Lipid is heterogeneously distributed in muscle and associates with low radiodensity in cancer patients

BACKGROUND: Low muscle radiodensity is associated with mortality in a variety of cancer types. Biochemical and morphological correlates are unknown. We aimed to evaluate triglyceride (TG) content and location as a function of computed tomography (CT)-derived measures of skeletal muscle radiodensity in cancer patients. METHODS: Rectus abdominis (RA) biopsies were collected during cancer surgery from 75 patients diagnosed with cancer. Thin-layer chromatography and gas chromatography were used for quantification of TG content of the muscle. Axial CT images of lumbar vertebra were used to measure muscle radiodensity. Oil Red O staining was used to determine the location of neutral lipids in frozen muscle sections. RESULTS: There was wide variation in RA radiodensity in repeated measures (CV% ranged from 3 to 55% based on 10 serial images) as well as within one slice (CV% ranged from 6 to 61% based on 10 subregions). RA radiodensity and total lumbar muscle radiodensity were inversely associated with TG content of RA (r = -0.396, P < 0.001, and r = -0.355, P = 0.002, respectively). Of the total percentage area of muscle staining positive for neutral lipid, 54 +/- 17% was present as extramyocellular lipids (range 23.5-77.8%) and 46 +/- 17% (range 22.2-76.5%) present as intramyocellular lipid droplets. CONCLUSIONS: Repeated measures revealed wide variation in radiodensity of RA muscle, both vertically and horizontally. Low muscle radiodensity reflects high level of TG in patients with cancer. Non-uniform distribution of intramyocellular and extramyocellular lipids was evident using light microscopy. These results warrant investigation of mechanisms resulting in lipid deposition in muscles of cancer patients.