A review of the ergot alkaloids found in endophyte-infected tall fescue and perennial ryegrass and their metabolism after ingestion by livestock

Abstract

Tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) are perennial cool-season grasses which are infected with the endophytic fungi, Neotyphodium coenophialum and N. lolii, respectively. These endophytes have been increasingly selected for, as they confer benefits such as pest resistance and drought tolerance to the plant. However, livestock grazing endophyte-infected (E+) grasses are negatively impacted by fungal ergot and lolitrem alkaloids, which are responsible for a variety of mammalian diseases including fescue toxicosis (summer syndrome, fescue foot and fat necrosis) and ryegrass staggers. Most likely, not all of the ergot alkaloids involved in fescue toxicosis have been identified to date. During sample processing for the diagnostic analysis of the endophyte toxin ergovaline, other unidentified peaks occasionally elute that appear to coincide with clinical disease. Analysis of unidentified chromatographic peaks was performed on feed samples by LCMS/ MS to determine their chemical structures and identities. Ergotamine, ergovaline, ergocornine, ergonovine, ergocryptine, ergocrystine and lysergol appeared in various samples and matched controls. Newly identified compounds included ergosine, ergostine and ergoptine. In addition, several samples showed one or more of fourteen new ergots ranging in size from 381-611 mw, with key mass spectral characteristics of ergot alkaloidsspecifically, m/z 223 and 208 corresponding to the ergoline ring system and its demethylated variant, respectively. Once ingested, ergot alkaloids are thought to be metabolised in the rumen and/ or liver of livestock species. Ruminal metabolism of ergovaline was studied in sheep offered Neotyphodium coenophialuminfected tall fescue straw at two ergovaline levels (<10 ppb and 500 ppb) for 28 days. Ergovaline concentration in rumen fluid expressed as a percent of intake increased over sampling time and sampling day (P<0.05). Lysergic acid concentration in rumen fluid expressed as a percent of intake increased over time from day 0 to day 3 (P<0.05) but was not different between day 3 and day 28 at any time point (P>0.10). The faeces contained an average of 0.41 μmol/day ergovaline and 0.87 μmol/day lysergic acid. Urine contained no detectable ergovaline; lysergic acid concentration was 0.213 μmol/day. The appearance of lysergic acid in the faeces, urine and rumen fluid is most likely due to the degradation of ergovaline in the rumen from microbial degradation and further break down in the lower digestive tract. Hepatic metabolism was studied using a mouse model, where the in vitro metabolism of ergotamine in mouse liver microsomes was characterised by LC-MS/MS. Microsomal incubations produced nine predominate peaks which were confirmed to be ergotamine, ergotamine epimer, monohydroxylated metabolites (M1, M2, M1e, M2e) and dihydroxylated metabolites (M3, M4, M5). Keywords: tall fescue, perennial ryegrass, endophyte, ergot alkaloids, metabolism, livestock