Technological advances for analyzing the content of organ-on-a-chip by mass spectrometry

Three-dimensional (3D) cell cultures, including organ-on-a-chip (OOC) devices, offer the possibility to mimic human physiology conditions better than 2D models. The organ-on-a-chip devices have a wide range of applications, including mechanical studies, functional validation, and toxicology investigations. Despite many advances in this field, the major challenge with the use of organ-on-a-chips relies on the lack of online analysis methods preventing the real-time observation of cultured cells. Mass spectrometry is a promising analytical technique for real-time analysis of cell excretes from organ-on-a-chip models. This is due to its high sensitivity, selectivity, and ability to tentatively identify a large variety of unknown compounds, ranging from metabolites, lipids, and peptides to proteins. However, the hyphenation of organ-on-a-chip with MS is largely hampered by the nature of the media used, and the presence of nonvolatile buffers. This in turn stalls the straightforward and online connection of organ-on-a-chip outlet to MS. To overcome this challenge, multiple advances have been made to pre-treat samples right after organ-on-a-chip and just before MS. In this review, we summarised these technological advances and exhaustively evaluated their benefits and shortcomings for successful hyphenation of organ-on-a-chip with MS

Reshaping Lipid Biochemistry by Pushing Barriers in Structural Lipidomics

Lipidomics is a rapidly growing field with numerous examples showing the importance of lipid molecules throughout biology. It has also shed light onto the vast and complex functions performed by many lipids that possess an immense diversity in molecular structures. Mass spectrometry (MS) is the tool of choice for analyzing lipids and has been the key catalyst driving the field forward. However, MS does not yet permit true molecular lipidomics wherein the identification and quantification of lipids having defined molecular structures can be routinely achieved. Here we describe recent advances in MS-based lipidomics that allow access to higher levels of molecular information in lipidomics experiments. These advances will form a key piece of the puzzle as the field moves towards systems characterization of lipids at the molecular level

Uncovering the behaviour of ions in the gas-phase to predict the ion mobility separation of isomeric steroid compounds

Bile acids are steroid compounds involved in biological mechanisms of neurodegenerative diseases making them potential biomarkers for diagnosis or treatment. These compounds exist as structural and conformational isomers, which hinder distinguishing them in physiological processes. We aimed to develop tandem mass spectrometry-ion mobility spectrometry (MS/MS-IMS) methodologies to explore and understand the behaviour of isomeric steroids in the gas-phase and rapidly separate them. Unlike previously published ion mobility data, various isomers were investigated in mixtures to better mimic complex (pre-) clinical samples. The experimental collision cross sections (CCS)s were compared to the theoretical CCS values for an in-depth analysis of isomeric ions' behaviour in the gas-phase. Based on density-functional theory, we identified the impact of adduct positioning on the 3D conformation of enantiomers, diastereomers and structural isomers. The curling of the large side chains hedged the small differences among the isomers and lowered the CCS values. On the other hand, fragmenting off the identical side branches as well as imposing the bending of the steroid ring resulted in ion mobility differentiation. Careful data evaluation revealed the tendency of isomers to form homo-cluster in the mixture solutions and assist the separation. Our fundamental and experimental findings enable the ion mobility separation of isomeric steroids to be predicted. The introduced rapid and optimal MS/MS-IMS analytical methodology can be applied to distinguish isomeric bile acids both in a solution and potentially in patients' tissue samples, and consequently, reveal their molecular pathways

Real-time drug detection using a diathermic knife combined to rapid evaporative ionisation mass spectrometry

Fast, accurate and sensitive detection of drugs in human tissue is of crucial importance in an investigation of a suspicious death. Here, we aimed to screen cocaine, diazepam, methadone and morphine in post-mortem muscle samples without sample preparation and in quasi-real time using rapid evaporative ionisation mass spectrometry (REIMS). REIMS enables the online MS analysis of vapours generated from tissue dissection by a diathermic knife. Human muscle samples were soaked in solutions of 4 drugs at different concentrations and multiple incubation times to check the feasibility of REIMS for this innovative application. Muscle samples soaked in blank saline were used as a control. The classification model was able to distinguish between 30 μg g-1 cocaine (m/z 304.2), 200 μg g-1 morphine (m/z 286.2), 10 μg g-1 methadone (m/z 310.2) and 10 μg g-1 muscle of diazepam (m/z 285.1). REIMS tandem MS confirmed that the mass peaks that contributed to the class separation, originated from the drugs of interest. As a proof-of-concept, a forensic case muscle sample from a methadone overdose was investigated using REIMS. Here, using our classification model, the recognition software was able to detect methadone, demonstrating that the REIMS method opens new possibilities in forensic toxicology and during autopsy, leading to faster crime solving and decreased costs