AN EXTRACT OF DESMODIUM-ADSCENDENS INHIBITS NADPH-DEPENDENT OXYGENATION OF ARACHIDONIC-ACID BY KIDNEY CORTICAL MICROSOMES

Cortical microsomes of human kidneys were used to study the effect of an extract of Desmodium adscendens on the cytochrome P450-dependent arachidonic acid (AA) metabolism. The phenolic compounds tyramine and hordenine, as well as triterpenoid saponins known to be present in the plant were also evaluated along with the extract, an n-butanol fraction (nBF) of the crude plant extract. The extract and the compounds were preincubated with the microsomal suspension before the addition of cofactors and radioactive AA. The products of the reactions and the unreacted AA were extracted, separtaed by HPLC and measured radiometrically. The total amount of radioactive AA converted, and the production of AA metabolites identified as epoxy-eicosatrienoic acids, monohydroxy-eicosatetraenoic acids, 19-, 20- and di-hydroxy derivatives of AA, were inhibited by nBF. The inhibition by nBF was shown to be dose-dependent. A saponin, sapogenin and the phenolic compounds present in D. adscendens did not inhibit this oxygenation of AA. The results indicate that this plant contains an as yet unidentified inhibitor for the third pathway of AA metabolism.