Death of smooth muscle cells and expression of mediators of apoptosis by T lymphocytes in human abdominal aortic aneurysms

Increased expression of phosphorylated c-Jun amino-terminal kinase and phosphorylated c-Jun in human cerebral aneurysms: role of the c-Jun amino-terminal kinase/c-Jun pathway in apoptosis of vascular walls

OBJECTIVE

Vascular remodeling via apoptotic mechanisms is an important factor in vascular diseases. c-Jun amino-terminal kinase (JNK) is a member of the mitogen-activated protein kinase family and initiates apoptosis mainly via phosphorylation of the c-Jun transcription factor. We performed this study to clarify the roles of the JNK/c-Jun pathway and apoptosis in the pathogenesis of cerebral aneurysms.

METHODS

Cerebral aneurysms from 12 patients and control vessels from 5 patients were studied. We analyzed the expression of phosphorylated JNK and phosphorylated c-Jun in cerebral aneurysms by using immunohistochemical methods.

RESULTS

Immunoreactivity for phosphorylated JNK and phosphorylated c-Jun was increased in the vascular walls of the cerebral aneurysms studied. Immunoreactivity for single-stranded deoxyribonucleic acid (a marker of deoxyribonucleic acid damage) was also increased in aneurysmal tissue, compared with control vessels, and was colocalized with that for phosphorylated JNK and phosphorylated c-Jun in smooth muscle cells.

CONCLUSION

These observations may lead to better understanding of the role of the JNK/c-Jun pathway in the development of cerebral aneurysms and to new strategies for treatment.

T(H)2 predominant immune responses prevail in human abdominal aortic aneurysm

T lymphocytes localize within lesions of two diametrically opposed expressions of atherosclerosis: stenosis-producing plaques and ectasia-producing abdominal aortic aneurysm (AAA). T(H)1 immune responses appear to predominate in human stenotic lesions. However, little information exists regarding the nature of the T-cell infiltrate in AAAs. We demonstrate here that AAAs predominantly express T(H)2-associated cytokines and correspondingly lack mediators associated with the T(H)1 response as determined by Western blot and immunohistochemical analysis. In particular, aneurysmal tissue expressed interleukin (IL)-4, IL-5, and IL-10, cytokines not or only faintly detected in nondiseased tissue or stenotic atheroma. In contrast, AAAs contained low levels of the T(H)1 characteristic cytokines IL-2 and IL-15, which are amply expressed in stenotic lesions. Notably, stenotic lesions, but not AAAs, contained mature forms of the interferon-gamma-inducing cytokines IL-12 and IL-18 as well as the IL-18-processing enzyme caspase-1. Moreover, aneurysmal tissue lacked the receptor for interferon-gamma, although both types of lesions contained this T(H)1-promoting cytokine. These findings suggest that the functional repertoire of T cells differs in stenotic and aneurysmal lesions, and provide a novel framework for understanding the mechanisms of these diametrically opposite expressions of atherosclerosis.

Increased medial TUNEL-positive staining associated with apoptotic bodies is linked to smooth muscle cell diminution during evolution of abdominal aortic aneurysms

Apoptosis has recently been identified as an important process in large vessel structural integrity. We examined whether the size of the abdominal aortic aneurysm might be associated with programmed cell death. We performed in situ labeling of the 3' ends of DNA fragments by apoptosis-associated endonucleases in 20 aneurysms, 10 controls with aortoiliac occlusive disease, and 4 controls with healthy aortas. Antibodies against a-smooth muscle actin were used to quantify smooth muscle cell alterations in the medial layer. Inflammatory cell characterization was made by using four monoclonal mouse antibodies (UCHL1, L26, PG-M1, and KP1). The results confirm the assumption that an apoptotic process may be of consequence for the loss of medial smooth muscle cells in the early evolution of an abdominal aortic aneurysm process.

Histological changes in canine aorta 1 year after stent-graft implantation: implications for the long-term stability of device anchoring zones

PURPOSE

To examine aortic histology 1 year after stent-graft implantation in a canine model as a means of assessing the durability of endograft fixation.

METHODS

Fourteen mongrel dogs each received 1 stent-graft and 1 bare stent placed endoluminally in the abdominal aorta. Eight animals were followed for 1 year, 3 for 4 to 8 weeks, and the remaining 3 for 24 to 48 hours. Aortic specimens were stained with hematoxylin-eosin, elastica-van Gieson, and Masson's trichrome and examined with light and electron microscopy and immunohistochemistry to identify smooth muscle cells (SMC), endothelialization, aortic wall ultrastructure, and changes at the device anchoring sites.

RESULTS

No dilatation or dissection was noted at any of the device anchoring sites. The aortic media at 1 year was remarkably decreased in thickness: 891 +/- 196 microm in the control tissue versus 388 +/- 70 microm for the proximal stent-grafted aorta and 457 +/- 148 microm for the bare-stented aortic segment. Other important histological features were reduced elastic lamellae in the stent-grafted aorta versus control (p<0.0001), increased SMC density in the stent-grafted aortic region (p<0.0001 versus control), and absence of inflammatory infiltrate. Complete neointimal covering and endothelialization of the luminal endograft surface were found. SMCs generally showed no ultrastructural features of necrosis.

CONCLUSIONS

Aortic stent-grafts induce distinctive histological changes in the aortic wall at 1 year, even when implanted in a healthy aorta. Although there is considerable medial elastin loss, an increased medial SMC density, an exuberant neointima, and a general absence of perigraft inflammation suggest an ongoing process of structural restoration at the device anchoring sites.

Human leukocyte antigen class II immune response genes, female gender, and cigarette smoking as risk and modulating factors in abdominal aortic aneurysms

OBJECTIVE

Aortic inflammation and the genes that regulate the immune response play an important role in abdominal aortic aneurysm pathogenesis. However, the modulating effects of such genetic and other environmental factors on the severity on aneurysm inflammation is not known. The objective of this study was to determine the influence of the human leukocyte antigen (HLA) class II genes, gender, and environmental factors on degree of abdominal aortic aneurysm tissue inflammation.

METHODS

Aneurysm specimens were obtained at the time of operation from 96 consecutive patients who underwent abdominal aortic aneurysm repair and were graded for degree of histologic inflammation. Multivariate analysis was used to determine the association of genetic and environmental factors with degree of inflammation and to determine the HLA-associated disease risk for aneurysm.

RESULTS

Active cigarette smoking and female gender were independently associated with high-grade tissue inflammation identified histologically (odds ratio [OR], confidence interval [CI]: 5.6, 1.6 to 19.3; and 6.0, 1.4 to 26.2, respectively), and a specific HLA allele (DR B1(*)01) was inversely associated with inflammation (OR, CI: 0.2, 0.04 to 0.7). Overall, the HLA-DR B1(*)02 and B1(*)04 alleles were significantly associated with disease risk, more than doubling risk for abdominal aortic aneurysm (OR, CI: 2.5, 1.4 to 4.3; and 2.1, 1.2 to 3.7, respectively).

CONCLUSION

Active cigarette smoking and female gender are significant disease-modulating factors associated with increased abdominal aortic aneurysm inflammation. In addition, the HLA class II immune response genes possess both disease modulating and disease risk properties, which may be useful in early aneurysm detection and surveillance.

Differential regulation of matrix metalloproteinase activities in abdominal aortic aneurysms

BACKGROUND

The increased synthesis of matrix metalloproteinases (MMPs) by aortic smooth muscle cells (SMCs) is thought to be involved in the etiopathogenesis of abdominal aortic aneurysms (AAAs), but the functional regulation and the activation states of these MMPs remain unclear. In this study, we assessed the expression levels and the functional regulation of several MMPs in the pathogenesis of AAAs.

METHODS

Human healthy aorta and AAA specimens were homogenized, and the proteolytic activities of MMP-2 and MMP-9 and of the macrophage metalloelastase (MMP-12) were assessed with zymography. Protein expression of MMP-1, MMP-12, membrane-type 1 MMP (MT1-MMP), tissue inhibitor of MMP 1 (TIMP-1), TIMP-2, TIMP-3, alpha-actin, and beta-actin was analyzed with electrophoresis on sodium dodecyl sulfate gels and immunoblotting.

RESULTS

MMP-1, MMP-9, and MMP-12 zymogen levels and proteolytic activities were increased in AAAs when compared with healthy aorta. A severe reduction in alpha-actin--positive vascular SMCs was observed in all the AAA specimens and was correlated with an increase in TIMP-3 but not TIMP-1 or TIMP-2 potential activities. Although pro--MMP-2 activity was decreased, the extent of activated MMP-2 remained unaffected in the AAAs. In accordance with this result, a highly activated MT1-MMP form was also observed in AAAs.

CONCLUSION

These data suggest that chronic aortic wall inflammation is mediated by macrophage infiltration, which may account for the destruction of medial elastin, as reflected by SMC down regulation, through increased levels of active MMP-1 and MMP-12. Moreover, altered MT1-MMP proteolytic turnover and differential regulation of TIMP expression in AAAs suggest that tight regulatory mechanisms are involved in the molecular regulation of MMP activation processes in the pathogenesis of AAAs.

Molecular signal transduction in vascular cell apoptosis

Apoptosis is a form of genetically programmed cell death, which plays a key role in regulation of cellularity in a variety of tissue and cell types including the cardiovascular tissues. Under both physiological and pathophysiological conditions, various biophysiological and biochemical factors, including mechanical forces, reactive oxygen and nitrogen species, cytokines, growth factors, oxidized lipoproteins, etc., may influence apoptosis of vascular cells. The Fas/Fas ligand/caspase death-signaling pathway, Bcl-2 protein family/mitochondria, the tumor suppressive gene p53, and the proto-oncogene c-myc may be activated in atherosclerotic lesions, and mediates vascular apoptosis during the development of atherosclerosis. Abnormal expression and dysfunction of these apoptosis-regulating genes may attenuate or accelerate vascular cell apoptosis and affect the integrity and stability of atherosclerotic plaques. Clarification of the molecular mechanism that regulates apoptosis may help design a new strategy for treatment of atherosclerosis and its major complication, the acute vascular syndromes.

Initial steps in the unifying theory of the pathogenesis of artery aneurysms

OBJECTIVES

The objective of this study was to investigate the changes in histology and proteolysis and the role of apoptosis in the development of peripheral artery aneurysms.

METHODS

Eighteen popliteal, 6 abdominal aortic, 10 iliac, 2 carotid, and 6 femoral artery aneurysm specimens were obtained from patients undergoing elective surgical repair. All were males with ages 48 to 93 (mean 71 years). Normal controls were obtained from patients matched for age, sex, and major risk factors. Vascular smooth muscle cells (VSMC), macrophages, T lymphocytes, and apoptosis-regulating molecules were detected immunohistochemically. Detection of apoptosis was by TUNEL assay. Proteolytic activity was determined by 10% gelatin gel zymography.

RESULTS

Paucity of VSMCs, increased amount of inflammatory infiltrate, and fragmentation of elastic lamellae were observed in aneurysmal tissues as compared to normal arteries (P < 0.02). There is increased gelatinolytic activity at 92, 84, 72, and 67 kDa in the aneurysmal tissues. There are fewer CD68+ macrophages and T cells in the media of controls than in the aneurysms (P = 0.01). Apoptosis is significantly high in aneurysm tissues (P < 0.01) and the degree of apoptosis was in the order AAA>FAA>PAA>IAA>CAA. There is increased expression of Bax, CPP-32, Fas, and p53 in PAA specimens as compared to normal popliteal arteries (P < 0.05).

CONCLUSIONS

These data confirm the apparent architectural disruption and loss of VSMCs that are hallmarks of aneurysm development, in peripheral artery aneurysms. Apoptosis and signaling molecules capable of initiating cell death may play a significant role in the pathogenesis of all aneurysms. Our data suggest a common etiology between the various types of aneurysms.

Mönckeberg's medial sclerosis and inorganic phosphate in uremia

Mönckeberg's medial sclerosis (MMS) is one of the characteristic calcified lesions of uremic artery disease and often exhibits osseous metaplasia. Although its pathogenic mechanism is largely unknown, MMS may contain two different pathologic processes: degenerative process leading to apoptosis or necrosis of medial smooth muscle cells and osteogenic process leading to formation of bone-like structures. It has long been known that calcification follows necrosis. Apoptotic/necrotic cells often release matrix vesicles or membranous cellular degradation products resulting from disintegration of the cells that frequently serve as the nidus of calcification. On the other hand, vascular cells may exhibit osteoblastic phenotype in vitro, and some of the markers for osteoblastic differentiation and noncollagenous proteins regulating mineralization have been demonstrated in calcified arterial lesions. As a possible etiologic factor inducing these two responses, hyperphosphatemia among various metabolic disturbances recognized in uremia may play an important role in the development of MMS in uremia.

The expression and localization of membrane type-1 matrix metalloproteinase in human abdominal aortic aneurysms

BACKGROUND AND OBJECTIVE

Matrix metalloproteinase-2 (MMP-2) degrades both fibrillar collagens and elastin. MMP-2 is secreted as a latent 72-kd proenzyme that must be proteolytically processed to the 62-kd active form. In our laboratory we demonstrated a significant increase of active, matrix-bound MMP-2 in abdominal aortic aneurysmal (AAA) tissue compared with nonaneurysmal aorta with arteriosclerotic occlusive disease and normal aortic tissue. This increase in active MMP-2 is considered to be important in aneurysm pathogenesis, but the mechanism of its activation in aortic tissue is unknown. Membrane type-1 MMP (MT-1 MMP) is known to be an activator of MMP-2. The purpose of this study was to determine MT-1 MMP expression and its involvement in pro-MMP-2 activation in human aneurysmal tissue.

METHODS

Infrarenal aortic tissue was obtained during the surgical repair of AAAs or the bypass of aortoiliac occlusive disease, or from nondiseased aorta, and the expression of MT-1 MMP messenger RNA was determined with Northern blot analysis. MT-1 MMP protein was determined with immunoblot and immunohistochemistry. The ability of aortic tissue to activate pro-MMP-2 was analyzed by incubating aortic tissue with exogenous radiolabeled pro-MMP-2.

RESULTS

MT-1 MMP messenger RNA and protein are increased in AAA (P <.05) compared with arteriosclerotic occlusive disease and normal aortic tissue. Immunohistochemical analysis localized MT-1 MMP to aortic smooth muscle cells and macrophages in aneurysmal tissue. AAA tissue demonstrated a greater capacity to activate exogenous pro-MMP-2 compared with atherosclerotic and normal aortic tissue (P <.05).

CONCLUSION

These studies demonstrate that MT-1 MMP is increased in AAA tissue and suggest that it may be important in AAA pathogenesis through its ability to activate pro-MMP-2

Apoptosis in atherosclerosis: pathological and pharmacological implications

Normal embryonic development, tissue differentiation and repair in the eukaryote requires a tightly regulated apoptosis, or programmed cell death. Apoptosis also plays an essential role in different pathological processes including atherosclerosis, in which it affects all cell types in the atherosclerotic lesion, including endothelial cells, vascular smooth muscle cells, and macrophages. During atherosclerosis progression, pro- and anti-apoptotic signals abound in the evolving lesion. Apoptosis limits the number of a particular cell type that accumulates in the lesion and slows down the overall progression of the lesion. On the other hand, it contributes to the production of unstable plaques. Many pharmacological agents used to treat cardiovascular and lipid disorders have pro- or/and anti-apoptotic effects. Pharmaceuticals that modulate apoptosis in specific types of cell can potentially serve as anti-atherogenic agents. However, to develop agents for clinical use requires a thorough knowledge of the pathophysiology of apoptosis in atheromatous lesions, a highly cell-specific process. Here we review our current understanding of the process to provide a background for future pharmacological research in the area.

Genetic similarity in inflammatory and degenerative abdominal aortic aneurysms: a study of human leukocyte antigen class II disease risk genes

PURPOSE

Clinically, abdominal aortic aneurysms (AAAs) display a spectrum of inflammation that extends from apparently noninflamed (degenerative) AAAs to the classic inflammatory variant. Genes encoded in the human leukocyte antigen (HLA) region are important in the development of both variants of AAA; however, their role in progression to the inflammatory variant is unknown. The purpose of this study was to compare HLA class II genes in patients with degenerative versus classic inflammatory AAAs and to quantify their impact as disease risk factors.

METHODS

Genotypes of the 12 major alleles of the HLA-DR B1 locus were determined in patients with degenerative (102) and inflammatory (40) AAAs who were compared with controls (118). Univariate and multivariate logistic regression analyses were used to determine allele distributions and to quantify disease risk.

RESULTS

Distribution of the HLA-DR B1 alleles was nonrandom and similar in both degenerative and inflammatory AAA groups compared with controls. The B1*02 and B1*04 alleles were enhanced in both degenerative (39.2% vs. 25.4%, P =.03; and 35.3% vs. 24.6%, P =.08 respectively) and inflammatory (47.5% vs. 25.4%, P =.01; and 32.5% vs. 24.6%, P =.09, respectively) AAAs compared with controls. The B1*02 and B1*04 alleles were associated with risk for both degenerative (odds ratio [OR] 2.2; 95% CI, 1.2-4.0; and OR 2.0; 95% CI, 1.1-3.7, respectively) and inflammatory AAAs (OR 3.7; 95% CI, 1.8-8.6; and OR 2.5; 95% CI, 1.1-6.1).

CONCLUSION

This study demonstrates that identical HLA alleles function as genetic risk factors for both inflammatory and degenerative AAAs. These results support the concept of a common, immune-mediated pathogenesis for AAAs that may be modulated by HLA-independent factors.

Examination of the apoptotic pathway and proteolysis in the pathogenesis of popliteal artery aneurysms

OBJECTIVES

to investigate the role of apoptosis, expression of death-promoting molecules and mediators of apoptosis in the development of popliteal artery aneurysms.

METHODS

ten popliteal artery aneurysm (PAA) specimens were obtained from patients undergoing elective surgical repair. Normal controls were popliteal arteries obtained from patients without PAA undergoing infrainguinal bypass surgery (n=8). Standard histochemistry techniques were used to assess elastic lamellae fragmentation and inflammatory infiltrate in PAA. Vascular smooth muscle cells (VSMC), macrophages, T lymphocytes, death-promoting molecules, CPP-32, Fas, p53, perforin, apoptosis-mediating Bcl-2 family proteins and apoptotic death substrate, poly(ADP-ribose) polymerase (PARP) were detected immunohistochemically. Detection of apoptosis was by TUNEL assay. Proteolytic activity was determined by 10% gelatin gel zymography.

RESULTS

there is a conspicuous disruption and fragmentation of elastic lamellae in PAA as compared to normal arteries. Increased gelatinolytic activity was observed at 92, 84, 72 and 67 kDa in PAA tissues. There is a significant decrease of VSMCs in the PAA walls (p=0.02). The control arteries had fewer CD68+ macrophages and CD3+ T cells in their media (p<0.01). There was a significant increase in the number of cells undergoing apoptosis in aneurysmal tissue than in the normal vessels, (p<0.02) as well as an increased expression of Bax, CPP-32, Fas, p53 and perforin.

CONCLUSIONS

the data confirm the architectural disruption of the PAA wall and illustrate an apparent biological response involving inflammatory infiltrate, apoptosis and signalling molecules capable of initiating cell death. In addition to compromising the mechanical integrity of the vessel wall, VSMC loss may contribute to imbalance in the protein profile, accelerating extracellular matrix degradation that could favour PAA development.

Elastin-laminin receptor and abdominal aortic aneurysms. New subject to study? A review

Abdominal aortic aneurysms and their management remain a significant health problem that is likely to assume greater importance with the expansion of the elderly population. Elastin fibres degradation and extracellular matrix remodelling seems to be the basic process in aneurysm formation. Recent investigations revealed the principal role of elastin-laminin receptor in extracellular matrix remodelling in aging and atherosclerosis. The correlation between events observed in animal aneurysm models, human aneurysms and in experiments on elastin-laminin receptor properties was discussed to propose the hypothesis about the role of elastin peptides and elastin-laminin receptor in aortic aneurysm formation.

Biologic effect and molecular regulation of vascular apoptosis in atherosclerosis

Apoptosis, a form of genetically programmed cell death, plays a key role in regulation of cellularity of the arterial wall. During atherogenesis, deregulated apoptosis may cause abnormalities of arterial morphogenesis, wall structural stability, and metabolisms. Many biophysiologic and biochemical factors, including mechanical forces, reactive oxygen and nitrogen species, cytokines, growth factors, oxidized lipoproteins, etc. may influence apoptosis of vascular cells. The Fas/Fas ligand/caspase death-signaling pathway, Bcl-2 protein family/mitochondria, the tumor suppressive gene p53, and the proto-oncogene c-myc may be activated in atherosclerotic lesions and mediate vascular apoptosis during the development of atherosclerosis. Abnormal expression and dysfunction of these apoptosis-regulating genes may attenuate or accelerate vascular cell apoptosis and affect the integrity and stability of plaques. Clarification of the molecular mechanism that regulates apoptosis may help design a new strategy for treatment of atherosclerosis and its major complication, the acute vascular syndromes.

Differential proteolytic activity and induction of apoptosis in fibrous versus atheromatous plaques in carotid atherosclerotic disease

PURPOSE

Atherosclerotic plaque instability may be a contributing factor to plaque complications, such as rupture, thrombosis, and embolization. Of the two types of plaques, atheromatous and fibrous, the atheromatous type has been reported to be vulnerable and unstable. This instability may be related to changes in the cell cycle and extracellular matrix degradation. Apoptosis may weaken the plaque structurally. In addition, alteration of the cellular component may lead to imbalances in associated proteolytic activity. Our study was designed to compare the two types of plaques in terms of apoptosis, apoptosis-inducing factors, namely Fas/CD95/APO-1 and CPP-32/YAMA/caspase-3, and proteolytic activity.

METHODS

Carotid artery plaques were obtained from patients undergoing endarterectomy and were classified as either atheromatous or fibrous on the basis of established criteria. Histologic study included hematoxylin and eosin staining, Verhoeff's van Gieson elastin staining, and trichrome staining. Detection of apoptosis was performed with the TUNEL assay. Immunohistochemical studies were performed to localize the expression of CPP-32/YAMA and Fas/CD95. Gelatin gel zymography was used to compare proteolytic activity levels in the two types of plaque.

RESULTS

Apoptosis was significantly higher (P <.001) in atheromatous plaques (4.90% +/- 1.27% [SEM]) as compared with fibrous plaques (0.86% +/- 0.46% [SEM]). Zymography demonstrated elevated levels of proteinases in atheromatous plaques. Immunohistochemistry revealed significant increases in the expression of Fas/CD95 (P <.04) and CPP-32/YAMA (P <.001) in atheromatous plaques as compared with that in fibrous plaques.

CONCLUSIONS

This is the first study comparing molecular factors that render atheromatous plaques more susceptible to rupture than fibrous plaques. The higher number of apoptotic cells seen in atheromatous plaques as compared with fibrous plaques could contribute to their greater instability. Immunoreactivity to cytoplasmic death domain, Fas/CD95 and CPP-32/YAMA, a prominent mediator of apoptosis, was consistent with the numbers of apoptotic cells detected. The increased levels of proteolytic activity in atheromatous plaques may make these plaques more prone to rupture. These data identifying some of the molecular events and biochemical pathways associated with plaque vulnerability may help in the development of new strategies to prevent plaque rupture.

Mutual exclusion of apoptosis and hsp70 in human vein intimal hyperplasia in vitro

BACKGROUND

Apoptosis of vascular smooth muscle cells (VSMC) plays a role in physiological vascular remodeling, as well as in disease states such as atherosclerosis and restenosis after angioplasty. Heat shock protein 70 (hsp70) may protect the cell against apoptosis and/or necrosis. In this study, we examined hsp70 expression and its temporal relationship to cell survival or death in a model of intimal vein hyperplasia in vitro.

METHODS

Segments of human saphenous veins were placed into culture. At different days vein segments were serum-starved or exposed to heat shock. Apoptosis and hsp70 expression were analyzed by Western blot, immunohistochemistry, and TUNEL assay.

RESULTS

A marked intimal vein hyperplasia developed after 14 days of culture when compared with baseline. hsp70 was present at baseline and disappeared during culture. Heating during culture could not up-regulate hsp70. The apoptotic markers were absent at baseline and present during normal culture. Conversely, serum starvation stimulated strong hsp70 expression coincidental with the disappearance of apoptotic markers.

CONCLUSIONS

Stimulation of veins during culture with serum resulted in hyperplasia, apoptosis, and inhibition of hsp70 expression. Down-regulation of hsp70 may permit apoptosis and vessel wall remodeling in this model.

Vascular-associated lymphoid tissue (VALT) involvement in aortic aneurysm

Vascular-associated lymphoid tissue (VALT) consisting of accumulations of immunocompetent and antigen presenting cells has recently been recognised in the arterial wall. In this study, we investigated the involvement of VALT in immune responses in abdominal aortic aneurysms (AAAs). Tissue samples were collected during operations from 31 patients with atherosclerotic infrarenal abdominal aortic aneurysms ranging in diameters from 5 to 8 cm. The specimens were immediately frozen and examined using single and double immunohistochemical staining. T-cell subpopulations, B-cells, dendritic cells and macrophages were identified using cell type specific antibodies. Cell contacts were examined by electron microscopy. Most inflammatory infiltrates were found in the adventitia. T-cells were the predominant cell type in a majority of inflammatory infiltrates but in seventeen cases, typical lymphoid follicles with B-cells forming germinative centres were also observed. In eight cases, the lymphoid follicles aggregated in lymph node-like structures. Dendritic cells were present within all inflammatory infiltrates and contacted lymphocytes. The present observations show that in aortic aneurysm, VALT is involved in immune responses and its activation mostly occurs in the adventitia. The formation of lymphoid follicles and lymph node-like structures in the adventitia suggests that VALT might locally serve the entire complex of both cellular and humoral immune responses in the aneurysmal wall.

Role of plaque rupture in acute coronary syndromes

Acute coronary syndromes are caused by plaque rupture. The conventional strategy of prevention of plaque rupture has been driven by the "lipid hypothesis"--if lipid levels are optimized to target levels, the risk of coronary events is decreased. Indeed, the hypothesis has been validated by the dramatic success of statin therapy. However, further major reductions in cardiac events is a realistic goal; various mechanistic and small clinical studies show that statins have beneficial effects in addition to their lipid-lowering properties. One of these beneficial effects is stabilization of plaque. Despite billions of dollars spent on randomized clinical trials, optimal therapy for coronary artery disease is yet to be tested. This therapy might include various combinations of the Mediterranean or low-fat diet, endothelial passivation, lipid-lowering drugs, antioxidants, antiplatelet agents and anti-inflammatory agents.

Contractile smooth muscle cell apoptosis early after saphenous vein grafting

BACKGROUND

The media of saphenous veins is composed of two cell populations: smooth muscle (SMC) and non-smooth muscle (NSMC) cells. Previous studies demonstrate a loss of SMCs by 3 days after grafting, despite an increase in cell proliferation. The purpose of this study is to determine the rates of apoptotic cell death versus cell proliferation for the two major cell populations of the media.

METHODS

Veins (six/time point) were examined at 0.5, 1, 2, 4, 8, 24, and 48 hours after grafting in crossbred pigs. Terminal transferase-mediated dUTP nick end labeling (TUNEL) and proliferating cell nuclear antigen (PCNA) stains were used to assess apoptosis and proliferation. Apoptosis was also corroborated with confocal and electron microscopy.

RESULTS

Apoptosis was high in both cell populations: at 8 hours, SMC and NSMC apoptosis peaked at 14.5% +/- 3.5% and 49.9% +/- 7.8%, respectively. In contrast, cell proliferation was different between the two populations. SMC proliferation was low at all time points, whereas NSMC proliferation rose to 22% +/- 5.4% by 48 hours.

CONCLUSIONS

Medial SMCs are removed through apoptosis and appear to be replaced by fibrous tissue (NSMCs) early after vein grafting. This reciprocal change between the medial SMC and NSMC populations may contribute to late vein graft degeneration.

Accelerated replicative senescence of medial smooth muscle cells derived from abdominal aortic aneurysms compared to the adjacent inferior mesenteric artery

BACKGROUND

Abdominal aortic aneurysms (AAAs) are associated with aging and atherosclerosis. AAAs arise through a degenerative process characterized in part by depletion of medial smooth muscle cells (SMC), suggesting that generalized aging and SMC senescence represent potential mechanisms contributing to aneurysmal degeneration. It is not yet known whether SMC from AAA tissue exhibit a difference in proliferative capacity compared to SMC from nonaneurysmal vessels or to what extent such differences might be due to aging alone or other patient-specific factors.

MATERIALS AND METHODS

Aneurysm wall tissues were obtained from 15 patients undergoing AAA repair. In each case, a segment of the adjacent (nonaneurysmal) inferior mesenteric artery (IMA) from the same patient was used as a control. Paired AAA- and IMA-derived SMC strains were obtained by explant techniques and their proliferative capacities were compared during serial passage in culture.

RESULTS

Sustainable SMC cultures were established from all IMA explants but from only 9 of 15 AAAs (P < 0.05). The interval required to achieve primary explant growth was longer for AAAs than IMAs (16.4 +/- 2 vs 6.4 +/- 1 days; P < 0.001), but it was unrelated to patient age, gender, or aneurysm size. AAA-derived SMC appeared larger and rounder than the corresponding IMA-derived SMC, even after repeated passage in culture, and their maximal proliferation was reduced by 44.2 +/- 8% (n = 5 pairs, P < 0.05). Serum-stimulated [(3)H]thymidine uptake in AAA-derived SMC was also reduced by 54.9 +/- 7% (n = 5 pairs, P < 0.01), but flow cytometry revealed no differences in SMC viability, apoptosis, or necrosis. While IMA-derived SMC continued to proliferate beyond passage 20 during serial subculture, all AAA-derived SMC developed replicative senescence by passage 12.

CONCLUSIONS

AAA-derived SMC exhibit a distinct morphologic appearance in culture, a diminished proliferative capacity compared to SMC from the adjacent IMA, and a limited in vitro life span. These differences reflect an intrinsic alteration in SMC growth capacity independent of age alone. Tissue-specific processes leading to accelerated replicative senescence may therefore contribute to the selective medial SMC depletion observed in AAAs.

Changing concepts of atherogenesis

This review discusses three stages in the life history of an atheroma: initiation, progression and complication. Recruitment of mononuclear leucocytes to the intima characterizes initiation of the atherosclerotic lesion. Specific adhesion molecules expressed on the surface of vascular endothelial cells mediate leucocyte adhesion: the selectins and members of the immunoglobulin superfamily such as vascular cell adhesion molecule-1 (VCAM-1). Once adherent, the leucocytes enter the artery wall directed by chemoattractant chemokines such as macrophage chemoattractant protein-1 (MCP-1). Modified lipoproteins contain oxidized phospholipids which can elicit expression of adhesion molecule and cytokines implicated in early atherogenesis. Progression of atheroma involves accumulation of smooth muscle cells which elaborate extracellular matrix macromolecules. These processes appear to result from an eventual net positive balance of growth stimulatory versus growth inhibitory stimuli, including proteins (cytokines and growth factors) and small molecules (e.g. prostanoids and nitric oxide). The clinically important complications of atheroma usually involve thrombosis. Arterial stenoses by themselves seldom cause acute unstable angina or acute myocardial infarction. Indeed, sizeable atheroma may remain silent for decades or produce only stable symptoms such as angina pectoris precipitated by increased demand. Recent research has furnished new insight into the molecular mechanisms that cause transition from the chronic to the acute phase of atherosclerosis. Thrombus formation usually occurs because of a physical disruption of atherosclerotic plaque. The majority of coronary thromboses result from a rupture of the plaque's protective fibrous cap, which permits contact between blood and the highly thrombogenic material located in the lesion's lipid core, e.g. tissue factor. Interstitial collagen accounts for most of the tensile strength of the plaque's fibrous cap. The amount of collagen in the lesion's fibrous cap depends upon its rate of biosynthesis stimulated by factors released from platelets (e.g. transforming growth factor beta or platelet-derived growth factor), but inhibited by gamma interferon, a product of activated T cells found in plaques. Degradation by specialized enzymes (matrix metalloproteinases) also influences the level of collagen in the plaque's fibrous cap. Such studies illustrate how the application of cellular and molecular approaches has fostered a deeper understanding of the pathogenesis of atherosclerosis. This increased knowledge of the basic mechanisms enables us to understand how current therapies for atherosclerosis may act. Moreover, the insights derived from recent scientific advances should aid the discovery of new therapeutic targets that would stimulate development of novel treatments. Such new treatments could further reduce the considerable burden of morbidity and mortality due to this modern scourge, and reduce reliance on costly technologies that address the symptoms rather than the cause of atherosclerosis.

Programmed cell death (Apoptosis) and its role in the pathogenesis of lower extremity varicose veins

The etiology of varicose veins remains elusive. We hypothesized that abnormal cell cycle events in the vein wall may contribute to changes in its structural integrity predisposing to varicosity development. Since cell cycle checkpoint controls are linked to the signaling and execution of apoptotic cascades, possibly apoptosis is a contributing factor in the pathophysiology of varicosities. The present study was designed to investigate whether programmed cell death varies in varicosities as compared to normal veins. Twenty-seven normal greater saphenous vein specimens were obtained from patients undergoing infrainguinal arterial bypass surgery, and 20 varicose vein specimens were retrieved from patients undergoing varicose vein excision. Apoptosis was detected by TUNEL assay. Expression of bcl-2 and cyclin D1 was noted by standard immunohistochemical techniques. Apoptotic cells were identified in 32 of the 47 specimens. Forty-eight percent of normal vein specimens displayed >3 apoptotic cells per 100 cells in the adventitia; 15% of the specimens of the varicose vein group showed such magnitude of apoptosis (p < 0.03). This increased apoptotic activity was not observed in media or intima of either vein group (p < 0.001). No significant difference in immunoreactivity to bcl-2 protein was observed in varicose vein specimens as compared to controls. Varicose vein specimens demonstrated increased nuclear expression of cyclin D1 whereas its cytoplasmic expression was significantly diminished (p </=0.02). These data show that programmed cell death is inhibited in varicose veins. Differential expression of cyclin D1 suggests that it may deregulate cell cycle events, thereby leading to varicosity formation.