Arteether neurotoxicity in the absence of deficits in behavioural performance in rats

Influence of Artemisia annua L. on toll-like receptor expression in brain of mice infected with Acanthamoeba sp

The treatment of acanthamoebiasis is a still a problem. Our previous studies showed that the application of extracts from Artemisia annua L. significantly prolonged the survival of mice infected by Acanthamoeba. This plant has medicinal properties in the treatment of human parasitic diseases. The aim of this study was to evaluate the effects of A. annua on expression of Toll-like receptors (TLRs) 2 and 4 in brain of mice with Acanthamoeba infection. Mice were infected with Acanthamoeba sp. strain Ac309 (KY203908) by intranasal inoculation without and after application of A. annua extract. The administration of extract from A. annua significantly reduced the level of expression of TLR2 and modified the level of expression of TLR4. A. annua extract is a natural substance that is well tolerated in animals and may be considered as a combination therapy in treatment of acanthamoebiasis. Our study suggested that A. annua extract may be used as an alternative therapeutic tool.

Anorectic Toxicity of Dih Ydroartemisinin, Artemether, and Arteether in Rats Following Multiple Intramuscular Doses

During studies of arteether (AE), artemether (AM), and dihydroartemisinin (DQHS) neurotoxicity, the effect of 7 daily intramuscular doses (25, 50, and 100 mg/ kg/d) of those antimalarial drugs on gastrointestinal function was investigated in rats. A modified Nichols' method was used to measure daily food and water consumption. To estimate gastric transit, the total length amaranth (administered 40 minutes prior to sacrifice) dye traveled through small intestine were measured, and to determine gastric retention, the tied-off stomach pouch was removed and the contents weighed 24 hours after the last dose or when a rat became moribund or died. AM and AE dose solutions were prepared using sesame oil, whereas 50% dimethylacetamide (DMAC) sesame oil was used for DQHS. The results showed that after dosing with 50 mg/ kg for 7 days, 50% inhibition of food consumption (ID50) occurred at 1.9 days for DQHS, 3.9 days for AM, and 4.1 days for AE. Similar data were observed for water intake. After 100 mg/kg dosing, the ID50 s for food and water consumption decreased to 2.8-2.9 days for AM and 3.1-3.7 days for AE. Food consumption and body weights were decreased following all three treatments, and rats exhibited neurologic symptoms at 25-100 mg/kg dose of DQHS and 50-100 mg/kg dose of AM and AE. In addition, the results constituted a 53% and 82% inhibition of gastric transit for AM and AE, respectively, at 25 mg/kg animals compared to control, and 100% inhibition was found in high doses (50 and 100 mg/kg) for all the three drugs. The gastric retention ratio (controls equal 1.0) was 26.0 for DQHS, 5.8 with AE, and 2.3 for AM rats following 50 mg/kg dosing. When the 100 mg/kg dose was administered, the gastric retention ratio doubled for AE (11.6) and AM (4.3). The consumption data indicated that DQHS was about 2-3 times more toxic to the anorexia than AM and AE at 25 and 50 mg/kg/day dose levels. Significant differences in gastric emptying and gastric transit activities between AE and AM were observed. Data demonstrated that after multiple intramuscular doses of DQHS, AM, or AE in rats, food consumption and gastric emptying were decreased, gastric transit was inhibited, as reflected in a significant body weight reduction and death. Since an exhibition of the anorectic symptoms of AM and AE was at a lower dose than the neurologic signs in rats, the anorexia could be an early portent or prediction of the neurotoxicity in animals or humans.

Effects of artemisinin in broiler chickens following chronic oral intake

Artemisinin has been used for centuries to treat malaria, intestinal tract helminthosis, diarrhea, and used as an antipyretic and sedative agent, but the usage in veterinary medicine is a new field. Recently, it has been used successfully to control experimental poultry coccidiosis. The present study aimed to determine the effects of different doses of artemisinin in broiler chickens with chronic usage. Sixty birds divided into one control and four treatment groups that fed rations mixed with artemisinin at doses of 17, 34, 68, and 136 ppm for 36 days. During the experiment, birds showed no clinical signs except anemia. In microscopic examinations, heart, lung, and spleen had no lesion, but liver, kidney, and brain showed various lesions. Degenerative lesions like intracytoplasmic eosinophilic inclusions were seen in both kidney and liver but fatty change was seen only in liver. There was no relationship between severity of the liver lesions and drug dosage. Central chromatolysis, scattered neuronal necrosis, and mild spongy changes were observed in five regions of the brain that were chosen for sectioning (motor cortex, cerebellar nuclei, midbrain nuclei, and hindbrain nuclei at two separate levels). Severity of lesions in brain was dose-dependent, and cerebral cortex was the most vulnerable area. Haematologic tests showed lower values for hematocrit and red blood cell count dose-dependently. In conclusion, artemisinin is a promising drug for prevention and control of coccidiosis in broiler chickens and its side effects are not too much serious especially at therapeutic doses.

Changes in antioxidant status and biochemical indices after acute administration of artemether, artemether-lumefantrine and halofantrine in rats

Artemether, artemether-lumefantrine, or coartem and halofantrine are alternative antimalarial drugs to chloroquine. Their efficacy and potential to delay drug resistance in falciparum malaria had led to their increased use. Although these drugs have proven to be well tolerated, there are adverse effects associated with them. This study was designed to examine the toxic potential of acute administration of these drugs in rats. Twenty-four rats were divided into four groups: group I (control) received distilled water; group II received artemether for 5 days with an initial dose of 3.2 g/kg body weight on day 1 and 1.6 mg/kg body weight on days 2-5; group III received coartem (27 mg/kg body weight/day) for 3 days, which was divided into two equal portions per day; and group IV received halofantrine (24 mg/kg body weight/day) in three equal portions. Administration of artemether, coartem and halofantrine caused significant decrease (P < 0.05) in reduced glutathione levels in the liver by 29%, 21% and 26%, respectively. In contrast, there were no significant differences (P > 0.05) in the kidney glutathione levels. Furthermore, artemether, coartem and halofantrine decreased the liver- and kidney-enzymatic antioxidant status of the animals. Precisely, artemether, coartem and halofantrine decreased liver superoxide dismutase and catalase activities by 45%, 50% and 57%; and 20%, 29% and 23%, respectively. While the kidney catalase activities were decreased by 41%, 28% and 30%, respectively, the drugs however did not produce significant effect (P > 0.05) on the kidney superoxide dismutase activities. In addition, artemether, coartem and halofantrine decreased the hepatic levels of glutathione S-transferase by 64%, 51% and 53%, respectively. Administration of artemether, coartem and halofantrine significantly increased (P < 0.05) liver and kidney lipid peroxidation levels by 67%, 50% and 81%; and 58%, 43% and 31%, respectively. This indicates that the liver is considerably more affected than the kidneys. Similarly, halofantrine treatment caused significant elevation (P < 0.05) in the levels of serum creatinine, aspartate and alanine aminotransferases and blood urea nitrogen by 73%, 66%, 61% and 63%, respectively. These data indicate that oral administration of artemether, coartem and halofantrine has adverse effects on both enzymic and non-enzymatic antioxidant status of the animals.

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.

Neurotoxic mode of action of artemisinin

We recently described a screening system designed to detect neurotoxicity of artemisinin derivatives based on primary neuronal brain stem cell cultures (G. Schmuck and R. K. Haynes, Neurotoxicity Res. 2:37-49, 2000). Here, we probe possible mechanisms of this brain stem-specific neurodegeneration, in which artemisinin-sensitive neuronal brain stem cell cultures are compared with nonsensitive cultures (cortical neurons, astrocytes). Effects on the cytoskeleton of brain stem cell cultures, but not that of cortical cell cultures, were visible after 7 days. However, after a recovery period of 7 days, this effect also became visible in cortical cells and more severe in brain stem cell cultures. Neurodegeneration appears to be induced by effects on intracellular targets such as the cytoskeleton, modulation of the energy status by mitochondrial or metabolic defects, oxidative stress or excitotoxic events. Artemisinin reduces intracellular ATP levels and the potential of the inner mitochondrial membrane below the cytotoxic concentration range in all three cell cultures, with these effects being most dominant in the brain stem cultures. Surprisingly, there were substantial effects on cortical neurons after 7 days and on astrocytes after 1 day. Artemisinin additionally induces oxidative stress, as observed as an increase of reactive oxygen species and of lipid peroxidation in both neuronal cell types. Interestingly, an induction of expression of AOE was only seen in astrocytes. Here, manganese superoxide dismutase (MnSOD) expression was increased more than 3-fold and catalase expression was increased more than 1.5-fold. In brain stem neurons, MnSOD expression was dose dependently decreased. Copper-zinc superoxide dismutase and glutathione peroxidase, two other antioxidant enzymes that were investigated, did not show any changes in their mRNA expression in all three cell types after exposure to artemisinin.

Assessment of the neurotoxicity of oral dihydroartemisinin in mice

High doses of the oil-soluble antimalarial artemisinin derivatives artemether and arteether, given by intramuscular injection to experimental mammals, produce an unusual pattern of selective damage to brainstem centres predominantly involved in auditory processing and vestibular reflexes. We have shown recently, in adult Swiss albino mice, that constant exposure either from depot intramuscular injection of oil-based artemisinin derivatives, or constant oral intake carries relatively greater neurotoxic potential than other methods of drug administration. Using the same model, oral dihydroartemisinin suspended in water was administered once or twice daily at different doses ranging from 50 to 300 mg/kg/day for 28 days. The neurotoxic potential of the oral dihydroartemisinin was assessed and compared to that of oral artemether and artesunate. Oral artemether, artesunate, and dihydroartemisinin had similar neurotoxic effects with no significant clinical or neuropathological evidence of toxicity at doses below 200 mg/kg/day. These data indicate that once and twice daily oral administration of artemether, artesunate and dihydroartemisinin is relatively safe when compared to intramuscular administration of the oil-based compounds.

The role of glutathione in the neurotoxicity of artemisinin derivatives in vitro

The role of antioxidants in the neurotoxicity of the antimalarial endoperoxides artemether and dihydroartemisinin was studied in vitro by quantitative image analysis of neurite outgrowth in the neuroblastoma cell line NB2a. Intracellular glutathione concentrations were measured by high performance liquid chromatography with fluorescence detection. Both dihydroartemisinin (1 microM) and a combination of artemether (0.3 microM) plus haemin (2 microM) significantly inhibited neurite outgrowth from differentiating NB2a cells to 11.5 +/- 11.0% (SD) and 19.6 +/- 15.2% of controls, respectively. The inhibition by artemether/haemin was prevented by the antioxidants superoxide dismutase (109.7 +/- 47.8% of control), catalase (107.0 +/- 29.3%) glutathione (123.8 +/- 12.4%), L-cysteine (88.0 +/- 6.3%), N-acetyl-L-cysteine (107.8 +/- 14.9%), and ascorbic acid (104.3 +/- 12.7%). Dihydroartemisinin-induced neurotoxicity was completely or partially prevented by L-cysteine (99.5 +/- 17.7% of control), glutathione (57.9 +/- 23.4% of control), and N-acetyl-L-cysteine (57.3 +/- 9.5%), but was not prevented by superoxide dismutase, catalase, or ascorbic acid. Buthionine sulphoximine, an inhibitor of gamma-glutamylcysteine synthetase, significantly increased the neurotoxic effect of non-toxic concentrations of artemether/haemin (0.1 microM/2 microM) and dihydroartemisinin (0.2 microM), suggesting that endogenous glutathione participates in the prevention of the neurotoxicity of artemether/haemin and dihydroartemisinin. Artemether/haemin completely depleted intracellular glutathione levels, whereas dihydroartemisinin had no effect. We conclude that although glutathione status is an important determinant in the neurotoxicity of endoperoxides, depletion of glutathione is not a prerequisite for their toxicity. This is consistent with their mechanisms of toxicity being free radical-mediated damage to redox-sensitive proteins essential for neurite outgrowth, or alteration of a redox-sensitive signalling system which regulates neurite outgrowth.

Behavioral and neural toxicity of the artemisinin antimalarial, arteether, but not artesunate and artelinate, in rats

Three artemisinin antimalarials, arteether (AE), artesunate (AS), and artelinate (AL) were evaluated in rats using an auditory discrimination task (ADT) and neurohistology. After rats were trained on the ADT, equimolar doses of AE (25 mg/kg, in sesame oil, n=6), AS (31 mg/kg, in sodium carbonate, n=6), and AL (36 mg/kg, in saline, n=6), or vehicle (sodium carbonate, n=6) were administered (IM) for 7 consecutive days. Behavioral performance was evaluated, during daily sessions, before, during, and after administration. Histological evaluation of the brains was performed using thionine staining, and damaged cells were counted in specific brainstem nuclei of all rats. Behavioral performance was not significantly affected in any rats treated with AS, AL, or vehicle. Furthermore, histological examination of the brains of rats treated with AS, AL, and vehicle did not show damage. In stark contrast, all rats treated with AE showed a progressive and severe decline in performance on the ADT. The deficit was characterized by decreases in accuracy, increases in response time and, eventually, response suppression. When performance on the ADT was suppressed, rats also showed gross behavioral signs of toxicity that included tremor, gait disturbances, and lethargy. Subsequent histological assessment of AE-treated rats revealed marked damage in the brainstem nuclei, ruber, superior olive, trapezoideus, and inferior vestibular. The damage included chromatolysis, necrosis, and gliosis. These results demonstrate distinct differences in the ability of artemisinins to produce neurotoxicity. Further research is needed to uncover pharmacokinetic and metabolic differences in artemisinins that may predict neurotoxic potential.

Establishment of an in vitro screening model for neurodegeneration induced by antimalarial drugs of the artemisinin-type

The establishment of an in vitro screening model for neurodegeneration inducing antimalarial drugs was conducted in stepwise fashion. Firstly, the in vivo selective neurotoxic potency of artemisinin was tested in neuronal cells in vitro in relation to the cytotoxic potency in other organ cell cultures such as liver and kidney or versus glial cells. Secondly, a comparison between different parts of the brain (cortex vs. brain stem) was performed and in the last step, a fast and sensitive screening endpoint was identified. In summary, non-neuronal cell lines such as hepatocytes (HEP-G2), liver epithelial cells (IAR), proximal tubular cells (LLC-PK(1)) and glial cells from the rat (C6) and human (GO-G-IJKT) displayed only moderate sensitivity to artemisinin and its derivatives. The same was found in undifferentiated neuronal cell lines from the mouse (N-18) and from human (Kelly), whereas during differentiation, these cells became much more sensitive. Primary astrocytes from the rat also were not specifically involved. In the comparison of primary neuronal cell cultures from the cortex and brain stem of the rat, the brain stem was found to be more sensitive than the cortex. The neurotoxic potential was determined by cytoskeleton elements (neurofilaments), which were degradated in vitro by diverse neurodegenerative compounds. In comparison of dog and rat primary brain stem cultures, the dog cells were found to be more sensitive to artemisinin than the rat cells. In addition to the primary brain stem cell cultures it was shown that the sprouting assay, which determines persistent delayed neurotoxic effects, is also useful for screening antimalarial drugs. To other compounds, artemether and artesunate, showed that use of the sprouting assay followed by primary brain stem cultures of the rat will be a good strategy to select candidate compounds.

Differential effects of orally versus parenterally administered qinghaosu derivative artemether in dogs

Artemether (AM) is an antimalarial drug derived from artemisinin (Qinghaosu), an extract of the herb Artemisia annua L., sweet wormwood. Its antiparasitic effect is that of a schizontocide and is explained by rapid uptake by parasitized erythrocytes and interaction with a component of hemoglobin degradation resulting in formation of free radicals. It has been shown to exhibit a high clinical cure rate. Previous animal safety studies with Qinghaosu derivatives revealed dose-dependent neurotoxicity with movement disturbances and neuropathic changes in the hindbrain of intramuscularly treated dogs, rats and monkeys. Such effects have not been seen in man. The objective of our present studies was to compare the effects of high levels of AM administered to dogs p.o. versus i.m. In a pilot study 20 mg/kg/day of AM was given i.m. to groups of 3 male Beagle dogs for 5 and 30 days, respectively. Clinical signs of neurotoxicity were noted in some individual dogs from test day 23 on. One dog had to be sacrificed pre-term. Hematologic findings indicated a hypochromic, microcytic anemia. Microscopic examination demonstrated neuropathic changes only at 30 days, but not at 5 days. The animals had neuronal and secondary axonal damage, most prominent in the cerebellar roof, pontine and vestibular nuclei, and in the raphe/paralemniscal region. The affected neurons showed loss of Nissl substance, cytoplasmic eosinophilia, shrinkage of the nucleus and in advanced stages scavenging by microglia. In a subsequent experiment, AM was administered to groups of 4 male and 4 female dogs, respectively, at 8 daily doses of 0, 20, 40 and 80 mg/kg i.m., or 0, 50, 150 and 600 mg/kg p.o. Neurologic signs were seen at high i.m. doses only. In most animals they were inconspicuous and consisted of reduced activity with convulsions seen in single dogs shortly before death. Neuronal damage occurred in all animals at 40 and 80 mg/kg following i.m. treatment. At 20 mg/kg minimal effects occurred in 5/8 dogs only, indicating that this level was close to tolerated exposure. No comparable lesions were observed after oral administration. Both i.m. and p.o. exposure at high dose levels was associated with a prolongation of mean QT interval of ECG, suggesting slowing of repolarization of the myocardium. Individual data indicated that in 1 of 4 females at 80 mg/kg i.m. this prolongation was above the 25% level considered as threshold for concern. After intramuscular administration pharmacokinetics indicated peak plasma levels of AM at 2 to 4 hours post-dose, slow elimination and a tendency to accumulate after repeated administration. Only low levels of the major metabolite, dihydroartemisinin (DHA), were found. AM levels in the cerebrospinal fluid (CSF) were < 10% of plasma levels. After oral administration AM concentrations were considerably lower than after i.m. administration. The concentration of DHA was high on day 1 but almost nil on day 7 indicating its fast inactivation in dogs. Two hours after the 8th oral administration neither AM nor DHA was detected in CSF which may explain the absence of neurotoxicity in dogs after oral administration of AM.

Dose-dependent brainstem neuropathology following repeated arteether administration in rats

Histopathological effects of the artemisinin antimalarial, beta-arteether, were evaluated in rats. Arteether (3.125-12.5 mg/kg/day, IM, in sesame oil) was administered for 7 consecutive days. Seven days following the last injection, histological evaluation of the brainstem was performed. Rats treated with 12.5 mg/kg showed significant neuropathology, including chromatolysis, in the nucleus trapezoideus and nucleus superior olive. To a lesser extent, neuropathology was present in the nucleus ruber. Mild neuropathology was also detected in other brainstem regions examined. Although no statistically significant neuropathology was found for the groups treated with 6.25 mg/kg/day and 3.125 mg/kg/day, substantial neuropathology was observed in a single rat in each of these treatment conditions. These results confirm and extend previous studies demonstrating brainstem neurotoxicity from artemisinin antimalarials. Furthermore, these results suggest that, in rats, brainstem auditory pathways may be particularly vulnerable. Early detection of arteether neuropathology may, therefore, require examination of auditory functions.

Enhanced in vitro neurotoxicity of artemisinin derivatives in the presence of haemin

The role of haem in the neurotoxicity of artemisinin derivatives has been studied in vitro by examining neurite outgrowth measured by image analysis and cellular metabolism of the tetrazolium salt MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) measured spectrophotometrically in the neuroblastoma cell line NB2a, and by examining binding of radiolabelled dihydroartemisinin to NB2a cell and rat brain proteins. In the cases of artemether, dihydroartemisinin, and arteether, haemin (ferriprotoporphyrin IX) significantly increased the dose-related inhibition of neurite outgrowth from differentiating NB2a cells and significantly increased the dose-dependent inhibition of MTT metabolism. Inhibition of neurite outgrowth and metabolism of MTT in the presence or absence of haemin ranged from 72% to 93% and from 27% to 49% at a drug concentration of 300 nM. Haemin also significantly increased the dose-related binding of radiolabelled dihydroartemisinin to proteins from NB2a cells approximately twofold and to rat brain between three- and sixfold. Haemin did not enhance the neurotoxicity of desoxyarteether, a structural analogue of arteether with an ether linkage in the place of the endoperoxide bridge. It is suggested that haemin may catalyse the transformation of these derivatives via an interaction with the endoperoxide bridge of the artemisinin derivative to produce free radicals or electrophilic intermediates that are toxic to neuronal cells.