Ovarian intrafollicular lipid environment of patients included in assisted reproduction programs: in search of reference values

Abstract

Thefunctional role of ovarian follicular lipids and intracellular sites forneutral lipid storage (lipid droplets) is relevant for lipid homeostasis ofcumulus-oocyte complexes but still an understudied topic. Until now, it is notclear if there is an association between plasma dyslipidemia and ovarianintrafollicular lipids or how this lipid environment affects oocyte maturation.In order to establish reference values or a reference metabolite profile thatbetter define oocyte normal environment, we characterized follicular fluids(FF) and granulosa cells (GC) of control patients with measured plasmaticlipids (women), including male and tubal factor infertility, donors and womenwith desire to gestate genetically related children. We analyzed: (i) neutrallipid composition, hyaluronic acid and products of lipid peroxidation from FFand (ii) hydrophobicity of intracellular lipids of GC. Total cholesterol,LDL-cholesterol, HDL-cholesterol and triglycerides (TG) content in plasmasamples of 34 patients (mean age 33.5±6.3 years) were compared to those in FFfrom the largest follicle and from a pool of smaller follicles. Lipid levelswere lower in both FF than in plasma. Positive correlations were found betweenplasmatic and follicular HDL-cholesterol and between both types of FF for alllipids analyzed. Mean values of TG for both types of FF were statisticallydifferent between women with or without dyslipidemia. Hyaluronic acid (ELISA) and4-hydroxinonenal (Western blot) were measured in FF from those patients withoutdyslipidemia (n=21). A single target protein modified by 4-hydroxinonenal wasfound in all patients. Hydrophobicity of intracellular lipids was evaluated byfluorescence spectroscopy using the lipophilic dye Nile Red. Fluorescencespectra from Nile Red stained GC revealed a coincident emission maximum (578nm). Human intrafollicular ovarian environment exhibits a distinctive lipidprofile compared to plasma, with basal lipoperoxidation levels and yellow-orangeNile Red emission of GC indicative of hydrophobic lipid droplets.