Unveiling the compositional variety of cardiolipins in Rhodobacter sphaeroides by liquid chromatography with electrospray ionization and multistage collision-induced dissociation mass spectrometry

Qualitative and quantitative lipidomic profiling of cardiolipin, oxidized cardiolipin, and monolysocardiolipin from human skeletal muscle by UPLC-Orbitrap-MSn

BACKGROUND

Cardiolipins (CL) are a mitochondria-specific family of phospholipids that play central roles in mitochondrial function. Imbalance in CL metabolism, especially excessive CL oxidation, leads to mitochondrial dysfunction, apoptosis, and inflammation, contributing to age-related diseases. As of yet no comprehensive methods have been developed to assess CL, oxidized CL (oxCL), and monolyso-CL (MLCL) species.

RESULTS

To fill this critical research gap, we combined untargeted and targeted lipidomic approaches to analyze CL species in human skeletal muscle samples. The method enabled in-depth structural characterization using exact mass measurement followed by multistage fragmentation (MSn) to achieve unequivocal structural elucidation at the molecular species level and sn-position level for some species. This novel methodology identified intact mono- and di-oxygenated L4CL species and allowed the differentiation of isomeric 9/13-HODE-L3CL and 9(10)/12(13)-EpOME-L3CL with unprocessed total lipid extracts. Overall, 220 molecular species (125 CL, 30 oxCL, and 65 MLCL) were detected. Our method includes a quantitation strategy that leveraged on establishing three-leveled matrix-matched calibration curves normalized by using internal standard M4CL and its isotopologues M+1 (13C-M4CL) and M+3 (13C3-M4CL) respectively. The analytical performance was also evaluated and found to be highly sensitive with LLOQs at fmol levels and reproducible with precision RSD <20 % for the majority.

SIGNIFICANCE AND NOVELTY

This is the first reported method to simultaneously provide broad coverage of CL, oxCL, and MLCL species from a single injection of total lipid extract in a complex biological sample. This method is also the first to demonstrate the presence of sn-positional isomers of CL in human skeletal muscle. It has been successfully applied to a pilot study of skeletal muscle biopsies and provided meaningful results. We anticipate the methodology will facilitate investigations of the cardiolipin lipidome leading to a better understanding of the complex and highly interactive biological processes that regulate mitochondria function and expand minor cardiolipin targets including oxCL and MLCL for biomarker discovery.

Analysis of glycosylated cardiolipins from thermophilic bacteria using GC-MS and LC-ESI-MS/MS methods

Unusual glucose-substituted cardiolipins (Glcx-CLs) in three genera of thermophilic bacteria, having more than one glycosidically linked glucose to the hydroxyl of the central glycerol of Glcx-CLs were identified for the first time in thermophilic bacteria of the genera Geobacillus, Meiothermus, and Thermus. The number of glucoses reached up to five units. The structure of glycosidically linked oligosaccharides was determined based on shotgun analysis MS (electrospray high-resolution tandem mass spectrometry), partially methylated alditol acetates were identified by GC-MS, both electron ionization (EI) and positive chemical ionization (PCI), hydrophilic interaction liquid chromatography (HILIC) separation and identification of CLs glycosides by high resolution MS-ESI, and digestion by specific glycosidases.

Detailed structural characterization of cardiolipins from various biological sources using a complex analytical strategy comprising fractionation, hydrolysis and chiral chromatography

Cardiolipins (1,3-bis(sn-3'-phosphatidyl)-sn-glycerol) (CLs) are widespread in many organisms, from bacteria to higher green plants and mammals. CLs were observed in Gram-positive bacterium of the genus Kocuria, brewer's yeast Saccharomyces, the green alga Chlamydomonas, spinach and beef heart. A mixture of molecular species of CLs was obtained from total lipids by hydrophilic interaction liquid chromatography (HILIC), and these were further separated and identified by reversed phase LC/MS with negative tandem electrospray ionization. The majority of CLs molecular species from each organism were cleaved using phospholipase C from Bacillus cereus. This phospholipase cleaves CLs into 1,2-diglycerols and phosphatidylglycerol 3-phosphates, which were then separated. After CLs cleavage, diacylglycerols such as sn-1,2-diacyl-3-acetyl-glycerols (i.e., triacylglycerols) were separated and identified by chiral chromatography/MS-positive tandem ESI. Significant differences in the composition of the molecular species between the 3-(3-sn-phosphatidyl) and 1-(3-sn-phosphatidyl) moieties of CLs were found in all organisms tested. Molecular species of CLs that contained four different fatty acids were identified in all five samples, and CLs containing very long chain fatty acids were identified in yeast. In addition, CLs containing both enantiomers (at the sn-2 carbon) were present in the bacterium tested. These findings were further supported by data already published in GenBank where, in the same family - Micrococcaceae - both enzymes responsible for chirality in the sn-2 position, glycerol-3-phosphate and glycerol-1-phosphate dehydrogenases, were present.