Acute effects of vasoactive medications in patients with parallel circulation awaiting hybrid or Norwood procedure.

Background: Vasoactive medications are frequently used in the preoperative stage to balance the pulmonary and systemic blood flow. However, not much is known about the effects of these agents during this stage. Aims: The primary objective of this study was to characterize the acute effects of vasoactive medications in children with parallel circulation before either the hybrid or Norwood procedure. Setting and Designs: This is a single-center, cross-sectional, retrospective study. Methods: Hemodynamic and systemic oxygen delivery data were captured from patients' vital signs, arterial blood gases, near-infrared spectroscopy monitoring (NIRS). Data for each patient were collected before the initiation of a vasoactive medication and again 6 h after. Statistical Analysis: Data were analyzed using paired t-tests, and analysis of covariance. Results: A total of 139 patients were identified. After data extraction the following patients were included before the initial intervention: 7 were on milrinone, 22 were on dopamine, and 17 were on dobutamine. Dopamine and dobutamine were found to significantly increase systolic blood pressure. Only dopamine increased pH (mean difference 0.04), decreased paCO2 (mean difference -7.1), decreased lactate (mean difference -0.6 mmol/L), and decreased in bedside Qp: Qs (mean difference -7.5) after continuous infusion for 6 h. Milrinone was not associated with any significant hemodynamic change. Conclusion: In this study, dopamine was independently associated with improvement in markers of systemic oxygen delivery 6 h after initiation. Dobutamine and dopamine were associated with increased in blood pressure. Well-powered studies are required to detect changes in lactate and NIRS.

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

CONTEXT: Nonpharmacologic treatments for attention-deficit/hyperactivity disorder (ADHD) encompass a range of care approaches from structured behavioral interventions to complementary medicines. OBJECTIVES: To assess the comparative effectiveness of nonpharmacologic treatments for ADHD among individuals 17 years of age and younger. DATA SOURCES: PubMed, Embase, PsycINFO, and Cochrane Database of Systematic Reviews for relevant English-language studies published from January 1, 2009 through November 7, 2016. STUDY SELECTION: We included studies that compared any ADHD nonpharmacologic treatment strategy with placebo, pharmacologic, or another nonpharmacologic treatment. DATA EXTRACTION: Study design, patient characteristics, intervention approaches, follow-up times, and outcomes were abstracted. For comparisons with at least 3 similar studies, random-effects meta-analysis was used to generate pooled estimates. RESULTS: We identified 54 studies of nonpharmacologic treatments, including neurofeedback, cognitive training, cognitive behavioral therapy, child or parent training, dietary omega fatty acid supplementation, and herbal and/or dietary approaches. No new guidance was identified regarding the comparative effectiveness of nonpharmacologic treatments. Pooled results for omega fatty acids found no significant effects for parent rating of ADHD total symptoms (n = 411; standardized mean difference -0.32; 95% confidence interval -0.80 to 0.15; I2 = 52.4%; P = .10) or teacher-rated total ADHD symptoms (n = 287; standardized mean difference -0.08; 95% confidence interval -0.47 to 0.32; I2 = 0.0%; P = .56). LIMITATIONS: Studies often did not reflect the primary care setting and had short follow-up periods, small sample sizes, variations in outcomes, and inconsistent reporting of comparative statistical analyses. CONCLUSIONS: Despite wide use, there are significant gaps in knowledge regarding the effectiveness of ADHD nonpharmacologic treatments.

Systematic review and meta-analysis of endovascular and surgical revascularization for patients with chronic lower extremity venous insufficiency and varicose veins.

BACKGROUND: Chronic lower extremity venous disease (LECVD) is twice as prevalent as coronary heart disease, and invasive therapies to treat LECVD accounted for an estimated $290 million in Medicare expenditures in 2015. Despite increasing use of these invasive therapies, their comparative effectiveness is unknown. METHODS: We conducted a systematic review and meta-analysis of treatments for patients (symptomatic and asymptomatic) with lower extremity varicosities and/or lower extremity chronic venous insufficiency/incompetence/reflux. We searched PubMed, Embase, and the Cochrane Database of Systematic Reviews for relevant English-language studies published from January 2000 to July 2016. We included comparative randomized controlled trials (RCTs) with >20 patients and observational studies with >500 patients. Short-, intermediate-, and long-term outcomes of placebo, mechanical compression therapy, and invasive therapies (surgical and endovascular) were included. Quality ratings and evidence grading was performed. Random-effects models were used to compute summary estimates of effects. RESULTS: We identified a total of 57 studies representing 105,878 enrolled patients, including 53 RCTs comprised of 10,034 patients. Among the RCTs, 16 were good quality, 28 were fair quality, and 9 were poor quality. Allocation concealment, double blinding, and reporting bias were inadequately addressed in 25 of 53 (47%), 46 of 53 (87%), and 15 of 53 (28.3%), respectively. Heterogeneity in therapies, populations, and/or outcomes prohibited meta-analysis of comparisons between different endovascular therapies and between endovascular intervention and placebo/compression. Meta-analysis evaluating venous stripping plus ligation (high ligation/stripping) compared with radiofrequency ablation revealed no difference in short-term bleeding (odds ratio [OR]=0.30, 95% CI -0.16 to 5.38, P=.43) or reflux recurrence at 1-2 years (OR=0.76, 95% CI 0.37-1.55, P=.44). Meta-analysis evaluating high ligation/stripping versus endovascular laser ablation revealed no difference in long-term symptom score (OR 0.02, 95% CI -0.19 to 0.23, P=.84) or quality of life at 2 years (OR 0.06, 95% CI -0.12 to 0.25, P=.50). CONCLUSIONS: The paucity of high-quality comparative effectiveness and safety data in LECVD is concerning given the overall rise in endovascular procedures. More high-quality studies are needed to determine comparative effectiveness and guide policy and practice.

Diagnostic Accuracy of Screening Tests and Treatment for Post-Acute Coronary Syndrome Depression: A Systematic Review.

BACKGROUND: Patients who have had an acute coronary syndrome (ACS) event have an increased risk for depression. PURPOSE: To evaluate the diagnostic accuracy of depression screening instruments and to compare safety and effectiveness of depression treatments in adults within 3 months of an ACS event. DATA SOURCES: MEDLINE, EMBASE, PsycINFO, CINAHL, and Cochrane Database of Systematic Reviews from January 2003 to August 2017, and a manual search of citations from key primary and review articles. STUDY SELECTION: English-language studies of post-ACS patients that evaluated the diagnostic accuracy of depression screening tools or compared the safety and effectiveness of a broad range of pharmacologic and nonpharmacologic depression treatments. DATA EXTRACTION: 2 investigators independently screened each article for inclusion; abstracted the data; and rated the quality, applicability, and strength of evidence. DATA SYNTHESIS: Evidence from 6 of the 10 included studies showed that a range of depression screening instruments produces acceptable levels of diagnostic sensitivity, specificity, and negative predictive values (70% to 100%) but low positive predictive values (below 50%). The Beck Depression Inventory-II was the most studied tool. A large study found that a combination of cognitive behavioral therapy (CBT) and antidepressant medication improved depression symptoms, mental health-related function, and overall life satisfaction more than usual care. LIMITATION: Few studies, no evaluation of the influence of screening on clinical outcomes, and no studies addressing several clinical interventions of interest. CONCLUSION: Depression screening instruments produce diagnostic accuracy metrics that are similar in post-ACS patients and other clinical populations. Depression interventions have an uncertain effect on cardiovascular outcomes, but CBT combined with antidepressant medication produces modest improvement in psychosocial outcomes. PRIMARY FUNDING SOURCE: Agency for Healthcare Research and Quality (PROSPERO: CRD42016047032).

Pharmacologic and behavioral interventions to improve cardiovascular risk factors in adults with serious mental illness: a systematic review and meta-analysis.

OBJECTIVE: Individuals with serious mental illness have high rates of cardiovascular disease (CVD) risk factors and mortality. This systematic review was conducted to evaluate pharmacologic and behavioral interventions to reduce CVD risk in adults with serious mental illness. DATA SOURCES: MEDLINE, EMBASE, PsycINFO, ClinicalTrials.gov, and Cochrane Database of Systematic Reviews were searched from January 1980 to July 2012 for English language studies. Examples of search terms used include schizophrenia, bipolar disorder, antipsychotics, weight, glucose, lipid, and cardiovascular disease. STUDY SELECTION: Two reviewers independently screened citations and identified 33 randomized controlled trials of at least 2 months' duration that enrolled adults with serious mental illness and evaluated pharmacologic or behavioral interventions targeting weight, glucose, or lipid control. DATA EXTRACTION: Reviewers extracted data, assessed applicability, and evaluated study quality; the team jointly graded overall strength of evidence. RESULTS: We included 33 studies. Most studies targeted weight control (28 studies). Compared with control groups, weight control was improved with behavioral interventions (mean difference = -3.13 kg; 95% CI, -4.21 to -2.05), metformin (mean difference = -4.13 kg; 95% CI, -6.58 to -1.68), anticonvulsive medications topiramate and zonisamide (mean difference = -5.11 kg; 95% CI, -9.48 to -0.74), and adjunctive or antipsychotic switching to aripiprazole (meta-analysis not possible). Evidence was insufficient for all other interventions and for effects on glucose and lipid control. The small number of studies precluded analyses of variability in treatment effects by patient characteristics. CONCLUSIONS: Few studies have evaluated interventions addressing 1 or more CVD risk factors in people with serious mental illness. Glucose- and lipid-related results were mainly reported as secondary outcome assessments in studies of weight-management interventions. Comparative effectiveness studies are needed to test multimodal strategies, agents known to be effective in nonserious mental illness populations, and antipsychotic-management strategies.

Rate- and rhythm-control therapies in patients with atrial fibrillation: a systematic review.

BACKGROUND: The comparative effectiveness of treatments for atrial fibrillation (AF) is uncertain. PURPOSE: To evaluate the comparative effectiveness of rate- and rhythm-control therapies. DATA SOURCES: English-language studies in PubMed, EMBASE, and the Cochrane Database of Systematic Reviews between January 2000 and November 2013. STUDY SELECTION: Two reviewers independently screened citations to identify comparative studies that assessed rate- or rhythm-control therapies in patients with AF. DATA EXTRACTION: Reviewers extracted data on study design, participant characteristics, interventions, outcomes, applicability, and quality. DATA SYNTHESIS: 200 articles (162 studies) involving 28,836 patients were included. When pharmacologic rate- and rhythm-control strategies were compared, strength of evidence (SOE) was moderate supporting comparable efficacy with regard to all-cause mortality (odds ratio [OR], 1.34 [95% CI, 0.89 to 2.02]), cardiac mortality (OR, 0.96 [CI, 0.77 to 1.20]), and stroke (OR, 0.99 [CI, 0.76 to 1.30]) in older patients with mild AF symptoms. Few studies compared rate-control therapies and included outcomes of interest, which limited conclusions. For the effect of rhythm-control therapies in reducing AF recurrence, SOE was high favoring pulmonary vein isolation versus antiarrhythmic medications (OR, 5.87 [CI, 3.18 to 10.85]) and the surgical maze procedure (including pulmonary vein isolation) done during other cardiac surgery versus other cardiac surgery alone (OR, 7.94 [CI, 3.63 to 17.36]). LIMITATION: Studies were heterogeneous in interventions, populations, settings, and outcomes. CONCLUSION: Pharmacologic rate- and rhythm-control strategies have comparable efficacy across outcomes in primarily older patients with mild AF symptoms. Pulmonary vein isolation is better than antiarrhythmic medications at reducing recurrences of AF in younger patients with paroxysmal AF and mild structural heart disease. Future research should address uncertainties related to subgroups of interest and the effect of different therapies on long-term clinical outcomes. PRIMARY FUNDING SOURCE: Agency for Healthcare Research and Quality.

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.

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.

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.

Oral contraceptive pills as primary prevention for ovarian cancer: a systematic review and meta-analysis.

OBJECTIVE: To estimate the overall reduction in ovarian cancer risk associated with the use of oral contraceptive pills (OCPs) and whether reduction in risk is affected by specifics of OCP use, such as formulation or duration of use. DATA SOURCES: We searched PubMed, Embase, the Cochrane Database of Systematic Reviews, and ClinicalTrials.gov for studies published from January 1990 to June 2012, with primary analysis of studies published since January 2000. 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 (in which the explicit or implicit indication for OCP use was prevention of pregnancy or ovarian cancer) compared with no use of OCPs. Two investigators independently reviewed the title and abstract and full-text of articles for inclusion or exclusion decision; discordant decisions were resolved by team review and consensus. TABULATION, INTEGRATION, AND RESULTS: Fifty-five studies met inclusion criteria. A random-effects meta-analysis of 24 case-control and cohort studies showed significant reduction in ovarian cancer incidence in ever-users compared with never-users (odds ratio 0.73, 95% confidence interval 0.66-0.81). There was a significant duration-response relationship, with reduction in incidence of more than 50% among women using OCPs for 10 or more years. The lifetime reduction in ovarian cancer attributable to the use of OCPs is approximately 0.54% for a number-needed-to-treat of approximately 185 for a use period of 5 years. CONCLUSION: Significant duration-dependent reductions in ovarian cancer incidence in the general population are associated with OCP use.

Priorities for comparative effectiveness reviews in cardiovascular disease.

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.

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

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.

Oral contraceptive use for the primary prevention of ovarian cancer.

OBJECTIVE: To estimate the overall balance of harms and benefits from the potential use of oral contraceptives (OCs) for the primary prevention of ovarian cancer DATA SOURCES: We searched PubMed®, Embase®, the Cochrane Database of Systematic Reviews, and ClinicalTrials.gov for English-language studies published from January 1990 to June 2012 that evaluated the potential benefits (reduction in ovarian, colorectal, and endometrial cancers) and harms (increase in breast and cervical cancer, and vascular complications) of OC use. REVIEW METHODS: Two investigators screened each abstract and full-text article for inclusion; the investigators abstracted data, and they performed quality ratings, applicability ratings, and evidence grading. Random-effects models were used to compute summary estimates of effects. A simulation model was used to estimate the effects of OC use on the overall balance of benefits and harms. RESULTS: We reviewed 55 studies relevant to ovarian cancer outcomes, 66 relevant to other cancers, and 50 relevant to vascular events. Ovarian cancer incidence was significantly reduced in OC users (OR [odds ratio], 0.73; 95% CI [confidence interval], 0.66 to 0.81), with greater reductions seen with longer duration of use. Breast cancer incidence was slightly but significantly increased in OC users (OR, 1.08; 95% CI, 1.00 to 1.17), with a significant reduction in risk as time since last use increased. The risk of cervical cancer was significantly increased in women with persistent human papillomavirus infection who used OCs, but heterogeneity prevented a formal meta-analysis. Incidences of both colorectal cancer (OR, 0.86; 95% CI, 0.79 to 0.95) and endometrial cancer (OR, 0.57; 95% CI, 0.43 to 0.76) were significantly reduced by OC use. The risk of vascular events was increased in current OC users compared with nonusers, although the increase in myocardial infarction was not statistically significant. The overall strength of evidence for ovarian cancer prevention was moderate to low, primarily because of the lack of randomized trials and inconsistent reporting of important characteristics of use, such as duration. The simulation model predicted that the combined increase in risk of breast and cervical cancers and vascular events was likely to be equivalent to or greater than the decreased risk in ovarian cancer, although the harm/benefit ratio was much more favorable when protection against endometrial and colorectal cancers was added, resulting in net gains in life expectancy of approximately 1 month. CONCLUSIONS: There is insufficient evidence to recommend for or against the use of OCs solely for the primary prevention of ovarian cancer. Although the net effects of the current patterns of OC use likely result in increased life expectancy when other noncontraceptive benefits are included, the harm/benefit ratio for ovarian cancer prevention alone is uncertain, particularly when the potential quality-of-life impact of breast cancer and vascular events are considered.

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

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).

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.

Outer Membrane Vesicles.

Outer membrane vesicles (blebs) are produced by Escherichia coli, Salmonella, and all other gram-negative bacteria both in vitro and in vivo. Most of the research in the field has focused on the properties of vesicles derived from pathogenic bacteria and their interactions with eukaryotic cells. These data indicate that vesicles are able to contribute to pathogenesis. Thus, it appears that pathogenic gram-negative bacteria have co-opted vesicles for the dissemination of virulence determinants. However, the role of vesicle production by nonpathogenic bacteria is less obvious. This section reviews the data demonstrating the mechanistic and physiological basis of outer membrane vesicle production by bacteria. Vesiculation can be seen as a mechanism for cells to react to conditions in the surrounding environment by carrying away unnecessary components and allowing rapid modification of the outer membrane composition. In addition, vesicles can transmit biological activities distant from the originating cell. Vesicles could act to bind and deplete host immune factors at the site of infection that would otherwise attack the bacteria. Vesicles in the area surrounding the cell may also provide the cell protection inside a human or animal host. The concept of vesicles as virulence factors has received considerable attention, and they are likely to play a significant role in the pathogenesis of gram-negative bacteria. By analysis of their composition, mechanism of formation, regulation, and physiological function, progress is being made in understanding the ubiquitous nature of outer membrane vesicles produced by gram-negative bacteria.