A missing link between a high salt intake and blood pressure increase

Bradykinin deficiency causes high blood pressure in mice

Bradykinin has a wide variety of physiological functions, including vasodilation and blood pressure reduction. However, the physiological roles of bradykinin are not fully understood. We used the CRISPR/Cas9 method to generate BKdelK1 and BKdelK2 mutant mice, targeting the BK portion of mouse kininogen1 and kininogen2 genes, respectively. The BKdelK1 and BKdelK2 mutant mice had about 50% reductions in plasma low molecular weight kininogen and trypsin-released BK, compared to wild mice. Both BKdelK1 and BKdelK2 mice had significantly elevated systolic blood pressure compared to WT mice. These results suggest that plasma LKNG is a source of KNG in the vascular kallikrein-kinin system and contributes to maintaining lower systolic blood pressure.

Green tea could improve elderly hypertension by modulating arterial stiffness, the activity of the renin/angiotensin/aldosterone axis, and the sodium-potassium pumps in old male rats

Hypertension is a major health problem common in the elderly people. Green tea is a popular beverage recommended in folk medicine for lowering blood pressure. However, the molecular mechanisms involved in the antihypertensive effects of green tea are not fully understood. Therefore, the aim of this study was to investigate the antihypertensive effects of green tea on high-salt diet-induced hypertension in old male rats. Forty old male rats were divided into five groups: control, hypertensive, and hypertensive-green tea (2, 4, and 6 g/kg). Heart rate (HR) and systolic blood pressure (SBP) were measured. Cardiac and renal histology were also performed. Lipid profile, NO, angiotensin II (Ang II), and aldosterone were determined, and the expression of eNOS, ATIR and ATIIR, aldosterone receptor, and Atp1a1 were measured. Green tea could significantly decrease HR and SBP, lipid profiles, renin-angiotensin II-aldosterone system activity, and Ang II signaling in kidney tissue of hypertensive rats (p < .01). It also increased Atp1a1, Nrf2, and eNOS expression along with antioxidant enzymes activity and NO concentration (p < .05) and decreased NF-ĸB and iNOS expression and IL-1β levels in the heart, kidneys, and aorta of rats with hypertension. It can be concluded that green tea can improve salt-induced blood pressure by modulating the function of the renin-angiotensin-aldosterone system, enhancing the synthesis of nitric oxide in the endothelium, increasing antioxidant activity and suppressing inflammation in the heart and kidney, improving the expression of the sodium-potassium pump, and reduction in serum lipids and glucose in aged male rats. PRACTICAL APPLICATIONS: The results of this study showed that green tea could improve hypertension in elderly rats by modulating (1) the expression of the sodium-potassium pump in the heart, kidney, and aortic tissues, (2) the activity of the renin-angiotensin II-aldosterone system in kidney, (3) enhancing antioxidant and anti-inflammatory activities in the heart, aorta, and kidneys, (4) enhancing the synthesis of nitric oxide in the endothelium, and (5) lowering lipid profile. The results of these studies show that the consumption of green tea and its products can be a good candidate for the prevention of cardiovascular diseases such as hypertension in the elderly. In addition, attention to its bioactive compounds can be considered by researchers as an independent therapeutic strategy or adjunctive therapy for the treatment of hypertension.

The Effect of Global Warming on Complex Disorders (Mental Disorders, Primary Hypertension, and Type 2 Diabetes)

Multiple studies imply a strong relationship between global warming (GW) and complex disorders. This review summarizes such reports concentrating on three disorders-mental disorders (MD), primary hypertension, and type 2 diabetes (T2D). We also attempt to point at potential mechanisms mediating the effect of GW on these disorders. Concerning mental disorders, immediate candidates are brain levels of heat-shock proteins (HSPs). In addition, given that heat stress increases reactive oxygen species (ROS) levels which may lead to blood-brain barrier (BBB) breakdown and, hence, enhanced protein extravasation in the brain, this might finally cause, or exacerbate mental health. As for hypertension, since its causes are incompletely understood, the mechanism(s) by which heat exposure affects blood pressure (BP) is an open question. Since the kidneys participate in regulating blood volume and BP they are considered as a site of heat-associated disease, hence, we discuss hyperosmolarity as a potential mediator. In addition, we relate to autoimmunity, inflammation, sodium excretion, and HSP70 as risk factors that might play a role in the effect of heat on hypertension. In the case of T2D, we raise two potential mediators of the effect of exposure to ambient hot environment on the disease's incidence-brown adipose tissue metabolism and HSPs.

Pathophysiology of essential hypertension: an update

INTRODUCTION

Hypertension is caused by increased cardiac output and/or increased peripheral resistance. Areas covered: The various mechanisms affecting cardiac output/peripheral resistance involved in the development of essential hypertension are covered. These include genetics; sympathetic nervous system overactivity; renal mechanisms: excess sodium intake and pressure natriuresis; vascular mechanisms: endothelial cell dysfunction and the nitric oxide pathway; hormonal mechanisms: the renin-angiotensin-aldosterone system (RAAS); obesity, obstructive sleep apnea (OSA); insulin resistance and metabolic syndrome; uric acid; vitamin D; gender differences; racial, ethnic, and environmental factors; increased left ventricular ejection force and hypertension and its association with increased basal sympathetic activity - cortical connections. Expert commentary: Maximum association of hypertension is found with sympathetic overactivity which is directly or indirectly involved in different mechanisms of hypertension including RAAS, OSA, obesity, etc.. It is not overt sympathetic activity but disturbed basal sympathetic tone. Basal sympathetic tone arises from hypothalamus; possibly affected by cortical influences. Therefore, hypertension is not merely a disease of circulatory system alone. Its pathogenesis involves alteration in ANS (autonomic nervous system) and likely in cortical-hypothalamic connections. Assessment of ANS and cortical-hypothalamic connections may be required for better understanding of hypertension.

Genetically‑modified stem cells in treatment of human diseases: Tissue kallikrein (KLK1)‑based targeted therapy (Review)

The tissue kallikrein-kinin system (KKS) is an endogenous multiprotein metabolic cascade which is implicated in the homeostasis of the cardiovascular, renal and central nervous system. Human tissue kallikrein (KLK1) is a serine protease, component of the KKS that has been demonstrated to exert pleiotropic beneficial effects in protection from tissue injury through its anti-inflammatory, anti-apoptotic, anti-fibrotic and anti-oxidative actions. Mesenchymal stem cells (MSCs) or endothelial progenitor cells (EPCs) constitute populations of well-characterized, readily obtainable multipotent cells with special immunomodulatory, migratory and paracrine properties rendering them appealing potential therapeutics in experimental animal models of various diseases. Genetic modification enhances their inherent properties. MSCs or EPCs are competent cellular vehicles for drug and/or gene delivery in the targeted treatment of diseases. KLK1 gene delivery using adenoviral vectors or KLK1 protein infusion into injured tissues of animal models has provided particularly encouraging results in attenuating or reversing myocardial, renal and cerebrovascular ischemic phenotype and tissue damage, thus paving the way for the administration of genetically modified MSCs or EPCs with the human tissue KLK1 gene. Engraftment of KLK1-modified MSCs and/or KLK1-modified EPCs resulted in advanced beneficial outcome regarding heart and kidney protection and recovery from ischemic insults. Collectively, findings from pre-clinical studies raise the possibility that tissue KLK1 may be a novel future therapeutic target in the treatment of a wide range of cardiovascular, cerebrovascular and renal disorders.

Dysregulation of microRNAs and renin-angiotensin system in high salt diet-induced cardiac dysfunction in uninephrectomized rats

Uninephrectomy is not associated with major adverse events in cardiovascular and renal functions of live kidney donors. The effect of high salt diet on the quality of life of live kidney donors is largely unknown. Hence in this study, we aimed to determine the effect of high salt diet on the alterations of renin-angiotensin system and microRNAs leading to CV and renal dysfunction in uninephrectomized rats. In order to mimic clinical scenario, uninephrectomized male Sprague Dawley rats were fed initially with normal pellet diet for 12 weeks and then for 20 weeks with high salt (10% w/w NaCl) diet. At the end of the study, biochemical, functional, histological and molecular parameters were measured. High salt diet feeding resulted in renal dysfunction & fibrosis, decreased baroreflex sensitivity, increased in vivo cardiovascular reactivity to angiotensin II owing to upregulation of angiotensin II type 1 receptors and L-type calcium channels leading to cardiovascular dysfunction in uninephrectomized rats (UNX+HSD) worse than that of normal (binephric) rats fed with high salt diet (HSD). Protein expression of functional and hypertrophic protein markers revealed decreased SERCA, p-AMPK and increased p-AKT. Interestingly, levels of miR-25, miR-451 and miR-155 increased and miR-99 decreased in heart of uninephrectomized rats fed with high salt. However, circulating miR-25 and miR-451 levels decreased and miR-99b increased in these animals. Our study points out that since tissue and circulating levels of miRNAs are not similar, caution must be exercised during the usage of miRs as diagnostic or prognostic biomarkers. To our knowledge, we are the first to show that epigenetic alterations result in cardiac dysfunction in uninephrectomized rats fed with high salt diet.

State of the Art Reviews: Relationship Between Diet/ Physical Activity and Health

Obesity and 4 of the leading causes of death—heart disease, cancer, stroke, and type 2 diabetes mellitus—are related to lifestyle. The combination of a healthy weight, prudent diet, and daily physical activity clearly plays a role in primary, secondary, and tertiary prevention of these and other chronic diseases. Because nearly 65% of the adult population is overweight or obese, weight loss and maintenance are central to this review article. Improved lipid profiles, blood pressure, insulin sensitivity, and euglycemia are associated with weight loss or a normal body weight; thus, maintaining a healthy weight is a universal recommendation for health. The methods for improving lifestyle described in the section on obesity include assessing nutritional status and stages of change of the client, setting realistic goals, eating a diet high in fruits and vegetables with low-fat sources of dairy and protein, and achieving appropriate physical activity levels. The importance of physicians discussing weight with clients and vice versa is stressed. The common features of lifestyle-related diseases make them amenable to similar lifestyle interventions.

Salt-Sensitive Hypertension: Perspectives on Intrarenal Mechanisms

Salt sensitive hypertension is characterized by increases in blood pressure in response to increases in dietary salt intake and is associated with an enhanced risk of cardiovascular and renal morbidity. Although researchers have sought for decades to understand how salt sensitivity develops in humans, the mechanisms responsible for the increases in blood pressure in response to high salt intake are complex and only partially understood. Until now, scientists have been unable to explain why some individuals are salt sensitive and others are salt resistant. Although a central role for the kidneys in the development of salt sensitivity and hypertension has been generally accepted, it is also recognized that hypertension is of multifactorial origin and a variety of factors can induce, or prevent, blood pressure responsiveness to the manipulation of salt intake. Excess salt intake in susceptible persons may also induce inappropriate central and sympathetic nervous system responses and increase the production of intrarenal angiotensin II, catecholamines and other factors such as oxidative stress and inflammatory cytokines. One key factor is the concomitant inappropriate or paradoxical activation of the intrarenal renin-angiotensin system, by high salt intake. This is reflected by the increases in urinary angiotensinogen during high salt intake in salt sensitive models. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for some individuals to retain salt and develop salt-dependent hypertension. In this review, we focus mainly on the renal contributions that provide the mechanistic links between chronic salt intake and the development of hypertension.

High salt-induced hypertension in B2 knockout mice is corrected by the ETA antagonist, A127722

BACKGROUND AND PURPOSE

The contribution of endothelin-1 (ET-1) in a B2KO mouse model of a high salt-induced arterial hypertension was investigated.

EXPERIMENTAL APPROACH

Wild-type (WT) or B2KO mice receiving a normal diet (ND) or a high-salt diet (HSD) were monitored by radiotelemetry up to a maximum of 18 weeks. At the 12th week of diet, subgroups under ND or HSD received by gavage the ETA antagonist A127722 during 5 days. In addition, blood samples were collected and, following euthanasia, the lungs, heart and kidneys were extracted, homogenized and assayed for ET-1 by RIA. In a separate series of experiments, the ETA antagonist, BQ123 was tested against the pressor responses to a NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) in anaesthetized WT and B2KO mice.

KEY RESULTS

In B2KO, but not WT mice, 12 weeks of HSD triggered a maximal increase of the mean arterial pressure (MAP) of 19.1 ± 2.8 mmHg, which was corrected by A127722 to MAP levels found in B2KO mice under ND. Significant increases in immunoreactive ET-1 were detected only in the lungs of B2KO mice under HSD. On the other hand, metabolic studies showed that sodium urinary excretion was markedly reduced in B2KO compared with WT mice under ND. Finally, BQ123 (2 mg·kg(-1)) reduced by 50% the pressor response to L-NAME (2 mg·kg(-1)) in B2KO, but not WT mice under anaesthesia.

CONCLUSIONS AND IMPLICATIONS

Our results support the concept that functional B2 receptors oppose high salt-induced increments in MAP, which are corrected by an ETA receptor antagonist in this mouse model of experimental hypertension.

Metabolomics approach reveals effects of antihypertensives and lipid-lowering drugs on the human metabolism

The mechanism of antihypertensive and lipid-lowering drugs on the human organism is still not fully understood. New insights on the drugs’ action can be provided by a metabolomics-driven approach, which offers a detailed view of the physiological state of an organism. Here, we report a metabolome-wide association study with 295 metabolites in human serum from 1,762 participants of the KORA F4 (Cooperative Health Research in the Region of Augsburg) study population. Our intent was to find variations of metabolite concentrations related to the intake of various drug classes and—based on the associations found—to generate new hypotheses about on-target as well as off-target effects of these drugs. In total, we found 41 significant associations for the drug classes investigated: For beta-blockers (11 associations), angiotensin-converting enzyme (ACE) inhibitors (four assoc.), diuretics (seven assoc.), statins (ten assoc.), and fibrates (nine assoc.) the top hits were pyroglutamine, phenylalanylphenylalanine, pseudouridine, 1-arachidonoylglycerophosphocholine, and 2-hydroxyisobutyrate, respectively. For beta-blockers we observed significant associations with metabolite concentrations that are indicative of drug side-effects, such as increased serotonin and decreased free fatty acid levels. Intake of ACE inhibitors and statins associated with metabolites that provide insight into the action of the drug itself on its target, such as an association of ACE inhibitors with des-Arg(9)-bradykinin and aspartylphenylalanine, a substrate and a product of the drug-inhibited ACE. The intake of statins which reduce blood cholesterol levels, resulted in changes in the concentration of metabolites of the biosynthesis as well as of the degradation of cholesterol. Fibrates showed the strongest association with 2-hydroxyisobutyrate which might be a breakdown product of fenofibrate and, thus, a possible marker for the degradation of this drug in the human organism. The analysis of diuretics showed a heterogeneous picture that is difficult to interpret. Taken together, our results provide a basis for a deeper functional understanding of the action and side-effects of antihypertensive and lipid-lowering drugs in the general population.

Bradykinin-forming components in Kuwaiti patients with type 2 diabetes

Diabetes is the most common risk factor in inducing hypertension, nephropathy and retinopathy. The bradykinin (BK)-forming system has been proposed to protect cardiovascular and renal functions. We therefore evaluated urinary active and proactive kallikrein, total kininogen, plasma tissue kallikrein, plasma creatinine, plasma glucose and plasma HbA1c in newly diagnosed untreated type 2 diabetic patients and healthy subjects. In diabetic patients, urinary and plasma tissue kallikrein concentrations were significantly increased. In addition, plasma prekallikrein levels were also significantly higher. However, urinary kininogen values were significantly reduced in diabetic patients when compared with healthy subjects. This is the first investigation among Kuwaiti Arab patients with type 2 diabetes showing abnormal activities in the BK-forming system. High levels of plasma prekallikrein may be a risk factor for developing high blood pressure as well as nephropathy. The urinary and plasma tissue kallikrein concentrations were higher in diabetic patients, which could indicate the hyperactivities of these components, and may result in increased levels of plasma glucose to induce diabetes. Furthermore, the urinary kininogen levels were reduced in diabetic patients. These alterations might reflect the utilization of urinary kininogen to form BK, a potent inflammatory agent. However, this hypothesis needs further investigation.

Tissue kallikrein-kinin therapy in hypertension and organ damage

Tissue kallikrein is a serine proteinase that cleaves low molecular weight kininogen to produce kinin peptides, which in turn activate kinin receptors to trigger multiple biological functions. In addition to its kinin-releasing activity, tissue kallikrein directly interacts with the kinin B2 receptor, protease-activated receptor-1, and gamma-epithelial Na channel. The tissue kallikrein-kinin system (KKS) elicits a wide spectrum of biological activities, including reducing hypertension, cardiac and renal damage, restenosis, ischemic stroke, and skin wound injury. Both loss-of-function and gain-of-function studies have shown that the KKS plays an important endogenous role in the protection against health pathologies. Tissue kallikrein/kinin treatment attenuates cardiovascular, renal, and brain injury by inhibiting oxidative stress, apoptosis, inflammation, hypertrophy, and fibrosis and promoting angiogenesis and neurogenesis. Approaches that augment tissue kallikrein-kinin activity might provide an effective strategy for the treatment of hypertension and associated organ damage.

Effects of Valsartan vs Amlodipin on renal function in salt loaded spontaneously hypertensive rats

The goal of this study was to compare the effects of valsartan and amlodipin on the systolic blood pressure and parameters specific to the renal function in salt loaded spontaneously hypertensive rats (SHR). 32 male SHR were used at age of 20 weeks and body weight ranging between 265-300 g. From 8 weeks of age tab water was replaced with a solution of NaCl (1%) given ad libitum. Rats were divided into 2 groups: valsartan treated group SHRVAL (n=16) in which valsartan was given at a dose of 10 mg/kg b. w. and amlodipine treated group SHRAMLO (n=16) in which amlodipine was given at a dose of 5 mg/kg b. w. For a period of 12 weeks we have evaluated the effect of the investigated drugs on systolic blood pressure, body weight and renal function tests. In salt loaded rats amlodipine was more effective in reducing the systolic blood pressure in contrast to valsartan who had more pronounced effect on renal parameters most evident in proteinuria. Since both treatment groups have different mechanism of action a combination therapy may be beneficial in improving renal function in SHR rats.

Renal (tissue) kallikrein-kinin system in the kidney and novel potential drugs for salt-sensitive hypertension

A large variety of antihypertensive drugs, such as angiotensin converting enzyme inhibitors, diuretics, and others, are prescribed to hypertensive patients, with good control of the condition. In addition, all individuals are generally believed to be salt sensitive and, thus, severe restriction of salt intake is recommended to all. Nevertheless, the physiological defense mechanisms in the kidney against excess salt intake have not been well clarified. The present review article demonstrated that the renal (tissue) kallikrein-kinin system (KKS) is ideally situated within the nephrons of the kidney, where it functions to inhibit the reabsorption of NaCl through the activation of bradykinin (BK)-B2 receptors localized along the epithelial cells of the collecting ducts (CD). Kinins generated in the CD are immediately inactivated by two kidney-specific kinin-inactivating enzymes (kininases), carboxypeptidase Y-like exopeptidase (CPY), and neutral endopeptidase (NEP). Our work demonstrated that ebelactone B and poststatin are selective inhibitors of these kininases. The reduced secretion of the urinary kallikrein is linked to the development of salt-sensitive hypertension, whereas potassium ions and ATP-sensitive potassium channel blockers ameliorate salt-sensitive hypertension by accelerating the release of renal kallikrein. On the other hand, ebelactone B and poststatin prolong the life of kinins in the CD after excess salt intake, thereby leading to the augmentation of natriuresis and diuresis, and the ensuing suppression of salt-sensitive hypertension. In conclusion, accelerators of the renal kallikrein release and selective renal kininase inhibitors are both novel types of antihypertensive agents that may be useful for treatment of salt-sensitive hypertension.

A common polymorphism in the tissue kallikrein gene is associated with increased urinary excretions of calcium and sodium in Japanese volunteers

Tissue kallikrein is an enzyme involved in the release of kinin in peripheral tissues. It is believed to regulate hemodynamics and electrolyte transport in the kidney. The present study analyzed polymorphisms of tissue kallikrein in Japanese volunteers and examined the associations between allele H in the promoter region, which has been shown to have decreased promoter activity, and urinary kallikrein activity and physiological parameters in subjects on an ad libitum diet. Ninety and 73 volunteers were analyzed for the promoter and coding regions of the tissue kallikrein gene, respectively. The allelic frequency of allele H was found to be 24%. One synonymous and three non-synonymous polymorphisms were found in the coding regions. Urinary kallikrein activity was not significantly decreased in subjects with allele H compared to those without allele H, although they were low in two homozygotes of allele H. Urinary excretions of calcium and sodium were larger in the subjects with allele H than in those without. It is concluded that allele H is a common polymorphism in Japanese and may contribute to decreased reabsorptions of calcium and sodium in the kidney. Further interventional studies are needed to clarify the phenotype of allele H with respect to renal electrolyte handling.

The role of the kallikrein-kinin system genes in the salt sensitivity of blood pressure: the GenSalt Study

The current study comprehensively examined the association between common genetic variants of the kallikrein-kinin system (KKS) and blood pressure salt sensitivity. A 7-day low-sodium followed by a 7-day high-sodium dietary intervention was conducted among 1,906 Han Chinese participants recruited from 2003 to 2005. Blood pressure was measured by using a random-zero sphygmomanometer through the study. A total of 205 single nucleotide polymorphisms (SNPs) covering 11 genes of the KKS were selected for the analyses. Genetic variants of the bradykinin receptor B2 gene (BDKRB2) and the endothelin converting enzyme 1 gene (ECE1) showed significant associations with the salt-sensitivity phenotypes even after adjustment for multiple testing. Compared with the major G allele, the BDKRB2 rs11847625 minor C allele was significantly associated with increased systolic blood pressure responses to low-sodium intervention (P = 0.0001). Furthermore, a haplotype containing allele C was associated with an increased systolic blood pressure response to high-sodium intervention (P = 0.0009). Seven highly correlated ECE1 SNPs were shown to increase the diastolic blood pressure response to low-sodium intervention (P values ranged from 0.0003 to 0.002), with 2 haplotypes containing these 7 SNPs also associated with this same phenotype (P values ranged from 0.0004 to 0.002). In summary, genetic variants of the genes involved in the regulation of KKS may contribute to the salt sensitivity of blood pressure.

Association and interaction of -58C>T and ±9 bp polymorphisms of BDKRB2 gene causing susceptibility to essential hypertension

INTRODUCTION

Bradykinin, a vasodilator by nature has been documented to have a protective role against hypertension and cardiovascular complications. Polymorphisms of bradykinin B2 receptor (BDKRB2) gene are reported to be predisposing factors for hypertension. Evaluation of the association between -58C>T and ±9 bp polymorphisms of BDKRB2 with essential hypertension (EHT) was attempted.

METHODS

Two hundred and fourteen primary hypertensives and 249 controls were genotyped for the selected markers by polymerase chain reaction, gel electrophoresis (±9 bp), and SSCP (-58C>T).

RESULTS

While -58C>T polymorphism did not reveal any association with EHT, ±9 bp polymorphism showed a significant association with high risk for heterozygotes (+9/-9) when tested against the pooled frequencies of homozygotes (OR [odds ratio] = 1.63, 95% confidence interval [CI] = 1.12-2.38, P = .02), and this risk was 1.7 folds high in males (OR = 1.74, 95% CI = 1.05-2.86, P = .06) and 1.9 folds high in familial cases (OR = 1.96, 95% CI = 1.09-3.53, P = .04). In contrast, significant protective effect was observed for -9/-9 genotype against EHT when tested under dominant model in general (OR = 0.59, 95% CI = 0.41-0.86, P = .01), in males (OR = 0.49, 95% CI = 0.30-0.82, P = .01), and in familial cases (OR = 0.50, 95% CI = 0.28-0.89, P = .04). Significant risk for +9 bp allele was observed in general (OR = 1.39, 95% CI = 1.05-1.86, P = .04) and in males (OR = 1.65, 95% CI = 1.13-2.41, P = .02). The interaction information analysis revealed a synergistic effect between the two polymorphisms contributing to EHT. +9/+9 genotype of ±9 bp polymorphism when present in combination with CC genotype of -58C>T polymorphism showed 2.2-fold higher risk for developing EHT.

CONCLUSIONS

The results suggest that allele +9 bp might be a risk factor for EHT in general and specially in males. Markers -58C>T and ±9 bp may act synergistically causing susceptibility to EHT.

The Effects of Captopril on Cardiac Regression, Blood Pressure and Bradykinin Components in Diabetic Wistar Kyoto Rats

The present study examined the left ventricular wall thickness (LVWT), total urinary kallikrein, total plasma kininogen and mean arterial blood pressure (MABP) in diabetic and non-diabetic Wistar Kyoto (WKY) rats. The MABP was significantly raised (P<0.01) in diabetic WKY rats compared to the respective controls. The LVWT was also significantly (P<0.01) increased in diabetic WKY rats than that of control WKY rats. The mean total urinary kallikrein level and the mean total plasma kininogen level were higher (P<0.01) in diabetic WKY rats, when these rats were treated with captopril (40 mg/kg and 80 mg/kg) against the mean value obtained from control WKY rats. In conclusion, this investigation suggests that diabetes induced in these rats can cause hypertension, increased LVWT and changes in the BK-forming components. Captopril treatment caused reduction in MABP, regression of LVWT and alterations in bradykinin (BK)-forming components. The possible significance of these observations is discussed.

High-salt diet and hypertension: focus on the renin-angiotensin system

A high-salt diet is one of the major risk factors in the development and maintenance of hypertension. Numerous experimental and observational studies have confirmed the association of sodium intake with blood pressure levels. The effects of a high-salt diet are related to the function of the renin-angiotensin system, which is normally suppressed by a high-salt diet. Endothelial dysfunction probably plays an important role in the influence of high sodium intake on blood pressure, although the exact mechanisms remain elusive. Genetic factors are known to be very important, and various consomic and congenic rat strains as animal models have proven to be very useful in bringing us a step closer to understanding the interaction between salt intake and hypertension. In this article, experimental data obtained in studies on animals and humans, as well as epidemiological data are reviewed.

Therapeutic targeting of mitochondrial superoxide in hypertension

RATIONALE

Superoxide (O2(-) ) has been implicated in the pathogenesis of many human diseases including hypertension; however, commonly used antioxidants have proven ineffective in clinical trials. It is possible that these agents are not adequately delivered to the subcellular sites of superoxide production.

OBJECTIVE

Because the mitochondria are important sources of reactive oxygen species, we postulated that mitochondrial targeting of superoxide scavenging would have therapeutic benefit.

METHODS AND RESULTS

In this study, we found that the hormone angiotensin (Ang II) increased endothelial mitochondrial superoxide production. Treatment with the mitochondria-targeted antioxidant mitoTEMPO decreased mitochondrial O2(-), inhibited the total cellular O2(-), reduced cellular NADPH oxidase activity, and restored the level of bioavailable NO. These effects were mimicked by overexpressing the mitochondrial MnSOD (SOD2), whereas SOD2 depletion with small interfering RNA increased both basal and Ang II-stimulated cellular O2(-). Treatment of mice in vivo with mitoTEMPO attenuated hypertension when given at the onset of Ang II infusion and decreased blood pressure by 30 mm Hg following establishment of both Ang II-induced and DOCA salt hypertension, whereas a similar dose of nontargeted TEMPOL was not effective. In vivo, mitoTEMPO decreased vascular O2(-), increased vascular NO production and improved endothelial-dependent relaxation. Interestingly, transgenic mice overexpressing mitochondrial SOD2 demonstrated attenuated Ang II-induced hypertension and vascular oxidative stress similar to mice treated with mitoTEMPO.

CONCLUSIONS

These studies show that mitochondrial O2(-) is important for the development of hypertension and that antioxidant strategies specifically targeting this organelle could have therapeutic benefit in this and possibly other diseases.

Activation of the Bradykinin System by Angiotensin-Converting Enzyme Inhibitors

The Bradykinin (BK) system has a very significant role in the regulation of blood pressure (BP). Hence, reduced activity of BK receptors mediated via decreased circulating endogenous kinin might explain the cause of high BP. This system also governs the activation of the angiotensin system at various axes in control of the physiological BP. The BK receptor antagonists can block the hypotensive action of angiotensin-converting enzyme inhibitors (ACEIs) in hypertensive and normotensive animals. The hypotensive action of BK is highly increased with ACEIs or kininase II inhibitor treatment. The development of specific BK agonists may provide a new direction to explore the experimental approach for examining the role of BK in hypertension.

A Novel Category of Anti-Hypertensive Drugs for Treating Salt-Sensitive Hypertension on the Basis of a New Development Concept

Terrestrial animals must conserve water and NaCl to survive dry environments. The kidney reabsorbs 95% of the sodium filtered from the glomeruli before sodium reaches the distal connecting tubules. Excess sodium intake requires the renal kallikrein-kinin system for additional excretion. Renal kallikrein is secreted from the distal connecting tubule cells of the kidney, and its substrates, low molecular kininogen, from the principal cells of the cortical collecting ducts (CD). Formed kinins inhibit reabsorption of NaCl through bradykinin (BK)-B₂ receptors, localized along the CD. Degradation pathway of BK by kinin-destroying enzymes in urine differs completely from that in plasma, so that ACE inhibitors are ineffective. Urinary BK is destroyed mainly by a carboxypeptidase-Y-like exopeptidase (CPY) and partly by a neutral endopeptidase (NEP). Inhibitors of CPY and NEP, ebelactone B and poststatin, respectively, were found. Renal kallikrein secretion is accelerated by potassium and ATP-sensitive potassium (KATP) channel blockers, such as PNU-37883A. Ebelactone B prevents DOCA-salt hypertension in rats. Only high salt intake causes hypertension in animals deficient in BK-B2 receptors, tissue kallikrein, or kininogen. Hypertensive patients, and spontaneously hypertensive rats, excrete less kallikrein than normal subjects, irrespective of races, and become salt-sensitive. Ebelactone B, poststatin, and KATP channel blockers could become novel antihypertensive drugs by increase in urinary kinin levels. Roles of kinin in cardiovascular diseases were discussed.

Immune regulation and vascular inflammation in genetic hypertension

Immune cells have been implicated in the pathogenesis of hypertension. We hypothesized that under the influence of chromosome (chr)2, T lymphocytes contribute to vascular inflammation in genetic salt-sensitive hypertension. Normotensive (Brown Norway), hypertensive (Dahl salt-sensitive), and consomic rats (SSBN2; in which chr2 has been transferred from Brown Norway to Dahl rats) were studied. Systolic blood pressure, measured by tail cuff, and aortic preproendothelin mRNA, measured by quantitative RT-PCR, were elevated in Dahl rats compared with Brown Norway rats and were reduced in SSBN2 rats compared with Dahl rats (P < 0.01). Compared with Brown Norway rats, Dahl rats exhibited increased inflammatory markers and mediators such as nuclear translocation of the aortic p65 subunit of NF-kappaB as well as VCAM-1, ICAM-1, chemokine (C-C motif) receptor 5, and CD4 mRNA, all of which were reduced in SSBN2 rats. Aortic CD8 mRNA was equally increased in Dahl and SSBN2 rats relative to Brown Norway rats. CD4(+) T cell infiltration in the aorta of SSBN2 rats was reduced compared with Dahl rats, whereas the aortic protein expression of Foxp3b and immunosuppressors transforming growth factor (TGF)-beta(1) and IL-10, the three markers associated with the regulatory T cell lineage, were enhanced in SSBN2 rats. Activation in vitro of T cells demonstrated that CD4(+)CD25(+) and CD8(+)CD25(+) cells (Tregs) produce IL-10 in SSBN2 rats. Thus, increased vascular inflammatory responses and hypertension in a genetic salt-sensitive hypertensive rodent model are reduced by transfer of chr2 from a normotensive strain, and this is associated with enhanced levels of immunosuppressive mediators.

Blood pressures, heart rate and locomotor activity during salt loading and angiotensin II infusion in protease-activated receptor 2 (PAR2) knockout mice

Background

In this study we used radiotelemetry to measure hemodynamic variables and locomotor activity in conscious unrestrained male Protease-Activated Receptor 2 (PAR-2) knockout mice in order to provide a detailed assessment of their blood pressure phenotype. In addition we tested for an influence of PAR-2 on salt-sensitivity (8% versus 0.5% NaCl diet, 2.5 weeks) and angiotensin II-induced hypertension (1 μg Ile⁵-angiotensin II/kg/min versus 0.25 μl/h saline, 2 weeks).

Results

Systolic arterial pressures of PAR-2 -/- (129 ± 1 mmHg, n = 21, P < 0.05) were statistically higher than those of C57BL/6J (124 ± 1 mmHg, n = 33) throughout the 24 h period under baseline conditions. Pulse pressures in PAR-2 -/- were also significantly elevated (33 ± 1 mmHg versus 30 ± 1 mmHg, P < 0.05), whereas diastolic arterial pressures were not. Heart rates in PAR-2 -/- were not significantly different than controls, with the exception that heart rate of PAR-2 -/- was 23 beats per min higher than controls (P < 0.001) during periods of nocturnal activity. The diurnal pattern and intensity of locomotor activity were not found to differ between strains. A high salt diet led to increased blood pressures, decreased heart rates, increased time spent active and decreased intensity levels of locomotor activity. Salt-induced changes in systolic and pulse pressures in PAR-2 -/- were less than in C57B/6J. Angiotensin II treatment increased pressures, decreased heart rates, decreased time spent active and decreased intensity levels of activity of PAR-2 -/-, all to the same extent as C57BL/6J. A trend of lower blood pressures during the middle period of angiotensin II treatment period was observed in individual PAR-2 -/-.

Conclusion

The data indicated gene knockout of PAR-2 was associated with a modest change in blood pressure phenotype. PAR-2 -/- mice exhibited moderate elevation of systolic arterial and pulse pressures, yet no increased diastolic arterial pressure, no increased blood pressure responses to high salt diet and a subtle difference in the time course of the blood pressure responses to angiotensin II infusion.

Are all individuals equally sensitive in the blood pressure to high salt intake? (Review article)

It has been reported that only one-third of normotensive subjects and half of hypertensive patients are salt-sensitive. Many causes of salt-sensitivity have been proposed. Our suggestion is that a reduced urinary kallikrein level may be one cause, since mutant kininogen-deficient rats, which cannot generate kinin in the urine, are salt-sensitive. Renal kallikrein is secreted by the connecting tubule cells of the kidney, which are located just distal to the macula densa or the tubuloglomerular feedback system. Excess amounts of sodium taken overflow into the distal tubules and are reabsorbed in the collecting ducts. Kinins generated inhibit sodium reabsorption in the collecting ducts. Both blacks and whites with essential hypertension excrete less urinary kallikrein than do their normotensive counterparts, but the mean value in "normotensive blacks" were not different from that in "hypertensive whites". African-Americans consume less potassium than whites. Potassium and ATP-sensitive potassium channel blockers are releasers of renal kallikrein. In a small-scale study, sodium loading caused more increase in the systolic blood pressure in urinary low-kallikrein group than in urinary high-kallikrein group. Large-scale clinical studies, under strict control of potassium intake, are needed to elucidate the relationship between salt-sensitivity and urinary kallikrein levels.

Recombinant adeno-associated virus-mediated human kallikrein gene therapy prevents high-salt diet-induced hypertension without effect on basal blood pressure

AIM

To investigate the effects of the expression of human kallikrein (HK) on basal level blood pressure and high-salt diet-induced hypertension.

METHODS

We delivered the recombinant adeno-associated viral (rAAV)-mediated HK (rAAV- HK) gene and rAAV-LacZ (as the control) to normal, adult Sprague-Dawley rats. The animals were administered a normal diet in the first 4 weeks, followed by a high-salt diet. The expression of HK in the rats was assessed by ELISA and RT- PCR. Blood pressure and Na+ and K+ urinary excretion were monitored.

RESULTS

Under the normal diet, no obvious changes in blood pressure and Na+ and K+ urinary excretion were observed. When the high-salt diet was administered, systolic blood pressure in the control animals receiving rAAV-LacZ increased from 122.3+/-1.13 mmHg to a stable 142.4+/-1.77 mmHg 8 weeks after the high-salt diet. In contrast, there was no significant increase in the blood pressure in the rAAV-HKtreated group, in which the blood pressure remained at 121.9+/-1.73 mmHg. In the rAAV-HK-treated group, Na+ and K+ urinary excretion were higher compared to those of the control group. The morphological analysis showed that HK delivery remarkably protected against renal damage induced by a high-salt intake.

CONCLUSION

Our study indicates that rAAV-mediated human tissue kallikrein gene delivery is a potentially safe method for the long-term treatment of hypertension. More importantly, it could be applied in the salt-sensitive population to prevent the occurrence of hypertension.

Pathogenesis of essential hypertension: historical paradigms and modern insights

Since its first identification in the late 1800s, a variety of etiologies for essential hypertension have been proposed. In this paper we review the primary proposed hypotheses in the context of both the time in which they were proposed as well as the subsequent studies performed over the years. From these various insights, we propose a current paradigm to explain the renal mechanisms underlying the hypertension epidemic today. Specifically, we propose that hypertension is initiated by agents that cause systemic and intrarenal vasoconstriction. Over time intrarenal injury develops with microvascular disease, interstitial T cell and macrophage recruitment with the induction of an autoimmune response, with local angiotensin II formation and oxidant generation. These changes maintain intrarenal vasoconstriction and hypoxia with a change in local vasoconstrictor-vasodilator balance favoring sodium retention. Both genetic and congenital (nephron number) mechanisms have profound influence on this pathway. As blood pressure rises, renal ischemia is ameliorated and sodium balance restored completely (in salt-resistant) or partially (in salt-sensitive) hypertension, but at the expense of a rightward shift in the pressure natriuresis curve and persistent hypertension.

State of the Art Reviews: Relationship Between Diet/ Physical Activity and Health

Obesity and 4 of the leading causes of death—heart disease, cancer, stroke, and type 2 diabetes mellitus—are related to lifestyle. The combination of a healthy weight, prudent diet, and daily physical activity clearly plays a role in primary, secondary, and tertiary prevention of these and other chronic diseases. Because nearly 65% of the adult population is overweight or obese, weight loss and maintenance are central to this review article. Improved lipid profiles, blood pressure, insulin sensitivity, and euglycemia are associated with weight loss or a normal body weight; thus, maintaining a healthy weight is a universal recommendation for health. The methods for improving lifestyle described in the section on obesity include assessing nutritional status and stages of change of the client, setting realistic goals, eating a diet high in fruits and vegetables with low-fat sources of dairy and protein, and achieving appropriate physical activity levels. The importance of physicians discussing weight with clients and vice versa is stressed. The common features of lifestyle-related diseases make them amenable to similar lifestyle interventions.

Pathophysiological Mechanisms of Salt-Dependent Hypertension

Changes in salt intake are associated in general with corresponding changes in arterial blood pressure. An exaggerated increment in blood pressure driven by a salt load is characteristic of salt-sensitive hypertension, a condition affecting more than two thirds of individuals with essential hypertension who are older than 60 years. In the last decade, significant insight was gained about the role of the kidney in the increment in blood pressure induced by sodium retention. The present review focuses on the pathophysiological characteristics of the blood pressure increase driven by expansion of extracellular fluid and the increment in plasma sodium concentration. In addition, we discuss systemic and renal conditions that result in decreased urinary sodium excretion and were implicated in the development of salt-sensitive hypertension.

The dopaminergic system in hypertension

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport, vascular smooth muscle contractility and production of reactive oxygen species and by interacting with the renin–angiotensin and sympathetic nervous systems. Dopamine receptors are classified into D1-like (D1 and D5) and D2-like (D2, D3 and D4) subtypes based on their structure and pharmacology. Each of the dopamine receptor subtypes participates in the regulation of blood pressure by mechanisms specific for the subtype. Some receptors regulate blood pressure by influencing the central and/or peripheral nervous system; others influence epithelial transport and regulate the secretion and receptors of several humoral agents. This review summarizes the physiology of the different dopamine receptors in the regulation of blood pressure, and the relationship between dopamine receptor subtypes and hypertension.