Abstract
Aims: Cancer cachexia is a syndrome which results in severe loss of muscle mass and marked fatigue. Conditioned media from cachexia-inducing cancer cells triggers metabolic dysfunction in skeletal muscle, including decreased mitochondrial respiration, which may contribute to fatigue. We hypothesized that Lewis lung carcinoma conditioned medium (LCM) would impair the mitochondrial electron transport chain (ETC) and increase production of reactive oxygen species, ultimately leading to decreased mitochondrial respiration. We incubated C2C12 myotubes with LCM for 30 min, 2, 4, 24 or 48 h. We measured protein content by western blot; oxidant production by 2′,7′-dichlorofluorescin diacetate (DCF), 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate (DAF), and MitoSox; cytochrome c oxidase activity by oxidation of cytochrome c substrate; and oxygen consumption rate (OCR) of intact myotubes by Seahorse XF Analyzer. Results: LCM treatment for 2 or 24 h decreased basal OCR and ATP-related OCR, but did not alter the content of mitochondrial complexes I, III, IV and V. LCM treatment caused a transient rise in reactive oxygen species (ROS). In particular, mitochondrial superoxide (MitoSOX) was elevated at 2 h. 4-Hydroxynonenal, a marker of oxidative stress, was elevated in both cytosolic and mitochondrial fractions of cell lysates after LCM treatment. Conclusion: These data show that lung cancer-conditioned media alters electron flow in the ETC and increases mitochondrial ROS production, both of which may ultimately impair aerobic metabolism and decrease muscle endurance.
Highlights
Cancer kills nearly 600,000 Americans annually, equating to approximately 1500 deaths every day (Society, 2012)
Thirty minutes of lung carcinoma conditioned medium (LCM) treatment did not affect electron transport chain (ETC) activity; 2 or 24 h of LCM treatment resulted in depressed basal respiration (Figure 1C)
To test our hypothesis that LCM treatment would alter the level of oxidants, we examined general oxidant production, reactive nitrogen species (RNS) production, and mitochondrial superoxide anion production in myotubes treated with LCM for 30 min, 4, 6, and 24 h
Summary
Cancer kills nearly 600,000 Americans annually, equating to approximately 1500 deaths every day (Society, 2012). Fifty percent of all cancer patients experience cachexia, a severe wasting syndrome that includes loss of muscle mass, weakness and fatigue (Tan and Fearon, 2008; Fearon et al, 2011). Some recent studies found evidence of mitochondrial dysfunction in cachexia, which may contribute to muscle pathology (Tan and Fearon, 2008; Constantinou et al, 2011; Fearon et al, 2011; Julienne et al, 2012, 2014; Wang et al, 2012; White et al, 2012; Dumas et al, 2013; Fontes-Oliveira et al, 2013; Tzika et al, 2013)
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