Zinc metabolism during captopril treatment

In 14 hypertensives the effect of captopril (angiotensin-converting enzyme inhibitor) treatment on red blood cell Na+, K+, Mg2+ and Zn2+ concentrations and on plasma Zn2+ concentrations were studied. Intraerythrocytic Zn2+ concentrations increased slightly, whereas plasma zinc concentrations decreased. The concurrence of hypozincemia with side effects resembling the symptoms of zinc deficiency such as loss of smell and taste suggests a role of alterations in zinc metabolism for the pharmacodynamics of captopril.     

Extracellular zinc triggers ERK-dependent activation of Na+/H+ exchange in colonocytes mediated by the zinc-sensing receptor

Extracellular zinc promotes cell proliferation and its deficiency leads to impairment of this process, which is particularly important in epithelial cells. We have recently characterized a zinc-sensing receptor (ZnR) linking extracellular zinc to intracellular release of calcium. In the present study, we addressed the role of extracellular zinc, acting via the ZnR, in regulating the MAP kinase pathway and Na+/H+ exchange in colonocytes. We demonstrate that Ca2+ release, mediated by the ZnR, induces phosphorylation of ERK1/2, which is highly metal-specific, mediated by physiological concentrations of extracellular Zn2+ but not by Cd2+, Fe2+, Ni2+, or Mn2+. Desensitization of the ZnR by Zn2+, is followed by approximately 90% inhibition of the Zn2+ -dependent ERK1/2 phosphorylation, indicating that the ZnR is a principal link between extracellular Zn2+ and ERK1/2 activation. Application of both the IP3 pathway and PI 3-kinase antagonists largely inhibited Zn2+ -dependent ERK1/2 phosphorylation. The physiological significance of the Zn2+ -dependent activation of ERK1/2 was addressed by monitoring Na+/H+ exchanger activity in HT29 cells and in native colon epithelium. Preincubation of the cells with zinc was followed by robust activation of Na+/H+ exchange, which was eliminated by cariporide (0.5 microm); indicating that zinc enhances the activity of NHE1. Activation of NHE1 by zinc was totally blocked by the ERK1/2 inhibitor, U0126. Prolonged acidification, in contrast, stimulates NHE1 by a distinct pathway that is not affected by extracellular Zn2+ or inhibitors of the MAP kinase pathway. Desensitization of ZnR activity eliminates the Zn2+ -dependent, but not the prolonged acidification-dependent activation of NHE1, indicating that Zn2+ -dependent activation of H+ extrusion is specifically mediated by the ZnR. Our results support a role for extracellular zinc, acting through the ZnR, in regulating multiple signaling pathways that affect pH homeostasis in colonocytes. Furthermore activation of both, ERK and NHE1, by extracellular zinc may provide the mechanism linking zinc to enhanced cell proliferation.     

Evidence for a zinc/proton antiporter in rat brain

The data presented in this paper are consistent with the existence of a plasma membrane zinc/proton antiport activity in rat brain. Experiments were performed using purified plasma membrane vesicles isolated from whole rat brain. Incubating vesicles in the presence of various concentrations of 65Zn2+ resulted in a rapid accumulation of 65Zn2+. Hill plot analysis demonstrated a lack of cooperativity in zinc activation of 65Zn2+ uptake. Zinc uptake was inhibited in the presence of 1 mM Ni2+, Cd2+, or CO2+. Calcium (1 mM) was less effective at inhibiting 65Zn2+ uptake and Mg2+ and Mn2+ had no effect. The initial rate of vesicular 65Zn2+ uptake was inhibited by increasing extravesicular H+ concentration. Vesicles preloaded with 65Zn2+ could be induced to release 65Zn2+ by increasing extravesicular H+ or addition of 1 mM nonradioactive Zn2+. Hill plot analysis showed a lack of cooperativity in H+ activation of 65Zn2+ release. Based on the Hill analyses, the stoichiometry of transport may include Zn2+/Zn2+ exchange and Zn2+/H+ antiport, the latter being potentially electrogenic. Zinc/proton antiport may be an important mode of zinc uptake into neurons and contribute to the reuptake of zinc to replenish presynaptic vesicle stores after stimulation.     

The extracellular zinc-sensing receptor mediates intercellular communication by inducing ATP release

Taste and salivary secretion disorders have been linked to zinc deficiency, indeed zinc is found in secretory granules in the salivary gland. The signaling role for the zinc release in this tissue, however, is poorly understood. Here, we address the signaling pathways and physiological role of the zinc-sensing receptor, ZnR, in the ductal salivary gland cell line, HSY. Exposure of these cells to zinc triggered intracellular Ca2+ release from thapsigargin-sensitive stores. The G alpha q inhibitor, YM-254890 (1 microM), eliminated the Zn2+-dependent Ca2+ response, demonstrating that ZnR is a G alpha q-coupled receptor. Dose-response curves yielded an apparent K0.5 of 36 microM and a Hill coefficient of 7 in the absence of extracellular Ca2+, and K0.5 of 55 microM with a Hill coefficient of 3 in its presence. This indicates that although Zn2+ is essential for ZnR activation, Ca2+ may affect the receptor co-operativity. The homologous desensitization pattern of ZnR was characterized by pre-exposure of cells to Zn2+ at concentrations found to activate the receptor. Re-exposure of cells to Zn2+ elicited an attenuated Zn2+-dependent Ca2+ response for at least 3 h, indicating that the ZnR is strongly desensitized by Zn2+. Finally, we studied the paracrine affects of ZnR using a co-culture consisting of the HSY cells and vascular smooth muscle cells (VSMCs). While no Zn2+-dependent Ca2+ release was observed in VSMC alone, application of Zn2+ to the co-culture induced a Ca2+ rise in both HSY cells and VSMC. This Ca2+ rise was inhibited by the ATP scavenger, apyrase. Taken together, our results demonstrate that ZnR activity is monitored in salivary cells and is modulated by extracellular Ca2+. We further show that ZnR enhances secretion of ATP, thereby linking zinc to key signaling pathways involved in modification of salivary secretions by the ductal cells.     

Interaction between dietary calcium supplementation and chronic waterborne zinc exposure in juvenile rainbow trout, Oncorhynchus mykiss

This study investigated the effects of dietary Ca2+ on branchial Ca2+ and Zn2+ uptake, new and total zinc accumulation in target tissues (gill, liver and kidney), calcium and zinc homeostasis, and acute tolerance to waterborne zinc in fish chronically exposed to waterborne zinc. Juvenile rainbow trout (Oncorhynchus mykiss) were maintained on a calcium-enriched diet [41.2 mg vs. 21.2 mg (control) calcium/g dry wt. of food] and chronic waterborne zinc exposure (2.3 micromol/L), both separately and in combination, for 28 days. Calcium-supplemented diet in the absence of waterborne zinc significantly reduced branchial Ca2+ and Zn2+ influx rates, and new and total zinc accumulations in target tissues relative to control. However it did not protect against the acute zinc challenge. In contrast, waterborne zinc exposure significantly increased branchial Ca2+ and Zn2+ influx rates, new and total zinc concentrations in target tissues, and acute zinc tolerance relative to control. Interestingly, no such changes in any of these parameters were recorded in fish treated simultaneously with elevated dietary Ca2+ and waterborne zinc, except acute zinc tolerance which was highest among all the treatments. Thus, we conclude that the interactions between elevated dietary Ca2+ and waterborne zinc can protect freshwater fish against waterborne zinc toxicity.     

Toxicity of zinc to fungi, bacteria, and coliphages: influence of chloride ions.

A 10 mM concentration of Zn2+ decreased the survival of Escherichia coli; enhanced the survival of Bacillus cereus; did not significantly affect the survival of Pseudomonas aeruginosa, Norcardia corallina, and T1, T7, P1, and phi80 coliphages; completely inhibited mycelial growth of Rhizoctonia solani; and reduced mycelial growth of Fusarium solani, Cunninghamella echinulata, Aspergillus niger, and Trichoderma viride. The toxicity of zinc to the fungi, bacteria, and coliphages was unaffected, lessened, or increased by the addition of high concentrations of NaCl. The increased toxicity of zinc in the presence of high concentrations of NaCl was not a result of a synergistic interaction between Zn2+ and elevated osmotic pressures but of the formation of complex anionic ZnCl species that exerted greater toxicities than did cationic Zn2+. Conversely, the decrease in zinc toxicity with increasing concentrations of NaCl probably reflected the decrease in the levels of Zn2+ due to the formation of Zn-Cl species, which was less inhibitory to these microbes than was Zn2+. A. niger tolerated higher concentrations of zinc in the presence of NaCl at 37 than at 25 degrees C.     

Stimulated release of exogenous GABA and glutamate from cerebral cortical synaptosomes and brain slices by bis (acetato) tetrakis (imidazole) copper(II) complex

Severe matermal zinc deficiency has a devastating effect on pregnancy outcome. Studies of humans and experimental animals show that matermal zinc deficiency can cause infertility, prolonged labor, intrauterine growth retardation, teratogenesis, severe immunological deficiencies, or fetal death. The additional need for zinc during pregnancy can be met by an increase in zinc intake. An increase in zinc supplements, when excessive, can cause a decrease in copper. Therefore, it is important to determine the zinc and copper concentrations in embryonic tissue in experimental models and their relationship with embryo number and viability. BALB/c mice were divided into groups according to zinc oral supplementation and gestational age. Phagocytosis was assesed in peritoneal macrophages from dams. The zinc and copper concentrations were obtained by inductively coupled plasma-optical emission spectrometry. Zn and Cu data concentrations in all the analyzed samples were above the detection limits. No spectral interferences were found in both elements (standard reference material was used). Zinc concentrations show a tendency to increase in embryos (14 gestational days and 21 gestational days) supplemented with zinc. Copper concentrations showed a noticeable tendency to diminish (36% and 27%, respectively) in the same period. In contrast, in placenta Zn values were increased by 30% and Cu values were decreased by 26%. We suggest a pivotal role of the placenta metabolism with its homeostatic mechanisms, in these findings. An important increment appeared in the +Zn embryo number (40%) relative to control (−Zn) embryos at 21 d gestational age. Embryo mortality was at 6% in +Zn embryos and at 20% in −Zn embryos. We consider these findings, both in the number and in the viability of +Zn embryos, outstanding.     

The zinc sensing receptor, a link between zinc and cell signaling

Zinc is essential for cell growth. For many years it has been used to treat various epithelial disorders, ranging from wound healing to diarrhea and ulcerative colon disease. The physiological/molecular mechanisms linking zinc and cell growth, however, are not well understood. In recent years, Zn2+ has emerged as an important signaling molecule, activating intracellular pathways and regulating cell fate. We have functionally identified an extracellular zinc sensing receptor, called zinc sensing receptor (ZnR), that is specifically activated by extracellular Zn2+ at physiological concentrations. The putative ZnR is pharmacologically coupled to a Gq-protein which triggers release of Ca2+ from intracellular stores via the Inositol 1,4,5-trisphosphate (IP3) pathway. This, in turn results in downstream signaling via the MAP and phosphatidylinositol 3-kinase (PI3 kinase) pathways that are linked to cell proliferation. In some cell types, e.g., colonocytes, ZnR activity also upregulates Na+/H+ exchange, mediated by Na+/H+ exchanger isoform 1 (NHE1), which is involved in cellular ion homeostasis in addition to cell proliferation. Our overall hypothesis, as discussed below, is that a ZnR, found in organs where dynamic zinc homeostasis is observed, enables extracellular Zn2+ to trigger intracellular signaling pathways regulating key cell functions. These include cell proliferation and survival, vectorial ion transport and hormone secretion. Finally, we suggest that ZnR activity found in colonocytes is well positioned to attenuate erosion of the epithelial lining of the colon, thereby preventing or ameliorating diarrhea, but, by signaling through the same pathways, a ZnR may enhance tumor progression in neoplastic disease.     

Inhibition of proton pumping by zinc ions during specific reaction steps in cytochrome c oxidase

Cytochrome c oxidase (CytcO) is a redox-driven proton pump in the respiratory chain of mitochondria and many aerobic bacteria. The results from several studies have shown that zinc ions interfere with both the uptake and release of protons, presumably by binding near the orifice of the proton entrance and exit pathways. To elucidate the effect of Zn2+ binding on individual electron and proton-transfer reactions, in this study, we have investigated the reaction of the fully reduced R. sphaeroides CytcO with O2, both with enzyme in detergent solution and reconstituted in phospholipid vesicles, and, with and without, Zn2+. The results show that addition of Zn2+ at concentrations of < or = 250 microM to the outside of the vesicles did not alter the transition rates between intermediates PR (P3)-->F3-->O4. However, proton pumping was impaired specifically during the P3-->F3, but not during the F3-->O4 transition at Zn2+ concentrations of < or = 25 microM. Furthermore, proton pumping during the P3-->F3 transition was typically impaired with the "as isolated" CytcO, which was found to contain Zn2+ ions at microM concentration. As has already been shown, Zn2+ was also found to obstruct proton uptake during the P3-->F3 transition, presumably by binding to a site near the orifice of the D-pathway. In this work we found a KI of approximately 1 microM for this binding site. In conclusion, the results show that Zn2+ ions bind on both sides of CytcO and that binding of Zn2+ at the proton output side selectively impairs proton release during the P3-->F3 transition.     

Effects of the Ca ionophore A23187 on zinc-induced apoptosis in C6 glioma cells

Zinc ions are essential, but at elevated concentrations, they also have toxic effects on mammalian cells. Zinc plays a crucial role in cell proliferation and differentiation and it even protects cells against apoptosis caused by various reagents. On the other hand, zinc at high concentrations causes cell death that was characterized as apoptotic by internucleosomal DNA fragmentation, formation of apoptotic bodies, and breakdown of the mitochondrial membrane potential. In the present work, a clone of rat C6 glioma cells that was resistant to toxic effects of ZnCl₂ up to 250 μM was employed to study the effect of the ionophore A23187 on zinc-induced apoptosis. Neither 150 μM Zn²⁺ nor 100 nM A23187 alone caused apoptosis as measured by internucleosomal DNA fragmentation. However, combined exposure of C6 cells to 100 nM A23187 and 150 μM Zn²⁺ for 48 h was effective in inducing apoptosis. Because the so-called calcium ionophore A23187 is not specific for Ca²⁺ ions but also transports Zn²⁺ with high selectivity over Ca²⁺, we investigated whether this substance promoted the uptake of Zn²⁺ ions into C6 cells. Employing the zinc-specific fluorescence probe Zinquin, we observed that the very low concentration of 1.9 nM A23187 significantly and rapidly raised the intracellular mobile Zn²⁺ content. Analysis by atomic absorption spectroscopy revealed that incubation with 1.9 nM A23187 caused a doubling of the total intracellular zinc level within 60 min. We conclude that the apoptosis evoked by the combined action of Zn²⁺ and A23187 was the result of enhanced Zn²⁺ influx evoked by the ionophore, resulting in higher intracellular zinc levels.     

Zinc metalloenzyme properties of active and latent collagenase from rabbit bone.

1. Inhibition of collagenase from rabbit bone cultures by the chelating agents 1,10-phenanthroline and EDTA is almost completely reversed by Zn2+; other metal cations are less effective in reversing the inhibition. Optimal restoration of activity is achieved at Zn2+ concentrations below that of the chelator, but excess of Zn2+ is inhibitory. 2. Prolonged incubation of collagenase with either chelator causes irreversible inactivation. This inactivation is prevented by Zn2+ at the same concentrations needed to reverse the primary inhibition. 3. Collagenase incorporates 65Zn by exchange when incubated with 1,10-phenanthroline and Zn2+ containing this radioactive isotope. The 65Zn2+ can be removed from its binding site in collagenase by 1,10-phenanthroline or EDTA. Irreversible inactivation of collagenase by chelators destroys its ability to incorporate 65Zn2+. 4. Latent collagenase, the inhibited form in which collagenase first appears in culture, behaves similarly to the active enzyme in 65Zn2+-exchange experiments, but is resistant to irreversible inactivation by chelators. 5. It is concluded that collagenase is a zinc metalloenzyme that forms an inactive and unstable apoenzyme on treatment with chelators. The bound inhibitor component of latent collagenase evidently stabilizes the apoenzyme.     

Evidence for a major route for zinc uptake in human red blood cells: [Zn(HCO3)2Cl]- influx through the [Cl-/HCO3-] anion exchanger

The initial rate of Zn2+ uptake in human red cells was measured by atomic absorption. A very important fraction of Zn2+ uptake was inhibited by DIDS with IC50 = 0.3 microM (and by furosemide and bumetanide with IC50 of 200 and 500 microM, respectively). DIDS-sensitive Zn2+ uptake exhibited the following properties: 1) It required the simultaneous presence of both external HCO3- and Cl-. 2) In Cl- containing media, it was strongly stimulated by external HCO3- following a sigmoidal (S-shaped) and saturable function, which was fitted by a Hanes equation, with n = 2 and an apparent dissociation constant (for external HCO3-) of 5.3 +/- 0.9 mM (mean +/- SD of four experiments). The maximal rate of Zn2+ uptake at saturating HCO3- concentrations was 50.7 +/- 4.8 mmol (liter cells x h)-1. 3) In HCO3- containing media, it was strongly stimulated by external Cl- following a Michaelis-like equation with an apparent dissociation constant (for external Cl-) of 88 +/- 11 mM (mean +/- SD of three experiments). 4) Bicarbonate-stimulated Zn2+ uptake was inhibited by physiological concentrations of phosphate (sulfate was a much less potent inhibitor than phosphate). A kinetic analysis of the data strongly suggested that zinc was transported by the anion carrier in the form of the monovalent anion complex: [Zn(HCO3)2Cl]-.     

The over-expression of TRPC6 channels in HEK-293 cells favours the intracellular accumulation of zinc

TRPC6 are plasma membrane cation channels. By means of live-cell imaging and spectroscopic methods, we found that HEK cells expressing TRPC6 channels (HEK-TRPC6) are enriched in zinc and sulphur and have a reduced copper content when compared to HEK cells and HEK cells expressing TRPC3 channels (HEK-TRPC3). Hence, HEK-TRPC6 cells have larger pools of mobilizable Zn2+ and are more sensitive to an oxidative stress. Synchrotron X-ray fluorescence experiments showed a higher zinc content in the nuclear region indicating that the intracellular distribution of this metal was influenced by the over-expression of TRPC6 channels. Their properties were investigated with the diacylglycerol analogue SAG and the plant extract hyperforin. Electrophysiological recordings and imaging experiments with the fluorescent Zn2+ probe FluoZin-3 demonstrated that TRPC6 channels form Zn2+-conducting channels. In cortical neurons, hyperforin-sensitive channels co-exist with voltage-gated channels, AMPA and NMDA receptors, which are known to transport Zn2+. The ability of these channels to regulate the size of the mobilizable pools of Zn2+ was compared. The data collected indicate that the entry of Zn2+ through TRPC6 channels can up-regulate the size of the DTDP-sensitive pool of Zn2+. By showing that TRPC6 channels constitute a Zn2+ entry pathway, our study suggests that they could play a role in zinc homeostasis.     

Zinc stimulates the activity of the insulin- and nutrient-regulated protein kinase mTOR

Recent studies indicate that zinc activates p70 S6 kinase (p70(S6k)) by a mechanism involving phosphatidylinositol 3-kinase (PI 3-kinase) and Akt (protein kinase B). Here it is shown that phenanthroline, a zinc and heavy metal chelator, inhibited both amino acid- and insulin-stimulated phosphorylation of p70(S6k). Both amino acid and insulin activations of p70(S6k) involve a rapamycin-sensitive step that involves the mammalian target of rapamycin (mTOR, also known as FRAP and RAFT). However, in contrast to insulin, amino acids activate p70(S6k) by an unknown PI 3-kinase- and Akt-independent mechanism. Thus the effects of chelator on amino acid activation of p70(S6k) were surprising. For this reason, we tested the hypothesis that zinc directly regulates mTOR activity, independently of PI 3-kinase activation. In support of this, basal and amino acid stimulation of p70(S6k) phosphorylation was increased by zinc addition to the incubation media. Furthermore, the protein kinase activities of mTOR immunoprecipitated from rat brain lysates were stimulated two- to fivefold by 10-300 microM Zn2+ in the presence of an excess of either Mn2+ or Mg2+, whereas incubation with 1,10-phenanthroline had no effect. These findings indicate that Zn2+ regulates, but is not absolutely required for, mTOR protein kinase activity. Zinc also stimulated a recombinant human form of mTOR. The stimulatory effects of Zn2+ were maximal at approximately 100 microM but decreased and became inhibitory at higher physiologically irrelevant concentrations. Micromolar concentrations of other divalent cations, Ca2+, Fe2+, and Mn2+, had no effect on the protein kinase activity of mTOR in the presence of excess Mg2+. Our results and the results of others suggest that zinc acts at multiple steps in amino acid- and insulin cell-signaling pathways, including mTOR, and that the additive effects of Zn2+ on these steps may thereby promote insulin and nutritional signaling.     

锌胁迫对铜锈环棱螺致死率、富集性、CAT和SOD活性的影响

以浙江省温州市瓯海茶山某河内的铜锈环棱螺Bellamya aeruginosa为受试生物,研究了不同浓度Zn2+胁迫下,铜锈环棱螺的致死效应、铜锈环棱螺对锌的富集性以及锌对铜锈环棱螺体内的过氧化氢酶(CAT)和超氧化物歧化酶(SOD)活性的影响.结果表明Zn2+对铜锈环棱螺具有较大的毒害影响.当Zn2+浓度达到3.0 mg/L时,就会引起个别铜锈环棱螺死亡,死亡率为2.66％.随着Zn2+浓度的增大(0.3 mg/L到2.4 mg/L)和处理时间的增加(2d到8d),除个别组外,铜锈环棱螺对锌的累积量均随之上升,具有一定的时间效应和剂量效应.铜锈环棱螺在锌胁迫下,肝胰腺的CAT和SOD活性受到较大的影响.当Zn2+浓度较低时,CAT和SOD活性均有较大的升高,但当Zn2+浓度较高时,CAT和SOD活性则受到一定的抑制.     

A sodium zinc exchange mechanism is mediating extrusion of zinc in mammalian cells

Zinc influx, driven by a steep inward electrochemical gradient, plays a fundamental role in zinc signaling and in pathophysiologies linked to intracellular accumulation of toxic zinc. Yet, the cellular transport mechanisms that actively generate or maintain the transmembrane gradients are not well understood. We monitored Na+-dependent Zn2+ transport in HEK293 cells and cortical neurons, using fluorescent imaging. Treatment of the HEK293 cells with CaPO4 precipitates induced Na+-dependent Zn2+ extrusion, against a 500-fold transmembrane zinc gradient, or zinc influx upon reversal of Na+ gradient, thus indicating that Na+/Zn2+ exchange is catalyzing active Zn2+ transport. Depletion of intracellular ATP did not inhibit the Na+-dependent Zn2+ extrusion, consistent with a mechanism involving a secondary active transporter. Inhibitors of the Na+/Ca2+ exchanger failed to inhibit Na+-dependent Zn2+ efflux. In addition, zinc transport was unchanged in HEK293 cells heterologously expressing functional cardiac or neuronal Na+/Ca2+ exchangers, thus indicating that the Na+/Zn2+ exchange activity is not mediated by the Na+/Ca2+ exchanger. Sodium-dependent zinc exchange, facilitating the removal of intracellular zinc, was also monitored in neurons. To our knowledge, the Na+/Zn2+ exchanger described here is the first example of a mammalian transport mechanism capable of Na+-dependent active extrusion of zinc. Such mechanism is likely to play an important role, not only in generating the transmembrane zinc gradients, but also in protecting cells from the potentially toxic effects of permeation of this ion.     

Growth and photosynthesis limitation of marine red tide alga Skeletonema costatum by low concentrations of Zn2+

The specific growth rate, cell final yields and extracellar carbonic anhydrase activity of the red tide alga Skeletonema costatum increased with increasing concentrations of Zn2+ from 0 to 12 pM, but decreased when Zn2+ was over 24 pM. However, cells grown under high concentrations of Zn2+ had higher activities of intracellular carbonic anhydrase than those grown under low concentrations of Zn2+. Chlorophyll a-specific light-saturated photosynthetic rate (P(Chla)), dark respiration rate (R(chla)) and apparent photosynthetic efficiency (alpha(chla)) significantly increased with increasing concentrations of Zn2+ from 0 to 3 pM, but decreased when increasing concentrations of Zn2+ from 3 to 66 pM. Photorespiration is the lowest when cells cultured in 3 pM Zn2+. The results suggest physiological activity of Skeletonema costatum is very sensitive to the prevailing concentration of Zn2+.     

The effect of dietary zinc - and polyphenols intake on DMBA-induced mammary tumorigenesis in rats

Background

The aim of the study was to investigate the effect of dietary supplementation with zinc and polyphenol compounds, i.e. resveratrol and genistein, on the effectiveness of chemically induced mammary cancer and the changes in the content of selected elements (Zn, Cu, Mg, Fe, Ca) in tumors as compared with normal tissue of the mammary gland.

Methods

Female Sprague-Dawley rats were divided into study groups which, apart from the standard diet and DMBA (7,12-dimethyl-1,2- benz[a]anthracene), were treated with zinc ions (Zn) or zinc ions + resveratrol (Zn + resveratrol) or zinc ions + genistein (Zn + genistein) via gavage for a period from 40 days until 20 weeks of age. The ICP-OES (inductively coupled plasma optical emission spectrometry) technique was used to analyze the following elements: magnesium, iron, zinc and calcium. Copper content in samples was estimated in an atomic absorption spectrophotometer.

Results

Regardless of the diet (standard; Zn; Zn + resveratrol; Zn + genistein), DMBA-induced breast carcinogenesis was not inhibited. On the contrary, in the Zn + resveratrol supplemented group, tumorigenesis developed at a considerably faster rate. On the basis of quantitative analysis of selected elements we found - irrespectively of the diet applied - great accumulation of copper and iron, which are strongly prooxidative, with a simultaneous considerable decrease of the magnesium content in DMBA-induced mammary tumors. The combination of zinc supplementation with resveratrol resulted in particularly large differences in the amount of the investigated elements in tumors as compared with their content in normal tissue.

Conclusions

Diet supplementation with zinc and polyphenol compounds, i.e. resveratrol and genistein had no effect on the decreased copper level in tumor tissue and inhibited mammary carcinogenesis in the rat. Irrespectively of the applied diet, the development of the neoplastic process in rats resulted in changes of the iron and magnesium content in the cancerous tissue in comparison with the healthy mammary tissue. The application of combined diet supplementation with zinc ions and resveratrol considerably promoted the rate of carcinogenesis and increased the number of DMBA-induced mammary tumors.     

Zinc availability from zinc lipoate and zinc sulfate in growing rats

The purpose of this study was to investigate the effect of zinc lipoate and zinc sulfate on zinc availability in growing rats. 6 . 6 male albino rats were fed purified diets based on corn starch, egg albumen, sucrose, soy bean oil and cellulose over a 4-week period (diet Ia: 10 mg Zn/kg as zinc sulfate, diet Ib: 10 mg Zn/kg as zinc lipoate, diet IIa: 10 mg Zn/kg as zinc sulfate +0.4% phytic acid, diet IIb: 10 mg Zn/kg as zinc lipoate +0.4% phytic acid, diet IIIa: 20 mg Zn/kg as zinc sulfate + 0.4% phytic acid, diet IIIb: 20 mg Zn/kg as zinc lipoate + 0.4% phytic acid). Zinc lipoate and zinc sulfate both proved to be highly available zinc sources. When 0.4% phytic acid were present in the diets, apparent zinc absorption was generally depressed but was higher from zinc lipoate in tendency than from zinc sulfate. Comparable results were evident for femur zinc, plasma zinc and metallothionein concentrations in liver tissues. This indicates that zinc lipoate could be a valuable zinc source under conditions of low zinc availability. Nevertheless the absence or presence of phytic acid was a more important factor influencing zinc availability than the type of zinc source investigated.