Ca(2+) mobilization evoked by chloroform in Madin-Darby canine kidney cells

The effect of chloroform on Ca(2+) mobilization in Madin-Darby canine kidney cells was examined by using Fura-2 as a Ca(2+) probe. Chloroform (24-248 mM) concentration dependently increased intracellular Ca(2+) concentration ([Ca(2+)](i)). Ca(2+) removal inhibited the Ca(2+) signals evoked by 93 to 248 mM chloroform by reducing both the initial rise and the sustained phase. In Ca(2+)-free medium, pretreatment with 93 mM chloroform abolished the Ca(2+) release induced by 1 microM thapsigargin, an endoplasmic reticulum Ca(2+) pump inhibitor, and partially reduced the Ca(2+) release induced by 2 microM carbonylcyanide m-chlorophenylhydrazone, a mitochondrial uncoupler. Pretreatment with carbonylcyanide m-chlorophenylhydrazone and thapsigargin to deplete the Ca(2+) stores in mitochondria and the endoplasmic reticulum, respectively, only partially inhibited chloroform-induced Ca(2+) release. This suggests that chloroform released Ca(2+) from multiple internal pools. The addition of 3 mM Ca(2+) increased [Ca(2+)](i) after pretreatment with 93 mM chloroform in Ca(2+)-free medium. La(3+) (1 mM) partially inhibited the [Ca(2+)](i) increase induced by 93 mM chloroform. Chloroform (93 mM)-induced Ca(2+) release was not altered when the formation of inositol-1,4,5-trisphosphate was abolished by U73122 (2 microM), a phospholipase C inhibitor, but was inhibited by 90% by inhibition of phospholipase A(2) with 40 microM aristolochic acid. Collectively, we found that 93 mM chloroform increased [Ca(2+)](i) in Madin-Darby canine kidney cells by releasing Ca(2+) from multiple stores in a manner independent of the formation of inositol-1,4,5-trisphosphate, followed by Ca(2+) entry from external medium. Other solvents, such as ethanol, methanol, and DMSO, did not affect the resting [Ca(2+)](i) at a concentration of 248 mM.

Lessons learned in applying the U.S. EPA proposed cancer guidelines to specific compounds

An expert panel was convened to evaluate the U.S. Environmental Protection Agency's "Proposed Guidelines for Carcinogen Risk Assessment" through their application to data sets for chloroform (CHCl3) and dichloroacetic acid (DCA). The panel also commented on perceived strengths and limitations encountered in applying the guidelines to these specific compounds. This latter aspect of the panel's activities is the focus of this perspective. The panel was very enthusiastic about the evolution of these proposed guidelines, which represent a major step forward from earlier EPA guidance on cancer-risk assessment. These new guidelines provide the latitude to consider diverse scientific data and allow considerable flexibility in dose-response assessments, depending on the chemical's mode of action. They serve as a very useful template for incorporating state-of-the-art science into carcinogen risk assessments. In addition, the new guidelines promote harmonization of methodologies for cancer- and noncancer-risk assessments. While new guidance on the qualitative decisions ensuing from the determination of mode of action is relatively straightforward, the description of the quantitative implementation of various risk-assessment options requires additional development. Specific areas needing clarification include: (1) the decision criteria for judging the adequacy of the weight of evidence for any particular mode of action; (2) the role of mode of action in guiding development of toxicokinetic, biologically based or case-specific models; (3) the manner in which mode of action and other technical considerations provide guidance on margin-of-exposure calculations; (4) the relative roles of the risk manager versus the risk assessor in evaluating the margin of exposure; and (5 ) the influence of mode of action in harmonizing cancer and noncancer risk assessment methodologies. These points are elaborated as recommendations for improvements to any revisions. In general, the incorporation of examples of quantitative assessments for specific chemicals would strengthen the guidelines. Clearly, any revisions should retain the emphasis present in these draft guidelines on flexibility in the use of scientific information with individual compounds, while simultaneously improving the description of the processes by which these mode-of-action data are organized and interpreted.

Re-evaluation of the 2-year chloroform drinking water carcinogenicity bioassay in Osborne-Mendel rats supports chronic renal tubule injury as the mode of action underlying the renal tumor response

Chloroform, generally regarded as a non-genotoxic compound, is associated with the induction of liver and/or kidney tumors in laboratory mice and rats. In particular, chloroform produced renal tubule tumors in low incidence in male Osborne-Mendel rats when administered by corn-oil gavage or in the drinking water. There is a lack of data on intermediate endpoints that may be linked to renal cancer development in this strain of rat, in contrast to mice. Specifically, evidence linking chloroform-induced liver and kidney tumors in mice with cytotoxicity and regenerative cell proliferation is very strong, but weak in the rat. In the present study, kidney tissue from a carcinogenicity bioassay of chloroform in Osborne-Mendel rats was re-evaluated for histological evidence of compound-induced cytotoxicity and cell turnover. All rats treated with 1800 ppm (160 mg/kg/day, high-dose group) in the drinking water for 2 years and half the rats treated with 900 ppm (81 mg/kg/day) had mild to moderate changes in proximal convoluted tubules in the mid to deep cortex indicative of chronic cytotoxicity. Tubule alterations specifically associated with chronic chloroform exposure included cytoplasmic basophilia, cytoplasmic vacuolation, and nuclear crowding consistent with simple tubule hyperplasia. Occasional pyknotic cells, mitotic figures in proximal tubules, and prominent karyomegaly of the renal tubule epithelium were present. These alterations were not present in control groups or at the 200-ppm (19 mg/kg/day) or 400-ppm (38 mg/kg/day) dose levels. This new information adds substantially to the weight of evidence that the key events in chloroform-induced carcinogenicity in rat kidney include sustained cellular toxicity and chronic regenerative hyperplasia.

Plasminogen deficiency leads to impaired remodeling after a toxic injury to the liver

Cellular proliferation and tissue remodeling are central to the regenerative response after a toxic injury to the liver. To explore the role of plasminogen in hepatic tissue remodeling and regeneration, we used carbon tetrachloride to induce an acute liver injury in plasminogen-deficient (Plg(o)) mice and nontransgenic littermates (Plg(+)). On day 2 after CCl(4), livers of Plg(+) and Plg(o) mice had a similar diseased pale/lacy appearance, followed by restoration of normal appearance in Plg(+) livers by day 7. In contrast, Plg(o) livers remained diseased for as long as 2.5 months, with a diffuse pale/lacy appearance and persistent damage to centrilobular hepatocytes. The persistent centrilobular lesions were not a consequence of impaired proliferative response in Plg(o) mice. Notably, fibrin deposition was a prominent feature in diseased centrilobular areas in Plg(o) livers for at least 30 days after injury. Nonetheless, the genetically superimposed loss of the Aalpha fibrinogen chain (Plg(o)/Fib(o) mice) did not correct the abnormal phenotype. These data show that plasminogen deficiency impedes the clearance of necrotic tissue from a diseased hepatic microenvironment and the subsequent reconstitution of normal liver architecture in a fashion that is unrelated to circulating fibrinogen.

Development of resistance to chloroform toxicity in male BDF1 mice exposed to a stepwise increase in chloroform concentration

To investigate the development of resistance to chloroform toxicity, a 4-week inhalation study was conducted in which BDF1 male mice were exposed to a low level of chloroform for an initial two-week period, and thereafter the exposure concentration was increased for a second two-week period. The animals were exposed to inhalation of chloroform vapor 6 hr per day, 5 days per week, with clinical observation and measurement of body weight conducted. These results demonstrate that pre-exposure to chloroform at a low dose level induced resistance to a higher dose of chloroform in male mice. This resistance was dependent on the pre-exposure concentration.

Hepatoprotection by dimethyl sulfoxide. II. Characterization of optimal dose and the latest time of administration for effective protection against chloroform and bromobenzene induced injury

Dimethyl sulfoxide (DMSO) has previously been shown to attenuate chloroform (CHCl3) and bromobenzene (BB) induced hepatotoxicity in the rat when a dose of 2.0 ml/kg is given 24 hr after the toxicants. However, the optimal dose of DMSO and the latest time at which DMSO can be administered and still provide effective protection have not been determined. In order to determine the latest time at which DMSO can interrupt the development of necrosis, male Sprague Dawley rats received either 0.75 ml/kg CHCl3 or 0.5 ml/kg BB, 20% in corn oil, p.o., followed by single dose of 2 ml/kg DMSO, 50% in saline, i.p., at 24, 26, 28 or 30 hr later. Positive control groups received either CHCl3 or BB and then 4.0 ml/kg saline, i.p., 24 hr later. All of the animals were then killed 48 hr after toxicant dosing. The extent of liver injury present when DMSO was administered was examined by killing animals at 24, 26, 28 or 30 hr after toxicant dosing. The optimal dose of DMSO for providing protection was estimated by administering either 0, 1.0, 2.0, 3.0 or 4.0 ml/kg DMSO at 24 hr after toxicant dosing and then killing the animals at 48 hr. Delaying DMSO administration to times later than 24 hr after toxicant dosing led to a loss of protection as indicated by both plasma ALT activity and the light microscopic appearance of liver tissue. The distinctive liver lesions present at 24 hr after CHCl3 or BB dosing rapidly expanded from being limited around central veins to bridging between centrilobular areas in only a few hours. This was accompanied by large increases in plasma ALT. With both toxicants, doses of DMSO greater than 2 ml/kg did not enhance its protective action while the lower dose of 1 ml/kg DMSO was not as effective. The loss of DMSO's antidotal action when given at times later than 24 hr after the toxicants indicates irreversible changes were underway as the centrilobular lesions progressed from being limited to more bridging in nature. Hopefully, further elucidation of the mechanism(s) by which DMSO interrupts the rapid progression of injury will both help to understand the steps involved in lesion development and provide insights into therapeutic interventions for drug and chemical induced hepatitis.

Metabolism of chloroform by cytochrome P450 2E1 is required for induction of toxicity in the liver, kidney, and nose of male mice

Chloroform is a nongenotoxic-cytotoxic liver and kidney carcinogen and nasal toxicant in some strains and sexes of rodents. Substantial evidence indicates that tumor induction is secondary to events associated with cytolethality and regenerative cell proliferation. Therefore, pathways leading to toxicity, such as metabolic activation, become critical information in mechanism-based risk assessments. The purpose of this study was to determine the degree to which chloroform-induced cytotoxicity is dependent on the cytochromes P450 in general and P450 2E1 in particular. Male B6C3F(1), Sv/129 wild-type (Cyp2e1+/+), and Sv/129 CYP2E1 knockout (Cyp2e1-/- or Cyp2e1-null) mice were exposed 6 h/day for 4 consecutive days to 90 ppm chloroform by inhalation. Parallel control and treated groups, excluding Cyp2e1-null mice, also received an i.p. injection (150 mg/kg) of the irreversible cytochrome P450 inhibitor 1-aminobenzotriazole (ABT) twice on the day before exposures began and 1 h before every exposure. Cells in S-phase were labeled by infusion of BrdU via an implanted osmotic pump for 3.5 days prior to necropsy, and the labeling index was quantified immunohistochemically. B6C3F(1) and Sv/129 wild-type mice exposed to chloroform alone had extensive hepatic and renal necrosis with significant regenerative cell proliferation. These animals had minimal toxicity in the nasal turbinates with focal periosteal cell proliferation. Administration of ABT completely protected against the hepatic, renal, and nasal toxic effects of chloroform. Induced pathological changes and regenerative cell proliferation were absent in these target sites in Cyp2e1-/- mice exposed to 90 ppm chloroform. These findings indicate that metabolism is obligatory for the development of chloroform-induced hepatic, renal, and nasal toxicity and that cytochrome P450 2E1 appears to be the only enzyme responsible for this cytotoxic-related metabolic conversion under these exposure conditions.

Time dependence of chloroform-induced metabolic alterations in the liver and kidney of B6C3F1 mice

The time course of some biochemical changes in the liver and in the kidney was studied in B6C3F1 male mice dosed with a single i.p. injection of 150 mg/kg body weight (b.w.) CHCl(3). Hepatic and renal microsomal cytochrome P450 (P450) content and some related monooxygenase activities, CHCl(3) oxidative and reductive metabolism, cytosolic reduced glutathione (GSH) content and serum markers of nephrotoxicity were measured. In the liver no biochemical changes were produced up to a week after chloroform treatment. On the contrary, the drug-metabolizing enzyme system in the kidney was dramatically and rapidly inactivated by chloroform treatment. Maximum loss of GSH (50%), P450 (80%) and of different enzymatic activities, including CHCl(3) bioactivation, occurred during the first 5 h. These biochemical alterations are early effects, not secondary to morphological tissue changes. Kidney parameters, altered by chloroform treatment, returned to control values at different times: renal function markers became normal in 48 h; GSH levels were recovered at 96 h and the drug-metabolizing enzyme activities at longer times. The present results clearly show that repeated daily doses of chloroform, as those used in carcinogenicity tests, find renal tubular cells not at their physiological status, due to the changes produced by the first chloroform dose. Therefore the similarity in P450-dependent chloroform metabolism shown in vitro by hepatic and renal microsomes from untreated B6C3F1 male mice or in vivo in animals treated once, is lost during repeated treatments. These features should be considered in understanding the different susceptibility of the liver and the kidney to chloroform-induced tumours.

Liver mitochondria alterations in chloroform-treated Sprague-Dawley rats

The formation of a chloroform adduct produced by the reaction of the oxidative chloroform metabolite phosgene with two molecules of phosphatidylethanolamine has been previously demonstrated in liver mitochondria of phenobarbital-pretreated Sprague-Dawley (SD) rats. The aim of our study was to assess the influence of chloroform adduct mitochondrial accumulation on the hepatic mitochondria morphology. Liver mitochondrial ultrastructural alterations were analyzed by electron microscopy in SD rats administered with increasing doses of chloroform. Variation in the morphology of mitochondria, consisting of an increase of intertwined organelles, only rarely seen in control specimens, was observed at the lowest chloroform dose (180 mg/kg). At higher doses, mitochondrial damage progressed with swelling of the organelles and formation of megamitochondria. These megamitochondria were characterized by a dilution of the matrix, and often membranous whorls were found inside the matrix. The two distinct forms of cell death, necrosis and apoptosis, were first observed at 300 mg/kg of chloroform. Our results suggest that the formation and the accumulation of a chloroform-modified phosphatidylethanolamine in mitochondria induce ultrastructural modifications of these organelles. In conclusion, mitochondria are involved in chloroform-induced hepatotoxicity.

Chloroform: An EPA test case

In March 1998, the U.S. Environmental Protection Agency (EPA) published a proposal to raise the drinking water maximum contaminant level goal (MCLG) for chloroform, a suspected human carcinogen, from zero to 300 parts per billion. The proposal marked a departure from the agency's traditional reliance on linear dose-response models in performing risk assessment, and reflected the new thinking contained in the 1996 draft update to the agency's cancer risk assessment guidelines. The updated guidelines emphasize mechanisms of action and descriptions of the conditions under which carcinogenic hazards are likely to be expressed.

V-Ha-ras gene expression in liver and kidney of transgenic Tg.AC mice following chemically induced tissue injury

The dermal Tg.AC transgenic mouse line is currently being used as a short-term alternative in vivo model for carcinogenicity screening of drugs and environmental chemicals. These mice carry multiple copies of an activated v-Ha-ras oncogene, making them susceptible to promotionally induced tumorigenesis caused by carcinogen exposure or deep skin wounding. Transgene expression is associated with tumor development in these animals. To determine whether tissue injury in organs other than the skin can induce transgene expression, we characterized the pattern of transgene expression in naive animals as well as mice treated by oral gavage with cytotoxic doses of chloroform. Hepatic BrdU labeling was increased 40-fold in females (240 mg/kg/day) and 20-fold in males (140 mg/kg/day) after 4 days of dosing with chloroform. An increase in renal BrdU labeling (7-fold) was observed only in male Tg.AC mice. Although chloroform did not induce v-Ha-ras expression, in either the liver or the kidney, a constitutive amount of transgene message was evident in the kidneys of Tg.AC mice. V-Ha-ras transgene expression also correlated with the expression of GATA-3, a transcription factor that binds the zeta-globin (zeta-globin) promoter of the Tg.AC transgene. These studies suggest that chemically induced tissue injury and regenerative cell proliferation per se are not sufficient for the induction of transgene expression in the liver and kidney of Tg.AC mice. Although organs like the kidney may contain the necessary transcription factors for transgene expression, other factors, yet unidentified, may impede v-Ha-ras-mediated tumorigenesis in these tissues.

Influence of oral administration of a quaternary mixture of trihalomethanes on their blood kinetics in the rat

Trihalomethanes (THMs; chloroform, bromoform, bromodichloromethane, dibromochloromethane), formed as by-products of chlorine disinfection, are found to occur in combination in drinking water supplies. THMs are metabolized by cytochromes P-450 and are likely substrates of CYP2E1. Therefore, it is possible that mixed exposure results in toxicokinetic interactions among THMs. The toxicokinetics of THMs during mixed exposures has not been investigated previously. The purpose of this study was to characterize the blood kinetics of the four THMs administered singly or in combination in the rat. A single dose of 0.25 mmol/kg or 0.5 mmol/kg b.w., of each THM alone, or of a quaternary mixture containing 0.25 mmol/kg of each THM (total dose of 1.0 mmol/kg) was administered by gavage. The venous blood concentrations of the THMs were measured by headspace gas chromatography (GC) at 20, 40, 60, 120, 180, 270 and 360 min post-administration. Results showed a nonlinear relationship between the area under the blood concentration versus time curves (AUCs) and administered doses of THMs, suggesting that metabolism is saturated in this dose range. The venous blood concentrations of THMs following administration of the quaternary mixture were significantly higher compared to single exposures. The altered kinetics of THMs during combined exposures is consistent with the occurrence of mutual inhibition of their hepatic metabolism. Simulation exercises conducted with physiologically based toxicokinetic models support metabolic inhibition as the possible mechanism of the interaction among THMs. The data reported in this study provide the starting point for evaluating the significance of interactions among THMs in the risk assessment process.

Hepatoprotection by dimethyl sulfoxide. I. Protection when given twenty-four hours after chloroform or bromobenzene

Dimethyl sulfoxide (DMSO) has previously been reported to protect against hepatotoxicity resulting from chloroform (CHCl3) or bromobenzene (BB) when given 10 hr after the toxicant. The object of these studies was to further demonstrate the latent protective ability of DMSO by administering it at a much later time (24 hr) following toxicant exposure. In addition, a more detailed evaluation of the lesions was performed to better characterize the lesion progression and resolution. Male Sprague-Dawley rats received a hepatotoxic oral dose of either CHCl3 (1.0 ml/kg) or BB (0.5 ml/kg) and then received 2 ml/kg DMSO intraperitoneally 24 hr later. With both toxicants, limited centrilobular lesions were already present by the time DMSO was administered. Without treatment, liver injury rapidly progressed so that by 48 hr it occupied 40-50% of the liver, with accompanying large increases in plasma alanine aminotransferase (ALT) activity. Administration of DMSO greatly attenuated lesion development for both toxicants; the area injured was reduced by more than 4-fold, accompanied by a decrease in 48 hr ALT activity of 8-16-fold. The ability of DMSO to intervene in the development of liver injury at such a late time appears to be unique and may provide insight into therapies for acute xenobiotic-induced hepatitis.

Toxicant-inflicted injury and stimulated tissue repair are opposing toxicodynamic forces in predictive toxicology

These studies were designed to investigate the dose response for liver injury and tissue repair induced by exposure to four structurally and mechanistically dissimilar hepatotoxicants, individually and as mixtures. The objective was to illuminate the impact of the extent and timeliness of tissue repair on the ultimate outcome of toxicity. Dose-response relationships for trichloroethylene (TCE), allyl alcohol (AA), thioacetamide (TA), and chloroform alone or as mixtures were studied. Male Sprague-Dawley rats (200-250 g) received a single intraperitoneal injection of individual toxicants as well as mixtures of these toxicants. Liver injury was monitored by plasma enzyme (ALT and SDH) levels and histopathology. Tissue regeneration was measured by [3H]thymidine incorporation into hepatic nuclear DNA. Individually, TCE, TA, and AA administration, over a 10- to 12-fold dose range, revealed a dose-related increase in injury as well as tissue repair up to a threshold dose. Beyond this threshold, tissue repair was delayed and attenuated, and liver injury progressed. Mixtures of the four chemicals at the higher doses used in individual dose-response studies resulted in 100% mortality. Hence, mixtures at the lower two doses were selected for further study. Additional lower doses were also included to better understand the dose-response relationship of mixtures. Results of these studies support the observations of individual chemicals. Higher and sustained repair was observed at low dose levels. These studies show that the extent of injury at early time points correlates well with the maximal stimulation of the opposing response of tissue repair. It appears that the toxicity of the mixture employed in these studies is roughly additive and correlates well with tissue repair response. These initial studies suggest that a biologically based mathematical model can be constructed and tested to extrapolate the outcome of toxicity from a given dose of individual compounds as well as their mixtures, where the responses measured are injury on the one hand and compensatory tissue repair on the other.

Alteration of protein kinase C isoform-specific expression during rat hepatocarcinogenesis after exposure to the peroxisome proliferator WY-14,643

The role of protein kinase C (PKC) isoforms in mediating peroxisome proliferator chemical- (PPC) induced hepatocarcinogenesis was examined. After an acute gavage exposure to WY-14,643 (WY) membrane-bound PKCdelta and cytosolic PKCbeta decreased, whereas the expression of the other isoforms was not altered. After a 13-week chronic exposure, membrane-bound PKCbeta, delta and zeta levels decreased. In WY-induced hepatocellular adenomas, PKCalpha was increased, and PKCbeta was further decreased in membrane fractions. These results, taken together with previous studies, indicate that alterations in PKCalpha, beta and delta isoforms, which regulate mitogenesis, could play important roles in perpetuating the high cell proliferative rate in PPC-induced hepatocellular adenomas.

Drinking water disinfection byproducts: review and approach to toxicity evaluation

There is widespread potential for human exposure to disinfection byproducts (DBPs) in drinking water because everyone drinks, bathes, cooks, and cleans with water. The need for clean and safe water led the U.S. Congress to pass the Safe Drinking Water Act more than 20 years ago in 1974. In 1976, chloroform, a trihalomethane (THM) and a principal DBP, was shown to be carcinogenic in rodents. This prompted the U.S. Environmental Protection Agency (U.S. EPA) in 1979 to develop a drinking water rule that would provide guidance on the levels of THMs allowed in drinking water. Further concern was raised by epidemiology studies suggesting a weak association between the consumption of chlorinated drinking water and the occurrence of bladder, colon, and rectal cancer. In 1992 the U.S. EPA initiated a negotiated rulemaking to evaluate the need for additional controls for microbial pathogens and DBPs. The goal was to develop an approach that would reduce the level of exposure from disinfectants and DBPs without undermining the control of microbial pathogens. The product of these deliberations was a proposed stage 1 DBP rule. It was agreed that additional information was necessary on how to optimize the use of disinfectants while maintaining control of pathogens before further controls to reduce exposure beyond stage 1 were warranted. In response to this need, the U.S. EPA developed a 5-year research plan to support the development of the longer term rules to control microbial pathogens and DBPs. A considerable body of toxicologic data has been developed on DBPs that occur in the drinking water, but the main emphasis has been on THMs. Given the complexity of the problem and the need for additional data to support the drinking water DBP rules, the U.S. EPA, the National Institute of Environmental Health Sciences, and the U.S. Army are working together to develop a comprehensive biologic and mechanistic DBP database. Selected DBPs will be tested using 2-year toxicity and carcinogenicity studies in standard rodent models; transgenic mouse models and small fish models; in vitro mechanistic and toxicokinetic studies; and reproductive, immunotoxicity, and developmental studies. The goal is to create a toxicity database that reflects a wide range of DBPs resulting from different disinfection practices. This paper describes the approach developed by these agencies to provide the information needed to make scientifically based regulatory decisions.

Drinking water disinfection byproducts: review and approach to toxicity evaluation

There is widespread potential for human exposure to disinfection byproducts (DBPs) in drinking water because everyone drinks, bathes, cooks, and cleans with water. The need for clean and safe water led the U.S. Congress to pass the Safe Drinking Water Act more than 20 years ago in 1974. In 1976, chloroform, a trihalomethane (THM) and a principal DBP, was shown to be carcinogenic in rodents. This prompted the U.S. Environmental Protection Agency (U.S. EPA) in 1979 to develop a drinking water rule that would provide guidance on the levels of THMs allowed in drinking water. Further concern was raised by epidemiology studies suggesting a weak association between the consumption of chlorinated drinking water and the occurrence of bladder, colon, and rectal cancer. In 1992 the U.S. EPA initiated a negotiated rulemaking to evaluate the need for additional controls for microbial pathogens and DBPs. The goal was to develop an approach that would reduce the level of exposure from disinfectants and DBPs without undermining the control of microbial pathogens. The product of these deliberations was a proposed stage 1 DBP rule. It was agreed that additional information was necessary on how to optimize the use of disinfectants while maintaining control of pathogens before further controls to reduce exposure beyond stage 1 were warranted. In response to this need, the U.S. EPA developed a 5-year research plan to support the development of the longer term rules to control microbial pathogens and DBPs. A considerable body of toxicologic data has been developed on DBPs that occur in the drinking water, but the main emphasis has been on THMs. Given the complexity of the problem and the need for additional data to support the drinking water DBP rules, the U.S. EPA, the National Institute of Environmental Health Sciences, and the U.S. Army are working together to develop a comprehensive biologic and mechanistic DBP database. Selected DBPs will be tested using 2-year toxicity and carcinogenicity studies in standard rodent models; transgenic mouse models and small fish models; in vitro mechanistic and toxicokinetic studies; and reproductive, immunotoxicity, and developmental studies. The goal is to create a toxicity database that reflects a wide range of DBPs resulting from different disinfection practices. This paper describes the approach developed by these agencies to provide the information needed to make scientifically based regulatory decisions.

The effect of surgical medicaments on peripheral nerve function

Surgical medicaments are often placed in close proximity to peripheral nerves and may be responsible for some postoperative sensory disturbances. In this study we investigated the effect of four medicaments -- BIPP, (bismuth iodoform paraffin paste), Whitehead's varnish (compound iodoform paint), Surgicel (oxidized regenerated cellulose) and Carnoy's solution (ethanol, chloroform and acetic acid) -- on peripheral nerve function. The experiments were carried out on the saphenous nerve in anaesthetized adult rats. Electrical stimuli (30 V, 0.1 ms duration) were applied to the saphenous nerve through electrodes placed distally (at the ankle) to evoke a compound action potential (CAP) which was recorded proximally (in the thigh). The CAP was recorded before, and for 2 h after, the application of the medicament to a 1 cm length of nerve between the electrodes. In other animals (n = 4 in each group) recordings were made after the medicament had been placed in a connective tissue pocket immediately overlying the nerve for a 2-week period. BIPP (n = 4) had no immediate or delayed effect on neural function, whereas Whitehead's varnish (n = 4) and Carnoy's (n = 4) solution both blocked neural conduction within 2 min of being placed adjacent to the nerve. The effect of Surgicel (n = 8) was more variable; axonal conduction was blocked within 2 h in five of the eight experiments undertaken. After the application of Whitehead's varnish or Surgicel for 2 weeks, the CAPs had regained characteristics which were similar to those of the controls, but after the application of Carnoy's solution they remained significantly diminished (P < 0.004). These results suggest that, with the exception of BIPP, the medicaments tested could be responsible for some postoperative sensory disturbances, and the effects of Carnoy's solution on neural function may be persistent.

Toxicity of chloroform

(1) Chloroform is strongly absorbed by the pulmonary, oral and cutaneous routes. (2) It has adverse cardiac, hepatic, renal, dermatological, neurological and ophthalmological effects. Deaths related to chloroform use have occurred. In animals, chloroform is carcinogenic and embryotoxic. (3) Since 1997, the European and French medicines agencies have no longer considered chloroform to be a simple solvent. Only minimal amounts are authorised in drug preparations (no more than 0.6 mg/day).

NOAEL and LOAEL determinations of acute hepatotoxicity for chloroform and bromodichloromethane delivered in an aqueous vehicle to F344 rats

Chloroform (CHCl3) and bromodichloromethane (BDCM) are generally the two most prevalent disinfection by-products formed during chlorination of drinking water, and both have been shown to be hepatotoxic, nephrotoxic, and carcinogenic in rodents. As the toxicity of these trihalomethanes (THMs) has most often been studied with corn oil as the vehicle of administration, the objectives of this study were to assess hepatotoxicity after exposure to single, low dosages of CHCl3 and BDCM given orally in an aqueous vehicle to estimate a lowest-observed-adverse-effect level (LOAEL) and a no-observed-adverse-effect level (NOAEL) and to compare toxic potency. Ninety-day-old male Fischer 344 rats were gavaged with either 0.125, 0.1875, 0.25, 0.5, 0.75, 1.0, or 1.5 mmol CHCl3 or BDCM/kg body weight in 10% Alkamuls EL-620 (5 ml/kg body weight). At 24 h postgavage, serum was collected for analysis of clinical chemistry indicators of liver damage. Both CHCl3 and BDCM induced dose-dependent hepatotoxicity; serum alanine aminotransferase, aspartate aminotransferase, and sorbitol dehydrogenase were elevated significantly over control at 1.5, 1.0, and 0.5 mmol/kg. At these dose levels after 24 h, the two THMs appeared to be equipotent hepatotoxicants. Additional assessments at later time points demonstrated that BDCM causes more persistent liver damage than CHCl3 (Lilly et al., 1997). At 0.25, 0. 1875, and 0. 125 mmol of either THM/kg, significant increases over control were not detected for any measured endpoint. Therefore, these data indicate that the acute, oral NOAELs and LOAELs for liver toxicity are 0.25 and 0.5 mmol/kg, respectively, for both CHCl3 and BDCM. These determinations should provide a basis to establish new exposure limits for One-Day Health Advisories for these prevalent THMs.

Occurrence of toxicity and cell proliferation after a single gavage administration of chloroform to male F344 rats

Chloroform, an industrial solvent and one of the most common environmental contaminants which produces carcinogenic effects in the liver and kidney of rodents, is not genotoxic in most traditional bacterial and mammalian test systems. Its carcinogenic potential appears attributable to the sustained cell turnover (regenerative hyperplasia) which results from chronic chloroform toxicity. In this present study, cell proliferation (replicative DNA synthesis, RDS) and histopathological changes in hepatocytes and renal tubular epithelial cells were assessed in male F344 rats following a single gavage chloroform exposure (50, 150 or 500 mg/kg). In addition, biochemical parameters (BUN, GOT, LDH and NAG) were examined using plasma and urine samples. Cell proliferation and histopathological changes (e.g. hypertrophy, necrosis, vacuolation) were only seen at the dose of 500 mg/kg in the liver and kidney. At the same dose, all biochemical markers were increased at the 24 to 48 hr time points. These results obtained are thus in line with earlier findings pointing to epigenetic carcinogenicity.

Effects of singly administered betaine on hepatotoxicity of chloroform in mice

Effects of a single dose of betaine on the chloroform-induced hepatotoxicity were examined in adult male ICR mice. Administration of betaine (1000 mg/kg, ip) 1 to 7 hr prior to a chloroform challenge (0.25 ml/kg, ip) resulted in remarkable enhancement of hepatotoxicity as indicated by increases in serum sorbitol dehydrogenase (SDH), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. The potentiation of hepatotoxicity was most significant when mice were treated with betaine 4 hr earlier than chloroform. However, a 24 hr prior administration of betaine protected the animals from induction of the chloroform hepatotoxicity. Thus, its effect appeared to be highly dependent on the time lapse from the betaine pretreatment to the challenge of mice with chloroform. Betaine treated either 4 or 24 hr prior to sacrifice did not alter the hepatic contents of cytochrome P-450, cytochrome b5, or NADPH cytochrome P-450 reductase activity. Accordingly the hepatic microsomal p-nitroanisole O-demethylase, aminopyrine N-demethylase, or p-nitrophenol hydroxylase activities were not influenced by the betaine pretreatment. Betaine was shown not to affect any of the enzyme activities associated with glutathione (GSH) conjugation reaction, such as glutathione S-transferases (GSTs), glutathione disulfide (GSSG) reductase and GSH peroxidase irrespective of the time of its administration. When betaine was administered to mice 2-6 hr prior to sacrifice, hepatic GSH level, but not plasma GSH, was decreased significantly. Enhancement of the chloroform hepatotoxicity by betaine correlated well with the reduction in hepatic GSH levels. Both hepatic and plasma GSH levels were elevated in mice 24 hr following the betaine treatment. The results suggest that betaine affects induction of the chloroform hepatotoxicity by modulating the availability of hepatic GSH, which appears to be associated with its role in the transsulfuration pathway in the liver.

In vitro assessment of the effect of halogenated hydrocarbons: chloroform, dichloromethane, and dibromoethane on embryonic development of the rat

Halogenated hydrocarbons are widely used in industry, the laboratory, and in the home. In the present study three of these solvents--chloroform, dichloromethane, and dibromoethane--were examined for embryotoxic/teratogenic potential using rat embryo culture. The results showed that each of the solvents had a concentration-dependent embryotoxic effect on the developing rat embryo in vitro. The effect and no-effect concentrations (expressed in mumol/ml culture medium), respectively, for each of the halogenated hydrocarbons tested were: dibromoethane--0.33, < 0.18; chloroform--2.06, 1.05; dichloromethane--6.54, 3.46. The levels of chloroform and dichloromethane found to be embryotoxic in the present study were compared to reported blood levels attained following controlled human exposure. In the industrial situation, if the current exposure levels are adhered to, chloroform and dichloromethane appear to have little potential for reproductive toxicity in the human. Fatal or near fatal solvent levels would be required in the mother for the embryotoxic level to be reached. For dibromoethane, there are no reports following controlled human exposure presumably due to its carcinogenicity. In an attempt to elucidate the mechanism of embryotoxicity, histological studies were performed after exposure of rat embryos to an embryotoxic level of each of the halogenated hydrocarbons studied, for increasing time periods up to the standard 40-hour culture. Marked cell death in the neuroepithelium of the developing neural tube was a prominent feature in all embryos exposed to an embryotoxic level of these solvents for periods of 16 hours of longer.

Repeated dosing with the peroxisome proliferator clofibrate decreases the toxicity of model hepatotoxic agents in male mice

Pretreatment of mice with clofibrate (CFB) has been shown to protect against acetaminophen (APAP) hepatotoxicity. To determine if pretreatment with CFB prevents the toxicity of other model hepatotoxicants, male C57BL6J or CD-1 mice received 500 mg CFB/kg, i.p., daily for 10 days, and then were challenged with either 250 mg bromobenzene (BrB)/kg, 0.025 ml carbon tetrachloride (CCl4)/kg or 0.5 ml chloroform (CHCl3)/kg. Liver and kidney injury was assessed by plasma sorbitol dehydrogenase activity (SDH) and blood urea nitrogen (BUN), respectively and histopathology. Challenge with BrB significantly elevated plasma SDH activity in C57Bl6J mice. This was prevented in CFB pretreated mice receiving the same dose of BrB. Changes in BUN were not detected in either group of BrB treated mice. Similarly, pretreatment of male CD-1 mice with CFB significantly reduced CCl4-induced elevation in plasma SDH activity, with no BUN elevation detected in either group. CFB pretreatment also diminished elevation in plasma SDH activity produced by CHCl3 in CD-1 mice, while BUN was significantly elevated in both groups, indicating that CFB did not protect against CHCl3-induced nephrotoxicity. Histopathological examination of liver and kidney sections confirmed these results. This study shows that mice pretreated with CFB were protected from toxicity at 24 h after challenge with other model hepatotoxic agents besides APAP.