Histidine supplementation suppresses food intake and fat accumulation in rats

The Diverse Network of Brain Histamine in Feeding: Dissect its Functions in a Circuit-Specific Way

Feeding is an intrinsic and important behavior regulated by complex molecular, cellular and circuit-level mechanisms, one of which is the brain histaminergic network. In the past decades, many studies have provided a foundation of knowledge about the relationship between feeding and histamine receptors, which are deemed to have therapeutic potential but are not successful in treating feeding- related diseases. Indeed, the histaminergic circuits underlying feeding are poorly understood and characterized. This review describes current knowledge of histamine in feeding at the receptor level. Further, we provide insight into putative histamine-involved feeding circuits based on the classic feeding circuits. Understanding the histaminergic network in a circuit-specific way may be therapeutically relevant for increasing the drug specificity and precise treatment in feeding-related diseases.

Potential therapeutic implications of histidine catabolism by the gut microbiota in NAFLD patients with morbid obesity

The gut microbiota contributes to the pathophysiology of non-alcoholic fatty liver disease (NAFLD). Histidine is a key energy source for the microbiota, scavenging it from the host. Its role in NAFLD is poorly known. Plasma metabolomics, liver transcriptomics, and fecal metagenomics were performed in three human cohorts coupled with hepatocyte, rodent, and Drosophila models. Machine learning analyses identified plasma histidine as being strongly inversely associated with steatosis and linked to a hepatic transcriptomic signature involved in insulin signaling, inflammation, and trace amine-associated receptor 1. Circulating histidine was inversely associated with Proteobacteria and positively with bacteria lacking the histidine utilization (Hut) system. Histidine supplementation improved NAFLD in different animal models (diet-induced NAFLD in mouse and flies, ob/ob mouse, and ovariectomized rats) and reduced de novo lipogenesis. Fecal microbiota transplantation (FMT) from low-histidine donors and mono-colonization of germ-free flies with Enterobacter cloacae increased triglyceride accumulation and reduced histidine content. The interplay among microbiota, histidine catabolism, and NAFLD opens therapeutic opportunities.

Integrated Metabolomics, Transcriptome and Functional Analysis Reveal Key Genes Are Involved in Tree Age-Induced Amino Acid Accumulation in Torreya grandis Nuts

Torreya grandis is native Chinese tree species of economic significance, renowned for its long lifespan and the rich nutritional value of its nuts. In this study, we analyzed the morphological characteristics, metabolites, associated gene expressions, and regulatory mechanism in nuts from young (10 years old) and old (1000 years old) T. grandis trees. We observed that the length, width, and weight of nuts from older trees were considerably greater than those from younger trees. Metabolomic analysis revealed that the concentrations of 18 amino acids and derivatives (including histidine and serine) in nuts from older trees were markedly higher than those in nuts from younger trees. Transcriptome and metabolomic correlation analysis identified 16 genes, including TgPK (pyruvate kinase), TgGAPDH (glyceraldehyde 3-phosphate dehydrogenase), and others, which exhibit higher expression levels in older trees compared to younger trees, as confirmed by qRT-PCR. These genes are associated with the biosynthesis of histidine, glutamic acid, tryptophan, and serine. Transient expression of TgPK in tobacco led to increased pyruvate kinase activity and amino acid content (histidine, tryptophan, and serine). Additionally, dual-luciferase assays and yeast one-hybrid results demonstrated that TgWRKY21 positively regulates TgPK expression by directly binding to the TgPK promoter. These findings not only demonstrate the nutritional differences between nuts from young and old trees but also offer fresh insights into the development of nutritional sources and functional components based on nuts from old trees, enriching our understanding of the potential benefits of utilizing nuts from older trees.

Untargeted metabolomic analysis investigating links between unprocessed red meat intake and markers of inflammation

BACKGROUND

Whether red meat consumption is associated with higher inflammation or confounded by increased adiposity remains unclear. Plasma metabolites capture the effects of diet after food is processed, digested, and absorbed, and correlate with markers of inflammation, so they can help clarify diet-health relationships.

OBJECTIVE

To identify whether any metabolites associated with red meat intake are also associated with inflammation.

METHODS

A cross-sectional analysis of observational data from older adults (52.84% women, mean age 63 ± 0.3 y) participating in the Multi-Ethnic Study of Atherosclerosis (MESA). Dietary intake was assessed by food-frequency questionnaire, alongside C-reactive protein (CRP), interleukin-2, interleukin-6, fibrinogen, homocysteine, and tumor necrosis factor alpha, and untargeted proton nuclear magnetic resonance (1H NMR) metabolomic features. Associations between these variables were examined using linear regression models, adjusted for demographic factors, lifestyle behaviors, and body mass index (BMI).

RESULTS

In analyses that adjust for BMI, neither processed nor unprocessed forms of red meat were associated with any markers of inflammation (all P > 0.01). However, when adjusting for BMI, unprocessed red meat was inversely associated with spectral features representing the metabolite glutamine (sentinel hit: β = -0.09 ± 0.02, P = 2.0 × 10-5), an amino acid which was also inversely associated with CRP level (β = -0.11 ± 0.01, P = 3.3 × 10-10).

CONCLUSIONS

Our analyses were unable to support a relationship between either processed or unprocessed red meat and inflammation, over and above any confounding by BMI. Glutamine, a plasma correlate of lower unprocessed red meat intake, was associated with lower CRP levels. The differences in diet-inflammation associations, compared with diet metabolite-inflammation associations, warrant further investigation to understand the extent that these arise from the following: 1) a reduction in measurement error with metabolite measures; 2) the extent that which factors other than unprocessed red meat intake contribute to glutamine levels; and 3) the ability of plasma metabolites to capture individual differences in how food intake is metabolized.

Regulation of metabolic health by dietary histidine in mice

Low-protein (LP) diets are associated with a decreased risk of diabetes in humans, and promote leanness and glycaemic control in both rodents and humans. While the effects of an LP diet on glycaemic control are mediated by reduced levels of the branched-chain amino acids, we have observed that reducing dietary levels of the other six essential amino acids leads to changes in body composition. Here, we find that dietary histidine plays a key role in the response to an LP diet in male C57BL/6J mice. Specifically reducing dietary levels of histidine by 67% reduces the weight gain of young, lean male mice, reducing both adipose and lean mass without altering glucose metabolism, and rapidly reverses diet-induced obesity and hepatic steatosis in diet-induced obese male mice, increasing insulin sensitivity. This normalization of metabolic health was associated not with caloric restriction or increased activity, but with increased energy expenditure. Surprisingly, the effects of histidine restriction do not require the energy balance hormone Fgf21. Histidine restriction that was started in midlife promoted leanness and glucose tolerance in aged males but not females, but did not affect frailty or lifespan in either sex. Finally, we demonstrate that variation in dietary histidine levels helps to explain body mass index differences in humans. Overall, our findings demonstrate that dietary histidine is a key regulator of weight and body composition in male mice and in humans, and suggest that reducing dietary histidine may be a translatable option for the treatment of obesity. KEY POINTS: Protein restriction (PR) promotes metabolic health in rodents and humans and extends rodent lifespan. Restriction of specific individual essential amino acids can recapitulate the benefits of PR. Reduced histidine promotes leanness and increased energy expenditure in male mice. Reduced histidine does not extend the lifespan of mice when begun in midlife. Dietary levels of histidine are positively associated with body mass index in humans.

Lysine Deprivation Suppresses Adipogenesis in 3T3-L1 Cells: A Transcriptome Analysis

Growing evidence proves that amino acid restriction can reverse obesity by reducing adipose tissue mass. Amino acids are not only the building blocks of proteins but also serve as signaling molecules in multiple biological pathways. The study of adipocytes' response to amino acid level changes is crucial. It has been reported that a low concentration of lysine suppresses lipid accumulation and transcription of several adipogenic genes in 3T3-L1 preadipocytes. However, the detailed lysine-deprivation-induced cellular transcriptomic changes and the altered pathways have yet to be fully studied. Here, using 3T3-L1 cells, we performed RNA sequencing on undifferentiated and differentiated cells, and differentiated cells under a lysine-free environment, and the data were subjected to KEGG enrichment. We found that the differentiation process of 3T3-L1 cells to adipocytes required the large-scale upregulation of metabolic pathways, mainly on the mitochondrial TCA cycle, oxidative phosphorylation, and downregulation of the lysosomal pathway. Single amino acid lysine depletion suppressed differentiation dose dependently. It disrupted the metabolism of cellular amino acids, which could be partially reflected in the changes in amino acid levels in the culture medium. It inhibited the mitochondria respiratory chain and upregulated the lysosomal pathway, which are essential for adipocyte differentiation. We also noticed that cellular interleukin 6 (IL6) expression and medium IL6 level were dramatically increased, which was one of the targets for suppressing adipogenesis induced by lysine depletion. Moreover, we showed that the depletion of some essential amino acids such as methionine and cystine could induce similar phenomena. This suggests that individual amino acid deprivation may share some common pathways. This descriptive study dissects the pathways for adipogenesis and how the cellular transcriptome was altered under lysine depletion.

Nano-melatonin and-histidine modulate adipokines and neurotransmitters to improve cognition in HFD-fed rats: A formula to study

The established correlation between obesity and cognitive impairment portrays pharmacological products aimed at both disorders as an important therapeutic advance. Modulation of dysregulated adipokines and neurotransmitters is hence a critical aspect of the assessment of in-use drugs. At the cellular level, repairments in brain barrier integrity and cognitive flexibility are the main checkpoints. The aim of this study was to investigate whether melatonin and histidine, alone or in combination, could produce weight loss, meanwhile improve the cognitive processes. In this study, obese rat model was established by feeding high fat diet (HFD) composed of 25% fats (soybean oil) for 8 weeks, accompanied by melatonin (10 mg/kg), histidine (780 mg/kg), and combination of both in conventional form and nanoform. At the end of the study, adiposity hormones, neuronal monoamines and amino acids, brain derived neurotrophic factor (BDNF) and zonula occluden-1 (ZO-1) were assessed. HFD feeding resulted in significant weight gain and poor performance on cognitive test. Coadministration of histidine in the nanoform increased the level of ZO-1; an indicator of improving the brain barrier integrity, along with adjusting the adipokines and neurotransmitters levels, which had a positive impact on learning tasks. Cotreatment with melatonin resulted in an increase in the level of BDNF, marking ameliorated synaptic anomalies and learning disabilities, while reducing weight gain. On the other hand, the combination of melatonin and histidine reinstated the synaptic plasticity as well as brain barrier junctions, as demonstrated by increased levels of BDNF and ZO-1, positively affecting weight loss and the intellectual function.

Beneficial effects of fish and fish peptides on main metabolic syndrome associated risk factors: Diabetes, obesity and lipemia

The definition of metabolic syndrome (MetS) fairly varies from one to another guideline and health organization. Per description of world health organization, occurrence of hyperinsulinemia or hyperglycemia in addition to two or more factors of dyslipidemia, hypoalphalipoproteinemia, hypertension and or large waist circumference factors would be defined as MetS. Conventional therapies and drugs, commonly with adverse effects, are used to treat these conditions and diseases. Nonetheless, in the recent decades scientific community has focused on the discovery of natural compounds to diminish the side effects of these medications. Among many available bioactives, biologically active peptides have notable beneficial effects on the management of diabetes, obesity, hypercholesterolemia, and hypertension. Marine inclusive of fish peptides have exerted significant bioactivities in different experimental in-vitro, in-vivo and clinical settings. This review exclusively focuses on studies from the recent decade investigating hypoglycemic, hypolipidemic, hypercholesterolemic and anti-obesogenic fish and fish peptides. Related extraction, isolation, and purification methodologies of anti-MetS fish biopeptides are reviewed herein for comparison purposes only. Moreover, performance of biopeptides in simulated gastrointestinal environment and structure-activity relationship along with absorption, distribution, metabolism, and excretion properties of selected oligopeptides have been discussed, in brief, to broaden the knowledge of readers on the design and discovery trends of anti-MetS compounds.Supplemental data for this article is available online at https://doi.org/10.1080/10408398.2022.2052261 .

Impacts of essential amino acids on energy balance

Background

Obesity develops due to an imbalance in energy homeostasis, wherein energy intake exceeds energy expenditure. Accumulating evidence shows that manipulations of dietary protein and their component amino acids affect the energy balance, resulting in changes in fat mass and body weight. Amino acids are not only the building blocks of proteins but also serve as signals regulating multiple biological pathways.

Scope of review

We present the currently available evidence regarding the effects of dietary alterations of a single essential amino acid (EAA) on energy balance and relevant signaling mechanisms at both central and peripheral levels. We summarize the association between EAAs and obesity in humans and the clinical use of modifying the dietary EAA composition for therapeutic intervention in obesity. Finally, similar mechanisms underlying diets varying in protein levels and diets altered of a single EAA are described. The current review would expand our understanding of the contribution of protein and amino acids to energy balance control, thus helping discover novel therapeutic approaches for obesity and related diseases.

Major Conclusions

Changes in circulating EAA levels, particularly increased branched-chain amino acids (BCAAs), have been reported in obese human and animal models. Alterations in dietary EAA intake result in improvements in fat and weight loss in rodents, and each has its distinct mechanism. For example, leucine deprivation increases energy expenditure, reduces food intake and fat mass, primarily through regulation of the general control nonderepressible 2 (GCN2) and mammalian target of rapamycin (mTOR) signaling. Methionine restriction by 80% decreases fat mass and body weight while developing hyperphagia, primarily through fibroblast growth factor 21 (FGF-21) signaling. Some effects of diets with different protein levels on energy homeostasis are mediated by similar mechanisms. However, reports on the effects and underlying mechanisms of dietary EAA imbalances on human body weight are few, and more investigations are needed in future.

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Dietary Essential Amino Acids (EAA) alterations affect energy homeostasis via distinct mechanisms.

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Alterations in dietary EAA intake can reduce fat mass and body weight.

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Increased circulating BCAAs have been observed in obese human and animal models.

Therapeutic Potential of Various Plant-Based Fibers to Improve Energy Homeostasis via the Gut Microbiota

Obesity is due in part to increased consumption of a Western diet that is low in dietary fiber. Conversely, an increase in fiber supplementation to a diet can have various beneficial effects on metabolic homeostasis including weight loss and reduced adiposity. Fibers are extremely diverse in source and composition, such as high-amylose maize, β-glucan, wheat fiber, pectin, inulin-type fructans, and soluble corn fiber. Despite the heterogeneity of dietary fiber, most have been shown to play a role in alleviating obesity-related health issues, mainly by targeting and utilizing the properties of the gut microbiome. Reductions in body weight, adiposity, food intake, and markers of inflammation have all been reported with the consumption of various fibers, making them a promising treatment option for the obesity epidemic. This review will highlight the current findings on different plant-based fibers as a therapeutic dietary supplement to improve energy homeostasis via mechanisms of gut microbiota.

Histidine dose-response effects on lactational performance and plasma amino acid concentrations in lactating dairy cows: 1. Metabolizable protein-adequate diet

The objective of this experiment was to determine the effect of increasing digestible His (dHis) doses on milk production, milk composition, and plasma AA concentrations in lactating dairy cows fed diets that meet or exceed their energy and metabolizable protein (MP) requirements. In a companion paper (Räisänen et al., 2021) results are presented on the effect of increasing dHis dose with an MP-deficient basal diet. In this experiment, 16 Holstein cows (72 ± 15 d in milk) were used in a replicated 4 × 4 Latin square design experiment with four 28-d periods. Treatments were as follows: (1) control, total mixed ration (TMR) with 1.8% dHis of MP (TMR1; dHis1.8); (2) a different TMR with 2.2% dHis (TMR2; dHis2.2); (3) TMR2 supplemented with rumen-protected His (RP-His) to supply 2.6% dHis (dHis2.6); and (4) TMR2 supplemented with RP-His to supply 3.0% dHis of MP (dHis3.0). Estimated dHis intakes calculated at the end of the experiment were 46, 58, 69, and 79 g/d for dHis1.8, dHis2.2, dHis2.6, and dHis3.0, respectively. Contrasts were used to compare TMR1 with TMR2 and to test the linear and quadratic effects of RP-His inclusion rate on TMR2. We detected no effects of TMR or dHis dose on dry matter intake or milk yield, whereas energy-corrected milk (ECM) yield was quadratically increased, being greatest for cows on treatment dHis2.6. Milk true protein and lactose concentrations and milk true protein yield were not affected by TMR or dHis dose. Milk fat concentration and yield increased quadratically, and lactose yield tended to increase quadratically with increasing dHis dose. Calculated apparent efficiency of His utilization decreased quadratically with increasing dHis supply. Further, plasma concentration of His was greater for cows on TMR2 compared with TMR1. When an MP-adequate diet was fed to dairy cows, milk true protein concentration and yield were not affected by dHis supply, but milk fat and ECM yields of dairy cows were optimized at dHis supply of 69 g/d or 2.65% of MP.

Of Mice and Men: Impacts of Calorie Restriction on Metabolomics of the Cerebellum

The main purpose of research in mice is to explore metabolic changes in animal models and then predict or propose potential translational benefits in humans. Although some researchers in the brain research field have mentioned that the mouse experiments results still lack the complex neuroanatomy of humans, caution is required to interpret the findings. In mice, we observed in article seventeenth of the series of the effects of graded levels of calorie restriction, metabolomic changes in the cerebellum indicated activation of hypothalamocerebellar connections driven by hunger responses. Therefore, the purpose of the current perspective is to set this latest paper into a wider context of the physiological, behavioral, and molecular changes seen in these mice and to compare and contrast them with previous human studies.

Effectiveness of Rice Germ Supplementation on Body Composition, Metabolic Parameters, Satiating Capacity, and Amino Acid Profiles in Obese Postmenopausal Women: A Randomized, Controlled Clinical Pilot Trial

Rice germ (RG) may be a safe and effective dietary supplement for obesity in menopause, considering its high protein content and considerable amounts of essential amino acids, good fatty acids, and fiber. This pilot randomized, blinded, parallel-group, placebo-controlled pilot trial investigated the effectiveness of 4-weeks RG supplementation (25 g twice a day) on body composition, as primary outcome, measured by Dual Energy X-Ray Absorptiometry (DXA), and metabolic parameters, as secondary outcomes, like amino acid profiles and satiating capacity, in obese postmenopausal women following a tailored hypocaloric diet (25–30% less than daily energy requirements). Twenty-seven women were randomly assigned to the supplemented group (14) or placebo group (13). There was a significant interaction between time and group for body mass index (BMI) (p < 0.0001), waist (p = 0.002) and hip circumferences (p = 0.01), total protein (0.008), albumin (0.005), Homeostasis Model Assessment index score (p = 0.04), glycine (p = 0.002), glutamine (p = 0.004), and histidine (p = 0.007). Haber’s means over time showed a clearly greater feeling of satiety for the supplemented compared to the placebo group. These findings indicate that RG supplementation in addition to a tailored diet counterbalanced the metabolic changes typical of menopause, with improvements in BMI, body composition, insulin resistance, amino acid profiles, and satiety.

Effect of Biochar on the Production of L-Histidine From Glucose Through Escherichia coli Metabolism

The organic compounds from biochar play a role of hormone analogs, stimulating the expression of metabolites by controlling related gene and protein. In this experiment, we reported the L-histidine biosysthesis was promoted by biochar treatment in E. coli unlike genetic engineering of the traditional method. The related results indicated the most optimal concentration was found to be 3%, and 7% is the lethal dose. E. coli was inhibited in the high-concentration treatment. On the other hand, docking technology was usually used as drug screening, basing on Lock-and-key model of protein in order to better understand mechanisms. So the organic compounds of biochar from GC-MS analysis that acted as ligands were connected to HisG protein controlling L-histidine biosysthesis in E. coli. The result showed that the three organic molecules interacted with HisG protein by hydrogen bond. So we considered that these three compounds play regulatory roles in L-histidine biosysthesis, and the hisG gene expression fully supports this conclusion.

Gene Expression and Histochemical Analyses in the Fatty Livers of Rats Fed a Histidine-Excess Diet

Triglyceride (TG) and cholesterol accumulation are known to occur in the liver of rats fed a histidine-excess (5%) diet, but there are few studies reporting histochemical and molecular biological analyses of the rat liver. The aim of this study was to elucidate the molecular basis of this lipid-accumulation mechanism. Lipid accumulations, tissue section images, and gene expression levels were compared in the livers of rats fed a control or histidine-excess diet for 5 wk (n=8/group). Serum levels of TGs, free fatty acids, total cholesterol, high-density lipoprotein cholesterol, glucose, albumin, and the enzyme activities of aspartate aminotransferase and alanine aminotransferase were also analyzed. In the livers of rats fed a histidine-excess diet, histochemical analyses showed what appeared to be a preliminary stage of nonalcoholic fatty liver, characterized by lipid accumulation around the central vein area and minor fibrosis. However, there were no changes in serum TG or free fatty acid levels. Quantitative PCR analyses showed the up-regulation of FAT/CD36, which is related to the uptake of fatty acids into cells, and the downregulation of two apolipoprotein genes, ApoC3 and ApoE. The mRNA levels of PPARγ, LXRα, and AMPKα in the liver were also reduced by excess histidine intake. The results of this study suggest that steatosis caused by excess histidine intake may be the result of an imbalance between lipid transport from the liver and the uptake of free fatty acids into hepatocytes.

Potential of 2D qNMR spectroscopy for distinguishing chicken breeds based on the metabolic differences

Two-dimensional quantitative NMR spectroscopy (2D qNMR) was set up and multivariate analyses were performed on metabolites obtained from breast meat extracts of broilers and four native chicken (KNC) strains. It can accurately identify more metabolites than 1D ¹H NMR via separation of peak overlap by dimensional expansion with good linearity, but has a problem of numerical quantification; Complementation of 1D and 2D qNMR is necessary. Among breeds, KNC-D had higher amounts of free amino acids, sugars, and bioactive compounds than others. Noticeable differences between KNCs and broilers were observed; KNCs contained higher amounts of inosine 5'-monophosphate, α-glucose, anserine, and lactic acid, and lower amounts of free amino acids and their derivatives. The 2D qNMR combined with multivariate analyses distinguished the breast meat of KNCs from broilers but showed similarities among KNCs. Also, 2D qNMR may provide fast metabolomics information compared to conventional analysis.

Highly Efficient Production of l-Histidine from Glucose by Metabolically Engineered Escherichia coli

l-Histidine is a functional amino acid with numerous therapeutic and ergogenic properties. It is one of the few amino acids that is not produced on a large scale by microbial fermentation due to the lack of an efficient microbial cell factory. In this study, we demonstrated the engineering of wild-type Escherichia coli to overproduce histidine from glucose. First, removal of transcription attenuation and histidine-mediated feedback inhibition resulted in 0.8 g/L histidine accumulation. Second, chromosome-based optimization of the expression levels of histidine biosynthesis genes led to a 4.75-fold increase in histidine titer. Third, strengthening phosphoribosyl pyrophosphate supply and rerouting the purine nucleotide biosynthetic pathway improved the histidine production to 8.2 g/L. Fourth, introduction of the NADH-dependent glutamate dehydrogenase from Bacillus subtilis and the lysine exporter from Corynebacterium glutamicum enabled the final strain HW6-3 to produce 11.8 g/L histidine. Finally, 66.5 g/L histidine was produced under fed-batch fermentation, with a yield of 0.23 g/g glucose and a productivity of 1.5 g/L/h. This is the highest titer and productivity of histidine ever reported from an engineered strain. Additionally, the metabolic strategies utilized here can be applied to engineering other microorganisms for the industrial production of histidine and related bioproducts.

Safety and efficacy of l-histidine monohydrochloride monohydrate produced by fermentation with Escherichia coli (NITE BP-02526) for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l‐histidine monohydrochloride monohydrate produced by fermentation with Escherichia coli (NITE BP‐02526) when used as a nutritional additive or as a feed flavouring compound in feed and water for drinking for all animal species. The product under assessment is l‐histidine HCl H₂O produced by fermentation with a genetically modified strain of E. coli (NITE BP‐02526). The production strain and its recombinant DNA were not detected in the final products. l‐Histidine HCl H₂O does not give rise to any safety concern to the production strain. The use of l‐histidine HCl H₂O is safe for the target species when used to supplement the diet in appropriate amounts. It is safe at the proposed use level of 25 mg/kg when used as a flavouring compound for all animal species. The use of l‐histidine HCl H₂O in animal nutrition raises no safety concerns for consumers of animal products. The additive is not irritating to the skin or eyes and is not a skin sensitiser. There is a risk for persons handling the additive from the exposure to endotoxins by inhalation. The use of l‐histidine as a feed additive does not represent a risk to the environment. The additive l‐histidine HCl H₂O is regarded as an effective source of the amino acid l‐histidine when used as a nutritional additive. For the supplemental l‐histidine to be as efficacious in ruminants as in non‐ruminant species, it requires protection against degradation in the rumen. It is also considered efficacious as a feed flavouring compound under the proposed conditions of use.

Histidine: A Systematic Review on Metabolism and Physiological Effects in Human and Different Animal Species

Histidine is an essential amino acid (EAA) in mammals, fish, and poultry. We aim to give an overview of the metabolism and physiological effects of histidine in humans and different animal species through a systematic review following the guidelines of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). In humans, dietary histidine may be associated with factors that improve metabolic syndrome and has an effect on ion absorption. In rats, histidine supplementation increases food intake. It also provides neuroprotection at an early stage and could protect against epileptic seizures. In chickens, histidine is particularly important as a limiting factor for carnosine synthesis, which has strong anti-oxidant effects. In fish, dietary histidine may be one of the most important factors in preventing cataracts. In ruminants, histidine is a limiting factor for milk protein synthesis and could be the first limiting AA for growth. In excess, histidine supplementation can be responsible for eating and memory disorders in humans and can induce growth retardation and metabolic dysfunction in most species. To conclude, the requirements for histidine, like for other EAA, have been derived from growth and AA composition in tissues and also have specific metabolic roles depending on species and dietary levels.

Histidine in Health and Disease: Metabolism, Physiological Importance, and Use as a Supplement

L-histidine (HIS) is an essential amino acid with unique roles in proton buffering, metal ion chelation, scavenging of reactive oxygen and nitrogen species, erythropoiesis, and the histaminergic system. Several HIS-rich proteins (e.g., haemoproteins, HIS-rich glycoproteins, histatins, HIS-rich calcium-binding protein, and filaggrin), HIS-containing dipeptides (particularly carnosine), and methyl- and sulphur-containing derivatives of HIS (3-methylhistidine, 1-methylhistidine, and ergothioneine) have specific functions. The unique chemical properties and physiological functions are the basis of the theoretical rationale to suggest HIS supplementation in a wide range of conditions. Several decades of experience have confirmed the effectiveness of HIS as a component of solutions used for organ preservation and myocardial protection in cardiac surgery. Further studies are needed to elucidate the effects of HIS supplementation on neurological disorders, atopic dermatitis, metabolic syndrome, diabetes, uraemic anaemia, ulcers, inflammatory bowel diseases, malignancies, and muscle performance during strenuous exercise. Signs of toxicity, mutagenic activity, and allergic reactions or peptic ulcers have not been reported, although HIS is a histamine precursor. Of concern should be findings of hepatic enlargement and increases in ammonia and glutamine and of decrease in branched-chain amino acids (valine, leucine, and isoleucine) in blood plasma indicating that HIS supplementation is inappropriate in patients with liver disease.

Lesser mealworm (Alphitobius diaperinus) powder as a novel baking ingredient for manufacturing high-protein, mineral-dense snacks

Increasing interest in consuming foods that are high in protein, vitamin, amino acid, and mineral contents is steering growth in the market for fortified snacks. The aim of the present study was to evaluate the use of lesser mealworm (Alphitobius diaperinus) powder (LP) (at 10 or 30% substitution for wheat flour) for the protein and mineral fortification of crunchy snacks (rusks). Hence, the technological, microbiological, nutritional, and sensory characteristics of the fortified rusks were evaluated. The protein content was enriched up to 99.3% in rusks with 30% substitution; moreover, a notable increase in the essential amino acids content was observed, with histidine fortification reaching up to 129.1% in rusks with 30% substitution. The incorporation of LP has led to an enrichment of almost all the minerals considered here, and especially Fe, P and Zn, with Zn showing fortification percentages of up to 300% in rusks with 30% substitution for LP. The experimental rusks showed pleasant sensory traits and low a_w values. In view of the potential industrial manufacturing of insect-based rusks, the proposed product can be assigned to level 4 (validation in a laboratory environment) of the Technology Readiness Level (TRL) scale, and it is thus ready to be tested in a simulated production environment.

Metabolism of Amino Acids in the Brain and Their Roles in Regulating Food Intake

Amino acids (AAs) and their metabolites play an important role in neurological health and function. They are not only the building blocks of protein but are also neurotransmitters. In the brain, glutamate and aspartate are the major excitatory neurotransmitters, whereas γ-aminobutyrate (GABA, a metabolite of glutamate) and glycine are the major inhibitory neurotransmitters. Nitric oxide (NO, a metabolite of arginine), H₂S (a metabolite of cysteine), serotonin (a metabolite of tryptophan) and histamine (a metabolite of histidine), as well as dopamine and norepinephrine (metabolites of tyrosine) are neurotransmitters to modulate synaptic plasticity, neuronal activity, learning, motor control, motivational behavior, emotion, and executive function. Concentrations of glutamine (a precursor of glutamate and aspartate), branched-chain AAs (precursors of glutamate, glutamine and aspartate), L-serine (a precursor of glycine and D-serine), methionine and phenylalanine in plasma are capable of affecting neurotransmission through the syntheses of glutamate, aspartate, and glycine, as well as the competitive transport of tryptophan and tyrosine across from the blood-brain barrier. Adequate consumption of AAs is crucial to maintain their concentrations and the production of neurotransmitters in the central nervous system. Thus, the content and balance of AAs in diets have a profound impact on food intake by animals. Knowledge of AA transport and metabolism in the brain is beneficial for improving the health and well-being of humans and animals.

Effects of histidine supplementation on amino acid metabolism in rats

Histidine (HIS) is investigated for therapy of various disorders and as a nutritional supplement to enhance muscle performance. We examined effects of HIS on amino acid and protein metabolism. Rats consumed HIS in a drinking water at a dose of 0.5 g/l (low HIS), 2 g/l (high HIS) or 0 g/l (control) for 4 weeks. At the end of the study, the animals were euthanized and blood plasma, liver, soleus (SOL), tibialis (TIB), and extensor digitorum longus (EDL) muscles analysed. HIS supplementation increased food intake, body weight and weights and protein contents of the liver and kidneys, but not muscles. In blood plasma there were increases in glucose, urea, and several amino acids, particularly alanine, proline, aspartate, and glutamate and in high HIS group, ammonia was increased. The main findings in the liver were decreased concentrations of methionine, aspartate, and glycine and increased alanine. In muscles of HIS-consuming animals increased alanine and glutamine. In high HIS group (in SOL and TIB) increased chymotrypsin-like activity of proteasome (indicates increased proteolysis); in SOL decreased anserine (beta-alanyl-N1-methylhistidine). We conclude that HIS supplementation increases ammonia production, alanine and glutamine synthesis in muscles, affects turnover of proteins and HIS-containing peptides, and increases requirements for glycine and methionine.

Amino acid signature predictive of incident prediabetes: A case-control study nested within the longitudinal pathobiology of prediabetes in a biracial cohort

OBJECTIVE

Circulating branched-chain amino acids (BCAAs, isoleucine, leucine, valine) and aromatic amino acids (AAAs, tyrosine and phenylalanine) predicted type 2 diabetes mellitus (T2DM) risk in a Caucasian population. Here, we assessed amino acid levels in relation to incident prediabetes among initially normoglycemic African Americans (AA) and European Americans (EA).

RESEARCH DESIGN AND METHODS

Using a nested case-control design, we studied 70 adults (35 AA, 35 EA) who developed prediabetes (progressors) and 70 matched participants who maintained normoglycemia (nonprogressors) during 5.5 years of follow-up in the Pathobiology of Prediabetes in a Biracial Cohort study. Assessments included plasma amino acid levels, insulin sensitivity, and beta-cell function.

RESULTS

The total level of all 18 amino acid assayed was significantly associated with lean mass (r = 0.36, P < 0.0001), waist circumference (r = 0.27, P = 0.001), fasting plasma glucose (r = 0.24, P = 0.005), HOMA-IR (r = 0.22, P = 0.01) and HDL cholesterol (r = -0.18, P = 0.03). Individual amino acid levels were significantly associated with insulin sensitivity and insulin secretion. Compared with nonprogressors, progressors had higher baseline levels of asparagine and aspartic acid (P <0.0001), glutamine/glutamic acid (P = 0.005) and phenylalanine (P = 0.02), and lower histidine (P = 0.02) levels. In fully-adjusted logistic regression models, aspartic acid/asparagine (OR 2.72 [95% CI 1.91-3.87]) and histidine (OR 0.90 [95% CI 0.85-0.96]) were the only amino acids that significantly predicted incident prediabetes.

CONCLUSIONS

Baseline plasma aspartic acid and asparagine levels predicted progression to prediabetes, whereas histidine levels were protective of prediabetes risk. Thus, the amino acid signature associated with prediabetes in a diverse population may be distinct from that previously linked to T2DM in Caucasians.

Effects of standardized ileal digestible histidine to lysine ratio on growth performance of 7- to 11-kg nursery pigs

Histidine may be the sixth limiting amino acid (AA) in practical nursery diets supplemented with high amounts of feed-grade AA. Therefore, 2 experiments were conducted to determine the standardized ileal digestible (SID) His:Lys ratio requirement estimate for growth performance of 7- to 11-kg nursery pigs. A total of 360 and 350 pigs (DNA 241 × 600, Columbus, NE; initially 7.1 ± 0.31 and 6.6 ± 0.36 kg) were used in Exp. 1 and 2, respectively. There were 5 pigs per pen with 12 replicates per treatment in Exp. 1 and 10 replicates per treatment in Exp. 2. After weaning, pigs were fed a common pelleted diet for 10 d in Exp. 1 and 7 d in Exp. 2. Then, pens were assigned to treatments in a randomized complete block design with body weight (BW) as the blocking factor. Dietary treatments consisted of SID His:Lys ratios of 24%, 28%, 32%, 36%, 40%, and 44% in Exp. 1 and 24%, 28%, 30%, 32%, 34%, 36%, and 42% in Exp. 2. Experimental diets were fed in pellet form for 10 or 14 d in Exp. 1 and 2, followed by a common mash diet for 15 or 14 d, respectively. Data were analyzed using the GLIMMIX and NLMIXED procedures of SAS, fitting data with heterogeneous variance when needed. The competing statistical models utilized were quadratic polynomial, broken-line linear (BLL), and broken-line quadratic. In Exp. 1, increasing SID His:Lys ratio increased (quadratic, P = 0.001) ADG, ADFI, G:F, and day 10 BW. In Exp. 2, ADG, G:F, and day 14 BW increased (quadratic, P = 0.001), and ADFI increased linearly (P = 0.001) with increasing SID His:Lys ratio. The best-fitting model for all response variables analyzed was the BLL. In Exp. 1, requirement estimates were 29.7%, 29.1%, and 29.8% SID His:Lys ratio for ADG, ADFI, and G:F, respectively. In Exp. 2, the SID His:Lys ratio requirement estimates were 31.0% for ADG and 28.6% for G:F. These results suggest that the SID His requirement estimate for growth performance is no more than 31% of Lys and that the NRC (2012) SID His requirement of 34% of Lys may be overestimated for 7- to 11-kg pigs.

Higher intakes of energy-adjusted dietary amino acids are inversely associated with obesity risk

We assessed the relationship between energy-adjusted amino acids (EAA) intakes and obesity risk using data on nutrient intakes derived from the Chinese food composition tables to determine dietary intakes (DI) among 1109 obese and 3009 normal weight subjects. Dietary patterns (DP) were identified using principal component analysis, multivariable-adjusted odds ratio (OR) and 95% confidence interval (CI) of obesity risk by quartiles of EAA intakes was estimated using logistic regression with two-sided P < 0.05. Multivariable-adjusted OR and 95% CI for obesity risk were 1.00, 0.801 (0.573, 1.119), 0.718 (0.504, 1.024) and 0.532 (0.353, 0.803) P-trend = 0.003 across energy-adjusted quartiles of total AA intakes. Similarly, higher DI of 13 AA; isoleucine, leucine, valine, lysine, cysteine, phenylalanine, tyrosine, threonine, histidine, aspartic acid, glutamic acid, proline, and serine were associated with lower risk of obesity. Furthermore, six DP; 'Wheaten food and Rice', 'Fruit, Vegetables and Milk', 'Snack, Beverage and Ice cream', 'Potatoes, Soybean & Egg', 'Livestock & Poultry meat' and 'Fish' were identified. Multivariable-adjusted OR and 95% CI across quartiles of DP adherence for obesity risk were 1.00, 0.737 (0.535, 1.017), 0.563 (0.406, 0.779), 0.724 (0.518, 1.011) P-trend = 0.018 for 'Fruit, Vegetables and Milk', 1.00, 0.734 (0.531, 1.013), 0.841(0.609, 1.161), 0.657 (0.478, 0.904) P-trend = 0.027 for 'Potatoes, Soybean & Egg' and 1.00, 1.106 (0.791, 1.548), 1.367(0.975, 1.917), 1.953 (1.399, 2.726) P-trend = 0.000 for 'Fish'. Additionally, lower adherence to 'Snack, Beverage and Ice cream' and 'Fish' patterns is associated with a protective higher AA intake-obesity risk relationship. Energy-adjusted AA intakes were inversely associated with obesity risk, but the associations appear modifiable by DP adherence of respondents.

Betahistine dihydrochloride transdermal delivery via optimized thermosensitive gels: percutaneous absorption evaluation using rat growth as a biomarker

The aim of this study was to develop and optimize a betahistine dihydrochloride (BH) thermoreversible bioadhesive gel intended for transdermal delivery. The gels were obtained via cold method. A full factorial design was employed to investigate the joint effect of Poloxamer 407 concentration (18 and 20%), adhesive polymer type (Polyvinyl pyrolidone, Hydroxypropyl methylcellulose, and Carbopol 934), and adhesive polymer concentration (0.5 and 1.5%) on gelling temperature, viscosity at 37 °C, and adhesion strength. Data collected were analyzed using multiple linear regression. A desirability index approach with relative importance weight was used to choose the most desirable formulation. F4 (20% Poloxamer+1.5% Carbopol) was selected for further characterization. F4 released 96.97% drug in 12 h across hairless rat skin. F4 gelation temperature and time were 36 ± 0.35 °C, and 6 ± 0.7 min, respectively. F4 adhesive force was 8835.68 dyne/cm². F4 was tested for its appetite suppressing effect in a rat model and it was evaluated histopathologically. Rats' chow intake and weight gain was significantly decreased with no signs of inflammation or lipolysis when the optimized BH gel formulation, F4, was compared with untreated animals and animals treated with BH free gel. The results suggest that BH is percutaneously absorbed from the gel base and that the BH gel is tolerable. The desirability index approach with relative importance weight of responses was effective in determination of the optimum formulation. BH is systemically effective and well-tolerated when applied topically in hydrogel-based systems. The Carbopol-Poloxamer gel is a promising modality for transdermal delivery of BH.

Satiety and gastrointestinal hormones during a Mixed Meal Tolerance Test after gastric bypass surgery: association with plasma amino acid concentrations

BACKGROUND

Circulating amino acids have been associated with both appetite and the secretion of anorexigenic hormones in healthy and obese populations. This effect has not been investigated in subjects having undergone Roux-en-Y gastric bypass surgery (RYGB).

OBJECTIVE

To investigate the association between postprandial plasma concentrations of amino acids and the anorexigenic hormones glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY), the orexigenic hormone ghrelin, and satiety and hunger in post-RYGB subjects.

SETTING

A Dutch surgical department.

METHODS

Participants after primary RYGB were studied during a Mixed Meal Tolerance Test (MMTT). Satiety and hunger were assessed every 30 minutes on visual analogue scales. Blood samples were collected at baseline, every 10 minutes during the first half hour and every 30 minutes until 210 minutes after the start. The samples were assessed for 24 amino acids and 3 gastrointestinal hormones. Incremental areas under the curve (iAUCs) were calculated. Exploratory analyses were performed in which subjects were divided into high and low responders depending on the median iAUC.

RESULTS

42 subjects, aged 48 ± 11 (mean ± SD) years, 31 to 76 months post-RYGB and with total weight loss of 30 ± 9% completed the MMTT. Subjects with high satiety scores had more than a 25% higher net iAUC of PYY and GLP-1 and at least a 10% higher net iAUC of 10 amino acids compared to subjects with low scores (P < 0.05). The net iAUC of five of these amino acids (i.e. arginine, asparagine, histidine, serine and threonine) was more than 10% higher in subjects with high responses on GLP-1 and/or PYY (P < 0.05).

CONCLUSIONS

Certain postprandial amino acids were associated with satiety and anorexigenic hormones and could therefore play a role in appetite regulation after RYGB; either by a direct effect on satiety, indirectly through gastrointestinal hormones, or both.

Effect of Amino Acids on Growth Performance, Carcass Characteristics, Meat Quality, and Carnosine Concentration in Broiler Chickens

The aim of this research was to investigate the deposition of carnosine in broiler muscles by feeding treatments comprising β-alanine, L-histidine, and magnesium oxide in various concentrations. The research was carried out on 120 Cobb 500 broilers divided into four groups. From weeks four to six, broilers were fed finisher mixtures as follows: P1, control group; P2, 0.5% β-alanine + 0.24% MgO; P3, 0.25% L-histidine + 0.24% MgO; and P4, 0.20% β-alanine + 0.10% L-histidine + 0.24% MgO. This paper presents the weights of broilers and their carcasses, portions of main parts of carcasses, technological quality of breast muscles, and concentrations of carnosine in breast and thigh muscles. The following traits of muscle tissue quality were measured: initial and final pH value (45 min after slaughtering pH₁, and 24 h after cooling pH₂), drip loss, color (Minolta colorimeter, expressed as CIE L*, CIE a*, and CIE b* values), meat softness, and cooking loss. Data on relative concentration of protein carbonyl (nmol/mg protein) in the muscles of breasts and thighs and levels of thiobarbituric acid-reactive substances (TBARS) in fresh and frozen breasts muscles (nmol/mg of tissue) are presented. Statistical analysis proved that feeding treatments had an effect on the live weight of broilers in the 4th, 5th, and 6th weeks of fattening (P<0.05), as well as on the carcass quality at slaughter (P<0.05; except the portion of wings), pH₁ value (P=0.035), CIE a* indicator (P=0.007), drip loss (P=0.002), and meat texture (P=0.008). Compared to the control group, synthesis and deposition of carnosine were increased in breast muscles in groups P2, P3, and P4 by 7.51%, 10.62%, and 62.93%, respectively, and in thigh muscles by 61.05%, 78.95%, and 89.52%, respectively. It was also confirmed that feeding treatments influenced the level of TBARS in frozen broiler breast muscles (P=0.014).

A novel transdermal nanoethosomal gel of betahistine dihydrochloride for weight gain control: in-vitro and in-vivo characterization

Background

Betahistine dihydrochloride (BDH) is a histamine analog used to control weight gain, with short elimination half-life and gastric irritation as side effects.

Objective

The aim of the current investigation is to formulate and optimize a topical BDH ethosomal gel for weight gain control.

Materials and methods

Box–Behnken design was applied to study the effect of independent variables: phosphatidylcholine (PC), propylene glycol (PG), and ethanol on vesicle size; entrapment efficiency; % drug release; and flux. The morphology and zeta potential of the optimized formulation were evaluated. The % drug release, flux, and pharmacodynamics of the optimized formulation gel were studied.

Results

The size and entrapment efficiency percent had a direct positive relationship with the concentration of PC and negative relationship with ethanol and PG. The % drug release and flux decreased with increasing PC and PG, while ethanol enhanced both responses. Regression modeling indicated a good correlation between dependent and independent variables, where F16 was chosen as the optimized formulation. F16 showed well-defined spherical vesicles and zeta potential of −24 mV, and % release from the gel exceeded 99.5% over 16 h with the flux of 0.28 mg/cm²/h. Food intake and weight gain of rats were significantly decreased after transdermal application of the BDH ethosomal gel when compared with control, placebo, and BDH gel. The histopathological findings proved the absence of inflammation and decrease in adipose tissue.

Conclusion

Results obtained showed a significant, sustained transdermal absorption of BDH ethosomal gel and, consequently, a decrease in food intake and weight gain.

Effects of intraperitoneally administered L-histidine on food intake, taste, and visceral sensation in rats

To evaluate relative factors for anorectic effects of L-histidine, we performed behavioral experiments for measuring food and fluid intake, conditioned taste aversion (CTA), taste disturbance, and c-Fos immunoreactive (Fos-ir) cells before and after i.p. injection with L-histidine in rats. Animals were injected with saline (9 ml/kg, i.p.) for a control group, and saline (9 ml/kg, i.p.) containing L-histidine (0.75, 1.5, 2.0 g/kg) for a L-histidine group. Injection of L-histidine decreased the average value of food intake, and statistically significant anorectic effects were found in animals injected with 1.5 or 2.0 g/kg L-histidine but not with 0.75 g/kg L-histidine. Taste abnormalities were not detected in any of the groups. Animals injected with 2.0 g/kg L-histidine were revealed to present with nausea by the measurement of CTA. In this group, a significant increase in the number of Fos-ir cells was detected both in the area postrema and the nucleus tractus solitarius (NTS). In the 0.75 g/kg L-histidine group, a significant increase in the number of Fos-ir cells was detected only in the NTS. When the ventral gastric branch vagotomy was performed, recovery from anorexia became faster than the sham-operated group, however, vagotomized rats injected with 2.0 g/kg L-histidine still acquired CTA. These data indicate that acute anorectic effects induced by highly concentrated L-histidine are partly caused by induction of nausea and/or visceral discomfort accompanied by neuronal activities in the NTS and the area postrema. We suggest that acute and potent effects of L-histidine on food intake require substantial amount of L-histidine in the diet.

Proline Decreases the Suppressive Effect of Histidine on Food Intake and Fat Accumulation

We recently suggested that proline might decrease the suppressive effect of histidine on food intake. Our purpose in the present study was to investigate the influence of proline on the suppressive effect of histidine on food intake and accumulation of body fat. Male Wistar rats were divided into four groups and allowed free access to the following diets for 3 wk: control (C), 5% proline (P), 5% histidine (H), or 5% histidine plus 10% proline (HP) diets. Food intake for 7 d and retroperitoneal fat tissue weight at the end of the experimental period of the HP diet group were greater than those of the H diet group, whereas no significant difference existed between the HP diet group and the C diet group. Our results indicate that proline inhibits the influence of histidine on food intake and accumulation of body fat.

Animal Models for the Study of the Relationships between Diet and Obesity: A Focus on Dietary Protein and Estrogen Deficiency

Obesity is an increasing major public health concern asking for dietary strategies to limit weight gain and associated comorbidities. In this review, we present animal models, particularly rats and mice, which have been extensively used by scientists to understand the consequences of diet quality on weight gain and health. Notably, modulation of dietary protein quantity and/or quality has been shown to exert huge effects on body composition homeostasis through the modulation of food intake, energy expenditure, and metabolic pathways. Interestingly, the perinatal window appears to represent a critical period during which the protein intake of the dam can impact the offspring’s weight gain and feeding behavior. Animal models are also widely used to understand the processes and mechanisms that contribute to obesity at different physiological and pathophysiological stages. An interesting example of such aspect is the situation of decreased estrogen level occurring at menopause, which is linked to weight gain and decreased energy expenditure. To study metabolic disorders associated with such situation, estrogen withdrawal in ovariectomized animal models to mimic menopause are frequently used. According to many studies, clear species-specific differences exist between rats and mice that need to be taken into account when results are extrapolated to humans.

Relationships of Dietary Histidine and Obesity in Northern Chinese Adults, an Internet-Based Cross-Sectional Study

Our previous studies have demonstrated that histidine supplementation significantly ameliorates inflammation and oxidative stress in obese women and high-fat diet-induced obese rats. However, the effects of dietary histidine on general population are not known. The objective of this Internet-based cross-sectional study was to evaluate the associations between dietary histidine and prevalence of overweight/obesity and abdominal obesity in northern Chinese population. A total of 2376 participants were randomly recruited and asked to finish our Internet-based dietary questionnaire for the Chinese (IDQC). Afterwards, 88 overweight/obese participants were randomly selected to explore the possible mechanism. Compared with healthy controls, dietary histidine was significantly lower in overweight (p < 0.05) and obese (p < 0.01) participants of both sexes. Dietary histidine was inversely associated with body mass index (BMI), waist circumference (WC) and blood pressure in overall population and stronger associations were observed in women and overweight/obese participants. Higher dietary histidine was associated with lower prevalence of overweight/obesity and abdominal obesity, especially in women. Further studies indicated that higher dietary histidine was associated with lower fasting blood glucose (FBG), homeostasis model assessment of insulin resistance (HOMA-IR), 2-h postprandial glucose (2 h-PG), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), C-reactive protein (CRP), malonaldehyde (MDA) and vaspin and higher glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and adiponectin of overweight/obese individuals of both sexes. In conclusion, higher dietary histidine is inversely associated with energy intake, status of insulin resistance, inflammation and oxidative stress in overweight/obese participants and lower prevalence of overweight/obesity in northern Chinese adults.

The Role of Circulating Amino Acids in the Hypothalamic Regulation of Liver Glucose Metabolism

A pandemic of diabetes and obesity has been developing worldwide in close association with excessive nutrient intake and a sedentary lifestyle. Variations in the protein content of the diet have a direct impact on glucose homeostasis because amino acids (AAs) are powerful modulators of insulin action. In this work we review our recent findings on how elevations in the concentration of the circulating AAs leucine and proline activate a metabolic mechanism located in the mediobasal hypothalamus of the brain that sends a signal to the liver via the vagus nerve, which curtails glucose output. This neurogenic signal is strictly dependent on the metabolism of leucine and proline to acetyl-coenzyme A (CoA) and the subsequent production of malonyl-CoA; the signal also requires functional neuronal ATP-sensitive potassium channels. The liver then responds by lowering the rate of gluconeogenesis and glycogenolysis, ultimately leading to a net decrease in glucose production and in concentrations of circulating glucose. Furthermore, we review here how our work with proline suggests a new role of astrocytes in the central regulation of glycemia. Last, we outline how factors such as the consumption of fat-rich diets can interfere with glucoregulatory mechanisms and, in the long term, may contribute to the development of hyperglycemia, a hallmark of type 2 diabetes.

The histaminergic system as a target for the prevention of obesity and metabolic syndrome

The control of food intake and body weight is very complex. Key factors driving eating behavior are hunger and satiety that are controlled by an interplay of several central and peripheral neuroendocrine systems, environmental factors, the behavioral state and circadian rhythm, which all concur to alter homeostatic aspects of appetite and energy expenditure. Brain histamine plays a fundamental role in eating behavior as it induces loss of appetite and has long been considered a satiety signal that is released during food intake (Sakata et al., 1997). Animal studies have shown that brain histamine is released during the appetitive phase to provide a high level of arousal preparatory to feeding, but also mediates satiety. Furthermore, histamine regulates peripheral mechanisms such as glucose uptake and insulin function. Preclinical research indicates that activation of H1 and H3 receptors is crucial for the regulation of the diurnal rhythm of food consumption; furthermore, these receptors have been specifically recognized as mediators of energy intake and expenditure. Despite encouraging preclinical data, though, no brain penetrating H1 receptor agonists have been identified that would have anti-obesity effects. The potential role of the H3 receptor as a target of anti-obesity therapeutics was explored in clinical trials that did not meet up to the expectations or were interrupted (clinicaltrials.gov). Nonetheless, interesting results are emerging from clinical trials that evaluated the attenuating effect of betahistine (an H1 agonist/H3 antagonist) on metabolic side effects associated with chronic antipsychotics treatment. Aim of this review is to summarize recent results that suggest the clinical relevance of the histaminergic system for the treatment of feeding disorders and provide an up-to-date summary of preclinical research. This article is part of the Special Issue entitled 'Histamine Receptors'.

Histidine supplementation alleviates inflammation in the adipose tissue of high-fat diet-induced obese rats via the NF-κB- and PPARγ-involved pathways

Obesity is considered to be accompanied by a chronic low-grade inflammatory state that contributes to the occurrence of many chronic diseases. Our previous study has demonstrated that histidine supplementation significantly ameliorates inflammation and oxidative stress in obese women. However, the in vivo potential mechanisms are not known. The present study was conducted to investigate the mechanisms underlying the effects of histidine on inflammation in a high-fat diet (HFD)-induced female obese rat model. An obese model was established in female Sprague–Dawley rats by HFD feeding for 8 weeks and followed by histidine supplementation for another 4 weeks. The results revealed that HFD-increased body weight and HFD-lowered serum histidine concentrations were significantly reversed by histidine supplementation (P< 0·05). In addition, the serum concentrations of TNF-α, IL-6, C-reactive protein (CRP) and malondialdehyde were significantly reduced and those of superoxide dismutase (SOD) were significantly increased by histidine supplementation when compared with those in obese rats (P< 0·05). Correspondingly, the mRNA expressions of TNF-α, IL-6 and CRP in the adipose tissue were significantly down-regulated and that of CuZnSOD was significantly up-regulated by histidine supplementation (P< 0·05). Histidine supplementation significantly reduced the HFD-induced translocation of NF-κB p65 into the nucleus (P= 0·032) by reducing the phosphorylation of the inhibitor of κBα in the adipose tissue. The results also revealed that the expression of adiponectin was markedly increased both in the serum and in the adipose tissue after histidine supplementation, accompanied by the activation of PPARγ (P= 0·021). These findings indicate that histidine is an effective candidate for ameliorating inflammation and oxidative stress in obese individuals via the NF-κB- and PPARγ-involved pathways.

Leptin signaling is required for leucine deprivation-enhanced energy expenditure

Leptin signaling in the hypothalamus is crucial in energy homeostasis. We have previously shown that dietary deprivation of the essential amino acid leucine in mice stimulates fat loss by increasing energy expenditure. The involvement of leptin signaling in this regulation, however, has not been reported. Here, we show that leucine deprivation promotes leptin signaling in mice maintained on an otherwise normal diet and restores leptin responses in mice maintained on a high fat diet, a regimen known to induce leptin resistance. In addition, we found that leucine deprivation stimulated energy expenditure, and fat loss was largely blocked in db/db mice homozygous for a mutation in leptin receptor and a knock-in mouse line Y3F with abrogation of leptin receptor Tyr(1138)-mediated signal transducer and activator transcript 3 signaling. Overall, our studies describe a novel link between hypothalamic leptin signaling and stimulation of energy expenditure under leucine deprivation.

Metabolic impacts of high dietary exposure to persistent organic pollutants in mice

Persistent organic pollutants (POPs) have been linked to metabolic diseases. Yet, the effects of high exposure to dietary POPs remain unclear. We therefore investigated whether elevated exposure to POPs provided by whale meat supplementation could contribute to insulin resistance. C57BL/6J mice were fed control (C) or very high-fat diet (VHF) containing low or high levels of POPs (VHF(+POPs)) for eight weeks. To elevate the dietary concentrations of POPs, casein was replaced by whale meat containing high levels of pollutants. Feeding VHF(+POPs) induced high POP accumulation in the adipose tissue of mice. However, compared with VHF-fed mice, animals fed VHF(+POPs) had improved insulin sensitivity and glucose tolerance, and reduced body weight. Levels of ectopic fat in skeletal muscles and liver were reduced in mice fed VHF(+POPs). These mice also gained less adipose tissue and had a tendency to reduced energy intake. In pair-feeding experiments, improved insulin action and reduced body weight gain were still observed in VHF(+POPs) compared to VHF pair-fed mice. We concluded that mice fed VHF contaminated with POPs derived from whale meat remain sensitive to insulin and glucose tolerant despite significant body burden of POPs. This indicates complex interactions between organic pollutants and nutrition in the development of metabolic disorders.

Transcriptomic and metabonomic profiling reveal synergistic effects of quercetin and resveratrol supplementation in high fat diet fed mice

Dietary quercetin and resveratrol have been frequently used in treating various diseases, but the underlying mechanisms are not entirely clear. Here, we report combined transcriptomic and metabonomic profiling that showed that the combined supplementation with quercetin and resveratrol produced synergistic effects on a high-fat diet-induced metabolic phenotype in mice. Histological and phenotypic improvements in serum and hepatic total cholesterol, insulin, fasting blood glucose, and HbA1c were also observed in mice receiving combined quercetin and resveratrol supplementation. This combined quercetin and resveratrol supplementation resulted in significant restoration of gene sets in functional pathways of glucose/lipid metabolism, liver function, cardiovascular system, and inflammation/immunity, which were altered by high fat diet feeding. The integration of transcriptomic and metabonomic data indicated quercetin and resveratrol supplementation enhanced processes of glycolysis and fatty acid oxidation, as well as suppressed gluconeogenesis. These alterations discovered at both the transcriptional and metabolic levels highlight the significance of combined "omics" platforms for elucidating mechanistic pathways altered by dietary polyphenols, such as quercetin and resveratrol, in a synergistic manner.

Peripheral and central mechanisms involved in the control of food intake by dietary amino acids and proteins

The present review summarises current knowledge and recent findings on the modulation of appetite by dietary protein, via both peripheral and central mechanisms. Of the three macronutrients, proteins are recognised as the strongest inhibitor of food intake. The well-recognised poor palatability of proteins is not the principal mechanism explaining the decrease in high-protein (HP) diet intake. Consumption of a HP diet does not induce conditioned food aversion, but rather experience-enhanced satiety. Amino acid consumption is detected by multiple and redundant mechanisms originating from visceral (during digestion) and metabolic (inter-prandial period) sources, recorded both directly and indirectly (mainly vagus-mediated) by the central nervous system (CNS). Peripherally, the satiating effect of dietary proteins appears to be mediated by anorexigenic gut peptides, principally cholecystokinin, glucagon-like peptide-1 and peptide YY. In the CNS, HP diets trigger the activation of noradrenergic and adrenergic neurons in the nucleus of the solitary tract and melanocortin neurons in the arcuate nucleus. Additionally, there is evidence that circulating leucine levels may modulate food intake. Leucine is associated with neural mechanisms involving mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK), energy sensors active in the control of energy intake, at least in the arcuate nucleus of the hypothalamus. In addition, HP diets inhibit the activation of opioid and GABAergic neurons in the nucleus accumbens, and thus inhibit food intake by reducing the hedonic response to food, presumably because of their low palatability. Future studies should concentrate on studying the adaptation of different neural circuits following the ingestion of protein diets.

Histidine and arginine are associated with inflammation and oxidative stress in obese women

The aims of the present study were to examine the serum amino acid profiles in obese and non-obese women and investigate the relationships between the serum amino acids and inflammation and oxidative stress in a human case–control study. Serum amino acids, inflammatory biomarkers (C-reactive protein and IL-6) and oxidative biomarkers (superoxide dismutase, malondialdehyde and glutathione peroxidase) were measured and compared in 235 obese women and 217 non-obese controls. The relationships between serum amino acids and inflammatory and oxidative biomarkers were examined using multiple linear regression. Among the amino acids determined, serum histidine, arginine, threonine, glycine, lysine and serine were found to be significantly lower in obese women as compared to non-obese controls (P < 0·001). The difference was the greatest for histidine (P < 0·001). In obese women, both histidine and arginine were negatively associated with inflammation and oxidative stress. In non-obese controls, histidine was negatively associated with oxidative stress. The findings in this study indicate that the metabolism of amino acids is abnormal in obese women in whom histidine and arginine have close relationships with inflammation and oxidative stress.