From Big Medical Encyclopedia

PHOTOSENSITIZATION (grech phos, photos light - j-a sensitization) — the sensitization of biological objects to action of energy of light radiation caused by course in them the photochemical reactions caused by introduction to a biological object (a cell or the whole organism) of molecules of a number of chemicals — dyes, pigments, etc.

Depending on type of substance and its localization of an effect F. can be shown at the molecular, cellular and organismal levels (see Light). In most cases they are expressed in damage of structure or functions biol. systems. It is accepted to call the damaging effect of light caused by a photosensitization fotodi-namichesky action (fotodinami-chesky effect). Fotodinamichesk of active connections

are among many dyes (xanthines, acridines, tia-zina), physiologically active and pharmacological agents (porphyrines, Riboflavinum, quinones, anthraquinones, anesthetics, antibiotics, barbiturates, haematoporphyrins, etc.). Such substances were called photosensitizers.

K F. practically all are sensitive biol. objects from separate biopolymers, viruses and cells of microorganisms to cells and fabrics of the higher plants and animals. The result of photodynamic effect at organismic level can variously be shown — mutagen and oncogenous reactions, suppression of process of protein synthesis and nucleinic to - t, cellular respiration, also the erythema, an allergy, a necrosis of skin, change of temperature, the ABP, etc. can be observed.

At the heart of F. a certain photochemical reaction lies (see. Photochemical reactions). In this regard the sequence of damage by light of these or those molecular and cellular structures depends by nature a photosensitizer, on features of an object — permeability of cells, microdistribution of a photosensitizer in cells, specificity of its linkng with cells of different types.

One of conditions of emergence F. illumination of cells in the presence of oxygen is. 11 ssledovan I

mechanism F. showed that the oxidation reactions of molecules proceeding with participation of active forms of oxygen, the excited singlet oxygen or euperoksidny radical About are the cornerstone of the majority of photosensitized damages (see Radicals a free, 2

Singlet state). However reactions, sensibilized for furocoumarins, proceeding without participation of oxygen and bringing to it biol are known. to effects, as an inactivation of viruses, bacterial cells, medical action at psoriasis.

Phenomenon F. is of great practical interest. First of all it is necessary to consider possible photodynamic effect of various drugs, to-rye are used in medical practice, but are not classical photosensitizers. Besides, many diseases of skin are connected with disbolism, accumulation in blood of the modified biochemical connections which are photosensitizers — haematoporphyrins, bilirubin (see Photodermatoses).

In medicine use ability of various photosensitizers to collect selectively in these or those cells and fabrics that leads to their selection damage at effect of light with lengths of waves absorbed by this substance. The derivatives of haematoporphyrin (see Lorfirina) having such important properties as the photosensitizing activity, ability in this respect are of the greatest practical interest it is easy to get into cells and to collect in different fabrics, including and tumoral.

Bibliography: Konev S. V. and In l about -

t about in with to and y I. D. Fotobiologiya, page 337, Minsk, 1979; Laser in photomedicine and photobiology, ed. by R. Pratesi a.

C. A. Sacchi, p. 58, V. a. o., 1980.

JI. B. Rubin.