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The transfer of 15N from urea to lysine in the human infant

Published online by Cambridge University Press:  09 March 2007

D. Joe Millward ,
Terrance Forrester ,
Eric Ah-Sing ,
Nana Yeboah ,
Neil Gibson ,
Asha Badaloo ,
M. Boyne ,
M. Reade ,
C. Persaud  and
Alan Jackson
D. Joe Millward*
Affiliation:
Centre for Nutrition and Food Safety, School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK
Terrance Forrester
Affiliation:
Tropical Metabolism Research Unit, University of the West Indies, Jamaica
Eric Ah-Sing
Affiliation:
Centre for Nutrition and Food Safety, School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK
Nana Yeboah
Affiliation:
Centre for Nutrition and Food Safety, School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK
Neil Gibson
Affiliation:
Centre for Nutrition and Food Safety, School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK
Asha Badaloo
Affiliation:
Tropical Metabolism Research Unit, University of the West Indies, Jamaica
M. Boyne
Affiliation:
Tropical Metabolism Research Unit, University of the West Indies, Jamaica
M. Reade
Affiliation:
Tropical Metabolism Research Unit, University of the West Indies, Jamaica
C. Persaud
Affiliation:
Institute of Human Nutrition, University of Southampton, Southampton SO16 6YD, UK
Alan Jackson
Affiliation:
Institute of Human Nutrition, University of Southampton, Southampton SO16 6YD, UK
*
*Corresponding author: Professor Joe Millward, fax + 44 (0) 1483 259 297, email [email protected]
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Abstract

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To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.To explore the nutritional significance of urea hydrolysis for human subjects, male infants being treated for severe undernutrition were given oral doses of 10 mg [15N15N]urea every 3 h for 36 h, on admission, during rapid growth and after repletion with either moderate or generous intakes of protein. Urea hydrolysis was calculated from the 15N enrichment of urinary urea, and where possible, lysine, alanine, glycine and histidine were isolated from urine by preparative ion-exchange chromatography for measurement of 15N enrichment. Sufficient N was obtained for 15N enrichment of lysine to be measured on fifteen occasions from six children. Urea hydrolysis accounted for half of all urea production with 130 (sd 85) mg N/kg hydrolysed per d, most of which appeared to be utilized in synthetic pathways. Of the samples analysed successfully, nine samples of lysine were enriched with 15N (mean atom percent excess 0·0102, range 0·0017–0·0208) with relative enrichment ratios with respect to lysine of 1·63 (range 0·18–3·15), 1·96 (range 0·7–3·73) and 0·9 (range 0·4–1·8) for glycine, alanine and histidine respectively. Enriched samples were identified at each treatment phase and 68 % of the variation in lysine enrichment was explained by the variation in urea enrichment with 54 % explained by the overall rate of delivery of 15N to the lower gastrointestinal tract. The results indicate a minimum of 4·7 mg lysine per kg body weight made available by de novo synthesis with the more likely value an order of magnitude higher. Thus, urea hydrolysis can improve the quality of the dietary protein supply by enabling an increased supply of lysine and other indispensable amino acids.

Keywords

UndernutritionUreaAmino acidsStable isotopes
Type
Research Article
Information
British Journal of Nutrition , Volume 83 , Issue 5 , May 2000 , pp. 505 - 512
Copyright
Copyright © The Nutrition Society 2000

References

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