Highly sensitive measurement of lipid molecular species from biological samples by fluorimetric detection coupled to high-performance liquid chromatography

Interest of fluorescence derivatization and fluorescence probe assisted post-column detection of phospholipids: a short review

Phospholipids are essential constituents of all living cell membranes. There are many analytical methods available for the quantitative and qualitative determination of phospholipids, but since these molecules lack chromophores, common absorbance based methods are of limited use. Beside mass spectrometry, some less specific approaches that are routinely used are evaporative light scattering detection or fluorescence, which exhibit sufficient sensitivity. Here, we focus on fluorescence, which remains an interesting way to quantify phospholipids. Two ways of detecting phospholipids by fluorescence are possible coupled with separation techniques such as thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE): firstly, pre-column derivatization procedures and secondly, probe assisted post-column detection with suitable fluorescence reagents. In both cases, the common purpose is to increase the detection sensitivity. It is shown that, whereas pre-column derivatization is characterized by selectivity due to the chemical functionality of the analyte involved in the derivatization process, in supramolecular post-column derivatization, the selectivity only proceeds from the capacity of the lipid to involve supramolecular assemblies with a fluorescence probe. The aim of this review is to summarize available experiments concerning fluorescence detection of phospholipids. The interest and limitation of such detection approaches are discussed.

A review of chromatographic methods for the assessment of phospholipids in biological samples

Phospholipids are important constituents of all living cell membranes. Lipidomics is a rapidly growing field that provides insight as to how specific phospholipids play roles in normal physiological and disease states. There are many analytical methods available for the qualitative and quantitative determination of phospholipids. This review provides a summary of the methods that were historically used such as thin layer chromatography, gas chromatography and high-performance liquid chromatography. In addition, an introduction to applications of interfacing these traditional chromatographic techniques with mass spectrometry is provided.

Mast cell- and dendritic cell-derived exosomes display a specific lipid composition and an unusual membrane organization

Exosomes are small vesicles secreted from multivesicular bodies, which are able to stimulate the immune system leading to tumour cell eradication. We have analysed lipids of exosomes secreted either upon stimulation from rat mast cells (RBL-2H3 cells), or constitutively from human dendritic cells. As compared with parent cells, exosomes displayed an enrichment in sphingomyelin, but not in cholesterol. Phosphatidylcholine content was decreased, but an enrichment was noted in disaturated molecular species as in phosphatidylethanolamines. Lyso(bis)phosphatidic acid was not enriched in exosomes as compared with cells. Fluorescence anisotropy demonstrated an increase in exosome-membrane rigidity from pH 5 to 7, suggesting their membrane reorganization between the acidic multivesicular body compartment and the neutral outer cell medium. NMR analysis established a bilayer organization of exosome membrane, and ESR studies using 16-doxyl stearic acid demonstrated a higher flip-flop of lipids between the two leaflets as compared with plasma membrane. In addition, the exosome membrane exhibited no asymmetrical distribution of phosphatidylethanolamines. Therefore exosome membrane displays a similar content of the major phospholipids and cholesterol, and is organized as a lipid bilayer with a random distribution of phosphatidylethanolamines. In addition, we observed tight lipid packing at neutral pH and a rapid flip-flop between the two leaflets of exosome membranes. These parameters could be used as a hallmark of exosomes.

Derivatization of phospholipids

Phospholipids are major components of biological membranes. Without chemical derivatization, it is difficult to identify and quantitate phospholipids in biological samples. Chemical derivatization can improve both the selectivity and sensitivity of the analytes. This paper gives a full review, through March, 2002, of derivatization methods used for phospholipids in HPLC, CE and GC as well as the spray reagent used for TLC in the early days.

Quantitative determination of fat emulsion using 1,6-diphenyl-1,3,5-hexatriene as fluorescence probe: application to the compounding of all-in-one parenteral nutrition admixtures

The potential contamination of binary bags by traces of fat emulsion stemmed from ternary bags prepared just before, led us to determine traces of lipids into the line set of the automated compounder MM23. Diphenylhexatriene (DPH) was chosen as fluorescence probe due to its strong fluorescence enhancement in a lipid environment. Optimization of experimental conditions (i.e. DPH amounts, pH of fat emulsion samples, ultrasounds use, light, temperature and contact duration) for fluorescence measurement and validation of analytical method were performed. This method was linear over 0.5-8.0 mg l(-1) (r=0.999) of fat emulsion. The intra-day and inter-day precisions were inferior to 2% for the 2.0 and 8.0 mg l(-1) standards. Under optimized conditions, the detection limit and quantitation limit were 0.10 and 0.29 mg l(-1) of lipids respectively. Compared to the colorimetric method using sodium dichromate, it is at least 100 times more sensitive. The proposed method permitted to rapidly measure fat emulsion traces in automated compounder line set for parenteral nutrition solutions and thus, to assess the risk of contamination of binary bags by lipids. At last, this method was shown to be conveniently applied to the analysis of fat emulsion in the final total parenteral nutrition bag.