Cigarette Smoke Extract Activates Tartrate-Resistant Acid Phosphatase-Positive Macrophage.

BACKGROUND: It has been reported that smoking is one of the strongest positive risk factors for abdominal aortic aneurysms (AAAs). Although many studies have been directed to decipher the effect of smoking on AAA, its effect on macrophage activation has not yet been explored. OBJECTIVES: We have reported the importance of osteoclastogenesis (OCG) in aneurysm formation. Therefore, we examined the effect of cigarette smoking on OCG and arterial aneurysmal formation by using cigarette smoke extract (CSE) in this study. METHODS: Macrophage cell lines were stimulated with CSE, and their activation and differentiation were examined in vitro. Since macrophages activated through the OCG pathway are identified by tartrate-resistant acid phosphatase (TRAP) expression, these cells are referred to as TRAP-positive macrophages (TPMs) in this study. We also applied CSE-contained PBS in the calcium chloride-induced mouse carotid aneurysm model in vivo. RESULTS: Macrophages stimulated with CSE expressed significantly higher levels of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), TRAP, cathepsin K, matrix metalloproteinase-9 and membrane-type metalloproteinase (MT1-MMP). CSE-treated mouse aneurysms showed increased aneurysm size with increased TPM infiltration and protease expression compared to non-CSE-treated mouse aneurysms. CONCLUSIONS: These results suggest that CSE intensifies OCG in macrophages and promotes arterial aneurysmal progression.

Functional Heterogeneity of Nadph Oxidases in Atherosclerotic and Aneurysmal Diseases.

NADPH oxidases (NOX) are enzymes that catalyze the production of reactive oxygen species (ROS). Four species of NOX catalytic homologs (NOX1, NOX2, NOX4, and NOX5) are reportedly expressed in vascular tissues. The pro-atherogenic roles of NOX1, NOX2, and their organizer protein p47ph°x were manifested, and it was noted that the hydrogen peroxide-generating enzyme NOX4 possesses atheroprotective effects. Loss of NOX1 or p47ph°x appears to ameliorate murine aortic dissection and subsequent aneurysmal diseases; in contrast, the ablation of NOX2 exacerbates the aneurysmal diseases. It is possible that the loss of NOX2 activates inflammatory cascades in macrophages in the lesions. Roles of NOX5 in vascular functions are currently undetermined, owing to the absence of this enzyme in rodents and the limitation of the experimental procedure. Thus, it is possible that the NOX family of enzymes exhibits heterogeneity in the atherosclerotic diseases. In this aspect, subtype-selective NOX inhibitor may be promising when NOX systems serve as a molecular target for atherosclerotic and aneurysmal diseases.

The role of matrix metalloproteinases and neutrophil gelatinase-associated lipocalin in central and peripheral arterial aneurysms.

INTRODUCTION: An association between arterial aneurysms and matrix metalloproteinases (MMPs) has been described previously. MMPs regulate extracellular structural proteins and tissue remodeling. Neutrophil gelatinase-associated lipocalin (NGAL) is involved in the regulation of MMP activity. The aim of this work was to study the relationship between the levels of MMPs and NGAL and arterial aneurysms. METHODS: In a multicenter, open-label, parallel groups, prospective study, patients with aneurysmal disease were divided into 2 groups: Group I (with ruptured aneurysm) and group II (with nonruptured aneurysm). Healthy volunteer patients were also enrolled and represented the control group (group III). RESULTS: We enrolled 307 patients (107 in group I and 200 in group II) with arterial aneurysm: 49 popliteal, 31 common femoral, 2 superficial femoral, 29 common iliac artery, 3 common carotid, and 193 abdominal aorta. Finally, 11 healthy volunteer patients (9 males and 2 females; age range, 40-70 years; median 56) were enrolled in group III. Enzyme-linked immunosorbent assay and Western blot analysis revealed greater levels of immunoreactive MMP-9 and NGAL in all patients with ruptured aneurysms, both central and peripheral aneurysms, and in the aneurismal vessels. CONCLUSION: These results provide potentially important insights to the understanding of the natural history of arterial aneurysms. MMPs and NGAL play a role in development of arterial aneurysms and may represent molecular markers for the prevention of aneurysmal rupture.

Network wiring of pleiotropic kinases yields insight into protective role of diabetes on aneurysm.

Recent studies suggest a protective role of diabetes in the development of aneurysm, but the biological mechanisms behind this are still unknown. This type of association is not present in the case of diabetes and atherosclerosis despite similar risk factors for aneurysm and atherosclerosis. We postulate the existence of genes that disrupt the pathways needed for the onset of aneurysm in the presence of diabetes. Motivated by the significance of genetic interactions in understanding disease-disease associations, we tackle this problem by integrating protein-protein interaction and genetic interaction data, i.e., we examine the biological pathways related to the three diseases that contain genes involved in the following genetic interactions: one gene in a genetic interaction is part of a diabetes pathway, the other gene is part of an aneurysm, or an atherosclerosis pathway. We create a protein-protein interaction sub-network that contains disease pathways described above. We then use a "brokerage" measure - a topological measure that identifies proteins in this sub-network whose removal severely affects the interconnectedness of their neighbourhood, enabling such proteins to disrupt the pathway they are in. We identify a set of proteins with high brokerage values and find this set to be enriched in biological functions, including cell-matrix adhesion, which facilitates mechanisms that have already been suggested as possible causes of diabetes-aneurysm association. We further narrow down our set to 16 proteins that are involved in an aneurysm or an atherosclerosis pathway and are encoded by genes participating in genetic interactions with a gene in a diabetes pathway. This set is enriched in kinases and phosphorylation processes, with two pleiotropic kinases that are involved in both aneurysm and atherosclerosis pathways. Kinases can turn on or off proteins, explaining how functional changes of such proteins could result in the disruption of pathways. So if in an aneurysm-related pathway a gene is turned off, the onset of the disease could be prevented. However, mutations of pleiotropic genes could have effects only on one of the traits, which explains why pleiotropic kinases that are involved in both aneurysm and atherosclerosis pathways could disrupt aneurysm pathways explaining the reduced risk of aneurysm in diabetes patients, but not affect the atherosclerosis pathways.

An important role of matrix metalloproteinase-8 in angiogenesis in vitro and in vivo.

AIMS: Growing evidence suggests a close association of plaque angiogenesis with atherosclerotic plaque formation and progression, and an important role of matrix metalloproteinase (MMP) in angiogenesis and atherosclerosis. We attempted to investigate the functional involvements of MMP8 in angiogenesis. METHODS AND RESULTS: Knockdown of MMP8 in human umbilical vein endothelial cells (HuVECs) with MMP-8 shRNA lentivirus resulted in a decrease in in vitro capillary-like network formation, cell proliferation and migration, and impaired its capacity of in vivo angiogenesis. Less nuclear accumulation of ß-catenin and lower ß-catenin target gene expression levels was observed in the HuVECs expressing lower levels of endogenous MMP8. Knockdown of endogenous MMP8 in HuVECs down-regulated platelet/endothelial cell adhesion molecule-1 (PECAM-1) expression by converting less angiotensin I to II, which is an inducer for PECAM-1 gene expression. Aortic rings isolated from MMP8(-/-)/apoE(-/-) mice had less endothelial cell sprouting, and endothelial cells in MMP8(-/-)/apoE(-/-) mice had a lower ability to migrate into Matrigel plugs and less capacity of proliferation and angiogenesis. Moreover, immunohistochemical analyses revealed that MMP8 was expressed in microvessels within human atherosclerotic plaques and aneurysm. Finally, analyses of MMP8(-/-)/apoE(-/-) and MMP8(+/+)/apoE(-/-) mice fed a Western diet for 12 weeks showed that MMP8-deficient mice had small lesion size and less endothelial cells within atherosclerotic lesions. CONCLUSION: We demonstrated for the first time that MMP8 plays an important role in angiogenesis in vitro and in vivo. Our findings provide new insights into the molecular mechanisms of plaque angiogenesis and suggest that MMP8 is a potential therapeutic target of cardiovascular diseases.

Matrix metalloproteinases in vascular physiology and disease.

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that primarily degrade components of the extracellular matrix (ECM). Remodeling of the ECM by MMPs is important in both physiological and pathological processes, including organ generation/regeneration, angiogenesis, wound healing, inflammation and tumor growth. In the vasculature, MMPs play a role in beneficial processes such as angiogenesis, collateral artery formation and thrombus resolution. However, MMP expression is also implicated in the pathogenesis of vascular diseases such as atherosclerosis, aortic aneurysms, plaque rupture and neointimal hyperplasia after balloon angioplasty. Here, we review the structure, functions and roles of MMPs in both neovascularization and vascular pathology and discuss the potential of, and challenges that face, adapting MMPs as therapeutic targets in vascular disease.

Matrix metalloproteinase-2 regulates the expression of tissue inhibitor of matrix metalloproteinase-2.

1. Matrix metalloproteinases (MMP) are associated with the vascular remodelling seen in atherosclerosis and aneurysm. The activation and activity of MMP-2 are regulated by the intrinsic tissue inhibitor of MMP-2 (TIMP-2). The aim of the present study was to examine whether, conversely, MMP-2 can affect the gene and protein expression of TIMP-2. 2. In the present study, we examined the mRNA and protein expression of MMP-2 and TIMP-2 in cultured smooth muscle cells (SMC) from the aortas of MMP-2(+/+) and MMP-2(-/-) mice. We also examined the roles of MMP-2 in SMC cellular events. 3. Western blotting showed that less TIMP-2 protein was present in the conditioned medium of MMP-2(-/-) SMC than in that of MMP-2(+/+) SMC. Real-time reverse transcription polymerase chain reaction analysis showed that MMP-2 deficiency reduced TIMP-2 mRNA expression in SMC. Recombinant MMP-2 enhanced the expression of TIMP-2 protein in cultured SMC from MMP-2(-/-) mice. Furthermore, a siRNA targeting MMP-2 impaired the gene and protein expression of MMP-2 in cultured SMC from MMP-2(+/+) mice. MMP-2 deficiency impaired SMC invasion, but not their proliferation, adhesion or migration. 4. Our findings suggest that MMP-2 is likely to be responsible, at least in part, for regulating TIMP-2 expression and is thus a potential target, in addition to TIMP-2, for therapeutics aimed at preventing cardiovascular remodelling in response to injury.

Carotid artery brain aneurysm model: in vivo molecular enzyme-specific MR imaging of active inflammation in a pilot study.

PURPOSE: To demonstrate the feasibility of using a myeloperoxidase (MPO)-specific paramagnetic magnetic resonance (MR) contrast agent to identify active inflammation in an animal model of common carotid artery (CCA) aneurysm. MATERIALS AND METHODS: All animal experiments were approved by the institutional animal care and use committee. Elastase-induced saccular aneurysms were created at the root of the right CCA in 16 New Zealand white rabbits. Intramural and perivascular injection of Escherichia coli lipopolysaccharide (LPS) was performed with an endovascular approach to induce aneurysm inflammation. After intraarterial injection of an MPO-specific (di-5-hydroxytryptamide of gadopentetate dimeglumine, 0.1 mmol per kilogram of bodyweight) or a non-MPO-specific (di-tyrosine of gadopentetate dimeglumine, 0.1 mmol/kg) contrast agent, animals underwent 3-T MR imaging. Intramural presence of MPO in aneurysms in which LPS had been injected was confirmed at immunohistologic analysis. Active MPO activity was verified by measuring the spectrophotometric oxidation of guaiacol. RESULTS: Endovascular injection of LPS resulted in inflammatory cell infiltration into the aneurysm wall, and there was a difference in active MPO expression between aneurysms in which LPS had been injected and control aneurysms (20.3 ng of MPO per milligram of tissue vs 0.12 ng of MPO per milligram of tissue, respectively; P < .002). MR imaging with di-5-hydroxytryptamide of gadopentetate dimeglumine revealed a difference in enhancement ratio between inflamed aneurysms in which LPS had been injected and control aneurysms (1.55 +/- 0.05 vs 1.16 +/- 0.10, respectively; P < .02). In inflamed aneurysms, di-5-hydroxytryptamide of gadopentetate dimeglumine exhibited delayed washout kinetics compared with the kinetics of di-tyrosine of gadopentetate dimeglumine. This finding enabled the verification of MPO specificity. CONCLUSION: The findings of this pilot study established the feasibility of an animal model of saccular aneurysm inflammation that can be seen with clinical-field-strength MR imaging and use of the enzyme-sensitive MR contrast agent di-5-hydroxytryptamide of gadopentetate dimeglumine, which is a paramagnetic MPO substrate that specifically enhances MR signal.

Metalloproteinase expression in venous aneurysms.

INTRODUCTION: Although recognized with increasing frequency, the pathogenesis of venous aneurysms (VA) remains poorly understood. We evaluated 8 patients with 10 VA for the presence, localization and activity of metalloproteinases (MMPs). METHODS: Tissue specimens from VA (n=8), normal saphenous vein (NSV n=7) and varicose veins (VV n=7 were compared by histology and immunohistochemistry (IHC). Histologic sections were stained with H&E, Movats pentachrome and toluidine blue, and IHC specimens with antibodies to CD68, MMP2, MMP9, and MMP13. Protein expression and enzyme activity were determined by Western immunoblotting and zymography. RESULTS: Three of 4 patients with popliteal VA presented with edema and leg pain and the remaining patient with deep venous thrombosis (DVT) and pulmonary embolism (PE). The 5 popliteal VA were treated by; excision and reanastomosis (n=2) lateral venorrhaphy (n=2) and spiral saphenous vein graft (n=1). The 3 patients with 4 upper extremity VA had discomfort over a compressible mass. Two of the VA were excised and the remaining patients aneurysm ruptured spontaneously. The mesenteric VA, an incidental finding at laparotomy was excised. Thrombus was present in 2 popliteal, 1 upper extremity and in the mesenteric aneurysm. Histologically, VA and VV were characterized by fragmentation of the elastic lamellae, loss of smooth muscle cells (SMCs) and attenuation of the venous wall when compared to NSV. Varicose veins and VA also demonstrated increased expression of MMP-2, MMP-9 and MMP-13 in endothelial cells (ECs), SMCs and adventitial microvessels compared to NSV. Both pro-MMP-2 and pro-MMP-9 were detected by zymography in VA,VV and NSV but only MMP-2 activity was demonstrable. CONCLUSIONS: The structural changes in the venous wall in addition to the increased expression of MMP-2, MMP-9 and MMP-13 in VA compared to NSV and VV suggests a possible causal role for these MMPs in their pathogenesis.

Endothelial nitric oxide synthase gene single-nucleotide polymorphism predicts cerebral vasospasm after aneurysmal subarachnoid hemorrhage.

Vasospasm is a major cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). Studies have shown a link between single-nucleotide polymorphisms (SNPs) in the endothelial nitric oxide synthase (eNOS) gene and the incidence of coronary spasm and aneurysms. Alterations in the eNOS T-786 SNP may lead to an increased risk of post-aSAH cerebral vasospasm. In this prospective clinical study, 77 aSAH patients provided genetic material and were followed for the occurrence of vasospasm. In multivariate logistic regression analysis, genotype was the only factor predictive of vasospasm. The odds ratio (OR) for symptomatic vasospasm in patients with one T allele was 3.3 (95% confidence interval (CI): 1.1 to 10.0, P=0.034) and 10.9 for TT. Patients with angiographic spasm were 3.6 times more likely to have a T allele (95% CI: 1.3 to 9.6, P=0.013; for TT: OR 12.6). Patients with severe vasospasm requiring endovascular therapy were more likely to have a T allele (OR 3.5, 95% CI: 1.3 to 9.5, P=0.016; for TT: OR 12.0). Patients with the T allele of the eNOS gene are more likely to have severe vasospasm. Presence of this genotype may allow the identification of individuals at high risk for post-aSAH vasospasm and lead to early treatment and improved outcome.

Matrix metalloproteinase-9 may play a role in recanalization and recurrence after therapeutic embolization of aneurysms or arteries.

PURPOSE: Matrix metalloproteinase (MMP)-9 plays various roles in vascular healing and angiogenesis. This study was conducted to determine if MMP-9 is involved in healing or recanalization after therapeutic occlusion of arteries or aneurysms. MATERIALS AND METHODS: Angiographic and pathologic changes were investigated in canine bilateral venous pouch carotid aneurysms embolized with gelatin sponges with or without previous endothelial denudation, a procedure that can prevent recanalization. To assess a potential role of MMP-9, messenger RNA (mRNA) and protein were compared in denuded and nondenuded aneurysms 4, 7, and 14 days after embolization. To assess if MMP-9 is essential to arterial recanalization, transmyocardial angiography and pathologic findings were compared 14 days after carotid occlusion with platinum coils in MMP-9-knockout and wild-type mice. RESULTS: Denudation of the endothelial lining led to improved angiographic results at 3 weeks (P < .001). Neointimal closure of the aneurysm neck was more complete in denuded versus nondenuded aneurysms. Denudation was followed by a decrease in MMP-9 mRNA (86%, P < .05) and protein (30%, P < .05) 7 days after embolization and a decrease in von Willebrand factor compared with nondenuded aneurysms. MMP-9 immunostaining of axial sections from embolized aneurysms confirmed MMP-9-positive endothelialized clefts, which were absent in denuded aneurysms. Transmyocardial angiography and pathologic examination showed recanalization of one of nine coiled carotid arteries of MMP-9-knockout mice, compared with five of seven controls (P = .035). CONCLUSIONS: MMP-9 may play a role in recanalization of arteries after coil occlusion and in recurrences after sponge embolization of aneurysms.

Matrix metalloproteinase-2: the forgotten enzyme in aneurysm pathogenesis.

The pathogenesis of abdominal aortic aneurysm (AAAs) involves progressive cycles of proteolysis and inflammation, the product of proteolysis driving subsequent inflammation. Little is yet known about the initiating events. We review the specific literature examining the possibility that MMP-2 may be the initial catalyst. Histologically, elastolysis is one of the earliest observable events in aneurysm genesis. Matrix metalloproteinase-2 (MMP-2), as the dominant gelatinase differentially expressed in aneurysmal tissue and cells derived from aneurysms, would be a good candidate. We report the results of in vivo and in vitro experiments, which lend support to the importance of MMP-2 as an aneurysmal initiator.

Diffusion of Alexa Fluor 488-conjugated dendrimers in rat aortic tissue.

In this study, the distribution of labeled dendrimers in native and aneurysmal rat aortic tissue was examined. Adult male rats underwent infrarenal aorta perfusion with generation 5 (G5) acetylated Alexa Fluor 488-conjugated dendrimers for varying lengths of time. In a second set of experiments, rats underwent aortic elastase perfusion followed by aortic dendrimer perfusion 7 days later. Aortic diameters were measured prior to and postelastase perfusion, and again on the day of harvest. Aortas were harvested 0, 12, or 24 h postperfusion, fixed, and mounted. Native aortas were harvested and viewed as negative controls. Aortic cross-sections were viewed and imaged using confocal microscopy. Dendrimers were quantified (counts/high-powered field). Results were evaluated by repeated measures ANOVA and Student's t-test. We found that in native aortas, dendrimers penetrated the aortic wall in all groups. For all perfusion times, fewer dendrimers were present as time between dendrimer perfusion and aortic harvest increased. Longer perfusion times resulted in increased diffusion of dendrimers throughout the aortic wall. By 24 h, the majority of the dendrimers were through the wall. Dendrimers in aneurysmal aortas, on day 0 postdendrimer perfusion, diffused farther into the aortic wall than controls. In conclusion, this study documents labeled dendrimers delivered intra-arterially to native rat aortas in vivo, and the temporal diffusion of these molecules within the aortic wall. Increasing perfusion time and length of time prior to harvest resulted in continued dendrimer diffusion into the aortic wall. These preliminary data provide a novel mechanism whereby local inhibitory therapy may be delivered locally to aortic tissue.

Vitamin k epoxide reductase: a protein involved in angiogenesis.

Vitamin K epoxide reductase (VKOR) is a newly identified protein which has been reported to convert the epoxide of vitamin K back to vitamin K, a cofactor essential for the posttranslational gamma-carboxylation of several blood coagulation factors. We found that the gene is expressed ubiquitously including vascular endothelial cells, smooth muscle cells, fibroblasts and cardiomyocytes, and is overexpressed in 11 tumor tissues on microarray. Stable transfection of VKOR cDNA into tumor cell line A549 and H7402 did not promote the cell proliferation. These results promoted us to hypothesize that VKOR may also be involved in angiogenesis. To test this hypothesis, the expression of VKOR was studied in different vascular cells in developmental and pathologic heart tissues. The effects of overexpression and suppressing expression of VKOR on endothelial cell proliferation, migration, adhesion, and tubular network formation were explored. We found that VKOR expression in arteries was prominent in vascular endothelial cells and was high in the ventricular aneurysm tissue of human heart and human fetal heart. In vitro studies showed that overexpression of VKOR slightly but significantly stimulated human umbilical vein endothelial cell proliferation (by 120%), migration (by 118%), adhesion (by 117%), as well as tubular network formation. Antisense to VKOR gene inhibited the proliferation (by 67%), migration (by 64%), adhesion (by 50%), and tubular network formation. Our findings support the impact of VKOR in the process of angiogenesis; hence, the molecule may have a potential application in cardiovascular disease and cancer therapy.

Role of leukocyte elastase in preventing cellular re-colonization of the mural thrombus.

To explore possible mechanisms responsible for the absence of cell re-colonization of mural thrombi in aneurysms, we analyzed the release and storage of leukocyte proteases in the most luminal layer versus intermediate and abluminal layers of 10 mural thrombi of human abdominal aortic aneurysms. The luminal layer contained many polymorphonuclear leukocytes (PMNs), which released pro-matrix metalloproteinase (MMP)-9 and MMP-8. Leukocyte elastase was also stored and released by the luminal layer (immunohistochemistry, activity on synthetic substrates, and casein zymography). Acid buffer allowed extraction of leukocyte elastase from the luminal layer, which was inhibited by elastase inhibitors. Casein zymography of luminal extracts and conditioned medium from formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMNs exhibited a similar lysis pattern, corresponding to elastase activity. Smooth muscle cell (SMC) seeding resulted in colonization of the intermediate thrombus layer ex vivo but not of the luminal layer. Extracts of the luminal layer induced loss of anchorage of both cultured human smooth muscle cells and stromal cells of bone marrow origin (anoikis). This anoikis was prevented by preincubation of the extracts with serine protease inhibitors. Moreover, adhesion of human SMCs and stromal bone marrow cells on fibrin gels was strongly inhibited when the gel was preincubated with pure elastase, medium of fMLP-stimulated PMNs, or extracts of luminal layers of mural thrombi. This loss of cell anchorage was prevented by the preincubation of the medium or extracts with alpha(1)-antitrypsin, but not when alpha(1)-antitrypsin was added after binding of elastase to the fibrin gel. In conclusion, elastase released by PMNs trapped within the mural thrombus impairs the spontaneous anchorage of mesenchymal cells to a fibrin matrix. This phenomenon could be one mechanism by which cellular healing of the mural thrombus in aneurysms is prevented.

Pathophysiology of arterial aneurysms.

Studies were performed to evaluate the contributions of elastin and collagen to the formation of arterial aneurysms. Dog carotid arteries and human external and internal iliac arteries were excised, mounted horizontally in a tissue bath, and were pressurized. Vessel diameter and longitudinal force were measured. the vessels were treated with elastase or collagenase. Those treated with elastase dilated, but never ruptured. Those treated with collagenase dilated still more and, in every case, ruptured. Circumferential stability resulted from recruitment of previously non-loaded collagen fibers, and from a change in geometry from a cylinder to a sphere. The laminated thrombus lining the lumen has little intrinsic strength and therefore does not confer strength to the aneurysmal wall. Treatment with elastase also reduces the retractive force exerted by the vessel in the longitudinal direction. Therefore loss of elastin permits the vessel to elongate and to become tortuous. In aged human arteries collagen also contributes a small portion of the retractive force. Progressive enlargement of aneurysms results from continued failure of wall connective tissues reflecting a) genetically defective collagen and or b) activity of the immune system.

Elastolytic and collagenolytic studies of arteries. Implications for the mechanical properties of aneurysms.

Studies were performed in vitro on cylindrical segments of 56 canine common carotid arteries, 32 human external iliac arteries, nine internal iliac arteries, and ten common iliac arteries, using purified elastase and purified collagenase. Treatment with elastase caused the canine vessels to dilate but to remain intact. Similar results were obtained with the human vessels, except that treatment with elastase caused only slight dilation. All canine and human vessels treated with collagenase ruptured. We concluded that wall integrity depends on intact collagen rather than elastin. Comparison between external iliac arteries and internal and common iliac arteries showed that the latter vessels exhibited dramatically greater dilatation and compliance changes after treatment with collagenase. This finding corresponds to the greater tendency of aneurysms to develop in internal and common iliac arteries.

Decreased lysyl oxidase activity in the aneurysm-prone, mottled mouse.

Inbred mice bearing certain alleles at the Mottled locus have defects in connective tissue which result in weakness of skin and of blood vessels. Previous studies have established that cross-links in collagen and elastin are decreased in these animals due to impaired formation of lysine-derived aldehydes. Lysyl oxidase activity in extracts of skin is markedly lower in those prepared from affected animals than control mice. An inhibitor of lysyl oxidase is present in equal amounts in affected and control skins and does not account for diminished activity found in affected animals.