Mushroom-derived preparations in the prevention of oxidative damage to cellular DNA

Mushroom-derived preparations (MDPs) were obtained from the fruit bodies of Auricularia auricula, Agaricus bisporus, Flammulina velutipes, Ganoderma lucidum, Hypsizygus marmoreus, Lentinula edodes, Pleurotus sajor-caju and Volvariella volvacea using two different extraction procedures. The MDPs were examined for their total antioxidant capacity by the ferric reducing antioxidant/power assay (FRAP assay), and for their ability to prevent oxidative strand breakage to cellular DNA in an in vitro system of cultured human B-lymphocyte (Raji) cells using the single-cell gel electrophoresis ("Comet") assay.;Both cold and hot water extracts from G. lucidum and V. volvacea exhibited relatively high levels of antioxidant power in the FRAP assay (between 1.5 to 2.5 mmol/L). Cold water extracts of A. bisporus and F. velutipes gave similar FRAP readings, which were about half (1.1--1.2 mmol/L) the values observed with cold water extracts of G. lucidum. Low FRAP values were obtained with all the other extracts tested. The contribution of ascorbic acid to the total antioxidant capacity of the MDPs was not more than 8% except for the two MDP's from F. velutipes where ascorbic acid accounted for about 25% of the FRAP value.;Screening of aqueous extracts of the sporophores of eight mushroom species for genoprotective activity using the Comet assay revealed a wide variation in the ability of the different MDPs to protect against oxidative DNA damage. Very high genoprotective activity was observed with cold and hot water extracts of A. bisporus and G. lucidum, respectively. In both cases, virtually complete protection against H2O2 -induced damage to cellular DNA was provided by concentrations of 0.5mg MDP per ml of tissue culture medium, and there were no cytotoxic effects per se. Intraperitoneal administration of Ab-cold also protected the DNA of rat lymphocytes against H2O2-induced damage in an ex vivo assay. However, Ab-cold could not protect Raji cells against damage to DNA induced by either bleomycin or ethyl methanesulphonate. No protective effects were observed with any of the other MDPs examined.;The protective effect of Ab-cold against H2O2-induced oxidative damage to cellular DNA was associated with a heat-labile protein present in the mushroom fruit body. The protein was purified using ammonium sulphate precipitation, DEAE-sepharose chromatography, hydrophobic interaction chromatography and hydroxyapatite chromatography, and was identified as tyrosinase on the basis of catalytic and electrophoretic properties as well as inhibition studies. The genoprotective effect of the tyrosinase was shown to be dependent upon the enzyme-catalysed hydroxylation of tyrosine to L-DOPA and the subsequent conversion of this metabolite to dopaquinone and other oxidation products.