Synthesis and characterization of deuterium-labelled dihexadecylglycerol and diphytanylglycerol phospholipids

A Molecular Toolkit for Highly Insulating Tethered Bilayer Lipid Membranes on Various Substrates

Tethered bilayer lipid membranes (tBLMs) are promising model architectures that mimic the structure and function of natural biomembranes. They provide a fluid, stable, and electrically sealing platform for the study of membrane related processes, specifically, the function of incorporated membrane proteins. This paper presents a generic approach toward the synthesis of functional tBLMs adapted for application to various surfaces. The central element of a tethered membrane consists of a lipid bilayer. Its proximal layer is covalently attached via a spacer unit to a solid support, either gold or silicon oxide. The membranes are characterized optically by using surface plasmon resonance spectroscopy (SPR) or ellipsometry and electrically by using electrochemical impedance spectroscopy (EIS). The bilayer membranes obtained show high electrical barrier properties and can be used to incorporate and study small membrane proteins in a functional form.

Surface properties of sulfur- and ether-linked phosphonolipids with and without purified hydrophobic lung surfactant proteins

Two novel C16:0 sulfur-linked phosphonolipids (S-lipid and SO(2)-lipid) and two ether-linked phosphonolipids (C16:0 DEPN-8 and C16:1 UnDEPN-8) were studied for surface behavior alone and in mixtures with purified bovine lung surfactant proteins (SP)-B and/or SP-C. Synthetic C16:0 phosphonolipids all had improved adsorption and film respreading compared to dipalmitoyl phosphatidylcholine, and SO(2)-lipid and DEPN-8 reached maximum surface pressures of 72mN/m (minimum surface tensions of <1mN/m) in compressed films on the Wilhelmy balance (23 degrees C). Dispersions of DEPN-8 (0.5mg/ml) and SO(2)-lipid (2.5mg/ml) also reached minimum surface tensions of <1mN/m on a pulsating bubble surfactometer (37 degrees C, 20cycles/min, 50% area compression). Synthetic lung surfactants containing DEPN-8 or SO(2)-lipid+0.75% SP-B+0.75% SP-C had dynamic surface activity on the bubble equal to that of calf lung surfactant extract (CLSE). Surfactants containing DEPN-8 or SO(2)-lipid plus 1.5% SP-B also had very high surface activity, but less than when both apoproteins were present together. Adding 10wt.% of UnDEPN-8 to synthetic lung surfactants did not improve dynamic surface activity. Surfactants containing DEPN-8 or SO(2)-lipid plus 0.75% SP-B/0.75% SP-C were chemically and biophysically resistant to phospholipase A(2) (PLA(2)), while CLSE was severely inhibited by PLA(2). The high activity and inhibition resistance of synthetic surfactants containing DEPN-8 or SO(2)-lipid plus SP-B/SP-C are promising for future applications in treating surfactant dysfunction in inflammatory lung injury.

Surface activity of a synthetic lung surfactant containing a phospholipase-resistant phosphonolipid analog of dipalmitoyl phosphatidylcholine

Surface activity and sensitivity to inhibition from phospholipase A2 (PLA2), lysophosphatidylcholine (LPC), and serum albumin were studied for a synthetic C16:0 diether phosphonolipid (DEPN-8) combined with 1.5% by weight of mixed hydrophobic surfactant proteins (SP)-B/C purified from calf lung surfactant extract (CLSE). Pure DEPN-8 had better adsorption and film respreading than the major lung surfactant phospholipid dipalmitoyl phosphatidylcholine and reached minimum surface tensions <1 mN/m under dynamic compression on the Wilhelmy balance and on a pulsating bubble surfactometer (37 degrees C, 20 cycles/min, 50% area compression). DEPN-8 + 1.5% SP-B/C exhibited even greater adsorption and had overall dynamic surface tension lowering equal to CLSE on the bubble. In addition, films of DEPN-8 + 1.5% SP-B/C on the Wilhelmy balance had better respreading than CLSE after seven (but not two) cycles of compression-expansion at 23 degrees C. DEPN-8 is structurally resistant to degradation by PLA2, and DEPN-8 + 1.5% SP-B/C maintained high adsorption and dynamic surface activity in the presence of this enzyme. Incubation of CLSE with PLA2 led to chemical degradation, generation of LPC, and reduced surface activity. DEPN-8 + 1.5% SP-B/C was also more resistant than CLSE to direct biophysical inhibition by LPC, and the two were similar in their sensitivity to biophysical inhibition by serum albumin. These findings indicate that synthetic surfactants containing DEPN-8 combined with surfactant proteins or related synthetic peptides have potential utility for treating surfactant dysfunction in inflammatory lung injury.

A tethered bilayer sensor containing alamethicin channels and its detection of amiloride based inhibitors

Alamethicin, a small transmembrane peptide, inserts into a tethered bilayer membrane (tBLM) to form ion channels, which we have investigated using electrical impedance spectroscopy. The number of channels formed is dependent on the incubation time, concentration of the alamethicin and the application of DC voltage. The properties of the ion channels when formed in tethered bilayers are similar to those for such channels assembled into black lipid membranes (BLMs). Furthermore, amiloride and certain analogs can inhibit the channel pores, formed in the tBLMs. The potency and concentration of the inhibitors can be determined by measuring the change of impedance. Our work illustrates the possibility of using a synthetic tBLM for the study of small peptide voltage dependent ion channels. A potential application of such a device is as a screening tool in drug discovery processes.

Chirospecific syntheses of 2H- and 13C-labeled 1-O-alkyl-2-O-alkyl'-sn-glycero-3-phosphoethanolamines and 1-O-alkyl-2-O-alkyl'-sn-glycero-3-phosphocholines

A convenient sequence for the synthesis of 1-O-alkyl-2-O-alkyl'-sn-glycero-3-phospholipids was demonstrated starting from 2,3-O-isopropylidene-sn-glycerol, which was first alkylated with 1-bromohexadecane, then converted to the corresponding benzylidene analog. Other less convenient methods to prepare 2,3-O-benzylidene-1-O-hexadecyl-sn-glycerol were also investigated. The key step in the synthesis was the reduction of 2,3-O-benzylidene-1-O-hexadecyl-sn-glycerol with lithium aluminum hydride-aluminum chloride to give 3-O-benzyl-1-O-hexadecyl-sn-glycerol as the major product in 79% yield. The syntheses of 1-O-hexadecyl-2-O-hexadecyl-(1',1'-d2,-sn-glycero-3-phosphoethanolamine and 1-O-hexadecyl-2-O-hexadecyl-(1'-13C)-sn-glycero-3-phosphoethanolamine as well as the correspondingly labeled sn-glycero-3-phosphocholine analogs were then performed. The optical purities of the synthetic intermediates and the ether lipids were established by a novel 1H-NMR method.