Preferential inhibition of bacterial elastase over human neutrophil elastase by leaf extracts of Psidium guajava: an in vitro study

Abstract

Background: The guava (Psidium guajava), belonging to family Myrtaceae, is a small tree grown widely for its fruit in tropical and subtropical countries. Apart from its nutritional value, it is also known for its medicinal value and the antimicrobial activities of its leaves. Aims and Objectives: To demonstrate the inhibitory effect of P. guajava leaf extracts (aqueous and methanolic) on bacterial elastase from Pseudomonas aeruginosa (MTCC3541) and human neutrophil elastase(HNE); to explore the presence of a protease inhibitor of protein nature in the aqueous leaf extract. Materials and Methods: Purified bacterial elastase from P. aeruginosa (MTCC3541) and commercially purchased HNE were used as enzyme sources with succinyl trialanyl p-nitroanilide as the substrate. Varying concentrations of methanolic and aqueous extracts of the leaves were used as the source of the inhibitor. Result: The results of the study show that the methanolic and aqueous extract of the leaves inhibited both bacterial elastase and HNE. Calculation of Ki and IC50 showed that the bacterial elastase was inhibited by smaller amounts of the inhibitor suggesting that the inhibitor was more potent toward bacterial elastase. However, an aqueous extract prepared after removal of phenolic compounds did not show any inhibitory activity ruling out the presence of inhibitor of protein nature. Conclusion: This observation indicated that the inhibitory activity exhibited by the leaf extract is exclusively owing to the phenolic compounds.