Genotoxicity of anthraquinone-glycosides - O-glycosides but not C-glycosides are metabolically activated

Hydroxyanthraquinones (HA) are widely distributed in the plant kingdom and are responsible for the pharmacological actions of many phytotherapeutics (e.g. Rubia tinctorum, Aloe, Senna, Frangula etc.). HA are predominantly found as O-glycosides or as C-glycosides. Since only HA-aglycones are genotoxic, we investigated whether bacterial or mammalian cells are capable of cleaving O-glycosides as well as C-glycosides to liberate the respective genotoxic aglycones. After incubation of O-glycosides (sennoside A and B, frangulin A, ruberythric acid and lucidinprimveroside) with rat liver S9 preparation, rat hepatocytes or rat coecal bacteria, the corresponding aglycones were liberated. Similarly incubated glycosides with a genotoxic aglycone (franguline A/ emodin and lucidinprimverosid/ lucidin) were mutagenic in the Salmonella/microsome assay and induced UDS in primary rat hepatocytes. With the C-glycosides (aloin and carminic acid) no enzymic liberation of the aglycones was demonstrated and the compounds did not exhibit genotoxic activity. In agreement, an aloe-extract containing the C-glykoside aloin but not the genotoxic aglycon, aloe-emodin, was inactive in these assays, whereas an extract of Cortex frangulae containing the O-glycosides, frangulin A and B, was active. It appears, therefore, that only O-glycosides of HA represent a genotoxic hazard