The role of the kidney in hypertension

Genetic and Epigenetic Mechanisms Regulating Blood Pressure and Kidney Dysfunction

The pioneering work of Dr Lewis K. Dahl established a relationship between kidney, salt, and high blood pressure (BP), which led to the major genetic-based experimental model of hypertension. BP, a heritable quantitative trait affected by numerous biological and environmental stimuli, is a major cause of morbidity and mortality worldwide and is considered to be a primary modifiable factor in renal, cardiovascular, and cerebrovascular diseases. Genome-wide association studies have identified monogenic and polygenic variants affecting BP in humans. Single nucleotide polymorphisms identified in genome-wide association studies have quantified the heritability of BP and the effect of genetics on hypertensive phenotype. Changes in the transcriptional program of genes may represent consequential determinants of BP, so understanding the mechanisms of the disease process has become a priority in the field. At the molecular level, the onset of hypertension is associated with reprogramming of gene expression influenced by epigenomics. This review highlights the specific genetic variants, mutations, and epigenetic factors associated with high BP and how these mechanisms affect the regulation of hypertension and kidney dysfunction.

The association between proton pump inhibitor use and risk of post-hospitalization acute kidney injury: a multicenter prospective matched cohort study

BACKGROUND

Proton Pump Inhibitors (PPI) are among the most commonly used drugs to treat acid-related gastrointestinal disorders in the USA. Although PPI use has been linked to acute interstitial nephritis, the side effects of post-hospitalization acute kidney injury (AKI) and the progression of kidney disease still are controversial. We conducted a matched cohort study to examine the associations between PPI use and the side effects, especially in post-hospitalization AKI.

METHODS

We investigated 340 participants from the multicenter, prospective, matched-cohort ASSESS-AKI study, which enrolled participants from December 2009 to February 2015. After the baseline index hospitalization, follow-up visits were conducted every six months, and included a collection of self-reported PPI use by participants. Post-hospitalization AKI was defined as the percentage increase from the nadir to peak inpatient SCr value was ≥ 50% and/or absolute increase ≥ 0.3 mg/dL in peak inpatient serum creatinine compared with baseline outpatient serum creatinine. We applied a zero-inflated negative binomial regression model to test the relationship between PPI use and post-hospitalization AKI. Stratified Cox proportional hazards regression models also were conducted to examine the association between PPI use and the risk of progression of kidney disease.

RESULTS

After controlling for demographic variables, baseline co-morbidities and drug use histories, there was no statistically significant association between PPI use and risk of post-hospitalization AKI (risk ratio [RR], 0.91; 95% CI, 0.38 to 1.45). Stratified by AKI status at baseline, no significant relationships were confirmed between PPI use and the risk of recurrent AKI (RR, 0.85; 95% CI, 0.11 to 1.56) or incidence of AKI (RR, 1.01; 95% CI, 0.27 to 1.76). Similar non-significant results also were observed in the association between PPI use and the risk of progression of kidney diseases (Hazard Ratio [HR], 1.49; 95% CI, 0.51 to 4.36).

CONCLUSION

PPI use after the index hospitalization was not a significant risk factor for post-hospitalization AKI and progression of kidney diseases, regardless of the AKI status of participants at baseline.

Evaluation of hypertension in systemic sclerosis and systemic lupus erythematosus overlap

Patients with systemic sclerosis and systemic lupus erythematosus serologies present a unique challenge to the clinician when hypertension is detected in the outpatient setting. Treatment choices for non-renal crisis hypertension are different for systemic sclerosis versus systemic lupus erythematosus. Urgent laboratory studies and, in the presence of certain symptoms, imaging assessment are indicated in systemic sclerosis and systemic lupus erythematosus overlap patients with systemic hypertension. Long-term assessment of systemic hypertension may be enhanced by advances in non-contrast imaging that serve as valuable biomarkers for progressive vasculopathy. In this review, the diagnostic approach to systemic sclerosis and systemic lupus erythematosus overlap patients presenting with hypertension is discussed.

Benincasa hispida extracts positively regulated high salt-induced hypertension in Dahl salt-sensitive rats: Impact on biochemical profile and metabolic patterns

Salt-induced hypertension is one of the major issues worldwide and one of the main factors involved in heart and kidney failure. The objective of this study was to investigate the potential role of Benincasa hispida extracts on high salt-induced hypertension in Dahl-salt sensitive (D-SS) rats and to find out the metabolic and biochemical pattern involved in the reduction of hypertension. Twenty-six Dahl salt-sensitive (D-SS) rats were selected and divided into four groups. The metabolic strategy was applied to test the extracts on salt-sensitive hypertension in kidney. Gas Chromatography-Mass spectrometry (GC-MS) was used to identify the potent biochemical profile in renal medulla and cortex of rat kidneys. The differential metabolites of cortex and medulla, enrichment analysis and pathway analysis were performed using metabolomics data. The GC-MS data revealed that 24 different antihypertensive metabolites was detected in renal cortex, while 16 were detected in renal medulla between different groups. The significantly metabolic pathways namely citrate cycle, glutathione metabolism, glycine, serine, and threonine metabolism, glyoxylate and dicarboxylate metabolism, glycerolipid metabolism, alanine, aspartate and glutamate metabolism in renal cortex and glycerolipid metabolism, pentose phosphate pathway, citrate cycle, glycolysis, glycerophospholipid metabolism, phenylalanine, tyrosine and tryptophan biosynthesis in renal medulla were involved in the process of Hypertension. The results suggest that the extract mainly alter the metabolic pathways of amino acid in Dahl salt-sensitive rats and its antioxidant potential reduced the hypertension patterns of Salt-sensitive rat. The antihypertensive components malic acid, aspartic acid, and glycine of extract can be used as therapeutic drugs to protect kidneys from salt-induced hypertension. PRACTICAL APPLICATIONS: Hypertension is a multifactorial disease and one of the risk factors for heart and kidney failure. Benincasa hispida is a widely used vegetable in China, which belongs to the Cucurbitaceae family. Benincasa hispida (wax gourd) has been used in traditional Chinese medicine for the treatment of inflammation and hypertension. The Benincasa hispida contains many compounds such as amino acids, carbohydrates, volatile compounds, vitamins, and minerals. The amino acid present in the pulp of Benincasa hispida are ornithine, threonine, aspartate, glutamate, serine, glycine, proline, alanine, valine, cysteine, isoleucine, tyrosine, leucine, lysine, phenylalanine, histidine, arginine, and γ-aminobutyric acid. Our results showed that Benincasa hispida is one of the potent natural antioxidants and can maintain normal blood pressure in Dahl salt-sensitive rats (D-SS). In conclusion, the current results provide good theoretical basis for the development and research using Benincasa hispida as an effective natural antioxidant for hypertension.

T Cell Immunometabolism and Redox Signaling in Hypertension

PURPOSE OF REVIEW

In this article, we summarize the current literature supporting metabolic and redox signaling pathways as important mechanisms underlying T cell activation in the context of hypertension.

RECENT FINDINGS

T cell immunometabolism undergoes dramatic remodeling in order to meet the demands of T cell activation, differentiation, and proliferation. Recent evidence demonstrates that the T cell oxidation-reduction (redox) system also undergoes significant changes upon activation, which can itself modulate metabolic processes and T cell function. Dysregulation of these signaling pathways can lead to aberrant T cell activation and inappropriate ROS production, both of which are linked to pathological conditions like hypertension. While the contribution of T cells to the progression of hypertension has been thoroughly investigated, how T cell metabolism and redox signaling changes, both separately and together, is an area of study that remains largely untouched. This review presents evidence from our own laboratory as well as others to highlight the importance of these two mechanisms in the study of hypertension.

Intratubular, Intracellular, and Mitochondrial Angiotensin II/AT1 (AT1a) Receptor/NHE3 Signaling Plays a Critical Role in Angiotensin II-Induced Hypertension and Kidney Injury

Hypertension is well recognized to be the most important risk factor for cardiovascular diseases, stroke, and end-stage kidney failure. A quarter of the world’s adult populations and 46% of the US adults develop hypertension and currently require antihypertensive treatments. Only 50% of hypertensive patients are responsive to current antihypertensive drugs, whereas remaining patients may continue to develop cardiovascular, stroke, and kidney diseases. The mechanisms underlying the poorly controlled hypertension remain incompletely understood. Recently, we have focused our efforts to uncover additional renal mechanisms, pathways, and therapeutic targets of poorly controlled hypertension and target organ injury using novel animal models or innovative experimental approaches. Specifically, we studied and elucidated the important roles of intratubular, intracellular, and mitochondrial angiotensin II (Ang II) system in the development of Ang II-dependent hypertension. The objectives of this invited article are to review and discuss our recent findings that (a) circulating and intratubular Ang II is taken up by the proximal tubules via the (AT₁) AT_1a receptor-dependent mechanism, (b) intracellular administration of Ang II in proximal tubule cells or adenovirus-mediated overexpression of an intracellular Ang II fusion protein selectively in the mitochonria of the proximal tubules induces blood pressure responses, and (c) genetic deletion of AT₁ (AT_1a) receptors or the Na⁺/H⁺ exchanger 3 selectively in the proximal tubules decreases basal blood pressure and attenuates Ang II-induced hypertension. These studies provide a new perspective into the important roles of the intratubular, intracellular, and mitochondrial angiotensin II/AT₁ (AT_1a) receptor signaling in Ang II-dependent hypertensive kidney diseases.

Amplification of Salt-Sensitive Hypertension and Kidney Damage by Immune Mechanisms

Humans with salt-sensitive (SS) hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Increasing evidence indicates that immune mechanisms play an important role in the full development of SS hypertension and associated renal damage. Recent experimental advances and studies in animal models have permitted a greater understanding of the mechanisms of activation and action of immunity in this disease process. Evidence favors a role of both innate and adaptive immune mechanisms that are triggered by initial, immune-independent alterations in blood pressure, sympathetic activity, or tissue damage. Activation of immunity, which can be enhanced by a high-salt intake or by alterations in other components of the diet, leads to the release of cytokines, free radicals, or other factors that amplify renal damage and hypertension and mediate malignant disease.

Renal metabolism and hypertension

Hypertension is a leading risk factor for disease burden worldwide. The kidneys, which have a high specific metabolic rate, play an essential role in the long-term regulation of arterial blood pressure. In this review, we discuss the emerging role of renal metabolism in the development of hypertension. Renal energy and substrate metabolism is characterized by several important and, in some cases, unique features. Recent advances suggest that alterations of renal metabolism may result from genetic abnormalities or serve initially as a physiological response to environmental stressors to support tubular transport, which may ultimately affect regulatory pathways and lead to unfavorable cellular and pathophysiological consequences that contribute to the development of hypertension.

Renoprotective and haemodynamic effects of adiponectin and peroxisome proliferator-activated receptor agonist, pioglitazone, in renal vasculature of diabetic Spontaneously hypertensive rats

Pioglitazone, a therapeutic drug for diabetes, possesses full PPAR-γ agonist activity and increase circulating adiponectin plasma concentration. Plasma adiponectin concentration decreases in hypertensive patients with renal dysfunctions. Present study investigated the reno-protective, altered excretory functions and renal haemodynamic responses to adrenergic agonists and ANG II following separate and combined therapy with pioglitazone in diabetic model of hypertensive rats. Pioglitazone was given orally [10mg/kg/day] for 28 days and adiponectin intraperitoneally [2.5μg/kg/day] for last 7 days. Groups of SHR received either pioglitazone or adiponectin in combination. A group of Wistar Kyoto rats [WKY] served as normotensive controls, whereas streptozotocin administered SHRs served as diabetic hypertensive rats. Metabolic data and plasma samples were taken on day 0, 8, 21 and 28. In acute studies, the renal vasoconstrictor actions of Angiotensin II [ANGII], noradrenaline [NA], phenylephrine [PE] and methoxamine [ME] were determined. Diabetic SHRs control had a higher basal mean arterial blood pressure than the WKY, lower RCBP and plasma adiponectin, higher creatinine clearance and urinary sodium excretion compared to WKY [all P<0.05] which were normalized by the individual drug treatments and to greater degree following combined treatment. Responses to intra-renal administration of NA, PE, ME and ANGII were larger in diabetic SHR than WKY and SHRs [P<0.05]. Adiponectin significantly blunted responses to NA, PE, ME and ANG II in diabetic treated SHRs by 40%, whereas the pioglitazone combined therapy with adiponectin further attenuated the responses to adrenergic agonists by 65%. [all P <0.05]. These findings suggest that adiponectin possesses renoprotective effects and improves renal haemodynamics through adiponectin receptors and PPAR-γ in diabetic SHRs, suggesting that synergism exists between adiponectin and pioglitazone. A cross-talk relationship also supposed to exists between adiponectin receptors, PPAR-γ and alpha adrenoceptors in renal vasculature of diabetic SHRs.

Endogenous miR-204 Protects the Kidney against Chronic Injury in Hypertension and Diabetes

BACKGROUND

Aberrant microRNA (miRNA) expression affects biologic processes and downstream genes that are crucial to CKD initiation or progression. The miRNA miR-204-5p is highly expressed in the kidney but whether miR-204-5p plays any role in the development of chronic renal injury is unknown.

METHODS

We used real-time PCR to determine levels of miR-204 in human kidney biopsies and animal models. We generated Mir204 knockout mice and used locked nucleic acid-modified anti-miR to knock down miR-204-5p in mice and rats. We used a number of physiologic, histologic, and molecular techniques to analyze the potential role of miR-204-5p in three models of renal injury.

RESULTS

Kidneys of patients with hypertension, hypertensive nephrosclerosis, or diabetic nephropathy exhibited a significant decrease in miR-204-5p compared with controls. Dahl salt-sensitive rats displayed lower levels of renal miR-204-5p compared with partially protected congenic SS.13^BN26 rats. Administering anti-miR-204-5p to SS.13^BN26 rats exacerbated interlobular artery thickening and renal interstitial fibrosis. In a mouse model of hypertensive renal injury induced by uninephrectomy, angiotensin II, and a high-salt diet, Mir204 gene knockout significantly exacerbated albuminuria, renal interstitial fibrosis, and interlobular artery thickening, despite attenuation of hypertension. In diabetic db/db mice, administering anti-miR-204-5p exacerbated albuminuria and cortical fibrosis without influencing blood glucose levels. In all three models, inhibiting miR-204-5p or deleting Mir204 led to upregulation of protein tyrosine phosphatase SHP2, a target gene of miR-204-5p, and increased phosphorylation of signal transducer and activator of transcription 3, or STAT3, which is an injury-promoting effector of SHP2.

CONCLUSIONS

These findings indicate that the highly expressed miR-204-5p plays a prominent role in safeguarding the kidneys against common causes of chronic renal injury.

Hyperosmolarity and Increased Serum Sodium Concentration Are Risks for Developing Hypertension Regardless of Salt Intake: A Five-Year Cohort Study in Japan

The potential contribution of serum osmolarity in the modulation of blood pressure has not been evaluated. This study was done to examine the relationship between hyperosmolarity and hypertension in a five-year longitudinal design. We enrolled 10,157 normotensive subjects without diabetes who developed hypertension subsequently as determined by annual medical examination in St. Luke's International Hospital, Tokyo, between 2004 and 2009. High salt intake was defined as >12 g/day by a self-answered questionnaire and hyperosmolarity was defined as >293 mOsm/L serum osmolarity, calculated using serum sodium, fasting blood glucose, and blood urea nitrogen. Statistical analyses included adjustments for age, gender, body mass index, smoking, drinking alcohol, dyslipidemia, hyperuricemia, and chronic kidney disease. In the patients with normal osmolarity, the group with high salt intake had a higher cumulative incidence of hypertension than the group with normal salt intake (8.4% versus 6.7%, p = 0.023). In contrast, in the patients with high osmolarity, the cumulative incidence of hypertension was similar in the group with high salt intake and in the group with normal salt intake (13.1% versus 12.9%, p = 0.84). The patients with hyperosmolarity had a higher incidence of hypertension over five years compared to that of the normal osmolarity group (p < 0.001). After multiple adjustments, elevated osmolarity was an independent risk for developing hypertension (OR (odds ratio), 1.025; 95% CI (confidence interval), 1.006-1.044), regardless of the amount of salt intake. When analyzed in relation to each element of calculated osmolarity, serum sodium and fasting blood glucose were independent risks for developing hypertension. Our results suggest that hyperosmolarity is a risk for developing hypertension regardless of salt intake.

Renal Effects of Fetal Reprogramming With Pentaerythritol Tetranitrate in Spontaneously Hypertensive Rats

Aims

Current antihypertensive therapies cannot cure hypertension and a life-long medication is necessary. Maternal treatment may represent a promising strategy for hypertension treatment. We have previously shown that maternal treatment of spontaneously hypertensive rats (SHR) with pentaerythritol tetranitrate (PETN) leads to a persistent blood pressure reduction in the female offspring. The underlying mechanisms include improved endothelial function resulting from long-lasting epigenetic changes. In the present study, we address the renal effects of maternal PETN treatment.

Methods and Results

F0 parental SHR were fed with either normal chow or PETN-containing (1 g/kg) chow ad libitum from the time point of mating to the end of lactation period. The F1 offspring received normal chow without PETN from the time point of weaning (at the age of 3 weeks). At the age of 16 weeks, female PETN offspring showed lower blood pressure than the control. No difference was observed in male offspring. All following experiments were performed with kidneys from 16-week-old female offspring. Maternal PETN treatment reduced the mRNA and protein expression of angiotensin-converting enzyme (ACE) and basic fibroblast growth factor (FGF2), resulting from epigenetic modifications found at the proximal promoter regions. The expression levels of mineralocorticoid receptor (MR) and factors in the MR signalling pathway (Rac1 and Sgk1) were also reduced by PETN. Major profibrotic cytokines, including Wnt4, TNF-alpha, TGF-beta, and MMP9, were downregulated by PETN, which was associated with reduced collagen deposition and glomerulus sclerosis in the kidney of PETN offspring. In addition, PETN treatment also decreased the markers of inflammation and immune cell infiltration in the kidneys.

Conclusions

PETN maternal treatment leads to epigenetic changes in the kidney of female SHR offspring. The reduced renal inflammation, alleviated kidney fibrosis, and decreased MR signalling are potential mechanisms contributing to the observed blood pressure-lowering effect.

Immune mechanisms of salt-sensitive hypertension and renal end-organ damage

Immune mechanisms have been recognized to have a role in the pathogenesis of hypertension, vascular disease and kidney damage in humans and animals for many decades. Contemporary advances in experimentation have permitted a deeper understanding of the mechanisms by which inflammation and immunity participate in cardiovascular disease, and multiple observations have demonstrated strong correlations between the discoveries made in animals and those made in patients with hypertension. Of note, striking phenotypic similarities have been observed in the infiltration of immune cells in the kidney and the development of end-organ damage in patients and animal models with sodium-sensitive hypertension. The available data suggest that an initial salt-induced increase in renal perfusion pressure, which is likely independent of immune mechanisms, induces the infiltration of immune cells into the kidney. The mechanisms mediating immune cell infiltration in the kidney are not well understood but likely involve tissue damage, the direct influence of salt to stimulate immune cell activation, sympathetic nerve stimulation or other factors. The infiltrating cells then release cytokines, free radicals and other factors that contribute to renal damage as well as increased retention of sodium and water and vascular resistance, which lead to the further development of hypertension.

MiR-192-5p in the Kidney Protects Against the Development of Hypertension

MicroRNA miR-192-5p is one of the most abundant microRNAs in the kidney and targets the mRNA for ATP1B1 (β1 subunit of Na⁺/K⁺-ATPase). Na⁺/K⁺-ATPase drives renal tubular reabsorption. We hypothesized that miR-192-5p in the kidney would protect against the development of hypertension. We found miR-192-5p levels were significantly lower in kidney biopsy specimens from patients with hypertension (n=8) or hypertensive nephrosclerosis (n=32) compared with levels in controls (n=10). Similarly, Dahl salt-sensitive (SS) rats showed a reduced abundance of miR-192-5p in the renal cortex compared with congenic SS.13^BN26 rats that had reduced salt sensitivity (n=9; P<0.05). Treatment with anti-miR-192-5p delivered through renal artery injection in uninephrectomized SS.13^BN26 rats exacerbated hypertension significantly. Mean arterial pressure on a 4% NaCl high-salt diet at day 14 post anti-miR-192-5p treatment was 16 mm Hg higher than in rats treated with scrambled anti-miR (n=8 and 6; P<0.05). Similarly, Mir192 knockout mice on the high-salt diet treated with Ang II (angiotensin II) for 14 days exhibited a mean arterial pressure 22 mm Hg higher than wild-type mice (n=9 and 5; P<0.05). Furthermore, protein levels of ATP1B1 were higher in Dahl SS rats than in SS.13^BN26 rats. Na⁺/K⁺-ATPase activity increased in the renal cortex of SS.13^BN26 rats 9 days posttreatment with anti-miR-192-5p compared with that of control anti-miR treated rats. Intrarenal knockdown of ATP1B1 attenuated hypertension in SS.13^BN26 rats with intrarenal knockdown of miR-192-5p. In conclusion, miR-192-5p in the kidney protects against the development of hypertension, which is mediated, at least in part, by targeting Atp1b1.

Two pharmacological epoxyeicosatrienoic acid-enhancing therapies are effectively antihypertensive and reduce the severity of ischemic arrhythmias in rats with angiotensin II-dependent hypertension

OBJECTIVE

We examined the effects of treatment with soluble epoxide hydrolase inhibitor (sEHi) and epoxyeicosatrienoic acids (EETs) analogue (EET-A), given alone or combined, on blood pressure (BP) and ischemia/reperfusion myocardial injury in rats with angiotensin II (ANG II)-dependent hypertension.

METHODS

Ren-2 transgenic rats (TGR) were used as a model of ANG II-dependent hypertension and Hannover Sprague-Dawley rats served as controls. Rats were treated for 14 days with sEHi or EET-A and BP was measured by radiotelemetry. Albuminuria, cardiac hypertrophy and concentrations of ANG II and EETs were determined. Separate groups were subjected to acute myocardial ischemia/reperfusion injury and the infarct size and ventricular arrhythmias were determined.

RESULTS

Treatment of TGR with sEHi and EET-A, given alone or combined, decreased BP to a similar degree, reduced albuminuria and cardiac hypertrophy to similar extent; only treatment regimens including sEHi increased myocardial and renal tissue concentrations of EETs. sEHi and EET-A, given alone or combined, suppressed kidney ANG II levels in TGR. Remarkably, infarct size did not significantly differ between TGR and Hannover Sprague-Dawley rats, but the incidence of ischemia-induced ventricular fibrillations was higher in TGR. Application of sEHi and EET-A given alone and combined sEHi and EET-A treatment were all equally effective in reducing life-threatening ventricular fibrillation in TGR.

CONCLUSION

The findings indicate that chronic treatment with either sEHi or EET-A exerts distinct antihypertensive and antiarrhythmic actions in our ANG II-dependent model of hypertension whereas combined administration of sEHi and EET-A does not provide additive antihypertensive or cardioprotective effects.

Salt-sensitive increase in macrophages in the kidneys of Dahl SS rats

Studies of Dahl salt-sensitive (SS) rats have shown that renal CD3⁺ T cells and ED-1⁺ macrophages are involved in the development of salt-sensitive hypertension and renal damage. The present study demonstrated that the increase in renal immune cells, which accompanies renal hypertrophy and albuminuria in high-salt diet-fed Dahl SS rats, is absent in Sprague-Dawley and SSBN13 rats that are protected from the SS disease phenotype. Flow cytometric analysis demonstrated that >70% of the immune cells in the SS kidney are M1 macrophages. PCR profiling of renal myeloid cells showed a salt-induced upregulation in 9 of 84 genes related to Toll-like receptor signaling, with notable upregulation of the Toll-like receptor 4/CD14/MD2 complex. Because of the prominent increase in macrophages in the SS kidney, we used liposome-encapsulated clodronate (Clod) to deplete macrophages and assess their contribution to salt-sensitive hypertension and renal damage. Dahl SS animals were administered either Clod-containing liposomes (Clod-Lipo), Clod, or PBS-containing liposomes as a vehicle control. Clod-Lipo treatment depleted circulating and splenic macrophages by ∼50%; however, contrary to our hypothesis, Clod-Lipo-treated animals developed an exacerbated salt-sensitive response with respect to blood pressure and albuminuria, which was accompanied by increased renal T and B cells. Interestingly, those treated with Clod also demonstrated an exacerbated phenotype, but it was less severe than Clod-Lipo-treated animals and independent of changes to the number of renal immune cells. Here, we have shown that renal macrophages in Dahl SS animals sustain a M1 proinflammatory phenotype in response to increased dietary salt and highlighted potential adverse effects of Clod-Lipo macrophage depletion.

The effects of estradiol and testosterone on renal tissues oxidative after central injection of angiotensin II in female doca - salt treated rats

Background Although numerous studies have proven that estrogen (Est) has a protective effect on the development of hypertension, more research needs to be done to show its detailed mechanism in a variety of hypertension. The important role of active oxygen species in blood pressure is well defined. We examined whether or not sex hormones change the growth of reactive oxygen species (ROS) ‎in kidneys after central microinjection of angiotensin II (Ang II).‎ Materials and methods Female Wistar rats, 8 weeks old (200 ± 10 g) were used in this study. The animal groups were (1) Sham, (2) Ovariectomy (OVX), (3) Sham-Hypertension (Sham-Hyper), (4) OVX-Hypertension (OVX-Hyper), (5) Sham-Hyper-Est, (6) OVX-Hyper-Est‎;‎ (7) Sham-Hyper-Testosterone (Tst) and (8) OVX-Hyper-Tst. Solutions of 1% NaCl and 0.1 KCl ‎were used and desoxycorticostrone (doca-salt) was injected (45 mg/kg) 3 times a week in Hypertension groups. Estradiol and Tst (2 mg/kg and ‎5 mg/kg‎; daily; subcutaneously) for 4 weeks. Ang II (50 μM, 5 μL) was microinjected by intracerebroventricular ( i.c.v.) infusion and malondialdehyde (MDA) and thiol in the kidneys were measured. Results MDA in the kidneys was increased by Ang II and doca-salt treatments. Both estradiol and Tst decreased the kidney's MDA. The level of thiol was higher in Hyper ‎groups and reversed after treatment with estradiol and Tst. Conclusions Our findings suggest that central effect of Ang II on blood pressure and kidney ‎disease is accompanied with increased levels of oxidative stress in the kidneys. Indeed sex hormones change the ROS level in the kidneys after central ‎microinjection of Ang II.‎‎.

Role of DNA De Novo (De)Methylation in the Kidney in Salt-Induced Hypertension

Numerous adult diseases involving tissues consisting primarily of nondividing cells are associated with changes in DNA methylation. It suggests a pathophysiological role for de novo methylation or demethylation of DNA, which is catalyzed by DNA methyltransferase 3 and ten-eleven translocases. However, the contribution of DNA de novo (de)methylation to these diseases remains almost completely unproven. Broad changes in DNA methylation occurred within days in the renal outer medulla of Dahl SS rats fed a high-salt diet, a classic model of hypertension. Intrarenal administration of anti-DNA methyltransferase 3a/ten-eleven translocase 3 GapmeRs attenuated high salt-induced hypertension in SS rats. The high-salt diet induced differential expression of 1712 genes in the renal outer medulla. Remarkably, the differential expression of 76% of these genes was prevented by anti-DNA methyltransferase 3a/ten-eleven translocase 3 GapmeRs. The genes differentially expressed in response to the GapmeRs were involved in the regulation of metabolism and inflammation and were significantly enriched for genes showing differential methylation in response to the GapmeRs. These data indicate a significant role of DNA de novo (de)methylation in the kidney in the development of hypertension in SS rats. The findings should help to shift the paradigm of DNA methylation research in diseases involving nondividing cells from correlative analysis to functional and mechanistic studies.

Mechanisms of sodium balance: total body sodium, surrogate variables, and renal sodium excretion

The classical concepts of human sodium balance include 1) a total pool of Na+ of ≈4,200 mmol (total body sodium, TBS) distributed primarily in the extracellular fluid (ECV) and bone, 2) intake variations of 0.03 to ≈6 mmol·kg body mass−1·day−1, 3) asymptotic transitions between steady states with a halftime (T½) of 21 h, 4) changes in TBS driven by sodium intake measuring ≈1.3 day [ΔTBS/Δ(Na+ intake/day)], 5) adjustment of Na+ excretion to match any diet thus providing metabolic steady state, and 6) regulation of TBS via controlled excretion (90–95% renal) mediated by surrogate variables. The present focus areas include 1) uneven, nonosmotic distribution of increments in TBS primarily in “skin,” 2) long-term instability of TBS during constant Na+ intake, and 3) physiological regulation of renal Na+ excretion primarily by neurohumoral mechanisms dependent on ECV rather than arterial pressure. Under physiological conditions 1) the nonosmotic distribution of Na+ seems conceptually important, but quantitatively ill defined; 2) long-term variations in TBS represent significant deviations from steady state, but the importance is undetermined; and 3) the neurohumoral mechanisms of sodium homeostasis competing with pressure natriuresis are essential for systematic analysis of short-term and long-term regulation of TBS. Sodium homeostasis and blood pressure regulation are intimately related. Real progress is slow and will accelerate only through recognition of the present level of ignorance. Nonosmotic distribution of sodium, pressure natriuresis, and volume-mediated regulation of renal sodium excretion are essential intertwined concepts in need of clear definitions, conscious models, and future attention.

Influence of dietary protein on Dahl salt-sensitive hypertension: a potential role for gut microbiota

High blood pressure affects 1.39 billion adults across the globe and is the leading preventable cause of death worldwide. Hypertension is a multifaceted disease with known genetic and environmental factors contributing to its progression. Our studies utilizing the Dahl salt-sensitive (SS) rat have demonstrated the remarkable influence of dietary protein and maternal environment on the development of hypertension and renal damage in response to high salt. There is growing interest in the relationship between the microbiome and hypertension, with gut dysbiosis being correlated to a number of pathologies. This review summarizes the current literature regarding the interplay among dietary protein, the gut microbiota, and hypertension. These studies may provide insight into the effects we have observed between diet and hypertension in Dahl SS rats and, we hope, lead to new perspectives where potential dietary interventions or microbiota manipulations could serve as plausible therapies for hypertension.

Genetic Association of Albuminuria with Cardiometabolic Disease and Blood Pressure

Excretion of albumin in urine, or albuminuria, is associated with the development of multiple cardiovascular and metabolic diseases. However, whether pathways leading to albuminuria are causal for cardiometabolic diseases is unclear. We addressed this question using a Mendelian randomization framework in the UK Biobank, a large population-based cohort. We first performed a genome-wide association study for albuminuria in 382,500 individuals and identified 32 new albuminuria loci. We constructed albuminuria genetic risk scores and tested for association with cardiometabolic diseases. Genetically elevated albuminuria was strongly associated with increased risk of hypertension (1.38 OR; 95% CI, 1.27-1.50 per 1 SD predicted increase in albuminuria, p = 7.01 × 10-14). We then examined bidirectional associations of albuminuria with blood pressure which suggested that genetically elevated albuminuria led to higher blood pressure (2.16 mmHg systolic blood pressure; 95% CI, 1.51-2.82 per 1 SD predicted increase in albuminuria, p = 1.22 × 10-10) and that genetically elevated blood pressure led to more albuminuria (0.005 SD; 95% CI 0.004-0.006 per 1 mmHg predicted increase in systolic blood pressure, p = 2.45 × 10-13). These results support the existence of a feed-forward loop between albuminuria and blood pressure and imply that albuminuria could increase risk of cardiovascular disease through blood pressure. Moreover, they suggest therapies that target albuminuria-increasing processes could have antihypertensive effects that are amplified through inhibition of this feed-forward loop.

MicroRNA-214-3p in the Kidney Contributes to the Development of Hypertension

BACKGROUND

In spite of extensive study, the mechanisms for salt sensitivity of BP in humans and rodent models remain poorly understood. Several microRNAs (miRNAs) have been associated with hypertension, but few have been shown to contribute to its development.

METHODS

We examined miRNA expression profiles in human kidney biopsy samples and rat models using small RNA deep sequencing. To inhibit an miRNA specifically in the kidney in conscious, freely moving rats, we placed indwelling catheters to allow both renal interstitial administration of a specific anti-miR and measurement of BP. A rat with heterozygous disruption of the gene encoding endothelial nitric oxide synthase (eNOS) was developed. We used bioinformatic analysis to evaluate the relationship between 283 BP-associated human single-nucleotide polymorphisms (SNPs) and 1870 human miRNA precursors, as well as other molecular and cellular methods.

RESULTS

Compared with salt-insensitive SS.13BN26 rats, Dahl salt-sensitive (SS) rats showed an upregulation of miR-214-3p, encoded by a gene in the SS.13BN26 congenic region. Kidney-specific inhibition of miR-214-3p significantly attenuated salt-induced hypertension and albuminuria in SS rats. miR-214-3p directly targeted eNOS. The effect of miR-214-3p inhibition on hypertension and albuminuria was abrogated in SS rats with heterozygous loss of eNOS. Human kidney biopsy specimens from patients with hypertension or hypertensive nephrosclerosis showed upregulation of miR-214-3p; the gene encoding miR-214-3p was one of several differentially expressed miRNA genes located in proximity to human BP-associated SNPs.

CONCLUSIONS

Renal miR-214-3p plays a functional and potentially genetic role in the development of hypertension, which might be mediated in part by targeting eNOS.

Tissue-specific effects of targeted mutation of Mir29b1 in rats

BACKGROUND

miR-29 is a master regulator of extracellular matrix genes, but conflicting data on its anti-fibrotic effect have been reported. miR-29 improves nitric oxide (NO) production in arterioles by targeting Lypla1. Mir29b1 targeted mutation exacerbates hypertension in a model derived from the Dahl salt-sensitive rat. We examined the effect of Mir29b1 mutation on tissue fibrosis and NO levels with a focus on kidney regions.

METHODS

Mir29b1 targeted mutant rats on the genetic background of SS-Chr13^BN rats were studied. Masson trichrome staining, molecular and biochemical assays, metabolic cage studies, and bioinformatic analysis of human genomic data were performed.

FINDINGS

The abundance of miR-29b and the co-transcribed miR-29a was substantially lower in mutant rats. Tissue fibrosis was significantly increased in the renal outer medulla, but not in the renal cortex, heart or liver in mutant rats on a 0.4% NaCl diet. Lypla1 protein abundance was significantly higher and NO levels lower in the renal outer medulla, but not in the renal cortex. After 14 days of a 4% NaCl diet, 24 h urine volume and urinary sodium excretion was significantly lower in mutant rats, and tissue fibrosis became higher in the heart. NO levels were lower in the renal outer medulla and heart, but not in the renal cortex. Human miR-29 genes are located in proximity with blood pressure-associated single nucleotide polymorphisms.

INTERPRETATION

The renal outer medulla might be particularly susceptible to the injurious effects of a miR-29 insufficiency, which might contribute to the development of hypertension in Mir29b1 mutant rats.

Gene Level Regulation of Na,K-ATPase in the Renal Proximal Tubule Is Controlled by Two Independent but Interacting Regulatory Mechanisms Involving Salt Inducible Kinase 1 and CREB-Regulated Transcriptional Coactivators

For many years, studies concerning the regulation of Na,K-ATPase were restricted to acute regulatory mechanisms, which affected the phosphorylation of Na,K-ATPase, and thus its retention on the plasma membrane. However, in recent years, this focus has changed. Na,K-ATPase has been established as a signal transducer, which becomes part of a signaling complex as a consequence of ouabain binding. Na,K-ATPase within this signaling complex is localized in caveolae, where Na,K-ATPase has also been observed to regulate Inositol 1,4,5-Trisphosphate Receptor (IP3R)-mediated calcium release. This latter association has been implicated as playing a role in signaling by G Protein Coupled Receptors (GPCRs). Here, the consequences of signaling by renal effectors that act via such GPCRs are reviewed, including their regulatory effects on Na,K-ATPase gene expression in the renal proximal tubule (RPT). Two major types of gene regulation entail signaling by Salt Inducible Kinase 1 (SIK1). On one hand, SIK1 acts so as to block signaling via cAMP Response Element (CRE) Binding Protein (CREB) Regulated Transcriptional Coactivators (CRTCs) and on the other hand, SIK1 acts so as to stimulate signaling via the Myocyte Enhancer Factor 2 (MEF2)/nuclear factor of activated T cell (NFAT) regulated genes. Ultimate consequences of these pathways include regulatory effects which alter the rate of transcription of the Na,K-ATPase β1 subunit gene atp1b1 by CREB, as well as by MEF2/NFAT.

Relationship between subtle urinary albumin excretion and risk of incident hypertension: modification by glomerular filtration rate

It has been reported that an increase in urinary albumin excretion (UAE) within the normal range could be a risk factor for incident hypertension. However, it remains unclear how the subtle increases in UAE and renal function interact in the development of hypertension. We examined the modification of UAE as a risk factor for incident hypertension by glomerular filtration rate (GFR) in the Japanese population. We prospectively followed 1281 normotensive individuals from Watari town (34.3% men; mean age, 58.0±12.3 years old) whose UAE was <30 mg g⁻¹· Cr. Hypertension was diagnosed as a systolic blood pressure (BP)⩾140 mm Hg and/or a diastolic BP⩾90 mm Hg, or antihypertensive medication use. The relationship between sex-specific quartiles of UAE and incident hypertension was examined with Cox proportional hazard analysis. During a mean follow-up of 3.7 years, 315 individuals developed hypertension. Multivariate Cox proportional hazard analysis revealed that a subtle increase in UAE was a risk factor for incident hypertension, but there was a significant interaction between UAE and estimated GFR (eGFR) (P=0.018). The risk of incident hypertension dose dependently increased in the highest eGFR quartile (⩾90 ml min⁻¹ per 1.73 m²). Decline in renal function alone increased the risk of incident hypertension but the increased risk with a subtle increase in UAE became smaller and less clear in the lower eGFR quartiles. The present data suggest that UAE as a risk factor for incident hypertension is largely dependent on eGFR levels.

Association of Kidney Function and Early Kidney Injury With Incident Hypertension in HIV-Infected Women

Subclinical kidney disease is associated with developing hypertension in the general population, but data are lacking among HIV-infected people. We examined associations of kidney function and injury with incident hypertension in 823 HIV-infected and 267 HIV-uninfected women in the Women's Interagency HIV Study, a multicenter, prospective cohort of HIV-infected and uninfected women in the United States. Baseline kidney biomarkers included estimated glomerular filtration rate using cystatin C, urine albumin-to-creatinine ratio, and 7 urine biomarkers of tubular injury: α-1-microglobulin, interleukin-18, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, liver fatty acid-binding protein, N-acetyl-β-d-glucosaminidase, and α1-acid-glycoprotein. We used multivariable Poisson regression to evaluate associations of kidney biomarkers with incident hypertension, defined as 2 consecutive visits of antihypertensive medication use. During a median follow-up of 9.6 years, 288 HIV-infected women (35%) developed hypertension. Among the HIV-infected women, higher urine albumin-to-creatinine ratio was independently associated with incident hypertension (relative risk =1.13 per urine albumin-to-creatinine ratio doubling, 95% confidence interval, 1.07-1.20), as was lower estimated glomerular filtration rate (relative risk =1.10 per 10 mL/min/1.73 m² lower estimated glomerular filtration rate; 95% confidence interval, 1.04-1.17). No tubular injury and dysfunction biomarkers were independently associated with incident hypertension in HIV-infected women. In contrast, among the HIV-uninfected women, urine albumin-to-creatinine ratio was not associated with incident hypertension, whereas higher urine interleukin-18, α1-acid-glycoprotein, and N-acetyl-β-d-glucosaminidase levels were significantly associated with incident hypertension. These findings suggest that early glomerular injury and kidney dysfunction may be involved in the pathogenesis of hypertension in HIV-infected people. The associations of tubular markers with hypertension in HIV-uninfected women should be validated in other studies.

Abnormal Circadian Blood Pressure Profile as a Prognostic Marker in Patients with Nonischemic Dilated Cardiomyopathy

OBJECTIVES

An abnormal circadian blood pressure (BP) profile is considered a risk factor for cardiovascular disease. However, its significance in heart failure patients with nonischemic etiology is unknown. Herein, we investigated the prognostic value of a circadian BP profile in patients with nonischemic dilated cardiomyopathy (NIDCM).

METHODS

We enrolled 114 NIDCM patients (76 males, mean age 53.1 years). The percent nighttime BP fall (%NBPF) was defined using ambulatory BP monitoring as a percent decrease in mean systolic BP in nighttime from daytime. All patients were divided into three groups: dipper (%NBPF ≥10), non-dipper (0 ≤ %NBPF < 10), and riser (%NBPF <0).

RESULTS

Riser patients had the highest serum creatinine levels (dipper, 0.78 ± 0.20 mg/dl; non-dipper, 0.85 ± 0.21 mg/dl; riser, 0.99 ± 0.23 mg/dl; p = 0.006). In survival analysis, riser patients had the highest cumulative cardiac-related deaths (log-rank, p = 0.001), which was an independent predictor of cardiac-related deaths (hazard ratio, 12.6; 95% confidence interval, 1.76-253; p = 0.01). Multivariate analysis revealed that the norepinephrine level at 24-hour collected urine (24 h U-NE) and the serum creatinine level were independent determinants of %NBPF (adjusted R2 = 0.20; 24 h U-NE, p = 0.0001; serum creatinine, p = 0.04).

CONCLUSIONS

The riser profile was associated with poor prognosis of NIDCM, which may reflect impaired sympathetic nervous system activity. Evaluating the circadian BP profile may be useful for risk stratification in NIDCM patients.

ISN Forefronts Symposium 2015: Maintaining Balance Under Pressure-Hypertension and the Proximal Tubule

Renal control of effective circulating volume (ECV) is key for circulatory performance. When renal sodium excretion is inadequate, blood pressure rises and serves as a homeostatic signal to drive natriuresis to re-establish ECV. Recognizing that hypertension involves both renal and vascular dysfunction, this report concerns proximal tubule sodium hydrogen exchanger 3 (NHE3) regulation during acute and chronic hypertension. NHE3 is distributed in tall microvilli (MV) in the proximal tubule, where it reabsorbs a significant fraction of the filtered sodium. NHE3 redistributes, in the plane of the MV membrane, between the MV body, where NHE3 is active, and the MV base, where NHE3 is less active. A high-salt diet and acute hypertension both retract NHE3 to the base and reduce proximal tubule sodium reabsorption independent of a change in abundance. The renin angiotensin system provokes NHE3 redistribution independent of blood pressure: The angiotensin-converting enzyme (ACE) inhibitor captopril redistributes NHE3 to the base and subsequent angiotensin II (AngII) infusion returns NHE3 to the body of the MV and restores reabsorption. Chronic AngII infusion presents simultaneous AngII stimulation and hypertension; that is, NHE3 remains in the body of the MV, due to the high local AngII level and inflammation, and exhibits a compensatory decrease in abundance driven by the hypertension. Genetically modified mice with blunted hypertensive responses to chronic AngII infusion (due to lack of the proximal tubule AngII receptors interleukin-17A or interferon-γ expression) exhibit reduced local AngII accumulation and inflammation and larger decreases in NHE3 abundance, which improves the pressure natriuresis response and reduces the need for elevated blood pressure to facilitate circulating volume balance.

Renal sodium transport in renin-deficient Dahl salt-sensitive rats

Objective:

The Dahl salt-sensitive rat is a well-established model of salt-sensitive hypertension. The goal of this study was to assess the expression and activity of renal sodium channels and transporters in the renin-deficient salt-sensitive rat.

Methods:

Renin knockout (Ren^−/−) rats created on the salt-sensitive rat background were used to investigate the role of renin in the regulation of ion transport in salt-sensitive hypertension. Western blotting and patch-clamp analyses were utilized to assess the expression level and activity of Na⁺ transporters.

Results:

It has been described previously that Ren^−/− rats exhibit severe kidney underdevelopment, polyuria, and lower body weight and blood pressure compared to their wild-type littermates. Here we found that renin deficiency led to decreased expression of sodium-hydrogen antiporter (NHE3), the Na⁺/H⁺ exchanger involved in Na⁺ absorption in the proximal tubules, but did not affect the expression of Na-K-Cl cotransporter (NKCC2), the main transporter in the loop of Henle. In the distal nephron, the expression of sodium chloride cotransporter (NCC) was lower in Ren^−/− rats. Single-channel patch clamp analysis detected decreased ENaC activity in Ren^−/− rats which was mediated via changes in the channel open probability.

Conclusion:

These data illustrate that renin deficiency leads to significant dysregulation of ion transporters.

Proton channels and renal hypertensive injury: a key piece of the Dahl salt-sensitive rat puzzle?

Hv1 is a voltage-gated proton channel highly expressed in phagocytic cells, where it participates in the NADPH oxidase-dependent respiratory burst. We have recently identified Hv1 as a novel renal channel, expressed in the renal medullary thick ascending limb that appears to importantly contribute to the pathogenesis of renal hypertensive injury in the Dahl salt-sensitive rat model. The purpose of this review is to describe the experimental approaches that we have undertaken to identify the source of excess reactive oxygen species production in the renal outer medulla of Dahl salt-sensitive rats and the resulting evidence that the voltage-gated proton channel Hv1 mediates augmented superoxide production and contributes to renal medullary oxidative stress and renal injury. In addition, we will attempt to point out areas of current controversy, as well as propose areas in which further experimental studies are likely to move the field forward. The content of the following review was presented as part of the Water and Electrolyte Homeostasis Section New Investigator Award talk at Experimental Biology 2014.

Evidence of the Importance of Nox4 in Production of Hypertension in Dahl Salt-Sensitive Rats

This study reports the consequences of knocking out NADPH (nicotinamide adenine dinucleotide phosphate) oxidase 4 (Nox4) on the development of hypertension and kidney injury in the Dahl salt-sensitive (SS) rat. Zinc finger nuclease injection of single-cell SS embryos was used to create an 8 base-pair frame-shift deletion of Nox4, resulting in a loss of the ≈68 kDa band in Western blot analysis of renal cortical tissue of the knock out of Nox4 in the SS rat (SS(Nox4-/-)) rats. SS(Nox4-/-) rats exhibited a significant reduction of salt-induced hypertension compared with SS rats after 21 days of 4.0% NaCl diet (134±5 versus 151±3 mm Hg in SS) and a significant reduction of albuminuria, tubular casts, and glomerular injury. Optical fluorescence 3-dimensional cryoimaging revealed significantly higher redox ratios (NADH/FAD [reduced nicotinamide adenine dinucleotide/flavin adenine dinucleotide]) in the kidneys of SS(Nox4-/-) rats even when fed the 0.4% NaCl diet, indicating greater levels of mitochondrial electron transport chain metabolic activity and reduced oxidative stress compared with SS rats. Before the development of hypertension, RNA expression levels of Nox subunits Nox2, p67(phox), and p22(phox) were found to be significantly lower (P<0.05) in SS(Nox4-/-) compared with SS rats in the renal cortex. Thus, the mutation of Nox4 seems to modify transcription of several genes in ways that contribute to the protective effects observed in the SS(Nox4-/-) rats. We conclude that the reduced renal injury and attenuated blood pressure response to high salt in the SS(Nox4-/-) rat could be the result of multiple pathways, including gene transcription, mitochondrial energetics, oxidative stress, and protein matrix production impacted by the knock out of Nox4.

Kidney-Specific Reduction of Oxidative Phosphorylation Genes Derived from Spontaneously Hypertensive Rat

Mitochondrial (Mt) dysfunction contributes to the pathophysiology of renal function and promotes cardiovascular disease such as hypertension. We hypothesize that renal Mt-genes derived from female spontaneously hypertensive rats (SHR) that exhibit hypertension have reduced expression specific to kidney cortex. After breeding a female Okamoto-Aoki SHR (SAP = 188mmHg) with Brown Norway (BN) males (SAP = 100 and 104 mmHg), hypertensive female progeny were backcrossed with founder BN for 5 consecutive generations in order to maintain the SHR mitochondrial genome in offspring that contain over increasing BN nuclear genome. Mt-protein coding genes (13 total) and nuclear transcription factors mediating Mt-gene transcription were evaluated in kidney, heart and liver of normotensive (NT: n = 20) vs. hypertensive (HT: n = 20) BN/SHR-mt^SHR using quantitative real-time PCR. Kidney cortex, but not liver or heart Mt-gene expression was decreased ~2–5 fold in 12 of 13 protein encoding genes of HT BN/SHR-mt^SHR. Kidney cortex but not liver mRNA expression of the nuclear transcription factors Tfam, NRF1, NRF2 and Pgc1α were also decreased in HT BN/SHR-mt^SHR. Kidney cortical tissue of HT BN/SHR-mt^SHR exhibited lower cytochrome oxidase histochemical staining, indicating a reduction in renal oxidative phosphorylation but not in liver or heart. These results support the hypothesis that renal cortex of rats with SHR mitochondrial genome has specifically altered renal expression of genes encoding mitochondrial proteins. This kidney-specific coordinated reduction of mitochondrial and nuclear oxidative metabolism genes may be associated with heritable hypertension in SHR.

Albuminuria, renal dysfunction and circadian blood pressure rhythm in older men: a population-based longitudinal cohort study

Background

Both albuminuria and kidney dysfunction may affect circadian blood pressure (BP) rhythm, while exacerbating each other's effects. We investigated associations and interactions of these two risk factors with circadian BP rhythm variation and non-dipper pattern progression in community-dwelling older men.

Methods

This was a cross-sectional and longitudinal analyses in the third and fourth cycles of the Uppsala Longitudinal Study of Adult Men, including 1051 men (age 71 years) with assessments on urinary albumin excretion rate (UAER), 24-h ambulatory BP monitoring (ABPM) and cystatin-C-estimated glomerular filtration rate (eGFR). Of these, 574 men attended re-examination after 6 years. Study outcomes were ABMP changes and non-dipping BP pattern (prevalence and progression).

Results

UAER associated with circadian BP rhythm both cross-sectionally and longitudinally. Longitudinally, significant interactions were observed between UAER and kidney dysfunction (eGFR < 60 mL/min/1.73 m²) in its association with the changes of both night-time systolic BP (SBP) and night–day SBP ratio. After stratification, UAER strongly predicted night–day SBP ratio change only in those with concurrent kidney dysfunction. At re-examination, 221 new cases of non-dipper were identified. In multivariable logistic models, high UAER associated with increased likelihood of non-dipper progression, but more strongly so among individuals with concurrent kidney dysfunction. These associations were evident also in the subpopulation of non-diabetics and in participants with normal range UAER.

Conclusions

UAER associates with circadian BP rhythm variation and non-dipper progression in elderly men. Concurrent renal dysfunction modifies and exacerbates these associations.

Vascular Type 1A Angiotensin II Receptors Control BP by Regulating Renal Blood Flow and Urinary Sodium Excretion

Inappropriate activation of the type 1A angiotensin (AT1A) receptor contributes to the pathogenesis of hypertension and its associated complications. To define the role for actions of vascular AT1A receptors in BP regulation and hypertension pathogenesis, we generated mice with cell-specific deletion of AT1A receptors in smooth muscle cells (SMKO mice) using Loxp technology and Cre transgenes with robust expression in both conductance and resistance arteries. We found that elimination of AT1A receptors from vascular smooth muscle cells (VSMCs) caused a modest (approximately 7 mmHg) yet significant reduction in baseline BP and exaggerated sodium sensitivity in mice. Additionally, the severity of angiotensin II (Ang II)-dependent hypertension was dramatically attenuated in SMKO mice, and this protection against hypertension was associated with enhanced urinary excretion of sodium. Despite the lower BP, acute vasoconstrictor responses to Ang II in the systemic vasculature were largely preserved (approximately 80% of control levels) in SMKO mice because of exaggerated activity of the sympathetic nervous system rather than residual actions of AT1B receptors. In contrast, Ang II-dependent responses in the renal circulation were almost completely eliminated in SMKO mice (approximately 5%-10% of control levels). These findings suggest that direct actions of AT1A receptors in VSMCs are essential for regulation of renal blood flow by Ang II and highlight the capacity of Ang II-dependent vascular responses in the kidney to effect natriuresis and BP control.

Urinary albumin as a marker of future blood pressure and hypertension in the general population

We investigated whether urinary albumin could predict the development of hypertension and future increases in blood pressure in the normotensive general population.Normotensive subjects who visited our hospital for a physical checkup (n = 6205, men 61.8%, 53.4 ± 11.4 years old) were enrolled in this study. Urine samples were collected for the measurement of albumin concentration, expressed as the ratio of urinary albumin to creatinine concentrations (UACR [mg/g Cr]). After the baseline examination, subjects were followed up for a median of 1089 days with the endpoint being the development of hypertension.Urinary albumin was in the normal range (UACR <30 mg/g Cr) in most subjects (97.5%). During the follow-up, hypertension developed in 1184 subjects (19.1%, 69.5 per 1000 person-years), with more men than women affected. The incidence of hypertension was increased across the quartiles of UACR by Kaplan-Meier analysis (log-rank, P < 0.0001) and the hazard ratio (lowest quartile [median UACR 1.14 mg/g Cr] as reference) was 1.53 (95% confidence intervals 1.30-1.80) in the highest quartile (median UACR 8.87 mg/g Cr). Multivariate Cox hazard analysis in which UACR was taken as a continuous variable identified UACR as a significant predictor of hypertension (hazard ratio 1.37, 95% CI 1.20-1.56). UACR was also an independent predictor of future increases in systolic blood pressure (P < 0.01).Urinary albumin is an independent predictor of hypertension and increases in blood pressure in the general population even in the normal range below the threshold defined for microalbuminuria.

Epigenetics and arterial hypertension: the challenge of emerging evidence

Epigenetic phenomena include DNA methylation, post-translational histone modifications, and noncoding RNAs, as major marks. Although similar to genetic features of DNA for their heritability, epigenetic mechanisms differ for their potential reversibility by environmental and nutritional factors, which make them potentially crucial for their role in complex and multifactorial diseases. The function of these mechanisms is indeed gaining interest in relation to arterial hypertension (AH) with emerging evidence from cell culture and animal models as well as human studies showing that epigenetic modifications have major functions within pathways related to AH. Among epigenetic marks, the role of DNA methylation is mostly highlighted given the primary role of this epigenetic feature in mammalian cells. A lower global methylation was observed in DNA of peripheral blood mononuclear cells of hypertensive patients. Moreover, DNA hydroxymethylation appears modifiable by salt intake in a Dahl salt-sensitive rat model. The specific function of DNA methylation in regulating the expression of AH-related genes at promoter site was described for hydroxysteroid (11-beta) dehydrogenase 2 (HSD11B2), somatic angiotensin converting enzyme (sACE), Na+/K+/2Cl- cotransporter 1 (NKCC1), angiotensinogen (AGT), α-adducin (ADD1), and for other crucial genes in endocrine hypertension. Post-translational histone methylation at different histone 3 lysine residues was also observed to control the expression of genes related to AH as lysine-specific demethylase-1(LSD1), HSD11B2, and epithelial sodium channel subunit α (SCNN1A). Noncoding RNAs including several microRNAs influence genes involved in steroidogenesis and the renin-angiotensin-aldosterone pathway. In the present review, the current knowledge on the relationship between the main epigenetic marks and AH will be presented, considering the challenge of epigenetic patterns being modifiable by environmental factors that may lead toward novel implications in AH preventive and therapeutic strategies.

Epoxyeicosatrienoic acid analogue lowers blood pressure through vasodilation and sodium channel inhibition

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.

20-HETE and blood pressure regulation: clinical implications

20-Hydroxy-5, 8, 11, 14-eicosatetraenoic acid (20-HETE) is a cytochrome P450 (CYP)-derived omega-hydroxylation metabolite of arachidonic acid. 20-HETE has been shown to play a complex role in blood pressure regulation. In the kidney tubules, 20-HETE inhibits sodium reabsorption and promotes natriuresis, thus, contributing to antihypertensive mechanisms. In contrast, in the microvasculature, 20-HETE has been shown to play a pressor role by sensitizing smooth muscle cells to constrictor stimuli and increasing myogenic tone, and by acting on the endothelium to further promote endothelial dysfunction and endothelial activation. In addition, 20-HETE induces endothelial angiotensin-converting enzyme, thus, setting forth a potential feed forward prohypertensive mechanism by stimulating the renin-angiotensin-aldosterone system. With the advancement of gene sequencing technology, numerous polymorphisms in the regulatory coding and noncoding regions of 20-HETE-producing enzymes, CYP4A11 and CYP4F2, have been associated with hypertension. This in-depth review article discusses the biosynthesis and function of 20-HETE in the cardiovascular system, the pharmacological agents that affect 20-HETE action, and polymorphisms of CYP enzymes that produce 20-HETE and are associated with systemic hypertension in humans.

Pharmacological manipulation of arachidonic acid-epoxygenase results in divergent effects on renal damage

Kidney damage is markedly accelerated by high-salt (HS) intake in stroke-prone spontaneously hypertensive rats (SHRSP). Epoxyeicosatrienoic acids (EETs) are epoxygenase products of arachidonic acid which possess vasodepressor, natriuretic, and anti-inflammatory activities. We examined whether up-regulation (clofibrate) or inhibition [N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH)] of epoxygenase would alter systolic blood pressure (SBP) and/or renal pathology in SHRSP on HS intake (1% NaCl drinking solution). Three weeks of treatment with clofibrate induced renal cortical protein expression of CYP2C23 and increased urinary excretion of EETs compared with vehicle-treated SHRSP. SBP and urinary protein excretion (UPE) were significantly lowered with clofibrate treatment. Kidneys from vehicle-treated SHRSP, which were on HS intake for 3 weeks, demonstrated focal lesions of vascular fibrinoid degeneration, which were markedly attenuated with clofibrate treatment. In contrast, 2 weeks of treatment with the selective epoxygenase inhibitor, MS-PPOH, increased UPE without significantly altering neither urinary EET levels nor SBP. Kidneys from vehicle-treated SHRSP, which were on HS intake for 11 days, demonstrated occasional mild damage whereas kidneys from MS-PPOH-treated rats exhibited widespread malignant nephrosclerosis. These results suggest that pharmacological manipulation of epoxygenase results in divergent effects on renal damage and that interventions to increase EET levels may provide therapeutic strategies for treating salt-sensitive hypertension and renal damage.

Mutation of Plekha7 attenuates salt-sensitive hypertension in the rat

PLEKHA7 (pleckstrin homology domain containing family A member 7) has been found in multiple studies as a candidate gene for human hypertension, yet functional data supporting this association are lacking. We investigated the contribution of this gene to the pathogenesis of salt-sensitive hypertension by mutating Plekha7 in the Dahl salt-sensitive (SS/JrHsdMcwi) rat using zinc-finger nuclease technology. After four weeks on an 8% NaCl diet, homozygous mutant rats had lower mean arterial (149 ± 9 mmHg vs. 178 ± 7 mmHg; P < 0.05) and systolic (180 ± 7 mmHg vs. 213 ± 8 mmHg; P < 0.05) blood pressure compared with WT littermates. Albumin and protein excretion rates were also significantly lower in mutant rats, demonstrating a renoprotective effect of the mutation. Total peripheral resistance and perivascular fibrosis in the heart and kidney were significantly reduced in Plekha7 mutant animals, suggesting a potential role of the vasculature in the attenuation of hypertension. Indeed, both flow-mediated dilation and endothelium-dependent vasodilation in response to acetylcholine were improved in isolated mesenteric resistance arteries of Plekha7 mutant rats compared with WT. These vascular improvements were correlated with changes in intracellular calcium handling, resulting in increased nitric oxide bioavailability in mutant vessels. Collectively, these data provide the first functional evidence that Plekha7 may contribute to blood pressure regulation and cardiovascular function through its effects on the vasculature.

Systemic and renal oxidative stress in the pathogenesis of hypertension: modulation of long-term control of arterial blood pressure by resveratrol

Hypertension affects over 25% of the global population and is associated with grave and often fatal complications that affect many organ systems. Although great advancements have been made in the clinical assessment and treatment of hypertension, the cause of hypertension in over 90% of these patients is unknown, which hampers the development of targeted and more effective treatment. The etiology of hypertension involves multiple pathological processes and organ systems, however one unifying feature of all of these contributing factors is oxidative stress. Once the body's natural anti-oxidant defense mechanisms are overwhelmed, reactive oxygen species (ROS) begin to accumulate in the tissues. ROS play important roles in normal regulation of many physiological processes, however in excess they are detrimental and cause widespread cell and tissue damage as well as derangements in many physiological processes. Thus, control of oxidative stress has become an attractive target for pharmacotherapy to prevent and manage hypertension. Resveratrol (trans-3,5,4'-Trihydroxystilbene) is a naturally occurring polyphenol which has anti-oxidant effects in vivo. Many studies have shown anti-hypertensive effects of resveratrol in different pre-clinical models of hypertension, via a multitude of mechanisms that include its function as an anti-oxidant. However, results have been mixed and in some cases resveratrol has no effect on blood pressure. This may be due to the heavy emphasis on peripheral vasodilator effects of resveratrol and virtually no investigation of its potential renal effects. This is particularly troubling in the arena of hypertension, where it is well known and accepted that the kidney plays an essential role in the long term regulation of arterial pressure and a vital role in the initiation, development and maintenance of chronic hypertension. It is thus the focus of this review to discuss the potential of resveratrol as an anti-hypertensive treatment via amelioration of oxidative stress within the framework of the fundamental physiological principles of long term regulation of arterial blood pressure.

Infiltrating immune cells in the kidney in salt-sensitive hypertension and renal injury

The importance of the immune system in hypertension, vascular disease, and renal disease has been appreciated for over 50 years. Recent experimental advances have led to a greater appreciation of the mechanisms whereby inflammation and immunity participate in cardiovascular disease. In addition to the experimental data, multiple studies in patients have demonstrated a strong correlation between the observations made in animals and humans. Of great interest is the development of salt-sensitive hypertension in humans with the concurrent increase in albumin excretion rate. Experiments in our laboratory have demonstrated that feeding a high-NaCl diet to Dahl salt-sensitive (SS) rats results in a significant infiltration of T lymphocytes into the kidney that is accompanied by the development of hypertension and renal disease. The development of disease in the Dahl SS closely resembles observations made in patients; studies were therefore performed to investigate the pathological role of infiltrating immune cells in the kidney in hypertension and renal disease. Pharmacological and genetic studies indicate that immune cell infiltration into the kidney amplifies the disease process. Further experiments demonstrated that infiltrating T cells may accentuate the Dahl SS phenotype by increasing intrarenal ANG II and oxidative stress. From these and other data, we hypothesize that infiltrating immune cells, which surround the blood vessels and tubules, can serve as a local source of bioactive molecules which mediate vascular constriction, increase tubular sodium reabsorption, and mediate the retention of sodium and water to amplify sodium-sensitive hypertension. Multiple experiments remain to be performed to refine and clarify this hypothesis.