Protein reservoir system

Figure 1. The hydrated state of a protein reservoir system. Key parameters controlling release are membrane composition, area, thickness, and concentration gradient.

The samples were mounted in the test cell with particular attention that they were not contaminated by contact with any liquids. The flow cell was then connected to a plumbing system that contained a protein solution reservoir, a wash buffer reservoir, and a three-way-valve. The flow cell, with the test materials mounted at the wedge surface, was connected to the system and filled with buffer. The system was purged of air, and degassed under vacuum. After the establishment of a flow of buffer through the cell, the three-way-valve was used to switch the input line to the sample protein reservoir for a selected period of time. Following the exposure of the surfaces to the protein solution, the valve was switched back to the buffer reservoir and the cell flushed with about 300 ml. of buffer. 

Another critical consideration in protein delivery from hydrogel systems is the potential for protein denaturation in the device. For diffusion-controlled delivery systems, where water is the main transporting medium, the protein solution stability governs the type of device. Extended releasing times can be achieved with reservoir systems (Fig. 1) for highly stable proteins (Langer, 1990). Alternatively, dehydrated delivery systems... 

Reservoir delivery systems have been developed in a variety of styles, ranging from microcapsules to hollow fibers to liposomes. Hayashi et al. (1994) produced delivery systems by encapsulating proteins and hormones inpoly-L-lactide microspheres by a solvent evaporation method. The release mechanism for hormones entrapped in liposomes was studied by Ho et al (1986). Progesterone and hydrocortisone skin permeation was enhanced by the presence ofthe liposomes no penetration ofthe liposomes was observed. Examples ofthe most common hydrogels employed in reservoir systems are crystalline-rubbery PEG, PAAm, celluloses, PAA, and PHEMA. 

The Higuchi equation (Eq. 22) has been applied to systems in which the initial protein concentration per unit volume (A) is above its solubility in that hydrogel matrix, c as found in a reservoir system. 

Though the above strategies are currently in use for a variety of treatment options, most efforts in the design of DDS have been focused on biodegradable reservoir systems for example, the treatment of prostate cancer and protein hormone delivery. In these materials, degradation occurs in four steps ... 

Bio-nanocomposites based on calcium phosphates can perform other innovative fundions such as acting as a reservoir for the controlled release of bioadive compounds once the material is implanted in the bone defect. For instance, the incorporation of a morphogenetic protein that promotes bone regeneration in an HAP-alginate-collagen system [110] or a vitamin in a Ca-deficient HAP-chitosan nanocomposite [111] are recent examples of this kind of application. 

Diafiltration is a process whereby an ultrafiltration system is utilized to reduce or eliminate low molecular mass molecules from a solution and is sometimes employed as part of biopharmaceuti-cal downstream processing. In practice, this normally entails the removal of, for example, salts, ethanol and other solvents, buffer components, amino acids, peptides, added protein stabilizers or other molecules from a protein solution. Diafiltration is generally preceded by an ultrafiltration step to reduce process volumes initially. The actual diafiltration process is identical to that of ultrafiltration, except for the fact that the level of reservoir is maintained at a constant volume. This is achieved by the continual addition of solvent lacking the low molecular mass molecules that are to be removed. By recycling the concentrated material and adding sufficient fresh solvent to the system such that five times the original volume has emerged from the system as permeate, over 99... 

Continuous systems use the same buffer, at constant pH, in the gel, sample, and electrode reservoirs. With continuous systems, the sample is loaded directly on the gel in which separation will occur. The sample application buffer is the same as the gel and electrode buffer, but at about half the concentration. The localized voltage drop that results from decreased conductivity in the sample solution helps drive sample proteins into the gel and sharpens protein bands. Once inside a gel, proteins are separated on the basis of their individual (gel-mediated) mobility differences. Bandwidths are highly dependent on the height of the applied sample... 

It is hard to believe that, in order to see how the enzyme works, or how the protein folds up, one must view the movie in its entirety. It is more plausible that there are only a few interesting parts, during which the system passes through critical bottlenecks in its configuration space the rest of the time being spent exploring large, equilibrated reservoirs between the bottlenecks. If the trajectory calculation were... 

Less than 25 pL of the solution of purified protein is mixed with an equal amount of the reservoir solution, giving precipitant concentration about 50% of that required for protein crystallization. This solution is suspended as a droplet underneath a cover glass, which is sealed onto the top of the reservoir grease. Because the precipitant is the major solute present, vapor diffusion in this closed system results in net transfer of water from the protein solution to the reservoir, until the precipitant concentration is the same in both solutions. Because the reservoir is much larger than the protein solution, the final concentration of the precipitant in the protein solution is nearly equal to that in the reservoir. When the system comes to equilibrium, net transfer of water ceases, and the protein solution is maintained at the optimal precipitant con-... 

As was indicated earlier, the circulatory system and components in the blood stream are primarily responsible for the transport of toxicants to target tissues or reservoirs. Erythrocytes and lymph can play important roles in the transport of toxicants, but compared to plasma proteins, their role in toxicant distribution is relatively minor for most toxicants. Plasma protein binding can affect distribution because only the unbound... 

There is emerging evidence that OSA may be a pro-inflammatory disorder with elevated circulating cytokines [60]. Abdominal visceral fat is a major reservoir of cytokines, and obesity is a leading risk factor for the presence of OSA [60], The mechanism(s) whereby pro-inflammatory cytokines are elevated in OSA is not fully elucidated, but may be related to the excessive sympathetic nervous system activation notable in OSA. Tumor necrosis factor (TNF)-a and interleukin (IL)-6 levels are elevated in OSA [61,62] and the circadian rhythm of TNF-a is disrupted in OSA [63]. IL-6 levels are higher again in OSA patients with systemic hypertension compared to normotensive apneics [60], IL-6 levels return to normal in OSA patients treated effectively with CPAP [64]. Other mediators of inflammation elevated in OSA include intercellular adhesion molecule-1 and C-reactive protein, the latter being synthesized primarily in hepatocytes in response to IL-6 [60], The presence of these and other pro-inflammatory cytokines may link to the increased prevalence of cardiovascular morbidity in OSA. 

---