Captopril and platelet-activating factor (PAF) antagonist prevent cardiac allograft vasculopathy in rats: Role of endogenous PAF and PAF-Like compounds

Accelerated coronary artery disease (CAD) is the leading cause of late mortality following cardiac transplantation. The vascular lesions are characterized by myointimal proliferation and perivascular mononuclear inflammatory infiltrates. Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent phospholipid mediator produced by inflammatory cells and activated endothelial cells. Angiotensin II is known to activate phospholipase A,, a critical enzyme in PAF synthesis. Using a rat heterotopic cardiac transplant model known to induce graft CAD, we previously reported that chronic administration of captopril, an angiotensin converting enzyme inhibitor, reduces intimal proliferation and maintains luminal patency. The purpose of the current study was to determine if captopril regulates vascular remodeling by suppressing PAF synthesis and whether administration of a PAF antagonist ameliorates graft CAD. Captopril was found to decrease levels of PAF and PAF-like compounds as well as reduce intimal lesions, decrease cellular rejection grade, and diminish allograft heart weights. Treatment with a PAF antagonist significantly decreased proliferation of the intimal component of the vasculopathy and caused regression of the cardiac hypertrophy, but had no significant effect on cellular rejection. In contrast, untreated animals had elevated plasma PAF levels, elevated heart weights, and severe myointimal proliferation with luminal stenosis 21 days post-transplantation. These observations suggest that graft CAD is mediated, in part, by PAF and PAF-like compounds, and suppression of endogenous PAF may prevent cardiac allograft vasculopathy.