Fructose-fed Sprague-Dawley Rats Research Articles

Natural mineral-rich water ingestion by ovariectomized fructose-fed Sprague-Dawley rats: effects on sirtuin 1 and glucocorticoid signaling pathways.

Prevention or induction of metabolic disorders and obesity depend on estrogen signaling and/or exogenous factors, such as mineral content in diet. The protective effects of a Portuguese natural mineral-rich water against the induction of metabolic syndrome in fructose-fed male Sprague-Dawley rats have been reported. The present study was designed to assess the impact of this mineral-rich water on fructose-fed estrogen-deficient female Sprague-Dawley rats. Ovariectomized rats had access to tap (TWO) or mineral-rich (MWO) waters, with and without 10% fructose (10-wk treatment). A sham-operated (tap water supplied) group was included and each of the five groups included six rats. Plasma biochemical and metabolic parameters were evaluated by routine clinical measurements. Western blotting was used to assess hepatic protein expression of sirtuins (Sirt) 1 and 3, phosphorylated AMP-activated protein kinase-α (p-AMPKα), peroxisome proliferator-activated receptor gamma coactivator-1-α (PGC1α), glucocorticoid receptor, and 11beta-hydroxysteroid dehydrogenase type 1 (11βHSD1). Ovariectomy increased plasma total cholesterol (46%/P < 0.05), but had no significant effects on hepatic protein expression. Fructose intake by ovariectomized rats increased PGC1α and 11βHSD1 (fructose in tap water [TWFO] vs TWO: 65%/P < 0.05 and 38%/P = 0.05, respectively) as well as glucocorticoid receptor (TWFO and fructose in natural mineral-rich water [MWFO] vs TWO and MWO: 107%/P = 0.05 and 182%/P < 0.05, respectively). Mineral-rich water ingestion exerted an increasing shape on Sirt1 (MWO vs TWO: 76%/P < 0.05; MWFO vs TWFO: 76%/P = 0.06), PGC1α (MWO vs TWO: 77%/P < 0.01), p-AMPKα (MWO vs TWO: 152%/P = 0.01; MWFO vs TWFO: 107%/P = 0.01), and 11βHSD1 (MWO vs TWO: 91%/P = 0.05; MWFO vs TWFO: 47%/P = 0.05). Mineral-rich water ingestion may have a prime role on the activation of Sirt1 signaling and the modulation of glucocorticoid signaling in the postmenopause.

Effects of tempol on altered metabolism and renal vascular responsiveness in fructose-fed rats.

This study investigated the effect of tempol (a superoxide dismutase mimetic) on renal vasoconstrictor responses to angiotensin II (Ang II) and adrenergic agonists in fructose-fed Sprague-Dawley rats (a model of metabolic syndrome). Rats were fed 20% fructose in drinking water (F) for 8 weeks. One fructose-fed group received tempol (FT) at 1 mmol·L(-1) in drinking water for 8 weeks or as an infusion (1.5 mg·kg(-1)·min(-1)) intrarenally. At the end of the treatment regimen, the renal responses to noradrenaline, phenylephrine, methoxamine, and Ang II were determined. F rats exhibited hyperinsulinemia, hyperuricemia, hypertriglyceridemia, and hypertension. Tempol reduced blood glucose and insulin levels (all p < 0.05) in FT rats compared with their untreated counterparts. The vasoconstriction response to all agonists was lower in F rats than in control rats by about 35%-65% (all p < 0.05). Vasoconstrictor responses to noradrenaline, phenylephrine, and methoxamine but not Ang II were about 41%-75% higher in FT rats compared with F rats (all p < 0.05). Acute tempol infusion blunted responses to noradrenaline, methoxamine, and Ang II in control rats by 32%, 33%, and 62%, while it blunted responses to noradrenaline and Ang II in F rats by 26% and 32%, respectively (all p < 0.05), compared with their untreated counterparts. Superoxide radicals play a crucial role in controlling renal vascular responses to adrenergic agonists in insulin-resistant rats. Chronic but not acute tempol treatment enhances renal vascular responsiveness in fructose-fed rats.

The Effect of Klotho Treatment on Atherogenesis, Blood Pressure, and Metabolic Parameters in Experimental Rodent Models.

Klotho is a transmembrane protein, expressed mainly in the kidneys and the choroid plexus. The extracellular domain of klotho is composed of 2 internal repeats, KL1 and KL2, which can be cleaved and act as hormones. Klotho-deficient mice develop a phenotype resembling human aging. Laboratory and clinical data suggest a favorable effect of klotho on atherosclerosis, high blood pressure, and metabolic syndrome. Therefore, we aimed to study the effect of klotho treatment on atherogenesis, blood pressure, and metabolic parameters in experimental rodent models. Fructose-fed Sprague-Dawley rats (metabolic syndrome model) and apolipoprotein E (apoE -/-) knock-out mice (atherosclerosis model) were treated with either klotho or its active domain KL1. In apoE -/- mice, klotho unexpectedly elevated plasma cholesterol and triglyceride levels compared to the control group. Yet, it did not increase the aortic sinus atherosclerotic lesion area. In fructose-fed Sprague-Dawley rats, klotho treatment did not lower blood pressure or plasma triglyceride levels. Although KL1 treatment did not lower blood pressure or plasma insulin levels, it significantly reduced the elevation of total plasma triglyceride levels (from 2.3-fold to 1.6-fold, p<0.05) due to lower triglyceride-rich VLDL levels. Klotho did not show any beneficial effects on atherosclerosis and components of the metabolic syndrome and was associated with increased plasma cholesterol levels. On the other hand, treatment with KL1 may lower plasma triglyceride levels independent of insulin. Additional studies are required in order to decipher the complex role of klotho and its active domains in the regulation of plasma lipid levels.

Natural mineral-rich water ingestion improves hepatic and fat glucocorticoid-signaling and increases sirtuin 1 in an animal model of metabolic syndrome.

We recently reported protection against metabolic syndrome (MetSyn) induction and endothelial dysfunction by natural mineral-rich water intake in fructose-fed Sprague-Dawley rats. As glucocorticoids are critical to MetSyn development, we aimed to further characterize the beneficial effects of mineral-rich water intake in that animal model, by assessing relevant effectors in glucocorticoid-signaling in liver and subcutaneous (SCAT) and visceral (VAT) adipose tissues, sites with a central role in metabolic (dys)regulation. Adult male rats had free access to standard diet and different drinking solutions (8 weeks): a) tap water (CONT), b) 10% fructose/tap water (FRUCT) or c) 10% fructose/mineral-rich water (FRUCTMIN). 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), glucocorticoid receptor (GR), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α) and sirtuin 1 (Sirt1) tissue protein expressions were evaluated by Western blot. Plasma corticosterone (ELISA) and non-esterified fatty acids (NEFA) levels were quantified spectrophotometrically. Expectedly, Sirt1 and PGC1-α significantly decreased in liver, 11β-HSD1 tended to increase in VAT and tended to decrease in liver and SCAT, and plasma corticosterone tended to increase in FRUCT vs. CONT. Mineral-rich water showed a trend towards a reduction of these fructose effects and significantly increased hepatic Sirt1 vs. CONT and FRUCT. GR significantly increased in VAT and plasma NEFA strongly tended to increase in FRUCTMIN vs. CONT and FRUCT. Glucocorticoid-signaling was different among SCAT and VAT and also in liver. Mineral-rich water modulation of fructose effects on glucocorticoid-signaling and Sirt1 underlines the better metabolic profile found earlier.

Effects of natural mineral-rich water consumption on the expression of sirtuin 1 and angiogenic factors in the erectile tissue of rats with fructose-induced metabolic syndrome

Consuming a high-fructose diet induces metabolic syndrome (MS)-like features, including endothelial dysfunction. Erectile dysfunction is an early manifestation of endothelial dysfunction and systemic vascular disease. Because mineral deficiency intensifies the deleterious effects of fructose consumption and mineral ingestion is protective against MS, we aimed to characterize the effects of 8 weeks of natural mineral-rich water consumption on the structural organization and expression of vascular growth factors and receptors on the corpus cavernosum (CC) in 10% fructose-fed Sprague-Dawley rats (FRUCT). Differences were not observed in the organization of the CC either on the expression of vascular endothelial growth factor (VEGF) or the components of the angiopoietins/Tie2 system. However, opposing expression patterns were observed for VEGF receptors (an increase and a decrease for VEGFR1 and VEGFR2, respectively) in FRUCT animals, with these patterns being strengthened by mineral-rich water ingestion. Mineral-rich water ingestion (FRUCTMIN) increased the proportion of smooth muscle cells compared with FRUCT rats and induced an upregulatory tendency of sirtuin 1 expression compared with the control and FRUCT groups. Western blot results were consistent with the dual immunofluorescence evaluation. Plasma oxidized low-density lipoprotein and plasma testosterone levels were similar among the experimental groups, although a tendency for an increase in the former was observed in the FRUCTMIN group. The mineral-rich water-treated rats presented changes similar to those observed in rats treated with MS-protective polyphenol-rich beverages or subjected to energy restriction, which led us to hypothesize that the effects of mineral-rich water consumption may be more vast than those directly observed in this study.

Relevance of a Hypersaline Sodium-Rich Naturally Sparkling Mineral Water to the Protection against Metabolic Syndrome Induction in Fructose-Fed Sprague-Dawley Rats: A Biochemical, Metabolic, and Redox Approach

The Metabolic Syndrome increases the risk for atherosclerotic cardiovascular disease and type 2 Diabetes Mellitus. Increased fructose consumption and/or mineral deficiency have been associated with Metabolic Syndrome development. This study aimed to investigate the effects of 8 weeks consumption of a hypersaline sodium-rich naturally sparkling mineral water on 10% fructose-fed Sprague-Dawley rats (Metabolic Syndrome animal model). The ingestion of the mineral water (rich in sodium bicarbonate and with higher potassium, calcium, and magnesium content than the tap water used as control) reduced/prevented not only the fructose-induced increase of heart rate, plasma triacylglycerols, insulin and leptin levels, hepatic catalase activity, and organ weight to body weight ratios (for liver and both kidneys) but also the decrease of hepatic glutathione peroxidase activity and oxidized glutathione content. This mineral-rich water seems to have potential to prevent Metabolic Syndrome induction by fructose. We hypothesize that its regular intake in the context of modern diets, which have a general acidic character interfering with mineral homeostasis and are poor in micronutrients, namely potassium, calcium, and magnesium, could add surplus value and attenuate imbalances, thus contributing to metabolic and redox health and, consequently, decreasing the risk for atherosclerotic cardiovascular disease.

Fiber-free white flour with fructose offers a better model of metabolic syndrome

BackgroundThe metabolic syndrome (MS) is a combination of metabolic abnormalities that lead to an increased risk of cardiovascular diseases. Due to its rising incidence and demanding life-long use of multiple drugs, there is a growing interest in testing and developing new allopathic, complementary and alternative therapies for controlling or curing disorders of MS. The discovery of new therapeutic modalities requires animal models of disease and currently available models have limitations. Developing an appropriate animal model for MS to achieve various therapeutic targets remains a challenge and this study aims to develop a rat model which closely depicts MS in humans.MethodologyRat model of MS was developed by replacing 60% of diet with fructose. Four groups of Sprague–Dawley rats were either given whole wheat or refined flour with and without fructose for 8 weeks. Data were analyzed on SPSS and Graphpad Prism using ANOVA with Tukey’s and Bonferonni tests for multiple group comparison. A p-value of less than 0.05 was considered significant for differences between groups.ResultsReplacing whole wheat with refined wheat flour in rat chow in 60% fructose-fed Sprague–Dawley rats resulted in hypertension (p 0.01), hyper-insulinemia (p < 0.001), hyperglycemia (p 0.03) and a reduction in HDL levels (p 0.002) at 4 weeks while hyper-triglyceridemia (p 0.001) with endothelial dysfunction was observed at 8 weeks.ConclusionIt is concluded that the refined wheat flour with 60% fructose in diet hastens the development of metabolic syndrome in 4 weeks and replacing whole wheat flour with refined flour in diet induces a more effective abnormality including a low HDL. Further studies may be directed to assess the associated pathological changes, which can be used to study the effect of different therapeutic modalities on an animal model of MS with low HDL.

The effect of losartan and carvedilol on renal haemodynamics and altered metabolism in fructose-fed Sprague–Dawley rats

The aim of this study is to assess the effects of losartan and carvedilol on metabolic parameters and renal haemodynamic responses to angiotensin II (Ang II) and adrenergic agonists in the model of fructose-fed rat. Thirty-six Sprague-Dawley rats were fed for 8 weeks either 20% fructose solution (F) or tap water (C) ad libitum. F or C group received either losartan or carvedilol (10 mg/kg p.o.) daily for the last 3 weeks of the study (FL and L) and (FCV and CV), respectively, then in acute studies the renal vasoconstrictor actions of Ang II, noradrenaline (NA), phenylephrine (PE) and methoxamine (ME) were determined. Data, mean±SEM were analysed using ANOVA with significance at P <0.05. Losartan and carvedilol decreased the area under the glucose tolerance curve of the fructose-fed group. The responses (%) to NA, PE, ME and Ang II in F were lower (P <0.05) than C (F vs. C, 17±2 vs. 38±3; 24±2 vs. 48±2; 12±2 vs. 34±2; 17±2 vs. 26±2), respectively. L had higher (P <0.05) responses to NA and PE while CV had blunted (P <0.05) responses to NA, PE and Ang II compared to C (L, CV vs. C, 47±3, 9±2 vs. 38±3; 61±3, 29±3 vs. 48±2; 16±3, 4±3 vs. 26±2), respectively. FL but not FCV group had enhanced (P <0.05) responses to NA, PE and ME compared to F (FL vs. F, 33±3 vs. 17±2; 45±3 vs. 24±2; 26±3 vs. 12±2), respectively. Losartan and carvedilol had an important ameliorating effect on fructose-induced insulin resistance. Losartan treatment could be an effective tool to restore normal vascular reactivity in the renal circulation of the fructose-fed rat.

Enalapril Increases the Local Extravasation of Macromolecules and Nitric Oxide Synthase in Pancreas of the Fructose-fed Insulin-resistant Rat Model

Angiotensin-converting enzyme (ACE) inhibitors have been associated with an increased risk of acute pancreatitis. The pathogenesis of this condition remains unclear, but an activation of the kinin system and a resultant localized angioedema have been implicated in the initial step leading to acute pancreatic damage. The goal of the present study was to explore the impact of ACE inhibition on pancreatic microcirculation and capillary permeability in normal and insulin-resistant rats. Chow- or fructose-fed Sprague-Dawley rats were treated with enalapril (dosage, 10 mg.kg.d) or vehicle for 4 weeks before measuring in vivo the extravasation of Evans blue (EB) dye in pancreas. Unanesthetized animals (n = 10-17 per group) were injected with EB 20 mg.kg in the caudal vein 10 minutes before killing, and EB dye was extracted from each pancreas by using formamide. Relative to controls, enalapril-treated animals showed a 5-fold increase in pancreatic extravasation of EB in the fructose-fed rat model (P < 0.001); smaller changes (2-fold) were observed in the chow-fed animals treated with enalapril (P < 0.001). The increase in pancreatic vasopermeability observed with enalapril in the fructose-fed animals was accompanied by a significant increase in total pancreatic nitric oxide synthase (NOS) activity compared to controls (Delta = +128%; P < 0.001). This increase in NOS activity seemed to be solely attributable to an upregulation of the endothelial NOS isoform because only the eNOS immunoreactive mass (as opposed to nNOS) seemed to be increased in the pancreas of these animals. Treatment with enalapril was not associated with any increase in serum amylase concentrations in either animal subgroup. Enalapril increases capillary permeability (extravasation of macromolecules) in the pancreas of the fructose-fed rat model. This suggests that ACE inhibition upregulates the eNOS isoform locally, increases vasopermeability of the pancreas, and can therefore result in local edema in the fructose-fed insulin-resistant rat model.

Oral taurine supplementation prevents fructose-induced hypertension in rats.

Taurine is known to have antihypertensive and lipid-lowering effects in some experimental models and patients. On the other hand, intracellular free calcium and magnesium play important roles in regulating the tonus of blood vessels and insulin sensitivity. We examined the effect of oral taurine supplementation on blood pressure, serum metabolic parameters, and platelet cytosolic free calcium ([Ca(2+)](i)) and magnesium ([Mg(2+)](i)) concentration in fructose-fed Sprague-Dawley rats. Systolic blood pressure and platelet [Ca(2+)](i) were significantly higher in rats fed a 60% fructose diet. Oral taurine supplementation (1% in drinking water) completely prevented the elevation of blood pressure and an increase in platelet [Ca(2+)](i), but exacerbated hyperinsulinemia, hypertriglyceridemia, and a decrease in platelet [Mg(2+)](i). In conclusion, taurine may ameliorate fructose-induced hypertension in rats by preventing an increase in intracellular free calcium concentration. The blood pressure-lowering effect of taurine appeared to be independent from its effect on glucose and lipid metabolism in this model.

Rosiglitazone increases extravasation of macromolecules and endothelial nitric oxide synthase in skeletal muscles of the fructose-fed rat model

Reduced extravasation of macromolecules in skeletal muscle has recently been documented in the fructose-fed rat model, corroborating a hypothesis that a functional obliteration of muscle regional microcirculation might lead to hypertension and restrict access of nutrients and hormones to their target cells. The goal of this study was to assess the impact of a treatment with rosiglitazone on the reduced muscle vasopermeability observed previously in the fructose-fed rat model. Fructose-fed Sprague–Dawley rats were gavaged with rosiglitazone (10 μmol kg −1 per day; n=21) or the vehicle only ( n=19) for 3 consecutive weeks before assessing the extravasation of Evans Blue (EB) dye in vivo in distinct muscle groups. Relative to control group, rosiglitazone reduced mean arterial blood pressure ( Δ=−16.7%, P<0.001), plasma insulin ( Δ=−39.1%, P<0.05) and plasma triglyceride ( Δ=−32.8%, P<0.01) concentrations in a significant manner. Plasma VEGF concentrations were significantly lower in the rosiglitazone-treated animals compared to the control animals (32.7±0.8 pg ml −1 versus 46.1±1.2 pg ml −1, P<0.001). While no changes were observed in the lungs or the kidneys, fructose-fed rats treated with rosiglitazone had a 30–50% increase ( P<0.005) in the extravasation of EB regardless of the skeletal muscle group studied (rectus femoris, soleus, gastrocnemius lateralis, vastus lateralis and tibialis cranalis). In homogenates of skeletal muscles (vastus lateralis) of fructose-fed rats, rosiglitazone resulted in a significant increase in NO synthase (NOS) activity ( Δ=+41.9%, P<0.003) as well as endothelial NOS immunoreactive mass ( Δ=+37.8%, P<0.01) compared to the control animals. There was no change in the immunoreactive level of the nNOS isoform, the most abundant muscle isoform, or in the immunoreactive levels of VEGF. In conclusion, rosiglitazone appears to restore a vascular dysfunction previously documented in the skeletal muscle microcirculation, as evidenced by improved skeletal muscle vasopermeability and upregulation of the muscle endothelium-NO system in the fructose-fed rat model. These effects on muscle per se might also result in a partial improvement of the insulin resistance phenomenon by improving the distribution of nutrients and insulin to skeletal muscle. This effect appears to be independent of circulating levels of VEGF since changes in plasma concentrations of this permeability factor were lower in the rosiglitazone-treated group.

Relationship Between Insulin Resistance and Hypertension

Patients with hypertension have been shown to be resistant to insulin-stimulated glucose uptake and to be both hyperinsulinemic and hypertriglyceridemic compared with matched normotensive control groups. These abnormalities are present before the institution of antihypertensive therapy and do not necessarily improve when blood pressure is effectively lowered. Insulin resistance, hyperinsulinemia, hypertriglyceridemia, and high blood pressure can be produced in fructose-fed Sprague-Dawley rats, but the development of these changes is inhibited by exercise training or somatostatin infusion. Furthermore, insulin-stimulated glucose uptake is lower in spontaneously hypertensive rats (SHRs) than Wistar-Kyoto rats, and this is associated with higher plasma triglyceride concentrations and blood pressure. In addition, a defect in insulin-stimulated glucose uptake can be shown in adipocytes isolated from SHRs, and the greater the degree of in vitro insulin resistance, the higher the plasma insulin concentration and blood pressure. These data strongly support the view that abnormalities of insulin and lipid metabolism are associated with high blood pressure in both patients and rodent models of experimental hypertension. In the latter context, endogenous hyperinsulinemia and hypertriglyceridemia are risk factors for coronary heart disease. The fact that antihypertensive treatment has not focused on correcting these metabolic abnormalities may explain why it has been difficult to show that lowering blood pressure decreases the risk of coronary heart disease. It can be argued that abnormalities of carbohydrate and lipoprotein metabolism play a role in both the etiology of hypertension and the clinical course of hypertensive patients.