![]() ![]() When the weights of individual tissues are taken into consideration, muscles, which make up 35 to 40% of total body weight, should contribute substantially to total body BCAA utilization. ![]() The BCKD activity is highest in the liver, intermediate in kidneys and heart, and low in muscles, adipose tissue, and brain. Changes in kinase activity may play a main role. Phosphorylation mediated by a specific kinase results in inactivation, while dephosphorylation by a specific phosphatase activates the enzyme. The BCKD is regulated by the phosphorylation-dephosphorylation mechanism. The second enzyme of BCAA catabolism, branched-chain α-keto acid dehydrogenase (BCKD), is a multienzyme complex located on the inner surface of the inner mitochondrial membrane, which catalyzes irreversible decarboxylation of the BCKA to the corresponding branched-chain acyl-CoA esters. GLN, ALA, and a significant portion of the BCKA are released from muscles to the blood. Glutamate then acts as an amino group source to form alanine (ALA) from pyruvate or as a substrate for ammonia detoxification to glutamine (GLN). The BCAT reaction involves the reversible transfer of the BCAA amino group to α-ketoglutarate (α-KG) to form glutamate and the corresponding branched-chain keto acids (BCKAs), α-ketoisocaproate (KIC, ketoleucine), α-keto-β-methylvalerate (KMV, ketoisoleucine), and α-ketoisovalerate (KIV, ketovaline). The initial site of most of the BCAA catabolism is skeletal muscle because of the BCAT high activity. As the main pathways of all three BCAAs are common and mixtures of all three BCAAs are used in most indications, the article does not describe the differences in effects of specific BCAAs. The intentions of this article are to: (i) review main metabolic pathways and supposed effects of BCAAs (ii) assess the causes of alterations in metabolism and BCAA levels in various healthy and pathological conditions and (iii) provide current views on their use as nutritional supplements for the main possible indications. However, until today, there is not consensus regarding their use as nutritional supplements. BCAA supplementation has been thought to promote anabolic pathways and therefore mitigate cachexia, prevent or treat signs of hepatic encephalopathy, attenuate fatigue during exercise, promote wound healing, and stimulate insulin production. The branched-chain amino acids (BCAAs), valine, leucine, and isoleucine are essential amino acids, which have been studied in a number of disorders, notably liver cirrhosis, renal failure, sepsis, trauma, burn injury, and cancer. It is concluded that alterations in BCAA metabolism have been found common in a number of disease states and careful studies are needed to elucidate their therapeutic effectiveness in most indications. Whether increased BCAA levels only markers are or also contribute to insulin resistance should be known before the decision is taken regarding their suitability in obese subjects and patients with type 2 diabetes. Further studies are needed to elucidate the effects of BCAA supplementation in burn, trauma, sepsis, cancer and exercise. ![]() New therapeutic strategies should be developed to enhance effectiveness and avoid adverse effects of BCAA on ammonia production in subjects with liver cirrhosis and urea cycle disorders. The studies indicate beneficial effects of BCAAs and BCKAs in therapy of chronic renal failure. Increased BCAA concentrations during brief starvation and type 1 diabetes are explained by amination of BCKAs in visceral tissues and decreased uptake of BCAA by muscles. Decreased BCKD activity is the main cause of increased BCAA levels and BCKAs in maple syrup urine disease, and plays a role in increased BCAA levels in diabetes type 2 and obesity. Increased BCKD activity is responsible for enhanced oxidation of BCAA in chronic renal failure, trauma, burn, sepsis, cancer, phenylbutyrate-treated subjects, and during exercise. Enhanced consumption of BCAA for ammonia detoxification to glutamine in muscles is the cause of decreased BCAA levels in liver cirrhosis and urea cycle disorders. In the article is demonstrated that the crucial roles in BCAA metabolism play: (i) skeletal muscle as the initial site of BCAA catabolism accompanied with the release of alanine and glutamine to the blood (ii) activity of branched-chain keto acid dehydrogenase (BCKD) and (iii) amination of branched-chain keto acids (BCKAs) to BCAAs. However, until today, there is no consensus regarding their therapeutic effectiveness. Branched-chain amino acids (BCAAs valine, leucine, and isoleucine) are essential amino acids with protein anabolic properties, which have been studied in a number of muscle wasting disorders for more than 50 years.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |