Cascade liposomal triggering: light-induced Ca2+ release from diplasmenylcholine liposomes triggers PLA2-catalyzed hydrolysis and contents leakage from DPPC liposomes.
We have previously reported a direct triggering approach [Thompson, D. H., et al. (1996) Biochim. Biophys. Acta 1279, 25-34; Gerasimov, O. V., et al. (1997) Biochim. Biophys. Acta 1324, 200-214] based on the facile degradation of plasmenylcholine and diplasmenylcholine vinyl ether linkages by either photooxidation or low-pH environments. This report describes a novel, cascade-type triggering technique that utilizes liposome photooxidation and contents release to activate an enzyme capable of destabilizing conventional phosphatidylcholine liposomes. Our application of this concept employs a mixture of two different liposome populations, one composed of synthetic diplasmenylcholine (1, 2-dihexadec-1'-enyl-sn-glycero-3-phosphocholine, DPPlsCho) containing Ca2+ as a signaling agent for phospholipase A2 (PLA2) and the second composed of 1, 2-dihexadecanoyl-sn-glycero-3-phosphocholine (DPPC) with encapsulated calcein as the reporter molecule. Bacteriochlorophyll (BChl)-sensitized photorelease of Ca2+ from PLA2-resistant DPPlsCho liposomes activates extravesicular PLA2, thereby promoting catalyzed DPPC hydrolysis in a secondary triggering reaction, leading to calcein release. BChl/DPPlsCho/DHC/DPPE-PEG5000/Ca2+IN (0.5:85:10:5) liposomes can be phototriggered using 800 nm excitation, resulting in Ca2+ release (t50% release = 15 min) that cocatalyzes the release of calcein (t50% release = 40 min) from DPPC liposomes (1.5 mM total lipid in DPPlsCho liposomes, 0.18 mM DPPC, 210 micro M final Ca2+ concentration, 90 units of PLA2/ml, 50 mM calcein, and 36 micro M EDTA). No appreciable calcein release occurs in the absence of either PLA2 or BChl/DPPlsCho/DHC/DPPE-PEG5000/CaIN liposomes. The implications of this cascade triggering technique on drug delivery approaches are briefly discussed.
Wymer
N J
NJ
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA.
Gerasimov
O V
OV
Thompson
D H
DH
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008081:Liposomes / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D017319:Photosensitizing Agents / Q000494:pharmacology; D010955:Plasmalogens / Q000378:metabolism*
D001429:Bacteriochlorophylls; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008081:Liposomes; D017319:Photosensitizing Agents; D010955:Plasmalogens; C032459:choline plasmalogens; D015060:1,2-Dipalmitoylphosphatidylcholine; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium; C007740:fluorexon