Synergistic effect of local endothelial shear stress and systemic hypercholesterolemia on coronary atherosclerotic plaque progression and composition in pigs

A dual-targeting therapeutic nanobubble for imaging-guided atherosclerosis treatment

Atherosclerosis is a cardiovascular disease that seriously endangers human health. Low shear stress (LSS) is recognized as a vital factor in causing chronic inflammatory and further inducing the occurrence and development of atherosclerosis. Targeting imaging and treatment are of substantial significance for the diagnosis and therapy of atherosclerosis. On this ground, a kind of ultrasound (US) imaging-guided therapeutic polymer nanobubbles (NBs) with dual targeting of magnetism and antibody was rationally designed and constructed for the efficiently treating LSS-mediated atherosclerosis. Under the combined targeting effect of an external magnetic field and antibodies, the drug-loaded therapeutic NBs can be effectively accumulated in the inflammatory area caused by LSS. Upon US irradiation, the NBs can be selectively disrupted, leading to the rapid release of the loaded drugs at the targeted site. Notably, the US irradiation generates a cavitation effect that induces repairable micro gaps in nearby cells, thereby enhancing the uptake of released drugs and further improving the therapeutic effect. The prominent US imaging, efficient anti-inflammatory effect and treatment outcome of LSS-mediated atherosclerosis had been verified in vivo on a surgically constructed LSS-atherosclerosis animal model. This work showcased the potential of the designed NBs with multifunctionality for in vivo imaging, dual-targeting, and drug delivery in the treatment of atherosclerosis.

Monocyte-endothelial cell interactions in vascular and tissue remodeling

Monocytes are circulating leukocytes of innate immunity derived from the bone marrow that interact with endothelial cells under physiological or pathophysiological conditions to orchestrate inflammation, angiogenesis, or tissue remodeling. Monocytes are attracted by chemokines and specific receptors to precise areas in vessels or tissues and transdifferentiate into macrophages with tissue damage or infection. Adherent monocytes and infiltrated monocyte-derived macrophages locally release a myriad of cytokines, vasoactive agents, matrix metalloproteinases, and growth factors to induce vascular and tissue remodeling or for propagation of inflammatory responses. Infiltrated macrophages cooperate with tissue-resident macrophages during all the phases of tissue injury, repair, and regeneration. Substances released by infiltrated and resident macrophages serve not only to coordinate vessel and tissue growth but cellular interactions as well by attracting more circulating monocytes (e.g. MCP-1) and stimulating nearby endothelial cells (e.g. TNF-α) to expose monocyte adhesion molecules. Prolonged tissue accumulation and activation of infiltrated monocytes may result in alterations in extracellular matrix turnover, tissue functions, and vascular leakage. In this review, we highlight the link between interactions of infiltrating monocytes and endothelial cells to regulate vascular and tissue remodeling with a special focus on how these interactions contribute to pathophysiological conditions such as cardiovascular and chronic liver diseases.

Shear Stress and Metabolic Disorders-Two Sides of the Same Plaque

Significance: Shear stress and metabolic disorder are the two sides of the same atherosclerotic coin. Atherosclerotic lesions are prone to develop at branches and curvatures of arteries, which are exposed to oscillatory and low shear stress exerted by blood flow. Meanwhile, metabolic disorders are pivotal contributors to the formation and advancement of atherosclerotic plaques. Recent Advances: Accumulated evidence has provided insight into the impact and mechanisms of biomechanical forces and metabolic disorder on atherogenesis, in association with mechanotransduction, epigenetic regulation, and so on. Moreover, recent studies have shed light on the cross talk between the two drivers of atherosclerosis. Critical Issues: There are extensive cross talk and interactions between shear stress and metabolic disorder during the pathogenesis of atherosclerosis. The communications may amplify the proatherogenic effects through increasing oxidative stress and inflammation. Nonetheless, the precise mechanisms underlying such interactions remain to be fully elucidated as the cross talk network is considerably complex. Future Directions: A better understanding of the cross talk network may confer benefits for a more comprehensive clinical management of atherosclerosis. Critical mediators of the cross talk may serve as promising therapeutic targets for atherosclerotic vascular diseases, as they can inhibit effects from both sides of the plaque. Hence, further in-depth investigations with advanced omics approaches are required to develop novel and effective therapeutic strategies against atherosclerosis. Antioxid. Redox Signal. 37, 820-841.

Effects of Postprandial Lipemia Combined With Disturbed Blood Flow on the Flow-Mediated Dilation, Oxidative Stress, and Endothelial Microvesicles in Healthy Subjects

Aims

Both postprandial lipemia (PPL) and disturbed blood flow (DBF) induce endothelial dysfunction. However, the interactive effect of these stimuli on endothelial function is currently unknown. In the present study, we tested whether PPL plus DBF causes a greater reduction in flow-mediated dilation (FMD) than PPL and if this response is associated with elevations in oxidative stress and endothelial microvesicles (EMVs).

Methods

Eighteen individuals (aged 28 ± 1yrs, 3 females, and BMI 24.43 ± 0.8kg/m²) randomly underwent two experimental sessions: PPL and PPL plus DBF. FMD and venous blood samples were obtained at baseline and 30, 70, and 110 min after stimulation. PPL was induced by fat overload via mozzarella pizza ingestion and DBF by forearm cuff inflation to 75 mm Hg per 30 min. Lipidic profile, oxidative stress (thiobarbituric acid reactive substances, TBARS; ferric reducing/antioxidant power, FRAP; hydrogen peroxide, H₂O₂) and EMVs were measured in blood samples.

Results

Hypertriglyceridemia was observed in both sessions. Retrograde shear rate and oscillatory index responses were significantly higher in the PPL plus DBF compared with PPL. PPL plus DBF evoked a greater reduction in FMD than did PPL and EMVs, NADPH oxidase, and H₂O₂ similarly increased in both sessions, but TBARS and FRAP did not change.

Conclusion

These data indicate that the association of PPL plus DBF additively impairs endothelium-dependent function in 110 min after stimulus in healthy individuals, despite a similar increase in oxidative stress and EMVs. Further studies are needed to understand the mechanisms associated with the induced-endothelial dysfunction by association of PPL and DBF.

Long noncoding RNA SNHG12 integrates a DNA-PK-mediated DNA damage response and vascular senescence

Long noncoding RNAs (lncRNAs) are emerging regulators of biological processes in the vessel wall; however, their role in atherosclerosis remains poorly defined. We used RNA sequencing to profile lncRNAs derived specifically from the aortic intima of Ldlr ^-/- mice on a high-cholesterol diet during lesion progression and regression phases. We found that the evolutionarily conserved lncRNA small nucleolar host gene-12 (SNHG12) is highly expressed in the vascular endothelium and decreases during lesion progression. SNHG12 knockdown accelerated atherosclerotic lesion formation by 2.4-fold in Ldlr ^-/- mice by increased DNA damage and senescence in the vascular endothelium, independent of effects on lipid profile or vessel wall inflammation. Conversely, intravenous delivery of SNHG12 protected the tunica intima from DNA damage and atherosclerosis. LncRNA pulldown in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that SNHG12 interacted with DNA-dependent protein kinase (DNA-PK), an important regulator of the DNA damage response. The absence of SNHG12 reduced the DNA-PK interaction with its binding partners Ku70 and Ku80, abrogating DNA damage repair. Moreover, the anti-DNA damage agent nicotinamide riboside (NR), a clinical-grade small-molecule activator of NAD⁺, fully rescued the increases in lesional DNA damage, senescence, and atherosclerosis mediated by SNHG12 knockdown. SNHG12 expression was also reduced in pig and human atherosclerotic specimens and correlated inversely with DNA damage and senescent markers. These findings reveal a role for this lncRNA in regulating DNA damage repair in the vessel wall and may have implications for chronic vascular disease states and aging.

Inflammation and enhanced atherogenesis in the carotid artery with altered blood flow in an atherosclerosis-resistant mouse strain

Ligation of the common carotid artery near its bifurcation in apolipoprotein E-deficient (Apoe^-/- ) mice leads to rapid atherosclerosis development, which is affected by genetic backgrounds. BALB/cJ (BALB) mice are resistant to atherosclerosis, developing much smaller aortic lesions than C57BL/6 (B6) mice. In this study, we examined cellular events leading to lesion formation in carotid arteries with or without blood flow restriction of B6 and BALB Apoe^-/- mice. Blood flow was obstructed by ligating the left common carotid artery near its bifurcation in one group of mice, and other group received no surgical intervention. Without blood flow interruption, BALB-Apoe^-/- mice formed much smaller atherosclerotic lesions than B6-Apoe^-/- mice after 12 weeks of Western diet (3,325 ± 1,086 vs. 81,549 ± 9,983 µm² /section; p = 2.1E-7). Lesions occurred at arterial bifurcations in both strains. When blood flow was obstructed, ligated carotid artery of both strains showed notable lipid deposition, inflammatory cell infiltration, and rapid plaque formation. Neutrophils and macrophages were observed in the arterial wall of BALB mice 3 days after ligation and 1 week after ligation in B6 mice. CD4 T cells were observed in intimal lesions of BALB but not B6 mice. By 4 weeks, both strains developed similar sizes of advanced lesions containing foam cells, smooth muscle cells, and neovessels. Atherosclerosis also occurred in straight regions of the contralateral common carotid artery where MCP-1 was abundantly expressed in the intima of BALB mice. These findings indicate that the disturbed blood flow is more prominent than high fat diet in promoting inflammation and atherosclerosis in hyperlipidemic BALB mice.

Multidirectional wall shear stress promotes advanced coronary plaque development: comparing five shear stress metrics

Aims

Atherosclerotic plaque development has been associated with wall shear stress (WSS). However, the multidirectionality of blood flow, and thus of WSS, is rarely taken into account. The purpose of this study was to comprehensively compare five metrics that describe (multidirectional) WSS behaviour and assess how WSS multidirectionality affects coronary plaque initiation and progression.

Methods and results

Adult familial hypercholesterolaemic pigs (n = 10) that were fed a high-fat diet, underwent imaging of the three main coronary arteries at three-time points [3 (T₁), 9 (T₂), and 10–12 (T₃) months]. Three-dimensional geometry of the arterial lumen, in combination with local flow velocity measurements, was used to calculate WSS at T₁ and T₂. For analysis, arteries were divided into 3 mm/45° sectors (n = 3648). Changes in wall thickness and final plaque composition were assessed with near-infrared spectroscopy–intravascular ultrasound, optical coherence tomography imaging, and histology. Both in pigs with advanced and mild disease, the highest plaque progression rate was exclusively found at low time-averaged WSS (TAWSS) or high multidirectional WSS regions at both T₁ and T₂. However, the eventually largest plaque growth was located in regions with initial low TAWSS or high multidirectional WSS that, over time, became exposed to high TAWSS or low multidirectional WSS at T₂. Besides plaque size, also the presence of vulnerable plaque components at the last time point was related to low and multidirectional WSS. Almost all WSS metrics had good predictive values for the development of plaque (47–50%) and advanced fibrous cap atheroma (FCA) development (59–61%).

Conclusion

This study demonstrates that low and multidirectional WSS promote both initiation and progression of coronary atherosclerotic plaques. The high-predictive values of the multidirectional WSS metrics for FCA development indicate their potential as an additional clinical marker for the vulnerable disease.

LncRNA VINAS regulates atherosclerosis by modulating NF-κB and MAPK signaling

Long noncoding RNAs (lncRNAs) play important roles in regulating diverse cellular processes in the vessel wall, including atherosclerosis. RNA-Seq profiling of intimal lesions revealed a lncRNA, VINAS (Vascular INflammation and Atherosclerosis lncRNA Sequence), that is enriched in the aortic intima and regulates vascular inflammation. Aortic intimal expression of VINAS fell with atherosclerotic progression and rose with regression. VINAS knockdown reduced atherosclerotic lesion formation by 55% in LDL receptor-deficient (LDLR-/-) mice, independent of effects on circulating lipids, by decreasing inflammation in the vessel wall. Loss- and gain-of-function studies in vitro demonstrated that VINAS serves as a critical regulator of inflammation by modulating NF-κB and MAPK signaling pathways. VINAS knockdown decreased the expression of key inflammatory markers, such as MCP-1, TNF-α, IL-1β, and COX-2, in endothelial cells (ECs), vascular smooth muscle cells, and bone marrow-derived macrophages. Moreover, VINAS silencing decreased expression of leukocyte adhesion molecules VCAM-1, E-selectin, and ICAM-1 and reduced monocyte adhesion to ECs. DEP domain containing 4 (DEPDC4), an evolutionary conserved human ortholog of VINAS with approximately 74% homology, showed similar regulation in human and pig atherosclerotic specimens. DEPDC4 knockdown replicated antiinflammatory effects of VINAS in human ECs. These findings reveal a potentially novel lncRNA that regulates vascular inflammation, with broad implications for vascular diseases.

Validation of Wall Shear Stress Assessment in Non-invasive Coronary CTA versus Invasive Imaging: A Patient-Specific Computational Study

Endothelial shear stress (ESS) identifies coronary plaques at high risk for progression and/or rupture leading to a future acute coronary syndrome. In this study an optimized methodology was developed to derive ESS, pressure drop and oscillatory shear index using computational fluid dynamics (CFD) in 3D models of coronary arteries derived from non-invasive coronary computed tomography angiography (CTA). These CTA-based ESS calculations were compared to the ESS calculations using the gold standard with fusion of invasive imaging and CTA. In 14 patients paired patient-specific CFD models based on invasive and non-invasive imaging of the left anterior descending (LAD) coronary arteries were created. Ten patients were used to optimize the methodology, and four patients to test this methodology. Time-averaged ESS (TAESS) was calculated for both coronary models applying patient-specific physiological data available at the time of imaging. For data analysis, each 3D reconstructed coronary artery was divided into 2 mm segments and each segment was subdivided into 8 arcs (45°).TAESS and other hemodynamic parameters were averaged per segment as well as per arc. Furthermore, the paired segment- and arc-averaged TAESS were categorized into patient-specific tertiles (low, medium and high). In the ten LADs, used for optimization of the methodology, we found high correlations between invasively-derived and non-invasively-derived TAESS averaged over segments (n = 263, r = 0.86) as well as arcs (n = 2104, r = 0.85, p < 0.001). The correlation was also strong in the four testing-patients with r = 0.95 (n = 117 segments, p = 0.001) and r = 0.93 (n = 936 arcs, p = 0.001).There was an overall high concordance of 78% of the three TAESS categories comparing both methodologies using the segment- and 76% for the arc-averages in the first ten patients. This concordance was lower in the four testing patients (64 and 64% in segment- and arc-averaged TAESS). Although the correlation and concordance were high for both patient groups, the absolute TAESS values averaged per segment and arc were overestimated using non-invasive vs. invasive imaging [testing patients: TAESS segment: 30.1(17.1-83.8) vs. 15.8(8.8-63.4) and TAESS arc: 29.4(16.2-74.7) vs 15.0(8.9-57.4) p < 0.001]. We showed that our methodology can accurately assess the TAESS distribution non-invasively from CTA and demonstrated a good correlation with TAESS calculated using IVUS/OCT 3D reconstructed models.

Role of the Platelets and Nitric Oxide Biotransformation in Ischemic Stroke: A Translative Review from Bench to Bedside

Ischemic stroke remains the fifth cause of death, as reported worldwide annually. Endothelial dysfunction (ED) manifesting with lower nitric oxide (NO) bioavailability leads to increased vascular tone, inflammation, and platelet activation and remains among the major contributors to cardiovascular diseases (CVD). Moreover, temporal fluctuations in the NO bioavailability during ischemic stroke point to its key role in the cerebral blood flow (CBF) regulation, and some data suggest that they may be responsible for the maintenance of CBF within the ischemic penumbra in order to reduce infarct size. Several years ago, the inhibitory role of the platelet NO production on a thrombus formation has been discovered, which initiated the era of extensive studies on the platelet-derived nitric oxide (PDNO) as a platelet negative feedback regulator. Very recently, Radziwon-Balicka et al. discovered two subpopulations of human platelets, based on the expression of the endothelial nitric oxide synthase (eNOS-positive or eNOS-negative platelets, respectively). The e-NOS-negative ones fail to produce NO, which attenuates their cyclic guanosine monophosphate (cGMP) signaling pathway and-as result-promotes adhesion and aggregation while the e-NOS-positive ones limit thrombus formation. Asymmetric dimethylarginine (ADMA), a competitive NOS inhibitor, is an independent cardiovascular risk factor, and its expression alongside with the enzymes responsible for its synthesis and degradation was recently shown also in platelets. Overproduction of ADMA in this compartment may increase platelet activation and cause endothelial damage, additionally to that induced by its plasma pool. All the recent discoveries of diverse eNOS expression in platelets and its role in regulation of thrombus formation together with studies on the NOS inhibitors have opened a new chapter in translational medicine investigating the onset of acute cardiovascular events of ischemic origin. This translative review briefly summarizes the role of platelets and NO biotransformation in the pathogenesis and clinical course of ischemic stroke.

Coronary artery plaque growth: A two-way coupled shear stress-driven model

Atherosclerosis in coronary arteries can lead to plaque growth, stenosis formation, and blockage of the blood flow supplying the heart tissue. Several studies have shown that hemodynamics play an important role in the growth of coronary artery plaques. Specifically, low wall shear stress (WSS) appears to be the leading hemodynamic parameter promoting atherosclerotic plaque growth, which in turn influences the blood flow and WSS distribution. Therefore, a two-way coupled interaction exists between WSS and atherosclerosis growth. In this work, a computational framework was developed to study the coupling between WSS and plaque growth in coronary arteries. Computational fluid dynamics (CFD) was used to quantify WSS distribution. Surface mesh nodes were moved in the inward normal direction according to a growth model based on WSS. After each growth stage, the geometry was updated and the CFD simulation repeated to find updated WSS values for the next growth stage. One hundred twenty growth stages were simulated in an idealized tube and an image-based left anterior descending artery. An automated framework was developed using open-source software to couple CFD simulations with growth. Changes in plaque morphology and hemodynamic patterns during different growth stages are presented. The results show larger plaque growth towards the downstream segment of the plaque, agreeing with the reported clinical observations. The developed framework could be used to establish hemodynamic-driven growth models and study the interaction between these processes.

Variation in Coronary Atherosclerosis Severity Related to a Distinct LDL (Low-Density Lipoprotein) Profile: Findings From a Familial Hypercholesterolemia Pig Model

OBJECTIVE

In an adult porcine model of familial hypercholesterolemia (FH), coronary plaque development was characterized. To elucidate the underlying mechanisms of the observed inter-individual variation in disease severity, detailed lipoprotein profiles were determined. Approach and Results: FH pigs (3 years old, homozygous LDLR R84C mutation) received an atherogenic diet for 12 months. Coronary atherosclerosis development was monitored using serial invasive imaging and histology. A pronounced difference was observed between mildly diseased pigs which exclusively developed early lesions (maximal plaque burden, 25% [23%-34%]; n=5) and advanced-diseased pigs (n=5) which developed human-like, lumen intruding plaques (maximal plaque burden, 69% [57%-77%]) with large necrotic cores, intraplaque hemorrhage, and calcifications. Advanced-diseased pigs and mildly diseased pigs displayed no differences in conventional risk factors. Additional plasma lipoprotein profiling by size-exclusion chromatography revealed 2 different LDL (low-density lipoprotein) subtypes: regular and larger LDL. Cholesterol, sphingosine-1-phosphate, ceramide, and sphingomyelin levels were determined in these LDL-subfractions using standard laboratory techniques and high-pressure liquid chromatography mass-spectrometry analyses, respectively. At 3 months of diet, regular LDL of advanced-diseased pigs contained relatively more cholesterol (LDL-C; regular/larger LDL-C ratio 1.7 [1.3-1.9] versus 0.8 [0.6-0.9]; P=0.008) than mildly diseased pigs, while larger LDL contained more sphingosine-1-phosphate, ceramides, and sphingomyelins. Larger and regular LDL was also found in plasma of 3 patients with homozygous FH with varying LDL-C ratios.

CONCLUSIONS

In our adult FH pig model, inter-individual differences in atherosclerotic disease severity were directly related to the distribution of cholesterol and sphingolipids over a distinct LDL profile with regular and larger LDL shortly after the diet start. A similar LDL profile was detected in patients with homozygous FH.

Decoding inflammation, its causes, genomic responses, and emerging countermeasures

Inflammation is the mechanism of diseases caused by microbial, autoimmune, allergic, metabolic and physical insults that produce distinct types of inflammatory responses. This aetiologic view of inflammation informs its classification based on a cause‐dependent mechanism as well as a cause‐directed therapy and prevention. The genomic era ushered in a new understanding of inflammation by highlighting the cell's nucleus as the centre of the inflammatory response. Exogenous or endogenous inflammatory insults evoke genomic responses in immune and non‐immune cells. These genomic responses depend on transcription factors, which switch on and off a myriad of inflammatory genes through their regulatory networks. We discuss the transcriptional paradigm of inflammation based on denying transcription factors’ access to the nucleus. We present two approaches that control proinflammatory signalling to the nucleus. The first approach constitutes a novel intracellular protein therapy with bioengineered physiologic suppressors of cytokine signalling. The second approach entails control of proinflammatory transcriptional cascades by targeting nuclear transport with a cell‐penetrating peptide that inhibits the expression of 23 out of the 26 mediators of inflammation along with the nine genes required for metabolic responses. We compare these emerging anti‐inflammatory countermeasures to current therapies. The transcriptional paradigm of inflammation offers nucleocentric strategies for microbial, autoimmune, metabolic, physical and other types of inflammation afflicting millions of people worldwide.

Low carotid endothelial shear stress associated with cerebral small vessel disease in an older population: A subgroup analysis of a population-based prospective cohort study

BACKGROUND AND AIMS

The association between carotid wall shear stress (WSS) and cerebral small vessel disease has yet to be fully elucidated. The major purpose of this study was to investigate this association in older subjects.

METHODS

Common carotid artery WSS, endothelial function, white matter hyperintensities (WMH), lacunes, and microbleeds were assessed in 1396 older adults. Participants were followed-up for an average of 69.7 months.

RESULTS

Mean (M) and peak (P) WSS and changes in endothelial function were independently associated with changes in WMH volume and fraction, lacune counts, and microbleed counts (all p < 0.05). The risks of new-incident Fazekas scale ≥2 [hazard ratio (HR) with 95% confidence interval (CI): 2.141 (1.469-3.119), p = 0.005 and 1.731 (1.197-2.505), p = 0.004, respectively], lacunes [HR (95% CI): 2.034 (1.369-3.022), p < 0.001 and 1.693 (1.151-2.490), p = 0.003, respectively], and microbleeds [HR (95% CI): 2.311 (1.509-3.541), p < 0.001 and 2.208 (1.299-3.751), p < 0.001, respectively] were significantly higher in the lowest quartile group than in the higher quartile group, as classified by either MWSS or PWSS, after adjustment for confounders.

CONCLUSIONS

Low carotid WSS is an independent risk factor for the progression of cerebral small vessel disease in older adults.

Atherosclerosis at arterial bifurcations: evidence for the role of haemodynamics and geometry

Atherosclerotic plaques are found at distinct locations in the arterial system, despite the exposure to systemic risk factors of the entire vascular tree. From the study of arterial bifurcation regions, emerges ample evidence that haemodynamics are involved in the local onset and progression of the atherosclerotic disease. This observed co-localisation of disturbed flow regions and lesion prevalence at geometrically predisposed districts such as arterial bifurcations has led to the formulation of a ‘haemodynamic hypothesis’, that in this review is grounded to the most current research concerning localising factors of vascular disease. In particular, this review focuses on carotid and coronary bifurcations because of their primary relevance to stroke and heart attack. We highlight reported relationships between atherosclerotic plaque location, progression and composition, and fluid forces at vessel’s wall, in particular shear stress and its ‘easier-tomeasure’ surrogates, i.e. vascular geometric attributes (because geometry shapes the flow) and intravascular flow features (because they mediate disturbed shear stress), in order to give more insight in plaque initiation and destabilisation. Analogous to Virchow’s triad for thrombosis, atherosclerosis must be thought of as subject to a triad of, and especially interactions among, haemodynamic forces, systemic risk factors, and the biological response of the wall.

Quantitative Evaluation of Coronary Plaque Progression by Computed Tomographic Angiography

Understanding plaque formation in patients at risk for coronary artery disease-the leading cause of morbidity and death in the world-enables physicians to better determine whether and how to treat these individuals. We used computed tomographic angiography to quantitatively evaluate the progression of nonculprit coronary plaques along the full length of the right coronary artery in 21 patients with acute coronary syndrome. Each right coronary artery was analyzed in sequential, 3-mm-long segments, and the minimum luminal area, plaque burden, and plaque volume within each segment were evaluated at baseline and at 12-month follow-up. Serial remodeling of the right coronary artery was also evaluated. In total, 625 arterial segments were analyzed. At 12-month follow-up, the plaque burden had increased slightly by 0.34% (interquartile range [IQR], -4.32% to 6.35%; P=0.02), and the plaque volume was not significantly changed (0.33 mm3; IQR, -3.05 to 3.54; P=0.213). The minimum luminal area decreased 0.05 mm2 (IQR, -1.33 to 0.87 mm2; P=0.012), and this was accompanied by vessel reduction, as evidenced by negative remodeling in 43% of the 625 segments. We conclude that serial computed tomographic angiography can be used to quantitatively evaluate the morphologic progression of coronary plaques.

Role of Low Endothelial Shear Stress and Plaque Characteristics in the Prediction of Nonculprit Major Adverse Cardiac Events: The PROSPECT Study

OBJECTIVES

This study sought to determine whether low endothelial shear stress (ESS) adds independent prognostication for future major adverse cardiac events (MACE) in coronary lesions in patients with high-risk acute coronary syndrome (ACS) from the United States and Europe.

BACKGROUND

Low ESS is a proinflammatory, proatherogenic stimulus associated with coronary plaque development, progression, and destabilization in human-like animal models and in humans. Previous natural history studies including baseline ESS characterization investigated low-risk patients.

METHODS

In the PROSPECT (Providing Regional Observations to Study Predictors of Events in the Coronary Tree) study, 697 patients with ACS underwent 3-vessel intracoronary imaging. Independent predictors of MACE attributable to untreated nonculprit (nc) coronary lesions during 3.4-year follow-up were large plaque burden (PB), small minimum lumen area (MLA), and thin-cap fibroatheroma (TCFA) morphology. In this analysis, baseline ESS of nc lesions leading to new MACE (nc-MACE lesions) and randomly selected control nc lesions without MACE (nc-non-MACE lesions) were calculated. A propensity score for ESS was constructed for each lesion, and the relationship between ESS and subsequent nc-MACE was examined.

RESULTS

A total of 145 lesions were analyzed in 97 patients: 23 nc-MACE lesions (13 TCFAs, 10 thick-cap fibroatheromas [ThCFAs]), and 122 nc-non-MACE lesions (63 TCFAs, 59 ThCFAs). Low local ESS (<1.3 Pa) was strongly associated with subsequent nc-MACE compared with physiological/high ESS (≥1.3 Pa) (23 of 101 [22.8%]) versus (0 of 44 [0%]). In propensity-adjusted Cox regression, low ESS was strongly associated with MACE (hazard ratio: 4.34; 95% confidence interval: 1.89 to 10.00; p < 0.001). Categorizing plaques by anatomic risk (high risk: ≥2 high-risk characteristics PB ≥70%, MLA ≤4 mm², or TCFA), high anatomic risk, and low ESS were prognostically synergistic: 3-year nc-MACE rates were 52.1% versus 14.4% versus 0.0% in high-anatomic risk/low-ESS, low-anatomic risk/low-ESS, and physiological/high-ESS lesions, respectively (p < 0.0001). No lesion without low ESS led to nc-MACE during follow-up, regardless of PB, MLA, or lesion phenotype at baseline.

CONCLUSIONS

Local low ESS provides incremental risk stratification of untreated coronary lesions in high-risk patients, beyond measures of PB, MLA, and morphology.

Low Endothelial Shear Stress Predicts Evolution to High-Risk Coronary Plaque Phenotype in the Future

Background—

Low endothelial shear stress (ESS) is associated with plaque progression and vulnerability. To date, changes in plaque phenotype over time in relation to ESS have not been studied in humans. The aim of this study was to investigate whether local ESS can predict subsequent changes to plaque phenotype using optical coherence tomography.

Methods and Results—

A total of 25 coronary arteries from 20 patients who underwent baseline and 6-month follow-up optical coherence tomography were included. Arteries were divided into serial 3-mm segments, and plaque characteristics were evaluated in each segment. A total of 145 segments were divided into low-ESS group (ESS <1 Pa) and higher-ESS group (ESS ≥1 Pa) based on baseline computational flow dynamics analyses. At baseline, low-ESS segments had significantly thinner fibrous cap thickness compared with higher-ESS segments (128.2±12.3 versus 165.0±12.0 μm; P =0.03), although lipid arc was similar. At follow-up, fibrous cap thickness remained thin in low-ESS segments, whereas it significantly increased in higher-ESS segments (165.0±12.0 to 182.2±14.1 μm; P =0.04). Lipid arc widened only in plaques with low ESS (126.4±15.2° to 141.1±14.0°; P =0.01). After adjustment, baseline ESS was associated with fibrous cap thickness (β, 9.089; 95% confidence interval, 2.539–15.640; P =0.007) and lipid arc (β, −4.381; 95% confidence interval, −6.946 to −1.815; P =0.001) at follow-up.

Conclusions—

Low ESS is significantly associated with baseline high-risk plaque phenotype and progression to higher-risk phenotype at 6 months.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01110538.

Intravascular hemodynamics and coronary artery disease: New insights and clinical implications

Intracoronary hemodynamics play a pivotal role in the initiation and progression of the atherosclerotic process. Low pro-inflammatory endothelial shear stress impacts vascular physiology and leads to the occurrence of coronary artery disease and its implications.

Role of biomechanical forces in the natural history of coronary atherosclerosis

Atherosclerosis remains a major cause of morbidity and mortality worldwide, and a thorough understanding of the underlying pathophysiological mechanisms is crucial for the development of new therapeutic strategies. Although atherosclerosis is a systemic inflammatory disease, coronary atherosclerotic plaques are not uniformly distributed in the vascular tree. Experimental and clinical data highlight that biomechanical forces, including wall shear stress (WSS) and plaque structural stress (PSS), have an important role in the natural history of coronary atherosclerosis. Endothelial cell function is heavily influenced by changes in WSS, and longitudinal animal and human studies have shown that coronary regions with low WSS undergo increased plaque growth compared with high WSS regions. Local alterations in WSS might also promote transformation of stable to unstable plaque subtypes. Plaque rupture is determined by the balance between PSS and material strength, with plaque composition having a profound effect on PSS. Prospective clinical studies are required to ascertain whether integrating mechanical parameters with medical imaging can improve our ability to identify patients at highest risk of rapid disease progression or sudden cardiac events.

Association of Wall Shear Stress with Coronary Plaque Progression and Transformation

Coronary endothelial function regulation by wall shear stress (WSS), the frictional force of blood exerted against the vessel wall, can help explain the focal propensity of plaque development in an environment of systemic atherosclerosis risk factors. Sustained abnormal pathologic WSS leads to a proatherogenic endothelial cell phenotype, plaque progression and transformation, and adaptive vascular remodeling in site-specific areas. Assessing dynamic coronary plaque compositional changes in vivo remains challenging; however, recent advances in intravascular image acquisition and processing may provide swifter WSS calculations and make possible larger prospective investigations on the prognostic value of WSS in patients with coronary atherosclerosis.

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.

How do we prevent the vulnerable atherosclerotic plaque from rupturing? Insights from in vivo assessments of plaque, vascular remodeling, and local endothelial shear stress

Coronary atherosclerosis progresses both as slow, gradual enlargement of focal plaque and also as a more dynamic process with periodic abrupt changes in plaque geometry, size, and morphology. Systemic vasculoprotective therapies such as statins, angiotensin-converting enzyme inhibitors, and antiplatelet agents are the cornerstone of prevention of plaque rupture and new adverse clinical outcomes, but such systemic therapies are insufficient to prevent the majority of new cardiac events. Invasive imaging methods have been able to identify both the anatomic features of high-risk plaque and the ongoing pathobiological stimuli responsible for progressive plaque inflammation and instability and may provide sufficient information to formulate preventive local mechanical strategies (eg, preemptive percutaneous coronary interventions) to avert cardiac events. Local endothelial shear stress (ESS) triggers vascular phenomena that synergistically exacerbate atherosclerosis toward an unstable phenotype. Specifically, low ESS augments lipid uptake and catabolism, induces plaque inflammation and oxidation, downregulates the production, upregulates the degradation of extracellular matrix, and increases cellular apoptosis ultimately leading to thin-cap fibroatheromas and/or endothelial erosions. Increases in blood thrombogenicity that result from either high or low ESS also contribute to plaque destabilization. An understanding of the actively evolving vascular phenomena, as well as the development of in vivo imaging methodologies to identify the presence and severity of the different processes, may enable early identification of a coronary plaque destined to acquire a high-risk state and allow for highly selective, focal preventive interventions to avert the adverse natural history of that particular plaque. In this review, we focus on the role of ESS in the pathobiologic processes responsible for plaque destabilization, leading either to accelerated plaque growth or to acute coronary events, and emphasize the potential to utilize in vivo risk stratification of individual coronary plaques to optimize prevention strategies to preclude new cardiac events.

ENDOTHELIAL MECHANOTRANSDUCTION MECHANISMS FOR VASCULAR PHYSIOLOGY AND ATHEROSCLEROSIS

Vascular physiology and disease progression, such as atherosclerosis, are mediated by hemodynamic force generated from blood flow. The hemodynamic force exerts on vascular endothelial cells (ECs), which could perceive the mechanical signals and transmit them into cell interior by multiple potential shear sensors, collectively known as mechanotransduction. However, we do not understand completely how these shear-sensitive components orchestrate physiological and atherosclerotic responses to shear stress. In this review, we provide an overview of biomechanical mechanisms underlying vascular physiology and atherosclerotic progression. Additionally, we summarize current evidences to illustrate that atherosclerotic lesions preferentially develop in arterial regions experiencing disturbance in blood flow, during which endothelial dysfunction is the initial event of atherosclerosis, inflammation plays dominant roles in atherosclerotic progression, and angiogenesis emerges as compensatory explanation for atherosclerotic plaque rupture. Especially in the presence of systemic risk factors (e.g., hyperlipidaemia, hypertension and hyperglycemia), the synergy between these systemic risk factors with hemodynamic factors aggravates atherosclerosis by co-stimulating some of these biomechanical events. Given the hemodynamic environment of vasculature, understanding how the rapid shear-mediated signaling, particularly in combination with systemic risk factors, contribute to atherosclerotic progression through endothelial dysfunction, inflammation and angiogenesis helps to elucidate the role for atherogenic shear stress in specifically localizing atherosclerotic lesions in arterial regions with disturbed flow.

Comprehensive plaque assessment by coronary CT angiography

Most acute coronary syndromes are caused by sudden luminal thrombosis due to atherosclerotic plaque rupture or erosion. Preventing such an event seems to be the only effective strategy to reduce mortality and morbidity of coronary heart disease. Coronary lesions prone to rupture have a distinct morphology compared with stable plaques, and provide a unique opportunity for noninvasive imaging to identify vulnerable plaques before they lead to clinical events. The submillimeter spatial resolution and excellent image quality of modern computed tomography (CT) scanners allow coronary atherosclerotic lesions to be detected, characterized, and quantified. Large plaque volume, low CT attenuation, napkin-ring sign, positive remodelling, and spotty calcification are all associated with a high risk of acute cardiovascular events in patients. Computation fluid dynamics allow the calculation of lesion-specific endothelial shear stress and fractional flow reserve, which add functional information to plaque assessment using CT. The combination of morphologic and functional characteristics of coronary plaques might enable noninvasive detection of vulnerable plaques in the future.