Implications of Rosiglitazone and Pioglitazone on Cardiovascular Risk in Patients with Type 2 Diabetes Mellitus

The role and therapeutic potential of macrophages in the pathogenesis of diabetic cardiomyopathy

This review provides a comprehensive analysis of the critical role played by macrophages and their underlying mechanisms in the progression of diabetic cardiomyopathy (DCM). It begins by discussing the origins and diverse subtypes of macrophages, elucidating their spatial distribution and modes of intercellular communication, thereby emphasizing their significance in the pathogenesis of DCM. The review then delves into the intricate relationship between macrophages and the onset of DCM, particularly focusing on the epigenetic regulatory mechanisms employed by macrophages in the context of DCM condition. Additionally, the review discusses various therapeutic strategies aimed at targeting macrophages to manage DCM. It specifically highlights the potential of natural food components in alleviating diabetic microvascular complications and examines the modulatory effects of existing hypoglycemic drugs on macrophage activity. These findings, summarized in this review, not only provide fresh insights into the role of macrophages in diabetic microvascular complications but also offer valuable guidance for future therapeutic research and interventions in this field.

Review: Potential protective effects of telmisartan on renal function deterioration

Experimental and clinical evidence is now available that antagonism of angiotensin II (Ang II) with both angiotensin-converting enzyme inhibitors and Ang II receptor antagonists (AIIAs) is effective in slowing the rate of renal functional loss in patients affected by proteinuric kidney diseases.Among AIIAs, telmisartan has been shown to be characterised by a potent and long lasting antihypertensive effect that may be associated with another specific effect of this molecule, the partial agonism of the peroxisome-activated receptor-gamma.Although this action has also been observed with other AIIAs, telmisartan seems to exert a more effective and specific action as in such a way to influence beneficially adipocyte metabolism, diabetes onset and insulin resistance. Recently, we have demonstrated, at the experimental and clinical level, that sustained blockade of Ang II biological activity with this class of compounds can potentially reduce the progression of renal dysfunction and in some circumstances induce the regression of renal functional and structural changes. In this review we analyse available experimental and clinical data that suggest that blocking Ang II with telmisartan may effectively ameliorate renal dysfunction in patients affected by the now frequently observed condition termed metabolic syndrome.

Transcriptomic analysis of insulin-sensitive tissues from anti-diabetic drug treated ZDF rats, a T2DM animal model

Gene expression changes have been associated with type 2 diabetes mellitus (T2DM); however, the alterations are not fully understood. We investigated the effects of anti-diabetic drugs on gene expression in Zucker diabetic fatty (ZDF) rats using oligonucleotide microarray technology to identify gene expression changes occurring in T2DM. Global gene expression in the pancreas, adipose tissue, skeletal muscle, and liver was profiled from Zucker lean control (ZLC) and anti-diabetic drug treated ZDF rats compared with those in ZDF rats. We showed that anti-diabetic drugs regulate the expression of a large number of genes. We provided a more integrated view of the diabetic changes by examining the gene expression networks. The resulting sub-networks allowed us to identify several biological processes that were significantly enriched by the anti-diabetic drug treatment, including oxidative phosphorylation (OXPHOS), systemic lupus erythematous, and the chemokine signaling pathway. Among them, we found that white adipose tissue from ZDF rats showed decreased expression of a set of OXPHOS genes that were normalized by rosiglitazone treatment accompanied by rescued blood glucose levels. In conclusion, we suggest that alterations in OXPHOS gene expression in white adipose tissue may play a role in the pathogenesis and drug mediated recovery of T2DM through a comprehensive gene expression network study after multi-drug treatment of ZDF rats.

Insulin resistance and metabolic derangements in obese mice are ameliorated by a novel peroxisome proliferator-activated receptor γ-sparing thiazolidinedione

Currently approved thiazolidinediones (TZDs) are effective insulin-sensitizing drugs that may have efficacy for treatment of a variety of metabolic and inflammatory diseases, but their use is limited by side effects that are mediated through ectopic activation of the peroxisome proliferator-activated receptor γ (PPARγ). Emerging evidence suggests that the potent anti-diabetic efficacy of TZDs can be separated from the ability to serve as ligands for PPARγ. A novel TZD analog (MSDC-0602) with very low affinity for binding and activation of PPARγ was evaluated for its effects on insulin resistance in obese mice. MSDC-0602 treatment markedly improved several measures of multiorgan insulin sensitivity, adipose tissue inflammation, and hepatic metabolic derangements, including suppressing hepatic lipogenesis and gluconeogenesis. These beneficial effects were mediated at least in part via direct actions on hepatocytes and were preserved in hepatocytes from liver-specific PPARγ(-/-) mice, indicating that PPARγ was not required to suppress these pathways. In conclusion, the beneficial pharmacology exhibited by MSDC-0602 on insulin sensitivity suggests that PPARγ-sparing TZDs are effective for treatment of type 2 diabetes with reduced risk of PPARγ-mediated side effects.

Endogenous inhibitory mechanisms and the regulation of platelet function

The response of platelets to changes in the immediate environment is always a balance between activatory and inhibitory signals, the cumulative effect of which is either activation or quiescence. This is true of platelets in free flowing blood and of their regulation of haemostasis and thrombosis. In this review, we consider the endogenous inhibitory mechanisms that combine to regulate platelet activation. These include those derived from the endothelium (nitric oxide, prostacyclin, CD39), inhibitory receptors on the surface of platelets (platelet endothelial cell adhesion molecule-1, carcinoembryonic antigen cell adhesion molecule 1, G6b-B - including evidence for the role of Ig-ITIM superfamily members in the negative regulation of ITAM-associated GPVI platelet-collagen interactions and GPCR-mediated signalling and in positive regulation of "outside-in" integrin α(IIb)β(3)-mediated signalling), intracellular inhibitory receptors (retinoic X receptor, glucocorticoid receptor, peroxisome proliferator-activated receptors, liver X receptor), and emerging inhibitory pathways (canonical Wnt signalling, Semaphorin 3A, endothelial cell specific adhesion molecule, and junctional adhesion molecule-A).

Metabolic effects of a conversion from rosiglitazone to pioglitazone in Native American patients with type 2 diabetes

In this retrospective electronic chart review, we evaluated the metabolic changes that occurred in Native American patients with type 2 diabetes who were treated with rosiglitazone and then converted to pioglitazone with no other changes in medication regimens for diabetes or dyslipidemia. Thirty-four patients were included in the analysis. After the conversion from rosiglitazone to pioglitazone, significant decreases in the levels of total cholesterol (10.1%), low-density lipoprotein cholesterol (11.7%), and triglycerides (15.3%) were seen. No significant changes occurred in weight, body mass index, fasting glucose, hemoglobin A(1c), high-densitylipoprotein cholesterol, blood pressure, or liver function tests. Significantly more patients achieved low-density lipoprotein cholesterol and triglyceride target goals when taking pioglitazone than when taking rosiglitazone. No drug discontinuations or adverse effects were reported among the evaluable population. These results are consistent with results of other studies evaluating these two drug therapies.

The PPAR-Platelet Connection: Modulators of Inflammation and Potential Cardiovascular Effects

Historically, platelets were viewed as simple anucleate cells responsible for initiating thrombosis and maintaining hemostasis, but clearly they are also key mediators of inflammation and immune cell activation. An emerging body of evidence links platelet function and thrombosis to vascular inflammation. peroxisome proliferator-activated receptors (PPARs) play a major role in modulating inflammation and, interestingly, PPARs (PPARβ/δ and PPARγ) were recently identified in platelets. Additionally, PPAR agonists attenuate platelet activation; an important discovery for two reasons. First, activated platelets are formidable antagonists that initiate and prolong a cascade of events that contribute to cardiovascular disease (CVD) progression. Dampening platelet release of proinflammatory mediators, including CD40 ligand (CD40L, CD154), is essential to hinder this cascade. Second, understanding the biologic importance of platelet PPARs and the mechanism(s) by which PPARs regulate platelet activation will be imperative in designing therapeutic strategies lacking the deleterious or unwanted side effects of current treatment options.

Non-genomic effects of PPARgamma ligands: inhibition of GPVI-stimulated platelet activation

BACKGROUND

Peroxisome proliferator-activated receptor-(gamma) (PPAR(gamma)) is expressed in human platelets although in the absence of genomic regulation in these cells, its functions are unclear.

OBJECTIVE

In the present study, we aimed to demonstrate the ability of PPAR(gamma) ligands to modulate collagen-stimulated platelet function and suppress activation of the glycoprotein VI (GPVI) signaling pathway.

METHODS

Washed platelets were stimulated with PPAR(gamma) ligands in the presence and absence of PPAR(gamma) antagonist GW9662 and collagen-induced aggregation was measured using optical aggregometry. Calcium levels were measured by spectrofluorimetry in Fura-2AM-loaded platelets and tyrosine phosphorylation levels of receptor-proximal components of the GPVI signaling pathway were measured using immunoblot analysis. The role of PPAR(gamma) agonists in thrombus formation was assessed using an in vitro model of thrombus formation under arterial flow conditions.

RESULTS

PPAR(gamma) ligands inhibited collagen-stimulated platelet aggregation that was accompanied by a reduction in intracellular calcium mobilization and P-selectin exposure. PPAR(gamma) ligands inhibited thrombus formation under arterial flow conditions. The incorporation of GW9662 reversed the inhibitory actions of PPAR(gamma) agonists, implicating PPAR(gamma) in the effects observed. Furthermore, PPAR(gamma) ligands were found to inhibit tyrosine phosphorylation levels of multiple components of the GPVI signaling pathway. PPAR(gamma) was found to associate with Syk and LAT after platelet activation. This association was prevented by PPAR(gamma) agonists, indicating a potential mechanism for PPAR(gamma) function in collagen-stimulated platelet activation.

CONCLUSIONS

PPAR(gamma) agonists inhibit the activation of collagen-stimulation of platelet function through modulation of early GPVI signalling.

Long-term pioglitazone therapy improves arterial stiffness in patients with type 2 diabetes mellitus

Pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, not only improves insulin resistance and glycemic control, but may also have additional beneficial vascular effects in patients with type 2 diabetes mellitus. We investigated whether pioglitazone had an influence on arterial stiffness, which is an independent predictor of cardiovascular events, in 204 patients with type 2 diabetes mellitus. A prospective, nonrandomized, open-label trial was performed that involved 41 patients treated with pioglitazone, 46 patients receiving sulfonylureas, 67 patients on insulin, and 50 patients on diet/exercise only. The follow-up period was 56 +/- 3 months. Arterial stiffness was evaluated by using the arterial stiffness index (ASI), which was based on analysis of the pulse wave amplitude pattern obtained during automated blood pressure measurement in the upper limb. The 4 groups had a similar baseline ASI, which was greater than the reference range in each group. Although antidiabetic therapies improved hemoglobin A(1c) and low-density lipoprotein cholesterol, ASI only decreased significantly in the pioglitazone group. Thus, pioglitazone improved abnormal arterial stiffness in patients with type 2 diabetes mellitus via a mechanism beyond the metabolic improvement. These findings may have important clinical implications in the use of pioglitazone in patients with type 2 diabetes mellitus.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

Clinical monitoring and management of the metabolic syndrome in patients receiving atypical antipsychotic medications

Individuals with major mental illness are a high-risk group for cardio-metabolic derangements due to genetic predisposition, developmental and environmental stressors, and lifestyle. This risk is compounded when they receive antipsychotic medications. Guidelines for screening, monitoring, and managing these patients for metabolic problems have been in place for several years. Despite this, recent reports document that this population continues to receive poor care in this regard. In this article, we review the metabolic profile of atypical antipsychotic medications and offer guidelines to reduce the metabolic complications of these agents.

Cardiovascular risk of rosiglitazone: another perspective

Rosiglitazone is an effective therapy for type 2 diabetes although concerns have grown about the incidence of oedema and cardiovascular adverse events in patients treated with the drug. The following review was conducted to evaluate further and complement the evidence linking rosiglitazone with an increased risk for cardiovascular adverse events by examining trials and case reports not included in recent meta-analyses. Rosiglitazone-related publications describing case reports and prospective and retrospective cohort analyses were identified using MEDLINE and EMBASE, from July 1999 to July 2007. Relevant reports cited in these publications were also obtained. A recently-published meta-analysis and a double-blind, randomized, placebo-controlled trial were also reviewed. This review of 20 case reports and 10 uncontrolled studies supports the need for added vigilance when prescribing rosiglitazone to patients for the treatment of type 2 diabetes who may be at risk for congestive heart failure. Clinical data from numerous case reports and uncontrolled studies suggested that patients receiving rosiglitazone should be monitored for the development of weight gain or oedema. Prudence should be observed in patients with a history or risk factors for congestive heart failure as they may be poor candidates for rosiglitazone therapy.

Control of lipids at baseline in the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) trial

In order to examine lipids, a major treatment parameter in those with diabetes and heart disease, the authors analyzed baseline data from the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) trial. The study consisted of 2368 participants with type 2 diabetes and coronary artery disease from 49 sites in 6 countries (2295 provided lipid measurements). Fifty-nine percent of participants had a low-density lipoprotein (LDL) cholesterol level < 100 mg/dL. Levels of total, LDL, and non-high-density lipoprotein (HDL) cholesterol and triglycerides differed by age group (younger than 55, 55-64, and 65 years and older); they were lowest in those aged 65 years. Women had higher total, LDL, and non-HDL cholesterol values. Education was associated with lower total, LDL, and non-HDL cholesterol levels. LDL cholesterol and triglyceride values were lower in the United States and Canada. Adjustment for age, sex, education level, randomization year, and medication did not eliminate these differences. Geographic variation was seen and was not fully accounted for by demographic or treatment characteristics (all P values < .05).

Targeting the pathophysiology of type 2 diabetes: rationale for combination therapy with pioglitazone and exenatide

OBJECTIVE

The objectives of this article are to review the pathophysiology of type 2 diabetes mellitus (T2DM), present the rationale for a pathophysiologically based treatment approach for patients with T2DM and discuss the role of the therapeutic combination of pioglitazone and exenatide in the management of T2DM.

METHODS

References were identified from searches of the PubMed database that were conducted in May 2007, October 2007 and March 2008 and updates to product labeling that occurred between May 2007 and December 2007. Information was selected for inclusion on the basis of its relevance to the pathophysiology of T2DM or the clinical use of thiazolidinediones or exenatide. Discussion of other anti-diabetic treatment strategies is not included.

RESULTS

T2DM results from a combination of insulin resistance and beta-cell dysfunction. The combination of a thiazolidinedione and an incretin mimetic offers a combination of characteristics (e.g., glycemic control, reduced insulin resistance, decreased weight, potential cardiovascular benefits, beta-cell preservation) that addresses many of the pathophysiologic underpinnings of T2DM. A recent small placebo-controlled study assessed the effects of exenatide used with a thiazolidinedione (TZD; pioglitazone or rosiglitazone) with or without metformin. Exenatide demonstrated a greater incidence of glycosylated hemoglobin (HbA(1c)) < 7%; greater reductions in fasting blood glucose, postprandial plasma glucose and body weight; and improved beta-cell function versus the TZD/placebo group. However, exenatide was associated with a high dropout rate, and the 16-week duration of treatment in this study precluded evaluation of the long-term effects of the exenatide/pioglitazone combination. Furthermore, exenatide/pioglitazone has not been compared with any other anti-diabetic combination in a head-to-head clinical study.

CONCLUSIONS

Dual effects on insulin sensitivity (TZD) and insulin secretion (exenatide) make the TZD/exenatide combination a rational treatment option for patients who do not attain glycemic control with a single agent. Studies undertaken to evaluate the effects on cardiovascular outcomes and the potential for prevention of T2DM with impaired glucose tolerance may reveal additional advantages of this combination approach.

Peroxisome proliferator-activated receptor gamma-independent effects of thiazolidinediones on human cardiac myofibroblast function

1. Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor (PPAR) gamma agonists that are used to lower insulin resistance in Type 2 diabetic patients. Although TZDs exhibit beneficial effects on the vasculature, their effects on the heart are less clear and are the subject of current clinical debate. Thiazolidinediones have been reported to reduce adverse myocardial remodelling, a pathology in which cardiac myofibroblasts (CMF) are pivotal. 2. The aim of the present study was to investigate whether TZDs modulate specific human CMF functions of importance to the myocardial remodelling process and to determine whether any of these effects were mediated via PPARgamma activation. 3. Immunoblotting of cultured human CMF homogenates revealed strong expression of PPARgamma (approximately 50 kDa). Three different TZDs (ciglitazone, rosiglitazone and troglitazone) and the endogenous PPARgamma ligand 15-deoxy-delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) inhibited CMF proliferation (cell number and expression of proliferating cell nuclear antigen) in a concentration-dependent manner (range 0.1-10 micromol/L) with similar potencies. This antiproliferative effect of TZDs was not reversed by the PPARgamma antagonists GW9662 or T0070907 (10-25 micromol/L). None of the TZDs or 15d-PGJ(2) affected cell migration or invasion (Boyden chamber assays without or with Matrigel barrier), matrix metalloproteinase-2 or -9 secretion (gelatin zymography) or the actin cytoskeleton (rhodamine/phalloidin fluorescent confocal microscopy). 4. In conclusion, TZDs reduce human CMF proliferation via a PPARgamma-independent mechanism. Although TZDs do not inhibit CMF invasion, their antiproliferative activity may contribute to the ability of this class of drugs to modulate adverse myocardial remodelling.

Future innovations in anti-platelet therapies

Platelets have long been recognized to be of central importance in haemostasis, but their participation in pathological conditions such as thrombosis, atherosclerosis and inflammation is now also well established. The platelet has therefore become a key target in therapies to combat cardiovascular disease. Anti-platelet therapies are used widely, but current approaches lack efficacy in a proportion of patients, and are associated with side effects including problem bleeding. In the last decade, substantial progress has been made in understanding the regulation of platelet function, including the characterization of new ligands, platelet-specific receptors and cell signalling pathways. It is anticipated this progress will impact positively on the future innovations towards more effective and safer anti-platelet agents. In this review, the mechanisms of platelet regulation and current anti-platelet therapies are introduced, and strong, and some more speculative, potential candidate target molecules for future anti-platelet drug development are discussed.

Arterial elasticity and plasma levels of adiponectin and leptin in type 2 diabetic patients treated with thiazolidinediones

BACKGROUND

Thiazolidinediones (TZDs) improve peripheral insulin sensitivity, but the effect on arterial stiffness is less clear. The aim of the present study was to assess the differential effect of pioglitazone or rosiglitazone on arterial stiffness and plasma levels of adiponectin and leptin in patients with type 2 diabetes mellitus.

METHODS

Thirty-five type 2 diabetic subjects were randomly assigned to receive pioglitazone (30 mg/day; n = 14), rosiglitazone (4 mg/day; n = 11), or placebo (medical nutrition therapy; n = 10) for 12 weeks. Changes in plasma glucose, glycosylated hemoglobin, insulin resistance (HOMA-IR), total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, adiponectin, and leptin were evaluated at baseline and after 12 weeks. In parallel, large arterial compliance (C1) and small arterial compliance (C2) were measured at baseline and at the end of treatment period.

RESULTS

At 12 weeks, the rosiglitazone (P = 0.026) and pioglitazone (P = 0.004) groups had a significant increase from baseline in adiponectin that was not seen in the medical nutrition therapy group. No significant changes in plasma leptin and in C1 and C2 elasticity indexes were observed over the entire study period in any of the treatment groups.

CONCLUSIONS

In this study of patients with type 2 diabetes, treatment with TZDs was associated with a significant improvement in adiponectin levels, although no significant effects were seen on leptin levels and arterial elasticity.

Pioglitazone use and heart failure in patients with type 2 diabetes and preexisting cardiovascular disease: data from the PROactive study (PROactive 08)

OBJECTIVE

PROspective pioglitAzone Clinical Trial In macroVascular Events (PROactive) enrolled patients with type 2 diabetes and preexisting cardiovascular disease. These patients were at high risk for heart failure, so any therapeutic benefit could potentially be offset by risk of associated heart failure mortality. We analyzed the heart failure cases to assess the effects of treatment on morbidity and mortality after reports of serious heart failure.

RESEARCH DESIGN AND METHODS

PROactive was an outcome study in 5,238 patients randomized to pioglitazone or placebo. Patients with New York Heart Association Class II-IV heart failure at screening were excluded. A serious adverse event of heart failure was defined as heart failure that required hospitalization or prolonged a hospitalization stay, was fatal or life threatening, or resulted in persistent significant disability or incapacity. Heart failure risk was evaluated by multivariate regression.

RESULTS

More pioglitazone (5.7%) than placebo patients (4.1%) had a serious heart failure event during the study (P = 0.007). However, mortality due to heart failure was similar (25 of 2,605 [0.96%] for pioglitazone vs. 22 of 2,633 [0.84%] for placebo; P = 0.639). Among patients with a serious heart failure event, subsequent all-cause mortality was proportionately lower with pioglitazone (40 of 149 [26.8%] vs. 37 of 108 [34.3%] with placebo; P = 0.1338). Proportionately fewer pioglitazone patients with serious heart failure went on to have an event in the primary (47.7% with pioglitazone vs. 57.4% with placebo; P = 0.0593) or main secondary end point (34.9% with pioglitazone vs. 47.2% with placebo; P = 0.025).

CONCLUSIONS

Although the incidence of serious heart failure was increased with pioglitazone versus placebo in the total PROactive population of patients with type 2 diabetes and macrovascular disease, subsequent mortality or morbidity was not increased in patients with serious heart failure.

Rosiglitazone prevents free fatty acid-induced vascular endothelial dysfunction

CONTEXT

Free fatty acids (FFAs) cause insulin resistance and vascular endothelial dysfunction. The peroxisome proliferator-activated receptor gamma agonist rosiglitazone acts as insulin sensitizer and could exert vasoprotective properties by preservation of endothelium-dependent vasodilation.

OBJECTIVE

We tested the effect of rosiglitazone on FFA-induced endothelial dysfunction of the forearm resistance vessels, insulin sensitivity, asymmetric dimethylarginine (ADMA), and high-sensitivity C-reactive protein concentrations in humans.

DESIGN AND SETTING

We conducted a double-blind, randomized, placebo-controlled parallel-group study at a university hospital.

PATIENTS AND INTERVENTIONS

Rosiglitazone 8 mg daily or placebo was administered to 16 healthy male subjects for 21 d. On the last day, triglycerides and heparin were infused iv to increase FFA plasma concentrations.

MAIN OUTCOME MEASURES

Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroglycerine were assessed using strain-gauge plethysmography at baseline, and on d 21 before and after 5 h of triglyceride/heparin infusion.

RESULTS

Forearm blood flow reactivity was not affected by rosiglitazone or placebo. Infusion of triglyceride/heparin substantially increased FFA concentrations (P < 0.001) and reduced endothelium-dependent vasodilation by 38 +/- 17% (P = 0.024). In the face of lower FFA elevation (P = 0.047 vs. controls), endothelium-dependent vasodilation was preserved in subjects receiving rosiglitazone (P = 0.016 vs. placebo). Endothelium-independent vasodilation and C-reactive protein were unchanged, whereas insulin sensitivity and plasma ADMA similarly decreased in both study groups after FFA elevation (both P < 0.05 vs. baseline).

CONCLUSIONS

Rosiglitazone mitigates the increase in FFA after infusion of triglyceride/heparin and prevents FFA-induced endothelial dysfunction. These effects are independent and possibly occur before any changes in insulin sensitivity and ADMA plasma concentrations in healthy subjects.

Evolution of Peroxisome Proliferator-Activated Receptor Agonists

OBJECTIVE:

To discuss the evolution of peroxisome proliferator-activated receptor (PPAR) agonists from single site to multiple subtype or partial agonists for the treatment of type 2 diabetes, dyslipidemia, obesity, and the metabolic syndrome.

DATA SOURCES:

Information was obtained from MEDLINE (1966-March 2007) using search terms peroxisome proliferator-activated receptor agonist, PPAR dual agonist, PPAR α/γ agonist, PPAR pan agonist, partial PPAR, and the specific compound names. Other sources included pharmaceutical companies, the Internet, and the American Diabetes Association 64th-66th Scientific Sessions abstract books.

STUDY SELECTION AND DATA EXTRACTION:

Animal data, abstracts, clinical trials, and review articles were reviewed and summarized.

DATA SYNTHESIS:

PPAR α, γ, and δ receptors play an important role in lipid metabolism, regulation of adipocyte proliferation and differentiation, and insulin sensitivity. The PPAR dual agonists were developed to combine the triglyceride lowering and high-density lipoprotein cholesterol elevation from the PPAR-α agonists (fibrates) with the insulin sensitivity improvement from the PPAR-γ agonists (thiazolidinediones). Although the dual agonists reduced hemoglobin A1C(A1C) and improved the lipid profile, adverse effects led to discontinued development. Currently, PPAR-γ agonists (GW501516 in Phase I trials), partial PPAR-γ agonists (metaglidasen in Phase II and III trials), and pan agonists (α, γ, δ netoglitazone in Phase II and III trials) with improved cell and tissue selectivity are undergoing investigation to address multiple aspects of the metabolic syndrome with a single medication. By decreasing both A1C and triglycerides, metaglidasen did improve multiple aspects of the metabolic syndrome with fewer adverse effects than compared with placebo. Metaglidasen is now being compared with pioglitazone.

CONCLUSIONS:

Influencing the various PPARs results in improved glucose, lipid, and weight management, with effects dependent on full or partial agonist activity at single or multiple receptors. Although the dual PPAR compounds have been associated with unacceptable toxicities, new PPAR agonist medications continue to be developed and investigated to discover a safe drug with benefits in multiple disease states.

The platelet as a therapeutic target for treating vascular diseases and the role of eicosanoid and synthetic PPARgamma ligands

The platelet was traditionally thought only to serve as the instigator of thrombus formation, but now is emerging as a pivotal player in cardiovascular disease and diabetes by inciting and maintaining inflammation. Upon activation, platelets synthesize eicosanoids such as thromboxane A2 (TXA2) and PGE2 and release pro-inflammatory mediators including CD40 ligand (CD40L). These mediators activate not only platelets, but also stimulate vascular endothelial cells and leukocytes. These autocrine and paracrine activation processes make platelets an important target for attenuating inflammation. The growing interest and recent discoveries in platelet biology has lead to the search for therapeutic platelet targets. Recently, platelets, although anucleate, were discovered to possess the transcription factor PPARgamma. Treatment with eicosanoid and synthetic PPARgamma ligands blunts platelet release of the bioactive mediators, soluble (s) CD40L and TXA2, in thrombin-activated platelets. PPARgamma ligand treatment may prove useful for dampening unwanted platelet activation and chronic inflammatory diseases such as cardiovascular disease.