The binding of bilirubin to albumin. A study using spin-labelled bilirubin

Bilirubin removal performance of immobilized albumin in a magnetically stabilized fluidized bed

Human serum albumin (HSA)-immobilised magnetic poly(2-hydroxyethyl methacrylate) (mPHEMA) particles were investigated as an adsorbent for selective bilirubin removal from human plasma in a magnetically stabilized fluidized bed system. mPHEMA particles were prepared by suspension polymerization in the presence of Fe3O4 particles. mPHEMA particles were characterized by scanning electron microscopy (SEM), surface area and pore size measurements. The mPHEMA beads have a spherical shape and porous structure. The specific surface area of the mPHEMA particles was found to be 50 m2/g with a size range of 80-120 microm in diameter and the swelling ratio was 45%. Then, HSA was covalently coupled to the cyanogen bromide (CNBr)-activated mPHEMA particles. The amount of coupled HSA was arranged by changing the activation degree of particles (i.e., CNBr concentration). In vitro bilirubin removal was investigated from hyperbilirubinemic human plasma on the mPHEMA particles containing different amounts of immobilised HSA (between 11 and 100 mg/g). The non-specific bilirubin adsorption on the bare mPHEMA particles was 0.47 mg/g. Higher bilirubin adsorption capacities, up to 88.3 mg/g, were obtained with the HSA-immobilised magnetic particles. Bilirubin capacity decreased significantly from 75.0 mg/g to 40.0 mg/g polymer with the increase of the flow-velocity from 0.5 ml/min to 4.0 ml/min. Bilirubin adsorption increased with increasing temperature. Adsorption behavior of bilirubin could be modelled using the Langmuir isotherm.

Adsorption of bilirubin with polylysine carrying chitosan-coated nylon affinity membranes

Microporous polyamide membranes were activated by bisoxirane and subsequently bound with chitosan (CS) to amplify reactive groups. Then polylysine (PLL) as ligand was immobilized onto the CS-coated nylon membranes. The contents of CS and PLL of PLL-attached membranes were 93.2 and 90.4 mg/g nylon membrane, respectively. Such PLL-attached membranes were used to adsorb bilirubin from the bilirubin-phosphate solution and bilirubin-albumin solution. The adsorption mechanism of bilirubin and the effects of temperature, initial concentration of bilirubin, albumin concentration and ionic strength on adsorption were investigated by batch experiments. The results showed that the adsorption capacity increased with increasing the temperature while decreased with increasing the NaCl concentration and albumin concentration, and the adsorption isotherm fitted the Freundlich model well. The result of dynamic experiment showed PLL-attached membranes can well remove the bilirubin from the bilirubin-albumin solution.

Adsorptive membranes for bilirubin removal

In this study, we employed ethylene vinyl alcohol (EVAL) adsorptive membranes with bovine serum albumin (BSA) as bioligand for affinity supports for bilirubin (BR) retention. Microfiltration membranes were prepared from ternary or quaternary water/(1-octanol)/DMSO/EVAL systems. To obtain active binding sites for BSA, the EVAL membranes were either chemically functionalized in aqueous and organic medium and by plasma dischargement or physically activated by entrapping of active particles. Static BR removal was determined for all EVAL-BSA membranes. BR retentions relevant for human plasma were gained for the mixed adsorber membranes and additionally investigated in the dynamic mode.

Synthesis and characterization of a biospecific adsorbent containing bovine serum albumin as a ligand and its use for bilirubin retention

Epoxy-activated gels from cross-linked polybutadiene-hydroxyethylmethacrylate (PB-HEMA) copolymer and epichlorohydrin (ECH) were prepared and characterized. Albumin was covalently bonded to the matrix and used as support of affinity chromatography in bilirubin (BR) retention experiments. PB-HEMA-ECH with different amounts of immobilized albumin (between 5.20 and 6.80 mg/g dry gel) were obtained. Bilirubin retention of 3.10 mg/g of these beads was observed at 5 degrees C.

Bilirubin removal from human plasma in a packed-bed column system with dye-affinity microbeads

A dye-ligand. Cibacron Blue F3GA. was covalently coupled with the poly(EGDMA-HEMA) microbeads. The affinity sorbent carrying 16.5 micromol Cibacron Blue F3GA per gram polymer was then used to remove bilirubin from human plasma in a packed-bed column system. Bilirubin adsorption from human plasma on the unmodified poly(EGDMA-HEMA) microbeads was 0.32 mg/g, while much higher adsorption values, up to 24.2 mg/g, were obtained with the dye-attached microbeads. The bilirubin adsorption capacity of the microbeads decreased with an increase in the recirculation rate of plasma. Bilirubin adsorption increased with increasing temperature, and the maximum adsorption achieved at 37 degrees C (32.5 mg bilirubin/g polymer). Bilirubin molecules interacted directly with the immobilized Cibacron Blue F3GA molecules. Contribution of albumin adsorption on bilirubin adsorption was also significant.

New sorbent for bilirubin removal from human plasma: Cibacron Blue F3GA-immobilized poly(EGDMA-HEMA) microbeads

Cibacron Blue F3GA-immobilized poly(EGDMA-HEMA) microbeads were investigated as a specific sorbent for bilirubin removal from human plasma. The poly(EGDMA-HEMA) microbeads were prepared by a modified suspension copolymerization technique. Cibacron Blue F3GA was covalently coupled to the poly(EGDMA-HEMA) microbeads via the nucleophilic reaction between the chloride of its triazine ring and the hydroxyl groups of the HEMA molecule, under alkaline conditions. Bilirubin adsorption was investigated from hyperbilirubinemic human plasma on the poly(EGDMA-HEMA) microbeads containing different amounts of immobilized Cibacron Blue F3GA, (between 5.0-16.5 micromol/g). The non-specific bilirubin adsorption on the unmodified poly(EGDMA-HEMA) microbeads were 0.32 mg/g from human plasma. Higher bilirubin adsorption values, up to 14.8 mg/g, were obtained with the Cibacron Blue F3GA-immobilized microbeads. Bilirubin molecules interacted with these sorbents directly. Contribution of albumin adsorption on the bilirubin adsorption was pronounced. Bilirubin adsorption increased with increasing temperature.

Kinetics of bilirubin transfer between serum albumin and membrane vesicles. Insight into the mechanism of organic anion delivery to the hepatocyte plasma membrane

Unconjugated bilirubin is transported in the plasma bound primarily to serum albumin, from which it is taken up and metabolized by the liver. To better characterize the mechanism of bilirubin delivery to the hepatocyte, stopped-flow techniques were utilized to study the kinetics of bilirubin transfer between serum albumin and both model phospholipid and native hepatocyte plasma membrane vesicles. The transfer process was best described by a single exponential function, with rate constants of 0.93 +/- 0.04, 0.61 +/- 0.03, and 0.10 +/- 0.01 s-1 (+/- S.D.) at 25 degrees C for human, rat, and bovine serum albumins, respectively. The observed variations in rate with respect to donor and acceptor concentrations provide strong evidence for the diffusional transfer of free bilirubin. Thermodynamic analysis suggests that the binding site on bovine serum albumin demonstrates higher specificity for the bilirubin molecule than that on human or rat serum albumin, which exhibit similar binding characteristics. Kinetic analysis of bilirubin transfer from rat serum albumin to isolated rat basolateral liver plasma membranes indicates that the delivery of albumin-bound bilirubin to the hepatocyte surface occurs via aqueous diffusion, rather than a collisional process, thereby mitigating against the presence of an "albumin receptor."

Adsorption of bilirubin with polypeptide-coated resins

Poly-L-lysine, poly-D-lysine and poly-L-ornithine have been coated covalently onto a water-swellable polyamide resin. These sorbents, especially the polylysine coated resins, exhibit high binding affinities for bilirubin in aqueous phosphate buffer solutions at 0 degrees C. The polylysine coated resins have an improved binding affinity for bilirubin over the sorbents with lysine containing oligopeptide pendants and much higher affinity than cholestyramine. The binding capacity is directly proportional to the number of lysine residues on the resin. Replacement of poly-L-lysine with poly-D-lysine does not affect the adsorption capacity.