Anti-Inflammatory Medicinal Plants As Anti-Oxidants And Inhibitors Of Proinflammatory Eicosanoid Biosynthesis

ABSTRACT Arachidonic acid (AA) metabolism that leads to the production of both anti- and pro-inflammatory eicosanoids is a standard assay used to investigate the basis for the therapeutic action of anti-inflammatory medicinal plants. Earlier investigations have established the efficacy of some herbal preparations in terms of their ability to increase the amounts of anti-inflammatory eicosanoids. Desm.od.ium adscendens and Parkitina sp. ('Tina A' ) increased PGE2 and PGI2 synthesis and inhibited phospholipase A2 activity while Thonningia sanguinea decreased the release of histamine and slow reacting substances of anaphylaxis (SRA-S). So far none of these extracts has shown any significant effect on thromboxane (TX) synthesis. The present study was conducted to evaluate the efficacy of four plant extracts, D. adscendens, Tina A, T. sanguinea and L. multi flora in decreasing the amounts of the pro-inflammatory eicosanoids, TXB2 and cysteinyl leukotrienes (cyst.LT), and their antioxidant properties to act as anti-oxidants. Isolated guinea pig lungs perfused via the trachea were used as a model to study the release and inhibition of the release of the TXB2 and cyst.LTs by the extracts. The organs were perfused with Kreb's solution with and without the plant extracts and TXB2 and cyst.LT released were estimated by an ELISA. There were significant decreases in the amounts of TX B2 and cyst.LT released from lungs perfused with the extract of 'Tina A' or T. sanguinea and lungs from animals treated with 'Tina A ' . Generally, the treatment of the animals with the extract decreased the release of TX more than LTs, while perfusion of the isolated lungs (i.e. short term treatment) had more effect on cyst.LT than TX. The effects of D. adscendens, 'Tina A' , L. multiflora and T. sanguinea on the in vitro synthesis of TXB2 using blood platelet microsomes were investigated. Microsomes for this study were prepared from blood platelets. Except L. multiflora, for which higher concentration showed minimum effects on TXB2 synthesis, there was a concentration-dependent inhibition of TXB2 by all the extracts. The effect of T. sanguinea became significant at a relatively higher concentration compared to that of D. adscendens or 'Tina A '. At the highest concentration of 100ug/ml, D. adscendens, 'Tina A ’ and T. sanguinea caused 81%, 81.6% and 87.5% decreases respectively in the amounts of TXB2 synthesized. The effects of the extracts on hydroxyl radical generation and total and watersoluble phenolic content were determined. There was a concentration-dependent inhibition of hydroxyl generation by all the extracts. Large amounts of phenolic compounds were identified in all the extracts. For 'Tina A', 74% of the total phenols was water soluble while T. sanguinea which gave the highest amount of total phenols had 31% being water soluble. There was a positive correlation between total phenolic content and inhibition of hydroxyl radical generation. T. sanguinea and D. adscendens which had the highest and lowest amounts of total phenols respectively, showed the highest and lowest inhibition of hydroxyl radical generations respectively at all concentrations studied. These findings suggest that the inhibition of both synthesis/release of pro-inflammatory eicosanoids and generation of reactive oxygen species by the plant extracts studied validates their use in folk medicine in the management of asthma and other inflammatory disorders.