d-Amphetamine-induced hepatotoxicity: possible contribution of catecholamines and hyperthermia to the effect studied in isolated rat hepatocytes
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Amphetamines are indirect-acting sympathomimetic drugs widely abused due to their physical and psychostimulating effects. However, the use of these drugs has been associated with numerous reports of hepatotoxicity. While glutathione depletion induced by amphetamines contributes to the exposure of hepatocytes to oxidative damage, other indirect effects attributed to amphetamines may have a role in cell injury. To examine this possibility, Wistar rats were used for plasma measurements of d-amphetamine and catecholamines (noradrenaline, adrenaline and dopamine) (15 min) after i.p. injection of d-amphetamine (5, 20 and 80 mg/kg). Freshly isolated rat hepatocytes were put into contact for 2 h with concentrations of d-amphetamine and catecholamines similar to those found in vivo. Since hyperthermia is a common consequence of acute amphetamine intake, the study using isolated hepatocytes was conducted at 37 °C and also at 41 °C in order to simulate high temperature levels. We found that hyperthermia was an important cause of cell toxicity: in vitro, a rise in incubation temperature from 37 to 41 °C causes oxidative stress in freshly isolated rat hepatocytes, as shown by a depletion of reduced glutathione (GSH; 23%), an increase of oxidized glutathione (GSSG; 157%), the induction of lipid peroxidation with 77% increase of thiobarbituric acid substances TBARS) and the consequent loss of cell viability (≤ 44%). Single treatment of isolated hepatocytes with catecholamines at 37 °C induced lipid peroxidation (29% increase of TBARS) but had no effect on glutathione or cell viability. Conversely, a single treatment with d-amphetamine induced glutathione depletion (≤ 24% depletion of GSH) with no effect on lipid peroxidation or cell viability. Also, d-amphetamine potentiated the induction by catecholamines of lipid peroxidation at 37 °C (≤ 48% increase of TBARS), while concomitant treatment of d-amphetamine and catecholamines potentiated cell death at 41 °C (≤ 56% of cell death) although no effect on viability was seen at 37 °C. It is concluded that the aforementioned modifications induced by d-amphetamine in vivo are cytotoxic to freshly isolated rat hepatocytes.
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