Surgical and pharmacological animal models used in drug metabolism and pharmacokinetics.

Mechanistic approaches in drug metabolism and pharmacokinetics during drug discovery depend upon animal models to increase the understanding of the absorption and disposition of new compounds. These animal models are also important to understand the complex interplay of biochemical and physiological events, and for the ability to answer questions in a reasonable time frame while interrogating numerous chemical structures. Many animal models have been described for understanding absorption, distribution, metabolism, and excretion and this review attempts to summarise some of these models. The focus is primarily on surgical and pharmacological models for pharmacokinetic studies in rodents with special emphasis on descriptive methodologies for researchers embarking on in vivo studies. In this review, the surgical approaches include the mechanical instrumentation of anatomical structures, e.g. abdominal cavity, marginal ear vein, while pharmacological models are restricted to chemical inhibition of the cytochrome P450 enzymes and P-gp to understand hepatic metabolism or brain penetration and intestinal absorption, respectively. The purpose of this review is not to exhaustively characterise each model but to serve as a general resource for investigators interested in performing these models.

Thromboelastography measurements of whole blood from factor VIII-deficient mice supplemented with rFVIII.

The rotational thromboelastography (ROTEG) assay system allows the real-time analysis of clot formation (fibrin formation) in a whole-blood assay format. The ROTEG system provides significant advantages over the current plasma-based assay systems as it includes the important interactions between cellular and plasmatic coagulation factors. We have employed the ROTEG system to characterize clot formation dynamics in factor VIII- deficient mouse whole blood and examined the ability of recombinant FVIII (rFVIII) supplementation to restore the normal phenotype. The ability to generate a clear dose-response relationship by adding rFVIII to FVIII-deficient murine whole blood (FVIII-/-) demonstrates the feasibility of this approach. A dose-response from 1 U to 0.00001 U mL(-1) demonstrates the enhanced sensitivity of the ROTEG system. Further characterization of this experimental approach may provide a potential tool for comparing the activity of FVIII concentrates and/or evaluating FVIII mutants.

Plasmin induces local thrombolysis without causing hemorrhage: a comparison with tissue plasminogen activator in the rabbit.

The direct fibrinolytic enzyme, plasmin, was compared with tissue plasminogen activator (TPA) in rabbit models of local thrombolysis and fibrinolytic hemorrhage. Plasmin was produced by solid-phase urokinase activation of plasminogen and purified on benzamidine Sepharose. Applied as an intra-arterial infusion into the thrombosed abdominal aorta under conditions of unimpeded blood flow, plasmin (4 mg/kg) and TPA (2 mg/kg) achieved equivalent clot dissolution and flow restoration. Using the model of restricted blood flow into the thrombosed aorta, which limits local plasminogen supply, plasmin was superior to TPA in clot lysis and vascular reperfusion. Using similar dosages of plasmin (2 or 4 mg/kg) and TPA (1 or 2 mg/kg) in the earpuncture rebleed model. TPA induced rebleeding in a dose-dependent manner from prior puncture sites in 9 of 10 animals, while none of the 10 animals exposed to plasmin rebled from these sites. These results suggest that plasmin is an effective, unique thrombolytic agent, distinguished from the plasminogen activators in current usage by its striking safety profile.