Studies on bilayer liposomes composed of 1,2-diacyl-3-succinylglycerol

Author

Ana Maria Tari

Date of Award

5-1992

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biochemistry and Cellular and Molecular Biology

Major Professor

Leaf Huang

Committee Members

Solon Georghiou, John Koontz, Dan Roberts

Abstract

Bilayer liposomes composed of 1,2-diacyl-3- succinylglycerol (DASG) were prepared. These liposomes destabilize upon incubation with acid and/or divalent cations. Differential scanning calorimetry showed that at pH 7.4, the chain-melting temperature (Tm) of 1,2-dipalmitoyl-3- succinylglycerol (DPSG) was 60.4°C and increased with decreasing pH (Tm 57.0°C and 62.7°C at pH 8.9 and 6.7, respectively). At pH 6.5, extensive phase separation was observed as the chain-melting peak split into three peaks. At pH 7.4, the Tm of DPSG also increased with increasing divalent cation concentrations. Under identical conditions, Mg²⁺ was more effective than Ca²⁺ in driving up the Tm. By further increasing the divalent cation concentration, DASG bilayers underwent a complete lamellar to hexagonal phase transition. The acid- and divalent cation-induced destabilization mechanisms were different. The former destabilization involved extensive phase separation while the latter destabilization involved a lamellar to hexagonal phase transition. Divalent cations acted synergistically with protons in destabilizing DASG bilayers. In the presence of divalent cations, phase separation of DPSG bilayers could be observed even at pH 6.8. Freeze fracture electron micrographs of 1,2-dioleoyl-3- succinylglycerol (DOSG) liposomes revealed that under acidic conditions, different final structures were formed by the divalent cations as hexagonal phase and cubic phase structures were observed in the presence of Ca²⁺ and Mg2+, respectively. DOSG immunoliposomes were efficient in cytoplasmic delivery. At 377deg;C DOSG liposomes, between 120 - 180 nm in diameter, were partially stable in plasma and partially acid-sensitive even after plasma incubation. Injected DOSG liposomes were rapidly removed from the circulation and taken up by the liver. Serum albumin was the major serum protein associated with DOSG liposomes. The association was dependent on divalent cations. The uptake of DOSG liposomes by differentiated THP-1 macrophages increased in the presence of serum albumin and divalent cations. We propose that DOSG liposomes mainly accumulate in the liver due to their preferential association with serum albumin, via an interaction of divalent cations. Thus, serum albumin is a divalent cation dependent, liver specific opsonin for DOSG liposomes.

Recommended Citation

Tari, Ana Maria, "Studies on bilayer liposomes composed of 1,2-diacyl-3-succinylglycerol. " PhD diss., University of Tennessee, 1992.
https://trace.tennessee.edu/utk_graddiss/11013