Inhibition of inducible nitric oxide synthase and cyclooxygenase-2 expression by phenolic compounds from roots of Rhododendron mucronulatum

Abstract

The roots of Rhododendron mucronulatum Turzaninov have been used in Oriental traditional medicine for the treatment of dysuria, fever, increase of digestive activity and tonics in China and Korea. Activity guided isolation of the roots of Rhododendron mucronulatum Turzaninov has led to the isolation of three flavonoids, one flavan 3-ol and one proanthocyanidin. Chemical investigation of the 80% Me2 CO extract from the roots of Rhododendron mucronulatum led to the isolation and identification of five compounds: taxifolin (1), taxifolin 3-O-β-D-glucopyranoside (2), quercetin 3-O-α-L-arabinofuranoside (3), (-)-epicatechin (4), procyanidin B-3 (5). To investigate the antioxidative and antiinflammatory effects of these compounds, their 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and the protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-stimulated HaCaT cells were also quantified by western blotting and their end products, nitric oxide (NO) and prostaglandin E2 (PGE2 ), respectively. Compounds (1-5) showed potent DPPH radical scavenging compared with positive controls (L-ascorbic acid). Also, compounds 1 and 2 dose-dependently inhibited the expressions of inflammatory mediators, NO and PGE2 , suggesting they are promising candidates as antiinflammatory agents.

Keywords: DPPH; Rhododendron mucronulatum; cyclooxygenase-2; flavan 3-ol; flavonoid; inducible nitric oxide synthase; proanthocyanidin.