Federica Sentinelli

Association of the human adiponectin gene and insulin resistance.

Adiponectin is an adipocyte-secreted protein that modulates insulin sensitivity and whose low circulating concentration is associated with insulin resistance. In the present study, we analysed the association between two single-nucleotide polymorphisms (SNPs) in the adiponectin gene and insulin resistance in 253 nondiabetic subjects. In addition, we investigated whether this association is modulated by body mass index (BMI) levels. The SNPs +45T>G and +276G>T in the human adiponectin gene were detected in real-time PCR with LightCycler. No association was found with the +45T>G SNP. The +276G>T SNP was associated with higher BMI (P<0.01), plasma insulin (P<0.02) and HOMAIR (P<0.02). To analyse the possible interaction between BMI and the adiponectin gene on insulin resistance, the study group was divided into two subgroups, according to the BMI below or above the median of 26.2 kg/m2. In both subgroups, subjects carrying the +276G>T SNP had higher HOMAIR; however, the difference was highly significant among leaner (P<0.001), but not among heavier individuals, indicating that BMI status and the adiponectin gene interact in modulating insulin resistance. Among individuals with BMI <26.2 kg/m2, the relative risk of insulin resistance was 9.7 (CI: 1.32–87.7, P<0.035). In a subgroup of 67 subjects, carriers of the +276G>T SNP had significantly (P<0.05) lower mean serum adiponectin levels (25.7 ng/ml) compared to noncarriers (37.0 ng/ml), suggesting a possible influence of the +276G>T SNP on adiponectin levels. In summary, we observed an association between the +276G>T SNP in the adiponectin gene and insulin resistance. In particular, among leaner individuals, the adiponectin gene appears to determine an increased risk to develop insulin resistance.

The 148M allele of the PNPLA3 gene is associated with indices of liver damage early in life

BACKGROUND & AIMS Childhood obesity is a growing problem worldwide. Non-alcoholic fatty liver disease (NAFLD) is frequently associated with obesity in children. Recently, the PNPLA3 gene I148M (rs738409) variant was demonstrated to be strongly associated with hepatic steatosis in obese adults. In this study we add further insight into the role of PNPLA3 by exploring whether this association begins early in life in obese children or becomes manifest only in adulthood. METHODS Four hundred and seventy-five obese/overweight children and adolescents were genotyped for the I148M allele. Clinical and biochemical parameters were collected for all participants, including indices of hepatic injury, glucose tolerance and insulin resistance. Ultrasound imaging of the liver was obtained to assess the degree of steatosis in a subset of children. RESULTS Carriers of two 148M alleles had a 52% increase in circulating ALT levels compared to carriers of two 148I alleles, with individuals with one 148M allele showing a 9.5% increase (p=0.001). AST concentration was also significantly higher in carriers of two and one M alleles (17.4% and 4%, respectively, p=0.022). A total of 36% of carries of two 148M alleles showed elevated ALT, defined as >30U/L, compared to only 10% of carriers of two 148I alleles (p<0.001). Liver steatosis was more prevalent in carriers of two 148M alleles. Glucose tolerance and insulin sensitivity were similar across all three genotypes. CONCLUSIONS Our data show that the PNPLA3 gene I148M variant is associated with increased levels of ALT/AST in obese children and adolescents, suggesting that it confers genetic susceptibility to liver damage from a young age.

The adiponectin gene SNP+276G>T associates with early-onset coronary artery disease and with lower levels of adiponectin in younger coronary artery disease patients (age ≤50 years)

Adiponectin, an adipocyte-derived protein, is an essential modulator of insulin sensitivity and several studies suggest an important role of adiponectin in the processes leading to atherosclerosis, thus indicating the adiponectin gene as a potential candidate for coronary artery disease (CAD). In the present study we have studied the association between two single nucleotide polymorphisms (SNPs) (+45T>G and +276 G>T) of the adiponectin gene and CAD, looking also into the possible influence of these SNPs on adiponectin plasma levels. The SNPs were analysed in a first cohort of 595 subjects, 325 with CAD and 270 matched controls. We observed a significant association (p<0.001) between the SNP +276G>T in the adiponectin gene and CAD. In multivariate analysis, carriers of the +276G>T SNP had an odds ratio (OR) for CAD of 4.99 (p<0.0007). A strong interaction between the +276G>T SNP and age was also present (OR, 1.03; p<0.0001). The increase in CAD risk was most evident among individuals with early-onset CAD (age ≤50 years), whereas in older CAD subjects other factors, and not the adiponectin SNP, were the major determinants. Furthermore, in CAD subjects with early-onset disease this SNP was also a significant determinant of lower levels of serum adiponectin levels. This association resulted independent from the other variables known to be associated with CAD in our population, including sex, body mass index, high-density lipoprotein and Homeostasis Model Assessment for insulin resistance. To confirm the results the +276G>T SNP was analysed in a second cohort of CAD and controls. The difference between CAD and controls in the +276G>T SNP frequencies showed a similar trend as before, although not significant. The combination of the two cohorts (1,046 subjects: 580 CAD and 466 controls) showed a statistically significant association, particularly in CAD subjects with early-onset of disease. In addition, we confirmed that in younger CAD subjects the SNP was a significant determinant of lower levels of adiponectin. In view of these results, it could be speculated that the adiponectin gene variant, or a mutation in linkage with it, determines lower adiponectin gene expression, causing in turn an increased risk to develop insulin resistance, atherosclerosis and cardiovascular disease. The significant association of the adiponectin gene in subjects with early-onset CAD also suggests that that genetic factors for late-onset diseases may exert a greater influence in younger persons, when other risk factors are not as prevalent as in older age groups.

The G972R variant of the insulin receptor substrate-1 (IRS-1) gene, body fat distribution and insulin-resistance.

Aims/hypothesis. Insulin resistance is recognised as the core factor in the pathogenesis of Type II (non-insulin-dependent) diabetes mellitus, hypertension and atherosclerosis. Several studies indicate the possible role of mutations of the insulin receptor substrate-1 (IRS-1) gene in the pathogenesis of insulin-resistance and suggest a possible interaction between the IRS-1 gene and obesity, either by an effect on the development of obesity or by causing or aggravating the obesity-associated insulin resistance. Therefore, the prevalence of the G972R mutation of the IRS-1 gene was compared in 157 non-diabetic obese subjects (BMI > 30 m/kg2) and in 157 lean subjects (BMI < 28 m/kg2). By investigating the relation between this IRS-1 mutation, measures of obesity and metabolic parameters, we explored the possible influence of this mutation on body fat distribution and insulin resistance. Methods. The G972R mutation was detected by PCR amplification and BstN-1 restriction enzyme digestion. Data were analysed by univariate and multivariate analysis. Results. The G972R allele was significantly more frequent in obese subjects than in lean subjects (p < 0.002); however, no difference was found between centrally and peripherally obese subjects. Obese G972R carriers had significantly higher BMI (p < 0.001), fasting insulin (p < 0.01), triglycerides (p < 0.03) and HOMAIR (p < 0.001) than obese non-carriers. No differences were observed between G972R carriers and non-carriers among control subjects. Multivariate analysis confirmed that the IRS-1 G972R mutation was significantly and independently associated with reduced insulin sensitivity (p < 0.009) in the obese group. Conclusion/interpretation. The G972R mutation of the IRS-1 gene associates with obesity, but not with fat distribution, in this Italian cohort, and within the obese subjects this IRS-1 variant strongly associates with metabolic parameters suggesting greater insulin-resistance. These findings indicate a possible interaction between the IRS-1 variant and obesity in worsening insulin sensitivity. [Diabetologia (2001) 44: 367–372]

The G-308A variant of the Tumor Necrosis Factor-α (TNF-α) gene is not associated with obesity, insulin resistance and body fat distribution

BackgroundTumor Necrosis Factor-α (TNF-α) has been implicated in the pathogenesis of insulin resistance and obesity. The increased expression of TNF-α in adipose tissue has been shown to induce insulin resistance, and a polymorphism at position -308 in the promoter region ofTNF-α has been shown to increase transcription of the gene in adipocytes. Aim of this study is to investigate the role of the G-308A TNFα variant in obesity and to study the possible influence of this mutation on body fat distribution and on measures of obesity (including Fat Free Mass, Fat Mass, basal metabolic rate), insulin resistance (measured as HOMAIR), and lipid abnormalities. The G-308A TNFα polymorphism has been studied in 115 patients with obesity (mean BMI 33.9 ± 0.5) and in 79 normal lean subjects (mean BMI 24.3 ± 0.3).MethodsThe G-308A variant, detected by PCR amplification and Nco-1 digestion, determines the loss of a restriction site resulting in a single band of 107 bp [the (A) allele].ResultsThe (A) allele frequencies of the G-308A TNFα polymorphism were 13.1% in the obese group and 14.6% in the lean subjects, with no significant difference between the two groups. Furthermore, no association was found with BMI classes, body fat distribution, HOMAIR, and metabolic abnormalities.ConclusionsOur study did not detect any significant association of the G-308A TNFα polymorphism with obesity or with its clinical and metabolic abnormalities in this population. Our data suggests that, in our population, the G-308A TNFα polymorphism is unlikely to play a major role in the pathogenesis of these conditions.

Oral glucose tolerance test in Italian overweight/obese children and adolescents results in a very high prevalence of impaired fasting glycaemia, but not of diabetes.

Very few studies on glucose abnormalities in European overweight/obese children and adolescents are available, and scientific evidence on the value of standard oral glucose tolerance test (OGTT) in childhood is lacking. We therefore aimed to establish prevalence and features of impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and type 2 diabetes (T2D) in a large cohort of Italian overweight/obese children and adolescents and to assess the validity of standard OGTT in the paediatric population.

Lack of effect of apolipoprotein C3 polymorphisms on indices of liver steatosis, lipid profile and insulin resistance in obese Southern Europeans.

BackgroundApolipoprotein C3 (APOC3) is a component of triglyceride-rich lipoproteins, and APOC3 rs2854116 and rs2854117 polymorphisms have been associated with non-alcoholic fatty liver disease, hypertriglyceridaemia, and insulin-resistance.ObjectiveTo determine if the APOC3 variants alter the susceptibility of obese subjects to develop liver damage, hypertrigliceridaemia, and insulin-resistance.MethodsThe study was carried out on 585 unrelated obese Italians (median body mass index BMI = 41 kg/m2) who were genotyped for the rs2854116 and rs2854117 variants. All participants underwent oral glucose tolerance tests (OGTT), with measurement of glucose, insulin, lipid parameters. Indices of insulin-resistance (HOMA and ISI) were calculated. Alanine transaminase (ALT) and aspartate transaminase (AST) were used as markers of liver injury.ResultsThe study subjects were divided into two groups: those homozygous for the wild-type alleles at both SNPs (-482C and -455T alleles) and those who were carriers of at least one variant allele or both (-482T, -455C or both). Also each SNP was analysed independently. No significant differences were found in ALT and AST levels and in the lipid profile between the two groups. Insulin concentrations, glucose tolerance and insulin sensitivity were similar in the two groups.ConclusionWe did not identify any significant association between APOC3 polymorphisms and fatty liver disease, lipids, and insulin-resistance in obese subjects, thus not confirming the suggested role of these APOC3 gene sequence variants.

The Gly482Ser Missense Mutation of the Peroxisome Proliferator-Activated Receptor γ Coactivator-1α (PGC-1α) Gene Associates with Reduced Insulin Sensitivity in Normal and Glucose-Intolerant Obese Subjects

Among the putative candidate genes for insulin resistance, the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a transcriptional coactivator of PPARγ and α, regulating a wide range of processes involved in energy production and utilization, such as thermogenesis, liver gluconeogenesis, glucose uptake in muscle. In population studies a Gly482Ser substitution in PGC-1α has been reported to be associated with increased risk of type diabetes 2 and insulin resistance. In the present study we have analysed the association between the Gly482Ser missense mutation of the PGC-1α gene and insulin sensitivity and glucose tolerance in a population of obese non-diabetic subjects. The Gly482Ser SNPs was detected by PCR-RFLP in a cohort of 358 Caucasian obese subjects (223 with normal glucose tolerance (NGT) and 125 with impaired glucose tolerance (IGT). We observed a significant association (p < 0.007) between carriers of the Gly482Ser variant of the PGC-1α gene and insulin resistance measured by HOMAIR. Multivariate analysis confirmed that the Gly482Ser SNP was a significant (p < 0.02) determinant of decreased insulin sensitivity, independently from other well-known modulators of insulin action. In conclusion, we have found significant association between the Gly482Ser variant of the PGC-1α gene and reduced insulin sensitivity in obese subjects. This association resulted independent from all other known modulators of insulin resistance, and suggests a primary role for the PGC-1α gene on the genetic susceptibility to insulin resistance in obesity.

Altered Glucose Homeostasis Is Associated with Increased Serum Apelin Levels in Type 2 Diabetes Mellitus

Background Apelin is an adipokine that plays a role in the regulation of glucose homeostasis and in obesity. The relationship between apelin serum concentration and dysmetabolic conditions such as type 2 diabetes (T2D) is still controversial. Aims of our study are: 1) determine the circulating levels of apelin in a large cohort of Italian subjects with T2D, T1D and in non-diabetic controls; 2) identify putative metabolic determinants of modified apelin concentrations, in order to search possible mechanism of apelin control; 3) investigate changes in apelin levels in response to sharp modifications of glucose/insulin metabolism in T2D obese subjects before and 3 days after bariatric surgery. Methods We recruited 369 subjects, 119 with T2D, 113 with T1D and 137 non-diabetic controls. All subjects underwent a complete clinical examination, including anthropometric and laboratory measurements. Serum apelin levels were determined by EIA (immunoenzyme assay). Results Patients with T2D had significantly higher serum apelin levels compared to controls (1.23±1.1 ng/mL vs 0.91±0.7 ng/mL, P<0.001) and to T1D subjects (0.73±0.39 ng/mL, P<0.001). Controls and T1D subjects did not differ significantly in apelin levels. Apelin concentrations were directly associated with fasting blood glucose (FBG), body mass index (BMI), basal Disposition Index (DI-0), age, and diagnosis of T2D at bivariate correlation analysis. Multiple regression analysis confirmed that diagnosis of T2D, basal DI-0 and FBG were all determinants of serum apelin levels independently from age and BMI. Bariatric surgery performed in a subgroup of obese diabetic subjects (n = 12) resulted in a significant reduction of apelin concentrations compared to baseline levels (P = 0.01). Conclusions Our study demonstrates that T2D, but not T1D, is associated with increased serum apelin levels compared to non-diabetic subjects. This association is dependent on impaired glucose homeostasis, and disappears after bariatric surgery, providing further evidence regarding the relationship between apelin and the regulation of glucose metabolism.

Association of FTO Polymorphisms with Early Age of Obesity in Obese Italian Subjects

Obesity is recognized as a major health problem worldwide. Genetic factors play a major role in obesity, and genomewide association studies have provided evidence that several common variants within the fat mass- and obesity-associated (FTO) gene are significantly associated with obesity. Very limited data is available on FTO in the Italian population. Aims of our study are to investigate: (1) the association of FTO gene SNPs rs9939609 and rs9930506 with body mass index (BMI) and obesity-related parameters in a large cohort (n = 752) of Italian obese subjects; (2) the association between the two FTO SNPs and age of onset of obesity. Our results demonstrate a strong association between FTO SNPs rs9939609 (P < 0.043) and rs9930506 (P < 0.029) with BMI in the Italian population. FTO rs9930506 was significantly associated with higher BMI in a G allele dose-dependent manner (BMI + 1.4 kg/m2 per G allele). We also observed that the association with BMI of the two FTO variants varied with age, with the carriers of the risk alleles developing an increase in body weight earlier in life. In conclusion, our study further demonstrates a role of the genetic variability in FTO on BMI in a large Italian population.