In Vivo Optical Analysis of Quantitative Changes in Collagen and Elastin During Arterial Remodeling¶

Selective Deletion of Heparan Sulfotransferase Enzyme, Ndst1, in Donor Endothelial and Myeloid Precursor Cells Significantly Decreases Acute Allograft Rejection

Early damage to transplanted organs initiates excess inflammation that can cause ongoing injury, a leading cause for late graft loss. The endothelial glycocalyx modulates immune reactions and chemokine-mediated haptotaxis, potentially driving graft loss. In prior work, conditional deficiency of the glycocalyx-modifying enzyme N-deacetylase-N-sulfotransferase-1 (Ndst1^f/f TekCre⁺) reduced aortic allograft inflammation. Here we investigated modification of heparan sulfate (HS) and chemokine interactions in whole-organ renal allografts. Conditional donor allograft Ndst1 deficiency (Ndst1^−/−; C57Bl/6 background) was compared to systemic treatment with M-T7, a broad-spectrum chemokine-glycosaminoglycan (GAG) inhibitor. Early rejection was significantly reduced in Ndst1^−/− kidneys engrafted into wildtype BALB/c mice (Ndst1^+/+) and comparable to M-T7 treatment in C57Bl/6 allografts (P < 0.0081). M-T7 lost activity in Ndst1^−/− allografts^, while M-T7 point mutants with modified GAG-chemokine binding displayed a range of anti-rejection activity. CD3+ T cells (P < 0.0001), HS (P < 0.005) and CXC chemokine staining (P < 0.012), gene expression in NFκB and JAK/STAT pathways, and HS and CS disaccharide content were significantly altered with reduced rejection. Transplant of donor allografts with conditional Ndst1 deficiency exhibit significantly reduced acute rejection, comparable to systemic chemokine-GAG inhibition. Modified disaccharides in engrafted organs correlate with reduced rejection. Altered disaccharides in engrafted organs provide markers for rejection with potential to guide new therapeutic approaches in allograft rejection.

Tropoelastin: A novel marker for plaque progression and instability

Background

Elastolysis and ineffective elastogenesis favor the accumulation of tropoelastin, rather than cross-linked elastin, in atherosclerotic plaques. We developed gadolinium-labeled tropoelastin-specific magnetic resonance contrast agents (Gd-TESMAs) for tropoelastin imaging in animal models.

Methods and Results

Two peptides, VVGSPSAQDEASPLS and YPDHVQYTHY were selected to target tropoelastin. In vitro binding, relaxivity, and biodistribution experiments enabled characterization of the probes and selecting the best candidate for in vivo MRI. MRI was performed in atherosclerotic apolipoprotein E-deficient (ApoE^-/-) mice and New Zealand white rabbits with stable and rupture-prone plaques using Gd-TESMA. Additionally, human carotid endarterectomy specimens were imaged ex vivo. The VVGSPSAQDEASPLS-based probe discriminated between tropoelastin and cross-linked elastin (64±7% vs 1±2%, P=0.001), had high in vitro relaxivity in solution (r_1-free=11.7±0.6mM^-1s^-1, r_{1-bound to tropoelastin} = 44±1mM^-1s^-1) and favorable pharmacokinetics. In vivo mice vascular enhancement (4wks=0.13±0.007mm², 8wks=0.22±0.01mm², 12wks=0.33±0.01mm², P<0.001) and R₁ relaxation rate (4wks=0.90±0.01 s^-1, 8wks=1.40±0.03 s^-1, 12wks=1.87±0.04s^-1, P<0.001) increased with atherosclerosis progression after Gd-TESMA injection. Conversely, statin-treated (0.13±0.01mm², R₁ =1.37±0.03s^-1) and control (0.10±0.005mm², R₁ =0.87±0.05s^-1) mice showed less enhancement. Rupture-prone rabbit plaques had higher R₁ relaxation rate compared with stale plaques (R₁=2.26±0.1s^-1vs R₁=1.43±0.02s^-1, P=0.001), after administration of Gd-TESMA that allowed detection of rupture-prone plaques with high sensitivity (84.4%) and specificity (92.3%). Increased vascular R₁ relaxation rate was observed in carotid endarterectomy plaques after soaking (R_1pre= 1.1±0.26 s^-1 vs R_1post= 3.0±0.1s^-1, P=0.01). Ex vivo analyses confirmed the MRI findings and showed uptake of the contrast agent to be specific for tropoelastin.

Conclusions

MRI of tropoelastin provides a novel biomarker for atherosclerotic plaque progression and instability.

Distribution of elastic fibers in the head and neck: a histological study using late-stage human fetuses

There is little or no information about the distribution of elastic fibers in the human fetal head. We examined this issue in 15 late-stage fetuses (crown-rump length, 220-320 mm) using aldehyde-fuchsin and elastica-Masson staining, and we used the arterial wall elastic laminae and external ear cartilages as positive staining controls. The posterior pharyngeal wall, as well as the ligaments connecting the laryngeal cartilages, contained abundant elastic fibers. In contrast with the sphenomandibular ligament and the temporomandibular joint disk, in which elastic fibers were partly present, the discomalleolar ligament and the fascial structures around the pterygoid muscles did not have any elastic fibers. In addition, the posterior marginal fascia of the prestyloid space did contain such fibers. Notably, in the middle ear, elastic fibers accumulated along the tendons of the tensor tympani and stapedius muscles and in the joint capsules of the ear ossicle articulations. Elastic fibers were not seen in any other muscle tendons or vertebral facet capsules in the head and neck. Despite being composed of smooth muscle, the orbitalis muscle did not contain any elastic fibers. The elastic fibers in the sphenomandibular ligament seemed to correspond to an intermediate step of development between Meckel's cartilage and the final ligament. Overall, there seemed to be a mini-version of elastic fiber distribution compared to that in adults and a different specific developmental pattern of connective tissues. The latter morphology might be a result of an adaptation to hypoxic conditions during development.

Three-dimensional imaging of the aortic vessel wall using an elastin-specific magnetic resonance contrast agent

OBJECTIVE

The aim of this study was to demonstrate the feasibility of high-resolution 3-dimensional aortic vessel wall imaging using a novel elastin-specific magnetic resonance contrast agent (ESMA) in a large animal model.

MATERIALS AND METHODS

The thoracic aortic vessel wall of 6 Landrace pigs was imaged using a novel ESMA and a nonspecific control agent. On day 1, imaging was performed before and after the administration of a nonspecific control agent, gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA; Bayer Schering AG, Berlin, Germany). On day 3, identical scans were repeated before and after the administration of a novel ESMA (Lantheus Medical Imaging, North Billerica, Massachusetts). Three-dimensional inversion recovery gradient echo delayed-enhancement imaging and magnetic resonance (MR) angiography of the thoracic aortic vessel wall were performed on a 1.5-T MR scanner (Achieva; Philips Medical Systems, the Netherlands). The signal-to-noise ratio and the contrast-to-noise ratio of arterial wall enhancement, including the time course of enhancement, were assessed for ESMA and Gd-DTPA. After the completion of imaging sessions, histology, electron microscopy, and inductively coupled plasma mass spectroscopy were performed to localize and quantify the gadolinium bound to the arterial vessel wall.

RESULTS

Administration of ESMA resulted in a strong enhancement of the aortic vessel wall on delayed-enhancement imaging, whereas no significant enhancement could be measured with Gd-DTPA. Ninety to 100 minutes after the administration of ESMA, significantly higher signal-to-noise ratio and contrast-to-noise ratio could be measured compared with the administration of Gd-DTPA (45.7 ± 9.6 vs 13.2 ± 3.5, P < 0.05 and 41.9 ± 9.1 vs 5.2 ± 2.0, P < 0.05). A significant correlation (0.96; P < 0.01) between area measurements derived from ESMA scans and aortic MR angiography scans could be found. Electron microscopy and inductively coupled plasma mass spectroscopy confirmed the colocalization of ESMA with elastic fibers.

CONCLUSION

We demonstrate the feasibility of aortic vessel wall imaging using a novel ESMA in a large animal model under conditions resembling a clinical setting. Such an approach could be useful for the fast 3-dimensional assessment of the arterial vessel wall in the context of atherosclerosis, aortic aneurysms, and hypertension.

Spectroscopic and histological evaluation of wound healing progression following Low Level Laser Therapy (LLLT)

The present study focuses on the evaluation of the effect of He-Ne laser on tissue regeneration by monitoring collagen synthesis in wound granulation tissues in Swiss albino mice using analysis of laser induced fluorescence (LIF) and light microscopy techniques. The spectral analyses of the wound granulation tissues have indicated a dose dependent increase in collagen levels during the post-wounding days. The histological examinations on the other hand have also shown a significant increase in collagen deposition along with the reduced edema, leukocytes, increased granulation tissue, and fibroblast number in the optimal laser dose treated group compared to the non-illuminated controls.

Detection of altered extracellular matrix in surface layers of unstable carotid plaque: an optical spectroscopy, birefringence and microarray genetic analysis

Erosion and rupture of surface layers in atherosclerotic plaque can cause heart attack and stroke; however, changes in luminal surface composition are incompletely defined. Laser-induced fluorescence spectroscopy (LIFS), with limited tissue penetration, was used to investigate the surface of unstable carotid plaque and correlated with microscopy, birefringence and gene expression. Arterial matrix collagens I, III and elastin were assessed in unstable plaques (n = 25) and reference left internal mammary arteries (LIMA, n = 10). LIFS in addition to selective histological staining with picrosirius red, Movat pentachrome and immunostaining revealed decreased elastin and increased collagen I and III (P < 0.05) in carotid plaque when compared with LIMA. Within plaque, collagen I was elevated in the internal carotid region versus the common carotid region. Polarized light microscopy detected layers of aligned collagen and associated mechanical rigidity of the fibrous cap. Microarray analysis of three carotid and three LIMA specimens confirmed up-regulation of collagen I, III and IV, lysyl oxidase and MMP-12. In conclusion, LIFS analysis coupled with microscopy revealed marked regional differences in collagen I, III and elastin in surface layers of carotid plaque; indicative of plaque instability. Birefringence measurements demonstrated mechanical rigidity and weakening of the fibrous cap with complementary changes in ECM gene expression.

Ultrastructural differences in rectus sheath of hernia patients and healthy controls

BACKGROUND

The etiology of inguinal hernia remains unclear. Research data indicate the presence of pathologic alterations within the connective tissue; their exact character remains the subject of dispute. The search for new methods to diagnose connective tissue abnormalities, and thoroughly explain the character of the ultrastructural alterations, continues.

MATERIALS AND METHODS

The study group included 10 male patients aged 18-60 y (five with primary inguinal hernia and five with acute appendicitis with no history of hernia). A specimen of the rectus muscle sheath was harvested from all of them upon surgery. The tissue samples were fixed and examined by spectrofluorometry and fluorescence microscopy, yielding fluorescence spectra and microscopic fluorescence images.

RESULTS

Both techniques have demonstrated significant differences between the biopsy samples harvested from hernia patients and healthy controls. The groups of fluorescence spectra were shifted relative to each other and showed maximum emission at different wavelengths after excitation with 350 nm light (arbitrarily chosen for one of the cross-link proteins). The spectra obtained for healthy controls were more homogenous, while the spectra of the hernia samples differed even between each other. In microscopic images, the difference was a more chaotic distribution of fluorophores in the samples obtained from hernia patients.

CONCLUSIONS

The evidence of significant differences between the samples harvested from the same location from hernia patients and healthy controls, found by fluorescence techniques, indicates the presence of abnormalities in the connective tissue forming the rectus muscle sheath. This area is not a part of the hernial defect, therefore, we can assume that the changes can be attributed to a generalized process.

MRI of coronary wall remodeling in a swine model of coronary injury using an elastin-binding contrast agent

BACKGROUND

The extracellular matrix (ECM) plays an important role in the pathogenesis of atherosclerosis and in-stent restenosis. Elastin is an essential component of the ECM. ECM degradation can lead to plaque destabilization, whereas enhanced synthesis typically leads to vessel wall remodeling resulting in arterial stenosis or in-stent restenosis after stent implantation. The objective of this study was to demonstrate the feasibility of MRI of vascular remodeling using a novel elastin-binding contrast agent (BMS-753951).

METHODS AND RESULTS

Coronary injury was induced in 6 pigs by endothelial denudation and stent placement. At day 28, delayed-enhancement MRI coronary vessel wall imaging was performed before and after injection of gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA). Two days later, DE-MRI was repeated after administration of BMS-753951. Contrast-to-noise-ratio and areas of enhancement were determined. Delayed-enhancement MRI with BMS-753951 caused strong enhancement of the aortic, pulmonary artery, and injured coronary artery walls, whereas Gd-DTPA did not. Delayed-enhancement MRI of the stented coronary artery with BMS-753951 yielded a 3-fold higher contrast-to-noise-ratio when compared with the balloon-injured and control coronary artery (21±6 versus 7±3 versus 6±4; P<0.001). The area of enhancement correlated well with the area of remodeling obtained from histological data (R(2)=0.86, P<0.05).

CONCLUSIONS

We demonstrate the noninvasive detection and quantification of vascular remodeling in an animal model of coronary vessel wall injury using an elastin-specific MR contrast agent. This novel approach may be useful for the assessment of coronary vessel wall remodeling in patients with suspected coronary artery disease. Further studies in atherosclerotic animal models and degenerative ECM disease are now warranted.

Multimodal CARS microscopy determination of the impact of diet on macrophage infiltration and lipid accumulation on plaque formation in ApoE-deficient mice

We characterized several cellular and structural features of early stage Type II/III atherosclerotic plaques in an established model of atherosclerosis-the ApoE-deficient mouse-by using a multimodal, coregistered imaging system that integrates three nonlinear optical microscopy (NLOM) contrast mechanisms: coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG), and two-photon excitation fluorescence (TPEF). Specifically, the infiltration of lipid-rich macrophages and the structural organization of collagen and elastin fibers were visualized by CARS, SHG, and TPEF, respectively, in thick tissue specimens without the use of exogenous labels or dyes. Label-free CARS imaging of macrophage accumulation was confirmed by histopathology using CD68 staining. A high-fat, high-cholesterol Western diet resulted in an approximate 2-fold increase in intimal plaque area, defined by CARS signals of lipid-rich macrophages. Additionally, analysis of collagen distribution within lipid-rich plaque regions revealed nearly a 4-fold decrease in the Western diet-fed mice, suggesting NLOM sensitivity to increased matrix metalloproteinase (MMP) activity and decreased smooth muscle cell (SMC) accumulation. These imaging results provide significant insight into the structure and composition of early stage Type II/III plaque during formation and allow for quantitative measurements of the impact of diet and other factors on critical plaque and arterial wall features.

Myxoma viral serpin, Serp-1, inhibits human monocyte adhesion through regulation of actin-binding protein filamin B

Serp-1 is a secreted myxoma viral serine protease inhibitor (serpin) with proven, highly effective, anti-inflammatory defensive activity during host cell infection, as well as potent immunomodulatory activity in a wide range of animal disease models. Serp-1 binds urokinase-type plasminogen activator (uPA) and the tissue-type PA, plasmin, and factor Xa, requiring uPA receptor (uPAR) for anti-inflammatory activity. To define Serp-1-mediated effects on inflammatory cell activation, we examined the association of Serp-1 with monocytes and T cells, effects on cellular migration, and the role of uPAR-linked integrins and actin-binding proteins in Serp-1 cellular responses. Our results show that Serp-1 associates directly with activated monocytes and T lymphocytes, in part through interaction with uPAR (P<0.001). Serp-1, but not mammalian serpin PA inhibitor-1 (PAI-1), attenuated cellular adhesion to the extracellular matrix. Serp-1 and PAI-1 reduced human monocyte and T cell adhesion (P<0.001) and migration across endothelial monolayers in vitro (P<0.001) and into mouse ascites in vivo (P<0.001). Serp-1 and an inactive Serp-1 mutant Serp-1(SAA) bound equally to human monocytes and T cells, but a highly proinflammatory mutant, Serp-1(Ala(6)), bound less well to monocytes. Serp-1 treatment of monocytes increased expression of filamin B actin-binding protein and reduced CD18 (beta-integrin) expression (P<0.001) in a uPAR-dependent response. Filamin colocalized and co-immunoprecipitated with uPAR, and short interference RNA knock-down of filamin blocked Serp-1 inhibition of monocyte adhesion. We report here that the highly potent, anti-inflammatory activity of Serp-1 is mediated through modification of uPAR-linked beta-integrin and filamin in monocytes, identifying this interaction as a central regulatory axis for inflammation.

Fluorescence spectroscopy and birefringence of molecular changes in maturing rat tail tendon

Tissue remodeling during maturation, wound healing, and response to vascular stress involves molecular changes of collagen and elastin in the extracellular matrix (ECM). Two optical techniques are effective for investigating these changes--laser-induced fluorescence (LIF) spectroscopy and polarizing microscopy. LIF spectroscopy integrates the signal from both elastin and collagen cross-linked structure, whereas birefringence is a measure of only collagen. Our purpose is (1) to evaluate the rat tail tendon (RTT) spectroscopy against data from purified extracted protein standards and (2) to correlate the two optical techniques in the study of RTT and skin. Spectra from tissue samples from 27 male rats and from extracted elastin and collagen were obtained using LIF spectroscopy (357 nm). Birefringence was measured on 5-mum histological sections of the same tissue. Morphometric analysis reveals that elastin represents approximately 10% of tendon volume and contributes to RTT fluorescence. RTT maximum fluorescence emission intensity (FEI(max)), which includes collagen and elastin, increases with animal weight (R(2)=0.64). Birefringence, when plotted against weight, increases to a plateau (nonlinear correlation: R(2)=0.90), tendon having greater birefringence than skin. LIF spectroscopy and collagen fiber birefringence are shown to provide complementary measurements of molecular structure (tendon birefringence versus FEI(max) at R(2)=0.60).

Classification of atherosclerotic rabbit aorta samples by mid-infrared spectroscopy using multivariate data analysis

Atherosclerotic and normal rabbit aorta samples show a marked difference in chemical composition governed by the water, lipid, and protein content. The strongly overlapping infrared absorption features of the different constituents, and the complexity of the tissue matrix, render tissue classification by direct evaluation of molecular spectroscopic characteristics obtained from IR reflectance or attenuated total reflectance (ATR) measurements virtually impossible. We apply multivariate analysis and classification techniques based on partial least squares regression (PLS) and linear discriminant analysis to IR spectroscopic data obtained by IR-ATR measurements and reflectance IR microscopy with high predictive accuracy during blind testing. Training data are collected from atherosclerotic and normal rabbit aorta samples. These results demonstrate the potential of IR spectroscopy combined with multivariate classification strategies for the in-vitro identification of normal and atherosclerotic aorta tissue. The prospect for future in-vivo measurement concepts is also discussed.

Optical coherence tomography for imaging the vulnerable plaque

While our understanding of vulnerable coronary plaque is still at an early stage, the concept that certain types of plaques predispose patients to developing an acute myocardial infarction continues to be at the forefront of cardiology research. Intracoronary optical coherence tomography (OCT) has been developed to both identify and study these lesions due to its distinct resolution advantage over other imaging modalities. We review clinical research conducted at the Massachusetts General Hospital over the past five years to develop, validate, and utilize this technology to improve our understanding of vulnerable plaque. Our results show that intracoronary OCT may be safely conducted in patients and that it provides abundant information regarding plaque microscopic morphology, which is essential to the identification and study of high-risk lesions. Even though many basic biological, clinical, and technological challenges must be addressed prior to widespread use of this technology, the unique capabilities of OCT ensure that it will have a prominent role in shaping the future of cardiology.