Abstract  Kupffer cells are resident macrophages of the liver and play an important role in its normal physiology and homeostasis as well as participating in the acute and chronic responses of the liver to toxic compounds. Activation of Kupffer cells directly or indirectly by toxic agents results in the release of an array of inflammatory mediators, growth factors, and reactive oxygen species. This activation appears to modulate acute hepatocyte injury as well as chronic liver responses including hepatic cancer. Understanding the role Kupffer cells play in these diverse responses is key to understanding mechanisms of liver injury. Idiosyncratic drug-induced liver disease results in morbidity and mortality, impacting severely on the development of new pharmacological agents. Modulation of the response of Kupffer cells by drugs has been suggested as a cause for the idiosyncratic response. Similarly, liver damage seen in chronic ethanol consumption appears to be modulated by Kupffer cell activation. More recent evidence has noted a contributory role of Kupffer cell activation in the process of hepatic carcinogenesis. Several nongenotoxic carcinogens, for example, activate Kupffer cells resulting in the release of cytokines and/or reactive oxygen species that induce hepatocyte cell proliferation and may enhance clonal expansion of preneoplastic cells leading to neoplasia. Kupffer cells therefore appear to play a central role in the hepatic response to toxic and carcinogenic agents. Taken together, the data presented in this symposium illustrate to the toxicologist the central role played by Kupffer cells in mediating hepatotoxicity.

Abstract  It was shown that 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio acetic acid (Wy-14,643), a potent peroxisome proliferator, caused rapid oxidant-dependent activation of nuclear factor kappaB (NF-kappaB) in Kupffer cells in vivo and activated superoxide production by isolated Kupffer cells. Here, we tested the hypothesis that NADPH oxidase (NADPH OX) is the source of oxidants increased by Wy-14,643. Indeed, both activation of NF-kappaB and increases in cell proliferation due to a single dose of Wy-14,643 (100 mg/kg) were prevented completely when rats were pretreated with diphenyleneiodonium (1 mg/kg), an inhibitor of NADPH OX. p47phox is a critical subunit of NADPH OX; therefore, p47phox knockout mice were used to specifically address the hypothesis of NADPH OX involvement. In livers of wild-type mice, Wy-14,643 activated NF-kappaB, followed by an increase in mRNA for tumor necrosis factor a. Importantly, these changes did not occur in p47phox knockouts. Moreover, when Kupffer cells were treated with Wy-14,643 in vitro, superoxide production was increased in cells from wild-type but not p47phox-null mice. Finally, when mice were fed a Wy-14,643-containing (0.1%) diet for 7 days, the increase in liver weight and cell proliferation caused by Wy-14,643 in wild-type mice was blocked in p47phox-null mice. Combined, these results are consistent with the hypothesis that Wy-14,643 activates NADPH OX, which leads to NF-kappaB-mediated production of mitogens that causes hepatocellular proliferation characteristic of this class of nongenotoxic carcinogens.

Abstract  The nuclear hormone receptor superfamily includes receptors for thyroid and steroid hormones, retinoids and vitamin D, as well as different "orphan" receptors of unknown ligand. Ligands for some of these receptors have been recently identified, showing that products of lipid metabolism such as fatty acids, prostaglandins, or cholesterol derivatives can regulate gene expression by binding to nuclear receptors. Nuclear receptors act as ligand-inducible transcription factors by directly interacting as monomers, homodimers, or heterodimers with the retinoid X receptor with DNA response elements of target genes, as well as by "cross-talking" to other signaling pathways. The effects of nuclear receptors on transcription are mediated through recruitment of coregulators. A subset of receptors binds corepressor factors and actively represses target gene expression in the absence of ligand. Corepressors are found within multicomponent complexes that contain histone deacetylase activity. Deacetylation leads to chromatin compactation and transcriptional repression. Upon ligand binding, the receptors undergo a conformational change that allows the recruitment of multiple coactivator complexes. Some of these proteins are chromatin remodeling factors or possess histone acetylase activity, whereas others may interact directly with the basic transcriptional machinery. Recruitment of coactivator complexes to the target promoter causes chromatin decompactation and transcriptional activation. The characterization of corepressor and coactivator complexes, in concert with the identification of the specific interaction motifs in the receptors, has demonstrated the existence of a general molecular mechanism by which different receptors elicit their transcriptional responses in target genes.

Abstract  Multiple modalities are available for treating acne scars, one of which is chemical peeling.

To evaluate the efficacy of medium-depth peels in the treatment of acne scars.

A total of 15 patients (14 women and 1 man) were seen between November 1998 and March 2000. A medium-depth chemical peel was performed. The peel was performed using a combination of Jessner's solution followed by the application of 35% trichloroacetic acid (TCA). The mean age of patients who entered the study was 28 years. A total of 42 peeling sessions were performed: 13 patients had the full three-session regiment, 1 patient had two sessions, and 1 had only one session.

Patients in our study had two forms of acne scars, the atrophic saucer or crater-like form and the pitted (ice-pick) form. Improvement occurred in all except one of our patients. Significant improvement (greater than 75% clearance of lesions) occurred in 1 patient (6.6%), moderate improvement (51-75% clearance) in 8 patients (53.3%), mild improvement (26-50% clearance) in 4 patients (26.6%), minimal improvement (1-25% clearance) in 1 patient (6.6%), and no response in 1 patient (6.6%). All patients had different combinations of the above two forms. Four patients (26.6%) had mainly pitted scars and deep atrophic scars. The clinical response in those patients was moderate, mild, minimal, and no response, respectively. The remainder of our patients had mainly atrophic scars of moderate depth. Nine patients (73.4%) suffered from transient postinflammatory hyperpigmentation. In two of them it was preceded by erythema that lasted for more than 1 month. All patients were free of noticeable pigmentation 3 months after the final peel. Patients in whom hyperpigmentation did not develop were of light brown complexion.

We conclude that medium-depth chemical peel is a safe and effective method of treating acne scars even in patients with dark complexion.

Abstract  Acne scarring is a common complication of acne and yet no appropriate and effective single treatment modality has been developed. We suggest a technique consisting of the focal application of higher trichloroacetic acid (TCA) concentrations by pressing hard on the entire depressed area of atrophic acne scars. This technique is called chemical reconstruction of skin scars (CROSS) by the authors.

To evaluate the clinical effects of CROSS on atrophic acne scars in dark-complexioned patients.

An analysis was conducted of 65 patients with atrophic acne scars who were treated with CROSS in our hospitals between July 1996 and July 2001. Thirty-three patients were treated with 65% TCA CROSS and 32 patients were treated with 100% TCA CROSS. All patients had Fitzpatrick skin types IV-V.

Patient treatment data indicated that 27 of 33 patients (82%) (the 65% TCA group) and 30 of 32 patients (94%) (the 100% TCA group) experienced a good clinical response. All patients in the 100% TCA group who received five or six courses of treatment showed excellent results. Good satisfaction rates in the 65% and 100% TCA groups were recorded. There were no cases of significant complication.

CROSS is a safe and very effective single modality for the treatment of atrophic acne scars with no significant complications.

Abstract  Hypomethylation signifies one end of a spectrum of DNA methylation states. In most cases hypomethylation refers to a relative state that represents a change from the "normal" methylation level. Hypomethylation, when approached from a topographical perspective, has been used to describe either overall decreases in the methylation status of the entire genome (global hypomethylation) or more localized relative demethylation of specific subsets of the genome, such as the promoter regions of protooncogenes or normally highly methylated repetitive sequences. Global hypomethylation accompanied by gene-specific hypermethylation is observed in at least two important settings: cancer and aging. Global hypomethylation is generally reflective of decreased methylation in CpGs dispersed throughout repetitive sequences as well as the bodies of genes. Hypomethylation of repetitive and parasitic DNA sequences correlates with a number of adverse outcomes. For example, decreased methylation of repetitive sequences in the satellite DNA of the pericentric region of chromosomes is associated with increased chromosomal rearrangements, a hallmark of cancer. Decreased methylation of proviral sequences can lead to reactivation and increased infectivity. However, hypomethylation in cancer can also affect the CpGs in the promoters of specific genes-namely, protooncogenes-leading to their overexpression and resulting in the functional outcome of increased cell proliferation. Thus, hypomethylation, in a variety of settings in which it represents a deviation from "normal," appears to correlate with progression to cancer and offers potential mechanisms to explain the carcinogenic process.

Abstract  The in vitro toxicity of the drinking water disinfection by products dichloroacetate (DCA) and trichloroacetate (TCA) were studied using the J774A.1 macrophage cell line. DCA and TCA were added to cell cultures at concentrations ranging between 8-32 mM and incubated for 24, 36 and 60 h. DCA and TCA effects on cellular viability, lactate dehydrogenase (LDH) release and superoxide anion (SA) production by the cells, as well as superoxide dismutase (SOD) activities of the cells were determined. DCA and TCA caused time- and concentration-dependent increases in cellular death, in LDH release and production of SA by the cells. The compounds also caused modulations in SOD activities of the cells, with increases observed at the lower concentrations and/or shorter periods of incubations and suppression with the higher concentrations and/or longer periods of incubation. The results of the study indicate that DCA and TCA induce macrophage activation and that the activation is associated with cellular toxicity. Also, DCA and TCA are found to be equitoxic to J774.A1 cells.

Abstract  Perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) have been detected globally in wildlife and humans. Data from a gene array indicate that PFOA decreases organic anion transporting polypeptides (Oatps) in liver. Na(+)-taurocholate cotransporting polypeptide (Ntcp) and Oatp1a1, 1a4, and 1b2 are major transporters responsible for uptake of bile acids (BAs) and other organic compounds into liver. The purpose of the present study was to determine the effects of two perfluorinated fatty acids, PFOA and PFDA, on mRNA and protein expression of hepatic uptake transporters Oatps and Ntcp, and to determine the underlying regulatory mechanisms by using peroxisome proliferator-activated receptor alpha (PPAR-alpha), constitutive androstane receptor, pregnane-X receptor, NF-E2-related factor 2, and farnesoid X receptor-null mouse models. After 2 days following a single i.p. administration, PFOA did not alter serum BA concentrations, but PFDA increased serum BA concentrations 300%. Furthermore, PFOA decreased mRNA and protein expression of Oatp1a1, 1a4, and 1b2, but not Ntcp in mouse liver. In contrast, PFDA decreased mRNA and protein expression of all four transporters, and decreased the mRNA expression in a dose-dependent manner, with the decrease of Oatp1a4 occurring at lower doses than the other three transporters. Multiple mechanisms are likely involved in the down-regulation of mouse Oatps and Ntcp by PFDA. By using the various transcription factor-null mice, PPAR-alpha was shown to play a central role in the down-regulation of Oatp1a1, 1a4, 1b2, and Ntcp by PFDA. The current studies provide important insight into understanding the mechanisms by which PFDA regulate the expression of hepatic uptake transporters. In conclusion, PFOA and PFDA decrease mouse liver uptake transporters primarily via activation of PPAR-alpha.

Abstract  The induction of phagocytic activation in response to prolonged treatment with different doses of dichloroacetate (DCA) and trichloroacetate (TCA) has been investigated in mice. Groups of B6C3F1 male mice were administered 7.7, 77, 154, and 410 mg of DCA or TCA/kg/day, postorally, for 4- and 13-weeks. Peritoneal lavage cells (PLCs) were isolated and assayed for the different biomarkers of phagocytic activation, including superoxide anion (SA), tumor necrosis factor-alpha (TNF-alpha), and myeloperoxidase (MPO). In addition, the role of superoxide dismutase (SOD) in the SA production was also assessed. DCA and TCA produced significant and dose-dependent increases in SA and TNF-alpha production and in MPO activity, but the increases in response to the high doses of the compounds (>77 mg/kg/day) in the 13-week treatment period were less significant than those produced in the 4-week treatment period. Also, dose-dependent increases in SOD activity were observed in both periods of treatments. In general, the results demonstrate significant induction of the biomarkers of phagocytic activation by doses of DCA and TCA that were previously shown to be noncarcinogenic, with significantly greater increases observed at the earlier period of exposure, as compared with later period. These findings may argue against the contribution of those mechanisms to the hepatotoxicity/hepatocarcinogenicity of the compounds and suggest them to be early adaptive/ protective mechanisms against their long-term effects.

Abstract  1. The structures of mammalian cytochrome P-450 isoenzymes have been compared with respect to micro-sequence heterogeneity and their haem-binding cysteinyl peptides. 2. Mechanisms of induction of several P450 gene families are described including transcriptional activation and mRNA stabilization in cytochrome P450 I, II and IV families. 3. The tissue expression and substrate specificity of the cytochrome P450 IV family in liver, kidney and lung have been discussed. 4. The role of hepatic cytochrome P450 IVA1 induction in peroxisome proliferation is presented, and emphasis placed on the identification of susceptible and non-susceptible species.

Abstract  Phagocytosis by polymorphonuclear leukocytes triggers a burst of oxidative metabolism resulting in hydrogen peroxide and superoxide production, and these active oxygen species function in the killing of microorganisms. A new cytochemical technique, based on a manganese dependent diaminobenzidine oxidation, has been developed to detect superoxide in these cells. It has been shown that superoxide generation is associated with the plasma membrane in cells activated by particulate (zymosan) and non-particulate (phorbol myristate acetate) stimuli. This membrane activity is maintained during invagination such that reduced oxygen is generated within the endocytic vacuoles. Reaction product is absent from unstimulated cells; additionally, formation of precipitate is blocked by omission of Mn++, low temperature, glutaraldehyde prefixation, and the presence of superoxide dismutase in the incubation medium.

Abstract  Glutathione transferase-P (GST-P) in rats is specifically expressed in precancerous lesions and in hepatomas induced by carcinogens or spontaneously arising hepatomas. GST-P expression in preneoplastic lesions is suppressed by peroxisome proliferators. To determine the mechanism of suppression of GST-P expression by peroxisome proliferators on a molecular level, we have analyzed the effects of peroxisome proliferators and their receptor (peroxisome proliferator-activated receptor alpha, PPAR alpha) on GST-P expression. GST-P gene expression linked to a reporter gene was specifically suppressed by cotransfection with a PPAR alpha expression plasmid in the presence of the peroxisome proliferator, clofibrate. The target element of the suppression was a 12-O-tetradecanoylphorbol-13-acetate-responsive element located 61 nucleotides upstream from the cap site, which is also internal to a Maf consensus binding sequence. Both Jun and Maf bind to this element and activate the gene having this element, but only Jun-activated expression was specifically inhibited by PPAR alpha. Expression of a transfected reporter gene linked to a PPAR-responsive element was inhibited by cotransfection with a Jun expression plasmid. These results suggest that PPAR alpha and Jun interact and share inhibitory activities, similar to Jun and the glucocorticoid receptor.

Abstract  While glutathione S-transferase P form (GST-P), a reliable marker for preneoplastic lesions induced by mutagenic hepatocarcinogens, is generally not expressed in rat liver foci, hyperplastic nodules and hepatomas induced by peroxisome proliferators (PPs), such lesions can be detected due to their peroxisomal enzyme-negative nature. For comparative purposes we examined the inducibility of enoyl CoA hydratase (ECH), a key peroxisomal enzyme, in rat hepatic preneoplastic lesions induced by mutagenic carcinogens. Clofibrate (CF) was therefore administered for 2 or 4 weeks following performance of the Solt-Farber protocol using diethylnitrosamine and 2-acetylaminofluorene. Immunohistochemical examination revealed no or only very weak expression of ECH within the induced foci in clear contrast to the strong staining of surrounding parenchyma. ECH expression was thus diametrically opposed to that of GST-P which was found only in foci. Although ECH was completely lacking in GST-P-strongly positive foci, it was expressed in GST-P-negative hepatocytes inside some foci otherwise positive for GST-P. CF administration resulted in a significant decrease in the numbers and areas of foci exhibiting strongly positive or positive GST-P staining; this being reflected in a lowering of GST-P protein levels. Furthermore, in primary cultured rat hepatocytes, clofibric acid as well as dexamethasone suppressed the expression of both GST-P and the oncogene, c-jun. These results taken together suggest that possible interaction of the PP receptor with JUN might be involved in loss of ECH expression in GST-P-strongly positive foci.

Abstract  Trichloroacetate (TCA), dichloroacetate (DCA), and bromodichloroacetate (BDCA) are byproducts of the chlorination of drinking water. TCA acts primarily as a peroxisome proliferator, but DCA produces tumors at doses less than required for peroxisome proliferation. BDCA does not induce peroxisome proliferation even at high doses. This study attempts to determine whether differences in the metabolism of the trihaloacetates (THAs) may contribute to their differing toxicological properties. Studies were performed in male B6C3F1 mice given [14C1,2]TCA, [14C1]BDCA, and [14C1,2]DCA by gavage. The replacement of a Cl by a Br greatly enhances THA metabolism. Much less radiolabel from BDCA is retained in the carcass after 24 hr than from TCA. Radiolabel from BDCA is largely found in the urine, with oxalate being the major metabolite. TCA is largely eliminated unchanged in the urine. There are dose-related changes in the rate of CO2 production from BDCA. The initial rate of CO2 production is reduced from 4.1 +/- 0.3 hr-1 at 5 and 20 mg/kg to 2.7 +/- 0.6 hr-1 at 100 mg/kg, but the net conversion to CO2 in 24 hr is greater at the highest dose. As would be predicted, substitution Br for Cl on TCA greatly increased its metabolism.

Abstract  HEEP COPYRIGHT: BIOL ABS. The organics in a Cincinnati, Ohio (USA) drinking water sample were concentrated by a reverse osmosis (RO) process. The diethyl ether soluble extract of the RO concentrate, which was mutagenic in studies using the Ames test (using Salmonella typhimurium), was partitioned into acid and base/neutral fractions. The unpartitioned ethyl ether concentrate, an acid and methylated acid fraction, the unpartitioned base/neutral extract, and 5 base/neutral eluants from a silica gel microcolumn were analzyed for the presence of organics using a computerized gas chromatography/mass spectrometry system (GC/COM) equipped with glass capilalry columns. Analysis of individual fractions indicated a predominance of polychlorinated biphenyls (PCB) and chlorinated aromatics in the 2nd base/neutral partition and many polynuclear aromatics (PNA) in the 4th base/neutral partition. Approximately 460 compounds were identified in this tap water extract, including 41 PNA, 15 PCB and a number of amines, amides and other halogenated species. (Human applicability is discussed. Some of the water impurities may be carcinogenic)./ANATOMY and HISTOLOGY

Abstract  Dichloroacetate (DCA) given gastrically as a single dose to healthy, fed rats caused transient lowering of blood glucose, lactate, and pyruvate. Chronic daily dosing caused lowering of these metabolites and a delay in the return of lactate to basal levels for 48 hr after the final dose. DCA caused activation of the pyruvate dehydrogenase complex (PDHC), with acute multiple dosing or chronic daily dosing. The elevated active PDHC persisted for 12 hr following the final dose. In addition, total PDHC activity was increased with chronic dosing and persisted for 48 hr following the final dose. This increase was not blocked by protein synthesis inhibitors. DCA increased isolated hepatocyte [14C-1]pyruvate oxidation and activated hepatocyte PDHC. Glyoxylate and oxalate, hepatic metabolites of DCA, were inhibitory at similar concentrations.

Abstract  Structurally unrelated peroxisome proliferators induce altered areas (AA), neoplastic nodules (NN), and hepatocellular carcinomas (HCC) in rats and mice. In this study we have examined several AA, NN, and HCC induced by Wy-14,643 and ciprofibrate in rats for gamma-glutamyltranspeptidase (GGT) and the placental form of glutathione S-transferase (GST-P) by histochemical and immunohistochemical procedures, respectively. In Wy-14,643-treated animals 96-100% of NN and HCC was negative for both GGT and GST-P. Eighty-seven % of the AA was negative for both GGT and GST-P, and only 2% was positive for both the marker enzymes. In ciprofibrate-treated animals 52% and 75% of AA were negative for GST-P and GGT, respectively, and 16% was positive for both the enzymes. However, a large majority of NN and HCC (more than 95%) was devoid of both these marker enzymes. Thus these studies clearly indicate that the hepatic lesions induced by peroxisome proliferators display different phenotypic properties as compared to the lesions induced by commonly used classical liver carcinogens. We conclude that GGT and GST-P are not the ideal markers for identifying AA, NN and HCC induced by peroxisome proliferators.

Abstract  Toxicology of disinfectants and disinfectant by-products. Disinfectants. Chlorine gas, chloramine and chlorine dioxide are strong respiratory irritants. Sodium hypochlorite (NaOC1) is also used as bleach and is frequently involved in human poisoning. These exposures, however, are not relevant to exposures in drinking-water. There have been relatively few evaluations of the toxic effects of these disinfectants in drinking-water in experimental animals or humans. Evidence from these animal and human studies suggests that chlorine, hypochlorite solutions, chloramine and chlorine dioxide themselves probably do not contribute to the development of cancer or any toxic effects. Attention has focused on the wide variety of by-products that result from reactions of chlorine and other disinfectants with NOM, which is found in virtually all water sources. Trihalomethanes. THMs induce cytotoxicity in the liver and kidneys of rodents exposed to doses of about 0.5 mmol/kg of body weight. The vehicle of administration significantly affects the toxicity of the THMs. The THMs have little reproductive and developmental toxicity, but BDCM has been shown to reduce sperm motility in rats consuming 39 mg/kg of body weight per day in drinking-water. Like chloroform, BDCM, when administered in corn oil, induces cancer in the liver and kidneys after lifetime exposures to high doses. Unlike chloroform and DBCM, BDCM and bromoform induce tumours of the large intestine in rats exposed by corn oil gavage. BDCM induces tumours at all three target sites and at lower doses than the other THMs. Since the publication of the 1994 WHO Environmental Health Criteria monograph on chloroform, additional studies have added to the weight of evidence indicating that chloroform is not a direct DNA-reactive mutagenic carcinogen. In contrast, the brominated THMs appear to be weak mutagens, probably as a result of GSH conjugation. Haloacetic acids. The HAAs have diverse toxicological effects in laboratory animals. Those HAAs of most concern have carcinogenic, reproductive and developmental effects. Neurotoxic effects are significant at the high doses of DCA that are used therapeutically. Carcinogenic effects appear to be limited to the liver and to high doses. The bulls of the evidence indicates that the tumorigenic effects of DCA and TCA depend on modifying processes of cell division and cell death rather than their very weak mutagenic activities. Oxidative stress is also a feature of the toxicity of the brominated analogues within this class. Both DCA and TCA cause cardiac malformations in rats at high doses. Haloaldehydes and haloketones. Chloral hydrate induces hepatic necrosis in rats at doses equal to or greater than 120 mg/kg of body weight per day. Its depressant effect on the central nervous system in humans is probably related to its metabolite trichloroethanol. Limited toxicity data are available for the other halogenated aldehydes and ketones. Chloroacetaldehyde exposure causes haematological effects in rats. Exposure of mice to 1,1-dichloropropanone (1,1-DCPN), but not 1,3-dichloropropanone (1,3-DCPN), results in liver toxicity. Chloral hydrate was negative in most but not all bacterial tests for point mutations and in in vivo studies on chromosomal damage. However, it has been shown that chloral hydrate may induce structural chromosomal aberrations in vitro and in vivo. Chloral hydrate has been reported to cause hepatic tumours in mice. It is not clear if it is the parent compound or its metabolites that are involved in the carcinogenic effect. The two chloral, hydrate metabolites, TCA and DCA, have induced hepatic tumours in mice. Some halogenated aldehydes and ketones are potent inducers of mutations in bacteria. Clastogenic effects have been reported for chlorinated propanones. Liver tumours were noted in a lifetime drinking-water study with chloroacetaldehyde. Other halogenated aldehydes, e.g., 2-chloropropenal, have been identified as tumour initiators in the skin of mice. The haloketones have not been tested for carcinogenicity in drinking-w ter. However, 1,3-DCPN acted as a tumour initiator in a skin carcinogenicity study in mice. Haloacetonitriles. Testing of these compounds for toxicological effects has been limited to date. Some of the groups are mutagenic, but these effects do not relate well to the activity of the chemicals as tumour initiators in the skin. There are only very limited studies on the carcinogenicity of this class of substances. Early indications of developmental toxicity of members of this class appear to be largely attributable to the vehicle used in treatment. Halogenated hydroxyfuranone derivatives. Based on experimental studies, the critical effects of MX appear to be its mutagenicity and carcinogenicity. Several in vitro studies have revealed that MX is mutagenic in bacterial and mammalian test systems. MX caused chromosomal aberrations and induced DNA damage in isolated liver and testicular cells and sister chromatid exchanges in peripheral lymphocytes from rats exposed in vivo. An overall evaluation of the mutagenicity data shows that MX is mutagenic in vitro and in vivo. A carcinogenicity study in rats showed increased tumour frequencies in several organs. Chlorite. The toxic action of chlorite is primarily in the form of oxidative damage to red blood cells at doses as low as 10 mg/kg of body weight. There are indications of mild neurobehavioural effects in rat pups at 5.6 mg/kg of body weight per day. There are conflicting data on the genotoxicity of chlorite. Chlorite does not increase tumours in laboratory animals in chronic exposure studies. Chlorate. The toxicity of chlorate is similar to that of chlorite, but chlorate is less effective at inducing oxidative damage. It does not appear to be teratogenic or genotoxic in vivo. There are no data from long-term carcinogenicity studies. Bromate. Bromate causes renal tubular damage in rats at high doses. It induces tumours of the kidney, peritoneum and thyroid in rats at doses of 6 mg/kg of body weight and above in chronic studies. Hamsters are less sensitive, and mice are considerably less sensitive. Bromate is also genotoxic in vivo in rats at high doses. Carcinogenicity appears to be secondary to oxidative stress in the cell. Epidemiological studies. Cardiovascular disease. Epidemiological studies have not identified an increased risk of cardiovascular disease associated with chlorinated or chloraminated drinking-water. Studies of other disinfectants have not been conducted. Cancer. The epidemiological evidence is insufficient to support a causal relationship between bladder cancer and long-term exposure to chlorinated drinking-water, THMs, chloroform or other THM species. The epidemiological evidence is inconclusive and equivocal for an association between colon cancer and long-term exposure to chlorinated drinking-water, THMs, chloroform or other THM species. The information is insufficient to allow an evaluation of the observed risks for rectal cancer and risks for other cancers observed in single analytical studies. Various types of epidemiological studies have attempted to assess the cancer risks that may be associated with exposure to chlorinated drinking-water. Chloraminated drinking-water was considered in two studies. Several studies have attempted to estimate exposures to total THMs or chloroform and the other THM species, but the studies did not consider exposures to other DBPs or other water contaminants, which may differ for surface water and groundwater sources. One study considered the mutagenicity of drinking-water as measured by the Salmonella typhimurium assay. Assessments of possible cancer risks that may be associated with drinking-water disinfected with ozone or chlorine dioxide have not been performed. Ecological and death certificate-based case-control studies have provided hypotheses for further evaluation by analytical studies that consider an individual's exposure to drinking-water and possible confounding factors. Analytical studies have reported weak to moderate increased relative risks of bladder, colon, rectal, pancreatic, breast, brain or lung can er associated with long-term exposure to chlorinated drinking-water. Single studies reported associations for pancreatic, breast or brain cancer; however, the evaluation of a possible causal relationship for epidemiological associations requires evidence from more than a single study. In one study, a small increased relative risk of lung cancer was associated with the use of surface water sources, but the magnitude of risk was too small to rule out residual confounding. A case-control study reported a moderately large association between rectal cancer and long-term exposure to chlorinated drinking-water or cumulative THM exposure, but cohort studies have found either no increased risk or a risk too weak to rule out residual confounding. Decreased bladder cancer risk was associated with increased duration of exposure to chloraminated drinking-water, but there is no biological basis for assuming a protective effect of chloraminated water. Although several studies found increased risks of bladder cancer associated with long-term exposure to chlorinated drinking-water and cumulative exposure to THMs, inconsistent results were reported among the studies for bladder cancer risks between smokers and non-smokers and between men and women. Estimated exposure to THMs was considered in three of these studies. In one study, no association was found between estimated cumulative exposure to THMs. In another study, a moderately strong increased relative risk was associated with increased cumulative exposure to THMs in men but not in women. The third study reported a weak increased relative risk associated with an estimated cumulative exposure of 1957-6425 ug of THMs per litre-year; weak to moderate associations were also reported for exposure to THM concentrations greater than 24, greater than 49 and greater than 74 ug/litre. No increased relative risk of bladder cancer was associated with exposure to chlorinated municipal surface water supplies, chloroform or other THM species in a cohort of women, but the follow-up period of 8 years was very short, resulting in few cases for study. Because inadequate attention has been paid to assessing exposure to water contaminants in epidemiological studies, it is not possible to properly evaluate the increased relative risks that were reported. Specific risks may be due to other DBPs, mixtures of by-products or other water contaminants, or they may be due to other factors for which chlorinated drinking-water or THMs may serve as a surrogate. Adverse pregnancy outcomes. Studies have considered exposures to chlorinated drinking-water, THMs or THM species and various adverse outcomes of pregnancy. A scientific panel recently convened by the US Environmental Protection Agency reviewed the epidemiological studies and concluded that the results of currently published studies do not provide convincing evidence that chlorinated water or THMs cause adverse pregnancy outcomes. Results of early studies are difficult to interpret because of methodological limitations or suspected bias. A recently completed but not yet published case-control study has reported moderate increased relative risks for neural tube defects in children whose mothers' residence in early pregnancy was in an area where THM levels were greater than 40 ug/litre. Replication of the results in another area is required before this association can be properly evaluated. A previously conducted study in the same geographic area reported a similar association, but the study suffered from methodological limitations. A recently reported cohort study found an increased risk of early miscarriage associated with heavy consumption of water (five or more glasses of cold tapwater per day) containing high levels ( > 75 ug/litre) of THMs. When specific THMs were considered, only heavy consumption of water containing BDCM ( > 18 ug/litre) was associated with a risk of miscarriage. As this is the first study to suggest an adverse reproductive effect associated with a brominated by-product, a scientific panel recommended that another study be conducted in a different geographic area to attempt to replicate these results and that additional efforts be made to evaluate exposures of the cohort to other water contaminants. Risk characterization. It should be noted that the use of chemical disinfectants in water treatment usually results in the formation of chemical by-products, some of which are potentially hazardous. However, the risks to health from these by-products at the levels at which they occur in drinking-water are extremely small in comparison with the risks associated with inadequate disinfection. Thus, it is important that disinfection not be compromised in attempting to control such by-products. Characterization of hazard and dose-response. Toxicological studies. Chlorine. A WHO Working Group for the 1993 Guidelines for drinking-water quality considered chlorine. This Working Group determined a tolerable daily intake (TDI) of 150 ug/kg of body weight for free chlorine based on a no-observed-adverse-effect level (NOAEL) of approximately 15 mg/kg of body weight per day in 2-year studies in rats and mice and incorporating an uncertainty factor of 100 (10 each for intra- and interspecies variation). There are no new data that indicate that this TDI should be changed. Monochloramine. A WHO Working Group for the 1993 Guidelines for drinking-water quality considered monochloramine. This Working Group determined a TDI of 94 ug/kg of body weight based on a NOAEL of approximately 9.4 mg/kg of body weight per day, the highest dose tested, in a 2-year bioassay in rats and incorporating an uncertainty factor of 100 (10 each for intra- and interspecies variation). There are no new data that indicate that this TDI should be changed. Chlorine dioxide. The chemistry of chlorine dioxide in drinking-water is complex, but the major breakdown product is chlorite. In establishing a specific TDI for chlorine dioxide, data on both chlorine dioxide and chlorite can be considered, given the rapid hydrolysis to chlorite. Therefore, an oral TDI for chlorine dioxide is 30 ug/kg of body weight, based on the NOAEL of 2.9 mg/kg of body weight per day for neurodevelopmental effects of chlorite in rats. Trihalomethanes. Cancer following chronic exposure is the primary hazard of concern for this class of DBPs. Because of the weight of evidence indicating that chloroform can induce cancer in animals only after chronic exposure to cytotoxic doses, it is clear that exposures to low concentrations of chloroform in drinking-water do not pose carcinogenic risks. The NOAEL for cytolethality andregenerative hyperplasia in mice was 10 mg/kg of body weight per day after administration of chloroform in corn oil for 3 weeks. Based on the mode of action evidence for chloroform carcinogenicity, a TDI of 10 ug/kg of body weight was derived using, the NOAEL for cytotoxicity in mice and applying an uncertainty factor of 1000 (10 each for inter- and intra-species variation and 10 for the short duration of the study). This approach is supported by a number of additional studies. This TDI is similar to the TDI derived in the 1998 WHO Guidelines for drinking-water quality, which was based on a 1979 study in which dogs were exposed for 7.5 years. Among the brominated THMs, BDCM is of particular interest because it produces tumours in rats and mice and at several sites (liver, kidneys, large intestine) after corn oil gavage. The induction of colon tumours in rats by BDCM (and by bromoform) is also interesting because of the epidemiological associations with colo-rectal cancer. BDCM and the other brominated THMs are also weak mutagens. It is generally assumed that mutagenic carcinogens will produce linear dose-response relationships at low doses, as mutagenesis is generally considered to be an irreversible and cumulative effect. In a 2-year bioassay, BDCM given by corn oil gavage induced tumours (in conjunction with cytotoxicity and increased proliferation) in the kidneys of mice and rats at doses of 50 and 100 mg/kg of body weight per day, respectively. The tumours in the large intestine of the rat occurred after exposure to both 50 and 100 mg/kg of body weight per day. Using the incidence of kidney tumours in male mice from this study, quantitative risk estimates have been calculated, yielding a slope factor of 4.8 x 10-3 [mg/kg of body weight per day]-1 and a calculated dose of 2.1 ug/kg of body weight per day for a risk level of 10-5. A slope factor of 4.2 x 10-3 [mg/kg of body weight per day]-3 (2.4 ug/kg of body weight per day for a 10-5 risk) was derived based on the incidence of large intestine carcinomas in the male rat. The International Agency for Research on Cancer (IARC) has classified BDCM in Group 2B (possibly carcinogenic to humans). DBCM and bromoform were studied in long-term bioassays. In a 2-year corn oil gavage study, DBCM induced hepatic tumours in female mice, but not in rats, at a dose of 100 mg/kg of body weight per day. In previous evaluations, it had been suggested that the corn oil vehicle may play a role in the induction of tumours in female mice. A small increase in tumours of the large intestine in rats was observed in the bromoform study at a dose of 200 mg/kg of body weight per day. The slope factors based on these tumours are 6.5 X 10-3 [mg/kg of body weight per day]-1 for DBCM, or 1.5 ug/kg of body weight per day for a 10-5 risk, and 1.3 x 10-3 [mg/kg of body weight per day]-1 or 7.7 ug/kg of body weight per day for a 10-5 risk for bromoform. These two brominated THMs are weakly mutagenic in a number of assays, and they were by far the most mutagenic DBPs of the class in the GST-mediated assay system. Because they are the most lipophilic THMs, additional concerns about whether corn oil may have affected their bioavailability in the long-term studies should be considered. A NOAEL for DBCM of 30 mg/kg of body weight per day has been established based on the absence of histopathological effects in the liver of rats after 13 weeks of exposure by corn oil gavage. IARC has classified DBCM in Group 3 (not classifiable as to its carcinogenicity to humans). A TDI for DBCM of 30 ug/kg of body weight was derived based on the NOAEL for liver toxicity of 30 mg/kg of body weight per day and an uncertainty factor of 1000 (10 each for inter- and intraspecies variation and 10 for the short duration of the study and possible carcinogenicity). Similarly, a NOAEL for bromoform of 25 mg/kg of body weight per day can be derived on the basis of the absence of liver lesions in rats after 13 weeks of dosing by corn oil gavage. A TDI for bromoform of 25 ug/kg of body weight was derived based on this NOAEL for liver toxicity and an uncertainty factor of 1000 (10 each for interand intraspecies variation and 10 for the short duration of the study and possible carcinogenicity). IARC has classified bromoform in Group 3 (not classifiable as to its carcinogenicity to humans). Haloacetic acids. The induction of mutations by DCA is very improbable at the low doses that would be encountered in chlorinated drinking-water. The available data indicate that DCA differentially affects the replication rates of normal hepatocytes and hepatocytes that have been initiated. The dose-response relationships are complex, with DCA initially stimulating division of normal hepatocytes. However, at the lower chronic doses used in animal studies (but still very high relative to those that would be derived from drinking-water), the replication rate of normal hepatocytes is eventually sharply inhibited. This indicates that normal hepatocytes eventually down-regulate those pathways that are sensitive to stimulation by DCA. However, the effects in altered cells, particularly those that express high amounts of a protein that is immunoreactive to a c-Jun antibody, do not seem to be able to down-regulate this response. Thus, the rates of replication in the pre-neoplastic lesions with this phenotype are very high at the doses that cause DCA tumours to develop with a very low latency. Preliminary data would suggest that this continued alteration in cell birth and death rates is also necessary for the tumours to progress to malignancy. This interpretation is supported by studies that employ initiation/promotion designs as well. On the basis of the above considerations, it is suggested that the currently available cancer risk estimates for DCA be modified by incorporation of newly developing information on its comparative metabolism and modes of action to formulate a biologically based dose-response model. These data are not available at this time, but they should become available within the next 2-3 years. The effects of DCA appear to be closely associated with doses that induce hepatomegaly and glycogen accumulation in mice. The lowest-observed-adverse-effect level (LOAEL) for these effects in an 8-week study in mice was 0.5 g/litre, corresponding to approximately 100 mg/kg of body weight per day, and the NOAEL was 0.2 g/litre, or approximately 40 mg/kg of body weight per day. A TDI of 40 ug/kg of body weight has been calculated by applying an uncertainty factor of 1000 to this NOAEL (10 each for inter- and intraspecies variation and 10 for the short duration of the study and possible carcinogenicity). IARC has classified DCA in Group 3 (not classifiable as to its carcinogenicity to humans). TCA is one of the weakest activators of the peroxisome proliferator activated receptor (PPAR) known. It appears to be only marginally active as a peroxisome proliferator, even in rats. Furthermore, treatment of rats with high levels of TCA in drinking-water does not induce liver tumours. These data strongly suggest that TCA presents little carcinogenic hazard to humans at the low concentrations found in drinking-water. From a broader toxicological perspective, the developmental effects of TCA are the end-point of concern. Animals appear to tolerate concentrations of TCA in drinking-water of 0.5 g/litre (approximately 50 mg/kg of body weight per day) with little or no signs of adverse effect. At 2 g/litre, the only sign of adverse effect appears to be hepatomegaly. Hepatomegaly is not observed in mice at doses of 0.35 g of TCA per litre in drinking-water, estimated to be equivalent to 40 mg/kg of body weight per day. In another study, soft tissue anomalies were observed at approximately 3 times the control rate at the lowest dose administered, 330 mg/kg of body weight per day. At this dose, the anomalies were mild and would clearly be in the range where hepatomegaly (and carcinogenic effects) would occur. Considering the fact that the PPAR interacts with cell signalling mechanisms that can affect normal developmental processes, a common mechanism underlying hepatomegaly and the carcinogenic effects and developmental effects of this compound should be, considered. The TDI for TCA is based on a NOAEL estimated to be 40 mg/kg of body weight per day for hepatic toxicity in a long-term study in mice. Application of an uncertainty factor of 1000 (10 each for interand intraspecies variation and 10 for possible carcinogenicity) to the estimated NOAEL gives a TDI of 40 ug/kg of body weight. IARC has classified TCA in Group 3 (not classifiable as to its carcinogenicity to humans). Data on the carcinogenicity of brominated acetic acids are too preliminary to be useful in risk characterization. Data available in abstract form suggest, however, that the doses required to induce hepatocarcinogenic responses in mice are not dissimilar to those of the chlorinated acetic acids. In addition to the mechanisms involved in the induction of cancer by DCA and TCA, it is possible that increased oxidative stress secondary to their metabolism might contribute to their effects. There are a significant number of data on the effects of dibromo-acetic acid (DBA) on male reproduction. No effects were observed in rats at doses of 2 mg/kg of body weight per day for 79 days, whereas an increased retention of step 19 spermatids was observed at 10 mg/kg of body weight per day. Higher doses led to progressively more severe effects, including marked atrophy of the seminiferous tubules with 250 mg/kg of body weight per day, which was not reversed 6 months after treatment was suspended. A TDI of 20 ug/kg of body weight was determined by allocating an uncertainty factor of 100 (10 each for inter- and intraspecies variation) to the NOAEL of 2 mg/kg of body weight per day. Chloral hydrate. Chloral hydrate at 1 g/litre of drinking-water (166 mg/kg of body weight per day) induced liver tumours in mice exposed for 104 weeks. Lower doses have not been evaluated. Chloral hydrate has been shown to induce chromosomal anomalies in several in vitro tests but has been largely negative when evaluated in vivo. It is probable that the liver tumours induced by chloral hydrate involve its metabolism to TCA and/or DCA. As discussed above, these compounds are considered to act as tumour promoters. IARC has classified chloral hydrate in Group 3 (not classifiable as to its carcinogenicity to humans). Chloral hydrate administered to rats for 90 days in drinking-water induced hepatocellular necrosis at concentrations of 1200 mg/litre and above, with no effect being observed at 600 mg/litre (approximately 60 mg/kg of body weight per day). Hepatomegaly was observed in mice at doses of 144 mg/kg of body weight per day administered by gavage for 14 days. No effect was observed at 14.4 mg/kg of body weight per day in the 14-day study, but mild hepatomegaly was observed when chloral hydrate was administered in drinking-water at 70 mg/litre (16 mg/kg of body weight per day) in a 90-day follow-up study. The application of an uncertainty factor of 1000 (10 each for inter- and intraspecies variation and 10 for the use of a LOAEL instead of a NOAEL) to this value gives a TDI of 16 ug/kg of body weight. Haloacetonitriles. Without appropriate human data or an animal study that involves a substantial portion of an experimental animal's lifetime, there is no generally accepted basis for estimating carcinogenic risk from the HANs. Data developed in subchronic studies provide some indication of NOAELs for the general toxicity of dichloroacetonitrile (DCAN) and dibromoacetonitrile (DBAN). NOAELs of 8 and 23 mg/kg of body weight per day were identified in 90-day studies in rats for DCAN and DBAN, respectively, based on decreased body weights at the next higher doses of 33 and 45 mg/kg of body weight per day, respectively. A WHO Working Group for the 1993 Guidelines for drinking-water quality considered DCAN and DBAN. This Working Group determined a TDI of 15 ug/kg of body weight for DCAN based on a NOAEL of 15 mg/kg of body weight per day in a reproductive toxicity study in rats and incorporating an uncertainty factor of 1000 (10 each for intra- and interspecies variation and 10 for the severity of effects). Reproductive and developmental effects were observed with DBAN only at doses that exceeded those established for general toxicity (about 45 mg/kg of body weight per day). A TDI of 23 ug/kg of body weight was calculated for DBAN based on the NOAEL of 23 mg/kg of body weight per day in the 90-day study in rats and incorporating an uncertainty factor of 1000 (10 each for intra- and interspecies variation and 10 for the short duration of the study). There are no new data indicating that these TDIs should be changed. LOAELs for trichloroacetonitrile (TCAN) of 7.5 mg/kg of body weight per day for embryotoxicity and 15 mg/kg of body weight per day for developmental effects were identified. However, later studies suggest that these responses were dependent upon the vehicle used. No TDI can be established for TCAN. There are no data useful for risk characterization purposes for other members of the HANs. MX. The mutagen MX has recently been studied in a long-term study in rats in which some carcinogenic responses were observed. These data indicate that MX induces thyroid and bile duct tumours. An increased incidence of thyroid tumours was seen at the lowest dose of MX administered (0.4 mg/kg of body weight per day). The induction of thyroid tumours with high-dose chemicals has long been associated with halogenated compounds. The induction of thyroid follicular tumours could involve modifications in thyroid function or a mutagenic mode of action. A dose-related increase in the incidence of cholangioma and cholangiocarcinomas was also observed, beginning at the low dose in female rats, with a more modest response in male rats. The increase in cholangiomas and cholangiocarcinomas in female rats was utilized to derive a slope factor for cancer. The 95% upper confidence limit for a 10-5 lifetime risk based on the linearized multistage model was calculated to be 0.06 ug/kg of body weight per day. Chlorite. The primary and most consistent finding arising from exposure to chlorite is oxidative stress resulting in changes in the red blood cells. This end-point is seen in laboratory animals and, by analogy with chlorate, in humans exposed to high doses in poisoning incidents. There are sufficient data available with which to estimate a TDI for humans exposed to chlorite, including chronic toxicity studies and a two-generation reproductive toxicity study. Studies in human volunteers for up to 12 weeks did not identify any effect on blood parameters at the highest dose tested, 36 ug/kg of body weight per day. Because these studies do not identify an effect level, they are not informative for establishing a margin of safety. In a two-generation study in rats, a NOAEL of 2.9 mg/kg of body weight per day was identified based on lower auditory startle amplitude, decreased absolute brain weight in the F1 and F2 generations, and altered liver weights in two generations. Application of an uncertainty factor of 100 (10 each for inter- and intraspecies variation) to this NOAEL gives a TDI of 30 ug/kg of body weight. This TDI is supported by the human volunteer studies. Chlorate. Like chlorite, the primary concern with chlorate is oxidative damage to red blood cells. Also like chlorite, 0.036 mg of chlorate per kg of body weight per day for 12 weeks did not result in any adverse effect in human volunteers. Although the database for chlorate is less extensive than that for chlorite, a recent well conducted 90-day study in rats identified a NOAEL of 30 mg/kg of body weight per day based on thyroid gland colloid depletion at the next higher dose of 100 mg/kg of body weight per day. A TDI is not derived because a long-term study is in progress, which should provide more information on chronic exposure to chlorate. Bromate. Bromate is an active oxidant in biological systems and has been shown to cause an increase in renal tumours, peritoneal mesotheliomas and thyroid follicular cell tumours in rats and, to a lesser extent, hamsters, and only a small increase in kidney tumours in mice. The lowest dose at which an increased incidence of renal tumours was observed in rats was 6 mg/kg of body weight per day. Bromate has also been shown to give positive results for chromosomal aberrations in mammalian cells in vitro and in vivo but not in bacterial assays for point mutation. An increasing body of evidence, supported by the genotoxicity data, suggests that bromate acts by generating oxygen radicals in the cell. In the 1993 WHO Guidelines for drinking-water quality, the linearized multistage model was applied to the incidence of renal tumours in a 2-year carcinogenicity study in rats, although it was noted that if the mechanism of tumour induction is oxidative damage in the kidney, application of the low-dose cancer model may not be appropriate. The calculated upper 95% confidence interval for a 10-5 risk was 0.1 ug/kg of body weight per day. The no-effect level for the formation of renal cell tumours in rats is 1.3 mg/kg of body weight per day. If this is used as a point of departure from linearity and if an uncertainty factor of 1000 (10 each for inter- and intraspecies variation and 10 for possible carcinogenicity) is applied, a TDI of 1 ug/kg of body weight can be calculated. This compares with the value of 0.1 ug/kg of body weight per day associated with an excess lifetime cancer risk of 10-5. At present, there are insufficient data to permit a decision on whether bromate-induced tumours are a result of cytotoxicity and reparative hyperplasia or a genotoxic effect. IARC has assigned potassium bromate to Group 2B (possibly

Abstract  Peroxisome proliferators activate nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha) and enhance the transcription of several genes in liver. We report here that synthetic PPARalpha ligands Wy-14,643, ciprofibrate, clofibrate, and others induce the nuclear translocation of constitutive androstane receptor (CAR) in mouse liver cells in vivo. Adenoviral-enhanced green fluorescent protein-CAR expression demonstrated that PPARalpha synthetic ligands drive CAR into the hepatocyte nucleus in a PPARalpha- and PPARbeta-independent manner. This translocation is dependent on the transcription coactivator PPAR-binding protein but independent of coactivators PRIP and SRC-1. PPARalpha ligand-induced nuclear translocation of CAR is not associated with induction of Cyp2b10 mRNA in mouse liver. PPARalpha ligands interfered with coactivator recruitment to the CAR ligand binding domain and reduced the constitutive transactivation of CAR. Both Wy-14,643 and ciprofibrate occupied the ligand binding pocket of CAR and adapted a binding mode similar to that of the CAR inverse agonist androstenol. These observations, therefore, provide information for the first time to indicate that PPARalpha ligands not only serve as PPARalpha agonists but possibly act as CAR antagonists.

Abstract  Nasal telangiectasia is a common disfiguring condition and may cause significant psychological distress. Although lasers are effective in treating such lesions, there are many disadvantages, such as purpura, scarring, and cost.

To assess the effectiveness of a combination therapy of CO2 laser and trichloroacetic acid (TCA) for nasal telangiectasia.

Twenty patients with nasal telangiectasia were treated with CO2 laser 2 weeks after modified sclerotherapy using 80% TCA.

After one treatment session, all patients had excellent results with more than 75% vessel clearance. There were mild side effects, such as transient erythema and fine frosting. After follow-up of 1 year, there were no relapses.

We conclude that CO2 laser after modified sclerotherapy using 80% TCA appears to be a simple, effective, and inexpensive method for the treatment of nasal telangiectasia.

Abstract  The disposition of dichloroacetic acid (DCA) was investigated in Fischer 344 rats over the 48 h after oral gavage of 282 mg/kg of 1- or 2-[14C]-DCA (1-DCA or 2-DCA) and 28.2 mg/kg of 2-DCA. DCA was absorbed quickly, and the major route of disposition was through exhalation of carbon dioxide and elimination in the urine. The dispositions of 1- and 2-DCA at 282 mg/kg were similar. With 2-DCA, the disposition differed with dose in that the percentage of the dose expired as carbon dioxide decreased from 34.4% (28.2 mg/kg) to 25.0% (282 mg/kg), while the percentage of the radioactivity excreted in the urine increased from 12.7 to 35.2%. This percentage increase in the urinary excretion was mostly attributable to the presence of unmetabolized DCA, which comprised more than 20% at the higher dose and less than 1% at the lower dose. The major urinary metabolites were glycolic acid, glyoxylic acid, and oxalic acid. DCA and its metabolites accumulated in the tissues and were eliminated slowly. After 48 h, 36.4%, 26.2%, and 20.8% of the dose was retained in the tissues of rats administered 28.2 and 282 mg/kg of 2-DCA and 282 mg/kg of 1-DCA, respectively. Of the organs examined, the liver (4.9-7.9% of dose) and muscle (4.5-9.9%) contained the most radioactivity, followed by skin (3.3-4.5%), blood (1.4-2.6%), and intestines (1.0-1.7%). One metabolite, glyoxylic acid, which is mutagenic, might be responsible for or contribute to the carcinogenicity of DCA.

Abstract  Trichloroacetic acid (TCA) and dichloroacetic acid (DCA) are environmental contaminants that are suspected human carcinogens. To obtain more detail on the role of the liver in the kinetics of TCA and DCA, experimental studies in the isolated perfused rat liver (IPRL) system were conducted. The IPRL system was dosed with either 5 or 50 micromol of either TCA or DCA (25 or 250 microM initial concentration, respectively). TCA and DCA concentrations were followed in perfusion medium and bile for 2 h. The chemical concentration in liver was determined at the end of exposure. Liver viability was monitored by measuring leakage of lactate dehydrogenase (LDH) into perfusion medium and the rate of bile production. Studies performed with TCA showed that the total TCA concentration in perfusion medium decreased slightly during the first 30 min of exposure and remained constant thereafter. Most TCA, greater than 90% of total, was bound to albumin in the perfusion medium. A low, linear excretion rate of TCA in bile was obtained. The calculated free TCA concentration in the liver intracellular water space was higher than the unbound TCA concentration in the perfusion medium. Parallel studies with DCA showed that the DCA concentration in perfusion medium decreased rapidly. Of the total DCA in the perfusion medium, 60% was bound to albumin. The concentration of DCA in bile decreased over time. There was no DCA detectable in the liver after 2 h of exposure at both DCA concentrations. Enzyme leakage and bile production did not change in the presence of TCA or DCA, indicating that these concentrations were not acutely cytotoxic to the liver.

Abstract  Induction of liver cancer by peroxisome proliferators such as nafenopin is frequently associated with increased liver growth, increased DNA synthesis and suppression of apoptosis. The cytokine, tumour necrosis factor alpha (TNF alpha), and non-parenchymal liver cells have been implicated in mediating the hepatic response to peroxisome proliferators. Here, we have investigated the dependency of the hepatocyte response to peroxisome proliferators on non-parenchymal cells, a major source of hepatic cytokines. Addition of non-parenchymal cells, or conditioned medium from non-parenchymal cell cultures, increased DNA synthesis (220% and 270% of control, respectively) and suppressed transforming growth factor beta(1)-induced hepatocyte apoptosis (32% and 54% of control, respectively). Removal of non-parenchymal cells from normal hepatocyte cultures prevented both the nafenopin- and TNF alpha-induced increase in DNA synthesis and suppression of hepatocyte apoptosis; this response was restored by returning non-parenchymal cells to the purified hepatocytes. TNF alpha was detected in the medium of non-parenchymal cell (3-15 pg/ml) and normal hepatocyte cultures (25-100 pg/ml) by bioassay using L929 cells. However, the contribution of TNF alpha released from non-parenchymal cells was small compared with that released spontaneously by hepatocytes. Nafenopin significantly increased the release of TNF alpha from non-parenchymal cells to 56 +/- 18 pg/ml, but had little effect on TNF alpha release by hepatocytes. However, the concentration of exogenous TNF alpha required to elicit a response in hepatocytes was 100 pg/ml and above. These data provide evidence that hepatic non-parenchymal cells are permissive for the growth response of hepatocytes in vitro to peroxisome proliferators and this may be mediated, at least in part by TNF alpha. However, the levels of TNF alpha released spontaneously or in response to peroxisome proliferators are insufficient per se to induce a growth response.