Recipient growth and nutritional status following transplantation of segmental small-bowel allografts

Advances in absorptive function of transplanted intestine

Intestinal transplantation (IT) is the only effective therapy for irreversible intestinal failure. Improvements in immunosuppression and surgical techniques have promoted the clinical use of IT, but small intestinal graft dysfunction limits the widespread use of IT. Small intestine has a crucial role in nutritive substances absorption. In order to study the effect of gastrointestinal growth factors on transplanted intestinal function, and assess digestive capabilities after IT, it is essential to investigate the intestinal recovery in structure and function after small bowel transplantation. This article summarizes the latest advances in this field, including the absorption of water, eletrolytes, carbohydrates, lipid and protein in the transplanted intestine.

Therapeutic efficacy of intestinal and multivisceral transplantation: survival and nutrition outcome

The clinical introduction of intestinal transplantation has added a new dimension and offered a valid therapeutic option for patients with irreversible intestinal failure. In the year 2000, the Center for Medicare & Medicaid Services (CMS) recognized intestinal, combined liver-intestinal, and multivisceral transplantation as the standard of care for patients with irreversible intestinal and parenteral nutrition (PN) failure. Accordingly, the indications for the procedure are currently limited to those who develop life-threatening PN complications. However, a recent improvement in survival similar to other solid organ transplant recipients should justify lifting the current restricted criteria, and the procedure should be considered before the development of PN failure. Equally important is the awareness of the recent evolution in nutrition management and outcome after transplantation. Early and progressive enteral feeding using a complex polymeric formula is safe and effective after successful transplantation. Full nutrition autonomy is universally achievable among most intestinal and multivisceral recipients, with enjoyment of unrestricted oral diet. Such a therapeutic benefit is commonly maintained among long-term survivors, with full rehabilitation and restoration of quality of life.

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.

Segmental small-intestinal transplantation: a comparison of jejunal and ileal grafts

Strong immune responses, such as rejection and graft-versus-host disease, have been major obstacles to achieving a successful intestinal transplantation. Segmental small-intestinal transplantation is considered to result in a weaker response than total length grafting. Problems relating to organ harvesting from a living donor and spacial constraints of the recipient's abdominal cavity are the other reasons why a segmental small intestinal transplantation is required. It is also important to select the most suitable part of the intestine to be used in transplantation; therefore, the jejunal and ileal grafts were comparatively reviewed from the aspects of native bowel characteristics, function, preservation, and immunological response. Immunologically, the jejunum is considered to have a slight advantage over the ileum. However, the control of rejection does not become inordinately more difficult for ileal grafts. Functionally, the ileum is considered to be better with regard to several parameters, such as greater absorptive capacities of fat, bile acids, and vitamins, and adaptation potential. Anatomically, an ileal graft is feasible for living-related transplantation. However, there is no conclusive factor for choosing the ileum as a suitable segmental graft. Further extensive studies are still needed to clarify various experimental as well as clinical aspects regarding intestinal transplantation.

Comparison of ileal and jejunal transplantation after 50% proximal intestinal resection

BACKGROUND

The ileum has a greater adaptive capacity than the jejunum after intestinal resection. Transposition studies suggest that this is, in part, related to increased exposure to nutrients. However, there may be regional differences in intestinal properties that contribute to this response as well. The aim of this study was to compare the outcome of replacing the jejunum with either ileal or jejunal transplants while preserving an intact ileum after 50% proximal resection.

METHODS

Twenty-one Lewis rats were included in the study. One group (n = 7) served as transection controls (TC). The other two groups (n = 7) had 50% proximal resection with syngeneic transplantation of a similar length of ileum (ITX) or jejunum (JTX). Nutritional status and adaptation were studied at 14 days.

RESULTS

JTX animals gained less weight than TC and ITX (104 +/- 2% vs 114 +/- 1 and 108 +/- 2% initial, P < 0.05). ITX and JTX groups had lower caloric intake and serum albumin levels compared with TC (7.4 +/- 0.4 and 7.2 +/- 0.8% vs 8.8 +/- 0.2% body weight and 2.6 +/- 0.1 and 2.4 +/- 0.9 g/dl vs 3.0 +/- 0.1 g/dl, P < 0.05). Mucosal thickness increased significantly in the ileal remnant of both ITX and JTX groups (9.2 +/- 2.1 and 8.8 +/- 0.6 micrometer vs 6.6 +/- 0.6 micrometer, P < 0.05). Transplanted ileum had mucosal thickness similar to that of jejunum.

CONCLUSIONS

Transplanted ileum achieves an intestinal structure similar to that of the jejunum in the same environment. Modest adaptation of the remnant occurs with transplantation. Replacing jejunum with ileum rather than jejunum resulted in better weight gain, suggesting that intrinsic absorptive, motor, or hormonal rather than structural differences are responsible.

Length of transplanted small bowel required for adequate weight gain in rats

Progress has been made toward developing a clinically successful small-bowel transplant procedure, but there has been little research concerning the functional aspects of the transplanted small bowel. Using a rat model, our study examined the length of transplanted small bowel required to provide adequate weight gain. The rats were divided into six groups; groups 1 and 2 were considered controls. Group 1 (n = 6) underwent a gastrostomy. Group 2 (n = 3) underwent a jejunoile-ectomy followed by re-establishment of intestinal continuity and anastomosis of the native proximal small bowel to an abdominal stoma and the distal portion to the ascending colon. Groups 3 (n = 5), 4 (n = 4), 5 (n = 5), and 6 (n = 4) underwent small-bowel transplantation, receiving 100%, 50%, 25%, and 15% transplants, respectively. The donor small-bowel anastomoses were the same as the native small-bowel anastomoses in group 2. All of the rats began to produce stool within 4 days of becoming dependent upon the transplanted small bowel. By the end of postoperative week 4, there was no significant difference between the percentages of preoperative body weight in groups 1-4 (range 125.7%-130.0%). Although the weight gain in group 5 was significantly less than that in groups 1-4 (P < 0.05), it was adequate (111.8%); group 6 animals lost weight (94.7%). It is concluded that a 50% or more small-bowel transplant with or without an ileocecal valve provides ample weight gain; minimally adequate weight gain is achieved by a 25% transplant without an ileocecal valve; and the graft begins to function soon after transplantation.

Tacrolimus (FK506)--its effects on intestinal glucose transport

Tacrolimus (FK506) is at present the mainstay of immunosuppression for small intestinal transplantation. This study investigates the effects of chronic treatment with varying dosages of tacrolimus on animal well-being, weight gain, intestinal permeability, and the active transport of nutrients as measured by in vitro studies quantifying glucose flux. The effect of acute treatment with high-dose tacrolimus on glucose flux was also investigated. In the chronic studies, juvenile male Lewis rats were given tacrolimus in a dosage of 0.1 mg/kg, 0.5 mg/kg, and 2 mg/kg q. second day by subcutaneous injection for five weeks. In the acute studies, animals were treated with 2 mg/kg given q. 24 hr [mult] 48 hr, 24 hr and 12 hr prior to sacrifice. In the acute treatment groups, tacrolimus caused no change in glucose flux. In the chronically treated animals, FK506 levels were within the clinically relevant range. Chronic treatment with 0.5 and 2 mg/kg caused a significant reduction in weight gain. These same groups of animals had a significant increase in intestinal permeability as measured by absorption of 99Te-DTPA. Glucose flux was affected in all chronically treated groups, with net flux increasing in the jejunum and decreasing in the ileum. These findings show that chronic treatment with low-dose tacrolimus is well tolerated, but in higher doses there are significant effects in intestinal permeability and nutrient uptake, and animal weight gain. We suggest that these changes are due to alterations in intestinal permeability that do not appear to be mediated by an acute drug effect and more likely represent chronic changes, possibly from alterations in gene expression. These findings suggest that further studies regarding the effects of tacrolimus on nutrient transport, intestinal permeability, and the known immunologically related functions of tacrolimus should be done.

Segmental small bowel transplantation in the rat: comparison of lipid absorption between jejunal and ileal grafts

BACKGROUND

From the immunological point of view, it is very important to evaluate the efficacy of segmental small bowel transplantation and to determine which part of the intestine, jejunum, or ileum should be used. In the present study, we investigated the absorptive function of the transplanted jejunum and ileum in the rat.

METHODS

Syngeneic segmental small bowel transplantation (jejunal or ileal grafting) was performed. After surgery, body weight and fecal fat excretions were measured. In addition, bile acid concentration in bile juice was measured, and the response of both serum lipase and bile flow rate after oleic acid stimulation was evaluated. Recanalization of the lymphatic vessels was investigated by lymphangiography.

RESULTS

There was no significant difference in body weight change between normal controls, jejunum-transplanted rats, and ileum-transplanted rats. In short gut rats, however, body weight was significantly impaired. Fecal fat excretion in short gut rats was the highest in the four groups, and it was significantly lower in ileal grafts than in jejunal grafts. Ileum-transplanted rats also showed a significantly higher bile acid concentration in bile juice than jejunum-transplanted rats. After oleic acid stimulation, serum lipase responded better in ileal transplants than in jejunal transplants, but the bile flow rate did not show significant change in either group. Recanalization of the lymphatic vessels was established on the 28th postoperative day.

CONCLUSIONS

These results clearly show that ileal transplantation is more conducive to lipid absorption than jejunal transplantation.

Impaired survival and growth in immunosuppressed young rats with lethal short gut syndrome and a small bowel transplant: an effect of cyclosporine

Neonates and growing individuals have increased nutritional demands as compared with adults. To determine the functional ability of an intestinal graft to allow survival and growth, an otherwise lethal short gut model should be used (resection of both the entire small bowel and the cecum). In this study the authors investigated the survival and growth in young rats (80 to 125 g) with this lethal short gut syndrome (SGS) and either syngeneic or allogeneic segmental small bowel transplantation (SBTx). Additionally they sought to determine the effect of therapeutical doses of cyclosporine (CyA) in young, growing rats. To avoid total parenteral nutrition in rats undergoing SBTx, surgery was carried out in two steps: after segmental SBTx of a 25-cm jejunal graft, SGS was created 2 weeks later. Lewis rats underwent 1: Syngeneic segmental SBTx + SGS (n = 7); 2: Allogeneic segmental SBTx (donor: Lewis Brown Norway F1) + SGS + CyA (15 mg/kg/d for 7 days, then every other day for 21 days) (n = 9); 3: Syngeneic segmental SBTx + SGS + CyA as in group 2 (n = 5); 4: SGS alone (n = 5): 5: small bowel resection alone (n = 5); 6: sham laparotomy twice (n = 5); 7: sham laparotomy twice + CyA as in group 2 (n = 6). Weight, general condition, and nutritional serum variables were followed up regularly for 4 months. Rats with resection of small bowel survived but did not grow. Rats with small bowel resection + cecectomy died within 5 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

The adaptive response of the rat small intestine after resection and segmental transplantation during the early postoperative phase

Organ harvesting from a living donor or spatial constraints in the recipient's abdominal cavity are the main factors to be considered in the segmental transplantation of the small intestine. It was the aim of the following study to gain insight into the functional characteristics of different portions of the small intestine either after partial resection or syngeneic and allogeneic transplantation during the early postoperative period. Nutritional parameters (serum albumin levels, serum triglyceride levels, maltose absorption, excretion of fecal fat) and fat-stimulated neurotensin release were determined in Lewis rats that underwent small bowel resection (n = 21), syngeneic (Lewis-->Lewis, n = 21), or allogeneic transplantation (Brown Norway-->Lewis, n = 24). The length of the remnant, isograft, or allograft was 27 cm (i.e. one third of the rat small intestine) and consisted of the proximal (n = 7), middle (n = 7), or distal (n = 7) portion. Three postoperative deaths were due to ileus or pneumonia. After allotransplantation, cyclosporine (15 mg/kg BW s.c.) was administered for graft acceptance. Controls were unoperated, weight- and age-matched Lewis rats (n = 7). We found that resection of two-thirds of the small intestine led to significantly lower levels of albumin and triglycerides in all the three portions investigated (P < 0.01) but did not affect maltose absorption. Excretion of fecal fat was elevated after distal resection (P < 0.05). When compared to resected animals, syngeneic transplantation did not affect the nutritional parameters, but caused a significantly higher hormone release (P < 0.05) in all three different intestinal grafts. Allogeneic transplantation was successful when the middle or distal portion was grafted. All recipients of proximal allografts showed a severe loss of body weight and died between day 8 and 10 after transplantation. Postmortem examination revealed no signs of acute rejection. When transplantation of short intestinal segments is considered, it is of vital importance to take into account the functional differences and the influence of immunosuppressive drug therapy in the regulatory bowel function.

[Metabolic parameters and neurotensin liberation after resection of the small intestine, syngeneic and allogeneic segment transplantation the rat]

The aim of the following study was to gain some insight into the functional characteristics of different portions of the small intestine after either partial resection or syngeneic and allogeneic transplantation 3 months postoperatively. Nutritional parameters (serum albumin levels, serum triglyceride levels, maltose absorption, excretion of fecal fat) and fat-stimulated neurotensin release were determined in Lewis rats that underwent small-bowel resection (n = 21), syngeneic (Lewis-->Lewis, n = 21), or allogeneic transplantation (Brown Norway-->Lewis, n = 24). The length of the remnant, isograft, or allograft was 27 cm (i.e., one-third of the rat small intestine) and consisted of the proximal (n = 7), middle (n = 7), or distal (n = 7) portion. Three postoperative deaths were due to ileus or pneumonia. After allotransplantation cyclosporine (15 mg/kg body wt. s.c.) was administered for graft acceptance. The control group was not operated upon, but was composed of weight- and age-matched Lewis rats (n = 7). We found that resection of two-thirds of the small intestine led to significantly lower levels of albumin and triglycerides in all three portions investigated (P < 0.01), but did not affect maltose absorption. Excretion of fecal fat was elevated significantly only after distal resection (P < 0.05). When compared to resected animals, syngeneic transplantation did not affect the nutritional parameters, but caused a significantly higher hormone release (P < 0.05) in all three different intestinal grafts. Allogeneic transplantation was successful when the middle or distal portion was grafted. All recipients of proximal allografts showed a severe loss of body weight and died between day 8 and 10 after transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional aspects of small-bowel transplantation in rats

Although clinical small-bowel transplantation is still severely hindered by rejection of the graft, prolonged graft survival can be achieved by using cyclosporin A in several experimental models of small-bowel transplantation. In an immunologically quiescent phase after transplantation, the important question arises whether a small-bowel allograft has enough functional capacity to maintain a normal nutritional status. We investigated the functional capacity of orthotopic small-bowel transplants and evaluated the ability of the total small-bowel transplant to absorb orally given cyclosporin in the early postoperative period and the effect of this oral cyclosporin treatment on allograft survival as compared with intramuscular administration. Between 3 and 7 months postoperatively, recipients of syngeneic and allogeneic total small-bowel transplants and syngeneic jejunal segmental grafts had significantly decreased serum triglyceride levels. Total serum protein and albumin concentrations, serum cholesterol values, fecal fat excretion, and percentage of split fatty acids were normal. One year after transplantation the weight in the groups transplanted with a total small-bowel graft was not different from age-matched untreated controls. Animals grafted with a segmental graft, however, showed a significantly impaired growth and had not reached a normal weight 1 year after transplantation. Growth was also significantly impaired after near-total small-bowel resection. These animals had to be killed because of their poor condition. Cyclosporin absorption after small-bowel transplantation equalled that in normal controls. Graft survival after intramuscular treatment, however, was significantly better than after oral treatment.

Jejunal and ileal absorptive function after a model of canine jejunoileal autotransplantation

The effects of intestinal transplantation on the physiologic functions of the gut are not well understood. Our aim was to determine the effect of a large animal model of small intestinal transplantation (disruption of all neural and lymphatic continuity) on selected absorptive functions of the jejunoileum. Seven dogs were studied before and at 1, 4, and 12 weeks after a model of jejunoileal autotransplantation, which avoids confounding factors of immune rejection, immunosuppression, and harvest ischemia. Jejunal function was assessed by quantitative [3H]-folate and D-xylose absorption and ileal function by quantitative 57Co-vitamin B12 absorption. The role of lymphatic continuity was assessed by fecal fat recovery following 5 days of a controlled, high fat diet (75 g/day). All dogs developed a profuse, watery diarrhea that persisted for 6 to 12 weeks and lost about 15% body weight; however, absorption of D-xylose, folate, and vitamin B12 was unaffected at any time point. Fat absorption postoperatively was only mildly abnormal (less than or equal to 8 g/day) at all time points in five of seven dogs despite complete lymphatic disruption. We concluded that jejunoileal autotransplantation does not markedly affect these specific jejunoileal absorptive functions. Fat absorption in most dogs surprisingly remains almost normal. Anatomic and physiologic consequences of intestinal transplantation do not appear to induce global abnormalities in all absorptive functions in the nonrejecting jejunoileum.

Influence of the length of the small bowel graft on the severity of graft versus host disease

The influence of the length and origin of a small bowel graft on graft versus host disease (GVHD) was studied in 33 (Lewis x brown Norway) F1 hybrids transplanted with different types of Lewis small bowel grafts. Recipients of an entire small bowel graft (N = 9), a jejunal graft (N = 6), or an ileal graft (N = 6) displayed a similar acute lethal GVHD, with 100% mortality rate and equivalent survival time (15 +/- 0.7, 16.8 +/- 0.9, and 16 +/- 0.6 days, respectively) (P greater than 0.01). On the other hand, 80% of the recipients of a segmental jejunal graft (N = 10) recovered from a transitory form of GVHD and regained weight similarly to the isografted rats (N = 4). It was concluded that the entire small bowel, jejunum, and ileum can provoke an equivalent GVHD after transplantation, whereas a segment of jejunum decreases the intensity of GVHD, probably by reducing the amount of transplanted lymphoid tissue.

VIP receptors and content after bowel transplantation

Advances in immunosuppressive therapy have renewed interest in small bowel transplantation. Little is known, however, about the functional capacity of transplanted intestine. To clarify the potential for normal function, we investigated whether elements of the enteric nervous system are preserved after denervation in our rat model of intestinal transplantation. We investigated whether VIP, a major peptide neurotransmitter of the enteric nervous system, and its receptors are preserved in the bowel after transplantation. In our model of transplantation, avascular fetal jejunum from term Fisher rats is transplanted to the subcutaneous tissues of host syngeneic rats. This "neogut" becomes vascularized and develops characteristics of native small bowel. VIP content was measured by RIA and the in situ distribution of VIP receptors was determined by the technique of receptor autoradiography. Neogut was studied 1 and 3 weeks after transplantation and compared with age-matched rat pup jejunum. Autoradiographs showed high silver grain density, representing VIP binding sites, in the mucosal layers of all tissues studied. VIP content in the transplanted bowel was comparable to that of native gut and showed a rise with developmental age similar to that of native gut. VIP levels (pmole/mg protein, x +/- SEM) were neogut 1 week, 0.26 +/- 0.14; jejunum 1 week, 0.25 +/- 0.07; neogut 3 weeks, 0.60 +/- 0.21; and jejunum 3 weeks, 0.69 +/- 0.16. These results show that VIP receptors and content are preserved in this model of transplantation. This suggests that the enteric nervous system and receptors for peptide neurotransmitters remain intact after transplantation and may retain the potential for regulatory function.

Current status of small-bowel transplantation

Patients who have lost such a large portion of their small bowel that they permanently require total parenteral nutrition for survival would greatly benefit by receiving a small-intestinal transplant. Over the past two decades, many experimental studies have delineated the specific problems surrounding small-bowel transplantation and provided strategies for their control. Control of rejection, the most difficult problem, may be achieved with a combination of cyclosporine, azathioprine, prednisone, antithymocyte globulin, and monoclonal antibodies. The threat of graft-versus-host disease originating from the allogeneic lymphatic tissues in the allograft is abolished by in vitro x-irradiation of the cold, nonperfused graft with 1000 rads. Monitoring of the intestinal allograft is possible with the combination of a function test (maltose absorption, glucose absorption, or any other function test) and repeated graft biopsy. Effective short-term preservation of small-bowel segments for up to 18 h is possible by intravascular flushing with a balanced electrolyte solution containing 3% fructose and by subsequent hypothermic storage. Clinical small-bowel transplantation is certainly not an imminent therapeutic tool. However, clinical trials in highly selected patients could be envisioned on the basis of our present understanding of small-bowel transplantation and of transplantation biology in general, and in view of the clinical successes achieved with duodenal grafts transplanted in conjunction with pancreatic grafts.