Academic literature on the topic 'Neotyphodium – Toxicology'

The ryegrass endophyte/plant interaction produces a number of toxic metabolites responsible for a range of toxicoses including ryegrass staggers. Although lolitrem B has long been considered the toxin responsible for ryegrass staggers in farm animals, it is only recently that we have demonstrated that oral administration of the pure toxin causes tremors in mice consistent with the symptoms of ryegrass staggers. Various levels of the toxin were incorporated into the diet of mice and tremor response measured regularly. Mice were very susceptible to the tremorgenic action of lolitrem B with a dose of only 1.1 mg/kg per day being sufficient to induce a tremor response. Analysis of faeces from a dosed mouse showed that approximately 40% of the toxin ingested was excreted unchanged. The profile of tremor response shows that tremors build up over a 24-hour period and then reach a dose dependent plateau suggesting that toxin turnover reaches a steady state. In experiments designed to test the possibility that tremorgens bind to specific receptors in the brain, mice were injected with the 14C-labelled tremorgen, paxilline. Paxilline was chosen as it is similar in structure and possible action to lolitrem B and could be more easily prepared with an isotopic label. Following injection of 14C-paxilline to mice their brains and spinal cord were sectioned and analysed for 14C content. Localised binding was not detected but rather an even distribution of isotope was observed. This is probably due to the lipophilicity of the tremorgens, which distribute randomly throughout the fatty brain matrix, masking any binding to specific regions or receptors. This study showed, however, that only a minute proportion of the administered tremorgen reached the brain and spinal cord, indicating that, if this is the site of action, the receptors involved in the initiation of staggers are extremely sensitive to the tremorgens. Keywords: endophyte, lolitrem, Lolium perenne, mycotoxin, Neotyphodium lolii, neurotoxin, oral dosing, ryegrass staggers, tremor, tremorgen

The main plant species relied on for forage supply to grazing animals in New Zealand and south-eastern Australia is perennial ryegrass (Lolium perenne L.). Perennial ryegrass has evolved with a fungal endophyte (Neotyphodium lolii, Latch, Christensen & Samuals) that occupies intercellular spaces, and is nourished by its host. The endophyte (referred to as standard or wild-type) provides the plant with protection from a range of insect pests by producing alkaloids, some of which are also toxic to grazing animals, causing ryegrass staggers and/or exacerbating heat stress. Over the last 20 years naturally occurring perennial ryegrass endophytes have been found in Europe that produce less of the alkaloids that cause animal health problems but have similar or enhanced effects as the standard endophyte on deterring insect attack on infected plants, when introduced into New Zealand and Australian-bred ryegrasses. This review provides a summary of endophyte research in New Zealand from the perspective of insect pests, plants (particularly perennial ryegrass) and the animals grazed on ryegrass-dominant pastures. The protocols used to evaluate perennial ryegrass/endophyte associations over the past 30 years are also discussed. Future testing of new grass/endophyte associations should include the utilisation of more environments for agronomic and entomological experiments; routinely carrying out small animal toxicology assays, and the running of short-term indoor feeding experiments with sheep and cows. Implementation of these changes provides the minimum requirements for strengthening the evaluation of new endophyte associations so farmers using these technologies, gain optimal benefits from their adoption.

‘Fescue toxicosis’ is a disease in livestock caused by ingestion of ergot alkaloids produced by the fungal endophyte Neotyphodium coenophialum in tall fescue; it is estimated to cost 1 billion USD in damages per year to the beef industry alone. Clinical signs include decreased reproductive fitness, necrosis of extremities, and reduced average daily gain and milk production. Little is known about the cellular mechanisms that mediate these toxic sequelae. We evaluated the effects of ergovaline-based fescue toxicosis on gene expression via oligonucleotide microarray. Liver biopsies were obtained from steers (n=4) pre- and post-exposure (0 and 29 days) to feed containing 579 ng/g ergovaline. Analyses were performed using both ANOVA with false discovery rate correction and Storey's optimal discovery procedure. Overall, down-regulation of gene expression was observed; heart contraction and cardiac development, apoptosis, cell cycle control, and RNA processing genes represented the bulk of differentially expressed transcripts. 2 CYPs (CYP2E1 and CYP4F6) were amongst the significantly upregulated results. Thus, exposure of cattle to toxic levels of ergovaline caused widespread changes in hepatic gene expression, which can both help explain macroscopic clinical signs observed in ruminant animals, and reinforce previous findings in monogastric models.

Ergot alkaloids are formed by Claviceps spp. on grains and grasses and by fungal endophytes such as Neotyphodium spp. in grasses, notably tall fescue and perennial ryegrass. Ergots from grains and grasses show a wide variation in alkaloid composition. The main ergot alkaloids are pharmacologically active lysergic acid derivatives – e.g. ergometrine (ergonovine), ergotamine, ergosine, ergocornine, α-ergocryptine, ergocristine, and ergovaline; derivatives of isolysergic acid, e.g. ergotaminine; and clavine alkaloids, e.g. agroclavine. Other structurally unrelated toxic alkaloids such as lolitrems are formed by fungal endophytes in grasses. The present review focuses more on how man and animals are exposed to ergot alkaloids than on toxicology and methods of analysis. Ergot poisoning in humans, well known in the Middle Ages, can be of two types: convulsive ergotism and gangrenous ergotism. Since the beginning of the last century there have been outbreaks in Russia, England, India, France and Ethiopia. The principal route of human exposure to ergot alkaloids is by consumption of contaminated food; another route is inhalation of grain dust. Toxicoses in animals due to ergot alkaloids are more common, particularly poisoning of livestock grazing on endophyte infected grasses. Analyses in Canada, Germany, Switzerland, Sweden and Denmark found ergot alkaloids in human foods such as wheat and rye flours, bread, and other grain foods, often at levels greater than 1000 µg/kg. Processing studies have confirmed that the alkaloids survive baking; they also remain to some extent after brewing of beer. There is little evidence for carryover of ergot alkaloids into animal tissue and milk. As an indication of the importance of controlling ergot for the health of animals and people, Canada, the European Union, Switzerland, USA, Japan, Australia and New Zealand have regulations for ergot in grains but only Uruguay and Canada have regulations for the actual ergot alkaloids in feed.

Perennial ryegrass (PRG, Lolium perenne) is a hardy cool-season grass that is infected with the endophytic fungus Neotyphodium lolii, which enables the plant to be insect repellant and drought resistant, lowering the use of insecticides and fertilizers. However, this fungus produces the compound lolitrem B (LB, m/z 686.4) which causes the tremorgenic neurotoxicity syndrome 'ryegrass staggers' in livestock consuming forage which contains <2000 ppb LB. Ergovaline (EV, m/z 534) is a vasoconstrictor normally associated with tall fescue (Festuca arudinacea), but has also been found in endophyte-infected PRG. Past research has shown a strong linear correlation between levels of LB and EV in PRG. The purpose of this study was to examine the linear relationship between EV and LB in feces and determine common metabolites. To accomplish this, four groups of steers (n=6/group) consumed endophyte- infected PRG over 70 days consumed the following averages of LB and EV: group I 2254ppb LB/633 ppb EV; group II 1554ppb LB/ 373ppb EV, group III 1011ppb LB/259ppb EV, and group IV 246ppb LB/<100ppb EV. Group I in week 4 was inadvertently given a washout period at which time the steers consumed the amount of LB and EV given to group IV (control). Both feed and feces samples were extracted using difference solid phase extraction methods and quantified by HPLC-fluorescence for LB and EV. Concentrations of EV and LB obtained through HPLC-fluorescence in both PRG and feces showed a linear relationship. Additional screening for metabolites was conducted LC-MS/MS and showed possible oxidation and reduction metabolites for both toxins.
Graduation date: 2013