Innovators in atherosclerosis research: A historical review

Journal Pre-proof Innovators in atherosclerosis research: A historical review

L. Maximilian Buja PII:

S0167-5273(19)35803-6

DOI:

https://doi.org/10.1016/j.ijcard.2020.02.016

Reference:

IJCA 28346

To appear in:

International Journal of Cardiology

Received date:

20 November 2019

Revised date:

23 January 2020

Accepted date:

6 February 2020

Please cite this article as: L.M. Buja, Innovators in atherosclerosis research: A historical review, International Journal of Cardiology(2018), https://doi.org/10.1016/ j.ijcard.2020.02.016

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Journal Pre-proof Innovators in Atherosclerosis Research: A Historical Review

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L. Maximilian Buja, MD Professor of Pathology and Laboratory Medicine Distinguished Teaching Professor McGovern Medical School The University of Texas Health Science Center at Houston (UTHealth) Chief, Cardiovascular Pathology Texas Heart Institute Houston, Texas

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Revisions in Red

Journal Pre-proof Abstract This review presents a retrospective analysis of the significance of the contributions of pathologists and kindred investigators in the latter half of the twentieth century to the advancement of understanding of atherosclerosis, a major disease and affliction of humankind. These outstanding investigators contributed importantly to the development of a large body of evidence encompassing populationbased autopsy studies, experimental animal studies and cell biological investigations that, coupled with

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insights from epidemiological studies, serve as the underpinning for the current dominant response to

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injury theory of atherogenesis. Their collective contributions have been highly meritorious and will

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remain seminally important into the future.

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Key Words: atherosclerosis, pathology, vascular biology, cardiovascular pathology

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Word Count (excluding references): 3437

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“The fundamental law should be engrained that the starting point of all treatment is in a knowledge of the natural history of a disease.” William Osler. The Reserves of Life. St. Mary’s Hosp Gaz 1907;13:95-98. “There are two essential factors in arterio-sclerosis – the quality of the tubing and the way it is treated.” William Osler. An Address of High Blood Pressure: Its Associations, Advantages, and Disadvantages. Brit Med J 1912;2:1733-7. “Longevity is a vascular question.” Martin CF. Osler as a clinician and teacher. Can Med Assoc J July, 1920;82-6.

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Introduction

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In the twentieth century, atherosclerosis research became scientifically rigorous and yielded a

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comprehensive analysis of atherosclerotic disease (1-4). As a result, atherosclerosis is now known to be

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an inflammatory and immunologically driven response of the arterial wall to multifactorial repetitive injury (3). This historical review focuses on the development of the substantial evidence in support of

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this construct and the cadre of pathologists and kindred investigators, active in the latter half of the

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twentieth century, who made major contributions to this process of discovery. Inevitably, others who have made noteworthy contributions to atherosclerosis research have not been included since this

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review is based on the influence exerted by the work of the selected investigators on the author’s

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understanding and research in cardiovascular pathology (see Personal Perspective in Supplement). The highlighted investigators were instrumental in the development of academic centers of excellence in atherosclerosis research in the United States and Canada, and they contributed to the advancement of atherosclerosis research nationally and internationally leading to the formation of the International Atherosclerosis Society (IAS) and affiliated organizations, including the Canadian Atherosclerosis Society (CAS) and the Council on Arteriosclerosis, Thrombosis and Vascular Biology (CATVB) of the American Heart Association (AHA). The review focuses on the contributions of these pathologists and allied investigators on the development of a comprehensive body of knowledge of the pathology and pathogenesis of atherosclerosis and its clinical consequences of coronary heart disease, stroke and

Journal Pre-proof peripheral arterial disease. (Table 1). (See the Supplement biographies and obituaries of the investigators and for supplemental references.) (Photographs of the leading pathologists are shown in Supplement Figure 1).

Beginnings There is a long record of autopsy studies documenting the very common occurrence of arteriosclerosis

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of the aorta and its distributing branches in humans. However, coherent concepts of pathogenesis only

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started to develop in the middle of the 19th century (2, 3). Experimental studies of atherosclerosis in

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animals began in the early 1900s, including the work of Nikolai Anitschkow, who identified cholesterol as the important dietary factor leading to the formulation of the lipid hypothesis of atherosclerosis (1,

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5).

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Epidemiological Studies

For many years, however, atherosclerosis generally was regarded to be an inevitable consequence of

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aging, and its importance as the substrate for morbidity and mortality in populations poorly defined (1).

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This viewpoint began to change with the advent of epidemiological studies which were begun in the

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1940ies. These epidemiological studies included efforts conducted by Dr. Jeremiah Stamler, who is credited with introduction of the concept of “risk factors” for cardiovascular disease (6), Ancel Keys and his Seven Countries Study (7), and the Framingham Heart Study under the sequential leadership of Dr. Gilein Meadors, Dr. Thomas Dawber and Dr. William Kannel (8). However, heightened attention of the medical establishment and general public regarding the potential epidemic of premature atherosclerosis and its likely morbid consequences was triggered by the report of autopsies documenting lesions of established atherosclerosis (atherosclerotic plaques) in the coronary arteries of casualties from the Korean Conflict; these studies were conducted by pathologists at the Armed Forces Institute of Pathology (9) This work raised major questions regarding the natural

Journal Pre-proof history of atherosclerosis, its onset and progression, in different regions of the vascular system, and the susceptibility to its occurrence in different populations. The challenge of addressing these important questions regarding a disease process with major public health implications was taken up by the pathologists who are featured in this review. Population-Based Pathology Studies The pathobiological basis for the epidemiological findings was addressed in three major population-

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based autopsy studies which yielded important information regarding the natural history of

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atherosclerosis. Beginning in the 1950ies, a focus on atherosclerosis was started in the department of

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pathology at the Louisiana State University (LSU) School of Medicine (SOM) due to the leadership of the then department chairman, Dr. Russell Holman (10). In the 1960ies, the International Atherosclerosis

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Project (IAP), also known as the Geographic Pathology of Atherosclerosis Study (GPAS), was initiated

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with the goal of collecting and analyzing specimens obtained at autopsy in several countries with different prevalence of clinical cardiovascular disease (11, 12). Dr. Jack Strong and Dr. Henry McGill

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were two pathologists in the department of pathology at the LSU SOM who lead the design and conduct

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of the IAP/GPAS, with their department serving as the repository for the specimens (11, 12). The

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IAP/GPAS study demonstrated major differences in occurrence of atherosclerosis in various geographic populations and linked pathology in the vessel wall to characteristics of these populations (11, 12). Interrelationships between fatty streaks as potential precursor lesions and lesions of established atherosclerosis were established (Figure 1). Links between risk factors and the prevalence and severity of atherosclerosis in different populations also were established. Stemming from this work, Dr. Strong is credited with discovering the link between cigarette smoking and atherogenesis (13). Another major population-based investigation is the Bogalusa Heart Study (BHS) lead by Dr. Gerald Berenson – a study which documented risk factors and pathological vascular changes in youths (14, 15). Observations made by Dr. Berenson and colleagues, including Dr. Strong, clearly showed that

Journal Pre-proof predisposition to adult heart disease, atherosclerosis, coronary heart disease, and essential hypertension begins in childhood, with anatomic changes documented to occur by 5 to 8 years of age (14, 15). Dr. Gerald Berenson received his medical degree and started his career at Tulane University SOM and then joined LSU SOM and worked there for 37 years before returning to Tulane in 1991 followed by appointment as a research professor at LSU in 2015. Dr. Berenson was a cardiologist with a strong interest in pathology leading to his engagement with a cadre of collaborating pathologists. He

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named his study after his birthplace, Bogalusa, Louisiana.

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The Pathological Determinants of Atherosclerosis in Youth study (PDAY) is the third manor population

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autopsy study started in the latter 20th century. Dr. Robert Wissler was instrumental in the design and

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launch of the PDAY study (16, 17). Dr. Jack Strong and Dr. Henry McGill were involved in this study as well. Dr. Robert Wissler and Dr. Seymour Glagov, his colleague, were leaders of a major center of

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atherosclerosis research in the pathology department of the University of Chicago SOM. Prior to the

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launch of PDAY, Dr. Wissler contributed outstanding research on the experimental pathobiology of atherosclerosis including proof of concept for regression of established atherosclerotic disease (18). Dr.

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Glagov specialized in quantitative morphological studies of human atherosclerotic arteries (19). Over

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the last 30 years, the PDAY investigators have generated important insights as to how the physicochemical components of risk factors actually interact with the arterial wall to generate atherosclerotic lesions (see supplemental references). Pathology of Atherosclerotic Lesions The population based autopsy studies provided material for detailed characterization and classification of different types of lesions found in the aorta and its distributing branches including the coronary arteries. This this work was facilitated by methodological advances in special stains for light microscopic histology, electron microscopy and lipid biochemistry (2). Dr. M. Daria Haust was a major contributor to

Journal Pre-proof the characterization of atherosclerotic lesions (20-22). Dr. Haust was the founding president of the IAS and has been a stalwart of the IAS and the CAS. After training at Queen’s University in Kingston, Ontario, Canada, Dr. Haust’s professional career has been with the department of pathology at the University of Western Ontario, London, Ontario, Canada. Dr. Haust’s early papers were with two other noteworthy pathologists, Dr. Robert More and Dr. Henry Movat (20). Dr. Haust conducted detailed histological and electron microscopic analysis which documented morphological features of early lesions (lesions of

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inception), identified as fatty dots and streaks, gelatinous elevations and microthrombi; advanced

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lesions, termed atherosclerotic plaques, and complicated lesions with secondary degenerative changes

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of calcification, ulceration and fissures, thrombosis and hemorrhage (21). Further characterization of atherosclerotic lesions came from biochemical studies of lesion composition, including the systematic

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work of Professor Elspeth Smith (23). Dr. Haust also confirmed the conclusion of Dr. Berensen that

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atherosclerosis is a pediatric problem (14, 15, 22).

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From 1985 to 1995, taking all information available at the time, an expert consensus panel of the AHA, led by Dr. Herbert Stary from LSU SOM, published and subsequently refined a lesion classification

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scheme for early and advanced lesions, and their interrelationships (Supplement Figures 2 and 3) (24).

(25).

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Interpretation of the nature and interrelationships of vascular lesions is a subject on ongoing interest

Experimental Animal Studies After a hiatus following the pioneering work of Ignatowski and Anitschkow, a renewed interest developed in the use of experimental animal models to study the pathobiology of atherosclerosis. Many investigators have conducted research using models involving dietary lipid manipulation (1-3). Dr. Robert Wissler, Dr. Draga Vesselinovitch and colleagues at the University of Chicago were leaders in the field of experimental atherogenesis, Wissler and Vesselinovitch established proof of concept for

Journal Pre-proof regression of established atherosclerotic disease (18). The potential for regression of coronary atherosclerosis in humans subsequently was established (26). These findings warranted a significant revision of the natural history construct developed in the GPAS study (Figure 2). Subsequent work has characterized animal models with spontaneous genetic mutations, particularly the Watanabe heritable hyperlipidemic (WHHL) rabbit (27, 28). Nowadays, gene deletion technology has resulted in the production of a variety of transgenic animal models closely mimicking various human

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lipoprotein disorders (28).

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Pathogenesis of Atherosclerosis

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Dr. Earl P. Benditt and Dr. Russell Ross made the pathology department at the University of Washington

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into a center for innovative research in atherosclerosis. Dr. Benditt was a medical graduate of Harvard

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Medical School who began his career at the University of Chicago before becoming chair of pathology at the University of Washington in 1957. He is noted for his innovative work in a number of areas including

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aging, atherosclerosis and amyloidosis. Dr. Benditt certainly was an original thinker leading to

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exploration of the infectious etiology and alternative pathogenesis of atherosclerosis (29, 30). Dr. Ross was a dentist with a PhD in experimental pathology who along with his colleague Dr. John Glomset

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developed a conceptual framework for atherogenesis, first proposed as the response to injury hypothesis (2, 31, 32).

It is noteworthy that these two pathologists working at the same institution championed different concepts of atherogenesis: Ross, the response to injury hypothesis with a focus on the primacy of endothelial injury and Benditt, the monoclonal hypothesis with a primacy on proliferation of SMC clones (2-4). Heterogenity of SMC in different vascular beds has been shown along with supportive evidence for the occurrence of SMC clones (33). However, the relevance of clonality in atherogenesis has not been

Journal Pre-proof established. The general view of the scientific community is that the preponderance of the evidence supports the response to injury construct (2-4). Vascular Cell Biology A new and innovative approach to atherosclerosis research was achieved by the development and application of modern vascular biology with a focus on mechanistic studies of endothelial cells and

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vascular smooth muscle cells. Investigators at the Brigham and Women’s Hospital of Harvard Medical School in Boston were leaders in this field. Dr. Ramzi Cotran was the chair of pathology at the Brigham

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and Women’s Hospital and Children’s Hospital of Harvard Medical School and one of the foremost

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academic pathologists of his generation. Dr. Cotran was an excellent renal pathologist. In 1979, Dr.

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Cotran became the senior author of the renowned textbook, Robbins Pathological Basis of Disease. Dr.

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Cotran was a catalyst and major force in establishing the experimental pathology discipline of contemporary vascular biology. He and his colleagues perfected methods for in vitro culture of

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endothelial and vascular smooth muscle cells (34). These culture systems then were utilized to investigate the roles of adhesion molecules and cytokines in regulating function of endothelial and

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vascular smooth muscle cells (35, 36). The work of Dr. Cotran and his colleagues provided a solid

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underpinning for understanding mechanisms responsible for phenomena observed during the progression of atherogenesis in experimental animals and man. His collaborator, Dr. Michael Gimbrone, subsequently established an experimental basis for the role of hemodynamic alterations in perturbation of endothelial cells (37). Another Boston contributor to the advancement of vascular cell biology was Dr. Judah Folkman, surgeon-in-chief at the Children’s Hospital in Boston, who identified the importance of angiogenesis in pathological processes, including tumor angiogenesis, bolstered by experimental evidence he obtained in collaboration with Dr. Cotran and his colleagues (38, 39). developed the concepts of tumor

Journal Pre-proof angiogenesis and anti-angiogenic drugs for cancer treatment (38). In collaboration with Drs. Cotran and Gimbrone, he obtained experimental evidence for his hypothesis (39). Ongoing research is addressing the complexities of tumor angiogenesis and anti-angiogenic therapy (see supplemental references). The legacy of Dr. Cotran and Dr. Folkman lives on in Boston in two subsequent generations of cardiovascular pathologists, including Dr. Michael Gimbrone and Dr. Richard (Rick) Mitchell (37, 40).

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Relationship of Atherosclerotic Lesions to Clinical Cardiovascular Disease The considerable body of descriptive observations regarding atherosclerosis provided the framework for

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pathologists to develop a synthesis of the natural history of atherosclerotic disease in different

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components of the arterial system, including the coronary arteries. Applying a morphometric approach,

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Dr. Seymour Glagov from the University of Chicago discovered that coronary arteries undergo

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remodeling resulting in compensatory preservation of luminal patency during intermediary stages in the progression of coronary atherosclerosis (41). This is now known as the “Glagov phenomenon or effect”.

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The Glagov phenomenon is considered to exert an important influence on the natural history and

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clinical expression of coronary atherosclerotic disease. Pathologists also analyzed coronary atherosclerosis in relationship to the development of acute cardiac

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clinical events, now known as acute coronary syndromes (ACS). This line of investigation led to the elucidation of the pivotal role of acute alterations in coronary arteries, including intramural hemorrhage as well as plaque fissures and capsule ruptures, with superimposed thrombosis as the major cause of acute myocardial infarction and sudden cardiac death (42, 43). Beginning in the early 20th century, several investigators made observational reports regarding features of culprit lesions, including Clark, Koch, Friedman, Constantinides, Wartman, Patterson and Winternitz (43). In 1981, this author confirmed that recent occlusive coronary thrombosis with associated plaque alterations is strongly linked to acute transmural acute myocardial infarction whereas acute subendocardial myocardial

Journal Pre-proof infarction often occurs without coronary thrombosis in relationship to other causes of poor coronary perfusion (44). The acute coronary lesions related to coronary thrombosis came to be designated as vulnerable or unstable plaques (43). In the 1980ies and 1990ies, Dr. Michael Davies from England and Dr. Erling Faulk from Denmark produced systematic studies that were instrumental in advancing the construct of the vulnerable plaque (43). Dr. Renu Virmani and colleagues from the CVPath Institute outside of Washington DC published extensive analyses of the relationship of coronary lesions to sudden

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cardiac death (42). Virmani and colleagues characterized the typical lesion with capsule rupture as a

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plaque with a fibrous capsule less than 65 micrometers in thickness and a large lipid-rich core, the thin

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cap fibroatheroma (TCFA) (42, 43). Dr. Peter Libby from the Brigham and Women’s Hospital and

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Harvard University provided synthetic analyses of mechanisms linking coronary lesions to ACS, (45,46). Two key processes were identified that are now considered basic mechanisms for the growth of

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advanced plaques: 1) outward abluminal expansion of the arterial wall (the Glagov phenomenon), and 2)

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subclinical plaque rupture of hemodynamically insignificant lesions, with incorporation of the mural thrombus into the lesion. Subsequently, a new plaque disruption can lead to occlusive thrombosis and

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sudden cardiac death or acute myocardial infarction. Virmani et al. developed a modification of the AHA

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classification to include the vulnerable plaque in the natural history of atherosclerotic disease (Table 2) (42). This is also reflected in a modification of the GPAS natural history construct (Figure 2). Status of Atherosclerosis Research in the late 20th Century and Now The comprehensive array of twelve articles published in a 1988 Festschrift honoring Dr. Robert Wissler provide documentation of insights into understanding of atherosclerosis obtained from major components of atherosclerosis research in the late 20th century (47). These articles encompass epidemiologic studies; studies of the role of lipids; human autopsy studies, both descriptive and mechanistic; animal models, and pathobiology of vascular smooth muscle cells. Contributing

Journal Pre-proof investigators reflected the global scope of the research, and included Dr. Stamler, Dr. Benditt and Dr. Berenson. Since 1988 and 2019, atherosclerosis research has provided much more detailed and specific information regarding the roles of inflammation and innate and acquired immunity in atherosclerosis and the molecular biology of mediators of these processes (3). Important confirmatory evidence for the role of inflammation in atherogenesis has come from the CANTOS trial conducted by Dr. Paul Ridker and

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collaborators. Results of this clinical trial showed significant reduction in clinical cardiovascular events in

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patients treated with the interleukin-1β inhibitor, canakinumab (48). This is a major outcome from the

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symbiosis of translational research and clinical trials confirming the importance of inflammation in

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atherogenesis in man and leading to new avenues for prevention and treatment of atherosclerotic

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diseases (48).

Recently, a link has been discovered between clonal hematopoiesis and increased cardiovascular risk (3,

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4). The expansion of myeloid cell clones in geriatric bone marrow (so-called clonal hematopoiesis of indeterminate potential or CHIP) has been correlated not only with an increased risk of hematologic

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malignancy but also with atherosclerotic disease risk (3, 4). This discovery provides a new and previously

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unsuspected link between systemic inflammation and aggravation of atherosclerosis. The relationship may be mediated by the selective expansion in inflammatory monocyte-macrophage lineages producing mediators such as interleukin-1 (IL-1). These studies of clonality may eventually provide the basis for a synthesis of the Ross and Benditt constructs of atherogenesis. Another major advance in the 21st century has been the application of contemporary genetics (next generation sequencing and whole genome analysis) to determine the interaction of genetic determinants with environmental factors in cardiovascular risk (49, 50). The changing focus of

Journal Pre-proof atherosclerosis research can be seen by comparison of the content of the 1988 Wissler Festschrift with the Compendium on Atherosclerosis published in 2016 (50). Today, the response to injury construct of atherogenesis is more accurately and more appropriately designated as a theory rather than a hypothesis. According to the Merriam Webster Dictionary, a hypothesis is a tentative assumption made in order to draw out and test its logical or empirical consequences, whereas a theory is a plausible or scientifically acceptable general principle or body of

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principles offered to explain phenomena. Scientific theories are distinguished from hypotheses, which

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of the way nature behaves under certain conditions.

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are individual empirically testable conjectures, and from scientific laws, which are descriptive accounts

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Conclusion

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The large scale and systematic pathology studies led by Drs. Strong, McGill, Berenson, and Wissler remain crucially important for characterizing the natural history of atherosclerosis in humans.

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Morphometric information was provided by Glagov and detailed characterization of lesions by Haust.

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The contemporanious epidemiological studies provided information regarding risk factors predisposing to clinical cardiovascular conditions whereas the pathology studies provided information regarding the

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actual underlying disease process. They are complimentary. The human pathology studies also have provided crucial confirmation of the importance of factors involved in atherogenesis which were brought to light from the experimental animal studies of Wissler and many others, the mechanistic studies of cultured vascular cells of Cotran and many others, and the experimental work of Folkman. This review confirms the great importance of medical autopsies in observational studies either to stimulate or confirm experimental mechanistic studies in the pathology laboratory (4). Together these modes of investigation provide a substantial body of coherent evidence confirming the response to injury theory of atherogenesis. The importance of coronary artery plaque rupture, fissure, and

Journal Pre-proof thrombosis in the pathogenesis of clinical cardiac illness was elucidated by the combined efforts of a number of investigators, including Drs. Davies, Falk, Libby and Virmani. Thus, pathologists working during the latter 20th century collectively achieved basic insights into the pathobiology of a major human disease and affliction, and these insights have served as the basis for improved prevention and clinical interventions resulting in substantial reduction in the morbidity and mortality from atherosclerosis and its clinical manifestations. The work of these pathologists have

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provided the framework for ongoing research into linking basic knowledge of atherosclerosis to progress

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in treatment and prevention of the disease.

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Personal Perspective

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I was stimulated to write this review upon learning of the recent passage of Dr. Jack Strong, a

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pathologist I knew and admired (see supplemental references). I had a particular interest in the work done at LSU SOM, founded in 1931. I am a graduate of Tulane University School of Medicine, a SOM

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with a long history of excellence in cardiovascular medicine and surgery since its founding in 1834.

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Faculty of the two New Orleans medical schools have made complimentary and lasting contributions to cardiovascular medicine.

While a faculty member at the University of Texas Southwestern Medical Center, I came to know and be guided by Dr. Robert Wissler. Therefore, I was honored to be selected to be an organizer and co-editor with Dr. Seymour Glagov of the Festschrift published in tribute to Dr. Robert Wissler on the occasion of his retirement (49). Regarding Dr. Cotran, he was a friend and great role model for me and many others. In 2000, I had the honor to recognize Dr. Cotran and present posthumously to his widow the Ben Qurrah Award from the Arab American Medical Association, Houston Chapter.

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Journal Pre-proof 31. Ross R, Glomset JA. Atherosclerosis and the arterial smooth muscle cell: Proliferation of smooth muscle is a key event in the genesis of the lesions of atherosclerosis. Science. 1973 Jun 29;180(4093):1332-9. PMID: 4350926 32. Ross R, Glomset J, Harker L. Response to injury and atherogenesis. Am J Pathol. 1977 Mar;86(3):67584. PMID: 842616

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(Paris). 1998 Mar;46(3):164-70. PMID: 9769911 37. Gimbrone MA Jr, García-Cardeña G. Endothelial Cell Dysfunction and the Pathobiology of Atherosclerosis. Circ Res. 2016 Feb 19;118(4):620-36. doi: 10.1161/CIRCRESAHA.115.306301. PMID: 26892962 38. Folkman J. Tumor angiogenesis: therapeutic implications. New Eng J Med 1971;285:1182-1186. PMID: 4938153

Journal Pre-proof 39. Gimbrone MA Jr, Leapman SB, Cotran RS, Folkman J. Tumor angiogenesis: iris neovascularization at a distance from experimental intraocular tumors. J Natl Cancer Inst. 1973 Jan;50(1):219-28. No abstract available. PMID: 4692862 40. Mitchell RN. Blood vessels. In: Kumar V, Abbas AK, Aster JC, editors. Robbins and Cotran Pathologic Basis of Disease, ninth edition. Philadelphia; Elsevier Saunders, 2015, pp.483-522. 41. Glagov S, Weisenberg E, Zarins CK, Stankunavicius R, Kolettis GJ. Compensatory enlargement of

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45. Libby P. Mechanisms of acute coronary syndromes and their implications for therapy. N Engl J Med. 2013;368(21):2004–2013. doi:10.1056/NEJMra1216063 46. Libby P, Pasterkamp G, Crea F, Jang IK. Reassessing the Mechanisms of Acute Coronary Syndromes. Circ Res. 2019;124(1):150–160. doi:10.1161/CIRCRESAHA.118.311098 47. Pathobiology of atherosclerosis: concepts and perspectives. A festschrift in tribute to Robert W. Wissler, PhD, MD. Arch Pathol Lab Med. 1988 Oct;112(10):973-1070. PMID: 3052356

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Journal Pre-proof Figure Legends Figure 1. Diagrammatic concept of the natural history of human atherosclerosis. From: Strong JP, Eggen DA, Oalmann MC. The natural history, geographic pathology, and epidemiology of atherosclerosis. In: Wissler RW, Geer JC, editors. The Pathogenesis of Atherosclerosis. Baltimore; The Williams and Wilkins Co, 1972, pp 20-40. (Figure 2.1, p 21)(Modified from McGill, H.C., Jr., Geer , J . C., and Strong, J.P. Natural history of human atherosclerotic lesions. In Atherosclerosis and Its Origin, edited by Sandler, M., and Bourn e,G. H., p. 42. New York , Academic Press, 1963.) With permission. Figure 2. The natural history of atherosclerosis construct modified by the author to include the concept of the potential for regression of established atherosclerotic lesions and the concept of the unstable/vulnerable plaque with associated thrombosis.

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Journal Pre-proof Author Agreement As sole author, I declare that the work described has not been published previously that it is not under consideration for publication elsewhere, and that, if accepted, it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright-holder. The work was funded entirely by local resources.

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I have no conflicts of interest related to the submission or publication of this article.

Journal Pre-proof Table 1. Major Lines of Evidence Acquired by Innovative Investigators Regarding the Pathology and Pathogenesis of Atherosclerosis Epidemiology Risk factor analysis (J Stamler) Seven Countries Study (A Keys)

Population-Based Pathology Korean Conflict Casualties (W Enos) International Atherosclerosis Project/Geographic Pathology of Atherosclerosis Study (J Strong, H McGill) Bogalusa Heart Study (G Berenson) Pathological Determinants of Atherosclerosis in Youth (R Wissler)

Framingham Study (G Meadors, T Dawber, W Kannel)

Pathology of Atherosclerotic Lesions Cytology and ultrastructure of lesions (MD Haust) Morphometrics of Aorta and Coronary Arteries (S Glagov) Unstable/vulnerable plaque (M Davies, E Faulk) Updated classification of atherosclerotic lesions and relationship to clinical events (R Virmani)

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Experimental Animal Studies Diet-induced models Genetic-based models (Multiple investigators)

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Pathogenesis Response to Injury Theory (R Ross) Hemodynamics (M Gimbrone) Roles of inflammation and innate and acquired immunity (P Libby, P Ridker) Monoclonal construct (E Benditt)

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Vascular Cell Biology Endothelial cells and smooth muscle cells (R Ross, R Wissler) Adhesion molecules and cytokines (R Cotran, M Gimbrone) Angiogenesis (J Folkman)

Journal Pre-proof Table 2. Modified AHA Classification Based on Morphological Description*! Description Thrombosi

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Journal Pre-proof Nonatherosclerotic intimal lesions Intimal thickening

The normal accumulation of smooth muscle cells (SMCs) in the intima in the absence of lipid or macrophage foam cells

Absent

Intimal xanthoma, or “fatty streak”

Luminal accumulation of foam cells without a necrotic core or fibrous cap. Based on animal and human data, such lesions usually regress.

Absen

SMCs in a proteoglycan-rich matrix with areas of extracellular lipid accumulation without necrosis

Absent

Luminal thrombosis; plaque same as above

Thrombus mostly mural and infrequently occlusive

Progressive atherosclerotic lesions Pathological intimal thickening Erosion

Plaque rupture Calcified nodule Fibrocalcific plaque

Absent Thrombus mostly mural and infrequently occlusive

A thin fibrous cap infiltrated by macrophages and lymphocytes with rare SMCs and an underlying necrotic core

Absent; may contain intraplaque hemorrhage/fibrin

Fibroatheroma with cap disruption; luminal thrombus communicates with the underlying necrotic core

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Thin fibrous cap atheroma

Well-formed necrotic core with an overlying fibrous cap Luminal thrombosis; plaque same as above; no communication of thrombus with necrotic core

Eruptive nodular calcification with underlying fibrocalcific plaque

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Erosion

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Fibrous cap atheroma

Collagen-rich plaque with significant stenosis usually contains

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large areas of calcification with few inflammatory cells; a necrotic core

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may be present.

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*From: Virmani R, Kolodgie FD, Burke AP, Farb A, Schwartz SM. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Arterioscler Thromb Vasc Biol. 2000;20(5):1262– 1275. doi:10.1161/01.atv.20.5.1262. With permission.

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!Compare with AHA Classification and Update, Supplement Figures 2 and 3

Thrombus usually occlusive Thrombus usually nonocclusive Absent

Journal Pre-proof Highlights In the later 20th century, pathologists and allied investigators made major contributions to atherosclerosis research. Their innovative research involved population-based autopsy studies, experimental animal studies and mechanistic in vitro work. The research provided the pathobiological basis for the roles of lipids, other risk factors, and inflammation. The research also provided the core evidence for the response to injury theory of atherosclerosis.

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The research also serves as the rationale for therapies, including lipid-lowering and new antiinflammatory drugs.

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