Transbilayer diffusion of divalent cations into liposomes mediated by lipidic particles of phosphatidate

Abstract

Liposomes formed from egg-yolk phosphatidylcholine:egg-yolk phosphatidate (molar ratio 2:1) containing pBR322 DNA and DNase I were induced to form, with divalent cations, bilayer/nonbilayer phase transitions of phosphatidate which allowed cation diffusion into liposomes; then cation diffusion was measured by the activation of the hydrolysis of DNase I on DNA. The formation of phosphatidate transitions on liposomes was demonstrated by freeze-fracture and 31P NMR, and a direct correlation between the formation of phosphatidate transitions and the transbilayer diffusion of cations was found: only Ca2+ and Mn2+, which induce phase transitions, were able to penetrate liposomes and triggered the DNase I activity; in addition, Ca2+ at higher concentrations (10 mM) caused fusion of liposomes, whereas Mn2+ did not, suggesting that transitions induced by Mn2+ participated only in the diffusion of this ion; furthermore, Mg2+ neither formed phase transitions nor triggered the enzymatic activity. The liposomes studied represent more dynamic structures that can form phosphatidate structures involved in both (1) the interchange of divalent cations with the surroundings, thereby modulating encapsulated enzymes, and (2) the fusion of lipid vesicles probably implicated in the enrichment of liposomal content in the early Precambian Earth.

Antibodies to non‐bilayer phospholipid arrangements induce a murine autoimmune disease resembling human lupus

“…1 (shift towards the left)]. These spectroscopic changes revealed the presence of NPA and were similar to those in which NPA were also demonstrated by EM [2,4]. Similar spectroscopic changes were observed after incubating liposomes with the cationic drugs chlorpromazine or procainamide, showing that these drugs induced NPA.…”

“…In contrast, the spectrum of rigid DPPC/PC/E. coli CL liposomes was more similar to that of multilamellar microvesicles with smooth bilayers [2,14], a spectrum unaltered by Ba 2+ or procainamide. Barium cations interact with smooth rigid liposomes but do not induce NPA formation [4].…”

“…1) similar to that of smooth unilamellar microvesicles with a diameter of 450 nm, which bear their phospholipids in bilayer arrangements [2,14]. After adding Ca 2+ to liposomes, the spectrum became sharper than that without cations and had a slight shift to a low magnetic field [ Fig.…”

“…Non-bilayer phospholipid arrangements (NPA) are transient intermediate structures of the anionic lipids cardiolipin (CL), phosphatidylserine (PS), diacylglycerol, and phosphatidic acid (PA), as well as the zwitterionic lipid phosphatidylethanolamine (PE), associated in the tubular Hexagonal H H (H H H ) phase, which by electron microscopy (EM) appear as protuberances on the surface of experimental membrane models such as liposomes [1][2][3]. NPA formation is induced by drugs, which trigger a lupus-like condition in humans such as chlorpromazine and procainamide, some antibiotics, apolar peptides, and the cations calcium and manganese [1].…”

Lepromatous leprosy patients produce antibodies that recognise non-bilayer lipid arrangements containing mycolic acids

“…Preparation of liposomes and liposomes with nonbilayer phospholipid arrangements -Unilamellar liposomes were prepared using the reverse-phase evaporation method (Szoka & Papahadjopoulos 1978) that was modified (Baeza et al 1994). The following lipids and lipid mixtures were dissolved in 1 mL of chloroform (Mallinckrodt Baker, Phillipsburg, NJ, USA), 3 µmol of phosphatidylcholine (PC), 2 µmol of PC and 1 µmol of PA (2:1 molar ratio), 2 µmol of PC and 1 µmol of MAs (2:1 molar ratio), and 2 µmol of PC, 0.5 µmol of PA and 0.5 µmol of MAs (2:0.5:0.5 molar ratio).…”