Year: 2013
Type: dissertation
Abstract: Initially, prostaglandins (PGs) were considered to only exist as free acid mediators. Although, formation of PG glycerol esters and PG ethanolamides by cellular cyclooxygenase (COX)-2 has been reported, generation of complex oxidised lipids via COX-1 has not been considered. In this study, formation of sixteen unique PG-containing phospholipids generated by agonist-activated human platelets is demonstrated using lipidomic approaches. Precursor scanning-tandem mass spectrometry identified a group of specific lipids comprising PGE2, PGD2 and two previously undescribed PG-like molecules (named PGb and PGc), attached to four phosphatidylethanolamine (PE) phospholipids (16:0p/, 18:1p/, 18:0p/ and 18:0a/). PGb and PGc were also detected as free eicosanoids and their structures remain to be characterised. These novel lipids formed within 2-5 minutes of platelet activation by thrombin, collagen or ionophore and required activation of several intracellular signalling intermediates, including cytosolic phospholipase A2 (cPLA2), p38 mitogen-activated protein kinase (MAPK), src tyrosine kinases, phospholipase C (PLC) and cytosolic calcium. Unlike free PGs that are secreted, PG-PEs remain cell associated, suggesting an autocrine mode of action. Aspirin supplementation in vivo (75 mg/day) or in vitro (1 mM) blocked their generation, indicating that COX-1 is required. Pharmacological studies using inhibitors of fatty acyl re-esterification significantly reduced formation of PG-PEs. Furthermore, purified COX-1 was unable to directly oxidise PE in vitro. Collectively, these indicate that PG-PEs are initially formed as free PGs via COX-1, and then rapidly esterified into PEs. In summary, this is the first demonstration of acute generation of PG-PEs in agonist-activated human platelets from endogenous substrate via COX-1. These unique lipids may represent additional bioactive molecules from this key platelet enzyme.
Author: Maceler Aldrovandi
Language: English
Subfield: Pharmacology (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: green
Funder: Vanderbilt University
OpenAlex ID: W1844903078