Dietary zinc absorption: A play of Zips and ZnTs in the gut

Biochemical Markers of Zinc Nutrition

Zinc is an important trace element involved in the biochemical and physiological functions of the organism and is essential in the human body. It has been reported that 17.3% of people around the world are at risk of many diseases due to zinc deficiency, which has already affected people's healthy lives. Currently, mild zinc deficiency is difficult to diagnose early due to the lack of typical clinical manifestations, so finding zinc biomarkers is crucial for people's health. The present article reviews the main representative zinc biomarkers, such as body fluid zinc levels, zinc-dependent proteins, tissue zinc, and zinc-containing enzymes, to provide a reference for actively promoting the study of zinc nutritional status and early clinical diagnosis.

The expression of Catsup in the hindgut is essential for zinc homeostasis in Drosophila melanogaster

Zinc excretion is crucial for zinc homeostasis. However, the mechanism of zinc excretion has not been well characterized. Zinc homeostasis in Drosophila seems well conserved to mammals. In this study, we screened all members of the zinc transporters ZnT (SLC30) and Zip (SLC39) for their potential roles in Drosophila hindgut, an insect organ that belongs to the excretory system. The results indicated that Catecholamines up (Catsup, CG10449), a ZIP member localized to the Golgi, is responsible for zinc homeostasis in the hindgut of Drosophila hindgut-specific knockdown of Catsup leads to a developmental arrest in the larval stage, which could be rescued well by human ZIP7. Further study suggested that Catsup RNAi in the hindgut reduced zinc levels in the excretory system (containing the Malpighian tubule and hindgut) but exhibited systemic zinc overload. Besides, more calculi were observed in the Malpighian tubules of Catsup RNAi flies. The developmental arrest and calculi in the Malpighian tubules of hindgut-specific Catsup RNAi flies could be rescued by dietary zinc restriction but hypersensitivity to zinc. These results will help us understand the fundamental process of zinc excretion in higher eukaryotes.

Zinc-glutathione mitigates alcohol-induced intestinal and hepatic injury by modulating intestinal zinc-transporters in mice

Long-term alcohol overconsumption impairs intestinal and hepatic structure and function, along with dysregulation of zinc homeostasis. We previously found that zinc-glutathione (Zn-GSH) complex effectively suppressed alcohol-induced liver injury in mice. This study was undertaken to test the hypothesis that Zn-GSH suppresses alcohol-induced liver injury by modulating intestinal zinc transporters. Mice were subjected to long-term ethanol feeding, as per the NIAAA model, with groups receiving either an ethanol diet alone or an ethanol diet supplemented with Zn-GSH. Treatment groups were carefully monitored for alcohol consumption and subjected to a final binge drinking exposure. The results showed that Zn-GSH increased the survival rate and decreased the recovery time from binge drinking-induced drunkenness. Histopathological analyses demonstrated a reduction in liver steatosis and the preservation of intestinal integrity by Zn-GSH. It was observed that Zn-GSH prevented the reduction of Zn and GSH levels while increasing alcohol dehydrogenase and aldehyde dehydrogenase in both liver and intestine. Importantly, the expression and protein abundance of zinc transporters ZnT-1, ZIP-1, ZIP-4, ZIP-6, and ZIP-14, all of which are critically involved in intestinal zinc transport and homeostasis, were significantly increased or preserved by Zn-GSH in response to alcohol exposure. This study thus highlights the critical role of Zn-GSH in maintaining intestinal zinc homeostasis by modulating zinc transporters, thereby preventing alcohol-induced intestinal and hepatic injury.

Investigation of the concentration and isotopic composition of Cu, Fe and Zn in human biofluids in the context of Alzheimer's disease via tandem and multi-collector inductively coupled plasma-mass spectrometry

Studies on essential trace elements in the context of Alzheimer's disease (AD) concluded that Cu, Fe and Zn interact with amyloid-β, accelerating plaque formation in the brain. Additionally, Cu and Fe in the vicinity of plaques produce reactive oxygen species (ROS) resulting in oxidative stress, whereas Zn plays a role in the antioxidant defence as a co-factor for antioxidants. In this work, the Cu, Fe and Zn concentrations and isotope ratios were determined in whole blood, blood serum and cerebrospinal fluid of 10 patients diagnosed with AD and 8 control individuals, using tandem (ICP-MS/MS) and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), respectively. In whole blood and blood serum of AD patients, a heavier Cu isotopic composition was observed (significant for whole blood only) compared to controls. Albumin levels in cerebrospinal fluid tend to increase with age, which could indicate an increased leakiness of the blood-brain barrier. In cerebrospinal fluid, a large variability was observed for the Cu and Fe isotope ratios, potentially resulting from that leakiness at the blood-brain barrier. Therefore, potential effects of AD on the concentration and isotopic composition of essential elements in cerebrospinal fluid related to amyloid-β formation could be hidden. Finally, in blood serum, Zn, urea and creatinine concentrations showed an increase with age and showed a significant difference between sexes.

The nutritional roles of zinc for immune system and COVID-19 patients

Zinc (Zn) is a vital micronutrient that strengthens the immune system, aids cellular activities, and treats infectious diseases. A deficiency in Zn can lead to an imbalance in the immune system. This imbalance is particularly evident in severe deficiency cases, where there is a high susceptibility to various viral infections, including COVID-19 caused by SARS-CoV-2. This review article examines the nutritional roles of Zn in human health, the maintenance of Zn concentration, and Zn uptake. As Zn is an essential trace element that plays a critical role in the immune system and is necessary for immune cell function and cell signaling, the roles of Zn in the human immune system, immune cells, interleukins, and its role in SARS-CoV-2 infection are further discussed. In summary, this review paper encapsulates the nutritional role of Zn in the human immune system, with the hope of providing specific insights into Zn research.

A network-based method for associating genes with autism spectrum disorder

Autism spectrum disorder (ASD) is a highly heritable complex disease that affects 1% of the population, yet its underlying molecular mechanisms are largely unknown. Here we study the problem of predicting causal genes for ASD by combining genome-scale data with a network propagation approach. We construct a predictor that integrates multiple omic data sets that assess genomic, transcriptomic, proteomic, and phosphoproteomic associations with ASD. In cross validation our predictor yields mean area under the ROC curve of 0.87 and area under the precision-recall curve of 0.89. We further show that it outperforms previous gene-level predictors of autism association. Finally, we show that we can use the model to predict genes associated with Schizophrenia which is known to share genetic components with ASD.

Effects of Long-Term Dietary Zinc Oxide Nanoparticle on Liver Function, Deposition, and Absorption of Trace Minerals in Intrauterine Growth Retardation Pigs

To investigate the long-term effects of dietary zinc oxide nanoparticle (Nano-ZnO, 20-40 nm) on the relative organ weight, liver function, deposition, and absorption of trace minerals in intrauterine growth retardation (IUGR) pigs, piglets were allocated to NBW (6 normal birth weight piglets fed basal diets), IUGR (6 IUGR piglets fed basal diets) and IUGR+NZ (6 IUGR piglets fed basal diets + 600 mg Zn/kg from Nano-ZnO) groups at weaning (21 days of age), which were sampled at 163 days of age. There were no noteworthy changes in the relative weight of organs, hepatic histomorphology, serum alkaline phosphatase, glutamic pyruvic transaminase and glutamic oxalacetic transaminase activities, and Mn, Cu, and Fe concentrations in leg muscle, the liver, the tibia, and feces among the IUGR, NBW, and IUGR+NZ groups (P>0.05), and no intact Nano-ZnO in the jejunum, liver, and muscle was observed, while dietary Nano-ZnO increased the Zn concentrations in the tibia, the liver, serum, and feces (P<0.05) and mRNA expression of metallothionein (MT) 1A, MT2A, solute carrier family 39 member (ZIP) 4, ZIP14, ZIP8, divalent metal transporter 1, solute carrier family 30 member (ZnT) 1, ZnT4 and metal regulatory transcription factor 1, and ZIP8 protein expression in jejunal mucosa (P<0.05). Immunohistochemistry showed that dietary Nano-ZnO increased the relative optical density of ZIP8 (mainly expressed in cells of brush border) and MT2A (mainly expressed in villus lamina propria and gland/crypt) (P<0.05). In conclusion, long-term dietary Nano-ZnO showed no obvious side effects on the development of the major organs, liver function, and metabolism of Cu, Fe, and Mn in IUGR pigs, while it increased the Zn absorption and deposition via enhancing the expression of transporters (MT, ZIP, and ZnT families) in the jejunum, rather than via endocytosis as the form of intact nanoparticles.

Structural Characterization of Zinc-Sucrose Complex and Its Ability to Promote Zinc Absorption in Caco-2 Monolayer Cells and Mice

Sucrose emerges as a metal-ion chelating agent with excellent stability that may increase metal-ion absorption. This study aimed to characterize the structure of zinc-sucrose complex and investigate its ability to promote zinc absorption in Caco-2 monolayer cells and mice. Based on the results of the inductively coupled plasma emission spectrometer (ICP-ES), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier transform infrared spectroscopy (FT-IR), it can be inferred that zinc and sucrose were chelated at a 1:1 ratio, with the hydroxyl groups playing a significant role. The Caco-2 monolayer cell model revealed that zinc-sucrose complex increased the amount of zinc uptake, retention, and transport in a dose- and time-dependent manner. Through the upregulation of genes and proteins for ZIP4, MT1, and DMT1, treatment with zinc-sucrose complex improved the proportion of absorbed zinc utilized for transport compared to ZnCl2 (26.21 ± 4.96 versus 8.50 ± 1.51%). Pharmacokinetic analysis of mice confirmed the zinc absorption-promoting effect of zinc-sucrose complex, as indicated by the considerably higher serum zinc level (4.16 ± 0.53 versus 2.56 ± 0.45 mg/L) and intestinal ZIP4, MT1, and DMT1 gene expression than ZnCl2. Further treatment of different zinc channel inhibitors and CETSA demonstrated the direct interaction of zinc-sucrose complex with ZIP4 protein and ZIP4-mediated cellular transport of zinc-sucrose complex. These findings provide a novel insight into the zinc absorption-promoting mechanism of zinc-sucrose complex, which could be used as an ingredient in functional foods to treat zinc deficiency.

An alternative ZnO with large specific surface area: Preparation, physicochemical characterization and effects on growth performance, diarrhea, zinc metabolism and gut barrier function of weaning piglets

High-dose ZnO is widely used to prevent diarrhea and promote growth of weaning piglets, which has led to serious problems of animal toxicity, bacterial resistance and environmental pollution. In this study, a novel alternative ZnO (AZO) was prepared and its physicochemical properties were characterized. Animal experiments were further conducted to evaluate the effects of the ZnO forms, the dose of AZO and the combinations with AZO on the growth performance, diarrhea, zinc metabolism and gut barrier function of weaning piglets. The results showed that the AZO, compared with ordinary ZnO (OZO), nano ZnO (NZO) and porous ZnO (PZO), had the largest surface area and reduced the release of Zn²⁺ into the gastric fluid. AZO showed better antibacterial activity on Escherichia coli K88, Staphylococcus aureus and Salmonella enteritidis but lower cytotoxicity on porcine intestinal epithelial cells. Animal experiments suggested that low-dose AZO, NZO and PZO (300 mg/kg) improved growth performance and reduced diarrhea in weaning piglets as well as high-dose OZO (3000 mg/kg). Notably, low-dose AZO had the lowest diarrhea incidence. Additionally, low-dose AZO in combination with probiotics improved digestibility and digestive enzyme activities. Low-dose AZO in combination with probiotics also upregulated the expression of the intestinal zinc transporter proteins ZIP4 and DMT1, increased zinc bioavailability, reduced faecal zinc emissions, and avoided zinc overload in the liver and oxidative damage caused by high-dose ZnO. Moreover, low-dose AZO in combination with probiotics improved the gut barrier function of weaning piglets by promoting the expression of tight junction proteins, mucins and antimicrobial peptides and increasing gut microbiota diversity and beneficial Lactobacillus. This study proposed a novel strategy to replace high-dose ZnO and antibiotics with low-dose AZO and probiotics in weaning piglets, which effectively improved growth performance and prevented diarrhea while reducing animal toxicity, bacterial resistance, heavy metal residues and zinc emission pollution.

Low Levels of Serum Zinc Associate with Malnutrition Risk Assessed by the Royal Free Hospital-Nutritional Prioritizing Tool in Cirrhosis

We have clarified that malnutrition risk evaluated by the Royal Free Hospital-Nutritional Prioritizing Tool (RFH-NPT) is prevalent in patients with cirrhosis. Mineral elements (zinc, iron, magnesium, copper, manganese, and calcium) are micronutrients essential for versatile physiological processes and cellular bioactivities. However, the association between these trace elements and integral nutritional status is unclear in decompensated cirrhotics. We collected blood samples from hospitalized patients with cirrhosis, and serum trace element concentrations were examined by inductively coupled plasma mass spectrometry. Association of trace element levels with high malnutrition risk was determined by multivariate logistic regression model. Sera from 141 patients with decompensated cirrhosis were analyzed for a total of six trace element concentrations. No significant differences were observed between high and low/moderate RFH-NPT malnutrition risk groups with the exception of zinc. The serum zinc concentrations were significantly decreased in patients at high malnutrition risk when compared to low/moderate subjects (57.9 vs 68.1 μg/dL, P = 0.006). In terms of receiver operating characteristics curve, zinc < 64 μg/dL represented best discriminative capability with an area of 0.635 (95% CI: 0.542, 0.728). Patients in the group with zinc < 64 μg/dL had elevated RFH-NPT and MELD score, higher proportion of Child-Pugh class C and ascites, higher CRP, lower albumin and sodium than in the group with zinc ≥ 64 μg/dL. Zinc < 64 μg/dL was an independent risk factor for high malnutrition risk. Low levels of serum zinc referring to less than 64 μg/dL were associated with poor integral nutritional status in cirrhosis.

Organic zinc with moderate chelation strength enhances zinc absorption in the small intestine and expression of related transporters in the duodenum of broilers

Our previous study demonstrated that the absorption of zinc (Zn) from the organic Zn proteinate with moderate chelation strength was significantly higher than that of Zn from the inorganic Zn sulfate in the in situ ligated duodenal segment of broilers, but the underlying mechanisms are unknown. The present study aimed to determine the effect of organic Zn with moderate chelation strength and inorganic Zn on the Zn absorption in the small intestine and the expression of related transporters in the duodenum of broilers. The Zn-deficient broilers (13 days old) were fed with the Zn-unsupplemented basal diets (control) containing 25.72 and 25.64 mg Zn/kg by analysis or the basal diets supplemented with 60 mg Zn/kg as the Zn sulfate or the Zn proteinate with moderate chelation strength (Zn-Prot M) for 26 days. The results showed that the plasma Zn contents from the hepatic portal vein of broilers at 28 days and 39 days of age were increased (p < 0.05) by Zn addition and greater (p < 0.05) in the Zn-Prot M than in the Zn sulfate. On d 28, Zn addition upregulated (p < 0.05) mRNA expression of zinc transporter 1 (ZnT1), Zrt-irt-like protein 5 (ZIP5), y + L-type amino transporter 2 (y + LAT2) and b^0,+-type amino acid transporter (rBAT), zinc transporter 4 (ZnT4) protein expression, and zinc transporter 9 (ZnT9) mRNA and protein expression in the duodenum. Moreover, ZnT9 mRNA expression, ZnT4, ZIP5, and rBAT protein expression, zinc transporter 7 (ZnT7), and y + LAT2 mRNA and protein expression in the duodenum of broilers on 28 days were higher (p < 0.05) in the Zn-Prot M than in the Zn sulfate. On d 39, supplemental Zn increased (p < 0.05) peptide-transporter 1 (PepT1) mRNA expression and y + LAT2 protein expression, while the mRNA expression of ZnT7 and Zrt-irt-like protein 3 (ZIP3) were higher (p < 0.05) for the Zn-Prot M than for the Zn sulfate in the duodenum. It was concluded that the Zn-Prot M enhanced the Zn absorption in the small intestine partially via upregulating the expression of ZnT4, ZnT7, ZnT9, ZIP3, ZIP5, y + LAT2, and rBAT in the duodenum of broilers.

The Role of Ferroptosis Signature in Overall Survival and Chemotherapy of Pancreatic Adenocarcinoma

Studies have shown that ferroptosis, an iron-dependent regulated cell death, is related to prognosis and chemotherapy, but the role of ferroptosis in pancreatic adenocarcinoma (PAAD) is still unclear. We aimed at constructing a ferroptosis-related gene (FRGs) model to predict the PAAD patients' overall survival (OS) and at exploring their values in chemotherapy. We downloaded the mRNA-sequencing data and corresponding clinical data of patients with PAAD from The Cancer Genome Atlas. Lasso-penalized Cox regression analysis was utilized to construct a prognostic risk model, including spermidine/spermine N1-acetyltransferase 1 (SAT1), SAT2, TFRC, SLC39A8, MAP1LC3A, ALOX15, and PROM2. Receiver operating characteristic curves were used to evaluate the prognostic model. International Cancer Genome Consortium cohorts were used to validate this model. Then, we used Genomics of Drug Sensitivity in Cancer and Gene Expression Omnibus databases to analyze the correlation between FRGs and drug sensitivity. Notably, SAT1 showed significant influence in cisplatin and gemcitabine resistance. Finally, in vitro experiments demonstrated that the combination of gemcitabine and cisplatin could induce ferroptosis in AsPC1 cells, probably through elevated SAT1 expression. Taken together, Our 7-gene signature has significant values in predicting the PAAD patients' OS, and it may help inform the clinical treatment of PAAD.

Aberrance of Zinc Metalloenzymes-Induced Human Diseases and Its Potential Mechanisms

Zinc, an essential micronutrient in the human body, is a component in over 300 enzymes and participates in regulating enzymatic activity. Zinc metalloenzymes play a crucial role in physiological processes including antioxidant, anti-inflammatory, and immune responses, as well as apoptosis. Aberrant enzyme activity can lead to various human diseases. In this review, we summarize zinc homeostasis, the roles of zinc in zinc metalloenzymes, the physiological processes of zinc metalloenzymes, and aberrant zinc metalloenzymes in human diseases. In addition, potential mechanisms of action are also discussed. This comprehensive understanding of the mechanisms of action of the regulatory functions of zinc in enzyme activity could inform novel zinc-micronutrient-supply strategies for the treatment of diseases.

Administration of zinc to preterm infants with hypozincemia does not reduce serum copper concentrations in most cases: a single-center retrospective observational study

Background

Zinc is an essential trace element involved in various physiological functions. In Japan, zinc acetate dihydrate is administered to neonates and infants with hypozincemia. Since serum copper concentrations are reduced by the administration of zinc, we retrospectively investigated changes in serum zinc and copper concentrations in preterm infants with hypozincemia receiving zinc acetate dihydrate.

Methods

Sixty-three preterm infants were included in the present study. Serum zinc and copper concentrations, doses, and other clinical characteristics were retrieved from electronic medical records.

Results

The medians and interquartile ranges of the dosage and duration of zinc acetate dihydrate were 2.1 (1.8–2.5) mg/kg/day and 12.0 (10.0–13.0) days, respectively. Its administration increased serum zinc concentrations in 39 patients (61.9%) and to more than 70 μg/dL in 16 patients (25.4%). The group with a serum zinc concentration of 70 μg/dL or higher after administration had a significantly higher zinc dose of 2.5 mg/kg/day than the group with a serum zinc concentration of less than 70 μg/dL. Serum copper concentrations did not decrease in 44 patients (69.8%). In the group with a decreased serum copper concentration, postmenstrual age and body weight were significantly lower, while serum zinc concentrations were significantly higher at the start of administration.

Conclusion

The present results showed that when zinc acetate dihydrate was administered to preterm infants with hypozincemia, it was possible to increase serum zinc concentrations without decreasing serum copper concentrations in many cases. However, caution may be required when administering zinc to preterm infants with a lower postmenstrual age or milder hypozincemia because serum copper concentrations may decrease.

Effects of Zinc Source and Enzyme Addition on the Fecal Microbiota of Dogs

Supplemental zinc from organic sources has been suggested to be more bioavailable than inorganic ones for dog foods. However, the bioavailability of zinc might be affected by dietary constituents such as phytates. The present study aimed to evaluate the effects of two zinc sources (zinc sulfate and zinc proteinate) and the addition of a multi-enzymatic complex from the solid-state fermentation of Aspergillus niger on end-products of fecal fermentation and fecal microbiota of adult Beagles fed a high-phytate diet. The experimental design consisted of three 4 × 4 Latin Squares with a 2 × 2 factorial arrangement of treatments (n = 12 Beagles), with four periods and four diets: zinc sulfate without (IZ) or with (IZ +) enzyme addition, and zinc proteinate without (OZ) or with (OZ +) enzyme addition. Enzyme addition significantly affected Faith’s phylogenetic diversity index, whereas zinc source did not affect either beta or alpha diversity measures. Linear discriminant analysis effect size detected nine taxa as markers for organic zinc, 18 for inorganic source, and none for enzyme addition. However, with the use of a negative binomial generalized linear model, further effects were observed. Organic zinc was associated with a significantly higher abundance of Firmicutes and lower Proteobacteria and Bacteroidetes, although at a genus level, the response varied. The DNA abundance of Clostridium cluster I, Clostridium cluster XIV, Campylobacter spp., Ruminococcaceae, Turicibacter, and Blautia was significantly higher in dogs fed IZ and IZ + diets. Higher abundance of genus Lactobacillus was observed in dogs fed enzyme-supplemented diets. End-products of fecal fermentation were not affected by zinc source or enzymes. An increase in some taxa of the phyla Actinobacteria and Firmicutes was observed in feces of dogs fed organic zinc with enzyme addition but not with inorganic zinc. This study fills a gap in knowledge regarding the effect of zinc source and enzyme addition on the fecal microbiota of dogs. An association of zinc bioavailability and bacteria abundance is suggested, but the implications for the host (dog) are not clear. Further studies are required to unveil the effects of the interaction between zinc sources and enzyme addition on the fecal microbial community.

Zinc is an important inter-kingdom signal between the host and microbe

Zinc (Zn) is an essential trace element in living organisms and plays a vital role in the regulation of both microbial virulence and host immune responses. A growing number of studies have shown that zinc deficiency or the internal Zn concentration does not meet the needs of animals and microbes, leading to an imbalance in zinc homeostasis and intracellular signalling pathway dysregulation. Competition for zinc ions (Zn²⁺) between microbes and the host exists in the use of Zn²⁺ to maintain cell structure and physiological functions. It also affects the interplay between microbial virulence factors and their specific receptors in the host. This review will focus on the role of Zn in the crosstalk between the host and microbe, especially for changes in microbial pathogenesis and nociceptive neuron-immune interactions, as it may lead to new ways to prevent or treat microbial infections.

Effect of pinealectomy and melatonin supplementation on metallothionein, ZnT2, ZIP2, ZIP4 and zinc levels in rat small intestine

We investigated the relations among levels of metallothionein (MT); zinc (Zn) transport proteins, ZnT2, ZIP2 (ZRT and IRT-like proteins); and ZIP4, which enable Zn absorption in the small intestine of rats. We also investigated tissue Zn levels in the small intestine. We used four groups of adult male rats: group 1, control; group 2, pinealectomy (Px); group 3, Px + melatonin (MEL); group 4, MEL only. Animals in groups 3 and 4 were administered 5 mg/kg/day MEL for four weeks. At the end of the study, all animals were sacrificed and samples of duodenum, jejunum and ileum were harvested to analyze ZnT2, ZIP2, ZIP4 and MT levels using immunohistochemistry, and tissue Zn levels were measured by atomic absorption spectrophotometry. The lowest ZnT2 levels in the duodenum, jejunum and ileum, and the lowest ZIP2 levels in the duodenum and ileum were found in group 2. The lowest ZIP4 levels were found in the duodenum and jejunum, and the lowest MT levels in the duodenum and ileum were found in group 2. The highest MT values in the ileum were found in group 4. We found that ZnT2, ZIP2, ZIP4 and MT levels were reduced in the ileum compared to controls following Px, but levels approached control values after MEL administration. By its effects on ZnT2, ZIP2, ZIP4 and MT levels, MEL participates in the absorption of Zn in the rat small intestine.

Zinc transporters and their functional integration in mammalian cells

Zinc is a ubiquitous biological metal in all living organisms. The spatiotemporal zinc dynamics in cells provide crucial cellular signaling opportunities, but also challenges for intracellular zinc homeostasis with broad disease implications. Zinc transporters play a central role in regulating cellular zinc balance and subcellular zinc distributions. The discoveries of two complementary families of mammalian zinc transporters (ZnTs and ZIPs) in the mid-1990s spurred much speculation on their metal selectivity and cellular functions. After two decades of research, we have arrived at a biochemical description of zinc transport. However, in vitro functions are fundamentally different from those in living cells, where mammalian zinc transporters are directed to specific subcellular locations, engaged in dedicated macromolecular machineries, and connected with diverse cellular processes. Hence, the molecular functions of individual zinc transporters are reshaped and deeply integrated in cells to promote the utilization of zinc chemistry to perform enzymatic reactions, tune cellular responsiveness to pathophysiologic signals, and safeguard cellular homeostasis. At present, the underlying mechanisms driving the functional integration of mammalian zinc transporters are largely unknown. This knowledge gap has motivated a shift of the research focus from in vitro studies of purified zinc transporters to in cell studies of mammalian zinc transporters in the context of their subcellular locations and protein interactions. In this review, we will outline how knowledge of zinc transporters has been accumulated from in-test-tube to in-cell studies, highlighting new insights and paradigm shifts in our understanding of the molecular and cellular basis of mammalian zinc transporter functions.

Overproduction of Human Zip (SLC39) Zinc Transporters in Saccharomyces cerevisiae for Biophysical Characterization

Zinc constitutes the second most abundant transition metal in the human body, and it is implicated in numerous cellular processes, including cell division, DNA and protein synthesis as well as for the catalytic activity of many enzymes. Two major membrane protein families facilitate zinc homeostasis in the animal kingdom, i.e., Zrt/Irt-like proteins (ZIPs aka solute carrier 39, SLC39, family) and Zn transporters (ZnTs), essentially conducting zinc flux in the opposite directions. Human ZIPs (hZIPs) regulate import of extracellular zinc to the cytosol, being critical in preventing overaccumulation of this potentially toxic metal, and crucial for diverse physiological and pathological processes, including development of neurodegenerative disorders and several cancers. To date, our understanding of structure-function relationships governing hZIP-mediated zinc transport mechanism is scarce, mainly due to the notorious difficulty in overproduction of these proteins for biophysical characterization. Here we describe employment of a Saccharomyces cerevisiae-based platform for heterologous expression of hZIPs. We demonstrate that yeast is able to produce four full-length hZIP members belonging to three different subfamilies. One target (hZIP1) is purified in the high quantity and homogeneity required for the downstream biochemical analysis. Our work demonstrates the potential of the described production system for future structural and functional studies of hZIP transporters.

Imipramine Influences Body Distribution of Supplemental Zinc Which May Enhance Antidepressant Action

Zinc (Zn) was found to enhance the antidepressant efficacy of imipramine (IMI) in human depression and animal tests/models of depression. However, the underlying mechanism for this effect remains unknown. We measured the effect of intragastric (p.o.) combined administration of IMI (60 mg/kg) and Zn (40 mg Zn/kg) in the forced swim test (FST) in mice. The effect of Zn + IMI on serum, brain, and intestinal Zn concentrations; Zn transporter (ZnT, ZIP) protein levels in the intestine and ZnT in the brain; including BDNF (brain-derived neurotrophic factor) and CREB (cAMP response element-binding protein) protein levels in the brain were evaluated. Finally, the effect of IMI on Zn permeability was measured in vitro in colon epithelial Caco-2 cells. The co-administration of IMI and Zn induced antidepressant-like activity in the FST in mice compared to controls and Zn or IMI given alone. This effect correlated with increased BDNF and the ratio of pCREB/CREB protein levels in the prefrontal cortex (PFC) compared to the control group. Zn + IMI co-treatment increased Zn concentrations in the serum and brain compared to the control group. However, in serum, co-administration of IMI and Zn decreased Zn concentration compared to Zn alone treatment. Also, there was a reduction in the Zn-induced enhancement of ZnT1 protein level in the small intestine. Zn + IMI also induced an increase in the ZnT4 protein level in the PFC compared to the control group and normalized the Zn-induced decrease in the ZnT1 protein level in the hippocampus (Hp). The in vitro studies revealed enhanced Zn permeability (observed as the increased transfer of Zn through the intestinal cell membrane) after IMI treatment. Our data indicate that IMI enhances Zn transfer through the intestinal tract and influences the redistribution of Zn between the blood and brain. These mechanisms might explain the enhanced antidepressant efficacy of combined IMI/Zn treatment observed in the FST in mice.

Zinc nutritional status influences ZnT1 and ZIP4 gene expression in children with a high risk of zinc deficiency

INTRODUCTION

Subclinical deficiency of zinc is associated with impairment of immune system function, growth, and cognitive development in children. Although plasma zinc is the best available biomarker of the risk of zinc deficiency in populations, its sensitivity for early detection of deficiency is limited. Therefore, we aimed to investigate zinc deficiency among preschool children and its relationship with whole blood gene expression of zinc transporters ZIP4 and ZnT1.

MATERIAL AND METHODS

This cross-sectional study included 139 children aged 32-76 months enrolled in philanthropic day-care centers. We performed an anthropometric evaluation, weighed food record and dietary record for dietary assessment, blood sample collection for zinc, and whole blood gene expression analyses of ZnT1 (SLC30A1) and ZIP4 (SLC39A4).

RESULTS

Zinc deficiency was observed in 26.6 % of the children despite adequate zinc intake and a phytate:zinc molar ratio < 18. Usual zinc intake did not affect whole blood gene expression of zinc transporters, but zinc status influenced ZnT1 and ZIP4 whole blood mRNA. Children with zinc deficiency exhibited 37.1 % higher ZnT1 expression and 45.3 % lower ZIP4 expression than children with adequate zinc (p < 0.05).

CONCLUSION

Children with plasma zinc deficiency exhibited higher expression of ZnT1 and lower expression of ZIP4 in whole blood mRNA, reinforcing the existence of strong regulation of mineral homeostasis according to the nutritional status, indicating that this analysis may be useful in the evaluation of dietary interventions.

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.

The role of zinc chelate of hydroxy analogue of methionine in cadmium toxicity: effects on cadmium absorption on intestinal health in piglets

Cadmium (Cd) is a toxic heavy metal that poses a threat to the health of humans and animals. It can cause serious damage to the small intestine, which is the main absorption site of Cd and the primary target organ after oral administration. Our previous study found that zinc chelate of hydroxy analogue of methionine (Zn-HMTB), a new type of feed additive, decreased Cd accumulation in the liver and kidneys. The aim of this study was to investigate the effect of Zn-HMTB on Cd absorption and Cd-induced toxicity in the small intestine of piglets. Twenty-four piglets (Landrace × Large White, 13.22 ± 0.58 kg BW) were randomly divided into four dietary treatment groups: basal diet, and diets containing 30 mg/kg Cd from CdCl2 and 0, 100 or 200 mg/kg Zn from Zn-HMTB. The experiment lasted 27 days. The feed intake and final BW of each piglet were recorded at the end of the experiment. Gastrointestinal (GI) tract tissue and samples of liver, kidney, spleen, heart, lung and longissimus muscle tissue and faeces were collected. The concentrations of Cd and metal trace elements in the GI tract and organs were analysed, as was the relative messenger RNA (mRNA) expression of inflammatory cytokines and metal element transporters in the small intestine, and epithelial apoptosis in the small intestine. The results showed that, compared with Cd-treated piglets, piglets in the Zn-HMTB and Cd cotreatment groups had less Cd deposition in the stomach, ileum, caecum, colon, liver, kidneys, spleen, lungs, heart and muscles (P < 0.05), and lower Cd concentrations in faeces (P < 0.05), suggesting that Zn-HMTB increased Cd absorption and the excretion of Cd in other forms (possibly urine). Zinc chelate of hydroxy analogue of methionine increased Zn deposition in the jejunum and the relative mRNA expression of divalent metal transporters 1 and zinc transporter 5 in the duodenum (P < 0.05), indicating that Zn-HMTB may promote the absorption and transportation of Cd and Zn together by upregulating metal element transporters. Competition between Zn and Cd may be responsible for accelerating Cd excretion. Furthermore, Zn-HMTB reduced Cd-induced apoptosis of enterocytes and inflammatory stimuli in the small intestine, suggesting that Zn-HMTB reduced Cd-induced toxicity to the small intestine. These results suggest that Zn-HMTB can be helpful in decreasing Cd accumulation in the GI tract and organs of piglets and relieving Cd-induced toxicity to the small intestine but cannot reduce the absorption of Cd.

Impact of dietary zinc:copper ratio on the postprandial net portal appearance of these minerals in pigs1

The present study compared the net intestinal absorption of zinc (Zn) and copper (Cu) after meals containing different dietary ratios among these trace elements. Ten 46-kg pigs were used in a cross-over design to assess the 10-h net portal-drained viscera (PDV) flux of serum Cu and Zn after ingestion of boluses containing ZnSO4 and CuSO4 in different Zn:Cu ratios (mg:mg): 120:20; 200:20; 120:8; and 200:8. Arterial Zn concentrations peaked within the first hour post-meal and responses were greater with 200 (0.9 to 1.8 mg/L) than with 120 mg (0.9 to 1.6 mg/L) of dietary Zn (dietary Zn × time, P = 0.05). Net PDV flux of Zn was greater (P = 0.02) with 200 than with 120 mg of dietary Zn and tended to be greater (P = 0.10) with 20 than with 8 mg of dietary Cu. The cumulative PDV appearance of Zn (% of dietary intake) was greater with 120 than 200 mg of dietary Zn from 8 h post-meal (P ≤ 0.04) and with 20 than 8 mg of dietary Cu from 7 h post-meal (P ≤ 0.05). At the end of the postprandial period (10 h), estimated PDV appearance of Zn was 16.0%, 18.4%, 12.0%, and 15.3% of Zn intake for 120:8, 120:20, 200:8, and 200:20 ratios, respectively. For Cu, irrespective of treatment, arterial values varied (P < 0.01) by less than 5% across postmeal times. Net PDV flux was not affected by treatments (P ≥ 0.12), but the value for ratio 120:20 was different from zero (P = 0.03). There was an interaction dietary Zn × dietary Cu on cumulative PDV appearance of Cu (% of dietary intake) at 30 min post-meal (P = 0.04) and thereafter at 3 h post-meal (P = 0.04). For the whole postprandial period (10 h), estimated PDV appearance of Cu was 61.9%, 42.1%, -17.1%, and 23.6% of Cu intake for 120:8, 120:20, 200:8, and 200:20 ratios, respectively. In conclusion, the present dietary amounts and ratios of Zn and Cu can affect the metabolic availability of both trace minerals for pigs. Ratios with 120 mg of dietary Zn maximized the postintestinal availability of both Zn and Cu.

Zinc and protein metabolism in chronic liver diseases

The capacity to metabolize proteins is closely related to the hepatic functional reserve in patients with chronic liver disease, and hypoalbuminemia and hyperammonemia develop along with hepatic disease progression. Zinc deficiency, which is frequently observed in patients with chronic liver disease, significantly affects protein metabolism. Ornithine transcarbamylase is a zinc enzyme involved in the urea cycle. Its activity decreases because of zinc deficiency, thereby reducing hepatic capacity to metabolize ammonia. Because the glutamine-synthesizing system in skeletal muscles compensates for the decrease in ammonia metabolism, hyperammonemia does not develop in the early stages of chronic liver disease. However, branched-chain amino acids (BCAAs) are consumed with the increase in glutamine-synthesizing system reactions, leading to a decreased capacity to synthesize proteins, including albumin, due to amino acid imbalance. Upon further disease progression, skeletal muscle mass decreases because of nutritional deficiency, as well as the further decreased capacity to metabolize ammonia in the liver, whereby the capacity to detoxify ammonia reduces as a whole, resulting in hyperammonemia. BCAA supplementation therapy for nutritional deficiency in liver cirrhosis improves survival by correcting amino acid imbalance via recovery of the capacity to synthesize albumin, while zinc supplementation therapy improves the capacity to metabolize ammonia in the liver. Here, the efficacy of a combination of BCAA and zinc preparation for nutritional deficiency in liver cirrhosis, as well as its theoretical background, was reviewed.

Maintenance of Intestinal Epithelial Homeostasis by Zinc Transporters

Zinc is an essential micronutrient for normal organ function, and dysregulation of zinc metabolism has been implicated in a wide range of diseases. Emerging evidence has revealed that zinc transporters play diverse roles in cellular homeostasis and function by regulating zinc trafficking via organelles or the plasma membrane. In the gastrointestinal tract, zinc deficiency leads to diarrhea and dysfunction of intestinal epithelial cells. Studies also showed that zinc transporters are very important in intestinal epithelial homeostasis. In this review, we describe the physiological roles of zinc transporters in intestinal epithelial functions and relevance of zinc transporters in gastrointestinal diseases.

The impact of apical and basolateral albumin on intestinal zinc resorption in the Caco-2/HT-29-MTX co-culture model

The molecular mechanisms of intestinal zinc resorption and its regulation are still topics of ongoing research. To this end, the application of suitable in vitro intestinal models, optimized with regard to their cellular composition and medium constituents, is of crucial importance. As one vital aspect, the impact of cell culture media or buffer compounds, respectively, on the speciation and cellular availability of zinc has to be considered when investigating zinc resorption. Thus, the present study aims to investigate the impact of serum, and in particular its main constituent serum albumin, on zinc uptake and toxicity in the intestinal cell line Caco-2. Furthermore, the impact of serum albumin on zinc resorption is analyzed using a co-culture of Caco-2 cells and the mucin-producing goblet cell line HT-29-MTX. Apically added albumin significantly impaired zinc uptake into enterocytes and buffered its cytotoxicity. Yet, undigested albumin does not occur in the intestinal lumen in vivo and impairment of zinc uptake was abrogated by digestion of albumin. Interestingly, zinc uptake, as well as gene expression studies of mt1a and selected intestinal zinc transporters after zinc incubation for 24 h, did not show significant differences between 0 and 10% serum. Importantly, the basolateral application of serum in a transport study significantly enhanced fractional apical zinc resorption, suggesting that the occurrence of a zinc acceptor in the plasma considerably affects intestinal zinc resorption. This study demonstrates that the apical and basolateral medium composition is crucial when investigating zinc, particularly its intestinal resorption, using in vitro cell culture.

Zinc requirements of broiler breeder hens

One hundred and twenty Cobb 500 hens, 20 wk of age, were randomly allocated into individual cages with the objective of estimating their Zn requirements. The study was composed of 3 phases: adaptation to cages (basal diet), depletion (deficient diet containing 18.7 ± 0.47 ppm Zn) for 7 wk, and experimental phases. Hens were fed diets with graded increments of Zn sulfate heptahydrate (ZnSO4·7H2O), totaling 18.7 ± 0.47, 50.3 ± 10.6, 77.3.0 ± 11.0, 110.2 ± 12.8, 140 ± 12.2, and 170.6 ± 13.2 ppm analyzed Zn in feeds for 12 wk (experimental phase). Requirements of Zn were done using quadratic polynomial (QP), broken line quadratic (BLQ), and exponential asymptotic (EA) models. In general, the non-linear statistical models were the ones that best fit the results in this study. Requirements obtained for hen day egg production and settable egg production were 83.3, 78.6 ppm and 61.4, 65.4 ppm for period of 33 to 36 wk, and 63.3, 53.1 and 60.4, 46.1 ppm for period of 37 to 40 wk, and 62.8, 52.8, and 67.7, 62.1 ppm for period of 41 to 44 wk, respectively, using BLQ and EA models. Total eggs and total settable eggs produced per hen had Zn requirements estimated as 75.7, 64.7 ppm, and 56.5, 41.5 ppm, respectively, for BLQ and EA models, whereas for alkaline phosphatase and eggshell percentage were 161.8, 124.9 ppm and 126.1, 122.4 ppm, using QP and BLQ models. Maximum responses for Zn in yolk for periods of 37 to 40 and 41 to 44 wk were 71.0, 78.1 and 64.5, 59.6 ppm, respectively, using BLQ and EA models. Breaking strength had Zn requirements estimated at 68.0 and 96.7 ppm, whereas eggshell palisade layer and eggshell thickness were maximized with 67.9, 67.9 ppm, and 67.7, 64.4 ppm, respectively, for BLQ and EA models. The average of all Zn requirement estimates obtained by EA and BLQ models in the present study was 72.28 ppm or 11.1 mg/hen/d.

Transition metals and host-microbe interactions in the inflamed intestine

Host-associated microbial communities provide critical functions for their hosts. Transition metals are essential for both the mammalian host and the majority of commensal bacteria. As such, access to transition metals is an important component of host-microbe interactions in the gastrointestinal tract. In mammals, transition metal ions are often sequestered by metal binding proteins to limit microbial access under homeostatic conditions. In response to invading pathogens, the mammalian host further decreases availability of these micronutrients by regulating their trafficking or releasing high-affinity metal chelating proteins, a process termed nutritional immunity. Bacterial pathogens have evolved several mechanisms to subvert nutritional immunity. Here, we provide an overview on how metal ion availability shapes host-microbe interactions in the gut with a particular focus on intestinal inflammatory diseases.

Zinc in Keratinocytes and Langerhans Cells: Relevance to the Epidermal Homeostasis

In the skin, the epidermis is continuously exposed to various kinds of external substances and stimuli. Therefore, epidermal barriers are crucial for providing protection, safeguarding health, and regulating water balance by maintaining skin homeostasis. Disruption of the epidermal barrier allows external substances and stimuli to invade or stimulate the epidermal cells, leading to the elicitation of skin inflammation. The major components of the epidermal barrier are the stratum corneum (SC) and tight junctions (TJs). The presence of zinc in the epidermis promotes epidermal homeostasis; hence, this study reviewed the role of zinc in the formation and function of the SC and TJs. Langerhans cells (LCs) are one of the antigen-presenting cells found in the epidermis. They form TJs with adjacent keratinocytes (KCs), capture external antigens, and induce antigen-specific immune reactions. Thus, the function of zinc in LCs was examined in this review. We also summarized the general knowledge of zinc and zinc transporters in the epidermis with updated findings.

Characterization of Caco-2 cells stably expressing the protein-based zinc probe eCalwy-5 as a model system for investigating intestinal zinc transport

Intestinal zinc resorption, in particular its regulation and mechanisms, are not yet fully understood. Suitable intestinal cell models are needed to investigate zinc uptake kinetics and the role of labile zinc in enterocytes in vitro. Therefore, a Caco-2 cell clone was produced, stably expressing the genetically encoded zinc biosensor eCalwy-5. The aim of the present study was to reassure the presence of characteristic enterocyte-specific properties in the Caco-2-eCalwy clone. Comparison of Caco-2-WT and Caco-2-eCalwy cells revealed only slight differences regarding subcellular localization of the tight junction protein occludin and alkaline phosphatase activity, which did not affect basic integrity of the intestinal barrier or the characteristic brush border membrane morphology. Furthermore, introduction of the additional zinc-binding protein in Caco-2 cells did not alter mRNA expression of the major intestinal zinc transporters (zip4, zip5, znt-1 and znt-5), but increased metallothionein 1a-expression and cellular resistance to higher zinc concentrations. Moreover, this study examines the effect of sensor expression level on its saturation with zinc. Fluorescence cell imaging indicated considerable intercellular heterogeneity in biosensor-expression. However, FRET-measurements confirmed that these differences in expression levels have no effect on fractional zinc-saturation of the probe.

Prospects of Zinc Supplementation in Autism Spectrum Disorders and Shankopathies Such as Phelan McDermid Syndrome

The loss of one copy of SHANK3 (SH3 and multiple ankyrin repeat domains 3) in humans highly contributes to Phelan McDermid syndrome (PMDS). In addition, SHANK3 was identified as a major autism candidate gene. Interestingly, the protein encoded by the SHANK3 gene is regulated by zinc. While zinc deficiency depletes synaptic pools of Shank3, increased zinc levels were shown to promote synaptic scaffold formation. Therefore, the hypothesis arises that patients with PMDS and Autism caused by Shankopathies, having one intact copy of SHANK3 left, may benefit from zinc supplementation, as elevated zinc may drive remaining Shank3 into the post-synaptic density (PSD) and may additional recruit Shank2, a second zinc-dependent member of the SHANK gene family. Further, elevated synaptic zinc levels may modulate E/I ratios affecting other synaptic components such as NMDARs. However, several factors need to be considered in relation to zinc supplementation such as the role of Shank3 in the gastrointestinal (GI) system-the location of zinc absorption in humans. Therefore, here, we briefly discuss the prospect and impediments of zinc supplementation in disorders affecting Shank3 such as PMDS and propose a model for most efficacious supplementation.

Zinc Detoxification: A Functional Genomics and Transcriptomics Analysis in Drosophila melanogaster Cultured Cells

Cells require some metals, such as zinc and manganese, but excess levels of these metals can be toxic. As a result, cells have evolved complex mechanisms for maintaining metal homeostasis and surviving metal intoxication. Here, we present the results of a large-scale functional genomic screen in Drosophila cultured cells for modifiers of zinc chloride toxicity, together with transcriptomics data for wild-type or genetically zinc-sensitized cells challenged with mild zinc chloride supplementation. Altogether, we identified 47 genes for which knockdown conferred sensitivity or resistance to toxic zinc or manganese chloride treatment, and >1800 putative zinc-responsive genes. Analysis of the 'omics data points to the relevance of ion transporters, glutathione (GSH)-related factors, and conserved disease-associated genes in zinc detoxification. Specific genes identified in the zinc screen include orthologs of human disease-associated genes CTNS, PTPRN (also known as IA-2), and ATP13A2 (also known as PARK9). We show that knockdown of red dog mine (rdog; CG11897), a candidate zinc detoxification gene encoding an ABCC-type transporter family protein related to yeast cadmium factor (YCF1), confers sensitivity to zinc intoxication in cultured cells, and that rdog is transcriptionally upregulated in response to zinc stress. As there are many links between the biology of zinc and other metals and human health, the 'omics data sets presented here provide a resource that will allow researchers to explore metal biology in the context of diverse health-relevant processes.

Mechanistic insights into the protective impact of zinc on sepsis

Sepsis, a systemic inflammation as a response to a bacterial infection, is a huge unmet medical need. Data accumulated over the last decade suggest that the nutritional status of patients as well as composition of their gut microbiome, are strongly linked with the risk to develop sepsis, the severity of the disease and prognosis. In particular, the essential micronutrient zinc is essential in the resistance against sepsis and has shown to be protective in animal models as well as in human patients. The potential mechanisms by which zinc protects in sepsis are discussed in this review paper: we will focus on the inflammatory response, chemotaxis, phagocytosis, immune response, oxidative stress and modulation of the microbiome. A full understanding of the mechanism of action of zinc may open new preventive and therapeutic interventions in sepsis.

Zinc Transporter Proteins

Zinc, which is involved in the structure of all enzyme classes, is a micro nutrient element and necessary for growth and development. The ability of zinc to function without causing toxic effects is depends on the protection of its homeostasis. Zinc transporter proteins are responsible for keeping zinc at certain concentrations. Based on their predicted membrane topology, Zn transporters are divided into two major families, SLC39s/ZIPs and SLC30s/ZnTs, which transport Zn in opposite directions through cellular and intracellular membranes. ZIPs increases the zinc concentration in the cytosol. For this, the ZIPs carries the zinc from extracellular and intracellular compartments to the cytosol. ZnTs, reduces the concentration of zinc in the cytosol. For this, ZnTs carries the zinc from the cytosol to extracellular and intracellular compartments. After being transported to the cell, 50% of the zinc is found in the cytoplasm, 30-40% in the nucleus, and 10% in the plasma and organelle membranes. The expression of many zinc transporter proteins in the cell is depending on the concentration of zinc and the physiological problems. The aim of this study is to give information about association of zinc transporter proteins with physiological events and health problems.

Recent Advances in the Role of SLC39A/ZIP Zinc Transporters In Vivo

Zinc (Zn), which is an essential trace element, is involved in numerous mammalian physiological events; therefore, either a deficiency or excess of Zn impairs cellular machineries and influences physiological events, such as systemic growth, bone homeostasis, skin formation, immune responses, endocrine function, and neuronal function. Zn transporters are thought to mainly contribute to Zn homeostasis within cells and in the whole body. Recent genetic, cellular, and molecular studies of Zn transporters highlight the dynamic role of Zn as a signaling mediator linking several cellular events and signaling pathways. Dysfunction in Zn transporters causes various diseases. This review aims to provide an update of Zn transporters and Zn signaling studies and discusses the remaining questions and future directions by focusing on recent progress in determining the roles of SLC39A/ZIP family members in vivo.

The essential roles of metal ions in insect homeostasis and physiology

Metal ions play distinct roles in living organisms, including insects. Some, like sodium and potassium, are central players in osmoregulation and 'blood and guts' transport physiology, and have been implicated in cold adaptation. Calcium is a key player as a second messenger, and as a structural element. Other metals, particularly those with multiple redox states, can be cofactors in many metalloenzymes, but can contribute to toxic oxidative stress on the organism in excess. This short review selects some examples where classical knowledge has been supplemented with recent advances, in order to emphasize the importance of metals as essential nutrients for insect survival.

Calcium and zinc decrease intracellular iron by decreasing transport during iron repletion in an in vitro model

PURPOSE

Iron is an essential micronutrient that participates in a number of vital reactions and its absorption may be altered by various nutritional factors such as other micronutrients. Our hypothesis is that iron absorption is decreased because of the interactions with zinc and calcium. We evaluated the interaction between calcium and zinc on iron uptake and transport, intracellular Fe and Zn levels and mRNA expression of DMT1, ferroportin, Zip4 and ZnT1 in an in vitro model.

METHODS

Caco-2 cells were cultivated with 1 mM Ca; 10 or 30 µM Zn and/or 10, 20 or 30 µM Fe for 24 h.

RESULTS

Intracellular Fe decreased in cells incubated with 30 µM Zn or with the mix Ca/10 µM Zn/Fe. Zn mostly increased under Ca, Zn and Fe treatment. DMT1 mRNA expression decreased when intracellular Fe increased. Ferroportin expression displayed no change in cells cultured with different Fe concentrations. The mix of Ca, Zn and Fe increased DMT1 and ferroportin expression mainly under high Zn concentration. Zip4 expression was mostly augmented by Ca and Fe; however, ZnT1 showed no change in all conditions studied. Fe uptake was higher in all the conditions studied compared to control cells; however, Fe transport increased only in cells incubated with Fe alone. In all the other conditions, Fe transport was lower than that in control cells.

CONCLUSIONS

The present findings suggest that Ca and Zn interfere with iron metabolism. This interference is through an increase in ferroportin activity, which results in a diminished net iron absorption.

New perspectives on the regulation of iron absorption via cellular zinc concentrations in humans

Iron deficiency is the most prevalent nutritional deficiency, affecting more than 30% of the total world's population. It is a major public health problem in many countries around the world. Over the years various methods have been used with an effort to try and control iron-deficiency anemia. However, there has only been a marginal reduction in the global prevalence of anemia. Why is this so? Iron and zinc are essential trace elements for humans. These metals influence the transport and absorption of one another across the enterocytes and hepatocytes, due to similar ionic properties. This paper describes the structure and roles of major iron and zinc transport proteins, clarifies iron-zinc interactions at these sites, and provides a model for the mechanism of these interactions both at the local and systemic level. This review provides evidence that much of the massive extent of iron deficiency anemia in the world may be due to an underlying deficiency of zinc. It explains the reasons for predominance of cellular zinc status in determination of iron/zinc interactions and for the first time thoroughly explains mechanisms by which zinc brings about these changes.

Role of Zinc in the Development/Progression of Alcoholic Liver Disease

OPINION STATEMENT

Many variables, aside from the amount and duration of alcohol consumption, play a role in the development and progression of alcoholic liver disease (ALD). One critical factor that can be modified is diet/nutrition. We have made major recent advances in our understanding of the interactions of nutrition and ALD. In this article, we review advances made in zinc metabolism/therapy for ALD. There is major zinc dyshomeostasis with ALD which is mediated, in part, by poor intake and absorption, increased excretion, and altered zinc transporters, especially ZIP14. Zinc deficiency plays an etiologic role in multiple mechanisms of ALD, ranging from intestinal barrier dysfunction to hepatocyte apoptosis. Zinc supplementation is highly effective at correcting these ALD mechanisms and preventing/treating experimental ALD. There is no Food and Drug Administration (FDA) approved therapy for any stage of ALD. Because animal and human data suggest that zinc deficiency occurs early in the course of ALD, we treat most ALD patients with daily oral zinc supplementation (220 mg zinc sulfate which contains 50 mg elemental zinc).

ICP-MS/MS-Based Ionomics: A Validated Methodology to Investigate the Biological Variability of the Human Ionome

We here describe the development, validation and application of a quantitative methodology for the simultaneous determination of 29 elements in human serum using state-of-the-art inductively coupled plasma triple quadrupole mass spectrometry (ICP-MS/MS). This new methodology offers high-throughput elemental profiling using simple dilution of minimal quantity of serum samples. We report the outcomes of the validation procedure including limits of detection/quantification, linearity of calibration curves, precision, recovery and measurement uncertainty. ICP-MS/MS-based ionomics was used to analyze human serum of 120 older adults. Following a metabolomic data mining approach, the generated ionome profiles were subjected to principal component analysis revealing gender and age-specific differences. The ionome of female individuals was marked by higher levels of calcium, phosphorus, copper and copper to zinc ratio, while iron concentration was lower with respect to male subjects. Age was associated with lower concentrations of zinc. These findings were complemented with additional readouts to interpret micronutrient status including ceruloplasmin, ferritin and inorganic phosphate. Our data supports a gender-specific compartmentalization of the ionome that may reflect different bone remodelling in female individuals. Our ICP-MS/MS methodology enriches the panel of validated "Omics" approaches to study molecular relationships between the exposome and the ionome in relation with nutrition and health.

Functional studies of Drosophila zinc transporters reveal the mechanism for zinc excretion in Malpighian tubules

Background

Zinc is an essential metal involved in many physiological processes. Previous work has identified a set of zinc transporters involved in Drosophila dietary zinc absorption. However, zinc excretion and reabsorption, the other two important processes to maintain zinc homeostasis, are not as well understood. In this work, we screened all the potential zinc transporter Zip (SLC39) and ZnT (SLC30) members for their likely roles in zinc excretion in Malpighian tubules, an insect organ functionally analogous to mammalian kidneys.

Results

Zip71B (CG10006, most homologous to hZIP5), in addition to the previously characterized ZnT35C (CG3994), was identified as being critical in zinc excretion. Tubule-specific knockdown of Zip71B/dZip5 reduces zinc accumulation in the tubules, but increases zinc levels in the body, resulting in survival defect under zinc excess conditions. Zip71B/dZip5 is localized to the plasma membrane at the basolateral side of the tubules, and is functionally epistatic to the apically localized ZnT35C in regulating the tubule zinc homeostasis. Our results indicate that Zip71B/dZip5 is involved in zinc import into the tubular cells from the circulation, and ZnT35C in turn effluxes the tubular zinc out. Notably, mammalian ZIP5, which is expressed in the kidney, functions analogously to Zip71B/dZip5 in the fly while hZIP4 cannot complement the loss of Zip71B/dZip5 function. Furthermore, Zip71B/dZip5 expression is regulated by zinc so that, in response to toxic levels of zinc, the tubules can increase zinc efflux capability. We also characterized the role of dZnT1 (CG17723) in zinc reabsorption in Malpighian tubules. Finally, using a tubule calcification model, we were able to show that knockdown of Zip71B/dZip5 or ZnT35C was able to mitigate stone formation, consistent with their roles in tubular zinc homeostasis.

Conclusions

Our results start to sketch out a relatively complete picture of the zinc excretion process in Drosophila Malpighian tubules, and may provide a reference for relevant mammalian studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0355-9) contains supplementary material, which is available to authorized users.

[Association between intracellular zinc levels and nutritional status in HIV-infected and uninfected children exposed to the virus]

INTRODUCTION

Malnutrition, growth retardation and opportunistic infections outlast the metabolic, immune and gastrointestinal disorders produced by HIV. Zinc deficiency has been associated with deteriorating nutritional status, growth failure, and risk of infection. The aim of this study is to determine the association between zinc levels in peripheral blood mononuclear cells (PBMC) and the nutritional status of HIV-infected and uninfected children exposed to the virus.

PATIENTS AND METHODS

An analytical, observational, cross-sectional study was conducted on 17 infected and 17 exposed children, aged 2-10 years. Anthropometric measurements, clinical and nutritional history, 24h recall, measurement of physical activity, and zinc in PBMC by flow cytometry analysis were recorded.

RESULTS

Height according to age, energy consumption and adequacy of energy, protein and dietary zinc were significantly higher in children exposed to the virus compared to those infected with HIV (P <.05). No significant differences were found in BMI, levels of zinc in monocytes, CD4 + and CD4- lymphocytes between the two study groups (P >.05). However, the median levels of zinc in monocytes of infected patients was higher (218.6) compared to the control group (217.0). No association was found between zinc intake and levels of intracellular zinc.

CONCLUSIONS

The deterioration of nutritional status and growth retardation in children were associated with HIV, but not with the levels of intracellular zinc. The dietary intake of this nutrient was not associated with levels of zinc in monocytes or CD4 + and CD4- lymphocytes.

The Expression of Zinc Transporters Changed in the Intestine of Weaned Pigs Exposed to Zinc Chitosan Chelate

This study was conducted to investigate the effect of zinc chitosan chelate (CS-Zn) on zinc transporter expression and content of tissue zinc in weaned piglets. A total of 90 weaned pigs (Duroc × Landrace × Yorkshire) were randomly allocated to treatment groups with supplementation of 100 mg/kg zinc as ZnSO₄, 100 mg/kg zinc as mixture of ZnSO₄ and chitosan, or 100 mg/kg zinc as CS-Zn, respectively. After 30 days of trial, 18 piglets (six pigs per treatment) were killed and the samples of duodenal mucosa were taken for analysis of zinc transporter mRNA expressions and protein abundance. The results show that CS-Zn more effectively increases (p < 0.05) the average daily gain (ADG) and serum zinc concentration. Zinc concentration in the liver and kidney did not differ between treatments. The mRNA expressions of ZnT1, ZIP4, and ZIP5 in CS-Zn treatment were all upregulated (p < 0.05) than ZnSO₄ or mixture of ZnSO₄ and chitosan groups. ZnT1 abundance was greater (p < 0.05) with CS-Zn as compared with ZnSO₄ and mixture of ZnSO4 and chitosan treatments, whereas ZIP4 and ZIP5 abundance was higher (p < 0.05) in ZnSO4 group. The results indicate that CS-Zn is more effective in serum zinc accumulation, and it might regulate zinc homeostasis by affecting zinc transporter mRNA expression and absorption mechanism might be different with ZnSO_4.

Effects of Long-Term Exposure to Zinc Oxide Nanoparticles on Development, Zinc Metabolism and Biodistribution of Minerals (Zn, Fe, Cu, Mn) in Mice

Zinc oxide nanoparticles (nano-ZnOs) are widely used and possess great potentials in agriculture and biomedicine. It is inevitable for human exposure to these nanoparticles. However, no study had been conducted to investigate the long term effects of nano-ZnOs. This study aimed at investigating effects of nano-ZnOs on development, zinc metabolism and biodistribution of minerals (Zn, Fe, Cu, and Mn) in mice from week 3 to 35. After the characteristics of nano-ZnOs were determined, they were added into the basal diet at 0, 50, 500 and 5000 mg/kg. Results indicated that added 50 and 500 mg/kg nano-ZnOs showed minimal toxicity. However, 5000 mg/kg nano-ZnOs significantly decreased body weight (from week 4 to 16) and increased the relative weights of the pancreas, brain and lung. Added 5000 mg/kg nano-ZnOs significantly increased the serum glutamic-pyruvic transaminase activity and zinc content, and significantly enhanced mRNA expression of zinc metabolism-related genes, including metallothionein 1(32.66 folds), metallothionein 2 (31.42 folds), ZIP8 (2.21folds), ZIP14 (2.45 folds), ZnT1 (4.76 folds), ZnT2 (6.19 folds) and ZnT4 (1.82 folds). The biodistribution determination showed that there was a significant accumulation of zinc in the liver, pancreas, kidney, and bones (tibia and fibula) after receiving 5000 mg/kg nano-ZnO diet, while no significant effects on Cu, Fe, and Mn levels, except for liver Fe content and pancreas Mn level. Our results demonstrated that long term exposure to 50 and 500 mg/kg nano-ZnO diets showed minimal toxicity. However, high dose of nano-ZnOs (5000 mg/kg) caused toxicity on development, and altered the zinc metabolism and biodistribution in mice.

Transportome Profiling Identifies Profound Alterations in Crohn's Disease Partially Restored by Commensal Bacteria

BACKGROUND AND AIMS

Several transport alterations have been described in intestinal inflammatory diseases. This is relevant because the primary function of the intestine is nutrient and mineral absorption. However, analysis of the transportome as a whole and the effect of commensal bacteria on it have not been addressed so far.

METHODS

Five healthy and 6 Crohn's disease (CD) samples were hybridized to human HT-12 V4 Illumina GeneChip. Results were validated by reverse transcription-polymerase chain reaction (RT-PCR) analysis and with additional array data. Organ culture assays were performed from mucosa ileal wall specimens collected at surgery. Samples were incubated with or without commensal bacteria for 4 hours. Finally, RNA was isolated for microarray processing.

RESULTS

The analysis of CD versus healthy ileal mucosa demonstrated upregulation of previously described genes involved in immunity and the inflammatory response in this disease. Interestingly, whole transcriptional analysis revealed profound alterations in the transportome profile. Sixty-two solute carrier (SLC) transporters displayed different expression patterns, most of them being downregulated. Changes were confirmed by RT-PCR in a randomly chosen subset of SLCs. A large number of amino acid transporters and most members of the enteric purinome were found to be altered. Most of these proteins were found at the apical membrane of the enterocyte, which could impair both amino acid absorption and purinergic signalling. Treatment of ileum specimen explants with commensal bacteria restored almost all CD transportome alterations.

CONCLUSIONS

These results describe the altered transportome profile in CD and open the possibility of restoring transportome complications with commensal bacteria.