ABSTRACT:Through the immobilization of polyethyleneimine (PEI) onto cellulose fibers, novel fibrous adsorbents (Cell-PEI fibers) for the removal of endotoxins were prepared. Anionexchange capacity and pore size (molecular mass exclusion, Mlim) of the Cell-PEI fibers were readily adjusted by changing the ratio of polyethyleneimine and sodium carbonate to cellulose during suspension. The adsorption of endotoxin by the fibers increased with anion-exchange capacity of the fibers, and decreased with increase in the ionic strength of the buffer. The Cell-PEI fibers (anion-exchange capacity 1.1 to 3.0meqg-1 ) showed high endotoxin-adsorbing activity at pH 5 to 9 and ionic strength ofµ= 0.05 to 0.2. The adsorbing activity for acidic protein such as bovine serum albumin (BSA) increased with Mlim and the anion-exchange capacity of the fibers, but decreased with increase in the ionic strength of the buffer. The Cell-PEI fibers (Mlim: 2000, anion-exchange capacity: 1. I meq g-1 ) selectively reduced endotoxins in various protein solutions containing endotoxins at pH 7 andµ= 0.05. The residual concentration of endotoxins in the protein solutions decreased to less than 0.1 ng m1-1 , and recovery rate of the protein was over 98% in all cases. KEY WORDSEndotoxin / Pyrogen / Lipopolysaccharide / Selective Removal / Cellulose Fiber / Polyethyleneimine / Bovine Serum Albumin / Endotoxins, constituents of the cell wall of gram-negative bacteria, are pyrogenic lipopolysaccharides (LPS). Their potent biological activity causes pyrogenic and shock reactions in mammals on intravenous injection even in nanogram amounts. 1 • 2 A number of attempts have been made to remove endotoxins from cell products used as drugs. 3 • 4 To remove them from protein solutions, adsorption has proven to be the most effective. Histidine-immobilized cellulose 5 • 6 and polymyxine-immobilized Sepharose 7 are presently sold as endotoxin adsorbents. However, these adsorbents cannot remove endotoxins selectively, since their adsorbing capacity is high for both endotoxins and acidic proteins such as bovine serum albumin (BSA) at low ionic strength ofµ= 0.05 and neutral pH. When the ionic strength of the buffer increased beyondµ= 0.2, the adsorption of BSA decreased, but the adsorption of endotoxins was slight. 6 t To whom correspondence should be addressed.Therefore, we attempted to develop endotoxin adsorbents capable of retaining high endotoxin-removing activity at a wide ionic strength range. We previously reported that aminated poly(y-methyl L-glutamate) (PMLG) spheres, 8 • 9 which have diaminoethane as a ligand, selectively remove endotoxins from various protein solutions at the high ionic strength of µ=0.2 to 0.8. However, the adsorption of an acidic protein can also be done at a low ionic strength ofµ= 0.05. 9 831 s. MORIMOTO et al.

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