Mika Tada

Scavenging or Quenching Effect of Melanin on Superoxide Anion and Singlet Oxygen

Although photoprotective properties of skin melanin have been well documented, a few studies on the effect of melanin on reactive oxygen species (ROS) generated by ultraviolet (UV) irradiation have been reported. To study the interaction of melanin with ROS, scavenging or quenching effect of melanin on O2•− and 1O2 was examined by electron spin resonance (ESR)-spin trapping methods and a spectrophotometric method, respectively. Melanin potently interacted with O2•− generated in a hypoxanthine (HPX)-xanthine oxidase (XOD) reaction, and with 1O2 generated from a peroxidase, H2O2, and halide system. In the HPX-XOD reaction, it was proved that melanin doses not interfere with the enzyme reaction. It is confirmed that one of the mechanisms by which melanin protects UV-induced skin damage is likely scavenging or quenching activity against ROS such as O2•− and 1O2.

Generation Mechanism of Radical Species by Tyrosine-Tyrosinase Reaction

Alleviated melanin formation in the skin through inhibition of tyrosine-tyrosinase reaction is one of the major targets of cosmetics for whitening ability. Since melanin has a pivotal role for photoprotection, there are pros and cons of inhibition of melanin formation. This study applying electron spin resonance (ESR)-spin trapping method revealed that •H and •OH are generated through tyrosine-tyrosinase reaction. When deuterium water was used instead of H2O, the signal of 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-H (a spin adduct of DMPO and •H) greatly decreased, whilst DMPO-OH (a spin adduct of DMPO and •OH) did not. Thus, it is suggested that •H was derived from H2O, and •OH through oxidative catalytic process of tyrosine to dopaquinone. Our study suggests that tyrosinase inhibitors might contribute to alleviate the oxidative damage of the skin by inhibiting •OH generation via the enzyme reaction.

Myristic Acid, A Side Chain of Phorbol Myristate Acetate (PMA), Can Activate Human Polymorphonuclear Leukocytes to Produce Oxygen Radicals More Potently than PMA.

Myristic acid (MyA), which is a saturated fatty acid (C14:0) and a side chain of phorbol 12-myristate 13-acetate (PMA), was examined if MyA stimulates human polymorphonuclear leukocytes (PMNs) to release oxygen radicals comparable to PMA by applying electron paramagnetic resonance (EPR)-spin-trapping method. When MyA was added to isolated human PMNs, spin adducts of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)-OH and DMPO-OOH were time-dependently observed. The amounts of these spin adducts were larger than those of PMNs stimulated by PMA. These results clearly show that MyA is more potent agent to prime human PMNs than PMA, in a point of view of not only O2·− but also ·OH production. This fact calls attention that too much intake of MyA that is known to be contained vegetable oils can lead to crippling effect through uncontrolled production of reactive oxygen species.

Fabrication of Cell-Adhesion Surface and Capillary Vessel Model by Photolithography

We have been developing scaffolds of three-dimensional (3D) synthetic vascular prosthesis in tailor-made. Human umbilical vein endothelial cells (HUVECs) attached on the inner surface of the scaffold have anticoagulant effects. Asperity structures of the inner surface are important to cell adhesion. It is important to quantify the inner surface asperity condition of the scaffold by observing HUVECs behavior and morphology. For this purpose, we recreated the inner surface profile of the scaffold on a poly(dimethilsiloxane) (PDMS) substrate by microfabrication. We made semiround convex patterns of resist that had 8 mum in diameter and 5 mum high using photolithography, and the concave pattern on the PDMS substrate by printing. We observed HUVECs adhering to the PDMS substrate having concave pattern on it surface. The distribution density of the concaves of the tested pattern is 1600 /mm2 or 40,000 in a 25 mm2 area. In addition, we fabricated a capillary vessel model by photolithography, creating a branched capillary tube model that had 13 mum in diameter. We confirmed that the capillary vessel model had no leakage using a methylene blue solution flow in the channel.

Transmitted laser beam power of the resin washed by experimental washing machine for dentures

We had developed the experimental washing machine for denture, and had examined the cleansing property of the machine. The washing machine was using hydrogen peroxide as cleansing solution activated by LED (375 nm) and ultrasonic energy. However, the effect of long-term use of this machine was not examined. The purpose of this study was to examine the color alteration using measurement of transmitted laser beam. This study showed that there was not a change in the measurement of transmitted laser beam after 100 h for washing. If the color alteration in the surface of the samples had occurred because of washing, it was thought that absorption and dispersion of the laser light were influenced. Consequently, this study indicated that this washing machine might not change on the surface of the resin.

Bactericidal effect of photodynamic therapy

Photodynamic therapy (PDT) is a procedure whereby undesired tissue can be destroyed by the combined action of light, oxygen, and a photosensitizer. It is thought that a photosensitizer excited by light with a specific wavelength transfers its excitation energy to ground state oxygen molecules resulting in the generation of singlet oxygen. Singlet oxygen is a reactive oxygen species with high oxidative reactivity. Therefore, the reaction of singlet oxygen with cellular constituents can result in oxidative damage leading to cell death. Although PDT is mainly used in cancer treatment, several studies have shown that PDT also has antimicrobial properties. It has been proposed that the bactericidal effect of singlet oxygen generated by PDT could be used in clinical dentistry. Applications of PDT for the treatment of periodontitis and peri-implantitis, endodontic disease, and caries are now under study.