Phenolic compounds present in medicinal mushroom extracts generate reactive oxygen species in human cells in vitro

Hot-water extracts of the higher Basidiomycetes Agaricus bisporus (J. Lge) Imbach, A. brasiliensis S. Wasser et al., Coprinus comatus (O.F. Mull.) Pers., Ganoderma lucidum (W. Curt.: Fr.) P. Karst., and Phellinus linteus (Berk. et Curt.) Teng were made, and the resulting polysaccharide mixtures were purified by DEAF-cellulose chromatography and ethanol precipitation. The extracts were noncytopathic. A. bisporus, A. brasiliensis, and G. lucidum strongly generated reactive oxygen species (ROS) in human PBMCs and K 562 cells. C. comatus and Ph. linteus extracts had low ROS-generating capacity. In A. bisporus extract, two different classes of polysaccharides were found. The colorless polysaccharide of MW > 250 kDa caused no intracellular ROS generation; acid hydrolysis followed by HPLC analysis showed it to consist of only glucose residues, thus being a pure glucan. The light brown polyphenol/polysaccharide complex of MW 75-200 kDa was found to strongly generate ROS. ROS generation by medicinal mushrooms could therefore be due to the presence of polyphenols rather than of glucan alone. A. bisporus polysaccharide extract showed a saturation level of ROS generation at 2 mg mL(-1). Generation appeared to continue in the presence of polysaccharide for more than 14 hours. Purified colorless polysaccharides of C. comatus and Ph. linteus showed no ROS generation in K562 cells; G. lucidum and A. brasiliensis polysaccharides could not completely be cleaned of phenolic compounds and remained active. Competitive inhibition of ROS generation by laminarin was not observed for any of the polysaccharide extracts, suggesting that polyphenol/glucan complexes isolated from higher Basidiomycetes mushrooms are able to generate ROS without binding to a dectin receptor