Efficacy and safety of next-generation tick transcriptome-derived direct thrombin inhibitors

Despite their limitations, unfractionated heparin (UFH) and bivalirudin remain standard-of-care parenteral anticoagulants for percutaneous coronary intervention (PCI). We discovered novel direct thrombin inhibitors (DTIs) from tick salivary transcriptomes and optimised their pharmacologic activity. The most potent, ultravariegin, inhibits thrombin with a K_i of 4.0 pM, 445-fold better than bivalirudin. Unexpectedly, despite their greater antithrombotic effect, variegin/ultravariegin demonstrated less bleeding, achieving a 3-to-7-fold wider therapeutic index in rodent thrombosis and bleeding models. When used in combination with aspirin and ticagrelor in a porcine model, variegin/ultravariegin reduced stent thrombosis compared with antiplatelet therapy alone but achieved a 5-to-7-fold lower bleeding time than UFH/bivalirudin. Moreover, two antibodies screened from a naïve human antibody library effectively reversed the anticoagulant activity of ultravariegin, demonstrating proof-of-principle for antidote reversal. Variegin and ultravariegin are promising translational candidates for next-generation DTIs that may reduce peri-PCI bleeding in the presence of antiplatelet therapy.

Electron microscopy examination of platelet whole mount preparations to quantitate platelet dense granule numbers: Implications for diagnosing suspected platelet function disorders due to dense granule deficiency

INTRODUCTION

Dense granule (DG) deficiency (DGD) is a feature of some platelet function disorders (PFD) with a prevalence similar to von Willebrand disease. Most laboratories assess for DGD using whole mount platelet preparations and electron microscopy (EM). We evaluated our experiences with this test and associations between DGD and bleeding.

METHODS

Dense granule EM records for 2006-2017 were examined for patients and simultaneously tested controls, and for an overlapping PFD study cohort to evaluate findings and their relationship to bleeding.

RESULTS

More patient than control samples had reduced DG counts (6.5% vs 0.3%, P < .01). DG counts showed no relationship to age or mean platelet volume and had acceptable within-subject variability that was higher for DGD than control participants (28% vs 12%). Repeat tests confirmed DGD in all persons with initial DG counts <4.0/platelet, but not in those with less severe reductions (4.0-4.8 DG/platelet) or normal DG counts (≥4.9 DG/platelet). Aggregometry and adenosine triphosphate release tests, respectively, had only ~52% and 70% sensitivity for DGD. Confirmed DGD by EM was associated with higher bleeding scores and a bleeding disorder.

CONCLUSION

Whole mount EM is useful for the evaluation of suspected PFD due to DGD and detects abnormalities associated with bleeding.

Variability in platelet dense granule adenosine triphosphate release findings amongst patients tested multiple times as part of an assessment for a bleeding disorder

INTRODUCTION

Lumi-aggregometry quantification of platelet dense granule adenosine triphosphate (ATP) release is commonly used for diagnosing platelet function disorders. As the test findings show considerable variability for healthy controls, we postulated that patient findings might also be variable and investigated patients who were assessed for dense granule ATP release defects more than once.

METHODS

Analyses were performed on prospectively collected data for first and second tests for subjects tested for dense granule ATP release defects more than once by the Hamilton Regional Laboratory Program (HRLMP) between January 2007 and June 2013 (cohort I). Similar analyses were performed for subjects who were recruited to a platelet disorder study (cohort II) and were assessed for ATP release defects more than once before October 2015.

RESULTS

A total of 150 unique subjects had multiple ATP release tests. Results with individual agonists were variable for many subjects. While normal findings with all tested agonists were often confirmed by the second test (cohort I: 83%; cohort II: 100%), impaired release with multiple agonists was confirmed in only some subjects (cohort I: 34%; cohort II: 54%). Inconsistent findings were common (cohort I: 36%; cohort II: 39%). ISTH bleeding scores showed no relationship to the test findings. The finding of impaired ATP release with 2 or more agonists on both tests was not associated with an increased likelihood of a definite bleeding disorder.

CONCLUSION

The variability in platelet dense granule ATP release findings amongst patients assessed for diagnostic purposes suggests that the test has limited value for diagnosing platelet disorders.

Microfluidic Chip–Based Online Screening Coupled to Mass Spectrometry

Thrombin and factor Xa (FXa) are critical enzymes of the blood coagulation cascade and are excellent targets of anticoagulant agents. Natural sources present an array of anticoagulants that can be developed as antithrombotic drugs. High-resolution, online screening techniques have been developed for the identification of drug leads from complex mixtures. In this study, we have developed and optimized a microfluidic online screening technique coupled to nano–liquid chromatography (LC) and in parallel with a mass spectrometer for the identification of thrombin and FXa inhibitors in mixtures. Inhibitors eluting from the nano-LC were split postcolumn in a 1:1 ratio; half was fed into a mass spectrometer (where its mass is detected), and the other half was fed into a microfluidic chip (which acts as a microreactor for the online assays). With our platform, thrombin and FXa inhibitors were detected in the assay in parallel with their mass identification. These methods are suitable for the identification of inhibitors from sample amounts as low as sub-microliter volumes.

Development of Plate Reader and On-Line Microfluidic Screening to Identify Ligands of the 5-Hydroxytryptamine Binding Protein in Venoms

The 5-HT3 receptor is a ligand-gated ion channel, which is expressed in the nervous system. Its antagonists are used clinically for treatment of postoperative- and radiotherapy-induced emesis and irritable bowel syndrome. In order to better understand the structure and function of the 5-HT3 receptor, and to allow for compound screening at this receptor, recently a serotonin binding protein (5HTBP) was engineered with the Acetylcholine Binding Protein as template. In this study, a fluorescence enhancement assay for 5HTBP ligands was developed in plate-reader format and subsequently used in an on-line microfluidic format. Both assay types were validated using an existing radioligand binding assay. The on-line microfluidic assay was coupled to HPLC via a post-column split which allowed parallel coupling to a mass spectrometer to collect MS data. This high-resolution screening (HRS) system is well suitable for compound mixture analysis. As a proof of principle, the venoms of Dendroapsis polylepis, Pseudonaja affinis and Pseudonaja inframacula snakes were screened and the accurate masses of the found bioactives were established. To demonstrate the subsequent workflow towards structural identification of bioactive proteins and peptides, the partial amino acid sequence of one of the bioactives from the Pseudonaja affinis venom was determined using a bottom-up proteomics approach.

Plasmodium falciparum cross-resistance between trimethoprim and pyrimethamine

Trimethoprim-sulfamethoxazole has been recommended as part of the standard package of care for people with HIV and AIDS in Africa. A similar antifolate combination, sulfadoxine-pyrimethamine, is now the first-line antimalarial drug in several of the African countries with the highest rates of HIV infection. We present evidence of Plasmodium falciparum cross-resistance between trimethoprim and pyrimethamine at the molecular level. The impact of trimethoprim-sulfamethoxazole on the efficacy of sulfadoxine-pyrimethamine needs to be assessed urgently, and alternative antimalarial treatment should be considered for people on trimethoprim-sulfamethoxazole prophylaxis.