Symposium‐in‐Print: Singlet Oxygen Invited Review

Abstract

Singlet oxygen (1O2) is unique amongst reactive oxygen species formed in cells in that it is an excited state molecule with an inherent upper lifetime of 4 micros in water. Whether the lifetime of 1O2 in cells is shortened by reactions with cellular molecules or reaches the inherent maximum value is still unclear. However, even with the maximum lifetime, the diffusion radius is only approximately 220 nm during three lifetimes (approximately 5% 1O2 remaining), much shorter than cellular dimensions indicating that the primary reactions of 1O2 will be subcellularly localized near the site of 1O2 formation. This fact has raised the question of whether spatially resolved cellular responses to 1O2 occur, i.e. whether responses can be initiated by generation and reaction of 1O2 at a particular subcellular location that would not have been produced by 1O2 generation at other subcellular sites. In this paper, we discuss examples of spatially resolved responses initiated by 1O2 as a function of distance from the site of generation of 1O2. Three levels are recognized, namely, a molecular level where the primary oxidation product directly modifies the behavior of a cell, an organelle level where the initial photo-oxidation products initiate mechanisms that are unique to the organelle and the cellular level where mediators diffuse from their site of formation to the target molecules that initiate the response. These examples indicate that, indeed, spatially resolved responses to 'O2 occur in cells.

Implicit and explicit prior information in near-infrared spectral imaging: accuracy, quantification and diagnostic value

“…Such approaches can be categorized into several different data types, as outlined in table 1. These [7][8][9] spectral derivative data multiple analyte analysis [10][11][12] fluorescence/excitation ratio fluorescence imaging [13][14][15] multi-distance data estimation of slopes with linear approximations robust tissue spectroscopy systems insensitive to slight shape changes [16][17][18] small-volume sampling scatter spectroscopy fibre probes with size less than effective scatter distance [19][20][21][22] absorption spectroscopy fibre probes sensitive to absorption only [23,24] fluorescence spectroscopy fibre probes sensitive to fluorescence and not tissue [25,26] temporal signals millisecond variations in tissue oxygen saturation and haemodynamic sampling [8,27,28] microsecond sampling flash photolysis analysis of biochemical changes in vivo [29,30] picosecond sampling ultrafast signals to reduce model dependence [31][32][33][34][35] high-frequency phase shift derivative with distance frequency-domain spectroscopy of tissue [36,37] lifetime-based signals fluorophore identification or microenvironment analysis [38] include: (i) ratiometric or derivative data at two or more different wavelengths, (ii) multiple-distance ratio or derivative data, (iii) small spatial volumes that either limit the effect of physical boundaries through scatter and/or absorption, or allow simpler empirical modelling, and (iv) temporal signals that are less sensitive to boundaries and/or more robustly insensitive to shape changes. The use of prior information about the tissue to be sampled is still essential in the design process with these systems, but can be implemented in the very first step o...…”

Photophysical properties and intracellular imaging of water-soluble porphyrin dimers for two-photon excited photodynamic therapy

“…The cellular response to PDT also depends on the primary organelle targeted by the photosensitiser. 7, 8 Most clinical photosensitisers induce apoptosis, generally via direct damage to the mitochondria; 7 however, a secondary apoptotic response can be achieved by initial damage to the lysosomes. 7 Photofrin ® , on the 60 other hand, localises in cell membranes and PDT with this photosensitiser is reported to induce necrosis.…”

Microbicidal Activity of Artificially Generated Hydroxyl Radicals

“…From this viewpoint, reaction involving homolytic fission is advantageous because the reaction can be terminated by cessation of irradiation of γ-ray, ultraviolet ligh or ultrasound. Since hydroxyl radicals have a very short lifetime (approximately 10 À9 s) [44,45,25], residual toxicity would be negligible after the termination of reaction. On the other hand, it might be difficult to control the reaction of one-electron reduction of H 2 O 2 during the disinfection treatment.…”

“…Our recent study demonstrated that hydroxyl radicals would not induce bacterial resistance as singlet oxygen does not [36]. In addition, hydroxyl radicals have higher oxidation power than singlet oxygen [25], resulting in higher antimicrobial activity. In this chapter, the generation systems of hydroxyl radicals and their microbicidal activity are discussed based on our recent works.…”

“…Once the photosensitizer is irradiated with light of a specific wavelength, it absorbs photons and transfers the excitation energy to molecular oxygen which is in turn metamorphosed to its diamagnetic form, singlet oxygen [24]. Since singlet oxygen is unstable and has high reactivity, it oxidizes bacterial cell components resulting in cell death [23,25]. The advantage of PDT is that it exerts bactericidal activity only when a photosensitizer is irradiated with light.…”