The Photodegradation of Porphyrins in Cells Can Be Used to Estimate the Lifetime of Singlet Oxygen

Abstract

NHIK 3025 cells were incubated with Photofrin II (PII) and/or tetra (3-hydroxyphenyl)porphyrin (3THPP) and exposed to light at either 400 or 420 nm, i.e. at the wavelengths of the maxima of the fluorescence excitation spectra of the two dyes. The kinetics of the photodegradation of the dyes were studied. When present separately in the cells the two dyes are photodegraded with a similar quantum yield. 3THPP is degraded 3-6 times more efficiently by light quanta absorbed by the fluorescent fraction of 3THPP than by light quanta absorbed by the fluorescent fraction of PII present in the same cells. The distance diffused by the reactive intermediate, supposedly mainly 1O2, causing the photodegradation was estimated to be on the order of 0.01-0.02 micron, which corresponds to a lifetime of 0.01-0.04 microsecond of the intermediate in the cells. PII has binding sites at proteins in the cells as shown by an energy transfer band in the fluorescence excitation spectrum at 290 nm. During light exposure this band decays faster than the Soret band of PII under the present conditions. Photoproducts (1O2 etc.) generated at one binding site contribute significantly in the destruction of remote binding sites.

Rose bengal uptake by E. faecalis and F. nucleatum and light-mediated antibacterial activity measured by flow cytometry

“…Because singlet oxygen is effective in the nanometer range (20 nm), photosensitizers that tightly bind or penetrate bacterial cells may elicit more antibacterial activity than those producing oxygen derivates nearby cells [14,16,33].…”

Repeated exposures to blue light-activated eosin Y enhance inactivation of E. faecalis biofilms, in vitro

“…Singlet oxygen ( 1 O 2 ) production is assumed to be the main mechanism involved in a-PDT. The half-life of singlet oxygen in biological systems is<40 ns, and therefore the radius of the action of singlet oxygen is of the order of 20 nm [39]. Also, the antimicrobial activity of photosensitizers mediated by highly reactive singlet oxygen was shown to have a direct effect on extracellular molecules.…”

Endoplasmic reticulum and Golgi apparatus are the preferential sites of Foscan® localisation in cultured tumour cells

“…Correlating the sites of dye location and sites of direct photodamage seems allowable since photochemically produced singlet oxygen is expected to diffuse intracellularly to distances limited by its short lifetime to 10 -20 nm (Moan and Berg, 1991).…”

“…The ultimate phototoxic effect of photosensitisers is governed by their photophysical properties as well as their intratumoural and intracellular uptake with subsequent translocation to various membrane-delimited compartments. Since singlet oxygen, the main cytotoxic species produced by PDT, is not able to diffuse over distances longer than 10 -20 nm during its excited state lifetime and cell dimensions are approximately 20 mm, the primary sites of photodynamic action should be strictly related to the specific intracellular sensitiser distribution (Moan and Berg, 1991). Still, the correlation between the sites of specific sensitiser localisation and primary light-induced damage sites should be established for every given photosensitiser.…”