Toxic interactions between carbon tetrachloride and chloroform in cultured rat hepatocytes

[11C]choline uptake in regenerating liver after partial hepatectomy or CCl4-administration

To characterize [methyl-(11)C]choline ([(11)C]choline) as an oncologic PET radiopharmaceutical, [(11)C]choline uptake in regenerating livers after partial hepatectomy as a model of typical proliferating tissue and after CCl(4) insult as that of proliferating tissue with inflammation, was studied in rats. [(11)C]Choline, [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [2-(14)C]thymidine ([(14)C]TdR) uptake was studied in regenerating rat liver after 70% partial hepatectomy or CCl(4)-administration. [(11)C]Choline uptake in regenerating liver after partial hepatectomy was significantly increased with [(14)C]TdR uptake as a marker of DNA synthesis at 18 hours after surgery. On the other hand, the uptake was not accelerated by CCl(4)-administration, though it significantly increased [(14)C]TdR uptake. There were no differences of [(11)C]choline uptake acceleration following partial hepatectomy among the three parts of the regenerating liver. [(18)F]FDG uptake was accelerated in the regenerating liver on either partial hepatectomy or CCl(4)-administration. The magnitude of the increase in [(18)F]FDG uptake in the regenerating liver induced by partial hepatectomy was greater than that for [(11)C]choline. [(11)C]Choline uptake in the liver was accelerated by partial hepatectomy, but not by CCl(4)-administration. This might be expected given that the differentiation between proliferating tissues such as tumor and inflammatory tissue was possible by [(11)C]choline-PET.

The role of glutathione and protein thiols in CBrCl3-induced cytotoxicity in isolated rat hepatocytes

The role of glutathione (GSH) and protein thiols in the pathobiochemical process of CBrCl3 cytotoxicity was investigated in isolated hepatocytes. Administration of 0.5, 1.0 and 1.5 mmol/l CBrCl3 affected cellular viability as assessed by trypan blue exclusion, release of lactate dehydrogenase and loss of intracellular potassium in a dose-dependent manner. Intracellular glutathione and the capacity to reduce 3-(4,5-dimethylthiazolyl-2-)-2,5-diphenyltetrazolium bromide (MTT, thiazolyl blue) decreased almost independently of the CBrCl3 concentration. Protein thiols were not markedly oxidized in the presence of CBrCl3. However, compromising cellular defence mechanisms by either inhibition of glutathione regeneration or depletion of glutathione enhanced the cytotoxicity of CBrCl3 and induced a loss of protein thiols in the late phase of cellular injury. Under these conditions the thiol-dependent Na+,K+ATPase revealed high sensitivity towards CBrCl3. Thus, glutathione proved to exert effective cytoprotection, and sulfhydryl groups of particular proteins were supposed to be an important target of radical attack.

Cytotoxic effects of gutta-percha solvents

Cytotoxicity of commonly used gutta-percha solvents was evaluated. Gutta-percha dissolved by chloroform, halothane, or turpentine was evaluated with the radiochromium release method using L929 mouse fibroblast cells. All solvents were toxic. Turpentine was most toxic followed by halothane and chloroform, which caused similar levels of cell injury.

The mechanism of chloroform toxicity in isolated rat hepatocytes

Chloroform (CHCl3) is widely used in the manufacture of drugs, cosmetics, plastics and cleaning agents. It is also found in chlorinated drinking water. This study was designed to investigate the toxic effect of CHCl3 on isolated male rat hepatocytes using several toxicity parameters. The hepatocytes were isolated by a collagenase perfusion technique and the cell viability was determined by Trypan blue exclusion. The leakage of cytosolic enzymes such as aspartate transaminase (AST) and alanine transaminase (ALT) after treatment with CHCl3 was measured. Reduced glutathione content (GSH) and its related enzymes, glutathione reductase (GSH-Rx) and glutathione peroxidase (GSH-Px), were also evaluated to study the effect of CHCl3 on hepatocytes. Exposure to 100 and 1000 ppm CHCl3 results in a significant decrease in cell after 30 min incubation. However, the effect of 1 and 10 ppm concentrations was observed at 60 min incubation. AST leakage was significantly increased in all treatment groups, while ALT was significantly increased at 100 and 1000 ppm CHCl3 after 60 and 30 min, respectively. As early as 15 min, GSH was decreased significantly at 1000 ppm, but at 100 and 10 ppm CHCl3 the decrease in GSH began after 30 and 120 min, respectively. GSH-Px activity did not changed. However, the activity of GSH-Rx was significantly decreased at 1000 ppm CHCl3 and at the same time GSH content was decreased. The data indicate that the toxic effect of CHCl3 was dose- and time-dependent. The degree of GSH depletion correlated with increased cytotoxicity and decreased GSH-Rx activity due to CHCl3.

An enzymatic explanation of the differential effects of oleate and gemfibrozil on cultured hepatocyte triacylglycerol and phosphatidylcholine biosynthesis and secretion

Incubation (1-4 h) of primary cultures of adult rat hepatocytes with gemfibrozil (0.1-1.0 mM) significantly decreased the: (1) incorporation of [1,3-14C]glycerol into cellular triacylglycerol (30%); (2) secretion of labeled (VLDL) triacylglycerol (4-fold); and (3) oleate-induced rise in triacylglycerol biosynthesis and secretion. Gemfibrozil also increased the: (1) incorporation of labeled glycerol into cellular phosphatidylcholine (2-fold); and (2) secretion of labeled (HDL) phosphatidylcholine (10-fold). The gemfibrozil-dependent increase in the flux of labeled diacylglycerol into phosphatidylcholine is rapid (15 min) and associated with a 2-fold increase in membrane-bound phosphocholine cytidylyltransferase activity. A phosphocholine cytidylyltransferase-mediated rise in cellular CDP choline content may explain the gemfibrozil-dependent rise in phosphatidylcholine biosynthesis since homogenates of monolayers incubated with CDP choline preferentially incorporate labeled diacylglycerol into phosphatidylcholine rather than triacylglycerol. Therefore, the triacylglycerol-lowering potential of gemfibrozil may be due in part to its ability to shunt liver cell diacylglycerol into phosphatidylcholine rather than triacylglycerol. These results suggest that CDP choline may be a key regulator of the diacylglycerol branchpoint, since diacylglycerol is primarily incorporated into phosphatidylcholine or triacylglycerol depending on whether CDP choline is or is not available.

Hepatotoxic interaction between carbon tetrachloride and chloroform in ethanol treated rats

The effect of coadministration of CHCl3 on CCl4-induced hepatic damage was investigated at low dose inhalation. Coexposure of CHCl3 did not influence CCl4-induced changes in any index of hepatic damage in control rats. Coadministration of CHCl3, however, enhanced CCl4 (10 ppm)-induced hepatic damage of ethanol treated rats in a dose- and duration-dependent manner: simultaneous exposure of 50 ppm CHCl3 potentiated CCl4-induced increase in plasma GPT activity and number of necrotic hepatocytes; the enhancement of CCl4-induced hepatic damage by 50 ppm CHCl3 was found over the 4 h exposure; simultaneous exposure of 10 and 25 ppm CHCl3 potentiated the CCl4-induced increase in liver malondialdehyde (MDA) content. In contrast, coadministration of 50 ppm trichloroethylene and 200 ppm 1,1,1-trichloroethane decreased CCl4-induced increase in plasma GPT activity, though these exposures did not influence the liver MDA content. These results suggest that the concentration of 10 ppm CCl4 may be significant for CHCl3 to potentiate the hepatic damage caused by CCl4 in ethanol-treated rats. Heavy drinkers may have a higher hepatotoxic risk for a mixture of CCl4 and CHCl3 than for a single exposure to CCl4 or CHCl3, and a particular attention should be therefore given to the joint exposure to CCl4 and CHCl3.

Lipid peroxidation and irreversible cell damage: synergism between carbon tetrachloride and 1,2-dibromoethane in isolated rat hepatocytes

The combination of 1,2-dibromoethane (DBE) with carbon tetrachloride (CCl4) in the isolated rat hepatocyte model produces a significant potentiation of both lipid peroxidation and plasma membrane damage induced by the latter compound. The increase in malondialdehyde production precedes the hepatocyte damage, evaluated in terms both of lactate dehydrogenase leakage and trypan blue exclusion. When hepatocytes are isolated from vitamin E pretreated rats, both the prooxidant and the cytotoxic effects of CCl4 are prevented. Also the synergism between CCl4 and DBE on lipid peroxidation disappears completely while that on cell damage is strongly reduced. The increased lipid peroxidation appears to be one of the mechanisms of the observed synergism between CCl4 and DBE on hepatocyte damage. Regarding the antioxidant status of the hepatocyte challenged with CCl4 and DBE, an early and significant consumption of vitamin E is observed only in the presence of the mixture of these xenobiotics. Total nonprotein thiol content is not significantly modified by CCl4 poisoning while DBE, alone and in association with CCl4, markedly decreases it. Vitamin E supplementation does not prevent but moderately delays total nonprotein thiol depletion due to DBE or to the mixture. Finally, glutathione transferase activity is significantly reduced by CCl4 treatment and not by DBE, and vitamin E supplementation totally prevents such inhibition. The increased prooxidant effect of CCl4 plus DBE compared to CCl4 alone seems related to the shift in DBE metabolism consequent to the CCl4-dependent inactivation of glutathione transferase.

A CCl4/CHCl3 interaction study in isolated hepatocytes: non-induced and phenobarbital-pretreated cells

The purpose of this study was to evaluate an isolated hepatocyte model for predicting the in vivo hepatotoxicity of carbon tetrachloride (CCl4) and chloroform (CHCl3), alone and in combination. Response surface methodology (RSM) was used to analyze and describe the data. The interaction was evaluated for % initial K+ (cell injury) and % LDH leakage (cell death) in non-induced (untreated) and phenobarbital-pretreated suspended hepatocytes. CCl4 and CHCl3 were delivered alone and in combination in dimethyl sulfoxide (DMSO) to suspended hepatocytes. The maximum observed no-effect level (MONEL) for CCl4 in non-induced cells was 1.0 mM (LDH and K+). In induced cells, the MONEL was 0.25 mM (K+) and 0.5 mM (LDH). The MONEL for CHCl3 in non-induced cells was 5.0 mM (LDH and K+) and in induced cells was 0.5 mM (K+) and 1.0 mM (LDH). Phenobarbital pretreatment enhanced the toxicity of both CCl4 and CHCl3, alone and in combination. RSM analysis of the % initial K+ and % LDH for CCl4 and CHCl3 in combination in noninduced and induced cells showed a greater than additive interaction. The isolated hepatocyte model appears to be a promising system for evaluating the toxicity of chemical mixtures and predicting their in vivo effects.