National Toxicology Program

National Toxicology Program
https://ntp.niehs.nih.gov/go/28483

Abstract for GMM-08

ABSTRACT

Toxicology and Carcinogenesis Study of Benzene (CAS No. 71-43-2) in Genetically Modified Haploinsufficient p16Ink4a/p19Arf Mice (Gavage Study)

Chemical Formula: C6H6 - Molecular Weight: 78.1

Benzene is used primarily as a solvent in the chemical and pharmaceutical industries, as a starting material and intermediate in the synthesis of numerous chemicals, and in gasoline. The major United States source of benzene is petroleum. Benzene has been previously evaluated in 2-year carcinogenicity studies by the National Toxicology Program (1986). In this study, the carcinogenic effects of benzene were studied in the haploinsufficient p16Ink4a/p19Arf mouse model as part of an ongoing NTP effort to seek improved model systems for toxicology and carcinogenesis studies, especially those that can provide mechanistic information relative to understanding an agent's mode of action. Male and female haploinsufficient p16Ink4a/p19Arf mice were administered benzene (greater than 99% pure) by gavage for 27 weeks. Genetic toxicology studies were conducted in mouse peripheral blood erythrocytes.
 

27-WEEK STUDY in MICE

Groups of 15 male and 15 female haploinsufficient p16Ink4a/p19Arf mice were administered 0, 25, 50, 100, or 200 mg benzene/kg body weight in corn oil by gavage 5 days per week for 27 weeks. All animals survived until the end of the study except one male administered 200 mg/kg. Mean body weights of males administered 50 mg/kg or greater were generally less than those of the vehicle controls throughout the study, and those of 25 mg/kg males were less after week 13. Mean body weights of 200 mg/kg females were less than those of the vehicle controls after week 17. Treatment-related clinical findings in 25 mg/kg or greater males and 50 mg/kg or greater females included black, brown, or gray discoloration (pigmentation) of the feet. The thymus weights of all dosed groups of males were significantly decreased. At weeks 13 and 27, a dose-related decrease in the erythron occurred in males and females. The erythron decrease was shown by decreases in the hematocrit, hemoglobin, and erythrocyte count values in all dosed males and in the 100 mg/kg or greater females. Decreased leukocyte counts, primarily lymphocyte counts, resulted in a dose-related leukopenia in males and females. In males, segmented neutrophil counts were also decreased.
 

The incidence of malignant lymphoma was significantly increased in 200 mg/kg males compared to the vehicle controls.

In the bone marrow, significantly increased incidences of minimal to mild atrophy occurred in the 100 and 200 mg/kg males compared to the vehicle controls. In the spleen, there were significantly increased incidences of lymphoid follicle atrophy in 100 and 200 mg/kg male mice. The incidence of hematopoietic cell proliferation was significantly increased in 200 mg/kg males. The incidences of atrophy of the thymus in the 100 and 200 mg/kg males were significantly greater than those in the vehicle controls. In the lymph nodes, significantly increased incidences of atrophy (mandibular, mediastinal, and mesenteric) occurred in 100 and 200 mg/kg males, and the incidence of atrophy of the mediastinal lymph node was significantly increased in the 100 mg/kg females. The incidences of skin pigmentation were significantly increased in all dosed groups of males and in females dosed with 50 mg/kg or greater.

GENETIC TOXICOLOGY

The frequency of micronucleated erythrocytes was assessed at four timepoints during the 27-week study. Significant increases in micronucleated cells were observed at all timepoints, and the magnitude of the response correlated with duration of treatment.

CONCLUSIONS

Under the conditions of this 27-week gavage study, there was clear evidence of carcinogenic activity of benzene in male haploinsufficient p16Ink4a/p19Arf mice based on the occurrence of malignant lymphoma. There was no evidence of carcinogenic activity of benzene in haploinsufficient p16Ink4a/p19Arf female mice administered 25, 50, 100, or 200 mg/kg.

Treatment of male and female haploinsufficient p16Ink4a/p19Arf mice with benzene was associated with toxicity to the hematopoietic system, lymphoid atrophy, and the accumulation of pigment in the extremities.

Synonyms: (6)-Annulene; benzol; benzole; benzolene; bicarburet of hydrogen; carbon oil; coal naphtha; cyclohexatriene; mineral naphtha; motor benzol; phene; phenyl hydride; pyrobenzol; pyrobenzole 


Summary of the 27-Week Carcinogenesis and Genetic Toxicology Studies of Benzene in Haploinsufficient p16Ink4a/p19Arf Mice
  Male Female
Concentrations in
corn oil by gavage
0, 25, 50, 100, or 200 mg/kg 0, 25, 50, 100, or 200 mg/kg
Body weights Dosed groups less than the vehicle control group 200 mg/kg group less than the vehicle control group
Survival rates 15/15, 15/15, 15/15, 15/15, 14/15 15/15, 15/15, 15/15, 15/15, 15/15
Nonneoplastic effects Bone marrow: atrophy (0/15, 0/15, 0/15, 10/15, 12/15); hemosiderin pigmentation (1/15, 13/15, 13/15, 15/15, 14/15)
Spleen: hematopoietic cell proliferation (0/15, 1/15, 0/15, 2/15, 8/15); lymphoid follicle atrophy (0/15, 0/15, 0/15, 15/15, 14/15)
Thymus: atrophy (0/15, 0/15, 0/15, 7/15, 13/15)
Lymph node (mandibular): atrophy (0/15, 0/15, 0/15, 6/14, 11/14)
Lymph node (mediastinal): atrophy (0/11, 0/11, 2/12, 6/9, 6/7)
Lymph node (mesenteric): atrophy (1/15, 2/15, 2/14, 13/15, 13/15)
Skin: pigmentation (0/15, 15/15, 15/15, 15/15, 14/15)
Lymph node (mesenteric): atrophy (0/15, 2/15, 3/15, 8/15, 6/15)
Skin: pigmentation (0/15, 1/15, 8/15, 15/15, 15/15)
Neoplastic effects Malignant lymphoma: (0/15, 0/15, 0/15, 0/15, 5/15) None
Level of evidence of carcinogenic activity Clear evidence No evidence
Genetic toxicology
Micronucleated erythrocytes
Mouse peripheral blood in vivo:

Positive in males and females at the 6.5-, 13-, 19.5-, and 27-week sampling times with the magnitude of the response increasing with increasing duration of treatment.


Report Date: October 2007

Pathology Tables, Survival and Growth Curves from NTP GMM Studies

Target Organs & Incidences from GMM Studies

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