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.     

Altered beta-endorphin, Met- and Leu-enkephalins, and enkephalin-containing peptides in pancreas and pituitary of genetically obese diabetic (db/db) mice during development of diabetic syndrome

We have recently shown that in addition to beta-endorphin the opioid peptides Met- and Leu-enkephalin and their apparent precursors are localized in islet endocrine cells of the rat pancreas. To begin evaluating a possible role for these pancreatic opiates in the pathophysiology of genetic diabetes in rodents, immunoreactive beta-endorphin and Met- and Leu-enkephalins were measured in acetic acid extracts of pancreas and pituitary of C57BL/KsJ db/db mice and their lean littermates. Groups of animals were studied during three phases of development of the diabetic syndrome in the mutant mice: at 4 (hyperinsulinemic and prediabetic); 6, 9, and 12 (frankly obese and diabetic); and 30 (hypoinsulinemic) wk of age. Elevations or decreases (P less than .05) were found in db/db mice (vs. lean littermates) as follows: pituitary content of Met-enkephalin was twofold higher at all ages studied; pituitary free Leu-enkephalin was lower at 4 wk and reversed to higher at 6-30 wk; pancreatic beta-endorphin was 30% lower at 4 wk and reversed to threefold higher at 6-12 wk; Met- and Leu-enkephalin-containing larger peptides were elevated at one or more points between 6 and 12 wk in both the pancreas and the pituitary. Thus, the onset of overt obesity between 4 and 6 wk of age was accompanied by a marked rise in both pancreatic beta-endorphin and pituitary Leu-enkephalin; similar elevations in these parameters have been reported previously in C57BL/6J ob/ob mice at approximately 12 wk of age.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

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)     

Genetic control of organ-reactive autoantibody production in mice by obesity (ob) diabetes (db) genes

Inbred strains of mice exhibited genetic and sex-dependent differences in spontaneous production of organ-reactive autoantibodies detected by indirect immunofluorescence. Antitestis autoreactivity was found primarily in sera from C57BL/6J (B6) mice, whereas antigastric autoreactivity was common to both CBA/J and 129/J strains. Autoantibodies against islet cell cytoplasmic antigens (ICAs) were uniquely expressed by C57BL/KsJ (BKs) males. Introduction of the diabetes (db) mutation into these various inbred-strain backgrounds induced expression of ICA, with stronger induction observed in males. The stress imposed by the db or obesity (ob) mutation induced ICA in BKs mice at a higher frequency than in B6 mice; this differential sensitivity was somehow related to a gene linked to the H-2 complex because BKs.B6 H-2b congenic mice resembled B6 mice. The db3J mutation increased the expression of these autoantibodies in 129/J mice, which, like B6, were H-2b and therefore presumably possessed the same H-2-linked inducibility allele as BKs. Cytotoxic autoantibodies against islet cell surface antigens were only observed in C3HeB/FeJ db/db males, and their presence was correlated with beta-cell necrosis. It is concluded that db and/or ob genes appear to play an important role in the production of autoantibodies to islet cells, and sex-linked factor(s) may modify the phenotypic expression of the autoantibodies.     

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.     

Molecular mimicry between insulin and retroviral antigen p73. Development of cross-reactive autoantibodies in sera of NOD and C57BL/KsJ db/db mice

Enzyme-linked immunosorbent assay (ELISA) was used to study temporal development of murine autoantibodies against insulin and both type C and intracisternal type A retroviral antigens. The nonobese diabetic (NOD) mouse, a model for autoimmune, insulin-dependent diabetes, was compared with a related, but diabetes-resistant, strain, nonobese normal (NON). Similarly, C57BL/KsJ db/db mice (insulin-resistant model of insulin-dependent diabetes and obesity) were compared with diabetes-resistant C57BL/6 db/db mice. NOD mice developed much higher autoantibody titers than did NON mice. Whereas type C autoantibodies in NOD developed to peak titer shortly after mice were weaned, autoantibodies against insulin and p73 (group-specific antigen of the intracisternal type A particle) did not develop until shortly before, or concomitant with, the development of hyperglycemia. Two NOD mice not developing hyperglycemia during the 40-wk study period were distinguished from the mice developing diabetes by a delayed onset of insulin (but not p73) autoantibodies. Our findings suggest that in NOD mice, the appearance of insulin and p73 autoantibodies signifies that extensive underlying necrosis of beta-cells occurred. C57BL/KsJ db/db mice (with extensive beta-cell necrosis and early hyperglycemia) developed much higher autoantibody titers to insulin and p73 than did the diabetes-resistant C57BL/6 db/db mice. However, the presence of autoantibodies in normoglycemic C57BL/KsJ +/db controls demonstrated that elevated autoantibody titers alone were insufficient to produce diabetes in this model. Absorption studies indicated that autoantibodies against p73 recognized a common epitope on insulin and IgE-binding factor. The potential significance of this molecular mimicry is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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)     

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.     

Abnormalities of GIP in spontaneous syndromes of obesity and diabetes in mice

The role of GIP in the pathogenesis of spontaneous syndromes of obesity-diabetes was examined in ob/ob mice of the Aston stock and db/db mice of the C57BL/KsJ background. Compared with lean controls, fed adult ob/ob and db/db mice, respectively, exhibited 1.8-fold and 2.1-fold increases in body weight, 1.8-fold and 2.8-fold elevations of plasma glucose, and 15.4-fold and 5.6-fold elevations of plasma insulin. As indicated by the relative magnitude of the hyperglycemia and hyperinsulinemia, db/db mice displayed a particularly severe form of diabetes. Plasma GIP concentrations of ob/ob and db/db mice were elevated 15.1-fold and 6.2-fold, respectively; the increments closely corresponded with the degrees of hyperinsulinemia. Small intestinal weight was increased 1.4-fold and 1.8-fold in ob/ob and db/db mice, respectively, but the intestinal GIP content expressed as microgram/g intestine or microgram/intestine was raised only in ob/ob mice (1.9-fold and 2.8-fold, respectively). Since glucose stimulation of insulin release is defective in both mutant strains, the results strongly implicate pathologically raised GIP concentrations in the hyperinsulinemia and related metabolic abnormalities of the obesity-diabetes syndromes. It is suggested that hypersecretion of GIP results in part from loss of normal feedback inhibition by endogenous insulin.     

Gene expression profiles of nondiabetic and diabetic obese mice suggest a role of hepatic lipogenic capacity in diabetes susceptibility

Obesity is a strong risk factor for the development of type 2 diabetes. We have previously reported that in adipose tissue of obese (ob/ob) mice, the expression of adipogenic genes is decreased. When made genetically obese, the BTBR mouse strain is diabetes susceptible and the C57BL/6J (B6) strain is diabetes resistant. We used DNA microarrays and RT-PCR to compare the gene expression in BTBR-ob/ob versus B6-ob/ob mice in adipose tissue, liver, skeletal muscle, and pancreatic islets. Our results show: 1) there is an increased expression of genes involved in inflammation in adipose tissue of diabetic mice; 2) lipogenic gene expression was lower in adipose tissue of diabetes-susceptible mice, and it continued to decrease with the development of diabetes, compared with diabetes-resistant obese mice; 3) hepatic expression of lipogenic enzymes was increased and the hepatic triglyceride content was greatly elevated in diabetes-resistant obese mice; 4) hepatic expression of gluconeogenic genes was suppressed at the prediabetic stage but not at the onset of diabetes; and 5) genes normally not expressed in skeletal muscle and pancreatic islets were expressed in these tissues in the diabetic mice. We propose that increased hepatic lipogenic capacity protects the B6-ob/ob mice from the development of type 2 diabetes.     

An H-2 alloantiserum preserves beta-cell function in mice made diabetic by low-dose streptozocin

The pancreatic beta-cell mass and function in C57BL/KsJ mice is markedly reduced the day after the last injection of five daily injections of a subdiabetogenic, 40 mg/kg, dose of streptozocin (STZ). In this study, we prepared an H-2 alloantiserum by injecting C57BL/6J mice (H-2b) with spleen lymphocytes from C57BL/KsJ (H-2d) mice. The alloantiserum given on five consecutive days, 5 h before each injection of STZ, did not prevent the initial beta-cytotoxic effect of STZ detected by perfusion of the pancreas and subsequent morphometric analysis of in situ dithizone-perfused pancreas. However, 12 days after the first injection of STZ, total insulin release in response to D-glucose, total pancreatic insulin, and pancreatic glucagon was greater in the alloantiserum-treated mice compared with controls receiving normal mouse serum. It is concluded that an H-2 alloantiserum may protect the function and amounts of beta-cells remaining after the initial five low-dose STZ injections.     

Genetic influence of the streptozotocin-induced insulitis and hyperglycemia.

Multiple injections of subdiabetogenic doses of streptozotocin (SZ) to CD-1 male mice produce a diabetic syndrome that includes a cell-mediated immune reaction against the pancreatic islet. The importance of the host genetic background in the pathogenesis of this model of diabetes was studied by comparing various inbred strains of mice. Of eight strains of mice studied, only C57BL/KsJ developed insulitis and hyperglycemia comparable to that observed in CD-1 mice. In two mouse strains (DBA/J and BALB/cJ) having an H-2d haplotype similar to the C57BL/KsJ, only mild insulitis and glucose intolerance were observed. These data suggest that major histocompatibility complex genes, as presently defined, cannot be the only determinant of the severity of hyperglycemia and insulitis in this model.     

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.     

Therapeutic effects of dehydroepiandrosterone (DHEA) in diabetic mice

Dehydroepiandrosterone (DHEA), a major adrenal secretory steroid in humans, was therapeutic when fed in a concentration of 0.4% to C57BL/KsJ mice with either non-insulin-dependent or insulin-dependent diabetes. Genetically diabetic (db/db) mice of both sexes develop obesity and a glucose intolerance and hyperglycemia associated with insulin resistance by 2 mo of age, and exhibit beta-cell necrosis and islet atrophy by 4 mo. In contrast, DHEA feeding initiated between 1 and 4 mo of age, while only moderately effective in preventing obesity, did prevent the other pathogenic changes and effected a rapid remission of hyperglycemia, a preservation of beta-cell structure and function, and an increased insulin sensitivity as measured by glucose tolerance tests. DHEA feeding was also therapeutic to normal C57BL/KsJ male mice made diabetic by multiple low doses of streptozotocin (SZ). While DHEA treatments did not block either the direct cytotoxic action of SZ on beta-cells or the development of insulitis, the steroid significantly moderated the severity of the ensuing diabetes (reduced hyperglycemia and water consumption, and increased plasma insulin and numbers of residual, granulated beta-cells.     

Behavioral manipulation of the diabetic phenotype in ob/ob mice

The genetically obese mouse (C57BL/6J ob/ob) is a commonly used model of non-insulin-dependent diabetes mellitus. However, our studies demonstrate that, while the animal is significantly hyperinsulinemic, it in fact does not show consistent hyperglycemia in the resting state. During stress, both obese animals and their lean littermates become hyperglycemic, but the magnitude of the hyperglycemia is exaggerated in the obese mice. Obese animals also show an exaggerated plasma glucose increase in response to epinephrine injection. This increase in plasma glucose is accompanied by a decrease in plasma insulin in response to both stress and epinephrine. Our findings suggest that environmental stimuli influence the expression of diabetes in the C57BL/6J obese mouse and therefore must be considered in studies of this animal model of diabetes.     

Pyruvate dehydrogenase activity in cardiac mitochondria from genetically diabetic mice

Pyruvate dehydrogenase (PDH) was studied in isolated heart mitochondria from genetically diabetic mice (C57BL/KsJ db/db) with progressive cardiomyopathy. Both the basal activity (active enzyme) and the total activity (the sum of active and inactive enzyme) were determined. In mitochondrial extracts from 8-18-wk-old db/db mice, there was a 73% decrease of basal activity accompanied by a 38% decrease of total activity as compared with controls. The lower basal activity at 8 wk of age suggests an increased conversion of the enzyme into the phosphorylated (inactive) form. Evidence is also given that the conversion of inactive (phosphorylated) enzyme into active (dephosphorylated) enzyme is inhibited in cardiac mitochondria prepared from 8-wk and older db/db mice. These changes coincide with the onset of defective oxidative metabolism and can explain the depressed pyruvate oxidation reported previously.