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 (β₂M) reduction ratio (RR), and to assess the impact of different in vitro test parameters on sieving coefficient values for albumin, β₂M, and myoglobin. Clinical albumin loss and β₂M 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, β₂M, 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 β₂M 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.

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 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.

Al(22)Cl(20).12L (L = THF, THP): the first polyhedral aluminum chlorides

Aluminum subhalides of the type Al(22)X(20).12L (X = Cl, Br; L = THF, THP) are the only known representatives of polyhedral aluminum subhalides and exhibit interesting multicenter bonding properties. Herein, we report on the synthesis and structural investigation of the first chlorides of this type. Additional investigations applying solid-state (27)Al NMR (MAS), XPS (of Al(4)Cp(4) and Al(22)X(20).12L), and quantum chemical calculations shed more light upon the structure of the molecules and possible Al modifications.

Structure assignment in the solid state by the coupling of quantum chemical calculations with NMR experiments: a columnar hexabenzocoronene derivative

We present a quantum chemical ab initio study which demonstrates a new combined experimental and theoretical approach, whereby a comparison of calculated and experimental (1)H NMR chemical shifts allows the elucidation of structural arrangements in solid-state molecular ensembles, taking advantage of the marked sensitivity of the (1)H chemical shift to intermolecular interactions. Recently, Brown et al. have shown that, under fast magic-angle spinning (MAS) at 35 kHz, the resolution in a (1)H NMR spectrum of the solid phase of an alkyl-substituted hexabenzocoronene (HBC) derivative is sufficient to observe the hitherto unexpected resolution of three distinct aromatic resonances ( J. Am. Chem. Soc. 1999, 121, 6712). Exploiting the additional information about proton proximities provided by (1)H double-quantum (DQ) MAS NMR spectroscopy, it was shown that the results are qualitatively consistent with the aromatic cores packing in a manner similar to that in unsubstituted HBC. Using the HBC-C(12) molecule as an example, we show here that the new combined experimental and theoretical approach allows the observed (1)H chemical shifts to be related in a quantitative manner to the intermolecular structure. In the quantum chemical calculations, a series of model systems of stacked HBC oligomers are used. On account of the marked dependence of the (1)H chemical shift to ring currents arising from nearby aromatic rings, the calculated (1)H chemical shifts are found to be very sensitive to the stacking arrangement of the HBC molecules. Moreover, the ring current effect is found to be particularly long range, with a considerable influence of the second neighbor, at a distance of 700 pm, being observed.

[Influence of Long-Term Stimulation on Pattern-Reversal Visual Evoked Cortical Potentials]

In 20 subjects, we recorded the pattern-reversal visual evoked cortical potential (VECP) over a period of 30 min. We could not find any remarkable alterations of the peak times, they were unchanged over the time. During the first 10 min, the amplitudes showed a clear tendency to decrease if one evaluated the averaging value of the whole group. After this time, there were no significant changes. But we learned a quite different behavior of amplitudes evaluating the record of each subject. We found 5 types of different behavioral modulated responses. The problems of long-term investigation are sophisticated and need further investigation to learn which different factors have an impact on VECP. From a clinical point of view, a long-term investigation shows no relevant potential alterations.

Cytokine-stimulation of prostaglandin synthesis from endogenous and exogenous arachidonic acids in polymorphonuclear leukocytes involving activation and new synthesis of cyclooxygenase

Peripheral blood-derived human polymorphonuclear leukocytes (PMNL) can be induced to synthesize prostaglandin E2 (PGE2) from endogenous and exogenous arachidonic acid (AA) when exposed to agents such as human recombinant (hr) granulocyte-macrophage (GM) colony-stimulating factor (CSF), hr tumor necrosis factor-alpha, hr granulocyte (G)-CSF, lipopolysaccharide and the chemoattractant N-formyl-methionyl-leucyl-phenylalanine. Treatment of PMNL with hr macrophage (M)-CSF and interleukin 3, however, did not result in detectable PGE2 synthesis. Cytokines stimulated PGE2 production during two distinct time intervals, an early peak of PGE2 that was detectable at 20 min and a late one detectable after 4 h. Inhibition of protein synthesis by cycloheximide (CHX) had virtually no effect on the early increase of PGE2 but prevented the late increase. Late addition of CHX to cultures after stimulation with hr GM-CSF at 4 h resulted in decline of PGE2 synthesis from exogenous arachidonic acid. Treatment of PMNL with GM-CSF had direct effects on cyclooxygenase (COx). PMNL depleted from COx by acetyl salicylic acid (ASA) recovered to synthesize PGE2 following exposure to GM-CSF. Recovery from COx inhibition by ASA could be prevented by CHX.

Inducible production of interleukin-6 by human polymorphonuclear neutrophils: role of granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-alpha

The recent demonstration of the ability of human polymorphonuclear neutrophils (PMN) to secrete various cytokines in response to the granulocyte activator granulocyte-macrophage colony-stimulating factor (GM-CSF) but not to other cytokines, has led to the identification of PMN as biosynthetically active cells. In this study we have investigated the ability of PMN to secrete interleukin-6 (IL-6), a molecule known to be involved in inflammatory reactions. Using RNA blotting analysis and bioassays, we show that PMN could be induced to synthesize transcripts specific for IL-6, indistinguishable in size from IL-6 mRNA produced by activated human macrophages. Consequently, PMN released IL-6-like activity into their culture supernatants that could be neutralized by monospecific anti-IL-6 antibody. Interleukin-6 secretion by PMN, however, required previous stimulation with GM-CSF or tumor necrosis factor-alpha (TNF-alpha), whereas other cytokines, including interleukin-3 (IL-3), granulocyte-CSF (G-CSF), macrophage-CSF (M-CSF), interferon gamma (IFN-gamma), and lymphotoxin (LT), failed to induce IL-6 mRNA accumulation and protein secretion by PMN. Similar to GM-CSF and TNF-alpha, other compounds, including the inhibitor of protein synthesis cyclohexemide (CHX), endotoxin (Escherichia coli-derived lipopolysaccharide), and phorbol myristate acetate (PMA) (but not the chemoattractant N-formyl-methionyl-leucyl-phenylalanine [FMLP]), induced detectable levels of IL-6 transcripts in PMN.