Acrodermatitis enteropathica: recent findings concerning clinical features, pathogenesis, diagnosis and therapy

Expression Analysis of Zinc Transporters in Nervous Tissue Cells Reveals Neuronal and Synaptic Localization of ZIP4

In the last years, research has shown that zinc ions play an essential role in the physiology of brain function. Zinc acts as a potent neuromodulatory agent and signaling ions, regulating healthy brain development and the function of both neurons and glial cells. Therefore, the concentration of zinc within the brain and its cells is tightly controlled. Zinc transporters are key regulators of (extra-) cellular zinc levels, and deregulation of zinc homeostasis and zinc transporters has been associated with neurodegenerative and neuropsychiatric disorders. However, to date, the presence of specific family members and their subcellular localization within brain cells have not been investigated in detail. Here, we analyzed the expression of all zinc transporters (ZnTs) and Irt-like proteins (ZIPs) in the rat brain. We further used primary rat neurons and rat astrocyte cell lines to differentiate between the expression found in neurons or astrocytes or both. We identified ZIP4 expressed in astrocytes but significantly more so in neurons, a finding that has not been reported previously. In neurons, ZIP4 is localized to synapses and found in a complex with major postsynaptic scaffold proteins of excitatory synapses. Synaptic ZIP4 reacts to short-term fluctuations in local zinc levels. We conclude that ZIP4 may have a so-far undescribed functional role at excitatory postsynapses.

Zinc Binding to MG53 Protein Facilitates Repair of Injury to Cell Membranes

Zinc is an essential trace element that participates in a wide range of biological functions, including wound healing. Although Zn(2+) deficiency has been linked to compromised wound healing and tissue repair in human diseases, the molecular mechanisms underlying Zn(2+)-mediated tissue repair remain unknown. Our previous studies established that MG53, a TRIM (tripartite motif) family protein, is an essential component of the cell membrane repair machinery. Domain homology analysis revealed that MG53 contains two Zn(2+)-binding motifs. Here, we show that Zn(2+) binding to MG53 is indispensable to assembly of the cell membrane repair machinery. Live cell imaging illustrated that Zn(2+) entry from extracellular space is essential for translocation of MG53-containing vesicles to the acute membrane injury sites for formation of a repair patch. The effect of Zn(2+) on membrane repair is abolished in mg53(-/-) muscle fibers, suggesting that MG53 functions as a potential target for Zn(2+) during membrane repair. Mutagenesis studies suggested that both RING and B-box motifs of MG53 constitute Zn(2+)-binding domains that contribute to MG53-mediated membrane repair. Overall, this study establishes a base for Zn(2+) interaction with MG53 in protection against injury to the cell membrane.

Development of a plasma zinc concentration cutoff to identify individuals with severe zinc deficiency based on results from adults undergoing experimental severe dietary zinc restriction and individuals with acrodermatitis enteropathica

Plasma zinc concentration (PZC) is a recommended biomarker to assess zinc status and the risk of zinc deficiency in populations. However, the relation between PZC and clinical signs of zinc deficiency remains uncertain. These analyses were conducted to evaluate the relation between PZC and clinical signs of zinc deficiency and to determine a cutoff for PZC below which individuals would have an increased likelihood of having clinical signs associated with zinc deficiency. Electronic bibliographic searches were conducted of literature indexed in PubMed, Embase, CINAHL Plus, and EBSCO and related to experimental zinc depletion studies in adults and case reports in children and adults (ages <1 mo-43 y) with acrodermatitis enteropathica (AE). Data extracted included demographic characteristics, PZCs, and the presence or absence of clinical signs likely associated with zinc deficiency (e.g., dermatitis, diarrhea). Mean PZC was significantly lower among adults consuming severely zinc-restricted diets (<1 mg Zn/d) who developed clinical signs compared with those who remained asymptomatic (36.0 ± 16.8 vs. 67.9 ± 13.3 μg/dL, P < 0.034). Likewise, patients with AE had a lower mean PZC when symptomatic compared with post-treatment PZC when they were asymptomatic (38.2 ± 20.7 vs. 102 ± 34.7 μg/dL, P < 0.01). Among individuals with restricted dietary zinc intake, PZC predicted clinical signs with 82% sensitivity and 92% specificity when using a cutoff of 50 μg/dL. Among individuals with AE, PZC predicted clinical signs with 80% sensitivity and 89% specificity when applying a cutoff of 50 μg/dL. These analyses demonstrate a clear relation between PZC and the presence of clinical signs associated with zinc deficiency among presumably healthy individuals undergoing periods of dietary zinc restriction, as well as in individuals with AE, further validating the usefulness of PZC as a biomarker of severe zinc deficiency.

Zinc: The Metal of Life

The importance of zinc was 1st reported for Aspergillus niger. It took over 75 y to realize that zinc is also an essential trace element for rats, and an additional 30 y went by before it was recognized that this was also true for humans. The adult body contains about 2 to 3 g of zinc. Zinc is found in organs, tissues, bones, fluids, and cells. It is essential for many physiological functions and plays a significant role in a number of enzyme actions in the living systems. Bioinformatics estimates report that 10% of the human proteome contains zinc-binding sites. Based on its role in such a plethora of cellular components, zinc has diverse biological functions from enzymatic catalysis to playing a crucial role in cellular neuronal systems. Thus, based on the various published studies and reports, it is pertinent to state that zinc is one of the most important essential trace metals in human nutrition and lifestyle. Its deficiency may severely affect the homeostasis of a biological system. This review compiles the role of zinc in prophylaxis/therapeutics and provides current information about its effect on living beings.

Zinc, its biological role and use in dermatology

This literature review detines the biological role ot zinc in the human body, immune homeostasis and skin physiology as well as pathophysiology ot skin diseases. It describes the current range ot systemic and topical zinc preparations and their pharmacological characteristics. The review also describes skin diseases that may be treated with the use ot zinc preparations on a grounded basis, and discloses the clinical experience ot the use ot these drugs described in the world literature. It sets out certain recommendations tor using zinc preparations in clinical practice.

A mouse model of acrodermatitis enteropathica: loss of intestine zinc transporter ZIP4 (Slc39a4) disrupts the stem cell niche and intestine integrity

Mutations in the human Zip4 gene cause acrodermatitis enteropathica, a rare, pseudo-dominant, lethal genetic disorder. We created a tamoxifen-inducible, enterocyte-specific knockout of this gene in mice which mimics this human disorder. We found that the enterocyte Zip4 gene in mice is essential throughout life, and loss-of-function of this gene rapidly leads to wasting and death unless mice are nursed or provided excess dietary zinc. An initial effect of the knockout was the reprogramming of Paneth cells, which contribute to the intestinal stem cell niche in the crypts. Labile zinc in Paneth cells was lost, followed by diminished Sox9 (sex determining region Y-box 9) and lysozyme expression, and accumulation of mucin, which is normally found in goblet cells. This was accompanied by dysplasia of the intestinal crypts and significantly diminished small intestine cell division, and attenuated mTOR1 activity in villus enterocytes, indicative of increased catabolic metabolism, and diminished protein synthesis. This was followed by disorganization of the absorptive epithelium. Elemental analyses of small intestine, liver, and pancreas from Zip4-intestine knockout mice revealed that total zinc was dramatically and rapidly decreased in these organs whereas iron, manganese, and copper slowly accumulated to high levels in the liver as the disease progressed. These studies strongly suggest that wasting and lethality in acrodermatitis enteropathica patients reflects the loss-of-function of the intestine zinc transporter ZIP4, which leads to abnormal Paneth cell gene expression, disruption of the intestinal stem cell niche, and diminished function of the intestinal mucosa. These changes, in turn, cause a switch from anabolic to catabolic metabolism and altered homeostasis of several essential metals, which, if untreated by excess dietary zinc, leads to dramatic weight loss and death.

Loss-of-function of the zinc transporter ZIP4 in the mouse intestine mimics the lethal human disease acrodermatitis enteropathica. This is a rare disease in humans that is not well understood. Our studies demonstrate the paramount importance of ZIP4 in the intestine in this disease and reveal that a root cause of lethality is disruption of the intestine stem cell niche and impaired function of the small intestine. This, in turn, leads to dramatic weight loss and death unless treated with exogenous zinc.

An update on mutations of the SLC39A4 gene in acrodermatitis enteropathica

Acrodermatitis enteropathica (AE) is a very rare inherited recessive disease caused by severe zinc deficiency. It typically occurs in early infancy and is characterized by periorificial and acral dermatitis, alopecia, and diarrhea. In 2002, both we and others identified the AE SLC39A4 gene located at 8q24.3, and described the first causative mutations for the disease. The SLC39A4 gene encodes a zinc-specific transporter belonging to the Zinc/Iron-regulated transporter-like family, which is highly expressed in the duodenum and jejunum. The SLC39A4 mutations are spread over the entire gene and include many different types of mutations. We report here the identification of five novel variants, including three likely pathogenic mutations. Since the first description, 31 mutations or unclassified variants of SLC39A4 have been reported in this gene. Although most of the patients with AE carry homozygous or compound heterozygous mutations, some of them have either no SLC39A4 mutation or only a monoallelic mutation. Thus, a genotype-phenotype correlation is not easily defined for all AE patients, and the molecular basis of the disease could be more complex than previously described. In cases unexplained by current genetic analyses, the most plausible molecular causes could be a dysregulation of the SLC39A4 gene transcription -- involving either metal response elements (MREs) or a modifier gene -- or the existence of another putative AE gene. In this review, we summarize the current knowledge of SLC39A4 mutations, as well as the future prospects to fully unravel the pathogenesis of AE.

Cooperation of metallothionein and zinc transporters for regulating zinc homeostasis in human intestinal Caco-2 cells

This investigation examined the effects of zinc status on cell proliferation and the synergic roles of the metallothionein (MT) and zinc transporter (ZnT) in the human colon adenocarcinoma cell line Caco-2. Cells were treated with 0 to 300 micromol/L ZnSO(4) or 0 to 10 micromol/L N,N,N',N'-tetrakis(2-phridylmethyl) ethylenediamine (TPEN). Cell proliferation was determined by MTT assay and apoptotic cells detected by flow cytometry (Hoechst 33258 dye). mRNA expression of MT1; ZnT1; zrt, irt-like protein 1, 4 (ZIP1, 4); and divalent metal transporter (DMT1) were determined by the reverse transcription polymerase chain reaction or real-time polymerase chain reaction. The results showed that either high or low zinc could inhibit the cell proliferation. The number of apoptotic cells increased with incremental increases in the concentrations of ZnSO(4) and TPEN. The mRNA expression of ZnT1 and MT1 responded significantly after 6 and 12 hours with 200 micromol/L zinc treatment, respectively, and increased gradually with zinc levels from 0 to 200 micromol/L. Compared with the unchanged ZIP1 mRNA expression, ZIP4 was closely dependent on TPEN treatment duration and concentration. The DMT1 mRNA expression was upregulated time-dependently but not concentration-dependently in the late TPEN treatment duration. The results suggest that ZIP4 and DMT1 mRNA expressions are susceptible to low extracellular zinc concentration and upregulated to enhance zinc absorption, whereas the ZnT1 and MT1 act as the key regulators under high zinc conditions to enhance the intracellular zinc efflux to maintain zinc homeostasis. We propose that in response to variations in zinc concentration, the cooperated regulative roles of ZnT1, MT1, DMT1, and ZIP4 contribute to zinc homeostasis.

Zinc in wound healing: theoretical, experimental, and clinical aspects

Zinc is an essential trace element in the human body and its importance in health and disease is appreciated. It serves as a cofactor in numerous transcription factors and enzyme systems including zinc-dependent matrix metalloproteinases that augment autodebridement and keratinocyte migration during wound repair. Zinc confers resistance to epithelial apoptosis through cytoprotection against reactive oxygen species and bacterial toxins possibly through antioxidant activity of the cysteine-rich metallothioneins. Zinc deficiency of hereditary or dietary cause can lead to pathological changes and delayed wound healing. Oral zinc supplementation may be beneficial in treating zinc-deficient leg ulcer patients, but its therapeutic place in surgical patients needs further clarification. Topical administration of zinc appears to be superior to oral therapy due to its action in reducing superinfections and necrotic material via enhanced local defense systems and collagenolytic activity, and the sustained release of zinc ions that stimulates epithelialization of wounds in normozincemic individuals. Zinc oxide in paste bandages (Unna boot) protects and soothes inflamed peri-ulcer skin. Zinc is transported through the skin from these formulations, although the systemic effects seem insignificant. We present here the first comprehensive account of zinc in wound management in relation to current concepts of wound bed preparation and the wound-healing cascade. This review article suggests that topical zinc therapy is underappreciated even though clinical evidence emphasizes its importance in autodebridement, anti-infective action, and promotion of epithelialization.

Zn2+-stimulated endocytosis of the mZIP4 zinc transporter regulates its location at the plasma membrane

Zinc is an essential nutrient for all organisms. Its requirement in humans is illustrated dramatically by the genetic disorder acrodermatitis enteropathica (AE). AE is caused by the reduced uptake of dietary zinc by enterocytes, and the ensuing systemic zinc deficiency leads to dermatological lesions and immune and reproductive dysfunction. The gene responsible for AE, SLC39A4, encodes a member of the ZIP family of metal transporters, hZIP4. The mouse ZIP4 protein, mZIP4, stimulates zinc uptake in cultured cells, and studies in mice have demonstrated that zinc treatment decreases mZIP4 mRNA levels in the gut. In this study, we demonstrated using transfected cultured cells that the mZIP4 protein is also regulated at a post-translational level in response to zinc availability. Zinc deficiency increased mZIP4 protein levels at the plasma membrane, and this was associated with increased zinc uptake. Significantly, treating cells with low micromolar zinc concentrations stimulated the rapid endocytosis of the transporter. Zinc-regulated localization of the human ZIP4 protein was also demonstrated in cultured cells. These findings suggest that zinc-regulated trafficking of human and mouse ZIP4 is a key mechanism controlling dietary zinc absorption and cellular zinc homeostasis.

The acrodermatitis enteropathica gene ZIP4 encodes a tissue-specific, zinc-regulated zinc transporter in mice

The human ZIP4 gene (SLC39A4) is a candidate for the genetic disorder of zinc metabolism acrodermatitis enteropathica. To understand its role in zinc homeostasis, we examined the function and expression of mouse ZIP4. This gene encodes a well conserved eight-transmembrane protein that can specifically increase the influx of zinc into transfected cells. Expression of this gene is robust in tissues involved in nutrient uptake, such as the intestines and embryonic visceral yolk sac, and is dynamically regulated by zinc. Dietary zinc deficiency causes a marked increase in the accumulation of ZIP4 mRNA in these tissues, whereas injection of zinc or increasing zinc content of the diet rapidly reduces its abundance. Zinc can also regulate the accumulation of ZIP4 protein at the apical surface of enterocytes and visceral endoderm cells. These results provide compelling evidence that ZIP4 is a zinc transporter that plays an important role in zinc homeostasis, a process that is defective in acrodermatitis enteropathica in humans.

Acrodermatitis enteropathica

A brief review of the clinical and biochemical features of Acrodermatitis enteropathica is given. This condition in now known to be caused by a systemic zinc deficiency secondary to a defect in the intestinal absorption of zinc and it illustrates the metabolic importance of this element in man.

Acrodermatitis enteropathica. II. Zinc deficiency and ultrastructural findings

The basic defect in acrodermatitis enteropathica (A.E.) is zinc deficiency caused by zinc malabsorption. The clinical symptoms disappear and serum zinc levels normalize after oral treatment with zinc. A report is given on two siblings suffering from A.E., both treated with oxyquinolines for a long period with changing clinical success. A permanent clinical remission could be achieved by treatment with zinc-sulphate at doses of 110-220 mg daily. The serum zinc levels normalized. The correlation between the zinc concentration of the hair and the kind of therapy was not very close. As we have shown in our first communication, the Paneth cells of the intestinal mucosa display ultrastructural changes in form of an unhomogeneous structure of the cytoplasm, formation of giant granules, and inclusion bodies. The zinc-therapy led to a complete normalization of the pathological changes in the Paneth cells. Thus, the changes in the Paneth cells in A.E. are the result and not the cause of zinc deficiency.