The exact mechanisms of fescue toxicity in animals have yet to be established, but it has been associated with an inability to thrive.
Ergovaline is the major ergopeptine
alkaloid associated with
fungal infections of tall fescue. Gastrointestinal (GI) toxicity of
ergovaline (10(-11) to 10(-4) M) was evaluated in Caco-2 cells (mimicking the GI epithelium) beginning on days 1, 8, and 18 of culture. Acute and chronic toxicity was assessed after 24 and 72 h of exposure. Treatment periods were chosen to study undifferentiated, semidifferentiated, and completely differentiated cells. Cell loss and metabolic activity were assessed by
thiazolyl blue reduction (3-(4,5-dimethylthiozole-2-yl)-2,5,-
biphenyl tetrazolium
bromide [MTT], mitochondrial
succinate dehyrdogenase activity),
alamarBlue assay (
cytochrome oxidase activity), and
deoxyribonucleic acid (
DNA) quantitation. Undifferentiated cells were sensitive to 1 x 10(-4) M
ergovaline after acute exposure (from 52 to 74% of control values depending on assay). After 72 h of exposure to 1 x 10(-4) M
ergovaline, in all three assays, treatment means were reduced to approximately 10% of the control means. By day 11 in culture,
ergovaline toxicity to cells had decreased. With 24 h exposure, an apparent paradoxical increase in MTT was seen at some concentrations. This increase in MTT was also found in fully differentiated cells (day 21), whereas
alamarBlue activity decreased. No change in
DNA was found until 72 h of exposure, when
DNA was reduced approximately 12% over most concentrations. These findings indicate differentiation state-dependent sensitivity of Caco-2 cells to
ergovaline, potential problems of the MTT assay as an
indicator of cellular toxicity, and usefulness of
alamarBlue assay over
DNA assay for toxicity assessment.