Assessment of fructose overload in the metabolic profile and oxidative/nitrosative stress in the kidney of senescent female rats

Probiotic Kefir Improves Renal Disorders in Ovariectomized Female SHR with High Fructose Intake-Induced Metabolic Syndrome

Women in postmenopausal period may present several comorbidities linked to metabolic syndrome (MetS). Our hypothesis is that kefir may prevent the deleterious effects in renal function in an experimental model of metabolic syndrome (MetS) and ovarian hormone deficiency. Young female spontaneously hypertensive rats (SHR) were divided into four groups: ovariectomized (OVX) control, OVX fructose, OVX kefir, and OVX kefir + fructose. They received kefir (5% w/v) via gavage for 8 weeks, while fructose (10% w/v) was available ad libitum. In ponderal parameters and glucose metabolism, we observe that fructose-overloaded groups (OF and OKF) showed increased weight, visceral fat, and fasting blood glucose. However, OKF partially reduced glycemic peak in the glucose tolerance test. Moreover, the standard method for the measurement of renal function showed that OF and OKF groups had a reduction in glomerular filtration rate, and surprisingly OKF exhibited increased renal flow (RBF and RPF) and decreased resistance (RVR). These might be associated with the findings in oxidative stress and nitric oxide (NO) bioavailability, in which kefir in the OKF group was capable of increasing total nitrogen oxides (NOx), attenuate the generation of hydrogen peroxide (DCF) and peroxynitrite (HPF), and also decreased the elevated microalbuminuria promoted by fructose even though the systemic blood pressure between the groups did not differ. Taking together our results, in the present study, kefir showed favorable effects in the model of metabolic syndrome and ovarian hormone deficiency (OKF), potentially protecting the kidney from the deleterious effects of fructose.

Effects of Liquid Fructose Supplementation and Chronic Unpredictable Stress on Uterine Contractile Activity in Nonpregnant Rats

Increased fructose consumption and chronic stress, the major characteristics of modern lifestyle, impact human health; however, the consequences of their combination on the uterus remain understudied. In this study, we investigated contractile activity, morphology, and intracellular activity of antioxidant enzymes in uteri from virgin Wistar rats subjected to liquid fructose supplementation and/or unpredictable stress over 9 weeks. Contractile activity and uterine response to oxytocin or adrenaline were examined ex vivo using isolated bath chambers. Fructose supplementation, irrespective of stress, affected uterine morphology by increasing endometrium while decreasing myometrium volume density, attenuated uterine response to increasing doses of oxytocin, and increased glutathione peroxidase activity. Stress, irrespective of fructose, attenuated dose-dependent adrenaline-induced uterine relaxation. Stress, when applied solely, decreased mitochondrial superoxide dismutase activity. In the combined treatment, irregular estrous cycles and both reduced response to oxytocin and to adrenaline (as a consequence of fructose consumption and exposure to stress), along with fructose-related alteration of uterine morphology, were detected. In conclusion, fructose and stress affect uterine contractile activity, irrespective of each other, by inducing completely distinct responses in isolated uteri. In the combined treatment, the effects of both factors were evident, suggesting that the combination exerts more detrimental effects on the uterus than each factor individually.

Deleterious Effect of Fructose on the Heart Function of Hypertriglyceridemic Rats

A high-fructose intake (HFI) in food, sweetened beverages, and soft drinks appears to be one of the risk factors that worsens human metabolic and cardiovascular health, although the more accurate mechanism remains unclear. Hypertriglyceridemic (HTG) rats represent a suitable animal model of metabolic syndrome where the consumption of an HFI could have an additional aggravating impact. We aimed to study the effect of fructose on the heart functions. Male HTG rats had HFI or a standard diet for five weeks. Heart function was tested ex vivo on the perfused heart using the Langendorff technique. Isolated hearts underwent 25 min ischemia (I) and 30 min reperfusion (R). Left ventricular developed pressure (LVDP), ventricular premature beats, and dysrhythmias were monitored during R. At the end of the R, ventricular fibrillation (VF) was evoked electrically. Systolic blood pressure, glucose level, serum total cholesterol (TC), triglycerides (TAG), and thiobarbituric acid reactive substances (TBARS) in the kidney were determined. The LVDP showed a reduced return to the input values, the duration of VF in R increased, and the threshold for VF induction decreased. Serum TC, TAG, and kidney TBARS were increased. The effect of HFI on heart ventricular impairment was associated with the reduced threshold for induction of VF and aggravated dyslipidemia. The results point to the adverse impact of dietary high-fructose intake in rats with hypertriglyceridemia.

Alterations in Oxidative Stress Markers and Na,K-ATPase Enzyme Properties in Kidney after Fructose Intake and Quercetin Intervention in Rats

The study aimed to characterize the consequences of a 15-week intake of 10% fructose on the kidney, with the focus on oxidative stress markers and properties of the Na,K-ATPase enzyme. Various antioxidants naturally occurring in common food were demonstrated to be protective against fructose-induced deterioration of kidneys. Therefore, we also aimed to observe the effect of 6-week quercetin administration (20 mg/kg/day) that was initiated following the 9-week period of higher fructose intake, by determining the concentration of sodium, potassium, creatinine, urea, and glucose in blood plasma and oxidative status directly in the renal tissue. Kinetic studies of renal Na,K-ATPase were utilized for a deeper insight into the molecular principles of expected changes in this enzyme activity under conditions of presumed fructose-induced renal injury. Fructose intake led to increase in body weight gain, plasma glucose and sodium levels, and deterioration of kidney properties, although some compensatory mechanisms were observable. Quercetin administration improved glycemic control in rats exposed to fructose overload. However, an increase in plasma creatinine, a decrease in GSH/GSSG ratio in renal tissue homogenate, and a controversial effect on renal Na,K-ATPase enzyme suggest that quercetin treatment may not be beneficial in the condition of pre-existing renal pathology.

Effects of Fructose and Stress on Rat Renal Copper Metabolism and Antioxidant Enzymes Function

The effects of a fructose-rich diet and chronic stress on copper metabolism in the kidneys are still understudied. We investigated whether fructose and/or chronic unpredictable stress modulate copper metabolism in a way that affects redox homeostasis, thus contributing to progression of metabolic disturbances in the kidney. We determined protein level of copper transporters, chaperones, and cuproenzymes including cytochrome c oxidase, as well as antioxidant enzymes function in the kidneys of male Wistar rats subjected to 20% liquid fructose supplementation and/or chronic stress. Liquid fructose supplementation increased level of copper chaperone of superoxide dismutase and decreased metallothionein level, while rendering the level of copper importer and copper chaperones involved in copper delivery to mitochondria and trans Golgi network unaffected. Stress had no effect on renal copper metabolism. The activity and expression of renal antioxidant enzymes remained unaltered in all experimental groups. In conclusion, fructose, independently of stress, decreased renal copper level, and modulated renal copper metabolism as to preserve vital cellular function including mitochondrial energy production and antioxidative defense, at the expense of intracellular copper storage.

Infliximab ameliorates tumor necrosis factor-alpha exacerbated renal insulin resistance induced in rats by regulating insulin signaling pathway

Infliximab (IFX), a monoclonal antibody for tumor necrosis factor-alpha (TNF-α), is known to restore blood glucose homeostasis. However, its effects on improving renal insulin resistance (IR) are not yet studied. So we investigate the impact of infliximab on renal insulin signaling pathway in IR rat model regarding to metformin (MET). The induced IR was confirmed by a high oral glucose tolerance test, an elevation of lipid profile and the homeostatic model assessment of insulin resistance 2 (HOMA-IR 2) values. Subsequently, IR rats were concurrently treated with either MET (100 mg/kg/day) or IFX (one dose 5 mg/kg) besides IR and normal control (NC) groups. Four weeks later, IR control rats displayed hyperglycemia, hyperinsulinemia and elevation in HOMA-IR 2, renal function markers and renal tissue TNF-α, interleukins-1β and 6 (Il-1β, IL-6) and suppressor of cytokines signaling 3 (SOCS3) contents as well as glomerulosclerosis when compared to NC group. Additionally, the phosphorylation of renal insulin receptor substrate 1 (IRS1), phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt) were markedly impaired. Treatment with either MET or IFX significantly improved IR and kidney functions. The effects of the drugs were achieved by the downregulation of renal inflammatory cytokines and SOCS3 levels and the amelioration of the renal IRS1/PI3K/Akt pathway. In conclusion, MET and IFX ameliorated the TNF-α worsening effect on IR in rat renal tissues by regulating insulin signaling. Interestingly, infliximab was superior to metformin in regulating insulin signaling pathway. Therefore, infliximab could be used as an adjuvant therapy in improving renal IR.