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51.
Burkhardt D Wiesner J Stoesser N Ramharter M Uhlemann AC Issifou S Jomaa H Krishna S Kremsner PG Borrmann S 《International journal for parasitology》2007,37(7):777-785
Clindamycin is safe and effective for the treatment of Plasmodium falciparum malaria, but its use as monotherapy is limited by unacceptably slow initial clinical response rates. To investigate whether the protracted action is due to an accumulative, time of exposure-dependent or a delayed effect on parasite growth, we studied the in vivo and in vitro pharmacodynamic profiles of clindamycin against P. falciparum. In vivo, elimination of young, circulating asexual parasite stages during treatment with clindamycin displayed an unusual biphasic kinetic: a plateau phase was followed by a precipitated decline of asexual parasite densities to nearly undetectable levels after 72 and 60 h in adult patients and asymptomatic children, respectively, suggesting an uninhibited capacity to establish a second, but not third, infectious cycle. In vitro, continuous exposure of a laboratory-adapted P. falciparum strain to clindamycin with concentrations of up to 100 microM for two replication cycles (96 h) did not produce inhibitory effects of >50% compared with drug-free controls as measured by the production of P. falciparum histidine-rich protein II (PfHRP2). PfHRP2 production was completely arrested after the second cycle (96-144h) (>10,000-fold decrease of mean half-inhibitory concentrations measured at 96-144h compared to 48-96h). Furthermore, incubation with clindamycin during only the first (0-48h) versus three (0-144h) parasite replication cycles led to comparable inhibition of PfHRP2 production in the third infectious cycle (96-144h) (mean IC(99) of 27 and 22nM, respectively; P=0.2). When parasite cultures were exposed to different concentrations of clindamycin ranging from 50 to 1,000nM for 72h and followed up in an experiment designed to simulate a typical 3-day treatment regimen, parasitaemia was initially suppressed below the microscopic detection threshold. Nonetheless, parasites reappeared in a dose-dependent manner after removal of drug at 72h but not in continuously drug-exposed controls. The delayed, but potent, antimalarial effect of clindamycin appears to be of greatest potential benefit in new combinations of clindamycin with rapidly acting antimalarial combination partners. 相似文献
52.
The GcpE enzyme converts 2-C-methyl-D-erythritol-2,4-cyclodiphosphate (MEcPP) into (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) in the penultimate step of the DOXP pathway for isoprene biosynthesis. Purification of the enzyme under exclusion of air leads to a preparation that contains solely [4Fe-4S] clusters. Kinetic studies showed that in the presence of the artificial reductant dithionite and MEcPP a new transient iron-sulfur-based signal is detected in electron paramagnetic resonance (EPR) spectroscopy. Similarity of this EPR signal to that detected in ferredoxin:thioredoxin reductase indicates that during the reaction an intermediate is directly bound to the active-site cluster. 相似文献
53.
在韩国境内Potentilla fragarioides var.sprengeliana的遗传多样 … 总被引:1,自引:0,他引:1
根据22个等位酶位点遗传变异,探讨了韩国境内委陵菜(Potentilla fragarioides L.var.sprengeliana)的遗传多样性和种群结构。酶位点的多态位点百分比为59.1%。种和种群水平上的遗传多样性比较高,分别为Hes=0.210,Hep=0.199;而种群的分化水平则相对较低(GST=0.074)。19个种群中随机交配的偏差为FIS=0.331。每代迁移数的间接估计 相似文献
54.
The synthesis and biological evaluation of novel N(6)-substituted adenosine derivatives is reported. The first series of compounds was obtained using an established procedure for the nucleophilic substitution of a 1-(6-chloro-purin-9-yl)-beta-D-1-deoxy-ribofuranose with various amines. In addition, attachment of two different amino-functionalised spacer arms at the N(6)-position of adenosine enabled derivatisation by an innovative polymer-assisted protocol. Thus, we were able to prepare three series of substituted derivatives that displayed activity versus the multiresistant Plasmodium falciparum strain Dd2 in cell culture experiments. 相似文献
55.
Reichenberg A Wiesner J Weidemeyer C Dreiseidler E Sanderbrand S Altincicek B Beck E Schlitzer M Jomaa H 《Bioorganic & medicinal chemistry letters》2001,11(6):833-835
The fosmidomycin derivative FR900098 represents an inhibitor of the 1-deoxy-D-xylulose 5-phosphate (DOXP) reductoisomerase with potent antimalarial activity. Prodrugs of FR900098 with increased activity after oral administration were obtained by chemical modification of the phosphonate moiety to yield phosphodiaryl esters. One diaryl ester prodrug demonstrated efficacy in mice infected with the rodent malaria parasite Plasmodium vinckei comparable to i.p. drug administration. 相似文献
56.
The complement system is a powerful tool of the innate immune system to eradicate pathogens. Both in vitro and in vivo evidence indicates that therapeutic anti-tumor monoclonal antibodies (mAbs) can activate the complement system by the classical pathway. However, the contribution of complement to the efficacy of mAbs is still debated, mainly due to the lack of convincing data in patients. A beneficial role for complement during mAb therapy is supported by the fact that cancer cells often upregulate complement-regulatory proteins (CRPs). Polymorphisms in various CRPs were previously associated with complement-mediated disorders.In this review the role of complement in anti-tumor mAb therapy will be discussed with special emphasis on strategies aiming at modifying complement activity. In the future, clinical efficacy of mAbs with enhanced effector functions together with comprehensive analysis of polymorphisms in CRPs in mAb-treated patients will further clarify the role of complement in mAb therapy. 相似文献
57.
Isoprenoid precursor biosynthesis occurs through the mevalonate or the methylerythritol phosphate (MEP) pathway, used i.e., by humans and by many human pathogens, respectively. In the MEP pathway, 2-C-methyl-d-erythritol-2,4-cyclo-diphosphate (MEcPP) is converted to (E)-1-hydroxy-2-methyl-but-2-enyl-4-diphosphate (HMBPP) by the iron-sulfur cluster enzyme HMBPP synthase (GcpE). The presented X-ray structure of the GcpE-MEcPP complex from Thermus thermophilus at 1.55 Å resolution provides valuable information about the catalytic mechanism and for rational inhibitor design. MEcPP binding inside the TIM-barrel funnel induces a 60° rotation of the [4Fe-4S] cluster containing domain onto the TIM-barrel entrance. The apical iron of the [4Fe-4S] cluster ligates with the C3 oxygen atom of MEcPP. 相似文献
58.
59.
B Altincicek A Kollas M Eberl J Wiesner S Sanderbrand M Hintz E Beck H Jomaa 《FEBS letters》2001,499(1-2):37-40
The mevalonate-independent 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis is essential in many eubacteria, plants, and the malaria parasite. Using genetically engineered Escherichia coli cells able to utilize exogenously provided mevalonate for isoprenoid biosynthesis by the mevalonate pathway we demonstrate that the lytB gene is involved in the trunk line of the MEP pathway. Cells deleted for the essential lytB gene were viable only if the medium was supplemented with mevalonate or the cells were complemented with an episomal copy of lytB. 相似文献
60.
In 1998–2000 a monitoring of the spectrum of Fusarium species on winter wheat was carried out in the Rhineland. The epidemic spread ofFusarium spp. on wheat plants during growing season was investigated as well as the grain contamination after harvest.F avenaceum was the Fusarium species isolated most frequently followed byF culmorum, F poae andF graminearum. Microdochium nivale occurred considerably only in 1998. Both, susceptibility and plant height of the cultivars were correlated to the incidence of Fusarium species /M nivale on harvested kernels; interactions with cropping intensities were detected. The incidence ofF poae seemed to be independent of the cultivar-specific Fusarium susceptibility. Despite the lack of disease symptoms, between growth stages 45–85 mycelium ofFusarium spp. was detectable in the leaves as well as conidia on the leaf surfaces. 相似文献