Wei-Chun Chin

Zinc oxide–engineered nanoparticles: Dissolution and toxicity to marine phytoplankton

It is now widely recognized that dissolution plays an important role in metallic nanoparticle toxicity, but to what extent remains unclear. In the present study, it was found that ZnO-engineered nanoparticle (ZnO-EN) toxicity to the marine diatom Thalassiosira pseudonana could be solely explained by zinc ion (Zn(2+) ) release. This is based on comparable inhibitive effects from ZnO-EN addition media, with or without the ultrafiltration through a 3-kD membrane, and from the media in which only Zn(2+) was added. Considering the importance of dissolution in ZnO-EN toxicity, Zn(2+) release kinetics was systematically examined under different conditions for the first time. It was found to be mainly influenced by pH as well as the specific surface area of the nanoparticles. In contrast, natural organic compounds either enhance or reduce Zn(2+) release, depending on their chemical composition and concentration. Compared with deionized water, ZnO-EN dissolution rates were accelerated in seawater, whereas ZnO-EN concentration itself only had a very small effect on Zn(2+) release. Therefore, dissolution as affected by several physicochemical factors should not be neglected in the effects, behavior, and fate of ENs in the environment.

Intracellular Uptake: A Possible Mechanism for Silver Engineered Nanoparticle Toxicity to a Freshwater Alga Ochromonas danica

The behavior and toxicity of silver engineered nanoparticles (Ag-ENs) to the mixotrophic freshwater alga Ochromonas danica were examined in the present study to determine whether any other mechanisms are involved in their algal toxicity besides Ag+ liberation outside the cells. Despite their good dispersability, the Ag-ENs were found to continuously aggregate and dissolve rapidly. When the initial nanoparticle concentration was lower than 10 µM, the total dissolved Ag+ concentration ([Ag+]T) in the suspending media reached its maximum after 1 d and then decreased suggesting that Ag+ release might be limited by the nanoparticle surface area under these conditions. Furthermore, Ag-EN dissolution extent remarkably increased in the presence of glutathione. In the Ag-EN toxicity experiment, glutathione was also used to eliminate the indirect effects of Ag+ that was released. However, remarkable toxicity was still observed although the free Ag+ concentration in the media was orders of magnitude lower than the non-observed effect concentration of Ag+ itself. Such inhibitive effects were mitigated when more glutathione was added, but could never be completely eliminated. Most importantly, we demonstrate, for the first time, that Ag-ENs can be taken in and accumulated inside the algal cells, where they exerted their toxic effects. Therefore, nanoparticle internalization may be an alternative pathway through which algal growth can be influenced.

A new role for bicarbonate in mucus formation

The impact of small anions on the physical properties of gel-forming mucin has been almost overlooked relative to that of cations. Recently, based on the coincident abnormalities in HCO(3)(-) secretion and abnormal mucus formed in the hereditary disease cystic fibrosis (CF), HCO(3)(-) was hypothesized to be critical in the formation of normal mucus by virtue of its ability to sequester Ca(2+) from condensed mucins being discharged from cells. However, direct evidence of the impact of HCO(3)(-) on mucus properties is lacking. Herein, we demonstrate for the first time that mucin diffusivity (∼1/viscosity) increases as a function of [HCO(3)(-)]. Direct measurements of exocytosed mucin-swelling kinetics from airway cells showed that mucin diffusivity increases by ∼300% with 20 mM extracellular HCO(3)(-) concentration. Supporting data indicate that HCO(3)(-) reduces free Ca(2+) concentration and decreases the amount of Ca(2+) that remains associated with mucins. The results demonstrate that HCO(3)(-) enhances mucin swelling and hydration by reducing Ca(2+) cross-linking in mucins, thereby decreasing its viscosity and likely increasing its transportability. In addition, HCO(3)(-) can function as a Ca(2+) chelator like EGTA to disperse mucin aggregates. This study indicates that poor HCO(3)(-) availability in CF may explain why secreted mucus remains aggregated and more viscous in affected organs. These insights bear on not only the fundamental pathogenesis in CF, but also on the process of gel mucus formation and release in general.

Aggregation, Dissolution, and Stability of Quantum Dots in Marine Environments: Importance of Extracellular Polymeric Substances

There is an increasing concern that a considerable fraction of engineered nanoparticles (ENs), including quantum dots (QDs), will eventually find their way into the marine environment and have negative impacts on plankton. As ENs enter the ocean, they will encounter extracellular polymeric substances (EPS) from microbial sources before directly interacting with plankton cells. In this study, EPS harvested from four phytoplankton species, Amphora sp., Dunaliella tertiolecta, Phaeocystis globosa, and Thalassiosira pseudonana, were examined for potential interactions with CdSe nonfunctionalized and functionalized (carboxyl- and amine-) QDs in artificial seawater. Our results show that EPS do not reduce the solubility of QDs but rather decrease their stability. The degradation rate of QDs was positively correlated to the protein composition of EPS (defined by the ratio of protein/carbohydrate). Two approaches showed significant inhibition to the degradation of carboxyl-functionalized QDs: (1) the presence of an antioxidant, such as N-acetyl cysteine, and (2) absence of light. Owing to the complexity in evaluating integrated effects of QDs intrinsic properties and the external environmental factors that control the stability of QDs, conclusions must be based on a careful consideration of all these factors when attempting to evaluate the bioavailability of QDs and other ENs in the marine environments.

A Mixture of Anatase and Rutile TiO2 Nanoparticles induces Histamine Secretion in Mast Cells

BackgroundHistamine released from mast cells, through complex interactions involving the binding of IgE to FcεRI receptors and the subsequent intracellular Ca2+ signaling, can mediate many allergic/inflammatory responses. The possibility of titanium dioxide nanoparticles (TiO2 NPs), a nanomaterial pervasively used in nanotechnology and pharmaceutical industries, to directly induce histamine secretion without prior allergen sensitization has remained uncertain.ResultsTiO2 NP exposure increased both histamine secretion and cytosolic Ca2+ concentration ([Ca2+]C) in a dose dependent manner in rat RBL-2H3 mast cells. The increase in intracellular Ca2+ levels resulted primarily from an extracellular Ca2+ influx via membrane L-type Ca2+ channels. Unspecific Ca2+ entry via TiO2 NP-instigated membrane disruption was demonstrated with the intracellular leakage of a fluorescent calcein dye. Oxidative stress induced by TiO2 NPs also contributed to cytosolic Ca2+ signaling. The PLC-IP3-IP3 receptor pathways and endoplasmic reticulum (ER) were responsible for the sustained elevation of [Ca2+]C and histamine secretion.ConclusionOur data suggests that systemic circulation of NPs may prompt histamine release at different locales causing abnormal inflammatory diseases. This study provides a novel mechanistic link between environmental TiO2 NP exposure and allergen-independent histamine release that can exacerbate manifestations of multiple allergic responses.

Effects of Engineered Nanoparticles on the Assembly of Exopolymeric Substances from Phytoplankton

The unique properties of engineered nanoparticles (ENs) that make their industrial applications so attractive simultaneously raise questions regarding their environmental safety. ENs exhibit behaviors different from bulk materials with identical chemical compositions. Though the nanotoxicity of ENs has been studied intensively, their unintended environmental impacts remain largely unknown. Herein we report experimental results of EN interactions with exopolymeric substances (EPS) from three marine phytoplankton species: Amphora sp., Ankistrodesmus angustus and Phaeodactylum tricornutum. EPS are polysaccharide-rich anionic colloid polymers released by various microorganisms that can assemble into microgels, possibly by means of hydrophobic and ionic mechanisms. Polystyrene nanoparticles (23 nm) were used in our study as model ENs. The effects of ENs on EPS assembly were monitored with dynamic laser scattering (DLS). We found that ENs can induce significant acceleration in Amphora sp. EPS assembly; after 72 hours EN-EPS aggregation reached equilibrium, forming microscopic gels of ∼4–6 µm in size. In contrast, ENs only cause moderate assembly kinetic acceleration for A. angustus and P. tricornutum EPS samples. Our results indicate that the effects of ENs on EPS assembly kinetics mainly depend on the hydrophobic interactions of ENs with EPS polymers. The cycling mechanism of EPS is complex. Nonetheless, the change of EPS assembly kinetics induced by ENs can be considered as one potential disturbance to the marine carbon cycle.

Mucin Secretion Induced by Titanium Dioxide Nanoparticles

Nanoparticle (NP) exposure has been closely associated with the exacerbation and pathophysiology of many respiratory diseases such as Chronic Obstructive Pulmonary Disease (COPD) and asthma. Mucus hypersecretion and accumulation in the airway are major clinical manifestations commonly found in these diseases. Among a broad spectrum of NPs, titanium dioxide (TiO2), one of the PM10 components, is widely utilized in the nanoindustry for manufacturing and processing of various commercial products. Although TiO2 NPs have been shown to induce cellular nanotoxicity and emphysema-like symptoms, whether TiO2 NPs can directly induce mucus secretion from airway cells is currently unknown. Herein, we showed that TiO2 NPs (<75 nm) can directly stimulate mucin secretion from human bronchial ChaGo-K1 epithelial cells via a Ca2+ signaling mediated pathway. The amount of mucin secreted was quantified with enzyme-linked lectin assay (ELLA). The corresponding changes in cytosolic Ca2+ concentration were monitored with Rhod-2, a fluorescent Ca2+ dye. We found that TiO2 NP-evoked mucin secretion was a function of increasing intracellular Ca2+ concentration resulting from an extracellular Ca2+ influx via membrane Ca2+ channels and cytosolic ER Ca2+ release. The calcium-induced calcium release (CICR) mechanism played a major role in further amplifying the intracellular Ca2+ signal and in sustaining a cytosolic Ca2+ increase. This study provides a potential mechanistic link between airborne NPs and the pathoetiology of pulmonary diseases involving mucus hypersecretion.

Functionalized Positive Nanoparticles Reduce Mucin Swelling and Dispersion

Multi-functionalized nanoparticles (NPs) have been extensively investigated for their potential in household and commercial products, and biomedical applications. Previous reports have confirmed the cellular nanotoxicity and adverse inflammatory effects on pulmonary systems induced by NPs. However, possible health hazards resulting from mucus rheological disturbances induced by NPs are underexplored. Accumulation of viscous, poorly dispersed, and less transportable mucus leading to improper mucus rheology and dysfunctional mucociliary clearance are typically found to associate with many respiratory diseases such as asthma, cystic fibrosis (CF), and COPD (Chronic Obstructive Pulmonary Disease). Whether functionalized NPs can alter mucus rheology and its operational mechanisms have not been resolved. Herein, we report that positively charged functionalized NPs can hinder mucin gel hydration and effectively induce mucin aggregation. The positively charged NPs can significantly reduce the rate of mucin matrix swelling by a maximum of 7.5 folds. These NPs significantly increase the size of aggregated mucin by approximately 30 times within 24 hrs. EGTA chelation of indigenous mucin crosslinkers (Ca2+ ions) was unable to effectively disperse NP-induced aggregated mucins. Our results have demonstrated that positively charged functionalized NPs can impede mucin gel swelling by crosslinking the matrix. This report also highlights the unexpected health risk of NP-induced change in mucus rheological properties resulting in possible mucociliary transport impairment on epithelial mucosa and related health problems. In addition, our data can serve as a prospective guideline for designing nanocarriers for airway drug delivery applications.

Ultrafine titanium dioxide nanoparticles induce cell death in human bronchial epithelial cells

Titanium dioxide (TiO2) nanoparticles (TNPs), once perceived as harmless, have been shown to induce cytotoxicity on various cell types under UV radiation. However, whether TNPs elicit cell death in the absence of UV has not been thoroughly studied. This study aims to investigate the TNPs-induced cell death mechanism in UV-absent condition by examining the reduction of cell viability and apoptotic cell death characteristics in the human bronchial epithelial cell line, Chago-K1. The Chago-K1 cells were exposed to TNPs for 24 h at concentrations ranging from 0.1 to 2 mg mL−1. CCK-8 and Live/Dead assays demonstrating diminishing cell viability indicate that peak cell death occurred around 2 mg mL−1 TNPs after 24 h treatment in darkness. Apoptotic related cell death mechanisms were demonstrated by chromatin condensation and translocation of phosphatidylserine with Annexin V staining. Here we demonstrate that ultrafine TNPs (75 nm) in darkness can induce significant cytotoxicity on the Chago-K1 cells possibly through apoptotic pathways.

Carbonaceous particles reduce marine microgel formation

An increase in ambient carbonaceous particle (CNP) levels has been found, potentially leading to significant environmental/health hazards. These particles will ultimately enter the oceanic environment and interact with dissolved organic carbon. However, a detailed mechanistic understanding of their behavior, transport, and fate in marine systems is still much needed. This study, using carbon black (CB, 14 nm) nanoparticles as a model, aimed to investigate the impact of CNPs on marine microgel formation, a critical shunt between DOC and particulate organic carbon that potentially represents a ~70-Gt organic carbon flux. We found that CB can enhance the stability of DOC polymers and reduce microgel equilibrium sizes in concentration as low as 1 μgL−1 CB, possibly due to negative surface charges on CB that decrease cross-linking bridges through Ca2+ bonds. The reduction of marine microgel formation induced by CB could lead to a decrease in the downward transportation of microbial substrates and nutrients, and therefore, could have a significant impact on the carbon cycle and the marine ecosystem.