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Biomedical subjects

Marc Zimmermann

Publications and source records attributed to Marc Zimmermann.

16 recordsLinked to original sources

Integration and mining of malaria molecular, functional and pharmacological data: how far are we from a chemogenomic knowledge space?

The organization and mining of malaria genomic and post-genomic data is important to significantly increase the knowledge of the biology of its causative agents, and is motivated, on a longer term, by the necessity to predict and characterize new biological targets and new drugs. Biological targets are sought in a biological space designed from the genomic data from Plasmodium falciparum, but using also the millions of genomic data from other species. Drug candidates are sought in a chemical space containing the millions of small molecules stored in public and private chemolibraries. Data management should, therefore, be as reliable and versatile as possible. In this context, five aspects of the organization and mining of malaria genomic and post-genomic data were examined: 1) the comparison of protein sequences including compositionally atypical malaria sequences, 2) the high throughput reconstruction of molecular phylogenies, 3) the representation of biological processes, particularly metabolic pathways, 4) the versatile methods to integrate genomic data, biological representations and functional profiling obtained from X-omic experiments after drug treatments and 5) the determination and prediction of protein structures and their molecular docking with drug candidate structures. Recent progress towards a grid-enabled chemogenomic knowledge space is discussed.

Animals↗

Towards assessing the sympathovagal balance.

Exact assessment of the autonomic nervous system's (ANS) activity by means of heart rate variability (HRV) is a long-standing challenge. Although many techniques have been proposed to take up the challenge, none ever proposed a rationale for the approach behind the technique or a satisfying discrimination of the two activities which underlie the autonomic control of HRV. We here propose a new method, providing both an understanding of the discrimination's nature and a framework which we believe leads to a thorough assessment of the sympathovagal balance, as a trajectory between points in a well-chosen space. The methodology assumes tools from scale invariance/covariance physics. The sympathovagal balance is obtained on a beat-to-beat basis with the dynamics portrayed through a trajectory. Furthermore, universal trajectories are sought which would comprehensively describe the effect of atropine and isoproterenol injections on systems underlying the heart pace variations. Non-invasive assessment of the respective activities of the sympathetic and parasympathetic subsystems of the ANS would be possible through cardiac autonomic measurements.

Atropine↗

[Management of atrial flutter in 2006].

Typical or common atrial flutter is a frequent cardiac arrhythmia related to a macroreentrant circuit located entirely within the right atrium. Risks associated with this supraventricular arrhythmia include 1 to 1 conduction with extremely rapid ventricular rates, tachycardia-mediated cardiomyopathy and thromboembolic events. Treatment of choice of atrial flutter is radiofrequency catheter ablation of the cavo-tricuspid isthmus, and this form of treatment may be considered either during the first episode or at the time of the first recurrence of atrial flutter. Anticoagulant therapy is the rule in the presence of atrial flutter because this arrhythmia favors thromboembolic complications and because atrial flutter is frequently associated with atrial fibrillation.

Anticoagulants↗

Permanent form of junctional reciprocating tachycardia in adults: peculiar features and results of radiofrequency catheter ablation.

AIM: PJRT occurs predominantly in infants and children and is limited to small series in adults. The aim of this study was to describe the clinical presentation, electrophysiological characteristics, feasibility and safety of radiofrequency ablation, and the long-term prognosis in a large group of adult patients with the permanent form of junctional reciprocating tachycardia (PJRT). METHODS AND RESULTS: Forty-nine adult patients (22 male and 27 female; mean age 43+/-16) with a diagnosis of PJRT confirmed at electrophysiological study were included. Eight patients (16%) presented with tachycardia-induced cardiomyopathy (TIC). Ventricular rate was 146+/-30 bpm. The arrhythmia was permanent or incessant in 23/49 cases (47%) and paroxysmal in 26/49 (53%). A significant correlation was found between symptom duration and tachycardia rate (r(2)=0.12, P=0.01). The accessory pathway (AP) was located in the right posteroseptal region in 37 cases (76%) and in atypical sites in 12 cases (24%). Patients with the incessant or permanent form of PJRT had longer duration of symptoms, more frequently TIC and a slower tachycardia rate. Radiofrequency catheter ablation was initially successful in 46 cases (94%) without any serious complication. Long-term success rate was 100% (49/49 patients) in the absence of any antiarrhythmic drug treatment (mean follow-up 49+/-38 months). Regression of TIC was observed in all cases (8/8). CONCLUSION: PJRT in adults is often paroxysmal (53%), and the retrograde slowly conducting, decremental AP is not infrequently in a non-posteroseptal location. Radiofrequency catheter ablation is highly effective and should be considered as the treatment of first choice in adult patients with PJRT.

Adolescent↗

Demonstration of in silico docking at a large scale on grid infrastructure.

WISDOM stands for World-wide In Silico Docking On Malaria. First step toward enabling the in silico drug discovery pipeline on a grid infrastructure, this CPU consuming application generating large data flows was deployed successfully on EGEE, the largest grid infrastructure in the world, during the summer 2005. 46 million docking scores were computed in 6 weeks. The proposed demonstration presents the submission of in silico docking jobs at a large scale on the grid. The demonstration will use the new middleware stack gLite developed within the EGEE project.

Europe↗

Multiple-ligand-based virtual screening: methods and applications of the MTree approach.

We present a novel approach for ligand-based virtual screening by combining query molecules into a multiple feature tree model called MTree. All molecules are described by the established feature tree descriptor, which is derived from a topological molecular graph. A new pairwise alignment algorithm leads to a consistent topological molecular alignment based on chemically reasonable matching of corresponding functional groups. These multiple feature tree models find application in ligand-based virtual screening to identify new lead structures for chemical optimization. Retrospective virtual screening with MTree models generated for angiotensin-converting enzyme and the alpha1a receptor on a large candidate database yielded enrichment factors up to 71 for the first 1% of the screened database. MTree models outperformed database searches using single feature trees in terms of hit rates and quality and additionally identified alternative molecular scaffolds not included in any of the query molecules. Furthermore, relevant molecular features, which are known to be important for affinity to the target, are identified by this new methodology.

Adrenergic alpha-1 Receptor Antagonists↗

Adenosine stimulates anabolic metabolism in developing castor bean (Ricinus communis L.) cotyledons.

In previous experiments it was shown that Castor-bean (Ricinus communis) endosperm releases carbohydrates, amino acids and nucleoside derivatives, which are subsequently imported into the developing cotyledons (Kombrink and Beevers in Plant Physiol 73:370-376, 1983). To investigate the importance of the most prominent nucleoside adenosine for the metabolism of growing Ricinus seedlings, we supplied adenosine to cotyledons of 5-days-old seedlings after removal of the endosperm. This treatment led to a 16% increase in freshweight of intact seedlings within 16 h, compared to controls. Using detached cotyledons, we followed uptake of radiolabelled adenosine and identified 40% of label in solubles (mostly ATP and ADP), 46% incorporation in RNA and 2.5% in DNA, indicating a highly active salvage pathway. About 7% of freshly imported adenosine entered the phloem, which indicates a major function of adenosine for cotyledon metabolism. Import and conversion of adenosine improved the energy content of cotyledons as revealed by a substantially increased ATP/ADP ratio. This effect was accompanied by slight increases in respiratory activity, decreased levels of hexose phosphates and increased levels of fructose-1,6-bisphosphate and triose phosphates. These alterations indicate a stimulation of glycolytic flux by activation of phosphofructokinase, and accordingly we determined a higher activity of this enzyme. Furthermore the rate of [(14)C]-sucrose driven starch biosynthesis in developing castor-bean is significantly increased by feeding of adenosine. In conclusion, our data indicate that adenosine imported from mobilizing endosperm into developing castor-bean cotyledons fulfils an important function as it promotes anabolic reactions in this rapidly developing tissue.

Adenosine↗

Sympathovagal balance prior to onset of repetitive monomorphic idiopathic ventricular tachycardia.

Repetitive monomorphic idiopathic (RMI) ventricular tachycardia (VT) occurs typically in patients without structural heart disease, originates in most cases from the right ventricular outflow tract, and can often be induced by exercise or isoproterenol. This study analyzed the dynamic changes in autonomic tone immediately before the spontaneous onset of RMIVT using frequency-domain heart rate variability (HRV) indices. We analyzed the ambulatory electrocardiographic recordings from 6 men and 8 women (mean age: 43 +/- 18 years; mean number of VT runs per day: 134 +/- 213; mean VT rate: 194 +/- 40 bpm; median VT run length: 4 cycles) with RMIVT. A total of 36 clusters of nonsustained episodes of RMIVT preceded by >/=1 hour of sinus rhythm without VT were analyzed (25 minutes before the onset of RMIVT divided into five 5-minute periods; 8 minutes before onset of RIMVT divided into eight 1-minute periods). During 25 minutes preceding the onset of VT, the mean RR interval decreased from 767 +/- 118 to 723 +/- 105 ms (P = 0.015) and the low-frequency (LF)/high-frequency (HF) ratio increased from 2.24 +/- 0.79 to 2.49 +/- 1.0 (P = 0.03). During the 8 minutes before VT onset, the mean RR interval decreased from 745 +/- 118 to 718 +/- 102 ms (P = 0.001) and the LF components increased from 205 +/- 72 to 253 +/- 113 ms (P = 0.014). No change in HF components was observed during the 25 or 8 minutes periods preceding the RMIVT onset. The changes in HRV indices suggest a strong time-dependent primary activation of sympathetic tone prior to the occurrence of RMIVT. Withdrawal of vagal tone does not appear essential to the initiation of RMIVT clusters.

Adult↗

Information extraction in the life sciences: perspectives for medicinal chemistry, pharmacology and toxicology.

Information extraction approaches have been successfully applied to mine the scientific literature in biology and medicine. So far, the main focus of research and development in this domain was on the recognition and extraction of gene and protein names in the context of molecular biology and genome research and on disease names and other medical terms in the context of clinical research. Similar to biology and medical sciences, medicinal chemistry, pharmacology and toxicology are descriptive sciences. However, information extraction approaches in these disciplines encounter a number of problems that are specific to the fact that these scientific areas are essentially centred at chemical compounds and their structures. In this review, we will give a short overview on general information extraction strategies in the life sciences and we will introduce new approaches to apply information extraction to the domain of pharmacology, medicinal chemistry and toxicology. Finally, we will emphasize on how information extraction approaches will support public and commercial research in medicinal chemistry, pharmacology and toxicology by linking information on chemical structures to biological information.

Biological Science Disciplines↗

Novel technologies for virtual screening.

There are several methods for virtual screening of databases of small organic compounds to find tight binders to a given protein target. Recent reviews in Drug Discovery Today have concentrated on screening by docking and by pharmacophore searching. Here, we complement these reviews by focusing on virtual screening methods that are based on analyzing ligand similarity on a structural level. Specifically, we concentrate on methods that exploit structural properties of the complete ligand molecules, as opposed to using just partial structural templates, such as pharmacophores. The in silico procedure of virtual screening (VS) and its relationship to the experimental procedure, HTS, is discussed, new developments in the field are summarized and perspectives on future research are offered.

Combinatorial Chemistry Techniques↗

EST-analysis of the thermo-acidophilic red microalga Galdieria sulphuraria reveals potential for lipid A biosynthesis and unveils the pathway of carbon export from rhodoplasts.

When we think of extremophiles, organisms adapted to extreme environments, prokaryotes come to mind first. However, the unicellular red micro-alga Galdieria sulphuraria (Cyanidiales) is a eukaryote that can represent up to 90% of the biomass in extreme habitats such as hot sulfur springs with pH values of 0-4 and temperatures of up to 56 degrees C. This red alga thrives autotrophically as well as heterotrophically on more than 50 different carbon sources, including a number of rare sugars and sugar alcohols. This biochemical versatility suggests a large repertoire of metabolic enzymes, rivaled by few organisms and a potentially rich source of thermo-stable enzymes for biotechnology. The temperatures under which this organism carries out photosynthesis are at the high end of the range for this process, making G. sulphuraria a valuable model for physical studies on the photosynthetic apparatus. In addition, the gene sequences of this living fossil reveal much about the evolution of modern eukaryotes. Finally, the alga tolerates high concentrations of toxic metal ions such as cadmium, mercury, aluminum, and nickel, suggesting potential application in bioremediation. To begin to explore the unique biology of G. sulphuraria , 5270 expressed sequence tags from two different cDNA libraries have been sequenced and annotated. Particular emphasis has been placed on the reconstruction of metabolic pathways present in this organism. For example, we provide evidence for (i) a complete pathway for lipid A biosynthesis; (ii) export of triose-phosphates from rhodoplasts; (iii) and absence of eukaryotic hexokinases. Sequence data and additional information are available at http://genomics.msu.edu/galdieria.

Algal Proteins↗

Effect of chronic amiodarone therapy on excitable gap during typical human atrial flutter.

INTRODUCTION: Class I antiarrhythmic drugs increase duration of the excitable gap (EG) during typical atrial flutter whereas intravenous class III drugs decrease the EG. The effect of chronic oral amiodarone therapy on the EG is unknown. METHODS AND RESULTS: EG was prospectively determined by introducing a premature stimulus and analyzing the response pattern during typical atrial flutter in 30 patients without antiarrhythmic drugs and in 20 patients under chronic oral amiodarone therapy. EG was calculated by the difference between the longest coupling interval leading to resetting and the effective atrial refractory period (EARP). A fully EG was defined by the portion of EG where the response curve of the return cycles was flat. A partially EG was defined by the portion of EG where the return cycle increases while coupling interval decreases. A resetting response curve was constructed by plotting the duration of the return cycle against the value of the coupling interval. Cycle length (CL; 222 +/- 17 vs 267 +/- 20 msec, P < 0.0001), EARP (128 +/- 16 vs 152 +/- 18 msec, P < 0.0001), and EG (54 +/- 19 vs 70 +/- 21 msec, P = 0.01) were significantly longer in patients taking amiodarone than in controls. Compared to CL, the relative part of the EARP (57 +/- 7 vs 57 +/- 6%, P = 0.96) and EG (24 +/- 7 vs 26 +/- 8%, P = 0.41) were comparable in both groups. The fully EG was larger in patients under chronic amiodarone therapy than in controls (39 +/- 21 vs 26 +/- 20 msec, P = 0.03). Neither duration of the partially EG (28 +/- 15 vs 31 +/- 15 msec, P = 0.42) nor slope of the ascending portion of the resetting response curve (1.15 +/- 0.5 vs 1.13 +/- 0.4 msec/msec, P = 0.71) differed between the two groups. CONCLUSION: EG in patients under chronic amiodarone therapy is significantly larger than in controls, mainly because of a longer fully EG. This observation may be explained by opposite effects on conduction velocity and refractoriness.

Administration, Oral↗

Autonomic tone variations before the onset of paroxysmal atrial fibrillation.

BACKGROUND: Mechanisms favoring the occurrence of paroxysmal atrial fibrillation (PAF) are complex and poorly defined. This study was designed to analyze dynamic changes in autonomic tone preceding the onset of PAF in a large group of patients. METHODS AND RESULTS: Holter tapes from 77 unselected consecutive patients (63 men and 14 women aged 58+/-12 years) with PAF were analyzed. A total of 147 episodes of sustained AF (>30 minutes) were recorded and submitted to time-domain and frequency-domain heart rate variability analyses; 6 periods were studied using repeated measures ANOVA: the 24-hour period, the hour preceding PAF, and the 20 minutes before PAF divided into four 5-minute periods. In the time-domain analyses, a linear decrease in mean RR interval from 925+/-16 to 906+/-16 ms (P<0.0002) was observed before the onset of PAF, together with a significant increase in the standard deviation of NN intervals from 65+/-4 to 70+/-4 ms (P<0.02). In the frequency-domain analyses, a significant increase in high-frequency (HF, HF-NU) components was observed before PAF (P<0.001 and P<0.0001, respectively), together with a progressive decrease in low-frequency components (LF, LF-NU) (P<0.0001 and P<0.004, respectively). The low/high frequency ratio showed a linear increase until 10 minutes before PAF, followed by a sharp decrease immediately before PAF, suggesting a primary increase in adrenergic tone followed by a marked modulation toward vagal predominance. No difference was observed in these heart rate variability changes between patients with "lone" PAF and patients with structural heart disease. CONCLUSIONS: The occurrence of PAF greatly depends on variations of the autonomic tone, with a primary increase in adrenergic tone followed by an abrupt shift toward vagal predominance.

Adrenergic beta-Antagonists↗

Atrial tachycardia with recipient-to-donor atrioatrial conduction and isthmus-dependent donor atrial flutter in a patient after orthotopic heart transplantation. Successful treatment by radiofrequency catheter ablation.

Atrial arrhythmias are common after orthotopic heart transplantation. We report an unusual case of a patient after heart transplantation with 2 types of atrial arrhythmias: one was a macro-reentrant, incisional, recipient-atrial tachycardia conducted to the donor atrium, and the other was a common-type, isthmus-dependent atrial flutter in the donor atrium. These 2 arrhythmias were successfully treated with selective radiofrequency catheter ablation.

Atrial Flutter↗