Changes induced by a fructose-rich diet on hepatic metabolism and the antioxidant system.
ABSTRACT 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.
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ABSTRACT: This study aimed to determine the cellular distribution of islet cannabinoid receptors (CBs) and their involvement in the development of metabolic and hormonal changes in rats fed a fructose-rich diet (F). In normal rat islets, we determined CBs (immunofluorescence and retrotranscription-polymerase chain reaction) and glucose-stimulated insulin secretion (GSIS) of isolated islets incubated with the CB1 antagonist rimonabant (R) and/or different CBs agonists. In 3-week F-fed rats, we determined the in vivo effect of R on serum glucose, triglyceride, and insulin levels; homeostasis model assessment for insulin resistance, GSIS, and CBs and insulin receptor substrate gene expression levels (real-time polymerase chain reaction). Cannabinoid receptors appeared exclusively in islet α cells. Whereas different CB agonists enhanced GSIS in normal rat islets, R did not affect it. F rats had higher serum triglyceride and insulin levels and homeostasis model assessment for insulin resistance than control rats; these alterations were prevented by R coadministration. Although R did not correct the increased GSIS observed in F islets, it modulated CBs and insulin receptor substrate gene expression. Islet CBs would exert an important modulatory role in metabolic homeostasis. Administration of R and F affected islet CB expression and prevented the development of F-induced metabolic impairment. Selective islet CB1 blockers could be useful to prevent/treat the alterations induced by the intake of unbalanced/unhealthy diets.Pancreas 09/2013; · 2.95 Impact Factor
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ABSTRACT: Background Islet NADPH oxidase activity is modulated by glucose and other insulin secretagogues and it might be part of the regulatory mechanism of insulin secretion. We studied its modulatory role of islet NADPH oxidase upon β-cell function in rats with fructose-induced oxidative stress. Methods Normal rats were fed for 3 weeks with a standard diet, a fructose-rich diet or both diets plus apocynin. We measured plasma glucose, insulin, triacylglycerol and lipid peroxidation levels and the homeostasis model assessment-insulin resistance (HOMA-IR) and HOMA-β indexes, and performed an oral glucose tolerance test. β-cell volume density and the number of islets per mm2 were determined by immunomorphometric analysis of the pancreas. Insulin secretion, glucose metabolism, glucokinase and NADPH oxidase activities were studied in islets isolated from each experimental group. Results Fructose-fed rats had increased plasma triacylglycerol, insulin and lipid peroxidation levels associated to an insulin resistance state; the reactive higher secretion was unable to cope with the increased demand of insulin, leading to an impaired glucose tolerance. They also have a lower number of islets per area unit with a decreased β-cell volume density. All these alterations were prevented by blocking NADPH oxidase activity with apocynin. Conclusion Fructose-induced changes are partly mediated by modulation of NADPH oxidase activity. General significance The metabolic dysfunctions and enhanced oxidative stress measured in fructose-fed rats resemble those recorded in human prediabetes; thus, successful strategies employed in this model could be later used to prevent the progression of this state towards type 2 diabetes in human beings.Biochimica et Biophysica Acta (BBA) - General Subjects 01/2014; · 3.85 Impact Factor
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ABSTRACT: A diet high in fructose (HFr) induces insulin resistance in animals. Free radicals are involved in the pathogenesis of HFr-induced insulin resistance. Carnosine (CAR) is a dipeptide with antioxidant properties. We investigated the effect of CAR alone or in combination with α-tocopherol (CAR + TOC) on HFr-induced insulin-resistant rats. Rats fed with HFr containing 60 % fructose received CAR (2 g/L in drinking water) with/without TOC (200 mg/kg, i.m. twice a week) for 8 weeks. Insulin resistance, serum lipids, inflammation markers, hepatic lipids, lipid peroxides, and glutathione (GSH) levels together with glutathione peroxidase (GSH-Px) and superoxide dismutase 1 (CuZnSOD; SOD1) activities and their protein expressions were measured. Hepatic histopathological examinations were performed. HFr was observed to cause insulin resistance, inflammation and hypertriglyceridemia, and increased triglyceride and lipid peroxide levels in the liver. GSH-Px activity and expression decreased, but GSH levels and SOD1 activity and expression did not alter in HFr rats. Hepatic marker enzyme activities in serum increased and marked macro- and microvesicular steatosis were seen in the liver. CAR treatment did not alter insulin resistance and hypertriglyceridemia, but it decreased steatosis and lipid peroxidation without any change in the antioxidant system of the liver. However, CAR + TOC treatment decreased insulin resistance, inflammation, hepatic steatosis, and lipid peroxidation and increased GSH-Px activity and expression in the liver. Our results may indicate that CAR + TOC treatment is more effective to decrease HFr-induced insulin resistance, inflammation, hepatic steatosis, and dysfunction and pro-oxidant status in rats than CAR alone.Journal of physiology and biochemistry 01/2014; · 1.65 Impact Factor