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 E(2) (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 (gammaT) reduced PGE(2) synthesis in both lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages and IL-1beta-treated A549 human epithelial cells with an apparent IC(50) of 7.5 and 4 microM, respectively. The major metabolite of dietary gammaT, 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), also exhibited an inhibitory effect, with an IC(50) of approximately 30 microM in these cells. In contrast, alpha-tocopherol at 50 microM slightly reduced (25%) PGE(2) formation in macrophages, but had no effect in epithelial cells. The inhibitory effects of gammaT 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, gammaT required an 8- to 24-h incubation period to cause the inhibition. The inhibitory potency of gammaT 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 gammaT in lipopolysaccharide-treated macrophages. These findings indicate that gammaT and its major metabolite possess anti-inflammatory activity and that gammaT at physiological concentrations may be important in human disease prevention.
Jiang
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Division of Biochemistry and Molecular Biology, University of California, Berkeley, CA 94720, USA.
Elson-Schwab
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Courtemanche
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Ames
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D001095:Arachidonic Acids / Q000378:metabolism; D002460:Cell Line; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D007536:Isomerism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009573:Nitrites / Q000378:metabolism; D017382:Reactive Oxygen Species; D014810:Vitamin E / Q000737:chemistry / Q000494:pharmacology*
D001095:Arachidonic Acids; D016861:Cyclooxygenase Inhibitors; D007375:Interleukin-1; D008070:Lipopolysaccharides; D009573:Nitrites; D017382:Reactive Oxygen Species; D014810:Vitamin E; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II