Thesis (doctoral)--Utrecht, 1981.

Thesis (M. Med. Sc.)--University of Hong Kong, 2005.

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 146-156).

Thesis (MTech (Biomedical Technology))--Cape Peninsula University of Technology, 2016. / Type 2 diabetes mellitus (T2DM) is a metabolic disorder which is characterised by insulin resistance, defective insulin secretion or both. The chronic state of hyperglycemia in diabetes is associated with microvascular complications and macrovascular complications which account for an estimated 80% of deaths as a result of cardiovascular complications. Type 2 diabetes mellitus is an inflammatory disease and pro- inflammatory stimuli in the form of activated endothelial cells, render the vascular endothelial surface attractive for both platelets and leukocytes. Activated platelets bind to the exposed extracellular matrix (ECM) and also to each other in both physiological haemostasis and pathological thrombosis. They can also adhere to leukocytes. Platelet leukocyte interactions are divided into 3 stages; these include the initiation of the interaction, stabilization of the aggregates and amplification of leukocyte activation. This study attempts to contribute to the current knowledge of T2DM by investigating the percentage of monocytes and neutrophils forming aggregates with platelets in pre-diabetes and diabetes and comparing this to non- diabetes individuals as well as the up regulation of pro-thrombotic and activation antigens on the surface of monocytes and neutrophils (Tissue Factor and CD69). Levels of platelet activation and function will be determined by both plate monocyte aggregates (PMA) and platelet neutrophil aggregates (PNA). A total of 124 individuals were recruited from Bellville South, Cape Town, South Africa. This comprised of diabetes (DM) (n=15), pre-diabetes (pre-T2DM) (n=25) and controls (n=84). All individuals were screened for diabetes using the oral glucose tolerance test (OGTT). Platelet leukocyte measurements were performed using the Navios 8-colour flow cytometer. The median percentage of circulating platelets bound to monocytes (%PMAs) was significantly increased in the T2DM 49.04[36.78-62] and the Pre-T2DM 48.96[36.72-61.2],groups, compared to the control group 7.2[5.4-9], p<0.0001. The median %PNAs, which show interactions between neutrophils and platelets, were significantly increased in the T2DM group 13.56[10.17-16.95] compared to the control group 6.01[4.51-7.51] p<0.0001. Platelet monocyte aggregates (PMAs) were higher in both the pre-T2DM and T2DM groups when compared to the control group indicating increased interactions between platelets and monocytes. In addition to forming aggregates with leukocytes, the platelets were able to initiate activation and phenotypic change to the leukocytes by increasing the expression of CD69 and TF (CD142). This finding provides further evidence that there is a link between the inflammatory process and the prothrombotic activity evident in diabetes and pre-diabetes individuals. Furthermore, we describe elevated levels of circulating activated neutrophils which directly correlate with increased PNA formation in both the pre-T2DM and T2DM group. / South African Medical Research Council

Orientador: Edson Antunes / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-11T20:19:41Z (GMT). No. of bitstreams: 1 Morganti_RafaelPrada_D.pdf: 740260 bytes, checksum: c6b0779cd2f8af7471aefb0da921a0a6 (MD5) Previous issue date: 2008 / Resumo: A sepsis é a segunda causa de morte em pacientes internados em unidades de tratamento intensivo não coronariano. Pacientes com sepsis apresentam anormalidades plaquetárias como trombocitopenia, prolongamento do tempo de coagulação, coagulação intravascular disseminada, trombose microvascular maciça e sangramentos. Entretanto, os mecanismos envolvidos nestas alterações plaquetárias ainda são mal compreendidos. O objetivo deste trabalho foi investigar as ações do lipopolissacarídeo (LPS) de E. coli, e de enterotoxinas de Staphylococcus aureus (SEA e SEB), na adesão e na agregação de plaquetas humanas, bem como os mecanismos envolvidos nesses fenômenos. As plaquetas foram expostas ao LPS, SEA ou SEB em diferentes concentrações e tempos de incubação para avaliação in vitro da adesão ou agregação. Além disso, realizou-se experimentos para verificar o papel do óxido nítrico (NO) e de espécies reativas de oxigênio nas ações induzidas pelo LPS, SEA e SEB, assim como a sinalização intracelular (mobilização de Ca+2) e ativação do receptor do fibrinogênio glicoproteína IIb/IIIa (GPIIb/IIIa). A incubação de plaquetas com LPS, SEA e SEB por períodos 5 a 120 min inibiu a adesão espontânea das plaquetas ao fibrinogênio, sendo esta inibição dependente da concentração e do tempo de incubação. A adesão de plaquetas ativadas com trombina também foi inibida após incubação com LPS, SEA ou SEB por 5 a 120 min. Porém, a inibição em plaquetas ativadas foi menor quando comparada à inibição da adesão espontânea. Esta inibição ocorreu de forma independente de aumentos intraplaquetários de GMPc e AMPc. Com o objetivo de se entender o mecanismo de ação envolvido na inibição da adesão plaquetária pelo LPS, SEA e SEB as plaquetas foram pré-tratadas com os seguintes agentes farmacológicos: superóxido dismutase (seqüestrador de ânion superóxido), polietilino glicol superóxido dismutase (seqüestrador de ânion superóxido intracelular), polietileno glicol catalase (degrada peróxido de hidrogênio), puromicina e ciclohexamida (inibidores de síntese protéica). Em conjunto, nossos dados mostraram que o efeito inibitório do LPS não envolve aumento de anion superóxido (O2 -) e de peróxido de hidrogênio (H2O2), nem a formação de proteínas neo-sintetizadas, e alterações na ativação da GPIIb/IIIa. Por outro lado, o LPS reduziu significativamente o influxo externo de cálcio, sem afetar a mobilização intracelular deste cátion. Em relação às enterotoxinas estafilocócicas, a síntese de neo-proteínas e aumento de O2 - não tem papel direto sobre a inibição plaquetária, embora um aumento nas concentrações de H2O2 intracelulares esteja ligado a esta resposta. Em conclusão, a exposição ao LPS inibiu a adesão a agregação plaquetária, dosee tempo-dependente, inibindo a influxo de cálcio; da mesma forma, a incubação com SEA ou SEB inibiu a adesão de plaquetas ao fibrinogênio, por um mecanismo que envolveria a formação de H2O2 / Abstract: Sepsis is the second major cause of death in intensive care unit. Septic patients show abnormalities in platelet like thrombocytopenia, prolongation in coagulation time, disseminated intravascular coagulation, deep venous thrombosis and bleedings. However, the mechanisms involved in these platelet alterations are not totally clear. The objective of this work was investigate the actions of lipopolysaccharide (LPS) from E. coli and enterotoxins from Staphylococcus aureus (SEA and SEB), in human platelet adhesion and aggregation, likewise the mechanism involved in these phenomenon. The platelets were exposed to LPS, SEA or SEB in different concentrations and times of incubation in vitro evaluations of adhesion and aggregation. Moreover, experiments to elucidate the participation of nitric oxide (NO) and reactive oxygen species in the actions of LPS, SEA and SEB, likewise the intracellular sinalization (calcium mobilization) and activation of fibrinogen receptor glycoprotein IIb/IIIa (GPIIb/IIIa) were carry out. The platelets incubation with LPS, SEA and SEB for 5 to 120 min, inhibited the spontaneous adhesion to fibrinogen and this inhibition was dependent of concentration and time of incubation. The thrombin activated adhesion of platelets was concentration and time dependently also inhibited after incubation with LPS, SEA and SEB for 5 to 120 min. However, the activated platelets inhibition was lower when compared to spontaneous adhesion inhibition. This inhibition was not dependent of intracellular levels increase of cGMP and cAMP. To understand the mechanism of action involved in the platelet adhesion inhibition by LPS, SEA and SEB, the platelets were previously treated with pharmacological agents like: superoxide dismutase (superoxide anion scavenger), superoxide dismutase-polyethylene glycol (superoxide anion intracellular scavenger), catalase-polyethylene glycol (Hydrogen peroxide intracellular scavenger), puromycin and cyclohexamide (protein synthesis inhibitors). Our data suggests that the inhibitory effect of LPS neither involve superoxide anion (O2 -) and hydrogen peroxide (H2O2) increase, nor the formation of neo-proteins, and alterations on activation of glycoprotein IIb/IIIa. In contrast, LPS significantly reduce the external calcium influx, without effecting calcium internal mobilization. With regard to staphylococcal enterotoxin, the protein synthesis and rise in O2 - do not play a role in the platelet inhibition; however the increase of H2O2 intracellular concentration was involved in this response. In conclusion, platelet aggregation and adhesion was inhibited after addition of LPS, concentration and time-dependently, inhibiting calcium influx; similary, incubation with SEA or SEB inhibited platelets adhesion to fibrinogen, by a mechanism involving H2O2 formation / Doutorado / Doutor em Farmacologia

Haemostasis is a highly regulated system, involving a myriad of cell types (endothelium, immune cells, platelets, etc.), proteins (enzymes, receptors, etc.) and signalling molecules (sterols, nucleotides, etc.). Haematophagous organisms, such as ticks, have evolved a number of strategies to overcome host haemostatic responses to feed effectively. Salivary apyrases are a class of nucleotide-metabolising enzymes that blood-feeding parasites utilise to modulate extracellular nucleotides, like ATP and ADP, to prevent platelet activation and aggregation. This specific enzyme function has evolved in blood-feeding parasites from the ecto-ATPdase/CD39 (E-NTPDases)-, Cimex-type- and 5’-nucleotidase/CD73 enzyme families. Furthermore, most arthropod apyrases are ascribed to the 5’-nucleotidase/CD73 enzyme family. The salivary apyrase from Ornithodoros savignyi has not been characterised to a specific enzyme family and the presence of 5’-nucleotidase homologs have not been demonstrated. Therefore, in this study 5’-nucleotidase homologous transcripts were identified from O. savignyi salivary gland DNA, using a 5’-nucleotidase specific degenerate primer and RACE protocols. Two full-length putative 5’-nucleotidase isoforms were identified that shared significant sequence identity and similarity to a 5’-nucleotidase from R. (B.) microplus and putative apyrases from I. scapularis and R. appendiculatus. Utilising computational tools, iso-electric points, molecular weights and cellular localisation were determined. The isoforms were predicted to be soluble secreted proteins, which correlated with the trend observed for parasitic apyrases in the 5’-nucleotidase family. Phylogenetic analysis of the 5’-nucleotidase family revealed that the O. savignyi 5’-nucleotidase isoforms claded monophyletically with the putative apyrases from I. scapularis and R. appendiculatus, excluding the 5’-nucleotidase from R. (B.) microplus. Molecular modelling of these two proteins showed a similar protein structure to a periplasmic ecto-5’-nucleotidase from E. coli. The similar architecture revealed a high conservation of key residues involved in dimetal coordination, catalysis and substrate binding, therefore a similar catalytic mechanism was proposed. It was hypothesised that the isoforms identified may be putative apyrases. To test this hypothesis, the 5’-nucleotidase isoform I was recombinantly expressed in yeast. Cross-reactivity was demonstrated with a polyclonal anti-apyrase antibody produced from O. savignyi native apyrase. The latter implied that the native apyrase may be a member of the 5’-nucleotidase enzyme family. However, no sequence information for native apyrase was available for comparison and therefore native enzyme was purified with ion exchange chromatography. Subsequent, Edman N-terminal sequencing and MS/MS analysis with purified enzyme identified peptide sequence fragments that shared a high degree of sequence identity with both 5’-nucleotidase isoforms. It was concluded that native apyrase is a mixture of the isoforms identified from O. savignyi salivary gland DNA. These results represent the first confirmation of a tick apyrase that belongs to the 5’-nucleotidase family of enzymes. Further confirmation will be achieved by testing activity of the recombinant protein and future experiments may assess the potential of this protein as a vaccine candidate. / Dissertation (MSc)--University of Pretoria, 2009. / Biochemistry / unrestricted

Charles University Faculty of Pharmacy in Hradec Králové Department of Pharmacology & Toxicology Student: Nikola Kopková Supervisor: Assoc. Prof. Přemysl Mladěnka, Pharm.D., Ph.D. Title of diploma thesis: Antiplatelet effects of flavonoids The most common antioxidants in ordinary food are flavonoids. They show antioxidant and anti-aggregation effects and other positive effects on cardiovascular diseases. Flavonoids are promising candidates to be antiplatelet drugs. Although several mechanisms responsible for antiplatelet activity have been suggesteed, only a few have been documented by published studies. The inhibition of blood platelet aggregation by flavonoids is reversible, which is another important factor. Data on thrombin-induced aggregation are controversial, some claim that flavonoids have no effect, the others says they have positive effects. (In the case of quercetin and genistein, inhibition of aggregation induced by thrombin was documented). The effect on arachidonic acid in the aggregation cascade is well documented, but there are several inconsistencies resulting from the use of different materials. Other mediators of aggregation are phospholipase A2, which plays a key role in the formation of inflammatory mediators. In this case, it has been shown that mainly genistein is capable of...

The active state of plasminogen activator inhibitor type-1 (PAI-1) is prolonged when it forms a complex with vitronectin (VN), a major serum protein. Active PAI-1 in the PAI-1:VN complex serves many functions related to fibrinolysis and cell migration but key to these effects is its extracellular distribution. PAI-1:VN complexes can bind to exposed vimentin (VIM) on activated platelet and platelet microparticles, resulting in the assembly of PAI-1:VN:VIM ternary complexes. However, the manner in which the vimentin cytoskeleton is presented extracellularlyi s not well understood. I hypothesized that PAI-1:VN:VIM ternary complex assembly occurs on cell surfaces when microparticle release leads to exposure of vimentin cytoskeleton which can lead to either assembly of the ternary complex or become involved in an autoimmune response specific for vimentin. To follow the intracellular and extracellular fate of PAI-1, I constructed an expression vector encoding PAI-1-dsRed, a fluorescent form of PAI-1, which would permit live cell tracking of PAI-1 in megakaryocytes and endothelial cells. Secondly, to study how vimentin is expressed on platelets and platelet microparticles, flow cytometry was used to isolate vimentin positive platelets or PMP's and atomic force microscopy was performed to image platelets or PMP's at nanoscale resolution. From these studies, I propose a model of vimentin expression in which the junction of microparticle release results in the exposure of cytoskeletal vimentin on both the cell and the microparticle. This exposed vimentin could potentially induce VN multimerization on the same cell surface leading to incorporation of multiple PAI-1:VN complexes. Finally, I investigated how anti-vimentin antibodies can induce platelet:leukocyte conjugate formation. To achieve this, in vitro tests were performed to determine the binding site of anti-vimentin antibodies (AVA's) and how they induce blood cell activation. Overall, my results suggest that vimentin exposure in our model of microparticle release can lead to ternary complex assembly if suitable quantities of PAI-1 are released during platelet activation. In the setting of transplant vasculopathy with high titres of AVA's, vimentin-positive granulocytes can bind these autoantibodies, which then leads to platelet activation and the formation of platelet:leukocyte conjugates. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

Treponema pallidum ssp. pallidum is the causative agent of syphilis, a multi-stage bacterial infection, transmitted sexually or from mother-to-child, with an unparalleled range of symptoms arising from the ability of treponemes to penetrate any tissue and cross immune privileged endothelial barriers to access the brain, the eye, and the fetus. Further, without treatment T. pallidum evades immune clearance and persists within the host to establish a chronic infection. These characteristics suggest that T. pallidum may have evolved unique mechanisms for immune escape and to mediate host-cell interactions. The findings presented in this dissertation contribute to our knowledge of T. pallidum pathogenesis by investigating a previously unexplored host-cell interaction, between T. pallidum and human platelets. These results validate the hypothesis that, as a pathogen which successfully utilizes vascular dissemination, T. pallidum would not only encounter, but interact with human platelets, complex cells now viewed as vascular sentinels that participate in many host-pathogen interactions. This is the first study to demonstrate that T. pallidum interacts with human platelets and to characterize and quantify these interactions using high resolution microscope imaging techniques (video and frame analysis). These interactions were shown to be complex, reversible and mediated by motile treponemes localizing to stationary, (slide-adhered) activated platelets, versus to free-floating, inactive platelets. In addition, it was found that T. pallidum discriminates between the level of platelet activation and preferentially localized to the most activated platelet. Treponema pallidum was also able to induce platelet activation following an extended lag period. Modified chemotaxis assays quantified by flow cytometry, were used to investigate the migration of T. pallidum in response to the plasma of platelets differentially activated with infection-relevant host components (thrombin, collagen). The results herein reveal that T. pallidum discriminates between different mechanisms of platelet activation, with a significant preference towards the secretions of collagen-activated platelets (under these experimental conditions), compared with that of inactive or thrombin-activated platelets. Previously, T. pallidum chemotaxis had been investigated through genomic characterization and molecular interaction studies with recombinant proteins. This investigation is the first time live T. pallidum was utilized for in vitro chemotaxis assays and is also the first study of pathogen chemotaxis in response to the secretions of differentially activated platelets. The body of work in this dissertation provides a foundation to further investigate the role of T. pallidum-platelet interactions during infection, adding a new host-cell interaction to our understanding of T. pallidum pathogenesis. The evidence that the molecular gradients of host components can affect T. pallidum migration suggests an important role for chemotaxis during T. pallidum infection. Together, the characterization of platelet-interactions and treponeme chemotaxis in response to host components, adds to our knowledge of T. pallidum-host interactions, and eludes to additional pathogenic strategies that may facilitate T. pallidum dissemination and immune evasion. / Graduate / 2022-01-14

Previous work on the binding of resting platelets to the basement membrane glycoprotein, laminin, has identified the Ic/IIa integrin c01aplex (CD49f/CD29), also known as VLA-6, as the receptor. There exists however, another protein with a molecular weight of 67kDa, that mediates this function on other cells. It is abundantly expressed on the membranes of breast cancer cells, where it plays a key role in both the localisation at, and penetration of vascular beds, by metastases. The objectives of this study were: * The development of a micro-titre assay similar to those used in previous studies, standardised and calibrated to characterize the adhesion of unstimulated normal human platelets to laminin-coated surfaces. * To determine the effect on adhesion of platelet activation, enzymatic surface-glycoprotein removal, antibodies to specific receptors and interaction with other adhesive proteins known to bind to platelet membranes. * To establish the in vivo relevance of the experimental findings, by the assay of adhesion of glycoprotein IIb/IIIa-deficient platelets of two patients with Glanzmann's Thrombasthenia. These studies serve d to distinguish specific binding sites for laminin from the known surface receptors of platelets. The methodology used to isolate laminin receptors from the membranes of breast carcinoma cells was then applied to platelet concentrates. Membranes were obtained by centrifuging the ultrasonic lysate of a unit of platelets. These were solubilized and passed over a laminin-Sepharose column. The bound components were eluted and identified by means of SDS-gel electrophoresis, after which a concentrate was tested for laminin binding by means of dot-blot methodology. The principle contribution of this work is the finding of a 67kDa receptor for laminin on the surface membranes of platelets. The combination of the various approaches applied to characterise the adhesion of platelets to laminin, show that this is a specific, Mg²⁺-dependent process, inhibited by Ca²⁺ and not enhanced by platelet activation. Adhesion was decreased by proteolysis with trypsin and chymotrypsin, showing that the adhesion is mediated by a surface glycoprotein. Proteolysis with the Serratia marcescens metalloprotease, which cleaves off glycoprotein lb, did not affect adhesion, proving that this well-known receptor for platelet adhesion is not involved in the adhesion. The receptors GPIV and glycocalicin were also excluded, as the presence of antibodies to these receptors had no effect. Prior incubation with fibrinogen or von Willebrand factor, which binds to specific receptors on the platelet membrane, inhibited adhesion, most likely due to spatial interference with the receptor site for laminin. The presence of the tetrapeptide recognised by the membrane receptors for many adhesive proteins, RGDS, at concentrations of up to 1mM, had no effect. The platelets of the two subjects with Glanzmann's Thrombasthenia adhered normally, definitively ruling out the involvement of GPIIb/IIIa, which is absent from these platelets. The isolation process recovered a membrane component from the laminin-Sepharose column with an elution pattern identical to that for the well characterised 67kDa receptor for laminin on the surface of breast carcinoma cells. They have the same molecular weights in both the reduced (67kDa) and non-reduced (53kDa) states. Blot identification demonstrated laminin binding by the eluate. In the last part of the work, collaborative studies using more sophisticated methodology have confirmed that platelet receptors for laminin play a role in their adhesion to living tissue. Anti-laminin Fab antibodies significantly decreased the adhesion when whole blood was perfused over isolated rabbit aortic segments. That these receptors are identical to the 67kDa receptor of breast carcinoma cells was shown by the specific, high affinity binding of antibodies directed at the carcinoma receptors to the surface of platelets when examined by flow cytometry. In addition, they inhibit platelet adhesion by 50-60% in the micro-titre assay. It is proposed that both the VLA-6 and the 67kDa receptors are required for platelet adhesion to laminin, possibly as a two-stage process, similar to the systems for adhesion to von Willebrand factor, where binding is initially to GPIb, followed by binding to GPIIb/IIIa. The possible relevance of this receptor in the pathophysiology of the metastatic process is discussed.