Comparative study of the antioxidant activity of some thiol-containing substances

Abstract

Background

Therapeutic thiol administration has been shown to have great potential in a variety of pathological conditions associated with oxidative stress. In the present study, the free radical scavenging effects against superoxide anion (${\rm O}_{2^ - }$) and hydroxyl (·OH) radicals of captopril were compared with those of cysteamine and mercaptoethanol. Methods: The ${\rm O}_{2^ - }$ and ·OH were generated in vitro. Deoxyribose (DR) was used as a detector of ·OH radicals. The degradation of DR was measured in terms of the formation of thiobarbituric acid reactive substances, which were quantified spectrophotometrically. Superoxide anion radicals were generated photochemically and ${\rm O}_{2^ - }$-produced nitro-blue tetrazolium (NBT) reduction was measured.

Results

Using two distinct ·OH generating systems, the DR test showed that in the absence of the chelator diethylene triamine pentaacetic acid (DTPA) cysteamine was much more potent inhibitor of the formation of thiobarbituric acid reactive substances (TBARs) than captopril and mercaptoethanol, and that in the presence of DTPA captopril and mercaptoethanol decreased the TBARs formation in presence of H₂O₂ better than cysteamine. Captopril in concentration of 9.34 mM and cysteamine in concentration of 1.21 mM inhibited the ${\rm O}_{2^ - }$ provoked NBT reduction by 50%. Mercaptoethanol up to 10 mM did not manifest an inhibitory effect.

Conclusions

Captopril and mercaptoethanol are potent free radical scavengers, reacting rapidly with ·OH, whereas cysteamine acts preferentially as a chelator of iron and in this way prevents the formation of ·OH.