NLRP3 (Nucleotide Oligomerization Domain-Like Receptor Family, Pyrin Domain Containing 3)-Caspase-1 Inflammasome Degrades Contractile Proteins: Implications for Aortic Biomechanical Dysfunction and Aneurysm and Dissection Formation.

OBJECTIVE: Increasing evidence suggests that contractile dysfunction in smooth muscle cells (SMCs) plays a critical role in aortic biomechanical dysfunction and aortic aneurysm and dissection (AAD) development. However, the mechanisms underlying SMC contractile dysfunction in sporadic AAD are poorly understood. In this study, we examined the role of the NLRP3 (nucleotide oligomerization domain-like receptor family, pyrin domain containing 3)-caspase-1 inflammasome, a key inflammatory cascade, in SMC contractile dysfunction in AAD. APPROACH AND RESULTS: We observed significant SMC contractile protein degradation in aortas from patients with sporadic thoracic AAD. The contractile protein degradation was associated with activation of the NLRP3-caspase-1 inflammasome cascade. In SMCs, caspase-1 bound and directly cleaved and degraded contractile proteins, leading to contractile dysfunction. Furthermore, Nlrp3 or caspase-1 deficiency in mice significantly reduced angiotensin II-induced contractile protein degradation, biomechanical dysfunction, and AAD formation in both thoracic and abdominal aortas. Finally, blocking this cascade with the inflammasome inhibitor, glyburide (an antidiabetic medication), reduced angiotensin II-induced AAD formation. CONCLUSIONS: Inflammasome-caspase-1-mediated degradation of SMC contractile proteins may contribute to aortic biomechanical dysfunction and AAD development. This cascade may be a therapeutic target in AAD formation. In addition, glyburide may have protective effects against AAD development.

AKT2 confers protection against aortic aneurysms and dissections.

RATIONALE: Aortic aneurysm and dissection (AAD) are major diseases of the adult aorta caused by progressive medial degeneration of the aortic wall. Although the overproduction of destructive factors promotes tissue damage and disease progression, the role of protective pathways is unknown. OBJECTIVE: In this study, we examined the role of AKT2 in protecting the aorta from developing AAD. METHODS AND RESULTS: AKT2 and phospho-AKT levels were significantly downregulated in human thoracic AAD tissues, especially within the degenerative medial layer. Akt2-deficient mice showed abnormal elastic fibers and reduced medial thickness in the aortic wall. When challenged with angiotensin II, these mice developed aortic aneurysm, dissection, and rupture with features similar to those in humans, in both thoracic and abdominal segments. Aortas from Akt2-deficient mice displayed profound tissue destruction, apoptotic cell death, and inflammatory cell infiltration that were not observed in aortas from wild-type mice. In addition, angiotensin II-infused Akt2-deficient mice showed significantly elevated expression of matrix metalloproteinase-9 (MMP-9) and reduced expression of tissue inhibitor of metalloproteinase-1 (TIMP-1). In cultured human aortic vascular smooth muscle cells, AKT2 inhibited the expression of MMP-9 and stimulated the expression of TIMP-1 by preventing the binding of transcription factor forkhead box protein O1 to the MMP-9 and TIMP-1 promoters. CONCLUSIONS: Impaired AKT2 signaling may contribute to increased susceptibility to the development of AAD. Our findings provide evidence of a mechanism that underlies the protective effects of AKT2 on the aortic wall and that may serve as a therapeutic target in the prevention of AAD.

D-dimer levels remain elevated in acute aortic dissection after 24 h.

BACKGROUND: D-dimer levels are elevated in patients with acute aortic dissection (AAD). Although D-dimer levels have been used to rule out AAD within 24 h of symptom onset, it is unknown whether they may be used reliably after 24 h but within the acute period. Here, we tested the hypothesis that D-dimer levels remain elevated in AAD patients for at least 10 d after dissection onset. MATERIALS AND METHODS: D-dimer levels were measured in preoperative heparinized plasma samples from 100 patients with confirmed AAD for up to 10 d after onset of dissection. When possible, serial samples were obtained for ≥2 d. D-dimer levels were measured in fibrinogen equivalent units using a BCS XP automated coagulation analyzer, which is approved for citrated samples. Therefore, we first validated our samples by comparing D-dimer levels in heparinized and citrated plasma samples from 29 individuals, including patients with and without aortic disease and healthy donors. RESULTS: The correlation between heparinized and citrated plasma samples was 0.991 (P ≤ 0.001). At a threshold of 1.6 µg/mL, the overall sensitivity of the D-dimer assay in AAD patients up to 10 d after onset of dissection was 95.3%. CONCLUSIONS: D-dimer levels remained elevated in AAD patients over a 10-d period after dissection onset and may be helpful in ruling out AAD in patients who seek treatment after the first 24 h but within the acute period. Heparinized plasma samples may be substituted for citrated samples when evaluating D-dimer levels using the BCS XP coagulation analyzer.

Matrix metalloproteinase levels in chronic thoracic aortic dissection.

BACKGROUND: Imbalance between matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) can lead to aortic wall failure. We hypothesized that patients with aneurysms resulting from chronic descending thoracic aortic dissection have elevated tissue and plasma levels of specific MMPs and decreased tissue levels of TIMPs. MATERIALS AND METHODS: Aortic tissue was obtained from 25 patients who required surgical repair of descending thoracic aortic aneurysm due to chronic aortic dissection and from 17 organ-donor controls without aortic disease. Tissue levels of MMP-1, -2, -3, -9, -12, and -13 and TIMP-1 and -2 were measured by colorimetric activity assay or enzyme-linked immunosorbent assay and confirmed by Western blot and immunohistochemistry. Blood obtained from the 25 patients and 15 controls without aortic diseases was used to compare plasma levels of MMP-3, -9, and -12. RESULTS: Total MMP-1, total MMP-9, and active MMP-9 levels were higher and total MMP-2 levels were lower in dissection tissue than in control tissue. Additionally, the MMP-9 to TIMP-1 and active to total MMP-2 ratios were higher and the MMP-2 to TIMP-2 ratio was lower in dissection tissue. Furthermore, patients had higher plasma active to total MMP-9 ratios than the controls. Age and hypertension were associated with increased MMP levels. CONCLUSIONS: Increased levels of several MMPs and increased MMP to TIMP ratios in aortic tissue from patients suggest an environment that favors proteolysis, which may promote progressive extracellular matrix destruction and medial degeneration after aortic dissection. An elevated active to total MMP-9 ratio in plasma may be a biomarker for end-stage aneurysm development in patients with chronic thoracic aortic disease.

Molecular mechanisms of thoracic aortic dissection.

Thoracic aortic dissection (TAD) is a highly lethal vascular disease. In many patients with TAD, the aorta progressively dilates and ultimately ruptures. Dissection formation, progression, and rupture cannot be reliably prevented pharmacologically because the molecular mechanisms of aortic wall degeneration are poorly understood. The key histopathologic feature of TAD is medial degeneration, a process characterized by smooth muscle cell depletion and extracellular matrix degradation. These structural changes have a profound impact on the functional properties of the aortic wall and can result from excessive protease-mediated destruction of the extracellular matrix, altered signaling pathways, and altered gene expression. Review of the literature reveals differences in the processes that lead to ascending versus descending and sporadic versus hereditary TAD. These differences add to the complexity of this disease. Although tremendous progress has been made in diagnosing and treating TAD, a better understanding of the molecular, cellular, and genetic mechanisms that cause this disease is necessary to developing more effective preventative and therapeutic treatment strategies.

Targeting the NLRP3 Inflammasome With Inhibitor MCC950 Prevents Aortic Aneurysms and Dissections in Mice.

Background Aortic aneurysms and dissections are highly lethal diseases for which an effective treatment strategy is critically needed to prevent disease progression. The nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3)-caspase-1 inflammasome cascade was recently shown to play an important role in aortic destruction and disease development. In this study, we tested the effects of MCC950, a potent, selective NLRP3 inhibitor, on preventing aortic destruction and aortic aneurysm and dissection formation. Methods and Results In a model of sporadic aortic aneurysm and dissection induced by challenging wild-type mice with a high-fat, high-cholesterol diet and angiotensin II infusion, MCC950 treatment significantly inhibited challenge-induced aortic dilatation, dissection, and rupture in different thoracic and abdominal aortic segments in both male and female mice. Aortic disease reduction by MCC950 was associated with the prevention of NLRP3-caspase-1 upregulation, smooth muscle cell contractile protein degradation, aortic cell death, and extracellular matrix destruction. Further investigation revealed that preventing matrix metallopeptidase 9 (MMP-9) expression and activation in macrophages is an important mechanism underlying MCC950's protective effect. We found that caspase-1 directly activated MMP-9 by cleaving its N-terminal inhibitory domain. Moreover, the genetic knockdown of Nlrp3 or Casp-1 in mice or treatment of mice with MCC950 diminished the challenge-induced N-terminal cleavage of MMP-9, MMP-9 activation, and aortic destruction. Conclusions Our findings suggest that the NLRP3-caspase-1 inflammasome directly activates MMP-9. Targeting the inflammasome with MCC950 is a promising approach for preventing aortic destruction and aortic aneurysm and dissection development.

Mitral Valve Repair Rate at a Veterans Affairs Hospital Utilizing a Multidisciplinary Heart Team.

Between 2000 and 2008, the mitral valve (MV) repair rate in patients with severe mitral regurgitation at our low-volume Veterans Affairs hospital was 21%. After instituting a multidisciplinary valve team in 2009, we determined whether this rate increased and characterized the outcomes of patients with degenerative disease. We retrospectively reviewed data from 103 MV operations performed at our hospital between 1/2009 and 8/2016. MV pathology was categorized as degenerative, rheumatic, endocarditis, ischemic, hypertrophic cardiomyopathy, or failed prior MV repair. The surgical techniques used for MV repair were reviewed. For the patients with degenerative disease who underwent MV repair, we assessed leaflet involvement and postoperative valve function. For the full cohort, the MV repair rate was 67% and the 30-day mortality rate was 0.97%. Of the 74 patients with degenerative disease, 64 (86.5%) underwent MV repair (none required reoperation). For these patients, the MV repair rate was significantly higher when the surgical approach was sternotomy rather than minimally invasive right minithoracotomy (92.5% vs 71.4%, P = 0.03). After MV repair, 95.3% of the degenerative disease patients had mild or less mitral regurgitation; median echocardiography follow-up time was 555 days. Anatomic features associated with a reduced MV repair rate in patients with degenerative disease were dystrophic leaflet calcification and severe mitral annular calcification. In an institution with a low volume of MV operations, preoperative surgical planning with a multidisciplinary valve team was associated with improved MV repair rates and excellent repair quality in patients with degenerative valve disease.

Postoperative Chylothorax After Thoracoabdominal Aortic Aneurysm Repair.

Chylothorax is a potentially deadly complication that can occur after thoracoabdominal aortic aneurysm (TAAA) repair. We describe our contemporary experience (2005-2014) with this complication, our efforts to identify perioperative variables associated with it, and our attempts to assess treatment outcomes. We reviewed the records of 1092 consecutive patients who underwent TAAA repair between 2005 and 2014. Standard bivariate analysis was used to test for between-group differences. Eleven patients (0.9%) developed postoperative chylothorax. Nonoperative management was used in 8 of these patients (73%); 1 patient died after a lengthy hospital stay (297 days). The other 3 patients required thoracotomy with direct ligation; 1 of these patients required a second operation. Patients who developed chylothorax appeared to be similar to other patients in age, sex, extent of aneurysm, and metabolic or cardiovascular comorbidities. Patients who developed postoperative chylothorax were more likely to require drainage of a pleural effusion (P = 0.005), tracheostomy (P = 0.02), and longer stays in the intensive care unit (median, 6 [2-24] days, P < 0.001) and the hospital (median, 35 [24-88] days, P = 0.001), and these patients were more likely to develop a graft infection (n = 2, P < 0.001). The extent of TAAA repair (Crawford I-IV), reoperation, and clamping proximal to the left subclavian artery were not significantly associated with postoperative chylothorax. Chylothorax after TAAA repair can often be managed nonoperatively. Development of postoperative chylothorax may lead to significant morbidity, longer hospitalization, and increased likelihood of graft infection.

Unplanned Readmissions After Open Thoracoabdominal Aortic Aneurysm Repair.

BACKGROUND: Although reducing the incidence of unplanned readmission after thoracoabdominal aortic aneurysm (TAAA) repair represents an important opportunity to improve outcomes, predictors of readmissions are not known. We sought to characterize and identify factors associated with unplanned readmission after discharge in survivors of open TAAA repair. METHODS: Through prospective phone contact and retrospective record review, we determined the frequency and characteristics of unplanned readmissions within 30 days of discharge in 363 patients who were discharged after open TAAA repair. We used univariate and multivariable analyses to identify factors associated with readmission. RESULTS: There were 44 unplanned readmissions in 40 patients (11%). After readmission, 11 patients underwent operations, and 17 underwent nonsurgical procedures, the most common of which was thoracentesis (n = 9). Readmitted patients tended to have lower preoperative estimated glomerular filtration rates (p = 0.045), higher frequencies of preoperative sleep apnea (p = 0.009) and postoperative pulmonary (p = 0.04) and infection (p = 0.02) complications, and longer hospital stays (p = 0.01) than patients without readmissions. Patient age, urgency of operation, and extent of TAAA repair were similar in patients with and without readmissions. Multivariable analysis identified sleep apnea (relative risk ratio [RRR] 3.21, 95% confidence interval [CI]: 1.51 to 6.82, p = 0.002), postoperative infection (RRR 4.34, 95% CI: 1.32 to 14.25, p = 0.02), renal failure necessitating dialysis (RRR 3.14, 95% CI: 1.04 to 9.46, p = 0.04), and visceral artery stenting (RRR 2.43, 95% CI: 1.09 to 5.44, p = 0.03) as significant predictors of readmission. CONCLUSIONS: Patients with renal dysfunction, sleep apnea, or postoperative infection were particularly likely to be readmitted; optimizing the management of these factors may reduce early readmission after TAAA repair.

Critical Role of ADAMTS-4 in the Development of Sporadic Aortic Aneurysm and Dissection in Mice.

Sporadic aortic aneurysm and dissections (AADs) are common vascular diseases that carry a high mortality rate. ADAMTS-4 (a disintegrin-like and metalloproteinase with thrombospondin motifs-4) is a secreted proteinase involved in inflammation and matrix degradation. We previously showed ADAMTS-4 levels were increased in human sporadic descending thoracic AAD (TAAD) samples. Here, we provide evidence that ADAMTS-4 contributes to aortic destruction and sporadic AAD development. In a mouse model of sporadic AAD induced by a high-fat diet and angiotensin II infusion, ADAMTS-4 deficiency (Adamts-4-/-) significantly reduced challenge-induced aortic diameter enlargement, aneurysm formation, dissection and aortic rupture. Aortas in Adamts-4-/- mice showed reduced elastic fibre destruction, versican degradation, macrophage infiltration, and apoptosis. Interestingly, ADAMTS-4 was directly involved in smooth muscle cell (SMC) apoptosis. Under stress, ADAMTS-4 translocated to the nucleus in SMCs, especially in apoptotic SMCs. ADAMTS-4 directly cleaved and degraded poly ADP ribose polymerase-1 (a key molecule in DNA repair and cell survival), leading to SMC apoptosis. Finally, we showed significant ADAMTS-4 expression in aortic tissues from patients with sporadic ascending TAAD, particularly in SMCs. Our findings indicate that ADAMTS-4 induces SMC apoptosis, degrades versican, promotes inflammatory cell infiltration, and thus contributes to sporadic AAD development.

Hepatopancreaticobiliary Values after Thoracoabdominal Aneurysm Repair.

BACKGROUND: After thoracoabdominal aortic aneurysm (TAAA) repair, blood tests assessing hepatopancreaticobiliary (HPB) organs commonly have abnormal results. The clinical significance of such abnormalities is difficult to determine because the expected postoperative levels have not been characterized. Therefore, we sought to establish expected trends in HPB laboratory values after TAAA repair. METHODS: This 5-year study comprised 155 patients undergoing elective Crawford extent II TAAA repair. In accordance with a prospective study protocol, all repairs involved left-sided heart bypass, selective visceral perfusion, and cold renal perfusion. Blood levels of aspartate transaminase (AST), alanine transaminase (ALT), γ-glutamyl transpeptidase (GGT), lactate dehydrogenase (LDH), total bilirubin, amylase, and lipase were measured before TAAA repair and for 7 days afterward. Ratios between postoperative and baseline levels were compared for each time point with 95% confidence intervals. RESULTS: Temporal patterns for the laboratory values varied greatly. Amylase, lipase, and AST underwent significant early increases before decreasing to preoperative levels. LDH increased immediately and remained significantly elevated, whereas ALT increased more gradually. GGT remained near baseline through postoperative day 4, and then increased to more than twice baseline. Total bilirubin never differed significantly from baseline. After adjusted analysis, the ischemic time predicted the maximum AST, lipase, GGT, and LDH values. CONCLUSIONS: Although most HPB laboratory values increase significantly after elective TAAA repair, the temporal trends for different values vary substantially. The ischemic time predicts the maximum AST, lipase, GGT, and LDH levels. These trends should be considered when laboratory values are assessed after TAAA repair.

Inflammatory Cell Infiltrates in Acute and Chronic Thoracic Aortic Dissection.

BACKGROUND: Thoracic aortic dissection (TAD) is a highly lethal cardiovascular disease. Injury to the intima and media allows pulsatile blood to enter the media, leading to dissection formation. Inflammatory cells then infiltrate the site of aortic injury to clear dead cells and damaged tissue. This excessive inflammation may play a role in aneurysm formation after dissection. METHODS: Using immunohistochemistry, we compared aortic tissues from patients with acute TAD (n = 11), patients with chronic TAD (n = 35), and donor controls (n = 20) for the presence of CD68+ macrophages, neutrophils, mast cells, and CD3+ T lymphocytes. RESULTS: Tissue samples from patients with acute or chronic TAD generally had significantly more inflammatory cells in both the medial and adventitial layers than did the control samples. In tissues from patients with acute TAD, the adventitia had more of the inflammatory cells studied than did the media. The pattern of increase in inflammatory cells was similar in chronic and acute TAD tissues, except for macrophages, which were seen more frequently in the adventitial layer of acute TAD tissue than in the adventitia of chronic TAD tissue. CONCLUSIONS: The inflammatory cell content of both acute and chronic TAD tissue was significantly different from that of control tissue. However, the inflammatory cell profile of aneurysmal chronic TAD was similar to that of acute TAD. This may reflect a sustained injury response that contributes to medial degeneration and aneurysm formation.

Stem cells in thoracic aortic aneurysms and dissections: potential contributors to aortic repair.

BACKGROUND: The hallmark of thoracic aortic aneurysms and dissections (TAAD) is progressive medial degeneration, which can result from excessive tissue destruction and insufficient repair. Although multipotent stem cells (SCs) are important in tissue repair, their role in TAAD is unknown. We sought to determine whether SCs are more abundant in TAAD tissue than in control tissues, and whether SCs within the diseased aortic wall differentiate into functionally relevant cell types. METHODS: Using immunohistochemistry, we compared the abundance of STRO-1+ cells, c-kit+ cells, and CD34+ cells in aortic tissue from patients with descending thoracic aortic aneurysms (n=12), patients with chronic descending thoracic aortic dissections (n=18), and age-matched organ donors (n=5). Using double immunofluorescence staining, we evaluated SC differentiation into smooth muscle cells, fibroblasts, and macrophages. RESULTS: All three cell types were significantly more abundant in the media and adventitia of TAAD tissues than in control tissues. We identified subsets of STRO-1+ cells, c-kit+ cells, and CD34+ cells that also expressed the smooth muscle cell marker SM22-α or fibroblast-specific protein-1, suggesting SC differentiation into smooth muscle cells or fibroblasts. Other STRO-1+ cells expressed the macrophage marker CD68, suggesting differentiation into inflammatory cells. CONCLUSIONS: Stem cells are more abundant in TAAD tissue than in normal aortic tissue. Differentiation of SCs into smooth muscle cells, fibroblasts, and inflammatory cells within the diseased aortic wall suggests that SCs might be involved in both reparative and destructive remodeling processes in TAAD. Understanding the regulation of SC-mediated aortic remodeling will be a critical step toward designing strategies to promote aortic repair and prevent adverse remodeling.