Effects of artesunate, dihydroartemisinin, and an artesunate-dihydroartemisinin combination against Toxoplasma gondii

Evaluation of the Combined Effect of Artemisinin and Ferroptosis Inducer RSL3 against Toxoplasma gondii

Toxoplasma gondii is a widespread intracellular pathogen that infects humans and a variety of animals. Dihydroartemisinin (DHA), an effective anti-malarial drug, has potential anti-T. gondii activity that induces ferroptosis in tumor cells, but the mechanism by which it kills T. gondii is not fully understood. In this study, the mechanism of DHA inhibiting T. gondii growth and its possible drug combinations are described. DHA potently inhibited T. gondii with a half-maximal effective concentration (EC₅₀) of 0.22 μM. DHA significantly increased the ROS level of parasites and decreased the mitochondrial membrane potential, which could be reversed by ferroptosis inhibitors (DFO). Moreover, the ferroptosis inducer RSL3 inhibited T. gondii with an EC₅₀ of 0.75 μM. In addition, RSL3 enhanced the DHA-induced ROS level, and the combination of DHA and RSL3 significantly increased the anti-Toxoplasma effect as compared to DHA alone. In summary, we found that DHA-induced ROS accumulation in tachyzoites may be an important cause of T. gondii growth inhibition. Furthermore, we found that the combination of DHA and RSL3 may be an alternative to toxoplasmosis. These results will provide a new strategy for anti-Toxoplasma drug screening and clinical medication guidance.

Formulation of Neem oil-loaded solid lipid nanoparticles and evaluation of its anti-Toxoplasma activity

BACKGROUND

Toxoplasmosis is caused by an intracellular zoonotic protozoan, Toxoplasma gondii, which could be lethal in immunocompromised patients. This study aimed to synthesize Neem oil-loaded solid lipid nanoparticles (NeO-SLNs) and to evaluate the anti-Toxoplasma activity of this component.

METHODS

The NeO-SLNs were constructed using double emulsification method, and their shape and size distribution were evaluated using transmission electron microscope (TEM) and dynamic light scattering (DLS), respectively. An MTT assay was employed to evaluate the cell toxicity of the component. The anti-Toxoplasma activity of NeO-SLNs was investigated using vital (trypan-blue) staining. Anti-intracellular Toxoplasma activity of NeO-SLNs was evaluated in T. gondii-infected Vero cells.

RESULTS

The TEM analysis represented round shape NeO-SLNs with clear and stable margins. DLS analysis showed a mean particle size 337.6 nm for SLNs, and most of nanoparticles were in range 30 to 120 nm. The cell toxicity of NeO-SLNs was directly correlated with the concentration of the component (P-value = 0.0013). The concentration of NeO-SLNs, which was toxic for at least 50% of alive T. gondii (cytotoxic concentration (CC50)), was > 10 mg/mL. The ability of NeO-SLNs to kill Toxoplasma was concentration-dependent (P-value < 0.0001), and all concentrations killed at least 70% of alive tachyzoites. Furthermore, the viability of T. gondii- infected Vero cells was inversely correlated with NeO-SLNs concentrations (P-value = 0.0317), and in the concentration 100 μg/mL at least 75% of T. gondii- infected Vero cells remained alive.

CONCLUSIONS

Overall, our findings demonstrated that the NeO-SLNs was able to kill T. gondii tachyzoites in concentration 100 μg/mL with a cell toxicity lower than 20%. Such results suggest that employing SLNs as carrier for NeO can effectively kill T. gondii tachyzoites with acceptable cell toxicity. Our findings also showed that SLNs capsulation of the NeO can lead to prolonged release of the extract, suggesting that NeO-SLNs could be also employed to clear cyst stages, which should be further investigated in animal models.

Impact of Plant-Based Foods and Nutraceuticals on Toxoplasma gondii Cysts: Nutritional Therapy as a Viable Approach for Managing Chronic Brain Toxoplasmosis

Toxoplasma gondii is an obligate intracellular parasite that mainly infects warm-blooded animals including humans. T. gondii can encyst and persist chronically in the brain, leading to a broad spectrum of neurological sequelae. Despite the associated health threats, no clinical drug is currently available to eliminate T. gondii cysts. In a continuous effort to uncover novel therapeutic agents for these cysts, the potential of nutritional products has been explored. Herein, we describe findings from in vitro and in vivo studies that support the efficacy of plant-based foods and nutraceuticals against brain cyst burden and cerebral pathologies associated with chronic toxoplasmosis. Finally, we discuss strategies to increase the translatability of preclinical studies and nutritional products to address whether nutritional therapy can be beneficial for coping with chronic T. gondii infections in humans.

Application of Amino Acids in the Structural Modification of Natural Products: A Review

Natural products and their derivatives are important sources for drug discovery; however, they usually have poor solubility and low activity and require structural modification. Amino acids are highly soluble in water and have a wide range of activities. The introduction of amino acids into natural products is expected to improve the performance of these products and minimize their adverse effects. Therefore, this review summarizes the application of amino acids in the structural modification of natural products and provides a theoretical basis for the structural modification of natural products in the future. The articles were divided into six types based on the backbone structures of the natural products, and the related applications of amino acids in the structural modification of natural products were discussed in detail.

Evolution of resistance in vitro reveals mechanisms of artemisinin activity in Toxoplasma gondii

Artemisinins are effective against a variety of parasites and provide the first line of treatment for malaria. Laboratory studies have identified several mechanisms for artemisinin resistance in Plasmodium falciparum, including mutations in Kelch13 that are associated with delayed clearance in some clinical isolates, although other mechanisms are likely involved. To explore other potential mechanisms of resistance in parasites, we took advantage of the genetic tractability of Toxoplasma gondii, a related parasite that shows moderate sensitivity to artemisinin. Resistant populations of T. gondii were selected by culture in increasing concentrations and whole-genome sequencing identified several nonconservative point mutations that emerged in the population and were fixed over time. Genome editing using CRISPR/Cas9 was used to introduce point mutations conferring amino acid changes in a serine protease homologous to DegP and a serine/threonine protein kinase of unknown function. Single and double mutations conferred a competitive advantage over wild-type parasites in the presence of drug, despite not changing EC50 values. Additionally, the evolved resistant lines showed dramatic amplification of the mitochondria genome, including genes encoding cytochrome b and cytochrome c oxidase I. Prior studies in yeast and mammalian tumor cells implicate the mitochondrion as a target of artemisinins, and treatment of wild-type parasites with high concentrations of drug decreased mitochondrial membrane potential, a phenotype that was stably altered in the resistant parasites. These findings extend the repertoire of mutations associated with artemisinin resistance and suggest that the mitochondrion may be an important target of inhibition of resistance in T. gondii.

Synthesis, in vitro and in vivo biological evaluation of dihydroartemisinin derivatives with potential anti-Toxoplasma gondii agents

In this study, four series of dihydroartemisinin derivatives were designed, synthesized, and evaluated for anti-toxoplasma gondii activity, and calculated the selectivity index (SI). It was the higher the SI, the better the effect of this compound against Toxoplasma gondii. Our goal was to filter out compounds that were bigger SI than the lead compound. The compound with the highest SI was selected for the anti-toxoplasmosis test in mice in vivo. Among the synthesized compounds, the (3R,5aS,6R,8aS,9R,12R,12aR)-3,6,9-trimethyl-decahydro-12H-3,12-epoxy[1,2]di-oxepino[4,3 -i]isochromen-10-yl-(te-rt-butoxycarbonyl)-l-alaninate (A2) exhibited the most potent anti-T. gondii activity and low cytotoxicity (SI: 6.44), yielding better results than the lead compound DHA (SI: 1.00) and the clinically used positive-control drug spiramycin (SI: 0.72) in vitro. Furthermore, compound A2 had better growth inhibitory effects on T. gondii in vivo than spiramycin did and significantly reduced the number of tachyzoites in the peritoneal cavity of mice (P < 0.01). The evaluation of the data generated in the T. gondii mouse infection model indicates that compound A2 treatment was a good inhibitor of T. gondii in vivo and that it was effective in relieving the liver damage induced by T. gondii. In addition, the results of a docking study revealed that A2 could become a better T. gondii calcium-dependent protein kinase1 (TgCDPK1) inhibitor. For this reason, compound A2 has potential as an anti-parasitic drug. Further studies are required to elucidate the mechanism of the action of compound A2, as well as to develop drug delivery systems for patients.

Treatment of Toxoplasmosis and Neosporosis in Farm Ruminants: State of Knowledge and Future Trends

Toxoplasmosis and neosporosis are closely related protozoan diseases that lead to important economic impacts in farm ruminants. Toxoplasma gondii infection mainly causes reproductive failure in small ruminants and is a widespread zoonosis, whereas Neospora caninum infection is one of the most important causes of abortion in cattle worldwide. Vaccination has been considered the most economic measure for controlling these diseases. However, despite vaccine development efforts, only a live-attenuated T. gondii vaccine has been licensed for veterinary use, and no promising vaccines against ne-osporosis have been developed; therefore, vaccine development remains a key goal. Additionally, drug therapy could be a valuable strategy for disease control in farm ruminants, as several drugs that limit T. gondii and N. caninum proliferation and dissemination have been evaluated. This approach may also be relevant to performing an initial drug screening for potential human therapy for zoonotic parasites. Treat-ments can be applied against infections in adult ruminants to minimize the outcomes of a primo-infection or the reactivation of a chronic infection during gestation or in newborn ruminants to avoid infection chronification. In this review, the current status of drug development against toxoplasmosis and neosporo-sis in farm ruminants is presented, and in an effort to promote additional treatment options, prospective drugs that have shown efficacy in vitro and in laboratory animal models of toxoplasmosis and neosporosis are examined

Apoptotic activity and anti-Toxoplasma effects of artemether on the tachyzoites and experimental infected Vero and J774 cell lines by Toxoplasma gondii

OBJECTIVES

Drugs used for toxoplasmosis have limited efficacy and also severe side effects. A new drug with good efficacy and limited side effects is need of the hour. We studied the effects of artemether on Toxoplasma gondii in vitro conditions.

MATERIALS AND METHODS

Artemether (methyl-ether-qinghaosu) was tested for tachyzoites, J774, and Vero cell lines infected by T. gondii. For evaluating the effect of drugs on Vero cells infected with T. gondii, we designed two separate experiments; in the first experiment, the Vero cells were infected with tachyzoites and then treated with artemether; while in the second one, the tachyzoites were exposed to artemether and then Vero cells were infected with treated tachyzoites. For evaluating the apoptotic effect of artemether on tachyzoites and infected J774 macrophages cell line with T. gondii, we used flow cytometry method. Inhibitory concentration (IC50) was evaluated by intracellular replication of tachyzoites in Vero cells.

RESULTS

IC50 for infected Vero cells with tachyzoites was determined as 49.13 μg/ml. In pretreated tachyzoites with artemether before entering into Vero cells, IC50 was calculated as 13.15 μg/ml. In both experiments, artemether showed a higher inhibitory effect than sulfadiazine (positive control). Artemether even at the highest concentrations only showed low cytotoxicity on Vero and J774 cell lines. Apoptosis in tachyzoites rise with an increasing concentration of artemether.

CONCLUSIONS

Our findings indicate that artemether is effective to control the tachyzoites of T. gondii in vitro and maybe a good alternative drug for toxoplasmosis.

The Potential Therapeutic Effects of Artesunate on Stroke and Other Central Nervous System Diseases

Artesunate is an important agent for cerebral malaria and all kinds of other severe malaria because it is highly efficient, lowly toxic, and well-tolerated. Loads of research pointed out that it had widespread pharmacological activities such as antiparasites, antitumor, anti-inflammation, antimicrobes activities. As we know, the occurrence and development of neurological disorders usually refer to intricate pathophysiologic mechanisms and multiple etiopathogenesis. Recent progress has also demonstrated that drugs with single mechanism and serious side-effects are not likely the candidates for treatment of the neurological disorders. Therefore, the pluripotent action of artesunate may result in it playing an important role in the prevention and treatment of these neurological disorders. This review provides an overview of primary pharmacological mechanism of artesunate and its potential therapeutic effects on neurological disorders. Meanwhile, we also briefly summarize the primary mechanisms of artemisinin and its derivatives. We hope that, with the evidence presented in this review, the effect of artesunate in prevention and curing for neurological disorders can be further explored and studied in the foreseeable future.

The efficacy of herbal medicines against Toxoplasma gondii during the last 3 decades: a systematic review

The objective of the current study was to systematically review papers discussing the efficacy of medicinal herbs against Toxoplasma gondii. Data were systematically collected from published papers about the efficacy of herbs used against T. gondii globally from 1988 to 2015, from PubMed, Google Scholar, ISI Web of Science, EBSCO, Science Direct, and Scopus. Forty-nine papers were included in the current systematic review reporting the evaluation of medicinal plants against T. gondii globally, both in vitro and in vivo. Sixty-one plants were evaluated. Most of the studies were carried out on Artemisia annua. The second highest number of studies were carried out on Glycyrrhiza glabra extracts. RH and ME49 were the predominant parasite strains used. Additionally, Swiss-Webster and BALB/c mice were the major animal models used. Alcoholic and aqueous extracts were used more than other types of extracts. Natural compounds mentioned here may be developed as novel and more effective therapeutic agents that improve the treatment of toxoplasmosis due to their lower side effects, higher availability, and better cultural acceptance compared with those of the chemical drugs that are currently being used.

Artemisinin and its derivatives in treating protozoan infections beyond malaria

Parasitic protozoan diseases continue to rank among the world's greatest global health problems, which are also common among poor populations. Currently available drugs for treatment present drawbacks, urging the need for more effective, safer, and cheaper drugs. Artemisinin (ART) and its derivatives are some of the most important classes of antimalarial agents originally derived from Artemisia annua L. However, besides the outstanding antimalarial and antischistosomal activities, ART and its derivatives also possess activities against other parasitic protozoa. In this paper we review the activities of ART and its derivatives against protozoan parasites in vitro and in vivo, including Leishmania spp., Trypanosoma spp., Toxoplasma gondii, Neospora caninum, Eimeria tenella, Acanthamoeba castellanii, Naegleria fowleri, Cryptosporidium parvum, Giardia lamblia, and Babesia spp. We conclude that ART and its derivatives may be good alternatives for treating other non-malarial protozoan infections in developing countries, although more studies are necessary before they can be applied clinically.

Endothelial-Leukocyte Interaction in Severe Malaria: Beyond the Brain

Malaria is the most important parasitic disease worldwide, accounting for 1 million deaths each year. Severe malaria is a systemic illness characterized by dysfunction of brain tissue and of one or more peripheral organs as lungs and kidney. The most severe and most studied form of malaria is associated with cerebral complications due to capillary congestion and the adhesion of infected erythrocytes, platelets, and leukocytes to brain vasculature. Thus, leukocyte rolling and adhesion in the brain vascular bed during severe malaria is singular and distinct from other models of inflammation. The leukocyte/endothelium interaction and neutrophil accumulation are also observed in the lungs. However, lung interactions differ from brain interactions, likely due to differences in the blood-brain barrier and blood-air barrier tight junction composition of the brain and lung endothelium. Here, we review the importance of endothelial dysfunction and the mechanism of leukocyte/endothelium interaction during severe malaria. Furthermore, we hypothesize a possible use of adjunctive therapies to antimalarial drugs that target the interaction between the leukocytes and the endothelium.

Clinically Available Medicines Demonstrating Anti-Toxoplasma Activity

Toxoplasma gondii is an apicomplexan parasite of humans and other mammals, including livestock and companion animals. While chemotherapeutic regimens, including pyrimethamine and sulfadiazine regimens, ameliorate acute or recrudescent disease such as toxoplasmic encephalitis or ocular toxoplasmosis, these drugs are often toxic to the host. Moreover, no approved options are available to treat infected women who are pregnant. Lastly, no drug regimen has shown the ability to eradicate the chronic stage of infection, which is characterized by chemoresistant intracellular cysts that persist for the life of the host. In an effort to promote additional chemotherapeutic options, we now evaluate clinically available drugs that have shown efficacy in disease models but which lack clinical case reports. Ideally, less-toxic treatments for the acute disease can be identified and developed, with an additional goal of cyst clearance from human and animal hosts.

Oxidative stress control by apicomplexan parasites

Apicomplexan parasites cause infectious diseases that are either a severe public health problem or an economic burden. In this paper we will shed light on how oxidative stress can influence the host-pathogen relationship by focusing on three major diseases: babesiosis, coccidiosis, and toxoplasmosis.

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.

Embryotoxicity and toxicokinetics of the antimalarial artesunate in rats

This study was conducted to investigate the potential embryo-fetal toxicity and toxicokinetics of the antimalarial agent artesunate (ARTS) in Sprague-Dawley rats. Pregnant rats were administered ARTS daily from gestational day 6~15 via oral gavage, at test doses of 0, 2, 4, or 8 mg/kg (22 females per group). The fetuses were examined for external, visceral, and skeletal abnormalities on gestational day 20. With regard to the dams, there were no deaths, treatment-related clinical signs, changes in body weight, or food intake in any of the treatment groups. There were no treatment-related gross findings at necropsy in any treatment group. In the 8 mg/kg group, there was a decrease in gravid uterine weight and in the weight of female fetuses. There was also an increase in fetal deaths (primarily late resorptions) and an increase in post-implantation losses (37%) at 8 mg/kg. An increase in the incidence of visceral and skeletal variations at 4 and 8 mg/kg was observed. These defects included minor changes in the appearance of the kidney and thymus, as well as absent ribs or thoracic vertebrae. Toxicokinetics were assessed in a parallel study, using 4 mated females per group. Using liquid chromatography-mass spectrometry (LC-MS) analysis, the concentration of ARTS and its metabolite dihydroartemisinin (DHA) were quantified in plasma from rats on gestational days 5, 6, 10, and 15. Amniotic fluid was assayed for ARTS and DHA on gestational day 15. There was evidence of rapid conversion of ARTS to the metabolite DHA in maternal plasma, since ARTS could not be consistently detected in plasma at the three doses tested. ARTS and DHA were not detected in amniotic fluid at gestational day 15, indicating limited placental transfer of the two agents. The embryofetal no-observable-adverse-effect level (NOAEL) of the test item was considered to be 8 mg/kg/day for dams, and 2 mg/kg/day for embryo-fetal development.

Is there a reduced sensitivity of dihydroartemisinin against praziquantel-resistant Schistosoma japonicum?

Praziquantel is currently the only drug of choice for the treatment of human schistosomiases. However, it has been proved that Schistosoma japonicum subjected to drug pressure may develop resistance to praziquantel. To evaluate the efficacy of dihydroartemisinin against praziquantel-resistant S. japonicum, mice infected with a praziquantel-resistant isolate and a praziquantel-susceptible isolate of S. japonicum were treated with dihydroartemisinin at a single oral dose of 300 mg/kg given once on each of 35-36 post-infection days, while infected but untreated mice served as controls. All mice were sacrificed 50 days post-infection, and the worm burden reductions were estimated. Administration of dihydroartemisinin at a single oral dose of 300 mg/kg on each of 35-36 post-infection days reduced total worm burdens of 69.8% and female worm burdens of 86% in mice infected with the praziquantel-susceptible isolate, and total worm burdens of 66.1% and female worm burdens of 85.1% in mice infected with the praziquantel-resistant isolate (both P values > 0.05). It is concluded that the sensitivity of artemisinin derivative dihydroartemisinin does not reduce in praziquantel-resistant S. japonicum.

Artesunate Exerts a Direct Effect on Endothelial Cell Activation and NF-κB Translocation in a Mechanism Independent of Plasmodium Killing

Artemisinin and its derivates are an important class of antimalarial drug and are described to possess immunomodulatory activities. Few studies have addressed the effect of artesunate in the murine malaria model or its effect on host immune response during malaria infection. Herein, we study the effect of artesunate treatment and describe an auxiliary mechanism of artesunate in modulating the inflammatory response during experimental malaria infection in mice. Treatment with artesunate did not reduce significantly the parasitemia within 12 h, however, reduced BBB breakdown and TNF-α mRNA expression in the brain tissue of artesunate-treated mice. Conversely, mefloquine treatment was not able to alter clinical features. Notably, artesunate pretreatment failed to modulate the expression of LFA-1 in splenocytes stimulated with parasitized red blood cells (pRBCs) in vitro; however, it abrogated the expression of ICAM-1 in pRBC-stimulated endothelial cells. Accordingly, a cytoadherence in vitro assay demonstrated that pRBCs did not adhere to artesunate-treated vascular endothelial cells. In addition, NF-κB nuclear translocation in endothelial cells stimulated with pRBCs was impaired by artesunate treatment. Our results suggest that artesunate is able to exert a protective effect against the P. berghei-induced inflammatory response by inhibiting NF-κB nuclear translocation and the subsequent expression of ICAM-1.

In vitro action of antiparasitic drugs, especially artesunate, against Toxoplasma gondii

INTRODUCTION: Toxoplasmosis is usually a benign infection, except in the event of ocular, central nervous system (CNS), or congenital disease and particularly when the patient is immunocompromised. Treatment consists of drugs that frequently cause adverse effects; thus, newer, more effective drugs are needed. In this study, the possible activity of artesunate, a drug successfully being used for the treatment of malaria, on Toxoplasma gondii growth in cell culture is evaluated and compared with the action of drugs that are already being used against this parasite. METHODS: LLC-MK2 cells were cultivated in RPMI medium, kept in disposable plastic bottles, and incubated at 36ºC with 5% CO2. Tachyzoites of the RH strain were used. The following drugs were tested: artesunate, cotrimoxazole, pentamidine, pyrimethamine, quinine, and trimethoprim. The effects of these drugs on tachyzoites and LLC-MK2 cells were analyzed using nonlinear regression analysis with Prism 3.0 software. RESULTS: Artesunate showed a mean tachyzoite inhibitory concentration (IC50) of 0.075µM and an LLC MK2 toxicity of 2.003µM. Pyrimethamine was effective at an IC50 of 0.482µM and a toxicity of 11.178µM. Trimethoprim alone was effective against the in vitro parasite. Cotrimoxazole also was effective against the parasite but at higher concentrations than those observed for artesunate and pyrimethamine. Pentamidine and quinine had no inhibitory effect over tachyzoites. CONCLUSIONS: Artesunate is proven in vitro to be a useful alternative for the treatment of toxoplasmosis, implying a subsequent in vivo effect and suggesting the mechanism of this drug against the parasite.

Curcumin-arteether combination therapy of Plasmodium berghei-infected mice prevents recrudescence through immunomodulation

Earlier studies in this laboratory have shown the potential of artemisinin-curcumin combination therapy in experimental malaria. In a parasite recrudescence model in mice infected with Plasmodium berghei (ANKA), a single dose of alpha,beta-arteether (ART) with three oral doses of curcumin prevented recrudescence, providing almost 95% protection. The parasites were completely cleared in blood with ART-alone (AE) or ART+curcumin (AC) treatments in the short-term, although the clearance was faster in the latter case involving increased ROS generation. But, parasites in liver and spleen were not cleared in AE or AC treatments, perhaps, serving as a reservoir for recrudescence. Parasitemia in blood reached up to 60% in AE-treated mice during the recrudescence phase, leading to death of animals. A transient increase of up to 2-3% parasitemia was observed in AC-treatment, leading to protection and reversal of splenomegaly. A striking increase in spleen mRNA levels for TLR2, IL-10 and IgG-subclass antibodies but a decrease in those for INFγ and IL-12 was observed in AC-treatment. There was a striking increase in IL-10 and IgG subclass antibody levels but a decrease in INFγ levels in sera leading to protection against recrudescence. AC-treatment failed to protect against recrudescence in TLR2(-/-) and IL-10(-/-) animals. IL-10 injection to AE-treated wild type mice and AC-treated TLR2(-/-) mice was able to prolong survival. Blood from the recrudescence phase in AE-treatment, but not from AC-treatment, was able to reinfect and kill naïve animals. Sera from the recrudescence phase of AC-treated animals reacted with several parasite proteins compared to that from AE-treated animals. It is proposed that activation of TLR2-mediated innate immune response leading to enhanced IL-10 production and generation of anti-parasite antibodies contribute to protective immunity in AC-treated mice. These results indicate a potential for curcumin-based combination therapy to be tested for prevention of recrudescence in falciparum and relapse in vivax malaria.

Toxoplasma gondii: effects of Artemisia annua L. on susceptibility to infection in experimental models in vitro and in vivo

Considering that the treatment for toxoplasmosis is based on drugs that show limited efficacy due to their substantial side effects, the purpose of the present study was to evaluate the effects of Artemisia annua on in vitro and in vivo Toxoplasma gondii infection. A. annua infusion was prepared from dried herb and tested in human foreskin fibroblasts (HFF) or mice that were infected with the parasite and compared with sulfadiazine treatment. For in vitro experiments, treatment was done on parasite before HFF infection or on cells previously infected with T. gondii and the inhibitory concentration (IC(50)) values for each treatment condition were determined. Viability of HFF cells in the presence of different concentrations of A. annua infusion and sulfadiazine was above 72%, even when the highest concentrations from both treatments were tested. Also, the treatment of T. gondii tachyzoites with A. annua infusion before infection in HFF cells showed a dose-response inhibitory curve that reached up to 75% of inhibition, similarly to the results observed when parasites were treated with sulfadiazine. In vivo experiments with a cystogenic T. gondii strain demonstrated an effective control of infection using A. annua infusion. In conclusion, our results indicate that A. annua infusion is useful to control T. gondii infection, due to its low toxicity and its inhibitory action directly against the parasite, resulting in a well tolerated therapeutic tool.

Calcium regulation and signaling in apicomplexan parasites

Apicomplexan parasites rely on calcium-mediated signaling for a variety of vital functions including protein secretion, motility, cell invasion, and differentiation. These functions are controlled by a variety of specialized systems for uptake and release of calcium, which acts as a second messenger, and on the functions of calcium-dependent proteins. Defining these systems in parasites has been complicated by their evolutionary distance from model organisms and practical concerns in working with small, and somewhat fastidious cells. Comparative genomic analyses of Toxoplasma gondii, Plasmodium spp. and Cryptosporidium spp. reveal several interesting adaptations for calcium-related processes in parasites. Apicomplexans contain several P-type Ca2+ ATPases including an ER-type reuptake mechanism (SERCA), which is the proposed target of artemisinin. All three organisms also contain several genes related to Golgi PMR-like calcium transporters, and a Ca2+/H+ exchanger, while plasma membrane-type (PMCA) Ca2+ ATPases and voltage-dependent calcium channels are exclusively found in T. gondii. Pharmacological evidence supports the presence of IP3 and ryanodine channels for calcium-mediated release. Collectively these systems regulate calcium homeostasis and release calcium to act as a signal. Downstream responses are controlled by a family of EF-hand containing calcium binding proteins including calmodulin, and an array of centrin and caltractin-like genes. Most surprising, apicomplexans contain a diversity of calcium-dependent protein kinases (CDPK), which are commonly found in plants. Toxoplasma contains more than 20 CDPK or CDPK-like proteases, while Plasmodium and Cryptosporidium have fewer than half this number. Several of these CDPKs have been shown to play vital roles in protein secretion, invasion, and differentiation, indicating that disruption of calcium-regulated pathways may provide a novel means for selective inhibition of parasites.

Artemisinin induces calcium-dependent protein secretion in the protozoan parasite Toxoplasma gondii

Intracellular calcium controls several crucial cellular events in apicomplexan parasites, including protein secretion, motility, and invasion into and egress from host cells. The plant compound thapsigargin inhibits the sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA), resulting in elevated calcium and induction of protein secretion in Toxoplasma gondii. Artemisinins are natural products that show potent and selective activity against parasites, making them useful for the treatment of malaria. While the mechanism of action is uncertain, previous studies have suggested that artemisinin may inhibit SERCA, thus disrupting calcium homeostasis. We cloned the single-copy gene encoding SERCA in T. gondii (TgSERCA) and demonstrate that the protein localizes to the endoplasmic reticulum in the parasite. In extracellular parasites, TgSERCA partially relocalized to the apical pole, a highly active site for regulated secretion of micronemes. TgSERCA complemented a calcium ATPase-defective yeast mutant, and this activity was inhibited by either thapsigargin or artemisinin. Treatment of T. gondii with artemisinin triggered calcium-dependent secretion of microneme proteins, similar to the SERCA inhibitor thapsigargin. Artemisinin treatment also altered intracellular calcium in parasites by increasing the periodicity of calcium oscillations and inducing recurrent, strong calcium spikes, as imaged using Fluo-4 labeling. Collectively, these results demonstrate that artemisinin perturbs calcium homeostasis in T. gondii, supporting the idea that Ca2+-ATPases are potential drug targets in parasites.

Artemisinin-resistant mutants of Toxoplasma gondii have altered calcium homeostasis

Artemisinin is a plant sesquiterpene lactone that has become an important drug for combating malaria, especially in regions where resistance to other drugs is widespread. While the mechanism of action is debated, artemisinin has been reported to inhibit the sarcoplasmic endoplasmic reticulum Ca(2+) ATPase (SERCA) in the malaria parasite. Artemisinin is also effective against Toxoplasma in vitro and in vivo, although it is less potent and, hence, is generally not used therapeutically to treat toxoplasmosis. To explore the mechanism of action, we generated chemically derived mutants of Toxoplasma gondii that were resistant to growth inhibition by this compound in vitro. Three artemisinin-resistant (ART(r)) mutant clones that differed in their sensitivities in vitro by three- to fivefold compared with that of the wild-type parasites were obtained. ART(r) mutants were cross-resistant to other derivatives of artemisinin, the most potent of which was artemisone. Resistance was not due to molecular alterations or differences in the expression of SERCA or other putative targets, such as proteins that code for multidrug resistance or translationally controlled tumor protein. ART(r) mutants were resistant to the induction of protein secretion from micronemes, a calcium-dependent process that is triggered by artemisinin. ART(r) mutants were not cross-resistant to secretion induced by thapsigargin but were more sensitive and were unable to regulate cytoslic calcium following treatment with this compound. These studies implicate calcium homeostasis in the mechanism of action of artemisinins against apicomplexan parasites.

Development and validation of a high-performance liquid chromatography–mass spectroscopy assay for determination of artesunate and dihydroartemisinin in human plasma

A sensitive method has been developed and validated for the determination of artesunate and its active metabolite dihydroartemisinin (DHA) in human plasma using artemisinin as an internal standard. Solid phase extraction (SPE) using Oasis HLB extraction cartridges was used for sample preparation and analysis was performed on a Shimadzu LCMS-2010 in single ion monitoring positive mode using atmospheric pressure chemical ionization (APCI) as an interface. Positive ions were measured using extracted ion chromatogram mode. The extracted ion for artesunate, alpha- and beta-DHA was m/z 221 and for artemisinin was m/z 283. Chromatography was carried out using a Synergi Max-RP, 4 mu, 75 mm x 4.6 mm column using glacial acetic acid 0.1%, acetonitrile and methanol mixture (38:46.5:15.5) as a mobile phase delivered at a flow rate of 0.5 mL/min. The retention times of artesunate, alpha- and beta-DHA and artemisinin were 17.4, 11.8, 18.7 and 13.4 min, respectively, with a total run time of 21 min. The assay was linear over the range 1-3000 ng/mL for artesunate and DHA. The analysis of quality control samples for artesunate 50, 300, 1300 and 2600 ng/mL demonstrated excellent precision with relative standard deviation of 14.3, 11.3, 7.5 and 12.1%, respectively (n=5). Recoveries at concentration of 50, 300, 1300 and 2600 ng/mL were 75, 94.5, 74.3 and 75.5%, respectively; similar results were obtained for precision and recovery of DHA. This liquid chromatography-mass spectroscopy (LC-MS) method for the determination of artesunate and DHA in human plasma has superior specification for sensitivity, sample throughput and robustness than previous methods and can reliably quantitate concentrations of both (artesunate and DHA) compounds as low as 1 ng/mL.