Deletion of the lactoperoxidase gene causes multisystem inflammation and tumors in mice

Strongly oxidative H2O2 is biologically important, but if uncontrolled, would lead to tissue injuries. Lactoperoxidase (LPO) catalyzes the redox reaction of reducing highly reactive H2O2 to H2O while oxidizing thiocyanate (SCN−) to relatively tissue-innocuous hypothiocyanite (OSCN−). SCN− is the only known natural, effective reducing-substrate of LPO; humans normally derive SCN− solely from food. While its enzymatic mechanism is understood, the actual biological role of the LPO-SCN− system in mammals remains unestablished. Our group previously showed that this system protected cultured human cells from H2O2-caused injuries, a basis for the hypothesis that general deficiency of such an antioxidative mechanism would lead to multisystem inflammation and tumors. To test this hypothesis, we globally deleted the Lpo gene in mice. The mutant mice exhibited inflammation and lesions in the cardiovascular, respiratory, digestive or excretory systems, neuropathology, and tumors, with high incidence. Thus, this understudied LPO-SCN− system is an essential protective mechanism in vivo.