Disease detection and lipid membrane analysis using spectrometric and spectroscopic measurements

The biological membrane functions as a semipermeable barrier regulating molecular flux from the cell and is a complex system with a diverse composition of lipids. Lipids are a varied class of biomolecules ranging from sterols to phospholipids. Both small changes in structure and relative amount of different lipids will affect membrane properties and processes. Importantly, phospholipid homeostasis is disrupted in many disease states, resulting in different membrane lipid compositions which is useful as a diagnostic tool and could be leveraged for drug-delivery. This dissertation explores the diversity and function of membrane lipids from two perspectives: as biomarkers for disease detection and as modulators of membrane-small molecule interactions and electric fields. The first section describes the use of a mass spectrometry-based sampling probe, the MasSpec Pen, for rapid analysis of lipids and metabolites. This probe was applied to acquire molecular profiles from bacteria and infected biospecimens which were then used to build statistical models for bacterial classification. The identification of a putatively assigned anesthetic metabolite, hexafluorisopropyl sulfonate, using this system is also described. Lastly, we report the development of an interface to facilitate clinical implementation of the MasSpec Pen and a proof-of-concept study distinguishing healthy liver tissue from hepatocellular carcinoma. The second section examines the implications of membrane lipid diversity for drug delivery and its impact on membrane electrostatics using fluorescence solvatochromism and vibrational stark effect (VSE) spectroscopy of model membrane systems. With complementary experiments and simulations, we propose charge separation on doubly positively charged peptides as a design principle for membrane permeating peptides. We also investigate the leaflet-dependent effects of anionic lipids on peptide-membrane interactions and identify outer leaflet anionic lipids as the dominant promoters of cationic peptide membrane insertion. The final chapter in this section probes the effect of cholesterol and 7-dehydrocholesterol (7DHC) on membrane electrostatics using VSE spectroscopy. While there was no significant difference in vibrational energy shifts for these two sterols, we demonstrate the significance of temperature for these measurements. Together, these efforts seek to expand the understanding of how biological membrane lipid diversity can be used to understand, diagnose, and treat disease states.