Peroxisome proliferator activated receptor gamma: a potential therapeutic target in the management of ischaemic heart disease

Cardioprotective effects of peroxisome proliferator activated receptor gamma activators on acute myocarditis: anti-inflammatory actions associated with nuclear factor kappaB blockade

OBJECTIVE

To test the hypothesis that activation of peroxisome proliferator activated receptor gamma (PPAR-gamma) reduces experimental autoimmune myocarditis (EAM) associated with inhibitor kappaB (IkappaB) alpha induction, blockade of nuclear factor kappaB (NF-kappaB), and inhibition of inflammatory cytokine expression.

METHODS

EAM was induced in Lewis rats by immunisation with porcine cardiac myosin. PPAR-gamma activators 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) and pioglitazone (PIO) were administered to rats with EAM.

RESULTS

Enhanced PPAR-gamma expression was prominently stained in the nuclear and perinuclear regions of infiltrating inflammatory cells. Administration of 15d-PGJ2 and PIO greatly reduced the severity of myocarditis and suppressed myocardial mRNA and protein expression of inflammatory cytokines in rats with EAM. In addition, treatment with PPAR-gamma activators enhanced IkappaB concentrations in the cytoplasmic fractions and nuclear fractions from inflammatory myocardium. Concurrently, NF-kappaB was greatly activated in myocarditis; this activation was blocked in the 15d-PGJ2 treated and PIO treated groups.

CONCLUSIONS

PPAR-gamma may have a role in the pathophysiology of EAM. Because an increase in IkappaB expression and inhibition of translocation of the NF-kappaB subunit p65 to the nucleus in inflammatory cells correlated with the protective effects of PPAR-gamma activators, these results suggest that PPAR-gamma activators act sequentially through PPAR-gamma activation, IkappaB induction, blockade of NF-kappaB activation, and inhibition of inflammatory cytokine expression. These results suggest that PPAR-gamma activators such as 15d-PGJ2 and PIO may have the potential to modulate human inflammatory heart diseases such as myocarditis.

Peroxisome proliferator activated-receptor agonism and left ventricular remodeling in mice with chronic myocardial infarction

1. Peroxisome proliferator activated receptor gamma (PPARgamma) has been implicated in several cellular pathways assumed to beneficially affect heart failure progression. In contrast, population-based studies demonstrate an increased incidence of heart failure in patients treated with PPARgamma agonists. Therefore, we examined the effect of pioglitazone, a PPARgamma agonist, on chronic left ventricular remodeling after experimental myocardial infarction (MI) in mice. 2. Mice were treated with placebo or pioglitazone (20 mg x kg(-1) by gavage) from week 1 to week 6 after ligation of the left anterior descending artery. Serial transthoracic echocardiography was performed at weeks 1, 3, and 6. 3. Over 6 weeks, there was no difference in mortality (placebo 12%, pioglitazone 10%). Echocardiography showed significant left ventricular dilatation in animals with MI (week 6, end-systolic area, placebo sham 9.6+/-1.3 vs placebo MI 14.4+/-2.5 mm(2)). However, there was no difference between the placebo and pioglitazone groups (week 6, end-systolic area, pioglitazone MI 14.8+/-2.9 mm(2), P=NS vs placebo). 4. Moreover, there were no changes in metabolic parameters, inflammation, and collagen deposition. Endothelial function in the aorta was not changed by PPARgamma activation. 5. In conclusion, PPARgamma activation did not adversely affect left ventricular remodeling and survival in mice with chronic MI. However, we were also not able to identify a protective effect of pioglitazone.

Thiazolidinediones in type 2 diabetes mellitus: current clinical evidence

Type 2 diabetes mellitus is characterised by insulin resistance as well as progressive pancreatic beta cell dysfunction. The cornerstone of current oral blood-glucose lowering therapy consists of metformin, which primarily lowers hepatic glucose production, and the sulphonylureas that act by stimulating pancreatic beta-cells to secrete insulin. Recently, a novel class of agents, the thiazolidinediones, has been introduced that favourably influence insulin sensitivity and possibly also pancreatic beta-cell function. The thiazolidinediones are synthetic ligands that bind to the nuclear peroxisome proliferator-activated receptor-gamma and exert their action by activating transcription of genes that, among others, regulate adipocyte differentiation and adipogenesis as well as glucose and lipid metabolism. To date, the precise mechanisms underlying the actions of thiazolidinediones are largely unknown. When given as monotherapy or in combination with sulphonylureas, metformin or insulin in patients with type 2 diabetes, the currently available thiazolidinediones (rosiglitazone and pioglitazone) ameliorate glycaemic control, by lowering fasting and postprandial blood glucose levels, and improve insulin sensitivity in placebo-controlled trials. They seem to have differential effects on dyslipidaemia in patients with type 2 diabetes; rosiglitazone increases total cholesterol as well as high-density lipoprotein (HDL) and low-density lipoprotein cholesterol levels and affects plasma triglyceride levels depending on the baseline values, whereas pioglitazone lowers triglycerides and increases HDL cholesterol levels. The adverse events of both agents that occur with greater frequency than in patients treated with placebo are fluid retention and oedema. As demonstrated, mainly in preclinical studies to date, rosiglitazone and pioglitazone possess beneficial effects on other cardiovascular risk factors associated with the insulin resistance syndrome. Thus, these agents were shown to decrease blood pressure, enhance myocardial function and fibrinolysis, as well as possess anti-inflammatory and other beneficial vascular effects. Long-term efficacy and surveillance of this promising class of drugs in patients, however, still need to be demonstrated in outcome trials.