Solomon W. Leung

Exposure to titanium dioxide and other metallic oxide nanoparticles induces cytotoxicity on human neural cells and fibroblasts

The use of titanium dioxide (TiO2) in various industrial applications (eg, production of paper, plastics, cosmetics, and paints) has been expanding thereby increasing the occupational and other environmental exposure of these nanoparticles to humans and other species. However, the health effects of exposure to TiO2 nanoparticles have not been systematically assessed even though recent studies suggest that such exposure induces inflammatory responses in lung tissue and cells. Because the effects of such nanoparticles on human neural cells are unknown, we have determined the putative cytotoxic effects of these nanoparticles on human astrocytes-like astrocytoma U87 cells and compared their effects on normal human fibroblasts. We found that TiO2 micro- and nanoparticles induced cell death on both human cell types in a concentration-related manner. We further noted that zinc oxide (ZnO) nanoparticles were the most effective, TiO2 nanoparticles the second most effective, and magnesium oxide (MgO) nanoparticles the least effective in inducing cell death in U87 cells. The cell death mechanisms underlying the effects of TiO2 micro- and nanoparticles on U87 cells include apoptosis, necrosis, and possibly apoptosis-like and necrosis-like cell death types. Thus, our findings may have toxicological and other pathophysiological implications on exposure of humans and other mammalian species to metallic oxide nanoparticles.

Functional enhancement of chitosan and nanoparticles in cell culture, tissue engineering, and pharmaceutical applications

As a biomaterial, chitosan has been widely used in tissue engineering, wound healing, drug delivery, and other biomedical applications. It can be formulated in a variety of forms, such as powder, film, sphere, gel, and fiber. These features make chitosan an almost ideal biomaterial in cell culture applications, and cell cultures arguably constitute the most practical way to evaluate biocompatibility and biotoxicity. The advantages of cell cultures are that they can be performed under totally controlled environments, allow high throughput functional screening, and are less costly, as compared to other assessment methods. Chitosan can also be modified into multilayer composite by combining with other polymers and moieties to alter the properties of chitosan for particular biomedical applications. This review briefly depicts and discusses applications of chitosan and nanoparticles in cell culture, in particular, the effects of chitosan and nanoparticles on cell adhesion, cell survival, and the underlying molecular mechanisms: both stimulatory and inhibitory influences are discussed. Our aim is to update the current status of how nanoparticles can be utilized to modify the properties of chitosan to advance the art of tissue engineering by using cell cultures.

Treatment of human astrocytoma U87 cells with silicon dioxide nanoparticles lowers their survival and alters their expression of mitochondrial and cell signaling proteins.

Recent evidence suggests silicon dioxide micro- and nanoparticles induce cytotoxic effects on lung cells. Thus, there is an increasing concern regarding their potential health hazard. Nevertheless, the putative toxicity of nanoparticles in mammalian cells has not yet been systematically investigated. We previously noted that several metallic oxide nanoparticles exert differential cytotoxic effects on human neural and nonneural cells. Therefore, we hypothesized that silicon dioxide nanoparticles induce cytotoxicity in U87 cells by lowering their survival by decreasing cell survival signaling and disturbing mitochondrial function. To investigate this hypothesis, we determined the activities of the key mitochondrial enzymes, citrate synthase and malate dehydrogenase, in astrocytoma U87 cells treated with silicon dioxide nanoparticles. In addition, we studied the expression of the mitochondrial DNA-encoded proteins, cytochrome C oxidase II and nicotinamide adenine dinucleotide (NADPH) dehydrogenase subunit 6, and cell signaling pathway protein extracellular signal-regulated kinase (ERK) and phosphorylated ERK in treated U87 cells. The activated form of ERK controls cell growth, differentiation, and proliferation. In parallel, we determined survival of U87 cells after treating them with various concentrations of silicon dioxide nanoparticles. Our results indicated that treatment with silicon dioxide nanoparticles induced decreases in U87 cell survival in a dose-related manner. The activities of citrate synthase and malate dehydrogenase in treated U87 cells were increased, possibly due to an energetic compensation in surviving cells. However, the expression of mitochondrial DNA-encoded cytochrome C oxidase subunit II and NADH dehydrogenase subunit 6 and the cell signaling protein ERK and phosphorylated ERK were altered in the treated U87 cells, suggesting that silicon dioxide nanoparticles induced disruption of mitochondrial DNA-encoded protein expression, leading to decreased mitochondrial energy production and decreased cell survival/proliferation signaling. Thus, our results strongly suggest that the cytotoxicity of silicon dioxide nanoparticles in human neural cells implicates altered mitochondrial function and cell survival/proliferation signaling.

An unidentified chloramine decomposition product. I: Chemistry and characteristics

Abstract This paper reports on a study of the chemistry and structural characteristics of an unidentified product found in organic free aqueous solution in the chloramination disinfection of drinking water. Mass balance on decomposing chloramine solutions were made using spectrophotometric, titrimetric and ion chromatographic methods in the presence and absence of added nitrite. The concentration of the unidentified product was determined from the difference of the measured and predicted chloramine spectra. Nitrite is believed to have an important role in the formation of the unidentified product. Added nitrite can dramatically increase the concentration of this product, and it is believed that nitrite may be involved in its formation during slow chloramine decomposition. Nitrite is not expected to be stable in the presence of chloramines as predicted from prior studies. Nitrite was observed, however, in rapidly decomposing solutions of dichloramine. Nitrate, chloride and nitrite were observed in photolysis of the unidentified product. The unidentified product contains both nitrogen and chlorine, and has an estimated molar absorptivity of 5000 M −1 cm −1 from the mass balance of chloride if one chlorine per molecule is assumed. Nitrate was also observed along with the unidentified product in slow chloramine decomposition at near or above neutral pH; however, the unidentified product was not detected in chloramine solutions at pH 3.5, but nitrite was observed. The formation of the unidentified product is not believed to be acid or base catalyzed, but is proportional to the total oxidant lost in slow monochloramine decomposition. Monochloramine is not likely involved in the rate-limiting step in the formation of the unidentified product.

An unidentified chloramine decomposition product-II. A proposed formation mechanism

Abstract This study proposed an empirical rate expression for the formation of an unidentified product generated in chloramine decomposition; the rate expression was incorporated into an existing model describing the fate and speciation in the chlorine-ammonia system. Specific rate constants were estimated based on experimental data and trial-and-errors computing technique. A simple mechanism was proposed for formation of the unidentified product. This mechanism hypothesized that an intermediate species was formed in the reactions of chloramine decomposition. The intermediate species was assumed reacting with nitrite to form the unidentified product, it also might react with HOCl to form other end-product(s). Concentration of the intermediate species and nitrite formed were estimated by pseudo steady-state assumption in the chlorine-ammonia system.

Critical Review of Removal of Nano Materials in Waste Streams

Industrial applications of nanomaterials (NMs) are rising drastically in recent years and the commercial value of these materials can reach over

Characterization of an ultra-high performance immunosensor modified with sol-gel nanogold particles and its applications

100 billion in 5 years. Major effort in nano research has been devoted to the utilities of the materials, only minimum effort has been directed to the disposal, reuse, and recycle of these new forms of materials. Due to their unique sizes and sharps, nanomaterials possess unique characteristics and toxicity that are not expected from their counterparts in meso/micro forms. At the present time, there are no regulations governing the handling and disposals of NMs, but recent research demonstrated that NMs are more hazardous than we realize. A main reason why less caution is being exercised by the general public regarding NMs is that the measurement and quantitation of NMs are difficult, which lead to difficulties in monitoring, thus regulation. This article critically reviewed over the issues stemming from the development of NMs, especially the challenges of measurement and disposal of these materials in landfills.

Fast-Response Smart Self-Assembling Biosensors for Biomarker Detection

Our research group is developing a series of biosensors that are capable of measuring metabolites and chemical species at extremely low levels for various biomedical and environmental applications, such as DNAs and biomarkers for cancer detections as well as pollutants for environmental monitoring. As a demonstrative model in this study, we are reporting an immunosensor fabricated in our laboratory for the detection of human immunoglobulin G (HIgG) which is the smallest but the most common anti-infection antibody that makes up of majority (75-80%) of all antibodies in our body. HIgG can bind with many pathogens and neutralizes invading toxins. The level of IgG concentration within an individual is a good indicator of the person’s immune status. The immunosensor consists of an anchoring electrode that is modified with a layer of biocomposite; the biocomposite comprises coatings of polymer (cysteamine/melamine), nano Au particles, and anti-HIgG. In this report, the detection range of this immunosensor from ...

Self-Cleansing Flexible Stent for Prevention of Clogging of Blood Vessels

The development of biosensors has been astronomical with the advent of the rapid growth of nanomaterials and nanotechnology. Nanobiosensors are becoming ubiquitous in numerous biomedical applications. Thus, there is a great impetus to exploit smart nanoparticles and other nanomaterials for designing and fabricating smart nanobiosensors that are ultrasensitive and biocompatible. We are developing smart self-assembling biosensors that can detect specific biomolecules (e.g., enzymes, cofactors, metabolites, drugs, hormones, etc.) from micro- to nanomolar levels. Applications of the biosensors include detection of organ dysfunction and/or failure (e.g., liver malfunction, heart failure, etc.), early detection of malignant cancers, toxicant identification, and other biomarkers of diseases. Although nanobiosensors that possess high sensitivity and specificity have been designed and marketed, one fundamental issue remains to be resolved. This important issue is one concerning biocompatibility. Thus, in our development of smart biosensors using nanomaterials, we have adopted a dual purpose approach. (i) On the one hand, it is necessary to systematically and comprehensively evaluate the material properties, characterize and model the signal sensing ability, and determine the biocompatibility of materials to be employed for the design of nanobiosensors. (ii) On the other hand, it is imperative to identify the ideal criteria for the designs of fast-response smart self-assembling nanobiosensors for biomarker detection. Based on a critical review of the literature and consideration of the biocompatibility, functional characterization, and other related issues discussed above, we have identify a set of criteria for the design of fast-response smart self-assembling nanobiosensors for detection of multiple biomarkers. We have also identified many biomedical areas where such nanobiosensors can be applied to detect biomarkers for various diseases. Our dual purpose approach will ultimately lead to the design of much more biocompatible and highly sensitive nanobiosensors and diagnostic equipment (nanobiosensor arrays).Copyright

Differential effects of anionic surfactants on activities of GDH, LDH, and MDH

Different types of stents are available to be implanted into blood-vessels (e.g., cardiovascular stent) or organs to maintain unobstructed blood flow or flow of tissue fluid through ducts (e.g., biliary and uretic stents and others). On the one hand, it is imperative to use smart material such that its mechanical and elastic properties meet those of the ideal stent. A smart stent can change the orientation of the material(s) either by sensing control, temperature, or blood pressure, thus alter the overall shape of the stent (wiggling). These wiggling motions can prevent or reduce the deposit of cholesterol inside the stent’s lumen. On the other hand, there is a need for a better physiological model of how the tensile and shear stresses of a blood vessel are altered as the blood pressure changes along a defined length of that vessel and how the shape changes of the blood vessel could prevent the deposits of lipid material on the vessel wall thereby possibly decrease the likelihood of stenosis. However, the design of an ideal stent is complicated by the lack of proper materials and modeling studies, and difficulties to have an optimized design because of complexities of environmental factors. In this literature review, we therefore propose that an optimal stents design should incorporate the use of highly biocompatible material(s) of well characterized properties and with an adequately modeled mechanical design. We have discussed the importance and relevance of these issues for future stent design and fabrication.Copyright