Electrospray ionization tandem mass spectrometry-based structure elucidation of lipid A molecules

Abstract

The main cause of death in intensive care units in hospitals around the world is septicemia, a serious bloodstream infection that may progress to sepsis and septic shock (Beutler and Rietschel, 2003). Septicemia happens when bacteria and their toxins enter the bloodstream from a bacterial infection in another part of the body, commonly the skin, lungs, kidneys, or bladder. People with chronic health conditions and weakened immune system are at a higher risk of septicemia due to their increased susceptibility to bacterial infections. In case of a Gram-negative bacterial infection, the uncontrolled growth and membrane lysis of bacteria results in the release of large amounts of membrane-associated lipopolysaccharide (LPS, endotoxin) in the bloodsream, which can, in turn, lead to exaggerated immune responses, called sepsis (Rietschel and Brade, 1992; Cavaillon, 2018). In serious cases, sepsis can result in dangerously low blood pressure, called septic shock, which can be fatal to the host. Paradoxically, under normal circumstances, Gram-negative bacteria (e.g., intestinal bacteria, or bacteria in home dust) have been known by upregulating the immune system by releasing small amounts of LPS that act as immunostimulants (Galanos and Delves, 1998; Gehring et al., 2020; Mbongue et al., 2022). Thus, in order to understand the diverse effects of LPS molecules on the human body, detection of their chemical structure, especially their lipid A portion – the primary immunostimulator of LPS (Zahringer et al., 1994) – is essential. At present, mass spectrometry is the most efficient method for exposing chemical structures of bacterial lipid A (Kilár et al., 2013) . Soft ionization techniques such as electrospray (ESI) and matrix-assisted laser desorption/ionization (MALDI) are used extensively to investigate the structural characteristics of these biomolecules. Tandem 9 mass spectrometry (MS/MS), and particularly, higher order tandem mass spectrometry (MSn ) in an ion trap mass analyzer is a powerful technique to demonstrate structural heterogeneity present in a lipid A extract. Not least, chemical structure information is especially important for the development of lipid A-based vaccine adjuvants.