EFFECT OF SERUM COMPONENTS ON THE PHYSICOCHEMICAL PROPERTIES OF CATIONIC LIPID OLIGONUCLEOTIDE COMPLEXES AND ON THEIR INTERACTIONS WITH CELLS/

The interactions among serum components and cationic lipid-nucleic aci d complexes are central to the understanding of how serum inhibits cel lular delivery of oligonucleotides in vitro and in vivo. In this study , we show that several serum proteins, in particular bovine serum albu min (BSA), lipoproteins (HDL and LDL) and macroglobulin, interact with cationic lipid/oligonucleotide complexes, alter the complex diameter and zeta potential (from positive to negative values), and significant ly interfere with the ability of 1,2-dioleoyl-3-trimethylammonium-prop ane (DOTAP) to deliver phosphorothioate oligonucleotides (ODN) into ce lls. Serum and BSA do not dissociate the ODN and lipid components, the refore inhibition of delivery cannot hp attributed tn a displacement n f cationic lipid from the ODN. Rather BSA at 2.5mg/ml, comparable to t he amount found in 10% serum, decreases the cell association of ODN by about 5-fold and nuclear uptake of ODN by greater than 20-fold, In co ntrast, immunoglobulin G, the other major serum component, alters the zeta potential from positive to near neutral, has a modest effect on t he diameter of the complex but does not affect cell association or nuc lear delivery of the ODN at amounts found in 10% serum. Other molecule s found in serum, specifically oleic acid and heparin, displace the OD N from the complex and thus interfere with delivery. This displacement is attenuated by first incubating the complex with BSA. Another manif estation of serum-complex interactions is that ODN significantly and c ationic liposomes slightly, activate complement. However, formation of the complex markedly reduces the complement activation of the ODN. Fi nally, the effect of serum can be partially counteracted by the select ion of the helper lipid (DOPE or cholesterol). Inclusion of a helper l ipid reduces the effective charge ratio (cationic groups/anionic thioa tes) required to deliver ODN into cells and permits delivery in the pr esence of greater percentages of serum in the culture medium. These re sults support the current view that the binding of serum proteins to t he complex is a significant factor in modulating the activity of catio nic lipid-ODN complexes in culture and after intravenous administratio n. (C) 1998 Elsevier Science B.V.