Determination of protein synthesis in human rectal cancer in situ
by continuous 1-13c-leucine infusion.
Hartl, Wolfgang H., Hans Demmelmair, Karl-Walter Jauch, Hanns-Ludwig
Schmidt, Berthold Koletzko, Friedrich W. Schildberg.
Department of Surgery, Klinikum Grosshadern, Kinderpoliklinik,
Klinikum Innenstadt, Ludwig-Maximilian University Munich, Department
of General Chemistry and Biochemistry, Technical University Munich,
Germany
APStracts 4:0024E, 1997.
Previous studies on human colorectal tumor protein synthesis in situ
relied on techniques which required intra- or perioperative sampling
to obtain a sufficient biopsy size. The purpose of the present study
was to develop a new technique using new mass spectrometry equipment
(capillary GC/combustion IRMS) which allows reduction of the
necessary sampling size. Thereby, tumor sampling could be done via
conventional recto-sigmoidoscopy, excluding the need for further
disturbing invasive measures. Fivteen postabsorptive patients with
localized rectal cancer received a primed-constant infusion of 1-13C
-leucine (0.16 [mu]mol/kg min, 9.6 [mu]mol/kg prime). Forceps biopsies
were taken after 3 and 6 hours. In five subjects, tumor tissue and
normal mucosa were studied simultaneously. Determination of protein
-bound leucine enrichment was done by GC/IRMS, and GC/quadrupole MS
was used to determine tracer/tracee ratios for free, intracellular
leucine. GC/MS data demonstrated achievement of a steady state in the
precursor pool enrichment after 3 hours of isotope infusion
(tracer/tracee ratio 3 hours: 6.34 +/- 0.46%, 6 hours: 6.58 +/- 0.38
%). Calculation of tumor protein synthesis yielded a fractional
synthetic rate of 1.06 +/- 0.11 %/h or 25.5 +/- 2.6 %/d, range 12.0
to 37.1 %/d. At any time, protein-bound leucine enrichment was
significantly higher in tumor tissue than in normal mucosa of the
same subject. However, protein synthetic rates were comparable
(tumor: 1.09 +/- 0.20 %/h, mucosa: 1.29 +/- 0.28 %/h). Thus, combined
GC/combustion IRMS and GC/quadrupole MS provide a simple, reliable
and minimally invasive method to determine tumor fractional synthetic
rate in situ, thereby excluding interferences common to previous
methods. Tumor and mucosa tissue are similar with respect to protein
synthesis, but apparently differ with respect to leucine extraction
from the arterial blood.
Received 18 October 1996; accepted in final form 2 January 1997.
APS Manuscript Number E516-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 19 February 1997