Inhibitory effects of Indonesian temu kunci (Boesenbergia rotunda) rhizome extract on nitric oxide synthase production and on the kidneys of Wistar rats

Abstract

Nitric oxide synthases (NOSs) are enzymes that function by generating nitric oxide (NO) from its substrate, L‑arginine, in human tissues. There are three known isoforms of NOS, eNOS (endothelial NOS), nNOS (neuronal NOS), and iNOS (inducible NOS). iNOS is released in response to inflammation. The human iNOS inhibitor, S‑ethylisothiourea (SEITU), has been found to attach to a Glu377 residue within the active‑site cavity of the enzyme. The discovery of iNOS inhibitors is always challenging. <em>Boesenbergia rotunda</em> (<em>B. rotunda</em>) has been reported to reduce inflammation in an animal model. The present study examined the inhibitory effects of <em>B. rotunda</em> rhizome ethanolic extract (BRE) on iNOS using the fluorometric method and investigated the histopathological effects of higher concentrations of BRE (1,000, 2,000 and 4,000 mg/kg body weight) on the kidneys of male Wistar rats. Molecular docking simulation of quercetin and kaempferol towards iNOS was also performed. The phytochemical screening of BRE indicated the presence of polyphenolics, flavonoids, triterpenoids, and saponins. The <em>in vitro</em> experiment confirmed that BRE reduced NO production with a half‑maximal inhibitory concentration value of 79.06 µg/ml. Both quercetin and kaempferol interacted with Glu377 by building hydrogen bonds. Furthermore, the animal experiment resulted in no mortality and no marked morphological changes in the rat kidneys at all concentrations, indicating the safety of BRE as regards this organ. Taken together, BRE may be further developed as a safe anti‑inflammatory drug candidate.