Synthesis of chalcone derivatives by Claisen-Schmidt condensation and in vitro analyses of their antiprotozoal activities

Chalcone is a molecule with known biological activities. Based on this, a series of chalcone derivatives bearing methyl, phenyl or furanyl substituents at different positions of A and B rings were synthesised, characterised, and evaluated regarding antiprotozoal activity. Molecules were synthesised via base catalyzed Claisen-Schmidt condensation and characterised by IR and NMR spectral data. Antiprotozoal activity against Phytomonas serpens, Leishmania amazonensis and Acanthamoeba polyphaga was performed. All compounds inhibited more than 50% of the growth of P. serpens while five had this effect on L. amazonensis and all of them no more than 35% of inhibition on A. polyphaga. Remarkably interesting antiprotozoal effects were recorded with compound 5, with IC50 of 1.59 µM for P. serpens and 11.49 µM for L. amazonensis. The addition of a naphthyl group to the B ring can be postulated to be the cause of the 10 times increase observed in its trypanocidal activity.

Chalcone Derivative Induces Flagellar Disruption and Autophagic Phenotype in Phytomonas serpens In Vitro

Phytomonas serpens is a trypanosomatid phytoparasite, found in a great variety of species, including tomato plants. It is a significant problem for agriculture, causing high economic loss. In order to reduce the vegetal infections, different strategies have been used. The biological activity of molecules obtained from natural sources has been widely investigated to treat trypanosomatids infections. Among these compounds, chalcones have been shown to have anti-parasitic and anti-inflammatory effects, being described as having a remarkable activity on trypanosomatids, especially in Leishmania species. Here, we evaluated the antiprotozoal activity of the chalcone derivative (NaF) on P. serpens promastigotes, while also assessing its mechanism of action. The results showed that treatment with the derivative NaF for 24 h promotes an important reduction in the parasite proliferation (IC50/24 h = 23.6 ± 4.6 µM). At IC50/24 h concentration, the compound induced an increase in reactive oxygen species (ROS) production and a shortening of the unique flagellum of the parasites. Electron microscopy evaluation reinforced the flagellar phenotype in treated promastigotes, and a dilated flagellar pocket was frequently observed. The treatment also promoted a prominent autophagic phenotype. An increased number of autophagosomes were detected, presenting different levels of cargo degradation, endoplasmic reticulum profiles surrounding different cellular structures, and the presence of concentric membranar structures inside the mitochondrion. Chalcone derivatives may present an opportunity to develop a treatment for the P. serpens infection, as they are easy to synthesize and are low in cost. In order to develop a new product, further studies are still necessary.

Effects of free and dipeptide forms of methionine supplementation on oxidative metabolism of broilers under high temperature

Our previous studies have shown that methionine supplementation could help to attenuate the effects of heat stress on the metabolism of broiler chickens. Here we investigated for the first time the effects of methionine supplementation in the form of DL-methionyl-DL-methionine on broilers subjected to heat stress during the growth phase. Broilers were divided into two groups; one group was reared under thermoneutral conditions and the other under continuous heat stress (30 ± 1 °C, 60% relative humidity). Both groups were subdivided into three dietary treatments: a methionine-deficient (MD) diet, a diet supplemented with free methionine (DL-M), and a diet supplemented with methionine dipeptide (DL-MM). Broilers raised under chronic heat stress had lower feed intake and weight gain than broilers raised under thermoneutral conditions (P < 0.05). There were no differences in animal performance between methionine-supplemented diets (DL-M and DL-MM). Heat-stressed birds had significantly higher heterophil/lymphocyte (H/L) ratio than thermoneutral birds. Under heat stress, broilers fed DL-M and DL-MM diets had lower H/L ratio than birds fed the MD diet. Higher concentrations of carbonylated proteins and lower concentration of reduced glutathione were observed in broilers raised under heat stress. In comparing heat-stressed broilers, we found that birds fed the DL-M diet had lower concentrations of thiobarbituric acid-reactive substances and carbonylated proteins than those fed the MD diet (P < 0.05). Higher expression of glutathione peroxidase (GPX) and glutathione synthetase (GSS) genes was observed in heat-stressed broilers (P < 0.05). Under heat stress, the MD diet increased GPX expression compared with other diets. Under thermoneutral conditions, the DL-M diet resulted in the highest GSS expression. There was a negative correlation between DNA methylation and GPX and GSS expression. Our results showed that supplementation of broiler diets with free methionine or methionine dipeptide may help attenuate the effects of heat stress through enhanced activation of genes related to the glutathione antioxidant system. Methionine effects were found for gene regulation, gene expression, and post-translational processing.

Ethanolic extract of Croton blanchetianus Ball induces mitochondrial defects in Leishmania amazonensis promastigotes

Leishmaniasis is a neglected disease caused by Leishmania. Chemotherapy remains the mainstay for leishmaniasis control; however, available drugs fail to provide a parasitological cure, and are associated with high toxicity. Natural products are promising leads for the development of novel chemotherapeutics against leishmaniasis. This work investigated the leishmanicidal properties of ethanolic extract of Croton blanchetianus (EECb) on Leishmania infantum and Leishmania amazonensis, and found that EECb, rich in terpenic compounds, was active against promastigote and amastigote forms of both Leishmania species. Leishmania infantum promastigotes and amastigotes presented IC50 values of 208.6 and 8.8 μg/mL, respectively, whereas Leishmania amazonensis promastigotes and amastigotes presented IC50 values of 73.6 and 3.1 μg/mL, respectively. Promastigotes exposed to EECb (100 µg/mL) had their body cellular volume reduced and altered to a round shape, and the flagellum was duplicated, suggesting that EECb may interfere with the process of cytokinesis, which could be the cause of the decline in the parasite multiplication rate. Regarding possible EECb targets, a marked depolarization of the mitochondrial membrane potential was observed. No cytotoxic effects of EECb were observed in murine macrophages at concentrations below 60 µg/mL, and the CC50 obtained was 83.8 µg/mL. Thus, the present results indicated that EECb had effective and selective effects against Leishmania infantum and Leishmania amazonensis, and that these effects appeared to be mediated by mitochondrial dysfunction.

Expression of glyceraldehyde 3-phosphate dehydrogenase is enhanced in Leishmania spp naturally resistant to nitric oxide

Leishmania spp are the causative agents of a spectrum of diseases termed leishmaniasis that affect mammals, including humans and dogs. Although reactive nitrogen species are employed in the control of parasitism by the immune system, it is known that Leishmania can withstand this oxidative stress. As the mechanism by which these species are resistant to nitric oxide (NO) is poorly understood, the main objective of this study was to evaluate the expression of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in Leishmania amazonensis and Leishmania chagasi promastigotes showing natural resistance to NO. GAPDH transcript levels were quantified by real-time polymerase chain reaction amplification, and GAPDH activity (assessed by levels of NADH oxidation) was measured by spectrophotometry. The level of nitration in total protein was assessed by immunoblotting. The results demonstrated an increase in GAPDH expression in resistant isolates of both species compared to susceptible isolates. The increase in GAPDH expression led to an increase in the activity of GAPDH in L. amazonensis human isolates resistant to NO. The pattern of protein nitration did not differ between sensitive and resistant isolates. Our results suggest that changes in expression of GAPDH may be responsible, at least in part, to natural resistance to NO found in human and canine Leishmania spp.

Identification of Suitable Reference Genes for Real Time Quantitative Polymerase Chain Reaction Assays on Pectoralis major Muscle in Chicken (Gallus gallus )

Thirteen reference genes were investigated to determine their stability to be used as a housekeeping in gene expression studies in skeletal muscle of chickens. Five different algorithms were used for ranking of reference genes and results suggested that individual rankings of the genes differed among them. The stability of the expression of reference genes were validated using samples obtained from the Pectoralis major muscle in chicken. Samples were obtained from chickens in different development periods post hatch and under different nutritional diets. For gene expression calculation the ΔΔCt approach was applied to compare relative expression of pairs of genes within each of 52 samples when normalized to mitochondrially encoded cytochrome c oxidase II (MT-CO2) target gene. Our findings showed that hydroxymethylbilane synthase (HMBS) and hypoxanthine phosphoribosyl transferase 1 (HPRT1) are the most stable reference genes while transferrin receptor (TFRC) and beta-2-microglobulin (B2M) ranked as the least stable genes in the Pectoralis major muscle of chickens. Moreover, our results revealed that HMBS and HPRT1 gene expression did not change due to dietary variations and thus it is recommended for accurate normalization of RT-qPCR data in chicken Pectoralis major muscle.

Evaluation of fosmidomycin analogs as inhibitors of the Synechocystis sp. PCC6803 1-deoxy-d-xylulose 5-phosphate reductoisomerase

Analogs of the antibiotic fosmidomycin, an inhibitor of the methylerythritol phosphate pathway to isoprenoids, were synthesized and evaluated against the recombinant Synechocystis sp. PCC6803 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR). Fosfoxacin, the phosphate analog of fosmidomycin, and its acetyl congener were found to be more potent inhibitors of DXR than fosmidomycin.

Kinetic characterization of Synechocystis sp. PCC6803 1-deoxy-d-xylulose 5-phosphate reductoisomerase mutants

The methylerythritol phosphate pathway to isoprenoids has been firmly established as an alternate to the mevalonate pathway in many bacteria, plants, algae, and the malaria parasite Plasmodium falciparum. The second enzyme in this pathway, deoxy-D-xylulose 5-phosphate reductoisomerase (DXR; E.C. 1.1.1.267), has been the focus of many investigations since it was found to be the target of the antibacterial and antimalarial compound, fosmidomycin. Several x-ray crystal structures of the Escherichia coli and Zymomonas mobilis DXR enzymes have provided important structural information about the residues potentially involved in substrate binding and catalysis. Site-directed mutagenesis studies can be used to complement the structural studies, providing kinetic data for specific changes of active site residues. Active site mutants were prepared of the recombinant Synechocystis sp. PCC6803 DXR, targeting residues D152, S153, E154, H155, M206, and E223. Alteration of the three acidic residues had major effects on catalysis, changes to S153 and M206 had variable effects on binding and catalysis, and a H155A mutation had only minimal effects on the kinetic parameters.

Mutation in the flexible loop of 1-deoxy-D-xylulose 5-phosphate reductoisomerase broadens substrate utilization

The second enzyme in the methylerythritol phosphate pathway to isoprenoids, 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR; EC 1.1.1.267) mediates the transformation of 1-deoxy-D-xylulose 5-phosphate (DXP) into 2-C-methyl-D-erythritol 4-phosphate. Several DXR mutants have been prepared to study amino acid residues important in binding or catalysis, but in-depth studies of many conserved residues in the flexible loop portion of the enzyme have not been conducted. In the course of our studies of this enzyme, an analog of DXP, 1,2-dideoxy-D-threo-3-hexulose 6-phosphate (1-methyl-DXP), was found to be a weak competitive inhibitor. Using the X-ray crystal structures of DXR as a guide, a highly conserved tryptophan residue in the flexible loop was identified that potentially blocks the use of this analog as a substrate. To test this hypothesis, four mutants of the Synechocystis sp. PCC6803 DXR were prepared and a W204F mutant was found to utilize the analog as a substrate.

The crystal structure of E.coli 1-deoxy-D-xylulose-5-phosphate reductoisomerase in a ternary complex with the antimalarial compound fosmidomycin and NADPH reveals a tight-binding closed enzyme conformation

The key enzyme in the non-mevalonate pathway of isoprenoid biosynthesis, 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) has been shown to be the target enzyme of fosmidomycin, an antimalarial, antibacterial and herbicidal compound. Here we report the crystal structure of selenomethionine-labelled Escherichia coli DXR in a ternary complex with NADPH and fosmidomycin at 2.2 A resolution. The structure reveals a considerable conformational rearrangement upon fosmidomycin binding and provides insights into the slow, tight binding inhibition mode of the inhibitor. Although the inhibitor displays an unusual non-metal mediated mode of inhibition, which is an artefact most likely due to the low metal affinity of DXR at the pH used for crystallization, the structural data add valuable information for the rational design of novel DXR inhibitors. Using this structure together with the published structural data and the 1.9 A crystal structure of DXR in a ternary complex with NADPH and the substrate 1-deoxy-D-xylulose 5-phosphate, a model for the physiologically relevant tight-binding mode of inhibition is proposed. The structure of the substrate complex must be interpreted with caution due to the presence of a second diastereomer in the active site.