Review of the mechanism underlying mefloquine-induced neurotoxicity.

Mefloquine, a potent blood schizontocide, is effective against drug-resistant Plasmodium falciparum. This property, along with its unique pharmacokinetic profile, makes mefloquine a widely prescribed antimalarial drug. However, several epidemiological studies have raised concerns on the safety of mefloquine as prophylaxis for malaria. Well-documented side-effects of mefloquine include abnormal dreams, insomnia, anxiety, and depressed mood, as well as nausea and dizziness (the last two most frequent effects). The mechanisms that underlie the neurological/psychiatric complications of mefloquine are poorly understood. The aim of this study was to review the literature on the neurotoxic mechanisms of action of mefloquine to better understand its potential toxicity in the central nervous system, highlighting the mechanisms that lead to its psychiatric disorders. Experimental studies on the neurotoxic effects of mefloquine discussed herein include brain transporters of mefloquine, alteration in neurotransmitters, disruption on calcium (Ca2+) homeostasis and neuroinflammation, generation of oxidative stress response in neurons (involving glutathione, increased F2-isoprostanes, accumulation of cytosolic lipid globules), and alteration of voltage-dependent channels, as well as gap junction intercellular communications. Although several hypotheses have been proposed for the mechanisms that mediate mefloquine-induced brain damage, they are not fully understood, necessitating additional studies in the future.

Safety assessment of MEFAS: an innovative hybrid salt of mefloquine and artesunate for malaria treatment.

Malaria is a global public health problem that causes approximately 445 000 deaths annually worldwide, especially in underdeveloped countries. Because of the high prevalence and mortality of the disease, new and less toxic therapeutic agents need to be developed, such as MEFAS, a low-cost hybrid salt that consists of artesunate and mefloquine. However, the efficacy of MEFAS has been systematically demonstrated, its safety requires further investigation. This study investigated the acute toxicity of MEFAS and its precursors, artesunate, and mefloquine. A total of 42 female Swiss mice were divided into seven groups (n = 6/group) that were treated orally by gavage with vehicle (filtered water, negative control), MEFAS (50, 500, and 1000 mg/kg), and 1:1 concentrations of artesunate + mefloquine (50, 500, and 1000 mg/kg). Clinical signs of toxicity were observed for 14 d after treatment. On day 15, the animals were weighed, deeply anesthetized with isoflurane, and euthanized for subsequent collection of the liver, spleen, and kidneys. The relative organ weights were determined, followed by histopathological analysis. Artesunate + mefloquine produced toxic effects compared with the negative control group, reflected by changes in clinical signs, relative organ weights, and histopathological alterations. In MEFAS-treated animals, no changes were observed compared with the negative control group. These findings demonstrate that MEFAS is safer than artesunate + mefloquine after acute administration in mice.

Modulation of the transient outward current (Ito) in rat cardiac myocytes and human Kv4.3 channels by mefloquine.

The antimalarial drug mefloquine, is known to be a potassium channel blocker, although its mechanism of action has not being elucidated and its effects on the transient outward current (Ito) and the molecular correlate, the Kv4.3 channel has not being studied. Here, we describe the mefloquine-induced inhibition of the rat ventricular Ito and of CHO cells co-transfected with human Kv4.3 and its accessory subunit hKChIP2C by whole-cell voltage-clamp. Mefloquine inhibited rat Ito and hKv4.3+KChIP2C currents in a concentration-dependent manner with a limited voltage dependence and similar potencies (IC50=8.9µM and 10.5µM for cardiac myocytes and Kv4.3 channels, respectively). In addition, mefloquine did not affect the activation of either current but significantly modified the hKv4.3 steady-state inactivation and recovery from inactivation. The effects of this drug was compared with that of 4-aminopyridine (4-AP), a well-known potassium channel blocker and its binding site does not seem to overlap with that of 4-AP.

Influence of mefloquine administration during early pregnancy on rat embryonic development.

Mefloquine (MQ) is a potent effective antimalarial drug against multiple drug-resistant Plasmodium falciparum. It has been proved that MQ can be given safely during the second and third trimesters. However, there is very limited information on the drug safety during the first trimester. The aim of the present work was to investigate the embryotoxicity and teratogenicity of MQ during critical periods of early development. Wistar rats were orally administered with a single dose of MQ (45 mg/kg bwt or 187 mg/kg bwt) on the 1st, 6th or 13th days of pregnancy. Cyclophosphamide (CPA) was chosen as a positive control. On the 21st day of gestation, standard parameters of reproductive performance and fetal examination were estimated. Malondialdehyde (MDA) level, glutathione reductase activity and glutathione (GSH) content were evaluated in placenta and liver homogenates of mothers and fetuses. The results indicated that MQ did not adversely affect the number of implantation, resorption, litter size and fetal body weight and length. Only groups treated with MQ on the 1st day of gestation exhibited significant decrease in fetal body weight. Examination of fetuses for external, visceral and skeletal changes showed minimal variations involving extension of lateral brain ventricles and renal pelvis and signs of delayed ossification. These variations were accompanied with significant elevation of MDA level and reduction of GSH content of fetal liver. Prenatal exposure to MQ at early pregnancy did not cause any embryolethal or teratogenic effect. It could slightly exacerbate minor variations.

Cellular targets of mefloquine.

Mefloquine is a quinoline-based compound widely used as an antimalarial drug, particularly in chemoprophylaxis. Although decades of research have identified various aspects of mefloquine's anti-Plasmodium properties, toxic effects offset its robust use in humans. Mefloquine exerts harmful effects in several types of human cells by targeting many of the cellular lipids, proteins, and complexes, thereby blocking a number of downstream signaling cascades. In general, mefloquine modulates several cellular phenomena, such as alteration of membrane potential, induction of oxidative stress, imbalance of ion homeostasis, disruption of metabolism, failure of organelle function, etc., leading to cell cycle arrest and programmed cell death. This review aims to summarize the information on functional and mechanistic findings related to the cytotoxic effects of mefloquine.

Anti-malarial activity of a non-piperidine library of next-generation quinoline methanols.

BACKGROUND: The clinical utility for mefloquine has been eroded due to its association with adverse neurological effects. Better-tolerated alternatives are required. The objective of the present study was the identification of lead compounds that are as effective as mefloquine, but exhibit physiochemical properties likely to render them less susceptible to passage across the blood-brain barrier. METHODS: A library of drug-like non-piperidine analogs of mefloquine was synthesized. These compounds are diverse in structure and physiochemical properties. They were screened in appropriate in vitro assays and evaluated in terms of their potential as lead compounds. The correlation of specific structural attributes and physiochemical properties with activity was assessed. RESULTS: The most potent analogs were low molecular weight unconjugated secondary amines with no heteroatoms in their side-chains. However, these compounds were more metabolically labile and permeable than mefloquine. In terms of physiochemical properties, lower polar surface area, lower molecular weight, more freely rotatable bonds and fewer H-bond acceptors were associated with greater potency. There was no such relationship between activity and LogP, LogD or the number of hydrogen bond donors (HBDs). The addition of an H-bond donor to the side-chain yielded a series of active diamines, which were as metabolically stable as mefloquine but showed reduced permeability. CONCLUSIONS: A drug-like library of non-piperidine analogs of mefloquine was synthesized. From amongst this library an active lead series of less permeable, but metabolically stable, diamines was identified.

Mefloquine binding to human acyl-CoA binding protein leads to redox stress-mediated apoptotic death of human neuroblastoma cells.

Malaria is an infectious disease that is caused by different species of Plasmodium. Several antimalarial drugs are used to counter the spread and infectivity of Plasmodium species. However, humans are also vulnerable to many of the antimalarial drugs, including the quinoline-based drugs. In particular, the antimalarial mefloquine has been reported to show adverse neuropsychiatric effects in humans. Though mefloquine is known to be neurotoxic, the molecular mechanisms associated with this phenomenon are still obscure. In this study, we show that mefloquine binds to and inactivates the human acyl-CoA binding protein (hACBP), potentially inducing redox stress in human neuroblastoma cells (IMR-32). Mefloquine occupies the acyl-CoA binding pocket of hACBP by interacting with several of the critical acyl-CoA binding amino acids. This leads to the competitive inhibition of acyl-CoA(s) binding to hACBP and to the accumulation of lipid droplets inside the IMR-32 cells. The accumulation of cytosolic lipid globules and oxidative stress finally correlates with the apoptotic death of cells. Taken together, our study deciphers a mechanistic detail of how mefloquine leads to the death of human cells by perturbing the activity of hACBP and lipid homeostasis.

Some Ototoxic Drugs Destroy Cochlear Support Cells Before Damaging Sensory Hair Cells.

A wide variety of ototoxic drugs are capable of damaging the sensory hair cells in the mammalian cochlea resulting in permanent hearing loss. However, the toxic properties of these drugs suggest that some could potentially damage cochlear support cells as well. To test the hypothesis, we treated postnatal day three rat cochlear cultures with toxic doses of gentamicin, cisplatin, mefloquine, and cadmium. Gentamicin primarily destroyed the hair cells and disrupted the intercellular connection with the surrounding support cells. Gentamicin-induced hair cell death was initiated through the caspase-9 intrinsic apoptotic pathway followed by activation of downstream executioner caspase-3. In contrast, cisplatin, mefloquine, and cadmium initially damaged the support cells and only later damaged the hair cells. Support cell death was initiated through the caspase-8 extrinsic apoptotic pathway followed later by downstream activation of caspase-3. Cisplatin, mefloquine, and cadmium significantly reduced the expression of actin and laminin, in the extracellular matrix, leading to significant disarray of the sensory epithelium.

Distinct patterns of gene and protein expression elicited by organophosphorus pesticides in Caenorhabditis elegans.

BACKGROUND: The wide use of organophosphorus (OP) pesticides makes them an important public health concern. Persistent effects of exposure and the mechanism of neuronal degeneration are continuing issues in OP toxicology. To elucidate early steps in the mechanisms of OP toxicity, we studied alterations in global gene and protein expression in Caenorhabditis elegans exposed to OPs using microarrays and mass spectrometry. We tested two structurally distinct OPs (dichlorvos and fenamiphos) and employed a mechanistically different third neurotoxicant, mefloquine, as an out-group for analysis. Treatment levels used concentrations of chemical sufficient to prevent the development of 10%, 50% or 90% of mid-vulval L4 larvae into early gravid adults (EGA) at 24 h after exposure in a defined, bacteria-free medium. RESULTS: After 8 h of exposure, the expression of 87 genes responded specifically to OP treatment. The abundance of 34 proteins also changed in OP-exposed worms. Many of the genes and proteins affected by the OPs are expressed in neuronal and muscle tissues and are involved in lipid metabolism, cell adhesion, apoptosis/cell death, and detoxification. Twenty-two genes were differentially affected by the two OPs; a large proportion of these genes encode cytochrome P450s, UDP-glucuronosyl/UDP-glucosyltransferases, or P-glycoproteins. The abundance of transcripts and the proteins they encode were well correlated. CONCLUSION: Exposure to OPs elicits a pattern of changes in gene expression in exposed worms distinct from that of the unrelated neurotoxicant, mefloquine. The functional roles and the tissue location of the genes and proteins whose expression is modulated in response to exposure is consistent with the known effects of OPs, including damage to muscle due to persistent hypercontraction, neuronal cell death, and phase I and phase II detoxification. Further, the two different OPs evoked distinguishable changes in gene expression; about half the differences are in genes involved in detoxification, likely reflecting differences in the chemical structure of the two OPs. Changes in the expression of a number of sequences of unknown function were also discovered, and these molecules could provide insight into novel mechanisms of OP toxicity or adaptation in future studies.

Synthesis and biological evaluation of the first pentafluorosulfanyl analogs of mefloquine.

Two novel SF5 analogs of the antimalarial agent mefloquine were synthesized in 5 steps and 10-23% overall yields and found to have improved activity and selectivity against malaria parasites. This work also represents the first report of SF5-substituted quinolines.

Synthesis, antimalarial activity, and intracellular targets of MEFAS, a new hybrid compound derived from mefloquine and artesunate.

A new synthetic antimalarial drug, a salt derived from two antimalarial molecules, mefloquine (MQ) and artesunate (AS), here named MEFAS, has been tested for its pharmacological activity. Combinations of AS plus MQ hydrochloride are currently being used in areas with drug-resistant Plasmodium falciparum parasites; although AS clears parasitemia in shorter time periods than any other antimalarial drug, it does not cure infected patients; in addition, MQ causes side effects and is rather expensive, important problems considering that malaria affects mostly populations in poor countries. Here, we show that MEFAS is more effective than the combination of AS and MQ, tested in parallel at different mass proportions, against P. falciparum (chloroquine-resistant clone W2 and chloroquine-sensitive clone 3D7) in vitro and in mice infected with Plasmodium berghei, promoting cure of this infection. MEFAS tested against HepG2 hepatoma cells exhibited lower toxicity than the antimalarials AS and MQ alone or combined. Possible targets of MEFAS have been studied by confocal microscopy using fluorescent probes (Fluo-4 AM and BCECF-AM) in P. falciparum synchronous culture of W2-infected red blood cells. Dynamic images show that MEFAS exhibited intracellular action increasing cytoplasmic Ca(2+) at 1.0 ng/ml. This effect was also observed in the presence of tapsigargin, an inhibitor of SERCA, suggesting an intracellular target distinct from the endoplasmic reticulum. Trophozoites loaded with BCECF-AM, when treated with MEFAS, were still able to mobilize protons from the digestive vacuole (DV), altering the pH gradient. However, in the presence of bafilomycin A1, an inhibitor of the H(+) pump from acidic compartments of eukaryotic cells, MEFAS had no action on the DV. In conclusion, the endoplasmic reticulum and DV are intracellular targets for MEFAS in Plasmodium sp., suggesting two modes of action of this new salt. Our data support MEFAS as a candidate for treating human malaria.

Synthesis and Antimalarial Activity of New Enantiopure Aminoalcoholpyrrolo[ 1,2-a]quinoxalines.

BACKGROUND: We prepared a novel series of enantiopure mefloquine analogues with pyrrolo[ 1,2-a]quinoxaline core in order to fight Plasmodium falciparum resistant strain. OBJECTIVES: To observe the influence of pyrrolo[1,2-a]quinoxaline core versus quinoline core on the antimalarial activity. METHOD: Four enantiopure aminoalcoholpyrrolo[1,2-a]quinoxalines 2 were synthetized via Sharpless asymmetric dihydroxylation reaction in eight steps. Their antimalarial activity was evaluated on two Plasmodium falciparum strains 3D7 and W2 with a SYBR Green I fluorescence-based method and their cytotoxicity was measured on four cell lines HepG2, THP-1, CHO and HFF. RESULTS: IC50 values of the four compounds 2 were close to the micromolar against the two P. falciparum strains. They were more active against P. falciparum strain W2 vs. P. falciparum strain 3D7. (R)- enantiomers were always more active than their (S)-counterpart whatever the strain. Selectivity indexes of compounds 2 were lower than 100. CONCLUSION: A novel series of enantiopure aminoalcohols with pyrrolo[1,2-a]quinoxaline core were synthesized in eight steps. They displayed IC50 values close to the micromolar against two P. falciparum strains 3D7 and W2. Although, In this series, 2,8-bistrifluoromethylquinoline was a best core than pyrrolo[1,2-a]quinoxaline for an optimal antimalarial activity, the pyrroloquinoxaline 2b showed an interesting antimalarial activity.

Mefloquine in the nucleus accumbens promotes social avoidance and anxiety-like behavior in mice.

Mefloquine continues to be a key drug used for malaria chemoprophylaxis and treatment, despite reports of adverse events like depression and anxiety. It is unknown how mefloquine acts within the central nervous system to cause depression and anxiety or why some individuals are more vulnerable. We show that intraperitoneal injection of mefloquine in mice, when coupled to subthreshold social defeat stress, is sufficient to produce depression-like social avoidance behavior. Direct infusion of mefloquine into the nucleus accumbens (NAc), a key brain reward region, increased stress-induced social avoidance and anxiety behavior. In contrast, infusion into the ventral hippocampus had no effect. Whole cell recordings from NAc medium spiny neurons indicated that mefloquine application increases the frequency of spontaneous excitatory postsynaptic currents, a synaptic adaptation that we have previously shown to be associated with increased susceptibility to social defeat stress. Together, these data demonstrate a role for the NAc in mefloquine-induced depression and anxiety-like behaviors.

A small-fish model for behavioral-toxicological screening of new antimalarial drugs: a comparison between erythro- and threo-mefloquine.

BACKGROUND: New antimalarial drugs need to be developed because over time resistance against the existing drugs develops. Furthermore, some of the drugs have severe side effects. Here we describe a behavioral small-fish model for early detection of neurotoxic effects of new drugs. As case example we compare the effects of two mefloquine diastereomers on the behavior of goldfish using an automated 3D tracking system. FINDINGS: In a preliminary experiment, the overall toxic effects in terms of motor and respiratory impairments were determined during a 3-hour exposure to the drugs at relatively high doses (21.5 and 43 mgL). In the second experiment, behavioral testing was performed 24 h after a 3.5-h drug exposure to a low dose (14.25 mgL) of either drug. For the two high doses, erythro-mefloquine resulted in severe motor problems and respiratory problems occurred. In goldfish treated with threo-mefloquine, at 43 mgL the motor/respiratory impairments were less severe and at 21.5 mgL no such problems were observed. For the lower dose (14.25 mgL), erythro-mefloquine reduced locomotion. There was also a tendency for increased freezing, and the preference for quadrant two of the observation container was increased. No behavioral effects of threo-mefloquine were found. CONCLUSIONS: The results demonstrate that in goldfish exposed to the drugs dissolved in the water, threo-mefloquine has less severe toxic effects as compared to erythro-mefloquine. These findings are consistent with other studies and support the usefulness of the small-fish model for predicting adverse effects of new antimalarial drugs during the initial phases of drug development.

Photophysical and photobiological behavior of antimalarial drugs in aqueous solutions.

This article describes the results of a combined photophysical and photobiological study aimed at understanding the phototoxicity mechanism of the antimalarial drugs quinine (Q), quinacrine (QC) and mefloquine (MQ). Photophysical experiments were carried out in aqueous solutions by stationary and time-resolved fluorimetry and by laser flash photolysis to obtain information on the various decay pathways of the excited states of the drugs and on transient species formed on irradiation. The results obtained showed that fluorescence and intersystem crossing account for all the adsorbed quanta for Q and MQ (quantum yield of about 0.1 and 0.9, respectively) and only for 24% in the case of QC, which has a negligible fluorescence quantum yield (0.001). Laser flash photolysis experiments evidenced, for QC and MQ, the occurrence of photoionization processes leading to the formation of the radical cations of the drugs. The effects of tryptophan and histidine on the excited states and transient species of the three drugs were also investigated. In parallel, the photoactivity of the antimalarial drugs was investigated under UV irradiation on various biological targets through a series of in vitro assays in the presence and in the absence of oxygen. Phototoxicity on 3T3 cultured fibroblasts and lipid photoperoxidation were observed for all the drugs. The photodamage produced by the drugs was also evaluated on proteins by measuring the photosensitized cross-linking of spectrin. The combined approaches were proven to be useful for understanding the mechanism of phototoxicity induced by the antimalarial drugs.

Assessment of interactions of the antimalarial drugs chloroquine and mefloquine with NaNO2 and HgCl2 in rodents.

Chloroquine and mefloquine are antimalarial drugs widely used in Brazil, especially in prospecting areas in the Amazonian region, where they may be associated with other compounds suspected to be genotoxic. Mefloquine was tested at doses of 150, 300, 600 and 1200 mg/kg body weight on Wistar rats and the animals were killed 6, 12 and 24 h later. No significant increase in chromatid gaps or breaks was induced by any of the treatments. The drugs were associated with NaNO2 and HgCl2, and a slight induction of chromatid aberration frequencies occurred with NaNO2, particularly when associated with chloroquine. The HgCl2 did not show clastogenic activity in bone marrow cells of Wistar rats or induce micronuclei in BALB/c mice. The association of chloroquine and mefloquine did not induce any clastogenic effect.

Effects of the combined artesunate and mefloquine antimalarial drugs on rat embryos.

Artemisinins combination therapy (ACT) is the first choice therapy for falciparum malaria. Data on the safety of ACTs in pregnancy are limited and controversial and the use is not recommended on the first trimester. To evaluate the effects of isolated and combined artesunate (AS)/mefloquine (MQ) on embryo rats, pregnant rats were treated orally with AS (15 and 40 mg/kg body weight (bwt)/day), MQ (30 and 80 mg/kg bwt/day) and AS/MQ (15/30 and 40/80 mg/kg bwt/day) on days 9-11 post coitum (pc). The dams were euthanized on day 12 pc and gestational and embryos histological parameters were evaluated. Embryolethality and histopathological anomalies were significant when AS was given alone or combined with MQ. Combination of AS and MQ did not enhance their toxicity compared to their separate administrations; on the other side, there was a reduction in the toxic effects of the AS when combined with MQ. Isolated MQ did not induce developmental toxicity.

Psychiatric side effects of mefloquine: applications to forensic psychiatry.

Mefloquine (previously marketed in the United States as Lariam®) is an antimalarial medication with potent psychotropic potential. Severe psychiatric side effects due to mefloquine intoxication are well documented, including anxiety, panic attacks, paranoia, persecutory delusions, dissociative psychosis, and anterograde amnesia. Exposure to the drug has been associated with acts of violence and suicide. In this article, we discuss the history of mefloquine use and describe plausible mechanisms of its psychotropic action. Mefloquine intoxication has not yet been successfully advanced in legal proceedings as a defense or as a mitigating factor, but it appears likely that it eventually will be. Considerations for the application of claims of mefloquine intoxication in forensic settings are discussed.

Study on the developmental toxicity of combined artesunate and mefloquine antimalarial drugs on rats.

Antimalarial drug combinations containing artemisinins (ACTs) have become first choice therapies for Plasmodium falciparum malaria. Data on safety of ACTs in pregnancy are limited and no previous study has been conducted on the developmental toxicity of artesunate-mefloquine combinations on the first trimester of gestation. To evaluate the developmental toxicity of an artesunate/mefloquine combination, pregnant rats were treated orally with artesunate (15 and 40 mg/kg bwt/day), mefloquine (30 and 80 mg/kg bwt/day) and artesunate/mefloquine (15/30 and 40/80 mg/kg bwt/day) on gestation days 9-11. Dams were C-sectioned on day 20, and their uteri and fetuses removed and examined for soft tissue and skeleton abnormalities. Artesunate increased embryolethality and the incidence of limb long bone malformations on the absence of overt maternal toxicity. Mefloquine (80 mg/kg bwt/day) was maternally toxic and enhanced fetal variations. Combination of artesunate and mefloquine did not enhance their toxicity compared to the toxicity observed after its separate administration. Embryotoxicity of artesunate was apparently attenuated when it is co-administered with mefloquine.

Mefloquine neurotoxicity is mediated by non-receptor tyrosine kinase.

Among several available antimalarial drugs, mefloquine has proven to be effective against drug-resistant Plasmodium falciparum and remains the drug of choice for both therapy and chemoprophylaxis. However, mefloquine is known to cause adverse neurological and/or psychiatric symptoms, which offset its therapeutic advantage. The exact mechanisms leading to the adverse neurological effects of mefloquine are poorly defined. Alterations in neurotransmitter release and calcium homeostasis, the inhibition of cholinesterases and the interaction with adenosine A(2A) receptors have been hypothesized to play prominent roles in mediating the deleterious effects of this drug. Our recent data have established that mefloquine can also trigger oxidative damage and subsequent neurodegeneration in rat cortical primary neurons. Furthermore, we have utilized a system biology-centered approach and have constructed a pathway model of cellular responses to mefloquine, identifying non-receptor tyrosine kinase 2 (Pyk2) as a critical target in mediating mefloquine neurotoxicity. In this study, we sought to establish an experimental validation of Pyk2 using gene-silencing techniques (siRNA). We have examined whether the downregulation of Pyk2 in primary rat cortical neurons alters mefloquine neurotoxicity by evaluating cell viability, apoptosis and oxidative stress. Results from our study have confirmed that mefloquine neurotoxicity is associated with apoptotic response and oxidative injury, and we have demonstrated that mefloquine affects primary rat cortical neurons, at least in part, via Pyk2. The implication of these findings may prove beneficial in suppressing the neurological side effects of mefloquine and developing effective therapeutic modalities to offset its adverse effects.