Branched-Chain Amino Acid (BCAA) and Iron Status Effects on Aging Skeletal Muscle
Date of Award
Doctor of Philosophy (PhD)
Aging, BCAA, Iron, Sarcopenia, Skeletal muscle
Medicine and Health Sciences
Sarcopenia, which is the loss of muscle mass and strength with advancing age, has been attracting the attention of many researchers in recent years which is likely the result of the demographic trend of an aging population. Notably, good health of aging individuals includes an adequate level of muscle mass and muscle function to allow performance of activities of daily living.
Our group and others have conjectured that elevated skeletal muscle iron status plays a causal role in the development of sarcopenia. The increase in muscle iron concentration with aging could trigger excess production of free radicals and induce oxidative stress and mitochondrial dysfunction. Thus, regulating muscle iron levels over the course of aging could be an important strategy to attenuate the onset and/or progression of sarcopenia.
Branched-chain amino acid (BCAA) administration is best known for the ability to increase protein synthesis in aging skeletal muscle through activation of mTOR signaling. Recent studies in heart tissue and cell culture suggest a possible link between mTOR and iron status. However, there are currently no studies to examine the effect of BCAA administration on the regulation of iron status in aging skeletal muscle. Thus, we had an interest to examine how low-iron and/or BCAA containing diets regulate muscle iron status, anabolic signaling, oxidative stress/mitochondrial dysfunction, as well as muscle mass of aging animals.
In this study, 29 month old male F344×Brown Norway rats were divided into two main groups (Control vs. BCAA diet groups) and further separated into subgroups by iron level in the diets (Regular-iron [RI] vs. Low-iron [LI] containing diet). Thus, animals were divided into the following groups: (1) Control + RI (CR; n=11), (2) Control + LI (CL; n=11), (3) 2×BCAA + RI (BR; n=10), and (4) 2×BCAA + LI (BL; n=12). All diets utilized the AIN-93M diet, either in its basic form (i.e., CR) or as a modified formulation (CL, BR, and BL). Low iron diets contained 2-6 ppm iron, compared to regular iron-containing diets (35 ppm iron). 2×BCAA diets contained twice the amount of BCAA compared to the CR and CL diets (BCAA ratio; leucine: isoleucine: valine = 1.5: 1: 1.1). Animals were on the respective diets for 12 weeks. Following the experimental period, animals were euthanized and we determined whether long-term dietary treatments with LI and/or 2×BCAA altered the aging plantaris: (1) muscle mass and muscle fiber size; (2) iron status (non-heme iron concentration and total non-heme iron content); (3) anabolic signaling (mTOR and p70S6K1); (4) mitochondrial biogenesis (PGC-1(alpha)) and oxidative capacity (CS and COX-2); and (5) oxidative stress (3-nitrotyrosine and 4-HNE).
Results showed no difference in body mass and muscle mass between groups after 12 weeks of the dietary treatments. However, histological analysis revealed that animal groups fed LI and/or 2×BCAA diets showed significantly larger plantaris muscle fiber size than that of the CR group. Although the effect of 2×BCAA on plantaris non-heme iron concentration did not reach statistical significance (p=0.150), animals consuming 2×BCAA containing diets showed lower total non-heme iron content compared to CR and CL groups (p<0.05). Moreover, a significant interaction between LI and 2×BCAA for p70S6K1 was identified in the aging skeletal muscle (p<0.05). Here, animals on low iron and/or 2×BCAA treatments had significantly greater p70S6K1 phosphorylation level compared to the CR group (p<0.05). Interestingly, significant interactions were also observed between LI and 2×BCAA for protein levels representative of mitochondrial biogenesis (PGC-1(alpha)) and oxidative capacity (CS and COX-2) (p<0.05). Both PGC-1(alpha) (p<0.05) and COX-2 (p=0.051) were slightly lower in the BL group than in the CL group. Moreover, although CS appeared to be slightly greater in the CL and BR groups than in the CR group (p>0.05), its level in the BL group was similar to the CR group. Hence, combining 2×BCAA with LI appeared to negate a possible positive influence of LI on mitochondrial capacity-related protein expression levels in aging muscle. There was no difference in oxidative stress (3-nitrotyrosine and 4-HNE protein levels) between groups (p>0.05), indicating that these long-term dietary treatments with LI and/or 2×BCAA did not link with oxidative stress in the plantaris muscle of old rats.
In conclusion, although there was no effect on muscle mass, the long-term dietary treatments with LI and/or 2×BCAA showed beneficial effects on muscle fiber size. This study found that while only 2×BCAA administration may play a role in the regulation of iron status, anabolic signaling (p70S6K1) was significantly activated by LI and 2×BCAA diets in aging skeletal muscle. However, neither LI nor 2×BCAA containing diets exhibited significant (simple) effects on increasing mitochondrial biogenesis and function of aging skeletal muscle. Interestingly, we found that co-administration of LI and BCAA was likely to negate the potential impact on mitochondrial biogenesis and oxidative capacity in the aging skeletal muscle as compared to either diet administered individually; suggesting possible interfering effects of the combined dietary interventions. Finally, long-term dietary treatment with LI and/or 2×BCAA appeared to have no effect on lowering markers of muscle oxidative stress. Collectively, future studies are needed to clarify the efficacy of LI and BCAA administration on muscle and mitochondrial function in aging skeletal muscle.
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Kim, Yu Ho, "Branched-Chain Amino Acid (BCAA) and Iron Status Effects on Aging Skeletal Muscle" (2015). Dissertations - ALL. 342.