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Coronary calcium: Cause or effect?

Posted Nov 28 2010 8:12am
Here's an interesting observation made by a British research group.

We all know that coronary calcium, as measured by CT heart scans, are a surrogate measure of atherosclerotic plaque "burden," i.e., an indirect yardstick for coronary plaque. The greater the quantity of coronary calcium, the higher the heart scan "score," the greater the risk for heart attack and other unstable coronary syndromes that lead to stents, bypass, etc.

But can calcium also cause plaque to form or trigger processes that lead to plaque formation and/or instability?

Nadra et al show, in an in vitro preparation, that calcium phosphate crystals are actively incorporated into inflammatory macrophages, which then trigger a constellation of inflammatory cytokine release (tumor necrosis factor-alpha, interleukins), fundamental processes underlying atherosclerotic plaque formation and inflammation.

Here's the abstract of the study Proinflammatory Activation of Macrophages by Basic Calcium Phosphate Crystals via Protein Kinase C and MAP Kinase Pathways
A Vicious Cycle of Inflammation and Arterial Calcification?

Basic calcium phosphate (BCP) crystal deposition underlies the development of arterial calcification. Inflammatory macrophagescolocalize with BCP deposits in developing atherosclerotic lesionsand in vitro can promote calcification through the release of TNF alpha. Here we have investigated whether BCP crystals can elicit a proinflammatory response from monocyte-macrophages.BCP microcrystals were internalized into vacuoles of human monocyte-derived macrophages in vitro. This was associated with secretion of proinflammatory cytokines (TNF{alpha}, IL-1ß and IL-8) capable of activating cultured endothelial cells and promoting capture of flowing leukocytes under shear flow. Critical roles for PKC, ERK1/2, JNK, but not p38 intracellular signaling pathways were identified in the secretion of TNF alpha, with activation of ERK1/2 but not JNK being dependent on upstream activation of PKC. Using confocal microscopy and adenoviral transfection approaches, we determined a specific role for the PKC-alpha isozyme.

The response of macrophages to BCP crystals suggests that pathological calcification is not merely a passive consequence of chronic inflammatory disease but may lead to a positive feed-back loop of calcification and inflammation driving disease progression.

This observation adds support to the notion that increasing coronary calcium scores, i.e., increasing accumulation of calcium within plaque, suggests active plaque. As I say in Track Your Plaque , "growing plaque is active plaque." Active plaque means plaque that is actively growing, inflamed and infiltrated by inflammatory cells like macrophages, eroding its structural components, and prone to "rupture," i.e., cause heart attack. Someone whose first heart scan score is, say, 100, followed by another heart scan score two years later of 200 is exposed to sharply increasing risk for cardiovascular events which may, in part, be due to the plaque-stimulating effects of calcium.

Conversely, reducing coronary calcium scores removes a component of plaque that would otherwise fuel its growth. So, people like our Freddie , who reduced his heart scan score by 75%, can be expected to enjoy a dramatic reduction of risk for cardiovascular events.

Less calcium, less plaque to rupture, less risk.

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