Lipoic and dihydrolipoic acids as antioxidants. A critical evaluation

Brigitte C. Scott, Okezie I. Aruoma, Patricia J. Evans, Charles O'neill, Albert Van Der Vliet, Carroll E Cross, Hans Tritschler, Barry Halliwell

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271 Scopus citations


A detailed evaluation of the antioxidant and pro-oxidant properties of lipoic acid (LA) and dihydrolipoic acid (DHLA) was performed. Both compounds are powerful scavengers of hypochlorous acid, able to protect α1-antiproteinase against inactivation by HOCl. LA was a powerful scavenger of hydroxyl radicals (OH-) and could inhibit both iron-dependent OH' generation and peroxidation of ox-brain phospholipid liposomes in the presence of FeCl3 -ascorbate, presumably by binding iron ions and rendering them redox-inactive. By contrast. DHLA accelerated iron-dependent OH- generation and lipid peroxidation, probably by reducing Fe3+ to Fe2+. LA inhibited this pro-oxidant action of DHLA. However, DHLA did not accelerate DNA degradation by a ferric bleomycin complex and slightly inhibited peroxidation of arachidonic acid by the myoglobin-H2O2 system. Under certain circumstances, DHLA accelerated the loss of activity of αantiproteinase exposed to ionizing radiation under a N2O/O2 atmosphere and also the loss of creatine kinase activity in human plasma exposed to gas-phase cigarette smoke. Neither LA nor DHLA reacted with superoxide radical (O2 -) or H2O2 at significant rates, but both were good scavengers of trichloromethylperoxyl radical (CCl3O2). We conclude that LA and DHLA have powerful antioxidant properties. However, DHLA can also exert pro-oxidant properties, both by its iron ion-reducing ability and probably by its ability to generate reactive sulphur-containing radicals that can damage certain proteins, such as α1-antiproteinase and creatine kinase.

Original languageEnglish (US)
Pages (from-to)119-133
Number of pages15
JournalFree Radical Research
Issue number2
StatePublished - 1994


  • Antioxidant
  • Dihydrolipoic acid
  • Hydroxyl radical
  • Hypochlorous acid
  • Lipid peroxidation
  • Lipoic acid
  • Superoxide
  • Trichloromethylperoxyl radical

ASJC Scopus subject areas

  • Biochemistry


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