Benzofuran is used as an intermediate in the polymerization of coumarone-indene resins found in various corrosion-resistant coatings such as paints and varnishes, in water-resistant coatings for paper products and fabrics, and in adhesives approved for use in food containers. Toxicology and carcinogenesis studies were conducted by administering benzofuran (approximately 99% pure) in corn oil by gavage to groups of F344/N rats and B6C3F1 mice of each sex for 14 days, 13 weeks, or 2 years. Genetic toxicology tests were conducted in Salmonella typhimurium, mouse lymphoma cells, and Chinese hamster ovary (CHO) cells.
Benzofuran doses for groups of five rats ranged from 63 to 1,000 mg/kg and from 16 to 250 mg/kg for mice. All male and female rats that received 1,000 mg/kg and one female rat that received 500 mg/kg died before the end of the studies. The final mean body weights of male rats that received 250 or 500 mg/kg were 13% or 21% lower than that of controls; the final mean body weight of female rats that received 500 mg/kg was 10% lower than that of controls. Final mean body weights of chemically exposed and control mice were similar. No compound-related histologic lesions were found in rats or mice.
Doses for groups of 10 rats and 10 mice ranged from 31 to 500 mg/kg. One female rat that received 500 mg/kg and one that received 250 mg/kg died before the end of the study. Final mean body weights of male rats that received 125, 250, or 500 mg/kg were 11%, 17%, or 27% lower than that of vehicle controls; the final mean body weight of female rats that received 500 mg/kg was 11% lower than that of vehicle controls. Histologic lesions observed in chemically exposed rats included minimal hepatocellular necrosis, increased severity of nephropathy, and cytoplasmic vacuolization of the adrenal cortex.
Seven male and three female mice that received 500 mg/kg and one male mouse that received 250 mg/kg died before the end of the 13-week studies. The final mean body weight of mice that received 500 mg/kg was 13% lower than that of vehicle controls. Nephrosis was observed in male mice that received 250 mg/kg.
Based on reduced mean body weights, increased severity of nephropathy, and hepatocellular necrosis, benzofuran doses selected for the 2-year studies in rats were 30 or 60 mg/kg for males and 60 or 120 mg/kg for female. Based on increased mortality and nephrosis in male mice, doses selected for the 2-year studies in mice were 60 or 120 mg/kg for males and 120 or 240 mg/kg for females.
Body Weights and Survival in the 2-Year Studies
Mean body weights of high dose rats and dosed male mice were 4%-11% lower than those of vehicle controls. Mean body weights of chemically exposed female mice were 8%-35% lower than those of vehicle controls. The survival of chemically exposed male rats was reduced after week 92 (survival at week 89: vehicle control, 47/50; low dose, 39/50; high dose, 38/50; final survival: vehicle control, 33/50; low dose, 12/50; high dose, 18/50). Survival of chemically exposed female rats and male mice was similar to that of vehicle controls after 2 years (female rats: 27/50; 23/50; 25/50; male mice: 33/50; 20/50; 28/50). Deaths of 10 low dose male mice at weeks 20-21 were caused by a dosing error; these animals were not included in survival and tumor analyses. Survival of chemically exposed female mice was reduced after week 89 (final survival: 37/50; 19/50; 21/50).
Nonneoplastic and Neoplastic Effects in the 2-Year Studies
Nephropathy occurred with increased severity in chemically exposed male rats. The incidences of parathyroid hyperplasia, fibrous osteodystrophy, mineralization of the pulmonary artery, renal cortical cysts, and hyperplasia of the pelvic epithelium were increased in chemically exposed male rats. The incidence of nephropathy was increased in chemically exposed female rats (vehicle control, 29/50; low dose, 48/50; high dose, 39/50). Renal atypical tubular cell hyperplasia and renal tubular cell adenocarcinomas occurred in chemically exposed female rats (atypical tubular cell hyperplasia: 0/50; 1/50; 3/50; tubular cell adenocarcinomas: 0/50; 1/50; 4/50). No renal tubular cell adenocarcinomas have been observed in 2,094 female corn oil vehicle control F344/N rats in National Toxicology Program studies.
Chronic inflammation, ulcers, and epithelial hyperplasia of the forestomach were observed at increased incidences in chemically exposed male rats (chronic inflammation: 1/50; 11/50; 6/49; ulcers: 1/50; 5/50; 8/49; epithelial hyperplasia: 9/50; 15/50; 18/49).
Metaplastic hepatocytes arising within pancreatic islets occurred at an increased incidence in high dose female rats (0/50; 1/50; 11/49).
The incidences of neurilemomas were markedly increased above the historical control incidences (0.1%-0.4%) in all groups of rats (male: 18/50; 13/50; 14/50; female: 7/50; 9/50; 3/50).
Syncytial alteration of the liver occurred at increased incidences in male mice exposed to benzofuran. The incidences of hepatocellular adenomas, hepatoblastomas (high dose male mice) and hepatocellular adenomas, hepatocellular carcinomas, or hepatoblastomas (combined) were increased in chemically exposed mice (male--adenomas: 4/49; 24/39; 34/48; hepatoblastomas: 0/49; 3/39; 18/48; carcinomas, adenomas, or hepatoblastomas, combined: 12/49; 31/39; 40/48; female--adenomas: 1/50; 22/48; 21/47; hepatoblastomas: 0/50; 1/48; 2/47; carcinomas, adenomas, or hepatoblastomas, combined: 4/50; 25/48; 22/47).
Squamous cell papillomas or carcinomas (combined) of the forestomach were increased in chemically exposed mice (male: 2/49; 11/39; 13/48; female: 2/50; 9/50; 5/50).
The incidences of epithelial hyperplasia of the bronchioles were increased in chemically exposed mice. The incidences of alveolar/bronchiolar adenomas or carcinomas (combined) in high dose males and chemically exposed females were increased (adenomas or carcinomas, combined--male: 10/49; 9/39; 19/48; female: 2/50; 9/48; 14/47).
Benzofuran was not mutagenic in S. typhimurium strains TA98, TA100, TA1535, or TA1537 in the presence or absence of exogenous metabolic activation. Benzofuran induced trifluorothymidine resistance in mouse L5178Y lymphoma cells treated in the absence of metabolic activation; this assay was not conducted with activation. Benzofuran induced sister chromatid exchanges but not chromosomal aberrations in CHO cells in the presence and absence of activation.
Under the conditions of these 2-year gavage studies, there was no evidence of carcinogenic activity of benzofuran for male F344/N rats receiving doses of 30 or 60 mg/kg per day. There was some evidence of carcinogenic activity of benzofuran for female F344/N rats, based on increased incidences of tubular cell adenocarcinomas of the kidney. There was clear evidence of carcinogenic activity for male and female B6C3F1 mice, based on increased incidences of neoplasms of the liver, lung, and forestomach.
Exposure to benzofuran increased the severity of nephropathy in male rats, increased the incidences of nephropathy in female rats, and induced hepatocellular metaplasia in the pancreas in female rats. Nonneoplastic lesions observed in mice exposed to benzofuran included syncytial alteration of the liver, bronchiolar epithelial hyperplasia, and epithelial hyperplasia of the forestomach.