Antioxidant status and biomarkers of oxidative stress in cats with diabetes mellitus

Increasing evidence implicates oxidative damage in the progression and pathologic complications of human diabetics. This study assessed antioxidant status and oxidative stress in cats with diabetes mellitus (DM). Antioxidant status was measured in diabetic (n = 10) and control (n = 10) cats by HPLC of vitamin E isomers, reduced (GSH) and oxidized glutathione (GSSG), and calculation of the GSH:GSSG ratio. Biomarkers of protein, lipid and DNA peroxidation (fructosamine, isoprostanes and Comet assay, respectively), and neutrophil function evaluated oxidative stress. Correlation between glycemic control and antioxidant status/ oxidative stress was also investigated. A diabetic index was generated using clinical signs, body condition score, insulin dose, fructosamine, fasted blood glucose and urinary glucose and ketones. Alpha tocopherol was increased (DM = 0.11 μg/mL, controls = 0.06 μg/mL; p = 0.0012) and gamma tocopherol was decreased (DM = 0.03 μg/mL, controls = 0.05 μg/mL; p = 0.0065) in diabetic vs. control cats. There was no difference in the GSH:GSH ratio between groups. Predictably, fructosamine was greater in diabetic vs. control cats (DM = 447 μmol/L, controls = 204 μmol/L; p < 0.0001). Antioxidant status/oxidative stress was not associated with glycaemic control in diabetic cats. Despite strong association of DM with oxidative stress in humans, this simple relationship is not found in diabetic cats. They have both increased and decreased parameters of systemic oxidative stress compared with control cats. This may be due to higher levels of antioxidants in feline therapeutic diets, the relatively short duration of disease in cats compared with humans, or other factors.