Carcinogenicity and testicular toxicity of 2-bromopropane in a 26-week inhalation study using the rasH2 mouse model

Abstract

2-Bromopropane (2-BP) is a colorless liquid at room temperature and is used in closed systems in factories, mainly as an intermediate for medicines, pesticides, and other chemicals. However, the carcinogenicity of 2-BP is still unknown. The CByB6F1-Tg(HRAS)2Jic (rasH2) transgenic mouse model has been established as an alternative to long-term studies (1.5 years-lifetime) to detect carcinogenicity in as short a time as six months. We performed a 26-week inhalation exposure study of 2-BP using the rasH2 mouse model. Male and female rasH2 mice were exposed to 0, 67, 200, or 600 ppm of 2-BP for 6 h/day, 5 days/week for 26 weeks. All tissues and blood were collected and subjected to biological and histopathological analyses. The results showed a concentration-dependent increase in lung tumor development in male and female rasH2 mice exposed by inhalation to 2-BP, which was significant by Peto's and Poly-3 trend tests. Furthermore, in male rasH2 mice, 2-BP was found to be a testicular toxin. This study is the first to demonstrate that 2-BP is carcinogenic in male and female mice and a testicular toxin in male mice using the rasH2 mouse model.

Figure 1

Characterization of 2-bromopropane (2-BP). (A) General properties. (B) Mass Spectrum.

Figure 2

Survival curves, Body Weight curves, and Food Intake of rasH2 mice exposed by inhalation to 2-BP (67, 200, or 600 ppm, 6 h/day, 5 days/week, 26 weeks). (A,C,E) Male mice. (B,D,F) Female mice.

Figure 3

Changes in the final body weights of rasH2 mice following inhalation exposure to 2-BP (67, 200, or 600 ppm, 6 h/day, 5 days/week, 26 weeks). Final body weights in males (A) and females (B) were measured at sacrifice. Dunnett’s multiple comparison test was used to compare weights with the age-matched control (0 ppm) groups: **p < 0.01 and ***p < 0.001.

Figure 4

Representative microscopic photographs of male rasH2 mouse lung tumors. Bronchiolo-alveolar adenoma (A,B,C,D) and carcinoma (E,F,G,H).

Figure 5

Representative reproductive organ toxicity of rasH2 mice following inhalation exposure to 2-BP (67, 200, or 600 ppm, 6 h/day, 5 days/week, 26 weeks). Testis organ weights (A,B) and ovary organ weights (C,D) are shown. Loupe images of testes exposed to 2-BP and magnified images (E). Typical histology of the head and tail of the epididymis (F). Summary of the results of various pathological findings of the testes (G) and epididymis (H) observed after 2-BP exposure. Dunnett’s multiple comparison test was used to compare the testes and ovary weights with age-matched control (0 ppm) groups: **p < 0.01 and ***p < 0.001. Significant difference: *p < 0.05; **p < 0.01; ***p < 0.001 by Chi square test compared with the respective controls for histological grading.

Figure 6

Representative hematopoietic organ toxicity of rasH2 mice following inhalation exposure to 2-BP (67, 200, or 600 ppm, 6 h/day, 5 days/week, 26 weeks). Typical histology of the bone marrow (A). Spleen weights of males (B,C) and females (D,E). Typical histology of the spleen (F). Summary of the results of various pathological findings of the bone marrow (G) and spleen (H) observed after 2-BP exposure. Dunnett’s multiple comparison test was used to compare the spleen weights with the age-matched control (0 ppm) groups: *p < 0.05.

Figure 7

Graphical abstract of this study.