Thiazolidinediones and the preservation of beta-cell function, cellular proliferation and apoptosis

Highly Enantioselective Rhodium-Catalyzed Transfer Hydrogenation of Tetrasubstituted Olefins: Application toward the Synthesis of GPR40 Agonist MK-2305

A highly efficient enantioselective synthesis for the potent G-protein-coupled receptor 40 agonist MK-2305 was developed. The key tetrasubstituted olefin was prepared via a stereoselective Mukaiyama aldol reaction/elimination sequence. The highly enantioselective rhodium-catalyzed transfer hydrogenation of the tetrasubstituted olefin afforded the target compound MK-2305 in excellent optical and chemical purity. The key asymmetric transfer hydrogenation proceeds in excellent yields and enantioselectivities for a variety of substrates. The superior reactivity of the tethered catalysts was revealed by NMR studies.

Treatment of Mitochondrial Diabetes with a Peroxisome Proliferator-activated Receptor (PPAR)-gamma Agonist

The 3243 A>G mutation in mitochondrial DNA is the most common cause of monogenic diabetes mellitus in Japan. A 45-year-old woman with mitochondrial diabetes and significant insulin resistance presented with hypoadiponectinemia despite a normal amount of visceral fat. Three months of treatment with pioglitazone (PIO) improved her blood glucose profile and response to the 75-g oral glucose tolerance test. These changes were accompanied by the amelioration of her insulin resistance and the impairment of early-phase insulin secretion. Her serum adiponectin levels increased to the normal range. In this case of mitochondrial diabetes, PIO was effective for glycemic control.

Oral antihyperglycemic treatment options for type 2 diabetes mellitus

Table 3 provides an overview of the oral antihyperglycemic drugs reviewed in this article. A 2011 meta-analysis by Bennett and colleagues found low or insufficient quality of evidence favoring an initial choice of metformin, SUs, glinides, TZDs, or (table see text) DPP-4 inhibitors (alpha-glucosidase inhibitors, bromocriptine mesylate, and SGLT2 inhibitors were not included in this meta-analysis) with regard to the outcomes measures of all-cause mortality, cardiovascular events and mortality, and incidence of microvascular disease (retinopathy, nephropathy, and neuropathy) in previously healthy individuals with newly diagnosed T2DM. Likewise, the Bennett and colleagues meta-analysis judged these drugs to be of roughly equal efficacy with regard to reduction of HbA1c (1%–1.6%) from the pretreatment baseline. The ADOPT clinical trial of 3 different and, at the time, popular, oral monotherapies for T2DM provides support for the consensus recommendation of metformin as first-line therapy. The ADOPT trial showed slightly superior HbA1c reduction for rosiglitazone compared with metformin, which was in turn superior to glyburide. However, significant adverse events, including edema, weight gain, and fractures, were more common in the rosiglitazone-treated patients. The implication of this trial is that the combination of low cost, low risk, minimal adverse effects, and efficacy of metformin justifies use of this agent as the cornerstone of oral drug treatment of T2DM. Judicious use of metformin in groups formerly thought to be at high risk for lactic acidosis (ie, those with CHF, chronic kidney disease [eGFR >30 mL/min/1.73 m2], and the elderly) may be associated with mortality benefit rather than increased risk. Secondary and tertiary add-on drug therapy should be individualized based on cost, personal preferences, and overall treatment goals, taking into account the wishes and priorities of the patient.

Do thiazolidinediones still have a role in treatment of type 2 diabetes mellitus?

Thiazolidinediones have been introduced in the treatment of type 2 diabetes mellitus (T2DM) since the late 1990s. Although troglitazone was withdrawn from the market a few years later due to liver toxicity, both rosiglitazone and pioglitazone gained widespread use for T2DM treatment. In 2010, however, due to increased risk of cardiovascular events associated with its use, the European Medicines Agency recommended suspension of rosiglitazone use and the Food and Drug Administration severely restricted its use. Thus pioglitazone is the only thiazolidinedione still significantly employed for treating T2DM and it is the only molecule of this class still listed in the American Diabetes Association-European Association for the Study of Diabetes 2012 Position Statement. However, as for the other thiazolidinediones, use of pioglitazone is itself limited by several side effects, some of them potentially dangerous. This, together with the development of novel therapeutic strategies approved in the last couple of years, has made it questionable whether or not thiazolidinediones (namely pioglitazone) should still be used in the treatment of T2DM. This article will attempt to formulate an answer to this question by critically reviewing the available data on the numerous advantages and the potentially worrying shortcomings of pioglitazone treatment in T2DM.

Glitazones exert multiple effects on β-cell stimulus-secretion coupling

Earlier studies suggest that glitazones exert beneficial effects in patients with type 2 diabetes by directly affecting insulin secretion of β-cells, besides improving the effectiveness of insulin in peripheral tissues. The effects of glitazones on stimulus-secretion coupling (SSC) are poorly understood. We tested the influence of troglitazone and pioglitazone on different parameters of SSC, including insulin secretion (radioimmunoassay), cell membrane potential, various ion currents (patch-clamp), mitochondrial membrane potential (ΔΨ), and cytosolic Ca(2+) concentration (fluorescence). Troglitazone exerted stimulatory, inhibitory, or no effects on insulin secretion depending on the drug and glucose concentration. It depolarized the ΔΨ, thus lowering ATP production, which resulted in opening of ATP-dependent K(+) channels (K(ATP) channels) and reduced insulin secretion. However, it also exerted direct inhibitory effects on K(ATP) channels that can explain enhanced insulin secretion. Troglitazone also inhibited the currents through voltage-dependent Ca(2+) and K(+) channels. Pioglitazone was less effective than troglitazone on all parameters tested. The effects of both glitazones were markedly reduced in the presence of bovine serum albumin. Glitazones exert multiple actions on β-cell SSC that have to be considered as undesired side effects because the influence of these compounds on β-cells is not controllable. The final effect on insulin secretion depends on many parameters, including the actual glucose and drug concentration, protein binding of the drug, and the drug by itself. Troglitazone and pioglitazone differ in their influence on SSC. It can be assumed that the effects of pioglitazone on β-cells are negligible under in vivo conditions.

Effects of KCNQ1 polymorphisms on the therapeutic efficacy of oral antidiabetic drugs in Chinese patients with type 2 diabetes

The aim of this study was to explore the impact of KCNQ1 variants on the responses to oral antidiabetic drugs in a Chinese study population. A 48-week randomized pharmacogenetics study compared the effects of repaglinide and rosiglitazone in 209 newly diagnosed patients with type 2 diabetes. In the repaglinide cohort, individuals who were rs2237892 TT homozygotes exhibited lower 2-h glucose levels and significantly higher cumulative attainment rates of target 2-h glucose levels (P(log-rank) = 0.0383) than the C allele carriers; patients with a greater number of rs2237892 C alleles showed larger augmentations in both fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) (P = 0.0166 and 0.0026, respectively); moreover, the rs2237895 C allele was also associated with greater increments in both fasting insulin and HOMA-IR (P = 0.0274 and 0.0259, respectively). In contrast, only an association between rs2237897 and decrease in 2-h glucose levels was detected in the rosiglitazone cohort (P = 0.0321). Our results indicated that KCNQ1 polymorphisms are associated with repaglinide efficacy, and might also be associated with rosiglitazone response, in Chinese patients with type 2 diabetes.

Effect of Rosiglitazone and Ramipril on {beta}-cell function in people with impaired glucose tolerance or impaired fasting glucose: the DREAM trial

OBJECTIVE The objective of this study was to determine the degree to which ramipril and/or rosiglitazone changed beta-cell function over time among individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) who participated in the Diabetes Reduction Assessment With Ramipril and Rosiglitazone Medication (DREAM) Trial, which evaluated whether ramipril and/or rosiglitazone could prevent or delay type 2 diabetes in high-risk individuals. RESEARCH DESIGN AND METHODS The present analysis included subjects (n = 982) from DREAM trial centers in Canada who had oral glucose tolerance tests at baseline, after 2 years, and at the end of the study. beta-Cell function was assessed using the fasting proinsulin-to-C-peptide ratio (PI/C) and the insulinogenic index (defined as 30-0 min insulin/30-0 min glucose) divided by homeostasis model assessment of insulin resistance (insulinogenic index [IGI]/insulin resistance [IR]). RESULTS Subjects receiving rosiglitazone had a significant increase in IGI/IR between baseline and end of study compared with the placebo group (25.59 vs. 1.94, P < 0.0001) and a significant decrease in PI/C (-0.010 vs. -0.006, P < 0.0001). In contrast, there were no significant changes in IGI/IR or PI/C in subjects receiving ramipril compared with placebo (11.71 vs. 18.15, P = 0.89, and -0.007 vs. -0.008, P = 0.64, respectively). The impact of rosiglitazone on IGI/IR and PI/C was similar within subgroups of isolated IGT and IFG + IGT (all P < 0.001). Effects were more modest in those with isolated IFG (IGI/IR: 8.95 vs. 2.13, P = 0.03; PI/C: -0.003 vs. -0.001, P = 0.07). CONCLUSIONS Treatment with rosiglitazone, but not ramipril, resulted in significant improvements in measures of beta-cell function over time in pre-diabetic subjects. Although the long-term sustainability of these improvements cannot be determined from the present study, these findings demonstrate that the diabetes preventive effect of rosiglitazone was in part a consequence of improved beta-cell function.

How safe is the use of thiazolidinediones in clinical practice?

BACKGROUND

Thiazolidinediones (TZDs) are widely used antidiabetic drugs with proven efficacy regarding mainly surrogate markers of diabetes management. However, efficacy on surrogate markers may not always translate into benefits in clinical outcomes. Thiazolidinediones are usually well tolerated; however, their use may be associated with several adverse effects. The first TZD, troglitazone, was withdrawn from the market owing to serious hepatotoxicity. However, this does not seem to be the case with newer TZDs.

OBJECTIVE

The aim of the present review is to discuss the safety profile of this drug class.

METHODS

We searched PubMed up to July 2008 using relevant keywords.

CONCLUSIONS

Common side effects associated with TZDs include edema, weight gain, macular edema and heart failure. Moreover, they may cause hypoglycemia when combined with other antidiabetic drugs as well as decrease hematocrit and hemoglobin levels. Increased bone fracture risk is another TZD-related side effect. Thiazolidinediones tend to increase serum low density lipoprotein cholesterol levels, with rosiglitazone having a more pronounced effect compared with pioglitazone. Moreover, rosiglitazone increases low density lipoprotein particle concentration in contrast to pioglitazone where a decrease is observed. Rosiglitazone has been associated with an increase in myocardial infarction incidence. On the other hand, pioglitazone may reduce cardiovascular events. Overall, TZDs are valuable drugs for diabetes management but physicians should keep in mind that they are associated with several adverse events, the most prominent of which is heart failure.

Tissue-specific regulation and expression of heat shock proteins in type 2 diabetic monkeys

The chaperone protein heat shock protein (HSP) 70 has been shown to protect against obesity-associated insulin resistance. Induction of HSPs is thus considered an exciting therapeutic strategy for diabetes (DM). The aims of this study were to (1) determine HSP levels in plasma, hepatic, and pancreatic tissues of type 2 DM primates and (2) assess the relationship between chaperone proteins of the HSP family and cellular protection. We collected plasma from 24 type 2 DM and 25 normoglycemic control (CTL) cynomolgus macaques. A subset of DM monkeys had liver and pancreas samples available which were compared to a second group of CTL monkeys. We found that DM monkeys had 32% lower HSP70 in circulation which remained significant even after adjustment for the greater age and bodyweight of these monkeys (p < 0.001). The liver demonstrated a similar reductions in both HSP70 and 90 that was related to 50% lower levels of the transcription factor, heat shock factor 1 (HSF1; p = 0.03). Pancreatic tissue had the opposite expression pattern with significantly higher HSF1 (p = 0.004) and accordingly higher HSP70 and 90. Pancreas from DM monkeys had less nitrosative oxidation (p = 0.03) which was unaccounted for by superoxide dismutases and was negatively associated with HSP levels (r = -0.57, p = 0.009). HSF1/HSP deficiency exists in DM liver which may contribute to hepatic insulin resistance and this deficiency was reflected in lower circulating concentrations. Pancreas maintains HSP levels despite hyperglycemia, likely in an attempt to protect vulnerable beta cells from exocrine pancreatic damage and from stress associated with insulin hypersecretion.

Impact of incretin therapy on islet dysfunction: an underlying defect in the pathophysiology of type 2 diabetes

Glucose homeostasis is governed by a complex interplay of hormonal signaling and modulation. Insulin, glucagon, amylin, the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and other hormones and enzymes interact to maintain glucose homeostasis and normal cellular metabolism. Derangements in these hormonal interactions, particularly insulin deficits and impaired insulin action, result in the development of type 2 diabetes-but only in individuals who have experienced significant dysfunction or loss of beta-cells, located in the pancreatic islets of Langerhans. Much less is known about the impact of alpha-cell dysregulation on glucose homeostasis, although it has been demonstrated that glucagon-secreting alpha-cells, also located in the pancreatic islets, play an important role in glucose metabolism. Because beta-cell dysfunction occurs early in the course of type 2 diabetes and is progressive, early intervention with therapies that improve beta-cell function is desirable. In addition to reducing HbA1c and fasting plasma glucose, the recently developed diabetes therapies GLP-1 receptor agonists (eg, exenatide, liraglutide) and dipeptidyl peptidase-4 (DPP-4) inhibitors (eg, sitagliptin, vildagliptin) appear to have beneficial effects on beta-cell dysfunction and, possibly, on alpha-cell dysregulation.