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S Bonner-Weir

Publications and source records attributed to S Bonner-Weir.

At least 73 records · Page 4Linked to original sources
PubMed1997

Reduced insulin, GLUT2, and IDX-1 in beta-cells after partial pancreatectomy.

Reduction of GLUT2 is associated with loss of glucose-induced insulin secretion in genetic and chemical diabetes and in transplanted islets exposed to chronic hyperglycemia. To examine the mechanisms for this loss of GLUT2 in normal islets exposed to hyperglycemia, we performed studies on Sprague Dawley rats 4 weeks after a 90% partial pancreatectomy (Px), a well-characterized model of hyperglycemia. GLUT2 immunofluorescence in the beta-cell of Px rats was greatly reduced. Western blot analysis of homogenates of isolated Px islets also showed a reduction in GLUT2 protein; densitometry measurements were 36 +/- 3% of values from islets of sham-operated controls. Insulin protein levels were decreased to a similar extent. Islet GLUT2 and insulin mRNA were measured with quantitative reverse transcriptase-polymerase chain reaction. The level of GLUT2 mRNA from Px islets was 24 +/- 4% of that of islets from sham-operated controls; similar results were obtained for insulin. Because both these beta-cell-specific messages were reduced, we analyzed the Px islets for the pancreas-duodenum-specific transcription factor IDX-1(IPF-1, STF-1, PDX-1) protein. It was markedly reduced (approximately 80%) in islets from the Px rats. These data suggest that 1) the loss of GLUT2 protein associated with hyperglycemia is at least partially explained by reduced levels of the GLUT2 gene transcripts; 2) the reduction of beta-cell insulin content during chronic hyperglycemia may not be completely due to degranulation (reduced levels of gene transcripts may play a role); and 3) the reduction in the transcription factor IDX-1 raises the possibility that dysregulation of transcription factors may contribute to the abnormal beta-cell function found in states of chronic hyperglycemia.

Animals↗
PubMed1997

Scientific and political impediments to successful islet transplantation.

Islet transplantation is a treatment for diabetes that has the potential to normalize glucose levels and prevent the development of complications. In spite of the simplicity of the concept and the urgent need to provide such a treatment to patients, there has been a frustrating lack of progress. This perspective delves into the scientific and political impediments to success. The scientific barriers are the need to find a satisfactory source of insulin-producing tissue and the requirement to prevent this tissue from being destroyed by immune rejection and autoimmunity. The problems and potential of allografts, xenografts, and the development of cell lines are discussed. Multiple approaches to the prevention of immune destruction are considered, including immunobarrier devices, immunosuppression, development of tolerance, and genetic manipulation. The political barriers discussed include the problems of high expectations, the controversy surrounding targeted research, the balance between basic and applied research, the roles of industry and academia, the concerns about xenotransplantation, and the difficulties in developing a planned approach to the problem.

Diabetes Mellitus↗
PubMed1997

Porcine neonatal pancreatic cell clusters (NPCCs): a potential source of tissue for islet transplantation.

This is a short review of porcine neonatal pancreatic cell clusters (NPCCs) which might eventually be useful for beta cell replacement therapy in people with diabetes. The current success with islet allograft transplantation is reviewed and is problematic because only partial success has been obtained and the shortage of human islet tissue means that only a small fraction of people with diabetes would be able to benefit. For these reasons there is considerable interest in xenotransplantation, with pigs being a particularly attractive source. The relative merits of early fetal, late fetal, neonatal and adult porcine tissue are discussed. Neonatal tissue has several attractive features, with their hardiness and potential for growth being especially noteworthy. NPCCs are harvested after digested and dispersed clumps of cells are kept in culture for 7 days. The NPCCs consist mainly of duct cells, protodifferentiated cells and mature endocrine cells. The protodifferentiated cells are either double or triple stained for insulin, cytokeratin 7, glucagon, pancreatic polypeptide, or somatostatin. When transplanted into diabetic nude mice it usually takes weeks before glucose levels are normalized, and during that time differentiation and growth of the graft can be observed. Potential strategies for controlling xenograft rejection are mentioned, with these being immunosuppression, induction of tolerance, immunobarrier devices, and gene transfer approaches.

Animals↗
PubMed1996

Outcome of subcutaneous islet transplantation improved by polymer device.

Syngeneic transplantation of rat islets into subcutaneous tissue failed to cure streptozocin diabetes. The reason is unknown, but poor vascularization may play a role. We hypothesize that if a well-vascularized subcutaneous site could be created, islet grafts would do well. Four hundred freshly isolated mouse islets were transplanted syngeneically under the renal capsule or into the intraperitoneal cavity and compared with 800 islets in subcutaneous tissue of streptozocin-diabetic mice. Four weeks after transplantation, 14 of 14 under the renal capsule, 4 of 8 in the intraperitoneal site, and 0 of 7 in the subcutaneous tissue site achieved normoglycemia. To create vascularized organoids, we transplanted 800 mouse islets into polyvinyl alcohol (PVA) or polyglycolic acid (PGA) polymers in subcutaneous tissue of streptozocin-diabetic mice either immediately (four in PVA and six in PGA) or 7 days (four in PVA and four in PGA) after implantation. Four weeks after transplantation, the mean blood glucose level and body weight had no change with PVA. However, the mean body weight increased significantly with PGA and 3/10 became normoglycemic. When transplanting 400 islets with PGA polymers intraperitoneally, all animals (n=5) remained hyperglycemic 3 months later. In contrast, four of five recipients transplanted with 800 islets with PGA polymers subcutaneously became normoglycemic. The grafts from successful animals contained numerous revascularized islets containing a substantial amount of insulin. These preliminary results indicate that subcutaneous islet transplantation using PGA polymers can improve the metabolic status and, in some cases, even cure diabetes in streptozocin-diabetic mice.

Animals↗
PubMed1996

Islet amyloid formation associated with hyperglycemia in transgenic mice with pancreatic beta cell expression of human islet amyloid polypeptide.

Pancreatic islet amyloid deposits are a characteristic pathologic feature of non-insulin-dependent diabetes mellitus and contain islet amyloid polypeptide (IAPP; amylin). We used transgenic mice that express human IAPP in pancreatic beta cells to explore the potential role of islet amyloid in the pathogenesis of non-insulin-dependent diabetes mellitus. Extensive amyloid deposits were observed in the pancreatic islets of approximately 80% of male transgenic mice > 13 months of age. Islet amyloid deposits were rarely observed in female transgenic mice (11%) and were never seen in nontransgenic animals. Ultrastructural analysis revealed that these deposits were composed of human IAPP-immunoreactive fibrils that accumulated between beta cells and islet capillaries. Strikingly, approximately half of the mice with islet amyloid deposits were hyperglycemic (plasma glucose > 11 mM). In younger (6- to 9-month-old) male transgenic mice, islet amyloid deposits were less commonly observed but were always associated with severe hyperglycemia (plasma glucose > 22 mM). These data indicate that expression of human IAPP in beta cells predisposes male mice to the development of islet amyloid and hyperglycemia. The frequent concordance of islet amyloid with hyperglycemia in these mice suggests an interdependence of these two conditions and supports the hypothesis that islet amyloid may play a role in the development of hyperglycemia.

Amyloid↗
PubMed1996

Translocation of glucokinase in pancreatic beta-cells during acute and chronic hyperglycemia.

Glucokinase (GK) plays a key role in the regulation of glucose-induced insulin secretion, and questions have been raised about its relationship to the glucose transporter GLUT2 and its function in diabetes. This study examined the location of immunostained GK and GLUT2 in beta-cells using confocal microscopy. On double stained sections from pancreases of normal fed rats, GLUT2 Texas Red staining was restricted to the plasma membrane, and GK fluorescein isothiocyanate staining was found in a limited area of cytoplasm that was perinuclear with slight extension toward the apical pole. The GK staining occupied 8.6 +/- 1.7% of total cytoplasmic area and was almost never adjacent to the GLUT2 staining of the plasma membrane. To determine whether the GK staining pattern is altered by metabolic perturbation, normal rats were made acutely hyperglycemic with iv glucose injections; after 20 min the GK staining changed from being localized to become diffusely distributed throughout the cytoplasm. To examine the influence of chronic hyperglycemia, rats were subjected to 90% partial pancreatectomy (Px), which produced glucose levels of 10.9-20.8 mM. When studied 6 or 14 days after Px, those rats with glucose levels greater than 17.7 mM had an altered GK staining pattern that was variable; in some beta-cells GK staining was diffuse and in others the localized staining pattern was preserved. GLUT2 staining was reduced overall, but variability between cells was observed, unlike the more uniform reductions seen with hyperglycemia of longer duration. Other rats received islet transplants to prevent hyperglycemia after Px; their GK and GLUT2 staining patterns were normal. These findings indicate that GK is translocated in association with acute and chronic hyperglycemia. The translocation of this key enzyme for glucose recognition by beta-cells may lead to altered rates of insulin secretion during acute perturbations of fuel provision and in the diabetic state.

Acute Disease↗
PubMed1996

Long-term normalization of GLUT-4 protein content in skeletal muscle of diabetic rats following islet transplantation.

Skeletal muscle GLUT-4 content is decreased in streptozotocin (STZ)-diabetic rats. This decrease is associated with impairment in glucose transport across the plasma membrane. In this study we investigated whether islet transplantation might normalize GLUT-4 content. Transplantation of syngeneic islets restored long-term near-normoglycemia in STZ-diabetic Lewis rats. Transplanted rats, followed up to 6 months, maintained slightly but significantly higher fasting and fed glucose levels when compared with age-matched normal controls. Although fasting insulin levels of transplanted rats were significantly higher than those of controls, insulin levels did not increase significantly with feeding. Plasma glucose levels following an oral glucose load (2 g/kg) were only slightly higher than in normal controls 2 months after transplantation, whereas after 6 months more severe glucose intolerance was detected. Transplanted rats completely lost the first-phase insulin release in response to i.v. glucose although they showed an increased second phase and preserved response to arginine. Six months after transplantation, endocrine beta cell mass of the grafts was similar to pretransplantation values. GLUT-4 protein content in skeletal muscle homogenates was reduced in untreated diabetic animals whereas it was completely restored by islet transplantation. In conclusion, achievement of long-term nearnormoglycemia after islet transplantation was associated with complete normalization of skeletal muscle GLUT-4 content in the diabetic animals, even in the presence of abnormal glucose tolerance and an altered pattern of insulin secretion.

Animals↗
PubMed1996

Vulnerability of islets in the immediate posttransplantation period. Dynamic changes in structure and function.

To learn more about islet vulnerability in the immediate posttransplant period, 400 syngeneic islets were transplanted under the kidney capsule of B6AF1 mice. Three groups of recipients were used: normal mice (normal), streptozotocin (STZ)-diabetic (diabetic), and STZ-diabetic kept hypo- or normoglycemic with insulin pellets (diabetic-normalized). Normoglycemia was achieved in all three groups 14 days after transplantation; however, in the diabetic and diabetic-normalized groups, blood glucose levels throughout the posttransplantation period were respectively higher and lower than in the normal group. Grafts were harvested 1, 3, 7, and 14 days after transplantation and analyzed for morphology, beta-cell death, beta-cell mass, insulin content, and insulin mRNA expression. In all groups, substantial damage in islet grafts was found on days 1 and 3 with apoptotic nuclei and necrotic cores; on day 3, beta-cell death was significantly higher in the diabetic group than in the other groups. Tissue remodelling occurred in all groups with stable graft appearance on day 14; the actual beta-cell mass of the grafts was lowest in the diabetic group. Graft insulin content decreased in all groups on day 1 and fell even further on days 3 and 7. Insulin mRNA levels of grafts retrieved from both the diabetic and diabetic-normalized group were lower than those from the normal group already by day 1 and remained lower on day 14. In conclusion, the first few days of islet transplantation, even under the most advantageous circumstances of excellent metabolic control, are characterized by dynamic changes, with substantial islet cell dysfunction and death followed by tissue remodelling and then stable engraftment.

Animals↗
PubMed1996

Islet transplantation in diabetic Lewis rats--a comparison of the transplantation sites kidney and spleen capsule.

Animal studies have been used to investigate different transplantation (Tx) sites to find best conditions for Tx in humans. A few long-term experiments of comparisons of different Tx-sites have been published. Therefore the aim of our study was to compare islet grafts transplanted under the kidney capsule (KTx) of male Lewis rats with grafts transplanted under the spleen capsule (STx) and to observe these animals over a period of 6 months. Diabetes was induced by Streptozotocin and rats were each transplanted with 2000 syngeneic islets under the kidney respectively the spleen capsule. 2 weeks after Tx all animals were normoglycemic. Over the following 6 months nearly normal plasma glucose levels could be maintained in the KTx group whereas the STx animals already became diabetic after 3 months. An oral glucose load after 2 months showed slightly elevated plasma glucose levels in the KTx group which only gained statistical significance in a similar test after 6 months. In the STx group definitely impaired glucose tolerance already prevailed at 2 months. An i.v. glucose tolerance test performed 6 months after Tx showed a loss of first phase insulin release in both Tx groups but an increased second phase release and a preserved response to L-arginine compared to controls. Insulin content remained unchanged in the KTx group, but was markedly reduced in the STx group after 6 months. In conclusion we may say that KTx is able to establish near-normoglycemia in streptozotocin-diabetic Lewis rats which can be maintained over a long period of time despite abnormal glucose tolerance and impaired insulin secretion STx could normalize plasma glucose only up to 3 months showing early impairment of glucose and insulin regulation. If KTx has immunological or local advantages (islet vascularization, innervation) compared to STx with higher dispersion of islets in spleen and portal vascular system remains unclear.

Animals↗
PubMed1995

A selective decrease in the beta cell mass of human islets transplanted into diabetic nude mice.

Streptozocin-induced diabetic nude mice (blood glucose 493 +/- 14 mg/dl) received aliquots of 2000 human islet equivalents (IE) under the kidney capsule and were then followed for up to 30 days with measurement of blood glucose concentration and body weight. Characterization of islet aliquots before the implantation included the assessment of the endocrine beta cell and nonbeta cell mass, estimated by point counting morphometry of immunostained sections. Islet transplantation was followed by a rapid decrease in blood glucose levels and by a progressive increase in body weight; 15 days after transplantation mean glycemic levels were 102 +/- 11 mg/dl and further decreased to 70 +/- 3 mg/dl at 30 days. Despite the progressive improvement in the glucose levels, the beta cell mass of the islet grafts significantly decreased over time from 2.63 +/- 0.2 mg, at the time of transplantation, to 1.16 +/- 0.1 and 0.86 +/- 0.1 mg 15 and 30 days, respectively, after transplantation. In contrast, the endocrine nonbeta cell mass remained stable from before the implantation to 30 days after. Therefore, the endocrine nonbeta cell/beta cell ratio increased from 14% at the time of transplantation, to 35% and 37%, 15 and 30 days, respectively, after transplantation. The rate of replication of the transplanted beta cells was similar in the grafts harvested at 15 and 30 days, with the percentage of beta cells positive for bromo-2' deoxyuridine (BrdU) incorporation being in the range of approximately 0.1% 6 hr after the BrdU injection. These data demonstrate that an important decrease in beta cell mass takes place immediately after islet transplantation--the most dramatic decrease occurring in the first 15 days and persisting even after revascularization has occurred. However, endocrine nonbeta cell mass remained stable indicating that engrafted nonbeta cells are less likely to die than beta cells. The finding that the nonbeta/beta cell ratio of a human islet graft can increase over time, raises questions about whether such a change in islet structure could have an influence upon function.

Animals↗
PubMed1995

Apoptosis contributes to the involution of beta cell mass in the post partum rat pancreas.

A significant reduction of beta cell mass has been described during the post partum period in the endocrine rat pancreas. We examined the mechanisms of this involution in Sprague Dawley rats by analyzing beta cell mass, beta cell replication, and beta cell size at end of pregnancy and 4 and 10 days after delivery. beta cell replication was significantly decreased at 4 days post partum but had returned back to nonpregnant levels by 10 days post partum. Similarly, beta cell size was significantly decreased at 4 and 10 days post partum as compared with the end of pregnancy, and at 10 days post partum was significantly decreased as compared with controls. At 4-6 days post partum, DNA fragmentation characteristic of apoptosis (programmed cell death) was detected in pancreatic islets, as assessed by in situ terminal deoxynucleotidyl transferase and nick translation assay. Only occasional cells were labeled with this assay in nonpregnant rats and at other time points after delivery. Condensed chromatin and apoptotic bodies, the morphological characteristics of apoptosis, were detected in beta cells of pancreatic islet at 3 and 4 days after delivery by electron microscopic analysis, confirming the occurrence of apoptosis in involuting islets. The expression of TRPM 2 and TGF beta 1, often enhanced in models of apoptosis, were studied during the post partum period by Northern blot analysis and immunohistochemistry. Levels of TRPM 2 gene and its protein, clusterin, were not different from controls; however, the TGF beta 1 gene and its protein expression were enhanced at 3 days post partum. Our study confirms the capability of beta cells to down-regulate their mass using the mechanisms of changes in rates of beta cell replication and of beta cell death, and changes in beta cell size to achieve homeostasis of the functional endocrine tissue.

Animals↗
PubMed1995

Function, mass, and replication of porcine and rat islets transplanted into diabetic nude mice.

Well-characterized aliquots of adult porcine and rat islets of comparable beta-cell mass were transplanted under the kidney capsule of streptozotocin-induced diabetic nude mice. In both porcine and rat islet grafts, beta-cell mass decreased significantly in the first 2 months and stabilized thereafter. As with beta-cell mass, insulin content decreased significantly in the first 2 months to almost 40% of that originally implanted. In porcine grafts, however, insulin content at 4 months was significantly higher than at 2 months. The endocrine non-beta-cell mass of grafts also decreased significantly after transplantation: in porcine grafts, the decrease was less than in rat and was limited to the first 2 months. beta-cell replication of engrafted islets was significantly lower in porcine than in rat grafts. Although beta-cell mass of porcine and rat grafts was similar at all time periods, recipients of porcine islets required a significantly longer time to reach normal glucose levels; nonetheless, their blood glucose levels continued to decrease and stabilized at levels significantly lower than those of normal mice. During oral and intraperitoneal glucose tolerance tests, blood glucose increased only slightly in both the recipients of porcine and rat grafts. When graft-bearing kidneys were perfused in situ, porcine islet grafts showed a 20-fold increase in insulin release in response to both glucose and arginine. In conclusion, this evidence that adult porcine islet grafts can bring glucose levels to those that are normal for humans provides further support of their potential for human islet replacement therapy.

Animals↗
PubMed1995

Loss of glucose-induced insulin secretion and GLUT2 expression in transplanted beta-cells.

Either 200 or 400 syngeneic islets were transplanted under the kidney capsule of normal or streptozocin-induced diabetic B6/AF1 mice. The diabetic mice with 400 islets became normoglycemic, but those with 200 islets, an insufficient number, were still diabetic after the transplantation (Tx). Two weeks after Tx, GLUT2 expression in the islet grafts was evaluated by immunofluorescence and Western blots, and graft function was examined by perfusion of the graft-bearing kidney. Immunofluorescence for GLUT2 was dramatically reduced in the beta-cells of grafts with 200 islets exposed to hyperglycemia. However, it was plentiful in grafts with 400 islets in a normoglycemic environment. Densitometric analysis of Western blots on graft homogenates demonstrated that GLUT2 protein levels in the islets, when exposed to chronic hyperglycemia for 2 weeks, were decreased to 16% of those of normal recipients. Moreover, these grafts had defective glucose-induced insulin secretion, while the effects of arginine were preserved. We conclude that GLUT2 expression in normal beta-cells is promptly down-regulated during exposure to hyperglycemia and may contribute to the loss of glucose-induced secretion of diabetes.

Animals↗
PubMed1995

Dynamics of beta-cell mass in the growing rat pancreas. Estimation with a simple mathematical model.

The growth and development of the endocrine pancreas has been studied for many years, but questions remain concerning the regulation of the mass of insulin-producing beta-cells both in the normal growing pancreas and during the pathogenesis of diabetes. The homeostatic control of beta-cell mass in both normal and pathophysiological conditions is based on the balance of cell proliferation, cell growth, and cell death. To gain insight into the relative contribution of each of these dynamic processes, we first mathematically analyzed the data available on the components involved in the maintenance of beta-cell mass, including rates of replication, beta-cell volume, and the beta-cell mass itself, at various ages in normal Sprague-Dawley rats. Then these data were combined in a simple mass balance equation to construct a mathematical model of the dynamics of the beta-cell mass in the normal growing rat pancreas. Such a model has allowed us to infer the contributions of fluxes that cannot be measured, i.e., neogenesis and cell death, to the known mass of beta-cells. Another important contribution of this model is to raise unanswered questions concerning the control of the balance of cell death and cell renewal in the endocrine pancreas.

Aging↗
PubMed1995

Long-term normalization of GLUT 4 protein content in skeletal muscle of streptozotocin-diabetic Lewis rats after islet transplantation.

Islet transplantation under the kidney capsule of STZ-diabetic Lewis rats was able to maintain near-normoglycemia over a period of 6 months. Fasting insulin in these animals was higher compared to controls but did not increase after feeding. Plasma glucose following an OGTT at 2 months was only slightly impaired, and after 6 months was more severely impaired in the Tx rats. An IVGTT 6 months after Tx confirmed impaired glucose tolerance and showed a loss of first phase insulin release. GLUT 4 protein content in skeletal muscle was completely restored in Tx animals. In conclusion, long-term near-normoglycemia after syngeneic islet transplantation under the kidney capsule of STZ-diabetic Lewis rats is associated with complete normalization of skeletal muscle GLUT 4 protein content, even in the presence of abnormal glucose tolerance and impaired insulin secretion.

Animals↗