Preparative isolation of middle molecular weight fractions from the hemofiltrate of patients with chronic uremia

Isolation of Unusually Composed Sialyl-Compounds from Hemofiltrate

Sialyl compounds are essential components of various biological fluids but relatively little is known about their occurrence in the extracellular fluid of patients with end-stage renal disease. As we have developed a macropreparative method for concentrating and desalting a wide range of fractions from diluted biological fluids we have been able to isolate and identify 5 sialooligosaccharides, 3 sialosugarphosphates, 2 monosialoglycopeptides and 1 disialoglycopeptide. The structures have been elucidated predominantly by one and two-dimensional NMR spectroscopy, enzymatic degradation and FAB mass spectrometry.

The accumulation of these compounds in uremic sera may be of particular interest as they may interact in the molecular biology of diseases typically associated with the uremic state, e.g., immune deficiency, neurological disorders, receptor binding abnormalities, complement system disturbances and cell membrane alterations.

Characteristics of the Cellulose Triacetate Membrane for Hemofiltration

The Permeation characteristics of the cellulose triacetate membrane used for hemofiltration were studied and compared with other commercially available sheet type membranes. The critical solute fractionation profile of the cellulose triacetate membrane was very similar to that of a glomerular basement membrane. The cellulose triacetate membrane showed a typical gel concentration polarization with a protein solution; however, the surface of the membrane is considered to be relatively homogeneous for permeation based on the relation between fluxes of the protein solution and saline: the flux of the protein solution is not much less than that of saline. This result differs from that observed with other membranes. Because of these desirable characteristics the cellulose triacetate membrane is considered to be suitable as a membrane for a hemofiltration system.

Combination of conventional and high-performance liquid chromatographic techniques for the isolation of so-called "uraemic toxins"

Using fluids from the artificial kidney as an example, a generally useful combination of separation techniques is described for the preparative isolation of biologically active subfractions from extremely heterogeneous and diluted biological fluids. Haemofiltrate (20 l) and dialysate (100 l), respectively, are desalted and concentrated in one step by reverse osmosis using membranes with a nominal cut-off of 500 Daltons. The retentate with high concentrations of "uraemic toxins" is fractionated by preparative ion-exchange chromatography (double column technique with detection at 206 nm) and size exclusion chromatography yielding large amounts of ninhydrin-positive subfractions which inhibit DNA synthesis of rat bone marrow and HeLa cells in vitro, respectively. These fractions were analyzed by reversed-phase and size exclusion high-performance liquid chromatography. Many of the isolated fractions were shown to contain peptides.

Electrodialysis and reverse osmosis as a regeneration system for hemofiltrate

The separation of urea from the hemofiltrate (or from spent dialysis fluid) must be considered the critical step in all regeneration systems. A promising solution for this problem is the combination of electrodialysis and reverse osmosis. A mathematical stimulation of the process and in vitro experiments have been carried out in order to determine operating conditions and design specifications. The experiments confirmed the predicted performance of the regeneration system with respect to the separation of urea and the recovery of electrolytes. As expected, some ionic toxins, such as uric acid, and some middle molecules are recovered also. These substances, however, can be easily removed by a small adsorption cartridge.

Evaluation of blood toxicity in chronic uremia by an improved chromatographic method

Biogel P2 gel chromatography of ultrafiltrate from chronic uremic patients leads to better resolution of the compounds present than so far reported in the literature. Reproducibility is good. Toxicity, evaluated by cell cultures, was detected in only one chromatographic fraction. Further purification of this fraction with HPLC on a RP18 column revealed two toxic fractions, to the better defined of which a polyol structure was ascribed.

A simple method for incorporating single pass dialysate delivery and controlled ultrafiltration with the RP-6 high flux dialyzer

A simple hemodialysis protocol has been developed to permit significant "middle molecule" clearance, yet retain normal low molecular weight clearance. The high flux RP-6 dialyzer has been combined with a single pass dialysate delivery system to provide accurate control of ultrafiltration without resorting to specialized or expensive equipment. By operating the RP-6 in the co-current mode, a simple valve on the dialysate output can be used to regulate ultrafiltration. At QB = 200 ml/min and QD = 500 ml/min, CU = 127 ml/min and CB12 = 56 ml/min at zero ultrafiltration rate; these values increase considerably with ultrafiltration. This protocol offers dialysis centers with standard equipment the opportunity to use high flux membranes in a routine manner.