Unsymmetrical cationic porphyrin-cyclodextrin bioconjugates for photoinactivation of Escherichia coli

Refining antimicrobial photodynamic therapy: effect of charge distribution and central metal ion in fluorinated porphyrins on effective control of planktonic and biofilm bacterial forms

Antibiotic resistance represents a pressing global health challenge, now acknowledged as a critical concern within the framework of One Health. Photodynamic inactivation of microorganisms (PDI) offers an attractive, non-invasive approach known for its flexibility, independence from microbial resistance patterns, broad-spectrum efficacy, and minimal risk of inducing resistance. Various photosensitizers, including porphyrin derivatives have been explored for pathogen eradication. In this context, we present the synthesis, spectroscopic and photophysical characteristics as well as antimicrobial properties of a palladium(II)-porphyrin derivative (PdF2POH), along with its zinc(II)- and free-base counterparts (ZnF2POH and F2POH, respectively). Our findings reveal that the palladium(II)-porphyrin complex can be classified as an excellent generator of reactive oxygen species (ROS), encompassing both singlet oxygen (Φ△ = 0.93) and oxygen-centered radicals. The ability of photosensitizers to generate ROS was assessed using a variety of direct (luminescence measurements) and indirect techniques, including specific fluorescent probes both in solution and in microorganisms during the PDI procedure. We investigated the PDI efficacy of F2POH, ZnF2POH, and PdF2POH against both Gram-negative and Gram-positive bacteria. All tested compounds proved high activity against Gram-positive species, with PdF2POH exhibiting superior efficacy, leading to up to a 6-log reduction in S. aureus viability. Notably, PdF2POH-mediated PDI displayed remarkable effectiveness against S. aureus biofilm, a challenging target due to its complex structure and increased resistance to conventional treatments. Furthermore, our results show that PDI with PdF2POH is more selective for bacterial than for mammalian cells, particularly at lower light doses (up to 5 J/cm2 of blue light illumination). This enhanced efficacy of PdF2POH-mediated PDI as compared to ZnF2POH and F2POH can be attributed to more pronounced ROS generation by palladium derivative via both types of photochemical mechanisms (high yields of singlet oxygen generation as well as oxygen-centered radicals). Additionally, PDI proved effective in eliminating bacteria within S. aureus-infected human keratinocytes, inhibiting infection progression while preserving the viability and integrity of infected HaCaT cells. These findings underscore the potential of metalloporphyrins, particularly the Pd(II)-porphyrin complex, as promising photosensitizers for PDI in various bacterial infections, warranting further investigation in advanced infection models.

In Vitro Photoinactivation of Fusarium oxysporum Conidia with Light-Activated Ammonium Phthalocyanines

Antimicrobial photodynamic therapy (aPDT) has been explored as an innovative therapeutic approach because it can be used to inactivate a variety of microbial forms (vegetative forms and spores) without causing significant damage to host tissues, and without the development of resistance to the photosensitization process. This study assesses the photodynamic antifungal/sporicidal activity of tetra- and octasubstituted phthalocyanine (Pc) dyes with ammonium groups. Tetra- and octasubstituted zinc(II) phthalocyanines (1 and 2) were prepared and tested as photosensitizers (PSs) on Fusarium oxysporum conidia. Photoinactivation (PDI) tests were conducted with photosensitizer (PS) concentrations of 20, 40, and 60 µM under white-light exposure at an irradiance of 135 mW·cm^-2, applied during 30 and 60 min (light doses of 243 and 486 J·cm^-2). High PDI efficiency corresponding to the inactivation process until the detection limit was observed for both PSs. The tetrasubstituted PS was the most effective, requiring the lowest concentration and the shortest irradiation time for the complete inactivation of conidia (40 µM, 30 min, 243 J·cm^-2). Complete inactivation was also achieved with PS 2, but a longer irradiation time and a higher concentration (60 µM, 60 min, 486 J·cm^-2) were necessary. Because of the low concentrations and moderate energy doses required to inactivate resistant biological forms such as fungal conidia, these phthalocyanines can be considered potent antifungal photodynamic drugs.

Anti-Viral Photodynamic Inactivation of T4-like Bacteriophage as a Mammalian Virus Model in Blood

The laboratorial available methods applied in plasma disinfection can induce damage in other blood components. Antimicrobial photodynamic therapy (aPDT) represents a promising approach and is approved for plasma and platelet disinfection using non-porphyrinic photosensitizers (PSs), such as methylene blue (MB). In this study, the photodynamic action of three cationic porphyrins (Tri-Py(+)-Me, Tetra-Py(+)-Me and Tetra-S-Py(+)-Me) towards viruses was evaluated under white light irradiation at an irradiance of 25 and 150 mW·cm^−2, and the results were compared with the efficacy of the approved MB. None of the PSs caused hemolysis at the isotonic conditions, using a T4-like phage as a model of mammalian viruses. All porphyrins were more effective than MB in the photoinactivation of the T4-like phage in plasma. Moreover, the most efficient PS promoted a moderate inactivation rate of the T4-like phage in whole blood. Nevertheless, these porphyrins, such as MB, can be considered promising and safe PSs to photoinactivate viruses in blood plasma.

Photodynamic inactivation of pathogenic Gram-negative and Gram-positive bacteria mediated by Si(IV) phthalocyanines bearing axial ammonium units

The photodynamic inactivation (PDI) of microorganisms has gained interest as an efficient option for conventional antibiotic treatments. Recently, Si(IV) phthalocyanines (SiPcs) have been highlighted as promising photosensitizers (PSs) to the PDI of microorganisms due to their remarkable absorption and emission features. To increase the potential of cationic SiPcs as PS drugs, one novel (1a) and two previously described (2a and 3a) axially substituted PSs with di-, tetra-, and hexa-ammonium units, respectively, were synthesized and characterized. Their PDI effect was evaluated for the first time against Escherichia coli and Staphylococcus aureus, a Gram-negative and a Gram-positive bacterium, respectively. The photodynamic treatments were conducted with PS concentrations of 3.0 and 6.0 μM under 60 min of white light irradiation (150 mW.cm^-2). The biological results show high photodynamic efficiency for di- and tetra-cationic PSs 1a and 2a (6.0 μM), reducing the E. coli viability in 5.2 and 3.9 log, respectively (after 15 min of dark incubation before irradiation). For PS 3a, a similar bacterial reduction (3.6 log) was achieved but only with an extended dark incubation period (30 min). Under the same experimental conditions, the photodynamic effect of cationic PSs 1a-3a on S. aureus was even more promising, with abundance reductions of ca. 8.0 log after 45-60 min of PDI treatment. These results reveal the high PDI efficiency of PSs bearing ammonium groups and suggest their promising application as a broad-spectrum antimicrobial to control infections caused by Gram-negative and Gram-positive bacteria.

Thermoresponsive Liposomes for Photo-Triggered Release of Hypericin Cyclodextrin Inclusion Complex for Efficient Antimicrobial Photodynamic Therapy

Antimicrobial strategies with high efficacy against bacterial infections are urgently needed. The development of effective therapies to control bacterial infections is still a challenge. Herein, near-infrared (NIR)-activated thermosensitive liposomes (TSL) were loaded with the NIR-dye 1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide (DiR) and the water-soluble hypericin (Hyp) β-cyclodextrin inclusion complex (Hyp-βCD). DiR and Hyp-βCD loaded thermosensitive liposomes (DHβCD-TSL) are functionalized for photothermal triggered release and synergistic photodynamic therapy to eliminate the gram-positive Staphylococcus saprophyticus. The dually active liposomes allow the production of heat and singlet oxygen species with the help of DiR and Hyp, respectively. The elevated temperature, generated by the NIR irradiation, irreversibly damages the bacterial membrane, increases the permeation, and melts the liposomes via a phase-transition mechanism, which allows the release of the Hyp-βCD complex. The photodynamic effect of Hyp-βCD eradicates the bacterial cells owing to its toxic oxygen species production. DHβCD-TSL measured the size of 130 nm with an adequate encapsulation efficiency of 81.3% of Hyp-βCD. They exhibited a phase transition temperature of 42.3 °C, while they remained stable at 37 °C, and 44% of Hyp-βCD was released after NIR irradiation (T > 47 °C). The bacterial viability dropped significantly after the synergistic treatment (>4 log₁₀), indicating that the NIR-activated TSL have immense therapeutic potential to enhance the antibacterial efficacy. The liposomes showed good biocompatibility, which was confirmed by the cellular viability of mouse fibroblasts (L929).

The Antimicrobial Photoinactivation Effect on Escherichia coli through the Action of Inverted Cationic Porphyrin-Cyclodextrin Conjugates

Photodynamic action has been used for diverse biomedical applications, such as treating a broad range of bacterial infections. Based on the combination of light, dioxygen, and photosensitizer (PS), the photodynamic inactivation (PDI) approach led to the formation of reactive oxygen species (ROS) and represented a non-invasive, non-toxic, repeatable procedure for pathogen photoinactivation. To this end, different tetrapyrrolic macrocycles, such as porphyrin (Por) dyes, have been used as PSs for PDI against microorganisms, mainly bacteria. Still, there is significant room for improvement, especially new PS molecules. Herein, unsymmetrical new pyridinone (3−5) and thiopyridyl Pors (7) were prepared with α-, β-, or γ-cyclodextrin (CD) units, following their quaternization to perform the corresponding free-base Pors (3a−5a and 7a), and were compared with the already-known Pors 6a and 8a, both bearing thiopyridinium and CD units. These water-soluble porphyrins were evaluated as PSs, and their photophysical and photochemical properties and photodynamic effects on E. coli were assessed. The presence of one CD unit and three positive charges on the Por structure (3a−5a and 7a) enhanced their aqueous solubility. The photoactivity of the cationic Pors 3a−5a and 6a−8a ensured their potential against the Gram-negative bacterium E. coli. Within each series of methoxypyridinium vs thiopyridinium dyes, the best PDI efficiency was achieved for 5a with a bacterial viability reduction of 3.5 log10 (50 mW cm−2, 60 min of light irradiation) and for 8a with a total bacterial viability reduction (>8 log10, 25 mW cm−2, 30 min of light irradiation). Here, the presence of the methoxypyridinium units is less effective against E. coli when compared with the thiopyridinium moieties. This study allows for the conclusion that the peripheral charge position, quaternized substituent type/CD unit, and affinity to the outer bacterial structures play an important role in the photoinactivation efficiency of E. coli, evidencing that these features should be further addressed in the pursuit for optimised PS for the antimicrobial PDI of pathogenic microorganisms.

Parietin Cyclodextrin-Inclusion Complex as an Effective Formulation for Bacterial Photoinactivation

Multidrug resistance in pathogenic bacteria has become a significant public health concern. As an alternative therapeutic option, antimicrobial photodynamic therapy (aPDT) can successfully eradicate antibiotic-resistant bacteria with a lower probability of developing resistance or systemic toxicity commonly associated with the standard antibiotic treatment. Parietin (PTN), also termed physcion, a natural anthraquinone, is a promising photosensitizer somewhat underrepresented in aPDT because of its poor water solubility and potential to aggregate in the biological environment. This study investigated whether the complexation of PTN with (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) could increase its solubility, enhance its photophysical properties, and improve its phototoxicity against bacteria. At first, the solubilization behavior and complexation constant of the PTN/HP-β-CD inclusion complexes were evaluated by the phase solubility method. Then, the formation and physicochemical properties of PTN/HP-β-CD complexes were analyzed and confirmed in various ways. At the same time, the photodynamic activity was assessed by the uric acid method. The blue light-mediated photodegradation of PTN in its free and complexed forms were compared. Complexation of PTN increased the aqueous solubility 28-fold and the photostability compared to free PTN. PTN/HP-β-CD complexes reduce the bacterial viability of Staphylococcus saprophyticus and Escherichia coli by > 4.8 log and > 1.0 log after irradiation, respectively. Overall, the low solubility, aggregation potential, and photoinstability of PTN were overcome by its complexation in HP-β-CD, potentially opening up new opportunities for treating infections caused by multidrug-resistant bacteria.

Applications of Fluorous Porphyrinoids: An Update†

Porphyrins and related macrocycles have been studied broadly for their applications in medicine and materials because of their tunable physicochemical, optoelectronic and magnetic properties. In this review article, we focused on the applications of fluorinated porphyrinoids and their supramolecular systems and summarized the reports published on these chromophores in the past 5-6 years. The commercially available fluorinated porphyrinoids: meso-perfluorophenylporphyrin (TPPF₂₀ ) perfluorophthalocyanine (PcF₁₆ ) and meso-perfluorophenylcorrole (CorF₁₅ ) have increased photo and oxidative stability due to the presence of fluoro groups. Because of their tunable properties and robustness toward oxidative damage these porphyrinoid-based chromophores continue to gain attention of researchers developing advanced functional materials for applications such as sensors, photonic devices, component for solar cells, biomedical imaging, theranostics and catalysts.

Design of Photosensitizing Agents for Targeted Antimicrobial Photodynamic Therapy

Photodynamic inactivation of microorganisms has gained substantial attention due to its unique mode of action, in which pathogens are unable to generate resistance, and due to the fact that it can be applied in a minimally invasive manner. In photodynamic therapy (PDT), a non-toxic photosensitizer (PS) is activated by a specific wavelength of light and generates highly cytotoxic reactive oxygen species (ROS) such as superoxide (O2-, type-I mechanism) or singlet oxygen (1O2*, type-II mechanism). Although it offers many advantages over conventional treatment methods, ROS-mediated microbial killing is often faced with the issues of accessibility, poor selectivity and off-target damage. Thus, several strategies have been employed to develop target-specific antimicrobial PDT (aPDT). This includes conjugation of known PS building-blocks to either non-specific cationic moieties or target-specific antibiotics and antimicrobial peptides, or combining them with targeting nanomaterials. In this review, we summarise these general strategies and related challenges, and highlight recent developments in targeted aPDT.