Ketoacids (KA) are known to improve muscle mass among patients with chronic kidney disease (CKD) on a low-protein diet (CKD-LPD), but the mechanism of its preventive effects on muscle atrophy still remains unclear. Since muscle atrophy in CKD may be attributable to the down-regulation of the Wnt7a/Akt/p70S6K pathway and the activation of the ubiquitin -proteasome system (UPS) and the apoptotic signalling pathway, a hypothesis can readily be drawn that KA supplementation improves muscle mass by up-regulating the Wnt7a/Akt/p70S6K pathway and counteracting the activation of the UPS and caspase-3-dependent apoptosis in the muscle of CKD-LPD rats. Rats with 5/6 nephrectomy were randomly divided into three groups, and fed with either 22 % protein (normal-protein diet; NPD), 6 % protein (LPD) or 5 % protein plus 1 % KA for 24 weeks. Sham-operated rats with NPD intake were used as the control. The results demonstrated that KA supplementation improved protein synthesis and increased related mediators such as Wnt7a, phosphorylated Akt and p70S6K in the muscle of CKD-LPD rats. It also inhibited protein degradation, withheld the increase in ubiquitin and its ligases MAFbx (muscle atrophy F-box) and MuRF1 (muscle ring finger-1) as well as attenuated proteasome activity in the muscle of CKD-LPD rats. Moreover, KA supplementation gave rise to a reduction in DNA fragment, cleaved caspase-3 and 14 kDa actin fragment via the down-regulation of the Bax:Bcl-2 ratio in the muscle of CKD-LPD rats. The beneficial effects unveiled herein further consolidate that KA may be a better therapeutic strategy for muscle atrophy in CKD-LPD.

The present study aimed to determine the effect of Astragalus polysaccharide (APS) in an in vivo and in vitro rat model of muscle atrophy (cachexia) caused by chronic renal failure (CRF), along with the potential corresponding roles of atroglin-1 and the ubiquitin-proteasome pathway. A rat model of CRF was established using subtotal bilateral nephrectomy. It was observed by reverse transcription-quantitative polymerase chain reaction and western blot analysis that APS and the specific inhibitor of nuclear factor (NF)-κB, pyrrolidine dithiocarbamate (PDTC), significantly reduced the expression of atrogin-1, ubiquitin and the NF-κB subunit p65 mRNA in rat skeletal muscle in vivo and in vitro, respectively (P<0.05). NF-κB and PDTC also markedly reduced the expression of atrogin-1, ubiquitin and p65 protein. In addition, cultured rat myoblasts pretreated with tumor necrosis factor (TNF)-α exhibited significantly reduced expression of atrogin-1, ubiquitin and p65 mRNA in vitro (P<0.05). Fluorescence microscopy was subsequently used to evaluate TNF-α-treated myoblasts administered with APS or PDTC, whereby no evidence of muscle cell atrophy was observed in cells treated with APS. These data suggest that APS may delay muscle cell atrophy associated with cachexia in CRF by targeting atrogin-1 and the ubiquitin-proteasome pathway.