Actin stress fiber content of regenerated endothelial cells correlates with intramural retention of intermediate plus low density lipoproteins in rat aorta after balloon injury

The rat aortic model of endothelial injury (balloon catheter induced) has been used to establish whether changes in protein intramural penetration in specific areas of the injured aorta were accompanied by phenotypic modifications of the regenerated endothelial cells covering these particular regions. Iodinated lipoproteins (IDL/LDL fraction) and albumin were used as tracers to localize protein permeability and retention in the aorta. Lipoproteins, but not albumin, were retained in the thickened areas covered with regenerated endothelium (i.e., 60 days after balloon induced injury). Neither lipoproteins nor albumin were retained in the other aortic areas studied, including the intimal thickening of de-endothelialized areas (15 days after injury). The relative volume of cytoplasmic stress fibers was significantly increased in regenerated endothelium covering thickened areas as compared with the other regions of the injured or normal aorta. The accumulation of lipids usually observed in atherosclerotic lesions, compatible with the trapping of lipoproteins by the matrix component of the intimal thickening, may be related to modulated features of endothelial cells regenerated over thickened areas of the aorta.     

Transendothelial transport and metabolism of adenosine and inosine in the intact rat aorta

This study was aimed at defining the role of vascular endothelium in the transport and metabolism of adenosine. For this purpose, endothelium-intact and endothelium-denuded isolated rat aortas, perfused at constant flow (2 ml/min), were prelabeled with 3H-adenosine or 3H-inosine for 10 minutes at concentrations of 0.012-100 microM. Sequestration of adenosine by endothelium was determined from radioactivity recovered during selective endothelial cell removal with deoxycholic acid (0.75% for 15 seconds). In the physiological concentration range of adenosine (0.012-1 microM), fractional sequestration by endothelium was 90-92% of the total adenosine incorporation by the aorta. Endothelial sequestration of inosine at 0.1 microM was 85%. At 100 microM adenosine or inosine, fractional sequestration by aortic endothelium was 33% and 39%, respectively. Analysis of the specific radioactivity of adenine nucleotides extracted from prelabeled aortas indicated that most of the adenosine was incorporated into endothelial adenine nucleotides. Incorporation of inosine into endothelial ATP was approximately 15% that of adenosine. Inhibition of aortic adenosine deaminase with erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) did not influence sequestration of 0.1 microM adenosine, but resulted in a 49% reduction of total endothelial incorporation at 100 microM adenosine. Transfer of radioactive purines from the endothelium to underlying smooth muscle after prelabeling was equivalent to only 1%/hr of total endothelial radioactivity. Our findings suggested that 1) macrovascular endothelium of the aorta constitutes a highly effective metabolic barrier for circulating adenosine and inosine; 2) transfer of labeled adenine nucleotides from endothelium to underlying smooth muscle is rather small and most likely proceeds via dephosphorylated purine compounds; and 3) measurement of adenosine trapping in endothelial and smooth muscle compartments overestimates the transendothelial adenosine concentration gradient.     

Patterns of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 expression in rabbit and mouse atherosclerotic lesions and at sites predisposed to lesion formation.

The recruitment of mononuclear leukocytes and formation of intimal macrophage-rich lesions at specific sites of the arterial tree are key events in atherogenesis. Inducible endothelial cell adhesion molecules may participate in this process. In aortas of normal chow-fed wild-type mice and rabbits, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1), but not E-selectin, were expressed by endothelial cells in regions predisposed to atherosclerotic lesion formation. En face confocal microscopy of the mouse ascending aorta and proximal arch demonstrated that VCAM-1 expression was increased on the endothelial cell surface in lesion-prone areas. ICAM-1 expression extended into areas protected from lesion formation. Hypercholesterolemia induced atherosclerotic lesion formation in rabbits, LDL receptor and apolipoprotein E knockout mice, and Northern blot analysis demonstrated increased steady-state mRNA levels of VCAM-1 and ICAM-1, but not of E-selectin. Immunohistochemical staining revealed that VCAM-1 and ICAM-1 were expressed predominantly by endothelium in early lesions and by intimal cells in more advanced lesions. In early and advanced lesions, staining was most intense in endothelial cells at and adjacent to lesion borders. ICAM-1 staining extended into the uninvolved aorta. These expression patterns were highly reproducible in both species. The only difference was that VCAM-1 expression in endothelium over the central portions of lesions was found frequently in rabbits and rarely in mice. The expression of VCAM-1 by arterial endothelium in normal animals may represent a pathogenic mechanism or a phenotypic marker of predisposition to atherogenesis.     

Increased chymase-dependent angiotensin II formation in human atherosclerotic aorta.

Locally formed angiotensin II (Ang II) and mast cells may participate in the development of atherosclerosis. Chymase, which originates from mast cells, is the major Ang II-forming enzyme in the human heart and aorta in vitro. The aim of the present study was to investigate aortic Ang II-forming activity (AIIFA) and the histochemical localization of each Ang II-forming enzyme in the atheromatous human aorta. Specimens of normal (n=9), atherosclerotic (n=8), and aneurysmal (n=6) human aortas were obtained at autopsy or cardiovascular surgery from 23 subjects (16 men, 7 women). The total, angiotensin-converting enzyme (ACE)-dependent, and chymase-dependent AIIFAs in aortic specimens were determined. The histologic and cellular localization of chymase and ACE were determined by immunocytochemistry. Total AIIFA was significantly higher in atherosclerotic and aneurysmal lesions than in normal aortas. Most of AIIFA in the human aorta in vitro was chymase-dependent in both normal (82%) and atherosclerotic aortas (90%). Immunocytochemical staining of the corresponding aortic sections with antichymase, antitryptase or anti-ACE antibodies showed that chymase-positive mast cells were located in the tunica adventitia of normal and atheromatous aortas, whereas ACE-positive cells were localized in endothelial cells of normal aorta and in macrophages of atheromatous neointima. The density of chymase- and tryptase-positive mast cells in the atherosclerotic lesions was slightly but not significantly higher than that in the normal aortas, and the number of activated mast cells in the aneurysmal lesions (18%) was significantly higher than in atherosclerotic (5%) and normal (1%) aortas. Our results suggest that local Ang II formation is increased in atherosclerotic lesions and that chymase is primarily responsible for this increase. The histologic localization and potential roles of chymase in the development of atherosclerotic lesions appear to be different from those of ACE.     

Primary culture of endothelial cells from atherosclerotic human aorta. Part 1. Identification, morphological and ultrastructural characteristics of two endothelial cell subpopulations

Endothelial cells (EC) were harvested by 0.1% collagenase treatment for adult human thoracic aortas obtained 1-3 h after sudden death. At least 35-70% of EC were removed from the intimal surface of aorta, 90-95% of them being viable. Plating efficiency was 70-80%. Monolayer formation was achieved at a seeding density of 5-8 X 10(2) cells/mm2. The cells were identified as endothelium by the presence of Factor VIII antigen, Weigel-Palade bodies and typically endothelial morphology at confluence. Unlike endothelial cultures derived from human umbilical veins and infant aortas, primary cultures obtained from human adult aortas contain multinuclear EC with Factor VIII antigen and Weibel-Palade bodies. The number of multinuclear EC in cultures isolated from aortas affected by atherosclerosis was 2-fold higher (P less than 0.05) than in cultures obtained from grossly normal aortas taken from donors of the same age. EC with numerous lipid inclusions revealed by oil-red-O staining were present in all the EC primary cultures derived from aortas affected by atherosclerosis. No oil-red-O-positive cells were detected among the EC cultured from infant aorta, aorta of young donors, and umbilical vein. An electron microscopic examination of EC from atherosclerotic aorta in culture and in situ failed to reveal any ultrastructural peculiarities distinguishing multinuclear EC from the mononuclear EC.     

Effect of Two Lipid Emulsions on Reversing High-Dose Levobupivacaine-Induced Reduced Vasoconstriction in the Rat Aortas

The goals of this study were to determine which lipid emulsion (Intralipid^® and Lipofundin MCT/LCT^®) is more effective in reversing high-dose levobupivacaine-induced reduced vasoconstriction in isolated rat aortas and to examine the associated cellular mechanisms with a particular focus on the endothelium. Two lipid emulsion concentration–response curves were generated using high-dose levobupivacaine-induced reduced vasoconstriction and vasodilation of isolated aortas pretreated with or without 60 mM KCl. Endothelial nitric oxide synthase (eNOS) and caveolin-1 phosphorylation were measured in rat aortic tissue treated with levobupivacaine in the presence or absence of lipid emulsion. Dichlorofluorescein oxidation, a measure of reactive oxygen species production, was measured in lipid emulsion-treated human umbilical vein endothelial cells. In levobupivacaine (0.3 mM)-induced reduced vasoconstriction of isolated aorta, the magnitude of the Intralipid^®- and Lipofundin MCT/LCT^®-mediated reversal was not significantly different. Lipid emulsion reversal of levobupivacaine-induced reduced vasoconstriction was greater in endothelium-intact aortas than in endothelium-denuded aortas. The two lipid emulsions similarly inhibited levobupivacaine-induced eNOS phosphorylation in aortic tissue. Pretreatment with both lipid emulsions increased dichlorofluorescein oxidation. Both Intralipid^® and Lipofundin MCT/LCT^® are equally effective for vascular tone recovery from high-dose levobupivacaine-induced reduced vasoconstriction. This reversal is mediated partially by decreasing nitric oxide bioavailability.     

Catheter-induced intimal injury during routine coronary catheterization in dogs

The location and progression of changes in arterial permeability and structure were studied in nine dogs over a 13-week period following left coronary catheterization with standard coronary catheters. Changes in arterial permeability were analyzed by quantitating Evans blue dye (EBD) uptake over the aortic luminal surface (blue areas). Structural changes were assessed by light and electron microscopy. In the catheterized animals, compared to uncatheterized controls, we observed a significant increase in aortic luminal EBD uptake that was maximal 4 hours after the procedure but still present up to 13 weeks later. Microscopic analysis of "blue areas" shortly after the procedure revealed widespread endothelial denudation, platelet and leukocyte adherence, with occasional intimal avulsions, disruption of the internal elastica, and thrombi. The EBD uptake patterns in association with the electron microscopic findings in these animals suggested that 67-89% of the aortic endothelium was removed by the catheter during the procedure. The proliferative response that occurred following this catheter-induced injury produced fibrocellular intimal thickening in the aortas and left main coronary arteries of animals studied 10 to 92 days after the procedure. In the aortic root, such thickening was associated with incomplete re-endothelialization, thrombogenicity, and grossly abnormal permeability patterns. We conclude that significant catheter-induced intimal injury can occur during coronary angiography. In the canine model, such injury is associated with widespread fibrocellular intimal thickening and abnormal permeability that persists for at least 13 weeks after the procedure.     

Endothelium-independent linkage of parathyroid hormone receptors of rat vascular tissue with increased adenosine 3',5'-monophosphate and relaxation of vascular smooth muscle

We examined the mechanisms involved in the relaxation of rat vascular smooth muscle by PTH. PTH increased intracellular cAMP 10-fold in cultured vascular smooth muscle cells from rat aorta. Forskolin, methylisobutylxanthine, and papaverine all potentiated PTH action. The cAMP responses to PTH were not altered by concurrent addition of propranolol, phentolamine, atropine, or [Sar1,Ile8]angiotensin II. Only the synthetic PTH antagonist analog [Nle8,Nle18,Tyr34] bovine PTH-(3-34) inhibited the cAMP and vascular relaxation responses to PTH. Isoproterenol produced increases in intracellular cAMP and adenylate cyclase activity which were additive to those produced by PTH. In contracted rat aortic strips, PTH caused a dose-dependent relaxation which was not altered by removal of the vessel intima or treatment with nordihydroguaiaretic acid. Also, membrane preparations from intact aortas or aortas with the endothelium or adventitia removed displayed identical PTH-stimulated adenylate cyclase activities. These findings indicate that the relaxant action of PTH in rat aorta does not require an intact endothelium and results from a direct effect on the vessel medial layer. Relaxation appears to be mediated by a receptor unique for PTH which is linked to the adenylate cyclase of vascular smooth muscle cells.     

Osteoprotegerin and RANKL differentially regulate angiogenesis and endothelial cell function

Osteoprotegerin (OPG) a soluble tumor necrosis factor receptor family molecule protects endothelial cells from apoptosis in vitro and promotes neovascularization in vivo. In this study, we assessed the role of OPG and its ligands, receptor activator of nuclear factor-κB ligand (RANKL) and tumor necrosis factor-related apoptosis inducing ligand (TRAIL), in microvessel formation using the rat aortic ring model of angiogenesis. OPG was found to promote a twofold increase in angiogenic sprouting in the aortic ring model, and this effect was inhibited by pre-incubation with a fivefold molar excess of either RANKL or TRAIL. While TRAIL had no effect upon angiogenesis on its own, RANKL was found to potently inhibit basal and vascular endothelial growth factor-induced angiogenesis. OPG increased the rate of endothelial cell proliferation in sprouting microvessels; in contrast, RANKL inhibited proliferation. RANKL was found to induce endothelial apoptosis at days 6, 7, and 10 in the aortic ring model and after incubation with human umbilical vein endothelial cells (HUVECs). Signaling studies showed that OPG induced ERK1/2 and Akt phosphorylation in HUVECs while RANKL had no effect. Our results indicate that OPG is a positive regulator of microvessel formation, while RANKL is an angiogenic inhibitor due to effects on regulation of endothelial cell proliferation, apoptosis, and signaling.     

Relation between lipopolysaccharide-induced endothelial cell injury and entry of macromolecules into the rat aorta in vivo

Lipopolysaccharide (LPS) causes endothelial cell injury both in vitro and in vivo. It is widely believed that this injury in vivo enhances the transport of macromolecules from plasma into the interstitial space of the underlying artery wall. A new technique was used in rats to obtain high resolution transmural profiles of macromolecules in vivo. We compared the time course of the macromolecular transport into the aortic tissue in vivo after LPS injection to that of LPS-induced endothelial cell death and the proliferative response of the endothelium to LPS injury. At a dose of 1 mg LPS/kg body wt, endothelial cell death reached a maximum by 36 hours after LPS injection and remained elevated for 96 hours; the peak of the S phase of endothelial cell proliferation was observed 48 hours after injection. To examine the effect of LPS on macromolecular accumulation, we measured aortic intimal and medial transmural concentration profiles of horseradish peroxidase (HRP) after circulation of HRP for 15 minutes. The data revealed a transient increase in total aortic accumulation (reflecting predominantly the media), which was maximal between 12 and 48 hours after LPS injection. Although total medial accumulation was found to return to near control levels by 72 hours after LPS injection, intimal accumulation remained elevated above control levels for 120 hours. When HRP was added to the perfusate of an in situ aorta preparation at a near zero transmural pressure gradient, the resulting transmural concentration profiles across aortas from control rats and from rats given LPS 24 hours previously were indistinguishable, whereas a pressure gradient of 60 mm Hg revealed LPS-altered concentration profiles analogous to those in vivo. This suggests that the accumulation of HRP observed in vivo was driven by increased convective transport. These results reveal that LPS enhances entry of macromolecules into the aorta wall in vivo. The changes in macromolecular transport do not, however, correlate temporally with endothelial cell death or proliferation. The results are consistent with an LPS-induced decrease in the endothelial barrier function, which precedes, and may be independent of, cell death and a transient increase in convective transport across the media due to alterations in the barrier function of the internal elastic lamina.     

Monocyte/macrophage accumulation and smooth muscle cell phenotypes in early atherosclerotic lesions of human aorta

In a search for early atherosclerotic lesions, we have investigated grossly normal areas of human thoracic aortas taken at autopsy from 40 trauma victims aged from 3 to 40 years. Two areas of aorta were compared: lesion predisposed to atherosclerosis (LP) area localized on the dorsal aspect of the vessel along the row of intercostal branching sites, and lesion resistant (LR) area located on the ventral aspect of the vessel. Accumulation of apolipoprotein B (apo B) was found in LP aortic area of each child older than 6 years. Similar retention of apo B in LR area appeared only in aortas of teenagers. The apo B staining increased with age in both areas tested but was usually of a greater extent in LP area than in LR area. Typical smooth muscle cells (SMCs) and a few monocytes/macrophages (Mn/Mph) were revealed in the intimal layer of all aortas examined. The number of Mn/Mph dramatically increased in LP areas of individuals over 17 years. Quantitative study of double stained sections has shown a 2- to 6-fold enhanced number of Mn/Mph in LP area compared with LR aortic area of 10 men over 21 years. Focal infiltration of Mn/Mph in aortas of young adults occurred without endothelial denudation. In addition, some intimal SMCs in LP area of 12 aortas out of 29 expressed desmin and contained well-developed endoplasmic reticulum, while such cells were seldom detected in LP area of the vessels. Thus, focal accumulation of apo B with subsequent Mn/Mph infiltration and SMC phenotypic modulation in LP aortic area of young adults may be causally involved in fatty streak and atherosclerotic plaque formation.     

Endostatin inhibits angiogenesis by stabilization of newly formed endothelial tubes

Endostatin decreased vascular endothelial growth factor (VEGF)-induced formation of endothelial tubes and microvessels sprouting from aortic rings and blocked their network. After cessation of treatment, the survival time of endostatin plus VEGF-treated tubes was approximately doubled in comparison to VEGF alone. Endostatin antibody blocked VEGF-induced endothelial tube formation and disrupted existing tubes. Endostatin immunostaining was localized between endothelium and basement membrane and in inter-endothelial junctions of new, but not of quiescent, blood vessels. In tumors grown in SCID mice, endostatin immunostaining was stronger accompanying blood vessel maturation and was significantly prominent in vessels of tumor marginal zone where angiogenesis is highly active. These data indicate a new antiangiogenic action of endostatin stabilizing and maturating endothelial tubes of newly formed blood vessels. Thus, strategies accelerating vascular stabilization and maturation could be promising in tumor therapy. This revised version was published online in June 2006 with corrections to the Cover Date.     

Changes in morphology of elastin fibers during development of the tunica intima of monkey aorta

Summary The normal development of elastin fibers in the thoracic aorta was studied in fetal, young, and adult monkeys. Tissue was examined by scanning electron microscopy (SEM) after NaOH treatment and by transmission electron microscopy (TEM). The NaOH treatment of fixed tissues effectively removed collagen fibers and enabled three-dimensional visualization of the elastin fibers. In intact fetal aortae, the internal elastic lamina (IEL) was situated immediately beneath the endothelium. This IEL consisted of superficial, longitudinally arranged bundles of elastin fibrils and an underlying solid sheet containing round fenestrations. In neonates, diffuse intimal thickening was observed. In the young and young-adult monkeys, the aortae exhibited intimal thickening with slender but split IEL. One of the most important findings of this study was that elastin fibers in the intimal thickening, as well as smooth muscle cells, ran in a longitudinal fashion. This was in contrast with the elastic laminae of the media which were mainly oriented circumferentially. Subendothelial elastin fibers in this intimal thickening combined with longitudinally arranged microfibrils which formed close associations with endothelial stress fibers. In some adult monkey aortae with well-developed intimal thickening, a complex meshwork of slender elastin fibers was also found beneath the endothelium. The development of the intimal elastin fibers is discussed in relation to hemodynamic forces.     

Scanning electron microscopy: arterial endothelial integrity after fixation at physiological pressure.

The luminal surface of normal rabbit aorta was examined by scanning electron microscopy (SEM) after outlining endothelial cells by staining intercellular junctions with silver. When aortas were fixed in situ at physiological pressure before processing for SEM, a reliable assessment of the morphological integrity of the endothelium was possible. In contrast, when aortas were excised and placed in fixative, contraction of the sub-endothelial structures made interpretation of endothelial integrity difficult.     

Effect of hypercholesterolemia on cholinephosphotransferase activity in rabbit and rat vessel walls

The activity of cholinephosphotransferase (EC 2.7.8.2, CPT) which catalyses de novo synthesis of phosphatidylcholine (PC) was studied in aortas of rabbits and rats, and in brain microvessels of rabbits with a cholesterol feeding-induced hypercholesterolemia. Cholesterol feeding produced a marked atheromatous change in rabbit aortas but not in rat aortas. The aortas of cholesterol-fed rabbits displayed a significantly higher CPT activity than the controls. On the other hand, the aortic CPT activity of cholesterol-fed rats was not different from that of control rats. The brain microvessels of cholesterol-fed rabbits having atheromatous aortic lesions did not show any lipid deposition, and CPT activity was similar to that of control rabbits. A tocopherol-deficient, high-cholesterol diet produced microscopical lipid deposits in rat aortas, and CPT activity of these aortas was significantly higher than that of aortas of rats on tocopherol-supplemented diets containing either a normal or high amount of cholesterol. The increase in CPT activity in atheromatous lesion might be closely related to lipid deposition in vessel walls and may be a cause of the increase in PC content in these lesions. Further studies are required to clarify the mechanism of activation of CPT activity in atheromatous conditions.     

Formation of 15-hydroxyeicosatetraenoic acid (15-HETE) as the predominant eicosanoid in aortas from Watanabe Heritable Hyperlipidemic and cholesterol-fed rabbits

Atherosclerotic plaque formation is accompanied by hyperproliferative events which have many features of an inflammatory response. A high-performance liquid chromatography procedure was developed to analyze the inflammatory prostaglandins, leukotrienes and hydroxyeicosatetraenoic acids (HETEs) produced by aortic segments. Normal rabbit aortas incubated with tritiated arachidonic acid synthesized 12-HETE as the principal lipoxygenase metabolite, and prostacyclin as the major cyclooxygenase product. In contrast, atherosclerotic aortas from both cholesterol-fed and Watanabe Heritable Hyperlipidemic rabbits showed major increases in synthesis of lipoxygenase-derived 15-HETE, which became the predominant eicosanoid in the aortas of both types of rabbit. No leukotrienes or other 5-lipoxygenase products were detected to the detection limit of 0.5 pmol/cm aorta. 15-HETE, which is chemotactic for smooth muscle cells, mitogenic for endothelial cells, and an inhibitor of prostacyclin synthesis may thus play a role in atherogenesis.