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PubMed1992

Human placental transfer of zinc: normal characteristics and role of ethanol.

The fetal alcohol syndrome is primarily an impairment of growth and development. Zinc deficiency also causes abnormal fetal growth. Moreover, alcohol has been shown in some rodent studies to impair placental transport of zinc. The purpose of this investigation was to define better normal human placental zinc transport and the effects of alcohol on this process. To do this we employed the isolated perfused single cotyledon human term placental model, as well as the cultured human cytotrophoblast. In the perfused placental studies, it was shown that zinc is transferred by the placenta very slowly, about 6% of the rate of transport of antipyrine, a freely diffusible marker. The transfer is comparable in both directions, maternal to fetal and the reverse. Zinc does not cross the placenta against a zinc concentration gradient, in either direction. Rather there is good evidence of significant uptake (storage) of the zinc by the placenta on the recirculating compartment side of gradient studies. Moreover, when the perfusion fluid was low (0.2 g/100 ml) in albumin, about twice as much zinc accumulated in the perfused cotyledon and there was less zinc in the maternal compartment, as compared to perfusion with ten-fold higher (2.0 g/100 ml) albumin concentrations. Thus, ligand binding in the perfusate importantly influences placental zinc uptake. Interestingly, however, the increased placental binding of zinc did not translate into greater transfer of zinc to the fetal compartment. Thus, normal zinc transfer is slow, equal bidirectionally, and dependent on ligand binding in perfusate and placenta.(ABSTRACT TRUNCATED AT 250 WORDS)

Culture Techniques↗
PubMed1998

Relation between diffuse axonal injury and internal head structures on blunt impact.

Diffuse axonal injury (DAI) is a severe head injury, which exhibits symptoms of consciousness disturbance and is thought to occur through rotational angular acceleration. This paper analyzes the occurrence of DAI when direct impacts with translational accelerations are applied to two-dimensional head models. We constructed a human model reproducing the human head structure, as well as modified human models with some internal head structures removed. Blunt direct impacts were applied from a lateral direction to the bottom of the third ventricle, considered to be the center of impact, using an impactor. The analysis was done by comparing the macroscopic manifestation of DAI with the shear stress as the engineering index. In the analytical data obtained from the human model, shear stresses were concentrated on the corpus callosum and the brain stem, in the deep area. This agrees with regions of the DAI indicated by small hemorrhages in the corpus callosum and the brain stem. The analytical data obtained by the modified human models show that the high shear stress on the corpus callosum is influenced by the falx cerebri, while the high shear stress on the brain stem is influenced by the tentorium cerebelli and the shape of the brain. These results indicate that DAI, generally considered to be influenced by angular acceleration, may also occur through direct impact with translational acceleration. We deduced that the injury mechanism of DAI is related to the concentration of shear stress on the core of the brain, since the internal head structures influence the impact stress concentration.

Acceleration↗
PubMed1999

Intranuclear trafficking of messenger RNA.

Within the nucleus, protein-encoding genes are transcribed into messenger RNA by RNA polymerase II. Messenger RNAs migrate to the cytoplasm, but before reaching their final destination the primary transcripts must undergo a series of modifications that include 5'-capping, splicing, and 3'-cleavage/polyadenylation. Errors in these processing events can originate aberrant products that, if translated, would produce abnormal proteins. Therefore, it is not surprising that eukaryotes have evolved a surveillance mechanism that recognizes and rapidly degrades aberrant mRNAs. Recent experiments provide exciting insights into how proper mRNAs are distinguished and selected for export. Transcription by RNA polymerase II is directly coupled to pre-mRNA processing, and the mechanism that targets the processing machinery to the polymerase complex suggests a model for co-transcriptional proofreading. Furthermore, there is evidence that at least some mRNAs move randomly throughout the nucleus, presumably by free diffusion. In this light, retention of aberrant mRNAs by the transcription/processing machinery is crucial to prevent their diffusion to the nuclear pores and eventual translocation to the cytoplasm.

Animals↗
PubMed2006

[Stochastic model for the spatial visualization of particle-deposition patterns in the lung and their significance in lung medicine].

The present paper provides a detailed description of an extension of the Monte Carlo computer model IDEAL, which enables the generation of spatial particle deposition patterns in the human lung. Randomly determined particle trajectories are transformed to a Cartesian coordinate system within which the orientation of the trachea corresponds to the z-direction. At the same time, the determination of particle deposition sites is carried out by application of a grid composed of specific volume elements (voxel). The calculation of particle deposition are based on the physical mechanisms of Brownian diffusion, sedimentation, and inertial impaction. After their storage in a matrix, the deposition data are subject to graphical processing. This allows the presentation of spatial particle distribution patterns (3d-density plots) and of the lung surface itself as well as the generation of two-dimensional distributions by sectioning the three-dimensional structures at pre-defined positions. The results of different model simulations (variation of particle size and breathing conditions) are discussed in detail.

Computer Simulation↗
PubMedDate not supplied

Photodynamic therapy of established prostatic adenocarcinoma with TOOKAD: a biphasic apparent diffusion coefficient change as potential early MRI response marker.

The goal of this study was to examine the use of diffusion-weighted magnetic resonance imaging (DW-MRI) for the assessment of early progression of photodamage induced by Pd-bacteriopheophorbide (TOOKAD)-based photodynamic therapy (PDT). TOOKAD is a novel second-generation photosensitizer for PDT of solid tumors developed in our laboratory and presently under clinical trials for prostate cancer (PC) therapy. Using the subcutaneous human prostate adenocarcinoma WISH-PC14 xenografts in nude mice as a model, a unique biphasic change in the apparent diffusion coefficient (ADC) was observed within the first 24 hours post-PDT, with initial decrease followed by an increase in ADC. Using DW-MRI, this phenomenon enables the detection of successful tumor response to PDT within 7 hours posttreatment. This process was validated by direct, histological, and immunohistochemical examinations and also by evaluation of serum prostate-specific antigen (PSA) levels that decreased significantly already 7 hours posttreatment. In vitro studies of multicellular cell spheroids confirmed a PDT-induced decrease in ADC, suggesting that lipid peroxidation (LPO) significantly contributes to ADC decline observed after PDT. These results demonstrate that TOOKAD-based PDT successfully eradicates prostate adenocarcinoma xenografts and suggests DW-MRI to be useful for the detection of early tumor response and treatment outcome in the clinical setting.

Adenocarcinoma↗
PubMed1979

A viscosity model of polyacrylamide gel electrophoresis.

In current theories of polyacrylamide gel electrophoresis, the idea prevails that molecular sieving relies on different accessibility of volume fractions and of cross-sectional area fractions (denoted "pores") to different-sized ions due to the effect of "geometric exclusion". This correlates with the assumption that all elements of a polyacrylamide network occupy fixed and unchangeable positions thus forcing colliding macro-ions to diffuse laterally in order to find an "accessible pore" and to resume motion in direction of the electrical field. However, the alternative conception would be equally well justified, i.e. the assumption that polyacrylamide chains represent smooth obstacles cleared aside under the electrokinetic pressure of a macro-ion. This explanation would even be preferable with respect to the molecular sieving effects occurring in solutions of "liquid polyacrylamide". Yet no theory exists as to describe such effects in quantitative terms. In the present article, a parameter is defined and discussed, which can be estimated by experiment, and which seems to be apt to characterize local resistivity of polymer structures against dislocation and deformation: the "fractional specific resistance". Definition of this parameter is based on the model of a "viscosity-emulsion" composed of two interpenetrating liquid compartments which are characterized by different levels of hydrodynamic friction and the spatial dimensions of which are inferred from Ogston's theory. This concept of "localized viscosity" may also serve as a link between theories of molecular sieving and of "macroscopic viscosity" of flexible polymers. The data of Morris, formerly taken as verifications of the "rigid-pore" concept, are now interpreted in terms of four factors responsible for sizediscrimination: collision frequency, duration of single contacts, size-dependent frictional force, and the extent of cooperation among fibres, due to crosslinking and to simultanous contacts of several fibres to a single macro-ion. Some functions relevant for problems of molecular weight determination by gel electrophoresis are discussed in relation to the suggested model.

Acrylamides↗
PubMed1994

On the "door-corridor" model of gel electrophoresis. III. The gel constant and resistance, and the net charge, friction, diffusion and electrokinetic force of the migrating molecules.

The door-corridor model of gel electrophoresis enabled an estimation of the net charge of DNA molecules run in various gels. When the runs were carried out in Trisacetate-EDTA buffer having a concentration from 10 to 120 mM, the net charge in 1% agarose gel varied from 1.1 to 0.58 e per base pair. The friction between migrating molecules and gel fibers was dependent on the gel type and concentration, as well as the electric field strength and temperature during electrophoresis. In the 123 to 1,474 bp size range, the friction in 1% agarose changed from 1.91 to 378.03 x 10(-10) N.m-1.s. It was found that the friction per 123 bp DNA segment is not constant, but raises with size. The gel resistance force increases at higher electric field strengths, indicating that elastic forces govern the migration of macromolecules through gels. In the gels studied, the friction, and therefore thermal diffusion, of DNA and protein-SDS complexes scale with from 2.20 to 2.32 power of size. The ratio of thermally induced diffusion and velocity in various gels shows that there is a profound reduction of diffusion compared to velocity with increasing DNA size. This is directly linked to the high exponent relating friction and size. The high resolving power of gel electrophoresis can be correlated to the difference between the frictional coefficients of a diffusing and migrating macromolecule.

DNA↗
PubMed1998

Therapeutic options directed against platelet activating factor, eicosanoids and bradykinin in sepsis.

Various autacoids, including the eicosanoids, platelet activating factor (PAF) and bradykinin, have been implicated in the pathogenesis of sepsis and septic shock. The precise role of these compounds as mediators of the diffuse inflammatory state characteristic of sepsis remains to be determined, but, in animal models, beneficial effects have been observed as a result of treatment with various inhibitors of eicosanoid biosynthesis or antagonists of PAF or bradykinin receptors. To date, however, it has been impossible to translate these encouraging results from animal models into convincingly positive results in the clinical setting.

Bradykinin↗
PubMed1997

Glutamine, alanine or glycine repeats inserted into the loop of a protein have minimal effects on stability and folding rates.

Natural proteins can contain flexible regions in their polypeptide chain. We have investigated the effects of glycine, alanine and glutamine repeats on the stability and folding of a protein by inserting stretches of 7 to 13 residues into a suitable position in a model system, the chymotrypsin inhibitor-2 (CI2). This folds by residues (1-40) docking with residues (41-64) to form a folding nucleus. The peptides GQ4GM, GQ6GM, GQ8GM, GQ10GM, GA2SA4SA2GM and G3SG4SG3M were inserted after residue 40. The stability of the mutant proteins changes only weakly with chain length and nature of insertion, suggesting that the presence of unstructured polypeptide chains in a protein does not have a great energetic penalty. This has implications in catalysis, for example, where floppy regions have been noted in active sites, and in DNA transcription where activators, transcription factors and intermediary proteins all show long repeats of glycine/serine and/or glutamine, which are thought to be important for function. We find that the rate of folding is very insensitive to the length of the linker. The changes in rate are close to those predicted from polymer theory for the loss of configuration entropy on closing a loop. This implies that all the diffusion steps are relatively rapid.

Alanine↗
PubMed2006

Brownian dynamics simulation of directional sliding of histone octamers caused by DNA bending.

Chromatin-remodeling complexes such as SWI/SNF and RSC of yeast can perturb the structure of nucleosomes in an ATP-dependent manner. Experimental results prove that this chromatin remodeling process involves DNA bending. We simulate the effect of DNA bending, caused by chromatin-remodeling complexes, on directional sliding of histone octamers by Brownian dynamics simulation. The simulation results show that, after a DNA loop being generated at the side of a nucleosome, the histone octamer slides towards this DNA loop until the loop disappears. The DNA loop size is an important factor affecting the process of directional sliding of the histone octamer.

Anisotropy↗
PubMed1977

Back-diffusion--fact or fiction?

Alterations in the concentration of acid in gastric juice secreted at different flow rates and disappearance of acid from the gastric lumen, when the gastric mucosa is exposed to acid luminal contents, have been interpreted as indicating "back-diffusion" of acid into the gastric mucosa from the luminal contents. The loss of acid from the gastric contents increases when the mucosa is exposed to certain drugs or is diseased, giving rise to the suggestion that the increased degree of "back-diffusion" of acid indicates mucosal damage, reflecting a breakdown of the gastric mucosal "barrier" to back-diffusion of acid from the gastric lumen. The change in the "barrier" properties of the gastric mucosa has been found to be associated with change in the electrical properties of the mucosa, so that alterations of the transmucosal potential difference has been considered to denote gastric mucosal damage. The case for every one of these hypotheses and for their underlying assumptions is discussed and found wanting for lack of direct evidence.

Animals↗
PubMed1995

Long-term chemotaxis studies on adherent cells: effect of platelet-derived growth factor-BB on human vascular smooth muscle cell migration.

Several chemotaxis methods have been developed which allow the study of different aspects of cell migration. The major limitation of such methods is the lack of a sustained chemotactic signal. Long-term chemotaxis phenomena which are known to take place in vivo have remained largely uninvestigated. Ways to maintain sustained chemotactic signals were sought and the used to investigate the long-term chemotactic effect of platelet-derived growth factor BB (PDGF-BB) on human vascular smooth muscle cells (HVSMC). PDGF-BB was adsorbed onto microcarrier beads and then embedded in agar. PDGF-BB diffusion was slow and a high and sustained local concentration was maintained in the agar. When PDGF-BB-loaded beads embedded in agar were placed at the edge of a tissue culture dish with HVSMC plated in the center, preferential movement was observed in the direction of the PDGF-BB source. This method was subsequently used to study directional movement of HVSMC arising from explants. This report demonstrates that PDGF-BB if present in an anisotropic concentration induces directional cell movement from such explants. By allowing the study of the effect of sustained chemotactic signals upon cultured cells or cells arising from explants, this method may provide a suitable model for investigating in vivo chemotaxis phenomena.

Cell Movement↗
PubMed2005

Kinetic modelling of the intestinal transport of sarafloxacin. Studies in situ in rat and in vitro in Caco-2 cells.

The absorption kinetics of sarafloxacin, as a model of fluoroquinolone structure, were studied in the rat small intestine and in Caco-2 cells. The objective of the study was to investigate the mechanistic basis of the drug's intestinal transport in comparison with other members of the fluoroquinolone family and to apply a mathematical modelling approach to the transport process. In the rat small intestine, sarafloxacin showed dual mechanisms of intestinal absorption with a passive diffusional component and an absorptive carrier-mediated component. The characteristics of the animal study design made it suitable for population analysis, thus allowing the accurate estimation of transport parameters and their inter and intra-individual variances. The transport system in the rat model was ATP-dependent, as sodium azide was able to decrease the absorption rate constant in a concentration-dependent fashion. The inhibition mechanism of sodium azide was modelled based on its ATP depletion capacity. The rationale of this approach was to consider the inhibitor-carrier interaction as a concentration- dependent response. This interaction was accurately described by a non-competitive mechanism. In Caco-2 cells, sarafloxacin showed a concentration dependent permeability in both directions apical to basal, and basal to apical. The permeability values and ratios of permeability values at different concentrations suggested the presence of two carriers (absorption and efflux carriers). The passive diffusion component in both systems was compared to that predicted by the absorption-partition correlation, previously established for two series of fluoroquinolones. The discrepancy between the experimental and predicted value suggested the presence of an efflux mechanism similar to that already described for other fluoroquinolones. The differences and similarities of the in situ and the in vitro results are discussed as well as the usefulness of the modelling approach.

Adenosine Triphosphate↗
PubMed1994

Kinetic and equilibrium studies of porphyrin interactions with unilamellar lipidic vesicles.

The interaction of deuteroporphyrin with dimyristoylphosphatidylcholine unilamellar vesicles of various sizes (ranging from 38 to 222 nm) has been studied using a stopped flow with fluorescence detection. Beside the kinetics of porphyrin incorporation into vesicles, the transfer of porphyrin from vesicles to human serum albumin has been investigated both experimentally and theoretically. The effects of both vesicle and albumin concentrations indicate that the transfer proceeds through the aqueous phase. It is governed by the rate of incorporation of porphyrin into the outer vesicle hemileaflet (kon), by the exit to the bulk aqueous medium (koff), and by the association (kas) and dissociation (kdis) constants relative to albumin. In both systems studied, a slower transbilayer flip-flop accounts for the biphasic character of the kinetics. This model is strongly supported by the effects of vesicle size, temperature, and cholesterol. The dependence of kon on the vesicle size indicates that the incorporation is diffusion controlled. The constant koff is found to be closely coupled to the phase state of the bilayer. The transbilayer flip-flop rate constant is approximately the same in both directions (approximately 0.4 s-1 at 32 degrees C and pH 7.4). It is strongly affected by the presence of cholesterol in vesicles and by the temperature, with a sharp enhancement around the phase transition. With the exception of very small vesicles obtained by sonication, no influence of the vesicle size on the flip-flop rate was observed. An accelerating effect of tetrahydrofuran, used to improve the solubility of porphyrin, has been noted. Steady-state measurements and kinetics results were in excellent agreement. The interest of systems involving albumin as a scavenger to extract important rate constants, is emphasized.

Deuteroporphyrins↗
PubMed2003

Fairweather and ESID: contemporary impact and a legacy for the twenty-first century.

This paper illustrates how the articles in this special issue demonstrate the central values, research, and action principles inherent in Fairweather's ESID model. The programs described in these articles address earlier social problems in new forms (e.g., previously, institutionalized mentally ill patients and now, the homeless mentally ill) and new issues (e.g., HIV prevention). Dissemination of innovative programs is abundant, but only recently has research begun in earnest to study the critical processes of dissemination. Moreover, Fairweather has pointed us in important, but yet unrealized directions for how to pursue a theory of social change on the basis of ecological concepts, innovative research methods and data analytic techniques, and salient change agent behaviors and principles.

Diffusion of Innovation↗
PubMed2003

Comparison between mono- and bi-exponential models for reaction kinetics in the immunoradiometric assay of neuron-specific enolase.

This paper studies the kinetics of the antigen-antibody reactions involved in the analytical determination of neuron-specific enolase (NSE) by means of radiometric immunoassay (IRMA). For the global process, kinetics were found to be dependent on analyte and labelled antibody concentrations, such dependence fitting with the models described in previous papers. Viscosity results clearly indicate its negative influence on the direct reaction rate. Ionic strength shows noticeable but not too relevant effects, which suggests that the variation caused by the glycerol addition is not due to the influence of the dielectric constant of the solutions used. The effect of temperature shows activation parameters similar to the viscous flow energy of water, which suggests diffusion control for the global process. The analysis of the kinetic data of the experiences conducted can be explained by admitting that the antigen-antibody binding takes place through two different binding site types.

Immunoradiometric Assay↗
PubMedDate not supplied

Flow and diffusion measurements in natural porous media using magnetic resonance imaging.

Flow and diffusion of water in natural porous media, quartz sand, and calcareous gravel were measured using a 1.5-T clinical magnetic resonance tomograph. The spatial resolution of the dynamic measurements was 1.32 x 1.32 x 5 mm3, and the time between two cross-sectional measurements was approximately 10 s. The measured coefficients of molecular diffusion for water were in good agreement with theoretical data. Flow was measured without any tracer at velocities between 0.15 and 6.67 mm/s. The results, based on a calibration within one part of the column, were in good agreement with data obtained from a tracer experiment and from a numerical model. It was possible to measure the flow velocity in larger pores and preferential flow paths directly. The results of the flow measurements in smaller pores reflected the mean velocity within that volume element. In that case the obtained values were close to the average linear velocity. Since the time resolution is high a monitoring of flow processes is possible. The pore space was imaged with a spatial resolution of 0.5 x 0.5 x 0.5 mm3. Here, the porosity of pores that are larger than 0.2 mm can be measured directly; for smaller pores a calibration is necessary.

Calibration↗
PubMed1998

Dynamic patterns of retinoic acid synthesis and response in the developing mammalian heart.

Retinoic acid (RA) has been implicated in cardiac morphogenesis by its teratogenic effects on the heart, although its role in normal cardiogenesis remains unknown. To define the parameters of RA action in cardiac morphogenesis, we analyzed the patterns of ligand synthesis, response, and inactivation in the developing mouse heart. Activation of a lacZ transgene controlled by an RA response element (RARE) was compared to the localization of the retinaldehyde-oxidizing dehydrogenase RALDH2, the earliest RA synthetic enzyme in the mouse embryo, and to the expression of a gene encoding an RA-degrading enzyme (P450RA). We observed that RALDH2 localization and RA response were virtually superimposable throughout heart development. Initially, both RALDH2 and RARE-LacZ activity were restricted to the sinus venosa in unlooped hearts, but were high in the dorsal mesocardium, while P450RA expression was restricted to the endocardium. Later stages were characterized by a sequential, noncontiguous progression of RALDH2 accumulation and RA response, from the sinus venosa to atria, dorsal-medial conotruncus, aortic arches, and the epicardium. This dynamic pattern of RA response was a direct result of localized RALDH2, since hearts of cultured embryos were uniformly competent to respond to an exogenous RA challenge. These observations support a model in which the influence of endogenous RA on heart development depends upon localized presentation of the ligand, with only limited diffusion from the source of its synthesis.

Aldehyde Oxidoreductases↗