The effect of ethanol exposure on cocaine toxicity in rat hepatocytes

Genetic depletion of p53 attenuates cocaine-induced hepatotoxicity in mice

Cocaine, an addictive drug, is known to induce hepatotoxicity via oxidative damage and proapoptosis. Since p53, a tumor suppressor gene, plays a major role in inducing oxidative stress and apoptosis, we examined the role of p53 inhibition against cocaine-induced hepatotoxicity. Cocaine treatment significantly increased oxidative parameters (i.e., reactive oxygen species, 4-hydroxylnonenal, and protein carbonyl) in the liver of wild type (WT) mice. We found that the pharmacological (i.e. pifithrin-α) and genetic (i.e. p53 knockout) inhibition of p53 significantly attenuates cocaine-induced hepatotoxicity. Cocaine treatment increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in the serum of mice, signifying hepatic damage. Consistently, these increases were attenuated by inhibition of p53, implying protection against cocaine-induced hepatic damage. In addition, cocaine treatment significantly increased PKCδ, cleaved PKCδ and p53 levels in the liver of WT mice. These increases were followed by the interaction between p53 and PKCδ, and pro-apoptotic consequences (i.e., cytosolic release of cytochrome c, activation of caspase-3, increase in Bax level and decreases in Bcl-2 and Bcl-xL levels). These changes were attenuated by p53 depletion, reflecting that the critical role of PKCδ in p53-mediated apoptotic potentials. Combined, our results suggest that the inhibition of p53 is important for protection against oxidative burdens, pro-apoptotic events, and hepatic degeneration induced by cocaine.

Protein kinase Cδ knockout mice are protected from cocaine-induced hepatotoxicity

We investigated whether protein kinase Cδ (PKCδ) mediates cocaine-induced hepatotoxicity in mice. Cocaine treatment (60 mg/kg, i.p.) significantly increased cleaved PKCδ expression in the liver of wild-type (WT) mice, and led to significant increases in oxidative parameters (i.e., reactive oxygen species, 4-hydroxylnonenal and protein carbonyl). These cocaine-induced oxidative burdens were attenuated by pharmacological (i.e., rottlerin) or genetic depletion of PKCδ. We also demonstrated that treatment with cocaine resulted in significant increases in nuclear factor erythroid-2-related factor 2 (Nrf-2) nuclear translocation and increased Nrf-2 DNA-binding activity in wild-type (WT) mice. These increases were more pronounced in the rottlerin-treated WT or PKCδ knockout mice than in the saline-treated WT mice. Although cocaine treatment increased Nrf-2 nuclear translocation, DNA binding activity, and γ-glutamyl cysteine ligases (i.e., GCLc and GCLm) mRNA expressions, while it reduced the glutathione level and GSH/GSSG ratio. These decreases were attenuated by PKCδ depletion. Cocaine treatment significantly increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in the serum of WT mice signifying the hepatic damage. These increases were also attenuated by PKCδ depletion. In addition, cocaine-induced hepatic degeneration in WT mice was evident 1 d post-cocaine. At that time, cocaine treatment decreased Bcl-2 and Bcl-xL levels, and increased Bax, cytosolic cytochrome c, and cleaved caspase-3 levels. Pharmacological or genetic depletion of PKCδ significantly ameliorated the pro-apoptotic properties and hepatic degeneration. Therefore, our results suggest that inhibition of PKCδ, as well as activation of Nrf-2, is important for protecting against hepatotoxicity induced by cocaine.

In vitro hepatotoxicity of alachlor and its by-products

During water treatment, potentially hazardous chemical by-products may be formed. Alachlor (2-chloro-N-(2, 6-diethylphenyl)-N-(methoxymethyl) acetamide) is a widely used pre-emergence herbicide. The present study investigated the toxicity of alachlor and its disinfection by-products on freshly isolated rat hepatocytes. Hepatocytes were harvested by a collagenase perfusion technique and were exposed to different concentrations of alachlor and its by-products for up to 2 h. Cell viability, the leakage of aspartate transaminase (AST) and alanine transaminase (ALT) and glutathione (GSH) depletion were determined throughout the incubation period. The cell viability of the hepatocytes exposed to 100 microg ml(-1) alachlor was decreased by 20% compared with the control after 60 min of incubation. At the same concentration of alachlor the leakage of ALT and AST was increased by 56% and 45%, respectively. Cell viability of the hepatocytes was decreased upon exposure to 2-chloro-N-(3-chloro-2,6-diethylphenyl)-N-(methoxymethyl) acetamide (CCDMA) and 2-chloro-N-(3-chloro-2,6-diethylphenyl) acetamide (CCDA)--the by-products of alachlor and chlorine--after 60 min of exposure. At 100 microg ml(-1) CCDMA the AST leakage was increased significantly (73%) after 30 min of incubation. The reaction mixture of alachlor (100 microg ml(-1)) and chlorine dioxide (1 ppm) caused significant increases in cell loss and ALT and AST levels by 22%, 40% and 34%, respectively, as early as 15 min incubation. Alachlor (100 and 200 microg ml(-1)) caused significant decreases in GSH contents (62%) in isolated hepatocytes. The reaction mixture of alachlor and chlorine dioxide led to significant glutathione depletion (44%) after 60 min of incubation. The by-products of alachlor and chlorine--CCDMA and CCDA--depleted GSH almost completely (93%). This investigation suggested that the by-products formed from the reaction of alachlor and chlorine decreased GSH and increased the leakage of liver enzymes, especially AST.

Ethanol does not increase the hepatotoxicity of cocaine in primary rat hepatocyte culture

Rat hepatocytes were utilized to investigate the role of cocaine metabolism and the contribution of ethylcocaine formation to cocaine-induced liver damage. Hepatocytes were prepared from rats pretreated with saline, phenobarbital or ethanol and exposed to cocaine, ethanol, or their combination. Hepatotoxicity was assessed by lactate dehydrogenase (LDH) leakage and was correlated with cocaine metabolism which was assessed quantitatively using HPLC. Only phenobarbital-pretreatment produced increases in LDH leakage from cultures exposed to cocaine. This increase in LDH release occurred simultaneous to a decrease in benzoylecognine formation and a marked increase in norcocaine generation. Exposing cultures to ethanol alone did not result in LDH leakage from hepatocytes. Furthermore, including ethanol in cultures treated with cocaine did not enhance the LDH leakage produced by cocaine alone. This study confirms quantitatively that cocaine-induced hepatotoxicity is mediated through cocaine oxidative events and is enhanced by microsomal induction produced by phenobarbital. The finding that ethylcocaine formation was maximal in the ethanol-pretreatment group where no toxicity was observed suggests that ethylcocaine is not the agent responsible for the hepatotoxicity observed in this study.