Mode of action of sesquiterpene lactones as anti-inflammatory agents

Sesquiterpene lactones containing an α-methylene-γ-lactone moiety were shown to be potent inhibitors of carrageenan-induced edema and chronic adjuvant-induced arthritis in rodents at 2.5 mg/kg/day. The mode of action of sesquiterpene lactones as anti-inflammatory agents appeared to be at multiple sites; for example, at 5 × 10⁻⁴ M, the sesquiterpene lactones effectively uncoupled the oxidative phosphorylation of human polymorphonuclear neutrophils and elevated the cyclic adenosine monophosphate levels of rat neutrophils and rat and mouse liver cells. Free and total lysosomal enzymatic activity was inhibited by these agents at 5 × 10⁻⁴ M, in both rat and mouse liver and rat and human neutrophils. Furthermore, the structure-activity relationships for the stabilization of lysosomal membrane for rat liver cathepsin activity followed the same structural requirement necessary for antiinflammatory activity; i.e., the α-methylene-γ-lactone moiety contributed the most activity, whereas the β-unsubstituted cyclopentenone and α-epoxycyclopentanone contributed only minor activity. Human polymorphonuclear neutrophil chemotaxis was inhibited at low concentrations (i.e., 5 × 10⁻⁵ and 5 × 10⁻⁶ M), whereas prostaglandin synthetase activity was inhibited at a higher concentration (i.e., 10⁻³ M) by the sesquiterpene lactones.