Percorrer por autor "Monks, Terrence J."
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- Hepatotoxicity of 3,4-methylenedioxyamphetamine and α-methyldopamine in isolated rat hepatocytes: formation of glutathione conjugatesPublication . Bastos, Maria de Lourdes; Carvalho, Márcia; Milhazes, Nuno; Remião, Fernando; Borges, Fernanda; Fernandes, Eduarda; Amado, Francisco; Monks, Terrence J.; Carvalho, FélixThe amphetamine designer drugs 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") and its N-demethylated analogue 3,4-methylenedioxyamphetamine (MDA or "love") have been extensively used as recreational drugs of abuse. MDA itself is a main MDMA metabolite. MDMA abuse in humans has been associated with numerous reports of hepatocellular damage. Although MDMA undergoes extensive hepatic metabolism, the role of metabolites in MDMA-induced hepatotoxicity remains unclear. Thus, the aim of the present study was to evaluate the effects of MDA and alpha-methyldopamine (alpha-MeDA), a major metabolite of MDA, in freshly isolated rat hepatocyte suspensions. The cells were incubated with MDA or alpha-MeDA at final concentrations of 0.1, 0.2, 0.4, 0.8, or 1.6 mM for 3 h. The toxic effects induced following incubation of hepatocyte suspensions with these metabolites were evaluated by measuring cell viability, the extent of lipid peroxidation, levels of glutathione (GSH) and glutathione disulfide (GSSG), the formation of GSH conjugates, and the activities of GSSG reductase (GR), GSH peroxidase (GPX), and GSH S-transferase (GST). MDA induced a concentration- and time-dependent GSH depletion, but had a negligible effect on lipid peroxidation, cell viability, or on the activities of GR, GPX, and GST. In contrast, alpha-MeDA (1.6 mM, 3 h) induced a marked depletion of GSH accompanied by a loss on cell viability, and decreases in GR, GPX and GST activities, although no significant effect on lipid peroxidation was found. For both metabolites, GSH depletion was not accompanied by increases in GSSG levels; rather, 2-(glutathion- S-yl)-alpha-MeDA and 5-(glutathion- S-yl)-alpha-MeDA were identified by HPLC-DAD/EC within cells incubated with MDA or alpha-MeDA. The results provide evidence that one of the early consequences of MDMA metabolism is a disruption of thiol homeostasis, which may result in loss of protein function and the initiation of a cascade of events leading to cellular damage.
- Role of metabolites in MDMA (ecstasy)-induced nephrotoxicity: an in vitro study using rat and human renal proximal tubular cellsPublication . Carvalho, Márcia; Hawksworth, Gabrielle; Milhazes, Nuno; Borges, Fernanda; Monks, Terrence J.; Fernandes, Eduarda; Carvalho, Félix; Bastos, Maria de LourdesThe metabolism of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) has recently been implicated in the mechanisms underlying ecstasy-induced neurotoxicity and hepatotoxicity. However, its potential role in ecstasy-induced kidney toxicity has yet to be investigated. Thus, primary cultures of rat and human renal proximal tubular cells (PTCs) were used to investigate the cytotoxicity induced by MDMA and its metabolites methylenedioxyamphetamine (MDA), alpha-methyldopamine (alpha-MeDA), and the glutathione (GSH) conjugates 5-(glutathion- S-yl)-alpha-MeDA and 2,5- bis(glutathion- S-yl)-alpha-MeDA. Cell viability was evaluated using the mitochondrial MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. MDMA and MDA were not found to be toxic to either rat or human PTCs at any concentration tested (100-800 micro M). In contrast, 800 micro M alpha-MeDA caused 60% and 40% cell death in rat and human PTCs, respectively. Conjugation of alpha-MeDA with GSH resulted in the formation of even more potent nephrotoxicants. Thus, exposure of rat and human PTC monolayers to 400 micro M 5-(glutathion- S-yl)-alpha-MeDA caused approximately 80% and 70% cell death, respectively. 5-(Glutathion- S-yl)-alpha-MeDA (400 micro M) was more toxic than 2,5- bis(glutathion- S-yl)-alpha-MeDA to rat renal PTCs but equally potent in human renal PTCs. Pre-incubation of rat PTCs with either acivicin, an inhibitor of gamma-glutamyl transpeptidase (gamma-GT), or bestatin, an inhibitor of aminopeptidase M, resulted in increased toxicity of 5-(glutathion- S-yl)-alpha-MeDA but had no effect on 2,5- bis(glutathion- S-yl)-alpha-MeDA-mediated cytotoxicity. The present data provide evidence that metabolism is required for the expression of MDMA-induced renal toxicity in vitro. In addition, metabolism of 5-(glutathion- S-yl)-alpha-MeDA by gamma-GT and aminopeptidase M to the corresponding cystein- S-yl-glycine and/or cystein- S-yl conjugates is likely to be associated with detoxication of this compound. Thus, it appears that toxicity induced by thioether metabolites of ecstasy at the apical membrane of renal proximal tubular cells is the result of extracellular events, presumably redox cycling.