European Journal of Clinical Investigation ( 1 990) 20, 3 10-3 12

A circadian rhythm of serum osteocalcin levels in postmenopausaI osteoporosis P. PIETSCHMANN, H. RESCH, W. WOLOSZCZUK & R. WILLVONSEDER, Department of Medicine 11, Un’iversity of Vienna, Department of Medicine, Hospital Barmherzige Briider, Ludwig BoltzmannInstitute for Clinical Endocrinology, and Ludwig Boltzmann-Institute of Gerontology, Vienna, Austria Received 15 June 1989 and in revised form 20 November 1989

Abstract. The serum levels of osteocalcin, a 49 amino acid bone matrix protein, have been found to be a specific biochemical parameter of bone formation. The aim of our study was to assess the variability of serum osteocalcin and parathyroid hormone levels in postmenopausal osteoporosis. In 16 patients with postmenopausal osteoporosis, serum levels of osteocalcin and parathyroid hormone were determined in 4-hourly intervals by radioimmunoassay. Whereas the serum parathyroid hormone levels were similar throughout the day, the serum osteocalcin levels showed a circadian rhythm, with lowest levels in the morning and maximal levels during the night. These findings might suggest a circadian variation of bone formation in patients with postmenopausal osteoporosis. Keywords. Bone formation, bone GLA protein, circadian rhythm, osteocalcin, osteoporosis. Introduction Osteocalcin (also termed bone GLA protein) is a 49 amino acid bone matrix protein, which is released into peripheral blood and can be measured by radioimmunoassay [l]. The serum levels of osteocalcin have been found to represent the de nooo synthesis of osteocalcin by the osteoblasts and thus to be a non-invasive biochemical parameter of bone formation [2]. Gundberg et al. described a circadian rhythmicity of serum osteocalcin levels in normal subjects [3]. As the determination of serum osteocalcin levels in patients with postmenopausal osteoporosis has become an interesting research tool [4], the aim of the present study was to assess whether circadian variations of serum osteocalcin levels occur in postmenopausal osteoporosis.

Patients and methods We studied 16 consecutive patients with postmenopausal osteoporosis after giving informed consent. The patients were referred for evaluation of osteoporosis and were untreated. All patients presented with at least one atraumatic vertebral fracture and had peripheral bone density values below the age-adjusted normal range. The presence of secondary osteoporosis was excluded by a detailed history, physical examination and routine laboratory studies including blood chemistrv, protein electrophoresis and basal TSH levels; in all patients renal and hepatic function was normal. Further details of the patients studied are given in Table I . On the study day, venous blood was sampled at 4hourly intervals. Blood samples were allowed to clot at room temperature for approximately 2 h. Thereafter serum was separated by centrifugation and stored at - 2 0 T . The patients received the usual calcium-rich diet and were encouraged to continue their normal lifestyles, including physical activity, meals and bedrest. Serum osteocalcin levels were determined by radioimmunoassay (CIS International, Gif sur Yvette, France) as described in detail earlier [5]. The minimal detectable concentration of osteocalcin was 0.2 ng ml-I. Serum parathyroid hormone (PTH) levels were measured by radioimmunoassay with midregion specificity using synthetic human PTH (43-68) as tracer and standard (Sorin Biomedica, Saluggia, Italy). The minimal detectable concentration of PTH was 20 pmol I - ’ . Both radioimmunoassays had intra-assay coefficients of variation less than 8% and interassay coefficients of variation less than 14%. All the data are presented as the mean fSEM. Paired Student’s t-test and analysis of variance were used for statistical analysis. Results

Correspondence: Dr P.Pietschmann, Department of Medicine 11, University of Vienna, Garnisongasse 13. 1090 Vienna, Austria.

310

The serum levels of osteocalcin and parathyroid hormone measured at different time points in the patients with postmenopausal osteoporosis are shown

CIRCADIAN RHYTHM O F SERUM OSTEOCALCIN

Figure 1. Serum levels of osteocalcin (OC, 0-0) and parathyroid hormone (PTH. 0postmenopausal osteoporosis measured at 4-hourly intervals. * P < 0.02 vs. baseline value.

Table 1. Clinical characteristics of the patients with

postmenopausal osteoporosis Age Serum calcium Serum phosphorus Serum alkaline phosphatase OH prolin excrction Bone mincral content

67 k 2 years 9.5kO.l nig dl 3.9 k 0.4 mg dl I 5 6 k 8.4 U I 3.8k0.8mg24h 26.0 & I .4 U -

'

-

'

in Fig. 1 . The mean serum osteocalcin levels remained relatively constant throughout the day but increased during the night and reached a peak at 24 h. The mean serum osteocalcin level measured at 24 h was 18% higher than the baseline level (8 h). The difference between the peak osteocalcin level (24 h) and the baseline osteocalcin level was statistically significant ( P< 0.02; Student's t-test); however, possibly due to the relatively large interindividual variations in the osteocalcin patterns in the analysis of variance, no statistically significant influence of time on the serum osteocalcin levels was found. The serum levels of PTH showed no statistically significant diurnal variation throughout the day.

Discussion In our study on patients with postmenopausal osteoporosis, serum levels of osteocalcin were found to be higher in the night than during daytime. Gundberg et ul. [3] described a diurnal rhythmicity of serum osteocalcin levels with maximum levels during the night in a group of 10 normal subjects with an age

-

~ 0 in) 16

31 I

patients with

range of 20-30 years. The magnitude of the osteocalcin amplitude in the young subjects studied by Gundberg et al. was considerably higher than in our elderly subjects with postmenopausal osteoporosis. In a very recently published study Guillemant & Guillemant described daily fluctuations of serum osteocalcin levels with an amplitude of 13% in elderly hospitalized control subjects, whereas in patients with primary and secondary hyperparathyroidism no circadian rhythmicity of serum osteocalcin levels could be found [ 6 ] .The circadian fluctuations of serum osteocalcin levels in our elderly osteoporotic patients occurred with an amplitude similar to that described by Guillemant & Guillemant [6] in elderly subjects ( 1 8% vs. 13%). In our study, similar to the studies of Gundberg et ul. and Guillemant & Guillemant, the maximal osteocalcin levels occurred during the night (in our study at 24 h, in the two studies on control subjects at 4 h). Thus our results might suggest that in elderly patients with osteoporosis a diurnal rhythmicity of serum osteocalcin levels similar to that described in elderly hospitalized control subjects is present. In animal studies, circulating osteocalcin has been found to be cleared mainly by kidney filtration [7]; thus we cannot exclude that a circadian rhythmicity might be due to diurnal variations in kidney function. However, as in all the patients studied, the renal function was normal and serum osteocalcin levels have been demonstrated to be normal in subjects with a glomerular filtration rate not lower than 30 mg min-' 1.37 m-? [8]. The possibility that minor variations in the renal function in the patients studied might have contributed to the rhythmicity of serum osteocalcin levels does not seem very probable. The serum levels of osteocalcin have been found to

3 12

P. PIETSCHMANN et al.

be a specific non-invasive biochemical parameter of bone formation. Both in patients with postmenopausal osteoporosis and in normal subjects, serum osteocalcin levels correlate very closely with the histomorphometric parameters of bone formation [4,9,10]. The diurnal pattern of osteocalcin in the patients with postmenopausal osteoporosis thus might suggest a circadian rhythm of bone formation with a maximum during the night. The assumption of a diurnal rhythm of bone metabolism is further substantiated by animal studies [ I 1,121. In contrast to data obtained in normal men [13], in our patients with osteoporosis no circadian rhythm of PTH was found. In this context it seems to be of interest that osteoporotic subjects were found to exhibit a disturbed pulse amplitude and frequency modulation of PTH with smaller and less pulses [14]. In clinical praxis our findings in patients with postmenopausal osteoporosis might have two consequences. 1 When the determination of serum osteocalcin levels

is applied in postmenopausal osteoporosis it is necessary to take account of the time of blood sampling, at least when blood samples are taken both during the day and at night in order to achieve comparable results. 2 As our results might suggest that maximal bone formation in postmenopausal osteoporosis occurs during the night, further studies should be undertaken in order to assess whether the affect of certain drugs applied in the treatment of the osteoporosis might be dependent on the time of administration. Acknowledgment

This study was supported in part by a research grant from the Lorenz Bohler-Stiftung (Wien).

References I Price PA, Parthemore JG, Deftos LJ. New biochemical marker for bone metabolism. Measurement by radioimmunoassay of bone GLA protein in the plasma of normal subjects and patients with bone disease. J Clin Invest 1980;66:878. 2 Price PA, Williamson MK, Lothringer JW. Origin of the vitamin K-dependent bone protein found in plasma and its clearance by kidney and bone. J Biol Chem 1981;256:12760. 3 Gundberg CM, Markowitz ME, Mizruchi M. Rosen JF. Osteocalcin in human serum: a circadian rhythm. J Clin Endocrinol Metab 1984;60:736-9. 4 Brown JP, Delmas PD, Malaval L, Edouard C. Chapuy MC. Meunier PJ. Serum bone GLa-protein a specific marker for bone formation in postmenopausal osteoporosis. Lancet 1984; I : 109 I . 5 Pietschmann P, Woloszczuk W. Panzer S, Kyrle P. Smolen J . Decreased serum osteocalcin levels in phenprocoumon-treated patients. J Clin Endocrinol Metab 1987;66: 107 I --4. 6 Guillemant J, Guillemant S. Plasma osteocalcin in primary and secondary hyperparathyroidism with regard to daily Ructuations. Horm metabol Res 1989;21:220-1. 7 Price PA, Williamson MK, Lothringer JW. Origin ofthe vitamin K-dependent bone protein found in plasma and its clearance by kidney and bone. J Biol Chem 1981;256:12760. 8 Delmas PD, Wilson DM, Mann KG, Riggs BL. Erect of renal function on plasma levels of bone Gla-protein. J Clin Endocrinol Metab 198237:1028-30. 9 Stracke H, Schulz A, Weber U, Ullmann J. Schatz H. Osteocalcin and Knochenhistologie bei Osteoporose. Klin Wochenschr 1978;65:1095-1100. 10 Garcia-Carrasco M, Gruson M, de Vernejoul MC. Denne MA, Miravet L. Osteocalcin and bone morphometric parameters in adults without bone disease. Calcif Tissue Int 1988;42:13- 17. 11 Simmons DJ. Daily rhythm of S-35 incorporation into epiphyseal cartilage in mice. Experientia I968;24:363. 12 Simmons DJ, Nichols G. Diurnal periodicity in the metabolic activity of bone tissue. Am J Physiol 1966;210:41I . 13 Markowitz ME, Arnaud S, Rosen JF, Thorphy M , Laximinarayan S. Temporal interrelationships between the circadian rhythms of serum parathyroid hormone and calcium concentrations. J Clin Endocrinol Metab 1988;67:1068-73. 14 Harms H, Kapteina U, Kulpmann T, Hesch RD. The pulse amplitude and frequency modulation of PTH secretion in man. Int Symp on Osteoporosis. Aalborg 1987;(abstract 232).

A circadian rhythm of serum osteocalcin levels in postmenopausal osteoporosis.

The serum levels of osteocalcin, a 49 amino acid bone matrix protein, have been found to be a specific biochemical parameter of bone formation. The ai...
243KB Sizes 0 Downloads 0 Views