Circular dichroism study of interactions of Fungizone or AmBisome forms of amphotericin B with human low density lipoproteins

Cochleate formulations of Amphotericin b designed for oral administration using a naturally occurring phospholipid

The purpose of this work was to formulate the poor soluble antifungal and antiparasitic agent Amphotericin B (AmB) in cost-effective lipid-based formulations suitable for oral use in developing countries, overcoming the limitations of poor water solubility, nephrotoxicity and low oral bioavailability. The antifungal agent was formulated, at different molar proportions, in cochleate nanocarriers prepared using an accessible naturally occurring phospholipid rich in phosphatidylserine (Lipoid PSP70). These nanoassemblies were prepared by condensation of negatively charged phospholipid membrane vesicles with divalent cations (Ca²⁺). Small-angle X-ray scattering studies revealed the Ca²⁺-triggered condensation of loosely packed multilamellar vesicles into tightly packed bilayers of strongly dehydrated multilamellar organization characterized by narrow Bragg peaks. Transmission electron microscopy and quasi-elastic light scattering studies demonstrated the formation of nanosized particles. AmB drug loading was above 55% in all formulations. Circular dichroism demonstrated the prevalence of monomeric and complexed forms of AmB over toxic aggregates. The stability of AmB in gastric medium was improved by loading in cochleates and its release in gastrointestinal media was retarded. Confocal microscopy studies revealed the in-vitro interactions of Lipoid PSP70-based cochleates with Caco2 intestinal cell monolayers. The results suggest that the low-cost AmB-loaded cochleates may increase the therapeutic range of this drug.

Self-assembled nanostructures of L-ascorbic acid alkyl esters support monomeric amphotericin B

Hypothesis

Amphotericin B (AmB) is a highly effective antimicrobial, with broad antimycotic and antiparasitic effect. However, AmB poor water-solubilisation and aggregation tendency limits its use for topical applications. We studied the capacity of nanostructures formed by alkyl esters of L-ascorbic acid (ASCn) to solubilise AmB and tested the relationship between the prevalence of the monomeric form of AmB and its effectiveness as antimicrobial agent.

Experiments

We developed self-assembled nanostructures formed by the commercial compound, palmitoyl ascorbic acid, as well as the shorter chained myristoyl and lauroyl ascorbic acid. AmB loaded ASCn nanostructures were studied by a combination of spectroscopic techniques, together with particle analysis, differential scanning calorimetry, microbiological tests, and Langmuir monolayer visualisation.

Findings

We found no direct relation between the antimicrobial capacity and the prevalence of the monomeric form of the drug. However, the later was related to chemical stability and colloidal robustness. Nanostructures formed by ASC16 in its anionic state provide an appropriate environment for AmB in its monomeric form, maintaining its antimicrobial capacity. Langmuir film visualisation supports spectrophotometric evidence, indicating that ASC16 allows the in-plane solubilisation of AmB. Coagels formed by ASC16 appear as promising for carrying AmB for dermal delivery.

Development of oil-in-water microemulsions for the oral delivery of amphotericin B

Amphotericin B (AmB) is a very efficient drug against serious diseases such as leishmaniasis and systemic fungal infections. However, its oral bioavailability is limited due to its poor solubility in water. Nevertheless, it is marketed as high-cost lipid parenteral formulations that may induce serious infusion-related side effects. In this study, oil-in-water (O/W) microemulsions (MEs) were developed and characterized with a view to their use as solubility enhancers and oral delivery systems for AmB. Therefore, different nonionic surfactants from the Tween(®) and Span(®) series were tested for their solubilization capacity in combination with several oils. Based on pseudoternary phase diagrams, AmB-loaded MEs with mean droplet sizes about 120 nm were successfully produced. They were able to improve the drug solubility up to 1000-fold. Rheological studies showed the MEs to be low-viscosity formulations with Newtonian behavior. Circular dichroism and absorption spectra revealed that part of the AmB in the MEs was aggregated as an AmB reservoir carrier. Cytotoxicity studies revealed limited toxicity to macrophage-like cells that may allow the formulations to be considered as suitable carriers for AmB.

Spectroscopic studies of amphotericin B-Cu²+ complexes

The aim of this research is to investigate amphotericin B (AmB)-Cu(2+) complexes in aqueous solution at different pH values. Electronic absorption, circular dichroism (CD), Raman and FTIR spectroscopies were used in this study. We found that different concentrations of AmB and Cu(2+) ions in solution leads to formation of complexes with stoichiometry of 2:1 and 1:1. The formation of AmB-Cu(2+) complexes at physiological pH values is accompanied by changes of the molecular organization of AmB especially disaggregation. These observed effects might be significant from a medical point of view.

Physicochemical characterization of molecular assemblies of miltefosine and amphotericin B

This study describes the interactions between two amphiphilic molecules with antileishmanial activity, amphotericin B (AmB) and miltefosine [hexadecylphosphocholine (HePC)], the latter being effective by the oral route. The effect of HePC on the aggregation state of AmB in aqueous solution and the interactions between the two agents were monitored using absorption spectroscopy and circular dichroism. Structural characterization of the mixed aggregates formed in water by dynamic light scattering (DLS) and cryofracture electron microscopy was performed. At concentrations above its critical micelle concentration, HePC was shown to interact with AmB, leading to an increase in the proportion of AmB in its monomeric form as a result of a micellar solubilization mechanism with a capacity of 26 +/- 3 mmol of AmB solubilized/mol of HePC, that is, nearly 40 molecules of HePC per molecule of AmB in the mixed micelles. These were revealed as individual and spherical aggregates close to 10 nm in diameter by both electron microscopy and DLS. Such a micellar formulation provides a new AmB-based system which might be useful in delivering AmB orally for visceral leishmaniasis bitherapy.

Interaction between miltefosine and amphotericin B: consequences for their activities towards intestinal epithelial cells and Leishmania donovani promastigotes in vitro

The aim of this study was to evaluate the potential of a combination of two antileishmanial drugs, miltefosine (HePC) and amphotericin B (AMB), when administered by the oral route. Caco-2 cell monolayers were used as a validated in vitro model of the intestinal barrier and Leishmania donovani promastigotes as a model for evaluating the effect of the drug combination. Spectroscopic measurements demonstrated that HePC and AMB associate, leading to the formation of mixed aggregates in which AMB is solubilized as monomers. The incubation of the association of HePC and AMB with Caco-2 cell monolayers, at a concentration higher than 5 microM, led to (i) a reduction of the HePC-induced paracellular permeability enhancement in Caco-2 cell monolayers, (ii) an inhibition of the uptake of both drugs, and (iii) a decrease in the transepithelial transport of both drugs, suggesting that a pharmacokinetic antagonism between HePC and AMB could occur after their oral administration. However, the combination did not exhibit any antagonism or synergy in its antileishmanial activity. These results demonstrated a strong physicochemical interaction between HePC and AMB, depending on the concentration of each, which could have important consequences for their biological activities, if they are administered together.

A case of chromoblastomycosis with an unusual clinical manifestation caused by Phialophora verrucosa on an unexposed area: treatment with a combination of amphotericin B and 5-flucytosine

Chromoblastomycosis is a cutaneous and subcutaneous mycotic disease caused by the dematiaceous (black) fungi. Five species of fungi are known generally to be the cause: Fonsecaea pedrosoi, Phialophora verrucosa, Cladosporium carrionii, F. compacta and Rhinocladiella cerphilum. In infected tissue they can appear as pigmented sclerotic bodies, commonly called 'copper pennies', which are pathognomonic of chromoblastomycosis. The infection usually occurs through traumatic skin inoculation, with the majority of lesions occurring on the feet and legs of outdoor workers. We report a patient in whom the lesions had begun on the right breast, which is an unexposed area, without a history of trauma. A uniform, reliable treatment does not exist but our patient was mycologically cured with the use of amphotericin B and the subsequent combination of 5-flucytosine and itraconazole.