This work is devoted to the investigation of reproductive toxicity of gold and silver nanoparticles. To evaluate not only stationary changes, but systemic physiological effects, we additionally up- and downregulated kisspeptinergic hypothalamic system – the main center for the regulation of hypothalamic-pituitary-gonadal axis.
It was shown that intraperitoneal injection of gold and silver nanoparticles resulted in significant decrease in the functional activity, as measured in hypothalamic arcuate neurons. At the same time, 1-month-old animals were still perceptive to the exogenous kisspeptin, while 6-month-old rats responded to the blockage of kisspeptinergic system only. This difference is probably due to the different sensitivity of neurons to nanometals at different stages of ontogenesis.
Pituitary gonadotrophs were also affected by nanoparticles – we observed significant decrease in the size of cytoplasm and secretory activity. Morphological findings included changes in the coloring of cytoplasm from light-blue to blue-purple and the appearance of the macule in the central part of cells. Exogenous kisspeptin had different effects, regarding the chemical nature of the nanoparticles. Nanosilver did not alter stimulatory effects of kisspeptin and inhibitory effects of its antagonist. On the contrary, nanogold attenuated those kisspeptin-related responses. We also found that pituitary toxicity of gold nanoparticles was much more observable in young animals.
We also investigated effects of nanoparticles on the testes. Both kinds of nanoparticles caused the development of structural changes in this organ. The most frequent histopathologic changes included local degeneration of spermatocytes, local desquamation of testicular epithelium, emergence of multinucleated cells of spermatogenic origin and degeneration of the Leydig cells. The same changes were observed in animals which received combinations of nanoparticles with kisspeptin or its antagonist. Supportive investigation of the blood testosterone levels showed surprising results: despite of the fact that exogenous kisspeptin, injected against the background of nanoparticle administration, had not altered morphometric parameters of the Leydig cells; the concentration of testosterone was significantly elevated. It is known that pituitary hormones affect Leydig cells in two ways: the fast one and the slow one. The fast changes are mainly due to the direct regulation of activity of testosterone-producing enzymes. Slow effects include changes in the transcription of specific genes. As a result, we may conclude that nanoparticles blocked the propagation of the long-term stimulation by pituitary hormones. Also, described effects are partially explained by the sensitization of the Leydig cells.
Changes in the epididymis induced by the gold nanoparticles included increase in the number of sperm-producing cells in the lumen of tubules and proliferation of connective tissue. However, these structural changes did not alter the responsiveness of the organ to kisspeptin-related stimuli. Nanosilver injection resulted in karyopyknosis in the main epithelial cells, increase in the number of leukocytes and overall qualitative changes in the content of lumen. Again, kisspeptin-mediated regulation was unaffected by these changes. As a conclusion, we may state that gold and silver nanoparticles inhibit the activity of epididymis by the direct influence on epithelial cells and connective stroma.
Prostate gland also showed signs of degeneration after the nanogold injections. We observed proliferation of connective tissue, decrease in the height of secretory cells and decrease in the amount of prostate secret. Nanosilver additionally caused leukocyte infiltration and severe local degeneration, which was recognized by the presence of large eosinophilic crystals in the lumen of the gland. But still, kisspeptin-mediated regulation was not significantly altered. Therefore, we may conclude that nanoparticles affect prostate gland in a direct way.
To sum up, we found out that gold and silver nanoparticles cause adverse effects to the morpho-functional state of hypothalamic-pituitary-gonadal system. It was shown that nanotoxicity is realized both through the direct cytotoxicity in target organs and indirect effects mediated by changes in other systems. Nanoparticles induced more significant changes in the organs of young animals, comparing to the adults.
