Effect of anserine ingestion on hyperglycemia and the autonomic nerves in rats and humans

Bibliometric and Visual Analysis of Global Research on Taurine, Creatine, Carnosine, and Anserine with Metabolic Syndrome: From 1992 to 2022

Red meat and animal-sourced protein are often disparaged as risk factors for developing metabolic syndrome, while emerging research has shown the beneficial effects of dietary taurine, creatine, carnosine, and anserine which are all exclusively abundant in red meat. Thus, it is imperative to highlight the available evidence to help promote red meat as part of a well-balanced diet to optimize human health. In this study, a bibliometric analysis was conducted to investigate the current research status of dietary taurine, creatine, carnosine, and anserine with metabolic syndrome, identify research hotspots, and delineate developmental trends by utilizing the visualization software CiteSpace. A total of 1094 publications were retrieved via the Web of Science Core Collection from 1992 to 2022. There exists a gradual increase in the number of publications on this topic, but there is still much room for research papers to rise. The United States has participated in the most studies, followed by China and Japan. The University of Sao Paulo was the research institute contributing the most; Kyung Ja Chang and Sanya Roysommuti have been identified as the most prolific authors. The analysis of keywords reveals that obesity, lipid profiles, blood pressure, and glucose metabolism, as well as ergogenic aid and growth promoter have been the research hotspots. Inflammation and diabetic nephropathy will likely be frontiers of future research related to dietary taurine, creatine, carnosine, and anserine. Overall, this paper may provide insights for researchers to further delve into this field and enlist the greater community to re-evaluate the health effects of red meat.

Acute balenine supplementation in humans as a natural carnosinase-resistant alternative to carnosine

Balenine possesses some of carnosine's and anserine's functions, yet it appears more resistant to the hydrolysing CN1 enzyme. The aim of this study was to elucidate the stability of balenine in the systemic circulation and its bioavailability in humans following acute supplementation. Two experiments were conducted in which (in vitro) carnosine, anserine and balenine were added to plasma to compare degradation profiles and (in vivo) three increasing doses (1-4-10 mg/kg) of balenine were acutely administered to 6 human volunteers. Half-life of balenine (34.9 ± 14.6 min) was respectively 29.1 and 16.3 times longer than that of carnosine (1.20 ± 0.36 min, p = 0.0044) and anserine (2.14 ± 0.58 min, p = 0.0044). In vivo, 10 mg/kg of balenine elicited a peak plasma concentration (Cmax) of 28 µM, which was 4 and 18 times higher than with 4 (p = 0.0034) and 1 mg/kg (p = 0.0017), respectively. CN1 activity showed strong negative correlations with half-life (ρ = - 0.829; p = 0.0583), Cmax (r = - 0.938; p = 0.0372) and incremental area under the curve (r = - 0.825; p = 0.0433). Overall, balenine seems more resistant to CN1 hydrolysis resulting in better in vivo bioavailability, yet its degradation remains dependent on enzyme activity. Although a similar functionality as carnosine and anserine remains to be demonstrated, opportunities arise for balenine as nutraceutical or ergogenic aid.

Oral anserine supplementation does not attenuate type-2 diabetes or diabetic nephropathy in BTBR ob/ob mice

Carnosine, a naturally occurring dipeptide present in an omnivorous diet, has been shown to ameliorate the development of metabolic syndrome, type-2 diabetes (T2D) and early- and advanced-stage diabetic nephropathy in different rodent models. Anserine, its methylated analogue, is more bio-available in humans upon supplementation without affecting its functionality. In this work, we investigated the effect of oral supplementation with anserine or carnosine on circulating and tissue anserine and carnosine levels and on the development of T2D and diabetic nephropathy in BTBR ob/ob mice. BTBR ob/ob mice were either supplemented with carnosine or anserine in drinking water (4 mM) for 18 weeks and compared with non-supplemented BTBR ob/ob and wild-type (WT) mice. Circulating and kidney, but not muscle, carnosine, and anserine levels were enhanced by supplementation with the respective dipeptides in ob/ob mice compared to non-treated ob/ob mice. The evolution of fasting blood glucose, insulin, fructosamine, triglycerides, and cholesterol was not affected by the supplementation regimens. The albumin/creatine ratio, glomerular hypertrophy, and mesangial matrix expansion were aggravated in ob/ob vs. WT mice, but not alleviated by supplementation. To conclude, long-term supplementation with anserine elevates circulating and kidney anserine levels in diabetic mice. However, anserine supplementation was not able to attenuate the development of T2D or diabetic nephropathy in BTBR ob/ob mice. Further research will have to elucidate whether anserine can attenuate milder forms of T2D or metabolic syndrome.

Carnosine, Small but Mighty-Prospect of Use as Functional Ingredient for Functional Food Formulation

Carnosine is a dipeptide synthesized in the body from β-alanine and L-histidine. It is found in high concentrations in the brain, muscle, and gastrointestinal tissues of humans and is present in all vertebrates. Carnosine has a number of beneficial antioxidant properties. For example, carnosine scavenges reactive oxygen species (ROS) as well as alpha-beta unsaturated aldehydes created by peroxidation of fatty acid cell membranes during oxidative stress. Carnosine can oppose glycation, and it can chelate divalent metal ions. Carnosine alleviates diabetic nephropathy by protecting podocyte and mesangial cells, and can slow down aging. Its component, the amino acid beta-alanine, is particularly interesting as a dietary supplement for athletes because it increases muscle carnosine, and improves effectiveness of exercise and stimulation and contraction in muscles. Carnosine is widely used among athletes in the form of supplements, but rarely in the population of cardiovascular or diabetic patients. Much less is known, if any, about its potential use in enriched food. In the present review, we aimed to provide recent knowledge on carnosine properties and distribution, its metabolism (synthesis and degradation), and analytical methods for carnosine determination, since one of the difficulties is the measurement of carnosine concentration in human samples. Furthermore, the potential mechanisms of carnosine's biological effects in musculature, metabolism and on immunomodulation are discussed. Finally, this review provides a section on carnosine supplementation in the form of functional food and potential health benefits and up to the present, neglected clinical use of carnosine.

Important roles of dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline in human nutrition and health

Taurine (a sulfur-containing β-amino acid), creatine (a metabolite of arginine, glycine and methionine), carnosine (a dipeptide; β-alanyl-L-histidine), and 4-hydroxyproline (an imino acid; also often referred to as an amino acid) were discovered in cattle, and the discovery of anserine (a methylated product of carnosine; β-alanyl-1-methyl-L-histidine) also originated with cattle. These five nutrients are highly abundant in beef, and have important physiological roles in anti-oxidative and anti-inflammatory reactions, as well as neurological, muscular, retinal, immunological and cardiovascular function. Of particular note, taurine, carnosine, anserine, and creatine are absent from plants, and hydroxyproline is negligible in many plant-source foods. Consumption of 30 g dry beef can fully meet daily physiological needs of the healthy 70-kg adult human for taurine and carnosine, and can also provide large amounts of creatine, anserine and 4-hydroxyproline to improve human nutrition and health, including metabolic, retinal, immunological, muscular, cartilage, neurological, and cardiovascular health. The present review provides the public with the much-needed knowledge of nutritionally and physiologically significant amino acids, dipeptides and creatine in animal-source foods (including beef). Dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline are beneficial for preventing and treating obesity, cardiovascular dysfunction, and ageing-related disorders, as well as inhibiting tumorigenesis, improving skin and bone health, ameliorating neurological abnormalities, and promoting well being in infants, children and adults. Furthermore, these nutrients may promote the immunological defense of humans against infections by bacteria, fungi, parasites, and viruses (including coronavirus) through enhancing the metabolism and functions of monocytes, macrophages, and other cells of the immune system. Red meat (including beef) is a functional food for optimizing human growth, development and health.

Responsiveness of Carnosine Homeostasis Genes in the Pancreas and Brain of Streptozotocin-Treated Mice Exposed to Dietary Carnosine

In excitable tissues, the endogenous dipeptide carnosine (CAR, β-Ala-l-His) sustains homeostatic responses to various challenges. By eliciting hypoglycemic effects via actions on the autonomic nervous system and protection of pancreatic beta-cells, CAR is also relevant in diabetes. We investigated the expression of genes involved in CAR biosynthesis, degradation, and membrane transport pathways, in the pancreas and brains of mice treated with streptozotocin (STZ) and then exposed to dietary CAR. We induced hyperglycemia by STZ intraperitoneal injections; then, STZ-treated mice received drinking water with or without CAR for two weeks. We report that CAR administration elicits beneficial effects on blood glucose levels and weight loss in STZ-treated mice and, remarkably, on the insulin gene products in the pancreas, preserving gene expression from STZ challenge. Also, we describe mRNA downregulation of the Slc15a2/Pept2 (dipeptide transporter) and Cndp2 (intracellular dipeptidase) genes in the pancreas of hyperglycemic mice, and dysregulation of Carns1 (CAR synthase), Pept2 and Cndp2 in brains; interestingly, dietary CAR elicits counteracting effects. These expression patterns associate with variations of CAR content in tissues of mice. Overall, our report suggests a direct role of CAR in the diabetes-affected pancreas and in the diabetes-targeted CNS, proposing (dys)regulation of CAR’s homeostasis as a marker condition.

Tuna extract reduces serum uric acid in gout-free subjects with insignificantly high serum uric acid: A randomized controlled trial

Long-term reduction of serum urate levels is vital in the treatment of gout. However, it is difficult to convince gout-free individuals of the necessity of treatment as few appropriate over-the-counter remedies and dietary supplements are available. Therefore, the present study aimed to investigate the antihyperuricemic efficacy and safety of a tuna extract containing the imidazole compounds to evaluate its potential as a functional food ingredient. A randomized, 4-week, double-blind, placebo-controlled study was conducted. A total of 48 male gout-free subjects with insignificantly high serum uric acid were randomly assigned to low- and high-dose tuna extract groups or a placebo group. The efficacy of the extract was assessed by measuring serum uric acid levels. Furthermore, a safety assessment was performed by physical parameters, hematology, blood biochemistry and urinalysis. The results indicated that the uric acid level was decreased at week 4 during the intervention in the tuna extract groups (low and high dose, -0.23 and -0.34 mg/dl, respectively) compared to the placebo group (-0.07 mg/dl). At week 4 after the intervention, a significant reduction in uric acid levels (-0.41 mg/dl; P<0.05) was observed in the high-dose tuna extract group compared with the placebo group (+0.11 mg/dl). No dose-related adverse events were observed during and following the intervention. Therefore, the present results suggest that oral administration of tuna extract containing the imidazole compounds has hypouricemic activity with no undesirable side effects.

Carnosine decreases IGFBP1 production in db/db mice through suppression of HIF-1

IGF binding protein 1 (IGFBP1) is a member of the binding proteins for the IGF with an important role in glucose homeostasis. Circulating IGFBP1 is derived essentially from the liver where it is mainly regulated negatively by insulin. Carnosine, a natural antioxidant, has been shown to improve metabolic control in different animal models of diabetes but its mechanisms of action are still not completely unraveled. We therefore investigate the effect of carnosine treatment on the IGFBP1 regulation in db/db mice. Db/db mice and heterozygous non-diabetic mice received for 4 weeks regular water or water supplemented with carnosine. Igfbp1 mRNA expression in the liver was evaluated using qPCR and the protein levels in plasma by western blot. Plasma IGF1 and insulin were analyzed using immunoassays. HepG2 cells were used to study the in vitro effect of carnosine on IGFBP1. The modulation of hypoxia inducible factor-1 alpha (HIF-1α) which is the central mediator of hypoxia-induction of IGFBP1 was analyzed using: WB, reporter gene assay and qPCR. Carnosine decreased the circulating IGFBP1 levels and the liver expression Igfbp1, through a complex mechanism acting both directly by suppressing the HIF-1α-mediated IGFBP1 induction and indirectly through increasing circulating insulin level followed by a decrease in the blood glucose levels and increased the plasma levels or IGF1. Reduction of IGFBP1 in diabetes through insulin-dependent and insulin-independent pathways is a novel mechanism by which carnosine contributes to the improvement of the metabolic control in diabetes.

UPF0586 Protein C9orf41 Homolog Is Anserine-producing Methyltransferase

Anserine (β-alanyl-N(Pi)-methyl-L-histidine), a methylated derivative of carnosine (β-alanyl-L-histidine), is an abundant constituent of vertebrate skeletal muscles. Although it has been suggested to serve as a proton buffer and radical scavenger, its physiological function remains mysterious. The formation of anserine is catalyzed by carnosine N-methyltransferase, recently identified in chicken as histamine N-methyltransferase-like (HNMT-like) protein. Although the HNMT-like gene is absent in mammalian genomes, the activity of carnosine N-methyltransferase was reported in most mammalian species. In the present investigation, we purified carnosine N-methyltransferase from rat muscles about 2600-fold. Three polypeptides of ∼ 45, 50, and 70 kDa coeluting with the enzyme activity were identified in the preparation. Mass spectrometry analysis of these polypeptides resulted in the identification of UPF0586 protein C9orf41 homolog as the only meaningful candidate. Rat UPF0586 and its yeast, chicken, and human orthologs were expressed in COS-7 cells and purified to homogeneity. Although all recombinant proteins catalyzed the formation of anserine, as confirmed by chromatographic and mass spectrometry analysis, rat UPF0586 was more active on carnosine than other orthologs. Confocal microscopy of HeLa cells expressing recombinant UPF5086 proteins revealed their presence in both cytosol and nucleus. Carnosine and Gly-His were the best substrates for all UPF0586 orthologs studied, although the enzymes also methylated other l-histidine-containing di- and tripeptides. Finally, cotransfection of COS-7 cells with rat or human UPF0586 and carnosine synthase transformed the cells into efficient anserine producers. We conclude that UPF0586 is mammalian carnosine N-methyltransferase and hypothesize that it may also serve as a peptide or protein methyltransferase in eukaryotes.

The effect of chicken extract on mood, cognition and heart rate variability

Chicken extract, which is rich in anserine and carnosine, has been widely taken in Asian countries as a traditional remedy with various aims, including attenuation of psychological fatigue. The effects of consuming BRAND’S Essence of Chicken (EOC) or a placebo on 46 young adults’ responses to a standard psychological “stressor” were considered. Heart rate variability (HRV), cortisol responses, mood and cognition were measured at baseline and after ten days supplementation. EOC resulted in feeling less anxious, depressed and confused and more agreeable and clearheaded. A decrease in HRV was observed after EOC but only in females. Cognition and cortisol levels were not influenced by EOC. Findings suggest that EOC may be a promising supplement to improve mood in a healthy population.

Carnosinases, their substrates and diseases

Carnosinases are Xaa-His dipeptidases that play diverse functions throughout all kingdoms of life. Human isoforms of carnosinase (CN1 and CN2) under appropriate conditions catalyze the hydrolysis of the dipeptides carnosine (β-alanyl-l-histidine) and homocarnosine (γ-aminobutyryl-l-histidine). Alterations of serum carnosinase (CN1) activity has been associated with several pathological conditions, such as neurological disorders, chronic diseases and cancer. For this reason the use of carnosinase levels as a biomarker in cerebrospinal fluid (CSF) has been questioned. The hydrolysis of imidazole-related dipeptides in prokaryotes and eukaryotes is also catalyzed by aminoacyl-histidine dipeptidases like PepD (EC 3.4.13.3), PepV (EC 3.4.13.19) and anserinase (EC 3.4.13.5). The review deals with the structure and function of this class of enzymes in physiological and pathological conditions. The main substrates of these enzymes, i.e., carnosine, homocarnosine and anserine (β-alanyl-3-methyl-l-histidine) will also be described.

Physiology and pathophysiology of carnosine

Carnosine (β-alanyl-l-histidine) was discovered in 1900 as an abundant non-protein nitrogen-containing compound of meat. The dipeptide is not only found in skeletal muscle, but also in other excitable tissues. Most animals, except humans, also possess a methylated variant of carnosine, either anserine or ophidine/balenine, collectively called the histidine-containing dipeptides. This review aims to decipher the physiological roles of carnosine, based on its biochemical properties. The latter include pH-buffering, metal-ion chelation, and antioxidant capacity as well as the capacity to protect against formation of advanced glycation and lipoxidation end-products. For these reasons, the therapeutic potential of carnosine supplementation has been tested in numerous diseases in which ischemic or oxidative stress are involved. For several pathologies, such as diabetes and its complications, ocular disease, aging, and neurological disorders, promising preclinical and clinical results have been obtained. Also the pathophysiological relevance of serum carnosinase, the enzyme actively degrading carnosine into l-histidine and β-alanine, is discussed. The carnosine system has evolved as a pluripotent solution to a number of homeostatic challenges. l-Histidine, and more specifically its imidazole moiety, appears to be the prime bioactive component, whereas β-alanine is mainly regulating the synthesis of the dipeptide. This paper summarizes a century of scientific exploration on the (patho)physiological role of carnosine and related compounds. However, far more experiments in the fields of physiology and related disciplines (biology, pharmacology, genetics, molecular biology, etc.) are required to gain a full understanding of the function and applications of this intriguing molecule.

Molecular identification of carnosine N-methyltransferase as chicken histamine N-methyltransferase-like protein (hnmt-like)

Anserine (beta-alanyl-N(Pi)-methyl-L-histidine), a naturally occurring derivative of carnosine (beta-alanyl-L-histidine), is an abundant constituent of skeletal muscles and brain of many vertebrates. Although it has long been proposed to serve as a proton buffer, radicals scavenger and transglycating agent, its physiological function remains obscure. The formation of anserine is catalyzed by carnosine N-methyltransferase which exhibits unknown molecular identity. In the present investigation, we have purified carnosine N-methyltransferase from chicken pectoral muscle about 640-fold until three major polypeptides of about 23, 26 and 37 kDa coeluting with the enzyme were identified in the preparation. Mass spectrometry analysis of these polypeptides resulted in an identification of histamine N-methyltransferase-like (HNMT-like) protein as the only meaningful candidate. Analysis of GenBank database records indicated that the hnmt-like gene might be a paralogue of histamine N-methyltransferase gene, while comparison of their protein sequences suggested that HNMT-like protein might have acquired a new activity. Chicken HNMT-like protein was expressed in COS-7 cells, purified to homogeneity, and shown to catalyze the formation of anserine as confirmed by both chromatographic and mass spectrometry analysis. Both specificity and kinetic studies carried out on the native and recombinant enzyme were in agreement with published data. Particularly, several compounds structurally related to carnosine, including histamine and L-histidine, were tested as potential substrates for the enzyme, and carnosine was the only methyl group acceptor. The identification of the gene encoding carnosine N-methyltransferase might be beneficial for estimation of the biological functions of anserine.

Carnosine treatment largely prevents alterations of renal carnosine metabolism in diabetic mice

Recently, we identified an allelic variant of human carnosinase 1 (CN1) that results in increased enzyme activity and is associated with susceptibility for diabetic nephropathy in humans. Investigations in diabetic (db/db) mice showed that carnosine ameliorates glucose metabolism effectively. We now investigated the renal carnosinase metabolism in db/db mice. Kidney CN1 activity increased with age and was significantly higher in diabetic mice compared to controls. Increased CN1 activity did not affect renal carnosine levels, but anserine concentrations were tenfold lower in db/db mice compared to controls (0.24±0.2 vs. 2.28±0.3 nmol/mg protein in controls; p<0.001). Homocarnosine concentrations in kidney tissue were low in both control and db/db mice (below 0.1 nmol/mg protein, p=n.s.). Carnosine treatment for 4 weeks substantially decreased renal CN1 activity in diabetic mice (0.32±0.3 in non-treated db/db vs. 0.05±0.05 μmol/mg/h in treated db/db mice; p<0.01) close to normal activities. Renal anserine concentrations increased significantly (0.24±0.2 in non-treated db/db vs. 5.7±1.2 μmol/mg/h in treated db/db mice; p<0.01), while carnosine concentrations remained unaltered (53±6.4 in non-treated vs. 61±15 nmol/mg protein in treated db/db mice; p=n.s.). Further, carnosine treatment halved proteinuria and reduced vascular permeability to one-fifth in db/db mice. In renal tissue of diabetic mice carnosinase activity is significantly increased and anserine concentrations are significantly reduced compared to controls. Carnosine treatment largely prevents the alterations of renal carnosine metabolism.