Lack of insulin resistance in fibroblasts from subjects with polycystic ovary syndrome

The study of the role of insulin resistance as etiological factor in polycystic ovarian syndrome: a case control study

Objectives

The relationship between insulin resistance (IR) and polycystic ovary syndrome (PCOS) has been consistently shown by several studies but what is the cause and what is the effect remained an unsolved issue. In recent years, IR has been suggested to be a key etiological factor which contributes to the severity of metabolic and reproductive features in PCOS. The aim of the present study is to determine the etiological role of IR in PCOS.

Methods

This is an analytical case control study where 30 newly diagnosed normoglycemic cases of PCOS (according to Rotterdam revised criteria 2003) between the age group of 15 and 35 years were enrolled. A total of 30 age matched, apparently healthy women were selected from volunteers as controls. Fasting glucose was analysed by spectrophotometry and fasting insulin by chemiluminescence immunoassay. HOMA-IR, Log HOMA-IR, QUICKI, G/I ratio and FIRI were calculated using standard formulae.

Results

The anthropometric parameters and markers of IR were high and QUICKI & G/I ratio were low in cases as compared to controls (p<0.05). Cases with BMI≥25 showed significantly higher IR markers and lower QUICKI & G/I ratio than BMI<25 cases and BMI matched controls. No significant difference was present in IR markers between high and low central obesity cases.

Conclusions

The findings of our study suggest that in normoglycemic PCOS women, raised IR markers in obese patients cannot be attributed to obesity or central obesity alone. Presence of IR in newly diagnosed cases at such an early stage i.e., even before development of hyperglycemia and hyperinsulinemia suggest IR to be a causative factor in development of PCOS.

A cross-sectional study to assess any possible linkage of C/T polymorphism in CYP17A1 gene with insulin resistance in non-obese women with polycystic ovarian syndrome

BACKGROUND & OBJECTIVES

Insulin resistance (IR) is a major confounding factor in polycystic ovarian syndrome (PCOS) irrespective of obesity. Its exact mechanism remains elusive till now. C/T polymorphism in the -34 promoter region of the CYP17 gene is inconsistently attributed to elucidate the mechanism of IR and its link to hyperandrogenemia in obese PCOS patients. In the present study we aimed to evaluate any association of this polymorphism with IR in non-obese women with PCOS.

METHODS

Polymorphism study was performed by restriction fragment length polymorphism (RFLP) analysis of the Msp A1 digest of the PCR product of the target gene in 75 PCOS cases against 73 age and BMI matched control women. Serum testosterone, BMI and HOMA-IR (homeostatic model of assessment-insulin resistance) were analyzed by standard techniques. A realistic cut-off value for the HOMA-IR was obtained through receiver operating characteristic (ROC) curve for exploring any possible link between IR and T/C polymorphism in the case group.

RESULTS

Significant increases in serum testosterone and HOMA-IR values were observed among the case group (P<0.001) without any significant elevation in BMI and FBG compared to controls. Cut-off value for IR in the PCOS patients was 1.40 against a maximum sensitivity of 0.83 and a minimum false positivity of 0.13. The analysis revealed an inconclusive link between the C/T polymorphic distribution and insulin resistant case subjects.

INTERPRETATION & CONCLUSIONS

The results showed that CYP17A1 gene was not conclusively linked to either IR or its associated increased androgen secretion in non-obese women with PCOS. We propose that an increased sensitivity of insulin on the ovarian cells may be the predominant reason for the clinical effects and symptoms of androgen excess observed in non-obese PCOS patients in our region.

Insulin resistance is not conserved in myotubes established from women with PCOS

Background

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder among premenopausal women, who often develop insulin resistance. We tested the hypothesis that insulin resistance in skeletal muscle of patients with polycystic ovary syndrome (PCOS) is an intrinsic defect, by investigating the metabolic characteristics and gene expression of in vitro differentiated myotubes established from well characterized PCOS subjects.

Methods

Using radiotracer techniques, RT-PCR and enzyme kinetic analysis we examined myotubes established from PCOS subjects with or without pioglitazone treatment, versus healthy control subjects who had been extensively metabolically characterized in vivo. Results Myotubes established from PCOS and matched control subjects comprehensively expressed all insulin-sensitive biomarkers; glucose uptake and oxidation, glycogen synthesis and lipid uptake. There were no significant differences between groups either at baseline or during acute insulin stimulation, although in vivo skeletal muscle was insulin resistant. In particular, we found no evidence for defects in insulin-stimulated glycogen synthase activity between groups. Myotubes established from PCOS patients with or without pioglitazone treatment also showed no significant differences between groups, neither at baseline nor during acute insulin stimulation, although in vivo pioglitazone treatment significantly improved insulin sensitivity. Consistently, the myotube cultures failed to show differences in mRNA levels of genes previously demonstrated to differ in PCOS patients with or without pioglitazone treatment (PLEK, SLC22A16, and TTBK).

Conclusion

These results suggest that the mechanisms governing insulin resistance in skeletal muscle of PCOS patients in vivo are not primary, but rather adaptive.

Trial Registration

ClinicalTrials.gov NCT00145340

Insulin and hyperandrogenism in women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a very common endocrine disorder characterized by chronic anovulation, clinical and/or biochemical hyperandrogenism, and/or polycystic ovaries. But most experts consider that hyperandrogenism is the main characteristic of PCOS. Several theories propose different mechanisms to explain PCOS manifestations: (1) a primary enzymatic default in the ovarian and/or adrenal steroidogenesis; (2) an impairment in gonadotropin releasing hormone (GnRH) secretion that promotes luteal hormone (LH) secretion; or (3) alterations in insulin actions that lead to insulin resistance with compensatory hyperinsulinemia. However, in the past 20 years there has been growing evidence supporting that defects in insulin actions or in the insulin signalling pathways are central in the pathogenesis of the syndrome. Indeed, most women with PCOS are metabolically insulin resistant, in part due to genetic predisposition and in part secondary to obesity. But some women with typical PCOS do not display insulin resistance, which supports the hypothesis of a genetic predisposition specific to PCOS that would be revealed by the development of insulin resistance and compensatory hyperinsulinemia in most, but not all, women with PCOS. However, these hypotheses are not yet appropriately confirmed, and more research is still needed to unravel the true pathogenesis underlying this syndrome. The present review thus aims at discussing new concepts and findings regarding insulin actions in PCOS women and how it is related to hyperandrogenemia.

Targeting insulin sensitivity in the treatment of polycystic ovary syndrome

Targeting insulin resistance may result in a list of benefits for women with PCOS, including hormonal, metabolic and ovulatory (and fertility) improvements. The therapeutic strategy to treat PCOS should however depend on the clinical situation, the phenotype, the degree of androgen excess, age, the presence of infertility and the woman's desire to conceive, the presence of obesity and, finally, the spectrum of metabolic abnormalities and the need to treat or prevent long-term associated comorbidities. According to the needs, therapeutic options include, alone or in combination, lifestyle management, particularly in the presence of obesity, the use of insulin sensitizers, metformin and thiazolidinediones, antiandrogens or estro-progestins.

Serum insulin patterns and the relationship between insulin sensitivity and glycaemic profile in women with polycystic ovary syndrome

OBJECTIVE

To evaluate serum insulin levels and insulin sensitivity in women with polycystic ovary syndrome (PCOS) in relation to their glycaemic status.

DESIGN

An observational study.

SETTING

A tertiary-level reproductive health centre in Sri Lanka.

SAMPLE

Infertile women diagnosed as having PCOS (n=168) on the basis of the Rotterdam criteria were included in the study.

METHODS

Glycaemic status and serum insulin values were assessed at fasting and at 2 hours after a 75-g oral glucose load and stratified as diabetes mellitus (DM) (10.12%), impaired glucose tolerance (IGT) (23.21%) and normoglycaemia (66.67%). The normoglycaemic group was restratified as groups A (10.7%), B (79.5%) and C (9.8%) on the basis of serum insulin levels, with group A having the lowest and group C the highest values. The Quantitative Insulin Sensitivity Check Index (QUICKI) scores of women with DM and IGT and those in groups A, B and C in the normoglycaemic category were compared.

MAIN OUTCOME MEASURES

Insulin sensitivity in these groups of women.

RESULTS

Body mass index (BMI) exceeded 23 kg/m(2) in 77.38% of the women. In normoglycaemic women with PCOS, insulin sensitivity was highest in group A. In groups B and C, insulin sensitivities corresponded to those found for women with IGT and DM respectively. This pattern was also reflected in the BMI.

CONCLUSIONS

Normoglycaemic women with PCOS are heterogeneous regarding insulin sensitivity. The treatment offered to those with DM and IGT could be extended to subgroups B and C of normoglycaemic subjects. Normoglycaemic women with PCOS with high insulin sensitivity (group A) would not qualify for this treatment.

Insulin resistance in polycystic ovary syndrome is associated with defective regulation of ERK1/2 by insulin in skeletal muscle in vivo

Insulin resistance is a recognized feature of PCOS (polycystic ovary syndrome). However, the molecular reason(s) underlying this reduced cellular insulin sensitivity is not clear. The present study compares the major insulin signalling pathways in skeletal muscle isolated from PCOS and controls. We measured whole-body insulin sensitivity and insulin signalling in skeletal muscle biopsies taken before and after acute exposure to hyperinsulinaemia in nine women diagnosed with PCOS and seven controls. We examined the expression, basal activity and response to in vivo insulin stimulation of three signalling molecules within these human muscle samples, namely IRS-1 (insulin receptor substrate-1), PKB (protein kinase B) and ERK (extracellular-signal-regulated kinase) 1/2. There was no significant difference in the expression, basal activity or activation of IRS-1 or PKB between PCOS and control subjects. However, there was a severe attenuation of insulin stimulation of the ERK pathway in muscle from all but two of the women with PCOS (the two most obese), and an accompanying trend towards higher basal phosphorylation of ERK1/2 in PCOS. These results are striking in that the metabolic actions of insulin are widely believed to require the IRS-1/PKB pathway rather than ERK, and the former has been reported as defective in some previous PCOS studies. Most importantly, the molecular defect identified was independent of adiposity. The altered response of ERK to insulin in PCOS was the most obvious signalling defect associated with insulin resistance in muscle from these patients.

Defects in insulin signaling pathways in ovarian steroidogenesis and other tissues in polycystic ovary syndrome (PCOS)

The polycystic ovary syndrome (PCOS) is the most common endocrinopathy in women of reproductive age today. Women with PCOS often demonstrate defective ovarian steroid biosynthesis and present with hyperandrogenemia. Moreover, 50-70% of PCOS women are insulin resistant and hyperinsulinemic. Insulin acts on the ovary via its own receptor and interacts with gonadotrophins, modulating steroidogenesis. The precise role of insulin and the molecular mechanisms that take place are not yet completely explicated. This review will be focused on insulin's action on the ovary and other target tissues, describing the intracellular signaling pathways implicated in steroidogenesis and their defects in women with PCOS.

Molecular mechanisms of insulin resistance in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrinopathy of unknown aetiology that affects women of reproductive age. During the past ten years, defective insulin activity in PCOS has been demonstrated in target tissues and causes insulin resistance and hyperinsulinaemia. Furthermore, presence of insulin receptors in the ovarian tissue and overproduction of androgens by theca cells leads to characteristic hyperandrogenaemia. Recent data suggest a divergence in post-receptor signalling pathways for insulin in its target tissues (muscle, adipocytes and ovarian tissue), where the metabolic pathway of insulin activity is defective, whereas the activation of steroidogenesis is maintained. Investigators are still searching for clues to understand the cause of this enigmatic syndrome, despite great advances in molecular medicine and genetics.

The relationship between polycystic ovary syndrome and antiepileptic drugs: a review of the evidence

Polycystic ovary syndrome (PCOS) is a serious endocrine disorder characterized by ovulatory dysfunction and hyperandrogenism that is thought to have a higher prevalence in women with epilepsy and perhaps bipolar disorder. Various theories have been offered to explain this higher prevalence of PCOS and other reproductive disorders in these patient populations, including the effects of the disease itself and of antiepileptic drugs, especially valproate, which may directly cause PCOS or indirectly lead to the disorder by causing weight gain that triggers insulin resistance, increased testosterone levels, and other reproductive abnormalities. A prospective, longitudinal study with larger cohorts in newly diagnosed women with epilepsy or bipolar disorder is needed to definitively characterize the relationship between antiepileptic drugs and PCOS. Until data from such a study are available, physicians need to be aware that there is a possibility of developing symptoms of PCOS in women of reproductive age who are treated with antiepileptic drugs. Despite this concern, the choice of antiepileptic drug for women with epilepsy or bipolar disorder should be based on the most effective agent for controlling neurologic symptoms.

Insulin augmentation of 17alpha-hydroxylase activity is mediated by phosphatidyl inositol 3-kinase but not extracellular signal-regulated kinase-1/2 in human ovarian theca cells

Polycystic ovary syndrome, characterized by hyperandrogenism and chronic anovulation, is frequently associated with insulin resistance. Ample evidence implicates a role for insulin in the genesis of ovarian hyperandrogenism. The objective of this study was to begin to define the intracellular signaling pathway(s) that mediates insulin regulation of 17alpha-hydroxylase activity in human ovarian theca cells. Third-passage theca cells, isolated from the ovaries of regularly cycling premenopausal women, were used. Insulin alone had no effect on 17alpha-hydroxylase activity or CYP17 mRNA expression but required costimulation with forskolin. At the insulin concentration used (10 ng/ml), a neutralizing antibody to the insulin receptor (but not an antibody to the type I IGF receptor) blocked the insulin stimulation of 17alpha-hydroxylase activity, demonstrating that the effects were mediated by the insulin receptor. Insulin stimulated both phosphatidylinositol-3-kinase (PI3-kinase) and extracellular signal-regulated kinase-1/2 (MAPK) pathways. Specific inhibition of MAPK kinase (MEK) with PD98059 or I0126 did not decrease the 17alpha-hydroxylase activity stimulated by forskolin or forskolin plus insulin. In contrast, the PI3-kinase inhibitor LY294002 completely blocked insulin-stimulated 17alpha-hydroxylase activity. Our data demonstrate that insulin stimulates PI3-kinase and extracellular signal-regulated kinase-1/2 activities in human theca cells, but only PI3-kinase mediates the insulin augmentation of forskolin-stimulated 17alpha-hydroxylase activity.

Current concepts in the polycystic ovary syndrome

Over the past 20 years, it has been clearly documented that the polycystic ovary syndrome (PCOS) has major metabolic sequelae related to insulin resistance and that insulin resistance plays an important role in the pathogenesis of the reproductive disturbances of the disorder. Family studies have indicated a genetic susceptibility to PCOS. Polycystic ovaries and hyperandrogenemia are present in approximately 50% of sisters of affected women. Increased androgen secretion and insulin resistance persist in cultured theca cells and skin fibroblasts, respectively, from women with PCOS; this finding suggests that these are intrinsic, presumably genetic, defects. Insulin resistance and elevated low-density lipoprotein (LDL) levels also cluster in the sisters of women with PCOS, consistent with genetic traits. Moreover, the brothers of women with PCOS have insulin resistance and elevated dehydroepiandrosterone sulfate (DHEAS) levels, which supports a genetic basis for these findings. Family-based studies of linkage and association have implicated several genes in the pathogenesis of PCOS. The strongest evidence to date points to a gene in the region of the insulin receptor. Insulin-sensitizing therapy mitigates the reproductive disturbances of PCOS.

Polycystic ovary syndrome, hyperandrogenism, and insulin resistance

Results from recent basic and clinical research investigations have greatly improved our understanding of insulin resistance in general and insulin resistance associated with PCOS in particular. With this understanding has come the possibility of using new methods to treat PCOS. This is particularly true when discussing the use of insulin-sensitizing drugs. Caution must be exercised in using these drugs because of unforeseen acute or remote adverse side effects. Postulated relationships among PCOS, hyperandrogenism, and insulin resistance do not completely solve the endocrinologic mystery of the patient with PCOS. For example, how does the partial destruction of the ovary (e.g., wedge biopsy or ovary drilling by laser or cautery), which does not affect insulin resistance, result in ovulatory cycles? Why does the administration of excessive exogenous insulin in the case of the insulin-dependent diabetic fail to cause hyperandrogenism? Certainly, much remains to be learned about the reproductive endocrine disturbance we now call PCOS.

Altered autophosphorylation of the insulin receptor in the ovary of a woman with polycystic ovary syndrome

OBJECTIVE

To determine whether the tyrosine autophosphorylation of the insulin receptor (IR) in the ovary of a woman with polycystic ovary syndrome (PCOS) was reduced compared to normal.

DESIGN

Experimental study.

SETTING

Tertiary care medical center.

PATIENT(S)

One woman with PCOS and one healthy control, both of whom underwent a hysterectomy and bilateral salpingo-oophorectomy.

INTERVENTION(S)

Plasma membrane fraction of ovarian tissue was isolated, and the IR was purified and concentrated.

MAIN OUTCOME MEASURE(S)

Western blots of the IR, which had been incubated with and without insulin, were prepared. Colorimetric and chemiluminescent methods were used to detect the presence of the IR beta-subunit and IR tyrosine autophosphorylation, respectively.

RESULT(S)

The presence of the beta-subunit of the IR was identified in both ovarian samples. The degree of insulin-stimulated IR tyrosine autophosphorylation, reflected by the mean (+/-SD) relative optical density of the 95 kd band, was 4.3-fold higher in the normal ovary compared to the PCOS ovary (0.56 +/- 0.18 optical density vs. 0.13 +/- 0.10 optical density, respectively).

CONCLUSION(S)

Tyrosine autophosphorylation of the IR may be decreased in the ovaries of women with PCOS, similar to the findings in other tissues. The mechanisms through which insulin acts to produce an excess in ovarian androgen production in the face of a decrease in ovarian IR autophosphorylation remain to be determined.

Insulin action in the polycystic ovary syndrome

Research on insulin action in PCOS has been intensive after the identification of insulin resistance as a feature of the syndrome in 1980. It is now clear that PCOS is a metabolic as well as a reproductive disorder and an important cause of type 2 diabetes mellitus in women. The cellular and molecular mechanisms of insulin resistance in PCOS are distinct from those in other insulin resistance syndromes. Elucidating these mechanisms promises to provide considerable insight into insulin receptor signal specificity. Conversely, insulin resistance is now known to have an important role in the pathogenesis of the reproductive disturbances of PCOS. It is thought that one or several genetic defects may cause both the insulin resistance and reproductive abnormalities characteristic of PCOS.