Marine foams impede metabolic and behavioural traits in the rough periwinkle Littorina saxatilis

Foams are a ubiquitous feature of marine environments. They can have major economic, societal and ecological consequences through their accumulation on the shore. Despite their pervasive nature and evidence that stable foam deposits play a pivotal role in the ecology of soft shore and estuaries, very limited amounts of information are available on their contribution to the structure and function at play in rocky intertidal ecosystems. This study shows that the metabolic rate of the high-shore gastropod Littorina saxatilis is significantly higher in individuals exposed to foams. Behavioural assays conducted under laboratory-controlled conditions further show that this species detects foam-born infochemicals both indirectly or directly, hence rely on both airborne and contact chemosensory cues. L. saxatilis also actively avoid areas covered in foam, and increase their activity in the presence of foam. These observations are interpreted in terms of foam-induced increased metabolic stress and increases behavioural anxiety and vigilance. They are further discussed in relation to the occurrence of two phytoplankton species known to produce repellent and/or toxic compounds such as domoic acid and dimethylsulfoniopropionate, the diatom Pseudo-nitzschia multistriata and the haptophyte Phaeocystis globosa, with the latter occurring at unusually high density. Taken together, these results suggest that the accumulation of foams on intertidal rocky shores may have major implications on taxa relying on both airborne and contact chemosensory cues to navigate, find food and mating partners. Specifically, the observed increased behavioural activity coupled with increased metabolic demands may impact species fitness and highlight potentially large ecological consequences in rocky intertidal ecosystems characterized by strong hydrodynamism and elevated organic matter content leading to the presence of long-lived foam.

Deformation of soap bubbles in uniform magnetic fields

The deformation of hemispherical sessile bubbles made of ferrofluid soap under vertical uniform magnetic fields was studied using Helmholtz coils. The deformation and the shape of the bubbles were monitored according to the amplitude of the magnetic field, the initial volume of the bubbles and the ferrofluid volume used to create them. The meniscus was found to bear most of the deformation, reshaping into a cylinder, with the remainder of the bubble forming a spherical cap, mainly adapting to the meniscus transformation. The growth of the meniscus height was rationalised using a simple model. More precisely, the meniscus shape depends on the competition between capillary, gravity and magnetic effects. These three ingredients can be rewritten to highlight two characteristic lengths of the system: the capillary and the magnetic lengths. Depending on the magnetic field intensity, the shape of the meniscus is described by one of the two lengths, thus revealing the existence of two distinct regimes.

Rebound and scattering of motile Chlamydomonas algae in confined chambers

Motivated by recent experiments demonstrating that motile algae get trapped in draining foams, we study the trajectories of microorganisms confined in model foam channels (section of a Plateau border). We track single Chlamydomonas reinhardtii cells confined in a thin three-circle microfluidic chamber and show that their spatial distribution exhibits strong corner accumulation. Using empirical scattering laws observed in previous experiments (scattering with a constant scattering angle), we next develop a two-dimension geometrical model and compute the phase space of trapped and periodic trajectories of swimmers inside a three-circles billiard. We find that the majority of cell trajectories end up in a corner, providing a geometrical mechanism for corner accumulation. Incorporating the distribution of scattering angles observed in our experiments and including hydrodynamic interactions between the cells and the surfaces into the geometrical model enables us to reproduce the experimental probability density function of micro-swimmers in microfluidic chambers. Both our experiments and models demonstrate therefore that motility leads generically to trapping in complex geometries.

Trapping of swimming microalgae in foam

Massive foam formation in aquatic environments is a seasonal event that has a significant impact on the stability of marine ecosystems. Liquid foams are known to filter passive solid particles, with large particles remaining trapped by confinement in the network of liquid channels and small particles being freely advected by the gravity-driven flow. By contrast, the potential role of a similar retention effect on biologically active particles such as phytoplankton cells is still relatively unknown. To assess if phytoplankton cells are passively advected through a foam, the model unicellular motile alga Chlamydomonas reinhardtii (CR) was incorporated in a bio-compatible foam, and the number of cells escaping the foam at the bottom was measured in time. Comparing the escape dynamics of living and dead CR cells, we found that dead cells are totally advected by the liquid flow towards the bottom of the foam, as expected since the diameter of CR remains smaller than the typical foam channel diameter. By contrast, living motile CR cells escape the foam at a significantly lower rate: after 2 hours, up to 60% of the injected cells may remain blocked in the foam, while 95% of the initial liquid volume in the foam has been drained out of the foam. Microscopic observation of the swimming CR cells in a chamber mimicking the cross-section of foam internal channels revealed that swimming CR cells accumulate near channels corners. A theoretical analysis based on the probability density measurements in the micro chambers has shown that this trapping at the microscopic scale contributes to explain the macroscopic retention of the microswimmers in the foam. At the crossroads of distinct fields including marine ecology of planktonic organisms, fluid dynamics of active particles in a confined environment and the physics of foam, this work represents a significant step in the fundamental understanding of the ecological consequences of aquatic foams in water bodies.

SAT0469 PROSPECTIVE STUDY ASSESSING BONE MINERAL DENSITY AND RISK FACTORS FOR OSTEOPOROSIS IN PATIENTS WITH ANDROGEN DEPRIVATION THERAPY. PRELIMINARY CROSS-SECTIONAL RESULTS

Background:

Few studies have analysed the incidence and risk factors for osteoporosis (OP) development in patients with prostate cancer (PC) and androgen deprivation therapy (ADT).

Objectives:

To assess risk factors for OP, bone turnover markers (BTM) and bone mineral density (BMD) in a cohort of patients with ADT, as well as the duration of ADT and previous treatments received for PC.

Methods:

Ongoing prospective study including patients with ADT for PC. Risk factors for OP, BTM (total ALP, bone ALP, CTx), spinal X-Ray and BMD (Lunar, DPX) were assessed yearly since inclusion in the study (April 2018). Patients with known OP or previous antiosteoporotic treatment were excluded. The study was approved by the ethics committee, and all patients gave their signed consent. Herein we present the preliminary cross-sectional study at inclusion.

Results:

Of the 83 patients attended at the Rheumatology Department during the study period, 75 were included with a mean age 75±5years and median ADT duration of 1 year. 18 were receiving concomitant radiotherapy and 7 docetaxel.

When assessing risk factors for OP: 28% had previous fragility fractures and 24% had current alcohol intake. After X-Ray assessment, 14% had morphometric vertebral fractures. Mean 25OHD at inclusion was 19±9ng/ml (73% had 25OHD <30ng/ml) and mean testosterone was 82±162ng/dL (75% had levels <50ng/dl). All patients had increased values of CTx and 9% had increased bone ALP levels.

BMD showed up to 28% with densitometric OP and osteopenia in 56%. Patients with OP were older (83±7 vs 74±8 years, p=0.021), had lower testosterone levels (16 vs 89 ng/dl, p=0.004), as expected lower BMD (at spine, proximal femur and even distal radius) and had more previous fragility fracture (75 vs 19%, p=0.022). But it should be noted that 16% had high bone mass (HBM) mostly affecting spine BMD (in 6 patients combined with femoral osteopenia). All patients with HBM had high bone metastatic disease, and no differences were observed between patients with/without HBM when comparing BTM or calcium-phosphate metabolism.

Conclusion:

Low bone mass (including osteoporosis and osteopenia) is frequent in patients with ADT as well as previous fragility fractures. Up to 16% had high bone mass, being mostly in patients with high volume metastatic disease. Thus, all patients with ADT should undergo a bone health assessment and start antiosteoporotic treatment if required.

Disclosure of Interests:

None declared

[Cystatin C: Biomarker of cardiovascular risk in HIV]

INTRODUCTION

Patients infected with the human immunodeficiency virus (HIV) have a higher cardiovascular risk (CVR). The development of cardiovascular disease (CVD) in this population involves traditional CVR factors and factors related to the infection itself, such as chronic inflammatory status, immune dysfunction, as well as the antiretroviral therapy received. Cystatin C (CC) has shown to be useful in assessing the presence of CVR factors and CVD established in the general population, the elderly population, and patients with chronic kidney disease. An analysis was performed on this association in an HIV positive population (HIV+).

MATERIAL AND METHODS

Analytical, observational, cross-sectional study was conducted, and included collecting information about CVR factors and CVD in HIV+, as well as measuring CC. The patients were divided into 2 groups: Group1=high CC (≥0.95mg/L) and Group2=normal CC (<0.95mg/L).

RESULTS

A total of 95 patients were included. Group1=27 (28.4%) and Group2=68 (71.5%). A value of CC≥0.95mg/L was related to the presence of CVD (P=.01). It was also related with and an increase in waist circumference (P=.05), neck circumference (P=.04), systolic blood pressure (P=.04), diastolic blood pressure (P=.01), Framingham score (P=.03), and Framingham score adapted for HIV (P=.01). After performing multivariate analysis with incorporation of variables associated with CVD in the bivariate analysis, only CC≥0.95mg/L continued to be related to CVD.

CONCLUSION

CC≥0.95mg/L was independently associated with CVD. This cut-off point was also linked to higher levels of blood pressure, and higher CVR at 10 years using the Framingham Score and Framingham Score adapted for HIV population.

Investigating the origin of acoustic attenuation in liquid foams

Liquid foams are known to be highly efficient to absorb acoustic waves but the origin of the sound dissipation remains unknown. In this paper, we present low frequency (0.5-4kHz) experimental results measured with an impedance tube and we confront the recorded attenuations with a simple model that considers the foam as a concentrate bubbly liquid. In order to identify the influence of the different parameters constituting the foams we probe samples with different gases, and various liquid fractions and bubble size distributions. We demonstrate that the intrinsic acoustic attenuation in the liquid foam is due to both thermal and viscous losses. The physical mechanism of the viscous term is not elucidated but the microscopic effective viscosity evidenced here can be described by a phenomenological law scaling with the bubble size and the gas density. In our experimental configuration a third dissipation term occurs. It comes from the viscous friction on the wall of the impedance tube and it is well described by the Kirchhoff law considering the macroscopic effective viscosity classically measured in rheology experiments.

Soap film vibration: origin of the dissipation

We investigate the complex dispersion relationship of a transverse antisymmetric wave on a horizontal soap film. Experimentally, the complex wave number k at a fixed forcing frequency is determined by measuring the vibrating amplitude of the soap film: the wavelength (linked to the real part of k) is determined by the spatial variation of the amplitude; the decay length (linked to the imaginary part of k) is determined by analyzing the resonance curves of the vibrating wave as a function of frequency. Theoretically, we compute the complex dispersion relationship taking into account the physical properties of the bulk liquid and gas phase, and of the gas-liquid interfaces. The comparison between the computation (developed to the leading order under our experimental conditions) and the experimental results confirms that the phase velocity is fixed by the interplay between surface tension, and liquid and air inertia, as reported in previous studies. Moreover, we show that the attenuation of the transverse antisymmetric wave originates from the viscous dissipation in the gas phase surrounding the liquid film. This result is an important step in understanding the propagation of an acoustic wave in liquid foam, using a bottom-up approach.

Acoustic characterisation of liquid foams with an impedance tube

Acoustic measurements provide convenient non-invasive means for the characterisation of materials. We show here for the first time how a commercial impedance tube can be used to provide accurate measurements of the velocity and attenuation of acoustic waves in liquid foams, as well as their effective "acoustic" density, over the 0.5-6kHz frequency range. We demonstrate this using two types of liquid foams: a commercial shaving foam and "home-made" foams with well-controlled physico-chemical and structural properties. The sound velocity in the latter foams is found to be independent of the bubble size distribution and is very well described by Wood's law. This implies that the impedance technique may be a convenient way to measure in situ the density of liquid foams. Important questions remain concerning the acoustic attenuation, which is found to be influenced in a currently unpredictible manner by the physico-chemical composition and the bubble size distribution of the characterised foams. We confirm differences in sound velocities in the two types of foams (having the same structural properties) which suggests that the physico-chemical composition of liquid foams has a non-negligible effect on their acoustic properties.

A technique for measuring velocity and attenuation of ultrasound in liquid foams

We describe an experimental setup specifically designed for measuring the ultrasonic transmission through liquid foams, over a broad range of frequencies (60-600kHz). The question of determining the ultrasonic properties of the foam (density, phase velocity and attenuation) from the transmission measurements is addressed. An inversion method is proposed, tested on synthetic data, and applied to a liquid foam at different times during the coarsening. The ultrasonic velocity and attenuation are found to be very sensitive to the foam bubble sizes, suggesting that a spectroscopy technique could be developed for liquid foams.

When a crack is oriented by a magnetic field

Upon drying, colloidal suspensions undergo a phase transformation from a "liquid" to a "gel" state. With further solvent evaporation, tensile stresses develop in the gel, which ultimately leads to fractures. These generally manifest themselves in regular cracking patterns which reflect the physical conditions of the drying process. Here we show experimentally and theoretically how, in the case of a drying droplet of magnetic colloid (ferrofluid), an externally applied magnetic field modifies the stress in the gel and therefore the crack patterns. We find that the analysis of the shape of the cracks allows one to estimate the value of the gel Young's modulus just before the crack nucleation.

Two-dimensional flow of foam around an obstacle: force measurements

A Stokes experiment for foams is proposed. It consists of a two-dimensional flow of a foam, confined between a water subphase and a top plate, around a fixed circular obstacle. We present systematic measurements of the drag exerted by the flowing foam on the obstacle versus various separately controlled parameters: flow rate, bubble volume, bulk viscosity, obstacle size, shape, and boundary conditions. We separate the drag into two contributions: an elastic one (yield drag) at vanishing flow rate and a fluid one (viscous coefficient) increasing with flow rate. We quantify the influence of each control parameter on the drag. The results exhibit in particular a power-law dependence of the drag as a function of the bulk viscosity and the flow rate with two different exponents. Moreover, we show that the drag decreases with bubble size and increases proportionally to the obstacle size. We quantify the effect of shape through a dimensional drag coefficient, and we show that the effect of boundary conditions is small.

Local rheological probes for complex fluids: application to Laponite suspensions

We present an experimental method allowing a direct measurement of the local rheological behavior of complex fluids. A magnetic probe is inserted into the bulk of the fluid and submitted to a controlled magnetic force or torque, which induces a mechanical perturbation of the fluid. The geometry of the perturbation can be varied using two kinds of probes: a magnetic bead submitted to a homogeneous magnetic force in one direction, and a magnetic needle that can turn inside the material under the effect of an applied magnetic torque. Two complex viscoelastic fluids are investigated. First, a surfactant solution, which has a linear mechanical behavior in the range of the applied stresses, is used to test and validate the experimental methodology. We then use the local probes to investigate a Laponite colloidal suspension, which exhibits nonlinear behavior such as thixotropy, shear thinning, and aging. In this latter fluid, we find an exponential growth of the rheological relaxation time versus the system age, a power-law dependence of the fluid viscosity on the applied stress, and a dynamical yield stress which saturates with the fluid aging time.

Overexpanded B cell clone mediating leukemic arthritis by abundant secretion of interleukin-1beta: a case report

The role of cytokines in leukemic arthritis is unknown. The presentation of a patient with B cell chronic lymphocytic leukemia and destructive arthritis of the wrist joints prompted us to study the synovial cytokine pattern by immunohistologic analysis. In addition, rearranged V(H) and V(L) immunoglobulin genes were sequenced to assess B cell clonality. Heavy infiltrations of CD20+ cells with lambda light chain restriction were found in the synovial tissue. Sequencing demonstrated overexpansion of a single B cell clone (DP58/D/J(H)4b and IGLV3S2/Jlambda2-Jlambda3 for V(H) and V(L), respectively) in the peripheral blood. Identical V(H) and V(L) rearrangements were found in the synovial infiltrates. Somatic mutations were found in both the peripheral blood and the synovial clone. Immunohistologic study revealed the presence of abundant interleukin-1beta (IL-1beta) and, to a lesser degree, tumor necrosis factor beta (TNFbeta) (lymphotoxin). In contrast, TNFalpha, interferon-gamma, IL-4, IL-6, and IL-10 were rarely found in the synovial infiltrates. Therefore, IL-1beta secreted in great amounts by leukemic B cells appears to be the major cytokine that mediates joint destruction in leukemic arthritis.

Immunization with recombinant Trypanosoma cruzi ribosomal P2beta protein induces changes in the electrocardiogram of immunized mice

Molecular expression cloning techniques revealed that patients with severe chronic Chagas heart disease showed a strong humoral response against the cloned C-terminal portion of the Trypanosoma cruzi ribosomal P2beta protein, previously named JL5. The main linear epitope of this polypeptide was mapped to the 13 C-terminal amino acid sequence EEEDDDMGFGLFD (named R13), which is almost identical to the mammalian ribosomal P consensus sequence EESDDDMGFGLFD (named H13). Enzyme-linked immunosorbent assay measurements demonstrated that sera from patients with chronic Chagas heart disease presented a very specific anti-P humoral response with high anti-R13, but low H13 antibody levels. We attempted to develop an animal model that would reproduce, at least partially, two features of the human infection: (1) the serological pattern of the anti-P response, and (2) specific cardiac symptoms. To this effect, mice were immunized with T. cruzi P2beta recombinant protein. Immunization reproduced the typical anti-P antibody profile defined for chronic infections, but did not induce cardiac inflammatory lesions. However, it altered significantly the electrocardiograms of immunized mice. It is suggested that this assay represents a functional test for assessing the biological activity of antibodies against T. cruzi ribosomal P protein on cardiac muscle.

Increased verbal interaction via group techniques with regressed schizophrenics

Verbal interaction on the tenth 50-min. session of remotivation therapy for 8 hospitalized male chronic schizophrenics ( Mage = 57.87) increased significantly over the level for 8 comparable schizophrenic patients who served as controls. Increased verbal interaction appeared on both a structured and an unstructured task. Although individual differences were marked, the efficacy of remotivation therapy with chronic schizophrenics is suggested.