Development of Screening Assays for Determining Toxicity of Grass-Associated Fungal Endophytes

Description

The research described in this thesis was focused on the indole diterpene mycotoxins produced by the perennial ryegrass-endophyte symbiotum. Perennial ryegrass is the major forage in south east Australia and New Zealand grazing systems. The indole diterpenoid mycotoxin lolitrem B is found in endophyte-infected perennial ryegrass and is present in around 90% of ryegrass
pastures. Ingestion causes a neurological syndrome in grazing livestock called “ryegrass staggers disease” where clinical signs include hyperexcitability, muscle tremors, ataxia (“staggers”) and, in severe cases, clonic seizures and death. Lolitrem B is only one of the lolitrems produced by endophytes and the toxicity of both analogues and biosynthetic pathway intermediates are largely undefined.
To better characterise toxicity, lolitrem B and several intermediates were purified from endophyte-infected perennial ryegrass using large scale extraction and isolation techniques.
Using a time-series analysis, the effects on movement and tremor in dosed mice were quantified for lolitrem B and terpendoles B, C and E. Animals exposed to lolitrem B showed significant and prolonged tremors and decreased stability during accelerated rotarod testing. Terpendole C induced severe short-term tremors, whereas terpendole B and E were inactive.
A metabolomics study was carried out on lolitrem B exposed mice at two key time points reflecting peak and post-peak tremors. A targeted approach was employed to determine the distribution of lolitrem B in the body and brain regions of toxin exposed mice and also to analyse the metabolic variation elicited in the brain. At peak tremor high levels of lolitrem B was found in
the cerebral cortex and although all brain regions show metabolic perturbation, the cerebral cortex showed the most profound effect with respect to activation of amino acids and neurotransmitters.
Characterisation of clinical signs and metabolic changes associated with exposure to indole diterpenoid toxins present in perennial ryegrass have provided useful information for generation of animal safe grass varieties for the dairy and meat industries.

Period	01 Jan 2015 → 12 Dec 2018
Examinee	Priyanka Reddy
Examination held at	La Trobe University
Degree of Recognition	National