Photodecontamination of blood components: advantages and drawbacks.

Photochemical methods using photosensitizing photoactive drugs are very promising for blood product decontamination. Depending on the nature of virus - or parasite - bound photosensitizers, direct photochemical addition to virus components (DNA, proteins and lipids) occurs or the photosensitizer produces singlet oxygen inactivating viruses or parasites. The main advantage of this method is the lack of dark toxicity of presently used photosensitizers (psoralens, methylene blue, merocyanine 540, porphyrins/chlorins, phthalocyanines). In blood, the uptake of photosensitizers is not fully specific for infected cells. Therefore, normal cells and plasma proteins may suffer from the photodynamic action. Consequently, cell metabolism, rheological properties and surface markers may be altered and a slow loss of functionality occurs during storage. Data regarding pathogen inactivation in plasma and blood proteins, platelets and RBC concentrates are presented in comparison with the effect of photosensitization on normal blood components. Means for protecting normal components from photosensitization are also evaluated.