The Relationship Between Insulin Resistance And Body Fat, Serum Lipid,Resistin And Interleukin-6in Obese Children

BackgroundObesity is a kind of aeipathia, that is, a condition where the body’s energy input exceeds its consumption, the redundant energy being stored in tissues as fat, consequently leading to excessive internal fat and supranormal body mass. Obesity have been becoming increasingly prevalent around the world,the tendency for the young to be inflicted by such diseases has clearly been increasing. The worldwide prevalence of obese and overweight preschool children increased from4.2%in1990to6.7%in2010. There has been an increase in the rates of obesity in children in China. In2000, the obesity rates of7to22-year-old urban boys, rural boys, urban girls and rural girls were4.37%,1.46%,2.32%and0.92%respectively. In2010,the obesity rates had increased to13.33%,5.64%,7.83%and3.78%, respectively. Ninety-five percent of cases of childhood obesity were simple obesity, caused by some kind of lifestyle factor, such as hyperphagia, personal lifestyle, physical inactivity,etc..Childhood obesity not only affects growth and development, but also closely relates to the incidence of adulthood metabolic syndrome (MS) or called insulin resistance syndrome(IRS). It is not only a manifestation of metabolic syndrome, but has great importance in the development of metabolic syndrome. NAFLD refers to certain varieties of liver damage caused by blood-lipid disorders, which have recently been considered to be amongst the symptoms of MS in liver, where insulin resistance (IR) forms the pathological basis of MS.For a long time the diagnostic criteria for childhood overweight and obesity in China was based on the median weight value for the same age, same sex or same sex height to weight ratio. Children with greater than20%of these median values were classified as obese. In1995, the World Health Organization (WHO) suggested the use of different diagnostic criteria for different ages of children and adolescents i.e. body mass index (BMI, kg/m2) for adolescents aged10-19; the Z score of height to weight for children under the age of10. The International Obesity Task Force(IOTF) suggested the use of BMI as global criteria for childhood overweight and obesity.In2003, The Working Group on Obesity in China (WGOC) formulated the normal children’s BMI value and its percentile. The WGOC suggested p85and p95as criteria for childhood overweight and obesity for those aged7-18. In2010, Li Hui etc. suggested the use of new criteria for overweight and obesity for children aged2to18, which was concordant with the adulthood overweight and obesity screening BMI cut off point. It had been already confirmed that BMI, waist circumference(WC), waist to hip ratio(WHR), waist to height ratio(WHtR) and subcutaneous fat thickness were reliable indices to measure body fat.Insulin Resistance is defined as an impaired ability for normal insulin in the blood to effectively promote peripheral glucose uptake, inhibit hepatic glucose output and inhibit very low density lipoprotein (VLDL) output. It is determined by insulin and glucose level tests, the commonest method using the homeostasis model assessment (HOMA)-IR index. It has already been confirmed that obese children exhibit the phenomenon of IR,which manifests mainly as hyperinsulinemia. As the study on IR has progressed further and further, the exploration of obesity and IR-related factors have become of great concern. Current research has proposed a new concept where in adipose tissue is an endocrine organ, and adipocytes are the key that relates type2diabetes mellitus (T2DM) and IR to obesity. Adipocytes secrete various substances such as resistin and IL-6, etc., which can cause peripheral tissues to develop IR.Resistin was first reported by Steppan et al in2001as a new polypeptide hormone secreted by adipose tissue. It is a protein with a relative molecular mass of12500, which is approximately composed of114amino acids and usually exists as a dimer, whose physiological effect is currently not completely clear. The human resistin gene coding sequence is on the19th chromosome. Giving mice intraperitoneal injections of resistin increased their blood glucose levels, while insulin levels displayed no significant change.The subsequent administration of resistin antibody injections caused insulin resistance where-in the blood glucose levels of the model mice recovered to the level before experiment. Furthermore, insulin sensitivity was significantly raised, suggesting resistin had the effect of causing IR. Some held the view that resistin was a type of hormone that connected obesity and IR. However, several experiments followed that found that there was no difference between the expressions of resistin in normal humans and IR or type2diabetes mellitus (T2DM) patients. At home and abroad currently, the study on resistin has only been limited to animal experiments, in-vitro experiments and genetics, while no large clinical studies have been performed. Therefore, whether human resistin is related to IR, the resistin signal transduction mechanism and its precise effect on metabolism are all the focus of current research.IL-6is a kind of multiple-effect cytokine.Adipose tissue is considered the main secretary tissue of IL-6, and adipocytes produce more IL-6with an increase in the degree of obesity. Plasma IL-6levels were raised in obese patients, however, the level declined after they lost weight. The plasma IL-6level was obviously related to IR, positively related to weight, BMI and body fat, but negatively related to insulin sensitivity. It was considered that plasma IL-6levels and the amount of IL-6secreted by adipocytes was closely related to obesity, IR and T2DM, and that IL-6was the main factor involved in the pathogenesis of IR.The Human IL-6gene is located on chromosome7p15-21, and its length is5kb with5extons and4introns, whose promoter region-174G/C gene polymorphism was found to be related to IR. Studies found that the distributions of the loci of IL-6genes and allelic gene frequencies vary considerably between races, and were related to age, sex and weight. However, currently our country has a lack of data on the relationship between childhood obesity and IL-6, especially with regards to IL-6gene polymorphism.ObjectiveTo observe IR, BMI, WC, WHR, WHtR, serum lipid concentration, resistin, IL-6concentration and gene polymorphism of IL-6-174G/C in children with simple obesity, to analyse their multiple correlations, and investigate the relationship between IR and the other indices. At the same time obese children with NAFLD were analysed, to investigate the relationship between NAFLD and IR, body fat and serum lipid concentration.MethodNinety children suffering from simple obesity were selected, who had seen a doctor between January,2010and December,2011at the pediatric endocrine clinic of Shenzhen Maternal and Child Health care Hospital. Among them were56boys and34girls aged2.5-14.3yrs, averaging (8.3±3.0) years old. They had undergone a physical, abdominal ultrasound and endocrine, hepatic, renal function examinations. Secondary obesity caused by other endocrine diseases, hereditary metabolic disease and central nervous system disease were excluded. Their height was in the normal range for the same age and sex. The obesity diagnostic criteria used was the Chinese2-18-year-old children overweight and obesity screening body mass index(BMI) cut off point method, which was concordant with the adulthood overweight and obesity screening BMI cut off point. Among the selected cases,45were chosen to test resistin, IL-6and its-174gene polymorphism,included25boys and20girls, aged2.5-14.3yrs, averaging (7.2±2.8) years old.According to Chinese Medical Association of Hepatology Fatty Liver and Alcoholic Liver Disease Study Group "Non-alcoholic fatty liver disease treatment guideline (2010Revision)", we diagnosed24cases of NAFLD in the90obese children (NAFLD group), which was26.67%of the obese children. The NAFLD group consisted of17boys and7girls, aged5.1-12.7, average (9.1±2.0) years old. Those without NAFLD (no NAFLD group) amounted to66, included39boys and27girls, aged2.5-14.3yrs, averaging (8.1±3.2) years old.In addition, we chose another35children who had visited this hospital in the same period and who were found to be healthy in the physical examination as the healthy control group. Body weight, liver and renal functions were all normal and they had no chronic diseases. Among them were17boys and18girls, aged4.2-12.5yrs, averaging (7.8±2.6) years old. There was no significant difference between all groups in age and sex.Physical indicators measurement: All the ages and genders were recorded. Between8AM and9AM before meals, all the children took off their shoes and hats and wore unlined garments. Height, weight, blood pressure, waist circumference, hip circumference, etc. of each child was measured, and their BMI =weight(kg)/height2(m2), WHR=waist circumference(cm)/hip circumference (cm), and WHtR=waist circumference(cm)/height(cm) were calculated.Specimen collection and laboratory tests:Between8AM and9AM before meals,4millilitre (ml) venous blood was exsanguinated. Fasting insulin(FINS), fasting blood glucose(FBG), total cholesterol(TC), triglycerides(TG), high density lipoprotein cholesterol(HDL-C), low density lipoprotein cholesterol(LDL-C), alanine aminotransferase(ALT) and aspartate aminotransferase(AST), etc. were measured immediately after the serum was separated. FINS was measured via an automatic fluorescence immunoassay analysis system; FBG, TC, TG, HDL-C, LDL-C, ALT and AST was measured by an automatic biochemical analyzer. HOMA-IR (=FINS×FBG/22.5) was calculated. Resistin and IL-6concentrations were determined by Enzyme-linked immunosorbent assay(ELISA). IL-6gene detection:2ml venous blood was exanguinated and anticoagulated by EDTA. Desoxyribose nucleic acid (DNA) was extracted by phenol-chloroform. IL-6gene polymorphism was tested in Beijing Genomics Institute by chain termination method (dideoxy method) for gene sequencing after Polymerase Chain Reaction (PCR) amplification.Statistical processingAll of the statistical analyses were performed with SPSS13.0software:data was tested to see if it was normally distributed. Skew distributed data were expressed as a median (P25,P75), normal distributions were expressed as X±S;HOMA-IR data which was not normal distribution, was translated as natural logarithm and then treated as a normal distribution. In comparing the two groups, two independent samples t test was applied to normal distributions (most medical physiology data is a normal distribution, this study’s sample was small, and although FBG and serum lipid were not normally distribution, we still treated them as normal distributions), while the rank sum test was applied to skew distribution data. Count data comparisons between groups were tested by chi-square test. Partial correlation analysis was performed, controlling for age.In comparing the three groups,one way analysis of variance (ANOVA) was applied to normal distributions;for further comparing per two groups,LSD test was applied to homogeneous variances,while Welch F test was applied to variances that were not homogeneous;Kruskal-Wallis H test was applied to skew distribution data.BMI, WC, WHR and WHtR used in diagnosing NAFLD was analyzed via the receiver operating characteristic (ROC) Curve. P<0.05was statistical difference.Result1、 Gender and age of both the simple obesity group and the healthy control group showed no significant difference,χ2/t=1.933,1.003, P=0.164,0.318, respectively. In the simple obese group, BMI, WHR, WC and WHtR were respectively24.97±3.77kg/m2,0.94±0.05,80.26±12.58cm and0.60±0.05, significantly higher than healthy control group, whose were17.28±3.30kg/m2,0.83±0.02,58.55±10.38cm,0.45±0.04,t=10.588,9.078,17.355,14.72, respectively, with P=0.000for all of them. There were statistical differences.2、 Fasting blood glucose was4.95±0.63mmol/L in the simple obesity group,4.93±0.44mmol/L in the healthy control group, t=0.195,P=0.846. There was no significant difference. Blood FINS in simple obesity group was108.48(66.05,140.57) pmol/L and Ln (IR) was3.08±0.56which were significantly higher than healthy control group, whose FINS was63.80(31.47,103.49) pmol/L and Ln (IR) was2.54±0.74, Z/t=-3.717,4.471, both P=0.000, there were obvious differences. TC, TG and LDL-C in the simple obesity group were4.03±1.00mmol/L,1.41±0.80mmol/L,2.14±0.87mmol/L respectively, significantly higher than healthy control group, whose were3.55±0.82mmol/L,0.97±0.52mmol/L,1.71±0.43mmol/L, respectively, t=2.515,3.593,3.683, P=0.013,0.001,0.000. There were statistical differences. HDL-C of both groups had no significant difference,t=1.007, P=0.319. HOMA-IR index was positively related to BMI, WC, WHR, WHtR, serum TG and LDL-C levels, r=0.400,0.351,0.265,0.331,0.245,0.183, P=0.000,0.000,0.003,0.000,0.006,0.042, respectively.3、 Resistin in the simple obesity group was27.76(17.35,53.23) ug/L, higher than healthy control group, whose was21.53(15.85,29.36)ug/L, Z=-2.076, P=0.038; there was a significant difference. There was no significant correlation between HOMA-IR and resistin, r=0.180, P=0.112. Resistin was positively related to BMI, WC, WHR, WHtR, TG, r=0.25,0.333,0.261,0.322,0.462, P=0.026,0.023,0.020,0.004,0.000, respectively.4、 IL-6in the simple obesity group was34.30(18.99,56.93)ng/L, significantly higher than the healthy control group, whose was20.90(13.10,39.75) ng/L,Z=-2.633, P=0.008; there was an obvious difference. There was no significant correlation between HOMA-IR and IL-6, r=0.177,P=0.118. IL-6was positively related to resistin, BMI, WC, WHtR, TG, r=0.504,0.260,0.413,0.231,0.387,0.248, P=0.000,0.021,0.000,0.041,0.000,0.028, respectively. All cases (including the simple obesity group and the healthy control group) IL-6-174G/C gene polymorphism showed that, they were all GG genotype, no C allele.5、 BMI, WC, WHR and WHtR of the NAFLD group were the highest of the three groups, respectively27.96±3.23kg/m2,90.08±8.84cm,0.97±0.04,0.63±0.05, followed by the no NAFLD group, whose were23.88±3.35kg/m2,76.69±11.85cm,0.93±0.05,0.58±0.05respectively, while the healthy control group’s were, respectively,17.28±3.30kg/m2,58.55±10.38cm,0.83±0.02,0.45±0.04, F=81.023,62.927,180.418,142.072, all P=0.000; there were significant differences. There were no obvious differences in FBG in all three groups, F=0.405, P=0.668. FINS and Ln (IR) in the NAFLD group were the highest of the three groups, respectively137.30 (99.11,141.97) pmol/L,3.29±0.44, followed by the no NAFLD group, whose were98.47(61.15,134.92)pmol/L,3.00±0.58, while the healthy control group’s were63.80(31.47,103.49)pmol/L,2.54±0.74, H/F=17.810,11.776, both P=0.000(except when comparing Ln(IR) in NAFLD group and no NAFLD group, P>0.05), there were significant differences. TG, TC and LDL-C of NAFLD group were,1.83±0.78mmol/L,4.44±0.99mmol/L and2.64±0.90mmol/L respectively, much higher than those of the no NAFLD group,1.25±0.76mmol/L,3.88±0.97mmol/L,1.95±0.79mmol/L, respectively, and healthy control group,0.97±0.52mmol/L,3.55±0.82mmol/L,1.73±0.43mmol/L respectively. F=10.862,5.844,11.684, P=0.000,0.004,0.000(except when comparing with those in the no NAFLD and the healthy control group,.P>0.05), there were significant differences. There was no significant difference in HDL-C in all three groups, F=0.519, P=0.598. The area under receiver operating characteristic (ROC) Curve of BMI, WC, WHR and WHtR diagnosing NAFLD were0.872,0.882,0.847,0.862, respectively-all of them were more than0.5, all P=0.000. Among them, the biggest area under ROC Curve was WC’s, i.e. WC was the most valuable predictor for NAFLD.ConclusionChildren with simple obesity had such phenomena as IR, and and increased BMI, WC, WHR, WHtR, blood-lipid disorders, mainly elevated TC, TG and LDL-C. They had elevated levels of resistin and IL-6, they were positively related to each other, and both positively related to BMI, WC, WHR, WHtR and TG.HOMA-IR in obese children was positively related to BMI, WC, WHR, WHtR, blood TG and LDL-C, but there was no significant correlation between HOMA-IR and resistin or IL-6. IL-6-174G/C gene sequencing showed that, they were all GG genotype, suggesting that there might be no significant relationship between IL-6-174G/C genotype and the development of obesity. The prevalence of NAFLD was related to obesity especially abdominal obesity, IR and high level of TC, TG and LDL-C. Controlling BMI, WC, WHR, WHtR and serum lipid could be propitious to control IR and the prevalence and development of NAFLD.