SAIL study of stroke, systemic embolism and bleeding outcomes with warfarin anticoagulation in non-valvular atrial fibrillation (S4-BOW-AF)

Aims

In patients with non-valvular atrial fibrillation (NVAF) prescribed warfarin, the association between guideline defined international normalised ratio (INR) control and adverse outcomes in unknown. We aimed to (i) determine stroke and systemic embolism (SSE) and bleeding events in NVAF patients prescribed warfarin; and (ii) estimate the increased risk of these adverse events associated with poor INR control in this population.

Methods and results

Individual-level population-scale linked patient data were used to investigate the association between INR control and both SSE and bleeding events using (i) the National Institute for Health and Care Excellence (NICE) criteria of poor INR control [time in therapeutic range (TTR) <65%, two INRs <1.5 or two INRs >5 in a 6-month period or any INR >8]. A total of 35 891 patients were included for SSE and 35 035 for bleeding outcome analyses. Mean CHA₂DS₂-VASc score was 3.5 (SD = 1.7), and the mean follow up was 4.3 years for both analyses. Mean TTR was 71.9%, with 34% of time spent in poor INR control according to NICE criteria.SSE and bleeding event rates (per 100 patient years) were 1.01 (95%CI 0.95-1.08) and 3.4 (95%CI 3.3-3.5), respectively, during adequate INR control, rising to 1.82 (95%CI 1.70-1.94) and 4.8 (95% CI 4.6-5.0) during poor INR control.Poor INR control was independently associated with increased risk of both SSE [HR = 1.69 (95%CI = 1.54-1.86), P < 0.001] and bleeding [HR = 1.40 (95%CI 1.33-1.48), P < 0.001] in Cox-multivariable models.

Conclusion

Guideline-defined poor INR control is associated with significantly higher SSE and bleeding event rates, independent of recognised risk factors for stroke or bleeding.

Incident atrial fibrillation and adverse clinical outcomes during extended follow-up of participants recruited to the remote heart rhythm sampling using the AliveCor heart monitor to screen for atrial fibrillation: the REHEARSE-AF study

Aims

Atrial fibrillation (AF) is an important risk factor for stroke, which is commonly asymptomatic, particularly in older patients, and often undetected until cardiovascular events occur. Development of novel technology has helped to improve detection of AF. However, the longer-term benefit of systematic electrocardiogram (ECG) screening on cardiovascular outcomes is unclear.

Methods and results

In the original REHEARSE-AF study, patients were randomized to twice-weekly portable electrocardiogram (iECG) assessment or routine care. After discontinuing the trial portable iECG assessment, electronic health record data sources provided longer-term follow-up analysis. Cox regression was used to provide unadjusted and adjusted hazard ratios (HR) [95% confidence intervals (CI)] for clinical diagnosis, events, and anticoagulant prescriptions during the follow-up period. Over the median 4.2-year follow-up, although a greater number of patients were diagnosed with AF in the original iECG group (43 vs. 31), this was not significant (HR 1.37, 95% CI 0.86-2.19). No differences were seen in the number of strokes/systemic embolisms or deaths between the two groups (HR 0.92, 95% CI 0.54-1.54; HR 1.07, 95% CI 0.66-1.73). Findings were similar when restricted to those with CHADS-VASc ≥ 4.

Conclusion

A 1-year period of home-based, twice-weekly screening for AF increased diagnoses of AF for the screening period but did not lead to increased diagnoses of AF or a reduction in cardiovascular-related events or all-cause death over a median of 4.2 years, even in those at highest risk of AF. These results suggest that benefits of regular ECG screening over a 1-year period are not maintained after cessation of the screening protocol.

Identifying unmet antithrombotic therapeutic need, and implications for stroke and systemic embolism in atrial fibrillation patients: a population-scale longitudinal study

Aims

Guidelines recommend anticoagulation (AC) in atrial fibrillation (AF) to reduce stroke and systemic embolism (SSE) risk; however, implementation has been slow across many populations. This study aimed to quantify the potential impact of changing prevalence of AF, associated risk, and AC prescribing on SSE hospitalizations and death.

Methods and results

We evaluated temporal trends of AF, CHA2DS2-VASc, antithrombotic prescriptions, SSE hospitalizations, death, and their associations between 2012 and 2018 in a longitudinal cohort of AF patients in Wales UK. Multi-state Markov models were used to estimate expected SSE rates given the AC coverage, adjusting for CHA2DS2-VASc scores. SSE rates were modelled for various past and future AC scenarios. A total of 107 137 AF patients were evaluated (mean age = 74 years, 45% female). AF prevalence increased from 1.75 to 2.22% (P-value <0.001). SSE hospitalizations decreased by 18% (2.34-1.92%, P-value <0.001). Increased AC coverage from 50 to 70% was associated with a 37% lower SSE rate, after adjustment for individual time-dependent CHA2DS2VASc scores. The observed AC increase accounted for approximately 80 fewer SSE hospitalizations per 100 000/year. If 90% AC coverage had been achieved since 2012, an estimated 279 SSE per 100 000/year may have been prevented. Our model also predicts that improving AC coverage to 90% over the next 9 years could reduce annual SSE rates by 9%.

Conclusion

We quantified the relationship between observed AC coverage, estimating the potential impact of variation in the timing of large-scale implementation. These data emphasize the importance of timely implementation and the considerable opportunity to improve clinical outcomes in the Wales-AF population.

Achievement of European Society of Cardiology/European Atherosclerosis Society lipid targets in very high-risk patients: Influence of depression and sex

AIMS

To explore differences in the use of lipid lowering therapy and/or achievement of lipid guideline targets in patients with and without prior depression and influence of sex in very high-risk coronary patients.

METHODS & FINDINGS

A retrospective observational cohort study was conducted using individual-level linked electronic health record data in patients who underwent percutaneous coronary intervention (2012-2017) in Wales. The cohort comprised of 13,781 patients (27.4% female), with 26.1% having prior depression. Lipid levels were recorded in 10,050 patients of whom 25% had depression. History of depression was independently associated with not having lipids checked (OR 0.79 95%CI 0.72-0.87 p<0.001). Patients with prior depression were less likely to achieve targets for low density lipoprotein cholesterol (LDL-C <1.8mmol/l), non-high density lipoprotein cholesterol (non-HDL-C <2.6mmol/l) and triglycerides (<2.3mmol/l) than patients without depression (OR 0.86 95%CI 0.78-0.96 p = 0.007, OR 0.80 95%CI 0.69-0.92 p = 0.003 & OR 0.69 95CI% 0.61-0.79 p<0.001 respectively). Females were less likely to achieve targets for LDL-C and non-HDL-C than males (OR 0.55 95%CI 0.50-0.61 p<0.001 & OR 0.63 95%CI 0.55-0.73 p<0.001). There was an additive effect of depression and sex; females with depression were not only least likely to be tested (OR 0.74 95%CI 0.65-0.84 p<0.001) but also (where levels were known) less likely to achieve LDL-C (OR 0.47 95%CI 0.41-0.55 p<0.001) and non-HDL-C targets (OR 0.50 95%CI 0.41-0.60 p<0.001). It was not possible to look at the influence of medication adherence on achievement of lipid targets due to limitations of the use of anonymised routinely-held clinical care data.

CONCLUSION

Patients with prior depression were less likely to have their lipids monitored and achieve guideline targets within 1-year. Females with depression are the least likely to be tested and achieve lipid targets, suggesting not only a greater risk of future events, but also an opportunity to improve care.

Achievement of European guideline-recommended lipid levels post-percutaneous coronary intervention: A population-level observational cohort study

AIMS

European Society of Cardiology/European Atherosclerosis Society 2019 guidelines recommend more aggressive lipid targets in high- and very high-risk patients and the addition of adjuvant treatments to statins in uncontrolled patients. We aimed to assess (a) achievement of prior and new European Society of Cardiology/European Atherosclerosis Society lipid targets and (b) lipid-lowering therapy prescribing in a nationwide cohort of very high-risk patients.

METHODS

We conducted a retrospective observational population study using linked health data in patients undergoing percutaneous coronary intervention (2012-2017). Follow-up was for one-year post-discharge.

RESULTS

Altogether, 10,071 patients had a documented LDL-C level, of whom 48% had low-density lipoprotein cholesterol (LDL-C)<1.8 mmol/l (2016 target) and (23%) <1.4 mmol/l (2019 target). Five thousand three hundred and forty patients had non-high-density lipoprotein cholesterol (non-HDL-C) documented with 57% <2.6 mmol/l (2016) and 37% <2.2 mmol/l (2019). In patients with recurrent vascular events, fewer than 6% of the patients achieved the 2019 LDL-C target of <1.0 mmol/l. A total of 10,592 patients had triglyceride (TG) levels documented, of whom 14% were ≥2.3 mmol/l and 41% ≥1.5 mmol/l (2019). High-intensity statins were prescribed in 56.4% of the cohort, only 3% were prescribed ezetimibe, fibrates or prescription-grade N-3 fatty acids. Prescribing of these agents was lower amongst patients above target LDL-C, non-HDL-C and triglyceride levels. Females were more likely to have LDL-C, non-HDL-C and triglyceride levels above target.

CONCLUSION

There was a low rate of achievement of the new European Society of Cardiology/European Atherosclerosis Society lipid targets in this large post-percutaneous coronary intervention population and relatively low rates of intensive lipid-lowering therapy prescribing in those with uncontrolled lipids. There is considerable potential to optimise lipid-lowering therapy further through statin intensification and appropriate use of novel lipid-lowering therapy, especially in women.

An observational study of international normalized ratio control according to NICE criteria in patients with non-valvular atrial fibrillation: the SAIL Warfarin Out of Range Descriptors Study (SWORDS)

AIMS 

In patients with non-valvular atrial fibrillation prescribed warfarin, the UK National Institute of Health and Care Excellence (NICE) defines poor anticoagulation as a time in therapeutic range (TTR) of <65%, any two international normalized ratios (INRs) within a 6-month period of ≤1.5 ('low'), two INRs ≥5 within 6 months, or any INR ≥8 ('high'). Our objectives were to (i) quantify the number of patients with poor INR control and (ii) describe the demographic and clinical characteristics associated with poor INR control.

METHOD AND RESULTS

Linked anonymized health record data for Wales, UK (2006-2017) was used to evaluate patients prescribed warfarin who had at least 6 months of INR data. 32 380 patients were included. In total, 13 913 (43.0%) patients had at least one of the NICE markers of poor INR control. Importantly, in the 24 123 (74.6%) of the cohort with an acceptable TTR (≥65%), 5676 (23.5%) had either low or high INR readings at some point in their history. In a multivariable regression female gender, age (≥75 years), excess alcohol, diabetes heart failure, ischaemic heart disease, and respiratory disease were independently associated with all markers of poor INR control.

CONCLUSION 

Acceptable INR control according to NICE standards is poor. Of those with an acceptable TTR (>65%), one-quarter still had unacceptably low or high INR levels according to NICE criteria. Thus, only using TTR to assess effectiveness with warfarin has the potential to miss a large number of patients with non-therapeutic INRs who are likely to be at increased risk.

Early Discontinuation of P2Y12 Antagonists and Adverse Clinical Events Post-Percutaneous Coronary Intervention: A Hospital and Primary Care Linked Cohort

Background

Early discontinuation of P2Y₁₂ antagonists post–percutaneous coronary intervention may increase risk of stent thrombosis or nonstent recurrent myocardial infarction. Our aims were to (1) analyze the early discontinuation rate of P2Y₁₂ antagonists post–percutaneous coronary intervention, (2) explore factors associated with early discontinuation, and (3) analyze the risk of major adverse cardiovascular events (death, acute coronary syndrome, revascularization, or stroke) associated with discontinuation from a prespecified prescribing instruction of 1 year.

Method and Results

We studied 2090 patients (2011–2015) who were recommended for clopidogrel for 12 months (+aspirin) post–percutaneous coronary intervention within a retrospective observational population cohort. Relationships between clopidogrel discontinuation and major adverse cardiac events were evaluated over 18‐month follow‐up. Discontinuation of clopidogrel in the first 4 quarters was low at 1.1%, 2.6%, 3.7%, and 6.1%, respectively. Previous revascularization, previous ischemic stroke, and age >80 years were independent predictors of early discontinuation. In a time‐dependent multiple regression model, clopidogrel discontinuation and bleeding (hazard ratio=1.82 [1.01–3.30] and hazard ratio=5.30 [3.14–8.94], respectively) were independent predictors of major adverse cardiac events as were age <49 and ≥70 years (versus those aged 50–59 years), hypertension, chronic kidney disease stage 4+, previous revascularization, ischemic stroke, and thromboembolism. Furthermore, in those with both bleeding and clopidogrel discontinuation, hazard ratio for major adverse cardiac events was 9.34 (3.39–25.70).

Conclusions

Discontinuation of clopidogrel is low in the first year post–percutaneous coronary intervention, where a clear discharge instruction to treat for 1 year is provided. Whereas this is reassuring from the population level, at an individual level discontinuation earlier than the intended duration is associated with an increased rate of adverse events, most notably in those with both bleeding and discontinuation.

Myocardial infarction and heart failure hospitalization rates in Maine, USA - variability along the urban-rural continuum

INTRODUCTION

Cardiovascular disease, including myocardial infarction (MI) and heart failure (HF), remains the leading cause of death in wealthy countries and is of increasing concern in low- and middle-income countries as risk factors such as smoking and obesity become more common around the globe. Within each country the health burden of MI and HF generally falls more heavily on those who live in rural areas and on those who live in communities with lower average socioeconomic status (SES). Hospitalization rates are an important measure of community health because high rates may indicate a high burden of poor health, while inappropriately low rates (low hospitalization rates absent evidence of average good health) may indicate underutilization of health services. The objective of this study was to determine the predictors of MI and HF hospitalization rates at town level in the State of Maine, USA. Maine has large variations in wealth and along the urban-rural continuum at town level. Because our results shed light on variations in health and health-seeking behavior for different Maine populations (such as those living closer vs further from hospitals) they may be of interest to providers of healthcare to people who live in areas remote from healthcare, and to people who face other barriers to good cardiovascular health.

METHODS

To determine predictors of HF and MI hospitalization in Maine, we constructed a geographic information system (GIS) for Maine's towns using publicly available electronic map layers, year 2000 census data, and electronic hospitalization records for all Maine hospitals. This GIS generated age-corrected MI and HF hospitalization rates for 1998-2002 as dependent variables and the following independent variables: poverty rate, unemployment rate, median income, educational attainment, rurality, physician density, and distance to the closest hospital. Univariable and multiple linear regression analysis were then performed to determine the significant predictors of MI and HF hospitalization rates.

RESULTS

During the 5-year study period there were 24 452 hospitalizations of Maine residents to Maine hospitals for MI and 20 330 for HF. In multiple linear regression analysis, greater unemployment, a larger fraction of the population living in poverty, and proximity to a hospital predicted higher MI hospitalization rate (p = 0.000, r-sq = 19.1%) while greater unemployment and proximity to a hospital predicted higher HF hospitalization rate (p = 0.000, r-sq = 8.4%).

CONCLUSIONS

Our finding that higher MI and HF hospitalization rates were predicted for towns that had lower SES is in agreement with many previous studies and shows the importance of these variables to health, even in a setting such as Maine with large variability in rurality. The negative relationship between the distance to a hospital and hospitalization rates likely does not represent better health in those living remotely from healthcare. Rather, it may indicate that people who live in communities distant from hospitals are less likely to seek hospitalization. This suggests that patient behavior as well as socioeconomic status may impact heart-related hospitalization in Maine. It highlights the importance of patient and provider education to ensure that people who live remotely from health care are hospitalized appropriately.

SCP1, a 356 023 bp linear plasmid adapted to the ecology and developmental biology of its host, Streptomyces coelicolor A3(2)

The sequencing of the entire genetic complement of Streptomyces coelicolor A3(2) has been completed with the determination of the 365,023 bp sequence of the linear plasmid SCP1. Remarkably, the functional distribution of SCP1 genes somewhat resembles that of the chromosome: predicted gene products/functions include ECF sigma factors, antibiotic biosynthesis, a gamma-butyrolactone signalling system, members of the actinomycete-specific Wbl class of regulatory proteins and 14 secreted proteins. Some of these genes are among the 18 that contain a TTA codon, making them targets for the developmentally important tRNA encoded by the bldA gene. RNA analysis and gene fusions showed that one of the TTA-containing genes is part of a large bldA-dependent operon, the gene products of which include three proteins isolated from the spore surface by detergent washing (SapC, D and E), and several probable metabolic enzymes. SCP1 shows much evidence of recombinational interactions with other replicons and transposable elements during its history. For example, it has two sets of partitioning genes (which may explain why an integrated copy of SCP1 partially suppressed the defective partitioning of a parAB-deleted chromosome during sporulation). SCP1 carries a cluster of probable transfer determinants and genes encoding likely DNA polymerase III subunits, but it lacks an obvious candidate gene for the terminal protein associated with its ends. This may be related to atypical features of its end sequences.

Complete genome sequence of the model actinomycete Streptomyces coelicolor A3(2)

Streptomyces coelicolor is a representative of the group of soil-dwelling, filamentous bacteria responsible for producing most natural antibiotics used in human and veterinary medicine. Here we report the 8,667,507 base pair linear chromosome of this organism, containing the largest number of genes so far discovered in a bacterium. The 7,825 predicted genes include more than 20 clusters coding for known or predicted secondary metabolites. The genome contains an unprecedented proportion of regulatory genes, predominantly those likely to be involved in responses to external stimuli and stresses, and many duplicated gene sets that may represent 'tissue-specific' isoforms operating in different phases of colonial development, a unique situation for a bacterium. An ancient synteny was revealed between the central 'core' of the chromosome and the whole chromosome of pathogens Mycobacterium tuberculosis and Corynebacterium diphtheriae. The genome sequence will greatly increase our understanding of microbial life in the soil as well as aiding the generation of new drug candidates by genetic engineering.

The C termini of constitutive nitric-oxide synthases control electron flow through the flavin and heme domains and affect modulation by calmodulin

The sequences of nitric-oxide synthase flavin domains closely resemble that of NADPH-cytochrome P450 reductase (CPR). However, all nitric-oxide synthase (NOS) isoforms are 20-40 residues longer in the C terminus, forming a "tail" that is absent in CPR. To investigate its function, we removed the 33 and 42 residue C termini from neuronal NOS (nNOS) and endothelial NOS (eNOS), respectively. Both truncated enzymes exhibited cytochrome c reductase activities without calmodulin that were 7-21-fold higher than the nontruncated forms. With calmodulin, the truncated and wild-type enzymes reduced cytochrome c at approximately equal rates. Therefore, calmodulin functioned as a nonessential activator of the wild-type enzymes and a partial noncompetitive inhibitor of the truncated mutants. Truncated nNOS and eNOS plus calmodulin catalyzed NO formation at rates that were 45 and 33%, respectively, those of their intact forms. Without calmodulin, truncated nNOS and eNOS synthesized NO at rates 14 and 20%, respectively, those with calmodulin. By using stopped-flow spectrophotometry, we demonstrated that electron transfer into and between the two flavins is faster in the absence of the C terminus. Although both CPR and intact NOS can exist in a stable, one-electron-reduced semiquinone form, neither of the truncated enzymes do so. We propose negative modulation of FAD-FMN interaction by the C termini of both constitutive NOSs.

Mortality impact of an integrated community cardiovascular health program

BACKGROUND

Preventing cardiovascular disease through community interventions makes theoretical sense but has been difficult to demonstrate. We set out to determine whether a community cardiovascular health program had an impact on mortality.

DESIGN

Program evaluation plus ecologic observational analysis of program encounters and mortality rates with external comparisons.

SETTING

Franklin County and two comparison counties in rural Maine.

PARTICIPANTS

Program encountered >50% of regional adults, broadly distributed by site, gender, and age.

INTERVENTIONS

From 1974 to 1994, a community program, integrated with primary medical care and staffed by professional nurses, provided education, screening, counseling, referral, tracking, and follow-up for cardiovascular risk factors.

MAIN OUTCOME MEASURES

Age-adjusted mortality rates (total, heart, coronary, cerebrovascular, cancer) for three counties and Maine, plus annual program encounters.

RESULTS

Relative to Maine, the Franklin heart disease death rate was 0.97 at baseline (1960-1969; 95% confidence interval, 0.91 to 1.03), 0.91 during the program (0.85 to 0.97), 0.83 during the 11 years of program growth (0.78 to 0.88), but 1.0 during the 10 years of decreasing encounters. Franklin's total death rate was 1.01 at baseline, 0.95 during the program (0.92 to 0.98), and 0.90 during program growth (0.86 to 0. 94). Results were similar for coronary disease, stroke, and cancer. Relative death rates did not fall in either comparison county. Nurse-client encounters totaled 120,280 over 21 years. Relative to Maine, heart disease death rates correlated inversely with program encounters (r = -0.53) but not with unemployment or physician supply.

CONCLUSIONS

Integrated with primary medical care, a comprehensive, nurse-mediated community cardiovascular health program in rural Maine has been associated with significant time-dependent and dose-dependent reductions in cardiovascular and total mortality.

Chandra X-Ray Observations of the Hydra A Cluster: An Interaction between the Radio Source and the X-Ray-emitting Gas

We present Chandra X-ray observations of the Hydra A cluster of galaxies, and we report the discovery of structure in the central 80 kpc of the cluster's X-ray-emitting gas. The most remarkable structures are depressions in the X-ray surface brightness, approximately 25-35 kpc in diameter, that are coincident with Hydra A's radio lobes. The depressions are nearly devoid of X-ray-emitting gas, and there is no evidence for shock-heated gas surrounding the radio lobes. We suggest that the gas within the surface brightness depressions was displaced as the radio lobes expanded subsonically, leaving cavities in the hot atmosphere. The gas temperature declines from 4 keV at 70 kpc to 3 keV in the inner 20 kpc of the brightest cluster galaxy (BCG), and the cooling time of the gas is approximately 600 Myr in the inner 10 kpc. These properties are consistent with the presence of an approximately 34 M middle dot in circle yr-1 cooling flow within a 70 kpc radius. Bright X-ray emission is present in the BCG surrounding a recently accreted disk of nebular emission and young stars. The star formation rate is commensurate with the cooling rate of the hot gas within the volume of the disk, although the sink for the material that may be cooling at larger radii remains elusive. A bright, unresolved X-ray source is present in the BCG's nucleus, coincident with the radio core. Its X-ray spectrum is consistent with a power law absorbed by a foreground NH approximately 4x1022 cm-2 column of hydrogen. This column is roughly consistent with the hydrogen column seen in absorption toward the less, similar24 pc diameter VLBA radio source. Apart from the point source, no evidence for excess X-ray absorption above the Galactic column is found.

Chandra X-Ray Detection of the Radio Hot Spots of 3C 295

An observation of the radio galaxy 3C 295 during the calibration phase of the Chandra X-Ray Observatory reveals X-ray emission from the core of the galaxy, from each of the two prominent radio hot spots, and from the previously known cluster gas. We discuss the possible emission processes for the hot spots and argue that a synchrotron self-Compton (SSC) model is preferred for most or all of the observed X-ray emission. SSC models with near-equipartition fields thus explain the X-ray emission from the hot spots in the two highest surface brightness FR II radio galaxies, Cygnus A and 3C 295. This lends weight to the assumption of equipartition and suggests that relativistic protons do not dominate the particle energy density.

In vivo native cellular fluorescence and histological characteristics of head and neck cancer

Native cellular fluorescence (NCF) represents the innate capacity of tissues to absorb and emit light of a specified wavelength. The ability to define the relationship of in vivo NCF with biological characteristics of neoplastic disease may allow for an improved understanding of the clinical course of disease. Head and neck cancers from 35 patients were evaluated in vivo for NCF characteristics using a xenon lamp-based spectrometer coupled to a handheld fiberoptic probe. Spectral assessment was limited to lambda 450-nm emission characteristics, in which tissues were excited at various wavelengths, ranging from lambda 290 nm to lambda 415 nm, and the intensity of lambda 450 nm emission was recorded. Each cancer was subsequently biopsied and assessed for histological differentiation by a pathologist who was blinded to NCF analysis. Considerable variation in spectral characteristics between head and neck cancers was identified, which was determined, in part, by NCF characteristics of the normal mucosa from the same patient. Poorly differentiated tumors were more likely than well- or moderately differentiated tumors to have lower excitation maxima (P < 0.05 by ANOVA). Most significantly, the tumor differentiation status, as well as the probability of demonstrating recurrent disease, could also be related to the NCF characteristics of the patient's normal mucosa from the same site within the upper aerodigestive tract. NCF analysis may represent an effective tool to identify biological characteristics of head and neck tumors in vivo without the need for invasive biopsies. Results suggest the need to explore the determinants of NCF characteristics expressed by clinically normal mucosa.

Lipid lowering in a multidisciplinary clinic compared with primary physician management

A multidisciplinary lipid reduction clinic achieved greater reduction of serum cholesterol when compared with primary physicians among patients with coronary heart disease. The lipid clinic was more likely than the primary physicians to prescribe lipid-lowering medication, to prescribe multiple medications, and to use drug doses in excess of the "starting dose."

An autoinhibitory control element defines calcium-regulated isoforms of nitric oxide synthase

Nitric oxide synthases (NOSs) are classified functionally, based on whether calmodulin binding is Ca2+-dependent (cNOS) or Ca2+-independent (iNOS). This key dichotomy has not been defined at the molecular level. Here we show that cNOS isoforms contain a unique polypeptide insert in their FMN binding domains which is not shared with iNOS or other related flavoproteins. Previously identified autoinhibitory domains in calmodulin-regulated enzymes raise the possibility that the polypeptide insert is the autoinhibitory domain of cNOSs. Consistent with this possibility, three-dimensional molecular modeling suggested that the insert originates from a site immediately adjacent to the calmodulin binding sequence. Synthetic peptides derived from the 45-amino acid insert of endothelial NOS were found to potently inhibit binding of calmodulin and activation of cNOS isoforms. This inhibition was associated with peptide binding to NOS, rather than free calmodulin, and inhibition could be reversed by increasing calmodulin concentration. In contrast, insert-derived peptides did not interfere with the arginine site of cNOS, as assessed from [3H]NG-nitro-L-arginine binding, nor did they potently effect iNOS activity. Limited proteolysis studies showed that calmodulin's ability to gate electron flow through cNOSs is associated with displacement of the insert polypeptide; this is the first specific calmodulin-induced change in NOS conformation to be identified. Together, our findings strongly suggest that the insert is an autoinhibitory control element, docking with a site on cNOSs which impedes calmodulin binding and enzymatic activation. The autoinhibitory control element molecularly defines cNOSs and offers a unique target for developing novel NOS activators and inhibitors.

Neuroimaging of AIDS. I. Fungal infections of the central nervous system

Fungal infections of the central nervous system are quite uncommon and most frequently occur in immunocompromised patients, such as those with AIDS. This article outlines the most common fungal infections that occur in the central nervous system. Even though fungal infections of the central nervous system, other than cryptococcosis, are rare in the AIDS population, one should recognize the findings and consider the diagnosis.

Neurosyphilis in patients with AIDS

Syphilis has become much more prevalent because of the dramatic increase in immunocompromised patients. The increase in immunocompromised patients is mainly secondary to AIDS. This article is put forth to refamiliarize the reader with syphilis, specifically neurosyphilis. The neurologic symptomatology and neuroimaging characteristics are presented so that one can recognize the findings and consider the diagnosis of neurosyphilis when confronted with a patient with AIDS.

Thiophosphorylation independently activates each head of smooth muscle myosin in vitro

To determine whether thiophosphorylation of the 20-kDa myosin light chain activates each head of smooth muscle myosin independently of the head with which it is paired, chicken gizzard smooth muscle myosin was randomly thiophosphorylated, producing a mixture of unphosphorylated and singly and doubly thiophosphorylated myosin. Thiophosphorylation levels were measured by glycerol-urea gels, and the activity of this myosin was determined by actin-activated adenosinetriphosphatase measurements and in an in vitro motility assay, where the velocity of actin filaments moving over a myosin-coated surface is measured. Activity at each thiophosphorylation level was similar to that previously observed for mixtures of unphosphorylated and doubly thiophosphorylated myosin (D. E. Harris, S. S. Work, R. K. Wright, N. R. Alpert, and D. M. Warshaw. J. Muscle Res. Cell Motil. 15: 11-19, 1994). All doubly thiophosphorylated myosin was then formed into filaments and removed from randomly thiophosphorylated myosin by centrifugation. The remaining myosin (mixture of unphosphorylated and singly phosphorylated myosin), which could not polymerize because of their conformation, retained approximately 70% activity compared with mixtures of unphosphorylated and doubly thiophosphorylated myosin. Thus a thiophosphorylated smooth muscle myosin head can produce substantial biochemical and mechanical activity, even when it is paired with an unphosphorylated partner.

Cardiac V1 and V3 myosins differ in their hydrolytic and mechanical activities in vitro

The two mammalian cardiac myosin heavy chain isoforms, alpha and beta, have 93% amino acid homology, but hearts expressing these myosins exhibit marked differences in their mechanical activities. To further understand the function of these cardiac myosins as molecular motors, we compared the ability of these myosins to hydrolyze ATP and to both translocate actin filaments and generate force in an in vitro motility assay. V1 myosin has twice the actin-activated ATPase activity and three times the actin filament sliding velocity when compared with V3 myosin. In contrast, the force-generating ability of these myosins is quite different when the total force produced by a small population of myosin molecules (> 50) is examined. V1 myosin produces only one half the average cross-bridge force of V3 myosin. With discrete areas of primary structural heterogeneity known to exist between alpha and beta heavy chains, the differences we report in the hydrolytic and mechanical activities of the motors are explored in the context of potential structural and kinetic differences between the V1 and V3 myosins.

The essential light chain is required for full force production by skeletal muscle myosin

Myosin, a molecular motor that is responsible for muscle contraction, is composed of two heavy chains each with two light chains. The crystal structure of subfragment 1 indicates that both the regulatory light chains (RLCs) and the essential light chains (ELCs) stabilize an extended alpha-helical segment of the heavy chain. It has recently been shown in a motility assay that removal of either light chain markedly reduces actin filament sliding velocity without a significant loss in actin-activated ATPase activity. Here we demonstrate by single actin filament force measurements that RLC removal has little effect on isometric force, whereas ELC removal reduces isometric force by over 50%. These data are interpreted with a simple mechanical model where subfragment 1 behaves as a torque motor whose leyer arm length is sensitive to light-chain removal. Although the effect of removing RLCs fits within the confines of this model, altered crossbridge kinetics, as reflected in a reduced unloaded duty cycle, probably contributes to the reduced velocity and force production of ELC-deficient myosins.

Smooth, cardiac and skeletal muscle myosin force and motion generation assessed by cross-bridge mechanical interactions in vitro

Differences in the mechanical properties of mammalian smooth, skeletal, and cardiac muscle have led to the proposal that the myosin isozymes expressed by these tissues may differ in their molecular mechanics. To test this hypothesis, mixtures of fast skeletal, V1 cardiac, V3 cardiac and smooth muscle (phosphorylated and unphosphorylated) myosin were studied in an in vitro motility assay in which fluorescently-labelled actin filaments are observed moving over a myosin coated surface. Pure populations of each myosin produced actin filament velocities proportional to their actin-activated ATPase rates. Mixtures of two myosin species produced actin filament velocities between those of the faster and slower myosin alone. However, the shapes of the myosin mixture curves depended upon the types of myosins present. Analysis of myosin mixtures data suggest that: (1) the two myosins in the mixture interact mechanically and (2) the same force-velocity relationship describes a myosin's ability to operate over both positive and negative forces. These data also allow us to rank order the myosins by their average force per cross-bridge and ability to resist motion (phosphorylated smooth > skeletal = V3 cardiac > V1 cardiac). The results of our study may reflect the mechanical consequence of multiple myosin isozyme expression in a single muscle cell.

Clinical effectiveness of behavioral signs for screening chronic low-back pain patients in a work-oriented physical rehabilitation program

This prospective study investigated the relationship between behavioral sign scores (from Waddell) and the return to work status of chronic low-back pain patients who completed a work-oriented physical rehabilitation program without formal facility-related psychologic or social services. Further, the authors monitored the effect of this program on changing these scores. The program consisted of physical reconditioning through resistive exercises, flexibility and aerobic training, posture and body mechanics education, and progressive work simulation tasks and activities of daily living. One hundred eighty-three nonworking or partially disabled low-back pain patients with an average duration of 8.7 months' disability were included in the study. The presence of each of eight behavioral signs was tested for on entry and again on completion of the program. Analysis showed a significant drop in behavioral sign scores for patients who successfully returned to work. There was no significant reduction in scores for patients who did not return to work. The results suggest these signs may predict the effectiveness of treating chronic low-back pain patients in a return-to-work physical rehabilitation program. Conversely, screening for behavioral signs may identify low-back pain patients who would benefit from intensive behavioral and psychiatric testing and intervention efforts.

Smooth and skeletal muscle myosin both exhibit low duty cycles at zero load in vitro

Smooth muscle's stress equals that of skeletal muscle with less myosin. Thus, under isometric conditions, smooth muscle myosin may spend a greater fraction of its cycle time attached to actin in a high force state (i.e. higher duty cycle). If so, then smooth muscle myosin may also have a higher duty cycle under unloaded conditions. To test this, we used an in vitro motility assay in which fluorescently labeled actin filaments move freely over a sparsely coated (5-100 micrograms/ml) myosin surface. Actin filament velocity (V) was a function of the number of cross-bridges capable of interacting with an actin filament (N) and the duty cycle (f), V = (a x Vmax) x (1-(1-f)N) (Uyeda et al., 1990; Harada et al., 1990). N was estimated from the myosin density on the motility surface and the actin filament length. Data for V versus N were fit to the above equation to predict f. The duty cycle of smooth muscle myosin (4.0 +/- 0.7%) was not significantly different from that of skeletal muscle myosin (3.8 +/- 0.5%) in agreement with values estimated by Uyeda et al. (1990) for skeletal muscle myosin under unloaded conditions. The duty cycles of smooth and skeletal muscle myosin may still differ under isometric conditions.

Smooth and skeletal muscle actin are mechanically indistinguishable in the in vitro motility assay

Smooth muscle produces as much stress as skeletal muscle with less myosin. To determine if the actin isoforms specific to smooth muscle contribute to the enhanced force generation, the motility of actin filaments from smooth and skeletal muscle were compared in an in vitro assay in which single fluorescently labeled actin filaments slide over a myosin-coated coverslip. No difference was observed between the velocity of smooth versus skeletal muscle actin filaments over either smooth or skeletal muscle myosin over a large range of assay conditions (changes in pH, ionic strength, and [ATP]). Similarly, no difference was observed between the two actins when the filaments moved under load over mixtures of phosphorylated smooth and skeletal muscle myosin. Thus, it appears that the actin isoforms of smooth and skeletal muscle are mechanically indistinguishable in the motility assay and that smooth muscle's enhanced force generation may originate within the myosin molecule specific to smooth muscle.

Nucleotide sequences of the rabbit alpha-smooth-muscle and beta-non-muscle actin mRNAs

We report the characterization of cDNAs encoding two actin isoforms (alpha-smooth muscle and beta-non-muscle) from the rabbit uterus. These isoforms have extensive amino acid and nucleotide sequence homology to the corresponding mouse and human isoforms.

Length vs. active force relationship in single isolated smooth muscle cells

The length vs. active force relationship (L-F) may provide information about changes in smooth muscle contractile protein interactions as muscle length changes. To characterize the L-F in single toad stomach smooth muscle cells, cells were attached to a force measurement system, electrically stimulated, and isometric force and elastic modulus (an estimate of the number of attached cross bridges) determined at different cell lengths. Cells generated maximum stress (Pmax = 152.5 mN/mm2) and elastic modulus (Eact = 0.68 x 10(4) mN/mm2) at their rest length (Lcell = 78.0 microns; distance between cell attachments). At shorter lengths, active force and elastic modulus declined proportionally with active force eliminated at 0.4 Lcell. Stretching the relaxed cells up to 1.4 Lcell shifted the subsequent L-F along the length axis by the amount of the stretch but did not change Pmax or the shape of the L-F. In activated cells, force was a function of cell length rather than of shortening history. We interpret these findings as evidence that 1) Lcell is close to the optimum length for force generation, 2) the decline in force at lengths less than Lcell results from a reduced number of attached cross bridges, and 3) stretching relaxed smooth muscle cells may not move the contractile units to new positions on their L-F.

Slowing of velocity during isotonic shortening in single isolated smooth muscle cells. Evidence for an internal load

In single smooth muscle cells, shortening velocity slows continuously during the course of an isotonic (fixed force) contraction (Warshaw, D.M. 1987. J. Gen. Physiol. 89:771-789). To distinguish among several possible explanations for this slowing, single smooth muscle cells were isolated from the gastric muscularis of the toad (Bufo marinus) and attached to an ultrasensitive force transducer and a length displacement device. Cells were stimulated electrically and produced maximum stress of 144 mN/mm2. Cell force was then reduced to and maintained at preset fractions of maximum, and cell shortening was allowed to occur. Cell stiffness, a measure of relative numbers of attached crossbridges, was measured during isotonic shortening by imposing 50-Hz sinusoidal force oscillations. Continuous slowing of shortening velocity was observed during isotonic shortening at all force levels. This slowing was not related to the time after the onset of stimulation or due to reduced isometric force generating capacity. Stiffness did not change significantly over the course of an isotonic shortening response, suggesting that the observed slowing was not the result of reduced numbers of cycling crossbridges. Furthermore, isotonic shortening velocity was better described as a function of the extent of shortening than as a function of the time after the onset of the release. Therefore, we propose that slowing during isotonic shortening in single isolated smooth muscle cells is the result of an internal load that opposes shortening and increases as cell length decreases.

Mechanical transients of single toad stomach smooth muscle cells. Effects of lowering temperature and extracellular calcium

Smooth muscle's slow, economical contractions may relate to the kinetics of the crossbridge cycle. We characterized the crossbridge cycle in smooth muscle by studying tension recovery in response to a small, rapid length change (i.e., tension transients) in single smooth muscle cells from the toad stomach (Bufo marinus). To confirm that these tension transients reflect crossbridge kinetics, we examined the effect of lowering cell temperature on the tension transient time course. Once this was confirmed, cells were exposed to low extracellular calcium [( Ca2+]o) to determine whether modulation of the cell's shortening velocity by changes in [Ca2+]o reflected the calcium sensitivity of one or more steps in the crossbridge cycle. Single smooth muscle cells were tied between an ultrasensitive force transducer and length displacement device after equilibration in temperature-controlled physiological saline having either a low (0.18 mM) or normal (1.8 mM) calcium concentration. At the peak of isometric force, after electrical stimulation, small, rapid (less than or equal to 1.8% cell length in 3.6 ms) step stretches and releases were imposed. At room temperature (20 degrees C) in normal [Ca2+]o, tension recovery after the length step was described by the sum of two exponentials with rates of 40-90 s-1 for the fast phase and 2-4 s-1 for the slow phase. In normal [Ca2+]o but at low temperature (10 degrees C), the fast tension recovery phase slowed (apparent Q10 = 1.9) for both stretches and releases whereas the slow tension recovery phase for a release was only moderately affected (apparent Q10 = 1.4) while unaffected for a stretch. Dynamic stiffness was determined throughout the time course of the tension transient to help correlate the tension transient phases with specific step(s) in the crossbridge cycle. The dissociation of tension and stiffness, during the fast tension recovery phase after a release, was interpreted as evidence that this recovery phase resulted from both the transition of crossbridges from a low- to high-force producing state as well as a transient detachment of crossbridges. From the temperature studies and dynamic stiffness measurements, the slow tension recovery phase most likely reflects the overall rate of crossbridge cycling. From the tension transient studies, it appears that crossbridges cycle slower and have a longer duty cycle in smooth muscle. In low [Ca2+]o at 20 degrees C, little effect was observed on the form or time course of the tension transients.(ABSTRACT TRUNCATED AT 400 WORDS)

Site-specific semisynthetic variant of human hemoglobin

A single round of Edman degradation was employed to remove the NH2-terminal valine from isolated alpha chains of human hemoglobin. Reconstitution of normal beta chains with truncated or substituted alpha chains was used to form truncated (des-Val1-alpha 1) and substituted ([[1-13C]Gly1]alpha 1) tetrameric hemoglobin analogs. Structural homology of the analogs with untreated native hemoglobin was established by using several spectroscopic and physical methods. Functional studies indicate that the reconstituted tetrameric protein containing des-Val1-alpha chains has a higher affinity for oxygen, is less influenced by chloride ions or 2,3-bisphosphoglycerate, and shows lower cooperativity than native hemoglobin. These results confirm the key functional role of the alpha-chain NH2 terminus in mediating cooperative oxygen binding across the dimer interface. The NH2-terminal pK1/2 value was determined for the [13C]glycine-substituted analog to be 7.46 +/- 0.09 at 15 degrees C in the carbon monoxide-liganded form. This value, measured directly by 13C NMR, agrees with the determination made by the less-direct 13CO2 method and confirms the role of this residue as a contributor to the alkaline Bohr effect; however, it is inconsistent with the presence of an NH2-terminal salt bridge to the carboxylate of Arg-141 of the alpha chain in the liganded form.

A new non-covalent complex of semisynthetically modified tryptic fragments of cytochrome c

We have prepared a semisynthetic analogue of fully acetimidylated horse cytochrome c, a complex in which the peptide bond between residues glycine-37 and arginine-38 is lacking. In contrast with the complex that we have previously described [Harris & Offord (1977) Biochem. J. 161, 12-25], in which the break in continuity is between residues arginine-38 and lysine-39, the new analogue has a nearly normal redox potential, and can more fully restore succinate oxidation to mitochondria depleted of cytochrome c. Studies of this and other analogues lead us to propose an explanation for the low biological activity of complex (1-38)-(39-104) and a role for the invariance of arginine-38.

Aliphatic semisynthetic variants of the amino-terminal residue of sperm whale myoglobin: enrichment with 13C and determination and interpretation of terminal pK values

The synthesis of a series of myoglobins substituted in the amino-terminal residue to provide variation in the aliphatic nature of the side chain and enrichment in 13C was accomplished by semisynthetic methods. The replacements for valine, the native first residue, included 13C-enriched glycine, alanine, valine, leucine, and isoleucine. The products were extensively characterized and found to be virtually indistinguishable by most physical methods. 13C NMR spectroscopy showed significant differences in the amino-terminal pK value, ranging from 7.72 for [Gly1]myoglobin to 7.15 for [Leu1]myoglobin. Consideration of the electrostatic effects of the charge matrix indicated a balance of interactions at this site not significantly altered by these variations in the side chain. By examination of the crystal structure, consideration of earlier work regarding the interactions of the side chain of Leu-2, and data regarding the motions of the terminal residue, it was concluded that the interaction of the side chain of the first residue with the hydrophobic cluster formed primarily by close contact of invariant residues Leu-2 and Leu-137 was the primary cause for the reduction in terminal pK values seen for the larger aliphatics. By restricting the freedom of the residue, this interaction limits the available hydration volume and consequently favors the unprotonated form of the amine. The concurrent observation of both functional elements in the series of alpha-amino-terminal residues brings out the interrelated consequences for the two categories of solvent interactions controlling structural and functional properties in a graded way.

The myoglobin of rodents Proechimys guairae (casiragua) and Mus musculus (house mouse)

The amino acid sequences of the myoglobins of two rodents, the casiragua and the house mouse, have been determined. The myoglobin of casiragua differs from that of viscacha (another hystricomorph) at 6 positions. Mouse myoglobin differs from that of mole-rat (another myomorph) at 17 positions, whereas casiragua and mouse differ at 22 positions. Mouse myoglobin possesses several features unique among all known myoglobins (Gly 31, Cys 66, Thr 74 and Glu 113) and one substitution unique among known mammalian myoglobins (Glu 53).

The preparation of fully N-epsilon-acetimidylated cytochrome c

We have re-examined the acetimidylation and subsequent deprotection of cytochrome c by published methods in the light of recent findings on the tendency of protein acetimidylation reactions to yield side products of differing net charges. We find that the protection methods do indeed yield a mixture of products, some of which have considerably diminished biological activity. Our observations support a postulated mechanism for the generation of side products, and we have been able to identify the major factor responsible for their formation by published methods. The deprotection method appears to be free of side reactions. We describe a new procedure for acetimidylation that will produce fully N-epsilon-acetimidylated cytochrome c. This derivative, lacking detectable side products and having good biological activity, is useful for structure-function studies and as an intermediate in the semisynthesis of cytochrome c analogues.

Ionization of tyrosine and lysine residues in native and modified horse cytochrome c

1H-n.m.r. and 13C-n.m.r. spectroscopy of horse cytochrome c and 1H-n.m.r. spectroscopy of the lysine-modified proteins N epsilon-acetimidyl-, N epsilon-amidino-, N epsilon-trifluoroacetyl- and N epsilon-maleyl-cytochrome c have shown that, although the lysine modifications do not greatly perturb the protein structure at pH7 and 27 degrees C, at higher temperature or at alkaline pH some parts of the structure are markedly perturbed. At pH7 and 27 degrees C the region of the protein about Ile-57 is affected in all the modified proteins, though not all to the same degree. N epsilon-Maleylation most seriously affects the protein structure, and the fully maleylated protein is readily unfolded. At 27 degrees C all four of the tyrosine residues of native horse cytochrome c have pKa values above 11, but in N epsilon-acetimidyl-cytochrome c the pKa of one tyrosine residue is 10.2.

Semisynthetic derivatives of glucagon: (des-His1)N epsilon-acetimidoglucagon and N alpha-Biotinyl-N epsilon-acetimidoglucagon

N epsilon-Acetimidoglucagon to be used for semisynthesis was prepared by reacting glucagon with methyl acetimidate hydrochloride at pH 10.2, favoring acetimidation of the sole epsilon-amino group. N epsilon-Acetimidoglucagon was isolated from the crude acetimidoglucagon mixture by anion-exchange chromatography at pH 9.4, producing a derivative which was identical with native glucagon on isoelectric focusing and which by amino acid analysis had greater than 98% of the lysine blocked. The yield was greater than that obtained when tetrahydrophthalic anhydride was used as a chromatographic handle to remove peptides with unreacted amino groups. N epsilon-Acetimidoglucagon closely resembled native glucagon in its biological activity and binding affinity, eliminating the need for deprotection. Semisynthetic N alpha-biotinyl-N epsilon-acetimidoglucagon, prepared by reacting (N-hydroxysuccinimido)biotin with N epsilon-acetimidoglucagon and purified by cation-exchange chromatography, was homogeneous upon isoelectric focusing (pI = 5.2) and exhibited 1.2% of the binding affinity, 2.4% of the biological potency, and 30% of the maximum activity of the native hormone. Preliminary fluorescence microscopy demonstrated binding of N alpha-biotinyl-N epsilon-acetimidoglucagon to glucagon specific receptors following exposure to fluorescein-labeled avidin. Capping of labeled receptors could be visualized with time. (Des-His1)N epsilon-acetimidoglucagon, prepared via a manual Edman degradation of N epsilon-acetimidoglucagon and isolated by cation-exchange chromatography, was homogeneous upon isoelectric focusing (pI = 5.2). The second residue, serine, has also been removed. Semisynthetic coupling of alternative residues to such derivatives will provide insight into the role of the amino-terminal residues in mediating the biological actions of the hormone.

Stepwise sequence determination from the carboxyl terminus of peptides

The thiocyanate method for stepwise degradation of peptides from their COOH termini [Stark, G. R. (1968) Biochemistry 7, 1796] has been investigated. The method involves first the reaction of the COOH-terminal residue with thiocyanate in an activation solvent of acetic acid and acetic anhydride and then cleavage of the COOH-terminal residue as its 2-thiohydantoin by acetohydroxamate in aqueous solution. The two steps of the degradation have been studied by using model peptides, and conditions have been developed for the rapid efficient removal and identification of the COOH-terminal residue of short peptides. The methods have been applied to peptides that have been covalently attached to insoluble supports. In this solid phase version of the degradation, a highly substituted porous glass activated with N,N'-carbonyldiimidazole has been prepared for use as the insoluble support. A number of peptides have been coupled to the porous glass, and several rounds of the degradation have been performed on immobilized peptides. High-pressure liquid chromatography provides a rapid, sensitive identification method for the 2-thiohydantoins. In addition, gas-liquid chromatography of the amino acid 2-thiohydantoins and reconversion to the parent amino acid have been used to identify the cleaved residues. The method of sequential degradation has been applied to a number of short model peptides such as Gly-Leu-Tyr, Met-enkephalin, and Val-Leu-Ser-Glu-Gly and has been used to determine the COOH-terminal sequence of 4 residues of a 22-residue cyanogen bromide fragment of pygmy sperm whale myoglobin.

A natural model of immunologic tolerance. Tolerance to murine C5 is mediated by T cells, and antigen is required to maintain unresponsiveness

A unique experimental model is described, where natural immunologic tolerance to a well-defined soluble native antigen (murine C5) is examined in congenic strains of mice that differ only by the presence or the absence of C5. A highly sensitive hemolytic assay was developed to detect nanogram amounts of C5 as well as an assay of anti-C5 inhibition of C5 hemolytic activity. The latter was more sensitive than immunodiffusion. Two reciprocal approaches were used to study the cellular basis of tolerance in irradiated hosts of either strain. In the first, lymphoid cells from either strain were transferred to irradiated B10.D2OSN hosts that were lacking C5 and so would not hinder detection of anti-C5 antibody upon challenge with murine C5. Second, lymphoid cells from either strain were transferred to irradiated B10.D2NSN hosts, whose native C5 provided the antigenic stimulus. The immune response of whole nonadherent spleen cell suspension as well as mixtures of T and B cells (separated on the basis of surface immunoglobulin) from either strain were studied. In addition, the duration of tolerance and the antigen requirement to maintain it in irradiated C5-deficient hosts repopulated with C5-sufficient spleen cells was examined. The positive control of irradiated C5-deficient hosts repopulated with syngeneic spleen cells showed a primary and secondary response to immunization. In contrast, C5-sufficient spleen cells failed to respond both in the primary and the secondary response. Because the unresponsiveness was not caused by antigen carryover and was not antigen specific, it represents central tolerance. In C5-sufficient irradiated hosts (where immunization was not required and antigen was present in natural form and physiological concentration), transfer of C5-deficient cells mediated a drop in C5 levels to 10-20% of that noted in unreconstituted controls. T and B cell mixing experiments from the two strains into deficient or sufficient hosts demonstrated that tolerance is T cell dependent and that C5-sufficient or -deficient B cells could cooperate with nontolerant C5-sufficient T cells to produce significant anti-C5 antibody or mediate a significant drop in C5 levels. In addition, the presence of antigen was necessary to maintain tolerance. In conclusion, these results show that (a) natural tolerance to C5 is an active process that is T cell dependent and requires the presence of antigen; (b) in this natural model, clonal abortion does not seem to occur; and (c) both tolerant and nontolerant B cells retain the capacity to produce autoantibody.

Cancer mortality in a cohort of naval shipyard workers in Hawaii: early findings

A retrospective cohort study was performed in Hawaii among 4,779 male shipyard workers exposed to asbestos and 2,757 similar male workers without known asbestos exposure. Observed deaths from cancer and other causes in the 2 groups were compared with expected deaths on the basis of the general population of Hawaii by the use of a modified life-table method of analysis. A risk ratio for lung cancer of 1.7 was found for the exposed group after 20 or more years of follow-up. No increased risk for lung cancer was seen in the nonexposed group. These findings could not be attributed to differences in smoking habits in the 2 shipyard groups or between the shipyard groups and the general population. Because the maximum duration of follow-up for this analysis was 24 years, greater risks for lung cancer may be seen in the exposed group when the follow-up period is extended.

Direct gas chromatographic determination of carbamate pesticides using Carbowax 20M-modified supports and the electrolytic conductivity detector

The gas chromatographic behavior of 32 carbamate pesticides was investigated using the Hall electrolytic conductivity detector. Relative retention indices were successfully determined for 24 carbamates on six different columns. Columns investigated included Ultra-Bond, 3% OV-101 on Ultra-Bond, 1% OV-17 on Ultra-Bond, 1% OV-210 on Ultra Bond, 1% Carbowax 20M on Ultra-Bond and 0.5% OV-210 + 0.65% OV-17 on Ultra-Bond. Chemical-ionization gas chromatography-mass spectrometry was used to verify that the carbamates were chromatographed intact. Chemical-ionization mass spectra are reported. Analytical procedures are demonstrated for the determination of carbamate residue in soil.

Mass spectrometric analyses and characterization of Kepone in environmental and human samples

A specific portion of our environment has been contaminated with Kepone, or chlordecone. Additionally, some specific human exposures to high concentrations of Kepone have been confirmed. Gas chromatography mass spectrometry involving chemical ionization and high resolution mass spectrometry were used to detect, identify and confirm the presence of Kepone, Kepone photoproducts and a reduction product of Kepone in environmental and human samples. Field desorption, field ionization and electron impact mass spectrometric methods, as well as infrared and nuclear magnetic resonance techniques were used to characterize and identify Kepone hydrate and hemiketal in benzene and methanol solutions, respectively.

A functioning complex between tryptic fragments of cytochrome c. A route to the production of semisynthetic analogues

We report the discovery of a functioning non-covalent complex between two peptides obtained from a limited tryptic digest of horse heart cytochrome c. We have used the phenomenon to produce three modified versions of the complex. We have replaced lysine-39 semisynthetically with ornithine in the first analogue, with p-fluorophenyl-alanine in the second, and removed it entirely in the third.