Cardioprotective effects of peroxisome proliferator activated receptor γ activators on acute myocarditis: Anti-inflammatory actions associated with nuclear factor κB blockade

Objective: To test the hypothesis that activation of peroxisome proliferator activated receptor γ(PPAR-γ) reduces experimental autoimmune myocarditis (EAM) associated with inhibitor κB (IκB) α induction, blockade of nuclear factor κ(NF-κB), and inhibition of inflammatory cytokine expression. Methods: EAM was induced in Lewis rats by immunisation with porcine cardiac myosin. PPAR-γ activators 15-deoxy-Δ^12/14-prostaglandin J₂ (15d-PGJ ₂) and pioglitazone (PIO) were administered to rats with EAM. Results: Enhanced PPAR-γ 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-γ activators enhanced IκB concentrations in the cytoplasmic fractions and nuclear fractions from inflammatory myocardium. Concurrently, NF-κB was greatly activated in myocarditis; this activation was blocked in the 15d-PGJ₂ treated and PIO treated groups. Conclusions: PPAR-γ may have a role in the pathophysiology of EAM. Because an increase in IκB expression and inhibition of translocation of the NF-κB subunit p65 to the nucleus in inflammatory cells correlated with the protective effects of PPAR-γ activators, these results suggest that PPAR-γ activators act sequentially through PPAR-γ activation, IκB induction, blockade of NF-κB activation, and inhibition of inflammatory cytokine expression. These results suggest that PPAR-γ activators such as 15d-PGJ₂ and PIO may have the potential to modulate human inflammatory heart diseases such as myocarditis.