Activities of anti-Toxoplasma drugs and compounds against tissue cysts in the last three decades (1987 to 2017), a systematic review

Cloning, expression, and purification of an α-carbonic anhydrase from Toxoplasma gondii to unveil its kinetic parameters and anion inhibition profile

Toxoplasmosis, induced by the intracellular parasite Toxoplasma gondii, holds considerable implications for global health. While treatment options primarily focusing on folate pathway enzymes have notable limitations, current research endeavours concentrate on pinpointing specific metabolic pathways vital for parasite survival. Carbonic anhydrases (CAs, EC 4.2.1.1) have emerged as potential drug targets due to their role in fundamental reactions critical for various protozoan metabolic processes. Within T. gondii, the Carbonic Anhydrase-Related Protein (TgCA_RP) plays a pivotal role in rhoptry biogenesis. Notably, α-CA (TcCA) from another protozoan, Trypanosoma cruzi, exhibited considerable susceptibility to classical CA inhibitors (CAIs) such as anions, sulphonamides, thiols, and hydroxamates. Here, the recombinant DNA technology was employed to synthesise and clone the identified gene in the T. gondii genome, which encodes an α-CA protein (Tg_CA), with the purpose of heterologously overexpressing its corresponding protein. Tg_CA kinetic constants were determined, and its inhibition patterns explored with inorganic metal-complexing compounds, which are relevant for rational compound design. The significance of this study lies in the potential development of innovative therapeutic strategies that disrupt the vital metabolic pathways crucial for T. gondii survival and virulence. This research may lead to the development of targeted treatments, offering new approaches to manage toxoplasmosis.

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Urtica dioica Extract Leads to Cyst Reduction, Enhanced Cell-Mediated Immune Response, and Antioxidant Activity in Experimental Toxoplasmosis

BACKGROUND

Toxoplasmosis is a cosmopolitan parasitic infection caused by Toxoplasma gondii which is commonly treated by pyrimethamine (PYR) plus sulfadiazine (SDZ) with several adverse side effects. The present study evaluated the therapeutic effects of Urtica dioica L. aqueous extract (UDE) on acute and chronic toxoplasmosis in mice.

METHODS

For this purpose, mice were infected with 20 cysts (acute infection) or 10 cysts (chronic infection) of T. gondii (Me49 strain). The mice were treated with 200 mg/kg of UDE intraperitoneally (IP) and intragastric route (IG). The UDE-treated mice were compared with the PYR + SDZ treatment. The histopathological changes, cyst count, total antioxidant capacity (TAC), malondialdehyde (MDA) assay, and serum INF-γ were also evaluated.

RESULTS

In the acute toxoplasmosis, UDE by IP and IG administration significantly reduced the number of brain cysts by 93.74 and 92.55%, respectively, and increased the survival rate to 80% compared with 60% in untreated controls. In the chronic infection, cyst burden decreased at 88.2 and 83.4%, respectively, for IP and IG treatments. Moreover, UDE significantly increased INF- γ levels in acute and chronic toxoplasmosis. Tissue inflammatory lesions were reduced in the UDE-treated subgroups compared to the untreated group. UDE treatment significantly reduced MDA levels and elevated TAC in both acute and chronic infections.

CONCLUSION

The results show that U. dioica possesses significant immunostimulant and antioxidant activity with a higher cyst reduction in the brain during acute toxoplasmosis. Further studies are required to investigate the fractionations of UDE against T. gondii and its combination with other standard drugs.

Anti-Toxoplasma gondii screening of MMV pandemic response box and evaluation of RWJ-67657 efficacy in chronically infected mice

Toxoplasmosis is a significant public health concern with limited therapeutic options. The medicines for malaria venture (MMV) developed the pandemic response box (PRB) containing 400 drug-like molecules with broad pathogen activity. The aim of this work is to evaluate PRB compounds for their anti-Toxoplasma gondii activity and identify promising candidates for further evaluation. Screening identified 42 selective compounds with half effective concentration (EC50) ranging from 2.4 to 913.1 nm and half cytotoxic concentration (CC50) ranging from 6 μm to >50 μm. Selectivity index (SI) values (CC50/EC50) ranged from 11 to 17 708. Based on its in silico and in vitro profile and its commercial availability, RWJ-67657 was selected for further studies. Molecular docking analysis showed RWJ-67657 is predicted to bind to T. gondii p38 mitogen-activated protein kinase (TgMAPK). Oral administration of RWJ-67657 (20 mg kg day−1/10 days) significantly reduced parasite burden in chronically infected mice compared to mock-treated group (P < 0.01). These findings highlight the PRB as a promising source for anti-T. gondii compounds, with several showing favourable drug properties, including MMV1634492, MMV002731, MMV1634491, MMV1581551, MMV011565, MMV1581558, MMV1578577, MMV233495 and MMV1580482, firstly described here as anti-T. gondii agents. RWJ-67657 emerges as a valuable drug candidate for experimental chronic cerebral toxoplasmosis therapy.

Successful treatment with doxycycline monotherapy for human infection with Babesia venatorum (Babesiidae, Sporozoa) in China: a case report and proposal for a clinical regimen

BACKGROUND

Human babesiosis is a worldwide disease caused by intraerythrocytic protozoa of the genus Babesia. It is transmitted by bites from ixodid ticks, and mechanically transmitted by blood transfusion. It is primarily treated with quinine and/or atovaquone, which are not readily available in China. In this study, we developed a novel treatment regimen involving doxycycline monotherapy in a patient with severe Babesia venatorum infection as an alternative therapeutic medication. The aim of our study is to provide a guidance for clinical practice treatment of human babesiosis.

CASE PRESENTATION

A 73-year-old man who had undergone splenectomy and blood transfusion 8 years prior, presented with an unexplained fever, headache, and thrombocytopenia, and was admitted to the Fifth Medical Center of the PLA General Hospital. He was diagnosed with B. venatorum infection by morphological review of thin peripheral blood smears, which was confirmed by multi-gene polymerase chain reaction (PCR), and sequencing of the entire 18s rRNA and partial β-tubulin encoding genes, as well as isolation by animal inoculation. The doxycycline monotherapy regimen (peros, 0.1 g bisindie) was administered following pharmacological guidance and an effective outcome was observed. The patient recovered rapidly following the doxycycline monotherapy. The protozoan load in peripheral blood samples decreased by 88% in hematocrit counts after 8 days, and negative PCR results were obtained after 90 days of follow-up at the hospital. The treatment lasted for 3 months without any side effects or sequelae. The nine-month follow-up survey of the patient did not reveal any signs of recrudescence or anti-babesial tolerance.

CONCLUSIONS

We have reported a clinical case of successful doxycycline monotherapy for human babesiosis caused by B. venatorum, which provides an optional medical intervention for human babesiosis.

Repurposing the Medicines for Malaria Venture's COVID Box to discover potent inhibitors of Toxoplasma gondii, and in vivo efficacy evaluation of almitrine bismesylate (MMV1804175) in chronically infected mice

Toxoplasmosis, caused by the obligate intracellular parasite Toxoplasma gondii, affects about one-third of the world's population and can cause severe congenital, neurological and ocular issues. Current treatment options are limited, and there are no human vaccines available to prevent transmission. Drug repurposing has been effective in identifying anti-T. gondii drugs. In this study, the screening of the COVID Box, a compilation of 160 compounds provided by the "Medicines for Malaria Venture" organization, was conducted to explore its potential for repurposing drugs to combat toxoplasmosis. The objective of the present work was to evaluate the compounds' ability to inhibit T. gondii tachyzoite growth, assess their cytotoxicity against human cells, examine their absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties, and investigate the potential of one candidate drug through an experimental chronic model of toxoplasmosis. Early screening identified 29 compounds that could inhibit T. gondii survival by over 80% while keeping human cell survival up to 50% at a concentration of 1 μM. The Half Effective Concentrations (EC50) of these compounds ranged from 0.04 to 0.92 μM, while the Half Cytotoxic Concentrations (CC50) ranged from 2.48 to over 50 μM. Almitrine was chosen for further evaluation due to its favorable characteristics, including anti-T. gondii activity at nanomolar concentrations, low cytotoxicity, and ADMET properties. Administering almitrine bismesylate (Vectarion®) orally at dose of 25 mg/kg/day for ten consecutive days resulted in a statistically significant (p < 0.001) reduction in parasite burden in the brains of mice chronically infected with T. gondii (ME49 strain). This was determined by quantifying the RNA of living parasites using real-time PCR. The presented results suggest that almitrine may be a promising drug candidate for additional experimental studies on toxoplasmosis and provide further evidence of the potential of the MMV collections as a valuable source of drugs to be repositioned for infectious diseases.

Efficacy of clofazimine against acute and chronic Toxoplasma gondii infection in mice

Toxoplasmosis is a zoonotic protozoal disease affecting approximately one-third of the world's population. The lack of current treatment options necessitates the development of drugs with good tolerance and effectiveness on the active and cystic stages of the parasite. The present study was established to investigate, for the first time, the potential potency of clofazimine (CFZ) against acute and chronic experimental toxoplasmosis. For this purpose, the type II T. gondii (Me49 strain) was used for induction acute (20 cysts in each mouse) and chronic (10 cysts in each mouse) experimental toxoplasmosis. The mice were treated with 20 mg/kg of CFZ intraperitoneally and orally. The histopathological changes, brain cyst count, total Antioxidant Capacity (TAC), malondialdehyde (MDA) assay, and the level of INF-γ were also evaluated. In the acute toxoplasmosis, both IP and oral administration of CFZ induced a significant reduction in brain parasite burden by 90.2 and 89%, respectively, and increased the survival rate to 100% compared with 60% in untreated controls. In the chronic infection, cyst burden decreased at 85.71 and 76.18% in CFZ-treated subgroups in comparison to infected untreated controls. In addition, 87.5% and 100% of CFZ-treated subgroups survived versus untreated control 62.5%. Moreover, CFZ significantly increased INF-γ levels in acute and chronic toxoplasmosis. Tissue inflammatory lesions were considerably reduced in the CFZ-treated chronic subgroups. CFZ treatment significantly reduced MDA levels and elevated TAC in both acute and chronic infections. In conclusion, CFZ showed a promising finding regarding the ability to reduce cyst burden in acute and chronic infection. Further studies are needed to investigate the therapeutic role of CFZ on toxoplasmosis using the long-term treatment and more advanced approaches. In addition, clofazimine may need to be accompanied by another drug to augment its effect and prevent the regrowth of parasites.

Animal venoms: a novel source of anti-Toxoplasma gondii drug candidates

Toxoplasma gondii (T. gondii) is a nucleated intracellular parasitic protozoan with a broad host selectivity. It causes toxoplasmosis in immunocompromised or immunodeficient patients. The currently available treatments for toxoplasmosis have significant side effects as well as certain limitations, and the development of vaccines remains to be explored. Animal venoms are considered to be an important source of novel antimicrobial agents. Some peptides from animal venoms have amphipathic alpha-helix structures. They inhibit the growth of pathogens by targeting membranes to produce lethal pores and cause membrane rupture. Venom molecules generally possess immunomodulatory properties and play key roles in the suppression of pathogenic organisms. Here, we summarized literatures of the last 15 years on the interaction of animal venom peptides with T. gondii and attempt to explore the mechanisms of their interaction with parasites that involve membrane and organelle damage, immune response regulation and ion homeostasis. Finally, we analyzed some limitations of venom peptides for drug therapy and some insights into their development in future studies. It is hoped that more research will be stimulated to turn attention to the medical value of animal venoms in toxoplasmosis.

Toxoplasma gondii vaccine candidates: a concise review

Toxoplasma gondii is an obligate intracellular parasite that causes toxoplasmosis. It has been shown that the severity of symptoms depends on the functioning of the host immune system. Although T. gondii infection typically does not lead to severe disease in healthy people and after infection, it induces a stable immunity, but it can contribute to severe and even lethal Toxoplasmosis in immunocompromised individuals (AIDS, bone marrow transplant and neoplasia). The antigens that have been proposed to be used in vaccine candidate in various studies include surface antigens and secretory excretions that have been synthesized and evaluated in different studies. In some studies, secretory antigens play an important role in stimulating the host immune response. Various antigens such as SAG, GRA, ROP, ROM, and MAG have been from different strains of T. gondii have been synthesized and their protective effects have been evaluated in animal models in different vaccine platforms including recombinant antigens, nanoparticles, and DNA vaccine. Four bibliographic databases including Science Direct, PubMed Central (PMC), Scopus, and Google Scholar were searched for articles published up to 2020.The current review article focuses on recent studies on the use and usefulness of recombinant antigens, nanoparticles, and DNA vaccines.

Metabolomics study of cat small intestine during the early stage of Toxoplasma gondii oocyst formation identifies potential biomarkers

Toxoplasma gondii (T. gondii) is a zoonotic intracellular protozoan parasite that can invade, replicate and survive in almost all cells of warm-blooded animals. T. gondii infection threatens the life of the fetus or can cause morbidity in the infant. As the only definitive host of T. gondii, felids spread the pathogen mainly by forming oocysts in the small intestines and discharging the oocysts into the ambient environment, consequently polluting water, vegetables, and meat products. In this study, we used untargeted metabolomics technology to study the changes in metabolites that occurred during the early stage of oocyst formation in the cat small intestine following T. gondii infection and attempted to identify metabolic biomarkers that could potentially be used as diagnostic molecular markers in the future. Domestic cats (Felis catus) were infected with T. gondii Pru tissue cysts, and samples of their small intestinal epithelium were collected at 2 and 4 days post-infection (DPI) for metabolic analysis. LC-MS/MS and multivariate statistical analysis were employed to detect metabolomic signatures that discriminated between the infected and control groups. A total of 1673 ions and 1201 ions were obtained in the positive and negative modes, respectively. Of these ions, 175 were up-regulated and 127 were down-regulated in the positive ion mode; whereas, 123 were up-regulated and 81 were down-regulated in the negative ion mode. Three commonly altered ions (0.74_313.0414 m/z, 8.82_615.2621 m/z and 8.16_325.2362 m/z) were determined to have potential research value. Seventy common metabolic pathways were enriched at two time points, with arginine biosynthesis, pyrimidine metabolism, pantothenate and CoA biosynthesis being the three most significant pathways related to T. gondii. The area under the curve (AUC) of differential metabolites combined with relevant literature analysis showed that N-Methylpelletierine and 3,3-Difluoro-17-methyl-5alpha-androstan-17beta-ol have higher predictability and better potential application value than other metabolites. Our analysis of metabolic markers during the early stage of T. gondii oocyst formation in the small intestine of the definitive host (cat) provided novel insight for understanding oocyst development and a theoretical basis for the application of potential biomarkers.

Ginger Is a Potential Therapeutic for Chronic Toxoplasmosis

Background:Toxoplasma gondii (T. gondii) is an opportunistic parasite that causes serious diseases in humans, particularly immunocompromised individuals and pregnant women. To date, there are limited numbers of therapeutics for chronic toxoplasmosis which necessitate the discovery of effective and safe therapeutics. In the present study, we aimed to evaluate the antitoxoplasmosis potential of ginger extract in mice with experimentally induced chronic toxoplasmosis. Results: Treatment with ginger extract significantly reduced cysts count in the brains of T. gondii-infected mice with a marked alleviation of edema and inflammation, and a reversal of neuronal injury. Moreover, ginger extract treatment reduced inflammation in liver and lungs and protected hepatocytes from infection-induced degeneration. Consistently, apoptosis was significantly mitigated in the brains of ginger extract-treated mice compared to infected untreated animals or spiramycin-treated animals. Methods: Four groups of Swiss albino mice (10 mice each) were used. The first group was not infected, whereas 3 groups were infected with Me49 T. gondii strains. One infected group remained untreated (infected untreated), whereas the other two infected groups were treated with either ginger extract (250 mg/kg) or spiramycin (positive control; 100 mg/kg), respectively. The therapeutic potential of ginger extract was evaluated by calculation of the parasite burden in infected animals, and examination of the infected tissues for reduced pathologic changes. Conclusions: Our results showed for the first time that ginger extract exhibited marked therapeutic effects in mice with chronic T. gondii infection which indicates that it can be used as a safe and effective treatment for chronic toxoplasmosis.

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.

Treatment of Human Babesiosis: Then and Now

Babesiosis is an emerging tick-borne disease caused by apicomplexan parasites of the genus Babesia. With its increasing incidence worldwide and the risk of human-to-human transmission through blood transfusion, babesiosis is becoming a rising public health concern. The current arsenal for the treatment of human babesiosis is limited and consists of combinations of atovaquone and azithromycin or clindamycin and quinine. These combination therapies were not designed based on biological criteria unique to Babesia parasites, but were rather repurposed based on their well-established efficacy against other apicomplexan parasites. However, these compounds are associated with mild or severe adverse events and a rapid emergence of drug resistance, thus highlighting the need for new therapeutic strategies that are specifically tailored to Babesia parasites. Herein, we review ongoing babesiosis therapeutic and management strategies and their limitations, and further review current efforts to develop new, effective, and safer therapies for the treatment of this disease.

Valproic acid inhibits chronic Toxoplasma infection and associated brain inflammation in mice

Individuals infected with Toxoplasma gondii (T. gondii) are prone to psycho-behavioral disorders, most notably schizophrenia and bipolar. Valproic acid reportedly inhibited the proliferation of T. gondii tachyzoites in vitro. However, animals treated with the drug neither lived longer during acute infection nor had fewer brain cysts upon chronic infection. In this study, a quantitative real-time PCR (qPCR) method was applied to quantify copy numbers of BAG1 (a bradyzoite-specific protein), REP529 DNA (a repetitive DNA fragment of the parasite), and SAG1 (a highly expressed tachyzoite-specific surface protein) in brains of chronically infected mice treated by valproic acid. The treatment inhibited the infection and decreased BAG1, SAG1, and REP529 copy numbers in mice brains (P < 0.0001), comparable to Trimethoprim/Sulfamethoxazole (TMP/SMZ), the common medication for Toxoplasmosis treatment. Moreover, valproic acid decreased brain TNF-α expression (P < 0.0001), comparable to TMP/SMZ. Histological examination of mice brains showed a marked reduction in cyst establishment, perivascular infiltration of lymphocytes, and glial nodules to the same level as the TMP/SMZ group. Our results provide direct evidence for the efficacy of valproic acid, a mood-stabilizing and antipsychotic drug against chronic Toxoplasma infection. These results might help modulate therapeutic regimens for neuropsychiatric patients and design more effective anti-Toxoplasma drugs.

A Novel Calcium-Dependent Protein Kinase 1 Inhibitor Potently Prevents Toxoplasma gondii Transmission to Foetuses in Mouse

Treatments currently used to prevent congenital toxoplasmosis are non-specific of Toxoplasma gondii and have grievous side effects. To develop a more specific and less toxic drug, we have designed SP230, an imidazo[1,2-b]pyridazine salt targeting the Toxoplasma gondii calcium-dependent protein kinase 1 (TgCDPK1) and active against acute toxoplasmosis in mice. Efficiency of SP230 to inhibit foetal transmission of the parasite was evaluated in a mouse model of congenital toxoplasmosis. Swiss mice were infected at mid-pregnancy with tachyzoites or cysts of the ME49 strain of T. gondii by intraperitoneal and oral route, respectively, and treated with SP230 at 50 mg/kg for 5 days by the same routes. Parasite burden in organs of dams and in foetuses was measured by quantitative PCR. Intraperitoneal administration of SP230 drastically reduced the number of parasites (more than 97% of reduction) in the brain and lungs of dams, and led to a reduction of 66% of parasite burden in foetuses. Oral administration of SP230 was particularly efficient with 97% of reduction of parasite burdens in foetuses. SP230 did not impact number and weight of offspring in our conditions. This inhibitor of TgCDPK1 is a promising candidate for the development of alternative therapeutics to treat infected pregnant women.

Oxidative Stress as a Possible Target in the Treatment of Toxoplasmosis: Perspectives and Ambiguities

Toxoplasma gondii is an apicomplexan parasite causing toxoplasmosis, a common disease, which is most typically asymptomatic. However, toxoplasmosis can be severe and even fatal in immunocompromised patients and fetuses. Available treatment options are limited, so there is a strong impetus to develop novel therapeutics. This review focuses on the role of oxidative stress in the pathophysiology and treatment of T. gondii infection. Chemical compounds that modify redox status can reduce the parasite viability and thus be potential anti-Toxoplasma drugs. On the other hand, oxidative stress caused by the activation of the inflammatory response may have some deleterious consequences in host cells. In this respect, the potential use of natural antioxidants is worth considering, including melatonin and some vitamins, as possible novel anti-Toxoplasma therapeutics. Results of in vitro and animal studies are promising. However, supplementation with some antioxidants was found to promote the increase in parasitemia, and the disease was then characterized by a milder course. Undoubtedly, research in this area may have a significant impact on the future prospects of toxoplasmosis therapy.

Modelling Toxoplasma gondii infection in human cerebral organoids

Pluripotent stem cell-derived cerebral organoids have the potential to recapitulate the pathophysiology of in vivo human brain tissue, constituting a valuable resource for modelling brain disorders, including infectious diseases. Toxoplasma gondii, an intracellular protozoan parasite, infects most warm-blooded animals, including humans, causing toxoplasmosis. In immunodeficient patients and pregnant women, infection often results in severe central nervous system disease and fetal miscarriage. However, understanding the molecular pathophysiology of the disease has been challenging due to limited in vitro model systems. Here, we developed a new in vitro model system of T. gondii infection using human brain organoids. We observed that tachyzoites can infect human cerebral organoids and are transformed to bradyzoites and replicate in parasitophorous vacuoles to form cysts, indicating that the T. gondii asexual life cycle is efficiently simulated in the brain organoids. Transcriptomic analysis of T. gondii-infected organoids revealed the activation of the type I interferon immune response against infection. In addition, in brain organoids, T. gondii exhibited a changed transcriptome related to protozoan invasion and replication. This study shows cerebral organoids as physiologically relevant in vitro model systems useful for advancing the understanding of T. gondii infections and host interactions.

Treatment Strategy in Human Ocular Toxoplasmosis: Why Antibiotics Have Failed

Background: There is currently no clear evidence of the effectiveness of antibiotic therapy in acute ocular toxoplasmosis (OT), but its effect as a secondary prophylaxis is undisputed. The majority of uveitis specialists advocate treatment. This meta-analytic review aims to critically analyze determinants of treatment success and to update current treatment strategies for OT in order to explain this discrepancy. Methods: A systematic literature search was performed in NCBI/PubMed, Clinical Trials, Google Scholar and ScienceDirect to retrieve pro- and retrospective studies using the key terms “ocular toxoplasmosis” or “retinochoroiditis” and “immunocompetent” and “treatment” or “therapy” and “human.” Of these, larger case series and prospective clinical studies and cross references identified from meta-analyses were selected by a manual search, and primary and secondary outcome parameters were extracted. Results: Ten case series and clinical trials reported success parameters for treatment outcomes, and four additional for recurrence prophylaxis. Five treatment studies were randomized clinical trials, three comparative and two noncomparative case series. Though several outcome parameters were reported, five of them defined time to healing, four visual gain and one lesion size as primary and secondary outcome parameters, recurrence rate as a secondary outcome parameter was reported once. No conclusive evidence was found for an antibiotic treatment effect. Four prophylaxis studies addressed the prevention of recurrences after treatment. The primary outcome in all studies was the effect of treatment and prophylaxis on recurrences, and all four found a significant effect on the risk of and time to recurrences. Conclusions: Antibiotic treatment of OT aims at controlling parasite proliferation. The absence of an effect on visual acuity and time to healing is thus not surprising. The fact that time to and number of recurrences respond to recurrence of prophylaxis proves the antibiotic effect on parasite activity.

Multi-pathogen infections and Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease associated with the overproduction and accumulation of amyloid-β peptide and hyperphosphorylation of tau proteins in the brain. Despite extensive research on the amyloid-based mechanism of AD pathogenesis, the underlying cause of AD is not fully understood. No disease-modifying therapies currently exist, and numerous clinical trials have failed to demonstrate any benefits. The recent discovery that the amyloid-β peptide has antimicrobial activities supports the possibility of an infectious aetiology of AD and suggests that amyloid-β plaque formation might be induced by infection. AD patients have a weakened blood-brain barrier and immune system and are thus at elevated risk of microbial infections. Such infections can cause chronic neuroinflammation, production of the antimicrobial amyloid-β peptide, and neurodegeneration. Various pathogens, including viruses, bacteria, fungi, and parasites have been associated with AD. Most research in this area has focused on individual pathogens, with herpesviruses and periodontal bacteria being most frequently implicated. The purpose of this review is to highlight the potential role of multi-pathogen infections in AD. Recognition of the potential coexistence of multiple pathogens and biofilms in AD's aetiology may stimulate the development of novel approaches to its diagnosis and treatment. Multiple diagnostic tests could be applied simultaneously to detect major pathogens, followed by anti-microbial treatment using antiviral, antibacterial, antifungal, and anti-biofilm agents.

Toxoplasma gondii α-amylase deletion mutant is a promising vaccine against acute and chronic toxoplasmosis

Individuals with inhibited immunity may develop lethal toxoplasmosis; thus, a safe and effective vaccine is urged to be developed. Toxoplasma gondii (T. gondii) α-amylase (α-AMY) is one of the enzymes responsible for starch digestion. In the present study, we first generated a ME49Δα-amy mutant and discovered that loss of α-AMY robustly grew in vitro but contributed to significant virulence attenuation in vivo. Therefore, we established a mouse model to explore the protective immunity of Δα-amy mutant against acute and chronic toxoplasmosis. The results indicated that the survival rates of short-term or long-term immunized mice re-infected with the tachyzoites of multiple T. gondii strains were nearly 100%. ME49Δα-amy not only could provide protective immunity against tachyzoites infection but also could resist the infection of tissue cysts. Furthermore, we detected that ME49Δα-amy vaccination could effectively eliminate the proliferation of parasites in mice and prevent the formation of cysts. The significant increases of Th1-type cytokines, Th2-type cytokines and specific total IgG and IgG subclasses (IgG2a and IgG1) confirmed efficiency of a combination of cellular and humoral immunity against infection. In conclusion, ME49Δα-amy attenuated strain can produce strong immune responses to provide efficient protection against toxoplasmosis, which signifies that ME49Δα-amy mutant may be a potential vaccine candidate.

Toxoplasma gondii AP2XII-2 Contributes to Proper Progression through S-Phase of the Cell Cycle

Toxoplasma gondii is a single-celled parasite that persists in its host by converting into a latent cyst stage. This work describes a new transcriptional factor called AP2XII-2 that plays a role in properly maintaining the growth rate of replicating parasites, which contributes to signals required for development into its dormant stage. Without AP2XII-2, Toxoplasma parasites experience a delay in their cell cycle that increases the frequency of latent cyst formation. In addition, we found that AP2XII-2 operates in a multisubunit complex with other AP2 factors and chromatin remodeling machinery that represses gene expression. These findings add to our understanding of how Toxoplasma parasites balance replication and dormancy, revealing novel points of potential therapeutic intervention to disrupt this clinically relevant process.

Toxoplasma gondii is a protozoan parasite that causes lifelong chronic infection that can reactivate in immunocompromised individuals. Upon infection, the replicative stage (tachyzoite) converts into a latent tissue cyst stage (bradyzoite). Like other apicomplexans, T. gondii possesses an extensive lineage of proteins called ApiAP2s that contain DNA-binding domains first characterized in plants. The function of most ApiAP2s is unknown. We previously found that AP2IX-4 is a cell cycle-regulated ApiAP2 expressed only in dividing parasites as a putative transcriptional repressor. In this study, we purified proteins interacting with AP2IX-4, finding it to be a component of the recently characterized microrchidia (MORC) transcriptional repressor complex. We further analyzed AP2XII-2, another cell cycle-regulated factor that associates with AP2IX-4. We monitored parallel expression of AP2IX-4 and AP2XII-2 proteins in tachyzoites, detecting peak expression during S/M phase. Unlike AP2IX-4, which is dispensable in tachyzoites, loss of AP2XII-2 resulted in a slowed tachyzoite growth due to a delay in S-phase progression. We also found that AP2XII-2 depletion increased the frequency of bradyzoite differentiation in vitro. These results suggest that multiple AP2 factors collaborate to ensure proper cell cycle progression and tissue cyst formation in T. gondii.

IMPORTANCEToxoplasma gondii is a single-celled parasite that persists in its host by converting into a latent cyst stage. This work describes a new transcriptional factor called AP2XII-2 that plays a role in properly maintaining the growth rate of replicating parasites, which contributes to signals required for development into its dormant stage. Without AP2XII-2, Toxoplasma parasites experience a delay in their cell cycle that increases the frequency of latent cyst formation. In addition, we found that AP2XII-2 operates in a multisubunit complex with other AP2 factors and chromatin remodeling machinery that represses gene expression. These findings add to our understanding of how Toxoplasma parasites balance replication and dormancy, revealing novel points of potential therapeutic intervention to disrupt this clinically relevant process.

Toxoplasma gondii: AnUnderestimated Threat?

Traditionally, the protozoan parasite Toxoplasma gondii has been thought of as relevant to public health primarily within the context of congenital toxoplasmosis or postnatally acquired disease in immunocompromised patients. However, latent T.gondii infection has been increasingly associated with a wide variety of neuropsychiatric disorders and, more recently, causal frameworks for these epidemiological associations have been proposed. We present assimilated evidence on the associations between T.gondii and various human neuropsychiatric disorders and outline how these may be explained within a unifying causal framework. We argue that the occult effects of latent T.gondii infection likely outweigh the recognised overt morbidity caused by toxoplasmosis, substantially raising the public health importance of this parasite.

Rosuvastatin reduced brain parasite burden in a chronic toxoplasmosis in vivo model and influenced the neuropathological pattern of ME-49 strain

This study evaluated the effects of rosuvastatin in vivo on toxoplasmosis chronic infection. Thirty-five Swiss mice were orally infected (ME-49 strain). After 50 days, the mice were separated into five groups: GI - non-infected, GII - infected, GIII - infected and treated with pyrimethamine and sulfadiazine (12.5 + 50 mg kg-1 body weight day-1), GIV and GV - infected and treated with rosuvastatin 10 and 40 mg kg-1 body weight day-1, respectively. After 21 days, we collected blood, liver, lungs, femoral biceps and brain were removed for Toxoplasma gondii DNA quantification by qPCR and histopathological analysis. GIV and GV did not present premature death or clinical changes, and the hepatic enzyme levels were lower compared to GI. Toxoplasma gondii DNA was detected mainly in brain and muscle, but the parasite load was significantly lower in GV compared to GII brains (P < 0.05). Histopathological changes were observed in brains, with T. gondii cysts as well as an inflammatory condition, including necrosis areas in GII and GIII. These data confirm active infection with tissue injury. This inflammatory condition was attenuated in the groups treated with rosuvastatin, especially R40 (GV). Our findings demonstrated the in vivo action of rosuvastatin in reducing cerebral parasitic load and indicate that this drug may interfere in chronic toxoplasmosis.

Development of an in vitro system to study the developmental stages of Toxoplasma gondii using a genetically modified strain expressing markers for tachyzoites and bradyzoites

Toxoplasma gondii, the agent of toxoplasmosis, is an intracellular parasite that can infect a wide range of vertebrate hosts. Toxoplasmosis causes severe damage to immunocompromised hosts and its treatment is mainly based on the combination of pyrimethamine and sulfadiazine, which causes relevant side effects primarily observed in AIDS patients, including bone marrow suppression and hematological toxicity (pyrimethamine) and/or hypersensitivity and allergic skin reactions (sulfadiazine). Thus, it is important to investigate new compounds against T. gondii, particularly those that may act on bradyzoites, which are present in cysts during the chronic disease phase. We propose an in vitro model to simultaneously study new candidate compounds against the two main causative stages of Toxoplasma infection in humans, using the EGS-DC strain that was modified from a type I/III strain (EGS), isolated from a case of human congenital toxoplasmosis in Brazil and engineered to express markers for both stages of development. One feature of this strain is that it presents tachyzoite and bradyzoite in the same culture system and in the same host cell under normal culture conditions. Additionally, this strain presents stage-specific fluorescent protein expression, allowing for easy identification of both stages, thus making this strain useful in different studies. HFF cells were infected and after 4 and 7 days post infection the cells were treated with 10 μM of pyrimethamine or atovaquone, for 48 or 72 h. We used high-throughput screening to quantify the extent of parasite infection. Despite a reduction in tachyzoite infection caused by both treatments, the atovaquone treatment reduced the bradyzoite infection while the pyrimethamine one increased it. Ultrastructural analysis showed that after treatment with both drugs, parasites displayed altered mitochondria. Fluorescence microscopy of cells labeled with MitoTracker CMXRos showed that the cysts present inside the cells lost their mitochondrial membrane potential. Our results indicate that this experimental model is adequate to simultaneously analyze new active compounds against tachyzoite and bradyzoite forms.

Perspective on current and emerging drugs in the treatment of acute and chronic toxoplasmosis

No new drugs for treatment of toxoplasmosis have been approved in over 60 years, despite the burden of toxoplasmosis on human society. The small selection of effective drugs is limited by important side effects, often limiting patient use. This perspective highlights promising late-stage drug candidates in the treatment of toxoplasmosis. Presently, drugs target the tachyzoite form of the parasite Toxoplasma gondii responsible for the acute infection but do not eradicate the tissue cyst form underlying chronic infection. Pyrimethamine - the first-line and only approved drug for treatment of toxoplasmosis in the United States - inhibits parasite DNA synthesis by inhibiting dihydrofolate reductase (DHFR). Two novel DHFR inhibitors with improved potency and selectivity for parasite DHFR over human DHFR are in clinical-stage development. One of the most advanced and promising therapeutic targets, demonstrating potential to treat both acute and chronic toxoplasmosis, is the calcium-dependent protein kinase 1 (CDPK1) which plays an essential role in the intracellular replicative cycle of the parasite, and has no direct mammalian homolog. Two CDPK1 inhibitor programs have identified potent and selective lead series, demonstrating acceptable systemic and CNS exposure, and in vivo efficacy in animal models of acute and chronic infection. Physicians need a better arsenal of parasiticidal drugs for the treatment of toxoplasmosis, particularly those active against tissue cysts.

Adjunctive bradyzoite-directed therapy for reducing complications of congenital toxoplasmosis

Congenital toxoplasmosis is caused by in utero infection of the fetus with the intracellular parasite Toxoplasma gondii. Upon infection, the parasite forms life-long cysts in fetal brain and eyes which are resistant to the currently accepted therapy of pyrimethamine and sulfadiazine. These cysts commonly reactivate later in life causing chorioretinitis and visual impairment, and rarely cause neurological complications. I hypothesize that adjunctive, bradyzoite-directed therapies have the potential to alleviate a significant burden of disease by reducing cyst burden in neonatal brain and eyes. Atovaquone is perhaps the most promising drug for further evaluation given its low side-effect profile, established safety, and efficacy in animal models reducing cyst burden. Very limited observational data in humans suggests atovaquone may prevent Toxoplasma-associated chorioretinitis recurrence. Clinical trials are needed to evaluate it and other potential drugs as adjunctive treatment in congenital toxoplasmosis.

In vitro and in vivo evaluation of kojic acid against Toxoplasma gondii in experimental models of acute toxoplasmosis

As current toxoplasmosis chemotherapies have many side effects along with toxicity on patients, we examined the anti-Toxoplasma effect of a biologically important natural antibiotic, kojic acid, in vitro and in vivo. Vero cells were incubated with different concentrations of kojic acid or pyrimethamine (positive control), and the cellular viability was determined. Next, Vero cells were infected with T. gondii (RH strain) and treated with drugs. Then, we calculated the infection index, T. gondii intracellular proliferation and the number and measure of plaque. Moreover, the effect of kojic acid on survival times, serum levels of IFN-γ and TNF-α and histopathological changes in the liver and spleen of Balb/c mice infected with T. gondii were determined. Kojic acid reduced the infection index, intracellular proliferation, the number and measure of plaque in vitro when compared to untreated infected cells. Kojic acid (100 mg/kg/day) also showed a better survival rate than infected untreated control mice (P < 0.05). IFN-γ and TNF-α secretions were significantly increased by kojic acid treatment in comparison to untreated groups (P < 0.05). In addition, its inhibitory effects on inflammatory alterations, apoptosis, and necrosis have been shown in sections of liver and spleen. We conclude that kojic acid exhibit potent anti-Toxoplasma activity with direct and indirect effects on the parasite, although further studies are needed before consideration of clinical trials.

Drug Resistance in Toxoplasma gondii

Toxoplasma gondii (T. gondii) is a global protozoan parasite infecting up to one-third of the world population. Pyrimethamine (PYR) and sulfadiazine (SDZ) are the most widely used drugs for treatment of toxoplasmosis; however, several failure cases have been recorded as well; suggesting the existence of drug resistant strains. This review aims to give a systematic and comprehensive understanding of drug resistance in T. gondii including mechanisms of resistance and sites of drug action in parasite. Analogous amino acid substitutions in the Toxoplasma enzyme were identified to confer PYR resistance. Moreover, resistance to clindamycin, spiramycin, and azithromycin is encoded in the rRNA genes of T. gondii. However, T. gondii SDZ resistance mechanism has not been proved yet. Recently there has been a slight increase in SDZ resistance. That is why the majority of studies were carried out using SDZ. Six strains resistant to SDZ were found in clinical cases between 2013 and 2017 which among Brazilian T. gondii isolates, TgCTBr11, Ck3, and Pg1 were identified in human toxoplasmosis, as well as in livestock intended for human consumption. In conclusion, recent experimental studies in clinical cases have clearly shown that drug resistance in Toxoplasma is ongoing. Thus, establishing a more effective therapeutic scheme in the treatment of toxoplasmosis is critically needed. The emergence of T. gondii strains resistant to current drugs, reviewed here, represents a concern not only for treatment failure but also for increased clinical severity in immunocompromised patients. To improve the therapeutic outcome in patients, a greater understanding of the exact mechanisms of drug resistance in T. gondii should be developed. Thus, monitoring the presence of resistant parasites, in food products, would seem a prudent public health program.