Abstract
Environmental exposure to nanomaterials is inevitable, as nanomaterials have become part of our daily life now. In this study, we firstly investigated the effects of silica nanoparticles on the spermatogenic process according to their time course in male mice. 48 male mice were randomly divided into control group and silica nanoparticle group with 24 mice per group, with three evaluation time points (15, 35 and 60 days after the first dose) per group. Mice were exposed to the vehicle control and silica nanoparticles at a dosage of 20 mg/kg every 3 days, five times over a 13-day period, and were sacrificed at 15, 35 and 60 days after the first dose. The results showed that silica nanoparticles caused damage to the mitochondrial cristae and decreased the levels of ATP, resulting in oxidative stress in the testis by days 15 and 35; however, the damage was repaired by day 60. DNA damage and the decreases in the quantity and quality of epididymal sperm were found by days 15 and 35; but these changes were recovered by day 60. In contrast, the acrosome integrity and fertility in epididymal sperm, the numbers of spermatogonia and sperm in the testes, and the levels of three major sex hormones were not significantly affected throughout the 60-day period. The results suggest that nanoparticles can cause reversible damage to the sperms in the epididymis without affecting fertility, they are more sensitive than both spermatogonia and spermatocytes to silica nanoparticle toxicity. Considering the spermatogenesis time course, silica nanoparticles primarily influence the maturation process of sperm in the epididymis by causing oxidative stress and damage to the mitochondrial structure, resulting in energy metabolism dysfunction.
Highlights
The biological properties of many nanomaterials, coupled with their rapidly expanding productions and usage, have generated concerns that nanoparticles may have unintended impacts when released into natural ecosystems
The characterization of silica nanoparticles The transmission electron microscope (TEM) images of silica nanoparticles indicated that the particles were spherical in shape with an average diameter of 64.43610.50 nm (Figure 1A), and their hydrodynamic sizes were measured in physiological saline because the exposure media is 107.5 nm
Changes in growth and in the testicular index in mice On days 15, 35 and 60 in the nanoparticle-treated groups, the average body weights, daily weight gains and the testicular index in silica nanoparticle-treated mice showed no significant differences compared with those values in the control mice (Figures S1A, S1B and S1C) (P.0.05); the analysis of covariance showed that the daily weight gains were significantly decreased in both the control group and the nanoparticle-treated group over time
Summary
The biological properties of many nanomaterials, coupled with their rapidly expanding productions and usage, have generated concerns that nanoparticles may have unintended impacts when released into natural ecosystems. The applications of silica nanoparticles in industry, biomedicine, food and environmental protection are extremely promising,such as silica nanoparticales are used in drug delivery as carriers because they display good stabilities and excellent biocompatibilities and easy modifications. Li et al showed that rats exposed to diesel exhaust rich in nanoparticles caused reduction of the weights of both the testis and prostate in male offsprings and disrupted the endocrine activity of the male reproductive system by decreasing the levels of testosterone, progesterone and corticosterone in the serum [6]. Ramdhan et al [7] found that the exposure to a low concentration of diesel exhaust rich in nanoparticles increased the levels of plasma testosterone, which contradict to Li et al.’s report [6]
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