Free radical reactions might contribute to severe alpha amanitin hepatotoxicity – A hypothesis

• Published in: Medical hypotheses Vol. 69; no. 2; pp. 361 - 367
• Main Authors: Zheleva, Antoaneta, Tolekova, Anna, Zhelev, Momchil, Uzunova, Veselina, Platikanova, Magdalena, Gadzheva, Vesselina
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 2007
• Subjects: Amanitins - metabolism; Amanitins - toxicity; Animals; Catalase - metabolism; Enzyme Activation - drug effects; Free Radicals - metabolism; Free Radicals - toxicity; Internal Medicine; Lethal Dose 50; Liver - drug effects; Liver - enzymology; Liver - metabolism; Male; Mice; Superoxide Dismutase - metabolism
• ISSN: 0306-9877; 1532-2777
• DOI: 10.1016/j.mehy.2006.10.066

Summary Alpha amanitin is a powerful natural hepatotoxin that belongs to the amatoxins isolated from deadly poisonous Amanita phalloides mushroom. The basic molecular mechanism of their toxicity was attributed to inhibition of RNA polymerase II of the eukaryotic cells. At present, the most effective clinical antidote to acute Amanita phalloides mushroom poisoning is silybin, an antioxidant possessing free radical scavenger activity and inhibiting lipid peroxidation, stabilizing membrane structure and protecting enzymes under conditions of oxidative stress. Bearing in mind the biological mechanism of silybin action and the fact that for different amatoxins (alpha, beta, and est. amanitins) does not established straight correlation between their in vivo LD50 and inhibitory constants (Ki) toward RNA polymerase III in vitro determined we supposed some additional toxic effects of these toxins might contribute to their severe hepatotoxicity. Our formerly in vitro experiments demonstrated that alpha amanitin could act either as an antioxidant or as a prooxidant depending on the treatment conditions and toxin concentration. By UV–visible spectroscopy we also shown that alpha amanitin was sensitive to oxidation by a system of lactoperoxidase/H2 O2 and assumed formation of free radical toxin intermediates. Having in mind some exogenic compounds including natural toxins can induce increased production of reactive oxygen species (ROS) we suggested similar generation of ROS provoked by alpha amanitin. Our recently in vitro studies have demonstrated that the alpha amanitin could increase superoxide dismutase (SOD) activity and inhibit catalase (CAT) activity to a considerable degree after together incubation of the toxin with any of enzymes. We have also shown that in vitro increased SOD activity was due to superoxide anion radical scavenging activity (SSA) of the toxin. This therefore informed the decision to study the in vivo effect of alpha amanitin on SOD and CAT activity and the level of lipid peroxidation (LPO) products in liver homogenates isolated from mice treated with the toxin. Statistical significant increased level of LPO products was found at the 6th day comparing to the 20th hour after mice treatment with a subletal dose of the toxin. Based on our previous in vitro and present in vivo studies we have made a hypothesize that in vivo during liver accumulation of the toxin it might be transformed to free radical intermediates causing increase in ROS levels. As a result a peroxidative process in hepatocytes might contribute to the severe alpha amanitin hepatotoxicity.