Silver nanoparticles induce oocyte maturation in zebrafish (Danio rerio)

Public concern regarding silver nanoparticles (AgNPs) in the environment has been increasing since they can cause adverse effects in some aquatic species. However, few data are actually available on the effects of AgNPs on the germ cells. In the present study, we used the zebrafish ovarian follicle as a model to assess the potentially adverse effects of AgNPs on oocyte maturation (germinal vesicle breakdown, GVBD) in vitro. Similar to the maturation inducing hormone (17α, 20β-dihydroxy-4-pregnen-3-one), AgNPs induced GVBD, and reduced the total cyclic adenosine monophosphate (cAMP) concentration in zebrafish ovarian follicles. The results from transmission electron microscope observation and Hoechst 33342 staining clearly indicated that AgNPs induced apoptosis in ovarian follicle cells surrounding the oocyte. Similar to AgNPs, AgNO3 also induced GVBD, decreased cAMP concentration and induced apoptosis of ovarian follicle cells. However, the results from gene expression analysis showed that transcript levels of oxidative stress related genes were more sensitive to AgNPs than AgNO3. Further more, H2O2 has an ability to induce zebrafish oocytes maturation by induction of apoptosis in ovarian follicle cells. Taken together, the results from our study indicated that oxidative stress appeared to be one of important mechanisms in AgNP induced apoptosis in ovarian follicle cells, which further triggered the GVBD.