Comparative toxicity of nickel oxide, nickel sulfate hexahydrate, and nickel subsulfide after 12 days of inhalation exposure to F344/N rats and B6C3F1 mice

The relative toxicity of nickel oxide (NiO), nickel sulfate hexahydrate. (NiSO4.6H2O), and nickel subsulfide (Ni3S2) was studied in F344/N rats and B6C3F1 mice after inhalation exposure for 6 h/day, 5 days/week for 12 exposure days. Exposure concentrations used (as mg Ni/m3) were 0.9-23.6 for NiO; 0.8-13.3 for NiSO4.6H2O, and 0.4-7.3 for Ni3S2. For each compound there were 5 exposure groups plus a control group. NiSO4.6H2O was the most toxic compound with exposure related mortality seen at exposure concentrations of 13.3 mg/m3 in rats and 1.6 mg/m3 and above in mice. For Ni3S2, mortality was seen in mice (but not in rats) at the highest exposure concentration (7.3 mg/m3). No mortality was seen after NiO exposure. Lesions of the lung and nasal cavity were seen in both rats and mice after exposure to NiSO4.6H2O and Ni3S2 at the 4 highest exposure concentrations. Lesions of the lung were seen primarily at the highest exposure concentrations after NiO exposure. The amount of nickel in the lungs at the end of exposure varied in relation to the water solubility of the compounds. Based on these 2-week studies, the toxicity ranking was NiSO4.6H2O greater than Ni3S2 much greater than NiO. Additional studies are in progress to assess the relative toxicities of these three nickel compounds after 90-day exposures.     

Lung Toxicity after 13-Week Inhalation Exposure to Nickel Oxide, Nickel Subsulfide, or Nickel Sulfate Hexahydrate in F344/N Rats and B6C3F1 Mice

Lung Toxicity after 13-Week Inhalation Exposure to Nickel Oxide,Nickel Subsulfide, or Nickel Sulfate Hexahydrate in F344/N Ratsand B6C3F₁ Mice. DUNNICK, J. K., ELWELL, M. BENSON, J. M., HOBBS,C. H., HAHN, F. F., HALY, P. J., CHENG, Y. S., AND EIDSON, A.F. (1989). Fundam. Appl. Toxicol. 12, 584–594. The relativetoxicity of nickel oxide (NiO), nickel sulfate hexahydrate (NiSO₄6H₂O)and nickel subsulfide (Ni₃S₂) was studied in F344/N rats andB6C3F₁ mice after inhalation exposure for 6 hr/day, 5 days/week,for 13 weeks. Exposure concentrations used (as mg Ni/m³ were0.4–7.9 for NiO, 0.02–0.4 for NiSO₄ 6H₂O and 0.11–1.8for Ni₃S₂. No exposure-related effects on mortality and onlyminor effects on body weight gain were seen in rats or mice.The most sensitive parameter for nickel toxicity was histopathologic change in the lungs of exposed animals where chronic activeinflammation, fibrosis, and alveolar macrophage hyperplasiawerez associated with nickel exposure. There was an exposure-related increase in lung weight in rats and mice. Equilibriumlevels of nickel in the lung were reached by 13 weeks of nickelsulfate and nickel subsulfide exposure, whereas lung levelsof nickel continued to increase throughout exposure to nickeloxide. Additional exposure-related histopathologic lesions intreated animals included atrophy of the olfactory epitheliumafter nickel sulfate and nickel subsulfide exposure. No nasallesions were seen after nickel oxide expo sure. Lymphoid hyperplasiaof the bronchial lymph nodes developed in animals exposed toall three nickel compounds. The order oftoxicity correspondedto the water solubility of the nickel compounds, with nickelsulfate being most toxic, followed by nickel subsulfide andnickel oxide.     

Biochemical responses of rat and mouse lung to inhaled nickel compounds

Nickel subsulfide (Ni3S2), nickel sulfate (NiSO4), and nickel oxide (NiO) are encountered occupationally in the nickel refining and electroplating industries, with inhalation being a common route of exposure. The purposes of this study were to evaluate the biochemical responses of lungs of rats and mice exposed for 13 weeks to occupationally relevant aerosol concentrations of Ni3S2, NiSO4, and NiO, to correlate biochemical responses with histopathologic changes, and to rank the compounds by toxicity. Biochemical responses were measured in bronchoalveolar lavage fluid (BALF) recovered from lungs of exposed animals. Parameters evaluated in BALF were lactate dehydrogenase (LDH), beta-glucuronidase (BG), and total protein (TP). Total and differential cell counts were performed on cells recovered in BALF. All compounds produced an increase in LDH, BG, TP, and total nucleated cells, and an influx of neutrophils, indicating the presence of a cytotoxic and inflammatory response in the lungs of exposed rats and mice. Increases in BG were greater than increases in LDH and TP for both rats and mice. Chronic active inflammation, macrophage hyperplasia, and interstitial phagocytic cell infiltrates were observed histologically in rats and mice exposed to all compounds. Statistically significant increases in BG, TP, neutrophils, and macrophages correlated well with the degree of chronic active inflammation. Results indicated a toxicity ranking of NiSO4 greater than Ni3S2 greater than NiO, based on toxicities of the compounds at equivalent mg Ni/m3 exposure concentrations.     

Strain differences in the responsiveness between Sprague-Dawley and Fischer rats to nephropathy induced by FYX-051, a xanthine oxidoreductase inhibitor

To determine a rat strain appropriate for carcinogenicity testing of FYX-051, a xanthine oxidoreductase inhibitor, we performed a 4-week oral toxicity study by administering 0.3, 1 and 3 mg/kg, and 1, 3 and 10 mg/kg of FYX-051 to male Sprague-Dawley (SD) and Fischer (F344) rats, respectively. Histopathology revealed that the degree of FYX-051-induced nephropathy was 3-fold stronger in SD rats than in F344 rats. Our previous study demonstrated that the key factor of species differences in FYX-051-induced nephropathy is purine metabolism. This observation led us to examine the involvement of purine metabolism in differences among two strains of rats. However, purine metabolism was proven not to be implicated as an important factor. Subsequently, other factors responsible for the strain differences were examined. FYX-051-induced increases in plasma xanthine concentrations were higher in SD rats than in F344 rats, suggesting more remarkable effects on pharmacodynamics in the former than the latter. Urinary volume was greater in F344 rats administered 10 mg/kg of FYX-051 (6.8 ml/h/kg) than in SD rats administered 3 mg/kg of FYX-051 (5.0 ml/h/kg), implying easier xanthine excretion in the former. Urinary xanthine solubility was 55 mg/dl in F344 rats aged 6 weeks, in contrast to 38 mg/dl in SD rats of the same age. Also, there were no significant differences in exposure levels at the same dose between SD and F344 rats. The outcomes of exposure levels and renal histopathology in both rats suggest the possibility that F344 rats could be exposed to a 3-fold higher amount of drug than SD rats in a carcinogenicity bioassay. The present study, therefore, suggested that strain differences of nephrotoxicity were caused by the combined effects of pharmacodynamics, xanthine excretion capacity, and urinary xanthine solubility. Furthermore, these results indicate that F344 rats would be a suitable strain for the carcinogenicity study of FYX-051.     

Carcinogenic activity of benzo[a]pyrene in a 2 year oral study in Wistar rats

Because of the relatively high human oral exposure to polycyclic aromatic hydrocarbons (PAHs) compared to the inhalation exposure, the known carcinogenicity of this type of compounds and the limited data from oral studies available with polycyclic aromatic hydrocarbons, an oral carcinogenicity study was performed using benzo[a]pyrene (B[a]P) as a PAH representative. Wistar rats, 52 animals per sex and group were exposed daily (5 days a week) to 0, 3, 10 or 30 mg B[a]P/kg bw/day by gavage for 104 weeks and were subject to gross- and histopathology. The main tumours observed were hepatocellular carcinomas and forestomach tumours. Other tumours induced in this study were tumours of the auditory canal, skin and appendages, oral cavity, small intestine, kidney, and soft tissue sarcomas. For hepatocellular carcinomas and forestomach tumours, the BMDL10 were 3 and 1 mg/kg bw/day, respectively. The incidence of altered hepatic foci was increased in the 3mg/kg bw/day group. The increase in liver tumours is considered the most relevant effect for human risk assessment in terms of pathogenesis and sensitivity, and is proposed as the basis for human cancer risk assessment for oral PAH exposure.     

Protective effects of zinc acetate toward the toxicity of nickelous acetate in rats

Zinc pretreatment is known to ameliorate the acute and chronic effects of the toxic heavy metal, cadmium. However, the ability of zinc to decrease the toxicity of other metals has not been widely investigated. Therefore, this study was designed to determine the effects of zinc pretreatment on the acute toxicity of nickel. Male Fischer rats received either nickel alone (i.p.), zinc alone (s.c.), zinc plus nickel, or saline (i.p. and s.c.; controls). In the lethality studies, the dose of nickel was 115 mumol nickel/kg (as nickel acetate) while for all other studies the dose was 95 mumol nickel/kg. Zinc was given in multiple doses of 300 mumol zinc/kg (as zinc acetate) at -24, 0 and +24 h relative to nickel (total zinc dose 900 mumol/kg) for lethality studies or -24 and 0 h for studies 24 h and under in duration (total dose 600 mumol/kg). Zinc pretreatment significantly increased the 14-day survival of nickel-related rats. Zinc did not, however, prevent the reduction in weight gain over 2 weeks seen with nickel treatment. Histopathologically, at 120 h following nickel exposure, kidneys in the group receiving nickel alone generally showed moderate nephropathy (multifocal proximal tubule degeneration with necrosis) while in the zinc plus nickel group the nephropathy was generally mild. Zinc pretreatment had no apparent effect on the pharmacokinetics of nickel over 24 h as assessed by urinary excretion, blood levels or organ distribution. Zinc pretreatment also did not alter the subcellular distribution of renal nickel 6 h after nickel exposure. Enhanced synthesis of metallothionein did not appear to play a critical role in the reduction of nickel toxicity, since renal concentrations of this metal-binding protein, although elevated compared to control, were not different in rats receiving zinc and nickel or zinc alone. Zinc pretreatment did, however, have marked effect on nickel-induced hyperglycemia, reducing both the duration and severity of elevated blood glucose levels. Results of this study show that zinc can prevent some of the toxic effects of nickel and that the mechanism of this action does not appear to involve either metallothionein or alterations in the pharmacokinetics of nickel.     

The effects of subchronic acrylamide exposure on gene expression, neurochemistry, hormones, and histopathology in the hypothalamus-pituitary-thyroid axis of male Fischer 344 rats

Acrylamide (AA) is an important industrial chemical that is neurotoxic in rodents and humans and carcinogenic in rodents. The observation of cancer in endocrine-responsive tissues in Fischer 344 rats has prompted hypotheses of hormonal dysregulation, as opposed to DNA damage, as the mechanism for tumor induction by AA. The current investigation examines possible evidence for disruption of the hypothalamic-pituitary-thyroid axis from 14 days of repeated exposure of male Fischer 344 rats to doses of AA that range from one that is carcinogenic after lifetime exposure (2.5 mg/kg/d), an intermediate dose (10 mg/kg/d), and a high dose (50 mg/kg/d) that is neurotoxic for this exposure time. The endpoints selected include: serum levels of thyroid and pituitary hormones; target tissue expression of genes involved in hormone synthesis, release, and receptors; neurotransmitters in the CNS that affect hormone homeostasis; and histopathological evaluation of target tissues. These studies showed virtually no evidence for systematic alteration of the hypothalamic-pituitary-thyroid axis and do not support hormone dysregulation as a plausible mechanism for AA-induced thyroid cancer in the Fischer 344 rat. Specifically, there were no significant changes in: 1) mRNA levels in hypothalamus or pituitary for TRH, TSH, thyroid hormone receptor alpha and beta, as well 10 other hormones or releasing factors; 2) mRNA levels in thyroid for thyroglobulin, thyroid peroxidase, sodium iodide symporter, or type I deiodinases; 3) serum TSH or T3 levels (T4 was decreased at high dose only); 4) dopaminergic tone in the hypothalamus and pituitary or importantly 5) increased cell proliferation (Mki67 mRNA and Ki-67 protein levels were not increased) in thyroid or pituitary. These negative findings are consistent with a genotoxic mechanism of AA carcinogenicity based on metabolism to glycidamide and DNA adduct formation. Clarification of this mechanistic dichotomy may be useful in human cancer risk assessments for AA.     

Worms as a Substitute for Rodents in Toxicology: Acute Toxicity of Three Nickel Compounds

In a continuing investigation of the use of the common earthworm (Lumbricus terrestris) as test subjects for metal toxicity, three nickel salts were evaluated. Saline solutions of either the chloride, the sulfate, or the acetate were injected into the coelom of the worm. Care was taken not to enter the gastrointestinal tract. The acute toxicities were determined by graphical methods using probit paper. The most consistent results were found when lethality was measured at 48 h rather than 24 h. The 48-h LD₅₀ values for the different salts of nickel are as follows: chloride, 52 mg/kg; sulfate, 54 mg/kg; and acetate, 69 mg/kg. The ratios of toxicity of nickel acetate to the chloride and sulfate salts in the worms are similar to those ratios noted in mice. The European Economic Commission (EEC) now suggests using earthworms for toxicity testing for legislation purposes.     

Subacute (28-day) toxicity of furfural in Fischer 344 rats: a comparison of the oral and inhalation route.

The subacute oral and inhalation toxicity of furfural vapour was studied in Fischer 344 rats to investigate whether route-to-route extrapolation could be employed to derive the limit value for inhalation exposure from oral toxicity data. Groups of 5 rats per sex were treated by gavage daily for 28 days at dose levels of 6-192 mg/kg bw/day, or exposed by inhalation to concentrations of 20-1280 mg/m3 (6 h/day, 5 days/week) or 160-1280 mg/m3 (3 h/day, 5 days/week) for 28 days. Controls received vehicle (corn oil) or were exposed to clean air. Daily oral treatment with the highest dose of furfural (initially 192 mg/kg bw/day, later reduced to 144 mg/kg bw/day and finally to 120 mg/kg bw/day) resulted in mortality, and in increases in absolute and relative kidney and liver weight in surviving females of this group. Exposure of rats by inhalation for 6 h/day, 5 days/week for 28 days induced mortality at concentrations of 640 mg/m3 and above within 1-8 days. At 640 mg/m3 (3 h/day) and at 320 mg/m3 (3 and 6 h/day) and below, however, exposure was tolerated without serious clinical effects. In contrast, histopathological nasal changes were seen even at the lowest concentration of 20 mg/m3. With increasing exposure concentration, the nasal effects increased in incidence and severity and also expanded from the anterior part to the posterior part, including the olfactory epithelium. It was concluded that the no-observed-adverse-effect level (NOAEL) for oral toxicity was 96 mg/kg bw/day. The NOAEL for systemic inhalation toxicity was comparable, i.e. 92 mg/kg bw/day (corresponding to 320 mg/m3 (6 h/day) or 640 mg/m3 (3 h/day)) assuming 100% absorption. The presence of the histopathological nasal changes at the lowest tested concentration of 20 mg/m3 (corresponding to 6 mg/kg bw/day) proves that for locally acting substances like furfural extrapolation from the oral to the inhalation route is not valid.     

Hepatoprotective role of naringin on nickel-induced toxicity in male Wistar rats

Aim of the present study was planned to determine the protective role of naringin in attenuating the toxicity induced by nickel sulfate in rat liver. In this investigation nickel sulfate (20 mg/kg body weight) was administered intraperitoneally for 20 days to induce toxicity. Naringin was administered orally (20, 40 and 80 mg/kg body weight) for 20 days with intraperitoneal administration of nickel sulfate. Liver injury was measured by the increased activities of serum hepatic enzymes namely aspartate transaminase, alanine transaminase, alkaline phosphatase, gamma glutamyl transferase, lactate dehydrogenase and total bilirubin along with increased elevation of lipid peroxidation markers, thiobarbituric reactive acid substances, lipid hydroperoxides, protein carbonyl content and conjugated dienes. The toxic effect of nickel was also indicated by significantly decreased activities of enzymatic antioxidants like superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase and glucose-6-phosphate dehydrogenase and non-enzymatic antioxidants like reduced glutathione, total sulfhydryl groups, vitamin C and vitamin E levels were significantly decreased. Naringin administered at a dose of 80 mg/kg body weight significantly reversed the activities of hepatic marker enzymes, decreasing lipid peroxidative markers, increasing the antioxidant cascade and decreasing the nickel concentration in the liver. The effect at a dose of 80 mg/kg body weight was more pronounced than that of other two doses (20 and 40 mg/kg body weight). All these changes were supported by histopathological observations. These results clearly demonstrate that naringin has the potential in alleviating the toxic effects of nickel in rat liver.     

Inhalation carcinogenicity study with nickel metal powder in Wistar rats

Epidemiological studies of nickel refinery workers have demonstrated an association between increased respiratory cancer risk and exposure to certain nickel compounds (later confirmed in animal studies). However, the lack of an association found in epidemiological analyses for nickel metal remained unconfirmed for lack of robust animal inhalation studies.In the present study, Wistar rats were exposed by whole-body inhalation to 0, 0.1, 0.4, and 1.0 mg Ni/m³ nickel metal powder (MMAD = 1.8 µm, GSD = 2.4 µm) for 6 h/day, 5 days/week for up to 24 months. A subsequent six-month period without exposures preceded the final euthanasia. High mortality among rats exposed to 1.0 mg Ni/m³ nickel metal resulted in the earlier termination of exposures in this group. The exposure level of 0.4 mg Ni/m³ was established as the MTD for the study. Lung alterations associated with nickel metal exposure included alveolar proteinosis, alveolar histiocytosis, chronic inflammation, and bronchiolar-alveolar hyperplasia.No increased incidence of neoplasm of the respiratory tract was observed. Adrenal gland pheochromocytomas (benign and malignant) in males and combined cortical adenomas/carcinomas in females were induced in a dose-dependent manner by the nickel metal exposure. The incidence of pheochromocytomas was statistically increased in the 0.4 mg Ni/m³ male group. Pheochromocytomas appear to be secondary to the lung toxicity associated with the exposure rather than being related to a direct nickel effect on the adrenal glands. The incidence of cortical tumors among 0.4 mg Ni/m³ females, although statistically higher compared to the concurrent controls, falls within the historical control range; therefore, in the present study, this tumor is of uncertain relationship to nickel metal exposure.The lack of respiratory tumors in the present animal study is consistent with the findings of the epidemiological studies.     

Inhalation toxicity and carcinogenicity studies of cobalt sulfate.

Cobalt sulfate is a water-soluble cobalt salt with a variety of industrial and agricultural uses. Several cobalt compounds have induced sarcomas at injection sites in animals, and reports have suggested that exposure to cobalt-containing materials may cause lung cancer in humans. The present studies were done because no adequate rodent carcinogenicity studies had been performed with a soluble cobalt salt using a route relevant to occupational exposures. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to aerosols containing 0, 0.3, 1.0, or 3.0 mg/m3 cobalt sulfate hexahydrate, 6 h/day, 5 days/week, for 104 weeks. Survival and body weights of exposed rats and mice were generally unaffected by the exposures. In rats, proteinosis, alveolar epithelial metaplasia, granulomatous alveolar inflammation, and interstitial fibrosis were observed in the lung in all exposed groups. Nonneoplastic lesions of the nose and larynx were also attributed to exposure to all concentrations of cobalt sulfate. In 3.0 mg/m3 male rats and in female rats exposed to 1.0 or 3.0 mg/m3, the incidences of alveolar/bronchiolar neoplasms were increased over those in the control groups. Lung tumors occurred with significant positive trends in both sexes. The incidences of adrenal pheochromocytoma in 1.0 mg/m3 male rats and in 3.0 mg/m3 female rats were increased. Nonneoplastic lesions of the respiratory tract were less severe in mice than in rats. In mice, alveolar/bronchiolar neoplasms in 3.0 mg/m3 males and females were greater than those in the controls, and lung tumors occurred with significantly positive trends. Male mice had liver lesions consistent with a Helicobacter hepaticus infection. Incidences of liver hemangiosarcomas were increased in exposed groups of male mice; however, because of the infection, no conclusion could be reached concerning an association between liver hemangiosarcomas and cobalt sulfate. In summary, exposure to cobalt sulfate by inhalation resulted in increased incidence of alveolar/bronchiolar neoplasms and a spectrum of inflammatory, fibrotic, and proliferative lesions in the respiratory tracts of male and female rats and mice. Adrenal pheochromocytomas were increased in female rats, and possibly in male rats.     

Effects of nickel sulfate on pulmonary natural immunity in Wistar rats

This study was designed to investigate the in vivo effect of nickel sulfate on the pulmonary non-specific immune defences. Groups of four male Wistar rats were treated with a single intratracheal instillation of NiSO(4) at different doses: 1, 2, 4 and 8 micromol of NiSO(4) per rat. Control rats received a corresponding instillation of the saline vehicle. The effect of NiSO(4) on the cytotoxic activity of the pulmonary natural killer (NK) cells and alveolar macrophages (AM), as well as the pulmonary production of cytokines such as alpha-tumor necrosis factor (TNF-alpha) and gamma-interferon (IFN-gamma), were examined 1, 2 and 7 days later. Spontaneous NK-cytotoxicity towards mouse-derived tumor cell line, Yac-1 was suppressed 1 day after treatment at doses of 2 micromol/rat and above with only one result significant (P<0.05); 2 days after treatment the suppression was increased with all results significant at the same doses; 1 week after treatment NK activity restoration was observed except for the highest dose, 8 micromol/rat. AM-mediated cytotoxicity towards mouse-derived tumor cell line, 3T12, did not show any significant difference in treated and untreated animals. In contrast, whereas moderate levels of TNF-alpha were detected in the broncho-alveolar lavage (BAL) fluid supernatants of controls, the NiSO(4) treatment highly suppressed TNF-alpha production with a maximum observed after 2 days. TNF-alpha suppression was found to be transient, at least with the lowest NiSO(4) dose, with levels returning to normal after 7 days. A non-significant increase in IFN-gamma was observed in the BAL fluids of treated animals at each time of examination. Taken together, these results indicate that NK cell activity and TNF-alpha secretion are sensitive targets for instilled NiSO(4) in Wistar rats.     

Oral bioaccessibility testing and read-across hazard assessment of nickel compounds

In vitro metal ion bioaccessibility, as a measure of bioavailability, can be used to read-across toxicity information from data-rich, source substances to data-poor, target substances. To meet the data requirements for oral systemic toxicity endpoints under the REACH Regulation in Europe, 12 nickel substances underwent bioaccessibility testing in stomach and intestinal fluids. A read-across paradigm was developed based on the correlation between gastric bioaccessibility and in vivo acute oral toxicity. The oral LD₅₀ values were well predicted by nickel release (R² = 0.91). Samples releasing <48% available nickel (mg Ni released/mg available Ni × 100) are predicted to have an LD₅₀ > 2000 mg/kg; while samples releasing >76% available nickel are expected to have an LD₅₀ between 300 and 2000 mg/kg. The hazard classifications (European Regulation on Classification, Labelling and Packaging of Chemical Substances and Mixtures) for all oral systemic endpoints were evaluated based on read-across from three source nickel compounds (sulfate, subsulfide, oxide). Samples releasing <48% available nickel were read-across from nickel oxides and subsulfide. Samples releasing >76% Ni were read-across from nickel sulfate. This assessment suggests that nickel chloride and dihydroxide should be less stringently classified and nickel sulfamate should receive a more stringent classification for oral systemic endpoints than currently assigned.     

Chronic toxicity and oncogenicity study on acrylamide incorporated in the drinking water of Fischer 344 rats

Male and female Fischer 344 rats were maintained on treated drinking water providing dosages of 0 (controls), 0.01, 0.1, 0.5, or 2.0 mg acrylamide/kg body wt/day for 2 years to assess the chronic toxicity and oncogenic potential of the chemical. The mean body weights of male and female rats receiving 2.0 mg/kg/day and of male rats receiving 0.5 mg/kg/day were minimally decreased when compared with controls. During the last 4 months of the study, there was an increase in mortality among male and female rats receiving 2.0 mg/kg/day. A target organ effect, characterized by degeneration of peripheral nerves, was observed in rats receiving 2.0 mg/kg/day. The incidence of several tumor types was increased in the rats receiving 2.0 mg/kg/day when compared with controls. In females, increased tumor incidences were observed in the mammary gland, central nervous system, thyroid gland-follicular epithelium, oral tissues, uterus, and clitoral gland. In males the incidence of tumors of the thyroid gland-follicular epithelium and scrotal mesothelium was increased. Male rats receiving 2.0 mg/kg/day also had increased incidence of central nervous system tumors when compared to historical controls but not when compared to concurrent controls. The only tumor incidence which was significantly increased at the 0.5 mg/kg/day level was scrotal mesothelioma. There was no statistically significant increase of any tumor type at the 0.1 or 0.01 mg/kg/day dose levels. However, the incidence of scrotal mesothelioma at the 0.1 mg/kg/day level was greater than that observed in the control group or historically reported in this laboratory.     

Effect of L-ascorbic acid on nickel-induced alterations in serum lipid profiles and liver histopathology in rats

Nickel exposure greatly depletes intracellular ascorbate and alters ascorbate-cholesterol metabolism. We studied the effect of the simultaneous oral treatment with L-ascorbic acid (50 mg/100 g body weight (BW) and nickel sulfate (2.0 mg/100 g BW, i.p) on nickelinduced changes in serum lipid profiles and liver histopathology. Nickel-treated rats showed a significant increase in serum low-density lipoprotein-cholesterol, total cholesterol, triglycerides, and a significant decrease in serum high-density lipoprotein-cholesterol. In the liver, nickel sulfate caused a loss of normal architecture, fatty changes, extensive vacuolization in hepatocytes, eccentric nuclei, and Kupffer cell hypertrophy. Simultaneous administration of L-ascorbic acid with nickel sulfate improved both the lipid profile and liver impairments when compared with rats receiving nickel sulfate only. The results indicate that L-ascorbic acid is beneficial in preventing nickel-induced lipid alterations and hepatocellular damage.     

Cancer risk assessment for oral exposure to PAH mixtures.

Cancer risk estimates for oral uptake of polycyclic aromatic hydrocarbons (PAHs) currently are based on risk estimates for benzo[a]pyrene (BAP). The potency of PAH mixtures often is calculated using relative potency values (BAP equivalency factors). We used recent oral carcinogenicity studies with BAP and coal tar mixtures, as well as older studies for a critical reappraisal of the current practice. A literature survey identified several carcinogenicity studies with oral and dermal exposure and lung implantation that allow a direct comparison of the carcinogenic potency of pure BAP and PAH mixtures. Moreover, when the PAH composition of the mixture has been analysed, prediction of the potency of PAH mixtures by BAP equivalency factors could be compared with the observed PAH potency. The analysis indicates that BAP equivalency factors do not describe adequately the potency of PAH mixtures and lead to underestimations of carcinogenic potency in most cases. Evaluation of several studies with various PAH mixtures revealed that the potency ratio between pure BAP and the PAH mixture in the same assay is highly dependent on the exposure pathway and the target organ, therefore potency estimates for PAH mixtures should be derived separately for oral, dermal and inhalative exposure using data from studies with the relevant pathway. A cancer slope factor for oral PAH exposure was derived based on data from a recent feeding study with coal tar mixtures. By using incidence data for all exposure-related tumours, a slope factor for humans of 11.5 (human excess risk per oral lifetime exposure with 1 mg BAP kg(-1)day(-1) in a PAH mixture) was obtained. Our analysis led to the conclusion that the contribution of BAP to the carcinogenic potency of the mixture depends on the exposure pathway and type of cancer observed but is relatively constant for various PAH mixtures from industrial sources. Thus, the derived oral slope factor is recommended to be used for the risk assessment of PAH-contaminated soils.     

The pharmacokinetics of dichloromethane. II. Disposition in Fischer 344 rats following intravenous and oral administration

The tissue distribution and metabolism of dichloromethane (DCM; CH2Cl2) was investigated in Fischer 344 rats following iv or oral administration. The route and level of exposure were found to have a significant effect on the disposition characteristics. A two-compartment model was used to describe the elimination of DCM from blood following single iv doses. The estimates of t1/2,beta were 11.9 and 23.5 min for doses of 10 and 50 mg/kg, respectively, and the disposition rate constants, beta were found to differ significantly at P less than 0.05. When DCM was administered orally (by gavage) in a daily dose of 50 or 200 mg/kg for 14 consecutive days, rapid absorption and distribution to the tissues characterized the disposition. Dose-dependent metabolism to 14CO2 and 14CO and rapid pulmonary clearance of unchanged 14CH2Cl2 were the dominant routes of elimination of DCM from the body following both iv and oral doses. No observable pharmacokinetic or metabolic effect resulted from repeated oral dosing.     

Chronic toxicity and oncogenicity bioassay of inhaled ethyl acrylate in Fischer 344 rats and B6C3F1 mice

Male and female Fischer 344 rats and B6C3F1 mice were exposed to 0, 25 or 75 ppm (0, 0.10 or 0.31 mg/l) ethyl acrylate vapors, 6 hours per day, 5 days per week, for a total of 27 months. Additional rats and mice were exposed to 225 ppm (0.92 mg/l) for 6 months and then held for 21 additional months post-exposure. Histopathologic changes in olfactory portions of the nasal mucosa were present in animals in all of these three exposure groups. These microscopic exposure-related changes were concentration-dependent, primarily in terms of distribution of the lesions within the nasal cavity. Generally those areas of the nasal mucosa normally lined by olfactory epithelium were altered, while the regions lined by respiratory epithelium were relatively unaffected. There was no indication of an oncogenic response in any organ or tissue in either rats or mice. A follow-up study in which Fischer 344 rats and B6C3F1 mice were exposed to 5 ppm (0.02 mg/l) for 24-months revealed no treatment-related changes in the nasal mucosa.     

The Developmental Toxicity of 2-Ethyihexanol Applied Dermally to Pregnant Fischer 344 Rats

Undiluted 2-ethylhexanol (2-EH) was administered by occludeddermal application for 6 hr per day on Gestation Days 6 through15 to pregnant Fischer 344 rats, in range-finding (R) and main(M) studies. The dermal route is considered to be the most relevantfor human exposure. Treatment levels were (R) 0.0, 0.5, 1.0,2.0, and 3.0 ml/kg/day (equivalent to 0, 420, 840, 1680, and2520 mg/kg/day) and (M) 0.0, 0.3, 1.0, and 3.0 ml/kg/day (equivalentto 0, 252, 840, and 2520 mg/kg/day). Controls (0.0 ml/kg/day,sham controls) received deionized water at 3.0 ml/kg/day. Dermal-positivecontrol groups received undiluted 2-methoxyethanol (2-ME) at(R) 0.5 and 1.5 ml/kg/day and (M) 1.0 ml/kg/day as a referencecompound in a similar regimen. An oral reference compound, valproicacid, was administered by gavage in the range-finding studyon Gestation Days 6 through 15 at 400 mg/kg/day. The range-findingstudy employed an untreated (naive) control group. Numbers ofplug-positive females per group were (R) 8 and (M) 25. Maternalweight gain was reduced for 2-EH at 1680 (R) and 2520 (R andM studies) mg/kg/day. Exfoliation and encrustation were seenat the application site in both studies at 840, 1680, and 2520mg/kg. Maternal liver, kidney, thymus, spleen, adrenal, anduterine weights, and gestational and fetal parameters were unaffectedby treatment with 2-EH. There were no treatment-related increasesin the incidence of individual or pooled external, visceral,and skeletal malformations or variations following the applicationof 2-EH. The NOAELs for the maternal toxicity of 2-EH were 252mg/kg/day based on skin irritation and 840 mg/kg/day based onsystemic toxicity. The developmental toxicity NOAEL was at least2520 mg/kg/day, with no teratogenicity. Administration of 2-MEat 840 mg/kg/day resulted in reduced maternal weight gain andfood consumption, increased postimplantation loss, reduced numbersof live fetuses per litter, and reduced fetal body weights perlitter. The incidence of fetal malformations and variationswas increased. Oral administration of VPA produced maternaltoxicity, developmental toxicity, and teratogenicity. The Fischer344 rat is thus susceptible to known rodent teratogens by boththe dermal and oral routes. It is concluded that 2-EH is notdevelopmentally toxic by the dermal route in the Fischer 344rat at and below treatment levels which produce maternal toxicity.