Protein synthesis measurement in cancer patients with 13C valine

The flooding dose technique is a method that uses tracer amino acids to measure the rate of protein synthesis in tissues in vivo. This technique involves the injection of a large amount of unlabelled amino acid together with the tracer to minimize difference in isotopic enrichment of the free amino acid in plasma and tissue compartments which represent the precursor pool of protein synthesis. Seven patients with localized colorectal carcinoma received a total parenteral nutrition before surgery and protein synthesis was measured in tumour and colon after administration of a large dose of valine (20% atom percent excess). The enrichment of free valine in plasma and tissues was measured by GCMS and the enrichment of protein-bound valine into tumour and colon by IRMS. The fractional synthesis rate in tumours was 13.44 +/- 6.9%/day compared to a value of 10.9 +/- 8.1%/day in healthy colon. The lack of significant difference probably relates to the low number of patients and the variability of protein synthesis rate in tumours.