Centrilobular Hepatocyte Necrosis Research Articles

Ischemic Hepatitis Arising in the Setting of Hitherto Undiagnosed Cirrhosis Secondary to Hemochromatosis

Ischemic hepatitis (IH) is characterized by an abrupt, marked but reversible increase in serum aminotransferase concentration(s) arising within a clinical setting of circulatory failure and systolic hypotension, in which other possible causes of hepatocellular necrosis can be excluded reliably. The histological hallmarks are centrilobular hepatocyte necrosis, central vein congestion and distortion of adjacent hepatic sinusoids. Prompt recovery may follow but the overall course is governed by underlying disease. It is unclear if the presence of end-stage liver disease (ESLD), whether as the result of hepatic congestion or otherwise, predisposes patients to develop IH more readily. A 45 year-old man with non-ischemic cardiomyopathy was transferred for management of cardiogenic shock. He was intubated, and had an intra-aortic balloon pump in situ. Despite inotropic support he remained hypotensive (mean BP: 82/46 mm Hg). Physical examination demonstrated no external evidence of ESLD. Laboratory data were as follows: aspartate aminotransferase 1860 IU/L (normal range [NR]: 10–60), alanine aminotransferase 1494 IU/L (NR: 10–60), prothrombin time 23.8 s (11.1–13.1) and total serum bilirubin 2.3 mg% (NR: 0.2–1.2). Acute hepatitis A, B and C virus infections were excluded on the basis of appropriate serologic testing. His antinuclear antibody titer was weakly positive (1:40). The serum ceruloplasmin concentration was 39 mg% (NR: 20–60). His serum ferritin concentration was 7774 ng/mL (NR: 30–300), and the iron saturation 68% (NR: 14–50). Liver histology revealed cirrhosis (Masson trichome stain), and grade 4/4 iron overload involving hepatocytes, Kupffer cells and the biliary epithelium (Prussian blue iron stain). In some centrilobular areas prior hepatocyte loss consistent with ischemic injury was evident, but not chronic passive congestion. Testing for the commonest mutations in the hemochromatosis (HC) gene was negative. Despite improvement in liver tests with further supportive care, he developed renal dysfunction. Continued systolic hypotension precluded hemodialysis, and the patient died 21 days after transfer from complications of ESLD. This man's clinical and laboratory picture at the time of transfer was entirely consistent with IH. However, cirrhosis secondary to HC was the dominant histologic abnormality, almost totally obscuring changes of IH. The diagnosis of HC, although unexpected, was important so as to avoid unnecessary efforts at cardiac transplant evaluation.

Final Report on the Safety Assessment of Capsicum Annuum Extract, Capsicum Annuum Fruit Extract, Capsicum Annuum Resin, Capsicum Annuum Fruit Powder, Capsicum Frutescens Fruit, Capsicum Frutescens Fruit Extract, Capsicum Frutescens Resin, and Capsaicin1

Final Report on the Safety Assessment of Capsicum Annuum Extract, Capsicum Annuum Fruit Extract, Capsicum Annuum Resin, Capsicum Annuum Fruit Powder, Capsicum Frutescens Fruit, Capsicum Frutescens Fruit Extract, Capsicum Frutescens Resin, and Capsaicin1

Acute Hepatitis and Liver Failure Associated With Influenza A Infection in Children

Acute Hepatitis and Liver Failure Associated With Influenza A Infection in Children

A Crucial Role of Nrf2 in In Vivo Defense against Oxidative Damage by an Environmental Pollutant, Pentachlorophenol

Our goal was to elucidate roles of Nrf2 in in vivo defense against pentachlorophenol (PCP), an environmental pollutant and hepatocarcinogen in mice. We examined oxidative stress and cell proliferation, along with other hepatotoxicological parameters, in the livers of nrf2-deficient (wild:+/+, heterozygous:+/-, homozygous:-/-) animals fed PCP in their diet at doses of 0, 150, 300, 600, or 1200 ppm for 4 weeks. For measurement of methoxyresorufin-O-demethylase (CYP 1A2), NAD(P):quinone oxidoreductase 1 (NQO1), and UDP-glucuronosyltransferase (UDP-GT), an additional study was performed with all but the 150-ppm dose. Significant elevation of 8-hydroxydeoxyguanosine (8-OH-dG) levels in the liver DNA was observed only in -/- mice treated with PCP at 1200 ppm. Levels of thiobarbituric-acid-reactive substances (TBARS) were also raised significantly compared to those of the relevant +/+ mice. Bromodeoxyuridine labeling indices (BrdU-LIs) of hepatocytes in -/- mice were significantly higher at all doses than those in the relevant +/+ mice. Relative liver weights were unchanged in mice lacking Nrf2, whereas liver weight in +/+ and +/- mice was increased. Significant elevations of serum ALP activity, but not ALT and AST activity, occurred at 600 ppm and above in -/- mice compared to the relevant +/+ mice. Histopathologically, centrilobular hepatocyte necrosis was severe in the -/- mice that received 600 ppm. Although CYP 1A2 activity was elevated in all treated mice, increases in NQO1 levels and UDP-GT activities did not occur only in -/- mice. These data suggest that Nrf2 plays a key role in prevention of PCP-induced oxidative stress and cell proliferation.

Are parenchymal changes in early post-transplant biopsies related to preservation-reperfusion injury or rejection?

The progression of parenchymal changes in liver allograft biopsies due to preservation-reperfusion injury (PRI) and their differentiation from rejection related changes is poorly understood. The aim of this study was to determine which changes in a 1-week posttransplant biopsy could be attributed to PRI and which to acute rejection. One week protocol liver transplant biopsies from patients with mild PRI (day 1 AST<400 IU/L) were compared with those from patients with severe PRI (day 1 AST>2000 IU/L). Parenchymal changes (cholestasis, ballooning, steatosis, necrosis) and rejection-related inflammatory features (portal tract inflammation, bile duct inflammation, portal vein endothelial inflammation, hepatic vein endothelial inflammation, and centrilobular inflammation) were blindly assessed semiquantitatively. Fat, cholestasis, and hepatocyte ballooning were significantly worse in the severe PRI group, and these features showed no correlation with histological features related to acute rejection. Centrilobular hepatocyte necrosis correlated with hepatic venular endothelial inflammation and centrilobular inflammation but not with rejection related features in portal tracts or with PRI. These findings suggest that centrilobular necrosis is a manifestation of a rejection-related parenchymal injury and may involve different pathogenetic mechanisms to rejection-related features in portal tracts. This study indicates that in early posttransplant biopsies, fat, cholestasis, and ballooning can largely be attributed to PRI. By contrast, centrilobular hepatocyte loss should be suspected as a rejection related phenomenon, even if typical portal tract changes are not prominent, and augmentation of immunosuppression should be considered.

MECHANISMS OF 1,1-DICHLOROETHYLENE-INDUCED CYTOTOXICITY IN LUNG AND LIVER*,†

Exposure to 1,1-dichloroethylene (DCE) causes lung and liver toxicities in mice. The lesions are characterized by damage preferentially to bronchiolar Clara cells in the lung and necrosis of centrilobular hepatocytes in the liver. The primary metabolites formed from DCE in lung and liver microsomal incubations are the epoxide, 2,2-dichloroacetaldehyde and 2-chloroacetyl chloride, which undergo hydrolysis and/or conjugation with glutathione (GSH). The major products formed are the epoxide-derived GSH conjugates 2-(S-glutathionyl) acetyl glutathione [B] and 2-S-glutathionyl acetate [C]. The hydrate of 2,2-dichloroacetaldehyde (acetal) is also detected. These metabolites are detected in vivo in murine lung and liver cytosol and in bile, and importantly, also in human lung and liver microsomal incubations. Formation of the epoxide is mediated mainly by CYP2E1. Immunohistochemical studies localized the epoxide-derived GSH conjugate [C] and cysteine-containing proteins in Clara cells and centrilobular hepatocytes. These findings are consistent with the premise that the lung and liver cytotoxicities induced by DCE are associated with in situ formation of the epoxide within the target cells.

Evidence for the involvement of N-methylthiourea, a ring cleavage metabolite, in the hepatotoxicity of methimazole in glutathione-depleted mice: structure-toxicity and metabolic studies.

In mice depleted of GSH by treatment with buthionine sulfoximine (BSO), methimazole (2-mercapto-1-methylimidazole, MMI) causes liver injury characterized by centrilobular necrosis of hepatocytes and an increase in serum alanine transaminase (SALT) activity. MMI requires metabolic activation by both P450 monooxygenase and flavin-containing monooxygenase (FMO) before it produces the hepatotoxicity. MMI and its analogues were examined for the ability to increase SALT activity in GSH-depleted mice. Saturation of the C-4,5 double bond in MMI resulted in a complete loss of hepatotoxicity. Similarly, ring fusion of a benzene nucleus to the C-4,5 double bond, forming 2-mercapto-1-methylbenzimidazole, abolished the toxic potency. As for MMI, 2-mercapto-1,4,5-trimethylimidazole, and 2-mercapto-1-methyl-4, 5-di-n-propylimidazole, the toxic potency decreased with the increasing bulk of the 4- and 5-alkyl substituents. Furthermore, methylation of the thiol group of MMI totally reduced its toxicity. These structural requirements and the known toxicity of thiono-sulfur compounds led us to the hypothesis that MMI would undergo epoxidation of the C-4,5 double bond by P450 enzymes and, after being hydrolyzed, the resulting epoxide would be then decomposed to form N-methylthiourea, a proximate toxicant. Before N-methylthiourea would produce toxicity, it would be further biotransformed to its S-oxidized metabolites mainly by FMO. Evidence for this hypothesis was provided by the facts that N-methylthiourea and glyoxal as the accompanying fragment were identified as urinary metabolites in mice treated with MMI and that N-methylthiourea caused a marked increase in SALT activity when administered to mice in combination with BSO.

Metabolism‐dependent hepatotoxicity of methimazole in mice depleted of glutathione

Methimazole (MMI) (>0.1 mmol kg−1, p.o.) given in combination withDL-buthionine sulphoximine (BSO) (3 mmol kg−1, i.p., 1 h before MMI administration), an inhibitor of glutathione (GSH) synthesis, caused liver injury in mice. The injury was characterized by centrilobular necrosis of hepatocytes and an increase in serum alanine transaminase (ALT) activity. Methionazole (2 mmol kg−1) alone resulted in only a marginal increase in serum ALT activity, but produced no histopathological changes in the liver. Pretreatment with hepatic cytochrome P-450 monooxygenase inhibitors—cobalt chloride, isosafrole, methoxsalen, metyrapone and piperonyl butoxide—prevented or tended to suppress the hepatotoxicity induced by MMI in combination with BSO. Treatment with N,N-dimethylaniline and ethyl methyl sulphide, competitive substrates of flavin-containing monooxygenases (FMO), also resulted in remarkable suppression of the hepatotoxicity caused by MMI in combination with BSO. These results suggest that MMI is activated by reactions mediated by both cytochrome P-450 monooxygenases and FMO, and that the inadequate rates of detoxification of the resulting metabolite are responsible for the hepatotoxicity in GSH-depleted mice. Copyright © 1999 John Wiley & Sons, Ltd.

Metabolism-dependent hepatotoxicity of methimazole in mice depleted of glutathione.

Methimazole (MMI) (>0.1 mmol kg(-1), p.o.) given in combination with DL-buthionine sulphoximine (BSO) (3 mmol kg(-1), i.p., 1 h before MMI administration), an inhibitor of glutathione (GSH) synthesis, caused liver injury in mice. The injury was characterized by centrilobular necrosis of hepatocytes and an increase in serum alanine transaminase (ALT) activity. Methionazole (2 mmol kg(-1)) alone resulted in only a marginal increase in serum ALT activity, but produced no histopathological changes in the liver. Pretreatment with hepatic cytochrome P-450 monooxygenase inhibitors--cobalt chloride, isosafrole, methoxsalen, metyrapone and piperonyl butoxide-prevented or tended to suppress the hepatotoxicity induced by MMI in combination with BSO. Treatment with N,N-dimethylaniline and ethyl methyl sulphide, competitive substrates of flavin-containing monooxygenases (FMO), also resulted in remarkable suppression of the hepatotoxicity caused by MMI in combination with BSO. These results suggest that MMI is activated by reactions mediated by both cytochrome P-450 monooxygenases and FMO, and that the inadequate rates of detoxification of the resulting metabolite are responsible for the hepatotoxicity in GSH-depleted mice.

Characterization of hepatocellular resistance and susceptibility to styrene toxicity in B6C3F1 mice.

Short-term inhalation exposure of B6C3F1 mice to styrene causes necrosis of centrilobular (CL) hepatocytes. However, in spite of continued exposure, the necrotic parenchyma is rapidly regenerated, indicating resistance by regenerated cells to styrene toxicity. These studies were conducted to test the hypothesis that resistance to repeated styrene exposure is due to sustained cell proliferation, with production of hepatocytes that have reduced metabolic capacity. Male mice were exposed to air or 500 ppm styrene (6 h/day); hepatotoxicity was evaluated by microscopic examination, serum liver enzyme levels, and bromodeoxyuridine (BrdU)-labeling index (LI). Metabolism was assessed by measurement of blood styrene and styrene oxide. Both single and repeated exposures to styrene resulted in mortality by Day 2; in mice that survived, there was CL necrosis with elevated BrdU LI at Day 6, and complete restoration of the necrotic parenchyma by Day 15. The BrdU LI in mice given a single exposure had returned to control levels by Day 15. Re-exposure of these mice on Day 15 resulted in additional mortality and hepatocellular necrosis, indicating that regenerated CL cells were again susceptible to the cytolethal effect of styrene following a 14-day recovery. However, in mice repeatedly exposed to styrene for 14 days, the BrdU LI remained significantly increased on Day 15, with preferential labeling of CL hepatocytes with enlarged nuclei (karyomegaly). If repeated exposures were followed by a 10-day recovery period, CL karyomegaly persisted, but the BrdU LI returned to control level and CL hepatocytes became susceptible again to styrene toxicity as demonstrated by additional mortality and acute necrosis after a challenge exposure. These findings indicated a requirement for continued styrene exposure and DNA synthesis in order to maintain this resistant phenotype. Analyses of proliferating-cell nuclear-antigen (PCNA) labeling were conducted to further characterize the cell cycle kinetics of these hepatocytes. The proportion of cells in S-phase was increased by repeated exposure. However, PCNA analysis also revealed an even larger increase in the G1 cell compartment with repeated exposures, without a concurrent increase in G2 phase or in mitotic cell numbers. These data indicate that resistance to styrene-induced necrosis under conditions of repeated exposure is not due to sustained cell turnover and production of new, metabolically inactive cells, but rather is due to some other, as yet unknown, protective phenotype of the regenerated cells.

Technical Report: Application of Rat Precision-cut Liver Slices for Toxicity Assessment In Vitro.

The usefulness of precision-cut liver slices for toxicological evaluation in vitro was confirmed with a representative hepatotoxic agent acetaminophen. Liver slices obtained from normal and in vivo phenobarbital-treated rats were incubated with 0, 1.25, 2.5, 5, and 10 mM of acetaminophen for 24 hours. Intracellular potassium concentration dose-dependently decreased and lactate dehydrogenase (LDH) leakage increased in the slices from phenobarbital-treated rats, whereas no changes were detected in the slices from normal rats. The cytotoxicity of acetaminophen was also shown in the slices from normal rats when the slices were preincubated with phenobarbital in vitro for one hour. The acetaminophen cytotoxicity in the liver slices was enhanced by the preincubation with diethyl maleate, a depressant of hepatic glutathione, tributyltin acetate, an inhibitor of glutathione S-transferase, and 2, 6-dichloro-4-nitrophenol, an inhibitor of sulfotransferase. These data suggest that the formation and accumulation of the toxic metabolite are essential to induce the acetaminophen hepatotoxicity. Histopathological observation revealed centrilobular hepatocyte necrosis on the slices from phenobarbital-treated rats 24 hours after the exposure to acetaminophen. These results coincide with those reported in in vivo acetaminophen toxicity. The application of precision-cut liver slices is considered to be useful in toxicological evaluation of chemicals.

The Effects of Glutathione Glycosidein Acetaminophen-Induced Liver Cell Necrosis

The hepatotoxic effects of high-dose acetaminophen (400 and 600 mg/kg body weight) were evaluated by determining the glutathione (GSH) and malondialdehyde (MDA) levels and the histological changes in the liver at 6 and 12 h, using C57BL/6J mice. Massive centrilobular hepatocyte necrosis associated with severe reduction of liver GSH and a significant increase in MDA levels were observed following acetaminophen intoxication. Administration of glutathione glycoside (GSH-glyc), a compound newly synthesized in our laboratory, 2 h after acetaminophen injection prevented changes in the GSH and MDA preserving their levels nearly to those of controls; in addition, histological evidence of hepatocyte necrosis was either abolished or severely reduced in the majority of animals. GSH-glyc is a nontoxic compound that can be used to transport GSH into cells, including those of brain and liver, and may prove to be useful for the prophylaxis and therapy of toxic tissue injury, including that induced by overdosage of acetaminophen.

Acetaminophen-Induced Hepatorenal Toxicity in High Fructose Diet-Fed Rats Is Sex-Dependent.

Male rats with fructose-induced hypertriglyceridemia become resistant to hepatotoxicity and more susceptible to nephrotoxicity of acetaminophen (APAP) as compared with normal male rats. To determine whether changes in APAP toxicity by fructose-treatment were sex-dependent, male and female rats were fed standard diet (non-pretreated rats) or high fructose diet (fructose-pretreated rats) for 3 weeks and then given a single ip dose of APAP at 800 mg/kg. At 24 hours after APAP dosing, they were sacrificed and examined histopathologically. Non-pretreated males showed severe hepatic lesions characterized by centrilobular hepatocyte necrosis and slight renal lesions characterized by single cell necrosis in the proximal straight tubules, while females showed no hepatic lesions and milder renal lesions than males. APAP-induced hepatotoxicity was prevented and APAP-induced nephrotoxicity was potentiated in fructose-pretreated males. In contrast, no apparent changes on APAP-induced toxicity were seen in fructose-pretreated females. Castration partially prevented such enhancement of APAP-induced nephrotoxicity in fructose-pretreated males. Furthermore, castration and estradiol treatment had greater protective effect against the enhancement of APAP-induced nephrotoxicity in fructose-pretreated males as compared with castration alone. Ovariectomy potentiated the enhancement of APAP-induced nephrotoxicity in females. These results indicate that the changes in APAP-induced hepatorenal toxicity by fructose-pretreatment are sex-dependent.

TOXICOLOGICAL EVALUATION OF THE PLANT Xanthium strumarium IN PIGS IN ZIMBABWE

Major clinical signs were depression, vomiting, abdominal pain, weakness, recumbency, paddling convulsions terminating in death from 6 to 96 hours after ingestion. Gross pathological findings included ascites with fibrin strands, enlarged, congested and friable livers with accentuation of lobulation on the capsule. Microscopically, acute hepatic congestion and hemorrhage, centrilobular hepatocyte necrosis, with occasional binucleation together with discoid lysis of skeletal and cardiac muscle fibers were remarkable changes. Binucleation of hepatocytes and degenerative changes in active muscles have not been reported before in relation to cocklebur plant toxicosis. These findings suggest that X. strumarium is a potential cause of sudden death in pigs extensively reared in Zimbabwe.

Modulation of chemical-induced lung and liver toxicity by all- trans-retinol in the male Sprague-Dawley rat

We have previously shown that retinol pretreatment limits the amount of pulmonary injury caused by 1-nitronaphthalene in male Sprague-Dawley rats. The main objective of this study was to determine if retinol pretreatment can protect the lung from the toxicity of other systemic pneumotoxicants. Furthermore because retinol has been shown to alter the hepatotoxicity of several chemicals, a secondary objective was to evaluate its effects on the liver injury caused by these toxicants. Rats were pretreated with all- trans-retinol (75 mg/kg/day p.o.) for 1 week, and given 2-nitronaphthalene (200 mg/kg i.p.) or paraquat (25 mg/kg i.p.). At 24 h after 2-nitronaphthalene treatment, pulmonary morphological changes associated with the bronchiolar epithelium, as well as a moderate pneumonitis were observed. Pretreatment of rats with retinol inhibited the majority of 2-nitronaphthalene-induced pulmonary damage including the infiltration of inflammatory cells and associated edema. However, these animals possessed limited lesions associated with their non-ciliated bronchiolar epithelial (Clara) cells. Interestingly, pretreatment with retinol also caused a significant potentiation of 2-nitronaphthalene-induced liver damage. The potentiated hepatotoxicity consisted of centrilobular hepatocyte necrosis with infiltration of inflammatory cells. Gadolinium chloride (GdCl 3), an inhibitor of Kupffer cell function, significantly decreased the potentiated hepatocellular injury. In paraquat-treated rats focal areas of damage to the alveolar parenchyma, consisting of inflammatory cell infiltration and alveolar sac remodeling, were observed at 48 h. Pretreatment with retinol caused significant protection from the pulmonary damaged caused by paraquat. Specifically, there was a lack of alveolar parenchymal cell damage and inflammatory cell infiltration in these animals. From these experiments, we conclude that retinol pretreatment decreases the severity of 2-nitronaphthalene and paraquat-induced pulmonary toxicity, apparently by inhibiting the inflammatory responses associated with the progression of toxic injury. In the liver, retinol potentiated 2-nitronaphthalene-induced hepatotoxicity by a mechanism which directly involves Kupffer cells.

Comparison of Styrene Hepatotoxicity in B6C3F1 and Swiss Mice

Comparison of Styrene Hepatotoxicity in B6C3F1 and Swiss Mice. Morgan, D. L., Mahler, J. F., Moorman, M. P., Wilson, R. E., Price, H. C., Jr., Richards, J. H., and O'Connor, R. W. (1995). Fundam. Appl. Toxicol. 27, 217-222. Inhalation exposure to styrene at concentrations that cause metabolic saturation results in significantly greater hepatotoxicity in B6C3F1 mice than in Swiss mice; females of both strains are more susceptible than males. These studies were conducted to investigate the mouse strain and gender differences in susceptibility to hepatotoxicity caused by repeated exposure to styrene at concentrations that do not cause metabolic saturation. Male and female B6C3F1 and Swiss mice (8 weeks old) were exposed to 0, 150, or 200 ppm styrene for 6 hr/day, 5 days/week, for up to 2 weeks. Changes in body and liver weights, serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) levels, liver histopathology, and total liver glutathione (GSH) were evaluated after 2, 3, 5, and 10 exposures (six mice/sex/strain/time point/concentration). Blood levels of styrene and styrene-7,8-oxide (SO) were measured in mice exposed to 200 ppm styrene for 2, 3, or 5 days (six mice/sex/strain/time point/concentration). Serum ALT and SDH levels were significantly elevated only in female B6C3F1 mice after 3 exposures to 200 ppm styrene; enzyme levels had returned to control levels when measured after 5 and 10 exposures. Degeneration and coagulative necrosis of centrilobular hepatocytes were observed in female B6C3F1 mice exposed 2, 3, and 5 days to 150 or 200 ppm styrene; incidences of these lesions were greater in the 200 ppm than in the 150 ppm dose group. After 10 days of exposure to 150 or 200 ppm styrene, hepatocellular lesions had resolved, although a residual chronic inflammation was present in livers of most female B6C3F1 mice. Degeneration of centrilobular hepatocytes was observed in one male B6C3F1 mouse after 3 exposures to 200 ppm, and no significant lesions were observed in livers of exposed Swiss mice. Significant dose-related decreases in hepatic GSH were observed in both sexes of both strains throughout the 2-week exposure. In general, hepatic GSH depletion was greatest in female B6C3F1 mice. Exposure to 200 ppm caused 60-70% GSH depletion in female B6C3F1 mice at each time point. GSH depletion generally decreased in B6C3F1 mice and increased in Swiss mice with continued exposure to 150 ppm styrene. With continued exposure to 200 ppm, GSH depletion generally decreased in all mice. Blood styrene and SO levels increased in all groups with the number of exposures. Styrene levels were significantly higher in B6C3F1 mice than in Swiss mice; however, within each strain gender differences were not significant. These data suggest that the transient hepatotoxicity in female B6C3F1 mice was related to greater hepatic GSH depletion and/or slower GSH regeneration in these animals.

A multidisciplinary approach to toxicological screening: I. Systemic toxicity.

The toxicity of 10 chemicals, including pesticides (carbaryl, chlordane, heptachlor, and triadimefon), solvents (carbon tetrachloride, dichloromethane, tetrachloroethylene, and trichloroethylene), and industrial chemicals [diethylhexylphthalate (DEHP) and phenol] was examined in the liver, kidneys, spleen, thymus, and adrenals of female F344 rats after 1 or 14 d of oral dosing. For each chemical, 4 doses were based on fractions of the acute LD50, which was estimated using an abbreviated (up-and-down) method. A multivariate analysis (MANOVA) was conducted for each organ using selected measures of toxicity. A post hoc contrast analysis was also conducted for significant MANOVA results in order to determine effective and ineffective doses. A single dose of heptachlor resulted in necrotic lymphocytes in the spleen and thymus at doses > or = 23 mg/kg. Triadimefon altered liver and spleen weights; this effect has not been described previously. Dichloromethane (> or = 337 mg/kg/d for 14 d) increased the incidence of necrosis of individual centrilobular hepatocytes. Trichloroethylene-induced hepatotoxicity was obtained at doses an order of magnitude lower than those reported in the literature. Acute DEHP (150 mg/kg) increased mitotic figures in hepatocytes, which were replaced by hepatocellular cytomegaly after 14 d of dosing at the same level. Following phenol exposure, there was an increased incidence in hepatocellular necrosis at 1 d, and an increased incidence of kidney lesions at 1 and 14 d; these findings were considered to be the result of vascular stasis. Overall, the algorithm used to select doses was effective for both 1- or 14-d dosing regimens. For all chemicals except carbon tetrachloride, the lowest effective dose for systemic toxicity was within the range of 3-56% of the LD50 for acute dosing, and 1-30% of the LD50 for repeated administration.

Effects of fructose-induced hypertriglyceridemia on hepatorenal toxicity of acetaminophen in rats.

The mode of hepatorenal toxicity of acetaminophen (AAP) was compared between fructose-induced hyper-triglyceridemic and normal rats. The hypertriglyceridemic and normal rats received a single dose of AAP (0, 750 and 900 mg/kg ip) at week 5 of fructose-treatment. At 24 hrs after AAP-dosing, they were sacrificed and examined blood biochemically and histopathologically. Hepatotoxicity as indicated by an increase in plasma ALT and AST activities and centrilobular necrosis of hepatocytes was more severe in the normal rats than in the hypertriglyceridemic ones. In contrast, nephrotoxicity as indicated by an increase in plasma urea nitrogen content and necrosis of epithelial cells in the proximal straight tubules was more severe in the hypertriglyceridemic rats than in normal ones. Thus, in the fructose-induced hypertriglyceridemic rats, as compared with normal ones, hepatotoxicity of AAP became apparently less severe, whereas nephrotoxicity of AAP became significantly more severe.

The Toxicity of 1-Week Exposures to Inhaled Chloroform in Female B6C3F1 Mice and Male F-344 Rats

The Toxicity of 1-Week Exposures to Inhaled Chloroform in Female B6C3F1 Mice and Male F-344 Rats. Larson, J. L., Wolf, D. C., Morgan, K. T., Mery, S., and Butterworth, B. E. (1994). Fundam. Appl. Toxicol. 22, 431-446.Detailed quantitative descriptions of the toxicity of inhaled chloroform are lacking, despite the fact that the majority of environmental exposures occur by this route. We investigated the ability of chloroform vapors to produce toxicity and regenerative cell proliferation in the livers and kidneys, the principal target organs for carcinogenicity of female B6C3F1 mice and male F-344 rats, respectively. Nasal passages were also examined for toxic responses. Rodents were exposed to chloroform vapors at concentrations of 0, 1, 3, 10, 30, 100, or 300 ppm for 6 hr/day for 7 consecutive days and necropsied on Day 8. Animals were administered bromodeoxyuridine (BrdU) via implanted osmotic pump for the previous 3.5 days before necropsy. Cell proliferation was quantitated as the percentage of cells in S-phase (labeling index; LI) measured by immunohistochemical detection of BrdU-labeled nuclei. Mice exposed to 100 or 300 ppm exhibited centrilobular hepatocyte necrosis and severe vacuolar degeneration of midzonal and periportal hepatocytes, while exposure to 10 or 30 ppm resulted in mild to moderate vacuolar changes in centrilobular hepatocytes. Slight, dose-related increases in the hepatocyte LI were observed for exposure concentrations of 10 and 30 ppm, while the LI was increased more than 30-fold in the 100 and 300 ppm groups. The kidneys of mice were affected only at the 300 ppm exposure, with approximately half of the proximal tubules lined by regenerating epithelium and an increased LI of tubule cells of 8-fold over control. In rats, mild centrilobular vacuolation was observed only in the livers of rats exposed to 300 ppm. The hepatocyte LI in rats were increased only at 100 and 300 ppm, 3- and 7-fold over control, respectively. In the kidneys of the male rats exposed to 300 ppm, about 25 to 50% of the proximal tubules were lined by regenerating epithelium. The LI for tubule cells in the cortex was increased at 30 ppm and above. In the nasal passages of rats, chloroform concentrations of 10 ppm and above induced histopathological changes that exhibited clear concentration-related severity. These lesions consisted of respiratory epithelial goblet cell hyperplasia and degeneration of Bowman's glands in olfactory mucosa with an associated osseous hyperplasia of the endoand ectoturbinates in the periphery of the ethmoid region. These nasal lesions were not observed in mice. Knowledge of the dose-dependent responses in rats and mice will be valuable in assessing the potential risks to humans posed by inhaled chloroform and in setting exposure concentrations for longer-term studies.

DEPRESSIVE EFFECT OF T-2 TOXIN ON HEPATOCYTE PROLIFERATION UNDER TWO EXPERIMENTAL CONDITIONS

The effect of T-2 mycotoxin on hepatocyte proliferation was investigated in mice using two models of hepatocyte regeneration, i.e. 2/3 partial hepatectomy (Ph) and CCl4-intoxication (CCl4). At 2 days after Ph or CCl4, mice were given T-2 toxin (2 or 4mg/kg, po). Five mice each were killed daily up to 7days after Ph or CCl4, and they were injected with BrdU (100mg/kg, ip) at I hour before sacrifice. T-2 toxin significantly delayed the recovery of liver weight loss after Ph Or CCl4, and it also significantly delayed the reduction in size of centrilobular hepatocyte necrosis after CCl4. In addition, T-2 toxin significantly depressed BrdU-uptake by hepatocytes in the early days after Ph or CCl4. It can be said that T-2 toxin depressed the proliferation of hepatocytes, resulting in the delay of recovery of liver weight loss. This seems to be related to the inhibitory effect of T-2 toxin on nuclear acid synthesis of hepatocytes.