Branched-chain Amino Acids: Catabolism in Skeletal Muscle and Implications for Muscle and Whole-body Metabolism

Branched- Chain Fatty Acids and Obesity: A Narrative Review

Branched- chain fatty acids (BCFAs) are a category of saturated fatty acids that are commonly present in various organisms and play a crucial role in a variety of metabolic reactions, including anticancer, lipid-lowering, anti-inflammatory, and neuroprotective actions. Currently, there is growing interest in the relationship between BCFAs and obesity. Branched- chain fatty acids regulate the gene expression of related enzymes by activating PPARα and sterol regulatory element-binding protein-1c, thereby reducing triglyceride synthesis in the body. Additionally, BCFAs reduce inflammation by decreasing the expression of pro-inflammatory factors in obesity such as cyclooxygenase-2, interleukin-6, and lipoxygenase-15 genes. Branched- chain fatty acids can also expedite the conversion of branched chain amino acids to BCFAs to regulate obesity-induced insulin resistance. In this article we provide a comprehensive review of research progress on how BCFAs affect obesity from the perspectives of lipid metabolism, inflammation, and insulin resistance.

Serum branched-chain amino acids are mainly associated with body mass index and waist circumference

BACKGROUND AND AIMS

To assess the associations between serum concentrations of branched-chain amino acids (BCAAs)-valine, leucine, and isoleucine-and different anthropometric markers, including leptin and adiponectin levels, as well as body composition.

METHODS AND RESULTS

This cross-sectional study used data from the CoLaus|PsyCoLaus and the OsteoLaus studies in Lausanne, Switzerland. Anthropometric markers included the conicity index (CI), body roundness index (BRI), a body shape index (ABSI), body mass index (BMI), and waist circumference, among others. Grip strength was used as a proxy for muscle mass. Bivariate analysis revealed that most anthropometric markers were positively correlated with BCAA, while adiponectin levels was negatively correlated with BCAA. These correlations were generally stronger in males than in females, with the exceptions of CI, ABSI, and adiponectin. After multivariable analysis, weight and BMI showed the strongest association coefficients with BCAA in males, while in females the strongest associations were found for waist circumference and waist-to-height ratio. No significant associations were found between the ABSI and BCAA levels in males, or between grip strength and BCAA levels in females. Stepwise linear regression identified BMI in males, and waist circumference in females as the anthropometric markers most strongly positively associated with BCAA.

CONCLUSION

We observed a significant difference in the association between BCAA levels and anthropometric markers by sex. BMI displayed the strongest positive association with BCAA levels in males while in females, waist circumference exhibited the strongest association.

Mitochondrial calcium signaling regulates branched-chain amino acid catabolism in fibrolamellar carcinoma

Metabolic adaptations are essential for survival. The mitochondrial calcium uniporter plays a key role in coordinating metabolic homeostasis by regulating mitochondrial metabolic pathways and calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial pathways has remained unexplored. Here, we investigate consequences of uniporter loss and gain of function using uniporter knockout cells and fibrolamellar carcinoma (FLC), which we demonstrate to have elevated mitochondrial calcium levels. We find that branched-chain amino acid (BCAA) catabolism and the urea cycle are uniporter-regulated pathways. Reduced uniporter function boosts expression of BCAA catabolism genes and the urea cycle enzyme ornithine transcarbamylase. In contrast, high uniporter activity in FLC suppresses their expression. This suppression is mediated by the transcription factor KLF15, a master regulator of liver metabolism. Thus, the uniporter plays a central role in FLC-associated metabolic changes, including hyperammonemia. Our study identifies an important role for the uniporter in metabolic adaptation through transcriptional regulation of metabolism and elucidates its importance for BCAA and ammonia metabolism.

Metabolic Markers Demonstrate the Heterogeneity of Walking Ability in Non-Disabled Community-Dwelling Older Adults

Background: Walking ability is important for the quality of life of older adults. A self-reported walking ability index (WAI) covering the difficulty and ease of walking captures a broader spectrum of walking ability in healthy older persons. Methods: Using metabolomics in the Health, Aging and Body Composition study, we identified Year 2 metabolites cross-sectionally and longitudinally related to WAI (0-9, higher scores indicate better walking ability) using probabilistic index models and multinomial logistic models, respectively. Results: Among 2334 participants (mean age 74.6 years, 51% women, 37% Black), 27% scored 0-5, 36% scored 6-8, and 37% scored 9 at Year 2. Over 4 years, 52% maintained a stable WAI, 6% improved, while 42% declined (22% 1-2 points and 20% >2 points decline). We identified 81 metabolites significantly associated with both poorer concurrent WAI and faster decline, including higher acylcarnitine species, shorter-chain saturated diglycerides and triglycerides, and TCA cycle intermediates (cis-aconitic, fumaric, and malic acids), and lower phospholipids levels. Eighteen additional metabolites were only associated with faster WAI decline: higher short-chain saturated triglycerides and energy metabolism markers (ATP/ADP/AMP) and lower margaric acid and glycine levels. Notably, those with improved WAI, despite poorer baseline WAI and lifestyles, showed more favorable metabolic profiles than others. Conclusions: Metabolites linked to the TCA cycle and energy metabolism, as well as inflammation and protein catabolism, were related to mobility function. Some metabolites might be particularly important for the early detection of older adults at risk of mobility decline. Metabolic profiles may also help identify older individuals (i.e., with improving WAI) with greater metabolic resilience to lifestyle risk factors and health conditions.

Apparent Saturation of Branched-Chain Amino Acid Catabolism After High Dietary Milk Protein Intake in Healthy Adults

CONTEXT

Milk protein contains high concentrations of branched-chain amino acids (BCAA) that play a critical role in anabolism and are implicated in the onset of obesity and chronic disease. Characterizing BCAA catabolism in the postprandial phase could elucidate the impact of protein intake on obesity risk established in the "early protein hypothesis."

OBJECTIVE

To examine the acute effects of protein content of young child formulas as test meals on BCAA catabolism, observing postprandial plasma concentrations of BCAA in relation to their degradation products.

METHODS

The TOMI Add-On Study is a randomized, double-blind crossover study in which 27 healthy adults consumed 2 isocaloric young child formulas with alternating higher (HP) and lower (LP) protein and fat content as test meals during separate interventions, while 9 blood samples were obtained over 5 hours. BCAA, branched-chain α-keto acids (BCKA), and acylcarnitines were analyzed using a fully targeted HPLC-ESI-MS/MS approach.

RESULTS

Mean concentrations of BCAA, BCKA, and acylcarnitines were significantly higher after HP than LP over the 5 postprandial hours, except for the BCKA α-ketoisovalerate (KIVA). The latter metabolite showed higher postprandial concentrations after LP. With increasing mean concentrations of BCAA, concentrations of corresponding BCKA, acylcarnitines, and urea increased until a breakpoint was reached, after which concentrations of degradation products decreased (for all metabolites except valine and KIVA and Carn C4:0-iso).

CONCLUSION

BCAA catabolism is markedly influenced by protein content of the test meal. We present novel evidence for the apparent saturation of the BCAA degradation pathway in the acute postprandial phase up to 5 hours after consumption.

BCAA metabolism in cancer progression and therapy resistance: The balance between fuel and cell signaling

Branched-chain amino acids (BCAAs), including leucine, isoleucine, and valine, play a crucial role in cellular metabolism and signaling. Recent studies have demonstrated that BCAA metabolic reprogramming is a key driver of tumor progression and treatment resistance in various cancers. BCAA metabolism supports cancer cell growth, survival, and proliferation by modulating pathways such as mTOR signaling and oxidative stress responses. By promoting immunosuppressive conditions and increasing the survival rate of cancer stem cells (CSCs), BCAAs contribute to immune evasion and resistance to therapies such as chemotherapy and immune checkpoint inhibitors. This article explores the different metabolic reprogramming patterns of BCAAs in various tumors and introduces BCAA-related metabolic targets for overcoming tumor resistance, offering new directions for precision cancer treatment, reducing resistance, and improving patient outcomes.

The Effect of Dexamethasone-Mediated Atrophy on Mitochondrial Function and BCAA Metabolism During Insulin Resistance in C2C12 Myotubes

Background: Muscle loss during sarcopenia and atrophy is also commonly associated with age-related insulin resistance. Interestingly, branched-chain amino acids (BCAA) which are known for stimulating muscle protein synthesis are commonly elevated during insulin resistance and sarcopenic obesity. Objectives: This study investigated the effects of the interplay between atrophy and insulin resistance on insulin sensitivity, mitochondrial metabolism, and BCAA catabolic capacity in a myotube model of skeletal muscle insulin resistance. Methods: C2C12 myotubes were treated with dexamethasone to induce atrophy. Insulin resistance was induced via hyperinsulinemia. Gene and expression were measured using qRT-PCR and Western blot, while mitochondrial and lipid content were assessed using fluorescent staining. Cell metabolism was analyzed via Seahorse metabolic assays. Results: Both dexamethasone-induced atrophy and insulin resistance independently reduced insulin-stimulated pAkt levels, as well as mitochondrial function and content. However, neither treatment affected gene or protein expression associated with mitochondrial biogenesis or content. Although dexamethasone independently reduced insulin sensitivity in otherwise previously insulin-sensitive cells, dexamethasone had no significant effect on extracellular BCAA content. Conclusions: Our findings indicate the metabolic interplay between atrophy and insulin resistance and demonstrate that both can reduce mitochondrial function, though only limited effects were observed on indicators of BCAA catabolism and utilization. This emphasizes the need for future studies to investigate the mechanisms that underlie atrophy and other metabolic disorders to develop new interventions.

Metabolomic analysis reveals key changes in amino acid metabolism in colorectal cancer patients

The number of colorectal cancer (CRC) patients is steadily growing worldwide, particularly in developing nations. Nonetheless, recent advances in early detection studies and therapy alternatives have reduced CRC mortality in affluent countries, despite rising incidence. Gut microbiota and their metabolites may contribute to tumor growth and reduced therapeutic efficacy. This preliminary study sought to uncover metabolic fingerprints in colorectal cancer patients. It also emphasizes the correlation between the gut microbiome, microbial metabolism, and altered metabolites in CRC. In this study, stool samples from 20 CRC patients and matched healthy controls were enrolled. Untargeted metabolomics approach based on an ultra-high-performance liquid chromatography high-resolution mass spectrometry (UHPLC-MS/MS) were applied. Statistical approaches, pathway enrichment analysis, and network analysis were employed to unleash CRC perturbed metabolic pathways and putative biomarkers. The study identified a distinct manually curated metabolite profile that is substantially linked to CRC. The steroidogenesis, aspartate, tryptophan (Trp), and urea cycle were the most significant pathways that concurrently contributed to CRC.Prominently, among other pathways, Trp metabolism was identified as a critical pathway, indicating a possible connection between the development of CRC and gut microbiota. In a nutshell the notable resulted metabolites reveal auspicious biomarkers for the initial diagnosis as well as surveilling of CRC progression. This preliminary study highlights the potential involvement that gut bacteria may contribute in CRC patients. Further investigation into the composition of the gut microbiome associated with this metabolic profile may lead to the identification of novel biomarkers for early detection and possible targets for treatment.

Serum metabolomics after exercise in ambulatory individuals with cerebral palsy

AIM

To evaluate whether serum metabolomics differ between ambulatory individuals with cerebral palsy (CP) compared with individuals with typical development and whether functional capacity is associated with metabolite abundance.

METHOD

Thirty-eight adolescents and young adults were enrolled (CP: n = 19; typical development: n = 19). After functional capacity testing (10-meter walk, sit-to-stand, and peak knee flexion/extension torques), blood was drawn. Targeted serum metabolomics on hydrophilic metabolites were performed by high-performance liquid chromatography coupled with high-resolution and tandem mass spectrometry. Metabolite dimensionality reduction, pathway analysis, fold change, and t-tests evaluated changes in metabolite abundance. Associations were tested between functional measures and metabolite abundance.

RESULTS

Individuals with CP had a significant increase in the abundance of essential amino acids, catabolic products of protein metabolism, and tricarboxylic acid cycle substrates, such as valine, tryptophan, kynurenic acid, and pyruvate (p < 0.05). Importantly, the abundance of numerous metabolites was only highly associated with functional capacity in individuals with CP such that greater abundance was associated with greater capacity, but not in those with typical development.

INTERPRETATION

Our findings show clear increases in serum metabolites in individuals with CP, which are associated with functional capacity for movement. The altered metabolite profile measured after exercise might reflect increased energy production needed for movement. Appropriate nutritional intake during exercise might be needed given increased energy requirements.

Research advances in branched-chain amino acid metabolism in tumors

The metabolic reprogramming of amino acids is an important component of tumor metabolism. Branched-chain amino acids (BCAAs) perform important functions in tumor progression. They are the important amino donor and are involved in the synthesis of various non-essential amino acids, nucleotides, and polyamines to satisfy the increased demand for nitrogen sources. This review summarizes the studies related to abnormalities in BCAA metabolism during tumorigenesis and the potential therapeutic targets. The expression of BCAA transporters was significantly upregulated in tumor cells, which increases BCAA uptake. High expression of the BCAA transaminases is prevalent in various tumors, however, the dehydrogenation step of BCAA catabolism is inhibited in tumors. This review shows that BCAA metabolic reprogramming is an important tumor metabolic feature, and metabolic genes of BCAAs play a crucial role in tumor metabolism, representing a good auxiliary target for early clinical diagnosis and treatment. In addition, BCAAs are indispensable for maintaining immune system function, and dietary supplementation with BCAAs can enhance the activity of immune cells. Therefore, BCAA supplementation in tumor patients may affect the interaction between the immune system and tumors.

The YEATS domain is a selective reader of histone methacrylation

Metabolically regulated lysine acylation modifications in proteins play a major role in epigenetic processes and cellular homeostasis. A new type of histone acylation, lysine methacrylation, has recently been identified but remains poorly characterized. Here, we show that lysine methacrylation can be generated through metabolism of sodium methacrylate and enzymatically removed in cells, and that the YEATS domain but not bromodomain recognizes this modification. Structural and biochemical analyses reveal the π-π-π-stacking mechanism for binding of the YEATS domain of ENL to methacrylated histone H3K18 (H3K18mc). Using mass spectrometry proteomics, we demonstrate that methacrylate induces global methacrylation of a set of proteins that differs from the set of methacrylated proteins associated with valine metabolism. These findings suggest that high levels of methacrylate may potentially perturb cellular functions of these proteins by altering protein methacrylation profiles.

Effects of Bioconverted Guava Leaf (Psidium guajava L.) Extract on Skeletal Muscle Damage by Regulation of Ubiquitin-Proteasome System and Apoptosis in Type 2 Diabetic Mice

Skeletal muscle atrophy is one of the serious complications of diabetes, which increases the risk of frailty, falls, and mortality. However, interventions for muscle atrophy are limited, and research is needed regarding the treatment of muscle wasting. Recently, the bioconversion of natural products by lactic acid bacteria has been highlighted as a possibility to improve the bioavailability of active ingredients. This process also produces metabolites, which are key signaling mediators for a variety of physiological functions. This study investigated the effect of bioconverted guava leaf (Psidium guajava L., GL) by Lactobacillus plantarum on hyperglycemia-induced skeletal muscle atrophy in type 2 diabetes mellites (T2DM) mice. Diabetes was induced by a high-fat diet with a two-time streptozotocin (STZ) injection (60 mg/kg BW) in male C57BL/6J mice. After diabetes was induced (a fasting blood glucose level (FBG) ≥ 300 mg/dL), the mice were administered with GL (100 mg/kg/day) or bioconverted GL (FGL) (50 mg/kg/day) by oral gavage for 14 weeks. FGL contains different substances such as hydroxyl-isocaproic acid and hydroxyl-isovaleric acid compared to GLE itself, which have potential to prevent muscle degradation in T2DM mice. GL and FGL supplementation reduced the FBG level in T2DM mice. In addition, GL and FGL supplementation enhanced muscle strength, the skeletal muscle cross-sectional area, and ameliorated ubiquitin-proteasome system (UPS)-related pathways in T2DM mice. On the other hand, GLE supplementation ameliorated glucose tolerance demonstrated by oral glucose tolerance test and enhanced insulin signaling pathway. In addition, only FGL supplementation attenuated skeletal muscle inflammation and apoptosis with an improved mammalian target of the rapamycin (mTOR)-autophagy-related pathway. Although administered at a half dose of GLE, FGL demonstrated greater efficacy in regulating the expression of these molecular markers. The result suggests that even GL itself has anti-diabetic effects, and the functionality would be enhanced by the bioconversion of GL with L. Plantarum, which has an additive or/and a synergistic effect. Taken together, FGL could be used as a potential nutraceutical to attenuate muscle degradation by the inhibition of inflammation, the UPS, and the apoptosis pathway.

Integration of UHPLC-MS and mass spectrometry imaging techniques revealed the protective mechanism of Gushudan in postmenopausal osteoporosis rats via branched-chain amino acid metabolism based on the 'kidney-bone' axis

According to the theory of traditional Chinese medicine, the kidney is regarded as governing the bones and dominating the storage of essence. Gushudan (GSD) is a traditional Chinese medicine prescription that has the effects of strengthening bone and nourishing the kidney. However, the mechanism of action of GSD in preventing postmenopausal osteoporosis (PMOP) rats based on the 'kidney-bone' axis remains to be further systematically investigated. In this study, an integrated kidney metabolomics method based on three MS detection modes of UHPLC-HRMS, UHPLC-MS/MS and AFADESI-MSI was developed to reveal the protective mechanism of GSD in PMOP rats. Firstly, the non-targeted metabolomics was investigated to comprehensively explore the metabolic changes in the kidneys of PMOP rats based on the UHPLC-Q-Orbitrap HRMS. Subsequently, UHPLC-MS/MS targeted metabolomics and Mass Spectrometry Imaging (MSI) techniques were combined to elucidate the preventive mechanism of GSD on PMOP through branched-chain amino acid (BCAA) metabolism. The results of the non-targeted metabolomics demonstrated that GSD significantly modulated the levels of 67 potential biomarkers, including leucine and valine, which are primarily involved in amino acid metabolism. Specifically, BCAA metabolism is notably enriched in amino acid metabolism. Compared to the control group, it was found that the levels of BCAAs were decreased and α-branched-chain keto acids (BCKAs) were increased in the model groups in the targeted metabolomics study. Moreover, MSI results showed that the changes in BCAAs content were mainly concentrated in the renal cortex. This finding confirmed the metabolic disorders of BCAA in the renal cortex of PMOP rats, and that GSD had a significant regulatory effect on this disorder. In conclusion, this study integrated three mass spectrometry techniques that validate and complement each other to revealed the anti-osteoporostic mechanism of GSD in PMOP rats and to elucidate the modern scientific connotation of the 'kidney-bone' axis based on the BCAA metabolism.

Genome-wide association study for circulating metabolic traits in 619,372 individuals

Interpreting genetic associations with complex traits can be greatly improved by detailed understanding of the molecular consequences of these variants. However, although genome-wide association studies (GWAS) for common complex diseases routinely profile 1M+ individuals, studies of molecular phenotypes have lagged behind. We performed a GWAS meta-analysis for 249 circulating metabolic traits in the Estonian Biobank and the UK Biobank in up to 619,372 individuals, identifying 88,604 significant locus-metabolite associations and 8,774 independent lead variants, including 987 lead variants with a minor allele frequency less than 1%. We demonstrate how common and low-frequency associations converge on shared genes and pathways, bridging the gap between rare-variant burden testing and common-variant GWAS. We used Mendelian randomisation (MR) to explore putative causal links between metabolic traits, coronary artery disease and type 2 diabetes (T2D). Surprisingly, up to 85% of the tested metabolite-disease pairs had statistically significant genome-wide MR estimates, likely reflecting complex indirect effects driven by horisontal pleiotropy. To avoid these pleiotropic effects, we used cis-MR to test the phenotypic impact of inhibiting specific drug targets. We found that although plasma levels of branched-chain amino acids (BCAAs) have been associated with T2D in both observational and genome-wide MR studies, inhibiting the BCAA catabolism pathway to lower BCAA levels is unlikely to reduce T2D risk. Our publicly available results provide a valuable novel resource for GWAS interpretation and drug target prioritisation.

Branched-Chain Amino Acids and Inflammation Management in Endurance Sports: Molecular Mechanisms and Practical Implications

Endurance athletes frequently experience muscle damage and inflammation due to prolonged, high-intensity exercise, which can impair recovery and hinder performance. This review examines the role of branched-chain amino acid (BCAA) supplementation in muscle repair, inflammation modulation, and immune regulation. BCAAs-particularly leucine and isoleucine-activate key molecular pathways, including the mechanistic target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK), to promote muscle protein synthesis and enhance energy metabolism. They also attenuate inflammatory responses by modulating the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), mitogen-activated protein kinase (MAPK), and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways, reducing levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). In addition, BCAAs influence immune function via mechanistic target of rapamycin complex 1 (mTORC1) signaling, enhance autophagy, and mitigate exercise-induced apoptosis. These molecular effects result in reduced muscle soreness, lower muscle damage biomarker levels (e.g., creatine kinase, lactate dehydrogenase), and improved recovery. Practical considerations such as optimal dosage, timing, and co-supplementation with carbohydrates, proteins, or omega-3s are also addressed. While BCAAs show promise as a nutritional strategy for enhancing recovery and controlling inflammation in endurance athletes, further research is needed to refine personalized protocols and clarify long-term effects.

Molecular Signatures of Exercise Adaptation in Arabian Racing Horses: Transcriptomic Insights from Blood and Muscle

Background/Objectives: Human-driven selection has shaped modern horse breeds into highly specialized athletes, particularly in racing. Arabian horses, renowned for their endurance, provide an excellent model for studying molecular adaptations to exercise. This study aimed to identify genes commonly influenced by physical exertion in the gluteus medius muscle and whole blood of Arabian horses during their first year of race training. Methods: RNA sequencing of sixteen pure-breed Arabian horses was used to analyze transcriptomic changes at three key training stages. Differentially expressed genes (DEGs) were identified to explore their role in endurance and metabolic adaptation. Results: Seven genes-RCHY1, PIH1D1, IVD, FABP3, ANKRD2, USP13, and CRYAB-were consistently deregulated across tissues and training periods. These genes are involved in muscle remodeling, metabolism, oxidative stress response, and protein turnover. ANKRD2 was associated with mechanosensing and muscle adaptation, FABP3 with fatty acid metabolism, and USP13 with ubiquitination-related pathways crucial for muscle recovery and energy regulation. The transcriptomic overlap between muscle and blood suggests potential systemic biomarkers for athletic performance and endurance. Conclusions: Our findings highlight the importance of multi-tissue transcriptomic profiling in understanding exercise-induced molecular adaptations. The identified genes warrant further investigation as potential molecular markers for monitoring training progression and athletic potential in endurance horses. This study contributes to the growing field of equine sports genetics and may offer translational insights into human sports performance.

Causal relationships of circulating amino acids with sarcopenia-related traits: A bidirectional Mendelian randomization study

BACKGROUND AND AIM

Recent studies have indicated a correlation between certain Amino acids (AAs) and sarcopenia. However, the exact causal relationship among these associations is still unclear. This study aims to elucidate the causal relationships between 20 types of AAs and the phenotypic characteristics associated with sarcopenia through Mendelian randomization (MR) analysis.

METHODS AND RESULTS

This MR study employed single nucleotide polymorphisms (SNPs) that were significantly associated with both AAs and the traits of sarcopenia as instrumental variables (IVs). The main method for estimating causal effects was the inverse-variance weighted (IVW) approach. To ensure the robustness of the findings, additional methods such as weighted median, weighted mode, and MR Egger regression were used. Sensitivity analyses included heterogeneity and pleiotropy tests. In this research, we discovered potential causal relationships between AAs and traits associated with sarcopenia. We not only found that AAs previously studied, such as Glutamine, Tyrosine, Glycine, and branched-chain amino acids, play positive roles in muscle metabolism. Additionally, our study identified the role of AAs previously neglected or not considered in earlier research, such as Alanine, Lysine, Cysteine, and Methionine, which exert potential effects on muscle metabolism and offer considerable research potential and value.

CONCLUSIONS

This MR study clarified the reciprocal effects between circulating levels of AAs and sarcopenia-related traits. These results indicate that AAs may be used as biomarkers for diagnosing sarcopenia or as intervention targets for its treatment in clinical practice.

Impact of formula protein quantity and source on infant metabolism: serum, urine, and fecal metabolomes of a randomized controlled study

BACKGROUND

Human milk offers significant health benefits for infants; however, when not feasible, infant formula serves as an alternative. The higher protein content in infant formula is thought to contribute to the distinct metabolic profiles observed in formula-fed infants compared with those fed human milk.

OBJECTIVES

This study investigates the impact of formula protein quantity and whey protein types on the serum, urine, and fecal metabolomes of infants.

METHODS

A secondary analysis was performed on a random subset of 200 well-characterized per-protocol infants who completed a prospective, randomized, double-blind controlled trial. Infants were randomly assigned to 1 of 3 groups: standard formula, protein-reduced formula with α-lactalbumin-enriched whey, or protein-reduced formula with casein glycomacropeptide-reduced whey, along with an observational reference group of exclusively breastfed infants. Serum, urine, and fecal metabolites were quantified using 1H nuclear magnetic resonance spectroscopy at baseline (1-2 mo), 4, and 6 mo of age. Dietary intake was assessed monthly ≤6 mo of age.

RESULTS

Formula protein content and type of whey protein used significantly influenced the amino acid profile and associated catabolic markers in serum and urine but had minimal impact on the fecal metabolome. Reduced protein formulas yielded metabolome profiles closer to those of breastfed infants compared with standard formula. Despite these improvements, infants fed human milk still demonstrated enhanced branched-chain amino acid (BCAA) oxidation and a greater capacity to eliminate catabolic waste products from BCAA metabolism over infants consuming protein-reduced formulas.

CONCLUSIONS

Comprehensive metabolomics profiling of serum, urine, and feces captures molecular-level changes and informs potential strategies for formula optimization. Both the quantity and source of protein significantly influenced the metabolic profiles of formula-fed infants. However, modifications in protein alone cannot fully resolve the metabolic differences between formula-fed and breastfed infants, highlighting the complexity of mimicking the human milk feeding-associated metabolic profile. This study was registered at clinicaltrials.gov as NCT02410057.

Transcriptome remodeling and adaptive preservation of muscle protein content in hibernating black bears

Hibernation is an energy-saving adaptation associated with physical inactivity. In contrast to most mammals, hibernating bears demonstrate limited loss of muscle mass and protein content over the prolonged periods of immobility and fasting during winter. This suggests that bears have natural adaptive mechanisms preserving muscle mass and functionality. To identify transcriptional changes that underlie molecular mechanisms attenuating muscle loss, we conducted a large-scale gene expression profiling (14,199 genes) by transcriptome sequencing in quadriceps of adult black bears, comparing hibernating animals (n=5) and summer active animals (n=5). Gene set enrichment analysis showed significant positive correlation between hibernating phenotype and expression changes of genes involved in translation, ribosome and the mTORC1 mediated signaling. In contrast, coordinated transcriptional reduction was detected for genes involved in catabolism of branched chain amino acid (BCAA) suggesting preservation of BCAA. These findings imply maintenance of protein biosynthesis through the mTORC1 signaling positively activated by availability of BCAA in muscle during hibernation. Support for this conclusion comes from overexpression of RRAGD and RRAGB , crucial regulator of the mTORC1 response to leucine availability, and up regulation of EIF4B , downstream target of the mTORC1 signaling. Consistent with the mTORC1 suppression of autophagy-dependent protein degradation, MAP1LC3A and ULK1 were down regulated in hibernating muscle. The maintenance of protein biosynthesis and decrease in protein catabolism through the mTORC1 signaling as response to BCAA availability likely contribute to the preservation of muscle protein through prolonged periods of immobility and fasting during hibernation.

Effect of Growth Hormone on Branched-Chain Amino Acids Catabolism in Males With Hypopituitarism

To investigate the impact of growth hormone (GH) on branched-chain amino acids (BCAAs) catabolism in males with hypopituitarism, we measured the concentration of amino acids in 133 males with hypopituitarism and 90 age-matched healthy controls using untargeted metabolome. A rat model of hypopituitarism was established through hypophysectomy, followed by recombinant human GH (rhGH) intervention. Targeted metabolomics and label-free quantitative phosphoproteomics were utilised to assess amino acid levels in rats and explore the mechanisms of GH's effect on BCAA catabolism. Hypopituitarism exhibited elevated concentrations of BCAAs, which correlated positively with triglyceride, fasting insulin and HOMA-IR. The BCAAs were significantly elevated following hypophysectomy and were substantially reduced upon rhGH intervention. Phosphorylation proteomics analysis in liver tissues revealed that differentially expressed phosphoproteins (DEPPs) after GH treatment were predominantly involved in 'RNA metabolic process', 'Diseases of signal transduction by growth factor receptors' and 'BCAAs degradation'. Notably, 12 proteins in the BCAA degradation pathway showed altered phosphorylation without whole protein changes. Importantly, the expression or phosphorylation modification of BCKDH, BCATs and MuRF1 were restored through rhGH intervention. Hypopituitarism exhibits elevated levels of circulating BCAAs. The increased circulating BCAAs in hypopituitarism may result from enhanced MuRF1-mediated muscle proteolysis, which greatly exceeds the BCAA degradation capacity. This study provides valuable insights into the effects of GH on BCAA catabolism at the scale of the proteomics level.

Single centre retrospective review of plasma branched-chain amino acid levels in children with urea cycle disorders: Impact of treatment modalities and disease severity

Branched-chain amino acids (BCAAs) are important for normal growth, development, and function. In urea cycle disorders (UCDs), plasma BCAA levels can be relatively low; this has been attributed variously to low protein intake, hyperammonaemia, and nitrogen scavenger treatment. We undertook a retrospective review of plasma BCAA levels in individuals with UCDs comprising ornithine carbamoyltransferase deficiency (OTCD n = 22), arginosuccinate lyase deficiency (ASLD n = 12), and argininosuccinate synthase deficiency (ASSD n = 6). Scavenger treatment groups comprised sodium benzoate (NaBz, n = 20), sodium phenylbutyrate (NaPBA, n = 5), NaBz+NaPBA (n = 14), and a control group receiving neither NaBz nor NaPBA (n = 14). In these treatment groups, respectively, median (IQR) plasma levels of leucine were 54 (32), 55 (25), 58 (19), and 91 (70) μmol/L (leucine was lower in the NaBz group than the control, p = 0.0282) and numbers of individuals (%) with leucine below normal were 10/20 (50 %), 1/4 (25 %), 10/14 (71 %), and 2/9 (20 %). The pattern was similar for isoleucine and valine. In the NaBz group, plasma BCAA levels were inversely correlated with protein intake (p ≤ 0.01 to p ≤ 0.001), plasma ammonia level (p ≤ 0.01 to p ≤ 0.0001), and scavenger dose (p ≤ 0.0001). We speculate that individuals with greater disease severity may be prone to BCAA deficiency, caused by BCAA consumption when alternative urea disposal pathways are used. Practical reflections on our audit were that to increase the proportion of plasma BCAA levels in the normal range, we needed to alter the biological value of protein intake, prescribe higher doses of scavenger to facilitate safe levels of protein intake, and give EAA supplements if indicated.

Alpha-ketoglutarate promotes anxiety, activates autophagy, and suppresses antioxidant enzymes in the cerebral cortex of female mice on cafeteria diet

Alpha-ketoglutarate (AKG), an intermediate of the tricarboxylic acid cycle, has been found to mitigate oxidative stress and inflammation. In turn, a cafeteria diet (CD), an obesogenic diet, is often associated with oxidative stress and inflammation. This study aimed to determine whether AKG can level the effects of CD on animal behavior, oxidative stress markers, glycolytic flow, and autophagy in the mouse cerebral cortex. Female C57BL/6 J mice were divided into two groups and fed either a standard diet or a CD for eight weeks. For the next four weeks, each group continued to be fed the previous diet; however, half of the individuals within each group received drinking water with 1 % AKG. Using an open field test, we found that the combination of CD and AKG promoted the development of anxiety signs. Both CD and AKG decreased the exploratory behavior of mice, with a significant additive effect in the combined diet. On diets supplemented with AKG, animals produced fewer fecal boli, a measure of emotionality. On all experimental diets, mice had lower activities of antioxidant and related enzymes, with no significant differences in the activities of glycolytic enzymes. The AKG-supplemented diet induced the transcription of autophagy-related genes and targets of the forkhead box O factor, involved in the regulation of carbohydrate metabolism. Transcriptional changes induced by AKG were partly abrogated by the CD. These findings suggest that AKG, particularly when combined with CD, may modulate behavioral responses and oxidative stress intensity in the brain by altering key metabolic and autophagic pathways.

Unveiling the tissue-specific landscape of nuclear-encoded mitochondrial genes involved in amino acid metabolism in buffalo

Mitochondria play a pivotal role in energy production, metabolism, and cellular signaling, serving as key regulators of cellular functions, including differentiation and tissue-specific adaptation. The interplay between mitochondria and the nucleus is crucial for coordinating these processes, particularly through the supply of metabolites for epigenetic modifications that facilitate nuclear-mitochondrial interactions. To investigate tissue-specific mitochondrial adaptations at the molecular level, we conducted RNA sequencing data analyses of kidney, heart, brain, and ovary tissues of female buffaloes, focusing on variations in mitochondrial gene expression related to amino acid metabolism. Our analysis identified 82 nuclear-encoded mitochondrial transcripts involved in amino acid metabolism, with significant differential expression patterns across all tissues. Notably, the heart, brain, and kidney-tissues with higher energy demands-exhibited elevated expression levels compared to the ovary. The kidney displayed unique gene expression patterns, characterized by up-regulation of genes involved in glyoxylate metabolism and amino acid catabolism. In contrast, comparative analysis of the heart and kidney versus the brain revealed shared up-regulation of genes associated with fatty acid oxidation. Gene ontology and KEGG pathway analyses confirmed the enrichment of genes in pathways related to amino acid degradation and metabolism. These findings highlight the tissue-specific regulation of mitochondrial gene expression linked to amino acid metabolism, reflecting mitochondrial adaptations to the distinct metabolic and energy requirements of different tissues in buffalo. Importantly, our results underscore the relevance of mitochondrial adaptations not only for livestock health but also for understanding metabolic disorders in humans. By elucidating the molecular mechanisms of mitochondrial function and their tissue-specific variations, this study provides insights that could inform breeding strategies for enhanced livestock productivity and contribute to therapeutic approaches for human metabolic diseases. Thus, our findings illustrate how mitochondria are specialized in a tissue-specific manner to optimize amino acid utilization and maintain cellular homeostasis, with implications for both animal welfare and human health.

Stress exposure in the mdx mouse model of Duchenne muscular dystrophy provokes a widespread metabolic response

Duchenne muscular dystrophy is a severe neuromuscular wasting disease that is caused by a primary defect in dystrophin protein and involves organism-wide comorbidities such as cardiomyopathy, metabolic and mitochondrial dysfunction, and nonprogressive cognitive impairments. Physiological stress exposure in the mdx mouse model of Duchenne muscular dystrophy results in phenotypic abnormalities that include locomotor inactivity, hypotension, and increased morbidity. Severe and lethal stress susceptibility in mdx mice corresponds to metabolic dysfunction in several coordinated metabolic pathways within dystrophin-deficient skeletal muscle, as well as prolonged elevation in mdx plasma corticosterone levels that extends beyond the wild-type (WT) stress response. Here, we performed a targeted mass spectrometry-based plasma metabolomics screen focused on biological stress pathways in healthy and dystrophin-deficient mdx mice exposed to mild scruff stress. One-third of the stress-relevant metabolites interrogated displayed significant elevation or depletion in mdx plasma after scruff stress and were restored to WT levels by skeletal muscle-specific dystrophin expression. The metabolic pathways of mdx mice altered by scruff stress are associated with regulation of the hypothalamic-pituitary-adrenal axis, locomotor tone, neurocognitive function, redox metabolism, cellular bioenergetics, and protein catabolism. Our data suggest that a mild stress triggers an exaggerated, multi-system metabolic response in mdx mice.

Branched-chain amino acids and specific phosphatidylinositols are plasma metabolite pairs associated with menstrual pain severity

Menstrual pain affects women's quality of life and productivity, yet objective molecular markers for its severity have not been established owing to the variability in blood levels and chemical properties of potential markers such as plasma steroid hormones, lipid mediators, and hydrophilic metabolites. To address this, we conducted a metabolomics study using five analytical methods to identify biomarkers that differentiate menstrual pain severity. This study included 20 women, divided into mild (N = 12) and severe (N = 8) pain groups based on their numerical pain rating scale. We developed pretreatment procedures that allowed all analyses from only 100 µL of finger-prick blood collected across the menstrual cycle. Among the 692 quantified metabolites, branched-chain amino acids and specific phosphatidylinositol (PI), especially PI(36:2), were identified as potential biomarkers. Furthermore, the ratio of PI(36:2) to each BCAA or total BCAA effectively discriminated between the severity levels of menstrual pain. These ratios correlated positively with NPRS, indicating high accuracy in pain assessment. This study highlights the potential of small molecular markers to objectively assess menstrual pain severity, aiding evidence-based support and intervention.

Metabolomic Profiling and Characterization of a Novel 3D Culture System for Studying Chondrocyte Mechanotransduction

Background/Objective

Articular chondrocytes synthesize and maintain the avascular and aneural articular cartilage. In vivo these cells are surrounded by a 3D pericellular matrix (PCM) containing predominantly collagen VI. The PCM protects chondrocytes and facilitates mechanotransduction. PCM stiffness is critical in transmitting biomechanical signals to chondrocytes. Various culture systems with different hydrogels are used to encapsulate chondrocytes for 3D culture, but many lack either the PCM or the in vivo stiffness of the cartilage matrix. This study aimed at establishing a culture system to investigate a) if chondrocytes cultured in alginate will develop a PCM and b) study mechanotransduction via metabolic changes induced in 3D agarose-embedded chondrocytes upon mechanical stimulation.

Methods

We cultured primary human and bovine chondrocytes in monolayers or as alginate encapsulated cells in media containing sodium L-ascorbate. PCM expression was analyzed by immunofluorescence and western blots. We further characterized the response of chondrocytes embedded in physiologically stiff agarose to dynamic compression through metabolomic profiling.

Results

We found that primary human and bovine chondrocytes, when cultured in alginate beads with addition of sodium L-ascorbate for 7 days, had a pronounced PCM, retained their phenotype, and synthesized both collagens VI and II. This novel culture system enables alginate-encapsulated chondrocytes to develop a robust PCM thereby creating a model system to study mechanotransduction in the presence of an endogenous PCM. We also observed distinct compression-induced changes in metabolomic profiles between the monolayer-agarose and alginate-released agarose-embedded chondrocytes indicating physiological changes in cell metabolism.

Conclusion/Significance

These data show that 3D preculture of chondrocytes in alginate before encapsulation in physiologically stiff agarose leads to pronounced development of pericellular matrix that is sustained in the presence of ascorbate. This model can be useful in studying the mechanism by which chondrocytes respond to cyclical compression and other types of loading simulating in vivo physiological conditions.

Rspo3-mediated metabolic liver zonation regulates systemic glucose metabolism and body mass in mice

The unique architecture of the liver consists of hepatic lobules, dividing the hepatic features of metabolism into 2 distinct zones, namely the pericentral and periportal zones, the spatial characteristics of which are broadly defined as metabolic zonation. R-spondin3 (Rspo3), a bioactive protein promoting the Wnt signaling pathway, regulates metabolic features especially around hepatic central veins. However, the functional impact of hepatic metabolic zonation, regulated by the Rspo3/Wnt signaling pathway, on whole-body metabolism homeostasis remains poorly understood. In this study, we analyze the local functions of Rspo3 in the liver and the remote actions of hepatic Rspo3 on other organs of the body by using murine models. Rspo3 expression analysis shows that Rspo3 expression patterns are spatiotemporally controlled in the murine liver such that it locates in the pericentral zones and converges after feeding, and the dynamics of these processes are disturbed in obesity. We find that viral-mediated induction of Rspo3 in hepatic tissue of obesity improves insulin resistance and prevents body weight gain by restoring attenuated organ insulin sensitivities, reducing adipose tissue enlargement and reversing overstimulated adaptive thermogenesis. Denervation of the hepatic vagus suppresses these remote effects, derived from hepatic Rspo3 induction, toward adipose tissues and skeletal muscle, suggesting that signals are transduced via the neuronal communication consisting of afferent vagal and efferent sympathetic nerves. Furthermore, the non-neuronal inter-organ communication up-regulating muscle lipid utilization is partially responsible for the ameliorations of both fatty liver development and reduced skeletal muscle quality in obesity. In contrast, hepatic Rspo3 suppression through Cre-LoxP-mediated recombination system exacerbates diabetes due to glucose intolerance and insulin resistance, promotes fatty liver development and decreases skeletal muscle quality, resulting in obesity. Taken together, our study results reveal that modulation of hepatic Rspo3 contributes to maintaining systemic glucose metabolism and body composition via a newly identified inter-organ communication mechanism.

Association of leucine and other branched chain amino acids with clinical outcomes in malnourished inpatients: a secondary analysis of the randomized clinical trial EFFORT

BACKGROUND

The essential branched-chain amino acids leucine, isoleucine and valine are considered anabolic and stimulate protein synthesis in the muscles as well in the liver. They also promote muscle recovery and contribute to glucose homeostasis. Recent studies in critically ill patients have demonstrated that depletion of plasma leucine is associated with increased mortality, but data in the non-critical care setting is lacking.

METHODS

This secondary analysis of the randomized controlled Effect of early nutritional support on Frailty, Functional Outcomes, and Recovery of malnourished medical inpatients Trial (EFFORT), investigated the impact of leucine, isoleucine, and valine metabolism on clinical outcomes. The primary endpoint was 180-day all-cause mortality.

RESULTS

Among 238 polymorbid patients with available metabolite measurements, low serum leucin levels were associated with a doubled risk of 180-day all-cause mortality in a fully adjusted regression model (adjusted HR 2.20 [95% CI 1.46-3.30], p < 0.001). There was also an association with mortality for isoleucine (1.56 [95% CI 1.03-2.35], p = 0.035) and valine (1.69 [95% CI 1.13-2.53], p = 0.011). When comparing effects of nutritional support on mortality in patients with high and low levels of leucine, there was no evidence of significant differences in effectiveness of the intervention. The same was true for isoleucine and valine.

CONCLUSION

Our data suggest that depletion of leucine, isoleucine, and valine among malnourished polymorbid patients is associated with increases in long-term mortality. However, patients with low metabolite levels did not show a pronounced benefit from nutritional support. Further research should focus on the clinical effects of nutritional support in patients with depleted stores of essential branched-chain amino acids.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov as NCT02517476 (registered 7 August 2015).

Low-calorie, high-protein diets, regardless of protein source, improve glucose metabolism and cardiometabolic profiles in subjects with prediabetes or type 2 diabetes and overweight or obesity

AIM

The aim was to study the effect of two low-calorie, high-protein (HP) diets, with most of the protein coming from animal or plant sources, on glycaemic and other cardiometabolic outcomes in subjects with overweight or obesity and glucose metabolism disorders.

MATERIALS AND METHODS

A total of 117 participants aged >18 years with body mass index over 27.5 kg/m2 and prediabetes or type 2 diabetes mellitus (T2DM) were randomized to one of two HP low-calorie diets (35% of total calories from protein), in which 75% of the protein was from either plant-based sources (HPP) or animal sources (HPA). For both diets, 30% and 35% of the total calories were from fat and carbohydrates, respectively. The dietary intervention lasted 6 months.

RESULTS

Both diets improved body composition to a similar extent, including weight loss (-8.05 ± 5.12 kg for the HPA diet and -7.70 ± 5.47 kg for the HPP diet at 6 months) and fat mass, mainly visceral fat. Both diets had a similar beneficial effect on glucose metabolism, including fasting glucose, insulin, homeostasis model assessment of insulin resistance index and glycated haemoglobin. Other biochemical parameters, including lipid profiles, liver enzymes, adipokines and inflammatory biomarkers, similarly improved in both groups. Fasting incretins, mainly glucagon-like peptide 1, decreased significantly in both groups, and this effect correlated with weight loss.

CONCLUSIONS

Low-calorie HP diets improved body composition, glucose metabolism and other cardiometabolic outcomes, regardless of protein source (either animal or plant sources), in outpatients with prediabetes or T2DM.

CLINICAL TRIAL REGISTRATION

The clinical trial was registered in ClinicalTrials.gov (identifier: NCT05456347) https://clinicaltrials.gov/study/NCT05456347?term=NCT05456347&rank=1.

Metabolic Reprogramming in Cancer: Implications for Immunosuppressive Microenvironment

Cancer is a complex and heterogeneous disease characterised by uncontrolled cell growth and proliferation. One hallmark of cancer cells is their ability to undergo metabolic reprogramming, which allows them to sustain their rapid growth and survival. This metabolic reprogramming creates an immunosuppressive microenvironment that facilitates tumour progression and evasion of the immune system. In this article, we review the mechanisms underlying metabolic reprogramming in cancer cells and discuss how these metabolic alterations contribute to the establishment of an immunosuppressive microenvironment. We also explore potential therapeutic strategies targeting metabolic vulnerabilities in cancer cells to enhance immune-mediated anti-tumour responses. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02044861, NCT03163667, NCT04265534, NCT02071927, NCT02903914, NCT03314935, NCT03361228, NCT03048500, NCT03311308, NCT03800602, NCT04414540, NCT02771626, NCT03994744, NCT03229278, NCT04899921.

Water deprivation induces a systemic procatabolic state that differentially affects oxidative and glycolytic skeletal muscles in male mice

Dehydration, characterized by the loss of total body water and/or electrolytes due to diseases or inadequate fluid intake, is prevalent globally but often underestimated. Its contribution to long-term chronic diseases and sarcopenia is recognized, yet the mechanisms involved in systemic and muscle protein metabolism during dehydration remain unclear. This study investigated metabolic adaptations in a 36-h water deprivation (WD) model of mice. Male C57BL/6 mice underwent 36-h WD or pair-feeding at rest, with assessments of motor skills along with biochemical and metabolic parameters. Dehydration was confirmed by hypernatremia, body mass loss, hyporexia, and increased activity of vasopressinergic and oxytocinergic neurons compared with controls. These results were associated with liver mass loss, decreased glycemia, and increased cholesterolemia. In addition, increased V̇o2 and a decreased respiratory exchange ratio indicated reduced carbohydrate consumption and potentially increased protein use during dehydration. Thus, skeletal muscle protein metabolism was evaluated due to its high protein content. In the oxidative muscles of the WD group, total and proteasomal proteolysis increased, which was associated with decreased Akt-mediated intracellular signaling. Interestingly, there was an increase in fiber cross-sectional area, likely due to higher muscle water content caused by increased intracellular osmolality induced by protein catabolism products. Conversely, no changes were observed in protein turnover or water content in glycolytic muscles. These findings suggest that short-term WD imposes a procatabolic state, depleting protein content in skeletal muscle. However, skeletal muscle may respond differently to dehydration based on its phenotype and might adapt for a limited time.NEW & NOTEWORTHY This study investigated the effects of WD on mouse homeostasis, focusing on energy substrates and skeletal muscle protein metabolism. Our findings revealed a shift toward reduced dependence on carbohydrate degradation and increased reliance on lipid oxidation, or even protein oxidation, as energy sources, since we observed increased proteolysis in one muscle phenotype. Despite body mass loss, soleus and EDL muscle masses were differently affected. These results indicate the procatabolic potential of short-term WD in mice.

Branched-Chain Amino Acid Supplements for Sarcopenia in Liver Cirrhosis: A Systematic Review and Meta-analysis

BACKGROUND

Sarcopenia, a key aspect of malnutrition in liver cirrhosis (LC), affects 30-70% of LC patients. Given the inconsistent results from RCTs on branched-chain amino acids (BCAAs) for treating sarcopenia in LC, we conducted a systematic review and meta-analysis to assess the efficacy and safety of BCAAs for sarcopenia management in LC patients.

METHODS

A systematic review and meta-analysis synthesizing evidence from RCTs obtained from PubMed, Embase, Cochrane, Scopus, and Web of Science from inception to April 2024. We used the fixed-effects model to report dichotomous outcomes using risk ratio (RR) and continuous outcomes using mean difference (MD), with a 95% confidence interval (CI). PROSPERO ID: CRD42024542761.

RESULTS

Five RCTs with 434 patients were included. BCAAs were significantly associated with decreased liver frailty index change (MD: -0.14 with 95% CI [-0.28, -0.01], P = 0.03). However, there was no significant difference between BCAAs and the control group regarding hand grip strength change (MD: 0.98 with 95% CI [-0.45, 2.41], P = 0.18). Also, BCAAs were associated with increased body mass index (BMI) change (MD: 0.99 with 95% CI [0.16, 1.82], P = 0.02) and increased QoL (standardized mean difference : 0.27 with 95% CI [0.03, 0.52], P = 0.03). However, there was no significant difference between BCAAs and the control group in model for end-stage liver disease (MELD) score change (MD: 0.65 with 95% CI [-1.20, 2.50], P = 0.49), skeletal muscle index change (MD: 0.21 with 95% CI [-0.23, 0.65], P = 0.35), and gait speed change (MD: 0.10 with 95% CI [-0.15, 0.34], P = 0.43).

CONCLUSION

BCAA supplementation in cirrhotic patients with sarcopenia reduced the liver frailty index, increased BMI and QoL, but did not affect handgrip strength, skeletal muscle index, gait speed, or MELD score. Outcome heterogeneity and study bias were noted, highlighting the need for further RCTs to confirm these results.

Metabolomics at the cutting edge of risk prediction of MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major public health threat globally. Management of patients afflicted with MASLD and research in this domain are limited by the lack of robust well-established non-invasive biomarkers for diagnosis, prognostication, and monitoring. The circulating metabolome reflects both the systemic metabo-inflammatory milieu and changes in the liver in affected individuals. In this review we summarize the available literature on changes in the different components of the metabolome in MASLD with a focus on changes that are linked to the presence of underlying steatohepatitis, severity of disease activity, and fibrosis stage. We further summarize the existing literature around biomarker panels that are derived from interrogation of the metabolome. Their relevance to disease biology and utility in practice are also discussed. We further highlight potential direction for future studies particularly to ensure they are fit for purpose and suitable for widespread use.

Vitamin D administration increases serum alanine concentrations in thermally injured mice

Thermal or burn injury results in profound metabolic changes in the body. This can contribute to muscle atrophy, bone loss, as well as suppression of the immune system. While the mechanisms that underlie this hypermetabolic response remain unclear, patients with burn injury often have low circulating levels of vitamin D. Vitamin D has been shown to regulate bone formation as well as regulate muscle function. We sought to clarify the effects of vitamin D administration on skeletal muscle function following thermal injury using a mouse model. We found that thermal injury resulted in decreased vitamin D levels as well as decreased bone mineral density. Branched chain amino acid (BCAA)s levels were also significantly enhanced in the serum following burn injury. Vitamin D administration reversed the decrease in bone marrow-derived mesenchymal stem cell (BM-MSC)s observed post burn injury. Interestingly, vitamin D administration also resulted in increased tricarboxylic acid cycle (TCA) cycle metabolites in muscle which was decreased after burn conditions, enhanced the supply of alanine and glutamine in the blood which could contribute to gluconeogenesis and wound healing. Therefore, vitamin D supplementation after burn injury may have effects not only in bone metabolism, but may affect substrate metabolism in other organs/tissues.

Mitochondrial Calcium Signaling Regulates Branched-Chain Amino Acid Catabolism in Fibrolamellar Carcinoma

Metabolic adaptations in response to changes in energy supply and demand are essential for survival. The mitochondrial calcium uniporter plays a key role in coordinating metabolic homeostasis by regulating TCA cycle activation, mitochondrial fatty acid oxidation, and cellular calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial pathways has remained unexplored. Here, we investigate metabolic consequences of uniporter loss- and gain-of-function using uniporter knockout cells and the liver cancer fibrolamellar carcinoma (FLC), which we demonstrate to have elevated mitochondrial calcium levels. Our results reveal that branched-chain amino acid (BCAA) catabolism and the urea cycle are uniporter-regulated metabolic pathways. Reduced uniporter function boosts expression of BCAA catabolism genes, and the urea cycle enzyme ornithine transcarbamylase (OTC). In contrast, high uniporter activity in FLC suppresses their expression. This suppression is mediated by reduced expression of the transcription factor KLF15, a master regulator of liver metabolism. Thus, uniporter responsive calcium signaling plays a central role in FLC-associated metabolic changes, including hyperammonemia. Our study identifies an important role for mitochondrial calcium signaling in metabolic adaptation through transcriptional regulation of metabolism and elucidates its importance for BCAA and ammonia metabolism in FLC.

Branched-chain amino acid supplementation and voluntary running have distinct effects on the serum metabolome of rats with high or low intrinsic aerobic capacity

Introduction

A growing body of literature associates branched-chain amino acid (BCAA) catabolism to increased fatty acid oxidation and better metabolic health. Hence, BCAA-rich diets may improve body composition and muscle protein synthesis. However, the role of individual characteristics such as a low aerobic fitness, a well-established risk factor for cardio-metabolic diseases, has not been studied.

Methods

This study examined 64 female rats from the high-capacity runner (HCR) and low-capacity runner (LCR) rat model. Rats from each line (HCR or LCR) were divided into four groups; differing from diet (CTRL or BCAA) and from the opportunity to voluntarily run on a running wheel (NONRUNNER or RUNNER). Groups were matched for body mass and maximal running capacity within each line. We measured maximal running capacity and metabolism before and after the intervention of diet and voluntary running activity. After the end of the experiment, serum samples were collected for metabolome analysis.

Results

We are the first to show that BCAA supplementation has a more pronounced impact on LCRs compared to HCRs. Specifically, in LCR rats, BCAA supplementation led to reduced daily voluntary running distance and an enrichment of serine metabolism in the serum metabolome. While voluntary running increased food intake and energy expenditure, its effects on the serum metabolome were minimal in HCRs.

Conclusion

The present research highlights the benefit achieved by combining BCAA supplementation with running activity, especially in the LCR line. Importantly, our results underscore the interconnected role of BCAAs and fatty acid metabolism in promoting overall metabolic health.

Volumetric body composition analysis of the Cancer Genome Atlas reveals novel body composition traits and molecular markers Associated with Renal Carcinoma outcomes

Clinically, the body mass index remains the most frequently used metric of overall obesity, although it is flawed by its inability to account for different adipose (i.e., visceral, subcutaneous, and inter/intramuscular) compartments, as well as muscle mass. Numerous prior studies have demonstrated linkages between specific adipose or muscle compartments to outcomes of multiple diseases. Although there are no universally accepted standards for body composition measurement, many studies use a single slice at the L3 vertebral level. In this study, we use computed tomography (CT) studies from patients in The Cancer Genome Atlas (TCGA) to compare current L3-based techniques with volumetric techniques, demonstrating potential limitations with level-based approaches for assessing outcomes. In addition, we identify gene expression signatures in normal kidney that correlate with fat and muscle body composition traits that can be used to predict sex-specific outcomes in renal cell carcinoma.

Metabolomic Fingerprints of Medical Therapy Versus Bariatric Surgery in Patients With Obesity and Type 2 Diabetes: The STAMPEDE Trial

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) are effective procedures to treat and manage type 2 diabetes (T2D). However, the underlying metabolic adaptations that mediate improvements in glucose homeostasis remain largely elusive. The purpose of this study was to identify metabolic signatures associated with biochemical resolution of T2D after medical therapy (MT) or bariatric surgery.

RESEARCH DESIGN AND METHODS

Plasma samples from 90 patients (age 49.9 ± 7.6 years; 57.7% female) randomly assigned to MT (n = 30), RYGB (n = 30), or SG (n = 30) were retrospectively subjected to untargeted metabolomic analysis using ultra performance liquid chromatography with tandem mass spectrometry at baseline and 24 months of treatment. Phenotypic importance was determined by supervised machine learning. Associations between change in glucose homeostasis and circulating metabolites were assessed using a linear mixed effects model.

RESULTS

The circulating metabolome was dramatically remodeled after SG and RYGB, with largely overlapping signatures after MT. Compared with MT, SG and RYGB profoundly enhanced the concentration of metabolites associated with lipid and amino acid signaling, while limiting xenobiotic metabolites, a function of decreased medication use. Random forest analysis revealed 2-hydroxydecanoate as having selective importance to RYGB and as the most distinguishing feature between MT, SG, and RYGB. To this end, change in 2-hydroxydecanoate correlated with reductions in fasting glucose after RYGB but not SG or MT.

CONCLUSIONS

We identified a novel metabolomic fingerprint characterizing the longer-term adaptations to MT, RYGB, and SG. Notably, the metabolomic profiles of RYGB and SG procedures were distinct, indicating equivalent weight loss may be achieved by divergent effects on metabolism.

Oligonol®, an Oligomerized Polyphenol from Litchi chinensis, Enhances Branched-Chain Amino Acid Transportation and Catabolism to Alleviate Sarcopenia

Branched-chain amino acids (BCAAs) are essential for muscle protein synthesis and are widely acknowledged for mitigating sarcopenia. Oligonol® (Olg), a low-molecular-weight polyphenol from Litchi chinensis, has also been found to attenuate sarcopenia by improving mitochondrial quality and positive protein turnover. This study aims to investigate the effect of Olg on BCAA-stimulated protein synthesis in sarcopenia. In sarcopenic C57BL/6 mice and senescence-accelerated mouse-prone 8 (SAMP8) mice, BCAAs were significantly decreased in skeletal muscle but increased in blood serum. Furthermore, the expressions of membrane L-type amino acid transporter 1 (LAT1) and branched-chain amino acid transaminase 2 (BCAT2) in skeletal muscle were lower in aged mice than in young mice. The administration of Olg for 8 weeks significantly increased the expressions of membrane LAT1 and BCAT2 in the skeletal muscle when compared with non-treated SAMP8 mice. We further found that BCAA deprivation via LAT1-siRNA in C2C12 myotubes inhibited the signaling of protein synthesis and facilitated ubiquitination degradation of BCAT2. In C2C12 cells mimicking sarcopenia, Olg combined with BCAA supplementation enhanced mTOR/p70S6K activity more than BCAA alone. However, blocked LAT1 by JPH203 reversed the synergistic effect of the combination of Olg and BCAAs. Taken together, changes in LAT1 and BCAT2 during aging profoundly alter BCAA availability and nutrient signaling in aged mice. Olg increases BCAA-stimulated protein synthesis via modulating BCAA transportation and BCAA catabolism. Combining Olg and BCAAs may be a useful nutritional strategy for alleviating sarcopenia.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) elicited dose-dependent shifts in the murine urinary metabolome associated with hepatic AHR-mediated differential gene expression

Epidemiological evidence suggests an association between dioxin and dioxin-like compound (DLC) exposure and human liver disease. The prototypical DLC, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been shown to induce the progression of reversible hepatic steatosis to steatohepatitis with periportal fibrosis and biliary hyperplasia in mice. Although the effects of TCDD toxicity are mediated by aryl hydrocarbon receptor (AHR) activation, the underlying mechanisms of TCDD-induced hepatotoxicity are unresolved. In the present study, male C57BL/6NCrl mice were gavaged every 4 days for 28 days with 0.03 - 30 μg/kg TCDD and evaluated for liver histopathology and gene expression as well as complementary 1-dimensional proton magnetic resonance (1D- 1H NMR) urinary metabolic profiling. Urinary trimethylamine (TMA), trimethylamine N-oxide (TMAO), and 1-methylnicotinamide (1MN) levels were altered by TCDD at doses ≤ 3 μg/kg; other urinary metabolites, like glycolate, urocanate, and 3-hydroxyisovalerate, were only altered at doses that induced moderate to severe steatohepatitis. Bulk liver RNA-seq data suggested altered urinary metabolites correlated with hepatic differential gene expression corresponding to specific metabolic pathways. In addition to evaluating whether altered urinary metabolites were liver-dependent, published single-nuclear RNA-seq (snRNA-seq), AHR ChIP-seq, and AHR knockout gene expression datasets provide further support for hepatic cell-type and AHR-regulated dependency, respectively. Overall, TCDD-induced liver effects were preceded by and occurred with changes in urinary metabolite levels due to AHR-mediated changes in hepatic gene expression.

Elevated BCAA catabolism reverses the effect of branched-chain ketoacids on glucose transport in mTORC1-dependent manner in L6 myotubes

Plasma levels of branched-chain amino acids (BCAA) and their metabolites, branched-chain ketoacids (BCKA), are increased in insulin resistance. We previously showed that ketoisocaproic acid (KIC) suppressed insulin-stimulated glucose transport in L6 myotubes, especially in myotubes depleted of branched-chain ketoacid dehydrogenase (BCKD), the enzyme that decarboxylates BCKA. This suggests that upregulating BCKD activity might improve insulin sensitivity. We hypothesised that increasing BCAA catabolism would upregulate insulin-stimulated glucose transport and attenuate insulin resistance induced by BCKA. L6 myotubes were either depleted of BCKD kinase (BDK), the enzyme that inhibits BCKD activity, or treated with BT2, a BDK inhibitor. Myotubes were then treated with KIC (200 μM), leucine (150 μM), BCKA (200 μM), or BCAA (400 μM) and then treated with or without insulin (100 nM). BDK depletion/inhibition rescued the suppression of insulin-stimulated glucose transport by KIC/BCKA. This was consistent with the attenuation of IRS-1 (Ser612) and S6K1 (Thr389) phosphorylation but there was no effect on Akt (Ser473) phosphorylation. The effect of leucine or BCAA on these measures was not as pronounced and BT2 did not influence the effect. Induction of the mTORC1/IRS-1 (Ser612) axis abolished the attenuating effect of BT2 treatment on glucose transport in cells treated with KIC. Surprisingly, rapamycin co-treatment with BT2 and KIC further reduced glucose transport. Our data suggests that the suppression of insulin-stimulated glucose transport by KIC/BCKA in muscle is mediated by mTORC1/S6K1 signalling. This was attenuated by upregulating BCAA catabolic flux. Thus, interventions targeting BCAA metabolism may provide benefits against insulin resistance and its sequelae.

Sex-Based Effects of Branched-Chain Amino Acids on Strength Training Performance and Body Composition

BACKGROUND

Branched-chain amino acids (BCAAs) are widely studied for their effects on muscle recovery and performance.

AIMS

This study examined the effects of BCAA supplementation on anthropometric data, physical performance, delayed onset muscle soreness (DOMS), and fatigue in recreational weightlifters.

METHODS

The trial involved 100 participants (50 men and 50 women), randomized into BCAA and placebo groups. Subjects in the BCAA group took five daily capsules of 500 mg L-leucine, 250 mg L-isoleucine, and 250 mg L-valine for six months. A two-way ANOVA was used to analyze the main and interaction effects of sex and treatment.

RESULTS

Notable findings include significant improvements in muscle recovery, as indicated by reduced DOMS, particularly in women who showed a decrement of 18.1 ± 9.4 mm compared to 0.8 ± 1.2 mm in the placebo group of a horizontal 100 mm line. Fatigue perception was also significantly lower in the BCAA group, with women reporting a greater decrease (2.6 ± 1.5 scores) compared to the placebo group (0.6 ± 0.7 scores). Strength gains were prominent, especially in men, with a 10% increase in bench press maximum observed in the BCAA group. The interaction between sex and treatment was significant, suggesting sex-specific responses to BCAA supplementation.

CONCLUSIONS

These results underscore the effectiveness of BCAA supplementation in enhancing muscle recovery, reducing fatigue, and improving strength. This study also highlights sex-specific responses, with women benefiting more in terms of DOMS and fatigue reduction, while men experienced greater strength gains, suggesting a need for tailored supplementation strategies.

Comparative Impact of Organic Grass-Fed and Conventional Cattle-Feeding Systems on Beef and Human Postprandial Metabolomics-A Randomized Clinical Trial

BACKGROUND/OBJECTIVES

Cattle-feeding systems may have health implications for consumers of beef products. Organic grass-fed (GRA) and conventional (CON) cattle-feeding systems may result in beef products with differing metabolite profiles and therefore could impact the postprandial metabolomic response of consumers. This study aims to measure whole beef metabolomics and postprandial metabolomic response of consumers between GRA and CON beef to elucidate potential health implications.

METHODS

This study followed a randomized double-blind crossover design with healthy male and female subjects (n = 10). Plasma samples were taken at fasting (0) and postprandially for four hours after consumption of a steak from each condition. Untargeted metabolomic analysis of whole beef and human plasma samples used LC/MS. Multivariate and pathway enrichment analysis in MetaboAnalyst was used to investigate metabolite and biochemical pathways that distinguished CON and GRA.

RESULTS

Cattle-feeding systems impacted both postprandial and whole beef steak metabolomic profiles. Metabolites that contributed to this variation included carnitine species (Proionylcarnitine), fatty acids, amino acids (L-valine), and Calamendiol. These metabolites have been associated with oxidative stress, inflammation, and cardiovascular health. Functional pathway enrichment analysis revealed numerous amino acid degradation pathways, especially branched-chain amino acids, and fatty acid degradation that changed throughout the postprandial time course.

CONCLUSIONS

These findings suggest that CON and GRA cattle-feeding systems differentially impact whole beef metabolomics, as well as consumer postprandial metabolic responses and the associated health implications.

Human Multi-Lineage Liver Organoid Model Reveals Impairment of CYP3A4 Expression upon Repeated Exposure to Graphene Oxide

Three-dimensional hepatic cell cultures can provide an important advancement in the toxicity assessment of nanomaterials with respect to 2D models. Here, we describe liver organoids (LOs) obtained by assembling multiple cell lineages in a fixed ratio 1:1:0.2. These are upcyte® human hepatocytes, UHHs, upcyte® liver sinusoidal endothelial cells, LSECs, and human bone marrow-derived mesenchymal stromal cells, hbmMSCs. The structural and functional analyses indicated that LOs reached size stability upon ca. 10 days of cultivation (organoid maturation), showing a surface area of approximately 10 mm2 and the hepatic cellular lineages, UHHs and LSECs, arranged to form both primitive biliary networks and sinusoid structures, alike in vivo. LOs did not show signs of cellular apoptosis, senescence, or alteration of hepatocellular functions (e.g., dis-regulation of CYP3A4 or aberrant production of Albumin) for the entire culture period (19 days since organoid maturation). After that, LOs were repeatedly exposed for 19 days to a single or repeated dose of graphene oxide (GO: 2-40 µg/mL). We observed that the treatment did not induce any macroscopic signs of tissue damage, apoptosis activation, and alteration of cell viability. However, in the repeated dose regimen, we observed a down-regulation of CYP3A4 gene expression. Notably, these findings are in line with recent in vivo data, which report a similar impact on CYP3A4 when mice were repeatedly exposed to GO. Taken together, these findings warn of the potential detrimental effects of GO in real-life exposure (e.g., occupational scenario), where its progressive accumulation is likely expected. More in general, this study highlights that LOs formed by many cell lineages can enable repeated exposure regimens (suitable to mimic accumulation); thus, they can be suitably considered alternative or complementary in vitro systems to animal models.

A 2-hydroxybutyrate-mediated feedback loop regulates muscular fatigue

Several metabolites have been shown to have independent and at times unexpected biological effects outside of their metabolic pathways. These include succinate, lactate, fumarate, and 2-hydroxyglutarate. 2-Hydroxybutyrate (2HB) is a byproduct of endogenous cysteine synthesis, produced during periods of cellular stress. 2HB rises acutely after exercise; it also rises during infection and is also chronically increased in a number of metabolic disorders. We show here that 2HB inhibits branched-chain aminotransferase enzymes, which in turn triggers a SIRT4-dependent shift in the compartmental abundance of protein ADP-ribosylation. The 2HB-induced decrease in nuclear protein ADP-ribosylation leads to a C/EBPβ-mediated transcriptional response in the branched-chain amino acid degradation pathway. This response to 2HB exposure leads to an improved oxidative capacity in vitro. We found that repeated injection with 2HB can replicate the improvement to oxidative capacity that occurs following exercise training. Together, we show that 2-HB regulates fundamental aspects of skeletal muscle metabolism.

Valsartan Rescues Suppressed Mitochondrial Metabolism during Insulin Resistance in C2C12 Myotubes

Elevated circulating branched-chain amino acids (BCAA) have been linked with the severity of insulin resistance across numerous populations, implicating heightened BCAA metabolism as a potential therapy for insulin resistance. Recently, the angiotensin II type 1 receptor (AT1R) inhibitor Valsartan (VAL) was identified as a potent inhibitor of branched-chain alpha-keto acid dehydrogenase kinase (BCKDK), a negative regulator of BCAA metabolism. This work investigated the effect of VAL on myotube metabolism and insulin sensitivity under both insulin sensitive and insulin resistant conditions. C2C12 myotubes were treated with or without VAL at 8 µM for 24 h, both with and without hyperinsulinemic-induced insulin resistance. Oxygen consumption and extracellular acidification were used to measure mitochondrial and glycolytic metabolism, respectively. Gene expression was assessed via qRT-PCR, and insulin sensitivity was assessed via Western blot. Insulin resistance significantly reduced both basal and peak mitochondrial function which were rescued to control levels by concurrent VAL. Changes in mitochondrial function occurred without substantial changes in mitochondrial content or related gene expression. Insulin sensitivity and glycolytic metabolism were unaffected by VAL, as was lipogenic signaling and lipid content. Additionally, both VAL and insulin resistance depressed Bckdha expression. Interestingly, an interaction effect was observed for extracellular isoleucine, valine, and total BCAA (but not leucine), suggesting VAL may alter BCAA utilization in an insulin sensitivity-dependent manner. Insulin resistance appears to suppress mitochondrial function in a myotube model which can be rescued by VAL. Further research will be required to explore the implications of these findings in more complex models.

Branched-chain amino acids: physico-chemical properties, industrial synthesis and role in signaling, metabolism and energy production

Branched-chain amino acids (BCAAs)-leucine (Leu), isoleucine (Ile), and valine (Val)-are essential nutrients with significant roles in protein synthesis, metabolic regulation, and energy production. This review paper offers a detailed examination of the physico-chemical properties of BCAAs, their industrial synthesis, and their critical functions in various biological processes. The unique isomerism of BCAAs is presented, focusing on analytical challenges in their separation and quantification as well as their solubility characteristics, which are crucial for formulation and purification applications. The industrial synthesis of BCAAs, particularly using bacterial strains like Corynebacterium glutamicum, is explored, alongside methods such as genetic engineering aimed at enhancing production, detailing the enzymatic processes and specific precursors. The dietary uptake, distribution, and catabolism of BCAAs are reviewed as fundamental components of their physiological functions. Ultimately, their multifaceted impact on signaling pathways, immune function, and disease progression is discussed, providing insights into their profound influence on muscle protein synthesis and metabolic health. This comprehensive analysis serves as a resource for understanding both the basic and complex roles of BCAAs in biological systems and their industrial application.

Interactions between Gut Microbiota and Natural Bioactive Polysaccharides in Metabolic Diseases: Review

The gut microbiota constitutes a complex ecosystem, comprising trillions of microbes that have co-evolved with their host over hundreds of millions of years. Over the past decade, a growing body of knowledge has underscored the intricate connections among diet, gut microbiota, and human health. Bioactive polysaccharides (BPs) from natural sources like medicinal plants, seaweeds, and fungi have diverse biological functions including antioxidant, immunoregulatory, and metabolic activities. Their effects are closely tied to the gut microbiota, which metabolizes BPs into health-influencing compounds. Understanding how BPs and gut microbiota interact is critical for harnessing their potential health benefits. This review provides an overview of the human gut microbiota, focusing on its role in metabolic diseases like obesity, type II diabetes mellitus, non-alcoholic fatty liver disease, and cardiovascular diseases. It explores the basic characteristics of several BPs and their impact on gut microbiota. Given their significance for human health, we summarize the biological functions of these BPs, particularly in terms of immunoregulatory activities, blood sugar, and hypolipidemic effect, thus providing a valuable reference for understanding the potential benefits of natural BPs in treating metabolic diseases. These properties make BPs promising agents for preventing and treating metabolic diseases. The comprehensive understanding of the mechanisms by which BPs exert their effects through gut microbiota opens new avenues for developing targeted therapies to improve metabolic health.

KIC (ketoisocaproic acid) and leucine have divergent effects on tissue insulin signaling but not on whole-body insulin sensitivity in rats

Plasma levels of branched-chain amino acids and their metabolites, the branched-chain ketoacids are increased in insulin resistance. Our previous studies showed that leucine and its metabolite KIC suppress insulin-stimulated glucose uptake in L6 myotubes along with the activation of the S6K1-IRS-1 pathway. Because other tissue and fiber types can be differentially regulated by KIC, we analyzed the effect of KIC gavage on whole-body insulin sensitivity and insulin signaling in vivo. We hypothesized that KIC gavage would reduce whole-body insulin sensitivity and increase S6K1-IRS-1 phosphorylation in various tissues and muscle fibers. Five-week-old male Sprague-Dawley rats were starved for 24 hours and then gavaged with 0.75ml/100g of water, leucine (22.3g/L) or KIC (30g/L) twice, ten minutes apart. They were then euthanized at different time points post-gavage (0.5-3h), and muscle, liver, and heart tissues were dissected. Other sets of gavaged animals underwent an insulin tolerance test. Phosphorylation (ph) of S6K1 (Thr389), S6 (Ser235/6) and IRS-1 (Ser612) was increased at 30 minutes post leucine gavage in skeletal muscles irrespective of fiber type. Ph-S6 (Ser235/6) was also increased in liver and heart 30 minutes after leucine gavage. KIC gavage increased ph-S6 (Ser235/6) in the liver. Neither Leucine nor KIC influenced whole-body insulin tolerance, nor ph-Akt (Ser473) in skeletal muscle and heart. BCKD-E1 α abundance was highest in the heart and liver, while ph-BCKD-E1 α (Ser293) was higher in the gastrocnemius and EDL compared to the soleus. Our data suggests that only leucine activates the S6K1-IRS-1 signaling axis in skeletal muscle, liver and heart, while KIC only does so in the liver. The effect of leucine and KIC on the S6K1-IRS-1 signaling pathway is uncoupled from whole-body insulin sensitivity. These results suggest that KIC and leucine may not induce insulin resistance, and the contributions of other tissues may regulate whole-body insulin sensitivity in response to leucine/KIC gavage.

Branched-Chain Amino Acids, Alanine, and Thyroid Function: A Cross-Sectional, Nuclear Magnetic Resonance (NMR)-Based Approach from ELSA-Brasil

The association of thyroid function with essential and non-essential amino acids is understudied, despite their common metabolic roles. Thus, our aim was to evaluate the association of thyroid function with the levels of branched-chain amino acids (BCAAs-leucine, isoleucine, and valine) and of alanine in the general population. We utilized data from the São Paulo research center of ELSA-Brasil, a longitudinal population-based cohort study. Thyroid parameters included thyroid stimulating hormone (TSH), free T4 and free T3 levels, and the FT4:FT3 ratio. BCAAs and alanine were analyzed on a fully automated NMR platform. The current analysis included euthyroid participants and participants with subclinical hyperthyroidism and hypothyroidism. We used Pearson's coefficient to quantify the correlation between thyroid-related parameters and amino acids. Linear regression models were performed to analyze whether thyroid parameters were associated with BCAAs and alanine levels. We included 4098 participants (51.3 ± 9.0 years old, 51.5% women) in this study. In the most adjusted model, higher levels of TSH were associated with higher levels of alanine, FT4 levels were inversely associated with isoleucine levels, FT3 levels were statistically significant and positively associated with valine and leucine, and the T3:T4 ratio was positively associated with all amino acids. We observed that subclinical hypothyroidism was positively associated with isoleucine and alanine levels in all models, even after full adjustment. Our findings highlight the association of subclinical hypothyroidism and thyroid-related parameters (including TSH, free T4, free T3, and FT4:FT3 ratio) with BCAAs and alanine. Further studies are needed to explore the mechanisms underlying this association. These insights contribute to our understanding of the influence of thyroid-related parameters on BCAA and alanine metabolism.