Anti-oxidative function of follicular fluid HDL and outcomes of modified natural cycle-IVF.

High density lipoproteins (HDL) are the main cholesterol carriers in follicular fluid (FF), the natural environment of oocyte development. Additionally, HDL have critical biological functions such as anti-oxidative capacity, which have not been studied in reproduction. Therefore, this study aimed to investigate whether the anti-oxidative function of FF-HDL is associated with fertility outcomes. From 253 women undergoing modified natural cycle (MNC)- IVF at a single academic centre FF and plasma were collected (n = 375 cycles). Anti-oxidative function of FF was mainly attributable to HDL (n = 8; 83%). FF-HDL had a higher anti-oxidative function than plasma HDL (n = 19, P < 0.001) coinciding with increased vitamin E and sphingosine 1 phosphate content (P = 0.028 each). Proteomic analysis indicated no significant differences in major anti-oxidative proteins such as paraoxonase 1, apolipoprotein (apo) A-I or apoA-IV between FF-HDL and matched plasma-HDL (n = 5), while apoC-III, apoE and apoC-II were relatively lower in FF-HDL. Finally, FF-HDL anti-oxidative function was related to a decrease in the odds of the oocyte undergoing normal fertilization, an association that persisted after adjustment for confounders (odds ratio 0.97 (0.93-1), P = 0.041). In conclusion, FF-HDL has considerable anti-oxidative properties that might be relevant for embryo quality.