Role of P-glycoprotein in the uptake/efflux transport of oral vitamin K antagonists and rivaroxaban through the Caco-2 cell model.

Vitamin K antagonists (VKAs) are prescribed worldwide and remain the oral anticoagulant of choice. These drugs are characterized by a narrow therapeutic index and a large inter- and intra-individual variability. P-glycoprotein could contribute to this variability. The aim of this study was to investigate the involvement of P-gp in the transport of acenocoumarol, phenprocoumon and warfarin using an in vitro Caco-2 cell monolayer model. These results were compared with those obtained with rivaroxaban, a new oral anticoagulant known to be a P-gp substrate. The transport of these four drugs was assessed at pH conditions 6.8/7.4 in the presence or absence of the P-gp inhibitor cyclosporine A (10 μM) and the more potent and specific P-gp inhibitor valspodar (5 μM). Analytical quantification was performed by LC/MS. With an efflux ratio of 1.7 and a significant decrease in the efflux (Papp B-A), in the presence of P-gp inhibitors at a concentration of 50 μM, acenocoumarol can be considered as a weak P-gp substrate. Concerning phenprocoumon, the results suggest that this molecule is a poor P-gp substrate. The P-gp inhibitors did not affect significantly the transport of warfarin. The efflux of rivaroxaban was strongly inhibited by the two P-gp inhibitors. In conclusion, none of the three VKAs tested are strong P-gp substrates. However, acenocoumarol can be considered as a weak P-gp substrate and phenprocoumon as a poor P-gp substrate.

Inhibition of bicarbonate transport protects embryonic heart against reoxygenation-induced dysfunction.

It has not been well established whether the mechanisms participating in pH regulation in the anoxic-reoxygenated developing myocardium resemble those operating in the adult. We have specially examined the importance of Na+/H+ exchange (NHE) and HCO3-dependent transports in cardiac activity after changes in extracellular pH (pHo). Spontaneously contracting hearts isolated from 4-day-old chick embryos were submitted to single or repeated anoxia (1 min) followed by reoxygenation (10 min). The chronotropic, dromotropic and inotropic responses of the hearts were determined in standard HCO3- buffer at pHo 7.4 and at pHo 6.5 (hypercapnic acidosis). In distinct experiments, acidotic anoxia preceded reoxygenation at pHo 7.4. NHE was blocked with amiloride derivative HMA (1 micro mol/l) and HCO3-dependent transports were inactivated by replacement of HCO3 or blockade with stilbene derivative DIDS (100 micro mol/l). Anoxia caused transient tachycardia, depressed mechanical function and induced contracture. Reoxygenation temporarily provoked cardiac arrest, atrio-ventricular (AV) block, arrhythmias and depression of contractility. Addition of DIDS or substitution of HCO3 at pHo 7.4 had the same effects as acidosis per se, i.e. shortened contractile activity and increased incidence of arrhythmias during anoxia, prolonged cardioplegia and provoked arrhythmias at reoxygenation. Under anoxia at pHo 6.5/reoxygenation at pHo 7.4, cardioplegia, AV block and arrhythmias were all markedly prolonged. Interestingly, in the latter protocol, DIDS suppressed AV block and arrhythmias during reoxygenation, whereas HMA had no effect. Thus, intracellular pH regulation in the anoxic-reoxygenated embryonic heart appears to depend predominantly on HCO3 availability and transport. Furthermore, pharmacological inhibition of anion transport can protect against reoxygenation-induced dysfunction.

Volcanic debris avalanche deposits of the upper Maronne valley (Cantal Volcano, France): evidence for contrasted formation and transport mechanisms

The deposits of two volcanic debris avalanches (VDA I and II) that occur in the upper Maronne valley, northwest sector of Cantal Volcano, France, were studied to establish their mechanisms of formation, transport and deposition. These two volcanic debris avalanches that clearly differ with regard to their structures, textures and extensions, exemplify the wide spectrum of events associated with large-scale sector collapse. VDA I is voluminous (similar to1 km(3) in the upper Maronne valley) and widespread. The deposits comprise two distinct facies: the block facies that forms the intermediate and upper part of the unit and the mixed facies that crops out essentially at the base of the unit. The block facies consists of more or less brecciated lava, block-and-ash-flow breccia and pumice-flow tuff megablocks set in breccias resulting from block disaggregation. Mixing and differential movements are almost absent in this part of the VDA. The mixed facies consists of breccias rich in fine particles that originate from block disagregation, as well as being picked up from the substratum during movement. Mixing and differential movements are predominant in this zone. Analysis of fractures on lava megablocks suggests that shear stress during the initial sliding is the principal cause of fracture. These data strongly indicate that VDA I is purely gravitational and argue for a model in which the initial sliding mass transforms into a flow due to differential in situ fragmentation caused by the shear stress. VDA II is restricted to low-topography areas. Its volume, in the studied area, is about 0.3 km(3). The deposits consist of brecciated, rounded blocks and megablocks set in a fine-grained matrix composed essentially of volcanic glass. This unit is stratified, with a massive layer that contains all the megablocks at the base and in the intermediate part, and in the upper part a normally graded layer that contains only blocks <1 m in size. The different lithologies present are totally mixed. These observations suggest that VDA II may be of the Bezymianny-type and that it underwent a flow transformation from a turbulent to a stratified flow consisting of a basal hyperconcentrated laminar body overlain by a dilute layer. (C) 2000 Elsevier Science B.V. All rights reserved.

Neuromonitorage après coma aigu aux soins intensifs [Multimodal neuromonitoring for the critical care management of acute coma].

Management of neurocritical care patients is focused on the prevention and treatment of secondary brain injury, i.e. the number of pathophysiological intracerebral (edema, ischemia, energy dysfunction, seizures) and systemic (hyperthermia, disorders of glucose homeostasis) events that occur following the initial insult (stroke, hemorrhage, head trauma, brain anoxia) that may aggravate patient outcome. The current therapeutic paradigm is based on multimodal neuromonitoring, including invasive (intracranial pressure, brain oxygen, cerebral microdialysis) and non-invasive (transcranial doppler, near-infrared spectroscopy, EEG) tools that allows targeted individualized management of acute coma in the early phase. The aim of this review is to describe the utility of multimodal neuromonitoring for the critical care management of acute coma.

Evolution of the epithelial sodium channel and the sodium pump as limiting factors of aldosterone action on sodium transport.

Despite large changes in salt intake, the mammalian kidney is able to maintain the extracellular sodium concentration and osmolarity within very narrow margins, thereby controlling blood volume and blood pressure. In the aldosterone-sensitive distal nephron (ASDN), aldosterone tightly controls the activities of epithelial sodium channel (ENaC) and Na,K-ATPase, the two limiting factors in establishing transepithelial sodium transport. It has been proposed that the ENaC/degenerin gene family is restricted to Metazoans, whereas the α- and β-subunits of Na,K-ATPase have homologous genes in prokaryotes. This raises the question of the emergence of osmolarity control. By exploring recent genomic data of diverse organisms, we found that: 1) ENaC/degenerin exists in all of the Metazoans screened, including nonbilaterians and, by extension, was already present in ancestors of Metazoa; 2) ENaC/degenerin is also present in Naegleria gruberi, an eukaryotic microbe, consistent with either a vertical inheritance from the last common ancestor of Eukaryotes or a lateral transfer between Naegleria and Metazoan ancestors; and 3) The Na,K-ATPase β-subunit is restricted to Holozoa, the taxon that includes animals and their closest single-cell relatives. Since the β-subunit of Na,K-ATPase plays a key role in targeting the α-subunit to the plasma membrane and has an additional function in the formation of cell junctions, we propose that the emergence of Na,K-ATPase, together with ENaC/degenerin, is linked to the development of multicellularity in the Metazoan kingdom. The establishment of multicellularity and the associated extracellular compartment ("internal milieu") precedes the emergence of other key elements of the aldosterone signaling pathway.

Sediment budget monitoring of debris-flow and bedload transport in the Manival Torrent, SE France

Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. Event-based sediment budget monitoring in the active Manival debris-flow torrent in the French Alps during a two-year period gave insights into the catchment-scale sediment routing during moderate rainfall intensities which occur several times each year. The monitoring was based on intensive topographic resurveys of low- and high-order channels using different techniques (cross-section surveys with total station and high-resolution channel surveys with terrestrial and airborne laser scanning). Data on sediment output volumes from the main channel were obtained by a sediment trap. Two debris-flows were observed, as well as several bedload transport flow events. Sediment budget analysis of the two debris-flows revealed that most of the debris-flow volumes were supplied by channel scouring (more than 92%). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitude is proposed.

Multimodal MRI analysis of structural and functional networks in the human brain : application to two clinical studies : driving abilities under THC intoxication and early white matter changes in FXTAS

Les approches multimodales dans l'imagerie cérébrale non invasive sont de plus en plus considérées comme un outil indispensable pour la compréhension des différents aspects de la structure et de la fonction cérébrale. Grâce aux progrès des techniques d'acquisition des images de Resonance Magnetique et aux nouveaux outils pour le traitement des données, il est désormais possible de mesurer plusieurs paramètres sensibles aux différentes caractéristiques des tissues cérébraux. Ces progrès permettent, par exemple, d'étudier les substrats anatomiques qui sont à la base des processus cognitifs ou de discerner au niveau purement structurel les phénomènes dégénératifs et développementaux. Cette thèse met en évidence l'importance de l'utilisation d'une approche multimodale pour étudier les différents aspects de la dynamique cérébrale grâce à l'application de cette approche à deux études cliniques: l'évaluation structurelle et fonctionnelle des effets aigus du cannabis fumé chez des consommateurs réguliers et occasionnels, et l'évaluation de l'intégrité de la substance grise et blanche chez des jeunes porteurs de la prémutations du gène FMR1 à risque de développer le FXTAS (Fragile-X Tremor Ataxia Syndrome). Nous avons montré que chez les fumeurs occasionnels de cannabis, même à faible concentration du principal composant psychoactif (THC) dans le sang, la performance lors d'une tâche visuo-motrice est fortement diminuée, et qu'il y a des changements dans l'activité des trois réseaux cérébraux impliqués dans les processus cognitifs: le réseau de saillance, le réseau du contrôle exécutif, et le réseau actif par défaut (Default Mode). Les sujets ne sont pas en mesure de saisir les saillances dans l'environnement et de focaliser leur attention sur la tâche. L'augmentation de la réponse hémodynamique dans le cortex cingulaire antérieur suggère une augmentation de l'activité introspective. Une investigation des ef¬fets au niveau cérébral d'une exposition prolongée au cannabis, montre des changements persistants de la substance grise dans les régions associées à la mémoire et au traitement des émotions. Le niveau d'atrophie dans ces structures corrèle avec la consommation de cannabis au cours des trois mois précédant l'étude. Dans la deuxième étude, nous démontrons des altérations structurelles des décennies avant l'apparition du syndrome FXTAS chez des sujets jeunes, asymptomatiques, et porteurs de la prémutation du gène FMR1. Les modifications trouvées peuvent être liées à deux mécanismes différents. Les altérations dans le réseau moteur du cervelet et dans la fimbria de l'hippocampe, suggèrent un effet développemental de la prémutation. Elles incluent aussi une atrophie de la substance grise du lobule VI du cervelet et l'altération des propriétés tissulaires de la substance blanche des projections afférentes correspondantes aux pédoncules cérébelleux moyens. Les lésions diffuses de la substance blanche cérébrale peu¬vent être un marquer précoce du développement de la maladie, car elles sont liées à un phénomène dégénératif qui précède l'apparition des symptômes du FXTAS. - Multimodal brain imaging is becoming a leading tool for understanding different aspects of brain structure and function. Thanks to the advances in Magnetic Resonance imaging (MRI) acquisition schemes and data processing techniques, it is now possible to measure different parameters sensitive to different tissue characteristics. This allows for example to investigate anatomical substrates underlying cognitive processing, or to disentangle, at a pure structural level degeneration and developmental processes. This thesis highlights the importance of using a multimodal approach for investigating different aspects of brain dynamics by applying this approach to two clinical studies: functional and structural assessment of the acute effects of cannabis smoking in regular and occasional users, and grey and white matter assessment in young FMR1 premutation carriers at risk of developing FXTAS. We demonstrate that in occasional smokers cannabis smoking, even at low concentration of the main psychoactive component (THC) in the blood, strongly decrease subjects' performance on a visuo-motor tracking task, and globally alters the activity of the three brain networks involved in cognitive processing: the Salience, the Control Executive, and the Default Mode networks. Subjects are unable to capture saliences in the environment and to orient attention to the task; the increase in Hemodynamic Response in the Anterior Cingulate Cortex suggests an increase in self-oriented mental activity. A further investigation on long term exposure to cannabis, shows a persistent grey matter modification in brain regions associated with memory and affective processing. The degree of atrophy in these structures also correlates with the estimation of drug use in the three months prior the participation to the study. In the second study we demonstrate structural changes in young asymptomatic premutation carriers decades before the onset of FXTAS that might be related to two different mechanisms. Alteration of the cerebellar motor network and of the hippocampal fimbria/ fornix, may reflect a potential neurodevelopmental effect of the premutation. These include grey matter atrophy in lobule VI and modification of white matter tissue property in the corresponding afferent projections through the Middle Cerebellar Peduncles. Diffuse hemispheric white matter lesions that seem to appear closer to the onset of FXTAS and be related to a neurodegenerative phenomenon may mark the imminent onset of FXTAS.

Protease-activated receptor 2 signalling promotes dendritic cell antigen transport and T-cell activation in vivo.

Deficiency of protease-activated receptor-2 (PAR2) modulates inflammation in several models of inflammatory and autoimmune disease, although the underlying mechanism(s) are not understood. PAR2 is expressed on endothelial and immune cells, and is implicated in dendritic cell (DC) differentiation. We investigated in vivo the impact of PAR2 activation on DCs and T cells in PAR2 wild-type (WT) and knockout (KO) mice using a specific PAR2 agonist peptide (AP2). PAR2 activation significantly increased the frequency of mature CD11c(high) DCs in draining lymph nodes 24 hr after AP2 administration. Furthermore, these DCs exhibited increased expression of major histocompatibility complex (MHC) class II and CD86. A significant increase in activated (CD44(+) CD62(-)) CD4(+) and CD8(+) T-cell frequencies was also observed in draining lymph nodes 48 hr after AP2 injection. No detectable change in DC or T-cell activation profiles was observed in the spleen. The influence of PAR2 signalling on antigen transport to draining lymph nodes was assessed in the context of delayed-type hypersensitivity. PAR2 WT mice that were sensitized by skin-painting with fluorescein isothiocyanate (FITC) to induce delayed-type hypersensitivity possessed elevated proportion of FITC(+) DCs in draining lymph nodes 24 hr after FITC painting when compared with PAR2 KO mice (0.95% versus 0.47% of total lymph node cells). Collectively, these results demonstrate that PAR2 signalling promotes DC trafficking to the lymph nodes and subsequent T-cell activation, and thus provides an explanation for the pro-inflammatory effect of PAR2 in animal models of inflammation.

Epithelial sodium transport and its control by aldosterone: the story of our internal environment revisited.

Transcription and translation require a high concentration of potassium across the entire tree of life. The conservation of a high intracellular potassium was an absolute requirement for the evolution of life on Earth. This was achieved by the interplay of P- and V-ATPases that can set up electrochemical gradients across the cell membrane, an energetically costly process requiring the synthesis of ATP by F-ATPases. In animals, the control of an extracellular compartment was achieved by the emergence of multicellular organisms able to produce tight epithelial barriers creating a stable extracellular milieu. Finally, the adaptation to a terrestrian environment was achieved by the evolution of distinct regulatory pathways allowing salt and water conservation. In this review we emphasize the critical and dual role of Na(+)-K(+)-ATPase in the control of the ionic composition of the extracellular fluid and the renin-angiotensin-aldosterone system (RAAS) in salt and water conservation in vertebrates. The action of aldosterone on transepithelial sodium transport by activation of the epithelial sodium channel (ENaC) at the apical membrane and that of Na(+)-K(+)-ATPase at the basolateral membrane may have evolved in lungfish before the emergence of tetrapods. Finally, we discuss the implication of RAAS in the origin of the present pandemia of hypertension and its associated cardiovascular diseases.

Recommendations for the use of multimodal monitoring in the neurointensive care unit.

PURPOSE OF REVIEW: Multimodal monitoring (MMM) is routinely applied in neurointensive care. Unfortunately, there is no robust evidence on which MMM-derived physiologic variables are the most clinically relevant, how and when they should be monitored, and whether MMM impacts outcome. The complexity is even higher because once the data are continuously collected, interpretation and integration of these complex physiologic events into targeted individualized care is still embryonic. RECENT FINDINGS: Recent clinical investigation mainly focused on intracranial pressure, perfusion of the brain, and oxygen availability along with electrophysiology. Moreover, a series of articles reviewing the available evidence on all the MMM tools, giving practical recommendations for bedside MMM, has been published, along with other consensus documents on the role of neuromonitoring and electroencephalography in this setting. SUMMARY: MMM allows comprehensive exploration of the complex pathophysiology of acute brain damage and, depending on the different configuration of the pathological condition we are treating, the application of targeted individualized care. Unfortunately, we still lack robust evidence on how to better integrate MMM-derived information at the bedside to improve patient management. Advanced informatics is promising and may provide us a supportive tool to interpret physiologic events and guide pathophysiological-based therapeutic decisions.