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Toxoplasma gondii is the etiological agent of toxoplasmosis, a common parasitic disease that affects nearly one-third of the human population. The primary infection can be asymptomatic in healthy individuals but may prove fatal in immunocompromised individuals. Available treatment options for toxoplasmosis patients are limited, underscoring the urg...
Citations
... The recommended treatment for Toxoplasma encephalitis (TE) is a combination of pyrimethamine and sulfadiazine, and trimethoprimsulfamethoxazole (TMP-SMX) plus azithromycin is an alternative therapeutic regimen [6][7]. However, standard treatment is associated with considerable side effects, especially prolonged suppressive treatment is essential to prevent relapse [8][9]. One of the important issues in the treatment of chronic T. gondii infection is poor brain penetration of standard treatments. ...
Toxoplasma gondii (T. gondii) is a protozoan parasite, which causes toxoplasmosis, a worldwide disease infecting all types of human cells. The efficacy of compound PPQ-6 against Toxoplasma gondii was examined in a murine model infected with a non-virulent (Me49) strain. Forty-eight female Swiss-albino mice (6 weeks old) were inoculated by mouth with 10 cysts/mouse and divided into 6 groups. Group I: was left untreated immunocomptent, group II: untreated immunocompromised, group III: infected immunocomptent, group IV: infected immunocompromised, group V: infected and treated with PPQ-6 and group VI: infected and treated with Pyrimethamine /sulfadiazine, treatment was started eight weeks post-infection and continued for 14 consecutive days. four mice from each group were sacrificed and the rest were observed for 30 days. Results showed that, the median survival duration of group I, II, V were 8.57 weeks, while the median survival duration of group III, IV, VI were 8.41, 7.26 and 8.16 weeks respectively (P >0.05). PPQ-6 induced a significant increase in serum level of IFN-γ more than with Pyrimethamine /sulfadiazine when compared with infected untreated group. Both PPQ-6 and Pyrimethamine / sulfadiazine-treated groups decrease of serum TNF-α level when compared with the untreated group. Conclusively, PPQ-6 shows promising results, hence it could be a potentially used alternatively with Pyrimethamine / sulfadiazine for treatment of reactivated toxoplasmosis.
... Strategies to identify new anti-parasitic compounds often use high throughput screening of small molecule libraries to identify inhibitors of parasite proliferation [21][22][23][24]. Adapting such high throughput screens to more specific assays offers a route to identifying inhibitors that target particular processes in the parasite. ...
Apicomplexans are widespread parasites of humans and other animals, and include the causative agents of malaria (Plasmodium species) and toxoplasmosis (Toxoplasma gondii). Existing anti-apicomplexan therapies are beset with issues around drug resistance and toxicity, and new treatment options are needed. The mitochondrial electron transport chain (ETC) is one of the few processes that has been validated as a drug target in apicomplexans. To identify new inhibitors of the apicomplexan ETC, we developed a Seahorse XFe96 flux analyzer approach to screen the 400 compounds contained within the Medicines for Malaria Venture 'Pathogen Box' for ETC inhibition. We identified six chemically diverse, on-target inhibitors of the ETC in T. gondii, at least four of which also target the ETC of Plasmodium falciparum. Two of the identified compounds (MMV024937 and MMV688853) represent novel ETC inhibitor chemotypes. MMV688853 belongs to a compound class, the aminopyrazole carboxamides, that were shown previously to target a kinase with a key role in parasite invasion of host cells. Our data therefore reveal that MMV688853 has dual targets in apicomplexans. We further developed our approach to pinpoint the molecular targets of these inhibitors, demonstrating that all target Complex III of the ETC, with MMV688853 targeting the ubiquinone reduction (Qi) site of the complex. Most of the compounds we identified remain effective inhibitors of parasites that are resistant to Complex III inhibitors that are in clinical use or development, indicating that they could be used in treating drug resistant parasites. In sum, we have developed a versatile, scalable approach to screen for compounds that target the ETC in apicomplexan parasites, and used this to identify and characterize novel inhibitors.
... In healthy individuals, Toxoplasma infection may go unnoticed, but in immunocompromised or pregnant individuals, it may result in morbidity and mortality [5]. Consuming tissue cysts (which contain the bradyzoite form) in undercooked meat or oocysts (which contain the sporozoite form) discharged in felid fecal material can lead to host infection [6]. The parasite develops into tachyzoites, which quickly infect the host's tissues, when an intermediate host contracts T. gondii infection. ...
... The emerging evidence indicates that testing a variety of substances for possible antiparasitic action is a viable strategy for identifying new treatment options for infectious diseases [1,7]. Recently, we screened chemical libraries containing 1143 compounds and discovered 32 "hit" compounds that inhibited T. gondii growth in vitro [6]. One of these hit compounds is a naturally occurring anthraquinone derivative known as emodin (1,3,8-trihydroxy-6-methylanthraquinone) ( Figure 1). ...
... Previously, we reported our findings on a group of natural molecules, which included emodin that caused strong and selective in vitro inhibition of T. gondii growth. To confirm this earlier report [6], we assessed emodin at various concentrations (between 0.0 and 1000 µg/mL) for an anti-parasitic efficacy and host cell cytotoxic potential. We added emodin to a freshly purified parasite suspension to a growing human foreskin fibroblast (HFF ATCC ® ) cell to assess its anti-T. ...
Currently, toxoplasmosis affects nearly one-third of the world’s population, but the available treatments have several limitations. This factor underscores the search for better therapy for toxoplasmosis. Therefore, in the current investigation, we investigated the potential of emodin as a new anti-Toxoplasma gondii while exploring its anti-parasitic mechanism of action. We explored the mechanisms of action of emodin in the presence and absence of an in vitro model of experimental toxoplasmosis. Emodin showed strong anti-T. gondii action with an EC50 value of 0.03 µg/mL; at this same effective anti-parasite concentration, emodin showed no appreciable host cytotoxicity. Likewise, emodin showed a promising anti-T. gondii specificity with a selectivity index (SI) of 276. Pyrimethamine, a standard drug for toxoplasmosis, had an SI of 2.3. The results collectively imply that parasite damage was selective rather than as a result of a broad cytotoxic effect. Furthermore, our data confirm that emodin-induced parasite growth suppression stems from parasite targets and not host targets, and indicate that the anti-parasite action of emodin precludes oxidative stress and ROS production. Emodin likely mediates parasite growth suppression through means other than oxidative stress, ROS production, or mitochondrial toxicity. Collectively, our findings support the potential of emodin as a promising and novel anti-parasitic agent that warrants further investigation.
... Many phytochemicals are currently believed to serve as protective agents for plants against invading enemies, so earthworms can derive secondary protective benefits from these phytochemicals when they are readily available in aqueous forms in the worm-casts [23]. Most of the phytochemicals identified in the earthworm cast had been previously implicated for a variety of medicinal value [24,25]. For example, tannins, phenols steroids, anthraquinones, and coumarins have been shown to possess medicinal properties such as antioxidant, anti-inflammatory, anti-parasitic, and antimicrobial among others [26e31]. ...
Background: Despite the continuous interest in the search for therapeutic agents, little attention has been given to the medicinal relevance of earthworm casts, with even less interest in over-seasoned worm-casts. Therefore, this study determined the phytochemical, antimicrobial, and cytotoxic properties of over-seasoned worm-casts of the earthworm Hyperiodrilus africanus (Eudrilidae). Methods: The earthworm casts were extracted with n-hexane, ethanol, and water and the crude extracts were evaluated for the presence of chemical constituents and antimicrobial properties. Cytotoxicity was inferred from the antimitotic effects of the extracts on the radicles of germinating seeds of Sorghum bicolor. Results: The chemical constituent determinations revealed the presence of alkaloids, anthraquinones, coumarins, steroids, terpenoids, tannins, cardiac glycosides, and phenols. Screening the extracts for chemical constituents revealed that the ethanolic and aqueous extracts had more chemical constituents than n-hexane extracts. The ethanolic extract showed antibacterial activity against Streptococcus sp. and Staphylococcus aureus; the aqueous extract showed antifungal activity against Aspergillus flavus and Aspergillus niger. Furthermore, both extracts showed antimitotic activity against healthy cells of S. bicolor in a manner similar to that of the reference drug (cyclophosphamide). Conclusion: The study provides evidence, lending credence to the antimicrobial and cytotoxic potential of overseasoned casts of H. africanus.
... Unfortunately, these drugs show an effect only in the active phase of the parasite, in addition to elicit adverse events in patients. Antibiotic medicines such as azithromycin, clarithromycin, and spiramycin used as alternative treatment options are poorly tolerated and also have no effect on the bradyzoite form of the parasite [21][22][23]. ...
Background
Therapeutic options for toxoplasmosis are limited. This fact underscores ongoing research efforts to identify and develop better therapy. Previously, we reported the anti-parasitic potential of a new series of derivatives of imidazole.
Objective
In the current investigation, we attempted the investigation of the possible action mechanism of few promising anti-parasite imidazole derivatives namely C1 (bis-imidazole), C2 (phenyl-substituted 1H-imidazole) and C3 (thiophene-imidazole)
Methods
We evaluated if oxidative stress, hypoxia as well as metabolic reprogramming of host l-tryptophan pathway form part of the parasite growth inhibition by imidazoles. Anti-parasite assay was performed for imidazoles at concentrations ranging from 0 to 10 μM, while pyrimethamine was used as reference drug to validate assay.
Results
Imidazole compounds restricted parasite growth dose-dependently. However, in the presence of an antioxidant (Trolox), l-tryptophan and/or CoCl2 (chemical inducer of hypoxia), the growth inhibitory efficacy of imidazoles was appreciably abolished. Further, imidazole treatment led to elevated level of reactive oxygen species, while reducing parasite mitochondrial membrane potential compared with control. In contrast, imidazole had no effect on host HIF-1α level suggesting its exclusion in the anti-parasite action.
Conclusion
Taken together, imidazole-based compounds might restrict parasite growth by causing oxidative stress. The findings provide new insight on the likely biochemical mechanisms of imidazoles as prospective anti-parasite therapy. Data gives new perspective that not only underscores the anti-parasite prospects of imidazoles, but implicates the host l-tryptophan pathway as a feasible treatment option for T. gondii infections.
... Encouraging results have been reported in other repurposing screens of existing drugs, in which several compounds were found to have new anti-T. gondii indications (218,221). ...
Toxoplasma gondii is known to infect a considerable number of mammalian and avian species and a substantial proportion of the world’s human population. The parasite has an impressive ability to disseminate within the host’s body and employs various tactics to overcome the highly regulatory blood-brain barrier and reside in the brain. In healthy individuals, T. gondii infection is largely tolerated without any obvious ill effects. However, primary infection in immunosuppressed patients can result in acute cerebral or systemic disease, and reactivation of latent tissue cysts can lead to a deadly outcome. It is imperative that treatment of life-threatening toxoplasmic encephalitis is timely and effective. Several therapeutic and prophylactic regimens have been used in clinical practice. Current approaches can control infection caused by the invasive and highly proliferative tachyzoites but cannot eliminate the dormant tissue cysts. Adverse events and other limitations are associated with the standard pyrimethamine-based therapy, and effective vaccines are unavailable. In this review, the epidemiology, economic impact, pathophysiology, diagnosis, and management of cerebral toxoplasmosis are discussed, and critical areas for future research are highlighted.
... gondii activity in vitro and in vivo. Besides, studies that have shown successful treatment for toxoplasmosis patients are limited, indicating the urgent need to identify and develop new therapies (Adeyemi et al., 2018) and data about the inhibition of T. gondii using lumefantrine is not available. Therefore, in this study, we evaluated the effect of lumefantrine treatment on T. gondii infection in vivo and in vitro. ...
Toxoplasma gondii is an obligate intracellular protozoan parasite, which can infect almost all warm-blooded animals, including humans, leading to toxoplasmosis. Currently, the effective treatment for human toxoplasmosis is the combination of sulphadiazine and pyrimethamine. However, both drugs have serious side-effects and toxicity in the host. Therefore, there is an urgent need for the discovery of new anti- T. gondii drugs with high potency and less or no side-effects. Our findings suggest that lumefantrine exerts activity against T. gondii by inhibiting its proliferation in Vero cells in vitro without being toxic to Vero cells ( P ≤ 0.01). Lumefantrine prolonged mice infected with T. gondii from death for 3 days at the concentration of 50 μ g L ⁻¹ than negative control (phosphate-buffered saline treated only), and reduced the parasite burden in mouse tissues in vivo ( P ≤ 0.01; P ≤ 0.05). In addition, a significant increase in interferon gamma (IFN-γ) production was observed in high-dose lumefantrine-treated mice ( P ≤ 0.01), whereas interleukin 10 (IL-10) and IL-4 levels increased in low-dose lumefantrine-treated mice ( P ≤ 0.01). The results demonstrated that lumefantrine may be a promising agent to treat toxoplasmosis, and more experiments on the protective mechanism of lumefantrine should be undertaken in further studies.
... This reduction in cellular MMP may not only lead to limited energy production in terms of ATP generation but cause mitochondrial damage committing to cell death. Meanwhile, investigations have shown that ROS and/or oxidative stress may lead to mitochondrial damage [13,17]. In addition, earlier findings have shown that intracellular ROS could negatively impact mitochondria leading to cell death [18,19]. ...
Background
Our previous reports demonstrated the prospects of a new series of imidazoles as a source of alternative anti-parasite treatments, thus warranting further studies that include toxicity profiling.
Objective
In this study, we evaluated three imidazoles: bis-imidazole (compound 1), phenyl-substituted 1H-imidazole (compound 2), and thiopene-imidazole (compound 3) for cellular toxicity and possible mechanisms.
Methods
The three (3) compounds were assessed for in vitro cytotoxic action. Additionally, we probed likely mechanistic actions of these imidazoles. Findings showed dose-dependent cellular toxicity by these imidazoles.
Results
In the presence of antioxidant (Trolox), cytotoxicity was improved for compounds 2 and 3 but not for compound 1. Meantime, compound 7 promoted reactive oxygen species (ROS) production, which was abated in the presence of a standard antioxidant (Trolox). Additionally, the three (3) imidazoles impaired mitochondrial membrane potential (MMP). While MMP was not restored after treatment removal, the addition of antioxidant (Trolox) improved MMP for compounds 2 and 3 treatment. Additionally, compound 1 elevated expression of hypoxia-inducing factor 1-alpha (HIF-1α). This may not be unconnected with the capacity of compound 1 to cause oxidative stress.
Conclusion
We show evidence that supports the cytotoxic action of imidazoles involves likely impairment to redox balance and mitochondrial membrane potential. The findings help our understanding of the mechanistic action of these imidazoles in living cells, and altogether may boost their prospects as new and alternative anti-protozoans.
... Screening an unbiased compound library is rapidly becoming a common approach to identify effective candidates to treat parasitic infection in the early stages of drug development [22][23][24]. However, drug development is an expensive and long-term process due to the lack of information about host toxicity and the actual mechanism of action of compounds. ...
... In the preliminary screening, the inhibition of parasite growth was determined using a luminescence-based β-galactosidase (β-Gal) activity assay as previously described [24,28,31]. Briefly, small molecular compounds were freshly reconstituted in culture medium to final concentrations of 5 μM and added to confluent monolayers of HFFs plated in 96-well half-area plates. ...
Background:
Toxoplasma gondii is a zoonotic pathogen that causes toxoplasmosis and leads to serious public health problems in developing countries. However, current clinical therapeutic drugs have some disadvantages, such as serious side effects, a long course of treatment and the emergence of drug-resistant strains. The urgent need to identify novel anti-Toxoplasma drugs has initiated the effective strategy of repurposing well-characterized drugs. As a principled screening for the identification of effective compounds against Toxoplasma gondii, in the current study, a collection of 666 compounds were screened for their ability to significantly inhibit Toxoplasma growth.
Methods:
The inhibition of parasite growth was determined using a luminescence-based β-galactosidase activity assay. Meanwhile, the effect of compounds on the viability of host cells was measured using CCK8. To assess the inhibition of the selected compounds on discrete steps of the T. gondii lytic cycle, the invasion, intracellular proliferation and egress abilities were evaluated. Finally, a murine infection model of toxoplasmosis was used to monitor the protective efficacy of drugs against acute infection of a highly virulent RH strain.
Results:
A total of 68 compounds demonstrated more than 70% parasite growth inhibition. After excluding compounds that impaired host cell viability, we further characterized two compounds, NVP-AEW541 and GSK-J4 HCl, which had IC50 values for parasite growth of 1.17 μM and 2.37 μM, respectively. In addition, both compounds showed low toxicity to the host cell. Furthermore, we demonstrated that NVP-AEW541 inhibits tachyzoite invasion, while GSK-J4 HCl inhibits intracellular tachyzoite proliferation by halting cell cycle progression from G1 to S phase. These findings prompted us to analyse the efficacy of the two compounds in vivo by using established mouse models of acute toxoplasmosis. In addition to prolonging the survival time of mice acutely infected with T. gondii, both compounds had a remarkable ability to reduce the parasite burden of tissues.
Conclusions:
Our findings suggest that both NVP-AEW541 and GSK-J4 could be potentially repurposed as candidate drugs against T. gondii infection.
... Additional screens using the approach presented here should help identify more lead compounds, and it is likely that one of these leads will result in a clinically effective new therapy for the treatment of the chronic infection. Furthermore, to meet the need for new antimicrobial therapies, we are driving the screening of wider ranges of chemical compounds to identify those with anti-parasitic activity (Adeyemi et al. 2017(Adeyemi et al. , 2018. ...
... Most of the hit compounds identified in this study have not been previously reported to have anti-T. gondii activity, except for daidzein which were reported previously by us (Adeyemi et al. 2018). Further study is required to unravel the mechanistic basis for the anti-T. ...
Toxoplasma gondii can infect virtually all warm-blooded animals, including humans. It can differentiate between rapidly replicating tachyzoites that cause acute infection and slowly growing bradyzoites in tissue cysts. Treatment options for toxoplasmosis are challenging because current therapies cannot eradicate the latent T. gondii infection that is mainly caused by the bradyzoite forms. Accordingly, recurrence of infection is a problem for immunocompromised patients and congenitally infected patients. Protein kinases have been widely studied in eukaryotic cells, and while little is known about signaling in Toxoplasma infection, it is likely that protein kinases play a key role in parasite proliferation, differentiation, and probably invasion. To identify optimized new kinase inhibitors for drug development against T. gondii, we screened a library of kinase inhibitor compounds for anti-Toxoplasma activity and host cell cytotoxicity. Pyrimethamine served as a positive control and 0.5% DMSO was used as a negative control. Among the 80 compounds screened, 6 compounds demonstrated ≥ 80% parasite growth inhibition at concentrations at which 5 compounds did not suppress host cell viability, while 3 kinase inhibitors (Bay 11-7082, Tyrphostin AG 1295 and PD-98059) had suppressive effects individually on parasite growth and host cell invasion, but did not strongly induce bradyzoite formation.
