Interior and surface of monomeric proteins

The solvent-accessible surface area (As) of 46 monomeric proteins is calculated using atomic co-ordinates from high-resolution and well-refined crystal structures. The As of these proteins can be determined to within 1 to 2% and that of their individual residues to within 10 to 20%. The As values of proteins are correlated with their molecular weight (Mr) in the range 4000 to 35,000: the power law As = 6.3 M0.73 predicts protein As values to within 4% on average. The average water-accessible surface is found to be 57% non-polar, 24% polar and 19% charged, with 5% root-mean-square variations. The molecular surface buried inside the protein is 58% non-polar, 39% polar and 4% charged. The buried surface contains more uncharged polar groups (mostly peptides) than the surface that remains accessible, but many fewer charged groups. On average, 15% of residues in small proteins and 32% in larger ones may be classed as "buried residues", having less than 5% of their surface accessible to the solvent. The accessibilities of most other residues are evenly distributed in the range 5 to 50%. Although the fraction of buried residues increases with molecular weight, the amino acid compositions of the protein interior and surface show no systematic variation with molecular weight, except for small proteins that are often very rich in buried cysteines. From amino acid compositions of protein surfaces and interiors we calculate an effective coefficient of partition for each type of residue, and derive an implied set of transfer free energy values. This is compared with other sets of partition coefficients derived directly from experimental data. The extent to which groups of residues (charged, polar and non-polar) are buried within proteins correlates well with their hydrophobicity derived from amino acid transfer experiments. Within these three groups, the correlation is low.

The origin of mutants

Nucleic acids are replicated with conspicuous fidelity. Infrequently, however, they undergo changes in sequence, and this process of change (mutation) generates the variability that allows evolution. As the result of studies of bacterial variation, it is now widely believed that mutations arise continuously and without any consideration for their utility. In this paper, we briefly review the source of this idea and then describe some experiments suggesting that cells may have mechanisms for choosing which mutations will occur.

East pacific rise: hot springs and geophysical experiments

Hydrothermal vents jetting out water at 380 degrees +/- 30 degrees C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galápagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation.

Surface, subunit interfaces and interior of oligomeric proteins

The solvent-accessible surface area (As) of 23 oligomeric proteins is calculated using atomic co-ordinates from high-resolution and well-refined crystal structures. As is correlated with the protein molecular weight, and a power law predicts its value to within 5% on average. The accessible surface of the average oligomer is similar to that of monomeric proteins in its hydropathy and amino acid composition. The distribution of the 20 amino acid types between the protein surface and its interior is also the same as in monomers. Interfaces, i.e. surfaces involved in subunit contacts, differ from the rest of the subunit surface. They are enriched in hydrophobic side-chains, yet they contain a number of charged groups, especially from Arg residues, which are the most abundant residues at interfaces except for Leu. Buried Arg residues are involved in H-bonds between subunits. We counted H-bonds at interfaces and found that several have none, others have one H-bond per 200 A2 of interface area on average (1 A = 0.1 nm). A majority of interface H-bonds involve charged donor or acceptor groups, which should make their contribution to the free energy of dissociation significant, even when they are few. The smaller interfaces cover about 700 A2 of the subunit surface. The larger ones cover 3000 to 10,000 A2, up to 40% of the subunit surface area in catalase. The lower value corresponds to an estimate of the accessible surface area loss required for stabilizing subunit association through the hydrophobic effect alone. Oligomers with small interfaces have globular subunits with accessible surface areas similar to those of monomeric proteins. We suggest that these oligomers assemble from preformed monomers with little change in conformation. In oligomers with large interfaces, isolated subunits should be unstable given their excessively large accessible surface, and assembly is expected to require major structural changes.

Comparison of first-line antiretroviral therapy with regimens including nevirapine, efavirenz, or both drugs, plus stavudine and lamivudine: a randomised open-label trial, the 2NN Study

BACKGROUND

The 2NN Study was a randomised comparison of the non-nucleoside reverse-transcriptase inhibitors (NNRTI) nevirapine and efavirenz.

METHODS

In this multicentre, open-label, randomised trial, 1216 antiretroviral-therapy-naive patients were assigned nevirapine 400 mg once daily, nevirapine 200 mg twice daily, efavirenz 600 mg once daily, or nevirapine (400 mg) and efavirenz (800 mg) once daily, plus stavudine and lamivudine, for 48 weeks. The primary endpoint was the proportion of patients with treatment failure (less than 1 log(10) decline in plasma HIV-1 RNA in the first 12 weeks or two consecutive measurements of more than 50 copies per mL from week 24 onwards, disease progression [new Centers for Disease Control and Prevention grade C event or death], or change of allocated treatment). Analyses were by intention to treat.

FINDINGS

Treatment failure occurred in 96 (43.6%) of 220 patients assigned nevirapine once daily, 169 (43.7%) of 387 assigned nevirapine twice daily, 151 (37.8%) of 400 assigned efavirenz, and 111 (53.1%) of 209 assigned nevirapine plus efavirenz. The difference between nevirapine twice daily and efavirenz was 5.9% (95% CI -0.9 to 12.8). There were no significant differences among the study groups in the proportions with plasma HIV-1 RNA concentrations below 50 copies per mL at week 48 (p=0.193) or the increases in CD4-positive cells (p=0.800). Nevirapine plus efavirenz was associated with the highest frequency of clinical adverse events, and nevirapine once daily with significantly more hepatobiliary laboratory toxicities than efavirenz. Of 25 observed deaths, two were attributed to nevirapine.

INTERPRETATION

Antiretroviral therapy with nevirapine or efavirenz showed similar efficacy, so triple-drug regimens with either NNRTI are valid for first-line treatment. There are, however, differences in safety profiles. Combination of nevirapine and efavirenz did not improve efficacy but caused more adverse events.

Effects of individualized breast cancer risk counseling: a randomized trial

BACKGROUND

Studies have shown that a majority of women with a family history of breast cancer have exaggerated perceptions of their own risk of this disease and experience excessive anxiety. In response to the need to communicate more accurate risk information to these women, specialized programs for breast cancer risk counseling have been initiated in medical centers across the United States.

PURPOSE

Our purpose was 1) to evaluate the impact of a standardized protocol for individualized breast cancer risk counseling on comprehension of personal risk among first-degree relatives of index breast cancer patients and 2) to identify women most and least likely to benefit from such counseling.

METHODS

This study is a prospective randomized trial comparing individualized breast cancer risk counseling to general health counseling (control). We studied 200 women aged 35 years and older who had a family history of breast cancer in a first-degree relative. Women with a personal history of cancer were excluded. Risk comprehension was assessed as the concordance between perceived "subjective" lifetime breast cancer risk and estimated "objective" lifetime risk.

RESULTS

The results of logistic regression analysis showed that women who received risk counseling were significantly more likely to improve their risk comprehension, compared with women in the control condition (odds ratio [OR] = 3.5; 95% confidence interval [CI] = 1.3-9.5; P = .01). However, in both groups, about two thirds of women continued to overestimate their lifetime risks substantially following counseling. Examination of subjects by treatment interaction effects indicated that risk counseling did not produce improved comprehension among the large proportion of women who had high levels of anxious preoccupation with breast cancer at base line (P = .02). In addition, white women were less likely to benefit than African-American women (OR = 0.34; 95% CI = 0.11-0.99; P = .05).

CONCLUSION

Efforts to counsel women about their breast cancer risks are not likely to be effective unless their breast cancer anxieties are also addressed.

IMPLICATIONS

Attention to the psychological aspects of breast cancer risk will be critical in the development of risk-counseling programs that incorporate testing for the recently cloned breast cancer susceptibility gene, BRCA1 (and BRCA2 when that gene has also been cloned).

Risks for incident human papillomavirus infection and low-grade squamous intraepithelial lesion development in young females

CONTEXT

Low-grade squamous intraepithelial lesions (LSILs) have been described as a benign cytological consequence of active human papillomavirus (HPV) replication. Several studies have reported that certain behavioral and biological risks exist for LSIL, suggesting that HPV alone is not sufficient for the development of LSIL. However, because most of these studies have been cross-sectional, it is not known whether behavioral and biological risks are simply risks for HPV infection itself.

OBJECTIVE

To prospectively examine risks of incident HPV infection in HPV-negative females and of incident LSIL development in females with HPV infection.

DESIGN

Prospective cohort study conducted between 1990-2000, with a median follow-up of 50 months.

SETTING AND PARTICIPANTS

Females aged 13 to 21 years who attended 2 family planning clinics in the San Francisco bay area; 496 had prevalent HPV infection and 105 were HPV-negative.

MAIN OUTCOME MEASURE

Incident development of HPV infection and LSIL, analyzed by various demographic, behavioral, and clinical risk factors.

RESULTS

Fifty-four incident HPV infections occurred in the 105 females who were HPV-negative at study entry (median duration of follow-up for those who remained HPV-negative was 26 months). Multivariable analysis showed that risks of HPV included sexual behavior (relative hazard [RH], 10.10; 95% confidence interval [CI], 3.24-31.50 per new partner per month), history of herpes simplex virus (RH, 3.54; 95% CI, 1.37-9.10), and history of vulvar warts (RH, 2.73; 95% CI, 1.27-5.87). Current use of oral contraceptives had a significantly protective effect (RH, 0.49; 95% CI, 0.28-0.86). Among the 496 individuals who were HPV-positive at baseline or in follow-up, there were 109 incident cases of LSIL during the follow-up interval, with a median follow-up time of 60 months for those who never developed LSIL. Human papillomavirus infection was the most significant risk factor for development of LSIL. The multivariable model showed the following risks for LSIL: HPV infection for less than 1 year (RH, 7.40; 95% CI, 4.74-11.57); HPV infection for 1 to 2 years (RH, 10.27; 95% CI, 5.64-18.69); HPV infection for 2 to 3 years (RH, 6.11; 95% CI, 1.86-20.06); and daily cigarette smoking (RH, 1.67; 95% CI, 1.12-2.48).

CONCLUSION

Our results indicate distinct risks for HPV and LSIL. In addition, most women with HPV infection in our study did not develop LSIL within a median follow-up period of 60 months. These findings underscore the hypothesis that certain biological risks thought to be associated with LSIL are, in fact, risks for acquisition of HPV. Cigarette smoking was a risk specific to LSIL, supporting the role of tobacco in neoplastic development.

The accessible surface area and stability of oligomeric proteins

Protein structures are stabilized by hydrophobic and van der Waals forces, and by hydrogen bonds. The relation between these thermodynamic quantities and the actual three-dimensional structure of proteins can not be calculated precisely. However, certain empirical relations have been discovered. Hydrophobic energy is gained by the reduction of surface in contact with water. For monomeric proteins, the area of the surface accessible to solvent, and of that buried in the interior, is a simple function of molecular weight. Proteins with different shapes and secondary structures, but of the same molecular weight, have the same accessible surface area. It has been argued that there is no similar relationship for large oligomeric proteins. In this paper we show that the surface areas of oligomeric proteins, and the areas of the surface buried within them, are directly related to relative molecular mass. Although oligomers of the same molecular weight bury the same amounts of surface, the proportions buried within and between subunits vary. This has important implications for the role of subunit interfaces in the stability and activity of oligomeric proteins.

Evidence of activity-dependent withdrawal of corticospinal projections during human development

OBJECTIVE

To characterize the development of ipsilateral corticospinal projections from birth and compare to 1) development of contralateral projections in the same subjects and 2) ipsilateral corticospinal projections in subjects with unilateral lesions of the corticospinal system acquired perinatally or in adulthood.

METHOD

Transcranial magnetic stimulation excited the motor cortex, and responses were recorded bilaterally in pectoralis major, biceps brachii, and the first dorsal interosseus muscles. Subjects studied included 9 neonates recruited at birth, studied longitudinally for 2 years; 85 healthy subjects aged from birth to adulthood; 10 subjects with hemiplegic cerebral palsy; and 8 with hemiplegia after stroke.

RESULTS

In neonates, ipsilateral responses had significantly shorter onsets than contralateral responses but similar thresholds and amplitudes. Thresholds within both pathways increased in the first 3 months. Differential development was present from 3 months so that by 18 months ipsilateral responses were significantly smaller and had significantly higher thresholds and longer onset latencies than contralateral responses. A similar pattern of smaller and later ipsilateral responses was observed after transcranial magnetic stimulation of the intact cortex in subjects with stroke. In contrast, subjects with hemiplegic cerebral palsy had ipsilateral responses with onsets, thresholds and amplitudes similar to those of contralateral responses. Significant branching of contralateral corticospinal axons from the intact motor cortex was excluded by cross-correlation analysis.

CONCLUSIONS

These data, together with previously published anatomic and radiologic studies, are consistent with activity-dependent corticospinal axonal withdrawal during development and maintenance of increased corticomotoneuronal projections from the intact hemisphere after unilateral perinatal lesions.

Behavioral and psychological signs and symptoms of dementia: a consensus statement on current knowledge and implications for research and treatment

The behavioral (e.g., repetitive questioning, hitting) and psychological (e.g., delusions, anxieties) signs and symptoms of dementia can result in suffering, premature institutionalization, increased costs of care, and significant loss in the quality of life for the patient and his or her family and caregivers.

Adverse effects of low dose amiodarone: a meta-analysis

OBJECTIVES

We sought to assess the odds of experiencing adverse effects with low dose amiodarone therapy compared with placebo.

BACKGROUND

An estimate of the likelihood of experiencing amiodarone-related adverse effects with exposure to low daily doses of the drug is lacking in the published reports, and little information is available on adverse effect event rates in control groups not receiving the drug.

METHODS

Data from four published trials involving 1,465 patients were included in a meta-analysis design. The criteria for inclusion were 1) double-blind, placebo-controlled design; 2) absence of a crossover design between patient groups; 3) mean follow-up of at least 12 months; 4) maintenance amiodarone dose < or = 400 mg/day; and 5) presence of an explicit description of adverse effects. Data were pooled after testing for homogeneity of treatment effects across trials, and summary odds ratios were calculated by the Peto-modified Mantel-Haenszel method for each adverse effect.

RESULTS

The mean amiodarone dose per day ranged from 152 to 330 mg; 738 patients were randomized to receive amiodarone and 727 placebo. Exposure to amiodarone in this dose range, for a minimal duration of 12 months, resulted in odds similar to those of placebo for hepatic and gastrointestinal adverse effects, but in significantly higher odds than those of placebo (p < 0.05) for experiencing thyroid (odds ratio [OR] 4.2, 95% confidence interval [CI] 2.0 to 8.7), neurologic (OR 2.0, 95% CI 1.1 to 3.7), skin (OR 2.5, 95% CI 1.1 to 6.2), ocular (OR 3.4, 95% CI 1.2 to 9.6) and bradycardic (OR 2.2, 95% CI 1.1 to 4.3) adverse effects. A trend toward increased odds of pulmonary toxicity was noted (OR 2.0, 95% CI 0.9 to 5.3), but this did not reach statistical significance (p = 0.07). The unadjusted total incidence of drug discontinuation was 22.9% in the amiodarone group and 15.4% in the placebo group. The odds of discontinuing the drug in the amiodarone group was approximately 1.5 times that of the placebo group (OR 1.52, 95% CI 1.2 to 1.9) (p = 0.003).

CONCLUSIONS

Compared with placebo, there is a higher likelihood of experiencing several amiodarone-related adverse effects with exposure to low daily doses of the drug. Thus, although low dose amiodarone may be well tolerated, it is not free of adverse effects.

A simple genetic basis for a complex psychological trait in laboratory mice

Psychological traits are commonly inferred from covariation in sets of behavioral measures that otherwise appear to have little in common. Emotionality in mice is such a trait, defined here by covariation in activity and defecation in a novel environment and emergence into the open arms of an elevated plus maze. Behavioral and quantitative trait analyses were conducted on four measures obtained from 879 mice from an F2 intercross. Three loci, on murine chromosomes 1, 12, and 15, were mapped that influence emotionality. This trait, inferred from studies of strain, sex, and individual differences in rodents, may be related to human susceptibility to anxiety or neuroticism.

Crystal structure of P22 tailspike protein: interdigitated subunits in a thermostable trimer

The tailspike protein (TSP) of Salmonella typhimurium phage P22 is a part of the apparatus by which the phage attaches to the bacterial host and hydrolyzes the O antigen. It has served as a model system for genetic and biochemical analysis of protein folding. The x-ray structure of a shortened TSP (residues 109 to 666) was determined to a 2.0 angstrom resolution. Each subunit of the homotrimer contains a large parallel beta helix. The interdigitation of the polypeptide chains at the carboxyl termini is important to protrimer formation in the folding pathway and to thermostability of the mature protein.

Mutations in mitochondrial cytochrome c oxidase genes segregate with late-onset Alzheimer disease

Mounting evidence suggests that defects in energy metabolism contribute to the pathogenesis of Alzheimer disease (AD). Cytochrome c oxidase (CO) is kinetically abnormal, and its activity is decreased in brain and peripheral tissue in late-onset AD. CO is encoded by both the mitochondrial and the nuclear genomes. Its catalytic centers, however, are encoded exclusively by two mitochondrial genes, CO1 and CO2 (encoding CO subunits I and II, respectively). We searched these genes, as well as other mitochondrial genes, for mutations that might alter CO activity and cosegregate with AD. In the present study, specific missense mutations in the mitochondrial CO1 and CO2 genes but not the CO3 gene were found to segregate at a higher frequency with AD compared with other neurodegenerative or metabolic diseases. These mutations appear together in the same mitochondrial DNA molecule and define a unique mutant mitochondrial genome. Asymptomatic offspring of AD mothers had higher levels of these mutations than offspring of AD fathers, suggesting that these mutations can be maternally inherited. Cell lines expressing these mutant mitochondrial DNA molecules exhibited a specific decrease in CO activity and increased production of reactive oxygen species. We suggest that specific point mutations in the CO1 and CO2 genes cause the CO defect in AD. A CO defect may represent a primary etiologic event, directly participating in a cascade of events that results in AD.

Excitation of the corticospinal tract by electromagnetic and electrical stimulation of the scalp in the macaque monkey

1. The responses evoked by non-invasive electromagnetic and surface anodal electrical stimulation of the scalp (scalp stimulation) have been studied in the monkey. Conventional recording and stimulating electrodes, placed in the corticospinal pathway in the hand area of the left motor cortex, left medullary pyramid and the right spinal dorsolateral funiculus (DLF), allowed comparison of the actions of non-invasive stimuli and conventional electrical stimulation. 2. Responses to electromagnetic stimulation (with the coil tangential to the skull) were studied in four anaesthetized monkeys. In each case short-latency descending volleys were recorded in the contralateral DLF at threshold. In two animals later responses were also seen at higher stimulus intensities. Both early and late responses were of corticospinal origin since they could be completely collided by appropriately timed stimulation of the pyramidal tract. The latency of the early response in the DLF indicated that it resulted from direct activation of corticospinal neurones: its latency was the same as the latency of the antidromic action potentials evoked in the motor cortex from the recording site in the DLF. 3. Scalp stimulation, which was also investigated in three of the monkeys, evoked short-latency volleys at threshold and at higher stimulus intensities these were followed by later waves. The short-latency volleys could be collided from the pyramid and, at threshold, had latencies compatible with direct activation of corticospinal neurones. The longer latency volleys were also identified as corticospinal in origin. 4. The latency of the early volley evoked by electromagnetic stimulation remained constant with increasing stimulus intensities. In contrast, with scalp stimulation above threshold the latency of the early volleys decreased considerably, indicating remote activation of the corticospinal pathway below the level of the motor cortex. In two monkeys both collision and latency data suggest activation of the corticospinal pathway as far caudal as the medulla. 5. The majority of fast corticospinal fibres could be excited by scalp stimulation with intensities of 20% of maximum stimulator output. Electromagnetic stimulation at maximum stimulator output elicited a volley of between 70 and 90% of the size of the maximal volley evoked from the pyramidal electrodes. 6. Electromagnetic stimulation was also investigated in one awake monkey during the performance of a precision grip task. Short-latency EMG responses were evoked in hand and forearm muscles. The onsets of these responses were approximately 0.8 ms longer than the responses evoked by electrical stimulation of the pyramid.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacological effects of Lu AA21004: a novel multimodal compound for the treatment of major depressive disorder

1-[2-(2,4-Dimethylphenyl-sulfanyl)-phenyl]-piperazine (Lu AA21004) is a human (h) serotonin (5-HT)(3A) receptor antagonist (K(i) = 3.7 nM), h5-HT(7) receptor antagonist (K(i) = 19 nM), h5-HT(1B) receptor partial agonist (K(i) = 33 nM), h5-HT(1A) receptor agonist (K(i) = 15 nM), and a human 5-HT transporter (SERT) inhibitor (K(i) = 1.6 nM) (J Med Chem 54:3206-3221, 2011). Here, we confirm that Lu AA21004 is a partial h5-HT(1B) receptor agonist [EC(50) = 460 nM, intrinsic activity = 22%] using a whole-cell cAMP-based assay and demonstrate that Lu AA21004 is a rat (r) 5-HT(7) receptor antagonist (K(i) = 200 nM and IC(50) = 2080 nM). In vivo, Lu AA21004 occupies the r5-HT(1B) receptor and rSERT (ED(50) = 3.2 and 0.4 mg/kg, respectively) after subcutaneous administration and is a 5-HT(3) receptor antagonist in the Bezold-Jarisch reflex assay (ED(50) = 0.11 mg/kg s.c.). In rat microdialysis experiments, Lu AA21004 (2.5-10.0 mg/kg s.c.) increased extracellular 5-HT, dopamine, and noradrenaline in the medial prefrontal cortex and ventral hippocampus. Lu AA21004 (5 mg/kg per day for 3 days; minipump subcutaneously), corresponding to 41% rSERT occupancy, significantly increased extracellular 5-HT in the ventral hippocampus. Furthermore, the 5-HT(3) receptor antagonist, ondansetron, potentiated the increase in extracellular levels of 5-HT induced by citalopram. Lu AA21004 has antidepressant- and anxiolytic-like effects in the rat forced swim (Flinders Sensitive Line) and social interaction and conditioned fear tests (minimal effective doses: 7.8, 2.0, and 3.9 mg/kg). In conclusion, Lu AA21004 mediates its pharmacological effects via two pharmacological modalities: SERT inhibition and 5-HT receptor modulation. In vivo, this results in enhanced release of several neurotransmitters and antidepressant- and anxiolytic-like profiles at doses for which targets in addition to the SERT are occupied. The multimodal activity profile of Lu AA21004 is distinct from that of current antidepressants.

Functional corticospinal projections are established prenatally in the human foetus permitting involvement in the development of spinal motor centres

From studies of subhuman primates it has been assumed that functional corticospinal innervation occurs post-natally in man. We report a post-mortem morphological study of human spinal cord, and neurophysiological and behavioural studies in preterm and term neonates and infants. From morphological studies it was demonstrated that corticospinal axons reach the lower cervical spinal cord by 24 weeks post-conceptional age (PCA) at the latest. Following a waiting period of up to a few weeks, it appears they progressively innervate the grey matter such that there is extensive innervation of spinal neurons, including motor neurons, prior to birth. Functional monosynaptic corticomotoneuronal projections were demonstrated neurophysiologically from term, but are also likely to be present from as early as 26 weeks PCA. At term, direct corticospinal projections to Group Ia inhibitory interneurons were also confirmed. Independent finger movements developed much later, between 6 and 12 months post-natally. These data do not support the proposal that in man, establishment of functional corticomotoneuronal projections occurs immediately prior to and provides the capacity for the expression of fine finger movement control. We propose instead that such early corticospinal innervation occurs to permit cortical involvement in activity dependent maturation of spinal motor centres during a critical period of perinatal development. Spastic cerebral palsy from perinatal damage to the corticospinal pathway secondarily involves disrupted development of spinal motor centres. Corticospinal axons retain a high degree of plasticity during axon growth and synaptic development. The possibility therefore exists to promote regeneration of disrupted corticospinal projections during the perinatal period with the double benefit of restoring corticospinal connectivity and normal development of spinal motor centres.

Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)

The coronavirus disease 2019 (COVID-19) pandemic has caused untold disruption throughout the world. Understanding the mechanisms for transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is key to preventing further spread, but there is confusion over the meaning of ‘airborne’ whenever transmission is discussed. Scientific ambivalence originates from evidence published many years ago which has generated mythological beliefs that obscure current thinking. This article collates and explores some of the most commonly held dogmas on airborne transmission in order to stimulate revision of the science in the light of current evidence. Six ‘myths’ are presented, explained and ultimately refuted on the basis of recently published papers and expert opinion from previous work related to similar viruses. There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. Experts from specialties encompassing aerosol studies, ventilation, engineering, physics, virology and clinical medicine have joined together to produce this review to consolidate the evidence for airborne transmission mechanisms, and offer justification for modern strategies for prevention and control of COVID-19 in health care and the community.

Osteogenic protein-1 prevents renal fibrogenesis associated with ureteral obstruction

Unilateral ureteral obstruction (UUO) is a model of renal injury characterized by progressive tubulointerstitial fibrosis and renal damage, while relatively sparing the glomerulus and not producing hypertension or abnormalities in lipid metabolism. Tubulointerstitial fibrosis is a major component of several kidney diseases associated with the progression to end-stage renal failure. Here we report that when a critical renal developmental morphogen, osteogenic protein-1 (OP-1; 100 or 300 microg/kg body wt), is administered at the time of UUO and every other day thereafter, interstitial inflammation and fibrogenesis are prevented, leading to preservation of renal function during the first 5 days after obstruction. Compared with angiotensin-converting enzyme inhibition with enalapril treatment, OP-1 was more effective in preventing tubulointerstitial fibrosis and in preserving renal function. The mechanism of OP-1- induced renal protection was associated with prevention of tubular atrophy, an effect not shared with enalapril, and was related to preservation of tubular epithelial integrity. OP-1 blocked the stimulation of epithelial cell apoptosis produced by UUO, which promoted maintenance of tubular epithelial integrity. OP-1 preserved renal blood flow (RBF) during UUO, but enalapril also stimulated RBF. Thus OP-1 treatment inhibited tubular epithelial disruption stimulated by the renal injury of UUO, preventing tubular atrophy and diminishing the activation of tubulointerstitial inflammation and fibrosis and preserving renal function.

Longitudinal study of central motor conduction time following stroke. 2. Central motor conduction measured within 72 h after stroke as a predictor of functional outcome at 12 months

A longitudinal study was performed on 118 first-ever stroke patients to evaluate neurophysiological measurements of central motor conduction time (CMCT) in the period immediately following stroke as predictors of functional outcome and mortality at 12 months. Measurements of CMCT were made as described in the accompanying article (Heald et al., 1993, Brain, 116, 1355-1370), in which the following three groups of patients were recognized within 12-72 h after the onset of symptoms: normal response group, delayed response group and no response group. Neurophysiological and clinical investigations were commenced 12-72 h (designated as day 1) after the onset of symptoms and repeated at set time intervals up to 12 months. The subjects were examined neurologically and assessed using the Motricity Index for muscle strength, the Nine-hole Peg Test to measure manual dexterity, the Barthel Score for activities of daily living and the modified Rankin Scale for functional outcome. The duration of stay in hospital and the occurrence of stroke-related death were noted. During the first week following stroke, absence of responses correlated closely with the patient's symptoms and neurological observations of abnormal muscle tone and tendon reflexes. Correlations were made in the three groups of patients of functional scores at day 1 and at 12 months. Patients with normal CMCT had consistently higher scores throughout the 12 month period and achieved significantly better functional recovery. Patients with no responses showed poor performance in neurological and functional tests throughout the 12 month period. Patients with delayed CMCT had neurological and functional scores intermediate between those of the other two groups, but outcome at 12 months was similar to those in the normal response group. Where the threshold to cortical stimulation was abnormally high, functional outcome was generally poor. Mortality was highest in the group with absent responses and the survivors spent the longest period in hospital. In conclusion, the observation of normal or delayed CMCT at day 1 identifies a group of patients with a high probability of survival and functional recovery. The absence of responses to cortical stimulation at day 1 identifies a group of patients who are at high risk of poor functional recovery at 12 months and greater probability of stroke-related death during this period.

The time course of minimal excitory post-synaptic potentials evoked in spinal motoneurones by group Ia afferent fibres

1. Group Ia EPSPs were recorded from lumbosacral motoneurones in anaesthetized cats after almost complete section of the relevant dorsal roots. The EPSPs were usually of small amplitude (median value of 230 muV) and an averaging device was used to improve the definition of their time course.2. From a total of over 500 averaged EPSPs a smaller number (342) were subjected to analysis. The other EPSPs were rejected either because they showed signs of multiple origin in the rising phase of their time course (see Methods) or because the resting membrane potential of the cell was less than 50 mV. All the selected EPSPs had their rise time (from the 10 to the 90% level) and half-width measured, and a semilogarithmic plot of their decay time course was made.3. 252 of the EPSPs showed an exponential decline in their later time course and the slope of this line was used to give an estimate of the membrane time constant. The range of the time constant for different motoneurones was 2.3-12.9 msec, with a mean value of 5.8 msec.4. In ten cells an EPSP was recorded which was judged to be generated exclusively by synaptic knobs located on the soma. On this assumption measurements of the normalized rise time, half-width and break point time were used to estimate alpha, rho(infinity) and L by the method suggested in Jack & Redman (1971b). The estimated value of alpha ranged from 18 to 65. A positive correlation was found between alpha and tau(m), indicating that for these EPSPs the duration of current injection was independent of the membrane time constant. The peak time of the wave form of current injection was between 0.1 and 0.25 msec. The estimates of rho(infinity) were not thought to be very accurate. A lower limit of 4 was assumed and the highest measured value was 12, but in three cells the time course of the EPSP could not be fitted even with a very high value of rho(infinity). Some possible explanations for this discrepancy are mentioned in the Discussion. The electrotonic length of the dendrites (L) was usually greater than 1.0 lambda and ranged between 0.75 and 1.5 lambda. Evidence for an open-circuit termination of the dendrites was found in some cells.5. The normalized values of the rise time and half-width were used to make an electrotonic distance allocation to the 246 EPSPs which were judged to be non-somatic. The method of allocation was not precise because individual values of rho(infinity) and L were not available for these motoneurones. Instead, a maximum possible range was assumed: for rho(infinity), 4-25; for L, 0.75-1.5. The range of alpha was also assumed, from 12 to 100. With these values the motoneurone model (Jack & Redman, 1971b) was used to set limits within which the normalized rise time and half-width of all EPSPs, generated by current at a single point, should lie. Twenty of the 246 EPSPs lay outside these boundary lines and hence they did not receive a distance allocation. The remaining 226 were assigned values between 0.2 and 1.6 lambda (in 0.2 lambda steps); the majority of the allocations (183) were to the proximal electrotonic part of the dendrites (0.2, 0.4 or 0.6 lambda). The relationship of these distance allocations to the histological results of Conradi (1969) is discussed.6. It is concluded that there is no good evidence against the view that the main time course of minimal Ia EPSPs can be explained by their generation by a brief pulse of synaptic current and subsequent passive spread.

Stroke prevention trial in sickle cell anemia

Stroke occurs in 7-8% of children with Sickle Cell Disease (Hb SS) and is a major cause of morbidity. Rates of recurrence have been reduced from 46-90% to less than 10% through chronic blood transfusions. Prevention of first stroke, however, would be preferable because even one stroke can cause irreversible brain injury. Transcranial Doppler (TCD) ultrasound can detect arterial blood flow rates associated with subsequent stroke risk. By combining TCD screening and a potentially effective treatment, first stroke may be prevented. The Stroke Prevention Trial in Sickle Cell Anemia (STOP) is the first stroke prevention trial in Hb SS and the first randomized, controlled use of transfusion in Hb SS. This multi-center trial is designed to test whether reducing sickle hemoglobin to 30% or less with periodic blood transfusions will reduce first-time stroke by at least 70% compared to standard care. Primary endpoints will be clinically evident symptoms of cerebral infarction with consistent findings on Magnetic Resonance Imaging and Angiography (MRI/MRA) or symptomatic intracranial hemorrhage. Secondary endpoints will be asymptomatic brain lesions detected by MRI in brain areas not involved in primary endpoints. The design calls for a 6-month start-up interval, 18 months of TCD screening and randomization, and observation for stroke from entry through month 54. Key features of the trial are standardized TCD and MRI/MRA protocols interpreted blindly, and blinded adjudication of endpoints. The sample size (60 per treatment group) is based on prospective data relating TCD velocity to risk of stroke. A time-averaged mean velocity of > or = 200 cm/sec is associated with a 46% risk of cerebral infarction over 39 months. The sample size is sufficient to detect 70% reduction in the primary endpoint at 90% power. This trial will determine if transfusion is effective in the primary prevention of stroke. Secondary aims may further the understanding of the effects of transfusion on the brain and guide future research into cerebrovascular disease in Hb SS.