Thiourea protects against copper-induced oxidative damage by formation of a redox-inactive thiourea-copper complex.
Although thiourea has been used widely to study the role of hydroxyl radicals in metal-mediated biological damage, it is not a specific hydroxyl radical scavenger and may also exert antioxidant effects unrelated to hydroxyl radical scavenging. Thus, we investigated the effects of thiourea on copper-induced oxidative damage to bovine serum albumin (1 mg/ml) in three different copper-containing systems: Cu(II)/ascorbate, Cu(II)/H(2)O(2), and Cu(II)/H(2)O(2)/ascorbate [Cu(II), 0.1 mM; ascorbate, 1 mM; H(2)O(2), 1 mM]. Oxidative damage to albumin was measured as protein carbonyl formation. Thiourea (0.1-10 mM) provided marked and dose-dependent protection against protein oxidation in all three copper-containing systems. In contrast, only minor protection was observed with dimethyl sulfoxide and mannitol, even at concentrations as high as 100 mM. Strong protection was also observed with dimethylthiourea, but not with urea or dimethylurea. Thiourea also significantly inhibited copper-catalyzed oxidation of ascorbate, and competed effectively with histidine and 1,10-phenanthroline for binding of cuprous, but not cupric, copper, as demonstrated by both UV-visible and low temperature electron spin resonance measurements. We conclude that the protection by thiourea against copper-mediated protein oxidation is not through scavenging of hydroxyl radicals, but rather through the chelation of cuprous copper and the formation of a redox-inactive thiourea-copper complex.
Zhu
Ben-Zhan
BZ
Linus Pauling Institute, Oregon State University, Corvallis 97331, USA.
Antholine
William E
WE
Frei
Balz
B
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D002417:Cattle; D003300:Copper / Q000633:toxicity*; D004249:DNA Damage / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers / Q000494:pharmacology*; D006639:Histidine / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D017665:Hydroxyl Radical; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D010618:Phenanthrolines / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000187:drug effects / Q000378:metabolism; D013890:Thiourea / Q000494:pharmacology*
D016166:Free Radical Scavengers; D010618:Phenanthrolines; D012710:Serum Albumin, Bovine; D017665:Hydroxyl Radical; D006639:Histidine; D003300:Copper; D006861:Hydrogen Peroxide; D013890:Thiourea; D001205:Ascorbic Acid