Alassaf, Fawaz A.
(2018)
The effect of quorum sensing molecules on vascular function.
PhD thesis, University of Nottingham.
Abstract
Bacteria communicate with each other by releasing chemicals called quorum sensing molecules. A common gram-negative bacteria, Pseudomonas aeruginosa, releases a number of such molecules including, N-3-(oxododecanoyl)-L-homoserine lactone (3OC12-HSL) and Pseudomonas quinolone signal (2-heptyl-3,4-dihydroxyquinoline, PQS). The quorum sensing molecules have immunomodulatory effects on mammalian cells in addition to their role in bacteria. There has been very little study of the vascular effects of quorum sensing molecules on the host. The aim of this thesis was; therefore, to investigate the effect of Pseudomonas aeruginosa quorum sensing molecules, 3OC12-HSL and PQS, on vascular function and endothelial cell permeability and to study the potential mechanisms involved.
Both 3OC12-HSL and PQS caused slowly developing vasorelaxation in arterial and venous preparations isolated from pigs. PQS was slightly more potent (pIC50) as a vasorelaxant than 3OC12-HSL. The endothelium was not a prerequisite for 3OC12-HSL-induced vasorelaxation since removal of endothelium and the nitric oxide synthase inhibitor (L-NAME) did not attenuate responses. Indeed, the opposite is true since 3OC12-HSL vasorelaxation responses were larger in the absence of the endothelium and nitric oxide. The mechanism of 3OC12-HSL does not involve either prostanoids, cyclic GMP, mitochondrial targets, calcium channels, chloride channels, PPAR-γ receptors, pannexin receptors, gap junctions or cystic fibrosis transmembrane conductance regulator. However, ouabain and depolarisation induced by potassium chloride decreased 3OC12-HSL responses suggest an impact on membrane potential.
Overnight exposure of the porcine coronary artery to wild type Pseudomonas aeruginosa (PAO-L), produced a selective reduction in the magnitude of contractions to potassium chloride. However, neither 3OC12-HSL nor PQS produced an inflammatory response with prolonged exposure since they did not modify tumor necrosis factor alpha or vascular tone under these conditions.
Both 3OC12-HSL and PQS increased endothelial cell permeability. Both caused a fall in endothelial resistance and an increase in FITC-dextran transport across human brain microvascular endothelial cells (HBMECs). The immunoblotting data showed that the levels of adherens junction and tight junction protein expression were decreased in HBMECs exposed to 3OC12-HSL, but not PQS. Rather PQS, but not 3OC12-HSL, caused a concentration-dependent phosphorylation of p38 MAPK, suggesting these molecules may modify vascular permeability by different mechanisms.
In summary, these data show that 3OC12-HSL and PQS affect mammalian vascular function by decreasing vascular tone and increasing endothelial permeability. The potential advantage of these effects of quorum sensing molecules on host cells allowing bacteria to promote increase local circulation or produce oedema or allow access to promote systemic infection.
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