Assessment of the role of pancreatic proteases in human abdominal aortic aneurysms and occlusive disease

Elastase and Collagenase Activities in the Wall of the Abdominal Aortic Aneurysm

Some patients with arteriosclerosis of the abdominal aorta develop occlusive lesions (group O) while others develop aneurysmal dilatation (group A). Defects in the tissue organization, possibly secondary to a familial factor, are demonstrated by enzyme imbalance in the aortic wall.

The authors report their own experience in comparing elastase and collagenase activ ities between the two groups. Tissue from the aortic wall of 24 consecutive patients undergoing surgery for either aneurysmal (8 patients) or occlusive aortic disease (16 patients) was subjected to suitable biochemical assays. Four samples from group O were excluded because of low tissue weight and/or zero protein content. Aortic wall elastase was found to be significantly higher in group A than in group O. When expressed in nmol/gram tissue, the median elastase content in group A was 8.211 (range: 3.4078-14.2049) compared with 3.049 (range: 0-5.6359 of group O (P = 0.0030). This difference was still significant if it was expressed in nmol/gram protein, the comparable figures being 2.303 (range: 0.616-5.171) and 0.559 (0-1.345) respectively (P = 0.0018). On the other hand the authors were unable to confirm previous findings suggesting a variation in collagenase levels between the two groups either by using additive substrate (P = 0.3348) or by using endogenous substrate (P = 0.2170).

This suggest that collagenase may not be implicated in the development of aneurysmal dilatation. Alternatively it may be tightly bound or inhibited in the aortic tissue protein matrix in such a way as to make measurement of its activity difficult, while still contributing to the pathological process. More refined techniques of detecting colla genase may therefore be required.

Multivariate statistical interpretation of laboratory clinical data

Laboratory aids are extensively used in the diagnosis of diseases, in preventive medicine, and as management tools. Reference values of clinically healthy people serve as a guide to the clinician in evaluating biochemical parameters. Determination of 21 biochemical parameters of healthy persons using standard methods of analysis. Cluster analysis and principal components analysis were applied on the above 21 biochemical parameters data. The application of a typical classification approach as cluster analysis proved that four major groups of similarity between all 21 clinical parameters are formed, which correspond to the authors assumption of the existence of several summarizing pattern of clinical parameters such as “enzyme,” “major component excretion”, “general health state,” and “blood specific” pattern. These patterns appear also in the subsets obtained by separation of the general dataset into “male”, “female”, “young”, and “adult” healthy groups. The results obtained from principal components analysis have additionally proved the validity of a similar assumption. The intelligent data analysis on the clinical parameter dataset has shown that when a complex system is considered as a multivariate one, the information about the system substantially increases. All these results support an idea that probably a general health indicator could be constructed taking into account the existing classification groups in the list of clinical parameters.

Activators of Plasminogen and the Progression of Small Abdominal Aortic Aneurysms

The aim of this study was to examine the role of activating pathways of plasminogen in the natural history of abdominal aortic aneurysms (AAA). To fulfill this objective 70 male patients with small AAA (> 3 cm) were interviewed and examined. Their blood samples were taken at diagnosis. The patients were scanned annually for a minimum period of 1 year and a maximum of 5 years (mean 2.5 years), and referred for surgery if the AAA exceeded 5 cm in diameter. Plasma levels of urokinase-like plasminogen activator (uPA), tissue-type plasminogen activator (tPA), plasminogen-activator-inhibitor-1 (PAI-1), macrophage-inhibiting factor (MIF), transforming-growth-factor-beta1 (TGF-beta1), homocysteine, and serum levels of IgA-antibodies against Chlamydia pneumoniae (IgA-CP) and cotinine (a nicotine metabolite) were measured. The annual expansion rate correlated positively with tPA, IgA-CP, and S-cotinine; rho = 0.37 (P = 0.004), 0.28 (P = 0.01), and 0.24 (P = 0.04), while PAI-1, uPA, TGF-beta1, homocysteine, and MIF did not. S-cotinine and PAI-1 also correlated positively with tPA, rho = 0.24 (P = 0.04), and 0.33 (P = 0.005). IgA-CP did not correlate with tPA. By receiver operating characteristics (ROC) curve analysis, tPA showed to be predictive of cases expanding to above 5 cm within the first 5 years with an optimal sensitivity and specificity of 0.73 and 0.71, respectively (P = 0.015). The aortic matrix degradation in AAA may be partly caused by an activation of plasminogen by tPA, but not by uPA, which usually dominates matrix degradation. Smoking seems to be an important factor for this pathway, while the pathway of IgA-CP seems different.

Detection of type III collagen fragments in specimens of abdominal aortic aneurysms

The purpose of this study was to analyze the collagens in aortic aneurysm walls and to investigate the mechanism of the formation of calcified abdominal aortic aneurysms (AAAs). Collagens were extracted from human aneurysmal aortic walls obtained during surgery, and from human nonaneurysmal aortic walls obtained at autopsy, using pepsin-acetic acid digestion. Electrophoresis and immunoblotting were performed. Type III collagen was found to be reduced in the arteriosclerotic aneurysmal aortic walls. The alpha1 chain of type II collagen/alpha1 chain of type I collagen ratio was 0.35+/-0.11 in the aortic aneurysms and 0.68+/-0.11 in the nonaneurysmal aortic walls (P=0.0111). All the calcified aneurysms were associated with type III collagen fragments having molecular mass of approximately 70 kDa and 30 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Thus, we concluded that AAAs with calcification may be caused by an abnormal degradation of type III collagen.

Expansion rates of abdominal aortic aneurysm: current limitations in evaluation

OBJECTIVES

Literature on the expansion rate of infrarenal aortic aneurysm is scant. This review was carried out to assess whether there is a normal rate of expansion for infrarenal aortic aneurysms.

DESIGN AND METHODS

Review of literature relating to abdominal aortic aneurysm (AAA) measurement and expansion rates. Articles were identified from a search of the computerised Medline database from 1966 onwards.

RESULTS

Nine studies produced expansion rates for 3.0-5.0 cm AAA ranging from 0.17 to 0.57 cm per year. Evaluation of these studies showed that they are not wholly comparable in terms of source population, sample size, disease definition and period of assessment.

CONCLUSIONS

It is not possible to discuss with confidence the "normal" expansion rate of infrarenal aortic aneurysms at any diameter. To elucidate fully the behaviour of AAA, a clear and universal definition of AAA is required in order that it may be used within a large, multicentered prospective cohort study.

Aminoterminal propeptide of type III procollagen in the follow-up of patients with abdominal aortic aneurysms

PURPOSE

We evaluate here whether serial changes in the concentration of the aminoterminal propeptide of type III procollagen (PIIINP) in serum bear any relationship to the rate of abdominal aortic aneurysm (AAA) expansion and whether serum PIIINP has any predictive value with respect to the rupture event.

METHODS

One hundred thirty-nine patients with asymptomatic AAAs were followed-up at intervals of 6 to 12 months by means of a clinical examination, B-mode ultrasound scan, and serum markers of collagen metabolism. Similar laboratory samples were also obtained from 18 patients who had a rupture of the AAA as their primary symptom soon after onset.

RESULTS

The primary correlation between serum PIIINP and AAA diameter was 0.22 (p = 0.01), and that between serum PIIINP and the thickness of the thrombus was 0.49 (p = 0.001). Toward the end of the follow-up, however, the correlation increased to 0.55 (p = 0.002) for serum PIIINP and diameter, but remained at 0.42 (p = 0.02) for serum PIIINP and the thickness of the thrombus. Serum PIIINP values were very high among the 18 patients who had ruptured AAAs.

CONCLUSIONS

Acceleration of AAA growth is reflected in serum PIIINP, and a marked elevation of serum PIIINP during follow-up of a patient with an AAA may predict an approaching rupture event.

Evidence for altered balance between matrix metalloproteinases and their inhibitors in human aortic diseases

BACKGROUND

Although abdominal aortic aneurysms (AAAs) exhibit increased expression of matrix metalloproteinases (MMPs), the functional balance between MMPs and their tissue inhibitors (TIMPs) remains uncertain. This report compares the proteolytic activity in normal aorta, aorto-occlusive disease (AOD), and AAA by use of a novel in situ zymographic technique.

METHODS AND RESULTS

Infrarenal aortic specimens were obtained from 25 patients undergoing surgery for AOD or AAA and were compared with normal aortic tissue (n = 7) obtained from cadavers. Immunohistochemical staining was performed for collagenase (MMP-1), gelatinase A (MMP-2), stromelysin (MMP-3), TIMP-1, and TIMP-2. Net proteolytic activity was determined with in situ zymography whereby aortic sections were incubated on fluorescently labeled substrate. Proteolytic activity was detected under epifluorescent examination. Compared with normal aortic tissue, AOD and AAA tissue demonstrated marked increases in MMP-1 and MMP-3 immunoreactivity, predominantly in the neointima, and modest increases in TIMP-1. MMP-2 was increased in the diseased aortas, and TIMP-2 was abundant in normal, AOD, and AAA samples. Zymography revealed proteolytic activity in AOD and AAA tissues with active digestion of casein and gelatin substrate, particularly on the luminal portion of the specimens. Normal specimens exhibited no lytic activity. Comparison of AOD and AAA specimens revealed no difference in MMP/TIMP immunoreactivity or net proteolytic activity.

CONCLUSIONS

MMP expression is markedly increased in AOD and AAA samples, and an imbalance between MMPs and their inhibitors results in similar proteolytic activity. The eventual formation of aneurysmal or occlusive lesions appears not to result from an ongoing difference in the proteolytic pattern.

Activated forms of MMP2 and MMP9 in abdominal aortic aneurysms

PURPOSE

This consistent observation of a reduction of the elastin concentration in abdominal aortic aneurysms (AAAs) has led us to investigate in AAA specimens two metalloproteinases that display elastase activity, MMP2 (gelatinase A/72kDa) and MMP9 (gelatinase B/92 kDa).

METHODS

Samples of full-thickness aortic wall, adherent thrombus, and serum were collected in 10 patients with AAAs. Samples of normal aortic wall and serum were taken from 6 age-matched control patients. Quantitative gelatin-zymography and gelatinolytic soluble assays after acetyl-phenyl mercuric acid activation were performed on serum and tissue extracts, and the results were expressed in units on a comparative wet-weight basis. Histologic analysis was performed in parallel to score the inflammatory infiltrate.

RESULTS

The luminal and parietal parts of the thrombus contained, respectively, 20- and 10-fold more gelantinolytic activity than the serum. The predominate form was MMP9. Although the total gelatinolytic activity was in the same range both in AAAs and in normal walls, a significantly higher proportion of MMP9 was found in the aneurysmal aortic walls. Furthermore, a significant proportion of MMP9 was under its processed active form, which was never observed in normal samples. A significantly higher proportion of MMP2 was also present as processed active form in AAA wall. This latter parameter positively correlated with the inflammatory score.

CONCLUSIONS

The presence of activated MMP9 and MMP2 might contribute to the degradation of the extracellular matrix proteins that occurs during the development of aneurysms.

Risk factors and segment-specific carotid arterial enlargement in the Atherosclerosis Risk in Communities (ARIC) cohort

BACKGROUND AND PURPOSE

B-mode ultrasound imaging affords the opportunity to quantify both intimal-medial thickness (IMT) and lumen diameter of extracranial carotid arteries in ambulatory populations. Since the relation of IMT to lumen diameter may be complex, we asked whether cardiovascular disease risk factors (previously shown to be associated with greater arterial IMT) are related to smaller lumen diameters.

METHODS

We used B-mode ultrasound to quantify lumen diameter, interadventitial diameter, and IMT of the extracranial carotid arteries and assessed the relationship of these measures to body mass index, smoking, low-density lipoprotein (LDL) and high-density lipoprotein cholesterol, hypertension, and diabetes in 6088 male and 7493 female participants in the Atherosclerosis Risk in Communities (ARIC) cohort.

RESULTS

Smoking, hypertension, and LDL cholesterol were consistently related to greater IMT in the common and internal carotid arteries of men and women, as has been previously reported. In the internal carotid artery, smoking, hypertension, and LDL cholesterol were consistently related to smaller lumens. In the common carotid artery, body mass index, smoking, and hypertension were related to significantly larger, and LDL cholesterol to smaller, lumens. Thus, only LDL cholesterol was consistently associated with smaller lumens in both the common and internal carotid arteries.

CONCLUSIONS

Risk factors relate positively to IMT in both the common and internal carotid arteries and inversely with lumen diameter in the internal carotid artery, in parallel with their relation to clinical events. However, their association with lumen diameters of the common carotid artery in population-based samples is more complex, and in some cases adverse levels of risk factors may be associated with larger lumens.

Identification of matrix metalloproteinases 3 (stromelysin-1) and 9 (gelatinase B) in abdominal aortic aneurysm

A prominent metalloproteinase activity with an apparent molecular mass of 80 kD and additional activities at 67 through 70, 50, and 32 kD have been observed on casein, gelatin, and elastin gel zymography in extracts from abdominal aortic aneurysms (AAAs). The forms at 80, 50, and 32 kD were isolated by affinity to recombinant tissue inhibitor of metalloproteinases, and the 80-kD and 50-kD components were shown to be derived from matrix metalloproteinase-9 (MMP-9). The relative electrophoretic mobility of these forms under reducing and nonreducing conditions corresponds to those of MMP-9 generated by MMP-3 (stromelysin-1) cleavage, and the active forms of MMP-3 at 45 and 35 kD were detected in aneurysmal extracts under reducing conditions by using specific antibody. Confirmation that the major proteolytic activity observed at 80 kD is MMP-9 was also demonstrated by immunoprecipitation of the activity with specific antibody. Comparative immunoblots of tissue extracts from 10 typical AAA patients, using specific antibody against MMP-9, revealed bands at 92, 82, 67, 51 through 53, 27, 23, and 20 kD under reducing conditions; six aortic control specimens displayed negligible immunoreactivity. This report is the first to show that known activated forms of MMP-3 and MMP-9 are present in the aneurysmal aortic wall and that they may play a role in the destruction of aortic matrix in AAA disease.

Serum-induced vascular smooth muscle cell elastolytic activity through tyrosine kinase intracellular signalling

In previous studies, we related increased elastolytic activity in pulmonary arteries (PA) with endothelial injury to the later development of PA hypertension in rats. As the mechanism causing the increased PA elastase was unknown, we hypothesized that serum factors which are accessible to vascular smooth muscle cells (SMC) following endothelial injury stimulate their elastolytic activity. To test this, we developed an in vitro assay in which we added [3H]-elastin to cultured vascular SMC after 24 h serum starvation and monitored elastolysis following a further 24 h incubation with fetal bovine serum (FBS). We observed that serum induced increased elastolytic activity in both PA and aorta-derived SMC but not in endothelial cells or SMC with low basal levels of elastolytic activity. Maximum stimulation of SMC elastolytic activity occurred with a concentration as low as 1% FBS and despite elastase inhibitors in serum, suggesting that the activity is confined to the immediate pericellular region where enzyme concentration is high. Serum-stimulated elastolytic activity was not reproduced by growth factors or cytokines known to be associated with vascular disease or to induce release of elastases in other cells. The serum inducing elastolytic activity was heat and acid labile. It was associated with increased elastin adhesion to the 67 kD elastin binding protein on SMC surfaces and was prevented by tyrosine kinase inhibitors but not protein kinase C or A inhibitors. Our studies therefore suggest a mechanism whereby serum induction of SMC elastase requires signalling through the elastin binding protein and activation of tyrosine kinase.

The composition and mechanical properties of abdominal aortic aneurysms

PURPOSE

The composition and mechanical properties of abdominal aortic aneurysms (AAAs) were studied.

METHODS

Stereologic study was used to measure volume fractions of the components of the aortic wall. Histochemical methods with picrosirus red and safranin O were developed to differentiate collagen from ground substance because they are difficult to distinguish from each other on histologic sections. Uniaxial tensile stress tests were carried out on a tensile-testing machine, and a stress-strain curve was plotted for each sample to study the mechanical properties of AAAs. The curves were fitted exponentially so sigma = aeb epsilon, where sigma is stress, epsilon is strain, and a and b are parameters.

RESULTS

In aneurysms (n = 8) the volume fraction of elastin was decreased from 22.7% +/- 5.7% to 2.4% +/- 2.2%, and the volume fraction of smooth muscle cells was decreased from 22.6% +/- 5.5% to 2.2% +/- 2.0%, whereas the volume fraction of collagen and ground substance combined was increased from 54.8% +/- 4.5% to 95.6% +/- 2.5% compared with nonaneurysmal aortas (n = 8). There was no significant difference (p > 0.05) in the ratio of collagen to ground substance (2.1 +/- 0.5 vs 2.0 +/- 0.4) between AAAs and nonaneurysmal aortas. The elastic diagrams showed that AAAs (n = 7) are less distensible and stiffer than nonaneurysmal aortas (n = 5). Parameter a was unchanged (p > 0.5), but parameter b was significantly greater (p < 0.002) for aneurysmal aortas.

CONCLUSIONS

Both the composition and mechanical properties of AAAs are different from those of nonaneurysmal aortas. The aneurysms were stiffer, and the volume fractions of collagen and ground substance were increased, whereas the volume fractions of elastin and muscle were decreased in aneurysms.

Pathogenesis of abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm involves many factors acting over time. However, destruction of elastin in the aortic wall is a key event that shifts the load produced by blood pressure on to collagen. This is exacerbated in the presence of hypertension. Smoking and age are further important factors, as is the site; elastic lamellae are relatively less common in the abdominal aorta. Once the shielding effect of elastin is lost, further dilatation and rupture of the aorta depend on the physical properties of the collagen present.

Matrix metalloproteinases in abdominal aortic aneurysm: characterization, purification, and their possible sources

One of the most consistent observations in abdominal aortic aneurysm (AAA) disease is the disorganization and disruption of elastin and other matrix components of the aortic wall. The enzymatic basis for the biochemical features of AAA has been investigated beginning with the demonstration on substrate gel enzymography of a typical "profile" of proteinase activities in AAA tissue extracts which degrade gelatin, casein and elastin. A recombinant TIMP-1 affinity column was developed and three of the elastolytic/caseinolytic activities with approximate molecular weights of approximately 80 kDa, approximately 50 kDa and approximately 32 kDa were partially purified from these extracts. Affinity for rTIMP-1 suggests that these enzymes are members of the matrix metalloproteinase (MMP) family. High molecular weight forms of two MMPs, collagenase (MMP-1) and stromelysin-1 (MMP-3), were also isolated from the AAA tissue on this column; active forms of MMP-1 could be demonstrated by immunoblotting techniques in this preparation under reducing conditions. Infiltrating inflammatory cells are known sources of these proteolytic activities; analysis of these cell populations in the aneurysmal aortic wall using fluorescence-activated cell counting revealed a fifty-fold increase in macrophages (a well-known source of matrix-degrading enzymes) as well as a significant increase in lymphocytes.

Modifications of the extracellular matrix of aneurysmal abdominal aortas as a function of their size

Collagen and elastin are the main extracellular matrix proteins providing the aortic wall with adequate mechanical properties and resistance for proper function. Our study aimed at investigating the relationship between the elastin concentration of the wall of normal and aneurysmal abdominal aortas (AAA), the collagen concentration, and its extractability, as a function of their size. Infrarenal aortas were collected from 30 patients undergoing operative repair of abdominal aortic aneurysm. Age-matched control samples were obtained from eight autopsies of individuals without vascular disease. Samples were divided into five groups according to the aortic diameter: control group (group N, n = 8); < 50 mm (group I, n = 6; between 50-75 mm (group II, n = 10); > 75 mm (group III, n = 7); and ruptured (group IV, n = 7). The collagen concentration in samples from group I was similar to the controls. An increased collagen concentration was observed in group II and remained at the same level in the largest and ruptured aneurysms. Extractability of collagen was found to be increased in group III and was even higher in group IV. A highly significant reduction in elastin concentration was observed in group I and there was progressive reduction with increasing diameter and rupture. A significant correlation could be established between aortic diameter, increased collagen extractability and decreased elastin content.

Content and turnover of extracellular matrix protein in human "nonspecific" and inflammatory abdominal aortic aneurysms

Inflammatory aneurysms (IAs) have peculiar macroscopic and histological aspects which make them very different from nonspecific aneurysms (NSAs). These morphological differences seem to be determined by significant modifications of the extracellular matrix. Extracellular matrix protein component concentrations were determined biochemically in infrarenal aortic biopsies from 10 NSAs, five IAs and five non-aneurysmal aortic controls. The concentration of each wall component was expressed in % w/w (relative concentration) and in mg/wall longitudinal cm (absolute concentration) with reference to total protein recovered after hydrolysis and amino acid analysis. The biochemical results were correlated with the histological and ultrastructural features of the specimens. A significant increase in total collagen was observed in the two groups of aneurysms, with respect to the controls (NSA = 285%, IA = 382%). In contrast the 80-90% decrease in the relative concentration of elastin observed in both types of aneurysm was less marked (NSA = 55%, IA = 39%). This fall was not significant when expressed in mg/cm, although elastin derived peptide (EDP) levels in the plasma of these patients was significantly higher than in age-matched controls. The concentration of the soluble collagen fraction appeared significantly higher (Mann-Whitney, p < 0.05) in the IAs with respect to the NSAs, whilst no differences were observed between the two groups regarding the concentration of insoluble elastin and of wall and plasma EDPs. As well as providing evidence of increased elastin turnover, this study emphasises the conspicuous modifications of collagen deposition in the wall of abdominal aortic aneurysms which appeared more marked in the inflammatory group.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of elastase and lysyl oxidase activity in spontaneous rupture of internal elastic lamina in rats

Rupture of the internal elastic lamina may occur spontaneously with age in certain arteries of the rat and to various extents in different strains. This phenomenon may have some bearing on certain aspects of arterial pathology. For this study, we investigated biochemically the mechanisms of formation of interruptions in the internal elastic lamina (IIEL) by comparing aortas of Brown Norway (BN) rats, which develop numerous IIEL in the abdominal aorta, with those of Long-Evans (LE) rats, which develop none. We isolated aortic elastin from BN and LE rats and determined its amino acid composition and its susceptibility to different elastases. No differences were found between the two strains, but the quantity of elastin isolated per aorta was lower in the BN than in the LE rats. Elastase-like activity (ELA) of whole aortic extracts, measured with Suc(Ala)3NA as a substrate, was greater in the BN rats than in the LE rats of both sexes. The assay of ELA in endothelium, media, and adventitia extracted separately showed very low levels in the media compared to the endothelium and adventitia. The endothelium accounts for about one-half of the total aortic ELA, but a difference between the two strains was detected only in the adventitia. With 3H-insoluble elastins prepared from BN and LE aortas as substrates, elastinolytic activity (EA) was detected only in extracts of endothelium after prior exposure to trypsin. Extracts from BN endothelium on BN elastin were more active than were those from LE endothelium on LE elastin. The assay of lysyl oxidase activity in aortic extracts from the two strains with 3H-collagen from chick embryo calvaria as the substrate showed a lower activity in the BN than in the LE rats. Taken together, these results suggest that increased elastase activity and decreased lysyl oxidase activity may be involved in the formation of IIEL.