Holmium as a faecal marker for copper absorption studies in adults

Abstract

The objective of the present study was to investigate the validity of using holmium as a faecal marker in a copper absorption study using a highly enriched (65)Cu stable isotope label. Ten volunteers (nine female, one male) aged 24-55 years were recruited from the Norwich area to take part in a free-living study. The study was conducted in the Human Nutrition Unit at the Institute of Food Research, Norwich, U.K., and involved feeding breakfast test meals containing foods labelled intrinsically or extrinsically with a highly enriched (65)Cu stable isotope label. A 1 mg oral dose of the rare earth element holmium was administered to volunteers simultaneously with an oral dose of highly enriched (65)Cu stable isotope as a label in the breakfast test meal. Complete faecal collections were made for 10 days after dosing, and the mean percentage holmium recovery (+/- S.D.) was 105 +/- 15%. After correcting for re-excreted copper label, the labelled copper and holmium had similar excretory profiles. It was concluded that holmium is a valid faecal marker in adult human copper absorption studies using stable isotopes.

Copper absorption from foods labelled intrinsically and extrinsically with Cu-65 stable isotope

“…True copper absorption was obtained by correcting the apparent copper absorption for endogenous losses of copper (Harvey et al, 2002). The reference dose was absorbed most efficiently (5479%) and was significantly higher than that from either the mushrooms, extrinsically labelled sunflower butter or extrinsically or intrinsically labelled soya bean test meals.…”

“…There was a minimum interval of 4 weeks between each test meal. An additional aim of the study was to validate the use of the rare earth element holmium as a faecal marker in copper absorption studies and these data have been published elsewhere (Harvey et al, 2002).…”

“…Apparent absorption is the difference between labelled copper intake and excretion in faeces and true absorption is calculated when an allowance is made for the copper which is firstly absorbed and then endogenously excreted into the gastrointestinal tract. The calculation of true absorption is described in a previous publication (Harvey et al, 2002). In summary, assuming that all subsequent stools, after the complete collection of holmium, only contain labelled copper which has been absorbed and then endogenously excreted, it is possible to plot the mole fraction of labelled copper against time for these latter stools, fit a straight line through the points (in the form y ¼ mx þ c) and extrapolate back to the time of dose administration.…”

“…Faecal samples were prepared for analysis as previously described (Harvey et al, 2002). Samples were quantitatively analysed for copper by AAS, calibrated with standards prepared from 1000 mg/l SpectrosoL (BDH) stock solution.…”

“…Isotopically enriched copper chloride (CuCl 2 ) was prepared from elemental Cu-65 (Europa Scientific Ltd, Crewe, UK) as previously described (Harvey et al, 2002). Individual doses were stored in plastic vials at À201C until required.…”