Thiazolidinedione derivatives in diabetes and cardiovascular disease: an update

Electrochemical Assays for the Determination of Antidiabetic Drugs-A Review

This article presents the current state of knowledge regarding electrochemical methods for determining the active substances within drugs that are used in the treatment of type 1 and type 2 diabetes. Electrochemical methods of analysis, due to their sensitivity and easiness, are a great alternative to other, usually more expensive analytical assays. The determination of active substances mentioned in this review is based on oxidation or reduction processes on the surface of the working electrode. A wide variety of working electrodes, often modified with materials such as nanoparticles or conducting polymers, have been used for the highly sensitive analysis of antidiabetic drugs. The presented assays allow us to determine the compounds of interest in various samples, such as pharmaceutical products or different human bodily fluids.

Mechanisms underlying drug-mediated regulation of membrane protein function

The hydrophobic coupling between membrane proteins and their host lipid bilayer provides a mechanism by which bilayer-modifying drugs may alter protein function. Drug regulation of membrane protein function thus may be mediated by both direct interactions with the protein and drug-induced alterations of bilayer properties, in which the latter will alter the energetics of protein conformational changes. To tease apart these mechanisms, we examine how the prototypical, proton-gated bacterial potassium channel KcsA is regulated by bilayer-modifying drugs using a fluorescence-based approach to quantify changes in both KcsA function and lipid bilayer properties (using gramicidin channels as probes). All tested drugs inhibited KcsA activity, and the changes in the different gating steps varied with bilayer thickness, suggesting a coupling to the bilayer. Examining the correlations between changes in KcsA gating steps and bilayer properties reveals that drug-induced regulation of membrane protein function indeed involves bilayer-mediated mechanisms. Both direct, either specific or nonspecific, binding and bilayer-mediated mechanisms therefore are likely to be important whenever there is overlap between the concentration ranges at which a drug alters membrane protein function and bilayer properties. Because changes in bilayer properties will impact many diverse membrane proteins, they may cause indiscriminate changes in protein function.

Development of Novel Glitazones as Antidiabetic Agents: Molecular Design, Synthesis, Evaluation of Glucose Uptake Activity and SAR Studies

Background:

Thiazolidinediones and its bioisostere, namely, rhodanines have become ubiquitous class of heterocyclic compounds in drug design and discovery. In the present study, as part of molecular design, a series of novel glitazones that are feasible to synthesize in our laboratory were subjected to docking studies against PPAR-γ receptor for their selection.

Methods and Results:

As part of the synthesis of selected twelve glitazones, the core moiety, pyridine incorporated rhodanine was synthesized via dithiocarbamate. Later, a series of glitazones were prepared via Knovenageal condensation. In silico docking studies were performed against PPARγ protein (2PRG). The titled compounds were investigated for their cytotoxic activity against 3T3-L1 cells to identify the cytotoxicity window of the glitazones. Further, within the cytotoxicity window, glitazones were screened for glucose uptake activity against L6 cells to assess their possible antidiabetic activity.

Conclusion:

Based on the glucose uptake results, structure activity relationships are drawn for the title compounds.

Sulfonimide and Amide Derivatives as Novel PPARα Antagonists: Synthesis, Antiproliferative Activity, and Docking Studies

An agonist-antagonist switching strategy was performed to discover novel PPARα antagonists. Phenyldiazenyl derivatives of fibrates were developed, bearing sulfonimide or amide functional groups. A second series of compounds was synthesized, replacing the phenyldiazenyl moiety with amide or urea portions. Final compounds were screened by transactivation assay, showing good PPARα antagonism and selectivity at submicromolar concentrations. When tested in cancer cell models expressing PPARα, selected derivatives induced marked effects on cell viability. Notably, 3c, 3d, and 10e displayed remarkable antiproliferative effects in two paraganglioma cell lines, with CC₅₀ lower than commercial PPARα antagonist GW6471 and a negligible toxicity on normal fibroblast cells. Docking studies were also performed to elucidate the binding mode of these compounds and to help interpretation of SAR data.

Synthesis of novel benzothiazole amides: Evaluation of PPAR activity and anti-proliferative effects in paraganglioma, pancreatic and colorectal cancer cell lines

The reduced activation of PPARs has a positive impact on cancer cell growth and viability in multiple preclinical tumor models, suggesting a new therapeutic potential for PPAR antagonists. In the present study, the benzothiazole amides 2a-g were synthesized and their activities on PPARs were investigated. Transactivation assay showed a moderate activity of the novel compounds as PPARα antagonists. Notably, in cellular assays they exhibited cytotoxicity in pancreatic, colorectal and paraganglioma cancer cells overexpressing PPARα. In particular, compound 2b showed the most remarkable inhibition of viability (greater than 90%) in two paraganglioma cell lines, with IC₅₀ values in the low micromolar range. In addition, 2b markedly impaired colony formation capacity in the same cells. Taken together, these results show a relevant anti-proliferative potential of compound 2b, which appears particularly effective in paraganglioma, a rare tumor poorly responsive to chemotherapy.

The Anticancer Potential of Peroxisome Proliferator-Activated Receptor Antagonists

The effects on cancer-cell proliferation and differentiation mediated by peroxisome proliferator-activated receptors (PPARs) have been widely studied, and pleiotropic outcomes in different cancer models and under different experimental conditions have been obtained. Interestingly, few studies report and little preclinical evidence supports the potential antitumor activity of PPAR antagonists. This review focuses on recent findings on the antitumor in vitro and in vivo effects observed for compounds able to inhibit the three PPAR subtypes in different tumor models, providing a rationale for the use of PPAR antagonists in the treatment of tumors expressing the corresponding receptors.

Effect of Sitagliptin and Metformin on Prediabetes Progression to Type 2 Diabetes - A Randomized, Double-Blind, Double-Arm, Multicenter Clinical Trial: Protocol for the Sitagliptin and Metformin in PreDiabetes (SiMePreD) Study

Background

The high prevalence and incidence of type 2 diabetes mellitus (DM), and its associated morbidity and mortality, has prompted growing international interest and effort in the primary prevention of this disease. Primary prevention is possible since type 2 DM is preceded by prediabetes, offering a window opportunity to treat patients, and prevent the emergence of advanced disease. Sitagliptin is an oral dipeptidyl peptidase-IV inhibitor that preserves existing beta cell function and increases beta cell mass. These two effects have been demonstrated both in vitro and in animal studies, and current clinical data show that sitagliptin is safe. Metformin, a biguanide, reduces insulin resistance and inhibits hepatic gluconeogenesis, and has an excellent safety profile. The combination of metformin and sitagliptin, targeting both characteristics of prediabetes (insulin resistance and progressive beta cell degeneration), may potentially slow or halt the progression from prediabetes to type 2 DM. This paper describes the rationale and design of the Sitagliptin and Metformin in PreDiabetes (SiMePreD) study.

Objective

The aim of this study is to determine the effect of sitagliptin and metformin on progression from prediabetes to type 2 DM. The objectives of the study are to determine the effects of metformin and placebo on glycemic endpoints, the effects of sitagliptin and metformin on glycemic endpoints, the effects of metformin and placebo on incidence of cardiovascular disease and death, and the effects of sitagliptin and metformin on incidence of cardiovascular disease and death.

Methods

This is a randomized, double-blind, multicenter clinical study that will determine if the combination of metformin and sitagliptin is effective in preventing the progression from prediabetes to type 2 DM. The study will contain two arms (metformin/sitagliptin and metformin/placebo). Primary endpoints include the number of subjects progressing from prediabetes to type 2 DM, the number of cardiovascular events, and the number of deaths. The planned duration of the study is five years, and 410 subjects will be included in each group. Data analyses will include clinically relevant measures (eg, numbers needed to treat and numbers needed to harm) and will be performed according to the intention-to-treat principle.

Results

This study is currently in the process of acquiring research funding.

Conclusions

The SiMePreD study is the first study to investigate the utility of sitagliptin in combination with metformin for the primary prevention of type 2 DM. 

Sildenafil does not enhance but rather attenuates vasorelaxant effects of antidiabetic agents

Type 2 diabetic men commonly experience erectile dysfunction for which phosphodiesterase-5 (PDE5) inhibitors like sildenafil (Viagra) are often recommended. By preventing degradation of cyclic guanosine monophosphate (cGMP) in vascular smooth muscle, these inhibitors also enhance arterial vasorelaxant effects of nitric oxide donors (which stimulate cGMP synthesis). In the present work, we confirmed this enhancing effect after co-administration of sildenafil with nitroprusside to freshly-isolated rat tail arterial tissues. However, in the same tissues we also observed that sildenafil does not enhance but rather attenuates vasorelaxant effects of three commonly-used antidiabetic drugs, i.e. the biguanide metformin and the thiazolidinediones pioglitazone and rosiglitazone. Indeed, sildenafil completely blocked vasorelaxant effects of low concentrations of these drugs. In addition, we found that this same novel anti-vasorelaxant interaction of sildenafil with these agents was abolished by either 1) omitting extracellular glucose or 2) inhibiting specific smooth muscle glycolytic pathways; pathways known to preferentially utilize extracellular glucose to fuel certain adenosine triphosphate (ATP)-dependent ion transporters: e.g. ATP-sensitive K channels, sarcoplasmic reticulum Ca-ATPase, plasma membrane Ca-ATPase and Na/K-ATPase. Accordingly, we suspect that altered activity of one or more of these ion transporters mediates the observed attenuating (anti-vasorelaxant) interaction of sildenafil with the antidiabetic drugs. The present results are relevant because hypertension is so common and difficult to control in Type 2 diabetes. The present data suggest that sildenafil might interfere with the known antihypertensive potential of metformin and the thiazolidinediones. However, they do not suggest that it will interact with them to cause life-threatening episodes of severe hypotension, as can occur when it is co-administered with nitrates.

Effects of sulfonylureas on lipids in type 2 diabetes mellitus: a meta-analysis of randomized controlled trials

OBJECTIVE

Previous studies suggested that dyslipidemia was potentially associated with anti-diabetic medications of sulfonylureas (SUs). The results were, however, inconsistent. Therefore, we conducted a meta-analysis of randomized controlled trials (RCTs) to assess the effects of SUs on the level of lipids in patients with type 2 diabetes mellitus (T2DM).

METHODS

We searched PubMed, EMBASE, and CENTRAL databases for RCTs that addressed the effects of second- and/or third-generation SUs used in T2DM patients on lipids profiles with study duration of at least 12 weeks. Two reviewers independently screened literature, collected data, and assessed methodological quality of included studies. The meta-analysis was performed by using the RevMan5.1 software.

RESULTS

A total of 59 RCTs were included, of which 52 were included for final meta-analysis. The results suggested that SUs statistically increased the levels of FFA (SMD = 0.24, 95%CI 0.06 to 0.42) and TG (MD = 0.06, 95%CI 0.02 to 0.10), but decreased HDL-C (MD = -0.07, 95%CI -0.11 to -0.04) and LDL-C (MD = -0.11, 95%CI -0.17 to -0.04); but the SUs had no effect on TC (MD = 0.01, 95%CI -0.05 to 0.08), ApoA1 (MD = 0.01, 95%CI -0.03 to 0.04), and Apo B (MD = -0.01, 95%CI -0.05 to 0.03). When compared to metformin, SUs could increase TC and LDL-C; compared to glinides, SUs increased TC and lowered HDL-C; compared to thiazolidinediones, SUs reduced TC, LDL-C, HDL-C, and increase TG.

CONCLUSIONS

SUs have a small effect on lipids, although they may statistically increase the level of FFA and TG, and decrease LDL-C and HDL-C.

A multicomponent nutrient bar promotes weight loss and improves dyslipidemia and insulin resistance in the overweight/obese: chronic inflammation blunts these improvements

This study determined if twice-daily consumption of a nutrient-dense bar intended to fill gaps in Western diets, without other dietary/lifestyle requirements, favorably shifted metabolic/anthropometric indicators of dysregulation in a healthy direction. Three 8-wk clinical trials in 43 healthy lean and overweight/obese (OW/OB) adults, who served as their own controls, were pooled for analysis. In less inflamed OW/OB [high-sensitivity C-reactive protein (hsCRP) <1.5], statistically significant decreases occurred in weight (-1.1 ± 0.5 kg), waist circumference (-3.1 ± 1.4 cm), diastolic blood pressure (-4.1 ± 1.6 mmHg), heart rate [HR; -4.0 ± 1.7 beats per minute (bpm)], triglycerides (-72 ± 38.2 mg/dl), insulin resistance (homeostatic model of insulin resistance) (-0.72 ± 0.3), and insulin (-2.8 ± 1.3 mU/L); an increase in HDL-2b (+303 ± 116 nM) and realignment of LDL lipid subfractions toward a less atherogenic profile [decreased small LDL IIIb (-44 ± 23.5 nM), LDL IIIa (-99 ± 43.7 nM), and increased large LDL I (+66 ± 28.0 nM)]. In the more inflamed OW/OB (hsCRP >1.5), inflammation was reduced at 2 wk (-0.66 mg/L), and HR at 8 wk (-3.4 ± 1.3 bpm). The large HDL subfraction (10.5-14.5 nm) increased at 8 wk (+346 ± 126 nM). Metabolic improvements were also observed in lean participants. Thus, favorable changes in measures of cardiovascular health, insulin resistance, inflammation, and obesity were initiated within 8 wk in the OW/OB by replacing deficiencies in Western diets without requiring other dietary or lifestyle modifications; chronic inflammation blunted most improvements.

PPARγ modulates vascular smooth muscle cell phenotype via a protein kinase G-dependent pathway and reduces neointimal hyperplasia after vascular injury

Vascular smooth muscle cells (VSMCs) undergo phenotypic changes in response to vascular injury such as angioplasty. Protein kinase G (PKG) has an important role in the process of VSMC phenotype switching. In this study, we examined whether rosiglitazone, a peroxisome proliferator-activated receptor (PPAR)-γ agonist, could modulate VSMC phenotype through the PKG pathway to reduce neointimal hyperplasia after angioplasty. In vitro experiments showed that rosiglitazone inhibited the phenotype change of VSMCs from a contractile to a synthetic form. The platelet-derived growth factor (PDGF)-induced reduction of PKG level was reversed by rosiglitazone treatment, resulting in increased PKG activity. This increased activity of PKG resulted in phosphorylation of vasodilator-stimulated phosphoprotein at serine 239, leading to inhibited proliferation of VSMCs. Interestingly, rosiglitazone did not change the level of nitric oxide (NO) or cyclic guanosine monophosphate (cGMP), which are upstream of PKG, suggesting that rosiglitazone influences PKG itself. Chromatin immunoprecipitation assays for the PKG promoter showed that the activation of PKG by rosiglitazone was mediated by the increased binding of Sp1 on the promoter region of PKG. In vivo experiments showed that rosiglitazone significantly inhibited neointimal formation after balloon injury. Immunohistochemistry staining for calponin and thrombospondin showed that this effect of rosiglitazone was mediated by modulating VSMC phenotype. Our findings demonstrate that rosiglitazone is a potent modulator of VSMC phenotype, which is regulated by PKG. This activation of PKG by rosiglitazone results in reduced neointimal hyperplasia after angioplasty. These results provide important mechanistic insight into the cardiovascular-protective effect of PPARγ.

Blocking the peroxisome proliferator-activated receptor (PPAR): an overview

Peroxisome proliferator-activated receptors (PPARs) have been studied extensively over the last few decades and have been assessed as molecular targets for the development of drugs against metabolic disorders. A rapid increase in understanding of the physiology and pharmacology of these receptors has occurred, together with the identification of novel chemical structures that are able to activate the various PPAR subtypes. More recent evidence suggests that moderate activation of these receptors could be favorable in pathological situations due to a decrease in the side effects brought about by PPAR agonists. PPAR partial agonists and antagonists are interesting tools that are currently used to better elucidate the biological processes modulated by this family of nuclear receptors. Herein we present an overview of the various molecular structures that are able to block each of the PPAR subtypes, with a focus on promising therapeutic applications.

Diabetes Mellitus: New Challenges and Innovative Therapies

Diabetes is a common chronic disease affecting an estimated 285 million adults worldwide. The rising incidence of diabetes, metabolic syndrome, and subsequent vascular diseases is a major public health problem in industrialized countries. This chapter summarizes current pharmacological approaches to treat diabetes mellitus and focuses on novel therapies for diabetes mellitus that are under development.

There is great potential for developing a new generation of therapeutics that offer better control of diabetes, its co-morbidities and its complications. Preclinical results are discussed for new approaches including AMPK activation, the FGF21 target, cell therapy approaches, adiponectin mimetics and novel insulin formulations. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications.

In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality of life in the near future.

A neutral risk on the development of new-onset diabetes mellitus (NODM) in Taiwanese patients with dyslipidaemia treated with fibrates

There are no data on the incidence of new-onset diabetes mellitus (NODM ) in nondiabetic dyslipidaemia patients treated with fibrates. The aim of our study was to clarify these issues, to investigate the relationship between NODM and fibrate and whether the fibrates lead to increased risk for developing NODM. A retrospective cohort study was conducted by analyzing the Longitudinal Health Insurance Database (LHID 2005) of the National Health Insurance Research Database (NHIRD) from 2005 to 2010 to investigate all fibrate prescriptions for patients with dyslipidaemia. We estimated the hazard ratios (HRs) of NODM associated with fibrate use. We identified 145 NODM patients among 3,815 dyslipidaemic patients in the database for the study period. The risk estimates for NODM for users of fenofibrate (HR 1.30; 95% CI 0.82, 2.05) and gemfibrozil (HR 0.771; 95% CI 0.49, 1.22) were not associated with an increased risk of developing NODM (P > 0.05). Our results revealed that patients with dyslipidaemia who took fenofibrate and gemfibrozil had a neutral risk of NODM. The reasons may be associated with the fibrates have the properties that activate PPARα and in some cases also activated PPARγ, leading to showing a neutral risk of NODM.

Effects of combining simvastatin with rosiglitazone on inflammation, oxidant stress and ambulatory blood pressure in patients with the metabolic syndrome: the SIROCO study

AIM

Individually, statins and thiazolidinediones (TZDs) show positive effects on atherosclerosis progression in cellular and animal models as well as patients with diabetes; however, their combined effects have not been studied. This study examines the effects of simvastatin combined with rosiglitazone on vascular inflammation, oxidant stress, ambulatory blood pressure (BP) and other atherosclerotic factors in patients with the metabolic syndrome.

METHODS

This is a randomized, double blind, placebo-controlled study in 53 subjects with the metabolic syndrome. Participants were randomized to simvastatin 40 mg/day plus placebo vs. simvastatin 40 mg/day plus rosiglitazone 4 mg/day for 6 months. The primary endpoint was the between-group difference in high-sensitivity C-reactive protein (hs-CRP) and secondary variables including urinary isoprostanes, serum malondialdehyde (MDA), ambulatory BP, adiponectin, and lipid and glycaemic profiles.

RESULTS

At study end, the group randomized to the simvastatin/rosiglitazone combination had a greater reduction in hs-CRP of 1.33 mg/dl, (p = 0.029) and showed a trend for a greater reduction in urinary isoprostane (-39%), (p = 0.056) compared to simvastatin/placebo group. Changes in MDA levels did not differed between groups (p = 0.81). 24-h systolic blood pressure (SBP) also showed a 4.5 mmHg reduction at 6 months (p = 0.06). Adiponectin levels increased by 3.91 µg/ml in the combination group over placebo, (p = 0.03) and blood glucose decreased in combination group vs. placebo.

CONCLUSION

Our data show that patients with the metabolic syndrome given a statin/TZD combination manifest greater reductions in markers of vascular inflammation and oxidant stress, 24-h ambulatory BP and increases in adiponectin as well as improved glycaemic indices.

Thiazolidinedione insulin sensitizers alter lipid bilayer properties and voltage-dependent sodium channel function: implications for drug discovery

The thiazolidinediones (TZDs) are used in the treatment of diabetes mellitus type 2. Their canonical effects are mediated by activation of the peroxisome proliferator–activated receptor γ (PPARγ) transcription factor. In addition to effects mediated by gene activation, the TZDs cause acute, transcription-independent changes in various membrane transport processes, including glucose transport, and they alter the function of a diverse group of membrane proteins, including ion channels. The basis for these off-target effects is unknown, but the TZDs are hydrophobic/amphiphilic and adsorb to the bilayer–water interface, which will alter bilayer properties, meaning that the TZDs may alter membrane protein function by bilayer-mediated mechanisms. We therefore explored whether the TZDs alter lipid bilayer properties sufficiently to be sensed by bilayer-spanning proteins, using gramicidin A (gA) channels as probes. The TZDs altered bilayer elastic properties with potencies that did not correlate with their affinity for PPARγ. At concentrations where they altered gA channel function, they also altered the function of voltage-dependent sodium channels, producing a prepulse-dependent current inhibition and hyperpolarizing shift in the steady-state inactivation curve. The shifts in the inactivation curve produced by the TZDs and other amphiphiles can be superimposed by plotting them as a function of the changes in gA channel lifetimes. The TZDs’ partition coefficients into lipid bilayers were measured using isothermal titration calorimetry. The most potent bilayer modifier, troglitazone, alters bilayer properties at clinically relevant free concentrations; the least potent bilayer modifiers, pioglitazone and rosiglitazone, do not. Unlike other TZDs tested, ciglitazone behaves like a hydrophobic anion and alters the gA monomer–dimer equilibrium by more than one mechanism. Our results provide a possible mechanism for some off-target effects of an important group of drugs, and underscore the importance of exploring bilayer effects of candidate drugs early in drug development.

Advances in the treatment of type 2 diabetes mellitus

There is a rising worldwide prevalence of diabetes, especially type 2 diabetes mellitus (T2DM), which is one of the most challenging health problems in the 21st century. The associated complications of diabetes, such as cardiovascular disease, peripheral vascular disease, stroke, diabetic neuropathy, amputations, renal failure, and blindness result in increasing disability, reduced life expectancy, and enormous health costs. T2DM is a polygenic disease characterized by multiple defects in insulin action in tissues and defects in pancreatic insulin secretion, which eventually leads to loss of pancreatic insulin-secreting cells. The treatment goals for T2DM patients are effective control of blood glucose, blood pressure, and lipids (if elevated) and, ultimately, to avert the serious complications associated with sustained tissue exposure to excessively high glucose concentrations. Prevention and control of diabetes with diet, weight control, and physical activity has been difficult. Treatment of T2DM has centered on increasing insulin levels, either by direct insulin administration or oral agents that promote insulin secretion, improving sensitivity to insulin in tissues, or reducing the rate of carbohydrate absorption from the gastrointestinal tract. This review presents comprehensive and up-to-date information on the mechanism(s) of action, efficacy, pharmacokinetics, pleiotropic effects, drug interactions, and adverse effects of the newer antidiabetic drugs, including (1) peroxisome proliferator-activated-receptor-γ agonists (thiazolidinediones, pioglitazone, and rosiglitazone); (2) the incretin, glucagon-like peptide-) receptor agonists (incretin-mimetics, exenatide. and liraglutide), (3) inhibitors of dipeptidyl-peptidase-4 (incretin enhancers, sitagliptin, and vildagliptin), (4) short-acting, nonsulfonylurea secretagogue, meglitinides (repaglinide and nateglinide), (5) amylin anlog-pramlintide, (6) α-glucosidase inhibitors (miglitol and voglibose), and (7) colesevelam (a bile acid sequestrant). In addition, information is presented on drug candidates in clinical trials, experimental compounds, and some plants used in the traditional treatment of diabetes based on experimental evidence. In the opinion of this reviewer, therapy based on orally active incretins and incretin mimetics with long duration of action that will be efficacious, preserve the β-cell number/function, and block the progression of diabetes will be highly desirable. However, major changes in lifestyle factors such as diet and, especially, exercise will also be needed if the growing burden of diabetes is to be contained.

Evidence of direct smooth muscle relaxant effects of the fibrate gemfibrozil

Fibrates are commonly employed to treat abnormal lipid metabolism via their unique ability to stimulate peroxisome proliferator-activated receptor alpha (PPARalpha). Interestingly, they also decrease systemic arterial pressure, despite recent evidence that PPAR alpha may contribute to expression of renin and related hypertension. Yet, mechanisms responsible for their potential antihypertensive activity remain unresolved. Rapid decreases in arterial pressure following bolus intravenous injections of bezafibrate strongly suggest they may relax arterial smooth muscle directly. But since bezafibrate is highly susceptible to photodegradation in aqueous media, it has never been critically tested for this possibility in vitro with isolated arterial smooth muscle preparations. Accordingly, we tested gemfibrozil which is resistant to photodegradation. We examined it over a therapeutically-relevant range (50-400 microM) for both acute and delayed relaxant effects on contractions of the isolated rat tail artery; contractions induced by either depolarizing its smooth muscle cell membranes with high potassium or stimulating its membrane-bound receptors with norepinephrine and arginine-vasopressin. We also examined these same gemfibrozil levels for effects on spontaneously-occurring phasic rhythmic contractile activity, typically not seen in arteries under in vitro conditions but commonly exhibited by smooth muscle of uterus, duodenum and bladder. We found that gemfibrozil significantly relaxed all induced forms of contraction in the rat tail artery, acutely at the higher test levels and after a delay of a few hours at the lower test levels. The highest test level of gemfibrozil (400 microM) also completely abolished spontaneously-occurring contractile activity of the isolated uterus and duodenum and markedly suppressed it in the bladder. This is the first evidence that a fibrate drug can directly relax smooth muscle contractions, either induced by various contractile agents or spontaneously-occurring. These findings are particularly relevant to both the recently renewed concern over the impact of fibrates on hypertension and a new understanding of their gastrointestinal side effects.

PPAR-γ agonism for cardiovascular and renal protection

Diabetes mellitus is an established risk factor for cardiovascular disease and the leading cause of end-stage renal disease in the Western World. Thiazolidinediones (TZDs) represent a class of antidiabetic agents that exert their glucose-lowering effects by reducing insulin resistance, through stimulation of a type of nuclear receptor, called peroxisome proliferator-activated receptor-γ. Apart from improving glycemic control, TZDs were shown to exert beneficial effects on several components of the metabolic syndrome and cardiovascular risk markers. Furthermore, background and human studies have shown that TZDs reduce urinary albumin and protein excretion and interfere with most of the pathogenentic pathways involved in the development and progression of diabetic nephropathy. On the other hand, currently used TZDs have side effects, most important of which is fluid retention leading to wait gain and heart failure deterioration. With regards to cardiovascular outcomes, the anticipated benefit of TZDs was demonstrated for pioglitazone, whereas a series of previous meta-analyses linking rosiglitazone treatment with increased risk of myocardial infarction and cardiovascular death raised uncertainty around the cardiovascular safety of rosiglitazone. This article will discuss the effects of TZDs on established and emerging cardiovascular risk factors, the data on possible beneficial renal effects of these compounds, and the existing evidence from large-scale clinical trials and meta-analyses on their effects on cardiovascular outcomes, aiming to provide an overview of the cardio- and renoprotective properties of these drugs.

Diabetes mellitus: new challenges and innovative therapies

Diabetes mellitus is a widespread disease prevalence and incidence of which increases worldwide. The introduction of insulin therapy represented a major breakthrough in type 1 diabetes; however, frequent hyper- and hypoglycemia seriously affects the quality of life of these patients. New therapeutic approaches, such as whole pancreas transplant or pancreatic islet transplant, stem cell, gene therapy and islets encapsulation are discussed in this review. Regarding type 2 diabetes, therapy has been based on drugs that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glucose production (biguanides), delay digestion and absorption of intestinal carbohydrate (alpha-glucosidase inhibitors) or improve insulin action (thiazolidinediones). This review is also focused on the newer therapeutically approaches such as incretin-based therapies, bariatric surgery, stem cells and other emerging therapies that promise to further extend the options available. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Some of these therapies rely on genetic modification of non-differentiated cells to express pancreatic endocrine developmental factors, promoting differentiation of non-endocrine cells into β-cells, enabling synthesis and secretion of insulin in a glucose-regulated manner. Alternative therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications. In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality-life and allow personalized therapy-planning in the near future.

Effect of thiazolidinediones on albuminuria and proteinuria in diabetes: a meta-analysis

BACKGROUND

Because of the major clinical and economic burden of diabetic nephropathy, new therapeutic tools to delay its progression are needed. Recent studies suggest that thiazolidinediones have renal benefits. We aimed to evaluate the effect of thiazolidinediones on urinary albumin and protein excretion in patients with diabetes mellitus.

STUDY DESIGN

Systematic review and meta-analysis by searching MEDLINE/PubMed, EMBASE, and Cochrane CENTRAL databases (1991 to September 2009).

SETTING & POPULATION

Patients with diabetes mellitus.

SELECTION CRITERIA FOR STUDIES

Randomized controlled trials.

INTERVENTION

Thiazolidinediones (rosiglitazone and pioglitazone) compared with placebo or other antidiabetic agents.

OUTCOMES

Weighted (WMDs) and standardized mean differences (SMDs) for changes in urine albumin or protein excretion between the thiazolidinedione and control groups.

RESULTS

Of 171 originally identified articles, 15 studies (5 with rosiglitazone and 10 with pioglitazone) involving 2,860 patients were included in the analysis. In participants with baseline normo- or microalbuminuria, the WMD of proportional changes between the thiazolidinedione and control groups in urinary albumin excretion measured using time-specified collections was -64.8% (95% CI, -75.6 to -53.9) and the WMD of changes in albumin-creatinine ratio was -24.8% (95% CI, -39.6 to -10.0). Overall, in participants with normo- and microalbuminuria, thiazolidinedione treatment was associated with a significant decrease in urinary albumin excretion (SMD, -0.6 units of standard deviation [SD]; 95% CI, -0.8 to -0.4). Similarly, thiazolidinediones were associated with a significant decrease in urinary protein excretion in patients with proteinuria (SMD, -1.1 units of SD; 95% CI, -1.8 to -0.4).

LIMITATIONS

Significant heterogeneity across included studies in several subgroup analyses; patient-level data not available.

CONCLUSIONS

Treatment with thiazolidinediones significantly decreases urinary albumin and protein excretion in patients with diabetes. This finding calls for clinical trials with hard renal outcomes to elucidate the potential benefits of thiazolidinediones on diabetic nephropathy.

Fixed-dose combination of sitagliptin and metformin for the treatment of type 2 diabetes

Janumet(TM,) a fixed dose combination of sitagliptin/metformin HCL manufactured by Merck Pharmaceuticals, has received US Food and Drug Administration approval for treatment of patients with type 2 diabetes, that are inadequately controlled, either by sitagliptin or metformin alone or together in free-dose combination form. Sitagliptin, an inhibitor of the enzyme DDP-4, assists patients with type 2 diabetes mellitus to achieve glycemic control. It has been shown to be safe and effective at 100 mg daily doses. The effect of giving sitagliptin in combination with metformin is thought to have a complimentary and possibly additive effect on glycemic control.

Treatment choice and effectiveness of adding sulphonylurea or glitazones to metformin for the treatment of type 2 diabetes mellitus

AIM

This study investigates the treatment choice between, and the effectiveness of, adding sulphonylurea or glitazone to ongoing metformin therapy for patients with type 2 diabetes mellitus in the clinical practice setting.

METHODS

A multicentre observational study using data from clinical records was conducted in Finland, France, Germany, Norway, Poland, Spain and the UK. Data were collected for patients who added sulphonylurea or glitazone to metformin. Effectiveness was defined as a change in haemoglobin A1c (HbA(1c)) from baseline to approximately 1 year after the initiation of additional therapy. To allow for comparisons between the two medication regimens, propensity score matching was employed. Treatment choice was analysed using a probit regression model. We hypothesized that treatment choice was associated with factors reflecting patient's characteristics, patient's experience with diabetes, patient's health or to physician's characteristics at baseline.

RESULTS

Compared with baseline, adding sulphonylurea to metformin reduced HbA(1c) by 0.8% (p < 0.0001), while adding glitazone to metformin reduced HbA(1c) by 0.9% (p < 0.0001). Percentage at HbA(1c) goal (6.5%) increased from 6.9 to 23.8% for the sulphonylurea group and 8.3 to 33.3% for the glitazone group. Both groups had similar changes in high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and triglycerides. In the probit regression model, age, HbA(1c), weight, treatment for weight reduction, history of macrovascular complications and type of physician were significant factors associated with treatment choice.

CONCLUSIONS

This study is consistent with the results of long-term randomized clinical trials in a clinical practice setting. Both regimens were able to reduce HbA(1c) by about 1%.