Systemic concentrations of antioxidants and biomarkers of macromolecular oxidative damage in horses with grass sickness.

Abstract

The aetiopathogenesis of equine grass sickness (EGS) is unknown. The role of free radical-mediated neuronal damage has not previously been investigated in this condition. To investigate the potential contribution of oxidative damage and antioxidant status to neurodegeneration in EGS. Systemic levels of surrogate biomarkers were determined in 10 horses with acute EGS and in 2 control populations; 10 healthy horses co-grazing with the 10 EGS horses at the onset of clinical disease, and 10 healthy mares grazing where EGS has not been reported. EGS horses had alterations in levels of several antioxidants, consistent with oxidative stress, the acute phase response and/or the secondary metabolic complications of EGS. EGS horses had elevated plasma dihydroxyphenylalanine (DOPA) levels. The elevated DOPA levels probably reflected a generalised disturbance of catecholamine metabolism rather than increased DOPA production via free radical-mediated oxidation of tyrosine. However, there was no evidence of systemic macromolecular oxidative damage. Further work is required to determine whether macromolecular oxidative damage occurring at the neuronal level contributes to EGS.