ABSTRACT
Most drugs need to interact with cell membrane to reach the biological target, so that membrane affinity assay is an important early screening step in drug discovery. However, at present, the traditional oil-water distribution method is still used, a new, simple and accurate method for membrane affinity assay is urgently needed. In this study, according to the colorimetric principle, a new assay model based on polydiacetylene vesicles was optimized through a series of experiments including different concentrations of vesicle solution, temperature, or pH reaction environment. On this basis, tetracaine hydrochloride, 2-methylimidazole and histamine were used as model drugs to measure the membrane affinity constants and verify the between-batch precision of the optimized assay model (relative standard deviation less than 5%). In addition, polydiacetylene vesicles were stable for up to 180 days, demonstrating the potential application of the assay model. This strategy is simple, stable, reliable, with high reproducibility, low cost and easy to promote, which provided a new tool and a new direction for the high-throughput assay of membrane affinity.
ABSTRACT
The conformation of nifedipine, a cardiac and smooth muscle calcium ion channel antagonist is studied in a hydrated bilayer of forty nine l,2-di-myristoyl-sn-glycero-3-phosphorylcholine (DMPC) molecules using molecular dynamics (MD) simulation technique. The simulation was carried out in conditions of constant number, volume and temperature (NVT) at 310 K, which is above the liquid crystalline (Lα) transition temperature of DMPC. The periodic boundary conditions were applied in three-dimensions. Thus the model represented an infinite bilayer. The important geometric parameters characteristic to DMPC and nifedipine molecules were calculated and compared with other theoretical and experimental results pertaining to nifedipine and other related dihydrophyridine (DHP) analogues. Our results suggest that conformational parameters required for antagonist activity are fairly conserved during the interaction of nifedipine with DMPC bilary and bilayer stabilizes the drug conformation in the bioactive form.
ABSTRACT
We present here results of molecular dynamics (MD) simulations on hydrated bilayers of 40 molecules of 1-2-dimyristoyl-sn-glycero-3-phosphatidyl choline (DMPC) in liquid crystalline (Lα) phase using two different models (i) with same (A) conformation for all DMPC molecules, (ii) with alternate rows having different (A and B reported in crystallographic studies on DMPC) conformations. The bilayers were hydrated using 776 and 1064 water molecules. Simulations have been carried out at 310K with AMBER 4·0 program, using united atom force field for 200 pico seconds (ps) after equilibration. During heating and equilibration constant pressure temperature (PT) conditions were maintained while in simulation of equillibrated bilayers constant volume temperature (VT) conditions were used. Subaveraged atomic coordinates were used to calculate geometric parameters of lipid molecules and lipid water interaction. Our results show larger flexibility of polar head group and glycerol region in Lα phase compared to gel or non-hydrated bilayers. Chain disorder was more towards end. Sn-2 chains were more disordered. Use of two types of starting conformations increased disorder. Trans fraction of chain torsional angle was higher in non-hydrated bilayer. However it was more disordered due to ‘swing’ movement of chains because of distortion in torsional angles α2 and 03 due to absence of water molecules. Trans fraction of the chains, order parameter and water penetration showed general agreement with the available experimental results. On the whole MD technique was found to be quite useful for depicting microscopic behaviour of liquid crystalline system and correlating the same with macroscopic changes observed experimentally.