Antimicrobial properties of porphyrins

What an Escherichia coli Mutant Can Teach Us About the Antibacterial Effect of Chlorophyllin

Due to the increasing development of antibiotic resistances in recent years, scientists search intensely for new methods to control bacteria. Photodynamic treatment with porphyrins such as chlorophyll derivatives is one of the most promising methods to handle bacterial infestation, but their use is dependent on illumination and they seem to be more effective against Gram-positive bacteria than against Gram-negatives. In this study, we tested chlorophyllin against three bacterial model strains, the Gram-positive Bacillus subtilis 168, the Gram-negative Escherichia coli DH5α and E. coli strain NR698 which has a deficient outer membrane, simulating a Gram-negative "without" its outer membrane. Illuminated with a standardized light intensity of 12 mW/cm², B. subtilis showed high sensitivity already at low chlorophyllin concentrations (≤10⁵ cfu/mL: ≤0.1 mg/L, 10⁶⁻10⁸ cfu/mL: 0.5 mg/L), whereas E. coli DH5α was less sensitive (≤10⁵ cfu/mL: 2.5 mg/L, 10⁶ cfu/mL: 5 mg/L, 10⁷⁻10⁸ cfu/mL: ineffective at ≤25 mg/L chlorophyllin). E. coli NR698 was almost as sensitive as B. subtilis against chlorophyllin, pointing out that the outer membrane plays a significant role in protection against photodynamic chlorophyllin impacts. Interestingly, E. coli NR698 and B. subtilis can also be inactivated by chlorophyllin in darkness, indicating a second, light-independent mode of action. Thus, chlorophyllin seems to be more than a photosensitizer, and a promising substance for the control of bacteria, which deserves further investigation.

Sensitization of Salmonella enterica with 5-aminolevulinic acid-induced endogenous porphyrins: a spectroscopic study

The fluorescence spectroscopy data reflecting time-dependent changes in the type and localization of endogenous porphyrins reveal the sensitization potential of a precursor 5-ALA for Gram-negative foodborne pathogen Salmonella enterica.

Role of clathrin-mediated endocytosis in the use of heme and hemoglobin by the fungal pathogen Cryptococcus neoformans

Heme is a major source of iron for pathogens of humans, and its use is critical in determining the outcome of infection and disease. Cryptococcus neoformans is an encapsulated fungal pathogen that causes life-threatening infections in immunocompromised individuals. C. neoformans effectively uses heme as an iron source, but the underlying mechanisms are poorly defined. Non-iron metalloporphyrins (MPPs) are toxic analogues of heme and are thought to enter microbial cells via endogenous heme acquisition systems. We therefore carried out a mutant screen for susceptibility against manganese MPP (MnMPP) to identify new components for heme uptake in C. neoformans. We identified several genes involved in signalling, DNA repair, sugar metabolism, and trafficking that play important roles in susceptibility to MnMPP and in the use of heme as an iron source. We focused on investigating the role of clathrin-mediated endocytosis (CME) and found that several components of CME including Chc1, Las17, Rvs161, and Rvs167 are required for growth on heme and hemoglobin and for endocytosis and intracellular trafficking of these molecules. We show that the hemoglobin uptake process in C. neoformans involves clathrin heavy chain, Chc1, which appears to colocalise with hemoglobin-containing vesicles and to potentially assist in proper delivery of hemoglobin to the vacuole. Additionally, C. neoformans strains lacking Chc1, Las17, Rvs161, or Rvs167 were defective in the elaboration of several key virulence factors, and a las17 mutant was avirulent in a mouse model of cryptococcosis. Overall, this study unveils crucial functions of CME in the use of heme iron by C. neoformans and reveals a role for CME in fungal pathogenesis.

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

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

Polyhedral Oligomeric Silsesquioxane (POSS)-Based Cationic Conjugated Oligoelectrolyte/Porphyrin for Efficient Energy Transfer and Multiamplified Antimicrobial Activity

Cationic quaternary ammonium (QA) groups and reactive oxygen species as two main approaches for antibacterial study have been intensively studied. Herein, we report a multifunctional antimicrobial agent (porphyrin-POSS-OPVE, PPO), which combines bacterial membrane intercalation, high density of local QA groups, efficient energy transfer, significantly reduced aggregation, and high water solubility into one single molecule. The light-harvesting PPO contains multiple donor-absorbing arms (oligo( p-phenylenevinylene) electrolytes, OPVEs) on its globular periphery and a central porphyrin acceptor in the core by using three-dimensional nanocages (polyhedral oligomeric silsesquioxanes, POSSs) as bridges. The antiaggregation ability of POSS and the highly efficient energy transfer from multiple OPVE arms to porphyrin could greatly amplify singlet oxygen generation in PPO. Particularly, OPVEs with QA terminal chains were able to intercalate into Escherichia coli membranes, which facilitated ¹O₂ diffusion and bacterial cell membrane disintegration by QA groups. The increased local cationic QA charges in OPVE arms can also enhance the biocidal activity of PPO. Benefiting from these satisfactory features, PPO exhibits multiamplified antibacterial efficacy under a very low concentration level and white light dose (400-700 nm, 6 mW·cm^-2, 5 min, 1.8 J·cm^-2) to Escherichia coli (8 μM) and Staphylococcus aureus (500 nM). Therefore, PPO shows great potential for photodynamic antimicrobial chemotherapy at a much lower irradiation light dose and photosensitizer concentration level compared to previous reports.

Co-protoporphyrin IX and Sn-protoporphyrin IX inactivate Zika, Chikungunya and other arboviruses by targeting the viral envelope

The global situation of diseases transmitted by arthropod-borne viruses such as Dengue (DENV), Yellow Fever (YFV), Chikungunya (CHIKV) and Zika (ZIKV) viruses is alarming and treatment of human infection by these arboviruses faces several challenges. The discovery of broad-spectrum antiviral molecules, able to inactivate different groups of viruses, is an interesting approach. The viral envelope is a common structure among arboviruses, being a potential target for antivirals. Porphyrins are amphipathic molecules able to interact with membranes and absorb light, being widely used in photodynamic therapy. Previously, we showed that heme, Co-protoporphyrin IX (CoPPIX) and Sn-protoporphyrin IX (SnPPIX) directly inactivate DENV and YFV infectious particles. Here we demonstrate that the antiviral activity of these porphyrins can be broadened to CHIKV, ZIKV, Mayaro virus, Sindbis virus and Vesicular Stomatitis virus. Porphyrin treatment causes viral envelope protein loss, affecting viral morphology, adsorption and entry into target cells. Also, light-stimulation enhanced the SnPPIX activity against all tested arboviruses. In summary, CoPPIX and SnPPIX were shown to be efficient broad-spectrum compounds to inactivate medically and veterinary important viruses.

Development in Assay Methods for in Vitro Antimalarial Drug Efficacy Testing: A Systematic Review

The emergence and spread of drug resistance are the major challenges in malaria eradication mission. Besides various strategies laid down by World Health Organization, such as vector management, source reduction, early case detection, prompt treatment, and development of new diagnostics and vaccines, nevertheless the need for new and efficacious drugs against malaria has become a critical priority on the global malaria research agenda. At several screening stages, millions of compounds are screened (1,000–2,000,000 compounds per screening campaign), before pre-clinical trials to select optimum lead. Carrying out in vitro screening of antimalarials is very difficult as different assay methods are subject to numerous sources of variability across different laboratories around the globe. Despite this, in vitro screening is an essential part of antimalarial drug development as it enables to resource various confounding factors such as host immune response and drug–drug interaction. Therefore, in this article, we try to illustrate the basic necessity behind in vitro study and how new methods are developed and subsequently adopted for high-throughput antimalarial drug screening and its application in achieving the next level of in vitro screening based on the current approaches (such as stem cells).

Mycoplasma tullyi sp. nov., isolated from penguins of the genus Spheniscus

A mycoplasma isolated from the liver of a dead Humboldt penguin (Spheniscus humboldti) and designated strain 56A97^T, was investigated to determine its taxonomic status. Complete 16S rRNA gene sequence analysis indicated that the organism was most closely related to Mycoplasma gallisepticum and Mycoplasma imitans(99.7 and 99.9 % similarity, respectively). The average DNA-DNA hybridization values between strain 56A97^T and M. gallisepticum and M. imitans were 39.5 and 30 %, respectively and the Genome to Genome Distance Calculator gave results of 29.10 and 23.50 %, respectively. The 16S-23S rRNA intergenic spacer was 72-73 % similar to M. gallisepticum strains and 52.2 % to M. imitans. A partial sequence of rpoB was 91.1-92 % similar to M. gallisepticum strains and 84.7 % to M. imitans. Colonies possessed a typical fried-egg appearance and electron micrographs revealed the lack of a cell wall and a nearly spherical morphology, with an electron-dense tip-like structure on some flask-shaped cells. The isolate required sterol for growth, fermented glucose, adsorbed and haemolysed erythrocytes, but did not hydrolyse arginine or urea. The strain was compared serologically against 110 previously described Mycoplasma reference strains, showing that, except for M. gallisepticum, strain 56A97^T is not related to any of the previously described species, although weak cross-reactions were evident. Genomic information, serological reactions and phenotypic properties demonstrate that this organism represents a novel species of the genus Mycoplasma, for which the name Mycoplasma tullyi sp. nov. is proposed; the type strain is 56A97^T (ATCC BAA-1432^T, DSM 21909^T, NCTC 11747^T).

Antimicrobial efficacy of irradiation with visible light on oral bacteria in vitro: a systematic review

AIM

Resistances to antibiotics employed for treatment of infectious diseases have increased to alarming numbers making it more and more difficult to treat diseases caused by microorganisms resistant to common antibiotics. Consequently, novel methods for successful inactivation of pathogens are required. In this instance, one alternative could be application of light for treatment of topical infections. Antimicrobial properties of UV light are well documented, but due to its DNA-damaging properties use for medical purposes is limited. In contrast, irradiation with visible light may be more promising.

METHODS

Literature was systematically screened for research concerning inactivation of main oral bacterial species by means of visible light.

RESULTS

Inactivation of bacterial species, especially pigmented ones, in planktonic state showed promising results. There is a lack of research examining the situation when organized as biofilms.

CONCLUSION

More research concerning situation in a biofilm state is required.

Antimicrobial effect of blue light using Porphyromonas gingivalis pigment

The development of antibiotics cannot keep up with the speed of resistance acquired by microorganisms. Recently, the development of antimicrobial photodynamic therapy (aPDT) has been a necessary antimicrobial strategy against antibiotic resistance. Among the wide variety of bacteria found in the oral flora, Porphyromonas gingivalis (P. gingivalis) is one of the etiological agents of periodontal disease. aPDT has been studied for periodontal disease, but has risks of cytotoxicity to normal stained tissue. In this study, we performed aPDT using protoporphyrin IX (PpIX), an intracellular pigment of P. gingivalis, without an external photosensitizer. We confirmed singlet oxygen generation by PpIX in a blue-light irradiation intensity-dependent manner. We discovered that blue-light irradiation on P. gingivalis is potentially bactericidal. The sterilization mechanism seems to be oxidative DNA damage in bacterial cells. Although it is said that no resistant bacteria will emerge using aPDT, the conventional method relies on an added photosensitizer dye. PpIX in P. gingivalis is used in energy production, so aPDT applied to PpIX of P. gingivalis should limit the appearance of resistant bacteria. This approach not only has potential as an effective treatment for new periodontal diseases, but also offers potential antibacterial treatment for multiple drug resistant bacteria.

Deferiprone and Gallium-Protoporphyrin Have the Capacity to Potentiate the Activity of Antibiotics in Staphylococcus aureus Small Colony Variants

Small colony variants (SCVs) of bacteria like Staphylococcus aureus are characterized by a reduced colony size and are linked to increased antibiotic tolerance and resistance. Their altered expression of virulence factors, slow growing properties and their ability to form biofilms make the eradication of SCVs challenging. In the context of biofilm-related infectious diseases involving S. aureus SCVs, a therapy targeting bacterial iron metabolism was evaluated. The combination of the iron-chelator deferiprone (Def) and the heme-analog gallium-protoporphyrin (GaPP), in solution and incorporated in a surgical wound gel, was tested for activity against planktonic and sessile SCVs. To this end, the activity of Def-GaPP was assessed against planktonic S. aureus SCVs, as well as against in vitro and in vivo biofilms in the colony biofilm model, an artificial wound model and a Caenorhabditis elegans infection model. While Def alone failed to show substantial antibacterial activity, GaPP and the combination of Def-GaPP demonstrated concentration- and strain-dependent antibacterial properties. Specifically, the Def-GaPP combination significantly reduced the bacterial load in an artificial wound model and increased the survival of S. aureus SCV infected C. elegans. When Def-GaPP were combined with gentamicin or ciprofloxacin, the triple combinations exceeded the antibiofilm activity of the individual compounds in the colony biofilm model. In targeting bacterial iron metabolism, Def-GaPP showed significant activity against planktonic and sessile SCVs. Moreover, Def-GaPP could potentiate the activity of gentamicin and ciprofloxacin. Delivered in a wound healing gel, Def-GaPP showed promise as a new topical strategy against infections with S. aureus SCVs.

A Topical Hydrogel with Deferiprone and Gallium-Protoporphyrin Targets Bacterial Iron Metabolism and Has Antibiofilm Activity

Many infectious diseases are associated with multidrug-resistant (MDR) bacteria residing in biofilms that require high antibiotic concentrations. While oral drug delivery is frequently ineffective, topical treatments have the potential to deliver higher drug concentrations to the infection site while reducing systemic side effects. This study determined the antibiofilm activity of a surgical wound gel loaded with the iron chelator deferiprone (Def) and the heme analogue gallium-protoporphyrin (GaPP), alone and in combination with ciprofloxacin. Activity against MDR Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Acinetobacter johnsonii biofilms was assessed in the colony biofilm and artificial wound model by enumeration of CFU and correlative light/electron microscopy. While Staphylococcus biofilms were equally susceptible to GaPP and Def-GaPP gels (log10 reduction of 3.8 and 3.7, respectively), the Def-GaPP combination was crucial for significant activity against P. aeruginosa biofilms (log10 reduction of 1.3 for GaPP and 3.3 for Def-GaPP). When Def-GaPP gel was combined with ciprofloxacin, the efficacy exceeded the activity of the individual compounds. Def-GaPP delivered in a surgical wound gel showed significant antibiofilm activity against different MDR strains and could enhance the gel's wound-healing properties. Moreover, Def-GaPP indicated a potentiation of ciprofloxacin. This antibiofilm strategy has potential for clinical utilization as a therapy for topical biofilm-related infections.

Mechanisms of Vesicular Stomatitis Virus Inactivation by Protoporphyrin IX, Zinc-Protoporphyrin IX, and Mesoporphyrin IX

Virus resistance to antiviral therapies is an increasing concern that makes the development of broad-spectrum antiviral drugs urgent. Targeting of the viral envelope, a component shared by a large number of viruses, emerges as a promising strategy to overcome this problem. Natural and synthetic porphyrins are good candidates for antiviral development due to their relative hydrophobicity and pro-oxidant character. In the present work, we characterized the antiviral activities of protoprophyrin IX (PPIX), Zn-protoporphyrin IX (ZnPPIX), and mesoporphyrin IX (MPIX) against vesicular stomatitis virus (VSV) and evaluated the mechanisms involved in this activity. Treatment of VSV with PPIX, ZnPPIX, and MPIX promoted dose-dependent virus inactivation, which was potentiated by porphyrin photoactivation. All three porphyrins inserted into lipid vesicles and disturbed the viral membrane organization. In addition, the porphyrins also affected viral proteins, inducing VSV glycoprotein cross-linking, which was enhanced by porphyrin photoactivation. Virus incubation with sodium azide and α-tocopherol partially protected VSV from inactivation by porphyrins, suggesting that singlet oxygen (¹O₂) was the main reactive oxygen species produced by photoactivation of these molecules. Furthermore, ¹O₂ was detected by 9,10-dimethylanthracene oxidation in photoactivated porphyrin samples, reinforcing this hypothesis. These results reveal the potential therapeutic application of PPIX, ZnPPIX, and MPIX as good models for broad antiviral drug design.

Photodynamic antimicrobial chemotherapy with the novel amino acid-porphyrin conjugate 4I: In vitro and in vivo studies

Photodynamic antimicrobial chemotherapy (PACT), as a novel and effective therapeutic modality to eradicate drug resistant bacteria without provoking multidrug resistance, has attracted increasing attention. This study examined the antimicrobial efficacy of the novel cationic amino acid-porphyrin conjugate 4I with four lysine groups against two different clinical isolated strains (drug sensitive and multidrug resistant) of the Acinetobacter baumannii species and its toxicity on murine dermal fibroblasts in vitro, as well as the therapeutic effect of PACT on acute, potentially lethal multidrug resistant strain excisional wound infections in vivo. The PACT protocol exposed 4I to illumination, exhibiting high antimicrobial efficacy on two different strains due to a high yield of reactive oxygen species (ROS) and non-selectivity to microorganisms. The photoinactivation effects of 4I against two different strains were dose-dependent. At 3.9 μM and 7.8 μM, PACT induced 6 log units of inactivation of sensitive and multidrug resistant strains. In contrast, 4I alone and illumination alone treatments had no visibly antimicrobial effect. Moreover, cytotoxicity tests revealed the great safety of the photosensitizer 4I in mice. In the in vivo study, we found 4I-mediated PACT was not only able to kill bacteria but also accelerated wound recovery. Compared with non-treated mice, over 2.89 log reduction of multidrug resistant Acinetobacter baumannii strain was reached in PACT treat mice at 24 h post-treatment. These results imply that 4I-mediated PACT therapy is an effective and safe alternative to conventional antibiotic therapy and has clinical potential for superficial drug-resistant bacterial infections.

Extracellular Heme Uptake and the Challenge of Bacterial Cell Membranes

Iron is essential for the survival of most bacteria but presents a significant challenge given its limited bioavailability. Furthermore, the toxicity of iron combined with the need to maintain physiological iron levels within a narrow concentration range requires sophisticated systems to sense, regulate, and transport iron. Most bacteria have evolved mechanisms to chelate and transport ferric iron (Fe³⁺) via siderophore receptor systems, and pathogenic bacteria have further lowered this barrier by employing mechanisms to utilize the host's hemoproteins. Once internalized, heme is cleaved by both oxidative and nonoxidative mechanisms to release iron. Heme, itself a lipophilic and toxic molecule, presents a significant challenge for transport into the cell. As such, pathogenic bacteria have evolved sophisticated cell surface signaling and transport systems to obtain heme from the host. In this review, we summarize the structure and function of the heme-sensing and transport systems of pathogenic bacteria and the potential of these systems as antimicrobial targets.

Innovative approaches to treat Staphylococcus aureus biofilm-related infections

Many bacterial infections in humans and animals are caused by bacteria residing in biofilms, complex communities of attached organisms embedded in an extracellular matrix. One of the key properties of microorganisms residing in a biofilm is decreased susceptibility towards antimicrobial agents. This decreased susceptibility, together with conventional mechanisms leading to antimicrobial resistance, makes biofilm-related infections increasingly difficult to treat and alternative antibiofilm strategies are urgently required. In this review, we present three such strategies to combat biofilm-related infections with the important human pathogen Staphylococcus aureus: (i) targeting the bacterial communication system with quorum sensing (QS) inhibitors, (ii) a ‘Trojan Horse’ strategy to disturb iron metabolism by using gallium-based therapeutics and (iii) the use of ‘non-antibiotics’ with antibiofilm activity identified through screening of repurposing libraries.

In Vitro Testing of Cyto- and Genotoxicity of New Porphyrin Water-Soluble Metal Derivatives

Porphyrins and porphyrin derivatives have an outstanding potential for discovery of novel pharmacological agents due to their ability for numerous chemical modifications and a variety of mechanisms of biological effects. New water-soluble Ag and Zn derivatives of tetrachloride meso-tetra (4- N-oxiethylpyridyl) porphyne were synthesized. Cyto- and genotoxicity of these substances were tested in vitro by the vital dye (trypan blue) exclusion and the micronucleus tests, respectively. Both metalloporphyrins were shown to be cytotoxic for Cos-7 (fibroblast-like African green monkey kidney cells transformed by simian virus 40 [SV40]), DU 145 (epithelial-like cells of human prostate carcinoma), and K-562 (human chronic myeloid leukemia cells) cell lines. At the same time they did not cause chromosome fragmentation in K-562 cell line at as high concentrations as IC50 (20 μmol/L for Ag and 70 μmol/L for Zn derivative). Thus, the metalloporphyrins tested meet at least two important demands to potential anticancer drugs as they combine the cytotoxicity with low genotoxicity. The three in vitro tumor models used are relevant to further in vitro and in vivo pre-clinical investigation of the studied metalloporphyrins as potential chemotherapeutics.

A Novel Electrostimulated Drug Delivery System Based on PLLA Composites Exploiting the Multiple Functions of Graphite Nanoplatelets

A novel drug delivery system based on poly(l-lactide) (PLLA), graphite, and porphyrin was developed. In particular, 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (THPP) was chosen because, besides its potential as codispersing agent of graphite, it is a pharmacologically active molecule. Graphite nanoplatelets, homogeneously dispersed in both the neat PLLA and the PLLA/porphyrin films, which were prepared by solution casting, turned out to improve the crystallinity of the polymer. Moreover, IR measurements demonstrated that unlike PLLA/porphyrin film, where the porphyrin was prone to aggregate causing variable concentration throughout the sample, the system containing also GNP was characterized by a homogeneous dispersion of the above molecule. The effect of graphite nanoplatelets on the thermal stabilization, electrical conductivity, and improvement of mechanical properties of the polymer resulted to be increased by the addition of the porphyrin to the system, thus demonstrating the role of the molecule in ameliorating the filler dispersion in PLLA. The porphyrin release from the composite film, occurring both naturally and with the application of an electrical field, was measured using an UV-vis spectrophotometer. Indeed, voltage application turned out to improve significantly the kinetic of drug release. The biocompatibility of the polymer matrix as well as the mechanical and thermal properties of the composite together with its electrical response makes the developed material extremely promising in biological applications, particularly in the drug delivery field.

A Perspective on the Trends and Challenges Facing Porphyrin-Based Anti-Microbial Materials

The emergence of multidrug resistant bacterium threatens to unravel global healthcare systems, built up over centuries of medical research and development. Current antibiotics have little resistance against this onslaught as bacterium strains can quickly evolve effective defense mechanisms. Fortunately, alternative therapies exist and, at the forefront of research lays the photodynamic inhibition approach mediated by porphyrin based photosensitizers. This review will focus on the development of various porphyrins compounds and their incorporation as small molecules, into polymers, fibers and thin films as practical therapeutic agents, utilizing photodynamic therapy to inhibit a wide spectrum of bacterium. The use of photodynamic therapy of these porphyrin molecules are discussed and evaluated according to their electronic and bulk material effect on different bacterium strains. This review also provides an insight into the general direction and challenges facing porphyrins and derivatives as full-fledged therapeutic agents and what needs to be further done in order to be bestowed their rightful and equal status in modern medicine, similar to the very first antibiotic; penicillin itself. It is hoped that, with this perspective, new paradigms and strategies in the application of porphyrins and derivatives will progressively flourish and lead to advances against disease.

Activity of Gallium Meso- and Protoporphyrin IX against Biofilms of Multidrug-Resistant Acinetobacter baumannii Isolates

Acinetobacter baumannii is a challenging pathogen due to antimicrobial resistance and biofilm development. The role of iron in bacterial physiology has prompted the evaluation of iron-modulation as an antimicrobial strategy. The non-reducible iron analog gallium(III) nitrate, Ga(NO₃)₃, has been shown to inhibit A. baumannii planktonic growth; however, utilization of heme-iron by clinical isolates has been associated with development of tolerance. These observations prompted the evaluation of iron-heme sources on planktonic and biofilm growth, as well as antimicrobial activities of gallium meso- and protoporphyrin IX (Ga-MPIX and Ga-PPIX), metal heme derivatives against planktonic and biofilm bacteria of multidrug-resistant (MDR) clinical isolates of A. baumannii in vitro. Ga(NO₃)₃ was moderately effective at reducing planktonic bacteria (64 to 128 µM) with little activity against biofilms (≥512 µM). In contrast, Ga-MPIX and Ga-PPIX were highly active against planktonic bacteria (0.25 to 8 µM). Cytotoxic effects in human fibroblasts were observed following exposure to concentrations exceeding 128 µM of Ga-MPIX and Ga-PPIX. We observed that the gallium metal heme conjugates were more active against planktonic and biofilm bacteria, possibly due to utilization of heme-iron as demonstrated by the enhanced effects on bacterial growth and biofilm formation.

Mechanism and In Vivo Evaluation: Photodynamic Antibacterial Chemotherapy of Lysine-Porphyrin Conjugate

Lysine-porphyrin conjugate 4i has potent photosensitive antibacterial effect on clinical isolated bacterial strains such as Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Pseudomonas aeruginosa. The mechanism of photodynamic antibacterial chemotherapy of 4i (4i-PACT) in vitro and the treatment effect in vivo was investigated in this paper. Atomic force microscopy (AFM) revealed that 4i-PACT can effectively destroy membrane and wall of bacteria, resulting in leakage of its content. This was confirmed by dual fluorescent staining with acridine orange/ethidium bromide and measuring materials absorption at 260 nm. Agarose gel electrophoresis measurement showed that 4i-PACT can damage genomic DNA. Healing of wound in rat infected by mixed bacteria showed that the efficiency of 4i-PACT is dependent on the dose of light. These results showed that 4i-PACT has promising bactericidal effect both in vitro and in vivo.

Amphiphilic cationic Zn-porphyrins with high photodynamic antimicrobial activity

AIM

Photodynamic inactivation of microbes can efficiently eradicate antibiotic-resistant strains. Systematic structural modification was used to investigate how porphyrin-based photosensitizers (PSs) could be designed for improved antibacterial activity.

MATERIALS & METHODS

Zinc(II)5,10,15,20-tetrakis(N-alkylpyridinium-2(3,4)-yl)porphyrins presenting systematic modifications at the periphery of the porphyrin ring were evaluated for toxicity and antimicrobial photodynamic activity by measuring metabolic activity, cell membrane integrity and viability using antibiotic-sensitive and resistant Escherichia coli strains as model Gram-negative targets.

RESULTS

Maximal sensitizer uptake, and, upon illumination, decrease of viable bacteria by >6 log10 were achieved by positively charged amphiphilic PSs with longer (six to eight carbon) alkyl substituents.

CONCLUSION

Antibacterial photoefficiency (throughout the text photoefficiency has been used as equivalent of photocytotoxic efficacy) can be increased by orders of magnitude by increasing the lipophilicity of cationic alkylmetalloporphyrin PSs.

Synthesis and conformation of a novel fluorescein–Zn-porphyrin dyad and intramolecular energy transfer

Modulations of the optical properties of a new porphyrin–fluorescein dyad were elucidated using experimental and theoretical techniques, with conformational rearrangements being studied.

Iron acquisition in the cystic fibrosis lung and potential for novel therapeutic strategies

Iron acquisition is vital to microbial survival and is implicated in the virulence of many of the pathogens that reside in the cystic fibrosis (CF) lung. The multifaceted nature of iron acquisition by both bacterial and fungal pathogens encompasses a range of conserved and species-specific mechanisms, including secretion of iron-binding siderophores, utilization of siderophores from other species, release of iron from host iron-binding proteins and haemoproteins, and ferrous iron uptake. Pathogens adapt and deploy specific systems depending on iron availability, bioavailability of the iron pool, stage of infection and presence of competing pathogens. Understanding the dynamics of pathogen iron acquisition has the potential to unveil new avenues for therapeutic intervention to treat both acute and chronic CF infections. Here, we examine the range of strategies utilized by the primary CF pathogens to acquire iron and discuss the different approaches to targeting iron acquisition systems as an antimicrobial strategy.

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.

Porphyrin-adsorbed Allograft Bone: A Photoactive, Antibiofilm Surface

BACKGROUND

Allograft bone is commonly used to augment bone stock. Unfortunately, allograft is prone to bacterial contamination and current antimicrobial therapies are inadequate. Photoactivated porphyrins combat bacterial growth by production of reactive oxygen species (ROS); however, to our knowledge, they have not been tested in the setting of allograft bone.

QUESTIONS/PURPOSES

We asked: (1) Does 5,10,15,20-tetrakis-(4-aminophenyl)-porphyrin (TAPP) stably adsorb to morselized, mineralized allograft? (2) Does Staphylococcus aureus acquire TAPP from TAPP-allograft? (3) Is TAPP-allograft antibacterial to S. aureus? (4) Is ROS production critical for antimicrobial activity? (5) Does illuminated TAPP-allograft dislodge biofilm? (6) Could other photoactive dyes (TAPP, TMPyP, TSP, THP, and methylene blue) confer antimicrobial properties to allograft?

METHODS

TAPP adsorption to allograft (TAPP-allograft), its localization in S. aureus, and TAPP-allograft long-term stability were determined spectrophotometrically. Antimicrobial activity was measured while activated with light or in the dark during incubation with S. aureus or after allograft biofilm formation. Glutathione was added to illuminated TAPP-allograft to quench ROS and antimicrobial activity was determined. Light-dependent antimicrobial activity of other photoactive dyes (TMPyP, TSP, THP, and methylene blue) adsorbed to allograft was also tested.

RESULTS

We found (1) porphyrins strongly adhere to bone allograft; and (2) the bacteria are not able to sequester TAPP from the TAPP-allograft; (3) when illuminated, TAPP-allograft is resistant to bacterial adherence; (4) the effects of TAPP are inhibited by the radical scavenger glutathione, indicating ROS-dependent antimicrobial activity; (5) illumination of TAPP-allograft disrupts biofilms; and, (6) other photoactive dyes impede biofilm formation on allograft bone in the presence of light.

CONCLUSIONS

Porphyrins stably associate with allograft and are inactive until illuminated. Illuminated TAPP-allograft markedly reduces bacterial colonization, which is restored in the presence of radical scavengers. Finally, illuminated TAPP-allograft disrupts biofilms.

CLINICAL RELEVANCE

The findings of this in vitro study suggest that loading bone allograft with biocompatible porphyrins before surgery might allow increased sterility of the allograft during implantation. Future testing in an animal model will determine if these in vitro activities can be used to prevent allograft-based infection in an establishing osteomyelitis.

Improved antibacterial phototoxicity of a neutral porphyrin in natural deep eutectic solvents

Neutral porphyrins for antibacterial photodynamic therapy (aPDT) have received little attention due to their tendency to aggregate in aqueous media and reports of low phototoxic effect. These compounds may be less toxic to cells than positively and negatively charged photosensitisers. The preparation of highly bacterial phototoxic formulations of neutral porphyrins remains an open field of research with great potential if achievable. The purpose of this study was to develop novel hydrophilic formulations of the neutral porphyrin 5,10,15,20-tetrakis(4-hydroxyphenyl)-porphyrin (THPP) by use of natural deep eutectic solvents (NADES) prepared by the solvent evaporation method. Physical and photochemical stability and in vitro photoinactivation of Enterococcus faecalis and Escherichia coli were investigated. Two of the 15 NADES investigated demonstrated superior solubilising properties of THPP. The photostability of THPP was higher in NADES than in methanol. A 100-fold dilution of the preparations with buffer to a final concentration of 0.5-5 nM THPP resulted in complete photoinactivation of E. faecalis and E. coli both in their exponential and stationary phase. THPP demonstrated significantly higher phototoxicity when formulated in NADES than in other aqueous preparations like phosphate buffered saline. NADES as a formulation concept for photosensitisers shows a great potential in aPDT.

Synthesis, characterization and in vitro photodynamic antimicrobial activity of basic amino acid-porphyrin conjugates

Photodynamic antimicrobial chemotherapy (PACT), as a novel and effective modality for the treatment of infection with the advantage of circumventing multidrug resistance, receives great attention in recent years. The photosensitizer is the crucial element in PACT, and cationic porphyrins have been demonstrated to usually be more efficient than neutral and negatively charged analogues towards bacteria in PACT. In this work, three native basic amino acids, l-lysine, l-histidine and l-arginine, were conjugated with amino porphyrins as cationic auxiliary groups, and 13 target compounds were synthesized. This paper reports their syntheses, structural characterizations, oil-water partition coefficients, singlet oxygen generation yields, photo-stability, as well as their photo inactivation efficacies against methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Pseudomonas aeruginosa in vitro. The preliminary structure-activity relationship was discussed. Compound 4i, with porphyrin bearing four lysine moieties, displays the highest photo inactivation efficacy against the tested bacterial strains at 3.91 μM with a low light dose (6 J/cm(2)), and it is stable in serum and lower cytotoxicity to A929 cells. These basic amino acid-porphyrin conjugates are potential photosensitizers for PACT.

Axially Ligated Zirconium(IV) Tetraphenylporphyrin: Synthesis, Characterization, and Biological Activity

A series of 5,10,15,20-tetraphenylporphinatozirconium(IV) acetylacetonatophenolates containing different phenols as axial ligands [Zr(TPP)(Y)(X)] (TPP = 5,10.15,20-tetraphenyl-21H, 23H-porphine; Y = acac; X = different phenolates) have been synthesized and characterized by various spectrochemical studies. The complexes were also screened for antimicrobial activities. Antifungal activity of some adducts has been carried out against the fungal strain Sclerotium rolfsii. Most of the complexes have shown good antibacterial activity.

Synthesis and Spectroscopic Characterization of Some New Axially Ligated Indium(III) Macrocyclic Complexes and Their Biological Activities

The synthesis and spectroscopic characterization of new axially ligated indium(III) porphyrin complexes were reported. Chloroindium(III) porphyrin (TPPIn-Cl) was obtained in good yield by treating the corresponding free base with indium trichloride. The action of the different phenols on chloroderivatives (TPPIn-Cl) led to the corresponding phenolato complexes (TPPIn-X). These derivatives were characterized on the basis of mass spectrometry, ¹H-NMR, IR, and UV-visible data. The separation and isolation of these derivatives have been achieved through chromatography. The spectral properties of free base porphyrin and its corresponding metallated and axially ligated indium(III) porphyrin compounds were compared with each other. A detailed analysis of UV-Vis, ¹H-NMR, and IR suggested the transformation from free base porphyrin to indium(III) porphyrin. Besides, ¹³C-NMR and fluorescence spectra were also reported and interpreted. The stability of these derivatives has also been studied through thermogravimetry. The complexes were also screened for anticancerous activities. Among all the complexes, 4-MePhO-InTPP shows highest anticancerous activity. The title complexe, TPPIn-X (where X = different phenolates), represents a five-coordinate indium(III) porphyrin complex in a square-pyramidal geometry with the phenolate anion as the axial ligand.

Simple biological systems for assessing the activity of superoxide dismutase mimics

SIGNIFICANCE

Half a century of research provided unambiguous proof that superoxide and species derived from it-reactive oxygen species (ROS)-play a central role in many diseases and degenerative processes. This stimulated the search for pharmaceutical agents that are capable of preventing oxidative damage, and methods of assessing their therapeutic potential.

RECENT ADVANCES

The limitations of superoxide dismutase (SOD) as a therapeutic tool directed attention to small molecules, SOD mimics, that are capable of catalytically scavenging superoxide. Several groups of compounds, based on either metal complexes, including metalloporphyrins, metallocorroles, Mn(II) cyclic polyamines, and Mn(III) salen derivatives, or non-metal based compounds, such as fullerenes, nitrones, and nitroxides, have been developed and studied in vitro and in vivo. Very few entered clinical trials.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Development of SOD mimics requires in-depth understanding of their mechanisms of biological action. Elucidation of both molecular features, essential for efficient ROS-scavenging in vivo, and factors limiting the potential side effects requires biologically relevant and, at the same time, relatively simple testing systems. This review discuses the advantages and limitations of genetically engineered SOD-deficient unicellular organisms, Escherichia coli and Saccharomyces cerevisiae as tools for investigating the efficacy and mechanisms of biological actions of SOD mimics. These simple systems allow the scrutiny of the minimal requirements for a functional SOD mimic: the association of a high catalytic activity for superoxide dismutation, low toxicity, and an efficient cellular uptake/biodistribution.

Synthesis and Spectroscopic and Biological Activities of Zn(II) Porphyrin with Oxygen Donors

Results of investigation of the physicochemical properties of zinc complexes containing substituted phenols as axial ligand having general formula [X-Zn-t(p-CH₃) PP] [where X = different phenolates as axial ligand] in impurity-free organic solvent are presented. The four-coordinated zinc porphyrin accepts one axial ligand in 1 : 1 molar ratio to form five-coordinated complex, which is purified by column chromatography and characterized by physicochemical, biological evaluation and TGA/DTA studies. Absorption spectra show two principal effects: a red shift for phenols bearing substituted electron releasing groups (−CH₃, −NH₂) and blue shift for phenols bearing electron withdrawing groups (−NO₂, −Cl) relative to Zn-t(p-CH₃) PP, respectively. ¹H NMR spectra show that the protons of the phenol ring axially attached to the central metal ion are merged with the protons of the porphyrin ring. Fluorescence spectra show two fluorescence peaks in the red region with emission ranging from 550 nm to 700 nm. IR spectra confirm the appearance of Zn-N_Por and Zn-O vibrational frequencies, respectively. According to the thermal studies, the complexes have a higher thermal stability and the decomposition temperature of these complexes depends on the axial ligation. The respective complexes of X-Zn^II-t(p-CH₃) PP were found to possess higher antifungal activity (up to 90%) and higher in vitro cytotoxicity against human cancer cells lines.

Insights on how the Mycobacterium tuberculosis heme uptake pathway can be used as a drug target

Mycobacterium tuberculosis (Mtb) acquires non-heme iron through salicylate-derived siderophores termed mycobactins whereas heme iron is obtained through a cascade of heme uptake proteins. Three proteins are proposed to mediate Mtb heme iron uptake, a secreted heme transporter (Rv0203), and MmpL3 and MmpL11, which are potential transmembrane heme transfer proteins. Furthermore, MhuD, a cytoplasmic heme-degrading enzyme, has been identified. Rv0203, MmpL3 and MmpL11 are mycobacteria-specific proteins, making them excellent drug targets. Importantly, MmpL3, a necessary protein, has also been implicated in trehalose monomycolate export. Recent drug-discovery efforts revealed that MmpL3 is the target of several compounds with antimycobacterial activity. Inhibition of the Mtb heme uptake pathway has yet to be explored. We propose that inhibitor design could focus on heme analogs, with the goal of blocking specific steps of this pathway. In addition, heme uptake could be hijacked as a method of importing drugs into the mycobacterial cytosol.

Synthesis, Spectroscopic, and Biological Studies on New Zirconium(IV) Porphyrins with Axial Ligand

A series of parasubstituted tetraphenylporphyrin zirconium(IV) salicylate complexes (SA/5-SSAZr(IV)RTPP, R = p-H, p-CH₃, p-NO₂, p-Cl, SA = salicylate, and 5-SSA = 5-sulfosalicylate) have been synthesized, and the spectral properties of free base porphyrins, their corresponding metallated, and axially ligated zirconium(IV) porphyrin compounds were compared with each other. A detailed analysis of ultraviolet-visible (UV-vis), proton nulcear magnetic resonance (¹H NMR) spectroscopy, infrared (IR) spectroscopy, and elemental analysis suggested the transformation from free base porphyrins to zirconium(IV) porphyrins. The ability of the metal in this complex for extra coordination of solvent molecules was confirmed by ESI-MS spectra. Besides the fluorescence, cyclic voltammetry, and thermogravimetric studies, the complexes were also screened for antimicrobial and anticancer activities. Among all the complexes, 5-SSAZr(p-NO₂TPP) shows high antibacterial activity.

Light based anti-infectives: ultraviolet C irradiation, photodynamic therapy, blue light, and beyond

Owing to the worldwide increase in antibiotic resistance, researchers are investigating alternative anti-infective strategies to which it is supposed microorganisms will be unable to develop resistance. Prominent among these strategies, is a group of approaches which rely on light to deliver the killing blow. As is well known, ultraviolet light, particularly UVC (200-280 nm), is germicidal, but it has not been much developed as an anti-infective approach until recently, when it was realized that the possible adverse effects to host tissue were relatively minor compared to its high activity in killing pathogens. Photodynamic therapy is the combination of non-toxic photosensitizing dyes with harmless visible light that together produce abundant destructive reactive oxygen species (ROS). Certain cationic dyes or photosensitizers have good specificity for binding to microbial cells while sparing host mammalian cells and can be used for treating many localized infections, both superficial and even deep-seated by using fiber optic delivered light. Many microbial cells are highly sensitive to killing by blue light (400-470 nm) due to accumulation of naturally occurring photosensitizers such as porphyrins and flavins. Near infrared light has also been shown to have antimicrobial effects against certain species. Clinical applications of these technologies include skin, dental, wound, stomach, nasal, toenail and other infections which are amenable to effective light delivery.

An encapsulation of iron homeostasis and virulence in Cryptococcus neoformans

Vertebrate hosts actively sequester iron, and fungal and other pathogens must therefore adapt to a severe limitation in iron availability to cause disease. Recent studies reveal that the pathogenic fungus Cryptococcus neoformans overcomes iron limitation by multiple mechanisms that target transferrin and heme. The regulation of iron uptake is mediated by an interconnected set of transcription factors that include the master iron regulator Cir1 and the pH-responsive factor Rim101. These factors integrate iron homeostasis with a myriad of other functions including pH sensing, nutrient and stress signaling pathways, virulence factor elaboration, and cell wall biogenesis.

Environmental heme utilization by heme-auxotrophic bacteria

Heme, an iron-containing porphyrin, is the prosthetic group for numerous key cellular enzymatic and regulatory processes. Many bacteria encode the biosynthetic enzymes needed for autonomous heme production. Remarkably, however, numerous other bacteria lack a complete heme biosynthesis pathway, yet encode heme-requiring functions. For such heme-auxotrophic bacteria (HAB), heme or porphyrins must be captured from the environment. Functional studies, aided by genomic analyses, provide insight into the HAB lifestyle, how they acquire and manage heme, and the uses of heme that make it worthwhile, and sometimes necessary, to capture this bioactive molecule.