Karen J. Ho

Nonnuclear Actions of Estrogen

Estrogen has long been observed to endow cardiovascular protective effects, as evidenced by sex-specific differences in the incidence of hypertensive and coronary artery disease, the development of atherosclerosis, and myocardial remodeling after infarction. To exert its tissue-specific effects, the classic estrogen receptor (ER) functions as a ligand-dependent transcription factor. However, there is growing evidence that in response to 17beta-estradiol and heterologous signals, the ER can also mediate signaling cascades at the membrane and in the cytoplasm via various second messengers, such as receptor-mediated protein kinases. This review summarizes the current understanding of nonnuclear ER signaling and discusses the relevance to eliciting the beneficial cardiovascular effects of estrogen. These include vasodilation, inhibition of response to vessel injury, limiting myocardial injury after infarction, and attenuating cardiac hypertrophy. Defining the full repertoire of ER function promises to expose novel, highly specific targets for pharmacological interventions and may ultimately lead to the primary and secondary prevention of cardiovascular diseases.

Restoration of Liver Mass after Injury Requires Proliferative and Not Embryonic Transcriptional Patterns

Normal adult liver is uniquely capable of renewal and repair after injury. Whether this response represents simple hyperplasia of various liver elements or requires recapitulation of the genetic program of the developing liver is not known. To study these possibilities, we examined transcriptional programs of adult liver after partial hepatectomy and contrasted these with developing embryonic liver. Principal component analysis demonstrated that the time series of gene expression during liver regeneration does not segregate according to developmental transcription patterns. Gene ontology analysis revealed that liver restoration after hepatectomy and liver development differ dramatically with regard to transcription factors and chromatin structure modification. In contrast, the tissues are similar with regard to proliferation-associated genes. Consistent with these findings, real-time polymerase chain reaction showed transcription factors known to be important in liver development are not induced during liver regeneration. These three lines of evidence suggest that at a transcriptional level restoration of liver mass after injury is best described as hepatocyte hyperplasia and not true regeneration. We speculate this novel pattern of gene expression may underlie the unique capacity of the liver to repair itself after injury.

Donor postextubation hypotension and age correlate with outcome after donation after cardiac death transplantation.

Background. Compared with standard donors, kidneys recovered from donors after cardiac death (DCD) exhibit higher rates of delayed graft function (DGF), and DCD livers demonstrate higher rates of biliary ischemia, graft loss, and worse patient survival. Current practice limits the use of these organs based on time from donor extubation to asystole, but data to support this is incomplete. We hypothesized that donor postextubation parameters, including duration and severity of hemodynamic instability or hypoxia might be a better predictor of subsequent graft function. Methods. We performed a retrospective examination of the New England Organ Bank DCD database, concentrating on donor factors including vital signs after withdrawal of support. Results. Prolonged, severe hypotension in the postextubation period was a better predictor of subsequent organ function that time from extubation to asystole. For DCD kidneys, this manifested as a trend toward increased DGF. For DCD livers, this manifested as increased rates of poor outcomes. Maximizing the predictive value of this test in the liver cohort suggested that greater than 15 min between the time when the donor systolic blood pressure drops below 50 mm Hg and flush correlates with increased rates of diffuse biliary ischemia, graft loss, or death. Donor age also correlated with worse outcome. Conclusions. Time between profound instability and cold perfusion is a better predictor of outcome than time from extubation to asystole. If validated, this information could be used to predict DGF after DCD renal transplant and improve outcomes after DCD liver transplant.

Predictive factors of 30-day unplanned readmission after lower extremity bypass

BACKGROUND Thirty-day unplanned readmission after lower extremity bypass represents a large cost burden and is a logical target for cost-containment strategies. We undertook this study to evaluate factors associated with unplanned readmission after lower extremity bypass. METHODS This is a retrospective analysis from a prospective institutional registry. All lower extremity bypasses for occlusive disease from January 1995 to July 2011 were included. The primary end point was 30-day unplanned readmission. Secondary end points included graft patency and limb salvage. RESULTS Of 1543 lower extremity bypasses performed, 84.5% were for critical limb ischemia and 15.5% were patients with intermittent claudication. Twenty-seven patients (1.7%) died in-house and were excluded from further analysis. Of 1516 lower extremity bypasses analyzed, 42 (2.8%) were in patients with a planned readmission within 30 days, and 349 (23.0%), in patients with an unplanned readmission. Most unplanned readmissions were wound related (62.9%). By multivariable analysis, preoperative predictive factors for unplanned readmission were dialysis dependence (odds ratio [OR], 1.73; P = .004), tissue loss indication (OR, 1.62; P = .0004), and history of congestive heart failure (OR, 1.43; P = .03). Postoperative predictors included distal inflow source (OR, 1.38; P = .016), in-hospital wound infection (OR, 8.30; P < .0001), in-hospital graft failure (OR, 3.20; P < .0001), and myocardial infarction (OR, 1.96; P < .04). Neither index length of stay nor discharge disposition independently predicted unplanned readmission. Unplanned readmission was associated with loss of assisted primary patency (hazard ratio, 1.39; 95% confidence interval, 1.08-1.80; P = .01) and long-term limb loss (hazard ratio, 1.68; 95% confidence interval, 1.23-2.29; P = .001). CONCLUSIONS Thirty-day unplanned readmission is a frequent occurrence after lower extremity bypass (23.0%). Stratifying patients by risk factors associated with unplanned readmission is essential for quality improvement and equitable resource allocation when disease-specific bundling strategies are being derived.

Lower extremity vein graft failure: a translational approach

Abstract Patients with the most severe manifestations of lower extremity arterial occlusive disease often require peripheral bypass surgery for limb salvage and preservation of function. Although good quality saphenous vein offers the most durable conduit for reconstruction, 5-year failure rates are 30–50% and have remained largely unchanged for the past two decades. The majority of these failures occur within the first year of implantation, which is regarded as the most biologically active time during which the vein graft adapts to the arterial environment. Although intimal hyperplasia is generally regarded as the primary culprit of vein graft failure, geometric remodeling of the healing vein graft has recently emerged as a potentially significant contributing factor. While hemodynamic forces, including an increase in shear stress and wall tension, are undoubtedly central to the magnitude and direction of vein graft remodeling, we have determined that these forces alone cannot account for the extent of variability noted in early remodeling patterns. Therefore, we hypothesize that circulating factors, such as mediators of inflammation, may modulate the vein graft response to mechanical forces. This article reviews the definition and diagnosis of vein graft failure and summarizes our current efforts to understand the mechanisms of normal and abnormal vein graft adaptation to the arterial environment.

Transcriptional ontogeny of the developing liver

BackgroundDuring embryogenesis the liver is derived from endodermal cells lining the digestive tract. These endodermal progenitor cells contribute to forming the parenchyma of a number of organs including the liver and pancreas. Early in organogenesis the fetal liver is populated by hematopoietic stem cells, the source for a number of blood cells including nucleated erythrocytes. A comprehensive analysis of the transcriptional changes that occur during the early stages of development to adulthood in the liver was carried out.ResultsWe characterized gene expression changes in the developing mouse liver at gestational days (GD) 11.5, 12.5, 13.5, 14.5, 16.5, and 19 and in the neonate (postnatal day (PND) 7 and 32) compared to that in the adult liver (PND67) using full-genome microarrays. The fetal liver, and to a lesser extent the neonatal liver, exhibited dramatic differences in gene expression compared to adults. Canonical pathway analysis of the fetal liver signature demonstrated increases in functions important in cell replication and DNA fidelity whereas most metabolic pathways of intermediary metabolism were under expressed. Comparison of the dataset to a number of previously published microarray datasets revealed 1) a striking similarity between the fetal liver and that of the pancreas in both mice and humans, 2) a nucleated erythrocyte signature in the fetus and 3) under expression of most xenobiotic metabolism genes throughout development, with the exception of a number of transporters associated with either hematopoietic cells or cell proliferation in hepatocytes.ConclusionsOverall, these findings reveal the complexity of gene expression changes during liver development and maturation, and provide a foundation to predict responses to chemical and drug exposure as a function of early life-stages.

BMP4 is a novel paracrine inhibitor of liver regeneration

Transforming growth factor (TGF)-β family members exert strong effects on restoration of liver mass after injury. Bone morphogenetic proteins (BMPs) are members of the TGF-β family and are found in the liver, suggesting that these proteins may play a role in liver regeneration. We examined BMP signaling in the liver during hepatectomy. We found that BMP4 is constitutively expressed in the peribiliary stroma and endothelial cells of the liver and that expression is decreased after hepatectomy. Mice driven to maintain BMP4 expression in the liver display inhibited hepatocyte proliferation and restoration of liver mass after hepatectomy, suggesting that reduced BMP4 is necessary for normal regeneration. Consistent with this finding, hepatocyte-specific deletion of the BMP receptor activin receptor-like kinase 3 (Alk3) enhances regeneration and reduces phosphorylation of SMAD1/5/8, a transducer of BMP signaling. In contrast to experiments in wild-type mice, maintaining BMP4 levels has no effect on liver regeneration in hepatocyte-specific Alk3 null mice, providing evidence that BMP4 signals through Alk3 to inhibit liver regeneration. Consistent with these findings, the BMP4 antagonist Noggin enhances regeneration. Furthermore, high-dose BMP4 inhibits proliferation of primary hepatocytes and HepG2 cells in culture. These findings elucidate a new, potentially clinically relevant paradigm in which a constitutively expressed paracrine inhibitory factor plays a critical role in liver regeneration.

Intermediate-term outcome of carotid endarterectomy with bovine pericardial patch closure compared with Dacron patch and primary closure

OBJECTIVE Multiple studies have established that patch angioplasty following carotid endarterectomy (CEA) reduces the risk of subsequent stroke and restenosis compared with primary closure. Previous reports have also demonstrated bovine pericardium to be associated with similar rates of postoperative complications and restenosis compared with other patch materials. Due to favorable handling and sonographic properties, bovine pericardium has become increasingly popular as a patch option in recent years. However, the intermediate- and long-term performance of this material remains incompletely defined. Through a retrospective analysis of our carotid endarterectomy experience, we sought to compare the bleeding, infection, and pseudoaneurysm rates with bovine pericardium patch closure to those with Dacron patch and primary closure. In this study, 1331 primary carotid endarterectomies performed in our institution between 1996 and 2008 were grouped according to the method of arteriotomy closure: primary closure (PC) (216, 16.3%), Dacron patch angioplasty (DPA) (642, 48.2%), and bovine pericardial patch angioplasty (BPA) (457, 34.3%). Demographic variable and postoperative outcome measures collected real-time via a designated database manager were assessed by univariate and multivariate analysis. RESULTS Mean follow-up for the entire cohort was 46.1 months. There were no statistically significant differences in rates of postoperative wound infection, hematoma, pseudoaneurysm formation, or 30-day stroke or 30-day mortality among the three groups. Combined 30-day stroke and death was significantly lower in the PC cohort (0.5% vs 2.3% DPA vs 2.4% BPA; P = .94, BPA vs DPA; P = .001, BPA vs PC; P = .001, DPA vs PC), while 5-year restenosis after both DPA (2.0% ± 0.6%) and BPA (1.1% ± 0.6%) was significantly lower compared with PC (5.2% ± 1.6%) (P = .03, DPA vs PC; P = .008, BPA vs PC; P = .14, BPA vs DPA). Five-year survival following BPA (77.9% ± 3.6%) was significantly improved compared with PC (66.9% ± 3.5%) and DPA (60.8% ± 2.1%) in univariate analysis (P = .24, DPA vs PC; P = .01, BPA vs PC; P = .03, BPA vs DPA), with statin use (P = .004) and male gender (P = .05) being positive predictors of enhanced survival on multivariate analysis. CONCLUSIONS This single-institution, retrospective review represents the largest reported experience with BPA after CEA to date and is the only report comparing outcomes after BPA to PC or to DPA. Our experience further demonstrates that patch angioplasty is protective against restenosis after CEA compared with PC. Equivalent rates of perioperative bleeding, infection, and pseudoaneurysm formation were seen with each closure strategy in this study.

Outcomes of Thoracic Endovascular Aortic Repair and Subclavian Revascularization Techniques

BACKGROUND Practice guidelines for management of the left subclavian artery (LSA) during thoracic endovascular aortic repair (TEVAR) are based on low-quality evidence, and there is limited literature that addresses optimal revascularization techniques. The purpose of this study was to compare outcomes of LSA coverage during TEVAR and revascularization techniques. STUDY DESIGN We performed a single-center retrospective cohort study from 2001 to 2013. Patients were categorized by LSA revascularization and by revascularization technique, carotid-subclavian bypass (CSB), or subclavian-carotid transposition (SCT). Thirty-day and mid-term stroke, spinal cord ischemia, vocal cord paralysis, upper extremity ischemia, primary patency of revascularization, and mortality were compared. RESULTS Eighty patients underwent TEVAR with LSA coverage, 25% (n = 20) were unrevascularized and the remaining patients underwent CSB (n = 22 [27.5%]) or SCT (n = 38 [47.5%]). Mean follow-up time was 24.9 months. Comparisons between unrevascularized and revascularized patients were significant for a higher rate of 30-day stroke (25% vs 2%; p = 0.003) and upper extremity ischemia (15% vs 0%; p = 0.014). However, there was no difference in 30-day or mid-term rates of spinal cord ischemia, vocal cord paralysis, or mortality. There were no statistically significant differences in 30-day or midterm outcomes for CSB vs SCT. Primary patency of revascularizations was 100%. Survival analysis comparing unrevascularized vs revascularized LSA was statistically significant for freedom from stroke and upper extremity ischemia (p = 0.02 and p = 0.003, respectively). After adjustment for advanced age, urgency, and coronary artery disease, LSA revascularization was associated with lower rates of perioperative adverse events (odds ratio = 0.23; p = 0.034). CONCLUSIONS During TEVAR, LSA coverage without revascularization is associated with an increased risk of stroke and upper extremity ischemia. When LSA coverage is required during TEVAR, CSB and SCT are equally acceptable options.

Optimized adeno-associated virus 8 produces hepatocyte-specific Cre-mediated recombination without toxicity or affecting liver regeneration

UNLABELLED Engineering viral vectors to produce liver-specific protein expression may help advance understanding of hepatic regeneration and disease states. In addition to introducing genes of interest to the liver, these vectors can be adapted for gene deletion when designed to express Cre recombinase. The ability to use this system requires high, liver-restricted expression, low toxicity, and no effect on the process of interest. We developed an adeno-associated virus 8 (AAV8) with a codon-optimized Cre recombinase under a hepatocyte-specific major urinary protein (MUP) promoter (MUP-iCre-AAV8) that fulfills these requirements. A single intravenous injection of ROSA26R reporter mice, which express lacZ after Cre-mediated recombination, demonstrated homogeneous beta-galactosidase expression limited to hepatocytes after only 7 days. Cre protein expression remained strong for at least 31 days. Serum liver function tests and histology demonstrated minimal liver toxicity. The presence of MUP-iCre-AAV8 did not affect hepatocyte proliferation after partial hepatectomy as measured by Ki67 staining. CONCLUSION AAV8 with the MUP promoter, by virtue of its lack of hepatic toxicity or effect on liver regeneration, may be an efficient alternative to complex transgenic methodologies for studies of the mouse liver.