Ions formed from lipids during electrospray ionization of crude lipid extracts have been mass-selected within a quadrupole linear ion trap mass spectrometer and allowed to react with ozone vapor. Gas-phase ion-molecule reactions between unsaturated lipid ions and ozone are found to yield two primary product ions for each carbon-carbon double bond within the molecule. The mass-to-charge ratios of these chemically induced fragments are diagnostic of the position of unsaturation within the precursor ion. This novel analytical technique, dubbed ozone-induced dissociation (OzID), can be applied both in series and in parallel with conventional collision-induced dissociation (CID) to provide near-complete structural assignment of unknown lipids within complex mixtures without prior fractionation or derivatization. In this study, OzID is applied to a suite of complex lipid extracts from sources including human lens, bovine kidney, and commercial olive oil, thus demonstrating the technique to be applicable to a broad range of lipid classes including both neutral and acidic glycerophospholipids, sphingomyelins, and triacylglycerols. Gas-phase ozonolysis reactions are also observed with different types of precursor ions including [M+H]+, [M+Li]+, [M+Na]+, and [M-H]-: in each case yielding fragmentation data that allow double bond position to be unambiguously assigned. Within the human lens lipid extract, three sphingomyelin regioisomers, namely SM(d18:0/15Z-24:1), SM(d18:0/17Z-24:1), and SM(d18:0/19Z-24:1), and a novel phosphatidylethanolamine alkyl ether, GPEtn(11Z-18:1e/9Z-18:1), are identified using a combination of CID and OzID. These discoveries demonstrate that lipid identification based on CID alone belies the natural structural diversity in lipid biochemistry and illustrate the potential of OzID as a complementary approach within automated, high-throughput lipid analysis protocols.

Electrospray ionisation tandem mass spectrometry has allowed the unambiguous identification and quantification of individual lens phospholipids in human and six animal models. Using this approach ca. 100 unique phospholipids have been characterised. Parallel analysis of the same lens extracts by a novel direct-insertion electron-ionization technique found the cholesterol content of human lenses to be significantly higher (ca. 6 times) than lenses from the other animals. The most abundant phospholipids in all the lenses examined were choline-containing phospholipids. In rat, mouse, sheep, cow, pig and chicken, these were present largely as phosphatidylcholines, in contrast 66% of the total phospholipid in Homo sapiens was sphingomyelin, with the most abundant being dihydrosphingomyelins, in particular SM(d18:0/16:0) and SM(d18:0/24:1). The abundant glycerophospholipids within human lenses were found to be predominantly phosphatidylethanolamines and phosphatidylserines with surprisingly high concentrations of ether-linked alkyl chains identified in both classes. This study is the first to identify the phospholipid class (head-group) and assign the constituent fatty acid(s) for each lipid molecule and to quantify individual lens phospholipids using internal standards. These data clearly indicate marked differences in the membrane lipid composition of the human lens compared to commonly used animal models and thus predict a significant variation in the membrane properties of human lens fibre cells compared to those of other animals.

Ozone-induced dissociation (OzID) exploits the gas-phase reaction between mass-selected lipid ions and ozone vapor to determine the position(s) of unsaturation. In this contribution, we describe the modification of a tandem linear ion-trap mass spectrometer specifically for OzID analyses wherein ozone vapor is supplied to the collision cell. This instrumental configuration provides spatial separation between mass-selection, the ozonolysis reaction, and mass-analysis steps in the OzID process and thus delivers significant enhancements in speed and sensitivity (ca. 30-fold). These improvements allow spectra revealing the double-bond position(s) within unsaturated lipids to be acquired within 1 s: significantly enhancing the utility of OzID in high-throughput lipidomic protocols. The stable ozone concentration afforded by this modified instrument also allows direct comparison of relative reactivity of isomeric lipids and reveals reactivity trends related to (1) double-bond position, (2) substitution position on the glycerol backbone, and (3) stereochemistry. For cis-and trans-isomers, differences were also observed in the branching ratio of product ions arising from the gas-phase ozonolysis reaction, suggesting that relative ion abundances could be exploited as markers for double-bond geometry. Additional activation energy applied to mass-selected lipid ions during injection into the collision cell (with ozone present) was found to yield spectra containing both OzID and classical-CID fragment ions. This combination CID-OzID acquisition on an ostensibly simple monounsaturated phosphatidylcholine within a cow brain lipid extract provided evidence for up to four structurally distinct phospholipids differing in both double-bond position and sn-substitution. (J Am Soc Mass Spectrom 2010, 21, 1989 . There are a wide range of lipid subclasses with different biochemical roles, including glycerophospholipids (GPLs) that act as primary building blocks of membranes and precursors for intracellular signaling molecules; fatty acids (FAs) and triacylglycerols (TAGs) that are the major source of energy in plants and animals; and sterols that modulate membrane stability and act as biochemical messengers [2]. The specific functions of lipid classes, and indeed individual lipids, are related to their chemical and physical properties that in turn depend on specific molecular features [3]. As such, even small changes in molecular structure can affect the role of a lipid within a living organism. Recent research has indicated that within living organisms, different lipid isomers play different, and in some cases contrasting, metabolic roles. For example, one study focusing on the effect of conjugated linoleic acid isomers on development of atherosclerosis in ApoE knockout mice revealed that while one isomer (10E,12Z-18:2) had a profound atherogenic effect, an alternate isomer (9Z, 11E-18:2) was anti-atherogenic [4]. While differences in molecular structure arising from double-bond position and/or stereoisomerism (vide infra) can be cha...

BackgroundWe present a lipidomics analysis of human Parkinson's disease tissues. We have focused on the primary visual cortex, a region that is devoid of pathological changes and Lewy bodies; and two additional regions, the amygdala and anterior cingulate cortex which contain Lewy bodies at different disease stages but do not have as severe degeneration as the substantia nigra.Methodology/Principal FindingsUsing liquid chromatography mass spectrometry lipidomics techniques for an initial screen of 200 lipid species, significant changes in 79 sphingolipid, glycerophospholipid and cholesterol species were detected in the visual cortex of Parkinson's disease patients (n = 10) compared to controls (n = 10) as assessed by two-sided unpaired t-test (p-value <0.05). False discovery rate analysis confirmed that 73 of these 79 lipid species were significantly changed in the visual cortex (q-value <0.05). By contrast, changes in 17 and 12 lipid species were identified in the Parkinson's disease amygdala and anterior cingulate cortex, respectively, compared to controls; none of which remained significant after false discovery rate analysis. Using gas chromatography mass spectrometry techniques, 6 out of 7 oxysterols analysed from both non-enzymatic and enzymatic pathways were also selectively increased in the Parkinson's disease visual cortex. Many of these changes in visual cortex lipids were correlated with relevant changes in the expression of genes involved in lipid metabolism and an oxidative stress response as determined by quantitative polymerase chain reaction techniques.Conclusions/SignificanceThe data indicate that changes in lipid metabolism occur in the Parkinson's disease visual cortex in the absence of obvious pathology. This suggests that normalization of lipid metabolism and/or oxidative stress status in the visual cortex may represent a novel route for treatment of non-motor symptoms, such as visual hallucinations, that are experienced by a majority of Parkinson's disease patients.

Background: Postoperative delirium is the most common complication of surgery particularly in older patients.Aims: The current study aimed to summarize the commonly used delirium assessment tools in assessing postoperative delirium (POD) and to estimate the incidence rates of POD.Methods: A systematic review that included empirical cohort studies reporting the use of delirium assessment tools in assessing POD between 2000 and 2019. Five core databases were searched for eligible studies. The methodological quality assessment of the included studies was undertaken using the Joanna Briggs Institute (JBI) critical appraisal checklist to examine the risk of bias. Pooled incidence estimates were calculated using a random effects model.Results: Nineteen studies with a total of 3,533 postsurgery older patients were included in this review. The confusion assessment method (CAM) and CAM-ICU were the most commonly used tools to assess POD among older postoperative patients. The pooled incidence rate of POD was 24% (95% CI [0.20, 0.29]). The pooled incidence estimates for mixed (noncardiac) surgery, orthopedic surgery, and tumor surgery were 23% (95% CI [0.15, 0.31]), 27% (95% CI [0.20, 0.33]), and 19% (95% CI [0.15, 0.22]), respectively. More than 50% of included studies used CAM to assess POD in different types of postoperative patients. Using CAM to assess delirium is less time-consuming and it was suggested as the most efficient tool for POD detection.