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Mechanisms of photodynamic inactivation of a gram-negative recombinant bioluminescent bacterium by cationic porphyrins.

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Tavares, Anabela Dias, Sandra R. S. Carvalho, Carla M. B. Faustino, Maria A. F. Tomé, João P. C. Neves, Maria G. P. M. S. Tomé, Augusto C. Cavaleiro, José A. S. Cunha, Ângela Gomes, Newton C. M. Alves, Eliana Almeida, Adelaide
Description	Country affiliation: Portugal Author Affiliation: Tavares A ( CESAM and Department of Biology, University of Aveiro, 3810-193, Aveiro, Portugal.)
Abstract	Photodynamic therapy is a very promising approach to inactivate pathogenic microorganisms. The photodamage of cells involves reactive oxygen species (ROS) which are generated in situ by two main mechanisms (type I and/or type II). The mechanism responsible for the photoinactivation (PI) of a bioluminescent recombinant Escherichia coli, induced by three different cationic porphyrins, was identified in this work using a rapid method based on the monitoring of the metabolic activity of this bacterium. The inhibitory effect of the photodynamic process in the presence of a singlet oxygen quencher (sodium azide) or free radical scavengers (d-mannitol and l-cysteine) was evaluated by exposing bacterial suspensions with 0.5 µM Tri-Py(+)-Me-PF, 5.0 µM Tetra-Py(+)-Me or 5.0 µM Tri-SPy(+)-Me-PF to white light. Strong bacterial protection was observed with sodium azide (100 mM) for the three cationic porphyrins. However, in the presence of Tri-Py(+)-Me-PF and Tetra-Py(+)-Me and the free radical scavengers (l-cysteine and d-mannitol) the reduction on the bacterial bioluminescence was significantly higher and similar to that obtained in their absence (5.4-6.0 log reduction). In the case of Tri-SPy(+)-Me-PF two distinct behaviours were observed when l-cysteine and d-mannitol were used as free radical scavengers: while the presence of l-cysteine (100 mM) lead to a bacterial protection similar to the one observed with sodium azide, in the presence of d-mannitol only a small protection was detected. The high inhibition of the PS activity by l-cysteine is not due to its radical scavenger ability but due to the singlet oxygen quenching by the sulfanyl group (-SH). In fact, the photodecomposition of 1,3-diphenylisobenzofuran in the presence of Tri-SPy(+)-Me-PF is completely suppressed when l-cysteine is present. The results obtained in this study suggest that singlet oxygen (type II mechanism) plays a very important role over free radicals (type I mechanism) on the PI process of the bioluminescent E. coli by Tri-Py(+)-Me-PF, Tetra-Py(+)-Me and Tri-SPy(+)-Me-PF. Although the use of scavengers is an adequate and simple approach to evaluate the relative importance of the two pathways, it is important to choose scavengers which do not interfere in both PI mechanisms. Sodium azide and d-mannitol seem to be good oxygen and free radical quenchers, respectively, to study the PI mechanisms by porphyrinic photosensitizers.
File Format	HTM / HTML
ISSN	1474905X
Issue Number	10
Volume Number	10
e-ISSN	14749092
Journal	Photochemical & Photobiological Sciences
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2011-10-01
Publisher Place	Great Britain (UK)
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Discipline Chemistry Discipline Biology Escherichia Coli Drug Effects Photosensitizing Agents Chemistry Pharmacology Porphyrins Pyridinium Compounds Cations Cysteine Genetics Metabolism Free Radical Scavengers Kinetics Light Luminescent Measurements Mannitol Photochemotherapy Photolysis Singlet Oxygen Sodium Azide Journal Article Research Support, Non-u.s. Gov't
Content Type	Text
Resource Type	Article
Subject	Physical and Theoretical Chemistry

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