Revascularization and function of pancreatic islet isografts in diabetic rats following transplantation

In pancreatic islet transplantation, revascularization is crucial for the graft's survival and function. In this study, the endothelium of isolated islets and revascularization and function of islet isografts in diabetic rat were investigated. Islets were isolated from Lewis rats by collagenase digestion method and were examined using immunohistochemistry (CD31 stain) on days 0, 1, 3, and 7 after isolation. The number of CD31-positive cells in these isolated islets was counted (mean +/- SD %). Isografts (freshly isolated islets: group A, and islets cultured for 7 days: group B) transplanted in the renal subcapsule of streptozotocin-induced diabetic Lewis rats were examined using immunohistochemistry (CD31 stain) on days 3, 5, and 7 after transplantation. Intravenous glucose tolerance tests (IVGTT) were performed on days 3 and 7 after transplantation. The number of CD31-positive cells in the isolated islets on days 0, 1, 3, and 7 after isolation were: 17.3 +/- 4.1%, 8.2 +/- 0.7%, 2.1 +/- 0.8%, and 0.8 +/- 0.5%, respectively (p < 0.05). On day 5 after transplantation, CD31-positive cells were not detected in group A and B grafts, but were detected in both groups in periphery of the islets. On day 7, CD31-positive microvessels were present throughout the entire graft. IVGTT values in groups A and B on days 3 and 7 after transplantation did not show significant differences. In renal subcapsular isografts in diabetic rats, revascularization into islet grafts occurs from the surrounding host tissue 5 days after transplantation, but has no influence on the response to glucose during this period.     

Intrasplenic islet isografts.

Sufficient numbers of pancreatic islets transplanted into the splenic pulp of streptozotocin-induced diabetic rats can result in complete reversal of hyperglycemia, glycosuria, and polyuria while promoting weight gain. These changes are constant for at least 3 months. Animals transplanted in this way, however, fail to exhibit a normal biphasic insulin response during an intravenous glucose tolerance test. This lack of biphasic response is in marked contrast to that observed in portal-vein--transplanted animals. Basal serum insulin in intrasplenic-transplanted animals is twice that observed in normal animals and portal-vein--transplanted animals which have received the same number of islet isografts. Direct injection of islets into the splenic pulp does not insure that subsequently all islets will remain in the splenic pulp, and, in fact, subsequent splenectomy suggests that in some cases a majority of transplanted tissue lodges in other organs--most likely, the liver.     

Long-term reversal of streptozotocin-induced diabetes in rats by intramuscular islet implantation

The ability of pancreatic islets implanted into abdominal muscle to effect a recovery from streptozotocin-induced diabetes was compared with that of i.p implants. Pancreases from 17 to 35 Lewis neonates were cultured for 6 days and placed in i.m. or i.p. sites in severely diabetic Lewis rats. Body weight, food and water intakes, urinary output, and 4-hr fasted plasma glucose levels returned to normal in both groups. Neither plasma insulin and glucose responses to intravenous glucose tolerance tests nor plasma glucose responses to oral glucose tolerance tests differed among i.m. or i.p. implant recipients and normal, age-matched controls, even after 1 week's prior challenge of insulin secretory capacity by a high sucrose diet. Plasma glucose levels were reduced after oral administration of tolbutamide in the three groups. Plasma glucagon of i.m. and i.p. implant recipients after a 4-hr fast or after an oral load of arginine were not significantly different from those of controls, although levels tended to be higher in the implant groups. Neither i.m. nor i.p. implant groups reverted to the diabetic state in the 10 months following pancreatic implantation. These findings validate the long-term efficacy of intramuscular implantation of cultured islets in reversing diabetes in inbred rats.     

Successful reversal of spontaneous diabetes in dogs by intraperitoneal microencapsulated islets.

Long-term euglycemia by intraperitoneal transplantation of microencapsulated islets has not been described in the diabetic large animal model. In this study, we report the successful long-term reversal of diabetes by this method in spontaneous diabetic dogs. We have identified fundamental mechanism(s) associated with alginate-based microcapsule fibrosis, and have devised methods to ameliorate this problem. These include the use of purified alginate of low mannuronic acid content and cytokine suppression. Ten insulin-dependent, spontaneous diabetic dogs (insulin requirement 1-4 units/kg/day; absence of circulating C-peptide and diabetic K-values of 0.6 +/- 0.4) were entered into the study. Islets from mongrel donor pancreata were isolated and transplanted intraperitoneally either as free islet controls (n = 3) or as microencapsulated islet allografts (n = 7). In all seven encapsulated islet recipients, euglycemia was achieved within 24 hr (serum glucose failing from 304 +/- 117 to 116 +/- 72 mg/dl). IVGTT performed 14 days after islet transplant demonstrated normalization of K-values changing from a pretransplant level of 0.6 +/- 0.4 to 2.6 +/- 0.6. All animals receiving encapsulated islets remained euglycemic, free of the need for exogenous insulin, for a period of 63-172 days, with a median insulin-independence for 105 days. In contrast, recipients receiving free islets rejected their graft within seven days of implantation. In conclusion, this is the first report of long-term successful reversal of spontaneous diabetes in the large animal model by an intraperitoneal injection of encapsulated islets. The potential exists for this form of therapy to be explored in the treatment of type I diabetes in man.     

Repeated intraportal injections of subtherapeutic islet cell isografts restore normoglycemia in streptozotocin-diabetic rats

Poor engraftment and consequent loss of β-cell mass could be one of the factors that are responsible for function loss after intraportal islet transplantation (Tx). Streptozotocin-diabetic rats were transplanted with syngeneic islets, which were injected into the portal vein via an indwelling catheter connected to a subcutaneous port. In Group I (n = 6), 1,000 islets were injected in a single dose into the liver. In Group II (n = 6), five doses of 200 islets were repeatedly injected over a period of 14 days, for a total of 1,000 islets. In Group III (n = 4), five decreasing doses of islets were injected over a period of 14 days, for a total of 750 islets. Nonfasting blood glucose (n-FBG) and body weight (b.wt.) were determined twice a week and an intravenous glucose tolerance test (IVGTT) was performed at 30 and 90 days. In Group I, n-FBG decreased in 2 wk from the time of first islet injection, averaging 110 ± 21.9 mg/dL at 1 mo (p < 0.05 vs. normal controls); this value was maintained throughout the 3-mo duration of the study. In Group II, n-FBG was normalized in 2 wk averaging 90.2 ± 25 mg/dL on day 12 (p = NS vs. normal controls) and 75.8 ± 14.6 mg/dL at 1 month (p = NS vs. normal controls); this value was maintained throughout the 3-mo duration of the study. In Group III, n-FBG decreased to normal values in 2 wk, averaging 77 ± 15.7 mg/dL at 1 mo (p = NS vs. normal controls), but normoglycemia was maintained for 40 days and then followed by a progressive increase. Only in Group II, K_G (percent/min decline in glucose level) was not significantly different from that of normal controls (1.702 ± 0.531 at 1 mo and 1.676 ± 0.891 at 3 mo), while it was significantly lower than normal controls in both Group I and III animals. Body weight increase after Tx correlated with the number of transplanted islets and at 90 days, Group III rats showed less increase than Groups I and II (p < 0.05), while no significant differences in b.wt. were recorded between Group I and II. The findings indicate that intraportal islet Tx, injected repeatedly and in small doses, produced better metabolic effects than injection of the same total number of islets in a single dose.     

A morphologic study of intrahepatic portal-vein islet isografts.

Isologous pancreatic islets were implanted into the portal vein of rats with streptozotocin-induced diabetes. At intervals of from one to 32 days after transplantation, the intrahepatic islet grafts were examined histologically and ultrastructurally, and their vascular supply was determined by later perfusion studies. Implanted islets were found widely dispersed throughout the liver in peripheral interlobular portal venules and surrounded by vacuolated liver cells containing large stores of glycogen. The endocrine cells were structurally normal in each interval examined. By the third day after transplantation the beta cells were depleted of secretory granules in aldehyde-fuchsin preparations. Regranulation returned by the 14th day and was associated with secretory organelle hypertrophy and hyperplasia. Islet cells were found outside the portal areas in direct apposition to hepatocytes forming distinct desmosomes by the first day. While hemoperfusion of the grafts occurred from the moment of implantation into the portal venule, a dual vascular supply derived from periportal arterial and venous sources developed by the 11th day after transplantation, establishing full vascularization of the grafts. Preliminary work is presented to show that an active ingrowth of nerves in the islet graft occurs in association with the process of vascularization.     

Effects of islet isografts on hemodynamic and vascular filtration changes in diabetic rats

To assess the reversibility of diabetes-induced increases in regional vascular albumin permeation and blood flow and changes in kidney filtration function, islet isografts were given via the portal vein after 2 mo of streptozocin-induced diabetes in male Lewis rats. One month later, vascular function was assessed in control rats, islet-transplanted diabetic rats, and untreated diabetic rats (6-9 rats/group). Untreated diabetic rats were markedly hyperglycemic, hyperphagic, and polyuric. Transplanted rats were euglycemic within 6 days; 24-h urine volumes were virtually normalized by 2 wk and food consumption was normalized 4 wk after transplantation. Vascular albumin permeation in diabetic rats was significantly increased 1.4- to 1.7-fold in anterior uvea, choroid, retina, sciatic nerve, new granulation tissue, and kidney and was increased 1.1- to 1.3-fold in diaphragm, cecum, and optic nerve. Albumin permeation was not increased in aorta, brain, heart, or forelimb skeletal muscle. Islet transplants significantly reduced but did not completely normalize vascular albumin permeation in most tissues in which it was increased by diabetes but had no effect on albumin permeation in optic nerve, sciatic nerve, and diaphragm. Urinary excretion of endogenous albumin and IgG in diabetic rats was significantly increased 19- and 14-fold, respectively, and was virtually normalized 4 days after islet transplantation. Marked (1.8-fold) increases in glomerular filtration rate (GFR) in diabetic rats were also substantially reduced by islet transplants but remained elevated 1.4-fold control values. Likewise, diabetes-induced increases in regional blood flow were reduced in general but not normalized by islet transplants. These observations indicate that 1) diabetes-induced hemodynamic changes and alterations in vascular filtration function are not rapidly reversed by euglycemia after islet transplantation, 2) diabetes-induced increases in urinary albumin and IgG excretion are more readily normalized by euglycemia than increases in GFR and renal 125I-labeled bovine serum albumin (125I-BSA) filtration, and 3) significant increases in GFR and renal 125I-BSA filtration may not be manifested by albuminuria.     

Detrimental effect of chronic diabetes on growth and function of fetal islet isografts in mice

We investigated (1), whether long-term (more than 6 months) streptozotocin-induced diabetes in mice had a detrimental effect on the function of pancreatic islet isografts; and (2), whether there was an effect on graft function in chronically diabetic mice of continuous pretransplant insulin infusion. BALB/c female mice that had been diabetic for more than 6 months were each transplanted with 1/2 of a 17-day fetal mouse pancreas that had been in organ culture for 14 days. All animals were grafted with same batch of tissue. One group of animals received continuous intraperitoneal infusion of regular insulin via an Alzet 2002 osmotic pump at the rate of 0.5 U/day for 14 days prior to grafting. Matched, chronically diabetic animals with pumps containing diluent alone, acutely diabetic animals of the same age, and acutely diabetic younger animals were used as controls. At 20 weeks after transplantation the grafts were removed and their insulin content measured. Following transplantation and removal of the pumps, all acutely diabetic animals returned to euglycemia within 6 weeks. The chronically diabetic animals which received diluent alone took 11 weeks to reach euglycemia compared to 7 weeks for their littermates that had received insulin. Graft insulin content was decreased from 16,300 +/- 4100 ng in the acutely diabetic animals to 9600 +/- 5200 ng in the chronically diabetic, non--insulin-treated group. The chronically insulin-treated group, however, had grafts with 16,400 +/- 5100 ng. Our studies suggest that there is a detrimental effect of chronic diabetes on graft insulin content that is ameliorated by pretransplant insulin therapy.     

Autologous islet transplantation to prevent diabetes after pancreatic resection.

BACKGROUND: Extensive pancreatic resection for small-duct chronic pancreatitis is often required for pain relief, but the risk of diabetes is a major deterrent. OBJECTIVE: Incidence of pain relief, prevention of diabetes, and identification of factors predictive of success were the goals in this series of 48 patients who underwent pancreatectomy and islet autotransplantation for chronic pancreatitis. PATIENTS AND METHODS: Of the 48 patients, 43 underwent total or near-total (> 95%) pancreatectomy and 5 underwent partial pancreatectomy. The resected pancreas was dispersed by either old (n = 26) or new (n = 22) methods of collagenase digestion. Islets were injected into the portal vein of 46 of the 48 patients and under the kidney capsule in the remaining 2. Postoperative morbidity, mortality, pain relief, and need for exogenous insulin were determined, and actuarial probability of postoperative insulin independence was calculated based on several variables. RESULTS: One perioperative death occurred. Surgical complications occurred in 12 of the 48 patients (25%): of these, 3 had a total (n = 27); 8, a near-total (n = 16); and 1, a partial pancreatectomy (p = 0.02). Most of the 48 patients had a transient increase in portal venous pressure after islet infusion, but no serious sequelae developed. More than 80% of patients experienced significant pain relief after pancreatectomy. Of the 39 patients who underwent total or near-total pancreatectomy, 20 (51%) were initially insulin independent. Between 2 and 10 years after transplantation, 34% were insulin independent, with no grafts failing after 2 years. The main predictor of insulin independence was the number of islets transplanted (of 14 patients who received > 300,000 islets, 74% were insulin independent at > 2 years after transplantation). In turn, the number of islets recovered correlated with the degree of fibrosis (r = -0.52, p = 0.006) and the dispersion method (p = 0.005). CONCLUSION: Pancreatectomy can relieve intractable pain caused by chronic pancreatitis. Islet autotransplantation is safe and can prevent long-term diabetes in more than 33% of patients and should be an adjunct to any pancreatic resection. A given patient's probability of success can be predicted by the morphologic features of the pancreas.     

Prevention of vascular complications of diabetes by pancreatic islet transplantation.

Isolated pancreatic islets from Wistar-Lewis rats were transplanted into the liver of diabetic allogeneic recipients to assess ability to prevent diabetic renal and ophthalmic complications. At nine months, the diabetic animals without transplants showed significant increase in PAS-positive material in the renal glomerular mesangium and thickening of glomerular arterioles as compared with normal nondiabetic animals. New vessel formation was also significant in the retina and retinal capillary dilation. Animals in which diabetes had been corrected by early pancreatic islet transplantation were completely protected from these changes, showing no significant pathologic change when compared with normal animals.     

Anti-CD154 (CD40L) prevents recurrence of diabetes in islet isografts in the DR-BB rat

Islet transplantation for the treatment of autoimmune diabetes is more difficult because of the additional barrier presented by the autoimmunity. We tested the ability of hamster anti-rat CD154 to prevent recurrence of diabetes in renal subcapsular islet isografts in DR-BB (RT1uu) rats with established autoimmune diabetes. Experimental animals with established diabetes received intravenous injections of 15 mg/kg anti-CD154 on a specified schedule starting 2 days before renal subcapsular transplantation of an islet isograft. Control animals received either saline or hamster IgG. Plasma glucose levels >250 mg/dl over 3 days were used to indicate the recurrence of diabetes. Rats that received saline (n = 5) or control antibody (n = 3) had a recurrence of diabetes 6-11 days after transplantation. Histological examination of islet isografts from these rats showed complete destruction of the insulin-producing portion of the isograft with residual cells positive for glucagon. Recipient rats that received anti-CD154 at the 15-mg/kg dosage (n = 6) did not have a recurrence of diabetes for 308-461 days after transplantation. Islet isografts removed from the rats showed low levels of insulin immunoreactivity, high levels of insulin mRNA, and focal infiltration with lymphocytes but no evidence of islet destruction. Mean peak antibody concentration was 266 microg/ml and returned to undetectable levels by 67-88 days after transplantation. Rats that received anti-CD154 starting at 4-7 days after transplantation had a recurrence of diabetes within 11 days of the isotransplantation. Therefore, anti-CD154 as the sole immunomodulator prevented the recurrence of diabetes in islet isografts in rats with established autoimmune diabetes. This suggests that CD40/CD154 blockade is effective in preventing the insulitis or the effector phase of autoimmune diabetes.     

Hyperinsulinemia and hyperglucagonemia following pancreatic islet transplantation in diabetic rats.

Fasting blood glucose (FBG), serum immunoreactive insulin (IRI), plasma immunoreactive glucagon (IRG), body weight, and caloric intake were measured in long-term islet-isografted rats eight to 10 months following intraperitoneal islet transplantation in in age-matched, sham-operated, concurrently followed normal and diabetic controls. Islet recipients had normal body weights, but they were significantly polyphagic, hyperinsulinemic, and hyperglucagonemic when compared with normals. Fasting blood glucose levels were reduced by 10 per cent. Several factors may be related to the occurrence of these abnormalities in long-term islet-isografted rats, including (1) the mass of islets transplanted, (2) the age of donor tissue, (3) the heterotopic location of islet grafts, and (4) the lack of normal innervation of transplanted islet cells.     

Fetal pancreas transplantation for reversal of streptozotocin-induced diabetes in rats.

Streptozotocin-induced diabetes in rats was completely reversed by transplantation of syngeneic fetal pancreases placed beneath the kidney capsule. To accomplish complete reversal of diabetes, four or more pancreases were necessary; three resulted in partial reversal, and two produced a slight but significant effect in some recipients. Removal of the transplants resulted in the prompt return of diabetes. The islets of Langerhans in the transplants functioned homeostatically; this was indicated by regular normal blood glucose values, in addition to normal findings in blood IRI response and glucose disappearance rate after glucose injection. Disappearance of exocrine elements, with only ducts and fibrous tissue remaining, resulted in a pure endocrine organ. The advantages of this technie, such as ease of accessibility for placement, observation, and removal, are of great importance for possible application to humans.