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Maares M, Haase H. A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models. Nutrients 2020; 12:E762. [PMID: 32183116 PMCID: PMC7146416 DOI: 10.3390/nu12030762] [Citation(s) in RCA: 146] [Impact Index Per Article: 36.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Revised: 02/23/2020] [Accepted: 03/09/2020] [Indexed: 12/17/2022] Open
Abstract
Zinc absorption in the small intestine is one of the main mechanisms regulating the systemic homeostasis of this essential trace element. This review summarizes the key aspects of human zinc homeostasis and distribution. In particular, current knowledge on human intestinal zinc absorption and the influence of diet-derived factors on bioaccessibility and bioavailability as well as intrinsic luminal and basolateral factors with an impact on zinc uptake are discussed. Their investigation is increasingly performed using in vitro cellular intestinal models, which are continually being refined and keep gaining importance for studying zinc uptake and transport via the human intestinal epithelium. The vast majority of these models is based on the human intestinal cell line Caco-2 in combination with other relevant components of the intestinal epithelium, such as mucin-secreting goblet cells and in vitro digestion models, and applying improved compositions of apical and basolateral media to mimic the in vivo situation as closely as possible. Particular emphasis is placed on summarizing previous applications as well as key results of these models, comparing their results to data obtained in humans, and discussing their advantages and limitations.
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Affiliation(s)
- Maria Maares
- Technische Universität Berlin, Chair of Food Chemistry and Toxicology, Straße des 17. Juni 135, 10623 Berlin, Germany
| | - Hajo Haase
- Technische Universität Berlin, Chair of Food Chemistry and Toxicology, Straße des 17. Juni 135, 10623 Berlin, Germany
- TraceAge-DFG Research Unit on Interactions of Essential Trace Elements in Healthy and Diseased Elderly, D-13353 Potsdam-Berlin-Jena, Germany
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Lebel A, Matte JJ, Guay F. Effect of mineral source and mannan oligosaccharide supplements on zinc and copper digestibility in growing pigs. Arch Anim Nutr 2014; 68:370-84. [PMID: 25179553 DOI: 10.1080/1745039x.2014.954357] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
This study aimed to compare the effects of organic (proteinate) and inorganic (sulphate) copper (Cu) and zinc (Zn) supplements, in presence or absence of a mannan oligosaccharide (MOS) supplement, on mineral solubility and digestibility in pigs. Twenty-eight barrows (25 ± 4 kg) assigned randomly to four treatment groups were fed a corn-wheat-soya bean meal diet with 10 mg/kg of Cu and 100 mg/kg of Zn supplied as organic or inorganic supplement, and supplemented or not with 0.1% MOS. After an adaptation period, total faeces and urine were collected for a period of 6-7 days. Pigs were then euthanatised and digesta from ileum and caecum were collected. Apparent digestibility was calculated in ileum and caecum using titanium dioxide. The organic mineral supplement improved total (faecal) digestibility and retained/ingested ratio of Cu (p < 0.05) while reducing apparent digestibility of Zn in the ileum (p < 0.05) without effect on total digestibility of Zn. Solubilities of Cu and Zn in liquid fraction of ileum and caecum were not affected by mineral sources. Although MOS supplement increased Cu solubility in the ileum (p < 0.05), it had no effect on digestibility of Zn and Cu in ileum, caecum and faeces, retained/ingested ratio of Zn and Cu, or pH and volatile fatty acid concentration in ileal and caecal digesta. In conclusion, organic mineral supplement improved total digestibility and retained/ingested ratio of Cu in pigs but this cannot be attributed to its solubility in ileal and caecal digesta. The MOS supplement did not interfere with digestibility or dietary utilisation of Zn and Cu in pigs fed above the Zn and Cu requirements.
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Affiliation(s)
- Alexandre Lebel
- a Département des sciences animals , Université Laval Québec , Québec , Canada G1V 0A6
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3
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Tako E, Rutzke MA, Glahn RP. Using the domestic chicken (Gallus gallus) as an in vivo model for iron bioavailability. Poult Sci 2010; 89:514-21. [PMID: 20181868 DOI: 10.3382/ps.2009-00326] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Iron fortification of foods and biofortification of staple food crops are strategies that can help to alleviate Fe deficiency. The broiler chicken may be a useful model for initial in vivo screening of Fe bioavailability in foods due to its growth rate, anatomy, size, and low cost. In this study, we assess the broiler as a model for hemoglobin (Hb) maintenance studies and present a unique duodenal loop technique for direct measurement of intestinal Fe absorption. One-week-old chicks were allocated into Fe-deficient versus Fe-adequate treatment groups. For 6 wk, blood Hb, feed consumption, and BW were measured. At wk 7, birds were anesthetized and their duodenal loops were exposed. The loop was isolated and a nonocclusive catheter was inserted into the duodenal vein for blood sampling. A stable isotope solution containing (58)Fe (1 mg of Fe in 10 mM ascorbic acid) was injected into the loop. Blood samples were collected every 5 min and for 120 min postinjection and analyzed by inductively coupled argon-plasma mass spectrometry for (58)Fe concentrations. In the low-Fe group, Hb concentrations, total body Hb Fe, and BW were lower and Hb maintenance efficiency (indicator for dietary Fe availability) was higher than in the high-Fe group (P < 0.05). Iron absorption was higher in the Fe-deficient birds (P < 0.05). In addition, expression of proteins involved in Fe uptake and transfer [i.e., divalent metal transporter 1 (Fe uptake transporter), ferroportin (involved in Fe transport across the enterocyte), and duodenal cytochrome B reductase (reduces Fe at brush border membrane)] were elevated in the low-Fe group. These results indicate that this model exhibits the appropriate responses to Fe deficiency and has potential to serve as a model for Fe bioavailability. Such a model should be most useful as an intermediate test of in vivo Fe bioavailability observations in preparation for subsequent human studies.
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Affiliation(s)
- E Tako
- Department of Science, Cornell University, Ithaca, NY 14853, USA.
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Bai SP, Lu L, Luo XG, Liu B. Kinetics of manganese absorption in ligated small intestinal segments of broilers. Poult Sci 2009; 87:2596-604. [PMID: 19038816 DOI: 10.3382/ps.2008-00117] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Two experiments were conducted with 28-day-old male commercial broilers to study mechanisms of Mn absorption and the effect of Mn treatment on divalent metal transporter 1 (DMT1) mRNA levels in ligated segments from different intestinal regions of broilers. The results from experiment 1 showed that the amount of Mn absorption was asymptotic with respect to time within 40 min after perfusion of the duodenal, jejunal, and ileal segments of broilers with 2.18 mmol/L of Mn as MnSO(4). In experiment 2, a kinetic study of Mn absorption was performed with duodenal, jejunal, and ileal loops perfused with solutions containing 0, 0.13, 0.27, 0.54, 1.09, 2.18, 4.37, or 8.74 mmol/L of Mn as MnSO(4). Manganese concentrations in perfusates were determined at 5 min after perfusion. In the control group and in the group treated with 2.18 mmol/L Mn as MnSO(4), DMT1 mRNA levels of ligated intestinal regions at 30 min after perfusion were analyzed by real-time reverse transcription PCR. The kinetic curves of Mn absorption showed that Mn absorption was a carrier-mediated process in the duodenum and jejunum. The maximum absorption rate (J(max)) in duodenal segments was greater (P < 0.05) than that in the jejunum (94.08 vs. 81.17 nmol/cm per min). There was no significant difference (P = 0.85) in the Michaelis-Menten constant (K(m)) values between the duodenum and jejunum (3.41 vs. 3.60 mmol/L). In the ileum of Mn-deficient broilers, the most probable mechanism of Mn absorption was a nonsaturable diffusion process, and the diffusive constant (P; means +/- SE) was 2.42 x 10(-2) +/- 5.22 x 10(-4) cm(2)/min. The DMT1 mRNA levels in the duodenum and jejunum of broilers were greater (P < 0.001) than the level in the ileum. The DMT1 mRNA level in the small intestine of broilers in the Mn treatment group decreased significantly (P < 0.001) compared with that of the control. The different mechanisms of Mn absorption found in different intestinal segments suggest that the ileum is the main site of Mn absorption in the small intestine of broilers.
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Affiliation(s)
- S P Bai
- Mineral Nutrition Research Division, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, P. R. China
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Swinkels JWGM, Kornegay ET, Verstegen MWA. Biology of Zinc and Biological Value of Dietary Organic Zinc Complexes and Chelates. Nutr Res Rev 2007; 7:129-49. [DOI: 10.1079/nrr19940009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Zinc uptake in swine intestinal brush border membrane vesicles using a 65Zn/69mZn duel isotope experiment. J Radioanal Nucl Chem 2007. [DOI: 10.1007/s10967-007-0421-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Shelton JL, Southern LL, LeMieux FM, Bidner TD, Page TG. Effects of microbial phytase, low calcium and phosphorus, and removing the dietary trace mineral premix on carcass traits, pork quality, plasma metabolites, and tissue mineral content in growing-finishing pigs. J Anim Sci 2005; 82:2630-9. [PMID: 15446480 DOI: 10.2527/2004.8292630x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
An experiment was conducted to determine the effects of phytase addition, reduced Ca and available P (aP), and removing the trace mineral premix (TMP) on growth performance, plasma metabolites, carcass traits, pork quality, and tissue mineral content in growing-finishing swine. One hundred twenty cross-bred pigs (initial and final BW of 22 and 109 kg, respectively) were allotted to five dietary treatments on the basis of weight within gender in a randomized complete block design. There were three replications of barrows and three replications of gilts, with four pigs per replicate pen. The dietary treatments were as follows: 1) corn-soybean meal (C-SBM), 2) C-SBM with reduced Ca and aP, 3) C-SBM with reduced Ca and aP plus 500 phytase units/kg of diet, 4) Diet 1 without the TMP, and 5) Diet 3 without the TMP. The Ca and aP were reduced by 0.10% in the low Ca and aP diets and the diets with added phytase. Daily gain, hot carcass weight, dressing percent, kilograms of carcass lean, bone ash percent, and bone strength were decreased (P = 0.10), but liver and kidney weight were increased (P = 0.10) in pigs fed diets with reduced Ca and aP; adding phytase reversed these responses (P = 0.10). The Commission Internationale de I'Eclairage L* was decreased (P = 0.09) in pigs fed the low Ca and aP diet plus phytase relative to those fed the control diet. Removing the TMP had no effect on overall growth performance, but it increased (P = 0.03) 10th-rib backfat thickness and fasting glucose and decreased (P = 0.03) carcass length and ham weight. Liver weight and liver weight as a percentage of final BW were not affected when phytase was added to the control diet, but removing the TMP increased liver weight and liver weight as a percentage of final BW; adding phytase reversed these responses (phytase x TMP, P = 0.06). Removing the TMP decreased (P = 0.08) Zn concentrations in the bone, muscle, and liver, and Cu and Fe concentrations in the bile but increased (P = 0.08) Mn concentrations in the bile and liver of pigs. The addition of phytase reversed the negative effects of the reduced Ca and aP diets. These data indicate that removing the TMP in diets for growing-finishing pigs has no negative effects on growth performance or pork quality, but it had negative effects on carcass traits and had variable effects on tissue mineral content.
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Affiliation(s)
- J L Shelton
- Department of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge 70803-4210, USA
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9
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Glover CN, Bury NR, Hogstrand C. Intestinal zinc uptake in freshwater rainbow trout: evidence for apical pathways associated with potassium efflux and modified by calcium. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1663:214-21. [PMID: 15157623 DOI: 10.1016/j.bbamem.2004.03.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2003] [Revised: 03/01/2004] [Accepted: 03/19/2004] [Indexed: 11/20/2022]
Abstract
Understanding the mechanisms of intestinal zinc uptake in fish is of considerable interest from both nutritional and toxicological perspectives. In this study, properties of zinc transport across the apical membrane of freshwater rainbow trout intestinal epithelia were examined using right-side-out brush border membrane vesicles (BBMV's). Extravesicular calcium was found to have complex actions on zinc uptake. At a low zinc concentration of 1 microM, calcium (0.1-2 mM) significantly stimulated zinc uptake. In contrast, calcium inhibited zinc uptake at higher zinc levels (100 microM). Lanthanum and cadmium in the external medium did not block zinc uptake, suggesting that interactions between zinc and calcium were not exerted at a calcium channel. Copper also failed to exercise any inhibitory action. Zinc association with the BBMV's was enhanced by an outward potassium gradient. This stimulatory effect was only present at a zinc concentration of 100 microM. The potassium channel blocker, tetraethylammonium chloride inhibited zinc uptake at this relatively high zinc concentration, suggesting the presence of a low affinity zinc uptake pathway linked to potassium efflux. The present study provides evidence that the mechanism of intestinal zinc uptake in rainbow trout is pharmacologically very different from that of the piscine gill and the mammalian intestine.
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Affiliation(s)
- Chris N Glover
- School of Health and Life Sciences, King's College London, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NN, UK.
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Glover CN, Bury NR, Hogstrand C. Zinc uptake across the apical membrane of freshwater rainbow trout intestine is mediated by high affinity, low affinity, and histidine-facilitated pathways. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1614:211-9. [PMID: 12896814 DOI: 10.1016/s0005-2736(03)00178-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Zinc is both a vital nutrient and an important toxicant to aquatic biota. In order to understand the interplay between nutrition and toxicity, it will be important to determine the mechanisms and the factors that regulate zinc uptake. The mechanism of apical intestinal Zn(II) uptake in freshwater rainbow trout and its potential modification by the complexing amino acid histidine was investigated using brush-border membrane vesicles (BBMVs). Following characterisation of the BBMV preparation, zinc uptake in the absence of histidine was both time- and concentration-dependent and consisted of two components. A saturable phase of uptake was described by an affinity constant of 57+/-17 microM and a transport capacity of 1867+/-296 nmol mg membrane protein(-1) min(-1). At higher zinc levels (>500 microM) a linear, diffusive component of uptake was evident. Zinc transport was also temperature-dependent, with Q10 values suggesting zinc uptake was a carrier-mediated process. Zinc uptake by vesicles in the presence of histidine was correlated to a mono-histidine species (Zn(His)+) at all Zn(II) concentrations examined.
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Affiliation(s)
- Chris N Glover
- School of Health and Life Sciences, King's College, London, 150 Stamford Street, London SE1 9NN, UK.
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11
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Pérès JM, Bureau F, Neuville D, Arhan P, Bouglé D. Inhibition of zinc absorption by iron depends on their ratio. J Trace Elem Med Biol 2001; 15:237-41. [PMID: 11846013 DOI: 10.1016/s0946-672x(01)80039-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Previous studies upon zinc-iron interactions gave conflicting results that could come from differences in protocol design or in trace element status of subjects. The present work assessed the influence of zinc : iron ratio and iron deficiency upon zinc absorption. The digestive absorption of zinc sulphate (100 micromol Zn/l) in presence of iron gluconate was studied in perfused jejunal loops (n = 6/group) of normal rats (range 0-1000 micromol Fe/l) and iron deficient rats (200-750 micromol Fe/l). In normal rats no significant iron inhibition on zinc absorption occurred at Fe:Zn ratio below 2:1. At higher ratios zinc uptake and net absorption decreased significantly (p<0.05). Between 2:1 and 5:1 a dose dependent inhibition of zinc absorption occurred and reached a plateau beyond this ratio. In iron deficient animals no changes in zinc uptake, mucosal retention and absorption compared to normal animals occurred at ratio 2:1. At higher ratios differences were observed at every zinc absorption step except for mucosal retention at 7.5:1 ratio. Iron-zinc interactions depend on their ratio and on previous trace elements status of subjects. Due to the wide and unknown variations that were likely to occur between the subjects of previous human and experimental studies, these results could explain some of the discrepancies between their results.
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Affiliation(s)
- J M Pérès
- Laboratoire de Physiologie Digestive et Nutritionnelle, CHU de Caen, France
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12
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Abstract
We examined the role of the large intestine in zinc absorption in rats in three separate experiments. In the first experiment, we examined apparent zinc absorption in rats fed diets containing graded levels of zinc carbonate (0.015-0.535 mmol Zn/kg diet) and evaluated zinc status on the basis of the zinc concentrations in serum and several tissues. The zinc absorption and the serum zinc concentration increased with the zinc content of the diet up to 0. 153 mmol Zn/kg diet. Femoral and pancreatic zinc levels increased linearly up to 0.229 mmol Zn/kg diet. In the second experiment, a zinc carbonate suspension was administered into the cecum via an implanted cannula or into the stomach via an orogastric tube, and the rats were fed diets with or without a highly fermentable fiber, guar gum hydrolysate (GGH, 50 g/kg diet), with coprophagy prevention. The amount of instilled zinc corresponded to the amount of zinc ingested as a component of the diet by the rats of a control group, 0.229 mmol Zn/kg diet. Apparent absorption of cecally instilled zinc was approximately half that observed when zinc was administered into the stomach in both diet groups. Serum and femur zinc concentrations in the cecum-administered groups were approximately 50 and 25% lower, respectively, than those in rats administered zinc into the stomach. The results demonstrate that, in vivo, the absorptive efficiency in the large intestine is not sufficient to satisfy the rat's zinc requirement and does not change when the luminal environment is substantially altered by feeding GGH. In Experiment 3, the effects of cecocolonectomy on zinc absorption were examined in rats with gastric acid suppression. In the cecocolonectomized groups, serum zinc concentration was lower as a result of treatment with a proton pump inhibitor, omeprazole, than in vehicle-treated rats, but not in sham-operated groups. These findings suggest that the cecum and colon contribute to zinc absorption when absorption in the small intestine is impaired.
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Affiliation(s)
- H Hara
- Department of Bioscience and Chemistry, Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
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13
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Abstract
The mechanism(s) by which zinc is transported into cells has not been identified. Since zinc uptake is inhibited by reducing the temperature, zinc uptake may depend on the movement of plasma membrane micoenvironments, such as endocytosis or potocytosis. We investigated the potential role of potocytosis in cellular zinc uptake by incubating normal and acrodermatitis enteropathica fibroblasts with nystatin, a sterol-binding drug previously shown to inhibit potocytosis. Zinc uptake was determined during initial rates of uptake (10 min) following incubation of the fibroblasts in 50 micrograms nystatin/mL or 0.1% dimethylsulfoxide for 10 min at 37 degrees C. The cells were then incubated with 1 to 30 microM 65zinc. Michaelis-Menten kinetics were observed for zinc uptake. Nystatin inhibited zinc uptake in both the normal and AE fibroblasts. Reduced cellular uptake of zinc was associated with its internalization, not its external binding. In normal fibroblasts, nystatin significantly reduced the K(m) 56% and the Vmax 69%. In the AE fibroblasts, nystatin treatment significantly reduced the Vmax 59%, but did not significantly affect the K(m). The AE mutation alone affected the Vmax for cellular zinc uptake. The control AE fibroblasts exhibited a 40% reduction in Vmax compared to control normal fibroblasts. We conclude that nystatin exerts its effect on zinc uptake by reducing the velocity at which zinc traverses the cell membrane, possibly through potocytosis. Furthermore, the AE mutation also affects zinc transport by reducing zinc transport.
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Affiliation(s)
- A Grider
- Division of Nutritional Sciences, University of Texas, Austin 78712, USA
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Lönnerdal B. Lactoferrin receptors in intestinal brush border membranes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1994; 357:171-5. [PMID: 7762428 DOI: 10.1007/978-1-4615-2548-6_16] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Lactoferrin from milk may have a physiological effect on the neonate by stimulating iron acquisition and/or mucosal growth. We have hypothesized that in order to achieve such an effect(s), lactoferrin will bind to a specific receptor located on the mucosal surface of the enterocyte. We have studied the presence of lactoferrin receptors in the brush border membrane from infant rhesus monkey intestine and from fetal and infant human intestine. The receptor exhibits saturation kinetics and the binding is specific for human and monkey lactoferrin--bovine lactoferrin or human transferrin do not bind to the receptor or compete with the binding of the primate lactoferrins. Enzymatic deglycosylation does not affect the binding of human lactoferrin to its receptor, suggesting that the glycan(s) is not needed for receptor recognition. Competitive binding experiments showed that holo-lactoferrin was more effective than less Fe-saturated forms of lactoferrin with regard to receptor binding. Mn-lactoferrin bound to the receptor, while we were unable to prepare Zn-lactoferrin in any physiological buffer. The human lactoferrin receptor was isolated and found to have a MW of approximately 110 kDa. This receptor has now been cloned and is being sequenced.
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Tacnet F, Lauthier F, Ripoche P. Mechanisms of zinc transport into pig small intestine brush-border membrane vesicles. J Physiol 1993; 465:57-72. [PMID: 8229851 PMCID: PMC1175419 DOI: 10.1113/jphysiol.1993.sp019666] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
1. The purpose of the present work was to examine certain membrane transport mechanisms likely to carry zinc across the brush-border membrane of pig small intestine, isolated in a vesicular form. 2. In initial velocity conditions, saturation kinetics revealed a great effect of pH on zinc transport: optimal conditions were observed with an intravesicular pH of around 6.6 with or without a H+ gradient; however, this did not allow us to conclude the existence of a neutral exchange between Zn2+ and H+ ions. 3. By measuring 36Cl uptakes, the presence of the Cl(-)-HCO3- or Cl(-)-OH-antiporter with typical 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) sensitivity was detected in vesicles; zinc did not alter this anionic exchange activity. A 65Zn time course, performed in conditions identical with those for 36Cl uptake, was DIDS insensitive and was greatly inhibited by an outward OH- gradient. This could argue against a transport of zinc as a complex with Cl- and HCO3- through the anion antiporter. 4. When external Cl- and HCO3- were replaced by SCN-, able to form a Zn(SCN)4(2-) complex, we observed a stimulating effect of outward HCO3- gradients on 65Zn uptake but neither DIDS nor diphenylamine-2-carboxylate (DPC) inhibited the transport in these conditions. This suggested that the intestinal anion antiporter was not a major route for zinc reabsorption. 5. The tripeptide Gly-Gly-His at low concentrations stimulated 65Zn uptake, then inhibited it in a dose-dependent manner either in the presence of an inward H+ gradient or in the presence of a membrane potential 'negative inside' or in both situations. These conditions are necessary for the active transport of the peptide and this strongly suggests that zinc can be transported as a [Gly-Gly-His-Zn] complex, utilizing the peptide carrier system.
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Affiliation(s)
- F Tacnet
- Département de Biologie Cellulaire et Moléculaire, SBCe, C.E. de Saclay, Gif sur Yvette, France
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Affiliation(s)
- B Sandström
- Research Department of Human Nutrition, Royal Veterinary and Agricultural University, Frederiksberg, Denmark
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Abstract
The mechanism of zinc (Zn) uptake by microvillous membrane vesicles prepared from human term placenta has been studied. The uptake was complex, with two processes being identified. In the first process, uptake was rapid, reaching equilibrium within 2 min, and was temperature dependent, with a Q10 of 1.5. Equilibrium Zn levels were sensitive to osmotic pressure, with Zn binding at infinite osmolarity being 69% iso-osmotic value. The uptake was saturable, with a Vmax of 58 +/- 2 nmol/mg protein/min and an apparent Kt of 128 +/- 13 microM. Uptake was inhibited by increasing extravesicular K+ concentration, dropping from 0.91 +/- 0.03 nmol/mg/min at 0 extravesicular K+ to 0.47 +/- 0.03 at an extravesicular K+ concentration of 150 mM ([Zn] = 1.0 microM). In the presence of both valinomycin, an electrogenic ionophore, and nigericin, an electroneutral exchanger, an outwardly directed K+ gradient stimulated Zn uptake. Similarly, preloading vesicles with Zn and imposing an inward gradient resulted in a temperature dependent efflux of Zn. The data suggest that there is a K+ dependent Zn transporter in vesicle membranes, and we suggest that the evidence is biased in favour of a Zn/K+ exchanger rather than Zn being dependent on the membrane potential.
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Affiliation(s)
- N Aslam
- Department of Child Health, University of Dundee, Ninewells Hospital and Medical School, Scotland
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Bobilya DJ, Briske-Anderson M, Reeves PG. Zinc transport into endothelial cells is a facilitated process. J Cell Physiol 1992; 151:1-7. [PMID: 1560036 DOI: 10.1002/jcp.1041510102] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The kinetics of zinc transport were examined by measuring the uptake of 65Zn into cultured endothelial cells. This served as a suitable model for characterizing the transport of zinc across a biological membrane (i.e., the plasma membrane). The transport process was saturable under physiological conditions, which indicates a facilitating transport mechanism. Within the physiological range of zinc concentrations, the maximum zinc transport rate was 27 pmoles zinc/(min x mg protein) and it was half maximal at 4.1 microM zinc. Cadmium competitively inhibited zinc transport (Ki = 6.5 microM), while equimolar concentrations of copper and manganese were ineffectual. The rate of zinc transport was substantially reduced at lower temperatures and in the presence of sulfhydryl blockers (sodium iodoacetate and N-ethylmaleimide). Inhibitors of energy metabolism (2,4-dinitrophenol and sodium azide) failed to disrupt zinc transport. These results demonstrate that zinc transport into endothelial cells is a facilitated process (i.e., it is carrier mediated and energy-independent).
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Affiliation(s)
- D J Bobilya
- United States Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, North Dakota 58202-7166
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Page KR, Abramovich DR, Aggett PJ, Bain M, Chipperfield AR, Durdy H, McLachlan J, Smale A. Uptake of zinc by human placental microvillus border membranes and characterization of the effects of cadmium on this process. Placenta 1992; 13:151-61. [PMID: 1631028 DOI: 10.1016/0143-4004(92)90030-w] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The uptake of Zinc (Zn) by microvillus border membrane vesicles formed from the trophoblast of term human placentae is markedly increased over brief periods of incubation with much slower increases persisting for up to 2 h of incubation. Zinc is both bound to membrane components and transported into intravesicular osmotically active space. Uptake is saturable, temperature dependent from 4 to 37 degrees C with a Q10 of 1.7, and is inhibited by the sulphydryl agent DTNB. About 20 per cent of the uptake is susceptible to inhibition by Cadmium (Cd) at concentrations from 5 to 50 microM, a significant part of the action of this metal being on the transmembrane component of Zn uptake.
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Affiliation(s)
- K R Page
- Physiology Division, School of Biomedical Sciences, University of Aberdeen, UK
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Turnbull AJ, Blakeborough P, Thompson RP. The effects of dietary ligands on zinc uptake at the porcine intestinal brush-border membrane. Br J Nutr 1990; 64:733-41. [PMID: 2265181 DOI: 10.1079/bjn19900075] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Intestinal brush-border-membrane vesicles were prepared from the porcine small bowel by magnesium precipitation and differential centrifugation, and were functionally intact. The influence of dietary ligands on 65Zn uptake was determined using a 65Zn concentration of 5 microM, an incubation time of 1 min and a reaction temperature of 27 degrees, with a rapid filtration technique. At this low Zn concentration the addition of an excess of folate, histidine or glucose had no effect on Zn uptake. Addition of picolinate, citrate and phytate to the incubation medium significantly reduced Zn uptake at all concentrations of ligand examined. Any inhibitory effects of folic acid in vivo may thus be due to a mucosal rather than lumen interaction. Those ligands inhibiting absorption may have done so through the formation of Zn-ligand complexes, which are either insoluble, or which reduce the binding of Zn to its mucosal receptor. This in vitro model of Zn absorption is useful for comparing the effects of potential Zn-binding ligands in the diet.
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Affiliation(s)
- A J Turnbull
- Gastrointestinal Laboratory, Rayne Institute, St Thomas' Hospital, London
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Blakeborough P, Neville SG, Rolls BA. The effect of diets adequate and deficient in calcium on blood pressures and the activities of intestinal and kidney plasma membrane enzymes in normotensive and spontaneously hypertensive rats. Br J Nutr 1990; 63:65-78. [PMID: 2317478 DOI: 10.1079/bjn19900092] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Basolateral and brush-border membranes were prepared from the intestines and kidneys of spontaneously hypertensive (SHR) and normotensive (WKY) rats fed on a calcium-adequate diet and assayed for their enzyme activities. In intestinal basolateral membranes the activities of Na+ K(+)-ATPase (EC 3.6.1.37) Ca2(+)-ATPase (EC 3.6.1.38) and alkaline phosphatase (EC 3.1.3.1) were lower in SHR rats when compared with WKY rats, whilst 5'-nucleotidase (EC 3.1.3.5) (a marker for basolateral membranes) was unaffected. In kidney basolateral membranes all enzymes were similar in activity in SHR and WKY rats. In intestinal brush-border membranes the activities of Ca2(+)-ATPase and alkaline phosphatase were lower in SHR rats when compared with WKY rats, whilst microvillus aminopeptidase (EC 3.4.11.2) (a marker for brush-border membranes) was unaffected. In kidney brush-border membranes all enzymes were similar in activity in SHR and WKY rats. The blood pressures of the SHR rats were considerably higher than those of the WKY rats. When SHR rats were fed on a Ca-deficient diet the activities of Na+K(+)-ATPase, Ca2(+)-ATPase and alkaline phosphatase in basolateral membranes and Ca2(+)-ATPase and alkaline phosphatase in brush-border membranes were all increased in the intestine when compared with SHR rats fed on a Ca-adequate diet. The equivalent enzymes in the kidneys of SHR rats, and the intestines and kidneys of WKY rats, were not affected by altering the Ca in the diet. The blood pressures of SHR rats fed on a Ca-deficient diet were higher than in those fed on a Ca-adequate diet. Blood pressures of WKY rats were not affected by altering the diet in this way. The results indicate that the absorption of Ca by active mechanisms may be reduced in SHR rats compared with WKY rats. Changing the level of Ca in the diet modified both blood pressure and the activities of enzymes which catalyse active Ca transport. The implications of these results to the aetiology, and possible nutritional treatment, of essential hypertension are discussed.
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Affiliation(s)
- P Blakeborough
- Department of Human Nutrition, AFRC Institute of Food Research, Reading Laboratory, Shinfield
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Abstracts of Communications. Proc Nutr Soc 1989. [DOI: 10.1079/pns19890044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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TURNBULL ALISTAIRJ, THOMPSON RICHARDPH. Zinc—a precious metal. NUTR BULL 1989. [DOI: 10.1111/j.1467-3010.1989.tb00302.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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