A modified technique for small-bowel transplantation in the rat

A practical guide for small bowel transplantation in rats-review of techniques and models

BACKGROUND

Animal models are a central aspect in research on small bowel transplantation (SBTx). Among them, rats are the preferred species because of their widespread availability and cost effectiveness. Because the complexity of the surgical procedure could per se influence the outcome of an experiment, a standardized and comparable technique is important. Based on of the vast amount of different models and surgical techniques published to this point, a review seemed necessary to guide investigators when choosing the suitable model.

MATERIALS AND METHODS

A systematic literature search of original articles published between 1965 and 2016 using the Medline Database regarding techniques of SBTx in rats was conducted according to the Preferred reporting Items for Systematic Reviews and Meta-Analyses guidelines. Articles describing a new technique or evaluating different techniques were considered.

RESULTS

A total of 38 publications fulfilled the selection criteria and were included. Data from these publications were regarded as too heterogeneous for statistical analysis. Depending on graft length and placement, full-length and reduced length heterotopic and orthotopic models were differentiated. Important factors concerning a good survival rate are the chosen model (heterotopic has a better outcome compared with orthotopic), a vascular flush of the graft in situ, a careful luminal flush of the graft, adequate fluid resuscitation, and a warm ischemia time of less than 40 min.

CONCLUSIONS

SBTx in rats remains a complex and challenging procedure, which necessitates a standardized technique as well as sufficient training. By choosing the optimal experimental model, applying established strategies, and proven techniques, a standardized and scientifically reliable model can be achieved.

Difficulties, guidelines and review of developing an acute rejection model after rat intestinal transplantation

Experimental small bowel transplantation (SBT) in rats has been proven to be a useful tool for the study of ischemia-reperfusion and immunological aspects related to solid organ transplantation. However, the model is not completely refined, specialized literature is scarce and complex technical details are typically omitted or confusing. Most studies related to acute rejection (AR) use the orthotopic standard, with small sample sizes due to its high mortality, whereas those studying chronic rejection (CR) use the heterotopic standard, which allows longer term survival but does not exactly reflect the human clinical scenario. Various animal strains have been used, and the type of rejection and the timing of its analysis differ among authors. The double purpose of this study was to develop an improved unusual AR model of SBT using the heterotopic technique, and to elaborate a guide useful to implement experimental models for studying AR. We analyzed the model's technical details and expected difficulties in overcoming the learning curve for such a complex microsurgical model, identifying the potential problem areas and providing a step-by-step protocol and reference guide for future surgeons interested in the topic. We also discuss the historic and more recent options in the literature.

Reduction of acute rejection by bone marrow mesenchymal stem cells during rat small bowel transplantation

Background

Bone marrow mesenchymal stem cells (BMMSCs) have shown immunosuppressive activity in transplantation. This study was designed to determine whether BMMSCs could improve outcomes of small bowel transplantation in rats.

Methods

Heterotopic small bowel transplantation was performed from Brown Norway to Lewis rats, followed by infusion of BMMSCs through the superficial dorsal veins of the penis. Controls included rats infused with normal saline (allogeneic control), isogeneically transplanted rats (BN-BN) and nontransplanted animals. The animals were sacrificed after 1, 5, 7 or 10 days. Small bowel histology and apoptosis, cytokine concentrations in serum and intestinal grafts, and numbers of T regulatory (Treg) cells were assessed at each time point.

Results

Acute cellular rejection occurred soon after transplantation and became aggravated over time in the allogeneic control rats, with increase in apoptosis, inflammatory response, and T helper (Th)1/Th2 and Th17/Treg-related cytokines. BMMSCs significantly attenuated acute cellular rejection, reduced apoptosis and suppressed the concentrations of interleukin (IL)-2, IL-6, IL-17, IL-23, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ while upregulating IL-10 and transforming growth factor (TGF)-β expression and increasing Treg levels.

Conclusion

BMMSCs improve the outcomes of allogeneic small bowel transplantation by attenuating the inflammatory response and acute cellular rejection. Treatment with BMMSCs may overcome acute cellular rejection in small bowel transplantation.

Study of morbidity in orthotopic small intestine transplantation with Wistar rats. Experimental study

BACKGROUND

Transplantation of the small intestine is a surgical procedure currently under investigation for its possible application in the treatment of patients with short bowel syndrome, aiming at the reintroduction of an oral diet.

AIM

To define the morbidity and mortality of intestinal transplantation in small animals using microsurgery. Intra and postoperative morbidity and mortality were studied in Wistar rats submitted to orthotopic intestinal allotransplantation.

MATERIAL AND METHOD

The animals were divided into three groups: group A (37 donor animals), group B (37 recipient animals), and group C (10 control animals). Group B was divided into three subgroups according to survival time. Subgroup TI consisted of animals that died during surgery or due to causes directly related to surgical intervention, subgroup T2 consisted of animals that died between the 4th and 29th postoperative day, and subgroup T3 consisted of animals that survived after 30 days. Transplanted animals were evaluated in terms of surgical technique used (vascular and intestinal anastomosis), graft quality, surgical time, and clinical parameters. The animals that died by the 29th postoperative day were submitted to autopsy and the remaining ones were sacrificed after 30 days.

RESULT

There was a high rate of complication of a surgical nature. Early mortality rate, i.e., mortality up to the third postoperative day, was 54% with vascular anastomosis being the major cause of death. Surgical time was evaluated in a restricted and homogeneous group and showed a strong prognostic value in terms of successful transplantation. Clinical parameters such as weight loss, reduction of ingestion, reduction of motor activity and diarrhea were directly correlated with acute rejection.

CONCLUSION

The experimented intestinal transplant is a procedure companied by considerable morbidity and mortality due to surgical complications in postoperative period, vascular anastomosis and total surgical time.

Secretory phospholipase A2 levels in rat small bowel

Preliminary studies on ischemia/reperfusion injury in transplanted small bowel grafts showed that secretory phospholipase A2 (sPLA2) may play a substantial role by breaking down membrane phospholipids. This study sought to determine the normal values of sPLA2 in the rat small bowel as a function of site and length as a baseline for future studies. The entire small bowel of male Lewis rats (200 g) was flushed with normal saline to eliminate solid contents. In group 1, the entire small bowel was divided into 5-cm segments (numbered 1-9), which were snap frozen and processed the same day for sPLA2. In group 2, a 25-cm segment of bowel (corresponding to segments 2-6 in group 1) was harvested from each animal, snap frozen, and immediately processed for sPLA2. To assess the effect of bowel storage on enzyme content, group 3 and group 4 grafts were stored for 7 and 14 days, respectively, at -85 degrees C prior to processing. All samples were homogenized in buffer, extracted with H2SO4 and assayed for sPLA2 activity using [1-14C]oleate-labeled autoclaved Escherichia coli as substrate. Results were analyzed statistically by ANOVA. sPLA2 activity rose from 85.46 +/- 14.46% hydrolysis/min fraction-1 in segment 1, to 476.38 +/- 176.75% hydrolysis/min fraction-1 in segment 9. The increase was linear and statistically significant (p < .0001). There was no significant difference in enzymatic activity between groups 2, 3, and 4. Group 2 activity was 263.02 +/- 43.74% hydrolysis/min fraction-1. This value was not statistically different from the mathematically calculated mean of segments 2-6 in group 1 (237.75). The results show that (1) sPLA2 activity increases predictably with distance from the ligament of Treitz (2) storage at -85 degrees C does not affect sPLA2, activity, and (3) 25-cm grafts may be evaluated in toto with reproducible baseline enzyme activity. Given the variability of enzyme activity along the course of the rat small bowel, it is imperative that exact location be identified in any studies evaluating sPLA2 activity.

Effect of flushing pressure on rat small bowel transplants

Excessive flushing pressure in rat small bowel transplants may cause graft failure, but the optimal pressure for manual flushing has not been established. The goal of this study was to determine a safe yet effective pressure for intravascular graft flushing and to evaluate the consequences of higher pressures. The "usual" manual flush was found to be at a pressure of approximately 40 mm Hg. After harvest, grafts were flushed manually with heparinized normal saline solution while connected to a transducer. Two groups of 25-cm jejunal grafts (n = 5 each) were harvested from Lewis rats (200 g) on a pedicle of superior mesenteric artery and vein. Group 1 grafts underwent 3 successive flushes at 50, 100, 200 mm Hg, respectively. After each flush, full-thickness biopsies were obtained for light and transmission electron microscopy. Two grafts underwent syngeneic small bowel transplantation (SBTx), and biopsies were taken after reperfusion. Group 2 grafts were flushed at 50 mm Hg and biopsies were obtained. All grafts underwent SBTx and biopsies as in group 1. After flushing at 50 mm Hg. biopsies were essentially normal. When flushed at 100 mm Hg, there was pronounced epithelial separation with dilatation of the core of the villus. Flushing at 200 mm Hg resulted in complete separation of the villi, with occasional disruption in the crypts. All group 1 transplanted grafts were grossly nonviable immediately after reperfusion, while transplanted grafts in group 2 were grossly normal. The findings were consistent within each group and the difference between groups was statistically significant (0 vs. 100%). The results suggest that flushing pressures of 50 mm Hg in rat SBTx provide optimal evacuation of blood with minimal, reversible tissue injury. Higher pressures cause progressive histologic damage and may produce nonviable grafts. Flushing pressures in the rat model of SBTx should therefore be maintained at approximately 50 mm Hg.

Vascular anastomotic techniques for experimental intestinal transplantation

A comparison of two techniques for the vascular anastomosis of intestinal transplants in the rat suggests that the use of an aortic segment with the graft leads to reduced operative time and improved technical success.

Vascular anastomotic techniques for experimental intestinal transplantation

A comparison of two techniques for the vascular anastomosis of intestinal transplants in the rat suggests that the use of an aortic segment with the graft leads to reduced operative time and improved technical success.

Cervical small bowel transplantation in the rat: a useful tool

Orthotopic intestinal transplantation in the rat is highly successful, but circumstances may require an extraabdominal graft location. We describe a microsurgical technique for cervical intestinal transplantation in the rat, which has been used to investigate the immune status of hosts already bearing an intraabdominal bowel transplant. A 10 cm segment of donor jejunum is harvested on a pedicle of superior mesenteric artery and superior mesenteric vein. In the recipient, the carotid artery (CA) and external jugular vein (EJV) are isolated. The venous anastomosis is performed end to end to the medial EJV branch, and the arterial anastomosis is completed end to side to the CA. Both anastomoses are performed with interrupted 10-0 nylon. The bowel is placed in a subcutaneous pocket in the neck, with both ends exteriorized. The procedure was performed in 11 donor-recipient pairs planned to elicit rejection, graft-vs.-host disease (GVHD) or graft acceptance. No technical complications were encountered. All rats survived long term, and their grafts were monitored histologically. The expected immune responses were observed, but rejection and GVHD were not fatal to the host with this model. We conclude that this technique is feasible and reliable to monitor the progress of isolated intestinal transplants. The location in the neck does not disrupt normal intestinal function of the recipient and may have multiple applications in the study of intestinal transplant immunology and physiology.

Small intestinal transplantation in the rat: effect on physiological properties of smooth muscle and nerves

The effect of transplantation on the physiological and pharmacologic properties of small intestine was evaluated in a syngeneic rat model. We examined the intrinsic contractile properties of the smooth muscle, the neural control of intestinal motility, and the sensitivity of the muscle and nerve endings to biologically active compounds in vitro, comparing transplanted tissue to controls. Both graft and control tissue contracted in a dose-dependent manner to cholinergic agonists, 5-hydroxytryptamine, and substance P and relaxed in response to noradrenaline. Contractile properties of smooth muscle and sensitivity to drugs were not altered by transplantation. Excitatory innervation was also similar in all specimens, but the inhibitory response was altered by transplantation. In the control intestine inhibition became maximal above 30 Hz, while in the graft maximal inhibition was obtained at 5 Hz. These findings imply an absence of extrinsic adrenergic inhibitory innervation in the graft. Intrinsic nonadrenergic inhibitory nerves and the excitatory innervation were intact after transplantation.

Small-bowel transplantation permits survival in rats with lethal short-gut syndrome

The functional integrity of transplanted bowel would most convincingly be demonstrated if transplantation after an otherwise lethal intestinal resection permitted survival and growth. In this experiment, we proposed to define the extent of bowel resection necessary for lethality and to show that transplantation allows salvage of these animals. Adult Brown-Norway rats (250 g) underwent extensive small-bowel resection (SBR) (ligament of Treitz to ileocecal valve) (n = 5), cecectomy only (CEC) (n = 3), SBR plus CEC (n = 6), or SBR plus CEC and syngeneic transplantation of 25 cm of jejunum (n = 6). All animals with SBR or CEC alone survived and grew; all animals with SBR plus CEC died within 2 weeks (mean, 6.4 days); and 6 of 6 animals with SBR plus CEC and transplant survived and grew. The difference in survival between the lethally resected rats and those with an intestinal transplant was highly significant (P less than 0.01). Dietary intake was similar in all groups. We conclude that in the rat, extensive small-bowel resection alone is not sufficient to be lethal; most of the small bowel and the cecum must be resected to obtain a lethal model. We have also shown that transplantation of small bowel into rats with an otherwise lethal extent of bowel resection will allow the animals to survive and grow. These results suggest the need for caution in correlating survival after intestinal transplantation in the rat with transplant function, since the preservation of too much native gut might permit survival even if the transplant has no nutritional function.

Monitoring of intestinal transplant rejection

Our results show that maltase, sucrase, and lactase activity are present at a normal level in nonrejecting small bowel transplants after an initial postoperative decline. This confirms that the disaccharide absorbing capacity of these grafts is intact. In allogeneic bowel, however, the levels of maltase and sucrase decline as histologic rejection occurs. These results suggest that serial maltase, sucrase, and possibly lactase levels in allogeneic intestinal transplants may serve as a useful adjunct in the monitoring of small bowel transplant rejection.

Technical aspects of intestinal transplantation in the rat

The microsurgical technique for rat intestinal transplantation used in our laboratory is described. A 25-cm segment of jejunum is harvested from the donor on a pedicle of superior mesenteric artery (SMA) and superior mesenteric vein (SMV). These vessels are then anastomosed end-to-side with 10-0 nylon to the infrarenal aorta and inferior vena cava of the recipient. The bowel ends are placed in isoperistaltic continuity with the host intestine. The procedure was performed in 423 animals with an 86 percent success rate and has been used to investigate all aspects of small bowel transplantation. The technique is described in detail with schematic drawings and intraoperative photographs, with the goal of making the procedure more understandable and accessible to other investigators wishing to study vascularized intestinal transplantation in the rat.

Small bowel transplantation in the rat: ultrastructural changes during the early phases of rejection

Small bowel transplantation has great potential for the treatment of short bowel syndrome, but the poorly understood rapid rejection of the bowel has hindered progress in this field. In this study, the rat model was used to evaluate the earliest detectable changes of bowel rejection. Eleven pairs of outbred rats underwent heterotopic transplantation of 10-15 cm segments of proximal jejunum on a pedicle of superior mesenteric artery and vein, anastomosed microsurgically to recipient aorta and inferior vena cava, respectively. The bowel extremities were exteriorized. Eight successfully transplanted rats were studied with serial punch biopsies, immediately post-transplantation and daily for 7 successive days. Biopsies were evaluated by light (LM) and transmission electron microscopy (TEM). Ultrastructural changes were evident before any gross or histologic changes. Endothelial damage, detected only by TEM, was common and resulted in exposure of the thrombus-promoting subendothelial components. Activated platelets as well as platelet aggregates adhered to these damaged areas. The lumen of some vessels was filled with tightly packed erythrocytes, at times showing intravascular hemolysis, suggestive of stasis. Extravascular features included edema and small numbers of immunocompetent cells. The epithelium showed a variable morphology depending on the degree of change in the underlying vessels and submucosa. The findings suggest that vascular damage and thrombosis as well as immunologic events are important in the early phase of the rejection process. Sustaining a viable segment of transplanted intestine may depend on suppressing both the microthrombotic aspect (with anticoagulants and/or antiplatelet agents) and the ensuing immunologic process with newer modalities such as cyclosporine.