COMPARATIVE FREE-RADICAL SCAVENGING ACTION OF ANGIOTENSIN-CONVERTING ENZYME-INHIBITORS WITH AND WITHOUT THE SULFHYDRYL RADICAL

The free radical scavenging effects of an angiotensin-converting enzym e (ACE) inhibitor containing sulfhydryl (SH; captopril) were compared with those of ACE inhibitors not containing SH (enalapril, enalaprilat , delapril and its de-esterified products). Electron spin resonance (E SR) using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin trap sho wed that enalapril and delapril (0.6-4.8 mmol/l) inhibited hydroxyl ra dicals concentration-dependently. Captopril (2.4-10 mmol/l), enalapril at and the de-esterified product of delapril (1.24. 8 mmol/l) also inh ibited hydroxyl radicals in a concentration-dependent manner. The effe cts of captopril and enalapril (2.4-4.8 mmol/l) on the scavenging of s uperoxide anion radical were also concentration-dependent. Delapril, i ts de-esterified product, and enalaprilat weakly inhibited superoxide anion radical. These results indicate that both SH- and non-SH-contain ing ACE inhibitors scavenge hydroxyl radical more strongly than the su peroxide anion radical and that the free radical scavenging action of ACE inhibitors is probably not related only to the presence of the SH radical.