Normal metabolic flexibility despite insulin resistance women with polycystic ovary syndrome

The Role of Glp-1 Receptor Agonists in Insulin Resistance with Concomitant Obesity Treatment in Polycystic Ovary Syndrome

Insulin resistance is documented in clamp studies in 75% of women with polycystic ovary syndrome (PCOS). Although it is not included in the diagnostic criteria of PCOS, there is a crucial role of this metabolic impairment, which along with hormonal abnormalities, increase each other in a vicious circle of PCOS pathogenesis. Insulin resistance in this group of patients results from defects at the molecular level, including impaired insulin receptor-related signaling pathways enhanced by obesity and its features: Excess visceral fat, chronic inflammation, and reactive oxygen species. While lifestyle intervention has a first-line role in the prevention and management of excess weight in PCOS, the role of anti-obesity pharmacological agents in achieving and maintaining weight loss is being increasingly recognized. Glucagon-like peptide-1 receptor agonists (GLP1-RAs) not only act by reducing body weight but also can affect the mechanisms involved in insulin resistance, like an increasing expression of glucose transporters in insulin-dependent tissues, decreasing inflammation, reducing oxidative stress, and modulating lipid metabolism. They also tend to improve fertility either by increasing LH surge in hypothalamus-pituitary inhibition due to estrogen excess connected with obesity or decreasing too high LH levels accompanying hyperinsulinemia. GLP1-RAs seem promising for effective treatment of obese PCOS patients, acting on one of the primary causes of PCOS at the molecular level.

Characterizing skeletal muscle dysfunction in women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine condition affecting women. It has traditionally been viewed as a primarily reproductive disorder; however, it is increasingly recognized as a lifelong metabolic disease. Women with PCOS are at increased risk of insulin resistance (IR), type 2 diabetes mellitus, non-alcoholic fatty liver disease and cardiovascular disease. Although not currently a diagnostic criterion, IR is a cardinal pathophysiological feature and highly prevalent in women with PCOS. Androgens play a bidirectional role in the pathogenesis of IR, and there is a complex interplay between IR and androgen excess in women with PCOS. Skeletal muscle has a key role in maintaining metabolic homeostasis and is also a metabolic target organ of androgen action. Skeletal muscle is the organ responsible for the majority of insulin-mediated glucose disposal. There is growing interest in the relationship between skeletal muscle, androgen excess and mitochondrial dysfunction in the pathogenesis of metabolic disease in PCOS. Molecular mechanisms underpinning defects in skeletal muscle dysfunction in PCOS remain to be elucidated, but may represent promising targets for future therapeutic intervention. In this review, we aim to explore the role of skeletal muscle in metabolism, focusing particularly on perturbations in skeletal muscle specific to PCOS as observed in recent molecular and in vivo human studies. We review the possible role of androgens in the pathophysiology of skeletal muscle abnormalities in PCOS, and identify knowledge gaps, areas for future research and potential therapeutic implications. Despite increasing interest in the area of skeletal muscle dysfunction in women with PCOS, significant challenges and unanswered questions remain, and going forward, novel innovative approaches will be required to dissect the underlying mechanisms.

Association Between Adipose Tissue Characteristics and Metabolic Flexibility in Humans: A Systematic Review

Adipose tissue total amount, distribution, and phenotype influence metabolic health. This may be partially mediated by the metabolic effects that these adipose tissue characteristics exert on the nearby and distant tissues. Thus, adipose tissue may influence the capacity of cells, tissues, and the organism to adapt fuel oxidation to fuel availability, i.e., their metabolic flexibility (MetF). Our aim was to systematically review the evidence for an association between adipose tissue characteristics and MetF in response to metabolic challenges in human adults. We searched in PubMed (last search on September 4, 2021) for reports that measured adipose tissue characteristics (total amount, distribution, and phenotype) and MetF in response to metabolic challenges (as a change in respiratory quotient) in humans aged 18 to <65 years. Any study design was considered, and the risk of bias was assessed with a checklist for randomized and non-randomized studies. From 880 records identified, 22 remained for the analysis, 10 of them measured MetF in response to glucose plus insulin stimulation, nine in response to dietary challenges, and four in response to other challenges. Our main findings were that: (a) MetF to glucose plus insulin stimulation seems inversely associated with adipose tissue total amount, waist circumference, and visceral adipose tissue; and (b) MetF to dietary challenges does not seem associated with adipose tissue total amount or distribution. In conclusion, evidence suggests that adipose tissue may directly or indirectly influence MetF to glucose plus insulin stimulation, an effect probably explained by skeletal muscle insulin sensitivity. Systematic Review Registration: PROSPERO [CRD42020167810].

Insulin-Mediated Substrate Use in Women With Different Phenotypes of PCOS: the Role of Androgens

CONTEXT

Few studies have explored in vivo insulin action on substrate use in women with PCOS. In particular, no data are available in women with different PCOS phenotypes.

OBJECTIVE

The aim of the study was to evaluate insulin action on glucose (Gox) and lipid (Lox) oxidation, nonoxidative glucose metabolism (Gnonox), and serum free fatty acids (FFAs) in different PCOS phenotypes.

METHODS

Participants included 187 nondiabetic women with PCOS diagnosed according to the Rotterdam criteria. Data from a historical sample of 20 healthy women were used as reference values. Whole-body substrate use data were obtained by the hyperinsulinemic euglycemic clamp associated with indirect calorimetry. Serum androgens were assessed by liquid chromatography-mass spectrometry and equilibrium dialysis.

RESULTS

During hyperinsulinemia, the increase of Gox (ΔGox), Gnonox, as well as the suppression of Lox (ΔLox) and serum FFA (Δ% FFA) were altered in each PCOS phenotype. Moreover, Gnonox and Δ% FFA were lower in women with the classic phenotype than in those with the ovulatory or the normoandrogenic phenotypes, and ΔGox was lower in women with the classic than in those with the ovulatory phenotype. In multivariable analysis fat mass and free testosterone were independent predictors of ΔGox, Gnonox, and Δ% FFA, whereas only fat mass predicted ΔLox.

CONCLUSION

In women with PCOS, regardless of phenotype, insulin-mediated substrate use is impaired. This phenomenon is greater in individuals with the classic phenotype. Free testosterone plays an independent role in insulin action abnormalities in glucose and lipid metabolism.

Metabolic inflexibility in women with polycystic ovary syndrome: a systematic review

Polycystic ovary syndrome (PCOS) is a risk factor for dysglycemia, insulin resistance, and type 2 Diabetes Mellitus (T2DM). Inefficient energy oxidation, metabolic inflexibility, is a marker of blunted metabolism. We conducted a systematic review on metabolic inflexibility in women with PCOS. We searched MEDLINE, EMBASE and Cochrane central (inception-October 2018) for studies evaluating metabolic inflexibility and reporting on changes in Respiratory Quotient (ΔRQ). We extracted data and assessed quality using The Newcastle-Ottawa Scale. We included five prospective cohort studies (461 women). Three compared PCOS women to unaffected subjects, one to women with obesity or T2DM, and one to adolescent girls; all had medium quality. Three studies showed higher metabolic inflexibility in women with PCOS (ΔRQ range 0.05-0.098) compared to unaffected subjects. Women with PCOS had similar metabolic inflexibility compared to those with T2DM (ΔRQ 0.05 ± 0.03 vs 0.06 ± 0.04, p = .98) and obesity (p = .06). Inflexibility was higher in hyperandrogenemic women with PCOS (ΔRQ 0.091 ± 0.060 vs 0.120 ± 0.010, p = .014). ΔRQ was lower in PCOS women with insulin resistance vs those with normal insulin sensitivity (0.04 ± 0.02 vs. 0.07 ± 0.04, p = .007). In conclusion, women with polycystic ovary syndrome appear to have higher metabolic inflexibility associated with hyperandrogenemia and insulin resistance.

Exercise as 'precision medicine' for insulin resistance and its progression to type 2 diabetes: a research review

Type 2 diabetes and obesity epidemics are in effect in the United States and the two pathologies are linked. In accordance with the growing appreciation that ‘exercise is medicine,’ it is intuitive to suggest that exercise can play an important role in the prevention and/or treatment of these conditions. However, if exercise is to truly be considered as a viable alternative to conventional healthcare prevention/treatment strategies involving pharmaceuticals, it must be prescribed with similar scrutiny. Indeed, it seems reasonable to posit that the recent initiative calling for ‘precision medicine’ in the US standard healthcare system should also be applied in the exercise setting. In this narrative review, we consider a number of explanations that have been forwarded regarding the pathological progression to type 2 diabetes both with and without the concurrent influence of overweight/obesity. Our goal is to provide insight regarding exercise strategies that might be useful as ‘precision medicine’ to prevent/treat this disease. Although the etiology of type 2 diabetes is complex and cause/consequence characteristics of associated dysfunctions have been debated, it is well established that impaired insulin action plays a critical early role. Consequently, an exercise strategy to prevent/treat this disease should be geared toward improving insulin sensitivity both from an acute and chronic standpoint. However, research suggests that a chronic improvement in insulin sensitivity only manifests when weight loss accompanies an exercise intervention. This has resonance because ectopic fat accumulation appears to represent a central component of disease progression regardless of whether obesity is also part of the equation. The cause/consequence characteristics of the relationship between insulin resistance, pathological fat deposition and/or mobilsation, elevated and/or poorly-distributed lipid within myocytes and an impaired capacity to use lipid as fuel remains to be clarified as does the role of muscle mitochondria in the metabolic decline. Until these issues are resolved, a multidimensional exercise strategy (e.g., aerobic exercise at a range of intensities and resistance training for muscular hypertrophy) could provide the best alternative for prevention/treatment.

Metabolic inflexibility in women with PCOS is similar to women with type 2 diabetes

Background

An ability to switch between primarily oxidizing fat in the fasted state to carbohydrate in the fed state, termed metabolic flexibility, is associated with insulin sensitivity. Metabolic flexibility has been explored previously in women with polycystic ovary syndrome (PCOS), yet the independent or synergistic contributions of androgen excess and/or insulin resistance is not yet known. Therefore, the purpose of this article was to characterize metabolic flexibility in women with PCOS compared to women of normal BMI, obesity, or type 2 diabetes (T2DM).

Methods

Eighty-six weight-stable women; thirty with either PCOS (n = 30), or fifty-six with obesity (n = 12), T2DM (n = 27), or normal BMI (n = 17) underwent a hyperinsulinemic euglycemic clamp and indirect calorimetry to measure insulin sensitivity and substrate oxidation via indirect calorimetry, respectively.

Results

All analyses were adjusted for differences in age, ethnicity, and BMI between groups. Women with PCOS were less metabolically flexible compared to healthy women with obesity (p < 0.0001), normal BMI (p < 0.0001), but after controlling for glucose disposal rate, were similar to women with T2DM (p = 0.99). When dividing women with PCOS above and below the mean cutoff for insulin resistance, the insulin resistant women with PCOS had lower rates of non-oxidative glucose metabolism (p = 0.0001), higher levels of percent free testosterone (p = 0.04), a higher free androgen index (p = 0.006), more visceral adipose tissue (p = 0.02), and were less metabolically flexible (p = 0.007).

Conclusions

Women with T2DM were as metabolically inflexible as women with PCOS. When stratifying women with PCOS into those who are metabolically flexible and inflexible, the women who are inflexible display greater amounts of visceral fat and androgen excess. The inability to alter substrate use given the physiological stimulus may lead to subsequent increases in adiposity in women with PCOS thereby further worsening the insulin resistance.

Trial registration number

Clinical Trials.gov, NCT01482286. Registered 30 November 2011.

Insulin suppression of fatty acid skeletal muscle enzyme activity in postmenopausal women, and improvements in metabolic flexibility and lipoprotein lipase with aerobic exercise and weight loss

BACKGROUND

Obesity and insulin resistance are characterized by metabolic inflexibility, a condition described as an inability to switch from fat oxidation during fasting to carbohydrate oxidation during hyperinsulinemia. The purpose of this study was to examine predictors of metabolic flexibility in 103 obese (37-59% fat), sedentary (VO₂max: 19.4 ± 0.5 ml/kg/min), postmenopausal (45-76 years) women, and changes in metabolic flexibility with exercise and weight loss interventions.

METHODS

Insulin sensitivity (M) and metabolic flexibility via an 80 mU/m²/min hyperinsulinemic-euglycemic clamp, VO₂max, and body composition were measured. Metabolic flexibility was measured after 6-months aerobic training + weight loss (AEX + WL: n = 43) or weight loss (WL: n = 31). Basal and insulin-stimulated vastus lateralis skeletal muscle samples were available from a subset of these women (n = 45).

RESULTS

Metabolic flexibility correlated inversely with glucose₁₂₀ min of OGTT, fasting insulin, and the percent change (insulin-basal) in lipoprotein lipase (LPL) activity and positively with M, but not with VO₂max, total body fat, visceral fat, or subcutaneous abdominal fat. Skeletal muscle acyl-CoA synthase and citrate synthase activities decreased during hyperinsulinemia. Metabolic flexibility increased after AEX + WL but not WL, and the percent change in metabolic flexibility was inversely related to the percent change in insulin's effect on LPL activity.

CONCLUSION

Metabolic flexibility is related to insulin sensitivity and insulin's action on LPL. Furthermore, metabolic flexibility and insulin suppression of skeletal muscle LPL activity increase with AEX + WL in overweight and obese, sedentary older women.

Impaired Lipolysis, Diminished Fat Oxidation, and Metabolic Inflexibility in Obese Girls With Polycystic Ovary Syndrome

Context

Metabolic flexibility reflects the ability to switch from lipid to carbohydrate oxidation during insulin stimulation manifested in increased respiratory quotient (RQ). Little is known about adipose tissue metabolism and metabolic flexibility in adolescent girls with polycystic ovary syndrome (PCOS).

Objective

We investigated whole-body lipolysis, substrate oxidation, and metabolic flexibility in obese girls with PCOS vs obese girls without PCOS.

Patients/Design

Twenty-one obese girls with PCOS and 21 obese girls without PCOS were pair-matched for age and race. Body composition, abdominal visceral adipose tissue (VAT), sex hormones, lipid profile, and adiponectin were measured. Whole-body lipolysis ([2H5]glycerol turnover), RQ, and substrate oxidation (indirect calorimetry) were evaluated during fasting and a hyperinsulinemic-euglycemic clamp together with assessment of insulin sensitivity (IS).

Results

Despite similar body mass index and percent body fat, girls with PCOS vs girls without PCOS had lower fasting lipolysis and fat oxidation, less increase in RQ during hyperinsulinemia with impaired suppression in lipolysis and lipid oxidation, and lower IS. In multiple regression, the best predictors of metabolic flexibility were [using clinical parameters: adiponectin, fasting triglycerides, and insulin (R2 = 0.618, P < 0.0001); using research parameters: IS, VAT, and baseline RQ (R2 = 0.756, P < 0.0001)].

Conclusions

Obese girls with PCOS vs obese girls without PCOS have decreased lipid mobilization, diminished fat oxidation, and metabolic inflexibility. Whether this metabolic phenotype of adipose tissue dysfunction, which is conducive to fat accretion, plays a role in the induction and maintenance of obesity in adolescent girls with PCOS remains to be determined.

Nesfatin-1 levels and metabolic markers in polycystic ovary syndrome

Nesfatin-1 is a novel hormone synthesized in hypothalamus and several other specific organs to regulate eating habits, appetite and is thought to be related to ovarian functions. In our study, we aimed to evaluate the nesfatin-1 levels with other metabolic parameters in polycystic ovary syndrome (PCOS), a condition that is known to be related to both ovarian functions and obesity. Study subjects were chosen from the women attended to the Obstetrics and Gynecology Department of Istanbul Bilim University, Avrupa Florence Nightingale Hospital. Thirty-five healthy control subjects and 55 PCOS patients were included. Blood samples were obtained on the 3rd day of the menstrual cycle. Luteinizing hormone (LH), follicle stimulating hormone (FSH), free testosterone (FT), dehydroepiandrosterone sulfate (DHEA-S), insulin, fasting blood glucose (FBG), high density lipoprotein (HDL), low density lipoprotein (LDL), triglycerides (TG), sex hormone binding globulin (SHBG) levels were measured; homeostatic model assessment-insulin resistance (HOMA-IR) value was calculated. The nesfatin-1 levels were measured by competitive inhibition ELISA method. Due to our results, PCOS patients were having lower nesfatin-1 levels compared to the control group and this was not seemed to be related to body mass index (BMI) levels. This is an important result to be investigated in larger study groups and is related to other metabolic markers.

Effect of a low-starch/low-dairy diet on fat oxidation in overweight and obese women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) affects between 4%-18% of reproductive-aged women and is associated with increased risk of obesity and obesity-related disease. PCOS is associated with hyperinsulinemia, which is known to impair fat oxidation. Research shows that carbohydrates from dairy and starch-based foods cause greater postprandial insulin secretion than carbohydrates from nonstarchy vegetables and fruits. The purpose of this study was to determine whether an ad libitum 8-week low-starch/low-dairy diet would improve fasting and postprandial fat oxidation after a high saturated fat liquid meal (HSFLM) in overweight and obese women with PCOS. Prospective 8-week dietary intervention using a low-starch/low-dairy diet in 10 women (body mass index ≥25 kg/m(2) and ≤45 kg/m(2)) with PCOS. Indirect calorimetry was used at fasting and for 5 h following consumption of the HSFLM to determine respiratory exchange ratio (RER), macronutrient oxidation, and energy expenditure (EE) at week 0 and week 8. Participants had a reduction in body weight (-8.1 ± 1.8 kg, p < 0.05) and fasting insulin (-19.5 ± 8.9 μg/mL, p < 0.05) after dietary intervention; however, these were not significantly correlated with improved fat oxidation. There was a reduction in fasting RER, and fasting and postprandial carbohydrate oxidation, and an increase in fasting and postprandial fat oxidation after adjusting for body weight. There was also significant difference in incremental area under the curve from pre- to post-diet for fat (0.06 ± 0.00 g/kg per 5 h; p < 0.001) and carbohydrate oxidation (-0.29 ± 0.06 g/kg per 5 h; p < 0.001), but not for RER or EE. In conclusion, an 8-week low-starch/low-dairy diet increased fat oxidation in overweight and obese women with PCOS.

Metabolic Evidence of Diminished Lipid Oxidation in Women With Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS), a common female endocrinopathy, is a complex metabolic syndrome of enhanced weight gain. The goal of this pilot study was to evaluate metabolic differences between normal (n=10) and PCOS (n=10) women via breath carbon isotope ratio, urinary nitrogen and nuclear magnetic resonance (NMR)-determined serum metabolites. Breath carbon stable isotopes measured by cavity ring down spectroscopy (CRDS) indicated diminished (p<0.030) lipid use as a metabolic substrate during overnight fasting in PCOS compared to normal women. Accompanying urinary analyses showed a trending correlation (p<0.057) between overnight total nitrogen and circulating testosterone in PCOS women, alone. Serum analyzed by NMR spectroscopy following overnight, fast and at 2 h following an oral glucose tolerance test showed that a transient elevation in blood glucose levels decreased circulating levels of lipid, glucose and amino acid metabolic intermediates (acetone, 2-oxocaporate, 2-aminobutyrate, pyruvate, formate, and sarcosine) in PCOS women, whereas the 2 h glucose challenge led to increases in the same intermediates in normal women. These pilot data suggest that PCOS-related inflexibility in fasting-related switching between lipid and carbohydrate/protein utilization for carbon metabolism may contribute to enhanced weight gain.