Search

Reactive oxygen species (ROS) are formed by virtually all tissues. In normal concentrations they facilitate many physiologic activities, but in excess they cause oxidative stress and tissue damage. Local antioxidant enzyme synthesis in cells is regulated by the cytoplasmic KEAP-1/Nrf2 complex, which is stimulated by ROS, to release Nrf2 for entry into the nucleus, where it upregulates antioxidant gene expression. Major antioxidant enzymes include glutathione peroxidase (GPx), catalase (CAT), superoxide dismutases (SOD), hemoxygenases (HO), and peroxiredoxins (Prdx). Notably, the pancreatic islet β-cell does not express GPx or CAT, which puts it at greater risk for ROS damage caused by postprandial hyperglycemia. Experimentally, overexpression of GPx in β-cell lines and isolated islets, as well as in vivo studies using genetic models of type 2 diabetes (T2D), has demonstrated enhanced protection against hyperglycemia and oxidative stress. Oral treatment of diabetic rodents with ebselen, a GPx mimetic that is approved for human clinical use, reproduced these findings. Prdx detoxify hydrogen peroxide and reduce lipid peroxides. This suggests that pharmacologic development of more potent, β-cell–specific antioxidants could be valuable as a treatment for oxidative stress due to postprandial hyperglycemia in early T2D in humans. Article Highlights: We examined evidence that postprandial hyperglycemia in early type 2 diabetes (T2D) causes oxidative stress. We addressed the question of whether cessation of high-fat diet and return to a normal diet in T2D rodents cause improved glucose control and less oxidative stress. Our findings are that oxidative stress is associated with functional and structural changes in β-cells and that this is met with an intrinsic response: translocate cytoplasmic Nrf2 to the nucleus to initiate gene expression of antioxidants. The results of our work imply that early treatment of T2D with avoidance of a high-fat diet and the use of antioxidants might be helpful in restoring β-cell function. [ABSTRACT FROM AUTHOR]

Glucagon is a peptide hormone that is produced primarily by the alpha cells in the islet of Langerhans in the pancreas, but also in intestinal enteroendocrine cells and in some neurons. Approximately 100 years ago, several research groups discovered that pancreatic extracts would cause a brief rise in blood glucose before they observed the decrease in glucose attributed to insulin. An overall description of the regulation of glucagon secretion requires the inclusion of its sibling insulin because they both are made primarily by the islet and they both regulate each other i n different ways. For example, glucagon stimulates insulin secretion, whereas insulin suppresses glucagon secretion. The mechanism of action of glucagon on insulin secre tion has been identified as a trimeric guanine nucleotide-binding protein (G-protein)-mediated event. The manner in which insulin suppresses glucagon release from the alpha cell is thought to be highly dependent on the peri-portal circulation of the islet through which blood flows downstream from beta cells to alpha cells. In this scenario, it is via the circulation that insulin is thought to suppress the release of glucagon. However, high levels of glucose also have been shown to suppress glucagon secretion. Consequently, the glucoselowering effect of insulin may be additive to the direct effects of insulin to suppress alpha cell function, so that in vivo both the discontinuation of the insulin signal and the condition of low glucose jointly are responsible for induction of glucagon secretion. [ABSTRACT FROM AUTHOR]

Context Chronic exposure of pancreatic islets to elevated glucose levels causes progressive declines in beta cell Pdx-1 and insulin gene expression, and glucose-induced insulin secretion. This has been shown to be associated with excessive islet reactive oxygen species and consequent damage to beta cell function, a process termed glucose toxicity. In short-term rodent in vivo studies, Nrf2 (Kelch-like ECH-associated protein 1:nuclear factor erythroid-derived-2 related factor complex) has been shown to play a central role in defending beta cells from oxidative damage via activation of antioxidant gene expression. Objective The current studies were primarily designed to examine the behavior of Nrf2 gene expression during longer term exposure of beta cells to glucose toxicity. Methods and Results We provide evidence that gene expression of Nrf2 in HIT-T15 cells, an insulin-secreting beta-cell line, undergoes a biphasic response characterized by an initial decrease followed by increased expression during prolonged culturing of these cells in a physiologic (0.8 mM) but not a supraphysiologic (16.0 mM) glucose concentration. This was associated with a slight rise in HO-1 gene expression. Pdx-1 and insulin mRNA levels also decreased but then stabilized in late passages of cells that had been cultured in low glucose concentrations. Conclusion These complex events support the concept that Nrf2 gene expression plays an important regulatory role in defending beta cells during prolonged exposure to oxidative stress. [ABSTRACT FROM AUTHOR]

This perspective examines the proposition that chronically elevated blood glucose levels caused by type 2 diabetes (T2D) harm body tissues by locally generating reactive oxygen species (ROS). A feed-forward scenario is described in which the initial onset of defective beta cell function T2D becomes sustained and causes chronic elevations in blood glucose, which flood metabolic pathways throughout the body, giving rise to abnormally high local levels of ROS. Most cells can defend themselves via a full complement of antioxidant enzymes that are activated by ROS. However, the beta cell itself does not contain catalase or glutathione peroxidases and thereby runs a greater risk of ROS-induced damage. In this review, previously published experiments are revisited to examine the concept that chronic hyperglycemia can lead to oxidative stress in the beta cell, how this relates to the absence of beta cell glutathione peroxidase (GPx) activity, and whether this deficiency might be ameliorated by genetic enrichment of beta cell GPx and by oral antioxidants, including ebselen, a GPx mimetic. [ABSTRACT FROM AUTHOR]

Clinical islet allotransplantation has been successfully regulated as tissue/organ for transplantation in number of countries and is recognized as a safe and efficacious therapy for selected patients with type 1 diabetes mellitus. However, in the United States, the FDA considers pancreatic islets as a biologic drug, and islet transplantation has not yet shifted from the experimental to the clinical arena for last 20 years. In order to transplant islets, the FDA requires a valid Biological License Application (BLA) in place. The BLA process is costly and lengthy. However, despite the application of drug manufacturing technology and regulations, the final islet product sterility and potency cannot be confirmed, even when islets meet all the predetermined release criteria. Therefore, further regulation of islets as drugs is obsolete and will continue to hinder clinical application of islet transplantation in the US. The Organ Procurement and Transplantation Network together with the United Network for Organ Sharing have developed separately from the FDA and BLA regulatory framework for human organs under the Human Resources & Services Administration to assure safety and efficacy of transplantation. Based on similar biologic characteristics of islets and human organs, we propose inclusion of islets into the existing regulatory framework for organs for transplantation, along with continued FDA oversight for islet processing, as it is for other cell/tissue products exempt from BLA. This approach would reassure islet quality, efficacy and access for Americans with diabetes to this effective procedure. [ABSTRACT FROM AUTHOR]

Background: The aims of this study were to 1. define the responses of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), glucagon, and peptide YY (PYY) to an oral meal and to intravenous L-arginine; and 2. examine correlation of enteroendocrine hormones with insulin secretion. We hypothesized a relationship between circulating incretin concentrations and insulin secretion. Methods: Subjects with normal glucose tolerance (NGT, n = 23), prediabetes (PDM, n = 17), or with type 2 diabetes (T2DM, n = 22) were studied twice, following a mixed test meal (470 kCal) (mixed meal tolerance test [MMTT]) or intravenous L-arginine (arginine maximal stimulation test [AST], 5 g). GLP-1 (total and active), PYY, GIP, glucagon, and β cell function were measured before and following each stimulus. Results: Baseline enteroendocrine hormones differed across the glucose tolerance (GT) spectrum, T2DM generally >NGT and PDM. In response to MMTT, total and active GLP-1, GIP, glucagon, and PYY increased in all populations. The incremental area-under-the-curve (0–120 min) of analytes like total GLP-1 were often higher in T2DM compared with NGT and PDM (35–51%; P < 0.05). At baseline glucose, L-arginine increased total and active GLP-1 and glucagon concentrations in all GT populations (all P < 0.05). As expected, the MMTT and AST provoked differential glucose, insulin, and C-peptide responses across GT populations. Baseline or stimulated enteroendocrine hormone concentrations did not consistently correlate with either measure of β cell function. Conclusions/interpretation: Both MMTT and AST resulted in insulin and enteroendocrine hormone responses across GT populations without consistent correlation between release of incretins and insulin, which is in line with other published research. If a defect is in the enteroendocrine/β cell axis, it is probably reduced response to rather than diminished secretion of enteroendocrine hormones. [ABSTRACT FROM AUTHOR]

Objective: Standardized, reproducible, and feasible quantification of β-cell function (BCF) is necessary for the evaluation of interventions to improve insulin secretion and important for comparison across studies. We therefore characterized the responses to, and reproducibility of, standardized methods of in vivo BCF across different glucose tolerance states.Research Design and Methods: Participants classified as having normal glucose tolerance (NGT; n = 23), prediabetes (PDM; n = 17), and type 2 diabetes mellitus (T2DM; n = 22) underwent two standardized mixed-meal tolerance tests (MMTT) and two standardized arginine stimulation tests (AST) in a test-retest paradigm and one frequently sampled intravenous glucose tolerance test (FSIGT).Results: From the MMTT, insulin secretion in T2DM was >86% lower compared with NGT or PDM (P < 0.001). Insulin sensitivity (Si) decreased from NGT to PDM (∼50%) to T2DM (93% lower [P < 0.001]). In the AST, insulin secretory response to arginine at basal glucose and during hyperglycemia was lower in T2DM compared with NGT and PDM (>58%; all P < 0.001). FSIGT showed decreases in both insulin secretion and Si across populations (P < 0.001), although Si did not differ significantly between PDM and T2DM populations. Reproducibility was generally good for the MMTT, with intraclass correlation coefficients (ICCs) ranging from ∼0.3 to ∼0.8 depending on population and variable. Reproducibility for the AST was very good, with ICC values >0.8 across all variables and populations.Conclusions: Standardized MMTT and AST provide reproducible and complementary measures of BCF with characteristics favorable for longitudinal interventional trials use. [ABSTRACT FROM AUTHOR]

The therapeutic potential of pancreatic islet allotransplantation, in which human donor islets are used, as a treatment for type 1 diabetes (T1D) has fascinated diabetes researchers and clinicians for decades. At the same time, the therapeutic potential of total pancreatectomy and islet autotransplantation (TPIAT) (in which one's own islets are used) as a preventive treatment for diabetes in patients who undergo total pancreatectomy for chronic, painful pancreatitis has received relatively less attention. This is ironic, since the latter has been much more effective than the former in terms of successful glucose management and duration of efficacy. The reasons for this disparity can be partially identified. TPIAT receives very little attention in textbooks of internal medicine and general surgery and surprisingly little print in textbooks of endocrinology and transplantation. T1D is much more predominant than TPIAT as a clinical entity. Provision of insulin or replacement of islets is mandatory and a primary goal in T1D. Provision of pain relief from chronic pancreatitis is the primary goal of total pancreatectomy in TPIAT, whereas treatment of diabetes, and certainly prevention of diabetes, has been more of a secondary consideration. Nonetheless, research developments in both fields have contributed to success in one another. In this Perspective, I will provide a brief history of islet transplantation and contrast and compare the procedures of allo- and autoislet transplantation from three major points of view 1) the procedures of islet procurement, isolation, and transplantation; 2) the role and complications of immunosuppressive drugs; and 3) the posttransplant consequences on β - as well as α-cell function. [ABSTRACT FROM AUTHOR]

The article discusses the study by J. C. Neuman and colleagues on prostaglandin E3 (PGE) to regulate the glucose-induced insulin secretion pathway. The study reportedly involved a series of experiments to learn whether shifting plasma membrane polyunsaturated fatty acid composition to favor eicosapentaeoic acid would change prostaglandin production reduce PGE signaling. Also explored are the role of polyunsaturated fatty acid on chronic conditions and islet function.

We used intravenous arginine with measurements of insulin, C-peptide, and glucagon to examine β-cell and α-cell survival and function in a group of 10 chronic pancreatitis recipients 1-8 years after total pancreatectomy and autoislet transplantation. Insulin and C-peptide responses correlated robustly with the number of islets transplanted (correlation coefficients range 0.81-0.91; P < 0.01-0.001). Since a wide range of islets were transplanted, we normalized the insulin and C-peptide responses to the number of islets transplanted in each recipient for comparison with responses in normal subjects. No significant differences were observed in terms of magnitude and timing of hormone release in the two groups. Three recipients had a portion of the autoislets placed within their peritoneal cavities, which appeared to be functioning normally up to 7 years posttransplant. Glucagon responses to arginine were normally timed and normally suppressed by intravenous glucose infusion. These findings indicate that arginine stimulation testing may be a means of assessing the numbers of native islets available in autologous islet transplant candidates and is a means of following posttransplant α- and β-cell function and survival. [ABSTRACT FROM AUTHOR]

We used intravenous arginine with measurements of insulin, C-peptide, and glucagon to examine β-cell and a-cell survival and function in a group of 10 chronic pancreatitis recipients 1-8 years after total pancreatectomy and autoislet transplantation. Insulin and C-peptide responses correlated robustly with the number of islets transplanted (correlation coefficients range 0.81-0.91; P < 0.01-0.001). Since a wide range of islets were transplanted, we normalized the insulin and C-peptide responses to the number of islets transplanted in each recipient for comparison with responses in normal subjects. No significant differences were observed in terms of magnitude and timing of hormone release in the two groups. Three recipients had a portion of the autoislets placed within their peritoneal cavities, which appeared to be functioning normally up to 7 years posttransplant. Glucagon responses to arginine were normally timed and normally suppressed by intravenous glucose infusion. These findings indicate that arginine stimulation testing may be a means of assessing the numbers of native islets available in autologous islet transplant candidates and is a means of following posttransplant α- and β-cell function and survival. [ABSTRACT FROM AUTHOR]

A key aspect of research into the prevention and treatment of type 2 diabetes is the availability of reproducible clinical research methodology to assess β-cell function. One commonly used method employs nonglycemic secretagogues like arginine (arg) or glucagon (glgn). This study was designed to quantify the insulin response to arg and glgn and determine test repeatability and tolerability. Obese overnight-fasted subjects with normal glucose tolerance were studied on 4 separate days: twice using arg (5 g iv) and twice with glgn (1 mg iv). Pre- and postinfusion samples for plasma glucose, insulin, and C-peptide were acquired. Arg and glgn challenges were repeated in the last 10 min of a 60-min glucose (900 mg/min) infusion. Insulin and C-peptide secretory responses were estimated under baseline fasting glucose conditions (AIRarg and AIRglgn) and hyperglycemic (AIRargMAX AIRglgnMAX) states. Relative repeatability was estimated by intraclass correlation coefficient (ICC). Twenty-three (12 men and 11 women) subjects were studied (age: 42.4 ± 8.3 yr; BMI: 31.4 ± 2.8 kg/m(2)). Geometric means (95% CI) for baseline-adjusted values AIRarg and AIRglgn were 84 (75-95) and 102 (90-115) μU/ml, respectively. After the glucose infusion, AIRargMAX and AIRglgnMAX were 395 (335-466) and 483 (355-658) μU/ml, respectively. ICC values were >0.90 for AIRarg andAIRargMAX. Glucagon ICCs were 0.83, 0.34, and 0.36, respectively, although the exclusion of one outlier increased the latter two values (to 0.84 and 0.86). Both glgn and arg induced mild adverse events that were transient. Glucagon, but not arginine, induced moderate adverse events due to nausea. Taken together, arginine is preferred to glucagon for assessment of β-cell function. [ABSTRACT FROM AUTHOR]

The article considers the epidemiologic and metabolic studies of the consequences of red wine drinking for people with type 2 diabetes (T2D). It determines whether the health effects of wine are intrinsic to grapes or a function of the alcohol in wine. Potential mechanisms of action for the beneficial effects of red wine are discussed. It is suggested that drinking red wine in moderation has no adverse effects on people with T2D.

We reported earlier that β-cell-specific overexpression of glutathione peroxidase (GPx)-1 significantly ameliorated hyperglycemia in diabetic mice and prevented glucotoxicity-induced db/db deterioration of β-cell mass and function. We have now ascertained whether early treatment of Zucker diabetic fatty (ZDF) rats with ebselen, an oral GPx mimetic, will prevent β-cell deterioration. No other antihyperglycemic treatment was given. Ebselen ameliorated fasting hyperglycemia, sustained nonfasting insulin levels, lowered nonfasting glucose levels, and lowered HbA1c levels with no effects on body weight. Ebselen doubled β-cell mass, prevented apoptosis, prevented expression of oxidative stress markers, and enhanced intranuclear localization of pancreatic and duodenal homeobox (Pdx)-1 and v-maf musculoaponeurotic brosarcoma oncogene family, protein A (MafA), two critical insulin transcription factors. Minimal β-cell replication was observed in both groups. These findings indicate that prevention of oxidative stress is the mechanism whereby ebselen prevents apoptosis and preserves intranuclear Pdx-1 and MafA, which, in turn, is a likely explanation for the beneficial effects of ebselen on β-cell mass and function. Since ebselen is an oral antioxidant currently used in clinical trials, it is a novel therapeutic candidate to ameliorate fasting hyperglycemia and further deterioration of β -cell mass and function in humans undergoing the onset of type 2 diabetes. [ABSTRACT FROM AUTHOR]

The FOXO1 (forkhead box O1) transcription factor influences many key cellular processes, including those important in metabolism, proliferation and cell death. Reversible phosphorylation of FOXO1 at Thr24 and Ser256 regulates its subcellular localization, with phosphorylation promoting cytoplasmic localization, whereas dephosphorylation triggers nuclear import and transcriptional activation. In the present study, we used biochemical and molecular approaches to isolate and link the serine/threonine PP2A (protein phosphatase 2A) holoenzyme containing the B55a regulatory subunit, with nuclear import of FOXO1 in pancreatic islet ß-cells under oxidative stress, a condition associated with cellular dysfunction in Type 2 diabetes. The mechanism of FOXO1 dephosphorylation and nuclear translocation was investigated in pancreatic islet INS-1 and ßTC-3 cell lines subjected to oxidative stress. A combined chemical cross-linking and MS strategy revealed the association of FOXO1 with a PP2A holoenzyme composed of the catalytic C, structural A and B55a regulatory subunits. Knockdown of B55a in INS-1 cells reduced FOXO1 dephosphorylation, inhibited FOXO1 nuclear translocation and attenuated oxidative stress-induced cell death. Furthermore, both B55a and nuclear FOXO1 levels were increased under hyperglycaemic conditions in db/db mouse islets, an animal model of type 2 diabetes. We conclude that B55a-containing PP2A is a key regulator of FOXO1 activity in vivo [ABSTRACT FROM AUTHOR]

Alloislet transplantation for the treatment of type 1 diabetes enjoyed highly favorable status in the first half of the last decade but declined in favor during the second half. In this Perspective, I will briefly review the literature published in this area from 2000 to 2010 for the purposes of extracting lessons we have learned, considering whether the procedure should be deemed a partial success or a partial failure, and offering several strategies to improve alloislet transplantation outcomes in the future. In the end, I hope to strike a positive note about where this procedure is going, and how it will be applied to establish insulin independence in patients with type 1 diabetes. [ABSTRACT FROM AUTHOR]

Alloislet transplantation for the treatment of type 1 diabetes enjoyed highly favorable status in the first half of the last decade but declined in favor during the second half. In this Perspective, I will briefly review the literature published in this area from 2000 to 2010 for the purposes of extracting lessons we have learned, considering whether the procedure should be deemed a partial success or a partial failure, and offering several strategies to improve alloislet transplantation outcomes in the future. In the end, I hope to strike a positive note about where this procedure is going, and how it will be applied to establish insulin independence in patients with type 1 diabetes. Diabetes 59:1285-1291, 2010 [ABSTRACT FROM AUTHOR]

Objective: The intraislet insulin hypothesis proposes that glucagon secretion during hypoglycemia is triggered by a decrease in intraislet insulin secretion. A more recent hypothesis based on in vivo data from hypoglycemic rats is that it is the decrease in zinc cosecreted with insulin from beta-cells, rather than the decrease in insulin itself, that signals glucagon secretion from alpha-cells during hypoglycemia. These studies were designed to determine whether closure of the alpha-cell ATP-sensitive K(+) channel (K(ATP) channel) is the mechanism through which the zinc switch-off signal triggers glucagon secretion during glucose deprivation.Research Design and Methods: All studies were performed using perifused isolated islets.Results: In control experiments, the expected glucagon response to an endogenous insulin switch-off signal during glucose deprivation was observed in wild-type mouse islets. In experiments with streptozotocin-treated wild-type islets, a glucagon response to an exogenous zinc switch-off signal was observed during glucose deprivation. However, this glucagon response to the zinc switch-off signal during glucose deprivation was not seen in the presence of nifedipine, diazoxide, or tolbutamide or if K(ATP) channel knockout mouse islets were used. All islets had intact glucagon responses to epinephrine.Conclusions: These data demonstrate that closure of K(ATP) channels and consequent opening of calcium channels is the mechanism through which the zinc switch-off signal triggers glucagon secretion during glucose deprivation. [ABSTRACT FROM AUTHOR]

OBJECTIVE--The intraislet insulin hypothesis proposes that glucagon secretion during hypoglycemia is triggered by a decrease in intraislet insulin secretion. A more recent hypothesis based on in vivo data from hypoglycemic rats is that it is the decrease in zinc cosecreted with insulin from β-cells, rather than the decrease in insulin itself, that signals glucagon secretion from α-cells during hypoglycemia. These studies were designed to determine whether closure of the α-cell ATP-sensitive K[sup +] channel (KATP channel) is the mechanism through which the zinc switch-off signal triggers glucagon secretion during glucose deprivation. RESEARCH DESIGN AND METHODS--All studies were performed using perifused isolated islets. RESULTS--In control experiments, the expected glucagon response to an endogenous insulin switch-off signal during glucose deprivation was observed in wild-type mouse islets. In experiments with streptozotocin-treated wild-type islets, a glucagon response to an exogenous zinc switch-off signal was observed during glucose deprivation. However, this glucagon response to the zinc switch-off signal during glucose deprivation was not seen in the presence of nifedipine, diazoxide, or tolbutamide or if K[sub ATP] channel knockout mouse islets were used. All islets had intact glucagon responses to epinephrine. CONCLUSIONS--These data demonstrate that closure of K[sub ATP] channels and consequent opening of calcium channels is the mechanism through which the zinc switch-off signal triggers glucagon secretion during glucose deprivation. Diabetes 59: 128-134, 2010 [ABSTRACT FROM AUTHOR]

OBJECTIVE--Glucagon responses to hypoglycemia from islets transplanted in the liver are defective. To determine whether this defect is related to intrahepatic glycogen, islets from inbred Lewis rats were transplanted into the hepatic sinus (H group), peritoneal cavity (P group), omentum (O group), and kidney capsule (K group) of recipient Lewis rats previously rendered diabetic with streptozotocin (STZ). RESEARCH DESIGN AND METHODS--Glucagon responses to hypoglycemia were obtained before and after transplantation under fed conditions and after fasting for 16 h and 48 h to deplete liver glycogen. RESULTS---Glucagon (area trader the curve) responses to hypoglycemia in the H group (8,839 ± 1,988 pg/ml per 90 min) were significantly less than in normal rats (40,777 ± 8,192; P < 0.01). Fasting significantly decreased hepatic glycogen levels. Glucagon responses in the H group were significantly larger after fasting (fed 8,839 ± 1,988 vs. 16-h fasting 24,715 ± 5,210 and 48-h fasting 29,639 ± 4,550; P < 0.01). Glucagon response in the H group decreased after refeeding (48-h fasting 29,639 ± 4,550 vs. refed 10,276 ± 2,750; P < 0.01.). There was no difference in glucagon response to hypoglycemia between the H and the normal control group after fasting for 48 h (H 29,639 ± 4,550 vs. control 37,632 ± 5,335; P = NS). No intragroup differences were observed in the P, O, and K groups,: or normal control and STZ groups, when comparing fed or fasting states. CONCLUSIONS--These data suggest that defective glucagon responses to hypoglycemia by intrahepatic islet α-cells is due to dominance of a suppressive signal caused by increased glucose flux and glucose levels within the liver secondary to increased glycogenolysis caused by systemic hypoglycemia. Diabetes 57: 1567-1574, 2008 [ABSTRACT FROM AUTHOR]

Background: Overexpression of antioxidant enzymes has been reported to protect rodent beta cells from oxidative stress. However, very little is known about protein expression and activity of antioxidant enzymes in human islets. Method/Results: Human islet protein levels by Western analysis and enzymatic activity for the key antioxidant enzymes superoxide dismutases (SODs), catalase, and glutathione peroxidase-1 (GPx) were examined. Enzyme protein expression and activity were in the order SODs > catalase > GPx. Human islet GPx protein expression was significantly less than that found for catalase (p < 0.0001) and levels of GPx activity were virtually undetectable. As glucose and estrogens have been proposed to alter antioxidant enzyme levels, we examined islet data from male and female donors separately and under varying glucose concentrations. We found significantly less (p < 0.001) GPx protein expression in islets from females compared to males, but no significant regulation by glucose in either gender. Conclusions: Human islets have very low protein and activity levels for GPx, the essential enzyme for protection against excessive levels of intracellular lipid peroxides. GPx mimetics may be especially valuable in providing human islets with the broadest spectrum of protection against oxidative stress during isolation and transplantation. [ABSTRACT FROM AUTHOR]

This Perspectives in Diabetes addresses the accuracy of metabolic testing as a measure of pancreatic islet β-cell mass in vivo in animals and in humans. The impetus for framing this question lies in the current intense interest in determining the fate of β-cell mass in transplanted islets, i.e., does it decrease, increase, or remain the same over time, as well as ascertaining whether drugs that enhance incretin levels, and consequently enhance glucose-induced insulin secretion, might also preserve β-cell mass. An important methodology recently making scientific strides in this arena is positron emission tomography (PET). The central question this Perspectives in Diabetes raises is whether it is likely that PET will provide significant advantages over the metabolic methods already in hand and routinely used to estimate β-cell mass. This article examines the fidelity with which published metabolic data correlate with independent measures of β-cell mass across multiple species. Correlation coefficients in the general range of r = 0.80 are routinely obtained and are robust for in vivo research. Whether PET can significantly improve on these correlations, given its inherent limitations in measurement sensitivity, remains to be seen. It is clear that investigators developing PET methodology to estimate β-cell mass should at the same time incorporate metabolic measures into their studies so that side-by-side comparisons of the accuracy of the two experimental approaches can be made. Diabetes 56:2420-2424, 2007 [ABSTRACT FROM AUTHOR]

Abstract: Pancreatic β-cell function continuously deteriorates in type 2 diabetes despite optimal treatment regimens, which has been attributed to hyperglycemia itself via formation of excess levels of reactive oxygen species (ROS). Glutathione peroxidase GPx), by virtue of its ability to catabolize both H2O2 and lipid peroxides, is uniquely positioned to protect tissues from ROS. The level of this antioxidant in β cells is extremely low and overexpression of GPx in islets provides enhanced protection against oxidative stress. This suggests that GPx mimetics may represent a valuable ancillary treatment that could add a novel layer of protection for the β-cell. [Copyright &y& Elsevier]

The intraislet insulin hypothesis proposes that the decrement in β-cell insulin secretion during hypoglycemia provides an activation signal for α-cells to release glucagon. A more recent hypothesis proposes that zinc atoms suppress glucagon secretion via their ability to open a-cell ATP-sensitive K[sup +] channels. Since insulin binds zinc, and zinc is cosecreted with insulin, we tested whether decreased zinc delivery to the a-cell activates glucagon secretion. In streptozotocin-induced diabetic Wistar rats, we observed that switching off intrapancreatic artery insulin infusions in vivo during hypoglycemia greatly improved glucagon secretion (area under the curve [AUC]: control group 240 ± 261 and experimental group 4,346 ± 1,259 pg ⋅ ml[sup -1] ⋅ 90 min[sup -1]; n = 5, P < 0.02). Switching off pancreatic artery infusions of zinc chloride during hypoglycemia also improved the glucagon response (AUC: control group 817 ± 107 and experimental group 3,445 ± 573 pg ⋅ ml[sup -1] ⋅ 90 min[sup -1]; n = 6, P < 0.01). However, switching off zinc-free insulin infusions had no effect. Studies of glucose uptake in muscle and liver cell lines verified that the zinc-free insulin was biologically active. We conclude that zinc atoms, not the insulin molecule itself, provide the switch-off signal from the β-cell to the α-cell to initiate glucagon secretion during hypoglycemia. Diabetes 56:1107-1112, 2007 [ABSTRACT FROM AUTHOR]

The insulin gene is expressed almost exclusively in pancreatic β-cells. Metabolic regulation of insulin gene expression enables the β-cell to maintain adequate stores of intracellular insulin to sustain the secretory demand. Glucose is the major physiologic regulator of insulin gene expression; it coordinately controls the recruitment of transcription factors [e.g., pancreatic/duodenal homeobox-1 (PDX-1), mammalian homologue of avian MafA/L-Maf (MafA), Beta2/Neuro D (B2), the rate of transcription, and the stability of insulin mRNA. However, chronically elevated levels of glucose (glucotoxicity) and lipids (lipotoxicity) also contribute to the worsening of β-cell function in type 2 diabetes, in part via inhibition of insulin gene expression. The mechanisms of glucotoxicity, which involve decreased binding activities of PDX-1 and MafA and increased activity of C/EBPβ, are mediated by high-glucose-induced generation of oxidative stress. On the other hand, lipotoxicity is mediated by de novo ceramide synthesis and involves inhibition of PDX-1 nuclear translocation and MafA gene expression. Glucotoxicity and lipotoxicity have common targets, which makes their combination particularly harmful to insulin gene expression and β-cell function in type 2 diabetes. [ABSTRACT FROM AUTHOR]

The "switch-off" hypothesis to explain beta-cell regulation of alpha-cell function during hypoglycemia has not been assessed previously in isolated islets, largely because they characteristically do not respond to glucose deprivation by secreting glucagon. We examined this hypothesis using normal human and Wistar rat islets, as well as islets from streptozotocin (STZ)-administered beta-cell-deficient Wistar rats. As expected, islets perifused with glucose and 3-isobutryl-1-methylxanthine did not respond to glucose deprivation by increasing glucagon secretion. However, if normal rat islets were first perifused with 16.7 mmol/l glucose to increase endogenous insulin secretion, followed by discontinuation of the glucose perifusate, a glucagon response to glucose deprivation was observed (peak change within 10 min after switch off = 61 +/- 15 pg/ml [mean +/- SE], n = 6, P < 0.01). A glucagon response from normal human islets using the same experimental design was also observed. A glucagon response (peak change within 7 min after switch off = 31 +/- 1 pg/ml, n = 3, P < 0.01) was observed from beta-cell-depleted, STZ-induced diabetic rats whose islets still secreted small amounts of insulin. However, when these islets were first perifused with both exogenous insulin and 16.7 mmol/l glucose, followed by switching off both the insulin and glucose perifusate, a significantly larger (P < 0.05) glucagon response was observed (peak change within 7 min after switch off = 71 +/- 11 pg/ml, n = 4, P < 0.01). This response was not observed if the insulin perifusion was not switched off when the islets were deprived of glucose or when insulin was switched off without glucose deprivation. These data uniquely demonstrate that both normal, isolated islets and islets from STZ-administered rats can respond to glucose deprivation by releasing glucagon if they are first provided with increased endogenous or exogenous insulin. These results fully support the beta-cell switch-off hypothesis as a key mechanism for the alpha-cell response to hypoglycemia. [ABSTRACT FROM AUTHOR]

The glucagon response is the first line of defense against hypoglycemia and is lost in insulin-dependent diabetes. The beta-cell "switch-off" hypothesis proposes that a sudden cessation of insulin secretion from beta-cells into the portal circulation of the islet during hypoglycemia is a necessary signal for the glucagon response from downstream alpha-cells. Although indirect evidence exists to support this hypothesis, it has not been directly tested in vivo by provision and then discontinuation of regional reinsulinization of alpha-cells at the time of a hypoglycemic challenge. We studied streptozotocin (STZ)-induced diabetic Wistar rats that had no glucagon response to a hypoglycemic challenge. We reestablished insulin regulation of the alpha-cell by regionally infusing insulin (0.025 microU/min) directly into the superior pancreaticoduodenal artery (SPDa) of STZ-administered rats at an infusion rate that did not alter systemic venous glucose levels. SPDa insulin infusion was switched off simultaneously when blood glucose fell to <60 mg/dl after a jugular venous insulin injection. This maneuver restored the glucagon response to hypoglycemia (peak change within 5-10 min = 326 +/- 98 pg/ml, P < 0.05; and peak change within 15-20 min = 564 +/- 148 pg/ml, P < 0.01). No response was observed when the SPDa insulin infusion was not turned off (peak change within 5-10 min = 44 +/- 85 pg/ml, P = NS; and peak change within 15-20 min = 67 +/- 97 pg/ml, P = NS) or when saline instead of insulin was infused and then switched off (peak change within 5-10 min = -44 +/- 108 pg/ml, P = NS; and peak change within 15-20 min = -13 +/- 43 pg/ml, P = NS). No responses were observed during euglycemia (peak change within 5-10 min = 48 +/- 35 pg/ml, P = NS; and peak change within 15-20 min = 259 +/- 129 pg/ml, P = NS) or hyperglycemia (peak change within 5-10 min = 49 +/- 62 pg/ml, P = NS; and peak change within 15-20 min = 138 +/- 87 pg/ml, P = NS). Thus, the glucagon response to hypoglycemia that was absent in rats made diabetic by STZ was restored by regional infusion and then discontinuation of insulin. These data provide direct in vivo support for the beta-cell "switch-off" hypothesis and indicate that the alpha-cell is not intrinsically abnormal in insulin-dependent diabetes because of STZ-induced destruction of beta-cells. [ABSTRACT FROM AUTHOR]

The glucagon response is the first line of defense against hypoglycemia and is lost in insulin-dependent diabetes. The β-cell "switch-off" hypothesis proposes that a sudden cessation of insulin secretion from β-cells into the portal circulation of the islet during hypoglycemia is a necessary signal for the glucagon response from downstream α-cells. Although indirect evidence exists to support this hypothesis, it has not been directly tested in vivo by provision and then discontinuation of regional reinsulinization of α-cells at the time of a hypoglycemic challenge. We studied streptozotocin (STZ)-induced diabetic Wistar rats that had no glucagon response to a hypoglycemic challenge. We reestablished insulin regulation of the α-cell by regionally infusing insulin (0.025 µU/min) directly into the superior pancreaticoduodenal artery (SPDa) of STZ-administered rats at an infusion rate that did not alter systemic venous glucose levels. SPDa insulin infusion was switched off simultaneously when blood glucose fell to <60 mg/dl after a jugular venous insulin injection. This maneuver restored the glucagon response to hypoglycemia (peak change within 5-10 min = 326 ± 98 pg/ml, P < 0.05; and peak change within 15-20 min = 564 ± 148 pg/ml, P < 0.01). No response was observed when the SPDa insulin infusion was not turned off (peak change within 5-10 min = 44 ± 85 pg/ml, P = NS; and peak change within 15-20 min = 67 ± 97 pg/ml, P = NS) or when saline instead of insulin was infused and then switched off (peak change within 5-10 min = -44 ± 108 pg/ml, P = NS; and peak change within 15-20 min = -13 ± 43 pg/ml, P = NS). No responses were observed during euglycemia (peak change within 5-10 min = 48 ± 35 pg/ml, P = NS; and peak change within 15-20 min = 259 ± 129 pg/ml, P = NS) or hyperglycemia (peak change within 5-10 min = 49 ± 62 pg/ml, P = NS; and peak change within 15-20 min = 138 ± 87 pg/ml, P = NS). Thus, the glucagon response to hypoglycemia that was absent in rats made diabetic by STZ was restored by regional infusion and then discontinuation of insulin. These data provide direct in vivo support for the β-cell "switch-off" hypothesis and indicate that the α-cell is not intrinsically abnormal in insulin-dependent diabetes because of STZ-induced destruction of β-cells. [ABSTRACT FROM AUTHOR]

The "switch-off" hypothesis to explain β-cell regulation of α-cell function during hypoglycemia has not been assessed previously in isolated islets, largely because they characteristically do not respond to glucose deprivation by secreting glucagon. We examined this hypothesis using normal human and Wistar rat islets, as well as islets from streptozotocin (STZ)-administered β-celldeficient Wistar rats. As expected, islets perifused with glucose and 3-isobutryl-1-methylxanthine did not respond to glucose deprivation by increasing glucagon secretion. However, if normal rat islets were first perifused with 16.7 mmol/l glucose to increase endogenous insulin secretion, followed by discontinuation of the glucose perifusate, a glucagon response to glucose deprivation was observed (peak change within 10 min after switch off = 61 ± 15 pg/ml [mean ± SE], n = 6, P < 0.01). A glucagon response from normal human islets using the same experimental design was also observed. A glucagon response (peak change within 7 rain after switch off = 31 ± 1 pg/ml, n = 3, P < 0.01) was observed from β-cell-depleted, STZ-induced diabetic rats whose islets still secreted small amounts of insulin. However, when these islets were first perifused with both exogenous insulin and 16.7 mmol/l glucose, followed by switching off both the insulin and glucose perifusate, a significantly larger (P < 0.05) glucagon response was observed (peak change within 7 min after switch off = 71 ± 11 pg/ml, n = 4, P < 0.01). This response was not observed if the insulin perifusion was not switched off when the islets were deprived of glucose or when insulin was switched off without glucose deprivation. These data uniquely demonstrate that both normal, isolated islets and islets from STZ-administered rats can respond to glucose deprivation by releasing glucagon if they are first provided with increased endogenous or exogenous insulin. These results fully support the β-cell switch-off hypothesis as a key mechanism for the α-cell response to hypoglycemia. [ABSTRACT FROM AUTHOR]

beta-Cell replacement in diabetes using pancreatic islets or beta-cell surrogates is a research area undergoing intense scrutiny. Once this approach is demonstrated to be reproducibly successful, the next major issue will be the length of time that success will be sustained. Whole and segmental pancreas transplants are now successful for up to two decades. Study of these grafts can provide insight into and predictions about beta-cell function and reserve when islet transplantation becomes a routine. The studies described herein investigated 102 human whole and segmental transplant recipients and control subjects to address the following five questions. 1) Is the usual reciprocal relationship between the acute insulin response to intravenous glucose (AIR(gluc)) and the level of fasting plasma glucose (FPG) maintained in pancreas transplant recipients? 2) Do recipients who have no AIR(gluc) have an acute insulin response to intravenous arginine (AIR(arg))? 3) Do recipients of whole pancreata from cadaveric donors have twice the amount of insulin secretory reserve as that found in recipients of 50% segmental grafts from living, related donors? 4) What clinically accessible measure of insulin secretion best correlates with glucose potentiation of arginine-induced insulin secretion (GPAIS)? 5) Do successful pancreas transplant recipients evince time-dependent declines in beta-cell function and glycemic regulation when studied long term and longitudinally? The results demonstrate that 1) the normal relationship between AIR(gluc) and fasting glucose levels is maintained despite systemic venous drainage of allografts and consequent hyperinsulinemia; 2) AIR(gluc) and AIR(arg) decrease in parallel as fasting glucose levels rise, although AIR(arg) is still present after AIR(gluc) disappears; 3) AIR(arg) and AIR(gluc) are strongly predictive of beta-cell mass; 4) AIR(arg) and AIR(gluc) are strongly predictive of insulin secretory reserve; and 5) transplant recipients who have successfully maintained normoglycemia for an average of 10 years and up to 22 years nonetheless experience time-related declines in beta-cell function. [ABSTRACT FROM AUTHOR]

β-Cell replacement in diabetes using pancreatic islets or β-cell surrogates is a research area undergoing intense scrutiny. Once this approach is demonstrated to be reproducibly successful, the next major issue will be the length of time that success will be sustained. Whole and segmental pancreas transplants are now successful for up to two decades. Study of these grafts can provide insight into and predictions about β-cell function and reserve when islet transplantation becomes a routine. The studies described herein investigated 102 human whole and segmental transplant recipients and control subjects to address the following five questions. 1) Is the usual reciprocal relationship between the acute insulin response to intravenous glucose (AIR[subgluc]) and the level of fasting plasma glucose (FPG) maintained in pancreas transplant recipients? 2) Do recipients who have no AIR[gluc] have an acute insulin response to intravenous arginine (AIR[arg])? 3) Do recipients of whole pancreata from cadaveric donors have twice the amountof insulin secretory reserve as that found in recipientsof 50% segmental grafts from living, related donors? 4)What clinically accessible measure of insulin secretion best correlates with glucose potentiation of arginine-induced insulin secretion (GPAIS)? 5) Do successful pancreas transplant recipients evince time-dependent declines in β-cell function and glycemic regulation when studied long term and longitudinally? The results demonstrate that 1) the normal relationship between AIR[subgluc]and fasting glucose levels is maintained despite systemic venous drainage of allografts and consequent hyperinsulinemia; 2) AIR[subgluc] and AIR[subarg] decrease in parallel as fasting glucose levels rise, although AIR[subarg] is still present after AIR[subgluc] disappears; 3) AIR[subarg] andAIR[subgluc] are strongly predictive of β-cell mass; 4) AIR[subarg]and AIR[subgluc] are strongly predictive of insulin secretory reserve; an... [ABSTRACT FROM AUTHOR]

The relentless decline in beta-cell function frequently observed in type 2 diabetic patients, despite optimal drug management, has variously been attributed to glucose toxicity and lipotoxicity. The former theory posits hyperglycemia, an outcome of the disease, as a secondary force that further damages beta-cells. The latter theory suggests that the often-associated defect of hyperlipidemia is a primary cause of beta-cell dysfunction. We review evidence that patients with type 2 diabetes continually undergo oxidative stress, that elevated glucose concentrations increase levels of reactive oxygen species in beta-cells, that islets have intrinsically low antioxidant enzyme defenses, that antioxidant drugs and overexpression of antioxidant enzymes protect beta-cells from glucose toxicity, and that lipotoxicity, to the extent it can be attributable to hyperlipidemia, occurs only in the context of preexisting hyperglycemia, whereas glucose toxicity can occur in the absence of hyperlipidemia. [ABSTRACT FROM AUTHOR]

The relentless decline in β-cell function frequently observed in type 2 diabetic patients, despite optimal drug management, has variously been attributed to glucose toxicity and lipotoxicity. The former theory posits hyperglycemia, an outcome of the disease, as a secondary force that further damages β-cells. The latter theory suggests that the often-associated defect of hy- perlipidemia is a primary cause of β-cell dysfunction. We review evidence that patients with type 2 diabetes continually undergo oxidative stress, that elevated glucose concentrations increase levels of reactive oxygen species in β-cells, that islets have intrinsically low antioxidant enzyme defenses, that antioxidant drugs and overexpression of antioxidant enzymes protect β-cells from glucose toxicity, and that lipotoxicity, to the extent it can be attributable to hyperlipidemia, occurs only in the context of preexisting hyperglycemia, whereas glucose toxicity can occur in the absence of hyperlipid- emia. Diabetes 53 (Suppl. 1):S119-S124, 2004 [ABSTRACT FROM AUTHOR]

Donors undergoing hemi-pancreatectomy to provide a pancreas segment for transplantation into a relative with type 1 diabetes acquire diminished insulin and glucagon responses to intravenous agonists. Some donors develop diabetes and require treatment for hyperglycemia. They become at risk for hypoglycemia when treatment includes sulfonylureas and insulin. However, no studies assessing the impact of hemi-pancreatectomy in humans on islet alpha-cell responses to hypoglycemia have been reported. Consequently, we performed stepped hypoglycemic clamps in 7 donors of varying glycemic control and compared their responses to 16 control subjects. Donors and control subjects reached similar nadirs of glycemia (45 +/- 3 and 41 +/- 1 mg/dl, respectively) during the clamp. The donors had significantly higher mean basal glucagon levels than control subjects (203 +/- 27 vs. 135 +/- 15 pg/ml; P < 0.03) but did not have significant differences in glucagon responses during the clamp. The donors also had significantly higher mean peak epinephrine responses during the clamp (1,231 +/- 134 vs. 730 +/- 68 pg/ml; P < 0.002), but there were no statistically significant differences in norepinephrine or symptom responses. The glucose thresholds at which hormonal and symptom responses began were not different. We conclude that although glucagon response to arginine and insulin response to glucose and arginine are diminished after hemi-pancreatectomy, no deficiency in glucagon responses were detected during hypoglycemia. [ABSTRACT FROM AUTHOR]

Chronic exposure to hyperglycemia can lead to cellular dysfunction that may become irreversible over time, a process that is termed glucose toxicity. Our perspective about glucose toxicity as it pertains to the pancreatic β-cell is that the characteristic decreases in insulin synthesis and secretion are caused by decreased insulingene expression. The responsible metabolic lesion appears to involve a posttranscriptional defect in pancreas duodenum homeobox-1 (PDX-1) mRNA maturation. PDX-1 is a critically important transcription factor for the insulin promoter, is absent in glucotoxic islets, and, when transfected into glucotoxic β-cells, improves insulin promoter activity. Because reactive oxygen species are produced via oxidative phosphorylation during anaerobic glycolysis, via the Schiff reaction during glycation, via glucose autoxidation, and via hexosamine metabolism under supraphysiological glucose concentrations, we hypothesize that chronic oxidative stress is an important mechanism for glucose toxicity. Support for this hypothesis is found in the observations that high glucose concentrations increase intraislet peroxide levels, that islets contain very low levels of antioxidant enzyme activities, and that adenoviral overexpression of antioxidant enzymes in vitro in islets, as well as exogenous treatment with antioxidants in vivo in animals, protect the islet from the toxic effects of excessive glucose levels. Clinically, consideration of antioxidants as adjunct therapy in type 2 diabetes is warranted because of the many reports of elevated markers of oxidative stress in patients with this disease, which is characterized by imperfect management of glycemia, consequent chronic hyperglycemia, and relentless deterioration of β-cell function. [ABSTRACT FROM AUTHOR]

Islet allotransplantation can provide prolonged insulin independence in selected individuals with type 1 diabetes. Whether islet transplantation also restores hypoglycemic counterregulation is unclear. To determine if hypoglycemic counterregulation is restored by islet transplantation, we studied hormone responses and hypoglycemic symptom recognition in seven insulin-independent islet transplant recipients using a 3-h stepped hypoglycemic clamp, and compared their responses to those of nontransplanted type 1 diabetic subjects and nondiabetic control subjects. Glucagon responses of islet transplant recipients to hypoglycemia were significantly less than that observed in control subjects (incremental glucagon [mean +/- SE]: -12 +/- 12 vs. 64 +/- 22 pg/ml, respectively; P < 0.05), and not significantly different from that of nontransplanted type 1 diabetic subjects (-17 +/- 10 pg/ml). Epinephrine responses and symptom recognition were also not restored by islet transplantation (incremental epinephrine [mean +/- SE]: 195 +/- 128 [islet transplant recipients] vs. 238 +/- 73 [type 1 diabetic subjects] vs. 633 +/- 139 pg/ml [nondiabetic control subjects], P < 0.05 vs. control; peak symptom scores: 3.3 +/- 0.9 [islet transplant recipients] vs. 3.1 +/- 1.1 [type 1 diabetic subjects] vs. 6.7 +/- 0.8 [nondiabetic control subjects]). Thus the results indicate that despite providing prolonged insulin independence and near-normal glycemic control in these patients with long-standing type 1 diabetes, hypoglycemic hormonal counterregulation and symptom recognition were not restored by intrahepatic islet transplantation. [ABSTRACT FROM AUTHOR]

Determines the role of glutathione peroxidase in protecting pancreatic Β cells against oxidative stress. Inhibition of glutamylcysteine synthetase by buthionine sulfoximine; Increase of intracellular oxidant load in human islets; Adverse consequences of ribose-induced oxidative stress on insulin messenger RNA.

Previous work has suggested that functional interrelationships may exist between inhibition of insulin secretion by interleukin (IL)-1beta and the endogenous synthesis of prostaglandin E(2) (PGE(2)) in the pancreatic islet. These studies were performed to ascertain the relative abundance of E prostaglandin (EP) receptor mRNAs in tissues that are major targets, or major degradative sites, of insulin; to identify which EP receptor type mediates PGE(2) inhibition of insulin secretion in pancreatic islets; and to examine possible sites of action through which sodium salicylate might affect IL-1beta/PGE(2) interactions. Real-time fluorescence-based RT-PCR indicated that EP3 is the most abundant EP receptor type in islets, liver, kidney, and epididymal fat. EP3 mRNA is the least, whereas EP2 mRNA is the most, abundant type in skeletal muscle. Misoprostol, an EP3 agonist, inhibited glucose-induced insulin secretion from islets, an event that was prevented by preincubation with pertussis toxin, by decreasing cAMP. Electromobility shift assays demonstrated that sodium salicylate inhibits IL-1beta-induced nuclear factor-kappaB (NF-kappaB) activation. Sodium salicylate also prevented IL-1beta from inducing EP3 and cyclooxygenase (COX)-2 gene expression in islets and thereby prevented IL-1beta from inhibiting glucose-induced insulin secretion. These findings indicate that the sites of action through which sodium salicylate inhibits these negative effects of IL-1beta on beta-cell function include activation of NF-kappaB as well as generation of PGE(2) by COX-2. [ABSTRACT FROM AUTHOR]

Type 2 diabetes is caused by a combination of beta-cell dysfunction and insulin resistance. Over time, hyperglycemia worsens, a phenomenon that has been attributed to deleterious effects of chronic hyperglycemia (glucotoxicity) or chronic hyperlipidemia (lipotoxicity) on beta-cell function and is often accompanied by increased islet triacylglycerol (TAG) content and decreased insulin gene expression. To examine these two potentially pathogenic forces, we studied Zucker rats (leptin receptor wild type, +/+; heterozygous, +/-; and mutant, -/-). First, +/+ and +/- Zucker rats were compared metabolically. At 6 weeks of age, the +/- rats had a lower level of islet insulin mRNA compared with +/+. At 12 weeks of age, differences were found in body weight and islet TAG content; however, levels of insulin mRNA were equivalent. Second, we examined whether worsening of the diabetic state in the homozygous mutant (-/-) Zucker diabetic fatty (ZDF) rat is related more to chronic hyperglycemia or to hyperlipidemia. The ZDF rats were treated for 6 weeks with either bezafibrate, a lipid-lowering drug that does not affect plasma glucose levels, or phlorizin, a drug that reduces plasma glucose without lowering lipid levels. Bezafibrate treatment lessened the rise in plasma TAG observed in nontreated rats (239 +/- 16 vs. 388 +/- 36 mg/dl, treated versus nontreated; P < 0.0001) but did not prevent the rise in fasting plasma glucose. Despite lowering plasma TAG, bezafibrate was not effective in preventing an increased islet TAG content and did not prevent the associated decrease in insulin mRNA levels. Phlorizin treatment prevented hyperglycemia (61 +/- 2 vs. 145 +/- 7 mg/dl, treated versus nontreated; P < 0.0001) and lowered islet TAG content (32.7 +/- 0.7 vs. 47.8 +/- 2.7 ng/islet, treated versus nontreated; P < 0.0001) and preserved insulin mRNA levels without preventing hypertriglyceridemia. Plasma free fatty acid level did not correlate with changes in islet TAG or insulin mRNA levels. We conclude that antecedent elevated plasma glucose levels, not plasma lipid levels, are associated with elevated islet TAG content and decreased insulin mRNA levels in ZDF animals. [ABSTRACT FROM AUTHOR]

Patients with chronic pancreatitis who undergo total pancreas resection inevitably become diabetic unless their islets are autotransplanted to prevent diabetes. We studied patients who underwent this procedure to assess its long-term efficacy in providing stable glucose regulation. Six patients were followed for up to 13 (6.2 +/- 1.7) years after intrahepatic islet autotransplantation. From 290,000 to 678,000 islets were transplanted and no patients received drugs to control glucose levels postoperatively. Islet function was assessed by measurements of fasting plasma glucose (FPG), intravenous glucose disappearance rate (KG), HbA1c, insulin responses to intravenous glucose and to arginine, and insulin secretory reserve. Patients were studied two to four times each to obtain longitudinal data. Five of six patients remained free of insulin treatment and maintained FPG <126 mg/dl and HbA1c levels <6.5%. As a group, they maintained stable insulin secretory reserve, but insulin responses to glucose tended to decrease over time in three patients. KG values correlated significantly with the number of islets originally transplanted. These data indicate that intrahepatic autoislet transplantation can successfully maintain stable beta-cell function and normal levels of blood glucose and HbA1c for up to 13 years after total pancreatectomy as treatment for chronic painful pancreatitis. This usually overlooked procedure of intrahepatic islet transplantation designed to prevent diabetes in patients undergoing pancreatectomy for chronic pancreatitis should be considered more often. [ABSTRACT FROM AUTHOR]

Reports on islet cells or pancreas transplantation for patients with diabetes. History; Techniques; Clinical results; Risk-benefit relationship of successful pancreas and pancreatic islet transplantation in hyperglemic patients with long-standing diabetes.

Historically, patients with diabetes have expanded tremendous effort in pursuing a return to normoglycemia. The relatively recent results of the Diabetes Control and Complications Trial, demonstrating an approximate 50% reduction in eye, nerve, and kidney complications in a group of patients receiving intensive treatment for hyperglycemia, have made this pursuit even more intense. Successful pancreas and islet transplantations are currently the only therapies that reproducibly achieve normoglycemia by reestablishing endogenous insulin secretion responsive to normal feedback regulation.

Chronic exposure of pancreatic islet beta-cell lines to supraphysiologic glucose concentrations causes defects in insulin gene expression and insulin secretion. To determine whether these in vitro phenomena have pathophysiologic relevance in vivo, we studied the Zucker diabetic fatty (ZDF) rat, an animal model of type 2 diabetes. The ZDF animals had relatively higher levels of glycemia and islet insulin mRNA at 6 weeks of age than age-matched Zucker lean control (ZLC) rats. As glycemia increased in 12- and 16-week-old ZDF rats, we observed decrements in glucose-induced insulin secretion during static incubations of pancreatic islets and in insulin mRNA levels, PDX-1 mRNA levels, and PDX-1 protein binding to the insulin promoter compared with age-matched ZLC rats and 6-week-old ZDF rats. To determine whether normalization of blood glucose levels would prevent these defects, ZDF rats were treated with troglitazone beginning at 6 weeks of age. Troglitazone prevented ZDF rats from becoming hyperglycemic and preserved glucose-induced insulin responses. Furthermore, troglitazone-treated ZDF animals had greater levels of insulin and PDX-1 mRNAs compared with untreated ZDF animals of the same ages at 12 and 16 weeks. Our results demonstrate that chronic and progressive hyperglycemia resulting from type 2 diabetes in ZDF rats is associated with loss of insulin and PDX-1 mRNAs and loss of glucose-stimulated insulin secretion. Prevention of hyperglycemia prevented the associated defects in insulin and PDX-1 gene expression and improved insulin secretion. These findings provide the first in vivo evidence that prevention of progressive hyperglycemia in a model of type 2 diabetes preserves insulin and PDX-1 gene expression. [ABSTRACT FROM AUTHOR]

Pancreas transplantation is a controversial form of therapy for type I diabetes. A major obstacle to acceptance of this procedure for many physicians is the lack of demonstrable long-term success. We performed these studies to assess the hypothesis that successful pancreas transplantation is efficacious in normalizing endogenous insulin secretion and glycemia in the long term (1-2 decades). Sixteen patients with a history of diabetic complications who had undergone a transplant 10-18 years earlier involving either a whole or a segment of pancreas were recruited for measurements of fasting plasma glucose, HbA1c, intravenous glucose tolerance, and insulin secretory reserve. All patients were taking immunosuppressive drugs, but none was using insulin or other hypoglycemic agents. All recipients had normal levels of fasting blood glucose, intravenous glucose tolerance, and HbA1c, and 15 of 16 stated that their quality of life had improved after transplantation. They had intact acute insulin responses to intravenous pulses of glucose and to arginine and insulin secretory reserve. Glucose potentiation of arginine-induced insulin secretion, the measure of insulin secretory reserve, correlated significantly (r = 0.095, P < 0.001) with the acute insulin response to intravenous glucose, rendering the latter a much simpler and valid measure of functional beta-cell mass. We conclude that successful pancreas transplants are efficacious for periods as long as 1-2 decades in returning euglycemia to type 1 diabetic patients by restoring endogenous insulin secretion and insulin secretory reserve. Thus, concern about long-term deterioration, as distinct from rejection, should not be a major obstacle when deciding whether to recommend pancreas transplantation. [ABSTRACT FROM AUTHOR]