REGULATION OF PROSTAGLANDIN-H SYNTHASE-2 EXPRESSION IN HUMAN MONOCYTES BY THE MARINE NATURAL-PRODUCTS MANOALIDE AND SCALARADIAL - NOVEL EFFECTS INDEPENDENT OF INHIBITION OF LIPID MEDIATOR PRODUCTION

The marine natural products manoalide and scalaradial are potent anti- inflammatory agents that inactivate the enzyme phospholipase A(2) (PLA (2)) in vitro. To study the mechanism of inhibition of prostaglandin E (2) (PGE(2)) production in human monocytes by manoalide and scalaradia l, lipopolysaccharide (LPS)-induced prostaglandin biosynthesis and ind uction of prostaglandin H synthase (PGHS) were evaluated. LPS (10 ng/m L) and interleukin-1 beta (IL-1 beta, 50-1000 ng/mL) but not tumor nec rosis factor alpha (TNF alpha, 300 ng/mL) induced the expression of th e PGHS-2 isoform as determined by immunoblot analysis with a specific polyclonal antibody for PGHS-2. Manoalide and scalaradial (1-10 mu M) inhibited LPS-induced endogeneous PGE(2) production, reduced the LPS-i nduced PGHS activity, and reduced the expression of PGHS-2. Indomethac in [a PGHS inhibitor (0.01 to 0.1 mu M)], zileuton [a 5-lipoxygenase i nhibitor (3-10 mu M)], and WEB-2806 [a platelet-activating factor (PAF ) antagonist (30 mu M)] did not affect the LPS-induced expression of P GHS-2 in human monocytes. These results suggest that modulation of lip id mediator production by manoalide or scalaradial may not be involved in the observed effects on the expression of PGHS-2 Manoalide and sca laradial also inhibited the release of IL-1 beta and TNF alpha from LP S-stimulated monocytes. Expression of PGHS-2 induced by either LPS or IL-1 beta was blocked by the IL-1 receptor antagonist (IL-1ra, 2 mu g/ mL) but not by rolipram, a phosphodiesterase IV inhibitor that inhibit s TNF alpha but not IL-1 beta release. Similar to LPS, IL-1 beta-induc ed PGHS-2 expression was apparently not regulated by lipid mediators s uch as prostaglandins, leukotrienes or PAF as determined with specific inhibitors and antagonists. Scalaradial and to some extent manoalide were capable of blocking the IL-1 beta-induced expression of PGHS-2. T hese results indicate that IL-1 beta is the predominant cytokine respo nsible for the induction of PGHS-2 in me human monocyte. Furthermore, marine natural products such as scalaradial have novel effects on the IL-1 beta-mediated induction of PGHS-2 in human monocytes, which appea rs to be independent of effects on lipid mediator production.