Branched-chain amino acid

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A branched-chain amino acid (BCAA) is an amino acid having aliphatic side-chains with a branch (a central carbon atom bound to three or more carbon atoms). Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine and valine.[1] Non-proteinogenic BCAAs include norvaline and 2-aminoisobutyric acid.

The three proteinogenic BCAAs are among the nine essential amino acids for humans, accounting for 35% of the essential amino acids in muscle proteins and 40% of the preformed amino acids required by mammals.[2]

Research[edit]

Dietary BCAA supplementation has been used clinically to aid in the recovery of burn victims. A 2006 paper suggests that the concept of nutrition supplemented with all BCAAs for burns, trauma, and sepsis should be abandoned for a more promising leucine-only-supplemented nutrition that requires further evaluation. [3]

Dietary BCAAs have been used in an attempt to treat some cases of hepatic encephalopathy.[4] They can have the effect of alleviating symptoms, but there is no evidence they benefit mortality rates, nutrition or overall quality of life.[5]

Certain studies suggested a possible link between a high incidence of amyotrophic lateral sclerosis among professional American football players and Italian soccer players, and certain sports supplements including BCAAs.[6] In mouse studies, BCAAs were shown to cause cell hyper-excitability resembling that usually observed in ALS patients. The proposed underlying mechanism is that cell hyper-excitability results in increased calcium absorption by the cell and thus brings about cell death, specifically of neuronal cells which have particularly low calcium buffering capabilities.[6] Yet any link between BCAAs and ALS remains to be fully established. While BCAAs can induce a hyperexcitability similar to the one observed in mice with ALS, current work does not show if a BCAA-enriched diet, given over a prolonged period, actually induces ALS-like symptoms.[6]

Blood levels of the BCAAs are elevated in obese, insulin resistant humans and in mouse and rat models of diet-induced diabetes, suggesting the possibility that BCAAs contribute to the pathogenesis of obesity and diabetes.[7][8] BCAA-restricted diets improve glucose tolerance and promote leanness in mice, and promotes insulin sensitivity in obese rats.[9][10]

Degradation[edit]

Degradation of branched-chain amino acids involves the branched-chain alpha-keto acid dehydrogenase complex (BCKDH). A deficiency of this complex leads to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products in the blood and urine, giving the condition the name maple syrup urine disease.

The BCKDH complex converts branched-chain amino acids into Acyl-CoA derivatives, which after subsequent reactions are converted either into acetyl-CoA or succinyl-CoA that enter the citric acid cycle.[11]

Enzymes involved are branched chain aminotransferase and 3-methyl-2-oxobutanoate dehydrogenase.

BCAA pathway

Claims in Bodybuilding[edit]

Bodybuilders make claims about the effectiveness of using BCAAs to aid recovery after a workout.[12] These claims[13] include prolonged mental and physical stamina[14] as well as a decrease in exercise-induced muscle breakdown and inflammation.[15] BCAAs are sold as bodybuilding supplements.

See also[edit]

References[edit]

  1. ^ Sowers, Strakie. "A Primer On Branched Chain Amino Acids" (PDF). Huntington College of Health Sciences. Retrieved 22 March 2011. 
  2. ^ Shimomura Y, Murakami T, Naoya Nakai N, Nagasaki M, Harris RA (2004). "Exercise Promotes BCAA Catabolism: Effects of BCAA Supplementation on Skeletal Muscle during Exercise". J. Nutr. 134 (6): 1583S–1587S. Retrieved 22 March 2011. 
  3. ^ De Bandt JP; Cynober L (2006). "Therapeutic use of branched-chain amino acids in burn, trauma, and sepsis". J. Nutr. 1 Suppl. 136 (30): 8S–13S. Retrieved 22 March 2011. 
  4. ^ Chadalavada R, Sappati Biyyani RS, Maxwell J, Mullen K (2010). "Nutrition in hepatic encephalopathy". Nutr Clin Pract. 25 (3): 257–64. doi:10.1177/0884533610368712. 
  5. ^ Gluud LL, Dam G, Les I, Córdoba J, Marchesini G, Borre M, Aagaard NK, Vilstrup H (2015). "Branched-chain amino acids for people with hepatic encephalopathy". Cochrane Database of Systematic Reviews. (2): CD001939. doi:10.1002/14651858.CD001939.pub2. PMID 25715177. 
  6. ^ a b c Manuel, Marin; Heckman, C.J. (2011). "Stronger is not always better: Could a bodybuilding dietary supplement lead to ALS?". Experimental Neurology. 228 (1): 5–8. doi:10.1016/j.expneurol.2010.12.007. ISSN 0014-4886. 
  7. ^ Lynch, Christopher J.; Adams, Sean H. (2014-12-01). "Branched-chain amino acids in metabolic signalling and insulin resistance". Nature Reviews. Endocrinology. 10 (12): 723–736. doi:10.1038/nrendo.2014.171. ISSN 1759-5037. PMC 4424797free to read. PMID 25287287. 
  8. ^ Newgard, Christopher B.; An, Jie; Bain, James R.; Muehlbauer, Michael J.; Stevens, Robert D.; Lien, Lillian F.; Haqq, Andrea M.; Shah, Svati H.; Arlotto, Michelle (2009-04-01). "A branched-chain amino acid-related metabolic signature that differentiates obese and lean humans and contributes to insulin resistance". Cell Metabolism. 9 (4): 311–326. doi:10.1016/j.cmet.2009.02.002. ISSN 1932-7420. PMC 3640280free to read. PMID 19356713. 
  9. ^ Fontana, Luigi; Cummings, Nicole E.; Arriola Apelo, Sebastian I.; Neuman, Joshua C.; Kasza, Ildiko; Schmidt, Brian A.; Cava, Edda; Spelta, Francesco; Tosti, Valeria (2016-06-21). "Decreased Consumption of Branched-Chain Amino Acids Improves Metabolic Health". Cell Reports. 16: 520–30. doi:10.1016/j.celrep.2016.05.092. ISSN 2211-1247. PMC 4947548free to read. PMID 27346343. 
  10. ^ White, Phillip J.; Lapworth, Amanda L.; An, Jie; Wang, Liping; McGarrah, Robert W.; Stevens, Robert D.; Ilkayeva, Olga; George, Tabitha; Muehlbauer, Michael J. "Branched-chain amino acid restriction in Zucker-fatty rats improves muscle insulin sensitivity by enhancing efficiency of fatty acid oxidation and acyl-glycine export". Molecular Metabolism. 5 (7): 538–551. doi:10.1016/j.molmet.2016.04.006. 
  11. ^ Sears DD, Hsiao G, Hsiao A, Yu JG, Courtney CH, Ofrecio JM, Chapman J, Subramaniam S (2009). "Mechanisms of human insulin resistance and thiazolidinedione-mediated insulin sensitization". Proc. Natl. Acad. Sci. USA. 106 (44): 18745–18750. doi:10.1073/pnas.0903032106. Retrieved 22 March 2011. 
  12. ^ [1]
  13. ^ "BCAA Supplements and Their Benefits". Macrospective. Retrieved 2016-03-23. 
  14. ^ Blomstrand, E.; Hassmén, P.; Ekblom, B.; Newsholme, E. A. (1991-01-01). "Administration of branched-chain amino acids during sustained exercise--effects on performance and on plasma concentration of some amino acids". European Journal of Applied Physiology and Occupational Physiology. 63 (2): 83–88. doi:10.1007/bf00235174. ISSN 0301-5548. PMID 1748109. 
  15. ^ Howatson, Glyn; Hoad, Michael; Goodall, Stuart; Tallent, Jamie; Bell, Phillip G.; French, Duncan N. (2012-01-01). "Exercise-induced muscle damage is reduced in resistance-trained males by branched chain amino acids: a randomized, double-blind, placebo controlled study". Journal of the International Society of Sports Nutrition. 9: 20. doi:10.1186/1550-2783-9-20. ISSN 1550-2783. PMC 3395580free to read. PMID 22569039. 

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