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PubMed1991

Intrinsic labelling of different foods with stable isotope of zinc (67Zn) for use in bioavailability studies.

Intrinsically-labelled foods are required to validate extrinsic-labelling techniques used to study the bioavailability of trace elements. Wheat (Triticum aestivum), peas (Pisum sativum), goat's milk, human milk, eggs and chicken meat were selected for intrinsic-labelling studies with 67Zn. Peas were grown hydroponically in enriched nutrient solution and wheat was grown in sand and watered with enriched nutrient solution. Some of the wheat plants were also given stem injections of 67Zn solution. Eggs and chicken meat were prepared by administering 67Zn intravenously to chickens, and human milk was collected after an oral dose of 67Zn in a cola drink. All the foods investigated were sufficiently enriched with 67Zn for Zn absorption studies except wheat prepared by the sand and water-culture method.

Animals↗
PubMed1998

Microwave method for preparing erythrocytes for measurement of zinc concentration and zinc stable isotope enrichment.

A microwave digestion method to prepare human erythrocytes for measurement of Zn concentration by atomic absorption spectrophotometry and stable isotope enrichment by mass spectrometry is described. Also described is a process for purifying digested erythrocyte samples enriched with Zn stable isotope for analysis by fast atom bombardment mass spectrometry. Microwave digestion was investigated as a way to increase sample throughput by replacing a more time-consuming conventional oven ashing/hot plate wet digestion method. Pooled red blood cells and NIST bovine liver standard reference material were digested by the two different methods and zinc recoveries compared by atomic absorption spectrophotometry. Microwave and conventional methods yielded 11.7 +/- 0.1 and 11.7 +/- 0.2 micrograms/g (wet wt), respectively, for the pooled erythrocytes, and Zn recovery from NIST bovine liver standard (certified 123 +/- 8 micrograms/g) was 128.2 +/- 1.2 and 127.4 +/- 1.3 micrograms/g, p > or = 0.282, respectively. Microwave digestion improved the processing of erythrocytes for atomic absorption spectrophotometry and mass spectrometry by reducing digestion time from 1 week to 2 h. In addition, a procedure for purifying digested erythrocyte samples by either extraction and ion-exchange chromatography in preparation for mass spectrometry analysis of Zn stable isotope enrichment is outlined.

Animals↗
PubMed2004

Zinc absorption as a function of the dose of zinc sulfate in aqueous solution.

BACKGROUND: Zinc supplements are used extensively in medicine and research and for public health purposes in the prevention and treatment of zinc deficiency. However, little is known about the efficiency of zinc utilization after different doses. OBJECTIVE: The objective was to determine the relation between dose of aqueous zinc and absorbed zinc (AZ) in healthy adults. DESIGN: Eight healthy adults (3 men and 5 women) aged 33.8 +/- 9.8 y (x +/- SD) received 3 pairs of zinc doses (2 and 5, 10 and 15, and 20 and 30 mg) in random order in 3 phases (1 pair per phase). There was a 3-wk washout between phases. Aqueous zinc sulfate labeled with 70Zn or 68Zn was orally administered in the postabsorptive state on days 1 and 6, respectively; intravenous 67Zn was administered 1 h after the first oral zinc dose. Two urine samples were collected daily from days 3 to 15; zinc isotopic ratios were determined by inductively coupled plasma mass spectrometry. Fractional absorption of zinc (FAZ) was determined by dual-isotope-tracer ratio; AZ was calculated by multiplying FAZ by dose. RESULTS: Mean (+/-SD) AZ values at doses of 2.2, 5.2, 10.4, 15.2, 20.3, and 30.1 mg ingested Zn were 1.6 +/- 0.4, 3.5 +/- 1.3, 7.4 +/- 1.0, 9.5 +/- 2.2, 11.0 +/- 4.4, and 11.2 +/- 2.1 mg, respectively. A saturable dose-response model, the Hill equation, was selected to model the relation of AZ to ingested zinc. Parameter estimation by nonlinear regression predicted a maximum zinc absorption of 13 mg for larger doses. CONCLUSIONS: Increases in aqueous zinc doses >20 mg result in relatively small and progressively diminishing increases in AZ postabsorptively in healthy adults.

Absorption↗
PubMed1989

Effect of low zinc intake on absorption and excretion of zinc by infants studied with 70Zn as extrinsic tag.

The effect of low dietary intake of zinc was studied in six normal infants with the use of 70Zn as an extrinsic tag. Of the two study formulas, one provided a zinc intake similar to that of customary infant formulas ("high" intake), whereas the other provided a "low" zinc intake. Two zinc absorption studies were performed with each formula (sequence: high-low-low-high). Extrinsically labeled formula was fed for 24 h and excreta were collected for 72 h. Zinc isotope ratios were determined by inductively coupled plasma mass spectrometry (ICP/MS). When zinc intake was high, net zinc absorption was 9.1 +/- 8.7% (mean +/- SD) of intake and net zinc retention was 74 +/- 91 micrograms/(kg.d). True zinc (70Zn) absorption was 16.8 +/- 5.8% of intake and fecal excretion of endogenous zinc was 78 +/- 56 micrograms/(kg.d). When zinc intake was low, net absorption of zinc increased significantly (P less than 0.001) to 26.0 +/- 13.0% of intake, but net retention was not significantly different at 42 +/- 33 micrograms/(kg.d). True absorption of zinc also increased significantly (P less than 0.001) to 41.1 +/- 7.8% of intake, whereas fecal endogenous zinc decreased (P less than 0.05) to 34 +/- 16 micrograms/(kg.d) during low zinc intake. Thus, infants maintain zinc balance in the face of low zinc intake through increased efficiency of absorption and decreased excretion of endogenous zinc.

Adaptation, Physiological↗
PubMed2001

Imaging synaptic zinc release in living nervous tissue.

Zinc enriched neurons have a pool of synaptic vesicles which contain free or loosely-bound zinc ions. The movement of the vesicular zinc ions into the synaptic clefts has been previously studied by microdialysis, fluorescence postmortem staining for zinc and radioactive zinc isotope. In this study the zinc fluorescence probe N-6-metoxy-p-toluensulfonamide quinoline (TSQ) has been applied as a tracer of synaptic release of zinc ions. This fluorochrome permeates cell membranes and when exposed to living brain slices gives rise to a staining pattern similar to that seen with autometallography. In the living brain slices, fluorescence emission persists after exposure to calcium saturated ethylen diamino-tetra-acetic acid (Ca-EDTA) because this chelator does not penetrate cell membranes, while sodium dethyldithiocarbamate (DEDTC), that does penetrate membranes, partially suppressed the fluorescence emission. Stimulation of slices bathed in the non-permeant chelator Ca-EDTA with 50 mM potassium chloride leads to a rapid and complete disappearance of fluorescence. In the absence of Ca-EDTA, however, potassium stimulation induces a sudden transitory increase in fluorescence. This increase is caused by a translocation of the fluorochrome (TSQ) zinc molecules from the weakly acid interior of the synaptic vesicles to the neutral extracellular space, whereby the fluorescence emission of the molecules is enhanced sufficiently to be recorded by a high sensitivity TV camera.

Aminoquinolines↗
PubMed2004

Zinc metabolism in adolescents with Crohn's disease.

Low serum zinc concentrations have been reported in Crohn's disease (CD) and overt zinc deficiency has been described, but little is known about the effect of CD on zinc metabolism in adolescents. The aim of this study was to measure zinc absorption, endogenous fecal zinc excretion, urinary zinc excretion, and zinc balance in children with stable CD and in matched controls. Subjects were 15 children, ages 8-18 y, with stable CD, and 15 healthy matched controls. Subjects were adapted to diets providing 12 mg/d elemental zinc for 2 wk, and then admitted for a 6-d metabolic study. Stable zinc isotopes were given intravenously and orally, and urine and feces collected for 6 d. Fractional zinc absorption, endogenous fecal zinc excretion, and zinc balance were calculated using established stable isotope methods. In subjects with CD, zinc absorption (10.9% +/- 6.1 versus 23.4 +/- 15.8, p = 0.008) and plasma zinc concentration (0.85 mg/dL +/- 0.15 versus 1.25 +/- 0.35, p = 0.004) were significantly reduced, compared with controls. Despite this, there were no significant differences in endogenous fecal zinc excretion (2.0 mg +/- 1.5 versus 1.5 +/- 1.5, p = 0.34) or urinary zinc excretion (0.9 mg +/- 0.7 versus 1.0 +/- 0.7, p = 0.47). Zinc balance was significantly lower in CD (-1.5 mg +/- 1.5) than in controls (+0.6 mg +/- 3.1, p < 0.0001). In conclusion, adolescents with CD have significantly reduced zinc absorption. Despite this, they were unable to reduce endogenous fecal zinc excretion to restore normal zinc balance and had a significantly worse zinc balance and lower plasma zinc concentration than controls.

Adolescent↗
PubMed1986

Stable isotope studies of zinc absorption and retention in young and elderly men.

Zinc absorption was determined with 67Zn and 70Zn, stable isotopes of zinc, in six young men and six elderly men who were confined to a metabolic unit for 12 wk. Their purified formula diets, supplemented with select food items, contained 15 mg of zinc per day. Zinc absorption was determined twice for each subject by combining zinc enriched with either 70Zn or 67Zn with the formula diet. Serum, urinary, and fecal zinc and zinc balance were determined by atomic absorption spectrometry. Zinc absorption averaged 17% in elderly men, significantly less than average zinc absorption of 31% in young men. Serum zinc was also lower in elderly men and increased in both groups during the course of the study. Zinc balance did not differ between groups, and endogenous zinc losses were less in the elderly than in the young men. The results suggest that while zinc absorption is less in elderly men than in young men, the lower absorption may reflect a lower requirement for absorbed zinc by the elderly. Alternatively, less efficient zinc absorption could result in decreased endogenous losses.

Absorption↗
PubMed2005

Isotopic discrimination of zinc in higher plants.

* The extent of isotopic discrimination of transition metals in biological processes is poorly understood but potentially has important applications in plant and biogeochemical studies. * Using multicollector inductively coupled plasma (ICP) mass spectrometry, we measured isotopic fractionation of zinc (Zn) during uptake from nutrient solutions by rice (Oryza sativa), lettuce (Lactuca sativa) and tomato (Lycopersicon esculentum) plants. * For all three species, the roots showed a similar extent of heavy Zn enrichment relative to the nutrient solution, probably reflecting preferential adsorption on external root surfaces. By contrast, a plant-species specific enrichment of the light Zn isotope occurred in the shoots, indicative of a biological, membrane-transport controlled uptake into plant cells. The extent of the fractionation in the shoots further depended on the Zn speciation in the nutrient solution. * The observed isotopic depletion in heavy Zn from root to shoot (-0.13 to -0.26 per atomic mass unit) is equivalent to roughly a quarter of the total reported terrestrial variability of Zn isotopic compositions (c. 0.84 per atomic mass unit). Plant uptake therefore represents an important source of isotopic variation in biogeochemical cycling of Zn.

Biological Transport↗
PubMed2001

Effect of acute zinc depletion on zinc homeostasis and plasma zinc kinetics in men.

BACKGROUND: Zinc homeostasis and normal plasma zinc concentrations are maintained over a wide range of intakes. OBJECTIVE: The objective was to identify the homeostatic response to severe zinc depletion by using compartmental analysis. DESIGN: Stable zinc isotope tracers were administered intravenously to 5 men at baseline (12.2 mg dietary Zn/d) and after 5 wk of acute zinc depletion (0.23 mg/d). Compartmental modeling of zinc metabolism was performed by using tracer and mass data in plasma, urine, and feces collected over 6-14 d. RESULTS: The plasma zinc concentration fell 65% on average after 5 wk of zinc depletion. The model predicted that fractional zinc absorption increased from 26% to essentially 100%. The rate constants for zinc excretion in the urine and gastrointestinal tract decreased 96% and 74%, respectively. The rate constants describing the distribution kinetics of plasma zinc did not change significantly. When zinc depletion was simulated by using an average mass model of zinc metabolism at baseline, the only change that accounted for the observed fall in plasma zinc concentration was a 60% reduction in the rate constant for zinc release from the most slowly turning over zinc pool. The large changes in zinc intake, excretion, and absorption-even when considered together-only explained modest reductions in plasma zinc mass. CONCLUSION: The kinetic analysis with a compartmental model suggests that the profound decrease in plasma zinc concentrations after 5 wk of severe zinc depletion was mainly due to a decrease in the rate of zinc release from the most slowly turning over body zinc pool.

Adult↗