Photodynamic reaction

Aminolevulinic acid (ALA HCl, Levulan Kerastick) is indicated for the treatment of nonhyperkeratotic actinic keratosis of the face and scalp. It has two components, an alcohol solution vehicle and ALA HCl as a dry solid. The two are mixed prior to application to the skin. When applied to human skin, ALA is metabolized to protoporphyrin, which accumulates and on exposure to visible light produces a photodynamic reaction that generates reactive oxygen species (ROS).The ROS produce cytotoxic effects that may explain therapeutic efficacy. Local burning and stinging of treated areas of skin due to photosensitization can occur. 

QUANTITATIVE DETECTION OF SINGLET OXYGEN WITH A CHEMILUMINESCENCE PROBE DURING PHOTODYNAMIC REACTIONS... 

However, the CL method also has shortcomings, such as the inefficiency of CL reactions. We have considered ways to improve CL detection. Thus during 02 detection with CL, correcting CL was considered. To implement this concept, ]02 was measured by FCLA in a photodynamic reaction to achieve correction. We have previously reported that the CL probe, FCLA, which can selectively detect singlet oxygen and superoxide.7 Here CL is measured and analyzed at different probe concentrations and a method of making the detection precise is discussed. 

Quenching of FCLA excitation state by FCLA oxide. The photodynamic reaction was performed with PPIX 5 pmol/L, FCLA 2 pmol/L and a laser setting of 20 mw/cm2. Fresh FCLA was used for the first experiment, and then the same reaction was done with added oxidized FCLA 2 pmol/L in solution. The experiment was repeated three times. 

Fig. 1. Relationship of chemiluminescence and probe concentrations in the photodynamic reaction. Fig.2A CL with 0.075 and 20 pmol/L FCLA Fig.2B initial CL with different FCLA concentrations (0.05- 20 pmol/L).

In conclusion, CL can reflect singlet oxygen in photodynamic reactions but some factors will affect the CL, including light absorption, self-quenching and concentration... 

Davidson and Cogdell (1981) showed that two carotenoids, neurosporene and spheroidene, could be incorporated into the B850 light-harvesting complexfromR6. sphaeroidesR-26.l by mixing the carotenoids with freeze-dried chromatophore membranes. They showed that carotenoids incorporated in this maimer were able to transfer energy to BChl and also protect the complex from the photodynamic reaction. 

A.C. Moor, J.W. Lagerberg, K. Tijssen, S. Eoley, T.G. Truscott, I.E. Kochevar, A. Brand, T. M. Dubbelman, J. VanSteveninck (1997). In vitro fluence rate effects in photodynamic reactions with AIPcS4 as sensitizer. Photochem. PhotobioL, 66, 860-865. 

About a decade ago, it was recognized that, under some circumstances, the oxygen in tissue could become depleted by the photodynamic reaction itself. 

Riboflavin or vitamin makes a prosthetic group of flavin enzymes where it can be reversibly reduced by hydrogen atoms (formula [38]). When exposed to light, riboflavin absorbs energy and reacts, via a triplet exited state, with other molecules such as protonated substrates or molecular oxygen, generating reactive species. In the type I photodynamic reaction, energy is transferred from a triplet sensi-tiser to O2 with the formation of O2. 

Photosensitization is an increase in susceptibility to iJtraviolet li it Free radicals produced by photodynamic reactions can damage cdl and lysosomal membranes... 

Chemical quenching is also known. A photodynamic reaction of Type I, for example, is a process in which a molecule in its triplet electronically excited state eventually transfers one electron to O2, producing superoxide anion radical OJ and a radical-cation derived from the sensitizer. 

These processes may play an important stimulatory or inhibitory role in the photosensitized induction of apoptosis. There are several modes by which photodynamic reactions can promote the activation of processes eventually leading to programmed cell death (for an excellent review, see Oleinick et al. ). The... 

Photodynamic reactions are to some extent temperature independent and have high quantum efficiency (O2 consumed/quanta absorbed). The rate is of zero order with respect to the sensitizer concentration. This proves that the dye acts as a catalyst. The latter might produce a peroxide or some kind of active oxygen. Classical examples are those of the increased death rate of Paramecium caudatum in the presence of oxygen and dyes and the work of Gaffron (1936) on bacteria. 

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