Original Paper Received: October 29, 2013 Accepted: March 24, 2014 Published online: October 23, 2014
Nephron Clin Pract DOI: 10.1159/000362456
Relationship between Serum Uric Acid and Serum Oxidative Stress Markers in the Japanese General Population Yuko Ishizaka a Minoru Yamakado a Akiko Toda a Mizuki Tani a Nobukazu Ishizaka b b
Center for Multiphasic Health Testing and Services, Mitsui Memorial Hospital, Tokyo, and Department of Cardiology, Osaka Medical College, Osaka, Japan
Key Words Oxidative stress · Antioxidant potentials · Uric acid
Abstract Background: Increased production of reactive oxygen species is a condition that is associated with, and plays a role in the progression of, various disorders such as hypertension, atherosclerosis, and diabetes. Purpose: To assess in vivo oxidative stress levels and antioxidant potential and to analyze the relationship with serum uric acid (UA) levels. Methods and Results: Oxidative stress levels (derivatives of reactive oxygen metabolites, d-ROMs) and antioxidant potential (biological antioxidant potential, BAP) were measured in individuals who underwent a general health screening test, and data were analyzed from 8,025 individuals (2,953 women and 5,072 men) who were free from UA-lowering medication. Higher serum UA levels were associated with increased levels of d-ROMs in both genders, and this trend was more prominent in women. In addition, higher UA levels were also associated with higher BAP in both genders, although the dose dependence was not apparent in men. These associations remained statistically significant after adjusting for age, blood pressure, renal function, albuminuria, C-reactive
© 2014 S. Karger AG, Basel 1660–2110/14/0000–0000$39.50/0 E-Mail [email protected] www.karger.com/nec
protein, and insulin resistance index. Conclusions: In individuals who underwent general health screening, serum UA levels were positively associated with both d-ROMs and BAP levels. Whether lowering of UA by lifestyle modification or by medication alters d-ROM/BAP levels awaits further investigations. © 2014 S. Karger AG, Basel
Introduction
Reactive oxygen species are generated during pathologic conditions as well as by normal physiological processes, and may play a role in the development of various life-threatening diseases such as atherosclerosis, cancer, and respiratory, immune and inflammatory disorders [1– 4]. Several antioxidant defense systems present in humans may act to correct a cellular redox imbalance; these include uric acid (UA), bilirubin, albumin, and reduced glutathione [5–7]. Unlike the endogenous antioxidants bilirubin and albumin, which have an inverse association with risk of atherosclerosis [8–10], subjects with higher serum UA levels may have a higher risk of atherosclerotic diseases [11]. This discrepancy might be explained by Nobukazu Ishizaka, MD Department of Cardiology, Osaka Medical College 2–7 Daigakumachi Takatsuki-shi, Osaka 569-8686 (Japan) E-Mail nobuishizka-tky @ umin.ac.jp
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a
Methods Ethics The study was approved by the ethical committees of Mitsui Memorial Hospital and Osaka Medical College. The data used in the current study was acquired exclusively from Center for Multiphasic Health Testing and Services, Mitsui Memorial Hospital. The database for the statistical analysis used in the current study was anonymized so that each individual enrolled was not identifiable. Although the used data were not publicly readily accessible, the same set of data would be accessed by other research group(s) upon the approval and agreement by the institute as well as by ethics committees. Study Population We have previously assessed the relationship between chronic kidney disease parameters and oxidant stress markers in 8,335 individuals who underwent general health screening between October 2008 and July 2012 including d-ROMs and BAP levels, IR, renal function, and albuminuria, whose characteristics were reported previously [14]. Among them, 310 subjects (3.7%) reported to be taking UA-lowering agents at the time of health check-up, and they were excluded from the current study. Thus, a total of 8,025 (2,953 women and 5,072 men) were enrolled in the current study. In Japan, regular health check-ups for employees are required by law and, therefore, the majority of these subjects did not have serious health problems. Blood pressure was measured after about 10 min of rest by an automated sphygmomanometer. Smoking status was categorized as never smoking, former smoking, or current smoking.
2
Nephron Clin Pract DOI: 10.1159/000362456
Data Measurement Systolic and diastolic blood pressure was measured in the morning twice by an automatic sphygmomanometer, and the mean of the two measurements was recorded as the individual’s data. For the assessment of albuminuria, spot urine was obtained in the morning after an overnight fast, and the ratio of urinary albumin to creatinine concentration was to assess the extent of albuminuria. Laboratory Analysis Blood samples were taken from the subjects after an overnight fast. Blood chemistry was performed as described previously [12]. Homeostasis model assessment (HOMA) of IR (HOMA-IR) was calculated according to the following formula: HOMA-IR = [fasting immunoreactive insulin (μU/ml) × fasting plasma glucose (mg/dl)]/405 [15]. Both the oxidative stress level and antioxidant properties in serum were determined by an automated method. The oxidative stress level was assessed via a d-ROMs test (Diacron Srl, Grosseto, Italy) in which the amount of organic hydroperoxide converted into radicals that oxidize N,N-diethyl-p-phenylenediamine hydroperoxide was measured [16]. In the antioxidant potential (BAP) test (Diacron Srl), antioxidant potential was assessed based on the capacity of the plasma sample to reduce ferric (Fe3+) ions to ferrous (Fe2+) ions [17]. Estimated glomerular filtration rate (eGFR) was calculated on the basis of the new Japanese coefficient-modified Modification of Diet in Renal Disease (MDRD) study equation [18]: eGFR (ml/ min/1.73 m2) = 194 × (serum creatinine)–1.094 × (age)–0.287 (× 0.739, when female). For the diagnosis of albuminuria, spot urine samples were collected and calculated on the basis of 1 g of urinary creatinine, designated urinary albumin excretion ratio (UAER), and micro- and macroalbuminuria was defined when UAER was 30–300 and ≥300 mg/g creatinine, respectively. High blood pressure was defined as systolic blood pressure of ≥140 mm Hg and/ or diastolic blood pressure of ≥90 mm Hg, irrespective of the depressor drug treatment. Statistical Analysis Data analysis was performed using IBM SPSS statistics version 21.0 software (SPSS, Inc., Chicago, Ill., USA). Data are expressed as the mean ± SD or median (IQR), unless stated otherwise. Differences between groups were calculated by analysis of variance (ANOVA), Mann-Whitney U test, Kruskal-Wallis test, and χ2 tests, where appropriate. Correlations between variables tested were assessed by Spearman’s correlation coefficient. Multivariate logistic regression analysis was performed for binominal variables. A value of p < 0.05 was taken to be statistically significant.
Results
Characteristics of Individuals The mean age of the subjects enrolled was 59.7 ± 10.1 years for women and 59.6 ± 10.6 years for men. Serum UA differed substantially between women and men; therefore, clinical and laboratory characteristics according to UA levels are shown for each gender separately (table 1). Only 16 subjects (5 women and 11 men) had extremely low UA Ishizaka /Yamakado /Toda /Tani /Ishizaka
Downloaded by: Ondokuz Mayis Universitesi 193.140.28.22 - 11/10/2014 2:28:58 PM
the association between serum UA and other atherogenic risk factors, such as insulin resistance (IR) and high blood pressure [12], or by superoxide production during the biosynthesis of UA via xanthine oxidase, one of the two functional forms of xanthine oxide dehydrogenase, which is posttranslationally converted from the other form, xanthine dehydrogenase [13]. If the unfavorable association between UA and lifestyle disease is attributed to the enhanced production of reactive oxygen species via xanthine oxidase, then two pharmacological UA-lowering strategies – xanthine oxidase inhibition and uricosuric agent – might have different impacts in terms of modulating the redox environment in the human body. On the other hand, information regarding the relationship between serum UA levels and in vivo oxidative stress seems to be limited, mainly due to a lack of reliable methods for the assessment of oxidative stress among a large-scale population. In the current study, by using automated measurement of derivatives of reactive oxygen metabolites (d-ROMs) and biological antioxidant potential (BAP), we assessed the relationship between serum UA and in vivo oxidant status in subjects undergoing general health screening.
Table 1. Baseline characteristics
Gender-specific UA quartiles first quartile Women UA, mg/dl, median (range) Subjects, n Age, years Body mass index Systolic BP, mm Hg Laboratory data HbA1C, % eGFR, ml/min/1.73 m2 Fasting glucose, mg/dl HOMA-IR d-ROM, Carr units BAP, mmol/l Smoking status, n (%) Never Former Current Medication, n (%) Antihypertensive Glucose-lowering Lipid-lowering Men UA, mg/dl, median (range) Subjects, n Age, years Body mass index Systolic BP, mm Hg Laboratory data HbA1C, % eGFR, ml/min/1.73 m2 Fasting glucose, mg/dl HOMA-IR d-ROM, Carr units BAP, mmol/l Smoking status, n (%) Never Former Current Medication, n (%) Antihypertensive Glucose-lowering Lipid-lowering
p value
second quartile
third quartile
fourth quartile
3.6 (0.6 – 4.0) 705 60.5 ± 10.6 21.9 ± 2.7 120 ± 18
4.4 (4.1 – 4.7) 745 58.0 ± 10.5 21.2 ± 2.8 118 ± 18
5.0 (4.8 – 5.3) 700 60.5 ± 9.6 21.9 ± 3.3 120 ± 18
5.9 (5.4 – 8.8) 803 62.3 ± 9.0 23.0 ± 3.8 125 ± 19
Nephron Clin Pract DOI: 10.1159/000362456
Relationship between Serum Uric Acid and Serum Oxidative Stress Markers in the Japanese General Population Yuko Ishizaka a Minoru Yamakado a Akiko Toda a Mizuki Tani a Nobukazu Ishizaka b b
Center for Multiphasic Health Testing and Services, Mitsui Memorial Hospital, Tokyo, and Department of Cardiology, Osaka Medical College, Osaka, Japan
Key Words Oxidative stress · Antioxidant potentials · Uric acid
Abstract Background: Increased production of reactive oxygen species is a condition that is associated with, and plays a role in the progression of, various disorders such as hypertension, atherosclerosis, and diabetes. Purpose: To assess in vivo oxidative stress levels and antioxidant potential and to analyze the relationship with serum uric acid (UA) levels. Methods and Results: Oxidative stress levels (derivatives of reactive oxygen metabolites, d-ROMs) and antioxidant potential (biological antioxidant potential, BAP) were measured in individuals who underwent a general health screening test, and data were analyzed from 8,025 individuals (2,953 women and 5,072 men) who were free from UA-lowering medication. Higher serum UA levels were associated with increased levels of d-ROMs in both genders, and this trend was more prominent in women. In addition, higher UA levels were also associated with higher BAP in both genders, although the dose dependence was not apparent in men. These associations remained statistically significant after adjusting for age, blood pressure, renal function, albuminuria, C-reactive
© 2014 S. Karger AG, Basel 1660–2110/14/0000–0000$39.50/0 E-Mail [email protected] www.karger.com/nec
protein, and insulin resistance index. Conclusions: In individuals who underwent general health screening, serum UA levels were positively associated with both d-ROMs and BAP levels. Whether lowering of UA by lifestyle modification or by medication alters d-ROM/BAP levels awaits further investigations. © 2014 S. Karger AG, Basel
Introduction
Reactive oxygen species are generated during pathologic conditions as well as by normal physiological processes, and may play a role in the development of various life-threatening diseases such as atherosclerosis, cancer, and respiratory, immune and inflammatory disorders [1– 4]. Several antioxidant defense systems present in humans may act to correct a cellular redox imbalance; these include uric acid (UA), bilirubin, albumin, and reduced glutathione [5–7]. Unlike the endogenous antioxidants bilirubin and albumin, which have an inverse association with risk of atherosclerosis [8–10], subjects with higher serum UA levels may have a higher risk of atherosclerotic diseases [11]. This discrepancy might be explained by Nobukazu Ishizaka, MD Department of Cardiology, Osaka Medical College 2–7 Daigakumachi Takatsuki-shi, Osaka 569-8686 (Japan) E-Mail nobuishizka-tky @ umin.ac.jp
Downloaded by: Ondokuz Mayis Universitesi 193.140.28.22 - 11/10/2014 2:28:58 PM
a
Methods Ethics The study was approved by the ethical committees of Mitsui Memorial Hospital and Osaka Medical College. The data used in the current study was acquired exclusively from Center for Multiphasic Health Testing and Services, Mitsui Memorial Hospital. The database for the statistical analysis used in the current study was anonymized so that each individual enrolled was not identifiable. Although the used data were not publicly readily accessible, the same set of data would be accessed by other research group(s) upon the approval and agreement by the institute as well as by ethics committees. Study Population We have previously assessed the relationship between chronic kidney disease parameters and oxidant stress markers in 8,335 individuals who underwent general health screening between October 2008 and July 2012 including d-ROMs and BAP levels, IR, renal function, and albuminuria, whose characteristics were reported previously [14]. Among them, 310 subjects (3.7%) reported to be taking UA-lowering agents at the time of health check-up, and they were excluded from the current study. Thus, a total of 8,025 (2,953 women and 5,072 men) were enrolled in the current study. In Japan, regular health check-ups for employees are required by law and, therefore, the majority of these subjects did not have serious health problems. Blood pressure was measured after about 10 min of rest by an automated sphygmomanometer. Smoking status was categorized as never smoking, former smoking, or current smoking.
2
Nephron Clin Pract DOI: 10.1159/000362456
Data Measurement Systolic and diastolic blood pressure was measured in the morning twice by an automatic sphygmomanometer, and the mean of the two measurements was recorded as the individual’s data. For the assessment of albuminuria, spot urine was obtained in the morning after an overnight fast, and the ratio of urinary albumin to creatinine concentration was to assess the extent of albuminuria. Laboratory Analysis Blood samples were taken from the subjects after an overnight fast. Blood chemistry was performed as described previously [12]. Homeostasis model assessment (HOMA) of IR (HOMA-IR) was calculated according to the following formula: HOMA-IR = [fasting immunoreactive insulin (μU/ml) × fasting plasma glucose (mg/dl)]/405 [15]. Both the oxidative stress level and antioxidant properties in serum were determined by an automated method. The oxidative stress level was assessed via a d-ROMs test (Diacron Srl, Grosseto, Italy) in which the amount of organic hydroperoxide converted into radicals that oxidize N,N-diethyl-p-phenylenediamine hydroperoxide was measured [16]. In the antioxidant potential (BAP) test (Diacron Srl), antioxidant potential was assessed based on the capacity of the plasma sample to reduce ferric (Fe3+) ions to ferrous (Fe2+) ions [17]. Estimated glomerular filtration rate (eGFR) was calculated on the basis of the new Japanese coefficient-modified Modification of Diet in Renal Disease (MDRD) study equation [18]: eGFR (ml/ min/1.73 m2) = 194 × (serum creatinine)–1.094 × (age)–0.287 (× 0.739, when female). For the diagnosis of albuminuria, spot urine samples were collected and calculated on the basis of 1 g of urinary creatinine, designated urinary albumin excretion ratio (UAER), and micro- and macroalbuminuria was defined when UAER was 30–300 and ≥300 mg/g creatinine, respectively. High blood pressure was defined as systolic blood pressure of ≥140 mm Hg and/ or diastolic blood pressure of ≥90 mm Hg, irrespective of the depressor drug treatment. Statistical Analysis Data analysis was performed using IBM SPSS statistics version 21.0 software (SPSS, Inc., Chicago, Ill., USA). Data are expressed as the mean ± SD or median (IQR), unless stated otherwise. Differences between groups were calculated by analysis of variance (ANOVA), Mann-Whitney U test, Kruskal-Wallis test, and χ2 tests, where appropriate. Correlations between variables tested were assessed by Spearman’s correlation coefficient. Multivariate logistic regression analysis was performed for binominal variables. A value of p < 0.05 was taken to be statistically significant.
Results
Characteristics of Individuals The mean age of the subjects enrolled was 59.7 ± 10.1 years for women and 59.6 ± 10.6 years for men. Serum UA differed substantially between women and men; therefore, clinical and laboratory characteristics according to UA levels are shown for each gender separately (table 1). Only 16 subjects (5 women and 11 men) had extremely low UA Ishizaka /Yamakado /Toda /Tani /Ishizaka
Downloaded by: Ondokuz Mayis Universitesi 193.140.28.22 - 11/10/2014 2:28:58 PM
the association between serum UA and other atherogenic risk factors, such as insulin resistance (IR) and high blood pressure [12], or by superoxide production during the biosynthesis of UA via xanthine oxidase, one of the two functional forms of xanthine oxide dehydrogenase, which is posttranslationally converted from the other form, xanthine dehydrogenase [13]. If the unfavorable association between UA and lifestyle disease is attributed to the enhanced production of reactive oxygen species via xanthine oxidase, then two pharmacological UA-lowering strategies – xanthine oxidase inhibition and uricosuric agent – might have different impacts in terms of modulating the redox environment in the human body. On the other hand, information regarding the relationship between serum UA levels and in vivo oxidative stress seems to be limited, mainly due to a lack of reliable methods for the assessment of oxidative stress among a large-scale population. In the current study, by using automated measurement of derivatives of reactive oxygen metabolites (d-ROMs) and biological antioxidant potential (BAP), we assessed the relationship between serum UA and in vivo oxidant status in subjects undergoing general health screening.
Table 1. Baseline characteristics
Gender-specific UA quartiles first quartile Women UA, mg/dl, median (range) Subjects, n Age, years Body mass index Systolic BP, mm Hg Laboratory data HbA1C, % eGFR, ml/min/1.73 m2 Fasting glucose, mg/dl HOMA-IR d-ROM, Carr units BAP, mmol/l Smoking status, n (%) Never Former Current Medication, n (%) Antihypertensive Glucose-lowering Lipid-lowering Men UA, mg/dl, median (range) Subjects, n Age, years Body mass index Systolic BP, mm Hg Laboratory data HbA1C, % eGFR, ml/min/1.73 m2 Fasting glucose, mg/dl HOMA-IR d-ROM, Carr units BAP, mmol/l Smoking status, n (%) Never Former Current Medication, n (%) Antihypertensive Glucose-lowering Lipid-lowering
p value
second quartile
third quartile
fourth quartile
3.6 (0.6 – 4.0) 705 60.5 ± 10.6 21.9 ± 2.7 120 ± 18
4.4 (4.1 – 4.7) 745 58.0 ± 10.5 21.2 ± 2.8 118 ± 18
5.0 (4.8 – 5.3) 700 60.5 ± 9.6 21.9 ± 3.3 120 ± 18
5.9 (5.4 – 8.8) 803 62.3 ± 9.0 23.0 ± 3.8 125 ± 19
