A biophysical approach to the optimisation of dendritic-tumour cell electrofusion

Electrofusion of tumour and dendritic cells (DCs) is a promising approach for production of DC-based anti-tumour vaccines. Although human DCs are well characterised immunologically, little is known about their biophysical properties, including dielectric and osmotic parameters, both of which are essential for the development of efficient electrofusion protocols. In the present study, human DCs from the peripheral blood along with a tumour cell line used as a model fusion partner were examined by means of time-resolved cell volumetry and electrorotation. Based on the biophysical cell data, the electrofusion protocol could be rapidly optimised with respect to the sugar composition of the fusion medium, duration of hypotonic treatment, frequency range for stable cell alignment, and field strengths of breakdown pulses triggering membrane fusion. The hypotonic electrofusion consistently gave a tumour-DC hybrid rate of up to 19%, as determined by counting dually labelled fluorescent hybrids in a microscope. This fusion rate is nearly twice as high as that usually reported in the literature for isotonic media. The experimental findings and biophysical approach presented here are generally useful for the development of efficient electrofusion protocols, especially for rare and valuable human cells.     

Comparing the efficiency of sensory systems: A biophysical approach

This article is an exposition of the view that the complexity of biological systems permitsintensive (as opposed toextensive) research on any level. Specifically, (i) new views onstructural information theory used to compare the efficiency of sensory systems in measuring the theoretically derived maximum amount of information in the sensory environment, (ii) the concept of the brain system involving the amygdaloid complex and the hypothalamus as acoupled harmonic oscillator system, and (iii) the concept of the cerebral cortex as ane.m. interferometric (holographic) structure, are outlined.     

Application of multivariate resolution methods to the study of biochemical and biophysical processes

Multivariate resolution methods make up a set of mathematical tools that may be applied to the analysis and interpretation of spectroscopic data recorded when monitoring a physical or chemical process with multichannel detectors. The goal of resolution methods is the recovery of chemical and/or physical information from the experimental data. Such data include, for example, the number of intermediates present in a reaction, the rate or equilibrium constants, and the spectra for each one of those intermediates. Multivariate resolution methods have been shown to be useful for the study of biophysical and biochemical processes such as folding/unfolding of proteins or nucleic acids. The present article reviews the most frequently used resolution methods, the limitations on their use, and their latest applications in protein and nucleic acid research.     

A biophysical approach to the Spatial Function of eye movements extraocular proprioception and the vestibulo-ocular reflex

The eyeball and the extraocular muscles are used as a paradigm to design a linear spatial model of a single joint with a redundant set of muscles. On the basis of this model relations are derived between orientation, torque, motor commands, and proprioceptive signals. These relations show that the tenet underlying the tensorial interpretation of neural signals in sensorimotor systems does not have general validity. A mechanism is proposed to show how proprioception may play a role in optimizing the coordination of muscles during spatial tasks. Further, a new concept is suggested that allows one to predict the neural connectivities mediating the redundant spatial vestibulo-ocular reflex. This concept has the advantage of minimizing both sensorial error and motor effort.     

Redox regulation of cellular processes: A biophysical model and experiment

A model for the redox regulation of the functional state of the cell has been constructed on the basis of representation of electron transfer processes by equivalent electric circuits. The mechanism of action of redox-active molecules on biosystems has been discussed in terms of circuit theory. A method for determining the parameters of cellular redox sensors has been proposed. It has been established that the concentration and redox potential of compounds entering the cell are the main regulatory parameters of redox signals for the cell. It has been experimentally shown that the calcium response to hydrogen peroxide in rat C6 glioma cells and human FL amnion cells depends on the redox-buffer capacity of cells.     

A flow cytometric approach to assessing the environmental and physiological status of phytoplankton

Individual particle analysis using a flow cytometer (FCM) was made on natural phytoplankton communities in oligotrophic waters. Our objective was to develop an assay to yield information on the nutrient history of individual cells using FCM. Results from nutrient assays showed that both biovolume and total red fluorescence are affected by the nutrient conditions in the incubator. The light effect was measured by changes in the chlorophyll content of the cells, and after the 12 h incubation the cells seemed well adapted to the light conditions. The estimated kinetic constant for the chlorophyll synthesis averaged 1.5 x 1.0(-2) h-1, whereas the growth rate calculated from the changes in the cell numbers changed from 0.14 to greater than 2.5 doubling per day. The smallest size fraction presented the highest growth rate (greater than 2.5 doublings per day). The relationship between the total red fluorescence as estimated with the FCM and the biovolume revealed that the cells from the 2 m samples at the beginning of the experiment were probably nutrient limited. Important changes in the size of the cells under nutrient limitation were also observed. The FCM data suggest that the FCM is a valuable tool for estimating the relative growth response and nutritional state of natural phytoplankton populations.     

A structured approach to design and operation of biotransformation processes

A structured approach to design and operation of biotransformation (bioconversion) processes, based on previous case studies, has been developed. This requires knowledge of the key characteristics of a biotransformation which determine the constraints on process selection. The approach is illustrated for five biotransformations, two enzymic and three microbial. Some generic problems such as low water solubility and volatility of reactants, reactant and product toxicity have been identified. The microblal oxidations of toluene and fluorobenzene to toluenecis-glycol and fluorocatechol respectively byPseudomonas putida have been used to illustrate how these constraints may be overcome by addition of tetradecane as a second liquid phase, use of a membrane oxygenator and introduction ofin situ product removal.     

A systematic approach to the simulation of short-term processes in the plant-environment complex

Abstract. A conceptual framework is presented for modelling short-term processes in the plant and its environment as an integrated system. Flows of water, water vapour, heat, momentum, CO₂, soluble carbohydrate and phosphorus are all described by equations of the same general type, i.e. in terms of diffusivity-type parameters, capacities and potential gradients. A representative volume of the crop is divided horizontally into layers and vertically between crop and environment for treatment by a finite-difference method. Vertical flow occurs in the atmosphere, soil, stems and larger roots, andilateral flow between leaves and air, and between finer roots and soil. The interception of direct sunlight and the flux densities of downward and upward diffuse radiation within layers are calculated by a step-wise procedure.
The conversions of materials within the plant are treated as functions of appropriate state variables. Schemes for carbon and phosphorus provide for flow to and from the translocation system, and for photosynthesis, respiration and growth.
A model of a fully-established lucerne crop is described and the sensitivity of model performance to changes in a number of parameter values explored. Simulation runs under varying conditions indicate realistic prediction of diurnal trends.     

A scaling approach to spatial variability in early diagenetic processes

The traditional approach to understanding early diagenetic processes in sediments has generally been to analyze pore water and solid phases from a single core on depth scales of centimeters. The resulting data is then modeled using the approximations of lateral homogeneity and steady-state conditions. However, the continuing advancement of the field of benthic biogeochemistry and development of new microelectrode analytic techniques are clearly demonstrating that in many sedimentary environments a more sophisticated approach to measure the spatial and temporal variability is necessary. Although no one approach is appropriate for all situations, a scaling method is presented, with examples, in this study for determining appropriate sampling intervals in time and space that has considerable utility for investigating early changes in sediment geochemistry in complex natural systems. This approach is derived from scaling techniques that have been developed by physical oceanographers for the study of processes in the water column where many analogous sampling problems are encountered.     

Determination of parameter identifiability in nonlinear biophysical models: A Bayesian approach

A major goal of biophysics is to understand the physical mechanisms of biological molecules and systems. Mechanistic models are evaluated based on their ability to explain carefully controlled experiments. By fitting models to data, biophysical parameters that cannot be measured directly can be estimated from experimentation. However, it might be the case that many different combinations of model parameters can explain the observations equally well. In these cases, the model parameters are not identifiable: the experimentation has not provided sufficient constraining power to enable unique estimation of their true values. We demonstrate that this pitfall is present even in simple biophysical models. We investigate the underlying causes of parameter non-identifiability and discuss straightforward methods for determining when parameters of simple models can be inferred accurately. However, for models of even modest complexity, more general tools are required to diagnose parameter non-identifiability. We present a method based in Bayesian inference that can be used to establish the reliability of parameter estimates, as well as yield accurate quantification of parameter confidence.     

A graph-based approach to investigating the influence of the landscape on population spread processes

Modelling of landscape connectivity is a key point in the study of the movement of populations within a given landscape. For studies focused on the preservation of biodiversity, graph-based methods provide an interesting framework to investigate the landscape influence on population spread processes. Such an approach is described here, based on the mapping of landscape categories in habitat patches, including a diachronic data set describing the population spread within the habitat patches. A minimum planar graph was built by computing spatial distances between all pairs of neighbouring patches. From this structure, two types of analysis are proposed: one focused on the links of the graph and consists in correlating spatial distances and gap indicators computed from the diachronic data. The other was based on the correlations between population data and connectivity metrics at the patch level. As an example, this approach was applied to the spread of the fossorial water vole on the Jura plateau (France), with annual population data covering eleven years from 1989 to 2000. Link analysis allowed to find an optimal set of resistance values used in the least-cost distances computations, and thus to build a relevant graph. From this graph, patch analysis displayed a cyclic correlation between a metric based on potential dispersal flux and the population density, outlining the strong role of landscape connectivity in the population spread. The present study clearly shows that landscape modelling and graph-based approach can produce parameters which are consistent with field observations and thus pave the way to simulating the effect of landscape modification on population dynamics.     

About a new biophysical approach to total vaccination of humans and animals

Biophysics - A new method of total nonspecific vaccination of humans and animals is presented, based on the experience of practical use of a powerful light pulse for air disinfection in laboratory...     

Interplay of mycolic acids,antimycobacterial compounds and pulmonary surfactant membrane: A biophysical approach to disease

This work focuses on the interaction of mycolic acids (MAs) and two antimycobacterial compounds (Rifabutin and N′-acetyl-Rifabutin) at the pulmonary membrane level to convey a biophysical perspective of their role in disease. For this purpose, accurate biophysical techniques (Langmuir isotherms, Brewster angle microscopy, and polarization-modulation infrared reflection spectroscopy) and lipid model systems were used to mimic biomembranes: MAs mimic bacterial lipids of the Mycobacterium tuberculosis (MTb) membrane, whereas Curosurf® was used as the human pulmonary surfactant (PS) membrane model. The results obtained show that high quantities of MAs are responsible for significant changes on PS biophysical properties. At the dynamic inspiratory surface tension, high amounts of MAs decrease the order of the lipid monolayer, which appears to be a concentration dependent effect. These results suggest that the amount of MAs might play a critical role in the initial access of the bacteria to their targets. Both molecules also interact with the PS monolayer at the dynamic inspiratory surface. However, in the presence of higher amounts of MAs, both compounds improve the phospholipid packing and, therefore, the order of the lipid surfactant monolayer. In summary, this work discloses the putative protective effects of antimycobacterial compounds against the MAs induced biophysical impairment of PS lipid monolayers. These protective effects are most of the times overlooked, but can constitute an additional therapeutic value in the treatment of pulmonary tuberculosis (Tb) and may provide significant insights for the design of new and more efficient anti-Tb drugs based on their behavior as membrane ordering agents.