Showing papers in "International Journal of Experimental Diabetes Research in 2001"
TL;DR: It is shown that early growth retardation due to maternal protein restriction leads to the development of diabetes in old male rat offspring, which is predominantly associated with insulin resistance.
Abstract: Restricted fetal growth is associated with increased risk for the future development of Type 2 diabetes in humans. The study aim was to assess the glucose tolerance of old (seventeen months) male rats, which were growth restricted in early life due to maternal protein restriction during gestation and lactation. Rat mothers were fed diets containing either 20% or 8% protein and all offspring weaned onto a standard rat diet. In old-age fasting plasma glucose concentrations were significantly higher in the low protein offspring: 8.4 (1.3)mmol/l v. 5.3 (1.3)mmol/l (p = 0.005), Areas under the curves were increased by 67% for glucose (p = 0.01) and 81% for insulin (p = 0.01) in these rats in intravenous glucose tolerance tests, suggesting (a degree of) insulin resistance. These results show that early growth retardation due to maternal protein restriction leads to the development of diabetes in old male rat offspring. The diabetes is predominantly associated with insulin resistance.
273 citations
TL;DR: Evidence indicates that BDNF activates the sympathetic nervous system via the central nervous system and regulates energy expenditure in obese diabetic animals.
Abstract: It has been previously demonstrated that brain-derived neurotrophic factor (BDNF) regulates glucose metabolism and energy expenditure in rodent diabetic models such as C57BL/KsJ-leprdb/leprdb (db/db) mice Central administration of BDNF has been found to reduce blood glucose in db/db mice, suggesting that BDNF acts through the central nervous system In the present study we have expanded these investigations to explore the effect of central administration of BDNF on energy metabolism Intracerebroventricular administration of BDNF lowered blood glucose and increased pancreatic insulin content of db/db mice compared with vehicle-treated pellet pair-fed db/db mice While body temperatures of the pellet pair-fed db/db mice given vehicle were reduced because of restricted food supply in this pair-feeding condition, BDNF treatment remarkably alleviated the reduction of body temperature suggesting the enhancement of thermogenesis BDNF enhanced norepinephrine turnover and increased uncoupling protein-1 mRNA expression in the interscapular brown adipose tissue Our evidence indicates that BDNF activates the sympathetic nervous system via the central nervous system and regulates energy expenditure in obese diabetic animals
116 citations
TL;DR: Fenugreek extracts had no effect on basal levels of glycogen phosphorylase a (HGPa) activity in rat hepatocyte suspensions and caused a marginal but statistically significant inhibition of glucagon induction of this enzyme suggesting a glucagon-antagonist effect.
Abstract: Fenugreek (Trigonella foenum-graecum L. seed) is a food with traditional medicinal use in diabetes. Beneficial effects have been demonstrated in diabetic animals and both insulin-dependent and non-insulin-dependent diabetic subjects. Effects of a lipid extract A, crude ethanolic extract B, further sub-fractions of B (saponin-free C, saponin D and sapogenin E) and a gum fibre fraction F on intestinal sodium-dependent glucose uptake were investigated in vitro using rabbit intestinal brush border membrane vesicles. All fractions except A inhibited glucose-uptake at 0.33 and/or 3.3 mg/mL (p < 0.001). Greatest inhibition was observed with fractions D and E. Diosgenin and trigonelline (compounds reported in fenugreek) also inhibited glucose-uptake (IC50 values approximately 3 mg/ml, equivalent to 8 mM and 19 mM respectively) but did not account for the activity of the crude extracts. Fenugreek extracts had no effect on basal levels of glycogen phosphorylase a (HGPa) activity in rat hepatocyte suspensions. However fractions C and E caused a marginal but statistically significant inhibition (18.9 and 15.1% respectively, p < 0.05) of glucagon induction of this enzyme suggesting a glucagon-antagonist effect. Diosgenin (1.65 mg/ml; 4 mM) inhibited glucagon-induced HGPa activity by 20% (p < 0.05), and was more effective than trigonelline (non significant inhibition of 9.4% at 1.65 mg/ml, 10 mM).
90 citations
TL;DR: It is concluded that hrC-peptide exerts a dose dependent protection on type 1 diabetic neuropathy in rats and that this effect is probably mediated by the partially conserved sequence of the active C-terminal pentapeptide.
Abstract: In order to explore the neuroprotective and crossspecies activities of.C-peptide on type 1 diabetic neuropathy, spontaneously diabetic BB/W-rats were given increasing doses of human recombinant Cpeptide (hrC-peptide). Diabetic rats received 10, 100, 500, or 1000 μg of hrC-peptide/kg body weight/ day from onset of diabetes. After 2 months of hrC-peptide administration, 100 μg and greater doses completely prevented the nerve conduction defect, which was associated with a significant but incomplete prevention of neural Na+/K+-ATPase activity in diabetic rats with 500 μg or greater C-peptide replacement. Increasing doses of hrC-peptide showed increasing prevention of early structural abnormalities such as paranodal swelling and axonal degeneration and an increasing frequency of regenerating sural nerve fibers. We conclude that hrC-peptide exerts a dose dependent protection on type 1 diabetic neuropathy in rats and that this effect is probably mediated by the partially conserved sequence of the active C-terminal pentapeptide
60 citations
TL;DR: Type 1 (insulin-dependent) diabetes mellitus, like other organ specific autoimmune diseases, results from a disorder of immunoregulation, and several approaches are being tested or under consideration for clinical trials to prevent or arrest complete autoimmune destruction of islet ß cells and insulin-dependent diabetes.
Abstract: Type 1 (insulin-dependent) diabetes mellitus, like other organ specific autoimmune diseases, results from a disorder of immunoregulation. T cells specific for pancreatic islet s cell constituents (autoantigens) exist normally but are restrained by regulatory mechanisms (self-tolerant state). When regulation fails, s cell-specific autoreactive T cells become activated and expand clonally. Current evidence indicates that islet s cell-specific autoreactive T cells belong to a T helper 1 (Th1) subset, and these Th1 cells and their characteristic cytokine products, IFNγ and IL-2, are believed to cause islet inflammation (insulitis) and s cell destruction. Immune-mediated destruction of s cells precedes hyperglycemia and clinical symptoms by many years because these become apparent only when most of the insulin-secreting s cells have been destroyed. Therefore, several approaches are being tested or are under consideration for clinical trials to prevent or arrest complete autoimmune destruction of islet s cells and insulin-dependent diabetes. Approaches that attempt to correct underlying immunoregulatory defects in autoimmune diabetes include interventions aimed at i) deleting s cell autoreactive Th1 cells and cytokines (IFNγ and IL-2) and/or ii) increasing regulatory Th2 cells and/or Th3 cells and their cytokine products (IL-4, IL-10 and TGFsI).
53 citations
TL;DR: The present findings suggest that nateglinide may exert a more physiologic effect on insulin secretion than comparator agents and thereby have less propensity to elicit hypoglycemia in vivo.
Abstract: Nateglinide, a novel D-phenylalanine derivative, stimulates insulin release via closure of KATP channels in pancreatic β-cell, a primary mechanism of action it shares with sulfonylureas (SUs) and repaglinide. This study investigated (1) the influence of ambient glucose levels on the insulinotropic effects of nateglinide, glyburide and repaglinide, and (2) the influence of the antidiabetic agents on glucose-stimulated insulin secretion (GSIS) in vitro from isolated rat islets. The EC50 of nateglinide to stimulate insulin secretion was 14 μM in the presence of 3mM glucose and was reduced by 6-fold in 8mM glucose and by 16-fold in 16mM glucose, indicating a glucose-dependent insulinotropic effect. The actions of glyburide and repaglinide failed to demonstrate such a glucose concentration-dependent sensitization. When tested at fixed and equipotent concentrations (~2x EC50 in the presence of 8mM glucose) nateglinide and repaglinide shifted the EC50s for GSIS to the left by 1.7mM suggesting an enhancement of islet glucose sensitivity, while glimepiride and glyburide caused, respectively, no change and a right shift of the EC50. These data demonstrate that despite a common basic mechanism of action, the insulinotropic effects of different agents can be influenced differentially by ambient glucose and can differentially influence the islet responsiveness to glucose. Further, the present findings suggest that nateglinide may exert a more physiologic effect on insulin secretion than comparator agents and thereby have less propensity to elicit hypoglycemia in vivo.
38 citations
TL;DR: While SAM may enhance the secretory potential of non-metabolized secretagogues, it may also serve as a preferential metabolic fuel in preference to other important physiological nutrients and compromise pancreatic beta cell function following prolonged exposure.
Abstract: Esters of succinic acid are potent insulin secretagogues, and have been proposed as novel antidiabetic agents for type 2 diabetes. This study examines the effects of acute and chronic exposure to succinic acid monomethyl ester (SAM) on insulin secretion, glucose metabolism and pancreatic beta cell function using the BRIN-BD11 cell line. SAM stimulated insulin release in a dose-dependent manner at both non-stimulatory (1.1mM) and stimulatory (16.7mM) glucose. The depolarizing actions of arginine also stimulated a significant increase in SAM-induced insulin release but 2-ketoisocaproic acid (KIC) inhibited SAM induced insulin secretion indicating a possible competition between the preferential oxidative metabolism of these two agents. Prolonged (18hour) exposure to SAM revealed decreases in the insulin-secretory responses to glucose, KIC, glyceraldehyde and alanine. Furthermore, SAM diminished the effects of nonmetabolized secretagogues arginine and 3-isobutyl-1-methylxanthine (IBMX). While the ability of BRIN-BD11 cells to oxidise glucose was unaffected by SAM culture, glucose utilization was substantially reduced. Collectively, these data suggest that while SAM may enhance the secretory potential of non-metabolized secretagogues, it may also serve as a preferential metabolic fuel in preference to other important physiological nutrients and compromise pancreatic beta cell function following prolonged exposure.
30 citations
TL;DR: The marked elevation of plasma leptin in obese SHR/N-cp rats suggests that obesity in this animal model is related to up-regulation of the ob gene and that hyperleptinemia is closely associated with several metabolic risk factors related to insulin resistance in the diabesity syndrome.
Abstract: The spontaneously hypertensive/NIH-corpulent (SHR/N-cp) rat is a genetic animal model that exhibits obesity, metabolic features of hyperinsulinemia, hyperglycemia, and hyperlipidemia, which are characteristic of type II diabetes and mild hypertension. To determine the role of leptin, the protein product of the ob gene, in the development of obesity and diabetes in this model, we measured steady-state circulating levels of leptin in obese and lean SHR/N-cp rats and examined the relation between plasma leptin levels and metabolic variables at the stage of established obesity in these animals. Mean fasting plasma leptin concentration was 8-fold higher in obese than in lean rats (p<0.01). This was associated with a 6-fold elevation in plasma insulin in the obese group. Fasting levels of plasma glucose, cholesterol, and triglyceride were all significantly higher in obese rats than in lean controls. Spearman correlation analysis showed a significant positive correlation between plasma leptin concentration and body weight among the animals (r=0.73, p<0.01). Similarly, plasma insulin concentration was significantly correlated with BW in all animals (r=0.54, p<0.05). There was also a significant positive.correlation between plasma leptin and plasma insulin in the entire group (r=0.70, p<0.01). However, this relationship was significant only for lean rats but not for obese rats (r=0.59, p<0.05 for lean rats, and r=0.23, p=NS, for obese rats). Plasma leptin also correlated positively with fasting plasma glucose (r=0.75, p<0.05), total cholesterol (r=0.63, p<0.05), and triglyceride (r=0.67, p <0.05). The marked elevation of plasma leptin in obese SHR/N-cp rats suggests that obesity in this animal model is related to up-regulation of the ob gene. Circulating leptin appears to be one of the best biological markers of obesity and that hyperleptinemia is closely associated with several metabolic risk factors related to insulin resistance in the diabesity syndrome.
27 citations
TL;DR: The reduction in the nuclear to cytoplasmic ratio of GK, an index of nuclear export, correlated with a >50% increase in glycogen cytochemical fluorescence over a 60min stimulation period, suggesting that a compartmentalization exists of both active GK and the initial sites of glycogen deposition at the hepatocyte surface.
Abstract: Hepatic glucokinase (GK) is acutely regulated by binding to its nuclear-anchored regulatory protein (GKRP). Although GK release by GKRP is tightly coupled to the rate of glycogen synthesis, the nature of this association is obscure. To gain insight into this coupling mechanism under physiological stimulating conditions in primary rat hepatocytes, we analyzed the subcellular distribution of GK and GKRP with immunofluorescence, and glycogen deposition with glycogen cytochemical fluorescence, using confocal microscopyand quantitative image analysis. Following stimulation, a fraction of the GK signal translocated from the nucleus to the cytoplasm. The reduction in the nuclear to cytoplasmic ratio of GK, an index of nuclear export, correlated with a >50% increase in glycogen cytochemical fluorescence over a 60min stimulation period. Furthermore, glycogen accumulation was initially deposited in a peripheral pattern in hepatocytes similar to that of GK. These data suggest that a compartmentalization exists of both active GK and the initial sites of glycogen deposition at the hepatocyte surface.
21 citations
TL;DR: MAP kinase is important for INS-1 cell proliferation but not for its insulin secretory response with respect to major initiators and modulators of insulin release with respectTo investigate whether PI3-kinase and cellular tyrosine kinase are involved in G-protein mediated effects on MAP kinase, inhibitors were used.
Abstract: MAP (mitogen-activated protein) kinase (also called Erk 1/2) plays a crucial role in cell proliferation and differentiation. Its impact on secretory events is less well established. The interplay of protein kinase C (PKC), PI3-kinase and cellular tyrosine kinase with MAP kinase activity using inhibitors and compounds such as glucose, phorbol 12-myristate 13-acetate (PMA) and agonists of G-protein coupled receptors like gastrin releasing peptide (GRP), oxytocin (OT) and glucose-dependent insulinotropic peptide (GIP) was investigated in INS-1 cells, an insulin secreting cell line. MAP kinase activity was determined by using a peptide derived from the EGF receptor as a MAP kinase substrate and [32P]ATP. Glucose as well as GRP, OT and GIP exhibited a time-dependent increase in MAP kinase activity with a maximum at time point 2.5 min. All further experiments were performed using 2.5 min incubations. The flavone PD 098059 is known to bind to the inactive forms of MEK1 (MAPK/ERK-Kinase) thus preventing activation by upstream activators. 20 microM PD 098059 (IC50 = 5 microM) inhibited MAP kinase stimulated by either glucose, GRP, OT, GIP or PMA. Inhibiton ("downregulation") of PKC by a long term (22 h) pretreatment with 1 microM PMA did not influence MAP kinase activity when augmented by either of the above mentioned compound. To investigate whether PI3-kinase and cellular tyrosine kinase are involved in G-protein mediated effects on MAP kinase, inhibitors were used: 100 nM wortmannin (PI3-kinase inhibitor) reduced the effects of GRP, OT and GIP but not that of PMA; 100 microM genistein (tyrosine kinase inhibitor) inhibited the stimulatory effect of either above mentioned compound on MAP kinase activation. Inhibition of MAP kinase by 20 microM PD 098059 did not influence insulin secretion modulated by either compound (glucose, GRP, OT or GIP). [3H]Thymidine incorporation, however, was severely inhibited by PD 098059. Thus MAP kinase is important for INS-1 cell proliferation but not for its insulin secretory response with respect to major initiators and modulators of insulin release. The data indicate that MAP kinase is active and under the control of MAP kinase. PKC is upstream of a genistein-sensitive tyrosine kinase and probably downstream of a PI3-kinase in INS-1 cells.
21 citations
TL;DR: The Israeli desert gerbil Psammomys obesus illustrates the probable antecedents of the development of worldwide diabetes epidemic in human populations emerging from food scarcity to nutritional affluence, inappriopriate to their metabolic capacity.
Abstract: Albert Renold strived to gain insight into the abnormalities of human diabetes by defining the pathophysiology of the disease peculiar to a given animal. He investigated the Israeli desert-derived spiny mice (Acomys cahirinus), which became obese on fat-rich seed diet. After a few months hyperplasia and hypertrophy of β-cells occurred leading to a sudden rupture, insulin loss and ketosis. Spiny mice were low insulin responders, which is probably a characteristic of certain desert animals, protecting against insulin oversecretion when placed on an abundant diet. We have compared the response to overstimulation of several mutant diabetic species and nutritionally induced nonmutant animals when placed on affluent diet. Some endowed with resilient β-cells sustain long-lasting oversecretion, compensating for the insulin resistance, without lapsing into overt diabetes. Some with labile beta cells exhibit apoptosis and lose their capacity of coping with insulin resistance after a relatively short period. The wide spectrum of response to insulin resistance among different diabetes prone species seems to represent the varying response of human beta cells among the populations. In search for the molecular background of insulin resistance resulting from overnutrition we have studied the Israeli desert gerbil Psammomys obesus (sand rat), which progresses through hyperinsulinemia, followed by hyperglycemia and irreversible beta cell loss. Insulin resistance was found to be the outcome of reduced activation of muscle insulin receptor tyrosine kinase by insulin, in association with diminished GLUT4 protein and DNA content and overexpression of PKC isoenzymes, notably of PKCe. This overexpression and translocation to the membrane was discernible even prior to hyperinsulinemia and may reflect the propensity to diabetes in nondiabetic species and represent a marker for preventive action. By promoting the phosphorylation of serine/threonine residues on certain proteins of the insulin signaling pathway, PKCe exerts a negative feedback on insulin action. PKCe was also found to attenuate the activity of PKB and to promote the degradation of insulin receptor, as determined by co-incubation in HEK 293 cells. PKCe overexpression was related to the rise in muscle diacylglycerol and lipid content, which are prevalent on lascivious nutrition especially if fat-rich. Thus, Psammomys illustrates the probable antecedents of the development of worldwide diabetes epidemic in human populations emerging from food scarcity to nutritional affluence, inappriopriate to their metabolic capacity.
TL;DR: It is shown that the standard laboratory diet administered to Psammomys obesus (sand rat) from Beni Abbes in Algeria, induced a non-insulin dependant diabetes, characterised by increase of body weight as well as hyperinsulinemia, hyperglycemia and hypercholesterolemia.
Abstract: In this report, we have shown that the standard laboratory diet administered to Psammomys obesus (sand rat) from Beni Abbes in Algeria, induced a non-insulin dependant diabetes, characterised by increase of body weight (p<0.001) as well as hyperinsulinemia, hyperglycemia and hypercholesterolemia. In cultured aortic smooth muscle cells (SMC) of sand rats, type I and type III collagen biosynthesis and insulin effects, at low dose, on these parameters were investigated. In all experimental conditions of cultured SMC study, The α chains of type I collagen were analysed by immunoblotting in media and cells.
Metabolic radiolabelling and Immunochemical procedures revealed that, in diabetic state, synthetic SMC (SMCs) actively produce type I and III collagen which are synthesised in the cells and secreted in the medium; type I collagen was predominant as compared with type III collagen. Diabetes enhanced the collagen synthesis. Low dose of Insulin added to the medium, during 48h of incubation, induced a marked reduction in the synthesis of collagen types, especially type I collagen.
TL;DR: The results strongly indicate that the ICA reaction represents simultaneous autoimmunity against several other antigens beside GAD65, IA-2 and insulin.
Abstract: To study the antigens involved in the islet cell antibody (ICA) reaction we selected 30 patient serum samples (ten in each group) positive for ICA and one other additional autoantibody, such as glutamic acid decarboxylase antibodies (GADA), thyrosine phosphatase antibodies (IA-2A) or insulin autoantibodies (IAA). The serum samples were incubated with the specific antigen (GAD65, IA-2 or insulin) and the ICA analysis and the corresponding immunoprecipitation assay were performed before and after the absorption. We could then demonstrate that specific autoantibodies against GAD65 and IA-2 could be absorbed with the corresponding antigen, since ten GADA positive and six IA-2A samples turned completely negative. However, the ICA reaction after absorption with GADA, IA-2A and insulin was still present, although at significantly lower levels. The results strongly indicate that the ICA reaction represents simultaneous autoimmunity against several other antigens beside GAD65, IA-2 and insulin.
TL;DR: All isoforms of TGF-β are increased in the diabetic rat kidney and inducible gene H3 mRNA was increased 35% in theabetic animals, consistent with increased activity of this growth factor.
Abstract: Transforming growth factor beta (TGF-β) is a major promoter of diabetic nephropathy. While TGF-β1 is the most abundaft renal isoform, types 2 and 3 are present as well and have identical in vitro effects. Whole kidney extracts were studied 2 weeks after induction of streptozocin diabetes and in control rats. Mean glomerular area was 25% greater in the diabetic animals. TGF-β1 showed a 2-fold increase in message with a 3-fold increase in protein. TGF-β2 mRNA increased approximately 6% while its protein doubled. TGF-β-message increased by 25%, producing a 35% increase in its protein. TGF-β- inducible gene H3 mRNA was increased 35% in the diabetic animals, consistent with increased activity of this growth factor. All isoforms of TGF-β are increased in the diabetic rat kidney. Future studies need to address the specific role that each isoform plays in diabetic nephropathy as well as the impact of therapies on each isoform.
TL;DR: Since repletion of the insulin deficiency that is present in non-acidotic, ambulatory patients with new onset Type 1 diabetes did not alter serum leptin, these results argue against an effect of insulin on serum leptin in the absence of the acute diabetic ketoacidosis.
Abstract: Leptin, the gene product of adipose tissue that signals caloric plentitude via central nervous system receptors, may also have diverse peripheral metabolic actions. Of paramount interest has been the potential interaction(s) between leptin and insulin. Insofar as insulin alters leptin secretion/action (or vice versa), dysregulation of this system could contribute to disease states such as diabetes.
TL;DR: It is concluded that IM delivery of the insulin gene in the NOD mouse was able to prevent clinical DM up to 14 weeks in a majority of treated animals, and suggests that gene therapy may be an alternative treatment for IDDM in the future.
Abstract: Using the Adeno-associated virus (AAV) as a gene delivery vehicle, we have constructed a recombinant vector containing the full length rat preproinsulin gene (vLP-1). Utilizing the well described non-obese diabetic (NOD) mouse model, an experimental group (n=10) of animals were intramuscularly (IM) injected with 107 rAAV virions containing the insulin gene and compared to a mock-injected control group (n=10). Blood glucose (glc) was then measured weekly for 16 weeks. Data showed that the experimental group contained 70% euglycemic animals (defined as glc <200mg/dL) versus 10% of the control animals (P<.05) at 14 weeks. Mean weight in the treated group was greater than the untreated group. Insulin mRNA was detected at the injection site of all of the treated animals, but not controls. Complete destruction of islets was confirmed by histology ruling out the possibility of spontaneous reversal of insulinitis. We conclude that IM delivery of the insulin gene in the NOD mouse was able to prevent clinical DM up to 14 weeks in a majority of treated animals. Our experimental data suggests that gene therapy may be an alternative treatment for IDDM in the future.
TL;DR: Overall the galactosemic rat model is not closely parallel to the diabetic rat model in extra-ocular tissues, and prudence should be exercised in the use of experimentally galactOSEmic rats as a model for diabetes until the correspondence of the models has been more fully characterized.
Abstract: Rats fed a galactose-rich diet have been used for several years as a model for diabetes to study, particularly in the eye, the effects of excess blood hexoses. This study sought to determine the utility of galactosemia as a model for oxidative stress in extraocular tissues by examining biomarkers of oxidative stress in galactose-fed rats and experimentally-induced diabetic rats. Sprague-Dawley rats were divided into four groups: experimental control; streptozotocin-induced diabetic; insulin-treated diabetic; and galactose-fed. The rats were maintained on these regimens for 30 days, at which point the activities of catalase, glutathione peroxidase, glutathione reductase, and superoxide dismutase, as well as levels of lipid peroxidation and reduced and oxidized glutathione were determined in heart, liver, and kidney. This study indicates that while there are some similarities between galactosemic and diabetic rats in these measured indices of oxidative stress (hepatic catalase activity levels and hepatic and renal levels of oxidized glutathione in both diabetic and galactosemic rats were significantly decreased when compared to normal), overall the galactosemic rat model is not closely parallel to the diabetic rat model in extra-ocular tissues. In addition, several effects of diabetes (increased hepatic glutathione peroxidase activity, increased superoxide dismutase activity in kidney and heart, decreased renal and increased cardiac catalase activity) were not mimicked in galactosemic rats, and glutathione concentration in both liver and heart was affected in opposite ways in diabetic rats and galactose- fed rats. Insulin treatment reversed/prevented the activity changes in renal and cardiac superoxide dismutase, renal and cardiac catalase, and hepatic glutathione peroxidase as well as the hepatic changes in lipid peroxidation and reduced and oxidized glutathione, and the increase in cardiac glutathione. Thus, prudence should be exercised in the use of experimentally galactosemic rats as a model for diabetes until the correspondence of the models has been more fully characterized.
TL;DR: In this communication, the cellular, physiological and clinical effects of C-peptide replacement in animal models and in patients with type 1 diabetes are reviewed and recommendations are presented as to the most urgent studies that should be pursued.
Abstract: In recent years the physiological role of the proinsulin C-peptide has received increasing attention, focusing on the potential therapeutic value of C-peptide replacement in preventing and ameliorating type 1 diabetic complications. In order to consolidate these new data and to identify the immediate directions of C-peptide research and its clinical usefulness, an International Symposium was held in Detroit, Michigan, on October 20–21, 2000, under the auspices of the Wayne State University/Morris Hood Jr. Comprehensive Diabetes Center. In this communication, we review the cellular, physiological and clinical effects of C-peptide replacement in animal models and in patients with type 1 diabetes. Finally, recommendations are presented as to the most urgent studies that should be pursued to further establish the biological action of C-peptide and its therapeutic value.
TL;DR: The functional enhancement of electrofusion-derived surrogate β-cells that were re-cultured for 20 days after implantation and restoration of normoglycaemia indicates that the in vivo environment could greatly assist β-cell engineering approaches to therapy for diabetes.
Abstract: Electrofusion-derived BRIN-BD11 cells are glucosesensitive insulin-secreting cells which provide an archetypal bioengineered surrogate β-cell for insulin replacement therapy in diabetes mellitus, 5x106 BRIN-BD11 cells were implanted intraperitoneally into severely hyperglycaemic (>24mmol/l) streptozotocin-induced insulin-treated diabetic athymic nude (nu/nu) mice. The implants reduced hyperglycaemia such that insulin injections were discontinued by 5–16 days (<17mmol/l) and normoglycaemia (<9mmol/l) was achieved by 7–20 days. Implanted cells were removed after 28 days and re-established in culture. After re-culture for 20 days, glucose-stimulated (16.7mmol/l) insulin release was enhanced by 121% (p<0.001) compared to non-implanted cells. Insulin responses to glucagon-like peptide-1 (10−9mol/l), cholecystokinin-8 (10−8 mol/l) and L-alanine (10 mmol/l) were increased by 32%, 31% and 68% respectively (p<0.05–0.01). Insulin content of the cells was 148% greater at 20 days after re-culture than before implantation (p<0.001), but basal insulin release (at 5.6 mmol/l glucose) was not changed. After re-culture for 40 days, insulin content declined to 68% of the content before implantation (p<0.01), although basal insulin release was unchanged. However, the insulin secretory responses to glucose, glucagonlike peptide-1, cholecystokinin-8 and L-alanine were decreased after 40 days of re-culture to 65%, 72%, 73% and 42% respectively of the values before implantation (p<0.05–0.01). The functional enhancement of electrofusion-derived surrogate β-cells that were re-cultured for 20 days after implantation and restoration of normoglycaemia indicates that the in vivo environment could greatly assist β-cell engineering approaches to therapy for diabetes.
TL;DR: The insulinotropic efficacy of NAT in islets desensitized to SUs may result from a distinct receptor/effector mechanism, which contributes to the unique pharmacological profile of NAT.
Abstract: Chronic exposure of pancreatic islets to sulfonylureas (SUs) is known to impair the ability of islets to respond to subsequent acute stimulation by SUs or glucose. Nateglinide (NAT) is a novel insulinotropic agent with a primarily site of action at β-cell KATP channels, which is common to the structurally diverse drugs like repaglinide (REP) and the SUs. Earlier studies on the kinetics, glucosedependence and sensitivity to metabolic inhibitors of the interaction between NAT and KATP channels suggested a distinct signaling pathways with NAT compared to REP, glyburide (GLY) or glimepiride (GLI). To obtain further evidence for this concept, the present study compared the insulin secretion in vitro from rat islets stimulated acutely by NAT, GLY, GLI or REP at equipotent concentrations during 1-hr static incubation following overnight treatment with GLY or tolbutamide (TOL). The islets fully retained the responsiveness to NAT stimulation after prolonged pretreatment with both SUs, while their acute response to REP, GLY, and GLI was markedly attenuated, confirming the desensitization of islets. The insulinotropic efficacy of NAT in islets desensitized to SUs may result from a distinct receptor/effector mechanism, which contributes to the unique pharmacological profile of NAT.
TL;DR: AG prevents the decrease of anionic charged molecules in the GBM and GBM thickening, which can be one of the mechanisms by which AG decreases albuminuria in diabetic rats.
Abstract: We investigated the effect of aminoguanidine (AG) administration on GBM thickness, glomerular heparan sulfate (HS) content, and urinary albumin and HS excretion in diabetic rats. After induction of diabetes, female Wistar rats were divided into 2 groups: Group AGDM (n=11) received 1g/L aminoguanidine bicarbonate in drinking water, group DC (n=12) was given only tap water. Control rats received AG (group AGH, n=8) or tap water (group HC, n=8). At the end of a period of 8 weeks, urinary albumin and glycosaminoglycan (GAG) excretion was detected. GBM heparan sulfate distribution and count was determined under the electron microscope. The AGDM group had lower urinary albumin and GAG excretion than diabetic controls. GBM thickness was increased in diabetic rats compared to groups of AGDM and HC. In AGDM group alcian blue stained particle distribution and count in the GBM was similar to healthy controls. In conclusion AG prevents the decrease of anionic charged molecules in the GBM and GBM thickening. This can be one of the mechanisms by which AG decreases albuminuria in diabetic rats.
TL;DR: The PDL rabbit model with chronic and severe glycemic disorders due to the predominant role of glucagon mimicked key features of the NIDDM syndrome secondary to exocrine disease.
Abstract: Plasma levels of glucose, insulin and glucagon were measured at various time intervals after pancreatic duct ligation (PDL) in rabbits. Two hyperglycemic periods were observed: one between 15–90 days (peak at 30 days of 15.1 ± 1.2mmol/l, p < 0.01), and the other at 450 days (11.2 ± 0.5 mmol/l, p < 0.02). The first hyperglycemic episode was significantly correlated with both hypoinsulinemia (41.8 ± 8pmol/l, r= –0.94, p < 0.01) and hyperglucagonemia (232 ± 21ng/l, r=0.95, p < 0.01). However, the late hyperglycemic phase (450 days), which was not accompanied by hypoinsulinemia, was observed after the hyperglucagonemia (390 days) produced by abundant immunostained A-cells giving rise to a 3-fold increase in pancreatic glucagon stores. The insulin and glucagon responses to glucose loading at 180, 270 and 450 days reflected the insensitivity of B- and A-cells to glucose. The PDL rabbit model with chronic and severe glycemic disorders due to the predominant role of glucagon mimicked key features of the NIDDM syndrome secondary to exocrine disease.
TL;DR: The association of progressive diabetic nephropathy with abnormal endothelium-dependent vasodilation may produce a high prevalence of hypertensive diabetes in diabetic rats treated with streptozotocin.
Abstract: The present study was designed to examine the development of hypertension in diabetic rats treated with streptozotocin (STZ, 1mg/g bw). The rats were studied at 3, 6, 9, 12 and 15 weeks. From the third week the rats were divided in diabetic rats according their glycemias and controls, along 15 weeks. After the third week a group, of rats showed increased urinary protein excretion (93, 134, 155 and 191%) compared to controls. In this group of rats the urinary kallikrein excretion was lower than control and the systolic blood pressure became significantly elevated between 3 and 6 weeks and persisted up to 15 weeks. On the other hand a group of diabetic rats were normotensive with urinary protein excretion similar to controls and urinary kallikrein lower compared to control but significantly higher compared diabetic hypertensive rats. These data suggest that the association of progressive diabetic nephropathy with abnormal endothelium-dependent vasodilation may produce a high prevalence of hypertensive diabetes.
TL;DR: In this model the in situ perfused placenta does not secrete significant quantities of lactate into the fetal compartment in either the control or diabetic group.
Abstract: Placental transfer of lactate, glucose and 2-deoxyglucose was examined employing the in situ perfused placenta. Control and streptozotocin induced diabetic Wistar rats were infused with [U-14C]-glucose and [3H]-2-deoxyglucose (2DG). The fetal side of the placenta was perfused with a cell free medium and glucose uptake was calculated in the adjacent fetuses. Despite the 5-fold higher maternal plasma glucose concentration in the diabetic dams the calculated fetal glucose metabolic index was not significantly different between the 2 groups. Placental blood flow was reduced in the diabetic animals compared with controls but reduction of transfer of [U-14C]-glucose and [3H]-2-deoxyglucose and endogenously derived [14C]-Lactate to the fetal compartment, could not be accounted for by reduced placental blood flow alone. There was no significant net production or uptake of lactate into the perfusion medium that had perfused the fetal side of the placenta in either group. The plasma lactate levels in the fetuses adjacent to the perfused placenta were found to be higher than in the maternal plasma and significantly higher in the fetuses of the diabetic group compared with control group. In this model the in-situ perfused placenta does not secrete significant quantities of lactate into the fetal compartment in either the control or diabetic group.
TL;DR: This issue of Experimental Diabetes Research is dedicated to providing coverage of the highlights of the lectures and communications presented at the 8th International Workshop on Lessons from Animal Diabetes, which felt that studies with animal models are opening new fields of diabetes research and significantly contribute to the understanding of pathogenesis of human diabetes and to the development of new therapeutic modalities.
Abstract: he 8th International Workshop on Lessons from Animal Diabetes was held July 24-26, 2001 at Nichidai Kaikan in Tokyo, the same venue where the 3rd Workshop took place in 1990. This issue of Experimental Diabetes Research is dedicated to providing coverage of the highlights of the lectures and communications presented at the workshop. The 8th LAD was organized jointly with the 15th annual meeting of Japan Association of Animal Diabetes Research (JAADR). JAADR is a research group initiated by Professor Yoshio Goto who established the famous GK rat model. There were over 200 participants about one half of them from Japan. Thus, the participants of 8th LAD had an opportunity to interact with many Japanese investigators. There was a novel session on \"Animal Models of Diabetes Established in Japan,\" which gave a special Japanese tone to the meeting. Twelve animal models were presented, many already widely known and others new that would get into international use soon. Among the important features was the 2nd Renold Memorial Lecture presented by Professor Eleazar Shafrir, entitled \"Molecular Background of Nutritionally Induced Insulin Resistance and Leading to Type 2 Diabetes from Animal Models to Humans\" (reprinted in this issue). We also had two plenary lectures by Doctor Palle Serup from Gentofte, Denmark on \"Pancreatic stem cells and islet cell differentiation\" and by Professor Takashi Kadowaki from the University of Tokyo on \"Molecular Pathogenesis of Type 2 diabetes in knockout mice models.\" LAD 8 comprised 4 symposia and 3 workshops in which we discussed the genetics and pathogenic mechanisms relevant to human type 1 and type 2 diabetes. We had 95 presentations, including short communications and posters not only related to pathogenesis of diabetes but also results of detailed mapping of genes, pathogenesis of complications and new therapeutic approaches. Abstracts of these communications appear in this volume. Listening and discussing these presentations, we felt that studies with animal models are opening new fields of diabetes research and significantly contribute to the understanding of pathogenesis of human diabetes and to the development of new therapeutic modalities. We thank all the participants for their contribution, especially those who came from outside Japan. We were able to make discussions as hot as the weather we had in Tokyo in July during the meeting.
TL;DR: In this issue, a Consensus Statement on proinsulin Cpeptide is published summarizing the deliberations of an international group of investigators, who met in Detroit in October 2000, and the demonstration of its specific binding to cell membranes by Riegler and collaborators at the Karolinska Institute strongly suggest a receptor-mediated mechanism for C-peptides action.
Abstract: n this issue, a Consensus Statement on proinsulin Cpeptide is published summarizing the deliberations of an international group of investigators, who met in Detroit in October 2000. This was preceded by the 3rd International Motor City Symposium, the theme of which was concerned with the clinical and biological effects of C-peptide. The abstracts of the presentations at the Symposium are also published in this issue of the International Journal of Experimental Diabetes Research. There is no doubt that the understanding of the actions of C-peptide has come a long way since its original discovery in the late 1960s. Ill A biological effect of C-peptide was suspected at the time. It was hypothesized that C-peptide would have an insulin-like glucose lowering effect. However, several studies failed to demonstrate such an effect and it was concluded that the only role played by Cpeptide was in the stereometric formation of insulin and that it lacked further biological activities. In the early 1990s, the interest in C-peptide was revitalized by Dr. John Wahren and his group at the Karolinska Institute in Stockholm.121 In short time C-peptide replacement studies in type diabetic patients demonstrated beneficial effects on incipient nephropathy with partial reversal of glomerular filtration rate and albumin secretion. Beneficial effects were also demonstrated in type patients with autonomic and sensory neuropathies. These findings were paralleled by effects on skin and muscle blood flow. These encouraging data energized the search for potential mechanisms, which followed with the demonstration of corrective effects on neural and renal tubular Na//K+-ATPase and microvascular nitric oxide. These findings appeared, at least in part, to explain the clinical effects. A further milestone in the C-peptide saga was the demonstration of its specific binding to cell membranesI31 by Riegler and collaborators at the Karolinska Institute. These findings strongly suggest a receptor-mediated mechanism for C-peptide’s action. Studies addressing the characterization of a specific C-peptide receptor are ongoing at the Karolinska Institute. Simultaneous studies at the Wayne State University/Morris Hood Diabetes Center in Detroit suggested an alternative and/or adjunct mechanism for C-peptide. Grunberger and collaboratorsI41 demonstrated activation of the insulin signaling pathway by C-peptide alone and with additive effects when incubated together with insulin. These results were supported by the finding that C-peptide autophosphorylates the insulin receptor. Since C-peptide does not compete with insulin at the receptor level, these findings may suggest a different ligand site for C-peptide. The receptor issue, particularly that of a specific C-peptide receptor, is not settled and remains one of the key issues to be firmly established, as stated in the recommendations by the Consensus Statement.
TL;DR: Data indicate that clinically significant severe insulin resistance does not modify the expression, regulation and activation of p21ras pathway in PBMC of patients with type II diabetes.
Abstract: Aims To asses whether clinically severe insulin resistance and poor metabolic control in patients with type II diabetes are associated with aberrant expression or function of the p21ras pathway.
TL;DR: Molecular pathogenesis of type 2 diabetes is dissected by generating several knockout mice models with a lack of each key molecules of signalling pathways of either insulin action or insulin Int.
Abstract: s of the 8th International Workshop on Lessons from Animal Diabetes Joint with The 15th Japan Association of Animal Diabetes Research TOKYO, JAPAN, JULY 24–26, 2001 Pancreatic Stem Cells and Islet Cell Differentiation PALLE SERUP, JAN JENSEN, JACOB HALD and OLE D. MADSEN Department of Developmental Biology, Hagedorn Research Institute, Gentofte, Denmark During the embryonic growth mechanisms that are not fully clear ensures that exoand endocrine cells are formed in the correct proportion. The embryonic endocrine progenitor cells are a subset of the developing Pdx1 pancreatic epithelial cells marked by the expression of Neurogenin3 (Ngn3). Ngn3 encodes a basic-Helix-Loop-Helix (bHLH) transcription factor (NGN3) that is required for the expression of NeuroD (as well as other transcription factor genes); moreover, ectopic Ngn3 expression can induce differentiation of embryonic pancreatic epithelium into α-cells at the expense of other pancreatic cell types. Notch signaling appears to control the activity of NGN3 and acts as a switch that determines the choice of the progenitor cells; the choice being to either remain as dividing precursor cells or to differentiate into endocrine cells. NGN3 is thought to activate transcription of the Notch ligand Dll–1. Once Dll–1 expression is induced in a differentiating cell it interacts with Notch, expressed on neighbouring cells. Notch activates a number of genes among which is the negatively acting bHLH gene Hes-1. This pathway (termed lateral inhibition) thus inhibits NGN3 activity and consequently endocrine differentiation and Dll–1 expression in the receiving cells. Lateral inhibition assures that only a few precursor cells differentiate and that a large fraction of the endocrine precursor cells in the pancreas are maintained in a dividing state until late stages of pancreatic development. In mice deficient for Notch pathway components, the precursor cells differentiate prematurely into endocrine cells. (Supported by NIH DK-55284) Molecular Pathogenesis of Type 2 Diabetes in Knockout Mice Models TAKASHI KADOWAKI, M.D., Ph.D. Department of Metabolic Diseases, Graduate School of Medicine, University of Tokyo Type 2 diabetes is a complex disease caused by interactions of multiple genes and environmental factors such as high-fat diet and sedentary life-style. Since type 2 diabetes is characterized by insulin resistance and relative insulin deficiency, we have tried to dissect molecular pathogenesis of type 2 diabetes by generating several knockout mice models with a lack of each key molecules of signalling pathways of either insulin action or insulin Int. Jnl. Experimental Diab. Res., Vol. 2, pp. 251–297 Copyright © 2001 Taylor & Francis, Inc. 1560-4284/01 $12.00 + .00