High-performance liquid chromatography separation of phospholipid classes and arachidonic acid on cyanopropyl columns

An HPLC-CAD/fluorescence lipidomics platform using fluorescent fatty acids as metabolic tracers

Fluorescent lipids are important tools for live imaging in cell culture and animal models, yet their metabolism has not been well-characterized. Here we describe a novel combined HPLC and LC-MS/MS method developed to characterize both total lipid profiles and the products of fluorescently labeled lipids. Using this approach, we found that lipids labeled with the fluorescent tags, 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY FL), 4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene [BODIPY(558/568)], and dipyrrometheneboron difluoride undecanoic acid (TopFluor) are all metabolized into varying arrays of polar and nonpolar fluorescent lipid products when they are fed to larval zebrafish. Quantitative metabolic labeling experiments performed in this system revealed significant effects of total dietary lipid composition on fluorescent lipid partitioning. We provide evidence that cholesterol metabolism in the intestine is important in determining the metabolic fates of dietary FAs. Using this method, we found that inhibitors of dietary cholesterol absorption and esterification both decreased incorporation of dietary fluorescent FAs into cholesterol esters (CEs), suggesting that CE synthesis in enterocytes is primarily responsive to the availability of dietary cholesterol. These results are the first to comprehensively characterize fluorescent FA metabolism and to demonstrate their utility as metabolic labeling reagents, effectively coupling quantitative biochemistry with live imaging studies.

Characterization of Staphylococcus aureus cardiolipin synthases 1 and 2 and their contribution to accumulation of cardiolipin in stationary phase and within phagocytes

In many bacteria, including Staphylococcus aureus, progression from the logarithmic to the stationary phase is accompanied by conversion of most of bacterial membrane phosphatidylglycerol (PG) to cardiolipin (CL). Phagocytosis of S. aureus by human neutrophils also induces the conversion of most bacterial PG to CL. The genome of all sequenced strains of S. aureus contains two open reading frames (ORFs) predicting proteins encoded with ∼30% identity to the principal CL synthase (cls) of Escherichia coli. To test whether these ORFs (cls1 and cls2) encode cardiolipin synthases and contribute to CL accumulation in S. aureus, we expressed these proteins in a cls strain of E. coli and created isogenic single and double mutants in S. aureus. The expression of either Cls1 or Cls2 in CL-deficient E. coli resulted in CL accumulation in the stationary phase. S. aureus with deletion of both cls1 and cls2 showed no detectable CL accumulation in the stationary phase or after phagocytosis by neutrophils. CL accumulation in the stationary phase was due almost solely to Cls2, whereas both Cls1 and Cls2 contributed to CL accumulation following phagocytosis by neutrophils. Differences in the relative contributions of Cls1 and Cls2 to CL accumulation under different triggering conditions suggest differences in the role and regulation of these two enzymes.

Quantification of phosphatidylserine, phosphatidic acid and free fatty acids in an ultrasound contrast agent by normal-phase high-performance liquid chromatography with evaporative light scattering detection

Sonazoid is a new contrast agent for ultrasound imaging. The product is an aqueous suspension of perfluorobutane microbubbles coated with phospholipids obtained from hydrogenated egg phosphatidylserine (H-EPS). A normal-phase high-performance liquid chromatographic (HPLC) method with evaporative light scattering detection was developed for quantification of free fatty acids, phosphatidylserine and phosphatidic acid in H-EPS and Sonazoid. Separation of the lipids was carried out on an HPLC diol column and a gradient of chloroform and methanol with 0.2% formic acid titrated to pH 7.5 with ammonia. The calibration standards contained stearic acid, distearoyl-phosphatidic acid (DSPA) and distearoyl-phosphatidylserine (DSPS) in the concentration range of 0.016-1.0mg/ml (0.4-25microg injected). The method was validated with a limit of quantification of the three lipids set to 0.4microg (approximately 20-60microM). The best fit of the three calibration curves were obtained when the logarithmic transformed theoretical lipid concentration was plotted against the logarithmic transformed area under the peak and fitted to a second order polynomial equation. Stearic acid, DSPA and DSPS were analysed with an intermediate precision ranging from 4.4% to 5.3% R.S.D. and they were extracted from an aqueous suspension with a recovery ranging from 103.3% to 113.3%. The sum of total phospholipid concentration determined in H-EPS ranged from 96.4% to 103.2% of the theoretical values. The lipids in the ultrasound product were quantitated with a repeatability ranging from 6.2% to 11.7% R.S.D.

Phospholipid composition of cell-derived microparticles determined by one-dimensional high-performance thin-layer chromatography

Microparticles in the circulation activate the coagulation system and may activate the complement system via C-reactive protein upon conversion of membrane phospholipids by phospholipases. We developed a sensitive and reproducible method to determine the phospholipid composition of microparticles. Samples were applied to horizontal, one-dimensional high-performance thin-layer chromatography (HPTLC). Phospholipids were separated on HPTLC by chloroform:ethyl acetate:acetone:isopropanol:ethanol:methanol:water:acetic acid (30:6:6:6:16:28:6:2); visualized by charring with 7.5% Cu-acetate (w/v), 2.5% CuSO(4) (w/v), and 8% H(3)PO(4) (v/v) in water; and quantified by photodensitometric scanning. Erythrocyte membranes were used to validate the HPTLC system. Microparticles were isolated from plasma of healthy individuals (n = 10). On HPTLC, mixtures of (purified) phospholipids, i.e., lysophosphatidylcholine, phosphatidylcholine (PC), sphingomyelin (SM), lysophosphatidylserine, phosphatidylserine, lysophosphatidylethanolamine, phosphatidylethanolamine (PE), and phosphatidylinositol, could be separated and quantified. All phospholipids were detectable in erythrocyte ghosts, and their quantities fell within ranges reported earlier. Quantitation of phospholipids, including extraction, was highly reproducible (CV < 10%). Microparticles contained PC (59%), SM (20.6%), and PE (9.4%), with relatively minor (<5%) quantities of other phospholipids. HPTLC can be used to study the phospholipid composition of cell-derived microparticles and may also be a useful technique for the analysis of other samples that are available only in minor quantities.

Reversed-phase liquid chromatographic method for the determination of 7-nitrobenz-2-oxa-1,3-diazol-4-yl-labelled lipid analogues

This paper reports the development of a dual column system for the simultaneous separation of fluorescent short-chain ceramide, 6-[(7-nitrobenz-2-oxa-1,3,-diazol-4-yl[NBD])amino]hexanoyl-sphingo sine and its metabolites, C6-NBD-sphingomyelin and C6-NBD-glucosylceramide, as well as the fluorescent derivatives of choline and serine phosphatides. The method enables the separation of these lipids in a single run on the basis of the polarity of their headgroups and hydrophobicity of their acyl backbone. The fluorescent properties of the NBD-label make it possible to quantitate small amounts of NBD-lipid analogues. The sensitivity of the presented method thus permits the use of small sample volumes and the determination of NBD-lipid analogues secreted into mouse bile directly, without prior extraction or concentration steps.

Isolation of a bioactive Ca(2+)-mobilizing complex lipid from bovine vitreous body

Vitreous body extracts show a potent Ca(2+)-mobilizing activity on fibroblast cells. This Ca2+ signal is complex, and due to the presence of two different bioactive substances. The first one was identified as acid FGF. The second one was shown to be a low molecular weight substance identified as a complex lipid by a combination of chromatographic and biochemical data. This finding raises the possibility that non-classical substances with growth factor-like activity might play a role in the regulation of proliferative processes in the eye.

Quantitative analysis of pulmonary surfactant phospholipids by high-performance liquid chromatography and light-scattering detection

An improved high-performance liquid chromatographic method for the separation and quantitation of nine phospholipid classes is described. It is based on normal-phase chromatography with silica gel as stationary phase and a binary gradient with mixtures of chloroform, methanol and water as mobile phase. The response of the evaporative light-scattering detector was non-linear. Peak areas were proportional to the power 1.7 of the masses. Phospholipids in lung lavage samples were enriched by liquid extraction prior to HPLC analysis. The described method is a rapid and accurate procedure for the quantitative analysis of phospholipid classes in biological samples.

Proton nuclear magnetic resonance lipid profiling of intact platelet membranes

A combination of high-resolution one-dimensional and two-dimensional proton nuclear magnetic resonance spectroscopic methods and high pressure liquid chromatography have been used to analyse qualitatively and quantitatively the phospholipids, cholesterol and fatty acid composition of normal human blood platelets. The major phospholipids present were identified and quantified. Information on the nature and composition of the different classes of structural phospholipids and unsaturated fatty acids was obtained and was similar to that reported by others using different analytical procedures. This work showed that the proton nuclear magnetic resonance spectroscopy approach to lipid analysis could provide rapid, comprehensive and detailed information on the roles of lipids in pathological conditions in which platelets have been implicated.

Characterization of phospholipid methylation in rat brain myelin

Highly purified rat brain myelin was solubilized in Triton X-100 and myelin phospholipid N-methyltransferase was characterized. The enzyme activities were separated by isoelectric focusing and ion-exchange chromatography. The phospholipid methyl-transferase has shown at least four peaks of activity with pIapp. values of 4.5, 5.2, 6.2 and 8.4. After affinity purification each of these activities revealed a close set of bands of approx. 65 kDa on SDS/PAGE. These data together with those from preparative SDS/PAGE separations suggested that rat brain myelin contains three acidic and at least one basic phospholipid-methylating isoenzymes and that the major isoenzyme in each case is approx. 65 kDa in size. While the predominant product of the reaction catalysed by all detected isoforms was monomethylated phosphatidylethanolamine, the least acidic isoform (pIapp. 6.2) also formed about 20% phosphatidylcholine, suggesting that these isoenzymes may play different roles in vivo.

High-performance liquid chromatography separation and light-scattering detection of phospholipids from cooked beef

A sensitive high-performance liquid chromatography (HPLC) method for the separation and quantitative analysis of major phospholipids (PLs) in biological systems is described. PLs were purified by solid-phase extraction with an amino (NH2) phase. Separation of PLs was carried out on an HPLC silica gel column, with a mobile phase consisting of chloroform, methanol and ammonium hydroxide, and detection was performed with a light-scattering evaporative detector. HPLC analysis of PLs extracted from ground beef cooked under different conditions and capillary gas chromatography of the fatty acid methyl esters showed that cooking treatments did not have a significant effect on the PL composition and fatty acid contents of the single PLs in ground beef.

Proton NMR lipid profile of Leishmania donovani promastigotes

The proton nuclear magnetic resonance (NMR) lipid profile of Leishmania donovani was obtained in the one-dimensional and two-dimensional modes. Partial assignments of lipid classes and individual lipids were obtained purely from the proton NMR spectrum of the mixture. A more complete assignment and quantitative analysis was achieved by prior separation of the lipids by high pressure liquid chromatography (HPLC) followed by proton NMR analysis of the fractions. This work showed that proton NMR spectroscopy could facilitate lipid analysis and classification of various parasitic protozoa and serve as a basis for rapid studies of comparative lipid metabolism in parasites.

The response of a human bronchial epithelial cell line to histamine: intracellular calcium changes and extracellular release of inflammatory mediators

Epithelial cells are likely to modulate inflammation and tissue repair in the airways, but the factors responsible for these processes remain unclear. Because human airway epithelia are infrequently available for in vitro studies, transformed epithelial cell lines are of interest as models. We therefore investigated the response of an SV-40/adenovirus-transformed human bronchial epithelial cell line (BEAS-2B) to histamine, a mediator with relevance for airway diseases. The intracellular calcium response to histamine (10(-4) M) was measured, using Fura-2 and microspectrofluorimetry. Histamine induced a transient increase in intracellular calcium that originated from intracellular sources; this effect was inhibited by the H1 receptor antagonist diphenhydramine, suggesting that BEAS cells retain functioning histamine receptors. BEAS cells were grown to confluence on microporous, collagen-coated filters, allowing measurement of vectorial release of soluble mediators. Monolayers exposed to histamine for 30 min released interleukin-6 and fibronectin in the apical direction, in a dose-dependent manner. Little eicosanoid production was induced by histamine, either in the apical or the basolateral direction, although BEAS cells constitutively produced small amounts of prostaglandin E2 and 15-HETE. However, these cells formed large amounts of eicosanoids in response to ozone exposure as a positive control. Comparison of our data with published reports for human airway epithelia in primary culture suggests that the BEAS cell line is, in a number of respects, a relevant model for the study of airway epithelial responses to a variety of stimuli.