Distribution of lipid and raised lesions in aortas of young people of different geographic origins (WHO-ISFC PBDAY Study). World Health Organization-International Society and Federation of Cardiology. Pathobiological Determinants of Atherosclerosis in Youth

Micro Spectroscopic Photoacoustic (μsPA) imaging of advanced carotid atherosclerosis

Atherosclerosis is a lipid-driven and an inflammatory disease of the artery walls. The composition of atherosclerotic plaque stratifies the risk of a specific plaque to cause a cardiovascular event. In an optical resolution photoacoustic microscopy setup, of 45 μm resolution, we extracted plaque lipid photoacoustic (PA) spectral signatures of human endarterectomy samples in the range of 1150-1240 nm, using matrix assisted laser desorption ionization mass spectrometry imaging as a reference. We found plaque PA signals to correlate best with sphingomyelins and cholesteryl esters. PA signal spectral variations within the plaque area were compared to reference molecular patterns and absorption spectra of lipid laboratory standards. Variability in the lipid spectroscopic features extracted by principal component analysis of all samples revealed three distinct components with peaks at: 1164, 1188, 1196 and 1210 nm. This result will guide the development of PA-based atherosclerosis disease staging capitalizing on lipidomics of atherosclerotic tissue.

The Importance of the Autopsy in Medicine: Perspectives of Pathology Colleagues

This article presents a perspective on the importance of the autopsy in medical practice and science based on experiences of the authors as physician-scientists involved in autopsy practice. Our perspectives are presented on the seminal contributions of the autopsy in the areas of cardiovascular disease, including congenital heart disease, atherosclerosis, coronary artery disease, and myocardial infarction, and infectious disease, including tuberculosis and viral infections. On the positive side of the future of the autopsy, we discuss the tremendous opportunities for important research to be done by application of advanced molecular biological techniques to formalin-fixed, paraffin-embedded tissue blocks obtained at autopsy. We also note with concern the countervailing forces impacting the influence of pathology in education and clinical practice at our academic medical centers, which also present impediments to increasing autopsy rates. Our challenge as academic pathologists, whose careers have been molded by involvement in the autopsy, is to counter these trends. The challenges are great but the benefits for medicine and society are enormous.

Prevalence and severity of atherosclerosis in different arterial territories and its relation with obesity

BACKGROUND

There is uneven association between obesity, traditional risk factors, and cardiovascular events. We aimed to analyze the relation between cardiovascular risk factors, including obesity, with the severity of atherosclerosis in different arterial territories.

METHODS

Arteries from five territories (circle of Willis, carotids, coronaries, aorta, and renal) were taken from 185 persons, newborn to 90 years undergoing autopsy in the Forensic Medical Service in Mexico City, to determine atherosclerotic lesions by histopathological study. Lesions were classified according to the American Heart Association grading system as early (types I-III) and advanced (types IV-VI). The degree of atherosclerosis was correlated with arterial territories and risk factors.

RESULTS

Frequencies of advanced lesions according to arterial territories were as follows: circle of Willis, 28%; right carotid, 36%; left carotid, 25%; right coronary, 71%; left coronary, 85%; right renal, 26%; left renal, 29%; and aorta, 52%; P=.0001, for all analyses. There was a higher risk for advanced lesions with increasing body mass index (BMI) (P=.004). However, after adjusting for age, gender, smoking status, hypertension, and diabetes mellitus, BMI was not independently associated with advanced lesions.

CONCLUSIONS

Coronary arteries are significantly more affected than other arterial territories regardless of risk factors, showing the effect of local and systemic factors in the severity of atherosclerosis. We did not find an independent association between advanced atherosclerotic lesions and obesity.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

The renal artery ostium flow diverter: structure and potential role in atherosclerosis

Initiation of renal atherosclerosis occurs primarily at the caudal region of the renal artery ostium. To date, no mechanism for initiation of atherosclerosis at this site has been substantiated. Herein, we identify a renal artery flow diverter on the caudal wall of the renal artery ostium that directs flow into the renal artery and selectively retains LDL, an initial step in atherosclerosis. High-resolution ultrasound revealed the generation of flow eddies by the caudal diverter in vivo, consistent with a role in directing aortic flow to the renal artery. Two-photon excitation en face microscopy of the diverter revealed a substantial reduction in the elastic lamina exposing potential retention sites for LDL. Fluorescent LDL was selectively retained by the renal artery diverter, consistent with its molecular structure. We propose that the rigid macromolecular structure of the renal artery ostium diverter is required for its vascular function and contributes to the initiation of renal atherosclerosis by the retention of LDL.

Three-dimensional analysis of segmental wall shear stress in the aorta by flow-sensitive four-dimensional-MRI

PURPOSE

To assess the distribution and regional differences of flow and vessel wall parameters such as wall shear stress (WSS) and oscillatory shear index (OSI) in the entire thoracic aorta.

MATERIALS AND METHODS

Thirty-one healthy volunteers (mean age = 23.7 +/- 3.3 years) were examined by flow-sensitive four-dimensional (4D)-MRI at 3T. For eight retrospectively positioned 2D analysis planes distributed along the thoracic aorta, flow parameters and vectorial WSS and OSI were assessed in 12 segments along the vascular circumference.

RESULTS

Mean absolute time-averaged WSS ranged between 0.25 +/- 0.04 N/m(2) and 0.33 +/- 0.07 N/m(2) and incorporated a substantial circumferential component (-0.05 +/- 0.04 to 0.07 +/- 0.02 N/m(2)). For each analysis plane, a segment with lowest absolute WSS and highest OSI was identified which differed significantly from mean values within the plane (P < 0.05). The distribution of atherogenic low WSS and high OSI closely resembled typical locations of atherosclerotic lesions at the inner aortic curvature and supraaortic branches.

CONCLUSION

The normal distribution of vectorial WSS and OSI in the entire thoracic aorta derived from flow-sensitive 4D-MRI data provides a reference constituting an important perquisite for the examination of patients with aortic disease. Marked regional differences in absolute WSS and OSI may help explaining why atherosclerotic lesions predominantly develop and progress at specific locations in the aorta.

Expression of cathepsin K is regulated by shear stress in cultured endothelial cells and is increased in endothelium in human atherosclerosis

Cathepsins, the lysosomal cysteine proteases, are involved in vascular remodeling and atherosclerosis. Genetic knockout of cathepsins S and K in mice has shown to reduce atherosclerosis, although the molecular mechanisms remain unclear. Because atherosclerosis preferentially occurs in arteries exposed to disturbed flow conditions, we hypothesized that shear stress would regulate cathepsin K expression and activity in endothelial cells. Mouse aortic endothelial cells (MAEC) exposed to proatherogenic oscillatory shear (OS, ± 5 dyn/cm2for 1 day) showed significantly higher cathepsin K expression and activity than that of atheroprotective, unidirectional laminar shear stress (LS, 15 dyn/cm2for 1 day). Western blot and active-site labeling studies showed an active, mature form of cathepsin K in the conditioned medium of MAEC exposed to OS but not in that of LS. Functionally, MAEC exposed to OS significantly increased elastase and gelatinase activity above that of LS. The OS-dependent elastase and gelatinase activities were significantly reduced by knocking down cathepsin K with small-interfering (si) RNA, but not by a nonsilencing siRNA control, suggesting that cathepsin K is a shear-sensitive protease. In addition, immunohistochemical analysis of atherosclerotic human coronary arteries showed a positive correlation between the cathepsin K expression levels in endothelium and elastic lamina integrity. These findings suggest that cathepsin K is a mechanosensitive, extracellular matrix protease that, in turn, may be involved in arterial wall remodeling and atherosclerosis.

Abdominal aortic hemodynamics in young healthy adults at rest and during lower limb exercise: quantification using image-based computer modeling

Localization of atherosclerotic lesions in the abdominal aorta has been previously correlated to areas of adverse hemodynamic conditions, such as flow recirculation, low mean wall shear stress, and high temporal oscillations in shear. Along with its many systemic benefits, exercise is also proposed to have local benefits in the vasculature via the alteration of these regional flow patterns. In this work, subject-specific models of the human abdominal aorta were constructed from magnetic resonance angiograms of five young, healthy subjects, and computer simulations were performed under resting and exercise (50% increase in resting heart rate) pulsatile flow conditions. Velocity fields and spatial variations in mean wall shear stress (WSS) and oscillatory shear index (OSI) are presented. When averaged over all subjects, WSS increased from 4.8 +/- 0.6 to 31.6 +/- 5.7 dyn/cm2 and OSI decreased from 0.22 +/- 0.03 to 0.03 +/- 0.02 in the infrarenal aorta between rest and exercise. WSS significantly increased, whereas OSI decreased between rest and exercise at the supraceliac, infrarenal, and suprabifurcation levels, and significant differences in WSS were found between anterior and posterior sections. These results support the hypothesis that exercise provides localized benefits to the cardiovascular system through acute mechanical stimuli that trigger longer-term biological processes leading to protection against the development or progression of atherosclerosis.

Distribution of early atherosclerotic lesions in the human abdominal aorta correlates with wall shear stresses measured in vivo

OBJECTIVES

to study the relationship between wall shear stresses measured in vivo and early atherosclerotic lesions in the abdominal aorta.

MATERIALS

eight young volunteers for in vivo wall shear-stress measurements. Abdominal aortas from 10 young adults without signs or history of atherosclerotic disease were obtained by autopsy for histomorphometric measurements.

METHODS

wall shear stresses were measured in the abdominal aorta above and below the renal arteries using a magnetic resonance technique with high resolution for imaging and blood velocity mapping. At identical abdominal aortic locations, intimal thickness was measured blindly using histomorphometric techniques and correlated to wall shear-stress variables using linear-regression analysis.

RESULTS

intimal thickness showed a linear decrease with mean wall shear stress (r=-0.90, p<0.01) and with maximum wall shear stress (r=-0.86, p<0.01).

CONCLUSIONS

intimal thickness in the normal abdominal aorta is associated with mean, maximum and oscillating wall shear stresses. These in vivo data corroborate previous in vitro studies suggesting that low and oscillating wall shear stresses are localising factors for intimal thickening and hence the early development of atherosclerosis.

A histomorphometric method for evaluating topographic differences in degree of early atherosclerosis within the human aorta

The aim of the study was to develop an unbiased topographically oriented method of evaluating early atherosclerotic lesions in the aorta and to apply this to a series of human aortas from young adults. A systematic sampling procedure and histomorphometric analysis of intimal thickening is described. Results from a group of 15 young adults (aged 18-40 years) showed a characteristic pattern with increasing intimal thickening when moving distally from the thoracic to the upper and finally to the lower abdominal aorta, but also a shift in the localization of the most pronounced intimal thickening from the posterior to the anterior and back to the posterior aspect. This pattern was found in aortas both with minimal and with more pronounced atherosclerosis, and supports the view that the early intimal thickening precedes the atherosclerotic lesions and marks the sites of predilection for the more advanced disease processes. An increase in intimal thickness with age could be demonstrated in the aortas without overt atherosclerosis. The simple sampling procedure, well-defined sampling sites, and ability to demonstrate and quantitate differences in intimal thickening and plaque morphology make this method well suited for relating morphometric data to other parameters of interest when studying the etiology and dynamics of atherosclerotic disease.

The role of taper on the distribution of atherosclerosis in the human infra-renal aorta

The role of vessel taper on the distribution of atherosclerotic lesions was examined in 11 photographs of human infra-renal aortas, aged 42-76. The aortas, opened anteriorly and pinned flat with the luminal surface facing up, were analysed using Mocha Imaging software. The circumference was measured at intervals of 10 mm and fitted with a third order polynomial function. Taper was calculated for three segments within each aorta as the angle produced by the slope of the decrease in circumference with length. The percent surface area covered by fatty streaks correlated strongly to the coefficients of the polynomial function, while the raised lesions showed a significant increase with an increase in taper angles in the different segments. The results suggest taper plays a role in the distribution of both fatty streaks and raised lesions, however, the nature of the cause and effect remains to be determined.

Women's health as a paradigm for understanding factors that mediate disease

Women's health research provides an opportunity to focus on the mechanisms underlying health and disease in both men and women. We propose that differences in risk between men and women and among individual women are primarily determined by biologic factors, such as sex steroid hormone metabolism, anatomy, immunologic function, genetic influences, and the effects of reproduction, interacting with external influences, such as psychologic development, sociocultural environment, and economic status. We provide examples whereby a comparison of disease frequencies between men and women and among women allows a focus on underlying mechanisms of disease. We then demonstrate the importance of posing questions about the genesis of differences in disease frequency.

Wall shear stress and early atherosclerotic lesions in the abdominal aorta in young adults

OBJECTIVES

To study the correlation between wall shear stress and early atherosclerotic lesions in the abdominal aorta.

DESIGN

Blinded histomorphometric studies. Comparison with in vitro data.

MATERIALS

Abdominal aortic haemodynamics were simulated in a realistic pulsatile flow model. Abdominal aortas from 10 young adults with no signs of atherosclerotic disease were obtained during autopsy.

METHODS

Quantitative wall shear stresses were measured at rest and exercise in one suprarenal and two infrarenal positions using laser Doppler anemometry. Intimal thickening indices were measured blindly at the corresponding locations using histomorphometric methods, and compared to wall shear stress variables using linear regression analysis.

RESULTS

Intimal thickness index increased significantly with age. Intimal thickness index was significantly lower in the suprarenal than the infrarenal aorta, and higher at the distal posterior vessel wall compared to the anterior wall. Intimal thickness index correlated significantly with mean, minimum and oscillating wall shear stresses measured at rest.

CONCLUSION

Intimal thickness in the undiseased abdominal aorta correlated significantly with mean, minimum and oscillating wall shear stresses at rest measured in a pulsatile flow model. No correlations were found with maximum shear stress parameters. Exercise changed the local wall shear stresses away from the characteristics associated with intimal thickness index.

In vivo wall shear stress measured by magnetic resonance velocity mapping in the normal human abdominal aorta

OBJECTIVE

To apply a new non-invasive method for quantification of in vivo wall shear stress (WSS) by magnetic resonance (MR) FAcE velocity mapping and measure WSS in the human abdominal aorta.

DESIGN

Prospective, open study.

MATERIAL

Six volunteers.

METHODS

MR FAcE velocity method was developed for measurements of mean, maximum, minimum WSS and oscillating shear index (OSI) values at the anterior and posterior walls of suprarenal and infrarenal abdominal aorta.

RESULTS

The mean, maximum and minimum WSS values were 0.63/0.28, 4.07/2.72 and -0.71/-1.00 N/m2, respectively, in the suprarenal/infrarenal aorta. The mean WSS was 0.35 N/m2 (p < 0.001) and the maximum WSS was 1.36 N/m2 (p < 0.0001) lower in the infrarenal aorta than in the suprarenal aorta. Mean, maximum minimum WSS and OSI values in the infrarenal position differed (p < 0.01) between the anterior and posterior walls.

CONCLUSION

WSS can be determined in vivo by MR FAcE velocity technique. Since the lowest WSS values were measured in the infrarenal, posterior blood-to-wall interface, the theory of more pronounced atherosclerosis development in low and oscillating WSS domains was not contradicted by the results of the present study.