Cytotoxicity of zinc in vitro

Gallium-doped zirconia coatings modulate microbiological outcomes in dental implant surfaces

Despite the significant recent advances in manufacturing materials supporting advanced dental therapies, peri-implantitis still represents a severe complication in dental implantology. Herein, a sol-gel process is proposed to easily deposit antibacterial zirconia coatings onto bulk zirconia, material, which is becoming very popular for the manufacturing of abutments. The coatings' physicochemical properties were analyzed through x-ray diffraction and scanning electron microscopy-energy-dispersive x-ray spectroscopy investigations, while their stability and wettability were assessed by microscratch testing and static contact angle measurements. Uniform gallium-doped tetragonal zirconia coatings were obtained, featuring optimal mechanical stability and a hydrophilic behavior. The biological investigations pointed out that gallium-doped zirconia coatings: (i) displayed full cytocompatibility toward human gingival fibroblasts; (ii) exhibited significant antimicrobial activity against the Aggregatibacter actinomycetemcomitans pathogen; (iii) were able to preserve the commensal Streptococcus salivarius. Furthermore, the proteomic analyses revealed that the presence of Ga did not impair the normal oral microbiota. Still, interestingly, it decreased by 17% the presence of Fusobacterium nucleatum, a gram-negative, strictly anaerobic bacteria that is naturally present in the gastrointestinal tract. Therefore, this work can provide a valuable starting point for the development of coatings aimed at easily improving zirconia dental implants' performance.

Glycyl-l-histidyl-l-lysine prevents copper- and zinc-induced protein aggregation and central nervous system cell death in vitro

Common features of neurodegenerative diseases are oxidative and inflammatory imbalances as well as the misfolding of proteins. An excess of free metal ions can be pathological and contribute to cell death, but only copper and zinc strongly promote protein aggregation. Herein we demonstrate that the endogenous copper-binding tripeptide glycyl-l-histidyl-l-lysine (GHK) has the ability to bind to and reduce copper redox activity and to prevent copper- and zinc-induced cell death in vitro. In addition, GHK prevents copper- and zinc-induced bovine serum albumin aggregation and reverses aggregation through resolubilizing the protein. We further demonstrate the enhanced toxicity of copper during inflammation and the ability of GHK to attenuate this toxicity. Finally, we investigated the effects of copper on enhancing paraquat toxicity and report a protective effect of GHK. We therefore conclude that GHK has potential as a cytoprotective compound with regard to copper and zinc toxicity, with positive effects on protein solubility and aggregation that warrant further investigation in the treatment of neurodegenerative diseases.

Antibacterial Calcium Phosphate Coatings for Biomedical Applications Fabricated via Micro-Arc Oxidation

A promising method for improving the functional properties of calcium-phosphate coatings is the incorporation of various antibacterial additives into their structure. The microbial contamination of a superficial wound is inevitable, even if the rules of asepsis and antisepsis are optimally applied. One of the main problems is that bacteria often become resistant to antibiotics over time. However, this does not apply to certain elements, chemical compounds and drugs with antimicrobial properties. In this study, the fabrication and properties of zinc-containing calcium-phosphate coatings that were formed via micro-arc oxidation from three different electrolyte solutions are investigated. The first electrolyte is based on calcium oxide, the second on hydroxyapatite and the third on calcium acetate. By adding zinc oxide to the three electrolyte solutions, antibacterial properties of the coatings are achieved. Although the same amount of zinc oxide has been added to each electrolyte solution, the zinc concentration in the coatings obtained vary greatly. Furthermore, this study investigates the morphology, structure and chemical composition of the coatings. The antibacterial properties of the zinc-containing coatings were tested toward three strains of bacteria-Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. Coatings of calcium acetate and zinc oxide contained the highest amount of zinc and displayed the highest zinc release. Moreover, coatings containing hydroxyapatite and zinc oxide show the highest antibacterial activity toward Pseudomonas aeruginosa, and coatings containing calcium acetate and zinc oxide show the highest antibacterial activities toward Staphylococcus aureus and methicillin-resistant Staphylococcus aureus.

Fabrication and Characterisation of Calcium Sulphate Hemihydrate Enhanced with Zn- or B-Doped Hydroxyapatite Nanoparticles for Hard Tissue Restoration

A composite based on calcium sulphate hemihydrate enhanced with Zn- or B-doped hydroxyapatite nanoparticles was fabricated and evaluated for bone graft applications. The investigations of their structural and morphological properties were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy techniques. To study the bioactive properties of the obtained composites, soaking tests in simulated body fluid (SBF) were performed. The results showed that the addition of 2% Zn results in an increase of 2.27% in crystallinity, while the addition of boron causes an increase of 5.61% compared to the undoped HAp sample. The crystallite size was found to be 10.69 ± 1.59 nm for HAp@B, and in the case of HAp@Zn, the size reaches 16.63 ± 1.83 nm, compared to HAp, whose crystallite size value was 19.44 ± 3.13 nm. The mechanical resistance of the samples doped with zinc was the highest and decreased by about 6% after immersion in SBF. Mixing HAp nanoparticles with gypsum improved cell viability compared to HAp for all concentrations (except for 200 µg/mL). Cell density decreased with increasing nanoparticle concentration, compared to gypsum, where the cell density was not significantly affected. The degree of cellular differentiation of osteoblast-type cells was more accentuated in the case of samples treated with G+HAp@B nanoparticles compared to HAp@B. Cell viability in these samples decreased inversely proportionally to the concentration of administered nanoparticles. From the point of view of cell density, this confirmed the quantitative data.

Antibacterial Effect of Low-Concentration ZnO Nanoparticles on Sulfate-Reducing Bacteria under Visible Light

The effect of ZnO nanoparticles (ZnO NPs), with different concentrations in simulated water, on the activity of sulfate-reducing bacteria (SRB) and their adhesion behaviour on stainless-steel surfaces, with and without visible light treatment, were investigated. The results showed that the concentration of ZnO NPs and light treatment greatly influenced the antibacterial performance of the NPs. In the water solution without light treatment, the low concentration (no more than 1 mg/L) of ZnO NPs in the aqueous solution promoted the growth of SRB, and the amount of biofilm attached to the stainless-steel surface increased. As the concentration increased, ZnO NPs exhibited antibacterial effects. In water under visible light irradiation, ZnO NPs showed antibacterial performance at all the concentrations studied (0.5~50 mg/L), and the antibacterial efficiency increased with the increase in the concentration of NPs. The determination results of the reactive oxygen species showed that light treatment can stimulate ZnO NPs in water to generate ·OH and O₂^·-, which exhibited good antibacterial properties. The adhesion amount of SRB on the stainless-steel surface was inversely proportional to the antibacterial efficiency of ZnO NPs.

Antimicrobial activity of ion-substituted calcium phosphates: A systematic review

In this systematic review, the antimicrobial effect of ion-substituted calcium phosphate biomaterials was quantitatively assessed. The literature was systematically searched up to the 6th of December 2021. Study selection and data extraction was performed in duplo by two independent reviewers with a modified version of the OHAT tool for risk of bias assessment. Any differences were resolved by consensus or by a referee. A mixed effects model was used to investigate the relation between the degree of ionic substitution and bacterial reduction. Of 1016 identified studies, 108 were included in the analysis. The methodological quality of included studies ranged from 6 to 16 out of 18 (average 11.4). Selenite, copper, zinc, rubidium, gadolinium, silver and samarium had a clear antimicrobial effect, with a log reduction in bacteria count of 0.23, 1.8, 2.1, 3.6, 5.8, 7.4 and 10 per atomic% of substitution, respectively. There was considerable between-study variation, which could partially be explained by differences in material formulation, study quality and microbial strain. Future research should focus on clinically relevant scenarios in vitro and the translation to in vivo prevention of PJI.

Seborrheic dermatitis: topical therapeutics and formulation design

Seborrheic dermatitis (SD) is a common dermatological disorder with symptoms that include skin flaking, erythema and pruritus. This review discusses the topical products available for treating SD, which target several aspects of disease pathobiology, including cutaneous microbial dysbiosis (driven by Malassezia yeast), inflammation, sebum production and skin barrier disruption. Among the various treatments available, zinc pyrithione (ZnPT) based products that exhibit anti-fungal action are the market leaders. A skin compartment approach is presented here for combining ZnPT exposure information with threshold levels for anti-fungal efficacy and toxicity, overall providing a comprehensive picture of ZnPT therapeutics and safety. While Malassezia yeast on the surface are effectively targeted, yeast residing beyond the superficial follicle may not receive adequate ZnPT for anti-fungal effect forming the basis for skin re-colonisation. Levels entering systemic circulation from topical delivery are well below toxic thresholds, however the elevated zinc levels within the viable epidermis warrants further investigation. Strategies to improve formulation design can be broadly classified as influencing 1) topical delivery, 2) therapeutic bioactivity, 3) skin mildness, and 4) sensory attributes. Successful SD treatment ultimately requires formulations that can balance efficacy, safety, and consumer appeal.

Metal-organic coordination polymers for delivery of immunomodulatory agents, and infectious disease and cancer vaccines

Metal-organic coordination polymers (CPs) are a broad class of materials that include metal-organic frameworks (MOFs). CPs are highly ordered crystalline materials that are composed of metal ions (or metal ion clusters) and multidentate organic ligands that serve as linkers. One-, two-, and three-dimensional CPs can be formed, with 2D and 3D structures referred to as MOFs. CPs have gained a lot of attention due to attractive structural features like structure versatility and tunability, and well-defined pores that enable the encapsulation of cargo. Further, CPs show a lot of promise for drug delivery applications, but only a very limited number of CPs are currently being evaluated in clinical trials. In this review, we outlined features that are desired for CP-based drug delivery platform, and briefly described most relevant characterization techniques. We highlighted some of the recent efforts directed toward developing CP-based drug delivery platforms with the emphasis on vaccines against cancer, infectious diseases, and viruses. We hope this review will be a helpful guide for those interested in the design and evaluation of CP-based immunological drug delivery platforms. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Soil and Freshwater Bioassays to Assess Ecotoxicological Impact on Soils Affected by Mining Activities in the Iberian Pyrite Belt

This study aims to use geochemical, mineralogical, ecotoxicological and biological indicators for a comprehensive assessment of the ecological risks related to the mobility, ecotoxicity and bioavailability of potentially harmful elements in the Lousal mining district. Particularly, toxicity was evaluated using four assays: algae, cytotoxicity assays with HaCaT cell line (dermal), earthworms and Daphnia magna. The geochemical and mineralogical characterization of the studied area shows that the mine wastes underwent intense weathering processes, producing important contamination of the adjacent soils, which also led to the release and mobilization of PHEs into nearby water courses. Total PTE results indicate that the soils affected by mining activities were highly contaminated with As and Cu, while Zn and Pb content ranged from low to very high, depending on the analyzed samples. Cadmium levels were found to be very low in most of the soil samples. The test using Daphnia magna was the most sensitive bioassay, while the Eisenia foetida test was the least sensitive. Except for the LOS07 soil sample, the rest of the soils were classified as “High acute toxicity” and “Very high acute toxicity” for aquatic systems. The results in HACaT cells showed results similar to the ecotoxicological bioassays. The application of biotests, together with geochemical and mineralogical characterization, is a very useful tool to establish the degree of contamination and the environmental risk of potentially harmful elements.

Indirect cytotoxicity evaluations of antibacterial raw silk fabric doped with calcium, copper and zinc on fibroblasts and osteoblasts

Antibacterial materials are widely used to prevent hospital-acquired infections. In our previous report, metal (calcium, copper or zinc)-doped raw silk fabrics were shown to possess strong antibacterial activities against Escherichia coli. However, antibacterial materials may occasionally be harmful to the human body; thus, in this study, we investigated the cytotoxicities of extracts from metal-doped raw silk fabrics with respect to fibroblasts and osteoblasts indirectly. Calcium-doped raw silk fabric demonstrated cytocompatibility with fibroblasts. Contrarily, copper- and zinc-doped raw silk fabrics remarkably decreased the cell densities of fibroblasts, indicating their cytotoxic effects. This observation could be attributed to the high concentrations of the released copper or zinc ions. However, calcium-, copper- and zinc-doped raw silk fabrics did not demonstrate any cytotoxic effects on osteoblasts because a high concentration of the serum alleviated the effects of these metal ions released from the fabrics. Thus, calcium-doped raw silk fabric is a promising antibacterial material that does not induce strong cytotoxicity. This study will facilitate the design of materials that are both antibacterial and safe.

Mechanical and antibacterial properties of ZnO/chitosan bio-composite films

In the current study, ZnO/chitosan bio-composite films were produced via solution-casting method. Two different ZnO powders, micrometer (d50 ≅ 1.5 μm) and nanometer sized (d50 ≅ 100 nm), were used to investigate the effect of ZnO particle size and concentration (0, 2, and 8% w/w of chitosan) on the mechanical and antibacterial properties of the ZnO/chitosan bio-composite films. The incorporation of the ZnO powders into the chitosan film resulted in an increase in the tensile strength (TS) and a decrease in the elongation at break (EB) values. Mechanical test results revealed that TS and EB properties were considerably affected (p < 0.05) by the concentration and particle size of the ZnO reinforcement. Disc diffusion method demonstrated good antibacterial activities of bio-composite films containing high amount of ZnO (8% w/w of chitosan) against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Bacillus subtilis. The growth-limiting effect of the films was more pronounced for S. aureus and K. pneumoniae. Due to enhanced TS and imparted antibacterial activity of the produced ZnO/chitosan bio-composite films, these materials are promising candidates for applications such as food packaging, wound dressing, and antibacterial coatings for various surfaces.

Targeted Delivery of Zinc Pyrithione to Skin Epithelia

Zinc pyrithione (ZnPT) is an anti-fungal drug delivered as a microparticle to skin epithelia. It is one of the most widely used ingredients worldwide in medicated shampoo for treating dandruff and seborrheic dermatitis (SD), a disorder with symptoms that include skin flaking, erythema and pruritus. SD is a multi-factorial disease driven by microbiol dysbiosis, primarily involving Malassezia yeast. Anti-fungal activity of ZnPT depends on the cutaneous availability of bioactive monomeric molecular species, occurring upon particle dissolution. The success of ZnPT as a topical therapeutic is underscored by the way it balances treatment efficacy with formulation safety. This review demonstrates how ZnPT achieves this balance, by integrating the current understanding of SD pathogenesis with an up-to-date analysis of ZnPT pharmacology, therapeutics and toxicology. ZnPT has anti-fungal activity with an average in vitro minimum inhibitory concentration of 10-15 ppm against the most abundant scalp skin Malassezia species (Malassezia globosa and Malassezia restrica). Efficacy is dependent on the targeted delivery of ZnPT to the skin sites where these yeasts reside, including the scalp surface and hair follicle infundibulum. Imaging and quantitative analysis tools have been fundamental for critically evaluating the therapeutic performance and safety of topical ZnPT formulations. Toxicologic investigations have focused on understanding the risk of local and systemic adverse effects following exposure from percutaneous penetration. Future research is expected to yield further advances in ZnPT formulations for SD and also include re-purposing towards a range of other dermatologic applications, which is likely to have significant clinical impact.

Bioabsorbable Osteofixation Materials for Maxillofacial Bone Surgery: A Review on Polymers and Magnesium-Based Materials

Clinical application of osteofixation materials is essential in performing maxillofacial surgeries requiring rigid fixation of bone such as trauma surgery, orthognathic surgery, and skeletal reconstruction. In addition to the use of titanium plates and screws, clinical applications and attempts using bioabsorbable materials for osteofixation surgery are increasing with demands to avoid secondary surgery for the removal of plates and screws. Synthetic polymeric plates and screws were developed, reaching satisfactory physical properties comparable to those made with titanium. Although these polymeric materials are actively used in clinical practice, there remain some limitations to be improved. Due to questionable physical strength and cumbersome molding procedures, interests in resorbable metal materials for osteofixation emerged. Magnesium (Mg) gained attention again in the last decade as a new metallic alternative, and numerous animal studies to evaluate the possibility of clinical application of Mg-based materials are being conducted. Thanks to these researches and studies, vascular application of Mg-based biomaterials was successful; however, further studies are required for the clinical application of Mg-based biomaterials for osteofixation, especially in the facial skeleton. The review provides an overview of bioabsorbable osteofixation materials in maxillofacial bone surgery from polymer to Mg.

In vitro evaluation of novel titania-containing borate bioactive glass scaffolds

Titanium-containing borate bioactive glass scaffolds (0, 5, 15, and 20 mol %, identified as BRT0, BRT1, BRT3, and BRT4) with a microstructure similar to that of human trabecular bone were prepared and evaluated in vitro for potential bone loss applications in revision total knee arthroplasty (rTKA). Methyl thiazolyl tetrazolium (MTT) cell viability assays of scaffold ion release extracts revealed that BRT0 scaffolds (0 mol % titanium) inhibited cell proliferation and activity at day 14. At day 30, all scaffold extracts decreased cell proliferation and activity significantly. However, live/dead cell assay results demonstrated that degradation products from all the scaffolds had no inhibitory effect on cell viability. Significant bactericidal efficacies of BRT3 extracts against Escherishia coli (Gram-negative) and BRT1 extracts against Staphylococcus aureus and Staphylococcus epidermidis (both Gram-positive bacteria) were demonstrated. Finally, evaluation of the cell/bioactive glass surface interactions showed well-spread cells on the surface of the BRT3 glass discs and BRT1 and BRT3 scaffolds, when compared to BRT0 and BRT4 scaffolds. The results indicate that by changing the Ti⁴⁺ :B³⁺ ratio, the ion release and consequently cell proliferation could be improved. in vitro results in this study demonstrate that BRT3 scaffolds could be a promising candidate for addressing bone loss in rTKAs; however, in vivo studies would be required to evaluate the effect of a dynamic environment on the cell and tissue response to the fabricated scaffolds.

Zinc supplementation during in vitro embryo culture increases inner cell mass and total cell numbers in bovine blastocysts1

Deficiencies in current embryo culture media likely contribute to the poor blastocyst development rates and pregnancy retention rates for in vitro produced (IVP) bovine embryos. Of special concern is the lack of micronutrients in these media formulations. One micronutrient of interest is zinc, an essential trace element involved with various enzyme and transcription factor activities. The objective of this work was to describe whether zinc sulfate supplementation during in vitro embryo culture affects bovine embryo development and blastomere numbers. Either 0, 2, 20, or 40 µM zinc sulfate was supplemented to presumptive zygotes cultured in synthetic oviductal fluid containing AAs and bovine serum albumin for 8 d. None of the treatments affected cleavage rates. Percentage of blastocysts on days 7 and 8 postfertilization was not affected by supplementing 2 or 20 µM zinc but were reduced (P < 0.05) with 40 µM zinc. In blastocysts harvested on day 8, inner cell mass (ICM) and total cell number were increased (P < 0.05) with 2 µM zinc supplementation but not with the other zinc concentrations. Numbers of trophectoderm cells were not affected by zinc treatment. In conclusion, supplementing zinc during bovine embryo culture did not impact blastocyst development but improved ICM cell numbers. This improvement in ICM cell number may have implications for improved pregnancy retention rates after IVP embryo transfer as smaller ICM sizes are associated with poor pregnancy success in cattle.

Live-Cell Imaging of Physiologically Relevant Metal Ions Using Genetically Encoded FRET-Based Probes

Essential biochemical reactions and processes within living organisms are coupled to subcellular fluctuations of metal ions. Disturbances in cellular metal ion homeostasis are frequently associated with pathological alterations, including neurotoxicity causing neurodegeneration, as well as metabolic disorders or cancer. Considering these important aspects of the cellular metal ion homeostasis in health and disease, measurements of subcellular ion signals are of broad scientific interest. The investigation of the cellular ion homeostasis using classical biochemical methods is quite difficult, often even not feasible or requires large cell numbers. Here, we report of genetically encoded fluorescent probes that enable the visualization of metal ion dynamics within individual living cells and their organelles with high temporal and spatial resolution. Generally, these probes consist of specific ion binding domains fused to fluorescent protein(s), altering their fluorescent properties upon ion binding. This review focuses on the functionality and potential of these genetically encoded fluorescent tools which enable monitoring (sub)cellular concentrations of alkali metals such as K⁺, alkaline earth metals including Mg²⁺ and Ca²⁺, and transition metals including Cu⁺/Cu²⁺ and Zn²⁺. Moreover, we discuss possible approaches for the development and application of novel metal ion biosensors for Fe²⁺/Fe³⁺, Mn²⁺ and Na⁺.

Penetration of an antimicrobial zinc-sugar alcohol complex into Streptococcus mutans biofilms

Mature biofilms are highly resistant to antimicrobial agents due to the presence of extracellular polymeric substances (EPS), which inhibit the penetration of external molecules. In this study, we developed a coordination compound consisting of zinc chloride and erythritol that exhibits penetrating and bactericidal activity against Streptococcus mutans biofilms. An in vitro biofilm model was established in microplates, and bactericidal activity against biofilms was evaluated using an Alamar blue assay. The cause of the antimicrobial activity of the zinc-erythritol mixture on mature biofilms was demonstrated using fast atom bombardment-mass spectrometry, confocal laser scanning microscopy and atomic force microscopy. We demonstrated that zinc chloride spontaneously formed cationic complexes with erythritol in water. The zinc-erythritol complexes reduced intra- and inter-molecular interactions between bacterial exopolysaccharides, a major component of EPS. This activity was confirmed by measuring the attenuation of the hardness of dried polysaccharides isolated from S. mutans biofilms. The reduction in the interactions between polysaccharides allowed the complexes to penetrate into biofilms and kill the embedded bacteria. While approximately 13% of biofilm-associated microbes were killed by a 10 min treatment with 6.6 mM zinc chloride, 45% were killed when a solution containing 19.8 mM erythritol and 6.6 mM zinc chloride was used. This strategy of leveraging the coordination properties of metal ions with sugar alcohols provides a simple way to effectively remove mature biofilms using only conventional substances without the need for intricate chemical synthesis processes.

The impact of nanomaterial characteristics on inhalation toxicity

During the last few decades, nanotechnology has evolved into a success story, apparent from a steadily increasing number of scientific publications as well as a large number of applications based on engineered nanomaterials (ENMs). Its widespread uses suggest a high relevance for consumers, workers and the environment, hence justifying intensive investigations into ENM-related adverse effects as a prerequisite for nano-specific regulations. In particular, the inhalation of airborne ENMs, being assumed to represent the most hazardous type of human exposure to these kinds of particles, needs to be scrutinized. Due to an increased awareness of possible health effects, which have already been seen in the case of ultrafine particles (UFPs), research and regulatory measures have set in to identify and address toxic implications following their almost ubiquitous occurrence. Although ENM properties differ from those of the respective bulk materials, the available assessment protocols are often designed for the latter. Despite the large benefit ensuing from the application of nanotechnology, many issues related to ENM behavior and adverse effects are not fully understood or should be examined anew. The traditional hypothesis that ENMs exhibit different or additional hazards due to their "nano" size has been challenged in recent years and ENM categorization according to their properties and toxicity mechanisms has been proposed instead. This review summarizes the toxicological effects of inhaled ENMs identified to date, elucidating the modes of action which provoke different mechanisms in the respiratory tract and their resulting effects. By linking particular mechanisms and adverse effects to ENM properties, grouping of ENMs based on toxicity-related properties is supposed to facilitate toxicological risk assessment. As intensive studies are still required to identify these "ENM classes", the need for alternatives to animal studies is evident and advances in cell-based test systems for pulmonary research are presented here. We hope to encourage the ongoing discussion about ENM risks and to advocate the further development and practice of suitable testing and grouping methods.

Exploring a wider range of Mg-Ca-Zn metallic glass as biocompatible alloys using combinatorial sputtering

In order to bypass the limitation of bulk metallic glasses fabrication, we synthesized thin film metallic glasses to study the corrosion characteristics of a wide atomic% composition range, Mg(35.9-63%)Ca(4.1-21%)Zn(17.9-58.3%), in simulated body fluid. We highlight a clear relationship between Zn content and corrosion current such that Zn-medium metallic glasses exhibit minimum corrosion. In addition, we found higher Zn content leads to a poor in vitro cell viability. These results showcase the benefit of evaluating a larger alloy compositional space to probe the limits of corrosion resistance and prescreen for biocompatible applications.

The cellular magnetic response and biocompatibility of biogenic zinc- and cobalt-doped magnetite nanoparticles

The magnetic moment and anisotropy of magnetite nanoparticles can be optimised by doping with transition metal cations, enabling their properties to be tuned for different biomedical applications. In this study, we assessed the suitability of bacterially synthesized zinc- and cobalt-doped magnetite nanoparticles for biomedical applications. To do this we measured cellular viability and activity in primary human bone marrow-derived mesenchymal stem cells and human osteosarcoma-derived cells. Using AC susceptibility we studied doping induced changes in the magnetic response of the nanoparticles both as stable aqueous suspensions and when associated with cells. Our findings show that the magnetic response of the particles was altered after cellular interaction with a reduction in their mobility. In particular, the strongest AC susceptibility signal measured in vitro was from cells containing high-moment zinc-doped particles, whilst no signal was observed in cells containing the high-anisotropy cobalt-doped particles. For both particle types we found that the moderate dopant levels required for optimum magnetic properties did not alter their cytotoxicity or affect osteogenic differentiation of the stem cells. Thus, despite the known cytotoxicity of cobalt and zinc ions, these results suggest that iron oxide nanoparticles can be doped to sufficiently tailor their magnetic properties without compromising cellular biocompatibility.

Formulation of polysaccharide-based nanoparticles for local administration into the oral cavity

The efficacy of treatments for oral ailments is often challenged by a low residence time of the conventional pharmaceutical formulations in the oral cavity. The residence time in the oral cavity could be improved by using bioadhesive formulations, such as preparations based on polysaccharides. This study describes the formulation and the evaluation of polysaccharide-based nanosystems as drug delivery systems addressed to the oral cavity. Nanoparticles based on chitosan, alginate or pectin were prepared through self-assembly by ionotropic gelation using oppositely charged crosslinkers (tripolyphosphate or zinc). Characteristics of nanoparticles at increasing crosslinker concentration provided the basis for selecting the most suitable formulations. The nanoparticles were tested for cytotoxicity against buccal cells (TR146) and for stability in a medium simulating pH, ionic strength, electrolyte composition and concentration of saliva. Alginate nanoparticles were the most stable in the salivary environment, while chitosan nanoparticles were the most cytocompatible. Alginate nanoparticles and pectin nanoparticles revealed possible cytotoxicity due to the presence of zinc. This knowledge is important in the early design of polymer-based nanoparticles for oral usage and for potential improving of the biocompatibility of the investigated nanoparticles with the oral environment.

Accelerating degradation rate of pure iron by zinc ion implantation

Pure iron has been considered as a promising candidate for biodegradable implant applications. However, a faster degradation rate of pure iron is needed to meet the clinical requirement. In this work, metal vapor vacuum arc technology was adopted to implant zinc ions into the surface of pure iron. Results showed that the implantation depth of zinc ions was about 60 nm. The degradation rate of pure iron was found to be accelerated after zinc ion implantation. The cytotoxicity tests revealed that the implanted zinc ions brought a slight increase on cytotoxicity of the tested cells. In terms of hemocompatibility, the hemolysis of zinc ion implanted pure iron was lower than 2%. However, zinc ions might induce more adhered and activated platelets on the surface of pure iron. Overall, zinc ion implantation can be a feasible way to accelerate the degradation rate of pure iron for biodegradable applications.

Bioluminescent bioreporter pad biosensor for monitoring water toxicity

Toxicants in water sources are of concern. We developed a tool that is affordable and easy-to-use for monitoring toxicity in water. It is a biosensor composed of disposable bioreporter pads (calcium alginate matrix with immobilized bacteria) and a non-disposable CMOS photodetector. Various parameters to enhance the sensor's signal have been tested, including the effect of alginate and bacterium concentrations. The effect of various toxicants, as well as, environmental samples were tested by evaluating their effect on bacterial luminescence. This is the first step in the creation of a sensitive and simple operative tool that may be used in different environments.

Degradation of zinc in saline solutions, plasma, and whole blood

The initial degradation of zinc has been investigated through exposures to simulated and real body fluids of increasing complexity: phosphate buffered saline (PBS), Ringer's saline solution, human plasma, and whole blood. Real body fluids were used to close the electrolyte gap between simulated and in vivo environment. Polarization of zinc in whole blood show a passive response not present in other electrolytes. The analysis shows a decrease in corrosion rate with time for plasma and whole blood and an increase for PBS and Ringer's. During exposure to plasma and whole blood a bi-layered corrosion product with poor adherence was formed over a uniformly corroding surface. The corrosion products comprise a mixture of inorganic material and biomolecules. Samples degrading in PBS were prone to localized corrosion and formed thick porous corrosion products of primarily zinc phosphates while in Ringer's solution a gel like layer of zinc carbonate was formed over an interface with shallow pits. The use of whole blood or plasma as electrolytes for short term in vitro evaluation of potential biodegradable metals may provide an improved understanding of the behavior in vivo, while Ringer's solution is preferred over PBS for long term degradation studies of zinc. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1141-1151, 2016.

Cytotoxicity evaluation of biodegradable Zn-3Mg alloy toward normal human osteoblast cells

The recent proposal of using Zn-based alloys for biodegradable implants was not supported with sufficient toxicity data. This work, for the first time, presents a thorough cytotoxicity evaluation of Zn-3Mg alloy for biodegradable bone implants. Normal human osteoblast cells were exposed to the alloy's extract and three main cell-material interaction parameters: cell health, functionality and inflammatory response, were evaluated. Results showed that at the concentration of 0.75mg/ml alloy extract, cell viability was reduced by ~50% through an induction of apoptosis at day 1; however, cells were able to recover at days 3 and 7. Cytoskeletal changes were observed but without any significant DNA damage. The downregulation of alkaline phosphatase protein levels did not significantly affect the mineralization process of the cells. Significant differences of cyclooxygenase-2 and prostaglandin E2 inflammatory biomarkers were noticed, but not interleukin 1-beta, indicating that the cells underwent a healing process after exposure to the alloy. Detailed analysis on the cell-material interaction is further discussed in this paper.

Zinc oxide as a new antimicrobial preservative of topical products: interactions with common formulation ingredients

Zinc oxide (ZnO) appears as a promising preservative for pharmaceutical or cosmetic formulations. The other ingredients of the formulations may have specific interactions with ZnO that alter its antimicrobial properties. The influence of common formulation excipients on the antimicrobial efficacy of ZnO has been investigated in simple model systems and in typical topical products containing a complex formulation. A wide variety of formulation excipients have been investigated for their interactions with ZnO: antioxidants, chelating agents, electrolytes, titanium dioxide pigment. The antimicrobial activity of ZnO against Escherichia coli was partially inhibited by NaCl and MgSO4 salts. A synergistic influence of uncoated titanium dioxide has been observed. The interference effects of antioxidants and chelating agents were quite specific. The interactions of these substances with ZnO particles and with the soluble species released by ZnO were discussed so as to reach scientific guidelines for the choice of the ingredients. The preservative efficacy of ZnO was assessed by challenge testing in three different formulations: an oil-in-water emulsion; a water-in-oil emulsion and a dry powder. The addition of ZnO in complex formulations significantly improved the microbiological quality of the products, in spite of the presence of other ingredients that modulate the antimicrobial activity.

Continuous microcarrier-based cell culture in a benchtop microfluidic bioreactor

Microfluidic bioreactors are expected to impact cell therapy and biopharmaceutical production due to their ability to control cellular microenvironments. This work presents a novel approach for continuous cell culture in a microfluidic system. Microcarriers (i.e., microbeads) are used as growth support for anchorage-dependent mammalian cells. This approach eases the manipulation of cells within the system and enables harmless extraction of cells. Moreover, the microbioreactor uses a perfusion function based on the biocompatible integration of a porous membrane to continuously feed the cells. The perfusion rate is optimized through simulations to provide a stable biochemical environment. Thermal management is also addressed to ensure a homogeneous bioreactor temperature. Eventually, incubator-free cell cultures of Drosophila S2 and PC3 cells are achieved over the course of a week using this bioreactor. In future applications, a more efficient alternative to harvesting cells from microcarriers is also anticipated as suggested by our positive results from the microcarrier digestion experiments.

Disrupted calcium homeostasis is involved in elevated zinc ion-induced photoreceptor cell death

Zinc (Zn), the second abundant trace element in living organisms, plays an important role in regulating cell metabolism, signaling, proliferation, gene expression and apoptosis. Meanwhile, the overload of Zn will disrupt the intracellular calcium homeostasis via impairing mitochondrial function. However, the specific molecular mechanism underlying zinc-induced calcium regulation remains poorly understood. In the present study, using zinc chloride (ZnCl2) as a stressor, we investigated the effect of exogenous Zn(2+) in regulating murine photoreceptor cell viability, reactive oxygen species (ROS), cell cycle distribution and calcium homeostasis as well as plasma membrane calcium ATPase (PMCA) isoforms (PMCA1 and PMCA2, i.e., ATP2B1, ATP2B2) expression. We found that the exogenous Zn(2+) in the exposure range (31.25-125.0 μmol/L) results in the overgeneration of ROS, cell cycle arrest at G2/M phases, elevation of cytosolic [Ca(2+)], inactivation of Ca(2+)-ATPase and reduction of both PMCA1 and PMCA2 in 661 W cells, and thus induces cell death. In conclusion, ZnCl2 exposure can elevate the cytosolic [Ca(2+)], disrupt the intracellular calcium homeostasis, further initiate Ca(2+)-dependent signaling pathway in 661 W cells, and finally cause cell death. Our results will facilitate the understanding of cell death induced by the zinc ion-mediated calcium homeostasis disruption.

Responses of hepatic metallothioneins and apoptotic activity in Carassius auratus gibelio witness a release of cobalt and zinc from waterborne nanoscale composites

The main goal of this study was to evaluate the ability of fish Carassius auratus tissues to release cobalt (Co) and zinc (Zn) cations present in the applied Co- and Zn-containing nanoscale composites (NCs). Male fish was subjected to 14day long action of Co- and Zn-NCs, as well as of Co(2+) and Zn(2+) or polymeric substance (PS) used for the NC preparation and derived from the vinylpyrrolidone. 50μg∙L(-1) of Co and 100μg∙L(-1) of Zn were applied either as a salt or a nanocomposite. Both Co and Co-NC increased (3.1 and 2.3 times, respectively) concentration of total Co, metallothionein-related Co (3.7 and 6.6 times, respectively) and thiols (by 71 and 95%, respectively), and caspase-3 activity (2.2 and 3.7 times, respectively) in the fish liver. At the same time, Co and Co-NC decreased glutathione level (1.8 and 1.9 times, respectively) and activated vitellogenesis (5.1 and 9.9 times, respectively) in the fish liver. Both Zn and Zn-NC increased markedly concentrations of metallothionein-related Zn (2.4 and 2.9 times, respectively) and Cu (2.8 and 3.2 times, respectively), and decreased metallothionein-related thiol (2.5 and 4.2 times, respectively), oxyradical (by 30.4 and 44.2%, respectively), and caspase-3 (3.0 and 5.3 times, respectively) levels in the fish liver. These peculiarities are common for metal and metal-NC and witness a release of metal from NS in fish organism. The differences in the levels of DNA strand breaks, biotransformation enzymes and total Zn levels in the liver were dependent on the kind of exposure.

Cytotoxicity of nanoscaled metal-organic frameworks

A series of fourteen porous Metal-Organic Frameworks (MOFs) with different compositions (Fe, Zn, and Zr; carboxylates or imidazolates) and structures have been successfully synthesised at the nanoscale and fully characterised by XRPD, FTIR, TGA, N₂ porosimetry, TEM, DLS and ζ-potential. Their toxicological assessment was performed using two different cell lines: human epithelial cells from foetal cervical carcinoma (HeLa) and murine macrophage cell line (J774). It appears that MOF nanoparticles (NPs) exhibit low cytotoxicity, comparable to those of other commercialised nanoparticulate systems, the less toxic being the Fe carboxylate and the more toxic being the zinc imidazolate NPs. The cytotoxicity values, higher in J774 cells than in HeLa cells, are mainly function of their composition and cell internalisation capacity. Finally, cell uptake of one of the most relevant Fe-MOF-NPs for drug vectorisation has been investigated by confocal microscopy studies, and indicates a faster kinetics of cell penetration within J774 compared to HeLa cells.

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.

Antimicrobial applications of nanotechnology: methods and literature

The need for novel antibiotics comes from the relatively high incidence of bacterial infection and the growing resistance of bacteria to conventional antibiotics. Consequently, new methods for reducing bacteria activity (and associated infections) are badly needed. Nanotechnology, the use of materials with dimensions on the atomic or molecular scale, has become increasingly utilized for medical applications and is of great interest as an approach to killing or reducing the activity of numerous microorganisms. While some natural antibacterial materials, such as zinc and silver, possess greater antibacterial properties as particle size is reduced into the nanometer regime (due to the increased surface to volume ratio of a given mass of particles), the physical structure of a nanoparticle itself and the way in which it interacts with and penetrates into bacteria appears to also provide unique bactericidal mechanisms. A variety of techniques to evaluate bacteria viability, each with unique advantages and disadvantages, has been established and must be understood in order to determine the effectiveness of nanoparticles (diameter ≤100 nm) as antimicrobial agents. In addition to addressing those techniques, a review of select literature and a summary of bacteriostatic and bactericidal mechanisms are covered in this manuscript.

Alveolar epithelial cell injury due to zinc oxide nanoparticle exposure

RATIONALE

Although inhalation of zinc oxide (ZnO) nanoparticles (NPs) is known to cause systemic disease (i.e., metal fume fever), little is known about mechanisms underlying injury to alveolar epithelium.

OBJECTIVES

Investigate ZnO NP-induced injury to alveolar epithelium by exposing primary cultured rat alveolar epithelial cell monolayers (RAECMs) to ZnO NPs.

METHODS

RAECMs were exposed apically to ZnO NPs or, in some experiments, to culture fluid containing ZnCl₂ or free Zn released from ZnO NPs. Transepithelial electrical resistance (R(T)) and equivalent short-circuit current (I(EQ)) were assessed as functions of concentration and time. Morphologic changes, lactate dehydrogenase release, cell membrane integrity, intracellular reactive oxygen species (ROS), and mitochondrial activity were measured.

MEASUREMENTS AND MAIN RESULTS

Apical exposure to 176 μg/ml ZnO NPs decreased R(T) and I(EQ) of RAECMs by 100% over 24 hours, whereas exposure to 11 μg/ml ZnO NPs had little effect. Changes in R(T) and I(EQ) caused by 176 μg/ml ZnO NPs were irreversible. ZnO NP effects on R(T) yielded half-maximal concentrations of approximately 20 μg/ml. Apical exposure for 24 hours to 176 μg/ml ZnO NPs induced decreases in mitochondrial activity and increases in lactate dehydrogenase release, permeability to fluorescein sulfonic acid, increased intracellular ROS, and translocation of ZnO NPs from apical to basolateral fluid (most likely across injured cells and/or damaged paracellular pathways).

CONCLUSIONS

ZnO NPs cause severe injury to RAECMs in a dose- and time-dependent manner, mediated, at least in part, by free Zn released from ZnO NPs, mitochondrial dysfunction, and increased intracellular ROS.

UV-A induced oxidative stress is more prominent in naturally pigmented aged human RPE cells compared to non-pigmented human RPE cells independent of zinc treatment

To investigate the effects of zinc supplementation on human amelanotic (ARPE-19) and native pigmented retinal pigment epithelial cells (hRPE) under normal light conditions and after ultraviolet A light exposure. hRPE cells, containing both melanin and lipofuscin granules, were prepared from human donor eyes of 60-70 year old patients. Cells of the amelanotic ARPE-19 cell line and pigmented hRPE cells were treated with zinc chloride and subjected to oxidative stress by UV-A irradiation. Intracellular H(2)O(2) formation was measured using a fluorescence oxidation assay. Additionally, apoptosis and viability assays were performed. Control cells were treated identically except for irradiation and zinc supplementation. Under normal light conditions, zinc treated hRPE cells produced less H(2)O(2) than unsupplemented hRPE cells. Viability and apoptosis events did not change. After UV-A irradiation, ARPE and hRPE cells were greatly impaired in all tests performed compared to the non-irradiated controls. No differences were found after zinc supplementation. hRPE cells showed a higher apoptosis and mortality rate than non-pigmented cells when stressed by UV-A light. ARPE cells never showed any zinc related effects. In contrast, without irradiation, zinc supplementation reduced H(2)O(2) production in pigmented hRPE cells slightly. We did not find any zinc effect in irradiated hRPE cells. After UV light exposure, pigmented cells showed a higher apoptosis and mortality than cells lacking any pigmentation. We conclude that cells with pigmentation consisting of melanin and lipofuscin granules have more prooxidative than antioxidative capacity when stressed by UV light exposure compared to cells lacking any pigmentation.

In vitro cytotoxicity of oxide nanoparticles: comparison to asbestos, silica, and the effect of particle solubility

Early indicators for nanoparticle-derived adverse health effects should provide a relative measure for cytotoxicity of nanomaterials in comparison to existing toxicological data. We have therefore evaluated a human mesothelioma and a rodent fibroblast cell line for in vitro cytotoxicity tests using seven industrially important nanoparticles. Their response in terms of metabolic activity and cell proliferation of cultures exposed to 0-30 ppm nanoparticles (microg g(-1)) was compared to the effects of nontoxic amorphous silica and toxic crocidolite asbestos. Solubility was found to strongly influence the cytotoxic response. The results further revealed a nanoparticle-specific cytotoxic mechanism for uncoated iron oxide and partial detoxification or recovery after treatment with zirconia, ceria, or titania. While in vitro experiments may never replace in vivo studies, the relatively simple cytotoxic tests provide a readily available pre-screening method.

Zinc uptake and storage: the role of fundus pigmentation

BACKGROUND

Age-related macular degeneration (AMD) is associated with lower melanin pigmentation and is more prevalent among the elderly Caucasian population than among Africans. A correlation between light iris colour, fundus pigmentation and the incidence of AMD is reported. Moreover, melanin represents the main storage of zinc in the eye. Zinc enhances antioxidant capacity through its function as a cofactor of important enzymes or by influencing gene expression of regulatory elements in the eye. In this study, we investigated the uptake and storage of zinc in the human choroid/retinal pigment epithelium (RPE) complexes in dependence on the fundus pigmentation as judged by the iris colour.

MATERIAL AND METHODS

Choroid/RPE complexes of blue and brown human eyes were used. Tissues without any substitution served as controls. Specimens from choroid/RPE complexes were incubated with 100 microM zinc chloride for 24 h. After incubation, pieces of the complexes were stored to investigate the uptake of zinc. The rest of the tissues were kept for 3 and 7 days in culture medium (DMEM) for storage examination. The concentration of zinc was measured by inductively coupled plasma mass spectrometry.

RESULTS

After 24 h of zinc treatment the concentration of zinc in the choroid/RPE complexes of blue eyes was not significantly increased. The concentration of zinc in highly pigmented tissues (brown eyes) was increased by the factor 5.1 after 24 h and remained at high levels after 3 days (factor 4.4) and 7 days (factor 2.8).

CONCLUSIONS

Zinc uptake in the choroid/RPE complex correlates to the iris colour. Alterations of the degree of iris pigmentation result in differences of zinc uptake and storage in the choroids. A potential protective role of zinc may be more prominent in dark- than in light-coloured eyes.

The Pigmentation of Human Iris Influences the Uptake and Storing of Zinc

Age-related macular degeneration (AMD) is more prevalent among the elderly Caucasians than in Africans. A significant association between light iris colour, fundus pigmentation and incidence of AMD is reported, suggesting a possible correlation with melanin pigment. Zinc is known to bind to melanin in pigmented tissues and to enhance antioxidant capacity by function as a cofactor or gene expression factor of antioxidant enzymes in the eye. In this in vitro study, we investigated the uptake and storage of zinc in human irides. Irides of blue and brown human eyes were used. The number of melanocytes was measured. Tissues without any treatment served as controls. The irides were incubated with 100 microM zinc chloride in culture medium for 24 h. Specimens of the tissues were stored for the uptake examination. The remained pieces were further incubated for 3 and 7 d to investigate the storage of zinc. The concentration of zinc was measured by inductively coupled plasma mass spectrometry (ICP-MS). Melanocytes count was significantly higher in the brown tissues (P < 0.0001). Zinc concentration of blue coloured irides after 24 h zinc treatment was close to the controls. We did not observe any significant storing. In contrast, the concentration of zinc in brown irides was significantly increased after 24 h (P < or = 0.01) and remained at a high level for 7 d. The uptake of zinc is likely dependent on the amount of pigmentation in human iris. Therefore, we assume that in patients suffering from AMD the degree of pigmentation of the irides and eventually fundi should be under consideration when the patients are treated with zinc supplementation.

In vitro assessment of copper-induced toxicity in the human hepatoma line, Hep G2

Copper, though essential, is highly toxic when present in excess, as in Wilson disease, a genetic disorder of hepatic copper metabolism. We hypothesized that mitochondria are a major target of copper-induced cytotoxicity in Wilson disease. We used the human hepatoma line Hep G2 to examine copper-mediated cytotoxicity and three different methods to assess organelle damage: MTT assay (mitochondria), neutral red (NR; lysosomes) and Trypan blue exclusion assay (TB; plasma membrane). For all assays, cells at approximately 60% confluence in microtitre plates were incubated with CuCl(2) (concentration range: 50-100-150-200 microM) for 24 or 48 h. Results were expressed as percent of untreated control. At 24 h, cytotoxicity as detected by NR assay was significantly higher at all concentrations of copper than for MTT or TB ( p<0.005 at all concentrations). Cytotoxicity as detected by MTT was higher than that detected by TB at all concentrations except at 200 microM (p<0.05 for 50 microM, p<0.005 for 100 microM, p = 0.001 for 150 microM). Results at 48 h were similar (NR versus others: p <0.001 MTT versus TB: NS except at 150 microM where p<0.01). We investigated reactive oxygen species (ROS) production in copper-associated hepatocytoxicity by incubating sub-confluent cells with 2('),7(')-dichlorodihydrofluorescein diacetate dye plus copper (concentration range: 0-200 microM) for 1-1.5 h. Copper, but not zinc, produced significant increases in ROS (p<0.001). In summary, Hep G2 lysosomes appeared more susceptible to Cu-mediated damage than mitochondria; the cell membrane was highly resistant to damage.