Acute alteration of chloroform-induced hepato- and nephrotoxicity by Mirex and Kepone

Bromotrichloromethane Hepatotoxicity. The Role of Stimulated Hepatocellular Regeneration in Recovery: Biochemical and Histopathological Studies in Control and Chlordecone Pretreated Male Rats

It has been shown that BrCCl3 is a more potent hepatotoxin than CCl4. Pretreatment with nontoxic dietary levels of chlordecone (CD) results in amplification of BrCCl3 hepatotoxicity. The objective of this research was to investigate and compare the histopathological alterations during a time course after a low dose of BrCCl3 alone and in combination with dietary CD. Male Sprague-Dawley rats were maintained on 10 ppm dietary CD or normal diet for 15 days. On day 16, they received a single ip dose (30 μ1/kg) of BrCCl3 in corn oil (CO) vehicle or corn oil alone. Blood and liver samples were collected at 0, 3, 6, 12, 24, 36, 48, 72, 96, and 120 hr for serum enzymes and histopathological examination, respectively. Serum enzymes (SDH, ALT, AST) were significantly ( p < 0.05) elevated in rats receiving the CD + BrCCl3 combination in comparison to BrCCl3 alone. For 48 hr, a continuous increase in serum enzyme activities was detected in rats treated with CD + BrCCl3 combination, but not in the rats receiving other treatments (ND + BrCCl3, ND + CO, or CD + CO). The most extensive hepatolobular necrosis was observed in rats treated with the CD + BrCCl3 combination. Thirty-six hr after the administration of BrCCl3 to rats maintained on normal diet, high mitotic activity was observed, which continued through 72 hr resulting in complete restoration of hepatolobular structure. In contrast, rats receiving the combination of CD + BrCCl3 exhibited minimal and belated hepatomitotic activity for a short period of time, resulting in progressive hepatic failure, culminating in animal death. In conclusion, hepatotoxicity of a low dose of BrCCl3 alone appeared to be overcome via stimulated hepatocellular regeneration and hepatolobular restoration. CD appears to amplify BrCCl3 hepatotoxicity via interference with this hormetic mechanism, permitting a progressive and continued hepatic injury leading to complete hepatic failure, culminating in animal death.

Chlorinated methanes and liver injury: highlights of the past 50 years

The chlorinated methanes, particularly carbon tetrachloride and chloroform, are classic models of liver injury and have developed into important experimental hepatoxicants over the past 50 years. Hepatocellular steatosis and necrosis are features of the acute lesion. Mitochondria and the endoplasmic reticulum as target sites are discussed. The sympathetic nervous system, hepatic hemodynamic alterations, and role of free radicals and biotransformation are considered. With carbon tetrachloride, lipid peroxidation and covalent binding to hepatic constituents have been dominant themes over the years. Potentiation of chlorinated methane-induced liver injury by alcohols, aliphatic ketones, ketogenic compounds, and the pesticide chlordecone is discussed. A search for explanations for the potentiation phenomenon has led to the discovery of the role of tissue repair in the overall outcome of liver injury. Some final thoughts about future research are also presented.

Toxicodynamics of low level toxicant interactions of biological significance: inhibition of tissue repair

Because of the complexity of studying the toxicological effects of mixtures of chemicals, much of the mechanistic information has become available through work with binary mixtures of toxic chemicals. Mechanisms derived from studies employing chemicals at individually nontoxic doses are more useful than the mechanisms of interactive toxicity at high doses from the perspective of environmental and public health. Several examples of chemical combinations and interactive toxicity at low doses are now available. Chlordecone-potentiated halomethane hepatotoxicity, where suppression of cell division and tissue repair response permits very high amplification of CCl4 injury culminating in animal mortality, is one such model. Phenobarbital-potentiated CCl4 injury does not lead to animal mortality in spite of much higher liver injury in comparison to the chlordecone+CCl4 model. Much higher stimulation of tissue repair allows the animals to survive despite higher liver injury. Similar interactions have been reported between alcohols and halomethane toxicants. These and other studies have revealed that infliction of toxicant-induced injury is accompanied by a parallel but opposing tissue repair stimulation response which allows the animals to overcome that injury up to a threshold dose. Beyond this threshold, tissue repair response is both diminished and delayed allowing unrestrained progression of injury. Large doses of chemicals can be predictably lethal owing to these two latter effects on tissue repair. Dose-response paradigms in which tissue repair response is measured as a parallel but opposing effect to toxic injury might be useful in more precise prediction of the ultimate outcome of toxic injury in risk assessment. Autoprotection experiments with CCl4, thioacetamide, 2-butoxyethanol and related chemicals as well as heteroprotection against acetaminophen-induced lethality with thioacetamide are examples where tissue repair stimulation has been shown to rescue the animals from massive and normally lethal liver injury. The concept of toxicodynamic interaction between inflicted injury and stimulated tissue repair offers mechanistic opportunity to fine-tune other aspects of human health risk assessment procedure. Tissue repair mechanisms may also offer a mechanistic basis to explain species and strain differences as well as to more accurately assess inter-individual differences in human sensitivity to toxic chemicals. Because tissue repair is affected by nutritional status, assessment of risk from exposure to chemicals without attention to nutritional status may be misleading. Finally, the concept of using maximum tolerated doses (MTDs) in long-term toxicity studies such as cancer bioassays may need to be re-examined. MTDs might be predictably expected to maximally stimulate cell division and it is known that increased cell division is likely to lead to increased number of errors in DNA replication thereby predisposing these animals to cancer. It is clear that detailed studies of toxicodynamic interaction between tissue injury and stimulated tissue repair are likely to yield significant dividends in fine-tuning risk assessment.

Injury and repair as opposing forces in risk assessment

Recent advances in our understanding of the toxicodynamic events that follow infliction of injury have helped us to bridge the link between the tissue injury and the final outcome of that injury. In addition to infliction of tissue injury, toxic chemicals induce a biological compensatory response of tissue repair intended to overcome tissue injury through healing. Since stimulation of tissue repair is a simultaneous response accompanying injury, measuring this response in addition to quantifying injury might be helpful in tomorrow's risk assessment. Studies with model hepatotoxicants such as thioacetamide and CCl4, where tissue repair as well as injury were measured, reveal that endogenous mechanisms that drive the tissue repair response are responsible for more than just compensation for tissue injury. Up to a threshold dose, tissue repair is stimulated in a dose-dependent manner, and above this threshold it is both delayed and diminished. During this delay, tissue injury progresses unabated leading to tissue destruction and animal death. While dose-related stimulation of tissue repair leads to recovery, delayed and diminished tissue repair seen at the high doses leads to tissue destruction and animal death. These findings impact on the currently used maximum tolerated doses (MTDs) in cancer bioassays. MTDs represent maximal stimulation of cell proliferation thereby enhancing the likelihood of errors in DNA replication. Measuring tissue repair and injury as simultaneous biological responses to toxic agents might increase the usefulness of dose-response paradigms in risk assessment.

ATSDR evaluation of health effects of chemicals. II. Mirex and chlordecone: health effects, toxicokinetics, human exposure, and environmental fate

This document provides public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective of the toxicology of mirex and chlordecone. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health. Additional substances will be profiled in a series of manuscripts to follow.

Ketone potentiation of haloalkane-induced hepato- and nephrotoxicity. I. Dose-response relationships

Carbon tetrachloride (CCl4) induced hepatotoxicity and chloroform (CHCl3) induced nephrotoxicity were evaluated in male Sprague-Dawley rats pretreated with acetone (A), methyl ethyl ketone (MEK), and methyl isobutyl ketone (MiBK). Dose-response relationships for A, MEK, and MiBK potentiation of CCl4-induced hepatotoxicity and CHCl3-induced nephrotoxicity were compared. A, MEK, and MiBK pretreatment at a dosage of 6.8 mmol/kg, given daily for 3 d, markedly potentiated CCl4-induced liver toxicity as indicated by a decrease in the CCl4 ED50 to 3.4, 4.6, and 1.8 mmol/kg, respectively, compared to vehicle-pretreated rats (17.1 mmol/kg). Similarly, pretreatment with these ketones (13.6 mmol/kg) potentiated CHCl3 kidney toxicity but to a lesser degree; CHCl3 ED50 values for vehicle-, A-, MEK-, and MiBK-pretreated rats were 3.4, 1.6, 2.1, and 2.2 mmol/kg, respectively. Our results indicate a potency ranking profile for the potentiation of CCl4 hepatotoxicity of MiBK > A > MEK and of A > MEK > or = MiBK for CHCl3 nephrotoxicity. These dissimilar ranking profiles could be due to differences in mechanisms of action for the two target sites.

Potentiation of halomethane hepatotoxicity by chlordecone: a hypothesis for the mechanism

A major toxicological issue today is the possibility of unusual toxicity due to interaction of toxic chemicals upon environmental or occupational exposures to two or more chemicals, at ordinarily harmless levels individually. While some laboratory models exist for such interactions for the simplest case of only two chemicals, progress in this area has suffered for want of a model where the two interactants are individually nontoxic. One such model is available, where prior exposure to nontoxic levels of the pesticide Kepone (chlordecone) results in a 67-fold amplication of CCl4 lethality in rats. Extensive hepatotoxicity observed in this interaction is characterized by histopathological alterations, perturbation of related biochemical parameters and is followed by complete hepatic failure. This propensity for chlordecone to potentiate hepatotoxicity of halomethanes such as CCl4, CHCl3, and BrCCl3 has been a subject of intense study to unravel the underlying mechanism. Mechanisms such as induction of microsomal cytochrome P-450 by chlordecone and greater lipid peroxidation are inadequate to explain the remarkably powerful potentiation of halomethane toxicity. Compelling experimental evidence supports the hypothesis that hepatocellular division during early time points after the administration of CCl4 is an important determinant of the progression (or repair of it) of the liver injury and consequent destruction (or restoration) of the hepatolobular architecture and function. This paper advances a hypothesis for the mechanism of hepatotoxic and lethal effect of CCl4 as being primarily related to the accelerated progression of liver injury due to suppressed hepatocellular regeneration and hepatolobular restoration. This is in contrast to the widely accepted putative mechanism, one which invokes only bioactivation followed by runaway lipid peroxidation as the events determining the course of the progressive phase of liver injury. The concept being advanced in this paper accepts bioactivation (and perhaps lipid peroxidation) as the primary initiating events of cell injury, but maintains that they are not the determinants of the progressive phase of liver injury. The biological issue of whether the cells are incapacitated from regenerating is the determinant of the progression of liver injury, and therefore, the ultimate outcome of hepatotoxicity and lethality.

Cytochrome P-450-dependent formation of reactive oxygen radicals: isozyme-specific inhibition of P-450-mediated reduction of oxygen and carbon tetrachloride

1. Ethanol-inducible P450 IIE1 exhibits a high rate of oxygen consumption and oxidase activity. The enzyme is selectively distributed in the liver centrilobular area, the acinar region specifically destroyed after treatment with P450 IIE1 substrates/inducers such as ethanol, carbon tetrachloride, chloroform, N-nitrosodimethylamine and paracetamol. 2. Twenty substrates and ligands for cytochrome P450 IIB4 and P450 IIE1 were evaluated for their ability to inhibit microsomal and reconstituted NADPH-dependent oxidase activity, and the P450 IIE1-catalysed reduction of carbon tetrachloride to chloroform. Type I ligands and substrates did not inhibit the processes whereas nitrogen-containing compounds such as octylamine, cimetidine, imidazole and tryptamine inhibited NADPH oxidation and H2O2 formation in microsomes from starved and acetone-treated rats by around 50%. 3. Tryptamine, octylamine, isoniazid and p-chloroamphetamine inhibited reconstituted P450 IIE1-dependent oxidase activity with half maximal effects at 14-170 microM. 4. Isoniazid, cimetidine and tryptamine inhibited the P450 IIE1-dependent reduction of carbon tetrachloride, whereas acetone was without effect. 5. The oxygen dependency of microsomal oxidase activity exhibited high-affinity and low-affinity phases, with partial saturation at 20 microM of O2. 6. It is concluded that microsomal oxidase activity takes place at physiological concentrations of O2 and that isozyme-specific type II ligands compete with oxygen or carbon tetrachloride for reduction by P-450 haem.

Bromotrichloromethane hepatotoxicity. The role of stimulated hepatocellular regeneration in recovery: biochemical and histopathological studies in control and chlordecone pretreated male rats

It has been shown that BrCCl3 is a more potent hepatotoxin than CCl4. Pretreatment with nontoxic dietary levels of chlordecone (CD) results in amplification of BrCCl3 hepatotoxicity. The objective of this research was to investigate and compare the histopathological alterations during a time course after a low dose of BrCCl3 alone and in combination with dietary CD. Male Sprague-Dawley rats were maintained on 10 ppm dietary CD or normal diet for 15 days. On day 16, they received a single ip dose (30 microliters/kg) of BrCCl3 in corn oil (CO) vehicle or corn oil alone. Blood and liver samples were collected at 0, 3, 6, 12, 24, 36, 48, 72, 96, and 120 hr for serum enzymes and histopathological examination, respectively. Serum enzymes (SDH, ALT, AST) were significantly (p less than 0.05) elevated in rats receiving the CD + BrCCl3 combination in comparison to BrCCl3 alone. For 48 hr, a continuous increase in serum enzyme activities was detected in rats treated with CD + BrCCl3 combination, but not in the rats receiving other treatments (ND + BrCCl3, ND + CO, or CD + CO). The most extensive hepatolobular necrosis was observed in rats treated with the CD + BrCCl3 combination. Thirty-six hr after the administration of BrCCl3 to rats maintained on normal diet, high mitotic activity was observed, which continued through 72 hr resulting in complete restoration of hepatolobular structure. In contrast, rats receiving the combination of CD + BrCCl3 exhibited minimal and belated hepatomitotic activity for a short period of time, resulting in progressive hepatic failure, culminating in animal death. In conclusion, hepatotoxicity of a low dose of BrCCl3 alone appeared to be overcome via stimulated hepatocellular regeneration and hepatolobular restoration. CD appears to amplify BrCCl3 hepatotoxicity via interference with this hormetic mechanism, permitting a progressive and continued hepatic injury leading to complete hepatic failure, culminating in animal death.

Evidence for the involvement of organelles in the mechanism of ketone-potentiated chloroform-induced hepatotoxicity

Ketones can potentiate the hepatotoxicity of haloalkanes in animals. This may be due, in part, to changes in organelle susceptibility. Male Sprague-Dawley rats were administered 15 mmol/kg (po) acetone, 2-butanone, 2-hexanone or 50 mg/kg (po) chlordecone or mirex (a nonketonic analog of chlordecone). Eighteen hours later, tests of organelle structure/function were performed (osmotic stress, respiration, and calcium pump activity). Other rats were given 14CHCl3 (0.5 or 1.0 ml/kg, po) 18 h after chlordecone or mirex administration. Three hours later, the organelle distribution of 14C was evaluated. In a final experiment, ketone-pretreated (chlordecone or 2-hexanone) animals were killed 6 h after CHCl3 administration and evaluated morphologically for evidence of modified organelle response. Acetone and chlordecone, when given alone, enhanced lysosomal fragility to osmotic stress; no changes in functional capacity of mitochondria or microsomes were observed. CHCl3-derived 14C in the mitochondrial fraction increased 2-fold in chlordecone-treated rats. Morphological evaluation suggested mitochondria respond differently to CHCl3 in ketone-pretreated (chlordecone or 2-hexanone) animals compared to corn oil-pretreated controls. These results support the concept that modifications of organelles contribute to the mechanism of ketone-potentiation of CHCl3-induced hepatotoxicity.

Mechanism of the lethal interaction of chlordecone and CCl4 at non-toxic doses

There is significant interest in the possibility of unusual toxicity due to interaction of toxic chemicals upon environmental or occupational exposures even though such exposures may involve levels ordinarily considered harmless individually. While many laboratory and experimental models exist for such interactions, progress in this area of toxicology has suffered for want of a model where the interactants are individually non-toxic. We developed such a model where prior exposure to non-toxic levels of the pesticide Kepone (chlordecone) results in a 67-fold amplification of CCl4 lethality in experimental animals. The mechanism(s) by which chlordecone amplifies the hepatotoxicity of halomethanes such as CCl4, CHCl3, and BrCCl3 has been a subject of intense study. The biological effects of this interaction include extensive hepatotoxicity characterized by histopathological alterations, hepatic dysfunction, and perturbation of related biochemical parameters. Close structural analogs of chlordecone such as mirex and photomirex do not share the propensity of chlordecone to potentiate halomethane toxicity. Mechanisms such as induction of microsomal cytochrome P-450 by chlordecone and greater lipid peroxidation are inadequate to explain the remarkably powerful potentiation of toxicity and lethality. Time-course studies in which liver tissue was examined 1-36 h after CCl4 administration were conducted. While animals receiving a normally nontoxic dose of CCl4 alone show limited hepatocellular necrosis by 6 h, proceeding to greater injury after 12 h, recovery phase ensues as revealed by greatly increased number of mitotic figures. Such regeneration and hepatic tissue repair processes are totally suppressed in animals exposed to chlordecone prior to CCl4. Thus, the arrested hepatocellular repair and renovation play a key role in the potentiation of CCl4 liver injury by chlordecone. These findings have allowed us to propose a novel hypothesis for the mechanism of chlordecone amplification of halomethane toxicity and lethality. While limited injury is initiated by the low dose of CCl4 by bioactivation followed by lipid peroxidation, this normally recoverable injury permissively progresses due to arrested hepatocellular regeneration and tissue repair processes. Recent studies designed to test this hypothesis have provided additional supporting evidence. Hepatocellular regeneration stimulated by partial hepatectomy was unaffected by 10 ppm dietary chlordecone, while these animals were protected from the hepatotoxic and lethal actions of CCl4 if administered at the time of maximal hepatocellular regeneration. The protection was abolished when CCl4 was administered upon cessation of hepatocellular regeneration.

The time course of liver injury and [3H]thymidine incorporation in chlordecone-potentiated CHCl3 hepatotoxicity

The mechanism by which chlordecone (CD) potentiates CHCl3 hepatotoxicity and lethality remains unknown. We examined the time course of the hepatotoxicity by following serum enzymes, liver histopathology, hepatocellular regeneration, and tissue repair by morphometric analysis and [3H]thymidine (3H-T) incorporation into nuclear DNA. Male mice fed control, or CD (10 ppm), mirex (Mx. 10 ppm), or phenobarbital (PB. 225 ppm) diets for 15 days and receiving a single ip dose of 0.1 ml CHCl3/kg in corn oil vehicle were used. Liver damage was assessed by plasma alanine and aspartate transaminases and by histopathology at 4, 12, 24, 36, 48, 72, and 96 hr after CHCl3 administration. None of the dietary pretreatments caused plasma transaminase elevations, any liver necrosis, or any increase in 3H-T incorporation in nuclear DNA at any time. CHCl3 alone caused only limited hepatocellular necrosis without any increase in plasma transaminases. The same dose of CHCl3 given to CD-pretreated mice resulted in greatly increased liver injury. Plasma transaminases were elevated starting at 4 hr, reaching a maximum value at 12 hr and a decline starting at 48 hr. Centrilobular and midzonal necroses were evident at 12 hr onward. PB pretreatment caused some increase in CHCl3-induced necrosis and a moderate rise in transaminases at 24 hr, but Mx pretreatment caused neither effect. 3H-T incorporation was increased at 72 and 96 hr after CHCl3 alone. The same dose of CHCl3 caused only a modest increase in PB and Mx and a significant and maximal biphasic increase at 36 and 72 hr CD-pretreated mice. Morphometry of liver sections indicated that hepatocellular regeneration is stimulated at 72 hr after CHCl3 alone. The same dose of CHCl3 results in a greater stimulation of hepatocellular regeneration in CD-pretreated mice, and this event is pushed forward at 48 hr, continuing through 96 hr to compensate for greater hepatocellular necrosis associated with this treatment. Lesser stimulation of hepatocellular regeneration was observed in PB + CHCl3 and Mx + CHCl3 groups of mice consonance with much lesser hepatotoxicity. These results suggest that the critical decisive event in the recovery from limited hepatocellular injury is the hepatocellular regeneration and tissue repair, which appear to be stimulated in proportion to the injury.

In vivo metabolism of CCl4 by rats pretreated with chlordecone, mirex, or phenobarbital

The propensity of chlordecone (CD) to potentiate hepatotoxic and lethal effects of CCl4 is well established. Mirex (M), a close structural analogue of CD, or phenobarbital (PB), powerful inducers of hepatic microsomal drug metabolizing enzymes, are much weaker potentiators of CCl4 toxicity. The purpose of this study was to test the possibility that CD potentiates the toxicity of CCl4 by increasing the metabolism of CCl4 to a greater degree than either PB or M. We compared the in vivo metabolism of CCl4 in rats pretreated with CD, M, or PB, by measuring the hepatic content of 14CCl4, the expiration of 14CCl4, expiration of 14CCl4-derived 14CO2, and lipid peroxidation. Male Sprague-Dawley rats (250-270 g) were pretreated with a single oral dose of CD (10 mg/kg), M (10 mg/kg), or corn oil vehicle (1 ml/kg). PB pretreatment consisted of an ip injection of sodium PB (80 mg/kg) in saline (0.9%) for 2 successive days. Twenty-four hours later, 14CCl4 (0.1 ml/kg; sp act: 0.04 mCi/mmol) was administered ip in corn oil and the radioactivity present in the expired air was collected for 6 hr. Excretion of the parent compound as represented by the 14C label in the toluene trap was unchanged by any of the pretreatments. Expiration of 14CO2 measured during the 6 hr after CCl4 administration was increased in animals pretreated with PB or CD. In vivo lipid peroxidation measured as diene conjugation in lipids extracted from the livers was increased to a similar extent in animals pretreated with PB and CD, whereas the serum transaminases (ALT, AST) were significantly elevated only in animals pretreated with CD.M did not affect 14CO2 production and was without a significant effect on the lipid peroxidation. The radiolabel present in the liver at 6 hr showed no difference in hepatic content of free 14CCl4 among the groups, but the covalently bound label present in the lipid fractions of the livers pretreated with PB was elevated in comparison to CD and M treatments. These data indicate that a single oral administration of CD (10 mg/kg) 24 hr prior to CCl4 administration (100 microliter/kg) enhances the oxidative metabolism of CCl4 but to a lesser extent than PB (80 mg/kg, ip, twice), which is in inverse relationship to the potentiation of the hepatotoxic and lethal effects of CCl4 associated with these pretreatments.

Amplification of chloroform hepatotoxicity and lethality by dietary chlordecone (kepone) in mice

Male Swiss Webster mice (25-30 g) maintained on powdered control diet, or on diets containing chlordecone (CD, 10 ppm), mirex (M, 10 ppm), or phenobarbital (PB, 225 ppm) were used in this study. At these low levels, chlorinated hydrocarbon pesticides are not toxic, they neither affect food or water consumption, nor the body weight of mice. After a 15-day dietary protocol, a single challenge dose of CHCl3 (0.1 ml/kg) was administered intraperitoneally in corn oil vehicle. Liver damage was assessed 24 hours later using serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities, histopathology, and lethality. For comparison, serum enzymes were measured in a separate group of mice receiving a high dose of CHCl3 (1.0 ml/kg) alone. None of the dietary treatments alone affected any of the serum transaminases. The serum enzymes were remarkably elevated in the mice treated with CD and CHCl3. A high dose of CHCl3 (1.0 ml/kg) elevated the serum enzymes more than 10-fold over those in the mice fed normal diet receiving only the corn oil vehicle. The histopathology of the liver indicated midzonal necrosis typical of liver injury from CHCl3 and depletion of PAS positive glycogen deposits. These effects were not evident in mice treated with 0.1 ml/kg CHCl3 alone. Additional histological alterations in the livers of the CD + CHCl3 group include the degenerated cells, loss of basophilic staining characteristics, and an increased degree of cytoplasmic vacuolation. The amplification of CHCl3 hepatotoxicity by CD was also reflected by a 4.2-fold increase in lethality determined by 48-hour LD50.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effect of chlordecone and mirex on the acute hepatotoxicity of acetaminophen in mice

1. Acetaminophen toxicity, as measured by leakage of intracellular enzymes, was increased by chlordecone and mirex with mirex having the greater effect. 2. These effects were confirmed by histological examination and by studies of enzyme leakage from isolated hepatocytes.

Taurolithocholate-induced intrahepatic cholestasis: potentiation by methyl isobutyl ketone and methyl n-butyl ketone in rats

Haloalkane-induced hepatonecrogenesis can be potentiated by the prior administration of methyl isobutyl ketone (MIBK) and methyl n-butyl ketone (MBK). We investigated the possibility that these ketones could potentiate the cholestasis induced by taurolithocholate (TLC) in rats. Daily ketone pretreatment for 3 or 7 days resulted in an enhancement of the diminution in bile flow observed after TLC challenge. When the ketones were administered without TLC challenge, cholestasis was not observed; in fact, slight increases in bile flow did occur. The data suggest that MIBK may be more effective than MBK as a potentiator. Preliminary experiments with 2,5-hexanedione (HD), a metabolite of MBK and a potent potentiator of haloalkane hepatonecrosis, were included in the study. HD appeared to be a less potent potentiator of TLC-induced cholestasis. Although some ketones can potentiate cholestatic as well as hepatonecrogenic reactions, different mechanisms of action appear to be involved in these two phenomena.

The joint neurotoxic action of inhaled methyl butyl ketone vapor and dermally applied O-ethyl O-4-nitrophenyl phenylphosphonothioate in hens: potentiating effect

The neurotoxic action of inhaled technical grade methyl butyl ketone and dermally applied (O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN) was studied. Three groups of five hens each were treated 5 days/week for 90 days with a dermal dose of 1.0 mg/kg of EPN (85%) on the unprotected back of the neck. These groups were exposed simultaneously to 10, 50, or 100 ppm of technical methyl butyl ketone (MBK; methyl n-butyl ketone:methyl isobutyl ketone, 7:3) in inhalation chambers. A fourth group was treated only with the dose of EPN and a fifth group with only 100 ppm MBK. The control consisted of a group of five hens treated with a dose of 0.1 ml acetone. Treatment was followed by a 30-day observation period. Simultaneous exposure to EPN and MBK greatly enhanced the neurotoxicity produced when compared to the neurotoxicity produced by either chemical when applied alone. Continued exposure to EPN and MBK resulted in earlier onset and more severe signs of neurotoxicity than exposure to either individual compound. The severity and characteristics of histopathologic lesions in hens given the same daily dermal dose of EPN in combination with inhaled MBK depended on the MBK concentration. Histopathologic changes were more severe and prevalent in the 100 ppm MBK:1 mg/kg EPN group than in the others. In this group, Wallerian-type degeneration was seen along with paranodal axonal swellings. The morphology and distribution of these lesions were characteristic of those induced by MBK. In the 50 ppm MBK:1 mg/kg EPN group axonal swelling was evident but not clearly identifiable as paranodal. Hens treated with 10 ppm MBK:1 mg/kg EPN had minimal lesions with low incidence of axonal swellings. These were not as large as those seen in MBK neurotoxicity, but instead resembled the histopathologic lesions caused by EPN. The results indicate that the combined treatment gave a value for neurotoxicity coefficient which was two times the additive neurotoxic effect of each treatment alone. Pretreatment with three daily ip doses of 5 mmol/kg technical grade MBK or methyl n-butyl ketone (MnBK), equally increased chicken hepatic microsomal cytochrome P-450 content. Also, hepatic microsomes from MBK-treated hens metabolized [14C]EPN in vitro to [14C]EPN oxon to a much greater extent than those from control hens. These results suggest that MBK potentiates the neurotoxic effect of EPN, at least in part, by increasing the metabolic activation of EPN to the more neurotoxic metabolite EPN oxon.(ABSTRACT TRUNCATED AT 400 WORDS)

Dose-response relationships in ketone-induced potentiation of chloroform hepato- and nephrotoxicity

Chloroform (CHCl3)-induced hepato- and nephrotoxicity was evaluated in male, Fischer 344 rats pretreated with various dosages (1.0 to 15.0 mmol/kg, po) of acetone (Ac), 2-butanone (Bu), 2-pentanone (Pn), 2-hexanone (Hx), or 2-heptanone (Hp). The CHCl3 challenge dosage (0.5 ml/kg, ip) produced slight centrilobular hydropic degeneration and patchy degeneration and necrosis in the proximal tubules of corn oil-pretreated rats. Each of the ketones studied produced a dose-related potentiation of CHCl3 liver and kidney injury. CHCl3 produced extensive tubular and centrilobular necrosis when administered to ketone-pretreated rats. The relationship between ketone dosage and the magnitude of the potentiated response was nonlinear. Maximum potentiation of CHCl3 toxicity occurred in the dosage range of 5.0 to 10.0 mmol ketone/kg. Ketone dosages greater than 10.0 mmol/kg were associated with a reduction in the degree of CHCl3 injury. At the lowest ketone dosage (1.0 mmol/kg), potentiating capacity appeared to be related to ketone carbon skeleton length. No differences in potentiating capacity were discernable between the ketones at dosages of 5.0 to 10.0 mmol/kg. Thus, whether or not there is a relationship with carbon chain length and potentiation depends upon the dosage of the ketone.

Mechanisms in 2-hexanone potentiation of chloroform hepatotoxicity

2-Hexanone (2-Hx) is known to potentiate chloroform (CHCl3) hepatotoxicity in part by increasing the bioactivation of CHCl3 to phosgene (COCl2). Treatment of rats with 2-Hx + CHCl3 in vivo did not initiate peroxidation of hepatic fatty acids as determined by formation of conjugated dienes or depletion of unsaturated fatty acids, or as determined by production of malondialdehyde (MDA) in vitro. A 5-fold decrease in the specific activity of succinate-dependent cytochrome c reductase in liver from rats treated in vivo with corn oil (vehicle) + CHCl3 and in rats treated with 2-Hx + CHCl3 indicated that a mechanism independent of CHCl3 bioactivation may add to the hepatotoxic effects which result from the metabolism of chloroform to phosgene.

Hepatic microsomal p-nitroanisole O-demethylase. Effects of chlordecone or mirex induction in male and female rats

The effects of chlordecone (CD) or mirex treatment on the hepatic microsomal monooxygenase system of male and female rats were investigated, and kinetic parameters (apparent Vmax and apparent Km) for p-nitroanisole O-demethylase were studied in detail. Both pesticides elevated the levels of cytochrome P-450 in a time- and dose-dependent manner. The maximum rate of p-nitroanisole metabolism in males was increased about 100 and 50% and the apparent Km was elevated about 40- and 18-fold by CD and mirex respectively. p-Nitroanisole metabolism in females was reduced slightly by treatment with either agent, and the apparent Km was increased about 14-fold by CD but was relatively unaffected by mirex treatment.

Destruction of hepatic mixed-function oxygenase parameters by CCl4 in rats following acute treatment with chlordecone, Mirex, and phenobarbital

Previous work has established the marked potentiation of CCl4 hepatoxicity by prior exposure to chlordecone (CD). This study was conducted to determine if prior exposure to CD results in enhancement of CCl4-induced destruction of the hepatic microsomal mixed-function oxygenase (MFO) system. Male Sprague-Dawley rats received a single oral dose of CD (10 mg/kg) or corn oil vehicle alone (1 ml/kg) 24 hr prior to a single ip injection of CCl4 (0-100 microliter/kg). Mirex (M; 10 mg/kg) and phenobarbital (PB; 80 mg/kg/day for two days) were used as negative and positive controls respectively for the potentiation of CCl4 hepatotoxicity. Hepatotoxicity was evaluated 24 hrs after CCl4 administration by elevations of three serum enzymes (GPT, GOT, and ICD). The key hepatic microsomal MFO parameters measured were microsomal protein, cytochrome P-450 content, glucose-6-phosphatase (G-6-Pase), and aminopyrine demethylase (APD). As previously demonstrated using a subchronic dietary pretreatment protocol, CD potentiated CCl4 hepatotoxicity over a range of CCl4 doses to a greater extent than PB or M, as judged by elevations in serum enzymes. PB caused the greatest increase in total P-450 content and the greatest increase in CCl4-mediated destruction of microsomal protein and APD activity. M caused the least destruction of total hepatic cytochrome P-450, despite the same level of cytochrome P-450 as in the PB group. CD treatment caused the greatest decrease in G-6-Pase activity in comparison to PB or M pretreatments and a similar degree of P-450 destruction as observed with the PB group. These findings suggest that in general, CCl4-induced destruction of hepatic MFO parameters measured in this study is disproportional to the known degree of potentiated hepatotoxicity by the pretreatments and does not accurately reflect the potentiation of CCl4 hepatotoxicity by CD.

Comparison of the effects of methyl-N-butyl ketone and phenobarbital on rat liver cytochromes P-450 and the metabolism of chloroform to phosgene

It was previously shown that treatment of rats with methyl-n-butyl ketone (MBK) produced an increase in the total level of liver microsomal cytochromes P-450 and an increase in the rate of metabolism of chloroform (CHCl3) to phosgene (COCl2). In the present study it was found that MBK also produced qualitative changes in the composition of microsomal cytochromes P-450 in rat liver as determined by anion-exchange chromatography. The degree of the chromatographic changes paralleled the effect of MBK on the rate of metabolism of CHCl3 to COCl2 and CHCl3-induced hepatotoxicity, suggesting that MBK potentiated the hepatotoxicity of CHCl3, at least in part, by inducing the formation of cytochromes P-450 that metabolized CHCl3 to the hepatotoxin COCl2. In this regard, reconstitution studies with a form of cytochrome P-450 isolated from rat liver microsomes from rats treated with MBK or phenobarbital (Pb) showed unequivocally that cytochrome P-450 can metabolize CHCl3 to COCl2. Although analysis of rat liver microsomes by SDS-polyacrylamide electrophoresis and anion-exchange chromatography suggested that MBK and Pb had similar effects on the composition of cytochromes P-450, metabolism studies indicated that differences did exist.

A semiquantitative morphologic assessment of chlordecone-potentiated chloroform hepatotoxicity

A semiquantitative morphologic procedure has been applied to chlordecone potentiation of CHCl3-induced liver injury in male Sprague-Dawley rats. The distance of the injured area from the terminal hepatic venule (THV) to the portal area was measured and the damaged cells were classified by type. The results were plotted graphically, along with elevations in plasma enzyme activities (GPT and OCT), to depict the pattern of damage. Chlordecone pretreatment enhanced the severity of the CHCl3-induced cellular changes and increased the number of cells affected. Dosages of 5 mg/kg of chlordecone did not potentiate CHCl3 toxicity, but higher dosages (10-50 mg/kg) enhanced the toxic response in a dose-dependent manner.

Possible nephrotoxic effect of carbon tetrabromide and its interaction with chlordecone

The hepatotoxic and nephrotoxic effects of CBr4 were studied in male Sprague-Dawley rats following a single i.p. administration in a dose range of 25 to 125 microliter/kg to animals maintained for 15 days either on normal diet or a diet containing 10 ppm chlordecone (CD). At these doses, CBr4 did not cause hepatotoxic effects when given alone or in combination with prior exposure to CD. CBr4 caused renal dysfunction characterized by oliguria, aciduria and hypo-osmolality, and these effects were abolished by dietary CD pretreatment. In vitro incubation of renal cortical slices obtained from CBr4-treated animals revealed a significant depression of organic anion transport, i.e., decreased transport of p-aminohippurate (PAH). Organic cation transport was unaffected as judged by accumulation of tetraethylammonium (TEA). CBr4-induced renal dysfunction appeared unrelated to depressed PAH transport since CD pretreatment which abolished renal dysfunction failed to restore PAH transport. These results show that CD does not potentiate CBr4 hepatotoxicity and the nephrotoxic effects of this halomethane are abolished by prior exposure to CD.

Potentiation of CCl4 hepatotoxicity and lethality by chlordecone in female rats

Female Sprague-Dawley rats (175-200 g) were maintained on a commercial powdered rat chow containing 0 or 10 ppm chlordecone (Kepone; CD). On day 15 of the dietary protocol, a single dose of CCl4 (5-100 microliters/kg) was administered i.p. in corn oil vehicle. Controls received corn oil vehicle only. Twenty-four hours after CCl4 administration, hepatotoxicity was assessed using biochemical, functional, and histopathological parameters. Serum enzymes (GPT, GOT, ICD and OCT) were elevated in a dose related manner in the animals receiving CD-CCl4 combination. CCl4 alone at the doses used had no marked effect. Centrilobular necrosis was observed in the animals receiving CD-CCl4 combination. Biliary excretion of phenolphthalein glucuronide (PG) and the rate of bile flow were decreased in a dose-dependent manner. Forty-eight hour LD50 of CCl4 was decreased 26-fold by CD pretreatment. These results indicate that CD potentiates CCl4 toxicity in female rats as well. Since the hepatic functional status is greatly compromised, the CD potentiated lethality is preceded by hepatic failure. Furthermore, female rats are sensitized to smaller doses of CCl4 in comparison to male rats.

Absence of potentiation of bromoform hepatotoxicity and lethality by chlordecone

Our previous studies indicated that the toxicity of chloro- or bromo-methanes is potentiated by chlordecone (CD). The present work was conducted to study the effect of prior dietary exposure to CD on toxicity of bromoform. Male S-D rats (175-200 g) were fed 0 or 10 ppm CD in the powdered ration for 15 days. Bromoform (25 to 300 microliters/kg) was given i.p. on day 15. 24 h later, hepatotoxicity was assessed by functional, biochemical and histopathological parameters. Excretion of phenolphthalein glucuronide in bile and the rate of bile flow were unaltered by either bromoform or CD-bromoform combination. Serum enzymes (GPT, GOT and isocitric dehydrogenase (ICD) were also not significantly elevated by any treatment. The results suggest that, unlike chloroform, CHBr3 does not act as a potent hepatotoxin and that its effects are not potentiated by CD to any significant extent.

Chlordecone-induced fat depletion in the male rat

The principal objective of this study was to quantitate the anatomical and biochemical parameters associated with the depletion of body fat by the pesticide, chlordecone (CD, or Kepone). Groups of 5 male Sprague-Dawley rats (150-175 g) were fed a control diet or a diet containing 100 ppm CD for 5, 15, or 20 d. After the treatment period, animals were killed by exsanguination. Weight of the period epididymal fat pads was taken as the anatomical marker for the depletion of body fat. Blood levels of acetoacetate, 3-hydroxybutyrate, and nonesterified fatty acids (NEFA) were measured as biochemical as biochemical markers for lipolysis of body fat depots. Serum enzymes (SGPT, ICD) and serum triglycerides were measured to assess liver damage. A consistent and significant difference was observed in the weight of epididymal fat pads between the control and each of the treatment groups. The reduction in epididymal fat reached a maximum of 60% in the CD-fed animals after 20 d. Circulating ketone bodies were not different in any of the treated-animal groups, indicating that CD treatment does not result in metabolic ketosis. Serum triglycerides and NEFA levels were not significantly different in treatment groups versus in controls. Serum transaminases and isocitrate dehydrogenase were not elevated by exposure to CD. These findings indicate that metabolic ketosis is not induced by dietary exposure to CD. Utilization of lipids as energy substrates appears to be the primary underlying mechanism responsible for the loss of body fat observed in CD-treated rats. It appears that CD induces a depletion of body fat stores as a consequence of altered energy balance of the animal.

Role of biotransformation in the potentiation of halocarbon hepatotoxicity by 2,5-hexanedione

2,5-Hexanedione (2,5-HD) pretreatment potentiated CHCl3-induced hepatotoxicity. 2,5-HD significantly increased hepatic cytochrome P-450, NADPH cytochrome c reductase, aniline hydroxylation, p-nitroanisole O-demethylation, and aminopyrine N-demethylation in both male and female mice. 2,5-HD pretreatment potentiated CHCl3-induced centrilobular necrosis and increased serum alanine amino transferase (ALT) activity by 20 times more than CHCl3 alone. Similarly, 2,5-HD pretreatment potentiated CDCl3-induced hepatotoxicity as well as CCl4-induced hepatotoxicity in male mice, but did not potentiate trichloroethylene-, 1,1,2-trichloroethane-, or perchloroethylene-induced hepatotoxicity. In female mice, 2,5-HD pretreatment potentiated CHCl3- and CDCl3-induced hepatotoxicity as well as trichloroethylene-, 1,1,2-trichloroethane-, and carbon tetrachloride-induced hepatotoxicity, but not perchloroethylene-induced hepatotoxicity. 2,5-HD pretreatment had no preferential effect on either CHCl3- or CDCl3-induced hepatotoxicity in females. However, phenobarbital pretreatment did differentiate CHCl3- and CDCl3-induced hepatotoxicity in females. 2,5-HD-induced potentiation of halocarbon hepatotoxicity is sex dependent.

Chlordecone-induced hepatic dysfunction

Chlordecone (Kepone) is a decachloroketone analog of the dodecachlorohydrocarbon mirex and is used as a stomach poison insecticide. Despite the structural similarity to mirex, chlordecone is unlike mirex in general organ-specific toxic properties. Chlordecone is primarily accumulated in the liver, where it causes a variety of morphological and biochemical alterations. Although less effective than mirex as a hepatotoxin, it causes liver enlargement, focal necrosis, mitochondrial changes, fatty infiltration of hepatocytes, and proliferation of endoplasmic reticulum. Chlordecone accumulation and morphological alterations in the liver were also observed in occupationally exposed human patients. Induction of hepatic microsomal mixed-function oxidases (MFOs) and impaired production and utilization of hepatocellular energy are the principal biochemical aberrations produced by chlordecone. Chronic exposure causes carcinogenesis in mice and rats. Hyperplastic nodules, which progress to hepatocellular carcinomas, are the principal pathological lesions. Acute and chronic exposures to chlordecone result in hepatobiliary dysfunction manifested as impaired excretion of anionic compounds accompanied by choleresis. Exposure to chlordecone results of greatly potentiated haloalkane hepatotoxicity, representing a most potent toxic interaction at otherwise individually nontoxic levels. In view of the demonstrated carcinogenic effect of chlordecone, such interactions at very low levels assume extraordinary significance in terms of chronic toxicological and pathological manifestations induced by combinations of toxic chemicals.

Nephrotoxicity and hepatotoxicity of chloroform in mice: effect of deuterium substitution

Chloroform (CHCl3) produces renal and hepatic damage in humans and experimental animals. Deuterium-labeled chloroform (CDCl3) has been reported to be less hepatotoxic than CHCl3 in rats. However, this isotope effect has not been determined in other species or in extrahepatic tissues. In this investigation, the effect of deuterium substitution on the nephrotoxicity and hepatotoxicity of CHCl3 was quantified in male ICR mice. Renal and hepatic damage were determined 24 h after administration on various doses of CHCl3 or CDCl3. Liver damage was estimated by measuring serum glutamic-pyruvic transaminase (SGPT) activity. Nephrotoxicity was evaluated by measuring blood urea nitrogen (BUN) and in vitro renal cortical accumulation of p-aminohippurate (PAH) and tetraethylammonium (TEA). Dose-related hepatotoxicity and nephrotoxicity were observed after administration of CHCl3 and CDCl3. CDCl3 produced less liver damage than CHCl3 in mice, suggesting that mouse liver metabolizes CHCl3 by the same mechanism as rat liver. CDCl3 was also less toxic to kidneys than CHCl3, suggesting that the kidney may metabolize CHCl3 in the same manner as the liver

Functional and biochemical correlates of chlordecone exposure and its enhancement of CCl4 hepatotoxicity

Animals pretreated with chlordecone exhibit a greatly increased hepatotoxic response to CCl4 challenge. Possible mechanisms underlying this interaction were examined. A single p.o. administration of chlordecone (5 mg/kg) was followed by CCl4 (200 microliter/kg) administered i.p. 48 h later. Twenty-four hours later, animals treated with chlordecone mccl4 had decreased hepatic excretory function (20% of controls) and elevated plasma transaminase activities and bilirubin. Hepatic mixed function oxidase activity was assessed as pentobarbital sleeping time and was not affected by chlordecone pretreatment. Irreversible binding of label from 14CCl4 to hepatic protein or lipid was not different in the chlordecone group compared to vehicle controls. Hepatic and renal glutathione concentrations were not affected by chlordecone alone (at 6 h, 1, 2, 3, 5 and 7 days) or by a combination of chlordecone (48 h) and CCl4 (24 h). CCl4-induced lipid peroxidation of liver tissue, measured in vitro or in vivo, was not increased by chlordecone treatment. Thus, while the mechanism for the enhanced toxicity remains to be elucidated, these results suggest that the interaction between chlordecone and CCl4 is a subtle one, not causally involving increased covalent binding of the toxin, increased susceptibility of tissue lipids to peroxidative damage or decreased hepatic GSH.