implicated in a number of human diseases, such as atherosclerosis (3), nonalcoholic fatty liver (4), diabetes (5), Alzheimer's disease (6), and cancer (7,8). Advances in lipidomic techniques and strategies, led by the LIPID MAPS consortium, have greatly enhanced our understanding of the distribution and biological roles of lipids (9-13). Modern mass spectrometry (MS), coupled with electrospray ionization (ESI), is the key to qualitative and quantitative lipidomic analysis. Typical MS-based lipidomic strategies are shotgun (i.e., direct infusion) lipidomics (9, 14) and liquid chromatography (LC)-MS lipidomics (11,15,16). Shotgun lipidomics relies on partial intrasource separation of lipid classes through varying the pH of the lipid solution and identification of lipid species by their characteristic fragmentation in tandem MS analysis (9,17). This approach has the advantage of being high-throughput, but it also has several disadvantages: a) suppression of low-abundant species by major polar lipids such as phosphatidylcholines; b) difficulty in analysis of lipid species that are poorly ionized by ESI; and c) inability to provide structural information on isobaric and isomeric species. The LC-MS-based strategy utilizes targeted analysis of each lipid class under conditions that are optimized for that particular class (11,15,16,18). This strategy has the advantages of being specific, sensitive, and comprehensive, but it also has limitations, such as being time consuming and less cost effective. To increase the throughput of the LC-MS lipidomics while maintaining the specificity and sensitivity, we desire improved chromatographic techniques and additional dimensions of separation that are orthogonal to LC and MS. Lipids play important roles in maintaining membrane structures and mediating signaling pathways (1, 2). Dysregulated lipid biosynthesis and metabolism have been Abstract Ion mobility-mass spectrometry (IM-MS) has proven to be a highly informative technique for the characterization of lipids from cells and tissues. We report the combination of hydrophilic-interaction liquid chromatography (HILIC) with traveling-wave IM-MS (TWIM-MS

In this study, we aim to identify environmental molecules that can inhibit cholesterol biosynthesis, potentially leading to the same biochemical defects as observed in cholesterol biosynthesis disorders, which are often characterized by congenital malformations and developmental delay. Using the Distributed Structure-Searchable Toxicity (DSSTox) Database Network developed by EPA, we first carried out in silico screening of environmental molecules that display structures similar to AY9944, a known potent inhibitor of 3β-hydroxysterol-Δ(7)-reductase (DHCR7)-the last step of cholesterol biosynthesis. Molecules that display high similarity to AY9944 were subjected to test in mouse and human neuroblastoma cells for their effectiveness in inhibiting cholesterol biosynthesis by analyzing cholesterol and its precursor using gas chromatography-mass spectrometry. We found that a common disinfectant mixture, benzalkonium chlorides (BACs), exhibits high potency in inhibiting DHCR7, as suggested by greatly elevated levels of the cholesterol precursor, 7-dehydrocholesterol (7-DHC). Subsequent structure-activity studies suggested that the potency of BACs as Dhcr7 inhibitors decrease with the length of their hydrocarbon chain: C10 > C12 ≫ C14 > C16. Real-time qPCR analysis revealed upregulation of the genes related to cholesterol biosynthesis and downregulation of the genes related to cholesterol efflux, suggesting a feedback response to the inhibition. Furthermore, an oxidative metabolite of 7-DHC that was previously identified as a biomarker in vivo was also found in cells exposed to BACs by liquid chromatography-mass spectrometry. Our findings suggest that certain environmental molecules could potently inhibit cholesterol biosynthesis, which could be a new link between environment and developmental disorders.

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Specific spontaneous heritable neurodegenerative diseases have been associated with lower serum and cerebrospinal fluid α-tocopherol (α-TOH) concentrations. Equine neuroaxonal dystrophy (eNAD) has similar histologic lesions to human ataxia with vitamin E deficiency caused by mutations in the α-TOH transfer protein gene (TTPA). Mutations in TTPA are not present with eNAD and the molecular basis remains unknown. Given the neuropathologic phenotypic similarity of the conditions, we assessed the molecular basis of eNAD by global transcriptome sequencing of the cervical spinal cord. Differential gene expression analysis identified 157 significantly (FDR<0.05) dysregulated transcripts within the spinal cord of eNAD-affected horses. Statistical enrichment analysis identified significant downregulation of the ionotropic and metabotropic group III glutamate receptor, synaptic vesicle trafficking and cholesterol biosynthesis pathways. Gene co-expression analysis identified one module of upregulated genes significantly associated with the eNAD phenotype that included the liver X receptor (LXR) targets CYP7A1, APOE, PLTP and ABCA1. Validation of CYP7A1 and APOE dysregulation was performed in an independent biologic group and CYP7A1 was found to be additionally upregulated in the medulla oblongata of eNAD horses. Evidence of LXR activation supports a role for modulation of oxysterol-dependent LXR transcription factor activity by tocopherols. We hypothesize that the protective role of α-TOH in eNAD may reside in its ability to prevent oxysterol accumulation and subsequent activation of the LXR in order to decrease lipid peroxidation associated neurodegeneration.

Benzalkonium chlorides (BACs) are widely used as disinfectants in cleaning products, medical products, and the food processing industry. Despite a wide range of reported toxicities, limited studies have been conducted on the metabolism of these compounds in animal models and none in human-derived cells or tissues. In this work, we report on the metabolism of BACs in human liver microsomes (HLM) and by recombinant human hepatic cytochrome P450 (CYP) enzymes. BAC metabolism in HLM was NADPH-dependent and displayed apparent half-lives that increased with BAC alkyl chain length (C 10 < C 12 < C 14 < C 16), suggesting enhanced metabolic stability of the more lipophilic, longer chain BACs. Metabolites of d 7-benzyl labeled BAC substrates retained all deuteriums and there was no evidence of N-dealkylation. MS/MS fragmentation of BAC metabolites confirmed oxidation occurs on the alkyl chain region. Major metabolites of C 10-BAC were identified as ω-hydroxy-, (ω−1)-hydroxy-, (ω, ω−1)-diol-, (ω−1)-ketone-, and ω-carboxylic acid-C 10-BAC by LC-MS comparison with synthetic standards. In a screen of hepatic CYP isoforms, recombinant CYP2D6, CYP4F2, and CYP4F12 consumed substantial quantities of BAC substrates and produced the major microsomal metabolites. The use of potent pan-CYP4 inhibitor HET0016, the specific CYP2D6 inhibitor quinidine, or both confirmed major contributions of CYP4-and CYP2D6-mediated metabolism in the microsomal disappearance of BACs. Kinetic characterization of C 10-BAC metabolite formation in HLM demonstrated robust Michaelis-Menten kinetic parameters for ω-hydroxylation (V max = 380 pmol/min/mg, K m = 0.69 μM) and (ω −1)-hydroxylation (V max = 126 pmol/min/mg, K m = 0.13 μM) reactions. This work illustrates important roles for CYP4-mediated ω-hydroxylation and CYP2D6/CYP4-mediated (ω−1)hydroxylation during the hepatic elimination of BACs, an environmental contaminant of emerging concern. Furthermore, we demonstrate that CYP-mediated oxidation of C 10-BAC mitigates the potent inhibition of cholesterol biosynthesis exhibited by this short-chain BAC.