Insulin-stimulated lactate production by granulosa cells (GC) appears to be compromised in polycystic ovary syndrome (PCOS), and this may have an adverse effect on the provision of 3-C units essential for oocyte development. The insulin-sensitiser, metformin, has been used successfully as an adjunct to gonadotrophin therapy in PCOS. Our objective was to establish whether metformin increased AMP kinase (AMPK) activity and lactate production in human GC.
GC were prepared from follicular aspirates obtained at oocyte collection from women undergoing an IVF programme. The collection protocol had received local ethical approval. GC were purified free of white blood cells and, in culture, were exposed to a range of additions including hCG, insulin and metformin using a defined medium. Insulin alone (1000 ng/ml) and hCG alone (100 ng/ml) significantly stimulated lactate production (P<0.001 in each case vs control). Metformin (500 micromolar), either alone or in the presence of insulin or hCG, elevated lactate by approximately 2540% (P<0.002 vs equivalent condition without metformin). Concentrations of metformin below approximately 125 micromolar were without effect on lactate production. Western analysis of protein extracts of GC previously cultured with metformin showed an increase (vs control) in phospho-AMPKalpha (thr172) indicating an activation of AMPK.
We conclude that metformin augments the production of lactate by human GC and that this action may be mediated by activation of AMPK. We speculate that these 3-C units (generated as lactate) may be made available to the developing oocyte perhaps through the mediation of cumulus cells known to provide 3-C units to the oocyte as pyruvate. It is possible that the beneficial effects of metformin action in the treatment of PCOS are associated with activation of AMPK in GC and improved production of lactate within the follicular environment of the oocyte.
06 - 07 Nov 2006
Society for Endocrinology