Effect of nanoparticle-rich diesel exhaust on testicular and hippocampus steroidogenesis in male rats

Background: Nanoparticle-rich diesel exhaust (NR-DE) has potentially adverse effects on testicular steroidogenesis. However, it is unclear whether NR-DE influences steroidogenic systems in the brain. Objective: To investigate the effect of NR-DE on hippocampal steroidogenesis of adult male rats in comparison with its effect on the testis. Methods: F344 male rats (8-week-old) were randomly divided into four groups (n = 8 or 9 per group) and exposed to clean air with 4.6 ± 3.2 μg/m in mass concentration, NR-DE with 38 ± 3 μg/m (a level nearly equivalent to the environmental standard in Japan (low NR-DE)), NR-DE with 149 ± 8 μg/m (high NR-DE), or filtered diesel exhaust with 3.1 ± 1.9 μg/m (F-DE), for 5 hours/day, 5 days/week, for 1, 2 or 3 months. F-DE was prepared by removing only particulate matters from high NR-DE with an HEPA filter. Results: Exposures to the high NR-DE for 1 month, and low NR-DE for 2 months, significantly increased or tended to increase plasma and testicular testosterone levels compared to clean air exposure, which might have resulted from the increased expression of mRNA of steroidogenic acute regulatory protein and its protein in the testes of rats. In the hippocampus, high NR-DE exposure for 1 month significantly increased the androstendione level compared to the clean air exposure, while no significant difference was observed in the steroidogenesis between fresh air exposure and any exposure to NR-DE or F-DE. Conclusion: NR-DE may influence steroidogenic enzymes in the testis, but not those in the hippocampus.