Peroxynitrite affects the cumulus cell defense of metaphase II mouse oocytes leading to disruption of the spindle structure in vitro

Objective: To demonstrate the effects of peroxynitrite (ONOO^-) on metaphase II mouse oocyte spindle structure and chromosomal alignment in presence and absence of cumulus cells. Design: Experimental study. Setting: University-based research laboratory. Animal(s): Metaphase II mouse oocytes (n = 440). Intervention(s): Metaphase II mouse oocytes, with and without cumulus cells, were exposed to ONOO^-, nitrite/nitrate, the final product of ONOO^-, and nontreated controls for 15 minutes. Oocytes were fixed and subjected to indirect immunofluorescence for detecting changes in the spindle and chromosomal alignment. Viability staining in exposed oocytes with and without cumulus cells was performed using the trypan blue dye exclusion method and compared with controls. Main Outcome Measure(s): Scoring the alterations in spindle and chromosomal alignment using immunofluorescent and confocal microscopy based on a previously validated system. Result(s): Most oocytes had poor scores for the spindle and chromosomal alignment with exposure to ONOO ^- in a dose-dependent manner compared with controls. Trypan blue staining revealed that most of the cumulus cells failed to survive treatment with ONOO^- compared with controls. Conclusion(s): ONOO^- affects the viability of cumulus cells and the oocyte spindle structure in a dose-dependent manner. Collectively, these effects compromise oocyte quality, which may lead to female infertility.