Temporal relationship of tissue somatostatin-like immunoreactivity to metabolic changes in genetically obese and diabetic mice

Somatostatin-like immunoreactivity (SRIF-LI) content in 2 N acetic acid extracts of hypothalamus, gastric antrum, and pancreas was measured in genetically obese (C57BL/6J ob/ob and db/db) and diabetic (C57BL/KsJ db/db and ob/ob) mice and normal littermate controls from 5 to 24 wk to determine the relationship of previously reported changes to the development of metabolic abnormalities. Hypothalamic SRIF-L concentration was similar in control, diabetic, and obese mice at all ages and increased progressively with age in all groups. Gastric antrum SRIF-LI was similar in all groups of mice at all ages. Obese mice gained weight progressively and showed moderate hyperglycemia and marked hyperinsulinemia from 5 wk of age. Pancreatic SRIF-LI content in obese (C57BL/6J) animals was similar to that in lean littermate controls, but pancreatic SRIF-LI concentration (expressed by weight or protein content) was decreased until 8 (6J ob/ob) and 10 (6J db/db) wk. Diabetic (C57BL/KsJ) mice showed a similar metabolic pattern until 10 wk with no change in pancreatic SRIF-LI content or concentration. Thereafter a progressive fall in serum insulin and a marked rise in serum glucose was associated with increasing pancreatic SRIF-LI content and concentration. These studies suggest that the genetically hyperphagic syndromes are unassociated with any change in hypothalamic or gastric SRIF-LI; that pancreatic SRIF-LI increases occur in response to, rather than as the cause of, relative hypoinsulinemia; and that the genetic background of the mice (KsJ or 6J) rather than the mutant gene (db or ob) determines the defect in carbohydrate metabolism and the pancreatic SRIF-LI response.     

Immunoreactive neurotensin in the pancreas of genetically obese and diabetic mice. A longitudinal study

Immunoreactive neurotensin (IR-NT) content in 2 N acetic acid extracts of pancreas was measured in genetically diabetic (C57BL/KsJ db/db and ob/ob) and obese (C57BL/6J ob/ob and db/db) mice and normal littermate controls from 5 to 24 wk of age to determine the relationship of any changes to the development of metabolic abnormalities. Pancreatic IR-NT in obese mice showed no consistent change compared with lean littermate controls. In contrast, diabetic mice demonstrated an increase in pancreatic IR-NT that occurred at 6-8 wk of age, and maximal about the time of islet B-cell failure (8-10 wk), and persisted over the study period. Pancreatic IR-NT eluted in two peaks on reverse phase high-pressure liquid chromatography, one of which exhibited a retention time similar to that of synthetic NT. These findings suggest that pancreatic IR-NT concentration is regulated by insulin, with elevated levels occurring in association with insulin deficiency and its metabolic consequences but not with insulin resistance. Taken together with the previous demonstration that NT influences pancreatic islet hormone secretion, the present findings support a possible role of endogenous NT in islet hormone regulation.     

Ciglitazone, a new hypoglycemic agent. I. Studies in ob/ob and db/db mice, diabetic Chinese hamsters, and normal and streptozotocin-diabetic rats

Ciglitazone, 5-[4-(1-methylcyclohexylmethoxy) benzyl]-thiazolidine-2,4-dione, is a new hypoglycemic agent orally active in the obese-hyperglycemic animal models. In C57BL/6J-ob/ob mice, treatment with 100 mg/kg ciglitazone for 2 days elicited a drastic fall in blood glucose. It also decreased plasma insulin, triglycerides, and free fatty acids and food intake without affecting the body weight. Its hypoglycemic activity was independent of its effect on food intake. Regranulation of islet beta-cells and increased pancreatic insulin content were observed in ob/ob mice treated for 41-44 days with 100 mg/kg/day ciglitazone. Ciglitazone showed no effect on food intake, blood glucose, or pancreatic islet beta-cells in a group of lean C57BL/6J-+/? mice concomitantly treated at a dose of 150 mg/kg/day. In C57BL/KsJ-db/db mice, ciglitazone decreased blood glucose and food intake. The untreated db/db mice lost weight despite hyperphagia, whereas the ciglitazone-treated db/db mice gained weight. In the spontaneously diabetic Chinese hamsters, ciglitazone showed no significant effect on food intake, body weight, blood glucose, or insulin content in either plasma or pancreas, but it lowered plasma lipids. In normal rats, ciglitazone failed to affect fasting blood glucose but improved glucose tolerance without increasing insulin secretory response to glucose. In streptozotocin-diabetic rats, it showed no effect on blood glucose or glycemic response to exogenous insulin. The hypoglycemic activity of ciglitazone was specific for obese-hyperglycemic and insulin-resistant animals.     

Quantitative analysis of pancreatic proinsulin mRNA in genetically diabetic (db/db) mice

C57BL/KsJ db/db mice develop hyperphagic obesity and nonketotic diabetes similar to non-insulin-dependent diabetes mellitus in humans. Initially the mice demonstrate an abundant beta-cell mass and hyperinsulinemia, which is followed by apparent beta-cell loss. As an index of insulin synthesis, this study assesses pancreatic proinsulin mRNA, measured by dot hybridization to cloned cDNA, during the development of diabetes in the mice. Changes in proinsulin mRNA from 5 to 13 wk of age are compared with serum insulin, pancreatic insulin content, and blood glucose. In control (+/db) mice, total proinsulin mRNA and pancreatic insulin content increased with age. Both changes were proportional to an increase in body weight. Obesity, hyperglycemia, and hyperinsulinemia were evident in diabetic (db/db) mice at 5 wk of age. Although pancreatic insulin content was comparable to that in the +/db controls at 5 wk, a fourfold relative elevation of proinsulin mRNA was observed. Despite an increase in body weight, proinsulin mRNA concentration and total proinsulin mRNA fell to levels similar to those of the control mice at 10 and 13 wk, associated with a loss of hyperinsulinemia, a mild decrease in pancreatic insulin content, and a marked increased in fasting blood glucose. A separate group of db/db mice was pair fed with the +/db controls from 4 to 13 wk. These diet-restricted diabetic mice were heavier than control mice and gained weight with age, but they weighed less than the unrestricted mice at all ages. Compared with the unrestricted db/db mice, a more modest fasting hyperglycemia was apparent, and a persistent hyperinsulinemia was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impairment of host resistance to Listeria monocytogenes infection in liver of db/db and ob/ob mice

Leptin is an adipocyte-derived hormone that regulates a number of physiological functions, including energy homeostasis and immune function. In immune responses, leptin plays a role in the induction of inflammation. We investigated a role of leptin in Listeria monocytogenes infection using leptin receptor-deficient db/db mice and leptin-deficient ob/ob mice. These mutant mice were highly susceptible to L. monocytogenes, and the elimination of bacteria from the liver was inhibited. After infection, the induction of monocyte chemoattractant protein-1 (MCP-1) and KC mRNA in the liver of db/db mice and the MCP-1 mRNA expression in the liver of ob/ob mice was decreased compared with their heterozygote littermates. Leptin replacement in ob/ob mice resulted in improvement of anti-listerial resistance and the MCP-1 mRNA expression. The elimination of L. monocytogenes was significantly enhanced, and the expression of MCP-1 and KC mRNA was completely reversed in db/db mice by insulin treatment. These results suggest that leptin is required for host resistance to L. monocytogenes infection and that hyperglycemia caused by leptin deficiency is involved in the inefficient elimination of bacteria from the liver. Moreover, defect of MCP-1 expression in the liver may be involved in the attenuated host resistance in these mutant mice.     

Effect of genetic background on the therapeutic effects of dehydroepiandrosterone (DHEA) in diabetes-obesity mutants and in aged normal mice

Dehydroepiandrosterone (DHEA) was fed at 0.1-0.4% in the diet to genetically diabetic (db/db) or obese (ob/ob) C57BL/KsJ (BL/Ks) or C57BL/6J (BL/6) mice. Treatment of BL/Ks-db/db or ob/ob mice with 0.4% DHEA prevented hyperglycemia, islet atrophy, and severe diabetes associated with this inbred background, but did not affect weight gain and food consumption. Homozygous obese (ob) or diabetes (db) mice on the BL/6 background were more sensitive to DHEA, and the mild, transient hyperglycemia associated with ob or db gene expression on the BL/6 inbred background could be prevented by 0.1% DHEA. Both body weight and food consumption were decreased in BL/6 mutants maintained on 0.1% DHEA whereas this effect was not seen in BL/Ks mutants fed up to 0.4% DHEA. Early therapy with 0.4% DHEA, initiated at 2 wk of age, prevented the development of most diabetes symptoms and decreased the rate of weight gain in pups of all genotypes. In addition to therapeutic effects on both obese mutants, DHEA effected significant changes in an aging study using normal BL/6 female mice. Four weeks of DHEA treatment initiated at 2 yr of age improved glucose tolerance and at the same time reduced plasma insulin to a "younger" level. This suggests that DHEA may act in insulin-resistant mutant mice and in aging normal mice to increase the sensitivity to insulin.     

An ascochlorin derivative, AS-6, reduces insulin resistance in the genetically obese diabetic mouse, db/db

An ascochlorin derivative, AS-6, is a new hypoglycemic agent orally active in both obese hyperinsulinemic and insulin-deficient diabetic animal models. AS-6, when given as a 0.025-0.2% admixture in the diet, dose-dependently ameliorated polydipsia, polyuria, and glycosuria in the genetically obese diabetic mouse, C57BL/KsJ db/db, while neither insulin nor tolbutamide showed any beneficial effects. The amelioration by AS-6 was associated with a marked decrease in serum glucose and triglyceride. The effects persisted at least 10 wk, accompanied by a steady decrease in drinking water consumption. The chronic treatment prevented pancreatic islet degeneration, e.g., degranulation of the beta-cells, basophilic appearance of the exocrine border around the islets, and small round cell infiltration. The isolated islets from AS-6-treated mice released much more insulin in response to glucose than those from untreated controls. A significant correlation between serum immunoreactive insulin and glucose/triglyceride from both treated and untreated mice suggests that AS-6 restores sensitivity and responsiveness to insulin to the mice. In fact, the combined treatment with insulin synergistically decreased serum glucose by 50% below AS-6 treatment alone. Furthermore, the epididymal fat pad slices from AS-6-treated db/db mice increased CO2 generation and lipogenesis over the untreated controls, and the glucose metabolic rate (CO2 generation plus lipogenesis from U-[14C]-glucose) in the slices and the serum glucose level inversely correlated at r = 0.8799.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alteration of islet cell populations in spontaneously diabetic mice.

Endocrine-cell populations in the islets of Langerhans of mutant mice with a severe hypoinsulinemic diabetes (ob/ob or db/db on the C57BL/KsJ background) or with a mild hyperinsulinemic diabetes (ob/ob or db/db on the C57BL/6J background) were studied quantitatively by immunofluorescence and morphometry. In severely diabetic mice, islets presented a reduced proportion of insulin containing cells but increased glucagon-, somatostatin-, and pancreatic polypeptide (PP)-containing cells, as compared with islets of control (+/+) mice. An inverse change was observed in islets of mildly diabetic mice: islets were hypertrophic and composed mostly of insulin-containing cells, with decreased proportions of glucagon-, somatostatin-, and PP-containing cells. In both types of diabetic syndromes, the changes in cell populations induced a qualitative alteration of cellular interrelationships in the affected islets.     

Inhibiting albumin glycation ameliorates diabetic nephropathy in the db/db mouse

Albumin modified by Amadori glucose adducts stimulates the expression of extracellular matrix proteins by glomerular mesangial and endothelial cells, and has been mechanistically linked to the pathogenesis of diabetic nephropathy. To test the hypothesis that inhibiting the formation of glycated albumin might beneficially influence the development of kidney disease in diabetes, we treated diabetic db/db mice for 12 weeks with a low-molecular-weight compound (EXO-226) that impedes the condensation of free glucose with lysine epsilon-amino groups in albumin. Administration of EXO-226 (3 mg/kg) twice daily by gavage normalized the plasma concentration of glycated albumin within days after initiation of treatment and maintained glycated albumin within the normal range throughout the study, despite persistent and severe hyperglycemia. Urine albumin excretion, which was markedly increased at the start of the study (age 12 weeks), was significantly reduced in treated diabetic animals compared with their untreated diabetic littermates. The fall in creatinine clearance that was observed in untreated diabetic animals was prevented in diabetic littermates that received treatment. Compared with the nondiabetic controls, the amount of glomerular mesangial matrix was threefold greater in untreated diabetic mice; in contrast, the mesangial matrix fraction was only 1. 5 times that of nondiabetic controls in the treated diabetic animals, representing a reduction in mesangial matrix accumulation of more than 50%. EXO-226 also reduced the overexpression of mRNA encoding for alpha1 (IV) collagen in renal cortex of db/db mice. We conclude that normalization of plasma glycated albumin concentrations with the glycation inhibitor EXO-226 ameliorates the glomerular structural and functional abnormalities associated with diabetic nephropathy in the db/db mouse.     

Phospholipid metabolism and protein phosphorylation in sciatic nerve from genetically diabetic (db/db) mouse

The incorporation of [32P]orthophosphate into phospholipids and proteins of sciatic nerve from genetically diabetic (db/db) and littermate control (db/m) C57BL/KsJ mice was studied. Nerves from animals of ages 12, 16, 22, 26, and 38 wk were incubated in vitro. Among phospholipids, the uptake of isotope into phosphatidic acid was higher at nearly all ages examined. Phosphorylation of several proteins, including the major myelin glycoprotein, P0, and the small myelin basic proteins Pr + P2, was significantly enhanced in nerves from both 12- and 38-wk-old diabetic mice. The altered pattern of protein phosphorylation, but not that of phospholipid metabolism, was similar to changes observed in sciatic nerve from streptozocin-induced diabetic rats. The relationship of the results to reported levels of myo-inositol, sorbitol, and Na+-K+-ATPase activity and to functional abnormalities in nerves of db/db mice is discussed. The findings suggest that caution should be exercised in reaching conclusions concerning which biochemical alterations observed in different animal models of diabetic neuropathy are invariably associated with the development of this disorder.     

T-lymphopenia and T-cell imbalance in diabetic db/db mice

The diabetic db/db mice of the C57 BL/KsJ strain display anti-islet immunity, thymic dysfunction, and lymphopenia. In the present work, lymphocytes, T-cells, and T-cell subsets were enumerated in thymus and spleen from diabetic db/db mice and their db/ + heterozygote littermates from the 10th day to the 10th month of life. A significant lymphopenia was detected in thymus and spleen from the second month on, involving specifically the T-cell compartment, as assessed by use of a monoclonal anti-Thy1 antibody in indirect fluorescence. The study of T-cell subsets by monoclonal anti-Lyt1 and anti-Lyt2 antibodies revealed a significant increase in Lyt1+ cells and a decrease in Lyt2+ cells, with a corresponding increase of the Lyt1+/Lyt2+ ratio. These anomalies appeared early in life, and were apparently linked neither with the degree of hyperglycemia nor with weight loss or infection. The T-cell depletion in thymus was more pronounced in young male (less than 3 mo) than in young female db/db mice. These alterations may correspond to an increase in the helper/suppressor-cytotoxic ratio and could be linked with the thymic anomalies present in these mice, contributing to the development of anti-islet autoimmunity.     

Effect of genetic obesity in mice on the induction of diabetes by encephalomyocarditis virus

The "M" variant of the encephalomyocarditis (EMC) virus causes a diabetes-like disease in some, but not all, strains of mice. The genetic basis for either resistance or susceptibility to the diabetogenic effect of the virus is not known. After infection with EMC, C57BL/6 mice seldom develop hyperglycemia and the insular lesions are subtle. To explore the possible effects of metabolic influences on the viral susceptibility of the islets, we studied C57BL/6 mice that were carriers of the ob gene. After virus inoculation, obese homozygous C57BL/6-ob/ob mice consistently developed hyperglycemia during the acute stages of infection, whereas nonobese littermates did not. Infection induced more severe lesions in the pancreatic islets of obese mice than in islets of the lean littermates. These studies suggest that the functional activity of the beta-cells influences the severity of the viral injury to the beta-cell, and the consequent occurrence of diabetes.     

Long-term treatment of glucagon-like peptide-1 analog exendin-4 ameliorates diabetic nephropathy through improving metabolic anomalies in db/db mice

Glucagon-like peptide-1 (GLP-1) is a gut incretin hormone and is a new clinically available class of agents for improving of insulin resistance in both animals and humans with type 2 diabetes. These studies aimed to determine whether long-term treatment with a long-acting GLP-1 analog, exendin-4, delayed the progression of diabetes. Male db/db mice and db/m mice at 8 wk of age were treated with exendin-4 for 8 wk, whereas the control db/db mice received only vehicle. Urinary albumin excretion was significantly decreased in db/db mice that were treated with 1 nmol/kg exendin-4 compared with those in db/db mice that were treated with 0.5 nmol/kg exendin-4 and control db/db mice (P < 0.005). Intraperitoneal glucose tolerance test was improved in db/db mice that were treated with 1 nmol/kg exendin-4 compared with other groups (P < 0.05). Despite this, fasting blood glucose, glycated hemoglobin, and creatinine concentrations were not significantly different among db/db mice. Renal histology studies further demonstrated that glomerular hypertrophy, mesangial matrix expansion, TGF-beta1 expression, and type IV collagen accumulation and associated glomerular lipid accumulation were significantly decreased in db/db mice that were treated with 1 nmol/kg exendin-4. Furthermore, there were fewer infiltrating inflammatory cells and apoptotic cells in the glomeruli of db/db mice that were treated with 1 nmol/kg exendin-4 compared with those in the other groups accompanied by an increase in the renal immunoreactivity of peroxisome proliferator-activated receptor alpha and GLP-1 receptor-positive cells and a decrease in 24-h urinary 8-hydroxy-deoxyguanosine levels (P < 0.01, respectively) along with decreases in lipid content. Taken together, exendin-4 treatment seems to ameliorate diabetic nephropathy together with improvement of the metabolic anomalies. These results suggest that exendin-4 could provide a therapeutic role in diabetic nephropathy that results from type 2 diabetes.     

Age-related changes in hepatic glycogen metabolism in the genetically diabetic (db/db) mouse

Hepatic glycogen metabolism was investigated in genetically diabetic C57BL/KsJ-db/db mice during their development. Initially, the development of obesity, hyperglycemia, hyperinsulinemia, and hyperglucagonemia in these mice was examined, which illustrated that the diabetes progressed normally. Little difference in hepatic glycogen concentrations was observed, averaging approximately 50 and 60 mg/g liver in diabetic (db/db) and control heterozygote (db/+) mice, respectively. Glycogen synthase activity (total and a-form) was significantly elevated by 5 wk in the diabetic mice relative to controls and reached maximum levels (two-fold higher than controls) around 8-9 wk. This activity then slowly declined during the rest of the 15-wk period examined. Both phosphorylase a and total phosphorylase activities were also elevated by 5 wk, reaching levels twofold higher than controls. These activities did not decline at the end of this 15-wk period, but instead continued to slowly increase. Glycogen synthase a activity showed a positive correlation (r = 0.54, N = 144) with circulating levels of insulin, and a similar correlation was seen for phosphorylase a activity and plasma glucagon levels (r = 0.64, N = 72). Protein kinase and phosphoprotein phosphatase activities were also measured, but no differences were detected between diabetic and control mice. This longitudinal study clarifies some of the changes in hepatic glycogen metabolism that occur during the progression of diabetes in the db/db mouse and indicates a role for circulating insulin and glucagon concentrations on the steady-state activities of glycogen synthase and phosphorylase, respectively.     

Increased hemoglobin AIc in diabetic mice.

The minor hemoglobins AIa, AIb, and AIc were studied in mice with either genetic or chemically induced diabetes. Hemoglobin AIc was elevated approximately twofold in all the phenotypically diabetic mice studied (C57BL/KsJ-db/db, C57BL/KsJ-ob/ob, C57BL/6J-db/db, and alloxan- and streptozotocin-treated mice). Elevation of the hemoglobin AIc in C57BL/6J-db/db mice was of short duration, reflecting the transitory diabetes characteristic of these mice. The degree of increase of hemoglobin AIc levels was unrelated to severity of hyperglycemia, duration of diabetes, age of mouse, or body weight. It is not known what factor(s) dictates the steady-state concentration of hemoglobin AIc.     

Reduction in glucagon receptor expression by an antisense oligonucleotide ameliorates diabetic syndrome in db/db mice

Excess glucagon levels contribute to the hyperglycemia associated with type 2 diabetes. Reducing glucagon receptor expression may thus ameliorate the consequences of hyperglucagonemia and improve blood glucose control in diabetic patients. This study describes the antidiabetic effects of a specific glucagon receptor antisense oligonucleotide (GR-ASO) in db/db mice. The ability of GR-ASOs to inhibit glucagon receptor mRNA expression was demonstrated in primary mouse hepatocytes by quantitative real-time RT-PCR. Intraperitoneal administration of GR-ASO at a dosage of 25 mg/kg twice a week in db/db mice for 3 weeks resulted in 1) decreased glucagon receptor mRNA expression in liver; 2) decreased glucagon-stimulated cAMP production in hepatocytes isolated from GR-ASO-treated db/db mice; 3) significantly reduced blood levels of glucose, triglyceride, and free fatty acids; 4) improved glucose tolerance; and 5) a diminished hyperglycemic response to glucagon challenge. Neither lean nor db/db mice treated with GR-ASO exhibited hypoglycemia. Suppression of GR expression was also associated with increased ( approximately 10-fold) levels of plasma glucagon. No changes were observed in pancreatic islet cytoarchitecture, islet size, or alpha-cell number. However, alpha-cell glucagon levels were increased significantly. Our studies support the concept that antagonism of glucagon receptors could be an effective approach for controlling blood glucose in diabetes.     

GLUT4 overexpression in db/db mice dose-dependently ameliorates diabetes but is not a lifelong cure

We previously reported that overexpression of GLUT4 in lean, nondiabetic C57BL/KsJ-lepr(db/+) (db/+) mice resulted in improved glucose tolerance associated with increased basal and insulin-stimulated glucose transport in isolated skeletal muscle. We used the diabetic (db/db) litter mates of these mice to examine the effects of GLUT4 overexpression on in vivo glucose utilization and on in vitro glucose transport and GLUT4 translocation in diabetic mice. We examined in vivo glucose disposal by oral glucose challenge and hyperinsulinemic-hyperglycemic clamps. We also evaluated the in vitro relationship between glucose transport activity and cell surface GLUT4 levels as assessed by photolabeling with the membrane-impermeant reagent 2-N-(4-(1-azi-2,2,2-trifluoroethyl)benzoyl)-1,3-bis(D-mannose-4-yloxy)-2-propylamine in extensor digitorum longus (EDL) muscles. All parameters were examined as functions of animal age and the level of GLUT4 overexpression. In young mice (age 10-12 weeks), both lower (two- to threefold) and higher (four- to fivefold) levels of GLUT4 overexpression were associated with improved glucose tolerance compared to age-matched nontransgenic (NTG) mice. However, glucose tolerance deteriorated with age in db/db mice, although less rapidly in transgenic mice expressing the higher level of GLUT4. Glucose infusion rates during hyperinsulinemic-hyperglycemic clamps were increased with GLUT4 overexpression, compared with NTG mice in both lower and higher levels of GLUT4 overexpression, even in the older mice. Surprisingly, isolated EDL muscles from diabetic db/db mice did not exhibit alterations in either basal or insulin-stimulated glucose transport activity or cell surface GLUT4 compared to nondiabetic db/+ mice. Furthermore, both GLUT4 overexpression levels and animal age are associated with increased basal and insulin-stimulated glucose transport activities and cell surface GLUT4. However, the observed increased glucose transport activity in older db/db mice was not accompanied by an equivalent increase in cell surface GLUT4 compared to younger animals. Thus, although in vivo glucose tolerance is improved with GLUT4 overexpression in young animals, it deteriorates with age; in contrast, insulin responsiveness as assessed by the clamp technique remains improved with GLUT4 overexpression, as does in vitro insulin action. In summary, despite an impairment in whole-body glucose tolerance, skeletal muscle of the old transgenic GLUT4 db/db mice is still insulin responsive in vitro and in vivo.     

Glucose-lowering and insulin-sensitizing actions of exendin-4: studies in obese diabetic (ob/ob, db/db) mice, diabetic fatty Zucker rats, and diabetic rhesus monkeys (Macaca mulatta).

Exendin-4 is a 39 amino acid peptide isolated from the salivary secretions of the Gila monster (Heloderma suspectum). It shows 53% sequence similarity to glucagon-like peptide (GLP)-1. Unlike GLP-1, exendin-4 has a prolonged glucose-lowering action in vivo. We compared the potency and duration of glucose-lowering effects of exendin-4 and GLP-1 in hyperglycemic db/db and ob/ob mice. Whereas reductions in plasma glucose of up to 35% vanished within 1 h with most doses of GLP-1, the same doses of exendin-4 resulted in a similar glucose-lowering effect that persisted for >4 h. Exendin-4 was 5,530-fold more potent than GLP-1 in db/db mice (effective doses, 50% [ED50s] of 0.059 microg/kg +/-0.15 log and 329 microg/kg+/-0.22 log, respectively) and was 5,480-fold more potent in ob/ob mice (ED50s of 0.136 microg/kg+/-0.10 log and 744 microg/kg+/-0.21 log, respectively) when the percentage fall in plasma glucose at 1 h was used as the indicator response. Exendin-4 dose-dependently accelerated glucose lowering in diabetic rhesus monkeys by up to 37% with an ED50 of 0.25 microg/kg +/-0.09 log. In two experiments in which diabetic fatty Zucker rats were injected subcutaneously twice daily for 5-6 weeks with doses of exendin-4 up to 100 microg x rat(-1) x day(-1) (approximately 250 microg/kg), HbA1c was reduced relative to saline-injected control rats. Exendin-4 treatment was also associated in each of these experiments with weight loss and improved insulin sensitivity, as demonstrated by increases of up to 32 and 49%, respectively, in the glucose infusion rate (GIR) in the hyperinsulinemic euglycemic clamp. ED50s for weight loss and the increase in clamp GIR were 1.0 microg/kg+/-0.15 log and 2.4 microg/kg+/-0.41 log, respectively. In conclusion, acute and chronic administration of exendin-4 has demonstrated an antidiabetic effect in several animal models of type 2 diabetes.     

Improved glycemic control in C57Bl/KsJ (db/db) mice after treatment with the thermogenic beta-adrenoceptor agonist, BRL 26830

BRL 26830, (R*,R*)-(+/-)-methyl-4-(2-[(2-hydroxy-2-phenylethyl)amino]propyl)-benzoa te, is a new type of beta-adrenoceptor receptor agonist that combines antihyperglycemic and thermogenic properties. In C57Bl/KsJ db/db mice, treatment with BRL 26830 (50 mg of the hemifumarate salt/kg diet) decreased blood glucose concentration and normalized water intake. As judged by the normalization of polydipsia, BRL 26830 was effective within 2 days and the effect was maintained throughout a treatment period of up to 11 wk. Treatment of db/db mice with BRL 26830 resulted in an increase in both plasma and pancreatic insulin concentrations and a partial restoration of first-phase insulin secretion by the isolated, perfused pancreas in response to a high (16.7 mM) glucose pulse. Given acutely, BRL 26830 increased energy expenditure in both fed and fasted db/db mice. When given chronically, BRL 26830 increased significantly the dietary and thermoregulatory component of metabolic rate. It is suggested that the antidiabetic and thermogenic properties of BRL 26830 are linked and that blood glucose acts either directly or indirectly as a substrate for thermogenesis.     

Expression and role of microRNA-155 in db/db mice

Objective To investigate the expression of microRNA-155 (miR-155) in serum and kidney of C57BLKS/db (db/db) mice and its role in the pathogenesis of diabetic kidney disease (DKD). Methods The db/db mice (n=24) were divided into 6, 8, and 10 weeks old groups (n=8) with age increasing according to the random number table, and C57BL/6 mice of the same age were used as control group. The expression of miR-155 in mouse serum and kidney tissue was determined using real-time quantitative PCR. The mRNA and protein expression of Ets-1, eNOS, AGTR1 in renal tissues was verified by real-time quantitative PCR, Western blotting and immunohistochemistry. Results Compared with the control group, the expression of miR-155 in serum of db/db mice at 6, 8 and 10 weeks of age were significantly increased (all P＜0.01), and the increase of miR-155 was most obvious at 10 weeks of age (P＜0.01). Meanwhile the expression of miR-155 in kidney tissues of 6, 8 and 10 weeks old db/db mice was significantly up-regulated (all P＜0.01), and the highest expression of miR-155 was at 10 weeks of age (P＜0.01). Immunohistochemistry showed that Ets-1, eNOS and AGTR1 were localized in glomerular endothelial cells. The results of real-time quantitative PCR showed that the mRNA expression of Ets-1, eNOS and AGTR1 were down-regulated in the kidney tissues of db/db mice at 6, 8 and 10 weeks of age compared to the control(all P＜0.05), and the level of down-regulation was the most obvious at 10 week. Western blotting results showed that there was no significant change in Ets-1, eNOS and AGTR1 in 6-week-old db/db mice compared to the control group; the eNOS protein expression was down-regulated at 8 weeks of age (P＜0.05); the expression of AGTR1 protein was down-regulated (P＜0.05), and the protein expression of Ets-1 and eNOS were significantly down-regulated at 10-week age (both P＜0.01). Conclusions The expression of miR-155 in serum and kidney tissues of db/db mice increases during the progression of DKD, while the expression of miR-155 target genes Ets-1, eNOS and AGTR1 decreases with the progression of DKD. MiR-155 may participate in the development and progression of DKD by inhibiting its target genes Ets-1, eNOS and AGTR1, affecting endothelial cell function.