The NAD⁺ precursor nicotinamide riboside protects against postovulatory aging in vitro

Postovulatory aging (POA) of oocytes is clinically significant as it mirrors the degeneration observed in maternally aged oocytes, leading to substantial impairments in oocyte quality and the success rates of artificial reproductive technology (ART). The molecular alterations associated with POA, such as the degeneration of the first polar body, an increase in perivitelline space, reactive oxygen species (ROS) accumulation, energy depletion, and chromosomal and DNA damage, underscore the urgency of finding interventions to mitigate these effects. This study aims to identify whether nicotinamide riboside (NR) can prevent POA during the process of in vitro culture and raise the success rates of ART.

Taking advantage of an in vitro postovulatory oocyte aging model, we examined the morphological integrity and NAD⁺ levels of ovulated mouse MII oocytes after 24 h of culturing. Following in vitro fertilization, we assessed the embryonic developmental potential of oocytes affected by POA. Using immunofluorescence and confocal microscopy, we measured the levels of ROS, mitochondrial function, and γH2AX. We also evaluated spindle assembly and chromosome alignment. Additionally, we detected the distribution of cortical granules to assess the metabolic and quality changes in POA oocytes with the supplementation of NR. To further our analysis, quantitative real-time PCR was conducted to measure the mRNA expression levels of antioxidant enzymes Sod1 and Gpx1 in the oocytes.

With 200 μM NR supplementation during in vitro culture for 24 h, the oocytes from POA demonstrated reduced signs of aging-related decline in oocyte quality, including reduced ROS accumulation, improved mitochondrial function, and corrected mis-localization of cortical granules. This improvement in oocyte quality is likely due to the inhibition of oxidative stress via the NAD⁺/SIRT1 signaling pathway, which also helped to restore normal spindle assembly and chromosome alignment, as well as reduce the elevated levels of γH2AX, thereby potentially enhancing the embryonic development potential.

Current research provides evidence that NR is an efficient and safe natural component that prevents the process of POA and is thus a potential ideal antiaging drug for raising the success rates of ART in clinical practice.