Effects Of TRPV1/PPAR Delta Activation On Renal Oxidative Stress Damage And Na-Glucose Transporter2

Background and objective:With the development of economy and society, hypertension has become one of themost common chronic diseases in the world. Hypertension is the main cause of stroke,kidney failure and other serious disease of cardio-cerebrovascular disease. The WorldHealth Organization (WHO) reported that hypertension is a leading cause of death ofcardiovascular disease worldwide. High blood pressure has become a major health problemdamaging our life and health, and its prevention and control has prominent significance andvalue. Genetic and environmental factors are associated with the pathogenesis ofhypertension. Studies show that dietary factors such as high-calorie food, the low-potassium and high-sodium food affect the development of hypertension importantly. Alarge number of studies show that high salt intake leads to blood pressure increase. Betweensalt intake and blood pressure has a clear dose-effect relationship, and reducing salt intakecan prevent hypertension and cardiovascular disease significantly. More effective dietaryintervention has important significance to improve hypertension and cardiovascular diseaseinduced by the high-salt diet.Transient Receptor Potential Vanilloid1(TRPV1) cation channel is a polymodelnonselective cation channel, and expresses in sensory neurons system and also presents innonneuronal tissues including blood vessels and kidneys. Capsaicin is the major pungentingredient in hot pepper. TRPV1is also known as the capsaicin receptor and its roles incardiovascular metabolic disease have been revealed in recent years. Our previous studiesfind that dietary capsaicin activation of endothelial TRPV1which mediates an increasedCa2+influx and subsequent phosphorylation of PKA and eNOS, increases nitric oxide (NO)and reduces blood pressure in spontaneously hypertensive rats; Activated TRPV1reducesthe oxidative stress and superoxide anion production caused by high dietary salt intake, andincreases the bioavailability of NO. TRPV1also improves the endothelium-dependentrelaxing dysfunction and decreases blood pressure caused by high salt intake. Other studies show that capsaicin has effects on anti-oxidative stress, reduction of the urinary sodiumexcretion, and maintenance of water-salt homeostasis. Antioxidant therapy improves theendothelial-dependent diastolic function in patients with hypertension and decreaseshigh blood pressure induced by salt-intake in mice significantly. But these studies mostlyconfined to acute animal experiments and clinical research, and the long-term effect andprognosis of capsaicin remain need further study.Kidney has a huge amount of capillary networks, so the effects of TRPV1activationwhich protect target-organ damage by the high salt need to be further studies.Deoxycorticosterone acetate (DOCA) salt hypertensive rat is a classic low reninhypertension model which increases superoxide anion and causes oxidative stress inendothelial cell, and leads to renal damage as well as fibrosis. It is not clear whethercapsaicin improves renal vascular oxidative stress and protect renal function inhypertensive animal. In this study, we built the DOCA-salt hypertension rat model, and fedwith normal or capsaicin diet, in order to investigate the effects of TRPV1agonist,capsaicin, on progression of renal injury in DOCA-salt hypertensive rats.The cluster of hypertension, diabetes mellitus, and dyslipidemia collectively referredto as the metabolic syndrome, is the most serious threats to public health. High dietary saltintake represents a risk factor for the development of cardiovascular disease that isindependent of its well-known ability to increase arterial pressure in some individuals.However, the effects of high-salt intake on glucose and lipid metabolism are still unclear.High sodium intake decreases high-density lipoprotein (HDL)-cholesterol and increasesplasma insulin, homeostasis model assessment of insulin resistance in hypertensive patients.But the study of salt intake in patients shows an increase in insulin-mediated glucosedisposal during euglycaemic clamp conditions that is significantly higher following thehigh-salt diet compared with the low-salt diet. The chronic salt overload in Wistar ratsenhances the adipocyte insulin sensitivity for glucose uptake and the insulin-inducedglucose metabolization. In normal individuals, glucose presents in the plasma is filtered bythe kidneys, but virtually all glucose are reabsorbed, such that＜1%of glucose is excretedin urine. Inhibition of reabsorption process is predicted to reduce the renal threshold forglucose, allowing the excretion of excess glucose in the urine and thus lowering plasmaglucose levels. The sodium glucose co-transporter (SGLT2) with low affinity is found almost exclusively in the kidney, and several mutations of SGLT2gene in human causesrenal glucosuria. Dapagliflozin, a SGLT2inhibitor, increases renal glucose excretion innormal and diabetic rats, improves glucose tolerance in normal rats, and reduces Zuckerdiabetic fatty (ZDF) rats’ hyperglycemia. Adipose tissue produces and secretes manybioactive substances, and one of which is adiponectin, an antiatherogenic and antidiabeticadipocytokine. Peroxisome proliferator activated receptors (PPARs) are ligand-activatedtranscription factors that belong to the nuclear receptor superfamily. Peroxisomeproliferator activated receptors delta (PPARδ) is one of the key transcriptional regulators ofnutrient metabolism and energy homeostasis. We reported previously that PPARδ activationby telmisartan prevents weight gain, obesity and improves insulin resistance. However, it isunknown whether PPARδ activation in adipocytes affects blood glucose and renal glucoseexcretion during long term high-salt diet. In this study, we hypothesized that high-salt dietreduced blood glucose through PPARδ and adiponectin activation in adipocytes mediatedby SGLT2inhibition in renal proximal tubule of mice.Materials and Methods:Experiment is divided into two parts, the first part is to observe the renoprotectiveeffects and mechanisms of activation of TRPV1in DOCA-salt Hypertensive RatsTwenty-four male Sprague-Dawley (SD) rats were used in this part. Sixteen rats wereunilaterally nephrectomized and randomly divided into2groups (normal diet group andcapsaicin diet group). The other8male SD rats were treated with sham operation (Shamgroup). Rats in normal diet group and sham group were fed with normal diet for8weeksand rats in capsaicin diet group were fed with dietary capsaicin (diet with0.2g/kg capsaicin)for8weeks.1. Tail blood pressure and body weight were measured in8thweek.2. After8weeks,24-hour proteinuria, Urea (BUN), serum creatinine (Scr), urinecreatinine (UCr), renal weight were measured.3. Renal arteries were separated, surperoxide anion and nitric oxide (NO) weredetected by fluorescent probe.4. The expressions of TRPV1, p-eNOS, Nitrotyrosine and Uncoupling Protein2(UCP2) in renal arteries were determined by Western-blot.The second part is to observe that the high-salt diet reduces blood glucose through adipocyte’s PPARδ upregulation mediated SGLT2inhibition in renal proximal tubule ofmice16male Wild type (WT) mice and Fabp4-PPARδ mice, were randomly divided into2groups at6weeks old, normal-salt (0.4%) diet group and and high-salt (8%) diet group for24weeks of feeding.1. Tail blood pressure and body weight were measured every two week.2. At the24thweek, glucose tolerance,24-hour urine volume, urine sodium excretion,urine glucose excretion were measured.3. At the24thweek, the acute SGLT2function were measured.4. Adiponectin level of blood plasma were determined with the ELISA method.5. The expressions of PPARδ, adiponectin, adipoR1in perirenal fat and theexpressions of adiponectin, adipoR1and SGLT2in renal were determine by Western-blot.Results1. The blood pressure, body weight in DOCA salt hypertensive rats were higher thanthe sham group. Capsaicin significantly reduced the blood pressure of the DOCA salthypertensive rat, it had no effect on the heart rate and body weight.2. According to24h urine examination and serum biochemical tests showed that singlerenal mass/body, urea nitrogen, creatinine and urinary protein in DOCA salt hypertensiverats were significantly higher than sham group, and the creatinine clearance decreased.Capsaicin significantly reduced single renal mass/body, urea nitrogen, creatinine, and urineprotein of DOCA salt hypertensive rats, and the creatinine clearance increased.3.The renal arteriole superoxide anion levels of DOCA salt hypertensive rats weresignificantly higher than sham group, while NO levels were significantly lower. Dietarycapsaicin reduced renal arteriole superoxide anion levels and improved NO levels.4. The expression of TRPV1and p-eNOS in salt hypertensive rats renal arteriole waslower compared with the sham group. Capsaicin obviously increased the expressions ofTRPV1and p-eNOS of the DOCA salt type hypertension rats5. The expressions of UCP2and3-nitrotyrosine (Nitrotyrosine) in salt hypertensive ratrenal arteriole was higher than sham group. Capsaicin significantly increased the expressionof UCP2and decreased the expression of Nitrotyrosine.6. High-salt diet reduced blood glucose and body weight of WT mice but not in Fabp4-PPARδ-/-mice.7. High-salt intake increased adiponectin levels of WT mice by PPARδ activation.8. High-salt intake down-regulated SGLT2through PPARδ/adiponectin pathway.Conclusion1. Capsaicin significantly can attenuated renal damage in DOCA-salt hypertensiverats probably by improving oxidative stress due to the increased expression of TRPV1andUCP2.2. Long term chronic high-salt diet can improved glucose homeostasis throughactivation of PPARδ/adiponectin in adipocytes and reduction of SGLT2-mediated glucosereabsorption in kidney.