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Biomedical subjects

Michael Klein

Publications and source records attributed to Michael Klein.

29 records · Page 2Linked to original sources
PubMed2003

Six-item screening tool is sensitive for dementia.

This study provides excellent evidence that a 6-item screening tool based on orientation to date and a 3-item short-term recall is sensitive for dementia. Clinicians should consider using this simple screen in an outpatient setting, keeping in mind that the final diagnosis of dementia is a clinical judgment after full assessment and that this screen was not intended for use in following patients over time. Caution also should be exercised in extending these results to patients in the hospital, who were not included in this trial.

Comment↗
PubMed2002

Synthesis and structure of a stabilized 10-membered cyclic enediyne.

The synthesis and structure of an acetal protected 10-membered cyclic enediyne-1,2-diol rac-10 is reported. The conformational constrain of the unsaturated macrocycle by the acetal protection group prevents the thermal cyclization reaction of the endiyne during synthesis and purification.

Journal Article↗
PubMed2002

Biliary dyskinesia in children.

Biliary dyskinesia (BD) is a well-recognized cause of chronic abdominal pain in adults, but is less common in children. We reviewed our experience with the diagnosis, treatment, and follow-up in a group of children treated with cholecystectomy from March 1995 to October 2000. We identified children with chronic upper abdominal pain, normal ultrasonography (US), and delayed cholecystokinin (CCK)-stimulated gallbladder emptying (<35%). All other diagnostic tests for their abdominal pain were reviewed. Their treatment, surgical intervention, and outcome were recorded. During the study period, 74 cholecystectomies were performed in our institution, 10 (13.5%) of them for BD. The duration of symptoms ranged between 1 and 60 months (mean 22). All patients had a normal plain abdominal radiograph, normal US, and delayed gallbladder ejection fraction (EF). All were treated by elective laparoscopic cholecystectomy. Symptoms were completely relieved in all patients during the follow-up period, which ranged between 9 and 24 months (mean 12.8). Cholecystectom should be considered in children with chronic upper-abdominal pain and delayed EF on CCK-HIDA scintigraphy. Laparoscopic cholecystectomy is the procedure of choice in these patients.

Abdominal Pain↗
PubMed2002

Endoplasmic reticulum calcium pool depletion-induced apoptosis is coupled with activation of the death receptor 5 pathway.

Thapsigargin (TG), by inducing perturbations in cellular Ca(2+) homeostasis, has been shown to induce apoptosis. The molecular mechanisms of Ca(2+) perturbation-induced apoptosis are not fully understood. In this study, we demonstrate for the first time that TG-mediated perturbations in Ca(2+) homeostasis are coupled with activation of the death receptor 5 (DR5)-dependent apoptotic pathway in human cancer cells. TG selectively upregulated DR5 but had no effect on the expression of the other TRAIL receptor, DR4. TG also upregulated the expression of the DR5 ligand TRAIL (tumor necrosis factor-related apoptosis inducing ligand), albeit in a cell-type specific manner. TG-induced apoptosis has been shown to be associated with activation of the mitochondrial pathway. We found that TG upregulation of DR5 and TRAIL was coupled with caspase 8 activation and Bid cleavage, suggesting that the TG-regulated DR5 pathway could be linked to the mitochondrial pathway. TG enhanced not only DR5 mRNA stability but also increased induction of the DR5 genomic promoter-reporter gene. The TG-induced increase in DR5 expression appeared to occur as a consequence of TG-induced endoplasmic reticulum (ER) Ca(2+) pool depletion. Thus, we report our novel findings that ER Ca(2+) pool depletion-induced apoptotic signals are mediated, at least in part, via a DR5-dependent apoptotic pathway and there appears to be a cross-talk between the death receptor and mitochondrial pathways.

Apoptosis↗
PubMed2002

Use of a pigtail catheter to engage a difficult internal mammary artery.

Increasing use of bilateral internal mammary arteries for coronary surgery will increase the number of interventions in these grafts. Such interventions may be technically challenging because of often tortuous and angulated vessels. We describe a technique to intubate an acutely angulated right internal mammary artery that was inaccessible with conventional catheters.

Catheterization↗
PubMed2002

Origins and diversification of sulfate-respiring microorganisms.

If the diversification of microbial life can be depicted as a single tree, as inferred by comparative sequencing of ribosomal RNAs, this could provide a framework for defining the order of emergence of new metabolic pathways. However, recent recognition that lateral gene transfer has been a significant force in microbial evolution has created uncertainty about the interpretation of taxonomies based on gene sequences. In this context, the origins and evolution of sulfate respiration will be evaluated considering the evolutionary history of a central enzyme in this process, the dissimilatory sulfite reductase. These studies suggest at least two major lateral transfer events during the early diversification of sulfate respiring microorganisms. The high sequence conservation of this enzyme has also provided a mechanism to directly explore the natural diversity of sulfate-respiring organisms using molecular techniques, avoiding the bias of culture-based identification. These studies suggest that the habitat range and evolutionary diversity of this key functional group of organisms is greater than now appreciated.

Evolution, Molecular↗
PubMed2000

The carboxyl terminus of the Bacillus subtilis SecA is dispensable for protein secretion and viability.

The Escherichia coli secretion-dedicated chaperone SecB targets a subset of proteins to the translocase by interacting with the carboxyl (C-) terminus of SecA. This region of SecA is highly conserved in Eubacteria, but despite its presence in the Bacillus subtilis SecA, the B. subtilis genome does not appear to contain a gene for a clear homologue of SecB. Deletion of the C-terminus of the B. subtilis SecA yields cells that have normal viability, but that exhibit a response reminiscent of oxidative stress and the loss of a number of secretory proteins from the culture supernatant. Semi-quantitative RT-PCR demonstrates that these proteins are expressed at lower levels. The C-terminus of SecA fused to glutathione S:-transferase (GST) specifically binds a cytosolic protein, termed MrgA. This protein has been reported to function in relation to oxidative stress, but deletion of the mrgA gene does not result in a secretion defect nor does it cause an oxidative stress response. It is concluded that the C-terminus of the B. subtilis SecA is not essential for secretion and viability.

Adenosine Triphosphatases↗
PubMedDate not supplied

Pesticide volatilization from soil: lysimeter measurements versus predictions of European registration models.

A comparison was drawn between model predictions and experimentally determined volatilization rates to evaluate the volatilization approaches of European registration models. Volatilization rates of pesticides (14C-labeled parathion-methyl, fenpropimorph, and terbuthylazine and nonlabeled chlorpyrifos) were determined in a wind-tunnel experiment after simultaneous soil surface application on Gleyic Cambisol. Both continuous air sampling, which quantifies volatile losses of 14C-organic compounds and 14CO2 separately, and the detection of soil residues allow for a mass balance of radioactivity of the 14C-labeled pesticides. Recoveries were found to be > 94% of the applied radioactivity. The following descending order of cumulative volatilization was observed: chlorpyrifos > parathion-methyl > terbuthylazine > fenpropimorph. Due to its high air-water partitioning coefficient, nonlabeled chlorpyrifos was found to have the highest cumulative volatilization (44.4%) over the course of the experiment. Volatilization flux rates were measured up to 993 microg m(-2) h(-1) during the first hours after application. Parameterization of the Pesticide Emission Assessment at Regional and Local Scales (PEARL) model and the Pesticide Leaching Model (PELMO) was performed to mirror the experimental boundary conditions. In general, model predictions deviated markedly from measured volatilization rates and showed limitations of current volatilization models, such as the uppermost compartment thickness, making an enormous influence on predicted volatilization losses. Experimental findings revealed soil moisture to be an important factor influencing volatilization from soil, yet its influence was not reflected by the model calculations. Future versions of PEARL and PELMO ought to include improved descriptions of aerodynamic resistances and soil moisture dependent soil-air partitioning coefficients.

Environmental Monitoring↗
PubMedDate not supplied

An improved description of pesticide volatilization: refinement of the pesticide leaching model (PELMO).

The consideration of pesticide volatilization from soil surfaces as an integral component of pesticide fate models is of importance, especially as part of the Predicted Environmental Concentrations (PEC) models used in the registration procedures for pesticides. The Pesticide Leaching Model (PELMO), which is used in the European registration process, was modified to allow for a reliable prediction of volatilization from soil. The previous PELMO version was upgraded by improving the spatiotemporal discretization at the soil surface, improving the empirical description of temperature dependence of Henry's law constants and including increased sorption of pesticides in dry soils. Comparison of predictions with experimental findings revealed the improvements of PELMO to contribute to a more realistic reflection of measurements, particularly at initial stages of the studies. The broad range of literature values of Henry's law constants was shown to have a significant effect on predicted volatilization fluxes. As a main refinement, the tendency of pesticides toward enhanced volatilization under moist conditions was correctly calculated by the improved model. Variations between model predictions and measurements were due to a lack of experimental data on soil sorption under dry conditions and indicated the need for further calibration of the model. The description of water content in the top layer was subject to uncertainty, which was exemplified by an overestimation of soil moisture during the last days of the field study. Thus, future model improvement will be dependent on experimental support to obtain more detailed information on soil-air-water partitioning of pesticides in the top soil layer.

Forecasting↗