泊沙康唑体内及体外活性研究进展

泊沙康唑是广谱三唑类抗真菌新药,对大多数酵母菌和丝状真菌体外高度敏感,如念珠菌属、新型隐球菌、曲霉属、镰刀霉属及接合菌属等。对部分双相型真菌和地方性真菌,泊沙康唑也具有体外活性。对免疫正常及免疫抑制动物的侵袭性感染,泊沙康唑都有广谱、高效的抗真菌活性。对光滑念珠菌、克柔念珠菌、土曲霉、镰刀霉及接合菌等,泊沙康唑的体内外活性优于其他唑类药物。在体内敏感度研究中,对不同免疫状态及不同部位的重度侵袭性感染,泊沙康唑预防和治疗用药都显示了良好的效果。     

Comparison of in vitro and in vivo antimalarial activities of 9-phenanthrenecarbinols

Analysis of the antimalarial activity of a selected series of 17 9-phenanthrenecarbinols against cultured strains of Plasmodium falciparum and against P. berghei in mice following oral administration indicated that the rankings of activities within the series were influenced by substituents on the 9-carbinol and the route of administration. Compounds with alkylamino-alkyl groups were ranked as most active by an in vitro screening system which assayed activity against chloroquine-sensitive and chloroquine-resistant strains of cultured P. falciparum by the inhibition of uptake of radiolabelled hypoxanthine. There were few differences in ranking of activities between the two strains. Although there was a significant difference between activities of an erythro- and a threo-racemate, activities of the four optical isomers of this compound were comparable. Among the series, compounds with a 2-piperidyl substituent on the 9-carbinol were ranked most active by the oral route of administration as assayed by the cure rates of mice infected with P. berghei. Correlation of these observations with previously published data on the activity of these compounds against P. falciparum in Owl monkeys and P. berghei in mice following subcutaneous administration suggested that neither species of host nor strains of parasite significantly influenced the ranking of activities of this class of compound.     

Potent antimalarial and transmission-blocking activities of centanamycin, a novel DNA-binding agent

Most treatments for malaria target the blood stage of infection in the human host, although few can also block transmission of the parasite to the mosquito. We show here that the compound centanamycin is very effective against blood-stage malarial infections in vitro and in vivo and has profound effects on sexual differentiation of the parasites in mosquitoes. After drug treatment, parasite development is arrested within the midguts of mosquitoes, failing to produce the infective forms that migrate to the salivary glands. The mechanism of parasite death is associated with modification of Plasmodium genomic DNA. We detected DNA damage in parasites isolated from mice 24 h after treatment with centanamycin, and, importantly, we also detected this DNA damage in parasites within mosquitoes that had fed on these mice 10 days earlier. This demonstrates that damage to parasite DNA during blood-stage infection persists from the vertebrate to the mosquito host and provides a novel biochemical strategy to block malaria transmission.     

瑞香素结构衍生物体内外抗疟活性的研究

目的 通过体外试验和鼠疟(Plamodium berghei)动物模型观察瑞香素结构衍生物的抗疟作用.方法 通过光学显微镜镜检和微量荧光法两种体外筛选系统筛检瑞香素类衍生物对恶性疟原虫(Plamodium falciparum)的体外抗疟作用;对体外筛检抗疟活性高的化合物,采用WHO推荐的"四天抑制试验"测定其对鼠伯氏疟原虫(ANKA株)的抗疟作用.结果 通过体外筛选系统筛选出DA78与DA79两种新型的瑞香素类抗疟化合物,两者的IC50分别为7.6 μmol/L和1.4 μmol/L,其体外抗疟活性与瑞香素在同一统计学水平(P＞0.05);体内试验伯氏鼠疟原虫ANKA株感染鼠,DA78 1、10、50、75 mg/kg·d×4 d剂量组D4减虫率与空白对照组比较差异有显著性(P＜0.01),而DA79 50或75 mg/kg·d×4 d剂量组D4减虫率与对照组相比较差异有显著性(P＜0.05),DA78 10或75 mg/kg·d×4 d剂量组D4减虫率高于同剂量的瑞香素组(P＜0.05).结论 以DA78与DA79为代表的瑞香素类衍生物作为一类新型的抗疟化合物,在体外和体内试验中均显示出一定的抗疟活性,为寻求更有效的抗疟化合物提供了方向和理论依据.     

Antipyretic and antimalarial activities of crude leaf extract and fractions of Enicostema littorale

ObjectiveTo evaluate the antiplasmodial and antipyretic activities of whole plant extract and fractions of Enicostemma littorale (E. littorale) for ascertaining the folkloric claim of its antimalarial and antipyretic activities.MethodsThe crude extract (260 – 780 mg/kg) and fractions (chloroform and acqeous; 520 mg/kg) of E. littorale were investigated for antiplasmodial activity against chloroquine-sensitive Plasmodium berghei (P. berghei) infections in mice and for antipyretic activity against dinitrophenol, amphetamine and yeast-induced pyrexia. The antiplasmodial activity during early and established infections as well as prophylactic were investigated. Artesunate (5 mg/kg) and pyrimethamine (1.2 mg/kg) were used as positive controls. Antipyretic activity of the crude extract was also evaluated against dinitrophenol, amphetamine and yeast-induced pyrexia.ResultsThe extract and fractions dose-dependently reduced parasitaemia induced by chloroquine-sensitive P. berghei infection in prophylactic, suppressive and curative models in mice. These reductions were statistically significant (P<0.001). They also improved the mean survival time from 11 to 27 days relative to control (P<0.01 – 0.001). The activities of extract/fractions were comparable to that of the standard drugs used (artesunate and pyrimethamine). On pyrexia induced by dinitrophenol, amphetamine and yeast, the extract caused inhibitions which were statistically significant (P<0.05 – 0.001) and in a dose-dependent fashion.ConclusionsThese plant extracts possess considerable antiplasmodial and antipyretic activities, which justify its use in ethnomedicine.     

Population biology and antimalarial resistance: The transmission of antimalarial drug resistance in Plasmodium falciparum

Malaria morbidity and mortality continue to increase across sub-Saharan Africa. This is largely as a result of the continued use of chloroquine and sulfadoxine-pyrimethamine, despite widespread resistance. Although eliminating the asexual stages of Plasmodium falciparum is the focus of treatment of individual symptomatic patients, at a population level, reducing the carriage of gametocytes - the sexual stage responsible for infection of the mosquito vector - is necessary to limit the transmission of malaria parasites and the spread of antimalarial resistance. The probability of a mosquito being infected depends on the prevalence, duration and density of viable gametocyte carriage in the human host, although additional humoral and leukocyte factors also affect transmissibility. There is a log-sigmoid relationship between gametocyte density in the patients' blood and infectivity to the mosquito. The infectivity and thus transmission potential associated with a particular antimalarial treatment can be characterised as a function of blood gametocyte density and time, summing these over the acute and all subsequent recrudescences of that infection. Gametocyte carriage and infectivity to mosquitoes is consistently higher in patients infected with drug resistant compared with drug sensitive malaria parasites. It is the ratio of transmission potential in drug resistant versus sensitive infections that drives the spread of resistance. Early access to highly effective antimalarial treatment reduces the risk of disease progression and limits gametocyte carriage. The remarkable spread of sulfadoxine-pyrimethamine (SP) resistance across vast regions results from the very high post-treatment prevalence and density of gametocyte carriage following SP treatment. In areas of low intensity malaria transmission, the gametocyte-reducing effect of widespread use of artemisinin-based combination therapy has resulted in a sustained decrease in malaria transmission and a decrease in the spread of resistance. Malaria treatment policy should be based primarily on therapeutic efficacy against asexual stages, but should also consider transmission reduction potential. Artemisinin-based combination therapies are the only antimalarials currently available which rapidly reduce both asexual and gametocyte stages of the P. falciparum lifecycle.     

Fractions of an antimalarial neem-leaf extract have activities superior to chloroquine, and are gametocytocidal

The antimalarial activities of two fractions (IRDN-A and IRDN-B) of an extract from the leaves of the neem tree (Azadirachta indica) were compared with those of chloroquine, in in-vitro assays against Plasmodium falciparum. The asexual stages of a chloroquine-sensitive clone (ITG2F6) and a chloroquine-resistant isolate (W2) and the gametocytes of the NF 54 (BD-7) isolate of P. falciparum were used as the drug targets. Activity against the asexual stages was generally evaluated as the concentrations inhibiting the parasitaemias recorded in the control cultures, after an incubation of 48-72 h, by 50% (IC50) or 100% (IC100). For the ITG2F6 strain, the IC50 and IC100 (in microg/ml) were, respectively, 10(-5) and 10(-4) for IRDN-A, 10(-3) and 10(-2) for IRDN-B, and 10(-2) and 1.0 for chloroquine. The corresponding values for the W2 strain were 10(-5) and 1.0 for IRDN-A, and 10.0 and >100 for chloroquine (even at 100 microg/ml, chloroquine only inhibited the parasitaemia by 85%).Each of the two neem-leaf fractions lysed 50% and 100% of developing gametocytes, at 10(-3) and 1.0 microg/ml, respectively; and 50% and 100% of mature gametocytes at 10(-3) and 10(2) microg/ml, respectively. If they are found safe and effective in vivo, the neem-leaf fractions may form the basis of new antimalarial drugs that not only cure chloroquine-sensitive and chloroquine-resistant malaria but also markedly reduce transmission.     

Cyclic GMP phosphodiesterase and guanylate cyclase activities in rabbit ovaries and the effect of in-vivo stimulation with LH

The activities of guanylate cyclase and cyclic GMP (cGMP) phosphodiesterase, enzymes that are responsible for maintaining tissue levels of cGMP, were determined in the ovaries of rabbits killed without treatment or 4 h after administration of LH. Ovarian activities of the two enzymes were determined in the 100 000 g supernatant fraction (cytosol) and the resulting pellet (particulate fraction). Significant phosphodiesterase and cyclase activities were detected in both the cytosol and particulate fractions. Administration of LH had no significant effect on phosphodiesterase activity in either of the tissue fractions. On the other hand, LH caused a significant drop in guanylate cyclase activity in the cytosol and particulate fractions. This drop in the cyclase activity may be the cause of the decreased rabbit ovarian concentrations of cGMP that we have previously observed after LH stimulation.     

Rifabutin reduces systemic exposure of an antimalarial drug 97/78 upon co-administration in rats:an in-vivo & in-vitro analysis

Objective: To determine the potential drug-drug interactions between anti-malarial candidate 97/78 and anti-tubercular drug rifabutin in-vivo in rats followed by in-vitro investigation of the underlying mechanisms of drug interaction. Methods: Single oral dose study was conducted in male and female rats at 40 mg/kg and 70 mg/kg for 97/78 and rifabutin respectively. Results: It was reported that rifabutin co-administration altered pharmacokinetics of 97/63(active metabolite of 97/78). A significant decrease was reported in the systemic exposure of 97/63 by a factor of 3-4. The AUC0-last values were(4.03 ± 0.60) and(5.44 ± 1.15) μg·h·m L-1 upon 97/78 administration alone, while the values were decreased to(1.13 ± 0.10) and(1.23 ± 1.13) μg·h·m L-1 upon rifabutin co-administration in male and female rats respectively. Statistically significant differences were also reported in Cmax and Tmax values upon rifabutin co-administration. In-vitro drug metabolism study in rat liver microsomes has shown that the metabolism of 97/63 was increased by 10%-12% upon rifabutin co-incubation. The extent of plasma protein binding of 97/63 was found to be decreased from 54%-55% to 6%-8% upon rifabutin addition. Conclusions: It was concluded that rifabutin co-administration altered PK parameters of 97/63 in SD rats. However, no intersex influences were reported in the interaction pattern. The results obtained in the in-vivo study were well correlated with the invitro findings and can further be applied to explore other aspects of potential drug interactions between these two drugs.     

The phenothiazinium chromophore and the evolution of antimalarial drugs

The phenothiazinium salt methylene blue [3,7-bis(dimethylamino)phenothiazinium chloride] is the oldest known synthetic antimalarial drug, its clinical efficacy having been reported in 1891. The role of methylene blue in the evolution of the modern antimalarial armoury is often unappreciated, yet it can be linked directly to standard drugs such as chloroquine and its congeners. Also, in the face of increasing plasmodial resistance to modern antimalarials, phenothiazinium derivatives have again featured as lead compounds in drug research. The precise mode of action of methylene blue and its commercial analogues against Plasmodium spp. remains a cause for conjecture, having been variously described as nucleic acid intercalation, food vacuole basification, parasite redox cycle interference and haem polymerization inhibition. That the activity of the series may be due to more than one route - i.e. a multifactorial activity - underlines the utility of these compounds in antimalarial research either as single drugs or as adjuvants (partners in a drug combination), particularly in the face of resistant parasitic strains.     

青蒿素类抗疟药的作用机制

70年代 ,我国学者自中草药黄花蒿中分离出抗疟药青蒿素之后 ,又陆续合成了蒿甲醚、青蒿琥酯和双氢青蒿素等有效衍生物。这类药物的问世 ,在抗疟药物研究史上树立了新的里程碑。在目前疟原虫对传统抗疟药普遍产生抗性情况下 ,青蒿素类抗疟药投入使用十余年 ,迄今尚未见抗药性出现 ,故其抗疟作用机制引起了学者的注意。青蒿素类药物具有独特的过氧桥结构 ,阐明其作用机制 ,对开发新一代高效低毒抗疟药具有重要意义。本文就近年来有关青蒿素类抗疟药作用机制方面的研究进展作一综述。1　铁介导的自由基生成及烷化蛋白质作用业已证明 ,铁 (包括…     

The effects of antimalarial drugs on ventricular repolarization

Cardiotoxicity has become a major concern during treatment with antimalarial drugs. Lengthening of the QTc and severe cardiac arrhythmia have been observed, particularly after treatment with halofantrine for chloroquine-resistant Plasmodium falciparum malaria. The purpose of this prospective study was to evaluate whether antimalarial agents alter dispersion of the QTc and ventricular repolarization dynamicity. Sixty patients with uncomplicated falciparum malaria were randomly allocated in four groups of 15 patients and treated with quinine, mefloquine, artemether, or halofantrine at recommended doses. Patients in treatment groups were compared with a group including 15 healthy controls with no history of malaria and/or febrile illness within the last month. QTc dispersion was measured on surface electrocardiograms. Repolarization dynamicity was analyzed from Holter recordings, which allow automatic beat-to-beat measurement of QT and RR intervals. Plasma drug concentration was determined by reversed-phase high-performance liquid chromatography. No change in QTc dispersion was observed after treatment with quinine, mefloquine, or artemether. Treatment with halofantrine was followed by a significant increase in QTc dispersion at 9 hours (P < 0.0001) and 24 hours (P < 0.01). Assessment of QT heart rate variability by QT/RR nychtohemeral regression slope demonstrated no significant difference between the artemether (mean +/- SEM = 0.170 +/- 0.048), mefloquine (0.145 +/- 0.044), and the control groups (0.172 +/- 0.039). A significant decrease in the Q-eT/RR slope was observed in the quinine group compared with the control and artemether groups (0.135 +/- 0.057; P < 0.04). With halofantrine, a significant increase in the QT/RR regression slope (0.289 +/- 0.118) was observed (P < 0.0002). QTc interval, QT dispersion, and QT regression slope were significantly correlated with halofantrine and quinine plasma concentration. Mefloquine and artemether did not alter ventricular repolarization. Quinine induced a significant decrease in QT/RR slope of the same order of magnitude as those previously observed with quinidine. Both QTc dispersion and QT/RR slope were significantly modified by halofantrine. These repolarization changes were related to a class-III antiarrhythmic drug effect and may explain the occurrence of ventricular arrhythmia and/or sudden deaths reported after halofantrine intake.     

The fluidity of blood in African elephants (Loxodonta africana)

The large cellular volume of erythrocytes and the increased plasma concentration of proteins in elephants are factors which potentially affect blood rheology adversely. To verify blood rheology, routine hemorheologic variables were analyzed in four African elephants (Loxodonta africana), housed in the zoo of Vienna. Whole blood viscosity at three different shear rates (WBV at low shear rate: WBV 0.7 s(-1) and WBV 2.4 s(-1); WBV at high shear rate: WBV 94 s(-1) done by LS30, Contraves) and erythrocyte aggregation (aggregation indices AI by LS30; aggregation indices M0, M1 by Myrenne aggregometer) were high (WBV 94 s(-1): 5.368 (5.246/5.648); WBV 2.4 s(-1): 16.291 (15.605/17.629); WBV 0.7 s(-1): 28.28 (25.537/32.173) mPa s; AI 2.4 s(-1): 0.25 (0.23/0.30); AI 0.7 s(-1): 0.24 (0.23/0.28); M0: 7.8 (6.4/8.4); M1: 30.2 (25/31)). Plasma viscosity (PV) was increased as well (1.865 (1.857/1.912) mPa s) compared to other mammalian species. These parameters would indicate a decrease in blood fluidity in elephants. However, erythrocyte rigidity (LORCA, Mechatronics) was decreased, which in contrast, has a promotive effect on peripheral perfusion. Blood rheology of the elephants was determined by a high whole blood and plasma viscosity as the result of pronounced erythrocyte aggregation and high plasma protein concentration. Thus, in the terminal vessels the resistance to flow will be increased. The large erythrocytes, which might impede blood flow further due to geometrical reasons, however, had a pronounced flexibility. We conclude that the effect of the increased inner resistance to peripheral blood flow was counteracted by the decreased rigidity of the erythrocytes to enable an adequate blood flow in African elephants.     

In-vitro and in-vivo electrophysiologic effects of encainide

The intracellular electrophysiologic effects of encainide (E) and its main metabolite, O-desmethyl-encainide (ODE), were studied in guinea-pig papillary muscle preparations and related to the in-vivo electrophysiologic effects observed after intravenous (IV) infusion of E in 11 patients undergoing electrophysiologic study (EPS).At equipotent concentrations of E and ODE, frequency-dependent reductions in V_max studied at pacing rates of 30–180 beats/min ranged from-11.5% to-53%, with maximum reductions of-53% and-47%, respectively at the highest frequency. The kinetics of onset of use-dependent V_max reduction were slower for ODE than for E at each studied pacing rate. The kinetics of total recovery from use-dependent block were still slower (120 seconds for E and 300 seconds for ODE at a 90 beats/min pacing rate).