Effects of Fructose and Stress on Rat Renal Copper Metabolism and Antioxidant Enzymes Function.

The effects of a fructose-rich diet and chronic stress on copper metabolism in the kidneys are still understudied. We investigated whether fructose and/or chronic unpredictable stress modulate copper metabolism in a way that affects redox homeostasis, thus contributing to progression of metabolic disturbances in the kidney. We determined protein level of copper transporters, chaperones, and cuproenzymes including cytochrome c oxidase, as well as antioxidant enzymes function in the kidneys of male Wistar rats subjected to 20% liquid fructose supplementation and/or chronic stress. Liquid fructose supplementation increased level of copper chaperone of superoxide dismutase and decreased metallothionein level, while rendering the level of copper importer and copper chaperones involved in copper delivery to mitochondria and trans Golgi network unaffected. Stress had no effect on renal copper metabolism. The activity and expression of renal antioxidant enzymes remained unaltered in all experimental groups. In conclusion, fructose, independently of stress, decreased renal copper level, and modulated renal copper metabolism as to preserve vital cellular function including mitochondrial energy production and antioxidative defense, at the expense of intracellular copper storage.

Effects of age and soybean isoflavones on hepatic cholesterol metabolism and thyroid hormone availability in acyclic female rats.

Soy-food and its isoflavones, genistein (G) and daidzein (D), were reported to exert mild cholesterol-lowering effect, but the underlying mechanism is still unclear. In this research, first we studied age-related alterations in hepatic cholesterol metabolism of acyclic middle-aged (MA) female rats. Then we tested if purified isoflavones may prevent or reverse these changes, and whether putative changes in hepatic thyroid hormone availability may be associated with this effect. Serum and hepatic total cholesterol (TChol), bile acid and cholesterol precursors, as well as serum TSH and T4 concentrations, hepatic deiodinase (Dio) 1 enzyme activity and MCT8 protein expression were determined by comparing data obtained for MA with young adult (YA) intact (IC) females. Effects of subcutaneously administered G or D (35mg/kg) to MA rats were evaluated versus vehicle-treated MA females. MA IC females were characterized by: higher (p<0.05) serum TChol, lower (p<0.05) hepatic TChol and its biosynthetic precursors, lower (p<0.05) hepatic 7α-hydroxycholesterol but elevated (p<0.05) 27- and 24-hydroxycholesterol in comparison to YA IC. Both isoflavone treatments decreased (p<0.05) hepatic 27-hydroxycholesterol, G being more effective than D, without affecting any other parameter of Chol metabolism. Only G elevated hepatic Dio1 activity (p<0.05). In conclusion, age-related hypercholesteremia was associated with lower hepatic Chol synthesis and shift from main neutral (lower 7α-hydroxycholesterol) to alternative acidic pathway (higher 27-hydroxycholesterol) of Chol degradation to bile acid. Both isoflavones lowered hepatic 27-hydroxycholesterol, which may be considered beneficial. Only G treatment increased hepatic Dio1 activity, thus indicating local increase in thyroid hormones, obviously insufficient to induce prominent cholesterol-lowering effect.

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.