Doxorubicin-induced skeletal muscle atrophy: Elucidating the underlying molecular pathways

Abstract

Aim: Loss of skeletal muscle mass is a common clinical finding in cancer patients. The purpose of this meta-analysis and systematic review was to quantify the effect of doxorubicin on skeletal muscle and report on the proposed molecular pathways possibly leading to doxorubicin-induced muscle atrophy in both human and animal models.

Methods: A systematic search of the literature was conducted in PubMed, EMBASE, Web of Science and CENTRAL databases. The internal validity of included studies was assessed using SYRCLE's risk of bias tool.

Results: Twenty eligible articles were identified. No human studies were identified as being eligible for inclusion. Doxorubicin significantly reduced skeletal muscle weight (ie EDL, TA, gastrocnemius and soleus) by 14% (95% CI: 9.9; 19.3) and muscle fibre cross-sectional area by 17% (95% CI: 9.0; 26.0) when compared to vehicle controls. Parallel to negative changes in muscle mass, muscle strength was even more decreased in response to doxorubicin administration. This review suggests that mitochondrial dysfunction plays a central role in doxorubicin-induced skeletal muscle atrophy. The increased production of ROS plays a key role within this process. Furthermore, doxorubicin activated all major proteolytic systems (ie calpains, the ubiquitin-proteasome pathway and autophagy) in the skeletal muscle. Although each of these proteolytic pathways contributes to doxorubicin-induced muscle atrophy, the activation of the ubiquitin-proteasome pathway is hypothesized to play a key role. Finally, a limited number of studies found that doxorubicin decreases protein synthesis by a disruption in the insulin signalling pathway.

Conclusion: The results of the meta-analysis show that doxorubicin induces skeletal muscle atrophy in preclinical models. This effect may be explained by various interacting molecular pathways. Results from preclinical studies provide a robust setting to investigate a possible dose-response, separate the effects of doxorubicin from tumour-induced atrophy and to examine underlying molecular pathways. More research is needed to confirm the proposed signalling pathways in humans, paving the way for potential therapeutic approaches.

Keywords: doxorubicin; mitochondrial dysfunction; muscle atrophy; reactive oxygen species; skeletal muscle; ubiquitin-proteasome pathway.

Figure 1

PRISMA Flow Diagram of the study selection process

Figure 2

Risk of bias graphs. Graph A displays the risk of selection, performance, detection, attrition and other biases, which were assessed in all included studies using SYRCLE’s risk of bias tool. Graph B displays the reporting of six key quality indicators. Review authors’ judgements about each item are presented as absolute numbers across all included studies

Figure 3

Forest plot of meta‐analysis estimates of the effect of doxorubicin on skeletal muscle weight (gram). Results are presented as percentage change in muscle weight with accompanying 95% CI. Subgroup analyses were conducted to assess the effect of doxorubicin on specific limb muscles

Figure 4

Forest plot of meta‐analysis estimates of the effect of doxorubicin on muscle fibre CSA (μm²). Results are presented as percentage change in muscle fibre size with accompanying 95% CI

Figure 5

A proposed schematic diagram of signalling pathways for doxorubicin‐induced muscle atrophy. Many intracellular pathways participate in doxorubicin‐induced muscle atrophy. The pathways are divided in three main pathways in this diagram: (a) The disrupted insulin signalling pathway leading to decreased protein synthesis, indicated in blue; (b) The autophagic signalling and ubiquitin‐proteasome proteolysis pathway leading to increased protein degradation, indicated in  green; and (c) Oxidative stress leading to mitochondrial degradation, indicated in  red. Insulin‐like growth factor 1 (IGF‐1) normally stimulates protein synthesis through Akt and mTOR. The insulin signalling pathway is disrupted in doxorubicin‐induced muscle atrophy and the expression of important proteins (ie GLUT4 and AMPK) involved in glucose uptake is decreased, which results in decreased protein synthesis. Myostatin (Mstn) increases protein degradation by activating forkhead (FOXO) family transcription factors. This allows for the increased transcription of important atrophy‐related genes (ie atrogin‐1/MaFbx and MuRF‐1). Furthermore, mitochondrial respiration is negatively affected by doxorubicin, resulting in excess ROS production. On the one hand this results in the activation of calpain‐1 and caspase‐3, which are proteases that are capable of, respectively, promoting muscle atrophy by cleaving structural proteins and degrading intact myofibrillar proteins. The activity of these two proteases is increased following doxorubicin administration, leading to proteolysis. On the other hand, it results in mitochondrial degradation, which leads to skeletal muscle atrophy. Note that underlined proteins are upregulated in response to chemotherapy