Haematology and Cell Biology
Permanent URI for this community
Browse
Browsing Haematology and Cell Biology by Subject "Baboons as laboratory animals"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Open Access The evaluation of tirofiban hydrochloride in a high shear rate arterial thrombosis model in baboons(University of the Free State, 2009-11) Janse van Rensburg, Walter James; Meiring, S. M.; Roodt, J. P.English: Background: Acute coronary syndrome (ACS) is a major cause of mortality and morbidity world-wide, and is responsible for roughly 2.5 million hospital admissions world-wide annually. ACS is commonly associated with platelet thrombus formation on disrupted atherosclerotic plaques, therefore effective and safe anti-platelet drugs are needed to help treat and prevent ACS. The current most popular anti-platelet drugs are associated with increased bleeding risk and reduced efficacy, thus drugs with a wider therapeutic window (more efficacy with less bleeding) need to be developed. Tirofiban hydrochloride is a small, short half-life molecule that inhibits platelet aggregation by antagonising the glycoprotein IIb/IIIa receptor on platelets preventing fibrinogen and von Willebrand factor to cross-link platelets, thereby inhibiting the final pathway of platelet aggregation. Tirofiban hydrochloride was believed to be a very promising drug due to its short half-life, as an antidote strategy is not needed to reverse adverse bleeding events, but it soon fell out of favour when it was found not to be as effective as for example abciximab in preventing ischaemic events. This was possibly due to the recommended dose being suboptimal. Methods and Results: We studied the efficacy of tirofiban hydrochloride to inhibit platelet thrombus formation on an injured and partially occluded artery by evaluating the effect of escalating doses on cyclic flow reduction (CFR) formation in a high shear arterial thrombosis model in baboons, and also evaluated its safety in two different bleeding models. We then compared our results to results found in the same model using clopidogrel. A significant effect on the number of CFRs was only observed after injection of three times (30 μg/kg bolus plus 0.45 μg/kg/min infusion) the therapeutic dose tirofiban, but it was a weak inhibitor at this dose. Only after injection of nine times (90 μg/kg bolus plus 1.35 μg/kg/min infusion) the recommended therapeutic dose, a strong complete inhibition was observed. A further dose of 27 times (270 μg/kg bolus plus 4.05 μg/kg/min infusion) the recommended therapeutic dose was given to evaluate the effect of an overdose on the bleeding tendency. A significant prolongation in bleeding time (3.05 minutes to 11.90 minutes) was observed after injection of nine times the therapeutic dose, an average 2.7 ± 2.44 fold increase in blood loss was also observed at this dose. A maximum increase in blood loss of an average of 3.4 ± 1.77 fold was seen after injection of 27 times the therapeutic dose. The efficacy of tirofiban hydrochloride was comparable to that of clopidogrel found in earlier studies, but the blood loss was much less when compared to the average 4.3 ± 2.6 fold increase with clopidogrel at 2.5 mg/kg and 8.0 ± 5.0 fold increase at 5 mg/kg. Conclusion: Tirofiban hydrochloride is an effective anti-platelet drug, but only offers adequate protection against arterial thrombosis at a dose between three and nine times the recommended therapeutic dose. However, it still remains safer in terms of bleeding than the most common anti-platelet drugs used today. We recommend that further in vivo studies be done to determine the optimal dose for tirofiban hydrochloride treatment, and that new clinical trials be done with higher dose tirofiban hydrochloride.Item Open Access Thrombogenecity of decellularized and re-endothelialized baboon arteries(University of the Free State, 2015-02) Khemisi, Mmakgabu Martha; Meiring, S. M.; Smit, F.English: The use of decellularized biological scaffolds for the reconstruction of small-diameter (< 6 mm) vascular grafts has been the focus of tissue engineering studies. These biological materials constructed through decellularization processes are thought to be ideal graft materials for replacement of diseased vessels. However thrombogenecity is a major cause of obstruction in these vascular constructs and result in early graft occlusion. Seeding of the decellularized vascular constructs with endothelial cells (ECs) is an attractive proposition as the endothelial layer incorporates many of the anti-thrombogenic properties of blood vessels. The aim of this study was to determine if we could successfully re-endothelialize decellularized baboon arteries, thereafter perfuse the newly engineered arteries with whole blood to investigate the possibility of thrombus formation. First, the histology of the decellularized baboon arteries were compared to normal arteries in order to assess the efficiency of the decellularization process. Collagen and elastin fibres were also stained to determine whether the remaining extracellular matrix scaffold was preserved after decellularization. Human umbilical vein endothelial cells (HUVECs) were then cultured under optimal conditions. The viability and proliferation rate of the cultured ECs were assessed using the MTT cell viability and proliferation assay. The cultured endothelial cells were then used to seed the luminal surfaces of decellularized baboon arteries. The confluent endothelial monolayer of the seeded decellularized arteries were then assessed using scanning electron microscopy (SEM) after 7 days. The seeded cells were then detached from the graft surfaces of small sections and tested for viability (metabolic activity and proliferation) using the MTT assay again. Afterwards, normal, decellularized and seeded decellularized arteries were perfused for 2 hours with baboon whole blood collected in 3.2% sodium citrate tubes. Thereafter, small artery sections were examined with SEM to determine whether thrombi was formed on the luminal surfaces of all arteries. Histology examinations showed that the decellularized arteries were not completely cell free. Nuclear and cellular remnants were still retained within the scaffold materials. Histology also revealed that the femoral arteries had retained more nuclear and cellular materials than the carotid and radial arteries which showed much less nuclear material remaining. However, the ECM of the decellularized arteries was preserved after the decllularization processes. Enough viable ECs were obtained in culture to seed three decellularized baboon arteries. After 7 days post seeding, a confluent endothelial monolayer was observed on the luminal surfaces of the decellularized scaffolds using SEM. The perfused normal artery and the seeded decellularized arteries showed no possible thrombus formation on their luminal surfaces. The decellularized arteries however showed wide-spread platelet adhesion and activation on the surface of the ECM. In conclusion, decellularization of arteries was not successfully and proved to be dependent on the thickness of the tissues used. However, the decellularization process produced morphologically preserved extracellular matrix. The endothelialization process was successful since the endothelialization of decellularized vascular grafts does prevent thrombus formation on artery surfaces after perfusion with whole blood, while a decellularized scaffold does promote thrombus formation.