Total pancreatectomy in dogs

Site for Unpurified Islet Transplantation is an Important Parameter for Determination of the Outcome of Graft Survival and Function

Transplantation of unpurified islets into the liver, unlike that of purified islets, causes portal hypertension and coagulopathy. The aim of this project was to determine the most suitable alternative site for transplantation of unpurified pancreatic islets in autotransplanted dogs. Twenty-five female mongrel dogs were divided into 5 groups depending on the site of islet transplantation: liver (3), spleen (7), skeletal muscle (5), omental pouch (6), and renal subcapsule (4). Pancreatic digestion of the total pancreatectomized specimen was carried out by distension of the pancreas with 1.5 mg/mL collagenase suspended in 250 mL Hanks' balanced salt solution using a semiautomatic method. The total number of islets equivalent isolated from 25 dogs was 90948 ± 6053. Only islets > 60 μm in diameter were counted, and the mean islet equivalent transplanted per kg body wt was 6762 ± 429. Islet function was achieved with transplantation into spleen in 71%, omental pouch in 50%, and muscle in 20%, but none in the renal subcapsule or liver groups. Glucose tolerance test at 30 d showed a mean K Value (decline in glucose, %/min) of 1.94 ± 0.73,0.79 ± 0.15 and 1.02 in the splenic, omental pouch and muscle groups, respectively. All animals in the liver group, 2 from the splenic group, and 2 from the renal subcapsule group died of diffuse bleeding. Four out of 5 dogs in the muscle group developed necrosis at the site of transplantation and the islets never functioned. This study demonstrates that in dogs, spleen and omental pouch appear to be suitable sites for transplantation of unpurified islets.

Pancreatic islet allograft in spleen with immunosuppression with cyclosporine. Experimental model in dogs

PURPOSE

To study the functional behavior of the allograft with immunosuppression of pancreatic islets in the spleen.

METHODS

Five groups of 10 Mongrel dogs were used: Group A (control) underwent biochemical tests; Group B underwent total pancreatectomy; Group C underwent total pancreatectomy and pancreatic islet autotransplant in the spleen; Group D underwent pancreatic islet allograft in the spleen without immunosuppressive therapy; Group E underwent pancreatic islet allograft in the spleen and immunosuppression with cyclosporine. All of the animals with grafts received pancreatic islets prepared by the mechanical-enzymatic method - stationary collagenase digestion and purification with dextran discontinuous density gradient, implanted in the spleen.

RESULTS

The animals with autotransplant and those with allografts with immunosuppression that became normoglycemic showed altered results of intravenous tolerance glucose (p < 0.001) and peripheral and splenic vein plasmatic insulin levels were significantly lower (p < 0.001) in animals that had allografts with immunosuppression than in those with just autotransplants.

CONCLUSIONS

In the animals with immunosuppression with cyclosporine subjected to allograft of pancreatic islets prepared with the mechanical-enzymatic preparation method (stationary collagenase digestion and purification with dextran discontinuous density gradient), the production of insulin is decreased and the response to intravenous glucose is altered.

Xenotransplantation of pig islets in diabetic dogs with use of a microcapsule composed of agarose and polystyrene sulfonic acid mixed gel

INTRODUCTION

The authors have designed a microcapsule composed of agarose and polystyrene sulfonic acid (PSSa) mixed gel that provides a protective barrier against complement attack. Xenografts of islets, encapsulated in an agarose-PSSa microcapsule, have been shown to normalize blood glucose in rodents with chemically induced diabetes for extended periods of time without immunosuppression.

AIM

To investigate the efficacy of agarose-PSSa microencapsulated pig islets in reversing diabetes in a large animal model.

METHODOLOGY

Diabetes was induced in beagle recipients by total pancreatectomy. Each recipient received three to five intraperitoneal injections of either encapsulated (n = 5) or nonencapsulated pig islets (n = 2).

RESULTS

In all dogs receiving microencapsulated islets, the graft function was achieved for 7.4 +/- 3.1 weeks (mean +/- standard error), as determined by elimination or reduction of exogenous insulin requirement. In three recipients, the fasting blood glucose levels were maintained at < or = 200 mg/dL without any exogenous insulin for a period of 6, 50, and 119 days. Circulating porcine C-peptide was detected in the sera of all dogs after transplantation of encapsulated islets. Immunohistologic examination revealed the presence of insulin-positive cells in the microcapsules. In contrast, in two dogs receiving nonencapsulated islets there was no graft function.

CONCLUSIONS

This preliminary study demonstrates that agarose-PSSa microencapsulated pig islets can survive and function for weeks or months in totally pancreatectomized diabetic dogs without immunosuppression.

Intrathymic islet transplantation in the canine: I. Histological and functional evidence of autologous intrathymic islet engraftment and survival in pancreatectomized recipients

BACKGROUND

Although an attractive alternative to daily insulin therapy, allogeneic pancreatic islet transplantation has yielded suboptimal results in clinical trials, in contrast to islet allotransplantation in animal models, which have demonstrated consistent success. The successful transplantation of isolated islets to the thymus, with a single concomitant dose of antilymphocyte serum, has been demonstrated in rodents, and more significantly, such intrathymic islet allografts have been shown to induce recipient tolerance toward subsequent extrathymic donor strain islet allografts. Intrathymic islet autotransplantation has been pursued, as a prelude to studies of allogeneic IT islet transplantation and tolerance induction, in canine, porcine, and non-human primate models, to assess the large animal thymus as a site capable of supporting a viable islet graft. However, little functional or histological evidence has established definitive survival of islets transplanted within the thymus of a phylogenetically advanced species, which may be requisite to tolerance induction. This study describes the successful intrathymic autotransplantation of isolated islets using a canine model.

METHODS

Purpose-bred juvenile dogs, aged 4-6 months, underwent partial (n=4), or total pancreatectomy (n=11), and transplantation of autologous islets. The pancreas (or pancreatic limb) was distended with collagenase solution, and digested using a modification of the semiautomated system of Ricordi. Islets were purified by discontinuous gradient centrifugation, using Euroficoll (ficoll in Euro-Collin's kidney preservation solution). Partially pancreatectomized canines underwent IT transplantation of purified autologous islets (8000+/-4000 IEs), and were killed 8 weeks posttransplant. Totally pancreatectomized canines underwent transplantation of autologous islets to the liver (via portal vein embolization, n=5, IPO group) or the thymus (via direct IT injection, n=6, IT group), and were serially evaluated for a period of 8 weeks posttransplant to assess fasting blood glucose (FBG), serum insulin (SI) levels, and i.v. glucose tolerance (IVGTTs). K values (defined as the %-decrease/minute of the log(e) of blood glucose values) were calculated from IVGTT results.

RESULTS

After autotransplantation in this cohort of animals, five of five IPO, and three of six IT islet recipients, remained normoglycemic (mean FBG< or =250 mg%) immediately posttransplant, and all recipients exhibited significantly elevated SI levels compared to apancreatic controls (n=10, followed 72 hr postpancreatectomy). Normal k values (=-1.1) were observed in two of five IPO, and in one of six IT recipients, 8 weeks after transplantation, and thymic tissue insulin content was increased compared to non-islet-bearing thymi (93.7+/-48.6 ng/g tissue vs. 0.7+/-0.4 ng/g tissue). At 8 weeks posttransplantation thymi from both partially and totally pancreatectomized animals were resected and processed for histological examination. Microscopic analysis of islet-bearing thymi revealed positive staining for islet-specific hormones (insulin and glucagon) within all IT recipients., Identification of islets within thymi of hyperglycemic IT recipients was problematic as islet beta cells were highly degranulated as a result of the recipients glycemic state.

CONCLUSIONS

These results indicate that autologous islets, transplanted to the canine thymus, engraft, function, and survive for up to 8 weeks after islet autotransplantation to the canine thymus and establish the feasibility of intrathymic islet transplantation in a phylogenetically advanced animal model. The ability of islets to survive within the thymic environment for a period of at least 8 weeks after transplantation suggests that the successful induction of specific unresponsiveness secondary to intrathymic transplantation will not be impaired or limited by the inability of a viable islet mass to survive within the thymus for a sufficient period.

Prevention of primary nonfunction of canine islet autografts by treatment with pravastatin

BACKGROUND

Nonspecific inflammation is the primary cause of early islet graft loss. We have shown in mice that pravastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, prevents primary nonfunction of islet isografts by reducing inflammatory reactions at the graft site. This study was designed to test the effectiveness of this agent in a large animal model, dogs, by transplanting autologous islets.

METHODS

After total pancreatectomy, islets were isolated by using a two-step digestion method, followed by discontinuous gradient centrifugation on EuroFicoll. A known number of freshly isolated islets were immediately transplanted back into the same dog via the portal vein.

RESULTS

First, we determined the minimal islet number required to reverse diabetes by transplanting 3,000-10,000 IEQ/kg with no additional treatment. The number was found to be 4,000 IEQ/kg, and islets less than 4,000 IEQ/kg consistently failed. To test the effect of pravastatin, 3,000 IEQ/kg were transplanted into dogs that either received no further treatment or were treated daily with 20 mg/kg of pravastatin from days -2 to 14. Without pravastatin, this number of islets lowered blood glucose only transiently, and all four of these dogs became hyperglycemic within 1 week. In contrast, four of the five dogs treated with pravastatin became normoglycemic (<150 mg/dL) and maintained this level during the observation period of 12 weeks (P<0.05). Postprandial plasma glucose and insulin levels returned to normal, and K values of intravenous glucose tolerance tests were significantly higher in pravastatin-treated dogs than in controls (P<0.04 at week 2 and P<0.01 at week 4).

CONCLUSION

Peritransplant pravastatin treatment reduced the number of autologous islets required to reverse diabetes in totally pancreatectomized dogs. These results suggest that pravastatin may also facilitate better islet graft survival and function in clinical transplantation.

Increased islet viability by addition of beraprost sodium to collagenase solution

The digestion of pancreatic tissue with collagenase is an essential part of the islet isolation procedure. However, the process exposes islets to various types of harmful factors, including collagenase contaminants, enzymes released from the acinar cells, warm ischemia, and mechanical agitation. Nitrogen oxide production and cytokine release may also contribute to islet cell damage. Protection of islets from such damage would improve the islet yield, survival, and function. Beraprost sodium (BPS) is a prostaglandin I2 analogue, is stable in aqueous solution, and has a cytoprotective effect on various types of cells. BPS has been shown to improve the yield and function of cryopreserved and/or cultured islets. These findings prompted us to examine its cytoprotective effect on islets during the islet isolation process. Canine islets were isolated by means of a two-step digestion method and purified on Euro-Ficoll density gradient solutions (the procedure used for human islets). BPS at a concentration of 100 nM was added to the collagenase solution. After purification, the islet yield was 434,561 +/- 35.691 islet number expressed as 150 microm equivalent size (IEQ)/pancreas or 8,799 +/- 345 IEQ/g of pancreas in the BPS group and 349,987 +/- 52,887 IEQ/pancreas or 7,998 +/-1610 IEQ/g of pancreas in the control group (n = 8, each). The percent viability was 88.5 +/- 0.7% in the BPS group and 82.0 +/-0.9% in the control group (P < 0.01). Therefore, the recovery of viable islets (calculated by islet number x % viability) was 384,586 +/- 46,804 IEQ/pancreas (7,743 IEQ/g) in the BPS group and 286,989 +/- 43,367 IEQ/pancreas (6,558 IEQ/g) in the control group (P < 0.02). After culture, significantly higher numbers of islets were also recovered in the BPS group than in the control group. The islet insulin content was significantly higher in the BPS group than controls (237.8 +/- 38.5 versus 92.3 +/- 25.6 microU/IEQ; P < 0.02), although islets of both groups responded with high stimulation indices (>6). These results indicate that the addition of BPS to the collagenase solution increases the recovery of viable islets, and improves beta cell function.

Distribuição anatômica da árvore ductal pancreática do cão: implicações para o isolamento das ilhotas de Langerhans

O conhecimento da anatomia normal da árvore ductal pancreática no cão e de sua variações reveste-se de importância para a execução dos protocolos de preparação e isolamento das ilhotas de Langerhans. A proposta deste estudo é demonstrar a configuração anatômica da dutal pancreática com especial atenção para as implicações sobre as técnicas de preparação do tecido pancreático para o transplante de ilhotas de Langerhans no cão. Os autores realizaram a dissecção do duto pancreático principal (Santorini) e a cateterização dos seus ramos ascendente e descendente. Em seguida procederam à pancreatectomia total sem duodenectomia. Através destes cateteres, infundiu-se solução de acetona no interior dos ductos e solução de tinta nanquim de cor azul no ramo ascendente e de cor vermelha no ramo descendente. Posteriormente, os autores dissecaram a árvore ductal pancreática com pinças delicadas e digitoclasia. Através desta técnica, os autores verificaram a distensão universal do parênquima pancreático devido ao envolvimento de toda a glândula pelos ramos tributários do ducto pancreático principal. O ramos descendente distendeu exclusivamente a região do processo uncinado, ao passo que o ramo ascendente distendeu exclusivamente as regiões do corpo e cauda do pâncreas canino. Esta constatação enfatiza a utilização destas vias para a infusão das soluções apropriadas nos procedimentos de isolamento das ilhotas de Langerhans no modelo canino.

[In vitro and in vivo studies of isolation, transplantation and function of Langerhans islets in the swine]

Limits and possibilities of the transplantation of islets of Langerhans in pigs were studied. 6 x 10(4) to 3 x 10(6) islets and insulin producing fragments per pancreas were obtained by intraductal collagenase digestion of the pancreatic gland following total pancreatectomy. Islets grafted into the spleen or liver rendered normoglycemia to the pancreatectomized animals as demonstrated by normal fasting blood sugars and normal intravenous glucose tolerance tests as compared to not operated animals permitting a survival time of up to one year. Apancreatic controls died of ketoacidosis and diabetic coma 10 to 12 days posttransplant. The number of isolated and transplanted islets correlated well to the normoglycemic state of the animal. Beyond that the in vitro challenge of the islets with glucose and resulting insulin secretion was a very important indicator for the functional status and integrity of the islets after transplantation. Thus the pig appears to be a suitable model for the preclinical studying of islet transplantation especially since immunologic, physiologic and anatomic features of the pig are similar to those in the human regarding pancreas and nutrition.

Cold storage preservation of pancreatic tissue prior to and after islet preparation in a dog autotransplantation model

Utilizing an intrasplenic canine islet autotransplant model, the effects of cold storage preservation on pancreatic tissue prior to and after collagenase dispersion were examined. A control series, in which freshly retrieved and prepared tissue was transplanted, yielded a 75% success rate (6/8). In contrast, when the pancreas was stored in modified silica gel filtered plasma (SGF I) for 24 hr, no autotransplant was successful (0/6). However, when the islet tissue was prepared following pancreatectomy and then stored in a mannitol-containing modification of SGF (SGF III), autotransplantation was successful in 83% (5/6) after 24 hr of preservation and in 60% (3/5) after 48 hr of preservation. Similarly, the islet tissue was stored in a hyperkalemic hydroxyethyl starch solution (HES) and this was successful in 20% (1/5) after 24 hr of preservation and in 50% (1/2) after 48 hr of preservation. Cold storage preservation techniques for the pancreas prior to islet isolation need to be refined, but dispersed islet-enriched pancreatic tissue can be successfully maintained at 4 degrees C for up to 48 hr prior to transplantation in dogs using established pancreas preservation solutions.

Combined subtotal pancreatectomy with selective streptozotocin infusion--a model for the induction of insulin deficiency in dogs

Standardized models of type I diabetes-like insulin deficiency in larger laboratory animals hardly exist. It was therefore investigated whether stable long-term insulin deficiency in dogs can be induced by selective beta-cell destruction in a safe and reliable procedure without damage of other organs. In Beagle dogs, the diabetogenic response to systemic streptozotocin administration (38.5-28 mg/kg b.wt.) was tested. In addition, resection of corpus and cauda pancreatis in combination with selective streptozotocin perfusion (25 mg/kg b.wt.) of the remaining pancreas tissue was evaluated. Whereas systemic streptozotocin administration failed to destroy insulin secretion, but led to a variety of intoxication symptoms even in comparatively low doses (28 mg/kg b.wt.), the latter procedure resulted in a complete and persistent insulin depletion (basal serum immunoreactive insulin less than or equal to 3 microU/ml, no stimulated response) without toxic organ damage or other serious side effects. The dogs developed type I-like diabetes, which required continuous exogenous insulin substitution. From these results, subtotal pancreatectomy with selective streptozotocin perfusion of the remaining pancreas is proposed as a safe model of insulin deficiency in dogs, which should be further evaluated in experimental diabetology.

A simple method of canine pancreatic islet isolation and intrahepatic transplantation

Clinical pancreatic islet transplantation has been impeded by the inability to isolate an adequate mass of functional tissue that will ameliorate diabetes. A simplified method of canine islet isolation was developed that allowed for either intrasplenic or intrahepatic transplantation. Following total pancreatectomy, parenchymal digestion was accomplished by intraductal collagenase perfusion and stationary incubation. The digested tissue was dispersed by filtration through a steel mesh (400 microns), washed, and separated on a discontinuous dextran density gradient. Enhanced islet tissue (2-4 ml) was recovered from the uppermost interface of the gradient and autotransplanted. The islet isolation procedure was tested in two series of dogs undergoing either intrasplenic or intrahepatic engraftment. Immediate and sustained normoglycemia (plasma glucose less than 200 mg%) was obtained in 5 of 8 dogs (63%) in the intrasplenic group and 6 of 8 dogs (75%) in the intrahepatic group. The mean fasting plasma glucose concentration 2 weeks after transplantation was 102.8 +/- 6.4 mg% in the intrasplenic group and 103.3 +/- 8.4 mg% in the intraportal group. The mean IVGTT K-values 2 weeks after transplantation were -1.41 +/- 0.35% and -1.21 +/- 0.13%, respectively. On the basis of insulin content, the islet yield was 33.0 +/- 3.7% of the total pancreas in the intrasplenic group and 33.0 +/- 3.1% in the intrahepatic group. Islet mass was enhanced 10.2 +/- 1.5 and 20.0 +/- 6.2 fold, respectively, on the basis of insulin/amylase ratios. The success rate in this canine model compared favorably with previously published results from other laboratories.(ABSTRACT TRUNCATED AT 250 WORDS)

Canine pancreaticoduodenal allotransplantation with cystoduodenostomy: an animal model with clinical application

Most techniques described in animal models of pancreatic transplantation use either segmental or autotransplants. We employ a technique of pancreaticoduodenal allotransplantation in the dog that closely resembles the operation used in humans. The arterial supply of the entire pancreatic graft is preserved by procuring a Carrel patch of aorta encompassing the origin of the celiac and the superior mesenteric arteries. Splenic, inferior pancreaticoduodenal, and superior pancreaticoduodenal arteries remain intact with the graft. Venous drainage is through a short segment of portal vein. A 6-cm cuff of duodenum is taken with the head of the pancreas. Engraftment proceeds by placing the allograft within the peritoneal cavity of the recipient. End-to-side vascular anastomoses are constructed to distal aorta and inferior vena cava. The duodenal cuff is anastomosed to the dome of the bladder for drainage and analysis of exocrine secretions and to provide a port of entry for cystoscopically directed needle biopsy. A total pancreatectomy is performed to induce a state of diabetes. The average operating time is 5 h. Twenty-two dogs have undergone allotransplantation using this technique. Six dogs had no complications and were sacrificed after meeting criteria of their study protocol. There were three technical failures, two arterial thromboses and one exsanguination, yielding an 86% rate of successful engraftment. Three other dogs died of intussusception and three dogs died of sepsis, one secondary to wound dehiscence and one due to inadvertent common bile duct ligation during pancreatectomy. Wound problems, four dehiscences and two superficial infections, occurred only in immunosuppressed dogs.

Cyclosporin A and islet function

Long-term cyclosporin A (CsA) administration in dogs was studied with respect to function of the islets of Langerhans. After 3 weeks of immunosuppression with therapeutic doses, the islets were isolated and assessed in vitro for insulin release in response to glucose challenge. Islet tissue retrieved from the CsA-treated animals showed a total insulin output significantly lower than that of the control animals (p less than 0.01). The first and second phases of insulin release were both impaired in animals treated with CsA compared with controls (p less than 0.001 and p less than 0.05, respectively). The negative impact of CsA on the beta cells was easily demonstrated in this in vitro study. Similar results are more difficult to achieve with purely in vivo models, probably due to the great redundancy of the islet mass in intact animals. The mechanism of this CsA toxicity remains to be defined.

Cyclosporine absorption in apancreatic dogs

The plasma concentration time course of orally administered cyclosporine was studied in apancreatic dogs with established islet autografts and compared with that in normal control dogs. After oral administration of cyclosporine (20 mg/kg), blood samples were collected at 0, 1, 2, 3, 4, 6, 8, and 24 hours, and the plasma cyclosporine concentrations were measured by radioimmunoassay. The plasma level of cyclosporine increased promptly in both groups after dosing. Peak plasma concentrations ranged from 435 to 1,542 ng/ml and were attained at between 2 and 6 hours in the apancreatic dogs, and concentrations from 602 to 4,414 ng/ml were attained at between 1 and 6 hours in the control dogs. Even though there was substantial variation among animals, the plasma concentration curve of the apancreatic group was quite comparable with that of the control group. The Student's test for unpaired data failed to show any significant differences over the time course. Area under the concentration-time curves, maximum concentration, and times of peak concentration were calculated. These data demonstrated the capacity of apancreatic dogs with islet autografts to absorb cyclosporine when they are stable, nutritionally normal, and have full endocrine reconstitution.

Proximal pancreatectomy: a comparison of electrocautery and contact and noncontact Nd:YAG laser techniques in the dog

Proximal pancreatectomy with duodenal preservation is technically difficult. It has often been performed experimentally in pancreatic transplantation studies. Preservation of the pancreaticoduodenal vessels and duodenum provides an excellent method of testing various operative techniques in pancreatic surgery which may lead to further clinical applications. The present study has compared the conventional noncontact Nd:YAG laser technique with electrocautery and a new contact Nd:YAG laser technique for proximal pancreatectomy. There were five dogs in each group, and the pancreatic duct was left open to drain into the abdominal cavity after pancreatic transection in all of the animals. Resection with the contact laser caused significantly less blood loss (109 +/- 74 ml) than the noncontact laser (228 +/- 81 ml), (p less than 0.05). A greater number of ligatures were used in the noncontact laser group (11 +/- 3 ligatures) as compared with the electrocautery group (2.2 +/- 1.6 ligatures) and the contact laser group (5.2 +/- 2.8 ligatures), (p less than 0.005). Noncontact laser and electrocautery resection techniques resulted in necrotizing pancreatitis and death in two animals. The new contact laser system provides a safe and effective method of performing pancreatic surgery.

Effect of cyclosporine on established islet autografts

Cyclosporine (CyA) is toxic to the function of isolated islets and this toxicity may, in part, explain the failure of islet allografts as well as autografts with CyA immunosuppression. Not only do canine allografts fail despite CyA immunosuppression, but control autografts given CyA from the day prior to transplantation have a very high failure rate. In this study, we investigated CyA effects on established islet autografts. Twenty mongrel dogs underwent total pancreatectomy and successful intrasplenic islet autotransplantation. Ten served as control autografts (Group 1); five were started on oral CyA on the 5th postoperative day (Group 2) and 5 dogs were given CyA from the 10th day after grafting (Group 3). Intravenous glucose tolerance tests were performed before operation, before starting CyA and after 3 weeks. Plasma insulin was determined by radioimmunoassay. Control dogs remained normoglycemic throughout the study as did Group 3 animals. In Group 2, 2 of 5 dogs failed, both on the 4th day of CyA, while the other 3 were normoglycemic throughout the study. No significant difference was shown among the K values, fasting blood glucose and peak plasma insulin values following IVGTT before and after treatment with CyA. CyA begun the day before autografting gravely compromises graft success. However, after the graft is well established, an adverse effect of CyA on islet cell function is not evident.