Ursodeoxycholic acid suppresses eosinophilic airway inflammation by inhibiting the function of dendritic cells through the nuclear farnesoid X receptor.

BACKGROUND: Ursodeoxycholic acid (UDCA) is the only known beneficial bile acid with immunomodulatory properties. Ursodeoxycholic acid prevents eosinophilic degranulation and reduces eosinophil counts in primary biliary cirrhosis. It is unknown whether UDCA would also modulate eosinophilic inflammation outside the gastrointestinal (GI) tract, such as eosinophilic airway inflammation seen in asthma. The working mechanism for its immunomodulatory effect is unknown. METHODS: The immunosuppressive features of UDCA were studied in vivo, in mice, in an ovalbumin (OVA)-driven eosinophilic airway inflammation model. To study the mechanism of action of UDCA, we analyzed the effect of UDCA on eosinophils, T cells, and dendritic cell (DCs). DC function was studied in greater detail, focussing on migration and T-cell stimulatory strength in vivo and interaction with T cells in vitro as measured by time-lapse image analysis. Finally, we studied the capacity of UDCA to influence DC/T cell interaction. RESULTS: Ursodeoxycholic acid treatment of OVA-sensitized mice prior to OVA aerosol challenge significantly reduced eosinophilic airway inflammation compared with control animals. DCs expressed the farnesoid X receptor for UDCA. Ursodeoxycholic acid strongly promoted interleukin (IL)-12 production and enhanced the migration in DCs. The time of interaction between DCs and T cells was sharply reduced in vitro by UDCA treatment of the DCs resulting in a remarkable T-cell cytokine production. Ursodeoxycholic acid-treated DCs have less capacity than saline-treated DCs to induce eosinophilic inflammation in vivo in Balb/c mice. CONCLUSION: Ursodeoxycholic acid has the potency to suppress eosinophilic inflammation outside the GI tract. This potential comprises to alter critical function of DCs, in essence, the effect of UDCA on DCs through the modulation of the DC/T cell interaction.

Exposure to chronic early-life stress lastingly alters the adipose tissue, the leptin system and changes the vulnerability to western-style diet later in life in mice.

Early-life stress (ES) increases the vulnerability to develop psychopathologies and cognitive decline in adulthood. Interestingly, this is often comorbid with metabolic disorders, such as obesity. However, it is unclear whether ES leads to lasting metabolic changes and to what extent this is associated with the ES-induced cognitive impairments. Here, we used an established chronic ES mouse model (from postnatal day (P) 2 to P9) to investigate the short- and long-term effects of ES exposure on parameters of the adipose tissue and the leptin system (i.e. circulating levels and gene expression of leptin and its receptor) in both sexes. Immediately following ES, the offspring exhibited reductions in white adipose tissue (WAT) mass, plasma leptin levels and in leptin mRNA expression in WAT. Furthermore, ES exposure led to increased brown adipose tissue and browning of WAT, which was evident by a drastic increase in uncoupling protein 1 mRNA expression in the inguinal WAT at P9. Notably, the ES-induced reductions in WAT mass, plasma leptin and leptin expression in WAT were sustained into adulthood and were accompanied by changes in body fat distribution, such as a higher ratio between mesenteric WAT and other WATs. Interestingly, while ES exposure increased leptin receptor mRNA expression in the choroid plexus, it was unaltered in the hippocampus. This suggests an adaptation to maintain central leptin homeostasis following ES exposure. In addition, chronic ES exposure resulted in the well-established cognitive impairment in object recognition performance during adulthood, which correlated positively with reductions in WAT mass observed in male, but not in female mice. Finally, to assess if ES leads to a different metabolic phenotype in a moderate obesogenic environment, we measured body fat accumulation of control and ES-exposed mice in response to a moderate western-style diet (WSD) that was provided during adulthood. ES-exposed mice subjected to WSD exhibit a higher increase in adiposity when compared to controls, suggesting that ES exposure might result in a higher vulnerability to develop obesity in a moderate obesogenic environment. To conclude, chronic ES exposure alters parameters of the adipose tissue, leads to central adaptations in leptin regulation and results in higher fat accumulations when exposed to a WSD challenge later in life. A better understanding of these metabolic effects induced by ES might open up new avenues for therapeutic (e.g. nutritional) interventions.

A novel approach to monitor glucose metabolism using stable isotopically labelled glucose in longitudinal studies in mice.

The aetiology of insulin resistance is still an enigma. Mouse models are frequently employed to study the underlying pathology. The most commonly used methods to monitor insulin resistance are the HOMA-IR, glucose or insulin tolerance tests and the hyperinsulinemic euglycaemic clamp (HIEC). Unfortunately, these tests disturb steady state glucose metabolism. Here we describe a method in which blood glucose kinetics can be determined in fasted mice without noticeably perturbing glucose homeostasis. The method involves an intraperitoneal injection of a trace amount of [6,6-(2)H2]glucose and can be performed repeatedly in individual mice. The validity and performance of this novel method was tested in mice fed on chow or high-fat diet for a period of five weeks. After administering the mice with [6,6-(2)H2]glucose, decay of the glucose label was followed in small volumes of blood collected by tail tip bleeding during a 90-minute period. The total amount of blood collected was less than 120 µL. This novel approach confirmed in detail the well-known increase in insulin resistance induced by a high-fat diet. The mice showed reduced glucose clearance rate, and reduced hepatic and peripheral insulin sensitivity. To compensate for this insulin resistance, ß-cell function was slightly increased. We conclude that this refinement of existing methods enables detailed information of glucose homeostasis in mice. Insulin resistance can be accurately determined while mechanistic insight is obtained in underlying pathology. In addition, this novel approach reduces the number of mice needed for longitudinal studies of insulin sensitivity and glucose metabolism.

Sustained activation of the mammalian target of rapamycin nutrient sensing pathway is associated with hepatic insulin resistance, but not with steatosis, in mice.

AIMS/HYPOTHESIS: Activation of nutrient sensing through mammalian target of rapamycin (mTOR) has been linked to the pathogenesis of insulin resistance. We examined activation of mTOR-signalling in relation to insulin resistance and hepatic steatosis in mice. MATERIALS AND METHODS: Chronic hepatic steatosis and hepatic insulin resistance were induced by high-fat feeding of male C57BL/6Jico mice for 6 weeks. In addition, acute hepatic steatosis in the absence of insulin resistance was induced by pharmacological blockade of beta-oxidation using tetradecylglycidic acid (TDGA). mTOR signalling was examined in liver homogenates. RESULTS: High-fat feeding caused obesity (p<0.001), hepatic steatosis (p<0.05) and hepatic insulin resistance (p<0.05). The phosphorylation of mTOR and its downstream targets p70S6 kinase and S6 ribosomal protein was two-fold higher in mice on a high-fat diet than in mice fed standard chow (all p<0.05) and associated with enhanced rates of protein synthesis. Acute induction of hepatic steatosis with TDGA had no effect on mTOR activity. The increased activity of the mTOR pathway in livers from mice on a high-fat diet could not be ascribed to diet-induced alterations in known modulators of mTOR activity such as circulating plasma leucine levels, phosphorylation of protein kinase B and AMP-activated protein kinase, and changes in mitochondrial function. CONCLUSIONS/INTERPRETATION: High-fat diet induces increase of the mTOR nutrient sensing pathway in association with hepatic insulin resistance, but not with hepatic lipid accumulation as such.

Enhanced glucose cycling and suppressed de novo synthesis of glucose-6-phosphate result in a net unchanged hepatic glucose output in ob/ob mice.

AIMS/HYPOTHESIS: Leptin-deficient ob/ob mice are hyperinsulinaemic and hyperglycaemic; however, the cause of hyperglycaemia remains largely unknown. METHODS: Glucose metabolism in vivo in 9-h fasted ob/ob mice and lean littermates was studied by infusing [U-(13)C]-glucose, [2-(13)C]-glycerol, [1-(2)H]-galactose and paracetamol for 6 h, applying mass isotopomer distribution analysis on blood glucose and urinary paracetamol-glucuronide. RESULTS: When expressed on the basis of body weight, endogenous glucose production (109+/-23 vs 152+/-27 micromol.kg(-1).min(-1), obese versus lean mice, p<0.01) and de novo synthesis of glucose-6-phosphate (122+/-13 vs 160+/-6 micromol.kg(-1).min(-1), obese versus lean mice, p<0.001) were lower in ob/ob mice than in lean littermates. In contrast, glucose cycling was greatly increased in obese mice (56+/-13 vs 26+/-4 micromol.kg(-1).min(-1), obese versus lean mice, p<0.001). As a result, total hepatic glucose output remained unaffected (165+/-31 vs 178+/-28 micromol.kg(-1).min(-1), obese vs lean mice, NS). The metabolic clearance rate of glucose was significantly lower in obese mice (8+/-2 vs 18+/-2 ml.kg(-1).min(-1), obese versus lean mice, p<0.001). Hepatic mRNA levels of genes encoding for glucokinase and pyruvate kinase were markedly increased in ob/ob mice. CONCLUSIONS/INTERPRETATION: Unaffected total hepatic glucose output in the presence of hyperinsulinaemia reflects hepatic insulin resistance in ob/ob mice, which is associated with markedly increased rates of glucose cycling. Hyperglycaemia in ob/ob mice primarily results from a decreased metabolic clearance rate of glucose.