MO650: In Vitro Performance Evaluation of a Filter Used for Hemodiafiltration by Using Β-Lactoglobulin

Abstract BACKGROUND AND AIMS Filters currently used for hemodiafiltration (HF) can remove sufficiently low to middle molecular weight solutes, like urea to β2 microglobulin (molecular weight: 11.800). Therefore, the removal rate of α1 microglobulin (α1-MG; molecular weight: 33.000) and albumin leakage are used as a guide to select a filter and to set appropriate operating conditions. Since α1-MG is very expensive, in vitro performance evaluation of the filters using α1-MG is not practical. In the present study, we aimed to investigate whether β-lactoglobulin (β-LG), which has a molecular weight of 18.400 and forms dimer (molecular weight: 36.800) under physiological conditions, can be used as a marker solute in the 30.000 molecular weight region. METHOD HF experiments were performed using 1.8 L of porcine whole blood (hematocrit: 30 ± 3%, total protein concentration: 6.5 ± 0.5 g/dL). The sieving coefficients of β-LG, separated from milk by membrane separation (untreated), made whey containing β-LG by acid treatment of milk and pH adjusted (acid-treated) and powdered reagent, were measured in porcine blood. In addition, HF experiments with permeate recycle were performed using three filters with different pore sizes (MFX-S, MFX-E and MFX-M; Nipro) at a blood flow rate of 250 mL/min and filtration flow rate of 42 mL/min for 240 min. The concentration of β-LG was measured by an enzyme-linked immunosorbent assay. RESULTS The sieving coefficient of acid-treated or powdered reagent β-LG added to the blood was almost equal to that of untreated β-LG. When the powdered reagent β-LG was treated with mercaptoethanol, the sieving coefficient became larger, meaning that the β-LG is tightly bound by disulfide bonds to form a stable dimer. In HF experiments using three filters with different pore sizes, the filter with a larger pore size resulted in lower transmembrane pressure. The sieving coefficients of β-LG decreased with time and were 0.15 ± 0.024, 0.39 ± 0.023, 0.75 ± 0.064 (mean ± SD, n = 3) at 60 min for MFX-M, MFX-E and MFX-S, respectively, indicating that the difference in filter performance was able to classify in the sieving coefficient of β-LG. CONCLUSION β-lactoglobulin existed stably as a dimer and was able to classify the performance of filters used for hemodiafiltration as a marker solute in the 30.000 molecular weight region.