Amanda J McBroom

Release of outer membrane vesicles by Gram-negative bacteria is a novel envelope stress response

Conditions that impair protein folding in the Gram‐negative bacterial envelope cause stress. The destabilizing effects of stress in this compartment are recognized and countered by a number of signal transduction mechanisms. Data presented here reveal another facet of the complex bacterial stress response, release of outer membrane vesicles. Native vesicles are composed of outer membrane and periplasmic material, and they are released from the bacterial surface without loss of membrane integrity. Here we demonstrate that the quantity of vesicle release correlates directly with the level of protein accumulation in the cell envelope. Accumulation of material occurs under stress, and is exacerbated upon impairment of the normal housekeeping and stress‐responsive mechanisms of the cell. Mutations that cause increased vesiculation enhance bacterial survival upon challenge with stressing agents or accumulation of toxic misfolded proteins. Preferential packaging of a misfolded protein mimic into vesicles for removal indicates that the vesiculation process can act to selectively eliminate unwanted material. Our results demonstrate that production of bacterial outer membrane vesicles is a fully independent, general envelope stress response. In addition to identifying a novel mechanism for alleviating stress, this work provides physiological relevance for vesicle production as a protective mechanism.

Outer Membrane Vesicle Production by Escherichia coli Is Independent of Membrane Instability

It has been long noted that gram-negative bacteria produce outer membrane vesicles, and recent data demonstrate that vesicles released by pathogenic strains can transmit virulence factors to host cells. However, the mechanism of vesicle release has remained undetermined. This genetic study addresses whether these structures are merely a result of membrane instability or are formed by a more directed process. To elucidate the regulatory mechanisms and physiological basis of vesiculation, we conducted a screen in Escherichia coli to identify gene disruptions that caused vesicle over- or underproduction. Only a few low-vesiculation mutants and no null mutants were recovered, suggesting that vesiculation may be a fundamental characteristic of gram-negative bacterial growth. Gene disruptions were identified that caused differences in vesicle production ranging from a 5-fold decrease to a 200-fold increase relative to wild-type levels. These disruptions included loci governing outer membrane components and peptidoglycan synthesis as well as the sigma(E) cell envelope stress response. Mutations causing vesicle overproduction did not result in upregulation of the ompC gene encoding a major outer membrane protein. Detergent sensitivity, leakiness, and growth characteristics of the novel vesiculation mutant strains did not correlate with vesiculation levels, demonstrating that vesicle production is not predictive of envelope instability.

Oral Contraceptive Use and Risk of Breast, Cervical, Colorectal, and Endometrial Cancers: A Systematic Review

Oral contraceptives may influence the risk of certain cancers. As part of the AHRQ Evidence Report, Oral Contraceptive Use for the Primary Prevention of Ovarian Cancer, we conducted a systematic review to estimate associations between oral contraceptive use and breast, cervical, colorectal, and endometrial cancer incidence. We searched PubMed, Embase, and Cochrane Database of Systematic Reviews. Study inclusion criteria were women taking oral contraceptives for contraception or ovarian cancer prevention; includes comparison group with no oral contraceptive use; study reports quantitative associations between oral contraceptive exposure and relevant cancers; controlled study or pooled patient-level meta-analyses; sample size for nonrandomized studies ≥100; peer-reviewed, English-language; published from January 1, 2000 forward. Random-effects meta-analyses were conducted by estimating pooled ORs with 95% confidence intervals (CIs). We included 44 breast, 12 cervical, 11 colorectal, and 9 endometrial cancers studies. Breast cancer incidence was slightly but significantly increased in users (OR, 1.08; CI, 1.00–1.17); results show a higher risk associated with more recent use of oral contraceptives. Risk of cervical cancer was increased with duration of oral contraceptive use in women with human papillomavirus infection; heterogeneity prevented meta-analysis. Colorectal cancer (OR, 0.86; CI, 0.79–0.95) and endometrial cancer incidences (OR, 0.57; CI, 0.43–0.77) were significantly reduced by oral contraceptive use. Compared with never use, ever use of oral contraceptives is significantly associated with decreases in colorectal and endometrial cancers and increases in breast cancers. Although elevated breast cancer risk was small, relatively high incidence of breast cancers means that oral contraceptives may contribute to a substantial number of cases. Cancer Epidemiol Biomarkers Prev; 22(11); 1931–43. ©2013 AACR.

Oral Contraceptives and Risk of Ovarian Cancer and Breast Cancer Among High-Risk Women: A Systematic Review and Meta-Analysis

PURPOSE To estimate the risks of ovarian cancer and breast cancer associated with oral contraceptive (OC) use among women at elevated risk owing to mutations in BRCA1/2 or a strong family history. METHODS We searched PubMed, Embase, the Cochrane Database of Systematic Reviews, and ClinicalTrials.gov for studies published 2000 to 2012 that evaluated associations between OC use and breast or ovarian cancer among women who are carriers of a BRCA1/2 mutation or have a family history of breast or ovarian cancer. RESULTS From 6,476 unique citations, we identified six studies examining ovarian cancer risk in BRCA1/2 mutation carriers and eight studies examining breast cancer risk in BRCA1/2 mutation carriers. For BRCA1/2 mutation carriers combined, meta-analysis showed an inverse association between OC use and ovarian cancer (odds ratio [OR], 0.58; 95% CI, 0.46 to 0.73) and a nonstatistically significant association with breast cancer (OR, 1.21; 95% CI, 0.93 to 1.58). Findings were similar when examining BRCA1 and BRCA2 mutation carriers separately. Data were inadequate to perform meta-analyses examining duration or timing of use. For women with a family history of ovarian or breast cancer, we identified four studies examining risk for ovarian cancer and three for breast cancer, but differences between studies precluded combining the data for meta-analyses, and no overall pattern could be discerned. CONCLUSION Our analyses suggest that associations between ever use of OCs and ovarian and breast cancer among women who are BRCA1 or BRCA2 mutation carriers are similar to those reported for the general population.

Risk of acute thromboembolic events with oral contraceptive use: a systematic review and meta-analysis.

OBJECTIVE: To estimate the risk of venous thromboembolism, stroke, or myocardial infarction (MI) associated with the use of oral contraceptive pills (OCPs) and to describe how these risks vary by dose or formulation. DATA SOURCES: We searched PubMed, Embase, the Cochrane Database of Systematic Reviews, and ClinicalTrials.gov for studies published from January 1995 through June 2012 that evaluated the association between OCP use and risk of venous thromboembolism, stroke, or MI. METHODS OF STUDY SELECTION: We reviewed 6,476 citations. We included English-language, controlled studies with human participants reporting a quantitative association between exposure to OCPs and outcomes of venous thromboembolism, stroke, or MI. Two investigators independently reviewed articles for inclusion or exclusion; discordant decisions were resolved by team review and consensus. Random-effects meta-analysis was used to generate summary odds ratios (ORs). TABULATION, INTEGRATION, AND RESULTS: Fifty studies met inclusion criteria. There were no randomized clinical trials. We found threefold increased odds of venous thromboembolism among current compared with noncurrent OCP users (14 studies; OR 2.97, 95% confidence interval [CI] 2.46–3.59). We found twofold increased odds of ischemic stroke (seven studies; OR 1.90, 95% CI 1.24–2.91). There was no evidence of increased risk of hemorrhagic stroke (four studies; OR 1.03, 95% CI 0.71–1.49) or MI (eight studies; OR 1.34, 95% CI 0.87–2.08). CONCLUSION: Current use of combined OCPs is associated with increased odds of venous thromboembolism and ischemic stroke but not hemorrhagic stroke or MI.

Rate- and Rhythm-Control Therapies in Patients With Atrial Fibrillation: A Systematic Review

Atrial fibrillation (AF) is a major public health problem in the United States. More than 2.3 million Americans are estimated to have AF (1). The known association between AF and substantial mortality, morbidity, and health care costs compounds the effect of this condition. Not only is the risk for death in patients with AF twice that of patients without it, but AF can result in myocardial ischemia and infarction, exacerbate heart failure (HF), and cause tachycardia-induced cardiomyopathy if the ventricular rate is not well-controlled (25). The most dreaded complication of AF is thromboembolism, especially stroke (6). In some patients, AF or therapies to manage this condition can severely depreciate quality of life (710). Furthermore, the management of AF and its complications is responsible for nearly

ECG-based signal analysis technologies for evaluating patients with acute coronary syndrome: a systematic review.

16 billion in additional costs to the U.S. health care system per year (11). Despite the substantial public health effect of AF, uncertainties around its management remain. In particular, the comparative safety and effectiveness of different rate- and rhythm-control therapies for patients with AF are unclear. We conducted this systematic review to evaluate the comparative safety and effectiveness of rate- versus rhythm-control strategies; medications used for ventricular rate control; strict versus more lenient rate-control strategies; nonpharmacologic rate-control therapies versus medications; electrical cardioversion and antiarrhythmic medications for restoration of sinus rhythm; and catheter ablation, surgical ablation, and antiarrhythmic medications for maintenance of sinus rhythm. Methods We developed and followed a standard protocol for our review. Full details of our methods, search strategies, results, and conclusions are presented in a comparative effectiveness review commissioned by the Agency for Healthcare Research and Quality (AHRQ) and are available at www.effectivehealthcare.ahrq.gov (12). Data Sources and Searches We searched PubMed, EMBASE, and the Cochrane Database of Systematic Reviews for studies published between 1 January 2000 and 12 November 2013. Data before 2000 have been summarized in an AHRQ report on the management of new-onset AF published in 2001 (1315). Study Selection We identified randomized, controlled trials (RCTs) published in English that were comparative assessments of pharmacologic or nonpharmacologic rate- or rhythm-control therapies aimed at treating adults with AF. Observational studies were also allowed for comparisons of strict versus lenient rate control or cardiac resynchronization therapy versus other rhythm-control therapies. The following outcomes were considered: restoration of sinus rhythm (conversion), maintenance of sinus rhythm, recurrence of AF at 12 months, development of cardiomyopathy, death (all-cause and cardiac), myocardial infarction, cardiovascular hospitalizations, HF symptoms, control of AF symptoms, quality of life, functional status, stroke and other embolic events, bleeding events, and adverse effects of therapy. Data Extraction and Quality Assessment One investigator abstracted and another confirmed data related to study setting and design, patient characteristics, details of treatment, comparators, and relevant outcomes. The quality of individual studies was evaluated using the approach described in AHRQs Methods Guide for Effectiveness and Comparative Effectiveness Reviews (16). Investigators also assessed factors that limited applicability of the evidence. Data Synthesis and Analysis For each treatment comparison and outcome of interest, we determined the feasibility of completing a quantitative synthesis (meta-analysis) based on the volume of relevant literature, conceptual homogeneity of the studies (both in terms of study population and outcomes), and completeness of the reporting of results. We considered meta-analysis for outcomes that at least 3 studies reported. For our evaluation of rate- versus rhythm-control strategies, we grouped all rate-control strategies together and all rhythm-control strategies together, regardless of the specific medication or procedure. We grouped pharmacologic interventions by class, considering rate-controlling calcium-channel blockers and all -blockers each to be similar enough to be grouped together. We categorized procedures into electrical cardioversion, atrioventricular node (AVN) ablation, AF ablation by pulmonary vein isolation (PVI) (by open surgical, minimally invasive, or transcatheter procedures), and different types of surgical maze procedures and explored comparisons among these categories. In addition, for the comparisons focusing on medications versus procedures, we also explored grouping all medications together and comparing them with all procedures. When a meta-analysis was appropriate, we used a random-effects model to synthesize the available evidence quantitatively using Comprehensive Meta-Analysis, version 2 (Biostat, Englewood, New Jersey). We used a standardized approach to rank the overall strength of evidence (SOE) for each outcome (16). Role of the Funding Source Primary funding was provided by AHRQ. Neither the technical experts nor AHRQ representatives had a role in the literature search, data analysis, interpretation of the data, or decision to submit the manuscript for publication. Results We screened 10495 abstracts, evaluated 570 full-text articles, and included 200 articles representing 162 studies involving 28836 patients (Figure 1). Tables 1 to 6 of the Supplement provide details about these studies and their populations for each topic described here. Table 7 of the Supplement lists identified and potential limitations of the studies. The full AHRQ report highlights additional findings (12). Figure 1. Summary of evidence search and selection. AAD = antiarrhythmic drug; CRT = cardiac resynchronization therapy; RCT = randomized, controlled trial. * Some studies were relevant to more than 1 topic. Supplement. Tables Rate- Versus Rhythm-Control Strategies We included 16 RCTs in this analysis: 13 compared pharmacologic rhythm-control versus rate-control strategies (1729) and 3 compared a rhythm-control strategy with PVI versus a rate-control strategy that involved AVN ablation and implantation of a pacemaker in 1 study (30) and rate-controlling medications in the other 2 (31, 32). Ten RCTs (17, 18, 2022, 2428) provided information on outcomes of interest and were combined quantitatively (Figure 2). Of these, 5 included only patients with persistent AF (2022, 25, 28), 1 included only patients with paroxysmal AF (17), and 4 included patients with paroxysmal or persistent AF (18, 24, 26, 27). Two studies (17, 22) compared a single-chamber pacemaker plus AVN ablation versus a dual-chamber pacemaker plus AVN ablation plus an antiarrhythmic medication; all others compared largely unspecified rate-control with rhythm-control strategies. Figure 2. Meta-analysis forest plots. AAD = antiarrhythmic drug; PVI = pulmonary vein isolation. A. All-cause mortality for rate- vs. rhythm-control strategies. B. Cardiovascular mortality for rate- vs. rhythm-control strategies. C. Stroke for rate- vs. rhythm-control strategies. D. Restoration of sinus rhythm for monophasic vs. biphasic waveforms. E. Maintenance of sinus rhythm for PVI vs. AAD therapy. Figure 2. Continued. Data from the included studies showed moderate SOE that pharmacologic rate- and rhythm-control strategies are of comparable efficacy with regard to their effect on all-cause mortality (odds ratio [OR], 1.34 [95% CI, 0.89 to 2.02]; Q= 21.71; P= 0.003) (Figure 2, A) (18, 2022, 24, 2628), cardiac mortality (OR, 0.96 [CI, 0.77 to 1.20]; Q= 3.55; P= 0.47) (Figure 2, B) (18, 21, 22, 24, 25), and stroke (OR, 0.99 [CI, 0.76 to 1.30]; Q= 7.02; P= 0.43) (Figure 2, C) (17, 18, 2022, 24, 27, 28). Although the meta-analysis for all-cause mortality showed a potential benefit, it did not reach statistical significance and 6 of the 8 studies (6069 patients [95%]) had ORs that crossed 1, resulting in a final moderate SOE. For cardiac mortality (Figure 2, B), point estimates were inconsistent and CIs were wide for 2 of the 5 studies (18, 21), but there was no evidence of heterogeneity; therefore, our SOE rating was not affected. For the outcome of stroke, there was no evidence of heterogeneity, but the findings were mostly driven by 1 large, good-quality RCT (4060 patients), which was inconsistent with several of the smaller studies, reducing our confidence in the finding and in the SOE. These studies largely included older patients with mild AF symptoms. Three RCTs compared pharmacologic rate-control strategies with rhythm-control strategies using antiarrhythmic medications (17, 18, 22). These RCTs showed fewer cardiovascular hospitalizations with the rhythm-control strategies (17, 18, 22). Although data from 5 RCTs suggest that there is no difference between pharmacologic rate- and rhythm-control strategies in their effect on HF symptoms (17, 22, 24, 26, 46) (Table 1), a prespecified substudy of the Atrial Fibrillation and Congestive Heart Failure study showed that a higher proportion of time spent in sinus rhythm was associated with a greater improvement in New York Heart Association class (29). Table 1. Summary of SOE and Effect Estimates for Rate- Versus Rhythm-Control Strategies Three studies compared a rhythm-control strategy involving catheter ablation with a rate-control strategy involving rate-controlling medications (32) or AVN ablation combined with implantation of a pacemaker (30) or rate-controlling medications (31). One study showed that catheter ablation was better than pharmacologic rate control at improving symptoms, neurohormonal status, and objective physiologic exercise capacity (32). Another study showed that PVI isolation was superior to AVN ablation and pacemaker implantation in improving quality of life, 6-minute walk distance, and ejection fraction (30). Another study showed that PVI resulted in long-term restoration o

Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers for treatment of ischemic heart disease: Future research needs prioritization

BACKGROUND/OBJECTIVES Timely identification of cardiac ischemia is critical in patients with acute coronary syndrome (ACS). The first test is often the standard, resting 12-lead ECG. Given its limitations, signal analysis enhancements have been proposed. We summarize the published evidence for commercially available ECG-based signal analysis technologies. METHODS This is a systematic review of the English-language published literature. RESULTS Published evidence meeting inclusion criteria was available for two devices: PRIME ECG and LP 3000. Meta-analysis of eight studies estimated a 68.4% sensitivity (95% CI, 35.1%-89.7%) and 91.4% specificity (CI, 83.6%-95.7%) for the PRIME ECG, compared with 40.5% sensitivity (CI, 19.6%-65.5%) and 95.0% specificity (CI, 87.9%-98.0%) for the standard 12-lead ECG. CONCLUSIONS Existing evidence is insufficient to confidently inform the appropriate use of ECG-based signal analysis technologies for detecting ischemia or infarct in ACS. Further research is needed to determine in what circumstances, if any, these devices might precede, replace, or add to the standard ECG in test strategies for detecting ischemia or infarct in ACS.

Priorities for Comparative Effectiveness Reviews in Cardiovascular Disease

BACKGROUND A recent review evaluated the comparative effectiveness of angiotensin-converting enzyme inhibitors (ACE-Is) and angiotensin II receptor blockers (ARBs) in patients with or at high risk for stable ischemic heart disease (IHD). The prioritization of future research needs has customarily been an informal process that is not responsive to the needs of all relevant stakeholders. METHODS As part of the Agency for Healthcare Research and Quality Effective Healthcare Program, the Duke Evidence-Based Practice Center engaged a diverse stakeholder group in 3 exercises designed to prioritize future research needs pertaining to the comparative effectiveness of ACE-I/ARB in patients with stable IHD. RESULTS Our stakeholders prioritized the following areas of research pertaining to the comparative effectiveness of ACE-I/ARB in stable IHD: (1) strategies to enhance greater evidence-based use, (2) impact of adherence on effectiveness or harms, (3) impact of comorbidities on effectiveness or harms, (4) medication impact on patient quality of life, (5) impact of demographic differences on effectiveness or harms, and (6) medication impact on incidence of new diagnoses. This project also yielded suggestions regarding potential study designs to address these future research needs. CONCLUSIONS Our stakeholders prioritized research designed to facilitate (1) tailored ACE-I/ARB treatment based on individual patient characteristics and (2) implementation of ACE-I/ARB use among patients most likely to benefit. With respect to suggested study designs, it was felt that analysis of existing data would sufficiently address many of the top-tier future research needs (FRNs).

Nonpharmacologic Treatments for Attention-Deficit/Hyperactivity Disorder: A Systematic Review

Background—Comparative effectiveness reviews offer a systematic method to critically appraise existing research and to identify unaddressed clinical areas in cardiovascular disease where significant morbidity, mortality, and variation in the use of resources persist. To delineate and help select areas where comparative effectiveness reviews are needed, the Effective Health Care Program of the Agency for Healthcare Research and Quality involved stakeholders in prioritization of the research agenda. Methods and Results—We involved a diverse panel of stakeholders representing a broad range of clinical, policy, and patient perspectives. To assist in prioritization of topics for evidence synthesis, we created a framework evaluating 12 cardiovascular disease subcategories that reflect American College of Cardiology/American Heart Association disease-based guidelines. We performed an environmental scan for each disease subcategory to populate this framework with existing knowledge, levels of evidence, and degrees of public interest. Through a formalized process, 4 disease subcategories were prioritized: chronic coronary artery disease, ventricular arrhythmias, heart failure, and cerebrovascular disease. Within these subcategories, 11 topics that address the comparative safety and effectiveness of existing treatments and evaluate emerging treatments were nominated by the stakeholder panel to proceed for feasibility assessment before developing comparative effectiveness reviews. Conclusions—Using a systematic process deriving consensus from multiple stakeholders across cardiovascular disease states, we generated a prioritized list of evidence synthesis topics to inform decision makers. The topics vetted through this process seek to determine the comparative safety and effectiveness of a range of treatments, both established and emerging, and are immediately relevant for prevalent disease states.