Insulin resistance, insulin sensitization and inflammation in polycystic ovarian syndrome
G Dhindsa, R Bhatia, M Dhindsa, Vishal Bhatia
Department of Internal Medicine, State University of New York, Buffalo, NY, USA
Department of Internal Medicine, State University of New York, Buffalo, NY
It is estimated that 5-10% of women of reproductive age have polycystic ovarian syndrome (PCOS). While insulin resistance is not part of the diagnostic criteria for PCOS, its importance in the pathogenesis of PCOS cannot be denied. PCOS is associated with insulin resistance independent of total or fat-free body mass. Post-receptor defects in the action of insulin have been described in PCOS which are similar to those found in obesity and type 2 diabetes. Treatment with insulin sensitizers, metformin and thiazolidinediones, improve both metabolic and hormonal patterns and also improve ovulation in PCOS. Recent studies have shown that PCOS women have higher circulating levels of inflammatory mediators like C-reactive protein, tumour necrosis factor- , tissue plasminogen activator and plasminogen activator inhibitor-1 (PAI-1 ). It is possible that the beneficial effect of insulin sensitizers in PCOS may be partly due to a decrease in inflammation.
|How to cite this article:|
Dhindsa G, Bhatia R, Dhindsa M, Bhatia V. Insulin resistance, insulin sensitization and inflammation in polycystic ovarian syndrome.J Postgrad Med 2004;50:140-144
|How to cite this URL:|
Dhindsa G, Bhatia R, Dhindsa M, Bhatia V. Insulin resistance, insulin sensitization and inflammation in polycystic ovarian syndrome. J Postgrad Med [serial online] 2004 [cited 2020 Apr 9 ];50:140-144
Available from: http://www.jpgmonline.com/text.asp?2004/50/2/140/8258
Polycystic ovarian syndrome (PCOS) is characterised by chronic anovulation and hyperandrogenism (hyperandrogenism can exist in the absence of hyperandrogenemia e.g. enhanced tissue sensitivity to androgens) in premenopausal women. According to revised guidelines of PCOS Consensus Workshop Group, to be diagnosed with PCOS, a woman must have 2 of the following 3 manifestations: irregular or absent ovulation, elevated levels of androgenic hormones and/or enlarged ovaries containing at least 12 follicles each. Polycystic ovaries are defined as those found on ultrasound to contain 12 or more follicles measuring 2 to 9 mm in diameter and/or have an increased volume of 10 mL or greater. Only one ovary fulfilling these criteria is enough to meet the definition of polycystic ovaries. Other hyperandrogenic disorders such as non-classical congenital adrenal hyperplasia and androgen-secreting tumours have to be excluded for the diagnosis of PCOS. It should be stressed that polycystic ovaries are not a necessary feature of PCOS and that many women with polycystic ovaries do not have PCOS. Women found to have incidental polycystic ovaries on an ultrasound performed for another indication should not be considered to have PCOS unless there is corroborating clinical evidence of the syndrome.
Androgen excess may be with or without skin manifestations. It is estimated that 5-10% of women of reproductive age have PCOS. Around 50% of PCOS women are obese and tend to have an android pattern of obesity.
Chronic anovulation may present as irregular menstrual periods or amenorrhea. It is not essential to document anovulation by ultrasonography or progesterone measurements in the presence of a clear clinical history. In fact, PCOS occurs in 85 to 90% of women with oligomenorrhea and in 30-40% of women with amenorrhea. Anovulation in PCOS women is associated with steady-state levels of gonadotropins and ovarian steroids. PCOS women are thus in a “chronic estrous state”. Constant estrogen exposure leads to proliferation and hyperplasia of the endometrium and this can lead to unpredictable bleeding episodes. Unopposed estrogen exposure can be confirmed by progesterone withdrawal test (medroxyprogesterone acetate 10mg/day for 10 days), done after a negative urine pregnancy test.
Hyperandrogenism is usually suggested by the presence of hirsutism (occurs in approximately 80% of PCOS women) and can be documented by measuring androgen levels in the blood. Free testosterone is the most frequently elevated steroid in the blood in PCOS. Circulating levels of total testosterone, androstenedione and Dehydroepiandrosterone (DHEA) are also elevated. In obese PCOS women, sex hormone binding globulin (SHBG) levels are decreased (a well-known effect of obesity per se) and this leads to an increase in free testosterone levels. Furthermore, insulin is a negative regulator of the production of SHBG by the liver, and SHBG levels are decreased in hyperinsulinemic conditions such as metabolic syndrome and visceral obesity., Interestingly, concentrations of sulfated DHEA (DHEAS) are also increased in the blood. DHEAS is secreted exclusively by the adrenal glands. The mechanism of increased DHEAS production by the adrenals is not yet known, although insulin and IGF-1 have been shown to upregulate adrenal 17-hydroxylase and 17,20-lyase activity. It was believed in the past that LH/FSH ratio of more than 2 was part of the diagnostic criteria of PCOS. Women with PCOS have higher mean concentrations of LH, increased bioactivity of LH and low to low-normal levels of follicle stimulating hormone (FSH)., However, obese PCOS women do not have elevated LH levels; therefore a normal LH level or normal LH/FSH ratio does not rule out PCOS. LH/FSH ratio is now not included in the diagnostic criteria of PCOS.
Under the influence of low but constant levels of FSH, multiple follicles of the ovary are stimulated but do not achieve maturation. The lifespan of the follicles may extend over several months, leading to multiple follicular cysts. Luteinized in response to constant and relatively high LH levels, these “arrested” follicles provide a constant supply of steroids. The atretic follicle becomes an androgenic follicle by default because atretic follicles are deficient in aromatase activity. Cultured follicular cells from the small follicles of polycystic ovaries produce small amounts of estradiol but show a dramatic increase in estrogen production when stimulated by FSH or IGF-1. FSH therapy induces a larger cohort of follicles to develop in women with PCOS when compared with other infertile women., A deficient in vivo ovarian response to FSH, possibly due to impaired interaction between signalling pathways associated with FSH and IGF-1, may be a key event in the pathogenesis of anovulation in PCOS.
Insulin Resistance and PCOS
The association between hyperinsulinemia and PCOS was first noted by Burghen et al in 1980 who found a significant positive correlation between insulin, androstenedione and testosterone levels among PCOS women. Subsequent studies confirmed insulin resistance as the cause of hyperinsulinemia. It is estimated that 20-40% of PCOS women have impaired glucose tolerance, a number approximately seven-fold higher than the rates in age and weight-matched women., Prevalence of type 2 diabetes mellitus is also increased in PCOS women (15% versus 2.3% in normal women). Lean PCOS women have lower rates of carbohydrate intolerance than obese PCOS women but even lean PCOS women have higher rates than age and weight-matched controls. Thus PCOS is associated with insulin resistance independent of total or fat-free body mass. Obese PCOS women are more insulin resistant than obese non-PCOS or non-obese PCOS women., Ehrmann et al demonstrated pancreatic beta cell secretory dysfunction in a subset of PCOS women and this subset probably has the highest risk of developing carbohydrate intolerance and type 2 diabetes., Rotterdam consensus panel recommends oral glucose tolerance tests for obese PCOS patients.
Conversely, in a small study, Nestler et al found PCOS in 8 out 30 premenopausal women with type 2 diabetes.
Insulin resistance is characterized by post-receptor defect in the action of insulin. The cause of this defect is still being elucidated. The first step in insulin's action involves binding to the cell-surface receptor. Following insulin binding, the receptor undergoes auto-phosphorylation on specific tyrosine residues (accomplished by activation of insulin receptor tyrosine kinase). The activated receptor then activates insulin receptor substrates (such as IRS-1,2 and 3) which in turn bind to signalling molecules such as PI3 kinase and activate downstream signalling leading to insulin-mediated glucose transport. Abnormalities in both insulin receptor tyrosine kinase (IRTK) activity and in mediators distal to the receptor are present in insulin resistance states. Serine phosphorylation of insulin receptor decreases IRTK activity.,
Studies in adipocytes from women with PCOS reveal adipocyte insensitivity to inhibition of lipolysis by insulin as well as a decrease in maximal rates of adipocyte glucose uptake., While these defects are also present in obesity and type 2 diabetes, they can occur in PCOS in the absence of obesity. Dunaif et al reported decreased insulin receptor auto-phosphorylation in 50% of fibroblasts removed from PCOS women and this was due to increased receptor serine phosphorylation. Serine phosphorylation, as noted above, has been associated with decreased insulin receptor tyrosine auto-phosphorylation. In fact, this is the probable mechanism of TNF-a induced insulin resistance. Since serine phosphorylation of P450c17 (the key regulatory enzyme of androgen biosynthesis) increases enzyme activity leading to androgen biosynthesis, it is possible that a single defect (serine phosphorylation) can produce both insulin resistance and hyperandrogenism in a subgroup of PCOS women. Lin et al showed reduced insulin stimulated lactate production in granulosa-lutein cells obtained from women with PCOS, whereas the same cells obtained from normal ovulatory subjects responded with increased lactate production after insulin exposure.
In vitro human theca cell studies have shown that insulin has direct stimulatory effects on ovarian steroidogenesis.,, Nestler et al showed that insulin produced a greater increase in androgen production by theca cells isolated from women with PCOS than in cells obtained from subjects without PCOS, and that this effect is mediated specifically through insulin receptor rather than through IGF receptor “cross-talk”. There is some data to suggest that insulin enhances the effect of LH on preovulatory ovarian follicles causing premature activation and subsequent follicle arrest. It is possible that hyperinsulinemia (due to insulin resistance) drives the LH effect on ovarian theca cells to cause androgen excess which are intrinsically programmed to produce more androgen. Excess androgens are known to interfere with the process of follicular maturation, thus inhibiting ovulation and producing more arrested follicles. It has been postulated that the PCOS ovaries are more resistant to the metabolic effects of insulin than to the steroidogenic effects of insulin., Further studies are needed to clarify the “selective insulin resistance” phenomenon.
Insulin Sensitization in PCOS
In the last decade many trials have been held showing the efficacy of insulin sensitizers biguanides and thiazolidinediones in improving many aspects of the multifactorial PCOS. Trials have been done with metformin and two thiazolidinediones, Troglitazone and Rosiglitazone. Metformin is a biguanide which reduces plasma glucose concentrations in type 2 diabetes patients. Metformin in type 2 diabetics does not lead to weight gain and can induce weight loss in some patients. Metformin predominantly works by reducing hepatic glucose production, inhibiting gluconeogenesis both directly and indirectly (by decreasing free fatty acid concentrations)., There is some data to suggest that it may slightly improve peripheral insulin sensitivity., Studies with metformin in PCOS revealed reductions in androgen levels and improvements in ovulation when metformin was given for a duration of 10-24 weeks (in various studies). However, only in some of these studies was the effect independent of the weight loss induced by metformin.,,, Metformin has also been found to reduce the high rates of gestational diabetes in PCOS.
Thiazolidinediones (TZDs) represent a novel class of drugs that decrease peripheral insulin resistance by enhancing insulin action in the skeletal muscle, liver and adipose tissue. These agents are believed to work through binding and modulating the activity of a family of nuclear transcription factors termed peroxisome proliferator-activated receptors (PPARS). Studies with TZD in PCOS subjects have shown an improvement of the androgen levels and ovulation rate and enhanced insulin sensitivity without any reduction in the weight of subjects.,, Troglitazone (withdrawn from the market in 2000 due to hepatotoxicity) was the first drug of this class to be studied. Studies have now been done with Rosiglitazone showing a decrease in testosterone, androstenedione and DHEA levels and an increase in SHBG (thereby causing a decrease in free testosterone levels) along with an improvement in insulin sensitivity., In a recent study by Ghazeeri et al, Rosiglitazone improved both spontaneous and clomiphene-induced ovulation rates. It is interesting that Troglitazone has recently been shown to have independent effects on ovarian steroidogenesis and thus a direct effect of TZD apart from improvement of insulin resistance cannot be ruled out.
PCOS, infertility and early miscarriages
PCOS is one of the commonest causes of infertility in females. It is known that anovulation or decreased ovulation is the primary cause of this infertility and as mentioned above, both metformin and TZDs increase the rates of ovulation. Metformin also improves the number of oocytes collected in PCOS women for in vitro fertilization after FSH stimulation. Metformin also improves pregnancy rates. Studies with TZDs on pregnancy rates are currently on.
PCOS women also suffer from early miscarriages. It is possible that PCOS women have a hostile uterine environmental milieu which causes decreased conception and/or early miscarriages. Elevated PAI-1 (plasminogen activator inhibitor-1, an endogenous inhibitor of fibrinolysis) levels have been independently associated with recurrent miscarriages in PCOS women. Hypofibrinolysis due to elevated PAI-1 levels may lead to placental microthrombi and therefore infertility. Metformin enhances luteal phase uterine vascularity and blood flow and has been shown to reduce the rate of first trimester spontaneous abortions., It is also possible that the reduced rate of pregnancy loss achieved with metformin may be because of better egg quality.
PCOS, inflammation and cardiovascular disease
Insulin resistance has been associated with an increased incidence of cardiovascular disease and atherosclerosis is now considered to be an inflammatory disorder., Insulin resistance has recently been associated with increased levels of inflammatory mediators in the blood., Studies have therefore been conducted to look at inflammation in PCOS. Gonzelez et al noted increased levels of tumour necrosis factor alpha (cytokine which causes insulin resistance and is secreted by the adipose tissue) in PCOS women as compared to controls. Interestingly, lean PCOS women had higher TNF-a levels than normal lean women while the levels were similar in obese PCOS and obese controls. Kelly et al noted increased C-reactive protein levels and tissue plasminogen activator (t-PA) levels in PCOS women as compared to healthy weight-matched controls., However when adjusted for insulin sensitivity, C-RP was no longer significantly different between groups but t-PA levels remained significantly different. Women with PCOS also have higher PAI-1 activity and higher fibrinogen levels than controls. However, in another study, PAI-1 levels were not significantly different from controls when adjusted for BMI. Glueck et al demonstrated that PAI-1 activity was an independent risk factor for miscarriages in PCOS.
While the above studies suggest that PCOS is associated with a state of increased inflammation, clinical studies have yet to definitively demonstrate an increased rate of cardiovascular disease in PCOS.
Thiazolidinediones have been shown to decrease inflammation in obese and diabetic subjects.,, TZDs have also been shown to reduce carotid intimal medial thickness, normalize vascular endothelial function and improve fibrinolytic and coagulation parameters. Rosiglitazone therapy for 26 weeks reduced MMP-9 (a matrix metalloproteinase, implicated in atherosclerotic plaque rupture) and C-RP levels in type 2 diabetics. In studies in PCOS women, Troglitazone reduced PAI-1 levels and improved endothelial-dependent vasodilation. It is possible that the beneficial effect of TZDs in PCOS may be partly due to the decrease in inflammation. Metformin has also been shown to decrease PAI-1 and C-RP levels in PCOS women.,
While insulin resistance is not a part of the diagnostic criteria for PCOS, its importance in the pathogenesis of PCOS cannot be denied. The treatment of PCOS in the past has largely centred on anti-androgen therapy for symptomatic control, cyclic hormones for regular menses and ovulation induction for infertility. While weight loss is helpful in the therapy of PCOS, it may be difficult to achieve. Furthermore, a significant percentage of PCOS women are lean but insulin resistant. Insulin sensitizers are unique in PCOS because they offer both metabolic and gynaecologic benefit. Although the use of insulin sensitizers in PCOS has not been approved by the FDA (Food and Drug Administration, USA) yet, it is probable that PCOS will be a recognized indication for TZDs and metformin in future.
|1||Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group. Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome. Fertil Steril 2004;81:19-25.|
|2||Dunaif A. Insulin resistance and the polycystic ovary syndrome: mechanism and implications for pathogenesis. Endocr Rev 1997;18:774-800.|
|3||Franks S. Polycystic ovary syndrome. N Engl J Med 1995;333:853-61.|
|4||Franks S, White DM. Prevalence of and etiological factors in polycystic ovarian syndrome. Ann N Y Acad Sci 1993;687:112-4.|
|5||Yki-Jarvinen H, Makimattila S, Utriainen T, Rutanen EM. Portal insulin concentrations rather than insulin sensitivity regulate serum sex hormone-binding globulin and insulin-like growth factor binding protein 1 in vivo. J Clin Endocrinol Metab 1995;80:3227-32.|
|6||Haffner SM, Karhapaa P, Mykkanen L, Laakso M. Insulin resistance, body fat distribution, and sex hormones in men. Diabetes 1994;43:212-9.|
|7||Laaksonen DE, Niskanen L, Punnonen K, Nyyssonen K, Tuomainen TP, Salonen R et al. Sex hormones, inflammation and the metabolic syndrome: a population-based study. Eur J Endocrinol 2003;149:601-8.|
|8||l'Allemand D, Penhoat A, Lebrethon MC, Ardevol R, Baehr V, Oelkers W, et al. Insulin-like growth factors enhance steroidogenic enzyme and corticotropin receptor messenger ribonucleic acid levels and corticotropin steroidogenic responsiveness in cultured human adrenocortical cells. J Clin Endocrinol Metab 1996;81:3892-7.|
|9||Venturoli S, Porcu E, Fabbri R, Magrini O, Gammi L, Paradisi R, et al. Episodic pulsatile secretion of FSH, LH, prolactin, oestradiol, oestrone, and LH circadian variations in polycystic ovary syndrome. Clin Endocrinol (Oxf) 1988;28:93-107.|
|10||Kletzky OA, Davajan V, Nakamura RM, Thorneycroft IH, Mishell DR, Jr. Clinical categorization of patients with secondary amenorrhea using progesterone-induced uterine bleeding and measurement of serum gonadotropin levels. Am J Obstet Gynecol 1975;121:695-703.|
|11||Arroyo A, Laughlin GA, Morales AJ, Yen SS. Inappropriate gonadotropin secretion in polycystic ovary syndrome: influence of adiposity. J Clin Endocrinol Metab 1997;82:3728-33.|
|12||Mason HD, Margara R, Winston RM, Seppala M, Koistinen R, Franks S. Insulin-like growth factor-I (IGF-I) inhibits production of IGF-binding protein-1 while stimulating estradiol secretion in granulosa cells from normal and polycystic human ovaries. J Clin Endocrinol Metab 1993;76:1275-9.|
|13||Homburg R, Eshel A, Kilborn J, Adams J, Jacobs HS. Combined luteinizing hormone releasing hormone analogue and exogenous gonadotrophins for the treatment of infertility associated with polycystic ovaries. Hum Reprod 1990;5:32-5.|
|14||Scheele F, Hompes PG, van der Meer M, Schoute E, Schoemaker J. The effects of a gonadotrophin-releasing hormone agonist on treatment with low dose follicle stimulating hormone in polycystic ovary syndrome. Hum Reprod 1993;8:699-704.|
|15||Burghen GA, Givens JR, Kitabchi AE. Correlation of hyperandrogenism with hyperinsulinism in polycystic ovarian disease. J Clin Endocrinol Metab 1980;50:113-6.|
|16||Dunaif A, Graf M, Mandeli J, Laumas V, Dobrjansky A. Characterization of groups of hyperandrogenic women with acanthosis nigricans, impaired glucose tolerance, and/or hyperinsulinemia. J Clin Endocrinol Metab 1987;65:499-507.|
|17||Legro RS, Kunselman AR, Dodson WC, Dunaif A. Prevalence and predictors of risk for type 2 diabetes mellitus and impaired glucose tolerance in polycystic ovary syndrome: a prospective, controlled study in 254 affected women. J Clin Endocrinol Metab 1999;84:165-9.|
|18||Dahlgren E, Johansson S, Lindstedt G, Knutsson F, Oden A, Janson PO, et al. Women with polycystic ovary syndrome wedge resected in 1956 to 1965: a long-term follow-up focusing on natural history and circulating hormones. Fertil Steril 1992;57:505-13.|
|19||Dunaif A, Segal KR, Futterweit W, Dobrjansky A. Profound peripheral insulin resistance, independent of obesity, in polycystic ovary syndrome. Diabetes 1989;38:1165-74.|
|20||Ehrmann DA, Sturis J, Byrne MM, Karrison T, Rosenfield RL, Polonsky KS. Insulin secretory defects in polycystic ovary syndrome. Relationship to insulin sensitivity and family history of non-insulin-dependent diabetes mellitus. J Clin Invest 1995;96:520-7.|
|21||Dunaif A, Finegood DT. Beta-cell dysfunction independent of obesity and glucose intolerance in the polycystic ovary syndrome. J Clin Endocrinol Metab 1996;81:942-7.|
|22||Peppard HR, Marfori J, Iuorno MJ, Nestler JE. Prevalence of polycystic ovary syndrome among premenopausal women with type 2 diabetes. Diabetes Care 2001;24:1050-2.|
|23||White MF, Kahn CR. The insulin signaling system. J Biol Chem 1994;269:1-4.|
|24||White MF. The IRS-signalling system: a network of docking proteins that mediate insulin action. Mol Cell Biochem 1998;182:3-11.|
|25||Caro JF, Ittoop O, Pories WJ, Meelheim D, Flickinger EG, Thomas F, et al. Studies on the mechanism of insulin resistance in the liver from humans with noninsulin-dependent diabetes. Insulin action and binding in isolated hepatocytes, insulin receptor structure, and kinase activity. J Clin Invest 1986;78:249-58.|
|26||Considine RV, Caro JF. Protein kinase C: mediator or inhibitor of insulin action? J Cell Biochem 1993;52:8-13.|
|27||Kruszynska YT, Olefsky JM. Cellular and molecular mechanisms of non-insulin dependent diabetes mellitus. J Investig Med 1996;44:413-28.|
|28||Ek I, Arner P, Bergqvist A, Carlstrom K, Wahrenberg H. Impaired adipocyte lipolysis in nonobese women with the polycystic ovary syndrome: a possible link to insulin resistance? J Clin Endocrinol Metab 1997;82:1147-53.|
|29||Rosenbaum D, Haber RS, Dunaif A. Insulin resistance in polycystic ovary syndrome: decreased expression of GLUT-4 glucose transporters in adipocytes. Am J Physiol 1993;264:E197-202.|
|30||Dunaif A, Xia J, Book CB, Schenker E, Tang Z. Excessive insulin receptor serine phosphorylation in cultured fibroblasts and in skeletal muscle. A potential mechanism for insulin resistance in the polycystic ovary syndrome. J Clin Invest 1995;96:801-10.|
|31||Hotamisligil GS. Mechanisms of TNF-alpha-induced insulin resistance. Exp Clin Endocrinol Diabetes 1999;107:119-25.|
|32||Zhang LH, Rodriguez H, Ohno S, Miller WL. Serine phosphorylation of human P450c17 increases 17,20-lyase activity: implications for adrenarche and the polycystic ovary syndrome. Proc Natl Acad Sci U S A 1995;92:10619-23.|
|33||Tsilchorozidou T, Overton C, Conway GS. The pathophysiology of polycystic ovary syndrome. Clin Endocrinol (Oxf) 2004;60:1-17.|
|34||Lin Y, Fridstrom M, Hillensjo T. Insulin stimulation of lactate accumulation in isolated human granulosa-luteal cells: a comparison between normal and polycystic ovaries. Hum Reprod 1997;12:2469-72.|
|35||Nestler JE, Jakubowicz DJ, de Vargas AF, Brik C, Quintero N, Medina F. Insulin stimulates testosterone biosynthesis by human thecal cells from women with polycystic ovary syndrome by activating its own receptor and using inositolglycan mediators as the signal transduction system. J Clin Endocrinol Metab 1998;83:2001-5.|
|36||Willis D, Mason H, Gilling-Smith C, Franks S. Modulation by insulin of follicle-stimulating hormone and luteinizing hormone actions in human granulosa cells of normal and polycystic ovaries. J Clin Endocrinol Metab 1996;81:302-9.|
|37||Barbieri RL, Makris A, Randall RW, Daniels G, Kistner RW, Ryan KJ. Insulin stimulates androgen accumulation in incubations of ovarian stroma obtained from women with hyperandrogenism. J Clin Endocrinol Metab 1986;62:904-10.|
|38||Franks S, Robinson S, Willis DS. Nutrition, insulin and polycystic ovary syndrome. Rev Reprod 1996;1:47-53.|
|39||Gilling-Smith C, Willis DS, Beard RW, Franks S. Hypersecretion of androstenedione by isolated thecal cells from polycystic ovaries. J Clin Endocrinol Metab 1994;79:1158-65.|
|40||Hillier SG, Tetsuka M. Role of androgens in follicle maturation and atresia. Baillieres Clin Obstet Gynaecol 1997;11:249-60.|
|41||Wu XK, Zhou SY, Liu JX, Pollanen P, Sallinen K, Makinen M, et al. Selective ovary resistance to insulin signaling in women with polycystic ovary syndrome. Fertil Steril 2003;80:954-65.|
|42||Wu MS, Johnston P, Sheu WH, Hollenbeck CB, Jeng CY, Goldfine ID, et al. Effect of metformin on carbohydrate and lipoprotein metabolism in NIDDM patients. Diabetes Care 1990;13:1-8.|
|43||Perriello G, Misericordia P, Volpi E, Santucci A, Santucci C, Ferrannini E, et al. Acute antihyperglycemic mechanisms of metformin in NIDDM. Evidence for suppression of lipid oxidation and hepatic glucose production. Diabetes 1994;43:920-8.|
|44||Fantus IG, Brosseau R. Mechanism of action of metformin: insulin receptor and postreceptor effects in vitro and in vivo. J Clin Endocrinol Metab 1986;63:898-905.|
|45||Inzucchi SE, Maggs DG, Spollett GR, Page SL, Rife FS, Walton V, et al. Efficacy and metabolic effects of metformin and troglitazone in type II diabetes mellitus. N Engl J Med 1998;338:867-72.|
|46||Velazquez EM, Mendoza S, Hamer T, Sosa F, Glueck CJ. Metformin therapy in polycystic ovary syndrome reduces hyperinsulinemia, insulin resistance, hyperandrogenemia, and systolic blood pressure, while facilitating normal menses and pregnancy. Metabolism 1994;43:647-54.|
|47||Nestler JE, Jakubowicz DJ. Decreases in ovarian cytochrome P450c17 alpha activity and serum free testosterone after reduction of insulin secretion in polycystic ovary syndrome. N Engl J Med 1996;335:617-23.|
|48||Nestler JE, Jakubowicz DJ. Lean women with polycystic ovary syndrome respond to insulin reduction with decreases in ovarian P450c17 alpha activity and serum androgens. J Clin Endocrinol Metab 1997;82:4075-9.|
|49||Haas DA, Carr BR, Attia GR. Effects of metformin on body mass index, menstrual cyclicity, and ovulation induction in women with polycystic ovary syndrome. Fertil Steril 2003;79:469-81.|
|50||Glueck CJ, Wang P, Kobayashi S, Phillips H, Sieve-Smith L. Metformin therapy throughout pregnancy reduces the development of gestational diabetes in women with polycystic ovary syndrome. Fertil Steril 2002;77:520-5.|
|51||Saltiel AR, Olefsky JM. Thiazolidinediones in the treatment of insulin resistance and type II diabetes. Diabetes 1996;45:1661-9.|
|52||Dunaif A, Scott D, Finegood D, Quintana B, Whitcomb R. The insulin-sensitizing agent troglitazone improves metabolic and reproductive abnormalities in the polycystic ovary syndrome. J Clin Endocrinol Metab 1996;81:3299-306.|
|53||Ehrmann DA, Schneider DJ, Sobel BE, Cavaghan MK, Imperial J, Rosenfield RL et al. Troglitazone improves defects in insulin action, insulin secretion, ovarian steroidogenesis, and fibrinolysis in women with polycystic ovary syndrome. J Clin Endocrinol Metab 1997;82:2108-16.|
|54||Hasegawa I, Murakawa H, Suzuki M, Yamamoto Y, Kurabayashi T, Tanaka K. Effect of troglitazone on endocrine and ovulatory performance in women with insulin resistance-related polycystic ovary syndrome. Fertil Steril 1999;71:323-7.|
|55||Ghazeeri G, Kutteh WH, Bryer-Ash M, Haas D, Ke RW. Effect of rosiglitazone on spontaneous and clomiphene citrate-induced ovulation in women with polycystic ovary syndrome. Fertil Steril 2003;79:562-6.|
|56||Zheng Z, Li M, Lin Y, Ma Y. [Effect of rosiglitazone on insulin resistance and hyperandrogenism in polycystic ovary syndrome]. Zhonghua Fu Chan Ke Za Zhi. 2002;37:271-3.|
|57||Mitwally MF, Witchel SF, Casper RF. Troglitazone: a possible modulator of ovarian steroidogenesis. J Soc Gynecol Investig 2002;9:163-7.|
|58||Fedorcsak P, Dale PO, Storeng R, Abyholm T, Tanbo T. The effect of metformin on ovarian stimulation and in vitro fertilization in insulin-resistant women with polycystic ovary syndrome: an open-label randomized cross-over trial. Gynecol Endocrinol 2003;17:207-14.|
|59||Sagle M, Bishop K, Ridley N, Alexander FM, Michel M, Bonney RC, et al. Recurrent early miscarriage and polycystic ovaries. BMJ 1988;297:1027-8.|
|60||Glueck CJ, Wang P, Fontaine RN, Sieve-Smith L, Tracy T, Moore SK. Plasminogen activator inhibitor activity: an independent risk factor for the high miscarriage rate during pregnancy in women with polycystic ovary syndrome. Metabolism 1999;48:1589-95.|
|61||Jakubowicz DJ, Seppala M, Jakubowicz S, Rodriguez-Armas O, Rivas-Santiago A, Koistinen H, et al. Insulin reduction with metformin increases luteal phase serum glycodelin and insulin-like growth factor-binding protein 1 concentrations and enhances uterine vascularity and blood flow in the polycystic ovary syndrome. J Clin Endocrinol Metab 2001;86:1126-33.|
|62||Glueck CJ, Wang P, Goldenberg N, Sieve-Smith L. Pregnancy outcomes among women with polycystic ovary syndrome treated with metformin. Hum Reprod 2002;17:2858-64.|
|63||Jakubowicz DJ, Iuorno MJ, Jakubowicz S, Roberts KA, Nestler JE. Effects of metformin on early pregnancy loss in the polycystic ovary syndrome. J Clin Endocrinol Metab 2002;87:524-9.|
|64||Ross R. Atherosclerosis-an inflammatory disease. N Engl J Med 1999;340:115-26.|
|65||Libby P, Ridker PM, Maseri A. Inflammation and atherosclerosis. Circulation. 2002;105:1135-43.|
|66||Festa A, D'Agostino R Jr, Howard G, Mykkanen L, Tracy RP, Haffner SM. Chronic subclinical inflammation as part of the insulin resistance syndrome: the Insulin Resistance Atherosclerosis Study (IRAS). Circulation 2000;102:42-7.|
|67||Haffner SM, Mykkanen L, Festa A, Burke JP, Stern MP. Insulin-resistant prediabetic subjects have more atherogenic risk factors than insulin-sensitive prediabetic subjects: implications for preventing coronary heart disease during the prediabetic state. Circulation 2000;101:975-80.|
|68||Gonzalez F, Thusu K, Abdel-Rahman E, Prabhala A, Tomani M, Dandona P. Elevated serum levels of tumor necrosis factor alpha in normal-weight women with polycystic ovary syndrome. Metabolism 1999;48:437-41.|
|69||Kelly CC, Lyall H, Petrie JR, Gould GW, Connell JM, Sattar N. Low grade chronic inflammation in women with polycystic ovarian syndrome. J Clin Endocrinol Metab 2001;86:2453-5.|
|70||Kelly CJ, Lyall H, Petrie JR, Gould GW, Connell JM, Rumley A, et al. A specific elevation in tissue plasminogen activator antigen in women with polycystic ovarian syndrome. J Clin Endocrinol Metab 2002;87:3287-90.|
|71||Atiomo WU, Bates SA, Condon JE, Shaw S, West JH, Prentice AG. The plasminogen activator system in women with polycystic ovary syndrome. Fertil Steril 1998;69:236-41.|
|72||Atiomo WU, Fox R, Condon JE, Shaw S, Friend J, Prentice AG, et al. Raised plasminogen activator inhibitor-1 (PAI-1) is not an independent risk factor in the polycystic ovary syndrome (PCOS). Clin Endocrinol (Oxf) 2000;52:487-92.|
|73||Wild S, Pierpoint T, McKeigue P, Jacobs H. Cardiovascular disease in women with polycystic ovary syndrome at long-term follow-up: a retrospective cohort study. Clin Endocrinol (Oxf) 2000;52:595-600.|
|74||Aljada A, Garg R, Ghanim H, Mohanty P, Hamouda W, Assian E, et al. Nuclear factor-kappaB suppressive and inhibitor-kappaB stimulatory effects of troglitazone in obese patients with type 2 diabetes: evidence of an antiinflammatory action? J Clin Endocrinol Metab 2001;86:3250-6.|
|75||Ghanim H, Garg R, Aljada A, Mohanty P, Kumbkarni Y, Assian E, et al. Suppression of nuclear factor-kappaB and stimulation of inhibitor kappaB by troglitazone: evidence for an anti-inflammatory effect and a potential antiatherosclerotic effect in the obese. J Clin Endocrinol Metab 2001;86:1306-12.|
|76||Garg R, Kumbkarni Y, Aljada A, Mohanty P, Ghanim H, Hamouda W, et al. Troglitazone reduces reactive oxygen species generation by leukocytes and lipid peroxidation and improves flow-mediated vasodilatation in obese subjects. Hypertension 2000;36:430-5.|
|77||Parulkar AA, Pendergrass ML, Granda-Ayala R, Lee TR, Fonseca VA. Nonhypoglycemic effects of thiazolidinediones. Ann Intern Med 2001;134:61-71.|
|78||Haffner SM, Greenberg AS, Weston WM, Chen H, Williams K, Freed MI. Effect of rosiglitazone treatment on nontraditional markers of cardiovascular disease in patients with type 2 diabetes mellitus. Circulation 2002;106:679-84.|
|79||Paradisi G, Steinberg HO, Shepard MK, Hook G, Baron AD. Troglitazone therapy improves endothelial function to near normal levels in women with polycystic ovary syndrome. J Clin Endocrinol Metab 2003;88:576-80.|
|80||Morin-Papunen L, Rautio K, Ruokonen A, Hedberg P, Puukka M, Tapanainen JS. Metformin reduces serum C-reactive protein levels in women with polycystic ovary syndrome. J Clin Endocrinol Metab 2003;88:4649-54.|
|81||Velazquez EM, Mendoza SG, Wang P, Glueck CJ. Metformin therapy is associated with a decrease in plasma plasminogen activator inhibitor-1, lipoprotein(a), and immunoreactive insulin levels in patients with the polycystic ovary syndrome. Metabolism 1997;46:454-7.|
|82||Iuorno MJ, Nestler JE. Insulin-lowering drugs in polycystic ovary syndrome. Obstet Gynecol Clin North Am 2001;28:153-64.|