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PubMed1989

Synergistic disaggregation of platelets by tissue-type plasminogen activator, prostaglandin E1, and nitroglycerin.

Endothelial cells produce at least three substances that can attenuate the platelet aggregation response: tissue-type plasminogen activator; the platelet inhibitory prostaglandins I2 and E1; and endothelium-derived relaxing factor, one form of which exhibits properties of nitric oxide. Since platelet aggregates formed in vivo are involved in the initiation of many clinically important occlusive vascular syndromes, we tested the hypothesis that these endothelial products act synergistically to disperse platelet aggregates. Our data reveal that tissue-type plasminogen activator, prostaglandin E1, and nitroglycerin (an organic nitrate activator of guanylate cyclase analogous to endothelium-derived relaxing factor) act synergistically to disaggregate platelets and do so in part by modulation of platelet cyclic nucleotides. These data suggest a potential mechanism by which the endothelium protects against the formation of platelet aggregates in vivo and offer a potential strategy for improving the efficacy of thrombolytic therapy.

Alprostadil↗

PubMed1974

Evidence for a structural requirement for the aggregation of platelets by collagen.

This study investigates whether soluble collagen can initiate platelet aggregation or whether a higher degree of polymerization is required. Purified rat skin collagen was prepared in four states. Soluble monomeric collagen, containing 2 muM calcium chloride, was maintained at 4 degrees C until use. A previously uncharacterized form of collagen, soluble microfibrillar collagen, was prepared from monomeric collagen containing calcium chloride by allowing it to polymerize at 23 degrees C. Viscometric and electron microscopic characterization of microfibrillar collagen indicated polymerization to ordered native filaments. Particulate native macrofibrillar collagen was prepared from monomeric collagen by allowing it to polymerize at 37 degrees C in the absence of calcium. Particulate collagen, in which the fibers were randomly associated, was prepared by salt precipitation of calcium-free monomeric collagen. Microfibrillar and native macrofibrillar collagen initiated platelet aggregation, with a lag phase of approximately 60 s. Monomeric collagen initiated aggregation with a lag phase of approximately 180 s. The duration of the lag phase for platelet aggregation initiated by monomeric collagen was independent of the dose. Salt-precipitated particulate collagen did not initiate platelet aggregation. Agents which prolong the transition from monomeric collagen to fibrillar collagen (urea, arginine) retarded or prevented the aggregation of platelets by monomeric collagen. Sodium borohydride, which stabilizes the intraand intermolecular cross-links of collagen did not affect platelet aggregation. Penicillamine, which displaces the intermolecular cross-links and binds the intramolecular cross-links of collagen, did not prevent platelet aggregation. The data suggest that an architectural requirement exists for the initiation of self-perpetuating platelet aggregation; that tropocollagen units do not fulfill this requirement; that a soluble collagen preparation, microfibrillar collagen, contains the minimal structural unit; and that cross-linkages within collagen do not play a critical role in platelet aggregation.

Animals↗

PubMed1999

Microfibrillar structure of PGG-glucan in aqueous solution as triple-helix aggregates by small angle x-ray scattering.

The conformation of polysaccharide PGG-Glucan, isolated from yeast cell walls, in aqueous solution was investigated by small angle x-ray scattering (SAXS) and multidetector gel permeation chromatography coupled with postcolumn delivery (GPC/PCD) techniques in comparison with scleroglucan. It was shown that both polysaccharides exhibit a rigid rod-like conformation in aqueous solution by SAXS experiments. The mass per unit length (M/L) and radius (R) of rod cross section of PGG-Glucan were measured to be 6300 daltons/nm and 1.89 nm, while those of scleroglucan are 2300 and 0.83, respectively. Utilizing a GPC/light scattering technique, the average aggregation number of PGG-Glucan is 9, while that of scleroglucan is around 3. From the comparison of the M/L and R of the respective rod cross sections as well as their aggregation number data, it is concluded that PGG-Glucan is composed of triple helices, which tend to aggregate as triplets in solution, whereas scleroglucan is composed of a single triple helix. The aggregation number distribution of PGG-Glucan was found to range from 1 to about 25 determined by GPC/PCD. From the observation of a Debye-Scherrer ring type of peak in the macroscopic scattering cross section of PGG-Glucan by SAXS, the existence of a small amount of ordered clusters of PGG-Glucan can be deduced. The "lattice parameter" of these ordered fasces-like clusters is consistent with the radius of the individual triple-helical rods forming a microfibrillar superstructure. These results indicate that higher aggregated forms of PGG-Glucan containing up to 8 triple helices behave as ordered fasces-like clusters. We conclude that PGG-Glucan is triple-helix aggregates formed by rigid rods stacking together side by side. We propose a molecular structural model for PGG-Glucan conformations.

Carbohydrate Conformation↗

PubMed1992

Interpretation of Scatchard plots for aggregating receptor systems.

Aggregation of cell surface receptors, with each other or with other membrane proteins, occurs in a variety of experimental systems. The list of systems where receptor aggregation appears to be important in understanding ligand binding and cellular responses is growing rapidly. In this paper we explore the interpretation of equilibrium binding data for aggregating receptor systems. The Scatchard plot is a widely used tool for analyzing equilibrium binding data. The shape of the Scatchard plot is often interpreted in terms of multiple noninteracting receptor populations. Such an analysis does not provide a framework for investigating the role of receptor aggregation and will be misleading if there is a relation between receptor aggregation and ligand binding. We present a general model for the equilibrium binding of a ligand with any number of aggregating receptor populations and derive theoretical expressions for observable Scatchard plot features. These can be used to test particular models and estimate model parameters. We develop particular models and apply the general results in the cases of six aggregating receptor systems where ligand binding and receptor aggregation are related: cross-linking of monovalent cell surface proteins by monoclonal antibodies, cross-linking of cell surface antibodies by bivalent ligand, antibody-induced co-cross-linking of cell surface antibodies and Fc gamma receptors, ligand-enhanced aggregation of identical epidermal growth factor receptors, aggregation of heterologous receptors for interleukin 2 to form a high-affinity receptor, and association of receptors, including those for interleukins 5 and 6, with nonbinding accessory proteins that influence receptor affinity or effector function.

Animals↗

PubMed2006

Cloning and characterisation of natriuretic peptides from the venom glands of Australian elapids.

The venom from Australian elapid snakes contains a complex mixture of polypeptide toxins that adversely affect multiple homeostatic systems within their prey in a highly specific and targeted manner. Included in these toxin families are the recently described venom natriuretic peptides, which display similar structure and vasoactive functions to mammalian natriuretic peptides. This paper describes the identification and detailed comparative analysis of the cDNA transcripts coding for the mature natriuretic peptide from a total of nine Australian elapid snake species. Multiple isoforms were identified in a number of species and represent the first description of a natriuretic peptide from the venom gland for most of these snakes. Two distinct natriuretic peptide isoforms were selected from the common brown snake (Pseudonaja textilis), PtNP-a, and the mulga (Pseudechis australis), PaNP-c, for recombinant protein expression and functional analysis. Only one of these peptides, PtNP-a, displayed cGMP stimulation indicative of normal natriuretic peptide activity. Interestingly, both recombinant peptides demonstrated a dose-dependent inhibition of angiotensin converting enzyme (ACE) activity, which is predictive of the vasoactive effects of the toxin. The natriuretic peptides, however, did not possess any coagulopathic activity, nor did they inhibit or potentiate thrombin, adenosine diphosphate or arachidonic acid induced platelet aggregation. The data presented in this study represent a significant resource for understanding the role of various natriuretic peptides isoforms during the envenomation process by Australian elapid snakes.

Amino Acid Sequence↗

PubMed2005

Quality and variability of osteoporosis data in general practice computer records: implications for disease registers.

OBJECTIVE: To determine the extent to which routinely collected general practitioner computer data could be used to create disease registers of patients with osteoporosis, and to report any improvement in data quality since previous studies. STUDY DESIGN: Audit using anonymized data extracted from general practice computer records from across England. METHODS: Morbidity Query Information and Export Syntax (MIQUEST) software was used to extract structured data from the 78 volunteer practices that participated in the study. The data were aggregated and analysed. RESULTS: There were 100-fold differences in the rates of recording of relevant data. Many patients receiving treatment had no diagnostic codes. Data about secondary causes of osteoporosis and fractures were more consistently recorded than data relating to falls. There were no data to indicate whether fractures were low impact. T-scores, the gold-standard measure of bone density, were very infrequently recorded. CONCLUSIONS: Sufficient data about secondary causes of osteoporosis exist, and these could be searched to identify patients at risk. Meanwhile, fracture recoding could be improved, including likely fragility fractures, and T-scores could be added to computer records. A systematic approach is needed to raise the computer records to a standard where they can be used as valid and reliable disease registers.

Accidental Falls↗

PubMed1977

Inhibition of human platelet thromboxane synthetase by 9,11-azoprosta-5,13-dienoic acid.

The synthetic prostaglandin analog 9,11-azoprosta-5,13-dienoic acid (azo analog I) has been found to be a potent inhibitor of human platelet thromboxane synthetase by three independent analytical methods: electron-capture gas chromatography, radioisotopic thin-layer chromatography, and radioimmunoassay. In the presence of azo analog I, human platelet aggregation induced by either the prostaglandin endoperoxide PGH2 or arachidonic acid was antagonized. The addition of azo analog I shifted the transformation of endoperoxides away from thromboxane synthesis and toward prostaglandin E2 synthesis. The specificity of azo analog I is demonstrated by its selective inhibition of the second wave of either ADP- or epinephrine-induced platelet aggregation. These data indicate that PGH2 must be converted to thromboxane A2 in order to induce human platelet aggregation.

Arachidonic Acids↗

PubMed2001

Implementing evidence-based medicine: the role of market pressures, compensation incentives, and culture in physician organizations.

OBJECTIVES: To assess the extent to which market pressures, compensation incentives, and physician medical group culture are associated with the use of evidence-based medicine practices in physician organizations. METHODS: Cross-sectional exploratory study of 56 medical groups affiliated with 15 integrated health systems from across the United States, involving 1,797 physician respondents. Larger medical groups and multispecialty groups were overrepresented compared with the United States as a whole. Data are from two sources: (1) surveys of physicians assessing the culture of the medical groups in which they work, and (2) surveys of medical directors and other managerial key informants pertaining to care management practices, compensation methods, and the management and governance of the medical groups. Physician-level data were aggregated to the group level to attain measures of group culture and then merged with the data regarding care management, incentives, and management and governance. Stepwise multiple regression was used to examine the study hypotheses. RESULTS: As hypothesized, the number of different types of compensation incentives used (cost containment, productivity, quality) was positively associated with the comprehensiveness of care management practices. The degree of salary control (ie, market-based salary grades and ranges versus the use of bookings or fees and individual negotiation) was also positively associated with the deployment of care management practices. As hypothesized, market pressures in the form of percentages of health maintenance and preferred provider organization patients seen were generally positively associated with the use of care management practices. Organizational culture had no association except that a patient-centered culture in combination with a greater number of different types of compensation incentives used was positively associated with greater use of care management practices. CONCLUSIONS: Both compensation incentives and managed care market pressures were significantly associated with the use of evidence-based care management practices. The lack of association for culture may be due to the relatively amorphous nature of most physician organizations at this point.

Cross-Sectional Studies↗

PubMed1983

Synergistic effect of heparin and chemotactic factor on polymorphonuclear leukocyte aggregation and degranulation.

The in vitro effects of therapeutic amounts of polyanionic heparin on human polymorphonuclear leukocytes (PMN) aggregation and on the release of cationic lactoferrin from PMN-specific granules were investigated. Incubation of 1 X 10(7) human PMNs with 0.3 unit/ml of heparin followed by stimulation with the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) 2 X 10(-7) M significantly increased PMN aggregation, compared with controls. Cytochalasin B potentiated aggregation, which was further increased by incubation of the PMNs with heparin. Similarly, heparin also increased PMN degranulation and lactoferrin release following stimulation with FMLP with or without cytochalasin B, compared with controls. In addition, human lactoferrin complexed with heparin on a sucrose density gradient and caused a significant shift in the migration of 3H-heparin. Finally, rabbits pretreated with intravenous heparin resulting in prolongation of their activated partial thromboplastin time (APTT) to 1.5 to 2.5 times baseline had more profound reduction in PMN counts following a challenge with the secretagogue phorbol myristate acetate (PMA). These studies demonstrate that heparin can interact synergistically with chemotactic stimuli known to evoke lactoferrin release, which in turn leads to enhancement of PMN aggregation. Our data further suggest that heparin may be contraindicated in the treatment of syndromes with increased PMN aggregation such as endotoxin-induced Schwartzman-type reactions.

Animals↗

PubMed1993

Violence by and against women: a comparative and cross-national analysis.

Drawing from different kinds and levels of analysis, this article synthesizes current knowledge on women's violent offending and victimization cross-nationally. Individual-level data indicate characteristics and situations that put women at risk for violence within particular countries. Aggregate-level data concentrate on women's risks of violent encounters across nations and the societal-level factors that are associated with these risks. This multinational, multilevel approach reveals substantial gaps between our understanding of the types of encounters in which women are at greatest risk for violence and the societal correlates that predict gender distributions in violence across nations.

Adolescent↗

PubMed2003

Spectroscopic investigation on gel-forming beta-sheet assemblage of peptide derivatives.

The conformational studies of peptide derivatives A and B in a gel state were studied by using circular dichroism (CD), Fourier transformed infrared (FTIR), and fluorescence spectroscopic techniques. Birefringence and electron microscopic studies were carried out to characterize the morphological aspects of the fibrils in the gel. The FTIR spectra of the peptides show the absence of free NH in the gel state, implying that the intermolecular hydrogen-bond formation is the driving force for the aggregation. The CD spectrum of the peptide gels shows the presence of antiparallel and parallel beta-sheet conformation for peptide derivatives A and B, respectively. Electron microscopic studies (EM) of the peptide derivatives A and B reveal that peptide A formed rigid, rod-like structures without cross-linking and peptide B formed loose fibrils organized into highly noncovalently cross-linked mesh-like structural aggregates. Peptide A was much more soluble in alcoholic solvents than peptide B, and no birefringence was observed with Congo red (CR) staining in the temperature range of 0-80 degrees C. The spectroscopic studies indicate that peptide B consists of domains having a significant amount of beta-sheet structure and exhibiting golden yellow birefringence between 53 and 56 degrees C when stained with Congo red. On the other hand, peptide A gives no evidence of birefringence under polarized light. Fluorescence probe binding studies with pyrene in gel state with peptides A and B indicates the polarity in the interior of the aggregates. The data presented in the present work indicate that peptide B forms fibrils, which is similar to amyloid aggregates that are present in biological systems.

Amino Acid Sequence↗

PubMed1978

A comparison of imidazole and 9,11-azoprosta-5,13-dienoic acid. Two selective thromboxane synthetase inhibitors.

Two selective thromboxane A2 synthetase inhibitors, imidazole and 9,11-azoprosta-5,13-dienoic acid (azo analog I) were compared to determine their effects on the quantitative formation of thromboxane B2 and prostaglandin E2 accompanying human platelet aggregation. Azo analog I was at least 200 times more potent, on a molar basis, than imidazole in suppressing thromboxane B2 formation in either platelet-rich plasma or washed platelet suspensions aggregated with arachidonic acid or prostaglandin H2. The inhibitors differed in their effect on the aggregation response itself. Azo analog I selectively suppressed thromboxane A2 formation with an accompanying, parallel, suppression of the platelet aggregation. Imidazole selectively suppressed thromboxane A2 formation, but only suppressed the accompanying aggregation in platelet rich plasma, and not washed platelet suspensions. The results indicate that azo analog I functions by competitive inhibition of prostaglandin H2 on the thromboxane synthetase, and that imidazole, while it suppresses thromboxane A2 formation, may have an associated agonist activity that enhances platelet aggregation. The data presented support this hypothesis, and they emphasize the importance of thromboxane A2 in arachidonate mediated platelet aggregation.

Arachidonic Acids↗

PubMed1990

Phospholipid independent phosphorylation of protamine by protein kinase C: effects of polyanions.

The ability of purified protein kinase C (PKC) to phosphorylate protamine sulphate was found to be totally independent of phospholipid cofactors, whereas the phosphorylation of protamine free base was markedly increased by the presence of phosphatidylserine (PS). The hypothesis of an activation of PKC by the sulphate groups of protamine sulphate was confirmed by the high phosphorylation of protamine free base in the presence of non-peptide polyanionic compounds, such as glycoaminoglycans or polynucleotides. The catalytic fragment of PKC supported protamine base phosphorylation with the same polyanionic dependency. Light scattering intensity measurements showed that this phosphorylation correlated to the substrate/cofactor aggregation. These data support the view that apparent phospholipid-independent activation of PKC results from the formation of aggregates in the assay and this could result in the non-specific activation of this enzyme through its catalytic domain.

Animals↗

PubMed2005

Humans appear no more sensitive than laboratory animals to the inhibition of red blood cell cholinesterase by dichlorvos.

Inhibition of red blood cell (RBC) cholinesterase is a consistent and sensitive indicator of exposure to dichlorvos (DDVP). Absent human data, default 10-fold adjustment factors for potential interspecies and intraspecies sensitivity differences would be used in developing a reference dose from the no observed effect levels for this endpoint obtained in toxicological assessments of laboratory animals. However, many studies of the cholinesterase-inhibiting effects associated with DDVP exposure have been conducted in humans, including healthy male volunteers, other healthy subpopulations, and diverse clinical subpopulations. Indeed, ample human data exist to permit a data-based assessment of potential interspecies sensitivity differences in RBC cholinesterase inhibition associated with DDVP exposure. In aggregate, these data demonstrate that the DDVP doses producing inhibition in humans are virtually identical to those eliciting the same levels of inhibition in laboratory rats, mice, monkeys, and dogs. Thus, healthy humans appear to be no more sensitive than laboratory animals to DDVP's effects on RBC cholinesterase, and an interspecies uncertainty factor of 1 is appropriate and scientifically warranted for use in DDVP risk assessments.

Algorithms↗

PubMed1987

A strategy for merging and analyzing work history data in industry-wide occupational epidemiological studies.

Study populations examined in epidemiologic investigations of occupational disease risks often are assembled by the pooling of employee data from several workplaces that share common exposure factors. The primary objectives of this approach are to enhance the representativeness of the overall study population and to obtain sufficient employee sample sizes in exposure subgroups of interest. Among the many epidemiologic aspects that must be considered carefully in such industry-wide studies is the inter- and intra-company or plant comparability of employee work history data. Currently, the literature is void of articles that specifically address the fundamental data reduction and statistical analysis issues related to merging work history data from several distinct cohorts. This paper describes the basic methodologic problems associated with the pooling of work history data and proposes a joint job title/job exposure-based uniform coding scheme (UCS) that facilitates the aggregation of data from similar or diverse cohorts in a variety of epidemiologic study settings. The utility of the UCS as both an efficient data coding structure and a flexible basis for statistical analysis is described within the context of a popular computer software program for analyzing occupational cohort data. The fundamental features of the UCS are illustrated using data from a recent industry-wide study of copper and zinc smelter workers.

Data Collection↗

PubMedDate not supplied

Can the social model explain all of disability experience? Perspectives of persons with chronic fatigue syndrome.

OBJECTIVE: The social model of disability has had a major influence on the academic field of disability studies and on contemporary understandings of the causes and experience of disability. The purpose of this study was to examine the adequacy of the social model for explaining the disability experience of persons with chronic fatigue syndrome (CFS). METHODS: This qualitative study examined the experiences of 47 adults with CFS participating in a research project that aimed to evaluate a participant-designed rehabilitation program. Data were aggregated from focus group interviews, open-ended questionnaires, progress notes, and from a program evaluation questionnaire. Data analysis was based on a grounded theory approach and used triangulation of multiple data sources and member checks to assure dependability of findings. RESULTS: Four themes emerged from the analysis: (1) minimization and mistrust of the disability; (2) negative experiences of impairment; (3) lack of identification with the disability community; and (4) the focus on advocacy as a quest for legitimacy. These themes varied in the extent to which they conformed to the principles set forth by the social model. CONCLUSIONS: Although the social model has important contributions to lend to occupational therapy practice, it is important to recognize that it may not capture the full reality of disability. In particular, the social model has serious limitations in describing the disability experience of individuals with disabilities who do not have visibly obvious disabilities and whose impairments do not conform to the traditional viewpoint of disability.

Adult↗

PubMed1996

Phosphatase inhibitors promote ICAM-1 and LFA-1 mediated homotypic aggregation of Jurkat and U937 cells.

Here we investigated the role of cellular phosphatases in activation of homotypic aggregation in leukocytes by adding the phosphatase inhibitors okadaic acid (OA) and calyculin A (CA) to cultures of the human monocytic U937 cell line and the human T-lymphocytic Jurkat cell line. We found that OA produces a 120-fold increase of homotypic aggregation with Jurkat cells and a 200-fold increase with U937 cells. Calyculin A increased aggregation of Jurkat cells 10-fold and U937 cells 88-fold. Monoclonal antibodies to LFA-1 completely inhibited the OA and CA induced aggregation in both cell lines, whereas the monoclonal antibody to ICAM-1 only inhibited U937 cell aggregation. These data suggest that phosphatase activity is important in the regulation of ICAM-1 and LFA-1 mediated homotypic aggregation in leukocytes.

Cell Aggregation↗

PubMed2002

Urea stress is more akin to EGF exposure than to hypertonic stress in renal medullary cells.

Although urea is considered to be a cell stressor even in renal medullary cells perpetually exposed to this solute in vivo by virtue of the renal concentrating mechanism, aspects of urea signaling resemble that of a peptide mitogen. Urea was compared with epidermal growth factor and hypertonic NaCl or hypertonic mannitol using a large-scale expression array-based approach. The expression profile in response to urea stress more closely resembled that of EGF treatment than hypertonic stress, as determined by hierarchical cluster analysis; the effect of urea+NaCl was equidistant from that of either solute applied individually. Among the most highly urea- and hypertonicity-responsive transcripts were genes that had previously been shown to be responsive to these solutes, validating this approach. Increased expression of the activating transcription factor 3 by urea was newly detected via expression array and confirmed via immunoblot analysis. Earlier, we noted an abrogation of tonicity-dependent gene regulation by urea, primarily in a transient transfection-based model (Tian W and Cohen DM. Am J Physiol Renal Physiol 280: F904-F912, 2001). Here we applied K-means cluster analysis to demonstrate that the genes most profoundly up- or downregulated by hypertonic stress were partially restored toward basal levels in the presence of urea pretreatment. These global expression data are consistent with our earlier biochemical studies suggesting that urea affords cytoprotection in this context. In the aggregate, these data strongly support the hypothesis that the urea effect in renal medullary cells resembles that of a peptide mitogen in terms of the adaptive program of gene expression and in terms of cytoprotection from hypertonicity.

Activating Transcription Factor 3↗