Tryptophan and purine catabolism metabolites in kidney tissue. Multiple tryptophan and purine catabolism metabolites were significantly elevated in cardiopulmonary bypass with deep hypothermic circulatory arrest (CPB/DHCA) animals without acute kidney injury (AKI) (group 1, green) compared with controls (group 0, red), with further increases seen in CPB/DHCA animals with AKI (group 2, blue). FDR, false discovery rate.