Photodynamic effects of antioxidant substituted porphyrin photosensitizers on gram-positive and -negative bacterial

Pentamidine enhances photosensitization of Acinetobacter baumannii using diode lasers with emission of light at wavelength of ʎ = 405 nm and ʎ = 635 nm

Antimicrobial photodynamic inactivation is currently one of the most promising trends in the modern bactericidal protocols. Under the conditions defined in our studies, we found that in vitro photosensitization of A. baumannii with 5-ALA as a precursor of protoporphyrin IX (photosensitizer) reduces the concentration of viable cells in planktonic cultures, and this process can be strongly enhanced by pentamidine. Diode lasers with the peak-power wavelength of ʎ = 405 nm (radiation intensity of 26 mW cm^-2) and ʎ = 635 nm (radiation intensity of 55 mW cm^-2) were used in this study. It was found that a blue laser light (energy fluence of 64 J cm^-2; no external photosensitizer) in the presence of pentamidine resulted in a reduction of CFU of 99.992 % compared to 99.97 % killing without pentamidine. When a red laser light was used in the experiments (energy fluence of 136 J cm^-2; no external photosensitizer), the mortality rate was 99.98 % in the presence of pentamidine compared to 99.93 % of those killed without the addition of this drug. The lethal effect with 5-ALA was achieved under blue light fluence of 16 J cm^-2 (in the presence of pentamidine) and 32 J cm^-2 (without pentamidine). In the case of laser light of 635 nm, the lethal effect with 5-ALA was attained with energy fluence of 51 J cm^-2 (with pentamidine) and 102 J cm^-2 (without pentamidine). The possible roles of pentamidine in enhancing photodynamic inactivation of A. baumannii have been discussed.

A peptide-based aggregation-induced emission bioprobe for selective detection and photodynamic killing of Gram-negative bacteria

A bioprobe with aggregation-induced emission characteristics is developed, which can visualize and photodynamically ablate Gram-negative bacteria in a selective manner.

Antibacterial Photoactivity and Thermal Stability of Tetra-cationic Porphyrins Immobilized on Cellulosic Fabrics

The thermal stability and photo-bactericidal effect of several tetra-cationic porphyrins and their zinc ion compounds immobilized onto cellulosic fabrics against S. aureus, P. aeruginosa, and E. coli were investigated and compared using a 100 W tungsten lamp. Immobilization of various concentrations of these photosensitizers onto cellulosic fabrics was carried out and characterized by ATR-FT-IR, DRS, TGA, and SEM. Applied cellulosic fabrics with the photosensitizers exhibited remarkable photo-stability, thermal stability, and antimicrobial activity against these studied strains.

Antibacterial activity of Cu(II) and Co(II) porphyrins: role of ligand modification

In this study, we report antibacterial activity of metalloporphyrins; 5, 10, 15, 20-tetrakis (para-X phenyl)porphyrinato M (II) [where X = H, NH₂ and COOMe for M = Cu and X = COOH  and OMe for M = Co]. The activity study of the as-synthesized metalloporphyrins toward two Gram-positive (S. aureus and S. pyogenes) and two Gram-negative (E. coli and K. pneumoniae) bacteria showed a promising inhibitory activity. Among the complexes under study, the highest antibacterial activity is observed for 5, 10, 15, 20-tetrakis (p-carboxyphenyl)porphyrinato cobalt (II), with inhibition zone of 16.5 mm against Staphylococcus aureus (S. aureus). This activity could be attributed to the high binding ability of COOH group to cellular components, membranes, proteins, and DNA as well as the lipophilicity of the complex. Moreover, consistent with literature report, the study revealed that metalloporphyrins with electron withdrawing group at para-positions have better antibacterial activity than metalloporphyrin which possess electron donating group at para position.

Photodynamic antimicrobial activity of new porphyrin derivatives against methicillin resistant Staphylococcus aureus

Methicillin resistant Staphylococcus aureus (MRSA) with multiple drug resistance patterns is frequently isolated from skin and soft tissue infections that are involved in chronic wounds. Today, difficulties in the treatment of MRSA associated infections have led to the development of alternative approaches such as antimicrobial photodynamic therapy. This study aimed to investigate photoinactivation with cationic porphyrin derivative compounds against MRSA in in-vitro conditions. In the study, MRSA clinical isolates with different antibiotic resistance profiles were used. The newly synthesized cationic porphyrin derivatives (P_M, P_E, P_PN, and P_PL) were used as photosensitizer, and 655 nm diode laser was used as light source. Photoinactivation experiments were performed by optimizing energy doses and photosensitizer concentrations. In photoinactivation experiments with different energy densities and photosensitizer concentrations, more than 99% reduction was achieved in bacterial cell viability. No decrease in bacterial survival was observed in control groups. It was determined that there was an increase in photoinactivation efficiency by increasing the energy dose. At the energy dose of 150 J/cm² a survival reduction of over 6.33 log₁₀ was observed in each photosensitizer type. While 200 μM P_M concentration was required for this photoinactivation, 12.50 μM was sufficient for P_E, P_PN, and P_PL. In our study, antimicrobial photodynamic therapy performed with cationic porphyrin derivatives was found to have potent antimicrobial efficacy against multidrug resistant S. aureus which is frequently isolated from wound infections.

Modulation of virulence in Acinetobacter baumannii cells surviving photodynamic treatment with toluidine blue

INTRODUCTION

Widespread resistance to antimicrobial agents has led to a dearth of therapeutic choices in treating Acinetobacter baumannii infections, leading to new strategies for treatment being needed. We evaluated the effects of photodynamic therapy (PDT) as an alternative antimicrobial modality on the virulence features of cell-surviving PDT.

MATERIALS AND METHODS

To determine the sublethal PDT (sPDT), a colistin-resistant, extensively drug-resistant A. baumannii (CR-XDR-AB) clinical isolate and A. baumannii and ATCC 19606 strains, photosensitized with toluidine blue O (TBO), were irradiated with light emitting diodes, following bacterial viability measurements. The biofilm formation ability, outer membrane (OM) integrity, and antimicrobial susceptibility profiles were assessed for cell-surviving PDT. The effects of sPDT on the expression of virulent genes were evaluated by real-time quantitative reverse transcription PCR (qRT-PCR).

RESULTS

sPDT resulted in the reduction of the biofilm formation capacity, and its metabolic activity in strains. The OM permeability and efflux pump inhibition of the sPDT-treated CR-XDR-AB cells were increased; however, there was no significant change in OM integrity in ATCC 19606 strain after sPDT. sPDT reduced the minimum inhibitory concentrations of the most tested antimicrobials by ≥2-fold in CR-XDR-AB. lpsB, blsA, and dnaK were upregulated after the strains were treated with sPDT; however, a reduction in the expression of csuE, epsA, and abaI was observed in the treated strains after sPDT.

CONCLUSION

The susceptibility of CR-XDR-AB to a range of antibiotics was enhanced following sPDT. The virulence of strains is reduced in cells surviving PDT with TBO, and this may have potential implications of PDT for the treatment of A. baumannii infections.

Advance in photosensitizers and light delivery for photodynamic therapy

The brief history of photodynamic therapy (PDT) research has been focused on photosensitizers (PSs) and light delivery was introduced recently. The appropriate PSs were developed from the first generation PS Photofrin (QLT) to the second (chlorins or bacteriochlorins derivatives) and third (conjugated PSs on carrier) generations PSs to overcome undesired disadvantages, and to increase selective tumor accumulation and excellent targeting. For the synthesis of new chlorin PSs chlorophyll a is isolated from natural plants or algae, and converted to methyl pheophorbide a (MPa) as an important starting material for further synthesis. MPa has various active functional groups easily modified for the preparation of different kinds of PSs, such as methyl pyropheophorbide a, purpurin-18, purpurinimide, and chlorin e6 derivatives. Combination therapy, such as chemotherapy and photothermal therapy with PDT, is shortly described here. Advanced light delivery system is shown to establish successful clinical applications of PDT. Phtodynamic efficiency of the PSs with light delivery was investigated in vitro and/or in vivo.

Emerging therapies for multidrug resistant Acinetobacter baumannii

The global emergence of multidrug resistant Acinetobacter baumannii has reduced the number of clinically available antibiotics that retain activity against this pathogen. For this reason, the development of novel prevention and treatment strategies for infections caused by A. baumannii is necessary. Several studies have begun to characterize nonantibiotic approaches that utilize novel mechanisms of action to achieve antibacterial activity. Recent advances in phage therapy, iron chelation therapy, antimicrobial peptides, prophylactic vaccination, photodynamic therapy, and nitric oxide (NO)-based therapies have all been shown to have activity against A. baumannii. However, before these approaches can be used clinically there are still limitations and remaining questions that must be addressed.

Eradication of Gram-positive and Gram-negative bacteria by photosensitizers immobilized in polystyrene

Immobilization of photosensitizers in polymers opens prospects for their continuous and reusable application. Methylene blue (MB) and Rose Bengal were immobilized in polystyrene by mixing solutions of the photosensitizers in chloroform with a polymer solution, followed by air evaporation of the solvent. This procedure yielded 15-140 μm polymer films with a porous surface structure. The method chosen for immobilization ensured 99% enclosure of the photosensitizer in the polymer. The antimicrobial activity of the immobilized photosensitizers was tested against Gram-positive and Gram-negative bacteria. It was found that both immobilized photosensitizers exhibited high antimicrobial properties, and caused by a 1.5-3 log10 reduction in the bacterial concentrations to their total eradication. The bactericidal effect of the immobilized photosensitizers depended on the cell concentration and on the illumination conditions. Scanning electron microscopy was used to prove that immobilized photosensitizers excited by white light caused irreversible damage to microbial cells. Photosensitizers immobilized on a solid phase can be applied for continuous disinfection of wastewater bacteria.

Mechanistic aspects of photoinactivation of Candida albicans by exogenous porphyrins

The mechanism of photoinactivation of Candida albicans by 3.5 μM uncharged, cationic or anionic porphyrins under blue light (407-420 nm) was found to be dependent on the uptake of porphyrins into yeast cells, and was also dependent on the presence or absence of proteins in the photosensitization medium. In a very protein-rich medium, a decrease in viability was observed only with the uncharged porphyrin. Photoinactivation by uncharged or cationic porphyrins in a protein-poorer medium resulted in total eradication, whereas no significant decrease was observed with the anionic porphyrin. Phototreatment in PBS resulted in eradication with all three porphyrins. X-ray microanalysis after phototreatment by the uncharged or cationic porphyrins in the protein-poor medium exhibited ion loss, indicating cell-membrane damage. Transmission electron microscopy indicated cellular and chromosomal damage. No ion loss or cell damage was observed in this medium with the anionic porphyrin. The efficiency of photoeradication of C. albicans is dependent on porphyrin uptake, which might lead (upon illumination) to processes that facilitate the formation of reactive oxygen species that damage the cells. Uptake of charged porphyrins is dependent on protein quantity and quality in the photosensitization microenvironment. This fact must be taken into account when using charged photosensitizers.

Optical method for monitoring of photodynamic inactivation of bacteria

Photodynamic inactivation is a new promising approach to treat bacterial infections. Usually, the evaluation of the efficacy of this method is done through time-consuming and labor-intensive microbiological test methods. This paper describes the development and implementation of an optical method to evaluate the photodynamic inactivation of bacteria based on non-invasive diffuse reflectance measurements. Five Staphylococcus aureus cultures and 15 mice have been used in this study. A skin lesion was created on the back of all animals, and it was contaminated with S. aureus (5.16 ± 0.013 log CFU/ml). Toluidine Blue O (c = 8.67 × 10 (- 3) M) has been used as a photosensitiser agent. The bacterial cultures and animals were exposed to laser radiation (λ = 635 nm, P = 15 mW, DE = 8.654 J/cm(2)) for 20 min. The photodynamic inactivation of bacteria was monitored by acquiring the wounds' reflection spectra at different time points and by microbiological exams on the bioptical material. The good correlation between the diffuse reflectance and colony-forming units demonstrates the value of this optical method based on diffuse reflectance measurements as a rapid technique to monitor photodynamic bacterial inactivation.

Photoactivated disinfection of Streptococcus intermedius through dentin disc at clinically relevant intervals: an in vitro study

In this present study we have tested the impact of porfimer sodium (Photofrin, AXCAN PHARMA Inc., Quebec, Canada) photoactivated disinfection (PD) on cells of Streptococcus intermedius in suspension. In order to provide basic data to support future clinical studies of PD in dentistry the study used exposure to Quartz-tungsten-halogen (QTH) dental curing light for clinically relevant time periods to activate Photofrin and measured its effectiveness under a variety of conditions including activation through dentin hard tissue. S. intermedius was grown in planktonic suspension for 48h. Nine groups were formed: three control groups (1-3) and six experimental groups (4-9). Groups 4-6 tested the use of Photofrin treatment combined with QTH light at various intervals of irradiation (5, 15 and 60s). Groups 7-9 were similar to groups 4-6 with the exception that irradiation commenced through a dentin disc. Following treatment, bacteria were plated. Colony counts were measured following 72h incubation at 37 degrees C. Statistical analysis was carried out by one-way ANOVA at a 95% confidence level. A significant reduction in S. intermedius colony counts was observed for all experimental groups and one control group. The reduction in numbers of colonies in the experimental groups varied from 79.28 to 99.40% with an average of 94.61%. Reduction in viable bacterial cells indicated a strong relationship between power density and irradiation interval. When curing light energy density was lower due to the irradiation through the 1mm dentin disc, prolonged irradiation interval enhanced bacterial kill. In conclusion, where direct irradiation is not possible for PD treatment, irradiation through dentin may still be done successfully within a clinically relevant interval.

Photodynamic antimicrobial chemotherapy by liposome-encapsulated water-soluble photosensitizers

Photodynamic antimicrobial chemotherapy is an alternative method for killing bacterial cells in view of the increasing problem of multi-antibiotic resistance. We examined the effect of three water-soluble photosensitizers (PhS): methylene blue (MB), neutral red (NR) and rose bengal (RB) on Gram-positive and Gram-negative bacteria. We compared the efficacy of PhS in their free form and encapsulated in liposomal formulations against various bacterial strains, and determined conditions for the effective use of encapsulated PhS. We found that all three PhS were able to eradicate the Gram-positive microbes Staphylococcus aureus and Sarcina lutea; and MB and RB were effective against St. epidermidis. In the case of the Gram-negative species, MB and RB were cytotoxic against the Shigella flexneri, NR-inactivated Escherichia coli and Salmonella para B, and BR was effective in killing Pseudomonas aeruginosa. None of the examined PhS showed activity against Klebsiella pneumoniae. MB and NR enclosed in liposomes gave a stronger antimicrobial effect than free PhS for all tested prokaryotes, whereas encapsulation of RB led to no increase in its activity. We suggest that encapsulation of PhS can increase the photoinactivation of bacteria.

Mechanistic insight of the photodynamic inactivation of Escherichia coli by a tetracationic zinc(II) phthalocyanine derivative

Photodynamic inactivation (PDI) of Escherichia coli has been studied in cultures treated with zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc(+4)) to obtain insight about the mechanism of damage. This phthalocyanine is rapidly bound to cells, reaching a value of approximately 0.8 nmol/10(6) cells when the cultures were incubated with 2 microM sensitizer. After 30 min of irradiation, a 4 log decrease of E. coli survival was observed. The photocytotoxic action was investigated in plasmid and genomic DNA by electrophoretic analysis. Absorption spectroscopic studies showed that this cationic phthalocyanine interacts strongly with DNA (K(DNA)=4.7 x 10(6)M(-1)). Photocleavage of calf thymus DNA sensitized by ZnPPc(+)4 was not found even after long irradiation periods. Similar results were also observed in genomic DNA extracted from E. coli cells after PDI treatment. Modifications of plasmid DNA isolated from bacteria were only observed after long irradiation periods. However, under these conditions transmission electron microscopy of the PDI bacteria revealed an aggregation of cytoplasmic macromolecules and irregularities in cell barriers. Also, scanning electron microscopy showed a shrunken appearance in cells after PDI. Even so, release of intracellular biopolymers was not detected by absorption. On the other hand, outer and inner membranes permeabilization assays showed an increase in the permeability. Consequently, alterations in the cell membrane functionality induced by ZnPPc(+4) appear to be the major cause of E. coli inactivation upon PDI.

A possible mechanism for visible light-induced wound healing

BACKGROUND AND OBJECTIVES

Chronic wounds resistant to conventional therapy have been treated successfully with low energy lasers and light emitting diodes (LEDs) in the visible and near IR region. It has been proposed that production of low level reactive oxygen species (ROS) following illumination is the first step of photobiomodulation. It was also shown that white light (400-800 nm) has similar stimulatory effects as lasers and LEDs. ROS at higher levels are toxic to cells and bacteria.

STUDY DESIGN/MATERIALS AND METHODS

In the present study, we examined the phototoxicity of broadband (400-800 nm, 120 J/cm(2)) visible light on the survival of several pathogenic bacteria: Staphylococcus aureus 195, Pseudomonas aeruginosa 1316, Escherichia coli 1313, and Serratia marcescens. These bacteria were chosen due to their high prevalence in infected wounds. The survival of bacterial cells following illumination was monitored by counting the number of colony forming units before and after exposure to light.

RESULTS

Illumination with white light, 120 J/cm(2), caused a reduction of 62%, 83%, and 56% in the colony count of E. coli 1313, S. aureus 195 and S. marcescens, respectively, though no reduction in the viability of P. aeruginosa 1316 was demonstrated. The phototoxic effect was found to involve induction of ROS production by the bacteria. It was also found that illumination of S. aureus 195 and E. coli 1313 in the presence of pyocyanin, known to be secreted by P. aeruginosa, had a stronger bactericidal effect compared to illumination alone.

CONCLUSION

Visible light at high intensity can kill bacteria in infected wounds. Thus, illumination of infected wounds with intense visible light, prior to low intensity illumination for stimulating wound closure, may reduce infection and promote healing.

Tandem dispersion and killing of bacteria from a biofilm

The combined effects of biofilm dispersion with a 2-aminoimidazole-triazole conjugate and bactericidal activity with a photodynamic inactivation agent suggest a novel combination therapy for treating diverse microbial infections.

Sensitivity of Staphylococcus aureus strains to broadband visible light

The phototoxic effect of illumination with broadband visible light on the viability of two Staphylococcus aureus strains was examined in the present study. A difference in the light sensitivity of the two strains was found. Illumination of the tested strains with a fluence rate of 180 J cm(-2) caused a reduction of up to 99.8% in the colony count of one of the strains (the "sensitive" strain). Illumination of the other strain (the "resistant" strain) resulted in a 55.5% reduction in viability. Proliferation of both strains was observed at low fluence rates of light. The phototoxic effect was found to be dependent on oxy radical production. The light-sensitive strain produced higher amounts of hydroxyl and superoxide radicals than the "resistant" strain. Adaptation to oxidative stress was exhibited only by the "resistant" strain. The "sensitive" strain produced ten times more endogenous porphyrins and secreted almost nine times more porphyrins than the resistant strain. Furthermore, the "resistant" strain produced twice as many carotenoids that protect the strain from illumination than the "sensitive" strain. These results indicate that high intensities of visible light cause bacterial photoeradication, a reaction which may assist wound healing by killing the infecting bacteria. On the other hand, low intensities of white light were found to enhance bacterial proliferation and thus prolong wound infection.

Photodynamic inactivation of recombinant bioluminescent Escherichia coli by cationic porphyrins under artificial and solar irradiation

A faster and simpler method to monitor the photoinactivation process of Escherichia coli involving the use of recombinant bioluminescent bacteria is described here. Escherichia coli cells were transformed with luxCDABE genes from the marine bioluminescent bacterium Vibrio fischeri and the recombinant bioluminescent indicator strain was used to assess, in real time, the effect of three cationic meso-substituted porphyrin derivatives on their metabolic activity, under artificial (40 W m(-2)) and solar irradiation (approximately 620 W m(-2)). The photoinactivation of bioluminescent E. coli is effective (>4 log bioluminescence decrease) with the three porphyrins used, the tricationic porphyrin Tri-Py+-Me-PF being the most efficient compound. The photoinactivation process is efficient both with solar and artificial light, for the three porphyrins tested. The results show that bioluminescence analysis is an efficient and sensitive approach being, in addition, more affordable, faster, cheaper and much less laborious than conventional methods. This approach can be used as a screening method for bacterial photoinactivation studies in vitro and also for the monitoring of the efficiency of novel photosensitizer molecules. As far as we know, this is the first study involving the use of bioluminescent bacteria to monitor the antibacterial activity of porphyrins under environmental conditions.

Mechanisms of Escherichia coli photodynamic inactivation by an amphiphilic tricationic porphyrin and 5,10,15,20-tetra(4-N,N,N-trimethylammoniumphenyl) porphyrin

The mechanistic aspects of Escherichia coli photodynamic inactivation (PDI) have been investigated in bacteria treated with 5,10,15-tris[4-(3-N,N,N-trimethylammoniumpropoxy)phenyl]-20-(4-trifluoromethylphenyl)porphyrin iodide (A3B3+) and visible light. The photosensitization activity of A3B3+ porphyrin was compared with that of 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin p-tosylate (TMAP4+), which is an active tetracationic sensitizer to eradicate bacteria. The PDI damages on plasmid and genomic DNA were analyzed by electrophoresis. DNA photocleavage was observed after a long period of irradiation, when the bacterial cells are largely photoinactivated. Transmission electron microscopy (TEM) revealed structural changes with appearance of low density areas into the cells and irregularities in cell barriers, which could affect the normal cell membrane functionality. Also, damages on the cell-wall were not detected by scanning electron microscopy (SEM) and release of intracellular biopolymers was not found after PDI. These results indicate that the photodynamic activity of these cationic porphyrins produces DNA photodamage after a long period of irradiation. Therefore, an interference with membrane functions could be the main cause of E. coli photoinactivation upon short PDI treatments.

Light sources for photodynamic inactivation of bacteria

Bacteria have an important role in human and animal morbidity, and a great number of them have developed antibiotic resistance. In the past recent years a new way of dealing with this problem has been studied: photodynamic inactivation. This method is based on administration of a photosensitizing substance that fixes itself in the bacterial cell followed by exposure to a light source. In the experiments done by many researchers on photodynamic inactivation of bacteria, both coherent and non-coherent light sources were used. This article is a review of these light sources and of some experimental results obtained by different authors.

Sewage bacteriophage photoinactivation by cationic porphyrins: a study of charge effect

Photodynamic therapy has been used to inactivate microorganisms through the use of targeted photosensitizers. Recently the inactivation of bacteria in residual waters has been reported, but nothing is known about photoinactivation of environmental bacteriophages, which are often used as indicators of human enteric viruses. In this study we tested the effect of six cationic porphyrin derivatives with two to four charges on the photoinactivation of a sewage bacteriophage. A phage suspension of 5 x 10(7) PFU mL(-1) was exposed to white light (40 W m(-2)), during 270 min, at three photosensitizer concentrations (0.5, 1.0 and 5.0 microM). Tetra- and tricationic porphyrins inactivated the T4-like sewage phage to the limits of detection, but dicationic porphyrins did not lead to a significant decrease in phage viability. At the highest photosensitizer concentration (5.0 microM), the phage was completely inactivated (>99.9999% of inactivation, reduction of 7.2 log) after 270 min by the tetracationic porphyrin. Two of the tricationic derivatives also led to phage inactivation to the limit of detection. The rate of bacteriophage photoinactivation and the efficiency of the photosensitizer appeared to vary with the charge and with the substituents in the meso-positions of the porphyrin macrocycle. Tetra- and tricationic porphyrins can, therefore, be used as a new method for inactivating sewage bacteriophages that are frequently used as human enteric virus indicators. The complete inactivation of viruses with low light intensity means that this methodology can be used even on cloudy days and during winter, opening the possibility to develop new technologies for wastewater treatment.

Low-Intensity Photosensitization May Enhance RecA Production

Three bacterial strains-Escherichia coli, Acinetobacter calcoaceticus, and the A. calcoaceticus RecA- mutant-underwent photosensitization by a low-concentration (0.73 micromol/L) tetramethyl pyridyl porphine (a cationic hydrophylic photosensitizer) and a 4-J/cm2 dose of 407 to 420 nm blue light. The viability of the first two strains decreased by approximately 60%. and that of the RecA- strain decreased by 90%. Increasing the amount of photosensitizer to 14.6 micromol/L at the same dose of blue light resulted in a 95% to 98% decrease in viability of the three strains. Very little damage to the bacterial DNA was observed after this treatment. Increasing the concentration photosensitizer under the same illumination conditions also resulted in very little damage to the DNA. Western blotting demonstrated that the low photosensitization procedures enhance RecA production for mending the damaged chromosomal DNA. RecA production as a result of low-dose photosensitization was confirmed and demonstrated by immunofluorescent staining and gold immunolabeling. Although DNA is not the primary target for photosensitization, this process of RecA production may provide a certain degree of DNA mending and may also affect the survival of bacterial cells on low-intensity photosensitization.

Inactivation of methicillin-resistant Staphylococcus aureus (MRSA) by liposome-delivered photosensitising agents

The uptake of two photosensitising agents (hematoporphyrin and chlorophyll a) by a highly pathogenic bacterium, namely methicillin-resistant Staphylococcus aureus (MRSA), has been studied by using unilamellar liposomes of different size, fluidity and electric charge as carriers. Optimal results are obtained by using hematoporphyrin embedded in fluid cationic vesicles composed by the monocationic lipid N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulfate (DOTAP), which yield an endocellular concentration of photosensitiser much higher than that obtained by incubation of the cells with the free porphyrin, yet promote a tighter binding and a more efficient photoinactivation of MRSA. Apparently, the photosensitiser is successfully transferred from the liposome to the bacterial cells when the presence of the tetrapyrrolic derivative does not appreciably perturb the native three-dimensional organisation of the lipid vesicle, such as it occurs with hematoporphyrin. On the other hand, chlorophyll, which causes a marked structural alteration of the DOTAP vesicles as shown by electron microscopy and fluorescence anisotropy measurements, does not show any detectable photocytotoxicity toward MRSA, contrary to what observed for the free dye.

Tunable DNA Photocleavage by an Acridine−Imidazole Conjugate

We report the synthesis and characterization of photonucleases N,N'-bis[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (7) and N-[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (10), consisting of a central 3,6-acridinediamine chromophore attached to 4 and 2 metal-coordinating imidazole rings, respectively. In DNA reactions employing 16 metal salts, photocleavage of pUC19 plasmid is markedly enhanced when compound 7 is irradiated in the presence of either Hg(II), Fe(III), Cd(II), Zn(II), V(V), or Pb(II) (low-intensity visible light, pH 7.0, 22 degrees C, 8-50 microM 7). We also show that DNA photocleavage by 7 can be modulated by modifying buffer type and pH. Evidence of metal complex formation is provided by EDTA experiments and by NMR and electrospray ionization mass spectral data. Sodium azide, sodium benzoate, superoxide dismutase, and catalase indicate the involvement of type I and II photochemical processes in the metal-assisted DNA photocleavage reactions. Thermal melting studies show that compound 7 increases the Tm of calf thymus DNA by 10 +/- 1 degrees C at pH 7.0 and that the Tm is further increased upon the addition of either Hg(II), Cd(II), Zn(II), or Pb(II). In the case of Fe(III) and V(V), a colorimetric assay demonstrates that compound 7 sensitizes one electron photoreduction of these metals to Fe(II) and V(IV), likely accelerating the production of type I reactive oxygen species. Our data collectively indicate that buffer, pH, Hg(II), Fe(III), Cd(II), Zn(II), V(V), Pb(II), and light can be used to "tune" DNA cleavage by compound 7 under physiologically relevant conditions. The 3,6-acridinediamine acridine orange has demonstrated great promise for use as a photosensitizer in photodynamic therapy. In view of the distribution of iron in living cells, compound 7 and other metal-binding acridine-based photonucleases should be expected to demonstrate excellent photodynamic action in vivo.

Mechanistic study of the photodynamic inactivation of Candida albicans by a cationic porphyrin

The growing resistance against antifungal agents has renewed the search for alternative treatment modalities, and antimicrobial photodynamic inactivation (PDI) is a potential candidate. The cationic porphyrin 5-phenyl-10,15,20-Tris(N-methyl-4-pyridyl)porphyrin chloride (TriP[4]) is a photosensitizer that in combination with light can inactivate bacteria, fungi, and viruses. For future improvement of the efficacy of PDI of clinically relevant fungi such as Candida albicans, we sought to understand the working mechanism by following the response of C. albicans exposed to PDI using fluorescence confocal microscopy and freeze-fracture electron microscopy. The following events were observed under dark conditions: TriP[4] binds to the cell envelope of C. albicans, and none or very little TriP[4] enters the cell. Upon illumination the cell membrane is damaged and eventually becomes permeable for TriP[4]. After lethal membrane damage, a massive influx of TriP[4] into the cell occurs. Only the vacuole membrane is resistant to PDI-induced damage once TriP[4] passes the plasma membrane. Increasing the incubation time of C. albicans with TriP[4] prior to illumination did not increase the influx of TriP[4] into the cell or the efficacy of PDI. After the replacement of 100% phosphate-buffered saline (PBS) by 10% PBS as the medium, C. albicans became permeable for TriP[4] during dark incubation and the efficacy of PDI increased dramatically. In conclusion, C. albicans can be successfully inactivated by the cationic porphyrin TriP[4], and the cytoplasmic membrane is the target organelle. TriP[4] influx occurred only after cell death.

Photodynamic therapy for Staphylococcus aureus infected burn wounds in mice

The rise of multiply antibiotic resistant bacteria has led to searches for novel antimicrobial therapies to treat infections. Photodynamic therapy (PDT) is a potential candidate; it uses the combination of a photosensitizer with visible light to produce reactive oxygen species that lead to cell death. We used PDT mediated by meso-mono-phenyl-tri(N-methyl-4-pyridyl)-porphyrin (PTMPP) to treat burn wounds in mice with established Staphylococcus aureus infections The third degree burn wounds were infected with bioluminescent S. aureus. PDT was applied after one day of bacterial growth by adding a 25% DMSO/500 microM PTMPP solution to the wound followed by illumination with red light and periodic imaging of the mice using a sensitive camera to detect the bioluminescence. More than 98% of the bacteria were eradicated after a light dose of 210 J cm(-2) in the presence of PTMPP. However, bacterial re-growth was observed. Light alone or PDT both delayed the wound healing. These data suggest that PDT has the potential to rapidly reduce the bacterial load in infected burns. The treatment needs to be optimized to reduce wound damage and prevent recurrence.

Photoinactivation ofEscherichia coliusing porphyrin derivatives with different number of cationic charges

The photodynamic effect of meso-substituted cationic porphyrins, 5-[4-(trimethylammonium)phenyl]-10,15,20-tris(2,4,6-trimethoxyphenyl)porphyrin iodide 1, 5,10-di(4-methylphenyl)-15,20-di(4-trimethylammoniumphenyl)porphyrin iodide 2 and 5-(4-trifluorophenyl)-10,15,20-tris(4-trimethylammoniumphenyl)porphyrin iodide 3, have been investigated in both homogeneous medium bearing photooxidizable substrates and in vitro on a typical gram-negative bacterium Escherichia coli. Absorption and fluorescence spectroscopic studies were compared in N,N-dimethylformamide. Fluorescence quantum yields (varphiF) of 0.10, 0.06 and 0.08 were calculated for porphyrins 1, 2 and 3, respectively. The singlet molecular oxygen, O2(1Deltag), production was evaluated using 9,10-dimethylanthracene yielding values of 0.66, 0.36 and 0.42 for porphyrins 1, 2 and 3, respectively. Guanosine 5'-monophosphate was used as biological substrate model. Similar decomposition of guanosine 5'-monophosphate was obtained using these cationic porphyrins as sensitizer. In biological medium, photosensitized inactivation of E. coli was analyzed using cells without and with one washing step. E. coli cultures were treated with sensitizer at 37 degrees C for 30 min in dark. In both procedures, a higher photoinactivation of cells (>99.999%) was found for cells treated with 10 microM of tricationic porphyrin 3 and irradiated for 5 min with visible light. Porphyrins 1 and 2 only show an important photodamage when the cells are irradiated without washing step. These results indicated that the tetracationic porphyrin 3 could be a promising sensitizer with potential applications in the photoinactivation of bacterial cells by photodynamic therapy.

Photosensitizers and antioxidants: a way to new drugs?

Photodynamic therapy (PDT) is a relatively new modality of treatment of diseases involving uncontrolled cell proliferation. It is based on the production of reactive species upon illumination of a photosensitizer in the presence of oxygen. Antioxidants are primarily reducing agents prone to scavenge reactive species in one way or another. Their presence in photodynamic reactions usually reduces the efficacy of PDT. Some antioxidants like ascorbic acid, alpha-tocopherol or butyl-4-hydroxyanisole, however, when added to cells at adequate concentrations may enhance the photodamaging activity of PDT. The presence of transition metals and precise timing of antioxidant administration may also be important factors in increasing the efficacy of PDT. Antioxidant carrier sensitizers have been designed, synthesised and tested for their antibacterial PDT activity. The promising results raise the question whether the introduction of antioxidant moieties into sensitizer molecules would lead to the synthesis of highly effective new drugs.