NTP Toxicology and Carcinogenesis Studies of p-Nitroaniline (CAS No. 100-01-6) in B6C3F1 Mice (Gavage Studies).
p-Nitroaniline is an intermediate in the preparation of several azo dyes used for coloring consumer products. Toxicology and carcinogenicity studies were conducted by administering p-nitroaniline (>99% pure) in corn oil by gavage to groups of male and female B6C3F1 mice for 14 days, 13 weeks, and 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, Chinese hamster ovary cells, mouse Iymphoma cells, and Drosophila melanogaster. 14-DAY STUDIES: Groups of five male and five female B6C3F1 mice received p-nitroaniline in corn oil by gavage at doses of 0, 10, 30, 100, 300, or 1,000 mg/kg body weight 5 days per week for 2 weeks. All mice that received 1,000 mg/kg died from chemical-related toxicity by day 4 of the studies. Final mean body weights of mice receiving 300 mg/kg or less were similar to those of the controls. Hematology results were consistent with chemical-related methemoglobinemia and regenerative anemia. Met hemoglobin concentrations in all groups of dosed mice were significantly higher than those in controls. Hematocrit values in mice that received 300 mg/kg and total erythrocyte counts in mice that received 100 or 300 mg/kg were significantly lower than those in controls. Reticulocyte counts in 300 mg/kg male mice and in 100 or 300 mg/kg females were significantly higher than controls. Heinz bodies were observed in erythrocytes of all 300 mg/kg mice and in two 100 mg/kg male mice. The absolute and relative spleen weights of 100 and 300 mg/kg mice were significantly greater than those of the controls. Hematopoiesis and pigment (hemosiderin) accumulation were observed in the splenic red pulp of males and females receiving 300 mg/kg; pigment (hemosiderin) accumulation in Kupffer cells of the liver was also seen in male mice at this dose level. 13-WEEK STUDIES: Groups of 20 male and 20 female B6C3F1 mice received p-nitroaniline in corn oil by gavage at doses of 0, 1, 3, 10, 30, or 100 mg/kg body weight 5 days per week for up to 13 weeks. Eight or nine mice in each group were evaluated at 7 weeks. There were no deaths associated with exposure to p-nitroaniline, and final mean body weights of dosed mice were similar to those of the controls. Hematologic and pathologic findings at 7 and 13 weeks were similar to those seen in the 14-day studies and occurred primarily in the 30 and 100 mg/kg groups. Met hemoglobin concentrations were increased and hematocrit levels and erythrocyte counts were decreased relative to those of the controls. Heinz bodies were observed in erythrocytes and nucleated erythrocytes and reticulocytes were increased in number. Absolute and relative spleen weights of male and female mice receiving 30 and 100 mg/kg were significantly greater than those of controls at 7 and 13 weeks. Absolute and relative liver weights of female mice necropsied at 7 weeks were significantly greater in the 30 and 100 mg/kg groups; by 13 weeks, both absolute and relative liver weights were similar to control values. The incidence or severity of splenic hematopoiesis and pigmentation (hemosiderin) increased with dose at the 7-week interim evaluations and at the end of the studies. Pigment (hemosiderin) was also present in Kupffer cells of the liver in dosed male mice. 2-YEAR STUDIES: Groups of 70 male and 70 female B6C3F1 mice received p-nitroaniline in corn oil by gavage at doses of 0, 3, 30, or 100 mg/kg body weight for 5 days per week for up to 103 weeks. The dose selection was based on the hematologic and pathologic findings of the 13-week studies. Nine or ten mice from each group were evaluated at 9 and 15 months for the presence of chemical-related lesions. Body Weights, Clinical Findings, Survival, and Hematology: Mean body weights of male and female mice that received p-nitroaniline were similar to those of control mice throughout the 2-year studies. There were no clinical findings associated with chemical exposure, and survival of dosed mice was similar to that of controls. The hematology findings at the 9 and 15-month interim evaluations were similar to those in the 14-day and 13-week s 13-week studies. The methemoglobin concentrations were significantly higher in all 30 or 100 mg/kg mice; sulfhemoglobin concentrations were significantly higher at 9 months in all 30 or 100 mg/kg female mice and at 15 months in 100 mg/kg females. Hematocrit and erythrocyte counts in 100 mg/kg mice were significantly lower than those in controls. By 9 months, reticulocyte counts were significantly higher in all 30 or 100 mg/kg mice. At 15 months, only the 100 mg/kg mice exhibited significantly higher reticulocyte counts. Neoplasms and Nonneoplastic Lesions: Lesions related to the administration of p-nitroaniline occurred in the spleen, liver, and bone marrow, primarily in mice receiving 30 or 100 mg/kg; these were observed at the 9- and 15-month interim evaluations and at the end of the studies. There were increases in the incidence or severity of splenic congestion, hematopoiesis, pigment (hemosiderin) accumulation, Kupffer cell pigmentation in the liver, and bone marrow hypercellularity (hyperplasia). The incidences of hemangiosarcoma of the liver (0 ppm, 0/50; 3 ppm, 1/50; 30 ppm, 2/50; 100 ppm, 4/50) and hemangioma or hemangiosarcoma (combined) at all sites (5/50, 3/50, 4/50, 10/50) were marginally increased in 100 mg/kg male mice. The incidence of hepatocellular adenoma or carcinoma (combined) was significantly decreased (25/50, 26/50, 25/50, 13/50) in 100 mg/kg male mice. GENETIC TOXICOLOGY: p-Nitroaniline is mutagenic in vitro. It was tested in two laboratories for induction of gene mutations in several strains of Salmonella typhimurium. Both studies showed positive results in strain TA98, with and without S9 activation; results were negative for all other strains. p-Nitroaniline was tested in two laboratories for induction of sister cremated exchanges and chromosomal aberrations in Chinese hamster ovary cells. In the sister cremated exchange study, one laboratory reported negative results without S9 and positive results with S9; the second laboratory reported equivocal results without S9 and negative results with S9. In the chromosomal aberrations study, both laboratories found positive results with S9. Without S9, one laboratory reported weakly positive results while the other reported negative results. p-Nitroaniline induced trifluorothymidine resistance in L5178Y mouse Iymphoma cells in the absence of S9; no induction of trifluorothymidine resistance was noted with S9. In contrast to the positive results in the previous tests, p-nitroaniline did not induce sex-linked recessive lethal mutations in germ cells of male Drosophila melanogaster when administered by feeding or injection to adult males or by feeding to larvae. CONCLUSIONS: Under the conditions of these 2-year gavage studies there was equivocal evidence of carcinogenic activity of p-nitroaniline in male B6C3F1 mice based on the increased incidences of hemangiosarcoma of the liver and hemangioma or hemangiosarcoma (combined) at all sites. There was no evidence of carcinogenic activity of p-nitroaniline in female B6C3F1 mice receiving doses of 3, 30, or 100 mg/kg.