Search PubMed⌕ Search

Biomedical subjects

G C Weir

Publications and source records attributed to G C Weir.

At least 19 recordsLinked to original sources
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

Islet transplantation under the kidney capsule fully corrects the impaired skeletal muscle glucose transport system of streptozocin diabetic rats.

Chronic insulin therapy improves but does not restore impaired insulin-mediated muscle glucose uptake in human diabetes or muscle glucose uptake, transport, and transporter translocation in streptozocin diabetic rats. To determine whether this inability is due to inadequate insulin replacement, we studied fasted streptozocin-induced diabetic Lewis rats either untreated or after islet transplantation under the kidney capsule. Plasma glucose was increased in untreated diabetics and normalized by the islet transplantation (110 +/- 5, 452 +/- 9, and 102 +/- 3 mg/dl in controls, untreated diabetics, and transplanted diabetics, respectively). Plasma membrane and intracellular microsomal membrane vesicles were prepared from hindlimb skeletal muscle of basal and maximally insulin-stimulated rats. Islet transplantation normalized plasma membrane carrier-mediated glucose transport Vmax, plasma membrane glucose transporter content, and insulin-induced transporter translocation. There were no differences in transporter intrinsic activity (Vmax/Ro) among the three groups. Microsomal membrane GLUT4 content was reduced by 30% in untreated diabetic rats and normal in transplanted diabetics, whereas the insulin-induced changes in microsomal membrane GLUT4 content were quantitatively similar in the three groups. There were no differences in plasma membrane GLUT1 among the groups and between basal and insulin stimulated states. Microsomal membrane GLUT1 content was increased 60% in untreated diabetics and normalized by the transplantation. In conclusion, an adequate insulin delivery in the peripheral circulation, obtained by islet transplantation, fully restores the muscle glucose transport system to normal in streptozocin diabetic rats.

Animals↗
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↗
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

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

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↗
PubMed1994

Pancreatic islet cell toxicity of amylin associated with type-2 diabetes mellitus.

The 37-amino-acid polypeptide amylin is the principal constituent of the amyloid deposits that form in the islets of Langerhans in patients with type-2 diabetes mellitus, but its role in the pathogenesis of this disease is unresolved. In view of the fact that the beta-amyloid protein that forms fibrils in Alzheimer's disease is toxic to neurons, we have investigated whether amylin fibrils could be toxic to pancreatic islet cells. We show here that human amylin is toxic to insulin-producing beta-cells of the adult pancreas of rats and humans. This toxicity is mediated by the fibrillar form of the amylin peptide and requires direct contact of the fibrils with the cell surface. The mechanism of cell death involves RNA and protein synthesis and is characterized by plasma membrane blebbing, chromatin condensation and DNA fragmentation, indicating that amylin induces islet cell apoptosis. These findings indicate that amylin fibril formation in the pancreas may cause islet cell dysfunction and death in type-2 diabetes mellitus.

Adult↗
PubMed1994

Transplanted beta cell response to increased metabolic demand. Changes in beta cell replication and mass.

We determined the capacity of transplanted beta cells to modify their replication and mass when stimulated by changes in metabolic demand. Five groups of Lewis rats were studied: group 1 (Tx-Px) had a 95% pancreatectomy 14 d after transplantation of 500 islets; group 2 (Px-Tx) had a 95% pancreatectomy 14 d before transplantation of 500 islets; group 3 (Tx) was transplanted with 500 islets; group 4 (Px) had a 95% pancreatectomy; and group 5 (normal) was neither transplanted nor pancreatectomized. Blood glucose was normal in Tx-Px and Tx groups at all times. Px-Tx and Px groups developed severe hyperglycemia after pancreatectomy that was corrected in Px-Tx group in 83% of rats 28 d after transplantation. Replication of transplanted beta cells increased in Tx-Px (1.15 +/- 0.12%) and Px-Tx (0.85 +/- 0.12%) groups, but not in Tx group (0.64 +/- 0.07%) compared with normal pancreatic beta cells (0.38 +/- 0.05%) (P < 0.001). Mean beta cell size increased in Tx-Px (311 +/- 14 microns2) and Px-Tx (328 +/- 13 microns2) groups compared with Tx (252 +/- 12 microns2) and normal (239 +/- 9 microns2) groups (P < 0.001). Transplanted beta cell mass increased in Tx-Px (1.87 +/- 0.51 mg) and Px-Tx (1.55 +/- 0.21 mg) groups compared with Tx group (0.78 +/- 0.17 mg) (P < 0.05). In summary, changes in transplanted beta cells prevented the development of hyperglycemia in Tx-Px rats. Transplanted beta cells responded to increased metabolic demand increasing their beta cell mass.

Animals↗
PubMed1994

Beneficial influence of glycemic control upon the growth and function of transplanted islets.

Syngeneic transplantation of 200 mouse islets under the kidney capsule usually fails to cure streptozocin-induced diabetes. We hypothesized that this number of islets, if engrafted in a normoglycemic environment, could expand their mass and improve their function to restore normoglycemia. Therefore, 200 freshly isolated mouse islets were transplanted under the capsule of each kidney of diabetic mice. Two weeks after transplantation, the recipients were normoglycemic, and one of the two grafts was removed. Removal of the graft was followed by transient hyperglycemia. At day 14 after graft removal, the beta-cell mass and insulin content of the remaining graft had increased 2.3- and 2.1-fold, respectively. At day 3 after graft removal, the replication rate of beta-cells increased threefold, and the mean individual beta-cell cross-sectional area, an indicator of cell size, was also increased. Perfusion of the kidney bearing the remaining graft showed biphasic insulin responses to high glucose and arginine 14 days after one graft removal. These data indicate that maintaining a period of near-normoglycemia after islet transplantation enhances the performance of an islet graft that would otherwise be expected to fail.

Animals↗