Metformin and Insulin Resistance: A Review of the Underlying Mechanisms behind Changes in GLUT4-Mediated Glucose Transport.

Metformin is the most commonly used treatment to increase insulin sensitivity in insulin-resistant (IR) conditions such as diabetes, prediabetes, polycystic ovary syndrome, and obesity. There is a well-documented correlation between glucose transporter 4 (GLUT4) expression and the level of IR. Therefore, the observed increase in peripheral glucose utilization after metformin treatment most likely comes from the induction of GLUT4 expression and its increased translocation to the plasma membrane. However, the mechanisms behind this effect and the critical metformin targets are still largely undefined. The present review explores the evidence for the crucial role of changes in the expression and activation of insulin signaling pathway mediators, AMPK, several GLUT4 translocation mediators, and the effect of posttranscriptional modifications based on previously published preclinical and clinical models of metformin's mode of action in animal and human studies. Our aim is to provide a comprehensive review of the studies in this field in order to shed some light on the complex interactions between metformin action, GLUT4 expression, GLUT4 translocation, and the observed increase in peripheral insulin sensitivity.

Glucose transporter 4 mRNA expression in subcutaneous adipose tissue of women with PCOS remains unchanged despite metformin withdrawal: is there a cellular metabolic treatment legacy effect?

PURPOSE: Metformin induces GLUT-4 mRNA expression in insulin target tissues in PCOS. It is unclear how long this impact is sustained after withdrawal of metformin. We aimed to compare the effect of metformin withdrawal on GLUT-4 mRNA expression in subcutaneous adipose tissue after prior short (ST, 1 year, N = 11) and long term (LT, at least 3 years, N = 13) treatment in obese PCOS women. METHODS: At baseline and 6 months after withdrawal, biopsy of subcutaneous adipose tissue followed by quantitative PCR analysis was performed to determine GLUT-4 mRNA expression. RESULTS: We found no time/effect differences in GLUT-4 mRNA expression in ST (2-dCt at baseline 0.42 (0.16-0.48) vs 2-dCt after 6 months 0.31 (0.22-0.56), p = 0.594) and no time/effect difference in LT group (2-dCt at baseline 0.24 (0.14-0.39) vs 2-dCt after 6 months 0.25 (0.20-0.38), p = 0.382). There was also no difference in GLUT-4 mRNA expression between both groups at baseline and after 6 months. CONCLUSIONS: In summary, 6 months after metformin withdrawal, GLUT-4 mRNA expression in subcutaneous adipose tissue remained stable, regardless of the prior treatment duration.

Effects of metformin withdrawal after long and short term treatment in PCOS: observational longitudinal study.

BACKGROUND: Metformin plays a consolidated role in the management of polycystic ovary syndrome (PCOS). However, there is no clear answer on how long we should treat and on how long its beneficial impact sustain after we stop treatment. We compared the effects of metformin withdrawal after long-term (LT) and short term (ST) treatment in PCOS women that had previously well responded to metformin. METHODS: We conducted observational longitudinal study including 44 PCOS women (31 (28-36) years and BMI 32.5 (27.7-34.9) kg/m2) that were followed for 6 months after metformin withdrawal. Prior inclusion, ST group had been treated with metformin on average for 1.03 ± 0.13 year, LT group for 5.07 ± 2.52 years. We followed anthropometric, metabolic, reproductive parameters and eating behavior as assessed by TFEQ-R18. RESULTS: After metformin withdrawal, ST group gained significant amount of weight (from 92 (75.5-107.3) kg to 96 (76-116) kg; p = 0.019). Weight tended to increase also in LT users (from 87 (75-103) to 87 (73-105) kg; p = 0.058). More women in LT group maintained stable weight (27% in LT group vs 15% in ST group). Eating behavior deteriorated in both groups. Withdrawal of metformin resulted in a decrease of menstrual frequency (6 (6-6) to 6 (4-6) menstrual bleeds per 6 months; p = 0.027) and in borderline increase of androstenedione (6.4 (4.6-7.6) to 7.8 (4.8-9.6) nmol/L; p = 0.053) in LT group. Waist circumference, HOMA and glucose homeostasis remained stable in both groups. There were no differences between groups at 6-month follow up. CONCLUSION: Collectively, present study implies some metabolic and endocrine treatment legacy in both groups as well as some group-specific deteriorations in clinical parameters 6 months after metformin withdrawal. TRIAL REGISTRATION: The study is registered at Clinical Trials with reference No. NCT04566718.

Long-term efficacy of metformin in overweight-obese PCOS: longitudinal follow-up of retrospective cohort.

OBJECTIVE: Long-term efficacy of metformin in polycystic ovarian syndrome (PCOS) apart from in those with impaired glucose tolerance or diabetes remains unproven. We aimed to evaluate the impact of metformin in overweight-obese patients with PCOS and normal baseline glycemic homeostasis. METHODS: A 10-year longitudinal follow-up of a retrospective cohort comprising 159 patients with PCOS defined by Rotterdam criteria, BMI ≥25 kg/m2 and normal initial glucose homeostasis (age 28.4 ± 6.4 years, BMI 34.9 ± 6.6 kg/m2) that had been receiving metformin 1000 mg BID. Collection data contained 6085 time-points including anthropometric, hormonal and metabolic parameters. RESULTS: After the first year body mass (BM) decreased for 3.9 ± 6.8 kg (P < 0.001) and remained stable during the following 3 years. Menstrual frequency (MF) increased to 3.0 ± 3.9 bleeds/year (P < 0.001) after first year to over 11 bleeds/year in the following years. The total testosterone and androstenedione decreased to 15.4 ± 47.9% and 11.3 ± 46.4% within first year, with further decrease in total testosterone and androstenedione to 37.8 ± 61.8 and 24.8 ± 40.5% at the fifth year of the follow-up. The total conversion rate to prediabetes and diabetes was extremely low throughout observation period. Less than 25% of patients continued with metformin for more than 5 years with further dropout to only 6% on metformin therapy at the tenth year of follow-up. CONCLUSIONS: Long-term metformin treatment of overweight-obese women with PCOS and normal baseline glycemic homeostasis resulted in reduction and stabilization of BM, improvements of MF and androgen profile and low conversion rate to diabetes.

SLC6A4 5HTTLPR Polymorphism Affects Insulin Secretion in Patients with Polycystic Ovary Syndrome.

PURPOSE: To investigate in a pilot study of genetic polymorphisms in serotonin system influencing basal- and glucose-stimulated insulin secretion in women with polycystic ovary syndrome (PCOS). METHODS: A cross-sectional study included 65 female patients with PCOS followed up at the endocrine outpatient clinic of the University Medical Center Ljubljana and a control group of 94 young healthy female blood donors. Oral glucose tolerance test was performed only in PCOS patients and basal- and glucose-stimulated blood glucose and insulin levels were measured. All the subjects were genotyped for 5HTR1A rs6295, 5HTR1B rs13212041, and SLC6A4 5HTTLPR polymorphisms in the serotonin system. RESULTS: Genotype distributions were in accordance with the Hardy-Weinberg equilibrium (HWE), except for 5HTR1A rs6295 in healthy controls and 5HTR1B rs13212041 in PCOS patients that were not consistent with HWE. SLC6A4 5HTTLPR polymorphism was significantly associated with insulin secretion (p = 0.030) and with the area under the curve of insulin blood levels during OGTT (p = 0.021). None of the investigated polymorphisms was significantly associated with basal- or glucose-stimulated blood glucose levels at any point in time during OGTT or with the basal insulin concentration. CONCLUSIONS: Serotonin system may play a role in glucose-stimulated insulin secretion in patients with insulin resistance (IR) and decreased insulin sensitivity. Further studies are needed to conclude whether the observed effect is characteristic for PCOS-related metabolic disturbances or for the identified mutation in different high metabolic risk populations.

Short-term effectiveness of low dose liraglutide in combination with metformin versus high dose liraglutide alone in treatment of obese PCOS: randomized trial.

BACKGROUND: Liraglutide 3 mg was recently approved as an anti-obesity drug. Metformin is weight neutral, yet it could enhance the therapeutic index of GLP-1 agonist. We compared weight-lowering potential of liraglutide 1.2 mg in combination with metformin to liraglutide 3 mg monotherapy in obese PCOS. METHODS: Thirty obese women with PCOS (aged 33.1 ± 6.1 years, BMI 38.3 ± 5.4 kg/m2) were randomized to combination (COMBO) of metformin (MET) 1000 mg BID and liraglutide 1.2 mg QD (N = 15) or liraglutide 3 mg (LIRA3) QD alone (N = 15) for 12 weeks. The primary outcome was change in anthropometric measures of obesity. RESULTS: Both treatments led to significant weight loss (-3.6 ± 2.5 kg, p = 0.002 in COMBO vs -6.3 ± 3.7 kg, p = 0.001 in LIRA3). BMI and waist circumference reduction in LIRA3 was greater than in COMBO (-2.2 ± 1.3 vs -1.3 ± 0.9 kg/m2, p = 0.05 and -4.2 ± 3.4 vs -2.2 ± 6.2 cm, p = 0.014, respectively). Both interventions resulted in a significant decrease of post-OGTT glucose levels. COMBO significantly reduced total testosterone and was associated with less nausea. CONCLUSIONS: Short-term interventions with COMBO and LIRA3 both led to significant improvement of measures of obesity in obese PCOS, LIRA3 being superior to COMBO. However, COMBO further improved androgen profile beyond weight reduction and was associated with better tolerability. TRIAL REGISTRATION: The study was retrospectively registered with ClinicalTrials.gov ( NCT02909933 ) on 16th of September 2016.

SORCS1 polymorphism and insulin secretion in obese women with polycystic ovary syndrome.

We investigated the influence of SORCS1 polymorphisms on insulin secretion in obese women with PCOS. Metabolic status was recorded in 50 clinically well characterized PCOS patients. Oral glucose tolerance test was performed and laboratory parameters of insulin resistance measured. All patients were genotyped for SORCS1 rs1358030, rs1416406 and rs11192966 polymorphisms. Statistical analysis was performed using the Mann-Whitney test. SORCS1 rs1416406 significantly influenced stimulated glucose plasma levels (p = 0.006) and increased glucose stimulated insulin secretion (p = 0.034). None of the polymorphisms influenced insulin resistance as measured by homeostatic model assessment. We report for the first time the relevance of SORCS1 polymorphisms for glycemic control and glucose stimulated insulin secretion in obese women with PCOS.

A 12-week treatment with the long-acting glucagon-like peptide 1 receptor agonist liraglutide leads to significant weight loss in a subset of obese women with newly diagnosed polycystic ovary syndrome.

OBJECTIVE: The long-acting glucagon-like peptide 1 receptor agonist liraglutide is linked to progressive and sustained weight loss in obese people with diabetes. However, its efficacy and safety in women with polycystic ovary syndrome (PCOS) has not yet been addressed. DESIGN: Thirty-two obese women (aged 27.6±7.2 years, BMI 39.5±6.2 kg/m(2)) with newly diagnosed PCOS were randomized to receive either liraglutide 1.2 mg QD sc (n=17) or metformin 1000 mg BID po (n=15) for 12 weeks; 28 patients completed the study (14 on liraglutide and 14 on metformin). The main outcome was change in body weight. RESULTS: Intention-to-treat analysis showed significant BMI (-0.98 kg/m(2); p<0.001), body weight (-2.52 kg; p<0.001), waist circumference (-3.38 cm; p<0.001) and whole-body fat mass (-1.26%; p<0.001) reduction in both treatment arms without significant differences between therapeutic groups. However, in a subgroup of patients (n=9) with insulin resistance (HOMA(IR) >2), severe obesity and higher odds ratio for the metabolic syndrome (OR=3.9), the patients fared much better with liraglutide than with metformin (mean BMI decreased 2.13 kg/m(2) vs. 0.62 kg/m(2), respectively). CONCLUSIONS: Short-term liraglutide treatment was associated with significant weight loss in a subset of obese patients with newly diagnosed PCOS and a higher metabolic risk profile.

Short-term intervention with liraglutide improved eating behavior in obese women with polycystic ovary syndrome.

AIM: Glucagon-like peptide 1 receptor agonists (GLP-1 RA) stimulate satiety leading to reductions in food intake and body weight. The effects of long- acting GLP-1 RA liraglutide on eating behavior of women with PCOS have not been investigated yet. METHODS: Thirty-six obese women with PCOS (mean ± SD, aged 31.2 ± 7.8 years, with BMI 38.7 ± 0.1 kg/m(2)), pretreated with metformin (1000 mg BID) were switched to liraglutide 1.2 mg QD sc for 12 weeks. Adiposity parameters and eating behavior as assessed by Three-Factor Eating Questionnaire (TFEQ-R18) were examined at baseline and after 12 weeks. RESULTS: Subjects treated with liraglutide lost on average 3.8 ± 0.1 kg (p < 0.001). Significant reductions of waist circumference and visceral adipose tissue (VAT) mass, volume and area were demonstrated from liraglutide induction to the end of the study. TFEQ-R18 scores were significantly different pre- and post-liraglutide intervention. After treatment with liraglutide the uncontrolled eating (UE) score decreased from 36.8 ± 24.5 to 19.6 ± 18.4 (p < 0.001) and emotional eating (EE) score decreased from 49.9 ± 33.3 to 28.5 ± 26.9 (p < 0.001). Scores for cognitive restraint (CR) were not changed. CONCLUSIONS: Short-term liraglutide treatment was associated with weight loss and significantly improved eating behavior in obese women with PCOS.

Short-term combined treatment with liraglutide and metformin leads to significant weight loss in obese women with polycystic ovary syndrome and previous poor response to metformin.

OBJECTIVE: The effect of metformin on weight reduction in polycystic ovary syndrome (PCOS) is often unsatisfactory. In this study, we investigated the potential add-on effect of treatment with the glucagon-like peptide-1 receptor agonist liraglutide on weight loss in obese nondiabetic women with PCOS who had lost <5% body weight during pretreatment with metformin. METHODS: A total of 40 obese women with PCOS, who had been pretreated with metformin for at least 6 months, participated in a 12-week open-label, prospective study. They were randomized to one of three treatment arms: metformin (MET) arm 1000 mg BID, liraglutide (LIRA) arm 1.2 mg QD s.c., or combined MET 1000 mg BID and LIRA (COMBI) 1.2 mg QD s.c. Lifestyle intervention was not actively promoted. The primary outcome was change in body weight. RESULTS: Thirty six patients (aged 31.3 ± 7.1 years, BMI 37.1 ± 4.6 kg/m²) completed the study: 14 on MET, 11 on LIRA, and 11 on combined treatment. COMBI therapy was superior to LIRA and MET monotherapy in reducing weight, BMI, and waist circumference. Subjects treated with COMBI lost on average 6.5 ± 2.8 kg compared with a 3.8 ± 3.7 kg loss in the LIRA group and a 1.2 ± 1.4 kg loss in the MET group (P<0.001). The extent of weight loss was stratified: a total of 38% of subjects were high responders who lost ≥5% body weight, 22% of them in the COMBI arm compared with 16 and 0% in the LIRA and MET arm respectively. BMI decreased by 2.4 ± 1.0 in the COMBI arm compared with 1.3 ± 1.3 in LIRA and 0.5 ± 0.5 in the MET arm (P<0.001). Waist circumference also decreased by 5.5 ± 3.8 cm in the COMBI arm compared with 3.2 ± 2.9 cm in LIRA and 1.6 ± 2.9 cm in the MET arm (P=0.029). Subjects treated with liraglutide experienced more nausea than those treated with metformin, but severity of nausea decreased over time and did not correlate with weight loss. CONCLUSIONS: Short-term combined treatment with liraglutide and metformin was associated with significant weight loss and decrease in waist circumference in obese women with PCOS who had previously been poor responders regarding weight reduction on metformin monotherapy.