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

Dissolution, solvation and diffusion in low-temperature zinc electrolyte design

Aqueous zinc-based batteries have garnered the attention of the electrochemical energy storage community, but they suffer from electrolytes freezing and sluggish kinetics in cold environments. In this Review, we discuss the key parameters necessary for designing anti-freezing aqueous zinc electrolytes. We start with the fundamentals related to different zinc salts and their dissolution and solvation behaviours, by highlighting the effects of anions and additives on salt solubility, ion diffusion and freezing points. We then focus on the complex structures and energetics of cation-anion-solvent interaction. We also evaluate the prevailing strategies to improve the performance of electrolytes at low temperatures, with a discussion on the kinetics of plating and stripping of zinc anodes and charge storage in various cathode materials. Furthermore, we consider the current challenges and envisage future research directions in cold-resistant aqueous electrolyte formulations for zinc batteries.

Excessive Zinc Ion Caused PC12 Cell Death Correlating with Inhibition of NOS and Increase of RAGE in Cells

Zinc ion (Zn²⁺) is an important functional factor; however, excessive Zn²⁺ can be toxic. To understand the neurotoxicity of excessive Zn²⁺ and the underlying mechanism, PC12 cells were treated with excessive Zn²⁺ and Zn²⁺ plus N, N, N', N'-Tetrakisethylenediamine (TPEN), a zinc ion chelator agent. Trypan blue and 3-(4,5-dimethyl-2- thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide, thiazolyl blue tetrazolium bromide (MTT) assays were used to test cell viability; the relative kits were used to detect the activity of NOS synthase and the content of the receptor for advanced glycation end product (RAGE) in cells. We observed that excessive zinc caused PC12 cell damage and that TPEN partially reversed cell damage caused by excessive zinc. In addition, excessive zinc decreased total nitric oxide synthase (TNOS) activity in cells, in which constitutive nitric oxide synthase (cNOS) activity was significantly reduced; however, inducible nitric oxide synthase (iNOS) activity was extremely promoted. Moreover, excessive zinc upregulated the expression of RAGE, and TPEN effectively reversed the increase in RAGE induced by excessive zinc ions. Therefore, we concluded that excessive zinc caused PC12 cell damage, correlating with the inhibition of NOS and increase of RAGE induced in cells.

Distinct Mechanisms of Cytotoxicity in Novel Nitrogenous Heterocycles: Future Directions for a New Anti-Cancer Agent

Electron-rich, nitrogenous heteroaromatic compounds interact more with biological/cellular components than their non-nitrogenous counterparts. The strong intermolecular interactions with proteins, enzymes, and receptors confer significant biological and therapeutic properties to the imidazole derivatives, giving rise to a well-known and extensively used range of therapeutic drugs used for infections, inflammation, and cancer, to name a few. The current study investigates the anti-cancer properties of fourteen previously synthesized nitrogenous heterocycles, derivatives of imidazole and oxazolone, on a panel of cancer cell lines and, in addition, predicts the molecular interactions, pharmacokinetic and safety profiles of these compounds. Method: The MTT and CellTiter-Glo® assays were used to screen the imidazole and oxazolone derivatives on six cancer cell lines: HL60, MDA-MB-321, KAIMRC1, KMIRC2, MCF-10A, and HCT8. Subsequently, in vitro tubulin staining and imaging were performed, and the level of apoptosis was measured using the Promega ApoTox-Glo® triplex assay. Furthermore, several computational tools were utilized to investigate the pharmacokinetics and safety profile, including PASS Online, SEA Search, the QikProp tool, SwissADME, ProTox-II, and an in silico molecular docking study on tubulin to identify the critical molecular interactions. Results: In vitro analysis identified compounds 8 and 9 to possess the most significant potent cytotoxic activity on the HL60 and MDA-MB-231 cell lines, supported by PASS Online anti-cancer predictions with pa scores of 0.413 and 0.434, respectively. In addition, compound 9 induced caspase 3/7 dependent-apoptosis and interfered with tubulin polymerization in the MDA-MB-231 cell line, consistent with in silico docking results, identifying binding similarity to the native ligand colchicine. All the derivatives, including compounds 8 and 9, had acceptable pharmacokinetics; however, the safety profile was suboptimal for all the tested derivates except compound 4. Conclusion: The imidazole derivative compound 9 is a promising anti-cancer agent that switches on caspase-dependent apoptotic cell death and modulates microtubule function. Therefore, it could be a lead compound for further drug optimization and development.

Polyphosphate in Chronic Wound Healing: Restoration of Impaired Metabolic Energy State

Many pathological conditions are characterized by a deficiency of metabolic energy. A prominent example is nonhealing or difficult-to-heal chronic wounds. Because of their unique ability to serve as a source of metabolic energy, inorganic polyphosphates (polyP) offer the opportunity to develop novel strategies to treat such wounds. The basis is the generation of ATP from the polymer through the joint action of two extracellular or plasma membrane-bound enzymes alkaline phosphatase and adenylate kinase, which enable the transfer of energy-rich phosphate from polyP to AMP with the formation of ADP and finally ATP. Building on these findings, it was possible to develop novel regeneratively active materials for wound therapy, which have already been successfully evaluated in first studies on patients.

Human Epidermal Zinc Concentrations after Topical Application of ZnO Nanoparticles in Sunscreens

Zinc oxide nanoparticle (ZnO NP)-based sunscreens are generally considered safe because the ZnO NPs do not penetrate through the outermost layer of the skin, the stratum corneum (SC). However, cytotoxicity of zinc ions in the viable epidermis (VE) after dissolution from ZnO NP and penetration into the VE is ill-defined. We therefore quantified the relative concentrations of endogenous and exogenous Zn using a rare stable zinc-67 isotope (67Zn) ZnO NP sunscreen applied to excised human skin and the cytotoxicity of human keratinocytes (HaCaT) using multiphoton microscopy, zinc-selective fluorescent sensing, and a laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) methodology. Multiphoton microscopy with second harmonic generation imaging showed that 67ZnO NPs were retained on the surface or within the superficial layers of the SC. Zn fluorescence sensing revealed higher levels of labile and intracellular zinc in both the SC and VE relative to untreated skin, confirming that dissolved zinc species permeated across the SC into the VE as ionic Zn and significantly not as ZnO NPs. Importantly, the LA-ICP-MS estimated exogenous 67Zn concentrations in the VE of 1.0 ± 0.3 μg/mL are much lower than that estimated for endogenous VE zinc of 4.3 ± 0.7 μg/mL. Furthermore, their combined total zinc concentrations in the VE are much lower than the exogenous zinc concentration of 21 to 31 μg/mL causing VE cytotoxicity, as defined by the half-maximal inhibitory concentration of exogenous 67Zn found in human keratinocytes (HaCaT). This speaks strongly for the safety of ZnO NP sunscreens applied to intact human skin and the associated recent US FDA guidance.

Evaluation of the effect of curcumin and zinc co-supplementation on glycemic measurements, lipid profiles, and inflammatory and antioxidant biomarkers in overweight or obese prediabetic patients: a study protocol for a randomized double-blind placebo-controlled phase 2 clinical trial

BACKGROUND

The prevalence of prediabetes is increasing worldwide. Unfortunately, prediabetes is related to non-communicable diseases. A high risk of developing type 2 diabetes mellitus (T2DM) is reported in people with prediabetes. Curcumin, a polyphenol, might lead to its therapeutic role in obesity and some obesity-related metabolic diseases. Zinc is a trace element that plays a key role in the synthesis and action of insulin, carbohydrate metabolism, and decreasing inflammation. There has been no clinical trial of zinc and curcumin co-supplementation in patients with prediabetes. In previous studies, the single administration of zinc or curcumin has not been conducted on many of the studied markers in prediabetic patients.

METHODS

The purpose of this randomized double-blind placebo-controlled clinical trial is to investigate the effect of curcumin and zinc co-supplementation on glycemic measurements, lipid profiles, and inflammatory and antioxidant biomarkers among 84 prediabetic patients with body mass index (BMI) between 25 and 35. Also, liver enzyme, serum zinc, urine zinc, blood pressure, anthropometric parameters, quality of life, adherence to co-supplementation, the side effects of co-supplementation, physical activity, and dietary intake will be assessed. Women or men (18-50 years old for men and 18 years to before menopause for women) will be followed for 3 months (90 days). This study will be conducted at Yazd Diabetes Research Clinic, Shahid Sadoughi University of Medical Sciences.

DISCUSSION

A diet rich in antioxidants, polyphenols, and phytochemicals has been shown to have a beneficial role in prediabetes. According to the beneficial properties of curcumin or zinc and inadequate evidence, RCTs are needed to assess the effect of curcumin and zinc co-supplementation in native prediabetes patients. We hope the results of the present trial, negative or positive, fill this gap in the literature and facilitate the approach for a much larger, multi-center clinical trial. In conclusion, a synergic effect of co-supplementation along with a weight-loss diet may delay the progression to type 2 diabetes mellitus.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials (IRCT) IRCT20190902044671N1 . Registered on 11 October 2019.

Toxicity assessment of zinc sulfate: A commonly used compound

Because zinc sulfate (ZnSO₄) is widely used in many fields such as biomedicine, electronics, and chemistry, it is important to evaluate its toxic effects. In this study, the cyto-genotoxic effects of ZnSO₄ on meristematic cells in the root tip of Allium cepa L. were investigated. After calculating the effective concentration (EC₅₀ = 70 ppm) of ZnSO₄, A. cepa root tip cells were suspended for 24, 48, 72, and 96 h in solutions of 35 ppm (EC₅₀/2), 70 ppm (EC₅₀), and 140 ppm (EC₅₀ × 2) concentrations. Using the counts of dividing cells, the mitotic index (MI) was calculated. Chromosome aberration index (CAI) was determined from percentages of abnormal cells. When the obtained data were statistically evaluated, it was determined that all application concentrations caused a significant decrease in MI and an increase in CAI compared to the control group (distilled water). It was concluded that increased ZnSO₄ dose concentrations and exposure times caused cytotoxicity and genotoxicity in the root cells of A. cepa L.

Comparing the Influence of High Doses of Different Zinc Salts on Oxidative Stress and Energy Depletion in IPEC-J2 Cells

The current study aimed to investigate the influence of four supplemental zinc salts (chelated: Zn glycine; non-chelated: Zn sulfate, Zn citrate, Zn gluconate) among different zinc concentrations (30-300 μM) on cell proliferation, oxidative stress, and energy depletion in intestinal porcine jejunum epithelial cells (IPEC-J2). Different zinc salts affected cell viability in a time- and dose-dependent manner, which was mainly dependent on the uptake of intracellular Zn²⁺. Intracellular Zn²⁺ of Zn sulfate has taken up almost twice as high as Zn glycine when cells were loaded with 100-200 μM zinc. After loading cells with 300 μM zinc, Zn glycine and Zn sulfate had a similar trend in accumulation of Zn²⁺. When the intracellular Zn²⁺ overloads, cells will gradually be damaged and subsequently die bearing biochemical features of necrosis or late apoptosis. Meanwhile, obviously, increased levels of intracellular ROS, mitochondrial ROS, MDA, and NO and decreased levels of GSH were observed. Excessive intracellular Zn²⁺ significantly decreased mitochondria membrane potential accompanied by an obvious loss of ATP and NAD⁺ levels. Overall, exposure to high doses of zinc salts caused cell damage, which was mainly dependent on the uptake of Zn²⁺. Zinc overload induced oxidative stress and energy depletion in IPEC-J2 cells, and the cell damage with non-chelated zinc addition was more serious than Zn glycine.

A physiologically active interpenetrating collagen network that supports growth and migration of epidermal keratinocytes: zinc-polyP nanoparticles integrated into compressed collagen

It is demonstrated that polyphosphate, as a component in wound healing mats together with Zn²⁺, is essential for growth and migration of skin keratinocytes.

The Protective Effect of Zinc Against Liver Ischaemia Reperfusion Injury in a Rat Model of Global Ischaemia

BACKGROUND

Ischaemia-reperfusion injury (IRI) is a major obstacle during liver transplantation and resection surgeries for cancer, with a need for effective and safe drugs to reduce IRI. Zinc preconditioning has been shown to protect against liver IRI in a partial (70%) ischaemia model. However, its efficacy against a clinically relevant Pringle manoeuvre that results in global liver ischaemia (100%) is unknown.

AIMS

The aim of this study was to test the efficacy of zinc preconditioning in a rat model of global liver ischaemia.

METHODS

Rats were preconditioned via subcutaneous injection of 10 mg/kg of ZnCl₂, 24 h and 4 h before ischaemia. Total liver ischaemia (100%) was induced by placing a clamp across the portal triad for 30 min. Liver injury was assessed by serum alanine transaminase (ALT) and aspartate transaminase (AST) levels in blood taken before ischaemia (baseline) and at 1, 2, 4, 24, 48, 72, 96 and 120 hours after ischaemia. Animals were culled after 7 days, and the harvested livers were histologically analysed.

RESULTS

On a two-way repeated-measures analysis of variance, there was a statistically significant (p = 0.025) difference in the mean ALT levels between saline- and ZnCl₂-treated groups. Specifically at 24 h after ischaemia, the ALT (341 ± 99 U/L) and AST (606 ± 78 U/L) in the zinc-treated group were significantly less than the ALT (2863 ± 828 U/L) and AST (3591 ± 948 U/L) values in the saline-treated group. Zinc significantly reduced neutrophil infiltration and necrosis compared with the saline control.

CONCLUSION

Zinc preconditioning reduces the overall hepatocellular damage from IRI. These results lay the foundation to assess the benefit of zinc preconditioning for clinical applications.

Why is it worth testing the ability of zinc to protect against ischaemia reperfusion injury for human application

Ischaemia (interruption in the blood/oxygen supply) and subsequent damage induced by reperfusion (restoration of blood/oxygen supply) ultimately leads to cell death, tissue injury and permanent organ dysfunction. The impact of ischaemia reperfusion injury (IRI) is not limited to heart attack and stroke but can be extended to patients undergoing surgeries such as partial nephrectomy for renal cancer, liver resection for colorectal cancer liver metastasis, cardiopulmonary bypass, and organ transplantation. Unfortunately, there are no drugs that can protect organs against the inevitable peril of IRI. Recent data show that a protocol incorporating specific Zn formulation, dosage, number of dosages, time of injection, and mode of Zn delivery (intravenous) and testing of efficacy in a large preclinical sheep model of IRI strongly supports human trials of Zn preconditioning. No doubt, scepticism still exists among funding bodies and research fraternity on whether Zn, a naturally occurring metal, will work where everything else has failed. Therefore, in this article, we review the conflicting evidence on the promoter and protector role of Zn in the case of IRI and highlight factors that may help explain the contradictory evidence. Finally, we review the literature related to the knowledge of Zn's mechanism of action on ROS generation, apoptosis, HIF activation, inflammation, and signal transduction pathways, which highlight Zn's likelihood of success compared to various other interventions targeting IRI.

An agonist of a zinc-sensing receptor GPR39 enhances tight junction assembly in intestinal epithelial cells via an AMPK-dependent mechanism

Intestinal barrier function depends on integrity of tight junctions, which serve as barriers to transepithelial influx of noxious substances/microorganisms from gut lumen. The G-protein coupled receptor 39 (GPR39) is a zinc-sensing receptor, which is expressed in several cell types including intestinal epithelial cells (IECs). The main objective of this study was to investigate the effect of GPR39 activation on tight junction assembly in IECs. Treatment with TC-G 1008 (1 μM -10 μM), a GPR39 agonist, and zinc (10 μM -100 μM) increased tight junction assembly in T84 cells. This effect was suppressed by pretreatment with compound C, an inhibitor of AMP-activated protein kinase (AMPK). In addition, western blot analysis revealed that treatment with TC-G 1008 induced AMPK activation in time- and concentration-dependent manners. Interestingly, inhibitors of phospholipase C (PLC) and calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ) abrogated the effect of TC-G 1008 on inducing AMPK activation, tight junction assembly and zonula occludens-1 re-organization. Collectively, this study reveals a novel role of GPR39 in enhancing tight junction assembly in IECs via PLC-CaMKKβ-AMPK pathways. GPR39 agonists may be beneficial in the treatment of diseases associated impaired intestinal barrier function.

Bioactive nano-metal-organic frameworks as antimicrobials against Gram-positive and Gram-negative bacteria

More effective antibiotics are needed to overcome the problem of multidrug resistance. The antibacterial efficacies of three Zn-based nano metal-organic frameworks (nMOFs) - IRMOF-3, MOF-5, and Zn-BTC - were explored, both alone and as mixtures with ampicillin and kanamycin. When tested against Escherichia coli, Staphylococcus aureus, Staphylococcus lentus, and Listeria monocytogenes, the nMOF/drug mixtures demonstrated synergistic (IRMOF-3/kanamycin) or additive (other nMOF/drug combinations) effects compared with the nMOFs or antibiotics alone. Zn-Based nMOFs can reduce the burden of the new discovery of antimicrobial pharmaceuticals by increasing the potency of existing antibiotics.

Enhanced antibacterial nanocomposite mats by coaxial electrospinning of polycaprolactone fibers loaded with Zn-based nanoparticles

ZnO and Zn acetate nanoparticles were embedded in polycaprolactone coaxial-fibers and uniaxial-fibers matrices to develop potential antibacterial nanocomposite wound dressings (mats). Morphology, composition, wettability, crystallinity and fiber structure of mats were characterized. Antibacterial properties of mats were tested against E. coli and S. aureus by turbidity and MTT assays. The effect of UVA illumination (prior to bacteria inoculation) on mats' antibacterial activity was also studied. Results showed that a coaxial-fibers design maintained nanoparticles distributed in the outer-shell of fibers and, in general, enhanced the antibacterial effect of the mats, in comparison to conventional uniaxial-fibers mats. Results indicated that mats simultaneously inhibited planktonic and biofilm bacterial growth by, probably, two main antibacterial mechanisms; 1) release of Zn²⁺ ions (mainly from Zn acetate nanoparticles) and 2) photocatalytic oxidative processes exerted by ZnO nanoparticles. Antibacterial properties of mats were significantly improved by coaxial-fibers design and exposure to UVA-light prior to bacteria inoculation.

Development of Epigallocatechin-3-gallate-Encapsulated Nanohydroxyapatite/Mesoporous Silica for Therapeutic Management of Dentin Surface

In dental clinic, unsatisfactory management of the dentin surface after dentin exposure often leads to the occurrence of dentin hypersensitivity and caries. Current approaches can occlude the tubules on the dentin surface to relieve dentin hypersensitivity; however, the blocked tubules are generally weak in combating daily tooth erosion and abrasion. Moreover, cariogenic bacteria, such as Streptococcus mutans, produce biofilm on the dentin surface, causing caries and compromising the tubules' sealing efficacy. To overcome this problem, the present study focused on establishing a versatile biomaterial, epigallocatechin-3-gallate-encapsulated nanohydroxyapatite/mesoporous silica nanoparticle (EGCG@nHAp@MSN), for therapeutic management of the dentin surface. The effectiveness of the biomaterial on dentinal tubule occlusion, including resistances against acid and abrasion, was evaluated by field-emission scanning electron microscopy (FESEM) and dentin permeability measurement. The inhibitory capability of the biomaterial on S. mutans biofilm formation was investigated by confocal laser scanning microscopy (CLSM), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony forming units (CFU) counts, and FESEM. Results demonstrated for the first time that the use of EGCG@nHAp@MSN on the dentin surface was capable of effectively occluding dentinal tubules, reducing dentin permeability, and achieving favorable acid- and abrasion-resistant stability. Furthermore, EGCG@nHAp@MSN held the capability to continuously release EGCG, Ca, and P, and significantly inhibit the formation and growth of S. mutans biofilm on the dentin surface. Thus, the development of EGCG@nHAp@MSN bridges the gap between multifunctional concept and dental clinical practice and is promising in providing dentists a therapeutic strategy for the management of the dentin surface to counter dentin hypersensitivity and caries.

Analysis of ZIP (Zrt-, Irt-related protein) transporter gene expression in murine neural stem/progenitor cells

Zinc plays important roles for brain development. Zrt-, Irt-related protein (ZIP) is a major transporter family to regulate the intracellular zinc levels. Neural stem/progenitor cells (NSPCs) are more sensitive than their differentiated progeny (neural/glial cells) to zinc in vitro (Nishikawa et al., 2015). We analyzed relative gene expression of 14 different ZIPs in murine NSPCs and differentiated cells by real-time polymerase chain reaction technique. Expression of Zip4 and that of Zip12 drastically increased, while that of Zip8 clearly decreased after differentiation of NSPCs. Downregulation of NSPC's marker (Nes) and upregulation of differentiated cell markers (Tubb3; neuron, Gfap; astrocyte) occurred simultaneously. ZIP8 protein was immunochemically detected both in cultured neurospheres consisting of NSPCs in vitro and in subventricular zone of embryonic mouse brain in vivo, like a novel surface marker of NSPCs. We considered that required types of ZIP changed during the differetiation of NSPCs.

Position on zinc delivery to olfactory nerves in intranasal insulin phase I-III clinical trials

Zinc in pancreatic insulin is essential for processing and action of the peptide, while in commercial preparations zinc promotes hexameric structure and prevents aggregate formation. In 2002, for the first time, insulin was delivered to humans intranasally with resulting cerebrospinal fluid insulin increases, but steady peripheral insulin levels. The novel method of increasing brain insulin levels without changes in the periphery resulted in an expansion of brain insulin research in clinical trials. As pre-clinical research has shown that brain insulin modulates a number functions, including food cravings and eating behavior, learning and memory functions, stress and mood regulation; realization of beneficial effects of insulin in modulating these functions in clinical populations became a possibility with the new direct-to-brain insulin delivery methodology. However, zinc, being integral to insulin structure and function, is neurotoxic, and has resulted in adverse effects to human health. In the last century, intranasal zinc was given preventively during the time of polio outbreak, and in the 21st century intranasal zinc was widely used over the counter to prevent common cold. In both cases, patients experienced partial or complete loss of smell. This paper is the first one to analyze zinc salts and concentrations of those two epidemiological adversities and directly compare formulations distributed to the public with animal toxicity data. The information gained from animal and epidemiological data provides a foundation for the formation of opinion given in this paper regarding safety of intranasal zinc in emerging clinical trials with intranasal insulin.

Structure, mechanical characteristics and in vitro degradation, cytotoxicity, genotoxicity and mutagenicity of novel biodegradable Zn-Mg alloys

Zn-(0-1.6)Mg (in wt.%) alloys were prepared by hot extrusion at 300 °C. The structure, mechanical properties and in vitro biocompatibility of the alloys were investigated. The hot-extruded magnesium-based WE43 alloy was used as a control. Mechanical properties were evaluated by hardness, compressive and tensile testing. The cytotoxicity, genotoxicity (comet assay) and mutagenicity (Ames test) of the alloy extracts and ZnCl2 solutions were evaluated with the use of murine fibroblasts L929 and human osteosarcoma cell line U-2 OS. The microstructure of the Zn alloys consisted of recrystallized Zn grains of 12 μm in size and fine Mg2Zn11 particles arranged parallel to the hot extrusion direction. Mechanical tests revealed that the hardness and strength increased with increasing Mg concentration. The Zn-0.8 Mg alloys showed the best combination of tensile mechanical properties (tensile yield strength of 203 MPa, ultimate tensile strength of 301 MPa and elongation of 15%). At higher Mg concentrations the plasticity of Zn-Mg alloys was deteriorated. Cytotoxicity tests with alloy extracts and ZnCl2 solutions proved the maximum safe Zn(2+) concentrations of 120 μM and 80 μM for the U-2 OS and L929 cell lines, respectively. Ames test with extracts of alloys indicated that the extracts were not mutagenic. The comet assay demonstrated that 1-day extracts of alloys were not genotoxic for U-2 OS and L929 cell lines after 1-day incubation.

Reduced zinc cytotoxicity following differentiation of neural stem/progenitor cells into neurons and glial cells is associated with upregulation of metallothioneins

We investigated zinc cytotoxicity in mouse neural stem/progenitor cells (NSPCs) and their differentiated progeny (neuronal/glial cells) in correlation with expression of metallothionein (MT) gene. Differentiated cells were less sensitive than NSPCs to ZnCl2 (IC50: 128μM vs. 76μM). Differentiation of immature NSPCs to the differentiated cells led to an increase in expression of MT family genes (Mt1, Mt2, Mt3, and Mt4). Zinc exposure induced a dose-dependent increase in expression level of Mt1 and that of Mt2 in both NSPCs and the differentiated cells. Our results showed that the reduced cytotoxicity of zinc associated with differentiation from NSPCs into their progeny was related to the upregulation of MTs.

Toxic effect of zinc nanoscale metal-organic frameworks on rat pheochromocytoma (PC12) cells in vitro

Metal-organic frameworks (MOFs) possess unique properties desirable for delivery of drugs and gaseous therapeutics, but their uncharacterized interactions with cells raise increasing concerns of their safety in such biomedical applications. We evaluated the adverse effects of zinc nanoscale MOFs on the cell morphology, cytoskeleton, cell viability and expression of neurotrophin signaling pathway-associated GAP-43 protein in rat pheochromocytoma PC12 cells. At the concentration of 25 μg/ml, zinc MOFs did not significantly affect morphology, viability and membrane integrity of the cells. But at higher concentrations (over 100 μg/ml), MOFs exhibited a time- and concentration-dependent cytotoxicity, indicating their entry into the cells via endocytosis where they release Zn(2+) into the cytosol to cause increased intracellular concentration of Zn(2+). We demonstrated that the toxicity of MOFs was associated with a disrupted cellular zinc homeostasis and down-regulation of GAP-43 protein, which might be the underlying mechanism for the improved differentiation in PC12 cells. These findings highlight the importance of cytotoxic evaluation of the MOFs before their biomedical application.

Zinc causes acute impairment of glutathione metabolism followed by coordinated antioxidant defenses amplification in gills of brown mussels Perna perna

Zinc demonstrates protective and antioxidant properties at physiological levels, although these characteristics are not attributed at moderate or high concentrations. Zinc toxicity has been related to a number of factors, including interference with antioxidant defenses. In particular, the inhibition of glutathione reductase (GR) has been suggested as a possible mechanism for acute zinc toxicity in bivalves. The present work investigates the biochemical effects of a non-lethal zinc concentration on antioxidant-related parameters in gills of brown mussels Perna perna exposed for 21 days to 2.6 μM zinc chloride. After 2 days of exposure, zinc caused impairment of the antioxidant system, decreasing GR activity and glutathione levels. An increase in antioxidant defenses became evident at 7 and 21 days of exposure, as an increase in superoxide dismutase and glutathione peroxidase activity along with restoration of glutathione levels and GR activity. After 7 and 21 days, an increase in cellular peroxides and lipid peroxidation end products were also detected, which are indicative of oxidative damage. Changes in GR activity contrasts with protein immunoblotting data, suggesting that zinc produces a long lasting inhibition of GR. Contrary to the general trend in antioxidants, levels of peroxiredoxin 6 decreased after 21 days of exposure. The data presented here support the hypothesis that zinc can impair thiol homeostasis, causes an increase in lipid peroxidation and inhibits GR, imposing a pro-oxidant status, which seems to trigger homeostatic mechanisms leading to a subsequent increase on antioxidant-related defenses.

Surface coatings of ZnO nanoparticles mitigate differentially a host of transcriptional, protein and signalling responses in primary human olfactory cells

BACKGROUND

Inhaled nanoparticles have been reported in some instances to translocate from the nostril to the olfactory bulb in exposed rats. In close proximity to the olfactory bulb is the olfactory mucosa, within which resides a niche of multipotent cells. Cells isolated from this area may provide a relevant in vitro system to investigate potential effects of workplace exposure to inhaled zinc oxide nanoparticles.

METHODS

Four types of commercially-available zinc oxide (ZnO) nanoparticles, two coated and two uncoated, were examined for their effects on primary human cells cultured from the olfactory mucosa. Human olfactory neurosphere-derived (hONS) cells from healthy adult donors were analyzed for modulation of cytokine levels, activation of intracellular signalling pathways, changes in gene-expression patterns across the whole genome, and compromised cellular function over a 24 h period following exposure to the nanoparticles suspended in cell culture medium.

RESULTS

ZnO nanoparticle toxicity in hONS cells was mediated through a battery of mechanisms largely related to cell stress, inflammatory response and apoptosis, but not activation of mechanisms that repair damaged DNA. Surface coatings on the ZnO nanoparticles mitigated these cellular responses to varying degrees.

CONCLUSIONS

The results indicate that care should be taken in the workplace to minimize generation of, and exposure to, aerosols of uncoated ZnO nanoparticles, given the adverse responses reported here using multipotent cells derived from the olfactory mucosa.

Toxicity of Ag, CuO and ZnO nanoparticles to selected environmentally relevant test organisms and mammalian cells in vitro: a critical review

Nanoparticles (NPs) of copper oxide (CuO), zinc oxide (ZnO) and especially nanosilver are intentionally used to fight the undesirable growth of bacteria, fungi and algae. Release of these NPs from consumer and household products into waste streams and further into the environment may, however, pose threat to the 'non-target' organisms, such as natural microbes and aquatic organisms. This review summarizes the recent research on (eco)toxicity of silver (Ag), CuO and ZnO NPs. Organism-wise it focuses on key test species used for the analysis of ecotoxicological hazard. For comparison, the toxic effects of studied NPs toward mammalian cells in vitro were addressed. Altogether 317 L(E)C50 or minimal inhibitory concentrations (MIC) values were obtained for algae, crustaceans, fish, bacteria, yeast, nematodes, protozoa and mammalian cell lines. As a rule, crustaceans, algae and fish proved most sensitive to the studied NPs. The median L(E)C50 values of Ag NPs, CuO NPs and ZnO NPs (mg/L) were 0.01, 2.1 and 2.3 for crustaceans; 0.36, 2.8 and 0.08 for algae; and 1.36, 100 and 3.0 for fish, respectively. Surprisingly, the NPs were less toxic to bacteria than to aquatic organisms: the median MIC values for bacteria were 7.1, 200 and 500 mg/L for Ag, CuO and ZnO NPs, respectively. In comparison, the respective median L(E)C50 values for mammalian cells were 11.3, 25 and 43 mg/L. Thus, the toxic range of all the three metal-containing NPs to target- and non-target organisms overlaps, indicating that the leaching of biocidal NPs from consumer products should be addressed.

Neuronal cytotoxicity and genotoxicity induced by zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO NPs) are one of the most abundantly used nanomaterials in consumer products and biomedical applications. As a result, human exposure to these NPs is highly frequent and they have become an issue of concern to public health. Although toxicity of ZnO NPs has been extensively studied and they have been shown to affect many different cell types and animal systems, there is a significant lack of toxicological data for ZnO NPs on the nervous system, especially for human neuronal cells and tissues. In this study, the cytotoxic and genotoxic effects of ZnO NPs on human SHSY5Y neuronal cells were investigated under different exposure conditions. Results obtained by flow cytometry showed that ZnO NPs do not enter the neuronal cells, but their presence in the medium induced cytotoxicity, including viability decrease, apoptosis and cell cycle alterations, and genotoxicity, including micronuclei production, H2AX phosphorylation and DNA damage, both primary and oxidative, on human neuronal cells in a dose- and time-dependent manner. Free Zn(2+) ions released from the ZnO NPs were not responsible for the viability decrease, but their role on other types of cell damage cannot be ruled out. The results obtained in this work contribute to increase the knowledge on the genotoxic and cytotoxic potential of ZnO NPs in general, and specifically on human neuronal cells, but further investigations are required to understand the action mechanism underlying the cytotoxic and genotoxic effects observed.

Involvement of MyD88 in zinc oxide nanoparticle-induced lung inflammation

Zinc oxide nanoparticles (ZnONP) have great potential for medical applications. However, ZnONP is reported to induce acute lung inflammation, which limits its application in humans. We designed in vivo and in vitro studies to clarify ZnONP inflammation and its associated molecular signals. ZnONP with a single dose of 80 μg/30 μl was instilled into the tracheas of mice sacrificed at days 2, 7, 14, and 28 after instillation. Bronchoalveolar lavage fluid showed increased neutrophils and macrophages after treatment. Lung pathology showed a mixed inflammatory infiltrate of neutrophils, lymphocytes, and macrophages primarily in the bronchioles and peribronchiolar areas. Proinflammatory gene expression of TNF-α, IL-6, CXCL1, and MCP-1 was increased at day 2 and decreased after 7 days. The lung pathology resolved at day 28, without fibrosis. It remains unclear whether this acute lung inflammation was caused by ZnONP themselves or Zn(2+) iron released from the nanoparticles. In vitro studies confirming the results of in vivo studies showed increased expression of proinflammatory genes in both MLE12 cells (mouse lung epithelial cells) and RAW264.7 cells (mouse macrophages) with either ZnONP or Zn(NO₃)₂ treatment; notably, increased levels of proinflammatory genes were obviously higher in cells treated with ZnONP than in cells treated with Zn(NO₃)₂ at the same molarity dose. TNF-α and MCP-1 were induced only in MLE12 cells. MyD88, an adaptor protein for most Toll-like receptors (TLR) signaling pathways, initiated the ZnONP or Zn(NO₃)₂-induced lung inflammation. Silencing MyD88 expression with siRNA significantly reduced ZnONP or Zn(NO₃)₂-induced proinflammatory gene expression in MLE12 and RAW264.7 cells. Single-dose exposure to ZnONP produced the short-term lung inflammation via a MyD88-dependent TLR pathway. These data suggest that although both ZnONP and zinc ion might participate in the inflammatory reactions, ZnONP more effectively induced MyD88-dependent proinflammatory cytokines than zinc ion in lung epithelial cells.

Zicam-induced damage to mouse and human nasal tissue

Intranasal medications are used to treat various nasal disorders. However, their effects on olfaction remain unknown. Zicam (zinc gluconate; Matrixx Initiatives, Inc), a homeopathic substance marketed to alleviate cold symptoms, has been implicated in olfactory dysfunction. Here, we investigated Zicam and several common intranasal agents for their effects on olfactory function. Zicam was the only substance that showed significant cytotoxicity in both mouse and human nasal tissue. Specifically, Zicam-treated mice had disrupted sensitivity of olfactory sensory neurons to odorant stimulation and were unable to detect novel odorants in behavioral testing. These findings were long-term as no recovery of function was observed after two months. Finally, human nasal explants treated with Zicam displayed significantly elevated extracellular lactate dehydrogenase levels compared to saline-treated controls, suggesting severe necrosis that was confirmed on histology. Our results demonstrate that Zicam use could irreversibly damage mouse and human nasal tissue and may lead to significant smell dysfunction.

Comparison of uptake and neuroprotective potential of seven zinc-salts

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