Hsin-Hou Chang

Visible-light-induced bactericidal activity of a nitrogen-doped titanium photocatalyst against human pathogens.

ABSTRACT The antibacterial activity of photocatalytic titanium dioxide (TiO2) substrates is induced primarily by UV light irradiation. Recently, nitrogen- and carbon-doped TiO2 substrates were shown to exhibit photocatalytic activities under visible-light illumination. Their antibacterial activity, however, remains to be quantified. In this study, we demonstrated that nitrogen-doped TiO2 substrates have superior visible-light-induced bactericidal activity against Escherichia coli compared to pure TiO2 and carbon-doped TiO2 substrates. We also found that protein- and light-absorbing contaminants partially reduce the bactericidal activity of nitrogen-doped TiO2 substrates due to their light-shielding effects. In the pathogen-killing experiment, a significantly higher proportion of all tested pathogens, including Shigella flexneri, Listeria monocytogenes, Vibrio parahaemolyticus, Staphylococcus aureus, Streptococcus pyogenes, and Acinetobacter baumannii, were killed by visible-light-illuminated nitrogen-doped TiO2 substrates than by pure TiO2 substrates. These findings suggest that nitrogen-doped TiO2 has potential application in the development of alternative disinfectants for environmental and medical usages.

The effects of the bacterial interaction with visible-light responsive titania photocatalyst on the bactericidal performance

Bactericidal activity of traditional titanium dioxide (TiO2) photocatalyst is effective only upon irradiation by ultraviolet light, which restricts the potential applications of TiO2 for use in our living environments. Recently carbon-containing TiO2 was found to be photoactive at visible-light illumination that affords the potential to overcome this problem; although, the bactericidal activity of these photocatalysts is relatively lower than conventional disinfectants. Evidenced from scanning electron microscopy and confocal Raman spectral mapping analysis, we found the interaction with bacteria was significantly enhanced in these anatase/rutile mixed-phase carbon-containing TiO2. Bacteria-killing experiments indicate that a significantly higher proportion of all tested pathogens including Staphylococcus aureus, Shigella flexneri and Acinetobacter baumannii, were eliminated by the new nanoparticle with higher bacterial interaction property. These findings suggest the created materials with high bacterial interaction ability might be a useful strategy to improve the antimicrobial activity of visible-light-activated TiO2.

Antiplatelet autoantibodies elicited by dengue virus non‐structural protein 1 cause thrombocytopenia and mortality in mice

Background: The mechanisms responsible for thrombocytopenia associated with dengue fever (DF) and dengue hemorrhage fever (DHF) remain unclear. Objective: In this study, we investigated the pathogenic effects of dengue virus (DENV) non‐structural protein 1 (NS1) on the elicitation of platelet cross‐reactive antibodies. Results: The results showed that anti‐DENV NS1 immunoglobulins (Igs) derived from both patients with DF/DHF and recombinant NS1‐immunized rabbits could opsonize normal human platelets and enhance platelet–macrophage engagements in vitro. In addition, treatments with anti‐NS1 Igs abnormally activated human platelets and induced thrombocytopenia in mice. These prothrombotic characteristics of anti‐NS1 Ig might increase the disease burden of coagulant‐aberrant DHF patients. To test this hypothesis, we injected anti‐NS1 Igs into C57BL/6J mice that were preconditioned into a hypercoagulable state by warfarin treatments. When given before but not after platelet‐lysate pre‐adsorption, the anti‐NS1 Igs injection treatments significantly increased mortality, fibrin deposition in lung, and plasma D‐dimer levels, but significantly decreased anticoagulant proteins C, protein S and antithrombin III. Conclusions: These results suggest that the platelet‐bound antibody fractions of anti‐NS1 Ig are prothrombotic, which might exacerbate the severity of disease in hosts with an imbalanced coagulant system.

Bactericidal Effects and Mechanisms of Visible Light-Responsive Titanium Dioxide Photocatalysts on Pathogenic Bacteria

This review focuses on the antibacterial activities of visible light-responsive titanium dioxide (TiO2) photocatalysts. These photocatalysts have a range of applications including disinfection, air and water cleaning, deodorization, and pollution and environmental control. Titanium dioxide is a chemically stable and inert material, and can continuously exert antimicrobial effects when illuminated. The energy source could be solar light; therefore, TiO2 photocatalysts are also useful in remote areas where electricity is insufficient. However, because of its large band gap for excitation, only biohazardous ultraviolet (UV) light irradiation can excite TiO2, which limits its application in the living environment. To extend its application, impurity doping, through metal coating and controlled calcination, has successfully modified the substrates of TiO2 to expand its absorption wavelengths to the visible light region. Previous studies have investigated the antibacterial abilities of visible light-responsive photocatalysts using the model bacteria Escherichia coli and human pathogens. The modified TiO2 photocatalysts significantly reduced the numbers of surviving bacterial cells in response to visible light illumination. They also significantly reduced the activity of bacterial endospores; reducing their toxicity while retaining their germinating abilities. It is suggested that the photocatalytic killing mechanism initially damages the surfaces weak points of the bacterial cells, before totally breakage of the cell membranes. The internal bacterial components then leak from the cells through the damaged sites. Finally, the photocatalytic reaction oxidizes the cell debris. In summary, visible light-responsive TiO2 photocatalysts are more convenient than the traditional UV light-responsive TiO2 photocatalysts because they do not require harmful UV light irradiation to function. These photocatalysts, thus, provide a promising and feasible approach for disinfection of pathogenic bacteria; facilitating the prevention of infectious diseases.

Role of Visible Light-Activated Photocatalyst on the Reduction of Anthrax Spore-Induced Mortality in Mice

Background Photocatalysis of titanium dioxide (TiO2) substrates is primarily induced by ultraviolet light irradiation. Anion-doped TiO2 substrates were shown to exhibit photocatalytic activities under visible-light illumination, relative environmentally-friendly materials. Their anti-spore activity against Bacillus anthracis, however, remains to be investigated. We evaluated these visible-light activated photocatalysts on the reduction of anthrax spore-induced pathogenesis. Methodology/Principal Findings Standard plating method was used to determine the inactivation of anthrax spore by visible light-induced photocatalysis. Mouse models were further employed to investigate the suppressive effects of the photocatalysis on anthrax toxin- and spore-mediated mortality. We found that anti-spore activities of visible light illuminated nitrogen- or carbon-doped titania thin films significantly reduced viability of anthrax spores. Even though the spore-killing efficiency is only approximately 25%, our data indicate that spores from photocatalyzed groups but not untreated groups have a less survival rate after macrophage clearance. In addition, the photocatalysis could directly inactivate lethal toxin, the major virulence factor of B. anthracis. In agreement with these results, we found that the photocatalyzed spores have tenfold less potency to induce mortality in mice. These data suggest that the photocatalysis might injury the spores through inactivating spore components. Conclusion/Significance Photocatalysis induced injuries of the spores might be more important than direct killing of spores to reduce pathogenicity in the host.

Facilitation of Cell Adhesion by Immobilized Dengue Viral Nonstructural Protein 1 (NS1): Arginine-Glycine-Aspartic Acid Structural Mimicry within the Dengue Viral NS1 Antigen

Dengue virus infection causes life-threatening hemorrhagic fever. Increasing evidence implies that dengue viral nonstructural protein 1 (NS1) exhibits a tendency to elicit potentially hazardous autoantibodies, which show a wide spectrum of specificity against extracellular matrix and platelet antigens. How NS1 elicits autoantibodies remains unclear. To address the hypothesis that NS1 and matrix proteins may have structural and functional similarity, cell-matrix and cell-NS1 interactions were evaluated using a cell-adhesion assay. The present study showed that dengue NS1 immobilized on coverslips resulted in more cell adhesion than did the control proteins. This cell adhesion was inhibited by peptides containing arginine-glycine-aspartic acid (RGD), a motif important for integrin-mediated cell adhesion. In addition, anti-NS1 antibodies blocked RGD-mediated cell adhesion. Although there is no RGD motif in the NS1 protein sequence, these data indicate that RGD structural mimicry exists within the NS1 antigen.

Antiplatelet Activities of Anthrax Lethal Toxin Are Associated with Suppressed p42/44 and p38 Mitogen-Activated Protein Kinase Pathways in the Platelets

Anthrax lethal toxin (LT) is the major virulence factor produced by Bacillus anthracis, but the mechanism by which it induces high mortality remains unclear. We found that LT treatment could induce severe hemorrhage in mice and significantly suppress human whole-blood clotting and platelet aggregation in vitro. In addition, LT could inhibit agonist-induced platelet surface P-selectin expression, resulting in the inhibition of platelet-endothelial cell engagements. Data from Western blot analysis indicated that LT treatment resulted in the suppression of p42/44 and p38 mitogen-activated protein kinase pathways in platelets. Combined treatments with LT and antiplatelet agents such as aspirin and the RGD-containing disintegrin rhodostomin significantly increased mortality in mice. Our data suggest that platelets are a pathogenic target for anthrax LT.

DNA Vaccination Using the Fragment C of Botulinum Neurotoxin Type A Provided Protective Immunity in Mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.

Dendritic cells modulate platelet activity in IVIg-mediated amelioration of ITP in mice

Intravenous immunoglobulin (IVIg) is an effective treatment against immune thrombocytopenia (ITP). Previous studies suggested that IVIg exerts this ameliorative role through 2 different leukocyte subsets. Dendritic cells (DCs) modulate the immunosuppression in an adoptive cell transfer model, and phagocytes up-regulate their inhibitory IgG Fc receptors (FcγR)IIB expression and thereby ameliorate the inflammatory response and platelet clearance. However, whether or not regulatory mechanisms exist among DCs, phagocytes, and platelets is still largely unknown. In this study we present findings that IVIg-primed splenic CD11c(+) DCs (IVIg-DCs) primarily mediate their anti-inflammatory effects at the level of the platelet rather than the phagocyte. IVIg-DCs did not ameliorate ITP in Fcgr2b(-/-), Fcgr3(-/-), nor P-Selp(-/-) mice, implicating the potential involvement of these pathways in IVIg action. As platelets are a component of DC regulatory circuits, these findings may suggest an alternative perspective for the use of IVIg treatment.

Bactericidal Performance of Visible-Light Responsive Titania Photocatalyst with Silver Nanostructures

Background Titania dioxide (TiO2) photocatalyst is primarily induced by ultraviolet light irradiation. Visible-light responsive anion-doped TiO2 photocatalysts contain higher quantum efficiency under sunlight and can be used safely in indoor settings without exposing to biohazardous ultraviolet light. The antibacterial efficiency, however, remains to be further improved. Methodology/Principal Findings Using thermal reduction method, here we synthesized silver-nanostructures coated TiO2 thin films that contain a high visible-light responsive antibacterial property. Among our tested titania substrates including TiO2, carbon-doped TiO2 [TiO2 (C)] and nitrogen-doped TiO2 [TiO2 (N)], TiO2 (N) showed the best performance after silver coating. The synergistic antibacterial effect results approximately 5 log reductions of surviving bacteria of Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus and Acinetobacter baumannii. Scanning electron microscope analysis indicated that crystalline silver formed unique wire-like nanostructures on TiO2 (N) substrates, while formed relatively straight and thicker rod-shaped precipitates on the other two titania materials. Conclusion/Significance Our results suggested that proper forms of silver on various titania materials could further influence the bactericidal property.