Macrophages are critical to the maintenance of IL-13-dependent lung inflammation and fibrosis.

The roles of macrophages in type 2-driven inflammation and fibrosis remain unclear. Here, using CD11b-diphtheria toxin receptor (DTR) transgenic mice and three models of interleukin 13 (IL-13)-dependent inflammation, fibrosis, and immunity, we show that CD11b(+) F4/80(+) Ly6C(+) macrophages are required for the maintenance of type 2 immunity within affected tissues but not secondary lymphoid organs. Direct depletion of macrophages during the maintenance or resolution phases of secondary Schistosoma mansoni egg-induced granuloma formation caused a profound decrease in inflammation, fibrosis, and type 2 gene expression. Additional studies with CD11c-DTR and CD11b/CD11c-DTR double-transgenic mice suggested that macrophages but not dendritic cells were critical. Mechanistically, macrophage depletion impaired effector CD4(+) T helper type 2 (Th2) cell homing and activation within the inflamed lung. Depletion of CD11b(+) F4/80(+) Ly6C(+) macrophages similarly reduced house dust mite-induced allergic lung inflammation and suppressed IL-13-dependent immunity to the nematode parasite Nippostrongylus brasiliensis. Consequently, therapeutic strategies targeting macrophages offer a novel approach to ameliorate established type 2 inflammatory diseases.

In vivo assessment of murine elastase-induced abdominal aortic aneurysm with high resolution magnetic resonance imaging.

OBJECTIVES: There are, to date, no published non-invasive or longitudinal studies performed in mice to measure aortic diameter and wall thickness in an elastase-induced abdominal aortic aneurysm. This MRI study at 11.75 T aimed at evaluating the reliability of longitudinal in vivo aortic diameter and wall thickness measurements in this particular model. METHODS: Adult male C57BL/6 mice underwent transient elastase or heat-inactivated elastase perfusion (controls). Aortic dilatation was measured before, during and immediately after elastase perfusion, and again 14 days after, with a calibrated ocular grid. MRI was performed just before initial surgery and at day 14 before harvest using an 11.75 T MR microscopy imager. RESULTS: Aortic diameter was significantly greater in elastase-perfused mice compared to controls as measured by optic grid (1.150 ± 0.153 mm vs 0.939 ± 0.07 mm, P = 0.038) and according to MRI measurement of the outer diameter on spin echo images (1.203 ± 0.105 mm vs 1070 ± 0.048 mm, P = 0.0067). Aortic wall thickness was found to be significantly increased in elastase-perfused mice at day 14. CONCLUSIONS: This study demonstrates in the mouse elastase-induced aneurysm model that characterization of aneurysm development by its inner and outer vessel diameter and vessel wall thickness can be carried out longitudinally using high resolution MRI without significant mortality.

Endoluminal graft repair for abdominal aortic aneurysms in high-risk patients and octogenarians: is it better than open repair?

OBJECTIVE: To analyze the short-term and midterm results of open and endoluminal repair of abdominal aortic aneurysms (AAA) in a large single-center series and specifically in octogenarians. METHODS: Between January 1997 and October 2000, 470 consecutive patients underwent elective repair of AAA. Conventional open repair (COR) was performed in 210 patients and endoluminal graft (ELG) repair in 260 patients. Ninety of the patients were 80 years of age or older; of these, 38 underwent COR and 52 ELG repair. RESULTS: Patient characteristics and risk factors were similar for both the entire series and the subgroup of patients 80 years or older. The overall complication rate was reduced by 70% or more in the ELG versus the COR groups. The postoperative death rate was similar for the COR and ELG groups in the entire series and lower (but not significantly) in the ELG 80 years or older subgroup versus the COR group. The 36-month rates of freedom from endoleaks, surgical conversion, and secondary intervention were 81%, 98.2%, and 88%, respectively. CONCLUSION: The short-term and midterm results of AAA repair by COR or ELG are similar. The death rate associated with this new technique is low and comparable, whereas the complication rate associated with COR in all patients and those 80 years or older in particular is greater and more serious than ELG repair. Long-term results will establish the role of ELG repair of AAA, especially in elderly and high-risk patients.

Nitric oxide inhibition increases matrix metalloproteinase-9 expression by rat aortic smooth muscle cells in vitro.

OBJECTIVE: The hypothesis to be tested was that diminished bioavailable nitric oxide (NO) affects matrix metalloproteinase (MMP) expression and activation in vascular smooth muscle cells (SMCs). METHODS: Cultivated rat aortic SMCs (RA-SMCs) were exposed to increasing concentrations of L-N-monomethyl arginine (L-NMMA), a nonselective inhibitor of NO synthase, in the presence of proinflammatory cytokines (50 ng/mL interleukin [IL]-1beta, 50 ng/mL interferon-gamma, and 30 microg/mL lipopolysaccharide). Nitrite and nitrate, two of the final end products of NO metabolism, were measured in media collected at 48 hours with the use of the Saville assay (n = 4). MMP activity was measured with 1% gelatin zymography (n = 4). In separate experiments in which 2 ng/mL of IL-1beta and L-NMMA was used, MMP protein and messenger RNA (mRNA) levels were determined with Western blot analysis (n = 3) and semiquantitative reverse transcriptase-polymerase chain reaction (n = 3), respectively. Data were analyzed with nonparametric analysis of variance. RESULTS: Increasing concentrations of the NO synthase inhibitor L-NMMA caused a dose-dependent decrease (P <.05) in nitrite and nitrate production by RA-SMCs after cytokine exposure. Zymography documented an early dosedependent increase (P <.05 compared with cytokines alone) in 92-kd MMP activity, with no significant changes in 72-kd MMP activity after treatment with L-NMMA (P >.05 compared with cytokines alone). Reverse transcriptase-polymerase chain reaction and Western blot analysis revealed that the addition of L-NMMA to IL-1beta-stimulated RA-SMCs led to significant increases in MMP-9 mRNA (n = 3, P <.01 for 1.0 mmol/L L-NMMA) and MMP-9 protein levels (n = 3, P <.05), respectively. No differences in MMP-2 mRNA or protein levels were demonstrated. CONCLUSIONS: Inhibition of cytokine-induced NO expression in RA-SMCs is associated with a selective, dose-dependent increase in MMP-9 expression and synthesis. These findings suggest that alterations in local NO synthesis may influence MMP-9-dependent vessel wall damage.

Simultaneous analysis of 1176 gene products in normal human aorta and abdominal aortic aneurysms using a membrane-based complementary DNA expression array.

BACKGROUND: A number of changes in gene expression have been described in abdominal aortic aneurysms (AAAs), but the spectrum of molecular alterations in this disease is unknown. The purpose of this study was to characterize the expression of approximately 1000 gene products in human AAA tissue and to compare the profile of genes expressed in AAAs with that observed in normal aorta. MATERIALS AND METHODS: Total RNA was isolated from abdominal aortic wall tissues (4 AAAs and 4 normal aortas), and array-specific [(32)P]-labeled complementary DNA (cDNA) probes were created with reverse transcription. The cDNA probes were hybridized with nylon membranes containing an array of 1176 cDNA clones (AtlasArray Human 1.2 I; Clontech, Palo Alto, Calif), and autoradiographs were scanned to identify the patterns of gene expression characteristic of each tissue type. Densitometric analysis was used to standardize the expression of individual genes to a panel of housekeeping controls, and differential gene expression was defined by a signal ratio of at least 2:1. RESULTS: One hundred forty-five (12.3%) of the 1176 genes were consistently expressed in aortic tissue. Thymosin beta-4 was the most abundant of 101 transcripts detected in both AAAs and normal aorta, whereas 44 genes exhibited differential patterns of expression (39 predominant in AAAs and 5 in normal aorta). Densitometric analysis confirmed differences in expression for 20 of these gene products between AAAs and normal aorta, with the greatest increases seen for myeloid cell nuclear differentiation antigen (31-fold), cathepsin H (30-fold), platelet-derived growth factor-A (23-fold), apolipoprotein E (13-fold), gelatinase B/matrix metalloproteinase-9 (12-fold), and interleukin-8 (11-fold). The only gene products substantially decreased in AAAs were myosin light chain kinase (39-fold) and beta-1 integrin (twofold). AAA tissues thereby exhibited a distinct pattern of gene expression reflecting chronic inflammation, extracellular matrix degradation, atherosclerosis, and smooth muscle cell depletion. CONCLUSIONS: cDNA expression arrays provide a powerful new approach to help identify the molecular mechanisms responsible for aneurysmal degeneration. Further studies will be needed to elucidate the functional and pathophysiologic significance of the individual genes that exhibit altered levels of expression in AAA tissue.

Increased expression of HDJ-2 (hsp40) in carotid artery atherosclerosis: a novel heat shock protein associated with luminal stenosis and plaque ulceration.

PURPOSE: Evidence suggests that both humoral and cellular autoimmune processes directed toward heat shock proteins (hsp) contribute to the pathogenesis of atherosclerosis. We characterized a human hsp distinct from those previously characterized in atherosclerotic lesions, termed HDJ-2. METHODS: To determine the role of HDJ-2 in atherosclerosis, we compared the level of HDJ-2 mRNA expression with the level of hsp60 and hsp70 mRNA expression in 26 carotid endarterectomy specimens and 17 normal arteries. The level of expression of HDJ-2 mRNA was also correlated to the presence of plaque ulceration and the degree of luminal stenosis associated with the lesion. RESULTS: The expression of HDJ-2 and hsp70 was significantly higher in carotid artery plaques as compared with normal arteries: HDJ-2, 6.7 +/- 1.6 vs 0.1 +/- 0.04, (P =.001); hsp70, 9.5 +/- 0.9 vs 3.7 +/- 0.8, (P =.002). There was no significant difference in hsp60 expression between carotid artery plaques and normal arteries (21.0 +/- 0.9 vs 20.6 +/- 0.8, P =.65). Increased HDJ-2 expression in carotid artery plaques was independent of hsp70 (Pearson correlation, r = 0.11; Bartlett chi(2) analysis, P =.71). Within the ulcerated plaque group, there was a correlation between degree of stenosis and high HDJ-2 mRNA expression (r = 0.896, P =.016). However, there was no correlation between degree of stenosis and high HDJ-2 mRNA expression within the nonulcerated plaque group (r = 0.530, P =.076) or within the entire group of patients (r = 0.0085, P =.97). CONCLUSION: These results demonstrate that expression of HDJ-2 is significantly increased in atherosclerotic carotid artery plaques as compared with hsp60 and hsp70 and correlates with luminal stenosis in ulcerated atherosclerotic carotid artery plaques.

Suppression of experimental abdominal aortic aneurysms in the rat by treatment with angiotensin-converting enzyme inhibitors.

PURPOSE: Pathologic remodeling of the extracellular matrix is a critical mechanism in the development and progression of abdominal aortic aneurysms (AAAs). Although angiotensin-converting enzyme (ACE) inhibitors are known to alter vascular wall remodeling in other conditions, their effects on AAAs are unknown. In this study we assessed the effect of ACE inhibitors in a rodent model of aneurysm development. METHODS: Male Wistar rats underwent transient aortic perfusion with porcine pancreatic elastase, followed by treatment with one of three ACE inhibitors (captopril [CP], lisinopril [LP], or enalapril [EP]), an angiotensin (AT)1 receptor antagonist (losartan [LOS]), or water alone (9 rats in each group). Blood pressure and aortic diameter (AD) were measured before elastase perfusion and on day 14, with an AAA defined as an increase in AD (DeltaAD) of more than 100%. The structural features of the aortic wall were examined by means of light microscopy. RESULTS: Aneurysmal dilatation consistently developed within 14 days of elastase perfusion in untreated rats, coinciding with the development of a transmural inflammatory response and destruction of the elastic media (mean DeltaAD, 223% +/- 28%). All three ACE inhibitors prevented AAA development (mean DeltaAD: CP, 67% +/- 4%; LP, 18% +/- 12%; and EP, 14% +/- 3%; each P <.05 vs controls). ACE inhibitors also attenuated the degradation of medial elastin without diminishing the inflammatory response. Surprisingly, the aneurysm-suppressing effects of ACE inhibitors were dissociated from their effects on systemic hemodynamics, and LOS had no significant effect on aneurysm development compared with untreated controls (mean DeltaAD, 186% +/- 19%). CONCLUSION: Treatment with ACE inhibitors suppresses the development of elastase-induced AAAs in the rat. Although this is associated with the preservation of medial elastin, the mechanisms underlying these effects appear to be distinct from hemodynamic alterations alone or events mediated solely by AT1 receptors. Further studies are needed to elucidate how ACE inhibitors influence aortic wall matrix remodeling during aneurysmal degeneration.

Evolution of vascular fellowship training in the new era of endovascular techniques.

PURPOSE: The endovascular technique has revolutionized the treatment of infrarenal abdominal aortic aneurysm (AAA). At our institution, we examined the impact of an endovascular program on the traditional operative training of the vascular fellows in the treatment of infrarenal AAA. METHODS: We examined the records of our vascular fellows' experience from July 1995 to May 2000. We introduced the endovascular treatment for infrarenal AAA in 1995. RESULTS: The fellows have performed increasing numbers of endovascular cases each year, with a predicted number of 124 cases for 1999-2000. However, despite an increase in the overall volume of patients with infrarenal AAA (102 cases in 1998-1999 and a predicted 160 cases in 1999-2000), the trainees will experience a reduction in the number of open AAAs from 61 cases in 1998-1999 to a predicted 36 cases in 1999-2000. However, the volume of open suprarenal AAA has also increased from eight cases in 1998 to 1999 to a predicted 24 cases in 1999-2000. With no significant change in the open aortoiliac occlusive cases from previous years, the current fellows will graduate with a similar volume of open aortic procedures as their predecessors. CONCLUSION: With the recent advances in endovascular technology, our traditional operative approach to the treatment of AAA disease may be lacking in the training of future vascular surgeons. At our institution, although fewer open infrarenal AAA cases were performed, the trainees have maintained the open aortic experience by performing an increased volume of suprarenal AAAs. We have to critically reevaluate and redefine what constitutes adequate vascular fellow experience in the surgical treatment of abdominal aortic aneurysms.

Functional importance of connective tissue repair during the development of experimental abdominal aortic aneurysms.

BACKGROUND: Abdominal aortic aneurysms (AAAs) involve an unfavorable balance between the destruction and the repair of connective tissue proteins. The purpose of this study was to assess the functional importance of connective tissue repair during experimental aneurysmal degeneration. METHODS: Male Wistar rats (n = 70) underwent transient intraluminal perfusion of the abdominal aorta with porcine pancreatic elastase. In Study I, the aortic diameter was measured before elastase perfusion and at days 0, 2, 7, and 14 (n = 6 rats at each interval). Aortic wall concentrations of desmosine (Des) and hydroxyproline (OHP) were measured at each interval, and the expression of tropoelastin (TE), alpha1(I) procollagen (PC), and lysyl oxidase genes was evaluated by reverse transcription-polymerase chain reaction. In Study II, 22 rats were treated with beta-aminopropionitrile (BAPN) to block connective tissue repair. In Study III (n = 30), rats were treated with doxycycline, a matrix metalloproteinase inhibitor, beginning 7 days after elastase perfusion. RESULTS: AAAs consistently developed between 7 and 14 days after elastase perfusion. Aortic wall Des concentration decreased markedly during aneurysm development, reaching 3% of normal by day 14 (377 +/- 22 pmol of Des/sample on day 0 vs 9 +/- 1 pmol of Des/sample on day 14; P <.05). Aortic wall OHP decreased to only 68% of normal at the same interval (121 +/- 10 nmol of OHP/sample on day 0 vs 82 +/- 14 nmol of OHP/sample on day 14; P <.05). TE and PC expression was undetectable in healthy aorta, but they both increased by day 7 (P <.05); while TE expression decreased again by day 14, PC continued to rise. Lysyl oxidase expression progressively decreased at all intervals after elastase perfusion. Treatment with beta-aminoproprionitrile resulted in acute aortic dissection in 81% of the rats (50% mortality). These early deaths occurred between days 3 and 6, coinciding with aortic infiltration by proteinase-secreting inflammatory cells. Delayed treatment with doxycycline suppressed the progression of aneurysmal dilatation between days 7 and 21 (P <.05 vs untreated controls). CONCLUSIONS: The development of elastase-induced AAAs is accompanied by an active process of connective tissue repair. While this reparative process is necessary to stabilize the developing aneurysm wall, it is insufficient to prevent aneurysm progression. In contrast, reducing the proteolytic destruction of connective tissue proteins promotes stabilization of the aneurysmal aorta.

Targeted gene disruption of matrix metalloproteinase-9 (gelatinase B) suppresses development of experimental abdominal aortic aneurysms.

Abdominal aortic aneurysms represent a life-threatening condition characterized by chronic inflammation, destructive remodeling of the extracellular matrix, and increased local expression of matrix metalloproteinases (MMPs). Both 92-kD gelatinase (MMP-9) and macrophage elastase (MMP-12) have been implicated in this disease, but it is not known if either is necessary in aneurysmal degeneration. We show here that transient elastase perfusion of the mouse aorta results in delayed aneurysm development that is temporally associated with transmural mononuclear inflammation, increased local production of several elastolytic MMPs, and progressive destruction of the elastic lamellae. Elastase-induced aneurysmal degeneration was suppressed by treatment with a nonselective MMP inhibitor (doxycycline) and by targeted gene disruption of MMP-9, but not by isolated deficiency of MMP-12. Bone marrow transplantation from wild-type mice prevented the aneurysm-resistant phenotype in MMP-9-deficient animals, and wild-type mice acquired aneurysm resistance after transplantation from MMP-9-deficient donors. These results demonstrate that inflammatory cell expression of MMP-9 plays a critical role in an experimental model of aortic aneurysm disease, suggesting that therapeutic strategies targeting MMP-9 may limit the growth of small abdominal aortic aneurysms.

Preoperative treatment with doxycycline reduces aortic wall expression and activation of matrix metalloproteinases in patients with abdominal aortic aneurysms.

PURPOSE: Matrix metalloproteinases (MMPs) are considered to play a central role in the pathogenesis of abdominal aortic aneurysms (AAAs). Doxycycline (Dox) has direct MMP-inhibiting properties in vitro, and it effectively suppresses the development of elastase-induced AAAs in rodents. The purpose of this study was to determine if treatment with Dox suppresses MMPs within human aneurysm tissue and to elucidate the molecular mechanisms underlying this effect. METHODS: Aneurysm tissues were obtained from 15 patients with an AAA, eight of whom had been treated with Dox before surgery (100 mg orally twice a day for 7 days). Protein extracts were examined by means of gelatin zymography and immunoblot analysis, and RNA was examined by means of reverse transcription-polymerase chain reaction (RT-PCR). The effects of Dox on MMP production were further examined in human THP-1 mononuclear phagocytes in vitro. RESULTS: No detectable difference was found between groups by using substrate zymography as a means of assessing total MMP activity, but Dox treatment was associated with a slight (24.4%) reduction in the activated fraction of 72-kDa gelatinase (MMP-2; P <.05). In contrast, a 2.5-fold reduction in the amount of extractable 92-kDa gelatinase (MMP-9) protein in Dox-treated patients was revealed by means of immunoblot analysis (P <.05). Also, a 5.5-fold (81.9%) reduction in MMP-9 messenger RNA (mRNA) in Dox-treated patients was demonstrated by means of quantitative competitive RT-PCR (mean +/- SE, mol MMP-9/mol beta-actin: 1.3 +/- 0.5 vs 7.2 +/- 3.1; P <.04). There was no significant difference between groups in the relative expression of MMP-2 protein or mRNA. In cultured THP-1 monocytes stimulated with phorbol ester, the expression of MMP-9 protein and mRNA were both decreased after exposure to relevant concentrations of Dox in vitro. CONCLUSION: In addition to its recognized effects as a direct MMP antagonist, Dox may influence connective tissue degradation within human aneurysm tissue by reducing monocyte/macrophage expression of MMP-9 mRNA and by suppressing the post-translational processing (activation) of proMMP-2. Through this complementary combination of mechanisms, treatment with Dox may be a particularly effective strategy for achieving MMP inhibition in patients with an AAA.

MMP inhibition in abdominal aortic aneurysms. Rationale for a prospective randomized clinical trial.

Abdominal aortic aneurysms (AAAs) represent a chronic degenerative condition associated with a life-threatening risk of rupture. The evolution of AAAs is thought to involve the progressive degradation of aortic wall elastin and collagen, and increased local production of several matrix metallo-proteinases (MMPs) has been implicated in this process. We have previously shown that tetracycline derivatives and other MMP inhibitors suppress aneurysm development in experimental animal models of AAA. Doxycycline also reduces the expression of MMP-2 and MMP-9 by human vascular wall cell types and by AAA tissue explants in vitro. To determine whether this strategy might have a role in the clinical management of small AAA, we examined the effect of doxycycline on aortic wall MMP expression in vivo. Patients were treated with doxycycline (100 mg p.o. bid) for 7 days prior to elective AAA repair, and aneurysm tissues were obtained at the time of surgery (n = 5). Tissues obtained from an equal number of untreated patients with AAA were used for comparison. By reverse transcription-polymerase chain reaction and Southern blot analysis, MMP-2 and MMP-9 were both found to be abundantly expressed in the aneurysm wall. Preoperative treatment with doxycycline was associated with a 3-fold reduction in aortic wall expression of MMP-2 and a 4-fold reduction in MMP-9 (p < 0.05 compared to untreated AAA). These preliminary results suggest that even short-term treatment with doxycycline can suppress MMP expression within human AAA tissues. Given its pleiotropic effects as an MMP inhibitor, doxycycline may be particularly effective in suppressing aortic wall connective tissue degradation. While it remains to be determined whether MMP inhibition will have a clinically significant impact on aneurysm expansion, it is expected that this question can be resolved by a properly designed prospective randomized clinical trial.

Source of elastin-degrading enzymes in mycotic aortic aneurysms: bacteria or host inflammatory response?

Elastolytic matrix metalloproteinases play a central role in the development of chronic atherosclerotic aortic aneurysms, but mycotic aortic aneurysms are a distinct and unusual form of aneurysm disease caused by bacterial infection. Mycotic aortic aneurysms follow a more rapid and unpredictable course than chronic aneurysm disease and they exhibit a predilection for the suprarenal aorta, further implying unique pathophysiologic mechanisms. The purpose of this study was to examine the nature and source of elastin-degrading enzymes in mycotic aortic aneurysm. Bacterial isolates and aortic tissues were obtained from four consecutive patients undergoing surgical repair of suprarenal mycotic aortic aneurysm. Using an in vitro 3H-labeled elastin degradation assay, elastin-degrading enzyme activity was only observed in the bacteria-conditioned medium from an isolate of Pseudomonas aeruginosa. Elastin-degrading enzyme activity in the aortic tissue homogenate of this patient was abolished by the serine protease inhibitor, phenylmethylsulfonyl fluoride, but it was not suppressed by the metalloproteinase inhibitor, ethylenediamine tetraacetic acid (EDTA). In contrast, elastin-degrading enzyme activity in the bacterial-conditioned medium was decreased by about half by both phenylmethylsulfonyl fluoride and EDTA. Elastin substrate zymography revealed two phenylmethylsulfonyl fluoride-inhibitable elastin-degrading enzyme activities in the aortic tissue homogenate that corresponded to human neutrophil elastase (approximately 30 kDa) and its stable complex with alpha 1-proteinase inhibitor (approximately 80 kDa), but no activity attributable to Pseudomonas elastase, a 33-kDa metal-dependent enzyme. Human neutrophil elastase was readily detected throughout mycotic aortic aneurysm tissues by immunohistochemistry, but elastolytic metalloproteinases were only occasionally observed. The results of this study suggest that the elastin-degrading enzyme produced in mycotic aortic aneurysm are largely serine proteases of host neutrophil origin, rather than elastases produced by the infecting microorganisms or the macrophage-derived metalloproteinases typically observed in atherosclerotic aneurysm disease. Further studies will be needed to extend these findings to a larger number of patients with mycotic aortic aneurysm and those caused by additional microorganisms.

Suppression of experimental abdominal aortic aneurysms by systemic treatment with a hydroxamate-based matrix metalloproteinase inhibitor (RS 132908).

BACKGROUND: Abdominal aortic aneurysms (AAAs) are associated with chronic inflammation, disruption of medial elastin, and increased local production of elastolytic matrix metalloproteinases (MMPs). The purpose of this study was to investigate how treatment with a hydroxamate-based MMP antagonist (RS 132908) might affect the development of experimental AAAs. METHODS: Male Wistar rats underwent intraluminal perfusion of the abdominal aorta with 50 units of porcine pancreatic elastase followed by treatment for 14 days with RS 132908 (100 mg/kg/day subcutaneously; n = 8) or with vehicle alone (n = 6). The external aortic diameter (AD) was measured in millimeters before elastase perfusion and at death, with AAA defined as an increase in AD (DeltaAD) of at least 100%. Aortic wall elastin and collagen concentrations were measured with assays for desmosine and hydroxyproline, and fixed aortic tissues were examined by light microscopy. RESULTS: AAAs developed in all vehicle-treated rats, with a mean AD (+/- SE) that increased from 1.60 +/- 0.03 mm before perfusion to 5.98 +/- 1.02 mm on day 14 (DeltaAD = 276.4 +/- 67.7%). AAAs developed in only five of eight animals (62.5%) after MMP inhibition, with a mean AD that increased from 1.56 +/- 0.05 mm to 3.59 +/- 0.34 mm (DeltaAD = 128.1 +/- 18.7%; P <.05, vs vehicle). The overall inhibition of aortic dilatation attributable to RS 132908 was 53.6 +/- 6.8%. Aortic wall desmosine fell by 85.4% in the vehicle-treated rats (1210.6 +/- 87.8 pmol/sample to 176.7 +/- 33.4 pmol/sample; P <.05) but only by 65.6% in the animals treated with RS 312908 (416.2 +/- 120.5 pmol/sample). In contrast, hydroxyproline was not significantly affected by either elastase perfusion or drug treatment. Microscopic examination revealed the preservation of pericellular elastin and a greater degree of fibrocollagenous wall thickening after MMP inhibition, with no detectable difference in the extent of inflammation. CONCLUSIONS: Systemic MMP inhibition suppresses aneurysmal dilatation in the elastase-induced rodent model of AAA. Consistent with its direct inhibitory effect on various MMPs, RS 132908 promotes the preservation of aortic elastin and appears to enhance a profibrotic response within the aortic wall. Hydroxamate-based MMP antagonists may therefore be useful in the development of pharmacologic approaches to the suppression of AAAs.

Expression and localization of macrophage elastase (matrix metalloproteinase-12) in abdominal aortic aneurysms.

Elastolytic matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of abdominal aortic aneurysms (AAA), a disorder characterized by chronic aortic wall inflammation and destruction of medial elastin. The purpose of this study was to determine if human macrophage elastase (HME; MMP-12) might participate in this disease. By reverse transcription-polymerase chain reaction, HME mRNA was consistently demonstrated in AAA and atherosclerotic occlusive disease (AOD) tissues (six of six), but in only one of six normal aortas. Immunoreactive proteins corresponding to proHME and two products of extracellular processing were present in seven of seven AAA tissue extracts. Total HME recovered from AAA tissue was sevenfold greater than normal aorta (P < 0.001), and the extracted enzyme exhibited activity in vitro. Production of HME was demonstrated in the media of AAA tissues by in situ hybridization and immunohistochemistry, but HME was not detected within the media of normal or AOD specimens. Importantly, immunoreactive HME was specifically localized to residual elastin fragments within the media of AAA tissue, particularly areas adjacent to nondilated normal aorta. In vitro, the fraction of MMP-12 sequestered by insoluble elastin was two- to fivefold greater than other elastases found in AAA tissue. Therefore, HME is prominently expressed by aneurysm-infiltrating macrophages within the degenerating aortic media of AAA, where it is also bound to residual elastic fiber fragments. Because elastin represents a critical component of aortic wall structure and a matrix substrate for metalloelastases, HME may have a direct and singular role in the pathogenesis of aortic aneurysms.

Pharmacologic suppression of experimental abdominal aortic aneurysms: acomparison of doxycycline and four chemically modified tetracyclines.

BACKGROUND: Matrix metalloproteinases (MMPs) likely contribute to the degradation of medial elastin in abdominal aortic aneurysms (AAAs), and tetracycline antibiotics exhibit MMP-inhibiting properties. The purpose of this study was to compare the effects of doxycycline and several non-antibiotic chemically modified tetracyclines (CMTs) in a rat model of elastase-induced AAA. METHODS: Fifty-two male Wistar rats underwent intraluminal perfusion of the abdominal aorta with porcine pancreatic elastase. The rats then were treated for 7 days with subcutaneous injections of saline solution, different doses of doxycycline, or 1 of 4 different CMTs. The aortic diameters were measured with microcalipers, and the fixed tissues were examined by means of light microscopy. Gelatin zymography was used to assess the MMP activity in the aortic tissue extracts. RESULTS: The mean aortic diameter in the control group increased by 126% +/- 14% on day 7 (from 1.57 +/- 0.04 mm to 3.54 +/- 0.27 mm; P <.05), and 5 of 6 animals (83%) had AAAs. Doxycycline appeared to inhibit aortic dilatation in a dose-dependent manner, and AAAs did not develop in any animals. Half-maximal effects were observed at a dose of approximately 6 mg/kg/day, and maximal effects were noted at greater than 30 mg/kg/day. No AAAs were observed in the animals that were treated with CMTs at 15 mg/kg/day. Each of the following CMTs exhibited an efficacy that was similar to that of doxycycline (percent inhibition of aortic dilatation vs control; all P <.05): CMT-3 (47.6%), CMT-4 (38.9%), CMT-7 (47.6%), CMT-8 (54.0%), and doxycycline (51.6%). Tissues from saline solution-treated controls exhibited a transmural inflammatory response and marked destruction of the medial elastic lamellae. Tetracycline derivatives limited the disruption of medial elastin without appearing to alter either the inflammatory response or the rat aortic wall production of metallogelatinases. CONCLUSION: Tetracycline derivatives suppress the development of AAAs after elastase-induced aortic injury in the rat. The aneurysm-suppressing effects of doxycycline appear to be dose-dependent and distinct from its antibiotic activities, and they coincide with the structural preservation of medial elastin fibers. Further studies are needed to explore the potential of MMP-inhibiting tetracyclines as a novel pharmacologic strategy for the suppression of aortic aneurysms.

Surgical management of subclavian-vein effort thrombosis as a result of thoracic outlet compression.

BACKGROUND: There is considerable variability and controversy in the current management of subclavian-vein effort thrombosis. The purpose of this study was to determine the long-term effectiveness and the functional outcome of our preferred treatment strategy of early thrombolysis/recanalization and prompt extensive supraclavicular decompression. PATIENTS AND METHODS: Thirty-three patients who ranged in age from 15 to 60 years underwent operative decompression of 34 primary subclavian-vein thromboses, one of which was bilateral. There were 21 patients with acute thrombosis 7 of whom had had prior unsuccessful balloon venoplasty, 1 with stent placement and 8 patients with chronic/recurrent thrombosis 5 of whom had had 9 unsuccessful prior operations for attempted decompression. Four patients had high-grade symptomatic stenosis and positional occlusion. A supraclavicular approach was used in 32 cases and, in 23 cases, was complemented by an infraclavicular (n = 21) or transaxillary (n = 2) incision. Complete subclavian-vein decompression was achieved by first-rib resection (n = 31), scalenectomy (n = 33), and circumferential venolysis (n = 34). RESULTS: Follow-up was obtained in 30 patients at a mean of 31 months. Twenty of the 21 patients with acute thrombosis had a complete resolution of symptoms with a return to full activity; the other patient was lost to follow-up. Four of the 8 patients with chronic thrombosis reported a mild relief of symptoms but still had limitations of activities of daily living. All of the patients with high-grade symptomatic stenosis with positional occlusion had a complete relief of symptoms and a return to full activity. CONCLUSION: The optimal management of acute effort thrombosis of the subclavian vein includes anticoagulation therapy, thrombolysis/recanalization, confirmatory positional venography, and early supraclavicular decompression of the subclavian vein. In the patients with chronic subclavian-vein thrombosis and positional venographic evidence of compression of first-rib bypass graft collaterals, the initial anticoagulation therapy should be followed by the surgical decompression of the collaterals. The supraclavicular approach alone or with an infraclavicular incision provides optimal exposure for scalenectomy, total first-rib resection, and circumferential venolysis.