Preclinical Development of a vWF Aptamer to Limit Thrombosis and Engender Arterial Recanalization of Occluded Vessels

Endothelial surface and circulating glycoprotein von Willebrand factor (vWF) regulates platelet adhesion and is associated with thrombotic diseases, including ischemic stroke, myocardial infarction, and peripheral vascular disease. Thrombosis, as manifested in these diseases, is the leading cause of disability and death in the western world. Current parenteral antithrombotic and thrombolytic agents used to treat these conditions are limited by a short therapeutic window, irreversibility, and major risk of hemorrhage. To overcome these limitations, we developed a novel anti-vWF aptamer, called DTRI-031, that selectively binds and inhibits vWF-mediated platelet adhesion and arterial thrombosis while enabling rapid reversal of this antiplatelet activity by an antidote oligonucleotide (AO). Aptamer DTRI-031 exerts dose-dependent inhibition of platelet aggregation and thrombosis in whole blood and mice, respectively. Moreover, DTRI-031 can achieve potent vascular recanalization of platelet-rich thrombotic occlusions in murine and canine carotid arteries. Finally, DTRI-031 activity is rapidly (<5 min) and completely reversed by AO administration in a murine saphenous vein hemorrhage model, and murine toxicology studies indicate the aptamer is well tolerated. These findings suggest that targeting vWF with an antidote-controllable aptamer potentially represents an effective and safer treatment for thrombosis patients having platelet-rich arterial occlusions in the brain, heart, or periphery.

Ferric Chloride-induced Canine Carotid Artery Thrombosis: A Large Animal Model of Vascular Injury

Occlusive arterial thrombosis leading to cerebral ischemic stroke and myocardial infarction contributes to ~13 million deaths every year globally. Here, we have translated a vascular injury model from a small animal into a large animal (canine), with slight modifications that can be used for pre-clinical screening of prophylactic and thrombolytic agents. In addition to the surgical methods, the modified protocol describes the step-by-step methods to assess carotid artery canalization by angiography, detailed instructions to process both the brain and carotid artery for histological analysis to verify carotid canalization and cerebral hemorrhage, and specific parameters to complete an assessment of downstream thromboembolic events by utilizing magnetic resonance imaging (MRI). In addition, specific procedural changes from the previously well-established small animal model necessary to translate into a large animal (canine) vascular injury are discussed.

Abstract 228: RNA Aptamer 9.14T79VRT7 Modifies Canine Ex vivo Platelet Reactivity

Objective: To compare the prophylactic and thrombolytic effects of RNA aptamer (9.14T79VRT7) on ex vivo canine platelet function.

Approach and Results: We previously demonstrated that inhibition of von Willebrand Factor (VWF) by a targeted RNA aptamer prevents thrombosis and thrombolyses stabilized clots in a FeCl 3 -induced murine vascular injury model suggesting a pivotal role for VWF in the pro-thrombotic and anti-thrombotic milieu. We hypothesize that 9.14T79VRT7, which demonstrated no hemorrhagic complications and greater re-perfusion compared to rTPA in murine and canine thrombotic models, may affect additional agonist pathways to mitigate platelet activation, aggregation, and adhesion. Platelet aggregation before and after 9.14T79VRT7 addition was analyzed utilizing WB aggregometry based on impedance in five adult beagles. Agonist concentrations were selected from previous publications which had optimized platelet reactivity in canine WB and included: collagen (3.2 ug/ul), ADP (20 uM), arachidonic acid (0.5 mM), and botrocetin (1 ug/ul). The 9.14T79VRT7 concentration used (25 nM) was selected as the most effective as assessed by Total Thrombus Analysis System (TTAS). Botrocetin elicited the greatest response before 9.14T79VRT7 addition, followed by Collagen, ADP, and Arachidonic acid. Impedance resulting from prophylactic addition of 9.14T79VRT7 before Collagen, ADP, and Botrocetin resulted in a 50.00%, 34.83%, and 38.26% change in amplitude, respectively and a 43.70%, 14.28%, and 35.14% change in slope, respectively (p<.0001). There was no significant difference in response after Arachidonic acid. Impedance resulting from thrombolytic addition of 9.14T79VRT7 after agonist response to Collagen, ADP, and Botrocetin resulted in a 78.66%, 94.08%, and 84.58% change in amplitude, respectively and a 67.28%, 61.28%, and 63.73% change in slope, respectively (p<.0001). Although amplitude and slope decreased with 9.14T79VRT7 addition after Arachidonic acid, the change was not significant. Both control groups (9.14T79VRT7 and platelet buffer diluent) resulted in no significant changes.

Conclusion: 9.14T79VRT7 markedly changes platelet response both before and after agonist treatment in canine ex vivo impedance analysis.

Vitamin D and type 2 diabetes mellitus

WHAT IS KNOWN AND OBJECTIVE

The deleterious effect of vitamin D deficiency on bone health has long been known. More recent studies suggest a deleterious effect of low vitamin D (hypovitaminosis D) on general health. And specific studies propose an association between hypovitaminosis D and the aetiology and progression of type 2 diabetes (T2DM). Given a commonly assumed lack of toxicity of vitamin D, routine measurement of plasma vitamin D and supplementation is rapidly becoming accepted general practice.

COMMENT

Authoritative practice guidelines have raised the level of vitamin D that is to be considered minimal for optimum health. This recommendation was based on a wealth of information and definitive evidence for skeletal benefits of vitamin D, but there was a lack of compelling evidence that hypovitaminosis D is causally related to extra-skeletal health outcomes such as diabetes. Hence, vitamin D supplementation for the purpose of achieving a level consistent with good health is evidence based, but measurement and supplementation for the purpose of preventing or treating T2DM is not.

WHAT IS NEW AND CONCLUSION

Although the maintenance of adequate vitamin D levels is desirable for all patients, we conclude that routine measurement of vitamin D level in every patient or initiating high-dose supplementation for the purpose of preventing or treating T2DM is not evidence based.

Transgenic swine: expression of human CD39 protects against myocardial injury

CD39 (ectonucleoside triphosphate diphosphohydrolase-1; ENTPD-1) rapidly hydrolyzes ATP and ADP to AMP; AMP is hydrolyzed by ecto-5'-nucleotidase (CD73) to adenosine, an anti-thrombotic and cardiovascular protective mediator. While expression of human CD39 in a murine model of myocardial ischemia/reperfusion (I/R) injury confers cardiac protection, the translational therapeutic potential of these findings requires further testing in a large animal model. To determine if transgenic expression of CD39 reduces infarct size in a swine model of myocardial ischemia/reperfusion injury, transgenic pigs expressing human CD39 (hCD39) were generated via somatic cell nuclear transfer and characterized. Expression of hC39 in cardiac tissue was confirmed by immunoblot and immunohistochemistry. Myocardial I/R injury was induced by intracoronary balloon inflation in the left anterior descending (LAD) artery for 60 min followed by 3 hours of reperfusion. The ischemic area was delineated by perfusion with 5% phthalo blue and the myocardial infarct size was determined by triphenyl tetrazolium chloride (TTC) staining. During ischemia, the rate-pressure product was significantly lower in control versus hCD39-Tg swine. Following reperfusion, compared to littermate control swine, hCD39-Tg animals displayed a significant reduction in infarct size (hCD39-Tg: 17.2 ± 4.3% vs.

CONTROL

44.7 ± 5.2%, P=0.0025). Our findings demonstrate for the first time that the findings in transgenic mouse models translate to large animal transgenic models and validate the potential to translate CD39 into the clinical arena to attenuate human myocardial ischemia/reperfusion injury.

Direct comparison of umbilical cord blood versus bone marrow-derived endothelial precursor cells in mediating neovascularization in response to vascular ischemia

Endothelial precursor cells (EPCs) cultured from adult bone marrow (BM) have been shown to mediate neovasculogenesis in murine models of vascular injury. We sought to directly compare umbilical cord blood (UCB)- and BM-derived EPC surface phenotypes and in vivo functional capacity. UCB and BM EPCs derived from mononuclear cells (MNC) were phenotyped by surface staining for expression of stromal (Stro-1, CXCR4, CD105, and CD73), endothelial (CD31, CD146, and vascular endothelial [VE]-cadherin), stem cell (CD34 and CD133), and monocyte (CD14) surface markers and analyzed by flow cytometry. The nonobese diabetic/severe combined immunodeficiency murine model of hind-limb ischemia was used to analyze the potential of MNCs and culture-derived EPCs from UCB and BM to mediate neovasculogenesis. Histologic evaluation of the in vivo studies included capillary density as a measure of neovascularization. Surface CXCR4 expression was notably higher on UCB-derived EPCs (64.29%+/-7.41%) compared with BM (19.69%+/-5.49%; P=.021). Although the 2 sources of EPCs were comparable in expression of endothelial and monocyte markers, BM-derived EPCs contained higher proportions of cells expressing stromal cell markers (CD105 and CD73). Injection of UCB- or BM-derived EPCs resulted in significantly improved perfusion as measured by laser Doppler imaging at days 7 and 14 after femoral artery ligation in nonobese diabetic/severe combined immunodeficiency mice compared with controls (P<.05). Injection of uncultured MNCs from BM or UCB showed no significant difference from control mice (P=.119; P=.177). Tissue samples harvested from the lower calf muscle at day 28 demonstrated increased capillary densities in mice receiving BM- or UCB-derived EPCs. In conclusion, we found that UCB and BM-derived EPCs differ in CXCR4 expression and stromal surface markers but mediate equivalent neovasculogenesis in vivo as measured by Doppler flow and histologic analyses.

The safety of autologous intracoronary stem cell injections in a porcine model of chronic myocardial ischemia

BACKGROUND

Intracoronary mononuclear cell therapy may produce angiogenesis in chronic myocardial ischemia. Potential complications include periprocedural infarction secondary to: reduced coronary blood flow; hyperviscosity from the cell preparation; or microvascular dysfunction. To date, no studies to evaluate these potential complications have been reported. The objective of this report was to study the safety and feasibility of intracoronary injections of autologous bone marrow mononuclear cells in a porcine chronic myocardial ischemia model.

METHODS

Domestic pigs (n = 5) underwent ameroid cuff placement of the left circumflex artery. Bone marrow-derived mononuclear cells [15 x 10(6) cells] labeled with CM dioctadecyl tetramethylindocarbocyanine were given by intracoronary injection. Animals were sacrificed, and hearts and vital organs were inspected grossly and by histopathology, and bone marrow underwent immunofluorescence microscopy.

RESULTS

Troponin I levels, gross inspection and histopathology did not reveal evidence of myocardial infarction. Labeled cells were observed in perivascular structures in myocardium at the injection site in all animals and in the spleen from one animal. Bone marrow aspirates indicated labeled cells.

CONCLUSIONS

Intracoronary injection of autologous mononuclear cells in a porcine chronic myocardial ischemia model appears safe. Intracoronary injection resulted in cell localization in the perivascular areas of myocardium supplied by the injected vessel. Cell localization was observed only in the spleen in just one animal. Labeled cells were identified in bone marrow aspirates from three animals following injection, suggesting a role for bone marrow engraftment and repopulation as a possible mechanism for progenitor cell localization in myocardium.

Septic arthritis in the geriatric population

Septic arthritis has emerged as an important infection in geriatric patients. Between 25% and 50% of all cases of nongonococcal bacterial arthritis in nonprosthetic joints occur in patients over the age of sixty years. Thirty-three percent of nongonococcal septic arthritis occurs in the geriatric population. In this retrospective study of geriatric septic arthritis, 22 patients were reviewed. The major predisposing factor was prior history of arthritis, with the knee being the most commonly affected joint. Staphylococcus aureus was the major pathogen, with gram-negative organisms accounting for a significant number of infections. We think that empiric antibiotic coverage for gram-negative organisms should be initiated at the time of treatment only in patients with multiple predisposing factors for septic arthritis. The disease also may be more indolent than previously reported, leading to delayed diagnosis, treatment, and increased morbidity and mortality.

Usher's syndrome. Ophthalmic and neuro-otologic findings suggesting genetic heterogeneity

The conditions of 70 patients with Usher's syndrome were studied by ophthalmic and neuro-otologic examinations. Two distinct clinical and presumed genetic types were discernible on the basis of differences in hearing impairment, vestibular sensitivity, and, to a lesser extent, deterioration in retinal photoreceptor function. Distinguishing these two types has relevance for both diagnosis and genetic counseling of patients with Usher's syndrome.

Problems in identifying an acoustically evoked potential to a single stimulus

The identification of evoked scalp potentials in man to a single acoustic stimulus such as a word becomes possible by combining several techniques. Either multiple EEG derivations from one subject or single derivations from several subjects, can be summed algebraically to yield a tracing with a significant increase (by a factor of 2 or more) in the size of the response relative to the background. A specific template has been found which, when cross correlated with the EEG, yields 2 dimensional (correlation and time) description of when the response occurs.