Pterin-6-aldehyde, an inhibitor of xanthine oxidase, has superoxide anion radical scavenging activity.

Superoxide anion radical (O2.-) scavenging activity of neopterin (NP) and its photodegraded products was studied. NP did not affect O2.- release in hypoxanthine/xanthine oxidase (HPX/XOD) reaction system, but pterin-6-aldehyde (P6A), one of photodegraded products of NP, suppressed it. The identification of P6A was successful by confirming inhibiting property of xanthine oxidase. In neutrophil/phorbol myristate acetate reaction system, NP did not affect the O2.- release but P6A suppressed it. The suppression by P6A was not associated with oxygen uptake, which indicated that P6A did not inhibit the generation of O2.- but directly scavenged it. These findings suggest that P6A has ameliorating effects on ischemic-reperfusion injury in which O2.-, which is generated both in HPX/XOD reaction and in activated neutrophil, is one of the major substances to damage the tissues.