ICURT PROCEEDINGS
Vitamin D Receptor Polymorphism in Chronic Kidney Disease Patients With Complicated Cardiovascular Disease Domenico Santoro, MD,* Silvia Lucisano, MD,* Giorgia Gagliostro, MD,* Angela Alibrandi, MD, Prof,† Salvatore Benvenga, MD, Prof,* Riccardo Ientile, MD,‡ Guido Bellinghieri, MD, Prof,* Michele Buemi, MD, Prof,* and Daniela Caccamo, MD, Prof‡ Several studies indicate a relationship between vitamin D and cardiovascular disease. Pleiotropic actions of vitamin D and its analogs are mediated by vitamin D receptor (VDR). VDRs have been identified in almost all tissues, including vascular smooth muscle cells, cardiomyocytes, and endothelial cells. The FokI and BsmI polymorphisms of the VDR gene are regarded as strong markers of disturbed vitamin D signaling pathway. Studies investigating the relationship between VDR genotypes and left ventricular hypertrophy revealed a highly significant association with the BsmI Bb heterozygous genotype. There are conflicting data on the action of vitamin D in left ventricular hypertrophy. Experimental as well as observational studies and small clinical trials have suggested that vitamin D administration may favorably influence left ventricular hypertrophy, whereas large randomized clinical trials have shown negative results. However, a beneficial effect on the left atrial volume index and the duration of hospitalization were observed in patients treated with vitamin D analogs. Larger clinical trials with robust clinical end points are needed to confirm that vitamin D is effective in preventing cardiovascular disease in chronic kidney disease patients and in general population. Ó 2015 by the National Kidney Foundation, Inc. All rights reserved.
T
HE GROWING IMPORTANCE of Vitamin D signaling in the last decades derives from studies that showed how several pathologic conditions can be associated with low levels of vitamin D. Indeed, vitamin D deficiency increases the risk of chronic diseases, including autoimmune diseases (e.g., type 1 diabetes, multiple sclerosis, and rheumatoid arthritis), malignancies (e.g., prostate, colon, and breast cancer), and cardiovascular diseases, including stroke. Vitamin D may help to modulate the immune system and fight infectious diseases including tuberculosis and upper respiratory tract infections.1-4 It has been reported that activators of vitamin D receptor (VDR) are also able to reduce proteinuria,5-7 in particular through the suppression of the renin-angiotensinaldosterone system and exert anti-inflammatory and immunomodulatory effects.8
*
Department of Clinical and Experimental Medicine, University of Messina, Italy. † Department of Economical, Business and Environmental Sciences and Quantitative Methods, University of Messina, Italy. ‡ Department of Biochemical, Physiological and Nutritional Sciences, University of Messina, Italy. Financial Disclosure: The authors declare that they have no relevant financial interests. Address correspondence to Domenico Santoro, MD, Department of Clinical and Experimental Medicine, University of Messina, Messina 98168, Italy. E-mail:
[email protected] Ó
2015 by the National Kidney Foundation, Inc. All rights reserved. 1051-2276/$36.00 http://dx.doi.org/10.1053/j.jrn.2014.10.022
Journal of Renal Nutrition, Vol 25, No 2 (March), 2015: pp 187-193
Moreover, human and experimental models of chronic kidney disease (CKD) as well as clinical trials suggest that active vitamin D and/or its analogs are renoprotective, resulting in an attenuation of proteinuria, inflammation, glomerulosclerosis and interstitial fibrosis, thus improving kidney functions.9 Pharmacologic supplementation of active vitamin D may be a rational strategy to halt the vicious cycle between its deficiency and decline in kidney function in CKD patients. VDRs have been identified in almost all tissues, including vascular smooth muscle cells, cardiomyocytes, and endothelial cells.10 Given the crucial importance of vitamin D in bone formation, it can be hypothesized that vitamin D may play a role in the development of vascular calcifications. Therefore, the potential benefit of vitamin D treatment is likely to include mechanisms related to the development of vascular calcifications, atherosclerosis, and cardiac dysfunction. In particular, activation of VDRs by vitamin D or its analogs may directly inhibit the production of proteins necessary for arterial calcification or stimulating proteins that inhibit mineralization.11 Left ventricle hypertrophy (LVH) is a strong cardiovascular risk marker in end-stage renal disease (ESRD) patients.12 Because of the recent evidence regarding the role of vitamin D in heart disease, the association between left ventricular mass (LVM) and VDR gene polymorphisms has been investigated in patients with CKD.13,14 The biological activity of 1,25-dihydroxyvitamin D (1,25(OH)2D3) is mediated by the activation of the highaffinity nuclear VDR bonds. The VDR heterodimerizes 187
188
SANTORO ET AL
Figure 1. Distribution of different single nucleotide polymorphisms (SNPs) in the vitamin D receptor (VDR) gene.
with the retinoid X receptor, binds to vitamin D response elements on genomic DNA, and forms a transcriptional preinitiation complex by recruiting other nuclear proteins.15 The VDR gene is located on chromosome 12q12.14 and is composed of 8 protein-coding exons (exons 2–9) and 6 untranslated exons (1a-1f) that are alternatively spliced (Fig. 1).
VDR Polymorphisms in CKD The molecular pathways regulated by 1,25(OH)2D3, i.e., those related to calcium and phosphate homeostasis, immune function, cell proliferation, differentiation, and apoptosis, may be altered by genetic defects of VDR.16 Several population-based studies have reported the association of polymorphisms in genes of the vitamin D pathway with different diseases, including increased risk of osteoporosis, cancer, autoimmune disease, infectious disease, type 1 and type 2 diabetes, hypertension, and heart diseases.17 Moreover, VDR gene polymorphisms were investigated in subjects with renal failure because of the complex role played by vitamin D in those patients.18 A high prevalence of hypovitaminosis of 25hydroxyvitamin D (25[OH]D), unrelated to vitamin D intake, as well as genetically determined decrement in VDR efficiency have been described in patients with chronic renal failure (CRF) and comorbidities13 (Table 1). The VDR BsmI gene polymorphism has been shown to influence parathyroid function in CRF, driving the progression toward secondary hyperparathyroidism (sHPT) or hypoparathyroidism. A Spanish study, on 170 hemodialysis (HD) patients, reported that the B-mutated allele and the BB genotype were significantly more frequent in the low parathormone (PTH) group (serum PTH levels ,12 pmol/L) than the b allele and bb genotype, which, instead, were overrepresented in the high PTH group (serum PTH levels .60 pmol/L).19 The mean serum PTH levels were also found lower in BB patients (86 6 102 pg/mL) than
in bb patients (148 6 217 pg/mL) among 877 Japanese HD patients.20 Another study, which stratified 99 HD patients into those with hypoparathyroidism (PTH,104 pg/mL or 11 pmol/L) and those with hyperparathyroidism (PTH .261 pg/mL or 27.5 pmol/L), demonstrated that individuals with the B allele and BB genotype had a significantly lower dialytic age and serum PTH levels than patients with the b allele and bb genotype.21 The BsmI polymorphism has also been reported to influence the response to calcitriol and to postpone parathyroidectomy in ESRD patients. Indeed, HD patients with the BB genotype showed a better response than bb to calcitriol 72 hours after the bolus (percentage relative to basal PTH value: BB: 63%, bb: 88.6%), even after adjusting for serum calcium and phosphorus.22 Moreover, while examining separately patients who had required early parathyroidectomy or late parathyroidectomy, it was observed that individuals with the BB genotype remained longer on HD before they need parathyroidectomy.23 In this study,23 the cutoff point for early and late parathyroidectomy was 89 months, this being the mean time on HD before parathyroidectomy. These results suggest that in ESRD, the VDR BsmI BB genotype may mark a higher risk of developing hypoparathyroidism, whereas the bb genotype predispose to severe secondary hyperparathyroidism. However, another study also showed that BB individuals had lower levels of PTH and higher calcitriol levels than bb individuals (5.3-9.3 vs. 5.4-21.9 pmol/L, and 24.1-47.1 vs. 20.4-32.6 pg/mL, respectively) in every stage of CRF, after excluding other factors affecting parathyroid function (diabetes, parathyroid hypofunction, hyperalbuminemia, and hypercalcemia).24 Even the VDR FokI polymorphism has been reported to affect serum PTH levels in CRF patients. Indeed, patients with the FF genotype had significantly higher PTH levels (16.8 6 2.7 pmol/L) than those with Ff or ff genotype (11.3 6 2.0 and 8.2 6 1.6 pmol/L, respectively).25
189
VDR POLYMORPHISM AND LVH IN CKD Table 1. Association of Vitamin D Receptor (VDR) Gene Polymorphic Variants With Renal Diseases and Comorbidities VDR Allele or Genotype
Associated Pathologic Findings
BsmI bb genotype
Higher incidence and faster progression of sHPT and earlier time of parathyroidectomy in HD patients
BsmI BB genotype
Hypoparathyroidism in every stage of CRF and HD
BsmI BB genotype BsmI BB genotype BsmI bb genotype BsmI B allele BsmI B allele FokI FF genotype FokI F allele FokI f allele FokI f allele FokI/BsmI haplotype
Increased risk for mortality and shorter life expectancy in HD patients Strong predictor for inadequate response to EPO administration in HD patients Higher rHuEPO doses needed for management of ESRD-related anemia Increased risk for ESRD Increased risk for diabetic nephropathy Higher PTH levels in CRF Transferrin saturation ,20% in HD patients Association with worse stages of CRF in type 2 diabetes Significant improvement of allograft survival in adult renal transplant recipients No association with allograft survival and acute rejection. Higher frequency of b/F in graft rejection
Reference Fernandez et al. 20 Nagaba et al. 21 Tagliabue et al. 22 s et al. 24 Borra Marco et al. 25, Marco et al. 23 Marco et al. 29 Erturk et al. 22 Sezer et al. 31 de Souza et al. 24 Zhang et al. 28 Vigo Gago et al. 26 Amato et al. 32 Yokoyama et al. 27 Santoro et al. 13 Santoro et al. 13 Santoro et al. 13
CRF, chronic renal failure; ESRD, end-stage renal disease; HD, hemodialysis; sHPT, secondary hyperparathyroidism; rHuEPO, recombinant human erythropoietin; PTH, parathyroid hormone.
Moreover, a significant interaction between 1,25OHD and FokI ff genotype was observed in type 2 diabetes patients with CRF, although FokI polymorphisms by themselves showed no significant associations with CRF stage. 1,25OHD levels, but not 25OHD levels, were negatively associated with CRF stage and positively associated with estimated glomerular filtration rate. Evidence that positive association between 1,25OHD and estimated glomerular filtration rate was steeper in FokI Ff and FF genotypes than in the FokI ff genotype suggests that higher 1,25OHD levels may be associated with better CRF stages in patients with type 2 diabetes, and that this association is modified by FokI genotypes.26 The onset of diabetic nephropathy (DN) is also influenced by VDR BsmI polymorphism as observed in a case–control study including 304 patients with type 2 diabetes mellitus and 100 control individuals belonging to the Han Chinese population.27 Results from this investigation showed that (1) BsmI BB 1 Bb genotypes and B allele frequency were significantly higher in diabetes with excessive albuminuria than in both the nonalbuminuric patients and controls (individuals with no diabetes); (2) BB 1 Bb genotype and B allele frequency were significantly higher in early onset DN occurring within 1 year than in lateonset DN after 5 years/no DN over the whole follow-up period of 5 years; (3) among patients with DN, albumin excretion rate in 24-hour urine was significantly higher in those having the BB 1 Bb genotypes than in those with bb phenotype; (4) BB 1 Bb genotype was not only correlated with type 2 DN, but also with early onset type 2 DN.27 The BsmI polymorphism, together with age, diabetes, and calcitriol treatment, strongly influences survival in HD patients. Patients with the bb genotype were more frequent in the group of survivors than in that of the
nonsurvivors (45.7% vs. 21.6%) and had a longer life expectancy than those with the Bb or BB genotype (1,290 vs. 1,152 or 983 days, respectively).28 The influence of the VDR BsmI polymorphism on mortality in CRF has been explained by postulating that the polymorphic variant acts by directly modifying protein levels of VDR or VDR sensitivity in target organs, i.e., cardiac and vascular tissues. It is also possible that other ESRD comorbid conditions, such as anemia, alteration of iron metabolism, increased cardiovascular risk, influence life expectancy in HD patients. In this regard, it has been shown that, in comparison with other VDR BsmI genotypes, the presence of BB genotype is associated with lower hemoglobin levels and a less effective management of anemia secondary to erythropoietin deficiency, which is a common comorbidity of ESRD.29 However, this is a controversial issue because other authors showed that the B allele is associated with higher hemoglobin levels and lower doses of recombinant human erythropoietin required to raise hemoglobin levels.30 It has also been shown that VDR polymorphisms may affect biochemical iron indices (serum iron, transferrin, transferrin saturation, and ferritin), the changes of which are highly predictive markers of cardiovascular morbidity and mortality in ESRD. In particular, an investigation in 88 HD patients who were routinely treated with vitamin D showed that the FokI F allele was significantly more represented among HD patients having transferrin saturation ,20% than among those having transferrin saturation .20%.31 Cardiovascular disease is the main cause of death among HD patients because of the presence of traditional cardiac risk factors as well as other factors related to ESRD, such as hyperphosphatemia, elevated calcium and phosphate
190
SANTORO ET AL
product, abnormal lipid metabolism, hyperhomocysteinemia, and chronic inflammation. Moreover, there is emerging evidence that deficiency of the 1,25OHD and acquired vitamin D resistance through the uremic state play a relevant role, by nonmineral homeostatic effects, in the pathogenesis of cardiac disease in ESRD. Vitamin D deficiency has long been known to affect cardiac contractility, vascular tone, cardiac collagen content, and cardiac tissue maturation. Notably, cardiac function and survival are improved in vitamin D–treated HD patients.32 Whether or not VDR polymorphisms may per se represent a risk factor for ESRD is a controversial issue because it has been shown that VDR BsmI b allele is protective against ESRD,33 and, on the other hand, individuals with F/b haplotype were found to have an 11.0-fold increased risk for ESRD compared with controls.34 In conclusion, these observations indicate that genotyping for VDR polymorphisms holds a great potential for the improvement of therapeutic approaches to CRF and the management of CRF comorbidities.
VDR and Cardiovascular Diseases in CKD Population There is growing evidence that low vitamin D status adversely affects cardiac function. In spite of its virtually ubiquitous expression in the body, the function of VDR in certain tissues has not been established. A receptor that binds the active metabolite 1,25-(OH)D3 has been identified in the rat heart.35 The cardiovascular effects of Vitamin D seem to be mediated by the renin-angiotensin system. Indeed, it has been shown a significant relationship between low circulating levels 1,25(OH)2D) and elevated serum renin.36 Decreased VDR activity increases circulating renin levels and blood pressure37 and causes hypertrophy of both the left ventricle and myocytes in genetically manipulated mouse models. Moreover, VDR-knockout mice show myocardial renin overexpression and marked cardiomyocyte hypertrophy.38 In addition to the general population, the relation between VDR activators and LVM has been fully investigated in patients with CKD. Experimental studies in Dahl rats, which are a reliable animal model of LVH and vitamin D deficiency, demonstrated that treatment with paricalcitol attenuates the development of LVH and LV dysfunction.39 Different types of studies have been performed in humans to find associations between low levels or altered vitamin D signaling and LVM. Observational studies reported associations between vitamin D deficiency and increased risk of cardiovascular events and between therapy with calcitriol or related analogs and reduced cardiovascular events.40-42 Small clinical trials showed that 1,25(OH)2D infusion in patients with CKD may regress LVH in HD patients with secondary hyperparathyroidism.43,44
Another option to explore the nature of the association between VDR and LVM is Mendelian randomization. Genotype is not altered by behavioral and environmental factors, and for this reason, gene polymorphisms association analyses have been used instead of classic epidemiology studies,45 thus representing a useful approach in studies targeted for the ESRD population. To test this hypothesis, the distribution of one polymorphism of the VDR (BsmI B/b) was examined in 100 consecutive patients with calcific aortic valve stenosis compared with a control group of 100 patients (paired match for age, sex, and the presence of coronary artery disease without calcified aortic valves). The authors found that the B allele had a higher prevalence in patients with calcific aortic stenosis (B 5 0.56, b 5 0.44) than in the control cohort (B 5 0.40, b 5 0.60).46 More recently, the association between VDR gene polymorphisms and LVM has been investigated. It has been reported that the VDR BsmI gene polymorphism is involved in LVH in ESRD patients.14,47 Indeed, VDR polymorphisms resulted independently related to LVH and LVH progression. In particular, the frequency of the B allele of the BsmI VDR gene polymorphism was independently related to LVH and associated with higher progression rate of LVH in dialysis patients.14 For this reason, the presence of BsmI mutated variant of VDR gene in ESRD patients has been proposed as a novel marker of disturbed vitamin D signaling pathway, a disturbance that leads to an increase in LVM.14 In a similar study, but carried out in a smaller HD population, the number of B alleles was positively correlated with the left ventricular mass index, suggesting that the B alleles of the BsmI polymorphism could be considered as novel markers of altered vitamin D signaling in ESRD patients, and that BB genotype is responsible for increase in left ventricle mass.47 Because changes in LVM are very frequent in HD patients and may be related both to pressure overload and several hemodynamic as well as nonhemodynamic factors, we chose to evaluate the effects of alterations in VDR signaling in a population of patients with CRF not yet on dialysis. Therefore, we carried out a genotyping approach investigating the distribution of FokI and BsmI VDR gene polymorphisms in a cohort of patients with CRF stage 3 to assess the relationships between VDR different alleles and genotypes and LVM in this population. Our study found that the VDR BsmI B-mutated allele is independently related to LVH in a population of CKD patients not on dialysis and may be considered as a risk genetic factor for the development of LVH at stage 3b of CKD. Indeed, we found that the presence of the BsmI B variant either in heterozygous or homozygous state confers a disease risk dramatically higher (21-40 fold) than the presence of the b wild-type state.48 These studies prompted us to postulate that altered vitamin D signaling is implicated in cardiovascular diseases (Table 2).
191
VDR POLYMORPHISM AND LVH IN CKD
Table 2. Genetic Association Studies Regarding the Relationship Between BsmI Polymorphism of Vitamin D Receptor Gene and Left Ventricular Mass Type of Population
No. of Patients 182
El-Shehaby AM et al 47
CKD5 in dialysis CKD5 in dialysis
Santoro D et al 48
CKD3b
145
Authors Testa A et al 14
80
Type of Study Cross-sectional and longitudinal Cross-sectional
Cross-sectional
Diagnostic Evaluation
Cardiac Alteration
Genotype or Allele Associated
P Value
Echocardiography
LVMI
B allele
.007
Echocardiography and intima-media thickness Echocardiography
LVMI
Bb
.004
% of patients with LVH
BB
.001
CKD, chronic kidney disease; LVH: left ventricular hypertrophy; LVMI 5 left ventricular mass index.
The ultimate test for establishing whether or not vitamin D is implicated in LVH in ESRD is randomized controlled clinical trials (RCTs). However, interventional randomized controlled clinical trial focused on the effect of VDR activators on cardiac mass did not confirm completely the previous interesting results. In the PRIMO trial, which included 227 patients with CKD stages 3 to 4 and LVH at echocardiography who were randomized to paricalcitol or placebo, the change in left ventricular mass index by magnetic resonance (MRI) after 12 months did not differ between the two groups. Anyway, the prespecified end point of cardiovascular-related hospitalizations was reduced in the paricalcitol-treated group (P 5.04) demonstrating a correlation between VDR activation and reduced cardiovascular events49 Recently, similar results were reported in the OPERA trial. In this study, patients with 3 to 5 CKD were randomly assigned to receive oral paricalcitol or placebo. After 52 weeks, VDR activation with paricalcitol significantly improved secondary hyperparathyroidism but failed to demonstrate any change in the measures of LV structure and function. However, the authors were able to demonstrate a reduction of the number of cardiovascular-related hospitalizations compared with placebo.50 Because exploratory analyses suggested an effect of paricalcitol on left atrial size, the authors of the PRIMO trial, in a post hoc analysis, assessed the effect of an activated vitamin D analog on left atrial volume index (LAVi). Over the study period, there was a significant decrease in LAVi in the paricalcitol group compared with the placebo group. The use of diuretics and body weight changes were similar between groups suggesting that the paricalcitol effect in LAVi was independent of the extracellular fluid volume. Moreover, paricalcitol attenuated the rise in levels of brain natriuretic peptide.51 In the opinion of the authors, a possible explanation for the discrepancy between change in BNP, LAVi, and the lack of apparent changes in diastolic dysfunction measurements was that the sample size was too small to account for the well-known variability of Doppler measurements. Moreover, the volume of the left atrium can be considered a surrogate marker of LV diastolic function.
Conclusions The FokI and BsmI VDR gene polymorphisms are regarded as reliable markers of disturbed vitamin D signaling pathway. BsmI polymorphism has been associated with increased LVM in ESRD patients14,47 and in patients with CRF not yet on dialysis.48 In particular, a highly significant association was found between the BsmI Bb heterozygous genotype and LVH. In patients with CRF stage 3, BsmI B allele is independently related to LVH. The presence of the same genetic association in different stages of CKD strengthens the hypothesis that altered vitamin D signaling is implicated in LVH in patients with renal diseases. LVH is a strong cardiovascular risk marker in ESRD patients. Thus, it is important to identify novel risk factors that affect a large part of the population and can be inexpensively addressed to limit CVD morbidity and mortality. If low vitamin D levels are, in fact, causally related to CVD
Figure 2. Studies evaluating the relationships between vitamin D receptor (VDR) and VDR Activators (VDRA) and cardiac structure and function alterations. See the text for such studies (Symbols. ‘‘1’’ means positive effects of VDR activation; ‘‘2’’ means increased risk of LVH in patients bearing B allele of BsmI gene polymorphisms; ‘‘5’’ sign means no association).
192
SANTORO ET AL
risk, then vitamin D supplementation might provide a new way for reducing CVD morbidity and mortality. Because a large part of the population, ranging from 40% to 60%, has suboptimal levels of vitamin D,52 the correction through supplementation or increased sun exposure is a major challenge that has to be implemented. Population-based strategies to increase vitamin D levels could include increased food fortification, greater concentrations of vitamin D in the supplements, and public health messages to encourage reasonable sun exposure and intake of oily fish. Because clinical trials showed that vitamin D replacement therapy is effective at high risk, then screening for, and treatment of, suboptimal vitamin D levels could be a primary prevention priority. Experimental studies, observational analyses, and small clinical trials suggested that vitamin D may favorably influence myocardial hypertrophy; larger randomized clinical trials showed negative results;49,50 however, a beneficial effect was observed in LAVi51 and in reduction of hospitalizations,50 in patients treated with vitamin D analogs (Fig. 2). Supplementation of vitamin D for CVD prevention and treatment possibilities is the next challenge. However, results from large clinical trials with hard clinical end points are needed to confirm that vitamin D is effective in preventing CVD in CKD and general population.
References 1. Melamed ML, Michos ED, Post W, Astor B. 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med. 2008;168:1629-1637. 2. Wang TJ, Pencina MJ, Booth SL, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation. 2008;117:503-511. 3. Manson JE, Mayne ST, Clinton SK. Vitamin D and prevention of cancer—ready for prime time? N Engl J Med. 2011;364:1385-1387. 4. Santoro D, Gitto L, Ferraro A, Satta E, Savica V, Bellinghieri G. Vitamin D status and mortality risk in patients with chronic kidney disease. Ren Fail. 2011;33:184-191. 5. Agarwal R, Acharya M, Tian J, et al. Antiproteinuric effect of oral paricalcitol in chronic kidney disease. Kidney Int. 2005;68:2823-2828. 6. Alborzi P, Patel NA, Peterson C, et al. Paricalcitol reduces albuminuria and inflammation in chronic kidney disease: a randomized double-blind pilot trial. Hypertension. 2008;52:249-255. 7. de Zeeuw D, Agarwal R, Amdahl M, et al. Selective vitamin D receptor activation with paricalcitol for reduction of albuminuria in patients with type 2 diabetes (VITAL study): a randomised controlled trial. Lancet. 2010;376:1543-1551. 8. Finch JL, Suarez EB, Husain K, et al. Effect of combining an ACE inhibitor and a VDR activator on glomerulosclerosis, proteinuria, and renal oxidative stress in uremic rats. Am J Physiol Renal Physiol. 2012;302:F141-F149. 9. Lucisano S, Buemi M, Passantino A, Aloisi C, Cernaro V, Santoro D. New insights on the role of vitamin D in the progression of renal damage. Kidney Blood Press Res. 2013;37:667-678. 10. Towler DA, Clemens TL. Vitamin D and cardiovascular medicine. In: Feldman D, Pike JW, Glorieux FH, eds. Vitamin D. 2nd ed. Amsterdam: Elsevier Academic Press; 2005. 11. Andress DL. Vitamin D in chronic kidney disease: a systemic role for selective vitamin D receptor activation. Kidney Int. 2006;69:33-43.
12. Zoccali C, Benedetto FA, Mallamaci F, et al. Prognostic impact of the indexation of left ventricular mass in patients undergoing dialysis. J Am Soc Nephrol. 2001;12:2768-2774. 13. Santoro D, Caccamo D, Gagliostro G, et al. Vitamin D metabolism and activity as well as genetic variants of the vitamin D receptor (VDR) in chronic kidney disease patients. J Nephrol. 2013;26:636-644. 14. Testa A, Mallamaci F, Benedetto FA, et al. Vitamin D receptor (VDR) gene polymorphism is associated with left ventricular (LV) mass and predicts left ventricular hypertrophy (LVH) progression in end-stage renal disease (ESRD) patients. J Bone Miner Res. 2010;25:313-319. 15. Haussler MR, Whitfield GK, Haussler CA, et al. The nuclear vitamin D receptor: biological and molecular regulatory properties revealed. J Bone Miner Res. 1998;13:325-349. 16. Valdivielso JM, Fernandez E. Vitamin D receptor polymorphisms and diseases. Clin Chim Acta. 2006;371:1-12. 17. Basit S. Vitamin D in health and disease: a literature review. Br J Biomed Sci. 2013;70:161-172. 18. Uitterlinden AG, Fang Y, Van Meurs JB, Pols HA, Van Leeuwen JP. Genetics and biology of vitamin D receptor polymorphisms. Gene. 2004;338:143-156. 19. Fernandez E, Fibla J, Betriu A, Piulats JM, Almirall J, Montoliu J. Association between vitamin D receptor gene polymorphism and relative hypoparathyroidism in patients with chronic renal failure. J Am Soc Nephrol. 1997;8:1546-1552. 20. Nagaba Y, Heishi M, Tazawa H, Tsukamoto Y, Kobayashi Y. Vitamin D receptor gene polymorphisms affect secondary hyperparathyroidism in hemodialyzed patients. Am J Kidney Dis. 1998;32:464-469. 21. Tagliabue J, Farina M, Imbasciati E, Vergani C, Annoni G. BsmI polymorphism of the vitamin D receptor gene in hyperparathyroid or hypoparathyroid dialysis patients. Am J Clin Pathol. 1999;112:366-370. 22. Marco MP, Martinez I, Betriu A, Craver L, Fibla MJ, Fernandez E. Influence of Bsml vitamin D receptor gene polymorphism on the response to a single bolus of calcitriol in hemodialysis patients. Clin Nephrol. 2001;56:111-116. 23. Borras M, Torregrossa V, Oliveras A, et al. BB genotype of the vitamin D receptor gene polymorphism postpones parathyroidectomy in hemodialysis patients. J Nephrol. 2003;16:116-120. 24. Marco MP, Martinez I, Amoedo ML, et al. Vitamin D receptor genotype influences parathyroid hormone and calcitriol levels in predialysis patients. Kidney Int. 1999;56:1349-1353. 25. Vigo Gago E, Cadarso-Suarez C, Perez-Fernandez R, Romero Burgos R, Devesa Mugica J, Segura Iglesias C. Association between vitamin D receptor FokI. Polymorphism and serum parathyroid hormone level in patients with chronic renal failure. J Endocrinol Invest. 2005;28:117-121. 26. Yokoyama K, Nakashima A, Urashima M, et al. Interactions between serum vitamin D levels and vitamin D receptor gene FokI polymorphisms for renal function in patients with type 2 diabetes. PLoS One. 2012;7:e51171. 27. Zhang H, Wang J, Yi B, et al. BsmI polymorphisms in vitamin D receptor gene are associated with diabetic nephropathy in type 2 diabetes in the Han Chinese population. Gene. 2012;495:183-188. 28. Marco MP, Craver L, Betriu A, Fibla J, Fernandez E. Influence of vitamin D receptor gene polymorphisms on mortality risk in hemodialysis patients. Am J Kidney Dis. 2001;38:965-974. 29. Erturk S, Kutlay S, Karabulut HG, et al. The impact of vitamin D receptor genotype on the management of anemia in hemodialysis patients. Am J Kidney Dis. 2002;40:816-823. 30. Sezer S, Tutal E, Bilgic A, Ozdemir FN, Haberal M. Possible influence of Vitamin D receptor gene polymorphisms on recombinant human erythropoietin requirements in dialysis patients. Transplant Proc. 2007;39:40-44. 31. Amato M, Pacini S, Aterini S, Punzi T, Gulisano M, Ruggiero M. Iron indices and vitamin D receptor polymorphisms in hemodialysis patients. Adv Chronic Kidney Dis. 2008;15:186-190. 32. Achinger SG, Ayus JC. The role of vitamin D in left ventricular hypertrophy and cardiac function. Kidney Int Suppl. 2005;95:S37-S42. 33. de Souza CM, Braosi AP, Luczyszyn SM, et al. Association between vitamin D receptor gene polymorphisms and susceptibility
VDR POLYMORPHISM AND LVH IN CKD to chronic kidney disease and periodontitis. Blood Purif. 2007;25: 411-419. 34. Tripathi G, Sharma R, Sharma RK, Gupta SK, Sankhwar SN, Agrawal S. Vitamin D receptor genetic variants among patients with end-stage renal disease. Ren Fail. 2010;32:969-977. 35. Walters MR, Wicker DC, Riggle PC. 1,25-Dihydroxyvitamin D3 receptors identified in the rat heart. J Mol Cell Cardiol. 1986;18:67-72. 36. Resnick LM, Muller FB, Laragh JH. Calcium-regulating hormones in essential hypertension. Relation to plasma renin activity and sodium metabolism. Ann Intern Med. 1986;105:649-654. 37. Li YC, Kong J, Wei M, et al. 1,25-dihydroxyvitamin D is a negative endocrine regulator of the renin-angiotensin system. J Clin Invest. 2002;110:229-238. 38. Xiang W, Kong J, Chen S, et al. Cardiac hypertrophy in vitamin D receptor knockout mice: role of the systemic and cardiac renin-angiotensin systems. Am J Physiol Endocrinol Metab. 2005;288:E125-E132. 39. Bodyak N, Ayus JC, Achinger S, et al. Activated vitamin D attenuates left ventricular abnormalities induced by dietary sodium in Dahl salt sensitive animals. Proc Natl Acad Sci USA. 2007;104:16810-16815. 40. Kalantar-Zadeh K, Kuwae N, Regidor DL, et al. Survival predictability of time-varying indicators of bone disease in maintenance hemodialysis patients. Kidney Int. 2006;70:771-780. 41. Teng M, Wolf M, Lowrie E, Ofsthun N, Lazarus JM, Thadhani RI. Survival of patients undergoing hemodialysis with paricalcitol or calcitriol therapy. N Engl J Med. 2003;349:446-456. 42. Teng M, Wolf M, Ofsthun MN, et al. Activated injectable vitamin D and hemodialysis survival: a historical cohort study. J Am Soc Nephrol. 2005;16:1115-1125. 43. Kim HW, Park CW, Shin YS, et al. Calcitriol regresses cardiac hypertrophy and QT dispersion in secondary hyperparathyroidism on hemodialysis. Nephron Clin Pract. 2006;102:c21-c29.
193
44. Park CW, Oh YS, Shin YS, et al. Intravenous calcitriol regresses myocardial hypertrophy in hemodialysis patients with secondary hyperparathyroidism. Am J Kidney Dis. 1999;33:73-81. 45. Davey SG, Ebrahim S. ‘‘Mendelian randomization’’: can genetic epidemiology contribute to understanding environmental determinants of disease? Int J Epidemiol. 2003;32:1-22. 46. Ortlepp JR, Hoffmann R, Ohme F, Lauscher J, Bleckmann F, Hanrath P. The vitamin D receptor genotype predisposes to the development of calcific aortic valve stenosis. Heart. 2001;85:635-638. 47. El-Shehaby AM, El-Khatib MM, Marzouk S, Battah AA. Relationship of BsmI polymorphism of vitamin D receptor gene with left ventricular hypertrophy and atherosclerosis in hemodialysis patients. Scand J Clin Lab Invest. 2013;73:75-81. 48. Santoro D, Gagliostro G, Alibrandi A, et al. Vitamin D receptor gene polymorphism and left ventricular hypertrophy in chronic kidney disease. Nutrients. 2014;6:1029-1037. 49. Thadhani R, Appelbaum E, Pritchett Y, et al. Vitamin D therapy and cardiac structure and function in patients with chronic kidney disease: the PRIMO randomized controlled trial. JAMA. 2012;307: 674-684. 50. Wang AY, Fang F, Chan J, et al. Effect of paricalcitol on left ventricular mass and function in CKD—The OPERA Trial. J Am Soc Nephrol. 2014;25:175-186. 51. Tamez H, Zoccali C, Packham D, et al. Vitamin D reduces left atrial volume in patients with left ventricular hypertrophy and chronic kidney disease. Am Heart J. 2012;164:902-909.e2. 52. Martins D, Wolf M, Pan D, et al. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States: data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2007;167:1159-1165.
Vitamin D Receptor Polymorphism in Chronic Kidney Disease Patients With Complicated Cardiovascular Disease Domenico Santoro, MD,* Silvia Lucisano, MD,* Giorgia Gagliostro, MD,* Angela Alibrandi, MD, Prof,† Salvatore Benvenga, MD, Prof,* Riccardo Ientile, MD,‡ Guido Bellinghieri, MD, Prof,* Michele Buemi, MD, Prof,* and Daniela Caccamo, MD, Prof‡ Several studies indicate a relationship between vitamin D and cardiovascular disease. Pleiotropic actions of vitamin D and its analogs are mediated by vitamin D receptor (VDR). VDRs have been identified in almost all tissues, including vascular smooth muscle cells, cardiomyocytes, and endothelial cells. The FokI and BsmI polymorphisms of the VDR gene are regarded as strong markers of disturbed vitamin D signaling pathway. Studies investigating the relationship between VDR genotypes and left ventricular hypertrophy revealed a highly significant association with the BsmI Bb heterozygous genotype. There are conflicting data on the action of vitamin D in left ventricular hypertrophy. Experimental as well as observational studies and small clinical trials have suggested that vitamin D administration may favorably influence left ventricular hypertrophy, whereas large randomized clinical trials have shown negative results. However, a beneficial effect on the left atrial volume index and the duration of hospitalization were observed in patients treated with vitamin D analogs. Larger clinical trials with robust clinical end points are needed to confirm that vitamin D is effective in preventing cardiovascular disease in chronic kidney disease patients and in general population. Ó 2015 by the National Kidney Foundation, Inc. All rights reserved.
T
HE GROWING IMPORTANCE of Vitamin D signaling in the last decades derives from studies that showed how several pathologic conditions can be associated with low levels of vitamin D. Indeed, vitamin D deficiency increases the risk of chronic diseases, including autoimmune diseases (e.g., type 1 diabetes, multiple sclerosis, and rheumatoid arthritis), malignancies (e.g., prostate, colon, and breast cancer), and cardiovascular diseases, including stroke. Vitamin D may help to modulate the immune system and fight infectious diseases including tuberculosis and upper respiratory tract infections.1-4 It has been reported that activators of vitamin D receptor (VDR) are also able to reduce proteinuria,5-7 in particular through the suppression of the renin-angiotensinaldosterone system and exert anti-inflammatory and immunomodulatory effects.8
*
Department of Clinical and Experimental Medicine, University of Messina, Italy. † Department of Economical, Business and Environmental Sciences and Quantitative Methods, University of Messina, Italy. ‡ Department of Biochemical, Physiological and Nutritional Sciences, University of Messina, Italy. Financial Disclosure: The authors declare that they have no relevant financial interests. Address correspondence to Domenico Santoro, MD, Department of Clinical and Experimental Medicine, University of Messina, Messina 98168, Italy. E-mail:
[email protected] Ó
2015 by the National Kidney Foundation, Inc. All rights reserved. 1051-2276/$36.00 http://dx.doi.org/10.1053/j.jrn.2014.10.022
Journal of Renal Nutrition, Vol 25, No 2 (March), 2015: pp 187-193
Moreover, human and experimental models of chronic kidney disease (CKD) as well as clinical trials suggest that active vitamin D and/or its analogs are renoprotective, resulting in an attenuation of proteinuria, inflammation, glomerulosclerosis and interstitial fibrosis, thus improving kidney functions.9 Pharmacologic supplementation of active vitamin D may be a rational strategy to halt the vicious cycle between its deficiency and decline in kidney function in CKD patients. VDRs have been identified in almost all tissues, including vascular smooth muscle cells, cardiomyocytes, and endothelial cells.10 Given the crucial importance of vitamin D in bone formation, it can be hypothesized that vitamin D may play a role in the development of vascular calcifications. Therefore, the potential benefit of vitamin D treatment is likely to include mechanisms related to the development of vascular calcifications, atherosclerosis, and cardiac dysfunction. In particular, activation of VDRs by vitamin D or its analogs may directly inhibit the production of proteins necessary for arterial calcification or stimulating proteins that inhibit mineralization.11 Left ventricle hypertrophy (LVH) is a strong cardiovascular risk marker in end-stage renal disease (ESRD) patients.12 Because of the recent evidence regarding the role of vitamin D in heart disease, the association between left ventricular mass (LVM) and VDR gene polymorphisms has been investigated in patients with CKD.13,14 The biological activity of 1,25-dihydroxyvitamin D (1,25(OH)2D3) is mediated by the activation of the highaffinity nuclear VDR bonds. The VDR heterodimerizes 187
188
SANTORO ET AL
Figure 1. Distribution of different single nucleotide polymorphisms (SNPs) in the vitamin D receptor (VDR) gene.
with the retinoid X receptor, binds to vitamin D response elements on genomic DNA, and forms a transcriptional preinitiation complex by recruiting other nuclear proteins.15 The VDR gene is located on chromosome 12q12.14 and is composed of 8 protein-coding exons (exons 2–9) and 6 untranslated exons (1a-1f) that are alternatively spliced (Fig. 1).
VDR Polymorphisms in CKD The molecular pathways regulated by 1,25(OH)2D3, i.e., those related to calcium and phosphate homeostasis, immune function, cell proliferation, differentiation, and apoptosis, may be altered by genetic defects of VDR.16 Several population-based studies have reported the association of polymorphisms in genes of the vitamin D pathway with different diseases, including increased risk of osteoporosis, cancer, autoimmune disease, infectious disease, type 1 and type 2 diabetes, hypertension, and heart diseases.17 Moreover, VDR gene polymorphisms were investigated in subjects with renal failure because of the complex role played by vitamin D in those patients.18 A high prevalence of hypovitaminosis of 25hydroxyvitamin D (25[OH]D), unrelated to vitamin D intake, as well as genetically determined decrement in VDR efficiency have been described in patients with chronic renal failure (CRF) and comorbidities13 (Table 1). The VDR BsmI gene polymorphism has been shown to influence parathyroid function in CRF, driving the progression toward secondary hyperparathyroidism (sHPT) or hypoparathyroidism. A Spanish study, on 170 hemodialysis (HD) patients, reported that the B-mutated allele and the BB genotype were significantly more frequent in the low parathormone (PTH) group (serum PTH levels ,12 pmol/L) than the b allele and bb genotype, which, instead, were overrepresented in the high PTH group (serum PTH levels .60 pmol/L).19 The mean serum PTH levels were also found lower in BB patients (86 6 102 pg/mL) than
in bb patients (148 6 217 pg/mL) among 877 Japanese HD patients.20 Another study, which stratified 99 HD patients into those with hypoparathyroidism (PTH,104 pg/mL or 11 pmol/L) and those with hyperparathyroidism (PTH .261 pg/mL or 27.5 pmol/L), demonstrated that individuals with the B allele and BB genotype had a significantly lower dialytic age and serum PTH levels than patients with the b allele and bb genotype.21 The BsmI polymorphism has also been reported to influence the response to calcitriol and to postpone parathyroidectomy in ESRD patients. Indeed, HD patients with the BB genotype showed a better response than bb to calcitriol 72 hours after the bolus (percentage relative to basal PTH value: BB: 63%, bb: 88.6%), even after adjusting for serum calcium and phosphorus.22 Moreover, while examining separately patients who had required early parathyroidectomy or late parathyroidectomy, it was observed that individuals with the BB genotype remained longer on HD before they need parathyroidectomy.23 In this study,23 the cutoff point for early and late parathyroidectomy was 89 months, this being the mean time on HD before parathyroidectomy. These results suggest that in ESRD, the VDR BsmI BB genotype may mark a higher risk of developing hypoparathyroidism, whereas the bb genotype predispose to severe secondary hyperparathyroidism. However, another study also showed that BB individuals had lower levels of PTH and higher calcitriol levels than bb individuals (5.3-9.3 vs. 5.4-21.9 pmol/L, and 24.1-47.1 vs. 20.4-32.6 pg/mL, respectively) in every stage of CRF, after excluding other factors affecting parathyroid function (diabetes, parathyroid hypofunction, hyperalbuminemia, and hypercalcemia).24 Even the VDR FokI polymorphism has been reported to affect serum PTH levels in CRF patients. Indeed, patients with the FF genotype had significantly higher PTH levels (16.8 6 2.7 pmol/L) than those with Ff or ff genotype (11.3 6 2.0 and 8.2 6 1.6 pmol/L, respectively).25
189
VDR POLYMORPHISM AND LVH IN CKD Table 1. Association of Vitamin D Receptor (VDR) Gene Polymorphic Variants With Renal Diseases and Comorbidities VDR Allele or Genotype
Associated Pathologic Findings
BsmI bb genotype
Higher incidence and faster progression of sHPT and earlier time of parathyroidectomy in HD patients
BsmI BB genotype
Hypoparathyroidism in every stage of CRF and HD
BsmI BB genotype BsmI BB genotype BsmI bb genotype BsmI B allele BsmI B allele FokI FF genotype FokI F allele FokI f allele FokI f allele FokI/BsmI haplotype
Increased risk for mortality and shorter life expectancy in HD patients Strong predictor for inadequate response to EPO administration in HD patients Higher rHuEPO doses needed for management of ESRD-related anemia Increased risk for ESRD Increased risk for diabetic nephropathy Higher PTH levels in CRF Transferrin saturation ,20% in HD patients Association with worse stages of CRF in type 2 diabetes Significant improvement of allograft survival in adult renal transplant recipients No association with allograft survival and acute rejection. Higher frequency of b/F in graft rejection
Reference Fernandez et al. 20 Nagaba et al. 21 Tagliabue et al. 22 s et al. 24 Borra Marco et al. 25, Marco et al. 23 Marco et al. 29 Erturk et al. 22 Sezer et al. 31 de Souza et al. 24 Zhang et al. 28 Vigo Gago et al. 26 Amato et al. 32 Yokoyama et al. 27 Santoro et al. 13 Santoro et al. 13 Santoro et al. 13
CRF, chronic renal failure; ESRD, end-stage renal disease; HD, hemodialysis; sHPT, secondary hyperparathyroidism; rHuEPO, recombinant human erythropoietin; PTH, parathyroid hormone.
Moreover, a significant interaction between 1,25OHD and FokI ff genotype was observed in type 2 diabetes patients with CRF, although FokI polymorphisms by themselves showed no significant associations with CRF stage. 1,25OHD levels, but not 25OHD levels, were negatively associated with CRF stage and positively associated with estimated glomerular filtration rate. Evidence that positive association between 1,25OHD and estimated glomerular filtration rate was steeper in FokI Ff and FF genotypes than in the FokI ff genotype suggests that higher 1,25OHD levels may be associated with better CRF stages in patients with type 2 diabetes, and that this association is modified by FokI genotypes.26 The onset of diabetic nephropathy (DN) is also influenced by VDR BsmI polymorphism as observed in a case–control study including 304 patients with type 2 diabetes mellitus and 100 control individuals belonging to the Han Chinese population.27 Results from this investigation showed that (1) BsmI BB 1 Bb genotypes and B allele frequency were significantly higher in diabetes with excessive albuminuria than in both the nonalbuminuric patients and controls (individuals with no diabetes); (2) BB 1 Bb genotype and B allele frequency were significantly higher in early onset DN occurring within 1 year than in lateonset DN after 5 years/no DN over the whole follow-up period of 5 years; (3) among patients with DN, albumin excretion rate in 24-hour urine was significantly higher in those having the BB 1 Bb genotypes than in those with bb phenotype; (4) BB 1 Bb genotype was not only correlated with type 2 DN, but also with early onset type 2 DN.27 The BsmI polymorphism, together with age, diabetes, and calcitriol treatment, strongly influences survival in HD patients. Patients with the bb genotype were more frequent in the group of survivors than in that of the
nonsurvivors (45.7% vs. 21.6%) and had a longer life expectancy than those with the Bb or BB genotype (1,290 vs. 1,152 or 983 days, respectively).28 The influence of the VDR BsmI polymorphism on mortality in CRF has been explained by postulating that the polymorphic variant acts by directly modifying protein levels of VDR or VDR sensitivity in target organs, i.e., cardiac and vascular tissues. It is also possible that other ESRD comorbid conditions, such as anemia, alteration of iron metabolism, increased cardiovascular risk, influence life expectancy in HD patients. In this regard, it has been shown that, in comparison with other VDR BsmI genotypes, the presence of BB genotype is associated with lower hemoglobin levels and a less effective management of anemia secondary to erythropoietin deficiency, which is a common comorbidity of ESRD.29 However, this is a controversial issue because other authors showed that the B allele is associated with higher hemoglobin levels and lower doses of recombinant human erythropoietin required to raise hemoglobin levels.30 It has also been shown that VDR polymorphisms may affect biochemical iron indices (serum iron, transferrin, transferrin saturation, and ferritin), the changes of which are highly predictive markers of cardiovascular morbidity and mortality in ESRD. In particular, an investigation in 88 HD patients who were routinely treated with vitamin D showed that the FokI F allele was significantly more represented among HD patients having transferrin saturation ,20% than among those having transferrin saturation .20%.31 Cardiovascular disease is the main cause of death among HD patients because of the presence of traditional cardiac risk factors as well as other factors related to ESRD, such as hyperphosphatemia, elevated calcium and phosphate
190
SANTORO ET AL
product, abnormal lipid metabolism, hyperhomocysteinemia, and chronic inflammation. Moreover, there is emerging evidence that deficiency of the 1,25OHD and acquired vitamin D resistance through the uremic state play a relevant role, by nonmineral homeostatic effects, in the pathogenesis of cardiac disease in ESRD. Vitamin D deficiency has long been known to affect cardiac contractility, vascular tone, cardiac collagen content, and cardiac tissue maturation. Notably, cardiac function and survival are improved in vitamin D–treated HD patients.32 Whether or not VDR polymorphisms may per se represent a risk factor for ESRD is a controversial issue because it has been shown that VDR BsmI b allele is protective against ESRD,33 and, on the other hand, individuals with F/b haplotype were found to have an 11.0-fold increased risk for ESRD compared with controls.34 In conclusion, these observations indicate that genotyping for VDR polymorphisms holds a great potential for the improvement of therapeutic approaches to CRF and the management of CRF comorbidities.
VDR and Cardiovascular Diseases in CKD Population There is growing evidence that low vitamin D status adversely affects cardiac function. In spite of its virtually ubiquitous expression in the body, the function of VDR in certain tissues has not been established. A receptor that binds the active metabolite 1,25-(OH)D3 has been identified in the rat heart.35 The cardiovascular effects of Vitamin D seem to be mediated by the renin-angiotensin system. Indeed, it has been shown a significant relationship between low circulating levels 1,25(OH)2D) and elevated serum renin.36 Decreased VDR activity increases circulating renin levels and blood pressure37 and causes hypertrophy of both the left ventricle and myocytes in genetically manipulated mouse models. Moreover, VDR-knockout mice show myocardial renin overexpression and marked cardiomyocyte hypertrophy.38 In addition to the general population, the relation between VDR activators and LVM has been fully investigated in patients with CKD. Experimental studies in Dahl rats, which are a reliable animal model of LVH and vitamin D deficiency, demonstrated that treatment with paricalcitol attenuates the development of LVH and LV dysfunction.39 Different types of studies have been performed in humans to find associations between low levels or altered vitamin D signaling and LVM. Observational studies reported associations between vitamin D deficiency and increased risk of cardiovascular events and between therapy with calcitriol or related analogs and reduced cardiovascular events.40-42 Small clinical trials showed that 1,25(OH)2D infusion in patients with CKD may regress LVH in HD patients with secondary hyperparathyroidism.43,44
Another option to explore the nature of the association between VDR and LVM is Mendelian randomization. Genotype is not altered by behavioral and environmental factors, and for this reason, gene polymorphisms association analyses have been used instead of classic epidemiology studies,45 thus representing a useful approach in studies targeted for the ESRD population. To test this hypothesis, the distribution of one polymorphism of the VDR (BsmI B/b) was examined in 100 consecutive patients with calcific aortic valve stenosis compared with a control group of 100 patients (paired match for age, sex, and the presence of coronary artery disease without calcified aortic valves). The authors found that the B allele had a higher prevalence in patients with calcific aortic stenosis (B 5 0.56, b 5 0.44) than in the control cohort (B 5 0.40, b 5 0.60).46 More recently, the association between VDR gene polymorphisms and LVM has been investigated. It has been reported that the VDR BsmI gene polymorphism is involved in LVH in ESRD patients.14,47 Indeed, VDR polymorphisms resulted independently related to LVH and LVH progression. In particular, the frequency of the B allele of the BsmI VDR gene polymorphism was independently related to LVH and associated with higher progression rate of LVH in dialysis patients.14 For this reason, the presence of BsmI mutated variant of VDR gene in ESRD patients has been proposed as a novel marker of disturbed vitamin D signaling pathway, a disturbance that leads to an increase in LVM.14 In a similar study, but carried out in a smaller HD population, the number of B alleles was positively correlated with the left ventricular mass index, suggesting that the B alleles of the BsmI polymorphism could be considered as novel markers of altered vitamin D signaling in ESRD patients, and that BB genotype is responsible for increase in left ventricle mass.47 Because changes in LVM are very frequent in HD patients and may be related both to pressure overload and several hemodynamic as well as nonhemodynamic factors, we chose to evaluate the effects of alterations in VDR signaling in a population of patients with CRF not yet on dialysis. Therefore, we carried out a genotyping approach investigating the distribution of FokI and BsmI VDR gene polymorphisms in a cohort of patients with CRF stage 3 to assess the relationships between VDR different alleles and genotypes and LVM in this population. Our study found that the VDR BsmI B-mutated allele is independently related to LVH in a population of CKD patients not on dialysis and may be considered as a risk genetic factor for the development of LVH at stage 3b of CKD. Indeed, we found that the presence of the BsmI B variant either in heterozygous or homozygous state confers a disease risk dramatically higher (21-40 fold) than the presence of the b wild-type state.48 These studies prompted us to postulate that altered vitamin D signaling is implicated in cardiovascular diseases (Table 2).
191
VDR POLYMORPHISM AND LVH IN CKD
Table 2. Genetic Association Studies Regarding the Relationship Between BsmI Polymorphism of Vitamin D Receptor Gene and Left Ventricular Mass Type of Population
No. of Patients 182
El-Shehaby AM et al 47
CKD5 in dialysis CKD5 in dialysis
Santoro D et al 48
CKD3b
145
Authors Testa A et al 14
80
Type of Study Cross-sectional and longitudinal Cross-sectional
Cross-sectional
Diagnostic Evaluation
Cardiac Alteration
Genotype or Allele Associated
P Value
Echocardiography
LVMI
B allele
.007
Echocardiography and intima-media thickness Echocardiography
LVMI
Bb
.004
% of patients with LVH
BB
.001
CKD, chronic kidney disease; LVH: left ventricular hypertrophy; LVMI 5 left ventricular mass index.
The ultimate test for establishing whether or not vitamin D is implicated in LVH in ESRD is randomized controlled clinical trials (RCTs). However, interventional randomized controlled clinical trial focused on the effect of VDR activators on cardiac mass did not confirm completely the previous interesting results. In the PRIMO trial, which included 227 patients with CKD stages 3 to 4 and LVH at echocardiography who were randomized to paricalcitol or placebo, the change in left ventricular mass index by magnetic resonance (MRI) after 12 months did not differ between the two groups. Anyway, the prespecified end point of cardiovascular-related hospitalizations was reduced in the paricalcitol-treated group (P 5.04) demonstrating a correlation between VDR activation and reduced cardiovascular events49 Recently, similar results were reported in the OPERA trial. In this study, patients with 3 to 5 CKD were randomly assigned to receive oral paricalcitol or placebo. After 52 weeks, VDR activation with paricalcitol significantly improved secondary hyperparathyroidism but failed to demonstrate any change in the measures of LV structure and function. However, the authors were able to demonstrate a reduction of the number of cardiovascular-related hospitalizations compared with placebo.50 Because exploratory analyses suggested an effect of paricalcitol on left atrial size, the authors of the PRIMO trial, in a post hoc analysis, assessed the effect of an activated vitamin D analog on left atrial volume index (LAVi). Over the study period, there was a significant decrease in LAVi in the paricalcitol group compared with the placebo group. The use of diuretics and body weight changes were similar between groups suggesting that the paricalcitol effect in LAVi was independent of the extracellular fluid volume. Moreover, paricalcitol attenuated the rise in levels of brain natriuretic peptide.51 In the opinion of the authors, a possible explanation for the discrepancy between change in BNP, LAVi, and the lack of apparent changes in diastolic dysfunction measurements was that the sample size was too small to account for the well-known variability of Doppler measurements. Moreover, the volume of the left atrium can be considered a surrogate marker of LV diastolic function.
Conclusions The FokI and BsmI VDR gene polymorphisms are regarded as reliable markers of disturbed vitamin D signaling pathway. BsmI polymorphism has been associated with increased LVM in ESRD patients14,47 and in patients with CRF not yet on dialysis.48 In particular, a highly significant association was found between the BsmI Bb heterozygous genotype and LVH. In patients with CRF stage 3, BsmI B allele is independently related to LVH. The presence of the same genetic association in different stages of CKD strengthens the hypothesis that altered vitamin D signaling is implicated in LVH in patients with renal diseases. LVH is a strong cardiovascular risk marker in ESRD patients. Thus, it is important to identify novel risk factors that affect a large part of the population and can be inexpensively addressed to limit CVD morbidity and mortality. If low vitamin D levels are, in fact, causally related to CVD
Figure 2. Studies evaluating the relationships between vitamin D receptor (VDR) and VDR Activators (VDRA) and cardiac structure and function alterations. See the text for such studies (Symbols. ‘‘1’’ means positive effects of VDR activation; ‘‘2’’ means increased risk of LVH in patients bearing B allele of BsmI gene polymorphisms; ‘‘5’’ sign means no association).
192
SANTORO ET AL
risk, then vitamin D supplementation might provide a new way for reducing CVD morbidity and mortality. Because a large part of the population, ranging from 40% to 60%, has suboptimal levels of vitamin D,52 the correction through supplementation or increased sun exposure is a major challenge that has to be implemented. Population-based strategies to increase vitamin D levels could include increased food fortification, greater concentrations of vitamin D in the supplements, and public health messages to encourage reasonable sun exposure and intake of oily fish. Because clinical trials showed that vitamin D replacement therapy is effective at high risk, then screening for, and treatment of, suboptimal vitamin D levels could be a primary prevention priority. Experimental studies, observational analyses, and small clinical trials suggested that vitamin D may favorably influence myocardial hypertrophy; larger randomized clinical trials showed negative results;49,50 however, a beneficial effect was observed in LAVi51 and in reduction of hospitalizations,50 in patients treated with vitamin D analogs (Fig. 2). Supplementation of vitamin D for CVD prevention and treatment possibilities is the next challenge. However, results from large clinical trials with hard clinical end points are needed to confirm that vitamin D is effective in preventing CVD in CKD and general population.
References 1. Melamed ML, Michos ED, Post W, Astor B. 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med. 2008;168:1629-1637. 2. Wang TJ, Pencina MJ, Booth SL, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation. 2008;117:503-511. 3. Manson JE, Mayne ST, Clinton SK. Vitamin D and prevention of cancer—ready for prime time? N Engl J Med. 2011;364:1385-1387. 4. Santoro D, Gitto L, Ferraro A, Satta E, Savica V, Bellinghieri G. Vitamin D status and mortality risk in patients with chronic kidney disease. Ren Fail. 2011;33:184-191. 5. Agarwal R, Acharya M, Tian J, et al. Antiproteinuric effect of oral paricalcitol in chronic kidney disease. Kidney Int. 2005;68:2823-2828. 6. Alborzi P, Patel NA, Peterson C, et al. Paricalcitol reduces albuminuria and inflammation in chronic kidney disease: a randomized double-blind pilot trial. Hypertension. 2008;52:249-255. 7. de Zeeuw D, Agarwal R, Amdahl M, et al. Selective vitamin D receptor activation with paricalcitol for reduction of albuminuria in patients with type 2 diabetes (VITAL study): a randomised controlled trial. Lancet. 2010;376:1543-1551. 8. Finch JL, Suarez EB, Husain K, et al. Effect of combining an ACE inhibitor and a VDR activator on glomerulosclerosis, proteinuria, and renal oxidative stress in uremic rats. Am J Physiol Renal Physiol. 2012;302:F141-F149. 9. Lucisano S, Buemi M, Passantino A, Aloisi C, Cernaro V, Santoro D. New insights on the role of vitamin D in the progression of renal damage. Kidney Blood Press Res. 2013;37:667-678. 10. Towler DA, Clemens TL. Vitamin D and cardiovascular medicine. In: Feldman D, Pike JW, Glorieux FH, eds. Vitamin D. 2nd ed. Amsterdam: Elsevier Academic Press; 2005. 11. Andress DL. Vitamin D in chronic kidney disease: a systemic role for selective vitamin D receptor activation. Kidney Int. 2006;69:33-43.
12. Zoccali C, Benedetto FA, Mallamaci F, et al. Prognostic impact of the indexation of left ventricular mass in patients undergoing dialysis. J Am Soc Nephrol. 2001;12:2768-2774. 13. Santoro D, Caccamo D, Gagliostro G, et al. Vitamin D metabolism and activity as well as genetic variants of the vitamin D receptor (VDR) in chronic kidney disease patients. J Nephrol. 2013;26:636-644. 14. Testa A, Mallamaci F, Benedetto FA, et al. Vitamin D receptor (VDR) gene polymorphism is associated with left ventricular (LV) mass and predicts left ventricular hypertrophy (LVH) progression in end-stage renal disease (ESRD) patients. J Bone Miner Res. 2010;25:313-319. 15. Haussler MR, Whitfield GK, Haussler CA, et al. The nuclear vitamin D receptor: biological and molecular regulatory properties revealed. J Bone Miner Res. 1998;13:325-349. 16. Valdivielso JM, Fernandez E. Vitamin D receptor polymorphisms and diseases. Clin Chim Acta. 2006;371:1-12. 17. Basit S. Vitamin D in health and disease: a literature review. Br J Biomed Sci. 2013;70:161-172. 18. Uitterlinden AG, Fang Y, Van Meurs JB, Pols HA, Van Leeuwen JP. Genetics and biology of vitamin D receptor polymorphisms. Gene. 2004;338:143-156. 19. Fernandez E, Fibla J, Betriu A, Piulats JM, Almirall J, Montoliu J. Association between vitamin D receptor gene polymorphism and relative hypoparathyroidism in patients with chronic renal failure. J Am Soc Nephrol. 1997;8:1546-1552. 20. Nagaba Y, Heishi M, Tazawa H, Tsukamoto Y, Kobayashi Y. Vitamin D receptor gene polymorphisms affect secondary hyperparathyroidism in hemodialyzed patients. Am J Kidney Dis. 1998;32:464-469. 21. Tagliabue J, Farina M, Imbasciati E, Vergani C, Annoni G. BsmI polymorphism of the vitamin D receptor gene in hyperparathyroid or hypoparathyroid dialysis patients. Am J Clin Pathol. 1999;112:366-370. 22. Marco MP, Martinez I, Betriu A, Craver L, Fibla MJ, Fernandez E. Influence of Bsml vitamin D receptor gene polymorphism on the response to a single bolus of calcitriol in hemodialysis patients. Clin Nephrol. 2001;56:111-116. 23. Borras M, Torregrossa V, Oliveras A, et al. BB genotype of the vitamin D receptor gene polymorphism postpones parathyroidectomy in hemodialysis patients. J Nephrol. 2003;16:116-120. 24. Marco MP, Martinez I, Amoedo ML, et al. Vitamin D receptor genotype influences parathyroid hormone and calcitriol levels in predialysis patients. Kidney Int. 1999;56:1349-1353. 25. Vigo Gago E, Cadarso-Suarez C, Perez-Fernandez R, Romero Burgos R, Devesa Mugica J, Segura Iglesias C. Association between vitamin D receptor FokI. Polymorphism and serum parathyroid hormone level in patients with chronic renal failure. J Endocrinol Invest. 2005;28:117-121. 26. Yokoyama K, Nakashima A, Urashima M, et al. Interactions between serum vitamin D levels and vitamin D receptor gene FokI polymorphisms for renal function in patients with type 2 diabetes. PLoS One. 2012;7:e51171. 27. Zhang H, Wang J, Yi B, et al. BsmI polymorphisms in vitamin D receptor gene are associated with diabetic nephropathy in type 2 diabetes in the Han Chinese population. Gene. 2012;495:183-188. 28. Marco MP, Craver L, Betriu A, Fibla J, Fernandez E. Influence of vitamin D receptor gene polymorphisms on mortality risk in hemodialysis patients. Am J Kidney Dis. 2001;38:965-974. 29. Erturk S, Kutlay S, Karabulut HG, et al. The impact of vitamin D receptor genotype on the management of anemia in hemodialysis patients. Am J Kidney Dis. 2002;40:816-823. 30. Sezer S, Tutal E, Bilgic A, Ozdemir FN, Haberal M. Possible influence of Vitamin D receptor gene polymorphisms on recombinant human erythropoietin requirements in dialysis patients. Transplant Proc. 2007;39:40-44. 31. Amato M, Pacini S, Aterini S, Punzi T, Gulisano M, Ruggiero M. Iron indices and vitamin D receptor polymorphisms in hemodialysis patients. Adv Chronic Kidney Dis. 2008;15:186-190. 32. Achinger SG, Ayus JC. The role of vitamin D in left ventricular hypertrophy and cardiac function. Kidney Int Suppl. 2005;95:S37-S42. 33. de Souza CM, Braosi AP, Luczyszyn SM, et al. Association between vitamin D receptor gene polymorphisms and susceptibility
VDR POLYMORPHISM AND LVH IN CKD to chronic kidney disease and periodontitis. Blood Purif. 2007;25: 411-419. 34. Tripathi G, Sharma R, Sharma RK, Gupta SK, Sankhwar SN, Agrawal S. Vitamin D receptor genetic variants among patients with end-stage renal disease. Ren Fail. 2010;32:969-977. 35. Walters MR, Wicker DC, Riggle PC. 1,25-Dihydroxyvitamin D3 receptors identified in the rat heart. J Mol Cell Cardiol. 1986;18:67-72. 36. Resnick LM, Muller FB, Laragh JH. Calcium-regulating hormones in essential hypertension. Relation to plasma renin activity and sodium metabolism. Ann Intern Med. 1986;105:649-654. 37. Li YC, Kong J, Wei M, et al. 1,25-dihydroxyvitamin D is a negative endocrine regulator of the renin-angiotensin system. J Clin Invest. 2002;110:229-238. 38. Xiang W, Kong J, Chen S, et al. Cardiac hypertrophy in vitamin D receptor knockout mice: role of the systemic and cardiac renin-angiotensin systems. Am J Physiol Endocrinol Metab. 2005;288:E125-E132. 39. Bodyak N, Ayus JC, Achinger S, et al. Activated vitamin D attenuates left ventricular abnormalities induced by dietary sodium in Dahl salt sensitive animals. Proc Natl Acad Sci USA. 2007;104:16810-16815. 40. Kalantar-Zadeh K, Kuwae N, Regidor DL, et al. Survival predictability of time-varying indicators of bone disease in maintenance hemodialysis patients. Kidney Int. 2006;70:771-780. 41. Teng M, Wolf M, Lowrie E, Ofsthun N, Lazarus JM, Thadhani RI. Survival of patients undergoing hemodialysis with paricalcitol or calcitriol therapy. N Engl J Med. 2003;349:446-456. 42. Teng M, Wolf M, Ofsthun MN, et al. Activated injectable vitamin D and hemodialysis survival: a historical cohort study. J Am Soc Nephrol. 2005;16:1115-1125. 43. Kim HW, Park CW, Shin YS, et al. Calcitriol regresses cardiac hypertrophy and QT dispersion in secondary hyperparathyroidism on hemodialysis. Nephron Clin Pract. 2006;102:c21-c29.
193
44. Park CW, Oh YS, Shin YS, et al. Intravenous calcitriol regresses myocardial hypertrophy in hemodialysis patients with secondary hyperparathyroidism. Am J Kidney Dis. 1999;33:73-81. 45. Davey SG, Ebrahim S. ‘‘Mendelian randomization’’: can genetic epidemiology contribute to understanding environmental determinants of disease? Int J Epidemiol. 2003;32:1-22. 46. Ortlepp JR, Hoffmann R, Ohme F, Lauscher J, Bleckmann F, Hanrath P. The vitamin D receptor genotype predisposes to the development of calcific aortic valve stenosis. Heart. 2001;85:635-638. 47. El-Shehaby AM, El-Khatib MM, Marzouk S, Battah AA. Relationship of BsmI polymorphism of vitamin D receptor gene with left ventricular hypertrophy and atherosclerosis in hemodialysis patients. Scand J Clin Lab Invest. 2013;73:75-81. 48. Santoro D, Gagliostro G, Alibrandi A, et al. Vitamin D receptor gene polymorphism and left ventricular hypertrophy in chronic kidney disease. Nutrients. 2014;6:1029-1037. 49. Thadhani R, Appelbaum E, Pritchett Y, et al. Vitamin D therapy and cardiac structure and function in patients with chronic kidney disease: the PRIMO randomized controlled trial. JAMA. 2012;307: 674-684. 50. Wang AY, Fang F, Chan J, et al. Effect of paricalcitol on left ventricular mass and function in CKD—The OPERA Trial. J Am Soc Nephrol. 2014;25:175-186. 51. Tamez H, Zoccali C, Packham D, et al. Vitamin D reduces left atrial volume in patients with left ventricular hypertrophy and chronic kidney disease. Am Heart J. 2012;164:902-909.e2. 52. Martins D, Wolf M, Pan D, et al. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States: data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2007;167:1159-1165.
