senecionine and 4-hydroxy-2-hexenal

The pyrrolizidine alkaloid senecionine has been shown to produce an increase in cytosolic free Ca2+ concentration in isolated hepatocytes that correlated with an increase in cellular toxicity. The cytotoxicity was greater in the absence of extracellular Ca2+ than in its presence, suggesting that alterations in intracellular Ca2+ distribution, and not an influx of extracellular Ca2+, were responsible for the senecionine-induced hepatotoxicity. The effect of senecionine, as well as the effects of trans-4-OH-2-hexenal (t-4HH), a microsomal metabolite of senecionine, and a related alkenal, trans-2-hexenal, on the sequestration of Ca2+ in mitochondrial and extramitochondrial compartments were examined in isolated hepatocytes. Each of the test compounds elicited a decrease in the available extramitochondrial Ca2+ stores that was inhibited by pretreatment with the thiol group reducing agent, dithiothreitol. Senecionine and t-4HH decreased the level of Ca2+ sequestered in the mitochondrial compartment of hepatocytes. The presence of a pyridine nucleotide reducing agent, beta-hydroxybutyrate, inhibited this reduction. These results suggest that both senecionine and t-4HH inhibit the sequestration of Ca2+ in extramitochondrial and mitochondrial compartments possibly by inactivating free sulfhydryl groups and oxidizing pyridine nucleotides respectively.

Topics: Aldehydes; Animals; Antineoplastic Agents, Phytogenic; Calcimycin; Calcium; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Dithiothreitol; In Vitro Techniques; Liver; Male; Pyrrolizidine Alkaloids; Rats; Rats, Inbred Strains

Lipid peroxidation was examined as a possible mechanism for cell injury by trans-4-OH-2-hexenal, the macrocyclic pyrrolizidine alkaloid senecionine and related alkenals in isolated rat hepatocytes. Each compound elicited a positive dose response for peroxidation of cellular lipids as measured by the formation of thiobarbituric acid-reactive products. The addition of the anti-oxidant N,N'-diphenyl-p-phenylenediamine to the hepatocyte suspensions inhibited the production of thiobarbituric acid-reactants. However, the presence of the anti-oxidant had no protective effects on the cell membrane integrity as evidenced by the leakage of lactate dehydrogenase from the cells into the surrounding media. These results suggest that lipid peroxidation which occurs in the presence of senecionine, trans-4-OH-2-hexenal or related alkenals is not entirely responsible for the cellular damage in isolated rat hepatocytes.

Topics: Aldehydes; Animals; Cells, Cultured; Lipid Peroxidation; Liver; Male; Pyrrolizidine Alkaloids; Rats; Rats, Inbred Strains

The toxicity of macrocyclic pyrrolizidine alkaloids in the livers of man and animals has been attributed to the formation of reactive pyrroles from dihydropyrrolizines. Now a novel metabolite, trans-4-hydroxy-2-hexenal, has been isolated from the macrocyclic pyrrolizidine alkaloid senecionine, in an in vitro hepatic microsomal system. Other alkenals such as trans-4-hydroxy-2-nonenal have previously been isolated from microsomal systems when treated with halogenated hydrocarbons or subjected to lipid peroxidation. The in vivo pathology caused by trans-4-hydroxy-2-hexenal appears to be identical to that previously attributed to reactive pyrroles. There are similarities between the toxic effects of this alkenal and those of centrilobular hepatotoxins such as CCl4 and other alkenals formed during lipid peroxidation.

Topics: Aldehydes; Animals; Biotransformation; Chemical and Drug Induced Liver Injury; In Vitro Techniques; Injections, Intravenous; Lipid Peroxides; Liver Diseases; Mice; Microsomes, Liver; Necrosis; Portal Vein; Pyrrolizidine Alkaloids; Rats