Penetration of dihydroartemisinin into cerebrospinal fluid after administration of intravenous artesunate in severe falciparum malaria

An Elusive Target: Inhibitors of JC Polyomavirus Infection and Their Development as Therapeutics for the Treatment of Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a rare demyelinating disease caused by infection with JC Polyomavirus (JCPyV). Despite the identification of the disease and isolation of the causative pathogen over fifty years ago, no antiviral treatments or prophylactic vaccines exist. Disease onset is usually associated with immunosuppression, and current treatment guidelines are limited to restoring immune function. This review summarizes the drugs and small molecules that have been shown to inhibit JCPyV infection and spread. Paying attention to historical developments in the field, we discuss key steps of the virus lifecycle and antivirals known to inhibit each event. We review current obstacles in PML drug discovery, including the difficulties associated with compound penetrance into the central nervous system. We also summarize recent findings in our laboratory regarding the potent anti-JCPyV activity of a novel compound that antagonizes the virus-induced signaling events necessary to establish a productive infection. Understanding the current panel of antiviral compounds will help center the field for future drug discovery efforts.

Artesunate Alleviates Paclitaxel-Induced Neuropathic Pain in Mice by Decreasing Metabotropic Glutamate Receptor 5 Activity and Neuroinflammation in Primary Sensory Neurons

Experimental studies on the pathogenetic process of paclitaxel-induced neuropathic pain (PINP) have been initially carried out, but PINP still has no effective therapy. Recently reported studies have highlighted the involvement of glutamate receptors and neuroinflammation in peripheral and central nociceptive transmission in PINP. Artesunate is a first-line antimalarial drug with established efficacy in alleviating pain in a variety of pathologies. The current work assessed whether artesunate inhibits PINP by modulating metabotropic glutamate receptor 5 (mGluR5) and neuroinflammation in mice. The anti-hyperalgesic effect of artesunate was verified by assessing mechanical frequency and thermal latency in the paw withdrawal test as well as spontaneous pain. The expression levels of mGluR5, pain-related receptors and neuroinflammatory markers in dorsal root ganglion (DRG) were examined. In addition, treatment with CHPG and 2-methyl-6-(phenyl ethynyl) pyridine (MPEP) (mGluR5 agonist and antagonist, respectively) was performed to determine mGluR5’s role in the anti-hyperalgesic properties of artesunate. We demonstrated artesunate prevented PINP in a dose-dependent manner, while exerting a clear anti-hyperalgesic effect on already existing PINP. Artesunate normalized paclitaxel-related expression changes in DRG mGluR5, NR1, and GluA2, as well as six paclitaxel related neuroinflammation markers. Intrathecal application of MPEP treated PINP by reversing NR1 and GluA2 expression changes but had no effects on chemokines and inflammatory factors. Furthermore, artesunate treatment reversed acute pain following CHPG application. In conclusion, this study revealed that artesunate alleviates paclitaxel-induced hyperalgesia and spontaneous pain by decreasing DRG mGluR5 expression and neuroinflammation in the mouse model of PINP.

Artemisinins and their impact on inhibitory neurotransmission

Artemisinin, a major extract of the annual mugwort Artemisia annua, and its semisynthetic derivatives represent state-of-the-art antimalarial drugs. These compounds also target, via poorly understood mechanisms, various mammalian pathways, thereby exhibiting anticancer and immunomodulatory properties. Recently, crystal structures of artemisinins with two mammalian targets were determined, namely, gephyrin, the prime scaffolding protein at inhibitory postsynapses, and pyridoxal kinase, a central metabolic enzyme synthesizing vitamin B6. These structures and corresponding functional studies demonstrate that artemisinins play a dual role in modulating inhibitory synapses, acting on postsynaptic sites by impeding inhibitory neurotransmitter receptor clustering and on presynaptic terminals by limiting the biosynthesis of the inhibitory neurotransmitter γ-aminobutyric acid. These studies pave the way for further investigations of artemisinins as inhibitory neurotransmission modulators in humans.

Pyridoxal kinase inhibition by artemisinins down-regulates inhibitory neurotransmission

The antimalarial artemisinins have also been implicated in the regulation of various cellular pathways including immunomodulation of cancers and regulation of pancreatic cell signaling in mammals. Despite their widespread application, the cellular specificities and molecular mechanisms of target recognition by artemisinins remain poorly characterized. We recently demonstrated how these drugs modulate inhibitory postsynaptic signaling by direct binding to the postsynaptic scaffolding protein gephyrin. Here, we report the crystal structure of the central metabolic enzyme pyridoxal kinase (PDXK), which catalyzes the production of the active form of vitamin B6 (also known as pyridoxal 5'-phosphate [PLP]), in complex with artesunate at 2.4-Å resolution. Partially overlapping binding of artemisinins with the substrate pyridoxal inhibits PLP biosynthesis as demonstrated by kinetic measurements. Electrophysiological recordings from hippocampal slices and activity measurements of glutamic acid decarboxylase (GAD), a PLP-dependent enzyme synthesizing the neurotransmitter γ-aminobutyric acid (GABA), define how artemisinins also interfere presynaptically with GABAergic signaling. Our data provide a comprehensive picture of artemisinin-induced effects on inhibitory signaling in the brain.

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.

Structure of Heteropentameric GABAA Receptors and Receptor-Anchoring Properties of Gephyrin

γ-Aminobutyric acid type A receptors (GABA_ARs) mediate the majority of fast synaptic inhibition in the central nervous system (CNS). GABA_ARs belong to the Cys-loop superfamily of pentameric ligand-gated ion channels (pLGIC) and are assembled from 19 different subunits. As dysfunctional GABAergic neurotransmission manifests itself in neurodevelopmental disorders including epilepsy and anxiety, GABA_ARs are key drug targets. The majority of synaptic GABA_ARs are anchored at the inhibitory postsynaptic membrane by the principal scaffolding protein gephyrin, which acts as the central organizer in maintaining the architecture of the inhibitory postsynaptic density (iPSD). This interaction is mediated by the long intracellular loop located in between transmembrane helices 3 and 4 (M3–M4 loop) of the receptors and a universal receptor-binding pocket residing in the C-terminal domain of gephyrin. In 2014, the crystal structure of the β3-homopentameric GABA_AR provided crucial information regarding the architecture of the receptor; however, an understanding of the structure and assembly of heteropentameric receptors at the atomic level was lacking. This review article will highlight recent advances in understanding the structure of heteropentameric synaptic GABA_ARs and how these structures have provided fundamental insights into the assembly of these multi-subunit receptors as well as their modulation by diverse ligands including the physiological agonist GABA. We will further discuss the role of gephyrin in the anchoring of synaptic GABA_ARs and glycine receptors (GlyRs), which are crucial for maintaining the architecture of the iPSD. Finally, we will also summarize how anti-malarial artemisinin drugs modulate gephyrin-mediated inhibitory neurotransmission.

Current scenario of artemisinin and its analogues for antimalarial activity

Human malaria, one of the most striking, reemerging infectious diseases, is caused by several types of Plasmodium parasites. Whilst advances have been made in lowering the numbers of cases and deaths, it is clear that a strategy based solely on disease control year on year, without reducing transmission and ultimately eradicating the parasite, is unsustainable. Natural products have served as a template for the design and development of antimalarial drugs currently in the clinic or in the development phase. Artemisinin combine potent, rapid antimalarial activity with a wide therapeutic index and an absence of clinically important resistance. The alkylating ability of artemisinin and its semi-synthetic analogues toward heme related to their antimalarial efficacy are underlined. Although impressive results have already been achieved in malaria research, more systematization and concentration of efforts are required if real breakthroughs are to be made. This review will concisely cover the clinical, preclinical antimalarial and current updates in artemisinin based antimalarial drugs. Diverse classes of semi-synthetic analogs of artemisinin reported in the last decade have also been extensively studied. The experience gained in this respect is discussed.

Effect of artemisinin on proliferation and apoptosis-related protein expression in vivo and in vitro

Artemisinin is the first-line drugs for the treatment of malaria. In recent years, a large number of reports showed that artemisinin exhibit anti-tumor activity. In this study, we used C6 glioma cells and rat C6 brain-glioma model to study anti-tumor activity of artemisinin in vivo and in vitro. We found that artemisinin inhibited the proliferation in C6 cells and induced cell cycle arrest and a caspase-3-dependent cell apoptosis. It also inhibited the growth of C6 brain-glioma in vivo and enhanced living state of rat brain-glioma model. These results suggested that artemisinin had significant anti-tumor activities on C6 cells both in vitro and in vivo. Artemisinin might be exploited as a promising clinical anti-cancer drug in future.

Methylene Homologues of Artemisone: An Unexpected Structure-Activity Relationship and a Possible Implication for the Design of C10-Substituted Artemisinins

We sought to establish if methylene homologues of artemisone are biologically more active and more stable than artemisone. The analogy is drawn with the conversion of natural O- and N-glycosides into more stable C-glycosides that may possess enhanced biological activities and stabilities. Dihydroartemisinin was converted into 10β-cyano-10-deoxyartemisinin that was hydrolyzed to the α-primary amide. Reduction of the β-cyanide and the α-amide provided the respective methylamine epimers that upon treatment with divinyl sulfone gave the β- and α-methylene homologues, respectively, of artemisone. Surprisingly, the compounds were less active in vitro than artemisone against P. falciparum and displayed no appreciable activity against A549, HCT116, and MCF7 tumor cell lines. This loss in activity may be rationalized in terms of one model for the mechanism of action of artemisinins, namely the cofactor model, wherein the presence of a leaving group at C10 assists in driving hydride transfer from reduced flavin cofactors to the peroxide during perturbation of intracellular redox homeostasis by artemisinins. It is noted that the carba analogue of artemether is less active in vitro than the O-glycoside parent toward P. falciparum, although extrapolation of such activity differences to other artemisinins at this stage is not possible. However, literature data coupled with the leaving group rationale suggest that artemisinins bearing an amino group attached directly to C10 are optimal compounds.

Antiviral effects of artesunate on JC polyomavirus replication in COS-7 cells

The human JC polyomavirus (JCPyV) causes the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). A growing number of patients with induced or acquired immunosuppression are at risk for infection, and no effective antiviral therapy is presently available. The widely used antimalarial drug artesunate has shown broad antiviral activity in vitro but limited clinical success. The aim of this study was to investigate the effect of artesunate on JCPyV replication in vitro. The permissivity for JCPyV MAD-4 was first compared in four cell lines, and the monkey kidney cell line COS-7 was selected. Artesunate caused a concentration-dependent decrease in the extracellular JCPyV DNA load 96 h postinfection, with a 50% effective concentration (EC50) of 2.9 μM. This effect correlated with a decreased expression of capsid protein VP1 and a reduced release of infectious viral progeny. For concentrations of <20 μM, transient reductions in cellular DNA replication and proliferation were seen, while for higher concentrations, some cytotoxicity was detected. A selective index of 16.6 was found when cytotoxicity was calculated based on cellular DNA replication in the mock-infected cells, but interestingly, cellular DNA replication in the JCPyV-infected cells was more strongly affected. In conclusion, artesunate is efficacious in inhibiting JCPyV replication at micromolar concentrations, which are achievable in plasma. The inhibition at EC50 probably reflects an effect on cellular proteins and involves transient cytostatic effects. Our results, together with the favorable distribution of the active metabolite dihydroartemisinin to the central nervous system, suggest a potential use for artesunate in patients with PML.

Subchronic toxicological study of two artemisinin derivatives in dogs

The objective of our study was to profile and compare the systematic changes between orally administered artesunate and intramuscularly injected artemether at a low dose over a 3-month period (92 consecutive days) in dogs. Intramuscular administration of 6 mg kg-1 artemether induced a decreased red blood cell (RBC) count (anemia), concurrent extramedullary hematopoiesis in the spleen and inhibition of erythropoiesis in the bone marrow. We also observed a prolonged QT interval and neuropathic changes in the central nervous system, which demonstrated the cortex and motor neuron vulnerability, but no behavioral changes. Following treatment with artesunate, we observed a decreased heart rate, which was most likely due to cardiac conduction system damage, as well as a deceased RBC count, extramedullary hematopoiesis in the spleen and inhibition of erythropoiesis in the bone marrow. However, in contrast to treatment with artemether, neurotoxicity was not observed following treatment with artesunate. In addition, ultra-structural examination by transmission electron microscopy showed mitochondrial damage following treatment with artesunate. These findings demonstrated the spectrum of toxic changes that result upon treatment with artesunate and artemether and show that the prolonged administration of low doses of these derivatives result in diverse toxicity profiles.

A conceptually new treatment approach for relapsed glioblastoma: coordinated undermining of survival paths with nine repurposed drugs (CUSP9) by the International Initiative for Accelerated Improvement of Glioblastoma Care

To improve prognosis in recurrent glioblastoma we developed a treatment protocol based on a combination of drugs not traditionally thought of as cytotoxic chemotherapy agents but that have a robust history of being well-tolerated and are already marketed and used for other non-cancer indications. Focus was on adding drugs which met these criteria: a) were pharmacologically well characterized, b) had low likelihood of adding to patient side effect burden, c) had evidence for interfering with a recognized, well-characterized growth promoting element of glioblastoma, and d) were coordinated, as an ensemble had reasonable likelihood of concerted activity against key biological features of glioblastoma growth. We found nine drugs meeting these criteria and propose adding them to continuous low dose temozolomide, a currently accepted treatment for relapsed glioblastoma, in patients with recurrent disease after primary treatment with the Stupp Protocol. The nine adjuvant drug regimen, Coordinated Undermining of Survival Paths, CUSP9, then are aprepitant, artesunate, auranofin, captopril, copper gluconate, disulfiram, ketoconazole, nelfinavir, sertraline, to be added to continuous low dose temozolomide. We discuss each drug in turn and the specific rationale for use- how each drug is expected to retard glioblastoma growth and undermine glioblastoma's compensatory mechanisms engaged during temozolomide treatment. The risks of pharmacological interactions and why we believe this drug mix will increase both quality of life and overall survival are reviewed.

Meningeal inflammation increases artemether concentrations in cerebrospinal fluid in Papua New Guinean children treated with intramuscular artemether

Although the artemisinin-associated neurotoxicity identified in vitro and in animal studies has not been confirmed clinically, only one adult study has measured cerebrospinal fluid (CSF) concentrations after administration of conventional doses. Potential artemisinin neurotoxicity could be serious in children, especially those with meningitis and, consequently, a compromised blood-brain barrier. We measured CSF/plasma artemether and dihydroartemisinin (DHA) concentrations in 32 Papua New Guinean children with a mean age of 39 months with suspected or proven severe falciparum malaria who underwent a single lumbar puncture after intramuscular artemether administration. CSF artemether concentrations were 0 to 43.5 μg/liter and CSF concentration/plasma concentration ratios were 0 to 38.1%. DHA was measurable in CSF in only two children. The seven children with meningeal inflammation (CSF white cell count > 20/mm(3)) had higher CSF artemether concentration/plasma artemether concentration ratios than those without (median, 6.7% [interquartile ratio, 2.5 to 27.8%]% versus 0.0% [interquartile ratio, 0.0 to 2.5%]; P = 0.002). Meningeal inflammation was associated with a 4.6-fold increase in the CSF artemether concentration/plasma artemether concentration ratio in a population pharmacokinetic model. These data suggest that pharmacovigilance should be heightened when intramuscular artemether is given to severely ill children with evidence of meningeal inflammation.

The pharmacokinetic evaluation of artemisinin drugs for the treatment of malaria in paediatric populations

INTRODUCTION

The use of artemisinin combination therapies to treat uncomplicated malaria is growing and, therefore, so is the number of children exposed to these agents. As a result, there is a huge drive to develop paediatric formulations. However, relatively limited data exist regarding the pharmacokinetic properties of these drugs in this vulnerable population.

AREAS COVERED

The article reviews the pharmacokinetic data for artemisinin drugs used for the treatment of malaria in paediatric populations. The authors discuss how developmental and environmental factors can produce significant variation in the pharmacokinetic properties of artemisinin drugs. The authors also discuss how this variation may lead to suboptimal therapeutic drug concentrations with implications on efficacy, safety and the development of parasite resistance to these drugs.

EXPERT OPINION

There is currently a lack of published studies on the pharmacokinetics of artemisinin drugs in children and this subject is complicated by several interdependent variables. Therefore, the construction of a systems-based model of this subject should be a priority area in order to identify gaps in current knowledge to ensure their continued effective and safe use.

Pitfalls in new artemisinin-containing antimalarial drug development

Artemisinin combination therapy (ACT) paves the way for new opportunities to eliminate malaria in the tropics. However, the huge increase of ACT consumption raises major concerns about their availability over the next few years. At the same time a decrease in their efficacy has already been reported. Alongside the deployment of multifocal control programs, the process ranging from artemisia crop production to accreditation of new ACT combinations urgently needs to be strengthened to supply sufficient quantities of high-quality drugs. New suppliers will have the opportunity to enter this market to develop new formulations, and bioequivalence studies are required to validate these new formulations. It is thus crucial for national malaria control teams to be able to better scrutinize the dossier of these new formulations.

Inhibitive effect of artemether on tumor growth and angiogenesis in the rat C6 orthotopic brain gliomas model

To explore the inhibitive effect of artemether on glioma growth and angiogenesis in brain tumor bearing SD rat. MTT assay was used to evaluate the inhibitory effect of artemether treatment on C6 glioma cells. Forty SD rats which were subcutaneous planted with SD rat C6 glioma cell to establish SD rat orthotopic glioma model were divided resourcefully into 5 groups. each group was 8 rats. Length-path (a mm) and short-path (b mm) of tumor each rat was measured. Tumor volume was calculated using the following formula: V (mm(3)) = a(2)bpi/6. Microvessel density (MVD) in different therapy groups was significantly lower than that in normal saline control group and brain glioma volume in different therapy groups was significantly smaller than that in normal saline control group. There were remarkably inhibitory effects of artmeter on brain glioma growth and angiogenesis in SD rats and the mechanism that artemether inhibited brain glioma growth might be penetrating the blood-brain barrier and inhibiting angiogenesis.

Are currently deployed artemisinins neurotoxic?

In vitro, animal, and human clinical studies suggest currently deployed artemisinins possess neurotoxic potential. A specific and consistent pattern of brainstem injuries that includes auditory processing centers has been reported from all laboratory animals studied. Hearing loss, ataxia, and tremor are reported from humans. Neurotoxicity appears mediated in part through artemisinin induced oxidative stress in exposed brainstems. In vitro studies suggest that artemisinin neurotoxicity does not manifest immediately upon exposure, but that once commenced it is inevitable and irreversible; extrapolation from in vitro data suggests that 14 days may possibly be required for full development, casting doubt upon some animal safety studies and human necropsy studies. Uncertainty remains over the neurotoxicity of currently deployed artemisinins, and their safety profile should be reviewed, especially in pediatric use. The development of non-neurotoxic artemisinins is possible and should be encouraged.

Conventional and experimental treatment of cerebral malaria

The most severe complication of Plasmodium falciparum infection is cerebral malaria (CM). Cerebral malaria implies the presence of neurological features, especially impaired consciousness. The treatment of CM is limited to: (i) a few conventional anti-malarial drugs (quinine or artemisinins), (ii) adjunctive treatments (initial stabilisation, blood exchange transfusion, osmotic diuretics and correction of hypoglycaemia, acidosis and hypovolaemia) and (iii) immunomodulation. There are clear procedures concerning treatment of CM, which include the use of the anti-plasmodial drugs. Adjunctive treatments are permissible but there is no single official guideline and immune intervention is a possibility currently being examined in rodent models only. The suggested immunomodulation approach is based on the strong likelihood that CM is the result of an immunopathological process. P. falciparum initiates the multifactorial chain of events leading to lethal CM and, after a certain stage, it is impossible to stop the progression even by using anti-malarial drugs. We present evidence that CM is a result of a dysregulated immune response. Therefore, it might be prevented by early modulation of discrete factors that participate in this process. In experimental systems, some immunomodulators delay or prevent CM without affecting the parasitaemia. Therefore, in the future the ultimate treatment of CM may be a combination of an anti-malarial and an immunomodulator. However, the overall effect of an immunomodulator would need to be carefully examined in view of concomitant infections, especially in malaria endemic areas.

Convenient Access Both to Highly Antimalaria-Active 10-Arylaminoartemisinins, and to 10-Alkyl Ethers Including Artemether, Arteether, and Artelinate

An economical phase-transfer method is used to prepare 10-arylaminoartemisinins from DHA and arylamines, and artemether, arteether, and artelinate from the corresponding alcohols. In vivo sc screens against Plasmodium berghei and P. yoelii in mice reveal that the p-fluorophenylamino derivative 5 g is some 13 and 70 times, respectively, more active than artesunate; this reflects the very high sc activity of 10-alkylaminoartemisinins. However, through the po route, the compounds are less active than the alkylaminoartemisinins, but still approximately equipotent with artesunate.

Artemisinin‐based combination therapies for uncomplicated malaria

There has been a relentless increase in resistance of malaria parasites to conventional antimalarial drugs, including chloroquine, sulfadoxine-pyrimethamine and mefloquine. In response to this situation, short-course artemisinin-based combination therapies (ACTs) have been developed. The World Health Organization has endorsed ACT as first-line treatment where the potentially life-threatening parasite Plasmodium falciparum is the predominant infecting species. ACTs combine the rapid schizontocidal activity of an artemisinin derivative (artesunate, artemether or dihydroartemisinin) with a longer-half-life partner drug. Although the use of chloroquine and sulfadoxine-pyrimethamine as partners in ACT improves their efficacy, this may only have value as a short-term measure in patients with a degree of immunity to malaria. Alternative currently available partner drugs include mefloquine, lumefantrine and piperaquine. Artesunate-mefloquine is highly effective but is expensive and side effects (mainly neurotoxicity) can be problematic. Artemether-lumefantrine, the only ACT available in Australia, appears less effective than artesunate-mefloquine and needs to be administered with food to ensure adequate bioavailability. Dihydroartemisinin-piperaquine is highly effective, well tolerated and relatively inexpensive. The goal of potent, safe, easy-to-administer and inexpensive ACTs may see trioxolanes in place of artemisinin derivatives, as well as novel partner drugs such as pyronaridine or naphthoquine, in the future.

Protein binding and alpha : beta anomer ratio of dihydroartemisinin in vivo

AIMS

To determine the ratio of alpha : beta anomers and the protein binding of dihydroartemisinin (DHA) in vivo.

METHODS

10-[(3)H]-DHA was synthesized by reduction of artemisinin with sodium boro-[(3)H]-hydride and purified with preparative thin layer chromatography. A solution of (3)H-DHA (2000 ng in 20 micro l) was added to 2 ml whole blood from 15 healthy volunteers and 22 Vietnamese patients with falciparum or vivax malaria. The blood was centrifuged and the plasma stored at -25 degrees C until analysed by HPLC with radiochromatographic detection. Protein-free ultrafiltrate of the plasma was assayed to determine the free fraction of DHA and the in vivo ratio of alpha-DHA : beta-DHA.

RESULTS

The DHA fraction unbound (mean +/- SD) was 0.068 +/- 0.032 in Vietnamese patients with falciparum malaria (n = 17), 0.065 +/- 0.009 in Vietnamese patients with vivax malaria (n = 5), 0.117 +/- 0.015 in Vietnamese volunteers (n = 7) and 0.092 +/- 0.020 in Caucasian volunteers (n = 8). The ratios of alpha-DHA : beta-DHA for the four groups were 6.3 +/- 0.9, 6.9 +/- 0.8, 6.9 +/- 0.6 and 5.4 +/- 0.8, respectively.

CONCLUSIONS

DHA is approximately 93% protein-bound in patients with malaria infection and there is a preferential existence in vivo of the alpha-DHA anomer. Knowledge of this stereochemistry may be valuable in elucidation of the mechanisms of DHA action and/or toxicity, and in the synthesis of new trioxane antimalarials.

Artemisinin derivatives: toxic for laboratory animals, safe for humans?

A discrepancy seems to prevail with regard to the toxicity and safety of the artemisinin family of antimalarials. While these compounds have been found to be virtually void of any serious side effects in humans, their neurotoxicity in animal models has raised concerns about their use. In this paper, we present selected examples of both pre-clinical and clinical studies dealing with adverse effects of artemisinin drugs. We suggest that the prolonged presence of artemisinins upon slow release from oil-based intramuscular formulations is the main cause of the observed toxicity in laboratory animals. In contrast, oral intake of these compounds, which is by far the most common formulation used for treatment of malaria patients, results in rapid clearance of these drugs and is thus unlikely to cause any toxicity in human subjects. Another plausible factor may be the relatively high doses of artemisinin compounds used in animal studies. In conclusion, the observation of the toxicity of artemisinin compounds in animals, but not in humans, is most likely due to different pharmacokinetic profiles after different routes of administrations.