Potentiation Of Carbon Tetrachloride Hepatotoxicity Research Articles

Potentiation of carbon tetrachloride hepatotoxicity and lethality in type 2 diabetic rats.

There is a need for well characterized and economical type 2 diabetic model that mimics the human disease. We have developed a type 2 diabetes rat model that closely resembles the diabetic patients and takes only 24 days to develop robust diabetes. Nonlethal doses of allyl alcohol (35 mg/kg i.p.), CCl(4) (2 ml/kg i.p.), or thioacetamide (300 mg/kg i.p.) yielded 80 to 100% mortality in diabetic rats. The objective of the present study was to investigate two hypotheses: higher CCl(4) bioactivation and/or inhibited compensatory tissue repair were the underlying mechanisms for increased CCl(4) hepatotoxicity in diabetic rats. Diabetes was induced by feeding high fat diet followed by a single dose of streptozotocin on day 14 (45 mg/kg i.p.) and was confirmed on day 24 by hyperglycemia, normoinsulinemia, and oral glucose intolerance. Time course studies (0-96 h) of CCl(4) (2 ml/kg i.p.) indicated that although initial liver injury was the same in nondiabetic and diabetic rats, it progressed only in the latter, culminating in hepatic failure, and death. Hepatomicrosomal CYP2E1 protein and activity, lipid peroxidation, glutathione, and (14)CCl(4) covalent binding to liver tissue were the same in both groups, suggesting that higher bioactivation-based injury is not the mechanism. Inhibited tissue repair resulted in progression of injury and death in diabetic rats, whereas in the nondiabetic rats robust tissue repair resulted in regression of injury and survival after CCl(4) administration. These studies show high sensitivity of type 2 diabetes to model hepatotoxicants and suggest that CCl(4) hepatotoxicity is potentiated due to inhibited tissue repair.

Potentiation of carbon tetrachloride hepatotoxicity by pentosan polysulfate in rats.

Few data are available in the literature regarding the effect of pentosan polysulfate (PPS) on normal and fibrotic rat livers. In addition, the combination of PPS and carbon tetrachloride (CCl4) has not been studied so far. The objective of this study was to assess the effect of PPS on rat livers treated or not with CCl4 for the induction of liver fibrosis. The study consisted of four stages: 1) hepatic fibrosis induction with CCl4 (N = 36 rats); 2) evaluation of the effect of PPS on CCl4-induced hepatic fibrosis (N = 36 rats); 3) evaluation of the effect of higher doses of PPS in combination with CCl4 (N = 50 rats); 4) evaluation of the presence of an enzymatic inductor effect by PPS (N = 18 rats) using the sodium pentobarbital test which indirectly evaluates hepatic microsomal enzyme activity in vivo. Adult (60 to 70 days) male Wistar rats weighing 180 to 220 g were used. All animals receiving 0.5 ml 8% CCl4 (N = 36) developed hepatic fibrosis, and after 8 weeks they also developed cirrhosis. No delay or prevention of hepatic fibrosis was observed with the administration of 5 mg/kg PPS (N = 8) and 1 mg/kg PPS (N = 8) 1 h after the administration of CCl4, but the increased hepatotoxicity resulting from the combination of the two substances caused massive hepatic necrosis in most rats (N = 45). PPS (40 mg/kg) alone caused hepatic congestion only after 8 weeks, but massive hepatic necrosis was again observed in association with 0.5 ml CCl4 after 1 to 4 weeks of treatment. Unexpectedly, sleeping time increased with time of PPS administration (1, 2, or 3 weeks). This suggests that PPS does not function as an activator of the hepatic microsomal enzymatic system. Further studies are necessary in order to clarify the unexpected increase in hepatotoxicity caused by the combination of CCl4 and high doses of PPS, which results in massive hepatic necrosis.

Adrenergic Modulation of Hepatotoxicity

Summaries of the interactions caused by altering adrenoreceptor activity in conjunction with the administration of selected hepatotoxicants are provided in Table 2 and Fig. 1. These hepatotoxicants can be divided into two groups, one whose toxicity is increased by adrenergic agonist drugs (group I) and the other whose toxicity is decreased by adrenergic antagonists (group II). Group I includes carbon tetrachloride, acetaminophen, and methylphenidate. Perhaps the most remarkable aspect these chemicals have in common is the striking potentiation that occurs with cotreatment with certain adrenergic agonist drugs. For each of these, cotreatment with the appropriate adrenergic agent can result in massive hepatocellular necrosis from an otherwise nontoxic dose. In terms of the specific adrenoreceptors involved and mechanisms of potentiation, however, they have little in common. Potentiation of carbon tetrachloride hepatotoxicity appears to be mediated by alpha(2)-adrenoceptor stimulation, acetaminophen is potentiated by alpha(1)-adrenoreceptor agonists, and methylphenidate responds to beta(2)-adrenoreceptor stimulation. Studies of the potentiation of carbon tetrachloride and acetaminophen agree that the timing of adrenergic stimulation relative to the hepatotoxicant dose is critically important to the interaction but markedly different for these two toxicants. Acetaminophen was potentiated only when the adrenergic drug was administered as a 3-h pretreatment. This is apparently a consequence of a mechanism of potentiation that involves adrenergic depression of hepatic glutathione content and a requirement that peak effects on glutathione of both the adrenergic agent and acetaminophen be coincident. The mechanism of potentiation of carbon tetrachloride hepatotoxicity is uncertain but clearly does not involve hepatic glutathione content. In contrast to acetaminophen, adrenergic effects must occur within a time window a few hours after the carbon tetrachloride dose for potentiation to occur. The importance of dose timing has not been evaluated for adrenergic potentiation of methylphenidate hepatotoxicity, but it is clear that this interaction is based on yet a third mechanism. While only three hepatotoxicants of the group I type have been examined in detail, the diversity of receptor types and mechanisms involved suggest that this phenomenon may be relevant for a wide variety of hepatotoxic drugs and chemicals. This interaction is also of interest because factors or events that lead to increased adrenergic stimulation are common in everyday life. Most over-the-counter cold and allergy preparations contain sympathomimetic drugs, and many prescription drugs produce adrenergic effects as either an extension of the intended therapeutic effect or as a side effect. Stress and some disease states can also lead to significant increases in peripheral adrenergic activity, creating the potential for increased susceptibility to hepatic injury from exposure to certain drugs or chemicals. Cocaine and bromobenzene represent group II, chemicals whose hepatotoxicity is diminished by cotreatment with adrenergic antagonist drugs. In the case of cocaine, adrenergic antagonist cotreatment was capable of reducing serum alanine aminotransferase activities by approximately 50%. For bromobenzene, the protection afforded by adrenergic antagonist cotreatment was more profound, with minimal hepatic lesions resulting from doses of bromobenzene that otherwise produced lethal hepatic necrosis. For the chemicals in group II, experimental observations are consistent with a phenomenon in which adrenergic potentiation of toxicity is supplied by the hepatotoxicant itself. Both cocaine and bromobenzene, in hepatotoxic doses increase endogenous catecholamine levels. When the effects of the elevated catecholamines are removed with the appropriate adrenergic antagonist, much lower toxicity (presumably due only to the direct hepatotoxic effects of the drug or chemical) is obse

Stimulated Tissue Repair Prevents Lethality in Isopropanol-Induced Potentiation of Carbon Tetrachloride Hepatotoxicity

Published reports on the alcohol potentiation of CCl4toxicity indicate that in spite of enhanced hepatotoxicity there is no increase in lethality. The objective of this study was to investigate the mechanism involved in animal survival despite significantly enhanced liver injury. Male Sprague–Dawley rats (175–225 g) were treated with isopropanol (ISOP, 2.5 ml/kg, 25% aqueous solution, po) 24 hr prior to CCl4(1 ml/kg, ip) administration. Plasma enzymes (ALT and SDH), hepatic glycogen levels, and [3H]thymidine (3H-T) incorporation into hepatonuclear DNA were measured during a time course (0–96 hr) after CCl4administration. Liver sections were examined for histopathology and cell cycle progression by proliferating cell nuclear antigen (PCNA) immunohistochemistry. Maximum injury was observed at 36 hr in both the groups as indicated by elevated plasma enzyme levels and by histopathology. The extent of injury in the ISOP + CCl4group was higher than that in the H2O + CCl4group. Plasma enzyme activity returned to control levels by 60 hr, indicating recovery from injury in both groups. Maximum3H-T incorporation occurred at 48 hr in both groups (ISOP + CCl4; vehicle + CCl4), indicating maximum stimulation of S-phase synthesis. PCNA studies revealed a corresponding stimulation of cell cycle progression. The wave of S-phase synthesis and cell cycle progression returned to control levels in the H2O + CCl4group by 60 hr but continued up to 72 hr in the ISOP + CCl4group. These findings support the hypothesis that in response to increased infliction of CCl4injury by isopropanol, augmented stimulation of cell division and tissue repair restrain the progression of injury and restore hepatic structure and function, thereby allowing the rats to survive. Further, antimitotic intervention with colchicine (1 mg/kg, ip) led to decreased S-phase synthesis, followed by 60% lethality in the isopropanol-pretreated group in contrast to 40% lethality in the group receiving CCl4alone (H2O + CCl4). These findings suggest that greater stimulation of tissue repair restrains the progression of ISOP-enhanced infliction of CCl4liver injury and accounts for recovery from enhanced liver injury and animal survival. The findings are consistent with a two-stage model of toxicity wherein liver injury is linked by progression or regression of injury, which is governed by the extent of tissue repair to the final outcome.

Methanol potentiation of carbon tetrachloride hepatotoxicity: The central role of cytochrome P450

Evidence to explain the enhanced hepatotoxicity of carbon tetrachloride (CCl 4) following methanol exposure by inhalation is presented. Hepatic microsomes prepared from male F344 rats exposed to methanol at concentrations up to 10000 ppm showed increased p-nitrophenol hydroxylase activity but no increase in pentoxyresorufin- O-dealkylase or ethoxyresorufin- O-deethylase activities. Hepatic antioxidant levels, glutathione levels and glutathione- S-transferase activity in methanol-treated animals were not different from controls. In vitro metabolism of CCl 4 was also increased in microsomes from methanol-treated animals. Pretreatment with allyl sulfone, a specific chemical inhibitor of cytochrome P450 2E1, abolished the difference in microsomal metabolism between exposed and control animals. This study shows that methanol exposure induces cytochrome P450 2E1, which appears to be the principal toxicokinetic mechanism responsible for the increased metabolism and thus the increased hepatotoxicity of CCl 4.

Potentiation of carbon tetrachloride hepatotoxicity by inhaled methanol: time course of injury and recovery.

Increases in the use of methanol (MeOH) as a transportation fuel would result in greater potential for inhalation exposure. Because oral exposure to MeOH potentiates the hepatotoxicity of carbon tetrachloride (CCl4), we examined the ability of inhaled MeOH to potentiate CCl4 hepatotoxicity and the time course of injury and recovery. Adult male F-344 rats were exposed to 0 or to 10,000 ppm MeOH by inhalation for 6 h and gavaged with 0.075 ml CCl4/kg 24 h later. Hepatotoxicity was assessed 0.5, 1, 1.5, 2, 3, 7, 15, 30, and 61 d after CCl4 exposure. For CCl4 alone, hepatotoxicity was most severe at 0.5 and 1 d, when minimal centrilobular hepatocellular necrosis and predominately mild centrilobular hepatocellular vacuolar degeneration occurred. By d 3, the livers from the CCl4 rats were histologically normal. For MeOH+CCl4, peak severity of hepatic injury was at 1 and 1.5 d, when moderate centrilobular necrosis and moderate/marked centrilobular degeneration occurred. MeOH+CCl4 resulted in serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) that were increased, relative to CCl4 alone, 171- and 113-fold, respectively, on d 1, and 166- and 140-fold, respectively, on d 1.5. Significant serum elevations in MeOH+CCl4 rats, relative to CCl4 alone rats, were present until d 7 and d 15 for AST and ALT, respectively. By d 3 and d 7, degeneration and necrosis, respectively, due to MeOH+CCl4 were essentially resolved. On d 7, the MeOH+CCl4 hepatic injury consisted mainly of chronic inflammation and centrilobular fibrosis. By d 30, the livers of MeOH+CCl4 rats were histologically normal. These data demonstrate that inhaled MeOH potentiates the hepatotoxicity of orally ingested CCl4, increasing the severity of CCl4 hepatotoxicity as well as the time required for recovery.

Mechanistic studies on the potentiation of carbon tetrachloride hepatotoxicity by methamphetamine

Recent studies have shown that methamphetamine is capable of potentiating the hepatotoxicity of carbon tetrachloride in mice. In the present study, it was found that this potentiation is sensitive to changes in the timing of the methamphetamine dose relative to the administration of carbon tetrachloride. Potentiation of hepatotoxicity, measured using serum alanine aminotransferase (ALT) activity, was observed only if the dose of methamphetamine (15 mg/kg, i.p.) was given with, or 3 h after, the carbon tetrachloride dose (0.005 ml/kg i.p.). No increase in carbon tetrachloride hepatotoxicity was evident when methamphetamine was administered 3 h before the carbon tetrachloride dose, or when given 6 or more hours after carbon tetrachloride. Increased covalent binding of carbon tetrachloride to proteins and lipids, shown previously to occur when methamphetamine and carbon tetrachloride are administered together, was not observed when methamphetamine was administered 3 h after the carbon tetrachloride dose and could not, therefore, account for the increased toxicity resulting from this treatment regimen. Pretreatment with the Kupffer cell inhibitor gadolinium chloride (10 mg/kg i.v.) significantly diminished the potentiation of carbon tetrachloride hepatotoxicity by methamphetamine, suggesting that potentiation by methamphetamine involves, at least in part, a stimulation of Kupffer cells. Mice administered a methamphetamine pretreatment regimen known to induce behavioral sensitization displayed an enhanced potentiation of carbon tetrachloride hepatotoxicity i.e. the extent of potentiation by methamphetamine was increased and the methamphetamine dose required for potentiation was diminished. Mice pretreated with a methamphetamine sensitization regimen were also found to be more responsive to the effects of morphine to enhance carbon tetrachloride hepatotoxicity. These observations suggest that there are important CNS, as well as hepatic, components in the potentiation of carbon tetrachloride-induced liver injury by methamphetamine and perhaps other drugs.

Potentiation of carbon tetrachloride hepatotoxicity by piperine.

The effect of piperine on CCl4-induced hepatotoxicity was investigated in rats. Piperine pretreatment potentiated the hepatotoxicity of CCl4 in a dose-dependent manner. The maximum potentiation occurred when piperine at a dose of 100 mg/kg BW was intragastrically administered 4 h prior to an intraperitoneal injection of CCl4, at which time the activities of plasma glutamic pyruvic transaminase (PGPT) and plasma glutamic oxaloacetic transaminase (PGOT) were elevated by 70-80%. Concurrent with the rise in PGPT and PGOT activities, the accumulation of hepatic triglyceride increased whereas the plasma level of triglyceride decreased. Piperine pretreatment also potentiated CCl4-induced lipid peroxidation in the liver. The extent of potentiation correlated well with the rise of hepatic enzyme activity in plasma. In the in vitro system in which the tissue was preincubated with piperine and CCl4 was added into the incubation medium, piperine also exhibited a concentration dependent potentiation on CCl4-induced lipid peroxidation and on the activity of NADPH-cytochrome c-reductase. The results indicated that piperine potentiated CCl4-induced hepatotoxicity by interacting with liver cells and increased the activity of NADPH-cytochrome c reductase. The increase in activity of this enzyme accelerated biotransformation of CCl4, thereby increasing lipid peroxidation and enhancing hepatotoxicity.

Vitamin A Potentiation of Carbon Tetrachloride Hepatotoxicity: Role of Liver Macrophages and Active Oxygen Species

Pretreatment of rats with large doses of vitamin A (VA) potentiates the hepatotoxicity of CCl 4. Because our previous studies indicate that VA treatment does not enhance CCl 4, metabolism but does enhance CCl 4-induced lipid peroxidation and activates liver Kupffer cells to release increased amounts of oxygen-centered free radicals, the current studies were designed to determine if VA treatment potentiates CCl 4-induced liver injury through increased release of reactive oxygen species. Plasma clearance of colloidal carbon, an index of Kupffer cell phagocytic activity, was enhanced two- to threefold in rats treated for 7 days with VA (retinol, 250,000 IU/kg per day). Accordingly, VA treatment alone caused Kupffer cell activation. To determine if these activated Kupffer cells could potentiate hepatic injury through release of reactive oxygen species upon Cd4 challenge, polyethylene glycol coupled-superoxide dismutase (PEG-SOD, 10,000 IU/kg) or -catalase (PEG-CAT, 40,000 IU/kg) was given iv 2 hr after CCl 4, (0.15 ml/kg, ip) to control or VA-pretreated rats to quench any released reactive oxygen. PEG-SOD and PEG-CAT effectively blocked VA potentiation of CCl 4, liver injury as assessed at 24 hr by change in plasma ALT. Methylpalmitate (MP, 2 g/kg), an inhibitor of Kupffer cell phagocytosis and related oxygen burst, also blocked the potentiation of liver injury when given iv 24 hr before CCI4 to VA-pretreated rats. At the doses used, PEG-SOD or PEG-CAT did not influence CCl 4 toxicity in control rats (at 0.15 or 2 ml CCl 4/kg). Importantly, SOD, CAT, and MP blocked the enhanced lipid peroxidation induced by CCl 4, in VA-pretreated rats. From these findings we conclude that the potentiation of CCl 4, liver injury by VA pretreatment is mediated, at least in part, by active oxygen species released from Kupffer cells and possibly other macrophages that are activated by VA. Supporting this conclusion is the failure of VA pretreatment to increase the release of LDH from suspension of hepatocytes incubated with CCl 4,.

Potentiation of carbon tetrachloride hepatotoxicity by phenylpropanolamine

Hepatic necrosis produced by carbon tetrachloride (0.02, 0.06, or 0.20 ml/kg, ip) in mice was found to be potentiated by simultaneous cotreatment with phenylpropanolamine (200 mg/kg, ip), a drug with catecholamine-like pharmacologic effects. The ability to potentiate carbon tetrachloride-induced hepatic necrosis was shared by a compound with agonist effects relatively selective for α 2-adrenoreceptors (clonidine, 5 mg/kg, ip), but not by specific α 1-adrenoreceptor agonists (phenylephrine, up to 100 mg/kg, ip and methoxamine, up to 50 mg/kg, ip) or by the β-adrenoreceptor agonist isoproterenol (up to 100 mg/kg, ip). Yohimbine (5 mg/kg, ip), a selective α 2-adrenoreceptor antagonist, completely blocked the potentiating effect of phenylpropanolamine on carbon tetrachloride hepatotoxicity, providing further evidence that the increased hepatotoxic response with phenylpropanolamine cotreatment was mediated through α 2-adrenoreceptor stimulation. Four potential mechanisms for phenylpropanolamine potentiation of liver injury from carbon tetrachloride were examined: (1) increased concentrations of carbon tetrachloride in the liver from greater absorption or altered distribution; (2) diminished food consumption leading to a starvation-like increase in responsiveness to carbon tetrachloride; (3) impaired detoxification through a depletion of hepatic glutathione content; and (4) enhanced toxicity produced by elevated core body temperature. None of these potential mechanisms was supported by the experimental results. It is concluded that phenylpropanolamine and related compounds potentiate carbon tetrachloride hepatotoxicity through a mechanism involving α 2-adrenoreceptor stimulation that has yet to be identified.

Potentiation of carbon tetrachloride hepatotoxicity by chlordecone: Dose‐response relationships and increased covalent binding in vivo

Chlordecone greatly potentiates carbon tetrachloride (CCl4) hepatotoxicity. In order to quantitate the degree of this potentiation, the effects of a range of doses of CCl4 on two microsomal enzymatic functions and liver enzyme release were examined in chlordecone-treated and control rats. Male Sprague-Dawley rats were pretreated with 15 mg chlordecone per kilogram body weight (BW) intragastrically or with vehicle. After 48 hours, 0 to 250 microliters CCl4 per 100 g body weight were given intraperitoneally (IP), and the rats were killed 24 hours later. Chlordecone treatment produced approximately a 17-fold potentiation of the CCl4-dependent loss of cytochrome P-450 and glucose-6-phosphatase activity, so that a dose of 6 microliters CCl4 per 100 g body weight in the chlordecone-treated animals resulted in a similar amount of damage as observed with 100 microliters CCl4 per 100 g body weight in controls. A similar potentiation by chlordecone was seen with CCl4 induced increases in serum glutamic-oxaloacetic transaminase (SGOT) levels. Chlordecone treatment also increased hepatic cytochrome P-450 levels by 67% and resulted in an increase in the covalent binding of [14-C]-CCl4-derived metabolites to microsomal protein and lipid in vivo.

Metabolites and ketone body production following methyl n-butyl ketone exposure as possible indices of MnBK potentiation of carbon tetrachloride hepatotoxicity

While the biotransformation of methyl n-butyl ketone (MnBK) in animals is well characterized, little is known about the quantitative relationship between hepatic and plasma MnBK concentrations. This study provides such information and emphasizes the usefulness of MnBK metabolite quantification, as well as MnBK-induced metabolic ketosis for the biological monitoring of MnBK exposure in rats. Elimination of MnBK was followed 24 hr after oral administration (0.95, 1.90, and 5.70 mmol/kg in corn oil) to male Sprague-Dawley rats. Two metabolites [2-hexanol (2HOL), and 2,5-hexanedione (2.5HD)] were also monitored and their kinetics determined. These data were compared to ketone body (KB) concentrations found in plasma and liver during the same period. Plasma concentrations of MnBK and 2,5HD correlated well with those in the liver. This was not the case for 2HOL. MnBK, 2HOL, and 2,5HD were no longer detected in plasma and liver 18 hr after dosing. Meanwhile, a marked ketosis was observed from 12 to 24 hr. This ketotic state was due to an increase in β-hydroxybutyrate (BOHB), while acetoacetate remained at its basal levels. These data indicate that MnBK can induce ketosis in rats and suggest that the resulting BOHB might be used as an alternative biological monitor of MnBK exposures at high concentrations.

Temporal analysis of rat liver injury following potentiation of carbon tetrachloride hepatotoxicity with ketonic or ketogenic compounds

The administration of some ketonic or ketogenic compounds prior to a challenging dose of CCl 4 potentiates the hepatic damage induced by this haloalkane. However, nothing is known about the recovery from the liver injury in these cases of chemically induced potentiation. To investigate this problem, we performed a temporal analysis of the hepatotoxic response of male Sprague-Dawley rats to CCl 4 following a single pretreatment (p.o.) with: n-hexane, 2-hexanone, 2,5-hexanedione (15 mmol/kg in corn oil), isopropanol, acetone (33 and 34 mmol/kg in water, respectively); or the vehicle alone (10 ml/kg). They received, 18 h later, an i.p. injection of CCl 4 (0.1, 0.75 or 1.0 ml/kg) and were killed 24–120 h later. Liver damage was assessed biochemically (ALT, OCT) and morphologically. A good correlation between biochemical and morphological results was observed. The ketonic or ketogenic compounds studied potentiated the liver injury produced by 0.1 ml/kg CCl 4. Relative ranking orders regarding severity of maximal hepatic damage induced and time needed for complete recovery of liver injury were established; time of recovery was dependent on the maximal severity of the lesion, regardless of the potentiation. The results show that the temporal evolution of CCl 4-induced liver injury is not markedly influenced by the administration of ketonic or ketogenic compounds as pretreatments, but rather depends on the severity of the maximal damage induced by the overall treatment.

Ethanol potentiation of carbon tetrachloride hepatotoxicity: Possible role for the in vivo inhibition of aldehyde dehydrogenase

1. 1. A potentiation of CCl 4-induced hepatotoxicity was observed in rats pretreated with ethanol 18 hr prior to CCl 4 exposure. 2. 2. Hepatic microsomal aldehyde dehydrogenase ( pLDH) was significantly inhibited in animals sacrificed 1 hr following the sequential exposure, however, no more so than in those animals receiving CCl 4 alone. 3. 3. The animals receiving ethanol alone had ALDH activity similar to vehicle treated controls. 4. 4. Twenty-four hours following a potentiating dose of ethanol and CCl 4 an 81 and 57% decline in NAD +-dependent microsomal and mitochondrial ALDH activity was observed, respectively. 5. 5. Similar results were observed for microsomal and mitochondrial NADP +-dependent ALDH activity. 6. 6. The decline in membrane-bound ALDH was greater in potentiated animals than in those receiving CCl 4 alone. 7. 7. A relatively smaller decline in cytosolic ALDH activity was observed in CCl 4 treated rats with or without ethanol pre-exposure. 8. 8. The data suggest that inhibition of membrane bound ALDH may be one of the major mechanisms of in vivo potentiation of CCl 4-induced hepatotoxicity by ethanol.

Potentiation of carbon tetrachloride hepatotoxicity by beta-phenethyl alcohol.

Carbon tetrachloride (CCl4)-induced hepatotoxicity was potentiated by pretreatment with beta-phenethyl alcohol, abundantly present in sake. The injury was determined by serum GPT levels and histological examination. Similar results were observed in ethanol- and phenobarbital-pretreated rats. Acetaminophen-induced hepatotoxicity was not accentuated by beta-phenethyl alcohol or ethanol pretreatment. The activities of liver microsomal enzymes, such as cytochrome P-450, cytochrome b5 reductase, aniline hydroxylase and aminopyrine demethylase, were not altered in beta-phenethyl alcohol-pretreated rats. Thus, CCl4-induced hepatotoxicity potentiation by beta-phenethyl alcohol administration is postulated to be due to a mechanism other than increased free radical generation.

Chlordecone-induced potentiation of carbon tetrachloride hepatotoxicity: A morphometric and biochemical study

The present study, conducted over a time course of 36 hr after CCl 4 administration, describes sequential morphometric and biochemical changes which occur in livers of rats exposed to a combination of low levels of chlordecone (10 ppm for 15 days) and a single ip injection of CCl 4 (0.1 ml/kg). Those changes were compared to hepatic alterations which occur in rats that received the same dose of chlordecone or CCl 4 alone. Biochemical studies showed only trivial increases in levels of glutamic-pyruvic transaminase (GPT), glutamic-oxalacetic transaminase (GOT), and moderate but temporary increases in isocitrate dehydrogenase (ICD) after CCl 4 alone. The combination of chlordecone and CCl 4 resulted in significantly greater elevations of all three serum enzymes at all time intervals examined. Morphometric data showed no difference between normal diet controls and animals exposed to chlordecone alone as far as numerical density of hepatocytes or volume densities of hepatocytes with glycogen, lipid, dilated rough endoplasmic reticulum (RER), pyknosis, or mitoses. Morphometric analysis of livers from animals that received CCl 4 alone showed decreases in numerical density, temporary decrease in precentage of hepatocytes containing glycogen, an increase in hepatocytes containing lipid, temporary increase in hepatocytes with dilated RER, and temporary increases in pyknotic nuclei. Soon after the initial hepatic injury was histologically evident between 4 and 6 hr, the number of mitoses increased dramatically and this progressed until complete recovery from CCl 4 damage. From all indices of damage, complete recovery was evident by 36 hr after CCl 4 administration. Morphometric analysis of livers from rats that received the chlordecone + CCl 4 combination showed decrease in numerical density, consistent and progressive decrease in percent of hepatocytes containing glycogen, progressive increase in hepatocytes containing lipid, progressive increase in cells with dilated RER, and a progressive increase in cells with pyknotic nuclei. Number of mitoses remained suppressed, in notable contrast to the animals receiving CCl 4 alone. These studies suggest that two aspects of chlordecone potentiation of CCl 4 hepatotoxicity might be of mechanistic interest: first, the initial, progressive, and remarkably greater CCl 4 injury in chlordecone-treated animals, and second, the mechanism for the suppression or prevention of hepatocellular repair and renovation, which leads to complete recovery of animals receiving CCl 4 alone while leading to total hepatic failure and death of animals receiving the combination treatment.

Chlordecone-induced potentiation of carbon tetrachloride hepatotoxicity: A light and electron microscopic study

Previous studies have shown that a chlorinated pesticide, chlordecone (Kepone), greatly potentiates carbon tetrachloride (CCl 4) hepatotoxicity and lethality (Curtis, L. R., Williams, W. L., and Mehendale, H. M. (1979). Toxicol. Appl. Pharmacol. 51, 283–293; Curtis, L. R., and Mehendale, H. M. (1980). Drug Metab. Dispos. 8, 23–27). The present study describes sequential morphologic changes which occurred in livers of rats given a “nontoxic” level of chlordecone (10 ppm for 15 days) followed by a single injection of CCl 4 (0.1 ml/kg). The hepatic alterations were examined 1 to 36 hr after exposure of the rats to CCl 4. Those changes were compared to hepatic alterations which occurred in rats that received the same dose of chlordecone (10 ppm for 15 days) or a single injection of CCl 4 (0.1 ml/kg) alone. The only change noted in livers from rats that received chlordecone alone was focal increase in smooth endoplasmic reticulum (SER) of hepatocytes at 24 hr and continuing throughout the time course of the experiment. Livers from animals that received CCl 4 alone showed morphologic changes at 6 hr consisting of glycogen loss, increase in SER, and dilatation of rough endoplasmic reticulum (RER) in pericentral hepatocytes. Accumulation of small lipid droplets was also noted in midzonal hepatocytes. After 6 hr, there was no further increase in severity of injury. At 12 hr recovery was noticeable and, by 36 hr, livers from the CCl 4 group appeared normal. Prior administration of chlordecone greatly potentiated pathologic changes in livers of animals that received CCl 4. By 4 hr, there was total loss of glycogen in hepatocytes throughout the entire lobule. Small lipid droplets were present in pericentral, midzonal and periportal hepatocytes. Hepatocytes with extremely dilated RER were randomly scattered throughout the entire lobule. At 6 hr, there was further accumulation of lipid in the form of large droplets in hepatocytes. Focal, necrotic cells surrounded by polymorphonuclear leukocytes were randomly distributed throughout the lobule. The number of necrotic foci had progressively increased at the 12- and 24-hr intervals. By 36 hr, confluent areas of necrosis in pericentral and midzonal areas were observed in livers of some animals. This study indicates that although the combination of chlordecone and CCl 4 produces much greater hepatic injury resembling damage due to a massive dose of CCl 4, histologically, some differences in the progression and distribution of hepatocellular damage within the lobular architecture of the liver are evident.

Phosgene: A possible role in the potentiation of carbon tetrachloride hepatotoxicity by 2-propanol

The metabolism of carbon tetrachloride to chloroform, carbon monoxide, carbon dioxide, and phosgene, as well as carbon tetrachloride-induced lipid peroxidation was studied in control, 2-propanol-, and phenobarbital-treated rats. Different effects were observed following 2-propanol and phenobarbital treatments. 2-Propanol treatment increased phosgene formation but had no effect on carbon tetrachloride-induced lipid peroxidation, while phenobarbital treatment had no effect on phosgene formation and potentiated carbon tetrachloride-induced lipid peroxidation. These data suggest that 2-propanol and phenobarbital treatments alter either the activity or composition of constitutive forms of cytochrome P-450 responsible for the metabolism of carbon tetrachloride and, in addition, suggest that phosgene may play a role in 2-propanol potentiation of carbon tetrachloride hepatotoxicity.

Potentiation of carbon tetrachloride hepatotoxicity in rats by pretreatment with polychlorinated biphenyls

Pretreatment of male rats with Aroclor 1254 at a dose of 25 mg/kg i.p. for 6 days resulted in potentiation of the hepatotoxicity of inhaled carbon tetrachloride (CCl 4) as evidenced by a decrease in liver glucose-6-phosphase and elevations of serum glutamic oxalacetic transaminace (SGOT), serum glutamic pyruvic transaminase (SGPT), isocitrate dehydrogenase, and sorbitol dehydrogenase. Aroclor 1254 alone did not demonstrate hepatotoxicity. Aroclor 1254 administration resulted in large increases in cytochrome c reductase, cytochrome P-450 (448) and p-nitroanisole demethylation. Subsequent exposure to CCl 4 vapor resulted in over 70% decreases in the latter two parameters. The potentiation was dose-dependent with a dose of 5 mg/kg or higher being effective. Aroclor 1260 administration gave results similar to those of Aroclor 1254, but Aroclor 1221 enhanced CCl 4 toxicity to a lesser extent.

Potentiation of carbon tetrachloride hepatotoxicity by ethanol and cold

Carbon tetrachloride (CCl 4) hepatotoxicity was investigated in ethanol-pretreated rats and in rats exposed to cold (18 hr at 4°C). Serum glutamic-pyruvate transaminase (SGPT) activity and liver triglyceride levels were used as indices of hepatotoxicity. In male and female rats the SGPT response to CCl 4 is increased after ethanol or cold exposure. Liver triglyceride accumulation after CCl 4 is not, however, potentiated by either ethanol or cold. Potentiation of the SGPT elevation by ethanol was blocked by pentolinium bitartrate (a ganglionic-blocking agent) and warmth (environmental temperature 31–33°C). Thyroidectomy did not block the potentiating effects of ethanol. The role of the pituitary in the potentiation phenomenon was not clarified because of increased mortality in hypophysectomized rats given ethanol. We postulate that ethanol-induced release of norepinephrine results in increased susceptibility of the liver to CCl 4.