Inhibition of Type A and Type B Monoamine Oxidases by Naturally Occurring Xanthones

Abstract

Eleven naturally occurring xanthones were tested for in vitro inhibition of type A and type B monoamine oxidases (MAO's), prepared by treating rat brain mitochondria with selective inhibitors. All compounds showed various potencies of inhibition for both types of MAO. 1-Hydroxy-3,8-dimethoxy-xanthone and 1,3-dihydroxy-7,8-dimethoxy-xanthone were most potent for type A MAO, while they were rather weak for type B MAO, showing that these compounds can be regarded as type A inhibitors. The xanthones bearing 1,3-dihydroxy-groups generally exhibited potent inhibition for both types. The 3-O-glucosides of xanthones were much weaker than their corresponding genuine aglycones for both types.