Photomodulation Approaches to Overcome Antimicrobial Resistance

Photopharmacology is an approach that aims to be an alternative to classical chemotherapy. Herein, the different classes of photoswitches and photocleavage compounds and their biological applications are described. Proteolysis targeting chimeras (PROTACs) containing azobenzene moieties (PHOTACs) and photocleavable protecting groups (photocaged PROTACs) are also mentioned. Furthermore, porphyrins are referenced as successful photoactive compounds in a clinical context, such as in the photodynamic therapy of tumours as well as preventing antimicrobial resistance, namely in bacteria. Porphyrins combining photoswitches and photocleavage systems are highlighted, taking advantage of both photopharmacology and photodynamic action. Finally, porphyrins with antibacterial activity are described, taking advantage of the synergistic effect of photodynamic treatment and antibiotic therapy to overcome bacterial resistance.

Sulfonamide Porphyrins as Potent Photosensitizers against Multidrug-Resistant Staphylococcus aureus (MRSA): The Role of Co-Adjuvants

Sulfonamides are a conventional class of antibiotics that are well-suited to combat infections. However, their overuse leads to antimicrobial resistance. Porphyrins and analogs have demonstrated excellent photosensitizing properties and have been used as antimicrobial agents to photoinactivate microorganisms, including multiresistant Staphylococcus aureus (MRSA) strains. It is well recognized that the combination of different therapeutic agents might improve the biological outcome. In this present work, a novel meso-arylporphyrin and its Zn(II) complex functionalized with sulfonamide groups were synthesized and characterized and the antibacterial activity towards MRSA with and without the presence of the adjuvant KI was evaluated. For comparison, the studies were also extended to the corresponding sulfonated porphyrin TPP(SO₃H)₄. Photodynamic studies revealed that all porphyrin derivatives were effective in photoinactivating MRSA (>99.9% of reduction) at a concentration of 5.0 μM upon white light radiation with an irradiance of 25 mW cm^-2 and a total light dose of 15 J cm^-2. The combination of the porphyrin photosensitizers with the co-adjuvant KI during the photodynamic treatment proved to be very promising allowing a significant reduction in the treatment time and photosensitizer concentration by six times and at least five times, respectively. The combined effect observed for TPP(SO₂NHEt)₄ and ZnTPP(SO₂NHEt)₄ with KI seems to be due to the formation of reactive iodine radicals. In the photodynamic studies with TPP(SO₃H)₄ plus KI, the cooperative action was mainly due to the formation of free iodine (I₂).

Photodynamic inactivation of microorganisms in different water matrices: The effect of physicochemical parameters on the treatment outcome

Wastewater (WW) insufficiently treated for the disinfection of microorganisms, including pathogenic ones, is a source of concern and a possible generator of public health problems. Traditional disinfection methods to reduce pathogens concentration (e.g., chlorination, ozonation, UV) are expensive, unsafe, and/or sometimes ineffective, highlighting the need for new disinfection technologies. The promising results of photodynamic inactivation (PDI) treatment to eradicate microorganisms suggest the efficacy of this treatment to improve WW quality. This work aimed to assess if PDI can be successfully extended to real contexts for the microbial inactivation in WW. For the first time, PDI experiments with 9 different water matrices compositions were performed to inquire about the influence of some of their physicochemical parameters on the effectiveness of microbial inactivation. Bacterial photoinactivation was tested in freshwater, aquaculture water, and seawater samples, as well as in influents and effluents samples from domestic, industrial, and a mixture of industrial and domestic WW receiving wastewater treatment plants (WWTPs). Additionally, PDI assays were performed in phosphate-buffered saline isotonic solution (PBS), used as an aqueous comparative matrix. To relate the PDI disinfection efficiency with the physicochemical compositions of the different used water matrices, a series of statistical analysis were performed, in order to support our main conclusions. Overall, the results showed that PDI is an effective and promising alternative to traditionally used WW disinfection methods, with a bacterial reduction of >3.0 log CFU/mL in all the water matrices within the first hour of PDI treatment, but also that the physicochemical composition of the aqueous matrices to be PDI-disinfected must be taken into account since they seem to influence the PDI efficacy, namely the pH, with acidic pH conditions seeming to be associated to a better PDI performance in general.

Porphyrin Photosensitizers Grafted in Cellulose Supports: A Review

Cellulose is the most abundant natural biopolymer and owing to its compatibility with biological tissues, it is considered a versatile starting material for developing new and sustainable materials from renewable resources. With the advent of drug-resistance among pathogenic microorganisms, recent strategies have focused on the development of novel treatment options and alternative antimicrobial therapies, such as antimicrobial photodynamic therapy (aPDT). This approach encompasses the combination of photoactive dyes and harmless visible light, in the presence of dioxygen, to produce reactive oxygen species that can selectively kill microorganisms. Photosensitizers for aPDT can be adsorbed, entrapped, or linked to cellulose-like supports, providing an increase in the surface area, with improved mechanical strength, barrier, and antimicrobial properties, paving the way to new applications, such as wound disinfection, sterilization of medical materials and surfaces in different contexts (industrial, household and hospital), or prevention of microbial contamination in packaged food. This review will report the development of porphyrinic photosensitizers supported on cellulose/cellulose derivative materials to achieve effective photoinactivation. A brief overview of the efficiency of cellulose based photoactive dyes for cancer, using photodynamic therapy (PDT), will be also discussed. Particular attention will be devoted to the synthetic routes behind the preparation of the photosensitizer-cellulose functional materials.

New Bis-Cyclometalated Iridium(III) Complexes with β-Substituted Porphyrin-Arylbipyridine as the Ancillary Ligand: Electrochemical and Photophysical Insights

An efficient synthetic access to new cationic porphyrin-bipyridine iridium(III) bis-cyclometalated complexes was developed. These porphyrins bearing arylbipyridine moieties at β-pyrrolic positions coordinated with iridium(III), and the corresponding Zn(II) porphyrin complexes were spectroscopically, electrochemically, and electronically characterized. The features displayed by the new cyclometalated porphyrin-bipyridine iridium(III) complexes, namely photoinduced electron transfer process (PET), and a remarkable efficiency to generate ¹O₂, allowing us to envisage new challenges and opportunities for their applications in several fields, such as photo(catalysis) and photodynamic therapies.

Photoinactivation of Phage Phi6 as a SARS-CoV-2 Model in Wastewater: Evidence of Efficacy and Safety

The last two years have been marked by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. This virus is found in the intestinal tract; it reaches wastewater systems and, consequently, the natural receiving water bodies. As such, inefficiently treated wastewater (WW) can be a means of contamination. The currently used methods for the disinfection of WW can lead to the formation of toxic compounds and can be expensive or inefficient. As such, new and alternative approaches must be considered, namely, photodynamic inactivation (PDI). In this work, the bacteriophage φ6 (or, simply, phage φ6), which has been used as a suitable model for enveloped RNA viruses, such as coronaviruses (CoVs), was used as a model of SARS-CoV-2. Firstly, to understand the virus’s survival in the environment, phage φ6 was subjected to different laboratory-controlled environmental conditions (temperature, pH, salinity, and solar and UV-B irradiation), and its persistence over time was assessed. Second, to assess the efficiency of PDI towards the virus, assays were performed in both phosphate-buffered saline (PBS), a commonly used aqueous matrix, and a secondarily treated WW (a real WW matrix). Third, as WW is generally discharged into the marine environment after treatment, the safety of PDI-treated WW was assessed through the determination of the viability of native marine water microorganisms after their contact with the PDI-treated effluent. Overall, the results showed that, when used as a surrogate for SARS-CoV-2, phage φ6 remains viable in different environmental conditions for a considerable period. Moreover, PDI proved to be an efficient approach in the inactivation of the viruses, and the PDI-treated effluent showed no toxicity to native aquatic microorganisms under realistic dilution conditions, thus endorsing PDI as an efficient and safe tertiary WW disinfection method. Although all studies were performed with phage φ6, which is considered a suitable model of SARS-CoV-2, further studies using SARS-CoV-2 are necessary; nevertheless, the findings show the potential of PDI for controlling SARS-CoV-2 in WW.

Synthesis, antioxidant and antitumoral activity of new 5′-arylchalcogenyl-3′-N-(E)-feruloyl-3′, 5′-dideoxy-amino-thymidine (AFAT) derivatives

A new multitarget arylchalcogenyl zidovudine derivative is disclosed. The compounds showed a prominent antioxidant and antitumoral activity with no overt sign of toxicity for in vivo evaluations.

Current Photoactive Molecules for Targeted Therapy of Triple-Negative Breast Cancer

Cancer is the second leading cause of death worldwide; therefore, there is an urgent need to find safe and effective therapies. Triple-negative breast cancer (TNBC) is diagnosed in ca. 15-20% of BC and is extremely aggressive resulting in reduced survival rate, which is mainly due to the low therapeutic efficacy of available treatments. Photodynamic therapy (PDT) is an interesting therapeutic approach in the treatment of cancer; the photosensitizers with good absorption in the therapeutic window, combined with their specific targeting of cancer cells, have received particular interest. This review aims to revisit the latest developments on chlorin-based photoactive molecules for targeted therapy in TNBC. Photodynamic therapy, alone or combined with other therapies (such as chemotherapy or photothermal therapy), has potential to be a safe and a promising approach against TNBC.

The Interactions of H2TMPyP, Analogues and Its Metal Complexes with DNA G-Quadruplexes-An Overview

The evidence that telomerase is overexpressed in almost 90% of human cancers justifies the proposal of this enzyme as a potential target for anticancer drug design. The inhibition of telomerase by quadruplex stabilizing ligands is being considered a useful approach in anticancer drug design proposals. Several aromatic ligands, including porphyrins, were exploited for telomerase inhibition by adduct formation with G-Quadruplex (GQ). 5,10,15,20-Tetrakis(N-methyl-4-pyridinium)porphyrin (H₂TMPyP) is one of the most studied porphyrins in this field, and although reported as presenting high affinity to GQ, its poor selectivity for GQ over duplex structures is recognized. To increase the desired selectivity, porphyrin modifications either at the peripheral positions or at the inner core through the coordination with different metals have been handled. Herein, studies involving the interactions of TMPyP and analogs with different DNA sequences able to form GQ and duplex structures using different experimental conditions and approaches are reviewed. Some considerations concerning the structural diversity and recognition modes of G-quadruplexes will be presented first to facilitate the comprehension of the studies reviewed. Additionally, considering the diversity of experimental conditions reported, we decided to complement this review with a screening where the behavior of H₂TMPyP and of some of the reviewed metal complexes were evaluated under the same experimental conditions and using the same DNA sequences. In this comparison under unified conditions, we also evaluated, for the first time, the behavior of the Ag^II complex of H₂TMPyP. In general, all derivatives showed good affinity for GQ DNA structures with binding constants in the range of 10⁶–10⁷ M⁻¹ and ligand-GQ stoichiometric ratios of 3:1 and 4:1. A promising pattern of selectivity was also identified for the new Ag^II derivative.

Photodynamic inactivation of Lasiodiplodia theobromae: lighting the way towards an environmentally friendly phytosanitary treatment

The fungus Lasiodiplodia theobromae is one of the main causal agents of trunk canker and dieback of grapevine. The objective of this work was to evaluate the efficiency of photodynamic inactivation (PDI) of L. theobromae with synthetic and natural photosensitizers and irradiation with either sunlight or artificial photosynthetically active radiation. Although the growth of the mycelium could not be completely prevented with natural sunlight irradiation, phenothiazine dyes (methylene blue, MB; toluidine blue O, TBO), riboflavin and a cationic porphyrin (Tetra-Py⁺-Me) caused complete inhibition under continuous irradiation with artificial light. Free radicals were the main cytotoxic agents in the PDI with MB, indicating the predominance of the type I mechanism. PDI with MB or Tetra-Py⁺-Me may represent a promising approach for the sanitation of vine material in greenhouse nurseries, in order to reduce the risk of infection upon grafting.

The Role of Porphyrinoid Photosensitizers for Skin Wound Healing

Microorganisms, usually bacteria and fungi, grow and spread in skin wounds, causing infections. These infections trigger the immune system and cause inflammation and tissue damage within the skin or wound, slowing down the healing process. The use of photodynamic therapy (PDT) to eradicate microorganisms has been regarded as a promising alternative to anti-infective therapies, such as those based on antibiotics, and more recently, is being considered for skin wound-healing, namely for infected wounds. Among the several molecules exploited as photosensitizers (PS), porphyrinoids exhibit suitable features for achieving those goals efficiently. The capability that these macrocycles display to generate reactive oxygen species (ROS) gives a significant contribution to the regenerative process. ROS are responsible for avoiding the development of infections by inactivating microorganisms such as bacteria but also by promoting cell proliferation through the activation of stem cells which regulates inflammatory factors and collagen remodeling. The PS can act solo or combined with several materials, such as polymers, hydrogels, nanotubes, or metal-organic frameworks (MOF), keeping both the microbial photoinactivation and healing/regenerative processes' effectiveness. This review highlights the developments on the combination of PDT approach and skin wound healing using natural and synthetic porphyrinoids, such as porphyrins, chlorins and phthalocyanines, as PS, as well as the prodrug 5-aminolevulinic acid (5-ALA), the natural precursor of protoporphyrin-IX (PP-IX).

Photodynamic inactivation of the phytopathogenic bacterium Xanthomonas citri subsp. citri

The present work intended to evaluate the applicability of photodynamic inactivation (PDI) of Xanthomonas citri subsp. citri with toluidine blue O (TBO), a commercial photosensitizer, as a strategy to control citrus canker. Assays were conducted with cell suspensions and biofilms, constructed either on polypropylene microtubes (in vitro assays) or on the surface of orange leaves (ex vivo assays), in the presence of TBO and under irradiation with artificial white light or natural sunlight. PDI assays using TBO alone caused a maximum 5·8 log10 reduction of X. citri viable cells in suspensions, and a much smaller inactivation (1·5 log10) in biofilms. However, concomitant use of KI potentiated the TBO photosensitization. Biofilms were inactivated down to the detection limit (>6 log10 reduction) with 5·0 µmol l^-1 TBO + 10 mmol l^-1 KI (in vitro) or 5·0 µmol l^-1 TBO + 100 mmol l^-1 KI (ex vivo) after artificial white light irradiation. Under natural sunlight, a reduction down to the detection limit of the Miles-Misra method was achieved with 50 µmol l^-1 TBO and 100 mmol l^-1 KI. PDI has potential to be applied in the control of citrus canker in field conditions although further studies are needed to show that there are no risks to plant physiology or fruit quality. SIGNIFICANCE AND IMPACT OF THE STUDY: Xanthomonas citri subsp. citri is a major cause of disease in citrus orchards. Because of the low efficacy and high environmental toxicity of copper-based treatments, there is growing interest on more sustainable phytosanitary approaches. Photodynamic inactivation (PDI) is being successfully used to control infectious agents and literature reports indicate that it is effective against some fungi and bacteria attacking fruit crops. The results of the present work open the perspective of using a low-cost photosensitizer and sunlight, as energy source, to control of the causative agent of citrus canker.

The Remarkable Effect of Potassium Iodide in Eosin and Rose Bengal Photodynamic Action against Salmonella Typhimurium and Staphylococcus aureus

Antimicrobial photodynamic therapy (aPDT) has been shown as a promising technique to inactivate foodborne bacteria, without inducing the development of bacterial resistance. Knowing that addition of inorganic salts, such as potassium iodide (KI), can modulate the photodynamic action of the photosensitizer (PS), we report in this study the antimicrobial effect of eosin (EOS) and rose bengal (RB) combined with KI against Salmonella enterica serovar Typhimurium and Staphylococcus aureus. Additionally, the possible development of bacterial resistance after this combined aPDT protocol was evaluated. The combination of EOS or RB, at all tested concentrations, with KI at 100 mM, was able to efficiently inactivate S. Typhimurium and S. aureus. This combined approach allows a reduction in the PS concentration up to 1000 times, even against one of the most common foodborne pathogenics, S. Typhimurium, a gram-negative bacterium which is not so prone to inactivation with xanthene dyes when used alone. The photoinactivation of S. Typhimurium and S. aureus by both xanthenes with KI did not induce the development of resistance. The low price of the xanthene dyes, the non-toxic nature of KI, and the possibility of reducing the PS concentration show that this technology has potential to be easily transposed to the food industry.

Wastewater chemical contaminants: remediation by advanced oxidation processes

Approximately 70% of the terrestrial area is covered with water, but only a small water fraction is compatible with terrestrial life forms. Due to the increment in human consumption, the need for water resources is increasing, and it is estimated that more than 40% of the population worldwide will face water stress/scarcity within the next few decades. Water recycling and reuse may offer the opportunity to expand water resources. For that, the wastewater treatment paradigm should be changed and adequately treated wastewater should be seen as a valuable resource instead of a waste product. It is easily understandable that the exact composition and constituent concentration of wastewater vary according to its different sources (industrial, agricultural, urban usage of water). Consequently, a variety of known and emerging pollutants like heavy metals, antibiotics, pesticides, phthalates, polyaromatic hydrocarbons, halogenated compounds and endocrine disruptors have been found in natural water reservoirs, due to the limited effectiveness of conventional wastewater treatment. The conventional approach consists of a combination of physical, chemical and biological processes, aiming at the removal of large sediments such as heavier solids, scum and grease and of organic content in order to avoid the growth of microorganisms and eutrophication of the receiving water bodies. However, this approach is not sufficient to reduce the chemical pollutants and much less the emerging chemical pollutants. In this review, after some considerations concerning chemical pollutants and the problematic efficiency of their removal by conventional methods, an update is presented on the successes and challenges of novel approaches for wastewater remediation based on advanced oxidation processes. An insight into wastewater remediation involving the photodynamic approach mediated by tetrapyrrolic derivatives will be underlined.

Evaluation of meso-substituted cationic corroles as potential antibacterial agents

Cationic derivatives of 5,10,15-tris[4-(pyridin-4-ylsulphanyl)-2,3,5,6-tetrafluorophenyl]-corrolategallium(III)pyridine and 5,10,15-tris[4-(pyridin-2-ylsulfanyl)-2,3,5,6-tetrafluorophenyl]-correlategallium(III)pyridine were synthesized and their photosensitizing properties against the naturally bioluminescent Gram-negative bacterium Allivibrio fischeri were evaluated. The cationic corrole derivatives exhibited antibacterial activity at micromolar concentrations against this Gram-negative bacterium strain.

An insight on the role of photosensitizer nanocarriers for Photodynamic Therapy

Photodynamic therapy (PDT) is a modality of cancer treatment in which tumor cells are destroyed by reactive oxygen species (ROS) produced by photosensitizers following its activation with visible or near infrared light. The PDT success is dependent on different factors namely on the efficiency of the photosensitizer deliver and targeting ability. In this review a special attention will be given to the role of some drug delivery systems to improve the efficiency of tetrapyrrolic photosensitizers to this type of treatment.

Antimicrobial Photodynamic Therapy against Endodontic Enterococcus faecalis and Candida albicans Mono and Mixed Biofilms in the Presence of Photosensitizers: A Comparative Study with Classical Endodontic Irrigants

Endodontic biofilms eradication from the infected root canal system remains as the primary focus in endodontic field. In this study, it was assessed the efficacy of antimicrobial Photodynamic Therapy (aPDT) with the Zn(II)chlorin e6 methyl ester (Zn(II)e₆Me) activated by red light against monospecies and mixed biofilms of Enterococcus faecalis and Candida albicans. The results were compared with the ones obtained with Rose Bengal (RB), Toluidine Blue-O (TBO), the synthetic tetracationic porphyrin (TMPyP) as well as classical endodontic irrigants (3% NaOCl, 17% EDTA and 2% CHX). The antimicrobial efficacy of aPDT toward monospecies and mixed biofilms was quantified resorting to safranin red method. The changes of biofilm organization and of cellular ultrastructure were evaluated through several microscopy techniques (light, laser confocal and transmission electron microscopy). Zn(II)e₆Me once activated with light for 60 or 90 s was able to remove around 60% of the biofilm’s biomass. It was more efficient than TBO and RB and showed similar efficiency to TMPyP and classical irrigants, CHX and EDTA. As desirable in a PS, Zn(II)e₆Me in the dark showed smaller activity than TMPyP. Only NaOCl revealed higher efficiency, with 70–90% of the biofilm’s biomass removal. The organization of biofilms and the normal microbial cell ultrastructure were extensively damaged by the presence of Zn(II)e₆Me. aPDT with Zn(II)e₆Me showed to be an efficient antimicrobial strategy deserving further studies leading to a future clinical usage in endodontic disinfection.

An easy synthetic access to new pyrazole spiro derivatives from 3-amino-1-phenyl-2-pyrazolin-5-one

Pyrazole and pyrazolone moieties have shown important biological activities.

Influence of external bacterial structures on the efficiency of photodynamic inactivation by a cationic porphyrin

The main targets of photodynamic inactivation (PDI) are the external bacterial structures, cytoplasmic membrane and cell wall. In this work it was evaluated how the external bacterial structures influence the PDI efficiency. To reach this objective 8 bacteria with distinct external structures were selected; 4 Gram-negative bacteria (Escherichia coli, with typical Gram-negative external structures; Aeromonas salmonicida, Aeromonas hydrophila both with an S-layer and Rhodopirellula sp., with a peptidoglycan-less proteinaceous cell wall and with cytoplasm compartmentalization) and 4 Gram-positive bacteria (Staphylococcus aureus, with typical Gram-positive external structures; Truepera radiovictrix, Deinococcus geothermalis and Deinococcus radiodurans, all with thick cell walls that give them Gram-positive stains, but including a second complex multi-layered membrane and structurally analogous to that of Gram-negative bacteria). The studies were performed in the presence of 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetraiodide (Tetra-Py(+)-Me) at 5.0 μM with white light (40 W m(-2)). The susceptibility of each bacteria to PDI by Tetra-Py(+)-Me was dependent on bacteria external structures. Although all Gram-positive bacteria were inactivated to the detection limit (reduction of ∼8 log) after 60-180 min of irradiation, the inactivation followed distinct patterns. Among the Gram-negative bacteria, E. coli was the only species to be inactivated to the detection limit (∼8 log after 180 min). The efficiency of inactivation of the two species of Aeromonas was similar (reduction of ∼5-6 log after 270 min). Rhodopirellula was less susceptible (reduction of ∼4 log after 270 min). As previously observed, the Gram-positive bacteria are more easily inactivated than Gram-negative strains, and this is even true for T. radiovictrix, D. geothermalis and D. radiodurans, which have a complex multi-layered cell wall. The results support the theory that the outer cell structures are major bacterial targets for PDI. Moreover, the chemical composition of the external structures has a stronger effect on PDI efficiency than complexity and the number of layers of the external coating, and lipids seem to be an important target of PDI.

Photoinactivation of Escherichia coli (SURE2) without intracellular uptake of the photosensitizer

AIM

This study was performed to investigate the possibility to photodynamically inactivate Gram-negative bacteria without intracellular uptake of the photosensitizer. The efficiency of the photodynamic growth inhibition of Escherichia coli (SURE2) was proved in a comparative study of a neutral and a cationic photosensitizer.

METHODS AND RESULTS

We used confocal laser scanning microscopy (CLSM) to investigate the uptake of the photosensitizer by the bacteria to show that both chlorin e(6) and TMPyP are not accumulated in the cells. Fluorescence lifetime imaging (FLIM) and phototoxicity experiments were used to investigate the photodynamic inactivation of the Gram-negative bacteria. The phototoxicity experiments were carried out using a white light LED-setup to irradiate the bacterial suspensions. The viability of the bacteria was obtained by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-assay. For the cationic TMPyP, photodynamic inactivation without intracellular uptake was observed, whereas for chlorin e(6) such behaviour was not found.

CONCLUSIONS

It was proven that in general, it is possible to photodynamically inactivate Gram-negative bacteria without photosensitizer accumulation in the bacterial cells. This fact is especially interesting, considering that the development of resistances may be prevented, leaving the active components outside the bacterium.

SIGNIFICANCE AND IMPACT OF THE STUDY

In a world with bacteria that gain the ability to withstand the effects of antibiotics and are able to transmit on these resistances to the next generation, it becomes necessary to develop new approaches to inhibit the growth of multi-resistant bacteria. The photodynamic inactivation of bacteria is based on a three-component system by which the growth of the bacterial cells is inhibited. The well-directed oxidative damage is initiated by visible light of a certain wavelength, which excites a nontoxic photoactive molecule, called photosensitizer. Its reaction with oxygen causes the generation of cytotoxic species like singlet oxygen, which is highly reactive and causes the inactivation of the growth of bacteria.

Photodynamic inactivation of mammalian viruses and bacteriophages

Photodynamic inactivation (PDI) has been used to inactivate microorganisms through the use of photosensitizers. The inactivation of mammalian viruses and bacteriophages by photosensitization has been applied with success since the first decades of the last century. Due to the fact that mammalian viruses are known to pose a threat to public health and that bacteriophages are frequently used as models of mammalian viruses, it is important to know and understand the mechanisms and photodynamic procedures involved in their photoinactivation. The aim of this review is to (i) summarize the main approaches developed until now for the photodynamic inactivation of bacteriophages and mammalian viruses and, (ii) discuss and compare the present state of the art of mammalian viruses PDI with phage photoinactivation, with special focus on the most relevant mechanisms, molecular targets and factors affecting the viral inactivation process.

Bioluminescence and its application in the monitoring of antimicrobial photodynamic therapy

Light output from bioluminescent microorganisms is a highly sensitive reporter of their metabolic activity and therefore can be used to monitor in real time the effects of antimicrobials. Antimicrobial photodynamic therapy (aPDT) is receiving considerable attention for its potentialities as a new antimicrobial treatment modality. This therapy combines oxygen, a nontoxic photoactive photosensitizer, and visible light to generate reactive oxygen species (singlet oxygen and free radicals) that efficiently destroy microorganisms. To monitor this photoinactivation process, faster methods are required instead of laborious conventional plating and overnight incubation procedures. The bioluminescence method is a very interesting approach to achieve this goal. This review covers recent developments on the use of microbial bioluminescence in aPDT in the clinical and environmental areas.

Porphyrin derivatives as photosensitizers for the inactivation of Bacillus cereus endospores

AIMS

In this study, we propose (i) to study the photodynamic inactivation (PDI) efficiency of neutral and cationic porphyrin derivatives, (ii) to characterize the kinetics of the inactivation process using Bacillus cereus as a model endospore-producing bacterium and (iii) to conclude on the applicability of porphyrin derivatives in the inactivation of bacterial endospores.

METHODS AND RESULTS

The study of PDI of Bacillus cereus endospores, taken as model-endospores, using porphyrin derivatives differing in the number of positive charges and in the meso-substituent groups, showed that neutral, monocationic and dicationic porphyrins are quite ineffective, in contrast with the tri- and tetra-cationic molecules. The most effective porphyrin is a tricationic porphyrin with a meso-pentafluorophenyl group. With this photosensitizer (PS), at 0.5 micromol l(-1), a reduction of 3.5 log units occurs after only 4 min of irradiation. None of the porphyrin derivatives showed toxicity in the absence of light.

CONCLUSIONS

Some porphyrin derivatives are efficient PSs for the inactivation of bacterial endospores and should be considered in further studies. Small modifications in the substituent groups, in addition to charge, significantly improve the effectiveness of the molecule as a PS for endospore inactivation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Tetrapyrrolic macrocycles should be regarded as worthy to explore for the PDI of spore-producing gram-positive bacteria. The development of molecules, more selective and effective, emerges as a new objective.

Study by liquid secondary ion and electrospray mass spectrometry of synthesized and formed-in-source metallocorroles

Liquid secondary ion and electrospray mass spectrometry were used to study the complexation in-source of 5,10,15-tris(pentafluorophenyl)corrole with several divalent transition-metal ions. The metallocorrole ions formed in-source were identified by comparing their product ion mass spectra with the spectra of the same ions formed from metallocorroles obtained from classical procedures. Positive metallocorrole ion formation is accompanied by oxidation of the metal centre. Mechanisms were proposed for the oxidation processes, and data from negative-ion spectra reinforced these mechanisms.

Interactions of cationic porphyrins with double-stranded oligodeoxynucleotides: a study by electrospray ionisation mass spectrometry

Electrospray ionisation mass spectrometry (ESI-MS), electrospray ionisation tandem mass spectrometry (ESI-MS/MS) and Ultraviolet-visible (UV-vis) spectroscopy were used to investigate the non-covalent interactions between small oligonucleotide duplexes with the GC motif and a group of cationic meso(N-methylpyridynium-4-yl)porphyrins (four free bases with one to four positive charges, and the zinc complex of the tetracationic free base). The results obtained point to outside binding of the porphyrins, with the binding strength increasing with the number of positive charges. Fragmentations involving losses from both chains were observed for the porphyrins with N-methylpyridinium-4-yl groups in opposite meso positions.

Characterization of dinitroporphyrin zinc complexes by electrospray ionization tandem mass spectrometry. Unusual fragmentations of beta-(1,3-dinitroalkyl) porphyrins

The zinc complexes of diaryl bis(p-nitrophenyl)porphyrins and beta-(1,3-dinitroalkyl)tetraphenylporphyrins were studied by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). All porphyrins showed the protonated molecule under ESI conditions. The protonated molecules were induced to fragment and the corresponding ESI tandem mass spectra were analysed. Porphyrins with two p-nitrophenyl groups showed, as expected, characteristic fragmentations including either loss of one nitro group, as the major fragment of the tandem mass spectra, and loss of both nitro groups. In contrast, MS/MS of the beta-(1,3-dinitroalkyl)porphyrins provided interesting and unexpected results such as the absence (or in insignificant abundance) of the ions formed by loss of one nitro group. However, these porphyrins show an abundant fragment due to combined loss of the two nitro groups. Also, the typical beta-cleavage of the alkyl chain is not observed per se, only when combined with loss of HNO2 or *NO2. Instead, alpha-cleavage, with loss of the beta-pyrrolic substituent, is the most favourable process.

Electrospray tandem mass spectrometry of new porphyrin amino acid conjugates

Porphyrin amino acid conjugates with one or two porphyrin units were analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The ESI-MS spectra of all the porphyrins studied, obtained in positive ion mode, show the presence of the corresponding protonated molecule [M+H]+; ESI-MS spectra of diporphyrinyl compounds also show the doubly charged ions [M+2H]2+. The fragmentations of these ions induced by collision with argon were studied (ESI-MS/MS). ESI-MS/MS gives detailed structural information about the amino acids associated with the porphyrin. Cleavage of the bonds in the vicinity of the porphyrin moiety and those involving the side chain of amino acid residues gives structural information about this type of association. A fragmentation common to all derivatives corresponds to the cleavage of the phenyl-CO bond. The expected cleavage of the amide bond, that links the porphyrin to the amino acid moiety, is a minor fragmentation, which in some cases is even absent. The MS/MS spectra of the monoporphyrinyl derivatives show product ions characteristic of the amino acid linked to the porphyrin; the fragmentation also indicates when the amino acids has a terminal carboxylic group or a terminal ester group. The fragmentations of the diporphyrinyl compounds occur mainly by the cleavage of the spacer, leading, in the case of the doubly charged ions, to predominantly mono-charged ions, indicating a preferential location of the two protons in separated porphyrinic units.