Studies from the last decades indicate that increased levels of ammonia contribute to muscle wasting in critically ill patients. The aim of the article is to examine the effects of two different causes of hyperammonemia-increased ATP degradation in muscles during strenuous exercise and impaired ammonia detoxification to urea due to liver cirrhosis. During exercise, glycolysis, citric acid cycle (CAC) activity, and ATP synthesis in muscles increase. In cirrhosis, due to insulin resistance and mitochondrial dysfunction, glycolysis, CAC activity, and ATP synthesis in muscles are impaired. Both during exercise and in liver cirrhosis, there is increased ammonia detoxification to glutamine (Glu + NH3 + ATP → Gln + ADP + Pi), increased drain of ketoglutarate (α-KG) from CAC for glutamate synthesis by α-KG-linked aminotransferases, glutamate, aspartate, and α-KG deficiency, increased oxidation of branched-chain amino acids (BCAA; valine, leucine, and isoleucine), and protein-energy wasting in muscles. It is concluded that ammonia can contribute to muscle wasting regardless of the cause of its increased levels and that similar strategies can be designed to increase muscle performance in athletes and reduce muscle loss in patients with hyperammonemia. The pros and cons of glutamate, α-KG, aspartate, BCAA, and branched-chain keto acid supplementation are discussed.

• Klíčová slova
• branched-chain amino acids, glutamic acid, glutamine, hyperammonemia,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

The aim of the article is to examine side effects of increased dietary intake of amino acids, which are commonly used as a dietary supplement. In addition to toxicity, mutagenicity and carcinogenicity, attention is focused on renal and gastrointestinal tract functions, ammonia production, and consequences of a competition with other amino acids for a carrier at the cell membranes and enzymes responsible for their degradation. In alphabetic order are examined arginine, beta-alanine, branched-chain amino acids, carnosine, citrulline, creatine, glutamine, histidine, beta -hydroxy- beta -methylbutyrate, leucine, and tryptophan. In the article is shown that enhanced intake of most amino acid supplements may not be risk-free and can cause a number of detrimental side effects. Further research is necessary to elucidate effects of high doses and long-term consumption of amino acid supplements on immune system, brain function, muscle protein balance, synthesis of toxic metabolites, and tumor growth and examine their suitability under certain circumstances. These include elderly, childhood, pregnancy, nursing a baby, and medical condition, such as diabetes and liver disease. Studies are also needed to examine adaptive response to a long-term intake of any substance and consequences of discontinuation of supplementation.

• MeSH
• aminokyseliny škodlivé účinky   metabolismus   MeSH
• arginin farmakologie   MeSH
• dítě MeSH
• glutamin * metabolismus   farmakologie   MeSH
• histidin metabolismus   MeSH
• kosterní svaly metabolismus   MeSH
• lidé MeSH
• potravní doplňky * škodlivé účinky   MeSH
• senioři MeSH
• těhotenství MeSH
• Check Tag
• dítě MeSH
• lidé MeSH
• senioři MeSH
• těhotenství MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• aminokyseliny MeSH
• arginin MeSH
• glutamin * MeSH
• histidin MeSH

Beta-hydroxy-beta-methyl butyrate (HMB) is a unique product of leucine catabolism with positive effects on protein balance. We have examined the effects of HMB (200 mg/kg/day via osmotic pump for 7 days) on rats with diabetes induced by streptozotocin (STZ, 100 mg/kg intraperitoneally). STZ induced severe diabetes associated with muscle wasting, decreased ATP in the liver, and increased α-ketoglutarate in muscles. In plasma, liver, and muscles increased branched-chain amino acids (BCAAs; valine, isoleucine, and leucine) and decreased serine. The decreases in mass and protein content of muscles and increases in BCAA concentration were more pronounced in extensor digitorum longus (fast-twitch muscle) than in soleus muscle (slow-twitch muscle). HMB infusion to STZ-treated animals increased glycemia and serine in the liver, decreased BCAAs in plasma and muscles, and decreased ATP in the liver and muscles. The effects of HMB on the weight and protein content of tissues were nonsignificant. We concluded that fast-twitch muscles are more sensitive to STZ than slow-twitch muscles and that HMB administration to STZ-treated rats has dual effects. Adjustments of BCAA concentrations in plasma and muscles and serine in the liver can be considered beneficial, whereas the increased glycemia and decreased ATP concentrations in the liver and muscles are detrimental.

• Klíčová slova
• ATP depletion, branched-chain amino acids, ketoglutarate, muscles, serine,
• MeSH
• aminokyseliny aplikace a dávkování   farmakologie   MeSH
• diabetes mellitus 1. typu chemicky indukované   farmakoterapie   metabolismus   MeSH
• injekce intraperitoneální MeSH
• injekce subkutánní MeSH
• játra účinky léků   metabolismus   MeSH
• kosterní svaly účinky léků   metabolismus   MeSH
• krysa rodu Rattus MeSH
• potkani Wistar MeSH
• streptozocin aplikace a dávkování   MeSH
• valeráty aplikace a dávkování   farmakologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• aminokyseliny MeSH
• beta-hydroxyisovaleric acid MeSH Prohlížeč
• streptozocin MeSH
• valeráty MeSH

Both regular exercise training and beta-hydroxy-beta-methylbutyrate (HMB) supplementation are shown as effective treatments to delay or reverse frailty and reduce cognitive impairment in older people. However, there is very little evidence on the true benefits of combining both strategies. The aim of this meta-analysis was to quantify the effects of exercise in addition to HMB supplementation, on physical and cognitive health in older adults. Data from 10 randomized controlled trials (RCTs) investigating the effect of HMB supplementation and physical function in adults aged 50 years or older were analyzed, involving 384 participants. Results showed that HMB supplementation in addition to physical exercise has no or fairly low impact in improving body composition, muscle strength, or physical performance in adults aged 50 to 80 years, compared to exercise alone. There is a gap of knowledge on the beneficial effects of HMB combined with exercise to preserve cognitive functions in aging and age-related neurodegenerative diseases. Future RCTs are needed to refine treatment choices combining HMB and exercises for older people in particular populations, ages, and health status. Specifically, interventions in older adults aged 80 years or older, with cognitive impairment, frailty, or limited mobility are required.

• Klíčová slova
• elderly, leucine, neuromuscular function, nutrition, resistance training, sarcopenia,
• MeSH
• cvičení fyziologie   MeSH
• lidé MeSH
• potravní doplňky * MeSH
• stárnutí * MeSH
• valeráty aplikace a dávkování   farmakologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• metaanalýza MeSH
• systematický přehled MeSH
• Názvy látek
• beta-hydroxyisovaleric acid MeSH Prohlížeč
• valeráty MeSH

Beta-hydroxy-beta-methylbutyrate (HMB) is a leucine metabolite with protein anabolic effects. We examined the effects of an HMB-enriched diet in healthy rats and rats with liver cirrhosis induced by multiple doses of carbon tetrachloride (CCl4). HMB increased branched-chain amino acids (BCAAs; valine, leucine and isoleucine) in blood and BCAA and ATP in muscles of healthy animals. The effect on muscle mass and protein content was insignificant. In CCl4-treated animals alterations characteristic of liver cirrhosis were found with decreased ratio of the BCAA to aromatic amino acids in blood and lower muscle mass and ATP content when compared with controls. In CCl4-treated animals consuming HMB, we observed higher mortality, lower body weight, higher BCAA levels in blood plasma, higher ATP content in muscles, and lower ATP content and higher cathepsin B and L activities in the liver when compared with CCl4-treated animals without HMB. We conclude that (1) HMB supplementation has a positive effect on muscle mitochondrial function and enhances BCAA concentrations in healthy animals and (2) the effects of HMB on the course of liver cirrhosis in CCl4-treated rats are detrimental. Further studies examining the effects of HMB in other models of hepatic injury are needed to determine pros and cons of HMB in the treatment of subjects with liver cirrhosis.

• Klíčová slova
• branched-chain amino acids, hepatic cachexia, insulin resistance, leucine, liver cirrhosis,
• MeSH
• chlorid uhličitý metabolismus   MeSH
• jaterní cirhóza metabolismus   MeSH
• játra účinky léků   metabolismus   MeSH
• kosterní svaly účinky léků   metabolismus   MeSH
• leucin metabolismus   MeSH
• potkani Wistar MeSH
• potravní doplňky MeSH
• valeráty farmakologie   MeSH
• větvené aminokyseliny metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• beta-hydroxyisovaleric acid MeSH Prohlížeč
• chlorid uhličitý MeSH
• leucin MeSH
• valeráty MeSH
• větvené aminokyseliny MeSH

Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the essential amino acid leucine that has been reported to have anabolic effects on protein metabolism. The aims of this article were to summarize the results of studies of the effects of HMB on skeletal muscle and to examine the evidence for the rationale to use HMB as a nutritional supplement to exert beneficial effects on muscle mass and function in various conditions of health and disease. The data presented here indicate that the beneficial effects of HMB have been well characterized in strength-power and endurance exercise. HMB attenuates exercise-induced muscle damage and enhances muscle hypertrophy and strength, aerobic performance, resistance to fatigue, and regenerative capacity. HMB is particularly effective in untrained individuals who are exposed to strenuous exercise and in trained individuals who are exposed to periods of high physical stress. The low effectiveness of HMB in strength-trained athletes could be due to the suppression of the proteolysis that is induced by the adaptation to training, which may blunt the effects of HMB. Studies performed with older people have demonstrated that HMB can attenuate the development of sarcopenia in elderly subjects and that the optimal effects of HMB on muscle growth and strength occur when it is combined with exercise. Studies performed under in vitro conditions and in various animal models suggest that HMB may be effective in treatment of muscle wasting in various forms of cachexia. However, there are few clinical reports of the effects of HMB on muscle wasting in cachexia; in addition, most of these studies evaluated the therapeutic potential of combinations of various agents. Therefore, it has not been possible to determine whether HMB was effective or if there was a synergistic effect. Although most of the endogenous HMB is produced in the liver, there are no reports regarding the levels and the effects of HMB supplementation in subjects with liver disease. Several studies have suggested that anabolic effects of HMB supplementation on skeletal muscle do not occur in healthy, non-exercising subjects. It is concluded that (i) HMB may be applied to enhance increases in the mass and strength of skeletal muscles in subjects who exercise and in the elderly and (ii) studies examining the effects of HMB administered alone are needed to obtain conclusions regarding the specific effectiveness in attenuating muscle wasting in various muscle-wasting disorders.

• Klíčová slova
• Cachexia, Exercise, HMB, Leucine, Sarcopenia, Supplements,
• MeSH
• kachexie dietoterapie   patofyziologie   MeSH
• kosterní svaly účinky léků   fyziologie   MeSH
• lidé MeSH
• potravní doplňky MeSH
• sarkopenie dietoterapie   patofyziologie   MeSH
• svalová atrofie dietoterapie   patofyziologie   MeSH
• svalová síla účinky léků   MeSH
• syndrom chřadnutí dietoterapie   patofyziologie   MeSH
• valeráty aplikace a dávkování   farmakologie   MeSH
• zdraví MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• beta-hydroxyisovaleric acid MeSH Prohlížeč
• valeráty MeSH

BACKGROUND: Many people believe in favourable effects of branched-chain amino acids (BCAAs; valine, leucine, and isoleucine), especially leucine, on muscle protein balance and consume BCAAs for many years. We determined the effects of the chronic intake of a BCAA- or leucine-enriched diet on protein and amino acid metabolism in fed and postabsorptive states. METHODS: Rats were fed a standard diet, a diet with a high content of valine, leucine, and isoleucine (HVLID), or a high content of leucine (HLD) for 2 months. Half of the animals in each group were sacrificed in the fed state on the last day, and the other half were sacrificed after overnight fast. Protein synthesis was assessed using the flooding dose method (L-[3,4,5-(3)H]phenylalanine), proteolysis on the basis of chymotrypsin-like activity (CHTLA) of proteasome and cathepsin B and L activities. RESULTS: Chronic intake of HVLID or HLD enhanced plasma levels of urea, alanine and glutamine. HVLID also increased levels of all three BCAA and branched-chain keto acids (BCKA), HLD increased leucine, ketoisocaproate and alanine aminotransferase and decreased valine, ketovaline, isoleucine, ketoisoleucine, and LDL cholesterol. Tissue weight and protein content were lower in extensor digitorum longus muscles in the HLD group and higher in kidneys in the HVLID and HLD groups. Muscle protein synthesis in postprandial state was higher in the HVLID group, and CHTLA was lower in muscles of the HVLID and HLD groups compared to controls. Overnight starvation enhanced alanine aminotransferase activity in muscles, and decreased protein synthesis in gastrocnemius (in HVLID group) and extensor digitorum longus (in HLD group) muscles more than in controls. Effect of HVLID and HLD on CHTLA in muscles in postabsorptive state was insignificant. CONCLUSIONS: The results failed to demonstrate positive effects of the chronic consumption of a BCAA-enriched diet on protein balance in skeletal muscle and indicate rather negative effects from a leucine-enriched diet. The primary effects of both diets are an activated catabolism of BCAAs, which leads to an enhanced production of BCKA, alanine and glutamine and their utilization in visceral tissues and an impaired protein synthesis in postabsorptive state, particularly in fast-twitch (white) muscles.

• Klíčová slova
• Glutamine, Muscle, Nutritional supplements, Protein synthesis, Proteolysis, Starvation,
• Publikační typ
• časopisecké články MeSH

Muscle wasting is a serious complication of various clinical conditions that significantly worsens the prognosis of the illnesses. Clinically relevant models of muscle wasting are essential for understanding its pathogenesis and for selective preclinical testing of potential therapeutic agents. The data presented here indicate that muscle wasting has been well characterized in rat models of sepsis (endotoxaemia, and caecal ligation and puncture), in rat models of chronic renal failure (partial nephrectomy), in animal models of intensive care unit patients (corticosteroid treatment combined with peripheral denervation or with administration of neuromuscular blocking drugs) and in murine and rat models of cancer (tumour cell transplantation). There is a need to explore genetically engineered mouse models of cancer. The degree of protein degradation in skeletal muscle is not well characterized in animal models of liver cirrhosis, chronic heart failure and chronic obstructive pulmonary disease. The major difficulties with all models are standardization and high variation in disease progression and a lack of reflection of clinical reality in some of the models. The translation of the information obtained by using these models to clinical practice may be problematic.

• MeSH
• kosterní svaly metabolismus   patologie   MeSH
• krysa rodu Rattus MeSH
• modely nemocí na zvířatech MeSH
• myši MeSH
• nádory komplikace   metabolismus   patologie   MeSH
• proteolýza MeSH
• sepse komplikace   metabolismus   patologie   MeSH
• svalová atrofie etiologie   metabolismus   patologie   MeSH
• syndrom chřadnutí etiologie   metabolismus   patologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

β-Hydroxy-β-methylbutyrate (HMB) is a leucine metabolite that may have a positive effect in protein catabolic conditions. Therefore, we hypothesized that HMB treatment could attenuate the sepsis-induced protein catabolic state. The aims of our study were to elucidate the effect of HMB in healthy and septic animals and to evaluate the differences in the action of HMB in different muscle types. Intact and septic (5 mg endotoxin/kg i.p.) rats were administered with HMB (0.5 g/kg/day) or saline. After 24 h, extensor digitorum longus (EDL) and soleus (SOL) muscles were isolated and used for determination of total and myofibrillar proteolysis, protein synthesis, leucine oxidation, activity of cathepsins B and L, chymotrypsin-like activity, and expression of α-subunits of proteasome. Our results indicate that the catabolic state induced by the endotoxin treatment was caused both by increase in protein breakdown (due to activation of proteasome system) and by attenuation of protein synthesis. The EDL (muscle composed of white, fast-twitch fibers) was more susceptible to these changes than the SOL (muscle composed of red, slow-twitch fibers). The HMB treatment had no effect in healthy animals but counteracted the changes in septic animals. The action of HMB was mediated by attenuation of proteasome activity and protein breakdown, not by stimulation of protein synthesis. More pronounced effect of the HMB treatment on myofibrillar proteolysis was observed in the SOL.

• MeSH
• časové faktory MeSH
• kathepsin B chemie   MeSH
• kathepsin L chemie   MeSH
• kosterní svaly účinky léků   metabolismus   MeSH
• krysa rodu Rattus MeSH
• kyslík chemie   MeSH
• leucin chemie   MeSH
• lyzozomy metabolismus   MeSH
• potkani Wistar MeSH
• proteasomový endopeptidasový komplex chemie   MeSH
• sepse farmakoterapie   metabolismus   MeSH
• valeráty farmakologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• beta-hydroxyisovaleric acid MeSH Prohlížeč
• kathepsin B MeSH
• kathepsin L MeSH
• kyslík MeSH
• leucin MeSH
• proteasomový endopeptidasový komplex MeSH
• valeráty MeSH