The use of 5-L-oxoproline excretion in urine as an index of glycine insufficiency

It has been shown that in normal adults there is a low excretion of 5-oxoproline (208 &mu;mol/day, 95% CI 189 to 277) which varies among and between individuals. Vegetarians were found to excrete increased levels of urinary 5-oxoproline (336 &mu;mol/day, 95% CI 278 to 392, p&lt;.01 compared to omnivores) compared with those on a mixed diet which included animal protein. When the dietary nitrogen intake of normal adults was controlled there was a significant increase in urinary 5-oxoproline (510 &mu;mol/day, 95% CI 318 to 710, p&lt;.001 compared to adequate protein intake) on the fifth day on a low protein diet. The excretion in the vegetarians was the same as that predicted from the response to that of controlled low protein intake.Further it was shown that when there is an unbalanced demand for glycine during growth (pregnancy, infancy, childhood and adolesence) there was an increase in urinary 5-oxoproline. In pregnancy and early infancy there was a wide variability between individuals and the rate of excretion could reach very high values. The basis of these differences is not clear, but there was a suggestion that maturity or difference in rates of growth might be important associates. When children recovering from severe malnutrition were given dietary supplementation of glycine for a short period of time there was evidence of benefit, although this was not clear cut. The appearance was that in the children who were growing most rapidly the supplement was not sufficient to satisfy all the demands associated with the most rapid weight gain.These data provide supporting evidences that glycine should be considered a conditionally essential amino acid during growth and marginal intake, when the demands for glycine are greater than the supply.</p

Effects of tuberculosis and HIV infection on whole-body protein metabolism during feeding, measured by the [15N]glycine method

Background: Tuberculosis (TB) and HIV infection are wasting diseases that frequently occur together and have severe consequences on nutritional status.Objective: The objective was to determine the effects of TB and HIV, separately and together, on protein metabolism.Design: Protein metabolism was determined in the fed state in 11 healthy control subjects, in 10 patients with HIV infection without TB or other active infection (HIV group), in 10 patients with active TB without HIV infection (TB group), and in 8 patients with HIV infection and active TB (HIVTB group) with the use of oral [15N]glycine and measurement of enrichment in urinary urea and ammonia.Results: Whole-body protein flux and degradation were lower in the HIV group than in the control group (mean flux: 3.53 ± 0.40 compared with 4.75 ± 0.97 g · kg lean body mass-1 · 12 h-1; P = 0.002). Protein flux, synthesis, and degradation were not significantly different between the control group and the TB and HIVTB groups. Net protein balance was strongly anabolic in the control, HIV, and TB groups but was neutral in the HIVTB group (P &lt; 0.001 for comparison between groups).Conclusions: HIV infection was associated with a significant down-regulation of whole-body protein flux. TB alone was not associated with abnormal protein metabolism, but net anabolism in the fed state was impaired in the HIVTB group