Analysis of phospholipids in bio-oils and fats by hydrophilic interaction liquid chromatography–tandem mass spectrometry

Direct infusion and ultra-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry analysis of phospholipid regioisomers

RATIONALE

Phospholipids are important components of cell membranes that are linked to several beneficial health effects such as increasing plasma HDL cholesterol levels, improving cognitive abilities and inhibiting growth of colon cancer. The role of phospholipid (PL) regioisomers in all these health effects is, however, largely not studied due to lack of analytical methods.

METHODS

Electrospray ionization mass spectrometry in negative mode produces structurally informative fragment ions resulting from differential dissociation of fatty acids (FAs) from the sn-1 and sn-2 positions, primarily high-abundance [RCOO]^- ions. The fragment ion ratios obtained with different ratios of regiopure phospholipid reference compounds were used to construct calibration curves, which allow determination of regioisomeric ratios of an unknown sample. The method was developed using both direct infusion mass spectrometry (MS) and ultra-high-performance liquid chromatography and hydrophilic interaction liquid chromatography mass spectrometry (UHPLC-HILIC-MS).

RESULTS

The produced calibration curves have high coefficients of determination (R²  >0.98) and the fragment ion ratios in replicate analyses were very consistent. A test mixture containing 60/40% ratios of all available regioisomer pairs was analyzed to test and validate the functionality of the calibration curves. The results were accurate and reproducible. However, regioisomeric quantification of certain chromatographically overlapping compounds is restricted by the relatively wide window in precursor ion selection of the MS instrument used.

CONCLUSIONS

This method establishes a framework for analysis of phospholipid regioisomers. Specific regioisomers can be quantified using the existing data, and method development will continue with improving chromatographic separation and exploring the fragmentation patterns and efficiencies of different PL classes and FA combinations, ultimately to refine this method for routine analysis of natural fats and oils.

Content and Composition of Phospholipids, Fatty Acids and Sterols in Commercial Natural Phospholipid Excipients

Background:

Phospholipids are widely used in food and pharmaceutical industry as functional excipients. In spite of the many analytical methods reported, there are very limited reports concerning systematic research and comparison of phospholipid excipients.

Objective:

To present a comprehensive evaluation of commercial natural phospholipid excipients (CNPEs).

Methods:

Seventeen batches of CNPEs from five manufacturing enterprises, isolated either from soybean or egg yolk, were investigated. The content and composition of phospholipids, fatty acids and sterols as a whole were considered as the evaluative index of CNPEs. Eight kinds of phospholipids were determined by Supercritical Fluid Chromatography (SFC), twenty-one kinds of fatty acids were determined by Gas Chromatography (GC) after boron trifluoride-methanol derivatization, and nine kinds of sterols were determined by High Performance Liquid Chromatography (HPLC) after separation and derivatization of the unsaponifiable matter. Cluster analysis was employed for the classification and identification of the CNPEs.

Results:

The results showed that each kind of CNPEs had its characteristic content and composition of phospholipids, fatty acids and sterols. Seventeen batches of samples were divided into eight groups in cluster analysis. CNPEs of the same type from different source (soybean or egg yolk) or enterprises presented different content and composition of phospholipids, fatty acids and sterols.

Conclusion:

Each type of CNPEs had its characteristic content and composition of phospholipid, fatty acid and sterol. The compositions of phospholipid, fatty acid and sterol as a whole can be applied as an indicator of the quality and characteristics for CNPEs.

Arsenosugar Phospholipids (As-PL) in Edible Marine Algae: An Interplay between Liquid Chromatography with Electrospray Ionization Multistage Mass Spectrometry and Phospholipases A1 and A2 for Regiochemical Assignment

The chemical identity of arsenosugar phospholipids (As-PL) as mono- (i.e., lyso, L-As-PL) and diacyl-arsenosugar PL in four edible and common marine alga samples, such as nori (Porphyra spp.), wakame (Undaria pinnatifida), dulse (Palmaria palmata), and kombu (Saccharina japonica), was successfully investigated. Adopting negative polarity electrospray ionization (ESI), not common for As-PL, conjugated with hydrophilic interaction liquid chromatography (HILIC) and mass spectrometry (MS), performed either at low resolution using a linear ion trap (LIT) with sequential MSn (n = 2, 3) or at high resolution using a high-resolution/high-accuracy Fourier-transform MS (FTMS), based on an orbital trap instrument, more than 20 As-PL and 2 L-As-PL species were identified. The absence of As-PL standard compounds encouraged us to generate an in-house-built database of As-PL/L-As-PL for a rapid and simple classification. Despite their compositional diversity, tandem MS of deprotonated As-PL and L-As-PL ([M - H]-) demonstrated the occurrence of a highly diagnostic product ion at m/z 389.0 ([AsC10H19O9P]-). The fatty acid composition and distribution of As-PL were easily assigned on the basis of the ratio intensity between sn-1 and sn-2 product ions. Indeed, the preferential formation of [R1C3H5O4P]- ions over [R2C3H5O4P]- ions, both containing the glycerol backbone, enabled the regiochemical assignment of As-PL. These outcomes were confirmed by MSn (n = 2, 3) analyses and using sn-1- and sn-2-regioselective hydrolase enzymes (i.e., phospholipases A1 and A2). The predominant As-PL's in samples of nori (red alga), wakame, and kombu (both brown algae) were identified as containing palmitic acyl chains (i.e., As-PL958 (As-PL 16:0/16:0) with ca. 66 ± 3, 82 ± 4, and 58 ± 3% as relative abundances, respectively), while the main species in dulse (red alga) samples was As-PL982 (As-PL 18:1/16:1) at ca. 38 ± 3%.

Evaluation of LC-MS and LC×LC-MS in analysis of zebrafish embryo samples for comprehensive lipid profiling

In this study, both conventional one-dimensional liquid chromatography (1DLC) and comprehensive two-dimensional liquid chromatography (2DLC) coupled to a high-resolution time-of-flight mass spectrometer (HR-TOF MS) were used for full-scale lipid characterization of lipid extracts from zebrafish embryos. We investigated the influence on annotated lipids and different separation mechanisms (HILIC, C18, and PFP), and their different orders arranged in the first and the second dimensions. As a result, the number of lipid species annotated by conventional one-dimensional LC-MS was between 212 and 448. In contrast, the number of individual lipids species annotated by C18×HILIC, HILIC×C18, and HILIC×PFP were 1784, 1059, and 1123, respectively. Therefore, it was evident that the performance of comprehensive 2DLC, especially the C18×HILIC method, considerably exceeded 1DLC. Interestingly, a comparison of the HILIC×C18 and C18×HILIC approaches showed, under the optimized conditions, similar orthogonality, but the effective separation power of the C18×HILIC was much higher. A comparison of the HILIC×C18 and the HILIC×PFP methods demonstrated that the HILIC×PFP separation had superior orthogonality with a small increase on its effective peak capacity, indicating that the HILIC×PFP combination maybe a promising platform for untargeted lipidomics in complex samples. Finally, from the comprehensive lipid profiling respective, the C18×HILIC was selected for further studies.

Separation and identification of phospholipids by hydrophilic interaction liquid chromatography coupled to tandem high resolution mass spectrometry with focus on isomeric phosphatidylglycerol and bis(monoacylglycero)phosphate

Changes in lipid composition of cells or tissue are often linked to various diseases. Studies indicate alterations of bis(monoacylglycero)phosphate (BMP) species in diseases such as cancer. Therefore, an extended phospholipid profiling method based on hydrophilic interaction liquid chromatography (HILIC) coupled to high-resolution mass spectrometry (MS) and data-dependent MS/MS acquisition was developed to separate and unambiguously identify BMP species. Lipid species identification was based on retention time, accurate mass and specific MS/MS fragments. The developed method was applied in a proof of concept study to lipid extracts of a cell culture model of conditional oncogene overexpression in MCF-7/NeuT breast cancer cells. Comparison of control and oncogene-induced MCF-7/NeuT breast cancer cells showed changes in BMP species distribution. Thereby, a shift from long-chain to shorter-chain fatty acid composition in BMP species was detected.