Photoinactivation ofEscherichia coliusing porphyrin derivatives with different number of cationic charges

Photodynamic inactivation of multidrug-resistant strains of Klebsiella pneumoniae and Pseudomonas aeruginosa in municipal wastewater by tetracationic porphyrin and violet-blue light: The impact of wastewater constituents

There is an increasing need to discover effective methods for treating municipal wastewater and addressing the threat of multidrug-resistant (MDR) strains of bacteria spreading into the environment and drinking water. Photodynamic inactivation (PDI) that combines a photosensitiser and light in the presence of oxygen to generate singlet oxygen and other reactive species, which in turn react with a range of biomolecules, including the oxidation of bacterial genetic material, may be a way to stop the spread of antibiotic-resistant genes. The effect of 5,10,15,20-(pyridinium-3-yl)porphyrin tetrachloride (TMPyP3) without light, and after activation with violet-blue light (VBL) (394 nm; 20 mW/cm2), on MDR strains of Pseudomonas aeruginosa, Klebsiella pneumoniae and K. pneumoniae OXA-48 in tap water and municipal wastewater was investigated. High toxicity (~2 μM) of TMPyP3 was shown in the dark on both strains of K. pneumoniae in tap water, while on P. aeruginosa toxicity in the dark was low (50 μM) and the PDI effect was significant (1.562 μM). However, in wastewater, the toxicity of TMPyP3 without photoactivation was much lower (12.5-100 μM), and the PDI effect was significant for all three bacterial strains, already after 10 min of irradiation with VBL (1.562-6.25 μM). In the same concentrations, or even lower, an anti-adhesion effect was shown, suggesting the possibility of application in biofilm control. By studying the kinetics of photoinactivation, it was found that with 1,562 μM of TMPyP3 it is possible to achieve the complete destruction of all three bacteria after 60 min of irradiation with VBL. This study confirmed the importance of studying the impact of water constituents on the properties and PDI effect of the applied photosensitiser, as well as checking the sensitivity of targeted bacteria to light of a certain wavelength, in conditions as close as possible to those in the intended application, to adjust all parameters and perfect the method.

The antibacterial activity of photodynamic agents against multidrug resistant bacteria causing wound infection

Antimicrobial photodynamic inactivation (aPDI) of multidrug-resistant (MDR) wound pathogens was evaluated with cationic porphyrin derivatives (CPDs). MDR bacterial strains including Pseudomonas aeruginosa, Escherichia coli, Acinetobacter baumannii, and Klebsiella pneumoniae were used. The CPDs named PM, PE, PN, and PL were synthesized as a photosensitizer (PS). A diode laser with a wavelength of 655 nm was used as a light source. aPDI of the combinations formed with different energy densities (50, 100, and 150 J/cm²) and PS concentrations (ranging from 3.125 to 600 µM) were evaluated on each bacterial strain. Dark toxicity, cytotoxicity, and phototoxicity were determined on fibroblast cells. In the aPDI groups, survival reductions of up to 5.80 log₁₀ for E. coli, 5.90 log₁₀ for P. aeruginosa, 6.11 log₁₀ for K. pneumoniae, and 6.78 log₁₀ for A. baumannii were obtained. The cytotoxic effect of PL and PM on fibroblast cells was very limited. PN was the type of CPD with the highest dark toxicity on fibroblast cells. In terms of providing broad-spectrum aPDI without or with very limited cytotoxic effect, the best result was observed in aPDI application with PL. The other CPDs need some modifications to show bacterial selectivity for use at 50 µM and above.

Rational Design of Self-Assembled Cationic Porphyrin-Based Nanoparticles for Efficient Photodynamic Inactivation of Bacteria

Bacterial infection has become an urgent health problem in the world. Especially, the evolving resistance of bacteria to antibiotics makes the issue more challenging, and thus new treatments to fight these infections are needed. Antibacterial photodynamic therapy (aPDT) is recognized as a novel and promising method to inactivate a wide range of bacteria with few possibilities to develop drug resistance. However, the photosensitizers (PSs) are not effective against Gram-negative bacteria in many cases. Herein, we use conjugated meso-tetra(4-carboxyphenyl)porphine (TCPP) and triaminoguanidinium chloride (TG) to construct self-assembled cationic TCPP-TG nanoparticles (NPs) for efficient bacterial inactivation under visible light illumination. The TCPP-TG NPs can rapidly adhere to both Gram-negative and Gram-positive bacteria and display promoted singlet oxygen (¹O₂) generation compared with TCPP under light irradiation. The high local positive charge density of TCPP-TG NPs facilitates the interaction between the NPs and bacteria. Consequently, the TCPP-TG NPs produce an elevated concentration of local ¹O₂ under light irradiation, resulting in an extraordinarily high antibacterial efficiency (99.9999% inactivation of the representative bacteria within 4 min). Furthermore, the TCPP-TG NPs show excellent water dispersity and stability during 4 months of storage. Therefore, the rationally designed TCPP-TG NPs are a promising antibacterial agent for effective aPDT.

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.

Peripheral tetra-cationic Pt(II) porphyrins photo-inactivating rapidly growing mycobacteria: First application in mycobacteriology

In this manuscript, we report, for the first time, the photoinactivation evaluation of tetra-cationic porphyrins with peripheral Pt (II)-bpy complexes in the photodynamic inactivation (PDI) of rapidly growing mycobacterial strains (RGM). Two different isomeric Pt (II)-porphyrins were synthetized and applied. PDI experiments in the strains of Mycobacteroides abscessus subsp. Abscessus (ATCC 19977), Mycolicibacterium fortuitum (ATCC 6841), Mycobacteroides abscessus subsp. Massiliense (ATCC 48898), and Mycolicibacterium smegmatis (ATCC 700084) conducted with adequate concentration (without aggregation) of photosensitizers (PS) under white-light illumination for 90 min showed that the most effective PS significantly reduced the concentration of viable mycobacteria. The present results show that positively charged porphyrins at the meta position (3-PtTPyP) are more efficient PS against M. abscessus, M. fortuitum, M. massiliense, and M. smegmatis. The effectiveness of the molecule as PS for PDI studies is also clear with mycobacteria, which is strongly related with the porphyrin peripheral charge and coordination platinum (II) compounds and consequently their solubility in physiological media. Tetra-cationic PS may be promising anti-mycobacterial PDI agents with potential applications in medical clinical cases and bioremediation.

An Insight into Advanced Approaches for Photosensitizer Optimization in Endodontics-A Critical Review

Apical periodontitis is a biofilm-mediated disease; therefore, an antimicrobial approach is essential to cure or prevent its development. In the quest for efficient strategies to achieve this objective, antimicrobial photodynamic therapy (aPDT) has emerged as an alternative to classical endodontic irrigation solutions and antibiotics. The aim of the present critical review is to summarize the available evidence on photosensitizers (PSs) which has been confirmed in numerous studies from diverse areas combined with several antimicrobial strategies, as well as emerging options in order to optimize their properties and effects that might be translational and useful in the near future in basic endodontic research. Published data notably support the need for continuing the search for an ideal endodontic photosensitizer, that is, one which acts as an excellent antimicrobial agent without causing toxicity to the human host cells or presenting the risk of tooth discoloration. The current literature on experimental studies mainly relies on assessment of mixed disinfection protocols, combining approaches which are already available with aPDT as an adjunct therapy. In this review, several approaches concerning aPDT efficiency are appraised, such as the use of bacteriophages, biopolymers, drug and light delivery systems, efflux pump inhibitors, negative pressure systems, and peptides. The authors also analyzed their combination with other approaches for aPDT improvement, such as sonodynamic therapy. All of the aforementioned techniques have already been tested, and we highlight the biological challenges of each formulation, predicting that the collected information may encourage the development of other effective photoactive materials, in addition to being useful in endodontic basic research. Moreover, special attention is dedicated to studies on detailed conditions, aPDT features with a focus on PS enhancer strategies, and the respective final antimicrobial outcomes. From all the mentioned approaches, the two which are most widely discussed and which show the most promising outcomes for endodontic purposes are drug delivery systems (with strong development in nanoparticles) and PS solubilizers.

New Materials Based on Cationic Porphyrins Conjugated to Chitosan or Titanium Dioxide: Synthesis, Characterization and Antimicrobial Efficacy

The post-functionalization of 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide, known as a highly efficient photosensitizer (PS) for antimicrobial photodynamic therapy (aPDT), in the presence of 3- or 4-mercaptobenzoic acid, afforded two new tricationic porphyrins with adequate carboxylic pending groups to be immobilized on chitosan or titanium oxide. The structural characterization of the newly obtained materials confirmed the success of the porphyrin immobilization on the solid supports. The photophysical properties and the antimicrobial photodynamic efficacy of the non-immobilized porphyrins and of the new conjugates were evaluated. The results showed that the position of the carboxyl group in the mercapto units or the absence of these substituents in the porphyrin core could modulate the action of the photosensitizer towards the bioluminescent Gram-negative Escherichia coli bacterium. The antimicrobial activity was also influenced by the interaction between the photosensitizer and the type of support (chitosan or titanium dioxide). The new cationic porphyrins and some of the materials were shown to be very stable in PBS and effective in the photoinactivation of E. coli bacterium. The physicochemical properties of TiO2 allowed the interaction of the PS with its surface, increasing the absorption profile of TiO2, which enables the use of visible light, inactivating the bacteria more efficiently than the corresponding PS immobilized on chitosan.

Photodynamic inactivation to prevent and disrupt Staphylococcus aureus biofilm under different media conditions

OBJECTIVE

The goal of this work was to investigate the photodynamic activity of 5,10,15,20-tetrakis[4-(3-N,N-dimethylaminopropoxy)phenyl]chlorin (TAPC) and zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine iodide (ZnPPc⁴⁺ ) as photosensitizers to inactivate Staphylococcus aureus biofilms and prevent their formations in different culture media.

METHODS

We incubated S aureus biofilms in different culture media: tryptic soy (TS), nutrient (N), Müeller Hinton (MH) broth, TS with glucose 2 and 5% (w/v) with 5 μM ZnPPc⁴⁺ or TAPC and irradiated with visible light (350-800 nm). Photodynamic inactivation (PDI) was determined by count of colony forming units (CFU) and crystal violet method. Furthermore, we studied PDI effect on biofilm development in TS broth. Finally, we examined the effects of PDI on the structure of S aureus biofilm.

RESULTS

Greater inactivation was achieved, using TAPC or ZnPPc⁴⁺ , when S aureus biofilm was grown in N or MH broths rather than in TS. Besides, glucose addition to the medium decreases the ability to develop biofilm and increase the photoinactivation capacity. Prevention of 3 log biofilm developments was obtained when S aureus cultures were treated with TAPC (10 μM) and 108 J/cm² in TS broth and the number of CFU was counted after 24 hours. Moreover, microscopy studies demonstrated modifications in biofilm architecture.

CONCLUSIONS

These results indicate that TAPC and ZnPPc⁴⁺ may be promising photosensitizers for photodynamic inactivation of S aureus biofilms or to prevent their formation.

Porphyrinoid photosensitizers mediated photodynamic inactivation against bacteria

The multi-drug resistant bacteria have become a serious problem complicating therapies to such a degree that often the term "post-antibiotic era" is applied to describe the situation. The infections with methicillin-resistant S. aureus, vancomycin-resistant E. faecium, third generation cephalosporin-resistant E. coli, third generation cephalosporin-resistant K. pneumoniae and carbapenem-resistant P. aeruginosa have become commonplace. Thus, the new strategies of infection treatment have been searched for, and one of the approaches is based on photodynamic antimicrobial chemotherapy. Photodynamic protocols require the interaction of photosensitizer, molecular oxygen and light. The aim of this review is to provide a comprehensive overview of photodynamic antimicrobial chemotherapy by porphyrinoid photosensitizers. In the first part of the review information on the mechanism of photodynamic action and the mechanism of the bacteria resistance to the photodynamic technique were described. In the second one, it was described porphyrinoids photosensitizers like: porphyrins, chlorins and phthalocyanines useable in photodynamic bacteria inactivation.

Controlled release of antibiotics from photopolymerized hydrogels: Kinetics and microbiological studies

The development of convenient synthetic methods and improved materials for the production of high load-capacity and biocompatible drug delivery systems is a challenging task with important implications in health sciences. In this work, acrylamide/2-hydroxyethylmethacrylate and N-isopropylacrylamide/2-hydroxyethylmethacrylate hydrogels were synthesized by photopolymerization using energy-efficient green-LEDs. A functionalized silsesquioxane was used as both crosslinker and co-initiator for the photopolymerization. The hybrid organic-inorganic nature of the silsesquioxane improved the resulting hydrogels' properties increasing their swelling capacity and biocompatibility. Additionally, the mild conditions used during the photopolymerization allowed the synthesis of hydrogels in the presence of antibiotics yielding high load-capacity materials in which the drug preserves its molecular structure and antimicrobial activity (as confirmed by HPLC and microbiological assays). The materials were characterized by FTIR, DSC and SEM. Additionally, the kinetics of gels´ swelling and drug release were studied under physiological conditions (pH 7.4 and 37 °C). The results demonstrate how hydrogel composition affects the antibiotics-release kinetics. The final drug release percentage increased with increasing molar fraction of acrylamide or N-isopropylacrylamide and in most cases exceeded 85%. Finally, the antibacterial effect of loaded gels was characterized using a number of assays against Gram negative and Gram positive bacteria. The observed antibacterial effect correlated well with swelling and drug release results. Furthermore, gels are not toxic for isolated erythrocytes as demonstrated by haemolytic tests. Overall, our results indicate that the produced hydrogels are promising materials to develop controlled drug-delivery devices such as capsules, dermatological patches and others.

Influence of Cationic meso-Substituted Porphyrins on the Antimicrobial Photodynamic Efficacy and Cell Membrane Interaction in Escherichia coli

Photodynamic inactivation (PDI) is a non-antibiotic option for the treatment of infectious diseases. Although Gram-positive bacteria have been shown to be highly susceptible to PDI, the inactivation of Gram-negative bacteria has been more challenging due to the impermeability properties of the outer membrane. In the present study, a series of photosensitizers which contain one to four positive charges (1–4) were used to evaluate the charge influence on the PDI of a Gram-negative bacteria, Escherichia coli (E. coli), and their interaction with the cell membrane. The dose-response PDI results confirm the relevance of the number of positive charges on the porphyrin molecule in the PDI of E. coli. The difference between the Hill coefficients of cationic porphyrins with 1–3 positive charges and the tetra-cationic porphyrin (4) revealed potential variations in their mechanism of inactivation. Fluorescent live-cell microscopy studies showed that cationic porphyrins with 1–3 positive charges bind to the cell membrane of E. coli, but are not internalized. On the contrary, the tetra-cationic porphyrin (4) permeates through the membrane of the cells. The contrast in the interaction of cationic porphyrins with E. coli confirmed that they followed different mechanisms of inactivation. This work helps to have a better understanding of the structure-activity relationship in the efficiency of the PDI process of cationic porphyrins against Gram-negative bacteria.

Kinetic and mechanistic aspects of solid state, nanostructured porphyrin diacid photosensitizers in photooxidation of sulfides

The kinetics and mechanism of aerobic photooxidation of sulfides in the presence of a series of electron-rich and electron-deficient porphyrins immobilized on Amberlyst 15 nanoparticles in the form of porphyrin diacids are reported.

An efficient formulation based on cationic porphyrins to photoinactivate Staphylococcus aureus and Escherichia coli

AIM

Antibiotic resistance is an increasingly serious worldwide problem that needs to be addressed with alternative tools. Antimicrobial photodynamic therapy seems a promising approach but in some cases the synthesis of highly efficient photosensitizers requires laborious processes burdened by extensive chromatographic purifications. In this study, we evaluate the suitability of a formulation (Form-1) containing porphyrins bearing different charges, obtained during the synthesis of the highly efficient photosensitizer 5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin tri-iodide.

RESULTS

Form-1 was equally effective in the photoinactivation of Escherichia coli and Staphylococcus aureus (reductions >5 log) as the best stand-alone photosensitizer.

CONCLUSION

The effective reduction of bacteria with Form-1 provided promising indications supporting its use, leading to a substantial decrease in costs and production time.

In Vitro Photodynamic Activity of N-Methylated and N-Oxidised Tripyridyl Porphyrins with Long Alkyl Chains and Their Inhibitory Activity in Sphingolipid Metabolism

A series of N-methylated and N-oxidised tripyridyl porphyrins were synthesised, characterised, and their PDT activity was studied with six cell lines. All the tested porphyrins with a long alkyl chain, except one, were more efficient for PDT than an N-methylated hydrophilic porphyrin and N-oxidised porphyrin without the long alkyl chain. Generally, N-methylated tripyridyl porphyrins were more active than those N-oxidised, but IC₅₀ values for phototoxicity of two N-oxides, named TOPyP3-C₁₇ H₃₃ O and TOPyP3-C₁₇ H₃₅ , were still in the nanomolar concentration range for most of the tested cell lines. However, TOPyP3-C₁₇ H₃₅ did not show phototoxicity on human foreskin fibroblast cells. Two methylated amphiphilic porphyrins, named TMPyP3-C₁₇ H₃₃ and TMPyP4-C₁₇ H_35, showed significant dark toxicity, whereas none of the oxidopyridyl porphyrins were toxic without light activation. The selected photosensitisers were shown to be apoptosis inducers, and had inhibitory effects on the clonogenic growth of HCT116 and HeLa cells. All three N-methylated amphiphilic porphyrins significantly reduced the migratory potential of HCT116 cells. Porphyrins TMPyP3-C₁₇ H₃₅ and TOPyP3-C₁₇ H₃₅ reduced the activity of acid ceramidase, whereas TOPyP3-C₁₇ H₃₃ O had a significant inhibitory effect on sphingosine kinase 1 activity in HeLa cells. Compounds with this dual activity were shown to be the most promising photosensitisers, with potential to treat invasive cancers.

Photodynamic inactivation of Escherichia coli - Correlation of singlet oxygen kinetics and phototoxicity

Photodynamic inactivation (PDI) of bacteria may play a major role in facing the challenge of the ever expanding antibiotic resistances. Here we report about the direct correlation of singlet oxygen luminescence kinetics and phototoxicity in E. coli cell suspension under PDI using the widely applied cationic photosensitizer TMPyP. Through direct access to the microenvironment, the time resolved investigation of singlet oxygen luminescence plays a key role in understanding the photosensitization mechanism and inactivation pathway. Using the homemade set-up for highly sensitive time resolved singlet oxygen luminescence detection, we show that the cationic TMPyP is localized predominantly outside the bacterial cells but in their immediate vicinity prior to photodynamic inactivation. Throughout following light exposure, a clear change in singlet oxygen kinetics indicates a redistribution of photosensitizer molecules to at least one additional microenvironment. We found the signal kinetics mirrored in cell viability measurements of equally treated samples from same overnight cultures conducted in parallel: A significant drop in cell viability of the illuminated samples and stationary viability of dark controls. Thus, for the system investigated in this work - a Gram-negative model bacteria and a well-known PS for its PDI - singlet oxygen kinetics correlates with phototoxicity. This finding suggests that it is well possible to evaluate PDI efficiency directly via time resolved singlet oxygen detection.

Porphyrin-based cationic amphiphilic photosensitisers as potential anticancer, antimicrobial and immunosuppressive agents

Photodynamic therapy (PDT) combines a photosensitiser, light and molecular oxygen to induce oxidative stress that can be used to kill pathogens, cancer cells and other highly proliferative cells. There is a growing number of clinically approved photosensitisers and applications of PDT, whose main advantages include the possibility of selective targeting, localised action and stimulation of the immune responses. Further improvements and broader use of PDT could be accomplished by designing new photosensitisers with increased selectivity and bioavailability. Porphyrin-based photosensitisers with amphiphilic properties, bearing one or more positive charges, are an effective tool in PDT against cancers, microbial infections and, most recently, autoimmune skin disorders. The aim of the review is to present some of the recent examples of the applications and research that employ this specific group of photosensitisers. Furthermore, we will highlight the link between their structural characteristics and PDT efficiency, which will be helpful as guidelines for rational design and evaluation of new PSs.

Novel oxazine and oxazone dyes: aggregation behavior and physicochemical properties

Novel compounds exhibited good properties in comparison with the corresponding starting reagent and satisfy the conditions of a potential drug.

Antimicrobial photodynamic inactivation with decacationic functionalized fullerenes: oxygen-independent photokilling in presence of azide and new mechanistic insights

Functionalized fullerenes are gaining wide interest for mediating photodynamic therapy (PDT) of diseases such as cancers and infections. We recently reported the synthesis of two new decacationic fullerene monoadducts: C60[>M(C3N6(+)C3)2]-(I(-))10(LC14) and its derivative with a light-harvesting antenna conjugated as a C60[>CPAF-(MN6(+)C3)2]-(I(-))10 nanostructure (LC15). We studied the ability of these compounds to mediate PDT of human cancer cells in vitro when excited by UVA light or by white light. Here we report the synthesis of a new fullerene derivative C60[>M(C3N6(+)C3)2][>M(C3N6C3)2]-(I(-))10 (LC16 derived from LC14), as a malonate bisadduct containing a covalently bound decatertiary amine arm. We investigated the relative abilities of the three compounds to generate singlet oxygen ((1)O2), hydroxyl radicals (HO·), and hydrogen peroxide (H2O2) after excitation by UVA or by white light. We used three different classes of pathogenic microbial cells (Gram-positive bacterium, methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative bacterium Escherichia coli, and fungal yeast Candida albicans). LC15 was the most powerful broad spectrum antimicrobial fullerenyl photosensitizer (FPS) followed by LC16, and LC14 was least powerful. Killing depended on both fullerene monoadduct concentration and light fluence. UVA was five times more effective than white light for killing, but not for generation of ROS and relative absorption was greater in white spectral region. Bacterial killing was not much inhibited by addition of azide anions and in some cases was potentiated. In the absence of oxygen, microbial photokilling was highly potentiated (up to 5 logs) by the addition of azide anions. We conclude that molecular functional addends that encourage a type I electron-transfer mechanism increase the ability of photoactivated fullerene monoadducts to kill microbial cells. Oxygen-independent photokilling is possible with fullerene monoadducts in the presence of azide anions, probably mediated by azidyl radicals. UVA excitation may kill bacteria partly by an electron-transfer mechanism directly into bacteria as well as by ROS.

Effects of divalent cations, EDTA and chitosan on the uptake and photoinactivation of Escherichia coli mediated by cationic and anionic porphyrins

The effect of divalent cations, EDTA and chitosan (CS) on the uptake and photoinactivation of Escherichia coli produced by 5,10,15,20-tetrakis(4-N,N,N-trimethylammoniumphenyl)porphyrin (TMAP(4+)), 5,10-di(4-methylphenyl)-15,20-di(4-N,N,N-trimethylammoniumphenyl)porphyrin (MPAP(2+)) and 5,10,15,20-tetra(4-sulphonatophenyl)porphyrin (TPPS(4-)) were examined under different conditions. These porphyrins were rapidly bound to E. coli cells (<2.5min) and the uptake of photosensitizers was not dependent on incubation temperature, reaching values of 0.61, 0.18 and 0.08nmol/10(8) cells for TMAP(4+), MPAP(2+) and TPPS(4-), respectively. The addition of Ca(2+) or Mg(2+) to the cultures enhanced the uptake of MPAP(2+) and TPPS(4-) by cells. In contrast, the amount of TMAP(4+) bound to cells was decreased. The presence of EDTA produced an increase in the uptake of porphyrins by cells, while CS mainly enhanced the amount of TPPS(4-) bound to E. coli. The photoinactivation of E. coli cells mediated by TMAP(4+) was highly effective even at low concentration (1μM) and short irradiation period (5min). However, a reduction in the phototoxicity was found for TMAP(4+) in presence of Ca(2+) and Mg(2+). In contrast, the phototoxic activity mediated by MPAP(2+) and TPPS(4-) was increased. Addition of EDTA did not show effect on the photoinactivation induced by cationic porphyrins, while a small enhance was found for TPPS(4-). Moreover, inactivation of E. coli cells was achieved in the presence CS. This cationic polymer was antimicrobial by itself in the dark. Using a slightly toxic CS concentration, the phototoxic activity induced by TMAP(4+) was diminished. This effect was mainly observed at lower concentration of TMAP(4+) (0.5-1μM). In contrast, an increase in E. coli photoinactivation was obtained for MPAP(2+) and TPPS(4-) in presence of CS. Thus, this natural polymeric destabilizer agent mainly benefited the photoinactivation mediated by TPPS(4-).

Photoinduced antibacterial activity of two dicationic 5,15-diarylporphyrins

Antimicrobial photodynamic treatment combines the use of photosensitizers (PSs) and visible light to kill bacterial cells. Cationic porphyrins are PSs largely used against bacteria and, among them, those featuring one positive charge on each of the 5,10,15,20-tetraaryl substituent (tetracationic) are the most used. The aim of this study was to synthesize two dicationic 5,15-di(N-alkyl-4-pyridyl)porphyrins, bearing methyl (PS 3) and benzyl (PS 4) N-alkylating groups, and to compare the efficiency in antibacterial photodynamic treatment, upon irradiation with a halogen-tungsten white lamp. The killing efficiency of the PS 4 was constantly found higher than that of the PS 3 against both pure and mixed cultures of laboratory model microorganisms as well as against wild wastewater microflora. The two PSs are comparable as regards singlet oxygen generation, but show a different repartition coefficient; the more lipophilic benzylated PS 4 shows a better interaction with the bacterial cells than the methylated one (PS 3). The data support the hypothesis that an efficient PS-cell binding is required to obtain significant effects. A correlation among cell binding, photoinactivation and PS lipophilicity is suggested.

Substituted zinc phthalocyanine as an antimicrobial photosensitizer for periodontitis treatment

In the last decades the worldwide rise in antibiotic resistance has intensified the development of new antimicrobial agents. Photodynamic antimicrobial chemotherapy (PACT) has been used successfully to inactivate bacteria. We herein report a new zinc phthalocyanine based photosensitizer conjugated with polylysine moiety ( ZnPc-PL ). This photosensitizer significantly inactivated Porphyromonas gingivalis, the primary pathogenic bacteria responsible for periodontitis. No obvious phototoxicity was found to either mammalian bone marrow stromal cells (BMSC) or human periodontal ligament cells (HPDLC), indicating the high selectivity of ZnPc -PL toward bacteria. Furthermore, we established an experimental periodontitis model on beagle dogs to test the antimicrobial efficacy in vivo. The amount of gingival crevicular fluid (GCF) and the activity of crevicular fluid aspartate aminotransferase (AST) were monitored and were found to reduce significantly in the ZnPc-PL treated group compared to the controls (laser only and no treatment). In addition, PACT with ZnPc -PL caused a reduction in the bacterial burden by 100-fold compared to controls. Taken together, these findings suggest ZnPc-PL is a promising antimicrobial photosensitizer for the treatment of periodontal diseases.

Reducing Vibrio load in Artemia nauplii using antimicrobial photodynamic therapy: a promising strategy to reduce antibiotic application in shrimp larviculture

We propose antimicrobial photodynamic therapy (aPDT) as an alternative strategy to reduce the use of antibiotics in shrimp larviculture systems. The growth of a multiple antibiotic resistant Vibrio harveyi strain was effectively controlled by treating the cells with Rose Bengal and photosensitizing for 30 min using a halogen lamp. This resulted in the death of > 50% of the cells within the first 10 min of exposure and the 50% reduction in the cell wall integrity after 30 min could be attributed to the destruction of outer membrane protein of V. harveyi by reactive oxygen intermediates produced during the photosensitization. Further, mesocosm experiments with V. harveyi and Artemia nauplii demonstrated that in 30 min, the aPDT could kill 78.9% and 91.2% of heterotrophic bacterial and Vibrio population respectively. In conclusion, the study demonstrated that aPDT with its rapid action and as yet unreported resistance development possibilities could be a propitious strategy to reduce the use of antibiotics in shrimp larviculture systems and thereby, avoid their hazardous effects on human health and the ecosystem at large.

Phage therapy and photodynamic therapy: low environmental impact approaches to inactivate microorganisms in fish farming plants

Owing to the increasing importance of aquaculture to compensate for the progressive worldwide reduction of natural fish and to the fact that several fish farming plants often suffer from heavy financial losses due to the development of infections caused by microbial pathogens, including multidrug resistant bacteria, more environmentally-friendly strategies to control fish infections are urgently needed to make the aquaculture industry more sustainable. The aim of this review is to briefly present the typical fish farming diseases and their threats and discuss the present state of chemotherapy to inactivate microorganisms in fish farming plants as well as to examine the new environmentally friendly approaches to control fish infection namely phage therapy and photodynamic antimicrobial therapy.

Designing photosensitizers for photodynamic therapy: strategies, challenges and promising developments

Photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT) are techniques that combine the effects of visible light irradiation with subsequent biochemical events that arise from the presence of a photosensitizing drug (possessing no dark toxicity) to cause destruction of selected cells. Despite its still widespread clinical use, Photofrin® has several drawbacks that limit its general clinical use. Consequently, there has been extensive research into the design of improved alternative photosensitizers aimed at overcoming these drawbacks. While there are many review articles on the subject of PDT and PACT, these have focused on the photosensitizers that have been used clinically, with little emphasis placed on how the chemical aspects of the molecule can affect their efficacy as PDT agents. Indeed, many of the PDT/PACT agents used clinically may not even be the most appropriate within a given class. As such, this review aims to provide a better understanding of the factors that have been investigated, while aiming at improving the efficacy of a molecule intended to be used as a photosensitizer. Recent publications, spanning the last 5 years, concerning the design, synthesis and clinical usage of photosensitizers for application in PDT and PACT are reviewed, including 5-aminolevulinic acid, porphyrins, chlorins, bacteriochlorins, texaphyrins, phthalocyanines and porphycenes. It has been shown that there are many important considerations when designing a potential PDT/PACT agent, including the influence of added groups on the lipophilicity of the molecule, the positioning and nature of these added groups within the molecule, the presence of a central metal ion and the number of charges that the molecule possesses. The extensive ongoing research within the field has led to the identification of a number of potential lead molecules for application in PDT/PACT. The development of the second-generation photosensitizers, possessing shorter periods of photosensitization, longer activation wavelengths and greater selectivity for diseased tissue provides hope for attaining the ideal photosensitizer that may help PDT and PACT move from laboratory investigation to clinical practice.

Charge effect on the photoinactivation of Gram-negative and Gram-positive bacteria by cationic meso-substituted porphyrins

BACKGROUND

In recent times photodynamic antimicrobial therapy has been used to efficiently destroy Gram (+) and Gram (-) bacteria using cationic porphyrins as photosensitizers. There is an increasing interest in this approach, namely in the search of photosensitizers with adequate structural features for an efficient photoinactivation process. In this study we propose to compare the efficiency of seven cationic porphyrins differing in meso-substituent groups, charge number and charge distribution, on the photodynamic inactivation of a Gram (+) bacterium (Enterococcus faecalis) and of a Gram (-) bacterium (Escherichia coli). The present study complements our previous work on the search for photosensitizers that might be considered good candidates for the photoinactivation of a large spectrum of environmental microorganisms.

RESULTS

Bacterial suspension (10(7) CFU mL(-1)) treated with different photosensitizers concentrations (0.5, 1.0 and 5.0 microM) were exposed to white light (40 W m(-2)) for a total light dose of 64.8 J cm(-2). The most effective photosensitizers against both bacterial strains were the Tri-Py+-Me-PF and Tri-Py+-Me-CO2Me at 5.0 microM with a light fluence of 64.8 J cm(-2), leading to > 7.0 log (> 99,999%) of photoinactivation. The tetracationic porphyrin also proved to be a good photosensitizer against both bacterial strains. Both di-cationic and the monocationic porphyrins were the least effective ones.

CONCLUSION

The number of positive charges, the charge distribution in the porphyrins' structure and the meso-substituent groups seem to have different effects on the photoinactivation of both bacteria. As the Tri-Py+-Me-PF porphyrin provides the highest log reduction using lower light doses, this photosensitizer can efficiently photoinactivate a large spectrum of environmental bacteria. The complete inactivation of both bacterial strains with low light fluence (40 W m(-2)) means that the photodynamic approach can be applied to wastewater treatment under natural light conditions which makes this technology cheap and feasible in terms of the light source.

Cytotoxicity of octal-bromide zinc phthalocyanine after photodynamic therapy with different light sources

OBJECTIVE

The objective of this study was to investigate the cytotoxicity of octal-bromide zinc phthalocyanine (ZnPcBr8) at different concentrations (0.25, 0.5, and 1 microM) after irradiating HEp-2 cell cultures with two different light sources: a diode semiconductor laser (660 nm, 30 mW) or an LED (640 nm, 70 mW). In order to obtain comparative results, the irradiation parameters of both light sources were adjusted so that the amount of energy density delivered would be the same (4.5 J/cm2).

BACKGROUND DATA

Numerous photosensitizers and light sources used in the treatment of human disease have been studied. Based on these studies, a comparative evaluation of two light sources used in photodynamic therapy (PDT) with ZnPcBr8 was proposed.

MATERIALS AND METHODS

HEp-2 cells were incubated with ZnPcBr8 at different concentrations (0.25, 0.5, or 1 microM) for 1 h, irradiated with the diode semiconductor laser (660 nm at 30 mW for 300 sec; 4.5 J/cm2) or the LED laser (640 nm at 70 mW for 128 sec; 4.5 J/cm2), and then incubated in MEM medium for 1 or 24 h. The cells were analyzed using the MTT and trypan blue dye exclusion tests.

RESULTS

The results demonstrated that the concentration of 1 microM of ZnPcBr8 was the most effective after PDT administered by both light sources. According to the MTT results, HEp-2-cell viability decreased by 97.96% 1 h after, and by 99.87% 24 h after irradiation with the diode semiconductor laser, and decreased by 94.03% 1 h after, and by 99.21% 24 h after irradiation with the LED. The results obtained using the trypan blue dye exclusion test confirmed the photodynamic efficacy of ZnPcBr8 employed with both light sources. With regard to HEp-2-cell viability, the following results were observed: a decrease of 98.73% 1 h after, and of 99.49% 24 h after irradiation with the diode semiconductor laser; and a decrease of 98.76% 1 h after, and of 99.23% 24 h after irradiation with the LED.

CONCLUSIONS

According to our results with the irradiation parameters studied here, both the LED and diode semiconductor laser can be used for PDT in vitro, since both light sources had excellent photodynamic efficacy.

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.

Interaction of cationic meso-porphyrins with liposomes, mitochondria and erythrocytes

Two series of cationic porphyrins meso-(3N-methylpyridinium)phenylporphyrin (3P1, 3P2c, 3P2t, 3P3 and 3P4) and meso-(4N-methylpyridinium)phenylporphyrin (4P1, 4P2c, 4P2t, 4P3 and 4P4) were studied to obtain a comprehensive understanding of factors that influence the binding of cationic porphyrins to liposomes and mitochondria, as well as their photodynamic efficiencies in erythrocytes. Binding and photodynamic efficiency were found to be inversely proportional to the number of positively charged groups and directly proportional to n-octanol/water partition coefficients (log P(OW)), except for the cis molecules 3P2c and 4P2c. In the cis molecules, binding and photodynamic efficiency were much higher than expected, indicating that specific interactions not accounted by log P(OW) enhance photodynamic efficiency. The effect of mitochondrial transmembrane electrochemical potentials on cationic porphyrin binding constants was estimated to be as large as 15%, and may be useful to selectively target this organelle when promoting photodynamic therapy to induce apoptosis.

Antibacterial activity of tetraaryl-porphyrin photosensitizers: an in vitro study on Gram negative and Gram positive bacteria

BACKGROUND

Photodynamic therapy exploits visible light and photosensitizers to inactivate cells and this methodology is currently used for the treatment of several types of malignancy. Although various tumours are successfully treated with PSs and light, the application on microorganisms (photodynamic antimicrobial chemotherapy) has not yet found specific medical applications and still remains an open field of fundamental research.

PURPOSE

The assessment of the effect of a panel of seven tetraaryl-porphyrins, two commercial (PS 1 and 2) and five synthetic (PS 3-7) in in vitro experiments against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus.

METHODS

Three of the new photosensitizers (PS 3, 4 and 5) are tetracationic porphyrins and were prepared by N-alkylation of 5,10,15,20-tetra-4-pyridylporphyrin with a large excess of different benzyl chlorides; compound 7 is a dicationic porphyrin and was obtained in a similar way using a lower excess of 4-methoxybenzyl chloride. The neutral porphyrin (PS 6) was previously described. Dose-response curves were obtained titrating the survivors of cell suspensions (10(8)cfu/ml) exposed to the PSs and irradiated with visible light (total fluence rate 266 J/cm2).

RESULTS

The non ionic porphyrin 6 was the least active PS against all the tested bacteria. Cationic PSs 3, 4, 5 and 7 were more active than the commercial 1 and 2. The Gram positive S. aureus was more sensitive to all the PSs than the Gram negative E. coli and P. aeruginosa, the latter being the more resistant one. Compound 7 was found particularly efficient against P. aeruginosa, causing a 7 log units reduction of survivors at a concentration of 8 microM.

CONCLUSIONS

The reported results confirm that the presence of positively charged groups on porphyrin frame is fundamental for PSs antibacterial activity, however our data suggest that a moderate degree of lipophilicity, achievable by the introduction of aromatic hydrocarbon side chains on the pyridyl moieties, may improve PSs efficiency. Furthermore dicationic porphyrin 7 seems to be more efficient than the corresponding tetracationic derivatives thus emphasizing an interesting feature involved in the PSs activity.

New photoantimicrobial films composed of porphyrinated lipophilic cellulose esters

Porphyrinated cellulose laurate esters have been prepared in homogeneous DMA/LiCl medium by "one-pot, two-step" reactions starting from cellulose, protoporphyrin IX, and lauric acid and using a TsCl/Pyridine system. The plastic films obtained after casting were shown to display photobactericidal activity against Gram positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. This new photobactericidal polymer has potential for industrial, medical, or household applications.