Age and Comorbidities Predict COVID-19 Outcome, Regardless of Innate Immune Response Severity: A Single Institutional Cohort Study

The COVID-19 pandemic has claimed over eight hundred thousand lives in the United States alone, with older individuals and those with comorbidities being at higher risk of severe disease and death. Although severe acute respiratory syndrome coronavirus 2-induced hyperinflammation is one of the mechanisms underlying the high mortality, the association between age and innate immune responses in COVID-19 mortality remains unclear.

DESIGN

Flow cytometry of fresh blood and multiplexed inflammatory chemokine measurements of sera were performed on samples collected longitudinally from our cohort. Aggregate impact of comorbid conditions was calculated with the Charlson Comorbidity Index, and association between patient factors and outcomes was calculated via Cox proportional hazard analysis and repeated measures analysis of variance.

SETTING

A cohort of severely ill COVID-19 patients requiring ICU admission was followed prospectively.

PATIENTS

In total, 67 patients (46 male, age 59 ± 14 yr) were included in the study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Mortality in our cohort was 41.8%. We identified older age (hazard ratio [HR] 1.09 [95% CI 1.07-1.11]; p = 0.001), higher comorbidity index (HR 1.24 [95% CI 1.14-1.35]; p = 0.039), and hyponatremia (HR 0.90 [95% CI 0.82-0.99]; p = 0.026) to each independently increase risk for death in COVID-19. We also found that neutrophilia (R = 0.2; p = 0.017), chemokine C-C motif ligand (CCL) 2 (R = 0.3; p = 0.043), and C-X-C motif chemokine ligand 9 (CXCL9) (R = 0.3; p = 0.050) were weakly but significantly correlated with mortality. Older age was associated with lower monocyte (R = -0.2; p = 0.006) and cluster of differentiation (CD) 16+ cell counts (R = -0.2; p = 0.002) and increased CCL11 concentration (R = 0.3; p = 0.050). Similarly, younger patients (< 65 yr) demonstrated a rise in CD4 (b-coefficient = 0.02; p = 0.036) and CD8 (0.01; p = 0.001) counts, as well as CCL20 (b-coefficient = 6.8; p = 0.036) during their ICU stay. This CD8 count rise was also associated with survival (b-coefficient = 0.01; p = 0.023).

CONCLUSIONS

Age, comorbidities, and hyponatremia independently predict mortality in severe COVID-19. Neutrophilia and higher CCL2 and CXCL9 levels are also associated with higher mortality, while independent of age.

Suppression of Fibrinolysis and Hypercoagulability, Severity of Hypoxemia, and Mortality in COVID-19 Patients: A Retrospective Cohort Study

BACKGROUND

COVID-19 causes hypercoagulability, but the association between coagulopathy and hypoxemia in critically ill patients has not been thoroughly explored. This study hypothesized that severity of coagulopathy would be associated with acute respiratory distress syndrome severity, major thrombotic events, and mortality in patients requiring intensive care unit-level care.

METHODS

Viscoelastic testing by rotational thromboelastometry and coagulation factor biomarker analyses were performed in this prospective observational cohort study of critically ill COVID-19 patients from April 2020 to October 2020. Statistical analyses were performed to identify significant coagulopathic biomarkers such as fibrinolysis-inhibiting plasminogen activator inhibitor 1 and their associations with clinical outcomes such as mortality, extracorporeal membrane oxygenation requirement, occurrence of major thrombotic events, and severity of hypoxemia (arterial partial pressure of oxygen/fraction of inspired oxygen categorized into mild, moderate, and severe per the Berlin criteria).

RESULTS

In total, 53 of 55 (96%) of the cohort required mechanical ventilation and 9 of 55 (16%) required extracorporeal membrane oxygenation. Extracorporeal membrane oxygenation-naïve patients demonstrated lysis indices at 30 min indicative of fibrinolytic suppression on rotational thromboelastometry. Survivors demonstrated fewer procoagulate acute phase reactants, such as microparticle-bound tissue factor levels (odds ratio, 0.14 [0.02, 0.99]; P = 0.049). Those who did not experience significant bleeding events had smaller changes in ADAMTS13 levels compared to those who did (odds ratio, 0.05 [0, 0.7]; P = 0.026). Elevations in plasminogen activator inhibitor 1 (odds ratio, 1.95 [1.21, 3.14]; P = 0.006), d-dimer (odds ratio, 3.52 [0.99, 12.48]; P = 0.05), and factor VIII (no clot, 1.15 ± 0.28 vs. clot, 1.42 ± 0.31; P = 0.003) were also demonstrated in extracorporeal membrane oxygenation-naïve patients who experienced major thrombotic events. Plasminogen activator inhibitor 1 levels were significantly elevated during periods of severe compared to mild and moderate acute respiratory distress syndrome (severe, 44.2 ± 14.9 ng/ml vs. mild, 31.8 ± 14.7 ng/ml and moderate, 33.1 ± 15.9 ng/ml; P = 0.029 and 0.039, respectively).

CONCLUSIONS

Increased inflammatory and procoagulant markers such as plasminogen activator inhibitor 1, microparticle-bound tissue factor, and von Willebrand factor levels are associated with severe hypoxemia and major thrombotic events, implicating fibrinolytic suppression in the microcirculatory system and subsequent micro- and macrovascular thrombosis in severe COVID-19.

EDITOR’S PERSPECTIVE

Key Pathogenic Factors in Coronavirus Disease 2019-Associated Coagulopathy and Acute Lung Injury Highlighted in a Patient With Copresentation of Acute Myelocytic Leukemia: A Case Report

The role of concurrent illness in coronavirus disease 2019 (COVID-19) is unknown. Patients with leukemia may display altered thromboinflammatory responses. We report a 53-year-old man presenting with acute leukemia and COVID-19 who developed thrombotic complications and acute respiratory distress syndrome. Multiple analyses, including rotational thromboelastometry and flow cytometry on blood and bronchoalveolar lavage, are reported to characterize coagulation and immune profiles. The patient developed chemotherapy-induced neutropenia that may have protected his lungs from granulocyte-driven hyperinflammatory acute lung injury. However, neutropenia also alters viral clearing, potentially enabling ongoing viral propagation. This case depicts a precarious equilibrium between leukemia and COVID-19.

Longitudinal Recovery and Reduced Costs After 120 Sessions of Locomotor Training for Motor Incomplete Spinal Cord Injury

OBJECTIVE

To determine the impact of long-term, body weight-supported locomotor training after chronic, incomplete spinal cord injury (SCI), and to estimate the health care costs related to lost recovery potential and preventable secondary complications that may have occurred because of visit limits imposed by insurers.

DESIGN

Prospective observational cohort with longitudinal follow-up.

SETTING

Eight outpatient rehabilitation centers that participate in the Christopher & Dana Reeve Foundation NeuroRecovery Network (NRN).

PARTICIPANTS

Individuals with motor incomplete chronic SCI (American Spinal Injury Association Impairment Scale C or D; N=69; 0.1-45y after SCI) who completed at least 120 NRN physical therapy sessions.

INTERVENTIONS

Manually assisted locomotor training (LT) in a body weight-supported treadmill environment, overground standing and stepping activities, and community integration tasks.

MAIN OUTCOME MEASURES

International Standards for Neurological Classification of Spinal Cord Injury motor and sensory scores, orthostatic hypotension, bowel/bladder/sexual function, Spinal Cord Injury Functional Ambulation Inventory (SCI-FAI), Berg Balance Scale, Modified Functional Reach, 10-m walk test, and 6-minute walk test. Longitudinal outcome measure collection occurred every 20 treatments and at 6- to 12-month follow-up after discharge from therapy.

RESULTS

Significant improvement occurred for upper and lower motor strength, functional activities, psychological arousal, sensation of bowel movement, and SCI-FAI community ambulation. Extended training enabled minimal detectable changes at 60, 80, 100, and 120 sessions. After detectable change occurred, it was sustained through 120 sessions and continued 6 to 12 months after treatment.

CONCLUSIONS

Delivering at least 120 sessions of LT improves recovery from incomplete chronic SCI. Because walking reduces rehospitalization, LT delivered beyond the average 20-session insurance limit can reduce rehospitalizations and long-term health costs.

Partial support for the central-marginal hypothesis within a population: reduced genetic diversity but not increased differentiation at the range edge of an island endemic bird

Large-scale population comparisons have contributed to our understanding of the evolution of geographic range limits and species boundaries, as well as the conservation value of populations at range margins. The central-marginal hypothesis (CMH) predicts a decline in genetic diversity and an increase in genetic differentiation toward the periphery of species' ranges due to spatial variation in genetic drift and gene flow. Empirical studies on a diverse array of taxa have demonstrated support for the CMH. However, nearly all such studies come from widely distributed species, and have not considered if the same processes can be scaled down to single populations. Here, we test the CMH on a species composed of a single population: the Island Scrub-Jay (Aphelocoma insularis), endemic to a 250 km² island. We examined microsatellite data from a quarter of the total population and found that homozygosity increased toward the island's periphery. However, peripheral portions of the island did not exhibit higher genetic differentiation. Simulations revealed that highly localized dispersal and small total population size, but not spatial variation in population density, were critical for generating fine-scale variation in homozygosity. Collectively, these results demonstrate that microevolutionary processes driving spatial variation in genetic diversity among populations can also be important for generating spatial variation in genetic diversity within populations.

Nitrogen enrichment modifies plant community structure via changes to plant-soil feedback

We tested the hypothesis that N enrichment modifies plant-soil feedback relationships, resulting in changes to plant community composition. This was done in a two-phase glasshouse experiment. In the first phase, we grew eight annual plant species in monoculture at two levels of N addition. Plants were harvested at senescence and the effect of each species on a range of soil properties was measured. In the second phase, the eight plant species were grown in multi-species mixtures in the eight soils conditioned by the species in the first phase, at both levels of N addition. At senescence, species performance was measured as aboveground biomass. We found that in the first phase, plant species identity strongly influenced several soil properties, including microbial and protist biomass, soil moisture content and the availability of several soil nutrients. Species effects on the soil were mostly independent of N addition and several were strongly correlated with plant biomass. In the second phase, both the performance of individual species and overall community structure were influenced by the interacting effects of the species identity of the previous soil occupant and the rate of N addition. This indicates that N enrichment modified plant-soil feedback. The performance of two species correlated with differences in soil N availability that were generated by the species formerly occupying the soil. However, negative feedback (poorer performance on the soil of conspecifics relative to that of heterospecifics) was only observed for one species. In conclusion, we provide evidence that N enrichment modifies plant-soil feedback relationships and that these modifications may affect plant community composition. Field testing and further investigations into which mechanisms dominate feedback are required before we fully understand how and when feedback processes determine plant community responses to N enrichment.

Quantitative model for prediction of hydrodynamic size of nonionic reverse micelles

The sizes of nonionic reverse micelles were investigated as a function of the molecular structure of the surfactant, the type of oil, the total concentration of surfactant [NP], the ratio of surfactant to total surfactant (r), the water to surfactant molar ratio (omega), temperature, salt concentration, and polar phase. The basis of our investigation was a mixture of nonylphenol polyethoxylates--NP4 and NP7, various polar phases, and several oils. Micelle sizes were determined using dynamic light scattering (DLS). A central composite experimental design was used to quantitatively model micelle size as a function of omega, surfactant concentration, and r. The model has demonstrated the capability of predicting the mean diameter of micelles from 4 to 13 with a precision of +/-2 nm as measured by DLS. This quantitative correlation between the size of reverse micelles and the synthetic variables provides the foundation for choosing experimental conditions to control reverse micelle size. In turn, this allows control of the size of nanoparticles synthesized within them.

Locomotor Training: Is Translating Evidence Into Practice Financially Feasible?

PURPOSE

Several lines of evidence suggest that locomotor training (LT) modalities, such as body weight-supported treadmill training (BWSTT), improves gait in individuals with incomplete spinal cord injury (SCI). Yet, manual BWSTT has been criticized for being cost prohibitive due to the number of staff required to perform this treatment. This study examined the financial viability of a LT program using manual BWSTT.

METHODS

This retrospective study analyzed data from individuals with motor incomplete SCI who had participated in manual BWSTT in a hospital-based outpatient clinic between 2003 and 2005. Individuals were between 18 and 68 years of age and were medically stable. Descriptive statistics were performed to determine the mean for each of the following: date of injury, age, impairment, gender, total number of visits, total procedures billed, charges, basic reimbursement information, and costs associated with the treatment.

RESULTS

The majority of individuals were male, classified as ASIA C, and had private insurance. Physical therapy evaluation, gait training, and therapeutic exercise were the most commonly billed procedures for all individuals. It was found that this locomotor training program, using the delivery model of one physical therapist, two physical therapy technicians, and one volunteer, was profitable.

CONCLUSIONS

The findings from this study suggest that LT using manual BWSTT in a hospital-based outpatient clinic can be financially feasible when provided by one trained physical therapist, two technicians, and one well-trained volunteer.

Predictors of HIV-specific lymphocyte proliferative immune responses induced by therapeutic vaccination

We treated a cohort of 38 HIV-infected individuals with a therapeutic vaccine (REMUNE, HIV-1 Immunogen) in an open label study. We then determined whether baseline parameters, such as CD4 cell count, viral load and IgG levels, were predictive of the magnitude of the HIV-specific lymphocyte proliferative responses (LPRs). We demonstrate herein that there is a significant enhancement from baseline for both HIV and p24 antigen-stimulated LPRs after immunization. Using a responder definition of a stimulation index of >5 on at least two post-immunization time-points, 29/38 (76%) responded to HIV-1 antigen while 27/38 (71%) responded to native p24 antigen. Viral load and total IgG were negatively correlated, while CD4 cell counts were positively associated with the magnitude of the HIV antigen LPR. In a multivariable analysis, baseline CD4 was the best predictor of HIV antigen LPR post-immunization.

Anti-F(ab')2 antibody in HIV type 1 infection: relationship to hypergammaglobulinemia and to antibody specific to the V3 loop region of glycoprotein 120

As HIV infection and autoimmune disease share certain similarities, it has been suggested that HIV may disrupt control of humoral immunity by the antiidiotype network, and that this may be evident as increased IgG antibody to F(ab')2. When anti-F(ab')2 was quantified by ELISA in sera of randomly chosen HIV-infected versus uninfected donors, some HIV-infected sera did contain increased anti-F(ab')2, resulting in a median amount twofold higher than in uninfected sera. Moreover, when data were grouped by blood CD4 lymphocyte count, anti-F(ab')2 in HIV+ groups appeared to rise as CD4 lymphocytes declined. However, increased anti-F(ab')2 mirrored the elevation in serum IgG closely, and normalization of anti-F(ab')2 to serum IgG concentration equalized the groups so that no relationship to CD4 lymphocytes remained. Hypergammaglobulinemia is therefore strongly implicated as a cause of variation in anti-F(ab')2. After dissociation of immune complexes, anti-F(ab')2 activity per microgram of monomeric IgG was slightly increased over normal only in the HIV-infected group with fewest CD4 lymphocytes, without statistical significance. In contrast, the proportion of IgG antibody to the V3-neutralizing determinant in HIV-1 decreased significantly as disease advanced. The same was true for 12 HIV+ individuals studied longitudinally for 500-1300 days. The data suggest that measuring serum anti-F(ab')2 is misleading when immune complexes are present: apparent increases as disease progresses are due to increased IgG and, possibly, to related technical artifacts. During HIV infection, the proportion of antiidiotypic IgG in fact remains unaltered or falls, making this an unlikely cause of suppressed humoral immunity to HIV-1.

Impairment of phagosome-lysosome fusion in HIV-1-infected macrophages

Phagosome-lysosome fusion is critical for intracellular killing of most organisms and is inhibited by some viruses, notably influenza. We explored the effects of infection in vitro with HIV-1 (IIIB or Ada-M) on phagosome-lysosome fusion in blood monocyte-derived macrophages. After 8 days of infection, fusion was assessed from the fluorescence change occurring up to 2 h after labeling the lysosome compartment with acridine orange and loading of phagosomes with opsonized yeast. Compared with mock-infected control macrophages, the proportion of cells showing fusion after infection was reduced from a mean of 70% to a mean of 47% (p = 0.0001). Inhibition was seen with heat-killed HIV-1 IIIB but not virus-free filtrate. It was mimicked by recombinant gp 120 and blocked by soluble CD4 or antibody to CD4 but not by a neutralizing antibody to the V3 loop of gp 120. The inhibitory effect was seen 8 days after the original, transient exposure to gp 120. These results suggest that a lasting abnormality of phagosome-lysosome fusion results from interaction between gp 120 and CD4, contributing, perhaps, to the increased susceptibility to opportunistic infections of people infected with HIV.

A role for urokinase-type plasminogen activator in human immunodeficiency virus type 1 infection of macrophages

Urokinase-type plasminogen activator (uPA), a proteinase which activates plasminogen by cleaving at -CPGR(arrow downward)V-, was shown to cleave the V3 loop in recombinant gp120 of human immunodeficiency virus type 1 (HIV-1) IIIB and MN strains, as well as a synthetic, cyclized peptide representing the clade B consensus sequence of V3. Proteolysis occurred at the homologous -GPGR(arrow downward)A-, an important neutralizing determinant of HIV-1. It required soluble CD4 and was prevented by inhibitors of uPA but not by inhibitors of likely contaminating plasma proteinases. It was accelerated by heparin, a known cofactor for plasminogen activation. In immune capture experiments, tight binding of uPA to viral particles, which did not depend on CD4, was also demonstrated. Active site-directed inhibitors or uPA diminished this binding, as did a neutralizing antibody to V3. Addition of exogenous uPA to the laboratory-adapted IIIB strain of HIV-1, the macrophage-tropic field strains JR-CSF and SF-162, or a fresh patient isolate of indeterminate tropism, followed by infection of macrophages with the various treated viruses, resulted in severalfold increases in subsequent viral replication, as judged by yields of reverse transcriptase activity and p24 antigen, as well as incorporation, as judged by PCR in situ. These responses were reversible by inhibitors or antibodies targeting the proteinase active site or the V3 loop. We propose that uPA, a transcriptionally regulated proteinase which is upregulated when macrophages are HIV infected, can be bound and utilized by the virus to aid in fusion and may be an endogenous component that is critical to the infection of macrophages by HIV-1.

Dibucaine elicits platelet procoagulant activity in factor VIII and factor X activation by a mechanism involving a sulfhydryl-dependent enzyme

Dibucaine, a potent inhibitor of platelet aggregation and platelet release, was found to enhance the ability of fresh gel-filtered or washed human platelets to support factor VIII activation and factor X activation. Dibucaine-treated platelets increased the peak of factor VIII clotting activity by 2-fold compared to activity with untreated platelets. Similarly platelets optimally stimulated by dibucaine (1.0-1.5 mM for 5 min at 37 degrees C) supported as much factor X activation by factors IXa and VIII (measured in a chromogenic assay) as platelets optimally stimulated by ionophore A23187 (15 microM). An assay of platelet calcium-dependent sulfhydryl proteases was devised and used to test the effect of various inhibitors on these platelet proteases. The membrane-permeable sulfhydryl inhibitor Thiolyte MB inhibited platelet calcium-dependent protease activity; whereas, membrane-impermeable Thiolyte MQ did not. Thiolyte MB also blocked the ability of dibucaine-stimulated platelets to support factor X activation. Incubation of fresh, gel-filtered platelets with calpain inhibitor II (N-Ac-L-L-Normethioninal) completely inhibited the calcium-dependent sulfhydryl protease activity of these platelets but did not affect their ability to support factor X activation after subsequent incubation with dibucaine. These data support the interpretation that an intracellular SH-dependent enzyme, which may not be calpain, is involved in the expression of platelet procoagulant activity in dibucaine-treated platelets.

Effect of breed and body weight on echocardiographic values in four breeds of dogs of differing somatotype

Eighty normal dogs of four morphologically disparate breeds (Pembroke Welsh Corgi, Miniature Poodle, Afghan Hound, Golden Retriever) (twenty of each breed), were studied by echocardiography to determine the importance of breed and weight in establishing normal echocardiographic reference ranges. Echocardiographic measurements included left-ventricular chamber dimension at systole and end-diastole, right-ventricular chamber dimension at end-diastole, interventricular septal thickness at systole and end-diastole, left-ventricular free wall thickness at systole and end-diastole, E-point septal separation, aortic root dimension at end-diastole, left atrial dimension, and fractional shortening. Analyses of covariance indicated that for all measurements except right-ventricular chamber dimension, the means were significantly different among breeds, after the differences in weight were taken into account. Echocardiographic measurements are variable even within the same breed. Breed must be considered in establishing echocardiographic measurement reference ranges. Echocardiographic values for each breed are presented.

Acromegaly in 14 cats

Acromegaly was diagnosed in 14 middle-aged to old cats of mixed breeding. Thirteen (93%) of the cats were male and one was female. The earliest clinical signs in the 14 cats included polyuria, polydipsia, polyphagia, all of which were associated with untreated diabetes mellitus. All developed severe insulin resistance within a few months; peak insulin dosages required to control severe hyperglycemia ranged from 20 to 130 U per day. Other clinical findings weeks to months after diagnosis included enlargement of one or more organs (e.g., liver, heart, kidneys, and tongue) (n = 14), cardiomyopathy (n = 13), increase in body size and weight gain (n = 8), nephropathy associated with azotemia and clinical signs of renal failure (n = 7), degenerative arthropathy (n = 6), and central nervous system signs (i.e., circling and seizures) caused by enlargement of the pituitary tumor (n = 2). The diagnosis of acromegaly was confirmed by demonstration of extremely high basal serum growth hormone concentrations (22 to 131 micrograms/l) in all cats. Computerized tomography disclosed a mass in the region of the pituitary gland and hypothalamus in five of the six cats in which it was performed. Two cats were treated by cobalt radiotherapy followed by administration of a somatostatin analogue (octreotide), whereas two cats were treated with octreotide alone. Treatment had little to no effect in decreasing serum GH concentrations in any of the cats. Eleven of the 14 cats were euthanized or died four to 42 months (median survival time, 20.5 months) after the onset of acromegaly because of renal failure (n = 2), congestive heart failure (n = 1), concomitant renal failure and congestive heart failure (n = 3), progressive neurologic signs (n = 2), persistent anorexia and lethargy of unknown cause (n = 1), the owner's unwillingness to treat the diabetes mellitus (n = 1), or unknown causes (n = 1). Results of necropsy examination in ten cats revealed a large pituitary acidophil adenoma (n = 10), marked left ventricular and septal hypertrophy (n = 7), dilated cardiomyopathy (n = 1), arthropathy affecting the shoulder, elbow, or stifle (n = 5), and glomerulopathy characterized by expansion of the mesangial matrix and variable periglomerular fibrosis (n = 10).

Airline Deregulation and Public Policy

An assessment of the effects of airline deregulation on travelers and carriers indicates that deregulation has provided travelers and carriers with $14.9 billion of annual benefits (1988 dollars). Airport congestion, airline safety, airline bankruptcy, and mergers are also analyzed and found in most cases to have reduced benefits. But, these costs should not be attributed to deregulation per se, but to failures by the government to pursue appropriate policies in these areas. Pursuit of policies that promote airline competition and efficient use of airport capacity would significantly increase the benefits from deregulation and would provide valuable guidance for other industries undergoing the transition to deregulation.

The presence of Campylobacter pylori in nonsteroidal antiinflammatory drug associated gastritis

Although Campylobacter pylori has recently been causally linked to active chronic gastritis and peptic ulcer disease, its relationship to nonsteroidal antiinflammatory drug (NSAID) associated gastritis is unclear. We performed a case-control study of 100 patients who had undergone gastritis biopsy. Blinded review of Giemsa stained slides demonstrated the presence of C. pylori in 32% of 19 NSAID treated cases with active chronic gastritis vs 3% of 36 controls with chronic gastritis not taking NSAID, and 69% of 45 "positive" controls with active chronic gastritis not taking NSAID (p less than 0.001). Our results suggest a possible multifactorial etiology of NSAID associated gastritis.

Hypersomatotropism and insulin-resistant diabetes mellitus in a cat

In this report, we described the clinical, radiographic, and echocardiographic findings in a cat with hypersomatotropism and insulin-resistant diabetes mellitus. Growth hormone determinations were made because of persistent hyperglycemia despite insulin requirements exceeding 2.2 U/kg of body weight, and the acromegalic features of the cat. Also, the results of a therapeutic trial in which a long-acting analogue of somatostatin was used are discussed.

Biofeedback to facilitate unassisted ventilation in individuals with high-level quadriplegia. A case report

The purpose of this case report is to discuss the effectiveness of electromyographic biofeedback in reeducating and strengthening the accessory breathing muscles in an individual with high-level (C1) complete quadriplegia. Six unassisted breathing sessions were performed with EMG biofeedback intervention. Six unassisted breathing sessions without EMG biofeedback intervention were also performed. In both conditions, the subject's vital capacity and the amount of time of unassisted ventilation were recorded. The study results indicated that EMG biofeedback may be a helpful modality in training accessory breathing muscles to enable an individual with high-level quadriplegia to become independent of mechanical ventilation for varying amounts of time.

Effect of limited modification of amino groups on the reactivity of human factor Xa

The basis of the specificity of human coagulation factor Xa has been probed with a reagent that reacts with nucleophiles, N-succinimidylpropionate. At pH 8.0 and 0.25 mM N-succinimidylpropionate, 0.4 microM factor Xa lost approx. 90% of its activity toward prothrombin in 4 min. The decay was first-order, k = 0.64 min-1, which increased to 0.98 min-1 in 1 mM Ca2+, and the dependence of k upon pH was consistent with primary amines being the target. The rate of modification was unaffected by the presence of a tetrapeptide substrate during modification; likewise, activity toward a tripeptide p-nitroanilide was unaltered during exposure of factor Xa to N-succinimidylpropionate with or without Ca2+. In addition, inhibition by antithrombin III was retained with a somewhat enhanced rate after modification; however, the acceleration of this by heparin was significantly less. Kinetic determination of the number of residues modified gave a reaction order of 2.0, while reaction with N-succinimidyl[3H]propionate yielded labeled factor Xa containing 1.0 mol N-succinimidylpropionate/mol factor Xa and 50% normal clotting activity, or 2.0 mol N-succinimidylpropionate/mol and 1% activity, respectively. Thus, one nucleophilic group is required for the reaction of factor Xa with prothrombin but not for the hydrolysis of peptides or recognition of antithrombin III. The decay of clotting activity of the factor X zymogen in N-succinimidylpropionate was much slower though still Ca2+-dependent. Conversely, the reaction of a related compound--N-succinimidyl(4-hydroxyphenyl)propionate or Bolton-Hunter reagent--with factor Xa broadly resembled that of N-succinimidylpropionate but the decay curves indicated more complex kinetics. Therefore, the target groups vary in their accessibility to modification according to the structural characteristics of both the protein and the reagent.

Origin of a fluorescence increase accompanying the limited proteolysis of fluorescein-labeled human prothrombin by Factor Xa

In a search for a probe which would report its proteolysis to thrombin, the human blood coagulation zymogen prothrombin was covalently labeled with fluorescein. Fluorescein isothiocyanate (FITC) and dichlorotriazinylaminofluorescein (DCTAF) both introduced approximately 1 molecule of dye, but labeling occurred at different locations, as FITC had no effect on clotting activity whereas DCTAF caused 95% inactivation. At pH 9.0 DCTAF, but not FITC, could induce labeling up to 4 mol/mol. All derivatives were activated normally by prothrombinase (the activating complex of Factor Xa, Factor V(a), Ca2+ and phospholipids), as indicated by the pattern of bands on SDS gel electrophoresis and an unaltered yield of activity toward a chromogenic substrate for thrombin. Upon undergoing this limited proteolysis, the most heavily labeled derivative showed a 40% increase in fluorescence of the fluorescein at 520 nm (lambda ex 480 nm). In contrast, the fluorescence of lightly labeled forms was more intense but increased by only 0-5% upon activation. The data suggest that the lower fluorescence of the most labeled form is due to an intramolecular quenching effect between the dye molecules on individual polypeptide chains that is partly relieved when activation occurs.

Tissue factor-dependent activation of tritium-labeled factor IX and factor X in human plasma

Recent investigations have suggested that the activation of factor IX by factor VII/tissue factor may be an important alternative route to the generation of factor Xa. Accordingly, we have compared the tissue factor-dependent activation of tritium-labeled factor IX and factor X in a human plasma system and have studied the role of proteases known to stimulate factor VII activity. Plasma was defibrinated by heating and depleted of its factors IX and X by passing it through antibody columns. Addition of human brain thromboplastin, Ca2+, and purified 3H-labeled factor X to the plasma resulted, after a short lag, in burst-like activation of the factor X, measured as the release of radiolabeled activation peptide. The progress of activation was slowed by both heparin and a specific inhibitor of factor Xa, suggesting a feedback role for this enzyme, but factor X activation could not be completely abolished by such inhibitors. In the case of 3H-factor IX activation, the rate also increased for approximately 3 min after addition of thromboplastin, but was not subsequently curtailed. A survey of proteases implicated as activators of factor VII in other settings showed that both factor Xa and (to a much smaller extent) factor IXa could accelerate the activation of factor IX. However, factor Xa was unique in obliterating activation when present at concentrations greater than approximately 1 nM. Heparin inhibited the tissue factor-dependent activation of factor IX almost completely, apparently through the effect of antithrombin on the feedback reactions of factors Xa and IXa on factor VII. These results suggest that a very tight, biphasic control of factor VII activity exists in human plasma, which is modulated mainly by factor Xa. Variation of the factor IX or factor X concentrations permitted kinetic parameters for each activation to be derived. At saturation of factor VIIa/tissue factor, factor IX activation was significantly more rapid than was previously found in bovine plasma under similar conditions. The activation of factor X at saturation was slightly more rapid than in bovine plasma, despite the presence of heparin.

Measurement of human activated factor X-antithrombin complex by an enzyme-linked differential-antibody immunosorbent assay

An enzyme-linked immunoabsorbent assay (ELISA) has been developed for the measurement of the complex of human antithrombin and Factor Xa. Rabbit anti-human Factor X antibodies are adsorbed to ELISA plates, and samples containing Xa-antithrombin complex are added. This is followed by the addition of F(ab')2 fragments of rabbit antibodies against human antithrombin, previously labeled with alkaline phosphatase, and subsequent measurement of the bound labeled antibody by hydrolysis of p-nitrophenylphosphate. The minimum level of complex detectable in a sample is ca. 0.1 nM. The assay has been used to follow the generation of Xa-antithrombin complex in kinetic situations by the addition of 1 microM Ile-Glu-Gly-Arg-chloro- methylketone to the ELISA sampling buffer, and it has also been used in plasma systems, where a 20-fold reduction in the sensitivity of the assay is observed. This reduction was shown to be entirely caused by the plasma Factor X. The assay has been used to follow generation of the Xa-antithrombin complex in defibrinated plasma upon activation of the clotting system with the Factor X-activating protein of Russell's Viper venom, and has been compared with the total generation of Factor Xa, measured by a radiopeptide assay of Factor X activation in the same mixtures.

The activation of Factor IX by tissue factor-Factor VII in a bovine plasma system lacking Factor X

The activation of Factor IX by tissue factor-Factor VII has been studied in a bovine plasma system under conditions that minimize the activation of Factor VII. The plasma was defibrinated, then passed twice through a column of anti-Factor X coupled to Sepharose in order to lower the Factor X level below its limit of assay (ca. 5 ng/ml), and once through an anti-Factor IX column to remove Factor IX. Varying levels of tritium-labelled Factor IX were then added back to the plasma, permitting measurement of its activation upon the addition of tissue factor and Ca2+. Despite the absence of significant levels of Factor X in the system, the course of Factor IX activation was initially characterized by some upward curvature, which suggested activation of the plasma Factor VII during the incubation. In order to obtain linear activation of Factor IX three proteolytic inhibitors were added to the system: 1) a Factor Xa inhibitor, 1,2-bis-(5-amidinobenzimidazole)-ethane, 2) aprotinin, and 3) heparin. Under these conditions the apparent Km of non-activated Factor VII (+ tissue factor) on Factor IX was 17.3 +/- 2.5 nM (SE), and the maximum velocity was 0.12 nM/min. In parallel experiments the plasma Factor VII was activated by first treating the plasma with Factor Xa for 30 seconds before the addition of inhibitors and the final addition of substrate. Under these conditions the maximum velocity rose to 4.2 nM/min, and the Km increased to 53.3 +/- 6.0 nM (SE). This change in the Km is highly significant (P less than 0.002), and indicates that the activation of Factor IX by nonactivated plasma Factor VII cannot be due only to traces of Factor VIIa in the plasma. At least in part, activation of Factor IX in the presence of tissue factor is suggested to be a result of the action of Factor VII itself.

Vitamin-A reversal of abnormal dark adaptation in cirrhosis. Study of effects on the plasma retinol transport system

Of 26 patients hospitalized with mild to moderate alcohol-associated cirrhosis, 14 had dark-adaptation abnormalities consistent with marginal vitamin-A status. The response of dark adaptation and the plasma retinol transport proteins, retinol-binding protein and prealbumin, was studied in 12 of these patients after daily oral vitamin-A supplements of 3300 microgram. Vitamin-A supplementation was associated with significant (p less than 0.05-0.005) improvement in dark adaptation and increased plasma concentrations of retinyl esters, retinol, and retinol-binding protein. Thus in patients with cirrhosis and marginal vitamin-A status, supplemental vitamin-A therapy appears to stimulate retinol-binding protein release from the liver. This enhancement of plasma retinol transport and delivery of retinol to peripheral tissues such as the retina is one of several factors that may serve to optimize vitamin-A nutritional status in patients with cirrhosis.

Zinc deficiency: a cause of abnormal dark adaptation in cirrhotics

Six stable alcoholic cirrhotics with serum zinc less than 70 microgram/100 ml had abnormal dark adaptation responses (mean dark adapted final threshold 3.2 +/- 0.6 versus 2.1 +/- 0.2 log lux in 21 age matched controls, P less than 0.01). Serum vitamin A ranged from 15 to 37 microgram/100 ml. Zinc sulfate (220 mg/day) was fed to three patients for 1 to 2 weeks and dark adapted final thresholds fell 0.9, 0.4, and 1.2 log lux without concurrent rises in serum vitamin A. Two patients were treated initially with oral vitamin A (10,000 IU/day) for 2 to 4 weeks, but their final thresholds fell to normal (2.1, 2.2 log lux) only after the addition of zinc for 1 to 2 weeks. The sixth patient, treated with vitamin A and zinc together, attained a normal final threshold in 2 weeks. The improvement in dark adaptation by zinc may be due to enhanced activity of previously depressed retinol dehydrogenase.