Inhibitory effects of ent-kauranes from the stems of Annona squamosa on superoxide anion generation by human neutrophils

Eleven ent-kauranes, isolated from the fresh stems of Annona squamosa L. (Annonaceae), were subjected to assays on the generation of superoxide anion (O₂^.-) by human neutrophils. Except for ent-kaur-16-en-19-oic acid, 16β,17-dihydroxy-ent-kauran-19-al, and 16α,17-dihydroxy-ent-kauran-19-al, all ent-kauranes showed significant inhibitory effect on O₂^.- generation in response to formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP/ CB). In contrast, phorbol myristate acetate (PMA)-induced O₂^.- generation was not suppressed by any ent-kauranes. Especially, ent-kaur-16-en-19-oic acid could significantly increase O₂^.- production. The structure-activity relationship of these compounds is also discussed herein. Furthermore, the effect of ent-kauranes on nitric oxide generation by NR8383 macrophages in response to lipopolysaccharide (LPS) was examined. None of the compounds showed an inhibitory effect on nitric oxide generation.