Adverse Effects of Prenatal Exposure to Oxidized Black Carbon Particles on the Reproductive System of Male Mice

Abstract

Ambient black carbon (BC), a main constituent of atmospheric particulate matter (PM), is a primary particle that is mainly generated by the incomplete combustion of fossil fuel and biomass burning. BC has been identified as a potential health risk via exposure. However, the adverse effects of exposure to BC on the male reproductive system remain unclear. In the present study, we explored the effects of maternal exposure to oxidized black carbon (OBC) during pregnancy on testicular development and steroid synthesis in male offspring. Pregnant mice were exposed to OBC (467 μg/kg BW) or nanopure water (as control) by intratracheal instillation from gestation day (GD) 4 to GD 16.5 (every other day). We examined the testicular histology, daily sperm production, serum testosterone, and mRNA expression of hormone synthesis process-related factors of male offspring at postnatal day (PND) 35 and PND 84. Histological examinations exhibited abnormal seminiferous tubules with degenerative changes and low cellular adhesion in testes of OBC-exposed mice at PND 35 and PND 84. Consistent with the decrease in daily sperm production, the serum testosterone level of male offspring of OBC-exposed mice also decreased significantly. Correspondingly, mRNA expression levels of hormone-synthesis-related genes (i.e., StAR, P450scc, P450c17, and 17β-HSD) were markedly down-regulated in male offspring of PND 35 and PND 84, respectively. In brief, these results suggest that prenatal exposure has detrimental effects on mouse spermatogenesis in adult offspring.

Keywords: atmospheric particulate matter; in utero exposure; male offspring; oxidized black carbon; spermatogenesis; steroidogenesis.

Figure 1

Effects of maternal exposure to oxidized black carbon (OBC) on the testicular tissue of PND 35 and PND 84 male offspring. (A) Representative H&E staining images of seminiferous tubule morphology in testis of male mice (magnification 40×). At two ages, seminiferous epithelial damage (arrows) was seen in the OBC group. Vacuolation was also seen with some seminiferous tubules (asterisks). (B) Enlarged view of seminiferous tubule from PND 35 male offspring showed some cellular abnormalities. Leydig cell (Lc), Sertoli cells (Sc), multinucleated giant cell (Mgc), spermatogonia types A (SpA) and B (SpB). (C) Examination of testicular damage was evaluated by counting the number of seminiferous tubules in cross-sections and determining the percentage of total degenerated seminiferous tubules in three cross-sections per testes. Values are means ± SEM (n = 9). * p < 0.05 and ** p < 0.01 vs. controls.

Figure 2

Effects of maternal exposure to oxidized black carbon (OBC) during pregnancy on daily sperm production of male offspring. At PND 35 (Control, n = 11; OBC, n = 11). At PND 84 (Control, n = 11; OBC, n = 10). Values are means ± SEM. * p < 0.05 and ** p < 0.01 versus controls.

Figure 3

Effects of maternal exposure to oxidized black carbon (OBC) during pregnancy on serum testosterone level of male offspring. At PND 35 (Control, n = 12; OBC, n = 11). At PND 84 (Control, n = 11; OBC, n = 10). All data were expressed as means ± SEM. n=12. * p < 0.05 and ** p < 0.01 as compared with control group.

Figure 4

Effects of maternal OBC exposure during pregnancy on testicular mRNA expression levels involved in steroid hormone biosynthesis in testis from male offspring. (A) StAR, (B) P450scc, (C) P450c17, (D) 17β-HSD, (E) 3-HSD, and (F) LHR. Values were expressed as means ± SEM of eight samples from eight litters. * p < 0.05 and ** p < 0.01 vs. controls.