Effect of manoalide on human 5-lipoxygenase activity.

The marine natural product manoalide (MLD) has been described to inactivate phospholipase A2 (PLA2) from several sources as well as to inhibit synthesis of eicosanoids in human polymorphonuclear leukocytes (HPMNL). MLD also reduces chemically-induced inflammation in vivo. In this investigation we have examined the effect of MLD on A23187-induced generation of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) in HPMNL as well as 5-lipoxygenase (5-LO) activity from HPMNL sonicated preparations. In the intact cell system, MLD inhibited with similar potency biosynthesis of LTB4 and TXB2 (IC50 1.7 and 1.4 microM, respectively). In order to discern if inhibition of 5-LO is involved in the effect of MLD, we examined the action of this compound on 5-LO activity from 10,000 x g and 100,000 x g supernatants of sonicated HPMNL homogenates. The enzymatic activity was not affected at concentrations of MLD up to 50 microM. These data indicate that MLD is not a direct inhibitor of 5-LO activity from HPMNL and support the hypothesis that its anti-inflammatory action could be related with a reduction of eicosanoid biosynthesis via inhibition of PLA2.