Jian Xie

Isolation and characterization of an Alcaligenes sp. strain DG-5 capable of degrading DDTs under aerobic conditions

In this study, an Alcaligenes sp. strain DG-5 that can effectively degrade dichlorodiphenyltrichloro-ethanes (DDTs) under aerobic conditions was isolated from DDTs-contaminated sediment. Various factors that affect the biodegradation of DDTs by DG-5 were investigated. About 88 %, 65 % and 45 % of the total DDTs were consumed within 120 h when their initial concentrations were 0.5, 5 and 15 mg L−1, respectively. However, almost no degradation was observed when their concentration was increased to 30 mg L−1, but the addition of nutrients significantly improved the degradation, and 66 % and 90 % of the total DDTs were degraded at 336 h in the presence of 5 g L−1 peptone and yeast extract, respectively. Moreover, the addition of 20 mM formate also enhanced the ability of DG-5 to transform DDTs, and its DDT transformation capacity (Tc) value was increased by 1.8 - 2.7 fold for the pure (p,p’-DDT or o,p’-DDT only) and mixed systems (p,p’-DDT, o,p’-DDT, p,p’-DDD and p,p’-DDE). Furthermore, it was found that competitive inhibition in the biodegradation by DDT compounds occurred in the mixed system.

Bilirubin adsorption properties of water-soluble adsorbents with different cyclodextrin cavities in plasma dialysis system

In this study, we explored the use of α-, β- or γ-cyclodextrin (CD)-grafted polyethyleneimine (PEI) as water-soluble adsorbent for removing excess plasma bilirubin. To evaluate the bilirubin-binding capacity of these adsorbents, bovine serum albumin (BSA) solution or plasma with high level of bilirubin were dialyzed against CD-PEI-spiked dialysate. In BSA solution with an initial biliurbin concentration of 171.5mg/L, α-CD-PEI, β-CD-PEI and γ-CD-PEI achieved adsorption capacities of 2.5, 5.8 and 3.8 mg/g, respectively. In a plasma dialysis system, 45.6% of bilirubin (260 mg/L) was removed from 200 mL plasma by 1L dialysate spiked with 10mg/mL β-CD-PEI, which was significantly higher than that removed by the same volume of BSA-spiked dialysate (P<0.05), demonstrating the strong bilirubin-binding ability of β-CD-PEI. The key feature of bilirubin adsorption was related to the CD functional group, not the PEI matrix. Subsequent molecular docking study indicated that the size of CD cavity could affect the affinity energy of CD-bilirubin complex. The cavity of β-CD was most suitable for accommodating the pyrrole rings of bilirubin. The inclusion complex of bilirubin and β-CD in the molar ratio of 1:2 was more logical in terms of affinity energy. All the results demonstrated the potential of β-CD-PEI (water-soluble adsorbent) as an effective agent for removing of bilirubin from plasma in dialysis system.

Water-soluble adsorbent β-cyclodextrin-grafted polyethyleneimine for removing bilirubin from plasma

A water-soluble adsorbent was developed for removing bilirubin from the plasma of hyperbilirubinemia patient. The adsorbent was synthesized by grafting β-cyclodextrin (β-CD) to branched polyethyleneimine (PEI) matrix. The resulting β-CD-PEI polymer had an average molecular weight of 163.7 kD, and it contained 56.3 β-CD functional groups. In β-CD-PEI-spiked dialysis, 35.8% of plasma bilirubin was removed, which was higher than that removed by the same concentration of bovine serum albumin. β-CD-PEI also removed aromatic amino acids and bile acids. The results indicated that β-CD-PEI could be an effective adsorbent for blood purification application aiming at the removal of toxins.

Removal of indoxyl sulfate by water-soluble poly-cyclodextrins in dialysis

Indoxyl sulfate (IS) is a uremic toxin related to the progression of chronic kidney diseases. Removal of IS from the plasma would reduce the risk of cardiovascular disease. In this study, crosslinked poly-β-cyclodextrins (PCDs) were used as a water-soluble adsorbent agent for IS in dialysis for the first time. The molecular weight of PCDs was found to be proportional to the crosslinking time between β-cyclodextrin monomers and epichlorohydrin, yet the proportion of β-cyclodextrin that reacted with epichlorohydrin decreased. It was observed that PCD after 2 h crosslinking yielded the best IS-binding capability in PBS, while reaching the binding equilibrium within 30 min and yielding a maximum binding capability of 45 mg g-1. Furthermore, the binding mechanism was investigated by two-dimensional nuclear magnetic resonance, Jobs plot method, and salt treatments. To simulate the clinical removal of IS we established a macro-dialysis and added PCD obtained from 2 h crosslinking (PCD1) to the dialysate. The removal of plasma IS from the dialysate by PCD1 was about twice as much as that removed from the dialysate without PCD1. Therefore, crosslinked poly-β-cyclodextrins may represent a simple, low-cost, and effective IS removal strategy with great potential for removing other hydrophobic plasma-bound toxins in dialysis. It could also serve as a supplement for the existing non-adsorbent added therapy.

Detection of Aβ-interacting proteins via a novel Aβ-adsorbents that use immobilized regular comb polymer

A detailed study of individual Aβ-interacting proteins has always been a difficult task because Aβ has a wide range of molecular weights and can easily form aggregates. In this study, we established a novel method for isolating Aβ-interacting proteins by utilizing regular comb polymer immobilized on Sepharose CL-4B. To achieve site-directed ligation of Aβ, a cysteine residue was added at the N-terminus of Aβ. Asp and Asp12, which have 2 and 13 carboxyl groups, respectively, were selected as the carriers for the regular comb polymer. Firstly, the N-termini of Asp and Asp12 were immobilized on Sepharose CL-4B. Next, modified Aβ molecules were coupled to the carboxyl groups of Asp and Asp12 using bromoethylamine as a spacer. To obtain homogeneous comb polymer, the efficiency of the reaction was controlled during the synthesis process. Thioflavin T staining indicated that homogeneous Aβ was achieved. The prepared Aβ-adsorbents were used to isolate Aβ-interacting proteins from mice brain extracts. The results showed that the adsorption capacity of the Aβ-adsorbents for proteins in mice brain extracts increased with the ages of the animals. SDS-PAGE analysis of the Aβ-interacting proteins showed that many kinds of brain proteins were selectively adsorbed by the Aβ adsorbents, and the levels of some of these proteins varied with the ages of the animals. The results indicated that Aβ-interacting proteins could be successfully obtained through the use of immobilized comb polymer. Similar method could also be used to isolate other amyloid-interacting proteins.

Effect of Structural Properties of Both Proteins and Stationary Phases to Adsorption Behavior of Proteins in Hydrophobic Interaction Chromatography

A series of specially designed agarose-based HIC adsorbents were examined using human immunoglobulin G (IgG) and human serum albumin (HSA) as model proteins, to investigate the effects of structural properties of both proteins and stationary phases on the adsorption behavior in HIC. The adsorbents examined differ from each other in terms of ligand density, spacer arm and ligand type. Dynamic binding capacity (DBC) was determined to reflect the retention of proteins on adsorbents. The results showed that the adsorption behaviors of IgG and HSA on hydrophobic adsorbents were in different manner. HSA tended to be retained in a HIC adsorbent with high local hydrophobicity within a small area, and their interaction was strictly salt-dependent; whereas IgG was sensitive to spatial accessibility of hydrophobic ligands rather than ligand type. This manner of adsorption enabled IgG to be adsorbed on adsorbents with relatively high ligand density in absence of water-structuring salt. The results were ascribed to the different structural flexibility, hydrophobic surface distribution and size of IgG and HSA, two proteins with different types of structure.