Effects of leucine supplementation and serum withdrawal on branched-chain amino acid pathway gene and protein expression in mouse adipocytes

Integrated physiological, transcriptome, and metabolome analyses of the hepatopancreas of Litopenaeus vannamei under cold stress

Temperature is a limiting factor in the growth of aquatic organisms and can directly affect many chemical and biological processes, including metabolic enzyme activity, aerobic respiration, and signal transduction. In this study, physiological, transcriptomic, and metabolomic analyses were performed to characterize the response of Litopenaeus vannamei to cold stress. We subjected L. vannamei to gradually decreasing temperatures (24 °C, 20 °C, 18 °C, 14 °C, and 12 °C) and studied the changes in the hepatopancreas. The results showed that extreme cold stress (12 °C) caused structural damage to the hepatopancreas of L. vannamei. However, shrimp exhibited response mechanisms to enhance cold tolerance, through regulating changes in key genes and metabolites in amino acid, lipid metabolism, and carbohydrate metabolism, including (a) increased level of methylation in cells to enhance cold tolerance; (b) increased content of critical amino acids, such as proline, alanine, glutamic acid and taurine, to ameliorate energy metabolism, protect cells from cold-induced osmotic imbalance, and promote ion transport and DNA repair; (c) accumulation of unsaturated fatty acids to improve cell membrane fluidity; and (d) regulation of the metabolic pattern shift to rely on anaerobic metabolism with a gradual decrease in aerobic metabolism and enhance glycolysis to produce enough ATP to maintain energy metabolic balance. When the temperature dropped further, cold stress impaired antioxidant and immune defense responses in shrimp. This study provides an integrated analysis of the physiology, transcriptome, and metabolome of L. vannamei in response to cold stress.

Research progress on branched-chain amino acid aminotransferases

Branched-chain amino acid aminotransferases, widely present in natural organisms, catalyze bidirectional amino transfer between branched-chain amino acids and branched-chain α-ketoacids in cells. Branched-chain amino acid aminotransferases play an important role in the metabolism of branched-chain amino acids. In this paper, the interspecific evolution and biological characteristics of branched-chain amino acid aminotransferases are introduced, the related research of branched-chain amino acid aminotransferases in animals, plants, microorganisms and humans is summarized and the molecular mechanism of branched-chain amino acid aminotransferase is analyzed. It has been found that branched-chain amino acid metabolism disorders are closely related to various diseases in humans and animals and plants, such as diabetes, cardiovascular diseases, brain diseases, neurological diseases and cancer. In particular, branched-chain amino acid aminotransferases play an important role in the development of various tumors. Branched-chain amino acid aminotransferases have been used as potential targets for various cancers. This article reviews the research on branched-chain amino acid aminotransferases, aiming to provide a reference for clinical research on targeted therapy for various diseases and different cancers.

The Emerging Importance of Mitochondria in White Adipocytes: Neither Last nor Least

The growing recognition of mitochondria's crucial role in the regulation of white adipose tissue remodeling and energy balance underscores its significance. The marked metabolic diversity of mitochondria provides the molecular and cellular foundation for enabling adipose tissue plasticity in response to various metabolic cues. Effective control of mitochondrial function at the cellular level, not only in thermogenic brown and beige adipocytes but also in energy-storing white adipocytes, exerts a profound influence on adipose homeostasis. Furthermore, mitochondria play a pivotal role in intercellular communication within adipose tissue via production of metabolites with signaling properties. A more comprehensive understanding of mitochondrial regulation within white adipocytes will empower the development of targeted and efficacious strategies to enhance adipose function, leading to advancements in overall metabolic health.

Branched chain amino acids-friend or foe in the control of energy substrate turnover and insulin sensitivity?

Branched chain amino acids (BCAA) and their derivatives are bioactive molecules with pleiotropic functions in the human body. Elevated fasting blood BCAA concentrations are considered as a metabolic hallmark of obesity, insulin resistance, dyslipidaemia, nonalcoholic fatty liver disease, type 2 diabetes and cardiovascular disease. However, since increased BCAA amount is observed both in metabolically healthy and obese subjects, a question whether BCAA are mechanistic drivers of insulin resistance and its morbidities or only markers of metabolic dysregulation, still remains open. The beneficial effects of BCAA on body weight and composition, aerobic capacity, insulin secretion and sensitivity demand high catabolic potential toward amino acids and/or adequate BCAA intake. On the opposite, BCAA-related inhibition of lipogenesis and lipolysis enhancement may preclude impairment in insulin sensitivity. Thereby, the following review addresses various strategies pertaining to the modulation of BCAA catabolism and the possible roles of BCAA in energy homeostasis. We also aim to elucidate mechanisms behind the heterogeneity of ramifications associated with BCAA modulation.

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

Branched-chain amino acids (BCAAs) are critical for skeletal muscle and whole-body anabolism and energy homeostasis. They also serve as signaling molecules, for example, being able to activate mammalian/mechanistic target of rapamycin complex 1 (mTORC1). This has implication for macronutrient metabolism. However, elevated circulating levels of BCAAs and of their ketoacids as well as impaired catabolism of these amino acids (AAs) are implicated in the development of insulin resistance and its sequelae, including type 2 diabetes, cardiovascular disease, and of some cancers, although other studies indicate supplements of these AAs may help in the management of some chronic diseases. Here, we first reviewed the catabolism of these AAs especially in skeletal muscle as this tissue contributes the most to whole body disposal of the BCAA. We then reviewed emerging mechanisms of control of enzymes involved in regulating BCAA catabolism. Such mechanisms include regulation of their abundance by microRNA and by post translational modifications such as phosphorylation, acetylation, and ubiquitination. We also reviewed implications of impaired metabolism of BCAA for muscle and whole-body metabolism. We comment on outstanding questions in the regulation of catabolism of these AAs, including regulation of the abundance and post-transcriptional/post-translational modification of enzymes that regulate BCAA catabolism, as well the impact of circadian rhythm, age and mTORC1 on these enzymes. Answers to such questions may facilitate emergence of treatment/management options that can help patients suffering from chronic diseases linked to impaired metabolism of the BCAAs.

Differences in gene expression of enzymes involved in branched-chain amino acid metabolism of abdominal subcutaneous adipose tissue between pregnant women with and without PCOS

OBJECTIVE

Polycystic ovary syndrome (PCOS) appears to be a common endocrine disorder of women in reproductive age. Adipose tissue (AT) is known as an active tissue in the metabolism of branched-chain amino acids (BCAA; Valine, Leucine, and Isoleucine) that they have associated with blood BCAA levels is a prognostic factor for insulin-resistant. Although the crucial roles of AT in women suffering from PCOS was reported, little information exists on the BCAA metabolism in AT of PCOS women. The aim was to assess and compare the expression of BCAAs metabolism pathway genes in abdominal subcutaneous AT of pregnant women with PCOS and non-PCOS pregnant women.

MATERIALS AND METHODS

AT samples from 13 PCOS were compared with samples collected from 6 non-PCOS women, all of whom underwent caesarean. Quantitative real-time PCR technique was used for gene expression of branched chain aminotransferase 2 mitochondrial (BCAT2), branched chain ketoacid dehydrogenase E1-alpha (BCKDHA), branched chain ketoacid dehydrogenase E1-Beta (BCKDHB), dihydrolipoamide branched chain transacylase E2 (DBT), dihydrolipoamide dehydrogenase E3 (DLD), branched chain ketoacid dehydrogenase kinase (BCKDK), Data were analyzed using t-test or U-test.

RESULTS

No significant differences were found in age and body mass index (BMI) between non-PCOS and PCOS women. The mRNA level of BCAT2 and DLD in PCOS group was not significantly different from non-PCOS group whereas mRNA level of BCKDHB and DBT was significantly increased in PCOS group (P < 0.0001). In contrast, mRNA level of BCKDHA (P = 0.0001) and BCKDK (P < 0.0001) was significantly decreased in PCOS group.

CONCLUSION

The alterations in gene expressions involved BCAA metabolism in age-matched and BMI- matched non-PCOS and PCOS pregnant women at delivery day was shown which warrants further studies regards functional activity. More attention should be given to AT of PCOS mothers that was previously ignored.

White adipose tissue mitochondrial metabolism in health and in obesity

White adipose tissue is one of the largest organs of the body. It plays a key role in whole-body energy status and metabolism; it not only stores excess energy but also secretes various hormones and metabolites to regulate body energy balance. Healthy adipose tissue capable of expanding is needed for metabolic well-being and to prevent accumulation of triglycerides to other organs. Mitochondria govern several important functions in the adipose tissue. We review the derangements of mitochondrial function in white adipose tissue in the obese state. Downregulation of mitochondrial function or biogenesis in the white adipose tissue is a central driver for obesity-associated metabolic diseases. Mitochondrial functions compromised in obesity include oxidative functions and renewal and enlargement of the adipose tissue through recruitment and differentiation of adipocyte progenitor cells. These changes adversely affect whole-body metabolic health. Dysfunction of the white adipose tissue mitochondria in obesity has long-term consequences for the metabolism of adipose tissue and the whole body. Understanding the pathways behind mitochondrial dysfunction may help reveal targets for pharmacological or nutritional interventions that enhance mitochondrial biogenesis or function in adipose tissue.

A leucine-rich diet modulates the mTOR cell signalling pathway in the gastrocnemius muscle under different Walker-256 tumour growth conditions

Background

The exact signalling mechanism of the mTOR complex remains a subject of constant debate, even with some evidence that amino acids participate in the same pathway as used for insulin signalling during protein synthesis. Therefore, this work conducted further study of the actions of amino acids, especially leucine, in vivo, in an experimental model of cachexia. We analysed the effects of a leucine-rich diet on the signalling pathway of protein synthesis in muscle during a tumour growth time-course.

Methods

Wistar rats were distributed into groups based on Walker-256 tumour implant and subjected to a leucine-rich diet and euthanised at three different time points following tumour development (the 7th, 14th and 21st day). We assessed the mTOR pathway key-proteins in gastrocnemius muscle, such as RAG-A-GTPase, ERK/MAP4K3, PKB/Akt, mTOR, p70S6K1, Jnk, IRS-1, STAT3, and STAT6 comparing among the experimental groups. Serum WF (proteolysis-induced factor like from Walker-256 tumour) and muscle protein synthesis and degradation were assessed.

Results

The tumour-bearing group had increased serum WF content, and the skeletal-muscle showed a reduction in IRS-1 and RAG activation, increased PKB/Akt and Erk/MAP4K3 on the 21st day, and maintenance of p70S6K1, associated with increases in muscle STAT-3 and STAT-6 levels in these tumour-bearing rats.

Conclusion

Meanwhile, the leucine-rich diet modulated key steps of the mTOR pathway by triggering the increased activation of RAG and mTOR and maintaining JNK, STAT-3 and STAT-6 levels in muscle, leading to an increased muscle protein synthesis, reducing the degradation during tumour evolution in a host, minimising the cancer-induced damages in the cachectic state.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Alterations in branched-chain amino acid kinetics in nonobese but insulin-resistant Asian men

Background

Branched-chain amino acids (BCAAs) are elevated in the insulin-resistant (IR) state. The reasons for this increase remain unclear, but it may be related to abnormalities in BCAA metabolism and free fatty acid (FFA) metabolism.

Objective

In this study, we quantified BCAA and FFA kinetics of IR and insulin-sensitive (IS) nonobese Asian men with the use of stable-isotope tracers. We hypothesized that in addition to greater substrate flux, the BCAA oxidative pathway is also impaired to account for the higher plasma BCAA concentration in the IR state.

Design

We recruited 12 IR and 14 IS nonobese and healthy Asian men. Oral-glucose-tolerance tests (OGTTs) were performed to quantify insulin sensitivity, and subjects underwent 2 stable-isotope infusion studies. [U-13C6]Leucine was infused to measure leucine flux and oxidation as indexes of BCAA metabolism, whereas [U-13C16]palmitate was infused to measure palmitate flux and oxidation to represent FFA metabolism, The 2H2O dilution method was used to estimate body composition.

Results

IR subjects had greater adiposity and significantly higher fasting and post-OGTT glucose and insulin concentrations compared with the IS group. However, none of the subjects were diabetic. Despite similar dietary protein intake, IR subjects had a significantly higher plasma BCAA concentration and greater leucine flux. Leucine oxidation was also greater in the IR group, but the relation between leucine oxidation and flux was significantly weaker in the IR group than in the IS group (r = 0.530 compared with 0.695, P < 0.0388 for differences between slope). FFA oxidation was, however, unaffected despite higher FFA flux in the IR group.

Conclusion

The higher plasma BCAA concentration in healthy nonobese individuals with IR is associated with a weaker relation between BCAA oxidation and BCAA flux and this occurs in the presence of accelerated FFA flux and oxidation.

Leucine Affects α-Amylase Synthesis through PI3K/Akt-mTOR Signaling Pathways in Pancreatic Acinar Cells of Dairy Calves

Dietary nutrient utilization, particularly starch, is potentially limited by digestion in dairy cow small intestine because of shortage of α-amylase. Leucine acts as an effective signal molecular in the mTOR signaling pathway, which regulates a series of biological processes, especially protein synthesis. It has been reported that leucine could affect α-amylase synthesis and secretion in ruminant pancreas, but mechanisms have not been elaborated. In this study, pancreatic acinar (PA) cells were used as a model to determine the cellular signal of leucine influence on α-amylase synthesis. PA cells were isolated from newborn Holstein dairy bull calves and cultured in Dulbecco's modifed Eagle's medium/nutrient mixture F12 liquid media containing four leucine treatments (0, 0.23, 0.45, and 0.90 mM, respectively), following α-amylase activity, zymogen granule, and signal pathway factor expression detection. Rapamycin, a specific inhibitor of mTOR, was also applied to PA cells. Results showed that leucine increased ( p < 0.05) synthesis of α-amylase as well as phosphorylation of PI3K, Akt, mTOR, and S6K1 while reduced ( p < 0.05) GCN2 expression. Inhibition of mTOR signaling downregulated the α-amylase synthesis. In addition, the extracellular leucine dosage significantly influenced intracellular metabolism of isoleucine ( p < 0.05). Overall, leucine regulates α-amylase synthesis through promoting the PI3K/Akt-mTOR pathway and reducing the GCN2 pathway in PA cells of dairy calves. These pathways form the signaling network that controls the protein synthesis and metabolism. It would be of great interest in future studies to explore the function of leucine in ruminant nutrition.

Leucine supplementation attenuates macrophage foam-cell formation: Studies in humans, mice, and cultured macrophages

Whereas atherogenicity of dietary lipids has been largely studied, relatively little is known about the possible contribution of dietary amino acids to macrophage foam-cell formation, a hallmark of early atherogenesis. Recently, we showed that leucine has antiatherogenic properties in the macrophage model system. In this study, an in-depth investigation of the role of leucine in macrophage lipid metabolism was conducted by supplementing humans, mice, or cultured macrophages with leucine. Macrophage incubation with serum obtained from healthy adults supplemented with leucine (5 g/d, 3 weeks) significantly decreased cellular cholesterol mass by inhibiting the rate of cholesterol biosynthesis and increasing cholesterol efflux from macrophages. Similarly, leucine supplementation to C57BL/6 mice (8 weeks) resulted in decreased cholesterol content in their harvested peritoneal macrophages (MPM) in relation with reduced cholesterol biosynthesis rate. Studies in J774A.1 murine macrophages revealed that leucine dose-dependently decreased cellular cholesterol and triglyceride mass. Macrophages treated with leucine (0.2 mM) showed attenuated uptake of very low-density lipoproteins and triglyceride biosynthesis rate, with a concurrent down-regulation of diacylglycerol acyltransferase-1, a key enzyme catalyzing triglyceride biosynthesis in macrophages. Similar effects were observed when macrophages were treated with α-ketoisocaproate, a key leucine metabolite. Finally, both in vivo and in vitro leucine supplementation significantly improved macrophage mitochondrial respiration and ATP production. The above studies, conducted in human, mice, and cultured macrophages, highlight a protective role for leucine attenuating macrophage foam-cell formation by mechanisms related to the metabolism of cholesterol, triglycerides, and energy production. © 2018 BioFactors, 44(3):245-262, 2018.

Administration of valine, leucine, and isoleucine improved plasma cholesterol and mitigated the preatherosclerotic lesions in rats fed with hypercholesterolemic diet

Hypercholesterolemia has a major contribution to the occurrence and progression of atherosclerotic lesions. Recent studies report the involvement of branched-chain amino acids in cholesterol methabolism. The aim of this research was to evaluate the role of valine, leucine and isoleucine on the occurrence and progression of atherosclerosis in rats receiving hypercholesterolic diet. Material and methods: 50 male Wistar rats distributed into five groups with the following type of diets: group I (control) received standard diet; group II - cholesterol; group III - cholesterol and valine; group IV - cholesterol and leucine; group V - cholesterol and isoleucine. The experimental study was conducted over a period of 2 months. The animals were evaluated for the serum levels of total cholesterol at the beginning of the experiment, after 1 month and after 2 months. The collected tissue fragments of heart and aorta were prepared for the examination by optical microscopy in order to identify the atherosclerotic changes. Results: The most increased values of serum cholesterol were recorded in rats from group II (p=0.001), for the second and third evaluation. The histological examination showed early histopathological lesions on the vascular intima for the groups treated with cholesterol, valine, leucine, and isoleucine. These early changes (the occurrence of some superficial endothelial erosions, adhesion of erythrocytes and platelets) were correlated with the degree of the arterial wall damage, of the leukocytes adhesion to the arterial intima, and the discontinuities of the internal elastic lamina. Conclusion: The comparative study of the effects of the three essential amino acids revealed that valine induced a faster response than leucine and isoleucine on the improvement of biochemical parameters, but there were no significant differences between the three amino acids in terms of their protective ability, demonstrated by the histopathological lesion assessment.

Emerging perspectives on branched-chain amino acid metabolism during adipocyte differentiation

PURPOSE OF REVIEW

Adipogenesis has been extensively studied in the context of carbohydrate and lipid metabolism. However, little information exists on the role of amino acid metabolism during adipocyte differentiation. Here, we review how branched-chain amino acid (BCAA) metabolism is modified during adipogenesis and, due to the limited information in the area, address questions that remain to be answered with further research.

RECENT FINDINGS

BCAAs are rapidly consumed during adipocyte differentiation and are indispensable for this process. Furthermore, we describe how BCAA catabolic enzymes and the metabolic fate of BCAAs are modified during adipogenesis.

SUMMARY

Obesity is a chronic disease characterized by increased adipose tissue due to either an increase in the size (hypertrophy) and/or number of adipocytes (hyperplasia). Hyperplasia is determined by the rate of adipogenesis. Therefore, understanding the mechanism that modulates adipogenesis in the context of amino acid metabolism will help to establish pharmacological and dietary interventions involving the type and amount of dietary protein for the treatment of obesity and its associated comorbidities.Video abstract http://links.lww.com/COCN/A11.

Systems view of adipogenesis via novel omics-driven and tissue-specific activity scoring of network functional modules

The investigation of the complex processes involved in cellular differentiation must be based on unbiased, high throughput data processing methods to identify relevant biological pathways. A number of bioinformatics tools are available that can generate lists of pathways ranked by statistical significance (i.e. by p-value), while ideally it would be desirable to functionally score the pathways relative to each other or to other interacting parts of the system or process. We describe a new computational method (Network Activity Score Finder - NASFinder) to identify tissue-specific, omics-determined sub-networks and the connections with their upstream regulator receptors to obtain a systems view of the differentiation of human adipocytes. Adipogenesis of human SBGS pre-adipocyte cells in vitro was monitored with a transcriptomic data set comprising six time points (0, 6, 48, 96, 192, 384 hours). To elucidate the mechanisms of adipogenesis, NASFinder was used to perform time-point analysis by comparing each time point against the control (0 h) and time-lapse analysis by comparing each time point with the previous one. NASFinder identified the coordinated activity of seemingly unrelated processes between each comparison, providing the first systems view of adipogenesis in culture. NASFinder has been implemented into a web-based, freely available resource associated with novel, easy to read visualization of omics data sets and network modules.

Mitochondrial function/dysfunction in white adipose tissue

The role of mitochondria in white adipocytes has long been neglected due in part to their lower abundance in these cells. However, accumulating evidence suggests that mitochondria are vital for maintaining metabolic homeostasis in white adipocytes because of their involvement in adipogenesis, fatty acid synthesis and esterification, branched-chain amino acid catabolism and lipolysis. It is therefore not surprising that white adipose tissue function can be perturbed by altering mitochondrial components or oxidative capacity. Moreover, studies in humans and animals with significantly altered fat mass, such as in obesity or lipoatrophy, indicate that impaired mitochondrial function in adipocytes may be linked directly to the development of metabolic diseases such as diabetes and insulin resistance. However, recent studies that specifically targeted mitochondrial function in adipocytes indicated dissociation between impaired mitochondrial oxidative capacity and systemic insulin sensitivity.