Myna Nakabashi

Synthesis and antiplasmodial activity of betulinic acid and ursolic acid analogues.

More than 40% of the World population is at risk of contracting malaria, which affects primarily poor populations in tropical and subtropical areas. Antimalarial pharmacotherapy has utilised plant-derived products such as quinine and artemisinin as well as their derivatives. However, worldwide use of these antimalarials has caused the spread of resistant parasites, resulting in increased malaria morbidity and mortality. Considering that the literature has demonstrated the antimalarial potential of triterpenes, specially betulinic acid (1) and ursolic acid (2), this study investigated the antimalarial activity against P. falciparum chloroquine-sensitive 3D7 strain of some new derivatives of 1 and 2 with modifications at C-3 and C-28. The antiplasmodial study employed flow cytometry and spectrofluorimetric analyses using YOYO-1, dihydroethidium and Fluo4/AM for staining. Among the six analogues obtained, compounds 1c and 2c showed excellent activity (IC50 = 220 and 175 nM, respectively) while 1a and b demonstrated good activity (IC50 = 4 and 5 μM, respectively). After cytotoxicity evaluation against HEK293T cells, 1a was not toxic, while 1c and 2c showed IC50 of 4 μM and a selectivity index (SI) value of 18 and 23, respectively. Moreover, compound 2c, which presents the best antiplasmodial activity, is involved in the calcium-regulated pathway(s).

Two series of new semisynthetic triterpene derivatives: differences in anti-malarial activity, cytotoxicity and mechanism of action

BackgroundThe discovery and development of anti-malarial compounds of plant origin and semisynthetic derivatives thereof, such as quinine (QN) and chloroquine (CQ), has highlighted the importance of these compounds in the treatment of malaria. Ursolic acid analogues bearing an acetyl group at C-3 have demonstrated significant anti-malarial activity. With this in mind, two new series of betulinic acid (BA) and ursolic acid (UA) derivatives with ester groups at C-3 were synthesized in an attempt to improve anti-malarial activity, reduce cytotoxicity, and search for new targets. In vitro activity against CQ-sensitive Plasmodium falciparum 3D7 and an evaluation of cytotoxicity in a mammalian cell line (HEK293T) are reported. Furthermore, two possible mechanisms of action of anti-malarial compounds have been evaluated: effects on mitochondrial membrane potential (ΔΨm) and inhibition of β-haematin formation.ResultsAmong the 18 derivatives synthesized, those having shorter side chains were most effective against CQ-sensitive P. falciparum 3D7, and were non-cytotoxic. These derivatives were three to five times more active than BA and UA. A DiOC6(3) ΔΨm assay showed that mitochondria are not involved in their mechanism of action. Inhibition of β-haematin formation by the active derivatives was weaker than with CQ. Compounds of the BA series were generally more active against P. falciparum 3D7 than those of the UA series.ConclusionsThree new anti-malarial prototypes were obtained from natural sources through an easy and relatively inexpensive synthesis. They represent an alternative for new lead compounds for anti-malarial chemotherapy.

The role of melatonin in parasite biology

Regarded as the circadian hormone in mammals, melatonin is a highly conserved molecule, present in nearly all species. In this review, we discuss the role of this indolamine and its precursors in the cell biology of parasites and the role of the molecule in the physiology of the host. In Plasmodium, melatonin can modulate intracellular concentrations of calcium and cAMP, which in turn can regulate kinase activity and cell cycle. In Trypanosoma infections, modulation of the immune system by melatonin is extremely important in controlling the parasite population. Melatonin also contributes to the inflammatory response to Toxoplasma gondii infection. Thus, there are a number of unique adaptations involving intricate connections between melatonin and the biology of the parasite-host relationship.

Estudo da germinação e crescimento in vitro de Hadrolaelia tenebrosa (Rolfe) Chiron & V.P. Castro (Orchidaceae), uma espécie da flora brasileira ameaçada de extinção

Orchids are seriously endangered species. For that reason, studies regarding their propagation and development are extremely important. Thus, the present study analyzed the influence of the culture medium on the in vitro germination of Hadrolaelia tenebrosa seeds, on the initial development of protocorms until they form seedlings and on seedling growth during the first twelve months in vitro. The results revealed that the ideal methodology for the in vitro culture of Hadrolaelia tenebrosa involves the use the Knudsons C medium for seed germination and seedling initial growth, and the subsequent transfer of six-month-old plants to VW medium where they should remain until acclimatization is carried out. The obtained data showed that the most efficient culture medium for seed germination of that species was not the most adequate for the development of their seedlings. Therefore, the outcomes of such studies are very important for the optimization of propagation techniques for orchid species.

Investigation of antimalarial activity, cytotoxicity and action mechanism of piperazine derivatives of betulinic acid.

To semisynthesise piperazine derivatives of betulinic acid to evaluate antimalarial activity, cytotoxicity and action mechanism.

Ribifolin, an Orbitide from Jatropha ribifolia, and Its Potential Antimalarial Activity

A new orbitide named ribifolin was isolated and characterized from Jatropha ribifolia using mass spectrometry, NMR spectroscopy, quantitative amino acid analysis, molecular dynamics/simulated annealing, and Raman optical activity measurements and calculations. Ribifolin (1) and its linear form (1a) were synthesized by solid-phase peptide synthesis, followed by evaluation of its antiplasmodial and cytotoxicity activities. Compound 1 was moderately effective (IC50 = 42 μM) against the Plasmodium falciparum strain 3D7.

Antimalarial activity of piperidine alkaloids from Senna spectabilis and semisynthetic derivatives

In our continuing work looking for new anti-infective lead compounds from Brazilian biomes, the two known piperidine alkaloids ( - )-cassine and ( - )-spectaline were isolated from the flowers of Senna spectabilis (syn. Cassia spectabilis). Their structures were elucidated using a combination of spectroscopic and spectrometric data analysis. Further, these compounds were acetylated yielding the derivatives ( - )-3-O-acetylcassine and ( - )-3-O-acetylspectaline. All compounds were screened against P. falciparum-infected red blood cells (RBC) in culture, aiming to identify antimalarial prototypes. Among all compounds screened, the first two alkaloids (IC50 1.82 µM and IC50 2.76 µM) were more effective than the derivatives (IC50 24.47 µM and IC50 25.14 µM) in comparison to the standard compound chloroquine (IC50 0.30 µM). These data show that piperidine alkaloids constitute a class of natural products that feature a broad spectrum of biological activities, and are, therefore, important templates for drug design, including antimalarial.

Mutator System Derivatives Isolated from Sugarcane Genome Sequence

Mutator-like transposase is the most represented transposon transcript in the sugarcane transcriptome. Phylogenetic reconstructions derived from sequenced transcripts provided evidence that at least four distinct classes exist (I–IV) and that diversification among these classes occurred early in Angiosperms, prior to the divergence of Monocots/Eudicots. The four previously described classes served as probes to select and further sequence six BAC clones from a genomic library of cultivar R570. A total of 579,352 sugarcane base pairs were produced from these “Mutator system” BAC containing regions for further characterization. The analyzed genomic regions confirmed that the predicted structure and organization of the Mutator system in sugarcane is composed of two true transposon lineages, each containing a specific terminal inverted repeat and two transposase lineages considered to be domesticated. Each Mutator transposase class displayed a particular molecular structure supporting lineage specific evolution. MUSTANG, previously described domesticated genes, are located in syntenic regions across Sacharineae and, as expected for a host functional gene, posses the same gene structure as in other Poaceae. Two sequenced BACs correspond to hom(eo)logous locus with specific retrotransposon insertions that discriminate sugarcane haplotypes. The comparative studies presented, add information to the Mutator systems previously identified in the maize and rice genomes by describing lineage specific molecular structure and genomic distribution pattern in the sugarcane genome.

Discovery of Marinoquinolines as Potent and Fast-Acting Plasmodium falciparum Inhibitors with in Vivo Activity

We report the discovery of marinoquinoline (3 H-pyrrolo[2,3- c]quinoline) derivatives as new chemotypes with antiplasmodial activity. We evaluated their inhibitory activities against P. falciparum and conducted a structure-activity relationship study, focusing on improving their potency and maintaining low cytotoxicity. Next, we devised quantitative structure-activity relationship (QSAR) models, which we prospectively validated, to discover new analogues with enhanced potency. The most potent compound, 50 (IC503d7 = 39 nM; IC50K1 = 41 nM), is a fast-acting inhibitor with dual-stage (blood and liver) activity. The compound showed considerable selectivity (SI > 6410), an additive effect when administered in combination with artesunate, excellent tolerability in mice (all mice survived after an oral treatment with a 1000 mg/kg dose), and oral efficacy at 50 mg/kg in a mouse model of P. berghei malaria (62% reduction in parasitemia on day 5 postinfection); thus, compound 50 was considered a lead compound for the discovery of new antimalarial agents.