PubMed · 14419900
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B MAGNUSSON. 1959-11-20. [Photodermatitis].. https://pubmed.ncbi.nlm.nih.gov/14419900/
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Clinically useful photosensitisers (PSs) are likely bound to subcellular and molecular targets during phototherapy. Binding to a macromolecule has the potential to change the photophysical and photochemical characteristics of the PSs that are crucial for their phototoxicity and cell-killing activity. We investigated the effects of binding of a specific PS (protoporphyrin IX or PPIX) to two proteins, human serum albumin (HSA) and a commercially available immunoglobulin (IgG). These two proteins provide two different environments for PPIX. The albumin binds PPIX in hydrophobic binding sites located in subdomain IIA and IIIA, conversely IgG leaves PPIX exposed to the solvent. We show that photophysical parameters such as emission maxima and fluorescence lifetime depend on the binding site. Our results indicate that the different binding site yields very different rates of formation of photoproducts (more than three times higher for PPIX bound to HSA than to IgG) and that different mechanisms of formation may be occurring. Our characterization shows the relevance of protein binding for the photochemistry and ultimately the phototoxicity of PSs.
The sun is essential for life. Yet, sunlight can also be a source of such deleterious effects as sunburn, and suntanning, as well as premalignant and malignant lesions. These may all occur in individuals with normal responses to sunlight. In addition, there exist a variety of 'abnormal' photosensitivity responses to sunlight that may result from either endogenous imbalances (e.g. the porphyrias) or from added exogenous factors (e.g. drug photosensitivity). The 'normal' responses to sunlight, by and large, are produced preferentially by UVB (290-320 nm), with minor contribution by UVA (320-400 nm) wavelengths. In contrast, the 'abnormal' photosensitivity responses are, for the most part, elicited predominantly by long UVA and, in some cases, visible light. In the last 20 years or so, considerable attention has been paid to the use of fabrics as photoprotective materials. The vast majority of work in this area has been concerned with fabric protection against sunburn. In addition to in vivo measurement of fabric SPF, in vitro evaluation of fabric UPF has been carried out in numerous laboratories around the world. The UPF is estimated from the wavelength-dependent transmission of the fabric, the solar UV spectrum and the erythemal action spectrum over the wavelength region 290-400 nm. Depending on the fabric, UPF values range from 2 to several thousand. More recently, it has become clear that such environmental influences as laundering, solarization, humidity, wetting and degree of stretching may play a major role in fabric protection. Protection also may be altered by addition of dyes, UV absorbers and fluorescent whitening agents. To date, there have been relatively few studies of fabric protection for endpoints other than sunburn erythema. Yet, many fabrics that provide good protection against sunburn may provide inadequate protection against photosensitization by intrinsic or extrinsic absorbing molecules or against (pre)malignant lesions. Future work should explicity address the efficacy of protective fabrics against photosensitivity diseases that are activated by long UVA or visible wavelengths.
Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHs) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calculated for ten PAHs by several ab initio methods. The main method used for these calculations was the Configuration Interaction approach, modeling excited states as combinations of single substitutions out of the Hartree-Fock ground state. These calculations correlate well with both experimentally measured singlet and triplet state energies and also previous HOMO-LUMO gap energies that approximate the singlet state energies. The excited state calculations then correlate well with general models of photo-induced toxicity based for the PAHs.