Arginase inhibitory properties of flavonoid compounds from the leaves of Mulberry (Morus alba, Moraceae).

OBJECTIVES: We aimed to isolate and identify bioactive molecules from Morus alba (Moraceae) leaves having arginase inhibitory activity towards the combat of clinical outcomes related to endothelial dysfunction. METHOD: Extraction and isolation were carried out by successive macerations, prepurification by using a Solid Phase Extraction (SPE) and separation using preparative PLC. The structures of the isolated components were established and confirmed by spectroscopic analyses, including the ESI-HRMS and NMR spectroscopic investigations. Biological evaluation was performed by using an in vitro assay with liver bovine purified arginase and by an ex vivo aortic ring study. KEY FINDINGS: We demonstrated that a phenolic extract from the leaves of M. alba possesses mammalian arginase inhibitory capacities. Investigation of the chemical constituents of its leaves results in the isolation and identification of ten compounds investigated in vitro for their arginase inhibitory capacities. Four compounds showed significant inhibition of arginase, with percentage inhibition ranging from 54% to 83% at 100 µm. In isolated rat aortic rings incubated with NO synthase inhibitor, Luteolin-7-diglucoside compound (2) was able to increase acetylcholine-induced relaxation. CONCLUSIONS: These results demonstrated the attractive ability of M. alba to be a potential source for the discovery of new active products on vascular system.

Arginase Inhibitors: A Rational Approach Over One Century.

Arginase (EC 3.5.3.1) is the bimanganese enzyme that converts L-arginine into ornithine and urea. This enzyme was discovered more than a century ago and early α-amino acids were identified as weak inhibitors. It was only during the 90s, after nitric oxide (NO) was reported as one of the most important biological mediators and when tight interrelation of arginase and NO synthase was found, that the development of arginase inhibitors was accelerated. The regulation of arginase activity by the N-hydroxy-L-arginine (3, NOHA) intermediate of the NO synthesis was the starting point of the N-hydroxy-nor-arginine (21, nor-NOHA) that proved to be the first micromolar inhibitor. The previously known manganese and arginase binding by borate inspired the 2(S)-amino-6-boronohexanoic acid (39, ABH) and S-(2-boronoethyl)-L-cysteine (40, BEC) now both considered as reference compounds in arginase inhibition. The high-resolution crystal structure of arginase and molecular modeling has rendered possible the recent design of (53) the strongest α,α-disubstituted derivatives of ABH. Simultaneously, traditional medicinal plants have contributed as a source of molecular diversity to the discovery of arginase inhibitors. This rational, step-by-step approach serves as guide in the present review where emphasis is placed on structure activity relationships. Highlights exhaustive review on arginase inhibitors highlight is made on rational approach to conception and structure activity relationships evaluation model is systematically mentioned with results.