Endophyte infected tall fescue (E+) is the base diet for nearly all beef cattle in the southern USA. It has been linked to a variety of toxicological conditions due to the presence of large numbers of ergot alkaloids. This study was designed to investigate the effects of E+ seed extract and selected ergot alkaloids on the detoxification pathway by cytochrome P450 (CYP3A4) enzyme system. Tests were performed using the P450- Glo CYP3A4 enzyme activity kit (Promega, WI), according to the manufacturer’s manual. Luminescence was measured using a single tube TD20/20 luminometer. Endophyte infected tall fescue seed was extracted with 50/50 methanol/25 mM ammonium carbonate, cleaned and concentrated on Strata-X reversed phase column (Phenomenex). The extracts were evaluated on an HPLC, and then tested using a serial dilution method. Commercially available ergonovine (EN), ergocorine (ER), bromocryptine (BC) and ergocryptine (EC) were tested individually using 0 to 44 nM concentrations. Seed extract of E+ produced a significant (P < 0.05) dose dependent inhibition of CYP3A4 enzyme activity similar to that produced by the commercially available ergot alkaloids EC, ER, BC and EN which inhibited CYP3A4 enzyme activity in a significant (P < 0.05) dose dependent manner with EC being most potent, followed by ER, BC, and then EN (70%, 40%, 30% and 10% at 44 nM concentration). The similarity of the inhibition curves of seed extract to that of the commercially available ergot alkaloids suggests a related mode of action and that the use of such ergot alkaloids and CYP3A4 assay is a good model to study the toxicity of tall fescue. Furthermore, it provides the foundation to identify the individual toxic components of purified endophyte infected tall fescue extract.
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