ABSTRACT
Incubation of 48 h concanavalin A stimulated spleen cells (T blasts) and murine peritoneal macrophages with the mycotoxin sporidesmin results in DNA fragmentation characteristic of apoptosis. Morphological changes, particularly condensed chromatin, observed following incubation of these cells with sporidesmin and the immunotoxin gliotoxin and related epipolythiodioxopiperazines (ETP) also show changes characteristic of apoptosis. The presence of Zn2+ salts in the culture medium at concentrations non toxic to the cells over the time period studied protects against DNA damage and morphological change. Interaction between Zn2+ and the reduced form of a simple ETP compound assessed by spectral changes demonstrated the formation of a weak complex between the two molecules. Complex formation between zinc and thiol however was insufficient to prevent oxidative damage to plasmid DNA in vitro by inhibiting auto-oxidation of the reduced ETP compound because of the looseness of the interaction. Cd2+, which appears to form a tighter complex with the dithiol does inhibit cleavage of plasmid DNA. These results establish that the toxicity of sporidesmin may be due in part to its ability to induce apoptosis or programmed cell death in sensitive cells. In addition the immunotoxin gliotoxin and related compounds have now been shown to induce the same characteristic morphological changes in cells of haemopoietic origin. The inhibition of apoptosis induced by ETP compounds by Zn2+ appears to be due to direct inhibition of apoptosis rather than Zn2+ acting as an antioxidant. These results demonstrate the inhibition of apoptosis induced by ETP compounds by Zn2+ and suggest an alternate explanation for the known prophylactic effect of Zn2+ on sporidesmin induced tissue damage.
Subject(s)
DNA Damage , Indoles/toxicity , Lymphocyte Activation/drug effects , Lymphocytes/drug effects , Macrophages/drug effects , Sporidesmins/toxicity , Zinc/pharmacology , Animals , Cadmium/pharmacology , Cell Survival/drug effects , Concanavalin A/pharmacology , Electrophoresis, Polyacrylamide Gel , Gliotoxin/antagonists & inhibitors , Gliotoxin/toxicity , Lymphocytes/ultrastructure , Macrophages/ultrastructure , Mice , Mice, Inbred BALB C , Piperazines/antagonists & inhibitors , Piperazines/pharmacology , Plasmids/drug effects , Sporidesmins/antagonists & inhibitorsABSTRACT
Sporidesmin, the mycotoxin responsible for "facial eczema" in ruminants, has previously been shown to generate superoxide free radical, the latter being formed during autoxidation of the reduced form of the mycotoxin, a dithiol. The autoxidation of reduced sporidesmin is catalysed by iron and by copper, although cobalt, nickel, manganese, cerium, vanadium and molybdenum were found to be without effect. The catalytic activity of copper was some 900-fold that of iron. Cyanide and certain organic complexing agents inhibit superoxide production from reduced sporidesmin by virtue of their ability to chelate copper. Some proteins behave likewise, again through binding of the metal catalyst, although amino acid-bound copper was found to be as effective as ionic copper in catalysing the autoxidation reaction. From the results of the present experiments, it is suggested that any superoxide production from sporidesmin in vivo would be mediated by the intracellular transport pool of copper. Furthermore, the ability of zinc to inhibit intestinal absorption of copper may be involved in the mechanism whereby salts of this metal afford protection against the harmful effects of sporidesmin in the living animal.
