Lipid formulations of polyene antifungal drugs and attenuation of associated nephrotoxicity

Nanodisks protect amphotericin B from ultraviolet light and oxidation-induced damage

BACKGROUND

Macrolide polyene antibiotics possess potent broad-spectrum antifungal properties. Use of these agents in the field or in controlled environments is impeded by their poor water solubility and susceptibility to oxidation- and/or light-induced degradation. While typically used for human disease therapy, there is potential to expand the utility of polyene macrolide antibiotics, such as amphotericin B, for control of fungal disease infestation in agricultural settings. Thus, the susceptibility of this antibiotic to exposure-induced activity loss was evaluated.

RESULTS

Incubation of the prototype polyene amphotericin B (AMB) with phospholipid vesicles and apolipoprotein A-I results in the formation of nanoscale complexes, termed nanodisks (NDs), capable of solubilizing significant quantities of AMB. To evaluate whether AMB incorporation into NDs conferred protection against light- or oxidation-induced damage, yeast growth inhibition assays were conducted. Compared with AMB solubilized in detergent micelles, AMB incorporated into NDs was protected from damage caused by exposure to UV light as well as by KMnO(4)-induced oxidation. Furthermore, AMB-NDs inhibited growth of the turfgrass fungus Marasmius oreades Fr.

CONCLUSION

Results suggest that this water-soluble formulation of a natural, biodegradable, antifungal agent represents a potential cost-effective, non-toxic and environmentally friendly substitute for chemical agents currently employed to control a range of fungal infestations.

Arabinogalactan protein from Arachis hypogaea: Role as carrier in drug-formulations

Arabinogalactan protein (AGP) a highly water-soluble glyco-conjugate from groundnut (Arachis hypogaea L.) seedling was isolated and purified by precipitation with beta-glucosyl Yariv reagent. Quantification of AGP was done by gel diffusion assay. Purified AGP was conjugated to amphotericin-B (AmB) by Schiff base reaction at pH 11.0, with aim to prepare a water-injectable lesser toxic AGP-AmB conjugate without affecting AmB antifungal potential. The AGP-AmB conjugate antifungal activity was assayed by serial broth dilution and disc method against several Candida albicans clinical isolates. Both AmB and AGP-AmB showed similar MICs and MFCs activities, indicating that AGP do not reduced the antifungal activity of AmB. However, the in vitro and in vivo toxicity assays revealed that AGP-AmB conjugate was lesser toxic than AmB, as high MTD (45 mg/kg body weight) was observed. It is suggested that AGP could be a potent carrier in AmB formulation, which may result in effective treatment of fungal infections.

Membrane interaction of amphotericin B as single-length assembly examined by solid state NMR for uniformly 13C-enriched agent

The membrane interaction of amphotericin B (AmB), one of the most important anti-fungal drugs, was investigated by solid state NMR measurements of uniformly 13C-enriched AmB, which was prepared by the culture of the drug-producing microorganism in the presence of [u-13C6]glucose. All the 13C NMR signals of AmB upon binding to DLPC membrane were successfully assigned on the basis of the 13C-13C correlation spectrum. 13C-31P RDX (Rotational-Echo Double Resonance for X-clusters) experiments clearly revealed the REDOR dephasing effects for carbon atoms residing in the both terminal parts, whereas no dephasing was observed for the middle parts including polyolefinic C20-C33 and hydroxyl-bearing C8/C9 parts. These observations suggest that AmB binds to DLPC membrane with a high affinity to the phospholipid and spans the membrane with a single molecular length.

Water-soluble amphotericin B-polyvinylpyrrolidone complexes with maintained antifungal activity against Candida spp. and Aspergillus spp. and reduced haemolytic and cytotoxic effects

OBJECTIVES

Poor solubility and toxicity severely hinder the clinical use of amphotericin B (AmB), in spite of its attractive chemotherapeutic properties. Water-soluble complexes of AmB and polyvinylpyrrolidone (AmB-PVP) could display lower cytotoxicity while maintaining antifungal activity.

METHODS

AmB-PVP [with PVP of 10, 24 and 40 kDa (AC1, AC2 and AC4)] were compared with free AmB for (i) activity against Candida spp. (five albicans; nine non-albicans) and Aspergillus spp. (four strains), (ii) haemolysis of sheep red blood cells, and (iii) release of lactate dehydrogenase from J774 macrophages [with further comparison with free PVP and a liposomal formulation of amphotericin (AmBisome)].

RESULTS

MICs and MFCs of AC1, AC2 and AC4 against Candida spp. and of AC2 and AC4 against Aspergillus spp. were similar to those of AmB (and even lower for some Candida strains). Killing kinetics (24 h) were also similar. Haemolytic activity of AC2 and AC4 was 2-fold lower than that of free AmB. Cytotoxicity of AC2 towards J774 macrophages was 8-fold lower, and that of AC4 5-fold lower than that of AmB and not significantly different from that of AmBisome. The lower cytotoxicity of AC2, AC4 was correlated with a lower cellular accumulation of amphotericin. Spectroscopic analysis shows that the lower toxicity of AmB-PVP was not owing to significant change in the monomeric/polymeric forms ratio of the drug.

CONCLUSIONS

AmB-PVP complexes compared favourably with AmB for antifungal activity, were less haemolytic and cytotoxic than AmB, and show a similar cytotoxicity profile to AmBisome.

Antifungal therapy--state of the art at the beginning of the 21st century

The most relevant information on the present state of the art of antifungal chemotherapy is reviewed in this chapter. For dermatomycoses a variety of topical antifungals are available, and safe and efficacious systemic treatment, especially with the fungicidal drug terbinafine, is possible. The duration of treatment can be drastically reduced. Substantial progress in the armamentarium of drugs for invasive fungal infections has been made, and a new class of antifungals, echinocandins, is now in clinical use. The following drugs in oral and/or intravenous formulations are available: the broad spectrum polyene amphotericin B with its new "clothes"; the sterol biosynthesis inhibitors fluconazole, itraconazole, and voriconazole; the glucan synthase inhibitor caspofungin; and the combination partner flucytosine. New therapy schedules have been studied; combination therapy has found a significant place in the treatment of severely compromised patients, and the field of prevention and empiric therapy is fast moving. Guidelines exist nowadays for the treatment of various fungal diseases and maintenance therapy. New approaches interfering with host defenses or pathogenicity of fungal cells are being investigated, and molecular biologists are looking for new targets studying the genomics of pathogenic fungi.