Carbon tetrachloride hepatotoxicity: an example of lethal cleavage

Bioactivation of halogenated hydrocarbons by cytochrome P4502E1

Numerous halogenated hydrocarbons of the alkane, alkene, and alkyne classes are metabolized by P450 enzymes to products that elicit cytotoxic and/or carcinogenic effects. Such halogenated hydrocarbons include anesthetics (e.g., halothane and enflurane) and industrial solvents (e.g., carbon tetrachloride, chloroform, and vinylidine chloride). Formation of reaction intermediates from these compounds occurs via P450-promoted dehalogenation, reduction, or reductive oxygenation, with certain hydrocarbons undergoing all three reaction types. Of the multiple forms of P450 present in liver microsomes, P4502E1 has been identified as the primary catalyst of hydrocarbon bioactivation in animals and, most likely, in humans as well. As hepatic concentrations of this P450 enzyme are highly inducible by ethanol and similar agents, prior exposure to 2E1-inducing compounds can play a pivotal role in halogenated hydrocarbon toxicity. Considering that metabolism governs the cytotoxicity and carcinogenicity of halogenated hydrocarbons, an understanding of the mechanism(s) underlying 2E1 induction in man becomes all the more important.

Lipid peroxidation. Biopathological significance

Peroxidation of unsaturated lipids, initially studied in the chemistry of oil and fat rancidity, has become a problem of increasing interest in the biological field, because of its proposed role in a variety of pathological conditions. The general mechanism of the process, the formation of toxic aldehydes capable to react with protein and non protein thiols, and the overall effects in cellular membranes are reviewed. The possible implications of lipid peroxidation as one of the main mechanisms of cellular damage in both toxic injury and other pathological conditions are discussed.

Use of 1H/23Na and 1H/31P double frequency tuned birdcage coils to study in vivo carbon tetrachloride-induced hepatotoxicity in rats

In vivo 1H and 23Na magnetic resonance imaging (MRI) and 31P magnetic resonance spectroscopy (MRS) techniques were used to study CCl4-induced acute hepatotoxicity in rats in situ. One or two hours following exposure to CCl4, a localized edematous region was detected in the liver by 1H MRI. The CCl4-induced edema was localized in a region surrounding the hepatic portal vein. With the use of a 23Na/1H double frequency tuned bird-cage imaging coil an increase in Na+ ion flux was also observed in the same region as the edematous region detected by 1H-MRI. Pretreatment with alpha-phenyl-tert-butyl nitrone (PBN), a free radical spin trap, 30 min prior to CCl4 exposure, was found to reduce the CCl4-induced edematous response in the liver observed in either 1H or 23Na-NMR images. Inhibition of the CCl4-induced edematous response in rat liver by PBN demonstrates that free radical intermediates, arising from the metabolism of CCl4, are possibly the key causal agents in the initiation of the edematous response. In addition, with the use of a 31P/1H double frequency tuned bird-cage imaging/spectroscopy coil, localized 31P spectra (ISIS) were obtained from the regions of CCl4-induced "tissue damage" observed in the 1H-MRI images. The most notable changes observed from the 31P spectra were an increase in inorganic phosphate (Pi) and a decrease in hepatocytosolic pH in the CCl4-treated rat livers in comparison to saline-treated control livers.

Metabolic zonation of the liver: regulation and implications for liver function

Liver parenchyma shows a remarkable heterogeneity of the hepatocytes along the porto-central axis with respect to ultrastructure and enzyme activities resulting in different cellular functions within different zones of the liver lobuli. According to the concept of metabolic zonation, the spatial organization of the various metabolic pathways and functions forms the basis for the efficient adaptation of liver metabolism to the different nutritional requirements of the whole organism in different metabolic states. The present review summarizes current knowledge about this heterogeneity, its development and determination, as well as about its significance for the understanding of all aspects of liver function and pathology, especially of intermediary metabolism, biotransformation of drugs and zonal toxicity of hepatotoxins.

The hepatotoxicity of chloroform in precision-cut rat liver slices

Chloroform hepatotoxicity was investigated in precision-cut liver slices from male Sprague-Dawley rats pretreated with phenobarbital to predispose animals to CHCl3 intoxication. Liver slices were exposed to 0.2, 0.5 and 1.0 mM chloroform for a total of 9 h in a roller culture system. Intracellular K+ loss was found to be concentration- and time-dependent over the duration of the experiment. Histopathological changes were also evident. Glucose 6-phosphate dehydrogenase and beta-glucuronidase were significantly decreased at 3 h relative to controls where a loss of 61% and 36% occurred, respectively. Enzyme levels of alanine aminotransferase and lactate dehydrogenase, both found predominantly in periportal hepatocytes, remained identical to controls over the duration of the experiment. A significant time-dependent depletion of glutathione occurred as early as 3 h following the administration of 0.5 mM chloroform. Mitochondrial viability, measured by the reduction of a specific dye, was significantly lower than controls in treated slices at 6 h following chloroform administration. Precision-cut liver slices appear to be especially useful for the biochemical and histopathological examination of site-specific hepatotoxicants such as CHCl3.

Evidence that interaction of hepatocytes with the collecting (hepatic) veins triggers position-specific transcription of the glutamine synthetase and ornithine aminotransferase genes in the mouse liver

We previously demonstrated that glutamine synthetase (GS) and ornithine aminotransferase (OAT) mRNAs are expressed in the mouse liver acinus preferentially in pericentral hepatocytes, that is, those immediately surrounding terminal central veins (A.L. Bennett, K.E. Paulson, R.E. Miller, and J.E. Darnell, Jr., J. Cell Biol. 105:1073-1085, 1987, and F.C. Kuo, W.L. Hwu, D. Valle, and J.E. Darnell, Jr., Proc. Natl. Acad. Sci. USA, in press). We now show that hepatocytes surrounding large collecting hepatic veins but not portal veins also express these two mRNAs. The pericentral hepatocytes are the most distal hepatocytes with respect to acinar blood flow, whereas this is not necessarily the case for hepatocytes next to the large collecting hepatic veins. This result implies that it is contact with some hepatic venous element which signals positional expression. In an effort to induce conditions that change relationships between hepatocytes and blood vessels, regenerating liver was studied. After surgical removal of two-thirds or more of the liver, there was no noticeable change in GS or OAT expression in the remaining liver tissue during regeneration. However, treatment with carbon tetrachloride (CCl4), which specifically kills pericentral hepatocytes, completely removed GS- and OAT-containing cells and promptly halted hepatic transcription of GS. Repair of CCl4 damage is associated with invasion of inflammatory and scavenging cells, which remove dead hepatocytes to allow regrowth. Only when hepatocytes resumed contact with pericentral veins were the pretreatment levels of OAT and GS mRNA and high levels of GS transcription restored.

Difference in liver and serum malathion carboxylesterase and glucose-6-phosphatase in detecting carbon tetrachloride-induced liver damage in rats

Microsome, cytosol and serum malathion carboxylesterase (MaCEst) activity was assessed in rats after single i.p. administration of carbon tetrachloride (CCl4) in doses ranging from 0.05 to 1 ml kg-1. MaCEst activities were compared with those of glucose-6-phosphatase (G6-Pase) as an indicator of endoplasmic reticulum damage and serum glutamate dehydrogenase (GLDH) and sorbitol dehydrogenase (SHD) as indicators of liver cytolysis. The data showed a dose-dependent increase in GLDH and SDH serum activities (175% and 68%) from 0.05 ml kg-1; an increase in serum G6-Pase (31%) and a decrease in microsomal G6-Pase (38%) was apparent only after 0.5 or 1.0 ml kg-1 doses. MaCEst activity was unaffected. The results demonstrate that, under these experimental conditions, serum and subcellular measurements of MaCEst activity failed to reveal the liver toxicity of CCl4.

Evidence that interaction of hepatocytes with the collecting (hepatic) veins triggers position-specific transcription of the glutamine synthetase and ornithine aminotransferase genes in the mouse liver

We previously demonstrated that glutamine synthetase (GS) and ornithine aminotransferase (OAT) mRNAs are expressed in the mouse liver acinus preferentially in pericentral hepatocytes, that is, those immediately surrounding terminal central veins (A.L. Bennett, K.E. Paulson, R.E. Miller, and J.E. Darnell, Jr., J. Cell Biol. 105:1073-1085, 1987, and F.C. Kuo, W.L. Hwu, D. Valle, and J.E. Darnell, Jr., Proc. Natl. Acad. Sci. USA, in press). We now show that hepatocytes surrounding large collecting hepatic veins but not portal veins also express these two mRNAs. The pericentral hepatocytes are the most distal hepatocytes with respect to acinar blood flow, whereas this is not necessarily the case for hepatocytes next to the large collecting hepatic veins. This result implies that it is contact with some hepatic venous element which signals positional expression. In an effort to induce conditions that change relationships between hepatocytes and blood vessels, regenerating liver was studied. After surgical removal of two-thirds or more of the liver, there was no noticeable change in GS or OAT expression in the remaining liver tissue during regeneration. However, treatment with carbon tetrachloride (CCl4), which specifically kills pericentral hepatocytes, completely removed GS- and OAT-containing cells and promptly halted hepatic transcription of GS. Repair of CCl4 damage is associated with invasion of inflammatory and scavenging cells, which remove dead hepatocytes to allow regrowth. Only when hepatocytes resumed contact with pericentral veins were the pretreatment levels of OAT and GS mRNA and high levels of GS transcription restored.

Enalapril cytotoxicity in primary cultures of rat hepatocytes. I. Effects of cytochrome P450 inducers and inhibitors

Enalapril maleate (EN) incubated with primary cultures of rat hepatocytes was cytotoxic in concentrations of 0.5 mM or greater. Toxicity was measured by release of lactate dehydrogenase (LDH) into the culture medium at 24 h. SKF525A, alpha-naphthoflavone (alpha NF) and metyrapone (MTP) reduced the toxicity of EN. In vivo pretreatment with phenobarbital (PB) and beta-naphthoflavone (beta NF) had minor protective effects on the responses of hepatocytes to EN exposure. However, in vivo pretreatment with pregnenolone-16 alpha-carbonitrile (PCN) substantially potentiated EN cytotoxicity. These results suggest that the cytocidal hepatotoxicity of EN in primary culture depends to some degree on metabolic activation by a cytochrome P450 species.

Colchicine antimitosis abolishes CCl4 autoprotection

A subtoxic dose of CCl4 is known to destroy liver microsomal cytochrome P-450 and this is widely accepted as the mechanism of CCl4 autoprotection. Circumstantial evidence suggests that while cytochrome P-450 is significantly decreased, this mechanism alone cannot explain the phenomenon of autoprotection. Previous studies have established that hepatocellular regeneration is stimulated as early as 6 hr after the administration of a low dose of CCl4. If the early phase stimulation of hepatocellular regeneration by the protective dose is indeed the mechanism of autoprotection, then ablation of this early phase of tissue healing by colchicine should result in an abolishment of autoprotection. Present studies were conducted to test this conceptual premise. The protection afforded by a low dose of CCl4 (LCCl4, 100 microliter/kg, ip) on the toxic effects of a subsequently administered moderately toxic dose of CCl4 (HCCL4, 2.5 ml/kg, ip) was established in male Sprague-Dawley rats. The protective dose provided 100% protection, whereas only 62.5% survival was observed when the corn oil vehicle was administered instead of the protective dose of LCCl4. Colchicine administration (1 mg/kg, ip in saline) 2 hr prior to the injection of LCCl4 led to a complete loss of autoprotection resulting in 100% mortality in rats given the HCCl4. Earlier studies have established that colchicine selectively suppresses the early phase of hepatocellular regeneration at 6 hr without influencing the second phase at 36-48 hr. The consequence of colchicine antimitosis on the toxicological endpoints of liver injury was evaluated by serum enzyme elevations and by histopathological examination of the liver during a time course of 6, 24, 48, 72, and 96 hr after the administration of HCCl4. In the autoprotection regime, after only a transient and modest elevation of serum alanine and aspartate transaminases, complete recovery occurred by 96 hr. Hepatocellular necrosis was consistently lower compared to all other groups. Colchicine preadministration in the autoprotection regime resulted in significantly greater and progressive elevation of the serum enzymes and a correspondingly commensurate progression of hepatic lesion. Toxic effects of HCCl4 alone were more rapidly and maximally augmented by colchicine preadministration. The role of hepatocellular regeneration in autoprotection was evaluated by 3H-thymidine incorporation in hepatocellular nuclear DNA and by morphometric estimation of mitotic index. While HCCl4 alone resulted in some stimulation of 3H-thymidine incorporation and mitosis, the regenerative activity observed with prior LCCl4 administration was remarkably greater, particularly at 48 hr. Colchicine preadministration in either of these 2 protocols decisively obtunded the stimulated regenerative activities essentially abolishing the tissue healing mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Bioartificial liver using hepatocytes on biosilon microcarriers: treatment of chemically induced acute hepatic failure in rats

An artificial liver support procedure based on hemoperfusion via hepatocytes cultured on microcarriers is described. The efficiency of the system was assessed by the survival rate of rats treated with either lethal dosage of 7% CCl4 [30 ml/kg body weight (b.w.)] or D-galactosamine (2.5 g/kg b.w.). In CCl4-treated rats, hemoperfusion via empty microcarriers (n = 16) revealed no surviving animals, whereas the use of the bioartificial liver (n = 11) resulted in 80% (p less than 0.01) and 60% (p less than 0.05) survival 48 and 168 h after hepatotoxin, respectively. For the same time periods, the survival rate in D-galactosamine-intoxicated rats after hemoperfusion with hepatocytes (n = 20) was approximately 60% (p less than 0.05) and was only 5% in those of rats treated with empty microcarriers (n = 20). Sublethal dosage of 7% CCl4 (15 ml/kg b.w.) caused 25% mortality and prolonged (48 h) increase of activity of the liver enzymes and bilirubin levels in the serum of surviving animals. In these rats (n = 8) at the end of 3 h of hemoperfusion via hepatocytes, the bilirubin concentration decreased by 45% as compared with the control group (n = 6) treated with empty microcarriers. Moreover, by 48 h after intoxication, the use of the bioartificial liver resulted in more than a three-fold decrease in glutamate-oxaloacetate transaminase and a 10-fold decrease in glutamate-pyruvate transaminase serum activity as well as a fivefold decline in total and a ninefold decline in conjugated bilirubin levels as compared with the control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo NMR, biochemical, and histologic evaluation of alcohol-induced fatty liver in rat and a comparison with CCl4 hepatotoxicity

Magnetic resonance imaging (MRI) and spectroscopy (MRS) were used to follow the time course of ethanol-induced fatty liver in a group of 10 rats fed a diet containing 12% alcohol (ethanol) over a 5-week period. The MR data consisted of T1-weighted images, in vivo 1H spectra, and in vivo T1 relaxation measurements. Changes in short TR images as a result of fatty accumulation were noted only as a slight increase in liver intensity relative to surrounding muscle. A poorly correlated (r = 0.54) increase in water T1 with time was observed. No statistically significant changes in lipid T1 were found. MRS derived lipid content was compared with biochemically derived total lipids and histology. MRS determined liver lipids were found to increase linearly with time (r = 0.91). Biochemically derived lipid content also increased with prolonged exposure to ethanol (r = 0.96). The averages of MRS derived lipid content agreed well with the average changes in biochemically determined total lipid concentration. Histologic examination revealed slight to moderate changes in fatty accumulation with significant variation in the group at the end of the study. On an individual basis the MRS and histologic evaluation were highly correlated (r = 0.94).

Enhancement of carbon tetrachloride-induced liver injury by a single dose of ethanol: proton magnetic resonance imaging (MRI) studies in vivo

Magnetic resonance imaging (MRI) and localized magnetic resonance spectroscopy (MRS) were used to study the effects of a single dose of ethanol, given 18 h prior to experiments, on CC14-induced acute hepatotoxicity in rats in situ. Localized edema in the centrilobular region of the liver, following exposure to ethanol and CCl4, was detected by 1H-MRI techniques. The edema was characterized by a volume selective spectroscopy (VOSY) method, which measured an increase in water concentration from ethanol and CCl4-treated rat livers, in comparison to control livers. Electron microscopy (EM) of the high intensity regions of the ethanol/CCl4 treated liver sections revealed dramatic subcellular changes such as fragmentation of the granular endoplasmic reticulum (ER), formation of large vacuoles and lipid droplets in the cytoplasmic matrix and extensive swelling of the mitochondria as well as disruption of the cristae. Pretreatment with alpha-phenyl tert-butyl nitrone (PBN), a free radical spin trap, prior to halocarbon exposure, was found to reduce the CC14-mediated high intensity region in the liver images. Electron microscopy of the PBN pretreated CCl4 exposed rat liver sections revealed only minor observable differences in subcellular organization, such as some swelling of the mitochondria, when compared to controls. In addition, these data suggest that ethanol may potentiate CCl4 hepatotoxicity by increased formation of free radical intermediates. Inhibition of the CCl4-induced edematous response in rat liver by PBN demonstrates that free radical intermediates, arising from the metabolism of CCl4, are possibly the causal factor in the initiation of the edema.

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.

Methylthiazolidine-4-carboxylate for treatment of acute T-2 toxin exposure

The effect of T-2 toxin on hepatic glutathione content and the protective effect of 2-methyl-thiazolidine-4-carboxylate (MTCA), an L-cysteine prodrug, were studied in mice. Acute exposure to T-2 toxin (4 mg kg-1, s.c.) resulted in a progressive decrease in glutathione content, reaching a minimum 6-8 h after toxin administration. Because T-2 toxin caused decreased food consumption, a condition known to deplete hepatic glutathione, glutathione was measured in both fed and fasted control and toxin-treated mice. Glutathione content (mumol g-1 tissue) was 9.01 +/- 0.66 (control) and 4.26 +/- 0.41 (toxin) for fed mice, 4.45 +/- 0.39 (control) and 2.45 +/- 0.26 (toxin) for 16-h fasted mice, and 7.18 +/- 0.26 (control) and 3.76 +/- 0.65 (toxin) for mice fed before, but fasted after exposure to toxin. In all cases, toxin treatment resulted in significant decreases in glutathione content compared to controls. Treatment of T-2-intoxicated mice with MTCA (750 mg kg-1, i.p.) not only maintained glutathione content at control levels or higher but significantly improved survival as well. Therefore, the toxicity and lethality of T-2 toxin may be associated with decreased hepatic glutathione content, since MTCA maintained glutathione content and improved survival.

Modification of hepatic vitamin E stores in vivo. I. Alterations in plasma and liver vitamin E content by methyl ethyl ketone peroxide

Since experiments with freshly isolated rat hepatocytes have shown that cellular vitamin E is consumed in response to insult by compounds that induce an oxidative stress only after cellular glutathione (GSH) concentrations have been substantially depleted, experiments were performed to determine whether this sequence of events occurred in response to oxidative insult in vivo. The role that plasma vitamin E plays in the response to chemically induced oxidative injury in vivo was also assessed. Treatments with 40 mg/kg of methyl ethyl ketone peroxide (MEKP) quickly induced lipid peroxidation in vivo and from one to 4 h after treatment caused a depression in the plasma content of vitamin E and the liver content of GSH, as well as signs of toxicity (elevations in serum activities of alanine and aspartate aminotransferases). At these time points however, the liver content of vitamin E was either indistinguishable from or slightly elevated from controls. By 12 to 24 h after treatment the liver content of vitamin E was reduced by 20-25% whereas values for all other indicators had returned toward control levels. Pretreatment of rats with L-buthionine-S,R-sulfoximine, an inhibitor of GSH by 4 or 24 h after treatment, did not alter the time course or extent of hepatic vitamin E depletion that was observed after treatment with MEKP. Other compounds that induce oxidative stress and lipid peroxidation to the liver, carbon tetrachloride and menadione, did not provoke an alteration in hepatic vitamin E levels as compared to controls 1 day after treatment. These findings indicate that depletion of hepatic vitamin E may not occur as an immediate consequence of oxidative insult to the liver and that the depletion of hepatic vitamin E levels may not be related to the extent of prior GSH depletion. Moreover, these findings suggest that alterations in the plasma concentration of vitamin E may not reflect concurrent alterations in hepatic vitamin E levels. A mechanism whereby liver vitamin E stores are mobilized for the maintenance of plasma vitamin E levels is proposed.

Correlation of changes in serum analytes and hepatic histopathology in rats exposed to carbon tetrachloride

Clinical pathology data can significantly contribute to the characterization of a disease process if suitable time points for sample collection are chosen and combined with the measurement of biochemical analytes that are sensitive and specific for damage to a potential target organ. Using a well-defined model for hepatotoxicity, we correlated histopathological lesions in the liver with changes in selected serum analytes. Groups of Fischer-344 rats were treated with carbon tetrachloride (280 mg/kg in corn oil) for 1, 2, 4, 6, 8 or 10 days. Subgroups were allowed to recover for 1, 5 or 8 days, at which time blood and liver specimens were collected. Histologically, necrosis was detected in livers from rats treated for 1 and 2 days and allowed to recover for 1 day. This was followed by generalized fatty change in animals treated for longer periods. The maximum severity of fatty change occurred 7-12 days (total experimental time). A sharp rise and fall (48 h) in cytosolic enzyme activities were seen in serum. This preceded gradual increases in all analytes measured which eventually peaked at 9-11 days (total experimental time). The pattern seen in biochemical analytes paralleled the development of marked fatty change. We discuss relationships between the histologic and biochemical findings and conclude that appropriate clinical biochemistry measurements in a toxicology experiment can provide valuable mechanistic information.

Free radical-induced liver injury. II. Effects of intraperitoneally administered 2,2'-azobis(2-amidinopropane) dihydrochloride on the fatty acid profiles of hepatic triacylglycerol and phospholipids

Liver injury induced by the radical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and carbon tetrachloride (CCI4) was examined by the analysis of lipids in the liver of rats. Increased triacylglycerol (TAG) was found in the liver within 24 hr following injection of these drugs. In AAPH-treated and CCI4-treated rats, it was 2.1 and 1.8 times that in the controls, respectively. TAG-palmitate and -oleate were found at particularly increased levels, while polyunsaturated fatty acid profiles of hepatic phospholipids were essentially the same for the treated and untreated rats. It is evident from these findings that radical initiators cause no decrease in polyunsaturated fatty acids in hepatic lipids, but accumulate TAG in the liver. Such a condition is the equivalent of liver injury in the rats in whose diets vitamin E has long been deficient.

Modulation of carbon tetrachloride hepatotoxicity and xenobiotic-metabolizing enzymes by corticosterone pretreatment, adrenalectomy and sham surgery

These investigations sought to determine the role of physiological concentrations of natural glucocorticoids in modulating chemical toxicity, and to ascertain if effects on toxicity may be due to alterations of chemical metabolizing enzymes by glucocorticoids. The hepatotoxic response to carbon tetrachloride (CCl4) in adrenalectomized or naive Long Evans rats treated with corticosterone was assessed. Alterations of hepatic cytochrome P-450 concentration, mono-oxygenase activities, NADPH-cytochrome (P-450)c reductase activity, and glutathione S-transferase activity were examined. Adrenalectomy and to a lesser extent sham surgery were protective, but corticosterone administration increased CCl4 hepatotoxicity. Corticosterone administration to adrenalectomized or sham-operated rats reduced the protective effect of these treatments. Correlating with the in vivo response, mono-oxygenase activities decreased after adrenalectomy and sham surgery, but increased with glucocorticoid administration. These studies suggest that basal, stress-associated, and pharmacological concentrations of a natural glucocorticoid can modify chemical toxicity and alter hepatic enzymes important to chemical metabolism.

Free radical-induced liver injury. I. Effects of dietary vitamin E deficiency on triacylglycerol level and its fatty acid profile in rat liver

Effects of dietary vitamin E deficiency on the fatty acid compositions of total lipids and phospholipids were studied in several tissues of rats fed a vitamin E-deficient diet for 4, 6, and 9 months. No significant differences were observed between the vitamin E deficiency and controls except in the fatty acid profiles of liver total lipids. Triacylglycerol (TAG) accumulation was found in the liver of rats fed a vitamin E-deficient diet. The levels of TAG-palmitate and -oleate increased particularly in the liver from such animals. The fatty acid compositions of hepatic phospholipids were not affected by the diet. Increased TAG observed in the liver of rats fed a vitamin E-deficient diet was restored to normal when the diet was supplemented with 20 mg alpha-tocopheryl acetate/kg diet. These findings indicate that dietary vitamin E deficiency causes TAG accumulation in the liver and that the antioxidant, vitamin E, is capable of preventing free radical-induced liver injury.

Role of hepatocellular regeneration in CCl4 autoprotection

The destruction of liver microsomal cytochromes P450 by a previously administered low dose of CCl4 has been widely accepted as the mechanism of CCl4 autoprotection. However, circumstantial evidence suggests that this mechanism cannot completely explain the phenomenon of autoprotection. The protective effect of a low dose of CCl4 (0.3 ml/kg, po) on the lethal effect of a subsequently administered high dose (5 ml/kg, po) was established in male Sprague Dawley rats. The protective dose permitted 100% survival, whereas only 15% survival was observed without it. Hepatotoxicity, measured by serum enzyme elevations (aspartate transaminase, alanine transaminase, and sorbitol dehydrogenase) and histopathological changes 24 hr after the treatment with high dose, was similar in both the groups, even though the protective dose had significantly decreased liver microsomal cytochromes P450 (to 62% of normal) and associated enzymes, aminopyrine demethylase and aniline hydroxylase. Rats pretreated with CoCl2 to decrease hepatic microsomal cytochrome P450 to 44% of normal levels did not show a significant protection from the hepatotoxicity of high dose of CCl4. Previous studies have established that hepatocellular regeneration is stimulated within 6 hr after the administration of a low dose of CCl4. Based on this observation, a premise that autoprotection results from augmented recovery from injury rather than decreased injury appears likely. Hence, the role of hepatocellular regeneration was evaluated by following 3H-thymidine incorporation in hepatocellular nuclear DNA, labelling index by autoradiography, and by morphometric estimation of mitotic index. After administration of the protective dose of CCl4, stimulated nuclear DNA synthesis measured by 3H-thymidine incorporation into nuclear DNA was increased and this remained high even after subsequent administration of high dose of CCl4. Forty-eight hr after the administration of a lethal dose of CCl4 alone (5 ml/kg, po), labelling index was slightly increased, but mitotic index was not increased. In the surviving rats (15%), both labelling index and mitotic index were significantly elevated after an additional 24 hr. In rats receiving the protective dose, a significantly greater elevation of labelling index as well as mitotic index occurred 48 hr after the administration of the same lethal dose of CCl4. These results suggest that hepatocellular regeneration stimulated by the protective dose, as a biological response recruited to overcome the accompanying limited injury, may augment and sustain tissue repair processes to permit tissue restoration even after the massive liver injury elicited by the subsequent large dose of CC14.

Role of mixed-function oxidases and non-protein sulfhydryl content in [14C]-2-chloro-4-acetotoluidide binding to liver and kidney in starlings

The compound 2-chloro-4-acetotoluidide (CAT) is highly toxic to many avian species, including the starling. In our earlier work, we demonstrated the covalent binding of radioactivity from [14C]-CAT to liver and kidneys of the starling. In the present study, the effects of inducers of mixed-function oxidase (MFO) and non-protein sulfhydryl (NPSH) depletor on the total and covalent binding of [14C]-CAT radioactivity to liver and kidney of the starling were examined. The total and covalently bound radioactivity from [14C]-CAT to liver and kidney were decreased significantly in the starling pretreated with the MFO inducer, 3-methylcholanthrene. However, pretreatment with phenobarbital, another inducer of MFO, had no effect. Pretreatment with the inhibitor of MFO, SKF 525-A, reduced the covalent binding of [14C]-CAT radioactivity to liver but not to kidney. There was no reduction in the NPSH content of liver or kidney following intravenous administration of CAT (3.5 mg kg-1). Reduction of NPSH levels in the liver or kidney following treatment with diethyl maleate caused a significant increase in the covalent binding of [14C]-CAT to kidney but not to liver.

Molecular mechanisms for bromotrichloromethane cytotoxicity in isolated rat hepatocytes

1. Bromotrichloromethane added to isolated rat hepatocytes resulted in increased cell death as determined by trypan blue uptake. Toxicity increased in a concentration-dependent fashion between 2.0-5.0 M bromotrichloromethane. 2. Lipid peroxidation (malondialdehyde) increased in a time-dependent fashion but in contrast to toxicity reached a maximum level at 2.0 mM bromotrichloromethane. 3. Hypoxia increased the toxicity of bromotrichloromethane three-fold but only decreased the amount of lipid peroxidation to a small degree. 4. In spite of this poor correlation between toxicity and lipid peroxidation, the antioxidant butylated hydroxyanisole and the iron chelator desferal protected the cells from toxicity under both aerobic and hypoxic conditions and prevented lipid peroxidation. 5. During treatment with bromotrichloromethane, cellular glutathione levels slowly decreased and oxidized glutathione appeared in the media. The addition of cystine to the incubation media prevented the formation of extracellular oxidized glutathione, indicating that cellular glutathione had leaked from the cell during treatment and was oxidized in the incubation media. Although this suggested that glutathione does not play a protective role against bromotrichloromethane toxicity, diethyl maleate-pretreatment of the cells to decrease glutathione levels markedly increased bromotrichloromethane toxicity. 6. The addition of ascorbic acid to the incubation media increased bromotrichloromethane toxicity. This was attributed to the reductive activation of bromotrichloromethane in an iron and oxygen-dependent reaction. 7. It was concluded that peroxidation of essential phospholipids contributes to bromotrichloromethane-induced hepatocyte cytotoxicity.

Effect of vitamin K on carbon tetrachloride-induced cellular damage in primary cultured rat hepatocytes

The effect of vitamin K on carbon tetrachloride-induced cellular damage of primary cultured hepatocytes was investigated by estimating prothrombin activity as a parameter of cellular function. Prothrombin activity was evaluated in primary cultured rat hepatocytes using synthetic fluorogenic peptide substrates (Boc-Val-Pro-Arg-MCA). Prothrombin activity significantly increased with the addition of vitamin K and decreased by the addition of warfarin (P less than 0.05). Carbon tetrachloride caused a significant decrease of prothrombin activity and cytotoxicity in a dose dependent manner. Prothrombin activity increased after addition of vitamin K when cells were previously exposed to carbon tetrachloride for a short period, but there was no change in cells treated for a long period. Carbon tetrachloride caused a modest increase of malondialdehyde formation after a short period of exposure and a significant increase following a long period of exposure. These results suggest that: 1) prothrombin activity is a good parameter for protein synthesis in cultured hepatocytes, 2) carbon tetrachloride-induced cytotoxicity results from different mechanisms in the early phase and the late phase of exposure, and 3) vitamin K has the ability to protect hepatocytes against the carbon tetrachloride-induced cellular damage in the early phase.

Mouse strain differences in susceptibility to sporidesmin-induced biliary tract injury

Biliary tract injury was examined in four inbred strains of mice orally dosed with 500 micrograms of the fungal toxin sporidesmin. Semiquantitative histological analysis was used to assess the grade of necroinflammatory changes in the gall bladder, intra- and extrahepatic biliary tree and lobular parenchyma. Injury was greatest in the C57BL/6 and C3H strain mice and was least in SJL/J mice. In these strains injury was greatest at 4 days and had regressed by 10 days. In BALB/c mice the damage, although similar to that in SJL/J mice at 4 days, persisted at the same severity at day 10 and was accompanied by periductal fibrosis and occasionally by obliteration of ducts typical of sclerosing cholangitis. Analysis of the time-course of development of the lesions in C57BL/6 mice showed that the primary target for the toxin is the biliary epithelium. The severity of the lesions within the liver increased centripetally and the worst affected ducts were found at the confluence of the lobar ducts with the common bile duct. The variation in the degree of damage and rate of healing between strains may be due to differences in sporidesmin excretion in bile or interactions with biliary epithelial cells and/or efficacy of protective cellular repair mechanisms.

Effect of carbon tetrachloride on hamster tracheal epithelial cells

This study was designed to assess effects of carbon tetrachloride (CCl4) in hamster tracheal epithelium. Adult, male, Syrian golden hamsters were treated with 2.5 ml/kg CCl4 ip, and controls received only the vehicle (peanut oil). Animals were sacrificed after 1, 4, 12, and 24 h. Tissue samples from upper and lower tracheal levels were fixed and embedded in glycol methacrylate for light microscopy. Some tracheal rings were also fixed in formaldehyde/glutaraldehyde cacodylate buffer for transmission electron microscopy. For histopathologic evaluation of the tracheal epithelial cells, each tracheal level was cut transversely at 3 microns and stained with toluidine blue. CCl4 produced injury to ciliated and nonciliated cells in all portions of hamster trachea, although the severity of CCl4-induced injury differed in various levels and regions. The number of damaged cells increased markedly after 1 h in the lower trachea, but not until after 4 h in the upper trachea. By 24 h, the number of injured cells had decreased so that no significant difference from control was evident. The ultrastructural alterations in epithelial cells were obvious as early as 1 h after CCl4 administration. Intracellular organelles, including smooth and rough endoplasmic reticulum, mitochondria, and Golgi apparatuses, were damaged by this chemical. Since CCl4-induced cell injury is dependent on metabolism by intracellular NADPH-dependent cytochrome P450 monooxygenases, these results suggest that hamster tracheal epithelial cells have the potential to activate CCl4 metabolically.

Prevention by silymarin of membrane alterations in acute CCl4 liver damage

The effect of silymarin on liver lipid peroxidation and membrane lipid alterations induced by an acute dose of CCl4 was studied. Four groups of animals were treated with CCl4, CCl4 + silymarin, silymarin and its vehicles. CCl4 was given orally (0.4 g 100 g-1 body wt.) and silymarin was administered i.p. All animals were sacrificed 24 h after the treatments. Liver lipid peroxidation was measured and plasma membranes were isolated. Alkaline phosphatase (AP) and gamma-glutamyl transpeptidase (GGTP) were measured in plasma membranes. Membrane lipids were extracted and then analysed by thin-layer chromatography by measuring the phosphorus of the phospholipids in each spot. Liver lipid peroxidation was increased about three times in the group receiving CCl4 only. Silymarin cotreatment prevented this increase. Phosphatidylethanolamine (PEA) decreased, while phosphatidylinositol (PI) increased in the plasma membranes isolated from the CCl4-treated group. Animals that received CCl4 + silymarin showed no decrease in PEA content. A partial prevention of the decrease in phosphatidylinositol content was also observed in plasma membranes of animals treated with silymarin in addition to CCl4. CCl4 decreased gamma-glutamyl transpeptidase (GGTP) and alkaline phosphatase (AP) membrane activities. Silymarin cotreatment prevented the AP (completely) and the GGTP (partially) falls caused by CCl4. Silymarin by itself increased AP membrane activity. A significant relationship between the membrane content of phosphatidylethanolamine (PEA) and the AP activity was observed in plasma membranes of treated animals and in normal liver membranes enriched with PEA. These results indicate that silymarin can protect against the alterations induced by CCl4 on the liver plasma membrane through its antioxidant properties by modifying the plasma membrane phospholipid content.

Hepatotoxicity of geniposide in rats

The hepatotoxic effects of geniposide were investigated in rats. Increases in serum alanine aminotransferase and aspartate aminotransferase activities as a result of oral administration of 320 mg geniposide/kg body weight were suppressed when geniposide was administered ip or when the rats were pretreated with chloramphenicol. The non-protein sulphydryl content of the liver 4 hr after oral administration of geniposide decrease in a dose-dependent manner. Genipin, the aglycone of geniposide, had a marked reactivity with sulphydryl groups of glutathione and cysteine in vitro. The hepatotoxic effects of ip administration of genipin at a dose of 80 mg/kg body weight were comparable with those of oral administration of geniposide at a dose of 320 mg/kg. Buthionine sulphoximine pretreatment enhanced the toxicity of geniposide, while cysteine pretreatment completely suppressed it. These results suggest that the conversion of geniposide to genipin is causally related to the hepatotoxicity of geniposide and that hepatic non-protein sulphydryls are important in modulating the toxicity.

Hypoxia and CCl4-induced liver injury, but not acidosis, impair metabolism of cysteinyl leukotrienes in perfused rat liver

Uptake, metabolism and biliary elimination of infused cysteinyl leukotrienes were investigated in single-pass perfused rat liver. Hypoxia did not impair uptake of infused [3H]leukotriene C4, but inhibited biliary excretion of radioactivity by about 50% compared with normoxic control experiments. In addition, the leukotriene metabolite pattern in bile was profoundly altered and was characterized in hypoxia by a 75% to 80% decrease of both leukotriene C4 and polar metabolites, representing omega-oxidation products, whereas the appearance of leukotriene D4 in bile was not affected. Reoxygenation was followed by a marked increase of biliary excretion of polar metabolites, indicating that leukotrienes taken up and stored in the liver cells during the hypoxic period now underwent omega-oxidation with subsequent elimination of the omega-oxidized products. Hypoxia also inhibited the biliary excretion of radioactivity after [3H]leukotriene E4 addition because of an almost complete absence of omega-oxidation products in bile, whereas N-acetyl-leukotriene E4 excretion was not affected. Induction of liver injury by carbon tetrachloride treatment decreased single-pass uptake of [3H]leukotriene C4 by 30%, and only 36% of the radioactivity taken up by the liver was eliminated into bile within 1 hr, compared with 78% in normal livers. The pattern of biliary leukotriene metabolites, however, was not significantly different. Lowering the pH in the perfusion medium from 7.4 to 7.1 had no effect on uptake, metabolism or biliary elimination of infused [3H]leukotriene C4. The data show that hypoxia and experimental liver injury, but not acidosis, impair hepatic processing of cysteinyl leukotrienes. Thus, in leukotriene-induced shock syndromes, leukotriene elimination and inactivation may be impaired giving rise to a "vicious circle."

Protection against carbon-tetrachloride-induced lymphoid organotoxicity in rats by protein A

In a previous study we described protection of rats from carbon tetrachloride (CCl4)-induced hepatotoxicity by protein A (PA). In the present report we described protection against CCl4-induced lymphoid organotoxicity in rats by PA. Our data indicate that CCl4 administration produced a significant increase in the number of total leukocytes and polymorphs in blood, a significant decrease in leukocyte count in bone marrow, and a significant loss in weight of spleen and adrenals. In the animals receiving PA prior to and after CCl4, these values were found to be near those of controls. Histological examination revealed thymocyte depletion in thymic lobe and degenerative changes of tissue in spleen of CCl4-exposed animals. PA treatment to CCl4-exposed animals exhibited improvement and recovery from the damage caused by CCl4. These observations throw a new light on the field of CCl4 toxicity to lymphoid organs and their protection by PA.

Phenobarbital pretreatment alters the localization of CCl4-induced changes in rat liver microsomal fatty acids

Phenobarbital treatment induces an isozyme(s) of liver microsomal cytochrome P450 susceptible to CCl4 and enhances the latter's lethality. We have now studied phenobarbital's effect on the specificity of phosphatidyl fatty acid changes in rat liver microsomes. Male Sprague-Dawley rats were pretreated with three daily ip doses of phenobarbital (50 mg/kg) or saline and then orally dosed with CCl4 (2.5 ml/kg). Liver microsomes were prepared 7.5 to 180 min after CCl4 treatment, the lipid fraction was extracted, diene conjugate content was determined, and phospholipids were separated by HPLC for fatty acid content determination. Protein, phospholipid, and phosphatidyl fatty acid residue loss occurred early (7.5 to 30 min) and in some cases later (60 to 180 min) in both pretreated groups, suggesting that two phases of CCl4-mediated injury occurred. Phenobarbital pretreatment accelerated the CCl4-induced formation of diene conjugates in the microsomal lipids. In studies on the separated phospholipids, phenobarbital alone altered microsomal fatty acid content, primarily decreasing arachidonic acid in favor of linoleate, particularly in phosphatidylserine. During the early phase of CCl4 injury, phenobarbital pretreatment shifted the major loss of arachidonic acid from phosphatidylserine to phosphatidylethanolamine. During the later phase, arachidonic acid loss was still prominent, but the most extensive CCl4-induced changes in fatty acids occurred in the neutral lipid fraction, regardless of pretreatment. These changes included loss of neutral lipid linoleic and docosahexanoic acids associated with an increase in palmitic acid. These data demonstrate that phenobarbital pretreatment is associated with a shift in the predominant phospholipid locus from phosphatidylserine to phosphatidylethanolamine for the early CCl4-induced fatty acid changes in rat liver microsomes.

Relation of Ca++ accumulation and lipid peroxidation with CCl4-induced toxicity in the rat liver

The relationship between lipid peroxidation and Ca++ content in liver and hepatic cellular disruption was studied in 24 hr-fasted rats. Microsomal lipid peroxidation of livers in rats treated with a single dose of 16 mg or 96 mg CCl4/kg was significantly increased by 22% or 49% as measured by the diene conjugation technique. Ca++ content of liver microsomes in rats treated with 96 mg CCl4/kg was significantly increased by 20%, while the Ca++ content in rats treated with 16 mg CCl4/kg was not changed. On the other hand mitochondrial Ca++ content was tremendously increased in both rats treated with 16 mg and 96 mg CCl4/kg. Furthermore, when the activity of plasma glutamic pyruvic transaminase (GPT), which is a liver-specific enzyme, was investigated 3 hr after CCl4 treatment, hepatotoxicity was evident in rats treated with 96 mg/kg but not evident in rats treated with 16 mg/kg. These results indicate that there was a good correlation between the microsomal Ca++ content and the hepatic cellular disruption but no correlation between the microsomal lipid peroxidation and the hepatic cellular disruption as measured by the diene conjugation.

CCl4-induced lipoperoxidation triggers a lethal defect in the liver plasma membranes

Loss of calcium regulation across the plasma membrane of hepatocytes is responsible for irreversible cell damage by CCl4. The mode of action of colchicine in CCl4 acute liver damage is not completely understood. We followed the time courses of the changes in lipoperoxidation, the activities of liver plasma membrane Ca2(+)-ATPase, gamma-glutamyl transpeptidase and alkaline phosphatase, as well as the time courses of serum markers of liver damage in rats acutely intoxicated with CCl4. We assessed the effects of colchicine in this model and evaluated the effect of this drug on liver cytochrome P-450. Increased lipoperoxidation is the earliest and shortest lasting effect of CCl4 in the liver and is followed by a decrease in the activities of plasma membrane-bound enzymes. The alterations in serum enzymes showed a slower onset and were more protracted. Colchicine pretreatment produced a small decrease in cytochrome P-450 in the liver but completely prevented most of the changes produced by CCl4 in lipoperoxidation, liver plasma membrane enzyme activities and serum enzyme activities. We conclude that CCl4 metabolites trigger lipoperoxidation and then produce a longer lasting change in the plasma membrane, which thus allows calcium accumulation. Colchicine prevents the early mechanisms of CCl4 damage, and its effect on cytochrome P-450 perhaps plays only a contributory role.

Sodium-23 and proton nuclear magnetic resonance imaging studies of carbon tetrachloride-induced liver damage in the rat

Magnetic resonance imaging techniques were used to investigate the response of the liver of the rat in situ to a toxicological challenge by carbon tetrachloride. Proton images were taken as transverse slices through the rat before and after intraperitoneal administration of the hepatotoxin. Two to three hours after carbon tetrachloride was given, a region of high proton signal intensity was observed where the portal vein enters the liver. Sodium-23 images were also taken, and a region of high sodium intensity was observed in the same location within the liver as the increased proton intensity. The results suggest that acute administration of carbon tetrachloride induces localized liver damage in the region where the hepatotoxin first enters the liver. This liver damage is manifest as edema with a buildup of sodium ion and water, which can be readily detected by sodium-23 and proton NMR imaging techniques, respectively.

Inhibition of carbon tetrachloride-induced lipid peroxidation by novel antioxidants in rat hepatic microsomes: dissociation from hepatoprotective effects in vivo

The ability of two novel antioxidants, U-74,006F and U-78,517G, as well as the known antioxidant N,N'-diphenyl-p-phenylenediamine to inhibit lipid peroxidation induced by carbon tetrachloride (CCl4) was investigated in Aroclor 1254-induced rat hepatic microsomes. All three compounds completely inhibited lipid peroxidation in microsomes as measured by the formation of thiobarbituric acid reactive substances (TBARS). Inhibition of lipid peroxidation was not a function of decreased bioactivation of CCl4, as the compounds did not substantially inhibit benzphetamine N-demethylase activity or covalent binding of [14-C]CCl4 to lipid or protein. Parallel studies examined the hepatoprotective effects of the compounds in vivo. Rats were pretreated with antioxidant or vehicle prior to administration of CCl4 (300 or 600 microL/kg i.p.). Sera were collected 24 h postadministration of CCl4 and analyzed for alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities and total bilirubin. Administration of CCl4 produced elevations in ALT, moderate changes in bilirubin, and no change in ALP activities. Histological examination of CCl4-treated livers revealed lipidosis and centrilobular necrosis. The antioxidants partially improved the clinical chemistry parameters, but had minimal effects on the histological lesion. In contrast to the complete inhibition of lipid peroxidation observed in the in vitro studies, none of the antioxidants markedly protected against CCl4-induced toxicity in vivo.

Effect of oral dosing vehicles on the acute hepatotoxicity of carbon tetrachloride in rats

Although carbon tetrachloride (CCl4) is of concern as a drinking water contaminant, it has been necessary in most oral toxicity studies to give CCl4 in an oil vehicle due to its limited water solubility. The primary objective of our study was to assess the influence of dosing vehicles on the acute hepatotoxicity of CCl4. Fasted 200- to 230-g rats were generally found to be more susceptible to CCl4 hepatotoxicity than fasted 300- to 330-g rats. A time-course study revealed that corn oil did not delay the onset or time of maximal liver injury by an oral 100 mg/kg dose of CCl4, but did reduce the extent of injury relative to that when the chemical was given undiluted or as an aqueous emulsion. Fasted 200- to 230-g male Sprague-Dawley rats were given 0, 10, 25, 50, 100, 250, 500, or 1000 mg CCl4/kg body wt by gavage: in corn oil; as an aqueous emulsion; as the undiluted chemical; and in the 10 and 25 mg/kg doses only, in water. Blood and liver samples were taken 24 hr after dosing for measurement of serum and microsomal enzymes. Pathological examination of liver samples was also conducted. Dose-dependent increases in serum enzyme levels and pathological changes and dose-dependent decreases in microsomal P450 and glucose-6-phosphatase activity were observed in each vehicle group. Both the 10 and 25 mg/kg oral doses of CCl4 in water caused significant elevations in serum enzymes and hepatic centrolobular vacuolation. The study revealed that acute hepatotoxicity was less pronounced at each dosage level in rats given CCl4 in corn oil than in other vehicle groups. These findings demonstrate that dosing vehicles can significantly influence the acute hepatotoxicity of CCl4 in rats and are a cause for additional consideration and review of the practice of routinely using vegetable oils as a diluent in studies of volatile organic compound (VOC) toxicity. The use of aqueous Emulphor emulsions appears more appropriate in acute toxicity studies of VOC drinking water contaminants such as CCl4, in that the emulsion did not substantially alter the toxicity of CCl4 from that of undiluted CCl4 or CCl4 ingested in water.

In vivo and in vitro 31P-NMR spectroscopy of rat liver treated with halocarbons

Both in vivo and in vitro 31P-NMR spectroscopy were used to demonstrate metabolic changes in rat liver as a function of time after exposure to either carbon tetrachloride (CCl4) or bromotrichloromethane (BrCCl3). The inorganic phosphate resonance, measured in vivo, moves upfield, which is associated with a decrease in cytosolic pH over a 12 or 20 h period (for BrCCl3 or CCl4, respectively). Intoxication by CCl4 or BrCCl3 causes an intracellular acidosis to pH 7.05 or 6.82 (+/- 0.05), respectively. Also, it has been found that halocarbon exposure increases the amounts of phosphomonoesters (PME) detected. High resolution in vitro 31P-NMR spectroscopy studies of perchloric acid extracts of CCl4-treated rat livers indicated a significant increase in the height of the phosphocholine resonance in the PME region 4-5 h after CCl4 exposure.

Effect of 2-butanol and 2-butanone on rat hepatic ultrastructure and drug metabolizing enzyme activity

The effect of a single oral dose of 2-butanol (2.2 ml/kg) or 2-butanone (1.87 ml/kg) on hepatic ultrastructure and drug-metabolizing enzyme activity was studied in the rat. A 135-197% increase in acetanilide hydroxylase activity was found in rats sacrificed 12-40 h after dosing with 2-butanol or 2-butanone. A 40-h pretreatment with 2-butanone produced a 155% increase in aminopyrine N-demethylase activity. NADPH-cytochrome c reductase activity and the concentrations of cytochromes P-450 and b5 were largely unaltered 2-40 h after dosing with either agent. Electron microscopic examination of hepatocytes from rats sacrificed 16 h after 2-butanol or 2-butanone revealed a marginal increase in the prevalence of smooth endoplasmic reticulum. However, by 40 h, there was a marked proliferation of the smooth endoplasmic reticulum and reduction in rough endoplasmic reticulum in response to both agents. The most marked potentiation of CCl4 hepatotoxicity occurred when rats were pretreated with 2-butanol or 2-butanone 16 h before CCl4 administration. The coincidental finding of maximal CCl4-induced hepatic injury and elevation of microsomal xenobiotic activity within the same time frame following 2-butanol or 2-butanone supports the hypothesis that aliphatic alcohols and ketones potentiate CCl4 hepatotoxicity by enhancing biotransformation of the halocarbon to cytotoxic metabolites.

Cellular analysis of c-Ha-ras gene expression in rat liver after CCl4 administration

Expression of the c-Ha-ras proto-oncogene is specifically enhanced during liver regeneration, in parallel with increased DNA replication, which suggests that c-Ha-ras may play a role in the control of regeneration. In this study, an in situ hybridization technique was applied for analysis of expression of the c-Ha-ras gene at the cellular level during liver regeneration induced by CCl4 administration. The in situ hybridization was compared with the observation for the p21c-Ha-ras protein, the corresponding protein of the c-Ha-ras gene, by immunohistochemistry. In normal rat liver, a few hepatocytes expressed the mRNAs and the corresponding proteins without any preferential localization. Zonal heterogeneity of c-Ha-ras gene expression first became evident at 12 hr after CCl4 administration, a higher number of gene products being detected in the pericentral zone than in the periportal zone. This heterogeneity became maximal at 24 hr after CCl4 administration. Zonal heterogeneity in the level of the p21c-Ha-ras protein paralleled that in the level of gene expression. Furthermore, both hepatocytes and nonparenchymal cells participated in expression of the c-Ha-ras gene during liver regeneration.

Toxic interactions between carbon tetrachloride and chloroform in cultured rat hepatocytes

Primary cultures of adult rat hepatocytes were incubated (1.5-16 hr) with various concentrations of CCl4 (less than or equal to 0.5 mM) and/or CHCl3 (less than or equal to 2.5 mM). Agent-dependent alterations in hepatocyte functions were assessed by measuring (1) [3H]choline incorporation into phosphatidylcholine (endoplasmic reticulum), (2) MTT (tetrazolium salt) reduction (mitochondria), and (3) AST release into medium (plasma membrane). Cultured hepatocytes incubated with 0.5 mM CCl4 displayed a significant (p less than or equal to 0.001) and rapid (1.5 hr) reduction (40%) in endoplasmic reticulum function that preceded significant (p less than or equal to 0.001) alterations in mitochondria (6-16 hr) and plasma membrane (6-16 hr) functions. CCl4-dependent alterations in liver cell functions are a result of CCl4 bioactivation since metyrapone inhibits the CCl4-mediated changes in cell functions. Response surface methods (RSM) were used to determine the influence of combinations of CCl4 and CHCl3 on liver cell MTT reduction and [3H]choline incorporation. Regression coefficients were determined for CCl4, CHCl3, and CCl4-CHCl3. All results were significant (p less than 0.0001) and implied that CCl4 was a more potent hepatotoxin in vitro than CHCl3. The RSM analysis also suggested that combinations of CHCl3 and CCl4 have greater than additive effects on MTT reduction and [3H]choline incorporation. These effects of CCl4 and/or CHCl3 on liver cell functions in vitro are consistent with liver alterations observed in vivo. Therefore, primary cultures of adult rat hepatocytes may be an appropriate model in vitro to assess the hepatotoxic potential of agents alone or in combination.

Methods for the study of liver cell heterogeneity

A large number of histological, histochemical and biochemical techniques are available for studying liver cell heterogeneity. Structural differences are recognized by morphometric analyses of electron micrographs. The zonal heterogeneity of enzyme activities can be demonstrated by histochemistry and more precisely by ultramicrobiochemical assays in microdissected periportal and perivenous tissue. Immunohistochemistry is useful for quantifying and localizing proteins, especially isoenzymes, without depending on their biological activity. The zonal quantification of specific mRNA can be achieved by in situ hybridization. The different structural and enzymic equipment of periportal and perivenous tissue found by these techniques has led to the concept of metabolic zonation. This hypothesis can be confirmed by determination of metabolic rates in perfused liver after selective zonal damage, in separated periportal and perivenous hepatocytes as well as in periportal and perivenous tissue of perfused liver by non-invasive techniques.

Carbon tetrachloride inhibits synthesis of pulmonary surfactant disaturated phosphatidylcholines and ATP production in alveolar type II cells

Other studies have shown that inhalation of carbon tetrachloride (CCl4) decreases the amount of pulmonary surfactant lining the alveolar surface. Therefore, we studied the effects of CCl4 on the synthesis of surfactant phosphatidylcholines (PCs) in rat alveolar type II cells in vitro. The rate of incorporation of choline, palmitate or glycerol into disaturated PC (DSPC) is decreased in a concentration-dependent manner. The CCl4 concentrations which cause maximal inhibition and 50% inhibition are similar for each substrate. The rate of incorporation of choline or glycerol into total PC is diminished to the same extent as their incorporation into DSPC. In addition, the rate of incorporation of glycerol into phosphatidylglycerol is decreased by the same extent as its incorporation into PC. All of these data suggest that there is a common site(s) at which CCl4 inhibits PC synthesis and that the inhibition occurs early in the biosynthetic pathway. However, individual enzymes involved in phospholipid synthesis do not seem to be affected by the solvent. Exposure of alveolar type II cells to CCl4 does cause a rapid and dramatic loss in cellular ATP, a cofactor required by some enzymes involved in PC synthesis. Studies with isolated lung mitochondria suggest that CCl4 inhibits the enzyme complex which catalyzes the synthesis of ATP from ADP. In addition, CCl4 causes a decrease in the amount of 3-O-methylglucose associated with type II cells, suggesting that glucose influx is impaired. This may also contribute to lower cellular ATP levels. The results of this study suggest that inhalation of CCl4 may impair surfactant phospholipid synthesis by decreasing ATP levels in alveolar type II cells.

Hepatic protection by 16, 16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1-induced injury in the rat

Studies were conducted to assess the possible protective action of 16,16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1 (AFB1) induced hepatic injury in the rat. Evaluation of liver damage by histopathologic techniques and clinical chemistry indicated that hepatic necrosis was ameliorated by treatment with DMPG even though binding of radiolabeled (3H)-AFB1 to hepatic DNA was unaffected by this prostaglandin. However, DMPG did not protect rats against AFB1-induced mortality. These data suggest that hepatic protection by DMPG was due to mechanisms other than an interference with the activation or hepatic binding of AFB1.

Relationship between hepatic glutathione content and carbon tetrachloride-induced hepatotoxicity in vivo

The relationship between carbon tetrachloride (CCl4)-induced hepatotoxicity and hepatic glutathione (GSH) content was investigated in fed and fasted rats. The elevation of serum glutamic-pyruvic transaminase (GTP) activity by CCl4 treatment was enhanced by fasting. Although the hepatic GSH content fo 12-hour-fasted rats was higher than that of fed rats determined at 6 p.m., the serum GPT activity of the former was higher than that of the latter. Starvation had no effect on the activities of hepatic glutathione peroxidase (GSH-Px) and glutathione reductase (GR). The results suggest that the potentiation of hepatic injury by CCl4 cannot be related to hepatic GSH content.

In vivo proton nuclear magnetic resonance imaging and spectroscopy studies of halocarbon-induced liver damage

Proton magnetic resonance imaging and localized NMR spectroscopy were used to study the rat liver in situ. Respiratory gating was used in both the imaging and the localized spectroscopy studies to control for the movement of the upper abdomen of the rat during breathing. After administration of carbon tetrachloride, bromotrichloromethane, or halothane, localized regions of high proton signal intensity were observed in the NMR images of the liver. Localized (VOSY) proton NMR spectra from within these regions indicated that the increase in a signal intensity was due to a longer T2 relaxation time for the water resonance, indicating acute edema in the region of tissue damage.

Carbon tetrachloride metabolism in partially hepatectomized and sham-operated rats pre-exposed to chlordecone (Kepone)

The potentiation of CCl4 toxicity by pre-exposure to chlordecone (CD) is well established. Chlordecone-induced metabolism of CCl4 and suppressed hepatocellular repair have been offered as possible mechanisms for this potentiation. Recent work using the partially hepatectomized (PH) rat as a model for an actively regenerating liver has provided supportive evidence for the latter hypothesis. The present study was initiated to determine if metabolism and disposition of 14CC14 is altered in the PH rat, and if this is a contributing factor to the reported protective effect afforded by the PH procedure. Male Sprague-Dawley rats (150-175 g) maintained on dietary CD (10 ppm) for 15 days were partially hepatectomized or sham-operated (SH) on day 15. Another group of CD-pretreated rats received 0.9% CoCl2 (60 mg/kg, sc, qd for 2 days) in lieu of the surgical procedure. On day 16 the rats were challenged with a single dose of CCl4 (100 microL/kg, ip) containing 20 muCi 14CCl4. A radiolabel inventory consisting of exhaled 14CCl4, 14CO2 production, total hepatic 14C, free 14CCl4 and covalently bound 14C was taken over a 6-hr time period. Lipid peroxidation and serum enzyme activities [aspartate aminotransferase (AST) and alanine aminotransferase (ALT)] were measured in indices of toxicity. Neither CD pretreatment alone nor CoCl2 treatment alone produced significant alterations in metabolism of low dose (100 microliters/kg) CCl4. No significant difference in 14CCl4 recovery or 14CO2 production was detected for PH versus SH rats. Hepatic 14CCl4-derived 14C (per gram tissue) was greater in PH rats. Values for free 14CCl4, covalently bound 14C, and lipid peroxidation were similar for SH and PH rats.(ABSTRACT TRUNCATED AT 250 WORDS)