The carbonyl content of specific plasma proteins is decreased by dietary copper deficiency in rats

Copper (Cu) deficiency is associated with increased susceptibility of tissue homogenates or lipoproteins to oxidation in vitro. Plasma is easily sampled and contains both lipid and protein components that may be susceptible to oxidation, making it appropriate to investigate plasma oxidation variables as biomarkers of in vivo oxidative stress. Oxidation of plasma proteins may be discernible as an increased content of carbonyl (aldehyde or ketone) groups on the proteins. Weanling male Long-Evans rats were fed sucrose-based modified AIN-93G diets with (+Cu, 6.2 mg Cu/kg diet) or without (-Cu, 0.4 mg/kg) added Cu for 4 wk before killing. Plasma and RBC Cu,Zn-superoxide dismutase activities and liver Cu concentration were significantly decreased and relative heart weight was significantly increased, confirming the Cu-deficient status of the -Cu rats. Dinitrophenylhydrazine (DNP) derivatization followed by SDS-PAGE and Western blotting using commercial anti-DNP antibody demonstrated that several plasma proteins in +Cu control rats showed evidence of carbonyl groups. The carbonyl content of these bands was lower in -Cu rats, not greater as would have been expected with oxidative damage to these proteins. Although dietary Cu deficiency may increase susceptibility to oxidative stress, it does not lead to accumulation of oxidized plasma proteins in this animal model.