Assessment of endothelialization of aneurysm wall over time in a rabbit model through CD31 scoring.

BACKGROUND: Intracranial aneurysms represent a significant health concern and are poorly understood despite decades of research. Our study focused on understanding temporal patterns of endothelial cell distribution in different spatial locations within the aneurysm early after creation in a rabbit model. METHODS: Elastase induced saccular aneurysms were created in rabbits and harvested on day 1 (n=3) and after 2 (n=5), 4 (n=4), 8 (n=5), and 12 (n=6) weeks. Sham operated controls (n=3) were harvested on the same day. Aneurysm and control tissue samples were subjected to en face whole mount CD31 staining for endothelial cells. Semiquantitative scoring was performed on the basis of endothelial coverage of the vessel wall (proximal, middle, and distal portions of the aneurysm dome). Mixed effects models were used to assess the effect of time and aneurysm section on endothelial coverage. RESULTS: Aneurysmal segments were near completely de-endothelialized at 4 and 8 weeks but had re-endothelialized by 12 weeks. Compared with controls, aneurysms at all time points showed decreased endothelialization, but the difference was only significant compared with the 4 and 8 week groups. Both time (P=0.03) and aneurysm section (P=0.07) were significantly associated with the degree of endothelialization. Proximal locations showed increased endothelialization compared with distal locations (P=0.03). CONCLUSION: In experimental aneurysms of rabbits, endothelial cells regress during the first month after creation, followed by ascending re-endothelialization that stays incomplete. These findings suggest that re-population of endothelial cells comes from resident cells in the adjacent parent artery and that deranged hemodynamics may affect full reconstitution of endothelial cells long term.

In vivo assessment of intraplaque and endothelial fibrin in ApoE(-/-) mice by molecular MRI.

OBJECTIVE: Molecular magnetic resonance imaging (MRI) has emerged as a promising non-invasive modality to characterize atherosclerotic vessel wall changes on a morphological and molecular level. Intraplaque and endothelial fibrin has recently been recognized to play an important role in the progression of atherosclerosis. This study aimed to investigate the feasibility of intraplaque and endothelial fibrin detection using a fibrin-targeted contrast-agent, FTCA (EPIX Pharmaceuticals, Lexington, MA), in a mouse model of atherosclerosis. METHODS: Male apolipoproteinE-knockout mice (ApoE(-/-)) were fed a high fat diet (HFD) for one to three months. MRI of the brachiocephalic artery was performed prior to and 90 min after the administration of FTCA (n=8 per group). Contrast to noise ratios (CNR) and longitudinal relaxation rates (R1) of plaques were determined and compared to ex vivo fibrin density measurements on immunohistological sections stained with a fibrin-specific antibody and gadolinium concentrations measured by inductively coupled mass spectroscopy (ICP-MS). RESULTS: Molecular MRI after FTCA administration demonstrated a significant increase (p<0.05) in contrast agent uptake in brachiocephalic artery plaques. In vivo CNR measurements were in good agreement with ex vivo fibrin density measurements on immunohistochemistry (y=2.4x+11.3, R(2)=0.82) and ICP-MS (y=0.95x+7.1, R(2)=0.70). Late stage atherosclerotic plaques displayed the strongest increase in CNR, R1, ex vivo fibrin staining and gadolinium concentration (p<0.05). CONCLUSION: This study demonstrated the feasibility of intraplaque and endothelial fibrin imaging using FTCA. Direct in vivo fibrin detection and quantification could be useful for characterization and staging of coronary and carotid atherosclerotic lesions, which may aid diagnosis and intervention.

Assessment of protein-incorporated arginine methylation in biological specimens by CZE UV-detection.

Protein arginine methyltransferases methylate post-translationally arginine residues in proteins to synthesize monomethylarginine (MMA), asymmetric dimethylarginine (ADMA), or symmetric dimethylarginine. Protein arginine methylation is involved in the regulation of signal transduction, RNA export, and cell proliferation. Moreover, upon proteolysis, arginines are released into the cytosol in which they exert important biological effects. Both MMA and ADMA are inhibitors of nitric oxide synthase and especially elevated levels of ADMA are associated with endothelial dysfunction and cardiovascular disease. Quantification of these analytes is commonly performed by HPLC after sample cleanup and derivatization. We propose a CE method in which these steps have been avoided and the procedure for sample preparation has been simplified. After acidic hydrolysis of proteins, samples were dried, resuspended in water, and directly injected in CE. A baseline separation of analytes was reached in a 60 cm x 75 microm id uncoated silica capillary, by using a Tris-phosphate run buffer at pH 2.15. This method allows an accurate assessment of protein arginine methylation degree in different biological samples such as whole blood, plasma, red blood cells, cultured cells, and tissue. Moreover, its good sensitivity permits to evaluate the methylation of a single protein type after the opportune purification steps. A method applicability concerns both clinical laboratories, where the evaluation of blood protein from numerous samples could be rapidly performed, and research laboratories where the factors affecting the arginine protein methylation degree could be easily studied.

Assessment of endogenous and therapeutic arteriogenesis by contrast ultrasound molecular imaging of integrin expression.

BACKGROUND: We hypothesized that molecular imaging with contrast-enhanced ultrasound (CEU) and microbubbles targeted to endothelial integrins could be used to noninvasively assess early angiogenic responses to ischemia and growth factor therapy. METHODS AND RESULTS: Hindlimb ischemia was produced in 48 rats by ligation of an iliac artery. Half of the animals received intramuscular sustained-release fibroblast growth factor-2 (FGF-2). Immediately after ligation and at subsequent intervals from 4 to 28 days, blood flow and oxygen tension in the proximal adductor muscles were measured by CEU perfusion imaging and phosphor quenching, respectively. Targeted CEU imaging of alpha(v)- and alpha5beta1-integrin expression was performed with microbubbles bearing the disintegrin echistatin. Iliac artery ligation produced a 65% to 70% reduction in blood flow and oxygen tension. In untreated ischemic muscle, muscle flow and oxygen tension partially recovered by days 14 to 28. In these animals, signal from integrin-targeted microbubbles was intense and peaked before flow increase (days 4 to 7). In comparison to untreated animals, FGF-2-treated muscle had a greater rate and extent of blood flow recovery and greater signal intensity from integrin-targeted microbubbles, which peaked before maximal recovery of flow. On immunohistology, arteriolar but not capillary density increased in the ischemic limb after ligation, the rate and degree of which were greater in FGF-2-treated rats. Immunofluorescence demonstrated intense staining for alpha(v) in arterioles, the temporal course of which correlated with targeted imaging. CONCLUSIONS: Targeted CEU can be used to assess endogenous and therapeutic arteriogenesis before recovery of tissue perfusion. These results suggest that molecular imaging of integrin expression may be useful for evaluating proangiogenic therapies.

The assessment of anti-endothelial cell antibodies in scleroderma-associated pulmonary fibrosis. A study of indirect immunofluorescent and western blot analysis in 49 patients with scleroderma.

We recently reported on the use of an indirect immunofluorescent method designated the rodent lung assay; this test assesses for the presence of circulating antibodies directed at components of the microvasculature. Serum samples from 49 patients with scleroderma were incubated with rodent lung tissue sections and visualized with fluoresceinated human anti-IgG. The assay also was performed on samples from a control group. Western blot analysis was performed with endothelial cell protein extracts using serum samples from patients with scleroderma and from healthy control subjects. The control subjects had a negative indirect immunofluorescent assay result. In the patients with scleroderma, there was a significant positive correlation between intensity of indirect immunofluorescent staining and pulmonary fibrosis (r = 0.316; P = .0347) and hypertension (r = 0.310; P = .0408). Western blot analysis revealed antibody binding to proteins in extracts of human endothelial cells in all patients in whom there was evidence of pulmonary disease. The indirect immunofluorescent rodent lung assay and Western blot data support a potential role of anti-endothelial cell antibodies in the propagation of scleroderma-associated pulmonary disease.

Contrast-enhanced transrectal color doppler ultrasonography (TRCDUS) for assessment of angiogenesis in prostate cancer.

BACKGROUND: The clinical relevance of tumor angiogenesis has been investigated in several human tumors, including prostate carcinoma (PC). Previously, we found angiogenesis, measured as microvessel density (MVD), to be an independent prognostic factor in PC. Therefore, we evaluated contrast-enhanced Transrectal Color Doppler Ultrasonography (TRCDUS) for assessment of angiogenesis in PC. MATERIALS AND METHODS: We investigated 15 patients with PC before radical prostatectomy (RP) and 3 control patients before radical cystoprostatectomy. TRCDUS was performed using a micro-bubble-based ultrasound enhancer Levovist for identifying hypervascularized areas within the prostate. Computer-assisted quantification of color pixel intensity (PI) was used to evaluate objectively the hypervascularized areas; resistive index (RI) measurements were also obtained in these areas. After histopathological examination of the entire prostate gland for tumor confirmation, immunohistochemical evaluation of MVD using a polyclonal antibody against factor VIII was performed as described by Weidner et al. (N Engl J Med 324: 1-8, 1991). TRCDUS findings were correlated with the immunohistochemical data. RESULTS: All patients showed hypervascularized areas (range: 1-9) on contrast-enhanced TRCDUS. Hypervascularized areas showed a sensitivity of 50.8% and a specificity of 95.2% for detecting PC. Analysis of TRCDUS data and immunohistochemistry revealed a significant correlation between PI and MVD in PC specimens, demonstrating a correlation coefficient of r2 = 0.977 (p<0.001). RI did not correlate with MVD. CONCLUSION: Contrast-enhanced TRCDUS showed a high specificity in identifying PC. PI correlated significantly with MVD. Therefore, quantification of color Doppler signals seems to be helpful for assessment of angiogenesis in PC.

Quantitative assessment of the normal cerebral microvasculature by endothelial barrier antigen (EBA) immunohistochemistry: application to focal cerebral ischemia.

Cerebrovascular endothelium participates importantly in the pathophysiology of ischemic injury. Endothelial barrier antigen (EBA) is a protein located in the luminal plasma membrane of normal central and peripheral nervous-system endothelium. In this study, we assessed the sensitivity and specificity of EBA as a quantitative marker of normal endothelium and characterized alterations of EBA immunohistochemistry following focal cerebral ischemia. Anesesthetized, non-ischemic control rats (N=6) were studied. Other animals (N=5) received 90 min of middle cerebral artery occlusion (MCAo) followed by 3-day survival. Brains were prepared by perfusion-fixation and paraffin-embedding. For EBA immunohistochemistry, a monoclonal antibody (1:2000 dilution) was used. Adjacent sections were reacted for activated microglia by isolectin immunochemistry. Morphometric image-analysis was carried out in standardized microscopic fields. In control brains, pial and parenchymal blood vessels of all sizes were distinctly and selectively immunolabeled for EBA; background staining was absent. EBA-positive vascular profiles occupied 4.3+/-0.36% (mean+/-S.D.) of the microscopic field. The mean area of each identified profile was 51+/-13 micromter(2). The low coefficients of variation for both numbers of profiles (17%) and fractional areas (8%) denoted high inter-animal consistency. In brains with prior MCAo, numbers of EBA-immunoreactive vascular profiles in infarcted cortex and striatum were reduced by 39 and 46%, respectively, and their fractional areas were decreased by 63 and 76%, respectively, compared to contralateral hemisphere. Activated microglia were prominent in zones of frank infarction and in adjacent paramedian cortex; the latter region, however, showed normal-appearing EBA-immunostaining. EBA-immunohistochemistry provides a sensitive and specific index of normal cerebrovascular endothelial structures of all sizes. The technique lends itself well to quantitative morphometry and is applicable to perfusion-fixed paraffin-embedded material. EBA immunoreactivity declines in zones of ischemic infarction.

Examining the technique of angiogenesis assessment in invasive breast cancer.

The intensity of angiogenesis as measured by the density of microvessels has been reported to be associated with a poor prognosis in invasive breast cancer in some, but not all, studies. The reasons for these discrepancies may be variations in the methodologies used. The monoclonal antibody used to identify the microvessels, the number of high-density areas or 'hotspots' counted and the type of value taken for statistical analysis (highest count or mean count) have varied between the different studies. We have assessed which of the three commonly used monoclonal antibodies provides the best visualization of microvessels in invasive breast cancer and have used methods that give reproducible data for the optimum number of 'hotspots' to count for each reagent. Thus, microvessels in formalin-fixed paraffin-embedded specimens from 174 primary breast cancers were immunohistochemically stained with monoclonal antibodies to FVIIIRAg, CD31 and CD34 and ten fields counted at 200 x magnification for each antibody. The highest count and the mean value of the highest of three, five and ten counts were used to examine the relationship between the density of microvessels and overall survival of patients with a median follow-up time of 7.1 years. Antibodies to CD31 and CD34 identified more vessels than antibodies to FVIIIRAg (median highest count per mm2: CD31 = 100, CD34 = 100, FVIIIRAg = 81). The monoclonal antibody to CD31, however, was the least reliable antibody, immunohistochemically staining only 87% of sections compared with 98% for the monoclonal to CD34 and 99% for the monoclonal to FVIIIRAg. There was a high degree of correlation between the number of vessels stained by the different antibodies, though there were some considerable differences in actual counts for serial sections of the same specimen stained by the different antibodies. Patients could be divided into two groups corresponding to those with high microvessel densities and those with low microvessel densities. Using Kaplan-Meier survival curves, there was a close association for all three antibodies between vessel density and survival whichever method of recording the highest vessel densities was used. Using log-rank tests and Cox's regression analysis, anti-CD34 gave the most significant results of the three antibodies, whereas a simple cut-off at the 75th percentile for the high and low groups produced the best association with patient survival. For anti-CD34 the highest microvessel density (P = 0.0014) and the mean value of the highest three microvessel densities (P = 0.004) showed a good correlation with patient death, whereas for anti-CD31 (P = 0.008) and anti-FVIIIRAg (P = 0.007) the highest count gave the best correlation using Cox's regression analysis.

Determination of 1-O-acyl-2-acetyl-sn-glyceryl-3-phosphorylcholine, platelet-activating factor and related phospholipids in biological samples by high-performance liquid chromatography--tandem mass spectrometry.

Combining normal-phase HPLC separation and tandem mass spectrometric detection, using an ion-spray HPLC-MS interface, a quantitative method for acyl-platelet activating factor (acyl-PAF), platelet-activating factor (PAF) and related phospholipids was developed. Mass spectra, positive ions, showed intense [M+H]+ ions; collision-induced dissociation of protonated molecular ions gave characteristic daughter ions corresponding to the polar head. Detection limits of 0.1-0.3 ng injected were obtained by multiple reaction monitoring. Samples of human endothelial cells treated with compounds modulating the levels of acyl-PAF and PAF have been analyzed by the present technique, proving that this approach is suitable for biochemical studies.

A method for the assessment of hypoxia in the arterial wall, with potential application in vivo.

According to the anoxemia theory of atherosclerosis, an imbalance between the demand for and supply of oxygen in the arterial wall is a key factor in the development of atherosclerotic lesions. Direct in vitro and in situ measurements have shown that PO2 is decreased in the inner part of the media, but the degree of hypoxia in vivo or the distribution of hypoxia along the arterial tree is not known. We applied a hypoxia marker, 7-(4'-(2-nitroimidazol-1-yl)-butyl)-theophylline (NITP), to develop a method for the detection of hypoxia in the arterial wall. Immunoperoxidase and immunofluorescence were used to detect the marker, and a clearly PO2-dependent staining was observed in the media of rabbit and swine aorta in vitro. The cutoff PO2 level was probably around 2 to 3 mm Hg. In experimental atherosclerotic lesions in the rabbit the marker seemed to bind to foam cells that were already at a higher surrounding PO2, which might reflect a higher local oxygen consumption. The binding of the marker to endothelial cells was not PO2 dependent. One explanation for this finding could be that the marker was metabolized via a non-oxygen-dependent pathway in these cells. We propose that this method may be used to assess arterial wall hypoxia in vivo. Furthermore, the spatial resolution allows the detection of local variations within the arterial tree.

A simplified and low-cost one-stage chromogenic assay for tissue factor dependent procoagulant activity of endothelial cells.

We developed a sensitive tissue factor (TF) chromogenic assay on a limited number of endothelial cells (EC), performed in microtiter plates, and which uses a normal pooled human plasma instead of purified concentrates as a source of coagulation factors. Primary cultures of human umbilical vein EC (HUVEC), both unstimulated and stimulated by lipopolysaccharide (LPS) were incubated with 50 microliters of of diluted normal human plasma (NHP) and 50 microliters of Factor Xa-specific chromogenic substrate (CBS 31-39, Stago, France). Hirudin was added at 4 U/ml to the plasma/CBS 31-39 mixture to inhibit thrombin generation. Optical densities were read at 405 nm and corresponding amounts of generated factor Xa were expressed in mU Xa/well using a standard curve established with purified human Factor Xa. The following parameters were then defined: the number of EC to plate (10(4) EC/well of a 96-well plate), the plasma-test dilution (1:20), the concentration of CBS 31-39 (0.50 mM) and the incubation time of reagents with EC (2 hours). The procoagulant activity (PCA) measured was only dependent on TF since it was no longer detectable either when FVII-deficient plasma was tested instead of normal human plasma or when PCA assays were performed in the presence of a blocking anti-human TF monoclonal antibody. This method allowed detection of a TF-dependent PCA on as few as 1000 EC per well. In addition, TF expression equal to 50% of maximal values was measured with LPS concentrations as low as 1 ng/ml, supporting the high sensitivity of the assay.