18Fluorodeoxyglucose Accumulation in Arterial Tissues Determined by PET Signal Analysis.

BACKGROUND: Arterial 18fluorodeoxyglucose (FDG) positron emission tomography (PET) is considered a measure of atherosclerotic plaque macrophages and is used for quantification of disease activity in clinical trials, but the distribution profile of FDG across macrophages and other arterial cells has not been fully clarified. OBJECTIVES: The purpose of this study was to analyze FDG uptake in different arterial tissues and their contribution to PET signal in normal and atherosclerotic arteries. METHODS: Wild-type and D374Y-PCSK9 transgenic Yucatan minipigs were fed a high-fat, high-cholesterol diet to induce atherosclerosis and subjected to a clinical FDG-PET and computed tomography scan protocol. Volumes of arterial media, intima/lesion, macrophage-rich, and hypoxic tissues were measured in serial histological sections. Distributions of FDG in macrophages and other arterial tissues were quantified using modeling of the in vivo PET signal. In separate transgenic minipigs, the intra-arterial localization of FDG was determined directly by autoradiography. RESULTS: Arterial FDG-PET signal appearance and intensity were similar to human imaging. The modeling approach showed high accuracy in describing the FDG-PET signal and revealed comparable FDG accumulation in macrophages and other arterial tissues, including medial smooth muscle cells. These findings were verified directly by autoradiography of normal and atherosclerotic arteries. CONCLUSIONS: FDG is taken up comparably in macrophage-rich and -poor arterial tissues in minipigs. This offers a mechanistic explanation to a growing number of observations in clinical imaging studies that have been difficult to reconcile with macrophage-selective FDG uptake.

Prior renovascular hypertension does not predispose to atherosclerosis in mice.

BACKGROUND: Hypertension is a major risk factor for development of atherosclerotic cardiovascular disease (ASCVD). Although lowering blood pressure with antihypertensive drugs reduces the increased risk of ASCVD, residual increased risk still remains, suggesting that hypertension may cause chronic changes that promote atherosclerosis. Thus, we tested the hypothesis that hypertension increases the susceptibility to atherosclerosis in mice even after a period of re-established normotension. METHODS: We used the 2-kidney, 1-clip (2K1C) technique to induce angiotensin-driven renovascular hypertension, and overexpression of the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene to cause severe hypercholesterolemia and atherosclerosis. RESULTS: First, we performed 2K1C (n = 8) or sham surgery (n = 9) in PCSK9 transgenic mice before they were fed a high fat diet for 14 weeks. As expected, 2K1C did not affect cholesterol levels, but induced cardiac hypertrophy and significantly increased the atherosclerotic lesion area compared to sham mice (1.8 fold, p < 0.01). Next, we performed 2K1C (n = 13) or sham surgery (n = 14) in wild-type mice but removed the clipped/sham-operated kidney after 10 weeks to eliminate hypertension, and subsequently induced hypercholesterolemia by way of adeno-associated virus-mediated hepatic gene transfer of PCSK9 combined with high-fat diet. After 14 weeks of hypercholesterolemia, atherosclerotic lesion areas were not significantly different in mice with or without prior 2K1C hypertension (0.95 fold, p = 0.35). CONCLUSION: Renovascular hypertension in mice does not induce pro-atherogenic changes that persist beyond the hypertensive phase. These results indicate that hypertension only promotes atherogenesis when coinciding temporally with hypercholesterolemia.

Stanniocalcin-2 overexpression reduces atherosclerosis in hypercholesterolemic mice.

BACKGROUND AND AIM: The metalloproteinase pregnancy-associated plasma protein-A (PAPP-A) has been suggested as a proatherogenic molecule by its ability to locally increase insulin-like growth factor signaling. Stanniocalcin-2 (STC2) was recently discovered to be a potent inhibitor of PAPP-A activity, but has not previously been implicated in vascular disease. The aim of this study was to substantiate the interaction between PAPP-A and STC2 as a potential local regulatory mechanism in the artery wall. METHODS AND RESULTS: We found that PAPP-A is secreted from cultured primary smooth muscle cells obtained from human aortas as a covalent complex with STC2, devoid of proteolytic activity. Extracts of human carotid atherosclerotic plaques contain both complexed and uncomplexed PAPP-A, and we show by immunohistochemistry that PAPP-A and STC2 are present in the tissue throughout early human lesion development. We then used adeno-associated virus-mediated expression of STC2 to increase the fraction of PAPP-A present in the inhibited state and found that it decreased the development of atherosclerosis by 47% (P = 0.0005) in apolipoprotein E-deficient mice challenged with a Western type diet compared to controls. CONCLUSIONS: This study is the first to suggest the involvement of STC2 in regulating PAPP-A activity during the development of atherosclerosis. Furthermore, we demonstrate that lesion development can be inhibited in an experimental model by driving the balance towards inhibited PAPP-A.

Inducing Persistent Flow Disturbances Accelerates Atherogenesis and Promotes Thin Cap Fibroatheroma Development in D374Y-PCSK9 Hypercholesterolemic Minipigs.

BACKGROUND: Although disturbed flow is thought to play a central role in the development of advanced coronary atherosclerotic plaques, no causal relationship has been established. We evaluated whether inducing disturbed flow would cause the development of advanced coronary plaques, including thin cap fibroatheroma. METHODS AND RESULTS: D374Y-PCSK9 hypercholesterolemic minipigs (n=5) were instrumented with an intracoronary shear-modifying stent (SMS). Frequency-domain optical coherence tomography was obtained at baseline, immediately poststent, 19 weeks, and 34 weeks, and used to compute shear stress metrics of disturbed flow. At 34 weeks, plaque type was assessed within serially collected histological sections and coregistered to the distribution of each shear metric. The SMS caused a flow-limiting stenosis, and blood flow exiting the SMS caused regions of increased shear stress on the outer curvature and large regions of low and multidirectional shear stress on the inner curvature of the vessel. As a result, plaque burden was ≈3-fold higher downstream of the SMS than both upstream of the SMS and in the control artery (P<0.001). Advanced plaques were also primarily observed downstream of the SMS, in locations initially exposed to both low (P<0.002) and multidirectional (P<0.002) shear stress. Thin cap fibroatheroma regions demonstrated significantly lower shear stress that persisted over the duration of the study in comparison with other plaque types (P<0.005). CONCLUSIONS: These data support a causal role for lowered and multidirectional shear stress in the initiation of advanced coronary atherosclerotic plaques. Persistently lowered shear stress appears to be the principal flow disturbance needed for the formation of thin cap fibroatheroma.

Diabetes with poor glycaemic control does not promote atherosclerosis in genetically modified hypercholesterolaemic minipigs.

AIMS/HYPOTHESIS: Diabetes is associated with an increased risk of atherosclerotic cardiovascular disease, but whether there is a direct and independent role for impaired glucose control in atherogenesis remains uncertain. We investigated whether diabetes with poor glycaemic control would accelerate atherogenesis in a novel pig model of atherosclerosis, the D374Y-PCSK9(+) transgenic minipig. METHODS: Nineteen minipigs were fed a cholesterol-enriched, high-fat diet; ten of these pigs were injected with streptozotocin to generate a model of diabetes. Restricted feeding was implemented to control the pigs' weight gain and cholesterol intake. After 49 weeks of high-fat feeding, the major arteries were harvested for a detailed analysis of the plaque burden and histological plaque type. RESULTS: Stable hyperglycaemia was achieved in the diabetic minipigs, while the plasma total and LDL-cholesterol and creatinine levels were unaffected. Diabetes failed to increase atherosclerosis in any of the vessels examined. The plaque burden in the aorta and right coronary artery was comparable between the groups, and was even reduced in the left anterior descending (LAD) coronary and iliofemoral arteries in the diabetic pigs compared with the controls. The distribution of plaque types and the collagen and macrophage contents were similar between the groups, except for a reduced infiltration of macrophages in the LAD arteries of the diabetic pigs. CONCLUSIONS/INTERPRETATION: Poorly controlled diabetes with no alterations in plasma cholesterol or creatinine concentrations did not augment the plaque burden or promote the development of more advanced lesions in this large-animal model of human-like atherosclerosis. This is consistent with clinical studies in patients with type 1 diabetes, indicating that hyperglycaemia per se is not an independent promoter of atherosclerotic disease, but that other diabetes-associated risk factors are important.