Biljana Bursać

Tissue-specific regulation of inflammation by macrophage migration inhibitory factor and glucocorticoids in fructose-fed Wistar rats.

High fructose consumption is commonly associated with insulin resistance, disturbed glucose homeostasis and low-grade inflammation. Increased glucocorticoid production within adipose tissue has been implicated in the pathogenesis of fructose-induced metabolic syndrome. Immunosuppressive actions of glucocorticoids can be counter-regulated by macrophage migration inhibitory factor (MIF), which is recognised as a key molecule in metabolic inflammation. In the present study, we hypothesised that coordinated action of glucocorticoids and MIF can mediate the effects of a high-fructose diet on adipose tissue and liver inflammation. We examined the effects of long-term consumption of a 10% fructose solution on corticosterone (CORT) and MIF levels in rat blood plasma, liver and adipose tissue, as well as MIF and TNF-a mRNA expression and NF-kB activation in the same tissues. The high-fructose diet led to an increase in both CORT and MIF in the adipose tissue, and a highly significant positive correlation between their levels was observed. The attenuated NF-kB activation and unaltered TNF-a mRNA expression noticed in the adipose tissue could be interpreted as an outcome of the opposing actions of CORT and MIF. In contrast to adipose tissue, inflammation in the liver was characterised by NF-kB activation, an increased TNF-a mRNA level and unchanged levels of MIF protein, MIF mRNA and CORT. Overall, these findings suggest that a high-fructose diet differently affects the levels of glucocorticoids and MIF in the adipose tissue and liver, implicating that fructose over-consumption has tissue-specific effects on regulation of metabolic inflammation.

Fructose consumption enhances glucocorticoid action in rat visceral adipose tissue.

The rise in consumption of refined sugars high in fructose appears to be an important factor for the development of obesity and metabolic syndrome. Fructose has been shown to be involved in genesis and progression of the syndrome through deregulation of metabolic pathways in adipose tissue. There is evidence that enhanced glucocorticoid regeneration within adipose tissue, mediated by the enzyme 11beta-hydroxysteroid dehydrogenase Type 1 (11βHSD1), may contribute to adiposity and metabolic disease. 11βHSD1 reductase activity is dependent on NADPH, a cofactor generated by hexose-6-phosphate dehydrogenase (H6PDH). We hypothesized that harmful effects of long-term high fructose consumption could be mediated by alterations in prereceptor glucocorticoid metabolism and glucocorticoid signaling in the adipose tissue of male Wistar rats. We analyzed the effects of 9-week drinking of 10% fructose solution on dyslipidemia, adipose tissue histology and both plasma and tissue corticosterone level. Prereceptor metabolism of glucocorticoids was characterized by determining 11βHSD1 and H6PDH mRNA and protein levels. Glucocorticoid signaling was examined at the level of glucocorticoid receptor (GR) expression and compartmental redistribution, as well as at the level of expression of its target genes (GR, phosphoenolpyruvate carboxyl kinase and hormone-sensitive lipase). Fructose diet led to increased 11βHSD1 and H6PDH expression and elevated corticosterone level within the adipose tissue, which was paralleled with enhanced GR nuclear accumulation. Although the animals did not develop obesity, nonesterified fatty acid and plasma triglyceride levels were elevated, indicating that fructose, through enhanced prereceptor metabolism of glucocorticoids, could set the environment for possible later onset of obesity.

High-fructose diet leads to visceral adiposity and hypothalamic leptin resistance in male rats — do glucocorticoids play a role?

Fructose overconsumption has been involved in the genesis and progression of the metabolic syndrome. Hypothalamus and adipose tissue, major organs for control of food intake and energy metabolism, play crucial roles in metabolic homeostasis. We hypothesized that glucocorticoid signaling mediates the effects of a fructose-enriched diet on visceral adiposity by acting on neuropeptide Y (NPY) in the hypothalamus and altering adipogenic transcription factors in the visceral adipose tissue. We analyzed the effects of 9-week consumption of 60% fructose solution on dyslipidemia, insulin and leptin sensitivity, and adipose tissue histology in male Wistar rats. Glucocorticoid signaling was assessed in both hypothalamus and visceral adipose tissue, while the levels of peroxisome-proliferator-activated receptor γ (PPARγ), sterol regulatory element-binding protein-1 (SREBP-1) and lipin-1, together with the levels of their target genes expression, were analyzed in the visceral adipose tissue. The results showed that long-term consumption of highly concentrated liquid fructose led to the development of visceral adiposity, elevated triglycerides and hypothalamic leptin resistance accompanied by stimulated glucocorticoid signaling and NPY mRNA elevation. Results from adipose tissue implied that fructose consumption shifted the balance between glucocorticoid receptor and adipogenic transcriptional factors (PPARγ, SREBP-1 and lipin-1) in favor of adipogenesis judged by distinctly separated populations of small adipocytes observed in this tissue. In summary, we propose that high-fructose-diet-induced alterations of glucocorticoid signaling in both hypothalamus and adipose tissue result in enhanced adipogenesis, possibly serving as an adaptation to energy excess in order to limit deposition of fat in nonadipose tissues.

The impact of different fructose loads on insulin sensitivity, inflammation, and PSA-NCAM-mediated plasticity in the hippocampus of fructose-fed male rats

Abstract Objectives High fructose diet has been shown to have damaging effects on the hippocampus, a brain region critical for learning and memory. Fructose-induced hippocampal dysfunction may arise from insulin resistance and inflammation, and from concomitant changes in plasticity-related presynaptic proteins. We hypothesized that long-term access to fructose (10% and 60% solutions over a period of 9 weeks) affects insulin sensitivity, hippocampal inflammation, and synaptic plasticity in male Wistar rats. Methods We used the area under curve (AUC) glucose value and inhibitory Ser307 phosphorylation of hippocampal insulin receptor substrate 1 (IRS-1) as hallmarks of insulin resistance. To examine inflammatory state, we analysed protein levels and intracellular redistribution of glucocorticoid receptor and nuclear factor-κB (NFκB), as well as mRNA levels of tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β). Polysialylated neural cell adhesion molecule (PSA-NCAM) protein was used as a synaptic plasticity marker. Results The results indicate different impacts of diverse fructose-enriched diets on insulin sensitivity and hippocampal inflammation and plasticity. Long-term ingestion of 10% fructose solution led to increase in AUC glucose value, as well as to elevation in hippocampal IRS-1 Ser307 phosphorylation and increase in IL-6 mRNA. In rats consuming 60% fructose, the level of PSA-NCAM was reduced, in parallel with augmented glucocorticoid signalization. Discussion The results showed that long-term consumption of 10% fructose solution induces hippocampal insulin resistance and inflammation, with no concomitant plasticity changes. Interestingly, rats fed with higher concentrations of fructose displayed impaired plastic response of the hippocampus, coinciding with augmented glucocorticoid signalling, which may provide a basis for cognitive deficits associated with metabolic syndrome.

Enhanced prereceptor glucocorticoid metabolism and lipogenesis impair insulin signaling in the liver of fructose-fed rats

Overconsumption of fructose, as a highly lipogenic sugar, may profoundly affect hepatic metabolism and has been associated with many components of the metabolic syndrome, particularly with insulin resistance and Type 2 diabetes. In this study, we proposed that high fructose diet may enhance lipogenesis and decrease insulin sensitivity in the liver through dysregulation of glucocorticoid signaling. Therefore, we examined the effects of long-term consumption of 10% fructose solution on triglyceridemia, liver histology and intracellular corticosterone level, as well as on 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and hexose-6-phosphate dehydrogenase (H6PDH) mRNA and protein levels in the rat liver. Glucocorticoid action was assessed by glucocorticoid receptor (GR) expression and intracellular redistribution. We also analyzed the expression of enzymes involved in gluconeogenesis and lipogenesis, phosphoenolpyruvate carboxykinase (PEPCK) and lipin-1. The results have shown that fructose-rich diet led to increase in 11βHSD1 and H6PDH protein levels, while hepatic corticosterone concentration remained unchanged. Concomitantly, GR was increasingly accumulated in the cytoplasm, whereas its nuclear level was unchanged and accompanied by diminished PEPCK mRNA level. Elevation of lipin-1 in the liver microsomes suggested that fructose diet led to an increase in lipogenesis and consequently to hypertriglyceridemia. The observed increase of insulin receptor supstrate-1 phosphorylation on Ser(307) represents a hallmark of impaired insulin signaling in the liver of fructose-fed rat and probably is a consequence of the alterations in 11βHSD1 and lipin-1 levels. Overall, our findings suggest that fructose-rich diet may perturb hepatic prereceptor glucocorticoid metabolism and lipogenesis, resulting in hypertriglyceridemia and attenuated hepatic insulin sensitivity.

Possible involvement of glucocorticoids in 5α-dihydrotestosterone-induced PCOS-like metabolic disturbances in the rat visceral adipose tissue

Polycystic ovary syndrome (PCOS) is a reproductive and metabolic disorder characterized by hyperandrogenism, ovulatory dysfunction, visceral obesity and insulin resistance. We hypothesized that changes in glucocorticoid metabolism and signaling in the visceral adipose tissue may contribute to disturbances of lipid metabolism in the rat model of PCOS obtained by 5α-dihydrotestosterone (DHT) treatment of prepubertal female Wistar rats. The results confirmed that DHT treatment caused anovulation, obesity and dyslipidemia. Enhanced glucocorticoid prereceptor metabolism, assessed by elevated intracellular corticosterone and increased 11 beta-hydroxysteroid dehydrogenase type 1 mRNA and protein levels, was accompanied by glucocorticoid receptor (GR) nuclear accumulation. In concert with the increased expression of GR-regulated prolipogenic genes (lipin-1, sterol regulatory element binding protein 1, fatty acid synthase, phosphoenolpyruvate carboxykinase), histological analyses revealed hypertrophic adipocytes. The results suggest that glucocorticoids influence lipid metabolism in the visceral adipose tissue in the way that may contribute to pathogenesis of metabolic disturbances associated with PCOS.

Involvement of glucocorticoid prereceptor metabolism and signaling in rat visceral adipose tissue lipid metabolism after chronic stress combined with high-fructose diet

Both fructose overconsumption and increased glucocorticoids secondary to chronic stress may contribute to overall dyslipidemia. In this study we specifically assessed the effects and interactions of dietary fructose and chronic stress on lipid metabolism in the visceral adipose tissue (VAT) of male Wistar rats. We analyzed the effects of 9-week 20% high fructose diet and 4-week chronic unpredictable stress, separately and in combination, on VAT histology, glucocorticoid prereceptor metabolism, glucocorticoid receptor subcellular redistribution and expression of major metabolic genes. Blood triglycerides and fatty acid composition were also measured to assess hepatic Δ9 desaturase activity. The results showed that fructose diet increased blood triglycerides and Δ9 desaturase activity. On the other hand, stress led to corticosterone elevation, glucocorticoid receptor activation and decrease in adipocyte size, while phosphoenolpyruvate carboxykinase, adipose tissue triglyceride lipase, FAT/CD36 and sterol regulatory element binding protein-1c (SREBP-1c) were increased, pointing to VAT lipolysis and glyceroneogenesis. The combination of stress and fructose diet was associated with marked stimulation of fatty acid synthase and acetyl-CoA carboxylase mRNA level and with increased 11β-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase protein levels, suggesting a coordinated increase in hexose monophosphate shunt and de novo lipogenesis. It however did not influence the level of peroxisome proliferator-activated receptor-gamma, SREBP-1c and carbohydrate responsive element-binding protein. In conclusion, our results showed that only combination of dietary fructose and stress increase glucocorticoid prereceptor metabolism and stimulates lipogenic enzyme expression suggesting that interaction between stress and fructose may be instrumental in promoting VAT expansion and dysfunction.

Fructose-rich diet differently affects angiotensin II receptor content in the nucleus and a plasma membrane fraction of visceral adipose tissue

The adipose tissue renin-angiotensin system (RAS) is proposed to be a pathophysiological link between adipose tissue dysregulation and metabolic disorders induced by a fructose-rich diet (FRD). RAS can act intracellularly. We hypothesized that adipocyte nuclear membranes possess angiotensin receptor types 1 and 2 (AT1R and AT2R), which couple to nuclear signaling pathways and regulate oxidative gene expression under FRD conditions. We analyzed the effect of consumption of 10% fructose solution for 9 weeks on biochemical parameters, adipocyte morphology, and expression of AT1R, AT2R, AT1R-associated protein (ATRAP), NADPH oxidase 4 (NOX4), matrix metalloproteinase-9 (MMP-9), and manganese superoxide dismutase (MnSOD) in adipose tissue of Wistar rats. We detected AT1R and AT2R in the nuclear fraction. FRD reduced the level of angiotensin receptors in the nucleus, while increased AT1R and decreased AT2R levels were observed in the plasma membrane. FRD increased the ATRAP mRNA level and decreased MnSOD mRNA and protein levels. No significant differences were observed for MMP-9 and NOX4 mRNA levels. These findings coincided with hyperleptinemia, elevated blood pressure and triglycerides, and unchanged visceral adipose tissue mass and morphology in FRD rats. Besides providing evidence for nuclear localization of angiotensin receptors in visceral adipose tissue, this study demonstrates the different effects of FRD on AT1R expression in different cellular compartments. Elevated blood pressure and decreased antioxidant capacity in visceral fat of fructose-fed rats were accompanied by an increased AT1R level in the plasma membrane, while upregulation of ATRAP and a decrease of nuclear membrane AT1R suggest an increased capacity for attenuation of excessive AT1R signaling and visceral adiposity.

Disturbances of systemic and hippocampal insulin sensitivity in macrophage migration inhibitory factor (MIF) knockout male mice lead to behavioral changes associated with decreased PSA-NCAM levels

ABSTRACT Macrophage migration inhibitory factor (MIF) is a multifunctional cytokine well known for its role in inflammation enhancement. However, a growing body of evidence is emerging on its role in energy metabolism in insulin sensitive tissues such as hippocampus, a brain region implicated in cognition, learning and memory. We hypothesized that genetic deletion of MIF may result in the specific behavioral changes, which may be linked to impairments in brain or systemic insulin sensitivity by possible changes of the hippocampal synaptic plasticity. To assess memory, exploratory behavior and anxiety, three behavioral tests were applied on Mif gene‐deficient (MIF−/−) and “wild type” C57BL/6J mice (WT). The parameters of systemic and hippocampal insulin sensitivity were also determined. The impact of MIF deficiency on hippocampal plasticity was evaluated by analyzing the level of synaptosomal polysialylated‐neural cell adhesion molecule (PSA‐NCAM) plasticity marker and mRNA levels of different neurotrophic factors. The results showed that MIF−/− mice exhibit emphasized anxiety‐like behaviors, as well as impaired recognition memory, which may be hippocampus‐dependent. This behavioral phenotype was associated with impaired systemic insulin sensitivity and attenuated hippocampal insulin sensitivity, characterized by increased inhibitory Ser307 phosphorylation of insulin receptor substrate 1 (IRS1). Finally, MIF−/− mice displayed a decreased hippocampal PSA‐NCAM level and unchanged Bdnf, NT‐3, NT‐4 and Igf‐1 mRNA levels. The results suggest that the lack of MIF leads to disturbances of systemic and hippocampal insulin sensitivity, which are possibly responsible for memory deficits and anxiety, most likely through decreased PSA‐NCAM‐mediated neuroplasticity rather than through neurotrophic factors. HIGHLIGHTSMacrophage migration inhibitory factor (MIF)−/− mice show anxiety‐like behaviorMIF−/− mice exhibit impaired recognition memoryMIF loss was associated with impaired systemic and hippocampal insulin sensitivityBehavioral changes are related to decreased synaptic plasticity

Enhanced Inflammation without Impairment of Insulin Signaling in the Visceral Adipose Tissue of 5α-Dihydrotestosterone-Induced Animal Model of Polycystic Ovary Syndrome

Polycystic ovary syndrome is a heterogeneous endocrine and metabolic disorder associated with abdominal obesity, dyslipidemia and insulin resistance. Since abdominal obesity is characterized by low-grade inflammation, the aim of the study was to investigate whether visceral adipose tissue inflammation linked to abdominal obesity and dyslipidemia could lead to impaired insulin sensitivity in the animal model of polycystic ovary syndrome.Female Wistar rats were treated with nonaromatizable 5α-dihydrotestosterone pellets in order to induce reproductive and metabolic characteristics of polycystic ovary syndrome. Glucose, triglycerides, non-esterified fatty acids and insulin were determined in blood plasma. Visceral adipose tissue inflammation was evaluated by the nuclear factor kappa B intracellular distribution, macrophage migration inhibitory factor protein level, as well as TNFα, IL6 and IL1β mRNA levels. Insulin sensitivity was assessed by intraperitoneal glucose tolerance test and homeostasis model assessment index, and through analysis of insulin signaling pathway in the visceral adipose tissue.Dihydrotestosterone treatment led to increased body weight, abdominal obesity and elevated triglycerides and non-esterified fatty acids, which were accompanied by the activation of nuclear factor kappa B and increase in macrophage migration inhibitory factor, IL6 and IL1β levels in the visceral adipose tissue. In parallel, insulin sensitivity was affected in 5α-dihydrotestosterone-treated animals only at the systemic and not at the level of visceral adipose tissue.The results showed that abdominal obesity and dyslipidemia in the animal model of polycystic ovary syndrome were accompanied with low-grade inflammation in the visceral adipose tissue. However, these metabolic disturbances did not result in decreased tissue insulin sensitivity.