Estimation of the carnosine content of different fibre types in the middle gluteal muscle of the thoroughbred horse

Targeted-metabolomic and untargeted-proteomic approaches reveal the effects of muscle fibre type and postmortem ageing on taste-active compounds in beef

The taste of beef is caused by taste-active compounds detected in the mouth during mastication. We hypothesised that the concentration of taste-active compounds in beef is influenced by muscle-fibre-type and postmortem ageing. To test this, and unravel the underlying mechanisms, we investigated the taste-active compounds, and proteomic profiles, in beef masseter [oxidative muscle, all type I fibres) and cutaneous trunci (glycolytic muscle, mostly type II fibres) before and after 14-days postmortem ageing. Our results showed that nucleotides were initially higher and degraded slower in cutaneous trunci (P < 0.05 for both), which could be explained by the profile of nucleotide metabolism enzymes. In contrast, free amino acids were initially higher and increased more in masseter compared to cutaneous trunci (P < 0.05 for all), which might be explained by the profile and activity of proteases in these two muscles. Our results indicate the taste of beef is affected by the muscle-fibre-type and postmortem ageing.

Liquid Chromatography-Mass Spectrometry-Based Metabolomics Reveals Dynamic Metabolite Changes during Early Postmortem Aging of Donkey Meat

BACKGROUND

Metabolic changes in donkey meat during the early postmortem period have not been previously reported.

METHODS

The LC-MS-based metabolomics technique was conducted to understand the metabolic profiles and identify the key metabolites of donkey meat in the first 48 h postmortem.

RESULTS

The pH values showed a decreasing trend followed by an increasing trend. Shear force was the lowest at 4 h and the highest at 24 h (p < 0.05). For the metabolome, some candidate biomarker metabolites were identified, such as adenine, inosine, n-acetylhistidine, citric acid, isocitrate, and malic acid. Predominant metabolic pathways, such as citrate cycle (TCA cycle), alanine, aspartate and glutamate metabolism, and purine metabolism, were affected by aging time. Overabundant n-acetylhistidine was identified in LT, declined at 12 h postmortem aging, and then increased. This may explain the significantly lower pH at 12 h postmortem. Adenine was higher at 4 h postmortem, then declined. Decreased ADP may indicate a fast consumption of ATP and subsequent purine metabolism in donkey meat.

CONCLUSIONS

The results of this study provided new insights into early postmortem aging of donkey meat quality.

Comparison of physiologically functional compounds in Sika deer Cervus nippon meats obtained from different regions in Japan

In Japan, the promotion of effective use of many wild deer as food resource has been conducted. However, they are not necessarily utilized effectively. Thus, we focused physiologically functional compounds to find characteristics of Sika deer meats (commercially available) obtained from different regions such as Hokkaido, Wakayama, Tokushima, and Miyazaki prefectures in Japan, making it a valuable resource for future studies and applications. The amount of carnosine, anserine, and balenine in muscle of deer from Wakayama prefecture was significantly lower than that in muscle of deer from other prefectures. The differences of amount of imidazole dipeptides in different prefectures seems to be caused by feed, rearing environment, and breed. The amount of carnitine in deer meat from Hokkaido was significantly lower than that in muscle of deer from other prefectures, while the amount of acetyl-carnitine in deer meat from Miyazaki prefectures was significantly higher than that from other prefectures. The amounts of glutamine, ornithine, and 3-methylhistidine in muscles of deer from Wakayama prefectures were significantly higher than those in muscle of deer from other prefectures. These results might be caused by differences in feeding habits, habitat, the muscle types, and subspecies of deer obtained from four regions in Japan.

Improving the enzymatic activity of l-amino acid α-ligase for imidazole dipeptide production by site-directed mutagenesis

Imidazole dipeptides, histidine-containing dipeptides, including carnosine (β-alanyl-l-histidine), anserine (β-alanyl-3-methyl-l-histidine), and balenine (β-alanyl-1-methyl-l-histidine) in animal muscles have physiological functions, such as significant antioxidant and antifatigue effects. They are obtained by extraction from natural raw materials, including chicken and fish meat. However, using natural raw materials entails stable supply and mass production limitations. l-amino acid α-ligase (Lal) catalyzes the formation of various dipeptides from unprotected l-amino acids by conjugating with adenosine 5'-triphosphate (ATP) hydrolysis reaction. In this study, site-directed mutagenesis of Lal was applied to establish an efficient method for producing imidazole dipeptides by the enzymatic process. We significantly improved the conversion rate from substrate amino acids compared with wild-type Lal.

Dietary guanidinoacetic acid supplementation improves water holding capacity and lowers free amino acid concentration of fresh meat in finishing pigs fed with various dietary protein levels

The current study was carried out to detect the effect of dietary guanidinoacetic acid (GAA) supplementation on carcass characteristics and meat quality in finishing pigs fed different dietary crude protein (CP) levels. Sixty-four barrows with an initial body weight of 73.05 ± 2.34 kg were randomly allocated into 1 of 4 dietary treatments in a 2 (100% vs. 125% NRC CP level) × 2 (0 vs. 300 mg/kg GAA) factorial arrangement (n = 7). The feeding trial lasted for 49 d. GAA supplementation significantly reduced drip loss (P = 0.01), free water distribution (T₂₃ peak area ratio) (P = 0.05) and the concentrations of free alanine, threonine, methionine and isoleucine (P < 0.05); but increased total glycine content (P = 0.03) in the longissimus dorsi muscle of finishing pigs regardless of the dietary CP levels. Furthermore, primary myogenic cell differentiation system was employed to investigate the influence of inclusion of GAA on free amino acid concentrations in myotubes (n = 4) and validate the finding in the animal feeding trial. We found that GAA inclusion in culture medium also decreased intracellular concentrations of free alanine, threonine, methionine, isoleucine, valine and proline in differentiated primary myogenic cells in vitro (P < 0.05). Meanwhile, relative to diets with 100% NRC CP level, the intake of diets with 125% NRC CP level improved sarcoplasmic protein solubility, increased the contents of carnosine and total free amino acids as well as flavor amino acids in the longissimus dorsi muscle and decreased backfat thickness at the 6–7th ribs in pigs (P < 0.05). In addition, we observed that the impact of dietary GAA supplementation on the last rib fat thickness, shear force, and free lysine content in the longissimus dorsi muscle was dependent on dietary CP levels (P < 0.05). Collectively, dietary GAA supplementation can reduce drip loss, decrease the concentrations of free amino acids and flavor amino acids of fresh meat independent of dietary CP levels.

Metabolomic Signatures Discriminate Horses with Clinical Signs of Atypical Myopathy from Healthy Co-grazing Horses

Atypical myopathy (AM) is a severe rhabdomyolysis syndrome that occurs in grazing horses. Despite the presence of toxins in their blood, all horses from the same pasture are not prone to display clinical signs of AM. The objective of this study was to compare the blood metabolomic profiles of horses with AM clinical signs with those of healthy co-grazing (Co-G) horses. To do so, plasma samples from 5 AM horses and 11 Co-G horses were investigated using untargeted metabolomics. Metabolomic data were evaluated using unsupervised, supervised, and pathway analyses. Unsupervised principal component analysis performed with all detected features separated AM and healthy Co-G horses. Supervised analyses had identified 1276 features showing differential expression between both groups. Among them, 46 metabolites, belonging predominantly to the fatty acid, fatty ester, and amino acid chemical classes, were identified by standard comparison. Fatty acids, unsaturated fatty acids, organic dicarboxylic acids, and fatty esters were detected with higher intensities in AM horses in link with the toxins' pathological mechanism. The main relevant pathways were lipid metabolism; valine, leucine, and isoleucine metabolism; and glycine metabolism. This study revealed characteristic metabolite changes in the plasma of clinically affected horses, which might ultimately help scientists and field veterinarians to detect and manage AM. The raw data of metabolomics are available in the MetaboLights database with the access number MTBLS2579.

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.

Exercise alters and β-alanine combined with exercise augments histidyl dipeptide levels and scavenges lipid peroxidation products in human skeletal muscle

Carnosine and anserine are dipeptides synthesized from histidine and β-alanine by carnosine synthase (ATPGD1). These dipeptides, present in high concentration in the skeletal muscle, form conjugates with lipid peroxidation products such as 4-hydroxy trans-2-nonenal (HNE). Although skeletal muscle levels of these dipeptides could be elevated by feeding β-alanine, it is unclear how these dipeptides and their conjugates are affected by exercise training with or without β-alanine supplementation. We recruited twenty physically active men, who were allocated to either β-alanine or placebo-feeding group matched for VO₂ peak, lactate threshold, and maximal power (W_max). Participants completed 2 weeks of conditioning phase followed by 1 week of exercise testing (CPET) and a single session followed by 6 weeks of high intensity interval training (HIIT). Analysis of muscle biopsies showed that the levels of carnosine and ATPGD1 expression were increased after CPET and decreased following a single session and 6 weeks of HIIT. Expression of ATPGD1 and levels of carnosine were increased upon β-alanine-feeding after CPET, while ATPGD1 expression decreased following a single session of HIIT. The expression of fiber type markers myosin heavy chain (MHC) I and IIa remained unchanged after CPET. Levels of carnosine, anserine, carnosine-HNE, carnosine-propanal and carnosine-propanol were further increased after 9 weeks of β-alanine supplementation and exercise training, but remained unchanged in the placebo-fed group. These results suggest that carnosine levels and ATPGD1 expression fluctuates with different phases of training. Enhancing carnosine levels by β-alanine feeding could facilitate the detoxification of lipid peroxidation products in the human skeletal muscle.

pH buffering of single rat skeletal muscle fibers in the in vivo environment

Homeostasis of intracellular pH (pHi) has a crucial role for the maintenance of cellular function. Several membrane transporters such as lactate/H(+) cotransporter (MCT), Na(+)/H(+) exchange transporter (NHE), and Na(+)/HCO3 (-) cotransporter (NBC) are thought to contribute to pHi regulation. However, the relative importance of each of these membrane transporters to the in vivo recovery from the low pHi condition is unknown. Using an in vivo bioimaging model, we pharmacologically inhibited each transporter separately and all transporters together and then evaluated the pHi recovery profiles following imposition of a discrete H(+) challenge loaded into single muscle fibers by microinjection. The intact spinotrapezius muscle of adult male Wistar rats (n = 72) was exteriorized and loaded with the fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-acetoxymethyl ester (10 μM). A single muscle fiber was then loaded with low-pH solution [piperazine-N,N'-bis(2-ethanesulfonic acid) buffer, pH 6.5, ∼2.33 × 10(-3) μl] by microinjection over 3 s. The rats were divided into groups for the following treatments: 1) no inhibitor (CONT), 2) MCT inhibition (by α-Cyano-4-hydroxyciannamic acid; 4 mM), 3) NHE inhibition (by ethylisopropyl amiloride; 0.5 mM), 4) NBC inhibition (by DIDS; 1 mM), and 5) MCT, NHE, and NBC inhibition (All blockade). The fluorescence ratio (F500 nm/F445 nm) was determined from images captured during 1 min (60 images/min) and at 5, 10, 15, and 20 min after injection. The pHi at 1-2 s after injection significantly decreased from resting pHi (ΔpHi = -0.73 ± 0.03) in CONT. The recovery response profile was biphasic, with an initial rapid and close-to-exponential pHi increase (time constant, τ: 60.0 ± 7.9 s). This initial rapid profile was not affected by any pharmacological blockade but was significantly delayed by carbonic anhydrase inhibition. In contrast, the secondary, more gradual, return toward baseline that restored CONT pHi to 84.2% of baseline was unimpeded by MCT, NHE, and NBC blockade separately but abolished by All blockade (ΔpHi = -0.60 ± 0.07, 72.8% initial pHi, P < 0.05 vs. CONT). After injection of H(+) into, or superfusion onto, an adjacent fiber pHi of the surrounding fibers decreased progressively for the 20-min observation period (∼7.0, P < 0.05 vs. preinjection/superfusion). In conclusion, these results support that, after an imposed H(+) load, the MCT, NHE, and NBC transporters are not involved in the initial rapid phase of pHi recovery. In contrast, the gradual recovery phase was abolished by inhibiting all three membrane transporter systems simultaneously. The alteration of pHi in surrounding fibers suggest that H(+) uptake by neighboring fibers can help alleviate the pH consequences of myocyte H(+) exudation.

Skeletal muscle adaptations and muscle genomics of performance horses

Skeletal muscles in horses are characterised by specific adaptations, which are the result of the natural evolution of the horse as a grazing animal, centuries of selective breeding and the adaptability of this tissue in response to training. These adaptations include an increased muscle mass relative to body weight, a great locomotor efficiency based upon an admirable muscle-tendon architectural design and an adaptable fibre-type composition with intrinsic shortening velocities greater than would be predicted from an animal of comparable body size. Furthermore, equine skeletal muscles have a high mitochondrial volume that permits a higher whole animal aerobic capacity, as well as large intramuscular stores of energy substrates (glycogen in particular). Finally, high buffer and lactate transport capacities preserve muscles against fatigue during anaerobic exercise. Many of these adaptations can improve with training. The publication of the equine genome sequence in 2009 has provided a major advance towards an improved understanding of equine muscle physiology. Equine muscle genomics studies have revealed a number of genes associated with elite physical performance and have also identified changes in structural and metabolic genes following exercise and training. Genes involved in muscle growth, muscle contraction and specific metabolic pathways have been found to be functionally relevant for the early performance evaluation of elite athletic horses. The candidate genes discussed in this review are important for a healthy individual to improve performance. However, muscle performance limiting conditions are widespread in horses and many of these conditions are also genetically influenced.

Comparison of Performance, Meat Lipids and Oxidative Status of Pigs from Commercial Breed and Organic Crossbreed

Simple Summary

In recent years, the development of alternative rearing methods, capable of satisfying requests regarding product quality, yet also taking animal welfare and environmental protection into consideration, is becoming an increasingly important consumer demand. When pigs are reared in free range and organic systems, outdoor access is given to pigs; and such rearing conditions increases energy demand for activity and thermoregulation, which reduces growth rate, but improves some meat quality characteristics, such as leaner meat with lower C14:0 and higher C20:1n9, and oxidative stability.

Abstract

The aim of this research was to determine the effect of rearing systems for pig production, as concerns performance, meat lipid content, the fatty acid profile, histidinic antioxidants, coenzyme Q10, and TBARs. One hundred pigs were assigned to one of three treatments: intensively reared commercial hybrid pig (I), free range commercial hybrid pig (FR) or organically reared crossbred pig (O), according to organic EU Regulations. I pigs showed the best productive performance, but FR and O increased: C20:1n9, Δ9-desaturase (C18) and thioesterase indices in meat. Lipid, dipeptides and CoQ10 appeared correlated to glycolytic and oxidative metabolic pathways. We can conclude that all studied parameters were influenced by the rearing system used, and that differences were particularly evident in the O system, which produced leaner meat with higher oxidative stability. In this respect, the organic pig rearing system promotes and enhances biodiversity, environmental sustainability and food quality.

Changes in endogenous bioactive compounds of Korean native chicken meat at different ages and during cooking

This study aimed to examine the effect of bird age on the contents of endogenous bioactive compounds, including carnosine, anserine, creatine, betaine, and carnitine, in meat from a certified meat-type commercial Korean native chicken strain (KNC; Woorimatdag). Additionally, the effects of the meat type (breast or leg meat) and the state of the meat (raw or cooked) were examined. Cocks of KNC were raised under similar standard commercial conditions at a commercial chicken farm. At various ages (10, 11, 12, 13, and 14 wk), breast and leg meats from a total of 10 birds from each age group were obtained. Raw and cooked meat samples were then prepared separately and analyzed for bioactive compounds. The age of the KNC had a significant effect only on the betaine content. The breast meat of KNC had higher amounts of carnosine and anserine but had lower amounts of betaine and carnitine than the leg meat (P < 0.05). The KNC meat lost significant amounts of all bioactive compounds during cooking (P < 0.05). Leg meat had high retention percentages of carnosine and anserine after cooking, whereas breast meat showed almost complete retention of betaine and carnitine. The results of this study provide useful and rare information regarding the presence, amounts, and determinants of endogenous bioactive compounds in KNC meat, which can be useful for selection and breeding programs, and also for popularizing indigenous chicken meat.

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.

Highly athletic terrestrial mammals: horses and dogs

Evolutionary forces drive beneficial adaptations in response to a complex array of environmental conditions. In contrast, over several millennia, humans have been so enamored by the running/athletic prowess of horses and dogs that they have sculpted their anatomy and physiology based solely upon running speed. Thus, through hundreds of generations, those structural and functional traits crucial for running fast have been optimized. Central among these traits is the capacity to uptake, transport and utilize oxygen at spectacular rates. Moreover, the coupling of the key systems--pulmonary-cardiovascular-muscular is so exquisitely tuned in horses and dogs that oxygen uptake response kinetics evidence little inertia as the animal transitions from rest to exercise. These fast oxygen uptake kinetics minimize Intramyocyte perturbations that can limit exercise tolerance. For the physiologist, study of horses and dogs allows investigation not only of a broader range of oxidative function than available in humans, but explores the very limits of mammalian biological adaptability. Specifically, the unparalleled equine cardiovascular and muscular systems can transport and utilize more oxygen than the lungs can supply. Two consequences of this situation, particularly in the horse, are profound exercise-induced arterial hypoxemia and hypercapnia as well as structural failure of the delicate blood-gas barrier causing pulmonary hemorrhage and, in the extreme, overt epistaxis. This chapter compares and contrasts horses and dogs with humans with respect to the structural and functional features that enable these extraordinary mammals to support their prodigious oxidative and therefore athletic capabilities.

Food restriction and refeeding in lambs influence muscle antioxidant status

Compensatory growth, a frequent phenomenon observed in ruminants due to seasonal variation in food availability, affects protein metabolism including protein oxidation. These oxidation processes may have an impact on animal health as well as on meat protein degradation during post mortem aging (ie meat maturation). Sixteen male lambs were randomly divided into four groups. One group was fed ad libitum (C) and one group was food-restricted to 60% of the intake of the C group (R). The last two groups were restricted similarly to the R group and refed either ad libitum (RAL) or similarly to the C group (pair-feeding) (RPF). Muscles samples were taken immediately after slaughter. The present study showed that the restriction/refeeding pattern had no effect on protein oxidation in the muscles studied (longissimus dorsi (LD), semitendinosus (ST) and supraspinatus (SP)). However, total antioxidant capacity decreased after food restriction (-51%, -43%, P < 0.01 for ST and LD muscles, respectively) and re-increased only after ad libitum refeeding. This alteration in the total antioxidant status can partially be explained by the similar pattern of change observed in the glutathione concentration of the muscles (-25%, P < 0.05 for ST muscle and NS for the other muscles). However, none of the concentrations of other water-soluble antioxidants studied (carnosine, anserine, glutathione peroxidase and superoxide dismutase) were altered during compensatory growth. This study showed that an inappropriate feeding level following a nutritional stress induced alterations in the total antioxidant status (particularly that of glutathione), which may have consequences on animal health. Other consequences of a decrease of the animal antioxidant status in vivo could be an alteration of the protein oxidation processes during meat maturation.

Free amino acids and dipeptides in porcine muscles: differences between `red' and `white' muscles

Three porcine muscles (m. longissimus dorsi, masseter and trapezius), chosen to represent the three main metabolic types, from 18 carcasses had their free amino acids and dipeptides quantified by reverse-phase high performance liquid chromatography (HPLC) in aqueous extracts derivatized with phenyl isothiocyanate. Of the 25 measured compounds, four amino acids and the dipeptide carnosine were closely related to the metabolic type of the three muscles. Masseter, a red oxidative muscle, had the highest contents of aspartic acid, glutamine and taurine. Longissimus dorsi, a white glycolytic muscle was characterised by the highest contents of β-alanine and carnosine. Trapezius, an intermediate muscle, had intermediate contents. These results show that free amino acid and dipeptide contents could partly explain differences in taste of muscles from the same species.

β-alanine supplementation improves isometric endurance of the knee extensor muscles

BACKGROUND

We examined the effect of four weeks of β-alanine supplementation on isometric endurance of the knee extensors at 45% maximal voluntary isometric contraction (MVIC).

METHODS

Thirteen males (age 23 ± 6 y; height 1.80 ± 0.05 m; body mass 81.0 ± 10.5 kg), matched for pre-supplementation isometric endurance, were allocated to either a placebo (n = 6) or β-alanine (n = 7; 6.4 g·d-1 over 4 weeks) supplementation group. Participants completed an isometric knee extension test (IKET) to fatigue, at an intensity of 45% MVIC, before and after supplementation. In addition, two habituation tests were completed in the week prior to the pre-supplementation test and a further practice test was completed in the week prior to the post-supplementation test. MVIC force, IKET hold-time, and impulse generated were recorded.

RESULTS

IKET hold-time increased by 9.7 ± 9.4 s (13.2%) and impulse by 3.7 ± 1.3 kN·s-1 (13.9%) following β-alanine supplementation. These changes were significantly greater than those in the placebo group (IKET: t(11) = 2.9, p ≤0.05; impulse: t(11) = 3.1, p ≤ 0.05). There were no significant changes in MVIC force in either group.

CONCLUSION

Four weeks of β-alanine supplementation at 6.4 g·d-1 improved endurance capacity of the knee extensors at 45% MVIC, which most likely results from improved pH regulation within the muscle cell as a result of elevated muscle carnosine levels.

Purification and identification of a novel primitive secretory enzyme catalyzing the hydrolysis of imidazole-related dipeptides in the jawless vertebrate Lethenteron reissneri

Imidazole-related dipeptides, such as carnosine and anserine, occur widely in skeletal muscles of jawed vertebrates. All of the known enzymes that catalyze the hydrolysis of these dipeptides belong to the M20A metallopeptidase subfamily; two secretory enzymes, serum carnosinase (EC 3.4.13.20) and anserinase (EC 3.4.13.5), and one non-secretory enzyme, cytosolic nonspecific dipeptidase (EC 3.4.13.18). Here we report the enzymatic characterization and molecular identification of an unidentified enzyme, which catalyzes the hydrolysis of these dipeptides, from the skeletal muscle of Far Eastern brook lamprey (Lethenteron reissneri). A 60-kDa subunit protein of the enzyme was purified to near homogeneity. We cloned two M20A genes from the skeletal muscle of Far Eastern brook lamprey; one was a secretory-type gene encoding for the 60-kD protein, and another was a non-secretory-type gene presumably encoding for cytosolic nonspecific dipeptidase. Our findings indicate that the purified enzyme is a N-glycosylated secretory M20A dipeptidase distributed specifically in the jawless vertebrate group, and may be derived from a common ancestor gene between serum carnosinase and anserinase. We propose that this dipeptidase is a novel secretory M20A enzyme and is classified as neither serum carnosinase nor anserinase.

Role of beta-alanine supplementation on muscle carnosine and exercise performance

In this narrative review, we present and discuss the current knowledge available on carnosine and beta-alanine metabolism as well as the effects of beta-alanine supplementation on exercise performance. Intramuscular acidosis has been attributed to be one of the main causes of fatigue during intense exercise. Carnosine has been shown to play a significant role in muscle pH regulation. Carnosine is synthesized in skeletal muscle from the amino acids l-histidine and beta-alanine. The rate-limiting factor of carnosine synthesis is beta-alanine availability. Supplementation with beta-alanine has been shown to increase muscle carnosine content and therefore total muscle buffer capacity, with the potential to elicit improvements in physical performance during high-intensity exercise. Studies on beta-alanine supplementation and exercise performance have demonstrated improvements in performance during multiple bouts of high-intensity exercise and in single bouts of exercise lasting more than 60 s. Similarly, beta-alanine supplementation has been shown to delay the onset of neuromuscular fatigue. Although beta-alanine does not improve maximal strength or VO2max, some aspects of endurance performance, such as anaerobic threshold and time to exhaustion, can be enhanced. Symptoms of paresthesia may be observed if a single dose higher than 800 mg is ingested. The symptoms, however, are transient and related to the increase in plasma concentration. They can be prevented by using controlled release capsules and smaller dosing strategies. No important side effect was related to the use of this amino acid so far. In conclusion, beta-alanine supplementation seems to be a safe nutritional strategy capable of improving high-intensity anaerobic performance.

Effects of beta-alanine on muscle carnosine and exercise performance: a review of the current literature

Muscle carnosine has been reported to serve as a physiological buffer, possess antioxidant properties, influence enzyme regulation, and affect sarcoplasmic reticulum calcium regulation. Beta-alanine (β-ALA) is a non-essential amino acid. β-ALA supplementation (e.g., 2-6 grams/day) has been shown to increase carnosine concentrations in skeletal muscle by 20-80%. Several studies have reported that β-ALA supplementation can increase high-intensity intermittent exercise performance and/or training adaptations. Although the specific mechanism remains to be determined, the ergogenicity of β-ALA has been most commonly attributed to an increased muscle buffering capacity. More recently, researchers have investigated the effects of co-ingesting β-ALA with creatine monohydrate to determine whether there may be synergistic and/or additive benefits. This paper overviews the theoretical rationale and potential ergogenic value of β-ALA supplementation with or without creatine as well as provides future research recommendations.

Beta-alanine supplementation reduces acidosis but not oxygen uptake response during high-intensity cycling exercise

The oral ingestion of beta-alanine, the rate-limiting precursor in carnosine synthesis, has been shown to elevate the muscle carnosine content. Carnosine is thought to act as a physiologically relevant pH buffer during exercise but direct evidence is lacking. Acidosis has been hypothesised to influence oxygen uptake kinetics during high-intensity exercise. The present study aimed to investigate whether oral beta-alanine supplementation could reduce acidosis during high-intensity cycling and thereby affect oxygen uptake kinetics. 14 male physical education students participated in this placebo-controlled, double-blind study. Subjects were supplemented orally for 4 weeks with 4.8 g/day placebo or beta-alanine. Before and after supplementation, subjects performed a 6-min cycling exercise bout at an intensity of 50% of the difference between ventilatory threshold (VT) and VO(2peak). Capillary blood samples were taken for determination of pH, lactate, bicarbonate and base excess, and pulmonary oxygen uptake kinetics were determined with a bi-exponential model fitted to the averaged breath-by-breath data of three repetitions. Exercise-induced acidosis was significantly reduced following beta-alanine supplementation compared to placebo, without affecting blood lactate and bicarbonate concentrations. The time delay of the fast component (Td(1)) of the oxygen uptake kinetics was significantly reduced following beta-alanine supplementation compared to placebo, although this did not reduce oxygen deficit. The parameters of the slow component did not differ between groups. These results indicate that chronic beta-alanine supplementation, which presumably increased muscle carnosine content, can attenuate the fall in blood pH during high-intensity exercise. This may contribute to the ergogenic effect of the supplement found in some exercise modes.

Influence of β-alanine supplementation on skeletal muscle carnosine concentrations and high intensity cycling capacity

Muscle carnosine synthesis is limited by the availability of beta-alanine. Thirteen male subjects were supplemented with beta-alanine (CarnoSyn) for 4 wks, 8 of these for 10 wks. A biopsy of the vastus lateralis was obtained from 6 of the 8 at 0, 4 and 10 wks. Subjects undertook a cycle capacity test to determine total work done (TWD) at 110% (CCT(110%)) of their maximum power (Wmax). Twelve matched subjects received a placebo. Eleven of these completed the CCT(110%) at 0 and 4 wks, and 8, 10 wks. Muscle biopsies were obtained from 5 of the 8 and one additional subject. Muscle carnosine was significantly increased by +58.8% and +80.1% after 4 and 10 wks beta-alanine supplementation. Carnosine, initially 1.71 times higher in type IIa fibres, increased equally in both type I and IIa fibres. No increase was seen in control subjects. Taurine was unchanged by 10 wks of supplementation. 4 wks beta-alanine supplementation resulted in a significant increase in TWD (+13.0%); with a further +3.2% increase at 10 wks. TWD was unchanged at 4 and 10 wks in the control subjects. The increase in TWD with supplementation followed the increase in muscle carnosine.

The absorption of orally supplied β-alanine and its effect on muscle carnosine synthesis in human vastus lateralis

Beta-alanine in blood-plasma when administered as A) histidine dipeptides (equivalent to 40 mg . kg(-1) bwt of beta-alanine) in chicken broth, or B) 10, C) 20 and D) 40 mg . kg(-1) bwt beta-alanine (CarnoSyn, NAI, USA), peaked at 428 +/- SE 66, 47 +/- 13, 374 +/- 68 and 833 +/- 43 microM. Concentrations regained baseline at 2 h. Carnosine was not detected in plasma with A) although traces of this and anserine were found in urine. Loss of beta-alanine in urine with B) to D) was <5%. Plasma taurine was increased by beta-alanine ingestion but this did not result in any increased loss via urine. Pharmacodynamics were further investigated with 3 x B) per day given for 15 d. Dietary supplementation with I) 3.2 and II) 6.4 g . d(-1) beta-alanine (as multiple doses of 400 or 800 mg) or III) L-carnosine (isomolar to II) for 4 w resulted in significant increases in muscle carnosine estimated at 42.1, 64.2 and 65.8%.

Profiling histidine-containing dipeptides in rat tissues by liquid chromatography/electrospray ionization tandem mass spectrometry

The histidine-containing dipeptides carnosine (CAR) and structurally related anserine (ANS) and homocarnosine (HCAR), widely distributed in vertebrate organisms, have recently been proposed as endogenous quenchers for highly cytotoxic alpha,beta-unsaturated aldehydes generated by peroxidation. A sensitive, selective, specific and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric assay was developed and validated for the simultaneous determination of these peptides in biological matrices in order to establish their plasma/tissue distribution. Samples (plasma or tissue homogenates from male rats) were prepared by protein precipitation with HClO(4) (1 : 1, v/v) containing H-Tyr-His-OH as internal standard. The supernatant was separated on a Phenomenex Sinergy polar-RP column with a mobile phase of water-acetonitrile-heptafluorobutyric acid (9 : 1 : 0.01, v/v/v) at a flow-rate of 0.2 ml min(-1), with a run time of 10 min. Detection was effected on an ion trap mass spectrometer equipped with an electrospray ionization interface operating in positive ionization mode. The acquisitions were in the multiple reaction monitoring mode using the following precursor --> product ion combinations: H-Tyr-His-OH (internal standard) m/z 319 --> 301; CAR m/z 227 --> 210 + 209; ANS m/z 241 --> 224 + 197 + 170; HCAR m/z 241 --> 156. The method was validated over the concentration range 15-1000 nmol g(-1) and the limit of quantification (LOQ) and limit of detection (LOD) were 12.5 and 4.2 pmol injected, respectively. The intra- and inter-day precisions were <10% (< or =17.47% at the LOQ) and the intra- and inter-assay accuracies were within +/-10% for all concentrations. The mapping profile in rat tissue gave the following results: the highest concentrations of CAR and ANS were found in skeletal muscles (soleus, gastrocnemius, tibialis), followed by the heart, cerebellum and brain (ANS below the LOQ). HCAR was found only in the brain and cerebellum. No histidine-containing dipeptides were detectable in plasma, liver, kidney and lung.

High level of skeletal muscle carnosine contributes to the latter half of exercise performance during 30-s maximal cycle ergometer sprinting

The histidine-containing dipeptide carnosine (beta-alanyl-L-histidine) has been shown to significantly contribute to the physicochemical buffering in skeletal muscles, which maintains acid-base balance when a large quantity of H(+) is produced in association with lactic acid accumulation during high-intensity exercise. The purpose of the present study was to examine the relations among the skeletal muscle carnosine concentration, fiber-type distribution, and high-intensity exercise performance. The subjects were 11 healthy men. Muscle biopsy samples were taken from the vastus lateralis at rest. The carnosine concentration was determined by the use of an amino acid autoanalyzer. The fiber-type distribution was determined by the staining intensity of myosin adenosinetriphosphatase. The high-intensity exercise performance was assessed by the use of 30-s maximal cycle ergometer sprinting. A significant correlation was demonstrated between the carnosine concentration and the type IIX fiber composition (r=0.646, p<0.05). The carnosine concentration was significantly correlated with the mean power per body mass (r=0.785, p<0.01) during the 30-s sprinting. When dividing the sprinting into 6 phases (0-5, 6-10, 11-15, 16-20, 21-25, 26-30 s), significant correlations were observed between the carnosine concentration and the mean power per body mass of the final 2 phases (21-25 s: r=0.694, p<0.05; 26-30 s: r=0.660, p<0.05). These results indicated that the carnosine concentration could be an important factor in determining the high-intensity exercise performance.

High levels of dietary carnosine are associated with increased concentrations of carnosine and histidine in rat soleus muscle

The aims of this investigation were to: 1) determine the effect of a moderately high dose of carnosine on muscle concentrations of carnosine, histidine and vitamin E at deficient, minimally adequate and sufficient levels of dietary vitamin E and 2) compare the effects of moderately high and pharmacological doses of carnosine on muscle concentrations of carnosine, histidine and vitamin E when dietary vitamin E is minimally adequate. Muscle concentrations of carnosine, histidine and vitamin E were measured in the lateral gastrocnemius and red and white vastus lateralis; carnosine and histidine concentrations were also measured in soleus muscle. Male Sprague-Dawley rats (n = 12/group) were fed a basal vitamin E-deficient diet supplemented with either 0, 0.001 or 0.01% vitamin E and 0, 0.1 or 1.8% carnosine. After 8 wk, 1.8% carnosine resulted in significant fivefold increases in carnosine and twofold increases in histidine in the soleus muscle (P < or = 0.05). Muscle vitamin E concentrations were not significantly affected by dietary carnosine. Thus, very high levels of dietary carnosine are associated with increases in carnosine and histidine concentrations in rat soleus muscle.

The influence of muscle fiber size and type distribution on electromyographic measures of back muscle fatigability

STUDY DESIGN

This was a cross-sectional study carried out on a group of 31 healthy, consenting volunteers with no history of low back pain (17 men, 14 women).

OBJECTIVES

To evaluate the relationship between electromyographic measures of erector spinae fatigability and the muscle's fiber type characteristics.

SUMMARY OF BACKGROUND DATA

Using electromyographic techniques, a pronounced fatigability of the muscles of patients with low back pain has been identified. It has been postulated that this is the result of an unfavorable back muscle fiber type distribution, although an association between electromyographic measures of fatigue and the muscle's fiber type characteristics has never been established.

METHODS

Two tests of back extensor fatigability were performed (on separate days), each to the limit of endurance: 1) maintenance of 60% total maximum voluntary contraction of the back extensors, and 2) performance of the Biering-Sørensen test. Pairs of surface electrodes were attached to the skin overlying the belly of the erector spinae, bilaterally, at T10 and L3. The median frequency was computed from the electromyographic power spectrum, and fatigability was given by the slope of the linear regression of median frequency on time (MFgrad; %.s-1). One week later, two percutaneous erector spinae muscle biopsy samples were obtained from the same sites described for electromyography (left side only). Samples were prepared for histochemistry for the identification of muscle fiber types. Fiber sizes (cross-sectional areas) were quantified using computerized image analysis.

RESULTS

The mean fiber size at each erector spinae region showed a significant correlation with maximum back extensor strength. In the thoracic region, the relative area of the muscle occupied by Type I fibers (which accounts for the relative size and distribution of the fiber types) showed a significant relationship with MFgrad recorded during each fatigue test. A similar relationship was observed for the lumbar region, but for the Biering-Sørensen test only.

CONCLUSIONS

The electromyographic changes recorded in back muscles during fatigue appear to be related to the underlying muscle fiber type area distribution. This confirms the usefulness of electromyography in reflecting such muscle characteristics in a noninvasive manner, when monitoring changes in function consequent to the development of, or rehabilitation from, low back pain.

Carnosine, anserine and taurine contents in individual fibres from the middle gluteal muscle of the camel

High muscle carnosine und anserine contents contribute significantly to intra-cellular physico-chemical buffering. Our aim was to measure carnosine, anserine and taurine contents directly in individual type I, IIA and IIB fibres from the middle gluteus muscle of the camel. Mean carnosine contents in type I, IIA and IIB were 24.6 +/- 9.2, 39.4 +/- 11.4 and 42.8 +/- 18.8 mmol kg-1 dry weight (dw), respectively. Mean anserine contents in type I, IIA and IIB fibres were 30.0 +/- 8.4, 37.3 +/- 10.1 and 34.5 +/- 9.7 mmol kg-1 dw, respectively. Mean taurine contents in type I, IIA and IIB fibres were 42.4 +/- 15.9, 20.3 +/- 12.9 and 24.7 +/- 15.9 mmol kg-1 dw, respectively. Higher carnosine contents in type II fibres emphasise the importance of carnosine to intra-muscular acid-base regulation. A specific role for taurine in type I fibres in unclear.

High-performance liquid chromatographic determination of imidazole dipeptides, histidine, 1-methylhistidine and 3-methylhistidine in equine and camel muscle and individual muscle fibres

The combined solid-phase extraction (Isolute PRS columns) and reversed-phase gradient HPLC method presented provides a sensitive, reproducible and selective quantification of carnosine, balenine, homocarnosine, histidine, 1-methylhistidine and 3-methylhistidine in equine and camel muscle and individual muscle fibres. Recoveries were 91-115%. Lower limits of detection were 0.005-0.010 mmol kg-1 dry muscle. The compounds were isolated from other physiological amino acids and small peptides and resolved within a single chromatographic run of 55 min. Concentrations of these compounds in equine myocardium, diaphragm, skeletal muscle, camel muscle and individual muscle fibres of both species are presented for the first time.

High-performance liquid chromatographic determination of N-alpha-acetyl-L-carnosine in equine plasma

N-alpha-Acetyl-L-carnosine (NAcCAR) in perchloric acid extracts of equine plasma was assayed by high-performance liquid chromatography on a 3 microns Hypersil ODS (150 x 4.6 mm I.D.) column eluted with 5 mM phosphoric acid-1 mM triethylamine, pH 2.58. NAcCAR was isolated by solid-phase extraction on Isolute PRS (propylsulphonyl) columns. The HPLC mean retention time for NAcCAR was 5.9 +/- 0.2 min. The recovery from plasma by solid-phase extraction was 93.9-99.7% and lower limit of detection in plasma was 0.18 microM. The normal NAcCAR concentration in equine plasma was 2.4 +/- 0.3 microM. The method was applied to the determination of plasma concentrations following oral and intravenous NAcCAR administration.

Skeletal muscle characteristics in 2 year-old race-trained thoroughbred horses

Skeletal muscle samples were obtained by needle biopsy from two depths of the m. gluteus medius of 50, young race-trained thoroughbred racehorses. Histochemical and biochemical characteristics of the muscle samples were analysed. Fibres were classified as type I, type IIa or type IIb on the basis of the pH dependent lability of the myosin ATPase reaction. The activities of citrate synthase (CS) and glycogen phosphorylase (Phos) were determined. Muscle fibre composition varied markedly between deep and superficial muscle samples and this was reflected in differences in the activities of citrate synthase (CS) and phosphorylase (Phos). CS activity was greater in samples taken from a depth of 90 mm (deep) than those taken from a depth of 40 mm (superficial: 122 +/- 19 compared with 88 +/- 16 mumol/g dry muscle/min at 25 degrees C). Phos activity was greater in superficial samples (137 +/- 20) compared with deep samples (117 +/- 21). Regression analysis was used to estimate the enzyme activities in the different fibre types. No significant correlations were observed between histochemical and biochemical measures and subsequent racing performance.