Essential Amino Acid-Enriched Diet Alleviates Dexamethasone-Induced Loss of Muscle Mass and Function through Stimulation of Myofibrillar Protein Synthesis and Improves Glucose Metabolism in Mice

Dexamethasone (DEX) induces dysregulation of protein turnover, leading to muscle atrophy and impairment of glucose metabolism. Positive protein balance, i.e., rate of protein synthesis exceeding rate of protein degradation, can be induced by dietary essential amino acids (EAAs). In this study, we investigated the roles of an EAA-enriched diet in the regulation of muscle proteostasis and its impact on glucose metabolism in the DEX-induced muscle atrophy model. Mice were fed normal chow or EAA-enriched chow and were given daily injections of DEX over 10 days. We determined muscle mass and functions using treadmill running and ladder climbing exercises, protein kinetics using the D2O labeling method, molecular signaling using immunoblot analysis, and glucose metabolism using a U-13C6 glucose tracer during oral glucose tolerance test (OGTT). The EAA-enriched diet increased muscle mass, strength, and myofibrillar protein synthesis rate, concurrent with improved glucose metabolism (i.e., reduced plasma insulin concentrations and increased insulin sensitivity) during the OGTT. The U-13C6 glucose tracing revealed that the EAA-enriched diet increased glucose uptake and subsequent glycolytic flux. In sum, our results demonstrate a vital role for the EAA-enriched diet in alleviating the DEX-induced muscle atrophy through stimulation of myofibrillar proteins synthesis, which was associated with improved glucose metabolism.

Effects of low concentration of proanthocyanidins and oxidation conditions on myofibrillar protein in chicken breast muscle

In this study, the effect of low concentration of proanthocyanidins (extracted from grape seeds) on the gel properties of chicken breast myofibrillar protein was studied. The addition of proanthocyanidins could strengthen the spatial structure of myofibrillar proteins and slow down the gel oxidation. The threshold value of the addition amount of proanthocyanidins refers to the threshold value of NaNO2, a commonly used food additive in meat products, closer to the actual production and application. In the threshold range, low concentration of proanthocyanidins had more stable water retention and slower structural decay. High concentration of proanthocyanidins’ gel (PG) had better stability in the first ten days, but a rapid decline occurred after 10 days. Raman microscope showed that the gel formed after adding proanthocyanidins had more compact spatial structure and smaller pore size, which was more conducive to maintaining water content. In this experiment, when the amount of proanthocyanidins exceeded the national standard threshold, the spatial structure of the gel was destroyed, and the data were disordered. Proanthocyanidins extracted from grape seeds (PFGS) could be appropriately added within the national standard threshold, which was beneficial to the stability, oxidation resistance and texture of the gel. Therefore, improving the stability of protein gel systems was important for the design and development of novel food products.