Consequences of Late-Stage Non–Small-Cell Lung Cancer Cachexia on Muscle Metabolic Processes

Muscle loss is common in advanced lung cancer, impairing quality of life and shortening life expectancy. The impact of cancer on muscle metabolism has not been well explored. The effects of late-stage non–small-cell lung cancer on key metabolic processes in muscle was studied. Changes consistent with impaired synthesis of new muscle proteins and reduced lipid storage were observed. Introduction The loss of muscle is common in patients with advanced non–small-cell lung cancer (NSCLC) and contributes to the high morbidity and mortality of this group. The exact mechanisms behind the muscle loss are unclear. Patients and Methods To investigate this, 4 patients with stage IV NSCLC who met the clinical definitions for sarcopenia and cachexia were recruited, along with 4 age-matched healthy volunteers. After an overnight fast, biopsy specimens were obtained from the vastus lateralis, and the key components associated with inflammation and the control of muscle protein, carbohydrate, and fat metabolism were assessed. Results Compared with the healthy volunteers, significant increases in mRNA levels for interleukin-6 and NF-κB signaling and lower intramyocellular lipid content in slow-twitch fibers were observed in NSCLC patients. Although a significant decrease in phosphorylation of the mechanistic target of rapamycin (mTOR) signaling protein 4E-BP1 (Ser⁶⁵) was observed, along with a trend toward reduced p70 S6K (Thr³⁸⁹) phosphorylation (P = .06), no difference was found between groups for the mRNA levels of MAFbx (muscle atrophy F box) and MuRF1 (muscle ring finger protein 1), chymotrypsin-like activity of the proteasome, or protein levels of multiple proteasome subunits. Moreover, despite decreases in intramyocellular lipid content, no robust changes in mRNA levels for key proteins involved in insulin signaling, glycolysis, oxidative metabolism, or fat metabolism were observed. Conclusion These findings suggest that examining the contribution of suppressed mTOR signaling in the loss of muscle mass in late-stage NSCLC patients is warranted and reinforces our need to understand the potential contribution of impaired fat metabolism and muscle protein synthesis in the etiology of cancer cachexia.