Characterization of a new L-carnosine synthase mined from deep-sea sediment metagenome.

L-Carnosine is a natural biologically active dipeptide with critical physiological functions, such as antioxidant, antiglycation, and cytoplasmic buffering properties. Direct enzymatic synthesis is a promising way for L-carnosine production. In this study, a new aminopeptidase (gene_236976) with synthetic activity toward L-carnosine was identified by a metagenome mining approach from deep-sea sediment and functionally expressed in Escherichia coli. The enzyme shared a low identity of 14.3% with reported L-carnosine dipeptidase (SmPepD) from Serratia marcescens. ß-Alanine methyl ester was proven to be the best substrate for the synthesis, and no ATP was needed for the enzymatic reaction. The enzyme activity was increased by structure-guided rational design. Only the mutant of G310 site gave positive results, and G310A mutant showed the best performance among the site-direct saturation mutagenesis, indicating that the additional CH3 group of mutant G310A was the main factor affecting the enzymatic activity. The engineered enzyme produced about 10 mM L-carnosine was produced from substrates of 50 mM ß-alanine methyl ester and 50 mM L-histidine, under a tentatively optimized condition. This study enriched the enzyme resources for developing the microbial synthesis process of L-carnosine production.

Novel Relationship Between Plasmalogen Lipid Signatures and Carnosine in Humans.

INTRODUCTION: Carnosine is a naturally occurring dipeptide abundant in the skeletal and cardiac muscle and brain, which has been shown to improve glucose metabolism and cardiovascular risk. This study showed that carnosine supplementation had positive changes on plasma lipidome. Here, this study aimed to establish the relationship of muscle carnosine and serum carnosinase-1 with cardiometabolic risk factors and the lipidome. METHODS AND RESULTS: This study profiles >450 lipid species in 65 overweight/obese nondiabetic individuals. Intensive metabolic testing is conducted using direct gold-standard measures of adiposity, insulin sensitivity and secretion, as well as measurement of serum inflammatory cytokines and adipokines. Muscle carnosine is negatively associated with 2-h glucose concentrations, whereas serum carnosinase-1 levels are negatively associated with insulin sensitivity and positively with IL-18. O-PLS and machine learning analyses reveal a strong association of muscle carnosine with ether lipids, particularly arachidonic acid-containing plasmalogens. Carnosinase-1 levels are positively associated with total phosphatidylethanolamines, but negatively with lysoalkylphosphatidylcholines, trihexosylceramides, and gangliosides. In particular, alkylphosphatidylethanolamine species containing arachidonic acid are positively associated with carnosinase-1. CONCLUSION: These associations reinforce the role of muscle carnosine and serum carnosinase-1 in the interplay among low-grade chronic inflammation, glucose homeostasis, and insulin sensitivity.

Carnosine in health and disease.

Carnosine was originally discovered in skeletal muscle, where it exists in larger amounts than in other tissues. The majority of research into the physiological roles of carnosine have been conducted on skeletal muscle. Given this and the potential for muscle carnosine content to be increased with supplementation, there is now a large body of research examining the ergogenic effects (or otherwise) of carnosine. More recent research, however, points towards a potential for carnosine to exert a wider range of physiological effects in other tissues, including the brain, heart, pancreas, kidney and cancer cells. Taken together, this is suggestive of a potential for carnosine to have therapeutic benefits in health and disease, although this is by no means without complication. Herein, we will provide a review of the current literature relating to the potential therapeutic effects of carnosine in health and disease.

The biological role of carnosine and its possible applications in medicine.

The article reviews current literature on the biological role of carnosine, its properties and use as a supplement in periods of intense physical activity. Studies carried out on laboratory animals and humans have shown that carnosine can have a beneficial influence on the organism. Carnosine is found naturally mainly in the skeletal muscles, central nervous system, olfactory neurons and in the lens of the eye in some vertebrates, including humans. Due to its antioxidant, protective, chelating, anti-glycation activity, this dipeptide can be used to prevent and treat diseases such as diabetes, neurodegenerative diseases, diseases of the sense organs and cancers. It may also cure or alleviate many other disorders thanks to its wide spectrum of activity. Carnosine is already used by athletes to achieve better results, due to its buffering feature, which contributes to the maintenance of the acid-base balance in the muscles. Future studies on the influence of carnosine on the human organism may lead to the therapeutic use of this dipeptide for many diseases, in addition to improving both amateur and professional athletes' results.

Physiology and pathophysiology of carnosine.

Carnosine (ß-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 ß-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 ß-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.

Β-alanine and l-histidine transport across the inner blood-retinal barrier: potential involvement in L-carnosine supply.

The supply of L-carnosine, a bioactive dipeptide of ß-alanine and l-histidine, to the retina across the blood-retinal barrier (BRB) was studied. The in vivo and in vitro studies revealed low uptake activities for [(3)H]Gly-Sar, a representative dipeptide, suggesting that l-carnosine transport plays only a minor role at the BRB. The in vivo study using rats showed approximately 18- and 23-fold greater retinal uptake indexes (RUI) for [(3)H]ß-alanine and [(3)H]l-histidine compared with that of a paracellular marker, respectively. The RUI of [(3)H]ß-alanine was taurine- and γ-aminobutyric acid-sensitive, and the in vitro uptake by TR-iBRB2 cells showed time- concentration- and temperature-dependent [(3)H]ß-alanine uptake, suggesting that a carrier-mediated process was involved in ß-alanine transport across the inner BRB. [(3)H]ß-Alanine uptake was inhibited by taurine and ß-guanidinopropionic acid, suggesting that taurine transporter (TAUT/SLC6A6) is responsible for the influx transport of ß-alanine across the inner BRB. Regarding l-histidine, the l-leucine-sensitive RUI of [(3)H]l-histidine was identified, and the in vitro [(3)H]l-histidine uptake by TR-iBRB2 cells suggested that a carrier-mediated process was involved in l-histidine transport across the inner BRB. The inhibition profile suggested that L-type amino acid transporter (LAT1/SLC7A5) is responsible for the influx transport of l-histidine across the inner BRB. These results show that the influx transports of ß-alanine and l-histidine across the inner BRB is carried out by TAUT and LAT1, respectively, suggesting that the retinal l-carnosine is supplied by enzymatic synthesis from two kinds of amino acids transported across the inner BRB.

Carnosine: from exercise performance to health.

Carnosine was first discovered in skeletal muscle, where its concentration is higher than in any other tissue. This, along with an understanding of its role as an intracellular pH buffer has made it a dipeptide of interest for the athletic population with its potential to increase high-intensity exercise performance and capacity. The ability to increase muscle carnosine levels via ß-alanine supplementation has spawned a new area of research into its use as an ergogenic aid. The current evidence base relating to the use of ß-alanine as an ergogenic aid is reviewed here, alongside our current thoughts on the potential mechanism(s) to support any effect. There is also some emerging evidence for a potential therapeutic role for carnosine, with this potential being, at least theoretically, shown in ageing, neurological diseases, diabetes and cancer. The currently available evidence to support this potential therapeutic role is also reviewed here, as are the potential limitations of its use for these purposes, which mainly focusses on issues surrounding carnosine bioavailability.

L-carnosine inhibits high-glucose-mediated matrix accumulation in human mesangial cells by interfering with TGF-ß production and signalling.

BACKGROUND: Transforming growth factor beta is recognized as a major cytokine in extracellular matrix (ECM) pathobiology as occurs in diabetic nephropathy. While experimental studies have advanced a protective role of carnosine for diabetic complications, a link between carnosine, TGF-ß and matrix accumulation remains to be elucidated. In the present study, we tested the hypothesis that L-carnosine inhibits TGF-ß production and signalling, thereby reducing hyperglycaemia-associated ECM accumulation. METHODS: Human mesangial cells (MC) were cultured in high-glucose (HG, 25 mM D-glucose) medium alone or in HG medium to which 20 mM L-carnosine was added. Collagen VI (Col6) and fibronectin (FN) deposition and messenger RNA expression were studied. In addition, TGF-ß production and activation of Smad1/5/8 (ALK1) and Smad2/3 (ALK5) pathways were assessed. RESULTS: Under HG conditions, deposition of Col6 and FN were increased 1.4- and 1.6-fold. This was significantly inhibited on the protein and messenger RNA level by L-carnosine. TGF-ß production increased under HG conditions but was completely normalized by addition of L-carnosine. Addition of exogenous TGF-ß could not overcome the effect of L-carnosine on Col6 and FN expression, indicating additionally interference with TGF-ß downstream signalling. Along the same line, L-carnosine reduced TGF-ß-mediated Smad2 phosphorylation, suggesting an inhibitory effect on ALK5 signalling. ALK1 signalling remained unchanged. Under HG conditions, pharmacologic inhibition of ALK5 prevented Col6 accumulation but did not change FN deposition. CONCLUSIONS: L-carnosine can modulate matrix accumulation in two ways. Firstly, inhibition of TGF-ß production might result in an overall inhibition of matrix accumulation and secondly, L-carnosine inhibits TGF-ß-induced matrix accumulation, most likely via inhibition of the ALK5 pathway.

Effects of sprint training combined with vegetarian or mixed diet on muscle carnosine content and buffering capacity.

Carnosine is an abundant dipeptide in human skeletal muscle with proton buffering capacity. There is controversy as to whether training can increase muscle carnosine and thereby provide a mechanism for increased buffering capacity. This study investigated the effects of 5 weeks sprint training combined with a vegetarian or mixed diet on muscle carnosine, carnosine synthase mRNA expression and muscle buffering capacity. Twenty omnivorous subjects participated in a 5 week sprint training intervention (2-3 times per week). They were randomized into a vegetarian and mixed diet group. Measurements (before and after the intervention period) included carnosine content in soleus, gastrocnemius lateralis and tibialis anterior by proton magnetic resonance spectroscopy ((1)H-MRS), true-cut biopsy of the gastrocnemius lateralis to determine in vitro non-bicarbonate muscle buffering capacity, carnosine content (HPLC method) and carnosine synthase (CARNS) mRNA expression and 6 × 6 s repeated sprint ability (RSA) test. There was a significant diet × training interaction in soleus carnosine content, which was non-significantly increased (+11%) with mixed diet and non-significantly decreased (-9%) with vegetarian diet. Carnosine content in other muscles and gastrocnemius buffer capacity were not influenced by training. CARNS mRNA expression was independent of training, but decreased significantly in the vegetarian group. The performance during the RSA test improved by training, without difference between groups. We found a positive correlation (r = 0.517; p = 0.002) between an invasive and non-invasive method for muscle carnosine quantification. In conclusion, this study shows that 5 weeks sprint training has no effect on the muscle carnosine content and carnosine synthase mRNA.

Effect of beta-alanine supplementation on muscle carnosine concentrations and exercise performance.

High-intensity exercise results in reduced substrate levels and accumulation of metabolites in the skeletal muscle. The accumulation of these metabolites (e.g. ADP, Pi and H(+)) can have deleterious effects on skeletal muscle function and force generation, thus contributing to fatigue. Clearly this is a challenge to sport and exercise performance and, as such, any intervention capable of reducing the negative impact of these metabolites would be of use. Carnosine (beta-alanyl-L-histidine) is a cytoplasmic dipeptide found in high concentrations in the skeletal muscle of both vertebrates and non-vertebrates and is formed by bonding histidine and beta-alanine in a reaction catalysed by carnosine synthase. Due to the pKa of its imidazole ring (6.83) and its location within skeletal muscle, carnosine has a key role to play in intracellular pH buffering over the physiological pH range, although other physiological roles for carnosine have also been suggested. The concentration of histidine in muscle and plasma is high relative to its K (m) with muscle carnosine synthase, whereas beta-alanine exists in low concentration in muscle and has a higher K (m) with muscle carnosine synthase, which indicates that it is the availability of beta-alanine that is limiting to the synthesis of carnosine in skeletal muscle. Thus, the elevation of muscle carnosine concentrations through the dietary intake of carnosine, or chemically related dipeptides that release beta-alanine on absorption, or supplementation with beta-alanine directly could provide a method of increasing intracellular buffering capacity during exercise, which could provide a means of increasing high-intensity exercise capacity and performance. This paper reviews the available evidence relating to the effects of beta-alanine supplementation on muscle carnosine synthesis and the subsequent effects on exercise performance. In addition, the effects of training, with or without beta-alanine supplementation, on muscle carnosine concentrations are also reviewed.

Molecular mechanisms of homocysteine toxicity.

Hyperhomocysteinemia is a risk factor for a number of cardiovascular and neurodegenerative processes as well as a complicating factor in normal pregnancy. Toxic effects of homocysteine and the product of its spontaneous oxidation, homocysteic acid, are based on their ability to activate NMDA receptors, increasing intracellular levels of ionized calcium and reactive oxygen species. Even a short-term exposure of cells to homocysteic acid at concentrations characteristic of hyperhomocysteinemia induces their apoptotic transformation. The discovery of NMDA receptors both in neuronal tissue and in several other tissues and organs (including immunocompetent cells) makes them a target for toxic action of homocysteine. The neuropeptide carnosine was found to protect the organism from homocysteine toxicity. Treatment of pregnant rats with carnosine under conditions of alimentary hyperhomocysteinemia increases viability and functional activity of their progeny.

Carnosine and its possible roles in nutrition and health.

The dipeptide carnosine has been observed to exert antiaging activity at cellular and whole animal levels. This review discusses the possible mechanisms by which carnosine may exert antiaging action and considers whether the dipeptide could be beneficial to humans. Carnosine's possible biological activities include scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS), chelator of zinc and copper ions, and antiglycating and anticross-linking activities. Carnosine's ability to react with deleterious aldehydes such as malondialdehyde, methylglyoxal, hydroxynonenal, and acetaldehyde may also contribute to its protective functions. Physiologically carnosine may help to suppress some secondary complications of diabetes, and the deleterious consequences of ischemic-reperfusion injury, most likely due to antioxidation and carbonyl-scavenging functions. Other, and much more speculative, possible functions of carnosine considered include transglutaminase inhibition, stimulation of proteolysis mediated via effects on proteasome activity or induction of protease and stress-protein gene expression, upregulation of corticosteroid synthesis, stimulation of protein repair, and effects on ADP-ribose metabolism associated with sirtuin and poly-ADP-ribose polymerase (PARP) activities. Evidence for carnosine's possible protective action against secondary diabetic complications, neurodegeneration, cancer, and other age-related pathologies is briefly discussed.

Effects of carnosine on long-term plasticity of medial perforant pathway/dentate gyrus synapses in urethane-anesthetized rats: an in vivo model.

The objective of this study was to examine the effect of carnosine on the hippocampal-dependent learning in perforant pathway/dentate gyrus synapses. The experiments were carried out on adult rats. A bipolar stimulating electrode was placed to the medial perforant path and a double-barrel glass micropipette was placed in the dentate gyrus as the recording electrode. Artificial cerebrospinal fluid (to control group) or carnosine (0.1, 1 microg/microL) was infused into the dentate gyrus via one of the barrels of the glass electrode. Our results showed that the I/O curve of excitatory postsynaptic potential (EPSP) slope or population spike (PS) amplitude was not significantly shifted by carnosine. Although carnosine infused prior to high-frequency stimulation (HFS) decreased the slope of EPSP and amplitude of PS, when infused after HFS, no effect was observed. In the present study, we speculated that carnosine decreased LTP by inhibiting sGC activation. The present experiment provides the first evidence that carnosine may play a role in synaptic plasticity in dentate gyrus in vivo.

Screening of dipeptides having central functions for excitation and sedation.

The naturally-occurring dipeptide carnosine (beta-alanyl-L-histidine) and the tripeptide glutathione (L-gammaglutamyl-L-cysteinylglycine) are found extensively in animal tissues such as brain and skeletal muscle. Central functions for excitation and sedation of them and their derivatives were screened.

On the enigma of carnosine's anti-ageing actions.

Carnosine (beta-alanyl-L-histidine) has described as a forgotten and enigmatic dipeptide. Carnosine's enigma is particularly exemplified by its apparent anti-ageing actions; it suppresses cultured human fibroblast senescence and delays ageing in senescence-accelerated mice and Drosophila, but the mechanisms responsible remain uncertain. In addition to carnosine's well-documented anti-oxidant, anti-glycating, aldehyde-scavenging and toxic metal-ion chelating properties, its ability to influence the metabolism of altered polypeptides, whose accumulation characterises the senescent phenotype, should also be considered. When added to cultured cells, carnosine was found in a recent study to suppress phosphorylation of the translational initiation factor eIF4E resulting in decreased translation frequency of certain mRNA species. Mutations in the gene coding for eIF4E in nematodes extend organism lifespan, hence carnosine's anti-ageing effects may be a consequence of decreased error-protein synthesis which in turn lowers formation of protein carbonyls and increases protease availability for degradation of polypeptides altered postsynthetically. Other studies have revealed carnosine-induced upregulation of stress protein expression and nitric oxide synthesis, both of which may stimulate proteasomal elimination of altered proteins. Some anti-convulsants can enhance nematode longevity and suppress the effects of a protein repair defect in mice, and as carnosine exerts anti-convulsant effects in rodents, it is speculated that the dipeptide may participate in the repair of protein isoaspartyl groups. These new observations only add to the enigma of carnosine's real in vivo functions. More experimentation is clearly required.

Inhibitory effect of carnosine on interleukin-8 production in intestinal epithelial cells through translational regulation.

The enhanced intestinal production of pro-inflammatory cytokines leads to inflammation and carcinogenesis, and therefore its down-regulation by nutrients could represent a promising therapeutic approach. We found for the first time that the secretion of interleukin-8 (IL-8) in intestinal epithelial cells stimulated by hydrogen peroxide or TNF-alpha was suppressed in the presence of carnosine (beta-Ala-His), a dietary dipeptide. Interestingly, carnosine had no influence on the stimulus-induced IL-8 mRNA expression, although the intracellular production and secretion of IL-8 were significantly inhibited by carnosine. The inhibitory effect of carnosine on the IL-8 secretion differed from that of other histidine-containing dipeptides like Gly-His, Ala-His, and anserine (beta-Ala-1-methyl-His), which inhibited both the hydrogen peroxide-induced secretion and mRNA expression of IL-8. These observations indicate that carnosine inhibited IL-8 secretion along a unique pathway, in which IL-8 production was suppressed at a post-transcriptional level, for instance, translation. The hypothesis that carnosine inhibited the translation of IL-8 mRNA is supported by the finding that the phosphorylation of eIF4E, an initiation factor, in stimulated Caco-2 cells was inhibited by carnosine. These results suggest that carnosine is a novel type of anti-inflammatory agent that down-regulates the inflammatory response in intestinal epithelial cells by a unique mechanism.

[Carnosine: endogenous physiological corrector of antioxidative system activity].

The results of research of camosine as an antioxidative system corrector in conditions of oxidative stress caused by the action of damaging factors (y-rays, overcooling, hypobaric hypoxia, brain ischemia, neurotoxin impact) are summarized in the present review. The effects of carnosine are characterized not only at the level of the whole organism but also in "in vitro" models with use of a whole series of enzymatic systems. The results of the experiments conducted displayed the ability of carnosine to protect animals from oxidative stress based on the combination of direct antioxidative effects and a modulation of enzymes' activities which participate in controlling of reactive oxygen species level in tissues.

Could carnosine or related structures suppress Alzheimer's disease?

Reactive oxygen species, reactive nitrogen species, copper and zinc ions, glycating agents and reactive aldehydes, protein cross-linking and proteolytic dysfunction may all contribute to Alzheimer's disease (AD). Carnosine (beta-alanyl-L-histidine) is a naturally-occurring, pluripotent, homeostatic agent. The olfactory lobe is normally enriched in carnosine and zinc. Loss of olfactory function and oxidative damage to olfactory tissue are early symptoms of AD. Amyloid peptide aggregates in AD brain are enriched in zinc ions. Carnosine can chelate zinc ions. Protein oxidation and glycation are integral components of the AD pathophysiology. Carnosine can suppress amyloid-beta peptide toxicity, inhibit production of oxygen free-radicals, scavenge hydroxyl radicals and reactive aldehydes, and suppresses protein glycation. Glycated protein accumulates in the cerebrospinal fluid (CSF) of AD patients. Homocarnosine levels in human CSF dramatically decline with age. CSF composition and turnover is controlled by the choroid plexus which possesses a specific transporter for carnosine and homocarnosine. Carnosine reacts with protein carbonyls and suppress the reactivity of glycated proteins. Carbonic anhydrase (CA) activity is diminished in AD patient brains. Administration of CA activators improves learning in animals. Carnosine is a CA activator. Protein cross-links (gamma-glutamyl-epsilon-amino) are present in neurofibrillary tangles in AD brain. gamma-Glutamyl-carnosine has been isolated from biological tissue. Carnosine stimulates vimentin expression in cultured human fibroblasts. The protease oxidised-protein-hydrolase is co-expressed with vimentin. Carnosine stimulates proteolysis in cultured myocytes and senescent cultured fibroblasts. These observations suggest that carnosine and related structures should be explored for therapeutic potential towards AD and other neurodegenerative disorders.

A leucine repeat in the carnosinase gene CNDP1 is associated with diabetic end-stage renal disease in European Americans.

BACKGROUND: Four linkage analyses have identified a region on chromosome 18q22-23 that appears to harbour a diabetic nephropathy (DN) susceptibility locus. A trinucleotide repeat sequence in exon 2 of the carnosinase gene (CNDP1) residing on 18q22.3 was subsequently associated with DN in European Caucasians and Arabs. METHODS: We evaluated the role of the CNDP1 5 leucine/5 leucine (5-5) polymorphism (CNDP1 Mannheim) in diabetic end-stage renal disease (ESRD) susceptibility in 858 European Americans: 294 with type 2 DN-associated ESRD (DN-ESRD), 258 with diabetes mellitus (DM) lacking nephropathy and 306 healthy controls. RESULTS: Subjects with DM lacking nephropathy were significantly more likely to be homozygous for the 5-leucine repeat CNDP1 genotype (5-5), compared with those with DN-ESRD (P=0.02). Healthy controls were also more likely to be homozygous for the 5-5 genotype, compared with those with DN-ESRD (P=0.008). No significant difference in 5-5 genotype frequency was observed between healthy controls and DM cases without nephropathy (P=0.74). CONCLUSION: European Americans homozygous for the 5-5 leucine repeat polymorphism in the CNDP1 gene are at significantly reduced risk for developing diabetic ESRD. This replicates the CNDP1 gene association with DN that was initially detected in European Caucasians and in Arabs, and further demonstrates that the CNDP1 gene and carnosine pathway appear to play a role in susceptibility to DN.