MODULATION OF EICOSANOEDS BIOSYNTHESES IN VIVO AS A MECHANISM-BASED EVALUATION OF PUTATIVE ANTI-INFLAMMATORY PLANT EXTRACTS

ABSTRACT

The eicosanoids are a group of oxygenated unsaturated 20-carbon chemical compounds produced from arachidonic acid (AA), that mediate almost every step in the inflammatory process naturally. Some of the eicosanoids are anti-inflammatory while others are proinflammatory. Desmodium adscendens, a medicinal plant used by local herbalists to manage asthma, had been shown to be anti-anaphylactic in vivo, and to modulate AA metabolism in vitro. In this work, the anti-inflammatory properties of D. adscendens in vivo were examined by measuring the effect of its aqueous extract on eicosanoid production. Two other putative anti-inflammatory medicinal plants, Parquetina sp {‘Tina A 0 and Cassia sieberiana (‘Kenkeri’) were also examined. The effects of the extracts on phospholipase A2 (PLA2), the enzyme responsible for the mobilization of arachidonic acid (AA) from membrane glycerophospholipid stores to initiate the de novo biosyntheses of the eicosanoids were also examined. Microsomal enzymes prepared from the lungs of both extract-treated (test) and untreated (control) male guinea pigs were used to catalyze the metabolism of arachidonic acid (AA), the natural substrate for eicosanoid synthesis, via the cyclo-. mono- and the lipoxygenase pathways to produce various eicosanoids. Reduced glutathione, GSH, was added to the reaction mixture for the cyclooxygenase pathway while NADPH was added xiii for the monoxygenase pathway. For the lipoxygenase pathway no cofactor was added. The monooxygenase metabolites were not quantified due to limited resources. However, the influence of added NADPH on the production of the metabolites of the other two pathways was evaluated. All synthesized eicosanoids were assayed by ELISA. As sources of secretory phospholipase A2 (sPLA2), blood samples were taken from the experimental animals and used to assess the effects of the plant extracts on PLA2 activity.