Acute and chronic treatment of L-isoleucine ameliorates glucose metabolism in glucose-intolerant and diabetic mice

BCAAs acutely drive glucose dysregulation and insulin resistance: role of AgRP neurons

BACKGROUND

High-protein diets are often enriched with branched-chain amino acids (BCAAs) known to enhance protein synthesis and provide numerous physiological benefits, but recent studies reveal their association with obesity and diabetes. In support of this, protein or BCAA supplementation is shown to disrupt glucose metabolism while restriction improves it. However, it is not clear if these are primary, direct effects of BCAAs or secondary to other physiological changes during chronic manipulation of dietary BCAAs.

METHODS

Three-month-old C57Bl/6 mice were acutely treated with either vehicle/BCAAs or BT2, a BCAA-lowering compound, and detailed in vivo metabolic phenotyping, including frequent sampling and pancreatic clamps, were conducted.

RESULTS

Using a catheter-guided frequent sampling method in mice, here we show that a single infusion of BCAAs was sufficient to acutely elevate blood glucose and plasma insulin. While pre-treatment with BCAAs did not affect glucose tolerance, a constant infusion of BCAAs during hyperinsulinemic-euglycemic clamps impaired whole-body insulin sensitivity. Similarly, a single injection of BT2 was sufficient to prevent BCAA rise during fasting and markedly improve glucose tolerance in high-fat-fed mice, suggesting that abnormal glycemic control in obesity may be causally linked to high circulating BCAAs. We further show that chemogenetic over-activation of AgRP neurons in the hypothalamus, as present in obesity, significantly impairs glucose tolerance that is completely normalized by acute BCAA reduction. Interestingly, most of these effects were demonstrated only in male, but not in female mice.

CONCLUSION

These findings suggest that BCAAs per se can acutely impair glucose homeostasis and insulin sensitivity, thus offering an explanation for how they may disrupt glucose metabolism in the long-term as observed in obesity and diabetes. Our findings also reveal that AgRP neuronal regulation of blood glucose is mediated through BCAAs, further elucidating a novel mechanism by which brain controls glucose homeostasis.

SGLT2 inhibitor improves kidney function and morphology by regulating renal metabolism in mice with diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is a secondary complication of diabetes mellitus and a leading cause of chronic kidney disease.

AIM

To investigate the impact of long-term canagliflozin treatment on DKD and elucidate its underlying mechanism.

METHODS

DKD model was established using high-fat diet and streptozotocin in male C57BL/6J mice (n = 30). Mice were divided into five groups and treated for 12 weeks. 1) normal control mice, 2) DKD model, 3) mice treated low-dose of canagliflozin, 4) high-dose of canagliflozin and 5) β-hydroxybutyrate. Mice kidney morphology and function were evaluated, and a metabolomics analysis was performed.

RESULTS

Canagliflozin treatment reduced blood creatinine and urine nitrogen levels and improved systemic insulin sensitivity and glucose tolerance in diabetic mice. Additionally, a decrease in histological lesions including collagen and lipid deposition in the kidneys was observed. β-hydroxybutyrate treatment did not yield a comparable outcome. The metabolomics analysis revealed that canagliflozin induced alterations in amino acid metabolism profiles in the renal tissue of diabetic mice.

CONCLUSION

Canagliflozin protects the kidneys of diabetic mice by increasing the levels of essential amino acids, promoting mitochondrial homeostasis, mitigating oxidative stress, and stimulating the amino acid-dependent tricarboxylic acid cycle.

Untargeted metabolomics of saliva in pregnant women with and without gestational diabetes mellitus and healthy non-pregnant women

Objective

The aim of this study was to compare the differences in salivary metabolites between pregnant women with gestational diabetes mellitus (GDM), healthy pregnant women (HPW), and healthy non-pregnant women (HNPW), and analyze the possible associations between the identified metabolites and gingivitis.

Method

The study included women with GDM (n = 9, mean age 28.9 ± 3.6 years, mean gestational age 30.1 ± 3.2 weeks), HPW (n = 9, mean age 27.9 ± 3.0 years, mean gestational age 28.6 ± 4.7 weeks), and HNPW (n = 9, mean age 27.7 ± 2.1 years). Saliva samples were collected from all participants and were analyzed with LC-MS/MS-based untargeted metabolomic analysis. Metabolite extraction, qualitative and semi-quantitative analysis, and bioinformatics analysis were performed to identify the differential metabolites and metabolic pathways between groups. The identified differential metabolites were further analyzed in an attempt to explore their possible associations with periodontal health and provide evidence for the prevention and treatment of periodontal inflammation during pregnancy.

Results

In positive ion mode, a total of 2,529 molecular features were detected in all samples, 166 differential metabolites were identified between the GDM and HPW groups (89 upregulated and 77 downregulated), 823 differential metabolites were identified between the GDM and HNPW groups (402 upregulated and 421 downregulated), and 647 differential metabolites were identified between the HPW and HNPW groups (351 upregulated and 296 downregulated). In negative ion mode, 983 metabolites were detected in all samples, 49 differential metabolites were identified between the GDM and HPW groups (29 upregulated and 20 downregulated), 341 differential metabolites were identified between the GDM and HNPW groups (167 upregulated and 174 downregulated), and 245 differential metabolites were identified between the HPW and HNPW groups (112 upregulated and 133 downregulated). A total of nine differential metabolites with high confidence levels were identified in both the positive and negative ion modes, namely, L-isoleucine, D-glucose 6-phosphate, docosahexaenoic acid, arachidonic acid, adenosine, adenosine-monophosphate, adenosine 5'-monophosphate, xanthine, and hypoxanthine. Among all pathways enriched by the upregulated differential metabolites, the largest number of pathways were enriched by four differential metabolites, adenosine, adenosine 5'-monophosphate, D-glucose 6-phosphate, and adenosine-monophosphate, and among all pathways enriched by the downregulated differential metabolites, the largest number of pathways were enriched by three differential metabolites, L-isoleucine, xanthine, and arachidonic acid.

Conclusion

Untargeted metabolomic analysis of saliva samples from pregnant women with GDM, HPW, and HNPW identified nine differential metabolites with high confidence. The results are similar to findings from previous metabolomics studies of serum and urine samples, which offer the possibility of using saliva for regular noninvasive testing in the population of pregnant women with and without GDM. Meanwhile, the associations between these identified differential metabolites and gingivitis need to be further validated by subsequent studies.

The role of the gut microbiota in health and cardiovascular diseases

The gut microbiota is critical to human health, such as digesting nutrients, forming the intestinal epithelial barrier, regulating immune function, producing vitamins and hormones, and producing metabolites to interact with the host. Meanwhile, increasing evidence indicates that the gut microbiota has a strong correlation with the occurrence, progression and treatment of cardiovascular diseases (CVDs). In patients with CVDs and corresponding risk factors, the composition and ratio of gut microbiota have significant differences compared with their healthy counterparts. Therefore, gut microbiota dysbiosis, gut microbiota-generated metabolites, and the related signaling pathway may serve as explanations for some of the mechanisms about the occurrence and development of CVDs. Several studies have also demonstrated that many traditional and latest therapeutic treatments of CVDs are associated with the gut microbiota and its generated metabolites and related signaling pathways. Given that information, we summarized the latest advances in the current research regarding the effect of gut microbiota on health, the main cardiovascular risk factors, and CVDs, highlighted the roles and mechanisms of several metabolites, and introduced corresponding promising treatments for CVDs regarding the gut microbiota. Therefore, this review mainly focuses on exploring the role of gut microbiota related metabolites and their therapeutic potential in CVDs, which may eventually provide better solutions in the development of therapeutic treatment as well as the prevention of CVDs.

Amino acid transporters as modulators of glucose homeostasis

Amino acids modulate glucose homeostasis. Cytosolic levels of amino acids are regulated by amino acid transporters, modulating insulin release, protein synthesis, cell proliferation, cell fate, and metabolism. In β-cells, amino acid transporters modulate incretin-stimulated insulin release. In the liver, amino acid transporters provide glutamine and alanine for gluconeogenesis. Intestinal amino acid transporters facilitate the intake of amino acids causing protein restriction when inactive. Adipocyte development is regulated by amino acid transporters through activation of mechanistic target of rapamycin (mTORC1) and amino acid-related metabolites. The accumulation and metabolism of branched-chain amino acids (BCAAs) in muscle depends on transporters. The integration between amino acid metabolism and transport is critical for the maintenance and function of tissues and cells involved in glucose homeostasis.

Metabolomic Analysis of Carbohydrate and Amino Acid Changes Induced by Hypoxia in Naked Mole-Rat Brain and Liver

Hypoxia poses a major physiological challenge for mammals and has significant impacts on cellular and systemic metabolism. As with many other small rodents, naked mole-rats (NMRs; Heterocephalus glaber), who are among the most hypoxia-tolerant mammals, respond to hypoxia by supressing energy demand (i.e., through a reduction in metabolic rate mediated by a variety of cell- and tissue-level strategies), and altering metabolic fuel use to rely primarily on carbohydrates. However, little is known regarding specific metabolite changes that underlie these responses. We hypothesized that NMR tissues utilize multiple strategies in responding to acute hypoxia, including the modulation of signalling pathways to reduce anabolism and reprogram carbohydrate metabolism. To address this question, we evaluated changes of 64 metabolites in NMR brain and liver following in vivo hypoxia exposure (7% O₂, 4 h). We also examined changes in matched tissues from similarly treated hypoxia-intolerant mice. We report that, following exposure to in vivo hypoxia: (1) phenylalanine, tyrosine and tryptophan anabolism are supressed both in NMR brain and liver; (2) carbohydrate metabolism is reprogramed in NMR brain and liver, but in a divergent manner; (3) redox state is significantly altered in NMR brain; and (4) the AMP/ATP ratio is elevated in liver. Overall, our results suggest that hypoxia induces significant metabolic remodelling in NMR brain and liver via alterations of multiple metabolic pathways.

Association between dietary essential amino acids intake and metabolic biomarkers: influence of obesity among Chinese children and adolescents

Essential amino acids (EAAs) are involved in growth and development in children and adolescents. This study was aimed at exploring the relationship between dietary EAA intakes and metabolic biomarker, and the influence of obesity in children and adolescents. A total of 3566 subjects were analysed. Participators were classified according to weight status. Metabolic biomarkers were determined using standardized methods and conditions. Normal, overweight, and obesity statuses were defined according to the Working Group on Obesity in China (WGOC) BMI cutoff points based on age- and sex-specific screening criteria. In normal-weight group, blood uric acid was negatively correlated with dietary Ile, Leu, Lys, Phe, Thr, Val, and His, and zinc was negatively correlated with Ile, Leu, Lys, Phe, Thr, Val, His, Met, and Trp. In overweight group, TC was negatively correlated with Ile, Leu, Phe, Val, and His, and LDL-C was negatively correlated with Ile, Leu, Lys, Phe, Thr, Val, His, and Met, while TG was positively correlated with Leu, Lys, Phe, Thr, Val, and Met. In obesity group, hemoglobin was positively related to Ile, Leu, Lys, Phe, Thr, Val, His, and Trp, while vitamin D was positively correlated with His and Trp. The serum creatinine was negatively correlated with Ile, Leu, Phe, Val, His, and Met in normal-weight group, and positively correlated with Ile, Leu, Lys, Phe, Thr, Val, His, Met, Trp, His, and Trp in obesity group. Dietary amino acid score (AAS) and Leu intake were protective factors for obesity. The association between fasting blood glucose and EAAs intake was weak and labile. Metabolic biomarkers and EAA intakes were only related under certain weight status. The dietary AAS is positively correlated with HDL-C, LDL-C, serum creatinine, albumin, serum vitamin D, and zinc. The subtle relationship of EAAs and kidney function should be explored further. There is a complex relationship between EAAs and metabolic biomarkers, and overweight and obesity have a certain influence on this relationship.

Reproductive performance, metabolism and oxidative stress profile in Chinese yellow-feathered broiler breeder hens fed multiple levels of isoleucine

1. This experiment was conducted to evaluate the effects of dietary isoleucine (Ile) on reproductive performance and certain indices of metabolism and oxidative stress in Chinese yellow-feathered broiler breeder hens.2. A total of 600, 40-week-old Chinese yellow-feathered broiler breeder hens were fed a basal diet formulated with maize, corn gluten meal and spray-dried blood cell meal containing 3.3 g/kg Ile, or supplemented to contain 4.5, 5.7, 6.9, or 8.1 g/kg Ile for five weeks. Each dietary treatment had six replicates with 20 birds per replicate. After three weeks of receiving the trial diets, 24 eggs were collected at random from each replicate to measure egg quality. Starting after four weeks of treatment, 50 settable eggs per replicate were collected for 7 d in succession for hatching. After five weeks of being fed the treatment diets, birds were slaughtered for tissue and organ collection.3. For the overall period, laying rate, egg weight, egg mass and hatchling weight linearly (P < 0.05) and quadratically (P < 0.05) increased with dietary Ile levels. Final body weight, feed intake and relative liver weight of birds fed 3.3 g/kg Ile was lower compared to birds fed the other diets (P < 0.05). There was no effect of Ile level on egg quality (P > 0.05). Hatchling weight was linearly (P < 0.05) and quadratically increased (P < 0.05) in line with dietary supplemental Ile.4. After three weeks on the trial diets, birds fed the diet containing 3.3 g/kg Ile had decreased blood TG concentrations compared to breeders fed 6.9 or 8.1 g/kg Ile (P < 0.05). Activities of CK were significantly higher in breeders fed the 3.3 g/kg Ile diet compared to all other levels of dietary Ile after five weeks of treatment. A quadratic effect (P < 0.05) was evident for glucose at 8.1 g/kg Ile level. After five weeks of treatment, plasma TG concentrations in birds fed 3.3 g/kg Ile were significantly lower than in birds fed all other levels of Ile. Glucose concentrations in breeder hens receiving the 3.3 g/kg Ile diet were lowest and the highest concentrations were in birds fed 5.7 g/kg Ile (P < 0.05). Plasma activities of LDH were highest in breeders on the 3.3 g/kg Ile diet but were only significantly different (P < 0.05) for birds fed 5.7 g/kg Ile.5. The current study indicated that Ile deficiency decreased reproductive performance and appeared to serve as a stressor. The optimal dietary Ile for Chinese yellow-feathered broiler breeder hens in the laying period was 5.79 g/kg feed (0.75 g/d).

Identification of biomarkers for essential hypertension based on metabolomics

AIM

Essential hypertension (EH) is one of the most important public health problems worldwide. However, the pathogenesis of EH is unclear and early diagnostic methods are lacking. Metabolomics demonstrates great potential for biomarker discovery and the mechanistic exploration of metabolic diseases.

DATA SYNTHESIS

This review included human and animal metabolomics studies related to EH in the PubMed and Web of Science databases between February 1996 and May 2020. The study designs, EH standards, and reported metabolic biomarkers were systematically examined and compared. The pathway analysis was conducted through the online software MetaboAnalyst 4.0. Twenty-two human studies and fifteen animal studies were included in this systematic review. There were many frequently reported biomarkers with consistent trends (e.g., pyruvate, lactic acid, valine, and tryptophan) in human and animal studies, and thus had potential as biomarkers of EH. In addition, several shared metabolic pathways, including alanine, aspartate, and glutamate metabolism, aminoacyl-tRNA biosynthesis, and arginine biosynthesis, were identified in human and animal metabolomics studies. These biomarkers and pathways, closely related to insulin resistance, the inflammatory state, and impaired nitric oxide production, were demonstrated to contribute to EH development.

CONCLUSIONS

This study summarized valuable metabolic biomarkers and pathways that could offer opportunities for the early diagnosis or prediction of EH and the discovery of the metabolic mechanisms of EH.

Nutraceuticals for the treatment of sarcopenia in chronic liver disease

BACKGROUND AND AIMS

Sarcopenia, defined as loss of muscle mass, strength and function, is associated with adverse clinical outcomes in patients with cirrhosis. Despite improved understanding of the multifaceted pathogenesis, there are few established therapies to treat or prevent muscle loss in this population. This narrative review examines the available literature investigating the role of nutraceuticals for the prevention or treatment of muscle wasting in chronic liver disease.

METHODS

A comprehensive search or Medline and PubMED databases was conducted. Reference lists were screened to identify additional articles.

RESULTS

A number of nutritional supplements and vitamins target the specific metabolic derangements that contribute to sarcopenia in cirrhosis including altered amino acid metabolism, hyperammonaemia and inflammation. Branched chain amino acid (BCAA) supplementation has proposed anabolic effects through dual pathways of enhanced ammonia clearance and stimulation of muscle protein synthesis. l-carnitine also has multimodal effects on muscle and shows promise as a therapy for muscle loss through anti-inflammatory, antioxidant and ammonia lowering properties. Other nutraceuticals including l-ornithine l-aspartate, omega-3 polyunsaturated fatty acids and zinc and vitamin D supplementation, may similarly have positive effects on muscle homeostasis, however further evidence to support their use in cirrhotic populations is required.

CONCLUSION

Nutraceuticals offer a promising and likely safe adjunct to standard care for sarcopenia in cirrhosis. While there is most evidence to support the use of BCAA and l-carnitine supplementation, further well-designed clinical trials are needed to elucidate their efficacy as a therapy for muscle loss in this population.

Intragastric administration of leucine and isoleucine does not reduce the glycaemic response to, or slow gastric emptying of, a carbohydrate-containing drink in type 2 diabetes

AIMS

In healthy individuals, intragastric administration of the branched-chain amino acids, leucine and isoleucine, diminishes the glycaemic response to a mixed-nutrient drink, apparently by stimulating insulin and slowing gastric emptying, respectively. This study aimed to evaluate the effects of leucine and isoleucine on postprandial glycaemia and gastric emptying in type-2 diabetes mellitus (T2D).

METHODS

14 males with T2D received, on 3 separate occasions, in double-blind, randomised fashion, either 10 g leucine, 10 g isoleucine or control, intragastrically 30 min before a mixed-nutrient drink (500 kcal; 74 g carbohydrates, 18 g protein, 15 g fat). Plasma glucose, insulin and glucagon were measured from 30 min pre- until 120 min post-drink. Gastric emptying of the drink was also measured.

RESULTS

Leucine and isoleucine stimulated insulin, both before and after the drink (all P < 0.05; peak (mU/L): control: 70 ± 15; leucine: 88 ± 17; isoleucine: 74 ± 15). Isoleucine stimulated (P < 0.05), and leucine tended to stimulate (P = 0.078), glucagon before the drink, and isoleucine stimulated glucagon post-drink (P = 0.031; peak (pg/mL): control: 62 ± 5; leucine: 70 ± 9; isoleucine: 69 ± 6). Neither amino acid affected gastric emptying or plasma glucose (peak (mmol/L): control: 12.0 ± 0.5; leucine: 12.5 ± 0.7; isoleucine: 12.0 ± 0.6).

CONCLUSIONS

In contrast to health, in T2D, leucine and isoleucine, administered intragastrically in a dose of 10 g, do not lower the glycaemic response to a mixed-nutrient drink. This finding argues against a role for 'preloads' of either leucine or isoleucine in the management of T2D.

The Effect of Isoleucine Supplementation on Body Weight Gain and Blood Glucose Response in Lean and Obese Mice

Chronic isoleucine supplementation prevents diet-induced weight gain in rodents. Acute-isoleucine administration improves glucose tolerance in rodents and reduces postprandial glucose levels in humans. However, the effect of chronic-isoleucine supplementation on body weight and glucose tolerance in obesity is unknown. This study aimed to investigate the impact of chronic isoleucine on body weight gain and glucose tolerance in lean and high-fat-diet (HFD) induced-obese mice. Male C57BL/6-mice, fed a standard-laboratory-diet (SLD) or HFD for 12 weeks, were randomly allocated to: (1) Control: Drinking water; (2) Acute: Drinking water with a gavage of isoleucine (300 mg/kg) prior to the oral-glucose-tolerance-test (OGTT) or gastric-emptying-breath-test (GEBT); (3) Chronic: Drinking water with 1.5% isoleucine, for a further six weeks. At 16 weeks, an OGTT and GEBT was performed and at 17 weeks metabolic monitoring. In SLD- and HFD-mice, there was no difference in body weight, fat mass, and plasma lipid profiles between isoleucine treatment groups. Acute-isoleucine did not improve glucose tolerance in SLD- or HFD-mice. Chronic-isoleucine impaired glucose tolerance in SLD-mice. There was no difference in gastric emptying between any groups. Chronic-isoleucine did not alter energy intake, energy expenditure, or respiratory quotient in SLD- or HFD-mice. In conclusion, chronic isoleucine supplementation may not be an effective treatment for obesity or glucose intolerance.

The Effects of BCAAs on Insulin Resistance in Athletes

The toxic catabolic intermediates of branched chain amino acids can cause insulin resistance, and are involved in different mechanisms in different metabolic tissues. In skeletal muscle, 3-hydroxy-isobutyrate produced by valine promotes skeletal muscle fatty acid uptake, resulting in the accumulation of incompletely oxidized lipids in skeletal muscle, causing skeletal muscle insulin resistance. In the liver, branched-chain α-keto acids decompose in large amounts, promote hepatic gluconeogenesis, and lead to the accumulation of multiple acylcarnitines, which damages the mitochondrial tricarboxylic acid cycle, resulting in the accumulation of incomplete oxidation products, oxidative stress in mitochondria, and hepatic insulin resistance. In adipose tissue, the expression of branched-chain amino acid catabolic enzymes (branched-chain amino acid transaminase, branched-chain α-keto acid dehydrogenase) is reduced, resulting in an increased level of plasma branched-chain amino acids, thereby causing massive decomposition of branched-chain amino acids in tissues such as skeletal muscle and liver, and inducing insulin resistance. However, branched-chain amino acids, as a common nutritional supplement for athletes, do not induce insulin resistance. A possible explanation for this phenomenon is that exercise can enhance the mitochondrial oxidative potential of branched-chain amino acids, alleviate or even eliminate the accumulation of branched-chain amino acid catabolic intermediates, and promotes branched-chain amino acids catabolism into beta-aminoisobutyric acid, increasing plasma beta-aminoisobutyric acid concentration, improving insulin resistance. This article reveals the mechanism of BCAA-induced insulin resistance and the relationship between exercise and BCAAs metabolism, adds a guarantee for the use of BCAAs, and provides a new explanation for the occurrence of diabetes and how exercise improves diabetes.

Combined systems pharmacology and fecal metabonomics to study the biomarkers and therapeutic mechanism of type 2 diabetic nephropathy treated with Astragalus and Leech

In our study, systems pharmacology was used to predict the molecular targets of Astragalus and Leech, and explore the therapeutic mechanism of type 2 diabetic nephropathy (T2DN) treated with Astragalus and Leech. Simultaneously, to reveal the systemic metabolic changes and biomarkers associated with T2DN, we performed 1H NMR-based metabonomics and multivariate analysis to analyze fecal samples obtained from model T2DN rats. In addition, ELISA kits and histopathological studies were used to examine biochemical parameters and kidney tissue, respectively. Striking differences in the Pearson's correlation of 22 biomarkers and 9 biochemical parameters were also observed among control, T2DN and treated rats. Results of systems pharmacology analysis revealed that 9 active compounds (3,9-di-O-methylnissolin; (6aR,11aR)-9,10-dimethoxy-6a,11a-dihydro-6H-benzofurano[3,2-c]chromen-3-ol; hirudin; l-isoleucine; phenylalanine; valine; hirudinoidine A-C) and 9 target proteins (l-serine dehydratase; 3-hydroxyacyl-CoA dehydrogenase; tyrosyl-tRNA synthetase; tryptophanyl-tRNA synthetase; branched-chain amino acid aminotransferase; acetyl-CoA C-acetyltransferase; isovaleryl-CoA dehydrogenase; pyruvate dehydrogenase E1 component alpha subunit; hydroxyacylglutathione hydrolase) of Astragalus and Leech were closely associated with the treatment of T2DN. Using fecal metabonomics analysis, 22 biomarkers were eventually found to be closely associated with the occurrence of T2DN. Combined with systems pharmacology and fecal metabonomics, these biomarkers were found to be mainly associated with 6 pathways, involving amino acid metabolism (leucine, valine, isoleucine, alanine, lysine, glutamate, taurine, phenylalanine, tryptophan); energy metabolism (lactate, succinate, creatinine, α-glucose, glycerol); ketone body and fatty acid metabolism (3-hydroxybutyrate, acetate, n-butyrate, propionate); methylamine metabolism (dimethylamine, trimethylamine); and secondary bile acid metabolism and urea cycle (deoxycholate, citrulline). The underlying mechanisms of action included protection of the liver and kidney, enhancement of insulin sensitivity and antioxidant activity, and improvement of mitochondrial function. To the best of our knowledge, this is the first time that systems pharmacology combined with fecal metabonomics has been used to study T2DN. 6 metabolites (n-butyrate, deoxycholate, propionate, tryptophan, taurine and glycerol) associated with T2DN were newly discovered in fecal samples. These 6 metabolites were mainly derived from the intestinal flora, and related to amino acid metabolism, fatty acid metabolism, and secondary bile acid metabolism. We hope the results of this study could be inspirational and helpful for further exploration of T2DN treatment. Meanwhile, our results highlighted that exploring the biomarkers of T2DN and therapeutic mechanisms of Traditional Chinese Medicine (TCM) formulas on T2DN by combining systems pharmacology and fecal metabonomics methods was a promising strategy.

BCAA Metabolism and Insulin Sensitivity - Dysregulated by Metabolic Status?

Branched-chain amino acids (BCAAs) appear to influence several synthetic and catabolic cellular signaling cascades leading to altered phenotypes in mammals. BCAAs are most notably known to increase protein synthesis through modulating protein translation, explaining their appeal to resistance and endurance athletes for muscle hypertrophy, expedited recovery, and preservation of lean body mass. In addition to anabolic effects, BCAAs may increase mitochondrial content in skeletal muscle and adipocytes, possibly enhancing oxidative capacity. However, elevated circulating BCAA levels have been correlated with severity of insulin resistance. It is hypothesized that elevated circulating BCAAs observed in insulin resistance may result from dysregulated BCAA degradation. This review summarizes original reports that investigated the ability of BCAAs to alter glucose uptake in consequential cell types and experimental models. The review also discusses the interplay of BCAAs with other metabolic factors, and the role of excess lipid (and possibly energy excess) in the dysregulation of BCAA catabolism. Lastly, this article provides a working hypothesis of the mechanism(s) by which lipids may contribute to altered BCAA catabolism, which often accompanies metabolic disease.

Branched-chain amino acids in liver diseases

Branched chain amino acids (BCAAs) are involved in various bioprocess such as protein metabolism, gene expression, insulin resistance and proliferation of hepatocytes. BCAAs have also been reported to suppress the growth of hepatocellular carcinoma (HCC) cells in vitro and to be required for immune cells to perform the function. In advanced cirrhotic patients, it has been clarified that serum concentrations of BCAA are decreased, whereas those of aromatic amino acids (AAAs) are increased. These alterations are thought to be the causes of hepatic encephalopathy (HE), sarcopenia and hepatocarcinogenesis and may be associated with the poor prognosis of patients with these conditions. Administration of BCAA-rich medicines has shown positive results in patients with cirrhosis.

An Amino Acids Mixture Attenuates Glycemic Impairment but not Affects Adiposity Development in Rats Fed with AGEs-containing Diet

Background: Unhealthy western dietary patterns lead to over-consumption of fat and advanced glycation end-products (AGEs), and these account for the developments of obesity, diabetes, and related metabolic disorders. Certain amino acids (AAs) have been recently demonstrated to improve glycemia and reduce adiposity. Therefore, our primary aims were to examine whether feeding an isoleucine-enriched AA mixture (4.5% AAs; Ile: 3.0%, Leu: 1.0%, Val: 0.2%, Arg: 0.3% in the drinking water) would affect adiposity development and prevent the impairments of glycemic control in rats fed with the fat/AGE-containing diet (FAD). Methods: Twenty-four male Sprague-Dawley rats were assigned into 1) control diet (CD, N = 8), 2) FAD diet (FAD, N = 8), and 3) FAD diet plus AA (FAD/AA, N = 8). After 9-weeks intervention, the glycemic control capacity (glucose level, ITT, and HbA1c levels), body composition, and spontaneous locomotor activity (SLA) were evaluated, and the fasting blood samples were collected for analyzing metabolic related hormones (insulin, leptin, adiponectin, and corticosterone). The adipose tissues were also surgically collected and weighed. Results: FAD rats showed significant increases in weight gain, body fat %, blood glucose, HbA1c, leptin, and area under the curve of glucose during insulin tolerance test (ITT-glucose-AUC) in compared with the CD rats. However, the fasting levels of blood glucose, HbA1c, leptin, and ITT-glucose-AUC did not differ between CD and FAD/AA rats. FAD/AA rats also showed a greater increase in serum testosterone. Conclusion: The amino acid mixture consisting of Ile, Leu, Val, and Arg showed clear protective benefits on preventing the FAD-induced obesity and impaired glycemic control.

Association of Polymorphisms in STRA6 and RARRES2 Genes with Type 2 Diabetes in Southern Han Chinese

Stimulated by retinoic acid gene homolog 6 (STRA6) and retinoic acid receptor responder 2 (RARRES2) are candidate genes involved in the pathogenesis of type 2 diabetes mellitus (T2DM). Three tag-SNPs in STRA6 and one in RARRES2 gene were selected and genotyped with TaqMan or PCR-RFLP method in 603 populations (571 patients with T2D versus 632 control subjects) in Southern Han Chinese. We estimated the interactions between T2DM risk and genetic variants in the STRA6 and RARRES2 genes using polymerase chain reaction. Rs736118 in STRA6 gene were significantly associated with T2DM occurrence in the recessive genetic model. The genotype of rs974456 was significantly associated with T2DM in the dominant genetic model correlated to sex, MBI, and triglyceride. However, the association of other SNPs with T2DM was not found. Furthermore, smoking history and other factors may be independent risk factors for the incidence of T2DM. This study suggested that a role of STRA6 polymorphism could also be of value in predicting the risk of T2DM while RARRES2 polymorphism could not predict the risk of T2DM.

The Ratio of Dietary Branched-Chain Amino Acids is Associated with a Lower Prevalence of Obesity in Young Northern Chinese Adults: An Internet-Based Cross-Sectional Study

This study aims to examine the association between the ratio of dietary branched chain amino acids (BCAA) and risk of obesity among young northern Chinese adults. A total of 948 randomly recruited participants were asked to finish our internet-based dietary questionnaire for the Chinese (IDQC). Associations between dietary BCAA ratio and prevalence of overweight/obesity and abdominal obesity were analyzed. Furthermore, 90 subjects were randomly selected to explore the possible mechanism. Dietary BCAA ratio in obese participants was significantly lower than non-obese participants. We found negative correlations between the ratio of dietary BCAA and body mass index (BMI) (r = −0.197, p < 0.001) or waist circumference (r = −0.187, p < 0.001). Compared with those in the first quartile, the multivariable-adjusted OR (95% CI) of the 3rd and 4th quartiles of dietary BCAA ratio for overweight/obesity were 0.508 (0.265–0.972) and 0.389 (0.193–0.783), respectively (all p < 0.05). After stratification by gender, the significance still existed in the 3rd and 4th quartile in males and the 4th quartile in females. For abdominal obesity, the multivariable-adjusted OR (95% CI) of the 3rd and 4th quartile of dietary BCAA ratio were 0.351 (0.145–0.845) and 0.376 (0.161–0.876), respectively (all p < 0.05). This significance was stronger in males. Further studies indicated that dietary BCAA ratio was inversely associated with 2-h postprandial glucose (2 h-PG) and status of inflammation. In conclusion, a higher ratio of dietary BCAA is inversely associated with prevalence of obesity, postprandial glucose and status of inflammation in young northern Chinese adults.

Tyrosine levels are associated with insulin resistance in patients with nonalcoholic fatty liver disease

OBJECTIVE

Amino acid imbalance is often found in patients with cirrhosis, and this imbalance is associated with insulin resistance. However, the mechanism underlying the relationship between amino acid imbalance and insulin resistance remains unclear. We evaluated serum amino acid concentrations in patients with nonalcoholic fatty liver disease to determine if any of the levels of amino acids were associated with the biochemical markers and fibrosis stage of nonalcoholic steatohepatitis (NASH).

METHODS

In 137 patients with nonalcoholic fatty liver disease who underwent liver biopsy, plasma levels of branched-chain amino acid (BCAA), tyrosine (Tyr), and the BCAA-to-Tyr ratio values were determined using mass spectroscopy. These values were then assessed for associations with fibrosis stage, anthropometric markers (age, sex, and body mass index), biochemical markers (alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transpeptidase, albumin, platelet count, total cholesterol, triglycerides, low-density lipoprotein cholesterol, and glycosylated hemoglobin), and relevant disease-specific biomarkers (homeostasis model assessment of insulin resistance [HOMA-IR], serum iron, ferritin, leptin, adiponectin, high-sensitivity C-reactive protein, and hyaluronic acid).

RESULTS

Serum albumin levels, plasma BCAA levels, and BCAA-to-Tyr ratio values were negatively associated with the fibrosis stage. In contrast, Tyr levels increased with increasing fibrotic staging. Tyr levels were also correlated with HOMA-IR results.

CONCLUSION

Plasma BCAA levels in patients with NASH decreased with increasing liver fibrosis, while Tyr levels increased with increasing fibrotic stage. These results suggest that amino acid imbalance and insulin resistance are intimately involved in a complex pathogenic mechanism for NASH.

Effects of acute exposure to increased plasma branched-chain amino acid concentrations on insulin-mediated plasma glucose turnover in healthy young subjects

BACKGROUND

Plasma branched-chain amino acids (BCAA) are inversely related to insulin sensitivity of glucose metabolism in humans. However, currently, it is not known whether there is a cause-and-effect relationship between increased plasma BCAA concentrations and decreased insulin sensitivity.

OBJECTIVE

To determine the effects of acute exposure to increased plasma BCAA concentrations on insulin-mediated plasma glucose turnover in humans.

METHODS

Ten healthy subjects were randomly assigned to an experiment where insulin was infused at 40 mU/m2/min (40U) during the second half of a 6-hour intravenous infusion of a BCAA mixture (i.e., BCAA; N = 5) to stimulate plasma glucose turnover or under the same conditions without BCAA infusion (Control; N = 5). In a separate experiment, seven healthy subjects were randomly assigned to receive insulin infusion at 80 mU/m2/min (80U) in association with the above BCAA infusion (N = 4) or under the same conditions without BCAA infusion (N = 3). Plasma glucose turnover was measured prior to and during insulin infusion.

RESULTS

Insulin infusion completely suppressed the endogenous glucose production (EGP) across all groups. The percent suppression of EGP was not different between Control and BCAA in either the 40U or 80U experiments (P > 0.05). Insulin infusion stimulated whole-body glucose disposal rate (GDR) across all groups. However, the increase (%) in GDR was not different [median (1st quartile - 3rd quartile)] between Control and BCAA in either the 40U ([199 (167-278) vs. 186 (94-308)] or 80 U ([491 (414-548) vs. 478 (409-857)] experiments (P > 0.05). Likewise, insulin stimulated the glucose metabolic clearance in all experiments (P < 0.05) with no differences between Control and BCAA in either of the experiments (P > 0.05).

CONCLUSION

Short-term exposure of young healthy subjects to increased plasma BCAA concentrations does not alter the insulin sensitivity of glucose metabolism.

Branched-chain amino acids supplementation protects streptozotocin-induced insulin secretion and the correlated mechanism

Significant evidence demonstrates that oxidative stress can impair insulin secretion and contribute to the development of type 2 diabetes. Branched-chain amino acids (BCAAs) are reported to be positively related to insulin secretion. This study aimed to determine how oxidative stress affects the function of islets and whether BCAAs can ameliorate the oxidative stress, and accompanying c-jun N-terminal kinase (JNK), protein kinase D1 (PKD1), and pancreatic/duodenal homeobox-1 (PDX-1) changes induced by streptozotocin (STZ). Plasma glucose, plasma insulin, and JNK, PKD1 and PDX-1 mRNA and protein expression were measured in rats treated with STZ and BCAAs. The glucose level in STZ-induced diabetic rats was much higher than that in control animals, and the elevated plasma glucose level in diabetic rats could be significantly inhibited by BCAAs treatment. Consistent with the change in glucose levels, the levels of insulin were also affected by BCAAs treatment. The mRNA and protein expression of JNK, PDX-1, and PKD1 were significantly altered in diabetic rats compared with the control group (P<0.01) and treatment with a low dose of BCAA reversed these changes in those above markers significantly (P<0.01). The present study demonstrated that STZ-induced oxidative stress could reduce serum insulin levels and alter the JNK, PDX-1, and PKD1 expression. BCAAs restored the levels of serum insulin reversed changes in JNK, PDX-1, and PKD1 expression.

The effect of an amino acid beverage on glucose response and glycogen replenishment after strenuous exercise

PURPOSE

We previously reported that an amino acid mixture (AA) was able to lower the glucose response to an oral glucose challenge in both rats and humans. Increased glucose uptake and glycogen storage in muscle might be associated with the faster blood glucose clearance. We therefore tested the effect of two different doses of AA provided with a carbohydrate supplement on blood glucose homeostasis and muscle glycogen replenishment in human subjects after strenuous aerobic exercise.

METHODS

Ten subjects received a carbohydrate (1.2 g/kg body weight, CHO), CHO/HAA (CHO + 13 g AA), or CHO/LAA (CHO + 6.5 g AA) supplement immediately and 2 h after an intense cycling bout. Muscle biopsies were performed immediately and 4 h after exercise.

RESULTS

The glucose responses for CHO/HAA and CHO/LAA during recovery were significantly lower than CHO, as was the glucose area under the curve (CHO/HAA 1259.9 ± 27.7, CHO/LAA 1251.5 ± 47.7, CHO 1376.8 ± 52.9 mmol/L 4 h, p < 0.05). Glycogen storage rate was significantly lower in CHO/HAA compared with CHO, while it did not differ significantly between CHO/LAA or CHO (CHO/HAA 15.4 ± 2.0, CHO/LAA 18.1 ± 2.0, CHO 21.5 ± 1.4 µmol/g wet muscle 4 h). CHO/HAA caused a significantly higher insulin response and a greater effect on mTOR and Akt/PKB phosphorylation compared with CHO. Phosphorylation of AS160 and glycogen synthase did not differ across treatments. Likewise, there were no differences in blood lactate across treatments.

CONCLUSIONS

The AA lowered the glucose response to a carbohydrate supplement after strenuous exercise. However, it was not effective in facilitating subsequent muscle glycogen storage.

Effects of branched-chain amino acids and zinc-enriched nutrients on prognosticators in HCV-infected patients: a multicenter randomized controlled trial

Branched‑chain amino acids (BCAAs) and trace element deficiencies are associated with poor prognosis in hepatitis C virus (HCV)‑infected patients. The aim of this study was to investigate the effects of BCAA and zinc‑enriched supplementation on prognostic factors in HCV‑infected patients. Fifty‑three HCV‑infected patients were enrolled in this multicenter randomized controlled trial. The patients were assigned to either the placebo (n=27) or supplement group (n=26; 6,400 mg/day BCAAs and 10 mg/day zinc) and were followed up for 60 days. Primary outcomes were prognostic factors for chronic liver disease, including the serum BCAA‑to‑tyrosine ratio (BTR), zinc levels and α‑fetoprotein (AFP) levels. There were no significant differences in any of the prognostic factors between the placebo and supplement groups at baseline. In the supplement group, the BTR and zinc levels were significantly increased compared with the placebo group (BTR: 5.14 ± 1.59 vs. 4.23 ± 1.14, P=0.0290; zinc: 76 ± 11 vs. 68 ± 11 µg/dl, P=0.0497). No significant differences were observed in AFP levels between the groups in the whole analysis. However, a stratification analysis showed a significant reduction in ΔAFP levels in the supplement group, with elevated AFP levels compared with the other groups (‑2.72 ± 3.45 ng/ml, P=0.0079). It was demonstrated that BCAA and zinc‑enriched supplementation increased the BTR and zinc levels in the HCV‑infected patients. Furthermore, the supplementation reduced the serum AFP levels in patients who had elevated serum AFP levels at baseline. Thus, BCAA and zinc‑enriched supplementation may prolong the survival of HCV‑infected patients by improving amino acid imbalance and zinc deficiency, and by partly downregulating AFP.

4-Hydroxyisoleucine ameliorates fatty acid-induced insulin resistance and inflammatory response in skeletal muscle cells

The 4-hydroxyisoleucine (4-HIL), an unusual amino acid isolated from the seeds of Trigonella foenum-graecum was investigated for its metabolic effects to ameliorate free fatty acid-induced insulin resistance in skeletal muscle cells. An incubation of L6 myotubes with palmitate inhibited insulin stimulated-glucose uptake and -translocation of glucose transporter 4 (GLUT4) to the cell surface. Addition of 4-HIL strongly prevented this inhibition. We then examined the insulin signaling pathway, where 4-HIL effectively inhibited the ability of palmitate to reduce insulin-stimulated phosphorylation of insulin receptor substrate-1 (IRS-1), protein kinase B (PKB/AKT), AKT substrate of 160 kD (AS160) and glycogen synthase kinase 3β (GSK-3β) in L6 myotubes. Moreover, 4-HIL presented strong inhibition on palmitate-induced production of reactive oxygen species (ROS) and associated inflammation, as the activation of NF-κB, JNK1/2, ERK1/2 and p38 MAPK was greatly reduced. 4-HIL also inhibited inflammation-stimulated IRS-1 serine phosphorylation and restored insulin-stimulated IRS-1 tyrosine phosphorylation in the presence of palmitate, leading to enhanced insulin sensitivity. These findings suggested that 4-HIL could inhibit palmitate-induced, ROS-associated inflammation and restored insulin sensitivity through regulating IRS-1 function.

Effects of individual branched-chain amino acids deprivation on insulin sensitivity and glucose metabolism in mice

OBJECTIVE

We recently discovered that leucine deprivation increases hepatic insulin sensitivity via general control nondepressible (GCN) 2/mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) pathways. The goal of the present study was to investigate whether the above effects were leucine specific or were also induced by deficiency of other branched chain amino acids including valine and isoleucine.

METHODS

Following depletion of BCAAs, changes in metabolic parameters and the expression of genes and proteins involved in regulation of insulin sensitivity and glucose metabolism were analyzed in mice and cell lines including human HepG2 cells, primary mouse hepatocytes and a mouse myoblast cell line C2C12.

RESULTS

Valine or isoleucine deprivation for 7 days has similar effect on improving insulin sensitivity as leucine, in wild type and insulin-resistant mice models. These effects are possibly mediated by decreased mTOR/S6K1 and increased AMPK signaling pathways, in a GCN2-dependent manner. Similar observations were obtained in in vitro studies. In contrast to leucine withdrawal, valine or isoleucine deprivation for 7 days significantly decreased fed blood glucose levels, possibly due to reduced expression of a key gluconeogenesis gene, glucose-6-phosphatase. Finally, insulin sensitivity was rapidly improved in mice 1 day following maintenance on a diet deficient for any individual BCAAs.

CONCLUSIONS

Our results show that while improvement on insulin sensitivity is a general feature of BCAAs depletion, individual BCAAs have specific effects on metabolic pathways, including those that regulate glucose level. These observations provide a conceptual framework for delineating the molecular mechanisms that underlie amino acid regulation of insulin sensitivity.

Pharmaceutical and nutraceutical approaches for preventing liver carcinogenesis: chemoprevention of hepatocellular carcinoma using acyclic retinoid and branched-chain amino acids

The poor prognosis for patients with hepatocellular carcinoma (HCC) is associated with its high rate of recurrence in the cirrhotic liver. Therefore, more effective strategies need to be urgently developed for the chemoprevention of this malignancy. The malfunction of retinoid X receptor α, a retinoid receptor, due to phosphorylation by Ras/mitogen-activated protein kinase is closely associated with liver carcinogenesis and may be a promising target for HCC chemoprevention. Acyclic retinoid (ACR), a synthetic retinoid, can prevent HCC development by inhibiting retinoid X receptor α phosphorylation and improve the prognosis for this malignancy. Supplementation with branched-chain amino acids (BCAA), which are used to improve protein malnutrition in patients with liver cirrhosis, can also reduce the risk of HCC in obese cirrhotic patients. In experimental studies, both ACR and BCAA exert suppressive effects on HCC development and the growth of HCC cells. In particular, combined treatment with ACR and BCAA cooperatively inhibits the growth of HCC cells. Furthermore, ACR and BCAA inhibit liver tumorigenesis associated with obesity and diabetes, both of which are critical risk factors for HCC development. These findings suggest that pharmaceutical and nutraceutical approaches using ACR and BCAA may be promising strategies for preventing HCC and improving the prognosis of this malignancy.

Branched-chain amino acids in liver diseases

Branched chain amino acids (BCAAs) have been shown to affect gene expression, protein metabolism, apoptosis and regeneration of hepatocytes, and insulin resistance. They have also been shown to inhibit the proliferation of liver cancer cells in vitro, and are essential for lymphocyte proliferation and dendritic cell maturation. In patients with advanced chronic liver disease, BCAA concentrations are low, whereas the concentrations of aromatic amino acids such as phenylalanine and tyrosine are high, conditions that may be closely associated with hepatic encephalopathy and the prognosis of these patients. Based on these basic observations, patients with advanced chronic liver disease have been treated clinically with BCAA-rich medicines, with positive effects.

Branched-chain amino acid supplementation: impact on signaling and relevance to critical illness

The changes that occur in mammalian systems following trauma and sepsis, termed systemic inflammatory response syndrome, elicit major changes in carbohydrate, protein, and energy metabolism. When these events persist for too long they result in a severe depletion of lean body mass, multiple organ dysfunction, and eventually death. Nutritional supplementation has been investigated to offset the severe loss of protein, and recent evidence suggests that diets enriched in branched-chain amino acids (BCAAs) may be especially beneficial. BCAAs are metabolized in two major steps that are differentially expressed in muscle and liver. In muscle, BCAAs are reversibly transaminated to the corresponding α-keto acids. For the complete degradation of BCAAs, the α-keto acids must travel to the liver to undergo oxidation. The liver, in contrast to muscle, does not significantly express the branched-chain aminotransferase. Thus, BCAA degradation is under the joint control of both liver and muscle. Recent evidence suggests that in liver, BCAAs may perform signaling functions, more specifically via activation of mTOR (mammalian target of rapamycin) signaling pathway, influencing a wide variety of metabolic and synthetic functions, including protein translation, insulin signaling, and oxidative stress following severe injury and infection. However, understanding of the system-wide effects of BCAAs that integrate both metabolic and signaling aspects is currently lacking. Further investigation in this respect will help rationalize the design and optimization of nutritional supplements containing BCAAs for critically ill patients.

Satiety hormone and metabolomic response to an intermittent high energy diet differs in rats consuming long-term diets high in protein or prebiotic fiber

Large differences in the composition of diet between early development and adulthood can have detrimental effects on obesity risk. We examined the effects of an intermittent high fat/sucrose diet (HFS) on satiety hormone and serum metabolite response in disparate diets. Wistar rat pups were fed control (C), high prebiotic fiber (HF) or high protein (HP) diets (weaning to 16 weeks), HFS diet challenged (6 weeks), and finally reverted to their respective C, HF, or HP diet (4 weeks). At conclusion, measurement of body composition and satiety hormones was accompanied by ¹H NMR metabolic profiles in fasted and postprandial states. Metabolomic profiling predicted dietary source with >90% accuracy. The HF group was characterized by lowest body weight and body fat (P < 0.05) and increased satiety hormone levels (glucagon-like peptide 1 and peptide-YY). Regularized modeling confirmed that the HF diet is associated with higher gut hormone secretion that could reflect the known effects of prebiotics on gut microbiota and their fementative end products, the short chain fatty acids. Rats reared on a HF diet appear to experience fewer adverse effects from an intermittent high fat diet in adulthood when rematched to their postnatal diet. Metabolite profiles associated with the diets provide a distinct biochemical signature of their effects.

The effect of a low-carbohydrate/high-monounsaturated fatty acid liquid diet and an isoleucine-containing liquid diet on 24-h glycemic variability in diabetes patients on tube feeding: a comparison by continuous glucose monitoring

OBJECTIVE

This study compare the effect of various liquid diets on 24-h glycemic variability in diabetes patients on tube feeding.

PATIENTS AND METHODS

The study included type 2 diabetes patients in whom percutaneous endoscopic gastrostomy had been performed for dysphagia as a sequela of cerebrovascular disease and who had been put on tube feeding with a standard high-carbohydrate liquid diet (HCD). Once stable glycemic control was achieved, these patients were continuously monitored for glucose levels for 5 days on continuous glucose monitoring. Of the 14 patients included, seven were given HCD on day 1, a low-carbohydrate/high-monounsaturated fatty acid liquid diet (LCD) on Days 2 and 3, and a isoleucine-containing liquid diet (ICD), which is known to promote glycemic uptake by skeletal muscle, thus suppressing increases in glucose levels, on Days 4 and 5, with the remaining seven given the same diets but ICD given on Days 2 and 3 and LCD given on Days 4 and 5. All comparisons were made under the same caloric conditions (caloric intake, 800-1200 kcal/day).

RESULTS

The 24-h mean glucose level was significantly lower with LCD and ICD than with HCD but was also significantly lower with LCD than with ICD. On the other hand, the SD of 288 glucose levels over a 24-h period, 24-h total area for glycemic fluctuations, and mean amplitude of glycemic excursion were significantly lower with LCD than with HCD or ICD, whereas they did not differ significantly between HCD and ICD.

CONCLUSIONS

LCD and ICD led to significant decreases in mean glucose levels, compared with HCD. However, of the diets compared, LCD had the greatest effect on glycemic variability in these patients on tube feeding.

Nutraceutical approach for preventing obesity-related colorectal and liver carcinogenesis

Obesity and its related metabolic abnormalities, including insulin resistance, alterations in the insulin-like growth factor-1 (IGF-1)/IGF-1 receptor (IGF-1R) axis, and the state of chronic inflammation, increase the risk of colorectal cancer (CRC) and hepatocellular carcinoma (HCC). However, these findings also indicate that the metabolic disorders caused by obesity might be effective targets to prevent the development of CRC and HCC in obese individuals. Green tea catechins (GTCs) possess anticancer and chemopreventive properties against cancer in various organs, including the colorectum and liver. GTCs have also been known to exert anti-obesity, antidiabetic, and anti-inflammatory effects, indicating that GTCs might be useful for the prevention of obesity-associated colorectal and liver carcinogenesis. Further, branched-chain amino acids (BCAA), which improve protein malnutrition and prevent progressive hepatic failure in patients with chronic liver diseases, might be also effective for the suppression of obesity-related carcinogenesis because oral supplementation with BCAA reduces the risk of HCC in obese cirrhotic patients. BCAA shows these beneficial effects because they can improve insulin resistance. Here, we review the detailed relationship between metabolic abnormalities and the development of CRC and HCC. We also review evidence, especially that based on our basic and clinical research using GTCs and BCAA, which indicates that targeting metabolic abnormalities by either pharmaceutical or nutritional intervention may be an effective strategy to prevent the development of CRC and HCC in obese individuals.

Branched-chain amino acids as pharmacological nutrients in chronic liver disease

Branched-chain amino acids (BCAAs) are a group of essential amino acids comprising valine, leucine, and isoleucine. A low ratio of plasma BCAAs to aromatic amino acids is a physiological hallmark of liver cirrhosis, and BCAA supplementation was originally devised with the intention of normalizing amino acid profiles and nutritional status. However, recent studies on BCAAs have revealed that, in addition to their role as protein constituents, they may have a role as pharmacological nutrients for patients with chronic liver disease. Large-scale, multicenter, randomized, double-blinded, controlled trials on BCAA supplementation have been performed in Italy and Japan, and results demonstrate that BCAA supplementation improves not only nutritional status, but also prognosis and quality of life in patients with liver cirrhosis. Moreover, accumulating experimental evidence suggests that the favorable effects of BCAA supplementation on prognosis may be supported by unforeseen pharmacological actions of BCAAs. This review summarizes the possible effects of BCAAs on albumin synthesis and insulin resistance from clinical and basic viewpoints. We also review the newly discovered clinical impact of BCAAs on hepatocellular carcinoma and the prognosis and quality of life of patients with liver cirrhosis.

Potential role of branched-chain amino acids in glucose metabolism through the accelerated induction of the glucose-sensing apparatus in the liver

Branched-chain amino acids (BCAAs) have a potential to improve glucose metabolism in cirrhotic patients; however, the contribution of liver in this process has not been clarified. To estimate the effect of BCAA on glucose metabolism in liver, we evaluated the mRNA expression levels of glucose-sensing apparatus genes in HepG2 cells and in rat liver after oral administration of BCAA. HepG2 cells were cultured in low glucose (100 mg/dl) or high glucose (400 mg/dl) in the absence or presence of BCAA. The mRNA expression levels and protein levels of GLUT2 and liver-type glucokinase (L-GK) were estimated using RT-PCR and immunoblotting. The expression levels of transcriptional factors, including SREBP-1c, ChREBP, PPAR-γm and LXRα, were estimated. The mRNA expression levels of transcriptional factors, glycogen synthase, and genes involved in gluconeogenesis were evaluated in rat liver at 3 h after the administration of BCAA. BCAA accelerated the expression of GLUT2 and L-GK in HepG2 cells in high glucose. Expression levels of ChREBP, SREBP-1c, and LXRα were also increased in this condition. BCAA administration enhanced the mRNA expression levels of L-GK, SREBP-1c, and LXRα and suppressed the expression levels of G-6-Pase in rat liver, without affecting the expression levels of glycogen synthase or serum glucose concentrations. BCAA administration enhanced the bioactivity of the glucose-sensing apparatus, probably via the activation of a transcriptional mechanism, suggesting that these amino acids may improve glucose metabolism through the accelerated utility of glucose and glucose-6-phosphate in the liver.

Impact of chromium histidinate on high fat diet induced obesity in rats

Background

Chromium (Cr) is an essential trace element that has garnered interest for use as a weight loss aid, but its molecular mechanism in obesity is not clear. In this study, an attempt has been made to investigate the effects of chromium histidinate (CrHis) on glucose transporter-2 (GLUT-2), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), nuclear factor-kappa B (NF-κB p65) and the oxidative stress marker 4-hydroxynonenal adducts (HNE) expressions in liver of rats fed high fat diet (HFD).

Methods

Male Wistar rats (n = 40, 8 wk-old) were divided into four groups. Group I was fed a standard diet (12% of calories as fat); Group II was fed a standard diet and supplemented with 110 μg CrHis/kg BW/d; Group III was fed a HFD (40% of calories as fat); Group IV was fed HFD and supplemented with 110 μg CrHis/kg BW/d.

Results

Rats fed HFD possessed greater serum insulin (40 vs.33 pmol/L) and glucose (158 vs. 143 mg/dL) concentration and less liver Cr (44 vs.82 μg/g) concentration than rats fed the control diet. However, rats supplemented with CrHis had greater liver Cr and serum insulin and lower glucose concentration in rats fed HFD (P < 0.05). The hepatic nuclear factor-kappa B (NF-κB p65) and HNE were increased in high fat group compared to control group, but reduced by the CrHis administration (P < 0.05). The levels of hepatic Nrf2 and HO-1 were increased by supplementation of CrHis (P < 0.05).

Conclusion

These findings demonstrate that supplementation of CrHis is protective against obesity, at least in part, through Nrf2-mediated induction of HO-1 in rats fed high fat diet.

Isoleucine prevents the accumulation of tissue triglycerides and upregulates the expression of PPARalpha and uncoupling protein in diet-induced obese mice

In this study, we investigated the effects of the branched-chain amino acid l-isoleucine (Ile) on both obesity and glucose/fat homeostasis in mice that were fed a high-fat (45% energy) diet. The mice were divided into different treatment groups and given a high-fat diet for 6 wk. During the last 4 wk, Ile was dissolved and added to the drinking water to a final concentration of 2.5%. The control mice received vehicle alone. The mice in the Ile group had an almost 6% lower body weight gain and 49% less epididymal white adipose tissue (WAT) mass with the control group (P < 0.05). The hepatic and skeletal muscle triglyceride (TG) concentrations and degree of hyperinsulinemia in the Ile group mice were also lower than the control group by 38, 47, and 39%, respectively (P < 0.05). The WAT leptin concentration was also lower, whereas that of adiponectin was higher, in the Ile group compared with the control group (P < 0.05). The hepatic levels of protein CD36/fatty acid translocase, PPARalpha, and uncoupling protein (UCP) 2 and the levels of UCP3 in skeletal muscle were all greater in the Ile group than in the control mice (P < 0.05). These results demonstrate that the liver and muscle TG concentrations are both lowered by Ile treatment. In addition, the PPARalpha and UCP expression levels in the mouse tissues were greater in the Ile group compared with the controls. Our current data thus suggest that supplementation with Ile might be useful in the treatment of metabolic syndrome.

High-fat diet and hydrochlorothiazide increase oxidative stress in brain of rats

This study evaluated the effect of possible synergic interaction between high fat diet (HF) and hydrochlorothiazide (HCTZ) on biochemical parameters of oxidative stress in brain. Rats were fed for 16 weeks with a control diet or with an HF, both supplemented with different doses of HCTZ (0.4, 1.0, and 4.0 g kg(-1) of diet). HF associated with HCTZ caused a significant increase in lipid peroxidation and blood glucose levels. In addition, HF ingestion was associated with an increase in cerebral lipid peroxidation, vitamin C and non-protein thiol groups (NPSH) levels. There was an increase in vitamin C as well as NPSH levels in HCTZ (1.0 and 4.0 g kg(-1) of diet) and HF plus HCTZ groups. Na(+)-K(+)-ATPase activity of HCTZ (4.0 g kg(-1) of diet) and HCTZ plus HF-fed animals was significantly inhibited. Our data indicate that chronic intake of a high dose of HCTZ (4 g kg(-1) of diet) or HF change biochemical indexes of oxidative stress in rat brain. Furthermore, high-fat diets consumption and HCTZ treatment have interactive effects on brain, showing that a long-term intake of high-fat diets can aggravate the toxicity of HCTZ.