Captopril inhibits the fluorescence development associated with glycation of proteins.

Albumin and immunoglobulin G (IgG) show increased visible fluorescence in diabetic patients, IgG fluorescence being correlated with the presence of diabetic retinopathy. Captopril, an angiotensin converting enzyme (ACE) inhibitor, has free radical scavenging ability, attributable to its thiol group. We compared the scavenging effect of captopril (at doses between 0.5 and 100 microM) with perindoprilat, enalapril and enalaprilat (ACE inhibitors without scavenging ability) and two thiol-containing compounds, mercaptopropionylglycine (MPG) and N-acetylcysteine (NAC) (scavengers with no effect on ACE). Three systems were used to generate visible fluorescence in albumin and IgG; glycation, exposure to copper/hydrogen peroxide and gamma radiation. All three thiol-containing compounds inhibited fluorescence development in IgG and albumin, when fluorescence was generated by glycation or gamma radiation. Other ACE inhibitors had no effect with IgG. Enalapril and perindoprilat showed less effect than captopril with albumin; enalaprilat had no effect. No compound had any effect on fluorescence generation by copper/hydrogen peroxide. Captopril may have an additional antioxidant effect compared to other ACE inhibitors.