Carcinogenicity and Toxicity of Inhaled Nitrobenzene in B6C3F1 Mice and F344 and CD Rats

The potential carcinogenicity and toxicity of inhaled nitrobenzenewere evaluated following chronic (2-year) exposure in mice andrats. Male and female B6C3F1 mice were exposed to 0, 5, 25,or 50 ppm nitrobenzene, while male and female F344 rats andmale CD rats were exposed to 0, 1, 5, or 25 ppm nitrobenzene.All exposures were for 6 hr/day, 5 days/week excluding holidays,for a total of 505 days over 2 years. Survival was not adverselyaffected by nitrobenzene exposure, and only mild exposure-relateddecreases in body weights (<10% of control) were occasionallynoted. Nitrobenaene exposure resulted in increased incidenceof neoplasia in male B6C3F1 mice (pulmonary alveolar/bronchiolarand thyroid follicular cell neoplasms), female B6C3FI mice (mammarygland neoplasms), male F344 rats (hepatocellular and renal neoplasms),female F344 rats (endometrial stromal neoplasms), and male CDrats (hepatocellu lar neoplasms). In addition, there were marginalincreases in the incidence of hepatocellular neoplasia in femaleB6C3F1 mice and thyroid follicular neoplasia in male F344 rats.Groups of nitrobenzene-exposed mice and rats with increasedincidence of renal and thyroid neoplasia also had increasedincidences of hyperplasia in these tissues. Toxicity resultingfrom chronic inhalation of nitrobenzene was manifested by methemoglobinemia,anemia, and adaptive or degenerative changes in the nose, liver,and testis. The results indicate that inhaled nitrobenzene iscarcinogenic and toxic in mice and rats, and that the spectrumof these responses in animals is dependent on species, sex,and genetic background.     

Systemic urocortin 2, but not urocortin 1 or stressin 1-A, suppresses feeding via CRF2 receptors without malaise and stress

BACKGROUND AND PURPOSE

Infusion of corticotropin-releasing factor (CRF)/urocortin (Ucn) family peptides suppresses feeding in mice. We examined whether rats show peripheral CRF/Ucn-induced anorexia and determined its behavioural and pharmacological bases.

EXPERIMENTAL APPROACH

Male Wistar rats (n = 5–12 per group) were administered (i.p.) CRF receptor agonists with different subtype affinities. Food intake, formation of conditioned taste aversion and corticosterone levels were assessed. In addition, Ucn 1- and Ucn 2-induced anorexia was studied in fasted CRF₂ knockout (n = 11) and wild-type (n = 13) mice.

KEY RESULTS

Ucn 1, non-selective CRF receptor agonist, reduced food intake most potently (∼0.32 nmol·kg⁻¹) and efficaciously (up to 70% reduction) in fasted and fed rats. The peptides'' rank-order of anorexic potency was Ucn 1 ≥ Ucn 2 > >stressin₁-A > Ucn 3, and efficacy, Ucn 1 > stressin₁-A > Ucn 2 = Ucn 3. Ucn 1 reduced meal frequency and size, facilitated feeding bout termination and slowed eating rate. Stressin₁-A (CRF₁ agonist) reduced meal size; Ucn 2 (CRF₂ agonist) reduced meal frequency. Stressin₁-A and Ucn 1, but not Ucn 2, produced a conditioned taste aversion, reduced feeding efficiency and weight regain and elicited diarrhoea. Ucn 1, but not Ucn 2, also increased corticosterone levels. Ucn 1 and Ucn 2 reduced feeding in wild-type, but not CRF₂ knockout, mice.

CONCLUSIONS AND IMPLICATIONS

CRF₁ agonists, Ucn 1 and stressin₁-A, reduced feeding and induced interoceptive stress, whereas Ucn 2 potently suppressed feeding via a CRF₂-dependent mechanism without eliciting malaise. Consistent with their pharmacological differences, peripheral urocortins have diverse effects on appetite.     

2,4-Dichloro-1-nitrobenzene exerts carcinogenicities in both rats and mice by two years feeding

Carcinogenicity and chronic toxicity of 2,4-dichloro-1-nitrobenzene (2,4-DCNB) were examined by dietary administration to F344/DuCrj rats and Crj:BDF₁ mice of both sexes for 2?years. Dietary administration commenced when the animals were 6?weeks old. The dietary concentration of 2,4-DCNB was 0 (control), 750, 1,500 and 3,000?ppm (w/w) for male and female rats; 0, 750, 1,500 and 3,000?ppm for male mice; and 0, 1,500, 3,000 and 6,000?ppm for female mice. In rats, there was a dose-dependent and significant induction of renal cell adenomas and carcinomas in both sexes and of preputial glands adenomas in males. In all the 2,4-DCNB-fed groups of both sexes, the incidence of atypical tubular hyperplasia, a pre-neoplastic lesion in the kidney, in the proximal tubule was significantly increased. In mice, there was a dose-dependent and significant induction of hepatocellular adenomas, hepatocellular carcinomas, hepatoblastomas and peritoneal hemangiosarcomas in both sexes. The incidence of acidophilic hepatocellular foci was also significantly increased in female mice. Thus, clear evidence of carcinogenic activity of 2,4-DCNB by 2-year feeding was demonstrated in both rats and mice.     

Toxicity and carcinogenicity of the water disinfection byproduct, dibromoacetic acid, in rats and mice

Dibromoacetic acid (DBA) is a water disinfection byproduct formed by the reaction of chlorine oxidizing compounds with natural organic matter in water containing bromide. Male and female F344/N rats and B6C3F₁ mice were exposed to DBA in drinking water for 2 weeks (N = 5), 3 months (N = 10), or 2 years (N = 50). Concentrations of DBA in drinking water were 0, 125, 250, 500, 1000, and 2000 mg/L in the 2-week and 3-month studies, and 0, 50, 500, and 1000 mg/L in the 2-year studies. Toxic effects of DBA in the prechronic studies were detected in the liver (hepatocellular cytoplasmic vacuolization in rats and mice) and testes (delayed spermiation and atypical residual bodies in male rats and mice, and atrophy of the germinal epithelium in rats). In the 2-year studies, neoplasms were induced at multiple sites in rats and mice exposed to DBA; these included mononuclear cell leukemia and abdominal cavity mesothliomas in rats, and neoplasms of the liver (hepatocellular adenoma or carcinoma and hepatoblastoma) and lung (alveolar adenoma or carcinoma) in mice. The increase in incidence of hepatocellular neoplasms in male mice was significant even at the lowest exposure concentration of 50 mg/L, which is equivalent to an average daily dose of approximately 4 mg/kg. These studies provide critical information for future re-evaluations of health-based drinking water standards for haloacetic acids.     

Reevaluation of a twenty-four-month chronic toxicity/carcinogenicity study of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in the B6C3F1 hybrid mouse

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been widely used as an explosive in U.S. army munitions formulations since World War II. Two-year carcinogenicity studies revealed RDX to be noncarcinogenic in two strains of rats, but a 2-year carcinogenicity study in B6C3F1 mice revealed an increased incidence of hepatocellular neoplasms in females. Based on results of the study in B6C3F1 mice, RDX has been classified as a possible carcinogen. The authors reevaluated the archived histological sections from the B6C3F1 mouse study, using current histopathologic diagnostic criteria and interpretations. The earlier evaluation showed a statistically significant increase in the incidence of hepatocellular adenoma/carcinoma in female mice from the three highest dose groups (7, 35, and 175/100 mg/kg/day). The revaluation yielded a slightly lower incidence at each of the dose levels in female mice. The reduced number of hepatocellular neoplasms was largely due to reclassification of hepatocellular adenomas as foci of cytoplasmic alteration, in compliance with current diagnostic criteria. The reevaluation was reviewed by a pathology working group (PWG), which arrived at a consensus classification of each lesion. Based on the consensus diagnoses of the PWG, only one female group (35 mg/kg/day) showed a significant increase when compared to controls. The incidence of hepatocellular neoplasms for all groups, including the 35 mg/kg/day group, was within the reported incidence range for spontaneous hepatocellular neoplasms in female B6C3F1 mice. The increased incidence of hepatocellular neoplasms in female mice given RDX at 35 mg/kg/day was interpreted as equivocal evidence of a carcinogenic effect.     

Toxicity and carcinogenicity of Elmiron in F344/N rats and B6C3F<Subscript>1</Subscript> mice following 2 years of gavage administration

Elmiron (sodium pentosan polysulfate) is used for the relief of urinary bladder pain associated with interstitial cystitis. The National Toxicology Program (NTP) tested this compound because of its orphan drug status and lack of information about its chronic toxicity and carcinogenicity. Groups of 50 male and 50 female F344/N rats were given Elmiron in de-ionized water by gavage at doses of 0, 14, 42, or 126 mg/kg to males and 0, 28, 84, or 252 mg/kg to females once daily, 5 days per week, for up to 2 years. The same numbers of male and female B6C3F₁ mice were dosed similarly with 0, 56, 168, or 504 mg/kg. Elmiron administration produced no effect on the body weight of rats, male mice, or low- and mid-dose groups of female mice. The body weights of the high-dose female mice were significantly decreased relative to those of controls. Pairwise comparison showed that survival of all dosed groups of rats and mice was similar to that of the controls. Elmiron was not carcinogenic in F344/N rats. An increased incidence of liver hemangiosarcoma provided evidence of some carcinogenic activity for Elmiron in male B6C3F₁ mice. Increased incidences of liver hemangiosarcoma, hepatocellular neoplasms (predominantly adenomas), and malignant lymphomas revealed carcinogenic activity of Elmiron in female B6C3F₁ mice. Elmiron administration produced elevated occurrences of nonneoplastic lesions, such as vacuolated histiocytes in the rectum, lung, spleen (males only), and mesenteric lymph node in rats and liver, rectum, mesenteric lymph node, and spleen in mice. Myxomatous change, chronic inflammation, and squamous metaplasia (mice only) were observed in the large intestine, and lymphohistiocytic hyperplasia was found to be increased in the spleen of rats of both sexes treated with the highest dose. In the latter lesion, the histiocytes contained pale, finely granular cytoplasm and were not considered to represent the same change as the vacuolated histiocytes seen in the mesenteric lymph node and rectum. Under the conditions of these 2-year studies, Elmiron was carcinogenic to mice but not rats.The studies were conducted at Battelle, Columbus, OH, USA.     

Hypolipidemic Activity of 3-Amino-1-(2,3,4-mononitro-, mono-, or dihalophenyl)propan-1-ones in Rodents

A series of 3-amino-1-(2,3,4-mononitro-, mono-, or dihalophenyl)propan-1-ones were synthesized and shown to be effective in lowering both serum cholesterol and triglyceride levels significantly in CF₁ mice and Sprague-Dawley rats. All analogs showed better activity than the standard drugs, lovastatin and clofibrate, in reducing the serum cholesterol and triglyceride levels in mice at 8 mg/kg/day intraperitoneally. The best active analogs, 3-morpholino-1-(3-nitrophenyl)propan-1-one ( 4 ) and 3-piperidino-1-(3-nitrophenyl)propan-1-one ( 5 ), exhibited 58% and 67% reduction of serum cholesterol levels, respectively, and 42% and 46% reduction of serum triglyceride levels, respectively, after 16 days of administration at 8 mg/kg/day intraperitoneally in CF₁ mice. In Sprague-Dawley rats at 8 mg/kg/day oral administration, both compounds ( 4 and 5 ) significantly decreased the serum cholesterol and triglyceride levels. Rat tissue lipid levels were reduced significantly by compound 4, while less effects resulted from compound 5. The cholesterol and triglyceride levels in chylomicrons, VLDL, and LDL fractions were reduced by both analogs while the HDL cholesterol levels were significantly increased. Compound 5 was also effective in lowering serum cholesterol and triglyceride levels in hyperlipidemic mice, at 8 mg/kg/day intraperitoneally, but not effective in hyperlipidemic rats at 8 mg/kg/day intraperitoneally, but not effective in hyperlipidemic rats at 8 mg/kg/day orally. Cholesterol and triglyceride lowering effects of the agents were correlated with inhibition of the activities of liver acetyl CoA synthetase, HMG CoA reductase, phosphatidylate phosphohydrolase, and lipoprotein lipase, and with elevation of the activity of cholesterol ester hydrolase.     

Peroxisome proliferation due to di (2-ethylhexyl) adipate, 2-ethylhexanol and 2-ethylhexanoic acid

The dose-response relationships for peroxisome proliferation due to Di (2-ethylhexyl) adipate (DEHA), 2-ethylhexanol (EH), 2-ethylhexanoic acid (EHA) have been investigated in rats and mice. Linear dose-response relationships were observed for induction of cyanide-insensitive palmitoyl CoA oxidation (PCO), used as a enzyme marker of peroxisome proliferation, by DEHA, EH and EHA in both species. Relative liver weights were also increased in a dose related manner. On a molar basis, DEHA was twice as potent as EH or EHA which were equipotent and PCO was stimulated to a greater extent in male mice than in rats or female mice. At doses above 8 mmol/kg/day, EH was toxic to rats (both sexes) and similarly EHA at 13.5 mmol/kg/day lead to the death of female rats. In a attempt to explain the species difference in carcinogenicity of DEHA previously reported, we also used Fischer 344 rats and B6C3F1 mice. DEHA administration (2.5 g/kg/day) to Fischer 344 rats and B6C3F1 mice lead to toxicity in female rats. Relative liver weights were increased in a dose related fashion by DEHA administration to both rats and mice, PCO but not catalase was markedly increased (up to 15 fold in male rats). Light microscopy examination indicated some glycogen loss, a dose related hypertrophy and increased eosinophilia in both rats and mice. Electron microscopy confirmed peroxisome proliferation accompanied by a marked reduction of lipid in the centrilobular hepatocytes. These data suggest EHA to be the proximate peroxisome proliferator derived from DEHA. These data indicate a higher sensitivity for Fischer 344 rats than B6C3F1 mice to hepatic peroxisome proliferation due to DEHA and ratio of PCO activity and catalase activity data suggest that more hydrogen peroxide (H₂O₂) could escape from peroxisomes in male Fischer 344 rats than B6C3F1 mice. These data obtained with B6C3F1 mice and Fischer 344 rats are not agreement with the carcinogenicity bioassays previously reported showing an incidence of hepatic tumours only in B6C3F1 mice.     

Oncogenicity Testing of 2-Ethylhexanol in Fischer 344 Rats and B6C3F1 Mice

2-Ethylhexanol (2EH) is a weak nongenotoxic hepatic peroxisomeproliferator in the rat. It is a high-volume chemical intermediatein the preparation of the plasticizers bis-(2-ethylhexyl) adipate(DEHA), bis-(2-ethylhexyl) phthalate (DEHP), and tris-(2-ethylhexyl)phosphate (TEHP), which are weak hepatocellular tumorigens infemale mice. In consequence, the oncogenic potential of 2EHwas evaluated in male (M) and female (F) rats and mice (50 animals/sex/group).Oral gavage doses of 2EH in 0.005% aqueous Cremophor EL (polyoxyl-35castor oil) were given five times a week to rats: 0 (water),0 (vehicle), 50, 150, and 500 mg/kg for 24 months, and to mice:0 (water), 0 (vehicle), 50, 200, and 750 mg/kg for 18 months.Statistical comparisons of data were made between vehicle controlsand treatment groups. There were no differences of biologicalsignificance between data from vehicle and water control groups.In rats, there were no dose-related changes at 50 mg/kg. Therewas reduced body weight gain at 150 mg/kg (M, 16; F, 12%) and500 mg/kg (M, 33; F, 31%) and an increased incidence of lethargyand unkemptness. There were dose-related increases in relativeliver, stomach, brain, kidney, and testis weights at sacrifice.Female rat mortality was markedly increased at 500 mg/kg. Therewas marked aspiration-induced bronchopneumonia in rats at 500mg/kg; hematologic, gross, and microscopic changes, includingtumors, were otherwise comparable among all rat groups. In miceat 50 and 200 mg/kg there were no dose-related changes and essentiallyno time-dependent or time-independent adverse trends in livertumor incidence at the 5% significance level. At 750 mg/kg mousebody weight gain was reduced (M, 26; F, 24%), and mortalityincreased (M and F, 30%) versus vehicle controls. At 750 mg/kgthere was a slight increase in nonneoplastic focal hyperplasiain the forestomach of mice (M 5/50, F 4/50) versus vehicle controls(M 1/50, F 1/50). There were increases in mouse relative liver(F, 21%) and stomach (M, 13%; F, 19%) weights at 750 mg/kg.There was a 12% incidence of hepatic basophilic foci and an18% incidence of hepatocellular carcinomas in male mice at 750mg/kg, not statistically significant compared with either controlby Fisher's exact test. There was a 12% incidence of hepaticbasophilic foci and a 10% incidence of hepatocellular carcinomasin female mice at 750 mg/kg, statistically significant (p <0.05) compared with vehicle but not with water controls by Fisher'sexact test. There were no metastases. Time-dependent and -independentstatistical analyses showed an adverse trend in the incidenceof hepatocellular carcinomas in male and female mice, correlatedwith toxicity (expressed as mortality) at 750 mg/kg. The time-adjustedincidence of hepatocellular carcinomas in male mice (18.8%)was within the historical normal range at the testing facility(0–22%), but that in females (13.1%) lay outside the normalrange (0–2%). Under the conditions of these studies 2EHwas not oncogenic in rats, but there were weak adverse trendsin hepatocellular carcinoma incidence in mice at high dose levelswhich may have been associated with toxicity. The major effectsof chronic dosing were mortality in female rats at 500 mg/kgand in male and female mice at 750 mg/kg, accompanied by reductionsin body weight gain in rats at 150 and 500 mg/kg and in miceat 750 mg/kg. Direct comparison of any tumorogenic effects of2EH given alone to female mice with those due to 2EH formedin vivo from DEHA, DEHP, or TEHP is limited by the high mortalitycaused by 2EH in female mice at equivalent doses of 2EH. While2EH may be a contributing factor in the hepatocellular carcinogenesisin female mice associated with the chronic administration ofDEHA and DEHP, it is unlikely to be the entire proximate carcinogen.     

Toxicology and carcinogenesis studies of o-nitrotoluene sulfone (CAS no. 88-72-2) in F344/N rats and B6C3F(1) mice (feed studies)

[structure: see text] o-Nitrotoluene is used to synthesize agricultural and rubber chemicals, azo and sulfur dyes, and dyes for cotton, wool, silk, leather, and paper. o-Nitrotoluene was nominated for study by NIOSH and the NTP based on its considerable human exposure as well as the absence of long-term studies of carcinogenicity in rodents. Male and female F344/N rats and B6C3F1 mice were exposed to o-nitrotoluene (greater than 99% pure) in feed for 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, rat and mouse bone marrow cells, and mouse peripheral blood erythrocytes. 2-YEAR STUDY IN RATS: In the core study, groups of 60 male and 60 female rats were fed diets containing 625, 1,250, or 2,000 ppm o-nitrotoluene (equivalent to average daily doses of approximately 25, 50, or 90 mg o-nitrotoluene/kg body weight to males and 30, 60, or 100 mg/kg to females) for 105 weeks. In a 3-month stop-exposure study, groups of 70 male rats were fed diets containing 2,000 or 5,000 ppm o-nitrotoluene (equivalent to average daily doses of approximately 125 or 315 mg/kg) for 13 weeks followed by undosed feed for the remainder of the study. A group of 70 male rats receiving undosed feed served as a control group for both male rat studies; 60 female rats receiving undosed feed were the control group for the female core study. Ten control males and 10 males from each stop-exposure group were sacrificed at 3 months. Survival, Body Weights, and Feed Consumption: All 2,000 ppm core study, all 5,000 ppm stop-exposure, and all but three core study 1,250 ppm male rats died before the end of the studies. Survival of 625 ppm core study and 2,000 ppm stop-exposure males and of 2,000 ppm females was significantly less than that of the controls. Mean body weights of all exposed groups of males except the 625 ppm group were generally less than those of the controls throughout the study. Mean body weights of 2,000 ppm females were less than those of the controls during year 2 of the study. Feed consumption by exposed groups of rats was similar to that by the controls. Biomarkers of Exposure: Three urinary metabolites were followed during the study as biomarkers of exposure. The ratios of o-nitrobenzoic acid to creatinine and of o-nitrobenzylmercapturic acid to creatinine determined at 2 weeks and at 3, 12, and 18 months were linearly related to exposure concentration in males and females. The ratio of o-aminobenzoic acid to creatinine was not related to exposure concentration. Pathology Findings: The incidences of malignant mesothelioma in male rats occurred with positive trends in both the core and stop-exposure studies and were significantly greater in exposed groups than in the controls. Incidences of subcutaneous skin neoplasms (fibroma, fibrosarcoma, and lipoma) were increased in exposed groups of males, while the incidences of fibroma or fibrosarcoma (combined) were increased in exposed females. In all exposed groups of males and females except 2,000 ppm core study males, the incidences of mammary gland fibroadenoma were significantly increased. The incidences of mammary gland hyperplasia were significantly increased in 625 and 1,250 ppm females. Increased incidences of mesothelioma, skin neoplasms, and mammary gland fibroadenoma in the stop-exposure males indicated that 3 months of dosing were sufficient to produce a carcinogenic effect. Liver weights of 5,000 ppm stop-exposure males were significantly greater than those of the controls at 3 months. The incidences of hepatocellular adenoma in 2,000 ppm core study males and females and of hepatocellular adenoma or carcinoma (combined) in 2,000 ppm core study and 5,000 ppm stop-exposure males were significantly increased. Cholangiocarcinoma occurred in three 5,000 ppm stop-exposure males, and a single hepatocholangiocarcinoma occurred in a 625 ppm male and in a 2,000 ppm core study male. Nonneoplastic lesions of the liver included eosinophilic, mixed cell, and clear cell foci in exposed groups of males and females and mixed cell infiltrate in exposed males and basophilic focus in exposed females. The incidences of alveolar/bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined) were significantly increased in 5,000 ppm stop-exposure males, as were alveolar/bronchiolar hyperplasia in most exposed groups of males and females. The incidences of hematopoietic cell proliferation of the spleen and of hyperplasia of the mandibular lymph node (females) and bone marrow were increased in exposed groups of males at 3 months and/or 2 years and in exposed groups of females at 2 years. The incidences of mononuclear cell leukemia were significantly decreased in all groups of males exposed to 1,250 ppm or greater and in all exposed groups of females; the incidence of testicular interstitial cell adenoma was significantly decreased in 5,000 ppm stop-exposure males. 2-YEAR STUDY IN MICE: Groups of 60 male and 60 female mice were fed diets containing 0, 1,250, 2,500, or 5,000 ppm o-nitrotoluene (equivalent to average daily doses of approximately 165, 360, or 700 mg/kg to males and 150, 320, or 710 mg/kg to females) for 105 weeks. Survival, Body Weights, and Feed Consumption: All 2,500 and 5,000 ppm males died before the end of the study. Survival of 1,250 ppm males and 5,000 ppm females was significantly less than that of the controls. Mean body weights of exposed males and 5,000 ppm females were generally less than those of the controls throughout the study, and those of 2,500 ppm females were less during the second year of the study. Feed consumption by 5,000 ppm males was less than that by the controls. Biomarkers of Exposure: Three urinary metabolites were followed during the study as biomarkers of exposure. The ratios of o-nitrobenzoic acid to creatinine determined at 2 weeks and at 3, 12, and 18 months were linearly related to exposure concentration in males and females. The concentrations of o-nitrobenzylmercapturic acid and o-aminobenzoic acid were below the limit of quantitation at most time points. Pathology Findings: The incidences of hemangiosarcoma in all exposed groups of males and in 5,000 ppm females were significantly greater than those in the controls. Large intestine (cecum) carcinomas were observed in all exposed groups except 5,000 ppm males. The incidences of hepatocellular neoplasms were significantly increased in 2,500 and 5,000 ppm females. Nonneoplastic liver lesions including eosinophilic and basophilic foci and minimal to mild necrosis were enhanced in exposed males and females. Also present were focal hepatocyte syncytial alteration in exposed males and hepatocyte necrosis and focal hepatocyte cytoplasmic vacuolization in 5,000 ppm females. Renal tubule pigmentation occurred more frequently in exposed groups of males and in 5,000 ppm females than in the controls. Olfactory epithelial degeneration occurred in every male and female mouse exposed to 2,500 or 5,000 ppm, and the severity of this lesion increased with increasing exposure concentration. GENETIC TOXICOLOGY: o-Nitrotoluene was not mutagenic in any of several strains of S. typhimurium, with or without metabolic activation enzymes (S9). Sister chromatid exchanges were significantly increased in cultured Chinese hamster ovary cells following exposure to o-nitrotoluene in the presence of S9; an equivocal response was seen without S9. o-Nitrotoluene did not induce chromosomal aberrations in cultured Chinese hamster ovary cells, with or without S9. o-Nitrotoluene did not induce a significant increase in the frequency of micronuclei in bone marrow polychromatic erythrocytes of male rats or male mice when administered by intraperitoneal injection. Results of a peripheral blood micronucleus test were equivocal for male mice and negative for female mice administered o-nitrotoluene in feed for 13 weeks. CONCLUSIONS: Under the conditions of these studies, there was clear evidence of carcinogenic activity* of o-nitrotoluene in male rats based on increased incidences of malignant mesothelioma, subcutaneous skin neoplasms, mammary gland fibroadenoma, and liver neoplasms. The increased incidences of lung neoplasms in male rats were also considered to be exposure related. There was clear evidence of carcinogenic activity of o-nitrotoluene in female rats based on increased incidences of subcutaneous skin neoplasms and mammary gland fibroadenoma. The increased incidence of hepatocellular adenoma in female rats was also considered to be exposure related. There was clear evidence of carcinogenic activity of -o-nitrotoluene in male and female mice based on increased incidences of hemangiosarcoma, carcinoma of the large intestine (cecum), and hepatocellular neoplasms (females only). Exposure to o--nitrotoluene caused increased incidences of nonneoplastic lesions of the mammary gland (females only), liver, bone marrow, spleen, lung, and mandibular lymph node (females only) in male and female rats and of the liver, kidney, and nose in male and female mice. Decreased incidences of mononuclear cell leukemia occurred in exposed groups of rats; the incidence of testicular interstitial cell adenoma was decreased in exposed male rats. [tables: see text]     

The 5-HT2C Receptor Agonist Lorcaserin Reduces Nicotine Self-Administration,Discrimination, and Reinstatement: Relationship to Feeding Behavior and Impulse Control

Lorcaserin ((1R)-8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine HCl) is a selective 5-HT_2C receptor agonist with clinical efficacy in phase-III obesity trials. Based on evidence that this drug class also affects behaviors motivated by drug reinforcement, we compared the effect of lorcaserin on behavior maintained by food and nicotine reinforcement, as well as the stimulant and discriminative stimulus properties of nicotine in the rat. Acutely administered lorcaserin (0.3–3 mg/kg, subcutaneous (SC)) dose dependently reduced feeding induced by 22-h food deprivation or palatability. Effects up to 1 mg/kg were consistent with a specific effect on feeding motivation. Lorcaserin (0.6–1 mg/kg, SC) reduced operant responding for food on progressive and fixed ratio schedules of reinforcement. In this dose range lorcaserin also reversed the motor stimulant effect of nicotine, reduced intravenous self-administration of nicotine, and attenuated the nicotine cue in rats trained to discriminate nicotine from saline. Lorcaserin also reduced the reinstatement of nicotine-seeking behavior elicited by a compound cue comprising a nicotine prime and conditioned stimulus previously paired with nicotine reinforcement. Lorcaserin did not reinstate nicotine-seeking behavior or substitute for a nicotine cue. Finally, lorcaserin (0.3–1 mg/kg) reduced nicotine-induced increases in anticipatory responding, a measure of impulsive action, in rats performing the five-choice serial reaction time task. Importantly, these results indicate that lorcaserin, and likely other selective 5-HT_2C receptor agonists, similarly affect both food- and nicotine-motivated behaviors, and nicotine-induced impulsivity. Collectively, these findings highlight a therapeutic potential for 5-HT_2C agonists such as lorcaserin beyond obesity into addictive behaviors, such as nicotine dependence.     

The effect of age and exposure duration on cancer induction by a known carcinogen in rats,mice, and hamsters

Female Golden Syrian hamsters, F-344 rats, Swiss CD-1 mice, and B6C3F1 hybrid mice were exposed 6 hr/day, 5 days/week to carcinogenic levels of vinyl chloride (VC) for 6, 12, 18, or 24 months (rats and hamsters only). Other groups of rodents were held for 6 or 12 months and then exposed for 6 or 12 months. At the end of the study the incidence of VC-induced neoplasms was compared in each of the groups to assess the effects of duration of exposure and age at the start of exposure on carcinogenicity of VC. In rats, with early initial exposure, hemangiosarcomas, hepatocellular carcinomas, and mammary gland carcinomas occurred with increasing incidence with longer exposure duration. Rats held for 6 months before exposure developed VC-related neoplasms, while rats held 12 months before the start of exposure failed to show a significantly increased incidence of these neoplasms. In hamsters, hemangiosarcomas, mammary gland carcinomas, gastric adenocarcinomas, and skin carcinomas resulted from VC exposure. The highest incidence of malignant neoplasms occurred in hamsters exposed for the first 12 months, whereas exposure begun after 12 months of age did not cause neoplasms. In both strains of mice, VC exposure during the first 6 months of the experiment induced a high incidence of hemangiosarcomas and mammary gland carcinomas. Swiss mice also developed lung carcinomas after only 6 months of exposure. In all three rodent species an initial 12 month exposure to VC was adequate to detect its carcinogenic potential, but the shortened survival of VC exposed mice and hamsters precluded a meaningful comparison with longer periods of exposure. Exposures were most effective when started early in life.     

Comparative Carcinogenicity of Polybrominated Biphenyls with or without Perinatal Exposure in Rats and Mice

Comparative Carcinogenicity of Polybrominated Biphenyls withor without Perinatal Exposure in Rats and Mice. CHHABRA, R.S., BUCHER, J. R., HASEMAN, J. K., ELWELL, M. R., KURTZ, P.J., AND CARLTON, B. D. (1993). Fundam. Appl. Toxicol. 21, 451–460. Chronic toxicity and carcinogenicity studies of a polybrominatedbiphenyl mixture (PBB) were conducted in F344/N rats and B6C3F1mice of each sex. The major objective of the study was to determineif exposure to PBB during the perinatal period, in additionto conventional exposure of animals for 2 years, enhances thesensitivity of the bioassay to identify the carcinogenic potentialof this chemical. The studies were designed to determine thetoxic and carcinogenic effects of dietary PBB in rats and micereceiving (i) perinatal exposure up to 8 weeks of age followedby control diet for 2 years, (ii) exposure for 2 years beginningat the age of 8 weeks, and (iii) combined perinatal/adult exposureto PBB (perinatal exposure to 8 weeks of age followed by adultexposure for 2 years). During the perinatal period, rats wereexposed to PBB at dose levels ranging from 1 to 10 ppm and adultexposure concentrations ranged from 3 to 30 ppm in the diet.In the mice, the dose levels ranged from 3 to 30 ppm in bothperinatal and adult exposure portions of the chronic studies.A total of eight dose groups (including controls) were usedwith 60 animals in each group. Liver was the major target organof PBB toxicity. Perinatal exposure alone (through dietary administrationof 10 ppm PBB to the dams) had no effect on the incidences ofneoplasms in female F344/N rats, but in male rats, perinatalexposure was associated with a marginally increased incidenceof hepatocellular adenomas that may have been related to chemicaladministration. In male and female B6C3F₁ mice, perinatal exposureto 30 ppm PBB resulted in significantly increased incidencesof hepatocellular neoplasms. In adult-only dietary exposurestudies, PBB was carcinogenic in male and female F344/N ratsand male and female B6C3F₁ mice based on increased incidencesof hepatocellular neoplasms. Combined perinatal and adult dietaryexposure to PBB confirmed the findings of the adult-only exposuresfor the increased incidences of hepatocellular neoplasms inrats and mice. In male rats, there were no enhancing effectsof combined perinatal and adult exposure. However, perinatalexposure enhanced the susceptibility of female rats receivingadult exposure of 10 or 30 ppm to the induction of liver neoplasms.For male and female rats, a combined analysis of the incidencesof leukemia in the adult-only, perinatal-only, and combinedperinatal and adult exposure groups revealed an apparent associationbetween increasing incidences of mononuclear cell leukemia andexposure to PBB. In male and female mice, it was not possibleto adequately assess the enhancing effects of combined perinataland adult exposure on hepatocellular tumors, because adult-onlyexposure to 10 or 30 ppm PBB resulted in high incidences (84–98%)of liver neoplasms. However, with increased perinatal exposure,there were increases in the numbers of mice with hepatocellularcarcinomas and in the numbers of mice with multiple hepatocellularadenomas, suggesting that combined perinatal and adult exposureincreases PBB-related hepatocellular carcinogenicity relativeto adult-only exposure.     

Biotransformation of a new synthetic retinoid, 4-[(5, 6, 7, 8-tetrahydro-5, 5, 8, 8-tetramethyl-2-naphthyl)carbamoyl] benzoic acid (Am-80), in the rat. Structure elucidation of the metabolites by mass and nmr spectrometry

1. The major metabolites of Am-80 in rat bile were examined by tlc-radiochromatography and hplc-radiochromatography after the intravenous administration of ¹⁴C-Am-80, and > 15 metabolites were detected.

2. Intact and Glusulase-treated bile were analysed by both tlc-radiochromatography and hplc-radiochromatography. As both samples gave similar patterns in both chromato-graphy systems, we have concluded that neither glucuronide nor sulphate conjugates were present.

3. ²H₃-Am-80 and ²H₆-Am-80 were administered to rats, and the major metabolites in bile were detected and their structures elucidated by GC-MS.

4. The chemical structures of seven major biliary metabolites, including unchanged Am-80, were identified by mass and two-dimensional nmr spectrometry, and included 6-hydroxy-Am-80 (M-3), 7-hydroxy-Am-80 (M-4), 6-oxo-Am-80 (M-5), unchanged Am-80 (M-0) and the taurine conjugates of M-3 (M-1), M-4 (M-2) and M-0 (M-6).     

咪苯嗪酮对花生四烯酸诱导的大鼠脑血栓形成的影响

花生四烯酸(AA)0.25～1 mg·kg~(-1)经颈内动脉注射能诱发大鼠同侧大脑半球脑内血栓形成,明显增加伊文思蓝通过血脑屏障渗入脑实质的量,峰值为205±s 50 mg·kg~1脑组织,相应对照组为10±s 5mg·kg~1,咪苯嗪酮0.25～0.5mg·kg~1 iv能对抗AA引起的大鼠脑血栓形成,显著降低脑实质内伊文思蓝的含量,作用呈剂量依赖性,且强于哒唑氧苯     

Peripheral endocannabinoid dysregulation in obesity: relation to intestinal motility and energy processing induced by food deprivation and re-feeding

Background and purpose:

Endocannabinoids in tissues controlling energy homeostasis are altered in obesity, thus contributing to metabolic disorders. Here we evaluate endocannabinoid dysregulation in the small intestine of mice with diet-induced obesity (DIO) and in peripheral tissues of Zucker and lean rats following food deprivation and re-feeding.

Experimental approach:

Intestinal transit, evaluated using rhodamine-B-labelled dextran, and small intestinal endocannabinoid levels, measured by liquid chromatography mass spectrometry, were measured in mice fed normal or high-fat diets (HFDs). Endocannabinoid levels were measured also in various tissues of lean and Zucker rats fed ad libitum or following overnight food deprivation with and without subsequent re-feeding.

Key results:

After 8 weeks of HFD, baseline intestinal transit was increased in DIO mice and enhanced by cannabinoid CB₁ receptor antagonism less efficaciously than in lean mice. Small intestinal anandamide and 2-arachidonoylglycerol levels were reduced and increased respectively. In Zucker rats, endocannabinoids levels were higher in the pancreas, liver and duodenum, and lower in the subcutaneous adipose tissue. Food deprivation increased endocannabinoid levels in the duodenum and liver of both rat strains, in the pancreas of lean rats and in adipose tissues of Zucker rats.

Conclusions and implications:

Reduced anandamide levels might account for increased intestinal motility in DIO mice. Regulation of endocannabinoid levels in rat peripheral tissues, induced by food deprivation and re-feeding, might participate in food intake and energy processing and was altered in Zucker rats. These data, together with previous observations, provide further evidence for dysregulation of peripheral endocannabinoids in obesity.     

Tumor induction in F344/N rats and B6C3F1 mice following inhalation exposure to ethylbenzene

Carcinogenesis studies of ethylbenzene were conducted because of its extensive use as a solvent and because it is structurally similar to the known carcinogen benzene. Groups of 50 male and 50 female Fischer rats and B6C3F1 mice were exposed to ethylbenzene by inhalation at 0, 75, 250, and 750 ppm 6 h per day, 5 days per week, for 2 years. The dose levels were selected based on the results of 13-week studies. In the 750 ppm group of male and female rats, body weights were slightly lower and incidences of renal hyperplasia and tubular neoplasms were significantly increased compared with controls. Incidence of testicular tumors was also significantly increased in male rats. Survival and body weights of the exposed groups of male and female mice and controls were comparable. Incidences of alveolar epithelium metaplasia, alveolar/bronchiolar adenoma, and hepatocyte hypertrophy and necrosis were significantly increased in the 750 ppm male mice and incidences of liver eosinophilic foci and hepatocellular neoplasms were significantly increased in the 750 ppm female mice compared with controls. Ethylbenzene is carcinogenic inducing neoplasms in kidneys and testes in Fischer rats and in lungs in male and liver in female B6C3F1 mice.     

Toxicology and carcinogenesis studies of isophorone in F344 rats and B6C3F1 mice

Toxicology and carcinogenesis studies of isophorone were conducted by administering 0, 250, or 500 mg/kg body weight per day by gavage in corn oil to groups of 50 F344/N rats and 50 B6C3F1 mice of each sex, 5 days/week, for 103 weeks. Dosed male rats developed proliferative lesions of the kidney including hyperplasia, adenoma, and adenocarcinoma of the renal tubule, and epithelial hyperplasia of the renal pelvis. Non-proliferative kidney lesions observed in dosed male rats included mineralization, and a more severe nephropathy in low dose animals than in controls or high dose animals. Carcinomas of the preputial gland occurred in high dose male rats. No isophorone-related lesions were observed in female rats. In male mice, isophorone exposure may have been associated with an increase in hepatocellular neoplasms and mesenchymal neoplasms of the integumentum in high dose animals, and with a marginally increased incidence of lymphoma in low dose male mice. In mice, no non-neoplastic lesions in males or females, or neoplastic lesions in females were considered associated with isophorone administration.     

Toxicity and carcinogenicity studies of nalidixic acid in rodents

Toxicity and carcinogenicity studies of nalidixic acid, an antimicrobial agent used to treat bacterial infections of the urinary tract, were conducted in F344/N rats and B6C3F1 mice of each sex for 13 weeks or 2 years. In the 13-week studies, nalidixic acid was administered at dietary concentrations ranging from 1,000 to 16,000 ppm. Body weights of both rats and mice were reduced in the groups receiving diet containing 8,000 and 16,000 ppm, and feed consumption of rats in the highest treatment groups was approximately two-thirds that of controls. Degeneration of the germinal epithelium in the seminiferous tubules of the testis was observed in male rats that received 16,000 ppm; no other compound-related histopathologic effects were observed in either species. Two-year studies were conducted by feeding diets containing 0, 2,000, or 4,000 ppm nalidixic acid to groups of 50 rats and mice/sex/group. The average daily feed consumption was slightly reduced compared to control groups and resulted in approximate daily doses of 82 or 175 mg nalidixic acid/kg for low dose and high dose rats, and 220 or 475 mg/kg for low dose and high dose mice. Mean body weights of dosed rats and mice were lower than those of controls, except for groups of low dose female rats and male mice. The incidences of preputial gland neoplasms in dosed male rats and of clitoral gland neoplasms in dosed female rats were significantly increased compared to those in controls; responses in low dose groups were similar to those in high dose groups. There were decreased incidences of leukemia and mammary gland neoplasms in dosed female rats and of pituitary gland neoplasms in dosed male rats. Subcutaneous tissue fibrosarcomas were marginally increased in dosed male mice. There were no increased incidences of neoplasms in dosed female mice. Under the conditions of these studies, the dietary administration of nalidixic acid was carcinogenic for rats, causing preputial gland or clitoral gland neoplasms in males and females, respectively. The association of subcutaneous neoplasms with administration of nalidixic acid to male mice was equivocal.