Metformin treatment reduces ovarian cytochrome P-450c17alpha response to human chorionic gonadotrophin in women with insulin resistance-related polycystic ovary syndrome

Metformin: new understandings, new uses

Metformin, a biguanide, has been available in the US for the treatment of type 2 diabetes mellitus for nearly 8 years. Over this period of time, it has become the most widely prescribed antihyperglycaemic agent. Its mechanism of action involves the suppression of endogenous glucose production, primarily by the liver. Whether the drug actually has an insulin sensitising effect in peripheral tissues, such as muscle and fat, remains somewhat controversial. Nonetheless, because insulin levels decline with metformin use, it has been termed an 'insulin sensitiser'. Metformin has also been shown to have several beneficial effects on cardiovascular risk factors and it is the only oral antihyperglycaemic agent thus far associated with decreased macrovascular outcomes in patients with diabetes. Cardiovascular disease, impaired glucose tolerance and the polycystic ovary syndrome are now recognised as complications of the insulin resistance syndrome, and there is growing interest in the management of this extraordinarily common metabolic disorder. While diet and exercise remain the cornerstone of therapy for insulin resistance, pharmacological intervention is becoming an increasingly viable option. We review the role of metformin in the treatment of patients with type 2 diabetes and describe the additional benefits it provides over and above its effect on glucose levels alone. We also discuss its potential role for a variety of insulin resistant and prediabetic states, including impaired glucose tolerance, obesity, polycystic ovary syndrome and the metabolic abnormalities associated with HIV disease.

Metformin administration modulates and restores luteinizing hormone spontaneous episodic secretion and ovarian function in nonobese patients with polycystic ovary syndrome

OBJECTIVE

To evaluate the effects of metformin administration on spontaneous LH episodic release in a group of nonobese polycystic ovary (PCOS) patients.

DESIGN

Controlled clinical study.

SETTING

PCOS patients in a clinical research environment.

PATIENT(S)

Twenty nonobese PCOS patients were enrolled after informed consent.

INTERVENTION(S)

All patients underwent hormonal evaluations and a pulsatility study (sampling every 10 minutes for 4 hours) before and at the sixth month of therapy (metformin, 500 mg, p.o. b.i.d.). Ultrasound examinations and Ferriman-Gallwey scoring were also performed.

MAIN OUTCOME MEASURE(S)

Measurements of plasma LH, FSH, estradiol (E(2)), androstenedione (A), 17-hydroxy-progesterone (17-OHP), and testosterone (T), glucose, insulin, and C-peptide concentrations.

RESULT(S)

After 6 months of metformin administration, the plasma LH, 17-OHP, A, and T levels and LH/FSH ratio were significantly reduced. Insulin sensitivity, expressed as the glucose-to-insulin ratio, was significantly improved under glucose load after 6 months of treatment. Spontaneous LH episodic release showed a significant reduction in pulse amplitude with no changes in pulse frequency. Menstrual cyclicity was restored in all amenorrheic and oligomenorrheic women. The ovarian volume and Ferriman-Gallwey scores also were significantly reduced.

CONCLUSION(S)

Metformin administration improves reproductive axis functioning in hyperandrogenic nonobese PCOS patients. By acting on the ovary and restoring normal ovarian activity, metformin positively modulates the reproductive axis (namely GnRH-LH episodic release).

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.

Obese patients with polycystic ovary syndrome: evidence that metformin does not restore sensitivity of the gonadotropin-releasing hormone pulse generator to inhibition by ovarian steroids

Women with polycystic ovary syndrome (PCOS) have reduced GnRH sensitivity to suppression by ovarian steroids, which can be ameliorated by androgen blockade. We studied nine PCOS women and nine controls to determine whether metformin could change feedback inhibition by estradiol (E(2)) and progesterone (P). LH was measured every 10 min, and FSH, E(2), P, and testosterone (T) were measured every 2 h. Frequently sampled iv glucose tolerance test was performed at the end of each admission. After the first admission, metformin (500 mg, three times a day) was started. The second admission occurred on d 8-11 of the next menstrual cycle in controls and on d 28 in PCOS patients. Patients subsequently took E(2) and P for 1 wk until the third admission. At baseline, PCOS women had higher T, free T, androstenedione, and estrone. After 4 wk of metformin, controls had a slight reduction in total T, but free T was unchanged. However, PCOS patients had reduced insulin, T, and E(2), and increased LH mean/amplitude and FSH. After ovarian steroids, controls had a greater reduction in LH pulse frequency than PCOS (61 vs. 25%). These results suggest that the beneficial effects of metformin on ovulatory function in obese PCOS women are probably not mediated by enhanced hypothalamic sensitivity.

Insulin-lowering agents in the management of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a medical condition that has brought multiple specialists together. Gynecologists, endocrinologists, cardiologists, pediatricians, and dermatologists are all concerned with PCOS patients and share research data and design clinical trials to learn more about the syndrome. Insulin resistance is a common feature of PCOS and is more marked in obese women, suggesting that PCOS and obesity have a synergistic effect on the magnitude of the insulin disorder. Hyperinsulinemia associated with insulin resistance has been causally linked to all features of the syndrome, such as hyperandrogenism, reproductive disorders, acne, hirsutism, and metabolic disturbances. Women with PCOS should be evaluated for cardiovascular risk factors, such as lipid profile and blood pressure. Modification of diet and lifestyle should be suggested to those who are obese. Several insulin-lowering agents have been tested in the management of PCOS. In particular, metformin is the only drug currently in widespread clinical use for treatment of PCOS. In a high percentage of patients, treatment with metformin is followed by regularization of menstrual cycle, reduction in hyperandrogenism and in cardiovascular risk factors, and improvement in response to therapies for induction of ovulation.

Metformin has direct effects on human ovarian steroidogenesis

OBJECTIVE

To investigate the possibility of direct effects of metformin on ovarian steroidogenesis.

DESIGN

Cultured ovarian cells.

SETTING

Academic research environment.

PATIENT(S)

Women undergoing bilateral salpingoophorectomy for benign gynecological disease.

MAIN OUTCOME MEASURE(S)

Estradiol and P were measured in granulosa cell (GC) conditioned medium and androstenedione (A) and P in theca conditioned medium.

RESULT(S)

The effect of addition of metformin alone to GCs was variable, but significant inhibition of both P and E2 was seen (range 0%-30%). Metformin dose-dependently inhibited gonadotrophin and insulin-stimulated P and E2 production (range 25%-50%). In theca, metformin inhibited A production (0%-40%) with no effect on P. In the presence of insulin, A was inhibited dose-dependently and P increased by a similar magnitude.

CONCLUSION(S)

These results demonstrate a direct effect of metformin on ovarian steroidogenesis. The inhibitory effects on androgen production in particular would be beneficial in polycystic ovary syndrome (PCOS).

Insulin-lowering treatment reduces aromatase activity in response to follicle-stimulating hormone in women with polycystic ovary syndrome

OBJECTIVE

To investigate the effects of reduction of insulin resistance and hyperinsulinemia associated with the polycystic ovary syndrome (PCOS) on FSH-stimulated ovarian aromatase activity.

DESIGN

Prospective study.

SETTING

Academic health center, Siena, Italy.

PATIENT(S)

Twenty women 18 to 26 years of age in whom PCOS was diagnosed on the basis of oligomenorrhea or amenorrhea and hyperandrogenemia.

INTERVENTION(S)

Recombinant FSH was administered. The next day, therapy with metformin (500 mg t.i.d.) was begun. After 35 to 40 days of treatment, the pretreatment protocol was repeated.

MAIN OUTCOME MEASURE(S)

Plasma levels of estradiol (E(2)), androstenedione (A), and testosterone (T). The ratios of basal levels and areas under the curve (AUCs) of products and substrates were compared before and after metformin administration to detect differences in aromatase activity.

RESULT(S)

Metformin treatment was associated with significant reduction in basal free testosterone plasma levels, insulin plasma levels, and insulin response to oral glucose tolerance testing. Administration of FSH was followed by a significantly lesser E(2) response after metformin therapy than before this therapy. The ratios of AUC(E2) to AUC(A) and to AUC(T), indicative of aromatase activity in response to FSH, were significantly lower after metformin therapy than before.

CONCLUSION(S)

Metformin therapy in women with PCOS is associated with a reduction in aromatase activity in response to FSH. Insulin affects production of both androgen and estrogen. Insulin therefore plays a central role in regulating the activity of thecal and granulosa cells.

Treatment of polycystic ovary syndrome with insulin-lowering agents

Early diagnosis and therapy of the underlying insulin resistance of heritable polycystic ovary syndrome (PCOS), often manifested at menarche, facilitate the reduction and/or reversal of the reproductive and metabolic morbidity of PCOS, as well as reduce the risk factors for cardiovascular disease. PCOS is characterised by oligoamenorrhoea, clinical and biochemical hyperandrogenism, infertility, recurrent miscarriage, insulin resistance, hyperinsulinaemia, gestational diabetes, impaired glucose tolerance, Type 2 diabetes, morbid obesity, hypertension, hypofibrinolysis, hypertriglyceridaemia, low levels of high density lipoprotein-cholesterol and a sevenfold risk increase in cardiovascular disease. Insulin sensitising-lowering agents reduce insulin resistance and hyperinsulinaemia, reverse PCOS endocrinopathy and ameliorate the reproductive, metabolic and cardiovascular morbidity of the disorder. The largest literature on the subject discusses metformin. Improved pregnancy outcomes in women with PCOS receiving metformin may be attributed to its ability to reduce insulin resistance, hyperinsulinaemia and hypofibrinolytic plasminogen activator inhibitor activity by the enhancement of folliculogenesis and improvement of oocyte quality.

Clinical, endocrine and metabolic effects of metformin added to ethinyl estradiol-cyproterone acetate in non-obese women with polycystic ovarian syndrome: a randomized controlled study

BACKGROUND

Oral contraceptive pills (OC) are usually the first choice of treatment for polycystic ovarian syndrome (PCOS), when fertility is not desired. However, they do not improve, or may even further induce impairment of insulin sensitivity, which is already impaired in women with PCOS. In this prospective, randomized study, we analysed the additional benefits of adding metformin to the OC treatment in non-obese women with PCOS.

METHODS

After a baseline work-up including body mass index (BMI), waist:hip ratio (WHR), Ferriman-Gallwey score, ovarian volume, serum gonadotrophin, androgen and sex hormone-binding globulin (SHBG) levels, and fasting lipid, glucose and insulin levels, 40 non-obese women with PCOS were assigned either to the OC or to the OC + metformin treatment by computer-assisted randomization. At the end of the 4 month follow-up period, subjects were re-evaluated.

RESULTS

The two groups were similar at baseline. After treatment, women in the OC + metformin group had significant decreases in BMI and WHR, and a significant increase in insulin sensitivity, in contrast to those in the OC group, who had insignificant changes in these parameters. Adding metformin also caused significant improvements in serum androstenedione and SHBG levels compared with the OC treatment alone.

CONCLUSIONS

Adding metformin to the OC treatment may improve the insulin sensitivity, and may further suppress the hyperandrogenaemia in non-obese women with PCOS.

Metformin and polycystic ovary syndrome: a literature review

Polycystic ovary syndrome (PCOS) is a common endocrine condition that affects women of reproductive age. Anovulation, menstrual irregularities, hirsutism, and infertility are common clinical presentations. Long-term health concerns such as type II diabetes mellitus and, possibly, cardiovascular disease, have been linked to PCOS. Metformin, an oral hypoglycemic agent, has been recently advocated as treatment for some women with PCOS due to the association of PCOS with hyperinsulinemia. Metformin is utilized as sole therapy for ovulation induction as well as in combination with traditional ovulation-induction therapies. This review identified 23 prospective studies addressing the effects of metformin on PCOS. Because of the heterogeneity of the published reports, only a qualitative assessment of the data was possible. Review of this literature confirms a beneficial role of metformin in reducing insulin resistance in some women with PCOS. Other favourable biochemical effects include reduced free testosterone levels and increased sex hormone-binding globulin (SHBG). Metformin may improve menstrual regularity, leading to spontaneous ovulation, and improve ovarian response to conventional ovulation-induction therapies. There is, however, little evidence supporting the use of metformin to facilitate weight reduction, or improve serum lipids or hirsutism. Further evaluation is required to define the long-term effectiveness of metformin, who will benefit from metformin treatment, and the optimal duration of metformin therapy.

Ovarian steroidogenic response to human chorionic gonadotrophin in obese women with polycystic ovary syndrome: effect of metformin

BACKGROUND

The aim of the present study was to investigate the steroidogenic response pattern to HCG in obese women with polycystic ovary syndrome (PCOS) and the possible effects of metformin treatment on it.

METHODS

A single injection of human chorionic gonadotrophin (HCG, 5000 IU) was given to 12 obese [body mass index (BMI) > or = 27 kg/m2] women with PCOS and to 27 control women. Blood samples for assays of 17alpha-hydroxyprogesterone (17-OHP), androstenedione, testosterone and oestradiol were collected at baseline and 1, 2 and 4 days after the injection. Responses to HCG were also assessed in the PCOS women after 2-month treatment with metformin (500 mg x 3 daily).

RESULTS

Serum 17-OHP and oestradiol concentrations peaked at 24 h in the PCOS women and preceded the maximum testosterone concentration, which was seen at 48 h. In the control women the maximum concentrations of all these steroids were reached 96 h after HCG. After metformin treatment, the basal serum testosterone concentration and the areas under the androstenedione (AUC(A)) and testosterone (AUC(T)) response curves after HCG decreased significantly.

CONCLUSIONS

The results demonstrate that obese PCOS women have a male-type steroidogenic response pattern to a single injection of HCG and a higher androgen secretory capacity than control women, which may be explained by the increased thecal cell activity in the polycystic ovary. The slight alleviation of hyperandrogenism brought about by metformin therapy appears to be due to its effect on ovarian steroidogenesis possibly mediated by decreased insulin action.

Metformin therapy in the management of polycystic ovary syndrome: endocrine, metabolic and reproductive effects

Polycystic ovary syndrome (PCOS) is a convergence of multisystem endocrine derangements. Impairment in insulin metabolism is a prominent feature of the syndrome and appears to play a key pathogenetic role precipitating the cascade of other disorders associated with PCOS. Recent studies report that insulin-sensitizing agents, such as metformin, reduce hyperinsulinemia, reverse the endocrinopathy of PCOS and normalize endocrine, metabolic and reproductive functions, leading to the resumption of menstrual cyclicity and ovulation. In this review, we report the most recent evidence regarding metformin usage in women with PCOS.

Insulin resistance in clomiphene responders and non-responders with polycystic ovarian disease and therapeutic effects of metformin

OBJECTIVES

To evaluate the clinical features, endocrine and metabolic profiles in clomiphene (CC) responders and non-responders with polycystic ovarian disease (PCOD), and to examine the effects of metformin (MTF) on the above parameters of CC resistance.

METHODS

A prospective clinical trial was undertaken at the infertility division of a university teaching hospital. Forty-one CC responders were selected and their hormonal and clinical features were determined. Forty-one CC-resistant PCOD women were also selected and clinical features; metabolic and hormonal profiles before and after treatment with MTF 1500 mg/day for 6-8 weeks were evaluated. Women who failed to conceive were treated by CC while continuing to take MTF.

RESULTS

CC responders had higher insulin levels while non-responders were hyperinsulinemic. Menstrual irregularities improved in 30%. Mean+/-S.D. area under curve of insulin decreased from 297.58+/-191.33 to 206+/-0.1 mIU/ml per min (P=0.005). Only 39.39% ovulated and 24.24% conceived.

CONCLUSION

PCOD is associated with insulin resistance (IR) particularly in CC-resistant women. Insulin resistance and androgen levels are significantly higher in obese patients. MTF therapy improved hyperandrogenemia, IR, and pregnancy rate.

Metformin directly inhibits androgen production in human thecal cells

OBJECTIVE

To examine the direct effect of metformin on thecal cell androgen production.

SETTING

Basic science research laboratory, University of Texas Southwestern, Dallas, Texas.

INTERVENTION(S)

Human ovarian theca-like tumor cells were treated with various concentrations of metformin in the presence and absence of forskolin for 48 hours.

MAIN OUTCOME MEASURE(S)

Media were collected, and radioimmunoassay (RIA) for progesterone, 17 alpha-hydroxyprogesterone (17OHP), androstenedione, and testosterone was performed. The effect of metformin on the expression of various enzymes involved in theca cell steroidogenesis was examined.

RESULT(S)

Metformin (50 microM and 200 microM) significantly inhibited androstenedione production from both forskolin-stimulated and unstimulated theca cells. Testosterone production was also significantly inhibited in forskolin-treated cells in the presence of 200 microM of metformin-treated compared with forskolin-only-treated cells. Western blot analysis revealed that metformin significantly inhibited the expression of steroidogenic acute regulatory (StAR) protein and 17 alpha-hydroxylase (CYP17) expression in cells stimulated with forskolin compared with forskolin treatment alone. There was no significant change in either 3beta-hydroxysteroid dehydrogenase (3 beta HSD) or cholesterol side-chain cleavage (CYP11A1) protein expression. Northern analysis revealed a significant decrease in the expression of CYP17 mRNA in forskolin-stimulated cells treated with metformin (200 microM) compared with forskolin-only-treated cells, however, there was no significant change in steroidogenic acute regulatory protein mRNA expression.

CONCLUSION(S)

Our results suggest that metformin may have a direct effect on thecal cells' androgen production.

Use of insulin-sensitizing agents in patients with polycystic ovary syndrome

OBJECTIVE

To review the subject of polycystic ovary syndrome and the therapeutic use of insulin-sensitizing agents in patients with this endocrinopathy.

METHODS

We present background information on this disorder and summarize the pertinent published literature.

RESULTS

Polycystic ovary syndrome affects approximately 7.5% of reproductive-age women in the United States. Although specific diagnostic criteria for this condition have not been established, the presence of three major factors-chronic anovulation, hyperandrogenemia, and clinical signs of hyperandrogenism-has been proposed as essential for consideration of the diagnosis. A high ratio of serum luteinizing hormone to follicle-stimulating hormone is found in 60 to 75% of women with this syndrome. Treatment with metformin may yield heterogeneous responses in differing populations with polycystic ovary syndrome, but most studies have shown evidence of restoration of ovulatory cycling. In addition, weight loss and decreases in free and total testosterone levels have been reported. Troglitazone therapy proved somewhat less efficacious than metformin for restoring menstrual cycles and similar to metformin in producing hormonal responses. Because troglitazone is no longer available for clinical use, studies will need to be extended to other thiazolidinediones. Patients treated with another insulin sensitizer, D-chiro-inositol, have demonstrated improved insulin sensitivity, ovulatory rates, and biochemical findings.

CONCLUSION

Current evidence suggests that the use of insulin-sensitizing agents in patients with polycystic ovary syndrome not only improves their sensitivity to the effects of insulin on glucose and lipid metabolism but also ameliorates clinical and biochemical manifestations of hyperandrogenism and increases rates of ovulation. Multicenter studies with larger numbers of patients are needed.

Metformin and intervention in polycystic ovary syndrome. Endocrine Society of Australia, the Australian Diabetes Society and the Australian Paediatric Endocrine Group

Polycystic ovary syndrome (PCOS) is classically characterised by ovarian dysfunction (oligomenorrhoea, anovulation and infertility), androgen excess (hirsutism and acne), obesity, and morphological abnormalities of the ovaries (cystic enlargement and stromal expansion). More recently, insulin resistance has been found to be common in PCOS, along with an increased prevalence of other features of the "metabolic syndrome", namely glucose intolerance, type 2 diabetes mellitus, and hyperlipidaemia. Hyperinsulinaemia is likely to contribute to the disordered ovarian function and androgen excess of PCOS. Reducing insulin resistance by lifestyle modifications such as diet and exercise improves endocrine and menstrual function in PCOS. These lifestyle modifications are the best initial means of improving insulin resistance. Metformin, an oral hypoglycaemic agent that increases insulin sensitivity, has been shown to reduce serum concentrations of insulin and androgens, to reduce hirsutism, and to improve ovulation rates. The effect of metformin alone on fertility rates is unknown. Some studies suggest that metformin will reduce total body weight to a small extent, but with a predominant effect on visceral adipose reduction. The effects of metformin on lipid abnormalities, hypertension or premature vascular disease are unknown, but the relative safety, moderate cost, and efficacy in reducing insulin resistance suggest that metformin may prove to be of benefit in combating these components of the "metabolic" syndrome in PCOS. Further properly planned randomised controlled trials are required.

Thiazolidinediones but not metformin directly inhibit the steroidogenic enzymes P450c17 and 3beta -hydroxysteroid dehydrogenase

Androgen biosynthesis requires 3beta-hydroxysteroid dehydrogenase type II (3betaHSDII) and the 17alpha-hydroxylase and 17,20-lyase activities of cytochrome P450c17. Thiazolidinedione and biguanide drugs, which are used to increase insulin sensitivity in type 2 diabetes, lower serum androgen concentrations in women with polycystic ovary syndrome. However, it is unclear whether this is secondary to increased insulin sensitivity or to direct effects on steroidogenesis. To investigate potential actions of these drugs on P450c17 and 3betaHSDII, we used "humanized yeast" that express these steroidogenic enzymes in microsomal environments. The biguanide metformin had no effect on either enzyme, whereas the thiazolidinedione troglitazone inhibited 3betaHSDII (K(I) = 25.4 +/- 5.1 microm) and both activities of P450c17 (K(I) for 17alpha-hydroxylase, 8.4 +/- 0.6 microm; K(I) for 17,20-lyase, 5.3 +/- 0.7 microm). The action of troglitazone on P450c17 was competitive, but it was mainly a noncompetitive inhibitor of 3betaHSDII. The thiazolidinediones rosiglitazone and pioglitazone exerted direct but weaker inhibitory effects on both P450c17 and 3betaHSDII. These differential effects of the thiazolidinediones do not correlate with their effects on insulin sensitivity, suggesting that distinct regions of the thiazolidinedione molecule mediate these two actions. Thus, thiazolidinediones inhibit two key enzymes in human androgen synthesis contributing to their androgen-lowering effects, whereas metformin affects androgen synthesis indirectly, probably by lowering circulating insulin concentrations.