PROTECTIVE EFFECTS OF DRIED FLOWER EXTRACTS OF HIBISCUS-SABDARIFFA L.AGAINST OXIDATIVE STRESS IN RAT PRIMARY HEPATOCYTES

Dried lower extracts of Hibiscus sabdarrifa L., a local soft drink mat erial and medical herb, was found to possess antioxidant activity in t he present study. In the preliminary studies, antioxidant potential of three fractions of the ethanol crude extract (HS-C: chloroform-solubl e fraction; HS-E: ethyl acetate soluble fraction; HS-R: residual fract ion) obtained from the dried flowers of Hibiscus sabdarrifa L. were ev aluated by their capacity of quenching 1,1-diphenyl-2-picrylhydrazyl ( DPPH) free radical and inhibiting xanthine oxidase (XO) activity. HS-E showed the greatest capacity of scavenging free radical (EC50=0.017 m g/ml), and HS-C showed the strongest inhibitory effect on XO activity (EC50=0.742 mg/ml). Furthermore, antioxidant bioactivities of these cr ude extracts were investigated using a model of tert-butyl hydroperoxi de (t-BHP)-induced oxidative damage in rat primary hepatocytes. All fr actions were found to inhibit significantly the unscheduled DNA synthe sis (UDS) induced by t-BHP at a concentration of 0.20 mg/ml. HS-C and HS-E also decreased the leakage of lactate dehydrogenase (LDH) and the formation of malondialdehyde (MDA) induced by t-BHP (1.5 mM) consider ably at a concentration of 0.10 and 0.20 mg/ml in the rat primary hepa tocyte cultures. These results indicated that the dried flower extract s (HS-C and HS-E) of H. sabdarrifa L. protect rat hepatocytes from I-B HP-induced cytotoxicity and genotoxicity by different mechanisms. (C) 1997 Elsevier Science Ltd. All rights reserved.