Mefloquine induces dose-related neurological effects in a rat model

Antiepileptogenic and neuroprotective effect of mefloquine after experimental status epilepticus

Acquired temporal lobe epilepsy (TLE) characterized by spontaneous recurrent seizures (SRS) and hippocampal inhibitory neuron dysfunction is often refractory to current therapies. Gap junctional or electrical coupling between inhibitory neurons has been proposed to facilitate network synchrony and intercellular molecular exchange suggesting a role in both seizures and neurodegeneration. While gap junction blockers can limit acute seizures, whether blocking neuronal gap junctions can modify development of chronic epilepsy has not been examined. This study examined whether mefloquine, a selective blocker of Connexin 36 gap junctions which are well characterized in inhibitory neurons, can limit epileptogenesis and related cellular and behavioral pathology in a model of acquired TLE. A single, systemic dose of mefloquine administered early after pilocarpine-induced status epilepticus (SE) in rat reduced both development of SRS and behavioral co-morbidities. Immunostaining for interneuron subtypes identified that mefloquine treatment likely reduced delayed inhibitory neuronal loss after SE. Uniquely, parvalbumin expressing neurons in the hippocampal dentate gyrus appeared relatively resistant to early cell loss after SE. Functionally, whole cell patch clamp recordings revealed that mefloquine treatment preserved inhibitory synaptic drive to projection neurons one week and one month after SE. These results demonstrate that mefloquine, a drug already approved for malaria prophylaxis, is potentially antiepileptogenic and can protect against progressive interneuron loss and behavioral co-morbidities of epilepsy.

Mefloquine-Induced Inner Ear Damage and Preventive Effects of Electrical Stimulation: An Electrophysiological Study

INTRODUCTION

Mefloquine is an antimalarial medicine used to prevent and treat malaria. This medicine has some side effects, including ototoxicity. This study, which was designed in two phases, aimed to investigate the side effects of mefloquine and evaluate the preventive effects of electrical stimulation on these side effects.

METHODS

In the first phase, two doses of mefloquine (50 and 200 μM) were injected into male rats, and after 7 days, they were evaluated by an auditory brainstem response (ABR) test. In the second phase, electrical stimulation was applied for 10 days, and then a toxic dose of mefloquine was injected. Similar to the first phase of the study, the animals were evaluated by an ABR test after 7 days.

RESULTS

In the first phase, the results showed that a high dose of mefloquine increased the ABR threshold and wave I latency; however, these changes were not observed in the second phase.

CONCLUSION

Application of electrical stimulation could prevent the ototoxic effects of mefloquine. According to the findings of the present study, electrical stimulation can be used as a preconditioner to prevent the ototoxic effects of mefloquine.

Ligand-Based Virtual Screening, Molecular Docking, and Molecular Dynamic Simulations of New β-Estrogen Receptor Activators with Potential for Pharmacological Obesity Treatment

Obesity is a pandemic and a serious health problem in developed and undeveloped countries. Activation of estrogen receptor beta (ERβ) has been shown to promote weight loss without modifying caloric intake, making it an attractive target for developing new drugs against obesity. This work aimed to predict new small molecules as potential ERβ activators. A ligand-based virtual screening of the ZINC15, PubChem, and Molport databases by substructure and similarity was carried out using the three-dimensional organization of known ligands as a reference. A molecular docking screening of FDA-approved drugs was also conducted as a repositioning strategy. Finally, selected compounds were evaluated by molecular dynamic simulations. Compounds 1 (-24.27 ± 0.34 kcal/mol), 2 (-23.33 ± 0.3 kcal/mol), and 6 (-29.55 ± 0.51 kcal/mol) showed the best stability on the active site in complex with ERβ with an RMSD < 3.3 Å. RMSF analysis showed that these compounds do not affect the fluctuation of the Cα of ERβ nor the compactness according to the radius of gyration. Finally, an in silico evaluation of ADMET showed they are safe molecules. These results suggest that new ERβ ligands could be promising molecules for obesity control.

Suspected Mefloquine Toxicity in a Colony of Humboldt Penguins (Spheniscus humboldti)

Avian malaria is an important cause of mortality in captive penguins housed in outdoor exhibits. Mefloquine was used as a prophylaxis to treat a colony of 19 Humboldt penguins (Spheniscus humboldti) for avian malaria. A target dose of 30 mg/kg was obtained from anecdotal literature for sphenisciforms that was not based on pharmacokinetic or toxicity studies. For this reason, preliminary plasma concentrations of mefloquine were acquired after the first dose in some penguins to ensure that plasma concentrations reached human malaria prophylactic concentrations. Afterward, each penguin in the entire colony received mefloquine (26-31 mg/kg [125 mg in toto] PO q7d). Regurgitation was frequently observed starting after the fourth weekly administration. Plasma concentrations of mefloquine after the seventh dose showed elevated concentrations, and the treatment was immediately terminated. Eight penguins died during and after the treatment period. The first fatality occurred after the fifth weekly administration, and 7 birds died within 7-52 days after the seventh weekly administration. Three penguins were found dead without previous symptoms. The other five presented with marked lethargy, dyspnea, poor appetite, and vomiting, and all died despite medical care. The remaining 11 penguins of the colony survived without any supportive care; 5 did not exhibit any clinical disease signs, while the other 6 showed a mild apathy and decreased appetite. Mefloquine toxicity was highly suspected on the basis of clinical signs, the elevated mefloquine plasma concentrations, and no other underlying pathologic disease conditions identified through postmortem examinations. Nonspecific lesions, including pulmonary congestion and edema and hepatic perivascular hematopoiesis, were noted in the birds that died. Additionally, 1 case presented with myocarditis, and mycobacteria were observed within granulomas in the respiratory tract of 2 penguins. Caution is advised, and further studies are encouraged before administering mefloquine to penguins.

Differential Stabilities of Mefloquine-Bound Human and Plasmodium falciparum Acyl-CoA-Binding Proteins

Toxic effects of pharmacological drugs restrict their robust application against human diseases. Although used as a drug in the combinatorial therapy to treat malaria, the use of mefloquine is not highly recommended because of its adverse effects in humans. Mefloquine inhibits the binding of acyl-CoAs to acyl-CoA-binding proteins of Plasmodium falciparum (PfACBPs) and human (hACBP). In this study, we have used molecular dynamics simulation and other computational approaches to investigate the differences of stabilities of mefloquine-PfACBP749 and mefloquine-hACBP complexes. The stability of mefloquine in the binding cavity of PfACBP749 is less than its stability in the binding pocket of hACBP. Although the essential tyrosine residues (tyrosine-30 and tyrosine-33 of PfACBP749 and tyrosine-29 and tyrosine-32 of hACBP) mediate the initial binding of mefloquine to the proteins by π-stacking interactions, additional temporally longer interactions between mefloquine and aspartate-22 and methionine-25 of hACBP result in stronger binding of mefloquine to hACBP. The higher fluctuation of mefloquine-binding residues of PfACBP749 contributes to the instability of mefloquine in the binding cavity of the protein. On the contrary, in the mefloquine-bound state, the stability of hACBP protein is less than the stability of PfACBP749. The helix-to-coil transition of the N-terminal hydrophobic region of hACBP has a destabilizing effect upon the protein's structure. This causes the induction of aggregation properties in the hACBP in the mefloquine-bound state. Taken together, we describe the mechanistic features that affect the differential dynamic stabilities of mefloquine-bound PfACBP749 and hACBP proteins.

Pentamidine sensitizes FDA-approved non-antibiotics for the inhibition of multidrug-resistant Gram-negative pathogens

Pentamidine sensitizes FDA-approved antibiotics to combat Gram-negative pathogens. We screened 1374 FDA-approved non-antibiotics for their ability to be sensitized by pentamidine against Escherichia coli. We identified mitomycin C and mefloquine as potent hits effective against multiple drug-resistant, Gram-negative bacteria. Killing kinetics and an in vivo model with Caenorhabditis elegans (C. elegans) revealed that such combinations produced synergy against colistin-resistant Enterobacter cloacae (E. cloacae). These findings suggest combinations of FDA-approved non-antibiotics, and pentamidine can be repurposed into new antimicrobial agents.

Neurological and psychiatric safety of tafenoquine in Plasmodium vivax relapse prevention: a review

BACKGROUND

Tafenoquine is an 8-aminoquinoline anti-malarial drug recently approved as a single-dose (300 mg) therapy for Plasmodium vivax relapse prevention, when co-administered with 3-days of chloroquine or other blood schizonticide. Tafenoquine 200 mg weekly after a loading dose is also approved as travellers' prophylaxis. The development of tafenoquine has been conducted over many years, using various dosing regimens in diverse populations.

METHODS

This review brings together all the preclinical and clinical data concerning tafenoquine central nervous system safety. Data were assembled from published sources. The risk of neuropsychiatric adverse events (NPAEs) with single-dose tafenoquine (300 mg) in combination with chloroquine to achieve P. vivax relapse prevention is particularly examined.

RESULTS

There was no evidence of neurotoxicity with tafenoquine in preclinical animal models. In clinical studies in P. vivax relapse prevention, nervous system adverse events, mainly headache and dizziness, occurred in 11.4% (36/317) of patients with tafenoquine (300 mg)/chloroquine versus 10.2% (19/187) with placebo/chloroquine; and in 15.5% (75/483) of patients with tafenoquine/chloroquine versus 13.3% (35/264) with primaquine (15 mg/day for 14 days)/chloroquine. Psychiatric adverse events, mainly insomnia, occurred in 3.8% (12/317) of patients with tafenoquine/chloroquine versus 2.7% (5/187) with placebo/chloroquine; and in 2.9% (14/483) of patients with tafenoquine/chloroquine versus 3.4% (9/264) for primaquine/chloroquine. There were no serious or severe NPAEs observed with tafenoquine (300 mg)/chloroquine in these studies.

CONCLUSIONS

The risk:benefit of single-dose tafenoquine/chloroquine in P. vivax relapse prevention is favourable in the presence of malaria, with a low risk of NPAEs, similar to that seen with chloroquine alone or primaquine/chloroquine.

Approval of Tafenoquine for Malaria Chemoprophylaxis

Malaria chemoprophylaxis has become increasingly prominent now that it is used for vulnerable populations in endemic regions in addition to nonimmune travelers to those regions. The objective would be a drug with > 95% efficacy and that is easily tolerated, including in children and pregnant women. For individuals who prefer weekly rather than daily drug administration, a further objective is a product that is administered weekly. The deficiencies of present agents are parasite resistance to chloroquine, neuropsychiatric liability of mefloquine, the need for daily dosing for atovaquone-proguanil, and daily dosing plus adverse reactions for doxycycline. A primaquine analogue, tafenoquine, has a 17-day half-life and was approved for weekly prophylaxis in the United States and in Australia in 2018. Weekly tafenoquine was equal to mefloquine in efficacy in nonimmunes. The tafenoquine label contains a contraindication for preexisting psychosis, but not for the broad number of other neuropsychiatric disorders which are listed as contraindications in the mefloquine label. As an 8-aminoquinoline, tafenoquine is contraindicated for glucose-6-phosphate dehydrogenase (G6PD)-deficient persons or in pregnancy if the fetus might be G6PD deficient. Other possible significant adverse reactions for tafenoquine are declines in hemoglobin levels reported in some G6PD-normal patients, asymptomatic elevations in methemoglobin, and minor psychiatric events. The lack of broad neuropsychiatric adverse reactions suggests that tafenoquine may have a role as the weekly prophylactic of choice for G6PD-normal persons.

Characterization of Lipid Binding Properties of Plasmodium falciparum Acyl-Coenzyme A Binding Proteins and Their Competitive Inhibition by Mefloquine

Malaria remains a worldwide concern in terms of morbidity and mortality. Limited understanding of the Plasmodium proteome makes it challenging to control malaria. Understanding of the expression and functions of different Plasmodium proteins will help in knowing this organism's virulence properties, besides facilitating the drug development process. In this study, we characterize the lipid binding and biophysical properties of the putative Plasmodium falciparum acyl-CoA binding proteins (PfACBPs), which may have intriguing functions in different stages of P. falciparum life cycle. While the PfACBPs can bind to long-chain fatty acyl-CoAs with high affinity, their affinity for short-chain fatty acyl-CoAs is weak. Base-stacking, electrostatic, and hydrophobic interactions between the aromatic rings, charged groups or residues, and hydrophobic chains or residues are responsible for acyl-CoA binding to PfACBPs. PfACBPs can also bind to phospholipids. PfACBPs cannot bind to the fatty acids and unphosphorylated fatty acid esters. PfACBPs are globular-helical proteins that contain a conserved acyl-CoA binding region. They exist in folded or unfolded conformations without attaining any intermediate state. In a systematic high-throughput in silico screening, mefloquine is identified as a potential ligand of PfACBPs. Binding affinities of mefloquine are much higher than those of fatty acyl-CoAs for all PfACBPs. Mefloquine binds to the acyl-CoA binding pocket of PfACBPs, thereby engaging many of the critical residues. Thus, mefloquine acts as a competitive inhibitor against fatty acyl-CoA binding to PfACBPs, leading to the prevention of P. falciparum growth and proliferation. Taken together, our study characterizes the functions of annotated PfACBPs and highlights the mechanistic details of their inactivation by mefloquine.

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.

Tafenoquine and primaquine do not exhibit clinical neurologic signs associated with central nervous system lesions in the same manner as earlier 8-aminoquinolines

BACKGROUND

Tafenoquine was recently approved for Plasmodium vivax radical cure (KRINTAFEL™) and malaria prevention (ARAKODA™).

METHODS

A review of the non-clinical and clinical literature was conducted to assess whether tafenoquine (and primaquine) exhibit the same neurologic lesions and associated clinical signs as earlier 8-aminoquinolines, as has been alleged in recent opinion pieces.

RESULTS

Plasmocid, pamaquine and pentaquine damage specific neuro-anatomical structures in Rhesus monkeys and humans leading to corresponding deficits in neurologic function. Neurologic therapeutic indices for these 3 drugs calculated based on monkey data were well correlated with human data. Despite 60 years of use, there is no evidence that primaquine exhibits similar neurotoxicity in humans.

DISCUSSION/CONCLUSIONS

Extrapolation of data from Rhesus monkeys to humans, and the available clinical data, suggest that tafenoquine also does not exhibit pamaquine, pentaquine or plasmocid-like clinical neurologic signs in humans.

Accidental hydroxychloroquine overdose resulting in neurotoxic vestibulopathy

Hydroxychloroquine is an oral antimalarial medication commonly used off-label for a variety of rheumatological conditions, including systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome and dermatomyositis. We present a case of a 64-year-old woman who presented with acute onset headache, bilateral tinnitus, and left-sided facial numbness and tingling in the setting of accidentally overdosing on hydroxychloroquine. By the next morning, the patient began to experience worsening in the tingling sensation and it eventually spread to her left arm, thigh and distal extremities. The patient also complained of new onset blurring of her peripheral vision and feeling 'off balance.' Despite a complete neurological and ophthalmological work-up with unremarkable imaging and blood work, the patient has had no improvement in her tinnitus, left-sided paresthesias, visual disturbance or ataxia. This is a unique case of hydroxychloroquine overdose resulting in permanent neurotoxic vestibulopathy.

Gap Junction Blockers: An Overview of their Effects on Induced Seizures in Animal Models

BACKGROUND

Gap junctions are clusters of intercellular channels allowing the bidirectional pass of ions directly into the cytoplasm of adjacent cells. Electrical coupling mediated by gap junctions plays a role in the generation of highly synchronized electrical activity. The hypersynchronous neuronal activity is a distinctive characteristic of convulsive events. Therefore, it has been postulated that enhanced gap junctional communication is an underlying mechanism involved in the generation and maintenance of seizures. There are some chemical compounds characterized as gap junction blockers because of their ability to disrupt the gap junctional intercellular communication.

OBJECTIVE

Hence, the aim of this review is to analyze the available data concerning the effects of gap junction blockers specifically in seizure models.

RESULTS

Carbenoxolone, quinine, mefloquine, quinidine, anandamide, oleamide, heptanol, octanol, meclofenamic acid, niflumic acid, flufenamic acid, glycyrrhetinic acid and retinoic acid have all been evaluated on animal seizure models. In vitro, these compounds share anticonvulsant effects typically characterized by the reduction of both amplitude and frequency of the epileptiform activity induced in brain slices. In vivo, gap junction blockers modify the behavioral parameters related to seizures induced by 4-aminopyridine, pentylenetetrazole, pilocarpine, penicillin and maximal electroshock.

CONCLUSION

Although more studies are still required, these molecules could be a promising avenue in the search for new pharmaceutical alternatives for the treatment of epilepsy.

Mefloquine-associated dizziness, diplopia, and central serous chorioretinopathy: a case report

Background

Many acute and chronic neurological sequelae from the quinoline derivative antimalarial drug mefloquine, including dizziness and effects on the visual system such as diplopia and blurred vision, may be attributable to focal central nervous system toxicity. Maculopathy has also been reported with use of mefloquine, although the mechanism of this effect has remained unclear. Identification of a common mechanism of toxicity plausibly underlying these visual and non-visual effects may provide broader insights into the acute and chronic neuropsychiatric effects of this and other quinoline antimalarial drugs.

Case presentation

This case report describes a 30-year-old man of Pakistani descent with sudden onset of dizziness and diplopia following the administration of mefloquine who developed macular changes diagnosed as acute central serous chorioretinopathy by angiography and optical coherence tomography. Similarities between the visual conditions observed in this case and those observed following administration of related quinoline derivative antimalarial drugs including quinine are considered, and plausible mechanisms for the observed drug-induced toxicity are discussed.

Conclusions

It is proposed that central serous chorioretinopathy be considered a potential ophthalmological sign of mefloquine central nervous system toxicity, and for this effect to potentially indicate susceptibility to other neuropsychiatric effects of mefloquine intoxication. Treating physicians should be aware of the potential for acute and chronic ocular effects resulting from administration of mefloquine and other quinoline antimalarial drugs.

Adverse neuropsychiatric effects of antimalarial drugs

INTRODUCTION

Antimalarial drugs are the primary weapon to treat parasite infection, save lives, and curtail further transmission. Accumulating data have indicated that at least some antimalarial drugs may contribute to severe neurological and/or psychiatric side effects which further complicates their use and limits the pool of available medications.

AREAS COVERED

In this review article, we summarize published scientific studies in search of evidence of the neuropsychiatric effects that may be attributed to the commonly used antimalarial drugs administered alone or in combination. Each individual drug was used as a search term in addition to keywords such as neuropsychiatric, adverse events, and neurotoxicity.

EXPERT OPINION

Accumulating data based on published reports over several decades have suggested that among the major commonly used antimalarial drugs, only mefloquine exhibited clear indications of serious neurological and/or psychiatric side effects. A more systematic approach to assess the neuropsychiatric adverse effects of new or repurposed antimalarial drugs on their safety, tolerability and efficacy phases of clinical studies and in post-marketing surveillance, is needed to ensure that these life-saving tools remain available and can be prescribed with appropriate caution and medical judgment.

Malaria Prevention, Mefloquine Neurotoxicity, Neuropsychiatric Illness, and Risk-Benefit Analysis in the Australian Defence Force

The Australian Defence Force (ADF) has used mefloquine for malaria chemoprophylaxis since 1990. Mefloquine has been found to be a plausible cause of a chronic central nervous system toxicity syndrome and a confounding factor in the diagnosis of existing neuropsychiatric illnesses prevalent in the ADF such as posttraumatic stress disorder and traumatic brain injury. Overall health risks appear to have been mitigated by restricting the drug's use; however serious risks were realised when significant numbers of ADF personnel were subjected to clinical trials involving the drug. The full extent of the exposure, health impacts for affected individuals, and consequences for ADF health management including mental health are not yet known, but mefloquine may have caused or aggravated neuropsychiatric illness in large numbers of patients who were subsequently misdiagnosed and mistreated or otherwise failed to receive proper care. Findings in relation to chronic mefloquine neurotoxicity were foreseeable, but this eventuality appears not to have been considered during risk-benefit analyses. Thorough analysis by the ADF would have identified this long-term risk as well as other qualitative risk factors. Historical exposure of ADF personnel to mefloquine neurotoxicity now also necessitates ongoing risk monitoring and management in the overall context of broader health policies.

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.

Anticonvulsant effects of mefloquine on generalized tonic-clonic seizures induced by two acute models in rats

Background

Mefloquine can cross the blood–brain barrier and block the gap junction intercellular communication in the brain. Enhanced electrical coupling mediated by gap junctions is an underlying mechanism involved in the generation and maintenance of seizures. For this reason, the aim of this study was to analyze the effects of the systemic administration of mefloquine on tonic-clonic seizures induced by two acute models such as pentylenetetrazole and maximal electroshock.

Results

All the control rats presented generalized tonic-clonic seizures after the administration of pentylenetetrazole. However, the incidence of seizures induced by pentylenetetrazole significantly decreased in the groups administered systematically with 40 and 80 mg/kg of mefloquine. In the control group, none of the rats survived after the generalized tonic-clonic seizures induced by pentylenetetrazole, but survival was improved by mefloquine. Besides, mefloquine significantly modified the total spectral power as well as the duration, amplitude and frequency of the epileptiform activity induced by pentylenetetrazole. For the maximal electroshock model, mefloquine did not change the occurrence of tonic hindlimb extension. However, this gap junction blocker significantly decreased the duration of the tonic hindlimb extension induced by the acute electroshock.

Conclusions

These data suggest that mefloquine at low doses might be eliciting some anticonvulsant effects when is systemically administered to rats.

Idiosyncratic quinoline central nervous system toxicity: Historical insights into the chronic neurological sequelae of mefloquine

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Regulators now warn adverse neurological effects from mefloquine may be irreversible.

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Many neurological effects resemble those of a common quinoline CNS toxidrome.

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The quinoline toxidrome is associated with a risk of CNS neuronal degeneration.

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CNS neuronal degeneration may underlie some neurological effects from mefloquine.

Mefloquine is a quinoline derivative antimalarial which demonstrates promise for the treatment of schistosomiasis. Traditionally employed in prophylaxis and treatment of chloroquine-resistant Plasmodium falciparum malaria, recent changes to the approved European and U.S. product labeling for mefloquine now warn of a risk of permanent and irreversible neurological sequelae including vertigo, loss of balance and symptoms of polyneuropathy. The newly described permanent nature of certain of these neurological effects challenges the conventional belief that they are due merely to the long half-life of mefloquine and its continued presence in the body, and raises new considerations for the rational use of the drug against parasitic disease. In this opinion, it is proposed that many of the reported lasting adverse neurological effects of mefloquine are consistent with the chronic sequelae of a well characterized but idiosyncratic central nervous system (CNS) toxicity syndrome (or toxidrome) common to certain historical antimalarial and antiparasitic quinolines and associated with a risk of permanent neuronal degeneration within specific CNS regions including the brainstem. Issues in the development and licensing of mefloquine are then considered in the context of historical awareness of the idiosyncratic CNS toxicity of related quinoline drugs. It is anticipated that the information presented in this opinion will aid in the future clinical recognition of the mefloquine toxidrome and its chronic sequelae, and in informing improved regulatory evaluation of mefloquine and related quinoline drugs as they are explored for expanded antiparasitic use and for other indications.

Formulation and evaluation of Pheroid vesicles containing mefloquine for the treatment of malaria

OBJECTIVES

Mefloquine (MQ) is an antimalarial drug with high efficacy, often used in the treatment and chemoprophylaxis of malaria. However, it has low solubility in water, a long elimination half-life (4 days), and is neurotoxic, which leads to unwanted side effects.

METHODS

We investigated a lipid-based drug delivery system, Pheroid vesicles, in combination with MQ (Pheroid MQ), to promote future clinical use. MQ was incorporated into Pheroid vesicles and the formulations characterized. The formulations were evaluated in terms of in-vitro efficacy and toxicity. In-vivo bioavailability studies were conducted in C57 BL6 mice.

KEY FINDINGS

The vesicles incorporated MQ with ~63% entrapment efficiency. The IC50 values of MQ after 48-h incubation in chloroquine-resistant (RSA11) and chloroquine sensitive (3D7) strains, were reduced by ~50% and ~30% respectively. In-vivo bioavailability study revealed no change in the pharmacokinetic parameters of MQ, and the incorporation of the drug in Pheroid vesicles reduced the in-vitro haemolytic activity by ~75%. Furthermore, the cytotoxicity against human neuroblastoma cells (SH-SY5Y) of the free drug was reduced by ~64% with Pheroid MQ.

CONCLUSIONS

Pheroid vesicles may therefore decrease the toxicity of MQ and thereby improve its therapeutic index, a strategy that may provide an effective alternative for malaria chemoprophylaxis and treatment.

New approaches for the identification of drug targets in protozoan parasites

Antiparasitic chemotherapy is an important issue for drug development. Traditionally, novel compounds with antiprotozoan activities have been identified by screening of compound libraries in high-throughput systems. More recently developed approaches employ target-based drug design supported by genomics and proteomics of protozoan parasites. In this chapter, the drug targets in protozoan parasites are reviewed. The gene-expression machinery has been among the first targets for antiparasitic drugs and is still under investigation as a target for novel compounds. Other targets include cytoskeletal proteins, proteins involved in intracellular signaling, membranes, and enzymes participating in intermediary metabolism. In apicomplexan parasites, the apicoplast is a suitable target for established and novel drugs. Some drugs act on multiple subcellular targets. Drugs with nitro groups generate free radicals under anaerobic growth conditions, and drugs with peroxide groups generate radicals under aerobic growth conditions, both affecting multiple cellular pathways. Mefloquine and thiazolides are presented as examples for antiprotozoan compounds with multiple (side) effects. The classic approach of drug discovery employing high-throughput physiological screenings followed by identification of drug targets has yielded the mainstream of current antiprotozoal drugs. Target-based drug design supported by genomics and proteomics of protozoan parasites has not produced any antiparasitic drug so far. The reason for this is discussed and a synthesis of both methods is proposed.

Mass administration of the antimalarial drug mefloquine to Guantánamo detainees: a critical analysis

Recently, evidence has emerged from an unusual form of mass drug administration practised among detainees held at US Naval Station Guantánamo Bay, Cuba ('Guantánamo'), ostensibly as a public health measure. Mefloquine, an antimalarial drug originally developed by the US military, whose use is associated with a range of severe neuropsychiatric adverse effects, was administered at treatment doses to detainees immediately upon their arrival at Guantánamo, prior to laboratory testing for malaria and irrespective of symptoms of disease. In this analysis, the history of mefloquine's development is reviewed and the indications for its administration at treatment doses are discussed. The stated rationale for the use of mefloquine among Guantánamo detainees is then evaluated in the context of accepted forms of population-based malaria control. It is concluded that there was no plausible public health indication for the use of mefloquine at Guantánamo and that based on prevailing standards of care, the clinical indications for its use are decidedly unclear. This analysis suggests the troubling possibility that the use of mefloquine at Guantánamo may have been motivated in part by knowledge of the drug's adverse effects, and points to a critical need for further investigation to resolve unanswered questions regarding the drug's potentially inappropriate use.

Recent highlights in anti-protozoan drug development and resistance research

This article summarizes the highlights of research presented in January, 2012, at the Keystone Symposium on "Drug Discovery for Protozoan Parasites" held in Santa Fe, New Mexico. This symposium which convenes approximately every 2 years provides a forum for leading investigators around the world to present data covering basic sciences to clinical trials relating to anti-protozoan drug development and drug resistance. Many talks focused on malaria, but other protozoan diseases receiving attention included African sleeping sickness, Chagas disease, leishmaniasis, cryptosporidiosis, and amoebiasis. The new research, most of it unpublished, provided insights into the latest developments in the field.

Limbic encephalopathy and central vestibulopathy caused by mefloquine: a case report

Mefloquine is a 4-methanolquinoline anti-malarial that in recent years has fallen out of favor for use as chemoprophylaxis against infection with chloroquine-resistant Plasmodium falciparum malaria owing in part to growing concerns of side effects and potential neurotoxicity. Despite over 20 years of licensed use, the pathophysiological mechanisms underlying mefloquine's neuropsychiatric and physical side effects and the clinical significance of the drug's neurotoxicity have remained poorly understood. In this report, an adverse reaction to mefloquine chemoprophylaxis is described characterized by prodromal symptoms of anxiety with subsequent development of psychosis, short-term memory impairment, confusion and personality change accompanied by complaints of disequilibrium and vertigo, with objective findings of central vestibulopathy. It is posited that these effects represent an idiosyncratic neurotoxic syndrome of progressive limbic encephalopathy and multifocal brainstem injury caused by the drug. This case provides insights into the clinical significance of mefloquine neuronal gap junction blockade and neurotoxicity demonstrated in animal models, points to recommendations for the management of affected patients including diagnostic considerations and appropriate referrals, and highlights critical implications for the continued safe use of the medication.

Central nervous system exposure of next generation quinoline methanols is reduced relative to mefloquine after intravenous dosing in mice

Background

The clinical use of mefloquine (MQ) has declined due to dose-related neurological events. Next generation quinoline methanols (NGQMs) that do not accumulate in the central nervous system (CNS) to the same extent may have utility. In this study, CNS levels of NGQMs relative to MQ were measured and an early lead chemotype was identified for further optimization.

Experimental design

The plasma and brain levels of MQ and twenty five, 4-position modified NGQMs were determined using LCMS/MS at 5 min, 1, 6 and 24 h after IV administration (5 mg/kg) to male FVB mice. Fraction unbound in brain tissue homogenate was assessed in vitro using equilibrium dialysis and this was then used to calculate brain-unbound concentration from the measured brain total concentration. A five-fold reduction CNS levels relative to mefloquine was considered acceptable. Additional pharmacological properties such as permeability and potency were determined.

Results

The maximum brain (whole/free) concentrations of MQ were 1807/4.9 ng/g. Maximum whole brain concentrations of NGQMs were 23 - 21546 ng/g. Maximum free brain concentrations were 0.5 to 267 ng/g. Seven (28%) and two (8%) compounds exhibited acceptable whole and free brain concentrations, respectively. Optimization of maximum free brain levels, IC90s (as a measure or potency) and residual plasma concentrations at 24 h (as a surrogate for half-life) in the same molecule may be feasible since they were not correlated. Diamine quinoline methanols were the most promising lead compounds.

Conclusion

Reduction of CNS levels of NGQMs relative to mefloquine may be feasible. Optimization of this property together with potency and long half-life may be feasible amongst diamine quinoline methanols.

Expanding the Antimalarial Drug Arsenal-Now, But How?

The number of available and effective antimalarial drugs is quickly dwindling. This is mainly because a number of drug resistance-associated mutations in malaria parasite genes, such as crt, mdr1, dhfr/dhps, and others, have led to widespread resistance to all known classes of antimalarial compounds. Unfortunately, malaria parasites have started to exhibit some level of resistance in Southeast Asia even to the most recently introduced class of drugs, artemisinins. While there is much need, the antimalarial drug development pipeline remains woefully thin, with little chemical diversity, and there is currently no alternative to the precious artemisinins. It is difficult to predict where the next generation of antimalarial drugs will come from; however, there are six major approaches: (i) re-optimizing the use of existing antimalarials by either replacement/rotation or combination approach; (ii) repurposing drugs that are currently used to treat other infections or diseases; (iii) chemically modifying existing antimalarial compounds; (iv) exploring natural sources; (v) large-scale screening of diverse chemical libraries; and (vi) through parasite genome-based ("targeted") discoveries. When any newly discovered effective antimalarial treatment is used by the populus, we must maintain constant vigilance for both parasite-specific and human-related factors that are likely to hamper its success. This article is neither comprehensive nor conclusive. Our purpose is to provide an overview of antimalarial drug resistance, associated parasite genetic factors (1. Introduction; 2. Emergence of artemisinin resistance in P. falciparum), and the antimalarial drug development pipeline (3. Overview of the global pipeline of antimalarial drugs), and highlight some examples of the aforementioned approaches to future antimalarial treatment. These approaches can be categorized into "short term" (4. Feasible options for now) and "long term" (5. Next generation of antimalarial treatment-Approaches and candidates). However, these two categories are interrelated, and the approaches in both should be implemented in parallel with focus on developing a successful, long-lasting antimalarial chemotherapy.

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.

Mefloquine damage vestibular hair cells in organotypic cultures

Mefloquine is an effective and widely used anti-malarial drug; however, some clinical reports suggest that it can cause dizziness, balance, and vestibular disturbances. To determine if mefloquine might be toxic to the vestibular system, we applied mefloquine to organotypic cultures of the macula of the utricle from postnatal day 3 rats. The macula of the utricle was micro-dissected out as a flat surface preparation and cultured with 10, 50, 100, or 200 μM mefloquine for 24 h. Specimens were stained with TRITC-conjugated phalloidin to label the actin in hair cell stereocilia and TO-PRO-3 to visualize cell nuclei. Some utricles were also labeled with fluorogenic caspase-3, -8, or -9 indicators to evaluate the mechanism of programmed cell death. Mefloquine treatment caused a dose-dependent loss of utricular hair cells. Treatment with 10 μM caused a slight reduction, 50 μM caused a significant reduction, and 200 μM destroyed nearly all the hair cells. Hair cell nuclei in mefloquine-treated utricles were condensed and fragmented, morphological features of apoptosis. Mefloquine-treated utricles were positive for the extrinsic initiator caspase-8 and intrinsic initiator caspase-9 and downstream executioner caspase-3. These results indicate that mefloquine can induce significant hair cell degeneration in the postnatal rat utricle and that mefloquine-induced hair cell death is initiated by both caspase-8 and caspase-9.

The evolution of metabolic profiling in parasitology

The uses of metabolic profiling technologies such as mass spectrometry and nuclear magnetic resonance spectroscopy in parasitology have been multi-faceted. Traditional uses of spectroscopic platforms focused on determining the chemical composition of drugs or natural products used for treatment of parasitic infection. A natural progression of the use of these tools led to the generation of chemical profiles of the parasite in in vitro systems, monitoring the response of the parasite to chemotherapeutics, profiling metabolic consequences in the host organism and to deriving host-parasite interactions. With the dawn of the post-genomic era the paradigm in many research areas shifted towards Systems Biology and the integration of biomolecular interactions at the level of the gene, protein and metabolite. Although these technologies have yet to deliver their full potential, metabolic profiling has a key role to play in defining diagnostic or even prognostic metabolic signatures of parasitic infection and in deciphering the molecular mechanisms underpinning the development of parasite-induced pathologies. The strengths and weaknesses of the various spectroscopic technologies and analytical strategies are summarized here with respect to achieving these goals.

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.

Epileptogenic potential of mefloquine chemoprophylaxis: a pathogenic hypothesis

Background

Mefloquine has historically been considered safe and well-tolerated for long-term malaria chemoprophylaxis, but prescribing it requires careful attention in order to rule out contraindications to its use. Contraindications include a history of certain neurological conditions that might increase the risk of seizure and other adverse events. The precise pathophysiological mechanism by which mefloquine might predispose those with such a history to seizure remains unclear.

Presentation of the hypothesis

Studies have demonstrated that mefloquine at doses consistent with chemoprophylaxis accumulates at high levels in brain tissue, which results in altered neuronal calcium homeostasis, altered gap-junction functioning, and contributes to neuronal cell death. This paper reviews the scientific evidence associating mefloquine with alterations in neuronal function, and it suggests the novel hypothesis that among those with the prevalent EPM1 mutation, inherited and mefloquine-induced impairments in neuronal physiologic safeguards might increase risk of GABAergic seizure during mefloquine chemoprophylaxis.

Testing and implications of the hypothesis

Consistent with case reports of tonic-clonic seizures occurring during mefloquine chemoprophylaxis among those with family histories of epilepsy, it is proposed here that a new contraindication to mefloquine use be recognized for people with EPM1 mutation and for those with a personal history of myoclonus or ataxia, or a family history of degenerative neurologic disorder consistent with EPM1. Recommendations and directions for future research are presented.

Properties of gap junction blockers and their behavioural, cognitive and electrophysiological effects: animal and human studies

Gap junctions play an important role in brain physiology. They synchronize neuronal activity and connect glial cells participating in the regulation of brain metabolism and homeostasis. Gap junction blockers (GJBs) include various chemicals that impair gap junction communication, disrupt oscillatory neuronal activity over a wide range of frequencies, and decrease epileptic discharges. The behavioural and clinical effects of GJBs suggest that gap junctions can be involved in the regulation of locomotor activity, arousal, memory, and breathing. Severe neuropsychiatric side effects suggest the involvement of gap junctions in mechanisms of consciousness. Unfortunately, the available GJBs are not selective and can bind to targets other than gap junctions. Other problems in behavioural studies include the possible adverse effects of GJBs, for example, retinal toxicity and hearing disturbances, changes in blood-brain transport, and the metabolism of other drugs. Therefore, it is necessary to design experiments properly to avoid false, misleading or uninterpretable results. We review the pharmacological properties and electrophysiological, behavioural and cognitive effects of the available gap junction blockers, such as carbenoxolone, glycyrrhetinic acid, quinine, quinidine, mefloquine, heptanol, octanol, anandamide, fenamates, 2-APB, several anaesthetics, retinoic acid, oleamide, spermine, aminosulfonates, and sodium propionate. It is concluded that despite a number of different problems, the currently used gap junction blockers could be useful tools in pharmacology and neuroscience.

Mefloquine neurotoxicity: a literature review

A literature review revealed that mefloquine neurotoxicity has been demonstrated at both the preclinical and clinical levels, with nausea, dizziness, sleep disturbances, anxiety and psychosis, amongst other adverse neuropsychiatric events, reported in users. Females and individuals of low body mass index (BMI) are at apparent greater risk. Mechanisms of possible neurotoxicity may include binding to neuroreceptors and cholinesterases, inhibition of sarcoendoplasmic reticulum ATPase (SERCA) and interference with cellular Ca(2+) homeostasis, accumulation in the CNS, and reductions in CNS efflux in individuals possessing certain MDR1 polymorphisms. It may be prudent to avoid mefloquine in females and low BMI individuals, and in combination with other potentially neurotoxic agents such as the artemisinin antimalarials.

Mefloquine-induced disruption of calcium homeostasis in mammalian cells is similar to that induced by ionomycin

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 dose-related 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.

Effect of Plasmodium yoelii nigeriensis infection on hepatic and splenic glutathione-S-transferase(s) in Swiss albino and db/+ mice: efficacy of mefloquine and menadione in antimalarial chemotherapy

The present report deals with the status of hepatic and splenic glutathione-S-transferase (GST) activities in mice during experimental infection with Plasmodium yoelii nigeriensis and subsequent treatment of infected mice with mefloquine (Mf) and menadione (Md). The infection caused significant decline in the hepatic and splenic glutathione-S-transferase (GST) activities of albino and db/+ mice. The decline was observed in the levels of both cytosolic and microsomal GST(s) of liver and spleen in both types of mice. Intraperitoneal administration of mefloquine at a dose of 5 mg/kg and menadione at a dose of 100 mg/kg, twice daily from day 1 p.i. (day 0) until day 10, caused restoration in the levels of hepatic as well as splenic GST(s), albeit to varying degrees. Mf was able to suppress parasitaemia by day 5 in the case of albino mice and by day 3 in the case of db/+ mice but was unable to cure both types of mice completely. On the other hand, Md caused a delay in maturation of infection in both cases, but could not cure the mice.

Utility of alkylaminoquinolinyl methanols as new antimalarial drugs

Mefloquine has been one of the more valuable antimalarial drugs but has never reached its full clinical potential due to concerns about its neurologic side effects, its greater expense than that of other antimalarials, and the emergence of resistance. The commercial development of mefloquine superseded that of another quinolinyl methanol, WR030090, which was used as an experimental antimalarial drug by the U.S. Army in the 1970s. We evaluated a series of related 2-phenyl-substituted alkylaminoquinolinyl methanols (AAQMs) for their potential as mefloquine replacement drugs based on a series of appropriate in vitro and in vivo efficacy and toxicology screens and the theoretical cost of goods. Generally, the AAQMs were less neurotoxic and exhibited greater antimalarial potency, and they are potentially cheaper than mefloquine, but they showed poorer metabolic stability and pharmacokinetics and the potential for phototoxicity. These differences in physiochemical and biological properties are attributable to the "opening" of the piperidine ring of the 4-position side chain. Modification of the most promising compound, WR069878, by substitution of an appropriate N functionality at the 4 position, optimization of quinoline ring substituents at the 6 and 7 positions, and deconjugation of quinoline and phenyl ring systems is anticipated to yield a valuable new antimalarial drug.