Interactions of phenytoin with lipids in mixed Langmuir monolayers

Structure Dependence of Pyridine and Benzene Derivatives on Interactions with Model Membranes

Pyridine-based small-molecule drugs, vitamins, and cofactors are vital for many cellular processes, but little is known about their interactions with membrane interfaces. These specific membrane interactions of these small molecules or ions can assist in diffusion across membranes or reach a membrane-bound target. This study explores how minor differences in small molecules (isoniazid, benzhydrazide, isonicotinamide, nicotinamide, picolinamide, and benzamide) can affect their interactions with model membranes. Langmuir monolayer studies of dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylethanolamine (DPPE), in the presence of the molecules listed, show that isoniazid and isonicotinamide affect the DPPE monolayer at lower concentrations than the DPPC monolayer, demonstrating a preference for one phospholipid over the other. The Langmuir monolayer studies also suggest that nitrogen content and stereochemistry of the small molecule can affect the phospholipid monolayers differently. To determine the molecular interactions of the simple N-containing aromatic pyridines with a membrane-like interface, ¹H one-dimensional NMR and ¹H-¹H two-dimensional NMR techniques were utilized to obtain information about the position and orientation of the molecules of interest within aerosol-OT (AOT) reverse micelles. These studies show that all six of the molecules reside near the AOT sulfonate headgroups and ester linkages in similar positions, but nicotinamide and picolinamide tilt at the water-AOT interface to varying degrees. Combined, these studies demonstrate that small structural changes of small N-containing molecules can affect their specific interactions with membrane-like interfaces and specificity toward different membrane components.

Influence of cadmium and selenate on the interactions between hormones and phospholipids

In this study, the influence of plant hormones, negatively charged indolilo-3-acetic acid (IAA) and positively charged zeatin, on lipid membranes was studied. As models of negatively and positively charged biological membranes, monolayers of 1,2-dimyristoyl-sn-glycero-3-[phospho-l-serine] (DMPS) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP) at the water/air interface were used, respectively. Additionally, the effect of cadmium and selenium ions on the interactions between hormones and lipids was studied. Surface pressure and surface potential measurements, Brewster angle microscopy (BAM), and grazing incidence X-ray diffraction (GIXD) were used for that purpose. Both IAA and zeatin led to an expansion of the lipid monolayer caused by electrostatic interactions between oppositely charged groups: negatively charged polar group of DMPS and positively charged zeatin or positive DPTAP headgroup and negative IAA. The addition of ions to the subphase containing hormones causes competitive interactions of both solutes with oppositely charged lipid polar heads. The largest effect was observed for IAA. While zeatin does not change the domain shape of DMPS, IAA causes the complete disappearance of characteristic DPTAP domains. Addition of SeO(4)(2-) ions causes restoration of DPTAP domains observed on pure water.

Effect of cholesterol and fatty acids on the molecular interactions of fengycin with Stratum corneum mimicking lipid monolayers

The combination of atomic force microscopy (AFM) and the Langmuir trough technique was used in this work to investigate the molecular interactions of fengycin with lipid monolayers constituted of the major lipid classes found in human stratum corneum (SC). AFM imaging o f spread SC lipids/fengycin monolayers showed that fengycin preferentially partitions into cholesterol-rich phases surrounding 2D domains mainly constituted of ceramide and fatty acid molecules. Penetration experiments of fengycin from the subphase into SC-mimicking monolayers clearly indicated that the lipopeptide insertion at the lipid interface is enhanced in the presence of cholesterol. AFM analysis of mixed SC lipids/fengycin monolayers obtained after lipopeptide penetration revealed that cholesterol strongly interacts with fengycin and undergoes specific molecular interactions with more disordered, loosely packed ceramide molecules. These results highlight the capacity of fengycin to interact with the lipid constituents of the extracellular matrix of SC and, in particular, with cholesterol.