Monisha Banerjee

Genome-wide association study for type 2 diabetes in Indians identifies a new susceptibility locus at 2q21.

Indians undergoing socioeconomic and lifestyle transitions will be maximally affected by epidemic of type 2 diabetes (T2D). We conducted a two-stage genome-wide association study of T2D in 12,535 Indians, a less explored but high-risk group. We identified a new type 2 diabetes–associated locus at 2q21, with the lead signal being rs6723108 (odds ratio 1.31; P = 3.32 × 10−9). Imputation analysis refined the signal to rs998451 (odds ratio 1.56; P = 6.3 × 10−12) within TMEM163 that encodes a probable vesicular transporter in nerve terminals. TMEM163 variants also showed association with decreased fasting plasma insulin and homeostatic model assessment of insulin resistance, indicating a plausible effect through impaired insulin secretion. The 2q21 region also harbors RAB3GAP1 and ACMSD; those are involved in neurologic disorders. Forty-nine of 56 previously reported signals showed consistency in direction with similar effect sizes in Indians and previous studies, and 25 of them were also associated (P < 0.05). Known loci and the newly identified 2q21 locus altogether explained 7.65% variance in the risk of T2D in Indians. Our study suggests that common susceptibility variants for T2D are largely the same across populations, but also reveals a population-specific locus and provides further insights into genetic architecture and etiology of T2D.

Interleukin-1 (IL-1) family of cytokines: Role in Type 2 Diabetes

Cytokines are small cell signaling protein molecules which encompass a large and diverse family. They consist of immunomodulating agents such as interleukins and inteferons. Virtually all nucleated cells, especially endo/epithelial cells and macrophages are potent producers of IL-1, IL-6 and TNF-α. IL-1 family is a group of cytokines which play a central role in the regulation of immune and inflammatory responses. Type 2 diabetes (T2D) has been recognized as an immune mediated disease leading to impaired insulin signaling and selective destruction of insulin producing β-cells in which cytokines play an important role. Disturbance of anti-inflammatory response could be a critical component of the chronic inflammation resulting in T2D. IL-1 family of cytokines has important roles in endocrinology and in the regulation of responses associated with inflammatory stress. The IL-1 family consists of two pro-inflammatory cytokines, IL-1α and IL-1β, and a naturally occurring anti-inflammatory agent, the IL-1 receptor antagonist (IL-1Ra or IL-1RN). This review is an insight into the different types of cytokines belonging to IL-1 family, their modes of action and association with Type 2 diabetes.

Vitamin D receptor (FokI, BsmI and TaqI) gene polymorphisms and type 2 diabetes mellitus: a North Indian study.

BACKGROUND The vitamin D receptor (VDR) gene is a candidate gene for susceptibility to several diseases. Studies on association between VDR polymorphisms and risk of type 2 diabetes (T2DM) in different ethnic populations are yet inconclusive. AIMS This study was conducted to evaluate association between VDR polymorphisms and genetic susceptibility to T2DM in the north Indian population. SETTINGS AND DESIGN One hundred clinically diagnosed T2DM patients and 160 healthy controls from the north Indian population were recruited for genetic association study. MATERIALS AND METHODS Genomic DNA was extracted from blood and genotyped for the single nucleotide polymorphism SNPs of FokI (T/C) [rs2228570], BsmI (A/G) [rs1544410] and TaqI (C/T) [rs731236] by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis. STATISTICAL ANALYSIS USED Genotype distribution and allelic frequencies were compared between patients and controls. Mean values and odds ratios (ORs) with 95% confidence interval (CI) were calculated using SPSS software (version 15.0). RESULTS The genotype distribution, allele and haplotype frequencies of VDR polymorphism did not differ significantly between patients and controls. Mean age and waist-hip ratio of patients were found to be associated with VDR polymorphism. Combination studies showed FFBbtt increased the risk of T2DM in north Indians. CONCLUSIONS Our data suggest that VDR gene polymorphism in combination of genotypes is associated with the risk of T2DM and thus requires further studies as a probable genetic risk marker for T2DM.

Association of glutathione S-transferase (GSTM1, T1 and P1) gene polymorphisms with type 2 diabetes mellitus in north Indian population

BACKGROUND Diabetes mellitus is associated with an increased production of reactive oxygen species (ROS) and a reduction in antioxidant defense. The oxidative stress becomes evident as a result of accumulation of ROS in conditions of inflammation and Type 2 diabetes mellitus (T2DM). The genes involved in redox balance, which determines the susceptibility to T2DM remain unclear. In humans, the glutathione S-transferase (GST) family comprises several classes of GST isozymes, the polymorphic variants of GSTM1, T1 and P1 genes result in decreased or loss of enzyme activity. AIMS The present study evaluated the effect of genetic polymorphisms of the GST gene family on the risk of developing T2DM in the North Indian population. SETTINGS AND DESIGN GSTM1, T1 and P1 polymorphisms were genotyped in 100 T2DM patients and 200 healthy controls from North India to analyze their association with T2DM susceptibility. MATERIALS AND METHODS Analysis of GSTM1 and GSTT1 gene polymorphisms was performed by multiplex polymerase chain reaction (PCR) and GSTP1 by PCR-Restriction Fragment Length Polymorphism (RFLP). STATISTICAL ANALYSIS Fishers exact test and chi2 statistics using SPSS software (Version-15.0). RESULTS We observed significant association of GSTM1 null (P=0.004, OR= 2.042, 95%CI= 1.254-3.325) and GSTP1 (I/V) (P=0.001, OR= 0.397, 95%CI=0.225-0.701) with T2DM and no significant association with GSTT1 (P=0.493). The combined analysis of the three genotypes GSTM1 null, T1 present and P1 (I/I) demonstrated an increase in T2DM risk (P= 0.005, OR= 2.431 95% CI=1.315-4.496). CONCLUSIONS This is the first study showing the association of a combined effect of GSTM1, T1 and P1 genotypes in a representative cohort of Indian patients with T2DM. Since significant association was seen in GSTM1 null and GSTP1 (I/V) and multiple association in GSTM1 null, T1 present and P1 (I/I), these polymorphisms can be screened in the population to determine the diabetic risk.

The macrophage Ox-LDL receptor, CD36 and its association with type II diabetes mellitus.

Type II diabetes mellitus (T2DM) is a common and serious metabolic disorder worldwide. It is the third leading cause of death after cancer and cardiovascular disease (CVD). Over time, diabetes mellitus can lead to different complications like atherosclerosis, coronary heart disease and many micro- and macrovascular diseases. CD36 is a class B scavenger receptor whose expression is prevalent in vascular lesions. It has been shown that high plasma low density lipoprotein (LDL) levels become atherogenic when oxidized to modified LDL (Ox-LDL) by inducing foam cell formation via enhanced CD36 expression on macrophages. In addition to Ox-LDL, raised levels of glucose, insulin resistance, low HDL cholesterol, increased levels of free fatty acid (FFA) all result in increased expression of CD36, thereby contributing to T2DM and related atherosclerosis. Adipocytokines such as tumor necrosis factor-alpha (TNF-α), C-reactive protein (CRP), adiponectin, leptin, resistin along with peroxisome proliferator activated receptor-γ (PPAR-γ) are important mediators in glucose homeostasis in association with CD36 and can be used as markers for T2DM and atherosclerosis. Several of these gene variants have shown association with lipid metabolism, T2DM and related complications. An attempt has been made to review the CD36 macrophage receptor and related molecules in association with T2DM.

Association of IL-4 and IL-1RN (receptor antagonist) gene variants and the risk of type 2 diabetes mellitus: a study in the north Indian population

BACKGROUND Inflammation is a key event closely associated with the pathophysiology of type 2 diabetes mellitus (T2DM). Association of genetic polymorphisms of inflammatory cytokines with T2DM is largely unknown. Our objective was to investigate the relationship of polymorphism of IL-1RN and IL-4, two important biomarkers of inflammation, with the risk of T2DM. SETTING AND DESIGN We recruited 120 clinically diagnosed T2DM patients and 150 normal healthy controls for this study in order to evaluate the nature of polymorphisms of IL-1RN and IL-4. MATERIALS AND METHODS Genomic DNA was isolated from the blood of all subjects, and the variable number of tandem repeat (VNTR) polymorphisms of IL-1RN and IL-4 genes was identified by polymerase chain reaction. STATISTICAL ANALYSIS USED Genotype distribution and allelic frequencies were compared between patients and control group. Means, as well as odds ratios (ORs) with 95% confidence intervals (CI), were calculated using SPSS software (version 11.5). RESULTS Our study revealed that distribution of both IL-4 and IL-1RN (VNTR) gene polymorphisms were significantly associated with T2DM subjects. We, however, failed to find any association of gene-gene (IL-4 and IL-1RN) interaction with T2DM. CONCLUSIONS Both IL-4 and IL-1RN (VNTR) gene polymorphisms were significantly associated with T2DM subjects. This may suggest that the genetic polymorphisms of IL-4 and IL-1RN genes could serve as susceptibility indicators for T2DM in the Indian population, but the actual mechanism of these associations will require more elaborate investigations. Lack of association of gene-gene (IL-4 and IL-1RN) interaction with T2DM may indicate the independent nature of influence of both these genes on the risk of T2DM.

Association of Superoxide dismutases (SOD1 and SOD2) and Glutathione peroxidase 1 (GPx1) gene polymorphisms with Type 2 diabetes mellitus

Abstract Type 2 diabetes mellitus (T2DM) is a metabolic disorder resulting from oxidative stress (OS), the root cause of insulin resistance, β-cell dysfunction, and impaired glucose tolerance. Antioxidant enzymes play key roles in cellular defense and can be used as important biomarkers for T2DM. The present study was undertaken to evaluate three genetic polymorphisms viz. SOD1 + 35A/C, SOD2 + 47C/T, and GPx + 599C/T in 207 T2DM cases and 210 healthy controls from North India. DNA was extracted from blood samples and genotyping was done by PCR-RFLP. Genotypic/allelic frequencies and haplotype/gene-gene interaction analysis were performed using SPSS (version 15.0) and SHEsis (v. online). Except age, all other biochemical parameters showed highly significant association in T2DM cases (P < 0.001). In North Indian population, SOD1 + 35A/C variant was monomorphic. Genotype/allele frequencies of SOD2 + 47C/T polymorphism and carriage rate of ‘C’ allele showed significant association (p < 0.05, < 0.001; OR 2.434). Genotype/allele frequencies of GPx1 + 599C/T and carriage rate showed no association although the odds ratio of GPx1 ‘C’ allele indicated a 1.362 times higher risk of T2DM. SOD2 ‘CT’ and GPx1 ‘CC’ genotypes showed maximum association with biochemical parameters. Haplotype/gene-gene interaction analysis in controls and cases showed that SOD2 + 47C/T and GPx1 + 599C/T were in linkage disequilibrium (D: 0.168; r2: 0.10) and individuals with this combination had a 1.273 times higher risk [OR; CI (95%)] of developing T2DM. Thus, we conclude that it is essential to assess the combinatorial association of gene variants with T2DM in order to identify risk haplotypes in a population.

Genetic polymorphisms of cytokine genes in type 2 diabetes mellitus.

Diabetes mellitus is a combined metabolic disorder which includes hyperglycemia, dyslipidemia, stroke and several other complications. Various groups all over the world are relentlessly working out the possible role of a vast number of genes associated with type 2 diabetes (T2DM). Inflammation is an important outcome of any kind of imbalance in the body and is therefore an indicator of several diseases, including T2DM. Various ethnic populations around the world show different levels of variations in single nucleotide polymorphisms (SNPs). The present review was undertaken to explore the association of cytokine gene polymorphisms with T2DM in populations of different ethnicities. This will lead to the understanding of the role of cytokine genes in T2DM risk and development. Association studies of genotypes of SNPs present in cytokine genes will help to identify risk haplotype(s) for disease susceptibility by developing prognostic markers and alter treatment strategies for T2DM and related complications. This will enable individuals at risk to take prior precautionary measures and avoid or delay the onset of the disease. Future challenges will be to understand the genotypic interactions between SNPs in one cytokine gene or several genes at different loci and study their association with T2DM.

Reactive metabolites and antioxidant gene polymorphisms in type 2 diabetes mellitus.

Type 2 diabetes mellitus (T2DM), by definition is a heterogeneous, multifactorial, polygenic syndrome which results from insulin receptor (IR) dysfunction. It is an outcome of oxidative stress caused by interactions of reactive metabolites (RMs) with lipids, proteins and other molecules of the human body. Production of RMs mainly superoxides (•O2−) has been found in a variety of predominating cellular enzyme systems including nicotinamide adenine dinucleotide phosphate oxidase, xanthine oxidase, cyclooxygenase, endothelial nitric oxide synthase (eNOS) and myeloperoxidase. The four main RM related molecular mechanisms are: increased polyol pathway flux; increased advanced glycation end-product formation; activation of protein kinase C isoforms and increased hexosamine pathway flux which have been implicated in glucose-mediated vascular damage. Superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and NOS are antioxidant enzymes involved in scavenging RMs in normal individuals. Functional polymorphisms of these antioxidant enzymes have been reported to be involved in the pathogenesis of T2DM. The low levels of antioxidant enzymes or their non-functionality results in excessive RMs which initiates stress related pathways thereby leading to IR and T2DM. An attempt has been made to review the role of RMs and antioxidant enzymes in oxidative stress resulting in T2DM.

Identification and characterization of Rv0494: a fatty acid-responsive protein of the GntR/FadR family from Mycobacterium tuberculosis

Escherichia coli FadR, a member of the GntR family of transcription factors, plays dual roles in fatty acid metabolism. FadR-DNA binding is inhibited by fatty acyl-CoAs, and thus FadR acts as a sensor of the fatty acid level in bacteria. We have identified FadR-binding sites in the upstream regions of genes showing altered expression after the disruption of fatty acid biosynthesis in Mycobacterium tuberculosis. A FadR homologue in M. tuberculosis, Rv0494, was identified, which binds to its operator in the upstream region of the kas operon. We have shown that FadRMt (Rv0494) directly binds to long-chain fatty acyl-CoA and that binding quenches the intrinsic fluorescence of the purified protein. FadR-DNA binding can be impaired by long-chain fatty acyl-CoA compounds. Overexpression of Rv0494 in Mycobacterium bovis BCG reduced the basal level expression of kas operon genes, thereby suggesting the repressor nature of this protein in fatty acid synthase II regulation. This is the first report, to the best of our knowledge, of a GntR/FadR family protein acting as a fatty acid-responsive transcriptional regulator in M. tuberculosis, suggesting a possible role for this protein in mycolic acid biosynthesis.