Antiatherogenic effects of thiazolidinediones?

Type 2 diabetes and atherosclerotic cardiovascular disease: do they share common antecedents?

It has been suggested that the association between type 2 diabetes and atherosclerotic cardiovascular disease might result from a shared antecedent — the `common soil' hypothesis. The antecedent could provide a fundamental link between type 2 diabetes and atherosclerosis via the metabolic (or insulin resistance) syndrome. The relative contributions of genes, fetal nutrition and environmental factors to this syndrome remain unclear. Although most patients with type 2 diabetes have insulin resistance, it is uncertain whether the insulin resistance-hyperinsulinaemia complex directly promotes atherogenesis, and whether type 2 diabetes and atheroma are connected via a common mediator such as central obesity, vascular endothelial dysfunction, or disordered lipid metabolism. Insulin sensitivity and cardiovascular risk may be influenced by adipocytokines (e.g. leptin and adiponectin), by excess fatty acids liberated from visceral fat, and inflammatory processes. Disturbances of the neuro-endocrine system, possibly mediated via visceral obesity, are also under investigation. Other putative links between type 2 diabetes and atheroma include polymorphisms in the genes for tumour necrosis factor-α,insulin-like growth factor-1 promoter, and lamin A/C. Trials with certain cardioprotective agents including inhibitors of the renin-angiotensin-aldosterone system and statins can improve cardiovascular outcomes and protect against the development of type 2 diabetes, lending support to the common soil hypothesis.

Effect of DHA-rich fish oil on PPARγ target genes related to lipid metabolism in type 2 diabetes: A randomized, double-blind, placebo-controlled clinical trial

BACKGROUND

The beneficial effects of omega-3 polyunsaturated fatty acids on lipid levels are well documented. However, the related molecular mechanisms are widely unknown. Omega-3 polyunsaturated fatty acids are natural ligand for peroxisome proliferator-activated receptor γ (PPARγ).

OBJECTIVE

The aim of this study was to evaluate the effect of docosahexaenoic acid (DHA)-rich fish oil supplementation on modulation of some PPARγ-responsive genes related to lipid metabolism.

METHODS

Patients with type 2 diabetes were randomly assigned to consume either DHA-rich fish oil (containing 2400 mg/d fish oil; DHA: 1450 mg and eicosapentaenoic acid: 400 mg) or placebo for 8 weeks. Lipid profile and glycemic control parameters as well as the gene expression of PPARγ, liver x receptor-a, ATP-binding cassette A1, and CD36 in peripheral blood mononuclear cells were measured at baseline and after 8 weeks.

RESULTS

DHA-rich fish oil supplementation resulted in decreased triglycerides (TG) level compared with placebo group, independently of the baseline value of TG (all patients (P = .003), hypertriglyceridemic subjects (P = .01), and normotriglyceridemic subjects (P = .02)). Moreover, a higher reduction in TG level was observed in hypertriglyceridemic subjects, comparing to normotriglyceridemic subjects with DHA-rich fish oil supplementation (P = .01). Other lipid parameters as well as the expression of PPARγ, liver x receptor-a, ATP-binding cassette A1, and CD36 were not affected by DHA-rich fish oil supplementation. Only in hypertriglyceridemic subjects, DHA-rich fish oil supplementation upregulated CD36 expression, compared with the placebo group (P = .01).

CONCLUSIONS

DHA-rich fish oil supplementation for 8 weeks increased CD36 expression in hypertriglyceridemic subjects, which might result to higher reduction in TG level, comparing with normotriglyceridemic subjects. However, this finding should be investigated in further studies.

Prevention of cardiovascular complications of the metabolic syndrome: focus on pharmacotherapy

The metabolic syndrome increases the risk of atherothrombotic cardiovascular disease (CVD) and diabetes. In turn, diabetes promotes the development of atheroma and is regarded as a coronary heart disease risk equivalent. A multifactorial therapeutic strategy is advocated for patients with the metabolic syndrome to improve cardiovascular risk factor profiles and to reduce the chances of developing type 2 diabetes. Individual components of the syndrome must be addressed using safe, efficacious, and cost-effective measures. There is general agreement that lifestyle modifications, including control of body weight, avoidance of central adiposity, adoption of an antiatherogenic diet, and regular physical activity, are crucial. However, as the magnitude of the individual components of the metabolic syndrome increases with time, lifestyle measures are often insufficient. An individual with metabolic syndrome will often require drug treatment for hyperglycemia, atherogenic dyslipidemia, and high blood pressure, together with antiplatelet therapy. Reducing the need for polypharmacy is an increasingly important consideration for clinicians and the pharmaceutical industry; to date, no single therapy has emerged that targets the root cause(s) of the syndrome. HMG-CoA reductase inhibitors are important agents that reduce CVD morbidity and mortality, in people with impaired fasting glucose or metabolic syndrome. Selective cannabinoid receptor antagonists appear promising because they improve or attenuate several key defects of the syndrome. Thiazolidinediones and metformin are presently licensed for treatment of type 2 diabetes but may prove to have a broader role in future. Novel insulin-sensitizing drugs are under investigation. Drugs that act to prevent or reverse endothelial dysfunction may be of particular utility in preventing cardiovascular disease, especially if initiated before tissue damage has become irreversible. Insulin therapy, which has antiinflammatory and endothelial protective properties, has been shown to reduce morbidity and mortality in high-risk nondiabetic patients during critical illness. Potential synergy between different classes of drugs with metabolic and/or cardiovascular protective properties merits further investigation.

Interactions between microvascular and macrovascular disease in diabetes: pathophysiology and therapeutic implications

Convention partitions the complications of diabetes into two main subtypes. First are the diabetes-specific microvascular complications of retinopathy, nephropathy and neuropathy; second are the atherothrombotic macrovascular complications that account for the majority of premature deaths. Pathological interactions between microvascular and macrovascular complications, for example, nephropathy and macrovascular disease, are common. Similar mechanisms and shared risk factors drive the development and progression of both small and large vessel disease. This concept has therapeutic implications. Mounting evidence points to the need for multifactorial strategies to prevent vascular complications in subjects with diabetes and/or the metabolic syndrome. We advocate a combined therapeutic approach that addresses small and large vessel disease. Preferential use should be made of drug regimens that (i) maximize vascular protection, (ii) reduce the risk of iatrogenic vascular damage and (iii) minimize the increasing problem of polypharmacy.

Cardiovascular effects of the thiazolidinediones

Thiazolidinediones, used for the treatment of diabetes mellitus type 2, modulate gene expression by binding to nuclear transcription factor, peroxisome proliferator-activated receptor-gamma. Peroxisome proliferator-activated receptor-gamma is expressed in several tissues, therefore, thiazolidinediones have biological effects on multiple organ systems. Here, we describe evidence that thiazolidinediones have beneficial effects on the cardiovascular system independent of their antidiabetic effect. Studies in animals have clearly shown that thiazolidinediones decrease blood pressure, left ventricular hypertrophy, development of atherosclerotic lesions, and protect myocardium from ischemia/reperfusion injury. Although relatively few studies in humans have been reported, the preponderance of available evidence suggests a beneficial effect of thiazolidinediones. Thus, by modulating gene expression, thiazolidinediones may provide a novel method for the prevention and treatment of cardiovascular diseases.

A potent activator of PPARα and γ reduces the vascular cell recruitment and inhibits the intimal thickning in hypercholesterolemic rabbits

Peroxisome proliferator-activated receptors (PPARs) regulate the vascular cell functions as well as systemic lipid and glucose metabolism. Here, we studied the effect of TAK-559, a newly developed potent activator both for PPARalpha and gamma, on the vascular cell recruitment. TNF-alpha- or interleukin-1beta (IL-1beta)-induced THP-1 cell attachment to cultured endothelial cells was significantly reduced in the presence of 10 microM TAK-559 (P < 0.05). The secretion of monocyte chemoattractant protein-1 (MCP-1) from endothelial cells is reduced by 36% in the presence of 10 microM TAK-559, accompanied with the decreased mRNA expression in the cells. The proliferation and migration of cultured smooth muscle cells (SMCs) were significantly decreased in the presence of TAK-559 (P < 0.05). TAK-559-treated hypercholesterolemic rabbits showed the significant reduction of intimal thickning after balloon catheterization by 51% compared with control (P < 0.05), although the plasma lipid and glucose level was not changed between them. The numbers of macrophage and SMCs were decreased to 34% and 49% in the hyperplastic intima of arteries from TAK-559-treated rabbits compared to those from control, respectively. These results suggest that the PPARalpha and gamma activator inhibits the recruitment of macrophages and SMCs in intima, possibly leading to the reduction of intimal hyperplasia in hypercholesterolemia.

Effets cardiovasculaires de la rosiglitazone

PROVEN EFFICACY

Since their launch on the French market in 2002, thiazolidinediones ("glitazones") prescribing conditions and therapeutic indications have progressively widened, although remaining strictly defined by the marketing licence. Clinical efficacy on glycemic control (HbA1c and glycemia), as well as beneficial metabolic effects (on lipids, insulinresistance and beta-cellular function) are now well established. Their side effects, generally minor or mild, are also well known. The problem of cardiovascular adverse events, although of a low incidence, should be known and recognized, notably fluid retention (and oedema) and risk of heart failure, more frequent in diabetic than in non diabetic patients. Clinicians must know and take into account the particular risk factors, clinical and diagnosis characteristics, possible pathophysiological mechanisms and their main preventive measures. POTENTIAL BENEFICIAL EFFECTS: On the other hand, numerous experimental and/or preliminary data in type 2 diabetic patients, including favourable effects on the various pathophysiological mechanisms involved in atherosclerosis and effects on cardiovascular risk factors or markers, justifies further large prospective long term clinical studies to assess glitazone effects on cardiovascular morbidity and mortality in type 2 diabetic patients at high cardiovascular risk. Several controlled studies are currently ongoing with rosiglitazone (ADOPT, BARI-2D, DREAM, RECORD, etc.), their results within the next coming Years will answer the questions on the anticipated benefits of rosiglitazone in terms of cardiovascular prevention and/or protection in type 2 diabetic patients.

Pioglitazone, insulinosensibilité et diabète de type 2 : données récentes

Thiazolidinediones ("glitazones") were recently added to the oral treatment of type 2 diabetes. Two glitazones are available in France, pioglitazone and rosiglitazone, which progressively were granted broader therapeutic indications since their launch in 2002. This review presents the most recent pioglitazone pharmacological and clinical data, with a particular emphasis on the QUARTET clinical study program results. Available information generates perspectives and hopes: prevention of the progressive decline in beta-pancreatic cell function (and possibly, prevention of type 2 diabetes in at-risk subjects), cardiovascular prevention in type 2 diabetic patients depending on the results of the ongoing prospective morbi-mortality studies in high risk type 2 diabetic patients.

Cœur, Diabète et Glitazones

Beneficial metabolic effects of rosiglitazone are now well established and its adverse events, generally minor or mild well known too. Following a brief review of these metabolic effects and main adverse events, we mainly describe fluid retention (and edema) and the heart failure risk, their risk factors, clinical and diagnosis characteristics, possible pathophysiological mechanisms and the main preventive measures are reviewed. Numerous experimental data and/or preliminary studies in type 2 diabetic patients, including effects on cardiovascular risk factors or markers, justify to conduct a large prospective long term clinical program to assess rosiglitazone effects on cardiovascular morbidity and mortality in type 2 diabetic patients at high cardiovascular risk, these studies are briefly described.

Lipoprotein abnormalities and their consequences for patients with type 2 diabetes

Dyslipidaemia is common in patients with Type 2 diabetes and is held to be responsible for considerable CVD-related morbidity and mortality. Patients with Type 2 diabetes are at high risk from complications associated with atherosclerosis and should therefore receive preventive interventions. At the level of the adipocyte, impaired insulin action leads to increased rates of intracellular hydrolysis of triglycerides with the release of NEFA. The rise in NEFA provides substrate for the liver that, in the presence of impaired insulin action and relative insulin deficiency, is associated with complex alterations in plasma lipids: * Plasma VLDL levels are raised. (i). Increased VLDL levels are associated with post-prandial hyperlipidaemia that is compounded by impaired LPL activity. The latter may be independently associated with CAD. (ii). Remnant particles can deliver more cholesterol to macrophages than LDL-C particles. Thrombogenic alterations in the coagulation system also ensue from hypertriglyceridaemia. * Plasma HDL-C levels are reduced. (i). The reduction in cardioprotective HDL-C means a reduction of cholesterol efflux from the tissues--the first step in reverse cholesterol transport to the liver from peripheral tissues. (ii). The antioxidant and antiatherogenic activities of HDL-C are reduced when circulating levels are low. * LDL-C particles become small and dense. Small, dense LDL-C particles are held to be more atherogenic than their larger, buoyant counterparts because they (a) are more liable to oxidation and (b) may more readily adhere to and subsequently invade the arterial wall. The atherogenicity of LDL-C may also be enhanced by nonenzymatic glycation. Metabolic and lipid abnormalities can often be improved with lifestyle changes, including dietary modification, weight loss, smoking cessation and increased exercise. Although attainment of better glycaemic control may improve diabetic dyslipidaemia, pharmacological intervention is usually required. Several large-scale clinical trials, including 4S and more recently HPS, have clearly demonstrated the benefits of statins in reducing cardiovascular events. By virtue of their high absolute risk of CVD, many patients with Type 2 diabetes may achieve a greater risk reduction than their non-diabetic counterparts. For example, in 4S there was a 43% reduction in total mortality risk among patients with diabetes compared with 29% for non-diabetics and a reduced risk of MI by 55% vs. 32% for diabetic and non-diabetics, respectively. In the diabetic subgroup in HPS, there were reductions of approximately 25-30% in the risk of first major vascular events. More recently, the lipid-lowering arm of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) was halted early because of a significant reduction in cardiovascular events compared with placebo. Surprisingly an analysis of subgroups failed to show significance among the diabetic population, although the sample size, shortened follow-up period and higher drop-in statin use among diabetics on placebo may have affected results. The Collaborative Atorvastatin Diabetes Study (CARDS), involving 2800 patients with Type 2 diabetes, was halted 2 years early in June 2003 because patients allocated atorvastatin had significant reductions in MI, stroke and surgical procedures compared with those receiving placebo. The UKPDS demonstrated that the appearance and progression of certain microvascular complications of Type 2 diabetes could be reduced by treatment directed at hyperglycaemia and hypertension. In addition, correction of dyslipidaemia in patients with diabetes is important in reducing the high toll from macrovascular disease. The subjects in the HPS had similar lipid profiles to the participants in UKPDS, suggesting that additional benefit would accrue from a therapeutic assault on the main cardiovascular risk factors simultaneously. We now have firm evidence that appropriate use of statins in patients with Type 2 diabetes can significantly reduce cardiovascular morbidity and mortality.

Antiatherogenic effect of pioglitazone in type 2 diabetic patients irrespective of the responsiveness to its antidiabetic effect

OBJECTIVE

Thiazolidinediones (TZDs), a class of insulin-sensitizing agents used clinically to treat type 2 diabetes, are also antiatherogenic. This study was designed to elucidate the relationship between the antiatherogenic and antidiabetic effects of pioglitazone, a TZD, in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A total of 136 Japanese type 2 diabetic patients were included and divided into two groups: the pioglitazone-treated group (30 mg daily for 3 months) (n = 70) and the untreated control group (n = 66). The changes in glycolipid metabolism as well as plasma high-sensitivity C-reactive protein (CRP), leptin, adiponectin, and pulse wave velocity (PWV) were monitored to analyze the relationship between the antiatherogenic and antidiabetic effects of pioglitazone.

RESULTS

The pioglitazone treatment significantly reduced hyperglycemia, hyperinsulinemia, and HbA(1c) levels and increased plasma adiponectin concentrations relative to the control group (P < 0.01). It also significantly decreased CRP and PWV (P < 0.01). The antiatherogenic effect was observed in both the nonresponders showing <1% of reduction in HbA(1c) (n = 30) and responders showing >1% of reduction (n = 40). ANCOVA revealed that treatment with pioglitazone was associated with a low CRP and PWV, independent of the changes in parameters related to glucose metabolism.

CONCLUSIONS

This study represents the first demonstration of the antiatherogenic effect of pioglitazone in both nonresponders and responders with respect to its antidiabetic effect and suggests that pioglitazone can exert its antiatherogenic effect independently of its antidiabetic effect.

Peroxisome proliferator-activated receptors: are they involved in atherosclerosis progression?

Peroxisome proliferator-activated receptors (PPAR) are nuclear receptors present in several organs and cell types. They are subdivided into PPAR alpha, PPAR gamma and PPAR delta (or beta). PPAR alpha and gamma are the two main categories of these receptors, which are both characterized by their ability to influence lipid metabolism, glucose homeostasis, cell proliferation, differentiation and apoptosis, as well as the inflammatory response, by transcriptional activation of target genes. PPAR alpha are activated by fatty acids, eicosanoids and fibrates, while PPAR gamma activators include arachidonic acid metabolites, oxidized low density lipoprotein and thiazolidinediones. Atherosclerosis is now considered a chronic inflammatory condition. Thus, PPAR activation appears a promising approach to favorably affect atherosclerosis development through both metabolic and anti-inflammatory effects. However, the clinical data in favor of an anti-atherosclerotic action of PPAR agonists are still scanty, and some experimental data would even indicate possible pro-atherogenic effects, or a lack of effect in the female sex. New controlled clinical studies will provide the information necessary to understand the true significance and usefulness of PPAR alpha, gamma and delta activators in the control of atherosclerotic disease.

Treatment of dyslipidemia in diabetes

Atherosclerosis kills more patients with diabetes than all other causes combined. Treatment must be focused on several targets: glycemic control, bulk reductions of LDL cholesterol, and shifting LDL particle size. Aggressive treatment and reversal of dyslipidemias is a proven prevention for coronary events in patients with type 2 diabetes. Glycemic control with diet, oral hypoglycemic agents, and insulin, when necessary, is often only partially effective in normalizing lipid values in type 2 diabetes. Intensive treatment with lipid-regulating agents, particularly statins, is often necessary to normalize diabetes-associated dyslipidemias. Statins are also the only agents thus far shown in prospective, controlled trials to reduce the risk of coronary events in diabetic patients definitively.