gamma-tocopherol and its major metabolite, in contrast to alpha-tocopherol, inhibit cyclooxygenase activity in macrophages and epithelial cells

Cyclooxygenase-2 (COX-2)-catalyzed synthesis of prostaglandin El (PGE(2)) p lays a key role in inflammation and its associated diseases, such as cancer and vascular heart disease. Here we report that gamma-tocopherol (gamma T) reduced PGE(2) synthesis in both lipopolysaccharide (LPS)-stimulated RAW26 4,7 macrophages and IL-1 beta-treated A549 human epithelial cells with an a pparent IC50 of 7.5 and 4 mu M, respectively. The major metabolite of dieta ry gamma T, 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-C EHC), also exhibited an inhibitory effect, with an IC50 of approximate to 3 0 mu M in these cells. In contrast, alpha-tocopherol at 50 mu M slightly re duced (25%) PGE(2) formation in macrophages, but had no effect in epithelia l cells. The inhibitory effects of gamma T and gamma-CEHC stemmed from thei r inhibition of COX-2 activity, rather than affecting protein expression or substrate availability, and appeared to be independent of antioxidant acti vity. gamma-CEHC also inhibited PGE(2) synthesis when exposed for 1 h to CO X-2-preinduced cells followed by the addition of arachidonic acid (AA), whe reas under similar conditions, gamma T required an 8- to 24-h incubation pe riod to cause the inhibition. The inhibitory potency of gamma T and gamma-C EHC was diminished by an increase in AA concentration, suggesting that they might compete with AA at the active site of COX-2, We also observed a mode rate reduction of nitrite accumulation and suppression of inducible nitric oxide synthase expression by gamma T in lipopolysaccharide-treated macropha ges, These findings indicate that gamma T and its major metabolite possess anti-inflammatory activity and that gamma T at physiological concentrations may be important in human disease prevention.