Antioxidant trace element reduction in an in vitro cardiopulmonary bypass circuit

Many complications occurring after cardiac surgery are attributed to an acute increase in reactive oxygen and reactive nitrogen species, which under normal conditions are balanced by the antioxidant response. Two key enzymes of the antioxidant response, glutathione peroxidase (GPx) and superoxide dismutase (SOD), rely on trace elements for normal function. It was hypothesized that circulation of blood through the cardiopulmonary bypass (CPB) circuit would 1) reduce trace element levels and antioxidant function, 2) increase oxidative stress, and that 3) prepriming circuits with albumin would ameliorate trace element loss. This hypothesis was investigated by circulating fresh human whole blood in an in vitro CPB circuit. Plasma selenium, copper, and zinc levels were measured, as were SOD and GPx and oxidative stress by thiobarbituric acid reactive substances (TBARS). In spite of significant decreases in copper and zinc levels, SOD levels increased with time. Significant decreases in selenium were associated with a trend to increase TBARS but no change in GPx. Prepriming with albumin provided no benefit as it did not reduce trace element loss nor alter levels of oxidative stress. This study confirms that CPB circuits cause significant depletion of trace elements (selenium, copper, and zinc) necessary to maintain redox homeostasis. The loss of trace elements is a potential contributor to cardiac surgical morbidities, and further studies in the cardiac patient population are needed to investigate this.