Effects of nicotinamide on follicular development and the quality of oocytes

Abstract

Background: Nicotinamide (NAM) is an important antioxidant, which is closely related to female fertility, but its role has not been clearly elucidated. The purpose of the present study was to investigate the effects of NAM on follicular development at different stages and the quality of oocytes.

Methods: The concentration of NAM in follicular fluid (FF) of 236 women undergoing in vitro fertilization (IVF) was ascertained by enzyme-linked immunosorbent assay (ELISA), and the correlation between NAM and clinical indexes was analyzed. During the in vitro maturation (IVM) of mice cumulus-oocyte complexes (COCs), different concentrations of NAM were added to check the maturation rate and fertilization rate. The reactive oxygen species (ROS) levels in the oocytes treated with different hydrogen peroxide (H₂O₂) and NAM were assessed. Immunofluorescence staining was performed to measure the proportion of abnormal spindles.

Results: The level of NAM in large follicles was significantly higher than that in small follicles. In mature FF, the NAM concentration was positively correlated with the rates of oocyte maturation and fertilization. Five mM NAM treatment during IVM increased maturation rate and fertilization rate in the oxidative stress model, and significantly reduced the increase of ROS levels induced by H₂O₂ in mice oocytes.

Conclusions: Higher levels of NAM in FF are associated with larger follicle development. The supplement of 5 mM NAM during IVM may improve mice oocyte quality, reducing damage caused by oxidative stress.

Keywords: Female infertility; Follicle size; Follicular fluid; Nicotinamide; Oocyte quality; Oxidative stress.

Fig. 1

a NAM concentration in the follicular fluid at different stages of development. b Follicle size: The area under the ROC curve for NAM was 0.685, p = 0.0023. c Oocyte maturation rate: The area under the ROC curve for NAM was 0.610, p = 0.0099. d Normal fertilization rate: The area under the ROC curve for NAM was 0.611, p = 0.0093

Fig. 2

Effects of different concentrations of NAM on oocyte maturation and fertilization. The effect of NAM on cumulus expansion was observed using a light microscope (a). Percentages of oocytes matured (b) and fertilized (c) in vitro following treatment with NAM. d, f Representative images of mature and immature oocytes. Pronucleus formation in fertilized oocytes (e). PB: Polar body; GV: germinal vesicle. Values are significantly different between groups (*P < 0.05, **P < 0.01). Scale bar = 200 μm

Fig. 3

Effects of different concentrations of H₂O₂ on maturation and fertilization. a Maturation rate of oocytes treated with different concentrations of H₂O₂ in vitro. b Fertilization rate of oocytes treated with different concentrations of H₂O₂ in vitro. The effects of NAM on the maturation rate of H₂O₂-exposed oocytes (c) and the fertilization rate (d). Values were significantly different between groups (*P < 0.05, **P < 0.01)

Fig. 4

NAM treatment impacted ROS levels and spindle abnormality in oocytes damaged by oxidative stress during IVM. Fluorescence staining for ROS (a) and relative fluorescence intensity (c) of MII oocytes in each group (Scale bar = 200 μm). b Typical images of spindle morphology and chromosome arrangements in different groups. d Spindle deformity rate in each group (Scale bar = 5 μm). The asterisk indicates a statistical significance (P < 0.05)