Platelets are relatively short-lived, anucleated cells that are essential for proper hemostasis. The regulation of platelet survival in the circulation remains poorly understood. The process of platelet activation and senescence in vivo is associated with processes similar to those observed during apoptosis in nucleated cells, including loss of mitochondrial membrane potential, caspase activation, phosphatidylserine (PS) externalization, and cell shrinkage. ABT-737, a potent antagonist of Bcl-2, Bcl-X L , and Bcl-w, induces apoptosis in nucleated cells dependent on these proteins for survival. In vivo, ABT-737 induces a reduction of circulating platelets that is maintained during drug therapy, followed by recovery to normal levels within several days after treatment cessation. Whole body scintography utilizing [111] Indium-labeled platelets in dogs shows that ABT-737-induced platelet clearance is primarily mediated by the liver. In vitro, ABT-737 treatment leads to activation of key apoptotic processes including cytochrome c release, caspase-3 activation, and PS externalization in isolated platelets. Despite these changes, ABT-737 is ineffective in promoting platelet activation as measured by granule release markers and platelet aggregation. Taken together, these data suggest that ABT-737 induces an apoptosis-like response in platelets that is distinct from platelet activation and results in enhanced clearance in vivo by the reticuloendothelial system.

ACUTE LAMINITIS has long been attributed to factors or events that precede the onset of laminitis. Between 1759 and 1907 the overconsumption of grain, inflammation of the feet, suppression of perspiration (anhydrosis), excessive rest, excessive bleeding, road concussion, poor shoeing, unilateral weight bearing, sudden environmental temperature changes, prolonged standing (in the cold and aboard ships), diarrhea, and postpartum complicat i o n~' -~ were all designated as causes. Today, commonly listed etiologic factors include ingestion of large amounts of grain, cold water, lush grass, or black walnut shavings, repeated concussion, endometritis or other severe infections, colic, exhaustion, stress, drug toxicities, and endocrine dysfunctions.8-'2 At Texas A&M University (Table 1) the factors recorded as the cause presume a causal relationship between some preceding event and the acute laminitis. Logically, any event that precedes laminitis might be a cause, but etiologic validity depends on the definition of "cause" and the role that coincidence might have in the appearance of the disease.The many "causes" of laminitis have led to the belief that laminitis is a complex disorder brought about by several interacting factors. The current understanding of the pathophysiology of laminitis does not explain how these diverse factors predispose the horse to laminitis. The diagnosis of acute laminitis is based on clinical signs. Because all horses develop similar clinical signs regardless of the cause of laminitis, a common pathophysiologic mechanism is believed to be responsible.Currently, metabolic abnormalities and endotoxemia are proposed as etiologies of acute laminitis. The meta- bolic hyp~thesis'~-'~ proposes that laminitis results from derangement of metabolic processes, resulting in structural failure of laminar epithelium. The restriction of histopathologic changes to the epidermal layers and the reduced incorporation of methionine into laminar epithelium of horses with acute laminitis is consistent with decreased keratin metab01isrn.I~ In this hypothesis inflammation, mechanical collapse of the digit and vascular pathologies occur as secondary events.

Vascular calcification is a mortality risk factor for stage 5 chronic kidney disease patients. We investigated the role of phosphorus and vitamin D analogs in the pathogenesis of vascular calcification using in vivo, ex vivo, and in vitro models. Our results demonstrate that uremic rats receiving a hyperphosphatemia-inducing diet did not exhibit aortic calcification despite elevated levels of serum phosphorus and calciumphosphorus (CaxP) product. The vitamin D analog 1␣-hydroxyvitamin-D 2 [1␣(OH)D 2 ] at 0.17 g/kg raised serum calcium, phosphorus, CaxP product, and aortic calcification in the uremic rats, but 19-nor-1␣,25(OH) 2 D 2 (19-nor) at the same dose had no significant effect. At 0.67 g/kg, both 1␣(OH)D 2 and 19-nor had similar effects on serum calcium, phosphorus, and CaxP product, but only 1␣(OH)D 2 induced significant aortic calcification. Only aortic rings from 1␣(OH)D 2 -treated uremic rats exhibited a significant increase in 45 Ca uptake ex vivo. When aortic rings from normal rats or a primary culture of human coronary artery smooth muscle cells were treated with phosphorus or vitamin D analogs in vitro, high phosphorus induced calcium accumulation and/or 45 Ca uptake in a dose-or time-dependent manner, whereas vitamin D analogs including 1␣(OH)D 2 up to 100 nM had no significant effect despite the presence of a functional vitamin D receptor. However, serum from 1␣(OH)D 2 -treated uremic rats induced 45 Ca uptake into smooth muscle cells cultured in high phosphorus. These results suggest that the regulation of vascular calcification in vivo cannot be easily replicated in the ex vivo or in vitro models, and high phosphorus and some vitamin D analogs such as 1␣(OH)D 2 exert interactive effects on modulating vascular calcification.

Objectives Efforts to develop and deploy effective vaccines against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) continue at pace. Here, we describe rational antigen design through to manufacturability and vaccine efficacy of a prefusion‐stabilised spike (S) protein, Sclamp, in combination with the licensed adjuvant MF59 ‘MF59C.1’ (Seqirus, Parkville, Australia). Methods A panel recombinant Sclamp proteins were produced in Chinese hamster ovary and screened in vitro to select a lead vaccine candidate. The structure of this antigen was determined by cryo‐electron microscopy and assessed in mouse immunogenicity studies, hamster challenge studies and safety and toxicology studies in rat. Results In mice, the Sclamp vaccine elicits high levels of neutralising antibodies, as well as broadly reactive and polyfunctional S‐specific CD4 + and cytotoxic CD8 + T cells in vivo . In the Syrian hamster challenge model ( n = 70), vaccination results in reduced viral load within the lung, protection from pulmonary disease and decreased viral shedding in daily throat swabs which correlated strongly with the neutralising antibody level. Conclusion The SARS‐CoV‐2 Sclamp vaccine candidate is compatible with large‐scale commercial manufacture, stable at 2–8°C. When formulated with MF59 adjuvant, it elicits neutralising antibodies and T‐cell responses and provides protection in animal challenge models.

Animal models of human disease are commonly utilized to gain insight into the potential efficacy and mode of action of novel pharmaceuticals. However, conventional (healthy) rodent and nonrodent models are generally utilized in nonclinical safety testing. Animal models of human disease may be helpful in understanding safety risks of compounds in nonclinical or clinical development, with their greatest value being in targeted or hypothesis-driven studies to help understand the mechanism of a particular toxicity. Limitations of animal models of disease in nonclinical safety testing include a lack of historical control, heterogeneity in disease expression, a limited life span, and confounding effects of the disease. In most instances, animal models of human disease should not be utilized to supplant testing in conventional animal models. While of potential benefit, testing in an animal model of human disease should only be taken after adequate consideration of relevance along with benefits and limitations of the proposed model.