Imperfect Tool Research Articles

Rapid re-expression of CD133 protein in colorectal cancer cell lines in vitro and in vivo

Studies related to the cancer stem cell hypothesis are challenging because of the imperfect tools to identify cell populations of interest and controversy on the usefulness of established cancer cell lines. We previously found CD133 to not be selective for a tumor-propagating or radioresistant population in a near-diploid, microsatellite-instable colorectal carcinoma (CRC) cell line. Because of discrepant literature data, we herein systematically analyzed the behavior of microsatellite-stable cell line subpopulations reflecting the more frequent carcinogenesis pathway in spontaneous CRC. CD133+ and CD133−/low populations were isolated by fluorescence-activated cell sorting and further processed. HT29 and SW620 cells were studied in detail in monolayer and/or spheroid culture assays and upon subcutaneous injection in NMRI (nu/nu) mice using a limiting dilution approach. CD133−/low HT29 cells showed a significantly lower clonogenic survival and reduced spheroid formation capacity than their CD133+ counterparts. However, the cell populations neither differed in growth kinetics and response to treatment in vitro nor in tumor formation capacity when injecting as low as 10 cells. CD133−/low HT29 cells rapidly re-expressed CD133 protein in vitro and in vivo as shown by flow cytometry and/or western blot analyses, and they also showed a particular survival benefit under tissue normoxic conditions. In contrast, CD133 protein in the CD133+ population was quite stable throughout culturing. The observation of CD133 re-expression and lack of difference in tumor take rate of subpopulations was confirmed in SW620 cells. Here, we found cell density to affect CD133 re-expression in the CD133−-sorted population. And even SW480 cells, classified as a CD133− cell line, presented some CD133 protein on their surface upon in vivo engraftment. We conclude that (i) CD133 protein expression shows high plasticity in CRC cell lines, and (ii) in vitro CD133 status on the cell surface neither determines tumorigenic potential nor CD133 profile in vivo.

Continuous glucose monitoring in type 1 diabetes

Continuous glucose monitors (CGM), devices that can measure interstitial glucose in "real time," have become widely available particularly for use in patients with diabetes, and their accuracy and ease of use have greatly improved over the last decade. A number of large and well-controlled clinical trials have firmly established their usefulness in improving metabolic control (as measured by HbA1C) and decreasing time spent in hypoglycemia in adults; however, data have been less robust proving benefit in children and adolescents. Benefits are clearly linked to near-continuous wear. Insulin dosing algorithms based on CGM glucose trends have proven useful in dissecting the large volume of data generated daily by these devices, although these are imperfect tools, particularly in children. The technology is likely to be most useful when integrated with insulin pump delivery systems (sensor augmented). In this review, we concentrate on the analysis of published results of the largest trials in adults and children, including the very young, with diabetes.

A new method for screening and surveillance colonoscopy: Combined water-exchange and cap-assisted colonoscopy

Colonoscopy plays an important and central role in current colorectal cancer screening and prevention programs, but it is an imperfect tool. Adjunct techniques may help improve the performance of colonoscopy to increase the detection of polyps with neoplastic potential. This study investigates the novel approach of combined water-exchange and cap-assisted colonoscopy (WCC) and its impact on adenoma detection. A single-center single-colonoscopist consecutive group observational study to compare WCC with conventional air insufflation colonoscopy was performed. Data were collected from 50 consecutive patients undergoing outpatient colorectal cancer screening or polyp surveillance with WCC. Adenoma detection rates (ADR) and adenomas detected per colonoscopy (APC) were compared to a control group of 101 consecutive patients examined with conventional air colonoscopy during the immediate prior period. Cecal intubation was achieved in all patients. As an emerging and alternative quality metric for colonoscopy, APC was significantly higher in the WCC group (3.08 vs. 1.50, p=0.0021). The conventional quality metric, overall ADR, was higher in the WCC group compared to the air colonoscopy group (70.0% vs. 59.4%, p=0.22). This difference was not statistically significant, likely due to a type II error. The observational data suggest APC is a more sensitive indicator of quality colonoscopy than ADR. WCC shows promise as a novel technique that merges two simple adjunct methods to help improve the performance of colonoscopy. The data suggest larger, prospective studies are necessary to determine the true impact of water-exchange combined with cap-assisted maneuvers.

CB2 cannabinoid receptors inhibit synaptic transmission when expressed in cultured autaptic neurons

The role of CB2 in the central nervous system, particularly in neurons, has generated much controversy. Fueling the controversy are imperfect tools, which have made conclusive identification of CB2 expressing neurons problematic. Imprecise localization of CB2 has made it difficult to determine its function in neurons. Here we avoid the localization controversy and directly address the question if CB2 can modulate neurotransmission. CB2 was expressed in excitatory hippocampal autaptic neurons obtained from CB1 null mice. Whole-cell patch clamp recordings were made from these neurons to determine the effects of CB2 on short-term synaptic plasticity. CB2 expression restored depolarization induced suppression of excitation to these neurons, which was lost following genetic ablation of CB1. The endocannabinoid 2-arachidonylglycerol (2-AG) mimicked the effects of depolarization in CB2 expressing neurons. Interestingly, ongoing basal production of 2-AG resulted in constitutive activation of CB2, causing a tonic inhibition of neurotransmission that was relieved by the CB2 antagonist AM630 or the diacylglycerol lipase inhibitor RHC80267. Through immunocytochemistry and analysis of spontaneous EPSCs, paired pulse ratios and coefficients of variation we determined that CB2 exerts its function at a presynaptic site of action, likely through inhibition of voltage gated calcium channels. Therefore CB2 expressed in neurons effectively mimics the actions of CB1. Thus neuronal CB2 is well suited to integrate into conventional neuronal endocannabinoid signaling processes, with its specific role determined by its unique and highly inducible expression profile.

Dyslexic students in higher education and virtual learning environments: an exploratory study

AbstractThis paper presents the results of an interview‐based study of the use of virtual learning environments (VLEs) among dyslexic students. Interviews were carried out with 12 informants who had been formally diagnosed as dyslexic. The informants were either enrolled in a university or college programme, or had graduated less than a year before the interview. The findings reveal that dyslexic students experience a number of challenges associated with VLE use, including information overload, imperfect word processing tools, inadequate search functions, and having to relate to more than one system at a time.

Holotranscobalamin: Not Ready for Prime Time

To the Editor: In their recent article in Clinical Chemistry (1), Valente and colleagues advocate that holotranscobalamin II (holoTC)1 become the primary diagnostic test of vitamin B12 status. I believe that study flaws undercut the authors' recommendation. Moreover, the validation difficulties extend to deeper, more basic issues that continue to limit translation of the holoTC concept, despite its theoretical attractiveness. Validation efforts have typically compared holoTC against serum B12 in general populations and have used imperfect tools with often-arbitrary cutpoints to define B12 status. Such approaches and their reliance on methylmalonic acid (MMA), despite its questionable diagnostic specificity, have been critiqued (2). Valente et al. reuse this model with just 1 modification, the substitution of erythrocyte vitamin B12 (RBC-B12) for MMA as the arbiter of B12 status. That innovation misfires, however, because RBC-B12 is probably an even poorer standard than MMA. No convincing data anywhere, including the references cited by Valente and colleagues, justify the report's assumption that RBC-B12 represents tissue B12 status. Very little is known about what RBC-B12 concentrations really mean. The measurement of RBC-B12 has been deemed insufficiently informative …

Design Considerations for a Two-stage Study with a Continuous Outcome and a Rare Exposure

We consider the scenario in which the severity of a disease is characterized by a normally distributed response and the chance of being exposed (yes/no) to the risk factor is extremely rare. A screening test is employed to oversample subjects who may be at risk for the disease because expensive laboratory tests are needed to measure the outcome of interest and to confirm the true exposure status. Considerations of sample size and cost are discussed for this type of two-stage design with the objectives of 1) minimizing the number of subjects in the Stage II, and 2) overcoming the problem of a rare exposure. In particular, with an imperfect screening tool, one must take into account the sensitivity and specificity of the screening test, and the uncertainty of the estimates of the exposure prevalence in the survey population. The Penn State Children Sleep Disorder Study (PSCSDS) is used for illustration.

Missing the Mark on Prostate-Specific Antigen Screening

THE US PREVENTIVE SERVICES TASK FORCE RECENTLY issued a draft recommendation against prostatespecific antigen (PSA) screening for prostate cancer. After performing a rigorous review of the relevant empirical literature, the task force concluded with “moderate certainty” that the harms of PSA-based detection (eg, biopsy-related complications) and early intervention (eg, incontinence, erectile dysfunction) exceed the potential benefits. For this reason, the task force now proposes discouraging PSA screening among men who are free of symptoms suspicious for prostate cancer. Most clinicians are aware that PSA is an imperfect tool for the early detection of prostate cancer. First, rather than being focused on patients most likely to benefit from early detection, the use of PSA as a screening test is often undiscerning. Second, PSA-based screening can be inconclusive. As a consequence, for some patients this process can lead to a cycle of repeated venipuncture and biopsy, as well as psychological distress often referred to as “PSA anxiety.” Third, there can be collateral harm to patients in whom PSA screening detects a cancer that was never destined to cause death or morbidity. Fourth, the adverse effects of prostate cancer therapies remain too high, further justifying concerns about the balance of benefits and harms associated with PSA-based screening and early intervention. Even though the process undertaken by the US Preventive Services Task Force was rigorous and these issues were considered, it seems that their recommendations still miss the mark. Over the last 2 decades, and concurrent with the dissemination of PSA screening, there has been a significant decline in prostate cancer–specific mortality in the United States. However, this advance apparently was barely recognized in the deliberations and communications from the task force. This well-established epidemiological trend is difficult, if not impossible, to explain without accepting that early detection strategies built around PSA screening have allowed the identification and successful treatment of patients who would otherwise have died of biologically aggressive, clinically significant prostate cancers. Current evidence suggests that younger men (ie, 70 years) and those with higher-grade cancers benefit from PSA screening and early intervention. Two screening trials reviewed by the task force demonstrated a small—but significant—survival benefit associated with screening for men younger than age 70 years. In contrast, the United States Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial showed no mortality benefits from PSA screening. However, PSA testing in the study’s usual care group was quite high (up to 52%), raising concerns about the study’s ability to answer the question of interest. In terms of treatment, the only trial deemed of “good quality” by the US Preventive Services Task Force (ie, the Scandinavian Prostate Cancer Study Group No. 4) showed that—with 15 years of follow-up—prostate cancer–specific mortality and allcause mortality were 38% and 25% lower, respectively, among men treated surgically compared with men managed with watchful waiting. Subgroup analyses suggested that the survival benefits were greatest for men aged 65 years or younger. In addition, even the limited data currently available from the Prostate Cancer Intervention Versus Observation Trial, portrayed by the task force as a largely negative study, demonstrate a signal favoring treatment among men with higher-risk cancers. So, for PSA screening, is the glass half empty or half full? The answer may depend on clinical experience. Many clinicians involved in the care of men living with and dying of prostate cancer may consider that the data reviewed by the task force reveal potentially meaningful survival benefits for younger men, for those whose PSA level or Gleason score indicate a higher-risk cancer, or both groups (collectively representing tens of thousands of men diagnosed with prostate cancer each year in the United States). Accordingly, the US Preventive Services Task Force recommendation discouraging the use of PSA screening, however well-intentioned, cannot go uncontested. By emphasizing the centrality of avoiding harms associated with detection and treatment (without question a laudable goal), members of the task force—none of whom were urologists, medical oncologists, or radiation therapists—are in es-

Application of appropriate use criteria for stress myocardial perfusion imaging at two academic medical centers: Compliance and association with image findings

Explore the extent to which stress myocardial perfusion imaging (MPI) studies for coronary heart disease detection met published appropriate use criteria (AUC), and the association between AUC classification and image findings. Retrospective, descriptive review of stress studies performed at the University of Washington Medical Center (UWMC n= 1377) and the Veterans Health Administration of Puget Sound (VA n= 1445) in the 31 months following AUC publication. At UWMC and VA, 69% and 89% of MPI studies, respectively, were classified as appropriate, 16% and 3% as inappropriate, and 15% and 8% as uncertain. All differences were significant, p < .001. At UWMC, 11% of appropriate studies and 10% of inappropriate or uncertain studies were abnormal (demonstrating myocardial ischemia or myocardial infarction), p= .93; these analyses were not performed on VA studies. Most studies at both sites were classified as appropriate. At UWMC, the likelihood of a study classified as appropriate demonstrating an abnormality was not significantly different from a study classified as uncertain or inappropriate. AUC are imperfect tools but are increasingly created and referenced; as such, it is vital that practicing nurse practitioners are knowledgeable about their creation, application, and evaluation.

Time-of-flight imaging of invisibility cloaks

As invisibility cloaking has recently become experimental reality, it is interesting to explore ways to reveal remaining imperfections. In essence, the idea of most invisibility cloaks is to recover the optical path lengths without an object (to be made invisible) by a suitable arrangement around that object. Optical path length is proportional to the time of flight of a light ray or to the optical phase accumulated by a light wave. Thus, time-of-flight images provide a direct and intuitive tool for probing imperfections. Indeed, recent phase-sensitive experiments on the carpet cloak have already made early steps in this direction. In the macroscopic world, time-of-flight images could be measured directly by light detection and ranging (LIDAR). Here, we show calculated time-of-flight images of the conformal Gaussian carpet cloak, the conformal grating cloak, the cylindrical free-space cloak, and of the invisible sphere. All results are obtained by using a ray-velocity equation of motion derived from Fermat's principle.

Imperfect tools for a difficult job: Colposcopy, ‘colpocytology’ and screening for cervical cancer in Brazil

The quasi-totality of social scientists who studied screening for cervical tumours identified such screening with a single method: the Pap smear (exfoliative cytology). This article explains that this method was not valid everywhere. The history of screening for cervical cancer in Brazil displays an alternative method for detecting cervical malignancies: a direct observation of the cervix with a specific instrument--the colposcope. The development of this method in Brazil in the 1940s and 1950s reflected a complex mixture of professional interests, government policies, and regional, local and charitable initiatives. While the use of colposcopy for cervical tumour screening was phased out in the 1970s and 1980s, the long lifespan and widespread diffusion of this method illuminates the irreducible contingency of specific developments in science, technology and medicine. Seen from the vantage point of Brazil, the Western model for preventing cervical malignancies no longer appears self-evident Alternative choices might have led to the development of different material and visual cultures of medicine, stimulated different patterns of medical specialization and division of medical labour, produced different links between malignancies, women, gynaecologists, epidemiologists and public health experts, and shaped different health policies.

A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming by Paul N. Edwards . Cambridge MA:MIT Press, 2010. 518 pp. ISBN: 978-0-262-01392-5, $32.95

A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming <i>by Paul N. Edwards</i> . Cambridge MA:MIT Press, 2010. 518 pp. ISBN: 978-0-262-01392-5, $32.95

Quality Assurance in Atmospheric Modeling

This paper summarizes a number of best practices associated with the use of numerical models of the atmosphere and is motivated by the rapid growth in the number of model users, who have a range of scientific and technical preparations. An underlying important message is that models are complex and imperfect tools, and model users must be aware of their strengths and weaknesses and be thorough in the process of model configuration and verification.

APP Transgenic Mice: Their Use and Limitations

Alzheimer's disease is the most widespread form of dementia. Its histopathological hallmarks include vascular and extracellular β-amyloid (Aβ) deposition and intraneuronal neurofibrillary tangles (NFTs). Gradual decline of cognitive functions linked to progressive synaptic loss makes patients unable to store new information in the earlier stages of the pathology, later becoming completely dependent because they are unable to do even elementary daily life actions. Although more than a hundred years have passed since Alois Alzheimer described the first case of AD, and despite many years of intense research, there are still many crucial points to be discovered in the neuropathological pathway. The development of transgenic mouse models engineered with overexpression of the amyloid precursor protein carrying familial AD mutations has been extremely useful. Transgenic mice present the hallmarks of the pathology, and histological and behavioural examination supports the amyloid hypothesis. As in human AD, extracellular Aβ deposits surrounded by activated astrocytes and microglia are typical features, together with synaptic and cognitive defects. Although animal models have been widely used, they are still being continuously developed in order to recapitulate some missing aspects of the disease. For instance, AD therapeutic agents tested in transgenic mice gave encouraging results which, however, were very disappointing in clinical trials. Neuronal cell death and NFTs typical of AD are much harder to replicate in these mice, which thus offer a fundamental but still imperfect tool for understanding and solving dementia pathology.

The Interpretive Movements of Language and Desire: Engagements of Poetry and Place in Qualitative Research

In this work, I seize on the movements of language engaged in the confusions of qualitative research. I examine the impressions and effects of a researcher’s desires, in which language serves simultaneously as a point of alienation, and as an imperfect enunciatory tool forever directed at satisfaction. Provoking a haunted analysis of autobiographical place, I also dwell in the poetic influences of topographical reading. The result is a methodological inquiry into the ways we move when we do educational re-search, and the curricular paths that languages help to inscribe in this performance.

Stroke Prevention in the High-risk Atrial Fibrillation Patient: Medical Management

Medical management of patients with atrial fibrillation (AF) at high risk for stroke is limited by problems of imperfect tools for assessment of thromboembolism and bleeding risks. Improved instruments, such as the CHA₂DS₂VASc and HAS-BLED risk stratification scores, have been incorporated into European practice guidelines. Until recently, the most effective therapy for stroke prevention has been anticoagulation with a vitamin K antagonist, but new oral anticoagulants in development, antiarrhythmic drugs that reduce adverse cardiovascular events in patients with AF, and interventional techniques for occlusion of the left atrial appendage represent promising options for stroke prevention. These new strategies will need focused evaluation in the most challenging AF patients-those with a high risk of bleeding, prior thromboembolism, or thrombosis-prone surfaces such as mechanical heart valve prostheses or drug-eluting coronary stents, for whom the limitations of currently available treatment options and a paucity of data are particularly acute.

A vast machine: computer models, climate data, and the politics of global warming

In A Vast Machine, Paul Edwards documents the evolution of a broad scientific field that began with the curiosity of a few 19th-century explorers and scholars and now spans a worldwide community of scientists, engineers, and other specialists working with huge quantities of data, immensely complex computer models, and many sophisticated instruments and measurement platforms. As a scholar in science and technology studies, Edwards provides historical context and insightful perspectives on how observations of Earth’s weather and climate have shaped scientific theories and models underpinning weather prediction and climate change—and how these in turn have dramatically affected our “knowledge infrastructure”: the ways in which environmental measurements are now made, analyzed, interpreted, and used both in science and in global debates about environmental policy. In particular, he elucidates what scientists often take for granted—that models and observational data together form an inseparable basis for scientific understanding and prediction—in the context of current policy debates that have often tried to characterize observational data as independent, immutable representations of “truth” and computer models as imperfect tools subject to scientific bias and error. A compelling aspect of A Vast Machine is Edwards’ careful history of the development of weather observations and prediction in conjunction with the simultaneous and often intertwined evolution of climate monitoring and modeling. Weather data networks and numerical weather prediction models have grown rapidly in response to immediate societal needs and interests, evolving into ubiquitous technologies and well-oiled systems for delivering useful information to a wide range of users. Climate data networks and climate models share many similar components and approaches, but require a shift in perspective in analyzing and using data and model predictions. For example, long time series of climate data need continual reassessment and reanalysis because improvements in our current knowledge and understanding of what determines and influences climate also affect how we interpret measurements made in the past. Because the global climate system is so complex and interconnected across land, oceans, atmosphere, the cryosphere, and the biosphere, the process of making observations collected from around the world—even through Earth-orbiting satellites—into truly “global” data sets requires significant innovation and investment. Edwards identifies different types of “data friction” that affect the flows and transformations of data and information, not only technical bottlenecks and constraints but also challenges stemming from coordinating scientists and systems across different disciplines, countries, and cultures. He also examines the institutional and structural histories of national agencies, international organizations, and other stakeholders that have shaped the evolution of weather and climate science and observational systems, including the strong influence of war, the military, politics, and the emergence of global environmental institutions and awareness. For anyone interested in global warming or more generally in climate or weather issues, A Vast Machine is well worth a careful read. It provides an unusually broad and long-term view of the development of climate science and associated climate data, models, and information infrastructure, supplemented by useful figures and very detailed notes and references. Edwards begins with helpful guidance on what chapters might be of strongest interest to some readers or too technical for others. For those more generally interested in science, science and technology policy, and data and information management issues, he offers a sprinkling of comparisons with analogous issues and pointers to relevant literature. As someone who has been closely involved for several decades in many of the research, data, and assessment activities and institutions documented in this volume, I found it indeed a rare and unexpected opportunity to learn so much about how these endeavors have fit into a vast and vibrant scientific enterprise that is of critical importance to the sustainability of our planet. The volume is also a testament to the vision and breadth of interests of the late Stephen Schneider of Stanford University, who helped Edwards with many aspects of his research (and who was a key mentor for this reviewer as well).

On the use of statistical models to predict crop yield responses to climate change

Predicting the potential effects of climate change on crop yields requires a model of how crops respond to weather. As predictions from different models often disagree, understanding the sources of this divergence is central to building a more robust picture of climate change's likely impacts. A common approach is to use statistical models trained on historical yields and some simplified measurements of weather, such as growing season average temperature and precipitation. Although the general strengths and weaknesses of statistical models are widely understood, there has been little systematic evaluation of their performance relative to other methods. Here we use a perfect model approach to examine the ability of statistical models to predict yield responses to changes in mean temperature and precipitation, as simulated by a process-based crop model. The CERES-Maize model was first used to simulate historical maize yield variability at nearly 200 sites in Sub-Saharan Africa, as well as the impacts of hypothetical future scenarios of 2 °C warming and 20% precipitation reduction. Statistical models of three types (time series, panel, and cross-sectional models) were then trained on the simulated historical variability and used to predict the responses to the future climate changes. The agreement between the process-based and statistical models’ predictions was then assessed as a measure of how well statistical models can capture crop responses to warming or precipitation changes. The performance of statistical models differed by climate variable and spatial scale, with time-series statistical models ably reproducing site-specific yield response to precipitation change, but performing less well for temperature responses. In contrast, statistical models that relied on information from multiple sites, namely panel and cross-sectional models, were better at predicting responses to temperature change than precipitation change. The models based on multiple sites were also much less sensitive to the length of historical period used for training. For all three statistical approaches, the performance improved when individual sites were first aggregated to country-level averages. Results suggest that statistical models, as compared to CERES-Maize, represent a useful if imperfect tool for projecting future yield responses, with their usefulness higher at broader spatial scales. It is also at these broader scales that climate projections are most available and reliable, and therefore statistical models are likely to continue to play an important role in anticipating future impacts of climate change.

Economics and Cognitive Science

The neo-classical approach to analyzing the performance of an economy assumes that in the face of pervasive scarcity individuals make choices reflecting a set of desires, wants or preferences. But valuable as this model has been for the development of an elegant body of theory it is a very imperfect tool for solving economic problems both at a moment of time but particularly over time. The puzzle I seek to unravel is how do humans evolve and believe in theories in the face of uncertainty.

Testing for Mutual Exclusivity

A test for two events being mutually exclusive is presented for the case in which there are known rates of misclassification of the events. The test can be utilized in other situations, such as to test whether a set is a subset of another set. In the test, the null value of the probability of the intersection is replaced by the expected value of the number determined to be in the intersection by the imperfect diagnostic tools. The test statistic is the number in a sample that is judged to be in the intersection. Medical testing applications are emphasized.