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Original articles

The effect of metformin therapy on serum leptin and resistin levels in women with polycystic ovary syndrome

Allam, Nahed E.; Mohamed Maarouf, Taiseer; Mostafa, Heba

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Evidence Based Women's Health Journal: August 2014 - Volume 4 - Issue 3 - p 135-140
doi: 10.1097/01.EBX.0000440888.46582.8f
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Polycystic ovary syndrome (PCOS) affects ∼6–10% of women of reproductive age. Many women with PCOS (38–88%) are overweight or obese 1. The prevalence of obesity in PCOS patients has increased similar to that observed in the general population, which indicates that obesity in PCOS reflects environmental factors to a considerable extent 2,3. A likely explanation for the mechanisms underlying the development of obesity in women with PCOS is the combined effect of a genetic predisposition to obesity with an obesogenic environment (poor diet and reduced exercise). There is no doubt that adiposity plays a crucial role in the development and maintenance of PCOS and strongly influences the severity of both its clinical and endocrine features in many women with the condition. Recent studies suggest that some hormones may mediate some of the adverse effects of obesity on ovarian function in PCOS 4. Obesity is accompanied by insulin resistance and compensatory hyperinsulinemia, suggesting that there is interaction between insulin and leptin 5. Leptin, the product of the ob(obese) gene, is a single-chain 16-kDa protein consisting of 146 amino acid residues. Leptin is produced mainly in adipose tissues and is involved in the regulation of energy homeostasis, reproduction, insulin action, and lipid metabolism; also, leptin levels decrease in response to weight loss. There is evidence of leptin and adipokines operating as endocrine–paracrine mediators, establishing a link between energy homeostasis and reproduction 6. The major site of these novel mediators of the appetite is the central nervous system, especially the hypothalamus and the pituitary, where they affect gonadotropin-releasing hormone (GnRH), pulsatility, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) production and secretion 7,8. The relationship between leptin and reproductive function is complex and not completely understood 9. Resistin, a novel cysteine-rich protein hormone, discovered by Steppan et al. 10, is secreted in adipocytes, and specifically expressed in white adipose tissues with an anti-insulin role. Resistin is produced by white and brown adipose tissues, but has also been identified in several other tissues, including the hypothalamus, the pituitary and adrenal glands, the pancreas, the gastrointestinal tract, myocytes, spleen, white blood cells, and plasma 11. Resistin seems to be actively involved in the pathogenesis of PCOS by a local paracrine action. It may be involved in multiple linkage of the insulin signaling pathway, supporting insulin resistance and aggravating clinical manifestations of PCOS (amenorrhea, obesity, higher LH/FSH, ovarian changes, etc.) 12. It was previously known that antidiabetic treatment increased plasma levels of adiponectin and decreased plasma levels of resistin in overweight/obese women with PCOS, and therefore, it might contribute to the improvement in fertility in PCOS 13.

Metformin, a drug belonging to the biguanide class and previously used in obese patients with type 2 diabetes mellitus, has been recently proposed as a first-line treatment in obese or overweight PCOS women with hyperinsulinemia. The administration of metformin is followed by improvement in insulin sensitivity, BMI, and menstrual pattern and a decrease in androgen levels in most women under treatment 14. The study aimed to investigate the effect of metformin on leptin and resistin levels in women with PCOS.

Patients and methods

The present case–control quasi-randomized clinical study performed between January 2013 and August 2013 was conducted on 96 patients in the reproductive age group (18–35 years) attending the Al-Zahraa University Hospital outpatient clinic; none of the patients had any systemic disease that could alter insulin sensitivity such as diabetes mellitus and any other endocrinal diseases and they were not using any medication such as hormonal replacement in the preceding months that could alter insulin sensitivity, sex steroid levels, or body fat distribution. Their consent was taken to participate in this prospective case−control study, and the local ethics committee approved the study. The patients were classified into the following groups:

The PCO cases (diagnosis based on the Rotterdam consensus criteria: two of three criteria of Rotterdam ESHRE/ASRM Consensus, 2004) were classified into two groups:

Group I: obese PCO (32 cases), BMI≥30 kg/m2.

Group II: lean PCO (24 cases), BMI≤25 kg/m2.

Group III included controls, who were obese (BMI≥30 kg/m2) non-PCO patients with regular menstrual cycles and no clinical or biochemical signs of hyperandrogenism. They attended the clinic for other gynecological complaints. Patients and controls were subjected to the following examination:

  • History: present history, menstrual history, past history
  • Physical examination: general and local examination was performed; BMI of all women was calculated as BMI=body weight (kg)/height2 (m2); the waist hip ratio (WHR) was determined: the waist circumference should be measured at the midpoint between the lower margin of the last palpable rib and the top of the iliac crest, and the hip circumference should be measured around the widest portion of the buttocks, with the tape parallel to the floor.
  • Ultrasound examination (transvaginal ultrasound): all participants in the study had a two-dimensional transvaginal pelvic ultrasound scan on the same day of hormonal measurements (third day of the cycle or the day of the visit in amenorrhic patients).
  • Blood samples were obtained for a hormonal profile after overnight fasting on the third day of the menstrual cycle or the day of the first visit in anovulatory women and for women with amenorrhea for the following tests:
    • FSH and LH,
    • serum leptin was determined by enzyme-linked immunosorbant assay,
    • serum prolactin,
    • thyroid-stimulating hormone,
    • E2,
    • fasting blood glucose,
    • fasting insulin,
    • insulin resistance: the Homeostatic Model Assessment (HOMA) was used to quantify insulin resistance. HOMA for insulin resistance was calculated from the following formula:
    • testosterone,
    • dehydroepiandrosterone (DHEAS),
    • serum progesterone was taken on day 21 of the same cycle.

After the first evaluation visit, PCOS patients started their treatment with metformin at a dose of 500 mg once a day, and the dose of metformin was increased stepwise up to a 500-mg tablet three times daily for the remaining period to reduce gastrointestinal side effects. Patients were instructed to maintain a diet containing 25–30 kcal/kg body weight and moderate physical activity throughout the trial. Six months later, on the third day of menstruation, patients returned to the hospital for the same clinical and biochemical assessments of leptin and resistin levels. Data were calculated and revised, verified, and then edited on a Microsoft Excel Sheet (Microsoft Corporation New York, USA). Data were then analyzed statically using SPSS statistical package, version 17 (Statistical Package for the Social science version 17; SPSS, USA). All the statistical data were described in terms of range, mean, and SD. Comparison between different groups in the present study was performed using the Student t-test. Correlation between various variables was determined using the Pearson moment correlation coefficient (r); a probability of less than 0.05 was considered significant.


There were 32 obese PCO (obese PCOs) cases in group I, 24 lean PCO (lean PCOs) cases in group II, and 40 obese non-PCO cases in group III (control). The age of patients was comparable in all three groups. Table 1 shows a statistically significant difference in the mean and SD of the LH, FSH/LH ratio, testosterone, DHEAS and FBS between lean PCO and obese PCO (P<0.05) patients. There was a statistically significant difference in the mean and SD of the FSH/LH ratio, E2, testosterone, FI, HOMA IR, leptin, and resistin between obese PCO patients and controls (P<0.05) (Table 2). Table 3 shows a statistically significant difference in the mean and SD of the LH, FSH-LH ratio, E2, testosterone and DHEAS, FI, HOMA IR, leptin and resistin between lean PCO patients (8.06±2.02) mIU/ml and controls (5.63±0.87) mIU/ml with P-value less than 0.05. Table 4 showed a decrease in the BMI after metformin treatment in both the obese PCO and the control groups (P<0.05). The decrease in the WHR after metformin treatment was significant only in the obese PCO group (P<0.05) as shown in Table 5. The decrease in the mean and SD of leptin after metformin treatment (9.33±2.26) pg/ml was highly significant (P<0.05) in the obese PCO group as shown in Table 6. The decrease in the mean and SD of resistin before and after metformin intake was not significant in all three groups as shown in Table 7. As shown in Table 8, there was a positive correlation between leptin and BMI, which was statistically significant in both the obese PCO (r=0.523, P <0.05) and the lean groups (r=0.655, P<0.05), whereas NS in the control group. Also, it is shown that there is no correlation between leptin and IR in any of the three groups. Table 9 shows a positive correlation between resistin and IR, which is statistically significant in both obese (r=0.715, P<0.05) and lean PCO groups (r=0.08, P<0.01), respectively, whereas NS in the control group.

Table 1:
A comparison between lean and obese PCO groups in laboratory measures
Table 2:
A comparison between the obese PCO group and the control group regarding laboratory measures
Table 3:
A comparison between the lean PCO group and the control group regarding laboratory measures
Table 4:
BMI before and after metformin therapy in the three groups
Table 5:
WHR before and after metformin therapy in the three groups
Table 6:
Leptin before and after metformin intake in the three groups
Table 7:
Resistin before and after metformin treatment in the three groups
Table 8:
Correlation between leptin with BMI and HOMA IR in the obese PCO group and the control group
Table 9:
Correlation between resistin with BMI and HOMA IR in the obese PCO group and the lean PCO group


After the discovery of the leptin hormone in 1994 and resistin in 2001, it has been confirmed that adipose tissue not only regulates energy metabolism in our body, it also releases many biological molecules collectively referred to as adipo(cyto)kines, which contribute to peripheral insulin sensitivity. The role of adipokines in the pathogenesis of the important features of PCOS, such as insulin resistance and central obesity, has attracted much attention. Studies are proceeding on the effect and benefit of drugs used in the treatment of this syndrome with regard to reducing insulin resistance 9.

This study was designed to determine the effect of metformin therapy on fasting serum leptin and resistin levels in women with polycystic ovarian syndrome in relation to their BMI and WHR. Findings from the current research show that the leptin level is significantly higher in PCO patients than in healthy controls, indicating that leptin is higher in PCO than in non-PCO patients, independent of BMI.

One factor that directly influences circulating leptin levels is obesity and more specifically BMI. It has been observed as described by Jéquier and Tappy 15 and Kowalska et al.16 that leptin levels are higher in obese individuals, correlating with their BMI; they have found significant correlation between BMI and leptin concentrations, which was only proved in the group of obese and overweight women (BMI>25). Other authors have failed to show any difference among PCOS and healthy women with regard to the leptin level 17,18. Higher leptin levels may play a role in the pathophysiology of PCOS. It has a dual effect on reproduction. The positive effect of leptin is its role as a trigger of puberty on the hypothalamic–pituitary axis by stimulating estrogen secretion. The negative impact of leptin, under conditions such as hyperleptinemia, is the inhibition of the ovarian response to gonadotrophin stimulation 19.

Most authors confirmed increased concentrations of leptin in the blood of PCOS patients, but at the same time, they emphasize a lack of explicit evidence for its role in the pathogenesis of this disease 20,21. Marciniak et al. 22, suggested that hyperleptinemia in PCOS does not depend on increased adipose tissue mass or insulin resistance only. Pusalkar et al. 23, reported that irrespective of the obesity status, leptin levels were significantly higher in PCOS women as compared with their control counterparts. However, BMI and/or obesity do not seem to be the only factors that contribute towards this increase in hormone levels in PCOS 22. However, Panidis et al. 24noticed that patients with PCOS and insulin resistance have considerably higher leptin concentrations, which means that leptin may play a role in the etiopathogenesis of this syndrome. These divergent results could be explained by differences in the age, anthropometric indices of groups, or the severity of the disease.

In the present study, the PCOS groups showed higher insulin levels, HOMA IR, and elevated testosterone than the healthy controls. In other words, peripheral (hepatic and skeletal muscle) insulin sensitivity and pancreatic β-cell function are improved by leptin action in these sites. Also, insulin stimulates both leptin biosynthesis and secretion from adipose tissues, creating an endocrine adipoinsular feedback loop called the ‘adipoinsular axis’ 25.

In the present study, treatment with metformin decreased leptin significantly in the obese PCO group and healthy controls. Kowalska et al. 16 also proved the efficiency of metformin therapy in PCOS patients. They noticed that metformin causes significant decrease in the concentrations of leptin in obese PCOS patients. However, Marciniak et al.22 observed that therapy with this agent led to a decrease in leptin concentrations mainly in nonobese women, as it does not affect leptin concentrations in women with PCOS and those with BMI higher than 25. It had been said that the leptin concentration is closely related to the body fat mass, but still the reduction in leptin levels cannot be fully explained by the reduction in BMI, because metformin was found to reduce leptin levels even in normal weight healthy individuals 16.

Resistin is an adipokine thought to be released in large amounts from macrophages and from human fatty tissue 16. In the present study, resistin levels were higher in the PCOS groups compared with healthy controls, and this difference was statistically significant. The elevated resistin levels are believed to be closely related to the development of IR in PCOS 12,26. Wang et al.27 found that the serum resistin level was higher in PCOS patients with IR than in non-IR women, but the difference was not statistically significant. However, Seow et al.28 found similar serum levels of resistin in PCOS (lean and obese) and controls. However, they determined that resistin mRNA expression in adipocytes was two-fold higher in the group of patients with PCOS than in the control group. This discrepancy of results may be explained by confounding factors, such as the body weight, the fat mass, the age, and the hormonal status. In the light of this finding, they suggested that resistin might exert a local paracrine effect in obesity and insulin resistance in PCOS. The Tarkun et al. 29 study could not determine any difference between BMI-matched PCOS patients and control groups in terms of serum resistin levels.

The present study found that, after administration of metformin, there was decrease in the resistin level, but it was a nonsignificant decrease in all groups patients. Steiner et al.30 investigated the effect of metformin treatment on resistin levels in patients with PCOS. They showed no changes in resistin levels and concluded that resistin determination does not provide a valuable monitor for insulin resistance and metabolic syndrome in the PCO patient population.

In the present study, the comparison of WHR between groups indicated that metformin decreases the WHR of PCO, but does so more markedly in the obese PCO group, indicating that metformin acts better on the WHR of obese PCO than obese non-PCO cases. Findings in others trials found evidence that metformin may enhance the degree of visceral fat loss, decreasing WHR, and also decreasing cardiovascular risk factors when taken concomitantly with a hypocaloric diet 5,28. In this study, the difference in the decrease between obese PCO cases and controls with regard to BMI indicated that metformin reduces BMI of obese PCO cases more than that of obese non-PCO cases. In agreement with this study, Agarwal et al.31 noted that metformin significantly reduced weight and waist circumference.

We concluded that metformin decreased leptin significantly in the obese PCO group, but there was no decrease in the resistin level except for a nonsignificant decrease in the obese PCO group. Also, metformin therapy decreased WHR and BMI significantly in the obese PCO group. The effect of leptin and resistin in the pathogenesis of PCOS may occur by ways other than the simple concentration of these hormones in circulation, particularly as leptin inserts its endocrine effects mostly through modulating insulin levels.


Conflicts of interest

There are conflicts of interest.


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homeostatic model assessment; leptin; polycystic ovary syndrome; resistin; waist hip ratio

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