Mechanistic investigation of doxycycline photosensitization by picosecond-pulsed and continuous wave laser irradiation of cells in culture
- Massachusetts General Hospital, Boston (USA)
In order to elucidate the photophysical mechanisms of cellular phototoxicity sensitized by doxycycline, MGH-U1 human bladder carcinoma cells in vitro were treated with 20.7 microM doxycycline and irradiated with either a pulsed (lambda = 355 nm, pulse duration = 24 ps) or a continuous wave (lambda = 351 nm) laser. Cumulative radiant exposure and irradiance were systematically varied in experiments with both lasers. Phototoxicity was assessed by epifluorescence microscopy of unfixed cells using rhodamine 123 labeling of mitochondria. With the continuous wave source, the cumulative radiant exposure required for induction of phototoxic injury was independent of irradiance. With the 24-ps-pulsed source, a significantly lower cumulative radiant exposure was required to induce the phototoxicity when the peak irradiance was 5.8 x 10(7) or 1.3 x 10(8) watts cm-2 compared with when peak irradiance was either lower (6.0 x 10(6) watts cm-2) or higher (7.6 x 10(8) watts cm-2). The measured fluorescence lifetimes of doxycycline in buffered saline solution were longer than the laser pulse duration of 24 ps. The increased efficiency of photosensitization at the optimal peak irradiance in the ps domain appears to result from sequential multiphoton absorption involving higher excited states of the singlet manifold. At the highest irradiance studied, on the other hand, reduced efficiency of photosensitization is attributed to increased photodegradation of doxycycline from higher excited states by processes such as photoionization. A model consistent with these observations is presented along with calculations, based on simple rate equations, that fit the essentials of the proposed model.
- OSTI ID:
- 6904647
- Journal Information:
- Journal of Biological Chemistry; (USA), Vol. 265:11; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
LASER RADIATION
BIOLOGICAL EFFECTS
TUMOR CELLS
SENSITIVITY
ANTIBIOTICS
CELL CULTURES
FLUORESCENCE
LASERS
MAN
MITOCHONDRIA
PHOTOLYSIS
RHODAMINES
AMINES
ANIMAL CELLS
ANIMALS
ANTI-INFECTIVE AGENTS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHEMICAL REACTIONS
DECOMPOSITION
DRUGS
DYES
ELECTROMAGNETIC RADIATION
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
LUMINESCENCE
MAMMALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANOIDS
PHOTOCHEMICAL REACTIONS
PRIMATES
RADIATIONS
REAGENTS
VERTEBRATES
560400* - Other Environmental Pollutant Effects