This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The polycystic ovary syndrome (PCOS) is a poorly understood disorder that affects approximately 6-10% of women of reproductive age. PCOS is characterized by chronic anovulation and hyperandrogenism, and is a leading cause of female infertility in the United States. Most women with PCOS are also characterized by insulin resistance, which plays a key role in the pathogenesis of PCOS and also places affected women at increased risk for developing type 2 diabetes. Our long-term goal is to elucidate the relationship between insulin resistance and PCOS. Some actions of insulin may be effected by putative inositolphosphoglycan (IPG) mediators of insulin action, and evidence suggests that a deficiency in a specific D-chiro-inositol-containing IPG (DCI-IPG) may contribute to insulin resistance in women with PCOS, as well as in other disorders characterized by insulin resistance such as impaired glucose tolerance or type 2 diabetes mellitus. Specifically in PCOS, three separate studies have shown that administration of D-chiro-inositol (DCI), the precursor to DCI-IPG, to both obese and non-obese women with PCOS improved glucose intolerance while reducing circulating insulin, improved ovulatory function, and decreased serum androgens. Serum triglycerides, HDL cholesterol and blood pressure improved in some of the studies as well. Collectively, these findings strongly suggest that administration of DCI improved insulin sensitivity in women with PCOS, and that insulin resistance in PCOS is due in part to impaired insulin-stimulated release of DCI-IPG.
Our aim during the present grant cycle was to determine if DCI metabolism is altered in PCOS, and if that alteration leads to DCI deficiency and diminished insulin-stimulated release of the putative DCI-IPG mediator of insulin action. To this end we successfully refined and validated a bioactivity assay for DCI-IPG, and assessed DCI metabolism and insulin sensitivity in both women with PCOS and a group of normal control women. We found that women with PCOS, when compared to normal women, had a 1) greater than 5-fold increase in the renal clearance of DCI, 2) 50% reduction in the circulating concentration of DCI, and 3) decreased insulin-stimulated release of DCI-IPG during an oral glucose tolerance test (OGTT). Moreover, insulin sensitivity (as determined by frequently sampled intravenous glucose tolerance test [FSIVGTT]) correlated inversely with renal clearance of DCI in all women. These findings are consistent with abnormal handling of DCI in PCOS that results in impaired release of the DCI-IPG mediator and, consequently, insulin resistance. The present proposal seeks to extend these findings by testing the hypothesis that DCI metabolism itself is regulated by insulin, such that hyperinsulinemia increases renal clearance of DCI, and that this occurs in PCOS but not in normal women. If this were the case, an initial """"""""insult"""""""" producing insulin resistance/hyperinsulinemia in a woman with PCOS would be amplified by a """"""""vicious cycle"""""""" in which renal DCI clearance is increased, yielding deficiencies in circulating DCI, intracellular DCI-IPG mediator, and insulin-stimulated DCI-IPG release. The latter, in turn, would further decrease insulin sensitivity. Such a mechanism could account for the observation that insulin resistance in women with PCOS is substantially greater than that of age- and BMI-matched healthy women.
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