Alcanivorax borkumensis biofilms enhance oil degradation by interfacial tubulation

During the consumption of alkanes, Alcanivorax borkumensis will form a biofilm around an oil droplet, but the role this plays during degradation remains unclear. We identified a shift in biofilm morphology that depends on adaptation to oil consumption: Longer exposure leads to the appearance of dendritic biofilms optimized for oil consumption effected through tubulation of the interface. In situ microfluidic tracking enabled us to correlate tubulation to localized defects in the interfacial cell ordering. We demonstrate control over droplet deformation by using confinement to position defects, inducing dimpling in the droplets. We developed a model that elucidates biofilm morphology, linking tubulation to decreased interfacial tension and increased cell hydrophobicity.

Dual energy-band excitation from a low power Rh anode X-ray tube for the simultaneous determination of low Z and high Z elements (Na-U) using total-reflection X-ray fluorescence analysis (TXRF)

This article presents results from an experimental setup for a dual energy-band vacuum spectrometer for total-reflection X-ray fluorescence analysis allowing simultaneous efficient excitation of low, medium, and high Z elements. The spectrometer is equipped with an air-cooled 35 W low power Rh X-ray tube and a 17 mm² silicon drift detector with a thin 8 µm beryllium window. A Pd/B₄C multilayer monochromator is used at the same time as a Bragg reflector for Rh-Kα radiation and as a high-energy cut-off reflector above 5 keV, where the characteristic Rh-L radiation is totally reflected and present in the spectrum of the exciting radiation. This leaves one broad low energy band below 5 keV and one high energy band around the energy of Rh-Kα. As Rh-L radiation would be absorbed on its path through air, a new beam entrance system was designed in order to guide the Rh-L photons into the vacuum chamber for efficient excitation of low Z elements. With this setup, elements down to sodium (Z = 11, E = 1.04 keV) could be detected. First results are presented, and spectra obtained in air as well as in vacuum are compared and discussed. Detection limits in the range of 1000 µg/kg for Na and around 140 µg/kg for Mg were achieved using the NIST SRM 1640 (trace elements in water).

Spontaneous shear flow in confined cellular nematics

In embryonic development or tumor evolution, cells often migrate collectively within confining tracks defined by their microenvironment 1,2. In some of these situations, the displacements within a cell strand are antiparallel 3, giving rise to shear flows. However, the mechanisms underlying these spontaneous flows remain poorly understood. Here, we show that an ensemble of spindle-shaped cells plated in a well-defined stripe spontaneously develop a shear flow whose characteristics depend on the width of the stripe. On wide stripes, the cells self-organize in a nematic phase with a director at a well-defined angle with the stripe's direction, and develop a shear flow close to the stripe's edges. However, on stripes narrower than a critical width, the cells perfectly align with the stripe's direction and the net flow vanishes. A hydrodynamic active gel theory provides an understanding of these observations and identifies the transition between the non-flowing phase oriented along the stripe and the tilted phase exhibiting shear flow as a Fréedericksz transition driven by the activity of the cells. This physical theory is grounded in the active nature of the cells and based on symmetries and conservation laws, providing a generic mechanism to interpret in vivo antiparallel cell displacements.

Soft inclusion in a confined fluctuating active gel

We study stochastic dynamics of a point and extended inclusion within a one-dimensional confined active viscoelastic gel. We show that the dynamics of a point inclusion can be described by a Langevin equation with a confining potential and multiplicative noise. Using a systematic adiabatic elimination over the fast variables, we arrive at an overdamped equation with a proper definition of the multiplicative noise. To highlight various features and to appeal to different biological contexts, we treat the inclusion in turn as a rigid extended element, an elastic element, and a viscoelastic (Kelvin-Voigt) element. The dynamics for the shape and position of the extended inclusion can be described by coupled Langevin equations. Deriving exact expressions for the corresponding steady-state probability distributions, we find that the active noise induces an attraction to the edges of the confining domain. In the presence of a competing centering force, we find that the shape of the probability distribution exhibits a sharp transition upon varying the amplitude of the active noise. Our results could help understanding the positioning and deformability of biological inclusions, e.g., organelles in cells, or nucleus and cells within tissues.

Maximal Fluctuations of Confined Actomyosin Gels: Dynamics of the Cell Nucleus

We investigate the effect of stress fluctuations on the stochastic dynamics of an inclusion embedded in a viscous gel. We show that, in nonequilibrium systems, stress fluctuations give rise to an effective attraction towards the boundaries of the confining domain, which is reminiscent of an active Casimir effect. We apply this generic result to the dynamics of deformations of the cell nucleus, and we demonstrate the appearance of a fluctuation maximum at a critical level of activity, in agreement with recent experiments [E. Makhija, D. S. Jokhun, and G. V. Shivashankar, Proc. Natl. Acad. Sci. U.S.A. 113, E32 (2016)PNASA60027-842410.1073/pnas.1513189113].

Cell-like pressure sensors reveal increase of mechanical stress towards the core of multicellular spheroids under compression

The surrounding microenvironment limits tumour expansion, imposing a compressive stress on the tumour, but little is known how pressure propagates inside the tumour. Here we present non-destructive cell-like microsensors to locally quantify mechanical stress distribution in three-dimensional tissue. Our sensors are polyacrylamide microbeads of well-defined elasticity, size and surface coating to enable internalization within the cellular environment. By isotropically compressing multicellular spheroids (MCS), which are spherical aggregates of cells mimicking a tumour, we show that the pressure is transmitted in a non-trivial manner inside the MCS, with a pressure rise towards the core. This observed pressure profile is explained by the anisotropic arrangement of cells and our results suggest that such anisotropy alone is sufficient to explain the pressure rise inside MCS composed of a single cell type. Furthermore, such pressure distribution suggests a direct link between increased mechanical stress and previously observed lack of proliferation within the spheroids core.

Synchrotron radiation micro X-ray fluorescence spectroscopy of thin structures in bone samples: comparison of confocal and color X-ray camera setups

In the quest for finding the ideal synchrotron-radiation-induced imaging method for the investigation of trace element distributions in human bone samples, experiments were performed using both a scanning confocal synchrotron radiation micro X-ray fluorescence (SR-µXRF) (FLUO beamline at ANKA) setup and a full-field color X-ray camera (BAMline at BESSY-II) setup. As zinc is a trace element of special interest in bone, the setups were optimized for its detection. The setups were compared with respect to count rate, required measurement time and spatial resolution. It was demonstrated that the ideal method depends on the element of interest. Although for Ca (a major constituent of the bone with a low energy of 3.69 keV for its Kα XRF line) the color X-ray camera provided a higher resolution in the plane, for Zn (a trace element in bone) only the confocal SR-µXRF setup was able to sufficiently image the distribution.

A novel vacuum spectrometer for total reflection x-ray fluorescence analysis with two exchangeable low power x-ray sources for the analysis of low, medium, and high Z elements in sequence

The extension of the detectable elemental range with Total Reflection X-ray Fluorescence (TXRF) analysis is a challenging task. In this paper, it is demonstrated how a TXRF spectrometer is modified to analyze elements from carbon to uranium. Based on the existing design of a vacuum TXRF spectrometer with a 12 specimen sample changer, the following components were renewed: the silicon drift detector with 20 mm(2) active area and having a special ultra-thin polymer window allowing the detection of elements from carbon upwards. Two exchangeable X-ray sources guarantee the efficient excitation of both low and high Z elements. These X-ray sources were two light-weighted easily mountable 35 W air-cooled low-power tubes with Cr and Rh anodes, respectively. The air cooled tubes and the Peltier-cooled detector allowed to construct a transportable tabletop spectrometer with compact dimensions, as neither liquid nitrogen cooling for the detector nor a water cooling circuit and a bulky high voltage generator for the X-ray tubes are required. Due to the excellent background conditions as a result of the TXRF geometry, detection limits of 150 ng for C, 12 ng for F, and 3.3 ng for Na have been obtained using Cr excitation in vacuum. For Rh excitation, the detection limits of 90 pg could be achieved for Sr. Taking 10 to 20 μl of sample volume, extrapolated detection limits in the ng/g (ppb) range are resulting in terms of concentration.

Growth, homeostatic regulation and stem cell dynamics in tissues

The regulation of cell growth in animal tissues is a question of critical importance: most tissues contain different types of cells in interconversion and the fraction of each type has to be controlled in a precise way, by mechanisms that remain unclear. Here, we provide a theoretical framework for the homeostasis of stem-cell-containing epithelial tissues using mechanical equations, which describe the size of the tissue and kinetic equations, which describe the interconversions of the cell populations. We show that several features, such as the evolution of stem cell fractions during intestinal development, the shape of a developing intestinal wall, as well as the increase in the proliferative compartment in cancer initiation, can be studied and understood from generic modelling which does not rely on a particular regulatory mechanism. Finally, inspired by recent experiments, we propose a model where cell division rates are regulated by the mechanical stresses in the epithelial sheet. We show that pressure-controlled growth can, in addition to the previous features, also explain with few parameters the formation of stem cell compartments as well as the morphologies observed when a colonic crypt becomes cancerous. We also discuss optimal strategies of wound healing, in connection with experiments on the cornea.

The actin cortex as an active wetting layer

Using active gel theory we study theoretically the properties of the cortical actin layer of animal cells. The cortical layer is described as a non-equilibrium wetting film on the cell membrane. The actin density is approximately constant in the layer and jumps to zero at its edge. The layer thickness is determined by the ratio of the polymerization velocity and the depolymerization rate of actin.

Fluctuation-response theorem for the active noisy oscillator of the hair-cell bundle

The hair bundle of sensory cells in the vertebrate ear provides an example of a noisy oscillator close to a Hopf bifurcation. The analysis of the data from both spontaneous and forced oscillations shows a strong violation of the fluctuation-dissipation theorem, revealing the presence of an underlying active process that keeps the system out of equilibrium. Nevertheless, we show that a generalized fluctuation-dissipation theorem, valid for nonequilibrium steady states, is fulfilled within the limits of our experimental accuracy and computational approximations, when the adequate conjugate degrees of freedom are chosen.

Tissue dynamics with permeation

Animal tissues are complex assemblies of cells, extracellular matrix (ECM), and permeating interstitial fluid. Whereas key aspects of the multicellular dynamics can be captured by a one-component continuum description, cell division and apoptosis imply material turnover between different components that can lead to additional mechanical conditions on the tissue dynamics. We extend our previous description of tissues in order to account for a cell/ECM phase and the permeating interstitial fluid independently. In line with our earlier work, we consider the cell/ECM phase to behave as an elastic solid in the absence of cell division and apoptosis. In addition, we consider the interstitial fluid as ideal on the relevant length scales, i.e., we ignore viscous stresses in the interstitial fluid. Friction between the fluid and the cell/ECM phase leads to a Darcy-like relation for the interstitial fluid velocity and introduces a new characteristic length scale. We discuss the dynamics of a tissue confined in a chamber with a permeable piston close to the homeostatic state where cell division and apoptosis balance, and we calculate the rescaled effective diffusion coefficient for cells. For different mass densities of the cell/ECM component and the interstitial fluid, a treadmilling steady state due to gravitational forces can be found.

Bidirectional motion of motor assemblies and the weak-noise escape problem

We present a detailed calculation that enables us to estimate the reversal time of a molecular motor assembly that displays bidirectional motion in the limit of weak noise. We derive a Fokker-Planck equation by taking a large volume expansion of a master equation, and we consider a simple choice of transition rates that enables us to reduce the number of variables to 2. We use the Wentzell-Freidlin theory to define an effective nonequilibrium potential and analytically estimate the reversal time. We also present the results of stochastic simulations that match very well our simulation results.

Instabilities of monolayered epithelia: shape and structure of villi and crypts

We study theoretically the shapes of a dividing epithelial monolayer of cells lying on top of an elastic stroma. The negative tension created by cell division provokes a buckling instability at a finite wave vector leading to the formation of periodic arrays of villi and crypts. The instability is similar to the buckling of a metallic plate under compression. We use the results to rationalize the various structures of the intestinal lining observed in vivo. Taking into account the coupling between cell division and local curvature, we obtain different patterns of villi and crypts, which could explain the different morphologies of the small intestine and the colon.

Dynamical behavior of molecular motor assemblies in the rigid and crossbridge models

We present a detailed analysis of the dynamical instabilities appearing in two kinetic theories for the collective behavior of molecular motors: the rigid two-state model and the two-state crossbridge (or power-stroke) model with continuous binding sites. We calculate force-velocity relations, discuss their stability, plot a diagram that summarizes the oscillation regimes, identify the location of the Hopf bifurcation with a memory effect, discuss the oscillation frequency and make a link with single-molecule experiments. We show that the instabilities present in these models naturally translate into non-linearities in force-displacement relations, and at linear order give forces that are similar to the delayed stretch activation observed in oscillating muscles. We also find that instabilities can appear for both apparent load-decelerated and load-accelerated detachment rates in a 3-state crossbridge model.

Motion reversal of molecular motor assemblies due to weak noise

Bidirectional motion is an example of collective behavior of molecular motors. It occurs at finite noise level in a nonequilibrium system. We consider this problem as a first exit problem. We identify the noise strength by doing an expansion of a master equation and apply the Wentzell-Freidlin theory to define an effective nonequilibrium potential and provide analytical estimates of the reversal time. Our results match very well with the results of stochastic simulations.

Polarity patterns of stress fibers

Stress fibers are contractile actomyosin bundles commonly observed in the cytoskeleton of metazoan cells. The spatial profile of the polarity of actin filaments inside contractile actomyosin bundles is either monotonic (graded) or periodic (alternating). In the framework of linear irreversible thermodynamics, we write the constitutive equations for a polar, active, elastic one-dimensional medium. An analysis of the resulting equations for the dynamics of polarity shows that the transition from graded to alternating polarity patterns is a nonequilibrium Lifshitz point. Active contractility is a necessary condition for the emergence of sarcomeric, alternating polarity patterns.

Dynamic instabilities in assemblies of molecular motors with finite stiffness

We propose a two-state "soft-motor" model for the collective behavior of molecular motors which takes into account both the internal motor stiffness and the periodic interaction with the filament. As in the Prandtl-Tomlinson model of tribology, the important parameter of the model is the pinning parameter, which compares the stiffness of the motors to the stiffness of the potential. The model predicts dynamic instabilities in two disconnected regions of parameter space. These parameter ranges correspond to two existing theories of motor assemblies, the rigid two-state model and the crossbridge model. The model also predicts a discontinuity of the slope of the force-velocity relation at small velocities.

Generalized fluctuation-dissipation theorem for steady-state systems

The fluctuation-dissipation theorem is a central result of statistical physics, which applies to any system at thermodynamic equilibrium. Its violation is a strong signature of nonequilibrium behavior. We show that for any system with Markovian dynamics, in a nonequilibrium steady state, a proper choice of observables restores a fluctuation-response theorem identical to a suitable version of the equilibrium fluctuation-dissipation theorem. This theorem applies to a broad class of dynamical systems. We illustrate it with linear stochastic dynamics and examples borrowed from the physics of molecular motors and Hopf bifurcations. Finally, we discuss general implications of the theorem.

Spontaneous movements and linear response of a noisy oscillator

A deterministic system that operates in the vicinity of a Hopf bifurcation can be described by a single equation of a complex variable, called the normal form. Proximity to the bifurcation ensures that on the stable side of the bifurcation (i.e. on the side where a stable fixed point exists), the linear-response function of the system is peaked at the frequency that is characteristic of the oscillatory instability. Fluctuations, which are present in many systems, conceal the Hopf bifurcation and lead to noisy oscillations. Spontaneous hair bundle oscillations by sensory hair cells from the vertebrate ear provide an instructive example of such noisy oscillations. By starting from a simplified description of hair bundle motility based on two degrees of freedom, we discuss the interplay of nonlinearity and noise in the supercritical Hopf normal form. Specifically, we show here that the linear-response function obeys the same functional form as for the noiseless system on the stable side of the bifurcation but with effective, renormalized parameters. Moreover, we demonstrate in specific cases how to relate analytically the parameters of the normal form with added noise to effective parameters. The latter parameters can be measured experimentally in the power spectrum of spontaneous activity and linear-response function to external stimuli. In other cases, numerical solutions were used to determine the effects of noise and nonlinearities on these effective parameters. Finally, we relate our results to experimentally observed spontaneous hair bundle oscillations and responses to periodic stimuli.

Hydrodynamics of cellular cortical flows and the formation of contractile rings

We propose a mechanism for the formation of contractile rings and the apparition of a flow in the cortical layer of cells undergoing cytokinesis at the end of cell division or during the healing of a wound in the cortex of Xenopus eggs. We generalize the hydrodynamic active gel theory along the lines of thin shell theory of continuum elasticity to describe the cell cortex. As in liquid crystal physics, the flow couples to the orientation of the actin filaments. The cortical flow is driven by an increased density of myosin motors in the cortex, and orients the filaments to form the ring.

Antioxidant effect of Ajuga iva aqueous extract in streptozotocin-induced diabetic rats

The purpose of this study was to investigate the possible antioxidant effect of an aqueous extract of Ajuga iva (Ai) in streptozotocin (STZ)-induced diabetic rats. Twelve diabetic rats were divided into two groups fed a casein diet supplemented or not with Ai (0.5%), for 4 weeks. In vitro, the Ai extract possessed a very high antioxidant effect (1 mg/ml was similar to those of trolox 300 mmol/l). The results indicated that plasma thiobarbituric acid reactive substances (TBARS) values were reduced by 41% in Ai-treated compared with untreated diabetic rats. TBARS concentrations were lower 1.5-fold in liver, 1.8-fold in heart, 1.9-fold in muscle and 2.1-fold in brain in Ai-treated than untreated group. In erythrocytes, Ai treatment increased significantly the activities of glutathione peroxidase (GSH-Px) (+25%) and glutathione reductase (GSSH-Red) (+22%). Superoxide dismutase activity was increased in muscle (+22%), while GSH-Px activity was significantly higher in liver (+28%), heart (+40%) and kidney (+45%) in Ai-treated compared with untreated group. Liver and muscle GSSH-Red activity was, respectively, 1.6- and 1.5-fold higher in Ai-treated than untreated diabetic group. Catalase activity was significantly increased in heart (+36%) and brain (+32%) in Ai-treated than untreated group. Ai treatment decreased plasma nitric oxide (-33%), carbonyls (-44%) and carotenoids (-68%) concentrations. In conclusion, this study indicates that Ajuga iva aqueous extract improves the antioxidant status by reducing lipid peroxidation and enhancing the antioxidant enzymes activities in plasma, erythrocytes and tissues of diabetic rats.

Generic theory of colloidal transport

We discuss the motion of colloidal particles relative to a two-component fluid consisting of solvent and solute. Particle motion can result from i) net body forces on the particle due to external fields such as gravity; ii) slip velocities on the particle surface due to surface dissipative phenomena. The perturbations of the hydrodynamic flow field exhibit characteristic differences in cases i) and ii) which reflect different patterns of momentum flux corresponding to the existence of net forces, force dipoles or force quadrupoles. In the absence of external fields, gradients of concentration or pressure do not generate net forces on a colloidal particle. Such gradients can nevertheless induce relative motion between particle and fluid. We present a generic description of surface dissipative phenomena based on the linear response of surface fluxes driven by conjugate surface forces. In this framework we discuss different transport scenarios including self-propulsion via surface slip that is induced by active processes on the particle surface. We clarify the nature of force balances in such situations.

Pushing off the walls: a mechanism of cell motility in confinement

We propose a novel mechanism of cell motility, which relies on the coupling of actin polymerization at the cell membrane to geometric confinement. We consider a polymerizing viscoelastic cytoskeletal gel confined in a narrow channel, and show analytically that spontaneous motion occurs. Interestingly, this does not require specific adhesion with the channel walls, and yields velocities potentially larger than the polymerization velocity. The contractile activity of myosin motors is not necessary to trigger motility in this mechanism, but is shown quantitatively to increase the velocity. Our model qualitatively accounts for recent experiments which show that cells without specific adhesion proteins are motile only in confined environments while they are unable to move on a flat surface, and could help in understanding the mechanisms of cell migration in more complex confined geometries such as living tissues.

Membrane tension lowering induced by protein activity

Using videomicroscopy we present measurements of the fluctuation spectrum of giant vesicles containing bacteriorhodopsin pumps. When the pumps are activated, we observe a significant increase of the fluctuations in the low wave vector region, which we interpret as due to a lowering of the effective tension of the membrane.

Thermal and non-thermal fluctuations in active polar gels

We discuss general features of noise and fluctuations in active polar gels close to and away from equilibrium. We use the single-component hydrodynamic theory of active polar gels built by Kruse and coworkers to describe the cytoskeleton in cells. Close to equilibrium, we calculate the response function of the gel to external fields and introduce Langevin forces in the constitutive equations with correlation functions respecting the fluctuation-dissipation theorem. We then discuss the breakage of the fluctuation-dissipation theorem due to an external field such as the activity of the motors. Active gels away from equilibrium are considered at the scaling level. As an example of application of the theory, we calculate the density correlation function (the dynamic structure factor) of a compressible active polar gel and discuss possible instabilities.

Viscous-fingering-like instability of cell fragments

We present a novel flow instability that can arise in thin films of cytoskeletal fluids if the friction with the substrate on which the film lies is sufficiently strong. We consider a two-dimensional, membrane-bound fragment containing actin filaments that polymerize at the edge and depolymerize in the fragment. Performing a linear stability analysis of the initial state due to perturbations of the fragment boundary, we find, in the limit of large friction, that the perturbed actin velocity and pressure fields obey the same laws governing the viscous fingering instability of an interface between immiscible fluids in a Hele-Shaw cell. A remarkable feature of this instability is that it is independent of the strength of the interaction between actin filaments and myosin motors.

Changes in antioxidant defense status in hypercholesterolemic rats treated with Ajuga iva

The aim of the study was to investigate the effect of aqueous extract of Ajuga iva (Ai) on serum and tissues lipid peroxidation as well as antioxidant enzymes activities in red blood cells (RBC) and tissues, in high hypercholesterolemic rats (HC). Male Wistar rats (n=12) were fed on 1% cholesterol-enriched diet for 15d. After this adaptation phase, hypercholesterolemic rats (total cholesterol=6.5+/-0.6mol/l) were divided into two groups fed the same diet and treated or not with Ai for 15d. Thiobarbituric acid reactive substances (TBARS) concentrations in serum, LDL-HDL(1), HDL(2) and HDL(3) were respectively, 5-, 7.8-, 2.3- and 5-fold lower in Ai treated than untreated hypercholesterolemic groups. TBARS concentrations were 1.4-fold lower in heart and 2.8-fold higher in kidney in Ai-HC treated than untreated HC group. Superoxide dismutase activity was respectively, 1.2- and 1.4-fold higher in RBC and muscle in Ai treated than untreated group. In RBC, Ajuga iva treatment enhanced glutathione peroxidase (GSH-Px) (+9%) and glutathione reductase (GSSH-Red) (+12%) in Ai-HC treated than untreated HC group. GSSH-Red activity was 1.4- and 1.5-fold higher in adipose tissue and heart, respectively and 3.7-fold lower in kidney in Ai treated than untreated group. Liver catalase activity was 1.6-fold higher in Ai treated than untreated group. Adipose tissue and muscle total glutathione content represented in Ai treated group 35% and 36% of the value noted in untreated group. Nitric oxide values of liver, adipose tissue and heart were 3.3-, 2.5- and 3.4-fold higher in Ai-HC than HC group. Ajuga iva treatment enhanced alpha-tocopherol contents (+25%) in Ai treated than untreated group. In conclusion, Ajuga iva treatment is more effective to improve the antioxidant capacity of RBC than that of tissues. Indeed, Ai is able to reduce the oxidative stress in hypercholesterolemic rats by increasing the antioxidant enzymes activity.

Serum lecithin: cholesterol acyltransferase activity, HDL2 and HDL3 composition in hypertensive mothers and their small for gestational age newborns

The aim of this study was to determine serum lecithin:cholesterol acyltransferase (LCAT) activity in parallel with HDL2 and HDL3 amounts and composition in pregnancy induced hypertension (PIH) and chronic hypertensive (CH) mothers and in their small for gestational age (SGA) newborns. LCAT activity was assayed by conversion of [3H] cholesterol to labelled cholesteryl ester. HDL2 and HDL3 were separated by ultracentrifugation. At term, cholesterol values were similar in PIH, CH and controls. However, higher levels of triglycerides were observed in PIH and CH (+20% and +21%, respectively) as compared with normotensive control mothers (NC). HDL2 and HDL3-phospholipids, HDL2-cholesterol concentrations and LCAT activity were lower in PIH and CH mothers than in NC mothers. Similar changes were also observed in SGA newborns of PHI mothers and in SGA newborns of CH mothers when compared to appropriate for gestational age newborns of control mothers (AGA-NC). In addition, SGA newborns showed low HDL2 and HDL3 apoA-I contents. Maternal hypertension and foetal intrauterine growth retardation are associated with profound abnormalities in HDL metabolism, consistent with an atherogenic risk. SGA lipoprotein profiles appear to implicate later metabolic diseases.

Serum lipoprotein composition, lecithin cholesterol acyltransferase and tissue lipase activities in pregnant diabetic rats and their offspring receiving enriched n-3 PUFA diet

The effects of dietary n-3 polyunsaturated fatty acids on lipoprotein concentrations and on lipoprotein lipase (LPL), hepatic triglyceride lipase (HTGL) and lecithin cholesterol acyltransferase (LCAT) activities were studied in streptozotocin-induced diabetic rats during pregnancy and in their macrosomic offspring from birth to adulthood. Pregnant diabetic and control rats were fed Isio-4 diet (vegetable oil) or EPAX diet (concentrated marine omega-3 EPA/DHA oil), the same diets were consumed by pups at weaning. Compared with control rats, diabetic rats showed, during pregnancy, a significant elevation in very low density lipoprotein (VLDL) and low and high density lipoprotein (LDL-HDL(1))-triglyceride, cholesterol and apoprotein B100 concentrations and a reduction in apoprotein A-I levels. HTGL activity was high while LPL and LCAT activities were low in these rats. The macrosomic pups of Isio-4-fed diabetic rats showed a significant enhancement in triglyceride and cholesterol levels at birth and during adulthood with a concomitant increase in lipase and LCAT activities. EPAX diet induces a significant diminution of VLDL and LDL-HDL(1) in mothers and in their macrosomic pups, accompanied by an increase in cholesterol and apoprotein A-I levels in HDL(2-3) fraction. It also restores LPL, HTGL and LCAT activities to normal range. EPAX diet ameliorates considerably lipoprotein disorders in diabetic mothers and in their macrosomic offspring.

[2-hydroxy-methyl-1(N-phtaloyltryptophyl) aziridine stimulates in vitro human lymphocyte proliferation and interleukin secretion]

AIM OF THIS WORK: Aziridines have been shown to possess marked immunotropic activity. In this study, the in vitro effects of a new aziridine, 2-hydroxy-methyl-1-(N-phtaloyltryptophyl) aziridine, were determined on the proliferative responses of human lymphocytes stimulated by mitogens and on interleukin (IL-2, IL-6) secretion.

MATERIAL AND METHODS

Peripheral blood lymphocytes were isolated using differential centrifugation on a density gradient of Ficoll-Paque. They were cultured with or without mitogens (Concanavalin A and lipopolysaccharide), and with different concentrations of the aziridine. Proliferation was monitored by direct cell counts and confirmed by MTT [3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. After different incubations, IL-2 and IL-6 were determined by using commercially available Elisa kits.

RESULTS

The aziridine tested significantly stimulated the resting and mitogen T and B lymphocyte proliferation at concentrations between 1 microM and 1 mM, in a dose-dependent manner. It also increased IL-2 and IL-6 secretion.

CONCLUSION

2-hydroxy-methyl-1-(N-phtaloyltryptophyl) aziridine displayed immunomodulatory properties and is potentially immunostimulant. It could be used to provide non-specific cell-mediated immune responses.

Effect of aqueous extract of Ajuga iva supplementation on plasma lipid profile and tissue antioxidant status in rats fed a high-cholesterol diet

The present study was designed to explore the possible antioxidant and hypolipidemic effects of the aqueous extract of Ajuga iva (0.5% in the diet) in rats fed a high-cholesterol (1%) diet (HCD). The results indicated that the HCD-Ai versus HCD treatment led to many changes in biochemical parameters. They showed a decrease of plasma total cholesterol (TC) and VLDL-cholesterol but an increase of HDL(2)-cholesterol. The triacylglycerol contents were reduced in plasma and in VLDL. The lipid peroxidation determined by TBARS was decreased by 75% in plasma. TBARS in liver, heart and kidneys were highly reduced excepted in the adipose tissue. Ajuga iva treatment enhanced superoxide dismutase activity in liver and kidney. Glutathione reductase activity was lowered in adipose tissue but increased in liver and in kidney. A significant increase was noted in glutathione peroxidase activity in liver, heart and kidney but a low value in adipose tissue was observed. In conclusion, the present study demonstrates that in addition to its potent TG and TC-lowering effects, Ajuga iva is effective in improving the antioxidant status by reducing lipid peroxidation in plasma and tissues and enhancing the antioxidant enzymes in rats fed high-cholesterol diet. Furthermore, Ajuga iva may reduce intestinal cholesterol absorption.

Effects of N-acyl-2-hydroxymethyl aziridines on in vitro proliferative responses of human lymphocytes stimulated by mitogens

Aziridines have been shown to possess marked immunotropic activity. The aim of this work was to study the in vitro effects of different concentrations of three novel aziridines, 2-hydroxy-methyl-1-(N-phtaloylglycyl) aziridine (aziridine 1), 2-hydroxy-methyl-1-(N-phtaloylalanyl) aziridine (aziridine 2) and 2-hydroxy-methyl-1-(N-phtaloylphenylalanyl) aziridine (aziridine 3), on the proliferative responses of human lymphocytes stimulated by mitogens (concanavalin A (Con A) and lipopolysaccharide (LPS)), and interleukin-2 (IL-2), interleukin-6 (IL-6) secretion. The results showed that aziridines 1 and 3 significantly stimulated the resting and Con A or LPS lymphocyte proliferation at concentrations between 1 micromol/l and 1 mmol/l, in a dose-dependent manner, the action of aziridine 3 being the highest. They also increased IL-2 and IL-6 secretion. However, aziridine 2 had no effect on the resting lymphocyte proliferation in the absence of mitogens, at any concentration used, reduced Con A-stimulated T lymphocyte proliferation and LPS- stimulated B lymphocyte proliferation in a dose dependent manner and diminished IL-2 and IL-6 production. None of the three aziridines affected cell viability. In conclusion, the three aziridines used in this study displayed immunomodulatory properties. Aziridines 1 and 3 are potentially immunostimulant while aziridine 2 is immunosuppressive and could be used to provide nonspecific cell-mediated immune responses.

[Gestational or essential hypertension in pregnant women limits the capacity to stock triglycerides by the placenta despite raised lipoprotein-lipase activity]

Placenta lipoprotein lipase (LPL) activity as well as serum VLDL and placenta lipids composition were determined in pregnant hypertensive women at term. 46 patients aged from 29 +/- 2 years with gravidic hypertension (HTA-G) and 38 patients with essential hypertension (HTA-E) aged 30 +/- 1 years were compared with 20 normotensive women aged 27 +/- 1 years. Serum triacylglycerols (TG) concentrations were 1.3-fold higher in the both hypertensive patients compared with controls. However, serum phospholipids (PL) and total cholesterol (TC) values were similar in the three groups. VLDL mass and their apolipoproteins, unesterified cholesterol (UC) and cholesteryl esters (CE) contents were significantly increased in hypertensive women compared with controls. In HTA-G and HTA-E patients, respectively. TG-VLDL concentrations were increased by +43% and +36% compared with those of controls (P < 0.01). In placenta, the values were lower 2.2- and 1.9-fold for TG, 2.8 and 2.5-fold for PL and two- and threefold for TC, in HTA-G and HTA-E patients than in controls. Placenta LPL activity was 2.7-fold higher in HTA-G and HTA-E patients compared with that of controls. In conclusion, although placenta LPL activity is higher it is not permit a decrease of serum TG-VLDL on the one hand, and an increase of placenta ability in TG storage on the other hand.

[Fish proteins moderate triacylglycerols, activities of hepatic triacylglycerol lipase and tissue lipoprotein lipases in hypertensive and diabetic rats]

Fish proteins effect compared with casein was determined on triacylglycerols (TG) metabolism and activities of hepatic triacylglycerol lipase (HTGL) and tissue lipoprotein lipases (LPL), in SHR and diabetic SHR. Two groups of rats (n=24) were fed, 2 months, diet containing 20% casein (CAS) or 20% fish proteins (FP). One month before sacrifice, diabetes was induced in one group of rats by a single intraperitoneal injection of streptozotocin (STZ) (60 mg/kg of body weight). FP vs. CAS showed a significant decrease of TG concentrations in plasma (-41%) and liver (-66%), in SHR-STZ. VLDL-LDL mass, which represented the amount of apolipoproteins, TG, phospholipids (PL), unesterified cholesterol (UC), and cholesteryl esters (CE), decreased by 21 and 16% with FP vs. CAS, in SHR and SHR-STZ, respectively, and was concomitant with its low TG. Indeed, TG values was 1.35- and 1.82-fold lower in SHR and SHR-STZ, respectively. In HDL2, a TG diminution of 13% was noted, in SHR with FP vs. CAS. In SHR-STZ with FP, TG and PL were enhanced by 11% and 27%, respectively compared to SHR. HTGL activity decreased by 22% in SHR fed FP compared to those fed CAS. In SHR-STZ with CAS vsSHR, this activity was decreased by 21%. LPL activity in heart was enhanced by 19% in SHR-STZ vs. SHR with FP, when that of muscle was diminished 1.5-fold in SHR with FP vs. CAS and 1.8-fold in SHR-STZ vs. SHR with CAS. Adipose LPL activity was 1.36-fold higher in SHR with FP than CAS. In conclusion, it appears that fish proteins have a hypotriglyceridemic effect, which the mechanism can differ in SHR or SHR-STZ. It may be of interest to propose these fish proteins as lipid metabolism regulator in diseases with hypertriglyceridemia.

Contractility and retrograde flow in lamellipodium motion

We present a phenomenological description of cell locomotion on a solid substrate. The material properties of the actin cytoskeleton in the lamellipodium are described by the constitutive equations of a viscous polar gel with intrinsic activity. The polymerization of the gel takes place in a localized region near the leading edge. Using a simple two-dimensional description, we calculate in the steady state the thickness profile of the lamellipodium which at the rear connects to the cell body; we also calculate the flow profiles and the forces exerted on the substrate. The cell velocity is estimated as a function of externally applied forces. Our description is consistent with experimentally observed properties of motile cells such as the existence of a retrograde flow in the lamellipodium and a dipolar force distribution exerted by the cell on the substrate.

Generic phase diagram of active polar films

We study theoretically the phase diagram of compressible active polar gels such as the actin network of eukaryotic cells. Using generalized hydrodynamics equations, we perform a linear stability analysis of the uniform states in the case of an infinite bidimensional active gel to obtain the dynamic phase diagram of active polar films. We predict, in particular, modulated flowing phases and a macroscopic phase separation at high activity. This qualitatively accounts for experimental observations of various active systems, such as actomyosin gels, microtubules and kinesins in vitro solutions, or swimming bacterial colonies.

N-3 Fatty acids modulate antioxidant status in diabetic rats and their macrosomic offspring

OBJECTIVE

We investigated the role of dietary n-3 polyunsaturated fatty acids (n-3 PUFA) in the modulation of total antioxidant status in streptozotocin (STZ)-induced diabetic rats and their macrosomic offspring.

DESIGN

Female wistar rats, fed on control diet or n-3 PUFA diet, were rendered diabetic by administration of five mild doses of STZ on day 5 and were killed on days 12 and 21 of gestation. The macrosomic (MAC) pups were killed at the age of 60 and 90 days.

MEASUREMENTS

Lipid peroxidation was measured as the concentrations of plasma thiobarbituric acid reactive substances (TBARS), and the total antioxidant status was determined by measuring (i) plasma oxygen radical absorbance capacity (ORAC), (ii) plasma vitamin A, E and C concentrations, and (iii) antioxidant enzymes activities in erythrocytes. The plasma lipid concentrations and fatty acid composition were also determined.

RESULTS

Diabetes increased plasma triglyceride and cholesterol concentrations, whereas macrosomia was associated with enhanced plasma cholesterol and triglyceride levels, which diminished by feeding n-3 PUFA diet. N-3 PUFA diet also reduced increased plasma TBARS and corrected the decreased ORAC values in diabetic rats and their macrosomic offspring. EPAX diet increased the diminished vitamin A levels in diabetic mothers and vitamin C concentrations in macrosomic pups. Also, this diet improved the decreased erythrocyte superoxide dismutase and glutathione peroxidase activities in diabetic and macrosomic animals.

CONCLUSION

Diabetes and macrosomia were associated with altered lipid metabolism, antioxidant enzyme activities and vitamin concentrations. N-3 PUFA diet improved hyperlipidemia and restored antioxidant status in diabetic dams and MAC offspring.

Antioxidant status in alcohol-related diabetes mellitus in Beninese subjects

In the present study, we investigated the antioxidant status in diabetes mellitus, related or not to alcohol consumption. A total of 38 type 1, 48 type 2 and 42 alcohol-related diabetic patients were selected. Total antioxidant status was assessed through the oxygen radical absorbance capacity of the plasma and the determination of enzymatic and non-enzymatic antioxidant molecules. Serum triglycerides, total cholesterol and HDL-cholesterol concentrations were determined and the lipid peroxydation was evaluated by measuring thiobarbituric acid reactive substances (TBARS) assay. Plasma total antioxidant capacity was more decreased in alcohol-related diabetes than that in type 1 and type 2 diabetes, regardless of the complications (retinopathy and renal failure). Plasma vitamin E concentrations were significantly decreased whereas those of vitamin C increased in all of the diabetic patients compared to the controls, irrespective to the complications. In addition, superoxide dismutase and glutathione peroxidase activities were reduced in all the patients (type 1, type 2 and alcohol-related), irrespective to the complications. Glutathione reductase activity was diminished in type 1 and alcohol-related, but not in type 2, diabetic patients. Glutathione (GSH) concentrations significantly decreased in all diabetic patients with a significant decrease in alcohol-related diabetic patients. Excessive alcohol consumption appears as an oxidative aggravating factor in diabetes mellitus. Besides, alcohol-related diabetes highly resembles to type 1 diabetes as far as the antioxidant parameters are concerned.

Motor proteins transporting cargos

Processive motor proteins such as kinesin and myosin-V are enzymes that use the energy of ATP hydrolysis to travel along polar cytoskeletal filaments. One of the functions of these proteins is the transport of vesicles and protein complexes that are linked to the light chains of the motors. Modeling the light chain by a linear elastic spring, and using the two-state model for one- and two-headed molecular motors, we study the influence of thermal fluctuations of the cargo on the motion of the motor-cargo complex. We solve numerically the Fokker-Planck equations of motor motion, and find that the mean velocity of the motor-cargo complex decreases monotonously as the spring becomes softer. This effect is due to the random force of thermal fluctuations of the cargo disrupting the operation of the motor. Increasing the size (thus, the friction coefficient) of the cargo also decreases the velocity. Surprisingly, we find that for a given size of the cargo, the velocity has a maximum for a certain friction of the motor. We explain this effect by the interplay between the characteristic length of thermal fluctuations of the cargo on a spring, the motor diffusion length, and the filament period. Our results may be relevant for the interpretation of single-molecule experiments with molecular motors (bead assays), where the motor motion is observed by tracking of a bead attached to the motor.