Origin of intact lactoferrin and its DNA-binding fragments found in the urine of human milk-fed preterm infants. Evaluation by stable isotopic enrichment.
The origin of intact (78-kD) lactoferrin found in the urine of human milk-fed preterm infants was investigated using human milk containing proteins enriched with [13C]leucine and [15N2]lysine or [2H4]lysine. Mothers of infants selected for the study were infused i.v. with [13C] leucine and [15N2]lysine or [2H4]lysine to label milk proteins. The labeled milk was collected from each mother, pooled, fortified with a lyophilized human milk fraction, and fed to her preterm infant by continuous orogastric infusion for a period of 48 h. Urine was collected from each infant for 96 h. Intact lactoferrin (78 kD) and DNA-binding lactoferrin fragments (51 and 39 kD) were purified from the urine by affinity chromatography on columns of immobilized single-stranded DNA-agarose. The concentration and isotopic enrichment of the intact lactoferrin and DNA-binding fragments were determined separately after their isolation by high-performance reverse-phase (phenyl) chromatography. Mass spectral analyses indicated that the isotopic enrichment of the purified urinary lactoferrin was 87 to 100% of that in the labeled human milk lactoferrin. Similar results were obtained for the isolated DNA-binding lactoferrin fragments. The ratios of isotopically labeled leucine to lysine in the purified milk lactoferrins and urinary lactoferrins were similar for each mother/infant pair. Isotopically labeled lysine, added to the milk as free amino acid, was not incorporated into the purified urinary lactoferrin. These results demonstrate that undegraded (78-kD) lactoferrin of maternal origin is absorbed by the gut and excreted intact in the urine of preterm infants; nearly all of the urinary lactoferrin was of maternal origin. The possible immunoregulatory functions of the absorbed intact, maternal lactoferrin are discussed.
Hutchens
T W
TW
Department of Pediatrics, Baylor College of Medicine Hospital, Houston, Texas.
Henry
J F
JF
Yip
T T
TT
Hachey
D L
DL
Schanler
R J
RJ
Motil
K J
KJ
Garza
C
C
D004268:DNA-Binding Proteins / Q000652:urine*; D004064:Digestive System / Q000378:metabolism; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D007554:Isotopes; D007781:Lactoferrin / Q000652:urine*; D007930:Leucine / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D008895:Milk, Human / Q000378:metabolism*; D010446:Peptide Fragments / Q000652:urine*
D004268:DNA-Binding Proteins; D007554:Isotopes; D010446:Peptide Fragments; D007781:Lactoferrin; D007930:Leucine; D008239:Lysine