Resistance as a tool in the study of old and new drug targets in Toxoplasma

Potential Anti-Toxoplasmosis Efficiency of Phoenix dactylifera Extracts Loaded on Selenium Nanoparticles

Background

Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii that infects humans and many types of mammals and birds.

Objective

To investigate the effect of selenium nanoparticles (SeNPs) and Phoenix dactylifera (Pd) extracts loaded on SeNPs as a new agent to combat chronic T. gondii infections in murine model as an alternative method to standard Spiramycin drug therapy.

Methods

A total of 64 female mice were randomly divided into eight groups: GI: Normal control, GII: Positive control, GIII: infected and treated with Spiramycin, GIV: infected and treated with SeNPs, GV: infected and treated with aqueous extract of Pd, GVI: infected and treated with methanolic extract of Pd, GVII: infected and treated with aqueous extract of Pd loaded on SeNPs, GVIII: infected and treated with methanolic extract of Pd loaded on SeNPs. Date palm (P. dactylifera) fruits were identified and collected from the farms of Saudi Arabia. Preparation and characterization of SeNPs were done. The parasitological, histopathological examinations and biochemical changes were evaluated in all groups.

Results

Parasitological results showed significant differences in GVII in comparison to GII while GVIII showed significant differences in comparison to GII and GIII. The histopathological section of the cerebral cortex showed obvious alterations in the infected compared with untreated control groups. Aqueous and methanolic extracts of P. dactylifera loaded on SeNPs treatment showed improvement that indicated by few perivascular cuffing with few inflammatory cell infiltrations. Few granule cells with mild intracellular vacuolation and edema few deformed neurons with deep pyknotic nuclei. Microglia cells expression of Iba-1 and inflammatory cytokines (IL-4, IL-10 and INF-γ) in serum of all groups was higher in GII and lowest in GVIII followed by GVII.

Conclusion

SeNPs and P. dactylifera extracts loaded on SeNPs could be a potent agent to combat T. gondii infections.

Surfactant vesicles for enhanced antitoxoplasmic effect of norfloxacin: in vitro and in vivo evaluations

The goal was to scrutinize niosomes as potential carriers for enhanced efficacy of norfloxacin against Toxoplasma gondii RH strain. This was assessed in vitro and in vivo. Standard niosomes of Span 60 and cholesterol were prepared. Gelucire 48/16 or Tween 80 was incorporated as hydrophilic fluidizer. The prepared vesicles were characterized for shape, size, viscosity and norfloxacin release. The in vitro anti-Toxoplasma was assessed by monitoring tachyzoites viability after incubation with niosomes. In vivo efficacy of niosomes encapsulated norfloxacin was evaluated on infected mice. Transmission electron micrographs showed nano-sized spherical vesicles. Norfloxacin release varied with niosomal composition to show faster liberation in presence of fluidizing agent. The half maximum effective concentration of norfloxacin against tachyzoites (EC50) was significantly reduced after niosomal encapsulation compared with simple drug solution with no significant difference between vesicular formulations. Tachyzoite count in the peritoneal fluid of infected mice was reduced by 45.2, 90.8, 88.3 and 84% after treatment with simple drug dispersion, standard niosomes, Gelucire containing and Tween containing vesicles, respectively compared to infected untreated mice. These results correlate with the in vitro data and reflects the efficacy of niosomes. The study introduced surfactant vesicles as a tool for enhanced efficacy of norfloxacin against toxoplasma.

Parasitological, Molecular, and Histopathological Investigation of the Potential Activity of Propolis and Wheat Germ Oil against Acute Toxoplasmosis in Mice

Toxoplasmosis is one of the most common parasitic zoonoses that affects all vertebrates. The drugs most commonly used against toxoplasmosis have many side effects, making the development of new antiparasitic drugs a big challenge. The present study evaluated the therapeutic effectiveness of novel herbal treatments, including propolis and wheat germ oil (WGO), against acute toxoplasmosis. A total of 50 albino mice were divided into five groups: group 1 (G1) (non-infected and non-treated); group 2 (G2) (infected without treatment); group 3 (G3) (treated with propolis); group 4 (G4) (treated with WGO); group 5 (G5) (treated with a combination of propolis and WGO). The effects of the herbal substances on different organs, mainly liver, spleen, and lungs, were investigated using parasitological, molecular, and histopathological examinations. The results of parasitological examination demonstrated statistically significant (p < 0.05) differences in the parasitic load between treated groups (G3, G4, and G5) compared to the control positive group (G2). These differences were represented by a significant reduction in the parasite load in stained tissue smears from the liver obtained from the animals treated with propolis (G3) compared to the parasite load in the positive control group. Similarly, animals (G4) treated with WGO exhibited a significant reduction in the parasite load versus the positive control group, while the lowest parasite load was found in G5, treated with propolis and WGO. Quantification of the parasite burden through molecular methods (PCR) revealed similar findings represented by reduction in the parasite burden in all treated groups with WGO and propolis as compared to the control group. Importantly, these previous parasitological and molecular findings were accompanied by a marked improvement in the histopathological picture of the liver, spleen, and lungs. In conclusion, propolis and WGO showed a good combination of therapeutic efficacy against acute toxoplasmosis.

Chemical and Pharmacological Properties of Decoquinate: A Review of Its Pharmaceutical Potential and Future Perspectives

Decoquinate (DQ) is an antimicrobial agent commonly used as a feed additive for birds for human consumption. Its use as an additive is well established, but DQ has the potential for therapy as an antimicrobial drug for veterinary treatment and its optimized derivatives and/or formulations, mainly nanoformulations, have antimicrobial activity against pathogens that infect humans. However, DQ has a high partition coefficient and low solubility in aqueous fluids, and these biopharmaceutical properties have limited its use in humans. In this review, we highlight the antimicrobial activity and pharmacokinetic properties of DQ and highlight the solutions currently under investigation to overcome these drawbacks. A literature search was conducted focusing on the use of decoquinate against various infectious diseases in humans and animals. The search was conducted in several databases, including scientific and patent databases. Pharmaceutical nanotechnology and medicinal chemistry are the tools of choice to achieve human applications, and most of these applications have been able to improve the biopharmaceutical properties and pharmacokinetic profile of DQ. Based on the results presented here, DQ prototypes could be tested in clinical trials for human application in the coming years.

The Experimental Role of Medicinal Plants in Treatment of Toxoplasma gondii Infection: A Systematic Review

BACKGROUND

Toxoplasma gondii is the global protozoa that could cause contamination in warm-blooded animals and is considered among the opportunistic pathogens in immunocompromised patients. Among the people at risk, toxoplasmosis infection can lead to the incidence of severe clinical manifestations, encephalitis, chorioretinitis, and even death.

PURPOSE

The present research is focused on the new research for the treatment of toxoplasmosis parasitic disease using medicinal herbs.

METHODS

The search was performed in five English databases, including Scopus, PubMed, Web of Science, EMBASE, and Google Scholar up from 2010 to December 2019. Studies in any language were entered in the searching step if they had an English abstract. The words and terms were used as a syntax with specific tags of each database.

RESULTS

Out of 1832 studies, 36 were eligible to be reviewed. The findings showed that 17 studies (47%) were performed in vitro, 14 studies (39%) in vivo, and 5 studies (14%) both in vivo and in vitro.

CONCLUSION

The studies showed that the plant extracts can be a good alternative in reducing the toxoplasmosis effects in the host and the herbal extracts can be used to produce natural product-based drugs affecting toxoplasmosis with fewer side-effects than synthetic drugs.

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.

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.

Current Therapy of Acquired Ocular Toxoplasmosis: A Review

Caused by the parasite Toxoplasma gondii, ocular toxoplasmosis (OT) is the most common form of posterior infectious uveitis. Combined antiparasitic therapy is the standard treatment for OT, but several other schemes have been proposed. The purpose of the present study was to review the literature on the treatment of OT and provide ophthalmologists with up-to-date information to help reduce OT-related visual morbidity. In conclusion, no ideal treatment scheme was identified; currently prescribed therapeutic schemes yield statistically similar functional outcomes.

Biochemical and molecular characterization of the pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase from Toxoplasma gondii

The pyrimidine biosynthesis pathway in the protozoan pathogen Toxoplasma gondii is essential for parasite growth during infection. To investigate the properties of dihydroorotate dehydrogenase (TgDHOD), the fourth enzyme in the T. gondii pyrimidine pathway, we expressed and purified recombinant TgDHOD. TgDHOD exhibited a specific activity of 84U/mg, a k(cat) of 89s(-1), a K(m)=60μM for l-dihydroorotate, and a K(m)=29μM for decylubiquinone (Q(D)). Quinones lacking or having short isoprenoid side chains yielded lower k(cat)s than Q(D). As expected, fumarate was a poor electron acceptor for this family 2 DHOD. The IC(50)s determined for A77-1726, the active derivative of the human DHOD inhibitor leflunomide, and related compounds MD249 and MD209 were, 91μM, 96μM, and 60μM, respectively. The enzyme was not significantly affected by brequinar or TTFA, known inhibitors of human DHOD, or by atovaquone. DSM190, a known inhibitor of Plasmodium falciparum DHOD, was a poor inhibitor of TgDHOD. TgDHOD exhibits a lengthy 157-residue N-terminal extension, consistent with a potential organellar targeting signal. We constructed C-terminally c-myc tagged TgDHODs to examine subcellular localization of TgDHOD in transgenic parasites expressing the tagged protein. Using both exogenous and endogenous expression strategies, anti-myc fluorescence signal colocalized with antibodies against the mitochondrial marker ATPase. These findings demonstrate that TgDHOD is associated with the parasite's mitochondrion, revealing this organelle as the site of orotate production in T. gondii. The TgDHOD gene appears to be essential because while gene tagging was successful at the TgDHOD gene locus, attempts to delete the TgDHOD gene were not successful in the KU80 background. Collectively, our study suggests that TgDHOD is an excellent target for the development of anti-Toxoplasma drugs.

An apicomplexan ankyrin-repeat histone deacetylase with relatives in photosynthetic eukaryotes

Cryptosporidium parvum is a member of the Apicomplexa that lacks a plastid and associated nuclear-encoded genes, which has hampered its use in evolutionary comparisons with algae and eliminated a pool of potentially useful drug targets. Here we show that apicomplexan parasites possess an unusual family of class II histone deacetylase (HDAC) proteins with orthologues that are present in other chromalveolates and primitive algae. A striking feature of these HDAC proteins is the presence of ankyrin repeats in the amino-terminus that appear to be required for enzyme activity. In vitro and in vivo analyses of the C. parvum orthologue indicate that this subclass of chromatin-remodelling proteins is targeted by the anti-cancer drug suberoylanilide hydroxamic acid and that these proteins are most likely involved in the essential process of H4 histone deacetylation that coincides with DNA replication. We propose that members of this novel class of histone deacetylase can serve as promising new targets for treatments against debilitating diseases such as cryptosporidosis, toxoplasmosis and malaria.

Prevention and treatment of congenital toxoplasmosis

Infection with Toxoplasma gondii is transmitted to man by infected meat or meat products and by contact with soil or surface water. In theory, prevention by hygienic measures is possible, but this has never been proved to work in practice. Therefore, pre- and postnatal screening has been implemented in several countries aiming at early diagnosis. However, data on the effect of treatment are limited and no randomized, controlled trials have been performed. The risk of T. gondii infection in Europe is declining and studies using historical controls from earlier decades cannot be used for decision making. The screening of pregnant women or neonates makes the assumption that any children diagnosed can be offered an effective treatment. There is an urgent need to test new drugs and demonstrate, using randomized, controlled trials, that the currently used drugs are effective.

Inhibitory effect of aureobasidin A on Toxoplasma gondii

The apicomplexan parasite Toxoplasma gondii is a leading opportunistic pathogen associated with AIDS and congenital birth defects. Due to the need for identifying new parasite-specific treatments, the possibility of targeting sphingolipid biosynthesis in the parasite was investigated. Aureobasidin A, an inhibitor of the enzyme synthesizing the sphingolipid inositol phosphorylceramide, which is present in fungi, plants, and some protozoa but absent in mammalian cells, was found to block in vitro T. gondii replication without affecting host cell metabolism. Aureobasidin A treatment did not induce tachyzoite to bradyzoite stage conversion in T. gondii but resulted in a loss of intracellular structures and vacuolization within the parasite. In addition, aureobasidin A inhibited sphingolipid synthesis in T. gondii. Sphingolipid biosynthetic pathways may therefore be considered targets for the development of anti-T. gondii agents.

Apicoplast fatty acid biosynthesis as a target for medical intervention in apicomplexan parasites

New chemotherapies for human and animal apicomplexan infections are needed as a component of future strategies to deal with these diseases. An extensive search for new treatments exploring the unique developmental physiology, metabolism and molecular structures of Apicomplexa is under way. The description of the full complement of about 5,300 Plasmodium falciparum genes and fast growing sequence databases for other Apicomplexa allow reconstruction of metabolic pathways of these parasites and thus accelerate identification and biochemical analysis of potential targets. The apicoplast de novo fatty acid biosynthetic pathway shows great potential as a target for small-molecule inhibitors in a stand-alone or combination chemotherapy. Three enzymatic activities, acetyl-CoA carboxylase, beta-ketoacyl-ACP synthase and enoyl-ACP reductase, respond to inhibitors previously identified for bacteria and plants, and deserve to be explored in depth. In this connection, screening systems have been established to seek more potent and specific antiparasitic compounds that are harmless to the host. To this end the interconnections of fatty acid biosynthesis in Apicomplexa with other metabolic and cellular processes must be investigated.

Dissecting apicoplast targeting in the malaria parasite Plasmodium falciparum

Transit peptides mediate protein targeting into plastids and are only poorly understood. We extracted amino acid features from transit peptides that target proteins to the relict plastid (apicoplast) of malaria parasites. Based on these amino acid characteristics, we identified 466 putative apicoplast proteins in the Plasmodium falciparum genome. Altering the specific charge characteristics in a model transit peptide by site-directed mutagenesis severely disrupted organellar targeting in vivo. Similarly, putative Hsp70 (DnaK) binding sites present in the transit peptide proved to be important for correct targeting.

Are cytochrome b gene mutations the only cause of atovaquone resistance in Pneumocystis?

There is evidence that exposure of the opportunistic pathogen Pneumocystis to atovaquone enhances the development of resistance to the drug. Atovaquone is a structural analog of ubiquinone, which binds to the mitochondrial cytochrome bc(1) complex and inhibits electron transport. Like the parasites Plasmodium and Toxoplasma, atovaquone resistance can result from mutations in the cytochrome b gene of Pneumocystis. However, atovaquone resistance cannot be explained by cytochrome b gene mutations in all cases. The discovery that atovaquone also inhibits biosynthesis of ubiquinone in P. carinii may unfold other mechanisms by which drug resistance develops.