Anti-/pro-oxidant effects of phenolic compounds in cells: are colchicine metabolites chain-breaking antioxidants?
Effective scavenging of reactive radicals and low reactivity of generated secondary antioxidant radicals towards vital intracellular components are two critical requirements for a chain-breaking antioxidant. Tubulin-binding properties aside, colchicine metabolites remain largely untested for other possible biological activities, including antioxidant activity. Mourelle et al. [Life Sci. 45 (1989) 891] proposed that colchiceine (EIN) acts as an antioxidant and protective agent against lipid peroxidation in a rat model of liver injury. Since EIN as well as two other colchicine metabolites, 2-demethylcolchicine (2DM) and 3-demethylcolchicine (3DM), possess a hydroxy-group on their carbon ring that could participate in radical scavenging, we tested whether they can act as chain-breaking antioxidants. Using our fluorescence-HPLC assay with metabolically incorporated oxidation-sensitive cis-parinaric acid (PnA) we studied the effects of colchicine metabolites on peroxidation of different classes of membrane phospholipids in HL-60 cells. None of the colchicine metabolites in concentrations ranging from 10(-6) to 10(-4) M was able to protect phospholipids against peroxidation induced by either azo-initiators of peroxyl radicals or via myeloperoxidase (MPO)-catalyzed reactions in the presence of hydrogen peroxide. However, the metabolites did exhibit dose-dependent depletion of glutathione, resembling the behavior of etoposide, a hindered phenol with antioxidant properties against lipid peroxidation. Electron spin resonance (ESR) experiments demonstrated that in a catalytic system containing horseradish peroxidase (HRP)/H(2)O(2), colchicine metabolites undergo one-electron oxidation to form phenoxyl radicals that, in turn, cause ESR-detectable ascorbate radicals by oxidation of ascorbate. Phenoxyl radicals of colchicine metabolites formed through MPO-catalyzed H(2)O(2)-dependent reactions in HL-60 cells and via HRP/H(2)O(2) in model systems can also oxidize GSH. Thus, colchicine metabolites possess the prerequisites of many antioxidants, i.e. a nucleophilic hydroxy-group on a carbon ring and the ability to scavenge reactive radicals and form a secondary radical. However, the latter retain high reactivity towards critical biomolecules in cells such as lipids, thiols, ascorbate, thereby, rendering colchicine metabolites effective radical scavengers but not effective chain-breaking antioxidants.
Department of Environmental and Occupational Health, University of Pittsburgh, FORBL Room 234, 3343 Forbes Avenue, Pittsburgh, PA 15260, USA. oregon@tunw.upol.cz
Martin
M
Modriansky
Yulia Y
YY
Tyurina
Vladimir A
VA
Tyurin
Tatsuya
T
Matsura
Anna A
AA
Shvedova
Jack C
JC
Yalowich
Valerian E
VE
Kagan
D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003078:Colchicine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D016166:Free Radical Scavengers; D005978:Glutathione / Q000378:metabolism; D018922:HL-60 Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015227:Lipid Peroxidation; D008563:Membrane Lipids / Q000032:analysis / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000494:pharmacology*
D000975:Antioxidants; D005231:Fatty Acids, Unsaturated; D005456:Fluorescent Dyes; D016166:Free Radical Scavengers; D008563:Membrane Lipids; D010743:Phospholipids; D017382:Reactive Oxygen Species; D005978:Glutathione; C012852:colchiceine; C013641:parinaric acid; D001205:Ascorbic Acid; D003078:Colchicine