Branched-chain amino acid interactions in growing pig diets1

Abstract

The branched-chain amino acids (BCAA) Leu, Ile, and Val share the first steps of their catabolism due to similarities in their structure. The BCAA are reversibly transaminated in skeletal muscle through the activity of branched-chain aminotransferase and then transported to the liver. They undergo an irreversible decarboxylation catalyzed by the branched-chain α-keto acid dehydrogenase complex. Both enzymes are common to Leu, Ile, and Val and increased enzymatic activity stimulated by an excess of one of them will increase the catabolism of all BCAA, which can result in antagonisms. Leucine and its keto acid are the most potent stimulators of BCAA catabolic enzymes. Moreover, BCAA and large neutral amino acids (LNAA) share common brain transporters. Research has shown that high concentrations of BCAA, especially Leu, can decrease the absorption of LNAA, such as Trp, which is a precursor of serotonin and can have a significant impact in feed intake regulation. Finally, high Leu concentrations have the ability to overstimulate the mTOR signaling pathway, resulting in an inhibitory effect on feed intake. Most of the research conducted to evaluate the impact of BCAA on growth performance of pigs seems to agree that high levels of Leu decrease weight gain, mostly due to a reduction in feed intake. However, some studies, mostly with finishing pigs, observed no evidence for an impact on growth performance even with extremely high levels of Leu. It could be hypothesized that these inconsistencies are driven by the entire dietary amino acid profile as opposed to only considering the level of Leu. Grow-finish diets typically contain high levels of Leu, but the other BCAA are also well above the requirement and could potentially mitigate the negative impact of Leu on BCAA catabolism. Indeed, some studies suggest that when diets contain high levels of Leu, more Ile and Val are needed to optimize growth performance. However, the precise relationship between BCAA and their balance in swine diets is not fully understood. More research is needed to understand and quantify the relationship between LNAA and BCAA.

Early lean mass sparing effect of high-protein diet with excess leucine during long-term bed rest in women

“…Among several potential mechanisms, including a leucine "desynchronization effect" (63) one possibility is that beyond a certain level, excess of leucine may stimulate key enzymes in BCAA catabolism (i.e., BCAA aminotransferase and branchedchain alpha-keto acid dehydrogenase) thus increasing the oxidation of serum leucine (79,80). Moreover, a surplus in leucine intake can decrease the plasma concentration of the other EAAs, an effect called BCAA antagonism (81)(82)(83). Further investigations are needed to confirm the "desynchronization effect" hypothesis.…”

Phosphorus and nitrogen nutrition in swine production

“…Among them, for N, there is strong interaction between AA such as valine, leucine, and isoleucine, the branched-chain amino acids required for protein synthesis but sharing the same enzymes for degradation with leucine that is generally in excess in swine diet ( NRC, 2012 ). Recently, studies showed that leucine excess may increase the need for dietary valine and Ile in piglets ( Cemin et al, 2019 ). For P, the interaction with calcium is well known and should be considered to optimize it’s use ( Létourneau-Montminy et al, 2012 ; NRC, 2012 ).…”

Understanding the interactive effects of dietary leucine with isoleucine and valine in the modern commercial broiler

“…Recent developments in feed grade manufacturing of L-Val, and to a lesser extent L-Ile, have resulted in prices that allow for more feasible use in feed formulation. Subsequently, interest has grown to better understand how all BCAA interact with one another under commercial conditions, not only in poultry ( Ospina-Rojas et al, 2017 ; Ospina-Rojas et al, 2018 ; Zeitz et al, 2019 ; Ospina-Rojas et al, 2020 ) but other monogastric species as well ( Cemin et al, 2019 ).…”