Exploring the permeability of Amphotericin B trough serum albumin dispersions and lipid nanocarriers for oral delivery.

Amphotericin B (AmB) is a potent polyenic antifungal agent with leishmanicidal activity. Due to its low solubility and permeability in the gastrointestinal tract, AmB is usually administered intravenously. In this context, various approaches have been used to try to improve these properties. Some of the systems developed have shown proven successful, but there is still a lack of knowledge about the pathways AmB takes after oral administration. Therefore, the aim of this work was not only to obtain aqueous dispersions containing AmB at different aggregation states, but also to entrap this molecule in nanocarriers, and evaluate the influence of these conditions on the jejunal permeability of AmB. To observe the aggregation states of AmB, physicochemical characterization of AmB-albumin complexes and AmB-loaded formulations was performed. Different degrees of AmB aggregation states were obtained. Thus, permeability tests were performed in the Ussing chamber and a decrease in AmB concentration in the donor compartment was observed. Electrophysiological measurements showed different responses depending on the AmB formulation. In conclusion, although control of the AmB aggregation state was observed by physicochemical characterization, this approach does not seem to have a sufficient effect on AmB permeability, but on its toxicity. For a complete understanding of AmB-loaded nanocarriers, other pathways, such as lymphatic absorption, should also be investigated.

The contribution of Raman scattering to the fluorescence of the polyene antibiotic amphotericin B.

Fluorescence has recently been applied to the analysis of the molecular organization state of the polyene antibiotic amphotericin B (AmB) in solution or in lipid membranes. The polyene chain of AmB monomer gives rise to two fluorescence emissions; S(1)(2(1)A(g)) → S(0)(1(1)A(g)) between 500 and 700 nm, S(2)(1(1)B(u)) → S(0)(1(1)A(g)) between 400 and 500 nm. However, Raman scattering might interfere with the S(2) → S(0) emission fluorescence due to the weak fluorescence quantum yield and close proximity to the exciting lines. In fact, we show here that a change in the excitation wavelength results in a shift of three emission bands, an effect which excludes their assignment to fluorescence. These bands originate from the water Raman at 3382 cm(-1)and AmB resonance Raman at 1556 and 1153 cm(-1). As a consequence, some former conclusions on the molecular organization state of AmB should be reconsidered.

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.

Cyclodextrin and polysaccharide-based nanogels: entrapment of two hydrophobic molecules, benzophenone and tamoxifen.

The entrapment of two hydrophobic molecules, benzophenone and tamoxifen, into self-assembling cyclodextrin (CD)-based nanogels has been studied. These nanogels formed spontaneously upon the association of a hydrophobically modified dextran (MD) and a cyclodextrin polymer (pbetaCD). The interactions of benzophenone and tamoxifen with MD and pbetaCD were investigated using phase solubility studies, circular dichroism, and isothermal titration calorimetry. Both hydrophobic molecules were included into the CD cavities of the pbetaCD and were also solubilized by MD into its hydrophobic microdomains. We took advantage of these interactions to form benzophenone- and tamoxifen-loaded nanogels. The highest benzophenone loadings were obtained by solubilizing it in both pbetaCD and MD solutions before mixing them to form nanogels. These studies open new possibilities of applications of the nanogels, mainly in the cosmetic field, as sun screen carriers prepared by a simple "green" technology.

Effect of high pressure homogenization on the structure and the interfacial and emulsifying properties of ß-lactoglobulin.

The effect of high pressure homogenization (HPH) on the structure of ß-lactoglobulin (ß-lg) was studied by combining spectroscopic, chromatographic, and electrophoretic methods. The consequences of the resulting structure modifications on oil/water (O/W) interfacial properties were also assessed. Moderated HPH treatment (100 MPa/4 cycles) showed no significant modification of protein structure and interfacial properties. However, a harsher HPH treatment (300 MPa/5 cycles) induced structural transformation, mainly from ß-sheets to random coils, wide loss in lipocalin core, and protein aggregation via intermolecular disulfide bridges. HPH-modified ß-lg displayed higher surface hydrophobicity leading to a faster adsorption rate at the interface and an earlier formation of an elastic interfacial film at Cß-lg = 0.1 wt%. However, no modification of the interfacial properties was observed at Cß-lg = 1 wt%. At this protein concentration, the prior denaturation of ß-lg by HPH did not modify the droplet size of nanoemulsions prepared with these ß-lg solutions as the aqueous phases. A slightly increased creaming rate was however observed. The effects of HPH and heat denaturations appeared qualitatively similar, but with differences in their extent.

Modulation of polyene antibiotics self-association by ions from the Hofmeister series.

The toxicity of the antifungal polyene antibiotic amphotericin B (AMB) has been related to its low solubility, more specifically to a self-associated form termed toxic aggregate. In addition, AMB in aqueous medium gives rise to concentration, ionic strength, and time-dependent polydisperse systems. For this reason different approaches, including the use of several lipid aggregates, have been used in attempts to improve the drug's solubility and increase its therapeutic index. In this context, understanding AMB's self-association properties should help in the preparation of less toxic formulations. Ions from the Hofmeister series alter water properties: while kosmotropes (water structure makers-sulfate, citrate, phosphate) decrease solute solubility, chaotropes (water structure breakers-perchlorate, thiocyanate, trichloroacetate, and the neutral molecule urea) have opposite effects. This work reports a study of the effect of Hofmeister ions and urea on the self-aggregation of AMB and some of its derivatives. Optical absorption and circular dichroism spectra were used to monitor monomeric and aggregated antibiotic. While kosmotropes increased aggregation in a concentration-dependent manner, the opposite was observed for chaotropes. It is shown, for the first time, that thiocyanate and trichloroacetate can induce complete AMB monomerization. The understanding of these processes at the physicochemical and molecular levels and the possibility of modulating the aggregation state of AMB and its derivatives should contribute to elucidate the mechanisms of action and toxicity of this widely used antibiotic and to develop more efficient and less toxic preparations.

New lipid formulation of amphotericin B: spectral and microscopic analysis.

UV-visible and dichroic spectrum analysis and electron microscopy have been used to characterize a new amphotericin B (AmB) lipid formulation prepared by a solvent displacement process. The composition was dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) in molar ratio DMPC/DMPG/AmB 7:3:5, a similar composition to that of Abelcet. Although the latter has a "ribbon-like" structure, our process gave a thin disc-like structure. Analysis of circular dichroism (CD) and UV-visible spectra of formulations containing different percentages of AmB revealed that a minimum of AmB self-association was observed with 7:3:5 molar ratio. Varying the lipid ratio (DMPC/DMPG) while maintaining the fixed ratio of AmB yielded similar results when DMPC was in excess (DMPC/DMPG from 10:0 to 6:4). However, when the ratio was between 5:5 to 3:7, AmB self-aggregation increased. For compositions rich in DMPG (2:8 and 0:10), inversion of the CD spectrum was observed. The influence of the lipid composition on the morphology of the complex was also evident in electron microscopy. DMPC/DMPG/AmB (10:0:5) gave large unfracturable lamellae. The presence of DMPG shortened the lamellae, which often appeared as disc-like structures. AmB content, the presence of DMPG and the preparation process all contribute to generating these original structures with particular CD spectra.

First enantioselective total synthesis and configurational assignments of suberosenone and suberosanone as potential antitumor agents.

The first enantioselective total syntheses of two marine sesquiterpenes (1R)-suberosenone and (1R)-suberosanone are achieved leading to revision of the AC of natural (1S)-suberosanone. Key elements of the synthesis include hyperbaric asymmetric Michael addition and highly efficient silver trifluoroacetate mediated α-alkylation for the formation of ring A.

Evidence for restrictive parameters in formulation of insulin-loaded nanocapsules.

Poly(isobutylcyanoacrylate) nanocapsules with an oily core were originally proposed for lipophilic drug encapsulation [Int. J. Pharm. 28 (1986) 125] but insulin, a hydrosoluble protein, has also been successfully encapsulated by Damgé et al. [Diabetes 37 (1988) 246]. The aim of this work was to understand if several parameters were restrictive for the encapsulation of insulin into the oily core of the nanocapsules prepared by interfacial polymerization. The encapsulation efficiency of insulin was not affected by the type of insulin since the peptides adopted the same association state after their addition to the organic phase. Formulation parameters mainly affected the size of the nanocapsules obtained but did not influence the insulin encapsulation efficiency. In contrast, the order of introduction of insulin and of the monomer in the organic phase was shown to control the formation and the characteristics of the nanocapsules. The key parameters, which were found to clearly influence the encapsulation efficiency of insulin, were the pH of the aqueous insulin solution and the origin of the monomer. Both of these parameters can affect the rate of the interfacial polymerization. Consequently, the ability of insulin to be entrapped into the oil containing nanocapsules appeared to be governed more by the rate of the monomer polymerization.

Effect of camphor/cyclodextrin complexation on the stability of O/W/O multiple emulsions.

Camphor (CA) encapsulation in oil/water/oil multiple emulsions prepared with cyclodextrin disturbs the emulsifier potential of alpha- and beta-natural cyclodextrins (CD). It was suggested that the size and geometrical fit between the CD cavity and CA could induce CD/CA complex formation in place of emulsifier formation leading to perturbation of emulsion stability. The complexation between CA and alpha-, beta- or gamma-CD in solution in the presence of oil phase are confirmed by phase-solubility diagrams, circular dichroism and 1H NMR. Furthermore, in order to mimic the emulsion system, CD/CA/soybean oil ternary dispersions were prepared to observe the complexation behavior of alpha-, beta- or gamma-CD/CA by circular dichroism. X-ray diffraction on emulsion samples prepared with alpha- and beta-CD confirms that the precipitates observed in emulsions are probably composed of crystals of CD/CA complexes. A preliminary study of the interaction between drug and CD before the formulation seems indispensable to prevent the risk of incompatibility.

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.

Bivalent sequential binding of docetaxel to methyl-ß-cyclodextrin.

New docetaxel (Dtx) and cyclodextrin (CD) inclusion complexes having improved apparent water solubility (up to 9.98mgmL(-1)) were obtained from phase solubility diagrams. γ-CD and SBE-ß-CD offered only poor solubility enhancements while considerable increases in apparent solubility were obtained with Me-ß-CD (20%, w/w) and HP-ß-CD (40%, w/w) (9.98mgmL(-1) and 7.43mgmL(-1), respectively). The complexation mechanism between Dtx and Me-ß-CD was investigated by circular dichroism spectrometry, two-dimensional (1)H NMR (NOESY) in D(2)O, isothermal titration calorimetry (ITC) and molecular docking calculations. Circular dichroism and NOESY confirmed the existence of non-covalent interactions between Dtx and Me-ß-CD and suggested that the tert-butyl group (C(6)-C(9)) and two aromatic groups (C(24)-C(29) and C(30)-C(35)) of Dtx interacted with the Me-ß-CD molecules. The combination of ITC results to molecular docking calculations led to the identification of an unconventional sequential binding mechanism between Me-ß-CD and Dtx. In this sequential binding, a Me-ß-CD molecule first interacted with both tert-butyl and C(30)-C(35) aromatic groups (K(1): 744M(-1)). Then a second Me-ß-CD molecule interacted with the C(24)-C(29) aromatic group (K(2): 202M(-1)). The entropy of the first interaction was positive, whereas a negative value of entropy was found for the second interaction. The opposite behavior observed for these two sites was explained by differences in the hydrophobic contact surface and functional group flexibility.

Heat-induced reformulation of amphotericin B-deoxycholate favours drug uptake by the macrophage-like cell line J774.

AIM: Heat treatment of deoxycholate-amphotericin B (AmB-DOC) leads to a therapeutically interesting supramolecular rearrangement (h-AmB-DOC); this reformulation improves the therapeutic index of AmB-DOC by reducing amphotericin B (AmB) toxicity in mammalian cell lines from 3- to 10-fold. Its activity in experimentally induced fungal infection in mice remains unchanged compared with AmB-DOC, whereas its activity is 2.5 times higher in Leishmania donovani-infected mice. This work investigates the in vitro mechanism that allows this improvement. METHODS: In this study, we analysed the role of serum components on the interaction of h-AmB-DOC with two cultured cell lines: murine peritoneal macrophage cells (J774) and kidney epithelial cells (LLCPK1). The methods used were: spectrophotometry for AmB uptake; MTT assay for cell viability; and lactate dehydrogenase release for membrane damage. RESULTS: In the presence of 10% fetal calf serum (FCS), the toxicity of AmB-DOC or h-AmB-DOC for both cell lines was null or weak. Interestingly, in J774 cells, the uptake of AmB in the form of h-AmB-DOC was much higher. In LLCPK1 cells, AmB uptake was more limited in both cases but remained higher with h-AmB-DOC. In the absence of FCS, no toxicity for either cell line was observed with h-AmB-DOC. CONCLUSIONS: These findings confirm the importance of serum proteins in AmB biodistribution and suggest that, in vivo, the reduced toxicity and the improved antileishmanial activity of AmB-DOC after moderate heating may be the result of its increased uptake by macrophages.