Journal of Clinical Endocrinology & Metabolism
, doi:10.1210/jc.2005-2856
The Journal of Clinical Endocrinology & Metabolism Vol. 91, No. 6 2133-2137
Copyright © 2006 by The Endocrine Society
Serum C-Reactive Protein and Its Relation to Cardiovascular Risk Factors and Adipocytokines in Japanese Children
Tomohide Yoshida,
Takuya Kaneshi,
Tadao Shimabukuro,
Makoto Sunagawa and
Takao Ohta
Department of Child Health and Welfare, Faculty of Medicine, University of the Ryukyus, Okinawa 903-0125, Japan
Address all correspondence and requests for reprints to: Dr. Takao Ohta, Department of Child Health and Welfare, Faculty of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa 903-0125, Japan. E-mail: tohta{at}med.u-ryukyu.ac.jp.
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Abstract
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Background: C-Reactive protein (CRP) is an independent risk factor for atherosclerotic coronary heart diseases (ACHD) in adults. To help prevent ACHD, it may be useful to understand risk factors during childhood.
Objective: The objective of this study was to investigate serum CRP and its relation to other risk factors for ACHD and adipocytokines (adiponectin, IL-6, and TNF-
) in Japanese children.
Methods: CRP, conventional risk factors for ACHD, and adipocytokines were determined in 568 children (340 boys and 228 girls, aged 7–10 yr). Serum concentrations of adipocytokines were measured by sandwich ELISA.
Results: Children with high CRP concentrations (highest tertile) had higher body mass index (BMI) SD scores, insulin, insulin resistance, uric acid, and adipocytokines and had more atherogenic lipoprotein profiles than other children. However, after being corrected by BMI SD, only high-density lipoprotein cholesterol, apolipoprotein A-I, IL-6, and TNF- for boys and high-density lipoprotein cholesterol, apolipoprotein B, uric acid, IL-6, and TNF- for girls were significantly correlated with CRP. IL-6 was the strongest predictive variable for CRP and accounted for 26.2 and 27.7% of the variability in serum concentrations of CRP in boys and girls, respectively. Serum concentrations of IL-6 were partly dependent on BMI SD and TNF- in both boys and girls.
Conclusion: Although serum concentrations of CRP are partly regulated by adipocytokines and conventional risk factors for ACHD, high CRP levels were associated with atherogenic profiles of cardiovascular risk factors in children. Our findings suggest that it may be important to control body weight to prevent an increase in serum CRP in children.
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Introduction
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C-REACTIVE PROTEIN (CRP) increases nonspecifically in inflammatory disorders. The recent development of a highly sensitive assay for serum CRP concentrations has led to the unexpected finding that elevation of CRP levels within the normal range is associated with an increased risk for atherosclerotic coronary heart diseases (ACHD) in apparently healthy subjects (1, 2, 3). Although the underlying mechanism by which CRP contributes to the development of ACHD is not yet clear, Sternik et al. (4) reported in an in vitro study that CRP induces vasorelaxation independent of the endothelium. In addition, it has been reported that CRP induced apoptosis in human coronary vascular smooth muscle cells (5). However, van den Berg et al. (6) recently reported that vasorelaxation induced by CRP may be an artifact caused by the reagent used in their experiment. CRP is correlated with many conventional risk factors for ACHD, such as insulin resistance, obesity, high-density lipoprotein cholesterol (HDL-C), etc. (7, 8). Because most of these epidemiological studies were performed in adults, ACHD risk factors acquired later in life, such as smoking, alcohol use, etc., may affect these relationships. In contrast to adults, children rarely drink alcohol or smoke and usually exercise regularly at school. Thus, environmental factors that affect the relationship between CRP and risk factors may have less of an effect in children than in adults. It seems reasonable to consider the relationship between serum CRP and risk factors for ACHD in schoolchildren. Several studies in children are currently available (9, 10, 11). Most of these have indicated that adiposity is the major determinant of CRP levels in children and have speculated that cytokines secreted from adipocytes may be responsible for the relationship between serum concentrations of CRP and adiposity. In the present study we investigated serum CRP and factors that influence serum CRP in children to better understand the roles of various risk factors in the development of atherosclerosis.
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Subjects and Methods
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Subjects
The present study was approved by the review board of University of the Ryukyus. Informed consent was obtained from the parents of all children. We studied 568 Japanese children (340 boys and 228 girls), aged 7–10 yr, who underwent screening and had been enrolled in a care program for lifestyle-related diseases since 2002 in Okinawa, Japan (Table 1
). Sex maturity stages in the children we studied were equal to or less than Tanner stage 2. The subjects were not patients who visited our hospital. Body mass index (BMI) was calculated as weight (kilograms)/height (meters)2. BMI SD scores adjusted for age and sex were obtained based on data for Japanese schoolchildren provided by the Ministry of Education, Culture, Sports, Science, and Technology (Murata, M., unpublished observations). None of the children studied were receiving therapy for weight reduction or drugs that affected lipid metabolism. None had a smoking habit. Venous blood was drawn after an overnight fast.
Laboratory measurements
The serum CRP concentration was measured by a highly sensitive immunoturbidimetric assay with the use of reagents and calibrators from Dade Behring Marbura GmbH (Marburg, Germany; the lower limit of detection for the serum CRP concentration was 0.05 mg/liter). IL-6 and TNF- were measured by ELISAs (R&D Systems, Inc., Minneapolis, MN). The serum adiponectin concentration was measured by sandwich ELISA (Otsuka Pharmaceutical Co., Ltd., Tokushima City, Japan). Serum insulin was measured by a two-step sandwich ELISA (SRL, Inc., Hachioji, Japan). Routine chemical methods were used to determine the serum concentrations of total cholesterol (TC), HDL-C, triglycerides (TG), uric acid, and glucose. Low-density lipoprotein-cholesterol (LDL-C) was calculated as TC – HDL-C – TG/5. Apolipoproteins (apoA-I and apoB) were measured by the turbidity immunoassay method (12). Insulin resistance was calculated using the homeostasis model approximation index (HOMA-R) (13). This equation, which is based on both fasting glucose and insulin, correlates well with insulin dynamics, as measured by the hyperinsulinemic clamp and the iv glucose tolerance test (13).
Statistical evaluation
For statistical analysis, serum concentrations of CRP below the limit of detection were assigned a value of 0.05 mg/liter (lower limit of detection). Gender-related differences were determined by the Mann-Whitney U test. Differences in parameters among subjects with low, middle, and high CRP concentrations (tertiles) were determined by the Kruskal-Wallis test. Parameters in these three groups were compared with Scheffé’s multiple comparison test. The distributions of HOMA-R and levels of CRP, insulin, TG, IL-6, and TNF- were markedly skewed. Thus, these parameters were normalized by log transformation. Pearson and partial correlation coefficients were computed to assess the associations between CRP and various parameters. A stepwise multiple regression analysis was performed by entering the independent variable with the highest partial correlation coefficient at each step until no variable remained with an F value of 4 or greater. Group differences or correlations with P < 0.05 were considered statistically significant. All statistical analysis was performed using StatView J-5.0 software (SAS Institute, Inc., Cary, NC).
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Results
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As shown in Table 1
, gender-related differences were found in several parameters (CRP, TC, LDL-C, HDL-C, apoA-I, and TNF-). Thus, we separated the data for boys and girls in the following analysis. To understand the relation between CRP and lipids and other parameters, subjects were divided into tertiles based on CRP concentrations (low, lowest tertile; middle, intermediate tertile; high, highest tertile; Tables 2 and 3). In boys, there were significant graded relationships among the three groups of CRP concentrations and all parameters except for glucose, TC, and TG. For parameters other than BMI SD, HDL-C, and IL-6, significant differences were found in one or two combinations (between low and high and/or between low and middle or between middle and high; Table 2). Table 3 shows the findings in girls. In contrast to the findings in boys, significant differences were not found in LDL-C, adiponectin, and TNF-, but were found in TG.
Tables 4 and 5 show Pearson and partial correlations between logCRP and the other parameters studied. In boys, logCRP was correlated with all parameters listed except TC (P = 0.000–0.010). After being corrected for BMI SD, logCRP was positively correlated with logIL-6 and logTNF- and was inversely correlated with HDL-C and apoA-I (P = 0.000–0.049; Table 4). In girls, logCRP was positively correlated with BMI SD, age, logInsulin, logHOMA-R, logTG, ApoB, uric acid, and logIL-6 and was inversely correlated with HDL-C (P = 0.000–0.016). After being corrected for BMI SD, logCRP was positively correlated with apoB, uric acid, logIL-6, and logTNF- (P = 0.000–0.031) and was inversely correlated with HDL-C (Table 5). Because each of these parameters can potentially contribute directly to the regulation of CRP, we performed a stepwise multiple regression analysis with logCRP as the dependent variable and the other parameters listed in Table 4 (HOMA-R was excluded because it was value calculated) as independent variables. In boys, BMI SD had the most significant association with logCRP and accounted for 24.3% of the variability in logCRP. HDL-C had additional effects (2.4%; Table 6, model 1, logIL-6 and TNF- were excluded). When logIL-6 and logTNF- were included in the model (Table 6, model 2), logIL-6 had the most significant association with logCRP and accounted for 26.2% of the variability in logCRP. BMI SD, HDL-C, and logTNF- had additional effects (9.7, 2.3, and 1.1%, respectively). In girls, BMI SD had the most significant association with logCRP and accounted for 13.2% of the variability in logCRP. ApoB had an additional effect (1.9%, respectively; Table 6, model 1). When logIL-6 and logTNF- were included in the model (Table 6, model 2), as in boys, logIL-6 had the most significant association with logCRP and accounted for 27.7% of the variability in logCRP. BMI SD and logTG had additional effects (3.6 and 2.2%, respectively).
To determine the relationship between IL-6 and the other parameters listed in Table 4, we performed a stepwise multiple regression analysis with logIL-6 as the dependent variable and the other parameters as independent variables. BMI SD was most significantly associated with IL-6 and accounted for 14.0 and 15.4% of the variabilities in IL-6 in boys and girls, respectively (r2 = 0.140 and 0.154; P < 0.0001). TNF- and age in boys and TNF- in girls had additional effects (5.4% in boys and 9.2% in girls).
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Discussion
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In the present study, we have shown that: 1) boys with high serum concentrations of CRP have more atherogenic clinical and chemical profiles than other children (high levels of BMI SD, insulin, HOMA-R, LDL-C, apoB, uric acid, IL-6, and TNF-, and low levels of HDL-C, apoA-I, and adiponectin); 2) girls with high serum concentrations of CRP show high levels of BMI SD, insulin, HOMA-R, TC, TG, apoB, uric acid, and IL-6, and low levels of HDL-C; 3) IL-6 had the most significant association with serum concentrations of CRP in children; and 4) BMI SD in children was the most powerful predictor of serum IL-6 concentrations.
In adults, serum concentrations of CRP are increased in subjects with obesity, insulin resistance, hypertension, and/or metabolic syndrome (1, 2, 3, 7, 8, 14, 15). These conditions are all well-known risk factors for ACHD. Two recent studies have suggested that serum concentrations of CRP were significant predictors of ACHD even after adjusting for conventional risk factors for ACHD, including serum lipid levels, smoking status, and BMI (3, 14). To date, there have been several large-scale studies of CRP levels in schoolchildren (9, 10, 11). Cook et al. (9) reported that serum concentrations of CRP were associated with BMI, heart rate, systolic blood pressure, fibrinogen, and HDL-C, but not with other lipid parameters. Ford (11) showed that serum concentrations of CRP were associated with BMI, systolic blood pressure, and TG, but not with glycosylated hemoglobin or glucose. Wu et al. (10) reported that BMI, TG, and HDL-C were associated with serum concentrations of CRP in schoolchildren in Taiwan. A common finding among these reports is that BMI was the most powerful predictor of serum concentrations of CRP in schoolchildren. In contrast to our study, adiponectin, IL-6, TNF-, and uric acid were not determined in these previous reports. When we removed cytokines and uric acid from our statistical analysis, in agreement with previous reports, BMI SD was the most powerful predictor of CRP in our children. After being corrected for BMI SD, age, HOMA-R, TG, LDL-C, apoB, and adiponectin in boys and age, HOMA-R, and TG in girls were no longer correlated with CRP. When we added uric acid to the statistical analysis, it was correlated with CRP in both boys and girls. However, a significant correlation was only found in girls after being corrected for BMI SD. Based on a recent report, human vascular smooth muscle cells and human umbilical vein endothelial cells are also sources of CRP production (16). CRP mRNA expression in human vascular smooth muscle cells, and human umbilical vein endothelial cells and the release of CRP into cell culture medium were both up-regulated by uric acid (16). Although additional studies are needed, our data for girls suggest that vascular cell damage induced by uric acid may begin in childhood.
With respect to cytokines, IL-6 and TNF- themselves have been reported to be risk factors for ACHD and type 2 diabetes mellitus, even after adjusting for BMI (17, 18). To date, IL-6 and TNF- are believed to mediate the relationship between BMI and CRP in children, because IL-6 and TNF- are the main inducers of the hepatic production of CRP and are expressed in and secreted from adipose tissue (19, 20, 21). To the best of our knowledge, no previous epidemiological evidence is available on the relation between CRP and these cytokines in children. In the present study IL-6 was the most significant predictor of CRP in both boys and girls. TNF- was not a significant predictor of CRP in girls. BMI SD was the most powerful predictor of serum IL-6 in children. Mohamed-Ali et al. (22) reported that in humans, although IL-6 and TNF- were both expressed in sc adipose tissues, only IL-6 was released from sc adipose tissues. However, in adults, serum concentrations of these cytokines were closely related to obesity, particularly central obesity (21). These findings suggest that sc fat may be responsible for the production of IL-6 in children, and the accumulation of visceral fat may be less evident in girls than in boys.
In conclusion, although serum concentrations of CRP are partly regulated by adipocytokines and conventional risk factors for ACHD, high CRP levels were associated with atherogenic profiles of cardiovascular risk factors in children. IL-6 was the most powerful predictor of serum CRP in children. BMI SD in both boys and girls was the most significant predictor of IL-6. These findings suggest that it may be important to control body weight to prevent an increase in serum CRP in children.
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Footnotes
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Abbreviations: ACHD, Atherosclerotic coronary heart disease; apo, apolipoprotein; BMI, body mass index; CRP, C-reactive protein; HDL-C, high-density lipoprotein cholesterol; HOMA-R, homeostasis model approximation index; LDL-C, low-density lipoprotein cholesterol; TC, total cholesterol; TG, triglycerides.
This work was supported by Health Sciences Research Grants (Research on Specific Diseases) from the Ministry of Health, Labor, and Welfare and by a Grant-in-Aid for Scientific Research (B:17390303) from the Ministry of Education, Culture, Sports, Science, and Technology.
All authors (T.Y., T.K., T.S., M.S., and T.O.) have nothing to declare.
First Published Online March 28, 2006
Received January 3, 2006.
Accepted March 17, 2006.
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References
|
|---|
- Ross R 1999 Atherosclerosis: an inflammatory disease. N Engl J Med 340:115–126[Free Full Text]
- Libby P, Ridker PM 1999 Novel inflammatory markers of coronary risk. Circulation 100:1148–1150[Free Full Text]
- Pai JK, Pischon T, Ma J, Manson JE, Hankinson SE, Joshipura K, Curhan GC, Rifai N, Cannuscio CC, Stampfer MJ, Rimm EB 2004 Inflammatory markers and risk of coronary heart disease in men and women. N Engl J Med 351:2599–2610[Abstract/Free Full Text]
- Sternik L, Samee S, Schaff HV, Zehr KJ, Lerman LO, Holmes DR, Herrmann J, Lerman A 2002 C-Reactive protein relaxes human vessels in vitro. Arterioscler Thromb Vasc Biol 22:1865–1868[Abstract/Free Full Text]
- Blaschke F, Bruemmer D, Yin F, Takata Y, Wang W, Fishbein MC, Okura T, Higaki J, Graf K, Fleck E, Hsueh WA, Law RE 2004 C-Reactive protein induces apoptosis in human coronary vascular smooth muscle cells. Circulation 110:579–587[Abstract/Free Full Text]
- van den Berg CW, Taylor KE, Lang D 2004 C-Reactive protein-induced in vitro vasorelaxation is an artifact caused by the presence of sodium azide in commercial preparations. Arterioscler Thromb Vasc Biol 24:e168–e171
- Mendal MA, Patel P, Ballam L, Strachan D, Northfield TC 1996 C-Reactive protein and its relation to cardiovascular risk factors: a population-based cross-sectional study. Br Med J 312:1061–1065[Abstract/Free Full Text]
- Haverkate F, Thompson SG, Pyke SD, Gallimore JR, Pepys MB 1997 Production of C-reactive protein and risk of coronary events in stable and unstable angina. European Concerted Action on Thrombosis and Disabilities Angina Pectoris Study Group. Lancet 349:462–466[CrossRef][Medline]
- Cook DG, Mendall MA, Whincup PH, Carey IM, Ballam L, Morris JE, Miller GJ, Strachan DP 2000 C-Reactive protein concentration in children: relationship to adiposity and other cardiovascular risk factors. Atherosclerosis 149:139–150[CrossRef][Medline]
- Wu DM, Chu NF, Shen MH, Chang JB 2003 Plasma C-reactive protein levels and their relationship to anthropometric and lipid characteristics among children. J Clin Epidemiol 56:94–100[CrossRef][Medline]
- Ford ES 2003 C-Reactive protein concentration and cardiovascular disease risk factors in children. Findings from the national health and nutrition examination survey 1999–2000. Circulation 108:1053–1058[Abstract/Free Full Text]
- Ikeda T, Shibuya U, Sugiuchi H, Araki S, Uji Y, Okabe H 1991 Automated immunoturbidimetric analysis of six serum apolipoproteins: correlation with radial immunodiffusion assays. J Clin Lab Anal 5:90–95[Medline]
- Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC 1985 Homeostasis model assessment: insulin resistance and ß-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 28:412–419[CrossRef][Medline]
- Danesh J, Wheeler JG, Hirschfield GM, Eda S, Eiriksdottir G, Rumley A, Lowe GD, Pepys MB, Gudnason V 2004 C-Reactive protein and other circulating markers of inflammation in the prediction of coronary heart disease. N Engl J Med 350:1387–1397[Abstract/Free Full Text]
- Rutter MK, Meigs JB, Sullivan LM, D’Agostino RB, Wilson PWF 2004 C-Reactive protein, the metabolic syndrome, and prediction of cardiovascular events in the Framingham offspring study. Circulation 110:380–385[Abstract/Free Full Text]
- Kang DH, Park SK, Lee IK, Johnson RJ 2005 Uric acid-induced C-reactive protein expression: Implication on cell proliferation and nitric oxide production of human vascular cell. J Am Soc Nephrol 16:3553–3562[Abstract/Free Full Text]
- Mendall MA, Patel P, Asante M, Ballam L, Morris J, Strachan DP, Camm AJ, Northfield TC 1997 Relation of serum cytokine concentrations to cardiovascular risk factors and coronary heart disease. Heart 78:273–277[Abstract/Free Full Text]
- Pradhan A, Manson JE, Rifai N, Buring JE, Ridker PM 2001 C-Reactive protein, interleukin 6, and risk of developing type 2 diabetes mellitus. JAMA 286:327–334[Abstract/Free Full Text]
- Heinrich PC, Castell JV, Andus T 1990 Interleukin-6 and the acute phase response. Biochem J 265:621–636[Medline]
- Warren RS, Starnes HF, Gabrilove JL, Oettgen HF, Brennan MF 1987 The acute metabolic effects of tumor necrosis factor administration in humans. Arch Surg 122:1396–1400[Abstract/Free Full Text]
- Yudkin JS, Stehouwer CDA, Emeis JJ, Coppack SW 1999 C-Reactive protein in healthy subjects: associations with obesity, insulin resistance, and endothelial dysfunction. A potential role for cytokines originating from adipose tissues. Arterioscler Thromb Vasc Biol 19:972–978[Abstract/Free Full Text]
- Mohamed-Ali V, Goodrick S, Rawesh A, Katz DR, Miles JM, Yudkin JS, Kein S, Coppack SW 1997 Subcutaneous adipose tissue releases interleukin-6, but not tumor necrosis factor-, in vivo. J Clin Endocrinol Metab 82:4196–4200[Abstract/Free Full Text]
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Abstract
Introduction
