Urinary zinc excretion and zinc status of patients with Β-thalassemia major

In this study, zinc status and urinary zinc excretion with and without desferrioxamine (DFO) infusion and the relationship between urinary zinc excretion and renal tubular dysfunction in thalassemia major (TM) patients were investigated. Forty TM patients were given four DFO infusions on alternate days over a 1-wk period prior to the transfusion. On each day that DFO was given, a 24-h urine collection initiated. DFO was omitted for 1-wk before the following transfusion and during the period four 24-h urine collections were performed. Twenty healthy children provided 24-h urine collection as controls. Blood samples were taken on each of two consecutive transfusion days of the patients and from the controls. Urinary zinc excretion was measured and plasma and red blood cell (RBC) zinc analysis were performed by inductively coupled plasma-atomic emission spectrophotometry. UrinaryN-acetyl-Β-D-glucosaminidase (NAG) activity and creatinine were determined in morning urine specimens. The mean plasma zinc concentration was significantly lower in the patients not given DFO compared to the values of the patients given DFO and the control group. The mean RBC zinc concentration (Μmol/g Hb) in the patients (with and without DFO) and the control group were similar. Urinary zinc excretion was significantly higher in the patients receiving DFO compared to the control group, whereas urinary zinc excretion in the patients not given DFO was not different from the controls. Urinary NAG indices (U/g Cr) were significantly higher in the patients compared to controls. Urinary zinc excretion was correlated with the urinary NAG indices.     

Müller cell zinc transporter-3 labeling suggests a role in outer retina zinc homeostasis

Labeling for zinc transporter protein-3 (ZnT-3), which can be found localized to glutamatergic vesicles elsewhere in the nervous system, has revealed an unexpectedly high concentration of this transporter protein in the outer limiting membrane region of the murine retina, a region that contains the mitochondria-rich portion of photoreceptor inner segments and is not involved with vesicle release. Having suggested the possibility that Müller cell apical villi forming the outer limiting membrane may be associated with the labeling observed, we used immunohistochemical techniques to look for ZnT-3 labeling of Müller cells isolated from rat and mouse retinas. With DAB labeling, rat Müller cell apical villi, soma, and endfeet exhibited ZnT-3 reactivity. FITC label and confocal analysis revealed that ZnT-3 protein appeared throughout the length of mouse Müller cells. We conclude from these observations that the dense labeling for ZnT-3 in the photoreceptor inner segment region of murine retinal slices is due to labeling of ZnT-3 protein associated with Müller cell apical villi. Based on these findings we suggest that Müller cells utilize ZnT-3 to regulate retinal zinc homeostasis and that this role is important to mitochondrial function in the photoreceptor inner segments.     

Dietary phytate × calcium/zinc millimolar ratios and zinc nutriture in some Ontario preschool children

Millimolar ratios of phytate/Zn, Ca x phytate/Zn, and Ca x phytate/Zn per 4.2 MJ were calculated from 3-d weighed-food records collected from 62 male (M) (mean age: 58 +/- 7 mo [mean +/- SD]) and 44 female (F) (mean age: 58 +/- 6 mo) preschool children from Southern Ontario. Food-composition values for phytate were based on laboratory analysis and the literature. No gender differences existed for median millimolar ratios of phytate/Zn (median: M, 5.3; F, 5.3), and Ca x phytate/Zn per 4.2 MJ (M, 68.1; F, 59.5), but median intakes of phytate (M, 399; F, 333 mg/d) and median millimolar ratios of Ca x phytate/Zn (median: M, 102.1; F, 72.3; p less than 0.01) were higher for boys than for girls. Of the children, only two (1M, 1F) and 22 (17 M, 5F) had millimolar ratios of phytate/Zn and Ca x phytate/Zn per 4.2 MJ, respectively, that were above critical values. Millimolar ratios of Ca x phytate/Zn (p = 0.06) and Ca x phytate/Zn per 4.2 MJ (p = 0.05) were higher in boys with hair zinc less than 1.07 mumol/g v greater than or equal to 1.07 mumol/g. Analysis of variance showed that height was influenced by an interaction between millimolar ratios of Ca x phytate/Zn per 4.2 MJ and sex (p = 0.0007), when age and midparent height were treated as covariates. Results suggest that dietary Ca x phytate/Zn millimolar ratios, when expressed per 4.2 MJ, influenced the zinc nutriture of these Southern Ontario boys.     

Serum zinc levels and Alzheimer’s disease

Concentrations of zinc in postmortem serum and four brain regions were measured by flame atomic absorption spectrometry and instrumental neutron activation analysis, respectively, in nine Alzheimer’s disease (AD) and eight control subjects. A statistically significant elevation of zinc serum was observed in AD subjects (136.4±66.8 μg/dL) compared with age-matched control subjects (71.1±35.0 μg/dL). No significant differences were observed between AD and control zinc concentrations in the amygdala, hippocampus, cerebellum, and superior and middle temporal gryi.     

Copper–zinc cross-modulation in prion protein binding

In this paper we report a systematic XAS study of a set of samples in which Cu(II) was progressively added to complexes in which Zn(II) was bound to the tetra-octarepeat portion of the prion protein. This work extends previous EPR and XAS analysis in which, in contrast, the effect of adding Zn(II) to Cu(II)–tetra-octarepeat complexes was investigated. Detailed structural analysis of the XAS spectra taken at both the Cu and Zn K-edge when the two metals are present at different relative concentrations revealed that Zn(II) and Cu(II) ions compete for binding to the tetra-octarepeat peptide by cross-regulating their relative binding modes. We show that the specific metal–peptide coordination mode depends not only, as expected, on the relative metal concentrations, but also on whether Zn(II) or Cu(II) was first bound to the peptide. In particular, it seems that the Zn(II) binding mode in the absence of Cu(II) is able to promote the formation of small peptide clusters in which triplets of tetra-octarepeats are bridged by pairs of Zn ions. When Cu(II) is added, it starts competing with Zn(II) for binding, disrupting the existing peptide cluster arrangement, despite the fact that Cu(II) is unable to completely displace Zn(II). These results may have a bearing on our understanding of peptide-aggregation processes and, with the delicate cross-regulation balancing we have revealed, seem to suggest the existence of an interesting, finely tuned interplay among metal ions affecting protein binding, capable of providing a mechanism for regulation of metal concentration in cells.     

Investigation of the zinc status of surgical patients—II. Influence of vascular reconstruction on the zinc status

Patients admitted for major vascular reconstruction operations received an i.v. dose of ⁶⁵Zn. From the increased whole-body retention of ⁶⁵Zn and the findings on other parameters it was concluded that the post-operative zinc metabolism of these patients differed from that of the control subjects. Unexpectedly, this difference persisted for several months. These patients can probably serve as controls in studies of patients who have undergone surgery of the intestinal tract. Increase of whole-body retention of ⁶⁵Zn may be a sensitive indicator for subclinical zinc deficiency, but application in practice is hampered by the long duration of the period required for the measurement. From the present results it seems likely that measurement of the retention of ⁶⁵Zn in the forearm as a function of time yields the same information but in a considerably shorter time.     

A new insulin-mimetic bis(allixinato)zinc(II) complex: structure–activity relationship of zinc(II) complexes

During the investigation of the development of insulin-mimetic zinc(II) complexes with a blood glucose-lowering effect in experimental diabetic animals, we found a potent bis(maltolato)zinc(II) complex, Zn(ma)₂, exhibiting significant insulin-mimetic effects in a type 2 diabetic animal model. By using this Zn(ma)₂ as the leading compound, we examined the in vitro and in vivo structure–activity relationships of Zn(ma)₂ and its related complexes. The in vitro insulin-mimetic activity of these complexes was determined by the inhibition of free fatty acid release and the enhancement of glucose uptake in isolated rat adipocytes treated with epinephrine. A new Zn(II) complex with allixin isolated from garlic, Zn(alx)₂, exhibited the highest insulin-mimetic activity among the complexes analyzed. The insulin-mimetic activity of the Zn(II) complexes examined strongly correlated (correlation coefficient=0.96) with the partition coefficient (logP) of the ligand, indicating that the activity of Zn(ma)₂-related complexes depends on the lipophilicity of the ligand. The blood glucose-lowering effects of Zn(alx)₂ and Zn(ma)₂ were then compared, and both complexes were found to normalize hyperglycemia in KK-A^y mice after a 14-day course of daily intraperitoneal injections. However, Zn(alx)₂ improved glucose tolerance in KK-A^y mice much more than did Zn(ma)₂, indicating that Zn(alx)₂ possesses greater in vivo anti-diabetic activity than Zn(ma)₂. In addition, Zn(alx)₂ improved leptin resistance and suppressed the progress of obesity in type 2 diabetic KK-A^y mice. On the basis of these observations, we conclude that the Zn(alx)₂ complex is a novel potent candidate for the treatment of type 2 diabetes mellitus.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00775-004-0590-8     

Ejection of structural zinc leads to inhibition of γ-butyrobetaine hydroxylase

γ-Butyrobetaine hydroxylase (BBOX) is a 2-oxoglutarate and Fe(II) dependent oxygenase that catalyses an essential step during carnitine biosynthesis in animals. BBOX is inhibited by ejection of structural zinc by a set of selenium containing analogues. Previous structural analyses indicated that an undisrupted N-terminal zinc binding domain of BBOX is required for catalysis. Ebselen is a relatively potent BBOX inhibitor, an observation which may in part reflect its cardioprotective properties.     

A role for zinc in postsynaptic density asSAMbly and plasticity?

Chemical synapses are asymmetric cell junctions that mediate communication between neurons. Multidomain scaffolding proteins of the Shank family act as major organizing elements of the "postsynaptic density"--that is, the cytoskeletal protein matrix associated with the postsynaptic membrane. A recent study has shown that the C-terminal sterile alpha-motif or "SAM domain" of Shank3 (also known as ProSAP2) can form two-dimensional sheets of helical fibers. Assembly and packaging of these fibers are markedly enhanced by the presence of Zn2+ ions. Zn2+ can be released together with glutamate from synaptic vesicles and can enter the postsynaptic cell through specific ionotropic receptors. Based on these observations, we propose a new model of synaptic plasticity in which Zn2+ influx directly and instantly modulates the structure and function of the postsynaptic density.     

Kinetics of demetallation of a zinc–salophen complex into liposomes

A Zn–salophen complex has been incorporated into POPC large unilamellar liposomes (LUV) obtained in phosphate buffer at pH 7.4. Fluorescence optical microscopy and anisotropy measurements show that the complex is located at the liposomal surface, close to the polar headgroups. The interaction of the POPC phosphate group with Zn^2 + slowly leads to demetallation of the complex. The process follows first order kinetics and rate constants have been measured fluorimetrically in pure water and in buffered aqueous solution.The coordination of the phosphate group of monomeric POPC with salophen zinc also occurs in chloroform as detected by ESI-MS measurements.The effect of the Zn–salophen complex on the stability of POPC LUV has been evaluated at 25 °C by measuring the rate of release of entrapped 5(6)-carboxyfluorescein (CF) in the presence and in the absence of Triton X-100 as the perturbing agent. It turns out that the inclusion of the complex significantly increases the stability of POPC LUV.     

Strong and weak zinc binding sites in human zinc-α2-glycoprotein

Zinc-α2-glycoprotein (ZAG) is an adipokine with an MHC class I-like protein fold. Even though zinc causes ZAG to precipitate from plasma during protein purification, no zinc binding has been identified to date. Using mass spectrometry, we demonstrated that ZAG contains one strongly bound zinc ion, predicted to lie close to the α1 and α2 helical groove. UV, CD and fluorescence spectroscopies detected weak zinc binding to holo-ZAG, which can bind up to 15 zinc ions. Zinc binding to 11-(dansylamino) undecanoic acid was enhanced by holo-ZAG. Zinc binding may be important for ZAG binding to fatty acids and the β-adrenergic receptor.