2-Hydroxyemodin, an active metabolite of emodin in the hepatic microsomes of rats.

The hepatic microsomes derived from rats transformed emodin (1,3,8-trihydroxy-6-methyl-anthraquinone), an anthraquinone present in fungal metabolites and constituent of rhubarb, into at least 10 anthraquinoid metabolites. Metabolite d proved to be mutagenic to Salmonella typhimurium TA1537 in the absence of activation system. MS, NMR, UV and mutagenicity test analysis revealed that metabolite d was 2-hydroxyemodin (1,2,3,8-tetrahydroxy-6-methyl-anthraquinone) and exhibited mutagenicity in doses of 2-20 micrograms/plate. In addition to this active metabolite, TLC analysis revealed the formation of 4-hydroxyemodin (metabolite a), 5-hydroxyemodin (metabolite b), 7-hydroxyemodin (metabolite d') and others. No mutagenicity of these monohydroxyemodins was demonstrated in the absence of activation system.