The present study was undertaken to evaluate the effects of chronic treatment with cis-4-[4-(3- adamantan-1-yl-ureido)cyclohexyl-oxy]benzoic acid (c-AUCB), a novel inhibitor of soluble epoxide hydrolase (sEH), which is responsible for the conversion of biologically active epoxyeicosatrienoic acids (EETs) to biologically inactive dihydroxyeicosatrienoic acids (DHETEs), on blood pressure (BP) and myocardial infarct size in male heterozygous Ren-2 transgenic rats (TGR) with established hypertension. Normotensive Hannover Sprague-Dawley (HanSD) rats served as controls. Myocardial ischemia was induced by coronary artery occlusion. Systolic BP was measured in conscious animals by tail-plethysmography. c-AUCB was administrated in drinking water. Renal and myocardial concentrations of EETs and DHETEs served as markers of internal production of epoxygenase metabolites. Chronic treatment with c-AUCB, which resulted in significant increases in the availability of biologically active epoxygenase metabolites in TGR – assessed as the ratio of EETs/DHETEs – was accompanied by a significant reduction in BP and significantly reduced infarct size in TGR as compared with untreated TGR. The cardioprotective action of c-AUCB treatment was completely prevented by acute administration of a selective EETs antagonist (14,15-epoxyeicosa5(Z)-enoic acid), supporting the notion that the improved cardiac ischemic tolerance conferred by sEH inhibition is mediated by EETs actions at the cellular level. These findings indicate that chronic inhibition of sEH exhibits antihypertensive and cardioprotective actions in this transgenic model of angiotensin II-dependent hypertension.

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.

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 epoxyecosatrienoic acid analog (EET-B) in Dahl SS hypertension. Dahl SS rats receiving high salt diet were treated with EET-B (10 mg/kg/d) 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 60–75% along with 30–60% reductions in glomerular injury, intra-tubular cast formation and kidney fibrosis without affecting blood pressure. In Dahl SS rats, EET-B treatment further caused marked reduction in oxidative stress with 25–30% 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 (ER) 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 ER stress, and this protection was independent of reducing blood pressure.

The aim was to determine whether increased oxidative stress during the adaptation to chronic intermittent hypoxia (CIH) plays a role in the induction of improved cardiac ischemic tolerance. Adult male Wistar rats were exposed to CIH in a hypobaric chamber (7,000 m, 8 h/day, 5 days/wk, 24-30 exposures). Half of the animals received antioxidant N-acetylcysteine (NAC; 100 mg/kg) daily before the exposure; the remaining rats received saline. Control rats were kept under normoxia and treated in a corresponding manner. One day after the last exposure (and/or NAC injection), anesthetized animals were subject to 20 min of coronary artery occlusion and 3 h of reperfusion for determination of infarct size. In parallel subgroups, biochemical analyses of the left ventricular myocardium were performed. Adaptation to CIH reduced infarct size from 56.7 +/- 4.5% of the area at risk in the normoxic controls to 27.7 +/- 4.9%. NAC treatment decreased the infarct size in the controls to 42.0 +/- 3.4%, but it abolished the protection provided by CIH (to 41.1 +/- 4.9%). CIH decreased the reduced-to-oxidized glutathione ratio and increased the relative amount of PKC isoform-delta in the particulate fraction; NAC prevented these effects. The expression of PKC-epsilon was decreased by CIH and not affected by NAC. Activities of superoxide dismutase, catalase, and glutathione peroxidase were affected by neither CIH nor NAC treatment. It is concluded that oxidative stress associated with CIH plays a role in the development of increased cardiac ischemic tolerance. The infarct size-limiting mechanism of CIH seems to involve the PKC-delta-dependent pathway but apparently not the increased capacity of major antioxidant enzymes.

The results suggest that opening of mitochondrial K(ATP) channels is involved in the cardioprotective mechanism conferred by long-term adaptation to intermittent high altitude hypoxia.

Endogenous cardiac protection against prolonged ischemic insult can be achieved by repeated brief episodes of ischemia (hypoxia) or by cardiac adaptation to various stresses such as chronic hypoxia. Activation of phosphatidylinositol 3-kinase (PI3K)/Akt is involved in antiapoptotic effects, however, it is not clear whether it is required for overall heart salvage including protection against myocardial infarction and arrhythmias. We focussed on the potential common role of PI3K/Akt in anti-infarct protection, in the experimental settings of long-term adaptation to chronic intermittent hypobaric hypoxia (IHH; 8 h/day, 25-30 exposures, in vivo rats) and acute ischemic preconditioning (IP; Langendorff-perfused hearts). In addition, we explored the role of PI3K/Akt in susceptibility to ischemic ventricular arrhythmias. In normoxic open-chest rats, PI3K/Akt inhibitor LY294002 (LY; 0.3 mg/kg) given 5 min before test occlusion/reperfusion (I/R) did not affect infarct size (IS) normalized to the size of area at risk (AR). In hypoxic rats, LY partially attenuated IS-limiting effect of IHH (IS/AR 59.7 +/- 4.1% vs. 51.8 +/- 4.4% in the non-treated rats; p > 0.05) and increased IS/AR to its value in normoxic rats (64.9 +/- 5.1%). In the isolated hearts, LY (5 muM) applied 15 min prior to I/R completely abolished anti-infarct protection by IP (IS/AR 55.0 +/- 4.9% vs. 15.2 +/- 1.2% in the non-treated hearts and 42.0 +/- 5.5% in the non-preconditioned controls; p < 0.05). In the non-preconditioned hearts, PI3K/Akt inhibition did not modify IS/AR, on the other hand, it markedly suppressed arrhythmias. In the LY-treated isolated hearts, the total number of ventricular premature beats and the incidence of ventricular tachycardia (VT) was reduced from 518 +/- 71 and 100% in the controls to 155 +/- 15 and 12.5%, respectively (p < 0.05). Moreover, bracketing of IP with LY did not reverse antiarrhythmic effect of IP. These results suggest that activation of PI3K/Akt cascade plays a role in the IS-limiting mechanism in the rat heart, however, it is not involved in the mechanisms of antiarrhythmic protection.

Although physiological responses to chronic hypoxia, including pulmonary hypertension and right ventricular hypertrophy, have been well described, the molecular mechanisms involved in cardiopulmonary adaptations are still not fully understood. We hypothesize that adaptive responses to chronic hypoxia are the result of altered transcriptional regulations in the right and left ventricles. Here we report results from the gene expression profiling of adaptive responses in a chronically hypoxic heart. Of 11 analyzed candidate genes, the expression of seven and four genes, respectively, was significantly altered in the right ventricle of hypoxic male and female mice. In the transcriptional profile of the left ventricle, we identified a single expression change in hypoxic males (Vegfa gene). To directly test the role of HIF1, we analyzed the expression profile in Hif1a partially deficient mice exposed to moderate hypoxia. Our data showed that Hif1a partial deficiency significantly altered transcriptional profiles of analyzed genes in hypoxic hearts. The expression changes were only detected in two genes in the right ventricle of Hif1a(+/-) males and in one gene in the right ventricle of Hif1a(+/-) females. First, our results suggest that hypoxia mainly affects adaptive expression profiles in the right ventricle and that each ventricle can respond independently. Second, our findings indicate that HIF1a plays an important role in adaptive cardiopulmonary responses and the dysfunction of HIF1 pathways considerably affects transcriptional regulation in the heart. Third, our data reveal significant differences between males and females in cardiac adaptive responses to hypoxia and indicate the necessity of optimizing diagnostic and therapeutic procedures in clinical practice, with respect to sex.

The objective of the work was to examine whether adaptation to intermittent high altitude hypoxia and ischaemic preconditioning provide additive protection of the heart against subsequent acute ischaemic injury. Adult male rats were exposed to hypoxia (7000 m, 8 h/day, 24-30 exposures) in a hypobaric chamber. Susceptibility of their hearts to ischaemia-induced ventricular arrhythmias and infarction was evaluated in open-chest animals subjected to 30-min coronary artery occlusion and 4-h reperfusion. Preconditioning was induced by either two (PC1) or five (PC2) occlusions of the same artery for 5 min, each followed by 5-min reperfusion. Adaptation to hypoxia decreased the arrhythmia score from 2.75 +/- 0.13 in normoxic controls to 2.17 +/- 0.18. Both PC1 and PC2 reduced the arrhythmia score in the controls (0.15 +/- 0.10 and 0.71 +/- 0.24, respectively), as well as in the hypoxic groups (0.40 +/- 0.15 and 0.27 +/- 0.15, respectively). The infarct size was reduced from 66.6 +/- 2.3% of the area at risk in the controls to 50.2 +/- 1.9% in the adapted rats. PC1 conferred further protection in adapted animals (38.4 +/- 2.8%) but this combined effect was of the same magnitude as that of preconditioning in the controls (37.5 +/- 1.6%). Similar results were obtained using PC2. It is concluded that adaptation to hypoxia decreases the efficiency of ischaemic preconditioning; cardioprotective effects of these two phenomena are not additive. The results are consistent with the view that the mechanisms of protection conferred by chronic hypoxia and preconditioning may share the same signalling pathway.