Richard A. Vanderpool

Selenium supplementation affects the retention of stable isotopes of selenium in human subjects consuming diets low in selenium

Twenty-nine women and fifteen men from an area of low Se intake (South Island of New Zealand) consumed 100 micrograms stable 74Se, as selenate given in water after an overnight fast, and blood was collected for 3 weeks. They were then divided into five groups and supplemented with 0, 10, 20, 30 and 40 micrograms Se/d (as selenomethionine) for 5 months. After 5 months, they received a second dose of 74Se identical to the first. Supplementation significantly altered retention of 74Se in the plasma, but not in the erythrocytes or platelets. Subjects receiving the placebo retained the greatest amount, and subjects receiving 30 micrograms supplemental Se/d retained the least 74Se. Supplementation resulted in relatively more isotope being retained in a medium molecular mass protein considered to be albumin, and relatively less in another fraction considered to be selenoprotein P. The lack of many observed changes in retention of stable Se, and the shift in retention among the plasma proteins, suggests that supplemental Se was not being used to replete critical pools of Se, probably because of adaptation to low Se intake.

Effect of bile/pancreatic secretions on absorption of radioactive or stable zinc : in vivo and in vitro studies

Biliary/pancreatic (B/P) secretions are a major component of endogenous secretions, and endogenously secreted Zn is a primary means of Zn homeostasis. This study examined whether B/P fluid alters the absorption/reabsorption of Zn and, in doing so, whether this contributes to homeostatic control of Zn. Animal experiments utilized rats fed 10 or 300 μg Zn/kg diet. An open-ended gut perfusion study in which65Zn-labeled B/P fluid or67Zn-labeled and digested diet found significantly decreased Zn absorption from B/P fluid. Although Zn absorption from both sources was less in animals fed diets higher in Zn, there was no interaction of treatment and diet. Further studies utilizing cultured human colon carcinoma cells (CACO-2) as in vitro models of gut enterocytes found that the presence of B/P fluid significantly decreased Zn retention and/or transport and resulted in a redistribution of cellular Zn after 1200 min of incubation. These studies show that a substance in B/P fluid can decrease the absorption of Zn and also suggest that dietary Zn and Zn associated with B/P secretions are absorbed from distinct pools. However, the lack of an interactive effect with diet, and the amount of time required to see differences in CACO-2 cells, suggest that differences in absorption are not a major contributor to Zn homeostasis.

Organ content and fecal excretion of cadmium in male and female rats consuming variable amounts of naturally occurring cadmium in confectionery sunflower kernels (Helianthus annuus L.)

Abstract Sunflowers ( Helianthus annuus L. ) tend to remove cadmium (Cd) from the soil and deposit it in their seeds. The availability of Cd in sunflower kernels for absorption and deposition in animal tissues was studied using a 15-week feeding trial with both male and female rats begun at weanling age. Diets included (1) purified basal diet with no sunflower kernels (85 μg Cd/kg), (2) basal diet containing 20% ground low-Cd sunflower kernels (120 μg Cd/kg), (3) basal diet containing 20% ground high-Cd sunflower kernels (195 μg Cd/kg), and (4) basal diet containing 20% ground low-Cd sunflower kernels plus Cd chloride (175 μg Cd/kg). In a second experiment, adult rats were fed sunflower kernels that contained an endogenous or exogenous label of 109 Cd. Cd availability was assessed by measuring 109 Cd excretion in feces and by measuring the amount of label accumulated in liver and kidney. Results were as follows: (1) Although all diets were of similar nutrient composition, female rats that consumed diets containing 20% ground sunflower kernels gained significantly ( P P 109 Cd was not different ( P > 0.1) than kernels labeled exogenously: 12% versus15%, respectively. Eight days after dosing, total liver 109 Cd was 1% of the initial dose; at 20 days it was only 0.3%. The corresponding amounts in kidney were 0.1% 8 days after dosing and 0.2% 20 days after dosing. The amount of label in liver and kidney was not affected by the method of labeling the kernels. This study clearly shows that Cd from sunflower kernels is available for absorption and accumulation in tissues of the rat, although in very small concentrations.

Determination, stable isotope enrichment and kinetics of direct-reacting copper in blood plasma

Abstract Direct-reacting Cu is defined as Cu2+ and other forms of Cu that readily exchange with Cu2+ in blood plasma. An analytical method was developed for 1) quantification of direct-reacting Cu by stable isotope dilution and 2) determination of 65Cu enrichment of direct-reacting Cu in plasma samples from in vivo tracer studies. The method involved addition of enriched 65Cu to plasma, extraction with sodium diethyldithiocarbamate in mineral oil, and analysis by inductively coupled plasma mass spectrometry. Optimum sodium diethyldithiocarbamate concentration for the extraction was 0.16 mM. Direct-reacting Cu (means ± SD) varied from 3.4 ± 0.5% of whole plasma Cu in dairy cows (n = 7) and 3.4 ± 0.3% in healthy men (n = 10) to 16.6 ± 3.7% in dogs (n = 3). After intravenous infusion of enriched 65Cu into two healthy men, biological half-lives of 8.7 and 12.3 min were determined for direct-reacting Cu.

Use of stable isotopic selenium as a tracer to follow incorporation of selenium into selenoproteins

Abstract Stable isotopes of selenium (Se) have been used in human studies to measure Se absorption, retention and excretion. The purpose of this study was to examine whether stable Se could also be used to follow the incorporation of Se into selenoproteins and whether selenoproteins are labeled with stable isotopes the same way they are with radioactive Se. Rats fed either a Se-deficient or a high-Se diet were injected with either a radioactive (75Se) or a stable isotope of Se (77Se), and the liver cytosol was chromatographed on Sephadex G-200. Compared with 75Se, a greater percentage of 77Se was incorporated into cytosol, but the distribution and the effect of dietary Se was similar for both isotopes. New Zealand long-eared rabbits were also injected with either 77Se or 75Se, and the plasma was chromatographed. More of the 75Se was incorporated into the plasma, but again the patterns of incorporation were similar for both isotopes. Plasma from a male subject who ingested 60 μg of 77Se was chromatographed, and the stable Se was detected in column fractions and showed a distribution similar to that observed for rabbit plasma. Finally, a polyacrylamide gel electrophoresis (PAGE) method was developed that allowed loading of sufficient protein to analyze for 77Se in individual protein fractions. The distribution of 77Se and 75Se in rabbit plasma was similar. Human plasma was electrophoresed by a similar method and peaks of 56 and 23 kDa were detected. These data show that stable isotopes of Se can be used for selenoprotein production in the same way as radioactive isotopes. They also show that, when physiological amounts of stable Se are ingested by humans, the isotope can be detected in blood-borne proteins separated by column chromatography and PAGE. [P.S.E.B.M. 1995, Vol 210]