SPIN-TRAPPING STUDY OF ANTIOXIDANT PROPERTIES OF NEOPTERIN AND 7,8-DIHYDRONEOPTERIN

Previously, it has been shown that pteridine derivatives are capable o f modulating the action of free radicals and both prooxidant and antio xidant properties have been described. However, the mechanism of manif estation of these properties is still unclear, We studied the radical scavenging properties of 7,8-dihydroneopterin and neopterin using the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). It was found that d ihydroneopterin acts generally as a radical scavenger. In the presence of dihydroneopterin the ESR signal was reduced by 30 to 90% compared to the control signal. The rate constants for the reactions of 7,8-dih ydroneopterin with superoxide (10(3) M-1 s?(-1)) and peroxyl radicals (10(7) M-1 s(-1)) were determined. Neopterin in contrast showed no red uction of the ESR signal except with superoxide radicals produced by x anthine oxidase. However, this effect was shown to be due to an inhibi tion of enzyme rather than to radical scavenging. Our results provide a basis for understanding previous observations of radical scavenger a ctivity of 7,8-dihydroneopterin. (C) 1997 Academic Press.