Injury and repair of smaller muscular and elastic arteries. Immunohistochemical demonstration of fibronectin and fibrinogen/fibrin and their degradation products in rabbit femoral and common carotid arteries following a dilatation injury

Monocyte adhesion to balloon-injured arteries: the influence of endothelial cell seeding

OBJECTIVE

Deendothelialization of injuries of the artery disrupts normal vascular homeostasis, affecting both the structural integrity of the blood vessel wall, as well as the interaction of the arterial surface with blood components such as platelets, leukocytes, and circulating proteins. Leukocyte and, in particular, monocyte recruitment to damaged vessels has been implicated in the pathogenesis of intimal hyperplasia. We hypothesize that reendothelialization is an important modulator of monocyte adhesion to healing arterial surfaces.

METHODS

New Zealand white rabbits (n = 20) were subjected to bilateral iliofemoral artery balloon injury. Cultured, autologous venous endothelial cells (ECs) were immediately seeded onto one vessel, whereas the contralateral artery received medium alone, to accelerate endothelial relining. Vessels were harvested (5-9 days after injury) for analysis of permeability (Evans Blue dye exclusion), endothelial coverage (anti-CD31 immunohistochemistry), monocyte adhesion (ex vivo binding of 51Na2CrO4-labeled monocytic THP-1 cells), and monocyte recruitment (RAM-11 immunohistochemistry).

RESULTS

Improved EC coverage was evidenced by positive staining for CD31 in the seeded vessels. Vessel wall permeability was markedly reduced in EC-seeded arteries (29% +/- 10% vs 99% +/- 0% surface Evans blue staining, P <.005), consistent with restoration of a functional endothelial barrier. EC seeding significantly reduced ex vivo THP-1 binding to vessels explanted at a mean of 8 days after injury (45,170 +/- 8939 vs 85,994 +/- 16,500 cells/cm2, P <.05). However, RAM-11 staining revealed no significant difference in overall macrophage accumulation between seeded and control vessels 1 week after injury (111 +/- 22 vs 95 +/- 14 cells/section, P =.36).

CONCLUSIONS

Immediate seeding of a balloon-injured rabbit artery with cultured ECs results in accelerated restoration of the endothelial lining. At 1 week, barrier function is improved, and the seeded vessel surface is less adhesive to activated monocytes ex vivo, as compared with injured controls. Nonetheless, EC-seeded and nonseeded arteries demonstrate similar total macrophage accumulation over 1 week. These data suggest that after mechanical arterial injury, endothelial coverage may be one important variable influencing leukocyte adhesion.

Immunolocalization of proliferating cells in the rabbit iliac artery after balloon angioplasty

PURPOSE

Experiments were performed to characterize the location of proliferating cells in the balloon-dilated rabbit iliac artery.

MATERIALS AND METHODS

Balloon angioplasty was performed on the external iliac arteries in each of four rabbits. The arteries were removed 3 days later, frozen, cryosectioned, and immunostained with Ki-67, an antibody that identifies proliferating cells. The sections were then examined to determine the patterns of cell proliferation within the arterial media and the ratio of proliferating to nonproliferating cells.

RESULTS

Of the 31 arterial cross-sections examined, cell proliferation was circumferential in five (16%), and focal in 26 (84%). Of the 86 foci of proliferation examined within the 31 cross-sections, proliferation was localized to the inner media in 30 (35%), to the outer media in four (5%), and was transmural in 52 (60%). The internal elastica lamina (IEL) appeared normal at 22 foci (26%), but appeared stretched or torn at 64 (74%). Proliferation was usually confined to the inner media at foci having no IEL injury (18 of 22; 82%), but was most often transmural where the IEL was stretched or torn (49 of 64; 77%). The ratio of proliferating to nonproliferating cells, which averaged 0.31 +/- .20, was greater (P < .01) in areas with IEL injury than in areas without IEL injury.

CONCLUSION

These results suggest that angioplasty-induced cell proliferation is typically focal rather than circumferential and is associated with stretching or tearing of the IEL.

Expression of type VIII collagen after cholesterol diet and injury in the rabbit model of atherosclerosis

This study presents an analysis of the expression of type VIII collagen mRNA in response to cholesterol diet and balloon injury in the rabbit iliac artery. The design of the animal experiments was as follows: 28 male New Zealand White rabbits were divided into the 3 different treatment groups. Group 1 received regular chow; group 2 was fed with a 1% cholesterol diet for 6 weeks and normal chow for 5 weeks; and group 3 underwent balloon injury, then 6 weeks of a 1% cholesterol diet, which was followed by 5 weeks of normal chow. The expression pattern of type VIII collagen mRNA was compared with that of the fibrillar collagen types I and III, transforming growth factor-beta1, a factor known to exert the most potent stimulatory effect on collagen synthesis in vitro, and matrix metalloproteinase 1, a collagen-degrading enzyme. The cholesterol diet resulted in an upregulation of type VIII collagen, fibrillar collagens, transforming growth factor-beta1, and matrix metalloproteinase I in the adventitia. Although the number of type VIII collagen mRNA-expressing cells in the media increased, no significant difference in overall expression levels was detectable by northern blot analysis. The ratio of medial smooth muscle cells expressing type VIII collagen mRNA to those expressing type I and type III collagen mRNA (CVIII:CI:CIII) changed from 1:1.88:0.03 in the normal media to 1:0.78:0.29. When cholesterol feeding was preceded by balloon injury, type VIII collagen mRNA expression concomitant with the fibrillar collagens was further upregulated over and above that level reported after cholesterol diet alone. In general, low levels of transforming growth factor-beta1 mRNA correlated with high expression of matrix metalloproteinase I. Our study indicates that a cholesterol diet resulted in a balanced reorganization of the collagen composition but did not result in marked collagen accumulation. This may provide an extracellular environment that favors migration and proliferation processes during early atherogenesis. It also demonstrates that type VIII collagen is highly expressed and deposited at later stages, and this may be linked to processes such as tissue reorganization during vascular repair and plaque stabilization.

Current concepts in giant cell (temporal) arteritis

Giant cell (temporal) arteritis continues to be a sight-threatening, systemic vasculitis with a poorly understood pathogenesis. The characteristic granulomatous inflammation of the vessel wall commonly leads to local ischemia. Recent advances in immunological investigations have characterized the cellular components of the disease process, but the etiology has so far remained unresolved. A reappraisal of the clinical features of giant cell (temporal) arteritis demonstrates the heterogeneity of the manifestations of the disease, including ischemic optic neuropathy. A range of new laboratory investigations and blood flow studies with color Doppler imaging have demonstrated promising roles, with respect to diagnosis and long-term follow-up. Prompt diagnosis and expeditious treatment require a high index of clinical suspicion, particularly for atypical cases. Corticosteroids remain the treatment of choice, other immuno-suppressive agents being used as second line steroid-sparing agents. Giant cell (temporal) arteritis leads to increased vascular and visual morbidity and, if untreated, may prove fatal. To maintain high standards of management of this enigmatic disorder, ophthalmologists need to be aware of the clinical spectrum of giant cell (temporal) arteritis and currently available diagnostic tests and treatment strategies.

Nonenzymatic glycation of fibronectin impairs adhesive and proliferative properties of human vascular smooth muscle cells

Nonenzymatic glycation of proteins is involved in the pathogenesis of diabetes vascular complications. Extracellular matrix proteins are a prominent target for nonenzymatic glycation because of their slow turnover rates. The aim of this study was to investigate the influence of human fibronectin (F) nonenzymatic glycation on adhesion and proliferation of cultured human vascular smooth muscle cells (hVSMC). Incubation of human F with 500 mmol/L D-glucose at 37 degrees C induced a time-dependent increase in fluorescence detectable at 440 nm after excitation at 363 nm. Nonenzymatic glycation did not affect binding of F itself to the plates. Adhesion of hVSMC to F increased with the increase of incubation time of the cells on the protein from 30 minutes up to 120 minutes and remained stable thereafter. Adhesion to glycated fibronectin (GF) was reduced in comparison to control F at all the different adhesion times. Adhesion of hVSMC to GF was reduced when F was exposed to glucose for 4, 9, or 28 days (P=.0417 to .0025), but not when F was exposed for 1 day. Adhesion of hVSMC to GF was reduced compared with adhesion to nonglycated F at all coating concentrations from 0.2 to 10 micrograms/mL (P=.05 to .014). Thus, nonenzymatic glycation of F impairs adhesion of hVSMC in vitro. Proliferation of hVSMC on F increased with increasing concentrations of the protein as coating agent (ANOVA:P<.0001 for both nonglycated F and GF). Proliferation with F glycated for 4, 9, and 28 days was reduced at concentrations of 1, 3, and 10 micrograms/mL as compared with proliferation with nonglycated F (P=.0253 to .0001). Proliferation on F glycated for only 1 day was not significantly reduced. When the number of hVSMC plated on control F was reduced by 25% to take into account the reduced adhesion, the number of cells that proliferated on F was still reduced. In conclusion, nonenzymatic glycation of F impairs adhesive and proliferative properties of hVSMC.

Vascular injury, repair, and restenosis after percutaneous transluminal angioplasty in the atherosclerotic rabbit

BACKGROUND

Several nonatherosclerotic animal models of restenosis exist and are used for the evaluation of the vascular response to angioplasty-induced injury. However, few studies have evaluated the response of an atherosclerotic vessel to angioplasty. The present study examined the radiographic, histological, immunohistochemical, and morphometric responses over time of atherosclerotic rabbit femoral arteries after percutaneous transluminal angioplasty (PTA).

METHODS AND RESULTS

Rabbits (n = 94) underwent arterial dissection and were fed a hypercholesterolemic diet for 3 weeks, and then PTA was performed. Arteries were obtained before PTA and 1, 3, 5, 7, 14, and 28 days after PTA. PTA caused radial stretching of the artery, medial compression, intramural hemorrhage, injury to normal arterial segments, and dissection within the intima and media. Thrombus filled and cellular accumulation repaired the dissection. Peak smooth muscle cell and macrophage DNA synthesis was noted at 3 to 5 days after angioplasty, generally at the dissection but also in normal sections of the artery. Adventitial injury and subsequent adventitial cellular proliferation and collagen production were observed. A rapid decrease in the radiographic minimal luminal diameter was noted at 3 days, resulting from vascular recoil or thrombus filling the dissection. At 7 to 14 days, only 24% to 33% of the luminal loss was accounted for by an increase in the intimal area, and 22% to 28% of the intima was neointima.

CONCLUSIONS

Restenosis in an atherosclerotic artery results from a variable combination of intimal proliferation, vascular remodeling/wound contraction, and recoil of the normal section of the artery. The variability of an atherosclerotic artery to PTA injury results from variable dissection, thrombus formation, and cellular response to injury as well as variable scar contraction and elastic recoil.

Differential distribution of 70-kD heat shock protein in atherosclerosis. Its potential role in arterial SMC survival

Smooth muscle cell death may contribute to necrotic plaque rupture and subsequent thromboembolus. Stress-induced synthesis of heat-shock proteins (HSPs) normally protects cells from death, but vascular HSPs may become insufficient as cytotoxicity increases in advanced plaques. To determine whether vascular HSP content is altered near necrosis, we compared 70-kD HSP (HSP70) distribution between fibrotic and necrotic plagues in immunostained carotid endarterectomy specimens. Average levels of HSP70 immunoreactivity were compared by video densitometry between fibrotic and necrotic plaques or between their underlying media. Both necrotic plaques and their underlying media contained significantly more HSP70 staining than did fibrotic tissues. To test whether cellular HSP70 correlated with resistance to toxicity in vitro, aortic smooth muscle cells (aSMCs) were heat shocked to induce endogenous HSPs or given 2 to 50 micrograms/mL purified HSP70. Cells were then serum deprived or exposed to 12 to 96 mumol/L cholestanetriol (C3ol) or 25-hydroxycholesterol, and survival was determined. Cellular HSP70 content was assayed by immunoblotting, and protein synthesis was monitored by 35S radiolabeling. Serum deprivation inhibited general protein synthesis but induced HSP70; C3ol exposure inhibited both overall protein and HSP70 synthesis, including post-heat shock. Induction of endogenous HSPs or 10 micrograms/mL exogenous HSP70 improved viability of serum-deprived cells (P < .05 and P < .01, respectively), while only exogenous HSP70 protected against C3ol (P < .002). The results suggest that insufficient HSP70 accumulates in aSMCs residing near necrosis to protect against plaque toxicity; aSMC death might then occur, allowing resident macrophages to degrade and destabilize the matrix, leading to rupture.

Cytoskeletal and extracellular matrix proteins in cerebral arteries following subarachnoid hemorrhage in monkeys

It is unclear if vasospasm after subarachnoid hemorrhage (SAH) is predominantly due to smooth-muscle contraction, proliferative vasculopathy, or other changes within the arterial wall such as fibrosis or change in smooth-muscle phenotype. In this study, immunohistochemistry was used to examine changes in extracellular and cytoskeletal proteins in cerebral arteries after SAH that might support one of these mechanisms. Following baseline cerebral angiography, bilateral SAH was created in nine monkeys. Three animals each were killed 7, 14, or 28 days after SAH. Cerebral angiography was repeated on Day 7 in all animals and immediately prior to sacrifice in animals killed on Days 14 and 28. Both middle cerebral arteries and four control basilar arteries were examined using fluorescent antibody techniques with antisera to alpha-actin, myosin, fibronectin, fibrinogen, vimentin, desmin, laminin, and collagens (types I, III, IV, and V). Angiography showed that vasospasm was most severe on Day 7, present but resolving on Day 14, and completely resolved by Day 28. Microscopic study of arterial sections and blinded review of microphotographs of arterial sections by five independent observers did not reveal changes in intensity of density of staining for collagens, desmin, myosin, laminin, or alpha-actin in the tunica media of tunica adventitia. Fibronectin immunoreactivity increased 14 days after SAH. Seven days after SAH, occasional areas of tunica media showed immunoreactivity to fibrinogen. On Day 28, intimal thickening was observed in four of six middle cerebral arteries and this tissue demonstrated immunoreactivity to alpha-actin, myosin, vimentin, desmin, fibronectin, laminin, and each type of collagen. No significant increases in the number of intimal cells showing immunoreactivity to alpha-actin were seen and no significant changes in the hydroxyproline content of cerebral arteries developed at any time after SAH. These results suggest that rigidity and lumen narrowing of vasospasm are not due to increased arterial collagen, although other proteins in the arterial wall or an alteration in cross-linking of existing proteins could produce these changes. There is no indication that smooth-muscle contractile proteins change during vasospasm or that increases in the number of alpha-actin-containing myointimal cells contribute to vasospasm. The occurrence of intimal thickening and increased tunica media fibronectin after vasospasm suggests that vasospasm damages smooth muscle, possibly as a result of intense prolonged smooth-muscle contraction.

Repair in arterial tissue 2 years after a severe single dilatation injury: the regenerative capacity of the rabbit aortic wall. The importance of endothelium and of the state of subendothelial connective tissue to reconstitution of the intimal barrier

The thoracic aortae from 11 rabbits that survived a single severe dilatation injury for 2 years were studied by vital staining with Evans blue, immunohistochemistry and transmission electron microscopy. Our results have shown almost total restitution of the thoracic aorta. Six of the 11 rabbits submitted to an injury had no blue-stained areas, indicating total reendothelialization. Five rabbits had a few blue areas often on the ventral side of the aorta. The reendothelialization from the first to the seventh pair of intercostal arteries ranged from 82% to 100%. There was intimal thickening inside the original internal elastic lamina in both white and blue areas. All blue areas had a surface composed of smooth muscle cells. Reendothelialized areas consisted of mature endothelium, reticular basal membrane, layered smooth muscle cells and an extracellular matrix consisting of pre-elastin, elastin, collagen and proteoglycans. An effective barrier had apparently been formed against penetration of macromolecules, judged from the absence of fibrinogen/fibrin and unmasked fibronectin. Intimal thickenings without endothelial cover were covered with smooth muscle cells without intercellular junctions. Our results indicate that an extracellular matrix of fibrin and fibronectin plays a role in forming an intimal thickening, and it is suggested that proteoglycans may modulate the biological role of the extracellular matrix in the healing process.

Fibronectin biosynthesis in the rat aorta in vitro. Changes due to experimental hypertension

This study was undertaken to determine if changes in fibronectin biosynthesis accompany the phenotypic changes that occur in aortic tissue following experimental hypertension. An in vitro procedure was developed to measure fibronectin synthesis in aortic rings obtained from normotensive or hypertensive rats. There was a three to sixfold increase in fibronectin biosynthesis by aortic rings taken from rats treated with deoxycorticosterone/salt for 7 and 21 d, the change being more pronounced at 21 d. In contrast, there was no major change at either time point in net incorporation into total protein. Studies comparing fibronectin biosynthesis in aortic rings from Wistar rats and spontaneously hypertensive rats at ages between 10 and 40 wk showed increased fibronectin biosynthesis in older animals of both strains, but only slight differences between strains. Studies using rats infused with angiotensin II showed a correlation between blood pressure elevation and increased aortic fibronectin biosynthesis. Western blot analysis of aortic extracts showed that the fibronectin content was increased in the hypertensive models. The in vitro procedure for measuring fibronectin biosynthesis appears to provide a reliable reflection of in vivo changes in fibronectin expression, and the methodology could prove useful for studying the factors influencing protein expression in vascular tissue.