α-Hydroxyisocaproic Acid Decreases Protein Synthesis but Attenuates TNFα/IFNγ Co-Exposure-Induced Protein Degradation and Myotube Atrophy via Suppression of iNOS and IL-6 in Murine C2C12 Myotube.

Koichiro Sumi,Kinya Ashida,Kentaro Nakamura,Kinuyo Munakata,Misato Sakuda

doi:10.3390/nu13072391

Abstract

There is ongoing debate as to whether or not α-hydroxyisocaproic acid (HICA) positively regulates skeletal muscle protein synthesis resulting in the gain or maintenance of skeletal muscle. We investigated the effects of HICA on mouse C2C12 myotubes under normal conditions and during cachexia induced by co-exposure to TNFα and IFNγ. The phosphorylation of AMPK or ERK1/2 was significantly altered 30 min after HICA treatment under normal conditions. The basal protein synthesis rates measured by a deuterium-labeling method were significantly lowered by the HICA treatment under normal and cachexic conditions. Conversely, myotube atrophy induced by TNFα/IFNγ co-exposure was significantly improved by the HICA pretreatment, and this improvement was accompanied by the inhibition of iNOS expression and IL-6 production. Moreover, HICA also suppressed the TNFα/IFNγ co-exposure-induced secretion of 3-methylhistidine. These results demonstrated that HICA decreases basal protein synthesis under normal or cachexic conditions; however, HICA might attenuate skeletal muscle atrophy via maintaining a low level of protein degradation under cachexic conditions.

Highlights

To examine whether hydroxyisocaproic acid (HICA) supplementation correlates with the acceleration of protein synthesis through the mTORC1 signaling pathway, we analyzed the phosphorylation of p70S6K, which is a major downstream target of mTORC1 [29]
The expression of muscle RING-finger protein-1 (MURF-1) was not affected to a significant effect by the treatment with cytokines or with HICA (Figure 6E). These results suggest that HICA cannot recover the decreased fractional synthesis rate (FSR) induced by tumor necrosis factor α (TNFα)/interferon γ (IFNγ) co-exposure, but it does attenuate increases in myotube protein degradation by inhibiting the increased activity of the ubiquitin–proteasome system, at least in part
We tested our hypothesis that HICA would attenuate the myotube atrophy that accompanies a decrease of protein synthesis using an in vitro cachexia model evoked by a co-exposure to TNFα and IFNγ

Summary

Introduction

Α-Hydroxyisocaproic acid (HICA, leucic acid or DL-2-hydroxy-4-methylvaleric acid) is an end-product of the microbial metabolism of leucine (Leu) [1]. The variability of HICA levels in commercial yogurts [4] may reflect the diversity of activities of hydroxyisocaproate dehydrogenase enzymes in the diverse Lactobacillus strains used in fermentation [3]. HICA cannot be degraded by many bacterial species, and its production may represent a survival strategy for Lactobacillus, because HICA displays antibacterial activity [5]. The contributions of HICA to skeletal muscle gain or maintenance have been examined. The impacts on muscle performance could have wide-ranging effects on athletic performances but, on the quality of life of frail or elderly individuals [9,10,11,12,13]

Methods

Results

Conclusion