α-Tocopherol and three derivatives in which the phytol chain is modified or deleted were examined for their effect on cultured keratinocyte arachidonic acid metabolism. 2,2,5,7,8-Pentamethyl-6-hydroxychromane (PMC), in which the phytol chain is replaced by a methyl group, inhibited basal, bradykinin (BK)- and A23187-stimulated prostaglandin E2 (PGE2) synthesis with an apparent K(i) of 1.3 μM. The K(i) of the analogue with six carbon atoms in the side chain (C6) was 5 μM while that of the C11 analogue was 10 μM. No effect of α-tocopherol was observed. The mechanism of inhibition was studied using PMC. The effect of PMC on phospholipase and cyclooxygenase activity was assayed using stable isotope mass measurements of PGE2 formation, which assesses arachidonate release and cyclooxygenase metabolism simultaneously. BK-stimulated formation of PGE2, derived from endogenous phospholipid, was decreased 60% by 5 μM PMC and eliminated by 50 μM PMC, compared with controls. No difference in PGE2 formed from exogenous arachidonic acid was observed, indicating no effect of PMC on cyclooxygenase activity. In contrast, no effect of 5 μM PMC was observed on BK-stimulated [3H]arachidonic acid release from prelabeled cultures. The capacity of PMC to inhibit phospholipase activity in vitro was also assessed. PMC inhibited hydrolysis of phospholipid substrate by up to 60%. These results suggest that α-tocopherol analogues with alterations in the phytol chain inhibit eicosanoid synthesis by preferential inhibition of phospholipase.
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1992|