Rheumatoid arthritis (RA) patients, in whom cryogelation occurs in the presence of
heparin, exhibit abnormally high concentrations of extra domain A containing
fibronectin [
EDA(+)FN] in their plasma. The selective removal of
EDA(+)FN from patient blood is therefore of potential therapeutic benefit.
Gellan-sulfate is a candidate
ligand for the removal of
EDA(+)FN due to its high affinity for FN. In this study, we prepare a novel adsorber for the direct removal of
EDA(+)FN from patient blood. The adsorber has both a plasma separation function and
EDA(+)FN trapping zones, and is prepared by cross-linking
gellan-sulfate with epichlorohydrine. The ratio of
gellan-sulfate to
gellan in the adsorber is 48%. The surface and internal structure of
gellan beads were observed by a range of microscopic techniques, and the beads were found to have a dilayer structure, consisting of a porous outer layer and an underlying
gellan-sulfate phase as the adsorber. The affinity constants of the
gellan-sulfate beads for
EDA(+)FN were almost the same in blood as in
buffer because the porous
gellan coating acts to separate plasma from the cellular fraction of the blood. The removal rate of
plasma proteins and blood cells from mock RA blood was measured for coated and uncoated
gellan-sulfate beads. Removal rates were 30-32% for
EDA(+)FN, 6-10% for
fibrinogen, 10-14% for
antithrombin III, 8% for C3, 4-7% for C4, and 0% for
albumin. The removal rates of uncoated beads were 11% for white blood cells, 0% for red blood cells and 33% for platelets, whereas removal rates of 0% for white blood cells, 0% for red blood cells and 20% for platelets were achieved for coated beads. The coating effectively inhibits the adsorption of white blood cells and platelets. Existing problems with direct adsorbers, including selectivity and plasma separation, have been solved by this material.