Labeling Hen's Egg with 74Se for Use in Human Metabolic Experiments

Experiments were conducted with laying hens to explore quantitative aspects of incorporation of 75Se (radioselenium) at various dosing levels and for different chemical forms of an orally administered tracer. Quantitative distribution of the incorporated isotope in egg white and egg yolk was strongly influenced by both the chemical form of the label and the dosing level. The ratio of egg yolk:egg white selenium decreased with increased level of administered dose of selenite. In addition, the rate of incorporation and the amount of selenium in whole egg were higher when [75Se]selenomethionine was given as compared to [75Se]selenite. Characterization of the chemical form of selenium in egg white and egg yolk labeled biologically by giving hens radioactive selenite or selenomethionine was performed by classification as: selenite, selenoprotein and fat-bound selenium. Studies were then undertaken to achieve intrinsic labeling of egg white and egg yolk with stable isotope 74Se for purposes of exploring selenium bioavailability in humans. Enrichments of 74Se in egg white and egg yolk of hens given high dose selenite (54.4 µg 74Se) were 20- and 28-fold, whereas in egg white and egg yolk of hens given low dose (10.9 µg 74Se) they were 4- and 10-fold the level of natural abundance, respectively. The stable isotope-labeling studies indicated that a 7-day sequential dosing protocol with 20–100 µg Se per dose permitted sufficient enrichment of egg white (only high dose) and of yolk with the stable isotope 74Se for use in human metabolic studies.