The thrombin generation capability of the Chacma baboon (Papio ursinus): implications for haemostatic disease models.

Baboon models are often used to investigate haemostatic diseases, such as acquired thrombotic thrombocytopenic purpura or bacterial sepsis-induced disseminated intravascular coagulation, and their potential treatment with novel drugs. Thrombin generation is vital for these models, and an important potential therapeutic target. We investigated the thrombin generation profile of the Chacma baboon (Papio ursinus - a common pre-clinical model) including the effects of sex and ABO blood group. Thrombin generation curves, lag times, peak heights, times-to-peak, velocity indexes and Endogenous Thrombin Potentials (ETPs) of 40 adult Chacma baboons were assessed and compared with normal human plasma, using a low concentration of tissue factor (1 pM) and phospholipids. Reference intervals were calculated, and results compared between O and non-O ABO blood groups, and between males and females. Lag times of all baboons fell within the human reference interval. Most animals (n = 32; 80%) had times-to-peak above, and velocity indexes and peak heights markedly below (n = 27; 68%) the human range. However, 97.5% of baboons had an ETP above the human reference interval, indicating greater overall thrombin generation. ABO blood group had no effect, but males (n = 14; 35%) had less potent thrombin generation than females (n = 26; 65%), with significantly longer lag times (p = 0.0475), lower peak thrombin concentrations (p = 0.0203), and lower ETPs (p = 0.0238). Chacma baboons have greater overall endogenous thrombin generation potentials than humans, which is even more prominent in females. This should be considered when designing future baboon model experiments involving the haemostatic system, or when evaluating novel therapies in these animals.

Eliminating exogenous insulin therapy in patients with type 2 diabetes by duodenal ablation and GLP-1RA decreases risk scores for cardiovascular events.

INTRODUCTION: Duodenal Mucosal Resurfacing (DMR) is an endoscopic ablation technique aimed at improving glycaemia and metabolic health in patients with type 2 diabetes mellitus (T2DM). DMR has an insulin sensitizing effect in patients with T2DM. Reducing hyperinsulinemia can improve cardiovascular health. In the INSPIRE trial, we combined a single DMR with a glucagon-like-peptide-1 receptor agonist (GLP-1RA) and demonstrated elimination of insulin treatment in 69% of patients at 6 months and 53% of patients at 18 months while improving glycaemic control and metabolic health. We hypothesized that this treatment approach is associated with improved cardiovascular health, by reducing hyperinsulinemia. METHODS: Before and 6 months after starting the combination treatment to replace insulin, the following assessments were performed to evaluate cardiovascular health: magnetic resonance imaging (MRI) to measure abdominal visceral adipose tissue volume, ambulatory 24 h blood pressure (ABPM) analysis, postprandial insulin and triglycerides, fasting lipid panel and urine microalbumin. The Atherosclerotic Cardiovascular Disease (ASCVD) score was calculated to estimate 10-year risk of cardiovascular disease or stroke and the diabetes lifetime-perspective prediction (DIAL) score was calculated to estimate years free of cardiovascular disease. RESULTS: Six months after replacing exogenous insulin by DMR and GLP-1RA, visceral adipose tissue decreased significantly by 24%. Postprandial triglyceride and insulin concentrations decreased significantly (p < 0.001), as did total cholesterol (from median 3.64 (IQR 3.34-4.89) to 3.48 (3.18-3.97) mmol/l, p = 0.008), LDL (from median 1.92 (IQR 1.49-2.30) to 1.79 (1.49-2.08 mmol/l, p = 0.044), and urine microalbumin (from median 7 (IQR 3-27) to 4 (3-8) mg/l, p = 0.018). All daytime blood pressure values decreased significantly. The ASCVD 10-year risk score decreased (from median 13.6 (IQR 5.7-26.0) to 11.5 (4.2-22.5) %, p = 0.030)) and the DIAL score increased (from median 82 (IQR 81-83) to 83 (81-84) years, (p = 0.039)). DISCUSSION: The combination of DMR and GLP-1RA to replace insulin therapy in patients with T2DM is associated with a positive effect on multiple parameters of cardiovascular health. Taken together, they show a pattern of overall improvement in cardiovascular health, as evidenced by decreased risk scores for cardiovascular complications. However, it is not yet clear whether these improvements will translate into a true reduction in cardiovascular events.

The effects of streptokinase in a Chacma baboon (Papio ursinus) model of acquired thrombotic thrombocytopenic purpura.

TTP is a life-threatening disorder with limited pharmaceutical treatment options. Recently, the potential of streptokinase in the treatment of acquired TTP was demonstrated in humans in vitro, and in vivo in a mouse model. We aimed to determine the in vitro and in vivo effects of streptokinase in an established Papio ursinus model of acquired TTP. In vitro: VWF activities & multimer patterns and thromboelastograms were assessed with increasing concentrations of streptokinase. In vivo: After induction of TTP, escalating streptokinase doses (ranging from 50,000 to 900,000 IU) were administered, and the effects of streptokinase assessed on peripheral blood counts, fibrinolysis, VWF activities & multimer patterns and thromboelastograms. In an extension of the study, high-dose streptokinase (1,500,000-3,000,000 IU) was administered to another baboon. After spiking, fibrinolysis with loss of large VWF multimers was observed at [2200 IU/mL]-roughly equivalent to 1,500,000 IU. However, administration of escalating intravenous streptokinase doses had no in vivo effect on the TTP phenotype, and in vivo increases in plasmin activity were mild when compared with baseline, even at high doses. Minimal effect on VWF multimer patterns was observed but only at doses ≥ 1500,000 IU. Streptokinase is not effective in resolving TTP in a Papio ursinus model of TTP, possibly due to limited activation of the baboon fibrinolytic system. Modifications to this model, the use of alternative higher animal models, or alternative thrombolytics, should be considered to establish proof-of-concept.

Comparison of ADAMTS13 and Von Willebrand factor levels and activities, and plasminogen levels, in plasma products currently available for the treatment of thrombotic thrombocytopenic purpura in South Africa.

OBJECTIVE: Thrombotic thrombocytopenic purpura (TTP) results from a deficiency in the Von Willebrand factor (VWF) cleaving protease, ADAMTS13. Treatment involves plasma exchange (PEX) therapy with either fresh frozen plasma (FFP), cryosupernatant (CSP) or solvent/detergent-treated plasma (SDP), available in South Africa as Bioplasma FDP. The aim of the study was to generate in vitro data on these products, and to explore possible differences between the products that may offer treatment advantages. METHODS: Twenty samples per product (FFP, CSP and Bioplasma FDP) were analysed for levels and activities of ADAMTS13 and VWF. Plasminogen levels, a proposed physiological back-up system for ADAMTS13, were also determined. FFP and CSP samples were subanalysed according to ABO blood group. Samples were analysed by means of commercially available ELISA assays. RESULTS: All samples had normal/high ADAMTS13 activity (Median activity for SDP = 94.0%, CSP = 80.5%, FFP = 122.0%) and plasminogen levels. The VWF content was mostly normal for Bioplasma FDP, typically deficient for CSP and mostly deficient for FFP, which was an unexpected finding. Depending on the parameter, Bioplasma FDP was the most standardised, with coefficients of variation (CV) from 14.1% to 27.3%, while FFP showed great inter-individual variation (CV 24.6% to 208.6%). Statistically significant differences were found across products (P ≤ 0.0095), and ABO blood groups (P = 0.0001). CONCLUSION: All three products can be used for the treatment of TTP. The choice of product depends on the need for additional viral safety, costs, product availability and the perceived impact of within-product variations.

The Use of Phage Display and Yeast Based Expression System for the Development of a Von Willebrand Factor Propeptide Assay: Development of a Von Willebrand Factor Propeptide Assay.

BACKGROUND: The diagnosis of von Willebrand disease is complex due to the heterogeneity of the disease. About eighty percent of von Willebrand disease patients are diagnosed with a quantitative defect of von Willebrand factor (VWF) where fifty percent is due to an increased clearance of von Willebrand factor. These patients do not respond well to the treatment of choice, Desmopressin (DDAVP) due to decreased efficacy. The ratio between the VWF propeptide and the mature VWF antigen is used to diagnose these patients. Commercial VWF propeptide assays are too expensive for use in developing countries. In this study, we developed a cost-effective ELISA assay. METHODS: We first displayed VWF propeptide on yeast. Antibody fragments were selected against the displayed VWF propeptide by using phage display technology. The antibodies were used to develop a cost-effective VWF propeptide assay and compared to a commercial VWF propeptide assay. RESULTS: Two of these antibody fragments bound specific to the VWF propeptide and not to the yeast used for the expression of the propeptides. These purified antibody fragments were able to detect VWF propeptide in normal plasma. CONCLUSION: Our assay performed well when compared to a commercial kit. It also showed a higher binding affinity for VWF propeptide in plasma at especially lower plasma concentrations.

Tirofiban versus abciximab: tirofiban is administered at suboptimal dosages when evaluated in an arterial thrombosis model in non-human primates.

To prevent thrombosis in high-risk acute coronary syndrome patients undergoing percutaneous coronary intervention for re-vascularisation, concomitant administration of a glycoprotein IIb/IIIa inhibitor, such as abciximab, tirofiban or eptifibatide, is recommended. Abciximab and eptifibatide are mostly preferred over tirofiban, which is less effective in preventing ischaemic events. We compared the efficacy and bleeding potential of escalating doses of tirofiban and abciximab in non-human primates. The efficacy of tirofiban and abciximab in inhibiting cyclic flow reductions (CFRs) was tested in a high shear arterial thrombosis model. Bleeding was evaluated with the template bleeding time and an incision bleeding model. Abciximab completely inhibited arterial thrombosis after injection of its therapeutic bolus dose. With tirofiban, a dose three times higher than the recommended therapeutic dose caused weak inhibition characterised by a return of CFRs after re-injury. At nine times the recommended therapeutic dose, complete inhibition was observed, and the efficacy of tirofiban was comparable to abciximab at its therapeutic bolus dose. Blood loss was less than with abciximab at its effective dose. In this model, tirofiban compared favourably with abciximab, although only at a dose of 3-9 times the therapeutic dose, and caused less bleeding than abciximab.

Sites of elimination and pharmacokinetics of recombinant [131I]lepirudin in baboons.

Lepirudin has a short half-life, and only 50-60% of the intravenously administered dose is excreted by the kidneys. The fate of the remainder is unknown. We designed a study to determine the fate of this lepirudin. In each of six baboons, [131I]lepirudin was given intravenously as a bolus or infused over 30 min, 24 h apart. The in vivo redistribution of [131I]lepirudin was determined and quantified by scintillation camera imaging. In all studies, the half-life of [131I]lepirudin, as determined from the disappearance of radioactivity, was 21 +/- 3 min. The half-life determined from the disappearance of lepirudin, measured by the Ecarin Clotting Time (ECT) method, was similar at 23 +/- 8 min. Results obtained with the labeled lepirudin are therefore comparable with those obtained using the plasma concentration of lepirudin. When lepirudin was administered as a bolus, the half-life was 18 +/- 4 min, and lepirudin was cleared from the plasma at a rate of 42 +/- 12 mL/min and by the kidneys at 23 +/- 2 mL/min. Following infusion over 30 min, the half-life and total and renal clearances were not significantly different. In both studies, between 50 and 60% of the administered lepirudin was excreted by the kidney. Studies on sacrificed baboons showed that appreciable amounts of lepirudin were present in the bile, indicating the liver as a contributor to the elimination of lepirudin.