Type 2 diabetes: principles of pathogenesis and therapy

Berberine reduces insulin resistance through protein kinase C-dependent up-regulation of insulin receptor expression

Natural product berberine (BBR) has been reported to have hypoglycemic and insulin-sensitizing activities; however, its mechanism remains unclear. This study was designed to investigate the molecular mechanism of BBR against insulin resistance. Here, we identify insulin receptor (InsR) as a target of BBR to increase insulin sensitivity. In cultured human liver cells, BBR increased InsR messenger RNA (mRNA) and protein expression in a dose- and time-dependent manner. Berberine increased InsR expression in the L6 rat skeletal muscle cells as well. Berberine-enhanced InsR expression improved cellular glucose consumption only in the presence of insulin. Silencing InsR gene with small interfering RNA or blocking the phosphoinositol-3-kinase diminished this effect. Berberine induced InsR gene expression through a protein kinase C (PKC)-dependent activation of its promoter. Inhibition of PKC abolished BBR-caused InsR promoter activation and InsR mRNA transcription. In animal models, treatment of type 2 diabetes mellitus rats with BBR lowered fasting blood glucose and fasting serum insulin, increased insulin sensitivity, and elevated InsR mRNA as well as PKC activity in the liver. In addition, BBR lowered blood glucose in KK-Ay type 2 but not in NOD/LtJ type 1 diabetes mellitus mice that were insulin deficient. Our results suggest that BBR is a unique natural medicine against insulin resistance in type 2 diabetes mellitus and metabolic syndrome.

Robust signaling networks of the adipose secretome

Type 2 diabetes is a prototypical complex systems disease that has a strong hereditary component and etiologic links with a sedentary lifestyle, overeating and obesity. Adipose tissue has been shown to be a central driver of type 2 diabetes progression, establishing and maintaining a chronic state of low-level inflammation. The number and diversity of identified endocrine factors from adipose tissue (adipokines) is growing rapidly. Here, I argue that a systems biology approach to understanding the robust multi-level signaling networks established by the adipose secretome will be crucial for developing efficient type 2 diabetes treatment. Recent advances in whole-genome association studies, global molecular profiling and quantitative modeling are currently fueling the emergence of this novel research strategy.

Decreased hepatic RBP4 secretion is correlated with reduced hepatic glucose production but is not associated with insulin resistance in patients with liver cirrhosis

OBJECTIVE

Patients with liver cirrhosis have a high incidence of insulin resistance and diabetes. This study was designed to determine circulating levels and hepatic production of retinol-binding protein 4 (RBP4) in relation to parameters of hepatic and systemic metabolism in patients with liver cirrhosis.

DESIGN AND METHOD

Circulating RBP4 levels were measured in 19 patients with liver cirrhosis at different clinical stages of the disease and in 20 age-, sex- and body mass index (BMI)-matched controls. Hepatic production rates of RBP4 and glucose were assessed by measuring the arterial hepatic venous concentration difference together with hepatic blood flow. Insulin resistance was determined by the Quantitative Insulin Sensitivity Check Index (QUICKI) and the homeostasis model assessment of insulin resistance (HOMA-IR), energy expenditure by indirect calorimetry and body composition by bioelectrical impedance analysis (BIA).

RESULTS

Compared with controls, RBP4 levels in cirrhosis were decreased (8.1 +/- 1.8 vs. 22.6 +/- 2.4 mg/l, P < 0.001) due to decreased hepatic production (P < 0.05). RBP4 correlated with hepatic protein synthesis capacity (P < 0.01), but not with insulin resistance, energy expenditure, BMI or body fat mass. Plasma RBP4 correlated with hepatic glucose production (P < 0.05).

CONCLUSIONS

These data demonstrate that RBP4 in cirrhosis (i) is decreased due to reduced hepatic production, (ii) is not associated with insulin resistance, and (iii) might have a beneficial role by decreasing hepatic glucose production and could thus also be regarded as a hepatokine.

Causes and metabolic consequences of Fatty liver

Type 2 diabetes and cardiovascular disease represent a serious threat to the health of the population worldwide. Although overall adiposity and particularly visceral adiposity are established risk factors for these diseases, in the recent years fatty liver emerged as an additional and independent factor. However, the pathophysiology of fat accumulation in the liver and the cross-talk of fatty liver with other tissues involved in metabolism in humans are not fully understood. Here we discuss the mechanisms involved in the pathogenesis of hepatic fat accumulation, particularly the roles of body fat distribution, nutrition, exercise, genetics, and gene-environment interaction. Furthermore, the effects of fatty liver on glucose and lipid metabolism, specifically via induction of subclinical inflammation and secretion of humoral factors, are highlighted. Finally, new aspects regarding the dissociation of fatty liver and insulin resistance are addressed.

Growth hormone excess and the effect of octreotide in cats with diabetes mellitus

In this prospective study 16 cats with diabetes mellitus were examined for concurrent acromegaly by measuring plasma growth hormone (GH) and insulin-like growth factor-I concentrations, and magnetic resonance imaging (MRI) of the pituitary fossa. Additionally, the effects of octreotide administration on the plasma concentrations of glucose, GH, alpha-melanocyte-stimulating hormone (alpha-MSH), adrenocorticotrophic hormone (ACTH), and cortisol were measured. Five cats were diagnosed with hypersomatotropism. The pituitary was enlarged in these 5 cats and in 2 other cats. Six cats that required a maximum lente insulin dosage >or=1.5 IU/kg body weight per injection had pituitary enlargement and 5 of these cats had acromegaly. Plasma concentrations of GH, ACTH, and cortisol decreased significantly after single intravenous administration of the somatostatin analogue octreotide in the acromegalic cats. The effect on GH concentrations was more pronounced in some of the acromegalic cats than in others. In the non-acromegalic cats only ACTH concentrations decreased significantly. In both groups plasma glucose concentrations increased slightly but significantly, whereas alpha-MSH concentrations were not significantly affected. In conclusion, the incidence of hypersomatotropism with concomitant pituitary enlargement appears to be high among diabetic cats with severe insulin resistance. Some of these cats responded to octreotide administration with a pronounced decrease in the plasma GH concentration, which suggests that octreotide administration could be used as a pre-entry test for treatment with somatostatin analogues.

New therapeutic approaches in type 2 diabetes

Type 2 diabetes is a progressive chronic disease resulting from a dynamic interaction between defects in insulin secretion and insulin action. New molecules have recently been launched and many others are under clinical investigation. Besides classical sulfonylureas and glinides, new insulin secretagogues are now available, which target the incretin gut hormone glucagon-like peptide-1 (GLP-1). Indeed, oral incretin enhancers acting as antagonists of the enzyme DPP-4 (dipeptidylpeptidase-4), which inactivates natural GLP-1,and injectable incretin mimetics (exenatide) or analogues (liraglutide), which reproduce the actions of GLP-1 while resisting to DPP-4, represent new opportunities to stimulate insulin secretion, without increasing the risk of hypoglycaemia and weight gain. Among insulin sensitizers, metformin remains unequivocally the first drug of choice for the treatment of type 2 diabetes, whereas promising drugs as thiazolidinediones (glitazones) were recently challenged because of various safety issues. When insulin is required, insulin analogues, both short-acting and basal ones, may offer some advantages regarding better control of postprandial hyperglycaemia, reduced risk of hypoglycaemia and/or lower weight gain in patients with type 2 diabetes. Emphasis should be put on early detection and intensive management of type 2 diabetes, individualized glucose lowering treatments and goals, stepwise pharmacological strategy avoiding therapeutic inertia, and multiple cardiovascular risk--targeted approach.

Predicting type 2 diabetes based on polymorphisms from genome-wide association studies: a population-based study

OBJECTIVE

Prediction of type 2 diabetes based on genetic testing might improve identification of high-risk subjects. Genome-wide association (GWA) studies identified multiple new genetic variants that associate with type 2 diabetes. The predictive value of genetic testing for prediction of type 2 diabetes in the general population is unclear.

RESEARCH DESIGN AND METHODS

We investigated 18 polymorphisms from recent GWA studies on type 2 diabetes in the Rotterdam Study, a prospective, population-based study among homogeneous Caucasian individuals of 55 years and older (genotyped subjects, n = 6,544; prevalent cases, n = 686; incident cases during follow-up, n = 601; mean follow-up 10.6 years). The predictive value of these polymorphisms was examined alone and in addition to clinical characteristics using logistic and Cox regression analyses. The discriminative accuracy of the prediction models was assessed by the area under the receiver operating characteristic curves (AUCs).

RESULTS

Of the 18 polymorphisms, the ADAMTS9, CDKAL1, CDKN2A/B-rs1412829, FTO, IGF2BP2, JAZF1, SLC30A8, TCF7L2, and WFS1 variants were associated with type 2 diabetes risk in our population. The AUC was 0.60 (95% CI 0.57-0.63) for prediction based on the genetic polymorphisms; 0.66 (0.63-0.68) for age, sex, and BMI; and 0.68 (0.66-0.71) for the genetic polymorphisms and clinical characteristics combined.

CONCLUSIONS

We showed that 9 of 18 well-established genetic risk variants were associated with type 2 diabetes in a population-based study. Combining genetic variants has low predictive value for future type 2 diabetes at a population-based level. The genetic polymorphisms only marginally improved the prediction of type 2 diabetes beyond clinical characteristics.

The diabetogenic effects of excessive ethanol: reducing beta-cell mass, decreasing phosphatidylinositol 3-kinase activity and GLUT-4 expression in rats

The diabetogenic impact of ethanol remains as a focal point of basic and clinical investigations. In this study, Wistar rats were subjected to daily intragastric ethanol administration (10 ml/kg body weight injection with 0 (control), 10, 20 and 33 % (v/v) ethanol in the injections, respectively) for 19 weeks. At the end of the administration, we found that the fasting plasma glucose level of the 33 % (v/v) ethanol-loaded group was 18 % higher than the control. Insulin sensitivity was decreased in a dose-dependent manner in all the ethanol-loaded groups (r - 0.842, P < 0.001) during intraperitoneal insulin tolerance test. Necrotic/haemorrhagic injury was detected in the pancreas and islet beta-cell mass was significantly reduced in the 33 % (v/v) ethanol-loaded rats by immunohistochemical and morphometric analysis. At the molecular level, we detected a dose-dependent attenuation of phosphatidylinositol 3-kinase activity (r - 0.956, P < 0.001) and GLUT-4 expression (GLUT-4 mRNA, r - 0.899, P < 0.001; GLUT-4 protein, r - 0.964, P < 0.001) in skeletal muscle. These results demonstrated that drinking is a conditional aetiological factor for diabetes and excessive ethanol intake is negatively associated with both insulin sensitivity and beta-cell mass. The whole-body insulin resistance might result from the ethanol-induced insulin signalling defects in muscle.

Type 2 diabetes: new genes, new understanding

Over the past two years, there has been a spectacular change in the capacity to identify common genetic variants that contribute to predisposition to complex multifactorial phenotypes such as type 2 diabetes (T2D). The principal advance has been the ability to undertake surveys of genome-wide association in large study samples. Through these and related efforts, approximately 20 common variants are now robustly implicated in T2D susceptibility. Current developments, for example in high-throughput resequencing, should help to provide a more comprehensive view of T2D susceptibility in the near future. Although additional investigation is needed to define the causal variants within these novel T2D-susceptibility regions, to understand disease mechanisms and to effect clinical translation, these findings are already highlighting the predominant contribution of defects in pancreatic beta-cell function to the development of T2D.

Retinol binding protein 4 and insulin resistance in apparently healthy elderly subjects

BACKGROUND

Insulin resistance (IR) increases with advancing age, yet the underlying mechanism is not well established. Although adipocytokine retinol binding protein 4 (RBP4) was recently shown to be linked to IR, their relationship remains controversial and relatively little information exists regarding their roles in the elderly subjects. We investigated the association between RBP4 and IR in obese and nonobese elderly subjects.

METHODS

A total of 111 (68 nonobese and 43 obese) apparently healthy elderly subjects, aged 75.9+/-4.8 y were included. IR was determined by homeostasis model assessment (HOMA-IR). Serum RBP4 was measured by enzyme-linked immunosorbent assay.

RESULTS

In all subjects, RBP4 levels were positively correlated with fasting insulin, HOMA-IR, and triglycerides. However, after subgroup analysis, RBP4 levels were positively correlated with fasting glucose, fasting insulin, and HOMA-IR in the obese group only. In step-wise multiple linear regression analysis, RBP4 was found to be independently associated with triglyceride levels in the nonobese group and independently associated with HOMA-IR in the obese group.

CONCLUSIONS

The reason for the differing metabolic role of RBP4 in obese and nonobese elderly subjects remains uncertain, but our findings suggest that RBP4 may be linked to IR and lipid metabolism, at least in the elderly.

Interindividual variability in oral antidiabetic drug disposition and response: the role of drug transporter polymorphisms

BACKGROUND

Numerous effective oral pharmacologic therapies are available to treat type 2 diabetes. However, a substantial number of patients do not achieve the expected glucose-lowering response, or may be predisposed to adverse effects, from these agents. The application of pharmacogenetics to the field of type 2 diabetes is one step towards the goal of improved pharmacotherapeutic management of this progressive disease.

METHODS

A PubMed literature search was conducted to identify clinical studies that have examined the extent to which drug-transporter gene polymorphisms influence interindividual variability in oral antidiabetic drug disposition and response in humans.

RESULTS/CONCLUSION

Available data suggest that drug transporters play an important role in the disposition of some oral antidiabetic drugs in the body, particularly the meglitinides and metformin. Moreover, polymorphisms in genes encoding drug transport proteins may alter the pharmacodynamic profile of these agents. Drug transporters, drug-metabolizing enzymes, and drug targets each play a distinct and important role in the disposition and action of many oral antidiabetic agents. Thus, future studies may need to take a pharmacogenomic (i.e., multiple gene) approach in order to comprehensively understand the extent to which genetic variation contributes to interindividual differences in oral antidiabetic drug clinical pharmacology.

Mechanisms of macrophage activation in obesity-induced insulin resistance

Chronic inflammation is now recognized as a key step in the pathogenesis of obesity-induced insulin resistance and type 2 diabetes mellitus. This low-grade inflammation is mediated by the inflammatory (classical) activation of recruited and resident macrophages that populate metabolic tissues, including adipose tissue and liver. These findings have led to the concept that infiltration by and activation of macrophages in adipose tissue are causally linked to obesity-induced insulin resistance. Studies have shown, however, that alternatively activated macrophages taking residence in adipose tissue and liver perform beneficial functions in obesity-induced metabolic disease. Alternatively activated macrophages reduce insulin resistance in obese mice by attenuating tissue inflammation and increasing oxidative metabolism in liver and skeletal muscle. The discovery that distinct subsets of macrophages are involved in the promotion or attenuation of insulin resistance suggests that pathways controlling macrophage activation can potentially be targeted to treat these comorbidities of obesity. Thus, this Review focuses on the stimuli and mechanisms that control classical and alternative activation of tissue macrophages, and how these macrophage activation programs modulate insulin action in peripheral tissues. The functional importance of macrophage activation is further discussed in the context of host defense to highlight the crosstalk between innate immunity and metabolism.

Insulin sensitivity: modulation by nutrients and inflammation

Insulin resistance is a major metabolic feature of obesity and is a key factor in the etiology of a number of diseases, including type 2 diabetes. In this review, we discuss potential mechanisms by which brief nutrient excess and obesity lead to insulin resistance and propose that these mechanisms of action are different but interrelated. We discuss how pathways that "sense" nutrients within skeletal muscle are readily able to regulate insulin action. We then discuss how obesity leads to insulin resistance via a complex interplay among systemic fatty acid excess, microhypoxia in adipose tissue, ER stress, and inflammation. In particular, we focus on the hypothesis that the macrophage is an important cell type in the propagation of inflammation and induction of insulin resistance in obesity. Overall, we provide our integrative perspective regarding how nutrients and obesity interact to regulate insulin sensitivity.

miR-375 targets 3'-phosphoinositide-dependent protein kinase-1 and regulates glucose-induced biological responses in pancreatic beta-cells

OBJECTIVE

MicroRNAs are short, noncoding RNAs that regulate gene expression. We hypothesized that the phosphatidylinositol 3-kinase (PI 3-kinase) cascade known to be important in beta-cell physiology could be regulated by microRNAs. Here, we focused on the pancreas-specific miR-375 as a potential regulator of its predicted target 3'-phosphoinositide-dependent protein kinase-1 (PDK1), and we analyzed its implication in the response of insulin-producing cells to elevation of glucose levels.

RESEARCH DESIGN AND METHODS

We used insulinoma-1E cells to analyze the effects of miR-375 on PDK1 protein level and downstream signaling using Western blotting, glucose-induced insulin gene expression using quantitative RT-PCR, and DNA synthesis by measuring thymidine incorporation. Moreover, we analyzed the effect of glucose on miR-375 expression in both INS-1E cells and primary rat islets. Finally, miR-375 expression in isolated islets was analyzed in diabetic Goto-Kakizaki (GK) rats.

RESULTS

We found that miR-375 directly targets PDK1 and reduces its protein level, resulting in decreased glucose-stimulatory action on insulin gene expression and DNA synthesis. Furthermore, glucose leads to a decrease in miR-375 precursor level and a concomitant increase in PDK1 protein. Importantly, regulation of miR-375 expression by glucose occurs in primary rat islets as well. Finally, miR-375 expression was found to be decreased in fed diabetic GK rat islets.

CONCLUSIONS

Our findings provide evidence for a role of a pancreatic-specific microRNA, miR-375, in the regulation of PDK1, a key molecule in PI 3-kinase signaling in pancreatic beta-cells. The effects of glucose on miR-375 are compatible with the idea that miR-375 is involved in glucose regulation of insulin gene expression and beta-cell growth.

Plasma fetuin-A levels and the risk of type 2 diabetes

OBJECTIVE

The liver-secreted protein fetuin-A induces insulin resistance in animals, and circulating fetuin-A is elevated in insulin resistance and fatty liver in humans. We investigated whether plasma fetuin-A levels predict the incidence of type 2 diabetes in a large prospective, population-based study.

RESEARCH DESIGN AND METHODS

A case-cohort study within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam study comprising 27,548 subjects was designed. We randomly selected a subcohort of 2,500 individuals of whom 2,164 were diabetes free at baseline and had anamnestic, anthropometrical, and metabolic data for analysis. Of the 849 incident diabetic case subjects identified in the full cohort during 7 years of follow-up, 703 remained for analyses after similar exclusions.

RESULTS

Plasma fetuin-A levels were positively associated with diabetes risk after adjustment for age (relative risk [RR] for extreme quintiles 1.75 [95% CI 1.32-2.31]; RR for 10 mug/ml 1.04 [1.03-1.06]). The association remained significant after adjustment for sex, BMI, waist circumference, and lifestyle risk factors (RR for 10 mug/ml 1.03 [1.01-1.06]). Adjustment for glucose, triglycerides, HDL cholesterol, A1C, gamma-glutamyltransferase, or high-sensitivity C-reactive protein or mutual adjustment for these biomarkers did not appreciably change this result (RR for 10 mug/ml full adjusted model 1.05 [1.02-1.07]). Furthermore, fetuin-A was associated with increased diabetes risk particularly in individuals with elevated plasma glucose.

CONCLUSIONS

Our data suggest that fetuin-A is an independent risk factor of type 2 diabetes.

Zinc signalling and subcellular distribution: emerging targets in type 2 diabetes

A finely tuned subcellular distribution of zinc (Zn), through the coordinated action of Zn transporters (ZnTs) and metallothioneins (MTs), is crucial for optimal cell function. Dysfunctions of these proteins might act as key causative or promoting factors in several chronic pathologies. Evidence of their involvement in the pathogenesis of type 2 diabetes (DM2) is emerging. The association of single nucleotide polymorphisms in genes encoding ZnT-8 and MT with DM2 has drawn attention to the relevance of Zn homeostasis for insulin secretory capacity and responsiveness. Here, we propose that potential mechanisms leading to altered subcellular Zn distribution rather than deficiency might be important in DM2. Increasing knowledge of the mechanisms of Zn homeostasis and signalling should promote the development of targeted interventions with the potential to reduce the burden of disease.

Diabetes in patients with idiopathic Parkinson's disease

OBJECTIVE

Previous observational studies reported inconsistent results on the association between diabetes and Parkinson's disease, and data on the risk of developing incident diabetes in relation to Parkinson's disease are scarce. We aimed at comparing the diabetes prevalence between patients with or without Parkinson's disease and at exploring the risk of developing incident diabetes associated with Parkinson's disease.

RESEARCH DESIGN AND METHODS

We used the U.K.-based General Practice Research Database (GPRD) to 1) compare the diabetes prevalence between Parkinson's disease cases and a matched comparison group free of Parkinson's disease between 1994 and 2005 and to 2) conduct a follow-up study with a nested case-control analysis to quantify the risk of developing new-onset diabetes in association with Parkinson's disease.

RESULTS

The diabetes prevalence was similar in patients with and without Parkinson's disease (adjusted odds ratio [OR] 0.95 [95% CI 0.80-1.14]). In the cohort analysis (incidence rate ratio [IRR] 0.55 [95% CI 0.38-0.81]) and in the nested case-control analysis (adjusted OR 0.53 [95% CI 0.33-0.87]), the risk of developing diabetes was lower in patients with Parkinson's disease than in subjects without. The adjusted OR for patients with Parkinson's disease who were current levodopa users of five or more prescriptions was 0.22 (0.10-0.48) and was 1.11 (0.50-2.45) for Parkinson's disease patients not using levodopa.

CONCLUSIONS

In this observational study, diabetes prevalence was closely similar between patients with Parkinson's disease and subjects without. The risk of developing incident diabetes was lower for patients with Parkinson's disease than for patients without, a finding that was limited to Parkinson's disease patients who were using levodopa.

High-risk patients with hypertension: Are we doing enough?

Despite the increasing risk of cardiovascular disease, especially in patients with multiple risk factors, blood pressure (BP) control remains suboptimal. This study investigated real-world BP goal attainment and prescribing patterns for high-risk patients. A retrospective chart review study was conducted in patients treated by eight large primary care physician group practices between December 2003 and May 2006. A total of 1,917 hypertensive patients were identified with >/=1 risk factors: African-American ethnicity (634); diabetes (851); advanced age (1,123); body mass index (BMI) 25 kg/m(2) (1,614). BP control rate was 46% overall, and similar in the advanced age and overweight/obese subpopulations, but substantially lower (28%) in the diabetic subpopulation. Systolic blood pressure >/=20 mm Hg above the Joint National Committee on Prevention, Detection, Evaluation, and Treatment Report recommendation was found in 13% of the overall, advanced age and overweight/obese subpopulations, and in 20% of diabetics and 18% of African-Americans. Overall, 62% of patients received >/=2 antihypertensive while 36% of diabetics, 31% of African-Americans, 28% of advanced age, and 26% of overweight/obese patients received >/=3 antihypertensive classes. Despite availability of multiple antihypertensive classes, BP control rates were still suboptimal in this study's high-risk patients. There is a need for awareness and more aggressive treatment in high-risk patients given their increased risk of poor outcomes.

Palmitate impairs and eicosapentaenoate restores insulin secretion through regulation of SREBP-1c in pancreatic islets

OBJECTIVE

Chronic exposure to fatty acids causes beta-cell failure, often referred to as lipotoxicity. We investigated its mechanisms, focusing on contribution of SREBP-1c, a key transcription factor for lipogenesis.

RESEARCH DESIGN AND METHODS

We studied in vitro and in vivo effects of saturated and polyunsaturated acids on insulin secretion, insulin signaling, and expression of genes involved in beta-cell functions. Pancreatic islets isolated from C57BL/6 control and SREBP-1-null mice and adenoviral gene delivery or knockdown systems of related genes were used.

RESULTS

Incubation of C57BL/6 islets with palmitate caused inhibition of both glucose- and potassium-stimulated insulin secretion, but addition of eicosapentaenoate (EPA) restored both inhibitions. Concomitantly, palmitate activated and EPA abolished both mRNA and nuclear protein of SREBP-1c, accompanied by reciprocal changes of SREBP-1c target genes such as insulin receptor substrate-2 (IRS-2) and granuphilin. These palmitate-EPA effects on insulin secretion were abolished in SREBP-1-null islets. Suppression of IRS-2/Akt pathway could be a part of the downstream mechanism for the SREBP-1c-mediated insulin secretion defect because adenoviral constitutively active Akt compensated it. Uncoupling protein-2 (UCP-2) also plays a crucial role in the palmitate inhibition of insulin secretion, as confirmed by knockdown experiments, but SREBP-1c contribution to UCP-2 regulation was partial. The palmitate-EPA regulation of insulin secretion was similarly observed in islets from C57BL/6 mice pretreated with dietary manipulations. Furthermore, administration of EPA to diabetic KK-Ay mice ameliorated impairment of insulin secretion in their islets.

CONCLUSIONS

SREBP-1c plays a dominant role in palmitate-mediated insulin secretion defect, and EPA prevents it through SREBP-1c inhibition, implicating a therapeutic potential for treating diabetes related to lipotoxicity.

Insulin resistance syndrome and glucose dysregulation in the elderly

The incidence of insulin resistance in the geriatric population is growing as this population grows. The management of hyperglycemia and its associated risk factors depends on an expanding understanding of the underlying pathophysiology and progression of disease and of the currently available and future therapeutics, which are continually evolving. There is a major need for studies in the long-term care setting to determine the appropriate standard of care in prevention and treatment of metabolic dysregulation.

Sodium glucose co-transporter 2 inhibitors: blocking renal tubular reabsorption of glucose to improve glycaemic control in patients with diabetes

BACKGROUND

The kidney plays a central role in the regulation of plasma glucose levels, although until recently this has not been widely appreciated or considered a target for therapeutic intervention. The sodium glucose co-transporter type 2 (SGLT2) located in the plasma membrane of cells lining the proximal tubule mediates the majority of renal glucose reabsorption from the tubular fluid, which normally prevents the loss of glucose in the urine. Competitive inhibitors of SGLT2 that provoke the renal excretion of glucose have been discovered, thereby providing a unique mechanism to potentially lower the elevated blood glucose levels in patients with diabetes.

OBJECTIVE

To explore the physiology of SGLT2 action and discuss several SGLT2 inhibitors that have entered early clinical development.

METHODS

All publicly available data were identified by searching the internet for 'SGLT2' and 'SGLT2 inhibitor' through 1 November 2007. Published articles, press releases and abstracts presented at national and international meetings were considered.

RESULTS/CONCLUSION

Sodium glucose co-transporter type 2 inhibition is a novel treatment option for diabetes, which has been studied in preclinical models and a few potent and selective SGLT2 inhibitors have been reported and are currently in clinical development. These agents appear to be safe and generally well tolerated, and will potentially be a beneficial addition to the growing battery of oral antihyperglycaemic agents.

An RBP4 promoter polymorphism increases risk of type 2 diabetes

AIMS/HYPOTHESIS

Retinol-binding protein 4 (RBP4), originally known for retinol transport, was recently identified as an adipokine affecting insulin resistance. The RBP4 -803GA promoter polymorphism influences binding of hepatic nuclear factor 1alpha and is associated with type 2 diabetes in case-control studies. We hypothesised that the RBP4 -803GA polymorphism increases type 2 diabetes risk at a population-based level. In addition, information on retinol intake and plasma vitamin A levels enabled us to explore the possible underlying mechanism.

METHODS

In the Rotterdam Study, a prospective, population-based, follow-up study, the -803GA polymorphism was genotyped. In Cox proportional hazards models, associations of the -803GA polymorphism and retinol intake with type 2 diabetes risk were examined. Moreover, the interaction of the polymorphism with retinol intake on type 2 diabetes risk was assessed. In a subgroup of participants the association of the polymorphism and vitamin A plasma levels was investigated.

RESULTS

Homozygous carriers of the -803A allele had increased risk of type 2 diabetes (HR 1.83; 95% CI 1.26-2.66). Retinol intake was not associated with type 2 diabetes risk and showed no interaction with the RBP4 -803GA polymorphism. Furthermore, there was no significant association of the polymorphism with plasma vitamin A levels.

CONCLUSIONS/INTERPRETATION

Our results provide evidence that homozygosity for the RBP4 -803A allele is associated with increased risk of type 2 diabetes in the Rotterdam population. This relationship was not clearly explained by retinol intake and vitamin A plasma levels. Therefore, we cannot differentiate between a retinol-dependent or -independent mechanism of this RBP4 variant.

Evaluation of the association between retinal binding protein 4 polymorphisms and type 2 diabetes in Chinese by DHPLC

Serum retinal binding protein 4 (RBP4) was recently described as a new liver- and adipocyte-derived signal that may contribute to Type 2 diabetes mellitus (T2DM) and insulin resistance. The aim of this study was to test whether the RBP4 gene could be used as a genetic marker to predict the development of T2DM amongst the Chinese population of Han. For this study, a normal control group of 115 healthy subjects and an experimental group of 107 patients with T2DM were examined. A combined method of denaturing high-performance liquid chromatography (DHPLC) and sequencing was applied to the detection of the RBP4 gene variants. Two SNPs, rs17484721 and rs36035572, were analyzed. Phenotypes and biochemical indicators related to the metabolism of glucose and lipid were measured. We found that there are significant differences between the control group and the patients group in terms of their respective distributions of genotype and allele frequency. The TG levels of the TT and II genotype was significantly higher than that of the TC + CC and ID + DD, respectively, in both patient group and control group. These findings suggest that the variations in the RBP4 gene may be associated with T2DM and serum triglyeride levels in the Han Chinese.

Serum retinol-binding protein 4 is not increased in obesity or obesity-associated type 2 diabetes mellitus, but is reduced after relevant reductions in body fat following gastric bypass

OBJECTIVE

Controversy exists regarding the elevation of serum retinol-binding protein 4 (RBP4) in human obesity and type 2 diabetes mellitus (T2DM). In the present study, we have compared serum RBP4 in lean and obese patients with or without T2DM, and analysed the effect of weight loss on serum RBP4.

DESIGN

Forty-two Caucasian subjects were included in the study. Serum RBP4 was measured by ELISA and Western blot. In addition, serum RBP4 was measured in 21 morbidly obese patients before and after 4, 8 and 15 months of weight loss following Roux-en-Y gastric bypass (RYGBP).

RESULTS

No significant effect of either obesity or diabetes on serum RBP4 was observed. Serum RBP4 concentrations (measured by either ELISA or Western blot) did not correlate with body mass index (BMI), body fat or any indicator of glucose metabolism or insulin resistance. Weight loss following RYGBP did not modify serum RBP4 at 15 months (P = 0.472). However, the variations in serum RBP4 were significantly associated with the reduction in body fat (r = 0.48; P = 0.026). Patients loosing over 20% of fat mass (n = 11) showed significantly different RBP4 concentrations compared to those individuals exhibiting smaller adiposity reductions (n = 10) (-11.0 +/- 6.4 vs.+5.8 +/- 3.6 mg/l; P = 0.036). Furthermore, RBP4 levels were significantly reduced at 4 (P = 0.006) and 8 (P = 0.015) months only in those patients loosing over 20% of fat mass.

CONCLUSION

Serum RBP4 concentrations are not increased in obese patients with or without T2DM. A decrease in RBP4 levels was only observed after surgically induced weight loss accompanied by relevant reductions in body fat. RBP4 might be considered as a dynamic marker of negative energy balance being reduced during weight loss when a negative energy balance threshold is reached. Furthermore, RBP4 variation in the first month after RYGBP may be a predictor of weight loss success.

Rediscovering the classic osteopathic literature to advance contemporary patient-oriented research: A new look at diabetes mellitus

Patient care experiences represent opportunities for establishing theories, testable hypotheses, and data to assess the potential use of osteopathic manipulative treatment in various disease conditions. The re-analysis of Bandeen's 1949 raw data described herein summarizes the effects of osteopathic manipulative treatment involving pancreatic stimulatory and inhibitory techniques in diabetic and non-diabetic patients seen over a 25-year period of clinical practice. Bandeen's data demonstrate a reduction in blood glucose levels at 30 and 60 minutes following pancreatic stimulation in 150 diabetic patients, and an elevation in blood glucose levels at 30 and 60 minutes following pancreatic inhibition in 40 non-diabetic patients. Such patient-oriented research conducted during the classic era of osteopathy in the United States provides a foundation and data for generating hypotheses about the potential mechanisms of action of osteopathic manipulative treatment. Osteopathic investigators would be well-served to rediscover the classic osteopathic literature to help advance contemporary evidence-based medicine.

Generalised reduction of putative endothelial progenitors and CXCR4-positive peripheral blood cells in type 2 diabetes

AIMS/HYPOTHESIS

In patients with type 2 diabetes, reduced levels of circulating endothelial progenitor cells have been reported and these have been correlated with disease severity. In this study, we examined a panel of markers widely used to identify progenitor and/or stem cells, and determined their association with disease severity in diabetic patients. Since expression of chemokine (C-X-C motif) receptor 4 (CXCR4) has been associated with mobilisation and recruitment of progenitor cells, CXCR4 expression was also analysed.

METHODS

Peripheral blood mononuclear cells (PBMCs) from 98 patients with type 2 diabetes and 39 control individuals were analysed by flow cytometry for surface marker expression.

RESULTS

Cells expressing different combinations of progenitor and/or stem cell markers were severely reduced in PBMCs of diabetic patients compared with those of control participants. Moreover, a number of these putative progenitor cell populations were negatively associated with disease severity. Reduced expression of CXCR4 and CD34/CXCR4-positive cells was also observed in diabetic patients. PBMCs expressing CXCR4 positively correlated with levels of progenitor cells in control participants but not in diabetic patients. Levels of putative progenitor and CXCR4-positive cells were further decreased in patients with diabetic complications, including cardiovascular and microvascular diseases.

CONCLUSIONS/INTERPRETATION

A generalised decrease in a range of progenitor cell populations was observed in type 2 diabetic patients. This reduction was also negatively associated with disease severity.

Meta-analysis approach identifies candidate genes and associated molecular networks for type-2 diabetes mellitus

Background

Multiple functional genomics data for complex human diseases have been published and made available by researchers worldwide. The main goal of these studies is the detailed analysis of a particular aspect of the disease. Complementary, meta-analysis approaches try to extract supersets of disease genes and interaction networks by integrating and combining these individual studies using statistical approaches.

Results

Here we report on a meta-analysis approach that integrates data of heterogeneous origin in the domain of type-2 diabetes mellitus (T2DM). Different data sources such as DNA microarrays and, complementing, qualitative data covering several human and mouse tissues are integrated and analyzed with a Bootstrap scoring approach in order to extract disease relevance of the genes. The purpose of the meta-analysis is two-fold: on the one hand it identifies a group of genes with overall disease relevance indicating common, tissue-independent processes related to the disease; on the other hand it identifies genes showing specific alterations with respect to a single study. Using a random sampling approach we computed a core set of 213 T2DM genes across multiple tissues in human and mouse, including well-known genes such as Pdk4, Adipoq, Scd, Pik3r1, Socs2 that monitor important hallmarks of T2DM, for example the strong relationship between obesity and insulin resistance, as well as a large fraction (128) of yet barely characterized novel candidate genes. Furthermore, we explored functional information and identified cellular networks associated with this core set of genes such as pathway information, protein-protein interactions and gene regulatory networks. Additionally, we set up a web interface in order to allow users to screen T2DM relevance for any – yet non-associated – gene.

Conclusion

In our paper we have identified a core set of 213 T2DM candidate genes by a meta-analysis of existing data sources. We have explored the relation of these genes to disease relevant information and – using enrichment analysis – we have identified biological networks on different layers of cellular information such as signaling and metabolic pathways, gene regulatory networks and protein-protein interactions. The web interface is accessible via .

Type 2 diabetes: the many facets of care

A review of Type 2 diabetes mellitus is presented. Lifestyle recommendations with a focus on currently available medications are discussed. A case study involving a patient with diabetes mellitus and a foot ulcer is discussed in relation to current treatment recommendations.

Oxidized to non-oxidized lipoprotein ratios are associated with arteriosclerosis and the metabolic syndrome in diabetic patients

BACKGROUND AND AIM

Type 2 diabetic patients have a greater prevalence of the metabolic syndrome, oxidative stress and accelerated atherosclerosis, compared to non-diabetics. We examined the association between biomarkers of lipid peroxidation and the presence of atherosclerosis and the metabolic syndrome in diabetic patients.

METHODS AND RESULTS

We studied oxidized LDL (OxLDL), OxLDL/LDL, OxLDL/HDL, lipoperoxides, autoantibodies against OxLDL (OxLDL-Ab), diene formation of LDL (lag phase), vitamin E, vitamin E/cholesterol and PON1 polymorphisms (-108C>T, 55T>A, and 192A>G) in 166 non-smoking type 2 diabetic patients, 119 fulfilling the criteria for the metabolic syndrome, 73 with atherosclerosis and 93 without atherosclerosis. Patients with macrovascular disease had higher values of OxLDL/LDL (11%; P=0.016), OxLDL/HDL (18%; P=0.024) and OxLDL-Ab (12%; P=0.046). OxLDL/LDL and OxLDL/HDL were correlated with the number of components of the metabolic syndrome (P<0.001). PON1 polymorphisms were not associated to LDL oxidation markers, only PON1 (-108TT) was weakly associated with higher OxLDL-Ab concentrations (22%; P=0.040) in patients with atherosclerosis.

CONCLUSION

OxLDL/LDL, OxLDL/HDL and OxLDL-Ab are the most useful clinical parameters of lipoprotein oxidation for discriminating the presence of macrovascular disease in diabetic patients. The presence of the metabolic syndrome in these patients is also associated with an increase in the oxidized lipoprotein ratios.

Vildagliptin: the evidence for its place in the treatment of type 2 diabetes mellitus

INTRODUCTION

Type 2 diabetes is increasing in prevalence worldwide and is a leading cause of morbidity and mortality, mainly due to the development of complications. Vildagliptin is an inhibitor of dipeptidyl peptidase 4 (DPP-4), a new class of oral antidiabetic agents.

AIMS

To evaluate the role of vildagliptin in the management of type 2 diabetes.

EVIDENCE REVIEW

Clear evidence shows that vildagliptin improves glycemic control (measured by glycosylated hemoglobin and blood glucose levels) more than placebo in adults with type 2 diabetes, either as monotherapy or in combination with metformin. Vildagliptin is as effective as pioglitazone and rosiglitazone, and slightly less effective than metformin, although better tolerated. Further glycemic control is achieved when adding vildagliptin to metformin, pioglitazone, or glimepride. There is evidence that vildagliptin improves beta-cell function and insulin sensitivity. Vildagliptin does not appear to be associated with weight gain or with a higher risk of hypoglycemia than placebo or other commonly used oral antidiabetic agents. Economic evidence is currently lacking.

PLACE IN THERAPY

Vildagliptin improves glycemic control with little if any weight gain or hypoglycemia in adult patients with type 2 diabetes when given alone or in combination with metformin, thiazolidinediones, or sulfonylureas. Since many diabetic patients require combination therapy, the complementary mechanism of action of vildagliptin and other commonly prescribed antidiabetic drugs represents an important new therapeutic option in diabetes management.

The genetic susceptibility to type 2 diabetes may be modulated by obesity status: implications for association studies

Background

Considering that a portion of the heterogeneity amongst previous replication studies may be due to a variable proportion of obese subjects in case-control designs, we assessed the association of genetic variants with type 2 diabetes (T2D) in large groups of obese and non-obese subjects.

Methods

We genotyped RETN, KCNJ11, HNF4A, HNF1A, GCK, SLC30A8, ENPP1, ADIPOQ, PPARG, and TCF7L2 polymorphisms in 1,283 normoglycemic (NG) and 1,581 T2D obese individuals as well as in 3,189 NG and 1,244 T2D non-obese subjects of European descent, allowing us to examine T2D risk over a wide range of BMI.

Results

Amongst non-obese individuals, we observed significant T2D associations with HNF1A I27L [odds ratio (OR) = 1.14, P = 0.04], GCK -30G>A (OR = 1.23, P = 0.01), SLC30A8 R325W (OR = 0.87, P = 0.04), and TCF7L2 rs7903146 (OR = 1.89, P = 4.5 × 10^-23), and non-significant associations with PPARG Pro12Ala (OR = 0.85, P = 0.14), ADIPOQ -11,377C>G (OR = 1.00, P = 0.97) and ENPP1 K121Q (OR = 0.99, P = 0.94). In obese subjects, associations with T2D were detected with PPARG Pro12Ala (OR = 0.73, P = 0.004), ADIPOQ -11,377C>G (OR = 1.26, P = 0.02), ENPP1 K121Q (OR = 1.30, P = 0.003) and TCF7L2 rs7903146 (OR = 1.30, P = 1.1 × 10^-4), and non-significant associations with HNF1A I27L (OR = 0.96, P = 0.53), GCK -30G>A (OR = 1.15, P = 0.12) and SLC30A8 R325W (OR = 0.95, P = 0.44). However, a genotypic heterogeneity was only found for TCF7L2 rs7903146 (P = 3.2 × 10^-5) and ENPP1 K121Q (P = 0.02). No association with T2D was found for KCNJ11, RETN, and HNF4A polymorphisms in non-obese or in obese individuals.

Conclusion

Genetic variants modulating insulin action may have an increased effect on T2D susceptibility in the presence of obesity, whereas genetic variants acting on insulin secretion may have a greater impact on T2D susceptibility in non-obese individuals.

Assay-dependent variability of serum insulin levels during oral glucose tolerance test: influence on reference intervals for insulin and on cut-off values for insulin sensitivity indices

BACKGROUND

The oral glucose tolerance test (oGTT) is the most common method to estimate indices of insulin sensitivity in clinical as well as in epidemiological studies. The aim of this study was to investigate the variability of insulin levels for reference intervals and of insulin sensitivity indices during oGTT by three different insulin immunoassays.

METHODS

Serum insulin levels were determined during oGTT of randomly selected adult subjects (total n=101, with n=68 with normal glucose tolerance) by the LIAISON (LIA), the Elecsys (EL) and the AutoDELFIA (AD) method.

RESULTS

Sensitivity and precision of all three insulin assays were comparable. Insulin levels demonstrated a close (p<0.001) interassay correlation (LIA vs. EL: r=0.987, LIA vs. AD: r=0.966, EL vs. AD: r=0.965). Insulin levels and insulin sensitivity indices (n=68) of the AD method were significantly different compared to the LIA or EL assay (p<0.001). Basal insulin levels demonstrated an assay-dependent significant body mass index (BMI) dependency (LIA: r=0.24, p=0.05; AD: r=0.44, p<0.001; EL: r=0.36, p<0.01) in the regression analysis. At 120 min post glucose, gender was the relevant influencing factor on insulin levels of the LIA (r=0.40, p<0.001), AD (r=0.37, p<0.01) and EL (r=0.40 p<0.001) method.

CONCLUSIONS

We conclude that assay-dependent reference intervals should be used for the clinical interpretation of insulin levels from oGTT and of insulin sensitivity indices. Moreover, BMI and gender have to be considered as influencing factors.

Mathematical modeling and analysis of insulin clearance in vivo

BACKGROUND

Analyzing the dynamics of insulin concentration in the blood is necessary for a comprehensive understanding of the effects of insulin in vivo. Insulin removal from the blood has been addressed in many studies. The results are highly variable with respect to insulin clearance and the relative contributions of hepatic and renal insulin degradation.

RESULTS

We present a dynamic mathematical model of insulin concentration in the blood and of insulin receptor activation in hepatocytes. The model describes renal and hepatic insulin degradation, pancreatic insulin secretion and nonspecific insulin binding in the liver. Hepatic insulin receptor activation by insulin binding, receptor internalization and autophosphorylation is explicitly included in the model. We present a detailed mathematical analysis of insulin degradation and insulin clearance. Stationary model analysis shows that degradation rates, relative contributions of the different tissues to total insulin degradation and insulin clearance highly depend on the insulin concentration.

CONCLUSION

This study provides a detailed dynamic model of insulin concentration in the blood and of insulin receptor activation in hepatocytes. Experimental data sets from literature are used for the model validation. We show that essential dynamic and stationary characteristics of insulin degradation are nonlinear and depend on the actual insulin concentration.

[Role of intestinal flora in insulin resistance and obesity]

Intestinal flora can be modified by diet in both humans and rodents. Excess caloric intake in obese humans and rodents promotes proliferation of the bacterial phylum Firmicutes. Bacteria of the Firmicutes phylum permit more efficient intestinal extraction of nutrients. Oral transplantation of Firmicutes flora into axenic mice is sufficient to make them obese. The translocation towards the general circulation of the lipopolysaccharides released by lysis of Gram-negative intestinal bacilli promotes systemic inflammation. This inflammation plays a role in the genesis of insulin resistance and hepatic steatosis in rodents. Pharmacological or dietary manipulation of intestinal flora may be a new strategy for treatment of overweight and its complications.

Whole grain intake and cardiovascular disease: a meta-analysis

BACKGROUND AND AIMS

Whole grain food sources have been associated with lowered risk of cardiovascular disease (CVD). Studies in recent years have strengthened this observation and elucidated potential mechanisms for this association. This study sought to quantitate the available observational evidence on whole grain intake and clinical cardiovascular events.

METHODS AND RESULTS

Seven prospective cohort studies with quantitative measures of dietary whole grains and clinical cardiovascular outcomes were identified from MEDLINE searches and a review of the literature. Based on event estimates adjusted for cardiovascular risk factors, greater whole grain intake (pooled average 2.5 servings/d vs. 0.2 servings/d) was associated with a 21% lower risk of CVD events [OR 0.79 (95% CI: 0.73-0.85)]. Similar estimates were noted for different CVD outcomes (heart disease, stroke, fatal CVD) and in sex-specific analyses. Conversely, refined grain intake was not associated with incident CVD events [1.07 (0.94-1.22)].

CONCLUSIONS

There is a consistent, inverse association between dietary whole grains and incident cardiovascular disease in epidemiological cohort studies. In light of this evidence, policy-makers, scientists, and clinicians should redouble efforts to incorporate clear messages on the beneficial effects of whole grains into public health and clinical practice endeavors.

Mycobacterium avium subspecies paratuberculosis is not associated with type-2 diabetes mellitus

Background

The role of pathogenic mycobacteria in diabetes has been a focus of speculation since a decade without any meaningful insights into the mechanism of diabetes causation vis a vis mycobacterial factors. Two of our studies based on PCR identification of mycobacterial DNA and detection of antibodies specific to the recombinant antigens and whole cell lysates of the Mycobacterium avium subsp. paratuberculosis (MAP) shown a clear association of MAP with the presence of type 1 diabetes mellitus (T1DM).

Methods

In this study, we sought to investigate if or not type 2 diabetes (T2DM) patients harbour humoral responses to MAP. Using three different MAP antigen preparations, humoral antibody profiles were estimated for 57 T2DM patients and 57 healthy controls. Statistical analysis was performed with the Chi-square test with Yates' corrections.

Results

We observed insignificant levels of humoral antibodies against recombinant heparin binding haemagglutinin (HbHA), glycosyl transferase (Gsd) and MAP whole cell lysate in the blood of subjects with T2DM as compared to healthy controls.

Conclusion

We found no obvious association of MAP with the incidence of T2DM in Sardinian patients.

A meta-analysis of QTL for diabetes-related traits in rodents

Crossbreeding studies in rodents have identified numerous quantitative trait loci (QTL) that are linked to diabetes-related component traits. To identify genetic consensus regions implicated in insulin action and glucose homeostasis, we have performed a meta-analysis of genomewide linkage scans for diabetes-related traits. From a total of 43 published genomewide scans we assembled a nonredundant collection of 153 QTL for glucose levels, insulin levels, and glucose tolerance. Collectively, these studies include data from 48 different parental strains and >11,000 individual animals. The results of the studies were analyzed by the truncated product method (TPM). The analysis revealed significant evidence for linkage of glucose levels, insulin levels, and glucose tolerance to 27 different segments of the mouse genome. The most prominent consensus regions [localized to chromosomes 2, 4, 7, 9, 11, 13, and 19; logarithm of odds (LOD) scores 10.5-17.4] cover approximately 11% of the mouse genome and collectively contain the peak markers for 47 QTL. Approximately half of these genomic segments also show significant linkage to body weight and adiposity, indicating the presence of multiple obesity-dependent and -independent consensus regions for diabetes-related traits. At least 84 human genetic markers from genomewide scans and >80 candidate genes from human and rodent studies map into the mouse consensus regions for diabetes-related traits, indicating a substantial overlap between the species. Our results provide guidance for the identification of novel candidate genes and demonstrate the presence of numerous distinct consensus QTL regions with highly significant LOD scores that control glucose homeostasis. An interactive physical map of the QTL is available online at http://www.diabesitygenes.org.

Cognition and diabetes: a lifespan perspective

Diabetes mellitus is associated with cognitive dysfunction and abnormalities that can be seen with brain imaging. Recent studies provide important new insights into the nature and severity of these cerebral complications that help to explain why some patients with diabetes have clinically relevant neurocognitive morbidity, whereas most are apparently unaffected. This Personal View investigates the hypothesis that clinically relevant diabetes-related cognitive decrements mainly occur at two crucial periods in life: when the brain is developing in childhood, and when the brain undergoes neurodegenerative changes associated with ageing. Outside of these periods cognitive decrements mainly occur in patients with notable diabetes-related comorbidities, in particular microvascular or macrovascular complications. The identification of crucial periods and conditions for the development of diabetes-related cognitive decrements helps to draw the attention of physicians to individuals at risk and can direct future studies into the mechanisms that underlie these conditions.

Platelet signalling abnormalities in patients with type 2 diabetes mellitus: a review

The hyperactivation of platelets is involved in the cardiovascular complications associated with type 2 diabetes mellitus. Altered platelet behavior contributes to the angiopathies associated with diabetes. A number of mechanisms involved in platelet activation are altered in diabetes. Platelets from type 2 diabetic patients show an enhanced endogenous reactive oxygen species production and a reduced antioxidant capability, which increase the activity of several tyrosine kinases, such as the Bruton's tyrosine kinase, MAP kinases or proteins of the SRC family. Oxidative stress is also involved in the abnormal intracellular calcium homeostasis observed in platelets from type 2 diabetics, including an enhanced resting cytosolic calcium concentration and calcium release and entry in response to agonists. Moreover, diabetes alters the bioavailability of nitric oxide in platelets. Basal nitric oxide synthase activity is reduced in homogenates of platelets obtained from patients with type 2 diabetes mellitus. The study of these abnormalities might be helpful in the development of new pharmacological strategies to reduce platelet activation in type 2 diabetes mellitus.