Habitual Myofibrillar Protein Synthesis Is Normal in Patients with Upper GI Cancer Cachexia.

ABSTRACT

PURPOSE: Skeletal muscle wasting and weight loss are characteristic features of cancer cachexia and contribute to impaired function, increased morbidity, and poor tolerance of chemotherapy. This study used a novel technique to measure habitual myofibrillar protein synthesis in patients with cancer compared with healthy controls. EXPERIMENTAL DESIGN: An oral heavy water (87.5 g deuterium oxide) tracer was administered as a single dose. Serum samples were taken over the subsequent week followed by a quadriceps muscle biopsy. Deuterium enrichment was measured in body water, serum alanine, and alanine in the myofibrillar component of muscle using gas chromatography-pyrolysis-isotope ratio mass spectrometry and the protein synthesis rate calculated from the rate of tracer incorporation. Net change in muscle mass over the preceding 3 months was calculated from serial CT scans and allowed estimation of protein breakdown. RESULTS: Seven healthy volunteers, 6 weight-stable, and 7 weight-losing (≥5% weight loss) patients undergoing surgery for upper gastrointestinal cancer were recruited. Serial CT scans were available in 10 patients, who lost skeletal muscle mass preoperatively at a rate of 5.6%/100 days. Myofibrillar protein fractional synthetic rate was 0.058%, 0.061%, and 0.073%/hour in controls, weight-stable, and weight-losing patients, respectively. Weight-losing patients had higher synthetic rates than controls (P = 0.03). CONCLUSION: Contrary to previous studies, there was no evidence of suppression of myofibrillar protein synthesis in patients with cancer cachexia. Our finding implies a small increase in muscle breakdown may account for muscle wasting.