Journal
REDOX REPORT
Volume 9, Issue 1, Pages 57-61Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1179/135100004225003923
Keywords
dihydrolipoic acid; redox activity; transition metals
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Funding
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [P01HL060886] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE ON AGING [R01AG017141] Funding Source: NIH RePORTER
- NCCIH NIH HHS [AT-00066] Funding Source: Medline
- NHLBI NIH HHS [HL-60886] Funding Source: Medline
- NIA NIH HHS [AG-17141] Funding Source: Medline
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alpha-Lipoic acid (LA) and its reduced form, dihydrolipoic acid (DHLA), have been suggested to chelate transition metal ions and, hence, mitigate iron- and copper-mediated oxidative stress in biological systems. However, it remains unclear whether LA and DHLA chelate transition metal ions in a redox-inactive form, and whether they remove metal ions from the active site of enzymes. Therefore, we investigated the effects of LA and DHLA on iron- or copper-catalyzed oxidation of ascorbate, a sensitive assay for the redox activity of these metal ions. We found that DHLA, but not LA, significantly inhibited ascorbate oxidation mediated by Fe(III)-citrate, suggesting that reduced thiols are required for iron binding. DHLA also strongly inhibited Cu(II)(histidine)(2)-mediated ascorbate oxidation in a concentration-dependent manner, with complete inhibition at a DHLA:Cu(II) molar ratio of 3:1. In contrast, no inhibition of copper-catalyzed ascorbate oxidation was observed with LA. To investigate whether LA and DHLA remove copper or iron from the active site of enzymes, Cu,Zn superoxide dismutase and the iron-containing enzyme aconitase were used. We found that neither LA nor DHLA, even at high, millimolar concentrations, altered the activity of these enzymes. Our results suggest that DHLA chelates and inactivates redox-active transition metal ions in small-molecular, biological complexes without affecting iron- or copper-dependent enzyme activities.
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