Fast regulation of the NF-κB signalling pathway in human skeletal muscle revealed by high-intensity exercise and ischaemia at exhaustion: Role of oxygenation and metabolite accumulation

Respiratory toxicity mechanism of 6PPD and 6PPD-quinone: An integrated study based on network toxicology and molecular docking

The widespread distribution of environmental contaminants poses a significant threat to public health. N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its ozone-derivative, 6PPD-quinone (6PPD-Q), are emerging pollutants that propagate through particulate matter and aerosols, exerting detrimental effects on the respiratory system. However, their specific pathogenic mechanisms remain unclear. This study employs integrated network toxicology and molecular docking to elucidate the molecular basis of 6PPD/6PPD-Q-induced respiratory toxicity. Respiratory hazard potential was predicted using ADMETlab 3.0 and ProTox-II. Potential targets were identified through multi-database mining (BindingDB, ChEMBL, SwissTargetPrediction, TargetNet), with disease-associated targets categorized into acute and chronic respiratory damage using GeneCards and OMIM. Intersectional analysis via Venn diagrams, STRING, and Cytoscape revealed compound-specific targets (EGFR for 6PPD; FYN for 6PPD-Q) and five shared targets (NR3C1, MAPK14, RELA, CYCS, JAK2). Enrichment analysis using DAVID indicated significant associations with mitochondrial energy metabolism, oxidative stress, apoptosis and neuroactive ligand-receptor interactions (p < 0.05). Molecular docking and molecular dynamics simulations confirmed that both compounds showed high affinity binding to key toxicity targets (binding energy <-20.92 kJ/mol), and revealed the interaction mode of these two compounds with the key target CYCS. Mechanistically, 6PPD and 6PPD-Q disrupt the mitochondrial electron transport chain, dysregulate apoptotic pathways, and activate NF-κB/JAK-STAT inflammatory cascades, leading to respiratory inflammation. This study establishes a comparative toxicological framework for 6PPD and 6PPD-Q, identifying actionable molecular targets and mechanistic pathways for respiratory toxicity, and highlights the utility of computational toxicology strategies in environmental health risk assessment.

OXA1L deficiency causes mitochondrial myopathy via reactive oxygen species regulated nuclear factor kappa B signalling pathway

BACKGROUND

OXA1L is crucial for mitochondrial protein insertion and assembly into the inner mitochondrial membrane, and its variants have been recently linked to mitochondrial encephalopathy. However, the definitive pathogenic link between OXA1L variants and mitochondrial diseases as well as the underlying pathogenesis remains elusive.

METHODS

In this study, we identified bi-allelic variants of c.620G>T, p.(Cys207Phe) and c.1163_1164del, p.(Val388Alafs*15) in OXA1L gene in a mitochondrial myopathy patient using whole exome sequencing. To unravel the genotype-phenotype relationship and underlying pathogenic mechanism between OXA1L variants and mitochondrial diseases, patient-specific human-induced pluripotent stem cells (hiPSC) were reprogrammed and differentiated into myotubes, while OXA1L knockout human immortalised skeletal muscle cells (IHSMC) and a conditional skeletal muscle knockout mouse model was generated using clustered regularly interspaced short palindromic repeats/Cas9 genomic editing technology.

RESULTS

Both patient-specific hiPSC differentiated myotubes and OXA1L knockout IHSMC showed combined mitochondrial respiratory chain defects and oxidative phosphorylation (OXPHOS) impairments. Notably, in OXA1L-knockout IHSMC, transfection of wild-type human OXA1L but not truncated mutant form rescued the respiratory chain defects. Moreover, skeletal muscle conditional Oxa1l knockout mice exhibited OXPHOS deficiencies and skeletal muscle morphofunctional abnormalities, recapitulating the phenotypes of mitochondrial myopathy. Further functional investigations revealed that impaired OXPHOS resulting of OXA1L deficiency led to elevated reactive oxygen species production, which possibly activated the nuclear factor kappa B signalling pathway, triggering cell apoptosis.

CONCLUSIONS

Together, our findings reinforce the genotype-phenotype association between OXA1L variations and mitochondrial diseases and further delineate the potential molecular mechanisms of how OXA1L deficiency causes skeletal muscle deficits in mitochondrial myopathy.

KEYPOINTS

OXA1L gene bi-allelic variants cause mitochondrial myopathy. OXA1L deficiency results in combined mitochondrial respiratory chain defects and OXPHOS impairments. OXA1L deficiency leads to elevated ROS production, which may activate the NF-κB signalling pathway, disturbing myogenic gene expression and triggering cell apoptosis.

Intracellular L-PGDS-Derived 15d-PGJ2 Inhibits CaMKII Through Lipoxidation to Alleviate Cardiac Ischemia/Reperfusion Injury

BACKGROUND

Myocardial ischemia/reperfusion (I/R) injury is a substantial challenge to the management of ischemic heart disease, the leading cause of mortality worldwide. Arachidonic acid (AA) is a prominent polyunsaturated fatty acid in the human body and plays an important role in various physiological and pathological conditions. AA metabolic enzymes determine AA levels; however, currently there is no comprehensive analysis of AA enzymes in cardiac I/R injury.

METHODS

The profiling of AA metabolic enzymes was analyzed with the RNA sequencing transcriptome data from the mouse heart tissues with I/R injury. Cultured neonatal and adult rat ventricular myocytes, human embryonic stem cell-derived cardiomyocytes, and in vivo mouse I/R models were used to confirm the role of L-PGDS (lipocalin-type prostaglandin D2 synthase)/15d-PGJ2 in I/R injury. A biotin-tagged 15d-PGJ2 analog combined with liquid chromatography-tandem mass spectrometry was used to identify the downstream signaling of L-PGDS/15d-PGJ2.

RESULTS

Based on the transcriptome data and experimental validations, L-PGDS, together with its downstream metabolite 15d-PGJ2, was downregulated in cardiac tissue with I/R injury. Functionally, L-PGDS overexpression mitigates myocardial I/R injury, whereas knockdown exacerbates the damage. Supplementation of 15d-PGJ2 alleviated I/R injury. Mechanistically, 15d-PGJ2 covalently bound to the Ca2+/CaMKII (calmodulin protein kinase II) and induced lipoxidation of its cysteine 495 (CaMKII-δ9) to dampen the formation of CaMKII oligomers and alleviate its overactivation, consequently ameliorating cardiomyocyte death and cardiac injury.

CONCLUSIONS

Our study uncovered L-PGDS/15d-PGJ2/CaMKII signaling as a new mechanism underlying I/R-induced cardiomyocyte death. This provides new mechanistic insights and therapeutic targets for myocardial I/R injury and subsequent heart failure. We also showed that lipoxidation is a new post-translational modification type for CaMKII, deepening our understanding of the regulation of its activity.

Redox signaling‑mediated muscle atrophy in ACL injury: Role of physical exercise (Review)

Muscle atrophy frequently occurs in patients with anterior cruciate ligament (ACL) injury, despite active participation in muscle strengthening programs. Without appropriate countermeasures such as exercise and pharmacological interventions, the atrophy may worsen. At the cellular and molecular levels, various protein synthesis‑related pathways and redox‑dependent molecules regulate processes associated with atrophy by activating or deactivating key signaling pathways. Muscle atrophy and the associated dysfunction can be reversed by physical exercise, which increases protein synthesis, thereby improving muscle strength and function around the ACL. However, the influence of different features of exercise protocols, including exercise type, intensity and duration, as well as the individual capacity of the patient, on the activity of the aforementioned pathways requires further investigation. Additionally, the mechanism by which redox‑sensitive molecules attenuate atrophy in ACL injury remains to be fully understood. The present review discusses exercise, signaling pathways and muscle atrophy in ACL injury, and highlights potential therapeutic strategies. These findings may also have implications for other joint diseases associated with ACL‑related injury.

Extracellular matrix-mimicking cryogels composed of methacrylated fucoidan enhance vascularized skeletal muscle regeneration following volumetric muscle loss

Volumetric muscle loss (VML) significantly impairs the inherent regenerative ability of skeletal muscle and results in chronic functional impairment. Polysaccharides in the muscle extracellular matrix are crucial for regulating cell proliferation and differentiation. Recent studies indicate that fucoidan has beneficial effects on musculoskeletal conditions. However, the impact of fucoidan on skeletal muscle regeneration remains poorly understood. In this study, methacrylated fucoidan (FuMA) was synthesized through chemical grafting of the methacryloyl group onto fucoidan. In vitro experiments demonstrated that treatment with FuMA significantly up-regulated the expression of myogenic markers and promoted the formation of myotubes in C2C12 myoblast cells. Importantly, FuMA treatment led to a significant enhancement in mitochondrial energy metabolism of myoblasts via activation of the NRF2 antioxidant signaling pathway. To further investigate the regenerative properties in repairing skeletal muscle defects, we fabricated a dual crosslinked cryogel consisting of FuMA and methacrylated gelatin (GelMA) with a porous and interconnected structure. In a rat tibialis anterior muscle VML model, implantation of the FuMA/GelMA cryogel effectively promoted the regeneration of muscle fibers, reduced collagen deposition, and facilitated the formation of new blood vessels. Hence, polysaccharide-based cryogels represent a promising implantable biomimetic scaffold for facilitating skeletal muscle regeneration following severe injuries.

CaMKII protein expression and phosphorylation in human skeletal muscle by immunoblotting: Isoform specificity

Calcium (Ca2+)/calmodulin-dependent protein kinase II (CaMKII) is activated during exercise by reactive oxygen species (ROS) and Ca2+ transients initiating muscle contraction. CaMKII modulates antioxidant, inflammatory, metabolic and autophagy signalling pathways. CaMKII is coded by four homologous genes (α, β, γ, and δ). In rat skeletal muscle, δD, δA, γD, γB and βM have been described while different characterisations of human skeletal muscle CaMKII isoforms have been documented. Precisely discerning between the various isoforms is pivotal for understanding their distinctive functions and regulatory mechanisms in response to exercise and other stimuli. This study aimed to optimize the detection of the different CaMKII isoforms by western blotting using eight different CaMKII commercial antibodies in human skeletal muscle. Exercise-induced posttranslational modifications, i.e. phosphorylation and oxidations, allowed the identification of specific bands by multitargeting them with different antibodies after stripping and reprobing. The methodology proposed has confirmed the molecular weight of βM CaMKII and allows distinguishing between γ/δ and δD CaMKII isoforms. The corresponding molecular weight for the CaMKII isoforms resolved were: δD, at 54.2 ± 2.1 kDa; γ/δ, at 59.0 ± 1.2 kDa and 61.6 ± 1.3 kDa; and βM isoform, at 76.0 ± 1.8 kDa. Some tested antibodies showed high specificity for the δD, the most responsive isoform to ROS and intracellular Ca2+ transients in human skeletal muscle, while others, despite the commercial claims, failed to show such specificity.

Unlocking peak performance: The role of Nrf2 in enhancing exercise outcomes and training adaptation in humans

Since the discovery of the nuclear factor erythroid-derived 2-like 2 (Nrf2) transcription factor thirty years ago, it has been shown that it regulates more than 250 genes involved in a multitude of biological processes, including redox balance, mitochondrial biogenesis, metabolism, detoxification, cytoprotection, inflammation, immunity, autophagy, cell differentiation, and xenobiotic metabolism. In skeletal muscle, Nrf2 signalling is primarily activated in response to perturbation of redox balance by reactive oxygen species or electrophiles. Initial investigations into human skeletal muscle Nrf2 responses to exercise, dating back roughly a decade, have consistently indicated that exercise-induced ROS production stimulates Nrf2 signalling. Notably, recent studies employing Nrf2 knockout mice have revealed impaired skeletal muscle contractile function characterised by reduced force output and increased fatigue susceptibility compared to wild-type counterparts. These deficiencies partially stem from diminished basal mitochondrial respiratory capacity and an impaired capacity to upregulate specific mitochondrial proteins in response to training, findings corroborated by inducible muscle-specific Nrf2 knockout models. In humans, baseline Nrf2 expression in skeletal muscle correlates with maximal oxygen uptake and high-intensity exercise performance. This manuscript delves into the mechanisms underpinning Nrf2 signalling in response to acute exercise in human skeletal muscle, highlighting the involvement of ROS, antioxidants and Keap1/Nrf2 signalling in exercise performance. Furthermore, it explores Nrf2's role in mediating adaptations to chronic exercise and its impact on overall exercise performance. Additionally, the influence of diet and certain supplements on basal Nrf2 expression and its role in modulating acute and chronic exercise responses are briefly addressed.

Reactive oxygen species promote endurance exercise-induced adaptations in skeletal muscles

The discovery that contracting skeletal muscle generates reactive oxygen species (ROS) was first reported over 40 years ago. The prevailing view in the 1980s was that exercise-induced ROS production promotes oxidation of proteins and lipids resulting in muscle damage. However, a paradigm shift occurred in the 1990s as growing research revealed that ROS are signaling molecules, capable of activating transcriptional activators/coactivators and promoting exercise-induced muscle adaptation. Growing evidence supports the notion that reduction-oxidation (redox) signaling pathways play an important role in the muscle remodeling that occurs in response to endurance exercise training. This review examines the specific role that redox signaling plays in this endurance exercise-induced skeletal muscle adaptation. We begin with a discussion of the primary sites of ROS production in contracting muscle fibers followed by a summary of the antioxidant enzymes involved in the regulation of ROS levels in the cell. We then discuss which redox-sensitive signaling pathways promote endurance exercise-induced muscle adaptation and debate the strength of the evidence supporting the notion that redox signaling plays an essential role in muscle adaptation to endurance exercise training. In hopes of stimulating future research, we highlight several important unanswered questions in this field.

Based on Sportomics: Comparison of Physiological Status of Collegiate Sprinters in Different Pre-Competition Preparation Periods

This study aimed to assess the impact of pre-competition training by comparing the differences of collegiate sprinters in physiological state between strengthening and tapering training period by sportomics and combining their sport performance. Fifteen collegiate sprinters were investigated or tested on their body composition, dietary habits, energy expenditure, sleep efficiency, heart rate and respiratory rate during training, blood (blood cells, biochemical and immune markers) and urine (urinalysis), gut microbiome distribution, microbiome and blood metabolites, and their functions during the strengthening (Group A) and tapering training period (Group B) prior to competing in the national competitions. We found that 26.67% of sprinters achieved personal bests (PB) after the competition. The limb skeletal muscle mass and lymphocyte ratio of male sprinters in Group B were lower than those in Group A, and the serum creatine kinase (CK) level was higher than Group A (p < 0.05). The levels of serum CK, interleukin-6 (IL-6), interleukin-1β (IL-1β), and urine-specific gravity (SG) of the two groups were higher than the upper limit of the reference value. The detection rates of urine white blood cell (WBC) and protein in Group B were higher than those in Group A. The gut microbiome health index (GMHI) of Group A was higher than that of Group B, and the microbial dysbiosis index was lower than that of Group B. The ratio of Firmicutes/Bacteroidota (F/B) in Group A was higher than that in Group B. There were 65 differential metabolites in the A/B group, and the enriched pathway was mainly the NF-kappa B signaling pathway (up); B/T cell receptor signaling pathway (up); Th1 and Th2 cell differentiation (up); phenylalanine metabolism (up); and growth hormone synthesis, secretion, and action (up). There were significant differences in blood metabolites between the A and B groups, with a total of 89 differential metabolites, and the enriched pathway was mainly the NF-kappa B signaling pathway (up), T cell receptor signaling pathway (up), Th1 and Th2 cell differentiation (up), and glycerophospholipid metabolism (down). In conclusion, the imbalance of the gut microbiome and inflammation and immune-related metabolites of collegiate sprinters during the pre-competition tapering training period may be the cause of their limited sports performance.

Phycocyanin attenuates skeletal muscle damage and fatigue via modulation of Nrf2 and IRS-1/AKT/mTOR pathway in exercise-induced oxidative stress in rats

Prolonged strenuous exercise induces oxidative stress, leading to oxidative damage, skeletal muscle fatigue, and reduced exercise performance. The body compensates for oxidative stress through antioxidant actions, while related enzymes alone may not overcome excessive oxidative stress during prolonged strenuous exercise. Phycocyanin is an important antioxidant supplement derived from blue-green algae, which may be helpful in this type of situation. This study determined the effects of phycocyanin on exercise performance from prolonged strenuous exercise. Forty Sprague Dawley male rats were divided into 5 groups (n = 8 /group); Control group (C), Exercise group (E), and Exercise with supplement groups receiving low dose (Phycocyanin = 100 mg/kg BW; ELP) and high dose (Phycocyanin = 200 mg/kg BW; EHP) or vitamin C (Vitamin C = 200 mg/kg BW; VC). Phycocyanin was found to decrease oxidative damage markers, muscle fatigue, and muscle atrophy through the activated AKT/mTOR pathway. This was also found to have greater increases in antioxidants via Nrf2 signaling and increases ATP synthesis, GLUT4 transporters, and insulin signaling due to increased IRS-1/AKT signaling. In conclusion, phycocyanin was found to reduce oxidative damage and muscle atrophy, including an increase in insulin signaling in skeletal muscles leading to increased exercise performance in rats.

Activation of macroautophagy and chaperone-mediated autophagy in human skeletal muscle by high-intensity exercise in normoxia and hypoxia and after recovery with or without post-exercise ischemia

Autophagy is essential for the adaptive response to exercise and physiological skeletal muscle functionality. However, the mechanisms leading to the activation of macroautophagy and chaperone-mediated autophagy in human skeletal muscle in response to high-intensity exercise remain elusive. Our findings demonstrate that macroautophagy and chaperone-mediated autophagy are stimulated by high-intensity exercise in normoxia (PIO2: 143 mmHg) and severe acute hypoxia (PIO2: 73 mmHg) in healthy humans. High-intensity exercise induces macroautophagy initiation through AMPKα phosphorylation, which phosphorylates and activates ULK1. ULK1 phosphorylates BECN1 at Ser15, eliciting the dissociation of BECN1-BCL2 crucial for phagophore formation. Besides, high-intensity exercise elevates the LC3B-II:LC3B-I ratio, reduces total SQSTM1/p62 levels, and induces p-Ser349 SQSTM1/p62 phosphorylation, suggesting heightened autophagosome degradation. PHAF1/MYTHO, a novel macroautophagy biomarker, is highly upregulated in response to high-intensity exercise. The latter is accompanied by elevated LAMP2A expression, indicating chaperone-mediated autophagy activation regardless of post-exercise HSPA8/HSC70 downregulation. Despite increased glycolytic metabolism, severe acute hypoxia does not exacerbate the autophagy signaling response. Signaling changes revert within 1 min of recovery with free circulation, while the application of immediate post-exercise ischemia impedes recovery. Our study concludes that macroautophagy and chaperone-mediated autophagy pathways are strongly activated by high-intensity exercise, regardless of PO2, and that oxygenation is necessary to revert these signals to pre-exercise values. PHAF1/MYTHO emerges as a pivotal exercise-responsive autophagy marker positively associated with the LC3B-II:LC3B-I ratio.

Exercise entrainment of musculoskeletal connective tissue clocks

The musculoskeletal system, crucial for movement and support, relies on the delicate balance of connective tissue homeostasis. Maintaining this equilibrium is essential for tissue health and function. There has been increasing evidence in the past decade that shows the circadian clock as a master regulator of extracellular matrix (ECM) homeostasis in several connective tissue clocks. Very recently, exercise has emerged as a significant entrainment factor for cartilage and intervertebral disk circadian rhythms. Understanding the implications of exercise on connective tissue peripheral clocks holds promise for enhancing tissue health and disease prevention. Exercise-induced factors such as heat, glucocorticoid release, mechanical loading, and inter-tissue cross talk may play pivotal roles in entraining the circadian rhythm of connective tissues. This mini review underscores the importance of elucidating the mechanisms through which exercise influences circadian rhythms in connective tissues to optimize ECM homeostasis. Leveraging exercise as a modulator of circadian rhythms in connective tissues may offer novel therapeutic approaches to physical training for preventing musculoskeletal disorders and enhancing recovery.

Demystifying roles of exercise in immune response regulation against acute respiratory infections: A narrative review

The benefits of physical activity and exercise, especially those classified as moderate-to-vigorous activity (MVPA), have been well-established in preventing non-communicable diseases and mental health problems in healthy adults. However, the relationship between physical activity and exercise and the prevention and management of acute respiratory infection (ARI), a global high-burden disease, has been inconclusive. There have been debates and disagreements among scientific publications regarding the relationship between exercise and immune response against the causative agents of ARI. This narrative review aims to explore the theory that sufficiently explains the correlation between exercise, immune response, and ARI. The potential root causes of discrepancies come from research associated with the "open window" hypothesis. The studies have several limitations, and future improvements to address them are urgently needed in the study design, data collection, exercise intervention, subject recruitment, biomarkers for infection and inflammation, nutritional and metabolism status, and in addressing confounding variables. In conclusion, data support the clinical advantages of exercise have a regulatory contribution toward improving the immune response, which in turn potentially protects humans fromARI. However, the hypothesis related to its negative effect must be adopted cautiously.

NF-κB in biology and targeted therapy: new insights and translational implications

NF-κB signaling has been discovered for nearly 40 years. Initially, NF-κB signaling was identified as a pivotal pathway in mediating inflammatory responses. However, with extensive and in-depth investigations, researchers have discovered that its role can be expanded to a variety of signaling mechanisms, biological processes, human diseases, and treatment options. In this review, we first scrutinize the research process of NF-κB signaling, and summarize the composition, activation, and regulatory mechanism of NF-κB signaling. We investigate the interaction of NF-κB signaling with other important pathways, including PI3K/AKT, MAPK, JAK-STAT, TGF-β, Wnt, Notch, Hedgehog, and TLR signaling. The physiological and pathological states of NF-κB signaling, as well as its intricate involvement in inflammation, immune regulation, and tumor microenvironment, are also explicated. Additionally, we illustrate how NF-κB signaling is involved in a variety of human diseases, including cancers, inflammatory and autoimmune diseases, cardiovascular diseases, metabolic diseases, neurological diseases, and COVID-19. Further, we discuss the therapeutic approaches targeting NF-κB signaling, including IKK inhibitors, monoclonal antibodies, proteasome inhibitors, nuclear translocation inhibitors, DNA binding inhibitors, TKIs, non-coding RNAs, immunotherapy, and CAR-T. Finally, we provide an outlook for research in the field of NF-κB signaling. We hope to present a stereoscopic, comprehensive NF-κB signaling that will inform future research and clinical practice.

The Acute, Short-, and Long-Term Effects of Endurance Exercise on Skeletal Muscle Transcriptome Profiles

A better understanding of the cellular and molecular mechanisms that are involved in skeletal muscle adaptation to exercise is fundamentally important to take full advantage of the enormous benefits that exercise training offers in disease prevention and therapy. The aim of this study was to elucidate the transcriptional signatures that distinguish the endurance-trained and untrained muscles in young adult males (24 ± 3.5 years). We characterized baseline differences as well as acute exercise-induced transcriptome responses in vastus lateralis biopsy specimens of endurance-trained athletes (ET; n = 8; VO2max, 67.2 ± 8.9 mL/min/kg) and sedentary healthy volunteers (SED; n = 8; VO2max, 40.3 ± 7.6 mL/min/kg) using microarray technology. A second cohort of SED volunteers (SED-T; n = 10) followed an 8-week endurance training program to assess expression changes of selected marker genes in the course of skeletal muscle adaptation. We deciphered differential baseline signatures that reflected major differences in the oxidative and metabolic capacity of the endurance-trained and untrained muscles. SED-T individuals in the training group displayed an up-regulation of nodal regulators of oxidative adaptation after 3 weeks of training and a significant shift toward the ET signature after 8 weeks. Transcriptome changes provoked by 1 h of intense cycling exercise only poorly overlapped with the genes that constituted the differential baseline signature of ETs and SEDs. Overall, acute exercise-induced transcriptional responses were connected to pathways of contractile, oxidative, and inflammatory stress and revealed a complex and highly regulated framework of interwoven signaling cascades to cope with exercise-provoked homeostatic challenges. While temporal transcriptional programs that were activated in SEDs and ETs were quite similar, the quantitative divergence in the acute response transcriptomes implicated divergent kinetics of gene induction and repression following an acute bout of exercise. Together, our results provide an extensive examination of the transcriptional framework that underlies skeletal muscle plasticity.

The Molecular Mechanisms of Fuel Utilization during Exercise

Exercise is widely recognized for its positive impact on human health and well-being. The process of utilizing substrates in skeletal muscle during exercise is intricate and governed by complex mechanisms. Carbohydrates and lipids serve as the primary fuel sources for skeletal muscle during exercise. It is now understood that fuel selection during exercise is not solely determined by physical activity itself but is also influenced by the overall metabolic state of the body. The balance between lipid and carbohydrate utilization significantly affects exercise capacity, including endurance, fatigue, and overall performance. Therefore, comprehensively understanding the regulation of substrate utilization during exercise is of utmost importance. The aim of this review is to provide an extensive overview of the current knowledge regarding the pathways involved in the regulation of substrate utilization during exercise. By synthesizing existing research, we can gain a holistic perspective on the intricate relationship between exercise, metabolism, and fuel selection. This advanced understanding has the potential to drive advancements in the field of exercise science and contribute to the development of personalized exercise strategies for individuals looking to optimize their performance and overall health.

Determinants of the maximal functional reserve during repeated supramaximal exercise by humans: The roles of Nrf2/Keap1, antioxidant proteins, muscle phenotype and oxygenation

When high-intensity exercise is performed until exhaustion a "functional reserve" (FR) or capacity to produce power at the same level or higher than reached at exhaustion exists at task failure, which could be related to reactive oxygen and nitrogen species (RONS)-sensing and counteracting mechanisms. Nonetheless, the magnitude of this FR remains unknown. Repeated bouts of supramaximal exercise at 120% of VO2max interspaced with 20s recovery periods with full ischaemia were used to determine the maximal FR. Then, we determined which muscle phenotypic features could account for the variability in functional reserve in humans. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation (near-infrared spectroscopy) were measured, and resting muscle biopsies were obtained from 43 young healthy adults (30 males). Males and females had similar aerobic (VO2max per kg of lower extremities lean mass (LLM): 166.7 ± 17.1 and 166.1 ± 15.6 ml kg LLM-1.min-1, P = 0.84) and anaerobic fitness (similar performance in the Wingate test and maximal accumulated oxygen deficit when normalized to LLM). The maximal FR was similar in males and females when normalized to LLM (1.84 ± 0.50 and 2.05 ± 0.59 kJ kg LLM-1, in males and females, respectively, P = 0.218). This FR depends on an obligatory component relying on a reserve in glycolytic capacity and a putative component generated by oxidative phosphorylation. The aerobic component depends on brain oxygenation and phenotypic features of the skeletal muscles implicated in calcium handling (SERCA1 and 2 protein expression), oxygen transport and diffusion (myoglobin) and redox regulation (Keap1). The glycolytic component can be predicted by the protein expression levels of pSer40-Nrf2, the maximal accumulated oxygen deficit and the protein expression levels of SOD1. Thus, an increased capacity to modulate the expression of antioxidant proteins involved in RONS handling and calcium homeostasis may be critical for performance during high-intensity exercise in humans.

Modified Curcuminoid-Rich Extract Liposomal CRE-SDInhibits Osteoclastogenesis via the Canonical NF-κB Signaling Pathway

Curcuminoids, namely curcumin, demethoxycurcumin, and bisdemethoxycurcumin, are the major active compounds found in Curcuma longa L. (turmeric). Although their suppressive effects on bone resorption have been demonstrated, their pharmacokinetic disadvantages remain a concern. Herein, we utilized solid dispersion of a curcuminoid-rich extract (CRE), comprising such curcuminoids, to prepare CRE-SD; subsequently, we performed liposome encapsulation of the CRE-SD to yield liposomal CRE-SD. In vitro release assessment revealed that a lower cumulative mass percentage of CRE-SD was released from liposomal CRE-SD than from CRE-SD samples. After culture of murine RANKL-stimulated RAW 264.7 macrophages, our in vitro examinations confirmed that liposomal CRE-SD may impede osteoclastogenesis by suppressing p65 and IκBα phosphorylation, together with nuclear translocation and transcriptional activity of phosphorylated p65. Blind docking simulations showed the high binding affinity between curcuminoids and the IκBα/p50/p65 protein complex, along with many intermolecular interactions, which corroborated our in vitro findings. Therefore, liposomal CRE-SD can inhibit osteoclastogenesis via the canonical NF-κB signaling pathway, suggesting its pharmacological potential for treating bone diseases with excessive osteoclastogenesis.

A Mango Leaf Extract (Zynamite®) Combined with Quercetin Has Exercise-Mimetic Properties in Human Skeletal Muscle

Zynamite PX^®, a mango leaf extract combined with quercetin, enhances exercise performance by unknown molecular mechanisms. Twenty-five volunteers were assigned to a control (17 males) or supplementation group (8 males, receiving 140 mg of Zynamite^® + 140 mg quercetin/8 h for 2 days). Then, they performed incremental exercise to exhaustion (IE) followed by occlusion of the circulation in one leg for 60 s. Afterwards, the cuff was released, and a 30 s sprint was performed, followed by 90 s circulatory occlusion (same leg). Vastus lateralis muscle biopsies were obtained at baseline, 20 s after IE (occluded leg) and 10 s after Wingate (occluded leg), and bilaterally at 90 s and 30 min post exercise. Compared to the controls, the Zynamite PX^® group showed increased basal protein expression of Thr²⁸⁷-CaMKIIδ_D (2-fold, p = 0.007) and Ser⁹-GSK3β (1.3-fold, p = 0.005) and a non-significant increase of total NRF2 (1.7-fold, p = 0.099) and Ser⁴⁰-NRF2 (1.2-fold, p = 0.061). In the controls, there was upregulation with exercise and recovery of total NRF2, catalase, glutathione reductase, and Thr²⁸⁷-CaMKIIδ_D (1.2-2.9-fold, all p < 0.05), which was not observed in the Zynamite PX^® group. In conclusion, Zynamite PX^® elicits muscle signaling changes in resting skeletal muscle resembling those described for exercise training and partly abrogates the stress kinases responses to exercise as observed in trained muscles.

Polyphenol Supplementation and Antioxidant Status in Athletes: A Narrative Review

Antioxidants in sports exercise training remain a debated research topic. Plant-derived polyphenol supplements are frequently used by athletes to reduce the negative effects of exercise-induced oxidative stress, accelerate the recovery of muscular function, and enhance performance. These processes can be efficiently modulated by antioxidant supplementation. The existing literature has failed to provide unequivocal evidence that dietary polyphenols should be promoted specifically among athletes. This narrative review summarizes the current knowledge regarding polyphenols' bioavailability, their role in exercise-induced oxidative stress, antioxidant status, and supplementation strategies in athletes. Overall, we draw attention to the paucity of available evidence suggesting that most antioxidant substances are beneficial to athletes. Additional research is necessary to reveal more fully their impact on exercise-induced oxidative stress and athletes' antioxidant status, as well as optimal dosing methods.