Decreased Toxicity of Liposomal Amphotericin B Due to Association of Amphotericin B with High‐Density Lipoproteins

Abstract

Previously, we have shown that liposomal amphotericin B (L‐AmpB) composed of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) was less nephrotoxic but equally as effective as Fungizone, which consists of amphotericin (AmpB) and deoxycholate. We have also observed that AmpB predominantly associates with high‐density lipoproteins (HDL) in human serum and that the amount of AmpB associated with HDL increases when AmpB is incorporated into negatively charged liposomes. Furthermore, we observe that AmpB was less toxic in vitro to pig kidney cells when associated with HDL, but still toxic when associated with LDL. To further understand why HDL‐associated AmpB causes reduced renal toxicity, we first examined LLC PK1 cells for the presence of LDL and HDL receptors and then the cytotoxic effects of HDL‐ and LDL‐associated AmpB following trypsin treatment of LLC PK1 renal cells, which removed only the high‐affinity LDL receptors. We found that LLC PK1 renal cells expressed high‐ and low‐affinity LDL receptors but only low‐affinity HDL receptors. Furthermore, when LLC PK1 cells were treated with trypsin, HDL‐ and LDL‐associated AmpB were less toxic to the cells than was AmpB. The reduced renal cell toxicity of HDL‐associated AmpB may be due to its lack of interaction with renal cells because of the absence of HDL receptors. Since AmpB interacts with cholesteryl esters (CE) whose transfer among lipoproteins is regulated by lipid transfer protein (LTP), the role of LTP on the distribution of AmpB to HDL and LDL was next investigated. We observed that LTP facilitated the transfer of AmpB, but not L‐AmpB, from HDL to LDL. Furthermore, we found that positively and negatively charged liposomes significantly reduced LTP‐mediated transfer on CE from HDL to LDL independent of the presence of AmpB, whereas free AmpB and deoxycholate significantly CE transfer only at one concentration tested (20 μg/mL). Therefore, we believe that the decreased renal toxicity of L‐AmpB is related to its predominant distribution to HDL, which is regulated by the inhibition of LTP activity.