Plasmepsin II inhibitory activity of alkoxylated and hydroxylated chalcones

Sixteen antimalarial alkoxylated and hydroxylated chalcones were tested for their ability to inhibit recombinant plasmepsin II in vitro. The best inhibitory compounds had either a chloro or dimethylamino group at the 4-position of phenyl ring A in the chalcone template. Combination of the chalcones with chloroquine showed additivity or mild antagonism of Plasmodium falciparum K1 growth in culture.     

非恶性疟人体疟原虫药物抗性分子标记研究进展

随着抗疟药的长期、广泛使用,疟原虫对抗疟药逐渐产生抗性。目前有关恶性疟原虫的抗药性分子标记研究较多,而对非恶性疟原虫关注度相对较小。为了更好地为临床治疗的合理用药提供科学依据,为非恶性疟人体疟原虫对抗疟药敏感性分子监测提供参考,本文就非恶性疟人体疟原虫常见抗药性相关分子标记的研究进展作一综述。     

恶性疟原虫:组氨酸富集蛋白基因反义寡脱氧核苷酸体外抗疟作用初步研究

[目的 ]研究反义寡脱氧核苷酸 (oligodeoxyribonucleotides,ODN)对恶性疟原虫组氨酸富集蛋白 (histidine richprotein ,HRP)Ⅱ和HRPⅢ基因表达的阻断作用 ,探讨抗疟新途径。 [方法 ]设计合成恶性疟原虫组氨酸富集蛋白翻译起始区的反义ODN、正义ODN和无义ODN ,研究其对红内期培养恶性疟原虫增殖和成熟的体外抑制作用。[结果 ]当ODN浓度较高时 (高于 1μmol L) ,反义ODN、正义ODN和无义ODN均能抑制恶性疟原虫的增殖和成熟 ,即ODN对疟原虫呈非特异性抑制。当ODN浓度在 0 0 1～ 0 5 μmol L时 ,与无义ODN对照组相比 ,反义ODN能显著抑制体外培养恶性疟原虫的增殖和裂殖体成熟 (P <0 0 1) ;且ODN浓度越高 ,抑制作用也就越强。正义ODN对虫体的抑制作用 ,与无义ODN相比其差异无显著性意义 (P >0 0 5 )。 [结论 ]HRPⅡ和HRPⅢ基因反义ODN可通过阻断基因的表达 ,抑制恶性疟原虫增殖和成熟的作用。     

Aspartic proteases from Plasmodium chabaudi: a rodent model for human malaria

Intraerythrocytic malaria parasites degrade haemoglobin to provide nutrients for their own growth and maturation. Plasmodium aspartic proteases known as plasmepsins play an important role on haemoglobin degradation and are being studied as drug targets for chemotherapy of malaria. The rodent model for human malaria, Plasmodium chabaudi, is an experimentally good model for therapy drug design. The gene encoding an aspartic protease precursor (proplasmepsin) from the rodent malaria parasite P. chabaudi was cloned and sequenced. A theoretical 3D structure model was constructed by comparative homology and used for superimposition with other known models. Analysis of the P. chabaudi and Plasmodium yoelli genomes revealed in both the presence of at least seven plasmepsins and each one has sequence similarity to its plasmepsin counterpart of the human malaria Plasmodium falciparum. The predicted proteins were confirmed as plasmepsins by detection on Blocks Database of three characteristic blocks of the eukaryotic and viral aspartic protease family. Analysis of the proline-rich loop amino acid sequence of these plasmepsins suggests that they constitute characteristic motifs of each plasmepsin group suggesting that these sequence variations are related with different substrate specificities.     

Insights into the pyrimidine biosynthetic pathway of human malaria parasite Plasmodium falciparum as chemotherapeutic target

Malaria is a major cause of morbidity and mortality in humans. Artemisinins remain as the first-line treatment for Plasmodium falciparum(P. falciparum) malaria although drug resistance has already emerged and spread in Southeast Asia. Thus, to fight this disease, there is an urgent need to develop new antimalarial drugs for malaria chemotherapy. Unlike human host cells, P. falciparum cannot salvage preformed pyrimidine bases or nucleosides from the extracellular environment and relies solely on nucleotides synthesized through the de novo biosynthetic pathway. This review presents significant progress on understanding the de novo pyrimidine pathway and the functional enzymes in the human parasite P. falciparum. Current knowledge in genomics and metabolomics are described, particularly focusing on the parasite purine and pyrimidine nucleotide metabolism. These include gene annotation, characterization and molecular mechanism of the enzymes that are different from the human host pathway. Recent elucidation of the three-dimensional crystal structures and the catalytic reactions of three enzymes: dihydroorotate dehydrogenase, orotate phosphoribosyltransferase, and orotidine 5'-monophosphate decarboxylase, as well as their inhibitors are reviewed in the context of their therapeutic potential against malaria.     

Differential regulation of IgG subclasses and IgE antimalarial antibody responses in complicated and uncomplicated Plasmodium falciparum malaria

The aim of this study was to assess the immunoglobulin (Ig)-subclass distribution of antimalarial antibody responses in 110 and 169 Thai patients with complicated and uncomplicated Plasmodium falciparum malaria, respectively. Antimalarial plasma IgG subclasses and IgE antibody levels against a crude malaria blood stages, and antigen preparation were determined using enzyme-linked immunosorbent assay (ELISA). On admission, the levels of anti-P. falciparum IgG1, IgG2 and IgG3 were significantly lower in patients with complicated malaria than uncomplicated malaria (IgG1, P < 0.0001; IgG2, P < 0.0001; IgG3, P < 0.0001). The levels of antimalarial IgE were slightly lower, but not statistically significant (P = 0.389) in the complicated malaria. After adjusting all antibody levels and age, anti-P. falciparum IgG3 levels remained significantly associated with complicated malaria. None of the other antibody concentrations showed statistically significant associations with complicated malaria. The anti-P. falciparum IgG3 levels were related to the IgG1 as well as IgG2 levels. A correlation between anti-P. falciparum IgG2 and IgE was observed in the complicated malaria group, and this may indicate their roles in the severity of disease. Our data suggest that anti-P. falciparum IgG3 is associated with a reduced risk of complicated malaria and that antimalarial Ig-subclasses are differently regulated in patients with complicated and uncomplicated malaria.     

Plasmodium falciparum infection in the pregnant patient

Malaria should be considered a risk factor in women who are pregnant, principally when the infection is Plasmodium falciparum. Moreover, the risk is greater if the woman is pregnant for the first time; if she has no immunity for malaria; if the diagnosis is made late; or if P. falciparum shows resistance to antimalarial drugs. This article presents the most significant aspects of P. falciparum malaria during pregnancy, including information about treatments and prophylaxis.     

Sensitivity of Plasmodium falciparum to antimalarial drugs in Colombia

Sensitivity of Plasmodium falciparum to several antimalarial drugs was determined by in vitro and in vivo tests. Chloroquine resistance in vitro was detected in 97 of 101 patients from different geographic areas of Colombia. Sensitivity to amodiaquine in vitro was observed in 29 of 30 P. falciparum isolates. In vitro sensitivity to amodiaquine was observed in 16 patients infected with chloroquine-resistant P. falciparum. In vitro sensitivity to quinine was demonstrated in 57 P. falciparum isolates. Two infections from the Amazon base (2/24) were resistant to mefloquine in vitro at concentrations of 5.7 and 16 pmol/well. Resistance to Fansidar, a sulfadoxine-pyrimethamine combination, was described in 9 patients from the Amazon region. One patient showed recrudescence of the infection 41 days after treatment. The current distribution and degree of resistance of P. falciparum to widely used antimalarial drugs requires the evaluation of therapeutic schemes based on combinations of fast blood schizontocides with slow acting drugs. These associations may reduce the development of multidrug-resistant isolates and retard the spread of resistant populations of P. falciparum parasites.     

Antimalarial activities of oligodeoxynucleotide phosphorothioates in chloroquine-resistant Plasmodium falciparum.

Synthetic oligonucleotides and their chemical modifications have been shown to inhibit viral and cellular gene expression by sequence-specific antisense hybridization to target mRNAs. We now report that oligodeoxynucleotide phosphorothioates and their nuclease-resistant modifications are effective in micromolar and submicromolar concentrations against the growth of both chloroquine-resistant and chloroquine-sensitive strains of Plasmodium falciparum in vitro. Parasitized human erythrocytes were found to be accessible to radioactively labeled oligodeoxynucleotides, whereas the uninfected erythrocytes did not permit any cellular entry of the same compounds. The dihydrofolate reductase-thymidylate synthase gene of P. falciparum was demonstrated to be a good target for sequence-dependent inhibition of plasmodial growth by exogenously administered modified oligonucleotides. The antimalarial activities observed in vitro were identical for chloroquine-sensitive and chloroquine-resistant strains of P. falciparum. The antimalarial activity of oligodeoxynucleotide phosphorothioates is related to sequence complementarity to certain regions of the plasmodial genome as well as to non-sequence-defined activities.     

In vitro antimalarial activity and cytotoxicity of some selected cuban medicinal plants

Terrestrial plants have been demonstrated to be sources of antimalarial compounds. In Cuba, little is known about antimalarial potentials of plant species used as medicinals. For that reason, we evaluated the antimalarial activity of 14 plant species used in Cuba as antimalarial, antipyretic and/or antiparasitic. Hydroalcoholic extracts were prepared and tested in vitro for the antimalarial activity against Plasmodium falciparum Ghana strain and over human cell line MRC-5 to determine cytotoxicity. Parasite multiplication was determined microscopically by the direct count of Giemsa stained parasites. A colorimetric assay was used to quantify cytotoxicity. Nine extracts showed IC50 values lower than 100 μg/mL against P. falciparum, four extracts were classified as marginally active (SI < 4), one as partially active (Parthenium hysterophorus) exhibiting SI equal to 6.2 and two extracts as active (Bambusa vulgaris and Punica granatum), showing SI > 10. B. vulgaris showed the most potent and specific antiplasmodial action (IC50 = 4.7 μg/mL, SI = 28.9). Phytochemical characterization of active extracts confirmed the presence of triterpenoids in B. vulgaris and polar compounds with phenol free groups and fluorescent metabolites in both extracts as major phytocompounds, by thin layer chromatography. In conclusion, antimalarial use of B. vulgaris and P. hysterophorus was validated. B. vulgaris and P. granatum extracts were selected for follow-up because of their strong antimalarial activity.     

海南省吊罗山地区恶性疟原虫对咯萘啶、磺胺多辛、乙胺嘧啶联用敏感性的5年监测

1986～1987年在抗氯喹恶性疟流行区海南省吊罗山地区,以咯萘啶(咯)800mg、磺胺多辛(磺)1 000mg、乙胺嘧啶(乙)50mg,2d分服,作为常规治疗恶性疟,1988年起改用咯500mg、磺1 000mg、乙50mg的单剂。1986～1990五年间共治疗恶性疟435例。经体内法测定,当地恶性疟原虫对咯、磺、乙伍用均保持敏感,治愈率均为100％。     

Artemisinin resistance or tolerance in human malaria patients

Malaria is a major cause of morbidity and mortality in the developing world. This situation is mainly due to emergence of resistance to most antimalarial drugs currently available. Artemisinin-based combination treatments are now first-line drugs for Plasmodium falciparum (P. falciparum) malaria. Artemisinin (qinghaosu) and its derivatives are the most rapid acting and efficacious antimalarial drugs. This review highlights most recent investigations into the emergence of artemisinin resistance in falciparum malaria patients on the Thai-Cambodian border, a historical epicenter for multidrug resistance spread spanning over 50 years. The study presents the first evidence that highlights the parasites reduced susceptibility to artemisinin treatment by prolonged parasite-clearance times, raising considerable concern on resistance development. Although the exact mechanism of action remains unresolved, development of resistance was proposed based from both in vitro experiments and human patients. Lines of evidence suggested that the parasites in the patients are in dormant forms, presumably tolerate to the drug pressure. The World Health Organization has launched for prevention and/or containment of the artemisinin-resistant malaria parasites. Taken together, the emergence of artemisinin resistance to the most potent antidote for falciparum malaria, poses a serious threat to global malaria control and prompts renewed efforts for urgent development of new antimalarial weapons.     

The enzyme-linked immunosorbent assay (ELISA) for malaria. I. The use of in vitro-cultured Plasmodium falciparum as antigen.

Using the Panama II strain of Plasmodium falciparum obtained from continuous in vitro culture as antigen, the micro enzyme-linked immunosorbent assay (ELISA) was used to test serum samples from 50 persons from the southeastern United States and serum specimens collected weekly from four non-immune and nine semi-immune patients infected with P. falciparum. None of the 50 sera from the United States had ELISA antibody titers greater than 1:80. The nine semi-immune patients had rapid ELISA antibody responses (titers greater than 1:2560) following patent parasitemia. ELISA titers remained elevated despite disappearance of patent parasitemia, and declined gradually following curative antimalarial therapy. The ELISA responses observed in the four non-immune patients were more variable, though positive titers appeared rapidly with patent parasitemia. Maximum titers were lower than those observed in semi-immune patients. These results demonstrate that P. falciparum obtained from continuous in vitro culture is an excellent antigen for the micro-ELISA test for malaria. However, further assessments of the ELISA are needed to identify the conditions associated with positive responses.     

A 5-year surveillance of sensitivity in vivo of Plasmodium falciparum to pyronaridine/sulfadoxine/pyrimethamine in Diaoluo area, Hainan Province

The surveillance of sensitivity of P. falciparum to pyronaridine/sulfadoxine/pyrimethamine has been carried out in Diaoluo area in Hainan Province where chloroquine-resistant falciparum malaria is endemic, covering an area of 406 square kilometers, with a population of 3745 in 1986. From 1986 all outpatients diagnosed as falciparum malaria were administered with PND/S/P as the only antimalarial. In vivo sensitivity of P. falciparum was measured in some patients who were treated in hospital. It was demonstrated that P. falciparum in the Diaoluo area has retained its sensitivity to a single oral dose of PND/S/P of 500/1,000/50 mg with 100% cure rate for at least 5 years.     

In vitro antimalarial drug susceptibility and pfcrt mutation among fresh Plasmodium falciparum isolates from the Lao PDR (Laos)

Recent drug trials in Laos have shown high levels of Plasmodium falciparum resistance to chloroquine, but there are no published data on in vitro antimalarial drug susceptibility. We used the double-site enzyme-linked pLDH immunodetection (DELI) assay to estimate the in vitro antimalarial drug susceptibility of 108 fresh P. falciparum isolates from southern Laos. The geometric mean (95% confidence interval) 50% inhibitory concentration values (nmol/L) were 152.4 (123.8-187.6) for chloroquine, 679.8 (533.8-863.0) for quinine, 45.9 (37.9-55.7) for mefloquine, 5.0 (4.4-6.4) for artesunate, 6.3 (4.5-8.9) for dihydroartemisinin, and 59.1 (46.4-75.3) for lumefantrine. The proportion of isolates defined as resistant were 65%, 40%, and 8% for chloroquine, quinine, and mefloquine, respectively. Of 53 isolates genotyped for the pfcrt T76K chloroquine-resistance mutation, 48 (91%) were mutants. P. falciparum in Laos is multi-drug resistant; antimalarial immunity resulting from the use of ineffective chloroquine before 2005 probably contributes significantly to the therapeutic responses in clinical trials.     

Inhibitors of Plasmodium falciparum methionine aminopeptidase 1b possess antimalarial activity

With >1 million deaths annually, mostly among children in sub-Saharan Africa, malaria poses one of the most critical challenges in medicine today. Although introduction of the artemisinin class of antimalarial drugs has offered a temporary solution to the problem of drug resistance, new antimalarial drugs are needed to ensure effective control of the disease in the future. Herein, we have investigated members of the methionine aminopeptidase family as potential antimalarial targets. The Plasmodium falciparum methionine aminopeptidase 1b (PfMetAP1b), one of four MetAP proteins encoded in the P. falciparum genome, was cloned, overexpressed, purified, and used to screen a 175,000-compound library for inhibitors. A family of structurally related inhibitors containing a 2-(2-pyridinyl)-pyrimidine core was identified. Structure/activity studies led to the identification of a potent PfMetAP1b inhibitor, XC11, with an IC(50) of 112 nM. XC11 was highly selective for PfMetAP1b and did not exhibit significant cytotoxicity against primary human fibroblasts. Most importantly, XC11 inhibited the proliferation of P. falciparum strains 3D7 [chloroquine (CQ)-sensitive] and Dd2 (multidrug-resistant) in vitro and is active in mouse malaria models for both CQ-sensitive and CQ-resistant strains. These results suggest that PfMetAP1b is a promising target and XC11 is an important lead compound for the development of novel antimalarial drugs.     

恶性疟原虫氯喹敏感株与抗性株对青蒿素类药物体外敏感性的研究

目的 测定恶性疟原虫氯喹敏感株与抗性株对青蒿素类药物的体外敏感性. 方法 运用体外微量法与酶联免疫吸附试验(enzyme-linked immunosorbent assay,ELISA)测定青蒿琥酯、蒿甲醚及双氢青蒿素等3种青蒿素类抗疟药物对体外培养的恶性疟原虫氯喹敏感株与氯喹抗性株的体外敏感性,并比较两种方法测定的IC50值. 结果 体外微量法测定的3种药物对恶性疟原虫氯喹敏感株的IC50值依次为3.12 nmol/L、4.30 nmol/L、2.18 nmol/L,对恶性疟原虫氯喹抗性株的IC50值依次为4.31nmol/L、3.90 nmol/L、3.17 nmol/L;同时,将体外微量法与ELISA法所获的结果进行相关性分析,两种方法结果基本一致(r2=0.93,P＜0.001). 结论 恶性疟原虫氯喹抗性株对青蒿素类药物无明显的交叉抗性;ELISA法可用于恶性疟原虫对抗疟药物的体外敏感性检测.     

A yeast-like mRNA capping apparatus in Plasmodium falciparum

Analysis of the mRNA capping apparatus of the malaria parasite Plasmodium falciparum illuminates an evolutionary connection to fungi rather than metazoans. We show that P. falciparum encodes separate RNA guanylyltransferase (Pgt1) and RNA triphosphatase (Prt1) enzymes and that the triphosphatase component is a member of the fungal/viral family of metal-dependent phosphohydrolases, which are structurally and mechanistically unrelated to the cysteine-phosphatase-type RNA triphosphatases found in metazoans and plants. These results highlight the potential for discovery of mechanism-based antimalarial drugs designed to specifically block the capping of Plasmodium mRNAs. A simple heuristic scheme of eukaryotic phylogeny is suggested based on the structure and physical linkage of the triphosphatase and guanylyltransferase enzymes that catalyze cap formation.     

Plasmodium falciparum and Plasmodium vivax infections in the owl monkey (Aotus trivirgatus). I. The courses of untreated infections.

This study, the first of three designed to determine the feasibility of using owl monkeys infected with human plasmodia in the search for new, more broadly active antimalarial drugs, dealt with the characteristics of untreated infections with eight strains of Plasmodium falciparum and two strains of P. vivax. Such infections, induced by standardized inocula of these strains in 1,733 monkeys, all Aotus trivirgatus griseimembra, were followed from day of inoculation to death of self-cure. The virulence of the various strains differed strikingly. Incidences of fatal reactions, ranging from 24.4--89.4% and 8.1--45.8%, respectively, in infections with strains of P. falciparum and P. vivax, were closely related to the rate at which parasitemia evolved, the height of parasitemia in the primary attack, and/or the time period over which a high parasite level was sustained. Antemortem symptom complexes and gross tissue and organ reactions in infections with P. falciparum varied with survival time, but within that boundary, were the same for infections with all eight strains of this plasmodium. Morbidity in both fatal and self-limited infections with both plasmodial species was related to height of parasitemia; however, at comparable parasite levels, symptoms exhibited in infections with P. vivax were more severe than in infections with P. falciparum. Overall, the characteristics of infections with these plasmodia in owl monkeys were remarkably similar to those of human infections. With respect to biological features, infections with P. falciparum and P. vivax in this simian host appear to have much to offer in the search for new antimalarial drugs.     

Generation of quinolone antimalarials targeting the Plasmodium falciparum mitochondrial respiratory chain for the treatment and prophylaxis of malaria

There is an urgent need for new antimalarial drugs with novel mechanisms of action to deliver effective control and eradication programs. Parasite resistance to all existing antimalarial classes, including the artemisinins, has been reported during their clinical use. A failure to generate new antimalarials with novel mechanisms of action that circumvent the current resistance challenges will contribute to a resurgence in the disease which would represent a global health emergency. Here we present a unique generation of quinolone lead antimalarials with a dual mechanism of action against two respiratory enzymes, NADH:ubiquinone oxidoreductase (Plasmodium falciparum NDH2) and cytochrome bc(1). Inhibitor specificity for the two enzymes can be controlled subtly by manipulation of the privileged quinolone core at the 2 or 3 position. Inhibitors display potent (nanomolar) activity against both parasite enzymes and against multidrug-resistant P. falciparum parasites as evidenced by rapid and selective depolarization of the parasite mitochondrial membrane potential, leading to a disruption of pyrimidine metabolism and parasite death. Several analogs also display activity against liver-stage parasites (Plasmodium cynomolgi) as well as transmission-blocking properties. Lead optimized molecules also display potent oral antimalarial activity in the Plasmodium berghei mouse malaria model associated with favorable pharmacokinetic features that are aligned with a single-dose treatment. The ease and low cost of synthesis of these inhibitors fulfill the target product profile for the generation of a potent, safe, and inexpensive drug with the potential for eventual clinical deployment in the control and eradication of falciparum malaria.