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Graft infection after endovascular abdominal aortic aneurysm repair

INTRODUCTION Although the natural history and management of infected open abdominal aortic aneurysm (AAA) repair is well described, only sporadic case reports have described the fate of patients with infected endografts placed in the abdominal aorta. The present study describes a tertiary referral centers experience with infected endovascular aneurysm repairs (EVARs). METHODS The medical records of 1302 open and endovascular aortic procedures were queried from January 2000 to January 2010. The cases were reviewed for prior aortic procedures, prosthetic implants, and etiology of current open procedure. Demographics, operative details, and perioperative courses were documented. RESULTS Nine patients (1 woman) with a mean age of 71 years had an EVAR that later required an open procedure for explantation and surgical revision for suspected infection. All grafts were explanted through a midline transperitoneal approach, with a mean time to explant of 33 months. The explanted endografts included 4 Zenith (Cook, Bloomington, Ind), 2 Ancure (Endovascular Technologies, Menlo Park, Calif), 2 Excluders (Gore, Flagstaff, Ariz), and 1 AneuRx (Medtronic, Minneapolis, Minn). Eight of the nine original EVARs were performed at other hospitals; 1 patient had EVAR and open explant at the University of Michigan. All patients had preoperative computed tomography scans, except one who was transferred in extremis with a gastrointestinal hemorrhage. Three patients also had a tagged leukocyte scan, and two had magnetic resonance imaging to further reinforce the suspicion of infection before explantation and bypass planning. Rifampin-soaked Hemashield (Boston Scientific) in situ grafts were used in four patients, with extra-anatomic (axillary-bifemoral) bypass used in the other five. The in situ group had no positive preoperative or postoperative cultures, with the exception of the unstable patient who died the day of surgery. For the other five patients, positive tissue cultures were found for Bacteroides, Escherichia coli, coagulase-negative Staphylococcus, Streptococcus, and Candida. Three patients were found to have aortic-enteric fistula, two of whom died before discharge from the hospital. The remaining seven survived to discharge. Average length of stay was 22 days, with a median follow-up of 11 months. CONCLUSION This series of infected EVARs is the largest group of infected AAA endografts reported to date. Because EVAR of AAAs is presently the most common method of repair, development of endograft infection, while rare, can be managed with acceptable mortality rates. Patients presenting with aortic-enteric fistula after EVAR appear to have a more virulent course.

Increased estrogen receptor alpha in experimental aortic aneurysms in females compared with males

BACKGROUND Estrogen receptor alpha (ERα) has been identified in the vessel wall, offering vasoprotective effects when upregulated. Estrogens are known to mediate the inflammatory milieu, and inflammation has long been associated with abdominal aortic aneurysm (AAA) formation. Therefore, it is theorized that increased estrogen receptor in females contributes to their relative resistance to AAAs. The objective of this study was to determine gender differences in ERα levels during experimental AAA formation. METHODS Infrarenal aortas of male and female C57 mice (n = 18 and n = 16, respectively) were infused with 0.4% elastase. Diameters were measured at days 0 and 14. Aortic messenger RNA expression of ERα was determined on day 3 by reverse transcription-polymerase chain reaction, whereas ERα protein levels were measured via Western blot. Immunohistochemistry using rabbit antibody for ERα was performed on day 14 samples and quantified. Zymography was done for matrix metalloproteinases (MMP)2 and 9 activity levels. Samples of human AAAs were collected and Western blot performed. Data were compared for significance using a student t-test. RESULTS Infrarenal aortic diameter increased in elastase-perfused males (ME) by 80% at 14 days after perfusion, whereas females (FE) increased by only 35% (P = 0.0012). FE had ×10 greater ERα messenger RNA expression compared with ME at day 3 (P = 0.003). Similarly, ERα protein levels were 100% higher in FE compared with those in ME on day 14 (P = 0.035). ERα protein levels were 80% higher in female human patients with AAA than those in their male counterparts (P = 0.029). ERα visualized via immunohistochemistry was 1.5 fold higher in FE than ME (P = 0.029). MMP2 and 9 activity levels were decreased in female compared with male aortas. CONCLUSIONS This study demonstrates an increase in aortic wall ERα in females compared with males that correlates inversely with MMP activity and AAA formation. These findings, coupled with observations that exogenous estrogen inhibits AAA formation in males, further suggest that estrogen supplementation may be important to prevent AAA formation and growth.

Phosphorylation of AKT and Abdominal Aortic Aneurysm Formation

It is hypothesized that differential AKT phosphorylation between sexes is important in abdominal aortic aneurysm (AAA) formation. Male C57BL/6 mice undergoing elastase treatment showed a typical AAA phenotype (80% over baseline, P < 0.001) and significantly increased phosphorylated AKT-308 (p308) and total-AKT (T-AKT) at day 14 compared with female mice. Elastase-treated Raw cells produced increased p308 and significant amounts of matrix metalloproteinase 9 (MMP-9), and these effects were suppressed by LY294002 treatment, a known AKT inhibitor. Male and female rat aortic smooth muscle cells treated with elastase for 1, 6, or 24 hours demonstrated that the p308/T-AKT and AKT-Ser-473/T-AKT ratios peaked at 6 hours and were significantly higher in the elastase-treated cells compared with controls. Similarly, male cells had higher phosphorylated AKT/T-AKT levels than female cells. LY294002 also inhibited elastase-induced p308 formation more in female smooth muscle cells than in males, and the corresponding cell media had less pro-MMP-9. AKT siRNA significantly decreased secretion of pro-MMP-9, as well as pro-MMP-2 and active MMP-2 from elastase-treated male rat aortic smooth muscle cells. IHC of male mice AAA aortas showed increased p308, AKT-Ser-473, and T-AKT compared with female mice. Aortas from male AAA patients had a significantly higher p308/T-AKT ratio than female AAA tissues. These data suggest that AKT phosphorylation is important in the upstream regulation of MMP activity, and that differential phosphorylation may be important in sex differences in AAA.

Increased PAI-1 in females compared with males is protective for abdominal aortic aneurysm formation in a rodent model

The serine proteases, along with their inhibitor plasmin activator inhibitor-1 (PAI-1), have been shown to play a role in abdominal aortic aneurysm (AAA) formation. The aim of this study is to determine if PAI-1 may be a protective factor for AAA formation and partially responsible for the gender difference observed in AAAs. Male and female wild-type (WT) C57BL/6 and PAI-1(-/-) mice 8-12 wk of age underwent aortic perfusion with porcine pancreatic elastase. Animals were harvested 14 days following perfusion and analyzed for phenotype, PAI-1 protein levels, and matrix metalloproteinase (MMP)-9 and -2 activity. WT males had an average increase in aortic diameter of 80%, whereas females only increased 32% (P < 0.001). PAI-1(-/-) males increased 204% and females 161%, significantly more than their WT counterparts (P < 0.001). Western blot revealed 61% higher PAI-1 protein levels in the WT females compared with the WT males (P = 0.01). Zymography revealed higher levels of pro-MMP-2 and active MMP-2 in the PAI-1(-/-) males and females compared with their WT counterparts. PAI-1(-/-) females had significantly higher serum plasmin levels compared with WT females (P = 0.003). In conclusion, WT female mice are protected from aneurysm formation and have higher levels of PAI-1 compared with males during experimental aneurysm formation. Additionally, both male and female PAI-1(-/-) animals develop significantly larger aneurysms than WT animals, correlating with higher pro- and active MMP-2 levels. These findings suggest that PAI-1 is protective for aneurysm formation in the elastase model of AAA and plays a role in the gender differences seen in AAA formation.

Increased JNK in Males Compared with Females in a Rodent Model of Abdominal Aortic Aneurysm

BACKGROUND In humans, there is a 4:1 male:female ratio in the incidence of abdominal aortic aneurysms (AAAs). c-Jun-N-terminal kinase (JNK) is an important upstream regulator of several enzymes involved in AAA formation, including the matrix metalloproteinases (MMPs). The purpose of this study was to determine if there is a gender difference between males and females in JNK during AAA formation. MATERIALS AND METHODS Male and female C57/B6 mice underwent aortic perfusion with elastase or heat inactivated elastase with aortas harvested at d 3 and 14 for phenotype determination, RT-PCR, Western blot, and zymography. Additionally, in vitro experiments using siRNA were conducted to define JNK regulation of matrix metalloproteinases (MMPs). A t-test was used to compare between groups. RESULTS Males formed larger AAAs at d 14 compared with females (P < 0.001), with significantly higher levels of JNK1 protein, proMMP9, proMMP2, and active MMP2. At d 3, males had more JNK1 mRNA, protein, and MMP activity. Knockdown of JNK 1 or 2 in vitro decreased MMP activity, while knockdown of JNK 1 and 2 together blocked all MMP activity. CONCLUSION Alterations in JNK between genders is partially responsible for the differential rates of experimental AAA formation, likely through differential regulation of MMPs.

Divergent effects of Tlr9 deletion in experimental late venous thrombosis resolution and vein wall injury

Deep-vein thrombosis (DVT) resolves via a sterile inflammatory response. Defining the inflammatory response of DVT may allow for new therapies that do not involve anticoagulation. Previously, we have shown that Toll-like receptor 9 (Tlr9) gene deleted mice had impaired venous thrombosis (VT) resolution. Here, we further characterise the role of Tlr9 signalling and sterile inflammation in chronic VT and vein wall responses. First, we found a human precedent exists with Tlr9+ cells present in chronic post thrombotic intraluminal tissue. Second, in a stasis VT mouse model, endogenous danger signal mediators of uric acid, HMGB-1, and neutrophil extracellular traps marker of citrullinated histone-3 (and extracellular DNA) were greater in Tlr9-/- thrombi as compared with wild-type (WT), corresponding with larger VT at 8 and 21 days. Fewer M1 type (CCR2+) monocyte/macrophages (MØ) were present in Tlr9-/- thrombi than WT controls at 8 days, suggesting an impaired inflammatory cell influx. Using bone marrow-derived monocyte (BMMØ) cell culture, we found decreased fibrinolytic gene expression with exposure to several endogenous danger signals. Next, adoptive transfer of cultured Tlr9+/+ BMMØ to Tlr9-/- mice normalised VT resolution at 8 days. Lastly, although the VT size was larger at 21 days in Tlr9-/- mice and correlated with decreased endothelial antigen markers, no difference in fibrosis was found. These data suggest that Tlr9 signalling in MØ is critical for later VT resolution, is associated with necrosis clearance, but does not affect later vein wall fibrosis. These findings provide insight into the Tlr9 MØ mechanisms of sterile inflammation in this disease process.

Deletion of Cysteine-Cysteine Receptor 7 Promotes Fibrotic Injury in Experimental Post-Thrombotic Vein Wall Remodeling

Objective—Deep vein thrombosis (VT) can result in vein wall injury, which clinically manifests as post-thrombotic syndrome. Postinjury fibrosis may be modulated in part through cellular cysteine-cysteine receptor 7 (CCR7)–mediated events. We tested the hypothesis that late vein wall fibrotic remodeling is dependent on CCR7. Approach and Results—CCR7−/− and C57BL/6 wild-type mice had inferior vena cava VT induced by nonstasis or stasis mechanisms. In both models, VT size was largest at day 1 and trended down by day 21, and CCR7+ cells peaked at day 8 in wild-type mice. No significant differences in VT resolution were found in CCR7−/− as compared with wild type in either model. In the nonstasis VT model, vein wall changes consistent with fibrotic injury were evidenced by significant increases in collagen I, III, matrix metalloproteinase 2, and transforming growth factor-&bgr; gene expression, increases in &agr;-smooth muscle actin and fibroblast specific protein-1 antigen, and total collagen at 8 days. Correspondingly, SM22&agr; and fibroblast specific protein-1, but not DDR2+ cells, were increased at 8 days. Early wild-type thrombus exposure inhibited profibrotic gene expression in CCR7−/− in ex vivo vein wall culture. Bone marrow chimera experiments further showed that circulating CCR7+ leukocytes partially rescued midterm profibrotic changes in CCR7−/− mice. In human histological sections of chronic thrombosed femoral veins, CCR7+ cells were present in the fibrotic areas. Conclusions—Post-thrombotic vein wall remodeling is impaired in CCR7−/− mice, with a profibrotic phenotype, is dependent on the thrombotic mechanism, and is mediated by circulating CCR7+ cells. Unlike other postinjury fibrotic responses, CCR7+ signaling may be important for positive vein wall remodeling after VT.

Differential gender- and species-specific formation of aneurysms using a novel method of inducing abdominal aortic aneurysms

BACKGROUND The objective of this study was to test a novel model of inducing abdominal aortic aneurysms (AAAs) in different mouse strains and genders. MATERIALS AND METHODS Male and female C57BL/6 and B6129 mice (n = 5 per group) underwent periaortic dissection and porcine pancreatic elastase (30 μL) or inactivated elastase application (5 min) to the aorta. Aortic measurements were taken on days 0 and 14. Aortic samples were analyzed for histology and zymography for matrix metalloproteinase (MMP) activity. Comparison statistics were performed using unpaired t-test. RESULTS AAA phenotype (50% aortic increase) occurred in external elastase-treated males (100%) and females (90%). No control animals developed AAAs. The aortic diameter was larger in C57BL/6 and B6129 elastase-treated versus control males (P = 0.0028 and P < 0.0001, respectively) and females (P < 0.0001 and P = 0.0458, respectively). Histology verified phenotype via disrupted internal elastic laminae. Macrophage counts in elastase-treated animals were >6-fold higher than in controls (all groups significant). MMP9 activity was greater in elastase-treated males and females in C57BL/6 (P = 0.0031, P = 0.0004) and B6129 (P = 0.025, P = 0.2) mice; MMP2 activity was greater in C57BL/6 versus B6129 male elastase-treated mice. CONCLUSIONS This rodent model produced AAAs in both genders and strains of mice. This model is simple, has little variability, and occurs in the infrarenal aorta, substantiating the external elastase model for future studies.