Biomedical subjects
Publications and source records attributed to T Martens.
The electrochemical oxidation of anticancer drugs ifosfamide and cyclophosphamide produced in high yield methoxylated analogues of the key hydroxy-metabolites of these oxazaphosphorine prodrugs. The cytotoxicity of these compounds was evaluated, and found to be as high as the hydroxy-metabolite.
A 290-million-year-old reptilian skeleton from the Lower Permian (Asselian) of Germany provides evidence of abilities for cursorial bipedal locomotion, employing a parasagittal digitigrade posture. The skeleton is of a small bolosaurid, Eudibamus cursoris, gen. et sp. nov. and confirms the widespread distribution of Bolosauridae across Laurasia during this early stage of amniote evolution. E. cursoris is the oldest known representative of Parareptilia, a major clade of reptiles.
OBJECTIVE: To compare the elimination of fluconazole by continuous veno-venous haemodiafiltration (CVVHD) and continuous veno-venous haemofiltration (CVVH) at different dosages. INTERVENTION: Patients received doses of 400 mg (n=3), 600 mg (n=1) or 800 mg (n=2) fluconazole as a short-time infusion once a day. Patients underwent CVVHD the first day and CVVH the second day. CVVHD and CVVH were performed using an acrylonitrile hollow-fibre filter at a constant blood flow of 90 ml/min and a substitution flow of 1000 ml/h (predilution). During CVVHD, the dialysate flow was 1000 ml/h. Ultrafiltration rates were 1158+/-90.5 ml/h during CVVHD and 1167+/-81.6 ml/h. Serum and ultrafiltrate/dialysate concentrations of fluconazole were determined on nine occasions over 24 h. PARTICIPANTS: Six critically ill patients with acute renal failure (ARF) and serious fungal infection. RESULTS: Extracorporeal clearance (CVVHD 30.5+/-6.0 ml/min, CVVH 17.5+/-4.0 ml/min) and total clearance of fluconazole (CVVHD 37.9+/-4.4 ml/min, CVVH 25.3+/-6.5 ml/min) were significantly higher during CVVHD (P < 0.05). During CVVHD, the sieving coefficient (S(CVVHD)) was 0.88 (range 0.54-1) and the elimination half-life (t1/2) was 14.8-35.1 h. During CVVH, the S(CVVH) was 0.96 (range 0.56-1.02) and t1/2 was 24.0-51.6 h. CONCLUSIONS: A daily dosage of 400-800 mg fluconazole is recommended in the treatment of life-threatening fungal infections in critically ill patients undergoing CVVHD since the clearance of CVVHD may considerably exceed the clearance in patients with normal renal function, which is about 20 ml/min. Drug monitoring is highly recommended for these patients.
The results of a study using questionnaires at two measuring points in high schools in North Germany are reported and discussed. This article analyzes the students' reasons and motivation for more or less environmentally friendly behavior. An integrated theoretical concept of motivation for human action formed the theoretical basis. The action genesis process was subdivided into the phases of forming motives, intentions and volition. Following a presentation of this theoretical concept and its definition with regard to competing and compatible theoretical hypotheses, the methodological procedure is described whereby the various motivation structures of the pupils questioned were analyzed. Mixed distribution models were used which allow modelling of complex multivariate relationships (latent class analysis and mixed Rasch models). The results show strong positive relationships among the variables of the motivation, the intention and the volition phases, but with isolated area-specific motivation patterns and moderator effects of certain cognitive variables.
The main factors influencing the microbial stability of chilled prepared food products for which there is an increased consumer interest-are temperature, pH, and water activity. Unlike the pH and the water activity, the temperature may vary extensively throughout the complete production and distribution chain. The shelf life of this kind of foods is usually limited due to spoilage by common microorganisms, and the increased risk for food pathogens. In predicting the shelf life, mathematical models are a powerful tool to increase the insight in the different subprocesses and their interactions. However, the predictive value of the sigmoidal functions reported in the literature to describe a bacterial growth curve as an explicit function of time is only guaranteed at a constant temperature within the temperature range of microbial growth. As a result, they are less appropriate in optimization studies of a whole production and distribution chain. In this paper a more general modeling approach, inspired by system theory concepts, is presented if for instance time varying temperature profiles are to be taken into account. As a case study, we discuss a recently proposed dynamic model to predict microbial growth and inactivation under time varying temperature conditions from a system theory point of view. Further, the validity of this methodology is illustrated with experimental data of Brochothrix thermosphacta and Lactobacillus plantarum. Finally, we propose some possible refinements of this model inspired by experimental results.
The diversity and quantities of vacuum packed and vacuum cooked prepared meals and menu components are rapidly growing on the European market. Because of the minimal heat processing, high water activity, absence of preservatives, and the use of many different often exotic ingredients, these products have a high risk potential. For this reason, Anglo-Saxon governments and industries are very sceptical about the safety of "sous vide" products. Industrial practice, as well as parallel tests and recent studies on inoculated packs have shown that, in many cases, it is more a potential than a real risk. Quality is the primary concern for "sous vide" products, and safety must be guaranteed by the application of the Hazard Analysis Critical Control Point (HACCP) concept, along with an adequate combination of different inhibitory factors (temperature of heating and cooling, pH, incorporation of starter cultures, bacteriocins and some particular enzymes).
To reduce the time required for product development, to avoid expensive experimental tests, and to quantify safety risks for fresh products and the consequence of processing there is a growing interest in computer aided food process design. This paper discusses the application of hybrid object-oriented and rule-based expert system technology to represent the data and knowledge of microbial experts and food engineers. Finite element models for heat transfer calculation routines, microbial growth and inactivation models and texture kinetics are combined with food composition data, thermophysical properties, process steps and expert knowledge on type and quantity of microbial contamination. A prototype system has been developed to evaluate changes in food composition, process steps and process parameters on microbiological safety and textual quality of foods.
The kinetic profile for the decomposition of ditiocarb sodium salt in aqueous solution was achieved with UV-visible absorption spectrometry. The kinetic profile indicates that the decomposition reaction is hydrogen ion-catalyzed over the entire 4-10 pH range and enables the determination of the value of the acid-base equilibrium constant (Ka = 4.0.10(-4) at 5 degrees C). Decomposition of ditiocarb produces volatile carbon disulfide, exclusive of hydrogen sulfide, as shown with electrochemical methods. This feature is of interest from a toxicological point of view.
Many sigmoidal functions to describe a bacterial growth curve as an explicit function of time have been reported in the literature. Furthermore, several expressions have been proposed to model the influence of temperature on the main characteristics of this growth curve: maximum specific growth rate, lag time, and asymptotic level. However, as the predictive value of such explicit models is most often guaranteed only at a constant temperature within the temperature range of microbial growth, they are less appropriate in optimization studies of a whole production and distribution chain. In this paper a dynamic mathematical model--a first-order differential equation--has been derived, describing the bacterial population as a function of both time and temperature. Furthermore, the inactivation of the population at temperatures above the maximum temperature for growth has been incorporated. In the special case of a constant temperature, the solution coincides exactly with the corresponding Gompertz model, which has been validated in several recent reports. However, the main advantage of this dynamic model is its ability to deal with time-varying temperatures, over the whole temperature range of growth and inactivation. As such, it is an essential building block in (time-saving) simulation studies to design, e.g., optimal temperature-time profiles with respect to microbial safety of a production and distribution chain of chilled foods.
In order to gain an interpretation of the schistosomicidal effect of 4-methyl 5-(2-pyrazinyl)-1,2-dithiole-3-thione (oltipraz), chemical, electrochemical and enzymatic hypotheses are discussed from a pharmacological standpoint. The enzymatic hypothesis is in good agreement with experimental results which ascertain that oltipraz behaves as a prodrug.
A decrease in glutathione reductase (GR) activity was observed in Schistosoma mansoni isolated from oltipraz(OPZ)-treated mice. Yeast and Schistosoma mansoni GR-activity was inhibited by OPZ derivatives only. These OPZ-derivatives showed in vitro schistosomicidal activity. Using yeast GR and dithiolium salts of OPZ, time-dependent inactivation and gel chromatography experiments revealed irreversible inhibition dependent on the redox state of the enzyme. Binding of radiolabelled ([3H]7-methyl-8-methylthio-pyrrolo[1,2-a]pyrazine disulphide 1b) obtained from OPZ was observed using exclusion chromatography and equilibrium dialysis. These results indicate that GR can be considered as the target of schistosomicidal activity of OPZ. The lack of inhibitory activity of OPZ and dithiole-thione analogues, and the potent activity of the corresponding pyrrolo-pyrazine derivatives, is consistent with the hypothesis that OPZ is a pro-drug.