Oxoproline kinetics and oxoproline urinary excretion during glycine- or sulfur amino acid-free diets in humans.
L-5-oxoproline (L-5-OP) is an intermediate in glutathione synthesis, possibly limited by cysteine availability. Urinary 5-OP excretion has been proposed as a measure of glycine availability. We investigated whether 5 days of dietary sulfur amino acid (SAA-free) or glycine (Gly-free) restriction affects plasma kinetics of 5-OP and urinary excretion of L- and D-5-OP in 6 healthy men. On day 6, L-5-[1-(13)C]oxoproline and [3,3-(2)H(2)]cysteine were infused intravenously for 8 h (3 h fast/5 h fed). In a control study (adequate amino acid mixture), plasma oxoproline fluxes were 37.8 +/- 13.8 (SD) and 38.4 +/- 14.8 micromol x kg(-1) x h(-1); oxidation accounted for 85% of flux. Cysteine flux was 47.9 +/- 8.5 and 43.2 +/- 8.5 micromol x kg(-1) x h(-1) for fast and fed phases, respectively. Urinary excretion of L- and D-5-OP was 70 +/- 34 and 31.1 +/- 13.3 micromol/mmol creatinine, respectively, during days 3-5, and 46.4 +/- 13.9 and 22.4 +/- 8.3 micromol/mmol over the 8-h tracer study. The 5-OP flux for the Gly-free diet was higher (P = 0. 018) and tended to be higher for the SAA-free diet (P = 0.057) when compared with the control diet. Oxidation rates were higher on the Gly-free (P = 0.005) and SAA-free (P = 0.03) diets. Cysteine fluxes were lower on the the Gly-free (P = 0.01) and the SAA-free diets (P = 0.001) compared with the control diet. Rates of L-5-OP excretion were unchanged by withdrawal of SAA or Gly for 5 days but increased on day 6 (P = 0.005 and P = 0.019, respectively). Thus acute changes in the dietary availability of SAA and Gly alter oxoproline kinetics and urinary 5-OP excretion.
Metges
C C
CC
Laboratory of Human Nutrition, School of Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. metges@www.dife.de
Yu
Y M
YM
Cai
W
W
Lu
X M
XM
Wong
S
S
Regan
M M
MM
Ajami
A
A
Young
V R
VR
D000328:Adult; D000603:Amino Acids, Sulfur / Q000008:administration & dosage / Q000172:deficiency*; D003404:Creatinine / Q000652:urine; D003545:Cysteine / Q000097:blood; D004032:Diet; D005215:Fasting; D005502:Food; D005998:Glycine / Q000008:administration & dosage / Q000172:deficiency*; D006801:Humans; D007700:Kinetics; D008297:Male; D010084:Oxidation-Reduction; D011761:Pyrrolidonecarboxylic Acid / Q000097:blood* / Q000652:urine*
D000603:Amino Acids, Sulfur; D003404:Creatinine; D003545:Cysteine; D011761:Pyrrolidonecarboxylic Acid; D005998:Glycine