Strengthening collaborations at the Biology-Physics interface: trends in antimicrobial photodynamic therapy

The unbridled use of antimicrobial drugs over the last decades contributed to the global dissemination of drug-resistant pathogens and increasing rates of life-threatening infections for which limited therapeutic options are available. Currently, the search for safe, fast, and effective therapeutic strategies to combat infectious diseases is a worldwide demand. Antimicrobial photodynamic therapy (APDT) rises as a promising therapeutic approach against a wide range of pathogenic microorganisms. APDT combines light, a photosensitizing drug (PS), and oxygen to kill microorganisms by oxidative stress. Since the APDT field involves branches of biology and physics, the strengthening of interdisciplinary collaborations under the aegis of biophysics is welcome. Given this scenario, Brazil is one of the global leaders in the production of APDT science. In this review, we provide detailed reports of APDT studies published by the Laboratory of Optical Therapy (IPEN-CNEN), Group of Biomedical Nanotechnology (UFPE), and collaborators over the last 10 years. We present an integrated perspective of APDT from basic research to clinical practice and highlight its promising use, encouraging its adoption as an effective and safe technology to tackle important pathogens. We cover the use of methylene blue (MB) or Zn(II) porphyrins as PSs to kill bacteria, fungi, parasites, and pathogenic algae in laboratory assays. We describe the impact of MB-APDT in Dentistry and Veterinary Medicine to treat different infectious diseases. We also point out future directions combining APDT and nanotechnology. We hope this review motivates further APDT studies providing intuitive, vivid, and insightful information for the readers.

New Insights in Phenothiazinium-Mediated Photodynamic Inactivation of Candida Auris

In recent years, Candida auris has emerged as a hazardous hospital-acquired pathogen. Its resistance to antifungal treatments makes it challenging, requiring new approaches to manage it effectively. Herein, we aimed to assess the impact of photodynamic inactivation mediated by methylene blue (MB-PDI) or 1,9-dimethyl MB (DMMB-PDI) combined with a red LED against C. auris. To evaluate the photoinactivation of yeasts, we quantified colony-forming units and monitored ROS production. To gain some insights into the differences between MB and DMMB, we assessed lipid peroxidation (LPO) and mitochondrial membrane potential (ΔΨm). After, we verified the effectiveness of DMMB against biofilms by measuring metabolic activity and biomass, and the structures were analyzed through scanning electron microscopy and optical coherence tomography. We also evaluated the cytotoxicity in mammalian cells. DMMB-PDI successfully eradicated C. auris yeasts at 3 μM regardless of the light dose. In contrast, MB (100 μM) killed cells only when exposed to the highest dose of light. DMMB-PDI promoted higher ROS, LPO and ΔΨm levels than those of MB. Furthermore, DMMB-PDI was able to inhibit biofilm formation and destroy mature biofilms, with no observed toxicity in fibroblasts. We conclude that DMMB-PDI holds great potential to combat the global threat posed by C. auris.

A Novel Strategy Based on Zn(II) Porphyrins and Silver Nanoparticles to Photoinactivate Candida albicans

Background

Photodynamic inactivation (PDI) is an attractive alternative to treat Candida albicans infections, especially considering the spread of resistant strains. The combination of the photophysical advantages of Zn(II) porphyrins (ZnPs) and the plasmonic effect of silver nanoparticles (AgNPs) has the potential to further improve PDI. Here, we propose the novel association of polyvinylpyrrolidone (PVP) coated AgNPs with the cationic ZnPs Zn(II) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin or Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin to photoinactivate C. albicans.

Methods

AgNPs stabilized with PVP were chosen to allow for (i) overlap between the NP extinction and absorption spectra of ZnPs and (ii) favor AgNPs-ZnPs interaction; prerequisites for exploring the plasmonic effect. Optical and zeta potential (ζ) characterizations were performed, and reactive oxygen species (ROS) generation was also evaluated. Yeasts were incubated with individual ZnPs or their respective AgNPs-ZnPs systems, at various ZnP concentrations and two proportions of AgNPs, then irradiated with a blue LED. Interactions between yeasts and the systems (ZnP alone or AgNPs-ZnPs) were evaluated by fluorescence microscopy.

Results

Subtle spectroscopic changes were observed for ZnPs after association with AgNPs, and the ζ analyses confirmed AgNPs-ZnPs interaction. PDI using ZnP-hexyl (0.8 µM) and ZnP-ethyl (5.0 µM) promoted a 3 and 2 log₁₀ reduction of yeasts, respectively. On the other hand, AgNPs-ZnP-hexyl (0.2 µM) and AgNPs-ZnP-ethyl (0.6 µM) systems led to complete fungal eradication under the same PDI parameters and lower porphyrin concentrations. Increased ROS levels and enhanced interaction of yeasts with AgNPs-ZnPs were observed, when compared with ZnPs alone.

Conclusion

We applied a facile synthesis of AgNPs which boosted ZnP efficiency. We hypothesize that the plasmonic effect combined with the greater interaction between cells and AgNPs-ZnPs systems resulted in an efficient and improved fungal inactivation. This study provides insight into the application of AgNPs in PDI and helps diversify our antifungal arsenal, encouraging further developments toward inactivation of resistant Candida spp.

Antileishmanial activity of tetra-cationic porphyrins with peripheral Pt(II) and Pd(II) complexes mediated by photodynamic therapy approaches

Leishmaniasis is a seriously neglected disease that impacts more than one billion people in endemic areas of the globe. Several drawbacks are associated with the currently existing drugs for the treatment as low effectiveness, toxicity, and the emergence of resistant strains that demonstrates the importance of looking for novel therapeutic alternatives. Photodynamic therapy (PDT) is a promising novel alternative for cutaneous leishmaniasis treatment because its topical application avoids potential side effects generally associated with oral/parenteral application. A light-sensitive compound known as photosensitizer (PS) interacts with light and molecular oxygen to generate reactive oxygen species (ROS), which promote cell death by oxidative stress through PDT approaches. Here, for the first time, we demonstrate the antileishmanial effect of tetra-cationic porphyrins with peripheral Pt(II)- and Pd(II)-polypyridyl complexes using PDT. The isomeric tetra-cationic porphyrins in the meta positions, 3-PtTPyP, and 3-PdTPyP, exhibited the highest antiparasitic activity against promastigote (IC_50-pro = 41.8 nM and 46.1 nM, respectively) and intracellular amastigote forms (IC_50-ama = 27.6 nM and 38.8 nM, respectively) of L. amazonensis under white light irradiation (72 J cm^-2) with high selectivity (SI > 50) for both forms of parasites regarding mammalian cells. In addition, these PS induced the cell death of parasites principally by a necrotic process in the presence of white light by mitochondrial and acidic compartments accumulation. This study showed that porphyrins 3-PtTPyP and 3-PdTPyP displayed a promising antileishmanial-PDT activity with potential application for cutaneous leishmaniasis treatment.

In vitro effects of lapachol and β-lapachone against Leishmania amazonensis

Leishmaniasis is a neglected disease that affects millions of people worldwide, and special attention should be given to treatment because the available drugs have limitations, which can lead to low therapeutic adherence and parasitic resistance. This study evaluated the activity of the bioactive naphthoquinones, lapachol and β-lapachone, against Leishmania amazonensis. The cell alterations were evaluated in vitro on promastigote and amastigote forms. The lethal dose (LD50) at 24, 48, and 72 h on the promastigote's forms using lapachol was 75.60, 72.82, and 58.85 μg/mL and for β-lapachone was 0.65, 1.24, and 0.71 μg/mL, respectively. The naphthoquinones significantly inhibited the survival rate of L. amazonensis amastigotes at 83.11, 57.59, and 34.95% for lapachol (82.28, 41.14, and 20.57 µg/mL), and 78.49, 83.25, and 80.22% for β-lapachone (3.26, 1.63, and 0.815 µg/mL). The compounds on the promastigote's forms led to the loss of mitochondrial membrane potential, induced changes in the integrity of the membrane, caused damage to cells suggestive of the apoptotic process, and showed inhibition of tumor necrosis factor (TNF)-α and interleukin (IL)-6 production. The results showed that these naphthoquinones are promising candidates for research on new drugs with anti-Leishmania activity derived from natural products.

Photoinactivation of Yeast and Biofilm Communities of Candida albicans Mediated by ZnTnHex-2-PyP4+ Porphyrin

Candida albicans is the main cause of superficial candidiasis. While the antifungals available are defied by biofilm formation and resistance emergence, antimicrobial photodynamic inactivation (aPDI) arises as an alternative antifungal therapy. The tetracationic metalloporphyrin Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (ZnTnHex-2-PyP⁴⁺) has high photoefficiency and improved cellular interactions. We investigated the ZnTnHex-2-PyP⁴⁺ as a photosensitizer (PS) to photoinactivate yeasts and biofilms of C. albicans strains (ATCC 10231 and ATCC 90028) using a blue light-emitting diode. The photoinactivation of yeasts was evaluated by quantifying the colony forming units. The aPDI of ATCC 90028 biofilms was assessed by the MTT assay, propidium iodide (PI) labeling, and scanning electron microscopy. Mammalian cytotoxicity was investigated in Vero cells using MTT assay. The aPDI (4.3 J/cm²) promoted eradication of yeasts at 0.8 and 1.5 µM of PS for ATCC 10231 and ATCC 90028, respectively. At 0.8 µM and same light dose, aPDI-treated biofilms showed intense PI labeling, about 89% decrease in the cell viability, and structural alterations with reduced hyphae. No considerable toxicity was observed in mammalian cells. Our results introduce the ZnTnHex-2-PyP⁴⁺ as a promising PS to photoinactivate both yeasts and biofilms of C. albicans, stimulating studies with other Candida species and resistant isolates.

Functionalized 1,2,3-triazolium salts as potential agents against visceral leishmaniasis

Visceral leishmaniasis (VL) is the most severe clinical form of leishmaniasis, being fatal if untreated. In search of a more effective treatment for VL, one of the main strategies is the development and screening of new antileishmanial compounds. Here, we reported the synthesis of seven new acetyl functionalized 1,2,3-triazolium salts, together with four 1,2,3-triazole precursors, and investigated their effect against different strains of L. infantum from dogs and humans. The 1,2,3-triazolium salts exhibited better activity than the 1,2,3-triazole derivatives with IC₅₀ range from 0.12 to 8.66 μM and, among them, compound 5 showed significant activity against promastigotes (IC₅₀ from 4.55 to 5.28 μM) and intracellular amastigotes (IC₅₀ from 5.36 to 7.92 μM), with the best selective index (SI ~ 6-9) and reduced toxicity. Our findings, using biochemical and ultrastructural approaches, demonstrated that compound 5 targets the mitochondrion of L. infantum promastigotes, leading to the formation of reactive oxygen species (ROS), increase of the mitochondrial membrane potential, and mitochondrial alteration. Moreover, quantitative transmission electron microscopy (TEM) revealed that compound 5 induces the reduction of promastigote size and cytoplasmic vacuolization. Interestingly, the effect of compound 5 was not associated with apoptosis or necrosis of the parasites but, instead, seems to be mediated through a pathway involving autophagy, with a clear detection of autophagic vacuoles in the cytoplasm by using both a fluorescent marker and TEM. As for the in vivo studies, compound 5 showed activity in a mouse model of VL at 20 mg/kg, reducing the parasite load in both spleen and liver (59.80% and 26.88%, respectively). Finally, this compound did not induce hepatoxicity or nephrotoxicity and was able to normalize the altered biochemical parameters in the infected mice. Thus, our findings support the use of 1,2,3-triazolium salts as potential agents against visceral leishmaniasis.

Photophysical characterization and in vitro anti-leishmanial effect of 5,10,15,20-tetrakis(4-fluorophenyl) porphyrin and the metal (Zn(II), Sn(IV), Mn(III) and V(IV)) derivatives

In this report 5 compounds were synthesized and structural and their photophysical characterization was performed (Φ_Δ and Φ_f). Furthermore, in this in vitro study, their biological activity against Leishmania panamensis was evaluated. The photophysical behavior of these compounds was measured and high Φ_Δ and low Φ_f was observed. Besides, DFT quantum calculations on the electronic structures were performed. Finally, the biological activity was determined by means of the compounds capacity to inhibit the viability of parasites using the MTT assay. The inclusion of the metal ions substantially modified the photophysical and biological properties in comparison with the free metal porphyrin (1). In fact, Zn²⁺ porphyrin derivative (2) showed a marked decrease of Φ_f and increase of Φ_Δ. In this sense, using TDDFT approaches, a luminescent process for Sn⁴⁺ derivative (3) was described, where emissive states involve the ML-LCT transition. So, this led to a decrease in the singlet oxygen production (0.82-0.67). Biological results showed that all compounds inhibit the viability of L. panamensis with high efficiency; the decrease in the viability was greater as the concentration of exposure increased. Finally, under light irradiation the IC₅₀ of L. panamensis against the Zn(II)-porphyrin (2) and V(IV)-porphyrin (5) was lower than the IC₅₀ of the Glucantime control (IC₅₀ = 2.2 and 6.95 μM Vs IC₅₀ = 12.7 μM, respectively). We showed that the use of porphyrin and metalloporphyrin-type photosensitizers with exceptional photophysical properties can be successful in photodynamic therapy (PDT) against L. panamensis, being the diamagnetic ion Zn²⁺ a candidate for the preparation of metalloporphyrins with high singlet oxygen production.

Thermal Stability Kinetics and Shelf Life Estimation of the Redox-Active Therapeutic and Mimic of Superoxide Dismutase Enzyme, Mn(III) meso-Tetrakis(N-ethylpyridinium-2-yl)porphyrin Chloride (MnTE-2-PyPCl5, BMX-010)

Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin chloride (MnTE-2-PyPCl5, BMX-010, and AEOL10113) is among the most studied superoxide dismutase (SOD) mimics and redox-active therapeutics, being currently tested as a drug candidate in a phase II clinical trial on atopic dermatitis and itch. The thermal stability of active pharmaceutical ingredients (API) is useful for estimating the expiration date and shelf life of pharmaceutical products under various storage and handling conditions. The thermal decomposition and kinetic parameters of MnTE-2-PyPCl5 were determined by thermogravimetry (TG) under nonisothermal and isothermal conditions. The first thermal degradation pathway affecting Mn-porphyrin structural integrity and, thus, activity and bioavailability was associated with loss of ethyl chloride via N-dealkylation reaction. The thermal stability kinetics of the N-dealkylation process leading to MnTE-2-PyPCl5 decomposition was investigated by using isoconversional models and artificial neural network. The new multilayer perceptron (MLP) artificial neural network approach allowed the simultaneous study of ten solid-state kinetic models and showed that MnTE-2-PyPCl5 degradation is better explained by a combination of various mechanisms, with major contributions from the contraction models R1 and R2. The calculated activation energy values from isothermal and nonisothermal data were about 90 kJ mol-1 on average and agreed with one another. According to the R1 modelling of the isothermal decomposition data, the estimated shelf life value for 10% decomposition (t 90%) of MnTE-2-PyPCl5 at 25°C was approximately 17 years, which is consistent with the high solid-state stability of the compound. These results represent the first study on the solid-state decomposition kinetics of Mn(III) 2-N-alkylpyridylporphyrins, contributing to the development of this class of redox-active therapeutics and SOD mimics and providing supporting data to protocols on purification, handling, storage, formulation, expiration date, and general use of these compounds.

Photophysical study and in vitro approach against Leishmania panamensis of dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV)

Background: Photodynamic therapy activity against different biological systems has been reported for porphyrins. Porphyrin modifications through peripheral groups and/or by metal insertion inside the ring are main alternatives for the improvement of its photo-physical properties. In this study, we synthesized and characterized 5,10,15,20-tetrakis(4-bromophenyl)porphyrin and the dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV).

Methods: Metal-free porphyrin was synthesized using the Alder method, while the Sn(IV)-porphyrin complex was prepared by combining metal-free porphyrin with stannous chloride in DMF; the reaction yields were 47% and 64% respectively. Metal-free porphyrin was characterized by UV-Vis, FT-IR, ESI-mass spectrometry and ¹³C-NMR. Additionally, the Sn(IV) -porphyrin complex was characterized using UV-Vis and FT-IR. Cyclic voltammetry tests in four different solvents. The fluorescence quantum yield (Φ _f) was measured using fluorescein as a standard, the singlet oxygen quantum yield (Φ _D) was estimated using the standard 5,10,15,20-(tetraphenyl)porphyrin (H2TPP) and the quencher of singlet oxygen 1,3-diphenylisobenzofuran (DPBF).

Results: UV-Vis assay showed typical Q and Soret bands for porphyrin and its metallo-porphyrin complex. Compounds showed photoluminescence at the visible range of electromagnetic spectrum. The inclusion of the metal in the porphyrin core changed the Φ _f from 0.15 to 0.05 and the Φ _D increased from 0.55 to 0.59. Finally, the effect of the compounds on the viability of L. panamensis was evaluated by means of the MTT test. The results showed that both compounds decreased the viability of the parasite; this inhibitory activity was greater under light irradiation; the porphyrin compound had IC ₅₀ of 16.5 μM and the Sn(IV)-porphyrin complex had IC ₅₀ of 19.2 μM.

Conclusion: The compounds were synthesized efficiently, their characterization was carried out by different spectroscopy techniques and their own signals were evidenced for both structures, both compounds decreased the cell viability of L. panamensis.

Progress in the photodynamic therapy treatment of Leishmaniasis

Leishmaniasis is a serious and endemic infectious disease that has been reported in more than 90 countries and territories. The classical treatment presents a series of problems ranging from difficulty in administration, development of resistance, and a series of side effects. Photodynamic therapy (PDT) has already shown great potential for use as a treatment for leishmaniasis that is effective and non-invasive, with very minor side effects. PDT can also be inexpensive and easy to administer. In this review, we will report the most recent developments in the field, starting with the chemical diversity of photosensitizers, highlighting important mechanistic aspects, and noting information that may assist in designing and developing new and promising photosensitizer molecules.

Photodynamic therapy for leishmaniasis: Recent advances and future trends

Leishmaniasis has infected more than 12 million people worldwide. This neglected tropical disease, causing 20,000-30,000 deaths per year, is a global health problem. The emergence of resistant parasites and serious side effects of conventional therapies has led to the search for less toxic and non-invasive alternative treatments. Photodynamic therapy is a promising therapeutic strategy to produce reactive oxygen species for the treatment of leishmaniasis. In this regard, natural and synthetic photosensitizers such as curcumin, hypericin, 5-aminolevulinic acid, phthalocyanines, phenothiazines, porphyrins, chlorins and nanoparticles have been applied. In this review, the recent advances on using photodynamic therapy for treating Leishmania species have been reviewed.

CELLULAR AND METABOLIC CHANGES AFTER PHOTODYNAMIC THERAPY IN LEISHMANIA PROMASTIGOTES

Leishmaniasis is a zoonotic disease, regarded by WHO as a public health problem that has presented a significant increase in the recent years. Conventional treatment is toxic and leads to serious side effects. Photodynamic therapy has been studied as a treatment to cutaneous leishmaniasis. This study aimed to evaluate the cell viability, morphological changes, type of cell death, production of reactive oxygen species, and changes in the mitochondrial membrane and DNA fragmentation in Leishmania braziliensis and Leishmania major promastigotes. Confocal microscopy was used to quantify the fluorescence emitted by JC-1, Annexin V, and propidium iodide reagents. The trypan blue exclusion test was used to evaluate the viability of the cells, the mitochondrial activity was verified with MTT, and the morphological changes were analyzed for SEM and DNA damage using the comet assay. PDT using curcumin at 500, 125, and 31,25 μg/mL decreased the viability of the parasites and induced changes in the mitochondrial membrane potential. The production of reactive oxygen species was dose-dependent and was observed only in the groups submitted to PDT. DNA damage was also observed in the parasite cells. The morphology of the cells was affected mainly at the highest curcumin concentration, resulting in rounded cells with a shortened flagellum. When the type of cell death was analyzed, the prevalence of apoptosis was noted. The results support the use of curcumin as photosensitizer in PDT against Leishmania promastigotes in the treatment for cutaneous leishmaniasis.

Evaluation of the Photodynamic Therapy with Curcumin on L. braziliensis and L. major Amastigotes

Cutaneous leishmaniasis (CL) is a neglected disease prevalent in tropical countries with the ability to cause skin lesions. Photodynamic therapy (PDT) represents a specific and topical option for the treatment of these lesions. This study evaluated the response of macrophages infected with L. braziliensis and L. major to PDT with curcumin. Curcumin concentrations were evaluated in serial dilutions from 500.0 to 7.8 µg/mL using LED (λ = 450 ± 5 nm), with a light dose of 10 J/cm². The Trypan blue viability test, ultrastructural analysis by scanning electron microscopy (SEM), mitochondrial polarity by Rhodamine 123 (Rho 123), curcumin internalization by confocal microscopy, and counting of the recovered parasites after the PDT treatment were performed. The lowest concentrations of curcumin (15.6 and 7.8 µg/mL) presented photodynamic inactivation. Cell destruction and internalization of curcumin in both macrophages and intracellular parasites were observed in microscopy techniques. In addition, an increase in mitochondrial membrane polarity and a decrease in the number of parasites recovered was observed in the PDT groups. This study indicates that PDT with curcumin has the potential to inactivate infected macrophages and might act as a basis for future in vivo studies using the parameters herein discussed.

Silver nanoprisms as plasmonic enhancers applied in the photodynamic inactivation of Staphylococcus aureus isolated from bubaline mastitis

Mastitis is a bacterial infection that affects all lactating mammals, and in dairy cattle, it leads to a reduction in their milk production and, in worse cases, it may lead to animal death. One viable therapeutic modality for overcoming bacterial resistance can be photodynamic inactivation (PDI), a therapeutic modality for bacterial infection treatment. One of the main factors that can lead to an efficient PDI process is the association of metallic nanoparticles in the close vicinity of photosensitizers, which has shown promising results due to localized surface plasmon resonance phenomena. In this work, methylene blue (MB) molecules were associated with Ag prismatic nanoplatelets (AgNPrs) to use as PDI photosensitizer against Staphylococcus aureus isolated from bubaline mastitis. The optical plasmonic activity of AgNPrs was tuned to the MB absorption region (600-700 nm) by inducing their growth into prismatic shapes by a seed-mediated procedure, using poly (sodium 4-styrene sulfonate) as the surfactant. A simulation on the plasmonic properties of the nanoprisms, applying particle size within the dimensions determined by TEM image analysis (d = 32 ± 6 nm), showed a 30 % increase of the incident field on the prismatic tips. Photodynamic results showed that the electrostatic AgNPr-MB conjugates promoted enhancement (ca. 15 %) of the reactive oxygen species production. Besides, PDI mediated by AgNPrs-MB led to the complete inactivation of the mastitis S. aureus strain after 6 min inactivation, in contrast to PDI mediated by MB, which reduced less than a 0.5 bacterial log. Thus, the results show this plasmonic enhanced photodynamic tool's potential to be applied in the inactivation of multi-resistant bacterial strains.

Efficient photodynamic inactivation of Leishmania parasites mediated by lipophilic water-soluble Zn(II) porphyrin ZnTnHex-2-PyP4

BACKGROUND

Photodynamic inactivation (PDI) is emerging as a promising alternative for cutaneous leishmaniasis (CL). The chemotherapy currently used presents adverse effects and cases of drug resistance have been reported. ZnTnHex-2-PyP⁴⁺ is a porphyrin with a high potential as a photosensitizer (PS) for PDI, due to its photophysical properties, structural stability, and cationic/amphiphilic character that can enhance interaction with cells. This study aimed to investigate the photodynamic effects mediated by ZnTnHex-2-PyP⁴⁺ on Leishmania parasites.

METHODS

ZnTnHex-2-PyP⁴⁺ stability was evaluated using accelerated solvolysis conditions. The photodynamic action on promastigotes was assessed by (i) viability assays, (ii) mitochondrial membrane potential evaluation, and (iii) morphological analysis. The PS-promastigote interaction was studied. PDI on amastigotes and the cytotoxicity on macrophages were also analyzed.

RESULTS

ZnTnHex-2-PyP⁴⁺, under submicromolar concentration, led to immediate inactivation of more than 95% of promastigotes. PDI promoted intense mitochondrial depolarization, loss of the fusiform shape, and plasma membrane wrinkling in promastigotes. Fluorescence microscopy revealed a punctate PS labeling in the parasite cytoplasm. PDI also led to reductions of ca. 64% in the number of amastigotes/macrophage and 70% in the infection index after a single treatment session. No noteworthy toxicity was observed on mammalian cells.

CONCLUSIONS

ZnTnHex-2-PyP⁴⁺ is stable against demetallation and more efficient as PS than the ethyl analogue ZnTE-2-PyP⁴⁺, indicating readiness for evaluation in in vivo studies as an alternative approach to CL.

GENERAL SIGNIFICANCE

This report highlighted promising photodynamic effects mediated by ZnTnHex-2-PyP⁴⁺ on Leishmania parasites, opening up perspectives for applications in CL pre-clinical assays and PDI of other microorganisms.

Photodynamic effect of palladium porphyrin derived from cashew nut shell liquid against promastigote forms of Leishmania braziliensis

Cutaneous leishmaniasis (CL) is a neglected tropical disease (NTD), endemic mainly in low-income countries that lack adequate basic health care. The emergence of resistant parasites to pentavalent antimonials has led to the search for new treatments for CL. Photodynamic therapy (PDT) is a promising non-invasive and less toxic alternative for the treatment of CL. The present work describes the synthesis, characterization and photodynamic effect against CL of a new metalloporphyrin Pd (II) meso-tetra[4-(2-(3-n-pentadecylphenoxy)ethoxy]phenylporphyrin (PdP) derived from the cashew nut shell liquid (CNSL). The PdP complex presented a singlet oxygen quantum yield of 0.49, favoring a type II photochemical reaction. The results of the photodynamic experiment carried out with PdP on the promastigote forms of Leishmania braziliensis indicated a mortality percentage of 70 % of the cells when compared to the control after exposure to blue light (λ = 420 nm). Besides this, the metalloporphyrin PdP did not show considerable toxicity to macrophages, indicating the cell viability of the compound. Therefore, this metalloporphyrin derived from biomass represents an interesting alternative as a potential therapeutic drug for the treatment of CL through PDT, especially for patients with intolerance to the chemotherapeutic drugs currently available.

meso-Thiophenium Porphyrins and Their Zn(II) Complexes: A New Category of Cationic Photosensitizers

A new category of cationic meso-thiophenium porphyrins are introduced as possible alternatives to the popular meso-pyridinium porphyrins. Combinations of cationic porphyrins bearing meso-2-methylthiophenium and meso-4-hydroxyphenyl moieties T₂(OH)₂M (A₂B₂ type) and T(OH)₃M (AB₃ type) along with their zinc(II) complexes T₂(OH)₂MZn and T(OH)₃MZn, are reported. The increase in the number of thienyl groups attached to the meso-positions of the porphyrin derivatives (A₂B₂ frame) has been shown to impart longer fluorescence lifetimes and stronger photocytotoxicity toward A549 lung cancer cells, as evident with T₂(OH)₂M and its corresponding diamagnetic metal complex T₂(OH)₂MZn. The photoactivated T₂(OH)₂MZn imparts an early stage reactive oxygen species (ROS) upregulation and antioxidant depletion in A549 cells and contributes to the strongest oxidative stress-induced cell death mechanism in the series. The DFT calculations of the singlet-triplet energy gap (ΔE) of all the four hydrophilic thiophenium porphyrin derivatives establish the potential applicability of these cationic photosensitizers as PDT agents.

Porphyrin Derivative Nanoformulations for Therapy and Antiparasitic Agents

Porphyrins and analogous macrocycles exhibit interesting photochemical, catalytic, and luminescence properties demonstrating high potential in the treatment of several diseases. Among them can be highlighted the possibility of application in photodynamic therapy and antimicrobial/antiparasitic PDT, for example, of malaria parasite. However, the low efficiency generally associated with their low solubility in water and bioavailability have precluded biomedical applications. Nanotechnology can provide efficient strategies to enhance bioavailability and incorporate targeted delivery properties to conventional pharmaceuticals, enhancing the effectiveness and reducing the toxicity, thus improving the adhesion to the treatment. In this way, those limitations can be overcome by using two main strategies: (1) Incorporation of hydrophilic substituents into the macrocycle ring while controlling the interaction with biological systems and (2) by including them in nanocarriers and delivery nanosystems. This review will focus on antiparasitic drugs based on porphyrin derivatives developed according to these two strategies, considering their vast and increasing applications befitting the multiple roles of these compounds in nature.

In Vitro Anti-Leishmanial Effect of Metallic Meso-Substituted Porphyrin Derivatives against Leishmania braziliensis and Leishmania panamensis Promastigotes Properties

In this study, a family of porphyrins based on 5,10,15,20-Tetrakis(4-ethylphenyl)porphyrin (1, Ph) and six metallo-derivatives (Zn²⁺(2, Ph-Zn), Sn⁴⁺(3, Ph-Sn), Mn²⁺ (4, Ph-Mn), Ni²⁺ (5, Ph-Ni), Al³⁺ (6, Ph-Al), and V³⁺ (7, Ph-V)) were tested as photosensitizers for photodynamic therapy against Leishmania braziliensis and panamensis. The singlet oxygen quantum yield value (Φ_Δ) for (1–7) was measured using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen trapping agent and 5,10,15,20-(tetraphenyl)-porphyrin (H2TPP) as a reference standard; besides, parasite viability was estimated by the MTT assay. After metal insertion into the porphyrin core, the Φ_Δ increased from 0.76–0.90 and cell viability changed considerably. The Φ_Δ and metal type changed the cytotoxic activity. Finally, (2) showed both the highest Φ_Δ (0.90) and the best photodynamic activity against the parasites studied (IC₅₀ of 1.2 μM).

Activation of artemisinin and heme degradation in Leishmania tarentolae promastigotes: A possible link

Endoperoxides (EPs) appear to be promising drug candidates against protozoal diseases, including malaria and leishmaniasis. Previous studies have shown that these drugs need an intracellular activation to exert their pharmacological potential. The efficiency of these drugs is linked to the extensive iron demand of these intracellular protozoal parasites. An essential step of the activation mechanism of these drugs is the formation of radicals in Leishmania. Iron is a known trigger for intracellular radical formation. However, the activation of EPs by low molecular iron or by heme iron may strongly depend on the structure of the EPs themselves. In this study, we focused on the activation of artemisinin (Art) in Leishmania tarentolae promastigotes (LtP) in comparison to reference compounds. Viability assays in different media in the presence of different iron sources (hemin/fetal calf serum) showed that IC50 values of Art in LtP were modulated by assay conditions, but overall were within the low micromolar range. Low temperature electron paramagnetic resonance (EPR) spectroscopy of LtP showed that Art shifted the redox state of the labile iron pool less than the EP ascaridole questioning its role as a major activator of Art in LtP. Based on the high reactivity of Art with hemin in previous biomimetic experiments, we focused on putative heme-metabolizing enzymes in Leishmania, which were so far not well described. Inhibitors of mammalian heme oxygenase (HO; tin and chromium mesoporphyrin) acted antagonistically to Art in LtP and boosted its IC50 value for several magnitudes. By inductively coupled plasma methods (ICP-OES, ICP-MS) we showed that these inhibitors do not block iron (heme) accumulation, but are taken up and act within LtP. These inhibitors blocked the conversion of hemin to bilirubin in LtP homogenates, suggesting that an HO-like enzyme activity in LtP exists. NADPH-dependent degradation of Art and hemin was highest in the small granule and microsomal fractions of LtP. Photometric measurements in the model Art/hemin demonstrated that hemin requires reduction to heme and that subsequently an Art/heme complex (λmax 474 nm) is formed. EPR spin-trapping in the system Art/hemin revealed that NADPH, ascorbate and cysteine are suitable reductants and finally activate Art to acyl-carbon centered radicals. These findings suggest that heme is a major activator of Art in LtP either via HO-like enzyme activities and/or chemical interaction of heme with Art.

The in vitro Photoinactivation of Helicobacter pylori by a Novel LED-Based Device

The rise of antibiotic resistance is the main cause for the failure of conventional antibiotic therapy of Helicobacter pylori infection, which is often associated with severe gastric diseases, including gastric cancer. In the last years, alternative non-pharmacological approaches have been considered in the treatment of H. pylori infection. Among these, antimicrobial PhotoDynamic Therapy (aPDT), a light-based treatment able to photoinactivate a wide range of bacteria, viruses, fungal and protozoan parasites, could represent a promising therapeutic strategy. In the case of H. pylori, aPDT can exploit photoactive endogenous porphyrins, such as protoporphyrin IX and coproporphyrin I and III, to induce photokilling, without any other exogenous photosensitizers. With the aim of developing an ingestible LED-based robotic pill for minimally invasive intragastric treatment of H. pylori infection, it is crucial to determine the best illumination parameters to activate the endogenous photosensitizers. In this study the photokilling effect on H. pylori has been evaluated by using a novel LED-based device, designed for testing the appropriate LEDs for the pill and suitable to perform in vitro irradiation experiments. Exposure to visible light induced bacterial photokilling most effectively at 405 nm and 460 nm. Sub-lethal light dose at 405 nm caused morphological changes on bacterial surface indicating the cell wall as one of the main targets of photodamage. For the first time endogenous photosensitizing molecules other than porphyrins, such as flavins, have been suggested to be involved in the 460 nm H. pylori photoinactivation.

Exploiting knowledge on pharmacodynamics-pharmacokinetics for accelerated anti-leishmanial drug discovery/development

Introduction: Being on the top list of neglected tropical diseases, leishmaniasis has been marked for elimination by 2020. In the light of small armamentarium of drugs and their associated drawbacks, the understanding of pharmacodynamics and/or pharmacokinetics becomes a priority to achieve and sustain disease elimination. Areas covered: The authors have looked into pharmacological aspects of existing and emerging drugs for treatment of leishmaniasis. An in-depth understanding of pharmacodynamics and pharmacokinetics (PKPD) provides a rationale for drug designing and optimizing the treatment strategies. It forms a key to prevent drug resistance and avoid drug-associated adverse effects. The authors have compiled the researches on the PKPD of different anti-leishmanial formulations that have the potential for improved and/or effective disease intervention. Expert opinion: Understanding the pharmacological aspects of drugs forms the basis for the clinical application of novel drugs. Tailoring drug dosage and individualized treatment can avoid the adverse events and bridge gap between the in vitro models and their clinical application. An integrated approach, with pragmatic use of technological advances can improve phenotypic screening and physiochemical properties of novel drugs. Concomitantly, this can serve to improve clinical efficacies, reduce the incidence of relapse and accelerate the drug discovery/development process for leishmaniasis elimination.

Potential of Pluronics® P-123 and F-127 as nanocarriers of anti-Leishmania chemotherapy

Leishmaniasis is a neglected disease and drugs approved for its treatment often lead to abandonment, failure of therapy and even death. Photodynamic therapy (PDT) has been shown to be a promising, non-invasive and selective for a target region without requiring high-cost technology. Usually, it is employed a photosensitizing agent (PS) incorporated into nanoparticles (NP). Pluronics^® P-123 and F-127 micelles are very interesting aqueous NP promoting efficient and selective delivery and less adverse effects. This study aimed to detect the activity of Pluronics^® P-123 and F-127 themselves since there is a scarcity of data on these NP activities without drugs incorporation. This study evaluated, in vitro, the activity of Pluronics^® against promastigotes and amastigotes of Leishmania amazonensis and also their cytotoxicities. Additionally, the determination of the mitochondria membrane potential in promastigotes, internalization of these Pluronics^® in the parasite membrane and macrophages and its stability in the culture medium was evaluated. Results showed that Pluronics^® did not cause significant damage to human red cells and promastigotes. The P-123 and F-127 inhibited the survival rate of L. amazonensis amastigotes, and also presented loss of mitochondrial membrane potential on promastigotes. The Pluronics^® showed low cytotoxic activity on J774A.1 macrophages, while only P-123 showed moderate cytotoxicity for BALB/c macrophages. The stability of P-123 and F-127 in culture medium was maintained for ten days. In conclusion, the NP studied can be used for incorporating potent leishmanicidal chemotherapy, due to their selectivity towards macrophages, being a promising system for the treatment of cutaneous leishmaniasis.