Aaron Z. Fernandis

Lipid-based biomarkers for cancer

Lipids play important and diverse roles in cells. Most obvious functions are storage of chemical energy, provision of structural support of biological membranes and signaling. All these cellular processes are of critical relevance to cells which undergo transformation, cancer progression and metastasis. Thus, it is likely that certain classes of lipids are reflective for the cellular physiology in cancer cells and tissue. Here we discuss key roles of lipids involved in cancer as well as challenges for development of novel lipid-based biomarkers. Special emphasis will be given to mass spectrometry based analysis of lipids. Such technology has been successfully used for qualitative and quantitative analysis of lipids with very different chemistries. Comparative analysis, often in case-control regimes, and either in non-targeted (e.g. by liquid chromatography-single stage mass spectrometry) or targeted (i.e. by tandem mass spectrometry) fashion yields vast arrays of information. Uni-variate (such as Students t-test or Mann-Whitney U-test) and multivariate statistics (principal components analysis, machine learning and regression analysis) are next used to identify variations in individual lipid species and/or to lower dimensions for visualization and grouping of cases and controls. As a result surrogate (single or multi-parameter) markers are identified which form the basis for functional validation as well as potential translation to alternative analytical readouts.

Membrane lipids as signaling molecules

Purpose of review Membrane lipids play important roles in signaling reactions. They are involved in most if not all cellular signaling cascades and in a wide variety of tissue and cell types. The purpose of this review is to highlight major pathways of signaling originating in membrane lipids. Details of lipid metabolism, and its relation to protein function, will thus advance understanding of the role of lipids in health and disease. Recent findings Major classes of lipids including glycerophospholipids, their metabolites (eicosanoids, endocannabinoids), and sphingolipids have recently generated interest in the field of signal transduction. These lipids are tightly regulated and have an impact on various physiological functions. Importantly, aberrant lipid metabolism often leads to onset of pathology, and thus the precise balance of signaling lipids and their effectors can serve as biomarkers. Summary Membrane lipids form precursors for second messengers and functional assembly matrices on membrane domains during cellular stimulation. Many of these modifications are rapid reactions at lipid headgroups. Metabolism of the fatty acyl portion of membrane lipids leads to the generation of a bewildering complexity of lipid mediators with extended effects in space and time.

Lipidomic analysis of human placental Syncytiotrophoblast microvesicles in adverse pregnancy outcomes

PROBLEM Syncytiotrophoblast microvesicles (STBM) are shed from placenta into the maternal circulation. STBM circulate in increased amounts in adverse pregnancies, e.g., preeclampsia and recurrent miscarriages (RM). Recently dysregulation of lipid metabolites has been proposed to be associated with their pathogenesis. Lipid composition of STBM in healthy and adverse pregnancies remains unknown. OBJECTIVE To determine lipid composition of STBM and whether STBM lipid composition differs in pathologic and normal pregnancies. STUDY DESIGN Patients with Preeclampsia (n = 6) or history of RM (n = 9) (>2 consecutive losses <20 weeks) and gestational age-matched normal pregnant controls (same number as cases) were recruited. STBM were prepared from placental explant culture supernatant. Lipid profiling of STBM was performed by mass spectrometry in combination with liquid chromatography. We quantified ∼200 lipids in STBM including (i) glycerophospholipids (phosphatidylcholine, PC; phosphatidylethanolamine, PE; phosphatidylinositol, PI; phosphatidylglycerol, PG; phosphatidylserine, PS; phosphatidic acid, PA); (ii) sphingolipids (sphingomyelin, SM; ceramide, Cer; Glucosylceramide, GluCer; ganglioside mannoside 3, GM3); (iii) free cholesterol and cholesteryl esters, CE. RESULTS The major lipid classes in STBM were SM, Chol, PS, PC and PI, along with PA and GM3 enrichments. SM/PC ratio showed a unique reversal (3:1) compared to that normally found in human cells or plasma. Level of total PS was significantly upregulated (p < 0.005) in preeclampsia patients, while PI (p < 0.0005), PA (p < 0.005), and GM3 (p < 0.05) were significantly downregulated. Similar trends were obtained in RM. CONCLUSIONS Differential lipid expression of STBM in preeclampsia or RM includes those that are implicated in immune response, coagulation, oxidative stress, and apoptosis.

Derivatization-independent cholesterol analysis in crude lipid extracts by liquid chromatography/mass spectrometry: Applications to a rabbit model for atherosclerosis

Direct measurement of various sterols in crude lipid extracts in a single experiment from limited biological samples is challenging. Current mass spectrometry (MS) based approaches usually require chemical derivatization before subjecting to MS analysis. Here, we present a derivatization-independent method for analyzing various sterols, including cholesterol and its congeners, using liquid chromatography and atmospheric pressure chemical ionization mass spectrometry. Based on the specific tandem mass spectrometry pattern of cholesterol, multiple reaction monitoring (MRM) transitions were used to quantify free cholesterol and its fatty acyl esters. Several cholesterol oxidation products could also be measured using the upfront liquid chromatography separation and specific MRM transitions. The method was validated alongside established enzymatic assays in measuring total cholesterol. As a proof of concept, we analyzed plasma sterols in rabbits administrated with a high cholesterol diet (HCD) which is a classical atherosclerotic model. Free cholesterol, cholesterol esters, 7-hydroxycholesterol, and 7-ketocholesterol were elevated in plasma of rabbits on HCD. This method could also serve as an excellent tool for quantitative analysis of other sterols such as ergosterol and sitosterol in other organisms beside mammalian. In Saccharomyces cerevisiae, our results indicated dramatic increases of the ratio of ergosterol esters to free ergosterol in both yeh2Δ and tgl1Δ cells, which are consistent with the function of the respective enzymes.

Profiling brain and plasma lipids in human apoe ε2, ε3, and ε4 knock - In mice using electrospray ionization mass spectrometry

It is known that apolipoprotein E (ApoE) is essential for normal lipid metabolism. ApoE is the major apolipoprotein in the central nervous system and plays a key role in neurobiology by mediating the transport of cholesterol, phospholipids, and sulfatides. We therefore examined APOE epsilon2, epsilon3, and epsilon4 knock-in mice, using electrospray ionization mass spectrometry to determine if APOE genotype or age leads to altered levels in the brain of a number of glycerophospholipids (phosphatidylinositol, PI; phosphatidylethanolamine, PE; phosphatidic acid, PA, phosphatidylserine, PS; phosphatidylcholine, PC), sphingolipids (sphingomyelin, SM; ceramide, Cer), cholesterol, and triacylglycerols. We observed slight changes within individual PI, PE, PC, Cer, and SM lipid levels in APOE epsilon2 and epsilon4 mice compared to APOE epsilon3 mice. However, overall, we did not observe any major effects in APOE epsilon4 knock-in mice for the levels of the glycerophospholipids measured, as compared to APOE epsilon2 and epsilon3 mice. Our findings indicate that variations in ApoE isoforms do not per se affect bulk lipid homeostasis in the brain. These findings indicate that APOE epsilon4 is not associated with disturbances in brain sterol or sphingolipids in the absence of environmental factors.

Identification and characterization of the lipid binding property of GrlR, a locus of enterocyte effacement regulator.

Lipocalins are a broad family of proteins identified initially in eukaryotes and more recently in Gram-negative bacteria. The functions of lipocalin or lipid-binding proteins are often elusive and very diverse. Recently, we have determined the structure of GrlR (global regulator of LEE repressor), which plays a key role in the regulation of LEE (locus of enterocyte effacement) proteins. GrlR adopts a lipocalin-like fold that is composed of an eight-stranded beta-barrel followed by an alpha-helix at the C-terminus. GrlR has a highly hydrophobic cavity region and could be a potential transporter of lipophilic molecules. To verify this hypothesis, we carried out structure-based analysis of GrlR, determined the structure of the lipid-GrlR complex and measured the binding of lipid to recombinant GrlR by ITC (isothermal titration calorimetry). In addition, we identified phosphatidylglycerol and phosphatidylethanolamine as the endogenously bound lipid species of GrlR using electrospray-ionization MS. Furthermore, we have shown that the lipid-binding property of GrlR is similar to that of its closest lipocalin structural homologue, beta-lactoglobulin. Our studies demonstrate the hitherto unknown lipid-binding property of GrlR.

A manual for biochemistry protocols

Protein Purification Protein Analysis Lipid Analysis Mammalian Cell Culture Microscopy Assays Autoradiography.

Lipidomics as a diagnostic and research tool

Lipids play an important role in signaling mechanisms, regulation of protein function and control of a wide variety of cellular responses. As these lipids are important regulators their levels are tightly controlled and fine tuned both spatially as well as temporally. An imbalance in these lipids, in particular those involved in cell signaling, could lead to various pathological disorders. Thus these lipids and their effectors can serve as biomarkers. Indeed, cardiovascular diseases, obesity, neurological disorders, as well as infectious diseases have been directly implicated with aberrant lipid metabolism. This indicates that careful inspection of lipid level using metabolic profiling could help in clinical diagnostics of these pathologies.