L-Carnitine Ameliorates the Muscle Wasting of Cancer Cachexia through the AKT/FOXO3a/MaFbx Axis

Abstract

Recent studies suggest potential benefits of applying L-carnitine in the treatment of cancer cachexia, but the precise mechanisms remain unknown. This study was conducted to determine the mechanism by which L-carnitine reduces cancer cachexia. We found that L-carnitine increased the gastrocnemius muscle (GM) weight in the CT-26-bearing cachexia mouse model and the cross-sectional fiber area (CFA) of the GM and myotube diameters of C2C12 cells treated with TNF-α. Additionally, L-carnitine reduced the protein expression of muscle RING-type E3 ubiquitin ligase 1 (MuRF1), muscle atrophy F-box protein (MaFbx) and FOXO3a, and increased the p-FOXO3a level in vivo and in vitro, indicating that L-carnitine inhibits muscle protein ubiquitination in models of cachexia. Inhibition of Akt, upstream of FOXO3a, reversed the effects of L-carnitine on the FOXO3a/MaFbx pathway and myotube diameters, without affecting FOXO3a/MuRF-1. In addition to regulating the ubiquitination of muscle proteins, L-carnitine also increased the levels of p-p70S6K and p70S6K, which are involved in protein synthesis. Akt inhibition did not reverse the effects of L-carnitine on p70S6K. Hence, L-carnitine ameliorated cancer cachexia via the Akt/FOXO3/MaFbx and p70S6K pathways. Moreover, L-carnitine reduced the serum levels of interleukin-1 (IL-1) and interleukin-6 (IL-6), factors known to induce cancer cachexia. However, there were minimal effects on TNF-α, another inducer of cachexia. Taken together, these results revealed a novel mechanism of action by which L-carnitine protects muscle cells and reduces inflammation related to cancer cachexia.