5-Aminolaevulinic acid (ALA) induced formation of different fluorescent porphyrins: a study of the biosynthesis of porphyrins by bacteria of the human digestive tract.

Aminolaevulinic acid (ALA) induces porphyrin formation in almost all living cells. The fluorescence spectra of porphyrins produced from a variety of 31 bacterial strains from the human oral cavity and other parts of digestive tract have been examined. Many of the bacteria exposed to ALA were able to induce protoporphyrin IX (PpIX) fluorescence, but under aerobic condition some bacteria can also produced different fluorescent porphyrins, in particular water-soluble porphyrins that can arise from an oxidation of the corresponding porphyrinogen precursors.

Internalization of aggregated photosensitizers by tumor cells: subcellular time-resolved fluorescence spectroscopy on derivatives of pyropheophorbide-a ethers and chlorin e6 under femtosecond one- and two-photon excitations.

Amphiphilic sensitizers self-associate in aqueous environments and form aggregated species that exhibit no or only negligible photodynamic activity. However, amphiphilic photosensitizers number among the most potent agents of photodynamic therapy. The processes by which these sensitizers are internalized into tumor cells have yet to be fully elucidated and thus remain the subject of debate.

[Tumors of the mouth cavity. Not all fluorescent tumors are malignant].

Early diagnosis and treatment of malignant tumors of the mouth and throat can greatly improve survival rates. Diagnostic fluorescence permits the reliable detection not only of oral cancer, but also of cancer precursor lesions. A problem here is the fact that although carcinomas can be detected with a high level of sensitivity, our own studies also demonstrate a considerable false-positive rate (35%).

[Visualizing carcinomas of the mouth cavity by stimulating synthesis of fluorescent protoporphyrin IX].

The fluorescence diagnosis based on the aminolavulinic acid-stimulated porphyrin synthesis allows the detection of superficial tumors in a very early stage even when they are very small tumors. A fluorescence diagnosis of tumors in the oral cavity can be simply performed by rinsing with a 0.4% ALA solution for 20 min.

Phototransformation of sensitisers: 3. Implications for clinical dosimetry.

Spectroscopic studies of aqueous solutions of haematoporphyrin-type sensitisers reveal that photobleaching during eposure to light is followed by the formation of stable red-absorbing photoproducts. Experiments in model systems (sensitisers bound to human serum albumin or in a suspension of resealed erythrocyte 'ghosts') and in tumour tissue show that similar photomodification takes place in all investigated environments. Loss of total absorption and emission intensities is accompanied by an increase of absorption in the red spectral region (630-650 nm) which is used for the treatment of tumours because of the deeper penetration of light into tissues.