Basic features of the polyamide membranes

In vivo secretome sampling technology for proteomics

Secretome is a critical mediator for cell-cell and microbe-cell interaction. Identification of secretome will endow researchers with important biomarkers and therapeutic targets as well as reinforce the current methods used in the systems biology research of cell-cell interactions. Here, we introduce an in vivo sampling technique using capillary ultrafiltration (CUF) probes that are capable of continuously collecting pure in vivo secretome from tissue microenvironments. Great benefits of CUF probes when compared with other current sampling techniques have been acknowledged. CUF probes can be designed to fit various in vivo models and they are easily adapted to different protein-detection systems including mass spectrometers. The future challenges and clinical advantages of CUF probe sampling are also highlighted in this review. Many prospective properties such as simple manipulation, dynamic sampling, pathogen clearance, online mass spectrometric coupling, and disease treatment and monitoring have made CUF probes attractive for clinical uses in the near future.

Adsorption of the uremic toxin p-cresol onto hemodialysis membranes and microporous adsorbent zeolite silicalite

Para-cresol CH3C6H4OH is a protein-bound solute which is not eliminated efficiently by hemodialysis systems. In this study, we present adsorption of p-cresol as a complementary process to hemodialysis. The kinetics and isotherms of adsorption onto cellulose-based membranes (cellulose diacetate and triacetate), synthetic membranes (polyamide, polysulfone, polyacrylonitrile and polymethylmethacrylate) and microporous zeolite silicalite (MFI), have been evaluated in static conditions. The results indicate that p-cresol has a low affinity to all membranes but polysulfone and polyamide and that the times to reach equilibrium conditions are slow. In contrast, equilibration time on silicalite is fast (2 min to eliminate 90%) while adsorption levels are high (maximum adsorption about 106 mg g(-1)). Adsorption onto microporous adsorbents could be a novel way to eliminate uremic toxins from blood.

Dialyzer membranes as determinants of the adequacy of dialysis

Hemodialysis membranes have undergone a gradual but substantial evolution over the past few decades. Classification of modern dialyzer membranes by chemical composition bears little relationship to their functional characteristics. The fundamental properties that determine the capacity of the membrane to remove solutes and fluids are its surface area, thickness, pore size, pore density, and potential to adsorb proteins. Dialyzer membrane performance is characterized clinically by its efficiency, defined as the potential to remove urea and presented as the mass-transfer area coefficient (KoA) and ultrafiltration coefficient (K(uf) ),defined as the potential to remove water adjusted for the transmembrane pressure. The parameter K(uf) usually, but not invariably, correlates with the membrane permeability, defined as the potential to remove middle molecules, with beta2-microglobulin being the currently popular marker. The sieving coefficient reflects the membrane potential to transport solutes by convection and is particularly useful for hemofiltration. Enhancing solute clearance is accomplished clinically by increasing blood and dialysate flow rates, strategies that also are applicable to middle molecules for highly permeable membranes. Novel designs of dialyzers include the optimization of fluid flow path geometry and increasing the membrane pore selectivity for solutes by using nanotechnology.

Hollow fiber shape alters solute clearances in high flux hemodialyzers

The mass transfer properties of hemodialyzers containing hollow fiber membranes are known to be influenced by membrane chemical composition, surface area, and pore size; however, the effects of hollow fiber shape (or configuration) and packing density within the dialyzer housing have not been well characterized. We determined, both in vitro and ex vivo (clinical), solute clearances and mass transfer-area coefficients (KoA) for high flux dialyzers containing polysulfone hollow fibers of identical chemical composition but different shapes. Hemoflow F80A (1.8 m2 of membrane surface area) dialyzers contained hollow fibers with a conventional shape, but Optiflux F180A (1.8 m2), F200A (2.0 m2), and F200NR (2.0 m2) dialyzers contained hollow fibers with a wavy shape. Clearances and KoA values determined in vitro for urea and creatinine increased with increasing dialysate flow rate and were higher for Optiflux F180A and F200A dialyzers than for Hemoflow F80A dialyzers. In vitro clearances for lysozyme and myoglobin were also higher for Optiflux F180A and F200A dialyzers than for Hemoflow F80A dialyzers, suggesting that a wavy hollow fiber shape increases mass transfer by increasing effective membrane surface area, conceivably by altering dialysate flow patterns. Urea clearances and KoA values determined ex vivo were higher for Optiflux F200NR dialyzers than for Hemoflow F80A dialyzers, confirming that the in vitro results are applicable to clinical hemodialysis. These increases in mass transfer efficiency for dialyzers containing hollow fibers with a wavy shape are consistent with improved mass transfer within the dialysate compartment as evidenced by the manufacturer-reported dialysate pressure-flow relationships. We conclude that the mass transfer characteristics of high flux dialyzers can be altered by the shape of the hollow fibers.

Properties of membranes used for hemodialysis therapy

Recent trends show a progressive increase in the use of modified cellulosic and synthetic dialyzers and a corresponding decrease in the utilization rate of unmodified cellulosic dialyzers. The purpose of this article is to describe current membrane and dialyzer technology, with the focus almost entirely on modified cellulosic and synthetic membranes. A general overview of membrane-related determinants of dialyzer performance is first presented, followed by a discussion of specific characteristics of some of the more commonly used membranes and dialyzers.

Does convective dialysis therapy applied daily approach renal blood purification?

Outcome studies in dialysis have generally failed to show an impact of changes in membrane flux or biocompatibility, and only dose increases up to a certain level have been shown to improve survival significantly. However, to see an effect of a potentially improved dialysis treatment, all available factors that make dialysis more physiological may need to be combined. A membrane that mimics the glomerular basement membrane in being hemocompatible, having a high hydraulic permeability and a generous sieving, yet not leading to albumin loss could be used. The dialysis fluid composition could be individualized, and the quality and volume appropriate for the selected application. The new system of online-prepared ultrapure dialysis fluid and sterile infusion solutions, as integral parts of the treatment, are cost effective and labor saving as well as biocompatible. Ideally, we should select a blood purification method that covers the same range of solutes as the kidney. Convection is equally effective for all solutes that can pass through the membrane, and the corresponding renal therapy is hemofiltration. For enhanced small solute removal, convection can be combined with diffusion as in hemodiafiltration, which has the potential to achieve the largest solute removal over a wide molecular weight spectrum among all forms of dialysis. Finally, the dialysis treatment should be applied as often as is practically possible-preferably daily-in order to reduce the peaks caused by uremic toxins, the exposure to acidosis and alkalosis, and the burden on the cardiovascular system by overhydration. While the designed therapy is already technically feasible today, a positive result from outcome studies will be needed to bring about the political and economic decisions required to change conventional dialysis into a treatment approaching true renal blood purification.

Beta2-microglobulin and low-flux synthetic dialyzers

The aim of this study was to compare the effect on beta2-microglobulin (beta2-M) plasma levels of dialyzers with 3 low-flux synthetic membranes and regenerated cellulose (Cuprophan) in 12 chronic dialysis patients. The synthetic membrane materials chosen were low-flux polymethylmethacrylate (PMMA), low-flux polysulfone (PS 400), and polycarbonate-polyether (Gambrane). Adequate and comparable removal of small solutes was provided by dialyzers with all 4 membrane materials used under similar conditions. A significant reduction of beta2-M plasma levels was seen only with Gambrane while the other 2 synthetic membrane materials gave rise to increases similar to those known to occur with Cuprophan. After correction for the hemoconcentration caused by ultrafiltration, dialysis with Gambrane showed a 24% lower plasma beta2-M level while the beta2-M concentrations with the other 3 membrane materials were practically unchanged. In addition, the efficiency of Gambrane dialyzers in beta2-M removal was able to significantly lower the predialysis plasma beta2-M levels after only 5 dialysis sessions. The hemocompatibility of the 3 synthetic low-flux membranes as judged by the white blood cell (WBC) count and complement activation was similar and therefore cannot be used to explain the different beta2-M plasma levels. In anticipation of gaining further insight into the mechanisms of accumulation and deposition of beta2-M in dialysis patients, a worthwhile approach may be to use a low-flux membrane such as Gambrane which combines removal with protection against potential activating factors in the dialysis fluid.

Effect of hemofiltration on hemodynamics and systemic concentrations of anaphylatoxins and cytokines in human sepsis

OBJECTIVE

To determine whether hemofiltration (HF) can eliminate cytokines and complement components and alter systemic hemodynamics in patients with severe sepsis.

DESIGN

Prospective observation study.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

16 patients with severe sepsis.

INTERVENTIONS

Continuous zero-balanced HF without dialysis (ultrafiltrate rate 2 l/h) was performed in addition to pulmonary artery catheterization, arterial cannulation, and standard intensive care treatment.

MEASUREMENTS AND MAIN RESULTS

Plasma and ultrafiltrate concentrations of cytokines (the interleukins IL-1 beta, IL-6, IL-8, and tumor necrosis factor alpha) and of complement components (C3adesArg, C5adesArg) were measured after starting HF (t0) and 4 h (t4) and 12 h later (t12). Hemodynamic variables including mean arterial pressure (MAP), mean central venous pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output were serially determined. During HF, cytokine plasma concentrations remained constant. However, C3adesArg and C5adesArg plasma concentrations showed a significant decline during 12-h HF (C3adesArg: t0 = 676.9 +/- 99.7 ng/ml vs t12 = 467.8 +/- 71, p < 0.01; C5adesArg: 26.6 +/- 4.7 ng/ml vs 17.6 +/- 6.2, p < 0.01). HF resulted in a significant increase over time in systemic vascular resistance (SVR) and MAP (SVR at t0: 669 +/- 85 dyne.s/cm5 vs SVR at t12: 864 +/- 75, p < 0.01; MAP at t0: 69.9 +/- 3.5 mmHg vs MAP at t12: 82.2 +/- 3.7, p < 0.01).

CONCLUSIONS

HF effectively eliminated the anaphylatoxins C3adesArg and C5adesArg during sepsis. There was also a significant rise in SVR and MAP during high volume HF. Therefore, HF may represent a new modality for removal of anaphylatoxins and may, thereby, deserve clinical testing in patients with severe sepsis.

Hemofiltration in human sepsis: evidence for elimination of immunomodulatory substances

Continuous hemofiltration is widely used for renal replacement therapy in patients with acute renal failure. It has been suggested that hemofiltration may also eliminate toxic mediators thought to be important in the pathophysiology of sepsis. The present study examined whether hemofiltration can activate or eliminate inflammatory mediators in patients with sepsis, and whether ultrafiltrate can alter specific functions of peripheral blood mononuclear leukocytes (PBMC) in vitro. Veno-venous hemofiltration was performed in 16 patients and in 5 healthy volunteers. Pre-filter (afferent), post-filter (efferent) and ultrafiltrate concentrations of cytokines (IL-1 beta, IL-6, IL-8, TNF alpha) and of complement components (C3, C3adesArg, C5adesArg, terminal complement complex) were measured after the beginning of hemofiltration (t0), and 60 minutes later (t60). PBMC, and monocyte and lymphocyte subfractions were incubated with ultrafiltrate, and cytokines were determined in the supernatants. Hemofiltration did not induce significant mediator activation. There was no evidence for significant cytokine elimination. However, pre-filter C3adesArg concentration showed a significant decline during hemofiltration (patients: t0 = 676.9 +/- 99.7 ng/ml, t60 = 545.4 +/- 83.2, P < 0.001; volunteers: t0 = 54.8 +/- 13.3 ng/ml, t60 = 33.9 +/- 10.7, P < 0.001). Ultrafiltrate from septic patients significantly stimulated PBMC and monocyte TNF alpha release, but suppressed lymphocyte IL-2 and IL-6 production. Ultrafiltrate from volunteers was without effect. Hemofiltration effectively eliminates certain mediators such as C3adesArg. Ultrafiltrate contains compounds with significant immunomodulatory qualities. Therefore, hemofiltration may represent a new modality for removal of immunomodulatory mediators.