Assessment of antimalarial medicinal plants used in Nigerian ethnomedicine reveals antimalarial potential of Cucurbita pepo leaf extract.

Medicinal plants are often used to treat malaria in different parts of Nigeria and exploiting these can unravel new therapeutic leads. This study evaluated the antiplasmodial potential of selected plants used to treat malaria in Nsukka, Enugu state, Nigeria. Leaves of three different plants (Cucurbita pepo, Hibiscus rosa-sinensis and Pennisetum purpureum) were collected for screening and two extracts viz., 70%v/v ethanol and dichloromethane/methanol (1:1 v/v), were prepared for each. An acute toxicity test was done in mice and cytotoxicity was assessed using human hepatoma cell line (HUH). The extracts were screened against chloroquine-sensitive P. falciparum (Pf3D7) in vitro, and chloroquine-resistant P. berghei ANKA in vivo using a 4 day-suppressive test in mice. Cucurbita pepo ethanol extract was further tested for hemolytic effect on human erythrocytes and in established infection in mice. Parameters assessed were post-treatment parasitemia, hematological indices, organ (brain, kidney, liver, and spleen) weights, and survival. The extracts were non-cytotoxic up to a test dose of 100 µg/ml and 2000 mg/kg fed - mice did not show acute or delayed toxicity. Cucurbita pepo ethanol extract (CpE) displayed excellent in vitro antiplasmodial activity with IC50 of 3.05 µg/ml. At an oral dose of 500 mg/kg, mice were observed to display significant (p < 0.01) ∼51% suppression of parasitemia. The extract did not produce any significant hemolytic effect up to a test concentration of 1 mg/ml. In established infection, a dose of 300 mg/kg significantly (p < 0.01) protected mice from anemia caused by low hematocrit. The extract produced significant (p < 0.05) elevation in red blood cells and platelet counts, and an increase in hemoglobin was evident at 100 and 300 mg/kg. Further, CpE in a dose-dependent manner, reversed liver and spleen weight increase seen in untreated, infected mice. These findings show C. pepo as a potential candidate for further studies to identify its bioactive principle(s) and possible mechanism(s) of antimalarial action.

Novel halogenated arylvinyl-1,2,4 trioxanes as potent antiplasmodial as well as anticancer agents: Synthesis, bioevaluation, structure-activity relationship and in-silico studies.

Herein, we have synthesized a series of lipophilic, halogenated-arylvinyl-1,2,4-trioxanes 8a-g (28 compounds) and assessed for their in vitro anti-plasmodial activity in Plasmodium falciparum culture using SYBRgreen-I fluorescence assay against chloroquine-resistant Pf INDO and artemisinin-resistant Pf Cam 3.1R539T (MRA-1240) strains. Alongside, the cell cytotoxic potential of 8a-g has also been determined against the HEK293 cell line in vitro. Out of twenty-eight halogenated-arylvinyl-1,2,4-trioxanes; ten analogues (8a2, 8a4, 8b2, 8b4, 8d4, 8e1, 8e2, 8e4,8f2, and 8g4) have shown potent in vitro antiplasmodial activity with IC50 < 27 nM (IC50 range = 4.48-26.58 nM). Also, the selectivity index (SI) for these ten analogues were found in the range of 72.00-3972.50 which indicates their selective potential towards Plasmodium cells. Results of the cell cycle stage specificity with two of the most potent compounds 8a4 {(IC50 = 4.48 nM; SI = 3972.50) more potent than chloroquine (IC50 = 546 nM; SI = 36.64) and artesunate (IC50 = 6.6 nM; SI = 4333.33)} and 8e2 (IC50 = 9.69 nM; SI = 1348) against Pf INDO indicated all three stages to be the target of the action of 8e2 while only rings and trophozoites appeared to be targeted by 8a4. Ring stage survival assay against artemisinin-resistant Pf Cam 3.1R539T indicated that 8a4 may be well suited to replace artemisinin from current ACTs which are experiencing in vivo delayed parasite clearance. With intraperitoneal (i.p.) and oral (p.o.) route at the dose of 50 mg/kg/day × 4 days; 8a4 has also shown 100% suppression of parasitemia in P. berghei ANKA infected Balb C mice. Further, the in vitro anticancer activity of 8a-g performed against human lung (A549) and liver (HepG2) cancer cell lines as also against immortalized normal lung (BEAS-2B) and liver (LO2) cell lines has revealed that most of the derivatives are endowed also with promising anticancer activity (IC50 = 0.69-15 µM; SI = 1.02-20.61) in comparison with standard drugs such as chloroquine (IC50 = 100 µM; SI = 0.03), artemisinin (IC50 = 100 µM), and artesunic acid (IC50 = 9.85 µM; SI = 0.76), respectively. All the derivatives have shown moderate anticancer activity against liver (HepG2) cancer cell lines. Arylvinyl-1,2,4-trioxanes 8f2 (IC50 = 0.69 µM; SI = 16.66), the most active compound of the series, has shown ∼145 fold more cytotoxic potential with higher selectivity in comparison to reference drugs chloroquine (IC50 = 100 µM; SI = 0.03) and artemisinin (IC50 = 100 µM), respectively against the lung (A549) cancer cell line. Finally, the in-silico docking studies of the potent halogenated 1,2,4-trioxanes along with reference drug molecules against epidermal growth factor receptor (EGFR; PDB ID: 1M17) have demonstrated the strong virtual interaction.

Design, Synthesis, Structure-Activity Relationship and Docking Studies of Novel Functionalized Arylvinyl-1,2,4-Trioxanes as Potent Antiplasmodial as well as Anticancer Agents.

A novel series of synthetic functionalized arylvinyl-1,2,4-trioxanes (8 a-p) has been prepared and assessed for their in vitro antiplasmodial activity against the chloroquine-resistant Pf INDO strain of Plasmodium falciparum by using a SYBR green-I fluorescence assay. Compounds 8 g (IC50 =0.051 µM; SI=589.41) and 8 m (IC50 =0.059 µM; SI=55.93) showed 11-fold and >9-fold more potent antiplasmodial activity, respectively, as compared to chloroquine (IC50 =0.546 µM; SI=36.63). Different in silico docking studies performed on many target proteins revealed that the most active arylvinyl-1,2,4-trioxanes (8 g and 8 m) showed dihydrofolate reductase (DHFR) binding affinities on a par with those of chloroquine and artesunate. The in vitro cytotoxic potentials of 8 a-p were also evaluated against human lung (A549) and liver (HepG2) cancer cell lines along with immortalized normal lung (BEAS-2B) and liver (LO2) cell lines. Following screening, five derivatives viz. 8 a, 8 h, 8 l, 8 m and 8 o (IC50 =1.65-31.7 µM; SI=1.08-10.96) were found to show potent cytotoxic activity against (A549) lung cancer cell lines, with selectivity superior to that of the reference compounds artemisinin (IC50 =100 µM), chloroquine (IC50 =100 µM) and artesunic acid (IC50 =9.85 µM; SI=0.76). In fact, the most active 4-naphthyl-substituted analogue 8 l (IC50 =1.65 µM; SI >10) exhibited >60 times more cytotoxicity than the standard reference, artemisinin, against A549 lung cancer cell lines. In silico docking studies of the most active anticancer compounds, 8 l and 8 m, against EGFR were found to validate the wet lab results. In summary, a new series of functionalized aryl-vinyl-1,2,4-trioxanes (8 a-p) has been shown to display dual potency as promising antiplasmodial and anticancer agents.

Rh(III)-Catalyzed C(8)-H Functionalization of Quinolines via Simultaneous C-C and C-O Bond Formation: Direct Synthesis of Quinoline Derivatives with Antiplasmodial Potential.

Here, a facile and efficient protocol for the synthesis of 3-hydroxyquinolin-8-yl propanoates via Rh(III)-catalyzed C(8)-H activation of 2-substituted quinolines has been developed. The reaction proceeds via C(8)-H activation, functionalization with acrylates, followed by intramolecular migration of the oxygen atom from quinoline N-oxides to the acrylate moiety. In this approach, N-oxide plays a dual role of a traceless directing group as well as a source of an oxygen atom for hydroxylation. This catalytic method involves simultaneous formation of new C-C and C-O bonds and is applicable only for C2-substituted quinolines. A catalytically competent five-membered rhodacycle has been characterized, thus revealing a key intermediate in the catalytic cycle. In silico docking studies against Falcipan-2 have revealed that 3a, 3b, 3g, and 3m have better scores. In vitro evaluation of selected compounds against CQ-sensitive pf3D7 and CQ-resistant pfINDO strains provided evidence that 3d (IC50 13.3 µM) and 3g (IC50 9.5 µM) had good promise against Plasmodium falciparum in the in vitro culture. Compound 3g was found to be the most potent on the basis of both in vitro antiplasmodial activity [IC50 9.5 µM ( Pf3D7) and 11.9 µM ( PfINDO), resistance index 1.25] and in silico studies.

Facile synthesis of vanillin-based novel bischalcones identifies one that induces apoptosis and displays synergy with Artemisinin in killing chloroquine resistant Plasmodium falciparum.

The inherent affinity of natural compounds for biological receptors has been comprehensively exploited with great success for the development of many drugs, including antimalarials. Here the natural flavoring compound vanillin has been used as an economical precursor for the synthesis of a series of novel bischalcones whose in vitro antiplasmodial activities have been evaluated against erythrocytic stages of Plasmodium falciparum. Bischalcones 9, 11 and 13 showed promising antiplasmodial activity {Chloroquine (CQ) sensitive Pf3D7 IC50 (µM): 2.0, 1.5 and 2.5 respectively}but only 13 displayed potent activities also against CQ resistant PfDd2 and PfIndo strains exhibiting resistance indices of 1.4 and 1.5 respectively. IC90 (8 µM) of 13 showed killing activity against ring, trophozoite and schizont stages. Further, 13 initiated the cascade of reactions that culminates in programmed cell death of parasites including translocation of phosphatidylserine from inner to outer membrane leaflet, loss of mitochondrial membrane potential, activation of caspase like enzyme, DNA fragmentation and chromatin condensation. The combinations of 13 + Artemisinin (ART) exhibited strong synergy (ΣFIC50:0.46 to 0.58) while 13 + CQ exhibited mild synergy (ΣFIC50: 0.7 to 0.98) to mild antagonism (ΣFIC50: 1.08 to 1.23) against PfIndo. In contrast, both combinations showed marked antagonism against Pf3D7(ΣFIC50: 1.33 to 3.34). These features of apoptosis and strong synergy with Artemisinin suggest that bischalcones possess promising antimalarial drug-like properties and may also act as a good partner drugs for artemisinin based combination therapies (ACTs) against Chloroquine resistant P. falciparum.

Leishmanicidal Activity of Piper nigrum Bioactive Fractions is Interceded via Apoptosis In Vitro and Substantiated by Th1 Immunostimulatory Potential In Vivo.

Visceral leishmaniasis (VL) is a life-threatening protozoal infection chiefly impinging the rural and poor population in the tropical and sub-tropical countries. The deadly affliction is rapidly expanding after its association with AIDS, swiftly defying its status of a neglected disease. Despite successful formulation of vaccine against canine leishmaniasis, no licensed vaccine is yet available for human VL, chemotherapy is in appalling state, and the development of new candidate drugs has been painfully slow. In face of lack of proper incentives, immunostimulatory plant preparations owing antileishmanial efficacy bear potential to rejuvenate awful antileishmanial chemotherapy. We have earlier reported profound leishmanicidal activity of Piper nigrum hexane (PNH) seeds and P. nigrum ethanolic (PNE) fractions derived from P. nigrum seeds against Leishmania donovani promastigotes and amastigotes. In the present study, we illustrate that the remarkable anti-promastigote activity exhibited by PNH and PNE is mediated via apoptosis as evidenced by phosphatidylserine externalization, DNA fragmentation, arrest in sub G0/G1 phase, loss of mitochondrial membrane potential and generation of reactive oxygen species. Further, P. nigrum bioactive fractions rendered significant protection to L. donovani infected BALB/c mice in comparison to piperine, a known compound present in Piper species. The substantial therapeutic potential of PNH and PNE was accompanied by elicitation of cell-mediated immune response. The bioactive fractions elevated the secretion of Th1 (INF-γ, TNF-α, and IL-2) cytokines and declined IL-4 and IL-10. PNH and PNE enhanced the production of IgG2a, upregulated the expression of co-stimulatory molecules CD80 and CD86, augmented splenic CD4(+) and CD8(+) T cell population, induced strong lymphoproliferative and DTH responses and partially stimulated NO production. PNH and PNE were devoid of any hepatic or renal toxicity. These encouraging findings merit further exploration of P. nigrum bioactive fractions as a source of potent and non-toxic antileishmanials.

Corrigendum: Leishmanicidal activities of Artemisia annua leaf essential oil against Visceral Leishmaniasis.

[This corrects the article on p. 626 in vol. 5, PMID: 25505453.].

Apoptosis mediated leishmanicidal activity of Azadirachta indica bioactive fractions is accompanied by Th1 immunostimulatory potential and therapeutic cure in vivo.

BACKGROUND: Exploration of immunomodulatory antileishmanials of plant origin is now being strongly recommended to overcome the immune suppression evident during visceral leishmaniasis (VL) and high cost and toxicity associated with conventional chemotherapeutics. In accordance, we assessed the in vitro and in vivo antileishmanial and immunomodulatory potential of ethanolic fractions of Azadirachta indica leaves (ALE) and seeds (ASE). METHODS: A. indica fractions were prepared by sequential extraction of the powdered plant parts in hexane, ethanol and water. Erythrosin B staining was employed to appraise the anti-promastigote potential of ALE and ASE. Cytostatic or cytocidal mode of action was ascertained and alterations in parasite morphology were depicted under oil immersion light microscopy. Study of apoptotic correlates was performed to deduce the mechanism of induced cell death and anti-amastigote potential was assessed in Leishmania parasitized RAW 264.7 macrophages. In vivo antileishmanial effectiveness was evaluated in L. donovani infected BALB/c mice, accompanied by investigation of immunomodulatory potential of ALE and ASE. Adverse toxicity of the bioactive fractions against RAW macrophages was studied by MTT assay. In vivo side effects on the liver and kidney functions were also determined. Plant secondary metabolites present in ALE and ASE were analysed by Gas chromatography-mass spectrometry (GC-MS). RESULTS: ALE and ASE (500 µg ml(-1)) exhibited leishmanicidal activity in a time- and dose-dependent manner (IC50 34 and 77.66 µg ml(-1), respectively) with alterations in promastigote morphology and induction of apoptosis. ALE and ASE exerted appreciable anti-amastigote potency (IC50 17.66 and 24.66 µg ml(-1), respectively) that was coupled with profound in vivo therapeutic efficacy (87.76% and 85.54% protection in liver and 85.55% and 83.62% in spleen, respectively). ALE exhibited minimal toxicity with selectivity index of 26.10 whereas ASE was observed to be non-toxic. The bioactive fractions revealed no hepato- and nephro-toxicity. ALE and ASE potentiated Th1-biased cell-mediated immunity along with upregulation of INF-γ, TNF-α and IL-2 and decline in IL-4 and IL-10 levels. GC-MS analysis revealed several compounds that may have contributed to the observed antileishmanial effect. CONCLUSION: Dual antileishmanial and immunostimulatory efficacy exhibited by the bioactive fractions merits their use alone or as adjunct therapy for VL.

Th1-biased immunomodulation and therapeutic potential of Artemisia annua in murine visceral leishmaniasis.

BACKGROUND: In the absence of vaccines and limitations of currently available chemotherapy, development of safe and efficacious drugs is urgently needed for visceral leishmaniasis (VL) that is fatal, if left untreated. Earlier we reported in vitro apoptotic antileishmanial activity of n-hexane fractions of Artemisia annua leaves (AAL) and seeds (AAS) against Leishmania donovani. In the present study, we investigated the immunostimulatory and therapeutic efficacy of AAL and AAS. METHODOLOGY/PRINCIPAL FINDINGS: Ten-weeks post infection, BALB/c mice were orally administered AAL and AAS for ten consecutive days. Significant reduction in hepatic (86.67% and 89.12%) and splenic (95.45% and 95.84%) parasite burden with decrease in spleen weight was observed. AAL and AAS treated mice induced the strongest DTH response, as well as three-fold decrease in IgG1 and two-fold increase in IgG2a levels, as compared to infected controls. Cytometric bead array further affirmed the elicitation of Th1 immune response as indicated by increased levels of IFN-γ, and low levels of Th2 cytokines (IL-4 and IL-10) in serum as well as in culture supernatant of lymphocytes from treated mice. Lymphoproliferative response, IFN-γ producing CD4+ and CD8+ T lymphocytes and nitrite levels were significantly enhanced upon antigen recall in vitro. The co-expression of CD80 and CD86 on macrophages was significantly augmented. CD8+ T cells exhibited CD62Llow and CD44hi phenotype, signifying induction of immunological memory in AAL and AAS treated groups. Serum enzyme markers were in the normal range indicating inertness against nephro- and hepato-toxicity. CONCLUSIONS/SIGNIFICANCE: Our results establish the two-prong antileishmanial efficacy of AAL and AAS for cure against L. donovani that is dependent on both the direct leishmanicidal action as well as switching-on of Th1-biased protective cell-mediated immunity with generation of memory. AAL and AAS could represent adjunct therapies for the treatment of leishmaniasis, either alone or in combination with other antileishmanial agents.

Leishmanicidal activities of Artemisia annua leaf essential oil against Visceral Leishmaniasis.

Visceral leishmaniasis (VL), the second-most dreaded parasitic disease after malaria, is currently endemic in 88 countries. Dramatic increases in the rates of infection, drug resistance, and non-availability of safe vaccines have highlighted the need for identification of novel and inexpensive anti-leishmanial agents from natural sources. In this study, we showed the leishmanicidal effect of essential oil from Artemisia annua leaves (AALEO) against Leishmania donovani in vitro and in vivo. AALEO was extracted by hydrodistillation and characterized by GC-MS, the most abundant compounds were found to be camphor (52.06 %) followed by ß-caryophyllene (10.95 %). AALEO exhibited significant leishmanicidal activity against L. donovani, with 50 % inhibitory concentration of 14.63 ± 1.49 µg ml(-1) and 7.3 ± 1.85 µg ml(-1), respectively, against the promastigotes and intracellular amastigotes. The effect was mediated through programmed cell death as confirmed by externalization of phosphatidylserine, DNA nicking by TdT-mediated dUTP nick-end labeling assay, dyskinetoplastidy, cell cycle arrest at sub-G0-G1 phase, loss of mitochondrial membrane potential and reactive oxygen species generation in promastigotes and nitric oxide generation in ex vivo model. AALEO presented no cytotoxic effects against mammalian macrophages even at 200 µg ml(-1). Intra-peritoneal administration of AALEO (200 mg/ kg.b.w.) to infected BALB/c mice reduced the parasite burden by almost 90% in the liver and spleen with significant reduction in weight. There was no hepato- or nephro-toxicity as demonstrated by normal levels of serum enzymes. The promising antileishmanial activity shown by camphor-rich AALEO may provide a new lead in the treatment of VL.

Synthesis and biological evaluation of some novel pyrido[1,2-a]pyrimidin-4-ones as antimalarial agents.

Novel pyrido[1,2-a]pyrimidin-4-ones have been synthesized and evaluated for their antimalarial activity by SYBR Green I assay against erythrocytic stages of chloroquine (CQ) sensitive Pf 3D7 strain. The antimalarial screening of 42 different compounds revealed that 3-Fluorobenzyl(4-oxo-4H-pyrido [1,2-a]pyrimidin-3-yl)carbamate (21, IC50 value 33 µM) and 4-Oxo-N-[4-(trifluoromethyl)benzyl]-4H-pyrido[1,2-a]pyrimidine-3-carboxamide (37, IC50 value 37 µM) showed moderate antimalarial activity. Cytotoxicity study was performed against mammalian cell line (Huh-7) by using the MTT assay for the moderately active compounds. Structural activity relationship (SAR) studies displayed that B-ring unsubstituted pyrido[1,2-a]pyrimidine scaffold is responsible for the antimalarial activities of the evaluated derivatives. This SAR based antimalarial screening supported that pyrido[1,2-a]pyrimidin-4-one can be considered as a lead heterocyclic structure for further development of more potent derivatives for antimalarial activity.

Apoptosis-like death in Leishmania donovani promastigotes induced by eugenol-rich oil of Syzygium aromaticum.

Leishmaniasis consists of a complex spectrum of infectious diseases with worldwide distribution of which visceral leishmaniasis or kala-azar caused by Leishmania donovani is the most devastating. In the absence of vaccines, chemotherapy remains the mainstay for the control of leishmaniasis. The drugs of choice are expensive and associated with multiple adverse side effects. Because of these limitations, the development of new antileishmanial compounds is imperative and plants offer prospects in this regard. The present work was conducted to study the antileishmanial potential of oil from Syzygium aromaticum flower buds (clove). The S. aromaticum oil was characterized by gas chromatography and GC-MS and eugenol as well as eugenyl acetate were found to be the most abundant compounds, composing 59.75 % and 29.24 %, respectively of the oil. Our findings have shown that eugenol-rich essential oil from S. aromaticum (EROSA) possesses significant activity against L. donovani, with 50 % inhibitory concentration of 21 ± 0.16 µg ml(-1) and 15.24 ± 0.14 µg ml(-1), respectively, against promastigotes and intracellular amastigotes. Alterations in cellular morphology and growth reversibility assay substantiated the leishmanicidal activity of EROSA. The leishmanicidal effect was mediated via apoptosis as confirmed by externalization of phosphatidylserine, DNA nicking by TdT-mediated dUTP nick-end labelling (TUNEL) assay, dyskinetoplastidy, cell cycle arrest at sub-G0-G1 phase, loss of mitochondrial membrane potential and reactive oxygen species generation. EROSA presented no adverse cytotoxic effects against murine macrophages even at 200 µg ml(-1). Our studies authenticate the promising antileishmanial activity of EROSA, which is mediated by programmed cell death, and, accordingly, EROSA may be a source of novel agents for the treatment of leishmaniasis.

Anti-plasmodial action of de novo-designed, cationic, lysine-branched, amphipathic, helical peptides.

BACKGROUND: A lack of vaccine and rampant drug resistance demands new anti-malarials. METHODS: In vitro blood stage anti-plasmodial properties of several de novo-designed, chemically synthesized, cationic, amphipathic, helical, antibiotic peptides were examined against Plasmodium falciparum using SYBR Green assay. Mechanistic details of anti-plasmodial action were examined by optical/fluorescence microscopy and FACS analysis. RESULTS: Unlike the monomeric decapeptides {(Ac-GXRKXHKXWA-NH2) (X = F,ΔF) (Fm, ΔFm IC50 >100 µM)}, the lysine-branched,dimeric versions showed far greater potency {IC50 (µM) Fd 1.5 , ΔFd 1.39}. The more helical and proteolytically stable ΔFd was studied for mechanistic details. ΔFq, a K-K2 dendrimer of ΔFm and (ΔFm)2 a linear dimer of ΔFm showed IC50 (µM) of 0.25 and 2.4 respectively. The healthy/infected red cell selectivity indices were >35 (ΔFd), >20 (ΔFm)2 and 10 (ΔFq). FITC-ΔFd showed rapid and selective accumulation in parasitized red cells. Overlaying DAPI and FITC florescence suggested that ΔFd binds DNA. Trophozoites and schizonts incubated with ΔFd (2.5 µM) egressed anomalously and Band-3 immunostaining revealed them not to be associated with RBC membrane. Prematurely egressed merozoites from peptide-treated cultures were found to be invasion incompetent. CONCLUSION: Good selectivity (>35), good resistance index (1.1) and low cytotoxicity indicate the promise of ΔFd against malaria.

Isopeptide ligation catalyzed by quintessential sortase A: mechanistic cues from cyclic and branched oligomers of indolicidin.

The housekeeping transpeptidase sortase A (SrtA) from Staphyloccocus aureus catalyzes the covalent anchoring of surface proteins to the cell wall by linking the threonyl carboxylate of the LPXTG recognition motif to the amino group of the pentaglycine cross-bridge of the peptidoglycan. SrtA-catalyzed ligation of an LPXTG containing polypeptide with an aminoglycine-terminated moiety occurs efficiently in vitro and has inspired the use of this enzyme as a synthetic tool in biological chemistry. Here we demonstrate the propensity of SrtA to catalyze "isopeptide" ligation. Using model peptide sequences, we show that SrtA can transfer LPXTG peptide substrates to the ε-amine of specific Lys residues and form cyclized and/or a gamut of branched oligomers. Our results provide insights about principles governing isopeptide ligation reactions catalyzed by SrtA and suggest that although cyclization is guided by distance relationship between Lys (ε-amine) and Thr (α-carboxyl) residues, facile branched oligomerization requires the presence of a stable and long-lived acyl-enzyme intermediate.

In vitro antimalarial activity of medicinal plant extracts against Plasmodium falciparum.

Malaria is a major global public health problem, and the alarming spread of drug resistance and limited number of effective drugs now available underline how important it is to discover new antimalarial compounds. In the present study, ten plants were extracted with ethyl acetate and methanol and tested for their antimalarial activity against chloroquine (CQ)-sensitive (3D7) and CQ-resistant (Dd2 and INDO) strains of Plasmodium falciparum in culture using the fluorescence-based SYBR Green assay. Plant extracts showed moderate to good antiparasitic effects. Promising antiplasmodial activity was found in the extracts from two plants, Phyllanthus emblica leaf 50% inhibitory concentration (IC50) 3D7: 7.25 µg/mL (ethyl acetate extract), 3.125 µg/mL (methanol extract), and Syzygium aromaticum flower bud, IC50 3D7:13 µg/mL, (ethyl acetate extract) and 6.25 µg/mL (methanol extract). Moderate activity (30-75 µg/mL) was found in the ethyl acetate and methanol extracts of Abrus precatorius (seed) and Gloriosa superba (leaf); leaf ethyl acetate extracts of Annona squamosa and flower of Musa paradisiaca. The above mentioned plant extracts were also found to be active against CQ-resistant strains (Dd2 and INDO). Cytotoxicity study with P. emblica leaf and S. aromaticum flower bud, extracts showed good therapeutic indices. These results demonstrate that leaf ethyl acetate and methanol extracts of P. emblica and flower bud extract of S. aromaticum may serve as antimalarial agents even in their crude form. The isolation of compounds from P. emblica and S. aromaticum seems to be of special interest for further antimalarial studies.

Antiplasmodial activity of botanical extracts against Plasmodium falciparum.

The absence of a vaccine and the rampant resistance to almost all antimalarial drugs have accentuated the urgent need for new antimalarial drugs and drug targets for both prophylaxis and chemotherapy. The aim of the study was to discover effective plant extracts against Plasmodium falciparum. In the present study, the hexane, chloroform, ethyl acetate, acetone, and methanol extracts of Citrus sinensis (peel), Leucas aspera, Ocimum sanctum, Phyllanthus acidus (leaf), Terminalia chebula (seed) were tested for their antimalarial activity against chloroquine (CQ)-sensitive (3D7) strain of P. falciparum which was cultured following the candle-jar method. Antimalarial evaluations of daily replacement of culture medium containing CQ and different plant crude extracts were performed on 96-well plates at 37°C for 24 and 48 h. Parasitemia was determined microscopically on thin-film Giemsa-stained preparations. Plant extracts were tested for their cytotoxicity using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay on human laryngeal cancer cell line (HEp-2) and normal cell line (Vero). Out of the 25 extracts tested, six showed good (IC(50) 4.76-22.76 µg/mL), 15 exhibited moderate (IC(50) 31.42-88.03 µg/mL), while four displayed mild (IC(50) > 100 µg/mL) antiplasmodial activity. The leaf ethyl acetate and methanol extracts of L. aspera; ethyl acetate, acetone, and methanol extracts of P. acidus; and seed acetone extract of T. chebula had good antiplasmodial activity (IC(50) = 7.81, 22.76, 9.37, 14.65, 12.68, and 4.76 µg/mL) with selectivity indices 5.43, 2.04, 4.88, 3.35, 3.42, and 9.97 for HEp-2 and >5.79, >2.20, >11.75, >3.41, >3.94, and >7.38 for Vero cells, respectively. These analyses have revealed for the first time that the components present in the solvent extracts of L. aspera, P. acidus, and T. chebula have antiplasmodial activity. The high antiplasmodial activity observed make these plants good candidates for isolation of anti-protozoal compounds which could serve as new lead structures for drug development.

Synthesis of novel alpha-pyranochalcones and pyrazoline derivatives as Plasmodium falciparum growth inhibitors.

Both the lack of a credible malaria vaccine and the emergence and spread of parasites resistant to most of the clinically used antimalarial drugs and drug combination have aroused an imperative need to develop new drugs against malaria. In present work, alpha-pyranochalcones and pyrazoline analogs were synthesized to discover chemically diverse antimalarial leads. Compounds were tested for antimalarial activity by evaluation of the growth of malaria parasite in culture using the microtiter plate based SYBR-Green-I assay. The (E)-3-(3-(2,3,4-trimethoxyphenyl)-acryloyl)-2H-chromen-2-one (Ga6) turned out to be the most potent analog of the series, showing IC(50) of 3.1 microg/ml against chloroquine-sensitive (3D7) strain and IC(50) of 1.1 microg/ml against chloroquine-resistant field isolate (RKL9) of Plasmodium falciparum. Cytotoxicity study of the most potent compounds was also performed against HeLa cell line using the MTT assay. All the tested compounds showed high therapeutic indices suggesting that they were selective in their action against the malaria parasite. Furthermore, docking of Ga6 into active site of falcipain enzyme revealed its predicted interactions with active site residues. This is the first instance wherein chromeno-pyrazolines have been found to be active antimalarial agents. Further exploration and optimization of this new lead could provide novel, antimalarial molecules which can ward off issues of cross-resistance to drugs like chloroquine.

De novo design and characterization of a helical hairpin eicosapeptide; emergence of an anion receptor in the linker region.

De novo design of supersecondary structures is expected to provide useful molecular frameworks for the incorporation of functional sites as in proteins. A 21 residue long, dehydrophenylalanine-containing peptide has been de novo designed and its crystal structure determined. The apolar peptide folds into a helical hairpin supersecondary structure with two right-handed helices, connected by a tetraglycine linker. The helices of the hairpin interact with each other through a combination of C-H.O and N-H.O hydrogen bonds. The folding of the apolar peptide has been realized without the help of either metal ions or disulphide bonds. A remarkable feature of the peptide is the unanticipated occurrence of an anion binding motif in the linker region, strikingly similar in conformation and function to the "nest" motif seen in several proteins. The observation supports the view for the possible emergence of rudimentary functions over short sequence stretches in the early peptides under prebiotic conditions.