Hypoxanthine is a purine-based organic compound in human muscle tissues, Hypoxanthine is formed during purine catabolism as a product of xanthine oxidase action on xanthine, and occasionally is found as a constituent of nucleic acids. The potent anti-inflammatory and cytoprotective effects of purines may be mediated by cell surface adenosine receptors. Hypoxanthine protects against oxidant-induced cell injury by inhibiting activation of nuclear poly(ADP-ribose) polymerase (PARP). (NCI04)