Heterotopic intestinal transplantation aggravates the insult of chronic rejection

Effect of chronic, extrinsic denervation on functional NANC innervation with vasoactive intestinal polypeptide and substance P in longitudinal muscle of rat jejunum

Intestinal denervation contributes to enteric motor dysfunction after intestinal transplantation [small bowel transplantation (SBT)]. Our aim was to determine long-term effects of extrinsic denervation on functional non-adrenergic, non-cholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P. Contractile activity of jejunal longitudinal muscle from six age-matched, naïve control rats (NC) and eight rats 1 year after syngeneic SBT were studied in tissue chambers. Spontaneous contractile activity did not differ between groups. Exogenous VIP inhibited contractile activity dose-dependently in both groups, greater in NC than in SBT. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) and the nitric oxide synthase inhibitor l-N(G)-nitro arginine prevented inhibition by exogenous VIP and electrical field stimulation (EFS) in both groups. Exogenous substance P increased contractile activity dose-dependently, greater in NC than in SBT. The substance P antagonist ([D-Pro(2),D-Trp(7,9)]-substance P) inhibited effects of exogenous substance P and increased the EFS-induced inhibitory response. Immunohistofluorescence showed staining for tyrosine hydroxylase in the jejunoileum 1 year after SBT suggesting sympathetic reinnervation. In rat jejunal longitudinal muscle after chronic denervation, response to exogenous VIP and substance P is decreased, while endogenous release of both neurotransmitters is preserved. These alterations in excitatory and inhibitory pathways occur despite extrinsic reinnervation and might contribute to enteric motor dysfunction after SBT.

Features of chronic allograft rejection on rat small intestine transplantation

The aim of this study was to develop a model of chronic rejection of the entire small intestine transplantation and to analyze the features of chronic rejection. Allogenic small bowel transplantation was performed in a rat combination of Lewis to F344. Intestines were procured at the 60th and the 90th day after operation. We compared the semiquantitative score of histological parameters. The immunological components involved in the chronic rejection process were evaluated by immunohistochemical staining and the cytokine levels in grafts. The significant characteristics of the allograft on histology were changes of villous architecture, interstitial fibrosis, leukocyte infiltration, and obliterative arteriopathy. Allografts on the 60th day post-transplantation had more score in inflammatory events, while the grafts on the 90th day after operation had more values in ischemia/fibrotic events. The number of infiltrating CD4, CD8 and macrophage cells in allografts progressively decreased over time. The level of intragraft cytokines such as IL-6, TNF-alpha and IL-10 in the 90th day after transplantation also decreased compared with that in the 60th day. These data suggested that in the early stage (POD 60), there were more active and intense inflammatory events; later (POD 90) allografts manifested less inflammation and more arterial obliteration and fibrosis.

Comparative study of allograft survival of heterotopic and orthotopic small bowel transplantation in rat

BACKGROUND

Small bowel allografts can either be placed heterotopically or orthotopically. In heterotopic small bowel transplantation (H-SBT), the host small intestine containing a substantial amount of gut-associated lymphoid tissue is removed, whereas in conventional orthotopic small bowel transplantation (O-SBT) it is retained. This study compared the allograft survival of H-SBT and O-SBT and evaluated the effect of retaining the host intestine in O-SBT in an altered O-SBT (AO-SBT) model.

METHODS

SBT was performed in a high-responder rat stain combination (blood group D Agouti --> Lewis). Immunosuppressive treatment consisting of a short course of FK506 (2 mg/kg/day IM for 3 days before transplantation and 0.3 mg/kg/day for 14 days after transplantation) was used.

RESULTS

Survival (mean +/- SD) of H-, O-, and AO-SBT untreated animals was 6.25+/-0.58 days, 6.5+/-0.58 days, and 6.7+/-0.25 days, respectively. With FK506 immunosuppression, survival of H-SBT animals was 49.3+/-13.17 days, whereas 75% (12/16) and 80% (4/5), respectively, of O-SBT and AO-SBT animals achieved indefinite survival (>120 days) with functioning grafts.

CONCLUSION

Our data suggest that heterotopic placement of intestinal allografts results in a more severe graft rejection than orthotopic placement. The indefinite survival of O-SBT is not due to of the removal of host intestine carrying a heavy load of gut-associated lymphoid tissue.

Impact of graft length on surgical damage after intestinal transplantation in rats

BACKGROUND

Intestinal grafts greatly affect nutrition and immunology in the host. The growth of the recipient and incidence of graft-versus-host disease depend on graft length. A larger graft may affect the host immune system, but little is known about how the length of the intestinal graft severely affects surgical intervention. We developed a cervical small bowel transplantation (SBT) rat model that minimized technical variations using a cuff method and studied the effects of graft length on surgical damage in SBT.

MATERIALS AND METHODS

We transplanted a whole (70 cm) or partial (15 cm) intestine into a syngeneic rat combination of LEW (MHC haplotype: RT1(l)) to LEW and evaluated changes in perioperative hemodynamics and the endogenous endotoxin level. Natural killer (NK) cell activity in the peripheral blood and the immunologic response of the recipient spleen were also studied.

RESULTS

In the whole SBT model, body weight loss was more severe than in the segmental SBT model; the rats in the former model often died, while all in the latter survived indefinitely. The systemic blood pressure markedly decreased in the whole SBT group immediately after reperfusion. The proliferative activity of splenic lymphocytes stimulated by concanavalin A was also more severely inhibited in the former model than in the latter postoperatively. NK cell activity in the whole SBT rats declined more severely than the segmental SBT rats 3 days postoperatively.

CONCLUSION

The longer graft severely induced surgical intervention; and influenced host immunosuppression, resulting in the higher mortality in rats undergoing whole SBT.

Impact of FK506 and steroids on adaptation after intestinal resection or segmental transplantation

Segmental small intestinal transplantation (SIT) using living related donors (LRD) is being evaluated as a therapy, clinically. Advantages of this technique include an increase in the donor pool, optimization of the timing of transplants, and potential immunologic benefits. However, the ability of a short segment of intestine to function after transplantation has not been investigated in large animal models. This study evaluates the impact of immunosuppression on the adaptive process and the ability of a transplanted segment of intestine to adapt. A pig model of segmental SIT was used. Animals were resected, leaving 150 cm of distal ileum (n = 5), resected and treated with FK506 (n = 4), or steroids (n = 4), or with FK506 + steroids (n = 7), or transplanted using a similar segment of ileum and treated with FK506 + steroid immunosuppression (n = 9). Animals undergoing resection, or resection plus steroid treatment, did well, gaining weight post-operatively (37% and 15% of preoperative weight, respectively). However, animals undergoing resection and treated with FK506 or FK506 + steroids did poorly, losing weight (-14% and -22% of preoperative weight, respectively) and showing significant impairment of intestinal adaptation, morphologically and functionally. Furthermore, FK506-treated animals developed inflammatory changes in the intestinal mucosa, mimicking rejection. Segmental SIT animals had a high rate of rejection (66%) and showed a similar impairment in adaptation. Hence, segmental SIT is a stringent physiological test of intestinal adaptation. FK506 appears to impair gut function after resection, either directly, or by interfering with the adaptive process. In this model of segmental SIT, FK506 and steroids at the doses tested did not provide adequate immunosuppression to prevent rejection and the graft did not function adequately to allow growth. Further studies are required to evaluate the mechanisms underlying these findings, and to determine if similar effects occur in humans.

Intestinal transplantation

Increasing experience with intestinal transplantation has led to the refinement of techniques to detect and treat rejection and infectious complications. Improved outcome has led to a broadening of the indications for intestinal transplantation, particularly solitary intestinal transplantation.