Skeletal muscle insulin resistance: role of mitochondria and other ROS sources

The relevance of the heme oxygenase system in alleviating diabetes-related hormonal and metabolic disorders

Heme oxygenase (HO) is an enzyme that catalyzes heme degradation. HO dysfunction is linked to various pathological conditions, including diabetes. Results of animal studies indicate that HO expression and activity are downregulated in experimentally induced diabetes. This is associated with severe hormonal and metabolic disturbances. However, these pathological changes have been shown to be reversed by therapy with HO activators. In animals with experimentally induced diabetes, HO was upregulated by genetic manipulation or by pharmacological activators such as hemin and cobalt protoporphyrin. Induction of HO alleviated elevated blood glucose levels and improved insulin action, among other effects. This effect resulted from beneficial changes in the main insulin-sensitive tissues, i.e., the skeletal muscle, the liver, and the adipose tissue. The action of HO activators was due to positive alterations in pivotal signaling molecules and regulatory enzymes. Furthermore, diabetes-related oxidative and inflammatory stress was reduced due to HO induction. HO upregulation was effective in various animal models of type 1 and type 2 diabetes. These data suggest the possibility of testing HO activators as a potential tool for alleviating hormonal and metabolic disorders in people with diabetes.

Obesity, Osteoarthritis, and Myokines: Balancing Weight Management Strategies, Myokine Regulation, and Muscle Health

Obesity and osteoarthritis (OA) are increasingly prevalent conditions that are intricately linked, with each exacerbating the other's pathogenesis and worsening patient outcomes. This review explores the dual impact of obesity on OA, highlighting the role of excessive weight in aggravating joint degeneration and the limitations OA imposes on physical activity, which further perpetuates obesity. The role of muscle tissue, particularly the release of myokines during physical activity, is examined in the context of OA and obesity. Myokines such as irisin, IL-6, and myostatin are discussed for their roles in metabolic regulation, inflammation, and tissue repair, offering insights into their potential therapeutic targets. This review emphasizes the importance of supervised weight management methods in parallel with muscle rehabilitation in improving joint health and metabolic balance. The potential for myokine modulation through targeted exercise and weight loss interventions to mitigate the adverse effects of obesity and OA is also discussed, suggesting avenues for future research and therapy development to reduce the burden of these chronic conditions.

Metabolic and hepatic phenotypes in sarcopenic obesity and impact of bariatric surgery

BACKGROUND & AIMS

Sarcopenic obesity (SO) is associated with cardiometabolic disorders and steatotic liver disease and carries major health risks. We assessed the hepatic and metabolic clinical phenotype associated with SO in patients with obesity undergoing bariatric surgery (BS). We also evaluated whether weight-loss and metabolic improvement post-surgery differ between patients with and without SO.

METHODS

972 consecutive patients from a single-center BS cohort who underwent whole-body dual-energy X-ray absorptiometry (DXA) and peri-operative liver biopsy were included. SO was diagnosed using the AIM-SO score, an AI-assisted unbiased clustering algorithm based on body composition. One-year post-surgery, 862 patients were reassessed for AIM-SO score changes.

RESULTS

Pre-operatively, 207 (21.3 %) patients were diagnosed with SO. These patients had significantly higher prevalence of type-2 diabetes (T2D), arterial hypertension and obstructive sleep apnea (OSA) compared to patients without SO (all p ≤ 0.003). Patients with SO had more severe liver damage: higher grades of moderate/advanced steatosis (64.2 % vs. 47.3 %), steatohepatitis (44.4 % vs. 32.3 %) and advanced fibrosis (12.1 % vs. 6.0 %) (all p ≤ 0.01). One-year post-BS, 58.5 % of patients had remission of SO. Patients with persistent SO exhibited less weight-loss than those with SO remission (-23.8 kg vs. -29.1 kg, p < 0.001) and had lower rates of remission for T2D (41.9 % vs. 69.8 %), arterial hypertension (20.8 % vs. 45.3 %), and metabolic syndrome (47.6 % vs. 75.0 %) (all p ≤ 0.009).

CONCLUSION

The DXA-based AIM-SO score identifies patients with SO who are at greater risk of hepatic and cardiometabolic comorbidities, and predicts less favorable weight-loss and metabolic improvements post-BS.

Effect of Weight Loss on Skeletal Muscle Bioactive Lipids in People With Obesity and Type 2 Diabetes

Muscle sn-1,2-diacylglycerol (DAG) and C18:0 ceramide accumulation in sarcolemmal and mitochondrial compartments have been proposed to regulate muscle insulin sensitivity. Here, we evaluated whether weight loss-induced improvements in insulin sensitivity were associated with changes in muscle sn-1,2-DAG and ceramide content in people with obesity and type 2 diabetes. We measured skeletal muscle insulin sensitivity, assessed by using the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled glucose tracer infusion, and skeletal muscle sn-1,2-DAG and ceramide contents by using liquid chromatography-tandem mass spectrometry after subcellular fractionation and DAG isomer separation in 14 adults with obesity and type 2 diabetes before and after marked (18.6 ± 2.1%) weight loss. Whole-body insulin sensitivity doubled after weight loss. Sarcolemmal sn-1,2-DAG and C18:0 ceramide contents after weight loss were not different from values before weight loss. In contrast, mitochondrial-endoplasmic reticulum (ER) C18:0 ceramide content decreased by ∼20% after weight loss (from 2.16 ± 0.08 to 1.71 ± 0.13 nmol/g, P < 0.005). These results suggest a decrease in muscle mitochondrial-ER C18:0 ceramide content could contribute to the beneficial effect of weight loss on skeletal muscle insulin sensitivity.

ARTICLE HIGHLIGHTS

Association between Pan-Immune Inflammation Value and Sarcopenia in Hypertensive Patients, NHANES 1999-2018

Sarcopenia worsens the prognosis in hypertensive patients, leading to complications such as proteinuria, osteoporosis, disability, and cognitive impairment. Early screening and intervention for sarcopenia in these patients may improve outcomes. This cross-sectional study utilized data from 9253 hypertensive patients in the 1999-2018 National Health and Nutrition Examination Survey (NHANES). We used logistic and linear regression models, restricted cubic splines (RCS), and subgroup analyses to evaluate the relationship between pan-immune-inflammation value (PIV) and sarcopenia. Patients were divided into quartiles based on PIV levels. After controlling for confounding factors, our study found that those in the highest PIV quartile faced a 36% greater risk of developing sarcopenia compared to those in the lowest quartile (OR = 1.36, 95% confidence interval [CI]: 1.04-1.77). The RCS analysis indicated a linear increase in sarcopenia risk as PIV levels rose (non-linear p = 0.130). Subgroup analysis demonstrated that diabetes synergistically increased sarcopenia risk (p for interaction = 0.007). Elevated PIV levels were identified as an independent risk factor for sarcopenia, with diabetes amplifying this risk. These findings highlight the importance of early identification and management of elevated PIV levels to improve outcomes for hypertensive patients at risk of sarcopenia.

A multiorgan map of metabolic, signaling, and inflammatory pathways that coordinately control fasting glycemia in mice

To identify the pathways that are coordinately regulated in pancreatic β cells, muscle, liver, and fat to control fasting glycemia we fed C57Bl/6, DBA/2, and Balb/c mice a regular chow or a high fat diet for 5, 13, and 33 days. Physiological, transcriptomic and lipidomic data were used in a data fusion approach to identify organ-specific pathways linked to fasting glycemia across all conditions investigated. In pancreatic islets, constant insulinemia despite higher glycemic levels was associated with reduced expression of hormone and neurotransmitter receptors, OXPHOS, cadherins, integrins, and gap junction mRNAs. Higher glycemia and insulin resistance were associated, in muscle, with decreased insulin signaling, glycolytic, Krebs' cycle, OXPHOS, and endo/exocytosis mRNAs; in hepatocytes, with reduced insulin signaling, branched chain amino acid catabolism and OXPHOS mRNAs; in adipose tissue, with increased innate immunity and lipid catabolism mRNAs. These data provide a resource for further studies of interorgan communication in glucose homeostasis.

Omega-3 Attenuates Disrupted Neurotransmission and Partially Protects Metabolic Dysfunction Caused by Obesity in Wistar Rats

Omega-3 (n3) is a polyunsaturated fatty acid well known for its anti-inflammatory and neuroprotective properties. Obesity is linked to chronic inflammation that disrupts metabolism, the intestine physiology and the central nervous system functioning. This study aims to determine if n3 supplementation can interfere with the effects of obesity on the mitochondrial activity, intestinal barrier, and neurotransmitter levels in the brain of Wistar rats that received cafeteria diet (CAF). We examined adipose tissue, skeletal muscle, plasma, intestine, and the cerebral cortex of four groups: CT (control diet), CTn3 (control diet with n3 supplementation), CAF, and CAFn3 (CAF and n3). Diets were offered for 13 weeks, with n3 supplementation in the final 5 weeks. Adipose tissue Electron Transport Chain complexes I, II, and III showed higher activity in CAF groups, as did complexes III and IV in skeletal muscle. Acetate levels in plasma were reduced in CAF groups, and Lipopolysaccharide (LPS) was higher in the CAF group but reduced in CAFn3 group. Claudin-5 in the intestine was lower in CAF groups, with no n3 supplementation effect. In the cerebral cortex, dopamine levels were decreased with CAF, which was reversed by n3. DOPAC, a dopamine metabolite, also showed a supplementation effect, and HVA, a diet effect. Serotonin levels increased in the CAF group that received supplementation. Therefore, we demonstrate disturbances in mitochondria, plasma, intestine and brain of rats submitted to CAF and the potential benefit of n3 supplementation in endotoxemia and neurotransmitter levels.

Japanese encephalitis virus infection causes reactive oxygen species-mediated skeletal muscle damage

Skeletal muscle wasting is a clinically proven pathology associated with Japanese encephalitis virus (JEV) infection; however, underlying factors that govern skeletal muscle damage are yet to be explored. The current study aims to investigate the pathobiology of skeletal muscle damage using a mouse model of JEV infection. Our study reveals a significant increment in viral copy number in skeletal muscle post-JEV infection, which is associated with enhanced skeletal muscle cell death. Molecular and biochemical analysis confirms NOX2-dependent generation of reactive oxygen species, leading to autophagy flux inhibition and cell apoptosis. Along with this, an alteration in mitochondrial dynamics (change in fusion and fission process) and a decrease in the total number of mitochondria copies were found during JEV disease progression. The study represents the initial evidence of skeletal muscle damage caused by JEV and provides insights into potential avenues for therapeutic advancement.

Lipid accumulation product and type 2 diabetes risk: a population-based study

BACKGROUND

The Lipid Accumulation Product (LAP) is a measure that indicates excessive fat accumulation in the body. LAP has been the focus of research in epidemiological studies aimed at forecasting chronic and metabolic diseases. This study aimed to evaluate the association between LAP and type 2 diabetes mellitus (T2DM) among adults in western Iran.

METHODS

The study involved 9,065 adults who participated in the initial phase of the Ravansar non-communicable diseases study (RaNCD) cohort. To investigate the association between LAP and T2DM, multiple logistic regressions were employed. Additionally, the receiver operating characteristic (ROC) curve was used to evaluate LAP's predictive ability concerning T2DM.

RESULTS

The participants had an average age of 47.24 ± 8.27 years, comprising 49.30% men and 50.70% women. The mean LAP was 53.10 ± 36.60 for the healthy group and 75.51 ± 51.34 for the diabetic group (P < 0.001). The multiple regression analysis revealed that the odds of T2DM in the second quartile of LAP were 1.69 (95% CI: 1.25, 2.29) times greater than in the first quartile. Furthermore, the odds in the third and fourth quartiles were 2.67 (95% CI: 2.01, 3.55) and 3.73 (95% CI: 2.83, 4.92) times higher, respectively. The ROC analysis for predicting T2DM showed that the LAP index had an area under the curve (AUC) of 0.66 (95% CI: 0.64, 0.68).

CONCLUSION

A strong association was identified between elevated LAP levels and T2DM in the adult population of western Iran. LAP is recommended as a potential tool for screening diabetes susceptibility.

The Association between Body Composition Phenotype and Insulin Resistance in Post-COVID-19 Syndrome Patients without Diabetes: A Cross-Sectional, Single-Center Study

BACKGROUND

The most frequent body composition alterations in post-COVID-19 syndrome include low muscle mass, dynapenia, sarcopenia, and obesity. These conditions share interconnected pathophysiological mechanisms that exacerbate each other. The relationship between body composition phenotypes and metabolic abnormalities in post-COVID-19 syndrome remains unclear.

OBJECTIVE

To evaluate the association between body composition phenotypes and insulin resistance (IR) and metabolic abnormalities in non-diabetic individuals with post-COVID-19 syndrome.

METHODS

A cross-sectional, single-center study involving 483 subjects with post-COVID-19 syndrome following moderate to severe acute COVID-19 requiring hospitalization. Individuals with diabetes, those who declined to participate, or those who could not be contacted were excluded. Body composition phenotypes were classified as normal weight, dynapenia, sarcopenia, dynapenic obesity, and sarcopenic obesity (SO).

RESULTS

The average age was 52.69 ± 14.75 years; of note, 67.08% were male. The prevalence of body composition phenotypes was as follows: 13.25% were of normal weight, 9.52% had dynapenia, 9.94% had sarcopenia, 43.69% had obesity, 18.84% had dynapenic obesity, and 4.76% had SO. Additionally, 58.18% had IR. Obesity (OR: 2.98, CI95%; 1.64-5.41) and dynapenic obesity (OR: 4.98, CI95%; 1.46-6.88) were associated with IR.

CONCLUSION

The most common body composition phenotypes were obesity, dynapenic obesity, and dynapenia. Furthermore, obesity and dynapenic obesity were associated with IR in post-COVID-19 syndrome.

Dapagliflozin improves skeletal muscle insulin sensitivity through SIRT1 activation induced by nutrient deprivation state

Lipid peroxidation and mitochondrial damage impair insulin sensitivity in skeletal muscle. Sirtuin-1 (SIRT1) protects mitochondria and activates under energy restriction. Dapagliflozin (Dapa) is an antihyperglycaemic agent that belongs to the sodium-glucose cotransporter-2 (SGLT2) inhibitors. Evidence shows that Dapa can induce nutrient deprivation effects, providing additional metabolic benefits. This study investigates whether Dapa can trigger nutrient deprivation to activate SIRT1 and enhance insulin sensitivity in skeletal muscle. We treated diet-induced obese (DIO) mice with Dapa and measured metabolic parameters, lipid accumulation, oxidative stress, mitochondrial function, and glucose utilization in skeletal muscle. β-hydroxybutyric acid (β-HB) was intervened in C2C12 myotubes. The role of SIRT1 was verified by RNA interference. We found that Dapa treatment induced nutrient deprivation state and reduced lipid deposition and oxidative stress, improved mitochondrial function and glucose tolerance in skeletal muscle. The same positive effects were observed after β-HB intervening for C2C12 myotubes, and the promoting effects on glucose utilization were diminished by SIRT1 RNA interference. Thus, Dapa promotes a nutrient deprivation state and enhances skeletal muscle insulin sensitivity via SIRT1 activation. In this study, we identified a novel hypoglycemic mechanism of Dapa and the potential mechanistic targets.

Excess Branched-Chain Amino Acids Suppress Mitochondrial Function and Biogenic Signaling but Not Mitochondrial Dynamics in a Myotube Model of Skeletal Muscle Insulin Resistance

Branched-chain amino acids (BCAA) are correlated with severity of insulin resistance, which may partially result from mitochondrial dysfunction. Mitochondrial dysfunction is also common during insulin resistance and is regulated in part by altered mitochondrial fusion and fission (mitochondrial dynamics). To assess the effect of BCAA on mitochondrial dynamics during insulin resistance, the present study examined the effect of BCAA on mitochondrial function and indicators of mitochondrial dynamics in a myotube model of insulin resistance. C2C12 myotubes were treated with stock DMEM or DMEM with additional BCAA at 0.2 mM, 2 mM, or 20 mM to achieve a continuum of concentrations ranging from physiologically attainable to supraphysiological (BCAA overload) both with and without hyperinsulinemia-mediated insulin resistance. qRT-PCR and Western blot were used to measure gene and protein expression of targets associated with mitochondrial dynamics. Mitochondrial function was assessed by oxygen consumption, and mitochondrial content was measured using mitochondrial-specific staining. Insulin resistance reduced mitochondrial function, peroxisome proliferator-activated receptor gamma coactivator 1-alpha mRNA, and citrate synthase expression mRNA, but not protein expression. Excess BCAA at 20 mM also independently reduced mitochondrial function in insulin-sensitive cells. BCAA did not alter indicators of mitochondrial dynamics at the mRNA or protein level, while insulin resistance reduced mitochondrial fission protein 1 mRNA, but not protein expression. Collectively, BCAA at excessively high levels or coupled with insulin resistances reduce mitochondrial function and content but do not appear to alter mitochondrial dynamics under the tested conditions.

Korean Red Ginseng Improves Oxidative Stress-Induced Hepatic Insulin Resistance via Enhancing Mitophagy

This study explored the potential of saponins from Korean Red Ginseng to target the PINK1/Parkin mitophagy pathway, aiming to enhance insulin sensitivity in hepatocytes-a key factor in metabolic disorders like metabolic dysfunction-associated steatotic liver disease (MASLD) and type 2 diabetes. Results from both in vitro and in vivo experiments showed increased expression of PINK1 and Parkin, activating mitophagy and reducing oxidative stress through reduction in mitochondrial and total reactive oxygen species. Additionally, improvements in insulin signaling were observed, including the upregulation of phosphorylated IRS and AKT, and downregulation of gluconeogenic enzymes, underscoring the saponins' efficacy in boosting insulin sensitivity. The findings highlighted Korean Red Ginseng-derived saponins as potential treatments for insulin resistance and related metabolic conditions.

Shining a spotlight on sarcopenia and myosteatosis in liver disease and liver transplantation: Potentially modifiable risk factors with major clinical impact

Muscle-wasting and disease-related malnutrition are highly prevalent in patients with chronic liver diseases (CLD) as well as in liver transplant (LT) candidates. Alterations of body composition (BC) such as sarcopenia, myosteatosis and sarcopenic obesity and associated clinical frailty were tied to inferior clinical outcomes including hospital admissions, length of stay, complications, mortality and healthcare costs in various patient cohorts and clinical scenarios. In contrast to other inherent detrimental individual characteristics often observed in these complex patients, such as comorbidities or genetic risk, alterations of the skeletal muscle and malnutrition are considered as potentially modifiable risk factors with a major clinical impact. Even so, there is only limited high-level evidence to show how these pathologies should be addressed in the clinical setting. This review discusses the current state-of-the-art on the role of BC assessment in clinical outcomes in the setting of CLD and LT focusing mainly on sarcopenia and myosteatosis. We focus on the disease-related pathophysiology of BC alterations. Based on these, we address potential therapeutic interventions including nutritional regimens, physical activity, hormone and targeted therapies. In addition to summarizing existing knowledge, this review highlights novel trends, and future perspectives and identifies persisting challenges in addressing BC pathologies in a holistic way, aiming to improve outcomes and quality of life of patients with CLD awaiting or undergoing LT.

Insulin signaling and mitochondrial phenotype of skeletal muscle are programmed in utero by maternal diabetes

Maternal diabetes may influence glucose metabolism in adult offspring, an area with limited research on underlying mechanisms. Our study explored the impact of maternal hyperglycemia during pregnancy on insulin resistance development. Adult female Sprague-Dawley rats from control and diabetic mothers were mated, and their female offspring were monitored for 150 days. The rats were euthanized for blood and muscle samples. Maternal diabetes led to heightened insulin levels, increased HOMA-IR, elevated triglycerides, and a raised TyG index in adult offspring. Muscle samples showed a decreased protein expression of AMPK, PI3K, MAPK, DRP1, and MFF. These changes induced intergenerational metabolic programming in female pups, resulting in insulin resistance, dyslipidemia, and glucose intolerance by day 150. Findings highlight the offspring's adaptation to maternal hyperglycemia, involving insulin resistance, metabolic alterations, the downregulation of insulin signaling sensors, and disturbed mitochondrial morphology. Maintaining maternal glycemic control emerges as crucial in mitigating diabetes-associated disorders in adult offspring.

Mitochondrial mechanisms in the pathogenesis of chronic inflammatory musculoskeletal disorders

Chronic inflammatory musculoskeletal disorders characterized by prolonged muscle inflammation, resulting in enduring pain and diminished functionality, pose significant challenges for the patients. Emerging scientific evidence points to mitochondrial malfunction as a pivotal factor contributing to these ailments. Mitochondria play a critical role in powering skeletal muscle activity, but in the context of persistent inflammation, disruptions in their quantity, configuration, and performance have been well-documented. Various disturbances, encompassing alterations in mitochondrial dynamics (such as fission and fusion), calcium regulation, oxidative stress, biogenesis, and the process of mitophagy, are believed to play a central role in the progression of these disorders. Additionally, unfolded protein responses and the accumulation of fatty acids within muscle cells may adversely affect the internal milieu, impairing the equilibrium of mitochondrial functioning. The structural discrepancies between different mitochondrial subsets namely, intramyofibrillar and subsarcolemmal mitochondria likely impact their metabolic capabilities and susceptibility to inflammatory influences. The release of signals from damaged mitochondria is known to incite inflammatory responses. Intriguingly, migrasomes and extracellular vesicles serve as vehicles for intercellular transfer of mitochondria, aiding in the removal of impaired mitochondria and regulation of inflammation. Viral infections have been implicated in inducing stress on mitochondria. Prolonged dysfunction of these vital organelles sustains oxidative harm, metabolic irregularities, and heightened cytokine release, impeding the body's ability to repair tissues. This review provides a comprehensive analysis of advancements in understanding changes in the intracellular environment, mitochondrial architecture and distribution, biogenesis, dynamics, autophagy, oxidative stress, cytokines associated with mitochondria, vesicular structures, and associated membranes in the context of chronic inflammatory musculoskeletal disorders. Strategies targeting key elements regulating mitochondrial quality exhibit promise in the restoration of mitochondrial function, alleviation of inflammation, and enhancement of overall outcomes.

The paradox of fatty-acid β-oxidation in muscle insulin resistance: Metabolic control and muscle heterogeneity

The skeletal muscle is a metabolically heterogeneous tissue that plays a key role in maintaining whole-body glucose homeostasis. It is well known that muscle insulin resistance (IR) precedes the development of type 2 diabetes. There is a consensus that the accumulation of specific lipid species in the tissue can drive IR. However, the role of the mitochondrial fatty-acid β-oxidation in IR and, consequently, in the control of glucose uptake remains paradoxical: interventions that either inhibit or activate fatty-acid β-oxidation have been shown to prevent IR. We here discuss the current theories and evidence for the interplay between β-oxidation and glucose uptake in IR. To address the underlying intricacies, we (1) dive into the control of glucose uptake fluxes into muscle tissues using the framework of Metabolic Control Analysis, and (2) disentangle concepts of flux and catalytic capacities taking into account skeletal muscle heterogeneity. Finally, we speculate about hitherto unexplored mechanisms that could bring contrasting evidence together. Elucidating how β-oxidation is connected to muscle IR and the underlying role of muscle heterogeneity enhances disease understanding and paves the way for new treatments for type 2 diabetes.

Exploring new mechanisms of Imeglimin in diabetes treatment: Amelioration of mitochondrial dysfunction

With the increasing prevalence of type 2 diabetes mellitus (T2DM), it has become critical to identify effective treatment strategies. In recent years, the novel oral hypoglycaemic drug Imeglimin has attracted much attention in the field of diabetes treatment. The mechanisms of its therapeutic action are complex and are not yet fully understood by current research. Current evidence suggests that pancreatic β-cells, liver, and skeletal muscle are the main organs in which Imeglimin lowers blood glucose levels and that it acts mainly by targeting mitochondrial function, thereby inhibiting hepatic gluconeogenesis, enhancing insulin sensitivity, promoting pancreatic β-cell function, and regulating energy metabolism. There is growing evidence that the drug also has a potentially volatile role in the treatment of diabetic complications, including metabolic cardiomyopathy, diabetic vasculopathy, and diabetic neuroinflammation. According to available clinical studies, its efficacy and safety profile are more evident than other hypoglycaemic agents, and it has synergistic effects when combined with other antidiabetic drugs, and also has potential in the treatment of T2DM-related complications. This review aims to shed light on the latest research progress in the treatment of T2DM with Imeglimin, thereby providing clinicians and researchers with the latest insights into Imeglimin as a viable option for the treatment of T2DM.

Physiological 4-phenylbutyrate promotes mitochondrial biogenesis and metabolism in C2C12 myotubes

Type 2 diabetes is characterized by elevated circulating blood metabolites such as glucose, insulin, and branched chain amino acids (BCAA), which often coincide with reduced mitochondrial function. 4-Phenylbutyrate (PBA), an ammonia scavenger, has been shown to activate BCAA metabolism, resolve endoplasmic reticulum (ER) stress, and rescue BCAA-mediated insulin resistance. To determine the effect of PBA on the altered metabolic phenotype featured in type 2 diabetes, the present study investigated the effect of PBA on various metabolic parameters including mitochondrial metabolism and mitochondrial biogenesis. C2C12 myotubes were treated with PBA at 0.5 mM (representing physiologically attainable blood concentrations) or 10 mM (representing physiologically unattainable/proof-of-concept levels) for up to 24 h. Mitochondrial and glycolytic metabolism were assessed via oxygen consumption and extracellular acidification rate, respectively. Mitochondrial content, lipid content, and ER stress were measured by fluorescent staining. Metabolic gene expression was measured by qRT-PCR. Both doses of PBA increased expression of indicators of mitochondrial biogenesis, though only PBA at 0.5 mM increased mitochondrial function and content while 10 mM PBA reduced mitochondrial function and content. PBA at 0.5 mM also rescued reduced mitochondrial function during insulin resistance, though PBA also caused a reduced insulin stimulated pAkt expression during insulin resistance. PBA treatment also increased extracellular BCAA accumulation during insulin resistance despite unchanged pBCKDH expression. Taken together, PBA may increase mitochondrial biogenesis, content, and function in a dose-dependent fashion which may have implications for prevention or treatment of metabolic disease such as insulin resistance.

Mitochondria and diabetes: insights and potential therapies

INTRODUCTION

Type 2 diabetes (T2D) presents significant global health and economic challenges, contributing to complications such as stroke, cardiovascular disease, kidney dysfunction, and cancer. The current review explores the crucial role of mitochondria, essential for fuel metabolism, in diabetes-related processes.

AREAS COVERED

Mitochondrial deficits impact insulin-resistant skeletal muscles, adipose tissue, liver, and pancreatic β-cells, affecting glucose and lipid balance. Exercise emerges as a key factor in enhancing mitochondrial function, thereby reducing insulin resistance. Additionally, the therapeutic potential of mitochondrial uncoupling, which generates heat instead of ATP, is discussed. We explore the intricate link between mitochondrial function and diabetes, investigating genetic interventions to mitigate diabetes-related complications. We also cover the impact of insulin deficiency on mitochondrial function, the role of exercise in addressing mitochondrial defects in insulin resistance, and the potential of mitochondrial uncoupling. Furthermore, a comprehensive analysis of Mitochondrial Replacement Therapies (MRT) techniques is presented.

EXPERT OPINION

MRTs hold promise in preventing the transmission of mitochondrial disease. However, addressing ethical, regulatory, and technical considerations is crucial. Integrating mitochondrial-based treatments requires a careful balance between innovation and safety. Ethical dimensions and regulatory aspects of MRT are examined, emphasizing collaborative efforts for the responsible advancement of human health.

Genetic risk score for insulin resistance based on gene variants associated to amino acid metabolism in young adults

Circulating concentration of arginine, alanine, aspartate, isoleucine, leucine, phenylalanine, proline, tyrosine, taurine and valine are increased in subjects with insulin resistance, which could in part be attributed to the presence of single nucleotide polymorphisms (SNPs) within genes associated with amino acid metabolism. Thus, the aim of this work was to develop a Genetic Risk Score (GRS) for insulin resistance in young adults based on SNPs present in genes related to amino acid metabolism. We performed a cross-sectional study that included 452 subjects over 18 years of age. Anthropometric, clinical, and biochemical parameters were assessed including measurement of serum amino acids by high performance liquid chromatography. Eighteen SNPs were genotyped by allelic discrimination. Of these, ten were found to be in Hardy-Weinberg equilibrium, and only four were used to construct the GRS through multiple linear regression modeling. The GRS was calculated using the number of risk alleles of the SNPs in HGD, PRODH, DLD and SLC7A9 genes. Subjects with high GRS (≥ 0.836) had higher levels of glucose, insulin, homeostatic model assessment- insulin resistance (HOMA-IR), total cholesterol and triglycerides, and lower levels of arginine than subjects with low GRS (p < 0.05). The application of a GRS based on variants within genes associated to amino acid metabolism may be useful for the early identification of subjects at increased risk of insulin resistance.

A Maternal Western-Style Diet Impairs Skeletal Muscle Lipid Metabolism in Adolescent Japanese Macaques

Maternal consumption of a Western-style diet (mWD) during pregnancy alters fatty acid metabolism and reduces insulin sensitivity in fetal skeletal muscle. The long-term impact of these fetal adaptations and the pathways underlying disordered lipid metabolism are incompletely understood. Therefore, we tested whether a mWD chronically fed to lean, insulin-sensitive adult Japanese macaques throughout pregnancy and lactation would impact skeletal muscle oxidative capacity and lipid metabolism in adolescent offspring fed a postweaning (pw) Western-style diet (WD) or control diet (CD). Although body weight was not different, retroperitoneal fat mass and subscapular skinfold thickness were significantly higher in pwWD offspring consistent with elevated fasting insulin and glucose. Maximal complex I (CI)-dependent respiration in muscle was lower in mWD offspring in the presence of fatty acids, suggesting that mWD impacts muscle integration of lipid with nonlipid oxidation. Abundance of all five oxidative phosphorylation complexes and VDAC, but not ETF/ETFDH, were reduced with mWD, partially explaining the lower respiratory capacity with lipids. Muscle triglycerides increased with pwWD; however, the fold increase in lipid saturation, 1,2-diacylglycerides, and C18 ceramide compared between pwCD and pwWD was greatest in mWD offspring. Reductions in CI abundance and VDAC correlated with reduced markers of oxidative stress, suggesting that these reductions may be an early-life adaptation to mWD to mitigate excess reactive oxygen species. Altogether, mWD, independent of maternal obesity or insulin resistance, results in sustained metabolic reprogramming in offspring muscle despite a healthy diet intervention.

ARTICLE HIGHLIGHTS

In lean, active adolescent offspring, a postweaning Western-style diet (pwWD) leads to shifts in body fat distribution that are associated with poorer insulin sensitivity. Fatty acid-linked oxidative metabolism was reduced in skeletal muscles from offspring exposed to maternal Western-style diet (mWD) even when weaned to a healthy control diet for years. Reduced oxidative phosphorylation complex I-V and VDAC1 abundance partially explain decreased skeletal muscle respiration in mWD offspring. Prior exposure to mWD results in greater fold increase with pwWD in saturated lipids and bioactive lipid molecules (i.e. ceramide and sphingomyelin) associated with insulin resistance.

Association between muscle quality index and pulmonary function in post-COVID-19 subjects

BACKGROUND

The SARS-CoV2 pandemic impacted many critically ill patients, causing sequelae, affecting lung function, and involving the musculoskeletal system. We evaluated the association between lung function and muscle quality index in severely ill post-COVID-19 patients.

METHODS

A cross-sectional study was conducted on a post-COVID-19 cohort at a third-level center. The study included patients who had experienced severe-to-critical COVID-19. Anthropometric measurements, such as body mass index (BMI) and handgrip strength, were obtained to calculate the muscle quality index (MQI). Additionally, spirometry, measurements of expiratory and inspiratory pressure, and an assessment of DLCO in the lungs were performed. The MQI was categorized into two groups: low-MQI (below the 50th percentile) and high-MQI (above the 50th percentile), based on sex. Group differences were analyzed, and a multivariate linear regression analysis was performed to assess the association between respiratory function and MQI.

RESULTS

Among the 748 patients analyzed, 61.96% required mechanical ventilation, and the median hospital stay was 17 days. In patients with a low MQI, it was observed that both mechanical respiratory function and DLCO were lower. The multivariate analysis revealed significantly lower findings in mechanical respiratory function among patients with a low MQI.

CONCLUSION

The Low-MQI is an independent predictor associated with pulmonary function parameters in subjects with Post-COVID-19 syndrome.

Sarcopenia in a type 2 diabetic state: Reviewing literature on the pathological consequences of oxidative stress and inflammation beyond the neutralizing effect of intracellular antioxidants

Sarcopenia remains one of the major pathological features of type 2 diabetes (T2D), especially in older individuals. This condition describes gradual loss of muscle mass, strength, and function that reduces the overall vitality and fitness, leading to increased hospitalizations and even fatalities to those affected. Preclinical evidence indicates that dysregulated mitochondrial dynamics, together with impaired activity of the NADPH oxidase system, are the major sources of oxidative stress that drive skeletal muscle damage in T2D. While patients with T2D also display relatively higher levels of circulating inflammatory markers in the serum, including high sensitivity-C-reactive protein, interleukin-6, and tumor necrosis factor-α that are independently linked with the deterioration of muscle function and sarcopenia in T2D. In fact, beyond reporting on the pathological consequences of both oxidative stress and inflammation, the current review highlights the importance of strengthening intracellular antioxidant systems to preserve muscle mass, strength, and function in individuals with T2D.

Resveratrol as a potential protective compound against skeletal muscle insulin resistance

The increasing prevalence of type 2 diabetes has become a major global problem. Insulin resistance has a central role in pathophysiology of type 2 diabetes. Skeletal muscle is responsible for the disposal of most of the glucose under conditions of insulin stimulation, and insulin resistance in skeletal muscle causes dysregulation of glucose homeostasis in the whole body. Despite the current pharmaceutical and non-pharmacological treatment strategies to combat diabetes, there is still a need for new therapeutic agents due to the limitations of the therapeutic agents. Meanwhile, plant polyphenols have attracted the attention of researchers for their use in the treatment of diabetes and have gained popularity. Resveratrol, a stilbenoid polyphenol, exists in various plant sources, and a growing body of evidence suggests its beneficial properties, including antidiabetic activities. The present review aimed to provide a summary of the role of resveratrol in insulin resistance in skeletal muscle and its related mechanisms. To achieve the objectives, by searching the PubMed, Scopus and Web of Science databases, we have summarized the results of all cell culture, animal, and human studies that have investigated the effects of resveratrol in different models on insulin resistance in skeletal muscle.

Mitochondrial transfer restores impaired liver functions by AMPK/ mTOR/PI3K-AKT pathways in metabolic syndrome

AIM

We investigated the effect of mitochondria transfer in high fat diet and streptozotocin (HFD + STZ) induced metabolic syndrome (MeS) in rats. The effect of mitochondria transfer in MeS with co-existing hypertension, hyperlipidaemia, diabetes and fatty liver together, has not been reported.

MATERIALS AND METHODS

Heathy mitochondria was transferred intravenously and the effect on several physiological parameters and biochemical parameters were examined in HFD + STZ rats. In addition, RNA-sequencing of healthy liver tissues was performed to elucidate the molecular pathways affected by mitochondria transfer in restoring metabolic health.

KEY FINDINGS

We observed reduction in both systolic and diastolic blood pressure levels, reduced blood glucose levels, and a marked reduction in serum lipid profiles. The levels of alanine transaminase (ALT) and aspartate transaminase (AST) also improved along with evident restoration of liver morphology demonstrated by histopathological analysis. Enhanced mitochondrial biogenetics and reduction in oxidative stress and inflammatory markers was also observed. The pathway enrichment analysis revealed reduction in insulin resistance, inflammatory markers, regulation of mitochondrial bioenergetics, calcium ion homeostasis, fatty-acid β-oxidation, cytokine immune regulators, and enhanced lipid solubilisation. The significant effect of healthy mitochondria transfer in restoration of metabolic functions was observed by the activation of PI3K-AKT, AMPK/mTOR pathways and cytokine immune regulators, suggesting that inflammatory mediators were also significantly affected after mitochondria transfer.

SIGNIFICANCE

This study, provides insights on molecular processes triggered by mitochondria transfer in fatty liver regeneration and improvement of overall metabolic health.

Partial skeletal muscle-specific Drp1 knockout enhances insulin sensitivity in diet-induced obese mice, but not in lean mice

OBJECTIVE

Dynamin-related protein 1 (Drp1) is the key regulator of mitochondrial fission. We and others have reported a strong correlation between enhanced Drp1 activity and impaired skeletal muscle insulin sensitivity. This study aimed to determine whether Drp1 directly regulates skeletal muscle insulin sensitivity and whole-body glucose homeostasis.

METHODS

We employed tamoxifen-inducible skeletal muscle-specific heterozygous Drp1 knockout mice (mDrp1+/-). Male mDrp1+/- and wildtype (WT) mice were fed with either a high-fat diet (HFD) or low-fat diet (LFD) for four weeks, followed by tamoxifen injections for five consecutive days, and remained on their respective diet for another four weeks. In addition, we used primary human skeletal muscle cells (HSkMC) from lean, insulin-sensitive, and severely obese, insulin-resistant humans and transfected the cells with either a Drp1 shRNA (shDrp1) or scramble shRNA construct. Skeletal muscle and whole-body insulin sensitivity, skeletal muscle insulin signaling, mitochondrial network morphology, respiration, and H2O2 production were measured.

RESULTS

Partial deletion of the Drp1 gene in skeletal muscle led to improved whole-body glucose tolerance and insulin sensitivity (P < 0.05) in diet-induced obese, insulin-resistant mice but not in lean mice. Analyses of mitochondrial structure and function revealed that the partial deletion of the Drp1 gene restored mitochondrial dynamics, improved mitochondrial morphology, and reduced mitochondrial Complex I- and II-derived H2O2 (P < 0.05) under the condition of diet-induced obesity. In addition, partial deletion of Drp1 in skeletal muscle resulted in elevated circulating FGF21 (P < 0.05) and in a trend towards increase of FGF21 expression in skeletal muscle tissue (P = 0.095). In primary myotubes derived from severely obese, insulin-resistant humans, ShRNA-induced-knockdown of Drp1 resulted in enhanced insulin signaling, insulin-stimulated glucose uptake and reduced cellular reactive oxygen species (ROS) content compared to the shScramble-treated myotubes from the same donors (P < 0.05).

CONCLUSION

These data demonstrate that partial loss of skeletal muscle-specific Drp1 expression is sufficient to improve whole-body glucose homeostasis and insulin sensitivity under obese, insulin-resistant conditions, which may be, at least in part, due to reduced mitochondrial H2O2 production. In addition, our findings revealed divergent effects of Drp1 on whole-body metabolism under lean healthy or obese insulin-resistant conditions in mice.

SAA1 exacerbates pancreatic β-cell dysfunction through activation of NF-κB signaling in high-fat diet-induced type 2 diabetes mice

Insufficient decompensated insulin secretion and insulin resistance caused by pancreatic β-cell dysfunction are the pathological bases of type 2 diabetes mellitus (T2DM). Glucolipotoxicity in pancreatic β-cells is an important factor leading to their dysfunction, closely related to inflammatory signals, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum stress (ERs). However, there may be other unproven regulatory mechanisms that govern pancreatic β-cell dysfunction. Therefore, further elucidation of the underlying mechanisms that lead to pancreatic β-cells dysfunction will provide a sufficient theoretical basis for the more effective prevention and treatment of T2DM. As a stress protein with pro-inflammatory properties, Serum Amyloid 1 (SAA1) promotes the progression of metabolic syndrome-related diseases by activating immune cells and damaging endothelial cells. In the development of T2DM, the activation of nuclear factor-kappa B (NF-κB) signaling aggravates pancreatic β-cells dysfunction under the stimulation of free fatty acids (FFAs), inflammatory factors, and chemokines. Moreover, the facilitating effect of SAA1 on the activation of the NF-κB signaling pathway has been demonstrated in other studies. In the present study, we demonstrated that SAA1 inhibits insulin secretion and promotes apoptotic molecular expression in pancreatic cells and islets and that NF-κB signaling inhibitors could reduce this effect of SAA1. SAA1 deficiency improved high-fat diet (HFD)-induced pancreatic β-cell dysfunction and decreased expression of NF-κB signaling molecules. Our findings suggested that HFD-induced SAA1 might exacerbate T2DM by enhancing pancreatic β-cell dysfunction; such a function of SAA1 might depend on NF-κB signaling activation.

Exercise ameliorates skeletal muscle insulin resistance by modulating GRK4-mediated D1R expression

Exercise has been recommended as a nonpharmaceutical therapy to treat insulin resistance (IR). Previous studies showed that dopamine D1-like receptor agonists, such as fenoldopam, could improve peripheral insulin sensitivity, while antipsychotics, which are dopamine receptor antagonists, increased susceptibility to Type 2 diabetes mellitus (T2DM). Meanwhile, exercise has been proved to stimulate dopamine receptors. However, whether the dopamine D1 receptor (D1R) is involved in exercise-mediated amelioration of IR remains unclear. We found that the D1-like receptor antagonist, SCH23390, reduced the effect of exercise on lowering blood glucose and insulin in insulin-resistant mice and inhibited the contraction-induced glucose uptake in C2C12 myotubes. Similarly, the opposite was true for the D1-like receptor agonist, fenoldopam. Furthermore, the expression of D1R was decreased in skeletal muscles from streptozotocin (STZ)- and high-fat intake-induced T2DM mice, accompanied by increased D1R phosphorylation, which was reversed by exercise. A screening study showed that G protein-coupled receptor kinase 4 (GRK4) may be the candidate kinase for the regulation of D1R function, because, in addition to the increased GRK4 expression in skeletal muscles of T2DM mice, GRK4 transgenic T2DM mice exhibited lower insulin sensitivity, accompanied by higher D1R phosphorylation than control mice, whereas the AAV9-shGRK4 mice were much more sensitive to insulin than AAV9-null mice. Mechanistically, the up-regulation of GRK4 expression caused by increased reactive oxygen species (ROS) in IR was ascribed to the enhanced expression of c-Myc, a transcriptional factor of GRK4. Taken together, the present study shows that exercise, via regulation of ROS/c-Myc/GRK4 pathway, ameliorates D1R dysfunction and improves insulin sensitivity.

Reactive Oxygen Species: A Crosslink between Plant and Human Eukaryotic Cell Systems

Reactive oxygen species (ROS) are important regulating factors that play a dual role in plant and human cells. As the first messenger response in organisms, ROS coordinate signals in growth, development, and metabolic activity pathways. They also can act as an alarm mechanism, triggering cellular responses to harmful stimuli. However, excess ROS cause oxidative stress-related damage and oxidize organic substances, leading to cellular malfunctions. This review summarizes the current research status and mechanisms of ROS in plant and human eukaryotic cells, highlighting the differences and similarities between the two and elucidating their interactions with other reactive substances and ROS. Based on the similar regulatory and metabolic ROS pathways in the two kingdoms, this review proposes future developments that can provide opportunities to develop novel strategies for treating human diseases or creating greater agricultural value.

Biomarkers of obesity-mediated insulin resistance: focus on microRNAs

Obesity and metabolic syndromes are becoming increasingly prevalent worldwide. Insulin resistance (IR) is a common complication of obesity. However, IR occurrence varies across individuals with obesity and may involve epigenetic factors. To rationalize the allocation of healthcare resources, biomarkers for the early risk stratification of individuals with obesity should be identified. MicroRNAs (miRNAs) are closely associated with metabolic diseases and involved in epigenetic regulation. In this review, we have summarized the changes in miRNA expression in the peripheral circulation and tissues of patients and animals with obesity-associated IR over the last 5 years and identified several candidate biomarkers that predict obesity-related IR. There are areas for improvement in existing studies. First, more than the predictive validity of a single biomarker is required, and a biomarker panel needs to be formed. Second, miRNAs are often studied in isolation and do not form a network of signaling pathways. We believe that early biomarkers can help clinicians accurately predict individuals prone to obesity-related IR at an early stage. Epigenetic regulation may be one of the underlying causes of different clinical outcomes in individuals with obesity. Future studies should focus on objectively reflecting the differences in miRNA profile expression in individuals with obesity-related IR, which may help identify more reliable biomarkers. Understanding the metabolic pathways of these miRNAs can help design new metabolic risk prevention and management strategies, and support the development of drugs to treat obesity and metabolic disorders.

Role of Oxidative Stress on Insulin Resistance in Diet-Induced Obesity Mice

Insulin resistance is the link between obesity and type 2 diabetes mellitus. The molecular mechanism by which obese individuals develop insulin resistance has not yet been fully elucidated; however, inconclusive and contradictory studies have shown that oxidative stress may be involved in the process. Thus, this study aimed to evaluate the effect of reactive species on the mechanism of insulin resistance in diet-induced obese mice. Obese insulin-resistant mice were treated with N-acetylcysteine (NAC; 50 mg/kg per day, for 15 days) by means of oral gavage. Twenty-four hours after the last NAC administration, the animals were euthanized and their tissues were extracted for biochemical and molecular analyses. NAC supplementation induced improved insulin resistance and fasting glycemia, without modifications in food intake, body weight, and adiposity. Obese mice showed increased dichlorofluorescein (DCF) oxidation, reduced catalase (CAT) activity, and reduced glutathione levels (GSH). However, treatment with NAC increased GSH and CAT activity and reduced DCF oxidation. The gastrocnemius muscle of obese mice showed an increase in nuclear factor kappa B (NFκB) and protein tyrosine phosphatase (PTP1B) levels, as well as c-Jun N-terminal kinase (JNK) phosphorylation compared to the control group; however, NAC treatment reversed these changes. Considering the molecules involved in insulin signaling, there was a reduction in insulin receptor substrate (IRS) and protein kinase B (Akt) phosphorylation. However, NAC administration increased IRS and Akt phosphorylation and IRS/PI3k (phosphoinositide 3-kinase) association. The results demonstrated that oxidative stress-associated obesity could be a mechanism involved in insulin resistance, at least in this animal model.

Repurposing Drugs for Diabetes Mellitus as Potential Pharmacological Treatments for Sarcopenia - A Narrative Review

Sarcopenia, the age-related loss of muscle strength and mass or quality, is a common condition with major adverse consequences. Although the pathophysiology is incompletely understood, there are common mechanisms between sarcopenia and the phenomenon of accelerated ageing seen in diabetes mellitus. Drugs currently used to treat type 2 diabetes mellitus may have mechanisms of action that are relevant to the prevention and treatment of sarcopenia, for those with type 2 diabetes and those without diabetes. This review summarises shared pathophysiology between sarcopenia and diabetes mellitus, including the effects of advanced glycation end products, mitochondrial dysfunction, chronic inflammation and changes to the insulin signalling pathway. Cellular and animal models have generated intriguing, albeit mixed, evidence that supports possible beneficial effects on skeletal muscle function for some classes of drugs used to treat diabetes, including metformin and SGLT2 inhibitors. Most human observational and intervention evidence for the effects of these drugs has been derived from populations with type 2 diabetes mellitus, and there is a need for intervention studies for older people with, and at risk of, sarcopenia to further investigate the balance of benefit and risk in these target populations. Not all diabetes treatments will be safe to use in those without diabetes because of variable side effects across classes. However, some agents [including glucagon-like peptide (GLP)-1 receptor agonists and SGLT2 inhibitors] have already demonstrated benefits in populations without diabetes, and it is these agents, along with metformin, that hold out the most promise for further investigation in sarcopenia.

A Narrative Review of Non-Pharmacological Strategies for Managing Sarcopenia in Older Adults with Cardiovascular and Metabolic Diseases

This narrative review examines the mechanisms underlying the development of cardiovascular disease (CVD) and metabolic diseases (MDs), along with their association with sarcopenia. Furthermore, non-pharmacological interventions to address sarcopenia in patients with these conditions are suggested. The significance of combined training in managing metabolic disease and secondary sarcopenia in type II diabetes mellitus is emphasized. Additionally, the potential benefits of resistance and aerobic training are explored. This review emphasises the role of nutrition in addressing sarcopenia in patients with CVD or MDs, focusing on strategies such as optimising protein intake, promoting plant-based protein sources, incorporating antioxidant-rich foods and omega-3 fatty acids and ensuring sufficient vitamin D levels. Moreover, the potential benefits of targeting gut microbiota through probiotics and prebiotic fibres in sarcopenic individuals are considered. Multidisciplinary approaches that integrate behavioural science are explored to enhance the uptake and sustainability of behaviour-based sarcopenia interventions. Future research should prioritise high-quality randomized controlled trials to refine exercise and nutritional interventions and investigate the incorporation of behavioural science into routine practices. Ultimately, a comprehensive and multifaceted approach is essential to improve health outcomes, well-being and quality of life in older adults with sarcopenia and coexisting cardiovascular and metabolic diseases.

The Effect of Omega-3 Fatty Acids on Insulin Resistance

Insulin resistance is a critical pathophysiological process in the onset and advancement of type 2 diabetes mellitus. It is well-recognized that alterations in the metabolism of lipids and aberrant fat buildup effectively trigger the development of resistance to insulin. Adjusting one's eating habits and managing weight appropriately are crucial for treating, controlling, and reducing the risk of T2DM because obesity and a lack of physical exercise are the primary factors responsible for the worldwide rise in T2DM. Omega-3 fatty acid is one of the polyunsaturated fatty acids (PUFA) that include long-chain omega-3 fatty acids such as eicosapentaenoic acid and docosahexaenoic acid, commonly found in fish oils. Omega-3 and omega-6 polyunsaturated fatty acids (PUFAs; 3 and 6 PUFAs) are essential for human health because they serve as metabolic precursors of eicosanoids, a class of signaling molecules that are essential for controlling a body's inflammation. Since humans are unable to produce any of the omega-3 or omega-6 PUFAs, they both constitute imperative nutritional ingredients. Long-standing concerns about long-chain omega-3 fatty acids' impact on diabetes management have been supported by experimental investigations that found significant increases in fasting glucose following omega-3 fatty acid supplementation and foods rich in PUFA and omega-3 fatty acid. Cellular explanations to explain the connection between inflammation and IR include mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and oxidative stress. Modifications in the lipid composition of mitochondrial membranes and/or receptor-mediated signaling may be part of the mechanism behind the activation of mitochondrial fusion by fish oil/omega-3 PUFA. The exact molecular processes by which omega-3 PUFAs control mitochondrial activity to defend against IR are still unknown.

Relationship between lipid accumulation product and new-onset diabetes in the Japanese population: a retrospective cohort study

Background

Diabetes has become a global public health problem. Obesity has been established as a risk factor for diabetes. However, it remains unclear which of the obesity indicators (BMI, WC, WhtR, ABSI, BRI, LAP, VAI) is more appropriate for monitoring diabetes. Therefore, the objective of this investigation is to compare the strength of the association of these indicators and diabetes and reveal the relationship between LAP and diabetes.

Methods

15,252 people took part in this research. LAP was quartered and COX proportional risk model was applied to explore the relationship between LAP and new-onset diabetes. Smooth curve fitting was employed to investigate the non-linear link between LAP and diabetes mellitus. Finally, the receiver operating characteristic (ROC) curve was used to evaluate the predictive ability of the aforementioned indicators for diabetes.

Results

After adjusting for confounding factors, multiple linear regression analysis showed that each unit increase in LAP was associated with a 76.8% increase in the risk of developing diabetes (HR=1.768, 95% CI: 1.139 to 2.746, P=0.011). In addition, LAP predicted new-onset diabetes better than other indicators, and the AUC was the largest [HR: 0.713, 95% CI: 0.6806-0.7454, P<0.001, in women; HR: 0.7922, 95% CI: 0.7396-0.8447; P<0.001, in men]. When LAP was used as a lone predictor, its AUC area was largest both men and women. However, after adding classical predictors (FPG, HbA1c, SBP, exercise, age) to the model, the LAP is better than the ABSI, but not better than the other indicators when compared in pairs.

Conclusions

High levels of LAP correlate very strongly with diabetes and are an important risk factor for diabetes, especially in women, those with fatty liver and current smokers. LAP was superior to other indicators when screening for diabetes susceptibility using a single indicator of obesity, both in men and in women. However, when obesity indicators were added to the model together with classical predictors, LAP did not show a significant advantage over other indicators, except ABSI.

Concomitant western diet and chronic-binge alcohol dysregulate hepatic metabolism

BACKGROUND AND AIMS

There is significant overlap between non-alcoholic fatty liver disease (NAFLD) and alcohol-associated liver disease (ALD) with regards to risk factors and disease progression. However, the mechanism by which fatty liver disease arises from concomitant obesity and overconsumption of alcohol (syndrome of metabolic and alcohol-associated fatty liver disease; SMAFLD), is not fully understood.

METHODS

Male C57BL6/J mice were fed chow diet (Chow) or high-fructose, high-fat, high-cholesterol diet (FFC) for 4 weeks, then administered either saline or ethanol (EtOH, 5% in drinking water) for another 12 weeks. The EtOH treatment also consisted of a weekly 2.5 g EtOH/kg body weight gavage. Markers for lipid regulation, oxidative stress, inflammation, and fibrosis were measured by RT-qPCR, RNA-seq, Western blot, and metabolomics.

RESULTS

Combined FFC-EtOH induced more body weight gain, glucose intolerance, steatosis, and hepatomegaly compared to Chow, EtOH, or FFC. Glucose intolerance by FFC-EtOH was associated with decreased hepatic protein kinase B (AKT) protein expression and increased gluconeogenic gene expression. FFC-EtOH increased hepatic triglyceride and ceramide levels, plasma leptin levels, hepatic Perilipin 2 protein expression, and decreased lipolytic gene expression. FFC and FFC-EtOH also increased AMP-activated protein kinase (AMPK) activation. Finally, FFC-EtOH enriched the hepatic transcriptome for genes involved in immune response and lipid metabolism.

CONCLUSIONS

In our model of early SMAFLD, we observed that the combination of an obesogenic diet and alcohol caused more weight gain, promoted glucose intolerance, and contributed to steatosis by dysregulating leptin/AMPK signaling. Our model demonstrates that the combination of an obesogenic diet with a chronic-binge pattern alcohol intake is worse than either insult alone.

Low-Carbohydrate Diet Modulates Glucose-Lipid Utilization in Skeletal Muscle of Diabetic Mice

Type 2 diabetes is associated with many complications, including skeletal muscle atrophy. Ketogenic diets and low-carbohydrate diets (LCD) have recently been introduced as dietary interventions in patients with diabetes, but their effects on glucose and lipid metabolism in skeletal muscle have not been studied. In the current study, we compared the effects of LCD and ketogenic diet on glucose and lipid metabolism in skeletal muscle of diabetic mice. C57BL/6J mice with type 2 diabetes, constructed by a high-fat diet combined with streptozotocin, were fed a standard diet, a high-fat diet, an LCD, or a ketogenic diet for 14 weeks, respectively. Here, we found that the LCD, rather than the ketogenic diet, retained skeletal muscle weight and suppressed the expression of atrophy-related genes in diabetic mice. In addition, the LCD had more glycolytic/type IIb myofiber content and inhibited forkhead box O1 and pyruvate dehydrogenase kinase 4 expression, leading to improved glucose utilization. However, the ketogenic diet maintained more oxidative/type I myofibers. Moreover, compared with the ketogenic diet, the LCD decreased intramuscular triglycerides content and muscle lipolysis, suggesting improvement in lipid metabolism. Taken together, these data suggested that the LCD improved glucose utilization, and inhibited lipolysis and atrophy in skeletal muscle of diabetic mice, while the ketogenic diet showed metabolic disorders in skeletal muscle.

Expressions of mRNA and encoded proteins of mitochondrial uncoupling protein genes (UCP1, UCP2, and UCP3) in epicardial and mediastinal adipose tissue and associations with coronary artery disease

Objective

To evaluate the expression of UCP1, UCP2, and UCP3 mRNA and encoded proteins in epicardial and mediastinal adipose tissues in patients with coronary artery disease (CAD).

Subjects and methods

We studied 60 patients with CAD and 106 patients undergoing valve replacement surgery (controls). Expression levels of UCP1, UCP2, and UCP3 mRNA and encoded proteins were measured by quantitative real-time PCR and Western blot analysis, respectively.

Results

: We found increased UCP1, UCP2, and UCP3 mRNA levels in the epicardial adipose tissue in the CAD versus the control group, and higher UCP1 and UCP3 mRNA expression in the epicardial compared with the mediastinal tissue in the CAD group. There was also increased expression of UCP1 protein in the epicardial tissue and UCP2 protein in the mediastinum tissue in patients with CAD. Finally, UCP1 expression was associated with levels of fasting plasma glucose, and UCP3 expression was associated with levels of high-density lipoprotein cholesterol and low-density cholesterol in the epicardial tissue.

Conclusion

Our study supports the hypothesis that higher mRNA expression by UCP genes in the epicardial adipose tissue could be a protective mechanism against the production of reactive oxygen species and may guard the myocardium against damage. Thus, UCP levels are essential to maintain the adaptive phase of cardiac injury in the presence of metabolic disorders.

Novel studies on Drosophila melanogaster model reveal the roles of JNK-Jak/STAT axis and intestinal microbiota in insulin resistance

The JNK pathway play a critical role in insulin resistance induced by a long-term high-sugar diet. However, the roles of up- and downstream molecules of the JNK pathway in insulin resistance are less known in vertebrates and invertebrates. As a classical organism in biological research, Drosophila melanogaster (D. melanogaster) has been widely applied to the studies of mechanism of insulin resistance. Based on previous studies, we found a novel predictive mechanism of the formation of insulin resistance in D. melanogaster. We found that JNK activated by high-sugar diet and dysregulated intestinal microbiota could mediate inflammation, and then the activated JNK released Upd3, which in turn stimulated Jak/STAT pathway to release ImpL2. ImpL2 can compete with Drosophila insulin-like peptides (Dilps) for binding with the insulin receptor and inhibit the activation of insulin pathway. In this study, we reviewed novel studies on the insulin signalling pathway based on the D. melanogaster model. The findings support our hypothesis. We, therefore, described how a long-term high-sugar diet disrupts intestinal microbiota to induce inflammation and the disruption of JNK-Jak/STAT axis. This description may offer some new clues to the formation of insulin resistance.

Skeletal muscle insulin resistance and adipose tissue hypertrophy persist beyond the reshaping of gut microbiota in young rats fed a fructose-rich diet

To investigate whether short term fructose-rich diet induces changes in the gut microbiota as well as in skeletal muscle and adipose tissue physiology and verify whether they persist even after fructose withdrawal, young rats of 30 d of age were fed for 3 weeks a fructose-rich or control diet. At the end of the 3-weeks period, half of the rats from each group were maintained for further 3 weeks on a control diet. Metagenomic analysis of gut microbiota and short chain fatty acids levels (faeces and plasma) were investigated. Insulin response was evaluated at the whole-body level and both in skeletal muscle and epididymal adipose tissue, together with skeletal muscle mitochondrial function, oxidative stress, and lipid composition. In parallel, morphology and physiological status of epididymal adipose tissue was also evaluated. Reshaping of gut microbiota and increased content of short chain fatty acids was elicited by the fructose diet and abolished by switching back to control diet. On the other hand, most metabolic changes elicited by fructose-rich diet in skeletal muscle and epididymal adipose tissue persisted after switching to control diet. Increased dietary fructose intake even on a short-time basis elicits persistent changes in the physiology of metabolically relevant tissues, such as adipose tissue and skeletal muscle, through mechanisms that go well beyond the reshaping of gut microbiota. This picture delineates a harmful situation, in particular for the young populations, posed at risk of metabolic modifications that may persist in their adulthood.

Independent, but not co-supplementation, with nitrate and resveratrol improves glucose tolerance and reduces markers of cellular stress in high-fat-fed male mice

Independent supplementation with nitrate (NIT) and resveratrol (RSV) enriches various aspects of mitochondrial biology in key metabolic tissues. Although RSV is known to activate Sirt1 and initiate mitochondrial biogenesis, the metabolic benefits elicited by dietary nitrate appear to be dependent on 5'-adenosine monophosphate-activated protein kinase (AMPK)-mediated signaling events, a process also linked to the activation of Sirt1. Although the benefits of individual supplementation with these compounds have been characterized, it is unknown if co-supplementation may produce superior metabolic adaptations. Thus, we aimed to determine if treatment with combined +NIT and +RSV (+RN) could additively alter metabolic adaptations in the presence of a high-fat diet (HFD). Both +RSV and +NIT improved glucose tolerance compared with HFD (P < 0.05); however, this response was attenuated following combined +RN supplementation. Within skeletal muscle, all supplements increased mitochondrial ADP sensitivity compared with HFD (P < 0.05), without altering mitochondrial content. Although +RSV and +NIT decreased hepatic lipid deposition compared with HFD (P < 0.05), this effect was abolished with +RN, which aligned with significant reductions in Sirt1 protein content (P < 0.05) after combined treatment, in the absence of changes to mitochondrial content or function. Within epididymal white adipose tissue (eWAT), all supplements reduced crown-like structure accumulation compared with HFD (P < 0.0001) and mitochondrial reactive oxygen species (ROS) emission (P < 0.05), alongside reduced adipocyte cross-sectional area (CSA) (P < 0.05), with the greatest effect observed after +RN treatment (P = 0.0001). Although the present data suggest additive changes in adipose tissue metabolism after +RN treatment, concomitant impairments in hepatic lipid homeostasis appear to prevent improvements in whole body glucose homeostasis observed with independent treatment, which may be Sirt1 dependent.

The impact of high-fat feeding and parkin overexpression on skeletal muscle mass, mitochondrial respiration, and H2O2 emission

Obesity is a major risk factor for developing various health problems, including insulin resistance and type 2 diabetes. Although controversial, accumulation of mitochondrial dysfunction, and notably an increase in mitochondrial reactive oxygen species (ROS) production, was proposed as a key contributor leading to obesity-induced insulin resistance. Here, our goal was to investigate whether Parkin overexpression, a key regulator of the removal of dysfunctional mitochondria through mitophagy, could confer protection against obesity-induced mitochondrial dysfunction. To this end, intramuscular injections of adeno-associated viruses (AAVs) were performed to overexpress Parkin in limb muscle of 6-mo-old mice fed a control diet (CD) or a high-fat diet (HFD) for 12 wk. An AAV-expressing the green fluorescent protein (GFP) was used as control. HFD increased fat mass, altered glycemia, and resulted in insulin resistance. Parkin overexpression resulted in an increase in muscle mass in both CD and HFD mice. In CD mice, Parkin overexpression increased maximal mitochondrial respiration and lowered H₂O₂ emission. HFD increased mitochondrial respiration and, surprisingly, also lowered H₂O₂ emission. Parkin overexpression did not significantly impact mitochondrial function in HFD mice. Taken altogether, our results indicate that Parkin overexpression positively impacts muscle and mitochondrial health under basal conditions and challenges the notion that intrinsic mitochondrial dysfunction is involved in the development of insulin resistance caused by high-fat feeding.

Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial

BACKGROUND

Elevated oxidative stress (OxS), mitochondrial dysfunction, and hallmarks of aging are identified as key contributors to aging, but improving/reversing these defects in older adults (OA) is challenging. In prior studies, we identified that deficiency of the intracellular antioxidant glutathione (GSH) could play a role and reported that supplementing GlyNAC (combination of glycine and N-acetylcysteine [NAC]) in aged mice improved GSH deficiency, OxS, mitochondrial fatty-acid oxidation (MFO), and insulin resistance (IR). To test whether GlyNAC supplementation in OA could improve GSH deficiency, OxS, mitochondrial dysfunction, IR, physical function, and aging hallmarks, we conducted a placebo-controlled randomized clinical trial.

METHODS

Twenty-four OA and 12 young adults (YA) were studied. OA was randomized to receive either GlyNAC (N = 12) or isonitrogenous alanine placebo (N = 12) for 16-weeks; YA (N = 12) received GlyNAC for 2-weeks. Participants were studied before, after 2-weeks, and after 16-weeks of supplementation to assess GSH concentrations, OxS, MFO, molecular regulators of energy metabolism, inflammation, endothelial function, IR, aging hallmarks, gait speed, muscle strength, 6-minute walk test, body composition, and blood pressure.

RESULTS

Compared to YA, OA had GSH deficiency, OxS, mitochondrial dysfunction (with defective molecular regulation), inflammation, endothelial dysfunction, IR, multiple aging hallmarks, impaired physical function, increased waist circumference, and systolic blood pressure. GlyNAC (and not placebo) supplementation in OA improved/corrected these defects.

CONCLUSION

GlyNAC supplementation in OA for 16-weeks was safe and well-tolerated. By combining the benefits of glycine, NAC and GSH, GlyNAC is an effective nutritional supplement that improves and reverses multiple age-associated abnormalities to promote health in aging humans. Clinical Trials Registration Number: NCT01870193.

Ginsenoside CK improves skeletal muscle insulin resistance by activating DRP1/PINK1-mediated mitophagy

Skeletal muscle insulin resistance is the main cause of type 2 diabetes, and mitochondria play a key role. Ginsenoside CK is the main active compound of ginseng with a variety of therapeutic effects, but few studies have reported on its mechanism towards skeletal muscle insulin resistance. Here, we found that CK significantly increased skeletal muscle insulin sensitivity, thereby alleviating hyperglycemia and insulin resistance. Furthermore, the effects of CK on skeletal muscle were associated with an improved mitochondrial fusion/fission dynamics balance and fatty acid oxidation. In fatty acid (FA)-induced C2C12 cells, CK promoted the translocation of GLUT4 to the cell membrane to improve glucose uptake and glycogen synthesis and also enhanced the mitochondrial quality. CK ameliorated the damaged mitochondrial membrane potential (ΔΨ_m), which was based on mitophagy activation. After the knockdown of mitophagy-related receptors, we found that DRP1/PINK1 was the key pathway of CK-induced mitophagy. These findings indicated that ginsenoside CK is a promising lead compound against diabetes.

Virgin coconut oil reverses behavioral phenotypes of letrozole-model of PCOS in Wistar rats via modulation of NRF2 upregulation

Objectives

Polycystic ovarian syndrome (PCOS) is an endocrine disorder associated with insulin resistance, hyperandrogenism, and sub-infertility. Virgin coconut oil (VCO) has been reported to have health benefits, such as anti-inflammatory, anti-oxidant, and antiviral properties. This study investigated the effects of dietary VCO supplementation on memory and cognitive impairment in female rats with letrozole induced PCOS.

Methods

Thirty female rats were randomly divided into five groups. All rats except controls were treated with letrozole for 21 days to induce PCOS and were subsequently treated for 14 days with 10% VCO, clomiphene (CLO), or VCO + CLO. Three neurobehavioral tests were conducted: elevated plus maze, Y maze, and novel object recognition tests.

Results

Our results indicated statistically elevated serum concentrations of sex hormones in rats with PCOS, compared with the control and treated groups. In addition, all treated groups showed significant reversal of the low serum concentrations of catalase and down-regulated gene expression of Nrf2 in the hippocampus seen in the PCOS rats. In addition, gene expression of acetylcholine esterase was up-regulated in PCOS rats, and was statistically reverted in the VCO treated groups.

Conclusion

Anxiety-like behavior and impaired short-term memory were observed in PCOS rats; however, VCO supplementation reversed these effects by modulating the gene expression of Nrf2 and AchE.

Overexpression of IGF2 affects mouse weight and glycolipid metabolism and IGF2 is positively related to macrosomia

Objective

To investigate the effects of insulin-like growth factor 2 (IGF2) on growth and glycolipid metabolism, as well as the underlying mechanism.

Methods

A mouse model of IGF2 overexpression was constructed to measure weight gain before adulthood, to obtain the values of adult glycolipid metabolism indicators in the peripheral blood and to detect the expression of genes in the IGF2 signaling pathway in different mouse tissues. The present study also explored the independent association between the IGF2 gene and macrosomia by detecting and comparing the expression levels of IGF2 mRNA/H19 RNA in maternal peripheral blood and fetal cord blood of 26 human pregnancies.

Results

In the mouse model, weights of the IGF2-overexpressing mice were significantly higher than those of the control mice at the age of 5-10 weeks. The glucose concentration, total cholesterol and high-density lipoprotein cholesterol (HDL-C) levels of IGF2-overexpressing mice were significantly lower than those of wild-type (WT) mice. Compared with the WT mice, the expression of H19 was significantly decreased in the pancreas and IGF1R was significantly decreased in the muscle of mice with IGF2 overexpression. The expression levels of STAT3 and AKT2 showed significant decrease in liver, muscle and increase in muscle of IGF2-overexpressing mice, respectively. GLUT2 expression showed significant increase in liver, kidney, muscle and decrease in pancreas of mice with IGF2 overexpression. This study also found that in normal mothers with the similar clinical characteristics, IGF2 expression in the maternal peripheral blood and fetal cord blood is an independent factor influencing macrosomia.

Conclusion

IGF2 expression was independently correlated with the occurrence of macrosomia, and overexpression of IGF2 significantly increased the weights of mice at the age of 5-10 weeks and significantly affected the values of adult glycolipid metabolism indicators, which might be the result of changes in the IGF2-IGF1R-STAT3/AKT2-GLUT2/GLUT4 pathway. These findings might suggest that IGF2 plays an important role in growth and glycolipid metabolism during both pregnancy and postnatal development.

Insulin resistance phenotype is associated with vascular risk phenotype at the end of the second decade of life: a population-based study

We hypothesize that early events of diabetes and cardiovascular disease continuums would be ongoing and associated in adolescents. We investigated the association between the Insulin Resistance Phenotype and the Vascular Risk Phenotype at the end of the second decade of life and indirect pathways from social vulnerability, alcohol consumption, and body fat mass. It is a population-based study in the RPS cohort of 18-19 years (n = 2,515), São Luís, Brazil. The theoretical model analyzed the association between Insulin Resistance Phenotype and Vascular Risk Phenotype by sex, using structural equation modeling (SEM). The Insulin Resistance Phenotype was a latent variable deduced from the correlations of Triglyceride to HDL ratio, Triglyceride Glycemic index, and VLDL; the Vascular Risk Phenotype was deduced from Systolic Blood Pressure, Diastolic Blood Pressure, and Pulse Wave Velocity. The Insulin Resistance Phenotype was directly associated with the Vascular Risk Phenotype in males (standardized coefficient SC = 0.183; p < 0.001) and females (SC = 0.152; p < 0.001). The Insulin Resistance Phenotype was an indirect pathway in the association of alcohol consumption and higher values of fat mass index with the Vascular Risk Phenotype. VLDL presented the highest factor loading, appearing as a marker of insulin resistance linked to cardiovascular risk in young people. Lower values of socioeconomic status, harmful use of alcohol, and high body fat values were also associated with higher values of the two phenotypes. The association of the Insulin Resistance Phenotype with the Vascular Risk Phenotype suggests common pathophysiological mechanisms present in early events in the continuums of diabetes and cardiovascular disease in adolescence.

Salvianolic acid A promotes mitochondrial biogenesis and mitochondrial function in 3T3-L1 adipocytes through regulation of the AMPK-PGC1α signalling pathway

Mitochondrial dysfunction is associated with insulin resistance and type 2 diabetes (T2DM). Decreased mitochondrial abundance and function were found in white adipose tissue (WAT) of T2DM patients. Therefore, promoting WAT mitochondrial biogenesis and improving adipocyte metabolism may be strategies to prevent and reverse T2DM. Salvianolic acid A (SAA) has been found to exert anti-diabetic and lipid disorder-improving effects. However whether SAA benefits mitochondrial biogenesis and function in adipose tissue is unclear. Here, we evaluated SAA's effect on mitochondrial biogenesis and function in 3T3-L1 adipocytes and investigated its potential regulatory mechanism. Results showed that SAA treatment significantly promoted the transcription and expression of peroxisome proliferator-activated receptor γ coactivator- 1α (PGC-1α), nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM). Meanwhile, SAA treatment significantly promoted mitochondrial biogenesis by increasing mitochondrial DNA (mtDNA) quantity, mitochondrial mass, and expression of mitochondrial respiratory chain enzyme complexes III and complex IV. These enhancements were accompanied by enhanced phosphorylation of AMPK and ACC and were suppressed by Compound C, a specific AMPK inhibitor. Furthermore, SAA treatment improved adipocytes mitochondrial respiration and stimulated ATP generation. These findings indicate that SAA exerts a potential therapeutic capacity against adipocytes mitochondrial dysfunction in diabetes by activating the AMPK-PGC-1α pathway.