Review: putative mutagens and carcinogens in foods. V. Cycad azoxyglycosides

Cycasin is a member of a family of azoxyglycosides produced by cycads. It is mutagenic and carcinogenic only when deglucosylated to release its principal metabolite, methylazoxymethanol (MAM). Methylazoxymethanol is also the aglycone of other cycad azoxyglycosides and is responsible for their toxicologic properties. The way in which people can be exposed to cycad azoxyglycosides is through the consumption of foods prepared from cycads. MAM induces genetic alterations in various test systems in bacteria, yeast, plants, Drosophila, and mammalian cells. An important aspect of the biological activities of cycasin and MAM is the intimate connection between their metabolism and their toxicologic effects. In adult mammals, the deglucosylation of cycasin is catalyzed only by enzymes of the microflora of the gut. Cycasin is therefore active when administered orally but not when administered parenterally. In contrast, MAM is active regardless of the route of exposure. Major uncertainties remain regarding the intermediates generated from MAM spontaneously and metabolically. More knowledge of these intermediates is required for a better understanding of the molecular mechanisms underlying the toxicity of cycasin, MAM, and related compounds.