Properties of human free apolipoprotein(a) and lipoprotein(a) after eitherfreezing or lyophilization in the presence and absence of cryopreservatives

Apolipoprotein(a), apo(a), the specific multikringle glycoprotein constitue nt of lipoprotein(a), Lp(a), occurs in the plasma mostly bound to apoB100-c ontaining lipoproteins but also in a free form. Often the properties of the se products are determined after storage in the cold; yet limited informati on is available on their stability at low temperatures. To shed light on th is subject, we examined the effect of two parameters, freezing and lyophili zation, in either the absence or the presence of cryopreservatives. Lp(a)s each having a single apo(a) size isoform containing either 14 or 17 kringle (K) IVs were isolated from the plasma of healthy donors by combining densi ty gradient ultracentrifugation and lysine-Sepharose column chromatography using solutions containing both antioxidants and proteolytic inhibitors. Ap o(a) was obtained from parent Lp(a) by a mild limited reductive procedure. Either freezing at -20 degreesC or lyophilization in the presence of 5% suc rose did not change the electrophoretic, immunochemical, and lysine-binding properties of Lp(a) including its ability to generate free apo(a). Irrespe ctive of source, apo(a) remained stable when either frozen at -20 and -80 d egreesC or lyophilized in the presence of 125 mM trehalose. In all cases, t he absence of cryopreservatives caused the samples to aggregate irreversibl y. Thawed or reconstituted samples of both free and bound apo(a) kept at 4 degreesC under sterile conditions in the presence of antioxidants, proteoly tic inhibitors, and cryopreservative exhibited no significant changes in pr operties within the time of observation. Both apo(a) isoforms gave comparab le results. We conclude that apo(a), either free or bound, can be kept stab le at low temperatures in the presence of appropriate cryopreservatives. (C ) 2001 Academic Press.