"On the one hand it’s important to find out whether a given plaque is stable or unstable before surgery, and on the other this method provides us with completely new ways of learning how plaques are formed", says Isabel Goncalves, senior lecturer at Lund University Diabetes Centre (LUDC) and physician at the clinical department of cardiology at Skåne University Hospital in Malmö. Together with researchers from the fields of nuclear physics and quaternary geology at Lund University, she now publishes the results of measurements performed using the carbon-14 method in Circulation Research.
All living organisms absorb carbon-14 from the atmosphere. When an organism such as a plant, an animal, or a person dies absorption stops and the carbon content disintegrates at a fixed rate with a half life of approximately 5,730 years. Basically, disintegration results are a kind of time table that moves backwards through time to tell us how old the material is. For example, the carbon-14 method fundamentally changed how archaeologists date ancient remains and fossils, from charcoal and bone to mummies.
Nuclear weapons testing at the end of the 1950s and in the early 1960s resulted in a significant increase in atmospheric carbon-14 content which was equally distributed around the globe. Since then, the amount has decreased relatively rapidly and at a known rate. "This decrease is not due to radioactive disintegration but to the fact that carbon-14 is absorbed primarily by our oceans", says senior lecturer in nuclear physics at Lund University, Kristina Stenström, who performed the measurements.
The scientists used carbon-14 originating from the bomb pulse just over 50 years ago and the subsequent rapidly decreasing content to date the fatty plaques in blood vessel walls that are responsible for cardiovascular diseases such as infarction, stroke, and vascular spasm. "Until now, we haven’t known how fast or slow atherosclerotic plaque is formed", says Isabel Goncalves.
Plaque building blocks consist of rancid fat from blood, inflamed tissue, and dead cells. The more unstable a plaque is, the more dangerous it is. If a plaque bursts in the cartoid artery, pieces of it can travel up to the brain, become stuck in a narrower vessel, and cause a stroke. If the same thing happens in the coronary artery in the heart, infarction is inevitable. A plaque can also become so large in situ that it almost completely blocks a blood vessel. "The risk when surgically removing plaques from the cartoid artery is that a piece becomes unstuck and travels up to the brain", says Isabel Goncalves and points out that the knowledge of how plaque is formed may be of great clinical importance. "This information enables us to focus on maximising the gain with the least possible level of risk", she continues.
In the recently published study, Isabel Goncalves and Kristina Stenström present dating results from different parts of ten plaques that were surgically removed from cartoid arteries. "Using an accelerator mass spectrometer, it is possible to precisely determine the amount of carbon-14 in plaque or other tissue. Only 25 microgram of carbon is needed in order to establish the age", says Kristina Stenström. Measurements show that plaque is formed over a long period of time. On average, the oldest parts of the plaque were ten years old. The youngest part with the most rapid growth rate and thus greatest instability was consistently the part some researchers refer to as ’the cap’. "This is perhaps the part that we ought to focus on in treatment", says Isabel Goncalves.
The new information relating to the slow development of plaque also explains why attempts at reducing plaque size using lipid-lowering statins, for example, have not been sufficiently effective in reducing plaque size.
The study was made possible by the fact that the scientists had access to one of Sweden’s two accelerator mass spectrometers in Lund and to a biobank containing approximately 500 surgically removed plaques that cardiovascular researchers at LUDC have collected.
The study has been published in the journal Circulation Research.
Dating Components of Human Atherosclerotic Plaques
http://circres.ahajournals.org/cgi/reprint/CIRCRESAHA.109.211201v1
Test: Tord Ajanki/Camilla Franks
For more information:
Isabel Goncalves: +46 40 39 12 07, +46 40 39 12 31, isabel [dot] goncalves [at] med [dot] lu [dot] se (Isabel Goncalves)
Kristina Stenström: +46 46 222 76 43, +46 70 814 77 26, kristina [dot] stenstrom [at] nuclear [dot] lu [dot] se (Kristina Stenström)