Melanin protects Paracoccidioides brasiliensis from the effects of antimicrobial photodynamic inhibition and antifungal drugs

Effect of proton pump inhibitors on susceptibility and melanogenesis of Sporothrix species

Introduction. Sporotrichosis is a subcutaneous infection caused by dimorphic Sporothrix species embedded in the clinical clade. Fungi have virulence factors, such as biofilm and melanin production, which contribute to their survival and are related to the increase in the number of cases of therapeutic failure, making it necessary to search for new options.Gap statement. Proton pump inhibitors (PPIs) have already been shown to inhibit the growth and melanogenesis of other fungi.Aim. Therefore, this study aimed to evaluate the effect of the PPIs omeprazole (OMP), rabeprazole (RBP), esomeprazole, pantoprazole and lansoprazole on the susceptibility and melanogenesis of Sporothrix species, and their interactions with itraconazole, terbinafine and amphotericin B.Methodology. The antifungal activity of PPIs was evaluated using the microdilution method, and the combination of PPIs with itraconazole, terbinafine and amphotericin B was assessed using the checkerboard method. The assessment of melanogenesis inhibition was assessed using grey scale.Results. The OMP and RBP showed significant MIC results ranging from 32 to 256 µg ml-1 and 32 to 128 µg ml-1, respectively. Biofilms were sensitive, with a significant reduction (P<0.05) in metabolic activity of 52% for OMP and 50% for RBP at a concentration of 512 µg ml-1 and of biomass by 53% for OMP and 51% for RBP at concentrations of 512 µg ml-1. As for the inhibition of melanogenesis, only OMP showed inhibition, with a 54% reduction.Conclusion. It concludes that the PPIs OMP and RBP have antifungal activity in vitro against planktonic cells and biofilms of Sporothrix species and that, in addition, OMP can inhibit the melanization process in Sporothrix species.

Sporothrix globosa melanin regulates autophagy via the TLR2 signaling pathway in THP-1 macrophages

Melanin, an important virulence factor of pathogenic fungi, has been shown to suppress host immune responses in multiple ways. Autophagy is a vital cellular mechanism underlying the host's innate immunity against microbial infections. However, the potential influence of melanin on autophagy has not been explored. We investigated the effect of melanin on autophagy in macrophages, which play a key role in controlling Sporothrix spp. infection, as well as the mechanism of melanin interaction with Toll-like receptor (TLR)-induced pathways. Sporothrix globosa conidia (wild-type and melanin-deficient mutant strains) or yeast cells were co-cultured with THP-1 macrophages to demonstrate that, although S. globosa infection led to the activation of autophagy-related proteins and increased autophagic flux, S. globosa melanin suppressed macrophage autophagy. Incubation with S. globosa conidia also increased the expression levels of reactive oxygen species and multiple proinflammatory cytokines (interleukin-6, tumor necrosis factor-α, interleukin-1β and interferon-γ) in macrophages. These effects were attenuated as melanin presented. Furthermore, while S. globosa conidia significantly increased the expression of both TLR2 and TLR4 in macrophages, the knockdown of TLR2, but not TLR4, with small interfering RNA suppressed autophagy. Overall, this study revealed the novel immune defense ability of S. globosa melanin to inhibit macrophage functionality by resisting macrophage autophagy through the regulation of TLR2 expression.

The protective role and mechanism of melanin for Aspergillus niger and Aspergillus flavus against chlorine-based disinfectants

Melanin is a critical component of fungal cell wall which protect fungi from adverse environmental tress. However, the role of melanin for fungi during the disinfection with chlorine-based disinfectants has not been elucidated. The results showed that the inactivation rate constants of Aspergillus niger with chlorine and chlorine dioxide decreased from 0.08 to 2.10 min^-1 to 0 after addition of 0.32 mg/L melanin. The results indicated addition of extracted fungal melanin inhibited the inactivation efficiency of chlorine and chlorine dioxide. In contrast, the k of Aspergillus niger after inactivation with monochloramine ranged from 1.50 to 1.78 min^-1 after addition of melanin which indicated effect of melanin on the inactivation efficiency of monochloramine was negligible. In addition, the extracted fungal melanin exhibited high reactivity with chlorine and chlorine dioxide but very low reactivity with monochloramine. The different inactivation mechanisms of chlorine-based disinfectants and different reactivity of melanin with chlorine-based disinfectants led to the different protective mechanism of melanin for A. niger and A. flavus spores against disinfection with chlorine-based disinfectants. The chlorine and chlorine dioxide appeared to react with functional groups of melanin in cell wall of spores, so sacrificial reactions between melanin and disinfectants decreased the available disinfectants and limited the diffusion of disinfectants to the reactive site on cell membrane, which led to the decrease of the disinfection efficiency for chlorine and chlorine dioxide. The monochloramine could penetrate into cell and damage DNA without the effect of melanin due to its strong penetration and low reactivity with melanin. Our results systematically demonstrate the protective roles of melanin on the fungal spores against chlorine-based disinfectants and the underlying mechanisms in resisting the environmental stress caused by chlorine-based disinfectants, which provides important implications for the control of fungi, especially for fungi producing melanin.

Effect of Melanin Biosynthesis Inhibition on the Antifungal Susceptibility of Chromoblastomycosis Agents

Chromoblastomycosis (CBM) is a chronic subcutaneous infection caused by genera of melanized fungi: Fonsecaea, Cladophialophora, Phialophora, Exophiala, and Rhinocladiella. Melanin is a virulence factor known to influence antifungal susceptibility. A specific inhibitor of melanin biosynthesis is tricyclazole. The aim of this study was to evaluate the effect of melanin inhibition on antifungal susceptibility of chromoblastomycosis agents and describe the susceptibility profiles of some unusual CBM agents. Seventy-six clinical isolates, representing 13 species of the five main genera of CBM agents, were studied. The antifungal susceptibility testing was performed according to the M38-A2 protocol of CLSI (Reference Method for Broth Dilution Antifungal Susceptibility Testing of Filamentous Fungi, 3rd ed., CLSI Standard M38, 2017). In the melanin inhibition test, 16 mg/liter of tricyclazole was added to the medium used in the inoculum preparation and the susceptibility assay. CBM agents were less susceptible to amphotericin B than azoles and terbinafine. The unusual species showed similar susceptibility profiles to those of other species of the same genera. With tricyclazole exposure, MICs of terbinafine, posaconazole, and itraconazole for Fonsecaea spp. significantly decreased (P < 0.05). For Phialophora spp., this reduction was significant for posaconazole and itraconazole. For the other genera, there was a reduction in MICs of terbinafine and itraconazole; however, the statistical tests were not significant. Melanin inhibition can increase the antifungal susceptibility of most CBM agents to itraconazole and terbinafine, the main drugs used in the disease treatment. This increased susceptibility may open up new possibilities for therapy in refractory cases of CBM and/or cases caused by resistant fungal strains. Further studies are needed to confirm the same results in vivo.

Melanin and chromoblastomycosis agents: Characterization, functions, and relation with antifungals

Melanins are a diverse group of dark pigments with similar properties. In fungi, the most studied is the dihydroxynaphtalene (DHN)-melanin, present in several species including all the chromoblastomycosis agents, a chronic, disabling, and recalcitrant subcutaneous mycosis. It is synthesized in a pathway known as the pentaketide pathway, which has the agrochemical tricyclazole as an inhibitor, widely used in in vitro studies because it does not prevent the growth of fungi. There are different methodologies for qualitative and quantitative analyses of DHN-melanin, which made it possible to discover its important structural and antioxidant functions, with melanin acting as a protective factor against the host's immune system. Also, it can interact with some of the main antifungals of medical interest, reducing its activity and the susceptibility of fungi to these agents. This review aims to discuss the aspects of DHN-melanin, focusing on chromoblastomycosis, bringing the main findings of the published scientific studies, and highlighting the need for further research to understand this important fungal pathogenicity and a virulence factor.

Deletion of pksA attenuates the melanogenesis, growth and sporulation ability and causes increased sensitivity to stress response and antifungal drugs in the human pathogenic fungus Fonsecaea monophora

Fonsecaea monophora, which is very similar to Fonsecaea pedrosoi in morphological features, has been commonly misdiagnosed as F. pedrosoi. Like F. pedrosoi, F. monophora has been also identified as a predominant pathogen of Chromoblastomycosis (CBM). Melanin has been recognized as a virulence factor in several fungi, however, it is still largely unknown about the biological role of melanin and how melanin is synthesized in F. monophora. In this study, we identified two putative polyketide synthase genes (pks), AYO21_03016 (pksA) and AYO21_10638, by searching against the genome of F. monophora. AYO21_03016 and AYO21_10638 were further targeted disrupted by Agrobacterium tumefaciens-mediated transformation (ATMT). We discovered that pksA gene was the major polyketide synthase required for melanin synthesis in F. monophora, rather than AYO21_10638. Phenotypic analysis showed that, knocking out of the pksA gene attenuated melanogenesis, growth rate, sporulation ability and virulence of F. monophora, as compared with wild-type and complementation strain (pksA-C). Furthermore, the ΔpksA mutant was confirmed to be more sensitive to the oxidative stress, extreme pH environment, and antifungal drugs including itraconazole (ITC), terbinafine (TER), and amphotericin B (AMB). Taken together, these findings enabled us to comprehend the role of pksA in regulating DHN-melanin pathway and its effect on the biological function of F. monophora.

5-Aminolevulinic acid-mediated photodynamic therapy has effective antifungal activity against Sporothrix globosa in vitro

BACKGROUND

An alternative therapy for sporotrichosis is necessary to reduce the treatment time and raise clinical efficacy. The 5-Aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) is a promising platform with which to treat mycoses. However, despite the worldwide prevalence of Sporothrix globosa, a causative agent of sporotrichosis, the effect of ALA-PDT on this pathogen has not been validated.

OBJECTIVES

The aim of this study was to evaluate the effect of ALA-PDT on S globosa and the protection of melanin through an in vitro study. The mechanisms involved were also investigated.

METHODS

To estimate the survival rate of S globosa treated with ALA-PDT and the protection offered by melanin, the conidia and yeast cells of wild-type S globosa (Mel+), other clinical strains, tricyclazole-treated Mel+ and an albino mutant strain (Mel-) were incubated with and without ALA or irradiation. Reactive oxygen species generation by Mel+ conidia induced by ALA-PDT was assayed. SEM and TEM were conducted to obverse ultrastructural changes in the conidia. A comet assay was performed to evaluate DNA damage.

RESULTS

The survival rate of S globosa conidia and yeast cells significantly decreased following incubation with 1.19M ALA and 162 J/cm² irradiation in vitro. Melanin was not only capable of protecting the conidia against ALA-PDT, but also against ALA or irradiation alone. After induction by ALA-PDT, alterations in reactive oxygen species generation, DNA damage and ultrastructural changes were observed.

CONCLUSIONS

ALA-PDT inhibits the survival of S globosa conidia in vitro and therefore has potential for the treatment of sporotrichosis.

The role of melanins in melanotic fungi for pathogenesis and environmental survival

Melanins provide fungi protection from environmental stressors, support their ecological roles, and can confer virulence in pathogens. While the function, structure, and synthesis of melanins in fungi are not fully understood, they have been shown to have varied roles. Recent research has revealed a wide range of functions, from radiation resistance to increasing virulence, shedding light on fungal diversity. Understanding fungal melanins can provide useful information, from harnessing the properties of these various melanins to targeting fungal infections.Key Points• Melanotic fungi are widespread in nature. • Melanin functions to protect fungi in the environment from a range of stresses. • Melanin contributes to pathogenesis and drug resistance of pathogenic fungi.

Photodynamic Antimicrobial Chemotherapy (PACT), using Toluidine blue (TBO) inhibits both growth and dimorphism in Paracoccidioides brasiliensis by a mechanism involving reactive oxygen species (ROS) production

BACKGROUND

The thermo-dimorphic fungus Paracoccidioides brasiliensis is the pathogen of Paracoccidioidomycosis, an important public health problem in Latin American with prevalence in Brazil. Photodynamic Antimicrobial Chemotherapy (PACT) is a process that combines a photosensitizer and light, producing reactive oxygen species (ROS) that can promote damages to treated cells.

METHODS

In this work was study the effect of PACT, using Toluidine blue (TBO) on both yeast and mycelial cells of P. brasiliensis.

RESULTS

It was observed that PACT decreased P. brasiliensis yeast growth, in a dependent manner of both TBO concentrations and fluence. In the presence of TBO 0.005 mg/mL, PACT reduced P. brasiliensis yeast growth in 63, 62 and 86%, using fluences of 20, 30 and 40 J/cm², respectively. After PACT, ROS production increased 2.80, 4.64 and 7.90 times, in the presence of TBO 0.001, 0.002 and 0.005 mg/mL, respectively. It was observed that after PACT, the cells are predominantly in mycelia form, indicating that mycelial cells irradiated in the presence of TBO, maintained their filamentous form and absence and/or decreased presence of transition structures.

CONCLUSIONS

These results demonstrated the potential of PACT, using TBO to inhibit both yeast and mycelium development of P. brasiliensis.

Antitumor effects of melanin from Lachnum YM226 and its derivative in H22 tumor-bearing mice

In the present study, we investigated the anti-tumor activities of the intracellular homogeneous melanin (LM) of Lachnum YM226 and its derivative (ALM) on liver cancer using murine H22 hepatocarcinoma model. The results showed that LM and ALM (50 and 200 mg kg-1) could effectively inhibit tumor growth of H22 tumour-bearing mice. The body weight, liver, spleen and thymus indices also improved in the LM and ALM treated groups. Moreover, the levels of alanine aminotransferase (ALT), aspartate aminotransaminase (AST), alkaline phosphatase (ALP), creatinine (CRE), blood urea nitrogen (BUN) and uric acid (UA) were lowered. Serum cytokines of interleukin-2 (IL-2), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) were increased on LM and ALM administration, while LM and ALM significantly decreased the vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) levels. The H&E staining indicated that LM and ALM exhibited antitumor activity in vivo by promoting apoptosis and inhibiting angiogenesis. The anti-tumor effect of ALM was more significant than that of LM for the same dose. In summary, the findings demonstrated that LM and ALM might be promising candidates for the prevention and treatment of HCC.

Exploration of Antifungal and Immunomodulatory Potentials of a Furanone Derivative to Rescue Disseminated Cryptococosis in Mice

Cryptococcus neoformans infection is quite complex with both host-pathogen interaction and host immune profile determining disease progress and therapeutic outcome. Hence in the present study, the potential utility of (E)-5-benzylidenedihydrofuran-2(3 H)-one (compound-6) was explored as an effective anticryptococcal compound with immunomodulatory potential. The efficacy of compound-6 in pulmonary cryptococosis model using H99 strain was investigated. The effective dose was found to provide 100% survival, with a significant reduction of yeast burden in lungs and brain. The biodistribution analysis provided evidence for the presence of higher concentration of compound-6 in major organs including lungs and brain. In addition, compound-6 treated mice had significantly higher expression of IL-6, IL-4 and IFN-γ in lung and brain. Similarly, elevated expression of TNF-α, IL-β1 and IL-12 were observed in lungs, suggesting the protective host response against C. neoformans. The reduction and clearance of fungal load in systemic organs and mouse survival are notable results to confirm the ability of compound-6 to treat cryptococcosis. In conclusion, the low molecular weight (174 Da), lipophilicity, its ability to cross blood brain barrier, and facilitating modulation of cytokine expression are the added advantages of compound-6 to combat against disseminated cryptococosis.

In vitro susceptibilities of Neoscytalidium spp. sequence types to antifungal agents and antimicrobial photodynamic treatment with phenothiazinium photosensitizers

Neoscytalidium spp. are ascomycetous fungi consisting of pigmented and hyaline varieties both able to cause skin and nail infection. Their color-based identification is inaccurate and may compromise the outcome of the studies with these fungi. The aim of this study was to genotype 32 isolates morphologically identified as Neoscytalidiumdimidiatum or N. dimidiatum var. hyalinum by multilocus sequence typing (MLST), differentiate the two varieties by their sequence types, evaluate their susceptibility to seven commercial antifungal drugs [amphotericin B (AMB), voriconazole (VOR), terbinafine (TER), 5-flucytosine (5FC), ketoconazole (KET), fluconazole (FLU), and caspofungin (CAS)], and also to the antimicrobial photodynamic treatment (APDT) with the phenothiazinium photosensitizers (PS) methylene blue (MB), new methylene blue (NMBN), toluidine blue O (TBO) and the pentacyclic derivative S137. The efficacy of each PS was determined, initially, based on its minimal inhibitory concentration (MIC). Additionally, the APDT effects with each PS on the survival of ungerminated and germinated arthroconidia of both varieties were evaluated. Seven loci of Neoscytalidium spp. were sequenced on MLST revealing eight polymorphic sites and six sequence types (ST). All N. dimidiatum var. hyalinum isolates were clustered in a single ST. AMB, VOR and TER were the most effective antifungal agents against both varieties. The hyaline variety isolates were much less tolerant to the azoles than the isolates of the pigmented variety. APDT with S137 showed the lowest MIC for all the isolates of both varieties. APDT with all the PS killed both ungerminated and germinated arthroconidia of both varieties reducing the survival up to 5 logs. Isolates of the hyaline variety were also less tolerant to APDT. APDT with the four PS also increased the plasma membrane permeability of arthroconidia of both varieties but only NMBN and S137 caused peroxidation of the membrane lipids.

Paracoccidioides Spp.: Virulence Factors and Immune-Evasion Strategies

Paracoccidioides spp. are dimorphic fungal pathogens responsible for one of the most relevant systemic mycoses in Latin America, paracoccidioidomycosis (PCM). Their exact ecological niche remains unknown; however, they have been isolated from soil samples and armadillos (Dasypus novemcinctus), which have been proposed as animal reservoir for these fungi. Human infection occurs by inhalation of conidia or mycelia fragments and is mostly associated with immunocompetent hosts inhabiting and/or working in endemic rural areas. In this review focusing on the pathogen perspective, we will discuss some of the microbial attributes and molecular mechanisms that enable Paracoccidioides spp. to tolerate, adapt, and ultimately avoid the host immune response, establishing infection.

Combining two antifungal agents does not enhance survival of Galleria mellonella larvae infected with Madurella mycetomatis

OBJECTIVE

To determine whether combination therapy would improve therapeutic outcome in eumycetoma caused by Madurella mycetomatis.

METHODS

Survival, colony-forming units (CFU), melanisation and histopathology in M. mycetomatis-infected Galleria mellonella larvae treated with amphotericin B, itraconazole, terbinafine or combinations thereof were determined.

RESULTS

Compared to larvae treated with 5% glucose, enhanced survival was obtained when M. mycetomatis-infected larvae were treated with amphotericin B, but not when they were treated with itraconazole or terbinafine. Combination therapy did not increase survival compared to 5% glucose-treated larvae, itraconazole-treated larvae or terbinafine-treated larvae. Compared to amphotericin B monotreatment, a significant decrease in survival was noted when this therapy was combined with either itraconazole or terbinafine. CFU, melanisation and histopathology did not differ between monotherapy, combination therapy or 5% glucose-treated larvae.

CONCLUSIONS

Combining different classes of antifungal agents did not enhance the survival of M. mycetomatis-infected G. mellonella larvae. Instead of improving the therapeutic outcome, combining either itraconazole or terbinafine with amphotericin B resulted in significantly lower survival rates of infected larvae than amphotericin B monotherapy. This experimental study does not provide support for the use of combined amphotericin B and itraconazole, combined itraconazole and terbinafine or combined terbinafine and amphotericin B and should be confirmed in other animal models.

Melanins Protect Sporothrix brasiliensis and Sporothrix schenckii from the Antifungal Effects of Terbinafine

Terbinafine is a recommended therapeutic alternative for patients with sporotrichosis who cannot use itraconazole due to drug interactions or side effects. Melanins are involved in resistance to antifungal drugs and Sporothrix species produce three different types of melanin. Therefore, in this study we evaluated whether Sporothrix melanins impact the efficacy of antifungal drugs. Minimal inhibitory concentrations (MIC) and minimal fungicidal concentrations (MFC) of two Sporothrix brasiliensis and four Sporothrix schenckii strains grown in the presence of the melanin precursors L-DOPA and L-tyrosine were similar to the MIC determined by the CLSI standard protocol for S. schenckii susceptibility to amphotericin B, ketoconazole, itraconazole or terbinafine. When MICs were determined in the presence of inhibitors to three pathways of melanin synthesis, we observed, in four strains, an increase in terbinafine susceptibility in the presence of tricyclazole, a DHN-melanin inhibitor. In addition, one S. schenckii strain grown in the presence of L-DOPA had a higher MFC value when compared to the control. Growth curves in presence of 2×MIC concentrations of terbinafine showed that pyomelanin and, to a lesser extent, eumelanin were able to protect the fungi against the fungicidal effect of this antifungal drug. Our results suggest that melanin protects the major pathogenic species of the Sporothrix complex from the effects of terbinafine and that the development of new antifungal drugs targeting melanin synthesis may improve sporotrichosis therapies.