Simultaneous Production of Superoxide Radical and Singlet Oxygen by Sulphonated Chloroaluminum Phthalocyanine Incorporated in Human Low-density Lipoproteins: Implications for Photodynamic Therapy¶

Kinetic analysis of nitroxide radical formation under oxygenated photolysis: toward quantitative singlet oxygen topology

Reaction kinetics for two sterically hindered secondary amines with singlet oxygen have been studied in detail.

Bactericidal action of photogenerated singlet oxygen from photosensitizers used in plaque disclosing agents

Background

Photodynamic therapy (PDT) has been suggested as an efficient clinical approach for the treatment of dental plaque in the field of dental care. In PDT, once the photosensitizer is irradiated with light of a specific wavelength, it transfers the excitation energy to molecular oxygen, which gives rise to singlet oxygen.

Methodology/Principal Findings

Since plaque disclosing agents usually contain photosensitizers such as rose bengal, erythrosine, and phloxine, they could be used for PTD upon photoactivation. The aim of the present study is to compare the ability of these three photosensitizers to produce singlet oxygen in relation to their bactericidal activity. The generation rates of singlet oxygen determined by applying an electron spin resonance technique were in the order phloxine > erythrosine ≒ rose bengal. On the other hand, rose bengal showed the highest bactericidal activity against Streptococcus mutans, a major causative pathogen of caries, followed by erythrosine and phloxine, both of which showed activity similar to each other. One of the reasons for the discrepancy between the singlet oxygen generating ability and bactericidal activity was the incorporation efficiency of the photosensitizers into the bacterial cells. The incorporation rate of rose bengal was the highest among the three photosensitizers examined in the present study, likely leading to the highest bactericidal activity. Meanwhile, the addition of L-histidine, a singlet oxygen quencher, cancelled the bactericidal activity of any of the three photoactivated photosensitizers, proving that singlet oxygen was responsible for the bactericidal action.

Conclusions

It is strongly suggested that rose bengal is a suitable photosensitizer for the plaque disclosing agents as compared to the other two photosensitizers, phloxine and erythrosine, when used for PDT.

Electron Paramagnetic Resonance - A Powerful Tool of Medical Biochemistry in Discovering Mechanisms of Disease and Treatment Prospects

In pathophysiological conditions related to oxidative stress, the application of selected antioxidants could have beneficial effects on human health. Electron paramagnetic resonance (EPR) spectroscopy is a technique that provides unique insight into the redox biochemistry, due to its ability to: (i) distinguish and quantify different reactive species, such as hydroxyl radical, superoxide, carbon centered radicals, hydrogen atom, nitric oxide, ascorbyl radical, melanin, and others; (ii) evaluate the antioxidative capacity of various compounds, extracts and foods; (iii) provide information on other important parameters of biological systems. A combination of EPR spectroscopy and traditional biochemical methods represents an efficient tool in the studies of disease mechanisms and antioxidative therapy prospects, providing a more complete view into the redox processes in the human organism.

Photosensitized oxidation of hypoxanthine and xanthine by aluminum phthalocyanine tetrasulfonate. Role of the alkylating quinone 2,5-dichloro-diaziridinyl-1,4-benzoquinone

Photoirradiation of nitrogen-saturated aqueous solutions containing aluminum phthalocyanine tetrasulfonate (AlPcS4) at 675 nm in the presence of 2,5-dichloro-diaziridinyl-1,4-benzoquinone (AZDClQ) and hypoxanthine (HX) produces the oxidized HX derivatives, xanthine (X) and uric acid (UA). Concentrations of the AZDClQ semiquinone, X and UA increase at the expense of HX with an increase in irradiation time. Almost negligible decomposition of HX, as well as very low amounts of X, are detected if photolysis occurs under identical conditions but in the absence of AZDClQ. Addition of calf-thymus DNA produces quinone-DNA covalent adducts after photolysis of anaerobic samples containing quinone, DNA and AlPcS4, in the presence or absence of HX and at pH 5.5. However, larger amounts of quinone-DNA adducts are detected if HX is present. The results presented here could have applications in the photodynamic treatment of hypoxic tissues such as solid tumors, under conditions of high HX concentration, where Type-I pathways could be more important than singlet oxygen generation.

Mechanisms of photochemistry and reactive oxygen production by fullerene suspensions in water

Buckminsterfullerene (C60) is a known photosensitizer that produces reactive oxygen species (ROS) in the presence of light; however, its properties in aqueous environments are still not well understood or modeled. In this study, production of both singlet oxygen and superoxide by UV photosensitization of colloidal aggregates of C60 in water was measured by two distinct methods: electron paramagnetic resonance (EPR) with a spin trapping compound, and spectrophotometric detection of the reduced form of the tetrazolium compound XTT. Both singlet oxygen and superoxide were generated by fullerol suspensions while neither was detected in the aqu/nC60 suspensions. A mechanistic framework for photosensitization that takes into account differences in C60 aggregate structure in water is proposed to explain these results. While theory developed for single molecules suggests that alterations to the C60 cage should reduce the quantum yield for the triplet state and associated ROS production, the failure to detect ROS production by aqu/nC60 is explained in part by a more dense aggregate structure compared with the hydroxylated C60.

In vitro photodynamic therapy on melanoma cell lines with phthalocyanine

Photodynamic therapy (PDT) is a new treatment modality of tumours. The photochemical interactions of sensitizer, light, and molecular oxygen produce singlet oxygen and other forms of active oxygen, such as peroxide, hydroxyl radical and superoxid anion. Phthalocyanine ClAlPcS(2), belonging among the promising second generation of sensitizers, was tested as an inducer of photodamage. We report the production of reactive oxygen species (ROS) and the phototoxicity of ClAlPcS(2) assessed using G361 melanoma cells. A semiconductor laser (lambda=675nm, output power 21mW) was used as a source for evocation of the photodynamic effect. ROS generation and H(2)O(2) release after PDT on G361 cells were detected using probe CM-H(2)DCFDA and recorded by luminescence spectrometer. Viability studies show, that the optimum phototoxic effect tested on G361 melanoma cells was determined in the combination of laser dose of 25Jcm(-2) and phthalocyanine ClAlPcS(2) concentration of 5microg/ml. This combination of phthalocyanine concentration and corresponding radiation dose was lethal for melanoma cells.

Fluorescence Spectroscopic Study of Hypericin-photosensitized Oxidation of Low-density Lipoproteins

By means of UV-VIS absorption and fluorescence spectroscopy, we demonstrate that the photosensitizer hypericin (Hyp) interacts nonspecifically with low-density lipoproteins (LDL), most probably with the lipid fraction of LDL. The molar ratio of monomeric Hyp binding to nonoxidized LDL and mildly oxidized LDL is 30:1. Increasing the Hyp concentration further leads to the formation of Hyp aggregates inside the LDL molecule. We also demonstrate that photoactivated Hyp oxidizes LDL in a light dose and excitation wavelength dependent manner. The level of oxidation of LDL depends on the amount of Hyp inside the LDL molecule. The maximum of the photosensitized oxidation of the LDL by Hyp is achieved for a 30:1 molar ratio, which corresponds to the maximum concentration of monomeric form of Hyp in LDL.