Renal and vascular oxidative stress and salt-sensitivity of arterial pressure

Individual and joint effects of organophosphate esters and hypertension or diabetes on renal injury among Chinese adults

Exposure to environmental contaminants and the development of hypertension and diabetes represent crucial risk factors for chronic kidney disease (CKD). Toxicological studies have revealed that organophosphate esters (OPEs) impair kidney function. However, the joint effects of OPE exposure on kidney injury and the interactions of OPE exposure with hypertension or diabetes on kidney injury remain unclear. Our study aimed to investigate the individual and joint effects of OPE exposure on renal injury, as well as the potential interaction between OPE exposure and hypertension or diabetes on kidney injury. The study enrolled 1938 participants from Wuhan, China. To explore the relationship between OPE exposure and renal injury, we conducted multivariate linear and logistic regression analysis. The results indicated that each unit increase in 4-hydroxyphenyl diphenyl phosphate (4-HO-DPHP), bis(2-butoxyethyl) phosphate (BBOEP), and tris(2-chloroethyl) phosphate (TCEP) (1 μg/L-ln transformed) was associated with a decreased 0.57 mL/min/1.73 m2 (95%CI: -1.05, -0.09), 0.85 mL/min/1.73 m2 (95%CI: -1.52, -0.19) and 1.24 mL/min/1.73 m2 (95%CI: -2.26, -0.23) of estimated glomerular filtration rate (eGFR), while each unit increase in 4-HO-DPHP and BBOEP (1 μg/L-ln transformed) was associated with 14% and 20% elevation of incident impaired renal function (IRF) risk. Notably the highest tertile of BCIPHIPP was positively associated with eGFR, although the p for trend ＞ 0.05. We employed Bayesian kernel machine regression (BKMR) and quartile-based g-computation (qgcomp) models to explore the joint effects of OPE mixtures on eGFR and IRF. Both the results of BKMR and qgcomp model consistently demonstrated negative associations between OPE mixtures and eGFR, and TCEP and 4-HO-DPHP were major contributors. Furthermore, we observed multiplicative interactions of diphenyl phosphate (DPHP), BBOEP, di-ocresyl phosphate (DoCP) & di-p-cresyl phosphate (DpCP), 1-hydroxy-2-propyl bis(1-chloro-2-propyl) phosphate (BCIPHIPP) and hypertension or diabetes on kidney injury (all P＜0.05). Those with diabetes or hypertension and higher OPE metabolite concentrations had increased risk of kidney function impairment compared to those who did not have diabetes or hypertension. These findings suggest that specific OPE exposure may elevate the risk of renal injury, particularly among hypertensive and diabetic populations.

Reactivity of renal and mesenteric resistance vessels to angiotensin II is mediated by NOXA1/NOX1 and superoxide signaling

Activation of NADPH oxidase (NOX) enzymes and the generation of reactive oxygen species and oxidative stress regulate vascular and renal function and contribute to the pathogenesis of hypertension. The present study examined the role of NOXA1/NOX1 function in vascular reactivity of renal and mesenteric resistance arteries/arterioles of wild-type and Noxa1-/- mice. A major finding was that renal blood flow is less sensitive to acute stimulation by angiotensin II (ANG II) in Noxa1-/- mice compared with wild-type mice, with a direct action on resistance arterioles independent of nitric oxide (NO) bioavailability. These functional results were reinforced by immunofluorescence evidence of NOXA1/NOX1 protein presence in renal arteries, afferent arterioles, and glomeruli as well as their upregulation by ANG II. In contrast, the renal vascular response to the thromboxane mimetic U46619 was effectively blunted by NO and was similar in both mouse genotypes and thus independent of NOXA1/NOX1 signaling. However, phenylephrine- and ANG II-induced contraction of isolated mesenteric arteries was less pronounced and buffering of vasoconstriction after acetylcholine and nitroprusside stimulation was reduced in Noxa1-/- mice, suggesting endothelial NO-dependent mechanisms. An involvement of NOXA1/NOX1/O2•- signaling in response to ANG II was demonstrated with the specific NOXA1/NOX1 assembly inhibitor C25 and the nonspecific NOX inhibitor diphenyleneiodonium chloride in cultured vascular smooth muscle cells and isolated mesenteric resistance arteries. Collectively, our data indicate that the NOX1/NOXA1/O2•- pathway contributes to acute vasoconstriction induced by ANG II in renal and mesenteric vascular beds and may contribute to ANG II-induced hypertension.NEW & NOTEWORTHY Renal reactivity to angiotensin II (ANG II) is mediated by superoxide signaling produced by NADPH oxidase (NOX)A1/NOX1. Acute vasoconstriction of renal arteries by ANG was blunted in Noxa1-/- compared with wild-type mice. NOXA1/NOX1/O2•- signaling was also observed in ANG II stimulation of vascular smooth muscle cells and isolated mesenteric resistance arteries, indicating that it contributes to ANG II-induced hypertension. A NOXA1/NOX1 assembly inhibitor (C25) has been characterized that inhibits superoxide production and ameliorates the effects of ANG II.

Biochemical Pathways of 8-Aminoguanine Production In Sprague-Dawley and Dahl Salt-Sensitive Rats

BACKGROUND

8-Aminoguanine exerts natriuretic and antihypertensive activity. Whether and how "free" 8-aminoguanine exists in vivo is unclear. Because 8-nitroguanosine is naturally occurring, we tested the hypothesis that 8-aminoguanine can arise from: pathway 1, 8-nitroguanosine→8-aminoguanosine→8-aminoguanine; and pathway 2, 8-nitroguanosine→8-nitroguanine→8-aminoguanine.

METHODS

8-Aminoguanine biosynthesis was explored in rats using renal microdialysis, mass spectrometry and enzyme kinetics.

RESULTS

In Sprague-Dawley rats, 8-nitroguanosine infusions increased kidney levels of 8-nitroguanine, 8-aminoguanosine and 8-aminoguanine; 8-nitroguanine infusions increased 8-aminoguanine. Purine nucleoside phosphorylase (PNPase) converted 8-nitroguanosine to 8-nitroguanine and 8-aminoguanosine to 8-aminoguanine. Forodesine (PNPase inhibitor) reduced metabolism of 8-nitroguanosine by pathway 2 and shunted metabolism of 8-nitroguanosine to 8-aminoguanosine. In Dahl salt-sensitive rats, 8-nitroguanosine infusions increased kidney levels of 8-nitroguanine, 8-aminoguanosine and 8-aminoguanine. These results indicate that both pathways 1 and 2 participate in the biosynthesis of 8-aminoguanine in Sprague-Dawley and Dahl rats. Endogenous 8-aminoguanine in kidneys and urine were elevated many-fold in Dahl, compared to Sprague-Dawley, rats. The increased levels of 8-aminoguanine in Dahl rats were not due to alterations in pathways 1 and 2 but were associated with increased urine levels of endogenous 8-nitroguanosine suggesting that the "upstream" production of 8-nitroguanosine was increased in Dahl rats. Dahl rats are known to have high levels of peroxynitrite, and peroxynitrite is known to nitrate guanosine in biomolecules. Here we confirm that a peroxynitrite donor increases kidney levels of 8-aminoguanine.

CONCLUSION

8-Aminoguanine occurs naturally via two distinct pathways and kidney levels of 8-aminoguanine are increased in Dahl rats, likely due to increased production of 8-nitroguanosine, a by-product of peroxynitrite chemistry.

Mechanism-based strategies to prevent salt sensitivity and salt-induced hypertension

High-salt diets are a major cause of hypertension and cardiovascular (CV) disease. Many governments are interested in using food salt reduction programs to reduce the risk for salt-induced increases in blood pressure and CV events. It is assumed that reducing the salt concentration of processed foods will substantially reduce mean salt intake in the general population. However, contrary to expectations, reducing the sodium density of nearly all foods consumed in England by 21% had little or no effect on salt intake in the general population. This may be due to the fact that in England, as in other countries including the U.S.A., mean salt intake is already close to the lower normal physiologic limit for mean salt intake of free-living populations. Thus, mechanism-based strategies for preventing salt-induced increases in blood pressure that do not solely depend on reducing salt intake merit attention. It is now recognized that the initiation of salt-induced increases in blood pressure often involves a combination of normal increases in sodium balance, blood volume and cardiac output together with abnormal vascular resistance responses to increased salt intake. Therefore, preventing either the normal increases in sodium balance and cardiac output, or the abnormal vascular resistance responses to salt, can prevent salt-induced increases in blood pressure. Suboptimal nutrient intake is a common cause of the hemodynamic disturbances mediating salt-induced hypertension. Accordingly, efforts to identify and correct the nutrient deficiencies that promote salt sensitivity hold promise for decreasing population risk of salt-induced hypertension without requiring reductions in salt intake.

Cooperation of augmented calcium sensitization and increased calcium entry contributes to high blood pressure in salt-sensitive Dahl rats

Salt hypertensive Dahl rats are characterized by sympathoexcitation and relative NO deficiency. We tested the hypothesis that the increased blood pressure (BP) response to fasudil in salt hypertensive Dahl rats is due to augmented calcium sensitization in the salt-sensitive strain and/or due to their decreased baroreflex efficiency. BP reduction after acute administration of nifedipine (an L-type voltage-dependent calcium channel blocker) or fasudil (a Rho kinase inhibitor) was studied in conscious intact rats and in rats subjected to acute NO synthase inhibition or combined blockade of the renin-angiotensin system (captopril), sympathetic nervous system (pentolinium), and NO synthase (L-NAME). Intact salt-sensitive (SS) Dahl rats fed a low-salt diet had greater BP responses to nifedipine (-31 ± 6 mmHg) or fasudil (-34 ± 7 mmHg) than salt-resistant (SR) Dahl rats (-16 ± 4 and -17 ± 2 mmHg, respectively), and a high-salt intake augmented the BP response only in SS rats. These BP responses were doubled after acute NO synthase inhibition, indicating that endogenous NO attenuates both calcium entry and calcium sensitization. Additional pentolinium administration, which minimized sympathetic compensation for the drug-induced BP reduction, magnified the BP responses to nifedipine or fasudil in all groups except for salt hypertensive SS rats due to their lower baroreflex efficiency. The BP response to the calcium channel blocker nifedipine can distinguish SS and SR rats even after calcium sensitization inhibition by fasudil, which was not seen when fasudil was administered to nifedipine-pretreated rats. Thus, enhanced calcium entry (potentiated by sympathoexcitation) in salt hypertensive Dahl rats is the abnormality that is essential for their BP increase, which was further augmented by increased calcium sensitization in salt-sensitive Dahl rats.

Oxidative Stress and Hypertension

A link between oxidative stress and hypertension has been firmly established in multiple animal models of hypertension but remains elusive in humans. While initial studies focused on inactivation of nitric oxide by superoxide, our understanding of relevant reactive oxygen species (superoxide, hydrogen peroxide, and peroxynitrite) and how they modify complex signaling pathways to promote hypertension has expanded significantly. In this review, we summarize recent advances in delineating the primary and secondary sources of reactive oxygen species (nicotinamide adenine dinucleotide phosphate oxidases, uncoupled endothelial nitric oxide synthase, endoplasmic reticulum, and mitochondria), the posttranslational oxidative modifications they induce on protein targets important for redox signaling, their interplay with endogenous antioxidant systems, and the role of inflammasome activation and endoplasmic reticular stress in the development of hypertension. We highlight how oxidative stress in different organ systems contributes to hypertension, describe new animal models that have clarified the importance of specific proteins, and discuss clinical studies that shed light on how these processes and pathways are altered in human hypertension. Finally, we focus on the promise of redox proteomics and systems biology to help us fully understand the relationship between ROS and hypertension and their potential for designing and evaluating novel antihypertensive therapies.

No evidence of racial disparities in blood pressure salt sensitivity when potassium intake exceeds levels recommended in the US dietary guidelines

On average, black individuals are widely believed to be more sensitive than white individuals to blood pressure (BP) effects of changes in salt intake. However, few studies have directly compared the BP effects of changing salt intake in black versus white individuals. In this narrative review, we analyze those studies and note that when potassium intake substantially exceeds the recently recommended US dietary goal of 87 mmol/day, black adults do not appear more sensitive than white adults to BP effects of short-term or long-term increases in salt intake (from an intake ≤50 mmol/day up to 150 mmol/day or more). However, with lower potassium intakes, racial differences in salt sensitivity are observed. Mechanistic studies suggest that racial differences in salt sensitivity are related to differences in vascular resistance responses to changes in salt intake mediated by vasodilator and vasoconstrictor pathways. With respect to cause and prevention of racial disparities in salt sensitivity, it is noteworthy that 1) on average, black individuals consume less potassium than white individuals and 2) consuming supplemental potassium bicarbonate, or potassium rich foods can prevent racial disparities in salt sensitivity. However, the new US dietary guidelines reduced the dietary potassium goal well below the amount associated with preventing racial disparities in salt sensitivity. These observations should motivate research on the impact of the new dietary potassium guidelines on racial disparities in salt sensitivity, the risks and benefits of potassium-containing salt substitutes or supplements, and methods for increasing consumption of foods rich in nutrients that protect against salt-induced hypertension.

Protective effect of oral histidine on hypertension in Dahl salt-sensitive rats induced by high-salt diet

AIMS

Salt-sensitive hypertension is a risk factor for cardiovascular disease. Previous studies have shown that insufficient arginine in the kidney caused by metabolic imbalance is an important factor in salt-sensitive hypertension. Whether the high nitrogen content of histidine can affect the balance of nitrogen metabolism in Dahl salt-sensitive (SS) rats. This article aimed to study the effects of oral histidine on salt-sensitive hypertension, kidney damage and metabolic patterns of high-salt diet in SS rats.

MAIN METHODS

Adult rats were divided into four groups, and blood pressure was measured using a non-invasive tail-cuff system. Gas chromatography-mass spectrometry analyzed metabolites in serum and kidney tissues.

KEY FINDINGS

High-salt diet significantly increased the blood pressure of rats and aggravated kidney damage. Of note, histidine can attenuate salt-sensitive hypertension and kidney damage by improving metabolic pattern, reducing Reactive Oxygen Species (ROS) and increasing nitric oxide levels in SS rats.

SIGNIFICANCE

These results suggest that histidine could be a potential adjuvant to prevent and control salt-sensitive hypertension.

Anti-Inflammatory, Antioxidant, and Antifibrotic Effects of Kefir Peptides on Salt-Induced Renal Vascular Damage and Dysfunction in Aged Stroke-Prone Spontaneously Hypertensive Rats

The increased prevalence of renal dysfunction and chronic kidney disease (CKD) and the high costs and poor outcomes of treatment are a significant health issue. The consequence of chronic high blood pressure is the increased prevalence of target organ end-stage renal disease, which has been proven to be a strong independent risk factor for adverse cardiovascular disease. A previous study showed that kefir products have anti-inflammatory and anti-hypertensive activities and immunological modulation functions. However, no data regarding the beneficial effects of kefir peptides (KPs) on salt-induced renal damage or related kidney diseases are available. In this study, KPs were orally administered to aged salt-induced stroke-prone spontaneously hypertensive (SHRSP) rats, and the effects of KPs against inflammation and oxidative stress and their ability to protect against renal dysfunction were evaluated. Fifty-five-week-old SHRSP rats under induction with 1% NaCl in drinking water for 4 weeks showed multiple renal injuries with increased renal inflammation, fibrosis, oxidative stress, tubular atrophy, and glomerulosclerosis. In contrast, oral gavage with KPs reduced the urine protein to creatinine (UPC) ratio, the fractional excretion of electrolytes (FeNa and FeCl), extracellular matrix deposition, and the interstitial fibrotic α-smooth muscle actin (α-SMA) levels in salt-induced SHRSP rats. The renal infiltration of inflammatory cells; the release of monocyte chemoattractant protein-1 (MCP-1), vascular cell adhesion molecule-1 (VCAM-1), endothelin-1 (ET-1), and the cytokine nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) and transforming growth factor-β (TGF-β); the reactive oxygen species (ROS) levels; and histopathological lesions were also decreased in salt-induced SHRSP rats. Furthermore, KP treatment significantly increased the renal superoxide dismutase (SOD) activity and the glomerular filtration rate (GFR), which exerted potent protection against salt-induced chronic kidney disease in SHRSP rats. The results of this study suggest that KPs ameliorate salt-induced renal damage, tubular atrophy, and glomerular dysfunction through anti-inflammatory, antioxidative stress, and antifibrotic activities, and might be a promising protective agent against high salt-induced renovascular-related diseases.

Effects of 12-Week Supplementation of a Polyherbal Formulation in Old Adults with Prehypertension/Hypertension: A Randomized, Double-Blind, Placebo-Controlled Trial

BACKGROUND

Uncontrolled blood pressure is the leading cause of mortality and disability due to associated cerebral and cardiovascular diseases and kidney failure. More than one-third of the old adult population have hypertension or prehypertension and many of their blood pressure are poorly controlled.

OBJECTIVE

We hypothesized that plant extracts-based antioxidants may benefit those with prehypertension/hypertension.

METHOD

One hundred age- and gender-matched healthy older adults were randomly assigned to receive HyperBalance capsules (n=50) or placebo (n=50) at Tang-Qiao Community Health Service Center, Shanghai. Blood pressure and severity scores of hypertension treatment-related symptoms (dizziness, headache, ringing/buzzing in ears, rapid heart rate, and chest tightness) were evaluated before and after the 12-week intervention.

RESULTS

Ninety-eight people completed the study, with 2 dropouts in the placebo group before the end of the study. Forty-one subjects (82%) of the HyperBalance group and 40 subjects (83.3%) of the placebo group had prehypertension (systolic blood pressures (SBP) between 130-139 and diastolic blood pressure (DBP) between 85-89mmHg), and 9 subjects (18%) in the HyperBalance group and 8 subjects (16.7%) in the placebo group had hypertension (≥140/90mmHg) before the intervention. HyperBalance significantly (P<0.01) reduced SBP from 136.18±4.38 to 124.14±3.96 mmHg and reduced DBP from 82.45±2.91 to 80.24±2.41mmHg, respectively, and reversed all 9 hypertension people to normotension or prehypertension state, whereas the placebo moderately reduced SBP from 135.79±4.22 to 132.35±4.656mmHg and reduced DBP from 82.90±3.07 to 82.27±3.01mmHg. All symptom severity scores became significantly lower in the HyperBalance group than in the placebo group after HyperBalance intervention: dizziness (0.82±0.44; vs 2.02±0.64, P<0.01); headache (0.46±0.50; vs 1.81±0.61, P<0.01); ringing/buzzing in ears (0.44±0.50; vs 1.04±0.29, P<0.01); and rapid heart rate and chest tightness (0.30±0.46; vs 0.92±0.28, P<0.01).

CONCLUSION

Polyherbal supplementation such as HyperBalance could benefit old adults with prehypertension/hypertension and improve treatment-related symptoms. Further studies are needed to validate the current findings.

Postulating the major environmental condition resulting in the expression of essential hypertension and its associated cardiovascular diseases: Dietary imprudence in daily selection of foods in respect of their potassium and sodium content resulting in oxidative stress-induced dysfunction of the vascular endothelium, vascular smooth muscle, and perivascular tissues

We hypothesize that the major environmental determinant of the expression of essential hypertension in America and other Westernized countries is dietary imprudence in respect of the consumption of daily combinations of foods containing suboptimal amounts of potassium and blood pressure-lowering phytochemicals, and supraphysiological amounts of sodium. We offer as premise that Americans on average consume suboptimal amounts of potassium and blood pressure-lowering phytochemicals, and physiologically excessive amounts of sodium, and that such dietary imprudence leads to essential hypertension through oxidative stress-induced vascular endothelial and smooth muscle dysfunction. Such dysfunctions restrict nitric oxide bioavailability, impairing endothelial cell-mediated relaxation of the underlying vascular smooth muscle, initiating and maintaining inappropriately increased peripheral and renal vascular resistance. The biochemical steps from oxidative stress to vascular endothelial dysfunction and its pernicious cardiovascular consequences are well established and generally accepted. The unique aspect of our hypothesis resides in the contention that Americans' habitual consumption of foods resulting in suboptimal dietary intake of potassium and supraphysiological intake of sodium result in oxidative stress, the degree of which, we suggest, will correlate with the degree of deviation of potassium and sodium intake from optimal. Because suboptimal intakes of potassium reflect suboptimal intakes of fruits and vegetables, associated contributors to oxidative stress include suboptimal intakes of magnesium, nitrate, polyphenols, carotenoids, and other phytochemical antioxidants for which fruits and vegetables contain abundant amounts. Currently Americans consume potassium-to-sodium in molar ratios of less than or close to 1.0 and the Institute of Medicine (IOM) recommends a molar ratio of 1.2. Ancestral diets to which we are physiologically adapted range from molar ratios of 5.0 to 10.0 or higher. Accordingly, we suggest that the average American is usually afflicted with oxidative stress-induced vascular endothelial dysfunction, and therefore the standards for normal blood pressure and pre-hypertension often reflect a degree of clinically significant hypertension. In this article, we provide support for those contentions, and indicate the findings that the hypothesis predicts.

The American Heart Association Scientific Statement on salt sensitivity of blood pressure: Prompting consideration of alternative conceptual frameworks for the pathogenesis of salt sensitivity?

: Recently, the American Heart Association (AHA) published a scientific statement on salt sensitivity of blood pressure which emphasized a decades old conceptual framework for the pathogenesis of this common disorder. Here we examine the extent to which the conceptual framework for salt sensitivity emphasized in the AHA Statement accommodates contemporary findings and views of the broader scientific community on the pathogenesis of salt sensitivity. In addition, we highlight alternative conceptual frameworks and important contemporary theories of salt sensitivity that are little discussed in the AHA Statement. We suggest that greater consideration of conceptual frameworks and theories for salt sensitivity beyond those emphasized in the AHA Statement may help to advance understanding of the pathogenesis of salt-induced increases in blood pressure and, in consequence, may lead to improved approaches to preventing and treating this common disorder.

Functional foods for augmenting nitric oxide activity and reducing the risk for salt-induced hypertension and cardiovascular disease in Japan

High salt intake is one of the major dietary determinants of hypertension and cardiovascular disease in Japan and throughout the world. Although dietary salt restriction may be of clinical benefit in salt-sensitive individuals, many individuals may not wish, or be able to, reduce their intake of salt. Thus, identification of functional foods that can help protect against mechanistic abnormalities mediating salt-induced hypertension is an issue of considerable medical and scientific interest. According to the "vasodysfunction" theory of salt-induced hypertension, the hemodynamic abnormality initiating salt-induced increases in blood pressure usually involves subnormal vasodilation and abnormally increased vascular resistance in response to increased salt intake. Because disturbances in nitric oxide activity can contribute to subnormal vasodilator responses to increased salt intake that often mediate blood pressure salt sensitivity, increased intake of functional foods that support nitric oxide activity may help to reduce the risk for salt-induced hypertension. Mounting evidence indicates that increased consumption of traditional Japanese vegetables and other vegetables with high nitrate content such as table beets and kale can promote the formation of nitric oxide through an endothelial independent pathway that involves reduction of dietary nitrate to nitrite and nitric oxide. In addition, recent studies in animal models have demonstrated that modest increases in nitrate intake can protect against the initiation of salt-induced hypertension. These observations are: (1) consistent with the view that increased intake of many traditional Japanese vegetables and other nitrate rich vegetables, and of functional foods derived from such vegetables, may help maintain healthy blood pressure despite a high salt diet; (2) support government recommendations to increase vegetable intake in the Japanese population.

Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats

This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other vessels), and describes techniques for evaluating tissue perfusion using Laser Doppler Flowmetry (LDF) and microvessel density utilizing fluorescently labeled Griffonia simplicifolia (GS1) lectin. Current methods for studying isolated resistance arteries at transmural pressures encountered in vivo and in the absence of parenchymal cell influences provide a critical link between in vivo studies and information gained from molecular reductionist approaches that provide limited insight into integrative responses at the whole animal level. LDF and techniques to selectively identify arterioles and capillaries with fluorescently-labeled GS1 lectin provide practical solutions to enable investigators to extend the knowledge gained from studies of isolated resistance arteries. This paper describes the application of these techniques to gain fundamental knowledge of vascular physiology and pathology in the rat as a general experimental model, and in a variety of specialized genetically engineered "designer" rat strains that can provide important insight into the influence of specific genes on important vascular phenotypes. Utilizing these valuable experimental approaches in rat strains developed by selective breeding strategies and new technologies for producing gene knockout models in the rat, will expand the rigor of scientific premises developed in knockout mouse models and extend that knowledge to a more relevant animal model, with a well understood physiological background and suitability for physiological studies because of its larger size.

Associations Between Genetic Variants of NADPH Oxidase-Related Genes and Blood Pressure Responses to Dietary Sodium Intervention: The GenSalt Study

BACKGROUND

The aim of this study was to comprehensively test the associations of genetic variants of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-related genes with blood pressure (BP) responses to dietary sodium intervention in a Chinese population.

METHODS

We conducted a 7-day low-sodium intervention followed by a 7-day high-sodium intervention among 1,906 participants in rural China. BP measurements were obtained at baseline and each dietary intervention using a random-zero sphygmomanometer. Linear mixed-effect models were used to assess the additive associations of 63 tag single-nucleotide polymorphisms in 11 NADPH oxidase-related genes with BP responses to dietary sodium intervention. Gene-based analyses were conducted using the truncated product method. The Bonferroni method was used to adjust for multiple testing in all analyses.

RESULTS

Systolic BP (SBP) response to high-sodium intervention significantly decreased with the number of minor T allele of marker rs6967221 in RAC1 (P = 4.51 × 10-4). SBP responses (95% confidence interval) for genotypes CC, CT, and TT were 5.03 (4.71, 5.36), 4.20 (3.54, 4.85), and 0.56 (-1.08, 2.20) mm Hg, respectively, during the high-sodium intervention. Gene-based analyses revealed that RAC1 was significantly associated with SBP response to high-sodium intervention (P = 1.00 × 10-6) and diastolic BP response to low-sodium intervention (P = 9.80 × 10-4).

CONCLUSIONS

These findings suggested that genetic variants of NADPH oxidase-related genes may contribute to the variation of BP responses to sodium intervention in Chinese population. Further replication of these findings is warranted.

Dietary Vitamin E Supplementation Attenuates Hypertension in Dahl Salt-Sensitive Rats

There is strong evidence that excess dietary salt (NaCl) is a major factor contributing to the development of hypertension. Salt-sensitive humans and rats develop hypertension even on a normal-salt diet. Salt sensitivity is associated with glucose intolerance and insulin resistance in both humans and animal models, including Dahl salt-sensitive (DSS) rats. In insulin resistance, impaired glucose metabolism leads to elevated endogenous aldehydes that bind sulfhydryl groups of membrane proteins, altering calcium channels, and increasing cytosolic free calcium ([Ca2+] i) and blood pressure. Vitamin E lowers tissue aldehyde conjugates, cytosolic [Ca2+] i, and blood pressure in spontaneously hypertensive rats and fructose-induced hypertensive Wistar Kyoto rats, models of insulin resistance. This study investigated the effect of a normal-salt diet on tissue aldehyde conjugates, cytosolic [Ca2+] i, and blood pressure in DSS rats and the effect of vitamin E supplementation on blood pressure and associated biochemical changes in these animals. Seven-week-old DSS rats were divided into 3 groups of 6 animals each and treated for 6 weeks with diets as follows: low-salt (0.4% NaCl); normal-salt (0.7% NaCl) and normal salt (0.7% NaCl) plus vitamin E (34 mg/kg feed). At completion, animals in the normal-salt group had significantly elevated systolic blood pressure, cytosolic [Ca2+] i, and tissue aldehyde conjugates compared with the low-salt group. They also showed smooth muscle cell hyperplasia in small arteries and arterioles of the kidney. Dietary vitamin E supplementation significantly attenuated the increase in systolic blood pressure and associated biochemical and histopathologic changes.

The protective effect of a buckwheat-enriched diet on renal injury in high salt-induced hypertension in rats

An excess of dietary salt is the most common factor that contributes to the pathogenesis of hypertension.

Probiotics Blunt the Anti-Hypertensive Effect of Blueberry Feeding in Hypertensive Rats without Altering Hippuric Acid Production

Previously we showed that feeding polyphenol-rich wild blueberries to hypertensive rats lowered systolic blood pressure. Since probiotic bacteria produce bioactive metabolites from berry polyphenols that enhance the health benefits of berry consumption, we hypothesized that adding probiotics to a blueberry-enriched diet would augment the anti-hypertensive effects of blueberry consumption. Groups (n = 8) of male spontaneously hypertensive rats were fed one of four AIN '93G-based diets for 8 weeks: Control (CON); 3% freeze-dried wild blueberry (BB); 1% probiotic bacteria (PRO); or 3% BB + 1% PRO (BB+PRO). Blood pressure was measured at weeks 0, 2, 4, 6, and 8 by the tail-cuff method, and urine was collected at weeks 4 and 8 to determine markers of oxidative stress (F2-isoprostanes), nitric oxide synthesis (nitrites), and polyphenol metabolism (hippuric acid). Data were analyzed using mixed models ANOVA with repeated measures. Diet had a significant main effect on diastolic blood pressure (p = 0.046), with significantly lower measurements in the BB- vs. CON-fed rats (p = 0.035). Systolic blood pressure showed a similar but less pronounced response to diet (p = 0.220), again with the largest difference between the BB and CON groups. Absolute increase in blood pressure between weeks 0 and 8 tended to be smaller in the BB and PRO vs. CON and BB+PRO groups (systolic increase, p = 0.074; diastolic increase, p = 0.185). Diet had a significant main effect on hippuric acid excretion (p<0.0001), with 2- and ~1.5-fold higher levels at weeks 4 and 8, respectively, in the BB and BB+PRO vs. PRO and CON groups. Diet did not have a significant main effect on F2-isoprostane (p = 0.159) or nitrite excretion (p = 0.670). Our findings show that adding probiotics to a blueberry-enriched diet does not enhance and actually may impair the anti-hypertensive effect of blueberry consumption. However, probiotic bacteria are not interfering with blueberry polyphenol metabolism into hippuric acid.

Pathophysiology and Medical Treatment of Carotid Artery Stenosis

Stroke is the third leading cause of mortality. Approximately 80 to 85% strokes are ischemic due to carotid artery stenosis (CAS). The prevalence of significant CAS is 7% in women and 9% in men. Severe asymptomatic CAS varies from 0 to 3.1%. Prevalence of symptomatic CAS is high in patients with peripheral arterial disease. CAS is due to atherosclerosis, the major risk factors for which include dyslipidemia, hypertension, diabetes, obesity, cigarette smoking, advanced glycation end products (AGEs) and its receptors (RAGE, soluble RAGE [sRAGE]), lack of exercise and C-reactive protein (CRP). This article discusses the basic mechanism of atherosclerosis and the mechanisms by which these risk factors induce atherosclerosis. The role of AGEs and its receptors in the development and progression of CAS has been discussed in detail. Lifestyle changes and medical treatment of CAS such as lifestyle changes, lipid-lowering agents, antihypertensive agents, antidiabetic drugs, anti-AGE therapy, measures to elevate soluble receptors of AGE (sRAGE, esRAGE). CRP-lowering agents have been discussed in detail. The drugs especially lipid-lowering agents, and antihypertensive and antidiabetic drugs suppress, regress, and slow the progression of CAS. The possible role of lowering the levels of AGEs and raising the levels of sRAGE in the treatment of CAS has been proposed. Lifestyle changes besides medical treatment have been stressed. Lifestyle changes and medical treatment not only would slow the progression of CAS but would also regress the CAS.

Chronic NF-κB blockade improves renal angiotensin II type 1 receptor functions and reduces blood pressure in Zucker diabetic rats

Background

Both angiotensin II type 1 receptor (AT₁R) and nuclear factor-kappa B (NF-κB) play significant roles in the pathogenesis of hypertension and type 2 diabetes. However, the role of NF-κB in perpetuating renal AT₁ receptors dysfunction remains unclear. The aim of the present study to determine whether blockade of NF-κB, could reverse the exaggerated renal AT₁R function, reduce inflammatory state and oxidative stress, lower blood pressure in Zucker diabetic fatty (ZDF) rats.

Methods

Pyrrolidine dithiocarbamate (PDTC), a NF-κB inhibitor (150 mg/kg in drinking water)or vehicle was administered orally to 12-weeks-old ZDF rats and their respective control lean Zucker (LZ) rats for 4 weeks. Blood pressure was measured weekly by tail-cuff method. AT₁R functions were determined by measuring diuretic and natriuretic responses to AT₁R antagonist (candesartan; 10 μg/kg/min iv). The mRNA and protein levels of NF-κB, oxidative stress maker and AT₁R were determined using quantitative real-time PCR and Western blotting, respectively. The NF-κB-DNA binding activity in renal cortex was measured by Electrophoretic mobility shift assay (EMSA).

Results

As compared with LZ rats, ZDF rats had higher blood pressure, impaired natriuresis and diuresis, accompanied with higher levels of oxidative stress and inflammation. Furthermore, AT₁R expression was higher in renal cortex from ZDF rats; candesartan induced natriresis and diuresis, which was augmented in ZDF rats. Treatment with PDTC lowered blood pressure and improved diuretic and natriuretic effects in ZDF rats; meanwhile, the increased oxidative stress and inflammation were reduced; the increased AT₁R expression and augmented candesartan-mediated natriuresis and diuresis were recoverd in ZDF rats. Our further study investigated the mechanisms of PDTC on AT₁R receptor expression. It resulted that PDTC inhibited NF-κB translocation from cytosol to nucleus, inhibited binding of NF-κB with AT₁R promoter, therefore, reduced AT₁R expression and function.

Conclusions

Our present study indicates blockade of NF-κB, via inhibition of binding of NF-κB with AT₁R promoter, reduces renal AT₁R expression and function, improves oxidative stress and inflammatory/anti-inflammatory balance, therefore, lowers blood pressure and recovers renal function in ZDF rats.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-015-0239-7) contains supplementary material, which is available to authorized users.

Superoxide enhances Ca2+ entry through L-type channels in the renal afferent arteriole

Reactive oxygen species regulate cardiovascular and renal function in health and disease. Superoxide participates in acute calcium signaling in afferent arterioles and renal vasoconstriction produced by angiotensin II, endothelin, thromboxane, and pressure-induced myogenic tone. Known mechanisms by which superoxide acts include quenching of nitric oxide and increased ADP ribosyl cyclase/ryanodine-mediated calcium mobilization. The effect(s) of superoxide on other calcium signaling pathways in the renal microcirculation is poorly understood. The present experiments examined the acute effect of superoxide generated by paraquat on calcium entry pathways in isolated rat afferent arterioles. The peak increase in cytosolic calcium concentration caused by KCl (40 mmol/L) was 99±14 nmol/L. The response to this membrane depolarization was mediated exclusively by L-type channels because it was abolished by nifedipine but was unaffected by the T-type channel blocker mibefradil. Paraquat increased superoxide production (dihydroethidium fluorescence), tripled the peak response to KCl to 314±68 nmol/L (P<0.001) and doubled the plateau response. These effects were abolished by tempol and nitroblue tetrazolium, but not by catalase, confirming actions of superoxide and not of hydrogen peroxide. Unaffected by paraquat and superoxide was calcium entry through store-operated calcium channels activated by thapsigargin-induced calcium depletion of sarcoplasmic reticular stores. Also unresponsive to paraquat was ryanodine receptor-mediated calcium-induced calcium release from the sarcoplasmic reticulum. Our results provide new evidence that superoxide enhances calcium entry through L-type channels activated by membrane depolarization in rat cortical afferent arterioles, without affecting calcium entry through store-operated entry or ryanodine receptor-mediated calcium mobilization.

Oxidative stress causes imbalance of renal renin angiotensin system (RAS) components and hypertension in obese Zucker rats

Background

Oxidative stress plays an important role in the pathogenesis of hypertension, especially in obesity‐related hypertension. The natriuretic and antinatriuretic components of the renal renin angiotensin system (RAS) maintain sodium homeostasis and blood pressure. Here, we test the hypothesis that increased oxidative stress leads to the imbalance of RAS components and hypertension in obese Zucker rats.

Methods and Results

Lean and obese rats received vehicle or tempol, a superoxide dismutase mimetic in the drinking water for 4 weeks. Compared with vehicle‐treated lean rats, vehicle‐treated obese rats exhibited higher blood pressure and increased renal oxidative stress, accompanied by increased diuretic and natriuretic responses to AT₁R antagonist (Candesartan) and AT₂R agonist (CGP‐42112A) and reduced diuretic and natriuretic response to MasR agonist (Ang‐[1 to 7]). Moreover, obese rats had higher ACE, AT₁R and AT₂R, lower ACE2 and MasR expressions in the kidney. All of the above‐mentioned abnormalities were reversed to some degree by tempol treatment. In primary cultures of renal proximal tubular (RPT) cells from lean and obese rats, tempol treatment also increased AT₂R, ACE2, and MasR expressions but decreased AT₁R and ACE expressions in obese rats.

Conclusions

Taken together, our study indicated that the imbalance of renal RAS components was associated with increased oxidative stress in obese rats. Furthermore, antioxidant treatment with tempol reversed the imbalance of renal RAS components and led to diuresis and natriuresis, which, at least in part, explains the blood pressure‐lowering effect of antioxidant supplementation in obesity‐related hypertension.

Transglutaminase activity is decreased in large arteries from hypertensive rats compared with normotensive controls

Transglutaminases (TGs) catalyze the formation of covalent cross-links between glutamine residues and amine groups. This cross-linking activity has been implicated in arterial remodeling. Because hypertension is characterized by arterial remodeling, we hypothesized that TG activity, expression, and functionality would be increased in the aorta, but not in the vena cava (which does not undergo remodeling), from hypertensive rats relative to normotensive rats. Spontaneously hypertensive stroke-prone rats (SHRSP) and DOCA-salt rats as well as their respective normotensive Wistar-Kyoto or Sprague-Dawley counterparts were used. Immunohistochemistry and Western blot analysis measured the presence and expression of TG1 and TG2, in situ activity assays quantified active TGs, and isometric contractility was used to measure TG functionality. Contrary to our hypothesis, the activity (52% DOCA-salt vs. control rats and 56% SHRSP vs. control rats, P < 0.05), expression (TG1: 54% DOCA-salt vs. control rats, P > 0.05, and TG2: 77% DOCA-salt vs. control rats, P < 0.05), and functionality of TG1 and TG2 were decreased in the aorta, but not in the vena cava, from hypertensive rats. Mass spectrometry identified proteins uniquely amidated by TGs in the aorta that play roles in cytoskeletal regulation, redox regulation, and DNA/RNA/protein synthesis and regulation and in the vena cava that play roles in cytoskeletal regulation, coagulation regulation, and cell metabolism. Consistent with the idea that growing cells lose TG2 expression, vascular smooth muscle cells placed in culture lost TG2 expression. We conclude that the expression, activity, and functionality of TG1 and TG2 are decreased in the aorta, but not in the vena cava, from hypertensive rats compared with control rats.

Protective Effects of Crocus Sativus L. Extract and Crocin against Chronic-Stress Induced Oxidative Damage of Brain, Liver and Kidneys in Rats

PURPOSE

Chronic stress has been reported to induce oxidative damage of the brain. A few studies have shown that Crocus Sativus L., commonly known as saffron and its active constituent crocin may have a protective effect against oxidative stress. The present work was designed to study the protective effects of saffron extract and crocin on chronic - stress induced oxidative stress damage of the brain, liver and kidneys.

METHODS

Rats were injected with a daily dose of saffron extract (30 mg/kg, IP) or crocin (30 mg/kg, IP) during a period of 21 days following chronic restraint stress (6 h/day). In order to determine the changes of the oxidative stress parameters following chronic stress, the levels of the lipid peroxidation product, malondialdehyde (MDA), the total antioxidant reactivity (TAR), as well as antioxidant enzyme activities glutathione peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD) were measured in the brain, liver and kidneys tissues after the end of chronic stress.

RESULTS

In the stressed animals that receiving of saline, levels of MDA, and the activities of GPx, GR, and SOD were significantly higher (P<0.0001) and the TAR capacity were significantly lower than those of the non-stressed animals (P<0.0001). Both saffron extract and crocin were able to reverse these changes in the stressed animals as compared with the control groups (P<0.05).

CONCLUSION

These observations indicate that saffron and its active constituent crocin can prevent chronic stress-induced oxidative stress damage of the brain, liver and kidneys and suggest that these substances may be useful against oxidative stress.

Reactive oxygen species as important determinants of medullary flow, sodium excretion, and hypertension

The physiological evidence linking the production of superoxide, hydrogen peroxide, and nitric oxide in the renal medullary thick ascending limb of Henle (mTAL) to regulation of medullary blood flow, sodium homeostasis, and long-term control of blood pressure is summarized in this review. Data obtained largely from rats indicate that experimentally induced elevations of either superoxide or hydrogen peroxide in the renal medulla result in reduction of medullary blood flow, enhanced Na(+) reabsorption, and hypertension. A shift in the redox balance between nitric oxide and reactive oxygen species (ROS) is found to occur naturally in the Dahl salt-sensitive (SS) rat model, where selective reduction of ROS production in the renal medulla reduces salt-induced hypertension. Excess medullary production of ROS in SS rats emanates from the medullary thick ascending limbs of Henle [from both the mitochondria and membrane NAD(P)H oxidases] in response to increased delivery and reabsorption of excess sodium and water. There is evidence that ROS and perhaps other mediators such as ATP diffuse from the mTAL to surrounding vasa recta capillaries, resulting in medullary ischemia, which thereby contributes to hypertension.

Female sex hormones protect against salt-sensitive hypertension but not essential hypertension

Initial studies found that female Dahl salt-sensitive (DS) rats exhibit greater blood pressure (BP) salt sensitivity than female spontaneously hypertensive rats (SHR). On the basis of the central role played by NO in sodium excretion and BP control, we further tested the hypothesis that blunted increases in BP in female SHR will be accompanied by greater increases in renal inner medullary nitric oxide synthase (NOS) activity and expression in response to a high-salt (HS) diet compared with DS rats. Gonad-intact and ovariectomized (OVX) female SHR and DS rats were placed on normal salt (NS; 0.4% salt) or HS (4% salt) diet for 2 wk. OVX did not alter BP in SHR, and HS diet produced a modest increase in BP. OVX significantly increased BP in DS rats on NS; HS further increased BP in all DS rats, although OVX had a greater increase in BP. Renal inner medullary NOS activity, total NOS3 protein, and NOS3 phosphorylated on serine residue 1177 were not altered by salt or OVX in either strain. NOS1 protein expression, however, significantly increased with HS only in SHR, and this corresponded to an increase in urinary nitrate/nitrite excretion. SHR also exhibit greater NOS1 and NOS3 protein expression than DS rats. These data indicate that female sex hormones offer protection against HS-mediated elevations in BP in DS rats but not SHR. We propose that the relative resistance to HS-mediated increases in BP in SHR is related to greater NOS expression and the ability to increase NOS1 protein expression compared with DS rats.

Testicular morphology in spontaneously hypertensive rat model: oxidant status and stereological implications

Studies by researchers suggest that reductions in blood flow to the testis could play an important role in the pathogenesis of male infertility. As this oxygen-dependent organ functions in a state of near anoxia, such a decrease in blood flow may very likely have profound effects on the tissue morphology that ultimately would predispose to various forms of hypo-spermatogenesis with consequent compromise in reproductive capability. With varying opinions expressed by experts as to the actual culprit or potential pathway and/or effects of pathophysiology of testicular haemodynamics, it still remains debatable whether the observed degenerative changes in testicular tissue are the result of major or minor reductions in flow or the consequence of other vascular pathologies or even extraneous factors. Again, increasing age and male gender have been identified as the single independent risk factors for the occurrence of cardiovascular pathologies with sexual dimorphism highly debated. The investigation of these factors occurring under hypertensive states using the spontaneously hypertensive rat (SHR) as an experimental model has attracted substantial attention in recent past. This review examines the relationships and potential morphologic changes in the testicular tissue under conditions of perturbations in blood flow as seen in the SHR with a view to the proper understanding of the role(s) of various factors that contributes to male subfertility. A suggestion to the use of stereological methods for quantitating various measurements in a highly active and dynamic structure like the testis with its arterial system has been added as this may facilitate a better understanding of the mechanisms implicated under hypertensive conditions.

Oxidative stress in hypertension: role of the kidney

SIGNIFICANCE

Renal oxidative stress can be a cause, a consequence, or more often a potentiating factor for hypertension. Increased reactive oxygen species (ROS) in the kidney have been reported in multiple models of hypertension and related to renal vasoconstriction and alterations of renal function. Nicotinamide adenine dinucleotide phosphate oxidase is the central source of ROS in the hypertensive kidney, but a defective antioxidant system also can contribute.

RECENT ADVANCES

Superoxide has been identified as the principal ROS implicated for vascular and tubular dysfunction, but hydrogen peroxide (H2O2) has been implicated in diminishing preglomerular vascular reactivity, and promoting medullary blood flow and pressure natriuresis in hypertensive animals.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Increased renal ROS have been implicated in renal vasoconstriction, renin release, activation of renal afferent nerves, augmented contraction, and myogenic responses of afferent arterioles, enhanced tubuloglomerular feedback, dysfunction of glomerular cells, and proteinuria. Inhibition of ROS with antioxidants, superoxide dismutase mimetics, or blockers of the renin-angiotensin-aldosterone system or genetic deletion of one of the components of the signaling cascade often attenuates or delays the onset of hypertension and preserves the renal structure and function. Novel approaches are required to dampen the renal oxidative stress pathways to reduced O2(-•) rather than H2O2 selectivity and/or to enhance the endogenous antioxidant pathways to susceptible subjects to prevent the development and renal-damaging effects of hypertension.

Hypertension: physiology and pathophysiology

Despite major advances in understanding the pathophysiology of hypertension and availability of effective and safe antihypertensive drugs, suboptimal blood pressure (BP) control is still the most important risk factor for cardiovascular mortality and is globally responsible for more than 7 million deaths annually. Short-term and long-term BP regulation involve the integrated actions of multiple cardiovascular, renal, neural, endocrine, and local tissue control systems. Clinical and experimental observations strongly support a central role for the kidneys in the long-term regulation of BP, and abnormal renal-pressure natriuresis is present in all forms of chronic hypertension. Impaired renal-pressure natriuresis and chronic hypertension can be caused by intrarenal or extrarenal factors that reduce glomerular filtration rate or increase renal tubular reabsorption of salt and water; these factors include excessive activation of the renin-angiotensin-aldosterone and sympathetic nervous systems, increased formation of reactive oxygen species, endothelin, and inflammatory cytokines, or decreased synthesis of nitric oxide and various natriuretic factors. In human primary (essential) hypertension, the precise causes of impaired renal function are not completely understood, although excessive weight gain and dietary factors appear to play a major role since hypertension is rare in nonobese hunter-gathers living in nonindustrialized societies. Recent advances in genetics offer opportunities to discover gene-environment interactions that may also contribute to hypertension, although success thus far has been limited mainly to identification of rare monogenic forms of hypertension.

The oxygen free radicals control MMP-9 and transcription factors expression in the spontaneously hypertensive rat

Oxygen free radical and matrix metalloproteinases-9 (MMP-9) play an important pathophysiological role in the development of chronic hypertension. MMP-9 activities are regulated at different levels. We hypothesize that as mediators of the expression of MMP-9 the transcription factors like nuclear factor kappa B (NF-κB), c-fos and retinoic acid receptors-α (RAR-α) with binding sites to the MMP-9 promoter are overexpressed in the spontaneously hypertensive rat (SHR) in a process that is regulated by oxygen free radicals. Transcription factor NF-κB, c-fos and RAR-α expression levels were determined by immunohistochemistry in renal, cardiac and mesentery microcirculation of the SHR and its normotensive control, the Wistar Kyoto (WKY) rat. The animals were treated with a superoxide scavenger (Tempol) for eight weeks. The elevated plasma levels of thiobarbituric acid reactive substances and MMP-9 levels in the SHR were significantly decreased by Tempol treatment (P<0.05). The NF-κB, c-fos and RAR-α expression levels in renal glomerular, heart and mesentery microvessels were enhanced in the SHR and could also be reduced by Tempol compared to untreated animals (P<0.05). The enhanced MMP-9 levels in SHR microvessels co-express with transcription factors. These results suggest that elevated NF-κB, c-fos and RAR-α expressions and MMP-9 activity in the SHR are superoxide-dependent.

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

α-MSH analogue attenuates blood pressure elevation in DOCA-salt hypertensive mice

Melanocyte-stimulating hormones, α-, β- and γ-MSH, regulate important physiological functions including energy homeostasis, inflammation and sodium metabolism. Previous studies have shown that α-MSH increases sodium excretion and promotes vascular function in rodents, but it is unexplored whether these characteristics of α-MSH could translate into therapeutic benefits in the treatment of hypertension. Therefore, we first assessed the diuretic and natriuretic properties of the stable α-MSH analogue [Nle(4), D-Phe(7)]-α-MSH (NDP-α-MSH) and investigated whether it has protective effects in deoxycorticosterone acetate (DOCA)-salt hypertensive mice. Adult male C57Bl/6N mice were subjected to DOCA-salt treatment and randomized to receive intraperitoneal injections of either saline as vehicle or NDP-α-MSH (0.3 mg/kg/day for 14 days) starting 7 days after the DOCA-salt treatment. Systemic hemodynamics, serum and urine electrolytes, and oxidative stress markers were assessed in control sham-operated and DOCA-salt mice. NDP-α-MSH elicited marked diuretic and natriuretic responses that were reversible with the MC3/4 receptor antagonist SHU9119. Chronic NDP-α-MSH treatment attenuated blood pressure elevation in DOCA-salt mice without affecting the blood pressure of normotensive control animals. Owing to the enhanced sodium excretion, NDP-α-MSH-treated mice were protected from DOCA-salt-induced hypernatremia. DOCA-salt treatment mildly increased oxidative stress at the tissue level, but NDP-α-MSH had no significant effects on the oxidative stress markers. In conclusion, treatment with NDP-α-MSH increases urinary sodium excretion and protects against DOCA-salt-induced hypertension. These findings point to the potential future use of α-MSH analogues in the treatment of hypertension.

Role of Rac1 GTPase in salt-sensitive hypertension

PURPOSE OF REVIEW

The aldosterone/mineralocorticoid receptor system plays an important role in the long-term blood pressure control through Na homeostasis. Its overactivation has been implicated in salt-sensitive hypertension. Excessive salt intake augments the function of mineralocorticoid receptor, despite lowering circulating aldosterone levels, but the mechanism had long been elusive. Recently, Rac1, a member of Rho family small GTP-binding proteins, has emerged as a novel ligand-independent modulator of mineralocorticoid receptor activity. In this review, the roles of Rac1 in the pathogenesis of salt-sensitive hypertension and kidney injury have been summarized.

RECENT FINDINGS

Genetic engineering studies have highlighted the new aspects of Rac1 and its regulators in salt-sensitive hypertension and cardiac and renal disease. New evidence shows the essential roles of Rac1 in salt-evoked paradoxical mineralocorticoid receptor activation observed in salt-sensitive models and in renal tubular Na reabsorption through reduced nicotinamide-adenine dinucleotide phosphate oxidase-mediated oxidative stress or direct regulation of Na transporters.

SUMMARY

The emerging concept of 'ligand-independent aberrant mineralocorticoid receptor activation by Rac1' in the pathogenesis of salt-sensitive hypertension and kidney injury has been reviewed. Rac inhibition, in addition to mineralocorticoid receptor blockade and salt restriction, would be a new promising strategy for the treatment of salt-sensitive hypertension.

L-arginine or tempol supplementation improves renal and cardiovascular function in rats with reduced renal mass and chronic high salt intake

AIM

Early life reduction in nephron number and chronic high salt intake cause development of renal and cardiovascular disease, which has been associated with oxidative stress and nitric oxide (NO) deficiency. We investigated the hypothesis that interventions stimulating NO signalling or reducing oxidative stress may restore renal autoregulation, attenuate hypertension and reduce renal and cardiovascular injuries following reduction in renal mass and chronic high salt intake.

METHODS

Male Sprague-Dawley rats were uninephrectomized (UNX) or sham-operated at 3 weeks of age and given either a normal-salt (NS) or high-salt (HS) diet. Effects on renal and cardiovascular functions were assessed in rats supplemented with substrate for NO synthase (L-Arg) or a superoxide dismutase mimetic (Tempol).

RESULTS

Rats with UNX + HS developed hypertension and displayed increased renal NADPH oxidase activity, elevated levels of oxidative stress markers in plasma and urine, and reduced cGMP in plasma. Histological analysis showed signs of cardiac and renal inflammation and fibrosis. These changes were linked with abnormal renal autoregulation, measured as a stronger tubuloglomerular feedback (TGF) response. Simultaneous treatment with L-Arg or Tempol restored cGMP levels in plasma and increased markers of NO signalling in the kidney. This was associated with normalized TGF responses, attenuated hypertension and reduced signs of histopathological changes in the kidney and in the heart.

CONCLUSION

Reduction in nephron number during early life followed by chronic HS intake is associated with oxidative stress, impaired renal autoregulation and development of hypertension. Treatment strategies that increase NO bioavailability, or reduce levels of reactive oxygen species, were proven beneficial in this model of renal and cardiovascular disease.

Role of the immune system in hypertension: modulation by dietary antioxidants

Hypertension is a major health problem worldwide. Individuals with hypertension are at an increased risk for stroke, heart disease, and kidney failure. Although the etiology of essential hypertension has a genetic component, lifestyle factors such as diet play an important role. Insulin resistance is a common feature of hypertension in both humans and animal models affecting glucose and lipid metabolism producing excess aldehydes including methylglyoxal. These aldehydes react with proteins to form conjugates called advanced glycation end products (AGEs). This alters protein structure and function and can affect vascular and immune cells leading to their activation and secretion of inflammatory cytokines. AGEs also act via receptors for advanced glycation end products on these cells altering the function of antioxidant and metabolic enzymes, and ion channels. This results in an increase in cytosolic free calcium, decrease in nitric oxide, endothelial dysfunction, oxidative stress, peripheral vascular resistance, and infiltration of vascular and kidney tissue with inflammatory cells leading to hypertension. Supplementation with dietary antioxidants including vitamins C, E, or B(6), thiols such as cysteine and lipoic acid, have been shown to lower blood pressure and plasma inflammatory cytokines in animal models and humans with essential hypertension. A well-balanced diet rich in antioxidants that includes vegetables, fruits, low fat dairy products, low salt, and includes whole grains, poultry, fish and nuts, lowers blood pressure and vascular inflammation. These antioxidants may achieve their antihypertensive and anti-inflammatory/immunomodulatory effects by reducing AGEs and improving insulin resistance and associated alterations. Dietary supplementation with antioxidants may be a beneficial, inexpensive, front-line alterative treatment modality for hypertension.

Association between circulating specific leukocyte types and incident chronic kidney disease: the Atherosclerosis Risk in Communities (ARIC) study

Progressive renal fibrosis is a characteristic of all the diseases that cause renal failure and is invariably accompanied by a prominent leukocyte infiltration in the kidney. The goal of this study was to determine the association between the circulating specific leukocyte types and incident chronic kidney disease (CKD). In a cohort of 10,056 middle-aged white and African American adults, levels of circulating neutrophils, lymphocytes, and monocytes were measured at baseline; blood pressure (BP) and serum creatinine were measured and estimated glomerular filtration rate (eGFR) was calculated at baseline and 3 and 9 years later; and surveillance for first hospitalization or death with CKD was carried out over a mean follow-up of 7.4 years (maximum, 11.9 years). Increased neutrophil levels and decreased lymphocyte levels were significantly associated with greater CKD incidence after adjustment for covariates. African Americans tended to have similar but stronger patterns of association between circulating leukocytes and CKD incidence than whites, although the differences between race groups were not statistically significant. We also found that eGFR and BP were higher at each visit in African Americans than whites between ages 45 and 65. These findings support a potential role for circulating specific leukocytes in the pathogenesis of kidney dysfunction, especially in African Americans, indicating the leukocyte-related renal mechanism of essential hypertension (HT).

Marinobufagenin and cyclic strain may activate endothelial NADPH oxidase, contributing to the adverse impact of salty diets on vascular and cerebral health

Limited but provocative ecologic epidemiology suggests that dietary salt may play a central role in the genesis of not only of stroke, but also dementia, including Alzheimer's disease. Impairment of nitric oxide bioactivity in the cerebral microvasculature is a likely mediator of this effect. Salted diets evoke increased adrenal secretion of the natriuretic steroid marinobufagenin (MBG), which promotes natriuresis via inhibition of renal tubular Na+/K+-ATPase; this effect is notably robust in salt-sensitive rodent strains in which other compensatory natriuretic mechanisms are subnormally efficient. MBG-mediated inhibition of sodium pumps in vascular smooth muscle likely plays a role in the hypertension induced by salty diets in these rodents. However, salt sensitivity in humans is associated with increased vascular mortality and ventricular hypertrophy independent of blood pressure; this suggests that MBG may be pathogenic via mechanisms unrelated to blood pressure control. Indeed, recent evidence indicates that MBG, via interaction with alpha1 isoforms of the sodium pump, can activate various intracellular signaling pathways at physiological concentrations too low to notably inhibit pump activity. An overview of current evidence suggests the hypothesis that MBG - as well as the cyclic strain induced by hypertension per se - may induce endothelial oxidative stress by activating NADPH oxidase. If so, this could rationalize the increase in vascular and systemic oxidative stress observed in salt-sensitive rodents fed salty diets, or in rodents infused with MBG; moreover, if this effect is a particularly prominent determinant of oxidative stress in cerebrovascular endothelium, it might help to explain the virtual absence of stroke and dementia in low-salt societies. As a corollary of this hypothesis, it can be predicted that spirulina-derived phycobilins, which appear to mimic the physiological role of bilirubin as an inhibitor of NAPDH oxidase complexes, may have potential for ameliorating the adverse health impacts of MBG and of salty diets. Potassium-rich diets are also likely to be protective in this regard, as they should suppress MBG production via their natriuretic impact, while their stimulatory effect on sodium pump activity may exert a hyperpolarizing effect on plasma membranes that suppresses NADPH oxidase activity.

A blueberry-enriched diet attenuates nephropathy in a rat model of hypertension via reduction in oxidative stress

OBJECTIVE AND BACKGROUND

To assess renoprotective effects of a blueberry-enriched diet in a rat model of hypertension. Oxidative stress (OS) appears to be involved in the development of hypertension and related renal injury. Pharmacological antioxidants can attenuate hypertension and hypertension-induced renal injury; however, attention has shifted recently to the therapeutic potential of natural products as antioxidants. Blueberries (BB) have among the highest antioxidant capacities of fruits and vegetables.

METHODS AND RESULTS

Male spontaneously hypertensive rats received a BB-enriched diet (2% w/w) or an isocaloric control diet for 6 or 12 weeks or 2 days. Compared to controls, rats fed BB-enriched diet for 6 or 12 weeks exhibited lower blood pressure, improved glomerular filtration rate, and decreased renovascular resistance. As measured by electron paramagnetic resonance spectroscopy, significant decreases in total reactive oxygen species (ROS), peroxynitrite, and superoxide production rates were observed in kidney tissues in rats on long-term dietary treatment, consistent with reduced pathology and improved function. Additionally, measures of antioxidant status improved; specifically, renal glutathione and catalase activities increased markedly. Contrasted to these observations indicating reduced OS in the BB group after long-term feeding, similar measurements made in rats fed the same diet for only 2 days yielded evidence of increased OS; specifically, significant increases in total ROS, peroxynitrite, and superoxide production rates in all tissues (kidney, brain, and liver) assayed in BB-fed rats. These results were evidence of "hormesis" during brief exposure, which dissipated with time as indicated by enhanced levels of catalase in heart and liver of BB group.

CONCLUSION

Long-term feeding of BB-enriched diet lowered blood pressure, preserved renal hemodynamics, and improved redox status in kidneys of hypertensive rats and concomitantly demonstrated the potential to delay or attenuate development of hypertension-induced renal injury, and these effects appear to be mediated by a short-term hormetic response.

Protective effects of peoniflorin against hydrogen peroxide-induced oxidative stress in human umbilical vein endothelial cells

Peoniflorin (PF), extracted from the root of Paeonia lactiflora Pall., has been reported to have anti-inflammation and antioxidant effects in several animal models. Herein, we investigated the protective effects of PF against hydrogen peroxide (H(2)O(2))-induced oxidative damage in human umbilical vein endothelial cells (HUVECs). HUVECs were treated by H(2)O(2) (240 µmol/L) with or without PF. PF significantly increased the percent cell viability of HUVECs injured by H(2)O(2) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. By flow cytometric analysis, PF markedly attenuated H(2)O(2)-induced apoptosis and intracellular reactive oxygen species production. In addition, PF also displayed a dose-dependent reduction of lactate dehydrogenase leakage, malondialdehyde formation, and caspase-3 proteolytic activities in H(2)O(2)-treated cells, which was accompanied with a restoration of the activities of endogenous antioxidants, including total superoxide dismutase and glutathione peroxidase. Finally, Western blot data revealed that H(2)O(2) upregulated phosphorylation of extracellular signal-regulated kinase 1/2 in HUVECs, which was almost completely reversed by PF. Taken together, our data provide the first evidence that PF has a protective ability against oxidative damage in HUVECs. PF may be a candidate medicine for the treatment of vascular diseases associated with oxidative stress.

Soluble guanylate cyclase stimulation prevents fibrotic tissue remodeling and improves survival in salt-sensitive Dahl rats

BACKGROUND

A direct pharmacological stimulation of soluble guanylate cyclase (sGC) is an emerging therapeutic approach to the management of various cardiovascular disorders associated with endothelial dysfunction. Novel sGC stimulators, including riociguat (BAY 63-2521), have a dual mode of action: They sensitize sGC to endogenously produced nitric oxide (NO) and also directly stimulate sGC independently of NO. Little is known about their effects on tissue remodeling and degeneration and survival in experimental malignant hypertension.

METHODS AND RESULTS

Mortality, hemodynamics and biomarkers of tissue remodeling and degeneration were assessed in Dahl salt-sensitive rats maintained on a high salt diet and treated with riociguat (3 or 10 mg/kg/d) for 14 weeks. Riociguat markedly attenuated systemic hypertension, improved systolic heart function and increased survival from 33% to 85%. Histological examination of the heart and kidneys revealed that riociguat significantly ameliorated fibrotic tissue remodeling and degeneration. Correspondingly, mRNA expression of the pro-fibrotic biomarkers osteopontin (OPN), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and plasminogen activator inhibitor-1 (PAI-1) in the myocardium and the renal cortex was attenuated by riociguat. In addition, riociguat reduced plasma and urinary levels of OPN, TIMP-1, and PAI-1.

CONCLUSIONS

Stimulation of sGC by riociguat markedly improves survival and attenuates systemic hypertension and systolic dysfunction, as well as fibrotic tissue remodeling in the myocardium and the renal cortex in a rodent model of pressure and volume overload. These findings suggest a therapeutic potential of sGC stimulators in diseases associated with impaired cardiovascular and renal functions.

Relative contributions of mitochondria and NADPH oxidase to deoxycorticosterone acetate-salt hypertension in mice

We assessed the relative contribution of the mitochondrial respiratory chain and NADPH (nicotinamide adenine dinucleotide phosphate) oxidase to deoxycorticosterone acetate (DOCA)-salt hypertension in mice. The daily mean arterial pressure was monitored by radiotelemetry in DOCA-salt-treated mice given vehicle or the mitochondrial respiratory chain complex I inhibitor rotenone. This treatment produced remarkable attenuation of DOCA-salt hypertension. Similar results were obtained with other inhibitors of mitochondrial function, including 5-hydroxydecanoate (specific for mitochondrial potassium-ATP channels), benzylguanidine (complexes I and III), and the cell-permeable manganese tetrakis (4-benzoic acid) porphyrin (a mimic of mitochondrial superoxide dismutase). In parallel with the blood pressure-lowering effect of rotenone, the DOCA-salt-induced increases in urinary 8-isoprostane excretion and in reactive oxygen species production of isolated kidney mitochondria were both significantly attenuated. Conversely, the DOCA-salt-induced reduction of urinary nitrate/nitrite excretion was significantly elevated. Following DOCA-salt treatment, mice deficient in NADPH oxidase subunits gp91(phox) or p47(phox) exhibited a partial attenuation of the hypertensive response at early but not later time points. Thus, the mitochondrial respiratory chain is a major source of oxidative stress in DOCA-salt hypertension, whereas NADPH oxidase may have a relatively minor role during the early stage of hypertension.

Salt-induced hemodynamic regulation mediated by nitric oxide

Excess daily salt intake impairs vasodilatation and enhances vasoconstriction, resulting in reduction of regional blood flow and elevation of blood pressure in healthy individuals and hypertensive patients with either salt sensitivity or not tested for salt sensitivity or not evaluated for salt sensitivity. The mechanism may involve decreased production of nitric oxide via endothelial nitric oxide synthase (eNOS), impaired bioavailability of nitric oxide, and elevated plasma levels of asymmetric dimethylarginine (ADMA). Experimental animals, irrespective of salt sensitivity, although less extensive in those with salt-resistance, fed a high-salt diet have deteriorated endothelial functions; the mechanisms involved include an impairment of eNOS activation, a decrease in eNOS expression, and an increase in oxidative stress and ADMA. The imbalance of interactions between nitric oxide and angiotensin II is also involved in salt sensitivity. Deficiency of nitric oxide formed via neuronal NOS and inducible NOS may contribute to salt-induced hypertension. Reduced daily salt intake, therefore, would be the most rational prophylactic measure against the development of hypertension.

Renal protective effects of N-acetyl-Ser-Asp-Lys-Pro in deoxycorticosterone acetate-salt hypertensive mice

BACKGROUND

Hypertension-induced renal injury is characterized by inflammation, fibrosis and proteinuria. Previous studies have demonstrated that N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP) inhibits renal damage following diabetes mellitus and antiglomerular basement membrane nephritis. However, its effects on low-renin hypertensive nephropathy are not known. Thus, we hypothesized that Ac-SDKP has renal protective effects on deoxycorticosterone acetate (DOCA)-salt hypertensive mice, decreasing inflammatory cell infiltration, matrix deposition and albuminuria.

METHOD

We uninephrectomized 16-week-old C57BL/6J mice and treated them with either placebo, DCOA (10 mg/10 g body weight subcutaneous) and 1% sodium chloride with 0.2% potassium chloride in drinking water (DOCA-salt) or DOCA-salt with Ac-SDKP (800 μg/kg per day) for 12 weeks. We measured blood pressure, urine albumin, glomerular matrix, renal collagen content, monocyte/macrophage infiltration and glomerular nephrin expression.

RESULTS

Treatment with DOCA-salt significantly increased blood pressure (P < 0.01), which remained unaltered by Ac-SDKP. Ac-SDKP decreased DOCA-salt-induced renal collagen deposition, glomerular matrix expansion and monocyte/macrophage infiltration. Moreover, DOCA-salt-induced increase in albuminuria was normalized by Ac-SDKP (controls, 10.8 ± 1.7; DOCA-salt, 41 ± 5; DOCA-salt + Ac-SDKP, 13 ± 3 μg/10 g body weight per 24 h; P < 0.001, DOCA-salt vs. DOCA-salt + Ac-SDKP). Loss of nephrin reportedly causes excess urinary protein excretion; therefore, we determined whether Ac-SDKP inhibits proteinuria by restoring nephrin expression in the glomerulus of hypertensive mice. DOCA-salt significantly downregulated glomerular nephrin expression (controls, 37 ± 8; DOCA-salt, 10 ± 1.5% of glomerular area; P < 0.01), which was partially reversed by Ac-SDKP (23 ± 4.0% of glomerular area; P = 0.065, DOCA-salt vs. DOCA-salt + Ac-SDKP).

CONCLUSION

We concluded that Ac-SDKP prevents hypertension-induced inflammatory cell infiltration, collagen deposition, nephrin downregulation and albuminuria, which could lead to renoprotection in hypertensive mice.

L/N-type calcium channel blocker cilnidipine ameliorates proteinuria and inhibits the renal renin-angiotensin-aldosterone system in deoxycorticosterone acetate-salt hypertensive rats

Cilnidipine, an N/L-type calcium channel blocker, has been reported to inhibit sympathetic nerve activity and has a greater renoprotective effect than L-type calcium channel blockers. To investigate the hypothesis that cilnidipine might ameliorate advanced hypertensive nephropathy and inhibit the renal renin-angiotensin-aldosterone system, cilnidipine (1 mg per kg per day) or amlodipine (1 mg per kg per day) was administered to uninephrectomized deoxycorticosterone (DOCA)-salt hypertensive rats (DOCA-salt) for 4 weeks by gavage. Although the blood pressure in the DOCA-salt group was higher than that of control, neither cilnidipine nor amlodipine had any effect on the increase in blood pressure in the DOCA-salt group. The DOCA (40 mg per kg per week, subcutaneously (s.c.)) and salt (1% NaCl in drinking water) treatment significantly aggravated the levels of urinary protein excretion and creatinine clearance and increased glomerulosclerosis and collagen deposition in the tubulointerstitial area of the kidney. These effects were attenuated by cilnidipine treatment. Reverse transcription-polymerase chain reaction analysis revealed that the renal expression of mRNA for collagen I/IV and transforming growth factor-β was enhanced in the DOCA-salt group and that the overexpression of these molecules was suppressed by cilnidipine. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived superoxide production in the kidney and urinary norepinephrine excretion, which were enhanced in the DOCA-salt group, were suppressed by cilnidipine. Cilnidipine also decreased the activity and expression of angiotensin-converting enzyme (ACE) and the aldosterone concentration in the renal homogenate. Although neither cilnidipine nor amlodipine had any effect on the increased blood pressure in the DOCA-salt group, these renal changes were not induced by treatment with amlodipine. In conclusion, cilnidipine inhibited renal dysfunction, sympathetic nerve activity and renal renin-angiotensin-aldosterone system in the DOCA-salt group.

High salt intake delayed angiotensin II-induced hypertension in mice with a genetic variant of NADPH oxidase

BACKGROUND

gp91(PHOX), a catalytic subunit of NAD(P)H oxidase, is involved in angiotensin II (Ang II)-induced superoxide (O₂⁻) generation. This study was designed to examine the hypothesis that an enhancement in O₂⁻ generation due to elevated Ang II induces salt-sensitivity, which contributes to the development of hypertension.

METHODS

Assessment of blood pressure and renal excretory responses to Ang II infusion (2.2 ng·min/g) for 2 weeks via osmotic minipump was made in knockout (KO; n = 20) mice lacking the gene for gp91(PHOX) which were fed on either normal-salt (NS; 0.04% NaCl) or high-salt (HS, 4% NaCl) diet and compared these responses with those in wild-type (WT; n = 23) mice.

RESULTS

Ang II induced increase in systolic blood pressure (SBP) was started within the 4th day in all groups except in HS fed KO mice in which SBP increased after the 10(th) day of Ang II infusion. The increases in SBP were lower in KO than WT mice at the end of 2-week infusion period. In Ang II + HS fed KO mice, the urinary excretion rate of nitrite/nitrate (U(NOx)V) markedly increased but 8-isoprostane excretion rate remained unchanged. These findings indicate that an increase in nitric oxide (NO) with a lack of O₂⁻ formation was involved in the delayed hypertension in Ang II + HS fed KO mice.

CONCLUSION

These data suggest that an enhanced O₂⁻ activity and its interaction with NO contribute to the early developmental phase of Ang II-induced salt-sensitive hypertension.American Journal of Hypertension (2011). doi:10.1038/ajh.2010.173.

Feeding blueberry diets inhibits angiotensin II-converting enzyme (ACE) activity in spontaneously hypertensive stroke-prone rats

Feeding flavonoid-rich blueberries to spontaneously hypertensive stroke-prone rats (SHRSP) lowers blood pressure. To determine whether this is due to inhibition of angiotensin-converting enzyme (ACE) activity, as seen with other flavanoid-rich foods, we fed blueberries to SHRSP and normotensive rats and analyzed ACE activity in blood and tissues. After 2 weeks on a control diet, the hypertensive rats showed 56% higher levels of ACE activity in blood as compared with the normotensive rats (p < 0.05). Feeding a 3% blueberry diet for 2 weeks lowered ACE activity in the SHRSP (p < 0.05) but not the normotensive rats. ACE activity in plasma of SHRSP was no longer elevated at weeks 4 and 6, but blueberry feeding inhibited ACE in SHRSP after 6 weeks. Blueberry diets had no effect on ACE activity in lung, testis, kidney, or aorta. Our results suggest that dietary blueberries may be effective in managing early stages of hypertension, partially due to an inhibition of soluble ACE activity.