Requirements and Pitfalls of Dialyzer Sieving Coefficients Comparisons.

Sieving coefficients reported in dialyzer data sheets and instructions for use (IFUs) indicate the potential of different solutes to pass across a particular membrane. Despite being measured in vitro, sieving coefficient data are often used as a predictor of the clinical performance of dialyzers. Although standards for the measurement of sieving coefficients exist, the stated methodologies do not offer sufficient guidance to ensure comparability of test results between different dialyzers. The aim of this work was to investigate the relationship between sieving coefficients and published clinical performance indicators for two solutes, albumin loss and beta-2 microglobulin (ß2 M) reduction ratio (RR), and to assess the impact of different in vitro test parameters on sieving coefficient values for albumin, ß2 M, and myoglobin. Clinical albumin loss and ß2 M RR for commercially available dialyzers used in hemodialysis (HD) and post-dilution hemodiafiltration (HDF) were extracted from the literature and plotted against sieving coefficients reported in data sheets and IFUs. Albumin, ß2 M, and myoglobin sieving coefficients of a selection of dialyzers were measured per the ISO 8637 standard. The impact of in vitro testing conditions was assessed by changing blood flow rate, ultrafiltration (UF) rate, sampling time, and origin of test plasma. Results showed variation in albumin loss and ß2 M RR for the same sieving coefficient across different dialyzers in HD and HDF. Changes in blood flow rates, UF rates, sampling time, and test plasma (bovine vs. human) caused marked differences in sieving coefficient values for all investigated solutes. When identical testing conditions were used, sieving coefficient values for the same dialyzer were reproducible. Testing conditions have a marked impact on the measurement of sieving coefficients, and values should not be compared unless identical conditions are used. Further, variability in observed clinical data in part reflects the lack of definition of test conditions.

In Vitro Dialysis of Cytokine-Rich Plasma With High and Medium Cut-Off Membranes Reduces Its Procalcific Activity.

Recently developed high-flux (HF) dialysis membranes with extended permeability provide better clearance of middle-sized molecules such as interleukins (ILs). Whether this modulation of inflammation influences the procalcific effects of septic plasma on vascular smooth muscle cells (VSMCs) is not known. To assess the effects of high cut-off (HCO) and medium cut-off (MCO) membranes on microinflammation and in vitro vascular calcification we developed a miniature dialysis model. Plasma samples from lipopolysaccharide-spiked blood were dialyzed with HF, HCO, and MCO membranes in an in vitro miniature dialysis model. Afterwards, IL-6 concentrations were determined in dialysate and plasma. Calcifying VSMCs were incubated with dialyzed plasma samples and vascular calcification was assessed. Osteopontin (OPN) and matrix Gla protein (MGP) were measured in VSMC supernatants. IL-6 plasma concentrations were markedly lower with HCO and MCO dialysis. VSMC calcification was significantly lower after incubation with MCO- and HCO-serum compared to HF plasma. MGP and OPN levels in supernatants were significantly lower in the MCO but not in the HCO group compared to HF. In vitro dialysis of cytokine-enriched plasma samples with MCO and HCO membranes reduces IL-6 levels. The induction of vascular calcification by cytokine-enriched plasma is reduced after HCO and MCO dialysis.

In vitro benchmark of cytokine removal by dialyzers with various permeability profiles.

PURPOSE: Removal of cytokines is relevant for dialysis patients as they are suspected to promote cardiovascular complications. The objective of this study was to benchmark membranes with different permeability profiles under standardized in vitro test conditions using miniaturized devices with respect to their ability to remove cytokines from human serum and to lower cell activating potential. METHODS: In vitro dialysis was used to dialyze cytokine enriched serum in 3 independent experiments per tested membrane. IL-6 in the serum and dialysate was measured at defined times by enzyme-linked immunosorbent assay. IL-8, IL-1ß, IL-6 and TNF-α in dialysate were measured by immunoassay. Dialysate samples were subjected to cultured tubular epithelial cells or human fibroblasts to study cell activation via IL-6 generation. Dialysate samples were added to human whole blood with subsequent analysis of granulocyte and monocyte activation by detection of CD11b. RESULTS: IL-6 decreased in serum and increased in dialysate during in vitro dialysis. IL-8, IL-1ß, and TNF-α were identified in dialysate. Dialysate added to cell cultures increased IL-6 concentration in culture medium or increased expression of CD11b. High cut-off membranes showed the strongest transfer of cytokines, albumin and total proteins from serum to dialysate and led to strongest cell activation. This effect was lower for medium cut-off membranes and lowest for conventional high-flux membranes. CONCLUSIONS: This study demonstrated an in vitro test by which membranes were benchmarked with respect to cytokine and cell activation removal capacity. Cell activation levels could be influenced by the choice of membrane by altering cytokine concentration levels.

Micro-computed tomography imaging of composite nanoparticle distribution in the lung.

Nanomedicine comprises a significant potential to approach the therapy of severe diseases. Knowledge of nanoparticle behavior at the target site would contribute to the development of specialized tools for respiratory medicine. Here, we were interested in the potential of micro-computed tomography (µCT) imaging to monitor the pulmonary distribution of polymeric nanoparticles. Composite nanoparticles were analyzed for physicochemical properties, morphology and composition. µCT was employed to visualize the pulmonary distribution of composite nanoparticles in an ex vivo lung model. Employed composite nanoparticles were composed of poly(styrene) cores coated by a thin shell of colloidal iron oxide. Particles were mainly located in the interstitial space and associated with pulmonary cells, as observed by light microscopy. µCT detected enhanced X-ray opacities in the conducting (linear pattern) and respiratory airways (aciniform X-ray attenuations). In conclusion, multifunctional nanoparticles will prompt the development of novel therapeutic and diagnostic tools in respiratory medicine.

Pulmonary targeting with biodegradable salbutamol-loaded nanoparticles.

BACKGROUND: Aerosol therapy using particulate drug carriers has become an increasingly attractive method to deliver therapeutic or diagnostic compounds to the lung. Polymeric nanoparticles are widely investigated carriers in nanomedicine. The targeted and controlled release of drugs from nanoparticles for pulmonary delivery, however, is a research field that has been so far rather unexploited. Therefore, the objective of this study was to compare the pulmonary absorption and distribution characteristics of salbutamol after aerosolization as solution or entrapped into novel polymeric nanoparticles in an isolated rabbit lung model (IPL). METHODS: Physicochemical properties, morphology, encapsulation efficiency, in vitro drug release, stability of nanoparticles to nebulization, as well as pulmonary drug absorption and distribution after nebulization in the IPL were investigated. RESULTS: Salbutamol-loaded poly(D,L-lactide-co-glycolide) (PLGA) and poly(vinyl sulfonate-co-vinyl alcohol)-graft-poly(D,L-lactide-co-glycolide) (VS(72)-10) nanoparticles were prepared by a modified solvent displacement technique with a mean particle size of approximately 120 nm and a polydispersity index below 0.150. VS(72)-10 nanoparticles showed a more negative zeta-potential of -54.2 +/- 3.3 mV compared to PLGA nanoparticles (-36.5 +/- 2.6 mV). Salbutamol encapsulation efficiency was 25.2 +/- 4.9% and 63.4 +/- 3.5% for PLGA and VS(72)-10 nanoparticles, respectively. After nebulization utilizing the MicroSprayer physicochemical properties of salbutamol-loaded VS(72)-10 nanoparticles were virtually unchanged, whereas nebulized salbutamol-loaded PLGA nanoparticles showed a significant increase in mean particle size and polydispersity. In vitro release studies demonstrated a sustained release of the encapsulated salbutamol from VS(72)-10 nanoparticles. In parallel, a sustained salbutamol release profile was observed after aerosol delivery of these particles to the IPL as reflected by a lower salbutamol recovery in the perfusate (40.2 +/- 5.8%) when compared to PLGA nanoparticles (55.2 +/- 9.1%) and salbutamol solution (62.8 +/- 7.1%). CONCLUSIONS: The current study suggests that inhalative delivery of biodegradable nanoparticles may be a viable approach for the treatment of respiratory diseases.

Pulmonary drug delivery with aerosolizable nanoparticles in an ex vivo lung model.

The use of colloidal carrier systems for pulmonary drug delivery is an emerging field of interest in nanomedicine. The objective of this study was to compare the pulmonary absorption and distribution characteristics of the hydrophilic model drug 5(6)-carboxyfluorescein (CF) after aerosolization as solution or entrapped into nanoparticles in an isolated rabbit lung model (IPL). CF-nanoparticles were prepared from a new class of biocompatible, fast degrading, branched polyesters by a modified solvent displacement method. Physicochemical properties, morphology, encapsulation efficiency, in vitro drug release, stability of nanoparticles to nebulization, aerosol characteristics as well as pulmonary dye absorption and distribution profiles after nebulization in an IPL were investigated. CF-nanoparticles were spherical in shape with a mean particle size of 195.3+/-7.1nm, a polydispersity index of 0.225+/-0.017 and a zeta-potential of -28.3+/-0.3mV. Encapsulation efficiencies of CF were as high as about 60% (drug loading of 3% (w/w)); 90% of the entrapped CF were released during the first 50min in vitro. Nanoparticle characteristics were not significantly affected by the aerosolization process utilizing a vibrating mesh nebulizer. After deposition of equal amounts of CF in the IPL, less CF was detected in the perfusate for CF-nanoparticles (plateau concentration 9.2+/-2.4ng/ml) when compared to CF aerosolized from solution (17.7+/-0.8ng/ml). In conclusion, the data suggest that inhalative delivery of biodegradable nanoparticles may be a viable approach for pulmonary drug delivery. Moreover, a targeting effect to the lung tissue is claimed.