Xenobiotics and the effects of eucalypt monoterpenes on the cytokine expression of koalas, Phascolarctos cinereus

Abstract

The koala is a specialist herbivore thriving on a diet of mainly eucalypts, which contain a toxic cocktail of highly absorbable monoterpenes that can affect health in various ways when ingested in high amounts. Specialist adaptations are required to protect animals from acute intoxication. Koalas apply amongst other strategies high metabolic detoxification capacities to deal with these components but increased exposure to anthropogenic environmental contamination is potentially effecting metabolic detoxification pathways and therefore can reduce food intake in this species. The aim of this thesis is to investigate the systemic exposure of koalas to a range of xenobiotics. The profile of main eucalypt monoterpenes in the ingesta of deceased koalas was investigated and tested for consistencies between animals and regions. A well-balanced monoterpene profile was found when mean profiles of different regions were compared. Blood exposure to selected monoterpenes was found continuous but low compared to other eucalypt feeders. Monoterpene profile in blood was similar to that in ingesta of koalas (but different to the profile of lymphatic tissue) suggesting a feeding behavior that balances toxin exposure in peripheral blood. Accumulation of frequently used pesticides, metal and trace elements were further investigated in koalas from different regions of NSW and Victoria. Hepatic accumulation of pesticides is uncommon in this species, but element exposure of koalas changes significantly with land use and region and less commonly with age and sex of the animals. This study also provides first insight into the effects of eucalypt monoterpenes on the immune function of this species. This study demonstrates that circulating concentrations of monoterpenes have dose dependent inhibitory effects (in vitro) on cytokine expression of koala peripheral blood mononuclear cells, suggesting a potential evolutionary adaptation in this species.