Effect of Membrane Structure on the Action of Polyenes: I. Nystatin Action in Cholesterol- and Ergosterol-Containing Membranes

Ergosterol promotes aggregation of natamycin in the yeast plasma membrane

Polyene macrolides are antifungal substances, which interact with cells in a sterol-dependent manner. While being widely used, their mode of action is poorly understood. Here, we employ ultraviolet-sensitive (UV) microscopy to show that the antifungal polyene natamycin binds to the yeast plasma membrane (PM) and causes permeation of propidium iodide into cells. Right before membrane permeability became compromised, we observed clustering of natamycin in the PM that was independent of PM protein domains. Aggregation of natamycin was paralleled by cell deformation and membrane blebbing as revealed by soft X-ray microscopy. Substituting ergosterol for cholesterol decreased natamycin binding and caused a reduced clustering of natamycin in the PM. Blocking of ergosterol synthesis necessitates sterol import via the ABC transporters Aus1/Pdr11 to ensure natamycin binding. Quantitative imaging of dehydroergosterol (DHE) and cholestatrienol (CTL), two analogues of ergosterol and cholesterol, respectively, revealed a largely homogeneous lateral sterol distribution in the PM, ruling out that natamycin binds to pre-assembled sterol domains. Depletion of sphingolipids using myriocin increased natamycin binding to yeast cells, likely by increasing the ergosterol fraction in the outer PM leaflet. Importantly, binding and membrane aggregation of natamycin was paralleled by a decrease of the dipole potential in the PM, and this effect was enhanced in the presence of myriocin. We conclude that ergosterol promotes binding and aggregation of natamycin in the yeast PM, which can be synergistically enhanced by inhibitors of sphingolipid synthesis.

Antibiotic Loaded Phytosomes as a Way to Develop Innovative Lipid Formulations of Polyene Macrolides

BACKGROUND

The threat of antibiotic resistance of fungal pathogens and the high toxicity of the most effective drugs, polyene macrolides, force us to look for new ways to develop innovative antifungal formulations.

OBJECTIVE

The aim of this study was to determine how the sterol, phospholipid, and flavonoid composition of liposomal forms of polyene antibiotics, and in particular, amphotericin B (AmB), affects their ability to increase the permeability of lipid bilayers that mimic the membranes of mammalian and fungal cells.

METHODS

To monitor the membrane permeability induced by various polyene-based lipid formulations, a calcein leakage assay and the electrophysiological technique based on planar lipid bilayers were used.

KEY RESULTS

The replacement of cholesterol with its biosynthetic precursor, 7-dehydrocholesterol, led to a decrease in the ability of AmB-loaded liposomes to permeabilize lipid bilayers mimicking mammalian cell membranes. The inclusion of plant flavonoid phloretin in AmB-loaded liposomes increased the ability of the formulation to disengage a fluorescent marker from lipid vesicles mimicking the membranes of target fungi. I-V characteristics of the fungal-like lipid bilayers treated with the AmB phytosomes were symmetric, demonstrating the functioning of double-length AmB pores and assuming a decrease in the antibiotic threshold concentration.

CONCLUSIONS AND PERSPECTIVES

The therapeutic window of polyene lipid formulations might be expanded by varying their sterol composition. Polyene-loaded phytosomes might be considered as the prototypes for innovative lipid antibiotic formulations.

Antifungal activity and mechanism of oxanthromicin against Verticillium dahliae

Oxanthromicin is an anthranone-type natural product isolated from Streptomyces sp. TRM 15522, which exhibits antifungal activity. However, the underlying mechanisms remain unclear. This study, therefore, aimed at investigating the mode of action of oxanthromicin against the phytopathogen Verticillium dahliae. We found that oxanthromicin substantially suppressed spore germination and mycelial growth in V. dahliae. Further, electron microscopy and staining with propidium iodide and Rhodamine 123 indicated that oxanthromicin causes cell membrane damage and induces changes in mitochondrial membrane potential. These findings suggest that oxanthromicin exhibits its antifungal activity by damaging fungal cell membranes. This discovery could potentially facilitate the development of oxanthromicin as a biological pesticide.

Natamycin interferes with ergosterol-dependent lipid phases in model membranes

Natamycin is an antifungal polyene macrolide that is used as a food preservative but also to treat fungal keratitis and other yeast infections. In contrast to other polyene antimycotics, natamycin does not form ion pores in the plasma membrane, but its mode of action is poorly understood. Using nuclear magnetic resonance (NMR) spectroscopy of deuterated sterols, we find that natamycin slows the mobility of ergosterol and cholesterol in liquid-ordered (Lo) membranes to a similar extent. This is supported by molecular dynamics (MD) simulations, which additionally reveal a strong impact of natamycin dimers on sterol dynamics and water permeability. Interference with sterol-dependent lipid packing is also reflected in a natamycin-mediated increase in membrane accessibility for dithionite, particularly in bilayers containing ergosterol. NMR experiments with deuterated sphingomyelin (SM) in sterol-containing membranes reveal that natamycin reduces phase separation and increases lipid exchange in bilayers with ergosterol. In ternary lipid mixtures containing monounsaturated phosphatidylcholine, saturated SM, and either ergosterol or cholesterol, natamycin interferes with phase separation into Lo and liquid-disordered (Ld) domains, as shown by NMR spectroscopy. Employing the intrinsic fluorescence of natamycin in ultraviolet-sensitive microscopy, we can visualize the binding of natamycin to giant unilamellar vesicles (GUVs) and find that it has the highest affinity for the Lo phase in GUVs containing ergosterol. Our results suggest that natamycin specifically interacts with the sterol-induced ordered phase, in which it disrupts lipid packing and increases solvent accessibility. This property is particularly pronounced in ergosterol containing membranes, which could underlie the selective antifungal activity of natamycin.

Polyene Antibiotics Physical Chemistry and Their Effect on Lipid Membranes; Impacting Biological Processes and Medical Applications

This review examined a collection of studies regarding the molecular properties of some polyene antibiotic molecules as well as their properties in solution and in particular environmental conditions. We also looked into the proposed mechanism of action of polyenes, where membrane properties play a crucial role. Given the interest in polyene antibiotics as therapeutic agents, we looked into alternative ways of reducing their collateral toxicity, including semi-synthesis of derivatives and new formulations. We follow with studies on the role of membrane structure and, finally, recent developments regarding the most important clinical applications of these compounds.

Undervirilized male infant with in utero exposure to maternal use of high dose antifungal therapy

Background

Antifungals act on fungal sterols structurally similar to human cholesterol. Ketoconazole reversibly suppresses steroidogenesis by inhibiting cytochrome P450 enzymes and interferes with dihydrotestosterone (DHT) activity by binding to the androgen receptor. Hypospadias was reported in infants exposed to nystatin in utero.

Case presentation

A male infant exposed to antepartum nystatin presented with severe under-undervirilization and transient adrenal corticosteroid abnormalities. He was born in USA at 31 weeks gestation to a mother treated with vaginal Polygynax capsules (nystatin-100,000 international units, neomycin sulphate-35,000 international units and polymyxin B-35,000 international units) for vaginal discharge in the Ivory Coast. She used approximately 60 capsules between the first trimester until delivery. The infant was born with micropenis, chordee, perineo-scrotal hypospadias and bifid scrotum with bilaterally palpable gonads. The karyotype was 46,XY. No Mullerian structures were seen on ultrasound. Serum 17-hydroxyprogesterone (17 OHP) on newborn screening was high (304 ng/ml, normal < 35). Cortisol response to cosyntropin on the 3rd day of life (DOL) was 10 mcg/ml; the subnormal cortisol response may have resulted from prematurity and the predelivery treatment with betamethasone. The elevation of several adrenal corticosteroids was not consistent with any specific enzymatic defect. Hydrocortisone and fludrocortisone were initiated at another hospital for suspected mild glucocorticoid and mineralocorticoid deficiencies. Genetic screening for adrenal and gonadal developmental defects performed when transferred to our care were normal. All medications were gradually discontinued over 5–8 months. Adrenal and testicular responses to cosyntropin and human chorionic gonadotropin (hCG) were normal at 8 months.

Conclusions

We report severe undervirilization in a 46,XY infant born to a mother treated with prolonged and high dose nystatin during pregnancy. This presentation suggests that prolonged antepartum use of high dose nystatin could lead to severe but transient defects in androgen synthesis and/or action possibly by acting as an endocrine disruptor. Further studies are warranted to confirm this finding. Thus, endocrine disruptors should be considered in male newborns with atypical genitalia not explained by common pathologies.

Effect of Chemically Transformed Macrocyclic Polyene Antibiotics on Tumor Cells

Comparative analysis of the effects of chemically transformed polyene antibiotics pimaricin, nystatin, lucensomycin, amphotericin B, and levorin on biological objects in vivo and in vitro revealed the greatest biological activity of original amphotericin B and levorin with its derivatives. The study also examined the effects of alkyl derivatives of amphotericin B and levorin modified in certain parts of the lactone ring on the lipid and biological membranes. It is established that methylated levorin possesses larger biological activity than the original antibiotic. Examination of the effects of alkyl derivatives of levorin and amphotericin B on cell cultures C6 (rat glioma) and HeLa (human cervical carcinoma) in vitro revealed the antitumor action of methylated levorin and original amphotericin B.

Electrical resonance of Amphotericin B channel activity in lipidic membranes

In our previous work [J. Membrane Biol. 237, 31 (2010)], we showed the dependence of the time average conductance of Nystatin channels as a function of the applied potential. Specifically, it was observed that greater potential induced enhanced channel activity. This indicates that the supramolecular structure could be stabilized by a large field, possibly by giving a preferential orientation to the monomers. In the present work, we entertain the notion that the process of pore formation in the lipidic membranes has an underlying deterministic component. To verify this hypothesis, experiments were performed under potentio-dynamic conditions, i.e., a square train of pulses of different frequencies (0.05-2 Hz) were applied to a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membrane having 30 mol. % cholesterol and the presence of 35 μM Amphotericin B. An emergence of a resonant frequency, in the present experiments, is tantamount to observing fingerprints of determinism in the activity of these channels in lipidic membranes.

The molecular mechanism of Nystatin action is dependent on the membrane biophysical properties and lipid composition

Nystatin-induced membrane permeabilization is related to its effects on membrane properties and organization.

An Amphotericin B Derivative Equally Potent to Amphotericin B and with Increased Safety

Amphotericin B is the most potent antimycotic known to date. However due to its large collateral toxicity, its use, although long standing, had been limited. Many attempts have been made to produce derivatives with reduced collateral damage. The molecular mechanism of polyene has also been closely studied for this purpose and understanding it would contribute to the development of safe derivatives. Our study examined polyene action, including chemical synthesis, electrophysiology, pharmacology, toxicology and molecular dynamics. The results were used to support a novel Amphotericin B derivative with increased selectivity: L-histidine methyl ester of Amphotericin B. We found that this derivative has the same form of action as Amphotericin B, i.e. pore formation in the cell membrane. Its reduced dimerization in solution, when compared to Amphotericin B, is at least partially responsible for its increased selectivity. Here we also present the results of preclinical tests, which show that the derivative is just as potent as Amphotericin B and has increased safety.

Solid lipid nanoparticles for antifungal drugs delivery for topical applications

Systemic and local infections caused by fungi, in particular those concerning the skin and nails, are increasing. Various drugs are used for mycoses treatment such as amphotericin B, nystatin and ketoconazole, fluconazole, itraconazole and fluconazole, among others. Unfortunately, many of these antifungal agents can cause side effects such as allergic and severe skin reaction. With the aim to reduce these side effects and maximize the antifungal drug activity, various drug-delivery systems have been formulated and been investigated in the last few years. In this context, solid lipid nanoparticles are attracting great attention. The aim of this review is to highlight the role of solid lipid nanoparticles as carriers of antifungal drugs for topical applications.

Cross-talk between Dopachrome Tautomerase and Caveolin-1 Is Melanoma Cell Phenotype-specific and Potentially Involved in Tumor Progression

l-Dopachrome tautomerase (l-DCT), also called tyrosinase-related protein-2 (TRP-2), is a melanoma antigen overexpressed in most chemo-/radiotherapeutic stress-resistant tumor clones, and caveolin-1 (CAV1) is a main regulator of numerous signaling processes. A structural and functional relationship between DCT and CAV1 is first presented here in two human amelanotic melanoma cell lines, derived from vertical growth phase (MelJuSo) and metastatic (SKMel28) melanomas. DCT co-localizes at the plasma membrane with CAV1 and Cavin-1, another molecular marker for caveolae in both cell phenotypes. Our novel structural model proposed for the DCT-CAV1 complex, in addition to co-immunoprecipitation and mass spectrometry data, indicates a possible direct interaction between DCT and CAV1. The CAV1 control on DCT gene expression, DCT post-translational processing, and subcellular distribution is cell phenotype-dependent. DCT is a modulator of CAV1 stability and supramolecular assembly in both cell phenotypes. During autocrine stimulation, the expressions of DCT and CAV1 are oppositely regulated; DCT increases while CAV1 decreases. Sub-confluent MelJuSo clones DCT(high)/CAV1(low) are proliferating and acquire fibroblast-like morphology, forming massive, confluent clusters as demonstrated by immunofluorescent staining and TissueFAXS quantitative image cytometry analysis. CAV1 down-regulation directly contributes to the expansion of MelJuSo DCT(high) subtype. CAV1 involved in the perpetuation of cell phenotype-overexpressing anti-stress DCT molecule supports the concept that CAV1 functions as a tumor suppressor in early stages of melanoma. DCT is a regulator of the CAV1-associated structures and is possibly a new molecular player in CAV1-mediated processes in melanoma.

Polymeric films as a promising carrier for bioadhesive drug delivery: Development, characterization and optimization

Bioadhesive films using tamarind seed polysaccharide were prepared for the treatment of candida vaginitis using nystatin as the model drug. Films were prepared by solvent casting method. A 3² factorial design was employed to study the effect of independent variables (polymer and plasticizer concentration) on a range of dependent variables namely mechanical, swelling, interfacial, and bioadhesive properties through response surface methodological approach, using Design Expert® software. Formulation composition that provided the most desired and optimized results was selected using desirability approach. Nystatin was solubilized using Tween 60 and was incorporated into the selected film. Drug solubilization and dispersion were confirmed by scanning electron microscopy and differential scanning calorimetry. The optimized film released 73.92 ± 2.54% of nystatin at the end of 8 h in simulated vaginal fluid and the release data showed best fit to Korsmeyer–Peppas model with R² of 0.9990 and the release mechanism to be super case-II. The optimized film also showed appropriate anti candida activity through appearance of zone of inhibition during antifungal activity testing study.

Evaluation of nystatin isolated from Streptomyces griseus SDX-4 against the ciliate, Ichthyophthirius multifiliis

The present study was conducted to evaluate the in vitro and in vivo antiparasitic efficacy of active compounds from the bacterial extracellular products of Streptomyces griseus SDX-4 against Ichthyophthirius multifiliis. Bioassay-guided fractionation and isolation of compounds with antiparasitic activity were performed on n-butanol extract of S. griseus yielding a pure bioactive compound, nystatin (Nys), identified by comparing spectral data (EI-MS, (1)H NMR, and (13)C NMR) with literature values. Results from in vitro antiparasitic assays revealed that Nys could be 100% effective against I. multifiliis theronts and encysted tomonts at the concentration of 6.0 mg L(-1), with the median effective concentration (EC50) values of 3.1 and 2.8 mg L(-1) for theronts and encysted tomonts (4 h), respectively. Results of in vivo test demonstrated that the number of I. multifiliis trophonts on the gold fish treated with Nys was markedly lower than the control group at 10 days after exposed to theronts (p < 0.05). In the control group, 85.7% mortality was observed owing to heavy I. multifiliis infection at 10 days after the exposure. On the other hand, only 23.8% mortality owing to parasite infection was recorded in the groups treated with the Nys (4.0 and 6.0 mg L(-1)). In addition, our results showed that the survival and reproduction of I. multifiliis tomont exited from the fish were significantly reduced after treated with the 6.0 mg L(-1) Nys. The median lethal dose (LD50) of Nys for goldfish was 16.8 mg L(-1). This study firstly demonstrated that Nys has potent antiparasitic efficacy against I. multifiliis, and it can be a good candidate drug for chemotherapy and control of I. multifiliis infections.

Cell penetrating peptides and cationic antibacterial peptides: two sides of the same coin

Cell penetrating peptides (CPP) and cationic antibacterial peptides (CAP) have similar physicochemical properties and yet it is not understood how such similar peptides display different activities. To address this question, we used Iztli peptide 1 (IP-1) because it has both CPP and CAP activities. Combining experimental and computational modeling of the internalization of IP-1, we show it is not internalized by receptor-mediated endocytosis, yet it permeates into many different cell types, including fungi and human cells. We also show that IP-1 makes pores in the presence of high electrical potential at the membrane, such as those found in bacteria and mitochondria. These results provide the basis to understand the functional redundancy of CPPs and CAPs.

The interaction of dipole modifiers with polyene-sterol complexes

Recently, we showed that the effect of dipole modifiers (flavonoids and styrylpyridinium dyes) on the conductance of single amphotericin B (AmB) channels in sterol-containing lipid bilayers primarily resulted from changes in the membrane dipole potential. The present study examines the effect of dipole modifiers on the AmB multi-channel activity. The addition of phloretin to cholesterol-containing membranes leads to a significant increase in the steady-state AmB-induced transmembrane current. Quercetin significantly decreases and RH 421 increases the current through ergosterol-containing bilayers. Other tested flavonoids and styrylpyridinium dyes do not affect the channel-forming activity of AmB independently on the sterol composition of the bilayers. The effects obtained in these trials may instead be attributed to the direct interaction of dipole modifiers with AmB/sterol complexes and not to the effect of dipole potential changes. The presence of double bonds in the Δ7 and Δ22 positions of sterol molecules, the number of conjugated double bonds and amino sugar residues in polyene molecules, and the conformation and adsorption plane of dipole modifiers are important factors impacting this interaction.

Effective endogenous gene silencing mediated by pH responsive peptides proceeds via multiple pathways

Cationic amphipathic histidine rich peptides possess high plasmid DNA and siRNA delivery capabilities. To further understand the pH responsive siRNA delivery process and evaluate the capabilities of such peptides we have investigated their ability to mediate specific silencing of endogenous GAPDH gene activity in MCF-7 and A549 cells and compared this with plasmid DNA delivery. A substantial and selective reduction of both GAPDH activity and expression was achieved using pH responsive peptide vectors, which compared favourably with that mediated by commercially available non-viral vectors in terms of efficacy and toxicity. Furthermore, by comparing the efficacy of both gene delivery and silencing mediated by a series of such peptides, their sensitivities to known inhibitors of endocytotic processes, and their route of uptake via confocal live cell imaging, we show that both plasmid DNA and siRNA are internalised via endocytosis. However siRNA entry facilitated by LAH4-L1, proceeds via a cholesterol dependent mechanism, in contrast to DNA transfer which is associated with clathrin dependent endocytosis. Furthermore, using peptides that respond at increasingly acidic pH, we demonstrate that the route of entry for the siRNA that ultimately mediates silencing is peptide specific and whilst some pH responsive peptides promote the escape of labelled siRNA from endosomes, others may promote entry via alternative mechanisms.