Sook Jeong Lee

Clioquinol induces autophagy in cultured astrocytes and neurons by acting as a zinc ionophore.

Recent studies have demonstrated that clioquinol, an antibiotic with an anti-amyloid effect, acts as a zinc ionophore under physiological conditions. Because increases in labile zinc may induce autophagy, we examined whether clioquinol induces autophagy in cultured astrocytes in a zinc-dependent manner. Within 1h of exposure to 0.1-10 μM clioquinol, the levels of microtubule-associated protein 1 light chain 3 (LC3)-II, a marker of autophagy, began to increase in astrocytes. Confocal live-cell imaging of GFP-LC3-transfected astrocytes showed the formation of LC3(+) autophagic vacuoles (AVs), providing a further indication that clioquinol induced autophagy. Addition of 3-methyladenine or small-interfering RNA against autophagy-related gene 6 (ATG6/Beclin-1) blocked clioquinol-induced increases in LC3-II. FluoZin-3 fluorescence microscopy showed that, like the zinc ionophore pyrithione, clioquinol increased intracellular zinc levels in the cytosol and AVs in an extracellular zinc-dependent manner. Zinc chelation with N,N,N,N-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN) reduced, and addition of zinc increased the levels of LC3-II and LC3(+) puncta, indicating that zinc influx plays a key role therein. Moreover, astrocytes and SH-SY5Y cells expressing mutant huntingtin (mHttQ74) accumulated less aggregates when treated with clioquinol, and this effect was reversed by TPEN. These results indicate that clioquinol-induced autophagy is likely to be physiologically functional. The present study demonstrates that clioquinol induces autophagy in a zinc-dependent manner and contributes to clearance of aggregated proteins in astrocytes and neurons. Hence, in addition to its metal-chelating effect in and around amyloid beta (Aβ) plaques, clioquinol may contribute to the reduction of Aβ loads by activating autophagy by increasing or normalizing intracellular zinc levels in brain cells.

Corrosion behavior and cytotoxicity of Mg-35Zn-3Ca alloy for surface modified biodegradable implant material.

This study was conducted to investigate the biocompatibility of Mg-Zn-Ca ternary alloy as a biodegradable material. The casting alloy underwent anodization in an alkaline electrolyte at current density 300 mA/cm(2) and frequency 50 Hz to obtain porous oxide layer. Plasma anodization film using pulse was shown to form irregular porous oxide film. As a result of corrosion test, the corrosion current was shown to decrease and the corrosion voltage was shown to increase in the anodized group, which showed the improvement of corrosion resistance after surface treatment. Sodium silicate (0.1 M) was directly oxidized due to high charges caused by spark and then formed SiO(2), and the compounds produced inside the film were shown MgO, Mg(2) SiO(4), and SiO(2.) In the histological examination in rats, all samples of the untreated group were shown to be absorbed 3 weeks later into the body. After the magnesium alloy was implanted, blood vessel expansion and tissue change were shown in the adjacent tissues. However, the changed tissues were shown to return to normal muscle tissues 4 weeks later when the alloy was completely absorbed. These results suggest that anodized Mg-35Zn-3Ca alloy has good biocompatibility in vivo and controls the absorption rate of biomaterials.

Effect of AOT-assisted multi-walled carbon nanotubes on antibacterial activity

The dispersing power of surfactant-modified multiwalled carbon nanotubes (MWCNTs) and their effect on the antibacterial activity were examined. The MWCNTs were modified using a dioctyl sodium sulfosuccinate (AOT) surfactant. UV-vis spectroscopy and transmission electron microscopy (TEM) were used to characterize the dispersion of MWCNTs in the aqueous phase. Fourier transform infrared spectroscopy confirmed the results of UV-vis spectroscopy and TEM, indicating that the AOT molecules had been adsorbed successfully onto the MWCNT surface. The highly dispersed AOT-modified MWCNTs showed strong antibacterial activity to Streptococcus mutans. The fluorescence images showed that the AOT-modified MWCNTs were capable of capturing bacteria and forming cell aggregates as well as killing them. The optical density growth curves and colony-forming units assays confirmed that the antibacterial activity of the AOT-modified MWCNTs was concentration-dependent and treatment time-dependent. This finding might be useful for applications of AOT-modified MWCNTs as an antibacterial agent to eliminate pathogens from a biocontaminated water phase.

The role of reciprocal activation of cAbl and Mst1 in the Oxidative death of cultured astrocytes

The protein kinase Mst1 (mammalian Sterile 20‐like kinase 1) likely plays a role in oxidative neuronal cell death as a target of its activator, cAbl. We previously found that H2O2‐induced death of astrocytes is mediated by cAbl in a metallothionein‐3 (Mt3)‐dependent manner. In the present study, we examined a possible role for Mst1 in the oxidative death of astrocytes. Treatment of cortical astrocytes with 170 µM H2O2 activated Mst1. Knockdown of Mst1 reduced H2O2‐induced cell death, indicating that Mst1 activation contributes to astrocytic cell death. STI571, an inhibitor of cAbl, blocked induction/activation of Mst1 and H2O2‐induced cell death. However, Mst1 silencing also inhibited induction/activation of cAbl, suggesting that the two kinases are regulated by a reciprocal activating mechanism. The zinc chelator TPEN blocked induction/activation of cAbl and Mst1, indicating that these phenomena are dependent on the rise of intracellular zinc. Moreover, H2O2 exposure did not increase free zinc levels in Mt3‐null astrocytes, suggesting that the increased levels of free zinc were largely from Mt3. Consistent with the involvement of FoxO1/3, which may play a role in the Mst1‐cell death cascade, we found an increase in the level of phosphorylated FoxO1/3 in H2O2‐treated astrocytes. Moreover, inhibition of cAbl or Mst1 reversed this effect. The present results suggest the interesting possibility that cAbl and Mst1 are reciprocally activated under oxidative stress conditions in astrocytes. Both kinases appear to be regulated by changes in the levels of free zinc originating from Mt3 and contribute to oxidative cell death through a FoxO‐dependent mechanism. GLIA 2014;62:639–648

Biodegradation and cytotoxic properties of pulse anodized Mg alloys

Magnesium has the potential to be used as an implant material owing to its non-toxicity. On the other hand, magnesium alloys corrode rapidly in subcutaneous gas bubbles. Consequently, the approach of using magnesium alloys as a biodegradable biomaterial is not well established. Therefore, the aim of this study was to provide corrosion protection by anodizing to surface for a biodegradable material. Micro-arc oxidation by pulsed DC was applied to AZ91D and AZ31B, and the cell bioactivity was defined. The anodic film was characterized by XRD and SEM. The specific mass loss variation from immersion test and potentiodynamic electrochemical test was performed for the quantification of corrosion resistance. Although the AZ91D had better corrosion resistance properties but the result of the in vitro tests showed low cell viability compared with the AZ31B. The results of the cell staining and agar overlay test revealed the AZ31B group had good biocompatibility and a low corrosion rate. In this study, the surfaces of AZ91D and AZ31B showed the formation of a uniform film by pulse power anodization improving corrosion resistance. Also, the cytotoxicity of the materials was examined by the aluminum content change of compound metal.

Characterization and biocompatibility of a calcium-containing AZ31B alloy as a biodegradable material

AbstractnMagnesium has attracted notability as a biodegradable material. Several studies have reported that magnesium containing calcium (Ca) had biosafety with higher mechanical properties. However, Mg–1Ca alloy showed non-uniform corrosion properties with bone. In this study, various Ca amounts were added to commercial magnesium alloy AZ31B to improve the corrosion resistance and microstructure. AZ31B billet was prepared by casting without Ca. The AZ31B alloy ingots were melted and recasted with Ca quantities at 1.5 and 2.5xa0wt%. Extrusion ingots were pressed out to a plate with thickness of 5xa0mm and width of 80xa0mm at 1650xa0°C. The microstructure of the alloy was observed by optical microscopy and SEM. The composition of the alloy was analyzed by EDX. To examine the corrosion properties, potentiodynamic polarization was used to measure the corrosion potential and current density. Osteoblast cells MC3T3-E1 were incubated with the samples to allow cell attachment and MTT assay. The microstructure of alloys was homogeneously distributed over the surface and observed phase boundary. Preliminary elemental analysis suggested that the second phases were Al2Ca and Mg2Ca. Grain refinement by extrude casting was obtained for AZ31B–xCa. The corrosion resistant of AZ31B–xCa by current density was greater than the AZ31B because the standard electrode potential of Mg phase was lower than Mg2Ca. In vitro studies showed that the reduction of corrosion resistance and mechanical ability of the magnesium alloy after addition of Ca were not correlated with bioactivity. In particular, AZ31B–1.5Ca had higher formation of biomimetic substances and lower cytotoxicity, even though it had more vulnerable mechanical properties than AZ31B. Based on this result, the effect of Ca ion on commercial alloy AZ31B, mechanical properties, and bioactivity as biodegradable implant were discussed.