A mathematical model for top-shelf vertigo: the role of sedimenting otoconia in BPPV

Benign Paroxysmal Positional Vertigo (BPPV) is a mechanical disorder of the vestibular system in which calcite particles called otoconia interfere with the mechanical functioning of the fluid-filled semicircular canals normally used to sense rotation. Using hydrodynamic models, we examine the two mechanisms proposed by the medical community for BPPV: cupulolithiasis, in which otoconia attach directly to the cupula (a sensory membrane), and canalithiasis, in which otoconia settle through the canals and exert a fluid pressure across the cupula. We utilize known hydrodynamic calculations and make reasonable geometric and physical approximations to derive an expression for the transcupular pressure $\Delta P_c$ exerted by a settling solid particle in canalithiasis. By tracking settling otoconia in a two-dimensional model geometry, the cupular volume displacement and associated eye response (nystagmus) can be calculated quantitatively. Several important features emerge: 1) A pressure amplification occurs as otoconia enter a narrowing duct; 2) An average-sized otoconium requires approximately five seconds to settle through the wide ampulla, where $\Delta P_c$ is not amplified, which suggests a mechanism for the observed latency of BPPV; and 3) An average-sized otoconium beginning below the center of the cupula can cause a volumetric cupular displacement on the order of 30 pL, with nystagmus of order $2^\circ$/s, which is approximately the threshold for sensation. Larger cupular volume displacement and nystagmus could result from larger and/or multiple otoconia.Comment: 15 pages, 5 Figures updated, to be published in J. Biomechanic

Lack of a p21waf1/cip-Dependent G1/S Checkpoint in Neural Stem and Progenitor Cells After DNA Damage In Vivo

The cyclin-dependent kinase inhibitor p21waf1/cip mediates the p53-dependent G1/S checkpoint, which is generally considered to be a critical requirement to maintain genomic stability after DNA damage. We used staggered 5-ethynyl-2′deoxyuridine/5-bromo-2′-deoxyuridine double-labeling in vivo to investigate the cell cycle progression and the role of p21waf1/cip in the DNA damage response of neural stem and progenitor cells (NSPCs) after exposure of the developing mouse cortex to ionizing radiation. We observed a radiation-induced p21-dependent apoptotic response in migrating postmitotic cortical cells. However, neural stem and progenitor cells (NSPCs) did not initiate a p21waf1/cip1-dependent G1/S block and continued to enter S-phase at a similar rate to the non-irradiated controls. The G1/S checkpoint is not involved in the mechanisms underlying the faithful transmission of the NSPC genome and/or the elimination of critically damaged cells. These processes typically involve intra-S and G2/M checkpoints that are rapidly activated after irradiation. p21 is normally repressed in neural cells during brain development except at the G1 to G0 transition. Lack of activation of a G1/S checkpoint and apoptosis of postmitotic migrating cells after DNA damage appear to depend on the expression of p21 in neural cells, since substantial cell-to-cell variations are found in the irradiated cortex. This suggests that repression of p21 during brain development prevents the induction of the G1/S checkpoint after DNA damage. Stem Cells 2012;30:537–54

Bone Marrow Stromal Cell Transplantation Mitigates Radiation-Induced Gastrointestinal Syndrome in Mice

Nuclear accidents and terrorism presents a serious threat for mass casualty. While bone-marrow transplantation might mitigate hematopoietic syndrome, currently there are no approved medical countermeasures to alleviate radiation-induced gastrointestinal syndrome (RIGS), resulting from direct cytocidal effects on intestinal stem cells (ISC) and crypt stromal cells. We examined whether bone marrow-derived adherent stromal cell transplantation (BMSCT) could restitute irradiated intestinal stem cells niche and mitigate radiation-induced gastrointestinal syndrome.Autologous bone marrow was cultured in mesenchymal basal medium and adherent cells were harvested for transplantation to C57Bl6 mice, 24 and 72 hours after lethal whole body irradiation (10.4 Gy) or abdominal irradiation (16-20 Gy) in a single fraction. Mesenchymal, endothelial and myeloid population were characterized by flow cytometry. Intestinal crypt regeneration and absorptive function was assessed by histopathology and xylose absorption assay, respectively. In contrast to 100% mortality in irradiated controls, BMSCT mitigated RIGS and rescued mice from radiation lethality after 18 Gy of abdominal irradiation or 10.4 Gy whole body irradiation with 100% survival (p<0.0007 and p<0.0009 respectively) beyond 25 days. Transplantation of enriched myeloid and non-myeloid fractions failed to improve survival. BMASCT induced ISC regeneration, restitution of the ISC niche and xylose absorption. Serum levels of intestinal radioprotective factors, such as, R-Spondin1, KGF, PDGF and FGF2, and anti-inflammatory cytokines were elevated, while inflammatory cytokines were down regulated.Mitigation of lethal intestinal injury, following high doses of irradiation, can be achieved by intravenous transplantation of marrow-derived stromal cells, including mesenchymal, endothelial and macrophage cell population. BMASCT increases blood levels of intestinal growth factors and induces regeneration of the irradiated host ISC niche, thus providing a platform to discover potential radiation mitigators and protectors for acute radiation syndromes and chemo-radiation therapy of abdominal malignancies

Benign Paroxysmal Positional Vertigo

Benign paroxysmal positional vertigo (BPPV) is characterized by brief recurrent episodes of vertigo triggered by changes in head position. BPPV is the most common etiology of recurrent vertigo and is caused by abnormal stimulation of the cupula by free-floating otoliths (canalolithiasis) or otoliths that have adhered to the cupula (cupulolithiasis) within any of the three semicircular canals. Typical symptoms and signs of BPPV are evoked when the head is positioned so that the plane of the affected semicircular canal is spatially vertical and thus aligned with gravity. Paroxysm of vertigo and nystagmus develops after a brief latency during the Dix-Hallpike maneuver in posterior-canal BPPV, and during the supine roll test in horizontal-canal BPPV. Positioning the head in the opposite direction usually reverses the direction of the nystagmus. The duration, frequency, and symptom intensity of BPPV vary depending on the involved canals and the location of otolithic debris. Spontaneous recovery may be expected even with conservative treatments. However, canalithrepositioning maneuvers usually provide an immediate resolution of symptoms by clearing the canaliths from the semicircular canal into the vestibule

Experimental concepts for toxicity prevention and tissue restoration after central nervous system irradiation

Several experimental strategies of radiation-induced central nervous system toxicity prevention have recently resulted in encouraging data. The present review summarizes the background for this research and the treatment results. It extends to the perspectives of tissue regeneration strategies, based for example on stem and progenitor cells. Preliminary data suggest a scenario with individually tailored strategies where patients with certain types of comorbidity, resulting in impaired regeneration reserve capacity, might be considered for toxicity prevention, while others might be "salvaged" by delayed interventions that circumvent the problem of normal tissue specificity. Given the complexity of radiation-induced changes, single target interventions might not suffice. Future interventions might vary with patient age, elapsed time from radiotherapy and toxicity type. Potential components include several drugs that interact with neurodegeneration, cell transplantation (into the CNS itself, the blood stream, or both) and creation of reparative signals and a permissive microenvironment, e.g., for cell homing. Without manipulation of the stem cell niche either by cell transfection or addition of appropriate chemokines and growth factors and by providing normal perfusion of the affected region, durable success of such cell-based approaches is hard to imagine

Implication of cardiac mitochondrial ROS production in cardiomyocyte signaling and cardiac rhythm

L’activation électrique des cardiomyocytes, via le courant de dépolarisation qu’elle induit, est primordiale dans la contraction cardiaque qui requiert l’adéquation de la production d'énergie par les mitochondries et des besoins énergétiques de l’appareil contractile. Les espèces radicalaires de l'oxygène (ROS) ont été récemment impliquées dans la régulation de nombreux acteurs du couplage excitation-contraction cardiaque. L’objectif de ce travail est d’explorer l'implication des ROS d'origine mitochondriale dans la régulation du couplage excitation-contraction au niveau du cardiomyocyte, en conditions physiologiques et pathologiques. C’est à cette fin qu’un modèle de surproduction endogène de ROS par addition de succinate - substrat énergétique mitochondrial - dans des cardiomyocytes isolés de cœur de rat a été mis au point. Différents protocoles pharmacologiques utilisant différents antioxydants (Trolox, MitoTEMPO et EUK) nous ont permis d’établir l'origine mitochondriale des ROS produits en présence de succinate. Enfin une étude pharmacologique utilisant la molécule OP2113 (inhibiteur spécifique de la production mitochondriale de ROS au niveau du complexe I de la chaine respiratoire- Brevet Philippe Diolez) nous a permis d'établir qu'environ 80% de cette production provenait du complexe I de la chaîne respiratoire. Notre travail s’est alors attaché à étudier, sur des cardiomyocytes isolés battants, les effets des ROS mitochondriaux sur différents paramètres du couplage excitation-contraction. Le succinate, via une surproduction de ROS mitochondriaux, provoque une baisse de 50% de l'amplitude de la contraction. L’amplitude de la contraction initiale est rétablie en présence de Trolox, MitoTEMPO ou OP2113, ce qui indique l'implication des ROS mitochondriaux et plus spécifiquement ceux produits au niveau du site IQ. Cette surproduction de ROS induit également une diminution de l’amplitude du transitoire calcique impliquant une diminution de la concentration en calcium systolique au cours de la contraction. Ces effets sont annulés en présence de Trolox et OP2113. Nous nous sommes alors attachés à moduler la concentration mitochondriale de calcium grâce à la cyclosporine A (inhibiteur du pore de transition mitochondrial) et au Ru360 (inhibiteur de l'entrée de calcium dans la mitochondrie). Il s’est avéré que ces inhibiteurs induisent une production de ROS insensible au Trolox et à OP2113 dont l'origine reste à établir. En conclusion une augmentation de la production mitochondriale de ROS se traduit par une diminution de la contraction intracytosolique et du transitoire calcique. L'ensemble de nos résultats illustre donc l’importance majeure de la mitochondrie dans le couplage excitation-contraction. Nos résultats ouvrent de nouvelles perspectives thérapeutiques dans le contexte de l’insuffisance cardiaque aigue ou chronique.The electrical activation of the cardiomyocyte through a generated depolarisation current is essential in the cardiac contraction, which requires the adequacy of the mitochondrial energy production and the energy needs of the contractile system. Radical oxygen species (ROS) have recently been involved in the regulation of many actors of the excitation-contraction coupling. The aim of this study was to explore the involvement of mitochondrial ROS in the regulation of the excitation-contraction coupling in cardiomyocytes, under physiological and pathological conditions. A model of endogenous ROS overproduction with the use of succinate was developed in isolated rat cardiomyocytes. Different pharmacological protocols, using various antioxidants (Trolox, Mito-Tempo,EUK and OP2113) allowed us to establish the mitochondrial origin of ROS production. Finally, the use of OP2113, (a specific inhibitor of mitochondrial ROS production, Patent P.Diolez) enabled us to establish that approximately 80 % of ROS production came from complex I in the respiratory chain. To start with, isolated cardiomyocytes were used to study the effects of mitochondrial ROS on different excitation-contraction coupling parameters. Succinate induced an overproduction of mitochondrial ROS, which lead to a drop of 50% of the contraction amplitude. The initial amplitude of contraction wasrecovered with addition of Trolox, Mito Tempo or OP2113, which demonstrates the implication of mitochondrial ROS produced at the site of Iq. Secondly, the overproduction of ROS leadsto a decrease of the calcium transient amplitude, due to a decrease of systolic calcium concentration during contraction. These effects were inhibited by Trolox and OP2113. Finally, mitochondrial calcium concentration was modulated with the use of Cyclosporin A (mitochondrial transition pore inhibitor) and Ru360 (mitochondrial calcium entry inhibitor). The inhibitors induced a ROS production unresponsive to Trolox and OP2113. The origin of which remains to be established. To conclude, an increase of mitochondrial ROS production results in a decrease of contraction amplitude and calcium transients. Our overall results demonstrate the critical significance of the mitochondrion in the excitation-contraction coupling. Our results open new therapeutic perspectives in the context of acute or chronic heart failure