In Vitro and In Vivo Evidence for Amphotericin B as a P-Glycoprotein Substrate on the Blood-Brain Barrier

Abstract

dAmphotericin B (AMB) has been a mainstay therapy for fungal infections of the central nervous system, but its use has been limited by its poor penetration into the brain, the mechanism of which remains unclear. In this study, we aimed to investigate the role of P-glycoprotein (P-gp) in AMB crossing the blood-brain barrier (BBB). The uptake of AMB by primary brain capillary endothelial cells in vitro was significantly enhanced after inhibition of P-gp by verapamil. The impact of two model P-gp inhibitors, verapamil and itraconazole, on brain/plasma ratios of AMB was examined in both uninfected CD-1 mice and those intracerebrally infected with Cryptococcus neoformans. In uninfected mice, the brain/plasma ratios of AMB were increased 15 min (3.5 versus 2.0; P < 0.05) and 30 min (5.2 versus 2.8; P < 0.05) after administration of verapamil or 45 min (6.0 versus 3.9; P < 0.05) and 60 min (5.4 versus 3.8; P < 0.05) after itraconazole administration. The increases in brain/plasma ratios were also observed in infected mice treated with AMB and P-gp inhibitors. The brain tissue fungal CFU in infected mice were significantly lower in AMB-plus-itraconazole or verapamil groups than in the untreated group (P < 0.005), but none of the treatments protected the mice from succumbing to the infection. In conclusion, we demonstrated that P-gp inhibitors can enhance the uptake of AMB through the BBB, suggesting that AMB is a P-gp substrate. Fungal infection of the central nervous system (CNS) is one of the most deadly forms of invasive fungal diseases. The most common pathogens that involve the CNS included Cryptococcus neoformans, Candida spp., and Aspergillus spp., while numerous other fungi had been reported as less common causes. New-generation triazoles with both broad antifungal spectrum and good CNS penetration, such as voriconazole and posaconazole, have expanded the choice for treatment of CNS fungal infections (1). Nonetheless, amphotericin B (AMB) remains the drug of choice for many forms of CNS fungal infection. In fact, AMB is strongly recommended for treatment of CNS cryptococcosis, histoplasmosis, blastomycosis, and mucormycosis (2). AMB plus flucytosine has demonstrated favorable efficacy in AIDS-associated cryptococcal meningitis and has been recommended as the first-line induction therapy (3). Ironically, AMB is well known for its poor ability to penetrate the blood-brain barrier (BBB), as the concentrations in the cerebrospinal fluid and brain tissue are almost undetectable (4). This has posed a dilemma to physicians dealing with CNS fungal infections using AMB, because increasing the dose of AMB in an effort to raise the CNS concentration would aggravate the severity of its multisystemic peripheral toxicities, especially nephrotoxicity.The manipulation of AMB penetration at the BBB is one strategy to improve outcome in CNS fungal infections, since the ability of antifungal drugs to achieve adequate concentrations in the CNS is one of the key factors influencing efficacy. However, despite advances in the understa...

Influence of Experimental Cryptococcal Meningitis in Wistar Rats on Voriconazole Brain Penetration Assessed by Microdialysis

“…Wu et al (26) investigated the influence of P-glycoprotein on the pharmacokinetics of amphotericin B in healthy and C. neoformans-infected mice. The brain/plasma ratios (brain data estimated from tissue homogenate) were 2.0 for healthy animals and 1.2 for infected animals, indicating that the infection reduced the drug distribution in the brain.…”

Pharmacokinetics of antifungal drugs: practical implications for optimized treatment of patients

“…After treatment with amphotericin B lipid formulations, amphotericin B target-site distribution in autopsy samples was similar to that reported after amphotericin B deoxycholate with tissue levels of ~100 µg/g in the liver and lowest concentrations in myocardium and cerebral cortex (~1 µg/g) [ 86 ]. In a preclinical study, enhanced cerebral amphotericin B uptake was achieved by exposure to P-glycoprotein (P-gp) inhibitors verapamil and itraconazole [ 87 ]. In P-gp knock-out mice, however, brain concentrations of amphotericin B were low [ 88 ].…”

Clinical Pharmacokinetics of Systemically Administered Antileishmanial Drugs

“…As described previously, miltefosine was found to be an intestinal P-gp inhibitor and AMB was reported to be a substrate for P-gp [ 129 ], although this has been contested [ 130 ]. As both miltefosine and AMB are amphiphilic molecules, AMB monomers were found to be incorporated in micellar formations of miltefosine if miltefosine is present at levels above its critical micelle concentration [ 131 ].…”