α-tocopherol decreases interleukin-1β release from activated human monocytes by inhibition of 5-lipoxygenase

Cardiovascular disease is the leading cause of morbidity and mortality in westernized populations. Low levels of alpha-tocopherol (AT) are associated with increased incidence of atherosclerosis and increased intakes appear to be protective. Recently, we showed that supplementation with AT resulted in significant decreases in monocyte superoxide anion release, lipid oxidation, interleukin-1 beta (IL-1 beta) release, and adhesion to endothelium. The reduction in superoxide and lipid oxidation by AT seemed to be mediated by inhibition of protein kinase C. The aim of this study was to investigate the mechanism(s) by which AT inhibits IL-1 beta release. Potential mechanisms examined included its effect as an antioxidant and its inhibitory effects on protein kinase C and. the cyclooxygenase-lipoxygenase pathways. Although AT decreased superoxide release from activated monocytes, superoxide dismutase and catalase had no effect on IL-1 beta release. Also, a similar antioxidant, beta-tocopherol, had no effect on IL-1 beta release. The protein kinase C inhibitor, bisindolylmaleimide, did not inhibit IL-1 beta release from activated monocytes, in spite of AT decreasing protein kinase C activity. Leukotriene B-4, a major product of 5-lipoxygenase, has been shown to augment IL-1 beta release. In the presence of AT, a significant reduction in leukotriene B-4 and IL-1 beta levels was observed, which was reversed by the addition of leukotriene Bq Similar observations were seen with specific inhibitors of S-lipoxygenase. The product of cyclooxygenase, prostaglandin E-2, has been shown to inhibit IL-1 beta activity in some systems. However, AT had no significant effect on prostaglandin E-2 levels in activated monocytes. In the presence of indomethacin, a cyclooxygenase inhibitor, AT inhibited IL-1 beta activity. Also, AT had no effect on IL-1 beta mRNA levels or stability, suggesting a posttranscriptional effect. Thus, in activated human monocytes, AT exerts a novel biological effect of inhibiting the release of the proinflammatory cytokine, IL-1 beta, via inhibition of the 5-lipoxygenase pathway.