Origin of Intact Lactoferrin and Its DNA-Binding Fragments Found in the Urine of Human Milk-Fed Preterm Infants. Evaluation by Stable Isotopic Enrichment

Abstract

ABSTRACT. 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 [13Cjle~cine and ['5N2]lysine or [2H4]lysine. Mothers of infants selected for the study were infused i.v. with [I3q leucine and ["N2]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 DNAbinding 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 motherfinfant 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. Lactofemn is a major constituent of human colostral milk and whey (I). This 78-kD secretory glycoprotein binds several different transition metal ions (2, 3), but is best characterized for its iron-binding properties and its association with host defense at mucosal surfaces (4). Perhaps more interesting are its postulated growth-promoting (5,6) and immune-modulating properties (7-1 1). The structures of human hololactofemn and apolactofemn are known (12, 13), but their full biologic significance and mechanisms of action remain the subject of continued investigations.Utilization of lactofemn by the immature gastrointestinal system of preterm and term infants is poorly characterized. Infants fed human milk excrete higher levels of fecal lactofemn than do infants fed bovine milk-based formulas (14-18). Fecal excretion, however, accounts for only a few percent (1-6%) of the lactofemn fed ( 16,17), and most fecal lactofemn is degraded to lower molecular mass forms (1 9-2 1). Investigators have also reported higher levels of lactofenin and lactoferrin fragments, free secretory component, and secretory IgA in the urine of infants fed human milk than in the urine of infants fed a bovine milk-based formula (21,22). The molecular sizes of these immune factors are larger than normally filtered by glomeruli (23). The serum levels of...

Oropharyngeal Colostrum Administration in Extremely Premature Infants: An RCT

“…The half-lives of sIgA and lactoferrin are 3 to 6 days, and their uptake from breast milk via neonatal gut mucosa with subsequent excretion of their intact maternal forms in the urine were well demonstrated in previous studies. 7,[20][21][22] This exceptional mucosal absorption might be expected to occur only in preterm infants, particularly before "gut closure," and our findings support this hypothesis. 23,24 On the other hand, in addition to mucosal absorption, the result of continued increase of urinary sIgA at 2 weeks of age might be reflective that oropharyngeal stimulation by colostrum enhances endogenous production and/or excretion of sIgA.…”

Lactoferrin: a review

“…Endocytosis performed by Kupffer cells, liver endothelial cells, and hepatocytes contributes to lactoferrin removal (Levay and Viljoen, 1995). Kidneys seem to be involved in the removal of lactoferrin from the circulation since lactoferrin and its fragments, mainly of maternal origin, have been found in the urine of breast-fed infants (Hutchens et al, 1991).…”

Identification of an alternative form of human lactoferrin mRNA that is expressed differentially in normal tissues and tumor-derived cell lines

“…However, in some malignancies, the levels of LF are lower (17,18). In addition, methylation patterns in and around the LF gene are altered in malignant compared with normal breast cells (19).…”