The revised JBI critical appraisal tool for the assessment of risk of bias for quasi-experimental studies

Systematic reviews of effectiveness offer a rigorous synthesis of the best evidence available regarding the effects of interventions or treatments. Randomized controlled trials are considered the optimal study design for evaluating the effectiveness of interventions and are the ideal study design for inclusion in a systematic review of effectiveness. In the absence of randomized controlled trials, quasi-experimental studies may be relied on to provide information on treatment or intervention effectiveness. However, such studies are subject to unique considerations regarding their internal validity and, consequently, the assessment of the risk of bias of these studies needs to consider these features of design and conduct. The JBI Effectiveness Methodology Group has recently commenced updating the suite of JBI critical appraisal tools for quantitative study designs to align with the latest advancements in risk of bias assessment. This paper presents the revised critical appraisal tool for risk of bias assessment of quasi-experimental studies; offers practical guidance for its use; provides examples for interpreting the results of risk of bias assessment; and discusses major changes from the previous version, along with the justifications for those changes.

Predatory journals and their practices present a conundrum for systematic reviewers and evidence synthesisers of health research: A qualitative descriptive study

Predatory journals are a blemish on scholarly publishing and academia and the studies published within them are more likely to contain data that is false. The inclusion of studies from predatory journals in evidence syntheses is potentially problematic due to this propensity for false data to be included. To date, there has been little exploration of the opinions and experiences of evidence synthesisers when dealing with predatory journals in the conduct of their evidence synthesis. In this paper, the thoughts, opinions, and attitudes of evidence synthesisers towards predatory journals and the inclusion of studies published within these journals in evidence syntheses were sought. Focus groups were held with participants who were experienced evidence synthesisers from JBI (previously the Joanna Briggs Institute) collaboration. Utilising qualitative content analysis, two generic categories were identified: predatory journals within evidence synthesis, and predatory journals within academia. Our findings suggest that evidence synthesisers believe predatory journals are hard to identify and that there is no current consensus on the management of these studies if they have been included in an evidence synthesis. There is a critical need for further research, education, guidance, and development of clear processes to assist evidence synthesisers in the management of studies from predatory journals.

Comparison of bias adjustment in meta-analysis using data-based and opinion-based methods

INTRODUCTION

Several methods exist for bias adjustment of meta-analysis results, but there has been no comprehensive comparison with unadjusted methods. We compare 6 bias-adjustment methods with 2 unadjusted methods to examine how these different methods perform.

METHODS

We re-analyzed a meta-analysis that included 10 randomized controlled trials. Two data-based methods (Welton's data-based approach and Doi's quality effects model) and 4 opinion-informed methods (opinion-based approach, opinion-based distributions combined statistically with data-based distributions, numerical opinions informed by data-based distributions, and opinions obtained by selecting areas from data-based distributions) were used to incorporate methodological quality information into the meta-analytical estimates. The results of these 6 methods were compared with 2 unadjusted models: the DerSimonian-Laird random effects model and Doi's inverse variance heterogeneity model.

RESULTS

The 4 opinion-based methods returned the random effects model estimates with wider uncertainty. The data-based and quality effects methods returned different results and aligned with the inverse variance heterogeneity method with some minor downward bias adjustment.

CONCLUSION

Opinion-based methods seem to only add uncertainty rather than bias adjust.

Implementing GRADE in systematic reviews that adhere to JBI methodological conduct

GRADE is a methodological approach used to establish certainty in a body of evidence and is now widely adopted among the evidence synthesis and guideline development community. JBI is an international evidence-based health care organization that provides guidance for a range of evidence synthesis approaches. The GRADE approach is currently endorsed for use in a subset of JBI systematic reviews; however, there is some uncertainty regarding when (and how) GRADE may be implemented in reviews that follow JBI methodology.

Common tool structures and approaches to risk of bias assessment: implications for systematic reviewers

There are numerous tools available to assess the risk of bias in individual studies in a systematic review. These tools have different structures, including scales and checklists, which may or may not separate their items by domains. There are also various approaches and guides for the process, scoring, and interpretation of risk of bias assessments, such as value judgments, quality scores, and relative ranks. The objective of this commentary, which is part of the JBI Series on Risk of Bias, is to discuss some of the distinctions among different tool structures and approaches to risk of bias assessment and the implications of these approaches for systematic reviewers.

Reporting of 3Rs Approaches in Preclinical Animal Experimental Studies-A Nationwide Study

The 3Rs aim to refine animal welfare, reduce animal numbers, and replace animal experiments. Investigations disclose that researchers are positive towards 3Rs recommendations from peers. Communication of 3Rs approaches via primary preclinical animal experimental literature may become a fast-forward extension to learn relevant 3Rs approaches if such are reported. This study investigates 3Rs-reporting in peer-reviewed preclinical animal research with at least one author affiliated to a Danish university. Using a systematic search and random sampling, we included 500 studies from 2009 and 2018. Reporting was low and improvement over time limited. A word search for 3R retrieved zero results in 2009 and 3.2% in 2018. Reporting on 3Rs-related sentences increased from 6.4% in 2009 to 18.4% in 2018, "reduction" increased from 2.4% to 8.0%, and "refinement" from 5.2% to 14.4%. Replacement was not reported. Reporting of the methodology was missing. For "reduction", methodology was mentioned in one study in 2009 and 11 studies in 2018, and for "refinement" in 9 and 21, respectively. Twenty-one studies stated compliance with ARRIVE-guidelines or similar without disclosure of details. Reporting of 3Rs approaches in preclinical publications is currently insufficient to guide researchers. Other strategies, e.g., education, interdisciplinary collaboration, and 3Rs funding initiatives, are needed.

Effectiveness of dual active ingredient insecticide-treated nets in preventing malaria: A systematic review and meta-analysis

Malaria vectors have demonstrated resistance to pyrethroid-based insecticides used in insecticide-treated nets, diminishing their effectiveness. This systematic review and meta-analysis investigated two forms of dual active-ingredient (DAI) insecticide-treated nets (ITN(s)) for malaria prevention. A comprehensive search was conducted on July 6th 2022. The databases searched included PubMed, Embase, CINAHL, amongst others. Trials were eligible if they were conducted in a region with ongoing malaria transmission. The first DAI ITN investigated were those that combined a pyrethroid with a non-pyrethroid insecticides. The second DAI ITN investigated were that combined a pyrethroid with an insect growth regulator. These interventions were compared against either a pyrethroid-only ITN, or ITNs treated with pyrethroid and piperonyl-butoxide. Assessment of risk of bias was conducted in duplicate using the Cochrane risk of bias 2 tool for cluster-randomised trials. Summary data was extracted using a custom data-extraction instrument. This was conducted by authors THB, JCS and SH. Malaria case incidence was the primary outcome and has been meta-analysed, adverse events were narratively synthesised. The review protocol is registered on PROSPERO (CRD42022333044). From 9494 records, 48 reports were screened and 13 reports for three studies were included. These studies contained data from 186 clusters and all reported a low risk of bias. Compared to pyrethroid-only ITNs, clusters that received pyrethroid-non-pyrethroid DAI ITNs were associated with 305 fewer cases per 1000-person years (from 380 fewer cases to 216 fewer cases) (IRR = 0.55, 95%CI: 0.44-0.68). However, this trend was not observed in clusters that received pyrethroid-insect growth regulator ITNs compared to pyrethroid-only ITNs (from 280 fewer cases to 135 more) (IRR = 0.90, 95%CI: 0.73-1.13). Pyrethroid-non-pyrethroid DAI ITNs demonstrated consistent reductions in malaria case incidence and other outcomes across multiple comparisons. Pyrethroid-non-pyrethroid DAI ITNs may present a novel intervention for the control of malaria.

Residual insecticide surface treatment for preventing malaria: a systematic review protocol

INTRODUCTION

Malaria presents a significant global public health burden, although substantial progress has been made, with vector control initiatives such as indoor residual surface spraying with insecticides and insecticide-treated nets. There now exists many different approaches to apply residual insecticide to indoor and outdoor surfaces in malaria-endemic settings, although no comprehensive systematic reviews exist evaluating these interventions. This manuscript outlines the protocol for a systematic review which aims to synthesise the best available evidence regarding full or partial indoor or outdoor residual insecticide surface treatment for preventing malaria.

METHODS AND ANALYSIS

This review will comprehensively search the literature (both published and unpublished) for any studies investigating the effectiveness of residual insecticide surface treatment for malaria. Studies will be screened to meet the inclusion criteria by a minimum of two authors, followed by assessment of risk of bias (using appropriate risk-of-bias tools for randomised and non-randomised studies) and extraction of relevant information using structured forms by two independent authors. Meta-analysis will be carried out where possible for epidemiological outcomes such as malaria, anaemia, malaria-related mortality, all-cause mortality and adverse effects. Certainty in the evidence will be established with GRADE assessments.

ETHICS AND DISSEMINATION

A full review report will be submitted to the Vector Control & Insecticide Resistance Unit, Global Malaria Program, WHO. A version of this report will be submitted for publication in an open access peer-reviewed journal. The report will inform the development of WHO recommendations regarding residual insecticide treatment for malaria. This systematic review does not require ethics approval as it is a review of primary studies.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO 293194.

Revising the JBI quantitative critical appraisal tools to improve their applicability: an overview of methods and the development process

JBI offers a suite of critical appraisal instruments that are freely available to systematic reviewers and researchers investigating the methodological limitations of primary research studies. The JBI instruments are designed to be study-specific and are presented as questions in a checklist. The JBI instruments have existed in a checklist-style format for approximately 20 years; however, as the field of research synthesis expands, many of the tools offered by JBI have become outdated. The JBI critical appraisal tools for quantitative studies (eg, randomized controlled trials, quasi-experimental studies) must be updated to reflect the current methodologies in this field. Cognizant of this and the recent developments in risk-of-bias science, the JBI Effectiveness Methodology Group was tasked with updating the current quantitative critical appraisal instruments. This paper details the methods and rationale that the JBI Effectiveness Methodology Group followed when updating the JBI critical appraisal instruments for quantitative study designs. We detail the key changes made to the tools and highlight how these changes reflect current methodological developments in this field.

Methodological quality assessment should move beyond design specificity

OBJECTIVE

This study aimed to assess the utility of a unified tool (MASTER) for bias assessment against design-specific tools in terms of content and coverage.

METHODS

Each of the safeguards in the design-specific tools was compared and matched to safeguards in the unified MASTER scale. The design-specific tools were the JBI, Scottish Intercollegiate Guidelines Network (SIGN), and the Newcastle-Ottawa Scale (NOS) tools for analytic study designs. Duplicates, safeguards that could not be mapped to the MASTER scale, and items not applicable as safeguards against bias were flagged and described.

RESULTS

Many safeguards across the JBI, SIGN, and NOS tools were common, with a minimum of 10 to a maximum of 23 unique safeguards across various tools. These 3 design-specific toolsets were missing 14 to 26 safeguards from the MASTER scale. The MASTER scale had complete coverage of safeguards within the 3 toolsets for analytic designs.

CONCLUSIONS

The MASTER scale provides a unified framework for bias assessment of analytic study designs, has good coverage, avoids duplication, has less redundancy, and is more convenient when used for methodological quality assessment in evidence synthesis. It also allows assessment across designs that cannot be done using a design-specific tool.

From critical appraisal to risk of bias assessment: clarifying the terminology for study evaluation in JBI systematic reviews

The foundations for critical appraisal of literature have largely progressed through the development of epidemiologic research methods and the use of research to inform medical teaching and practice. This practical application of research is referred to as evidence-based medicine and has delivered a standard for the health care profession where clinicians are equally as engaged in conducting scientific research as they are in the practice of delivering treatments. Evidence-based medicine, now referred to as evidence-based health care, has generally been operationalized through empirically supported treatments, whereby the choice of treatments is substantiated by scientific support, usually by means of an evidence synthesis. As evidence synthesis methodology has advanced, guidance for the critical appraisal of primary research has emphasized a distinction from the assessment of internal validity required for synthesized research. This assessment is conceptualized and branded in various ways in the literature, such as risk of bias, critical appraisal, study validity, methodological quality, and methodological limitations. This paper provides a discussion of the definitions and characteristics of these terms, concluding with a recommendation for JBI to adopt the term "risk of bias" assessment.

Assessing the risk of bias of quantitative analytical studies: introducing the vision for critical appraisal within JBI systematic reviews

A key step in the systematic review process is the assessment of the methodological quality (or risk of bias) of the included studies. At JBI, we have developed several tools to assist with this evaluation. As evidence synthesis methods continue to evolve, it has been necessary to revise and reflect on JBI's current approach to critical appraisal and to plan a strategy for the future. In this first paper of a series focusing on risk of bias assessment, we introduce our vision for risk of bias assessment for JBI. In future papers in this series, the methodological approach taken for this revision process will be discussed, along with the revised tools and guidance for using these tools.

Reporting quality and risk of bias in JBI systematic reviews evaluating the effectiveness of interventions: a methodological review protocol

OBJECTIVE

The objective of this methodological review is to evaluate the adherence of systematic reviews of effectiveness published in JBI Evidence Synthesis to reporting guidelines and methodological quality.

INTRODUCTION

Systematic reviews of effectiveness are essential tools for health practitioners and policy-makers. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines and the Risk of Bias in Systematic Reviews (ROBIS) tool are used to ensure maintenance of high reporting standards and methodological quality, respectively. This review will utilize these tools to identify strengths and shortfalls in the reporting quality of JBI systematic reviews of effectiveness.

INCLUSION CRITERIA

This review will include the 20 most recent systematic reviews of effectiveness published in JBI Evidence Synthesis .

METHODS

This review will search MEDLINE (PubMed) for effectiveness reviews published in JBI Evidence Synthesis . Abstract and full-text screening will be performed by 2 independent reviewers, and the most recent 20 studies will be selected for inclusion. Data regarding adherence to PRISMA 2020 and ROBIS will be extracted by 2 independent reviewers. Data will be presented descriptively with tables and synthesized narratively.

The revised JBI critical appraisal tool for the assessment of risk of bias for randomized controlled trials

JBI recently began the process of updating and revising its suite of critical appraisal tools to ensure that these tools remain compatible with recent developments within risk of bias science. Following a rigorous development process led by the JBI Effectiveness Methodology Group, this paper presents the revised critical appraisal tool for the assessment of risk of bias for randomized controlled trials. This paper also presents practical guidance on how the questions of this tool are to be interpreted and applied by systematic reviewers, while providing topical examples. We also discuss the major changes made to this tool compared to the previous version and justification for why these changes facilitate best-practice methodologies in this field.

Investigating different typologies for the synthesis of evidence: a scoping review protocol

OBJECTIVE

The objective of this scoping review is to identify evidence synthesis types and previously proposed classification systems, typologies, or taxonomies that have guided evidence synthesis.

INTRODUCTION

Evidence synthesis is a constantly evolving field. There is now a plethora of evidence synthesis approaches used across many different disciplines. Historically, there have been numerous attempts to organize the types and methods of evidence synthesis in the form of classification systems, typologies, or taxonomies. This scoping review will seek to identify all the available classification systems, typologies, or taxonomies; how they were developed; their characteristics; and the types of evidence syntheses included within them.

INCLUSION CRITERIA

This scoping review will include discussion papers, commentaries, books, editorials, manuals, handbooks, and guidance from major organizations that describe multiple approaches to evidence synthesis in any discipline.

METHODS

The Evidence Synthesis Taxonomy Initiative will support this scoping review. The search strategy will aim to locate both published and unpublished documents utilizing a three-step search strategy. An exploratory search of MEDLINE has identified keywords and MeSH terms. A second search of MEDLINE, Embase, CINAHL with Full Text, ERIC, Scopus, Compendex, and JSTOR will be conducted. The websites of relevant evidence synthesis organizations will be searched. Identified documents will be independently screened, selected, and extracted by two researchers, and the data will be presented in tables and summarized descriptively.

DETAILS OF THIS REVIEW PROJECT ARE AVAILABLE AT

Open Science Framework https://osf.io/qwc27.

How should we handle predatory journals in evidence synthesis? A descriptive survey-based cross-sectional study of evidence synthesis experts

Synthesizers of evidence are increasingly likely to encounter studies published in predatory journals during the evidence synthesis process. The evidence synthesis discipline is uniquely positioned to encounter novel concerns associated with predatory journals. The objective of this research was to explore the attitudes, opinions, and experiences of experts in the synthesis of evidence regarding predatory journals. Employing a descriptive survey-based cross-sectional study design, these experts were asked a series of questions regarding predatory journals to explore these attitudes, opinions, and experiences. Two hundred and sixty four evidence synthesis experts responded to this survey. Most respondents agreed with the definition of a predatory journal (86%), however several (19%) responded that this definition was difficult to apply practically. Many respondents believed that studies published in predatory journals are still eligible for inclusion into an evidence synthesis project. However, this was only after the study had been determined to be 'high-quality' (39%) or if the results were validated (13%). While many respondents could identify common characteristics of these journals, there was still hesitancy regarding the appropriate methods to follow when considering including these studies into an evidence synthesis project.

Bias Assessment in Outcomes Research: The Role of Relative Versus Absolute Approaches

OBJECTIVES

Bias assessment tools vary in content and detail, and the method used for assessment may produce different assessment results in a study if not carefully considered. Therefore, taking an approach to the assessment of studies that produces a similar result regardless of the tool used for assessment (tool independence) is important.

METHODS

A preexisting study that used 25 different quality scales was assessed to examine tool dependence of 2 common approaches to bias assessments-absolute value judgments (defined as the qualitative risk of bias judgment based on a threshold across studies) and relative ranks (defined as the relative probability toward bias of a study relative to the best assessed study). Agreement between each of the 25 scales and a composite scale (that includes all unique safeguards across all scales) was computed (using the intraclass correlation coefficient [ICC]; consistency). Tool dependence was considered present when the ICCs were inconsistent across the 25 scales for the same study.

RESULTS

We found that using relative ranks for tools with different numbers and types of items produced consistent results, with only small differences in the agreement for the various tools with the composite tool, whereas consistency (measured by the ICC) varied considerably when using absolute judgments. Inconsistency is problematic because it means that the assessment result is linked to the scale and not to the study.

CONCLUSIONS

Tool independence is an important attribute of a bias assessment tool. On the basis of this study, the use of relative ranks retains tool independence and therefore produces consistent ranks for the same study across tools.

The MethodologicAl STandards for Epidemiological Research (MASTER) scale demonstrated a unified framework for bias assessment

OBJECTIVE

This paper presents a unified framework for assessment of the methodological quality of analytic study designs.

STUDY DESIGN AND SETTING

A systematic review of 393 methodological quality assessment tools that updated a previous assessment with 100 tools. Tool items were extracted, examined and reworded. Bias domains and finally methodological standards to be fulfilled were defined.

RESULTS

There were 36 unique methodological safeguards that were categorized into seven methodological standards to be fulfilled in the MASTER scale. These methodological standards reflect initial and ongoing equivalence in particular areas, including equal recruitment, equal retention, equal ascertainment, equal implementation, equal prognosis, sufficient analysis, and temporal precedence.

CONCLUSION

This approach unifies existing methods for methodological quality assessment and will be useful for (1) clinical researchers when a bias assessment of clinical research studies is required across analytical designs, (2) promoting a unified framework for bias assessment.

Comparison of bias adjustment methods in meta-analysis suggests that quality effects modeling may have less limitations than other approaches

BACKGROUND

The quality of primary research is commonly assessed before inclusion in meta-analyses. Findings are discussed in the context of the quality appraisal by categorizing studies according to risk of bias. The impact of appraised risk of bias on study outcomes is typically judged by the reader; however, several methods have been developed to quantify this risk of bias assessment and incorporate it into the pooled results of meta-analysis, a process known as bias adjustment. The advantages, potential limitations, and applicability of these methods are not well defined.

STUDY DESIGN AND SETTING

Comparative evaluation of the applicability of the various methods and their limitations are discussed using two examples from the literature. These methods include weighting, stratification, regression, use of empirically based prior distributions, and elicitation by experts.

RESULTS

Use of the two examples from the literature suggest that all methods provide similar adjustment. Methods differed mainly in applicability and limitations.

CONCLUSION

Bias adjustment is a feasible process in meta-analysis with several strategies currently available. Quality effects modelling was found to be easily implementable with fewer limitations in comparison to other methods.

Leg-Length Discrepancy After Total Hip Arthroplasty: Comparison of Robot-Assisted Posterior, Fluoroscopy-Guided Anterior, and Conventional Posterior Approaches

Total hip arthroplasty (THA) effectively provides adequate pain relief and good long-term outcomes in patients with hip osteoarthritis. However, leg-length discrepancy (LLD) remains the most common cause of patient dissatisfaction and malpractice litigation in hip arthroplasty. We conducted a study to compare LLD in patients who underwent THA performed with a robot-assisted posterior approach (RTHA), a fluoroscopy-guided anterior approach (ATHA), or a conventional posterior approach (PTHA). We reviewed all RTHA, ATHA, and PTHA cases performed by Dr. Domb between September 2008 and December 2012. Patients included in the study had a primary diagnosis of hip osteoarthritis and proper postoperative anteroposterior pelvis radiographs available. Two blinded observers calibrated and measured all radiographs twice. After exclusions, 67 RTHA, 29 ATHA, and 59 PTHA cases remained in the study. There were strong interobserver and intraobserver correlations for all LLD measurements (r > 0.9; P < .001). Mean (SD) LLD was 2.7 (1.8) mm (95% CI, 2.3-3.2) in the RTHA group, 1.8 (1.6) mm (95% CI, 1.2-2.4) in the ATHA group, and 1.9 (1.6) mm (95% CI, 1.5-2.4) in the PTHA group (P = .01). When LLD of more than 3 mm was set as an outlier, percentage of outliers was 37.3% (RTHA), 17.2% (ATHA), and 22% (PTHA) (P = .06-.78). When LLD of more than 5 mm was set as an outlier, percentage of outliers was 10.4% (RTHA), 6.9% (ATHA), and 8.5% (PTHA) (P = .72 to > .99). No patient in any group had LLD of 10 mm or more. RTHA, ATHA, and PTHA did not differ in obtaining minimal LLD. All 3 techniques are effective in achieving accuracy in LLD.

Comorbidities, Exposure to Medications, and the Risk of Community-Acquired Clostridium difficile Infection: a systematic review and meta-analysis

BACKGROUND

Clostridium difficile infection (CDI) has been extensively described in healthcare settings; however, risk factors associated with community-acquired (CA) CDI remain uncertain. This study aimed to synthesize the current evidence for an association between commonly prescribed medications and comorbidities with CA-CDI.

METHODS

A systematic search was conducted in 5 electronic databases for epidemiologic studies that examined the association between the presence of comorbidities and exposure to medications with the risk of CA-CDI. Pooled odds ratios were estimated using 3 meta-analytic methods. Subgroup analyses by location of studies and by life stages were conducted.

RESULTS

Twelve publications (n=56,776 patients) met inclusion criteria. Antimicrobial (odds ratio, 6.18; 95% CI, 3.80-10.04) and corticosteroid (1.81; 1.15-2.84) exposure were associated with increased risk of CA-CDI. Among the comorbidities, inflammatory bowel disease (odds ratio, 3.72; 95% CI, 1.52-9.12), renal failure (2.64; 1.23-5.68), hematologic cancer (1.75; 1.02-5.68), and diabetes mellitus (1.15; 1.05-1.27) were associated with CA-CDI. By location, antimicrobial exposure was associated with a higher risk of CA-CDI in the United States, whereas proton-pump inhibitor exposure was associated with a higher risk in Europe. By life stages, the risk of CA-CDI associated with antimicrobial exposure greatly increased in adults older than 65 years.

CONCLUSIONS

Antimicrobial exposure was the strongest risk factor associated with CA-CDI. Further studies are required to investigate the risk of CA-CDI associated with medications commonly prescribed in the community. Patients with diarrhea who have inflammatory bowel disease, renal failure, hematologic cancer, or diabetes are appropriate populations for interventional studies of screening.

[Squamous neoplasia of the ocular surface in patients with pterygium in Peru]

OBJECTIVES

To estimate the frequency of unsuspected ocular surface squamous neoplasia (OSSN) in pterygium, the accuracy of clinical diagnosis, and associated demographic and clinical characteristics.

MATERIALS AND METHODS

We reviewed histopathological reports of patients with a clinical diagnosis of pterygium and/or OSSN who were surgically treated between March 2009 and December 2012 at the National Eye Institute in Lima, Peru. The accuracy of the clinical diagnosis of OSSN was assessed by sensitivity, specificity, and likelihood ratios. Models of negative log-log regression were performed to identify demographic and clinical characteristics associated with increased odds of diagnosing OSSN.

RESULTS

3,021 histopathological reports were reviewed. The frequency of unsuspected OSSN in pterygium was 0.65%. Clinical diagnosis had a sensitivity of 85%, a specificity of 99%, a positive likelihood ratio of 111.89, and a negative likelihood ratio of 0.15. Associated characteristics were male gender (OR =1.15; 95% CI: 1.01 to 1.30), age group of 61-80 years (OR = 1.54, 95% CI: 1.28 to 1.85) ≥ 81 years (OR = 3.10; 95% CI: 2.09 to 4.58), presence of recurrent lesions (OR = 1.59; 95% CI: 1.03 to 2.46) and temporal location lesions (OR = 3.57; 95% CI: 2.63 to 4.85). These characteristics were associated with a greater likelihood of OSSN.

CONCLUSIONS

A low frequency of unsuspected OSSN was found; however, it is recommended to routinely perform histopathology studies to avoid misdiagnosis of OSSN as pterygium.

Putting the diabetes risk due to statins in perspective: a re-evaluation using the complementary outcome

AIMS

Statins are used extensively to treat dyslipidemia and have been associated with significant clinical benefit that increases with dose. However, recent studies have associated statins with an excess risk of developing diabetes mellitus, which may offset the clinical benefit to patients. Adverse events related to intensive-dose statin therapy were revisited in light of recent data regarding the use of relative risks.

DATA SYNTHESIS

A meta-analysis was replicated with the event of interest redefined as the complementary outcome (no-onset of diabetes). Five randomised controlled trials that compared the risk of intense-dose with moderate-dose of statin therapy for the onset of diabetes with a follow-up greater than 12 months were included in the analysis. A reduction in the risk for no-onset of diabetes was found when intensive-dose statin therapy was compared with moderate-dose statin therapy, revealing a relative risk of 0.9908 (95%CI: 0.9849-0.99679). Over two years, one more patient was harmed by diabetes onset for every 237 patients exposed to intensive-dose statin therapy (95%CI: 123-3847) compared with standard dose statin therapy.

CONCLUSIONS

Statins are associated with only a very small increase in risk of diabetes mellitus. Previous research selected the outcomes with the lower baseline risks and therefore the actual risk associated with statins has been largely over-estimated.

Estrogen and selective estrogen receptor modulators (SERMs) for the treatment of acromegaly: a meta-analysis of published observational studies

Estrogen and selective estrogen receptor modulator (SERM) treatments for acromegaly have received limited attention since the development of newer pharmacologic therapies. There has been ongoing research evidence suggesting their utility in the biochemical control of acromegaly. Therefore, the aim of this meta-analysis was to synthesise current evidence with a view to determining to what extent and in which acromegalic patient subsets do estrogen and SERMs reduce IGF-1 levels. A literature search was conducted (finished December 2012), which included all studies pertaining to estrogen or SERM treatment and IGF-1. Seven patient subsets were identified from six published observational studies, and were pooled using meta-analytic methods. Overall, the pooled mean loss in IGF-1 was -29.09 nmol/L (95 % CI -37.23 to -20.95). A sensitivity analysis indicated that women receiving estrogen had a substantially greater reduction in IGF-1 levels compared with women receiving SERMs, with a weighted mean loss in IGF-1 of -38.12 nmol/L (95 % CI -46.78 to -29.45) compared with -22.91 nmol/L (95 % CI -32.73 to -13.09). There was a trend that did not reach statistical significance for men receiving SERM treatment at -11.41 nmol/L (95 % CI -30.14 to 7.31). It was concluded that estrogen and SERMs are a low cost and effective treatment to achieve control of IGF-1 levels in acromegalic women either as concomitant treatment for refractory disease, or where access to conventional therapy is restricted. Their use in men requires further study.

Radiographic, histologic, and arthroscopic findings in amorphous calcifications of the hip labrum

PURPOSE

The purpose of this study was to evaluate the clinical, radiographic, histologic, and intraoperative findings of an amorphous calcification involving the acetabular labrum.

METHODS

From October 2008 to April 2013, all patients who underwent arthroscopic hip surgery for symptomatic intra-articular hip disorders and were found to have the characteristic calcific deposit involving the acetabular labrum were included. These patients were reviewed retrospectively on prospectively collected data. Radiographs were retrospectively evaluated for morphologic features of impingement and characteristics of labral calcification.

RESULTS

Sixteen patients were identified as having amorphous calcification at the time of arthroscopy. There were 15 women and 1 man. Mean age was 37.3 years (range, 30 to 50 years). Symptoms were present for a mean of 9.3 months (range, 3 to 48 months). All patients reported anterior groin pain. Fifteen (94%) patients had positive anterior impingement and 9 (56%) had positive results for lateral impingement. Calcifications measured on average 3.2 mm (range, 1.9 mm to 5.6 mm), and 14 had a clear separation from the rim with increased opacity compared with neighboring trabecular bone. Intraoperatively, the characteristic amorphous calcium deposit was located in the anterosuperior labrum, with the deposit found to be accessible from the capsule-labral recess in all cases. All patients had labral tears and all patients had at least one component of femoroacetabular impingement (FAI).

CONCLUSIONS

Calcification in the anterosuperior acetabular labrum presents with a consistent patient demographic and distinct radiographic and arthroscopic presentation that is different from os acetabuli. As with os acetabuli, one should have a high suspicion for FAI when this lesion is encountered.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Hip arthroscopy for labral tears in workers' compensation: a matched-pair controlled study

BACKGROUND

Workers' compensation (WC) status has been related to clinical outcomes; however, no comparative studies have been performed to assess 2-year outcomes between hip arthroscopy patients based on WC status.

PURPOSE

To evaluate 2-year outcomes of patients receiving WC who underwent hip arthroscopy for labral tears and to compare outcomes with those of a matched control group not receiving WC.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

During the study period between June 2008 and August 2010, data were collected on all patients treated with hip arthroscopy. Inclusion criteria for the study group were diagnosis of labral tear and WC status. All patients were assessed pre- and postoperatively with 4 patient-reported outcome (PRO) measures: the modified Harris Hip Score (mHHS), Non-Arthritic Hip Score (NAHS), Hip Outcome Score-Activities of Daily Living (HOS-ADL), and Hip Outcome Score-Sport-Specific Subscales (HOS-SSS). Pain was estimated on the visual analog scale (VAS), and satisfaction was measured on a scale from 0 to 10. A matched-pair group of patients not associated with WC was selected in a 1:1 ratio according to age within 3 years, sex, surgical procedures, and radiographic findings.

RESULTS

Twenty-one hips were included in each group. Patients with WC status had significantly lower preoperative PRO scores for all measures (P < .001). However, there was no significant difference between VAS pain scores between the groups. Of the WC patients, 86% returned to work at a median 82 days postoperatively. For the WC group, the score improvement from preoperative to 2-year follow-up was 46 to 67.7 for mHHS, 39.3 to 66 for NAHS, 39.7 to 69.5 for HOS-ADL, and 15.3 to 49.8 for HOS-SSS. For the control group, the score improvement from preoperative to 2-year follow-up was 67.9 to 85.8 for mHHS, 62.6 to 84.4 for NAHS, 69.8 to 86.9 for HOS-ADL, and 41.9 to 73.8 for HOS-SSS. Both groups demonstrated statistically significant postoperative improvement in all scores, and the average amount of change of preoperative to postoperative scores between the 2 groups was only significantly different for the HOS-ADL in the control group (P = .043). However, the WC group demonstrated greater improvement in aggregate scores in the HOS-ADL. Pain scores decreased from 7 to 3.9 in the WC group and 5.8 to 3.2 in the control group and were not significantly different between the groups. Patient satisfaction was 6.8 for the WC group and 7.7 for the control group, with no significant difference between groups.

CONCLUSION

Our study demonstrated that WC patients had significantly lower baseline PRO scores when compared with a matched-pair control group. However, both groups demonstrated statistically significant postoperative improvement in all scores. Patients with WC status started and ended with lower absolute scores but benefited from arthroscopic intervention for hip injuries. While patient and physician expectations may be adjusted accordingly, these results may reflect favorably on the use of hip arthroscopy for labral tears in the WC population.

Regulation of Ras in lymphocytes: get a GRP

RasGRPs (guanine nucleotide releasing proteins) are a family of four GEFs (guanine nucleotide-exchange factors) (Ras GEFs) that positively regulate Ras and related small GTPases. RasGRP1 possesses a catalytic region consisting of a REM (Ras exchange motif) and a CDC25 (cell division cycle 25) domain. RasGRP1 also possesses a DAG (diacylglycerol)-binding C1 domain and a pair of EF hands that bind calcium. RasGRP1 is selectively expressed in lymphocytes as well as in some cells of the brain, kidney and skin. Functional analysis supports the hypothesis that RasGRP1 serves to couple TCR (T-cell receptor) stimulation and phospholipase C activation with Ras signalling. In B-cells, both RasGRP1 and RasGRP3 play a similar role downstream of the B-cell receptor. RasGRP2 acts on the Ras-related protein Rap and functions in platelet adhesion. RasGRP4 is expressed in mast cells and certain myeloid leukaemia cells. Membrane DAG regulates RasGRPs directly by recruitment to cellular membranes, as well as indirectly by protein kinase C-mediated phosphorylation. The properties of RasGRPs provide a novel view of Ras regulation in lymphocytes and explain several earlier observations. Many experimental results obtained with DAG analogues could be reviewed in light of these findings.

The aging hippocampus: A multi-level analysis in the rat

In the current experiment we conducted a multi-level analysis of age-related characteristics in the hippocampus of young adult (3 months), middle-aged (12 months), and old (24 months) Fisher 344xBrown Norway hybrid (FBNF1) rats. We examined the relationships between aging, hippocampus, and memory using a combination of behavioral, non-invasive magnetic resonance imaging and spectroscopy, and postmortem neuroanatomical measures in the same rats. Aging was associated with functional deficits on hippocampus-dependent memory tasks, accompanied by structural alterations observed both in vivo (magnetic resonance imaging-hippocampal volume) and postmortem (dentate gyrus neuronal density and neurogenesis). Neuronal metabolic integrity, assessed by levels of N-acetylaspartate with magnetic resonance spectroscopy, was however, preserved. Further, our results suggest that neurogenesis (doublecortin) seems to be related to both performance deficits on hippocampus-dependent tasks and hippocampal volume reduction. The observed pattern of age-related alterations closely resembles that previously reported in humans and suggests FBNF1 rats to be a useful model of normal human aging.

Presence of Ras guanyl nucleotide-releasing protein in striosomes of the mature and developing rat

Ras signal transduction pathways have been implicated as key regulators in neuroplasticity and synaptic transmission in the brain. These pathways can be modulated by Ras guanyl nucleotide exchange factors, (GEF) which activate Ras proteins by catalysing the exchange of GDP for GTP. Ras guanyl nucleotide-releasing protein (RasGRP), a recently discovered Ras GEF, that links diacylglycerol and probably calcium to Ras signaling pathways, is expressed in brain as well as in T-cells. Here, we have used a highly selective monoclonal antibody against RasGRP to localize this protein within the striatum and related forebrain structures of developing and adult rats. RasGRP immunolabeling was found to be widespread in the mature and developing rat forebrain. Most notably, it presented a prominent patchy distribution throughout the striatum at birth and at all postnatal ages examined. These patches were found to correspond with the striosomal compartment of the striatum, as identified by micro-opioid receptor labeling in the adult. RasGRP-immunoreactivity was also observed in the matrix-like compartment surrounding these patches/striosomes but appeared later in development and was always weaker than in the patches. In both striatal compartments, RasGRP was exclusively expressed by medium-sized spiny neurons and showed no preference for neurons that project either directly or indirectly to the substantia nigra. At the ultrastructural level, immunogold labeling of RasGRP was confined to the cell bodies and dendritic shafts of these output neurons. We conclude that the prominent expression of RasGRP in striosomes may be of significance for diacylglycerol signaling in the striatum, and could be of importance for the processing of limbic-related activity within the basal ganglia.

Cellular and subcellular localization of Ras guanyl nucleotide-releasing protein in the rat hippocampus

Ras guanyl nucleotide-releasing protein (RasGRP) is a recently discovered Ras guanyl nucleotide exchange factor that is expressed in selected regions of the rodent CNS, with high levels of expression in the hippocampus. Biochemical studies suggest that RasGRP can activate the Ras signal pathway in response to changes in diacylglycerol and possibly calcium. To investigate potential sites for RasGRP signaling, we have determined the cellular and subcellular localization of RasGRP protein in adult rat hippocampus, and have also examined the appearance of RasGRP mRNA and protein during hippocampal development. RasGRP immunoreactivity is predominately localized to those neurons participating in the direct cortico-hippocampo-cortical loop. In both hippocampal and entorhinal neurons, RasGRP protein appeared to be localized to both dendrites and somata, but not to axons. Electron microscopy of hippocampal pyramidal cells confirmed RasGRP immunoreactivity in neuronal cell bodies and dendrites, where it appeared to be associated with microtubules. The localization of RasGRP to dendrites suggests a role for this pathway in the regulation of dendritic function. Examination of developing hippocampal structures indicated that RasGRP mRNA and protein appear synchronously during the first 2 weeks of postnatal development as these neurons become fully mature. This result indicates that the RasGRP signal transduction pathway is not required during early hippocampal development, but is a feature of mature neurons during the later stages of development.

Iridals are a novel class of ligands for phorbol ester receptors with modest selectivity for the RasGRP receptor subfamily

Since 1990, the National Cancer Institute has performed extensive in vitro screening of compounds for anticancer activity. To date, more than 70 000 compounds have been screened for their antiproliferation activities against a panel of 60 human cancer cell lines. We probed this database to identify novel structural classes with a pattern of biological activity on these cell lines similar to that of the phorbol esters. The iridals form such a structural class. Using the program Autodock, we show that the iridals dock to the same position on the C1b domain of protein kinase C delta as do the phorbol esters, with the primary hydroxyl group of the iridal at the C3 position forming two hydrogen bonds with the amide group of Thr12 and with the carbonyl group of Leu 21 and the aldehyde oxygen of the iridal forming a hydrogen bond with the amide group of Gly23. Biological analysis of two iridals, NSC 631939 and NSC 631941, revealed that they bound to protein kinase C alpha with K(i) values of 75.6 +/- 1.3 and 83.6 +/- 1.5 nM, respectively. Protein kinase C is now recognized to represent only one of five families of proteins with C1 domains capable of high-affinity binding of diacylglycerol and the phorbol esters. NSC 631939 and NSC 631941 bound to RasGRP3, a phorbol ester receptor that directly links diacylglycerol/phorbol ester signaling with Ras activation, with K(i) values of 15.5 +/- 2.3 and 41.7 +/- 6.5 nM, respectively. Relative to phorbol 12,13-dibutyrate, they showed 15- and 6-fold selectivity for RasGRP3. Both compounds caused translocation of green fluorescent protein tagged RasGRP3 expressed in HEK293 cells, and both compounds induced phosphorylation of ERK1/2, a downstream indicator of Ras activation, in a RasGRP3-dependent fashion. We conclude that the iridals represent a promising structural motif for design of ligands for phorbol ester receptor family members.

Phorbol esters modulate the Ras exchange factor RasGRP3

RasGRP represents the prototype of a new class of guanine nucleotide exchange factors that activate small GTPases. The guanyl nucleotide-releasing protein (GRP) family members contain catalytic domains related to CDC25, the Ras exchange factor of Saccharomyces cerevisiae. They also contain a motif resembling a pair of calcium-binding EF-hands and a C1 domain similar to the diacylglycerol interaction domain of protein kinase C. The sequence of KIAA0846, identified in a human brain cDNA library, encodes a member of the GRP family that we refer to as RasGRP3. We show here that RasGRP3 bound phorbol esters with high affinity. This binding depended on anionic phospholipids, which is characteristic of phorbol ester binding to C1 domain proteins. In addition, phorbol esters also caused activation of the RasGRP3 exchange activity in intact cells, as determined by an increase in RasGTP and phosphorylation of the extracellular-regulated kinases. Finally, both phorbol 12-myristate 13-acetate and the diacylglycerol analogue 1,2-dioctanoyl-sn-glycerol induced redistribution of RasGRP3 to the plasma membrane and/or perinuclear area in HEK-293 cells, as demonstrated using a green fluorescent fusion protein. We conclude that RasGRP3 serves as a PKC-independent pathway to link the tumor-promoting phorbol esters with activation of Ras GTPases.

Evidence for protein kinase C-dependent and -independent activation of mitogen-activated protein kinase in T cells: potential role of additional diacylglycerol binding proteins

Activation of mitogen-activated protein kinases (MAPK) is a critical signal transduction event for CTL activation, but the signaling mechanisms responsible are not fully characterized. Protein kinase C (PKC) is thought to contribute to MAPK activation following TCR stimulation. We have found that dependence on PKC varies with the method used to stimulate the T cells. Extracellular signal-regulated kinase (ERK) activation in CTL stimulated with soluble cross-linked anti-CD3 is completely inhibited by the PKC inhibitor bisindolylmaleimide (BIM). In contrast, only the later time points in the course of ERK activation are sensitive to BIM when CTL are stimulated with immobilized anti-CD3, a condition that stimulates CTL degranulation. Surprisingly, MAPK activation in response to immobilized anti-CD3 is strongly inhibited at all time points by the diacylglycerol (DAG)-binding domain inhibitor calphostin C implicating the contribution of a DAG-dependent but PKC-independent pathway in the activation of ERK in CTL clones. Chronic exposure to phorbol ester down-regulates the expression of DAG-responsive PKC isoforms; however, this treatment of CTL clones does not inhibit anti-CD3-induced activation of MAPK. Phorbol ester-treated cells have reduced expression of several isoforms of PKC but still express the recently described DAG-binding Ras guanylnucleotide-releasing protein. These results indicate that the late phase of MAPK activation in CTL clones in response to immobilized anti-CD3 stimulation requires PKC while the early phase requires a DAG-dependent, BIM-resistant component.

RasGRP is essential for mouse thymocyte differentiation and TCR signaling

The Ras signaling pathway plays a critical role in thymopoiesis and T cell activation, but the mechanism of Ras regulation is controversial. At least one mode of Ras regulation in T cells involves the messenger diacylglycerol (DAG). RasGRP, a Ras activator with a DAG-binding C1 domain, is expressed in T cells and thymocytes. Here we show that thymi of RasGRP-null mutant mice have approximately normal numbers of immature thymocytes but a marked deficiency of mature, single-positive (CD4+CD8- and CD4-CD8+) thymocytes. In Ras signaling and proliferation assays, mutant thymocytes showed a complete lack of response to DAG analogs or T cell receptor (TCR) stimulation by antibodies. Thus, TCR and DAG are linked through RasGRP to Ras signaling.

Distribution of ras guanyl releasing protein (RasGRP) mRNA in the adult rat central nervous system

In the nervous system, Ras signal transduction pathways are involved in cellular differentiation, neuronal survival and synaptic plasticity. These pathways can be modulated by Ras guanyl nucleotide exchange factors (Ras GEFs), which activate Ras protein by catalyzing the exchange of GDP for GTP. RasGRP, a recently discovered Ras GEF is expressed in brain as well as in T cells. In addition to the catalytic domain which catalyzes dissociation of Ras-GDP, RasGRP has a pair of calcium-binding EF hands and a diacylglycerol binding domain. The structure of RasGRP suggests that it serves to link calcium and lipid messengers to Ras signaling pathways. We have used an RNase protection assay to detect RasGRP mRNA in various regions of the rat brain and we have determined the cellular distribution of RasGRP mRNA by in situ hybridization. RasGRP mRNA is widely distributed and is present in both interneurons and projection neurons but not confined to any neuronal type or neurotransmitter phenotype. The presence of RasGRP mRNA in archicortical neurons suggests that this pathway may be important in phylogenetically older regions of the CNS. The restriction of RasGRP mRNA to subsets of neurons suggests that activation of Ras by RasGRP has a specific function in certain neuronal types. We did not detect RasGRP in glial cells.

RasGRP links T-cell receptor signaling to Ras

Stimulation of the T-cell receptor (TCR) alters a number of intracellular signaling pathways including one that involves protein tyrosine kinases, phospholipase C-gamma1 (PLC-gamma1), diacylglycerol (DAG), and calcium messengers. By a divergent pathway, TCR-stimulated protein tyrosine kinase activity is thought to result independently in recruitment of the Ras activator Sos to the plasma membrane, leading to Ras activation. Here we show that RasGRP, a Ras activator that contains calcium-binding EF hands and a DAG-binding domain, is expressed in T cells. A PLC-gamma1 inhibitor diminished activation of Ras following TCR stimulation. Membranes from TCR-stimulated Jurkat T cells exhibited increased RasGRP and increased Ras-guanyl nucleotide association activity that was inhibited by antibodies directed against RasGRP. Overexpression of RasGRP in T cells enhanced TCR-Ras-Erk signaling and augmented interleukin-2 secretion in response to calcium ionophore plus DAG analogues phorbol ester myristate or bryostatin-1. Thus, RasGRP links TCR and PLC-gamma1 to Ras-Erk signaling, a pathway amenable to pharmacologic manipulation.

The guanine nucleotide exchange factor RasGRP is a high -affinity target for diacylglycerol and phorbol esters

RasGRP is a recently described guanine nucleotide exchange factor (GEF) that possesses a single C1 domain homologous to that of protein kinase C (PKC). The phorbol ester [(3)H]phorbol 12, 13-dibutyrate ([(3)H]PDBu) bound to this C1 domain (C1-RasGRP) with a dissociation constant of 0.58 +/- 0.08 nM, similar to that observed previously for PKC. Likewise, the potent PKC activator bryostatin 1, a compound currently in clinical trials, showed high affinity binding for C1-RasGRP. Structure activity analysis using several phorbol ester analogs showed both similarities and differences in ligand selectivity compared with PKC; the differences were comparable in magnitude to those between different PKC isoforms. Similarly, the potency of the PKC inhibitor calphostin C to inhibit [(3)H]PDBu binding to C1-RasGRP was similar to that observed for PKC. In contrast to the relative similarities in ligand recognition, the lipid cofactor requirements differed between RasGRP and PKC. The C1 domain plus the EF-hand motif of RasGRP (C1EF-RasGRP) was markedly less dependent on acidic phospholipids than was PKCalpha. The differences in lipid requirements were reflected in differential ligand selectivity under conditions of limiting lipid. Despite the presence of twin EF-hand like motifs, calcium did not affect the binding of [(3)H]PDBu to C1EF-RasGRP. We conclude that RasGRP is a high affinity receptor for phorbol esters and diacylglycerol. RasGRP thus provides a direct link between diacylglycerol generation or phorbol ester/bryostatin treatment and Ras activation.

Hypothermic stress leads to activation of Ras-Erk signaling

The small GTPase Ras is converted to the active, GTP-bound state during exposure of vertebrate cells to hypothermic stress. This activation occurs more rapidly than can be accounted for by spontaneous nucleotide exchange. Ras-guanyl nucleotide exchange factors and Ras GTPase-activating proteins have significant activity at 0 degrees C in vitro, leading to the hypothesis that normal Ras regulators influence the relative amounts of Ras-GTP and Ras-GDP at low temperatures in vivo. When hypothermic cells are warmed to 37 degrees C, the Raf-Mek-Erk protein kinase cascade is activated. After prolonged hypothermic stress, followed by warming to physiologic temperature, cultured fibroblasts assume a rounded morphology, detach from the substratum, and die. All of these biologic responses are attenuated by pharmacologic inhibition of Mek. Previously, it had been found that low temperature blocks acute growth factor signaling to Erk. In the present study, we found that this block occurs at the level of Raf activation. Temperature regulation of Ras signaling could help animal cells respond appropriately to hypothermic stress, and Ras-Erk signaling can be manipulated to improve the survival of cells in cold storage.

A novel pathway for tumor necrosis factor-alpha and ceramide signaling involving sequential activation of tyrosine kinase, p21(ras), and phosphatidylinositol 3-kinase

Treatment of confluent rat2 fibroblasts with C2-ceramide (N-acetylsphingosine), sphingomyelinase, or tumor necrosis factor-alpha (TNFalpha) increased phosphatidylinositol (PI) 3-kinase activity by 3-6-fold after 10 min. This effect of C2-ceramide depended on tyrosine kinase activity and an increase in Ras-GTP levels. Increased PI 3-kinase activity was also accompanied by its translocation to the membrane fraction, increases in tyrosine phosphorylation of the p85 subunit, and physical association with Ras. Activation of PI 3-kinase by TNFalpha, sphingomyelinase, and C2-ceramide was inhibited by tyrosine kinase inhibitors (genistein and PP1). The stimulation of PI 3-kinase by sphingomyelinase and C2-ceramide was not observed in fibroblasts expressing dominant-negative Ras (N17) and the stimulation by TNFalpha was decreased by 70%. PI 3-kinase activation by C2-ceramide was not modified by inhibitors of acidic and neutral ceramidases, and it was not observed with the relatively inactive analog, dihydro-C2-ceramide. It is proposed that activation of Ras and PI 3-kinase by ceramide can contribute to signaling effects of TNFalpha that occur downstream of sphingomyelinase activation and result in increased fibroblasts proliferation.

RasGRP, a Ras activator: mouse and human cDNA sequences and chromosomal positions

We recently reported the molecular cloning of a novel transforming rat brain cDNA, rbc7, that encodes a Ras activator (Ebinu et al. Science 280, p. 1082, 1998). We proposed that this cDNA is a 5' and 3' truncated version of a larger normal transcript that encodes a predicted 90-kDa protein which we called RasGRP (Ras guanyl nucleotide releasing protein). We have now studied the structure of the mouse and human sequences and confirmed our conclusions about the nature of the 5' truncation. The human gene has been localized to 15q15 by an in situ hybridization technique, while the mouse gene has been positioned on Chr 2 near thrombospondin by linkage analysis. The relatedness of RasGRP to another human sequence and a hypothetical nematode protein are also discussed.

Premature senescence involving p53 and p16 is activated in response to constitutive MEK/MAPK mitogenic signaling

Oncogenic Ras transforms immortal rodent cells to a tumorigenic state, in part, by constitutively transmitting mitogenic signals through the mitogen-activated protein kinase (MAPK) cascade. In primary cells, Ras is initially mitogenic but eventually induces premature senescence involving the p53 and p16(INK4a) tumor suppressors. Constitutive activation of MEK (a component of the MAPK cascade) induces both p53 and p16, and is required for Ras-induced senescence of normal human fibroblasts. Furthermore, activated MEK permanently arrests primary murine fibroblasts but forces uncontrolled mitogenesis and transformation in cells lacking either p53 or INK4a. The precisely opposite response of normal and immortalized cells to constitutive activation of the MAPK cascade implies that premature senescence acts as a fail-safe mechanism to limit the transforming potential of excessive Ras mitogenic signaling. Consequently, constitutive MAPK signaling activates p53 and p16 as tumor suppressors.

RasGRP, a Ras guanyl nucleotide- releasing protein with calcium- and diacylglycerol-binding motifs

RasGRP, a guanyl nucleotide-releasing protein for the small guanosine triphosphatase Ras, was characterized. Besides the catalytic domain, RasGRP has an atypical pair of "EF hands" that bind calcium and a diacylglycerol (DAG)-binding domain. RasGRP activated Ras and caused transformation in fibroblasts. A DAG analog caused sustained activation of Ras-Erk signaling and changes in cell morphology. Signaling was associated with partitioning of RasGRP protein into the membrane fraction. Sustained ligand-induced signaling and membrane partitioning were absent when the DAG-binding domain was deleted. RasGRP is expressed in the nervous system, where it may couple changes in DAG and possibly calcium concentrations to Ras activation.

Interaction of activated Ras with Raf-1 alone may be sufficient for transformation of rat2 cells

v-H-ras effector mutants have been assessed for transforming activity and for the ability of the encoded proteins to interact with Raf-1-, B-Raf-, byr2-, ralGDS-, and CDC25-encoded proteins in the yeast two-hybrid system. Transformation was assessed in rat2 cells as well as in a mutant cell line, rv68BUR, that affords a more sensitive transformation assay. Selected mutant Ras proteins were also examined for their ability to interact with an amino-terminal fragment of Raf-1 in vitro. Finally, possible cooperation between different v-H-ras effector mutants and between effector mutants and overexpressed Raf-1 was assessed. Ras transforming activity was shown to correlate best with the ability of the encoded protein to interact with Raf-1. No evidence for cooperation between v-H-ras effector mutants was found. Signaling through the Raf1-MEK-mitogen-activated protein kinase cascade may be the only effector pathway contributing to RAS transformation in these cells.

Increased concentrations of phosphatidate, diacylglycerol and ceramide in ras- and tyrosine kinase (fps)-transformed fibroblasts

Concentrations of the bioactive lipids, phosphatidate and diacylglycerol, increased with time in culture in ras- and tyrosine kinase (fps)-transformed fibroblasts but not in control fibroblasts. On Day 3, diacylglycerol and phosphatidate concentrations were about 3.3- and 5.5-fold higher respectively in the ras-transformed compared to control fibroblasts. These concentrations in fps-transformed fibroblasts were increased about twofold. The changes in phosphatidate and diacylglycerol resulted from enhanced phospholipid turnover rather than from synthesis de novo. The increased ratio of phosphatidate to diacylglycerol is explained by decreased activities of two distinct phosphatidate phosphohydrolases and increased diacylglycerol kinase in ras-transformed fibroblasts. Ceramide concentrations were about 2.5- and threefold higher in the fps- and ras-transformed cells respectively on Day 3 compared to the controls. Incubating control fibroblasts from Days 1 to 3 with phosphatidylcholine-specific phospholipase C increased diacylglycerol, phosphatidate and ceramide concentrations, and decreased Mg2+-independent-phosphatidate phosphohydrolase activity. 8-(4-chlorophenylthio)-cAMP had a cytostatic effect in ras-transformed cells, it decreased the concentrations of phosphatidate and diacylglycerol, but increased that of ceramide. The consequences of increased ceramide and phosphatidate concentrations in ras-transformed cells are discussed in relation to signal transduction, cell division and the transformed phenotype.

Stimulation of ras GTPase activity by an anti-ras monoclonal antibody

Wild-type ras has GTPase activity, and this activity is accelerated substantially by GTPase-activating proteins (GAPs). Oncogenic ras species have an abnormally low intrinsic GTPase activity, and this activity is insensitive to GAPs. We confirmed that the anti-ras monoclonal antibody Y13-238 inhibited GAP activity in vitro, but we also noted that this antibody had GAP activity of its own. We studied the GAP activity of Y13-238 in circumstances in which ras GTPase activity was influenced by the GTPase-inhibitory antibody Y13-259 or by substitutions in ras. The GTPase-inhibitory antibody Y13-259 blocked the GAP associated with Y13-238. A ras species with a substitution in the effector loop that blocked conventional GAP activity was sensitive to stimulation by Y13-238. Both Y13-238 and Y13-259 stimulated the autophosphorylation of Ala59Thr ras. We interpreted these data in terms of a model in which the extrinsic factors influence the ras GTPase reaction by affecting the balance between "committed" and "uncommitted" states. We suggest that there is a mechanism distinct from that exploited by conventional GAPs for stimulating ras GTPase activity.

ras effector loop mutations that dissociate p120GAP and neurofibromin interactions

ras proteins are positively regulated by nucleotide exchange factors and negatively regulated by GTPase-activating proteins (GAPs). Two GAPs have been found in mammalian cells, p120GAP and neurofibromin, the product of the type 1 neurofibromatosis (NF1) gene. A library of substitutions in the effector loop region of ras in an Escherichia coli plasmid expression system was screened for c-Ha-ras species with altered GAP interactions. Several substitutions preferentially disrupted the interaction of ras with p120GAP as compared with the interaction with the recombinant GAP-related domain of neurofibromin (NF1-GRD). The most extreme example, Tyr32His, encoded a ras species that was unaffected by p120GAP but was stimulated normally by NF1-GRD. Tyr32His was weakly transforming in Rat2 cells. Tyr32His ras was primarily GDP-bound in quiescent Rat2 cells, although it rapidly associated with GTP after treatment of cells with epidermal growth factor. These results show that the NF1 product has less stringent requirements than p120GAP for ras effector domain structure and that negative regulation of ras can be achieved in rat fibroblasts by the product of NF1.

RAS signalling is abnormal in a c-raf1 MEK1 double mutant

A mutant rat cell clone that suppresses the transformation defects of RAS effector loop substitutions is heterozygous for mutations in c-raf1 and MEK1. The mutant cells can be transformed by many otherwise defective RAS effector mutants, including RAS genes with the effector regions of distantly related GTPases, even though the encoded RAS proteins do not interact with either the mutant or wild-type RAF in Saccharomyces cerevisiae. While the significance of the c-raf1 mutation is unclear, the MEK1 mutation increases MEK1 activity and leads to activation of mitogen-activated protein kinase. The mutant MEK1 is coupled to the epidermal growth factor pathway but exhibits decreased physical interaction with RAF. When overexpressed, the MEK1 mutation is transforming and causes hyperphosphorylation of RAF. Signalling from RAS to MEK1 may be mediated by something other than RAF alone, but signalling through MEK1 is probably sufficient for RAS transformation.