Inhibitory Effect of Alkaloids Extracted from the Stem Bark of Hunteria zeylanica on 5-Lipoxygenase Activity in Vitro

Abstract

The effects of alkaloid extract from the stem bark of Hunteria zeylanica GARD. (H. zeylanica) on the activities of cyclooxygenase and 5-lipoxygenase in A23187-stimulated rat mast cells were investigated. H. zeylanica alkaloid extract (0.3-300μg/ml) inhibited leukotriene C₄ (LTC₄) production by 5-lipoxygenase in a concentration-dependent manner and it blocked the production by 50% at 300 μg/ml. On the other hand, the extract had no effect on prostaglandin D₂ (PGD₂) production by cyclooxygenase. Neither (-)-eburnamine nor pleiomutinine, major constituents of H. zeylanica alkaloid extract, inhibited the production of PGD₂ and LTC₄ in the A23187-stimulated mast cells. The inhibition of arachidonic acid metabolism via 5-lipoxygenase pathway may be due to minute amounts of other components as stated in the Discussion.