1-palmitoyl-2-oleoylphosphatidylcholine and merocyanine-dye

The lipophilic dye merocyanine 540 (MC540) was used to model small molecule-membrane interactions using micropatterned lipid bilayer arrays (MLBAs) prepared using a 3D Continuous Flow Microspotter (CFM). Fluorescence microscopy was used to monitor MC540 binding to fifteen different bilayer compositions simultaneously. MC540 fluorescence was two times greater for bilayers composed of liquid-crystalline (l.c.) phase lipids (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC),1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)) compared to bilayers in the gel phase (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)). The effect cholesterol (CHO) had on MC540 binding to the membrane was found to be dependent on the lipid component; cholesterol decreased MC540 binding in DMPC, DPPC and DSPC bilayers while having little to no effect on the remaining l.c. phase lipids. MC540 fluorescence was also lowered when 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (sodium salt) (DOPS) was incorporated into DOPC bilayers. The increase in the surface charge density appears to decrease the occurrence of highly fluorescent monomers and increase the formation of weakly fluorescent dimers via electrostatic repulsion. This paper demonstrates that MLBAs are a useful tool for preparing high density reproducible bilayer arrays to study small molecule-membrane interactions in a high-throughput manner.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Algorithms; Binding, Competitive; Cell Membrane; Chlorobenzenes; Cholesterol; Dimyristoylphosphatidylcholine; Gels; Kinetics; Lipid Bilayers; Microarray Analysis; Microscopy, Fluorescence; Molecular Structure; Phase Transition; Phosphatidylcholines; Pyrimidinones; Reproducibility of Results; Spectrometry, Fluorescence

Absorption and fluorescence emission spectroscopy was applied to study the changes in albumin modified incorporation of merocyanine 540 into liposomes composed of different lecithins (DMPC, DPPC, POPC, and egg PC). Our results confirmed high affinity of merocyanine molecules toward albumin and revealed that albumin competed with all phospholipids used for binding merocyanine 540 molecules. However, the extent of this competition was determined by the kind of phospholipid. Albumin competed very successfully with lecithins containing saturated fatty acid chains (DPPC, DMPC) and weakly with unsaturated lecithins (POPC, egg PC) for binding merocyanine 540 molecules.

Topics: Albumins; Animals; Binding Sites; Binding, Competitive; Biophysical Phenomena; Biophysics; Cattle; Fluorescent Dyes; In Vitro Techniques; Liposomes; Phosphatidylcholines; Pyrimidinones; Spectrometry, Fluorescence; Spectrophotometry

The photochemistry of merocyanine 540 (MC 540), a sensitizing dye that binds preferentially to leukemia and electrically excitable cells, has been investigated. MC 540-mediated photooxidation of histidine, arachidonate, and unsaturated phospholipid vesicles was assessed by spin label oximetry and shown to involve type II (singlet oxygen) chemistry. The dye was also shown to be a potent sensitizer of lipid peroxidation in a natural cell membrane, the erythrocyte ghost. Inhibition by azide, stimulation by 2H2O, and identification of the cholesterol product 5 alpha-cholest-6-ene-3 beta,5-diol in this system, all were consistent with singlet oxygen intermediacy. Finally, MC 540 was found to be considerably more phototoxic to K-562 leukemia cells in 2H2O than in H2O. We conclude that singlet oxygen plays a major role in the phototherapeutic effects of this dye.

Topics: Cell Line; Cell Membrane; Dimyristoylphosphatidylcholine; Electron Spin Resonance Spectroscopy; Erythrocyte Membrane; Fluorescent Dyes; Humans; Leukemia, Myeloid; Liposomes; Oxygen; Phosphatidylcholines; Photochemistry; Pyrimidinones; Singlet Oxygen