抄録
Low density lipoprotein (LDL) is well recognized as one of the major risk factors for developing coronary heart diseases. In spite of intensive development of LDL-lowering drugs, there still exist those patients with refractory hyperlipidemia, whose plasma LDL level is not sufficiently lowered by drugs. LDL apheresis—direct removal of plasma LDL from circulating blood—is expected as the most promising treatment for those refractory patients. Various techniques, such as immunoadsorbent utilizing anti-LDL antibody, have been tried to achieve the selective removal of LDL. However, none of them were widely used, because of complication, poor selectivity and so forth.
To establish a safe and effective LDL apheresis system, we chose synthetic affinity adsorbent as the LDL-removing device of the system. Synthetic polyanion compounds were employed as the affinity ligands for LDL adsorbent to simulate anion-rich sequences of LDL binding sites in human LDL receptor. Among various polyanion compounds, those polyanions with sulfate or sulfonate groups and hydrophilic backbone were found to have strong affinity for LDL. On the other hand, polyanions with carboxyl groups showed poorer affinity. Dextransulfate (DS) was selected as the affinity ligand of LDL adsorbent for its high affinity and low toxicity. The influence of its charge density and molecular weight on the affinity for LDL was studied. The affinity rapidly increased with an increase of charge density, then reached at constant value. Little affinity was found for both DS monomer (glucosesulfate) and DS with higher molecular weight than 104 dalton, while DS with middle molecular weight showed strong affinity.
Middle molecular weight DS was immobilized on cellulose hard gel to give LDL adsorbent for clinical application. The adsorbent demonstrated an excellent selectivity for LDL and VLDL in vitro. Adsorption of HDL and major plasma proteins was almost negligible. Further study on the LDL binding mechanism revealed that DS directly interacts with positively charged site on LDL, which demonstrates the nature of the interaction is same as that of LDL receptor.
LDL adsorption column (LiposorberTM) packed with the LDL adsorbent and polysulfone hollow fiber plasma separator (SulfluxTM) were developed for efficient LDL apheresis system. Clinical investigation proved this system is capable of intensively lowering plasma LDL level without affecting major plasma components.
