The potential for photodynamic therapy in the treatment of localized infections

The potential of photodynamic therapy (PDT)-Experimental investigations and clinical use

Photodynamic therapy (PDT) is an intensively studied part of medicine based on free radicals. These reactive species, extremely harmful for whole human organism, are used for eradication numerous diseases. Specific structure of ill tissues causes accumulation free radicals inside them without attack remaining healthy tissues. A rapid development of medicine and scientific research has led to extension of PDT towards treatment many diseases such as cancer, herpes, acne and based on antimicrobials. The presented review article is focused on the aforementioned disorders with accurate analysis of the newest available scientific achievements. The discussed cases explicitly indicate on high efficacy of the therapy. In most cases, free radicals turned out to be solution of many afflictions. Photodynamic therapy can be considered as promising treatment with comparable effectiveness but without side effects characteristic for chemotherapy.

Assessment of the quantity of microorganisms associated with bronchiectasis in saliva, sputum and nasal lavage after periodontal treatment: a study protocol of a randomised controlled trial

INTRODUCTION

The association between periodontal disease (PD) and chronic obstructive pulmonary disease (COPD) has been widely studied, with aspiration of periodontal pathogens being one of the most accepted causal mechanisms for pulmonary exacerbation. Periodontal treatment (PT) was associated with a decrease in these exacerbations. Bronchiectasis is a pulmonary disease that has many similarities to COPD; however, there are no studies correlating this condition to PD thus far. This study will evaluate if PT reduces proinflammatory cytokines in serum and saliva, as well as halitosis and the amount of microorganisms associated with exacerbation of bronchiectasis in saliva, sputum and nasal lavage 3 months after PT.

METHODS AND ANALYSIS

A total of 182 patients with PD and bronchiectasis will be randomly allocated to group 1 (positive control; scaling and root planing (SRP)+oral hygiene (OH)) or group 2 (experimental; SRP+photodynamic therapy+OH). After 3 months, samples of saliva, nasal lavage and sputum will be collected to determine the level of Pseudomonas aeruginosa, Staphylococcus aureus and Porphyromonas gingivalis by quantitative PCR. This protocol will determine the efficacy of PT in reducing the most likely niches of bronchiectasis exacerbation by comparing pre- and post-treatment microbiology samples. Furthermore, there will be assessment of oral halitosis and verification of inflammatory cytokines in serum and saliva.

ETHICS AND DISSEMINATION

This protocol has been approved by the Research Ethics Committee of Universidade Nove de Julho. Data will be published in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT02514226.

Synergistic antimicrobial effect of photodynamic therapy and ciprofloxacin

The occurrence of a variety of pathogens resistant to current antibiotics remains the major problem in medical care, especially when bacterial infections are established as biofilms. In this study, we propose the use of photodynamic therapy (PDT) as a monotherapy and associated with antibiotic as an alternative treatment. The aim of this study was to analyze the effects of PDT mediated by methylene blue (MB) on Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) in both biofilm and planktonic phases. Several concentrations of MB and light doses were tested. The bactericidal effects of PDT as a monotherapy did not increase with the concentration of photosensitizer, but were light dose-dependent. In addition, bacteria in biofilms were less affected than cells in the planktonic phase. Although not concentration-dependent, the disruption effect of PDT on biofilms was clearly illustrated by scanning electron microscopy (SEM). We also carried out experiments that evaluated the synergistic effect of photodynamic therapy and the antibiotic ciprofloxacin. The best results were obtained after combination treatment of photodynamic therapy followed by ciprofloxacin on biofilms, which increased bacterial reduction on biofilms, resulting in a 5.4 log reduction for S. aureus biofilm and approximately 7 log for E. coli biofilm.

Use of Photosensitizers in Semisolid Formulations for Microbial Photodynamic Inactivation

Semisolid formulations, such as gels, creams and ointments, have recently contributed to the progression of photodynamic therapy (PDT) and microbial photodynamic inactivation (PDI) in clinical applications. The most important challenges facing this field are the physicochemical properties of photosensitizers (PSs), optimal drug release profiles, and the photosensitivity of surrounding tissues. By further integration of nanotechnology with semisolid formulations, very promising pharmaceuticals have been generated against several dermatological diseases (PDT) and (antibiotic-resistant) pathogenic microorganisms (PDI). This review focuses on the different PSs and their associated semisolid formulations currently found in both the market and clinical trials that are used in PDT/PDI. Special emphasis is placed on the advantages that the semisolid formulations bring to drug delivery in PDI. Lastly, some potential considerations for improvement in this field are also discussed.

Protoporphyrin IX: the Good, the Bad, and the Ugly

Protoporphyrin IX (PPIX) is ubiquitously present in all living cells in small amounts as a precursor of heme. PPIX has some biologic functions of its own, and PPIX-based strategies have been used for cancer diagnosis and treatment (the good). PPIX serves as the substrate for ferrochelatase, the final enzyme in heme biosynthesis, and its homeostasis is tightly regulated during heme synthesis. Accumulation of PPIX in human porphyrias can cause skin photosensitivity, biliary stones, hepatobiliary damage, and even liver failure (the bad and the ugly). In this work, we review the mechanisms that are associated with the broad aspects of PPIX. Because PPIX is a hydrophobic molecule, its disposition is by hepatic rather than renal excretion. Large amounts of PPIX are toxic to the liver and can cause cholestatic liver injury. Application of PPIX in cancer diagnosis and treatment is based on its photodynamic effects.

Carboranyl-Chlorin e6 as a Potent Antimicrobial Photosensitizer

Antimicrobial photodynamic inactivation is currently being widely considered as alternative to antibiotic chemotherapy of infective diseases, attracting much attention to design of novel effective photosensitizers. Carboranyl-chlorin-e₆ (the conjugate of chlorin e₆ with carborane), applied here for the first time for antimicrobial photodynamic inactivation, appeared to be much stronger than chlorin e₆ against Gram-positive bacteria, such as Bacillus subtilis, Staphyllococcus aureus and Mycobacterium sp. Confocal fluorescence spectroscopy and membrane leakage experiments indicated that bacteria cell death upon photodynamic treatment with carboranyl-chlorin-e₆ is caused by loss of cell membrane integrity. The enhanced photobactericidal activity was attributed to the increased accumulation of the conjugate by bacterial cells, as evaluated both by centrifugation and fluorescence correlation spectroscopy. Gram-negative bacteria were rather resistant to antimicrobial photodynamic inactivation mediated by carboranyl-chlorin-e₆. Unlike chlorin e₆, the conjugate showed higher (compared to the wild-type strain) dark toxicity with Escherichia coli ΔtolC mutant, deficient in TolC-requiring multidrug efflux transporters.

In vitro effect photodynamic therapy with differents photosensitizers on cariogenic microorganisms

BACKGROUND

Antimicrobial photodynamic therapy has been proposed as an alternative to suppress subgingival species. This results from the balance among Streptococcus sanguis, Streptococcus mutans and Candida albicans in the dental biofilm. Not all the photosensitizers have the same photodynamic effect against the different microorganims. The objective of this study is to compare in vitro the photodynamic effect of methylene blue (MB), rose Bengal (RB) and curcumin (CUR) in combination with white light on the cariogenic microorganism S. mutans, S. sanguis and C. albicans.

RESULTS

Photodynamic therapy with MB, RB and CUR inhibited 6 log 10 the growth of both bacteria but at different concentrations: 0.31-0.62 μg/ml and 0.62-1.25 μg/ml RB were needed to photoinactivate S. mutans and S. sanguis, respectively; 1.25-2.5 μg/ml MB for both species; whereas higher CUR concentrations (80-160 μg/ml and 160-320 μg/ml) were required to obtain the same reduction in S. mutans and S. sanguis viability respectively. The minimal fungicidal concentration of MB for 5 log10 CFU reduction (4.5 McFarland) was 80-160 μg/ml, whereas for RB it ranged between 320 and 640 μg/ml. For CUR, even the maximum studied concentration (1280 μg/ml) did not reach that inhibition. Incubation time had no effect in all experiments.

CONCLUSIONS

Photodynamic therapy with RB, MB and CUR and white light is effective in killing S. mutans and S. sanguis strains, although MB and RB are more efficient than CUR. C. albicans required higher concentrations of all photosensitizers to obtain a fungicidal effect, being MB the most efficient and CUR ineffective.

Antibacterial photodynamic therapy with 808-nm laser and indocyanine green on abrasion wound models

Infections with pathogens could cause serious health problems, such as septicemia and subsequent death. Some of these deaths are caused by nosocomial, chronic, or burn-related wound infections. Photodynamic therapy (PDT) can be useful for the treatment of these infections. Our aim was to investigate the antibacterial effect of indocyanine green (ICG) and 808-nm laser on a rat abrasion wound model infected with the multidrug resistant Staphylococcus aureus strain. Abrasion wounds were infected with a multidrug resistant clinical isolate of S. aureus. ICG concentrations of 500, 1000, and 2000 μg∕ml were applied with a 450 J∕cm2 energy dose. Temperature change was monitored by a thermocouple system. The remaining bacterial burden was determined by the serial dilution method after each application. Wounds were observed for 11 days posttreatment. The recovery process was assessed macroscopically. Tissue samples were also examined histologically by hematoxylin–eosin staining. Around a 90% reduction in bacterial burden was observed after applications. In positive control groups (ICG-only and laser-only groups), there was no significant reduction. The applied energy dose did not cause any thermal damage to the target tissue or host environment. Results showed that ICG together with a 808-nm laser might be a promising antibacterial method to eliminate infections in animals and accelerate the wound-healing process.

How green is green chemistry? Chlorophylls as a bioresource from biorefineries and their commercial potential in medicine and photovoltaics

Chlorophylls are the natural green pigments par excellence and offer potential as therapeutics and in energy generation. This perspective outlines the state-of-the-art, their possible applications and indicates future directions in the context of green chemistry and their production from biorefineries.

Specific features of early stage of the wound healing process occurring against the background of photodynamic therapy using fotoditazin photosensitizer-amphiphilic polymer complexes

There is a growing demand on the studies of the wound healing potentials of photodynamic therapy. Here we analyze the effects of Fotoditazin, an e6 chlorine derivative, and its complexes with amphiphilic polymers, on the early stage of wound healing in a rat model. A skin excision wound model with prevented contraction was developed in male albino rats divided into eight groups according to the treatment mode. All animals received injections of one of the studied compositions into their wound beds and underwent low-intensity laser irradiation or stayed un-irradiated. The clinical monitoring and histological examination of the wounds were performed. It has been found that all the Fotoditazin formulations have significant effects on the early stage of wound healing. The superposition of the inflammation and regeneration was the main difference between groups. The aqueous solution of Fotoditazin alone induced a significant capillary hemorrhage, while its combinations with amphiphilic polymers did not. The best clinical and morphological results were obtained for the Fotoditazin-Pluronic F127 composition. Compositions of Fotoditazin and amphiphilic polymers, especially Pluronic F127, probably, have a great potential for therapy of wounds. Their effects can be attributed to the increased regeneration and suppressed reactions changes at the early stages of repair.

Evaluation of the interplay among the charge of porphyrinic photosensitizers, lipid oxidation and photoinactivation efficiency in Escherichia coli

Photodynamic inactivation (PDI) is a simple and controllable method to destroy microorganisms based on the production of reactive oxygen species (ROS) (e.g., free radicals and singlet oxygen), which irreversibly oxidize microorganism's vital constituents resulting in lethal damage. This process requires the combined action of oxygen, light and a photosensitizer (PS), which absorbs and uses the energy from light to produce ROS. For a better understanding of the photoinactivation process, the knowledge on how some molecular targets are affected by PDI assumes great importance. The aim of this work was to study the relation between the number and position of positive charges on porphyrinic macrocycles and the changes observed on bacterial lipids. For that, five porphyrin derivatives, bearing one to four positive charges, already evaluated as PS on Escherichia coli inactivation, have been tested on lipid extracts from this bacterium, and also on a simple liposome model. The effects were evaluated by the quantification of lipid hydroperoxides and by analysis of the variation of fatty acyl profiles. E. coli suspensions and liposomes were irradiated with white light in the presence of each PS (5.0 μM). Afterwards, total E. coli lipids were extracted and quantified by phosphorus assay. Lipid oxidation on bacteria and on liposomes was quantified by ferrous oxidation in xylenol orange (FOX2 assay) and the analysis of the fatty acid profile was done by gas chromatography (GC). As previously observed for E. coli viability, an overall increase in the lipid hydroperoxides content, depending on the PS charge and on its distribution on the macrocycle, was observed. Analysis of the fatty acid profile has shown a decrease of the unsaturated fatty acids, corroborating the relation between lipid oxidation and PDI efficiency. Bacterial membrane phospholipids are important molecular targets of photoinactivation and the number of charges of the PS molecule, as well as their distribution, have a clear effect on the lipid oxidation and on the efficiency of PDI. The distinct extent of the formation of lipid hydroperoxy derivatives, depending on the PS used, is a good indicator of this process. The FOX2 assay allowed the detection of lipid peroxidation of E. coli membrane after PDI with all the five porphyrins, however, it was not the most appropriated method to quantify the relative lipid oxidation caused by PS with different efficiencies. The fatty acid analysis used to quantify the extent of lipid oxidation by the different PS provided better results. The same results were observed for the liposome model. Consequently, the model system based on liposomes is a fast and simple method that can be used for the screening of the efficiency of new PS, before proceeding with the more complex studies on bacterial models.

Photodynamic therapy versus ultrasonic irrigation: interaction with endodontic microbial biofilm, an ex vivo study

INTRODUCTION

Photodynamic therapy was introduced as an adjuvant to conventional chemo-mechanical debridement during endodontic treatment to overcome the persistence of biofilms. The aim of this study was to evaluate the ability of photodynamic therapy (PDT) to disrupt an experimental microbial biofilm inside the root canal in a clinically applicable working time.

MATERIALS AND METHODS

Thirty extracted teeth were prepared and then divided in three groups. All samples were infected with an artificially formed biofilm made of Enterococcus faecalis, Streptococcus salivarius, Porphyromonas gingivalis and Prevotella intermedia bacteria. First group was treated with Aseptim Plus® photo-activated (LED) disinfection system, second group by a 650 nm Diode Laser and Toluidine blue as photosensitizer, and the third group, as control group, by ultrasonic irrigation (PUI) using EDTA 17% and NaOCl 2.6% solutions. The working time for all three groups was fixed at 3 min. Presence or absence of biofilm was assessed by aerobic and anaerobic cultures.

RESULTS

There was no statistically significant difference between results obtained from groups treated by Aseptim Plus® and Diode Laser (P<0.6267). In cultures of both groups there was a maximal bacterial growth. The group that was treated by ultrasonic irrigation and NaOCl and EDTA solutions had the best results (P<0.0001): there was a statistically significant reduction of bacterial load and destruction of microbial biofilm.

CONCLUSION

Under the condition of this study, Photodynamic therapy could not disrupt endodontic artificial microbial biofilm and could not inhibit bacterial growth in a clinically favorable working time.

Photodynamic therapy as a novel antimicrobial strategy against biofilm-based nosocomial infections: study protocols

Hospital-acquired infections (HAIs), also known as nosocomial infections, are one of the most serious health-care issues currently influencing health-care costs. Among them, those sustained by microbial biofilm represent a major public health concern. Here, we describe the experimental protocols for microbial biofilm inactivation relying on antimicrobial photodynamic therapy (APDT) as a new strategy for the control of these kinds of infections.

Synthesis of a novel water-soluble zinc phthalocyanine and its CT DNA-damaging studies

A novel 3-(4-methoxybenzylamino) propanoic acid substituted water-soluble zinc phthalocyanine (CNPcZn) was synthesized. The interaction between CNPcZn with calf thymus DNA (CT DNA) was studied using spectroscopic methods. The studies indicated that CNPcZn has strong affinity to CT DNA, and furthermore, CNZnPc showed excellent photodamaging activity to CT DNA. Above results indicated that such CNPcZn has great potential to be used as an effective photosensitizer in the field of photodynamic therapy.

Photodynamic inactivation of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus with Ru(II)-based type I/type II photosensitizers

BACKGROUND

The introduction of new disinfection and sterilization methods, such as antimicrobial photodynamic therapy, is urgently needed for the healthcare industry, in particular to address the pervasive problem of antibiotic resistance. This study evaluated the efficacy and the mechanisms of photodynamic antimicrobial chemotherapy (PACT), also known as photodynamic inactivation (PDI) of microorganisms, induced by novel Ru(II)-based photosensitizers against Staphylococcus aureus and methicillin-resistant S. aureus strains.

METHODS

The photodynamic antibacterial effects of a new class of Ru(II)-based photosensitizers (TLD1411 and TLD1433) were evaluated against a strain of S. aureus (ATCC 25923) and a methicillin-resistant strain of S. aureus (MRSA, ATCC 33592). Bacterial samples were dosed with a range of photosensitizer concentrations (0.3-12 μM) and exposed to 530 nm light (90J cm(-2)) in normoxic conditions (ambient atmosphere) and in hypoxic conditions (0.5% O2).

RESULTS

Both photosensitizers exerted photodynamic inactivation (PDI) of the microorganisms in normoxia, and this activity was observed in the nanomolar regime. TLD1411 and TLD1433 maintained this PDI potency under hypoxic conditions, with TLD1433 becoming even more active in the low-oxygen environment.

CONCLUSION

The observation of activity in hypoxia suggests that there exists an oxygen-independent, Type I photoprocess for this new class of compounds in addition to the typical Type II pathway mediated by singlet oxygen. The intrinsic positive charge of the Ru(II) metal combined with the oxygen independent activity demonstrated by this class of photosensitizers presents a new strategy for eradicating both gram-positive and gram-negative bacteria regardless of oxygenation level.

Synthesis of decacationic [60]fullerene decaiodides giving photoinduced production of superoxide radicals and effective PDT-mediation on antimicrobial photoinactivation

We report a novel class of highly water-soluble decacationic methano[60]fullerene decaiodides C60[>M(C3N6(+)C3)2]-(I(-))10 [1-(I(-))10] capable of co-producing singlet oxygen (Type-II) and highly reactive hydroxyl radicals, formed from superoxide radicals in Type-I photosensitizing reactions, upon illumination at both UVA and white light wavelengths. The O2(-)·-production efficiency of 1-(I(-))10 was confirmed by using an O2(-)·-reactive bis(2,4-dinitrobenzenesulfonyl)tetrafluorofluorescein probe and correlated to the photoinduced electron-transfer event going from iodide anions to (3)C60*[>M(C3N6(+)C3)2] leading to C60(-)·[>M(C3N6(+)C3)2]. Incorporation of a defined number (ten) of quaternary ammonium cationic charges per C60 in 1 was aimed to enhance its ability to target pathogenic Gram-positive and Gram-negative bacterial cells. We used the well-characterized malonato[60]fullerene diester monoadduct C60[>M(t-Bu)2] as the starting fullerene derivative to provide a better synthetic route to C60[>M(C3N6(+)C3)2] via transesterification reaction under trifluoroacetic acid catalyzed conditions. These compounds may be used as effective photosensitizers and nano-PDT drugs for photoinactivation of pathogens.

Decacationic [70]Fullerene Approach for Efficient Photokilling of Infectious Bacteria and Cancer Cells

Photodynamic inactivation of pathogenic bacteria and cancer cells by novel water-soluble decacationic fullerene monoadducts, C60[>M(C3N6+C3)2] and C70[>M(C3N6+C3)2], were investigated. In the presence of a high number of electron-donating iodide anions as parts of quaternary ammonium salts in the arm region, we found that C70[>M(C3N6+C3)2] produced more highly reactive HO• radical than C60[>M(C3N6+C3)2], in addition to singlet oxygen (1O2). This finding offers an explanation of the preferential killing of Gram-positive and Gram-negative bacteria by C60[>M(C3N6+C3)2] and C70[>M(C3N6+C3)2], respectively. The hypothesis is that 1O2 can diffuse more easily into porous cell walls of Gram-positive bacteria to reach sensitive sites, while the less permeable Gram-negative bacterial cell wall needs the more reactive HO• to cause real damage.

Sonodynamic excitation of Rose Bengal for eradication of gram-positive and gram-negative bacteria

Photodynamic antimicrobial chemotherapy based on photosensitizers activated by illumination is limited by poor penetration of visible light through skin and tissues. In order to overcome this problem, Rose Bengal was excited in the dark by 28 kHz ultrasound and was applied for inactivation of bacteria. It is demonstrated, for the first time, that the sonodynamic technique is effective for eradication of gram-positive Staphylococcus aureus and gram-negative Escherichia coli. The net sonodynamic effect was calculated as a 3-4 log10 reduction in bacteria concentration, depending on the cell and the Rose Bengal concentration and the treatment time. Sonodynamic treatment may become a novel and effective form of antimicrobial therapy and can be used for low-temperature sterilization of medical instruments and surgical accessories.

Prospective study of topical 5-aminolevulinic acid photodynamic therapy for the treatment of moderate to severe acne vulgaris in Chinese patients

BACKGROUND

Topical photodynamic therapy (PDT) mediated with 5-aminolevulinic acid (ALA) offers an alternative option for the treatment of acne vulgaris.

OBJECTIVE

To study the effects of ALA dose, incubation time, and lesion type on protoporphyrin IX (PpIX) production and treatment outcomes.

METHODS

To examine the time course of PpIX production, 10% ALA was applied to inflammatory papules for 1 to 5 hours and followed by in situ fluorescence examination. To determine the effects of ALA dose and lesion type, 3, 5, and 10% ALA was applied to acne lesions in split-face fashion for 3 hours followed by whole-face light irradiation at 633 nm and 30 to 70 J/cm2. Treatment was repeated twice at 2-week intervals.

RESULTS

PpIX reached a stable level after 3 hours of incubation. Similar PpIX levels were seen in areas receiving 3, 5, and 10% ALA. Poisson regression analyses indicated that lesion counts decreased by 0.791 times for a one-unit increase in treatment times (95% CI 0.782-0.799 < .0001) but only by 0.999 times for a one-unit increase in ALA dose (95% CI 0.998-1.000  =  .22).

CONCLUSION

The combination of low-dose ALA and a red light is a safe and effective option for the treatment of moderate to severe acne.

Singlet oxygen generation enhanced by silver-pectin nanoparticles

We demonstrate the potential application of silver-pectin nanoparticles on photodynamic therapy, on a solution-base platform. Photodynamic therapy is a medical technique which uses a combination of photosensitizing drugs and light to induce selective damage on the target tissue, by electronically excited and highly reactive singlet state of oxygen. Metal enhanced singlet oxygen generation in riboflavin water solution with silver-pectin nanoparticles was observed and quantified. Here 13 nm silver nanospheres enclosed by a pectin layer were synthesized and it interaction with riboflavin molecule was analyzed. Pectin, a complex carbohydrate found in plants primary cell walls, was used to increase the biocompatibility of the silver nanoparticles and to improve metal enhanced singlet oxygen generation (28.5 %) and metal-enhanced fluorescence (30.7 %) processes at room temperature. The singlet oxygen sensor fluorescent green reagent was used to quantify the enhancement of the riboflavin singlet oxygen production induced by the silver colloid. We report a 1.7-fold increase of riboflavin emission and a 1.8-fold enhancement of singlet oxygen production.

Synthesis and characterization of positively charged pentacationic [60]fullerene monoadducts for antimicrobial photodynamic inactivation

We designed and synthesized two analogous pentacationic [60]fullerenyl monoadducts, C₆₀(>ME₁N₆⁺C₃) (1) and C₆₀(>ME₃N₆⁺C₃) (2), with variation of the methoxyethyleneglycol length. Each of these derivatives bears a well-defined number of cationic charges aimed to enhance and control their ability to target pathogenic Gram-positive and Gram-negative bacterial cells for allowing photodynamic inactivation. The synthesis was achieved by the use of a common synthon of pentacationic N,N′,N,N,N,N-hexapropylhexa(aminoethyl)amine arm (C₃N₆⁺) having six attached propyl groups, instead of methyl or ethyl groups, to provide a well-balanced hydrophobicity-hydrophilicity character to pentacationic precursor intermediates and better compatibility with the highly hydrophobic C₆₀ cage moiety. We demonstrated two plausible synthetic routes for the preparation of 1 and 2 with the product characterization via various spectroscopic methods.

Synthesis and photodynamic effect of new highly photostable decacationically armed [60]- and [70]fullerene decaiodide monoadducts to target pathogenic bacteria and cancer cells

Novel water-soluble decacationically armed C(60) and C(70) decaiodide monoadducts, C(60)- and C(70)[>M(C(3)N(6)(+)C(3))(2)], were synthesized, characterized, and applied as photosensitizers and potential nano-PDT agents against pathogenic bacteria and cancer cells. A high number of cationic charges per fullerene cage and H-bonding moieties were designed for rapid binding to the anionic residues displayed on the outer parts of bacterial cell walls. In the presence of a high number of electron-donating iodide anions as parts of quaternary ammonium salts in the arm region, we found that C(70)[>M(C(3)N(6)(+)C(3))(2)] produced more HO(•) than C(60)[>M(C(3)N(6)(+)C(3))(2)], in addition to (1)O(2). This finding offers an explanation of the preferential killing of Gram-positive and Gram-negative bacteria by C(60)[>M(C(3)N(6)(+)C(3))(2)] and C(70)[>M(C(3)N(6)(+)C(3))(2)], respectively. The hypothesis is that (1)O(2) can diffuse more easily into porous cell walls of Gram-positive bacteria to reach sensitive sites, while the less permeable Gram-negative bacterial cell wall needs the more reactive HO(•) to cause real damage.

Antimicrobial photodynamic activity of porphyrin derivatives: potential application on medical and water disinfection

In this highlight an overview of the advances performed by the Aveiro group on the design and synthesis of tetrapyrrolic photosensitizers with potential photodynamic antimicrobial activity is presented.

Synthesis, properties and photodynamic activities of some zinc(II) phthalocyanines against Escherichia coli and Staphylococcus aureus

Two new zinc phthalocyanine derivatives bearing four 3,5-di-tert-butyl-4-hydroxyphenyl (ZnPc1) and 3,5-dimethylphenoxy (ZnPc2) have been synthesized and proved by elemental analyses and UV-vis, 1H NMR, FTIR and MALDI-TOF mass spectra as spectroscopic determination. Thermal stabilities of these neutral Zn -phthalocyanines were performed by thermal gravimetric analysis and, significantly, were found stable up to 373 °C for ZnPc1 and 550 °C for ZnPc2. In addition, the photostability of the sensitizers was quite successful within 240 min. Furthermore, photodynamic therapy has been investigated using these neutral phthalocyanines. Singlet oxygen generation capacities of ZnPc1 and ZnPc2 were studied using 1,3-diphenyl-iso-benzofuran (50.0 μM) as a selective singlet oxygen trap in DMSO and both of them demonstrated very high singlet oxygen generation capacity. Photodynamic therapy is of considerable interest for its potential as an antimicrobial therapy on the grounds that the photodynamic activity of these compounds was tested against a Gram-negative bacteria, Escherichia coli and a Gram-positive bacteria, Staphylococcus aureus. Suspensions of the microorganisms were irradiated for 240 min in the presence of ZnPc1 (with hydrophilic group) and ZnPc2 phthalocyanines. In order to simulate solar radiation, we used a 750 W xenon lamp. Minimum photosensitizer concentration was used as 0.1 mg.10 mL-1 in 1% dimethylsulfoxide/phosphate buffer saline solution (DMSO/PBS). Moreover, the photostability of these compounds has been investigated and the effect of the amount of DMSO tested against selected bacteria. In the dark, with and without Pcs, bacterial inactivation did not occur. Bacterial inactivation by light with ZnPc1 was observed in response to Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus, whereas the photoinactivation studies with ZnPc2 have revealed that the lack of its activity is due to its poor affinity for either of the organisms. These results suggest that a neutral amphiphilic photosensitizer may be easily used in an application concerning photoinactivation of bacterial cells as well as ionic photosensitizers.

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.

Photodynamic therapy based on 5-aminolevulinic acid and its use as an antimicrobial agent

Exogenous 5-aminolevulinic acid (ALA) is taken up directly by bacteria, yeasts, fungi, and some parasites, which then induces the accumulation of protoporphyrin IX (PPIX). Subsequent light irradiation of PPIX leads to the inactivation of these organisms via photodamage to their cellular structures. ALA uptake and light irradiation of PPIX produced by host cells leads to the inactivation of other parasites, along with some viruses, via the induction of an immune response. ALA-mediated PPIX production by host cells and light irradiation result in the inactivation of other viruses via either the induction of a host cell response or direct photodynamic attack on viral particles. This ALA-mediated production of light-activated PPIX has been extensively used as a form of photodynamic therapy (PDT) and has shown varying levels of efficacy in treating conditions that are associated with microbial infection, ranging from acne and verrucae to leishmaniasis and onychomycosis. However, for the treatment of some of these conditions by ALA-based PDT, the role of an antimicrobial effect has been disputed and in general, the mechanisms by which the technique inactivates microbes are not well understood. In this study, we review current understanding of the antimicrobial mechanisms used by ALA-based PDT and its role in the treatment of microbial infections along with its potential medical and nonmedical applications.

HPLC-FLD methods to quantify chloroaluminum phthalocyanine in nanoparticles, plasma and tissue: application in pharmacokinetic and biodistribution studies

Analytical and bioanalytical methods of high-performance liquid chromatography with fluorescence detection (HPLC-FLD) were developed and validated for the determination of chloroaluminum phthalocyanine in different formulations of polymeric nanocapsules, plasma and livers of mice. Plasma and homogenized liver samples were extracted with ethyl acetate, and zinc phthalocyanine was used as internal standard. The results indicated that the methods were linear and selective for all matrices studied. Analysis of accuracy and precision showed adequate values, with variations lower than 10% in biological samples and lower than 2% in analytical samples. The recoveries were as high as 96% and 99% in the plasma and livers, respectively. The quantification limit of the analytical method was 1.12 ng/ml, and the limits of quantification of the bioanalytical method were 15 ng/ml and 75 ng/g for plasma and liver samples, respectively. The bioanalytical method developed was sensitive in the ranges of 15-100 ng/ml in plasma and 75-500 ng/g in liver samples and was applied to studies of biodistribution and pharmacokinetics of AlClPc.

Effects of toluidine blue-mediated photodynamic therapy on periopathogens and periodontal biofilm: in vitro evaluation

Photodynamic therapy (PDT) is a selective modality of killing targeted cells, mostly known for its application in neoplasms. PDT can be considered to be an alternative method for the elimination of periodontal bacteria from the pocket without harms for the resident tissues. Therefore, PDT may replace systemic antibiotics and enhance the effect of mechanical treatments of periodontal defects. This effort focused on the in vitro sensitization of periopathogens (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Fusobacterium nucleatum and Prevotella intermedia ) Toluidine Blue mediated and on the use of a Diode laser emitting source. The objective of this research was to evaluate the bactericidal in vitro effect of laser diodes 830 nm (as the light source) after photosensitization with Toluidine Blue (TBO) on the following periopathogenic bacteria: Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Fusobacterium nucleatum and Prevotella intermedia. After evaluating the effect on the single bacterial strain, the ability of Diode Laser to disrupt the structure of biofilms produced by A. actinomycetemcomitans after photosensitization with TBO was also analyzed. The study suggests that the association of TBO and diode laser light 830 nm is effective for the killing of bacteria strains and determines the photoinactivation of Aggregatibacter biofilms. In summary, photodynamic therapy has effectively shown its capabilities and, therefore, it can be considered a valid alternative approach to antimicrobial therapy of periodontitis.

Susceptibility of planktonic cultures of Streptococcus mutans to photodynamic therapy with a light-emitting diode

The objective of this study was to evaluate the effect of photodynamic therapy with erythrosine and rose bengal using a light-emitting diode (LED) on planktonic cultures of S. mutans. Ten S. mutans strains, including nine clinical strains and one reference strain (ATCC 35688), were used. Suspensions containing 10⁶ cells/mL were prepared for each strain and were tested under different experimental conditions: a) LED irradiation in the presence of rose bengal as a photosensitizer (RB+L+); b) LED irradiation in the presence of erythrosine as a photosensitizer (E+L+); c) LED irradiation only (P-L+); d) treatment with rose bengal only (RB+L-); e) treatment with erythrosine only (E+L-); and f) no LED irradiation or photosensitizer treatment, which served as a control group (P-L-). After treatment, the strains were seeded onto BHI agar for determination of the number of colony-forming units (CFU/mL). The results were submitted to analysis of variance and the Tukey test (p ≤ 0.05). The number of CFU/mL was significantly lower in the groups submitted to photodynamic therapy (RB+L+ and E+L+) compared to control (P-L-), with a reduction of 6.86 log₁₀ in the RB+L+ group and of 5.16 log₁₀ in the E+L+ group. Photodynamic therapy with rose bengal and erythrosine exerted an antimicrobial effect on all S. mutans strains studied.

Chemiluminescence as a PDT light source for microbial control

The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem® concentration varied from 0 to 75 μg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at μW/cm² level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources.

New halogenated water-soluble chlorin and bacteriochlorin as photostable PDT sensitizers: synthesis, spectroscopy, photophysics, and in vitro photosensitizing efficacy

Chlorin and bacteriochlorin derivatives of 5,10,15,20-tetrakis(2-chloro-5-sulfophenyl)porphyrin have intense absorptions in the phototherapeutic window, high water solubility, high photostability, low fluorescence quantum yield, long triplet lifetimes, and high singlet oxygen quantum yields. Biological studies revealed their negligible dark cytotoxicity, yet significant photodynamic effect against A549 (human lung adenocarcinoma), MCF7 (human breast carcinoma) and SK-MEL-188 (human melanoma) cell lines upon red light irradiation (cutoff λ<600 nm) at low light doses. Time-dependent cellular accumulation of the chlorinated sulfonated chlorin reached a plateau at 2 h, as previously observed for the related porphyrin. However, the optimal incubation time for the bacteriochlorin derivative was significantly longer (12 h). The spectroscopic, photophysical, and biological properties of the compounds are discussed in relevance to their PDT activity, leading to the conclusion that the bacteriochlorin derivative is a promising candidate for future in vivo experiments.

Identification of methicillin-resistant Staphylococcus aureus-specific peptides for targeted photoantimicrobial chemotherapy

The increasing prevalence of multi-drug resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), necessitates development of alternative modes of bacterial targeting which are not hindered by antibiotic resistance and minimise collateral damage. To achieve this, the FliTrx™ bacterially-displayed peptide library was panned against MRSA and randomly selected clones (n = 20) were DNA sequenced. One selected peptide was synthesised as both cyclic and linear constructs. Binding of the cyclic construct was observed by flow cytometry against isolates of MRSA whilst the linear construct showed low affinity. Low reactivity was observed with other Staphylococcal sp., gram-negative bacteria and human keratinocytes. The selected peptide was also cloned in-frame, within the thioredoxin gene into the pPROTet.E 6xHN vector for protein expression. A porphyrin photosensitiser (5-(4-isothiocyanatophenyl)-10,15,20-tris(4-N-methylpyridiniumyl)porphyrin trichloride) was conjugated to the recombinant protein and the in vitro cytotoxic effect of the resulting bioconjugate was determined against MRSA and other non-specific bacterial and mammalian cell lines. Photoantimicrobial chemotherapy (PACT) using the bioconjugate showed a 66% reduction in MRSA growth in comparison with non-irradiated cells. This work demonstrates the potential to isolate peptides with binding specificity against MRSA that can be used for targeted PACT, providing an effective alternative to antibody targeting.