Dysprosium as a nonabsorbable marker for studies of mineral absorption with stable isotope tracers in human subjects.

Abstract

Two studies were conducted to determine if dysprosium (Dy) could be used as a quantitative fecal marker for studies of zinc-70 (70Zn), copper-65 (65Cu) and magnesium-26 (26Mg) absorption in humans. In the first experiment, Dy excretion was shown to be complete (104 +/- 9%; mean +/- SD, n = 6) and the kinetics of fecal Dy excretion closely paralleled that of 70Zn but not 65Cu. Because of the similarity in 70Zn and Dy excretion kinetics, a method for estimating 70Zn absorption was developed which used 70Zn and Dy data from only the first two stools passed after isotope administration. Average estimates of 70Zn absorption based on the two-stool (partial pool) vs total pool (5-day composite) method were not different (28.0 +/- 5.2 vs 24.4 +/- 4.1%, respectively; means +/- SEM; p > 0.10). In the second study, the same questions was addressed relative to 26Mg absorption. 26Mg and Dy also exhibited nearly identical excretion patterns. Average estimates of 26Mg absorption based on the partial pool vs total pool method were comparable yielding mean values of 22.7 +/- 3.4 vs 23.2 +/- 2.5% and 26.1 +/- 1.8 vs 24.3 +/- 1.8%, respectively, from magnesium-26 oxide (26MgO) and 26Mg glycinate. Advantages and limitations of the partial pool method for estimating mineral absorption are discussed.

Measurement of magnesium absorption and retention in type 2 diabetic patients with the use of stable isotopes

“…Ytterbium is a rare earth element, the absorption of which is < 0.05% when administered orally (50). Rare elements have been evaluated in studies of iron and magnesium (26,27,51) and have been shown to be useful tools to correct for incomplete stool collection. Bohn (26) showed that the excretion of ytterbium and the magnesium isotopic label was significantly correlated.…”

Holmium as a faecal marker for copper absorption studies in adults

“…Dysprosium has been used as a quantitative faecal marker in human mineral absorption studies, where the excretion kinetics were found to parallel those of zinc and magnesium, but not copper [10]. However, in all cases dysprosium recovery from the faeces was complete.…”

“…However, when an allowance is made for the re-excreted copper, the term true absorption is used. Previous studies have used rare earth elements as non-absorbable faecal markers to delineate the excretion of unabsorbed isotope from endogenous secretion, and also to correct for completeness of collection [10,11]. To date, however, there has been no validation of the reliability of using the rare earth element holmium as a faecal marker in '&Cu stable isotope studies.…”

“…Two 0.5 g replicates of each powdered faecal sample were microwave-digested until a clear solution was obtained. For quantitative analysis of copper and holmium, 1 ml of the acid digest was diluted to 10 ml Holmium as a faecal marker 10 3 mg of 65 Cu and 1 mg of Ho added to a mushroom soup (350 g of mushrooms blended with 6.5 g of butter, 143 g of demineralized water and seasoning) Extrinsically labelled sunflower seeds 8 1 mg of 65 Cu in 37.5 g of sunflower seed butter (25 g of finely chopped sunflower seeds with 12.5 g of butter) served on 35 g of toasted white bread ; 1 mg of Ho was given simultaneously in 125 ml of diet cola Intrinsically labelled sunflower seeds 8 1 mg of 65 Cu in 75 g of sunflower seed butter (50 g of finely chopped intrinsically labelled sunflower seeds with 25 g of butter) served on 70 g of toasted white bread ; 1 mg of Ho was given simultaneously in 125 ml of diet cola Extrinsically labelled soya beans 5 3 mg of 65 Cu and 1 mg of Ho in 450 g of cooked and homogenized soya beans Intrinsically labelled soya beans 9 0.3 mg of 65 Cu and 1 mg of Ho in 450 g of cooked and homogenized soya beans certified reference material tea (Cu 17.3p3 µg\g) for copper gave a mean value of 16.2p1.0 µg\g (n l 4). Samples were analysed quantitatively for copper by AAS using a Thermo-Unicam Solaar 969 atomic absorption spectrophotometer, which had been calibrated with standards prepared from 1000 mg\l SpectrosoL (BDH) stock solution.…”

The double isotope tracer method is a reliable measure of fractional zinc absorption

“…Rare earth elements follow a similar excretory pattern to unabsorbed stable isotopes of iron and, by inference, other inorganic nutrients like zinc (Schuette et al, 1993).…”