Reversion of down-regulation of intestinal multidrug resistance-associated protein 2 in fructose-fed rats by geraniol and vitamin C: Potential role of inflammatory response and oxidative stress

Intestinal multidrug resistance-associated protein 2 is an ABC transporter that limits the absorption of xenobiotics ingested orally, thus acting as essential component of the intestinal biochemical barrier. Metabolic Syndrome (MetS) is a pathological condition characterized by dyslipidemia, hyperinsulinemia, insulin resistance, chronic inflammation, and oxidative stress (OS). In a previous study we demonstrated that MetS-like conditions induced by fructose in drinking water (10% v/v, during 21 days), significantly reduced the expression and activity of intestinal Mrp2 in rats. We here evaluated the potential beneficial effect of geraniol or vitamin C supplementation, natural compounds with anti-inflammatory and anti-oxidant properties, in reverse fructose-induced Mrp2 alterations. After MetS-like conditions were induced (21 days), animals were cotreated with geraniol or vitamin C or vehicle for another 14 days. Decreased expression of Mrp2 protein and mRNA due to fructose administration was reversed by geraniol and by vitamin C, consistent with restoration of Mrp2 activity evaluated in everted intestinal sacs. Concomitantly, increased intestinal IL-1β and IL-6 levels induced by fructose were totally and partially counterbalanced, respectively, by geraniol administration. The intestinal redox unbalance generated by fructose was improved by geraniol and vitamin C, as evidenced by decreasing lipid peroxidation products and activity of Superoxide Dismutase and by normalizing glutathione reduced/oxidized glutathione ratio. The restoration effects exhibited by geraniol and vitamin C suggest that local inflammatory response and OS generated under MetS-like conditions represent important mediators of the intestinal Mrp2 down-regulation. Additionally, both agents could be considered of potential therapeutic value to preserve Mrp2 function under MetS conditions.

Intestinal multidrug resistance-associated protein 2 is down-regulated in fructose-fed rats

Expression and activity of jejunal multidrug resistance-associated protein 2 (Mrp2) and glutathione-S-transferase (GST) were examined in fructose fed Wistar rats, an experimental model of metabolic syndrome. Animals were fed on (a) control diet or (b) control diet plus 10% w/vol fructose in the drinking water. Mrp2 and the α class of GST proteins as well as their corresponding mRNAs were decreased, suggesting a transcriptional regulation by fructose. Confocal microscopy studies reaffirmed down-regulation of Mrp2. Everted intestinal sacs were incubated with 1-chloro-2,4-dinitrobenzene in the mucosal compartment, and the glutathione-conjugated derivative, dinitrophenyl- S-glutathione (DNP-SG; model Mrp2 substrate), was measured in the same compartment to estimate Mrp2 activity. Excretion of DNP-SG was substantially decreased by fructose treatment, consistent with simultaneous down-regulation of Mrp2 and GST. In addition, the effect of fructose on intestinal barrier function exerted by Mrp2 was evaluated in vivo using valsartan, a recognized Mrp2 substrate of therapeutic use. After intraduodenal administration as a bolus, intestinal absorption of valsartan was increased in fructose-drinking animals. Fructose administration also induced oxidative stress in intestinal tissue as demonstrated by significant increases of intestinal lipid peroxidation end products and activity of the antioxidant enzyme superoxide dismutase, by a decreased GSH/GSSG ratio. Moreover, fructose treatment conduced to increased intestinal levels of the proinflammatory cytokines IL-β1 and IL-6. Collectively, our results demonstrate that metabolic syndrome-like conditions, induced by a fructose-rich diet, result in down-regulation of intestinal Mrp2 expression and activity and consequently in an impairment of its barrier function.

Brain, liver, and serum salusin-alpha and -beta alterations in Sprague-Dawley rats with or without metabolic syndrome

BACKGROUND

This metabolic syndrome (MetS) study was designed to investigate changes in expression of the neuropeptides salusin-α (Sal-α) and salusin-β (Sal-β) in brain and liver tissue in response to obesity and related changes induced by high-fructose diet and explored how these changes were reflected in the circulating levels of Sal-α and Sal-b, as well as revealing how the lipid profile and concentrations of glucose and uric acid were altered.

MATERIAL/METHODS

The study included 14 Sprague-Dawley rats. The control group was fed ad libitum on standard rat pellets, while the intervention group was given water with 10% fructose in addition to the standard rat pellet for 3 months. Sal-α and Sal-β concentrations in the serum and tissue supernatants were measured by ELISA, and immunohistochemical staining was used to demonstrate expression of the hormones in brain and liver.

RESULTS

Sal-α and Sal-β levels in both the serum and the brain and liver tissue supernatants were lower in the MetS group than the control group. Sal-α and Sal-β were shown by immunohistochemistry to be produced in the brain epithelium, the supraoptic nucleus of the hypothalamus, and the liver hepatocytes.

CONCLUSIONS

The decrease in Sal-α and Sal-β might be involved in the etiopathology of the metabolic syndrome induced by fructose.

Responses of iliac conduit artery and hindlimb resistance vessels to luminal hyperfructosemia in the anaesthetized pig

AIMS

High fructose levels are found in diabetes mellitus, associated with high corn syrup diets, and have been claimed to cause hypertension. As the direct effects on conduit and resistance arteries have not been previously reported, we measured these in vivo in the anaesthetized pig with instrumented iliac arteries.

METHODS

Experiments were performed on the iliac artery preparation in the anaesthetized pig: blood flow, diameter and pressure were measured in the iliac.

RESULTS

The change in diameter of an occluded iliac artery segment filled with hyperfructosemic (15 μm) blood was 89.5 ± 22.1 μm (mean ± SE), contrasted with 7.7 ± 13.06 μm control (P = 0.005, paired t-test, n = 6). There was no significant difference when compared with blood containing both hyperfructosemic blood and the nitric oxide synthesis inhibitor, N(G)-nitro-l-arginine methyl ester (250 μg mL(-1)). Step changes in pressure and flow were achieved by progressive arterial stenosis during control saline and 15 μm min(-1) fructose downstream intra-arterial infusions. Linear regression of the step changes in blood pressure versus the instantaneous step changes in blood flow showed a statistically significant decrease in slope of the conductance (P < 0.001, analysis of covariance), indicating an increase in instantaneous peripheral vascular resistance. Peripheral autoregulation and conduit artery shear-stress-mediated dilatation were not significantly altered.

CONCLUSION

An elevated level of fructose caused dilatation of a conduit artery but constriction of resistance vessels. The latter effect could account, if maintained long-term, for the hypertension claimed to be due to hyperfuctosemia.