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

Cyclooxygenase-2 (COX-2)-catalyzed synthesis of prostaglandin El (PGE(2)) plays 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 RAW264,7 macrophages and IL-1 beta-treated A549 human epithelial cells with an apparent IC50 of 7.5 and 4 mu M, respectively. The major metabolite of dietary gamma T, 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), also exhibited an inhibitory effect, with an IC50 of approximate to 30 mu M in these cells. In contrast, alpha-tocopherol at 50 mu M slightly reduced (25%) PGE(2) formation in macrophages, but had no effect in epithelial cells. The inhibitory effects of gamma T and gamma-CEHC stemmed from their inhibition of COX-2 activity, rather than affecting protein expression or substrate availability, and appeared to be independent of antioxidant activity. gamma-CEHC also inhibited PGE(2) synthesis when exposed for 1 h to COX-2-preinduced cells followed by the addition of arachidonic acid (AA), whereas under similar conditions, gamma T required an 8- to 24-h incubation period to cause the inhibition. The inhibitory potency of gamma T and gamma-CEHC 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 moderate reduction of nitrite accumulation and suppression of inducible nitric oxide synthase expression by gamma T in lipopolysaccharide-treated macrophages, 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.