Whole-body protein turnover in peritoneal dialysis patients: a comparison of the [15N]glycine end product and the [13C]leucine precursor methods.
BACKGROUND
Two well-described methods for measuring whole-body protein turnover (WBPT) are the precursor method using a primed continuous infusion of [1-(13)C]leucine and the end-product method with a single oral dose of [(15)N]glycine. We previously measured the effects of amino acid (AA)-containing dialysate on protein anabolism in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) using the [1-(13)C]leucine technique. Here, we examine whether the less invasive [(15)N]glycine method could also be appropriate for studying nutritional interventions.


METHODS
We compared the results of WBPT measurements using a single oral dose of [(15)N]glycine with those obtained with the primed continuous infusion of [1-(13)C]leucine during AA and glucose (G) dialysis and G-only dialysis in 12 CAPD patients in the fed state.


RESULTS
The end-product method showed a wide variation for protein synthesis and breakdown measurements. It did not detect a small but significant increase in protein synthesis with AA-containing dialysate as shown by the precursor method. However, a significant relation was found between both methods for net protein synthesis (i.e. protein synthesis minus breakdown) during AA and G (r = 0.75, P = 0.005) or during G-only dialysis (r = 0.86, P < 0.001). The agreement between the two methods for the net protein balance was good [intra-class correlation coefficient (ICC) = 0.88] with G-only dialysate and moderate (ICC = 0.70) with AA and G dialysate.


CONCLUSIONS
While the precursor method shows less variation, the more convenient end-product method may be useful in larger groups of selected patients including those on PD.
Tjiong
Hoey Lan
HL
Department of Internal Medicine, Erasmus MC's, University Medical Center Rotterdam, The Netherlands. h.tjiong@erasmusmc.nl
Swart
Roel
R
Rietveld
Trinet
T
Wattimena
Josias L
JL
Hop
Wim C
WC
Fieren
Marien W
MW
van den Berg
Jacobus W
JW
D000328:Adult; D000368:Aged; D002247:Carbon Isotopes; D015314:Dialysis Solutions; D005260:Female; D005998:Glycine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006801:Humans; D007930:Leucine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D009587:Nitrogen Isotopes; D010531:Peritoneal Dialysis, Continuous Ambulatory; D011506:Proteins / Q000378:metabolism*
D002247:Carbon Isotopes; D015314:Dialysis Solutions; D009587:Nitrogen Isotopes; D011506:Proteins; D007930:Leucine; D005998:Glycine