Highlights
- Calcific Aortic Valve Disease (CAVD) may not be a valvular equivalent of atherosclerosis
- Current treatment for stenosis is considered to be valve replacement
- Stages of Valve Disease progression has to studied to stop CAVD in its tracks and avoid valve replacement surgery
A team led by Masters has jumped a longstanding hurdle in that search with a study published today (Dec. 25, 2017) in the journal Proceedings of the National Academy of Sciences. The researchers teased apart, for the first time, the early cascade of events that may eventually cause stenosis, a severe narrowing of the aortic valve that reduces blood flow to body tissues and weakens the heart.
The only current treatment for stenosis is valve replacement, which typically requires risky and expensive open-heart surgery.
"Our study sheds new light on the differences between atherosclerosis and CAVD, especially regarding bottleneck events that we can target with drugs," says Masters, whose work is supported by the National Institutes of Health and the American Heart Association.
"With a better understanding of how the disease progresses from early to later stages, we may eventually be able to stop CAVD in its tracks and avoid valve replacement surgery."
Their valves provided a snapshot of early CAVD that is challenging to capture in humans, showing that it typically begins with the accumulation of certain sugar molecules called glycosaminoglycans (GAGs) in valve tissue. But to examine exactly how this tissue responds to increasing levels of GAGs, the researchers needed a greater amount of valve tissue than living pigs could provide.
When the researchers changed only the amount of GAGs these native valve cells were exposed to, while keeping all other conditions the same, they observed surprising results that challenged previous assumptions.
"We thought the GAGs would play a major role in driving the disease process, but the more we added, the fewer inflammatory factors the cells produced and the happier they were," says Masters. "When we examined this unexpected finding more closely, we noticed two distinct effects: GAGs directly increased a chemical needed to grow new blood vessels, and also trapped low-density lipoprotein (LDL) molecules."
Neither of these effects was immediately detrimental for valve cells, but the trapping made it more likely for oxygen to react with LDL molecules, and the accumulation of oxidized LDL appeared to be a bottleneck event for a multi-stage process toward valve cell damage, Masters says.
This multi-stage process may explain why 25 percent of adults over the age of 65 have CAVD with partially blocked aortic valves, but only one percent goes on to develop stenosis due to a valve that can no longer open and close properly. The fact that native valve cells cannot oxidize LDL themselves, while smooth muscle cells in blood vessels can, also highlights a key distinction between CAVD and atherosclerosis.
The study, which included first author Ana Porras, a postdoctoral in Masters' lab, has important implications for the development of new drugs that may prevent early CAVD from progressing to stenosis by making GAGs less likely to bind LDL. "The take-home message of our study is that CAVD is a multi-stage process and that healthy valve cells respond differently to LDL than blood vessel cells," Masters says.
"The ability to examine multiple steps in this novel in vitro model for early CAVD opens up several promising avenues for developing drugs that are distinct from those for atherosclerosis."
Reference:
New hope for stopping an understudied heart disease in its tracks - (https://news.wisc.edu/new-hope-for-stopping-an-understudied-heart-disease-in-its-tracks/)
Source-Eurekalert