Arginase inhibitory activity of several natural polyphenols using a novel in vitro test on purified bovine arginase

Abstract

Interest in arginase, metalloenzyme hydrolyzing L-arginine into L-ornithine and urea, was stimulated by the finding that arginases might compete with nitric oxide synthases for their common substrate, L-arginine and therefore regulate NO availability. Thus, emerged the concept that selective arginase inhibitors might be a valuable strategy for the treatment of various diseases associated to decreased NO [1,2]. Therefore, research of new candidates targeting on arginase has been attracting scientists but the methods used, in terms of models and of biochemical conditions for the arginase assay are currently too different from one study to another to allow valid comparisons. In this work, we developed a novel in vitro microplate colorimetric assay for evaluation of arginase inhibitory effect using commercially available purified liver bovine arginase 1. This assay adapted from [3], is based on the reaction of urea with α-isonitrosopropiophenone and allows using low quantities (0.5 U) of arginase. The evaluation of S-(2-boronoethyl)-L-cystein, a known reversible competitive arginase inhibitor, validated our method (IC50= 12,0µM) that is thus applicable for routine screening analyses. This assay was used to evaluate several natural polyphenols (IC50): rutoside (458.2µM), epicatechin (94µM), taxifolin (79.25µM), piceatannol (37.7µM), chlorogenic acid (37.4µM) and its two moieties caffeic (571.4µM) and quinic (5500µM) acids. These results suggested that piceatannol and chlorogenic acid are suitable as lead compounds to develop new natural or semi-synthetic arginase inhibitors and that caffeoyl part is crucial for the activity.