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G L Warnock

Publications and source records attributed to G L Warnock.

At least 91 records · Page 5Linked to original sources
PubMed1990

Prolonged function of canine pancreatic fragments autotransplanted to the spleen by venous reflux.

The long-term viability and function of pancreatic islets transplanted as nonvascularized dispersed grafts has not been well established. We report maintenance of nondiabetic carbohydrate metabolism for up to 36 months (17.8 +/- 1.4 months) in 77% of 40 consecutive canine recipients of nonpurified islet grafts transplanted to the spleen by venous reflux. Spontaneous loss of graft function occurred in 9 dogs during the follow-up period. Failure usually occurred within 1 year of implantation and was predicted by low K value and low insulin output on intravenous glucose tolerance tests 1 and 3 months postimplant. High K values and insulin output correlated strongly with maintenance of function beyond 24 months. A sufficient mass of implanted islets can provide satisfactory metabolic control for prolonged periods.

Animals↗
PubMed1990

Reversal of diabetes in dogs by transplantation of pure cryopreserved islets.

We have autotransplanted highly purified cryopreserved canine islets into pancreatectomized dogs. Islets were frozen by slow cooling (0.25 degrees C/min) to -40 degrees C, stored at -196 degrees C and thawed rapidly (200 degrees C/min). A total of 7868 +/- 665 (means +/- SE) cryopreserved islets/kg body weight were implanted to the spleen (n = 7) by venous reflux, and seven other control dogs received 6811 +/- 653 fresh islets/kg (P versus cryo., NS). Fasting plasma glucose [( PG] mg/dl, +/- SEM) and intravenous glucose tolerance were determined before and at 1 and 3 months postimplantation. Six dogs that received cryopreserved islets and all seven control animals promptly became normoglycemic, with PGs of 133 +/- 23 and 110 +/- 4, respectively, at 1 week postimplantation (NS). During follow-up one normoglycemic animal from each group died due to small bowel volvulus and one recipient of fresh islets became diabetic at 14 days. The remaining dogs remained normoglycemic with PGs of 89 +/- 3 and 92 +/- 3 in dogs receiving cryopreserved and fresh islets, respectively, at 3 months postimplantation (NS). Mean K value (decline of glucose, %/min +/- SEM) at ivGTT for all dogs was 2.5 +/- 0.3 preoperatively. At 1 and 3 months postimplantation, the K values of dogs receiving cryopreserved islets were 1.3 +/- 0.1 and 1.4 +/- 0.2, respectively, compared with 1.3 +/- 0.2 and 2.0 +/- 0.2 for control dogs (NS). These data demonstrate prompt and sustained function of a defined quantity of frozen-thawed purified islets in a large mammal. Cryopreservation is an effective method for the long-term storage of purified islet tissue.

Animals↗
PubMed1990

Glucoregulatory response to moderate exercise in long-term islet cell autografted dogs.

The glucoregulatory response to moderate treadmill exercise (approximately 60% maximum heart rate; 60 min at 100 m/min, 12% grade) was examined in six controls and six pancreatectomized dogs that had been normoglycemic and insulin independent for more than 1 year since autograft of isolated islets of Langerhans (Tx). There were no significant intergroup differences in plasma glucose levels during exercise, but return to baseline after exercise was delayed in Tx (p less than 0.05). In Tx, the initially suppressed insulin levels rose above baseline from 30 to 60 min. Within Tx, exercise-induced levels of plasma glucagon and epinephrine were more variable than control and strongly correlated (r = 0.81, p less than 0.001), perhaps indicating that the A cells within the grafted islets were regulated by circulating beta-adrenergic agonists. We conclude that the isolated islets were removed from direct central control. In Tx dogs, the variable counterregulatory responses and the diminished recovery of plasma glucose after exercise indicate reliance on alternative glucoregulatory mechanisms.

Adrenal Glands↗
PubMed1990

Cytotoxic effects of cytokines on human pancreatic islet cells in monolayer culture.

Interleukin-1 (IL-1), tumor necrosis factor (TNF), and interferon-gamma (IFN gamma) inhibit insulin release and may be cytotoxic to isolated rodent pancreatic islets. In this study we examined the effects of IL-1, TNF, and IFN gamma on the viability and hormone secretion of islets isolated from adult human pancreas and maintained in monolayer culture. IL-1 and TNF were cytotoxic to the islet cells (20-30% cell lysis) in a 51Cr release cytotoxicity assay, and IFN gamma had only small effects (less than 10% lysis). Combination of maximally cytotoxic concentrations of IL-1 (10 U/mL) and TNF (10(3) U/mL) produced an additive cytotoxic effect. IFN gamma (10(3) U/mL) acted synergistically with IL-1 and TNF, and the three cytokines added together produced maximal islet cell lysis (46.4 +/- 4.3%). Assay of insulin and glucagon in the islet monolayers revealed that IL-1, TNF, and IFN gamma inhibited both B- and A-cell secretory functions; however, only IL-1 and TNF produced permanent decreases in insulin and glucagon contents in the islet cultures. These findings indicate that IL-1 and TNF, as single agents, are cytotoxic to human islet cells, and that this cytotoxicity can be amplified by combining the cytokines and/or adding IFN gamma. However, the lack of specificity for B-cells in vitro suggests that additional factors might be operative in vivo for the cytokine products of macrophages and lymphocytes infiltrating islets to produce the B-cell-specific damage characteristic of type 1 diabetes.

Adult↗
PubMed1990

Isolation of purified large mammal and human islets of Langerhans.

Previous studies have shown that the yield and viability of islets obtained from human or large mammal pancreas depends upon techniques used for islet isolation and upon factors that affect the quality of the donor pancreas. In the present studies, the efficacy of collagenase digestion by ductal perfusion or automated techniques was compared in a canine model of purified islet isolation. The ductal perfusion technique was then developed for human pancreas which was excised before (n = 8) or after (n = 8) multiple organ procurement and without in situ arterial perfusion of hypothermic preservation solution or significant cold storage. Studies with canine pancreas showed that ductal perfusion yielded 2.0 +/- 0.7 microL of islets/g of pancreas and when combined with automated digestion, yields improved to 3.6 +/- 0.8 microL/g (versus perfusion alone, not significant). The yield and viability of human islets was improved when the pancreas was excised before procurement of other donor organs. Results of islet isolation from eight consecutive human pancreases procured in this manner revealed a total yield of 355.2 +/- 44 x 10(3) islets, corresponding to 5345 +/- 600 islets/g (+/- SEM, mean islet diameter 150 microns). Six of eight Ficoll purification attempts succeeded, yielding 186.6 +/- 31 x 10(3) islets of purity ranging from 45-60%. Perifusion with glucose elicited biphasic insulin secretion with a three-fold rise. Islets from two of the isolations were utilized to initiate a clinical trial of islet transplantation in insulin-dependent diabetes mellitus.

Animals↗
PubMed1990

Critical mass of islets that function after implantation in a large mammalian.

A major problem that limits clinical islet transplantation is insufficient information on the critical quantity of islets needed to reverse insulin dependence. To address this problem, we have previously identified the critical number of purified islets of known size that consistently induced normoglycemia in a large mammal model of type I diabetes. In the present studies, we found that the dose-response relationship between the volume of islets transplanted and consistent normoglycemia in dogs corresponded to greater than 4.1 microliters islet tissue per kilogram body weight. The functional outcome of similar quantities of purified islets was then examined after autoimplantation into splenic or hepatic sites and after splenic implantation by venous reflux or pulp injection. During prolonged follow-up, four of five initially normoglycemic recipients of intrahepatic islets became hyperglycemic within 1 year and the other failed at 26 months. In contrast, function of intrasplenic islets was more durable with delayed onset of hyperglycemia observed in only two of six grafts at 13 and 18 months. Sustained normoglycemia was induced by splenic venous reflux of islets in six of seven dogs, but intrapulp injection succeeded in only two of six. Islet allografts implanted to the spleen (n = 10) or to the kidney capsule (n = 6) of Cyclosporine-treated recipients induced normoglycemia in all, but sustained function ensued in only the intrasplenic group when the islet mass was augmented by 40%. These data define the critical islet volume needed to induce normoglycemia in a large mammal. Islets implanted by venous reflux to spleen provide more durable long-term function than the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Immunosuppression and pancreatic islet transplantation.

Azathioprine-prednisone immunosuppression has proven ineffective in rodent, canine, and human islet transplantation. ALS has demonstrated beneficial effects in rodent islet transplantation, but high dose CsA monotherapy remains the most effective immunosuppressive modality in canine islet allotransplantation. Nephrotoxicity prevents effective utilization of such an approach in human islet transplantation. We have been unable to demonstrate additional benefit from the addition of azathioprine and prednisone to CsA immunosuppression in large animal islet allotransplantation. CsA, azathioprine and prednisone all appear to have the potential for adverse effects variously on islet engraftment, insulin secretion, and/or peripheral insulin activity. The effects of CsA appear to be dose related and may be reversible. Our approach in clinical islet transplantation has been to achieve potent induction immunosuppression with Minnesota antilymphocyte globulin, delayed CsA administration, and ongoing maintenance with low dose triple immunotherapy. Initial results are encouraging.

Animals↗
PubMed1990

The evaluation of solutions for pancreas preservation prior to islet isolation.

We have demonstrated the U.W. solution to be superior to commonly used solutions for storage of the pancreas prior to islet isolation in a rodent model with respect to both the number of islets recovered, and the in vitro functional integrity of those islets. For prolonged storage, delivery of the U.W. solution via a ductal injection was superior to delivery via in situ flush. Current methods of multiorgan harvesting may not allow for optimal storage of cadaver pancreas prior to islet isolation. Preliminary studies demonstrate that large numbers of viable islets can be recovered from the human pancreas up to 20 hr after in situ flush with and storage in the U.W. solution. While these studies with rat and human pancreas demonstrate improved results with the U.W. solution, considerable room clearly exists for improvement in pancreas storage prior to islet isolation.

Adenosine↗
PubMed1990

Islet cryopreservation.

As methods for human islet isolation improve and clinical trials become widespread, some form of storage will be needed. Cryopreservation would offer many advantages: storage in a tissue bank to provide sufficient islets to transplant to individual recipients; modulation of tissue immunogenicity; purification; and, facilitate shipment from center to center. Since 1976, much work has been done on islet cryopreservation with cooling rates of 0.025 degrees C/min to 75 degrees C/min being reported as optimum. In rats we have found that slow cooling to -40 degrees C with rapid thawing from -196 degrees C gives the highest survival as measured in-vitro and in-vivo. This freeze-thaw protocol also provides viable pancreatic microfragments and pure dog islets which can both induce prolonged normoglycemia. This freezing procedure also gives prolonged survival of islet xenografts and purifies the pancreatic microfragments of the unwanted exocrine contaminants. This method of freezing is now being used for human islets. Low temperature storage of human islets will greatly help the clinical use of islet transplantation.

Animals↗
PubMed1990

Islet isolation from human pancreas stored in UW solution for 6 to 26 hours.

1. Viable and functional islets can be recovered from human pancreata stored for prolonged periods (up to 18 hours) with either the UW solution or EC. 2. Function of islets from pancreas stored in UW solution appeared superior. However, the difference in these preliminary studies does not appear nearly so dramatic as in transplantation of vascularized pancreas. 3. Function of islets from human pancreas stored for longer than 18 hours after UW in situ flush was uniformly poor. 4. Considerable room for improvement in the storage of human pancreas before isolation exists. Progress in this area will be important for the development of any large-scale program of clinical islet transplantation.

Adenosine↗
PubMed1990

Comparison of automated and manual methods for islet isolation.

The authors used the principal features of a collagenase perfusion technique and an automated dissociation technique to determine if islets could be isolated from the large mammal pancreas and to compare the effects of the two methods on isolated islets. The pancreases of 16 dogs were cannulated and perfused with collagenase at 4 degrees C, then warmed to 37 degrees C. Group 1 (eight) pancreases were perfused at 37 degrees C until digested, then dissociated manually by teasing and trituration. Group 2 (eight) pancreases were transferred to a closed chamber for continued collagenase digestion and dissociation at 37 degrees C. Islets were purified using identical Ficoll gradients. Aliquots were stained with dithizone and evaluated for number, size and purity. Total islet volume was calculated. Group 2 pancreases were thoroughly digested leaving only a few residual ducts, but undigested fragments persisted in group 1 pancreases. Islet size was similar in both groups. There was a greater islet volume before and after Ficoll purification in group 2, but the difference was not significant. Purity was greater than 90% in both groups. Perifusion with 28 mM glucose elicited a biphasic insulin release from islets in both groups. The data show that the combined protocol enables mass isolation of purified islets from the canine pancreas. Compared with the manual technique, the automated protocol for pancreas dissociation tends to improve the yield of islets without compromising islet size and viability. It provides the advantages of a closed system with increased control over the extent of collagenase digestion.

Animals↗
PubMed1989

Effects of precryopreservation culture on survival of rat islets transplanted after slow cooling and rapid thawing.

Despite the frequent use of in vitro tissue culture before islet cryopreservation, no study has evaluated the ability of this procedure to improve the recovery or in vivo function of frozen-thawed islets. To evaluate this, quantities of 2500 Wistar-Furth (WF) rat islets were allocated to each of four groups (n = 8 each): group 1, freshly isolated; group 2, 48 hr in vitro culture; group 3, cryopreservation; group 4, cryopreservation after 48 hr in culture. Islets were frozen slowly at 0.25 degrees C/min and thawed rapidly at 200 degrees C/min. The number of islets recovered after culture or cryopreservation was determined and viability was assessed by measuring weekly indices of plasma glucose (PG), urine glucose (UG), urine volume (UV), and weight after implantation into the portal vein of streptozotocin-diabetic WF recipients. Islet recovery was 97% after culture, 95% after cryopreservation, and 94% after culture-then cryopreservation. After implantation of group 1 and 2 islets, PG was less than 150 mg/dl at 1 week and UG and UV were normal by 1-2 weeks. Group 3 islets restored normoglycemia at 3 weeks and other indices of diabetes were reversed by 4 weeks; group 4 islets restored normoglycemia at 4 weeks and indices returned to basal after 4 weeks. At intravenous glucose tolerance testing (ivGTT), the K values (mean decline in glucose, %/min, +/- SE) were group 1, 1.6 +/- 0.3; group 2, 1.5 +/- 0.3; group 3, 0.6 +/- 0.1; and group 4, 0.7 +/- 0.2. These data show that cryopreservation preserves freshly isolated or cultured islets that reverse the indices of diabetes after implantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Transplantation of purified single-donor canine islet allografts with cyclosporine.

We evaluated the survival of highly purified freshly isolated pancreatic islets transplanted from single canine donors into 20 outbred mongrel dogs immunosuppressed with cyclosporine or untreated. The grafts (mean weight +/- SE, 0.5 +/- 0.1 g, containing 122 +/- 8 X 10(3) islets; purity 91% by electron microscopy) were transplanted into 3 groups of dogs: group 1, autograft without CsA (5444 +/- 688 islets/kg body weight, n = 6); group 2, allograft without CsA (6669 +/- 1744, n = 4); and group 3, allograft with CsA (8645 +/- 1149, n = 10). The CsA was injected i.m. daily for 4 days before and 30 days after transplantation. Fasting plasma glucose (PG, mg/dl) and serum CsA trough values were determined daily. Intravenous glucose tolerance tests were done before and after transplantation, for calculation of K values (decline in glucose, %/min; preoperatively, mean K = 3.9 +/- 0.2). In group 1 all 6 dogs were normoglycemic (PG = 98 +/- 2 and K = 1.8 +/- 0.2) at 1 month; in group 2 the graft failed in all 4 dogs, at 4 +/- 1.2 days; in group 3 all 10 dogs were normoglycemic initially. Of the group 3 dogs, 4 died (intussusception developed in 2, and the graft failed at 3 and 9 days in 2 the CsA values of which were less than 300 micrograms/L preoperatively), but the other 6 were still normoglycemic when the CsA was stopped at 30 days (mean PG = 132 +/- 16 and K = 0.9 +/- 0.2; P less than 0.05 vs. group 1). Their CsA values were 708 +/- 197 before and 359 +/- 41 micrograms/L during the third week after transplantation; their grafts failed 12.3 +/- 3.4 days after the cessation of CsA. This data is unique in demonstrating prolonged function of purified allogeneic islets transplanted from individual outbred canine donors, but glucose tolerance was impaired. CsA at serum levels greater than 300 micrograms/L induced prolonged survival of purified canine islets and rejection was prompt when it was stopped.

Animals↗