Large-scale drug screening against Babesia divergens parasite using a fluorescence-based high-throughput screening assay

Comparative chemical genomics in Babesia species identifies the alkaline phosphatase PhoD as a determinant of antiparasitic resistance

Babesiosis is an emerging zoonosis and widely distributed veterinary infection caused by 100+ species of Babesia parasites. The diversity of Babesia parasites and the lack of specific drugs necessitate the discovery of broadly effective antibabesials. Here, we describe a comparative chemogenomics (CCG) pipeline for the identification of conserved targets. CCG relies on parallel in vitro evolution of resistance in independent populations of Babesia spp. (B. bovis and B. divergens). We identified a potent antibabesial, MMV019266, from the Malaria Box, and selected for resistance in two species of Babesia. After sequencing of multiple independently derived lines in the two species, we identified mutations in a membrane-bound metallodependent phosphatase (phoD). In both species, the mutations were found in the phoD-like phosphatase domain. Using reverse genetics, we validated that mutations in bdphoD confer resistance to MMV019266 in B. divergens. We have also demonstrated that BdPhoD localizes to the endomembrane system and partially with the apicoplast. Finally, conditional knockdown and constitutive overexpression of BdPhoD alter the sensitivity to MMV019266 in the parasite. Overexpression of BdPhoD results in increased sensitivity to the compound, while knockdown increases resistance, suggesting BdPhoD is a pro-susceptibility factor. Together, we have generated a robust pipeline for identification of resistance loci and identified BdPhoD as a resistance mechanism in Babesia species.

Antiparasitic activity of FLLL-32 against four Babesia species, B. bovis, B. bigemina, B. divergens and B. caballi, and one Theileria species, Theileria equi in vitro, and Babesia microti in mice

Introduction: FLLL-32, a synthetic analog of curcumin, is a potent inhibitor of STAT3's constitutive activation in a variety of cancer cells, and its anticancer properties have been demonstrated both in vitro and in vivo. It is also suggested that it might have other pharmacological activities including activity against different parasites. Aim: This study therefore investigated the in vitro antiparasitic activity of FLLL-32 against four pathogenic Babesia species, B. bovis, B. bigemina, B. divergens, and B. caballi, and one Theileria species, Theileria equi. In vivo anti-Babesia microti activity of FLLL-32 was also evaluated in mice. Methods: The FLLL-32, in the growth inhibition assay with a concentration range (0.005-50 μM), was tested for it's activity against these pathogens. The reverse transcription PCR (RT-PCR) assay was used to evaluate the possible effects of FLLL-32 treatment on the mRNA transcription of the target B. bovis genes including S-adenosylhomocysteine hydrolase and histone deacetylase. Results: The in vitro growth of B. bovis, B. bigemina, B. divergens, B. caballi, and T. equi was significantly inhibited in a dose-dependent manner (in all cases, p < 0.05). FLLL-32 exhibits the highest inhibitory effects on B. bovis growth in vitro, and it's IC50 value against this species was 9.57 μM. The RT-PCR results showed that FLLL-32 inhibited the transcription of the B. bovis S-adenosylhomocysteine hydrolase gene. In vivo, the FLLL-32 showed significant inhibition (p < 0.05) of B. microti parasitemia in infected mice with results comparable to that of diminazene aceturate. Parasitemia level in B. microti-infected mice treated with FLLL-32 from day 12 post infection (pi) was reduced to reach zero level at day 16 pi when compared to the infected non-treated mice. Conclusion: The present study demonstrated the antibabesial properties of FLLL-32 and suggested it's usage in the treatment of babesiosis especially when utilized in combination therapy with other antibabesial drugs.

Evaluation of the Inhibitory Effect of Moringa oleifera Leaves Methanolic Extract against In Vitro Growth of Several Babesia Species and Theileria equi and the In Vivo Growth of Babesia microti

The current study evaluated the inhibitory effect of Moringa oleifera leaves methanolic extract (MOL) against the in vitro growth of Babesia bovis (B. bovis), B. caballi, B. bigemina, and Theileria equi (T. equi), as well as in vivo growth of B. microti in mice. Active principles of MOL extract were determined using liquid chromatography mass spectrometry (LC-MS). MOL's anti-piroplasm efficacy was assessed both in vitro and in vivo using the SYBR Green I fluorescence assay. Every 96 hours, the hematological parameters, including red blood cell count (RBCs; 104/UL), hemoglobin content (HGB; g/dl), and hematocrit percent (HCT; %), in the treated mice were monitored using a Celltac MEK6450 automated hematological analyzer. LC-MS of MOL revealed that the most abundant polyphenolic catechism found in the MOL extract was isoquercetin and rutin. MOL inhibited B. bovis, B. caballi, B. bigemina, and T. equi in vitro growth in a dose-dependent way, with IC50 values of 45.29 ± 6.14, 19.16 ± 0.45, 137.49 ± 16.07, and 9.29 ± 0.014 μg/ml, respectively. MOL's in vitro antibabesial activity was enhanced when administrated simultaneously with either diminazene aceturate (DA) or MMV665875 compound from malaria box. In mice infected by B. microti, a combination of MOL and a low dose of DA (12.5 mg·kg-1) resulted in a significant (P < 0.05) reduction in B. microti growth. These findings suggest that MOL is an effective herbal anti-piroplasm therapy, especially when combined with a low dosage of either DA or MMV665875.

Diminazene aceturate and imidocarb dipropionate-based combination therapy for babesiosis – A new paradigm

In the present study, the effect of a combination therapy consisting of diminazene aceturate (DA) and imidocarb dipropionate (ID) on the in vitro growth of several parasitic piroplasmids, and on Babesia microti in BALB/c mice was evaluated using a fluorescence-based SYBR Green I test. We evaluated the structural similarities between the regularly used antibabesial medications, DA and ID, and the recently found antibabesial drugs, pyronaridine tetraphosphate, atovaquone, and clofazimine, using atom pair fingerprints (APfp). The Chou-Talalay approach was used to determine the interactions between the two drugs. A Celltac MEK-6450 computerized hematology analyzer was used to detect hemolytic anemia every 96 hours in mice infected with B. microti and in those treated with either mono- or combination therapy. According to the APfp results, DA and ID have the most structural similarities (MSS). DA and ID had synergistic and additive interactions against the in vitro growth of Babesia bigemina and Babesia bovis, respectively. Low dosages of DA (6.25 mg kg^-1) and ID (8.5 mg kg^-1) in conjunction with each other inhibited B. microti growth by 16.5 %, 32 %, and 4.5 % more than 25 mg kg^-1 DA, 6.25 mg kg^-1 DA, and 8.5 mg kg^-1 ID monotherapies, respectively. In the blood, kidney, heart, and lung tissues of mice treated with DA/ID, the B. microti small subunit rRNA gene was not detected. The obtained findings suggest that DA/ID could be a promising combination therapy for treating bovine babesiosis. Also, such combination may overcome the potential problems of Babesia resistance and host toxicity induced by utilizing full doses of DA and ID.

Comparative chemical genomics in Babesia species identifies the alkaline phosphatase phoD as a novel determinant of resistance

Babesiosis is an emerging zoonosis and widely distributed veterinary infection caused by 100+ species of Babesia parasites. The diversity of Babesia parasites, coupled with the lack of potent inhibitors necessitates the discovery of novel conserved druggable targets for the generation of broadly effective antibabesials. Here, we describe a comparative chemogenomics (CCG) pipeline for the identification of novel and conserved targets. CCG relies on parallel in vitro evolution of resistance in independent populations of evolutionarily-related Babesia spp. ( B. bovis and B. divergens ). We identified a potent antibabesial inhibitor from the Malaria Box, MMV019266. We were able to select for resistance to this compound in two species of Babesia, achieving 10-fold or greater resistance after ten weeks of intermittent selection. After sequencing of multiple independently derived lines in the two species, we identified mutations in a single conserved gene in both species: a membrane-bound metallodependent phosphatase (putatively named PhoD). In both species, the mutations were found in the phoD-like phosphatase domain, proximal to the predicted ligand binding site. Using reverse genetics, we validated that mutations in PhoD confer resistance to MMV019266. We have also demonstrated that PhoD localizes to the endomembrane system and partially with the apicoplast. Finally, conditional knockdown and constitutive overexpression of PhoD alter the sensitivity to MMV019266 in the parasite: overexpression of PhoD results in increased sensitivity to the compound, while knockdown increases resistance, suggesting PhoD is a resistance mechanism. Together, we have generated a robust pipeline for identification of resistance loci, and identified PhoD as a novel determinant of resistance in Babesia species.

Highlights

Use of two species for in vitro evolution identifies a high confidence locus associated with resistance Resistance mutation in phoD was validated using reverse genetics in B. divergens Perturbation of phoD using function genetics results in changes in the level of resistance to MMV019266Epitope tagging reveals localization to the ER/apicoplast, a conserved localization with a similar protein in diatoms Together, phoD is a novel resistance determinant in multiple Babesia spp .

Evaluating the inhibitory effect of resveratrol on the multiplication of several Babesia species and Theileria equi on in vitro cultures, and Babesia microti in mice

Introduction: Histone post-translational modification is one of the most studied factors influencing epigenetic regulation of protozoan parasite gene expression, which is mediated by histone deacetylases (KDACs) and acetyltransferases (KATs). Objective and methods: The present study investigated the role of resveratrol (RVT) as an activator of histone deacetylases in the control of various pathogenic Babesia sp. and Theileria equi in vitro, as well as B. microti infected mice in vivo using fluorescence assay. Its role in mitigating the side effects associated with the widely used antibabesial drugs diminazene aceturate (DA) and azithromycin (AZM) has also been investigated. Results: The in vitro growth of B. bovis, B. bigemina, B. divergens, B. caballi and Theileria equi (T. equi) was significantly inhibited (P < 0.05) by RVT treatments. The estimated IC50 values revealed that RVT has the greatest inhibitory effects on B. bovis growth in vitro, with an IC50 value of 29.51 ± 2.46 µM. Reverse transcription PCR assay showed that such inhibitory activity might be attributed to resveratrol's stimulatory effect on B. bovis KDAC3 (BbKADC3) as well as its inhibitory effect on BbKATS. RVT causes a significant decrease (P < 0.05) in cardiac troponin T (cTnT) levels in heart tissue of B. microti- infected mice, thereby indicating that RVT may play a part in reducing the cardiotoxic effects of AZM. Resveratrol showed an additive effect with imidocarb dipropionate in vivo. Treatment of B. microti-infected mice with a combined 5 mg/kg RVT and 8.5 mg/kg ID resulted in an 81.55% inhibition at day 10 postinoculation (peak of parasitemia). Conclusion: Our data show that RVT is a promising antibabesial pharmacological candidate with therapeutic activities that could overcome the side effects of the currently used anti-Babesia medications.

In vivo activity and atom pair fingerprint analysis of MMV665941 against the apicomplexan parasite Babesia microti, the causative agent of babesiosis in humans and rodents

The effect of MMV665941 on the growth of Babesia microti (B. microti) in mice, was investigated in this study using a fluorescence-based SYBR Green I test. Using atom Pair signatures, we investigated the structural similarity between MMV665941 and the commonly used antibabesial medicines diminazene aceturate (DA), imidocarb dipropionate (ID), or atovaquone (AV). In vitro cultures of Babesia bovis (B. bovis) and, Theileria equi (T. equi) were utilized to determine the MMV665941 and AV interaction using combination ratios ranged from 0.75 IC50 MMV665941:0.75 IC50 AV to 0.50 IC50 MMV665941:0.50 IC50 AV. The used combinations were prepared depending on the IC50 of each drug against the in vitro growth of the tested parasite. Every 96 h, the hemolytic anemia in the treated mice was monitored using a Celltac MEK-6450 computerized hematology analyzer. A single dose of 5 mg/kg MMV665941 exhibited inhibition in the B. microti growth from day 4 post-inoculation (p.i.) till day 12 p.i. MMV665941 caused 62.10%, 49.88%, and 74.23% inhibitions in parasite growth at days 4, 6 and 8 p.i., respectively. Of note, 5 mg/kg MMV665941 resulted in quick recovery of hemolytic anemia caused by babesiosis. The atom pair fingerprint (APfp) analysis revealed that MMV665941 and atovaquone (AV) showed maximum structural similarity. Of note, high concentrations (0.75 IC50) of MMV665941 and AV caused synergistic inhibition on B. bovis growth. These findings suggest that MMV665941 might be a promising drug for babesiosis treatment, particularly when combined with the commonly used antibabesial drug, AV.

In Vitro Inhibitory Effects and Bioinformatic Analysis of Norfloxacin and Ofloxacin on Piroplasm

PURPOSE

The in vitro inhibitory effect of two fluroquinolone antibiotics, norfloxacin and ofloxacin, was evaluated in this study on the growth of several Babesia and Theileria parasites with highlighting the bioinformatic analysis for both drugs with the commonly used antibabesial drug, diminazene aceturate (DA), and the recently identified antibabesial drugs, luteolin, and pyronaridine tetraphosphate (PYR).

METHODS

The antipiroplasm efficacy of screened fluroquinolones in vitro and in vivo was assessed using a fluorescence-based SYBR Green I assay. Using atom Pair signatures, we investigated the structural similarity between fluroquinolones and the antibabesial drugs.

RESULTS

Both fluroquinolones significantly inhibited (P < 0.05) the in vitro growths of Babesia bovis (B. bovis), B. bigemina, B. caballi, and Theileria equi (T. equi) in a dose-dependent manner. The best inhibitory effect for both drugs was observed on the growth of T. equi. Atom Pair fingerprints (APfp) results and AP Tanimoto values revealed that both fluroquinolones, norfloxacin with luteolin, and ofloxacin with PYR, showed the maximum structural similarity (MSS). Two drug interactions findings confirmed the synergetic interaction between these combination therapies against the in vitro growth of B. bovis and T. equi.

CONCLUSION

This study helped in discovery novel potent antibabesial combination therapies consist of norfloxacin/ofloxacin, norfloxacin/luteolin, and ofloxacin/PYR.

Imidazo[1,2-a]pyridine: a Highly Potent Therapeutic Agent Clears Piroplasm Infection In Vitro

BACKGROUND AND PURPOSE

The imidazo[1,2-a] pyridines have huge applications in medicinal chemistry with potent activity against wide spectrum of infectious agents. The efficacy of imidazo[1,2-a]pyridine on the in vitro growth of different piroplasms, including Babesia bovis, B. bigemina, B. divergens, B. caballi, and Theileria equi, was investigated in this study.

METHODS

The anti-piroplasm efficacy of imidazo[1,2-a] pyridines was assessed using a fluorescence-based SYBR Green I assay. Furthermore, efficacy of imidazo[1,2-a]pyridine against piroplasms following discontinuation of treatment was also assessed using a viability assay. In vitro cultures of B. bovis and T. equi were used to assess the imidazo[1,2-a]pyridine and diminazene aceturate (DA) interaction.

RESULTS

In vitro, imidazo[1,2-a]pyridine inhibited the growth of B. bovis, B. bigemina, B. caballi, and T. equi in a dose-dependent manner. The highest inhibitory effects of imidazo[1,2-a]pyridine were detected on the growth of B. caballi with IC₅₀ value of 0.47 ± 0.07. Interestingly, the efficacy of imidazo[1,2-a]pyridine was higher against B. bigemina (IC₅₀: 1.37 ± 0.15) compared to the positive-control DA (IC₅₀: 2.29 ± 0.06). The viability test findings indicate that imidazo[1,2-a]pyridine had a long-lasting inhibitory effect on bovine Babesia parasites in vitro growth up to 4 days after treatment. Notably, when coupled with DA at 0.75 or 0.50 IC₅₀, a high concentration (0.75 IC₅₀) of imidazo[1,2-a]pyridine produced additive suppression of B. bovis growth which suggest that imidazo[1,2-a]pyridine/DA could be a promising combination therapy for the treatment of B. bovis.

CONCLUSION

The obtained encouraging findings pave the way for in vitro and in vivo efficacy trials of imidazo[1,2-a]pyridine derivatives against several piroplasmids.

Measurement of Babesia bovis infected red blood cells using flow cytometry

Rapid and accurate tools are needed for high-throughput in vitro antibabesial drug testing. In this study, flow cytometry for the measuring of Babesia bovis in vitro culture, was developed using SYBR Green I and compared against the results of fluorescence-based assay and microscopic assay. A high correlation of measured parasitemia was observed with high R² value (R² = 0.9991) between flow cytometry and microscopic analysis. The degree of antibabesial drug sensitivity against B. bovis determined by flow cytometry was 0.424 ± 0.173 μM. Similar to the results of previously published studies involving fluorescence spectrometry-based assay (0.408 ± 0.011 μM) and microscopy-based assay (0.400 ± 0.017 μM). The outcomes of this present study suggest that flow cytometry assay using SYBR Green I can potentially be useful in determining parasitemia and can serve as a rapid alternative method to antibabesial drug testing.

Pomegranate (Punica granatum) Peel Inhibits the In Vitro and In Vivo Growth of Piroplasm Parasites

Pomegranate (Punica granatum) peel has seen a rapid surge in attention as a medical and nutritional product over the last decade. The impact of pomegranate peel methanolic extract monotherapy and combination therapy on the in vitro growth of Babesia (B.) bovis, B. bigemina, B. divergens, B. caballi, and Theileria (T.) equi, as well as B. microti in mice, was investigated in this work. Fluorescence-based SYBR green I assay was used for evaluating the inhibitory antibabesial efficacy of pomegranate (Punica granatum) peel against the growth of several piroplasm parasites in vitro and in vivo. Celltac α MEK-6450 computerized haematology analyzer was used for monitoring the haematological parameters of treated mice every 4 days. Pomegranate peel inhibited the in vitro growth of B. bovis, B. bigemina, B. divergens, T. equi, and B. caballi in a dose-dependent manner, with IC₅₀ values of 154.45 ± 23.11, 40.90 ± 9.35, 72.71 ± 14.77, 100 ± 16.20, and 77.27 ± 16.94 μg/ml, respectively. On a B. bovis culture, the in vitro inhibitory effect of pomegranate peel was amplified when it was combined with diminazene aceturate (DA). Combination therapy of pomegranate peel and a low dose of DA (15 mg kg⁻¹) inhibited B. microti growth significantly (P < 0.05) higher than the treatment with the full dose of DA (25 mg kg⁻¹) in B. microti-infected mice. These findings suggest that pomegranate peel might be a potential medicinal plant for babesiosis treatment, especially when combined with a low dosage of DA.

Effect of methanolic extract from Capsicum annuum against the multiplication of several Babesia species and Theileria equi on in vitro cultures, and Babesia microti in mice

Background and Aim: Piroplasmosis is a serious disease that infects animals, inflicting significant economic losses in the livestock industry and animal trade worldwide. Anti-piroplasm drugs now on the market have demonstrated host toxicity and parasite resistance. As a result, developing more effective and safer anti-piroplasm drugs becomes an urgent issue. This study aimed to evaluate the inhibitory effect of Capsicum annuum methanolic extract (CA) against the growth of Babesia bovis, Babesia divergens, Babesia caballi, and Theileria equi in vitro and against B. microti in mice. Materials and Methods: Fluorescence-based SYBR Green I assay was used to evaluate CA's inhibitory effect in vitro and in vivo when used either as a monotherapy or combined with diminazene aceturate (DA). The hematological parameters (HCT, hemoglobin, and red blood cells counts) were determined in the blood of mice every 96 h using Celltac α MEK-6450 electronic hematology analyzer. Results: The in vitro growth of B. bovis, B. divergens, T. equi, and B. caballi was inhibited by CA in a dose-dependent manner with IC50 values of 4.87±1.23, 44.11±8.03, 8.23±2.54, and 1.26±0.50 mg/mL, respectively. In B. microti-infected mice, a combination therapy consisting of CA and a low dose of DA showed a significant (p<0.05) inhibition of B. microti growth nearly similar to those obtained by treatment with the full dose of DA. Conclusion: The obtained results indicate that CA might be a promising medicinal plant for treating babesiosis, especially when used with a low dose of DA.

Identification and Characterization of P0 Protein as a Vaccine Candidate Against Babesia divergens, Blood Parasite of Veterinary and Zoonotic Importance

The molecular identification and antigenic characterization of P0 protein in Babesia divergens, a blood parasite of veterinary and zoonotic importance, were carried out in this study for use in developing subunit vaccines against B. divergens infection. Recombinant protein encoding P0 (BdP0) was developed in Escherichia coli, and its antiserum was generated in mice for further molecular characterization. Anti-rBdP0 serum had a specific interaction with the corresponding legitimate B. divergens protein, as confirmed by Western blotting and indirect fluorescent antibody tests. ELISA was used to assess the immunogenicity of BdP0 in a group of 68 bovine field samples, and significant immunological reactivity was found in 19 and 20 positive samples of rBdp0 and B. divergens lysate, respectively. The in vitro growth of B. divergens cultures treated with anti-rBdP0 serum was significantly inhibited (p < 0.05). Furthermore, after 6 h of incubation with 2 mg/ml anti-rBdP0 serum, the ability of pre-incubated free merozoites to invade bovine erythrocytes was reduced by 59.88%. The obtained data suggest the possible use of rBdP0 as diagnostic antigen and may serve as a vaccine candidate against babesiosis caused by B. divergens either in animal or human.

Evaluation of the inhibitory effect of Zingiber officinale rhizome on Babesia and Theileria parasites

The effect of Zingiber officinale rhizome methanolic extract (ZOR) on the in vitro growth of bovine Babesia (B. bovis, B. bigemina, and B. divergens) and equine piroplasm (B. caballi, and Theileria equi) parasites and on the growth of B. microti in mice was evaluated in this study. The possible in vitro synergistic interaction between ZOR and either diminazene aceturate (DA) or potent Medicines for Malaria Venture (MMV) hits from the malaria box was also investigated. In vitro, ZOR reduced the growth of B. bovis, B. bigemina, T. equi, and B. caballi in a dose-dependent manner. B. divergens was the most susceptible parasite to the in vitro inhibitory effect of ZOR. DA and MMV compounds enhanced the in vitro inhibitory antibabesial activity of ZOR. 12.5 mg/kg DA when administrated in combination with ZOR in mice exhibited a significant inhibition (P < 0.05) in B. microti growth better than those observed after treatment with 25 mg/kg DA monotherapy. These findings suggest that ZOR could be a viable medicinal plant for babesiosis treatment, particularly when combined with a modest dose of either DA or powerful anti-B. bigemina MMV hits.

Compounds from the Medicines for Malaria Venture Box Inhibit In Vitro Growth of Babesia divergens, a Blood-Borne Parasite of Veterinary and Zoonotic Importance

Babesiosis is an infectious disease with an empty drug pipeline. A search inside chemical libraries for novel potent antibabesial candidates may help fill such an empty drug pipeline. A total of 400 compounds (200 drug-like and 200 probe-like) from the Malaria Box were evaluated in the current study against the in vitro growth of Babesia divergens (B. divergens), a parasite of veterinary and zoonotic importance. Novel and more effective anti-B. divergens drugs than the traditionally used ones were identified. Seven compounds (four drug-like and three probe-like) revealed a highly inhibitory effect against the in vitro growth of B. divergens, with IC₅₀s ≤ 10 nanomolar. Among these hits, MMV006913 exhibited an IC₅₀ value of 1 nM IC₅₀ and the highest selectivity index of 32,000. The atom pair fingerprint (APfp) analysis revealed that MMV006913 and MMV019124 showed maximum structural similarity (MSS) with atovaquone and diminazene aceturate (DA), and with DA and imidocarb dipropionate (ID), respectively. MMV665807 and MMV665850 showed MMS with each other and with ID. Of note, a high concentration (0.75 IC₅₀) of MMV006913 caused additive inhibition of B. divergens growth when combined with DA at 0.75 or 0.50 IC₅₀. The Medicines for Malaria Venture box is a treasure trove of anti-B. divergens candidates according to the obtained results.

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.

Activity Comparison of Epigenetic Modulators against the Hemoprotozoan Parasites Babesia divergens and Plasmodium falciparum

Babesiosis is a tick-borne parasitic disease of humans and livestock that has dramatically increased in frequency and geographical range over the past few decades. Infection of cattle often causes large economic losses, and human infection can be fatal in immunocompromised patients. Unlike for malaria, another disease caused by hemoprotozoan parasites, limited treatment options exist for Babesia infections. As epigenetic regulation is a promising target for new antiparasitic drugs, we screened 324 epigenetic inhibitors against Babesia divergens blood stages and identified 75 (23%) and 17 (5%) compounds that displayed ≥90% inhibition at 10 and 1 μM, respectively, including over a dozen compounds with activity in the low nanomolar range. We observed differential activity of some inhibitor classes against Babesia divergens and Plasmodium falciparum parasites and identified pairs of compounds with a high difference in activity despite a high similarity in chemical structure, highlighting new insights into the development of epigenetic inhibitors as antiparasitic drugs.

Impact of using pyronaridine tetraphosphate- based combination therapy in the treatment of babesiosis caused by Babesia bovis, B. caballi, and B. gibsoni in vitro and B. microti in mice

The inhibitory efficacies of pyronaridine tetraphosphate (PYR), when used in combination with two novel and potent antibabesial drugs; clofazimine (CF), and MMV396693 were evaluated in the current study against the growth of Babesia bovis, B. caballi, and B. gibsoni in vitro and B. microti in mice. The in vitro study against the selected parasites was performed using combination of PYR with either CF or MMV396693 in ratios ranged from 0.75:0.75 to 0.25:0.25. Combined application of PYR/MMV396693 revealed additive and indifferent interactions against the in vitro growth of all screened Babesia parasites. PYR in combination with CF, achieved indifferent and antagonistic interactions with all used concentration ratios against the in vitro growth of B. bovis and B. caballi. Treatment with PYR-CF combination therapy caused significant inhibition (P < 0.05) of the fluorescence values at days 12, 14, 16, 18, and 22 p.i. in comparison with control mice. Of note, treatment with combination therapy exhibited inhibition in the growth of B. microti (23.16%) greater than those caused by PYR alone. In summary, the obtained results highlight the improvement in the in vivo antibabesial efficacy of PYR when used in combination with CF rather than using PYR alone but such inhibition is still lower than those caused by either DA or CF monotherapies.

Pyronaridine: An update of its pharmacological activities and mechanisms of action

Pyronaridine (PYR) is an erythrocytic schizonticide with a potent antimalarial activity against multidrug-resistant Plasmodium. The drug is used in combination with artesunate for the treatment of uncomplicated P. falciparum malaria, in adults and children. The present review briefly retraces the discovery of PYR and recent antimalarial studies which has led to the approval of PYR/artesunate combination (Pyramax) by the European Medicines Agency to treat uncomplicated malaria worldwide. PYR also presents a marked antitumor activity and has revealed efficacy for the treatment of other parasitic diseases (notably Babesia and Trypanosoma infections) and to mitigate the Ebola virus propagation. On the one hand, PYR functions has an inhibitor of hemozoin (biomineral malaria pigment, by-product of hemoglobin digestion) formation, blocking the biopolymerization of β-hematin and thus facilitating the accumulation of toxic hematin into the digestive vacuole of the parasite. On the other hand, PYR is a bona fide DNA-intercalating agent and an inhibitor of DNA topoisomerase 2, leading to DNA damages and cell death. Inhibition of hematin polymerization represents the prime mechanism at the origin of the antimalarial activity, whereas anticancer effects relies essentially on the interference with DNA metabolism, as with structurally related anticancer drugs like amsacrine and quinacrine. In addition, recent studies point to an immune modulatory activity of PYR and the implication of a mitochondrial oxidative pathway. An analogy with the mechanism of action of artemisinin drugs is underlined. In brief, the biological actions of pyronaridine are recapitulated to shed light on the diverse health benefits of this unsung drug.

Alsinol, an arylamino alcohol derivative active against Plasmodium, Babesia, Trypanosoma, and Leishmania: past and new outcomes

Malaria, babesiosis, trypanosomosis, and leishmaniasis are some of the most life-threatening parasites, but the range of drugs to treat them is limited. An effective, safe, and low-cost drug with a large activity spectrum is urgently needed. For this purpose, an aryl amino alcohol derivative called Alsinol was resynthesized, screened in silico, and tested against Plasmodium, Babesia, Trypanosoma, and Leishmania. In silico Alsinol follows the Lipinski and Ghose rules. In vitro it had schizontocidal activity against Plasmodium falciparum and was able to inhibit gametocytogenesis; it was particularly active against late gametocytes. In malaria-infected mice, it showed a dose-dependent activity similar to chloroquine. It demonstrated a similar level of activity to reference compounds against Babesia divergens, and against promastigotes, and amastigotes stages of Leishmania in vitro. It inhibited the in vitro growth of two African animal strains of Trypanosoma but was ineffective in vivo in our experimental conditions. It showed moderate toxicity in J774A1 and Vero cell models. The study demonstrated that Alsinol has a large spectrum of activity and is potentially affordable to produce. Nevertheless, challenges remain in the process of scaling up synthesis, creating a suitable clinical formulation, and determining the safety margin in preclinical models.

Myrrh Oil in Vitro Inhibitory Growth on Bovine and Equine Piroplasm Parasites and Babesia microti of Mice

The present experimental study was conducted for the assessment of the efficacy of in vitro inhibition of myrrh oil on the propagation of Babesia bovis, B. divergens, B. bigemina, Theileria equi, and B. caballi and in vivo efficacy on B. microti in mice through fluorescence assay based on SYBR green I. The culture of B. divergens B. bovis and was used to evaluate the in vitro possible interaction between myrrh oil and other commercial compound, such as pyronaridine tetraphosphate (PYR), diminazene aceturate (DA), or luteolin. Nested-polymerase chain reaction protocol using primers of the small-subunit rRNA of B. microti was employed to detect any remnants of DNA for studied parasitic species either in blood or tissues. Results elucidated that; Myrrh oil significantly inhibit the growth at 1% of parasitic blood level for all bovine and equine piroplasm under the study. Parasitic regrowth was inhibited subsequently by viability test at 2 µg/mL for B. bigemina and B. bovis, and there was a significant improvement in the in vitro growth inhibition by myrrh oil when combined with DA, PYR, and luteolin. At the same time; mice treated with a combination of myrrh oil/DA showed a higher inhibition in emitted fluorescence signals than the group that challenged with 25 mg/kg of diminazene aceturate at 10 and 12 days post-infection. In conclusion, this study has recommended the myrrh oil to treat animal piroplasmosis, especially in combination with low doses of DA.

Closing the empty anti-Babesia gibsoni drug pipeline in vitro using fluorescence-based high throughput screening assay

In the current study, we evaluated the usefulness of a SYBR Green I (SG I) fluorescence assay for evaluation of the inhibitory effects of antibabesial drugs against the in vitro growth of Babesia gibsoni. Linearity and high-throughput screening (HTS) assays exhibited the validity of the SG I fluorescence assay for B. gibsoni parasite when performed at low hematocrits (HCTs) (2.5% and 5%) without daily changing of the medium. Interestingly, 5% HCT showed the highest value of the signal/noise ratio. Of note, there were no significant differences (P > .05) in the IC₅₀s of the commonly used antibabesial drugs (diminazene aceturate and/or imidocarb dipropionate) that calculated by either the SG I fluorescence assay with and without daily medium changing or by the fluorescence and microscopy methods at 2.5% and 5% HCTs. Such results confirmed that both HCTs are valid for mass drug screening against the in vitro growth of B. gibsoni. While the results of the HTS assay add merit to the assay when performed at 5% HCT especially when incubating the plates for 2 h in a dark after adding lysis buffer with SG I stain. Next, nine different drugs were screened to confirm the assay's usefulness. MMV396693, pyronaridine tetraphosphate and nerolidol drugs exhibited the highest effectiveness against the in vitro growth of B. gibsoni, next to diminazene aceturate. In summary, SG I fluorescence assay with 5% HCT without daily changing of the medium for B. gibsoni offers a novel approach for the large-scale screening of huge chemical libraries in in vitro cultures.

Assay methods for in vitro and in vivo anti-Babesia drug efficacy testing: Current progress, outlook, and challenges

Absence of an effective high-throughput drug-screening system for Babesia parasites is considered one of the main causes for the presence of a wide gap in the treatment of animal babesiosis when compared with other hemoprotozoan diseases, such as malaria. Recently, a simple, accurate, and automatic fluorescence assay was established for large-scale anti-Babesia (B. bovis, B. bigemina, B. divergens, B. caballi and T. equi) drug screening. Such development will facilitate anti-Babesia drug discovery, especially in the post-genomic era, which will bring new chemotherapy targets with the completion of the Babesia genome sequencing project currently in progress. In this review, we present the current progress in the various assays for in vitro and in vivo anti-Babesia drug testing, as well as the challenges, highlighting new insights into the future of anti-Babesia drug screening.

A Comprehensive Insight on the Health Benefits and Phytoconstituents of Camellia sinensis and Recent Approaches for Its Quality Control

Tea, Camellia sinensis, which belongs to the family Theaceae, is a shrub or evergreen tree up to 16 m in height. Green tea is very popular because of its marked health benefits comprising its anticancer, anti-oxidant, and antimicrobial activities, as well as its effectiveness in reducing body weight. Additionally, it was recognized by Chinese people as an effective traditional drink required for the prophylaxis against many health ailments. This is due to the complex chemical composition of green tea, which comprises different classes of chemical compounds, such as polyphenols, alkaloids, proteins, minerals, vitamins, amino acids, and others. The beneficial health effects of green tea ultimately led to its great consumption and increase its liability to be adulterated by either low-quality or non-green tea products with concomitant decrease in activity. Thus, in this review, green tea was selected to highlight its health benefits and phytoconstituents, as well as recent approaches for its quality-control monitoring that guarantee its incorporation in many pharmaceutical industries. More research is needed to find out other more biological activities, active constituents, and other simple and cheap techniques for its quality assurance that ascertain the prevention of its adulteration.

Cocktail Babesia bovis antigens for global detection of Babesia bovis infection in cattle

The diagnostic performance of a cocktail formula consisting of two Babesia (B.) bovis recombinant proteins, including spherical body protein 1 (BbSBP-1) and spherical body protein 4 (BbSBP-4), was evaluated in the present study for the global detection of B. bovis infection in cattle and for the differentiation between B. bovis and B. bigemina infections. The efficacy and the practicality of the rBbSBP-1 and rBbSBP-4 cocktail formula for differentiation between the infection caused by both parasites were assessed using indirect enzyme-linked immunosorbent assay (iELISA) with serum samples collected from cattle experimentally infected by B. bovis (n = 33) or B. bigemina (n = 30). Cocktail antigen exhibited the highest optical density (OD) values with B. bovis-infected sera and the lowest OD values with normal bovine sera or B. bigemina-infected sera in comparison with the single antigen. A total of 581 field serum samples collected from four countries with known B. bovis endemicity: Ghana (n = 154), Egypt (n = 162), Thailand (n = 96), and South Africa (n = 169) were screened also in the current study using iELISA and the results were compared to those of indirect fluorescent antibody test (IFAT) as a reference. A cocktail formula (rBbSBP-1 and rBbSBP-4) exhibited the highest concordance rate (89.90%) and kappa value (0.73). The obtained results revealed the reliability of the rBbSBP-1 and rBbSBP-4 cocktail antigen for the detection of specific antibodies to B. bovis in cattle and demonstrated the usefulness of cocktail antigen for differentiation between B. bovis and B. bigemina infections compared with the single antigen in cattle, which will be useful for epidemiological surveys and control of bovine babesiosis.

Discovering the in vitro potent inhibitors against Babesia and Theileria parasites by repurposing the Malaria Box: A review

There is an innovative approach to discovering and developing novel potent and safe anti-Babesia and anti-Theileria agents for the control of animal piroplasmosis. Large-scale screening of 400 compounds from a Malaria Box (a treasure trove of 400 diverse compounds with antimalarial activity has been established by Medicines for Malaria Venture) against the in vitro growth of bovine Babesia and equine Babesia and Theileria parasites was performed, and the data were published in a brief with complete dataset from 236 screens of the Malaria Box compounds. Therefore, in this review, we explored and discussed in detail the in vitro inhibitory effects of 400 antimalarial compounds (200 drug-like and 200 probe-like) from the Malaria Box against Babesia (B.) bovis, B. bigemina, B. caballi, and Theileria (T.) equi. Seventeen hits were the most interesting with regard to bovine Babesia parasites, with mean selectivity indices (SIs) greater than 300 and half maximal inhibitory concentration (IC₅₀s) ranging from 50 to 410 nM. The most interesting compounds with regard to equine Babesia and Theileria parasites were MMV020490 and MMV020275, with mean SIs > 258.68 and >251.55, respectively, and IC₅₀s ranging from 76 to 480 nM. Ten novel anti-B. bovis, anti-B. bigemina, anti-T. equi, and anti-B. caballi hits, MMV666093, MMV396794, MMV006706, MMV665941, MMV085203, MMV396693, MMV006787, MMV073843, MMV007092, and MMV665875, with nanomole levels of IC₅₀ were identified. The most interesting hits were MMV396693, MMV073843, MMV666093, and MMV665875, with mean SIs greater than 307.8 and IC₅₀s ranging from 43 to 630 nM for both bovine Babesia and equine Babesia and Theileria parasites. Screening the Malaria Box against the in vitro growth of Babesia and Theileria parasites helped with the discovery of new drugs than those traditionally used, diminazene aceturate and imidocarb dipropionate, and indicated the potential of the Malaria Box in finding new, potent antibabesial drugs.

Evaluation of the in vitro and in vivo inhibitory effect of thymoquinone on piroplasm parasites

BACKGROUND

Developing new antibabesial drugs with a low toxic effect to the animal and with no resistance from Babesia parasites is in urgent demand. In this concern, the antimalarial, anticancer and antioxidant effect of thymoquinone (TQ), a phytochemical compound found in the plant Nigella sativa, has been reported. Therefore, in the present study, the antibabesial effect of this compound was evaluated on the growth of piroplasm parasites.

RESULTS

Significant inhibition (P < 0.05) of the in vitro growth of piroplasm parasites were observed after treatment by TQ with IC₅₀ values of 35.41 ± 3.60, 7.35 ± 0.17, 0.28 ± 0.016, 74.05 ± 4.55 and 67.33 ± 0.94 μM for Babesia bovis, Babesia bigemina, Babesia divergens, Theileria equi and Babesia caballi, respectively. The in vitro inhibitory effect of TQ was significantly enhanced (P < 0.05) when used in combination with either diminazene aceturate on bovine Babesia and equine Babesia and Theileria cultures. In B. microti-infected mice, oral and intraperitoneal administrations of TQ showed significant (P < 0.05) inhibition of parasite growth at a dose of 70 mg/kg and 50 mg/kg, respectively, compared to the control group.

CONCLUSIONS

The obtained results indicate that thymoquinone might be a promising medicinal compound for use in the treatment of animal piroplasmosis.

Inhibitory effects of fluoroquinolone antibiotics on Babesia divergens and Babesia microti, blood parasites of veterinary and zoonotic importance

Aim

This study aimed to evaluate the inhibitory effects of fluoroquinolone antibiotics, including enrofloxacin, enoxacin, trovafloxacin, norfloxacin, and ofloxacin, on the in vitro and in vivo growth of Babesia divergens and Babesia microti parasites, respectively.

Materials and methods

The in vitro and in vivo inhibitory effects of fluoroquinolone antibiotics against B. divergens and B. microti, respectively were evaluated using fluorescence-based assay. Additionally, combination therapies of highly effective fluoroquinolone antibiotics (enrofloxacin, enoxacin, and trovafloxacin) with diminazene aceturate, luteolin, or pyronaridine tetraphosphate were tested on the in vitro cultures of B. divergens.

Results

Enrofloxacin, trovafloxacin, and enoxacin were the most effective fluoroquinolones against the in vitro growth of B. divergens, followed by norfloxacin and ofloxacin. Furthermore, a combination of enoxacin or trovafloxacin with either diminazene aceturate, luteolin, or pyronaridine tetraphosphate significantly enhanced the inhibitory effect on the growth of B. divergens in in vitro cultures. In mice infected by B. microti, enoxacin and diminazene aceturate combination therapy exhibited a potential antibabesial effect.

Conclusion

These results suggest that safe and cheap fluoroquinolone, such as enoxacin, might be used for the treatment of clinical cases caused by Babesia spp. in animals or humans.

17-DMAG inhibits the multiplication of several Babesia species and Theileria equi on in vitro cultures, and Babesia microti in mice

Heat shock protein 90 (Hsp90) is a chaperone protein that stabilizes cells during stress or non-stress responses. Previous reports have shown that Hsp90 is a potential drug target to suppress the multiplication of several protozoan parasites. In this study, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), an Hsp90 inhibitor, was evaluated for its inhibitory effect on five in vitro cultures of Babesia and Theileria species, including B. bovis, B. bigemina, B. divergens, B. caballi, and T. equi, and on the multiplication of a B. microti–infected mouse model. 17-DMAG showed the inhibitory effect in all of the species tested. The half maximum inhibition concentration (IC₅₀) of 17-DMAG on B. bovis, B. bigemina, B. divergens, B. caballi, and T. equi was 77.6 ± 2.9, 62.4 ± 1.9, 183.8 ± 3.2, 88.5 ± 9.6, and 307.7 ± 7.2 nM, respectively. The toxicity assay on MDBK and NIH/3T3 cell lines showed that 17-DMAG affected the viability of cells with an IC₅₀ of 15.5 ± 4 and 8.8 ± 2 μM, respectively. Since the IC₅₀s were much lower on the parasites than on the host cell lines, the selectivity index were high for all tested species. Furthermore, the two-drug combination of 17-DMAG with diminazene aceturate (DA) and atovaquone (AV) showed synergism or addition on in vitro cultures of Babesia and Theileria parasites. In the mouse model, 17-DMAG at a concentration of 30 mg/kg BW effectively inhibited the multiplication of B. microti. Moreover, if combined with DA or AV, 17-DMAG showed a comparable inhibition at the half dose. Taken together, these results indicate that 17-DMAG is a potent drug for treating piroplamosis. The data warrant further evaluation of 17-DMAG as an antibabesial drug and as an option in combination with atovaquone for the treatment of human babesiosis.

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17-DMAG inhibits the in vitro multiplication of Babesia and Theileria parasites.

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Combination of 17-DMAG with diminazene aceturate or atovaquone were also effective.

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17-DMAG also inhibits the multiplication of B. microti in mice.

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17-DMAG is a new treatment option for babesiosis in animal and human.

Performance and consistency of a fluorescence-based high-throughput screening assay for use in Babesia drug screening in mice

In this study, we evaluated the validity of a fluorescence-based assay using SYBR Green I (SG I) stain for screening antibabesial compounds against B. microti in mice. Two different hematocrits (HCTs; 2.5% and 5%) were used. Correlating relative fluorescence units (RFUs) with parasitemia showed significant linear relationships with R² values of 0.97 and 0.99 at HCTs of 2.5% and 5%, respectively. Meanwhile, the Z′ factors in a high-throughput screening (HTS) assay were within the permissible limit (≥0.5) at 2.5% HCT and lower than this value at 5% HCT. Taken together, the highest signal-to-noise (S/N) ratios were obtained at 2.5% HCT; therefore, we concluded that 2.5% was the best HCT for applying fluorescence assay in antibabesial drug screening in mice. Additionally, positive control mice and those treated with diminazene aceturate, pyronaridine tetraphosphate, and an allicin/diminazene aceturate combination showed peak parasitemia and fluorescence values on the same day post-inoculation. Moreover, using different concentrations of SG I revealed that the optimal concentration was 2x. In summary, considering that all experiments were applied under optimal laboratory conditions, fluorescence assay at 2.5% HCT using 2x SG I for B. microti parasite offers a novel approach for drug screening in mice.

Molecular identification and antigenic characterization of Babesia divergens Erythrocyte Binding Protein (BdEBP) as a potential vaccine candidate

Host cell invasion is the only step where Babesia parasites are extracellular, and their survival is menaced during this step. Therefore, interfering with this critical stage is a target for an anti-Babesia intervention strategy. In this regard, recombinant protein encoding Babesia divergens Erythrocyte Binding Protein (BdEBP) was produced in Escherichia coli in the current study, and its antiserum was prepared in mice for further molecular characterization. Western blotting and indirect fluorescent antibody test (IFAT) revealed the specific reaction of the anti-rBdEBP serum with a corresponding authentic protein of B. divergens. Next, bovine RBCs were incubated with a B. divergens lysate, and anti-rBdEBP serum was produced in mice to detect the ability of BdEBP to bind with host cells. Bands corresponding to 29.6-kDa proteins in the protein-bound erythrocyte lysate were detected by specific immune rBdEBP using Western blotting. These results suggest that BdEBP is functional in the merozoite stage and may be involved in attachment to bovine RBCs. A significant inhibition of the in vitro growth of B. divergens culture treated with anti-rBdEBP serum was observed. Moreover, the efficacy of pre-incubated free merozoites to invade bovine erythrocytes was inhibited by 60% after incubation with 2mg/ml of anti-rBdEBP serum for 6h. The obtained data suggest the possible use of rBdEBP as a vaccine candidate against bovine babesiosis.

Evaluation of the inhibitory effect of N-acetyl-L-cysteine on Babesia and Theileria parasites

N-acetyl-L-cysteine is known to have antibacterial, antiviral, antimalarial, and antioxidant activities. Therefore, the in vitro inhibitory effect of this hit was evaluated in the present study on the growth of Babesia and Theileria parasites. The in vitro growth of Babesia bovis, Babesia bigemina, Babesia divergens, Theileria equi, and Babesia caballi that were tested was significantly inhibited (P < 0.05) by micromolar concentrations of N-acetyl-L-cysteine. The inhibitory effect of N-acetyl-L-cysteine was synergistically potentiated when used in combination with diminazene aceturate on B. bovis and B. caballi cultures. These results indicate that N-acetyl-L-cysteine might be used as a drug for the treatment of babesiosis, especially when used in combination with diminazene aceturate.