Major buffering constituents in animal muscle

A comprehensive review on physiological and biological activities of carnosine: turning from preclinical facts to potential clinical applications

Carnosine, a compound with plethora of benefits, was originally discovered in 1900 and is formed by the amide linkage of β-alanine and L-histidine. Carnosine production is limited by β-alanine whereas the imidazole ring of histidine moiety makes it a suitable buffer in physiological pH range. It is reported to be found in the skeletal muscle, brain, heart, and gastrointestinal tissues of humans. This review focuses on the biological properties of carnosine including pH buffering ability, antioxidant activity, anti-inflammatory activity, anti-aging effect, enhancement of cognitive function, and immunomodulation. The relevance of carnosine in muscle function attributing to enhancement of physical performance has also been highlighted. Studies spanning several years have proved the preclinical effectiveness of carnosine in treating diverse pathological diseases. A complete summary of all key activities of carnosine from in vivo investigations and clinical trials has been compiled. Considering its numerous advantages, carnosine may be a promising option for the development of a nutraceutical.

An investigation on the structure and group vibrations of balenine molecule by matrix isolation IR spectroscopy, DFT and MP2 based calculations

Stable conformers of neutral balenine were scanned through molecular dynamics simulations and energy minimizations using Allinger's MM2 force field. For each of the found minimum-energy conformers, geometry optimization and thermochemistry calculations were performed by using B3LYP, MP2, G3MP2B3 methods, 6-31G(d), 6-311++G(d,p) and aug-cc-pvTZ basis sets. The calculation results have indicated that balenine has about twenty stable conformers whose relative energies are in the range of 0-9.5 kcal/mol. Three of these are thought to provide the major contribution to matrix isolation IR spectra of the molecule. Our solvent calculations using the polarized continuum model revealed the stable zwitterion structures which are predicted to dominate IR spectra of balenine in water and heavy water (D₂O) solvents. Pulay's SQM-FF method was used in scaling of the harmonic force constants and vibrational spectral data calculated for the neutral and zwitterion structures. These refined calculation data together with those obtained from anharmonic frequency calculations enabled us to correctly interpret the matrix isolation IR spectrum of balenine and the tautomerism-based changes observed in its KBr IR and solution (D₂O) IR spectra. The results revealed the crucial role of conformation and zwitterionic tautomerism on the structure and vibrational spectral data of the molecule.

Buffering capacity of wet texturized plant proteins in comparison to pork meat

There is an increasing demand to develop and characterize high moisture extrudates from alternative plant proteins due to their increased use in various foods. In this study, wet texturized proteins from two pea isolates and four oilseed flours from pumpkin and sunflower were subjected to an acid titration to gain insights into their buffering capacity. Results were compared to pork meat with a special emphasis on compositional differences. Wet texturized pumpkin and sunflower proteins had the highest buffering capacity, especially in between pH7.0 and pH4.5, while pea protein extrudates and pork meat were more prone to acidification and similar in buffering capacity. A multiple linear regression model further revealed that ash and select minerals and amino acids are key influencing factors on the overall buffering capacity, while the effect of protein and non-protein nitrogen depends on the evaluated pH-regime. The obtained results underline the importance for a more in-depth physicochemical characterization of texturized plant proteins and their raw materials and suggest a need for recipe and process adjustment to achieve stable pH values.

Survival rates and physiological recovery responses in the lesser-spotted catshark (Scyliorhinus canicula) after bottom-trawling

In 2019, Europe will adopt a no-discards policy in fisheries. This entails the landing of captured species unless strong evidence is provided supporting their survival and recovery after fishing. Thus, research on this topic is gaining momentum. Bottom-trawling, as a non-selective fishing method, is characterized by a high proportion of discards including vulnerable key species, such as demersal sharks. Their survival may also depend on capture depth. By paralleling onboard and laboratory experiments with the small-spotted catshark, Scyliorhinus canicula, we offer a robust experimental design to assess the survival of discarded sharks. Catsharks were captured by bottom-trawling at two depths (shallow ~89 m and deep ~479 m). Blood samples were collected following trawl capture and analyzed for stress biomarkers (lactate, osmolality, phosphate, urea). During recovery in onboard tanks, behavior was video-recorded and fish were re-sampled after 24 h. A second experiment was conducted in laboratory facilities to simulate air-exposure after trawling and to analyze the physiological recovery. Our results showed that 95.7% of the animals survived 24 h after trawling. We confirmed that trawling elicited acute stress responses in catshark but that they managed to recover. This was demonstrated by lactate concentrations that were 2.6 mM upon capture, but recovered to assumed baselines after 24 h (0.2 mM). Non-invasive video monitoring revealed behavioral differences with depth, whereby those captured at 89 m depth required longer to recover than those captured at 479 m depth. Implementation of standardized survival studies by fishery managers can benefit from holistic physiological approaches, such as the one proposed here.

Reduced non-bicarbonate skeletal muscle buffering capacity in mice with the mini-muscle phenotype

Muscle pH decreases during exercise, which may impair function. Endurance training typically reduces muscle buffering capacity as a result of changes in fiber-type composition, but existing comparisons of species that vary in activity level are ambiguous. We hypothesized that high-runner (HR) lines of mice from an experiment that breeds mice for voluntary wheel running would have altered muscle buffering capacity as compared with their non-selected control counterparts. We also expected that 6 days of wheel access, as used in the selection protocol, would reduce buffering capacity, especially for HR mice. Finally, we expected a subset of HR mice with the 'mini-muscle' phenotype to have relatively low buffering capacity as a result of fewer type IIb fibers. We tested non-bicarbonate buffering capacity of thigh muscles. Only HR mice expressing the mini-muscle phenotype had significantly reduced buffering capacity, females had lower buffering capacity than males, and wheel access had no significant effect.

Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt

The aim of the present study was to investigate cataract development in diploid (2N) and triploid (3N) Atlantic salmon smolts and post-smolts at two water temperatures (10 and 16 °C) given diets with different histidine supplementation (LH, 10.4 and HH, 13.1 g kg^-1 ) before and after seawater transfer. In freshwater, a severe cataract outbreak was recorded in both ploidies reared at 16 °C. The cataract score was significantly higher in triploids compared to diploids, and the severity was lower in both ploidies fed the HH diet. The cataract development at 10 °C was minor. Low gill Na⁺ , K⁺ -ATPase activity in fish reared at 16 °C before seawater transfer was followed by osmoregulatory stress with elevated plasma electrolyte concentrations and high mortality in sea water. Both diploids and triploids reared at 10 °C developed cataracts during the seawater period, with higher severities in triploids than diploids and a reduced severity in the fish fed the HH diet. The findings of this study demonstrate the importance of environmental conditions in the husbandry of Atlantic salmon, and particularly triploids, with regard to smoltification and adjusted diets to mitigate cataract development in fresh and sea water.

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.

The buffering capacity of porcine muscles

The aim of this study was to investigate the buffering capacity (BC) of five porcine muscles. The pH of muscles with zero lactate was also estimated. The BC was calculated on the basis of the amount of lactate accumulating in the muscle between two sampling times and the simultaneous pH decline. Two muscle samples were obtained from each muscle (n=13-36): one as soon as possible after slaughter and the other 24 h post-mortem. The BCs (mmol lactate/(pHkg)) were in the light gluteus superficialis, longissimus dorsi and semimembranosus muscles 48.3±8.8, 48.6±9.2 and 46.8±13.0, and in the dark infraspinatus and masseter muscles 45.3±13.1 and 32.0±11.5, respectively. The dark masseter muscle differed significantly from the other muscles studied (p<0.01). The estimated pH values of muscles with zero lactate were in the gluteus, longissimus dorsi, semimembranosus muscles 7.14±0.06; 7.18±0.06; 7.38±0.08, and in the infraspinatus and masseter muscles 6.87±0.07; 7.03±0.08, respectively. It was suggested since lactate is continuously formed in the muscles, the resting pH of living light and dark muscles may, however, be the same. The approach used in this study to determine the BC resulted in values which are close to values previously reported in the literature (measured by using titration curves).

Low O2 avoidance is associated with physiological perturbation but not exhaustion in the snapper (Pagrus auratus: Sparidae)

It is already known that the New Zealand snapper (Pagrus auratus, Sparidae) does not avoid hypoxia until reaching an oxygen partial pressure (PO(2)) of 3.1±1.2 kPa at 18 °C. Avoidance at this level of PO(2) and temperature is below the critical oxygen partial pressure of the species (P(crit)=5.8±0.6 kPa, 43.5±4.5 mmHg) and is therefore expected to result in major physiological stress. Results from the current study showed that avoidance was associated with numerous physiological perturbations, including a significant endocrine response, haematological changes, osmoregulatory disturbance and metabolic adjustments in the heart, liver and muscle. Snapper clearly experienced physiological stress at the point of avoidance but they were not however in a state of physiological exhaustion since some fuel reserves were still available. In addition to avoidance, snapper also showed a subtle reduction in swimming speed - this energy-saving response may have helped snapper minimise the physiological challenge of low O(2) residence. It is therefore concluded that snapper can reside in water below their P(crit) threshold for brief periods of time and, without any evidence of physiological exhaustion at the point of avoidance, fish should recover quickly once normoxia is selected. Lastly, with signs of anaerobic metabolism in cardiac tissue at the point of avoidance, we tentatively suggest that snapper may leave hypoxia to protect heart function.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Inhibitory effect of carnosine and N-acetyl carnosine on LPS-induced microglial oxidative stress and inflammation

Chronic inflammation and oxidative stress have been implicated in the pathogenesis of neurodegenerative diseases. A growing body of research focuses on the role of microglia, the primary immune cells in the brain, in modulating brain inflammation and oxidative stress. One of the most abundant antioxidants in the brain, particularly in glia, is the dipeptide carnosine, beta-alanyl-L-histidine. Carnosine is believed to be involved in cellular defense such as free radical detoxification and inhibition of protein cross-linking. The more stable N-acetyl derivative of carnosine has also been identified in the brain. The aim of the present study was to examine the role of carnosine and N-acetyl carnosine in the regulation of lipopolysaccharide (LPS)-induced microglial inflammation and oxidative damage. In this study, BV2 microglial cells were stimulated with bacterial LPS, a potent inflammatory stimulus. The data shows that both carnosine and N-acetyl carnosine significantly attenuated the LPS-induced nitric oxide synthesis and the expression of inducible nitric oxide synthase by 60% and 70%, respectively. By competitive spectrophotometric measurement and electrospray mass spectrometry analysis, we demonstrated a direct interaction of N-acetyl carnosine with nitric oxide. LPS-induced TNFalpha secretion and carbonyl formation were also significantly attenuated by both compounds. N-acetyl carnosine was more potent than carnosine in inhibiting the release of the inflammatory and oxidative stress mediators. These observations suggest the presence of a novel regulatory pathway through which carnosine and N-acetyl carnosine inhibit the synthesis of microglial inflammatory and oxidative stress mediators, and thus may prove to play a role in brain inflammation.

Protection of neuronal cells against reactive oxygen species by carnosine and related compounds

Carnosine and related compounds were compared in terms of their abilities to decrease the levels of reactive oxygen species (ROS) in suspensions of isolated neurons activated by N-methyl-D-aspartic acid (NMDA) using both stationary fluorescence measurements and flow cytometry. Carnosine was found to suppress the fluorescent signal induced by ROS production and decreased the proportion of highly fluorescent neurons, while histidine showed opposite effects. N-Acetylated derivatives of both carnosine and histidine demonstrated weak (statistically indistinguishable) suppressive effects on the ROS signal. N-Methylated derivatives of carnosine suppressed intracellular ROS generation to the same extent as carnosine. This rank of effectiveness is distinct from that previously obtained for the anti-radical ability of CRCs (anserine>carnosine>ophidine). These differences suggest that the similar ability of carnosine and its N-methylated derivatives to protect neuronal cells against the excitotoxic effect of NMDA is not solely related to the antioxidant properties of these compounds.

The buffering power of plasma in brown bullhead (Ameiurus nebulosus)

Brown bullhead (Ameiurus nebulosus) blood plasma was found to exhibit an unusually high non-bicarbonate buffer capacity (beta) in relation to that of other teleost fish. In brown bullhead, the non-bicarbonate buffer capacity of plasma (beta(plasma)), at -5.72 +/- 0.34 mmol l(-1) pH unit(-1) (mean +/- S.E.M., N=30), constituted 37% of whole blood beta and was 2.5 times higher than beta(plasma) in rainbow trout (-2.33 +/- 0.42 mmol l(+/-1) pH unit(-1); N=7). The strong buffering power of bullhead plasma was not the result of unusually high plasma protein levels. Size separation chromatography in conjunction with a spectrophotometric assay for buffering capacity were used to isolate a plasma fraction of high buffering power. SDS-polyacrylamide gel electrophoresis revealed that this fraction contained four proteins, but was dominated by a protein of approximately 68-70 kDa molecular mass. On the basis of the amino acid composition of this fraction, the dominant protein was identified as albumin. In comparison to other fish albumins, bullhead albumin appears to be histidine-rich (6.7%). Thus, the unusually high non-bicarbonate buffer capacity of bullhead plasma appears to stem from the presence in the plasma of a histidine-rich albumin.

Metabolic transformation of neuropeptide carnosine modifies its biological activity

1. The ability of carnosine and carnosine-related compounds (CRCs) to interact with several free oxygen radicals is analyzed. 2. Carnosine, the CRCs (imidazole, histidine, anserine), and ergothioneine were found to be equally efficient in singlet oxygen quenching. During generation of hydroxyl radicals from hydrogen peroxide in the Fenton reaction, carnosine was found to be more effective than the CRCs tested. 3. By measuring the chemiluminescence produced by carnosine and CRCs in rabbit leukocytes in the presence of luminol or lucigenin, we conclude that carnosine and other CRCs play a stimulating role in superoxide oxygen production while suppressing the myeloperoxidase system. 4. ADP-induced aggregation of human platelets is slightly stimulated by carnosine but is inhibited by acetylanserine. 5. The following rank order of efficiency of CRCs was demonstrated while measuring the oxidation of human serum lipoproteins: acetylcarnosine < acetylanserine < homocarnosine = ophidine < carnosine < anserine. 6. The results obtained demonstrate that metabolic transformation of carnosine into CRCs in tissues may play an important role in regulating the native antioxidant status of the organism.

Effects of carnosine and related compounds on generation of free oxygen species: a comparative study

The effect of carnosine and related compounds on the luminol- and lucigenin-dependent luminescence of rabbit leukocytes, activated by BaSO4, has been studied. Carnosine was found to modify BaSO4-induced chemiluminescence of leukocytes via suppression of hypochlorous anion generation with simultaneous stimulation the system of oxygen superoxide anion. Additionally to this effect carnosine prevents enzymic dismutation of O2.. Anserine, acetylanserine, and homocarnosine also possess the ability to activate O.2 production by leukocytes. The effect is not inherent to imidazole used in the same concentrations. Suppression of myeloperoxidase reaction by carnosine and related compounds is explained by both inhibiting action on the enzyme itself, and direct neutralization of hypochlorous anion due to formation of stable chloroamine complexes. Methylation of carnosine at N1 nitrogen of imidazole ring, leading to anserine, forced inhibition of myeloperoxidase system, whereas its acetylation at the free beta-amino group weakened this effect.

Human urinary excretion of L-histidine-related compounds after ingestion of several meats and fish muscle

1. After oral administration of the muscle of skipjack tuna, about 90% of ingested anserine (Ans) was excreted quickly into urine as Ans (8%) and pi-methylHis (82%), indicating the fast decomposition of Ans into pi-methylHis. This was also the case for chicken muscle ingestion. 2. After eel muscle ingestion, carnosine (Car) excretion was only 1% of the ingested whereas almost no increase was found in His, a constituent of Car, indicating the re-utilization of this essential amino acid. Similar results were also obtained from beef and pork ingestion. 3. In all cases, the urinary excretion of these compounds reached a maximum within 7 hr after ingestion and returned to the level of meat-free diet within 40 hr.