Photosensitization: Basic Principles

Authored by: Giulio Jori

CRC Handbook of Organic Photochemistry and Photobiology

Print publication date:  March  2012
Online publication date:  March  2012

Print ISBN: 9781439899335
eBook ISBN: 9781466561250
Adobe ISBN:


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The first scientific documentation that sunlight or visible light can be detrimental for cells and more complex biological systems was provided by Marcacci in the late nineteenth century [1]; this investigator reported that the fermentation of plant alkaloids and amphibian eggs is drastically impaired under exposure to UV/visible light. Shortly thereafter, Raab [2], a medical student working in the laboratory of Prof. H. von Tappeiner in Munich, demonstrated that the presence of some exogenously added visiblelight-absorbing compounds, for example, acridine orange, was necessary for sunlight to promote the death of paramecia. In a second paper, von Tappeiner [3] associated this property with fluorescence, postulating that the necrotic effects were consequent to the transfer of energy from the light-activated chemical compounds to other sites in their close surroundings. These photoactivatable substances were defined as photosensitizers. The overall scenario was completed by the observation [4] that the presence of oxygen is often a necessary requisite for photosensitization to occur. The combined effect of the three elements, namely, light, photosensitizer, and oxygen, has been termed “photodynamic action” [5]. Finally, von Tappeiner in collaboration with a dermatologist named Jesionek showed that the photodynamic processes could be quite useful in medicine by using topically applied eosin and visible light to positively treat skin tumors [6]. This finding prompted a wealth of studies aimed at defining the pharmacokinetic properties of photosensitizing agents in vivo and devising suitable strategies for promoting the selective or preferential localization of the photosensitizer in specific diseased tissues. The results thus obtained eventually paved the way to the development of the so-called photodynamic therapy (PDT) for several pathologies, including solid tumors, actinic keratosis, atheromas, rheumatoid arthritis, infectious diseases of microbial origin, sterilization of blood products, age-related macular degeneration, and a variety of skin diseases [7,8]. At the same time, photodynamic processes are now showing very promising features for addressing important problems connected with the protection of the environment and the preservation of biodiversity [9,10].

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