Nicotinic acid protects germinal vesicle oocyte meiosis in mice and humans against toxicity of benzo(a)pyrene during maturation

Abstract

AbstractBackgroundApproximately 5 nM -7 nM internal exposure concentration of BaP was detected in women who mainstream smoke or suffering assisted reproductive failure. In this study, we evaluated the effects of benzo(a)pyrene (BaP) on mouse and human germinal vesicle (GV) oocyte maturation in 5 nM BaP. Then, we tested whether nicotinic acid (NA) could restore GV meiotic failure caused by the BaP or not during in vitro maturation (IVM)?MethodsClinically discarded GV oocytes from young women (aged < 35 years) undergoing intracytoplasmic sperm injection (ICSI) / in vitro fertilization (IVF) and GV oocytes from 6–8 weeks old female CD1 mice were used. Oocyte quality was estimated by GV oocyte maturation, morphological observation, and mitochondrial functions. The subcellular structures were further evaluated using immunostaining, fluorescent intensity quantification or western blot to analyze spindle organization, chromosome arrangement, actin polymerization, mitochondrial distribution, DNA damage and the Sirt1 protein level during mouse oocyte meiotic.ResultsWe found 5 nM/50 nM BaP exposure significantly reduced first polar body extrusion during mouse GV oocytes maturation. Sirt1 protein expression decreased after BaP treatment in mouse oocytes. Moreover, BaP exposure disorganized spindle and chromosome arrangement, disrupted cortical actin cap, impaired mitochondrial redistribution, and caused DNA damage in IVM metaphase II (MII) mouse oocytes. Importantly, NA supplementation (15µM) increased Sirt1 expression and significantly rescued most of the abnormal effects. We then explored the effect of 5 nM BaP on human GV oocytes, a concentration close to that in human ovarian follicular fluid, and found that BaP caused GV meiotic failure by increasing mitochondrial membrane potential and markedly elevating reactive oxygen species (ROS) levels. Finally, we showed that 15 µM NA supplementation partially rescued human GV oocytes from the toxicity of 5 nM BaP during IVM.ConclusionsCollectively, our study indicated that internal exposure concentrations of BaP could seriously disrupt GV oocyte IVM and caused GV meiotic defects in both mouse and human. NA partially protected GV oocyte meiosis against toxicity of BaP during IVM.