Should patients with polycystic ovary syndrome be treated with metformin?

Benefits of insulin sensitizing drugs in polycystic ovary syndrome—beyond ovulation induction

Laurel A. Stadtmauer1, Benjamin C. Wong and Sergio Oehninger

The Howard and Georgeanna Jones Institute for Reproductive Medicine, 601 Colley Avenue, Norfolk, VA 23507, USA


    Abstract
 Top
 Abstract
 Introduction
 How does metformin work?
 Metformin with gonadotrophins
 Elevated PAI-1 as a...
 Conclusions
 References
 
The debate on metformin use in polycystic ovary syndrome (PCOS) has mainly focused on its treatment for infertility in ovulation induction and menstrual cyclicity. Here we will summarize the data supporting the effect of metformin on improving hyperandrogenaemia and hyperinsulinaemia in PCOS patients. We propose that metformin benefits PCOS patients undergoing gonadotrophin therapy and IVF as well as ovulation induction. We also advocate the use of insulin sensitizing drugs to reduce miscarriage rates, and risks associated with coronary artery disease, gestational diabetes and obesity.

Key words: hyperandrogenism/insulin resistance/metformin/polycystic ovary syndrome


    Introduction
 Top
 Abstract
 Introduction
 How does metformin work?
 Metformin with gonadotrophins
 Elevated PAI-1 as a...
 Conclusions
 References
 
Polycystic ovary syndrome (PCOS) is an extremely common disorder with a prevalence rate of 3–7% in the general population (Asunción et al., 2000Go; Knochenhauer et al., 1998Go) and as high as 20% in the infertile population (Dunaif et al., 1997; Diamanti-Kandarakis et al., 1998Go). It is characterized by hyperandrogenaemia and hyperinsulinaemia. The chronic hyperinsulinaemia leads to overproduction of ovarian androgens including testosterone, and to a decrease in the serum sex hormone-binding globulin (SHBG) leading to an increase in serum-free testosterone concentrations (Barbieri et al., 1988Go). The high levels of androgens lead to chronic anovulation, menstrual disturbances and hirsuitism. These patients typically have elevated LH levels, and LH:FSH ratios as well as insulin resistance. The hyperandrogenism is closely tied with the insulin resistance and the decline in insulin levels leads to decreased androgen production (Dunaif et al., 1987Go; Franks, 1989Go; Utiger, 1996Go). However, lowering the androgen levels does not lead to an improvement in insulin resistance (Lanzone et al., 1990Go), evidence that the insulin resistance is core in the development of PCOS. The hyperandrogenism leads to abnormal folliculogenesis and endometrial development. The associated insulin resistance leads to increased risk for developing glucose intolerance, type 2 diabetes mellitus and gestational diabetes mellitus (Dahlgren et al., 1992aGo,bGo; Franks et al., 1999Go; Legro et al., 1999Go).

Although it is not yet known whether patients with PCOS have increased severity of cardiovascular morbidity and mortality, these patients certainly have an increased prevalence of cardiovascular risk factors such as diabetes mellitus, dyslipidaemia, obesity and hypertension (Wild et al., 1985Go; Slowinska-Srzednicka et al., 1991Go; Legro et al., 2001Go). Clinicians caring for patients with PCOS need to pay attention to the potential long-term medical implications of the disease as described above, as well as endometrial hyperplasia and carcinoma. There is also evidence of a positive correlation between serum insulin levels and plasminogen activator inhibitor-1 (Dahlgren et al., 1994Go; Andersen et al., 1995Go; Sampson et al., 1996Go) and the latter has been implied in the pathogenesis of cardiovascular disease and spontaneous abortion in patients with PCOS.

There have been two recent reviews summarizing the evidence for use of insulin-sensitizing agents to treat the infertility of PCOS (Homburg, 2002Go; Nestler, 2002Go). These papers review the evidence for the role of metformin alone or in combination with clomiphene citrate in increasing the incidence of ovulation induction and menstrual cyclicity. Although none of the insulin-sensitizing drugs have Food and Drug Administration (FDA) approval for use in PCOS patients, the scientific evidence in clinical trials, including some randomized placebo-controlled studies, is convincing. What is less clear is its use in conjunction with gonadotrophins and its use throughout pregnancy. Questions that still remain unanswered from these two reviews include: are fasting glucose-to-insulin ratios useful in predicting which patients will benefit from the insulin-sensitizing drugs or will all women with PCOS benefit? Are lean women with PCOS different from obese women in terms of their benefit from metformin? Should metformin be used on all patients who are undergoing gonadotrophin stimulation for ovulation induction or IVF? Does metformin reduce risk of miscarriages? Is there an increase in cardiovascular disease among women with PCOS and if so, does metformin reduce the risk of diabetes and cardiovascular disease that is increased in these patients? We do not have all the answers, but will review the evidence to support the use of these drugs in the PCOS patients to correct the metabolic derangement of PCOS.


    How does metformin work?
 Top
 Abstract
 Introduction
 How does metformin work?
 Metformin with gonadotrophins
 Elevated PAI-1 as a...
 Conclusions
 References
 
Metformin, an oral biguanide insulin-sensitizing agent, acts by inhibiting hepatic glucose production without hypoglycaemia because it does not increase insulin secretion (Velazquez et al., 1997aGo; Nestler et al., 1998Go). This drug enhances the effects of insulin on glucose uptake in skeletal muscles and adipocytes (Hundal et al., 1992Go; Klip et al., 1992Go; Wiernsperger and Bailey, 1999Go) and decreases intestinal absorption of glucose (Wilcock and Bailey, 1991Go; Ikeda et al., 2000Go). In addition, it increases glucose uptake in the muscle in the insulin-stimulated state after meals. The medication has been used widely as an oral hypoglycemic in patients with type 2 diabetes mellitus. The most common side effect of metformin is gastrointestinal upset, which can be reduced by taking metformin with meals and increasing the dose slowly to the effective dose of 1.5–2 gm/day. Lactic acidosis, a serious side effect, is extremely rare and has only been seen in women with renal insufficiency, which causes lactate to accumulate to high concentrations, or serious medical problems, which can lead to severe hypoxia and mitochondrial dysfunction such as congestive heart failure. Therefore, serum blood urea nitrogen (BUN) and creatinine should be measured in all patients with medical problems that may compromise renal function before treatment.

A recent review (Kirpichnikov et al., 2002Go) summarized the studies on the subject. The mechanisms that decrease hepatic glucose production are found to be secondary to a reduction in hepatic gluconeogenesis based on findings in in-vitro (Wollen and Bailey, 1988Go) and in-vivo animal studies (Radizuk et al., 1997). In the latter study, the molecular mechanism was believed to be via inhibition of lactate uptake. Other proposed mechanisms include a decrease of adenosine triphosphate leading to an increase in pyruvate flux (Argaud et al., 1993Go), and inhibition of pyruvate carboxylase-phosphoenolpyruvate carboxykinase activity with a resultant decrease in gluconeogenesis (Large and Baylot, 1999).

In PCOS patients, the majority of studies show that metformin decreases insulin resistance and endocrine parameters. It has been shown to reduce the insulin, testosterone and LH concentrations, which are elevated in these patients (Velazquez et al., 1994Go, 1997aGo; Diamanti-Kandarakis et al., 1998Go; Nestler et al., 1998Go; Glueck et al., 1999aGo; Kolodziejcyk et al., 2000; Moghetti et al., 2000Go). Hyperinsulinaemia has been proposed to play an essential role in the development of the hyperandrogenism that is observed in women with PCOS. Velazquez et al. proposed that the improvement in free testosterone may be due to a decrease in insulin affecting hepatic SHBG production (Velazquez et al., 1997aGo). Insulin has a direct effect on ovarian steroidogenesis by the stimulation of androgen production by the thecal cells (Barbieri et al., 1984Go, Dunaif et al., 1992Go). Hyperinsulinaemia can inhibit insulin-like growth factor-1 (IGF-1)-binding protein production by the liver with a subsequent increase in IGF-1. This IGF-1 in conjunction with LH could stimulate ovarian thecal cell androgen production (Leroith et al., 1995Go). This may be the mechanism for insulin driven increase in androgens in women with PCOS.

In PCOS patients, metformin has been shown to be beneficial in reducing hyperinsulinaemia and hyperandrogenaemia while facilitating normal menses and pregnancy (Velasquez et al., 1994, 1997a; Morin-Papunen et al., 1998aGo; Nestler et al., 1998Go; Glueck et al., 1999aGo; Moghetti et al., 2000Go). In addition, it has been shown to improve insulin response during the oral glucose tolerance test. However, the reduction in insulin levels and improvement in the insulin sensitivity in some of these studies does not appear extensive enough to explain the decrease in androgen levels and improvement in the menstrual regularity. Therefore, metformin may be acting directly on the thecal cells decreasing steroid production. Attia et al. showed that metformin had a direct inhibitory effect on androstenedione production in human ovarian thecal-like androgen-producing tumour cells (Attia et al., 2001Go). These findings could explain the mechanism for the decrease in androgen levels with the use of metformin.

Insulin acts by binding a cell surface receptor and activating a tyrosine kinase. (Petruzzelli et al., 1985). Tyrosine phosphorylation activates the receptor and serine phosphorylation inactivates the receptor (Stadtmauer and Rosen, 1986Go; Dunaif et al., 1995Go). It is believed that insulin resistance is due mostly to a post-receptor defect in signal transduction rather than a defect in insulin receptor number or affinity (Dunaif et al., 1995Go). This defect leads to reduced tyrosine autophosphorylation and increased serine phosphorylation in the ß subunit of the insulin receptor. This increase in serine phosphorylation has also been shown to augment both adrenal and ovarian CYP17 activity, with a subsequent increase in androgen production (Zhang et al., 1995Go). This increase in CYP17 represents a key point in the androgen synthesis in steroidogenic cells. Metformin, by impairing hyperinsulinaemia, has been shown to reduce CYP17 activity in women thereby decreasing the ovarian androgen production (Nestler and Jakubowicz, 1997aGo,bGo; la Marca et al., 2000Go). Specifically, Nestler and Jakubowicz performed a placebo-controlled study in 24 obese women [mean body mass index (BMI) 34 kg/m2] and reported that metformin 500 mg three times daily decreased area under plasma insulin levels versus time curve after oral glucose administration (Nestker and Jakubowicz, 1997a). They found an increase in the SHBG level, a decrease in LH and free testosterone and reduced basal and leuprolide stimulated 17-hydroxy progesterone levels. They found the same results in lean PCOS women (Nestler and Jakubowicz, 1997bGo). This fall in insulin levels in response to metformin with a concomitant fall in ovarian androgens support the hypothesis that the hyperinsulinaemia contributes to the hyperandrogenism.

The molecular mechanism of action of metformin is still not certain. Studies have also suggested the primary site of action of metformin to be hepatocyte mitochondria and gluconeogenesis was decreased by inhibition of respiratory chain oxidation of complex I substrates (Dominguez et al., 1996Go; Yli-Järvinen et al., 1999Go). The action of metformin in muscle cells has been found to be via its facilitation of glucose transport (Hundal et al., 1992Go; Klip et al., 1992Go), activation of tyrosine kinase activity (Dominguez et al., 1996Go) and stimulation of inositol 1,4,5-triphosphate production and glycogen synthesis (Stith et al., 1996Go).

There is also evidence to suggest a direct inhibition of androgen production in a human ovarian thecal-like androgen-producing tumour (HOTT) cell culture study (Attia et al., 2001Go). While the hyperandrogenaemia in PCOS patients has been attributed to hyperinsulinaemia, other mechanisms such as dysregulation of the CYP11a gene (Gharani et al., 1997Go) and the VNTR gene polymorphism (Waterworth et al., 1997Go) have also been proposed as a cause. Hence, the modulation of metformin on the serum androgen level may involve mechanisms other than its effects on insulin levels.

Metformin appears to benefit PCOS patients independently of weight loss. In the study by Velazquez et al. there was a 2% decrease in weight in the metformin treated patients, but this most likely is not enough to show that the menstrual regulation and decrease in androgens was related to weight loss alone (Velazquez et al., 1997aGo). Diamanti-Kandarakis et al. also found improved insulin-stimulated glucose utilization as well as improvements in ovarian hyperandrogenism such as free testosterone and androstendione independent of weight loss (Diamanti-Kandarakis et al., 1998Go). In addition, metformin decreased plasma plasminogen activator inhibitor-1 and lipoprotein A levels with a significant association with decreased fasting insulin levels.

A few studies failed to observe any statistically significant effect on endocrine studies or insulin response (Crave et al., 1995Go; Acibay and Gundogdu, 1996Go; Ehrmann et al., 1997aGo; Pirwany et al., 1999Go). These studies differ in the patient inclusion criteria, ethnic background, methods of measuring insulin sensitivity, as well as the BMI of the patients and dose and length of treatment of metformin, making comparisons difficult. The majority of these studies showing no improvement of metformin on the insulin sensitivity or hyperandrogenaemia were in severely obese women. The incidence of insulin resistance is known to differ in obese verses thin PCOS patients (Acien et al., 1999Go). The study by Flemming et. al. showed that metformin is much less effective in women whose BMI is >37 kg/m2 than those with BMI <37 kg/m2 (Flemming et al., 2002). In this randomized controlled trial of metformin in ovulation induction, metformin had an impact on weight loss and lowered serum leptin levels, with metabolic and cardiovascular risk factor benefits in all groups except for the severely obese group (BMI >37 kg/m2). When comparing studies, there is no consensus as to the most accurate measurement of insulin sensitivity. The hyperinsulinaemic euglycemic clamp technique is still regarded as the gold standard diagnostic test. However, its routine use in the clinical setting is not practical. Other indices such as fasting insulin, fasting glucose, fasting glucose-to-insulin ratio, i.v. glucose tolerance test (IVGTT), homeostasis assessment model (HOMA) and quantative insulin sensitivity check index (QUICKI) have also been used but to date there is no direct comparison of their sensitivities and specificities (Radziuk, 2000Go). There is inconsistency among clinical studies on whether insulin resistance was documented and how it was documented among PCOS patients.

We propose that metformin, through its effect on lowering insulin and androgen levels, benefits PCOS patients at multiple levels. It is important that when we analyse previous studies, and for future investigation, we look at the composition of patients: lean verses obese, the degree of hyperandrogenaemia, and the way insulin resistance is measured, since the types of PCOS patients may differ. Although metformin has been shown to reduce the androgen levels among PCOS patients, its efficacy in the treatment of hirsutism remains controversial since the studies show conflicting results. In order to detect a change in hirsutism, the patients need to be followed for longer than 6 months and this would probably explain the negative results in some studies. It is also possible that despite the lowering of serum androgen levels, the variable degree of increased 5-{alpha}-reductase activity in the hirsute PCOS patients (Serafini et al., 1985Go; Miles et al., 1992Go) leads to persistent hirsutism in some patients.

Modulation of leptin levels by metformin
Leptin, a peptide secreted by fat cells in adipose tissue, acts on the neurons in the central nervous system and is involved with regulation of eating behaviour and energy balance. It is the product of the `ob' gene and a deficiency in the protein or mutation in the gene leads to obesity (Caro et al., 1996Go). Leptin deficiency as well as high leptin levels are both associated with infertility (Barash et al., 1996Go). High levels of leptin may suppress neuropeptide Y in the hypothalamus, leading to the high GnRH and LH levels seen in PCOS. Several studies found high levels of leptin in PCOS patients (Brechffa et al., 1996; El Orabi et al., 1999Go), suggesting that it may play a role in the pathophysiology of the disease. However, leptin levels are directly related to obesity, so it is very important to exclude the effect of BMI on the leptin levels, as mean leptin levels are significantly higher in the obese groups (El Orabi et al., 1999Go). Numerous studies (Morin-Papunen et al., 1998bGo, 2000Go; Pasquali et al., 2000Go; Koivunen et al., 2001Go) show metformin treatment is associated with a decrease in leptin levels. Freemark and Bursy showed that in obese adolescent girls with hyperinsulinaemia, metformin lowered BMI and serum leptin levels (Fremark and Bursy, 2001). Although these studies are promising, unfortunately they were carried out on an obese subgroup of PCOS patients, so it is unclear whether the decrease in leptin levels is related to a decrease in obesity or to an improvement in the pathogenesis of PCOS.


    Metformin with gonadotrophins
 Top
 Abstract
 Introduction
 How does metformin work?
 Metformin with gonadotrophins
 Elevated PAI-1 as a...
 Conclusions
 References
 
Administration has been shown to improve ovarian response to exogenous gonadotrophin in women with clomiphene-resistant PCOS (De Leo et al., 1999Go). This study examined whether metformin affects the response to FSH therapy among PCOS patients resistant to clomiphiene citrate. Clomiphene resistance was defined as failure to ovulate or conceive on a dose of up to 150 mg of clomiphene citrate for three cycles or more. Twenty women with PCOS were randomized to two groups. The first group (n = 10) received FSH alone for two cycles and then metformin for 1 month before undergoing a combined metformin and FSH cycle. The second group of 10 was treated with metformin for 1 month before receiving a combination of FSH and metformin for one cycle. The patients were not screened for insulin resistance. The step-up protocol was used and the FSH was increased slowly until an ovarian response was evident. In this study, FSH-only (19 cycles) and metformin plus FSH (18 cycles) were compared. Because PCOS patients have a risk of hyper-responding requiring cancellation, the authors looked at the number of follicles that developed, estradiol levels and the incidence of cancelled cycles.

The results in a study by De Leo et al. showed that the daily dose needed to cause a detectable ovarian response was similar in the FSH-only and the metformin plus FSH groups as well as the total dose (De Leo et al., 1999Go). However, the estradiol level for the FSH-only cycles was significantly higher at 720 pg/ml verses 450 pg/ml. The number of follicles in the FSH only cycles was significantly higher (4.5 versus 2.5). The number of cancelled cycles due to too many follicles was 31% in the FSH-only cycles, compared with none in the FSH-metformin cycles. The pregnancy rates were similar for both the FSH-only cycles (10.5%) and FSH-metformin cycles (16.6%). The hyperstimulation rates were also similar (26.3% for the FSH only cycles and 16.6% for the FSH-metformin cycles). However, there may be insufficient power to reach statistical significance. Metformin showed a more orderly growth of follicles and a reduction in the multifollicular development. The average FSH dose in the study was similar. This study is limited by its low numbers of patients and by the study design of crossing over the first group with the second group.

Stadtmauer et al. also found a more orderly ovarian stimulation in IVF patients, after metformin treatment with 500 mg three times a day prior to and during leuprolide acetate and gonadotrophin treatment (Stadtmauer et al., 2001Go). There appeared to be a shift in follicle size with a reduction of the number of small follicles in the recruited cohort. There was also improvement in the endocrine parameters in terms of a decrease in follicular fluid and serum testosterone and insulin levels. It is possible to hypothosize that the decrease in the androgen and insulin levels locally in the ovary may be important factors leading to more normal folliculogenesis, homogeneous development of follicles and atresia of the small cohort of follicles. This is consistent with a direct effect of metformin on the androgen producing thecal cells.

In a prospective randomized trial Yarali et al. also evaluated the impact of metformin on ovarian response when co-administered with FSH (Yarali et al., 2002Go). Their study involved 32 obese patients with clomiphene citrate-resistant PCOS (average BMI of 29 km/m2). Following completion of baseline studies, patients were randomized to oral placebo or metformin for 6 weeks before exogenous gonadotrophin treatment at 850 mg twice daily and continued until ovulation or day of hCG administration. A low-dose step-up protocol was used starting at 75 IU of FSH for 14 days and increased by 37.5 IU at weekly intervals. Cycles were cancelled if there were more than three follicles >=15 mm or if there was no response within 35 days. Their results did not show a significant improvement in peripheral insulin resistance using fasting insulin concentration, fasting glucose:insulin ratio, and AUCinsulin, after 6 weeks of treatment. They did find that one patient on placebo and six on metformin ovulated. They also found a decrease in mean serum free testosterone concentration. Although this study using a low-dose step-up protocol did not show significant improvements in insulin sensitivity, the trends were towards lower duration of stimulation, fewer total numbers of vials and lower estradiol level on the day of hCG in the metformin group. It is possible that the difference may reach significant level if more patients were included in the study.

Metformin with gonadotrophins in IVF
Little is known about metformin use in IVF because there are only two retrospective studies by the primary author in this area and prospective studies are now ongoing. The first study reviewed 72 cycles of IVF in patients with clomiphene-resistant PCOS. In half of the cycle, patients received 500 mg metformin three times daily for 6 weeks prior to gonadotrophin stimulation. The study showed a beneficial effect on the number of mature oocytes, fertilization rates, embryos cleaved and pregnancy rates following metformin treatment and IVF. In addition, follicular fluid IGF levels, insulin and testosterone levels were affected by metformin use (Stadtmauer et al., 2001Go). This suggests that metformin may have an effect on modulating local levels of ovarian androgens, insulin and the insulin-like growth factors and may be related to the mechanism for improvement of ovarian stimulation and follicular development in metformin treated patients.

In the study by Stadtmauer et al. ovarian simulation in metformin treated and untreated groups were compared in the 59 coasted cycles of patients undergoing IVF and embryo transfer (Stadtmauer et al., 2002Go). The decreased number of days of coasting and lower peak E2 levels seen in metformin patients had a positive impact on both fertilization and pregnancy rates. The number of patients with moderate or severe ovarian hyperstimulation syndrome was the same in each group. Looking at the subset of patients with no coasting or coasting for <3 days the pregnancy rates are not significantly different. Therefore the improvement in the stimulation and folliculogenesis with less coasting and lower maximum estradiol levels may account for improvement in the oocytes and embryos leading to improved pregnancy rates. However the true mechanism has not been elicited.

Long-term implication of cardiovascular diseases in PCOS patients
Few studies have been done to date to assess the long-term cardiovascular risk to women with PCOS. Patients with PCOS have an increased incidence of risk factors associated with cardiovascular diseases, such as hypertension, diabetes mellitus, dyslipidaemia and family history of cardiovascular disease, similar to that of Syndrome X (Talbott et al., 2001Go). Cibula et al. found a significant increase in the prevalence of coronary artery disease in PCOS women compared with the controls obtained by response to questionnaires sent out to patients (Cibula et al., 2000Go). The result was further confounded by the increased prevalence of non-insulin dependent diabetes mellitus in the PCOS group. Dahlgren et al. demonstrated, using a risk factor model, a seven-fold increased incidence of myocardial infarction among women with PCOS compared with age-matched referents in a prospective population study (Dahlgren et al., 1992aGo). Independent risk factors used in the model included age, hypertension, diabetes mellitus, central obesity and dyslipidaemia. Increased risk of hypertension in PCOS was demonstrated in a retrospective cohort study by the same author (Dahlgren et al., 1992bGo). Total cholesterol, low density lipoprotien (LDL)-cholesterol, triglyceride, very low density lipoprotein (VLDL)-cholesterol and apolipoprotein B levels have been found to increase significantly among the non-obese PCOS women while high density lipoprotein-fraction 2 (HDL2)-cholesterol levels and apolipoprotein A-I/A-II ratios decrease (Wild et al., 1985Go; Slowinska-Srzednicka et al., 1991Go; Talbott et al., 1995Go; Legro et al., 2001Go). This increase in prevalence of cardiovascular risk factors likely contributes to the increase in cardiovascular disease although the long-term cardiovascular morbidity and mortality of PCOS has yet to be determined. The majority of data from studies on surrogate markers of cardiovascular disease such as carotid intima-media thickness by ultrasonography (Talbott et al., 1995Go; Guzick et al., 1996Go) and endothelial functions by blood flow measurement suggests that PCOS patients are predisposed to the development of atherosclerosis (Paradisi et al., 2001Go). Of note, a study performed by Mather and co-workers on healthy PCOS patients without cardiovascular risk factors revealed normal endothelial dysfunction in PCOS patients (Mather et al., 2000Go). Since patients with PCOS represent a heterogeneous group of patients, variation in cardiovascular function is expected among different study populations. Future research should focus on cardiovascular risk stratification in PCOS patients so that patients who will benefit from lifestyle and medical intervention can be identified.

Alteration in plasminogen activator inhibitor-1 (PAI-1) level in insulin resistance
PAI-1 is a 52 kDa glycoprotein that inhibits plasmin formation during plasminogen activation and fibrinolysis and is the most potent inhibitor of fibrinoloysis (Velazquez et al., 1997bGo; Glueck et al., 1999bGo). There is an increasing amount of observational data in the literature supporting an association between raised systemic PAI-1 level and PCOS (Sampson et al., 1996Go) and a positive correlation between PAI-1 level and insulin levels (Dahlgren et al., 1994Go; Ibáñez et al., 2002Go). In a cross-sectional study using weight-matched controls (Atiomo et al., 2000Go) PAI-1 level was found not to be elevated independently of the effect from obesity. In a prospective study, Andersen et al. demonstrated that weight loss by dieting in nine women with PCOS resulted in significant reductions of fasting glucose and insulin as well as PAI-1 (Andersen et al., 1995Go). Improvement of insulin sensitivity by metformin has been correlated with a decrease in PAI-1 in a prospective pilot study of 22 women with PCOS (Velazquez et al., 1997; Glueck et al., 2000Go). Similar results have been noted with the treatment of insulin resistance by troglitazone (Ehrmann et al., 1997bGo). Due to these findings, the elevated PAI-1 levels in PCOS have been suggested as a pathogenic process for ischemic heart diseases and spontaneous abortion in this patient group (Velazquez et al., 1997bGo).

Long-term use of metformin in PCOS patients for cardiovascular risk modification
There is no direct evidence available to support the long-term use of metformin in PCOS patients to reduce the cardiovascular morbidity and mortality to date. Studies on the use of metformin to treat cardiovascular risk factors showed conflicting results (Velazquez et al., 1994Go; Morin-Papunen et al., 1998aGo; Chu et al., 2002Go) except for the reduced incidence of diabetes (Diabetes Prevention Program Research Group, 2002Go). A recent review article (Nestler, 2002Go) concluded that there is accumulating evidence to support the use of insulin sensitizers for prevention of type 2 diabetes mellitus in high risk individuals, PCOS patients being considered to be in this group. Interestingly, in the above study (Diabetes Prevention Program Research Group, 2002Go), lifestyle changes such as low- carbohydrate diet and exercise were found to be more effective than metformin in the reduction of risk of diabetes. Therefore, weight loss should always be encouraged prior to and during metformin treatment. While metformin has been used for a long time among patients with type 2 diabetes patients, the safety of its long-term use in PCOS patients, which might require chronic use of the medication from as early as the teenage years, needs to be studied. There is no data on the length of time the patients should be kept on metformin once the medication is started. Although PCOS is a chronic disease with the symptoms of menstrual irregularity, hyperandrogenaemia and/or hyperandrogenism persist till menopause, future study should also investigate the benefit of continuing the medication well into the menopausal period since the insulin resistance and the cardiovascular risk factors persist into that period.

While considering the appropriateness of the long-term use of metformin in PCOS patients, it is also important to challenge the traditional management of PCOS patients with oral contraceptives. In a review by Livingstone and Collison, the potential negative effects of supraphysiologic dose of estrogen on insulin resistance was suggested (Livingstone and Collison, 2002Go). The evidence, however, remains indirect since there is no data on patients with PCOS. The authors quoted a study on the administration of ethinyl estradiol to male-to-female transsexuals with a resultant increase in insulin resistance (Polderman et al., 1994Go). Another study quoted involved measuring the change of insulin resistance among patients on oral contraceptives (OCs) and noted an increase in insulin resistance (Godsland et al., 1992Go; Godsland and Crooke, 1994). Morin-Papunen et al. compared metformin therapy with OCs with 35 µg ethinyl estradiol and cyproterone acetate and found that the OCs worsened glucose tolerance with increased total and LDL-cholesterol and triglyceride levels (Morin-Papunen et al., 2000Go). These studies overall suggest at least a theoretical cardiovascular concern in the use of OCs among PCOS patients and further studies are needed to confirm this. In the mean time, clinicians should monitor these patients closely when they are on OCs and recommend its discontinuation if there is a worsening in the severity of the cardiovascular risk factors.


    Elevated PAI-1 as a pathogenic factor for ischaemic heart disease
 Top
 Abstract
 Introduction
 How does metformin work?
 Metformin with gonadotrophins
 Elevated PAI-1 as a...
 Conclusions
 References
 
Due to the frequent co-existence of cardiac risk factors in women with PCOS (Haffner et al., 1992Go; Talbott et al., 1995Go; Haffner, 1996Go) and the lack of clinical studies that investigate the association between elevated PAI-1 level and incidence of myocardial infarction corrected for other confounding factors, the pathogenic role of PAI-1 remains speculative at this point. PAI-1 is not the only proposed mechanism for ischaemic heart disease in PCOS. A recent cross-sectional study demonstrated a significant relationship between insulin resistance and plasma concentrations of asymmetric dimethylarginine (ADMA) (Stühlinger et al., 2002Go). ADMA is an endogenous nitric oxide synthase inhibitor and increased levels have been associated with endothelial dysfunction and increased risk of cardiovascular disease (Miyazaki et al., 2000Go). Women with PCOS were also found to have elevated levels of endothelin-1, a marker of vasculopathy, and metformin treatment reduced this elevation (Diamanti-Kandarakis et al., 2001Go). Yarali et al. have also suggested that the increased serum homocysteine concentrations in PCOS patients contribute to the cardiovascular risk with a decrease in these levels with metformin use (Yarali et al., 2001Go). While different pathogenic theories have been suggested, further prospective long term clinical studies are needed to assess more precisely the risk of cardiovascular disease in PCOS women.

Elevated PAI-1 as a pathogenic factor for spontaneous abortions
Elevated PAI-1 levels in PCOS have been found to be an independent reversible risk factor for early spontaneous abortion (Glueck et al., 1999bGo). Women with PCOS are more likely to have a hereditary hypofibrinolysis with homozygous or heterozygous for the 4G polymorphism in the promoter sequence of the PAI-1 gene (Glueck et al., 1999aGo). 4G/5G polymorphism of the PAI-1 gene independently accounted for 14% of the variance of PAI activity. The concentration of the glycoprotein PAI-1 is raised in insulin resistance and its high levels have been shown to cause spontaneous abortion through the mechanism of hypofibrinolysis (Glueck et al., 1999bGo; Kupferminc et al., 1999Go). Insulin has been shown to directly augment the expression of PAI-1 in vivo and in vitro (Alessi et al., 1988Go; Schneider and Sobet, 1991; Nordt et al., 1995Go). The genetic cause of elevated PAI-1 level, together with its augmentation by hyperinsulinaemia in PCOS may be the pathogenic mechanism for the early reproductive loss in this group. Several studies have investigated the potential use of metformin in early pregnancy to reduce the incidence of spontaneous abortions. In a retrospective study, metformin administration during pregnancy reduced first-trimester pregnancy loss significantly (Jakubowicz et al., 2002Go). A total of 65 women received metformin during pregnancy and 31 did not. The early pregnancy loss in the meformin group was 6/68, or 8.8% compared with 13/31, or 41.9% in the control group. In a subset of patients with a prior history of miscarriage, the early pregnancy loss rate was also lower in the metformin group when compared with the control group (11.1 versus 58.3%). Metformin has been shown to lower the PAI-1 levels and the latter has been associated with a decreased early spontaneous abortion rate. Glueck et al., published a case report of a 32-year old woman with PCOS and familial hypofibrinolysis with 4G/4G polymorphism of the PAI-1 gene with resulting high PAI-1 activity (Glueck et al., 2000Go). After treatment with metformin, PAI-1 activity normalized in conjunction with normalization of her insulin and a decrease in her weight. A prospective pilot study with historic controls was subsequently performed on the use of metformin in early pregnancy to reduce first trimester spontaneous abortion in PCOS (Glueck et al., 2001Go). Ten PCOS women with 22 previous pregnancies and 16 first-trimester spontaneous abortions in the past had 10 pregnancies with one spontaneous abortion after being treated with metformin. Fasting serum insulin level was positively correlated with PAI-1 activity before metformin therapy and reduction in fasting serum insulin during metformin therapy, and before conception was also positively correlated with reduction in PAI-1 activity. The correlation between a reduction in the plasma insulin levels and PAI-1 levels after treatment with metformin in early pregnancy, and the suggestive findings of improved pregnancy outcome with its use, support the proposed pathogenic role of PAI-1. Further prospective randomized controlled trials are needed to confirm these findings. If further studies support a reduction of miscarriage rate by metformin, the latter will become the only known treatment that appears to decrease the increased miscarriage rate in PCOS women to date. Although metformin has not been shown to have any adverse effects when used in pregnancy, careful records and neonatal follow-up needs to be conducted on all women who have conceived on or taken metformin throughout pregnancy.

Use of metformin in pregnancy
Traditionally, the group of oral hypoglycaemic agents have been regarded as teratogenic and therefore contra-indicated in pregnancy. Although an earlier animal study showed an increase risk of teratogenicity with use of oral hypoglycemic agents in pregnancy (Schardein, 1993Go; Shepard et al., 1995) an increasing amount of data support the safe use of metformin throughout pregnancy. In a prospective pilot study of 22 non-diabetic PCOS women taking metformin 1.5–2.55 g/day throughout pregnancy, no birth defects have occurred (Glueck et al., 2001Go). A study by Glueck et al. followed 154 infants whose mothers had PCOS and took metformin during pregnancy and did not see any adverse outcome (Glueck et al., 2002aGo). Further multi-centre studies involving much larger number of patients to document the safety of this medication in pregnancy should be performed. Information on the use of other insulin-sensitizers such as rosaglitazone is lacking, however they are characterized as category C drugs, so caution must be used. The decision to use metformin in pregnancy (a category B drug) therefore depends on an assessment of the balance between potential benefits against risks.

Gestational diabetes mellitus
In women with PCOS, Glueck et al. reported that patients who took metformin throughout their pregnancy had a 10-fold reduction in the risk of gestational diabetes (Glueck et al., 2002bGo). They found that 1/33 (3%) pregnant patients who took metformin versus 22/72 (31%) pregnant women who did not take metformin developed gestational diabetes. Since PCOS patients are at increased risk for gestational diabetes mellitus in pregnancy, this is another potential benefit of keeping patients on metformin throughout the pregnancy.

Diabetes mellitus and chronic treatment
In a recent review and continuation of the debate on metformin use in PCOS, Dr Nestler summarized the evidence supporting the use of metformin rather than OCPS for chronic therapy in PCOS patients at increased risk for developing type 2 diabetes (Nestler, 2002Go). We also support his position.


    Conclusions
 Top
 Abstract
 Introduction
 How does metformin work?
 Metformin with gonadotrophins
 Elevated PAI-1 as a...
 Conclusions
 References
 
There is strong evidence for the use of metformin in the regulation of cycle and ovulation induction among PCOS patients who desire fertility. The impact of using metformin as an adjunct to controlled ovarian stimulation and IVF is promising and requires further study. The use of metformin for long-term medical benefits such as reduction of risk of type 2 diabetes mellitus and cardiovascular disease requires further prospective studies to confirm the clinical impact but remains an area with great potential. Based on a few studies metformin appears to reduce the risk of gestational diabetes and early pregnancy losses when its use is continued in pregnancy, and it appears to be safe. The studies reporting the benefits of metformin outweigh those reporting the risks, so we are justified in treating patients with metformin throughout pregnancy. Other insulin-sensitizing drugs, including the thiazolidiones such as rosiglitazone, are commonly used in diabetes, but their safety in pregnancy has not been established. These drugs deserve a study comparison after teratogenicity and placental crossing studies have been completed. In order to know which subsets of patients will most benefit from metformin treatment, future studies have to have specific diagnostic criteria in their groups with respect to age, BMI, hyperinsulinaemina and hyperandrogenaemia to allow uniformity in the study groups. In comparison with oral contraceptives, which traditionally have been used as a first-line treatment for PCOS patients not interested in fertility, we agree with Dr Nestler in his debate (Nestler, 2002Go) that metformin is theoretically a better choice in this group of patients. He reviews the evidence for the effect of OCPs on glucose tolerance and the effect of the progestins on the lipids. Studies that directly compare the two treatments will certainly help to clarify this speculation. We do not know the effect of long-term metformin treatment on obese adolescent girls with PCOS. However, the risk factors of obesity and insulin resistance in developing type 2 diabetes are so strong that the hope of breaking this inevitable cycle is worth a try.


    Notes
 
1 To whom correspondence should be addressed. E-mail: stadtmla{at}evms.edu Back


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 Elevated PAI-1 as a...
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