Abstract
Elevated endothelin (ET)-1 has been implicated in cerebrovascular complications following brain trauma characterized by dysregulation of endothelial nitric oxide synthase (eNOS), protein kinase C (PKC), and cerebral function. Recently, vascular expression of PPARalpha has been observed and suggested to improve vascular dysfunction. We speculate that activation of PPARalpha in cerebral microvessels can improve cerebral dysfunction following trauma, and we tested the hypothesis that activation of cerebral endothelial peroxisome proliferator-activated receptor (PPAR)alpha will attenuate ET-1 production via a mechanism involving nitric oxide (NO) and PKC. Phorbol 12-myristate 13-acetate (PMA) (1 microM), bradykinin (BK, 1 microM), angiotensin II (AII, 1 microM), or hemoglobin (Hem, 10 microM) increased ET-1 levels by 24-, 11.4-, 3.6-, or 1.3-fold increasing ET-1 levels from 0.36 +/- 0.08 to 8.6 +/- 0.8, 4.1 +/- 0.7, 1.30 +/- 0.1, or 0.47 +/- 0.03 fmol/microg protein (p < 0.05), respectively. Clofibrate (10 microM) reduced basal ET-1 from 0.36 +/- 0.08 (control) to 0.03 +/- 0.01 and blunted vasoactive agent-induced increase to 0.12 +/- 0.07 (PMA), 0.6 +/- 0.04 (BK), 0.25 +/- 0.03 (AII), or 0.12 +/- 0.03 (Hem) fM/microg protein (p < 0.05). L-arginine methyl ester (100 microM) inhibited clofibrate-induced reduction in basal ET-1 production. Clofibrate increased PPARalpha expression, accompanied by increased NO production and eNOS expression. PKC inhibition by calphostin C (10 microM) blocked these effects, whereas activation by PMA reduced basal PPARalpha expression. Thus, PPARalpha activation attenuated ET-1 production by agents that mediate brain injury through mechanisms that probably result from PPARalpha-induced increase in eNOS expression/NO production and complex PKC signaling pathways. Therefore, PPARalpha activators can be appropriate therapeutic agents to alleviate cerebrovascular dysfunction following cerebral vasospasm.