Mild pressure induces resistance of erythrocytes to hemolysis by snake venom phospholipase A2

Recombinant human scFv antibody fragments against phospholipase A2 from Naja naja and Echis carinatus snake venoms: In vivo neutralization and mechanistic insights

Snake envenomation results in a range of clinical sequelae, and widely used animal-based conventional antivenoms exhibit several limitations including the adverse immunological effects in human snake bite victims. Therefore, human monoclonal anti-snake venom antibodies or fragments can be an alternate therapy for overcoming the existing limitations. We developed venom-neutralizing humanized scFv antibodies and analyzed biochemical mechanisms associated with the inhibition of toxicity. Tomlinson I and J human scFv antibody libraries were screened against Naja naja and Echis carinatus venoms, and seven unique scFv antibodies were obtained. Further, specific toxins of snake venom interacting with each of these scFvs were identified, and phospholipase A2 (PLA2) was found to be prominently captured by the phage-anchored scFv antibodies. Our study indicated PLA2 to be one of the abundant toxins in Naja naja and Echis carinatus venom samples. The scFvs binding to PLA2 were used to perform in vivo survival assay using the mouse model and in vitro toxin inhibition assays. scFv N194, which binds to acidic PLA2, protected 50% of mice treated with Naja naja venom. Significant prolongation of survival time and 16% survival were observed in Echis carinatus venom-challenged mice treated with scFv E113 and scFv E10, respectively. However, a combination comprised of an equal amount of two scFvs, E113 and E10, both interacting with basic PLA2, exhibited synergistically enhanced survival of 33% in Echis carinatus venom-challenged mice. No such synergistically enhanced survival was observed in the case of combinatorial treatment with anti-Naja naja scFvs, N194, and N248. These scFvs demonstrated partial inhibition of venom-induced myotoxicity, and E113 also inhibited hemolysis by 50%, which corroborates the enhanced survival during combinatorial treatment in Echis carinatus venom-challenged mice.

Noninvasive cardiac absolute pressure sensing: a fundamentally new approach

Noninvasive cardiac pressure sensing using an imaging modality to ascertain changes in absolute pressure would be of immense benefit as a replacement for the Swan-Ganz catheter in current use. However, very little research has been published in this area. This paper reviews the small number of relevant studies to date, points out the many gaps in the research record, and discusses possible new avenues of approach in solving the problem.

The transduction of very small hydrostatic pressures

This paper reviews experiments in which cells, subjected to hydrostatic pressures of 20 kPa or less, (micro-pressures), demonstrate a perturbation in growth and or metabolism. Similarly, the behavioural responses of aquatic animals (lacking an obvious compressible gas phase) to comparable pressures are reviewed. It may be shown that in both cases the effect of such very low hydrostatic pressures cannot be mediated through the thermodynamic mechanisms which are invoked for the effects of high hydrostatic pressure. The general conclusion is that cells probably respond to micro-pressures through a mechanical process. Differential compression of cellular structures is likely to cause shear and strain, leading to changes in enzyme and/or ion channel activity. If this conclusion is true then it raises a novel question about the involvement of 'micro-mechanical' effects in cells subjected to high hydrostatic pressure. The responses of aquatic animals to micro-pressures may be accounted for, using the model case of the crab, by the mechanical, bulk, compression of hair cells in the statocysts, the organ of balance. If this is true, it raises the interesting question of why the putative cellular mechanisms of micro-pressure transduction appear to have been superseded by the statocyst.

Human red blood cell shape and volume are changed by physiological levels of hydrostatic pressure

Application of hydrostatic pressure of several atmospheres (atm), such as that applied in diving or hyperbaric treatment, has been previously shown to induce the release of membrane components into the extracellular medium. As the shape of red blood cells (RBC) is sensitive to membrane composition, this might imply a subsequent change in RBC shape and volume. The present study demonstrates that application of hydrostatic pressure of up to 15 atm changes the shape of RBC from the normal discoids to stomatocytes (cup-shaped) and accordingly increases their volume. Changes in RBC shape and volume are known to impair physiological and cellular function. Thus, these changes might be pertinent to hemodynamic and physiological disorders observed in humans subjected to elevated pressure.

Methane-induced haemolysis of human erythrocytes

Human erythrocytes were exposed to high concentrations of methane and nitrogen through the application of elevated partial pressures of these gas molecules. Cell leakage (haemolysis) was measured for cells exposed to these gases under a wide range of experimental conditions. Application of methane produces haemolysis at pressures far below the hydrostatic pressures known to disrupt membrane or protein structure. The effects of changes in buffer, temperature, diffusion rate and detergents were studied. Methane acts co-operatively with detergents to produce haemolysis at much lower detergent concentration than is required in the absence of methane or in the presence of nitrogen. At sufficiently high concentrations of methane, all cells are haemolysed. Increased temperature enhances the effect. Methane produces 50% haemolysis at a concentration of about 0.33 M compared with about 7.5 M methanol required for the same degree of haemolysis.

Red blood cell aggregability is enhanced by physiological levels of hydrostatic pressure

The effect of hydrostatic pressure of up to 15 bars on the aggregability of rat and human red blood cells (RBC), i.e., their capability to form aggregates, was studied using computerized image analysis. The aggregate size distribution was determined under ambient pressure, following application of hydrostatic pressure for various durations up to 2 h. It was found that RBC aggregability markedly increases, up to three-fold, as the pressure which had been applied was increased. Accordingly, higher shear stress is required for dispersing the aggregates of pressure-treated RBC than those of untreated cells. The median size of human RBC aggregates was about three times higher than that of rat RBC, and this ratio was maintained following pressure treatment. RBC aggregability is a major determinant in blood flow, especially in the microcirculation. Pressure at the levels used in this study occurs in physiological states such as hyperbaric treatment or diving. The enhanced aggregability induced by application of such pressure implies that blood flow in microvessels might be altered under conditions associated with elevated hydrostatic pressure.

Direct visualization of phosphorylase-phosphorylase kinase complexes by scanning tunneling and atomic force microscopy

In skeletal muscle the activation of phosphorylase b is catalyzed by phosphorylase kinase. Both enzymes occur in vivo as part of a multienzyme complex. The two enzymes have been imaged by atomic force microscopy and the results compared to those previously found by scanning tunneling microscopy. Scanning tunneling microscopy and atomic force microscopy have been used to view complexes between the activating enzyme phosphorylase kinase and its substrate phosphorylase b. Changes in the size and shape of phosphorylase kinase were observed when it bound phosphorylase b.