The proximal nephron reabsorbs 60% to 70% of the fluid and sodium and most of the filtered bicarbonate via Na/H exchanger 3. Enhanced proximal nephron transport is implicated in hypertension. Our findings show that a fructose-enriched diet causes salt sensitivity. We hypothesized that fructose stimulates luminal Na/H exchange activity and sensitizes the proximal tubule to angiotensin II. Na/H exchange was measured in rat proximal tubules as the rate of intracellular pH (pH _i ) recovery in fluorescent units/s. Replacing 5 mmol/L glucose with 5 mmol/L fructose increased the rate of pH _i recovery (1.8±0.6 fluorescent units/s; P <0.02; n=8). Staurosporine, a protein kinase C inhibitor, blocked this effect. We studied whether this effect was because of the addition of fructose or removal of glucose. The basal rate of pH _i recovery was first tested in the presence of a 0.6-mmol/L glucose and 1, 3, or 5 mmol/L fructose added in a second period. The rate of pH _i recovery did not change with 1 mmol/L but it increased with 3 and 5 mmol/L of fructose. Adding 5 mmol/L glucose caused no change. Removal of luminal sodium blocked pH _i recovery. With 5.5 mmol/L glucose, angiotensin II (1 pmol/L) did not affect the rate of pH _i recovery (change, –1.1±0.5 fluorescent units/s; n=9) but it increased the rate of pH _i recovery with 0.6 mmol/L glucose/5 mmol/L fructose (change, 4.0±2.2 fluorescent units/s; P <0.02; n=6). We conclude that fructose stimulates Na/H exchange activity and sensitizes the proximal tubule to angiotensin II. This mechanism is likely dependent on protein kinase C. These results may partially explain the mechanism by which a fructose diet induces hypertension.

Nephrotoxicity severely limits the use of the anticancer drug cisplatin. Oxidative stress, inflammation, and endoplasmic reticulum (ER) stress contribute to cisplatin‐induced nephrotoxicity. We developed novel orally active epoxyeicosatrienoic acid (EET) analogs and investigated their prophylactic effect in cisplatin‐induced nephrotoxicity in rats. Cisplatin‐induced nephrotoxicity was manifested by increases in blood urea nitrogen, plasma creatinine, urinary N ‐acetyl‐β‐( d )‐glucosaminidase activity, kidney injury molecule 1, and histopathology. EET analogs (10 mg/kg/d) attenuated cisplatin‐induced nephrotoxicity by reducing these renal injury markers by 40–80% along with a 50–70% reduction in renal tubular cast formation. This attenuated renal injury is associated with reduced oxidative stress, inflammation, and ER stress evident from reduction in related biomarkers and in the renal expression of genes involved in these pathways. Moreover, we demonstrated that the attenuated nephrotoxicity correlated with decreased apoptosis that is associated with 50–90% reduction in Bcl‐2 protein family mediated proapoptotic signaling, reduced renal caspase‐12 expression, and a 50% reduction in renal caspase‐3 activity. We further demonstrated in vitro that the protective activity of EET analogs does not compromise the anticancer effects of cisplatin. Collectively, our data provide evidence that EET analogs attenuate cisplatin‐induced nephrotoxicity by reducing oxidative stress, inflammation, ER stress, and apoptosis without affecting the chemotherapeutic effects of cisplatin.—Khan, Md. A. H., Liu, J., Kumar, G., Skapek, S. X., Falck, J. R. Imig, J. D., Novel orally active epoxyeicosatrienoic acid (EET) analogs attenuate cisplatin nephrotoxicity. FASEB J. 27, 2946–2956 (2013). www.fasebj.org

Epoxyeicosatrienoic acids (EETs) contribute to haemodynamics, electrolyte homoeostasis and blood pressure regulation, leading to the concept that EETs can be therapeutically targeted for hypertension. In the present study, multiple structural EET analogues were synthesized based on the EET pharmacophore and vasodilator structure-activity studies. Four EET analogues with 91–119% vasodilatory activity in the isolated bovine coronary artery (EC₅₀: 0.18–1.6 μM) were identified and studied for blood-pressure-lowering in hypertension. Two EET analogues in which the COOH group at carbon 1 of the EET pharmacophore was replaced with either an aspartic acid (EET-A) or a heterocyclic surrogate (EET-X) were administered for 14 days [10 mg/kg per day intraperitoneally (i.p.)]. Both EET-A and EET-X lowered blood pressure in spontaneously hypertensive rats (SHRs) and in angiotensin II (AngII) hypertension. On day 14, the mean arterial pressures in EET analogue-treated AngII-hypertensive and SHRs were 30–50 mmHg (EET-A) and 15–20 mmHg (EET-X) lower than those in vehicle-treated controls. These EET analogues (10 mg/kg per day) were further tested in AngII hypertension by administering orally in drinking water for 14 days and EET-A lowered blood pressure. Additional experiments demonstrated that EET-A inhibits epithelial sodium channel (ENaC) activity in cultured cortical collecting duct cells and reduced renal expression of ENaC subunits in AngII hypertension. In conclusion, we have characterized EET-A as an orally active antihypertensive EET analogue that protects vascular endothelial function and has ENaC inhibitory activity in AngII hypertension.

Background. Hydrogen sulfide (H2S), an endogenous vasoactive agent, is produced by cystathionine γ-lyase (CGL) and cystathionine β-synthase (CBS) enzym

Salt-sensitive hypertension leads to kidney injury. The Dahl salt–sensitive hypertensive rat (Dahl SS) is a model of salt-sensitive hypertension and progressive kidney injury. The current set of experimental studies evaluated the kidney protective potential of a novel epoxyeicosatrienoic acid analog (EET-B) in Dahl SS hypertension. Dahl SS rats receiving high-salt diet were treated with EET-B (10 mg/kg per day) or vehicle in drinking water for 14 days. Urine, plasma, and tissue samples were collected at the end of the treatment protocol to assess kidney injury, oxidative stress, inflammation, and endoplasmic reticulum stress. EET-B treatment in Dahl SS rats markedly reduced urinary albumin and nephrin excretion by 60% to 75% along with 30% to 60% reductions in glomerular injury, intratubular cast formation, and kidney fibrosis without affecting blood pressure. In Dahl SS rats, EET-B treatment further caused marked reduction in oxidative stress with 25% to 30% decrease in kidney malondialdehyde content along with 42% increase of nitrate/nitrite and a 40% reduction of 8-isoprostane. EET-B treatment reduced urinary monocyte chemoattractant protein-1 by 50% along with a 40% reduction in macrophage infiltration in the kidney. Treatment with EET-B markedly reduced renal endoplasmic reticulum stress in Dahl SS rats with reduction in the kidney mRNA expressions and immunoreactivity of glucose regulatory protein 78 and C/EBP homologous protein. In summary, these experimental findings reveal that EET-B provides kidney protection in Dahl SS rats by reducing oxidative stress, inflammation, and endoplasmic reticulum stress, and this protection was independent of reducing blood pressure.

Cardiometabolic syndrome occurs with obesity and consists of pathophysiological factors that increase the risk for cardiovascular events. Soluble epoxide hydrolase inhibition (sEHi) is a novel therapeutic approach that exerts renal and cardiovascular protection. Although sEHi as a therapeutic approach is promising, it could be more effective for the treatment of cardiometabolic syndrome when combined with peroxisome proliferator activated receptor γ (PPARγ) agonists. We hypothesized that the PPARγ agonist, rosiglitazone in combination with a sEHi (tAUCB) will provide synergistic actions to decrease blood pressure, improve vascular function, decrease inflammation, and prevent renal damage in spontaneously hypertensive obese rats (SHROB). SHROB were treated with rosiglitazone, tAUCB or the combination of tAUCB and rosiglitazone for four-weeks and compared with spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Blood pressure increased in SHROB (164±7 mmHg) and decreased 10 mmHg when treated with rosiglitazone, tAUCB, or tAUCB and rosiglitazone. Mesenteric artery dilation to the KATP channel opener pinacidil was attenuated in SHROB (E_Max =77±7%), compared with WKY (E_Max =115±19) and SHR (E_Max = 93±12%). Vasodilation to pinacidil was improved by rosiglitazone (E_Max = 92±14%) but not tAUCB. Renal macrophage infiltration increased in SHROB and significantly decreased with rosiglitazone or tAUCB and rosiglitazone treatment. Albuminuria was increased in SHROB (90±20 mg/d) and was significantly decreased by the combination of tAUCB and rosiglitazone (37±9 mg/d). Glomerular injury in SHROB was also significantly decreased by tAUCB and rosiglitazone. These results indicate that even though sEHi or PPARγ agonist have benefits when used individually, the combination is more beneficial for the multidisease features in cardiometabolic syndrome.