Association of IL-6 and CRP gene polymorphisms with obesity and metabolic disorders in children and adolescents

Pâmela F. Todendi Elisa I. Klinger Michele B. Ferreira Cézane P. Reuter Miria S. Burgos Lia G. Possuelo Andréia R.M. Valim About the authors

Abstracts

Activation of adipose tissue inflammation is associated with obesity caused by lipid accumulation in adipocytes. Through this activation, proinflammatory cytokines, such as Interleukin-6 (IL-6) and C-reactive protein (CRP) seem to influence metabolic disorders. The present study evaluated whether polymorphisms in the CRP (rs1205) and IL-6 (rs1800795, rs2069845) genes are associated with the development of metabolic disorders in children and adolescents. A cross-sectional study was performed, consisting of 470 students from the municipality of Santa Cruz do Sul, Brazil, aged 7-17 years. Body mass index (BMI) was classified according to overweight and obesity. Genotyping was performed by real-time Polymerase Chain Reaction(PCR). Anthropometric characteristics, biochemical markers, immunological markers and blood pressure were assessed. Descriptive statistics, chi-square and logistic regression were used for the analyses. No association was detected between the rs1800795 polymorphism and the assessed variables. Individuals with the risk genotype in the rs1205 gene were associated with the risk of developing hypercholesterolemia (OR 2.79; CI 1.40, 5.57; p = 0.003). Carriers of the risk genotype in the rs2069845 gene are associated with the risk of developing obesity (OR 3.07; CI 1.08, 8.72; p = 0.03). The polymorphism rs2069845 was associated with obesity and rs1205 was associated with the risk of developing hypercholesterolemia in Brazilian schoolchildren.

Inflammation; obesity; polymorphisms; risk; schoolchildren


A ativação da inflamação do tecido adiposo está relacionada com a obesidade, causada pelo acúmulo de lipídios nos adipócitos. Através dessa ativação, citocinas pró-inflamatórias como Interleucina-6 (IL-6) e Proteína C-Reativa (CRP) parecem influenciar as desordens metabólicas. O presente estudo avaliou se polimorfis mos nos genes da CRP (rs1205) e da IL-6(rs1800795 rs2069845) estão relacionados com o desenvolvimento de alterações metabólicas em crianças e adolescentes. Estudo transversal, foi feito com 470 escolares do município de Santa Cruz do Sul, Brasil, com idades entre 7 a 17 anos. O índice de massa corporal (IMC) foi classificado de acordo com sobrepeso e obesidade. A genotipagem foi realizada através da Reação em Cadeia de Polimerase (PCR) em tempo real. Características antropométricas, indicadores bioquímicos, marcadores imunológicos e a pressão arterial foram avaliados. Estatísticas descritivas, qui-quadrado e regressão logística foram utilizadas para as análises. Nenhuma associação foi detectada entre o polimorfismo rs1800795 e as variáveis avaliadas. Indivíduos com o genótipo de risco no gene rs1205 foram associados ao risco de desenvolver hipercolesterolemia (OR = 2,79; IC: 1,40, 5,57; p = 0,003). Portadores do genótipo de risco no gene rs2069845 estão associados com o risco de desenvolver obesidade (OR = 3,07; IC: 1,08, 8,72; p = 0,03). O polimorfismo rs2069845 foi relacionado com obesidade e o rs1205 associado ao risco de desen volver hipercolesterolemia em escolares brasileiros.

Inflamação; obesidade; polimorfismos; risco; escolares


INTRODUCTION

The increase in size and number of adipose cells is associated with obesity, which leads to metabolic disorders (Greenberg and Obin 2006GREENBERG AS and OBIN MS. 2006. Obesity and the role of adipose tissue in inflammation and metabolism. Am J Clin Nutr 83(2): 461S-465S.). Childhood obesity that persists into adolescence results in physiological and pathological effects that increase morbidity and mortality in adulthood (Bastien et al. 2014BASTIEN M, POIRIER P, LEMIEUX I and DESPRÉS JP. 2014. Overview of epidemiology and contribution of obesity to cardiovascular disease. Prog Cardiovasc Dis 56(4): 369-381., Nickelson et al. 2014NICKELSON J, LAWRENCE JC, PARTON JM, KNOWLDEN AP and MCDERMOTT RJ. 2014. What proportion of preschool-aged children consume sweetened beverages? J Sch Health 84(3): 185-194., Raj 2012RAJ M. 2012. Obesity and cardiovascular risk in children and adolescents. Indian J Endocrinol Metab 16(1): 13-19., Rodrigues et al. 2011RODRIGUES PA, MARQUES MH, CHAVES MGAM, SOUZA CF and CARVALHO MF. 2011. Prevalência e fatores associados a sobrepeso em escolares da rede pública. Ciênc & Saúde Coletiva 16: 1581-1588.) and is considered an early risk factor associated with hypertension, type 2 diabetes mellitus (DM2) (Alderete et al. 2014ALDERETE TL, TOLEDO-CORRAL CM and GORAN MI. 2014. Metabolic basis of ethnic diferences in diabetes risk in overweight and obese youth. Curr Diab Rep 14(2): 455., Kaneko et al. 2011KANEKO K, KIMATA T, TSUJI S, SHIRAISHI K, YAMAUCHI K, MURAKAMI M and KITAGAWA T. 2011. Impact of obesity on childhood kidney. Pediatr Rep 3(4): e27, 108-110.), heart disease, atherosclerosis (Baker et al. 2007BAKER JL, OLSEN LW and SORENSEN TI. 2007. Childhood body-mass index and the risk of coronary heart disease in adulthood. N Engl J Med 357(23): 2329-2337.), osteoarthritis, some types of cancer (Abrantes et al. 2002ABRANTES M, LAMOUNIER JA and COLOSIMO EA. 2002. Prevalência de sobrepeso e obesidade em crianças e adolescentes das regiões Sudeste e Nordeste. J Pediatr 78(4): 335-340.), non-alcoholic fatty liver disease, infertility and psychiatric diseases (Kelsey et al. 2014KELSEY MM, ZAEPFEL A, BJORNSTAD P and NADEAU KJ. 2014. Age-Related Consequences of Childhood Obesity. Gerontology 60(3): 222-228.). Considering that the risk factors of obesity are multifactorial, the identification of these risks is crucial to prevent the epidemic of childhood obesity (Dev et al. 2013DEV DA, MCBRIDE BA, FIESE BH, BLAKE LJ and CHO H. 2013. Risk Factors for Overweight/Obesity in Preschool Children: An Ecological Approach. Child Obes 9(5): 399-408.).

Obesity has been associated with chronic low-grade inflammation (Carolan et al. 2014CAROLAN E, HOGAN AE, CORRIGAN M, GAOTSWE G, O`CONNELL J, FOLEY N, O´NEILL LA, CODY D and O´SHEA D. 2014. The impact of childhood obesity on inflammation, innate immune cell frequency and metabolic microRNA expression. J Clin Endocrinol Metab 99(3): E474-478.), triggered by white adipose tissue (WAT), which was previously considered as a passive fat depot (Roth et al. 2011ROTH CL, KRATZ M, RALSTON MM and REINEHR T. 2011. Changes in adipose-derived inflammatory cytokines and chemokines after successful lifestyle intervention in obese children. Metabolism 60(4): 445-452.). However, recent data has shown that the WAT is an active factor in the metabolism linked to the production of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF- α), interleukins (IL-1 and IL-6) and C-reactive Protein (CRP) (Petersen and Pedersen 2005PETERSEN AM and PEDERSEN BK. 2005. The anti-inflammatory effect of exercise. J Appl Physiol (1985) 98(4): 1154-1162., Genest 2010GENEST J. 2010. C-reactive protein: Risk factor, biomarker and/or therapeutic target? Can J Cardiol 26(2010): 41a-44a., Roth et al. 2011, Shi et al. 2014SHI C et al. 2014. IL-6 and TNF-α Induced Obesity-Related Inflammatory Response Through Transcriptional Regulation of miR-146b. J Interferon Cytokine Res 34(5): 342-348.). Together with adipocytes, endothelial cells, fibroblasts and immune cells located in adipose tissue, can all contribute to inflammatory cytokine secretion (Roth et al. 2011). Studies on genes encoding different cytokines have shown the presence of several single-nucleotide polymorphisms (SNPs), which may be useful in studies of allele and genotype frequencies in different populations (Mendoza-Carrera et al. 2010MENDOZA-CARRERA F, RAMÍREZ-LÓPEZ G, AYALA-MARTÍNEZ NA, GARCÍA-ZAPIÉN AG, FLORES-MARTÍNEZ SE and SÁNCHEZ-CORONA J. 2010. Influence of CRP, IL6 and TNFA gene polymorphisms on circulating levels of C-reactive protein in Mexican adolescents. Arch Med Res 41(6): 472-477., Corpeleijn et al. 2010CORPELEIJN E et al. 2010. Obesity-related polymorphisms and their associations with the ability to regulate fat oxidation in obese Europens: the NUGENOB study. Obesity (Silver Spring). 18(7): 1369-1377., Franceschi et al. 2009FRANCESCHI DAS, VIEL DO, SELL AM, TSUNETO LT and VISENTAINER JEL. 2009. Otimização de metodologia PCR-SSP para identificação de polimorfismos genéticos de TNF e IL2. Rev Bras Hematol Hemoter 31(4): 241-246., Tabassum et al. 2012TABASSUM R, MAHENDRAN Y, DWIVEDI OP, CHAUHAN G, GHOSH S, MARWAHA RK, TANDON N and BHARADWAJ D. 2012. Variants of IL6, LEPR, and PBEF1 Are Associated With Obesity in Indian Children. Diabetes 61(3): 626-631.).

The available evidence suggests that variations in the metabolic modulation ofCRP and IL-6 genes may play a relevant role in the etiology of metabolic disorders related to obesity. Based on this assumption, the present study evaluated whether the gene polymorphisms IL-6rs1800795, IL-6 rs2069845 and CRP rs1205 are related to the development of metabolic abnormalities and obesity in children and adolescents in southern Brazil.

MATERIALS AND METHODS

STUDY SUBJECTS AND DESIGN

A retrospective, cross-sectional study consisting of 470 children (aged 7-9 years) and adolescents (aged 10-17 years), 54% girls, from five schools in the municipality of Santa Cruz do Sul, state of Rio Grande do Sul, Brazil. This study is part of a larger project, whose sample size was calculated according to the formula of the Division of Research Nea (Christensen 1980CHRISTENSEN LB. 1980. Experimental methodology. 2nd ed., Boston: Allyn/Bacon 14(3).) of which a population of 20,540 from the public and private education system in Santa Cruz do Sul-RS, were considered. 470 students were selected as a convenience sample in this preliminary sampling. The population of this research is predominantly of Germanic origin (Filho and Monasterio 2012FILHO IC and MONASTERIO LM. 2012. Immigration and the Origins of Regional Inequality: Government-Sponsored European Migration to Southern Brazil Before World War I. Reg Sci Urban Econ 42(5): 794-807.). All study participants reported their free participation in the study by having the free and informed consent form signed by their parents or guardians. This study was reviewed by the Research Ethics Committee of the Universidade Santa Cruz do Sul, under protocol number 120.090/2012.

Anthropometric measurements were performed using the Body Mass Index (BMI), based on the curves of percentiles from the Centers for Disease Control and Prevention/National Center for Health Statistics (CDC/NCHS 2000NATIONAL INSTITUTES OF HEALTH: International HapMap Project. Disponível em: http://www.ncbi.nlm.nih.gov [acesso em 12 de dezembro de 2012].
http://www.ncbi.nlm.nih.gov...
), according to gender and age, considering underweight ( < p5 ), normal weight ( ≥ p5 and < p85 ), overweight ( p ≥ 85 and < p95) and obesity ( ≥ p95). Waist Circumference (WC) was measured with an inelastic tape, using as reference the narrowest part of the trunk between the ribs and the iliac crest and hip at the greater trochanter level and, subsequently, classified according to the criteria established by Taylor et al. (2000)TAYLOR RW, JONES IE, WILLIANS SM and GOULDING A. 2000. Evaluation of waist circumference, waist-to-hip ratio, and the conicity index as screening tools for high trunk fat mass, as measured by dual-energy X-ray absorptiometry, in children aged 3-19 y. Am J Clin Nutr 72: 490-495.according to gender and age, which considers as a normal circumference a percentile ≤ 80 and obesity a percentile > 80. The percentage of body fat (%BF) was calculated using the equation of Slaughter et al. (1988)SLAUGHTER MH, LOHMAN TG, BOILEAU RA, HORSWILL RJ, STILLMAN MN, VANLOAN MD and BEMBEN DA. 1988. Skinfold Equations for Estimation of Body Fatness in Children and Youth. Hum Biol 60(5): 709-723. and subsequently classified according to Lonman's data (1987), cited by Heyward and Stolarczyk (2000)HEYWARD VH and STOLARCZYK LM. 2000. Avaliação da composição corporal aplicada. São Paulo: Manole, 241 p., into two categories: 1) very low, low and optimal; and 2) moderately high, high and very high.

Blood pressure (BP) was assessed according to the parameters established at the VI Brazilian Guidelines on Hypertension (SBC 2010SBC - Sociedade Brasileira de Cardiologia / Sociedade Brasileira de Hipertensão/Sociedade Brasileira de Nefrologia. 2010. VI Diretrizes Brasileiras de Hipertensão. Arq Bras Cardiol 95(1): 1-51.), using the auscultatory method and previously calibrated aneroid devices consisting of three cuffs of different sizes, making it possible to consider the width/length ratio of 1:2 for each arm circumference. Values below the 90th percentile were considered normotensive, as long as they were < 120/80 mmHg; between percentiles 90-95th, they were considered borderline; and ≥ 95th percentile, as arterial hypertension; it is noteworthy that any value ≥ 120/80 mmHg in adolescents, even if below the 95th percentile, was considered borderline.

LABORATORY ANALYSES

Blood was collected after at least 12 hours of fasting by venipuncture. Blood samples (10 mL) were separated into aliquots and then stored in a freezer at -20°C.

Measurements of total cholesterol (TC), HDL-C cholesterol, triglycerides (TG) and glucose were performed using Kovalent commercial kits (Kovalent do Brazil Ltda) and CRP was measured using DiaSys kits (DiaSys Diagnostic Systems, Germany), in Miura One equipment (ISE, Rome, Italy). For TC, LDL-C cholesterol and TG, values ​​were classified as: acceptable, borderline and high; for HDL-C, as acceptable, borderline and low (NHLBI 2012NHLBI - National Heart, Lung, and Blood Institute. 2012. NHLBI Expert panel on integrated guidelines for cardiovascular health and risk reduction in children and adolescents. NHI publicação no. 12-7486A. Disponível em: http://www.nhlbi.nih.gov/guidelines/cvd_ped/peds_guidelines_sum.pdf [acesso em 12 de maio de 2013].
http://www.nhlbi.nih.gov/guidelines/cvd_...
). LDL-C cholesterol was calculated using the Friedewald et al. equation (1972)FRIEDEWALD WT, LEVY RI and FREDRICKSON DS. 1972. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem 18: 499-502.. Glucose was considered normal at < 100 mg/dL and as pre-diabetes with levels from 100 mg/dL to 125 mg/dL (ADA 2011ADA - American Diabetes Association. 2011. Diagnosis and classification of diabetes mellitus. Diabetes Care 34(1): S62-69.). CRP levels were considered as low, medium and high, with values corresponding to < 1.0; 1.0 to 3.0 and > 3.0 mg/L, respectively (Shine et al. 1981SHINE B, DE BEER FC and PEPYS MB. 1981. Solid phase radioimmunoassays for human C-reactive protein. Clin Chim Acta 117(1): 13-23., Pearson et al. 2003PEARSON TA et al. 2003. Markers of inflammation and cardiovascular disease: application to clinical and public health practice: a statement for healthcare professionals from the Centers for Disease Control and Prevention and the American Heart Association. Circulation 107: 499-511.) and subsequently reclassified as normal and high.

Serum CRP levels were measured using a high-sensitivity assay. Students with CRP levels > 10 mg/L were excluded from the study, as they suggested an acute inflammatory process (Pearson et al. 2003).

GENOTYPING

DNA extraction was carried out in whole blood anticoagulated with EDTA, using the Salting out method described by Miller et al. (1988)MILLER SA, DYKES DD and POLESKY HF. 1988. A simple salting out procedure for extracting DNA from human nucleated cells. Nucleic Acids Res 16(3): 1215.. DNA quantification was carried out in the NanoDrop 2000c Spestrophotometer equipment (ThermoScientific, Wilmington, USA).

IL-6 rs1800795, IL-6 rs2069845 andCRP rs1205 polymorphisms were genotyped and the choice of these genes occurred after searching the literature and evaluating allele frequency in the National Institutes of Health: International HapMap Project (http://www.ncbi.nlm.nih.gov), considering that the study population is predominantly of German origin (Filho and Monasterio 2012). The technique used for genotyping was real-time PCR in StepOne Plus(r) equipment (Applied Biosystems, Foster City, CA, USA) according to the manufacturer's instructions, using allelic discrimination assays. Probes TaqManTM rs1205, rs2069845, rs1800795 (customized assay) and Master Mix PCR Universal were purchased from Applied Biosystems (Foster City, CA, USA). Genotyping was performed in duplicate, with an accuracy of 100%.

STATISTICAL ANALYSES

Descriptive analysis based on the mean and standard deviation was used to specify the subjects' characteristics. Bivariate and multivariate logistic regression analyses were performed to estimate odds ratios between polymorphisms rs1800795, rs2069845 and rs1205 and anthropometric characteristics, biochemical markers and blood pressure levels of the subjects. The Hardy-Weinberg equilibrium (HWE) was analyzed for all polymorphisms and the p value was calculated by the chi-square test. The statistical analysis of the data was carried out using SPSS 20.0 software (IBM, Chicago, USA). P values < 0.05 were considered significant.

RESULTS

PATIENTS CHARACTERISTICS

Descriptive characteristics of the 470 students, as well as the allele and genotype frequencies for the IL-6 and CRP genes can be seen on Table I. Among the selected sample subjects, it was observed that the overall mean age was 13.13 (± 2.99 years), 15.3% were overweight and 9.8% were classified as obese. Visceral fat, measured by WC was elevated in 13.2% of the students and 37% were classified as having moderately high, high and very high %BF. Laboratory analysis showed that 21% had elevated TC, 35% had altered LDL-C, 20% were classified as having pre-diabetes or altered glucose levels and 12% had high CRP levels. The genotypic proportions observed were in Hardy-Weinberg equilibrium (data not shown) for the three analyzed polymorphisms. The observed allelic frequencies for the polymorphisms were 32.8% for rs1800795/C, 36.8% for rs2069845/G and 39% for rs1205/T (Table II).

Table 1.
Descriptive characteristics of the subjects.
Table 2.
Descriptive allele and genotype frequencies.

ASSOCIATION AMONG CLINICAL FACTORS AND GENOTYPES

The bivariate logistic regression analysis (Table III) showed that individuals with the risk genotype rs1205CRP gene have a greater association with the risk of developing hypercholesterolemia (OR = 2.12; 95% CI: 1.28, 3.51, p = 0.003), after performing multivariate logistic regression analysis it was noted that subjects with the risk genotype rs1205 in the CRP gene had a risk factor for developing hypercholesterolemia (OR = 2.79; 95% CI: 1.40, 5.57;p = 0.003) and the risk genotype rs2069845 in theIL-6 gene showed an association with the risk of developing obesity (OR = 3.07; 95% CI: 1.08, 8.72; p = 0.03) in Brazilian children and adolescents. The rs1800795 polymorphism indicated no significant association in the analyzed model.

Table 3.
Association of IL-6 polymorphisms and CRP with anthropometric measurements, biochemical markers and blood pressure in individuals with altered variables.

DISCUSSION

According to the inflammatory markers related to the risk of developing metabolic disorders in healthy individuals, we assessed the effect of polymorphisms rs2069845 (IL-6), rs1800795 (IL-6) and rs1205 (CRP) as they are associated with obesity and metabolic disorders in children and adolescents (Feng et al. 2003FENG N, ADLER-WAILES D, ELBERG J, CHIN JY, FALLON E, CARR A, FRAZER T and YANOVSKI JA. 2003. Sequence variants of the POMC gene and their associations with body composition in children. Obes Res 11: 619-624., Kolz et al. 2008KOLZ M et al. 2008. DNA variants, plasma levels and variability of C-reactive protein in myocardial infarction survivors: results from the AIRGENE study. Eur Heart J 29(10): 1250-1258., Tabassum et al. 2012). Increasing evidence suggests that polymorphisms associated with low-grade inflammation may be a determining factor for metabolic complications commonly associated with obesity (Roth et al. 2011, Shoelson et al. 2006SHOELSON ES, LEE J and GOLDFINE BA. 2006. Inflammation and insulin resistance. J Clin Invest 116(7): 1793-1801., Wexler et al. 2005WEXLER DJ, HU FB, MANSON JE, RIFAI N and MEIGS JB. 2005. Mediating effects of inflammatory biomarkers on insulin resistance associated with obesity. Obes Res 13(10): 1772-1783., Yudkin et al. 2004YUDKIN JS et al. 2004. Low-grade inflammation may play a role in the etiology of the metabolic syndrome in patients with coronary heart disease: the HIFMECH study. Metabolism 53(7): 852-857., Tabassum et al. 2012).

The study observed that carriers of the risk genotype rs1205 in theCRP gene were associated with hypercholesterolemia (Table III). Hu et al. (2010)HU M, LEE MH, MAK VW and TOMLINSON B. 2010. Effect of central obesity, low high-density lipoprotein cholesterol and C-reactive protein polymorphisms on C-reactive protein levels during treatment with Rosuvastatin (10 mg Daily). Am J Cardiol 106(11): 1588-1593. also showed associations between the rs1205 polymorphism and waist circumference, diabetes, TG and HDL-C in Chinese adult individuals; however, there was no association between this polymorphism and the parameters established for obesity. A study carried out in six European cities (Athens, Rome, Barcelona, Augsburg, Stockholm and Helsinki) with adult subjects showed that rs1205 was associated with lower serum concentrations of CRP. Regarding the clinical covariates, BMI and total cholesterol were associated with higher CRP values.

A dose-dependent effect is suggested for rs1205, which is located in the 3'UTR flanking region, considered a region possibly controlled by RNA cleavage and intracellular stability, export and localization (Kolz et al. 2008). In a study with 448 Mexican adolescents, the analysis of metabolic traits was performed, in which the rs1205 CRP gene showed no significant association with TG, but was associated with HOMA and fasting glucose; however the statistical significance did not persist after correction for multiple tests (Duran-Gonzalez et al. 2011DURAN-GONZALEZ J et al. 2011. Association Study of Candidate Gene Polymorphisms and Obesity in a Young Mexican-American Population from South Texas. Arch Med Res 42(6): 523-531.).

In Table III, comparisons showed that being a carrier of the rs2069845 risk variant increased by 3.07-fold the chance of developing obesity (p <0.05). IL-6 is a physiological regulator that has several functions in different organs, including the central nervous system, cardiovascular, immune and hepatic systems, among others; its dysregulation affects several pathological conditions (Hong et al. 2007HONG DS, ANGELO LS and KURZROCK R. 2007. Interleukin-6 and its receptor in cancer: implications for translational therapeutics. Cancer 110(9): 1911-1928., Guimarães et al. 2007).

The presence of high concentrations of IL-6 is related to inflammation, whereas polymorphisms such as rs1800795 and rs2069845 are associated with obesity and other diseases such as insulin resistance, metabolic syndrome and type 2 diabetes mellitus (Mendoza-Carrera et al. 2010, Corpeleijn et al. 2010, Steemburgo et al. 2009STEEMBURGO T, AZEVEDO MJ and MARTÍNEZ JA. 2009. Gene-nutrient interaction and its association with obesity and diabetes mellitus. Arq Bras Endocrinol Metabol 53(5): 497-508., Tabassum et al. 2012). In a study carried out in India with children and adolescents aged 11 to 17 years, theIL-6 polymorphism rs2069845 had its risk allele associated with overweight/obesity, whereas in this same study IL-6 polymorphism rs1800795 was not associated with overweight/obesity (Tabassum et al. 2012). In recent years, the results of genetic variation between diet and chronic diseases have been studied and the presence of several IL-6 polymorphisms constitutes a major role in the obesity phenotypes (Steemburgo et al. 2009).

Associations between the IL-6 rs1800795 gene and biochemical markers, blood pressure and anthropometric characteristics were not significant in our study. However, some studies show that carriers of the C allele for theIL-6 polymorphism rs1800795 have higher BMI, IL-6, CRP, insulin resistance and lipoprotein levels, identified in children, adolescents and adults (Eklund et al. 2006EKLUND C, NENONEN A, KUKKONEN-HARJULA K, BORG P, FOGELHOLM M, LAINE S, HUHTALA H, LEHTIMÄKI T and HURME M. 2006. Association of the IL6-174(G/C) polymorphism with C-reactive protein concentration after weight loss in obese men. Eur Cytokine Netw 17(2): 131-135., Goyenechea et al. 2006GOYENECHEA E, PARRA MD and MARTÍNEZ JA. 2006. Weight regain after slimming induced by an energy-restricted diet depends on interleukin-6 and peroxisome-proliferator-activated-receptor-γ2 gene polymorphisms. Br J of Nutr 96(5): 965-972., Jones et al. 2001JONES AB. 2001. Peroxisome proliferator-activated receptor (PPAR) modulators: Diabetes and beyond. Med Res Rev 21(6): 540-552.).

A study carried out in London with 571 Caucasian adults found that 76% of CC carriers had metabolic syndrome (MS), when compared to 56% of individuals with GG genotype; consonant with that, the C allele frequency was significantly higher in individuals with MS, when compared to those without the syndrome (Stephens et al. 2007STEPHENS JW, HUREL SJ, LOWE G, RUMLEY A and HUMPHRIES SE. 2007. Association between plasma IL-6, the IL6 -174G>C gene variant and the metabolic syndrome in type 2 diabetes mellitus. Mol Genet Metab 90(4): 422-428.). In disagreement with these observations, other studies indicate that the G allele has been associated with increased IL-6 secretion, lipid disorders (Fernández-Real et al. 2000), insulin resistance and diabetes (Hamid et al. 2005HAMID YH, ROSE CS, URHAMMER SA, GLÜMER C, NOLSOE R, KRISTIANSEN OP, MANDRUP-POULSEN T, BORCH-JOHNSEN K, JORGENSEN T, HANSEN T and PEDERSEN O. 2005. Variations of the interleukin-6 promoter are associated with features of the metabolic syndrome in Caucasian Danes. Diabetologia 48(2): 251-260.). The present study did not evaluate insulin.

The allelic frequencies of SNPs analyzed in this study (Table II) are mostly similar to those found in previous publications with Caucasian populations (Dedoussis et al. 2004DEDOUSSIS GVZ, MANIOS Y, CHOUMERIANOU DM, YIANNAKOURIS N, PANAGIOTAKOS DB, SKENDERI K and ZAMPELAS A. 2004. The IL-6 Gene G-174C Polymorphism Related to Health Indices in Greek Primary School Children. Obes Res 12: 1037-1041., Duran-Gonzalez et al. 2011, Ljungman et al. 2009LJUNGMAN P et al. 2009. Modification of the Interleukin-6 Response to Air Pollution by Interleukin-6 and Fibrinogen Polymorphisms. Environ Health Perspect 117(9): 1373-1379., Goyenechea et al. 2007, Sousa et al. 2012SOUSA AL, FAVA VM, SAMPAIO LH, MARTELLI CM, COSTA MB, MIRA MT and STEFANI MM. 2012. Genetic and immunological evidence implicates interleukin 6 as a susceptibility gene for leprosy type 2 reaction. J Infect Dis 205(9): 1417-1424.), showing a frequency distribution similar to the one of this present study.

Regarding the anthropometric and clinical characteristics of the subjects evaluated in the study, it was observed that 25.3% of the study subjects were overweight or obese and 13.2% had elevated WC (Table I). In a previous study of this population, the prevalence of overweight and obesity was 25.3% among boys and 25.6% among girls, whereas 19% had elevated WC (Reuter et al. 2013REUTER CP, BURGOS LT, CAMARGO MD, POSSUELO LG, RECKZIEGEL MB, REUTER ÉM, MEINHARDT FP and BURGOS MS. 2013. Prevalence of obesity and cardiovascular risk among children and adolescents in the municipality of Santa Cruz do Sul, Rio Grande do Sul. São Paulo Med J 131(5): 323-330.).

In this study, obese individuals showed significant values ​when compared withIL-6 risk genotypes rs2069845, whereas in relation to otherCRP (rs1205) and IL-6 (rs1800795) polymorphisms, this association was not significant. An explanation for this fact might be the sample size, even though they are representative for the studied population. The analysis also showed that having the risk genotype for theCRP rs1205 gene is associated with hypercholesterolemia and thus, we suggest further studies of CRP polymorphisms in our population, as it is believed that CRP levels add prognostic value to the lipid parameters, being able to identify subjects at risk for future cardiovascular events.

The results suggest that the risk genotype of CRP rs1205 gene is associated with the deve lopment of hypercholesterolemia and the risk genotype ofIL-6 rs2069845 gene is associated with the development of obesity in Brazilian children and adolescents. No association was found betweenIL-6 rs1800795 polymorphism and the anthropometric parameters, blood pressure levels and biochemical markers assessed in the study.

We emphasize the importance of studies capable of identifying the influence of a particular gene on a phenotype in a certain population with different eating habits and lifestyles that can supposedly affect this phenotype. All students received their biochemical profile analysis after their participation in the study and those with abnormal results were referred for appropriate treatment.

We also suggest future studies to demon strate the association of inflammatory markers and comorbidities related to obesity in childhood and adolescence, as well as investigate other variations in the studied genes and other polymorphisms associated with metabolic disor ders in the Brazilian population, aiming at clarifying issues that may lead to an inflammatory-metabolic imbalance and possibly, to future health complications.

ACKNOWLEDGMENTS

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS). We declare that the experiments comply with current Brazilian legislation. The authors declare no actual or potential financial interest.

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Publication Dates

  • Publication in this collection
    15 May 2015
  • Date of issue
    Apr-Jun 2015

History

  • Received
    15 July 2014
  • Accepted
    25 Nov 2014
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