Name: Inferior Vena Cava (IVC) Ligation for Venous Thrombosis Analysis in Mouse
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inferior vena cava (ivc) ligation for venous thrombosis analysis in mouse

Optimized Venous Thrombosis Assay in a Mouse Cancer Model Using Vascular Clips

Cancer-associated venous thromboembolism (VTE) 
Venous thromboembolism (VTE) risk is 4 to 7 times higher in cancer survivors compared to the general population1,2,3. This condition proves fatal in one out of seven patients with cancer. The incidence of VTE varies depending on the type of cancer and the tumor burden and is highest among patients with pancreatic and gastric cancers4.
Cancer-associated VTE in cancer patients has prognostic significance. It is associated with unfavorable overall survival in the first year after a cancer diagnosis, even after adjusting for age, race, and stage of underlying cancer5. These findings highlight the importance of examining cancer associated VTE and the need to probe its mechanism using an animal model. The translational relevance of this area is further emphasized by the fact that VTE in cancer patients is preventable and treatable with thromboprophylaxis and antithrombotic therapy6.
Animal models of cancer and venous thrombosis 
Cancer models are conventionally termed xenografts, which entail the injection of cancer cells in mice. The injection of cancer cells at a site like its origin is referred to as an orthotopic model, while at a different site (subcutaneous plane over the flank) is known as a heterotopic model. The species of origin of cancer cells determines them as an allogeneic model, such as the HT-29 cell line (human colon cancer)7,8,9. On the contrary, syngeneic models use the murine cancer cell lines, including RenCa and MC-38 cell lines3,10.
The literature has described arterial, venous, and capillary thrombosis models in rodents. Venous thrombosis is induced in the inferior vena cava (IVC) by mechanical injury (guide wire) or complete IVC ligation, chemical (Ferric chloride), or electrolytic injury. Ferric chloride-induced thrombosis or IVC ligation represents complete occlusion models. The latter results in the stasis of blood and inflammatory infiltrates in veins11,12,13. The complete ligation model results in a high rate of thrombosis formation in 95% to 100% of mice. The partial IVC ligation model might include interruption of lateral iliolumbar branches, and the venous return is abrogated by applying suture ligations in the distal target points of IVC12. Sometimes, a space holder is used to interrupt the venous return partially. However, the thrombus weight is inconsistent in the current partial occlusion model, resulting in high variability in clot weights and heights12,14.
Both these large vein mechanical models (partial and complete) have limitations. First, IVC ligation (stasis model) often results in hypotension. The blood gets shunted through vertebral veins. Though in experienced hands, the mortality with this model ranges from 5%-30%, with the higher rate expected during the learning curve. Importantly, the complete occlusion model does not reproduce deep vein thrombosis (DVT) in humans, where a thrombus typically is nonocclusive. Complete occlusion is likely to alter hemorheological factors and pharmacodynamic parameters, altering the bioavailability of compounds at the local site. Due to these limitations, complete occlusion models may not be optimal for testing novel chemical compounds for therapeutic purposes and drug discoveries12.
It should be noted that to provide a more clinically relevant murine model of venous thrombosis with decreased flow with endothelial damage, a venous thrombosis model has been introduced, where DVT is triggered by the restriction of blood flow in the absence of endothelial disruption. The model was validated by scanning electron microscopy15. A preferred clinically relevant thrombosis model is one with near complete thrombosis that enables drug discoveries. The clot formation in the current partial occlusion models is inconsistent, resulting in high variability in the clot weight and heights12,16. Furthermore, the clot weight is variable with the conventional methods, requiring&#160;more&#160;mice per studies12.
Previous cancer-associated thrombosis models focused on colon, pancreatic, and lung cancer and were all complete occlusion models17,18,19. This manuscript modifies the partial occlusion thrombosis model to provide clots with lower variability and mouse mortality (Figure 1). Former studies used allogeneic cancer cell lines on immunocompromised athymic mice background19,20,21. This manuscript uses an MC-38 cell syngeneic xenograft in C57Bl6/J mice, which allows the use of immunocompetent mice and examination of immune components to thrombogenesis.

Author Spotlight: Advancing Cancer Associated Thrombosis Research in Rodent Models 

Venous Thrombosis Assay in a Mouse Model of Cancer

This research aims to enhance the rodents model for venous thrombosis focusing on cancer-associated thrombosis. It introduces a refined surgical technique using vascular clips in a syngeneic colon cancer xenograft mouse model to improve consistency and reproducibility, advancing cancer-associated thrombosis mechanistic understanding and drug discovery. Although the flow reduction model was introduced in the IVT stenotic models in 2012, no significant progress has been made in cancer-associated thrombosis models in the last 10 years.This was the rationale for this endeavor. In the field of cancer-associated thrombosis research, current technologies include advanced imaging techniques, like scanning, electron microscopic images, molecular biology tools, such as immunofluorescent staining, precision surgical instrument, data analysis software and data interpretation, and animal welfare. The current experimental challenges include variability in clot weights, a high mortality rate, and a prolonged learning curve in rodent models of venous thrombosis.Additionally, the venous flow direction and clot formation mechanisms differ from clinical cases. Our research protocol bridges gaps in rodent models of cancer-associated thrombosis. It introduces a novel surgical technique using vascular clips in xenograft models, yielding more consistent and reproducible thrombosis outcomes.This enhances our understanding of cancer-related thrombosis and drug discovery in translational research.

Watch this Scientific Journal Video about Inferior Vena Cava IVC Ligation for Venous Thrombosis Analysis in Mouse at JoVE.com

Inferior Vena Cava (IVC) Ligation for Venous Thrombosis Analysis in Mouse  

To begin, use a pair of fine scissors to make an incision on the abdominal skin of an anesthetized mouse, starting from the xiphoidal eminence to the bladder. With a pair of atraumatic forceps, pinch the peritoneum halfway along the skin incision, ensuring an adequate gap between the incision and the overlying intestines. Next, open the peritoneum longitudinally along the avascular linea alba.Then use wet cotton tips to pull out the intestines carefully. Then drop 200 to 300 microliters of normal saline over the intestines, and explore the route of the ureters inferior vena cava, or IVC, aorta, and renal veins. Cauterize the bilateral branches distal to the confluence of the left renal vein and infrarenal inferior vena cava.Check the ureters and vasculature for any oozing. To prevent potential complications of spinal ischemia and claudication, leave the lumbar branches intact. Check for the side branches, including the bilateral uterine horn and hypogastric vessels.Next, use a closed tip atraumatic forceps to gently pass a six-zero polypropylene suture through the avascular plane two to three times. Apply gentle pressure with a cotton tip tamponade to control any oozing. Finally, pass a five-zero polypropylene suture through the plane with gentle coddle to cranial movements to widen it.Place the vascular clamps over the suture to guarantee adequate space. Clot weights of the xenografted experimental group displayed a 1.5 fold increase relative to the control mice. Immunofluorescence assays showed that the IVC from the control group had intact CD31 and fibrin partially occupying the vessel lumen.The CD31 expression was not intact in the experimental group, with the wall showing fibrin staining. The control group had significantly lower fibrin expression compared to the experimental group. Ultrasonic graphic analysis of the mice showed the ligated infrarenal vena cava of a control group mouse had a partial clot.The experimental group, however, had a large clot nearly occluding the infrarenal vena cava.

inferior-vena-cava-ivc-ligation-for-venous-thrombosis-analysis

Research

JoVE Journal

Cancer Research

This methodology paper highlights the surgical nuances of a rodent model of venous thrombosis, specifically in the context of cancer-associated thrombosis (CAT). Deep venous thrombosis is a common complication in cancer survivors and can be potentially fatal. The current murine venous thrombosis models typically involve a complete or partial mechanical occlusion of the inferior vena cava (IVC) using a suture. This procedure induces a total or partial stasis of blood and endothelial damage, triggering thrombogenesis. The current models have limitations such as higher variability in clot weights, significant mortality rate, and prolonged learning curve. This report introduces surgical refinements using vascular clips to address some of these limitations. Using a syngeneic colon cancer xenograft mouse model, we employed customized vascular clips to ligate the infrarenal vena cava. These clips allow residual lip space similar to a 5-0 polypropylene suture after IVC ligations. Mice with the suture method served as controls. The vascular clip method resulted in a consistent reproducible partial vascular occlusion and greater clot weights with less variability than the suture method. The larger clot weights, greater clot mass, and clot to the IVC luminal surface area were expected due to the higher pressure profile of the vascular clips compared to a 6-0 polypropylene suture. The approach was validated by gray scale ultrasonography, which revealed consistently greater clot mass in the infrarenal vena cava with vascular clips compared to the suture method. These observations were further substantiated with the immunofluorescence staining. This study offers an improved method to generate a venous thrombosis model in mice, which can be employed to deepen the mechanistic understanding of CAT and in translational research such as drug discovery.

This article aims to present an optimized method for assessing venous thrombosis in a mouse cancer model, using vascular clips to achieve venous ligation. Optimization minimizes variability in thrombosis-related measurements and enhances relevance to human cancer-associated venous thrombosis.

This methodology paper highlights the surgical nuances of a rodent model of venous thrombosis, specifically in the context of cancer-associated thrombosis ...