DL-ethionine treatment of adult pancreatic donors. Amelioration of diabetes in multiple recipients withe tissue from a single donor

Exocrine contamination of isolated islets of Langerhans deteriorates the process of revascularization after free transplantation

BACKGROUND

We investigated the influence of exocrine tissue contamination on the process of vascularization of isolated pancreatic islets of Langerhans after free transplantation into Syrian golden hamsters.

METHODS

After isolation by a modified collagenase digestion technique, a total of 45 individual islets contaminated with exocrine tissue were transplanted syngeneically into striated muscle of dorsal skinfold chambers of nine animals. Sixty-six purified islet grafts transplanted into nine additional animals served as controls. Islet engraftment as well as the process of angiogenesis and revascularization were analyzed at days 3, 5, 9, and 13 after transplantation using intravital fluorescent microscopic techniques.

RESULTS

Islet grafts contaminated with exocrine tissue showed a significantly (P<0.05) lower take rate initially after transplantation when compared with purified islet grafts. In addition, functional capillary density, which served as an indicator of graft vascularization, was found significantly (P<0.05) decreased in contaminated compared with purified islets. Exocrine tissue contamination was further associated with marked leukocyte-endothelial cell interaction within the grafts' postcapillary venules, which finally resulted in six of nine animals in an overwhelming unspecific inflammation of the transplantation site with successive loss of the islet transplants.

CONCLUSIONS

These findings support the view that exocrine tissue contamination is detrimental for the process of angiogenesis and vascularization of freely transplanted pancreatic islets when grafted to a confined site such as striated muscle tissue.

[Isogenic islet transplantation on the rat liver (method for isolation and purification of the Langerhans islets)]

The major indication for pancreas or islet transplantation is diabetes mellitus type I. This process has to supply the insulin necessity keeping glucose under control. We have studied isogenic islet transplantation on the rat (WAG-RT1u) liver. The method of isolation and purification of the islets obtained 2.834 +/- 551.64 islets with purity of 83 +/- 2.45%. Diabetes was induced by streptozotocin and seric glucose prior transplantation was 35 mmol/L. The islet transplantation of 2.834 +/- 551.64 islets in the rat liver has normalized glucose test from 9.62 +/- 2.65 mmol/L 10 days after transplantation to 7.43 +/- 0.27 mmol/L later in the follow-up (P < 0.05). The median survival time of the islets was 73 days. In conclusion both the method of isolation and purification of the islets and islet transplantation was effective in the control of the diabetes induced by streptozotocin with median survival time of both islet and rat more than 73 days when rats were sacrified.

In vivo depletion of pancreatic acinar tissue simplifies islet preparation for transplantation

A copper deficient diet is reported to reduce acinar tissue in vivo. We investigated the suitability of this method to reduce in vivo acinar tissue mass of a rat pancreas prior to transplantation of dispersed pancreatic tissue. We also studied islet function in the acinar depleted pancreas and the outcome of transplantation of islets from such pancreata. Eighty-two Wistar Furth rats were divided into two groups with 42 animals in the control group receiving regular diet, and 40 receiving copper deficient diets (Cudt) plus tetraethylene- pentamine penta-hydrochloride (TEPA) as a chelating agent. All animals in the control group and 34 (85%) in the Cudt group tolerated this diet and survived for 60 days or longer. At the end of 60 days, all experimental animals were converted to a regular diet until the pancreata were harvested for islet transplantation. Eight rats in the Cudt group, which were converted to a regular diet for 2 weeks, and 2 in the control group were randomly selected and sacrificed to study the pancreas for acinar depletion and islet morphology. An intravenous glucose tolerance test (IVGTT) in the control group (n=24) and the Cudt group (n=25) showed K-values of 1.891+/-0.7 and 1.107+/-0.47, respectively (P-ns). Histology of pancreata showed normal acinar tissue in the control group and reduction of acinar tissue mass in the Cudt group. Furthermore, immunohistochemistry for insulin, glucagon, and somatostatin showed positively staining, while amylase was negative in the Cudt group, compared with the positive stain for cells in the control group. Standard collagenase digestion of the pancreas showed islets were surrounded by scant amounts of acinar tissue in the Cudt group compared with the control group. The islet count in the control group was 523+/-126 and 611+/-52 in the Cudt group. The mean volumes of dispersed pancreatic tissue were 0.3875+/-0.14 and 0.0668+/-0.029 ml per rat in the control and Cudt groups, respectively (P<0.05). Transplantation of dispersed pancreatic tissue from the control group into the spleen of two diabetic Wistar Furth rats resulted in the death of the recipients within 24 hr. To avoid this complication, purified islets from the control group were used for transplantation. Purified islets from 5 donor pancreata from the control group and dispersed pancreatic tissue from 3 pancreata in the Cudt group were transplanted into each recipient. Islet function was seen in 75% of the rats transplanted with purified islets from the control group, and in 67% receiving dispersed pancreatic tissue from the Cudt group. Rats with sustained islet function for 30 days following islet transplantation developed diabetes following splenectomy. The islet cells were positively stained for insulin these splenectomy specimens. This study demonstrates that rats maintained on a copper deficient diet for 60 days show depletion of collagenase digested volume of whole pancreatic tissue occurred in the Cudt as compared with the control group. Transplantation of dispersed pancreatic tissue from the acinar depleted pancreas was successful in reversing diabetes. We conclude that Cudt containing TEPA depletes exocrine tissue and facilitates pancreas digestion for successful transplantation of islets into the portal system.

Pancreatic islet transplantation: is purification necessary?

Successful islet allotransplantation in diabetic patients has been slow to develop. In the past, it has been assumed that the low success rates are, in part, due to difficulty in obtaining high-quality human islet preparations. The assumption has been that purified islets are essential because exocrine contamination hampers engraftment and makes islets more vulnerable to rejection by increasing graft immunogenicity. We reviewed the existing experimental data on the consequences of exocrine contamination and concluded that most clinical trials of islet allotransplantation have involved efforts to over-purify the allograft. Until antigen-specific tolerance or the biohybrid artificial pancreas is a reality, the best strategy for clinical trials is to test new immunosuppressive protocols in a search for a more effective way of modifying the host's immune response while maximizing islet yield by using less pure preparations.

Islet cell isolation in experimental d,l-ethionine pancreatitis in dogs

Bulk isolation of islets of Langerhans for biochemical studies or transplantation has generally been associated with significant or even prohibitive contamination by acinar tissue. High-purity islet preparations are associated with an extremely low yield. The acinar tissue can be ablated with d,l-ethionine, but previously, this tactic has been restricted to rodents because of toxicity problems in larger animals. A dosage regimen in dogs which reduces amylase content of the pancreas to 0.3% of normal with complete preservation of insulin content is reported. Ductal perfusion with collagenase permits the recovery of 45% of the islet cell mass as determined by extractable insulin. These islets prove functional in in vitro perifusion studies and in allografts.

[Further developments in pancreatic islet transplantation I. Induction of selective morphological changes in the exocrine pancreas]

For pancreatic islet transplantation to become clinically applicable, chemical agents are needed which cause selective morphological alterations in the exocrine part of the organ within a few hours after application. DL-ethionine (Aet), cerulein (Cd), seleno-DL-methionine (SeMet) and seleno-DL-ethionine (SeAet) were given to rats during various time periods. At 4 h after i.p. injection, 40 mg/kg SeMet caused the greatest selective morphological alterations in the exocrine pancreas. Acinar structure disappeared, the exocrine cells were abnormal and their nuclei had various dimensions and forms. There were, however, no alterations in the islet cells. At this time, neither Aet, Cd, nor SeAet produced similar changes. SeMet was the most toxic substance and was taken up in the shortest time and in the greatest amount. This selective destructive SeMet effect allows better isolation of the islets from exocrine tissue thereby increasing islet yield and decreasing transplantation volume. Better islet purification may prevent an early rejection.

Effect of total lymphoid irradiation and pretransplant blood transfusion on pancreatic islet allograft survival

Total lymphoid irradiation (TLI) has been shown to have a strong immunosuppressive effect both experimentally and clinically. Pretransplant blood transfusions have also been shown to have a strong beneficial effect in the outcome of organ transplantation. A study was made of the effect of TLI and pretransplant blood transfusions, alone and in combination, as an immunosuppressive modality in the isolated pancreatic islet transplant in the rat model. Donor rats (Fischer RT1v1) were kept on a 50% DL-ethionine supplemented diet for 4-6 weeks prior to pancreas removal. Recipient rats (Lewis RT1) were made diabetics prior to transplantation by iv injection of streptozotocin (45 mg/kg). Transfusion protocol consisted of a biweekly transfusion of 2 ml of either donor specific or third party transfusions. Total lymphoid irradiation was carried out by daily administration of 200 rads during one week prior to transplantation. Transplantation of the isolated islets was performed by intraportal injection. Syngeneic transplant of one and a half donor pancreata in each recipient reverted the diabetic condition indefinitely (greater than 100 days). Untreated allogenic grafts had a mean survival time (MST) of 5.2 days. Total lymphoid irradiation in dosages of 800, 1000, and 1200 rads, as the only immunosuppressive regimen, prolonged the MST of allografts to 15.3, 16.5, and 21.8 days, respectively (P less than .05). Pretransplant third party blood transfusion had no effect on allograft survival (MST 6.0). When donor specific blood transfusions were given, the MST was prolonged to 25.3 days (P less than .05). When TLI was administered to recipients of donor specific transfusions, the MST of the allografts did not show any statistical significant difference when compared with untreated animals. This abrogation of the beneficial effect of specific blood transfusion was observed in all dosages of TLI employed: 800 rad (MST 3.0), 1000 rad (MST 8.0), 1200 rad (MST 5.18). Total lymphoid irradiation and pretransplant blood transfusions have a similar immunosuppressive effect on islets allograft survival, but their mechanisms of action are antagonistic when both modalities of pretreatment are used in the sequence described in this study.

Transplantation of cryopreserved and fresh rat islets and canine pancreatic fragments: comparison of cryopreservation protocols

(1) The freezing protocol we have devised for rat islets results in normal clinical indices and almost normal glucose tolerance in diabetic recipients of the same inbred strain. (2) Cryopreservation of canine islet-containing pancreatic tissue required a higher temperature than rat islets during exposure to the protective agent. (3) Because of the similar compactness of the pancreas in man and dog, we consider this canine model useful for formulating optimal cryopreservation techniques for the human pancreas. (4) Cryopreservation may partially purify islet-containing tissue of its exocrine content.

A high yield method for isolating rat islets of Langerhans using differential sensitivity to freezing

Conventional methods of isolating islets of Langerhans rely upon the differential sensitivity of the pancreatic acinar tissue vs islets to enzymatic dissociation by crude collagenase, however, the yield of intact islets obtainable with this technique is quite low. Higher yields of islets can be obtained with pharmacological or surgical methods which either destroy acinar cells or cause them to release their zymogen granules. However, because of the requirement to pretreat the donor, these methods cannot be scaled-up for potential clinical use. To overcome the limitations of the conventional isolation procedures, we exploited the differential sensitivity of acinar cells and islet cells to freezing damage. Using this approach we are able to isolate greater than 2500 islets from the pancreas of a single rat. Basically, we rapidly mince pancreatic tissue, subject the tissue to a short collagenase digestion, briefly freeze the tissue at -30 degrees C in the presence of glycerol, and immediately thaw it. Subsequent enzyme treatment digests the residual acinar tissue, collagen, DNA, and proteins. Preliminary results indicate that the islets are morphologically indistinguishable from islets isolated using conventional digestion techniques.

Technical aspects of segmental pancreatic grafting in rats

Four techniques for segmental pancreatic transplantation were used sequentially in rats. The success rate and the incidence and type of technical complications that developed in each group of recipients were determined and attempts were made to improve the microsurgical technique. A strict comparison of the relative merits of the four different techniques was not made, but rather the development of an approach to an original technique that resulted in a high success is rate presented. The various modifications and details of this experience are documented. The various complications, each of which results in a typical postoperative pattern of weight and plasma glucose changes and each of which is preventable by the use of proper microsurgical techniques, are also analyzed.