High dietary salt decreases antioxidant defenses in the liver of fructose-fed insulin-resistant rats.

In this study we investigated the hypothesis that a high-salt diet to hyperinsulinemic rats might impair antioxidant defense owing to its involvement in the activation of sodium reabsorption to lead to higher oxidative stress. Rats were fed a standard (CON), a high-salt (HS), or a high-fructose (HF) diet for 10 weeks after which, 50% of the animals belonging to the HF group were switched to a regimen of high-fructose and high-salt diet (HFS) for 10 more weeks, while the other groups were fed with their respective diets. Animals were then euthanized and their blood and liver were examined. Fasting plasma glucose was found to be significantly higher (approximately 50%) in fructose-fed rats than in the control and HS rats, whereas fat liver also differed in these animals, producing steatosis. Feeding fructose-fed rats with the high-salt diet triggered hyperinsulinemia and lowered insulin sensitivity, which led to increased levels of serum sodium compared to the HS group. This resulted in membrane perturbation, which in the presence of steatosis potentially enhanced hepatic lipid peroxidation, thereby decreasing the level of antioxidant defenses, as shown by GSH/GSSG ratio (HFS rats, 7.098±2.1 versus CON rats, 13.2±6.1) and superoxide dismutase (HFS rats, 2.1±0.05 versus CON rats, 2.3±0.1%), and catalase (HFS rats, 526.6±88.6 versus CON rats, 745.8±228.7 U/mg ptn) activities. Our results indicate that consumption of a salt-rich diet by insulin-resistant rats may lead to regulation of sodium reabsorption, worsening hepatic lipid peroxidation associated with impaired antioxidant defenses.

Dornas WC ，de Lima WG ，dos Santos RC ，Guerra JF ，de Souza MO ，Silva M ，Souza e Silva L ，Diniz MF ，Silva ME ... -  《-》

Influence of alpha-lipoic acid on lipid peroxidation and antioxidant defence system in blood of insulin-resistant rats.

High fructose feeding induces insulin resistance and hyperinsulinaemia in rats. A role for oxidative stress in the occurrence of insulin resistance has been suggested by several workers. The aim of this study was to investigate the effect of alpha-lipoic acid (LA) on oxidant-antioxidant balance in rats fed on a high-fructose diet that showed characteristic features of insulin resistance. Male Wistar rats weighing 150-170 g were divided into seven groups. The control group received the control diet containing starch. The fructose group was given a high-fructose diet (>60% of total calories). The third and fourth groups were given fructose diet and were administered two different doses of LA at a low dose (35 mg/kg body weight) and high dose (70 mg/kg body weight) using olive oil as vehicle. The fifth group received fructose diet and olive oil. The sixth group received control diet and was administered LA (70 mg/kg body weight). And, the seventh group received the control diet and olive oil. Products of lipid peroxidation and activities of enzymic antioxidants, namely superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase, in red blood cells were assayed. Levels of non-enzymic antioxidants alpha-tocopherol, ascorbic acid and reduced glutathione were determined in plasma. The levels of lipid peroxides, diene conjugates and thiobarbituric acid-reactive substances were significantly higher in fructose-fed rats. Inadequate antioxidant system was observed in high-fructose-fed rats. Treatment of fructose rats mitigated the imbalance between peroxidation and antioxidant defence system at both the doses tested. Increases in glucose, triglycerides, free fatty acids, insulin and insulin resistance were observed in fructose-fed rats. LA administration prevented these alterations and improved insulin sensitivity. Significant positive correlations were obtained between insulin resistance and lipid peroxidation indices. Increased lipid peroxidation and deficient antioxidant system are observed in high-fructose-fed rats. LA administration preserves the antioxidant system and lowers lipid peroxidation. The findings suggest an interrelationship between lipid peroxidation and insulin resistance.

Thirunavukkarasu V ，Anuradha CV 《DIABETES OBESITY & METABOLISM》

Changes induced by a fructose-rich diet on hepatic metabolism and the antioxidant system.

The effect of a three-week fructose-rich diet (FRD) upon gene expression, protein and activity levels of liver antioxidant system and carbohydrate metabolism was studied. Serum glucose (fasting and after a glucose load), triglyceride and insulin levels of normal male Wistar rats were measured. In liver, we measured gene/protein expression and enzyme activity of catalase (CAT), copper-zinc-superoxide dismutase (CuZnSOD) and glutathione peroxidase (GSHPx); reduced glutathione (GSH); protein carbonyl content; thiobarbituric acid reactive substances (TBARS) content and microsomal membrane susceptibility to lipid peroxidation; glucokinase (GK), glucose-6-phosphatase (G-6-Pase) and glucose-6-phosphate dehydrogenase (G-6-PDH) activity; and glycogen, pyruvate, lactate and triglyceride content. Similar body weights and caloric intake were recorded in both groups. FRD rats had higher serum glucose, insulin and triglyceride levels, molar insulin:glucose ratio, HOMA-IR values and impaired glucose tolerance, whereas CAT, CuZnSOD and GSHPx relative gene expression levels were significantly lower. CAT and CuZnSOD protein expression, CAT activity and GSH content were also lower, while protein carbonyl content was higher. No differences were recorded in CuZnSOD, MnSOD and GSHPx activity, TBARS content and membrane susceptibility to lipid peroxidation. Glycogen, lactate and triglyceride content and GK, G-6-Pase and G-6-PDH activity were significantly higher in FRD rats. In the presence of oxidative stress, the liver exhibits changes in the carbohydrate and lipid metabolic pathways that would decrease reactive oxygen species production and their deleterious effect, thus inducing little impact on specific antioxidant mechanisms. This knowledge could facilitate the design and implementation of strategies to prevent oxidative stress-induced liver damage.

Francini F ，Castro MC ，Schinella G ，García ME ，Maiztegui B ，Raschia MA ，Gagliardino JJ ，Massa ML ... -  《-》

Attenuation of insulin resistance, metabolic syndrome and hepatic oxidative stress by resveratrol in fructose-fed rats.

Metabolic syndrome and oxidative stress are common complications of type 2 diabetes mellitus. The present study was designed to determine whether resveratrol, a widely used nutritional supplement, can improve insulin sensitivity, metabolic complication as well as hepatic oxidative stress in fructose-fed rats. Male Sprague Dawley rats (180-200 g) were divided into four groups with 8 animals each. Fructose-fed insulin resistant group (Dia) animals were fed 65% fructose (Research diet, USA) for a period of 8 weeks, whereas control group (Con) animals were fed 65% cornstarch (Research Diet, USA). Resveratrol, 10 mg/kg/day (Dia+Resv) or metformin 300 mg/kg/day (Dia+Met) were administered orally to the 65% fructose-fed rats for 8 weeks. At the end of the feeding schedule, Dia group had insulin resistance along with increased blood glucose, triglyceride, uric acid and nitric oxide (NO) levels. Significant (p<0.05) increase in hepatic TBARS and conjugated dienes, and significant (p<0.05) decrease in hepatic SOD and vitamin C was observed in Dia group compared to Con group. Administration of metformin or resveratrol significantly (p<0.05) normalized all the altered metabolic parameters. However, a marked insulin sensitizing action was only observed in the Dia+Resv group. Similarly, while metformin administration failed to normalize the increased TBARS levels and decreased SOD activity, resveratrol showed a more promising effect of all oxidative stress parameters measured in the present study. Attenuation of hepatic oxidative stress in fructose-fed rat liver after resveratrol administration was associated with significant (p<0.05) increase in nuclear level of NRF2 compared with other groups. The present study demonstrates that resveratrol is more effective than metformin in improving insulin sensitivity, and attenuating metabolic syndrome and hepatic oxidative stress in fructose-fed rats.

Bagul PK ，Middela H ，Matapally S ，Padiya R ，Bastia T ，Madhusudana K ，Reddy BR ，Chakravarty S ，Banerjee SK ... -  《-》

Globularia alypum aqueous extract decreases hypertriglyceridemia and ameliorates oxidative status of the muscle, kidney, and heart in rats fed a high-fructose diet.

Fructose is widely used as a food ingredient and has potential to increase oxidative stress. Moreover, the beneficial health effects of plant polyphenols are frequently attributed to their potent antioxidant effects. We hypothesized that administration of Globularia alypum (Ga) aqueous extract would reduce metabolic disorders and oxidative stress induced in rats fed a high-fructose diet. Male Wistar rats (n = 24) weighing 242 ± 13 g were divided into 4 groups and fed, during 14 week, diets containing 20% casein and 61% cornstarch (control diet, or C) or fructose (F), and Ga supplementation (0.5%; CGa and FGa). Compared with control group, rats fed a high-fructose diet increased plasma triglycerides (TG; +48%) and very low-density lipoprotein-TG (+45%) levels. In addition, thiobarbituric acid reactive substances were increased in the liver (+31%), heart (+55%), and muscle (+58%). Moreover, activities of superoxide dismutase in the liver and heart, catalase in liver and glutathione peroxidase in the heart were diminished. In the FGa group, a hypertriglyceridemic effect was observed concomitantly with a low level of TG in very low-density lipoprotein and high-density lipoprotein 2, compared with the F group. Thiobarbituric acid reactive substance concentrations were reduced in the kidney (-42%)and muscle (-76%), and antioxidant enzymes activity was increased for superoxide dismutase in the muscle (+81%) and heart (+28%), and for glutathione peroxidase, in the kidney (+70%) and heart (+30%). In conclusion, the Ga extract has a beneficial effect on plasma TG and gives a promising perspective for hypertriglyceridemia treatment. Moreover, in the muscle and kidney, Ga is effective by lowering lipid peroxidation and improves antioxidant enzymes.

Taleb-Dida N ，Krouf D ，Bouchenak M 《-》