Inherited thrombocytopenias, including inherited giant platelet disorders (IGPD) or macro thrombocytopenias are relatively rare, but their prevalence is likely underestimated from complexities of diagnosis and a spectrum of subclinical phenotypes. Harris platelet syndrome (HPS) is the most common IGPD reported from the Indian subcontinent. Of note there are an increased number of hemoglobinopathies reported from the geographic location. We analysed red blood cell and platelet indices of blood donors with HPS from the north eastern part of India and compared them with blood indices of blood donors of south India. We found a statistically significant lower platelet count in blood donors with HPS (median, range) 132 (71-267) vs. 252 (160-478) as compared to donors from south India (P < 0.001). Mean platelet volume (MPV) was higher in donors with HPS 13.1, (range 12-21.9 fl) as compared to donors from south India 7.35 (range 6-9.2 fl) (P < 0.001). This study showed that blood donors with HPS had a low median platelet bio-mass 0.17 (0.10-0.38%) vs. 0.19 (0.13-0.28%) in donors from south India. The platelet distribution width (PDW) was 17.4 (14.9-19.6) in donors with HPS vs. 16.38 (15.2-18.5) in south Indian blood donors (P < 0.001). Thirty-three donors with HPS had a normal platelet count with MPV more than 12 fL. Only donors with HPS had giant platelets and thrombocytopenia on peripheral blood smear examination. None of these donors had Dohle body inclusion in their leukocytes. Compared to donors from south India, donors with HPS had a significantly lower hemoglobin 13.8 (12-16.3 gm/dL) vs. 14.8 (12-18) respectively (P < 0.001) while red distribution width (RDW) was higher in HPS 13.6 (11.5-16.7) vs. 12.8 (11.4-15.1). However we did not find any statistically significant difference in MCV, MCH, MCHC between the two groups. Peripheral blood smear did not show any obvious abnormal red blood cell morphology. In the blood donors with HPS we found a statistically higher MPV, RDW and a lower platelet count and platelet biomass. A population-based study will be helpful in determining the existence of any hemoglobinopathies among subjects with HPS.

According to the World Health Organization (WHO), Cardiovascular Disease (CVD) is the leading cause of death in the world. Biomechanics and fluid dynamics of blood flow play an important role in CVD mediation. Shear stress plays a major role in platelet-substrate interactions and thrombus formation and growth in blood flow, where under both pathological and physiological conditions platelet adhesion and accumulation occur. In this study, a three-dimensional dynamic model of platelet-rich thrombus growth in stenosed vessels using computational fluid dynamics (CFD) methods is introduced. Platelet adhesion, aggregation and activation kinetics are modeled by solving mass transport equations for blood components involved in thrombosis. The model was first verified under three different shear conditions and at two heparin levels. Three-dimensional simulations were then carried out to evaluate the performance of the model for severely damaged (stripped) aortas with mild and severe stenosis degrees. For these cases, linear shear-dependent functions were developed for platelet-surface and platelet-platelet adhesion rates. It was confirmed that the platelet adhesion rate is not only a function of Reynolds number (or wall shear rate) but also the stenosis severity of the vessel. General correlations for adhesion rates of platelets as functions of stenosis and Reynolds number were obtained based on these cases. The model was applied to different experimental systems and shown to agree well with measured platelet deposition. Then, the Arbitrary Lagrangian Eulerian (ALE) formulation was used to model dynamic growth by including geometry change in the simulation procedure. The wall boundaries were discretely moved based on the amount of platelet deposition that occurs on the vessel wall. To emulate the dynamic behavior of platelet adhesion kinetics during thrombus growth, the validated model for platelet adhesion, which calculates platelet-surface adhesion rates as a function of stenosis severity and Reynolds number, was applied to the model. The model successfully predicts the nonlinear growth of thrombi in the stenosed area. These simulations provide a useful guide to understand the effect of growing thrombus on platelet deposition rate, platelet activation kinetics and occurrence of thromboembolism (TE) in highly stenosed arteries. / Ph. D.

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M.Sc.(Med.), Faculty of Health Sciences, University of the Witwatersrand, 2008 / Introduction It is widely recognised that stroke is a multi-factorial disorder in which platelets play a crucial role in thrombus formation resulting in ischaemic stroke. Platelet adhesion and aggregation are initiated by the interaction of various platelet glycoproteins (GP’s) such as GPIbα, which binds to von Willebrand Factor and GPIIb/IIIa a fibrinogen receptor. Recent studies have shown that the GP’s are polymorphic and the polymorphisms described within GPIbα such as Kozak- 5T/C, the variable number of tandem repeats (VNTR) and the Human Platelet antigen 2 (HPA2), have been implicated in the development of stroke, while the PIA polymorphism of GPIIb/IIIa was found to contribute to “aspirin resistance”. Therefore, these polymorphisms may be potentially important for early detection and early intervention and thus setting the need to provide for a high volume genotype testing at health care centres. One of the most used techniques to determine platelet function is platelet aggregometry. However, the major disadvantages of platelet aggregation is that it is influenced by a number of environmental factors and its access is limited to tertiary health centres. Platelet aggregation measures the functional expression of platelets, which is known to deteriorate over time. It is for this reason that new methods at molecular level such as polymerase chain reaction (PCR) are needed to explore the role of genotypic expressions, which are not influenced by environmental factors. Currently, conventional PCR is used to detect platelet polymorphisms in the research settings and has limitations as a routine diagnostic test. Furthermore, it is time consuming and is prone to contamination. With the recent advances in real-time PCR it is possible to genotype large sample batches rapidly without compromising on the quality, accuracy and precision of results. This study aims to adapt conventional PCR methodology onto a real-time platform for detecting platelet polymorphisms that have been implicated in both stroke and aspirin resistance. Materials and methods A total of 60 caucasian patients classified as having ischaemic stroke by virtue of MRI and Doppler analysis from the Stroke Clinic at the Johannesburg Hospital were enrolled for this study. Healthy caucasian individuals (38), age and gender matched were enrolled as controls. DNA samples were extracted from all the subjects and the prevalence of the Kozak –5T/C, HPA-2, VNTR and GPIIIa PIA polymorphisms were determined first by using conventional PCR and then the real-time LightCycler TM PCR method. Results The frequency of the unfavourable alleles ( the PIA2 allele for the GPIIIa PIA polymorphism, the T allele for the Kozak –5T/C polymorphism, the B allele for the HPA-2 polymorphism and the C allele for the VNTR polymorphism) of the different GP’s were higher in the stroke patients when compared to the control subjects but did not reach statistical significance. There was complete statistical agreement between the results obtained for the conventional PCR as compared to the results obtained for real-time PCR except for the VNTR polymorphism, due to the difficulty in designing and the unavailability of probes for the real-time PCR assay. However, it is important to note that adapting the real-time PCR as a new methodology would greatly benefit both the patients and the clinicians by providing early detection and the possibility of early therapeutic intervention. Conclusion Therefore in conclusion, it is possible to perform not only conventional PCR for platelet polymorphism but also real-time PCR on a large scale without compromising on the quality, accuracy and precision on platelet polymorphisms that play a significant role in stroke and aspirin resistance. However, a larger population based study needs to be performed to confirm the findings.

This study investigated the role of NMDARs in the differentiation of MEG-01 cells and in the activation of human platelets. This investigation demonstrated that the NR1, NR2D and NR3 subunit proteins are expressed in human platelets, with the NR1 subunit also expressed in MEG-01 cells. The NR2A subunit protein was not detectable in either MEG-01 cells or human platelets. PMA-induced differentiation of MEG-01 cells did not appear to stimulate changes in expression of any of the subunit proteins tested. Using assays to measure the changes in [Ca2+]i and ATP secretion, it was determined that donors could be separated into those who responded to the agonists applied and those who did not; responses also decreased over time in both assays. Human platelets from responding donors demonstrate an increase in [Ca2+]i in response to extracellular glutamate, and that increases in ATP secretion are detected at a 10-fold lower concentration. The same is also true with extracellular glycine. Increases in [Ca2+]i were elicited on the addition of extracellular NMDA; extracellular D-serine had no effect. NMDAR inhibitors, MK-801 and D-AP5, inhibited ATP secretion evoked by either glutamate alone or in combination with glycine. D-serine inhibited responses elicited by extracellular glycine. NMDARs play a role in MK differentiation, with the adhesion of MEG-01 cells cultured on a fibrinogen-surface and differentiated with PMA reduced by both inhibitors. PMA-treated MEG-01 cells increased both in size and irregularity, with the addition of NMDAR-specific inhibitors having no effect. S-nitrosylation also inhibits activation of NMDAR, and a new molecule has been developed which can detect S-nitrosylated proteins through a single step process in live cells. Overall, this study has shown that both human platelets and MEG-01 cells express NMDAR subunits, which have been demonstrated to form functional receptors in human platelets.

The study of platelet messenger and micro-RNAs is of increasing interest owing to the fact that platelets contain the machinery to splice and translate mRNA into proteins in response to inhibitory or activating signals. However, the relatively small size (roughly 4000-5000 transcripts) and short half-life of the platelet transcriptome makes this a technically challenging aspect of platelet biology to investigate. The aims of these thesis investigations were therefore to optimise protocols for the isolation of platelets for downstream RNA analyses and function testing, to investigate the functional capabilities of platelet subpopulations rich in RNA, and to understand the functional and transcriptomic impact of gene mutations predicted to influence platelet function. I found that the optimal method for isolating platelets from whole blood is to use simple single step centrifugation to obtain platelet rich plasma. This method is as effective as more involved methods at reducing white blood cell contamination whilst causing minimal platelet activation. Using this method in combination with flow cytometric cell sorting techniques I was able to isolate the newly formed reticulated platelet sub-population and to confirm the link between reticulation status and increased RNA content. Furthermore, using a range of platelet function assays I demonstrated that reticulated platelets are more reactive than non-reticulated platelets. By obtaining blood samples from a patient with a PLA2G4A mutation I was able to show that loss of cPLA2α enzymatic activity alters both platelet function and the expression of certain mRNA transcripts. My investigations using samples from a range of patients with bleeding tendencies show the benefit of combining deep platelet phenotyping with next generation sequencing to understand the causation of bleeding disorders. Together these investigations highlight the utility of genomic DNA and platelet specific mRNA studies in providing novel insights in to pathways regulating platelet reactivity.

Stroke is the third most common leading cause of death worldwide and is a major cause of serious long-term disability among adults. Platelet activation and it¡¦s interaction with leukocytes plays an important role in the pathophysiology of ischemic stroke. Anti-platelet drugs are widely used for secondary prevention after cerebral ischemia of non-cardioembolic origin and different anti-platelet drugs exert different pharmacologic effects on platelets. Several stimulations cause elevation of cytosolic Ca2+ level ([Ca2+]i), activating the secondary messenger in the platelet, and then leading to platelet activation. The majority of damage following acute stroke does not occur immediately, but rather develops gradually over the course of the following hours. Leukocytes are believed to liberate inflammatory cytokines and other neurotoxins in the ischemic brain and to promote microvascular occlusion through platelet-leukocyte-endothelium interactions in the ischemic penumbra. In this thesis, we tested the serial changes of platelet [Ca2+]i movement in patients after acute ischemic stroke. We evaluated platelet activation markers, leukocyte adhesion molecules and platelet-leukocyte interaction in patients with acute ischemic stroke. We also analyzed the relationship between these biomarkers and the clinical outcome. Furthermore, we compared the antiplatelet effect of aspirin and clopidogrel in patients after acute stroke Dysregulation of Ca2+ Movement in Platelets from Patients with Acute Ischemic Stroke Thirty-one patients with acute ischemic stroke and 27 at-risk controls were enrolled in this study. The platelet [Ca2+]i was measured using a fluorescent dye fura-2 after stimulation with arachidonic acid (AA), adenosine diphosphate (ADP), platelet-activation factor (PAF), and thrombin. The basal [Ca2+]i was higher in the stroke group than in the at-risk controls irrespective of the presence or absence of extracellular Ca2+. In the Ca2+-containing medium, both PAF and ADP, but not AA and thrombin, significantly increased the platelet [Ca2+]i in the stroke patients than in the at-risk controls. However, in the Ca2+-free medium, only PAF significantly increased the platelet [Ca2+]i in the stroke patients than in the at-risk controls. The basal [Ca2+]i and PAF-induced platelet [Ca2+]i rises were still higher in the stroke patients at the subacute stage than in the at-risk controls. Levels and Value of Platelet Activation Markers in Different Subtypes of Acute Non-Cardio-Embolic Ischemic Stroke Platelet activation markers (CD62P, CD63, and CD40L) and platelet-leukocyte interaction were measured by flow cytometry at different time points in 54 (32 small-vessel and 22 large-vessel diseases) acute ischemic stroke patients, 28 convalescent stroke patients (3 to 9 months after acute stroke), and 28 control subjects. Patients with ischemic stroke had significantly increased circulating CD62P, CD63, platelet-monocyte interaction, and platelet-lymphocyte interaction in the acute stage compared with the convalescent stage and control groups. Levels of CD62P and CD63 were significantly higher in the large-vessel disease group than in the small-vessel disease group, and differences in CD62P were significant even at one month. The CD40L level in the poor outcome group was significantly higher than that in the good outcome group. The Value of Leukocyte Adhesion Molecules in Patients after Ischemic Stroke We examined serially the change of PSGL-1, Mac-1, and LFA-1 expression on leukocytes by using flow cytometry at various time points in 65 acute ischemic stroke patients and 60 controls. PSGL-1 expression on neutrophils and monocytes was significantly higher from Day 1 to Day 90 after stroke as compared with control subjects. The expression of monocyte Mac-1, LFA-1, and neutrophil Mac-1 were more significantly increased on Day 1 and 7 after stroke as compared with the control subjects. Furthermore, the neutrophil PSGL-1 expression on admission was independently associated with early neurologic deterioration. Serial Changes in Platelet Activation Markers with Aspirin and Clopidogrel after Acute Ischemic Stroke We designed a prospectively randomized case-control study and 70 patients with non-cardioembolic stroke who were treated with either aspirin (100 mg/d) or clopidogrel (75 mg/d) after acute ischemic stroke were evaluated. Ischemic stroke patients had significantly increased circulating CD62P, CD63, and CD40L in the acute stage as compared to the control group. Levels of CD62P, CD63 and CD40L were more significantly reduced in the clopidogrel group than in the aspirin group in the first week after stroke. Furthermore, differences in CD62P and CD63 levels were significant even at one-month post-stroke. Conclusion Stroke patients have enhanced platelet activity and platelet-leukocyte interaction in acute and convalescent phase of ischemic stroke compared with controls. Large-vessel cerebral infarction elicits higher platelets activation than small-vessel infarction in the acute phase of stroke. The dysregulation of Ca2+ movement, through the PAF- and ADP- receptor mediated pathway, in platelets may persist up to the subacute stage of ischemic stroke. It is possible that clopidogrel, an ADP-receptor inhibitor, elicit stronger antiplatelet effect than aspirin in the acute and convalescent phases after ischemic stroke. Sustained leukocyte-endothelium interaction, as reflected by expression of Mac-1 and LFA-1 on circulating leukocytes, may cause substantial inflammatory reaction and lead to secondary injury of potentially salvageable neurons after cerebral infarction. Ischemic stroke patients presenting with a higher CD40L level on admission were associated with a 3-month poor outcome.

Thesis (M. Med. Sc.)--University of Queensland, 2001. / Includes bibliographical references.