Abstract
The interaction of four long-chain nicotinates, compounds that are of interest as potential chemopreventive agents, with dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayers at the air-water interface and in fully hydrated bilayers. For the monolayer studies, the compression isotherms of mixtures of the respective nicotinate with DPPC were recorded at various compositions on a hydrochloric acid subphase (pH 1.9-2.1, 37 +/- 2 degrees C). The headgroup of the nicotinates (24-29 A2/molecule) is larger than that of the hydrophobic tail (20 A2/molecule). The pure nicotinates exhibit a temperature- and chain length-dependent transition from an expanded to a condensed phase. Analysis of the concentration dependence of the average molecular area at constant film pressure and the concentration dependence of the breakpoint of the phase transition from the expanded to the condensed state suggests that all four DPPC-nicotinate mixtures are partially miscible at the air-water interface. Although a complex phase behavior with several phase transitions was observed, differential scanning calorimetry studies of the four mixtures are also indicative of the partial miscibility of DPPC and the respective nicotinate. Overall, the complex phase behavior most likely results from the head-tail mismatch of the nicotinates and the geometric packing constraints in the two-component lipid bilayer.
Highlights
The interaction of four long-chain nicotinates, compounds that are of interest as potential chemopreventive agents, with dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayers at the air-water interface and in fully hydrated bilayers
This study used a combination of monolayer and differential scanning calorimetry (DSC) studies to gain a better insight into the interaction of dipalmitoylphosphatidylcholine (DPPC), an important biological phospholipid, and several long-chain nicotinates
The present study investigates the mixing behavior of four nicotinates with DPPC in insoluble monolayers at the air-water interface and in completely hydrated mixtures using DSC
Summary
The interaction of four long-chain nicotinates, compounds that are of interest as potential chemopreventive agents, with dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayers at the air-water interface and in fully hydrated bilayers. There is significant interest in the pulmonary administration of several chemopreventive agents, such as steroids and retinoids, directly to the lung because of reduced systemic toxicity [7,8,9,10,11] This route of administration may be advantageous for the administration of nicotinic acid esters, by using either an aerosol or a perfluorocarbon vehicle [12, 13]. The interaction of various chemopreventive agents, especially retinoids, with phospholipids has been investigated [14, 15], there is no current knowledge about the factors that determine the interaction (i.e., phase behavior) of nicotinates with biological lipids such as the phospholipids present in pulmonary surfactant. This technique allows the study of the effect of a compound dispersed in a (model) biological membrane on the gel-to-liquid or main transition contains supplemental information
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