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Branched-Chain Amino Acids (BCAA)

 BCAA are a group of three ketogenic essential amino acids (leucine, valine and isoleucine). They are called branched-chain because their structure has a “branch” off the main body of the molecule. The combination of these three essential amino acids makes up approximately one-third of skeletal muscle in the human body in form of protein, even though BCAA are present in the skeletal muscle in free (non-protein) form only in marginal amounts. Commercial form of BCAA is a white crystal or crystalline powder, odorless and with slightly bitter taste. All of the BCAA are readily soluble in formic acid, sparingly in water and practically insoluble in alcohol.

Differently from many other amino acids, BCAA are metabolized only in the muscle, since the enzyme BCAA amino-transferase is not present in the liver where many other amino acids are converted. The rate-limiting enzyme of BCAA metabolism is branched-chain alpha-ketodehydrogenase is also located in the muscle and effectively activated by physical exercise or fasting. BCAA are used in various combinations and amounts, among them, leucine is the most readily oxidized one and therefore the most effective at secreting insulin from the pancreas. It lowers elevated blood sugar levels and aids in growth hormone production.

In the pharmaceutical field, BCAA are being used in gastrectomized patients to maintain nitrogen in the body and treat various forms of hepatic injury. Three possible targets of BCAA supplementation in hepatic diseases are: (1) hepatic encephalopathy, (2) liver regeneration, and (3) liver cirrhosis (i.e., Urata, 2007, Kawamura, 2009). The BCAA may ameliorate hepatic encephalopathy by promoting ammonia detoxification, correction of the plasma amino acid imbalance, and by reduced brain influx of aromatic amino acids. The influence of BCAA supplementation on hepatic encephalopathy could be especially effective in chronic hepatic injury with hyperammonemia and low concentrations of BCAA in blood. The favorable effect of BCAA on liver regeneration and nutritional state of the body is related to their stimulatory effect on protein synthesis, secretion of hepatocyte growth factor, glutamine production and inhibitory effect on proteolysis (Holecek, 2010).

There is substantial scientific debate on whether BCAA have an anabolic effect during/after exercise in healthy humans, with some recent clinical studies indicating that exercise-induced muscle damage and muscle soreness may be suppressed by oral load of BCAA (Shimomura, 2010; Jackman, 2010), leading to an improved long-term muscle performance. However, the subject of anabolism is still insufficiently studied, also due to disparity of methodologies applied to study muscle performance and differences in BCAA dose, respectively the ratio among leucine, isoleucine and valine.

In respect to upper levels in human diet, no human data indicate adverse effects caused by an increased ingestion of BCAA in healthy humans (the 4th Workshop on the Assessment of Adequate Intake of Dietary Amino Acids). The only “model” of extremely high BCAA exposure is a very rare genetic disorder, maple syrup urine disease, a feature of which is substantial brain dysfunction, but that cannot serve as a useful model of excessive BCAA intake in general population (for review see, Fernstrom, 2005). In patients with liver cirrhosis, high doses (app. 12 gram BCAA per day) were applied for prolonged periods of severl months without any reports of side effects (for review, see, Marchesini, 2005). A recent project sponsored by ICAAS (Elango, 2010) has indicated that the mean upper metabolic limit to oxidize leucine in healthy humans was as high as 0.56 gram per kg body weight per day, which would indicate that the homeostatic control of the intake of one of the BCAA, leucine, is very well developed in humans.

 

Reference:
  1. Elango, R., Chapman, K., Rafii, M., Ball, R. O., Pencharz, P. B. (2010). Abstract for the Experimental Biology.
  2. Fernstrom, J. D. (2005). J. Nutrition, 135S, 1539 – 1546.
  3. Holecek, M. (2010). Nutrition, 26, 482-490.
  4. Jackman, S. R., Witard, O. C., Jeukendrup, A. E., Tipton, K. D. (2010). Med Sci Sports Exercice, 42, 962-970.
  5. Kawamura, E., Habu, D., Morikawa, H., Enomoto, M., Kawabe, J., Tamori, A., Sakaguchi, H., Saeki, S., Kawada, N., Shiomi. S. (2009). Liver Transpl., 15, 790-797.
  6. Marchesini, G., Marzocchi, R., Noia, M., Bianchi, G. (2005). J. Nutrition, 135S, 1596 – 1601.
  7. Shimomura, Y., Inaguma, A., Watanabe, S., Yamamoto, Y., Muramatsu, Y., Bajotto, G., Sato, J., Shimomura, N., Kobayashi, H., Mawatari, K. (2010). Int J Sport Nutr Exerc Metabolism,  20, 236-244.
  8. The 4th Workshop on the Assessment of Adequate Intake of Dietary Amino Acids (2005). J. Nutrition, 135S.
  9. Urata, Y., Okita, K., Korenaga, K., Uchida, K., Yamasaki, T., Sakaida, I. (2007). Hepatol Research, 37, 510-516.
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