Improved Oral Bioavailability and Gastrointestinal Stability of Amphotericin B through Fatty Acid Conjugation Approach

Abstract

Amphotericin B (AmB) is one of the most effective drugs used in the treatment of leishmaniasis and systemic fungal infections. Considering the global burden of leishmaniasis, ∼90% of disease cases occur in developing countries, suggestive of the need for an affordable AmB therapy. However, owing to the physicochemical properties of AmB, all the clinically available formulations must be administered by intravenous route, thereby creating a significant hurdle in patients’ access to AmB due to pharmacoeconomic considerations. We have previously demonstrated that lipid conjugation (e.g., fatty acids) to AmB significantly decreases the toxicity of resulting prodrug by a favorable alteration in the aggregation pattern. The hypothesis of the present work was to investigate the potential of the previously established AmB-lipid conjugate [AmB-oleyl conjugate (AmB-OA)] in improving the physicochemical properties such as gastric instability and lower intestinal permeability that otherwise limits the oral delivery of AmB. The synthesized AmB-OA conjugate was remarkably stable at gastric pH in contrast to AmB and exhibited significantly higher permeation across the Caco-2 monolayer (indicative of intestinal permeability). Mechanistic studies revealed that AmB-OA retained an equivalent antifungal activity. Also, AmB-OA was found to interact preferentially with intracellular membranes of Saccharomyces cerevisiae, while AmB interacted with the plasma membrane. The results of Caco-2 monolayer permeation experiments were further confirmed by in vivo pharmacokinetics, which showed that AmB-OA exhibited a 3.13-fold increase in the C max and a 4.88-fold increase in AUCTot as compared to AmB. In conclusion, the lipid conjugation approach may provide an effective solution for current challenges in designing drug delivery systems intended for oral AmB therapy.

Lipid Systems for the Delivery of Amphotericin B in Antifungal Therapy

“…Metabolism of the AmB-OA conjugate in liver homogenate was higher than 80% [162], which warrants prodrug bioconversion after oral administration. AmB-OA was stable in simulated gastric fluid (pH 1.2) and displayed enhanced permeation across the human colon adenocarcinoma (Caco-2) cell monolayer as an intestinal barrier model compared to the free drug [162]. Cytotoxicity concerns resulting from enhanced intestinal permeability were also evaluated and cell viability of Caco-2 monolayers upon exposure to AmB-OA for 3 h was found to be higher than 90% [162].…”

“…Oral administration of AmB-OA conjugate to rats (10 mg/kg in phosphate buffer saline (PBS) as gavage vehicle) resulted in significant increase in C max and AUC compared to i.v. AmB and AmB-OA admixture [162].…”

“…Further in silico studies showed that monomers in AmB-OA dimers accommodate in a head-to-head arrangement in contrast to head-to-tail arrangement in AmB dimers [161]. Moreover, AmB-OA in the aggregated state retained selectivity for ergosterol over cholesterol, which was lost in AmB aggregates [161], and in vitro antifungal activity of the parent drug was retained in the AmB-OA conjugate [162]. These results suggest that lipid conjugation can be a promising strategy for oral delivery of AmB.…”

“…Oleic acid (OA), a known skin and intestinal permeation enhancer, has been conjugated to AmB via amide bond formation with the carboxylic acid group of the drug using standard carbodiimide chemistry [161]. Metabolism of the AmB-OA conjugate in liver homogenate was higher than 80% [162], which warrants prodrug bioconversion after oral administration. AmB-OA was stable in simulated gastric fluid (pH 1.2) and displayed enhanced permeation across the human colon adenocarcinoma (Caco-2) cell monolayer as an intestinal barrier model compared to the free drug [162].…”

“…AmB-OA was stable in simulated gastric fluid (pH 1.2) and displayed enhanced permeation across the human colon adenocarcinoma (Caco-2) cell monolayer as an intestinal barrier model compared to the free drug [162]. Cytotoxicity concerns resulting from enhanced intestinal permeability were also evaluated and cell viability of Caco-2 monolayers upon exposure to AmB-OA for 3 h was found to be higher than 90% [162]. A reversible reduction in transepithelial electrical resistance (TEER) values was observed, indicating monolayer integrity retention.…”