Long-term fructose-enriched diet introduced immediately after weaning does not induce oxidative stress in the rat liver

Protective effects of green tea on blood and liver of rats fed with high fructose diet

This study was designed to investigate the effects of green tea on lipid profile, liver tissue damage, and oxidative stress in rats fed a diet including high fructose. Sprague-Dawley rats were randomly divided into four groups: Control (C), Fructose (F), Green Tea (GT), and F+GT. F and F+GT groups were given 20% fructose in the drinking water for eight weeks. Green tea (2 mg kg−1) was administrated to GT and F+GT groups by oral gavage for eight weeks. Biochemical parameters in serum and oxidative stress markers in the liver were analysed. The liver sections were stained with haematoxylin-eosin. As of the 3rd week of the experiment, the body weight of rats in the F group showed a statistically significant increase in comparison with the F+GT group. The serum glucose and triglyceride levels of the F+GT group significantly decreased when compared with the F group. The fructose-induced degenerative changes in the liver were reduced with green tea. Green tea may serve a protective role against hyperlipidaemia and liver injury in rats fed a high fructose diet.

Fructose-Rich Diet Attenuates Stress-Induced Metabolic Disturbances in the Liver of Adult Female Rats

BACKGROUND

Both fructose consumption and chronic stress contribute to the development of metabolic disorders. The consequences of such combination are not fully understood.

OBJECTIVE

We investigated whether fructose supplementation and chronic stress synergistically disturb hepatic lipid and glucose metabolism. The role of energy sensing, redox, and inflammatory status during development of metabolic disturbances was investigated.

METHODS

Female Wistar rats, aged 2.5 mo, were divided into 4 experimental groups: control (C) fed a standard diet (commercial food and drinking water); fructose (F) fed the same food and 10% fructose solution; stress (S) fed the standard diet and subjected to chronic unpredictable stress and, stress + fructose (SF) combining conditions F and S as above. Stress included daily stressors: cold water forced swimming, physical restraint, cold room, wet bedding, rocking, switching, or tilting cages. After 9 wk, hepatic enzymes and transcription factors involved in gluconeogenesis, lipogenesis, fatty acid oxidation, antioxidative defence, energy sensing, and cytokines were assessed by qPCR, Western blotting, and spectrophotometry and analyzed by 2-factor ANOVA.

RESULTS

Fructose increased AMP-activated protein kinase (AMPK) phosphorylation (40%; P < 0.05) and the ratio of inhibitory phosphorylation to total acetyl-CoA carboxylase (46%; P < 0.01), and decreased sterol regulatory element binding protein 1c nuclear translocation by 30% (P < 0.05) in F and SF compared with C rats. Increased phosPck (phoenolpyruvate carboxykinase) (85%) and G6pase(glucose-6-phosphatase) (55%) was observed in S rats (P < 0.05). A 40% decrease in Apob (apolipoprotein B-100) and an increase in hepatic lipids (P < 0.05), together with a double increase in TNF-α (P < 0.001), were observed in S rats, but without liver histopathological changes. These stress effects on lipid accumulation and TNF-α were abolished in SF rats (P < 0.05).

CONCLUSIONS

Fructose does not enhance stress effects on hepatic lipid and glucose metabolism but attenuates its effects on hepatic lipid accumulation and inflammation, suggesting that, in female rats, AMPK activation prevails over stress-induced effects.

Fructose Consumption Affects Glucocorticoid Signaling in the Liver of Young Female Rats

The effects of early-life fructose consumption on hepatic signaling pathways and their relation to the development of metabolic disorders in later life are not fully understood. To investigate whether fructose overconsumption at a young age induces alterations in glucocorticoid signaling that might contribute to development of metabolic disturbances, we analysed glucocorticoid receptor hormone-binding parameters and expression of its target genes involved in gluconeogenesis (phosphoenolpyruvate carboxykinase and glucose-6-phosphatase) and lipid metabolism (lipin-1), as well as redox and inflammatory status in the liver of female rats subjected to a fructose-rich diet immediately after weaning. The fructose diet increased hepatic corticosterone concentration, 11β-hydroxysteroid dehydrogenase type 1 level, glucocorticoid receptor protein level and hormone-binding activity, as well as lipin-1 level. The expression of glucose-6-phosphatase was reduced in fructose-fed rats, while phosphoenolpyruvate carboxykinase remained unaltered. The fructose-rich diet increased the level of fructose transporter GLUT2, while the expression of fructolytic enzymes fructokinase and aldolase B remained unaltered. The diet also affected pro-inflammatory pathways, but had no effect on the antioxidant defence system. In conclusion, a fructose-rich diet applied immediately after weaning promoted lipogenesis and enhanced hepatic glucocorticoid signaling, possibly to protect against inflammatory damage, but without an effect on gluconeogenesis and antioxidant enzymes. Yet, prolonged treatment might ultimately lead to more pronounced metabolic disturbances.

Exercise Training Prevents Cardiovascular Derangements Induced by Fructose Overload in Developing Rats

The risks of chronic diseases associated with the increasing consumption of fructose-laden foods are amplified by the lack of regular physical activity and have become a serious public health issue worldwide. Moreover, childhood eating habits are strongly related to metabolic syndrome in adults. Thus, we aimed to investigate the preventive role of exercise training undertaken concurrently with a high fructose diet on cardiac function, hemodynamics, cardiovascular autonomic modulation and oxidative stress in male rats after weaning. Male Wistar rats were divided into 4 groups (n = 8/group): Sedentary control (SC), Trained control (TC), Sedentary Fructose (SF) and Trained Fructose (TF). Training was performed on a treadmill (8 weeks, 40–60% of maximum exercise test). Evaluations of cardiac function, hemodynamics, cardiovascular autonomic modulation and oxidative stress in plasma and in left ventricle (LV) were performed. Chronic fructose overload induced glucose intolerance and an increase in white adipose tissue (WAT) weight, in myocardial performance index (MPI) (SF:0.42±0.04 vs. SC:0.24±0.05) and in arterial pressure (SF:122±3 vs. SC:113±1 mmHg) associated with increased cardiac and vascular sympathetic modulation. Fructose also induced unfavorable changes in oxidative stress profile (plasmatic protein oxidation- SF:3.30±0.09 vs. SC:1.45±0.08 nmol/mg prot; and LV total antioxidant capacity (TRAP)- SF: 2.5±0.5 vs. SC:12.7±1.7 uM trolox). The TF group showed reduced WAT, glucose intolerance, MPI (0.35±0.04), arterial pressure (118±2mmHg), sympathetic modulation, plasmatic protein oxidation and increased TRAP when compared to SF group. Therefore, our findings indicate that cardiometabolic dysfunctions induced by fructose overload early in life may be prevented by moderate aerobic exercise training.

The expression and activity of antioxidant enzymes in the liver of rats exposed to high-fructose diet in the period from weaning to adulthood

BACKGROUND

Increased fructose consumption correlates with rising prevalence of various metabolic disorders, some of which were linked to oxidative stress. The relationship between fructose consumption and oxidative stress is complex and effects of a fructose-rich diet on the young population have not been fully elucidated. The aim of this study was to investigate whether high-fructose diet applied in the period from weaning to adulthood induces oxidative stress in the liver, thus contributing to induction or aggravation of metabolic disturbances in later adulthood. To that end we examined the effects of high-fructose diet on expression and activity of antioxidant enzymes, markers of lipid peroxidation and protein damage in the liver as the main fructose metabolizing tissue.

RESULTS

High-fructose diet increased only SOD2 (mitochondrial manganese superoxide dismutase) activity, with no effect on other antioxidant enzymes, lipid peroxidation or accumulation of damaged proteins in the liver.

CONCLUSION

The results show that fructose-induced metabolic disturbances could not be attributed to oxidative stress, at least not at young age. The absence of oxidative stress in the liver observed herein implies that young organisms are capable of maintaining redox homeostasis when challenged by fructose-derived energy overload.