Bioavailability of zinc from zinc-histidine complexes. I. Comparison with zinc sulfate in healthy men

Glycoprotein Matrix Zinc Exhibits Improved Absorption: A Randomized Crossover Trial

Biotransformation of minerals via glycosylation by microorganisms such as yeast and/or probiotics yields nutrients bound to a food matrix, resulting in increased bioavailability. The purpose of this study was to compare the effects of glycoprotein matrix-bound zinc (GPM) on absorption compared to inorganic zinc oxide. Sixteen participants ingested 11 mg of zinc as either GPM™ Soy-Free Zinc (GPM, Ashland, Kearny, NJ, USA) or zinc oxide (USP). Blood samples were taken at 0 (i.e., baseline), 30, 60, 90, 120, 180, 240, 300, 360, 420, and 480 min post-ingestion. GPM zinc concentrations were significantly higher at 120 min (p = 0.02; 12.4 ± 5.1 mcg/dL), 180 min (p = 0.002; 16.8 ± 5.1 mcg/dL), and 240 min (p = 0.007; 14.6 ± 5.1 mcg/dL) in comparison to USP zinc oxide. In addition, GPM zinc significantly increased iAUC by 40% (5840 ± 2684 vs. 4183 ± 1132 mcg/dL * 480 min, p = 0.02), and Cmax values were 10% higher in GPM compared to USP (148 ± 21 mcg/dL vs. 135 ± 17.5 mcg/dL, p = 0.08). Tmax was 12% slower in GPM compared to USP (112.5 ± 38.7 min vs. 127.5 ± 43.1 min); however, differences in Tmax failed to reach statistical significance (p = 0.28). Zinc bound to a glycoprotein matrix significantly increased absorption compared to zinc oxide.

Preliminary Comparison of Fractional Absorption of Zinc Sulphate, Zinc Gluconate, and Zinc Aspartate after Oral Supple-Mentation in Healthy Human Volunteers

(1) Background: Zinc is generally used as a nutritional supplement for individuals at nutritional risk, such as older adults. This preliminary study investigated the fractional Zn absorption (FZA) after the supplementation on eight healthy volunteers with three different Zn complexes acquired with milk. (2) Methods: The design was a double-blind, three-period crossover trial. The volunteers were randomly divided into three groups. Each individual consumed 200 mL of bovine milk and rotated through a simultaneous administration of a single oral dose of ⁷⁰ZnSO₄, ⁷⁰Zn-Gluconate (⁷⁰Zn-Glu), and ⁷⁰Zn-Aspartate (⁷⁰Zn-Asp), equivalent to 2.0 mg ⁷⁰Zn, followed by 2 weeks of wash-out. An estimation of the FZA for comparative purposes was computed by the isotopic ratio between ⁶⁶Zn and ⁷⁰Zn in urine collected before and 48 h after administration. (3) Results: The estimated FZA was found to be significantly higher for ⁷⁰Zn-Asp when compared to the other forms, while the FZA of ⁷⁰Zn-Glu was found to be significantly higher than ⁷⁰ZnSO₄. (4) Conclusions: The results of this study suggest that complexing Zn with aspartate in milk could be a useful tool to improve FZA in individuals at risk of Zn deficiency. These results provide a rationale for conducting further studies on Zn-Asp preparations.

The Molecular Basis for Zinc Bioavailability

Zinc is an essential micronutrient, and its deficiency is perhaps the most prevalent and least understood worldwide. Recent advances have expanded the understanding of zinc’s unique chemistry and molecular roles in a vast array of critical functions. However, beyond the concept of zinc absorption, few studies have explored the molecular basis of zinc bioavailability that determines the proportion of dietary zinc utilized in zinc-dependent processes in the body. The purpose of this review is to merge the concepts of zinc molecular biology and bioavailability with a focus on the molecular determinants of zinc luminal availability, absorption, transport, and utilization.

Zinc Fortification: Current Trends and Strategies

Zinc, through its structural and cofactor roles, affects a broad range of critical physiological functions, including growth, metabolism, immune and neurological functions. Zinc deficiency is widespread among populations around the world, and it may, therefore, underlie much of the global burden of malnutrition. Current zinc fortification strategies include biofortification and fortification with zinc salts with a primary focus on staple foods, such as wheat or rice and their products. However, zinc fortification presents unique challenges. Due to the influences of phytate and protein on zinc absorption, successful zinc fortification strategies should consider the impact on zinc bioavailability in the whole diet. When zinc is absorbed with food, shifts in plasma zinc concentrations are minor. However, co-absorbing zinc with food may preferentially direct zinc to cellular compartments where zinc-dependent metabolic processes primarily occur. Although the current lack of sensitive biomarkers of zinc nutritional status reduces the capacity to assess the impact of fortifying foods with zinc, new approaches for assessing zinc utilization are increasing. In this article, we review the tools available for assessing bioavailable zinc, approaches for evaluating the zinc nutritional status of populations consuming zinc fortified foods, and recent trends in fortification strategies to increase zinc absorption.

Enhancement of the Water Affinity of Histidine by Zinc and Copper Ions

Histidine (His) is widely involved in the structure and function of biomolecules. Transition-metal ions, such as Zn²⁺ and Cu²⁺, widely exist in biological environments, and they are crucial to many life-sustaining physiological processes. Herein, by employing density function calculations, we theoretically show that the water affinity of His can be enhanced by the strong cation–π interaction between His and Zn²⁺ and Cu²⁺. Further, the solubility of His is experimentally demonstrated to be greatly enhanced in ZnCl₂ and CuCl₂ solutions. The existence of cation–π interaction is demonstrated by fluorescence, ultraviolet (UV) spectroscopy and nuclear magnetic resonance (NMR) experiments. These findings are of great importance for the bioavailability of aromatic drugs and provide new insight for understanding the physiological functions of transition metal ions.

Nutritional Interventions and the Gut Microbiome in Children

The gut microbiome plays an integral role in health and disease, and diet is a major driver of its composition, diversity, and functional capacity. Given the dynamic development of the gut microbiome in infants and children, it is critical to address two major questions: (a) Can diet modify the composition, diversity, or function of the gut microbiome, and (b) will such modification affect functional/clinical outcomes including immune function, cognitive development, and overall health? We synthesize the evidence on the effect of nutritional interventions on the gut microbiome in infants and children across 26 studies. Findings indicate the need to study older children, assess the whole intestinal tract, and harmonize methods and interpretation of findings, which are critical for informing meaningful clinical and public health practice. These findings are relevant for precision health, may help identify windows of opportunity for intervention, and may inform the design and delivery of such interventions. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Zinc(II) Complexes of Amino Acids as New Active Ingredients for Anti-Acne Dermatological Preparations

Zinc compounds have a number of beneficial properties for the skin, including antimicrobial, sebostatic and demulcent activities. The aim of the study was to develop new anti-acne preparations containing zinc–amino acid complexes as active ingredients. Firstly, the cytotoxicity of the zinc complexes was evaluated against human skin fibroblasts (1BR.3.N cell line) and human epidermal keratinocyte cell lines, and their antimicrobial activity was determined against Cutibacterium acnes. Then, zinc complexes of glycine and histidine were selected to create original gel formulations. The stability (by measuring pH, density and viscosity), microbiological purity (referring to PN-EN ISO standards) and efficacy of the preservative system (according to Ph. Eur. 10 methodology) for the preparations were evaluated. Skin tolerance was determined in a group of 25 healthy volunteers by the patch test. The preparations containing zinc(II) complexes with glycine and histidine as active substances can be topically used in the treatment of acne skin due to their high antibacterial activity against C. acnes and low cytotoxicity for the skin cells. Dermatological recipes have been appropriately composed; no irritation or allergy was observed, and the preparations showed high microbiological purity and physicochemical stability.

Tolerance to graded dosages of histidine supplementation in healthy human adults

BACKGROUND

Histidine is an essential amino acid with health benefits that may warrant histidine supplementation; however, the clinical safety of histidine intake above the average dietary intake (1.52-5.20 g/d) needs to be vetted.

OBJECTIVES

We aimed to determine the tolerance to graded dosages of histidine in a healthy adult population.

METHODS

Healthy adults aged 21-50 y completed graded dosages of histidine supplement (4, 8, and 12 g/d, Study 1) (n = 20 men and n = 20 women) and/or a 16-g/d dosage of histidine (Study 2, n = 21 men and n = 19 women); 27 participants (n = 12 men and n = 15 women) completed both studies. After study enrollment and baseline measures, participants consumed encapsulated histidine for 4 wk followed by a 3-wk recovery period. Primary outcomes included vitals, select biochemical analytes, anthropometry, serum zinc, and body composition (via DXA).

RESULTS

No changes in vitals or body composition occurred with histidine supplementation in either study. Plasma histidine (measured in subjects who completed all dosages for Studies 1 and 2) was elevated at the 12- and 16-g/d dosages (compared with 0-8 g/d, P < 0.05) and blood urea nitrogen increased with dosage (P = 0.013) and time (P < 0.001) in Study 1 and with time in Study 2 (P < 0.001). In Study 1, mean ferritin concentrations were lower in 12 g/d (46.0 ng/mL; 95% CI: 34.8, 60.9 ng/mL) than in 4 g/d (51.6 ng/mL; 95% CI: 39.0, 68.4 ng/mL; P = 0.038). In Study 2, 16 g/d increased mean aspartate aminotransferase from baseline (19 U/L; 95% CI: 17, 22 U/L) to week 4 (24 U/L; 95% CI: 21, 27 U/L; P < 0.001) and mean serum zinc decreased from baseline (0.75 μg/dL; 95% CI: 0.71, 0.80 μg/dL) to week 4 (0.70 μg/dL; 95% CI: 0.66, 0.74 μg/dL; P = 0.011).

CONCLUSIONS

Although values remained within the normal reference ranges for all analytes measured, in all dosages tested, the human no-observed adverse effect level was determined to be 8 g/d owing to changes in blood parameters at the 12-g/d dosage.This trial was registered at clinicaltrials.gov as NCT04142294.

Benefits and Adverse Effects of Histidine Supplementation

Histidine is a nutritionally essential amino acid with many recognized benefits to human health, while circulating concentrations of histidine decline in pathologic conditions [e.g., chronic obstructive pulmonary disease (COPD) and chronic kidney disease (CKD)]. The purpose of this review is to examine the existing literature regarding the benefits of histidine intake, the adverse effects of excess histidine, and the upper tolerance level for histidine. Supplementation with doses of 4.0-4.5 g histidine/d and increased dietary histidine intake are associated with decreased BMI, adiposity, markers of glucose homeostasis (e.g., HOMA-IR, fasting blood glucose, 2-h postprandial blood glucose), proinflammatory cytokines, and oxidative stress. It is unclear from the limited number of studies in humans whether the improvements in glucoregulatory markers, inflammation, and oxidative stress are due to reduced BMI and adiposity, increased carnosine (a metabolic product of histidine with antioxidant effects), or both. Histidine intake also improves cognitive function (e.g., reduces appetite, anxiety, and stress responses and improves sleep) potentially through the metabolism of histidine to histamine; however, this relation is ambiguous in humans. At high intakes of histidine (>24 g/d), studies report adverse effects of histidine such as decreased serum zinc and cognitive impairment. There is limited research on the effects of histidine intake at doses between 4.5 and 24 g/d, and thus, a tolerable upper level has not been established. Determining tolerance to histidine supplementation has been limited by small sample sizes and, more important, a lack of a clear biomarker for histidine supplementation. The U-shaped curve of circulating zinc concentrations with histidine supplementation could be exploited as a relevant biomarker for supplemental histidine tolerance. Histidine is an important amino acid and may be necessary as a supplement in some populations; however, gaps in knowledge, which this review highlights, need to be addressed scientifically.

Comprehensive Analysis of Zinc Derivatives Pro-proliferative, Anti-Apoptotic and Antimicrobial Effect on Human Fibroblasts and Keratinocytes in a Simulated, Nutrient-deficient Environment In Vitro

Zinc as therapeutic agent in skin and wound care has been known for centuries, but its role is controversial and comprehensive investigations in nutrient-deficient environments are lacking. We aimed to provide a broad analysis of different zinc derivatives on proliferation, apoptosis and antimicrobial properties in a simulated nutrient-deficient environment in vitro. Human fibroblasts (CRL2522) and keratinocytes (HaCaT) were treated with a broad concentration range (10 – 0.0001 µg/mL) of zinc-sulfate (ZnSO₄), -gluconate (ZnGluc) and -histidine (ZnHis) for 1-6 days under nutrient-deficient media conditions. Cell proliferation was investigated by XTT assay. Targeted analyzes in proliferation (E2F1, PCNA) and apoptosis (TP53) associated genes were performed via qRT-PCR and apoptosis was determined via FACS (annexin V/7-AAD staining). Antimicrobial efficacy was investigated using a quantitative suspension method against S. aureus, P. aeruginosa, E. coli, and C. albicans. The results indicated that 0.1 to 0.001 µg/mL Zn increased cell proliferation in both cell lines. Fibroblasts were more susceptible with significant proliferation peaks on days 2 & 6, and days 1 & 4 for keratinocytes. No relevant changes in gene expression were detected for E2F1 and PCNA nor for TP53. Annexin-V/7-AAD-staining of fibroblasts revealed a small, yet insignificant reduction of apoptosis induction for ZnGluc and ZnSO₄. ZnGluc and ZnSO₄ (0.1%) achieved high microbial reductions (4-5 log₁₀ reductions) against tested pathogens. ZnGluc and ZnSO₄ showed relevant pro-proliferative and antimicrobial, as well as tendential anti-apoptotic features in a simulated nutrient-deficient microenvironment in vitro. This further validates a potential benefit of local zinc treatment in deficient wound microenvironments.

Zinc deficiency in low- and middle-income countries: prevalence and approaches for mitigation

This review addresses the prevalence of zinc deficiency in Low- and Middle-income Countries (LMICs) and assesses the available strategies for its alleviation. The paucity of national-level data on the zinc deficiency in LMICs is partially a result of the lack of a reliable biomarker. Zinc deficiency appears to be a public health problem in almost all the LMICs, irrespective of the recommended indicators (plasma zinc concentration, dietary zinc adequacy and stunting prevalence) used. Based on plasma/serum zinc concentration (PZC), which is the most appropriate indicator at present, the prevalence of zinc deficiency in LMICs is of concern. Among the 25 countries for which national PZC data were available, 23 had a zinc deficiency prevalence of >20% for at least one physiological group. Zinc supplementation is largely restricted as an adjunct therapy for diarrhoea management in children, and the best platform and the most effective way of preventive zinc supplementation delivery remains to be established. Impact assessment for current zinc fortification programmes in LMICs and the effectiveness of zinc supplementation as part of a multi-micronutrient powder is to be determined. Dietary diversification, though promising for LMICs, is in the nascent stages of development at present. Inclusion of meat and animal products can be an important way of improving zinc status. Programmatic experience with the promotion of home processing techniques to increase absorbable zinc in the diet is lacking. Conventional biofortification techniques are gaining recognition in LMICs; however, transgenic biofortification as a strategy remains controversial.

Histidine: A Systematic Review on Metabolism and Physiological Effects in Human and Different Animal Species

Histidine is an essential amino acid (EAA) in mammals, fish, and poultry. We aim to give an overview of the metabolism and physiological effects of histidine in humans and different animal species through a systematic review following the guidelines of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). In humans, dietary histidine may be associated with factors that improve metabolic syndrome and has an effect on ion absorption. In rats, histidine supplementation increases food intake. It also provides neuroprotection at an early stage and could protect against epileptic seizures. In chickens, histidine is particularly important as a limiting factor for carnosine synthesis, which has strong anti-oxidant effects. In fish, dietary histidine may be one of the most important factors in preventing cataracts. In ruminants, histidine is a limiting factor for milk protein synthesis and could be the first limiting AA for growth. In excess, histidine supplementation can be responsible for eating and memory disorders in humans and can induce growth retardation and metabolic dysfunction in most species. To conclude, the requirements for histidine, like for other EAA, have been derived from growth and AA composition in tissues and also have specific metabolic roles depending on species and dietary levels.

A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models

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.

Speciation and accumulation of Zn in sweetcorn kernels for genetic and agronomic biofortification programs

In sweetcorn (Zea mays L.), embryo Zn is accumulated mainly as Zn-phytate, whereas endosperm Zn is complexed with a N- or S-containing ligand. Understanding the speciation of Zn in crop plants helps improve the effectiveness of biofortification efforts. Kernels of four sweetcorn (Zea mays L.) varieties were analysed for Zn concentration and content. We also assessed the speciation of the Zn in the embryo, endosperm, and pericarp in situ using synchrotron-based X-ray absorption spectroscopy. The majority of the Zn was in the endosperm and pericarp (72%), with the embryo contributing 28%. Approximately 79% of the Zn in the embryo accumulated as Zn-phytate, whereas in the endosperm most of the Zn was complexed with a N- or S-containing ligand, possibly as Zn-histidine and Zn-cysteine. This suggests that whilst the Zn in the endosperm and pericarp is likely to be bioavailable for humans, the Zn in the embryo is of low bioavailability. This study highlights the importance of targeting the endosperm of sweetcorn kernels as the tissue for increasing bioavailable Zn concentration.

Zinc preconditioning protects against renal ischaemia reperfusion injury in a preclinical sheep large animal model

Ischaemia-reperfusion injury (IRI) during various surgical procedures, including partial nephrectomy for kidney cancer or renal transplantation, is a major cause of acute kidney injury and chronic kidney disease. Currently there are no drugs or methods for protecting human organs, including the kidneys, against the peril of IRI. The aim of this study was therefore to investigate the reno-protective effect of Zn²⁺ preconditioning in a clinically relevant large animal sheep model of IRI. Further the reno-protective effectiveness of Zn²⁺ preconditioning was tested on normal human kidney cell lines HK-2 and HEK293. Anaesthetised sheep were subjected to uninephrectomy and 60 min of renal ischaemia followed by reperfusion. Sheep were preconditioned with intravenous injection of zinc chloride prior to occlusion. Serum creatinine and urea were measured before ischaemia and for 7 days after reperfusion. HK-2 and HEK293 cells were subjected to in vitro IRI using the oxygen- and glucose-deprivation model. Zn²⁺ preconditioning reduced ischaemic burden determined by creatinine and urea rise over time by ~ 70% in sheep. Zn²⁺ preconditioning also increased the survival of normal human kidney cells subjected to cellular stress such as hypoxia, hydrogen peroxide injury, and serum starvation. Overall, our protocol incorporating specific Zn²⁺ dosage, number of dosages (two), time of injection (24 and 4 h prior), mode of Zn²⁺ delivery (IV) and testing of efficacy in a rat model, a large preclinical sheep model of IRI and cells of human origin has laid the foundation for assessment of the benefit of Zn²⁺ preconditioning for human applications.

Zinc Absorption from Milk Is Affected by Dilution but Not by Thermal Processing, and Milk Enhances Absorption of Zinc from High-Phytate Rice in Young Dutch Women

Background: Milk has been suggested to increase zinc absorption. The effect of processing and the ability of milk to enhance zinc absorption from other foods has not been measured directly in humans.Objective: We aimed to assess zinc absorption from 1) milk undergoing various processing and preparatory steps and 2) from intrinsically labeled high-phytate rice consumed with milk or water.Methods: Two randomized crossover studies were conducted in healthy young women [age:18-25 y; body mass index (in kg/m²): 20-25]: 1) a milk study (n = 19) comparing the consumption of 800 mL full-fat ultra-high temperature (UHT) milk [heat-treated milk (HTM)], full-fat UHT milk diluted 1:1 with water [heat-treated milk and water (MW)], water, or unprocessed (raw) milk (UM), each extrinsically labeled with ⁶⁷Zn, and 2) a rice study (n = 18) comparing the consumption of 90 g intrinsically ⁶⁷Zn-labeled rice with 600 mL of water [rice and water (RW)] or full-fat UHT milk [rice and milk (RM)]. The fractional absorption of zinc (FAZ) was measured with the double-isotope tracer ratio method. In vitro, we assessed zinc extraction from rice blended into water, UM, or HTM with or without phytate.Results: FAZ from HTM was 25.5% (95% CI: 21.6%, 29.4%) and was not different from UM (27.8%; 95% CI: 24.2%, 31.4%). FAZ from water was higher (72.3%; 95% CI: 68.7%, 75.9%), whereas FAZ from MW was lower (19.7%; 95% CI: 17.5%, 21.9%) than HTM and UM (both P < 0.01). FAZ from RM (20.7%; 95% CI: 18.8%, 22.7%) was significantly higher than from RW (12.8%; 95% CI: 10.8%, 14.6%; P < 0.01). In vitro, HTM and UM showed several orders of magnitude higher extraction of zinc from rice with HTM than from rice with water at various phytate concentrations.Conclusions: Milk enhanced human FAZ from high-phytate rice by 62% compared with water. Diluting milk with water decreases its absorption-enhancing proprieties, whereas UHT processing does not. This trial was registered at the Dutch trial registry as NTR4267 (http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=4267).

A novel thiolated human-like collage zinc complex as a promising zinc supplement: physicochemical characteristics and biocompatibility

To improve zinc binding ability to human-like collagen (HLC) and stability of metal complex, HLC was thiolated by mercaptosuccinylation reaction with S-acetylmercaptosuccinic anhydride (S-AMSA) at pH8.0. One mole of thiolated HLC-Zn (SHLC-Zn) complex possessed 24.3mol zinc ions when pH was 8.0 and zinc concentration was 15 mM. The physicochemical properties and biocompatibility of thiolated HLC-Zn (SHLC-Zn) complex were investigated by UV-vis, CD, electrophoresis analysis, differential scanning calorimetry (DSC) and cell viability assay, respectively. The results showed that SHLC-Zn complex(1) exhibited higher zinc ions than that of native HLC and still maintained the secondary structure of HLC though interaction occurred between SHLC and zinc ions, (2) increased the apparent molecular weight when compared with native HLC, (3) exhibited greater thermal stability than native HLC, and (4) presented toxicity free for BHK cells. This study suggests that the SHLC-Zn complex is a potential nutrition as well as zinc supplement in the medical application.

Altered amino acid homeostasis and the development of fatigue by breast cancer radiotherapy patients: A pilot study

OBJECTIVES

To examine altered amino acid homeostasis as a predisposing factor of fatigue in female radiotherapy breast cancer patients.

DESIGN AND METHODS

Participants underwent breast-conserving surgery and adjuvant breast irradiation and were free from significant fatigue pre-radiotherapy. The Functional Assessment of Cancer Therapy fatigue subscale was used to assess fatigue pre- and post-radiotherapy. Blood biochemistry factors and urinary and plasma amino acid levels were measured.

RESULTS

One third of 27 patients developed fatigue and were designated as the fatigued cohort. It was possible to differentiate between fatigued subjects pre- and post-radiotherapy based upon their urinary amino acid profiles. Univariate analysis supported altered amino acid homeostasis within the fatigued cohort. Urinary levels of histidine and alanine were increased pre-radiotherapy whilst threonine, methionine, alanine, serine, asparagine and glutamine levels were higher after 5weeks of radiotherapy for the fatigued cohort.

CONCLUSIONS

Fatigue was accompanied by altered amino acid homeostasis with increased amino acid excretion suggestive of a catabolic response.

Comparison of uptake and neuroprotective potential of seven zinc-salts

Zinc plays an important role as an antioxidant in different cells treated with various kinds of oxidative stressors. Although intracellular Zn(2+) is important in many cellular events, little is known about the cellular uptake of this trace metal and the intracellular status that is required for its optimal function. Since previous reports usually employed only one type of zinc-salt, in this work was compared cellular uptake and antioxidative potential of seven zinc-salts in order to discriminate whether different counterions and ligands may influence its function. Oxidative stress was induced by peroxide or iron in neuronal PC12 cells. We compared uptake of zinc-salts into the labile Zn(2+) pool of PC12 cells as well as their effects on the prevention of cell death, glutathione depletion, lipid peroxidation and ROS production. Zinc-salts provided better protection against oxidative stress-induced in PC12 cultures by peroxide than by iron. Preincubations with zinc-salts displayed better neuroprotection in all cases than coincubations. Zinc-histidine complex was shown to be the most potent compound. Our results indicated that protective effect of zinc is not related to its uptake into PC12 cells, what is indicated by the rather low salt concentrations required for the cell protection and by the observation that despite a superior antioxidant effect of zinc-histidine, the uptake of this salt by PC12 cells was remarkably lower in comparison with other zinc-salts. Although zinc-sulfate exerted weak neuroprotective potential, accumulation of Zn(2+) from this salt within cells was significantly higher compared to other salts. The differences in accumulation of zinc-salts were not specific and unique to PC12 cells, since similar results were obtained in rat primary hepatocytes and endothelial HUVEC cells.

Comparative in vitro toxicity of seven zinc-salts towards neuronal PC12 cells

Currently much attention has been given to the neurotoxicity of zinc, yet little is known about the influence of the counterions present. Therefore, we investigated the influence of different Zn(2+)-salts (concentrations range 0.05-0.3 mM) on cell viability, ATP and glutathione concentration and caspase activation in differentiated PC12 cells as a model for neuronal cells. Generally, at concentrations of 0.05 mM most Zn(2+)-salts were not cytotoxic except for zinc-citrate. At concentrations between 0.1 and 0.3 mM Zn(2+) a significant decrease in GSH and ATP levels preceded cell death induced by all salts, except of zinc-histidinate. Zinc-citrate and zinc-sulphate turned out to be the most toxic salts particularly at low concentrations. Analyses of caspase 3/7 activity showed that dependent on the concentration and the type of the salt used cell death may show more or less signs of both, necrosis and apoptosis. Interestingly, the uptake of Zn(2+) from zinc-sulphate and zinc-citrate was significantly higher than that of other salts, implicating a correlation between uptake and toxicity. In conclusion, Zn(2+)-salts could be divided into three categories with high (zinc-citrate, zinc-sulphate), moderate (zinc-orotate, zinc-acetate, zinc-chloride(,) zinc-gluconate) and low cytotoxicity (zinc-histidinate).

Effect of dietary ligands and food matrices on zinc uptake in Caco-2 cells: implications in assessing zinc bioavailability

The kinetics, depletion/repletion of zinc, and effects of dietary ligands/food matrices on (65)Zn uptake was studied in Caco-2 cells. The uptake of zinc showed a saturable and nonsaturable component, depending upon the media zinc concentrations. Intracellular depletion increased zinc uptake, whereas zinc loading did not. Phytic acid and histidine inhibited zinc uptake, while tannic acid, tartaric acid, arginine, and methionine increased zinc uptake. Tannic acid at a 1:50 molar ratio promoted zinc uptake from wheat- and rice-based food matrices. Further, Caco-2 cells responded similarly with zinc and iron uptake when fed Indian bread prepared from low- and high-extraction wheat flour, representing low and high phytate content. However, inclusion of tea extract or red grape juice as a source of polyphenols enhanced the uptake of zinc while decreasing that of iron. These results suggest that the Caco-2 cells predict the correct direction of response to dietary ligands even from complex foods.

Zinc bioavailability is improved by the micronised dispersion of zinc oxide with the addition of L-histidine in zinc-deficient rats

Zinc fortification of milk or soft drinks is usually used to combat zinc deficiencies in developing countries. Water-soluble zinc compounds, such as zinc sulfate or zinc citrate, are better absorbed but have an unacceptable taste. A micronised, dispersible zinc oxide (MDZnO), which does not have such a problem concerning taste, had higher solubility compared to ZnO (zinc oxide) in an artificial gastric solution. MDZnO was tested for its bioavailability using zinc-deficient Wistar rats. Prior to the experiment, rats were fed zinc-deficient diet for 3 wk and were orally administered control (distilled water) or zinc solutions (ZnO, ZnO+L-histidine (His), MDZnO, MDZnO+His, 1 mg zinc/kg or 3.2 mg His/kg body weight). Compared to ZnO, MDZnO showed a lag in peak time and a lengthy period of continued high plasma zinc concentration after the single oral administration of zinc compounds. Addition of His to MDZnO elevated serum zinc concentration. Serum zinc concentration (area under the curve) in rats administered MDZnO with His was significantly higher than in rats administered distilled water (p<0.05). Liver zinc level was significantly higher in rats administered MDZnO with His compared with control rats (p<0.05), although the level was not affected by the administration with ZnO alone, ZnO+His, or MDZnO alone. In conclusion, the solubility of ZnO was elevated by the micronised dispersion tecnique and an in vivo study using zinc-deficient rats confirmed that its bioavailability was significantly improved compared to ZnO and the coadministration of His additively enhanced the bioavailability of MDZnO.

Nutrition intervention strategies to combat zinc deficiency in developing countries

Widespread zinc deficiency is likely to exist in developing countries where staple diets are predominantly plant based and intakes of animal tissues are low. The severe negative consequences of zinc deficiency on human health in developing countries, however, have only recently been recognized. An integrated approach employing targeted supplementation, fortification and dietary strategies must be used to maximize the likelihood of eliminating zinc deficiency at a national level in developing countries. Supplementation is appropriate only for populations whose zinc status must be improved over a relatively short time period, and when requirements cannot be met from habitual dietary sources. As well, the health system must be capable of providing consistent supply, distribution, delivery and consumption of the zinc supplement to the targeted groups. Uncertainties still exist about the type, frequency, and level of supplemental zinc required for prevention and treatment of zinc deficiency. Salts that are readily absorbed and at levels that will not induce antagonistic nutrient interactions must be used. At a national level, fortification with multiple micronutrients could be a cost effective method for improving micronutrient status, including zinc, provided that a suitable food vehicle which is centrally processed is available. Alternatively, fortification could be targeted for certain high risk groups (e.g. complementary foods for infants). Efforts should be made to develop protected fortificants for zinc, so that potent inhibitors of zinc absorption (e.g. phytate) present either in the food vehicle and/or indigenous meals do not compromise zinc absorption. Fortification does not require any changes in the existing food beliefs and practices for the consumer and, unlike supplementation, does not impose a burden on the health sector. A quality assurance programme is required, however, to ensure the quality of the fortified food product from production to consumption. In the future, dietary modification/diversification, although long term, may be the preferred strategy because it is more sustainable, economically feasible, culturally acceptable, and equitable, and can be used to alleviate several micronutrient deficiencies simultaneously, without danger of inducing antagonistic micronutrient interactions. Appropriate dietary strategies include consumption of zinc-dense foods and those known to enhance zinc absorption, reducing the phytic acid content of plant based staplesviaenzymic hydrolysis induced by germination/fermentation or nonenzymic hydrolysis by soaking or thermal processing. All the strategies outlined above should be integrated with ongoing national food, nutrition and health education programmes, to enhance their effectiveness and sustainability, and implemented using nutrition education and social marketing techniques. Ultimately the success of any approach for combating zinc deficiency depends on strong advocacy, top level commitment, a stable infrastructure, long term financial support and the capacity to control quality and monitor and enforce compliance at the national or regional level. To be cost effective, costs for these strategies must be shared by industry, government, donors and consumers.

Effects of cyclo (his-pro) plus zinc on glucose metabolism in genetically diabetic obese mice

AIMS

The specific objective of this study was to determine acute and long-term effects of cyclo (his-pro) (CHP) plus zinc and l-histidine (CZH) treatment on glucose metabolism in genetically obese (ob/ob), type 2 diabetic mice.

METHODS

Acute effects of 0.3 mg of CHP plus 10 mg of zinc and 0.5 mg of l-histidine/kg body weight (BW) on fed blood glucose concentrations and 3-h average of above fasting blood glucose concentrations (TAFGCs), an index of oral glucose tolerance test, in lean and ob/ob mice were determined. To evaluate long-term effects of CZH on TAFGCs, lean and ob/ob mice were treated with drinking water containing increasing doses of CHP (0, 0.5, 1.0 or 1.5 mg/l) plus 10 mg zinc and 0.5 mg of l-histidine/l for 3 weeks. During the treatment period, fed blood glucose concentrations, BW and food and water intake were determined. At the end of the treatment, fasting blood glucose concentrations, TAFGC and fed plasma insulin concentrations were determined.

RESULTS

Blood glucose concentrations significantly decreased when CZH was administered acutely via gastric gavage in food-deprived ob/ob mice. Similarly, 1.0 mg/l CHP treatment of mice with fixed amounts of 10 mg zinc and 0.5 mg l-histidine/l was optimal to decrease fed blood glucose and plasma insulin concentrations during a 3-week treatment period in ob/ob mice. TAFGC values in these mice also improved most significantly with the same combination of CHP, zinc and l-histidine used to test for fed blood glucose and plasma insulin levels. Fasting blood glucose concentrations and BW gains also decreased in ob/ob mice treated with 1.0 mg of CHP/l plus the same amount of zinc and l-histidine used in the above experiments. No effects of CZH treatment in lean mice were observed.

CONCLUSIONS

CZH is effective in decreasing blood glucose concentrations in genetically obese (ob/ob), type 2 diabetic mice. These data support our working hypothesis that CZH may be an important anti-hyperglycaemic agent.

Dietary factors influencing zinc absorption

Marginal zinc deficiency and suboptimal zinc status have been recognized in many groups of the population in both less developed and industrialized countries. Although the cause in some cases may be inadequate dietary intake of zinc, inhibitors of zinc absorption are most likely the most common causative factor. Phytate, which is present in staple foods like cereals, corn and rice, has a strong negative effect on zinc absorption from composite meals. Inositol hexaphosphates and pentaphosphates are the phytate forms that exert these negative effects, whereas the lower phosphates have no or little effect on zinc absorption. The removal or reduction of phytate by enzyme (phytase) treatment, precipitation methods, germination, fermentation or plant breeding/genetic engineering markedly improves zinc absorption. Iron can have a negative effect on zinc absorption, if given together in a supplement, whereas no effect is observed when the same amounts are present in a meal as fortificants. Cadmium, which is increasing in the environment, also inhibits zinc absorption. The amount of protein in a meal has a positive effect on zinc absorption, but individual proteins may act differently; e.g., casein has a modest inhibitory effect of zinc absorption compared with other protein sources. Amino acids, such as histidine and methionine, and other low-molecular-weight ions, such as EDTA and organic acids (e.g., citrate), are known to have a positive effect on zinc absorption and have been used for zinc supplements. Knowledge about dietary factors that inhibit zinc absorption and about ways to overcome or remove these factors is essential when designing strategies to improve the zinc nutrition of vulnerable groups.

Interactions related to trace elements in parenteral nutrition

Trace elements (TE) are now commonly added into the nutritive admixtures used in total parenteral nutrition (TPN) to prevent deficiencies which can be observed in patients undergoing long-term intravenous feeding. Although the needs in TE are not exactly known during a TPN, some of them must be considered as essential according to the results of studies dealing with general nutritional deficiencies. Among essential TE copper, iron and zinc are found at relatively high levels in organism. Chromium, manganese and selenium are also very important even though they are present at lower levels. In the case of a parenteral nutrition, the composition of the mixture is precisely defined and both digestion and absorption steps are shunted. Nevertheless, beneficial and/or negative physicochemical and metabolic interactions can occur between TE and the other nutrients. These interactions must be studied and taken into account because they can modify the bioavailability of the trace elements. In this article, our aim is to review the main recent bodies of knowledge which could be helpful to understand and prevent nutritional problems linked to these interactions during parenteral nutrition.

Free zinc concentration in bovine milk measured by analytical affinity chromatography with immobilized metallothionein

A new analytical affinity chromatography method was developed for measuring the free [Zn2+] concentration in bovine milk. The column was generated by immobilizing avidin and attaching biotinylated metallothionein (MT) on controlled-pore glass beads. Zinc bound to the MT column at physiological free [Zn2+] concentration and was dissociated again in an elution buffer of pH 2. The distributions of extrinsically added 65Zn and native zinc in different fractions of milk were virtually identical, validating the use of extrinsic labeling in studies of the free [Zn2+] concentration in milk. Extrinsically labeled whey fractions were mixed with standard solutions whose free [Zn2+] concentrations were calculated by computer model. 65Zn retained by the column provided an indication of free [Zn2+] concentration in the mixture, and by interpolation, in the original milk. The free [Zn2+] concentration measured by the affinity chromatography method in the milk of a group of six cows was 90.4 +/- 29.7 pM. This value is similar to estimates of free [Zn2+] concentrations in other biological fluids by entirely different methods. Measurement of free [Zn2+] may be helpful in understanding the physiology and biochemistry of zinc metabolism.

Dietary regulation of copper absorption and storage in rats: effects of sodium, zinc and histidine-zinc

Zinc (Zn) and L-histidine (His) are known competitors of intestinal copper (Cu) uptake. Sodium (Na) appears to be an enhancer of the luminal phase of Cu absorption. We investigated whether dietary treatment with these modifiers would alter Cu absorption and tissue stores of Zn and Cu in rats. Juvenile male rats were fed semipurified diets with adequate amounts of Cu, Zn and Na (Ctl), or with the addition of either excess Na (Hi Na), Zn (Hi Zn), or Zn plus His (Hi Zn+His) for 3 weeks. The jejunum was perfused in situ with 0.1 mM Cu, 1 mM His to determine Cu and water absorption rates. The lowest Cu absorption rate was observed in the Hi Zn+His group, and both the Hi Zn and Hi Zn+His had greater Cu accumulation in the small intestine than did Ctl or Hi Na rats. Hi Na had no effect on Cu transport. There was excess Cu accumulation in the kidneys of Hi Zn+His rats, and hepatic and kidney metallothioneins were also elevated. These results indicate that while a high Na intake does not affect Cu absorption, excess dietary Zn and His have greater effect than does Zn only in the limitation of Cu uptake.

Recent advances in the role of reactive oxygen intermediates in ischemic injury. I. Evidence demonstrating presence of reactive oxygen intermediates; II. Role of metals in site-specific formation of radicals

This article has attempted to bring the reader up to date on advances in selected facets of the area of reactive oxygen intermediate-induced ischemic injury. Specifically, we have discussed the more recent reports that provide evidence for the presence of these species in reperfused ischemic tissue. In addition, we have attempted to introduce the reader to the relatively new concept of "site-specific" formation of radicals and how the use of "push-pull" techniques, such as chelation by high-affinity chelators or displacement by non-redox-active metals such as zinc, may decrease postischemic reperfusion injury. Finally, we have identified a class of compounds that affect the oxidation state of redox-active metals, and have demonstrated how these compounds may also represent a new therapeutic modality. In conclusion, both academic and nonacademic surgeons should have profited from reading this article. For the academic surgeon, who may do research, several new cytoprotectants requiring further study in both in vitro and in vivo models have been identified. For the nonacademic surgeon in clinical practice the realization that there are several promising areas of research that may yield new therapies to mitigate postischemic reperfusion injury should have been gained.

Distinct mechanisms of zinc uptake at the apical and basolateral membranes of caco-2 cells

Zinc uptake mechanisms at the apical and basolateral membrane borders of caco-2 cells were examined. This human-derived cell line possesses many morphological and functional characteristics of absorptive small intestinal cells. By day 14, confluent and well-differentiated monolayers were formed when the cells were grown on porous polycarbonate filters. Labelled zinc was placed on the apical or basal side of the monolayer and its uptake by the cells, as well as its transport across the monolayer, were measured. Zinc uptake by the cells from the apical side was found to be a saturable process (Kt = 41 microM; Vmax = 0.3 nmols/cm2/10 min) with a diffusional term at higher concentrations (1.0 sec/cm). Apical uptake was not affected by metabolic inhibitors or potential zinc ligands. Zinc uptake from the basolateral side was concentration dependent (Kd = 1.3 sec/cm) and was partially inhibited (30%) by ouabain and vanadate, suggesting that the (Na-K)-ATPase on the basolateral membrane is involved in the serosal uptake of zinc by the cell. Transport of zinc across the monolayers from the apical or basolateral compartment was concentration dependent and was not affected by metabolic inhibitors. Zinc transport from the basolateral side was greater than 2-fold greater than apical transport. Hence, separate mechanisms can be distinguished with respect to zinc uptake at the apical and basolateral membranes of caco-2 cells.

A preliminary study of the bioavailability of iron- and zinc-glycine chelates

Groups of rats were fed diets containing marginal levels of Fe and Zn as glycine chelates (tradename 'Chelazome', Albion Laboratories, Verona, New Jersey, USA), or the same level of mineral as ferrous sulphate or zinc carbonate. The Fe diets were fed to weanling rats for 4 weeks and the Zn diets to young adult rats for 5 weeks. Blood Hb concentrations were significantly higher in the group fed Fe-chelazome than ferrous sulphate, 149 and 128 g/l respectively (P less than 0.001), but PCV and liver Fe concentrations were similar between the two groups. No difference in plasma Zn, pancreas, testes or femur Zn concentrations were observed between the two Zn groups, indicating that Zn-chelazome has no advantage over zinc carbonate. The results of this preliminary study indicate that Fe-chelazome has a higher bioavailability than ferrous sulphate and merits further study.

The effects of dietary ligands on zinc uptake at the porcine intestinal brush-border membrane

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.