(-)-Lasiocarpine

Lasiocarpine is toxic to liver cells but not to lung cells, which is unable to metabolize the pyrrolizidine alkaloids to pyrroles. The application of lasiocarpine to human liver cells in culture is followed by inhibition of DNA, RNA and protein synthesis; vacuolation of the cells, the prevention of mitosis and the formation of giant cells (“megalocytes”). (A15431) Effects on the liver include hemorrhagic necrosis of parenchymal cells, marked enlargement of parenchymal cells and of their nuclei and nucleoli, fibrosis or cirrhosis, depression of cell division, and possibly neoplasia. (A15432) The inducibility of tryptophan pyrrolase activity by hydrocortisone, in the livers of rats treated chronically with lasiocarpine is an indication that translational mechanisms are intact. However, the increased uptake of 3H-thymidine by megalocytes, in the absence of observable mitotic activity, suggests that these cells are in the process of hypertrophy. They may act as prolonged, potent inhibitors of mitosis in hepatocytes, they are mutagenic in Drosophila and cause chromosome breakage in leukocytes. One of the unusual results of chronic poisoning by lasiocarpine and other members of the pyrrolizidine alkaloids is progressive enlargement of liver cells to up to three times the normal diameter, with an accompanying proportionate increase in nuclear diameter. The term megalocytosis has been applied to this abnormality which may be associated with mild fibrosis of central veins and proliferation of bile ducts. The prominence of rough ER in enlarged hepatocytes is s a sign of increased metabolic activity. (A15433)