C-174G polymorphism in the promoter of the interleukin-6 gene is associated with insulin resistance

Nontraditional atherosclerotic risk factors and extent of coronary atherosclerosis in patients with combined impaired fasting glucose and impaired glucose tolerance

Partially inconsistent data exist on mutual relations between nontraditional atherosclerotic risk factors, including the magnitude of insulin resistance (IR), as well as on their relevance for atherogenesis in the metabolic syndrome. Subjects exhibiting combined impaired fasting glucose and impaired glucose tolerance (IFG/IGT) are exposed to an exceptionally high risk for atherogenesis and development of type 2 diabetes mellitus. Because of islet Beta-cell dysfunction, the usefulness of commonly used indices of IR is limited in IFG/IGT. Our aim was to assess the relationship between extent of angiographic coronary artery disease (CAD) and nontraditional atherosclerotic risk factors (including IR by a clamp-based golden standard method) in IFG/IGT. Fifty-three subjects (32 men, 21 women; mean age, 55 +/- 11 years) with stable angina, preserved left ventricular systolic function, and IFG/IGT were divided into 3 groups: group A (no coronary stenoses >50%, n = 22), group B (1-vessel CAD, n = 15), and group C (2/3-vessel CAD, n = 16). Insulin sensitivity was quantified by a hyperinsulinemic euglycemic clamp technique and expressed as M. M value, plasma homocysteine (Hcy) level, and asymmetric dimethyl-L-arginine (ADMA)/L-arginine ratio were independent determinants of CAD extent as shown by forward stepwise discriminant function analysis. Compared with group A (M = 32.7 +/- 9.3 micromol/kg fat-free mass [FFM] per minute; Hcy, 8.1 +/- 1.4 micromol/L), lower M and higher Hcy levels were found in group B (M = 16.9 +/- 8.2 micromol/kg FFM per minute, P < .001; Hcy, 11.2 +/- 2.9 micromol/L, P = .003) and C (M = 16.4 +/- 7.8 micromol/kg FFM per minute, P < .001; Hcy, 12.8 +/- 3.9 micromol/L, P < .001). The ADMA/L-arginine ratio was increased in group C (0.0078 +/- 0.0011) compared with group A (0.0063 +/- 0.0013, P = .03) and B (0.0058 +/- 0.0012, P = .01). Multivariate correlates (P < .05) of plasma Hcy concentrations were M (beta = -.34 +/- .12, P = .008), creatinine clearance (beta = -.23 +/- .10, P = .03) and fasting insulin (beta = .25 +/- .12, P = .04). This indicates an additive contribution of IR, plasma Hcy, and elevated ADMA/L-arginine ratio to the extent of angiographic CAD in combined IFG/IGT.

Carotid artery intima-media thickness is associated with insulin-mediated glucose disposal in nondiabetic normotensive offspring of type 2 diabetic patients

The aim of this study was to investigate whether insulin resistance is independently associated with early manifestations of atherosclerosis. To this end, 176 normotensive offspring of type 2 diabetic patients were subjected to euglycemic hyperinsulinemic clamp to assess insulin sensitivity. Early atherosclerosis was studied by ultrasonography of the common carotid artery. Of the total 176 subjects, 145 were glucose tolerant, 18 had impaired fasting glucose, and 13 had impaired glucose tolerance. Univariate correlations showed that age, body mass index, waist, blood pressure, 2-h postchallenge glucose, fasting insulin, triglycerides, interleukin-6, fibrinogen, and white blood cell count were significantly correlated with carotid intima-media thickness (IMT), whereas HDL cholesterol and glucose disposal showed a negative correlation. A stepwise multivariate regression analysis including sex, age, waist circumference, smoking status, systolic blood pressure, diastolic blood pressure, triglyceride, HDL cholesterol, 2-h postchallenge glucose, plasma IL-6, fibrinogen, white blood cell count, insulin-stimulated glucose disposal, and fasting insulin showed that the four variables that remained significantly associated with carotid IMT were waist circumference, insulin-stimulated glucose disposal, white blood cell count, and diastolic blood pressure, accounting for 33.7% of its variation. These findings support the concept that insulin sensitivity, rather than plasma insulin levels, is associated with early atherosclerosis in nondiabetic normotensive offspring of type 2 diabetic patients.

Dietary fat, genes and insulin sensitivity

Both insulin resistance and dyslipidaemia are determined by genetic and environmental factors. Depending on their expression and their function, gene variants may influence either insulin action or dyslipidaemia. The purpose of this review was to give some examples from recent studies of gene variants that influence insulin signalling and the interaction between gene and diet to predispose insulin resistance. Recent findings indicate a major role for genetic susceptibility to the insulin resistance syndrome. Nutrition also plays an important role in the development and progression of the condition. Genetic background may interact with habitual dietary fat composition, affecting predisposition to the insulin resistance syndrome and individual responsiveness to changes in dietary fat intake. Due to the complex nature of gene-environment interactions, therefore, therapeutic dietary therapy may require a 'personalized' nutrition approach in the future. Although results have not always been consistent, gene variants that affect primary insulin action or dyslipidaemia, and particularly their interaction with the environment, are important modulators of glucose metabolism and insulin resistance syndrome.

The PEA15 gene is overexpressed and related to insulin resistance in healthy first-degree relatives of patients with type 2 diabetes

AIMS/HYPOTHESIS

Overexpression of the gene encoding phosphoprotein enriched in astrocytes 15 (PEA15), also known as phosphoprotein enriched in diabetes (PED), causes insulin resistance and diabetes in transgenic mice and has been observed in type 2 diabetic individuals. The aim of this study was to investigate whether PEA15 overexpression occurs in individuals at high risk of diabetes and whether it is associated with specific type 2 diabetes subphenotypes.

SUBJECTS AND METHODS

We analysed PEA15 expression in euglycaemic first-degree relatives (FDR) of type 2 diabetic subjects.

RESULTS

The expression of PEA15 in peripheral blood leucocytes (PBLs) paralleled that in fat and skeletal muscle tissues. In PBLs from the FDR, PEA15 expression was two-fold higher than in euglycaemic individuals with no family history of diabetes (control subjects), both at the protein and the mRNA level (p < 0.001). The expression of PEA15 was comparable in FDR and type 2 diabetic subjects and in each group close to one-third of the subjects expressed PEA15 levels more than 2 SD higher than the mean of control subjects. Subjects with IFG with at least one type 2 diabetes-affected FDR also overexpressed PEA15 (p < 0.05). In all the groups analysed, PEA15 expression was independent of sex and unrelated to age, BMI, waist circumference, systolic and diastolic BP, and fasting cholesterol, triacylglycerol and glucose levels. However, in euglycaemic FDR of type 2 diabetic subjects, PEA15 expression was inversely correlated with insulin sensitivity (r = -557, p = 0.01).

CONCLUSIONS/INTERPRETATION

We conclude that PEA15 overexpression represents a common defect in FDR of patients with type 2 diabetes and is correlated with reduced insulin sensitivity in these individuals.

Genetic variation in IL6 gene and type 2 diabetes: tagging-SNP haplotype analysis in large-scale case-control study and meta-analysis

Interleukin-6 (IL-6, gene symbol IL6) is a proinflammatory cytokine. High circulating IL-6 levels have been associated with insulin resistance and greater risk of type 2 diabetes. Using a linkage disequilibrium (LD)-based approach, we sought to investigate the associations of the common polymorphisms comprehensively defining the genetic variability at the IL6 locus with diabetes risk. We conducted a case-control study of 2691 cases of type 2 diabetes (1692 women and 999 men) and 3237 control subjects (2238 women and 999 men) from the Nurses' Health Study and the Health Professional Follow-up Study. Pairwise LD analysis indicated that all the IL6 polymorphisms (rs2069827, rs1800797, rs1800795, rs1554606, rs2069849, rs2069861 and rs1818879) were in strong LD. We did not find significant associations between IL6 polymorphisms and the risk of type 2 diabetes in women or men, individually or in haplotypes. In addition, none of the IL6 polymorphisms was significantly associated with the plasma levels of IL-6 in the control subjects. Our meta-analysis of 5383 diabetes case and 12 069 controls indicated a null association between the best-studied 5' promoter polymorphism--174G>C (rs1800795)--and diabetes risk. Diversity in adiposity, age and sex could not account for the heterogeneity across different studies. In summary, the data in this study do not support substantial associations between the common polymorphisms in IL6 gene and circulating IL-6 levels and the risk of type 2 diabetes.