Drug-induced reactive oxygen species-mediated inhibitory effect on growth of Trypanosoma evansi in axenic culture system

Intracellular ROS production and apoptotic effect of quinoline and isoquinoline alkaloids on the growth of Trypanosoma evansi

Trypanosoma evansi, a hemoflagellate poses huge economic threat to the livestock industry of several countries of Asia, Africa, South America and Europe continents of the world. Limited number of available chemical drugs, incidents of growing drug resistance, and related side effects encouraged the use of herbal substitutes. In the present investigation, the impact of six alkaloids of quinoline and isoquinoline group was evaluated on the growth and multiplication of Trypanosoma evansi and their cytotoxic effect was examined on horse peripheral blood mononuclear cells in an in vitro system. Quinine, quinindine, cinchonine, cinchonidine, berbamine and emetine showed potent trypanocidal activities with IC50/24 h values 6.631 ± 0.244, 8.718 ± 0.081, 16.96 ± 0.816, 33.38 ± 0.653, 2.85 ± 0.065, and 3.12 ± 0.367 µM, respectively, which was comparable to the standard anti-trypanosomal drug, quinapyramine sulfate (20 µM). However, in the cytotoxicity assay, all the drugs showed dose dependent cytotoxic effect and quinine, berbamine and emetine showed selectivity index more than 5, based of ration of CC50 to IC50. Among the selected alkaloids, quinidine, berbamine and emetine exhibited higher apoptotic effects in T. evansi. Likewise, drug treated parasites showed a dose-dependent and time-dependent increase in reactive oxygen species (ROS) production. Therefore, increased apoptosis in combination with ROS generation could be responsible for the observed trypanocidal effect which could be further evaluated in T. evansi-infected mice model.

In vitro anti-trypanosomal effect of ivermectin on Trypanosoma evansi by targeting multiple metabolic pathways

High cytotoxicity and increasing resistance reports of existing chemotherapeutic agents against T. evansi have raised the demand for novel, potent, and high therapeutic index molecules for the treatment of surra in animals. In this regard, repurposing approach of drug discovery has provided an opportunity to explore the therapeutic potential of existing drugs against new organism. With this objective, the macrocyclic lactone representative, ivermectin, has been investigated for the efficacy against T. evansi in the axenic culture medium. To elucidate the potential target of ivermectin in T. evansi, mRNA expression profile of 13 important drug target genes has been studied at 12, 24, and 48 h interval. In the in vitro growth inhibition assay, ivermectin inhibited T. evansi growth and multiplication significantly (p < 0.001) with IC₅₀ values of 13.82 μM, indicating potent trypanocidal activity. Cytotoxicity assays on equine peripheral blood mononuclear cells (PBMCs) and Vero cell line showed that ivermectin affected the viability of cells with a half-maximal cytotoxic concentration (CC₅₀) at 17.48 and 22.05 μM, respectively. Data generated showed there was significant down-regulation of hexokinase (p < 0.001), ESAG8 (p < 0.001), aurora kinase (p < 0.001), casein kinase 1 (p < 0.001), topoisomerase II (p < 0.001), calcium ATPase 1 (p < 0.001), ribonucleotide reductase I (p < 0.05), and ornithine decarboxylase (p < 0.01). The mRNA expression of oligopeptidase B remains refractory to the exposure of the ivermectin. The arginine kinase 1 and ribonucleotide reductase II showed up-regulation on treatment with ivermectin. The ivermectin was found to affect glycolytic pathways, ATP-dependent calcium ATPase, cellular kinases, and other pathway involved in proliferation and maintenance of internal homeostasis of T. evansi. These data imply that intervention with alternate strategies like nano-formulation, nano-carriers, and nano-delivery or identification of ivermectin homologs with low cytotoxicity and high bioavailability can be explored in the future as an alternate treatment for surra in animals.

Gene expression study to elucidate the anti-trypanosomal activity of quinapyramine methyl sulphate (QPS)

The kinetoplastid protozoan parasite, Trypanosoma evansi causes a fatal disease condition known as Surra in equines throughout the globe. Disease condition being acute in nature, entrust a huge economic and health impact on the equine industry. Till date, quinapyramine methyl sulphate (QPS) is the first line of treatment and a panacea for the T. evansi infection in equines. Still after the >70 years of its discovery, there is no clue about the mode of action of QPS in T. evansi. The establishment of in vitro cultivation of T. evansi in HMI-9 media has provided opportunity to study the alteration in mRNA expression of parasite on exposure to the drug. With this research gap, the present study aimed to investigate the relative mRNA expression of 13 important drug target genes to elucidate the anti-trypanosomal activity of QPS against T. evansi. The IC₅₀ of QPS against a pony isolate of T. evansi was determined as 276.4 nM(147.21 ng/ mL) in the growth inhibitory assay. The in vitro cultured T. evansi population were further exposed to IC₅₀ of QPS and their relative mRNA expression was studied at 12 h, 24 h and 48 h interval.The mRNA expression of several genes such as hexokinase, trypanothione reductase, aurora kinase, oligopeptidase B and ribonucleotide reductase II were found refractory (non-significant, p > 0.1234) to the exposure of QPS. Significant up-regulation of trans-sialidase (p < 0.0001), ESAG8 (p < 0.0021), ribonucleotide reductase I (p < 0.0001), ornithine decarboxylase (p < 0.0001), topoisomerase II (p < 0.0021) and casein kinase I (p < 0.0021) were recorded after exposure with QPS. The arginine kinase 1 and calcium ATPase I showed highly significant (p < 0.0001) down-regulation in the drug kinetics. Therefore, the arginine kinase 1 and calcium ATPase I can be explored further to elucidate the trypanocidal activity of QPS. The preliminary data generated provide the potential of arginine kinase 1 and calcium ATPase I mRNA mediated pathway of trypanocidal action of QPS. Further, transcriptomics approach is required to investigate the possible mechanism of action of drugs at molecular level against the targeted organism.

In vitro and in vivo evaluation of kinase and protease inhibitors against Trypanosoma evansi

Trypanosoma evansi is a causative agent of chronic wasting and fatal disease of livestock and wild animals known as surra. In this study, repurposing approach based on drug target was used to investigate the efficacy of kinase inhibitors (Barasertib-HQPA, BAR and Palbociclib isethionate, PAL) and protease inhibitors (Z-pro-prolinal, Z-PRO and Leupeptin hemisulphate, LEU) against T. evansi in HMI-9 medium. BAR, PAL and Z-PRO exhibited IC₅₀ values of 13.52 µM, 0.6375 µM and 63.20 µM against T. evansi in terms of growth inhibition, in the contrary, LEU failed to exhibit a significant growth inhibition at any time interval. Furthermore, oligopeptidase B and aurora kinase genes of T. evansi were targeted to determine the effect of these drugs on quantitative mRNA expression, which showed significant (p < 0.01) up-regulation of both genes in the BAR and PAL-exposed population at 12 h of exposure, whereas, Z-PRO showed only significant (p < 0.05) up-regulation of aurora kinase gene at 12 h interval. In cytotoxicity assay, BAR exhibited 52% and 41% cytotoxicity at 50 μM concentration (about five folds the IC₅₀ value₎ on equine PBMC's and Vero cell line, respectively. Similarly, the cytotoxicity of 25% and 24% were recorded at 10 μM concentration (about ten folds to the IC₅₀ value) of PAL in equine PBMC's and Vero cell line, respectively. Of these, BAR and PAL, which were found effective under in vitro trials, raised the longevity of mice at higher doses during in vivo trials. Data generated showed that kinase inhibitors have higher potential to explore therapeutic molecules against surra organism.

Gum-based nanocapsules comprising naphthoquinones enhance the apoptotic and trypanocidal activity against Trypanosoma evansi

Nanoencapsulation is a promising approach to enhance the therapeutic potential of a drug. Herein, three selected naphthoquinone (NTQ) derivatives, based on the IC₅₀ value against Trypanosoma evansi, were encapsulated using gum damar as biocompatible and biodegradable natural gum via nanoprecipitation method. Nanoformulation of NTQs (NNTQs) was less than 150 nm in size, was found to be stable and released the drug in a sustained manner. All the three NNTQs exhibited significant antitrypanosomal effect and morphological changes at approximately two to three times lesser drug concentrations. The nanoformulations exhibited enhanced production of reactive oxygen species (ROS) in the axenic culture of T. evansi and less cytotoxic effect on horse peripheral blood mononuclear cells relative to pure NTQs. As evidenced by flow cytometry, the NNTQs showed dose-dependent and time-dependent increased transition of live cells (AV^-PI^-) to early apoptotic cells (AV⁺PI^-), late apoptotic cells (AV^-PI⁺), and necrotic cells (AV⁺PI⁺) using annexin V/propidium iodide probe analysis. The results concluded that NNTQs induced more ROS, apoptosis and necrotic effects that exhibited more inhibitory effect on the growth of T. evansi with respect to respective NTQ by themselves.

Discovery and Validation of Lmj_04_BRCT Domain, a Novel Therapeutic Target: Identification of Candidate Drugs for Leishmaniasis

Since many of the currently available antileishmanial treatments exhibit toxicity, low effectiveness, and resistance, search and validation of new therapeutic targets allowing the development of innovative drugs have become a worldwide priority. This work presents a structure-based drug discovery strategy to validate the Lmj_04_BRCT domain as a novel therapeutic target in Leishmania spp. The structure of this domain was explored using homology modeling, virtual screening, and molecular dynamics studies. Candidate compounds were validated in vitro using promastigotes of Leishmania major, L. amazonensis, and L. infantum, as well as primary mouse macrophages infected with L. major. The novel inhibitor CPE2 emerged as the most active of a group of compounds against Leishmania, being able to significantly reduce the viability of promastigotes. CPE2 was also active against the intracellular forms of the parasites and significantly reduced parasite burden in murine macrophages without exhibiting toxicity in host cells. Furthermore, L. major promastigotes treated with CPE2 showed significant lower expression levels of several genes (α-tubulin, Cyclin CYCA, and Yip1) related to proliferation and treatment resistance. Our in silico and in vitro studies suggest that the Lmj_04_BRCT domain and its here disclosed inhibitors are new potential therapeutic options against leishmaniasis.

Naphthoquinone derivatives exhibit apoptosis-like effect and anti-trypanosomal activity against Trypanosoma evansi

Trypanosoma evansi is an extracellular flagellate blood protozoan parasite and an etiological agent of animal trypanosomosis. Presently, only a few drugs are registered and have been used for the treatment of animal trypanosomosis, but they show severe toxic effects and also face the problem of drug resistance. Naphthoquinones (NTQ) are considered as fortunate structures in the field of medicinal chemistry as they have been reported for their antitrypanosomal potential against other trypanosomes-T. brucei and T. cruzi. In the present study, six naphthoquinones (NTQ1-NTQ6) derivatives were evaluated for anti-trypanosomal activity by demonstrating their growth inhibitory effect against T. evansi. All NTQs significantly (p < 0.001) exhibited activity against parasite growth and multiplication with IC₅₀ values of 11.48 μM, 373.6 μM, 12.97 μM, 21.97 μM, 18.19 μM and 5.758 μM but NTQ1, NTQ3 and NTQ6 were selected based on their IC₅₀ value for further studies. The dose-and time-dependent morphological effect on parasite was evaluated including the measurement of reactive oxygen species (ROS) by spectrofluorometery and measurement of apoptosis by flow cytometry. The selected NTQs exhibited a significant production of ROS and displayed a significant AV⁺ and PI⁺ labelled cells in the axenic culture of T. evansi than quinapyramine methyl sulphate (QPS), as reference control. NTQs also showed more cytotoxic effect on horse peripheral blood mononuclear cells as compare to QPS. Therefore, we confirmed the antitrypanosomal activity and apoptotic-like mechanism of NTQs in an axenic culture of T. evansi.