Inhibitory effects of sesquiterpenes from bay leaf on nitric oxide production in lipopolysaccharide-activated macrophages: Structure requirement and role of heat shock protein induction

The methanolic extract from the leaves of Laurus nobilis (bay leaf, laurel) was found to inhibit nitric oxide (NO) production in lipopolysaccharide (LPS)-activated mouse peritoneal macrophages. Through bioassay-guided separation, fourteen known sesquiterpenes were isolated from the active fraction and were examined for ability to inhibit the NO production. Seven sesquiterpene lactones (costunolide, dehydrocostus lactone, eremanthine, zaluzanin C, magnolialide, santamarine and spirafolide) potently inhibited LPS-induced NO production (IC50 - 1.2 similar to 3.8 mu M). Other sesquiterpene constituents also showed the inhibitory activity (IC50 greater than or equal to 21 mu M), but their inhibitory activities were less than those of sesquiterpene lactones. alpha-Methylene-gamma-butyrolactone also showed inhibitory activity (IC50 - 9.6 mu M), while mokko lactone and watsonol A etc., reductants of the alpha-methylene-gamma-butyrolactone moiety by NaBH4 or DIBAL, and a 2-mercaptoethanol adduct of dehydrocostus lactone showed little activity (IC50 greater than or equal to 18 mu M). These results indicated that the alpha-methylene-gamma-butyrolactone moiety is important for the activity. Furthermore, costunolide and dehydrocostus lactone inhibited inducible nitric oxide synthase (iNOS) induction in accordance with induction of heat shock protein 72 (HSP 72). These results suggested that, as one of their mechanisms of action, sesquiterpene lactones induce HSP 72 thereby preventing nuclear factor-kappa B activation followed by iNOS induction.