Empagliflozin protects mice against diet-induced obesity, insulin resistance and hepatic steatosis.

AIMS/HYPOTHESIS: Sodium-glucose cotransporter 2 (SGLT2) inhibitors are widely used in the treatment of type 2 diabetes, heart failure and chronic kidney disease. Their role in the prevention of diet-induced metabolic deteriorations, such as obesity, insulin resistance and fatty liver disease, has not been defined yet. In this study we set out to test whether empagliflozin prevents weight gain and metabolic dysfunction in a mouse model of diet-induced obesity and insulin resistance. METHODS: C57Bl/6 mice were fed a western-type diet supplemented with empagliflozin (WDE) or without empagliflozin (WD) for 10 weeks. A standard control diet (CD) without or with empagliflozin (CDE) was used to control for diet-specific effects. Metabolic phenotyping included assessment of body weight, food and water intake, body composition, hepatic energy metabolism, skeletal muscle mitochondria and measurement of insulin sensitivity using hyperinsulinaemic-euglycaemic clamps. RESULTS: Mice fed the WD were overweight, hyperglycaemic, hyperinsulinaemic and insulin resistant after 10 weeks. Supplementation of the WD with empagliflozin prevented these metabolic alterations. While water intake was significantly increased by empagliflozin supplementation, food intake was similar in WDE- and WD-fed mice. Adipose tissue depots measured by MRI were significantly smaller in WDE-fed mice than in WD-fed mice. Additionally, empagliflozin supplementation prevented significant steatosis found in WD-fed mice. Accordingly, hepatic insulin signalling was deteriorated in WD-fed mice but not in WDE-fed mice. Empagliflozin supplementation positively affected size and morphology of mitochondria in skeletal muscle in both CD- and WD-fed mice. CONCLUSIONS/INTERPRETATION: Empagliflozin protects mice from diet-induced weight gain, insulin resistance and hepatic steatosis in a preventative setting and improves muscle mitochondrial morphology independent of the type of diet.

Changing the dietary composition improves inflammation but not adipocyte thermogenesis in diet-induced obese mice.

Pronounced weight loss was shown to improve adipocyte dysfunction and insulin sensitivity in obese subjects. While bariatric surgery is frequently accompanied by adverse side effects, weight loss due to caloric restriction is often followed by weight regain. Here we aimed to determine whether switching the diet from a metabolically harmful Western type diet to a balanced standard diet is sufficient to reverse adipocyte dysfunction in diet-induced obese mice. Male C57BL/6 mice were fed a Western diet for 10 weeks and afterwards switched to a standard diet for eight more weeks (WD/SD mice) or continued to be fed a Western diet (WD/WD mice) ad libitum. Mice fed SD for 18 weeks served as control group (SD/SD). Insulin sensitivity was similar in WD/SD and SD/SD mice despite increased body weight in WD/SD mice. Beiging markers Ucp-1, Cidea and Cox8b were drastically reduced in subcutaneous adipose tissue of WD/SD mice when compared with SD/SD mice. Also, in brown adipose tissue morphologic features and markers of thermogenesis were still altered in both WD/SD and WD/WD mice. However, adipocyte size, Hif1α and macrophage infiltration were significantly lower in both, brown and white adipose tissues of WD/SD compared to WD/WD mice and additionally, a shift toward anti-inflammatory M2 phenotype was found in WD/SD mice only. In conclusion our data suggest that switching the diet is sufficient to improve adipose tissue inflammation, while western diet negatively affects thermogenic capacity of brown adipose tissue, and inhibits beiging of white adipose tissue in the long-term.

Apolipoprotein A5 controls fructose-induced metabolic dysregulation in mice.

BACKGROUND AND AIMS: Western dietary habits are partially characterized by increased uptake of fructose, which contributes to metabolic dysregulation and associated liver diseases. For example, a diet enriched with fructose drives insulin resistance and non-alcoholic fatty liver disease (NAFLD). The molecular hubs that control fructose-induced metabolic dysregulation are poorly understood. Apolipoprotein A5 (apoA5) controls triglyceride metabolism with a putative role in hepatic lipid deposition. We explored apoA5 as a rheostat for fructose-induced hepatic and metabolic disease in mammals. METHODS AND RESULTS: ApoA5 knock out (-/-) and wildtype (wt) mice were fed with high fructose diet or standard diet for 10 weeks. Afterwards, we conducted a metabolic characterization by insulin tolerance test as well as oral glucose tolerance test. Additionally, hepatic lipid content as well as transcription patterns of key enzymes and transcription factors in glucose and lipid metabolism were evaluated. Despite comparable body weight, insulin sensitivity was significantly improved in high fructose diet fed apoA5 (-/-) when compared to wildtype mice on the same diet. In parallel, hepatic triglyceride content was significantly lower in apoA5 (-/-) mice than in wt mice. No difference was seen between apoA5 (-/-) and wt mice on a standard diet. CONCLUSION: ApoA5 is involved in fructose-induced metabolic dysregulation and associated hepatic steatosis suggesting that apoA5 may be a novel target to treat metabolic diseases.

Cardioprotective effects of short-term empagliflozin treatment in db/db mice.

Sodium glucose transporter (SGLT)-2 inhibitors have consistently shown cardioprotective effects independent of the glycemic status of treated patients. In this study we aimed to investigate underlying mechanisms of short-term empagliflozin treatment in a mouse model of type II diabetes. Male db/db mice were fed a western type diet with or without enrichment with empagliflozin for 7 days. While glucose tolerance was significantly improved in empagliflozin treated mice, body weight and fasting insulin levels were comparable in both groups. Cardiac insulin signaling activity indicated by reduced proteinkinase B (AKT) phosphorylation was significantly decreased in the empagliflozin treated group. Remarkably, mitochondrial mass estimated by citrate synthase activity was significantly elevated in empagliflozin treated mice. Accordingly, mitochondrial morphology was significantly altered upon treatment with empagliflozin as analysed by transmission electron microscopy. Additionally, short-term empagliflozin therapy was associated with a changed cardiac tissue cytokine expression in favor of an anti-inflammatory pattern. Our data suggest that early cardioprotection in empagliflozin treated mice is independent of a reduction in body weight or hyperinsulinemia. Ameliorated mitochondrial ultrastructure, attenuated cardiac insulin signaling and diminished cardiac inflammation might contribute to the cardioprotective effects of empagliflozin.

Metabolic effects of reduced growth hormone action in fatty liver disease.

BACKGROUND: Adult growth hormone (GH) deficiency is associated with fatty liver disease and shows several features of the metabolic syndrome. Vice versa obesity is characterized as a state of low GH function. Here, we aimed to define the role of hepatic GH signaling and its metabolic consequences in non-alcoholic fatty liver disease. METHODS: In humans, GHR and IGF-1 levels were determined in liver samples of 29 obese patients with non-alcoholic steatohepatitis (NASH) or simple steatosis. Cellular effects of GH on insulin signaling were investigated in GH receptor (GHR) knockdown HepG2 cells. RESULTS: Hepatic IGF-1 expression levels reflecting GH action were significantly lower and fasting glucose concentrations higher in patients with NASH than in patients with simple steatosis. GHR knockdown in hepatocytes resulted in a scenario of high glucose output displayed by reduced glycogen content, increased gluconeogenesis and diminished insulin signaling. CONCLUSIONS: Our data suggest that GH signaling in the liver is diminished in patients with NASH and associated with deteriorated hepatic insulin sensitivity and metabolic activity. Reduced hepatic GH action might contribute to insulin resistance in obese patients with NASH.

Fat-enriched rather than high-fructose diets promote whitening of adipose tissue in a sex-dependent manner.

Adipose tissue is a critical regulator of energy metabolism and an effector organ of excessive caloric intake. We studied the effects of high-fructose (HFruD), high-fat (HFD) and mixed high-sucrose and high-fat diet (HFHSD) on adipocyte morphology and biology and consecutive metabolic effects in male and female C57BL/6 mice. Forty male and 40 female mice were randomly assigned to one of four dietary groups and fed for 10 weeks ad libitum. After 10 weeks of feeding, mice were analyzed in regard to glucose metabolism, insulin sensitivity and alteration in adipocyte morphology and function. Weight gain and diminished insulin sensitivity in HFD- and HFHSD-fed mice were accompanied by increased adipocyte size and a shift in size distribution towards larger adipocytes in all mice. The latter effect was also found but less pronounced in HFruD-fed mice, while insulin sensitivity and body weight remained unaffected. In male mice, expansion of white adipocytes along with decreased uncoupling protein 1 (UCP-1) expression and alterations of mitochondrial biogenesis was found after HFD and HFHSD feeding, while in female mice, UCP-1 expression was also reduced in the HFruD dietary group. Diet-induced cellular alterations were less pronounced in female mice. Our data demonstrate that high-fat rather than high fructose consumption drives metabolically disadvantageous alterations of adipocyte differentiation involving whitening and insulin resistance in a sex-dependent manner with most deleterious effects seen upon administration of combined sucrose and fat-enriched diet in male mice.

Dipeptidyl peptidase-4 impairs insulin signaling and promotes lipid accumulation in hepatocytes.

Dipeptidyl-peptidase 4 [DPP-4) has evolved into an important target in diabetes therapy due to its role in incretin hormone metabolism. In contrast to its systemic effects, cellular functions of membranous DPP-4 are less clear. Here we studied the role of DPP-4 in hepatic energy metabolism. In order to distinguish systemic from cellular effects we established a cell culture model of DPP-4 knockdown in human hepatoma cell line HepG2. DPP-4 suppression was associated with increased basal glycogen content due to enhanced insulin signaling as shown by increased phosphorylation of insulin-receptor substrate 1 (IRS-1), protein kinase B/Akt and mitogen-activated protein kinases (MAPK)/ERK, respectively. Additionally, glucose-6-phosphatase cDNA expression was significantly decreased in DPP-4 deficiency. Reduced triglyceride content in DPP-4 knockdown cells was paralleled by enhanced expressions of peroxisome proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase -1 (CPT-1) while sterol regulatory element-binding protein 1c (SREBP-1c) expression was significantly decreased. Our data suggest that hepatic DPP-4 induces a selective pathway of insulin resistance with reduced glycogen storage, enhanced glucose output and increased lipid accumulation in the liver. Hepatic DPP-4 might be a novel target in fatty liver disease in patients with glucose intolerance.