Effects of Amanita Phalloides toxins on insulin release: in vivo and in vitro studies

The clinical picture of Amanita phalloides poisoning includes hypoglycaemia, usually related to hepatic damage. In fact, Amanita toxins induce hepatic glycogen depletion in humans and animals. However, in animals morphological changes of pancreatic beta cells are reported, suggesting that an alteration of insulin secretion might be involved in the pathogenesis of hypoglycaemia. Therefore, we determined fasting glucose, insulin and C-peptide levels in ten patients intoxicated by Amanita phalloides and in ten control subjects. Fasting blood samples were drawn on 3 consecutive days, beginning 48-72 h after mushroom ingestion, and glucose, insulin and C-peptide concentrations were determined by routine methods. Serum glucose concentrations did not differ between poisoned subjects and controls, whereas insulin and C-peptide concentrations were significantly higher in poisoned subjects (P<0.01), with a significant positive correlation (R=0.97, P<0.001). We also evaluated the effects of alpha-amanitin, the main amatoxin, on in vitro insulin release. Rat islets were incubated with 5 and 50 mg/l alpha-amanitin, in the presence or absence of 5.6 mM glucose. In another protocol, islets were preincubated for 2 h with 5 and 50 mg/l alpha-amanitin in medium containing 5.6 mM glucose. After lavage, islets were incubated with increasing glucose (2.8-22.0 mM) to evaluate insulin release. In vitro, both concentrations of toxin induced insulin release (5 mg/l P<0.02, 50 mg/l P<0.01 vs controls), in the presence of 5.6 mM glucose. Islets preincubated with 5 mg/l alpha-amanitin showed a pattern of glucose-stimulated insulin release similar to controls, whereas islets preincubated with 50 mg/l alpha-amanitin showed an increased basal release with a reduced response to glucose stimulation. These observations show that Amanita toxins might play a role in the clinical context of Amanita poisoning. We demonstrate, for the first time, that alpha-amanitin induces insulin release and may exert a cytotoxic effect on beta cells.