Cellular products such as DNA vaccines and proteins, produced by recombinant gene technology, are usually contaminated with endotoxin (lipopolysaccharide; LPS). To separate LPS from bio-product solution containing DNA, copolymeric adsorbents were prepared. The adsorbents comprise copolymer particles derived from g-cyclodextrin (CyD) and 1,6-hexamethylene diisocyanate (HMDI), toluene diisocyanate (TDI) or chloromethyloxirane (CMO)¹⁾. For the hydrophobic adsorption of LPS, we expected that the cavities of the g-CyD tube (diameter: 0.85 nm) could include the hydrophobic chains of LPS because the center-to-center distance of the hydrophobic chains is about 0.49 nm (Figure 1).To develop a DNA-purification system, we compared the chromatographic LPS-separation activity of the copolymer adsorbents with that of cationic polymer beads or hydrophobic particles.

   The selective adsorption of LPS from a bio-product solution by various adsorbents was determined by a batch method. The cationic adsorbents (poly(ε-lysine)-immobilized cellulose beads) and the activated charcoal had high adsorption activities for both LPS and DNA at a physiological condition. Therefore, each could not selectively adsorb LPS at any pH and ionic strength. By contrast, the g-CyD/CMO=7/93, the g-CyD/TDI=12/88 and the g-CyD/HMDI=20/80 copolymers selectively adsorbed LPS without the adsorption of DNA, but the g-CyD/CMO=7/93 and the g-CyD/TDI=12/88 showed poor LPS-removing activity. As a result, only the g-CyD/HMDI=20/80 (20 mol% ratio of g-CyD) could selectively removed LPS from a DNA solution containing LPS. The residual concentration of LPS in each sample (LPS: 15 EU/ml, DNA: 50 mg/ml,pH 4-6, ionic strength m = 0.05-0.2) was <0.1 EU, and recovery of the DNA was >99%. In addition, the g-CyD/HMDI=20/80 removed selectively LPS from various protein solutions containing LPS, without adsorption of protein.