The Distribution of Nifurtimox Across the Healthy and Trypanosome-Infected Murine Blood-Brain and Blood-Cerebrospinal Fluid Barriers

Abstract

Nifurtimox, an antiparasitic drug, is used to treat American trypanosomiasis (Chagas disease) and has shown promise in treating central nervous system (CNS)-stage human African trypanosomiasis (HAT; sleeping sickness). In combination with other antiparasitic drugs, the efficacy of nifurtimox against HAT improves, although why this happens is unclear. Studying how nifurtimox crosses the blood-brain barrier (BBB) and reaches the CNS may clarify this issue and is the focus of this study. To study the interaction of nifurtimox with the blood-CNS interfaces, we used the in situ brain/choroid plexus perfusion technique in healthy and trypanosome-infected mice and the isolated incubated choroid plexus. Results revealed that nifurtimox could cross the healthy and infected blood-brain and blood-cerebrospinal fluid (CSF) barriers (K in brain parenchyma was 50.8 Ϯ 9.0 l ⅐ min Ϫ1 ⅐ g Ϫ1 ). In fact, the loss of barrier integrity associated with trypanosome infection failed to change the distribution of [ 3 H]nifurtimox to any significant extent, suggesting there is not an effective paracellular barrier for [ 3 H]nifurtimox entry into the CNS. Our studies also indicate that [ 3 H]nifurtimox is not a substrate for P-glycoprotein, an efflux transporter expressed on the luminal membrane of the BBB. However, there was evidence of [ 3 H]nifurtimox interaction with transporters at both the blood-brain and blood-CSF barriers as demonstrated by cross-competition studies with the other antitrypanosomal agents, eflornithine, suramin, melarsoprol, and pentamidine. Consequently, CNS efficacy may be improved with nifurtimox-pentamidine combinations, but over time may be reduced when nifurtimox is combined with eflornithine, suramin, or melarsoprol.

The Drugs of Sleeping Sickness: Their Mechanisms of Action and Resistance, and a Brief History

“…This was consistent with an earlier study in rats, which found that 35 S-nifurtimox is rapidly distributed throughout the host, and that both the blood-brain or placental barriers were permeable to the drug [175]. This could be the result of its lipophilicity (octanol-saline partition coefficient = 5.46 [173]), which might allow a simple diffusion across membranes. Certainly, no transporter for nifurtimox uptake has, to date, been identified, either in the host or in trypanosomes, including with RNAi library screens [171].…”

“…The accumulation of nifurtimox across the BBB was investigated by Sarah Thomas using both a murine perfusion system and an in vitro model based on immortalised human BBB cells [173,174]. Nifurtimox readily crossed the BBB and blood-CSF barriers and this was not significantly different in healthy mice or infected mice where the barrier integrity had been compromised [173]. This almost certainly means that the uptake of nifurtimox at the BBB is trans-cellular rather than paracellular (i.e., between cells).…”

“…Yet, nifurtimox, bearing a polar nitro group, is not very lipophilic, the trans-cellular uptake at the BBB is consistent with a transporter, and it has been argued that almost all drugs require a transport mechanism [176] and that absence of proof for the involvement of a transporter simply means we haven't looked well enough [177]. Moreover, Jeganathan et al reported a higher concentration of 3 H-nifurtimox in the CNS compared with plasma [173], which would be hard to explain without active import, especially since there is also a component of extrusion across the barrier (see below). Of potential importance for NECT, eflornithine reduced CNS accumulation of 3 H-nifurtimox by > 50%, presumably by interfering at the level of a transporter at the barrier [173], although that result could not be reproduced in the later study with cultured human BBB cells [174].…”

Nifurtimox Is Effective Against Neural Tumor Cells and Is Synergistic with Buthionine Sulfoximine

“…1) and the known ability of nifurtimox to penetrate the blood brain barrier2425, we pursued further studies of nifurtimox in neural tumor cell lines. In order to determine the mechanism of decreased neural tumor cell viability after treatment with nifurtimox, we performed assays for DNA ladder formation and for cleavage of PARP to establish whether nifurtimox treatment induced apoptosis.…”

“…Nifurtimox has been previously shown to penetrate the BBB in preclinical models2425, and nifurtimox has demonstrated efficacy in late stage African trypanosomiasis (African sleeping sickness), defined by the presence of active CNS infection3536. It is unclear whether the penetrability of the BBB is similar in patients with infection compared to those with malignancies.…”