RICERCA ITALIANA     

Genetic and molecular determinants of the role of COX-2 in atherothrombosis.

Università degli Studi "G. d'Annunzio" Chieti-Pescara

Abstract

Cyclooxygenase (COX)-2 plays a key role both in endothelial dysfunction, "primus movens" of atherosclerosis, and in atherosclerotic plaque rupture, final step of atherosclerotic disease.
There is strong evidence that reduced endothelial nitric oxide (NO) release may play a critical role in the evolution of endothelial dysfunction. Thus, all mediators inducing NO perturbation could promote endothelial dysfunction. One of them is COX-2, which may reduce NO biosynthesis by inducing oxidative stress. This is confirmed by the observation that COX-2 blockade can restore normal endothelial function. Different enzymatic systems can modulate endothelial susceptibility to COX-2-dependent oxidative stress. In fact, p66Shc protein modulates the endothelial oxidative stress response, and mice carrying a targeted mutation of the p66Shc gene show an increased resistance to oxidative stress.
However, the role of COX-2 in vascular walls is more complex, as it can exert both anti- and pro-atherogenic effects depending on the cellular type and on the prostaglandin (PG) produced. In fact, COX-2 in endothelial cells (ECs) catalyses PGI2 production. This may be the case in the presence of high density lipoprotein (HDL)3 that increases release of PGI2, but not of the pro-atherogenic PGE2.
In addition to its role in endothelium homeostasis, COX-2 has been shown to be involved in atherosclerotic progression toward instability. In fact, in atherosclerotic plaques, COX-2 can >>>

Principal Investigator

Franco CUCCURULLO Università degli Studi "G. d'Annunzio" CHIETI-PESCARA

Research Objectives

This Research Program is focused on different research activities in the area of cardiovascular disease.
There is strong evidence that inflammation plays a key role in the events leading to plaque rupture. In fact, inflammation is more common in symptomatic plaques, with a greater number of macrophages (Mf) and T cells infiltration, and plaque rupture is related to increased inflammation within the plaque rather than plaque morphology, or degree of vessel stenosis. Mf synthesizes metalloproteinases (MMPs) that are enzymes capable of degrading plaque constituents. Increased expression of MMPs has been reported in Mf in vulnerable regions of unstable plaques. Thus, localized MMP increase may cause acute plaque disruption, and the identification of pathways that regulate MMPs is critical to the formulation of strategies for plaque stabilization. Production of MMPs by Mf is induced through a prostaglandin (PG)E2-dependent pathway. In contrast, MMP biosynthesis may be suppressed by PGD2 metabolite via mechanisms involving both Peroxisome Proliferator Activated Receptor (PPAR)-gamma activation and NF-kB inhibition. Signaling through these pathways involves cyclooxygenase (COX), the enzyme that catalyzes the conversion of arachidonic acid (AA) to PGH2, then further metabolized by PGE synthase (PGES) or PGD synthase (PGDS) (isomerases) to opposing prostanoids (PGE2 and PGD2). It is important to note that COX-2 is expressed in Mf in human atherosclerotic plaques. Thus, COX-2 >>>

First Results

Studies on endothelial dysfunction.
It is expected that this 12-months period of study will allow the identification and the recruitment of a number of patients with different cardiovascular risk profiles adequate to obtain a statistical power. Sample size of the different research activities was usually determined by power analyses as follows: power = 0.95 and alpha= 0.05. In the different statistical calculations, we have estimated the means value of analyzed parameters based on previously published data by Unit #4, and assuming differences of 25% between groups of patients with different risk profile with respect to diverse molecular markers of endothelial function. The supposed difference in molecular marker was always a conservative estimate.

Studies on plaque instability.
It is expected that this 12-months period of study will permit the identification and the recruitment of a number of patients with symptomatic and asymptomatic carotid atherosclerotic plaques adequate to obtain a statistical power.
Sample size of the different research activities was usually determined by power analyses as follows: power = 0.95 and alpha= 0.05. In the different statistical calculations, we have estimated the means value of analyzed parameters based on previously published data, and assuming differences ranging from 30% to 60% between symptomatic and asymptomatic groups with respect to diverse molecular markers, the required sample of patients per >>>

Timescale

24 months

National and international background

1.Arachidonic acid metabolism via the PGH-synthase pathway.
Arachidonic acid (AA; 20:4, n-6) is an essential polyunsaturated fatty acid; its oxidation generates prostanoids and leukotrienes, collectively designated as "eicosanoids". When tissues are exposed to diverse physiological and pathological stimuli, AA is liberated from membrane phospholipids and converted to prostanoids like the prostaglandins and thromboxane (TX) A2, by the action of PGH-synthase (PGHS), known as cyclooxygenase as well. The cyclooxygenase and hydroperoxidase catalytic activities of this bifunctional enzyme result in the sequential formation of unstable endoperoxide intermediates, PGG2 and PGH2, which in turn is metabolized to PGD2, PGE2, PGF2alpha, PGI2 and TXA2 by cell-specific isomerases and synthases.
Two distinct isoforms of PGHS have been recognized since 1991, also designated as COX-1 and COX-2. Both COXs are membrane-anchored proteins existing as dimers and have remarkable structural similarity. The AA gains access to the active site via a hydrophobic channel, but this access can be blocked by drugs, which reversibly anchor to strategically located residues or irreversibly modify them. COX-1 is expressed constitutively in many tissues of the body and plays a central role in platelet aggregation and gastric cytoprotection. COX-2 is predominantly induced during inflammation, wound healing and neoplastic transformation, although it is expressed constitutively in the human kidney >>>