Oxidized phospholipids on alkyl-amide scaffold demonstrate anti-endotoxin and endothelial barrier-protective properties

Olga V Oskolkova,Alma Hodzic,Pratap Karki,Bernd Gesslbauer,Yunbo Ke,Dina C Hofer,Juliane G Bogner-Strauss,Jean-Marie Galano,Camille Oger,Anna Birukova,Thierry Durand,Konstantin Birukov,Valery Bochkov

doi:10.1016/j.freeradbiomed.2021.07.041

Abstract

Oxidized phospholipids (OxPLs) containing enzymatically or non-enzymatically oxidized fatty acids (oxylipins) are increasingly recognized as lipid mediators involved in pathogenesis of diseases. Further understanding of structure-activity relationship and molecular mechanisms activated by OxPLs is hampered by the complexity of synthesis of individual molecular species. Although dozens of individual free oxylipins are commercially available, their attachment to the phospholipid scaffold requires relatively harsh conditions during activation of carboxy-group, which may lead to decomposition of unstable oxylipins. Furthermore, additional protection-deprotection steps are required for oxylipins containing hydroxy-groups. In this work we describe synthesis of OxPLs containing oxylipins bound at the sn-2-position via an amide-bond that is characteristic of sphingophospholipids. Activation of oxylipins and attachment to the phospholipid scaffold are performed under mild conditions and characterized by high yield. Hydroxy-groups of oxylipins do not interfere with reactions and therefore no protection/deprotection steps are needed. In order to prevent oxylipin migration, a fatty acid residue at the sn-1 was bound through an alkyl bond, which is a common bond present in a large proportion of naturally occurring phospholipids. An additional advantage of combining alkyl and amide bonds in a single phospholipid molecule is that both types of bonds are phospholipase A1/A2-resistant, which may be expected to improve biological stability of OxPLs and thus simplify analysis of their effects. As proof of principle, several alkyl-amide oxidized phosphatidylcholines (OxPCs) containing either linear or prostane ring oxylipins have been synthesized. Importantly, we show here that alkyl-amide-OxPCs demonstrated biological activities similar to those of di-acyl-OxPCs. Alkyl-amide-OxPCs inhibited pro-inflammatory action of LPS and increased endothelial cellular barrier in vitro and in mouse models. The effects of alkyl-amide and di-acyl-OxPCs developed in a similar range of concentrations. We hypothesize that alkyl-amide-OxPLs may become a useful tool for deeper analysis of the structure-activity relationship of OxPLs.

Highlights

Oxidation of lipids is a common mechanism generating biologically active molecules
Synthesis of alkyl-amide-oxidized phosphocholine (OxPC) was performed in 2 stages
To ensure that the anti-LPS activity is not limited to PLs containing a cyclic prostane ring, linear fatty acids with a ω-terminal hydroxide have been attached to the alkyl-amide-OxPC scaffold

Summary

Introduction

Oxidation of lipids is a common mechanism generating biologically active molecules. Some lipid oxidation products are genuine mediators that are recognized by cellular receptors (e.g., prostaglandins and iso prostanes), while other act less by non-selective modification of biomolecules leading to activation of signaling stress pathways. We describe a relatively simple and fast method for synthesis of alkyl-amide OxPLs. A broad variety of oxylipins, including those containing hydroxyl groups, can be attached to the PL In order to check if alkyl-amide-OxPCs demonstrate biological ac tivities described for their di-acyl homologs, we first tested if alkylamide-OxPCs can inhibit pro-inflammatory effects of LPS [17,18,19].

Results

Conclusion