High-throughput fluorescence screening assay for the identification and comparison of antimicrobial peptides’ activity on various yeast species

Can BioSAXS detect ultrastructural changes of antifungal compounds in Candida albicans?-an exploratory study

The opportunistic yeast Candida albicans is the most common cause of candidiasis. With only four classes of antifungal drugs on the market, resistance is becoming a problem in the treatment of fungal infections, especially in immunocompromised patients. The development of novel antifungal drugs with different modes of action is urgent. In 2016, we developed a groundbreaking new medium-throughput method to distinguish the effects of antibacterial agents. Using small-angle X-ray scattering for biological samples (BioSAXS), it is now possible to screen hundreds of new antibacterial compounds and select those with the highest probability for a novel mode of action. However, yeast (eukaryotic) cells are highly structured compared to bacteria. The fundamental question to answer was if the ultrastructural changes induced by the action of an antifungal drug can be detected even when most structures in the cell stay unchanged. In this exploratory work, BioSAXS was used to measure the ultrastructural changes of C. albicans that were directly or indirectly induced by antifungal compounds. For this, the well-characterized antifungal drug Flucytosine was used. BioSAXS measurements were performed on the synchrotron P12 BioSAXS beamline, EMBL (DESY, Hamburg) on treated and untreated yeast C. albicans. BioSAXS curves were analysed using principal component analysis (PCA). The PCA showed that Flucytosine-treated and untreated yeast were separated. Based on that success further measurements were performed on five antifungal peptides {1. Cecropin A-melittin hybrid [CA (1-7) M (2-9)], KWKLFKKIGAVLKVL; 2. Lasioglossin LL-III, VNWKKILGKIIKVVK; 3. Mastoparan M, INLKAIAALAKKLL; 4. Bmkn2, FIGAIARLLSKIFGKR; and 5. optP7, KRRVRWIIW}. The ultrastructural changes of C. albicans indicate that the peptides may have different modes of action compared to Flucytosine as well as to each other, except for the Cecropin A-melittin hybrid [CA (1-7) M (2-9)] and optP7, showing very similar effects on C. albicans. This very first study demonstrates that BioSAXS shows promise to be used for antifungal drug development. However, this first study has limitations and further experiments are necessary to establish this application.

Light-induced antifungal activity of nanoparticles with an encapsulated porphyrin photosensitizer

The strong antifungal effect of sulfonated polystyrene nanoparticles (NPs) with an encapsulated tetraphenylporphyrin (TPP) photosensitizer is reported here. TPP is activated by visible light, resulting in the generation of singlet oxygen. Its antifungal action is potentiated in the presence of potassium iodide, yielding I₂/I₃⁻, another antifungal species. The NPs exhibit no dark toxicity, but a broad spectrum of antifungal photodynamic effects. The efficiency of this rapid killing (on the order of minutes) depends on the concentration of TPP NPs, potassium iodide, yeast species and temperature. A strong antifungal activity of TPP NPs is demonstrated on eleven pathogenic and opportunistic pathogenic yeast species (six Candida species and other yeast species, including melanized Hortaea werneckii). The composition and architecture of yeast cell envelope structures clearly influence the efficacy of photodynamic therapy. Candida krusei is the most sensitive to photodynamic therapy. Despite expectations, melanin does not provide Hortaea cells with marked resistance compared to white yeast species. The kinetics of the interaction of NPs with yeast cells is also described. This study may inspire and promote the fabrication of a new type of antiseptic for various skin injuries in clinical medicine.

Antimicrobial Peptides with Anti-Candida Activity

Mycoses are accountable for millions of infections yearly worldwide. Invasive candidiasis is the most usual, presenting a high morbidity and mortality. Candida albicans remains the prevalent etiologic agent, but the incidence of other species such as Candida parapsilosis, Candida glabrata and Candida auris keeps increasing. These pathogens frequently show a reduced susceptibility to commonly used antifungal drugs, including polyenes, triazoles and echinocandins, and the incidence of emerging multi-drug-resistant strains of these species continues to increase. Therefore, the need to search for new molecules that target these pathogenic species in a different manner is now more urgent than ever. Nature is an almost endless source of interesting new molecules that could meet this need. Among these molecules, antimicrobial peptides, present in different sources in nature, possess some advantages over conventional antifungal agents, even with their own drawbacks, and are considered as a promising pharmacological option against a wide range of microbial infections. In this review, we describe 20 antimicrobial peptides from different origins that possess an activity against Candida.

Debaryomyces hansenii: an old acquaintance for a fresh start in the era of the green biotechnology

The halophilic yeast Debaryomyces hansenii has been studied for several decades, serving as eukaryotic model for understanding salt and osmotic tolerance. Nevertheless, lack of consensus among different studies is found and, sometimes, contradictory information derived from studies performed in very diverse conditions. These two factors hampered its establishment as the key biotechnological player that was called to be in the past decade. On top of that, very limited (often deficient) engineering tools are available for this yeast. Fortunately Debaryomyces is again gaining momentum and recent advances using highly instrumented lab scale bioreactors, together with advanced –omics and HT-robotics, have revealed a new set of interesting results. Those forecast a very promising future for D. hansenii in the era of the so-called green biotechnology. Moreover, novel genetic tools enabling precise gene editing on this yeast are now available. In this review, we highlight the most recent developments, which include the identification of a novel gene implicated in salt tolerance, a newly proposed survival mechanism for D. hansenii at very high salt and limiting nutrient concentrations, and its utilization as production host in biotechnological processes.

Styrylpyridinium Derivatives as New Potent Antifungal Drugs and Fluorescence Probes

The incidence of Candida glabrata infections increases every year due to its higher resistance to commonly used antifungal drugs. We characterized the antifungal mechanism of action of eight new styrylpyridinium derivatives, with various N-alkyl chains (-C₆H₁₃, -C₈H₁₇, -C₁₀H₂₁, -C₁₂H₂₅) and different substituents, on C. glabrata strains differing in their drug resistance due to the presence or absence of two major drug-efflux pumps. We found that the tested styrylpyridinium compounds affected the growth of C. glabrata cells in a compound- and strain-dependent manner, and apparently they were substrates of CgCdr1 and CgCdr2 pumps. Further, we determined the impact of the tested compounds on plasma membrane integrity. The ability to cause damage to a plasma membrane depended on the compound, its concentration and the presence of efflux pumps, and corresponded well with the results of growth and survival tests. We also tested possible synergism with three types of known antifungal drugs. Though we did not observe any synergism with azole drugs, styrylpyridinium compounds 5 and 6 together with FK506 demonstrated excellent antifungal properties, whereas compounds 2, 3, 5, and 6 exhibited a significant synergistic effect in combination with terbinafine. Based on our results, derivatives 2 and 6 turned out to be the most promising antifungal drugs. Moreover, compound 6 was not only able to effectively permeabilize the yeast plasma membrane, but also exhibited significant synergism with FK506 and terbinafine. Finally, we also characterized the spectroscopic properties of the tested styrylpyridinium compounds. We measured their absorption and fluorescence spectra, determined their localization in yeast cells and found that their fluorescence characteristics differ from the properties of current commercial vacuolar styrylpyridinium markers and allow multi-color staining. Compounds 1, 3, 7, and 8 were able to accumulate in plasma and vacuolar membranes, and compounds 2, 5, and 6 stained the whole interior of dead cells. In summary, of the eight tested compounds, compound 6 is the most promising antifungal drug, compound 8, due to its minimal toxicity, is the best candidate for a new vacuolar-membrane probe or new benchmark substrate of C. glabrata Cdr pumps, and derivative 5 for a new vital dye.

Combined effect of lasioglossin LL-III derivative with azoles against Candida albicans virulence factors: biofilm formation, phospholipases, proteases and hemolytic activity

Candida albicans has several virulence factors at its disposal, including yeast–hyphal transition associated with biofilm formation, phospholipases, proteases and hemolytic activity, all of which contribute to its pathogenesis. We used synthetic derivative LL-III/43 of antimicrobial peptide lasioglossin LL-III to enhance effect of azoles on attenuation of C. albicans virulence factors. LL-III/43 was able to inhibit initial adhesion or biofilm formation of C. albicans strains at 50 µM. Azoles, however, were ineffective at this concentration. Using fluorescently labeled LL-III/43, we observed that peptide covered C. albicans cells, partially penetrated through their membranes and then accumulated inside cells. LL-III/43 (25 µM) in combination with clotrimazole prevented biofilm formation already at 3.1 µM clotrimazole. Neither LL-III/43 nor azoles were able to significantly inhibit phospholipases, proteases, or hemolytic activity of C. albicans. LL-III/43 (25 µM) and clotrimazole (50 µM) in combination decreased production of these virulence factors, and it completely attenuated its hemolytic activity. Scanning electron microscopy showed that LL-III/43 (50 µM) prevented C. albicans biofilm formation on Ti-6Al-4 V alloy used in orthopedic surgeries and combination of LL-III/43 (25 µM) with clotrimazole (3.1 µM) prevented biofilm formation on urinary catheters. Therefore, mixture of LL-III/43 and clotrimazole is suitable candidate for future pharmaceutical research.

Antifungal activity of analogues of antimicrobial peptides isolated from bee venoms against vulvovaginal Candida spp

Candida albicans is the main causative agent of vulvovaginal candidiasis (VVC), a common mycosis in women, relapses of which are difficult to manage due to biofilm formation. This study aimed at developing novel non-toxic compounds active against Candida spp. biofilms. We synthesised analogues of natural antifungal peptides LL-III (LL-III/43) and HAL-2 (peptide VIII) originally isolated from bee venoms and elucidated their structures by nuclear magnetic resonance spectroscopy. The haemolytic, cytotoxic, antifungal and anti-biofilm activities of LL-III/43 and peptide VIII were then tested. LL-III/43 and VIII showed moderate cytotoxicity to HUVEC-2 cells and had comparable inhibitory activity against C. albicans and non-albicans spp. The lowest minimum inhibitory concentration (MIC90) of LL-III/43 was observed towards Candida tropicalis (0.8 µM). That was 8-fold lower than that of antimycotic amphotericin B. Both peptides can be used to inhibit Candida spp. bio film f ormation. Biofilm inhibitory concentrations (BIC50) ranged from 0.9 to 58.6 µM and biofilm eradication concentrations (BEC50) for almost all tested Candida spp. strains ranged from 12.8 to 200 µM. Als o pro ven were the peptides’ abilities to reduce the area colonised by biofilms , inhibit hyphae formation and permeabilise cell membranes in biofil ms . LL-III/43 and VIII are promising candidates for further development as therapeutics against VVC.

Characterization, Preparation, and Purification of Marine Bioactive Peptides

Marine bioactive peptides, as a source of unique bioactive compounds, are the focus of current research. They exert various biological roles, some of the most crucial of which are antioxidant activity, antimicrobial activity, anticancer activity, antihypertensive activity, anti-inflammatory activity, and so forth, and specific characteristics of the bioactivities are described. This review also describes various manufacturing techniques for marine bioactive peptides using organic synthesis, microwave assisted extraction, chemical hydrolysis, and enzymes hydrolysis. Finally, purification of marine bioactive peptides is described, including gel or size exclusion chromatography, ion-exchange column chromatography, and reversed-phase high-performance liquid chromatography, which are aimed at finding a fast, simple, and effective method to obtain the target peptides.