Cellular membrane phospholipids act as a depository for quaternary amine containing drugs thus competing with the acetylcholine/nicotinic receptor

An In Vitro Study of Aromatic Stacking of Drug Molecules

In this paper, drug-drug chemical interactions between two different aromatic compounds were studied by mass spectrometry. Specifically, we examined non-covalent complexes (NCX) between paclitaxel, a chemotherapeutic compound, and medications widely used in palliative care for depression, psychosis, and anxiety. It is unknown whether psychotropic medications directly interact with paclitaxel. Here, we use a simple and rapid electrospray ionization mass spectrometry in vitro assay, which has been predictive in the case of neuropeptides, to measure the relative strength of non-covalent interactions. This chemical interaction is most likely due to the overlap of aromatic rings of π-orbitals between paclitaxel and five commonly used medications: diazepam, clonozepam, sertraline, fluoxetine, and haloperidol. Molecular modeling illustrates that differences in the stability of the NCXs are likely due to the distance between the aromatic rings present in both the paclitaxel and antidepressant medications. Graphical Abstract.

A microscopic view of phospholipid insertion into biological membranes

Understanding the process of membrane insertion is an essential step in developing a detailed mechanism, for example, for peripheral membrane protein association and membrane fusion. The highly mobile membrane mimetic (HMMM) has been used to accelerate the membrane association and binding of peripheral membrane proteins in simulations by increasing the lateral diffusion of phospholipid headgroups while retaining an atomistic description of the interface. Through a comparative study, we assess the difference in insertion rate of a free phospholipid into an HMMM as well as into a conventional phospholipid bilayer and develop a detailed mechanistic model of free phospholipid insertion into biological membranes. The mechanistic insertion model shows that successful irreversible association of the free phospholipid to the membrane interface, which results in its insertion, is the rate-limiting step. Association is followed by independent, sequential insertion of the acyl tails of the free phospholipid into the membrane, with splayed acyl tail intermediates. Use of the HMMM is found to replicate the same intermediate insertion states as in the full phospholipid bilayer; however, it accelerates overall insertion by approximately a factor of 3, with the probability of successful association of phospholipid to the membrane being significantly enhanced.

Imaging of noncovalent complexes by MALDI-MS

Noncovalent interactions govern how molecules communicate. Mass spectrometry is an important and versatile tool for the analysis of noncovalent complexes (NCX). Electrospray mass spectrometry (ESI-MS) is the most widely used MS technique for the study of NCXs because of its softer ionization and easy compatibility with the solution phase of NCX mixtures. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has also been used to study NCXs. However, successful analysis depends upon several experimental factors, such as matrix selection, solution pH, and instrumental parameters. In this study, we employ MALDI imaging mass spectrometry to investigate the location and formation of NCXs, involving both peptides and proteins, in a MALDI sample spot.