Metallopeptidase inhibitors arrest vital biological processes in the fungal pathogen Scedosporium apiospermum

Active Cu(II), Mn(II) and Ag(I) 1,10-phenanthroline/1,10-phenanthroline-5,6-dione/dicarboxylate chelates: effects on Scedosporium

Background: Scedosporium/Lomentospora species are human pathogens that are resistant to almost all antifungals currently available in clinical practice. Methods: The effects of 16 1,10-phenanthroline (phen)/1,10-phenanthroline-5,6-dione/dicarboxylate chelates containing Cu(II), Mn(II) and Ag(I) against Scedosporium apiospermum, Scedosporium minutisporum, Scedosporium aurantiacum and Lomentospora prolificans were evaluated. Results: To different degrees, all of the test chelates inhibited the viability of planktonic conidial cells, displaying MICs ranging from 0.029 to 72.08 μM. Generally, Mn(II)-containing chelates were the least toxic to lung epithelial cells, particularly [Mn2(oda)(phen)4(H2O)2][Mn2(oda)(phen)4(oda)2].4H2O (MICs: 1.62-3.25 μM: selectivity indexes >64). Moreover, this manganese-based chelate reduced the biofilm biomass formation and diminished the mature biofilm viability. Conclusion: [Mn2(oda)(phen)4(H2O)2][Mn2(oda)(phen)4(oda)2].4H2O opens a new chemotherapeutic avenue for the deactivation of these emergent, multidrug-resistant filamentous fungi.

Extracellularly Released Molecules by the Multidrug-Resistant Fungal Pathogens Belonging to the Scedosporium Genus: An Overview Focused on Their Ecological Significance and Pathogenic Relevance

The multidrug-resistant species belonging to the Scedosporium genus are well recognized as saprophytic filamentous fungi found mainly in human impacted areas and that emerged as human pathogens in both immunocompetent and immunocompromised individuals. It is well recognized that some fungi are ubiquitous organisms that produce an enormous amount of extracellular molecules, including enzymes and secondary metabolites, as part of their basic physiology in order to satisfy their several biological processes. In this context, the molecules secreted by Scedosporium species are key weapons for successful colonization, nutrition and maintenance in both host and environmental sites. These biologically active released molecules have central relevance on fungal survival when colonizing ecological places contaminated with hydrocarbons, as well as during human infection, particularly contributing to the invasion/evasion of host cells and tissues, besides escaping from the cellular and humoral host immune responses. Based on these relevant premises, the present review compiled the published data reporting the main secreted molecules by Scedosporium species, which operate important physiopathological events associated with pathogenesis, diagnosis, antimicrobial activity and bioremediation of polluted environments.

Cloning, expression and characterization of metalloproteinase HypZn from Aspergillus niger

A predicted metalloproteinase gene, HypZn, was cloned from Aspergillus niger CGMCC 3.7193 and expressed in Pichia pastoris GS115, and the physicochemical characteristics of recombinant HypZn were investigated after separation and purification. The results showed that the specific activity of the purified HypZn reached 1859.2 U/mg, and the optimum temperature and pH value of HypZn were 35°C and 7.0, respectively. HypZn remained stable both at 40°C and at pH values between 5.0 and 8.0. The preferred substrate of HypZn was soybean protein isolates, and the Km and Vmax values were 21.5 μmol/mL and 4926.6 μmol/(mL∙min), respectively. HypZn was activated by Co2+ and Zn2+ and inhibited by Cu2+ and Fe2+. The degree of soybean protein isolate hydrolysis reached 14.7%, and the hydrolysates were of uniform molecular weight. HypZn could tolerate 5000 mM NaCl and completely lost its activity after 30 min at 50°C. The enzymological characterizations indicated that HypZn has great application potential in the food industry, especially in fermented food processing.

Biofilms formed by Scedosporium and Lomentospora species: focus on the extracellular matrix

In the present study, the composition of the extracellular matrix (ECM) of the biofilm formed by Scedosporium apiospermum, S. aurantiacum, S. minutisporum and Lomentospora prolificans on a polystyrene surface was investigated. Confocal laser scanning microscopy revealed a dense mycelial mass, with an ECM covering/interspersing the fungal cells and containing carbohydrate-rich molecules (e.g. glycoproteins) and extracellular DNA. The ECMs that were chemically extracted from mature biofilms formed by each of these fungi was predominantly composed of polysaccharides, followed by proteins, nucleic acids and sterols. In general, the amount of biofilm ECM was significantly greater in S. minutisporum and S. aurantiacum than in S. apiospermum and L. prolificans. Corroborating these results, the disarticulation of mature biofilms with enzymes, sodium metaperiodate and chelating agents occurred mainly in S. minutisporum and S. aurantiacum. Collectively, these results have revealed for the first time the composition of the ECM of the biofilms formed by Scedosporium/Lomentospora species and the role it plays in their architecture.

Transcriptional profiling of Scedosporium apiospermum enzymatic antioxidant gene battery unravels the involvement of thioredoxin reductases against chemical and phagocytic cells oxidative stress

Scedosporium species rank the second, after Aspergillus fumigatus, among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF). Development of microorganisms in the respiratory tract depends on their capacity to evade killing by the host immune system, particularly through the oxidative response of macrophages and neutrophils, with the release of reactive oxygen species (ROS) and reactive nitrogen species (RNS). This is particularly true in the airways of CF patients which display an exacerbated inflammatory reaction. To protect themselves, pathogens have developed various enzymatic antioxidant systems implicated in ROS degradation, including superoxide dismutases, catalases, cytochrome C peroxidases, chloroperoxidases and enzymes of the glutathione and thioredoxin systems, or in RNS degradation, that is, flavohemoglobins, nitrate reductases, and nitrite reductases. Here we investigated the transcriptional regulation of the enzymatic antioxidant gene battery in 24-h-old hyphae of Scedosporium apiospermum in response to oxidative stress induced chemically or by exposure to activated phagocytic cells. We showed that 21 out of the 33 genes potentially implicated in the oxidative or nitrosative stress response were overexpressed upon exposure of the fungus to various chemical oxidants, while they were only 13 in co-cultures with macrophages or neutrophils. Among them, genes encoding two thioredoxin reductases and to a lesser extent, a peroxiredoxin and one catalase were found to be overexpressed after chemical oxidative stress as well as in co-cultures. These results suggest that thioredoxin reductases, which are known to be virulence factors in other pathogenic fungi, play a key role in pathogenesis of scedosporiosis, and may be new drug targets.

Scedosporium and Lomentospora: an updated overview of underrated opportunists

Species of Scedosporium and Lomentospora are considered as emerging opportunists, affecting immunosuppressed and otherwise debilitated patients, although classically they are known from causing trauma-associated infections in healthy individuals. Clinical manifestations range from local infection to pulmonary colonization and severe invasive disease, in which mortality rates may be over 80%. These unacceptably high rates are due to the clinical status of patients, diagnostic difficulties, and to intrinsic antifungal resistance of these fungi. In consequence, several consortia have been founded to increase research efforts on these orphan fungi. The current review presents recent findings and summarizes the most relevant points, including the Scedosporium/Lomentospora taxonomy, environmental distribution, epidemiology, pathology, virulence factors, immunology, diagnostic methods, and therapeutic strategies.

Scedosporium boydii CatA1 and SODC recombinant proteins, new tools for serodiagnosis of Scedosporium infection of patients with cystic fibrosis

Scedosporium species rank the second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF), after Aspergillus fumigatus. In CF, these fungi may cause various respiratory infections similar to those caused by A. fumigatus, including bronchitis and allergic broncho-pulmonary mycoses. Diagnosis of these infections relies on the detection of serum antibodies using crude antigenic extracts. However, many components of these extracts are common to Scedosporium and Aspergillus species, leading to cross-reactions. Here, 5 recombinant proteins from S. apiospermum or S. boydii were produced, and their value in serodiagnosis of Scedosporium infections was investigated by enzyme-linked immunosorbent assay. Two of them, corresponding to the Scedosporium catalase A1 or cytosolic Cu,Zn-superoxyde dismutase, allowed the detection of Scedosporium infection, and the differentiation with an Aspergillus infection. These recombinant proteins therefore may serve as a basis for the development of a standardized serological test.

Conidial germination in Scedosporium apiospermum, S. aurantiacum, S. minutisporum and Lomentospora prolificans: influence of growth conditions and antifungal susceptibility profiles

In the present study, we have investigated some growth conditions capable of inducing the conidial germination in Scedosporium apiospermum, S. aurantiacum, S. minutisporum and Lomentospora prolificans. Germination in Sabouraud medium (pH 7.0, 37ºC, 5% CO2) showed to be a typically time-dependent event, reaching ~75% in S. minutisporum and > 90% in S. apiospermum, S. aurantiacum and L. prolificans after 4 h. Similar germination rate was observed when conidia were incubated under different media and pHs. Contrarily, temperature and CO2 tension modulated the germination. The isotropic conidial growth (swelling) and germ tube-like projection were evidenced by microscopy and cytometry. Morphometric parameters augmented in a time-dependent fashion, evidencing changes in size and granularity of fungal cells compared with dormant 0 h conidia. In parallel, a clear increase in the mitochondrial activity was measured during the transformation of conidia-into-germinated conidia. Susceptibility profiles to itraconazole, fluconazole, voriconazole, amphotericin B and caspofungin varied regarding each morphotype and each fungal species. Overall, the minimal inhibitory concentrations for hyphae were higher than conidia and germinated conidia, except for caspofungin. Collectively, our study add new data about the conidia-into-hyphae transformation in Scedosporium and Lomentospora species, which is a relevant biological process of these molds directly connected to their antifungal resistance and pathogenicity mechanisms.

Identification of Scedosporium boydii catalase A1 gene, a reactive oxygen species detoxification factor highly expressed in response to oxidative stress and phagocytic cells

Scedosporium boydii is an opportunistic filamentous fungus which may be responsible for a large variety of infections in both immunocompetent and immunocompromised individuals. This fungus belongs to the Scedosporium apiospermum species complex which usually ranks second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF). Species of the S. apiospermum complex are able to chronically colonize the CF airways suggesting pathogenic mechanisms allowing persistence and growth of these fungi in the respiratory tract. Few putative virulence factors have been purified and characterized so far in the S. apiospermum complex including a cytosolic Cu,Zn-superoxide dismutase (SOD) and a monofunctional catalase (catalase A1). Upon microbial infection, host phagocytes release reactive oxygen species (ROS), such as hydrogen peroxide, as part of the antimicrobial response. Catalases are known to protect pathogens against ROS by degradation of the hydrogen peroxide. Here, we identified the S. boydii catalase A1 gene (CATA1) and investigated its expression in response to the environmental conditions encountered in the CF airways and to the oxidative stress. Results showed that S. boydii CATA1 gene expression is not affected by hypoxia, hypercapnia or pH changes. In contrast, CATA1 gene was overexpressed in response to a chemically induced oxidative stress with a relative gene expression 37-fold higher in the presence of 250 μM H(2)O(2), 20-fold higher with 250 μM menadione and 5-fold higher with 2 mM paraquat. Moreover, S. boydii CATA1 gene expression progressively increased upon exposure to activated THP-1-derived macrophages, reaching a maximum after 12 h (26 fold). Activated HL60-derived neutrophils and activated human peripheral blood neutrophils more rapidly induced S. boydii CATA1 gene overexpression, a maximum gene expression level being reached at 75 min (17 fold) and 60 min (15 fold), respectively. In contrast expression of the gene encoding the Cu,Zn-SOD (SODC gene) was not affected by H(2)O(2), menadione, paraquat or in co-culture with phagocytic cells. These results suggest that S. boydii CATA1 gene is highly stimulated by the oxidative burst response whereas SODC gene is constitutively expressed.

1,10-phenanthroline inhibits the metallopeptidase secreted by Phialophora verrucosa and modulates its growth, morphology and differentiation

Phialophora verrucosa is one of the etiologic agents of chromoblastomycosis, a fungal infection that affects cutaneous and subcutaneous tissues. This disease is chronic, recurrent and difficult to treat. Several studies have shown that secreted peptidases by fungi are associated with important pathophysiological processes. Herein, we have identified and partially characterized the peptidase activity secreted by P. verrucosa conidial cells. Using human serum albumin as substrate, the best hydrolysis profile was detected at extreme acidic pH (3.0) and at 37 °C. The enzymatic activity was completely blocked by classical metallopeptidase inhibitors/chelating agents as 1,10-phenanthroline and EGTA. Zinc ions stimulated the metallo-type peptidase activity in a dose-dependent manner. Several proteinaceous substrates were cleaved, in different extension, by the P. verrucosa metallopeptidase activity, including immunoglobulin G, fibrinogen, collagen types I and IV, fibronectin, laminin and keratin; however, mucin and hemoglobin were not susceptible to proteolysis. As metallopeptidases participate in different cellular metabolic pathways in fungal cells, we also tested the influence of 1,10-phenanthroline and EGTA on P. verrucosa development. Contrarily to EGTA, 1,10-phenanthroline inhibited the fungal viability (MIC 0.8 µg/ml), showing fungistatic effect, and induced profound morphological alterations as visualized by transmission electron microscopy. In addition, 1,10-phenanthroline arrested the filamentation process in P. verrucosa. Our results corroborate the supposition that metallopeptidase inhibitors/chelating agents have potential to control crucial biological events in fungal agents of chromoblastomycosis.

In vitro and in vivo studies into the biological activities of 1,10-phenanthroline, 1,10-phenanthroline-5,6-dione and its copper(ii) and silver(i) complexes

1,10-Phenanthroline (phen, 5), 1,10-phenanthroline-5,6-dione (phendione, 6), [Cu(phendione)3](ClO4)2·4H2O (12) and [Ag(phendione)2]ClO4 (13) are highly active, in vitro, against a range of normal and cancerous mammalian cells, fungal and insect cell lines, with the metal complexes offering a clear enhancement in activity. Cytoselectivity was not observed between the tumorigenic and non-tumorigenic mammalian lines. In in vivo tests, using Galleria mellonella and Swiss mice, all four compounds were well tolerated in comparison to the clinical agent, cisplatin. In addition, blood samples taken from the Swiss mice showed that the levels of the hepatic enzymes, aspartate aminotransferase (AST) and alanine aminotransferase (ALT), remained unaffected. Immunocompromised nude mice showed a much lower tolerance to 13 and, subsequently, when these mice were implanted with Hep-G2 (hepatic) and HCT-8 (colon) human-derived tumors, there was no influence on tumor growth.