Phospholipases and Reactive Oxygen Species Derived Lipid Biomarkers in Healthy and Diseased Humans and Animals – A Focus on Lysophosphatidylcholine

Phospholipids (PL) are converted into lipid biomarkers by the action of phospholipases and reactive oxygen species (ROS), which are activated or released under certain physiological and pathophysiological conditions. Therefore, the in vivo concentration of such lipid biomarkers [e.g., lysophospholipids (LPLs)] is altered in humans and animals under different conditions such as inflammation, stress, medication, and nutrition. LPLs are particularly interesting because they are known to possess pro- and anti-inflammatory properties and may be generated by two different pathways: either by the influence of phospholipase A2 or by different reactive oxygen species that are generated in significant amounts under inflammatory conditions. Both lead to the cleavage of unsaturated acyl residues. This review provides a short summary of the mechanisms by which lipid biomarkers are generated under in vitro and in vivo conditions. The focus will be on lysophosphatidylcholine (LPC) because usually, this is the LPL species which occurs in the highest concentration and is, thus, easily detectable by chromatographic and spectroscopic methods. Finally, the effects of lipid biomarkers as signaling molecules and their roles in different human and animal pathologies such as infertility, cancer, atherosclerosis, and aging will be shortly discussed.

Circulating Free Fatty Acid and Phospholipid Signature Predicts Early Rapid Kidney Function Decline in Patients With Type 1 Diabetes

<b>Objectives:</b> Patients with type 1 diabetes (T1D) exhibit modest lipid abnormalities as measured by traditional metrics. This study aimed to identify lipidomic predictors of rapid decline of kidney function in T1D. <p><b>Research Design and Methods: </b>In a Case-Control study, 817 T1D patients from 3 large cohorts were randomly split into training and validation subsets. Case was defined as >3 mL/min/1.73 m²/year decline in estimated glomerular filtration rate (eGFR) while Control was defined as <1 mL/min/1.73 m²/year decline over a minimum 4-year follow up. Lipids were quantified in baseline serum samples using a targeted mass spectrometry lipidomic platform. </p> <p><b>Results: </b>At individual lipids, free fatty-acid (FFA)20:2 was directly, and phosphatidylcholine (PC)16:0/22:6 was inversely and independently associated with rapid eGFR decline. When examined by lipid class, rapid eGFR decline was characterized by higher abundance of unsaturated FFAs, phosphatidylethanolamine (PE)-Ps and PCs with an unsaturated acyl chain at the sn1 carbon, and by lower abundance of saturated FFAs, longer triacylglycerols, and PCs, PEs, PE-Ps, and PE-Os with an unsaturated acyl chain at the sn1 carbon at eGFR ≥90 mL/min. A multi-lipid panel consisting of unsaturated FFAs and saturated PE-Ps predicted rapid eGFR decline better than individual lipids (C-statistic, 0.71) and improved C-statistic of clinical model from 0.816 to 0.841 (p=0.039). Observations were confirmed in the validation subset. </p> <p><b>Conclusion: </b>Distinct from previously reported predictors of GFR decline in type 2 diabetes, these findings suggest differential incorporation of FFAs at sn1 carbon of the phospholipids’ glycerol backbone as independent predictor of rapid GFR decline in T1D. </p>

Circulating Free Fatty Acid and Phospholipid Signature Predicts Early Rapid Kidney Function Decline in Patients With Type 1 Diabetes

<b>Objectives:</b> Patients with type 1 diabetes (T1D) exhibit modest lipid abnormalities as measured by traditional metrics. This study aimed to identify lipidomic predictors of rapid decline of kidney function in T1D. <p><b>Research Design and Methods: </b>In a Case-Control study, 817 T1D patients from 3 large cohorts were randomly split into training and validation subsets. Case was defined as >3 mL/min/1.73 m²/year decline in estimated glomerular filtration rate (eGFR) while Control was defined as <1 mL/min/1.73 m²/year decline over a minimum 4-year follow up. Lipids were quantified in baseline serum samples using a targeted mass spectrometry lipidomic platform. </p> <p><b>Results: </b>At individual lipids, free fatty-acid (FFA)20:2 was directly, and phosphatidylcholine (PC)16:0/22:6 was inversely and independently associated with rapid eGFR decline. When examined by lipid class, rapid eGFR decline was characterized by higher abundance of unsaturated FFAs, phosphatidylethanolamine (PE)-Ps and PCs with an unsaturated acyl chain at the sn1 carbon, and by lower abundance of saturated FFAs, longer triacylglycerols, and PCs, PEs, PE-Ps, and PE-Os with an unsaturated acyl chain at the sn1 carbon at eGFR ≥90 mL/min. A multi-lipid panel consisting of unsaturated FFAs and saturated PE-Ps predicted rapid eGFR decline better than individual lipids (C-statistic, 0.71) and improved C-statistic of clinical model from 0.816 to 0.841 (p=0.039). Observations were confirmed in the validation subset. </p> <p><b>Conclusion: </b>Distinct from previously reported predictors of GFR decline in type 2 diabetes, these findings suggest differential incorporation of FFAs at sn1 carbon of the phospholipids’ glycerol backbone as independent predictor of rapid GFR decline in T1D. </p>

Intrinsic lipid curvatures of mammalian plasma membrane outer leaflet lipids and ceramides

We developed a global X-ray data analysis method to determine the intrinsic curvatures of lipids hosted in inverted hexagonal phases. In particular, we combined compositional modelling with molecular shape-based arguments to account for non-linear mixing effects of guest-in-host lipids on intrinsic curvature. The technique was verified by all-atom molecular dynamics simulations and applied to sphingomyelin and a series of phosphatidylcholines and ceramides with differing composition of the hydrocarbon chains. We report positive lipid curvatures for sphingomyelin and all phosphatidylcholines with disaturated and monounsaturated hydrocarbons. Substitution of the second saturated hydrocarbon with an unsaturated acyl chain in turn shifted the intrinsic lipid curvatures to negative values. All ceramides, with chain lengths varying between C2:0 and C24:0, displayed significant negative lipid curvature values. Moreover, we report non-additive mixing for C2:0 ceramide and sphingomyelin. Our findings manifest the high and manifold potential of lipids to modulate physiological membrane function.

Syntheses of Spiro(2-oxopyrrolidinyl)-5,4′-pyrazolones via Organocatalyzed Michael/Ammonolysis Cascade Reaction of 4-Aminopyrazolones and α,β-Unsaturated Acyl Phosphates

The efficient organocatalyzed Michael/ammonolysis cascade reaction of N-protected 4-aminopyrazolones and α,β-unsaturated acyl phosphates has been developed. This tactic gives rise to architecturally multifarious spiro(2-oxopyrrolidinyl)-5,4′-pyrazolones in good productiveness (up to 88% yield) and with moderate to good diastereoselectivities (up to 20:1 dr). These novel hybrid heterocycles would be promising candidates for drug-discovery programs and chemical biology.

NHC-catalyzed enantioselective C2-functionalization of 3-hydroxychromenones via α,β-unsaturated acyl azoliums

The first direct and highly enantioselective C2-functionalization of a 3-hydroxychromenone skeleton via NHC-catalyzed generation of chiral α,β-unsaturated acyl azoliums and a following Coates-Claisen rearrangement.

Synergy between 15-lipoxygenase and secreted PLA2promotes inflammation by formation of TLR4 agonists from extracellular vesicles

Damage-associated endogenous molecules induce innate immune response, thus making sterile inflammation medically relevant. Stress-derived extracellular vesicles (stressEVs) released during oxidative stress conditions were previously found to activate Toll-like receptor 4 (TLR4), resulting in expression of a different pattern of immune response proteins in comparison to lipopolysaccharide (LPS), underlying the differences between pathogen-induced and sterile inflammation. Here we report that synergistic activities of 15-lipoxygenase (15-LO) and secreted phospholipase A2(sPLA2) are needed for the formation of TLR4 agonists, which were identified as lysophospholipids (lysoPLs) with oxidized unsaturated acyl chain. Hydroxy, hydroperoxy, and keto products of 2-arachidonoyl-lysoPI oxidation by 15-LO were identified by mass spectrometry (MS), and they activated the same gene pattern as stressEVs. Extracellular PLA2activity was detected in the synovial fluid from rheumatoid arthritis and gout patients. Furthermore, injection of sPLA2promoted K/BxN serum-induced arthritis in mice, whereby ankle swelling was partially TLR4 dependent. Results confirm the role of oxidized lysoPL of stressEVs in sterile inflammation that promotes chronic diseases. Both 15-LO and sPLA2enzymes are induced during inflammation, which opens the opportunity for therapy without compromising innate immunity against pathogens.

α,β-Unsaturated acyl ammonium species as reactive intermediates in organocatalysis: an update

α,β-Unsaturated acyl ammonium species are versatile intermediates that have been applied in a variety of transformation including Michael additions, domino reactions and cycloadditions. Many of these transformations are promoted by...