Skeletal muscle mitochondrial function in polycystic ovarian syndrome

Resting energy expenditure in women with polycystic ovary syndrome

STUDY QUESTION

Is resting energy expenditure (REE) altered in women with polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

Women with PCOS have a reduction in REE, when corrected for fat-free mass, independent of PCOS clinical phenotypes and BMI categories.

WHAT IS KNOWN ALREADY

Obesity is an important issue in women with PCOS, in terms of frequency and pathophysiological implications. It has been hypothesized that obesity may be favoured by alterations in REE, but the studies have been limited and conflicting.

STUDY DESIGN, SIZE, DURATION

This case-control study was a comparison of 266 women with PCOS and 51 healthy controls, recruited in the Verona 3P study from 2010 to 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women with PCOS diagnosed by the Rotterdam criteria, with normal thyroid function and no interfering medications, were referred to the outpatient clinic of a tertiary care centre of endocrinology and metabolism for a measurement of REE. Healthy controls were recruited in the same period and submitted to the same procedure. In all subjects, REE was measured by indirect calorimetry and serum androgens were measured by LC-MS/MS. In women with PCOS, insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp.

MAIN RESULTS AND THE ROLE OF CHANCE

REE was similar in women with PCOS and controls. However, REE corrected for fat-free mass (REE/FFM) was significantly lower in women with PCOS than in controls (31.8 ± 4.0 vs 35.4 ± 3.9 kcal/kgFFM·day, P < 0.001). REE/FFM did not differ between normal-weight, overweight, or obese women with PCOS, and each of these subgroups showed lower REE/FFM values than controls. Reduced REE/FFM values were found in each phenotype of the syndrome. In multiple regression analysis, REE/FFM was independently associated with age and PCOS status, but not with fat mass. In PCOS women, REE/FFM was independently and directly associated with ovarian follicle number.

LIMITATIONS, REASONS FOR CAUTION

Limitations of the study are the cross-sectional design, which limits the causal inference of the results, and the unavailability of precise information about lifestyle factors, which may be potential confounders. Further prospective studies are needed to establish the importance of this phenomenon in contributing to the weight excess of PCOS.

WIDER IMPLICATIONS OF THE FINDINGS

A reduction of REE could potentially favour weight gain in women with PCOS and possibly contribute to the altered metabolic profile typical of this condition, even counteracting the therapeutic strategies aimed to reduce excess body fat in these women. Nevertheless, the presence of this abnormality in both obese/overweight and normal-weight patients suggests that other factors must play a role in this phenomenon.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by academic grants to PM from the University of Verona (FUR 2010-2022). All authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Resveratrol ameliorates mitochondrial biogenesis and reproductive outcomes in women with polycystic ovary syndrome undergoing assisted reproduction: a randomized, triple-blind, placebo-controlled clinical trial

BACKGROUND

This study was designed to examine the effect of resveratrol on mitochondrial biogenesis, oxidative stress (OS), and assisted reproductive technology (ART) outcomes in individuals with polycystic ovary syndrome (PCOS).

METHODS

Fifty-six patients with PCOS were randomly assigned to receive 800 mg/day of resveratrol or placebo for 60 days. The primary outcome was OS in follicular fluid (FF). The secondary outcome involved assessing gene and protein expression related to mitochondrial biogenesis, mitochondrial DNA (mtDNA) copy number, and adenosine triphosphate (ATP) content in granulosa cells (GCs). ART outcomes were evaluated at the end of the trial.

RESULTS

Resveratrol significantly reduced the total oxidant status (TOS) and oxidative stress index (OSI) in FF (P = 0.0142 and P = 0.0039, respectively) while increasing the total antioxidant capacity (TAC) (P < 0.0009). Resveratrol consumption also led to significant increases in the expression of critical genes involved in mitochondrial biogenesis, including peroxisome proliferator-activated receptor gamma coactivator (PGC-1α) and mitochondrial transcription factor A (TFAM) (P = 0.0032 and P = 0.0003, respectively). However, the effect on nuclear respiratory factor 1 (Nrf-1) expression was not statistically significant (P = 0.0611). Resveratrol significantly affected sirtuin1 (SIRT1) and PGC-1α protein levels (P < 0.0001 and P = 0.0036, respectively). Resveratrol treatment improved the mtDNA copy number (P < 0.0001) and ATP content in GCs (P = 0.0014). Clinically, the resveratrol group exhibited higher rates of oocyte maturity (P = 0.0012) and high-quality embryos (P = 0.0013) than did the placebo group. There were no significant differences between the groups in terms of chemical or clinical pregnancy rates (P > 0.05).

CONCLUSIONS

These findings indicate that resveratrol may be a promising therapeutic agent for patients with PCOS undergoing assisted reproduction.

TRIAL REGISTRATION NUMBER

http://www.irct.ir ; IRCT20221106056417N1; 2023 February 09.

Polymorphisms of mtDNA in the D-loop region moderate the associations of BMI with HOMA-IR and HOMA-β among women with polycystic ovary syndrome: a cross-sectional study

PURPOSE

Polycystic ovary syndrome (PCOS) is one of the leading causes of infertility in women of childbearing age, and many patients with PCOS have obesity and insulin resistance (IR). Although obesity is related to an increased risk of IR, in clinical practice, PCOS patients exhibit different effects on improving insulin sensitivity after weight loss. Therefore, in the present study, we aimed to examine the moderating effect of polymorphisms of mtDNA in the D-loop region on the associations of body mass index (BMI) with the homeostasis model assessment of insulin resistance index (HOMA-IR) and pancreatic β cell function index (HOMA-β) among women with PCOS.

METHODS

Based on a cross-sectional study, women with PCOS were recruited from the Reproductive Center of the First Affiliated Hospital of Anhui Medical University from 2015 to 2018. A total of 520 women who were diagnosed with PCOS based on the revised 2003 Rotterdam criteria were included in the study. Peripheral blood was collected from these patients, followed by DNA extraction, PCR amplification, and sequencing at baseline. HOMA-IR and HOMA-β were calculated according to blood glucose-related indices. Moderating effect models were performed with BMI as an independent variable, polymorphisms of mtDNA in the D-loop region as moderators, and ln (HOMA-IR) and ln (HOMA-β) as dependent variables. To verify the stability of moderating effect, sensitivity analysis was performed with the quantitative insulin sensitivity check index (QUICKI), fasting plasma glucose/fasting insulin (G/I), and fasting insulin as dependent variables.

RESULTS

BMI was positively associated with ln (HOMA-IR) and ln (HOMA-β) (β = 0.090, p < 0.001; β = 0.059, p < 0.001, respectively), and the relationship between BMI and ln (HOMA-IR) or ln (HOMA-β) was moderated by the polymorphisms of mtDNA in the D-loop region. Compared with the respective wild-type, the variant -type of m.16217 T > C enhanced the association between BMI and HOMA-IR, while the variant-type of m.16316 A > G weakened the association. On the other hand, the variant-type of m.16316 A > G and m.16203 A > G weakened the association between BMI and HOMA-β, respectively. The results of QUICKI and fasting insulin as dependent variables were generally consistent with HOMA-IR, and the results of G/I as dependent variables were generally consistent with HOMA-β.

CONCLUSION

Polymorphisms of mtDNA in the D-loop region moderate the associations of BMI with HOMA-IR and HOMA-β among women with PCOS.

Oxidative stress and mitochondrial dysfunction of granulosa cells in polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is one of the leading causes of anovulatory infertility in women, affecting 5%-15% of women of reproductive age worldwide. The clinical manifestations of patients include ovulation disorders, amenorrhea, hirsutism, and obesity. Life-threatening diseases, such as endometrial cancer, type 2 diabetes, hyperlipidaemia, hypertension, and cardiovascular disease, can be distant complications of PCOS. PCOS has diverse etiologies and oxidative stress (OS) plays an important role. Mitochondria, as the core organelles of energy production, are the main source of reactive oxygen species (ROS). The process of follicular growth and development is extremely complex, and the granulosa cells (GCs) are inextricably linked to follicular development. The abnormal function of GCs may directly affect follicular development and alter many symptoms of PCOS. Significantly higher levels of OS markers and abnormal mitochondrial function in GCs have been found in patients with PCOS compared to healthy subjects, suggesting that increased OS is associated with PCOS progression. Therefore, the aim of this review was to summarize and discuss the findings suggesting that OS and mitochondrial dysfunction in GCs impair ovarian function and induce PCOS.

Acetate circumvents impaired metabolic switch in skeletal muscle of letrozole-induced PCOS rat model by suppression of PDK4/NLRP3

OBJECTIVES

Endocrine disorders in women of childbearing age, including polycystic ovarian syndrome (PCOS), have been linked to skeletal muscle insulin resistance with multiple post-receptor intracellular defects, disrupting metabolic flexibility. Short-chain fatty acids, such as acetate have been suggested as a metabolic modulator. However, the effects of acetate on aberrant metabolic switch in skeletal muscle of individuals with PCOS are unknown. This study therefore hypothesized that acetate would circumvent impaired metabolic switch in the skeletal muscle of a letrozole-induced PCOS rat model, probably by suppression of PDK4/NLRP3.

METHODS

Eight-wk-old female Wistar rats were assigned into three groups (n = 6), which received vehicle, letrozole (1 mg/kg), and letrozole plus acetate (200 mg/kg), respectively. The administrations were done by oral gavage for 21 d. .

RESULTS

Animals with PCOS had insulin resistance, increased testosterone, and leptin, as well as decreased adiponectin level. Additionally, the skeletal muscle was also characterized with increased lipid deposition, malondialdehyde, inflammatory mediators (nuclear factor-κB and tumor necrosis factor-α), lactate dehydrogenase, lactate/pyruvate ratio, HDAC and PDK 4 with corresponding decrease in glycogen synthesis, glutathione and NrF2. Besides, immunohistochemical evaluation showed severe expression of inflammasome and apoptosis in PCOS animals. Nonetheless, supplementation with acetate significantly attenuated these perturbations.

CONCLUSIONS

The present results demonstrate aberrant metabolic switch in the skeletal muscle of PCOS animals, which is accompanied by excessive inflammation, oxidative stress and elevated levels of histone deacetylase and PDK4. The results suggested that histone deacetylase inhibitor, acetate circumvents impaired metabolic switch in the skeletal muscle of PCOS rats by suppression of PDK4/NLRP3 inflammasome.

Genetic associations with polycystic ovary syndrome: the role of the mitochondrial genome; a systematic review and meta-analysis

Background

Polycystic ovary syndrome (PCOS) remains the most common female reproductive endocrine disorder. Genetic studies have predominantly focused on the role of the nuclear genome, while the contribution of mitochondrial genetics in PCOS remains largely unknown.

Aim

This study aims to systematically evaluate the literature regarding the associations between the mitochondrial genome and PCOS.

Methods

A literature search focused on PCOS and mitochondrial genetics was conducted on (1) MEDLINE, (2) EMBASE and (3) The Cochrane Library (CENTRAL and Cochrane Reviews). Search results were screened for eligibility, and data involving genetic variants of mitochondrial DNA (mtDNA) were extracted. Quantitative data were presented in forest plots, and where this was not possible, data were analysed in a qualitative manner. Quality of studies was assessed using the Q-Genie tool.

Results

Of the 13 812 identified studies, 15 studies were eligible for inclusion, with 8 studies suitable for meta-analysis. Women with PCOS showed higher frequencies of a 9 bp deletion, and aberrant single nucleotide polymorphisms (SNPs) in the ND5, A6 and 7 transfer RNA-encoding genes. They also showed lower frequencies of two SNPs in the D-loop of the genome. Women with PCOS also exhibited significantly lowered mtDNA copy number.

Conclusion

Women with PCOS harbour genetic variants in coding and non-coding regions of the mitochondrial genome. This may disrupt the electron transport chain and lead to oxidative stress, causing apoptosis of cells and further genetic damage. However, further studies of higher quality are required to confirm these associations.

PROSPERO registration number

CRD42021267991.

The mitochondrial profile in women with polycystic ovary syndrome: impact of exercise

Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting pre-menopausal women and involves metabolic dysregulation. Despite the high prevalence of insulin resistance, the existence of mitochondrial dysregulation and its role in the pathogenesis of PCOS is not clear. Exercise is recommended as the first-line therapy for women with PCOS. In particular, high-intensity interval training (HIIT) is known to improve metabolic health and enhance mitochondrial characteristics. In this narrative review, the existing knowledge of mitochondrial characteristics in skeletal muscle and adipose tissue of women with PCOS and the effect of exercise interventions in ameliorating metabolic and mitochondrial health in these women are discussed. Even though the evidence on mitochondrial dysfunction in PCOS is limited, some studies point to aberrant mitochondrial functions mostly in skeletal muscle, while there is very little research in adipose tissue. Although most exercise intervention studies in PCOS report improvements in metabolic health, they show diverse and inconclusive findings in relation to mitochondrial characteristics. A limitation of the current study is the lack of comprehensive mitochondrial analyses and the diversity in exercise modalities, with only one study investigating the impact of HIIT alone. Therefore, further comprehensive large-scale exercise intervention studies are required to understand the association between metabolic dysfunction and aberrant mitochondrial profile, and the molecular mechanisms underlying the exercise-induced metabolic adaptations in women with PCOS.

Non-cell autonomous mechanisms control mitochondrial gene dysregulation in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder associated with insulin resistance and impaired energy metabolism in skeletal muscle, the aetiology of which is currently unclear. Here, we mapped the gene expression profile of skeletal muscle from women with PCOS and determined if cultured primary myotubes retain the gene expression signature of PCOS in vivo. Transcriptomic analysis of vastus lateralis biopsies collected from PCOS women showed lower expression of genes associated with mitochondrial function, while the expression of genes associated with the extracellular matrix was higher compared to controls. Altered skeletal muscle mRNA expression of mitochondrial-associated genes in PCOS was associated with lower protein expression of mitochondrial complex II-V, but not complex I, with no difference in mitochondrial DNA content. Transcriptomic analysis of primary myotube cultures established from biopsies did not display any differentially expressed genes between controls and PCOS. Comparison of gene expression profiles in skeletal muscle biopsies and primary myotube cultures showed lower expression of mitochondrial and energy metabolism-related genes in vitro, irrespective of the group. Together, our results show that the altered mitochondrial-associated gene expression in skeletal muscle in PCOS is not preserved in cultured myotubes, indicating that the in vivo extracellular milieu, rather than genetic or epigenetic factors, may drive this alteration. Dysregulation of mitochondrial-associated genes in skeletal muscle by extracellular factors may contribute to the impaired energy metabolism associated with PCOS.

Mitochondrial Dysfunction and Chronic Inflammation in Polycystic Ovary Syndrome

Polycystic ovarian syndrome (PCOS) is the most common endocrine-metabolic disorder affecting a vast population worldwide; it is linked with anovulation, mitochondrial dysfunctions and hormonal disbalance. Mutations in mtDNA have been identified in PCOS patients and likely play an important role in PCOS aetiology and pathogenesis; however, their causative role in PCOS development requires further investigation. As a low-grade chronic inflammation disease, PCOS patients have permanently elevated levels of inflammatory markers (TNF-α, CRP, IL-6, IL-8, IL-18). In this review, we summarise recent data regarding the role of mtDNA mutations and mitochondrial malfunctions in PCOS pathogenesis. Furthermore, we discuss recent papers dedicated to the identification of novel biomarkers for early PCOS diagnosis. Finally, traditional and new mitochondria-targeted treatments are discussed. This review intends to emphasise the key role of oxidative stress and chronic inflammation in PCOS pathogenesis; however, the exact molecular mechanism is mostly unknown and requires further investigation.

Mitochondrial dysfunction: An emerging link in the pathophysiology of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder characterized by irregular menstrual cycles, hyperandrogenism and subfertility. Due to its complex manifestation, the pathogenic mechanism of PCOS is not well defined. Cumulative effect of altered genetic and epigenetic factors along with environmental factors may play a role in the manifestation of PCOS leading to systemic malfunction. With failure of genome-wide association study (GWAS) and other studies performed on nuclear genome to provide any clue for precise mechanism of PCOS pathogenesis, attention has been diverted to mitochondria. Mitochondrion plays an important role in cellular metabolic functions and is linked to Insulin Resistance (IR). Recently, increasing reports suggest that mitochondrial dysfunction may be a contributing factor in the pathogenesis of PCOS. Hence, in this review, we have discussed mitochondrial biology in brief and emphasizes on genetic and epigenetic aspects of mitochondrial dysfunction studied in PCOS women and PCOS-like animal models. We also highlight underlying mechanism behind mitochondrial dysfunction contributing to PCOS and its related complications such as obesity, diabetes, cardiovascular diseases, metabolic syndrome, non-alcoholic fatty liver disease (NAFLD) and cancer. Furthermore, contrasting remarks against involvement of mitochondrial dysfunction in PCOS pathophysiology have also been presented. This review enhances our understanding in relation to mitochondrial dysfunction in the etiology of PCOS and stimulates further research to explore a clear link between mitochondrial dysfunction and PCOS pathogenesis and progression. Understanding pathogenic mechanisms underlying PCOS will open new windows to develop promising therapeutic strategies against PCOS.

Molecular Mechanisms of Insulin Resistance in Polycystic Ovary Syndrome: Unraveling the Conundrum in Skeletal Muscle?

CONTEXT

Polycystic ovary syndrome (PCOS) is a common endocrine condition affecting 8% to 13% of women across the lifespan. PCOS affects reproductive, metabolic, and mental health, generating a considerable health burden. Advances in treatment of women with PCOS has been hampered by evolving diagnostic criteria and poor recognition by clinicians. This has resulted in limited clinical and basic research. In this study, we provide insights into the current and future research on the metabolic features of PCOS, specifically as they relate to PCOS-specific insulin resistance (IR), that may affect the most metabolically active tissue, skeletal muscle.

CURRENT KNOWLEDGE

PCOS is a highly heritable condition, yet it is phenotypically heterogeneous in both reproductive and metabolic features. Human studies thus far have not identified molecular mechanisms of PCOS-specific IR in skeletal muscle. However, recent research has provided new insights that implicate energy-sensing pathways regulated via epigenomic and resultant transcriptomic changes. Animal models, while in existence, have been underused in exploring molecular mechanisms of IR in PCOS and specifically in skeletal muscle.

FUTURE DIRECTIONS

Based on the latest evidence synthesis and technologies, researchers exploring molecular mechanisms of IR in PCOS, specifically in muscle, will likely need to generate new hypothesis to be tested in human and animal studies.

CONCLUSION

Investigations to elucidate the molecular mechanisms driving IR in PCOS are in their early stages, yet remarkable advances have been made in skeletal muscle. Overall, investigations have thus far created more questions than answers, which provide new opportunities to study complex endocrine conditions.

Advances in PCOS Pathogenesis and Progression-Mitochondrial Mutations and Dysfunction

Polycystic ovary syndrome (PCOS) is a common female endocrine disorder, which still remains largely unsolved in terms of etiology and pathogenesis despite important advances in our understanding of its genetic, epigenetic, or environmental factor implications. It is a heterogeneous disease, frequently associated with insulin resistance, chronic inflammation, and oxidative stress and probably accompanied with subclinical cardiovascular disease (CVD) and some malignant lesions as well, such as endometrial cancer. Discrepancies in the clinical phenotype and progression of PCOS exist between different population groups, which nuclear genetic studies have so far failed to explain. Over the last years, mitochondrial dysfunction has been increasingly recognized as an important contributor to an array of diseases. Because mitochondria are under the dual genetic control of both the mitochondrial and nuclear genomes, mutations within either DNA molecule may result in deficiency in respiratory chain function that leads to a reduced ability to produce cellular adenosine-5'-triphosphate and to an excessive production of reactive oxygen species. However, the association between variants in mitochondrial genome, mitochondrial dysfunction, and PCOS has been investigated to a lesser extent. May mutations in mitochondrial DNA (mtDNA) become an additional target of investigations on the missing PCOS heritability? Are mutations in mtDNA implicated in the initiation and progression of PCOS complications, e.g., CVDs, diabetes mellitus, cancers?

Mitochondrial respiratory capacity remains stable despite a comprehensive and sustained increase in insulin sensitivity in obese patients undergoing gastric bypass surgery

AIM

It has been proposed, but not yet demonstrated by convincing evidence in published articles, that insulin resistance and mitochondrial respiratory function are causally related physiological phenomena. Here, we tested the prediction that weight loss-induced increase in insulin sensitivity will correlate with a corresponding change in mitochondrial respiratory capacity over the same time period.

METHODS

Insulin sensitivity was evaluated using the hyperinsulinaemic-euglycaemic clamp technique, and skeletal muscle mitochondrial respiratory capacity was evaluated by high-resolution respirometry in 26 patients with obesity. Each experiment was performed ~2 months and 1-2 weeks before, and ~4 and ~19 months after Roux-en-Y gastric bypass (RYGB) surgery.

RESULTS

A substantial weight loss was observed in all patients, and insulin sensitivity increased in all patients over the 21-months time period of the study. In contrast, skeletal muscle mitochondrial respiratory capacity, intrinsic mitochondrial respiratory capacity and mitochondrial content remained unchanged over the same time period.

CONCLUSION

Among obese patients with and without type 2 diabetes undergoing RYGB surgery, intrinsic mitochondrial respiratory capacity in skeletal muscle is not correlated with insulin sensitivity before or after the surgical intervention. Mitochondrial respiratory function may not be germane to the pathophysiology and/or aetiology of obesity and/or type 2 diabetes.

Impact of mitochondrial DNA copy number and displacement loop alterations on polycystic ovary syndrome risk in south Indian women

Sequencing of mitochondrial displacement-loop (D-loop) of polycystic ovary syndrome (PCOS) patients and (n=118) and controls (n=114) of south Indian origin showed significant association of D310 (P=0.042) and A189G (P=0.018) SNPs with PCOS. qRT-PCR analysis revealed significantly diminished mtDNA copy number in PCOS patients compared to controls (P=0.038). Furthermore, mtDNA copy number was significantly lower in PCOS cases carrying D310 and 189G alleles when compared to non-carriers (P=0.001 and 0.006 respectively). The D310 carriers also showed significantly elevated LH/FSH ratio (P=0.026). In conclusion, mtDNA D-loop and copy number alterations may constitute an inheritable risk factor for PCOS in south Indian women.

Altered cardiorespiratory response to exercise in overweight and obese women with polycystic ovary syndrome

In polycystic ovary syndrome (PCOS), cardiovascular risk is increased. Peak O2 uptake (V˙O2peak) predicts the cardiovascular risk. We were the first to examine the contribution of systemic O2 delivery and arteriovenous O2 difference to V˙O2peak in overweight and obese women with PCOS. Fifteen overweight or obese PCOS women and 15 age-, anthropometry-, and physical activity-matched control women performed a maximal incremental cycling exercise test. Alveolar gas exchange (volume turbine and mass spectrometry), arterial O2 saturation (pulse oximetry), and cardiac output (CO) (impedance cardiography) were monitored. Hb concentration was determined. Arterial O2 content and arteriovenous O2 difference (C(a-v)O2) (Fick equation) were calculated. Insulin resistance was evaluated by homeostasis model assessment (HOMA-IR). PCOS women had lower V˙O2peak than controls (40 ± 6 vs. 46 ± 5 mL/min/kg fat-free mass [FFM], P = 0.011). Arterial O2 content was similarly maintained in the groups throughout the exercise test (P > 0.05). Linear regression analysis revealed a pronounced response of CO to increasing V˙O2 in PCOS women during the exercise test: A ∆CO/∆V˙O2 slope was steeper in PCOS women than in controls (β = 5.84 vs. β = 5.21, P = 0.004). Eventually, the groups attained similar peak CO and peak CO scaled to FFM (P > 0.05). Instead, C(a-v)O2 at peak exercise was lower in PCOS women than in controls (13.2 ± 1.6 vs. 14.8 ± 2.4 mL O2/100 mL blood, P = 0.044). HOMA-IR was similar in the groups (P > 0.05). The altered cardiorespiratory responses to exercise in overweight and obese PCOS women indicate that PCOS per se is associated with alterations in peripheral adjustments to exercise rather than with limitations of systemic O2 delivery.

Defects in mitochondrial efficiency and H2O2 emissions in obese women are restored to a lean phenotype with aerobic exercise training

The notion that mitochondria contribute to obesity-induced insulin resistance is highly debated. Therefore, we determined whether obese (BMI 33 kg/m(2)), insulin-resistant women with polycystic ovary syndrome had aberrant skeletal muscle mitochondrial physiology compared with lean, insulin-sensitive women (BMI 23 kg/m(2)). Maximal whole-body and mitochondrial oxygen consumption were not different between obese and lean women. However, obese women exhibited lower mitochondrial coupling and phosphorylation efficiency and elevated mitochondrial H2O2 (mtH2O2) emissions compared with lean women. We further evaluated the impact of 12 weeks of aerobic exercise on obesity-related impairments in insulin sensitivity and mitochondrial energetics in the fasted state and after a high-fat mixed meal. Exercise training reversed obesity-related mitochondrial derangements as evidenced by enhanced mitochondrial bioenergetics efficiency and decreased mtH2O2 production. A concomitant increase in catalase antioxidant activity and decreased DNA oxidative damage indicate improved cellular redox status and a potential mechanism contributing to improved insulin sensitivity. mtH2O2 emissions were refractory to a high-fat meal at baseline, but after exercise, mtH2O2 emissions increased after the meal, which resembles previous findings in lean individuals. We demonstrate that obese women exhibit impaired mitochondrial bioenergetics in the form of decreased efficiency and impaired mtH2O2 emissions, while exercise effectively restores mitochondrial physiology toward that of lean, insulin-sensitive individuals.

Peripheral insulin resistance in obese girls with hyperandrogenism is related to oxidative phosphorylation and elevated serum free fatty acids

Hyperandrogenic syndrome (HAS) is associated with insulin resistance (IR) and type 2 diabetes. Muscle IR in type 2 diabetes is linked with defects in mitochondrial oxidative capacity. In vivo muscle mitochondrial function has not been studied in HAS, especially in youth, who are early in the disease process. Our goal was to measure muscle mitochondrial oxidative function and peripheral IR in obese youth with HAS. Obese girls without HAS [n = 22, age 15(13,17) yr, BMI Z-score 2.05 ± 0.37] and with HAS [n = 35, age 15(14,16) yr, BMI Z-score 2.18 ± 0.30] were enrolled. Mitochondrial function was assessed with (31)phosphorus MR spectroscopy before, during, and after near-maximal isometric calf exercise, and peripheral IR was assessed with an 80 mU·m(-2)·min(-1) hyperinsulinemic euglycemic clamp. Girls with HAS had higher androgens [free androgen index 7.9(6.6,15.5) vs. 3.5(3.0,4.0), P < 0.01] and more IR [glucose infusion rate 9.4(7.0, 12,2) vs. 14.5(13.2,15.8) mg·kg lean(-1)·min(-1), P < 0.01]. HAS girls also had increased markers of inflammation including CRP, platelets, and white blood cell count and higher serum free fatty acids during hyperinsulinemia. Mitochondrial oxidative phosphorylation was lower in HAS [0.11(0.06,0.19) vs. 0.18(0.12,0.23) mmol/s, P < 0.05], although other spectroscopy markers of mitochondrial function were similar between groups. In multivariate analysis of the entire cohort, IR related to androgens, oxidative phosphorylation, and free fatty acid concentrations during hyperinsulinemia. These relationships were present in just the HAS cohort as well. Obese girls with HAS have significant peripheral IR, which is related to elevated androgens and free fatty acids and decreased mitochondrial oxidative phosphorylation. These may provide future options as targets for therapeutic intervention.

Metabolic risk in PCOS: phenotype and adiposity impact

Polycystic ovary syndrome (PCOS) is a common condition in reproductive-aged women, with reproductive, cardiometabolic, and psychological features. The heterogeneity in insulin resistance, obesity, and cardiometabolic features has led to controversy on the independent contributions of PCOS status, diagnostic criteria, phenotype, and adiposity. It now appears that women with PCOS have an increased risk of insulin resistance and cardiometabolic features, which is independent of, but worsened by, adiposity and central adiposity, and is unrelated to reproductive phenotype. Obesity may be more prevalent in the more severe phenotypes, which suggests either an exacerbation of the reproductive features or a more likely diagnosis in overweight women with PCOS. Therefore, all women with PCOS should be targeted for prevention, screening, and management of cardiometabolic features.

The polycystic ovary syndrome: a position statement from the European Society of Endocrinology

Polycystic ovary syndrome (PCOS) is the most common ovarian disorder associated with androgen excess in women, which justifies the growing interest of endocrinologists. Great efforts have been made in the last 2 decades to define the syndrome. The presence of three different definitions for the diagnosis of PCOS reflects the phenotypic heterogeneity of the syndrome. Major criteria are required for the diagnosis, which in turn identifies different phenotypes according to the combination of different criteria. In addition, the relevant impact of metabolic issues, specifically insulin resistance and obesity, on the pathogenesis of PCOS, and the susceptibility to develop earlier than expected glucose intolerance states, including type 2 diabetes, has supported the notion that these aspects should be considered when defining the PCOS phenotype and planning potential therapeutic strategies in an affected subject. This paper offers a critical endocrine and European perspective on the debate on the definition of PCOS and summarises all major aspects related to aetiological factors, including early life events, potentially involved in the development of the disorder. Diagnostic tools of PCOS are also discussed, with emphasis on the laboratory evaluation of androgens and other potential biomarkers of ovarian and metabolic dysfunctions. We have also paid specific attention to the role of obesity, sleep disorders and neuropsychological aspects of PCOS and on the relevant pathogenetic aspects of cardiovascular risk factors. In addition, we have discussed how to target treatment choices based according to the phenotype and individual patient's needs. Finally, we have suggested potential areas of translational and clinical research for the future with specific emphasis on hormonal and metabolic aspects of PCOS.

Mitochondrial respiratory capacity and content are normal in young insulin-resistant obese humans

Considerable debate exists about whether alterations in mitochondrial respiratory capacity and/or content play a causal role in the development of insulin resistance during obesity. The current study was undertaken to determine whether such alterations are present during the initial stages of insulin resistance in humans. Young (∼23 years) insulin-sensitive lean and insulin-resistant obese men and women were studied. Insulin resistance was confirmed through an intravenous glucose tolerance test. Measures of mitochondrial respiratory capacity and content as well as H(2)O(2) emitting potential and the cellular redox environment were performed in permeabilized myofibers and primary myotubes prepared from vastus lateralis muscle biopsy specimens. No differences in mitochondrial respiratory function or content were observed between lean and obese subjects, despite elevations in H(2)O(2) emission rates and reductions in cellular glutathione. These findings were apparent in permeabilized myofibers as well as in primary myotubes. The results suggest that reductions in mitochondrial respiratory capacity and content are not required for the initial manifestation of peripheral insulin resistance.

Women with polycystic ovary syndrome have intrinsic insulin resistance on euglycaemic-hyperinsulaemic clamp

STUDY QUESTION

What is the prevalence of insulin resistance (IR) and the contributions of intrinsic and extrinsic IR in women diagnosed with polycystic ovary syndrome (PCOS) according to the Rotterdam criteria?

SUMMARY ANSWER

We report novel clamp data in Rotterdam diagnosed PCOS women, using World Health Organization criteria for IR showing that women with PCOS have a high prevalence of IR, strengthening the evidence for an aetiological role of IR in both National Institutes of Health (NIH) and Rotterdam diagnosed PCOS in lean and overweight women.

WHAT IS KNOWN ALREADY

PCOS is a complex endocrine condition with a significant increased risk of gestational diabetes and type 2 diabetes.

STUDY DESIGN, SIZE, DURATION

Using a cross-sectional study design, 20 overweight and 20 lean PCOS (Rotterdam criteria), 14 overweight and 19 lean body mass index (BMI)-matched control non-PCOS women underwent clinical measures of IR after a 3-month withdrawal of insulin sensitizers and the oral contraceptive pill.

MATERIALS, SETTING, METHODS

In an academic clinic setting, glucose infusion rate (GIR) on euglycaemic-hyperinsulinaemic clamp was investigated as a marker of insulin sensitivity.

MAIN RESULTS AND THE ROLE OF CHANCE

PCOS women were more IR than BMI-matched controls (main effect for BMI and PCOS; P < 0.001). IR was present in 75% of lean PCOS, 62% of overweight controls and 95% of overweight PCOS. Lean controls (mean ± SD; GIR 339 ± 76 mg min⁻¹ m⁻²) were less IR than lean PCOS (270 ± 66 mg min⁻¹ m⁻²), overweight controls (264 ± 66 mg min⁻¹ m⁻²) and overweight PCOS (175 ± 96 mg min⁻¹ m⁻²). The negative relationship between BMI and IR reflected by GIR was more marked in PCOS (y = 445.1 - 7.7x, R² = 0.42 (P < 0.0001) than controls (y = 435.5 - 4.6x, R² = 0.04 (P < 0.01)).

LIMITATIONS, REASONS FOR CAUTION

The study did not use glucose tracer techniques to completely characterize the IR, as well as the lack of matching for body composition and age.

WIDER IMPLICATIONS OF THE FINDINGS

IR is exacerbated by increased BMI, supporting intrinsic IR in PCOS. BMI impact on IR is greater in PCOS, than in controls, irrespective of visceral fat, prioritizing lifestyle intervention and the need for effective therapeutic interventions to address intrinsic IR and prevent diabetes in this high-risk population.

STUDY FUNDING/COMPETING INTEREST(S)

This investigator-initiated trial was supported by grants from the National Health & Medical Research Council (NHMRC) Grant number 606553 (H.J.T., N.K.S. and S.K.H.) as well as Monash University and The Jean Hailes Foundation. H.J.T. is an NHMRC Research Fellow. N.K.S. is supported through the Australian Government's Collaborative Research Networks (CRN) programme. A.E.J. is a Jean Hailes and NHMRC scholarship holder. The authors declare that there is no conflict of interest associated with this manuscript.

Insulin resistance and mitochondrial function in skeletal muscle

The mechanism(s) behind the decreased ability of insulin to facilitate glucose uptake in insulin sensitive tissues as seen in type 2 diabetes is not resolved. With the rapidly increasing prevalence of this disease world-wide, and the many complications that follow the disease, large resources are used in the attempt to resolve the mechanisms of insulin resistance. In this context, a dysfunction of mitochondria in the skeletal muscle has been suggested to play a pivotal role. It has been postulated that a decrease in the content of mitochondria in the skeletal muscle can explain the insulin resistance. Complementary to this also specific defects of components in the respiratory chain in the mitochondria have been suggested to play a role in insulin resistance. A key element in these mechanistic suggestions is inability to handle substrate fluxes and subsequently an accumulation of ectopic intramyocellular lipids, interfering with insulin signaling. In this review we will present the prevailing view-points and argue for the unlikelihood of this scenario being instrumental in human insulin resistance. This article is part of a Directed Issue entitled: Bioenergetic dysfunction.