Genetic models for non insulin dependent diabetes mellitus in rodents

High-fructose and high-fat diet-induced disorders in rats: impact on diabetes risk, hepatic and vascular complications

BACKGROUND

As a result of the increased consumption of sugar-rich and fatty-products, and the increase in preference for such products, metabolic disorders are becoming more common at a younger age. Fructose is particularly used in prepared foods and carbonated beverages. We investigated the impact of regular consumption of fructose, in combination or not with fatty food, on the onset of metabolic syndrome and type 2 diabetes (T2D). We evaluated the metabolic, oxidative, and functional effects on the liver and blood vessels, both related to diabetes complications.

METHODS

High-fat diet (HFD), high-fructose beverages (HF) or both (HFHF) were compared to rats fed with normal diet (ND) for 8 months to induce T2D and its metabolic, oxidative, and functional complications. Metabolic control was determined by measuring body weight, fasting blood glucose, C-peptide, HOMA2-IR, leptin, and cholesterol; oxidative parameters were studied by lipid peroxidation and total antioxidant capacity in plasma and the use of ROS labelling on tissue. Histological analysis was performed on the liver and endothelial function was performed in main mesenteric artery using organ-baths.

RESULTS

After 2 months, HFHF and HFD increased body weight, leptin, HOMA2-IR associated to steatosis, oxidative stress in plasma and tissues, whereas HF had only a transient increase of leptin and c-peptide. Only HFHF induced fasting hyperglycaemia after 6 months and persistent hyperinsulinaemia and fasting hyperglycaemia with complicated steatosis (inflammation and fibrosis) after 8 months. HFHF and HFD induced endothelial dysfunction at 8 months of diet.

CONCLUSIONS

Six months, high fat and high carbohydrate induced T2D with widespread tissues effects. We demonstrated the role of oxidative stress in pathogenesis as well as in complications (hepatic and vascular), reinforcing interest in the use of antioxidants in the prevention and treatment of metabolic diseases, including T2D.

Glucose intolerance and reduced islet blood flow in transgenic mice expressing the FRK tyrosine kinase under the control of the rat insulin promoter

The FRK tyrosine kinase has previously been shown to transduce beta-cell cytotoxic signals in response to cytokines and streptozotocin and to promote beta-cell proliferation and an increased beta-cell mass. We therefore aimed to further evaluate the effects of overexpression of FRK tyrosine kinase in beta-cells. A transgenic mouse expressing kinase-active FRK under control of the insulin promoter (RIP-FRK) was studied with regard to islet endocrine function and vascular morphology. Mild glucose intolerance develops in RIP-FRK male mice of at least 4 mo of age. This effect is accompanied by reduced glucose-stimulated insulin secretion in vivo and reduced second-phase insulin secretion in response to glucose and arginine upon pancreas perfusion. Islets isolated from the FRK transgenic mice display a glucose-induced insulin secretory response in vitro similar to that of control islets. However, islet blood flow per islet volume is decreased in the FRK transgenic mice. These mice also exhibit a reduced islet capillary lumen diameter as shown by electron microscopy. Total body weight and pancreas weight are not significantly affected, but the beta-cell mass is increased. The data suggest that long-term expression of active FRK in beta-cells causes an in vivo insulin-secretory defect, which may be the consequence of islet vascular abnormalities that yield a decreased islet blood flow.

Diabetic modifier QTLs identified in F2 intercrosses between Akita and A/J mice

To identify novel genetic modifiers of type 2 diabetes (T2D), we performed quantitative trait loci (QTL) analysis on F(2) progeny of hypoinsulinemic diabetic Akita mice, heterozygous for the Ins2 gene Cys96Tyr mutation, and nondiabetic A/J mice. We generated 625 heterozygous (F(2)-Hetero) and 338 wild-type (F(2)-Wild) mice with regard to the Ins2 mutation in F(2) intercross progeny. We measured quantitative traits, including plasma glucose and insulin concentrations during the intraperitoneal glucose tolerance test (IPGTT), and body weight (BW). We observed three significant QTLs in hypoinsulinemic hyperglycemic male F(2)-Hetero mice, designated Dbm1, Dbm3, and Dbm4 on Chromosomes 6, 14, and 15, respectively. They showed linkage to plasma glucose concentrations, with significant maximum logarithm of odds (LOD) scores of 4.12, 4.17, and 6.17, respectively, all exceeding threshold values by permutation tests. In normoinsulinemic normoglycemic male F(2)-Wild mice, Dbm1 on Chromosome 6 showed linkage to both plasma insulin concentrations and BW, and Dbm2 on Chromosome 11 showed linkage to plasma glucose concentrations only, with LOD scores of 4.52 and 6.32, and 5.78, respectively. Based on these results, we concluded that Dbm1, Dbm2, Dbm3, and Dbm4 represent four major modifier QTLs specifically affecting T2D-related traits and that these diabetic modifier QTLs are conditional on the heterozygous Ins2 gene mutation and sex to exert their modifier functions. Identification of the genes responsible for these QTLs would provide new drug development targets for human T2D.

Role of islet amyloid in type 2 diabetes mellitus

Diabetes mellitus is one of the most common metabolic diseases worldwide and its prevalence is rapidly increasing. Due to its chronic nature (diabetes mellitus can be treated but as yet not cured) and its serious complications, it is one of the most expensive diseases with regard to total health care costs per patient. The elevated blood glucose levels in diabetes mellitus are caused by a defect in production and/or secretion of the polypeptide hormone insulin, which normally promotes glucose-uptake in cells. Insulin is produced by the pancreatic 'beta-cells' in the 'islets of Langerhans', which lie distributed within the exocrine pancreatic tissue. In type 2 diabetes mellitus, the initial defect in the pathogenesis of the disease in most of the patients is believed to be 'insulin resistance'. Hyperglycemia (clinically overt diabetes mellitus) will not develop as long as the body is able to produce enough insulin to compensate for the reduced insulin action. When this compensation fails ('beta-cell failure') blood glucose levels will become too high. In this review, we discuss one of the mechanisms that have been implicated in the development of beta-cell failure, i.e. amyloid formation in the pancreatic islets. This islet amyloid is a characteristic histopathological feature of type 2 diabetes mellitus and both in vitro and in vivo studies have revealed that its formation causes death of islet beta-cells. Being a common pathogenic factor in an otherwise heterogeneous disease, islet amyloidosis is an attractive novel target for therapeutic intervention in type 2 diabetes mellitus.

Feline Models of Type 2 Diabetes Mellitus

Feline diabetes mellitus (FDM) closely resembles human type 2 diabetes mellitus (T2DM) in many respects including clinical, physiological, and pathological features of the disease. These features include age of onset of FDM in middle age, association with obesity, residual but declining insulin secretion, development of islet amyloid deposits, loss of approximately 50% of beta-cell mass, and development of complications in several organ systems including peripheral polyneuropathy and retinopathy. Many of the pathological aspects of the disease are also experimentally inducible, facilitating study of the pathogenesis of these lesions. Physiological aspects of FDM and obesity are also well studied in the cat and provide an excellent basis for comparative studies of human T2DM. The relatively short generation time of cats along with breed predispositions to development of FDM may allow for more rapid screening and identification of genetic markers for diabetes susceptibility. FDM, in both spontaneous and inducible forms, therefore provides a good animal model of human T2DM and may provide additional insights into the pathogenesis of this important condition.

Development of insulin resistance and obesity in mice overexpressing cellular glutathione peroxidase

Insulin resistance, a hallmark of type 2 diabetes, is associated with oxidative stress. However, the role of reactive oxygen species or specific antioxidant enzymes in its development has not been tested under physiological conditions. The objective of our study was to investigate the impact of overexpression of glutathione peroxidase 1 (GPX1), an intracellular selenoprotein that reduces hydrogen peroxide (H(2)O(2)) in vivo, on glucose metabolism and insulin function. The GPX1-overexpressing (OE) and WT male mice (n = 80) were fed a selenium-adequate diet (0.4 mg/kg) from 8 to 24 weeks of age. Compared with the WT, the OE mice developed (P < 0.05) hyperglycemia (117 vs. 149 mg/dl), hyperinsulinemia (419 vs. 1,350 pg/ml), and elevated plasma leptin (5 vs. 16 ng/ml) at 24 weeks of age. Meanwhile, these mice were heavier (37 vs. 27 g, P < 0.001) and fatter (37% vs. 17% fat, P < 0.01) than the WT mice. At 30-60 min after an insulin challenge, the OE mice had 25% less (P < 0.05) of a decrease in blood glucose than the WT mice. Their insulin resistance was associated with a 30-70% reduction (P < 0.05) in the insulin-stimulated phosphorylations of insulin receptor (beta-subunit) in liver and Akt (Ser(473) and Thr(308)) in liver and soleus muscle. Here we report the development of insulin resistance in mammals with elevated expression of an antioxidant enzyme and suggest that increased GPX1 activity may interfere with insulin function by overquenching intracellular reactive oxygen species required for insulin sensitizing.

Mice heterozygous for Atp10c, a putative amphipath, represent a novel model of obesity and type 2 diabetes

Atp10c is a novel type IV P-type ATPase and is a putative phospholipid transporter. The purpose of this study was to assess the overall effect of the heterozygous deletion of Atp10c on obesity-related phenotypes and metabolic abnormalities in mice fed a high-fat diet. Heterozygous mice with maternal inheritance of Atp10c were compared with heterozygous mice with paternal inheritance of Atp10c and wild-type controls. Body weight, adiposity index, and plasma insulin, leptin and triglyceride concentrations were significantly greater in the mutants inheriting the deletion maternally compared with their sex- and age-matched control male mice fed a 10% fat (% energy) diet and female mice fed a 45% fat (% energy) diet. Glucose and insulin tolerance tests were performed after mice consumed the diets for 4 and 8 wk. Mutants had altered glucose tolerance and insulin response compared with controls, suggesting insulin resistance in both sexes. Mice were killed at 12 wk and routine gross and histological evaluations of the liver, pancreas, adipose tissue, and heart were performed. Histological evaluation showed micro- and macrovesicular lipid deposition within the hepatocytes that was more severe in the mutant mice than in age-matched controls. Although sex differences were observed, our data suggest that heterozygous deletion along with an unusual pattern of maternal inheritance of the chromosomal region containing the single gene, Atp10c, causes obesity, type 2 diabetes, and nonalcoholic fatty liver disease in these mice.

Combinations of nondiabetic parental genomes elicit impaired glucose tolerance in mouse SMXA recombinant inbred strains

Type 2 diabetes in humans is not a single gene disorder but a multifactorial disease caused by the interaction of multiple genes and environmental factors. Recombinant inbred (RI) strains are a powerful tool for analyzing not only single genetic traits but also multifactorial genetic traits. By using the SMXA RI mice, we genetically dissected diabetes-related traits (BMI, nonfasting blood glucose concentration, and blood glucose concentration during intraperitoneal glucose tolerance tests). For minimizing the variation of glucose tolerance in each strain, all mice were fed the high-carbohydrate diet and subjected to phenotypic and genetic analyses. The parental strains, SM/J and A/J, were nondiabetic, and the differences of the mean values of diabetes-related traits were small. In contrast, an impaired glucose tolerance was observed in (SM x A)F1 mice, and marked differences in diabetes-related traits were observed in 19 SMXA RI strains. In particular, several SMXA RI strains showed markedly impaired glucose tolerance and hyperglycemia. Quantitative trait locus (QTL) analysis revealed a locus on chromosome (Chr) 10 contributing significant effect on nonfasting blood glucose concentration, as well as six diabetes-related loci on four chromosomes with suggestive evidence of linkage with diabetes-related phenotypes. The A/J-derived QTLs on Chr 2 and 18 and an SM/J-derived QTL on Chr 10 contributed to the impairment of glucose tolerance and/or the increase of blood glucose concentration. The present study indicates that QTLs derived from parental SM/J and A/J genomes, both of which are nondiabetic, interact in the RI genomes, leading to the development of hyperglycemia and diabetic phenotypes. Genetic dissection of this kind of diabetogenesis will increase our understanding of the complex gene-gene interaction and mode of inheritance in human type 2 diabetes.

Defining the genetic contribution of type 2 diabetes mellitus

Type 2 diabetes mellitus is a common multifactorial genetic syndrome, which is determined by several different genes and environmental factors. It now affects 150 million people world wide but its incidence is increasing rapidly because of secondary factors, such as obesity, hypertension, and lack of physical activity. Many studies have been carried out to determine the genetic factors involved in type 2 diabetes mellitus. In this review we look at the different strategies used and discuss the genome wide scans performed so far in more detail. New technologies, such as microarrays, and the discovery of SNPs will lead to a greater understanding of the pathogenesis of type 2 diabetes mellitus and to better diagnostics, treatment, and eventually prevention.

Genetic analysis of a new mouse model for non-insulin-dependent diabetes

The TallyHo (TH) mouse strain is a newly established model for non-insulin-dependent diabetes mellitus (NIDDM). TH mice show obesity, hyperinsulinemia, hyperlipidemia, and male-limited hyperglycemia. A genetic dissection of the diabetes syndrome has been carried out using male backcross 1 progeny obtained from crosses between (C57BL/6J x TH)F1 and TH mice or (CAST/Ei x TH)F1 and TH mice. A genome-wide scan reveals three quantitative trait loci (QTLs), Tanidd1-3 (TH-associated NIDDM) linked to hyperglycemia. The major QTL (common in both crosses), Tanidd1, maps to chromosome (Chr) 19. Additionally, gene-gene interactions contributing to hyperglycemia have been observed between Tanidd1 and a locus on Chr 18 as well as between Tanidd2 and a locus on Chr 16. The overt hyperglycemia in TH mice is, therefore, likely due to a mutation in a major diabetes susceptibility locus on Chr 19, which interacts with additional genes to lead to an observable phenotype.

The use of transgenic mice in pharmacokinetic and pharmacodynamic studies

Transgenic technology has made it possible to alter the genetic make-up of a laboratory mouse through the removal or insertion of selected genes. The resulting transgenic mouse provides a means for determining the developmental and functional contributions of selected genes and the proteins they encode. The current article reviews examples of the use of transgenic mice in pharmacokinetic and pharmacodynamic studies. In addition to examining current applications of transgenic technology in the areas of pharmacokinetics and pharmacodynamics, the potential for future advancements as well as limitations of the technology are discussed.

Fenofibrate and rosiglitazone lower serum triglycerides with opposing effects on body weight

Activators of peroxisome proliferator activated receptors (PPARs) are effective drugs to improve the metabolic abnormalities linking hypertriglyceridemia to diabetes, hyperglycemia, insulin-resistance, and atherosclerosis. We compared the pharmacological profile of a PPARalpha activator, fenofibrate, and a PPARgamma activator, rosiglitazone, on serum parameters, target gene expression, and body weight gain in (fa/fa) fatty Zucker rats and db/db mice as well as their association in db/db mice. Fenofibrate faithfully modified the expression of PPARalpha responsive genes. Rosiglitazone increased adipose tissue aP2 mRNA in both models while increasing liver acyl CoA oxidase mRNA in db/db mice but not in fatty Zucker rats. Both drugs lowered serum triglycerides yet rosiglitazone markedly increased body weight gain while fenofibrate decreased body weight gain in fatty Zucker rats. KRP 297, which has been reported to be a PPARalpha and gamma co-activator, also affected serum triglycerides and insulin in fatty Zucker rats although no change in body weight gain was noted. These results serve to clearly differentiate the metabolic finality of two distinct classes of drugs, as well as their corresponding nuclear receptors, having similar effects on serum triglycerides.