Photodynamic sensitizers

For photosensitization to occur light must be absorbed by the photosensitizer and cause a reaction to take place in the biological system ( ). Two main types of photosensltlzatlon are known to occur. Those involving O2 are called photodynamic sensitizations and are mediated by the bulk of the 400 synthetic and natural photosensitizers known O). The second type of photosensltlzatlon does not Involve O2 and is associated with the furanocoumarlns. 

Eosin generates singlet oxygen upon irradiation with visible light. Its ability to act as a photodynamic sensitizer has been known for many years [125], Irradiation of Eosin in the presence of oxygen is found to deactivate viruses [126] and yeasts [127] and to damage the photosystem II of leaf tissue [128,129], Eosin covalently immobilized in polystyrene beads has been used to remove E. coli from drinking water [130],... 

A number of workers have looked at the effect of photooxidation and photodynamic sensitizers on DNA. Rose Bengal photosensitizes strand breaks in double-stranded, supercoiled, pBR322 DNA the effect follows first-order kinetics with respect to light fluence and dye concentration. The reaction is substantially more efficient in the absence of oxygen, but the quantum yield of strand breaks in air is only 10 8. The results are consistent with the initiation of chain scission by Rose Bengal triplet, with some additional mechanism coming into play in the presence of oxygen. 

Photodynamic sensitizers in plants have long been suspected to act by generating singlet oxygen, and this has now been confirmed by studies with cercosporin (Dobrowolski and Foote). 

Bellnier DA, Dougherty. Protection of murine skin and transplantable tumor against Photofrinll mediated photodynamic sensitization with WR-2721. J Photochem Photobiol 1989 49 369-72. 

Boyle, R. W., Dolphin, D., Structure and Biodistribution Relationships of Photodynamic Sensitizers, Photochem. Photobiol. 1996, 64, 469 485. 

Walrant, R and Santus, R., N-formyl-kynurenine, a tryptophan photooxidation product, as a photodynamic sensitizer, Photochem. Photobiol., 411, 1974, 1974. 

Roberts, W.G., Smith, K.M., McCullough, J.L., and Bems, M.W. (1989) Skin photosensitivity and photodestruction of several potential photodynamic sensitizers, Photochem. Photobiol., 49 431-438. 

Photosensitive liposomes may contain a photosensitizer that can induce peroxidation of the membrane lipids by type I and/or type II photodynamic sensitization (Srinath and Jain, 1994). In the type I process, the electronically excited sensitizer reacts directly with the lipids. The result is the formation of radicals that can react further with molecular oxygen or other components present at the reaction site. In the type II process, the electronically excited sensitizer reacts directly with molecular oxygen via energy transfer to produce singlet oxygen. 

CPSC regulations elaborate on the statutory definition of strong sensitizer by specifically differentiating between allergic and photodynamic sensitization. According to 16 C.F.R. 1500.3(c)(5), an allergic sensitization develops by means of an antibody mechanism. A photodynamic sensitizer, by contrast, is defined as... 

R.W. Boyle, D. Dolphin (1996). Structure and biodistribution relationships of photodynamic sensitizers. Photochem. PhotobioL, 64, 469-485. 

J.K. Hoober, T.W. Sery, N. Yamamoto (1988). Photodynamic sensitizers from chlorophyll purpurin-18 and chlorin-p6. J. Photochem. Photobiol. B, 48, 579-582. 

I. Rosenthal (1991). Phthalocyanines as photodynamic sensitizers. Yearly review. Photochem. PhotobioL, 53, 859-870. 

The response of tissue to PDT treatment clearly depends on the dose factors of local light fluence (rate), photosensitizer concentration and microlocalization and free oxygen availability. It also depends on the intrinsic photodynamic sensitivity of the tissue. That is, how much of the cytotoxic photoproduct (e.g. O2) must be generated locally in the tissue in order to produce a specified biological endpoint, such as apoptosis or necrosis If this could be known and the various dose factors could be measured during treatment, then the response could be predicted. 

In tryptophan (5g), the flve-membered, nitrogen-containing ring Is cleaved, and N-formylkynurenlne ( ), a remarkable photodynamic sensitizer (237), Is formed as the primary product ... 

TABLE 146.3 Cell Response to Visible Light Irradiation in the Presence of Photodynamic Sensitizers... 

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