Possible mechanisms underlying copper-induced damage in biological membranes leading to cellular toxicity.
It is generally accepted that copper toxicity is a consequence of the generation of reactive oxygen species (ROS) by copper ions via Fenton or Haber-Weiss reactions. Copper ions display high affinity for thiol and amino groups occurring in proteins. Thus, specialized proteins containing clusters of these groups transport and store copper ions, hampering their potential toxicity. This mechanism, however, may be overwhelmed under copper overloading conditions, in which copper ions may bind to thiol groups occurring in proteins non-related to copper metabolism. In this study, we propose that indiscriminate copper binding may lead to damaging consequences to protein structure, modifying their biological functions. Therefore, we treated liver subcellular membrane fractions, including microsomes, with Cu2+ ions either alone or in the presence of ascorbate (Cu2+/ascorbate); we then assayed both copper-binding to membranes, and microsomal cytochrome P450 oxidative system and GSH-transferase activities. All assayed sub-cellular membrane fractions treated with Cu2+ alone displayed Cu2+-binding, which was significantly increased in the presence of Zn2+, Hg2+, Cd2+, Ag+1 and As3+. Treatment of microsomes with Cu2+ in the microM range decreased the microsomal thiol content; in the presence of ascorbate, Cu2+ added in the nM concentrations range induced a significant microsomal lipoperoxidation; noteworthy, increasing Cu2+ concentration to > or =50 microM led to non-detectable lipoperoxidation levels. On the other hand, microM Cu2+ led to the inhibition of the enzymatic activities tested to the same extent in either presence or absence of ascorbate. We discuss the possible significance of indiscriminate copper binding to thiol proteins as a possible mechanism underlying copper-induced toxicity.
Letelier
María Eugenia
ME
Laboratory of Pharmacology, Department of Pharmacological and Toxicological Chemistry, Chemical and Pharmaceutical Sciences School, University of Chile, Olivos 1007, Independencia, Santiago, Chile. mel@ciq.uchile.cl
Lepe
Ana María
AM
Faúndez
Mario
M
Salazar
Julia
J
Marín
Rigoberto
R
Aracena
Paula
P
Speisky
Hernán
H
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D003300:Copper / Q000633:toxicity*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005982:Glutathione Transferase / Q000378:metabolism; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000187:drug effects* / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010101:Oxygen Consumption; D011506:Proteins / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013438:Sulfhydryl Compounds / Q000032:analysis / Q000378:metabolism
D011506:Proteins; D013438:Sulfhydryl Compounds; D003300:Copper; D003577:Cytochrome P-450 Enzyme System; D005982:Glutathione Transferase; D001205:Ascorbic Acid