Resistance of a rodent malaria parasite to a thymidylate synthase inhibitor induces an apoptotic parasite death and imposes a huge cost of fitness

Base pairs with 5-chloroorotic acid and comparison with the natural nucleobase. Structural and spectroscopic study, and three suggested antiviral modified nucleosides

A structural and spectroscopic study of 5-chloroorotic acid (5-ClOA) biomolecule was carried out by IR and FT-Raman and the results obtained were compared to those achieved in 5-fluoroorotic acid and 5-aminoorotic acid compounds. The structures of all possible tautomeric forms were determined using DFT and MP2 methods. To know the tautomer form present in the solid state, the crystal unit cell was optimized through dimer and tetramer forms in several tautomeric forms. The keto form was confirmed through an accurate assignment of all the bands. For this purpose, an additional improvement in the theoretical spectra was carried out using linear scaling equations (LSE) and polynomic equations (PSE) deduced from uracil molecule. Base pairs with uracil, thymine and cytosine nucleobases were optimized and compared to the natural Watson-Crick (WC) pairs. The counterpoise (CP) corrected interaction energies of the base pairs were also calculated. Three nucleosides were optimized based on 5-ClOA as nucleobase, and their corresponding WC pairs with adenosine. These modified nucleosides were inserted in DNA:DNA and RNA:RNA microhelices, which were optimized. The position of the -COOH group in the uracil ring of these microhelices interrupts the DNA/RNA helix formation. Because of the special characteristic of these molecules they can be used as antiviral drugs.Communicated by Ramaswamy H. Sarma.

Drug selection pressure and fitness cost for artemether-resistant Plasmodium berghei ANKA parasites in vivo

BACKGROUND

The clinical use of artemisinin-based combination therapies is threatened by increasing failure rates due to the emergence and spread of multiple drug resistance genes in most human Plasmodium strains. The aim of this study was to generate artemether-resistant (AMR) parasites from Plasmodium berghei ANKA (AMS), and determine their fitness cost.

METHODS

Artemether resistance was generated by increasing drug pressure doses gradually for 9 months. Effective doses (ED50 and ED90) were determined using the 4-day suppressive test, and the indices of resistance (I) at 50% and 90% (I50 and I90) were determined using the ratio of either ED50 or ED90 of AMR to AMS, respectively. The stability of the AMR parasites was evaluated by: five drug-free passages (5DFPs), 3 months of cryopreservation (CP), and drug-free serial passages (DFSPs) for 4 months. Analysis of variance was used to compare differences in growth rates between AMR and AMS with 95% confidence intervals.

RESULTS

ED50 and ED90 of AMS were 0.61 and 3.43 mg/kg/day respectively. I50 and I90 after 20 cycles of artemether selection pressure were 19.67 and 21.45, respectively; 5DFP values were 39.16 and 15.27, respectively; 3-month CP values were 29.36 and 10.79, respectively; and DFSP values were 31.34 and 12.29, respectively. The mean parasitaemia value of AMR (24.70% ± 3.60) relative to AMS (37.66% ± 3.68) at Day 7 post infection after DFSPs revealed a fitness cost of 34.41%.

CONCLUSION

A moderately stable AMRP. berghei line was generated. Known and unknown mutations may be involved in modulating artemether resistance, and therefore molecular investigations are recommended.

Overexpression of the HECT ubiquitin ligase PfUT prolongs the intraerythrocytic cycle and reduces invasion efficiency of Plasmodium falciparum

The glms ribozyme system has been used as an amenable tool to conditionally control expression of genes of interest. It is generally assumed that insertion of the ribozyme sequence does not affect expression of the targeted gene in the absence of the inducer glucosamine-6-phosphate, although experimental support for this assumption is scarce. Here, we report the unexpected finding that integration of the glms ribozyme sequence in the 3′ untranslated region of a gene encoding a HECT E3 ubiquitin ligase, termed Plasmodium falciparum ubiquitin transferase (PfUT), increased steady state RNA and protein levels 2.5-fold in the human malaria parasite P. falciparum. Overexpression of pfut resulted in an S/M phase-associated lengthening of the parasite’s intraerythrocytic developmental cycle and a reduced merozoite invasion efficiency. The addition of glucosamine partially restored the wild type phenotype. Our study suggests a role of PfUT in controlling cell cycle progression and merozoite invasion. Our study further raises awareness regarding unexpected effects on gene expression when inserting the glms ribozyme sequence into a gene locus.

Hematologic changes and splenic index on malaria mice models given Syzygium cumini extract as an adjuvant therapy

Aims:

This research aimed to determine the efficacy of Syzygium cumini L. as an adjuvant therapy on blood changes and splenic index of mice model malaria.

Materials and Methods:

Mice were infected intraperitoneally with 0.2 ml red blood cell (RBC) that contains 1×10⁶Plasmodium berghei. 35 mice were divided into seven treatment groups: Group K0: Mice were not infected; K1: Mice were infected; K2: Mice were infected and given chloroquine; P1: Mice were infected and given S. cumini leaf extract; P2: Mice were infected and given chloroquine and also S. cumini leaf extract; P3: Mice was infected and given S. cumini stem bark extract; and P4: Mice were infected and given chloroquine and S. cumini stem bark extract. Treatment was given for 4 days 24 h post -P. berghei infection. 21^st day post-P. berghei infection, blood was taken from the heart for hematological examination, and the spleen was taken to examine the splenic index and also to measure the weight and length of the spleen. Hematological data and splenic index were analyzed by analysis of variance test, and if there is a difference, the test is continued by Duncan’s multiple range test with 5% level.

Results:

The K0 group has normal hemoglobin (HGB), RBC, and hematocrit (HCT) and significantly different (p<0.05) than other groups. HGB, RBC, and HCT of K1 group were under normal range, lowest, and significantly different (p<0.05) than other groups. Mean corpuscular volume and mean corpuscular HGB values of K2 groups showed a decrease. The number of leukocytes, lymphocytes, and monocytes of K1 groups was increasing and significantly different (p<0.05) with K2 and treatment group. The length, width, weight, and splenic index of K1 group were significantly different (p<0.05) with K0 group. K2 and treatment groups showed that the length and width of spleens were significantly different (p<0.05) with K1.

Conclusion:

The combination of chloroquine with leaf and chloroquine with stem bark extract of S. cumini as adjuvant therapy may increase the amount of erythrocyte; decrease the number of leukocytes, lymphocytes, and monocytes; and decrease the length, width, and splenic index on malaria mice models.

Phenotypic approach artemisinin resistance in malaria rodent as in vivo model

Aim:

The aim of this study is to prove the development of artemisinin resistance phenotypically in malaria rodent as an in vivo resistance development model in humans.

Materials and Methods:

Plasmodium berghei was infected intraperitoneally in mice, then artemisinin was given with “4-day-test” with effective dose (ED) 99% dose for 3 days which begins 48 h after infection (D2, D3, and D4). Parasite development was followed during 5^th until 10^th days of infection. After parasitemia >2% of red blood cell which contains parasites on 1 mice, that mice were used as donor to be passaged on the new 5 mice. After that, parasitemia was calculated. ED₅₀ and ED₉₀ were examined with parasite clearance time (PCT), recrudescence time (RT), and also morphology development examination of intraerythrocytic cycle of P. berghei with transmission electron microscope.

Results:

Among the control group compare with the treatment group showed significant differences at α=0.05 on 5^th day (D5) until 10^th day (D10). The control group of 4^th passage (K4) with passage treatment group of 4^th passage (P4) on the 10^th days (D10) post infection showed no significant differences in the α=0.05. The average percentage of inhibition growth was decreasing which is started from 5^th to 10^th day post infection in P1, P2, P3, and P4. On the development of P. berghei stage, which is given repeated artemisinin and repeated passage, there was a formation of dormant and also vacuoles in Plasmodium that exposed to the drug.

Conclusion:

Exposure to artemisinin with repeated passages in mice increased the value of ED₅₀ and ED₉₀, decreased the PCT and RT and also changes in morphology dormant and vacuole formation.

Efficacy and safety evaluation of a novel trioxaquine in the management of cerebral malaria in a mouse model

Background

The emergence of multidrug-resistant strains of Plasmodium falciparum poses a great threat of increased fatalities in cases of cerebral and other forms of severe malaria infections in which parenteral artesunate monotherapy is the current drug of choice. The study aimed to investigate in a mouse model of human cerebral malaria whether a trioxaquine chemically synthesized by covalent linking of a 4,7-dichloroquinoline pharmacophore to artesunate through a recent drug development approach termed ‘covalent bitherapy’ could improve the curative outcomes in cerebral malaria infections.

Methods

Human cerebral malaria rodent model, the C57BL/6 male mice were infected intraperitoneally (ip) with Plasmodium berghei ANKA and intravenously (iv) treated with the trioxaquine from day 8 post-infection (pi) at 12.5 and 25 mg/kg, respectively, twice a day for 3 days. Treatments with the trioxaquine precursors (artesunate and 4,7-dichloroquine), and quinine were also included as controls. In vivo safety evaluation for the trioxaquine was done according to Organization for Economic Co-operation and Development (OECD) guidelines 423, where female Swiss albino mice were orally administered with either 300 or 2000 mg/kg of the trioxaquine and monitored for signs of severity, and or mortality for 14 days post-treatment.

Results

The trioxaquine showed a potent and a rapid antiplasmodial activity with 80% parasite clearance in the first 24 h for the two dosages used. Long-term parasitaemia monitoring showed a total parasite clearance as the treated mice survived beyond 60 days post-treatment, with no recrudescence observed. Artesunate treated mice showed recrudescence 8 days post-treatment, with all mice in this group succumbing to the infection. Also, 4,7-dichloroquinoline and quinine did not show any significant parasitaemia suppression in the first 24 h post-treatment, with the animals succumbing to the infection.

Conclusion

Covalent bitherapy proves to be a viable source of urgently needed new anti-malarials for management of cerebral malaria, and this polypharmacology approach could be a potential strategy to protect artesunate from parasite resistance and in potentially improving clinical outcomes in severe forms of malaria infections.

Wanted Plasmodium falciparum, dead or alive

Mechanisms of cell death in unicellular parasites have been subjects of debate for the last decade, with studies demonstrating evidence of apoptosis or non-apoptosis like mechanisms, including necrosis, and autophagy. Recent clarifications on the definition of regulated or accidental cell death by The Nomenclature Committee on Cell Death provides an opportunity to reanalyze some data, re-evaluate conclusions in the light of parasite diversity, and to propose alternative arguments in the context of malaria drug resistance, considering lack of really new drugs in the pipeline. Deciphering the mechanisms of death may help in detection of new drug targets and the design of innovative drugs. However, classifications have been evolving rapidly since initial description of "programmed cell death", leading to some uncertainty as to whether Plasmodium cell death is accidental or regulated.

Structural and immunological effects of skin cryoablation in a mouse model

Cryoablation is therapeutically applied for various disorders in several organs, and skin diseases are typical targets as this cryotherapy has been widely used for viral warts, benign tumors, and actinic keratosis. The main mechanisms of cryoablation consist of direct freezing effect on skin constituents, thrombosis formation in microcirculation, and subsequent immunological responses. Among them, however, the immunological mechanism remains unelucidated, and it is an issue how the direct freezing injury induces immunological consequences. We established a mouse cryoablation model with liquid nitrogen applied to the shaved back skin, and used this system to study the immunological excitement. After application of liquid nitrogen, the thermal decrease ratio was -25°C/sec or less and the lowest temperature was less than -100°C, which was sufficient to induce ulceration. Destruction of cornified layer and necrosis of epidermal cells were observed in transmission electron microscopy image, and increased transepidermal water loss and skin permeability were detected by the functional measurements. By flow cytometry, antigen-presenting dendritic cells (DCs), including PDCA1+B220+CD19- plasmacytoid DCs (pDCs) and CD11c+ myeloid DCs, as well as neutrophils and macrophages were increased in subcutaneous tissue. In parallel, the mRNA expressions of interferon α1 which are known as pDC-producing cytokines, was elevated. We also found marked degranulation of mast cells, providing a possibility that released histamine attracts pDCs. Finally, FITC migration assay revealed that pDCs and CD11c+ DCs emigrated from the cryoablated skin to the draining lymph nodes. Our study suggests that cryoablation induces destruction of the barrier/epidermis, accumulation of pDCs and CD11c+ DCs to the skin, and migration of DCs to regional lymph nodes. Viral elements or tumor cell lysates released from damaged keratinocytes may stimulate the DCs, thereby leading to antiviral or antitumor effect.

Fitness cost of resistance for lumefantrine and piperaquine-resistant Plasmodium berghei in a mouse model

Background

The evolution of drug-resistant parasites is a major hindrance to malaria control, and thus understanding the behaviour of drug-resistant mutants is of clinical relevance. The study aimed to investigate how resistance against lumefantrine (LU) and piperaquine (PQ), anti-malarials used as partner drugs in artemisinin-based combination therapy (ACT), impacts parasite fitness. This is important since resistance to ACT, the first-line anti-malarial regimen is increasingly being reported.

Methods

The stability of Plasmodium berghei ANKA strain that was previously selected for LU and PQ resistance was evaluated using the 4-day assay and established infection test in mice. Fitness cost of resistance was determined by comparing parasites proliferation rates in absence of drug pressure for the drug-exposed parasites between day 4 and 7 post-infection (pi), relative to the wild-type. Statistical analysis of data to compare mean parasitaemia and growth rates of respective parasite lines was carried out using student’s t-test and one-way analysis of variance, with significance level set at p<0.05.

Results

During serial passaging in the absence of the drug, the PQ-resistant parasite maintained low growth rates at day 7 pi (mean parasitaemia, 5.6% ± 2.3) relative to the wild-type (28.4% ± 6.6), translating into a fitness cost of resistance of 80.3%. Whilst resistance phenotype for PQ was stable, that of LU was transient since after several serial passages in the absence of drug, the LU-exposed line assumed the growth patterns of the wild-type.

Conclusions

The contrasting behaviour of PQ- and LU-resistance phenotypes support similar findings which indicate that even for drugs within the same chemical class, resistance-conferred traits may vary on how they influence parasite fitness and virulence. Resistance-mediating polymorphisms have been associated with less fit malaria parasites. In the absence of drug pressure in the field, it is therefore likely that the wild-type parasite will out-compete the mutant form. This implies the possibility of reintroducing a drug previously lost to resistance, after a period of suspended use. Considering the recent reports of high failure rates associated with ACT, high fitness cost of resistance to PQ is therefore of clinical relevance as the drug is a partner in ACT.

FT-IR and FT-Raman spectra of 5-fluoroorotic acid with solid state simulation by DFT methods

FT-Raman and FT-IR studies of the biomolecule 5-fluoroorotic acid in the solid state were carried out. The unit cell found in the crystal was simulated as a tetramer form by density functional calculations. They were performed to clarify wavenumber assignments of the experimental observed bands in the spectra. Correlations with the molecule of uracil were made, and specific scale equations were employed to scale the wavenumbers of 5-fluoroorotic acid. Good reproduction of the experimental wavenumbers is obtained and the % error is very small in the majority of the bands. This fact confirms our simplified solid state model. The molecular structure was fully optimized using DFT and MP2 methods. The relative stability of both the syn and anti conformations was investigated, and the anti-form was found to be slightly more stable, by 7.49 kJ/mol at the MP2 level. The structures of all possible tautomeric forms were determined. The keto-form appeared as the most stable one. The NBO atomic charges and several thermodynamic parameters were also calculated.

Intra-subtype variation in enteroadhesion accounts for differences in epithelial barrier disruption and is associated with metronidazole resistance in Blastocystis subtype-7

Blastocystis is an extracellular, enteric pathogen that induces intestinal disorders in a range of hosts including humans. Recent studies have identified potential parasite virulence factors in and host responses to this parasite; however, little is known about Blastocystis-host attachment, which is crucial for colonization and virulence of luminal stages. By utilizing 7 different strains of the parasite belonging to two clinically relevant subtypes ST-4 and ST-7, we investigated Blastocystis-enterocyte adhesion and its association with parasite-induced epithelial barrier disruption. We also suggest that drug resistance in ST-7 strains might result in fitness cost that manifested as impairment of parasite adhesion and, consequently, virulence. ST-7 parasites were generally highly adhesive to Caco-2 cells and preferred binding to intercellular junctions. These strains also induced disruption of ZO-1 and occludin tight junction proteins as well as increased dextran-FITC flux across epithelial monolayers. Interestingly, their adhesion was correlated with metronidazole (Mz) susceptibility. Mz resistant (Mzr) strains were found to be less pathogenic, owing to compromised adhesion. Moreover, tolerance of nitrosative stress was also reduced in the Mzr strains. In conclusion, the findings indicate that Blastocystis attaches to intestinal epithelium and leads to epithelial barrier dysfunction and that drug resistance might entail a fitness cost in parasite virulence by limiting entero-adhesiveness. This is the first study of the cellular basis for strain-to-strain variation in parasite pathogenicity. Intra- and inter-subtype variability in cytopathogenicity provides a possible explanation for the diverse clinical outcomes of Blastocystis infections.

Apoptotic-like activity of staurosporine in axenic cultures of Trypanosoma evansi

Trypanosoma evansi is a blood protozoan parasite of the genus Trypanosoma which is responsible for surra (Trypanosomosis) in domestic and wild animals. This study addressed apoptotic-like features in Trypanosoma evansi in vitro. The mechanism of parasite death was investigated using staurosporine as an inducing agent. We evaluated its effects through several cytoplasmic features of apoptosis, including cell shrinkage, phosphatidylserine exposure, maintenance of plasma membrane integrity, and mitochondrial trans-membrane potential. For access to these features we have used the flow cytometry and fluorescence microscopy with cultures in the stationary phase and adjusted to a density of 10(6) cells/mL. The apoptotic effect of staurosporine in T. evansi was evaluated at 20 nM final concentration. There was an increase of phosphatidylserine exposure, whereas mitochondrial potential was decreased. Moreover, no evidence of cell permeability increasing with staurosporine was observed in this study, suggesting the absence of a necrotic process. Additional studies are needed to elucidate the possible pathways associated with this form of cell death in this hemoparasite.