Serum C-reactive Protein and Thioredoxin Levels in Subjects with Mildly Reduced Glomerular Filtration Rate

Shoko Tsuchikura; Tetsuo Shoji; Naoko Shimomura; Ryusuke Kakiya; Masanori Emoto; Hidenori Koyama; Eiji Ishimura; Masaaki Inaba; Yoshiki Nishizawa

Disclosures

BMC Nephrology. 2010;11:7 

In This Article

Methods

Subjects

The subjects were recruited from 264 consecutive participants of a health check-up program at the Osaka Health Promotion Center, Osaka, Japan. Twenty-three individuals refused to participate, and 241 subjects gave written informed consent to take part in the study. From the 241 people, we excluded 8 subjects with reduced eGFR < 60 mL/min/1.73 m2 and 51 subjects taking medications for diabetes mellitus, hypertension, and/or dyslipidemia, to avoid possible influence of these medications to oxidative stress biomarkers. The remaining 182 individuals were the final subjects of this study (Figure 1). Table 1 summarizes the characteristics of the final subjects. No one had proteinuria by a dip-stick method. According to the criteria by the Kidney Disease Improving Global Outcomes (KDIGO),[36] 79 subjects had normal eGFR (90 ml/min/1.73 m2 or higher), and 103 subjects showed mildly reduced eGFR (60–89 ml/min/1.73 m2). This study was carried out in compliance with the Helsinki Declaration, and approved by the ethics committee at Osaka City University Graduate School of Medical School.

Figure 1.

Recruitment and selection of the subjects. Abbreviations: DM, diabetes mellitus; HT, hypertension; DL, dyslipidemia.

Estimation of Glomerular Filtration Rate

Glomerular filtration rate (GFR) was estimated by the following equation:

where Cr is serum creatinine level by an enzymatic method. This equation was validated against the gold standard inulin clearance methods among Japanese individuals.[37]

Blood Collection and Measurements

Venous blood was collected after overnight fast into plastic tubes. After clotting at room temperature for 10 minutes, the tubes were chilled in ice, and serum was separated by centrifugation for 20 minutes at 4°C. Serum levels of TRX were measured within 3 days after sampling using frozen sera at -30°C. Other assays were performed immediately. CRP was assayed by a sensitive Latex-immunoassay (Denka Seiken, Tokyo) with a detection limit of 0.01 mg/dL. Serum TRX was quantified using a commercial ELISA kit for human TRX (Redox Bioscience Inc, Kyoto) with a detection limit of 2 ng/mL. Serum creatinine and total cholesterol was measured by enzymatic methods. HDL-cholesterol were determined by homogenous assays (Denka Seiken, Tokyo), and Non-HDL-cholesterol was calculated by subtracting HDL-cholesterol from total cholesterol. Body mass index (BMI) was calculated as body weight (kg) divided by squared height (m2).

Statistics

Because skewed distribution was found for CRP and TRX in preliminary analyses, all continuous data were summarized as median (25th-75th percentile levels). Categorical data were given in number or percentage. Correlation was evaluated by non-parametric Spearman's rank correlation test. Difference in median levels between groups was examined by Mann-Whitney's U-test. Multiple regression models were used to evaluate independent associations, to which CRP and TRX were entered after log-transformation to fit the linear models. P-values less than 0.05 was taken to be statistically significant. All these calculations were performed with StatView 5 software (SAS Institute Inc., Cary, NC) for Windows personal computers.

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