Sodium sulfite and N-acetylcysteine: new additives to dialysate for inhibiting formation of glucose degradation products and advanced glycation end-products.

The present study evaluated the inhibiting effect of various chemicals on the advanced glycation end-product (AGEs) cross-linking caused in protein by glucose degradation products (GDPs). We evaluated a few dozen organic and inorganic chemicals--in addition to previously reported AGE inhibitors, such as thiazolium derivatives and aminoguanidine--for their inhibiting effect. Collagen IV (from human placenta) or human serum albumin (HSA) was incubated with an AGE accelerator and one of the selected chemicals in phosphate buffer solution at 37 degrees C for as long as 14 days. Fluorescence intensity (440 nm) was determined after a given incubation time. Among 36 chemicals tested, 8 new chemicals and 5 previously known AGE inhibitors significantly suppressed the increase in fluorescence intensity seen after incubation of HSA with methylglyoxal. We believe that 6 chemicals may effectively quench GDPs and inhibit AGE cross-link formation, in a manner different from that of aminoguanidine and thiazolium.

Can recovered protein from the CAPD patient's own dialysis effluent substitute for dextrose?

Albumin has been evaluated as an osmotic agent for peritoneal dialysis as being physiologically safe and having modest colloidal osmotic pressure. However its extremely high cost inhibits clinical applications, and hypoalbuminemia is often seen in continuous ambulatory peritoneal dialysis (CAPD) patients, especially those with high peritoneal equilibration test (PET) values and who lose a large quantity of albumin everyday. This study aims at recovering protein from CAPD effluent and reusing it safely at reasonable cost as a substitute for dextrose. The dialysis effluent was collected and concentrated with a semipermeable membrane. Uremic toxins and low-molecular-weight solutes were removed by repeated filtration and water dilution. The concentrate was acidified with hydrochloric acid down to pH 2, thence de-acidified with water dialysis up to pH 5. At this point, the isoelectric point of albumin, at which precipitate was deposited, the precipitate was separated from the supernatant and re-dissolved into electrolyte solution. The acidified concentrate exhaled an unpleasant odor, like that of decayed food. The precipitate solution, however, did not smell at all. The initial ultrafiltration rate of the recovered protein solution was measured and compared with that of dextrose and dextran by using a high-sensitivity differential manometer, one end of which was connected with the test solution cell, and the other with the serum cell. The ends were separated by a semipermeable membrane. The recovered protein solution at 20 g/dL concentration was almost equivalent in initial ultrafiltration rate to the 2.0 g/dL dextrose solution and to 20 g/dL dextran (MW: 75,000 dalton) solution.

Measurement of back clearance.

With improvement in dialysis membranes, back filtration becomes the focus of study. Because new membranes that remove low molecular weight proteins, such as beta 2-microglobulin by diffusion are now available for clinical use, both back filtration and back diffusion become problems. This paper gives the mass transfer rate of solutes from the dialysate to blood compartment. As markers of toxic or antigenic substances, inulin (MW 5,200), lysozyme (MW 14,300), and alpha-lactoalbumin (MW 14,400) were used. The dialyzers tested were the CLSU-12W, AM-FP10, BK-1.0P, and FB-110U. The UFR controller set the flow rate on the blood side at 200, dialysate at 500, and ultrafiltration (QF) as 0 to 50 ml/min. Under these conditions, the inulin back clearance is 16 (CLSU) to 26 ml/min (FB), even if the QF is 50 ml/min, and is 10 to 34 ml/min for lysozyme at QF = 0 ml/min. Although a substantial amount of solute moves into the blood compartment, back clearance does not drastically decrease with increase in QF. To avoid contamination of the blood side, clean-up techniques for the dialysis line or online protein adsorber should be followed.

Effects of zeta potential on the permeability of dialysis membranes to inorganic phosphate.

Some patients on hemodialysis have elevated plasma phosphate values. The chemical and physical properties of dialysis membranes may cause reduced inorganic phosphate clearance, leading to hyperphosphatemia. The zeta potential was determined by a streaming potential method using an electrolytic, aqueous solution to elucidate discrepancies in phosphate ion transport through cellulosic and polymethylmethacrylate membranes. The authors also carried out dialysis experiments at 310K to obtain solute permeability for H32PO4(2-), overall mass transfer coefficient for HPO4(2-), and pure water permeability. This study demonstrates that permeability to inorganic phosphate ion does not vary with zeta potential for cellulosic membranes, but polymethylmethacrylate membranes with highly negative zeta potentials may suppress phosphate removal from patients on hemodialysis.

Nondestructive evaluation by x-ray computed tomography of dialysate flow patterns in capillary dialyzers.

It is hard to evaluate dialysate flow patterns inside the fiber bundle of capillary dialyzers. The current study describes a novel determination of dialysate flow by x-ray computed tomography. The authors did steady and nonsteady state tracer experiments with adipiodone to observe the dialysate flow pattern in capillary dialyzers held vertically and horizontally. The hollow fibers were filled with paraffin to avoid permeation of adipiodone from the dialysate to blood compartment. In steady state tracer experiments, adipiodone solution (50 vol%) was injected into the dialysate compartment at a flow rate of 1.5 ml/min. Horizontal sectional dialysate flow patterns were observed every 2 cm from the point of the adipiodone injection. Adipiodone solution flowed along broken and twisted fiber bundles at dialysate flow rates ranging from 200 to 600 ml/min. In nonsteady state tracer experiments, dialysate was switched from pure water to adipiodone solution by solenoid-controlled valves after a steady state was reached, and adipiodone solution (2.4 vol%) was infused into the dialysate compartment for 30 sec at a flow rate of 500 ml/min. Vertical sectional dialysate flow patterns were observed every 2 sec after the start of adipiodone infusion. Values for dialysate flow velocity at the outer and inner regions of the fiber bundle were 3.5 and 0.6 cm/sec for the CA-170, and 1.4 and 0.7 cm/sec for the HF-200 capillary dialyzer, respectively. This study demonstrates the usefulness of x-ray computed tomography in visually and quantitatively determining dialysate flow patterns in capillary dialyzers.

Effects of membrane structure on removal of low molecular weight proteins.

Much attention is being devoted to the efficient removal of beta 2-microglobulin from patients on hemodialysis as it may cause amyloidosis. The objective of the present article is to clarify the beta 2-microglobulin removal characteristics of dialysis membranes having varying water contents and pore radii. For membranes of regenerated cellulose, polymethylmethacrylate (PMMA) and ethylenevinyl alcohol (EVA), solute and pure water permeability and water content were determined by the standard methods. Data analysis using a tortuous pore model allows determination of pore radius, surface porosity, and tortuosity, and hence, the sieving coefficient as a function of Stokes radius. Based on the tortuous pore model calculation, little beta 2-microglobulin is removed from patients on hemodialysis by regenerated cellulose and PMMA membranes, but EVA membranes, with a sieving coefficient of 0.5, are capable of removing it. The solute permeability for urea is about 2 orders greater than that for beta 2-microglobulin.

Varying methods of sterilisation, and their effects on the structure and permeability of dialysis membranes.

This study elucidates changes in membrane structure and permeability due to the methods of sterilisation and the conditions under which they are carried out. Tubular dialysis membranes of regenerated cellulose having various values for porosity were sterilised by ethylene oxide gas, autoclave or gamma irradiation under varying conditions. Non-sterilised membranes were included as controls. The solute permeability of the membranes was determined using 14C-urea. The membranes tested showed no difference in clearance of urea or creatinine. Gamma-ray sterilisation under dry conditions greatly reduced the vitamin B12 clearance and hydraulic permeability of membranes with a water content of below 60%. Hydraulic permeability increased with gamma irradiation for membranes sterilised under wet conditions. A reduction in vitamin B12 clearance for membranes with a water content of above 60% resulted after autoclave sterilisation. Pore model calculation reveals that membrane shrinkage resulted from sterilisation both by gamma-rays under dry conditions, and by autoclave. Thus, the structure of dialysis membranes varies with the method of sterilisation and the conditions under which the sterilisation is carried out.