ABSTRACT
Metallothionein (MT) and reduced glutathione (GSH) play an important role in the intracellular handling of copper by preventing the generation and favouring the removal of copper-derived free radicals. The present study addressed the changes in MT and GSH that follow chronic (2 or 5 weeks) exposure of human hepatoblastoma cells (HepG2) to excess copper. Copper treatment (100 microM, 2 weeks) led to a 28-fold elevation in intracellular copper. Concomitantly, cells exhibited a seven-fold increase in total MT and an increment in its saturation with copper from 45 to 86%. Around 38% of copper in the cytosolic fraction could be accounted for by MT. GSH equivalents were substantially lowered (to 37% of basal levels) in treated cells, with only part of it being accounted for by an increase in GSSG. Copper-treatment induced no changes in catalase or GSH-peroxidase activities but it was associated with a small reduction in SOD (20%) and GSH-reductase (26%) activities. Copper-loaded cells did not differ from controls in their basal oxidative tone; however, when exposed to tert-butylhydroperoxide they exhibited a markedly greater susceptibility to undergo both oxidative stress and cell lysis. It is proposed that chronic exposure of HepG2 cells to excess copper is accompanied by "adaptive changes" in GSH and MT metabolism that would render cells substantially more susceptibility to undergo oxidative stress-related cytotoxicity.
Subject(s)
Copper/toxicity , Glutathione/metabolism , Hepatoblastoma/enzymology , Liver Neoplasms/enzymology , Metallothionein/biosynthesis , Adaptation, Physiological/drug effects , Cell Death/drug effects , Cytosol/drug effects , Cytosol/metabolism , Dose-Response Relationship, Drug , Enzyme Induction , Humans , Oxidative Stress/drug effects , Tumor Cells, Cultured , tert-Butylhydroperoxide/pharmacologyABSTRACT
O presente trabalho se valeu de células de hepatoma humano Hep G2 para estudar se existe algum efeito das vastatinas sobre a atividade das enzimas que governam a hidrólise hepática do coleterol: colesterol éster hidrolases lisossomal, citosólica e microssomal. As enzimas foram incubadas com ou sem amostras de vastatina, dissovidas em dimetilsulfóxido. A adiçao das vastatinas ofereceu distintos resultados, conforme a maneira que se apresentou o substrato às enzimas. No caso da colesterol éster hidrolase lisossomal, obteve-se inibiçao em substrato Hajjar, com sais biliares, e estimulaçao em substrato Brecher, desprovido de sais biliares. A hidrolase citosólica teve sua atividade inibida em substrato Hajjar e constante em substrato Brecher.