A novel approach to assess the spontaneous gastrointestinal bleeding risk of antithrombotic agents using Apc(min/+) mice.

Assessment of the bleeding risk of antithrombotic agents is usually performed in healthy animals with some form of vascular injury to peripheral organs to induce bleeding. However, bleeding observed in patients with currently marketed antithrombotic drugs is typically spontaneous in nature such as intracranial haemorrhage (ICH) and gastrointestinal (GI) bleeding, which happens most frequently on top of preexisting pathologies such as GI ulcerations and polyps. Apc(min/+) mice are reported to develop multiple adenomas through the entire intestinal tract and display progressive anaemia.In this study, we evaluated the potential utility of Apc(min/+) mice as a model for assessing spontaneous GI bleeding with antithrombotic agents. Apc(min/+) mice exhibited progressive blood loss starting at the age of nine weeks. Despite the increase in bleeding, Apc(min/+) mice were in a hypercoagulable state and displayed an age-dependent increase in thrombin generation and circulating fibrinogen as well as a significant decrease in clotting times. We evaluated the effect of warfarin, dabigatran etexilate, apixaban and clopidogrel in this model by administering them in diet or in the drinking water to mice for 1-4 weeks. All of these marketed drugs significantly increased GI bleeding in Apc(min/+) mice, but not in wild-type mice. Although different exposure profiles of these antithrombotic agents make it challenging to compare the bleeding risk of compounds, our results indicate that the Apc(min/+) mouse may be a sensitive preclinical model for assessing the spontaneous GI bleeding risk of novel antithrombotic agents.

Brain penetration of aprepitant, a substance P receptor antagonist, in ferrets.

The pharmacokinetics, metabolism, and brain penetration of the neurokinin 1 (NK1) receptor antagonist (substance P receptor antagonist), aprepitant (MK-0869), were examined in ferrets. This species exhibits human-type NK1receptor pharmacology and is of proven value in the identification of clinically useful drugs for the treatment of chemotherapy-induced nausea and vomiting in humans. After a single p.o. dose of aprepitant at 1 or 2 mg/kg, plasma levels of the compound were between approximately 200 and 270 ng/ml, 24 h after dosing. In the brain cortex, concentrations of aprepitant reached between approximately 80 and 150 ng/g of tissue 24 h after dosing. The predominant radioactive component present in the plasma and the brain of ferrets at 24 or 48 h after a single oral dose of [14C]aprepitant at 3 mg/kg was the parent compound itself. The slow plasma clearance of aprepitant ( approximately 1.5 ml/min/kg) and its abundance in ferret brain were in accord with its efficacy in blocking the retching and vomiting at 24 and 48 h postdose when ferrets were challenged with the emetic anticancer drug, cisplatin. When aprepitant and some of its metabolites were assessed for their in vitro binding affinity to the human NK1receptor, aprepitant demonstrated the highest affinity. Collectively, these data suggested that aprepitant, rather than its metabolites, was responsible, primarily, for the antiemetic activity of this compound in the male ferret.

Alteration of lymphocyte trafficking by sphingosine-1-phosphate receptor agonists.

Blood lymphocyte numbers, essential for the development of efficient immune responses, are maintained by recirculation through secondary lymphoid organs. We show that lymphocyte trafficking is altered by the lysophospholipid sphingosine-1-phosphate (S1P) and by a phosphoryl metabolite of the immunosuppressive agent FTY720. Both species were high-affinity agonists of at least four of the five S1P receptors. These agonists produce lymphopenia in blood and thoracic duct lymph by sequestration of lymphocytes in lymph nodes, but not spleen. S1P receptor agonists induced emptying of lymphoid sinuses by retention of lymphocytes on the abluminal side of sinus-lining endothelium and inhibition of egress into lymph. Inhibition of lymphocyte recirculation by activation of S1P receptors may result in therapeutically useful immunosuppression.

Identification of metabolites of a substance P (neurokinin 1 receptor) antagonist in rat hepatocytes and rat plasma.

[3R,5R,6S]-3-(2-cyclopropyloxy-5-trifluoromethoxyphenyl)-6-phenyl-1-oxa-7-azaspiro[4.5]decane is a substance P (Neurokinin 1 receptor) antagonist. Substance P antagonists are proven in concept to have excellent potential for the treatment of major depression, and they allow superior and sustained protection from acute and delayed chemotherapy-induced emesis. The metabolism of this compound was investigated in rat hepatocytes, and circulating rat plasma metabolites were identified following oral and intravenous dosing. The turnover in rat hepatocytes within 4 h was about 30%, and the major metabolites were identified as two nitrones and a lactam associated with the piperidine ring. Although these metabolites were also observed in rat plasma, the major circulating metabolite was a keto acid following oxidative de-amination of the piperidine ring. Liquid chromatography/tandem mass spectrometry and nuclear magnetic resonance were used to confirm the structure of the latter metabolite. A mechanism leading to the formation of the keto acid metabolite has been suggested, and most intermediates were observed in rat plasma.