PROJECT SUMMARY/ABSTRACT
Calcification of arteries, especially in the coronaries (CAC), progresses with age and is associated with
increased risk. However, evidence shows that CAC progression is promoted by statins, leading some to
believe that CAC is protective. This leaves a clinical dilemma for the elderly with CAC, from being told: 1) to
start statins to reduce their high-risk CAC and 2) that statins reduce risk by increasing CAC. We posit that
calcification reduces risk only in older individuals with high coronary calcium. Clinically, numerous small
deposits are associated with higher risk than large, contiguous deposits of the same volume. The link between
CAC and risk is most likely plaque rupture due to compliance mismatch at the interface between compliant
vascular tissue and rigid calcium mineral. Theoretically, surfaces of calcium deposits that face toward
mechanical stress have increased rupture risk, which should increase as mineral surface area (SA) increases.
Thus, SA is predicted to increase initially with progression of calcification, but, eventually, when deposits
coalesce they may reduce SA and presumably risk. This results in a roughly bell-shaped curve for the
relationship of risk to calcification. Older individuals, who generally have more calcification, may be on the
downslope of this curve. Therefore, SA may be a useful indicator of vulnerable plaque. In support of this,
clinical PET imaging with fluoride (18F-NaF), which preferentially labels the surface of calcium deposits, was
shown to identify vulnerable plaque. Based on these studies, we have developed a novel way to quantitatively
assess changes in SA of aortic calcium deposits in mice and found that the opposite trends in 18F-NaF
incorporation by microPET vs. in mineral content by microCT would suggest coalescence of calcium
deposits. We propose the novel hypothesis that calcification reduces risk only in older individuals, who have
enough calcium content for progression to lead to coalescence. We propose 2 aims. AIM 1. DETERMINE IF
AGING CAUSES PARADOXICAL CHANGES IN AORTIC CALCIUM CONTENT VS. MINERAL SURFACE AREA IN MICE. We will
assess changes over 2 years in mineral SA vs. calcium content in hyperlipidemic (Apoe-/- and Ldlr-/-) mice by
serial, 18F-microPET/microCT imaging and quantitative histochemical analyses using automated edge-
detection. AIM 2. DETERMINE IF MORPHOLOGIC RUPTURE RISK OF AORTIC CALCIUM DEPOSITS CHANGES
DIFFERENTIALLY IN OLD VS. YOUNG MICE ON STATINS. Aortas of hyperlipidemic mice on and off statins for 5
months will be subjected to the imaging and histological analysis, as in Aim1. In addition, after euthanasia, we
will determine plaque rupture threshold from stress-strain recordings and assess high resolution, 3D, laser
light-sheet fluorescence microscopy to overcome any sampling limitation of histology. Results will reveal
whether aging transforms the risk of calcification progression through coalescence and reduction of
surface area, compliance mismatch, and mechanical rupture stress. If progression is found to reduce
risk, it would have a profound impact on clinical management in the aging population.