Normal Arterial Wall Research Articles

Intimal Tissue Factor Activity Is Released from the Arterial Wall after Injury

Tissue factor (TF), the initiator of coagulation, has been implicated as a critical mediator of arterial thrombosis. Previous studies have demonstrated that TF is rapidly induced in the normal rodent arterial wall by balloon injury, but is not associated with fibrin deposition. A second injury, however, performed 10-14 days after the first, is followed by small platelet-fibrin microthrombi. This study was undertaken to better localize active TF in balloon-injured rat arteries and to explore possible mechanisms underlying the apparent discrepancy between injury-induced TF expression and the lack of large platelet-fibrin thrombi. By immunohistochemistry, TF antigen was first detected in the media 24 h after injury to rat aortas, and subsequently accumulated in the neointima. Using an ex vivo flow chamber, no TF activity (Factor Xa generation) was found on the luminal surface of normal or injured aortas. Wiping the luminal surface with a cotton swab exposed TF activity in all vessels; levels were increased approximately 3-fold in arteries containing a neointima. The exposed TF activity was rapidly washed into the perfusate, rendering the luminal surface inactive. The loss of luminal TF into the circulation may attenuate thrombosis at sites of arterial injury.

Neurogenic regulation of basal tone of coronary artery with mild atherosclerosis in humans: observation using two-dimensional intravascular ultrasound.

The purpose of this study was to assess the role of the autonomic nervous system in the regulation of basal coronary artery tone in normal and atherosclerotic plaque segments by using intravascular ultrasound in humans. In each of 21 patients, a short-axis image at one site of coronary artery was imaged by means of a 3.2F, 30-MHz intravascular ultrasound before and after intracoronary administration of 2 mg isosorbide dinitrate (ISDN). The authors identified the perimeters of the vessel wall segments with normal or atherosclerotic plaque on ultrasound images and evaluated the basal tone in each segment as a percent increase in each perimeter produced by ISDN. Using heart rate variability analysis for 512 seconds recorded immediately before ISDN administration, they evaluated cardiac sympathetic and vagal activities at rest as the integrated power of fast Fourier transform (FFT) spectrum for the low-frequency (LF: 0.04 to 0.15 Hz), and high-frequency (HF: 0.15 to 0.4 Hz) components, respectively. Of 29 segments examined by ultrasound, 16 were normal and 13 were atherosclerotic plaque. In all 29 segments, ISDN produced an increase in the perimeter of the vessel wall. At the normal 16 segments, the increase in perimeter by ISDN exhibited a significant correlation to the power of HF (r = 0.749, p = 0.0008) but no significant correlation to LF. At 13 plaque segments, however, no significant correlation between the response to ISDN and autonomic nerve activity was observed. In conclusion, the basal tone of normal coronary arterial wall segment is closely related to parasympathetic nerve, whereas the relation is impaired in mild atherosclerotic segments.

Expression of inducible nitric oxide synthase in macrophages and smooth muscle cells in various types of human atherosclerotic lesions.

Nitric oxide (NO) is an important regulatory agent in blood vessels. We studied the expression of inducible nitric oxide synthase (iNOS) in different types of human atherosclerotic lesions using simultaneous in situ hybridization and immunocytochemistry. Since nitric oxide and its derivates or reaction products can have both oxidative and antioxidative effects, we also studied the presence of oxidized low-density lipoproteins (ox-LDL) and peroxynitrite-modified proteins in the same lesions as indicators of oxidative damage. Twenty-seven aortic samples were studied from seven autopsies. Samples were classified microscopically as normal areas, initial lesions (type I), fatty streaks (type II), intermediate lesions (type III), atheroma (type IV), fibroatheroma lesions (type Va) and fibrotic lesions (type Vc). In normal arterial wall iNOS mRNA was expressed at a low level in smooth muscle cells (SMCs). Absence of, or a low level of, epitopes characteristic of ox-LDL was found in the normal arterial wall. The expression of iNOS mRNA and protein was induced in macrophages and SMCs in the majority of early lesions and in all advanced atherosclerotic lesions. Epitopes characteristic of ox-LDL and peroxynitrite-modified proteins tended to be colocalized in iNOS-positive lesions. We consider that iNOS and oxidative injuries may play an important part in atherogenesis.

Nε-(carboxymethyl)lysine in atherosclerotic vascular lesions as a marker for local oxidative stress

Previous studies suggested that N ε-(carboxymethyl)lysine (CML), as the major product of oxidative degradation of glycated proteins and unsaturated fatty acids, represents an integrative biomarker for oxidative stress. In the present study, the level of CML in morphologically normal as well as atherosclerotic vessel walls are immunohistochemically analyzed and the in vitro formation of CML determined from glycoxidation and lipid peroxidation processes. The analysis revealed negative staining results in normal arterial walls of fetal, juvenile and young adult origin. A minor positive staining was seen in normal arteries from adults between 40 and 60 years of age with a rise in the CML-staining further increasing with rising individual age. This staining was mainly restricted to the intimal extracellular matrix and there was no intracellular staining. In arteriosclerotic vessels, in contrast, the extracellular CML-staining was significantly increased by approximately 3-fold also affecting the vascular media and adventitia. A strong intracellular staining was seen in macrophages. The degree of CML-staining correlated with the extent of the atherosclerotic changes. The in vitro studies showed a slow formation of CML of glycated proteins under aerobic conditions. No CML was formed under anaerobic conditions. Unsaturated fatty acids revealed a much faster formation of CML which reached high levels. The addition of vitamin E did not substantially suppress the CML-formation. The data suggest that the endogenous biomarker CML for oxidative stress accumulates slowly in normal arterial walls. This process is significantly increased in atherosclerosis. While the accumulation of CML in the extracellular matrix seemed to be the result of ongoing glycoxidation, the significant intracellular CML-formation in macrophages may have resulted from lipid peroxidation.

Characterization of the dose perturbation by stents as a function of x-ray beam energy

Purpose. External beam irradiation of coronary arteries has been shown to be detrimental in an animal model for the prevention of neointimal hyperplasia in the presence of stents when orthovoltage x-ray beams are used. The present study investigated the effect of beam energy on the dose distribution in the wall of the artery in the presence of stents. Materials and Methods. We used 250-kVp x-rays and 6-MV x-rays to irradiate a stent placed in a homogeneous phantom. Radiochromic film densitometry and Monte Carlo calculations were used to measure and to simulate the dose distribution in the proximity of the stent. Result. External beam irradiation not only failed to prevent neointimal hyperplasia, but actually accentuated the neointimal response to a prompt mechanical injury in the artery. The photoelectric effect, which dominates low-energy x-ray interactions, produces recoil electrons in the stent, which enhance the dose surrounding the intima. The photoelectrons generated in nickel and iron have an extremely short range in normal tissue, approximately 0.1 mm. Initial estimates of orthovoltage x-ray interactions with the stent indicate a dose enhancement in the orthovoltage range by a factor of 2–6 due to the rise in the photoelectric cross section in this energy range depending on the elemental composition of the stent. Film densitometry verifies this dose enhancement. The Monte Carlo calculation yields a dose enhancement and the dose fall-off with distance from the stent when irradiated with orthovoltage x-rays. Conversely when the tissue and stent are irradiated with megavoltage x-rays, the dose enhancement in this region is a factor of 1.15 in close proximity to the stent and 1.0 at distances greater than 0.1 mm. The 6-MV photon interactions in tissue and Ni/Ti are predominantly through Compton scattering. The Compton effect is dependent on the electron density in the medium, in contrast to the atomic number, which is more relevant for photoelectric absorption. The dose estimates for megavoltage x-rays adjacent to the stent are complicated by the lack of charged particle equilibrium. Conclusions. There is a limited but definite increase in the dose delivery to the arterial wall when stents are irradiated with orthovoltage x-ray energies. This increase may explain the negative response in other studies. The presence of the stent does perturb the character and magnitude of the dose in the normal arterial wall as a function of beam quality.

Intravascular Ultrasound Evidence for Coarctation Causing Symptomatic Renal Artery Stenosis

A recent study of human cadaveric renal arteries revealed that renal artery narrowing could be due not only to atherosclerotic plaque compensated for by adaptive remodeling, but also to hitherto undescribed focal narrowing of an otherwise normal renal arterial wall (ie, coarctation). The present study investigated whether vessel coarctation could be identified in patients with symptomatic renal artery stenosis (RAS). Consecutive symptomatic patients with angiographically proven atherosclerotic RAS who were referred for stent placement were studied by 30-MHz intravascular ultrasound before intervention (n=18) or after predilatation (n=18). Analysis included assessment of the media-bounded area and plaque area (PLA) at the most stenotic site and at a distal reference site (most distal cross-section in the main renal artery with normal appearance). Coarctation was considered present whenever the target/reference media-bounded area was </=85%. Before intervention, coarctation was observed in 9 of 18 patients and adaptive remodeling in 9 of 18 patients. Coarctation lesions had a significantly smaller PLA than adaptive remodeled lesions (P=0.001). Similarly, despite predilatation, coarctation was seen in 8 of 18 patients who had significantly smaller PLAs (P=0. 008) when compared with those patients who had adaptive remodeled lesions. No differences in severity of RAS or angiographic or clinical parameters were observed. Low-plaque coarctation may cause a considerable proportion of symptomatic RAS, which is angiographically and clinically indistinguishable from plaque-rich RAS.

Expression of Tissue Factor Pathway Inhibitor in Vascular Smooth Muscle Cells and Its Regulation by Growth Factors

Tissue factor pathway inhibitor (TFPI) in vivo is thought to be synthesized mainly by endothelial cells. To date, no significant regulator of TFPI synthesis has been described. Vascular smooth muscle cells (VSMC) express tissue factor in vitro and in vivo, which may contribute to vascular thrombosis. We hypothesized that VSMC might also express TFPI. To determine this, we examined growth-arrested coronary VSMC in culture and found that VSMC secreted an amount of TFPI similar to that seen in endothelial cells. Immunohistochemistry of normal human coronary arteries showed TFPI staining throughout the media and intima of the vessel with localization to VSMC and endothelial cells. To determine regulation of TFPI expression in VSMC, we examined the effects of serum stimulation on TFPI secretion and found that FBS induced a 5-fold increase in TFPI antigen and activity levels in conditioned medium at 48 hours (P<0.001) when compared with serum-free conditions. A similar stimulatory effect was seen with 10% pooled human serum. Moreover, epidermal growth factor and platelet-derived growth factor-B increased TFPI secretion by 4- to 5-fold and 2- to 3-fold, respectively (P<0.05), and these growth factors accounted for approximately 50% of the TFPI secretion effects of human serum. The serum effect was associated with a 3-fold increase in TFPI mRNA 24 hours after release from growth arrest and a 50% decrease in TFPI secretion after treatment with actinomycin D. Taken together, this study suggests that there is significant TFPI expression in VSMC in culture and in VSMC within the intima and media of the normal coronary artery wall. We present the first evidence for TFPI regulation by serum in VSMC and more specifically by its constituent growth factors, epidermal growth factor and platelet-derived growth factor-B.

Arterial heparan sulfate proteoglycans inhibit vascular smooth muscle cell proliferation and phenotype change in vitro and neointimal formation in vivo

Purpose: The aim of this study was to determine whether heparan sulfate proteoglycans (HSPGs) from the normal arterial wall inhibit neointimal formation after injury in vivo and smooth muscle cell (SMC) phenotype change and proliferation in vitro. Methods: Arterial HSPGs were extracted from rabbit aortae and separated by anion-exchange chromatography. The effect of HSPGs, applied in a periadventitial gel, on neointimal formation was assessed 14 days after balloon catheter injury of rabbit carotid arteries. Their effect on SMC phenotype and proliferation was measured by point-counting morphometry of the cytoplasmic volume fraction of myofilaments (Vvmyo) and 3H-thymidine incorporation in SMCs in culture. Results: Arterial HSPGs (680 μg) reduced neointimal formation by 35% at 14 days after injury ( P = .029), whereas 2000 μg of the low-molecular-weight heparin Enoxaparin was ineffective. HSPGs at 34 μg/mL maintained subconfluent primary cultured SMCs with the same high Vvmyo (52.1% ± 13.8%) after 5 days in culture as did cells freshly isolated from the arterial wall (52.1% ± 15.1%). In contrast, 100 μg/mL Enoxaparin was ineffective in preventing phenotypic change over this time period (Vvmyo 38.9% ± 14.6%, controls 35.9% ± 12.8%). HSPGs also inhibited 3H-thymidine incorporation into primary cultured SMCs with an ID 50 value of 0.4 μg/mL compared with a value of 14 μg/mL for Enoxaparin ( P < .01). Conclusion: When used periadventitially in the rabbit arterial injury model, natural arterial HSPGs are effective inhibitors of neointimal formation. In vitro, the HSPGs maintain SMCs in a quiescent state by inhibiting phenotypic change and DNA synthesis. This study suggests that HSPGs may be a natural agent for the treatment of clinical restenosis. (J Vasc Surg 1998;28:308-18)

Chlamydial heat shock protein 60 localizes in human atheroma and regulates macrophage tumor necrosis factor-alpha and matrix metalloproteinase expression.

Recent evidence has implicated Chlamydia pneumoniae in the aggravation of atherosclerosis. However, the mechanisms by which this agent affects atherogenesis remain poorly understood. Chlamydiae produce large amounts of heat shock protein 60 (HSP 60) during chronic, persistent infections, and C pneumoniae localizes predominantly within plaque macrophages. Several studies have furnished evidence that endogenous (human) HSP 60 may play a role in atherogenesis. We tested here the hypothesis that atheroma contains chlamydial HSP 60 and that this bacterial product might stimulate macrophage functions considered relevant to atherosclerosis and its complications, such as production of proinflammatory cytokines as tissue necrosis factor-alpha (TNF-alpha) and matrix-degrading metalloproteinases (MMPs). Surgical specimens of human carotid atherosclerotic arteries (n = 19) and normal arterial wall samples (n=7, 2 carotid arteries and 5 aortas) were tested immunohistochemically for the presence of chlamydial HSP 60 and human HSP 60. Macrophage localization of these antigens was assessed by double immunostaining. Murine peritoneal macrophages, maintained in serum-free conditions for 48 hours after harvesting, were incubated with C pneumoniae, chlamydial HSP 60, human HSP 60, or Escherichia coli lipopolysaccharide (LPS). Culture supernatants, collected at 24 hours for concentration-dependence experiments and at up to 72 hours for time-dependence experiments, were analyzed for TNF-alpha by ELISA and for MMP by gelatin zymography. Atherosclerotic lesions showed immunoreactive chlamydial HSP 60 in 47% (9 of 19) of the cases and human HSP 60 in 89% (17 of 19) of the cases. Chlamydial HSP 60 colocalized with human HSP 60 within plaque macrophages in 77% (7 of 9) of the cases. Nonatherosclerotic samples contained neither HSP. Both C pneumoniae and recombinant chlamydial HSP 60 induced TNF-alpha production by mouse macrophages in a concentration- and time-dependent fashion. E coli LPS and human HSP 60 produced similar effects. Similarly, C pneumoniae and HSPs induced MMPs in a concentration- and time-dependent manner. Heat treatment abolished the effect of C pneumoniae and HSPs on both TNF-alpha and MMP production, but it did not alter the ability of E coli LPS to induce these functions. Chlamydial HSP 60 frequently colocalizes with human HSP 60 in plaque macrophages in human atherosclerotic lesions. Chlamydial and human HSP 60 induce TNF-alpha and MMP production by macrophages. Chlamydial HSP 60 might mediate the induction of these effects by C pneumoniae. Induction of such macrophage functions provides potential mechanisms by which chlamydial infections may promote atherogenesis and precipitate acute ischemic events.

Enhanced endothelium-dependent relaxations after gene transfer of recombinant endothelial nitric oxide synthase to rabbit carotid arteries.

We tested the effects of overexpression of the endothelial nitric oxide synthase (eNOS) gene in the normal arterial wall by adenoviral-mediated gene transfer. Rabbit carotid arteries were surgically isolated and exposed to adenoviral vectors encoding eNOS (AdeNOS) or beta-galactosidase (Ad betaGal) on the contralateral side. Vector solutions at a concentration of 1 x 10(10) plaque forming units/mL were instilled for 20 minutes before restoration of flow. Arteries were harvested 4 days later for immunostaining, measurement of cGMP, and vasomotor studies. Endothelium-specific gene transfer was confirmed by staining for beta-galactosidase in the Ad betaGal arteries. Immunostaining of en face endothelial cell imprints from AdeNOS-transduced arteries with a monoclonal antibody to eNOS showed increased immunoreactivity. Basal cGMP levels were significantly greater in the AdeNOS-transduced arteries (18.4+/-4.6 versus 4.2+/-0.5 pmol/mg protein; P<.05). Contractions to phenylephrine were significantly reduced in the AdeNOS-transduced arteries (area under curve, 106+/-5 versus 119+/-7; P<.05), but in the presence of the eNOS inhibitor, N(G)-monomethyl-L-arginine (L-NMMA, 3 x 10(-4) mol/L), there was no difference between the two (area under curve, 148+/-5 versus 153+/-6; P=NS). Relaxations to acetylcholine obtained during submaximal contractions to phenylephrine were significantly enhanced in the AdeNOS-transduced arteries (EC50, 7.45+/-0.05 versus 7.23+/-0.03; P<.05). We conclude that overexpression of eNOS in the endothelium results in diminished contractile responses, as well as enhanced endothelium-dependent relaxations. These findings imply a possible role for vascular eNOS gene transfer in the treatment of vasospasm and endothelial dysfunction.

Platelet-derived growth factor ligand and receptor expression in response to altered blood flow in vivo.

Blood flow and the tractive force shear stress are important determinants of artery caliber, and reduced shear predisposes arteries to intimal thickening and atherosclerosis. The molecular basis for shear-induced changes in artery wall structure is poorly defined. A number of factors associated with normal and pathological artery wall remodeling are induced by shear stress in endothelial cell cultures. These include platelet-derived growth factor (PDGF), a potent mitogen, chemoattractant, and vasoconstrictor. To determine whether similar changes occur in vivo, we examined the effects of reduced blood flow on endothelial cell PDGF expression and proliferation in the rat carotid artery. Branches of the right internal and external carotid arteries were ligated, reducing common carotid artery blood flow from 8.0+/-0.6 to 0.5+/-0.1 mL/min while increasing flow in the left carotid from 7.1+/-0.6 to 10.8+/-0.7 mL/min. Shear stress following the procedure was 1.4+/-0.2 and 33.4+/-1.1 dyne/cm2 in carotids with reduced blood flow (RF) and increased blood flow (IF), respectively. Arteries were harvested 6, 24, 48, or 72 hours after ligation, perfusion-fixed, and opened longitudinally. Endothelial cell proliferation (bromodeoxyuridine [BrdU] labeling) was assessed en face at 24, 48, and 72 hours; expression of mRNA for PDGF-A and -B chains and PDGF alpha- and beta-receptors (in situ hybridization) was determined at 6, 48, and 72 hours after unilateral flow reduction. RF induced endothelial cell proliferation, which peaked at 48 hours (RF BrdU labeling: 24 hours, 0.4+/-0.2%; 48 hours, 7.2+/-2.0%; and 72 hours, 4.1+/-0.6%; n=5). PDGF-B expression increased in RF compared with IF endothelium within 48 hours and persisted at 72 hours (percent labeling [RF/IFx100]: 6 hours, 76+/-20%; 48 hours, 395+/-179%; and 72 hours, 208+/-44%; n=3). PDGF-A expression was similarly increased in RF endothelium. In contrast, expression of PDGF alpha- and beta-receptors was undetectable in RF and IF endothelium at all times. We conclude that endothelial cell PDGF ligand expression is induced by reduced shear stress in vivo and may play an important role in flow-mediated remodeling and atherogenesis.

The nuclear factor kappa-B signaling pathway participates in dysregulation of vascular smooth muscle cells in vitro and in human atherosclerosis.

In the lesions of atherosclerosis, vascular smooth muscle cells (SMC) display many functions characteristic of cytokine activation that likely contribute importantly to ongoing inflammation during human atherogenesis. The transcription factor nuclear factor kappa-B (NFkappaB) often mediates the effects of cytokines on target cells, but the identity of Rel family members important in human SMC activation remains uncertain. In vitro, human SMC express multiple Rel family members. Of these, dimers of p65 and p50, but not a putative SMC-Rel, comprise basal and inducible NFkappaB binding activities. SMC express two inhibitor proteins IkappaBbeta and IkappaBalpha. Interleukin-1beta stimulation caused transient loss of IkappaBalpha and a sustained decrease of IkappaBbeta that correlated with increased and persistent levels of p65/p50 protein and binding activity in the nucleus. SMC cultured under serum-free conditions displayed little NFkappaB activity, but addition of serum or platelet-derived growth factor did activate NFkappaB. In situ analyses showed no evidence for basal NFkappaB activity in SMC in vivo as nonatherosclerotic arteries did not contain nuclear p65 or p50 protein. However, the nuclei of intimal SMC within human atheroma did contain both Rel proteins. We conclude that (i) dimers of p65 and p50, but not SMC-Rel, comprise NFkappaB complexes in human SMC; (ii) stimulatory components in serum activate NFkappaB and likely account for previously reported "constitutive" NFkappaB activity in cultured SMC; and (iii) exposure to inflammatory cytokines may produce prolonged NFkappaB activation in SMC because of sustained decreases in the inhibitory subunit IkappaB-beta.

Perspectives of coronary excimer laser angioplasty: Multiplexing, saline flushing, and acoustic ablation control

Background and Objective Bubble formation, pressure wave generation, and cavitations constitute major factors influencing the outcome of clinical Excimer laser angioplasty. Thus, the rationale of this study was to determine the extent of pressure waves occurring during excimer laser ablation and to discuss possibilities that allow a less traumatic plaque removal in the coronary circulation. Study Design/Materials and Methods Conventional and experimental Xenon-Chlorid-Excimer lasers emitting light at a wave-length of 308nm and a pulse duration of 115ns were used for testing of signals. Whereas the conventional excimer laser light source transmits light through all fibres of a 1.7 mm laser catheter simultaneously, the prototype excimer laser divides the laser beam into several areas of uniform energy fluence by scanning the beam from one section to the other using the intermission between two laser discharges. Hydrophones consisting of piezoelectric films detected the acoustic signals, which were obtained on normal arterial wall and atherosclerotic plaque. Results Multiplexing decreases maximum pressures for both normal arterial wall and calcified plaque significantly, whereas pressure rise time remains comparable. During ablation of pure blood, a linear increase of peak pressures of 1 MPa at 10 mJ/mm2 to 7.5 MPa at 50 mJ/mm2 is found. Contrast media intensifies the extent of pressure wave formation. At 20 mJ/mm2, 60% contrast media added to blood results in an increase of maximum pressures from 1.5 MPa up to 5 MPa. Dilution with saline solution is effective; however, high concentrations of > 90% are required to achieve a significant pressure wave reduction. Conclusion Peak pressures of several thousand kPa occur during excimer laser ablation of contrast media, blood, calcified plaque, and normal arterial wall in a decreasing order. Multiplexing and saline flushing are capable of reducing the intensity of the generated acoustic signals during tissue ablation. It has to be taken into consideration, however, that high concentrations of saline solution are necessary to achieve a significant reduction of peak pressures. Lasers Surg. Med. 21:72–78, 1997. © 1997 Wiley-Liss, Inc.

Perspectives of coronary excimer laser angioplasty: multiplexing, saline flushing, and acoustic ablation control.

Bubble formation, pressure wave generation, and cavitations constitute major factors influencing the outcome of clinical Excimer laser angioplasty. Thus, the rationale of this study was to determine the extent of pressure waves occurring during excimer laser ablation and to discuss possibilities that allow a less traumatic plaque removal in the coronary circulation. Conventional and experimental Xenon-Chlorid-Excimer lasers emitting light at a wave-length of 308 nm and a pulse duration of 115 ns were used for testing of signals. Whereas the conventional excimer laser light source transmits light through all fibers of a 1.7 mm laser catheter simultaneously, the prototype excimer laser divides the laser beam into several areas of uniform energy fluence by scanning the beam from one section to the other using the intermission between two laser discharges. Hydrophones consisting of piezoelectric films detected the acoustic signals, which were obtained on normal arterial wall and atherosclerotic plaque. Multiplexing decreases maximum pressures for both normal arterial wall and calcified plaque significantly, whereas pressure rise time remains comparable. During ablation of pure blood, a linear increase of peak pressures of 1 MPa at 10 mJ/mm2 to 7.5 MPa at 50 mJ/mm2 is found. Contrast media intensifies the extent of pressure wave formation. At 20 mJ/mm2, 60% contrast media added to blood results in an increase of maximum pressures from 1.5 MPa up to 5 MPa. Dilution with saline solution is effective; however, high concentrations of > 90% are required to achieve a significant pressure wave reduction. Peak pressures of several thousand kPa occur during excimer laser ablation of contrast media, blood, calcified plaque, and normal arterial wall in a decreasing order. Multiplexing and saline flushing are capable of reducing the intensity of the generated acoustic signals during tissue ablation. It has to be taken into consideration, however, that high concentrations of saline solution are necessary to achieve a significant reduction of peak pressures.

Effect of Rotational Atherectomy in Noncalcified Atherosclerotic Plaque: A Volumetric Intravascular Ultrasound Study

Objectives. This study used pre-rotational and post-rotational atherectomy volumetric intravascular ultrasound analysis to determine whether rotational atherectomy causes ablation of noncalcified atherosclerotic plaque.Background. Rotational atherectomy is currently the preferred treatment for heavily calcified coronary lesions. However, the mechanism of lumen enlargement in noncalcified lesions has not been studied in detail. Intravascular ultrasound allows detailed, cross-sectional imaging of the coronary arteries in vivo. The normal coronary artery wall, the major components of the atherosclerotic plaque and the quantitative changes in vessel, lumen and plaque cross-sectional areas and volumes that occur as a result of the atherosclerotic disease process and during transcatheter therapy can be studied in a manner otherwise not possible.Methods. Eighteen noncalcified native vessel lesions in 18 patients were imaged before and after rotational atherectomy using intravascular ultrasound systems incorporating motorized transducer pullback through a stationary imaging sheath. External elastic membrane, lumen and plaque plus media cross-sectional areas were measured every 1 mm of lesion length (for a total of 10 image slices), and external elastic membrane, lumen and plaque plus media volumes were calculated using Simpson's rule.Results. After rotational atherectomy, the minimal lumen cross-sectional area increased from 1.37 ± 0.50 to 2.99 ± 0.60 mm2 (mean value ± 1 SD, p < 0.0001). Lumen volume increased from 23.2 ± 9.0 to 38.0 ± 8.0 mm3 (p < 0.0001) as a result of a decrease in plaque plus media volume (from 102.2 ± 50.9 to 85.8 ± 47.7 mm3, p < 0.0001), with no change in total vessel (external elastic membrane) volume (125.3 ± 54.2 to 123.8 ± 52.9 mm3, p = 0.119).Conclusions. Rotational atherectomy effectively ablates noncalcified plaque in non-calcium-containing lesions.

Smooth muscle DNA replication in response to angiotensin II is regulated differently in the neointima and media at different times after balloon injury in the rat carotid artery. Role of AT1 receptor expression.

We have reported that angiotensin II (Ang II) infusion to rats during the third and fourth weeks after vascular injury stimulates DNA replication in a larger proportion of smooth muscle cells (SMCs) in the arterial neointima than in the underlying media or the normal arterial media. Whether this increased responsiveness to Ang II is a transient or stable property of neointimal cells after vascular injury remained unclear. The present study examined smooth muscle DNA replication in response to Ang II infusion (250 ng.kg-1.min-1 for 2 weeks) at 3 to 4, 9 to 10, or 27 to 28 weeks after balloon injury to the rat carotid artery. Control rats received Ringer's lactate. BrdU (0.8 mg.kg-1.d-1) was coinfused to label replicating DNA. The increased replicative response to Ang II in the neointima versus the normal arterial media did not persist beyond the period of rapid lesion growth shortly after injury, even in neointimal areas without endothelial regeneration. By 9 to 10 weeks after injury, replication frequencies were comparable in the neointima and the normal arterial wall. In the presence of a regenerated endothelium, neointimal DNA replication was lowered but not abolished. After the early period, however, the most marked difference may be the loss of ability of medial SMCs to respond mitogenically to systemic Ang II. As a consequence, Ang II-induced DNA replication in injured arteries was greater in the neointima than in the underlying media at all times studied after injury. DNA replication levels correlated with AT1 receptor levels in the injured artery neointima but not media, as shown by receptor binding in vascular sections at 3 and 10 weeks after injury. The growth response to systemic Ang II is differentially regulated in adjacent smooth muscle layers in the injured arterial wall in vivo via mechanisms that include, but are not restricted to, the regulation of AT1 receptor expression in SMCs.

Significance of automated stenosis detection during quantitative angiography. Insights gained from intracoronary ultrasound imaging.

Automated stenosis analysis is a common feature of commercially available quantitative coronary angiography (QCA) systems, allowing automatic detection of the boundaries of the stenosis, interpolation of the expected dimensions of the coronary vessel at the point of obstruction, and angiographically derived estimation of atheromatous plaque size. However, the ultimate meaning of this type of analysis in terms of the degree of underlying atherosclerotic disease remains unclear. We investigated the relationship between stenosis analysis performed with QCA and the underlying degree of atherosclerotic disease judged by intracoronary ultrasound (ICUS) imaging. In 40 coronary stenoses, automated identification of the sites of maximal luminal obstruction and the start of the stenosis was performed with QCA by use of curvature analysis of the obtained diameter function. Plaque size at these locations also was estimated with ICUS, with an additional ICUS measurement immediately proximal to the start of the stenosis. Crescentlike distribution of plaque, indicating an atheroma-free arc of the arterial wall, was recorded. At the site of the obstruction, total vessel area measured with ICUS was 16.65 +/- 4.04 mm2, whereas an equivalent measurement obtained from QCA-interpolated reference dimensions was 7.48 +/- 3.30 mm2 (P = .0001). Plaque area derived from QCA data was significantly less than that calculated from ICUS (6.32 +/- 3.21 and 13.29 +/- 4.22 mm2, respectively; mean difference, 6.92 +/- 4.43 mm2; P = .0001). At the start of the stenosis identified by automated analysis, ICUS plaque area was 9.38 +/- 3.17 mm2, and total vessel area was 18.77 +/- 5.19 mm2 (50 +/- 11% total vessel area stenosis). The arterial wall presented a disease-free segment in 28 proximal locations (70%) but in only 5 sites (12%) corresponding to the start of the stenosis and none at the obstruction (P = .0001). At the site of obstruction, all vessels showed a complete absence of a disease-free segment, and the atheroma presented a cufflike or all-around distribution with a variable degree of eccentricity. At the site of maximal obstruction, QCA underestimated plaque size as measured with ICUS. Atherosclerotic disease was consistently present at the start of the stenosis and was used as a reference site by automated stenosis analysis. At the start of the stenosis, ICUS demonstrated a mean 50 +/- 11% total vessel area stenosis, with a characteristic loss of disease-free arcs of arterial wall present in proximal locations. Thus, the site identified by automated stenosis analysis as the start of the stenosis does not represent a disease-free site but rather the place where compensatory vessel enlargement fails to preserve luminal dimensions, a phenomenon that seems related to the observed loss of a remnant arc of normal arterial wall.

Langhans cells of human arterial intima: uniform by stellate appearance but different by nature

The stellate cells in human arterial intima known as Langhans cells were investigated. Arterial specimens were obtained during carotid endarterectomy and aortic reconstruction and included atherosclerotic lesions as well as areas of the adjacent normal appearing arterial wall. Following immunohistochemical and electron microscopic analysis, most of the stellate cells were found to inhabit the elastic-hyperplastic layer of the intima in the normal arterial wall but in atherosclerotic lesions, stellate cells were distributed throughout all intimal layers. Immunohistochemical examination revealed that different types of intimal cells, including smooth muscle cells (HHF-35; smooth muscle alpha-actin +) and vascular dendritic cells (CD1a +, S-100 +), exhibited a typical stellate appearance but the cell processes of macrophages (HAM56 +, CD68 +) were too short for macrophages to be considered as stellate. No other intimal cells formed processes which could be detected under immunohistochemical examination. In atherosclerotic lesions, some smooth muscle cells transforming to foam cells retained their stellate shape. Smooth muscle cells interacted with each other through gap junctions while other intimal cells including vascular dendritic cells contacted each other without forming any specialized structures. We conclude that Langhans cells comprise two histological types of intimal cells, namely, smooth muscle cells and vascular dendritic cells.

Inhibitors of fibrinolysis are elevated in atherosclerotic plaque.

The proteins of the fibrinolytic system have been examined in the human normal and atherosclerotic arterial wall by immunohistochemical techniques and by quantitative immunoassay of extracts. The concentration of plasminogen activator inhibitor-1 (PAI-1) increased significantly during the progression from normal vessels to fatty streaks to the developed atherosclerotic plaque. Staining for PAI-1 was strongly positive, particularly in the areas adjacent to the plaque. In these areas, PAI-1 appeared to colocalized with its binding protein vitronectin. Alpha2-antiplasmin (alpha2-AP) was present in the aorta at even higher concentrations than PAI-1; a small but significant increase was seen in some atherosclerotic compared with normal vessel walls. Tissue plasminogen activator (TPA) showed the opposite trend, being lowest in lesions with plaque. Thus, higher concentrations of the two principal inhibitors of fibrinolysis, PAI-1 and alpha2-AP, together with lower levels of TPA, are characteristic of advanced atheromatous lesions. Alteration in the balance of the fibrinolytic system, favoring its inhibition, may predispose to the development or maintenance of atherosclerotic plaque.

Limitations of Angiography in the Assessment of Plaque Distribution in Coronary Artery Disease

Plaque distribution (eccentricity) may be a determinant of the success of transcatheter therapy, and certain devices may be better suited to treating severely eccentric lesions than others. However, no study has compared methods for assessing plaque distribution or systematically studied the validity of the angiographic assessment of plaque distribution. We studied 1446 native vessel target lesions in 1349 patients by intravascular ultrasound and coronary angiography. Angiographic and intravascular ultrasound criteria for lesion eccentricity were compared. Angiography showed that 795 of 1446 (55.0%) of target lesions were eccentric. When intravascular ultrasound was used, only 219 lesions (15.1%) had an arc of normal arterial wall within the lesion (equivalent to the pathological definition of lesion eccentricity). When an eccentricity index of >/= 3.0 was used, intravascular ultrasound classified 659 lesions (45.6%) as eccentric. The concordance rates of classification were only 47.7% (versus lesions containing an arc of normal arterial wall) and 53.8% (versus lesions with an ultrasound eccentricity index of >/= 3.0). More eccentric lesions had larger lumen cross-sectional areas, smaller plaque plus media and external elastic membrane cross-sectional areas, and smaller arcs of calcium, suggesting that they may represent less advanced atherosclerotic disease. There was significant discordance between angiography and ultrasound in assessing plaque distribution. Angiography appeared to detect lesion eccentricity more often than intravascular ultrasound. Furthermore, markedly eccentric lesions, in which there is an arc of normal vessel wall, were uncommon.