Incidence and Risk Factors for Hepatocellular Carcinoma in Cirrhosis: The Multicenter Hepatocellular Carcinoma Early Detection Strategy (HEDS) Study

BACKGROUND & AIMS

Worldwide, hepatocellular carcinoma (HCC) is a common malignancy. We aimed to prospectively determine the incidence and risk factors of HCC in a U.S.

COHORT

METHODS

The multicenter Hepatocellular Carcinoma Early Detection Strategy study of the National Institutes of Health prospectively enrolled patients with cirrhosis who underwent standard surveillance for HCC. Demographics, medical and family history, etiology of liver disease, and clinical features were evaluated for associations with HCC.

RESULTS

Between April 10, 2013 and December 31, 2021, 1723 patients were enrolled and confirmed eligible. During median follow-up of 2.2 years (range, 0-8.7 years), there were 109 incident cases of HCC for an incidence rate of 2.4 per 100 person-years: 88 (81%) patients with very early/early Barcelona Clinic Liver Cancer stage (0, A), 20 (18%) intermediate stage (B), and 1 (1%) unknown stage. Risk factor analyses were restricted to 1325 patients, including 95 incident HCC, with at least 6 months of follow-up. The majority were men (53.2%), obese or severely obese (median body mass index, 30.2 kg/m2), and white (86.3%); 42.0% had history of hepatitis C virus infection, 20.7% had alcoholic liver disease, and 24.9% had nonalcoholic fatty liver disease. Fourteen risk factors for HCC were significant (P < .05) in univariate analyses, and a multivariate subset was selected using stepwise logistic regression. The multivariate subset contained gender (P < .001; male; odds ratio [OR], 2.47; 95% confidence interval [CI], 1.54-4.07), years with cirrhosis (P = .004; OR, 1.06; 95% CI, 1.02-1.1), family history of liver cancer (P = .02; yes; OR, 2.69; 95% CI, 1.11-5.86), age (per 5 years; P = .02; OR, 1.17; 95% CI, 1.03-1.33), obesity (P = .02; yes; OR, 1.7; 95% CI, 1.08-2.73), aspartate aminotransferase (log(1+AST); P = .06; OR, 1.54; 95% CI, 0.97-2.42), alpha-fetoprotein (log(1+AFP); P = .07; OR, 1.32; 95% CI, 0.97-1.77), and albumin (P = .10; OR, 0.7; 95% CI, 0.46-1.07).

CONCLUSIONS

Thus far, this is the largest prospective and geographically diverse study of a U.S. cohort of patients with cirrhosis that validates known risk factors for HCC (gender, age, obesity, years with cirrhosis, family history of liver cancer, baseline AFP, albumin, and AST). The incidence of HCC was 2.4% per 100 person-years.

Mortality Benefit of a Blood-Based Biomarker Panel for Lung Cancer on the Basis of the Prostate, Lung, Colorectal, and Ovarian Cohort

PURPOSE

To investigate the utility of integrating a panel of circulating protein biomarkers in combination with a risk model on the basis of subject characteristics to identify individuals at high risk of harboring a lethal lung cancer.

METHODS

Data from an established logistic regression model that combines four-marker protein panel (4MP) together with the Prostate, Lung, Colorectal, and Ovarian (PLCO) risk model (PLCOm2012) assayed in prediagnostic sera from 552 lung cancer cases and 2,193 noncases from the PLCO cohort were used in this study. Of the 552 lung cancer cases, 387 (70%) died of lung cancer. Cumulative incidence of lung cancer death and subdistributional and cause-specific hazard ratios (HRs) were calculated on the basis of 4MP + PLCOm2012 risk scores at a predefined 1.0% and 1.7% 6-year risk thresholds, which correspond to the current and former US Preventive Services Task Force screening criteria, respectively.

RESULTS

When considering cases diagnosed within 1 year of blood draw and all noncases, the area under receiver operation characteristics curve estimate of the 4MP + PLCOm2012 model for risk prediction of lung cancer death was 0.88 (95% CI, 0.86 to 0.90). The cumulative incidence of lung cancer death was statistically significantly higher in individuals with 4MP + PLCOm2012 scores above the 1.0% 6-year risk threshold (modified χ2, 166.27; P < .0001). Corresponding subdistributional and lung cancer death-specific HRs for test-positive cases were 9.88 (95% CI, 6.44 to 15.18) and 10.65 (95% CI, 6.93 to 16.37), respectively.

CONCLUSION

The blood-based biomarker panel in combination with PLCOm2012 identifies individuals at high risk of a lethal lung cancer.

Blood-Based Biomarker Panel for Personalized Lung Cancer Risk Assessment

PURPOSE

To investigate whether a panel of circulating protein biomarkers would improve risk assessment for lung cancer screening in combination with a risk model on the basis of participant characteristics.

METHODS

A blinded validation study was performed using prostate lung colorectal ovarian (PLCO) Cancer Screening Trial data and biospecimens to evaluate the performance of a four-marker protein panel (4MP) consisting of the precursor form of surfactant protein B, cancer antigen 125, carcinoembryonic antigen, and cytokeratin-19 fragment in combination with a lung cancer risk prediction model (PLCO_m2012) compared with current US Preventive Services Task Force (USPSTF) screening criteria. The 4MP was assayed in 1,299 sera collected preceding lung cancer diagnosis and 8,709 noncase sera.

RESULTS

The 4MP alone yielded an area under the receiver operating characteristic curve of 0.79 (95% CI, 0.77 to 0.82) for case sera collected within 1-year preceding diagnosis and 0.74 (95% CI, 0.72 to 0.76) among the entire specimen set. The combined 4MP + PLCO_m2012 model yielded an area under the receiver operating characteristic curve of 0.85 (95% CI, 0.82 to 0.88) for case sera collected within 1 year preceding diagnosis. The benefit of the 4MP in the combined model resulted from improvement in sensitivity at high specificity. Compared with the USPSTF2021 criteria, the combined 4MP + PLCO_m2012 model exhibited statistically significant improvements in sensitivity and specificity. Among PLCO participants with ≥ 10 smoking pack-years, the 4MP + PLCO_m2012 model would have identified for annual screening 9.2% more lung cancer cases and would have reduced referral by 13.7% among noncases compared with USPSTF2021 criteria.

CONCLUSION

A blood-based biomarker panel in combination with PLCO_m2012 significantly improves lung cancer risk assessment for lung cancer screening.

Applying sequential surveillance methods that use regression adjustment or weighting to control confounding in a multisite, rare-event, distributed setting: Part 2 in-depth example of a reanalysis of the measles-mumps-rubella-varicella combination vaccine and seizure risk

OBJECTIVE

In-depth example of two new group sequential methods for postmarket safety monitoring of new medical products.

STUDY DESIGN AND SETTING

Existing trial-based group sequential approaches have been extended to adjust for confounders, accommodate rare events, and address privacy-related constraints on data sharing. Most adaptations have involved design-based confounder strategies, for example, self-controlled or exposure matching, while analysis-based approaches like regression and weighting have received less attention. We describe the methodology of two new group sequential approaches that use analysis-based confounder adjustment (GS GEE) and weighting (GS IPTW). Using data from the Food and Drug Administration's Sentinel network, we apply both methods in the context of a known positive association: the measles-mumps-rubella-varicella vaccine and seizure risk in infants.

RESULTS

Estimates from both new approaches were similar and comparable to prior studies using design-based methods to address confounding. The time to detection of a safety signal was considerably shorter for GS IPTW, which estimates a risk difference, compared to GS GEE, which provides relative estimates of excess risk.

CONCLUSION

Future group sequential safety surveillance efforts should consider analysis-based confounder adjustment techniques that evaluate safety signals on the risk difference scale to achieve greater statistical power and more timely results.

A Plasma Biomarker Panel to Identify Surgically Resectable Early-Stage Pancreatic Cancer

Background

Blood-based biomarkers for early detection of pancreatic ductal adenocarcinoma (PDAC) are urgently needed. Current biomarkers lack high sensitivity and specificity for population screening. The gold-standard biomarker, CA 19-9, also fails to demonstrate the predictive value necessary for early detection.

Methods

To validate a functional genomics-based plasma migration signature biomarker panel, plasma tissue factor pathway inhibitor (TFPI), tenascin C (TNC-FN III-C), and CA 19-9 levels were measured by enzyme-linked immunosorbent assays in three early-stage PDAC plasma cohorts, including two independent blinded validation cohorts containing a total of 43 stage I, 163 stage II, 86 chronic pancreatitis, 31 acute biliary obstruction, and 108 controls. Logistic regression models developed classification rules combining TFPI and/or TNC-FN III-C with CA 19-9 for patient cases and control subjects, with or without adjustment for age and diabetes status. Model classification performance was evaluated and analyses repeated among subpopulations without diabetes and pancreatitis history. Two-sided P values were calculated using bootstrap method.

Results

The TFPI/TNC-FN III-C/CA 19-9 panel improved CA 19-9 performance in all early-stage cohorts, including discriminating stage IA/IB/IIA, stage IIB, and all early-stage cancer from healthy controls. Statistical significance was reached for a number of subcohorts, including for all early-stage cancer vs healthy controls (cohort 1 AUC = 0.92, 95% CI = 0.86 to 0.96, P  = .04; cohort 3 AUC = 0.83, 95% CI = 0.76 to 0.89, P  = .045). Among subcohorts without diabetes and pancreatitis history, the panel approaches potential clinical utility for early detection to discriminate early-stage PDAC from healthy controls including an area under the curve (AUC) of 0.87 (95% CI = 0.77 to 0.95) for stage I/IIA, an AUC of 0.93 (95% CI = 0.87 to 0.98) for stage IIB, and a statistically significant AUC of 0.89 (95% CI = 0.82 to 0.95) for all early-stage cancer ( P  = .03).

Conclusions

TFPI/TNC-FN III-C migration signature adds statistically significantly to CA 19-9's predictive power to detect early-stage PDAC and may have clinical utility for early detection of surgically resectable PDAC, as well as for enhanced survival from this routinely lethal cancer.

Oxidative pentose phosphate pathway inhibition is a key determinant of antimalarial induced cancer cell death

Despite immense interest in using antimalarials as autophagy inhibitors to treat cancer, it remains unclear whether these agents act predominantly via autophagy inhibition or whether other pathways direct their anti-cancer properties. By comparing the treatment effects of the antimalarials chloroquine (CQ) and quinacrine (Q) on KRAS mutant lung cancer cells, we demonstrate that inhibition of the oxidative arm of the pentose phosphate pathway (oxPPP) is required for antimalarial induced apoptosis. Despite inhibiting autophagy, neither CQ treatment nor RNAi against autophagy regulators (ATGs) promote cell death. In contrast, Q triggers high levels of apoptosis, both in vitro and in vivo, and this phenotype requires both autophagy inhibition and p53-dependent inhibition of the oxPPP. Simultaneous genetic targeting of the oxPPP and autophagy is sufficient to trigger apoptosis in lung cancer cells, including cells lacking p53. Thus, in addition to reduced autophagy, oxPPP inhibition serves as an important determinant of antimalarial cytotoxicity in cancer cells.

Validation sampling can reduce bias in health care database studies: an illustration using influenza vaccination effectiveness

OBJECTIVES

Estimates of treatment effectiveness in epidemiologic studies using large observational health care databases may be biased owing to inaccurate or incomplete information on important confounders. Study methods that collect and incorporate more comprehensive confounder data on a validation cohort may reduce confounding bias.

STUDY DESIGN AND SETTING

We applied two such methods, namely imputation and reweighting, to Group Health administrative data (full sample) supplemented by more detailed confounder data from the Adult Changes in Thought study (validation sample). We used influenza vaccination effectiveness (with an unexposed comparator group) as an example and evaluated each method's ability to reduce bias using the control time period before influenza circulation.

RESULTS

Both methods reduced, but did not completely eliminate, the bias compared with traditional effectiveness estimates that do not use the validation sample confounders.

CONCLUSION

Although these results support the use of validation sampling methods to improve the accuracy of comparative effectiveness findings from health care database studies, they also illustrate that the success of such methods depends on many factors, including the ability to measure important confounders in a representative and large enough validation sample, the comparability of the full sample and validation sample, and the accuracy with which the data can be imputed or reweighted using the additional validation sample information.

Apples and oranges: a comparison of costing methods for obesity

Obesity has escalated to epidemic proportions over the past 30 years resulting in increased disease burden and healthcare costs. The aim of this paper was to analyse different costing methods for obesity. Several databases have been searched to identify eligible literature estimating obesity cost. These were categorized into databases, patient-attributable fraction (PAF) and modelling studies. Studies from the United States were used to explore effects of study designs on cost outcomes. Our results show that cost outcomes are largely affected by underlying study designs, such as population size, age, cost categories (medical expenditure vs. total costs), length of the data collection and body mass index cut-offs. Three study types are likely to have an impact on reported costs, with modelling studies providing the most conservative estimates. Database studies can help to increase the overall awareness of the economic burden of obesity. PAF studies can make the obesity disease more tangible by drawing connections to diseases. Decision makers need to be aware of the different purposes and weaknesses of the studies when interpreting cost outcomes. Further research is needed to refine the existing methods and provide high-quality data accounting for the complexity of the disease.

Vaccination site and risk of local reactions in children 1 through 6 years of age

OBJECTIVE

Our objective was to assess whether the occurrence of medically attended local reactions to intramuscularly administered vaccines varies by injection site (arm versus thigh) in children 1 to 6 years of age.

METHODS

This is a retrospective cohort study of children in the Vaccine Safety Datalink population from 2002 to 2009. Site of injection and the outcome of medically attended local reactions were identified from administrative data.

RESULTS

The study cohort of 1.4 million children received 6.0 million intramuscular (IM) vaccines during the study period. The primary analyses evaluated the IM vaccines most commonly administered alone, which included inactivated influenza, hepatitis A, and diphtheria-tetanus-acellular pertussis (DTaP) vaccines. For inactivated influenza and hepatitis A vaccines, local reactions were relatively uncommon, and there was no difference in risk of these events with arm versus thigh injections. The rate of local reactions after DTaP vaccines was higher, and vaccination in the arm was associated with a significantly greater risk of this outcome compared with vaccination in the thigh, both for children 12 to 35 months (relative risk: 1.88 [95% confidence interval: 1.34-2.65]) and 3 to 6 years of age (relative risk: 1.41 [95% confidence interval: 0.84-2.34]), although this difference was not statistically significant in the older age group.

CONCLUSIONS

Injection in the thigh is associated with a significantly lower risk of a medically attended local reaction to a DTaP vaccination among children 12 to 35 months of age, supporting current recommendations to administer IM vaccinations in the thigh for children younger than 3 years of age.

Modelling obesity trends and related diseases in Eastern Europe

Obesity has increased at an alarming rate across the world and, in turn, rates of non-communicable diseases have escalated. In Eastern Europe, this epidemic has probably occurred at a later stage than the West due to the economic transition following the demise of communism. Knowing how these trends will change is important. We used a micro-simulation model to project obesity trends and related incidence of coronary heart disease and stroke, cancer and type 2 diabetes 20 and 40 years into the future. Where nationally representative data were available, obesity levels were shown to increase with most prominent increases seen amongst men in Latvia and Estonia, and amongst women in Croatia and Latvia. The exception was Lithuania where a decrease in overweight and obesity was observed in both men and women. We showed that interventions effective in reducing obesity would have a significant impact upon the number of new cases of each disease. It is necessary to improve surveillance of obesity and disease incidence as well as implement policies that are effective in reducing body fat.

Contrast ureteropyelography in theatre: standardised flowchart reporting

INTRODUCTION

Urologists perform retrograde contrast studies of the ureters and pelvicalyceal systems in the operating theatre, both for diagnostic purposes and to guide instrumentation. We describe the development of a set of guidelines that aim to standardise the diagnostic quality of these studies and to reduce radiation dose to the patient and theatre staff. The guidelines incorporate a reporting template that allows a urologist's written report to be made available on the picture archiving and com- munication system (PACS) for subsequent multidisciplinary review.

METHODS

Three cycles of audit were conducted to assess the implementation of the guidelines. An independent reviewer rated image quality and screening times. During the audit cycle, the presentation of the guidelines was honed. The end prod- uct is a flowchart and reporting template for use by urologists in the operating theatre.

RESULTS

Phase 1 of the audit included 63 studies, phase 2 included 42 studies and phase 3 included 46 studies. The results demonstrate significant improvements in the number of good quality studies and in the recording of control, contrast and post-procedure images. The mean screening time decreased from 5.0 minutes in phase 1 to 3.2 minutes in phase 3. In phase 3, when in-theatre reporting of the studies by the urologist was added, the handwritten report was scanned in and made available on PACS in 43 of 46 cases (93%). CONCLUSIONS Introduction of guidelines improved retrograde contrast study quality and reduced screening times. A system has been developed to store appropriate pictures and a urologist's report of the study on PACS.

Simulation models of obesity: a review of the literature and implications for research and policy

Simulation models (SMs) combine information from a variety of sources to provide a useful tool for examining how the effects of obesity unfold over time and impact population health. SMs can aid in the understanding of the complex interaction of the drivers of diet and activity and their relation to health outcomes. As emphasized in a recently released report of the Institute or Medicine, SMs can be especially useful for considering the potential impact of an array of policies that will be required to tackle the obesity problem. The purpose of this paper is to present an overview of existing SMs for obesity. First, a background section introduces the different types of models, explains how models are constructed, shows the utility of SMs and discusses their strengths and weaknesses. Using these typologies, we then briefly review extant obesity SMs. We categorize these models according to their focus: health and economic outcomes, trends in obesity as a function of past trends, physiologically based behavioural models, environmental contributors to obesity and policy interventions. Finally, we suggest directions for future research.

The Ribosomal Database Project: improved alignments and new tools for rRNA analysis

The Ribosomal Database Project (RDP) provides researchers with quality-controlled bacterial and archaeal small subunit rRNA alignments and analysis tools. An improved alignment strategy uses the Infernal secondary structure aware aligner to provide a more consistent higher quality alignment and faster processing of user sequences. Substantial new analysis features include a new Pyrosequencing Pipeline that provides tools to support analysis of ultra high-throughput rRNA sequencing data. This pipeline offers a collection of tools that automate the data processing and simplify the computationally intensive analysis of large sequencing libraries. In addition, a new Taxomatic visualization tool allows rapid visualization of taxonomic inconsistencies and suggests corrections, and a new class Assignment Generator provides instructors with a lesson plan and individualized teaching materials. Details about RDP data and analytical functions can be found at http://rdp.cme.msu.edu/.

Evaluation for the design of experience in virtual environments: modeling breakdown of interaction and illusion

New and emerging media technologies have the potential to induce a variety of experiences in users. In this paper, it is argued that the inducement of experience presupposes that users are absorbed in the illusion created by these media. Looking to another successful visual medium, film, this paper borrows from the techniques used in "shaping experience" to hold spectators' attention in the illusion of film, and identifies what breaks the illusion/experience for spectators. This paper focuses on one medium, virtual reality (VR), and advocates a transparent or "invisible style" of interaction. We argue that transparency keeps users in the "flow" of their activities and consequently enhances experience in users. Breakdown in activities breaks the experience and subsequently provides opportunities to identify and analyze potential causes of usability problems. Adopting activity theory, we devise a model of interaction with VR--through consciousness and activity--and introduce the concept of breakdown in illusion. From this, a model of effective interaction with VR is devised and the occurrence of breakdown in interaction and illusion is identified along a continuum of engagement. Evaluation guidelines for the design of experience are proposed and applied to usability problems detected in an empirical study of a head-mounted display (HMD) VR system. This study shows that the guidelines are effective in the evaluation of VR. Finally, we look at the potential experiences that may be induced in users and propose a way to evaluate user experience in virtual environments (VEs) and other new and emerging media.

Performance-improvement strategies can reduce costs

Hospitals continue to be challenged to reduce costs while providing high-quality care. Cost-reduction methods that hospitals can use successfully include cost data, interdisciplinary approaches, benchmarking, clinical pathways, physician profiling, and case management. Cost reduction also can be achieved through performance inprovement. One performance-improvement-strategy is the FOCUS-PDCA model. The letters in the model's name refer to the following steps: Find a process that needs improvement, Organize a team that knows the process, Clarify current knowledge of the process, Understand the process and learn the causes of the variation, Select the improvement opportunities, Plan the change, Do, Check the results, and Act by implementing the change. The FOCUS-PDCA model was used by an East Texas regional hospital to reduce the costs relaed to cholecystectomy surgeries performed there.

The intrinsic factor-vitamin B12 receptor, cubilin, is assembled into trimers via a coiled-coil alpha-helix

A large protein was purified from bovine kidney, using selective extraction with EDTA to solubilize proteins anchored by divalent cation-dependent interactions. An antiserum raised against the purified protein labeled the apical cell surface of the epithelial cells in proximal tubules and the luminal surface of small intestine. Ten peptide sequences, derived from the protein, all matched the recently published sequences for rat (Moestrup, S. K., Kozyraki, R., Kristiansen, M., Kaysen, J. H., Holm Rasmussen, H., Brault, D., Pontillon, F., Goda, F. O., Christensen, E. I., Hammond, T. G., and Verroust, P. J. (1998) J. Biol. Chem. 273, 5235-5242) and human cubilin, a receptor for intrinsic factor-vitamin B12 complexes, identifying the protein as bovine cubilin. In electron microscopy, a three-armed structure was seen, indicating an oligomerization of three identical subunits. This model was supported by the Mr values of about 1,500,000 for the intact protein and 440,000 for its subunits obtained by analytical ultracentrifugation. In a search for a potential assembly domain, we identified a region of heptad repeats in the N-terminal part of the cubilin sequence. Computer-assisted analysis supported the presence of a coiled-coil alpha-helix between amino acids 103 and 132 of the human cubilin sequence and predicted the formation of a triple coiled-coil. We therefore conclude that cubilin forms a noncovalent trimer of identical subunits connected by an N-terminal coiled-coil alpha-helix.

Expression of cyclo-oxygenase 2 in rat brain following kainate treatment

The transcriptional expression of the mitogen-inducible cyclo-oxygenase (COX-2) was investigated by in situ hybridization of kainate-treated rat brains. Kainate treatment rapidly induced COX-2 mRNA in neurons throughout the forebrain which was blocked by pretreatment with MK-801 or NBQX. Transient expression of COX-2 mRNA lasting about 8 h occurred in areas that were resistant to neuronal necrosis, while COX-2 mRNA expression persisted for 24-72 h in regions that were vulnerable. These results show that seizures result in increased COX-2 expression and support the hypothesis that COX-2 could be an important factor in the pathogenesis of delayed neuronal necrosis due to kainate excitotoxicity.

Characterization of native laminin from bovine kidney and comparison with other laminin variants

A comprehensive characterization of laminin isoforms requires access to native preparations of laminins of a defined subunit composition. For this purpose an optimized isolation procedure was developed and shown to be broadly applicable to normal mammalian tissues. The protocol does in addition yield side fractions highly enriched in collagens XII and XIV. The major laminin purified from bovine kidney is indistinguishable from mouse Engelbreth-Holm-Swarm (EHS) tumor laminin in electron microscopy, but contains an A chain that migrates in a position intermediate to the Ae and the Am chains on SDS/PAGE. Antisera raised against mouse EHS-tumor laminin crossreact with B chains, but not with the A chain, of kidney laminin. Further, this A chain is not recognized by antisera raised against the Am chain. Laminins from heart and kidney both contain a significant subpopulation with a 190-kDa polypeptide identified as the B1s chain. The Am-containing laminins from heart and placenta differ morphologically from the Ae-containing EHS laminin in having one short arm that does not have the characteristic globule-rod-globule appearance. Further, the Am-containing laminins show a significantly higher thermal stability of the coiled-coil alpha-helical region in the long arm than does Ae-containing EHS laminin, indicating that certain combinations of laminin chains interact more strongly than others.

Colloidal gold particles as an incompressible atomic force microscope imaging standard for assessing the compressibility of biomolecules

Colloidal gold particles have multiple uses as three-dimensional atomic force microscopy imaging standards because they are incompressible, monodisperse, and spherical. The spherical nature of the particles can be exploited to characterize scanning tip geometry. As uniform spheres, colloidal gold particles may be used to calibrate the vertical dimensions of atomic force microscopy at the nanometer level. The monodisperse and incompressible nature of the gold can be used to characterize the vertical dimensions of coadsorbed biomolecules. Simultaneous measurements of gold with tobacco mosaic virus show that, at the same applied vertical force, the tobacco mosaic virus is undamaged by blunt tips but is compressed or disintegrated under sharper scanning styli, suggesting that specimen degradation is partly a pressure-dependent effect.

A biomechanical comparison of the topspin and backspin forehand approach shots in tennis

Three-dimensional (3-D) high-speed cinematographic techniques were used to record topspin and backspin forehand approach shots hit down-the-line by high-performance players. The direct linear transformation (DLT) technique was used in the 3-D space reconstruction from 2-D images recorded via laterally placed phase-locked cameras operating at 200 Hz. A Mann-Whitney U-test was calculated for the different aspects of the topspin and backspin shots to test for significance (P less than 0.05). A significant difference was recorded between topspin and backspin shots in the angle of the racket at the completion of the backswing. The racket was taken 0.48 rad past a line drawn perpendicular to the back fence for topspin trials, but only rotated 0.86 rad from a line parallel to the net in the backspin shot. Maximum racket velocities occurred prior to impact and were significantly higher in topspin (26.5 m s-1) compared to backspin (16.6 m s-1) trials. This resulted in the topspin trials recording a significantly higher ball velocity compared to backspin trials (27.6 m s-1 vs 21.7 m s-1). Pre-impact racket trajectories revealed that in topspin shots the racket moved on an upward path of 0.48 rad while in backspin shots it moved down at an angle of 0.34 rad. In the topspin trials impact occurred significantly further forward of the front foot than in backspin shots (0.26 m vs 0.05 m) while the angle of the racket was the same for both strokes (0.14 rad behind a line parallel to the net). The mean angle of the racket-face at impact was inclined backwards by 0.11 rad for backspin strokes and rotated forward by 0.13 rad for topspin strokes. Angles of incidence and reflection of the impact between the ball and the court showed that backspin trials had larger angles of incidence and reflection than topspin strokes.

The ribonucleoprotein substrate for a ribosomal RNA-processing nuclease

The Bacillus subtilis RNase M5 activity, responsible for the endonucleolytic maturation of 5 S rRNA, requires two proteins, alpha and beta. The beta component has been purified to homogeneity and shown to correspond to ribosomal protein BL16. The BL16 protein evidently corresponds functionally to Escherichia coli ribosomal protein EL18, as that latter protein also will complement the B. subtilis alpha protein in the RNase M5 reaction. A filter binding assay for the formation of B. subtilis 5 S rRNA-protein complexes was characterized and used to evaluate the association of BL16 protein with some RNAs. A native precursor of 5 S rRNA, containing extra sequences at both termini of the mature domain, binds the ribosomal protein no better than the mature 5 S rRNA; the precursor sequences do not facilitate that interaction. A model is considered in which the precursor segments facilitate, by refolding, the dissociation of processing products prior to the RNase M5 step. Electrostatic versus nonelectrostatic contributions to the BL16-5 S rRNA complex formation were inspected by analyzing variation in apparent association constants as a function of ionic strength. Electrostatic interactions were seen to contribute approximately 65% to the overall binding energy.

The RNA moiety of ribonuclease P is the catalytic subunit of the enzyme

The RNA moieties of ribonuclease P purified from both E. coli (M1 RNA) and B. subtilis (P-RNA) can cleave tRNA precursor molecules in buffers containing either 60 mM Mg2+ or 10 mM Mg2+ plus 1 mM spermidine. The RNA acts as a true catalyst under these conditions whereas the protein moieties of the enzymes alone show no catalytic activity. However, in buffers containing 5-10 mM Mg2+ (in the absence of spermidine) both kinds of subunits are required for enzymatic activity, as shown previously. In the presence of low concentrations of Mg2+, in vitro, the RNA and protein subunits from one species can complement subunits from the other species in reconstitution experiments. When the precursor to E. coli 4.5S RNA is used as a substrate, only the enzyme complexes formed with M1 RNA from E. coli and the protein moieties from either bacterial species are active.

Effect of protein deprivation and a reduced diet on the regenerating rat liver

In rats fed a protein-free, calorie rich diet DNA synthesis is reduced, the mitotic index diminished and the proliferative response imparied. Nevertheless protein deficient hepatocytes retain a remarkable ability to hypertrophy and proliferate after partial hepatectomy. In pair-fed rats on a reduced semi-stravation diet deficient in calories these same parameters are not only diminished but their onset is also delayed. Electron microscopy revealed that the glycogen in the liver cells of these rats was severely depleted. This depletion was considered to be a critical factor in the delayed response to partial hepatectomy. Both groups showed a marked reduction of organelles, especially ribosomes and rough endoplasmic reticulum (RER). Golgi complexes persisted and were conspicuous. Rough endoplasmic reticulum was promptly reformed following partial hepatectomy.