Saturation diving; physiology and pathophysiology

In saturation diving, divers stay under pressure until most of their tissues are saturated with breathing gas. Divers spend a long time in isolation exposed to increased partial pressure of oxygen, potentially toxic gases, bacteria, and bubble formation during decompression combined with shift work and long periods of relative inactivity. Hyperoxia may lead to the production of reactive oxygen species (ROS) that interact with cell structures, causing damage to proteins, lipids, and nucleic acid. Vascular gas-bubble formation and hyperoxia may lead to dysfunction of the endothelium. The antioxidant status of the diver is an important mechanism in the protection against injury and is influenced both by diet and genetic factors. The factors mentioned above may lead to production of heat shock proteins (HSP) that also may have a negative effect on endothelial function. On the other hand, there is a great deal of evidence that HSPs may also have a "conditioning" effect, thus protecting against injury. As people age, their ability to produce antioxidants decreases. We do not currently know the capacity for antioxidant defense, but it is reasonable to assume that it has a limit. Many studies have linked ROS to disease states such as cancer, insulin resistance, diabetes mellitus, cardiovascular diseases, and atherosclerosis as well as to old age. However, ROS are also involved in a number of protective mechanisms, for instance immune defense, antibacterial action, vascular tone, and signal transduction. Low-grade oxidative stress can increase antioxidant production. While under pressure, divers change depth frequently. After such changes and at the end of the dive, divers must follow procedures to decompress safely. Decompression sickness (DCS) used to be one of the major causes of injury in saturation diving. Improved decompression procedures have significantly reduced the number of reported incidents; however, data indicate considerable underreporting of injuries. Furthermore, divers who are required to return to the surface quickly are under higher risk of serious injury as no adequate decompression procedures for such situations are available. Decompression also leads to the production of endothelial microparticles that may reduce endothelial function. As good endothelial function is a documented indicator of health that can be influenced by regular exercise, regular physical exercise is recommended for saturation divers. Nowadays, saturation diving is a reasonably safe and well controlled method for working under water. Until now, no long-term impact on health due to diving has been documented. However, we still have limited knowledge about the pathophysiologic mechanisms involved. In particular we know little about the effect of long exposure to hyperoxia and microparticles on the endothelium.

Pressure cycling technology in systems biology

Systems biologists frequently seek to integrate complex data sets of diverse analytes into a comprehensive picture of an organism's biological state under defined environmental conditions. Although one would prefer to collect these data from the same sample, technical limitations with traditional sample preparation methods often commit the investigator to extracting one type of analyte at the expense of losing all others. Often, volume further constrains the range of experiments that can be collected from a single sample. The practical solution employed to date has been to rely on information collected from multiple replicate experiments and similar historical or reported data. While this approach has been popular, the integration of information collected from disparate single-analyte sample preparation streams increases uncertainty due to nonalignment during comparative analysis, and such gaps accumulate quickly when combining multiple data sets. Regrettably, discontinuities between separate data streams can confound a whole understanding of the biological system being investigated. This difficulty is further compounded for researchers handling highly pathogenic samples, in which it is often necessary to use harsh chemicals or high-energy sterilization procedures that damage the target analytes. Ultra-high pressure cycling technology (PCT), also known as barocycling, is an emerging sample preparation strategy that has distinct advantages for systems biology studies because it neither commits the researcher to pursuing a specific analyte nor leads to the degradation of target material. In fact, samples prepared under pressure cycling conditions have been shown to yield a more complete set of analytes due to uniform disruption of the sample matrix coupled with an advantageous high pressure solvent environment. Fortunately, PCT safely sterilizes and extracts complex or pathogenic viral, bacterial, and spore samples without adversely affecting the constituent biomolecules valued as informative and meaningful analytes. This chapter provides procedures and findings associated with incorporating PCT into systems biology as a new and enabling approach to preanalytical sample treatment.

Development of high hydrostatic pressure in biosciences: pressure effect on biological structures and potential applications in biotechnologies

Compared to temperature, the development of pressure as a tool in the research field has emerged only recently (at the end of the XIXth century). Following several developments in Physics and Chemistry during the first half of the XXth century (in particular the synthesis of diamond in 1953-1954), high pressures were applied in Food Science, especially in Japan. The main objective was then to achieve the decontamination of foods while preserving their organoleptic properties. Now, a new step is engaged: the biological applications of high pressures, from food to pharmaceuticals and biomedical applications. This paper will focus on three main points: (i) a brief presentation of the pressure parameter and its characteristics, (ii) a description of the pressure effects on biological constituents from simple to more complex structures and (iii) a review of the different domains for which the application of high pressures is able to initiate potential developments in Biotechnologies.

A perfusion-based micro opto-fluidic system (PMOFS) for continuously in-situ immune sensing

This paper proposes a novel perfusion-based micro opto-fluidic system (PMOFS) as a reusable immunosensor for in-situ and continuous protein detection. The PMOFS includes a fiber optic interferometry (FOI) sensor housed in a micro-opto-fluidic chip covered with a microdialysis membrane. It features a surface regeneration mechanism for continuous detection. Gold nanoparticles (GNPs) labeled anti-rabbit IgG were used to enhance the immune conjugation signal by the elongated optical path from GNPs conjugation. Surface regeneration of the sensor was achieved through local pH level manipulation by means of a photoactive molecule, o-Nitrobenzaldehyde (o-NBA), which triggered the elution of immune complexes. Experimental results showed that the pH level of the o-NBA solution can be reduced from 7 to 3.5 within 20 seconds under UV irradiation, sufficient for an effective elution process. The o-NBA molecules, contained within poly(ethylene glycol) diacrylate (PEG) complexes, were trapped within the sensing compartment by the microdialysis membrane and would not leak into the outside environment. The pH variation was also limited in the neighborhood of the sensor surface, resulting in a self-contained sensing system. In-situ immune detection and surface regeneration of the sensing probe has been successfully carried out for two identical cycles by the same sensing probe, and the cycle time can be less than 8 minutes, which is so far the fastest method for continuous monitoring on protein/peptide molecules. In addition, the interference fringe shift of the sensor is linearly related to the concentration of anti-cytochrome C antibody solution and the detection limit approaches 10 ng/ml.

The use of high pressure for separation and production of bioactive molecules

Due to its action on the forces governing inter- and intramolecular interactions, the application of high pressure to biopurification or bio-elaboration of a product are of interest. The two closely thermodynamically related parameters, pressure and temperature, render processes based on their action clean, as no chemical reagents have to be added (and thus further removed) when they are applied. The use of high pressure in the development of desorption methods for the purification of bioactive molecules, particularly in the immunoaffinity field, is reviewed and discussed. Also mentioned is the application of the pressure parameter during the synthesis of a bioreagent. Finally, integrated processes relative to the synthesis and purification of these compounds are proposed.

Effects of high hydrostatic pressures on living cells: a consequence of the properties of macromolecules and macromolecule-associated water

Sixty percent of the Earth's biomass is found in the sea, at depths greater than 1000 m, i.e., at hydrostatic pressures higher than 100 atm. Still more surprising is the fact that living cells can reversibly withstand pressure shifts of 1000 atm. One explanation lies in the properties of cellular water. Water forms a very thin film around macromolecules, with a heterogeneous structure that is an image of the heterogeneity of the macromolecular surface. The density of water in contact with macromolecules reflects the physical properties of their different domains. Therefore, any macromolecular shape variations involving the reorganization of water and concomitant density changes are sensitive to pressure (Le Chatelier's principle). Most of the pressure-induced changes to macromolecules are reversible up to 2000 atm. Both the effects of pressure shifts on living cells and the characteristics of pressure-adapted species are opening new perspectives on fundamental problems such as regulation and adaptation.

Aromatic residues mediate the pressure-induced association of digoxigenin and antibody 26-10

We have previously found that the complex between fluorescently labeled digoxigenin and the monoclonal antibody 26-10 forms with a decrease in volume of approximately 30 ml/mol, leading to increased association of these species under applied hydrostatic pressure. In the present study, we have utilized a panel of mutant antibodies and Fab fragments, previously characterized for their importance in the binding affinity of digoxin:26-10, to probe the molecular basis of pressure sensitivity in this complex, as measured by fluorescence polarization spectroscopy. Several mutations that result in marked decreases in affinity exerted little or no significant effect on the association volume. Mutation at any of several key aromatic residues of the 26-10 Fab heavy chain led to a decrease in the pressure-induced association, and two mutants with Trp-->Arg mutations at heavy chain residue 100 exhibited pressure-induced dissociation. The effect of charged groups was found to depend on their proximity to contacting aromatic groups. The ability to understand and control the pressure sensitivity of antigen-antibody complexes has numerous potential applications in immunoseparations and immunosensors.

Effect of pressure on antigen-antibody complexes: modulation by temperature and ionic strength

Changes in the equilibrium binding affinity of antigen-antibody complexes subjected to hydrostatic pressures of about 2000 bar provide a potential means for the separation and recovery under mild conditions of biological molecules from immunoadsorbents or immunosensors. We have investigated the ability of temperature and ionic strength to modulate the pressure sensitivity of several antigen-antibody complexes in solution. For two different protein:monoclonal antibody complexes (BSA:9.1 and HEWL:HyHEL-10) exhibiting pressure-induced dissociation (positive association volume), we find little temperature dependence to the association volume. For another complex (digoxigenin:26-10) exhibiting pressure-induced association, the association volume increases with temperature, which, via a Maxwell relation, indicates that enthalpic changes drive the pressure effect. An increase in ionic strength decreases the affinity of binding the HEWL:HyHEL-5 complex, which contains several salt bridges. At low ionic strengths (<0.3 M), no pressure dependence of the free energy of association is observed, but at higher ionic strengths, significant pressure-induced association is observed, suggesting that positive contributions to the association volume provided by the salt bridges are counterbalanced by other (e.g., aromatic stacking) interactions that lead to negative association volumes. These results suggest that ionic strength may be used to modulate the pressure sensitivity of antigen antibody complexes, which may be useful in designing processes that exploit this phenomenon for immunoseparations.

A bioseparation apparatus with high-pressure fluid injection and fluid sampling

A novel apparatus in which fluids may be injected and sampled at high pressure is described. Bioseparation applications of the apparatus were demonstrated in three model systems: (1) lambdaDNA was eluted under pressure from an anion exchange column into a low-salt (0.25 M) buffer, thereby eliminating conventional time-consuming desalting procedures required for downstream analysis of the DNA; (2) RNA was separated under pressure from a RNA/DNA mixture, thereby enabling rapid differential preparation of nucleic acids; and (3) an antibody was purified from a protein mixture by affinity capture at one pressure and dissociation from the antigen binding partner at a second pressure, thereby enabling the immunoreactivities of both antibody and antigen to be preserved during the separation process.