A nuclear magnetic resonance study of the interactions of the antimalarials chloroquine, quinacrine, quinine and mefloquine with dipalmitoylphosphatidylcholine bilayers

The antimalarial drug quinine has been shown to impair human polymorphonuclear leukocyte (PMN) functions. To gain insight into the mechanism of this phenomenon, we investigated quinine uptake by PMN with a fluorometric assay based on the fluorescence properties of this drug. After 30 min of incubation at 37°C in the presence of 1 and 10 ,ug of quinine per ml, PMN-associated quinine reached 90 6 and 780 + 150 ng/2.5 x 106 PMN, respectively, giving a cellular-to-extracellular concentration ratio of 140 to 150. A steady state was reached within 5 min. Uptake was partially dependent on temperature, cell viability, and extracellular pH. Fractionation studies showed that 30 to 40% of the PMN-associated quinine was located in the particulate fraction. The efflux of PMN-associated quinine was rapid and complete when the incubation mixture was replaced by drug-free medium. These data suggest that several mechanisms are involved in the uptake of quinine by PMN, including a viability-and energy-independent process possibly related to reversible association of quinine to cell structures (particularly the membrane). Other mechanisms could involve trapping by protonation and/or active PMN transport systems. Thus, most of the quinine taken up by resting PMN is found in the soluble fraction of disrupted cells. This may partly explain the depressive properties of quinine.Numerous data are available concerning the intracellular pharmacokinetic behavior of antibacterial agents (6,7,10,14), whereas other anti-infective agents, in particular antimalarial agents, have been little explored in this respect, with the exception of chloroquine (22,23). However, such studies are undoubtedly of interest for the following reasons. (i) They may provide a valuable pharmacokinetic parameter, since because of their large numbers leukocytes may represent an important drug reservoir. (ii) Since most antimalarial drugs depress leukocyte functions, knowledge of their possible uptake by phagocytes may provide insight into the mechanisms underlying such effects. (iii) Cell-penetrating antimalarial drugs may be useful tools for studying the mechanisms of phagocyte activation and function, as has been proposed for chloroquine (11,25). We and others (3,8,21) have previously observed that quinine, the oldest still widely used antimalarial agent, strongly depresses polymorphonuclear neutrophil (PMN) functions in vitro at concentrations (<10 ,ug/ml) relevant to those therapeutically achievable in plasma (30). Quinine was one of the first drugs found to fluoresce and is widely used as a reference standard for fluorescence assays (28); this property has also been used to study the pharmacokinetic profile of quinine after extraction or high-performance liquid chromatographic separation from biologic samples (2). We used this natural property of quinine to investigate the association of quinine with PMN. Studies conducted with other fluorescing antibacterial agents, namely quinolones (19,20), have shown that the sensitivity of this technique is similar to that ...

Section: Resultssupporting

confidence: 83%

Quinine uptake by human polymorphonuclear neutrophils

Benna

Pasquier

Labro

1991

“…There are no reports in the literature of which we are aware that have evaluated the possibility that mefloquine induces direct ionophoric effects. However, mefloquine possesses one of the key characteristics of ionophores-it is lipophilic and readily penetrates and accumulates in biological membranes (10,16,36). This effect is less marked in other aminoalcohols (quinine) and is not observed with chloroquine (36).…”

Section: Discussionmentioning

confidence: 98%

“…First, mefloquine accumulates in the CNS to levels (90 M equivalent) that exceed the threshold concentration of mefloquine required for the induction of an ionophoric effect (Table 4). Second, given the affinity of mefloquine for lipids, it is likely that much of the mefloquine in the CNS is partitioned into cell membranes (10,16,36). Finally, the nature of the histopathological changes observed suggests that mefloquine causes neuronal degeneration consistent with the necrotic ef- entry through voltage-gated channels is most likely excluded as a possible mechanism, since its profile of Ca 2ϩ entry is dissimilar to that of mefloquine.…”

Section: Discussionmentioning

confidence: 99%

“…However, mefloquine possesses one of the key characteristics of ionophores-it is lipophilic and readily penetrates and accumulates in biological membranes (10,16,36). This effect is less marked in other aminoalcohols (quinine) and is not observed with chloroquine (36). Structur- ally, these effects have been attributed to the planar shape of mefloquine (which allows membrane intercalation), the presence of an ionizable piperidinium nitrogen that may bond with anionic phosphate, H bonding between the hydroxyl group of mefloquine and H bond acceptor groups in the lipid phase, and van der Waals forces between the carbon skeleton of mefloquine and the lipid hydrocarbon chains (16).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Mefloquine-Induced Disruption of Calcium Homeostasis in Mammalian Cells Is Similar to That Induced by Ionomycin

Caridha

Yourick

Cabezas

et al. 2008

In previous studies, we have shown that mefloquine disrupts calcium homeostasis in neurons by depletion of endoplasmic reticulum (ER) stores, followed by an influx of external calcium across the plasma membrane. In this study, we explore two hypotheses concerning the mechanism(s) of action of mefloquine. First, we investigated the possibility that mefloquine activates non-N-methyl-D-aspartic acid receptors and the inositol phosphate 3 (IP3) signaling cascade leading to ER calcium release. Second, we compared the disruptive effects of mefloquine on calcium homeostasis to those of ionomycin in neuronal and nonneuronal cells. Ionomycin is known to discharge the ER calcium store (through an undefined mechanism), which induces capacitative calcium entry (CCE). In radioligand binding assays, mefloquine showed no affinity for the known binding sites of several glutamate receptor subtypes. The pattern of neuroprotection induced by a panel of glutamate receptor antagonists was dissimilar to that of mefloquine. Both mefloquine and ionomycin exhibited doserelated and qualitatively similar disruptions of calcium homeostasis in both neurons and macrophages. The influx of external calcium was blocked by the inhibitors of CCE in a dose-related fashion. Both mefloquine and ionomycin upregulated the IP3 pathway in a manner that we interpret to be secondary to CCE. Collectively, these data suggest that mefloquine does not activate glutamate receptors and that it disrupts calcium homeostasis in mammalian cells in a manner similar to that of ionomycin.Mefloquine is an antimalarial with utility for chemoprophylaxis and treatment. The drug has been associated with adverse central nervous system (CNS) effects in a dose-related manner (reviewed in reference 14). As a consequence, its continued use in an otherwise healthy population for prophylaxis is controversial. The precise etiology of mefloquine-induced adverse effects is unknown. There is clinical evidence that P glycoprotein polymorphisms are associated with adverse neurological outcomes (1). Numerous putative CNS targets have been proposed (reviewed in reference 12) in either in vitro or ex vivo contexts. Recent studies in our laboratory demonstrated mefloquine induction of brain stem histopathology consistent with direct cellular neurotoxicity in rats (12) and disruption of neuronal calcium homeostasis in vitro (14). The latter effect involves discharge of the endoplasmic reticulum (ER) calcium store and induction of a subsequent influx of calcium into the cell from the extracellular space (14). Initially we suspected that this effect might occur as a consequence of the inhibition of the thapsigargin-sensitive sarcoplasmic reticulum/ER Ca 2ϩ -ATPase (SERCA), followed by subsequent triggering of capacitative calcium entry (CCE). However, in subsequent gene expression studies, we observed that mefloquine failed to induce the downstream stress responses typical of thapsigargininduced ER calcium depletion (13). These observations suggested either that the interaction of mefloquine ...

“…It supports the notion that quinolines share FP binding as a mode of action and suggests that their differential effects on the Hb endocytic pathway may be manifestations of differences in the physiochemical properties of the individual quinoline-FP complexes. The residual endocytosis inhibition by quinoline-methanols in the presence of PIs may be due to their additional propensity to bind phospholipid membranes (3,13,23), which could disrupt the plasma membrane properties required for endocytic vesicle formation. The Hb dependence of quinoline action may potentially be explored by using erythrocyte-free parasites (15).…”

mentioning

confidence: 99%

Differential Effects of Quinoline Antimalarials on Endocytosis inPlasmodium falciparum

Roberts

Egan

Joiner

et al. 2008

The effects of quinoline antimalarials on endocytosis by Plasmodium falciparum was investigated by measuring parasite hemoglobin levels, peroxidase uptake, and transport vesicle content. Mefloquine, quinine, and halofantrine inhibited endocytosis, and chloroquine inhibited vesicle trafficking, while amodiaquine shared both effects. Protease inhibitors moderated hemoglobin perturbations, suggesting a common role for heme binding.Despite problems associated with drug resistance and side effects, quinolines remain widely used for the treatment of severe malaria and malaria prophylaxis, in artemisinin combination therapy regimens, and for the development of novel quinoline drug candidates (1,2,11,16,19). The mechanism of action of the 4-aminoquinoline chloroquine (CQ) has been extensively investigated. Intraerythrocytic malarial parasites ingest the erythrocytic cytosol by endocytosis and deliver it to the parasite food vacuole via hemoglobin (Hb) transport vesicles. Hb digestion in the vacuole releases ferriprotoporphyrin IX (FP), which is detoxified by incorporation into inert hemozoin crystals (6). CQ concentrates in the food vacuole and is thought to dimerize with FP to cause an inhibition of hemozoin formation and the lethal accumulation of toxic FP or FP-CQ complexes (5,9,14,21,22). Other quinolines have also been found to inhibit hemozoin formation in vitro at concentrations that correlate with their parasite-inhibitory concentrations (4, 5, 7-9, 13, 14), which supplies a strong argument that they share the mechanism of action of CQ and produce toxic levels of FP by disrupting hemozoin formation. This conclusion is confounded, however, by their disparate effects on the parasite Hb endocytic pathway (10). We have previously found that CQ inhibits Hb transport vesicle trafficking, with a resultant accumulation of Hb and vesicles, while mefloquine (MQ) inhibits Hb endocytosis (15). In this study, we investigated the extent to which these differential effects extend to other therapeutically relevant quinolines, i.e., quinine (Q), halofantrine (H), and amodiaquine (AQ).Early trophozoite-stage cultures of Plasmodium falciparum (strain 3D7) were incubated for 8 h with the quinolines at concentrations 5 times their 50% inhibitory concentration values, the parasites were released from the infected erythrocytes by saponin lysis, and the parasite Hb content was determined by Western blotting (15, 20) (Fig. 1A). Consistent with the notion that MQ inhibits fluid phase endocytosis in malaria parasites (10, 15), the Hb content in MQ-treated parasites was reduced by 83%. The structurally related quinoline-methanols Q and H also reduced Hb content, by 64% and 84%, respectively. By contrast, the Hb content in CQ-treated parasites increased to 283% compared to that in the untreated controls. Being a 4-aminoquinoline related to CQ, AQ was expected to act similarly (10). However, the Hb levels in AQ-treated parasites were comparable to that in the controls or slightly reduced (statistically insignificant; P ϭ 0.37). In parallel ...