Sporidesmin — Hepatocyte interactions affecting bile secretion

The cellular and molecular toxicity of sporidesmin

The fungal metabolite sporidesmin is responsible for the hepatogenous photosensitising disease facial eczema in livestock. Toxicity is due to a sulfur-bridged epidithiodioxopiperazine ring that has wide biological reactivity. The ways in which the toxin causes hepatobiliary and other tissue damage have not been established. Hypotheses include direct interaction with cellular thiols including protein cysteine residues or production of reactive oxygen species resulting in oxidative stress. Comparison with the cellular effects of the structurally related compound gliotoxin suggests additional mechanisms including interaction with cell adhesion complexes and possible downstream consequences for regulated necrosis as a response to tissue injury. Revision of hypotheses of how sporidesmin affects cells has the potential to generate new strategies for control of facial eczema including through identification of proteins and genes that are associated with resistance to the disease.

Mouse strain differences in susceptibility to sporidesmin-induced biliary tract injury

Biliary tract injury was examined in four inbred strains of mice orally dosed with 500 micrograms of the fungal toxin sporidesmin. Semiquantitative histological analysis was used to assess the grade of necroinflammatory changes in the gall bladder, intra- and extrahepatic biliary tree and lobular parenchyma. Injury was greatest in the C57BL/6 and C3H strain mice and was least in SJL/J mice. In these strains injury was greatest at 4 days and had regressed by 10 days. In BALB/c mice the damage, although similar to that in SJL/J mice at 4 days, persisted at the same severity at day 10 and was accompanied by periductal fibrosis and occasionally by obliteration of ducts typical of sclerosing cholangitis. Analysis of the time-course of development of the lesions in C57BL/6 mice showed that the primary target for the toxin is the biliary epithelium. The severity of the lesions within the liver increased centripetally and the worst affected ducts were found at the confluence of the lobar ducts with the common bile duct. The variation in the degree of damage and rate of healing between strains may be due to differences in sporidesmin excretion in bile or interactions with biliary epithelial cells and/or efficacy of protective cellular repair mechanisms.

Use of indirect immunofluorescence to show changes in liver actin microfilament staining in inbred mice strains exposed to the mycotoxin sporidesmin

The distribution of microfilaments in cryostat sections of liver from BALB/c and C57BL/6 mice was compared using the F-actin binding probe rhodaminyl phalloidin and indirect immunofluorescence using a human serum containing antiactin autoantibodies. The immunological reactivity of this serum was established by its capacity to immunoprecipitate purified skeletal muscle actin and by its ability to immunoprecipitate a protein which migrated electrophoretically with actin from 35S-labeled liver cells. Oral administration of the liver toxin sporidesmin did not substantially alter the binding of rhodaminyl phalloidin to microfilaments but the reactivity of the anti-actin serum with the liver cytoskeleton was diminished 3 h after, and enhanced within 24 h of toxin ingestion. Amounts of actin measured by DNAse inhibition were not altered. The results are assessed in terms of their significance for understanding the way in which sporidesmin causes liver damage.