Lewis K. Dahl Memorial Lecture. The renin system and four lines fo hypertension research. Nephron heterogeneity, the calcium connection, the prorenin vasodilator limb, and plasma renin and heart attack

The NADPH Oxidase Isoform 1 Contributes to Angiotensin II-Mediated DNA Damage in the Kidney

In higher concentrations, the blood pressure regulating hormone angiotensin II leads to vasoconstriction, hypertension, and oxidative stress by activating NADPH oxidases which are a major enzymatic source of reactive oxygen species (ROS). With the help of knockout animals, the impact of the three predominant NADPH oxidases present in the kidney, i.e., Nox1, Nox2 and Nox4 on angiotensin II-induced oxidative damage was studied. Male wildtype (WT) C57BL/6 mice, Nox1-, Nox2- and Nox4-deficient mice were equipped with osmotic minipumps, delivering either vehicle (PBS) or angiotensin II, for 28 days. Angiotensin II increased blood pressure and urinary albumin levels significantly in all treated mouse strains. In Nox1 knockout mice these increases were significantly lower than in WT, or Nox2 knockout mice. In WT mice, angiotensin II also raised systemic oxidative stress, ROS formation and DNA lesions in the kidney. A local significantly increased ROS production was also found in Nox2 and Nox4 knockout mice but not in Nox1 knockout mice who further had significantly lower systemic oxidative stress and DNA damage than WT animals. Nox2 and Nox4 knockout mice had increased basal DNA damage, concealing possible angiotensin II-induced increases. In conclusion, in the kidney, Nox1 seemed to play a role in angiotensin II-induced DNA damage.

Angiotensin II type 1a receptor-deficient mice develop angiotensin II-induced oxidative stress and DNA damage without blood pressure increase

Hypertensive patients have an increased risk of developing kidney cancer. We have shown in vivo that besides elevating blood pressure, angiotensin II causes DNA damage dose dependently. Here, the role of blood pressure in the formation of DNA damage is studied. Mice lacking one of the two murine angiotensin II type 1 receptor (AT1R) subtypes, AT1aR, were equipped with osmotic minipumps, delivering angiotensin II during 28 days. Parameters of oxidative stress and DNA damage of kidneys and hearts of AT1aR-knockout mice were compared with wild-type (C57BL/6) mice receiving angiotensin II, and additionally, with wild-type mice treated with candesartan, an antagonist of both AT1R subtypes. In wild-type mice, angiotensin II induced hypertension, reduced kidney function, and led to a significant formation of reactive oxygen species (ROS). Furthermore, genomic damage was markedly increased in this group. All these responses to angiotensin II could be attenuated by concurrent administration of candesartan. In AT1aR-deficient mice treated with angiotensin II, systolic pressure was not increased, and renal function was not affected. However, angiotensin II still led to an increase of ROS in kidneys and hearts of these animals. Additionally, genomic damage in the form of double-strand breaks was significantly induced in kidneys of AT1aR-deficient mice. Our results show that angiotensin II induced ROS production and DNA damage even without the presence of AT1aR and independently of blood pressure changes.

Effect of aliskiren on vascular remodelling in small retinal circulation

BACKGROUND

In hypertension, changes in small arterial structure are characterized by an increased wall-to-lumen ratio (WLR). These adaptive processes are modulated by the rennin-angiotensin system. It is unclear whether direct renin inhibitors exert protective effects on small arteries in hypertensive patients.

METHODS

In this double-blind, randomized, placebo-controlled study (http://www.clinicaltrials.gov: NCT01318395), 114 patients with primary hypertension were randomized to additional therapy with either placebo or aliskiren 300 mg for 8 weeks after 4 weeks of standardized open-label treatment with valsartan 320 mg (run-in phase). Parameter of arteriolar remodelling was WLR of retinal arterioles (80 - 140 μm) assessed noninvasively and in vivo by scanning laser Doppler flowmetry (Heidelberg Engineering, Germany). In addition, pulse wave analysis (SphygmoCor, AtCor Medical, Australia) and pulse pressure (PP) amplification were determined.

RESULTS

In the whole study population, no clear effect of additional therapy with aliskiren on vascular parameters was documented. When analyses were restricted to patients with vascular remodelling, defined by a median of WLR more than 0.3326 (n = 57), WLR was reduced after 8 weeks by the treatment with aliskiren compared with placebo (-0.044 ± 0.07 versus 0.0043 ± 0.07, P = 0.015). Consistently, after 8 weeks of on-top treatment with aliskiren, there was an improvement of PP amplification compared with placebo (0.025 ± 0.07 versus -0.034 ± 0.08, P = 0.013), indicative of less stiff arteries in the peripheral circulation.

CONCLUSION

Thus, our data indicate that treatment with aliskiren, given on top of valsartan therapy, improves altered vascular remodelling in hypertensive patients.

Angiotensin II induces DNA damage via AT1 receptor and NADPH oxidase isoform Nox4

Epidemiological studies revealed increased renal cancer incidences and higher cancer mortalities in hypertensive individuals. Activation of the renin-angiotensin-aldosterone system leads to the formation of reactive oxygen species (ROS). In vitro, in renal cells, and ex vivo, in the isolated perfused mouse kidney, we could show DNA-damaging potential of angiotensin II (Ang II). Here, the pathway involved in the genotoxicity of Ang II was investigated. In kidney cell lines with properties of proximal tubulus cells, an activation of NADPH oxidase and the production of ROS, resulting in the formation of DNA strand breaks and micronuclei induction, was observed. This DNA damage was mediated by the Ang II type 1 receptor (AT1R), together with the G protein G ( α-q/11 ) . Subsequently, phospholipase C (PLC) was activated and intracellular calcium increased. Both calcium stores of the endoplasmic reticulum and extracellular calcium were involved in the genotoxicity of Ang II. Downstream, a role for protein kinase C (PKC) could be detected, because its inhibition hindered Ang II from damaging the cells. Although PKC was activated, no involvement of its known target, the NADPH oxidase isoform containing the Nox2 subunit, could be found, as tested by small-interfering RNA down-regulation. Responsible for the DNA-damaging activity of Ang II was the NADPH oxidase isoform containing the Nox4 subunit. In summary, in kidney cells the DNA-damaging activity of Ang II depends on an AT1R-mediated activation of NADPH oxidase via PLC, PKC and calcium signalling, with the NADPH subunit Nox4 playing a crucial role.

Role of angiotensin in the rostral ventrolateral medulla in the development and maintenance of hypertension

Whilst crucial for behavioural and homeostatic responses to environmental challenges, chronic elevation of sympathetic nervous system activity to specific vascular beds is associated with hypertension. Indeed such elevated activity may drive the increase in blood pressure seen in some people and in some experimental models of hypertension. This review discusses the neural circuitry involved in generating and modulating sympathetic efferent nerve activity, focusing on the premotor neurons of the rostral ventrolateral medulla. Neurons in the rostral ventrolateral medulla show altered responses to angiotensin II in experimental models of hypertension, suggesting that this might be an important node for interaction between these two systems that are crucial for regulation of blood pressure.

Systemic and uteroplacental renin--angiotensin system in normal and pre-eclamptic pregnancies

Pregnancy is characterized by an increase in many of the different components of the circulating renin-angiotensin system (RAS). However, the physiological mechanisms of stimulated RAS activity during pregnancy are unknown. Even less understood is how this system may be altered in pre-eclampsia, a hypertensive disorder of pregnancy. Additional studies have shown the presence of a local tissue specific RAS in the uteroplacental unit of normal and pre-eclamptic pregnancies. Differences in normal pregnant and pre-eclamptic RAS component regulation may provide insight into the mechanisms responsible for the clinical pathological features of pre-eclampsia. Specifically, this review summarizes the key findings in the circulating and uteroplacental RAS in normal and pre-eclamptic pregnancies.

Angiotensin II-induced genomic damage in renal cells can be prevented by angiotensin II type 1 receptor blockage or radical scavenging

Hypertensive patients exhibit elevated cancer incidence, especially of cancers of the kidney. Elevated levels of ANG II, the active peptide of the renin-angiotensin system, regulating blood pressure and cardiovascular homeostasis, are known to cause hypertension and kidney diseases. There is evidence that ANG II is an activator of NAD(P)H oxidase, leading to the formation of free radicals, which are known to participate in the induction of DNA damage. This study was undertaken to characterize ANG II-induced DNA damage. DNA damage was measured by comet assay and micronucleus frequency test. Incubation of pig kidney cells (LLC-PK(1)) in vitro with ANG II concentrations between 85 and 340 nM led to a 6- to 15-fold increase of DNA damage compared with the control as revealed by comet assay analysis. Micronuclei were induced about fourfold compared with the control in pig and rat kidney cells (LLC-PK(1), NRK) and in human promyelocytic cells (HL-60). ANG II-induced DNA damage could be prevented by coincubation with the ANG II type 1 receptor blocker candesartan and the antioxidants N-acetylcysteine and alpha-tocopherol. The ANG II type 2 receptor antagonist PD123319 could not reduce ANG II-induced DNA damage. Measurement of reactive oxygen species (ROS) by flow cytometry showed an enhanced formation after exposure to ANG II and a reduction of ROS after candesartan, N-acetylcysteine, and alpha-tocopherol. The present findings support our hypothesis that ANG II causes DNA damage via ANG II type 1 receptor binding and subsequent formation of oxidative stress.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Gender-related differences in target organ damage in untreated patients with essential hypertension

We examined the gender-related differences in target organ damage in 220 untreated patients with essential hypertension (106 men and 114 women). As the indices of target organ damage, we examined the left ventricular mass index and the intima-media thickness in the carotid and femoral arteries obtained from echocardiography. In a multiple regression model, there was a significant positive correlation between the intima-media thickness and age in both groups. In men, there was a significant positive correlation between the left ventricular mass index and age, as well as the diastolic blood pressure, and body mass index. In women, there was a significant positive correlation between the left ventricular mass index and age, as well as plasma renin activity and smoking. In conclusion, there are gender-related differences in the contributing factors, which relate to left ventricular hypertrophy in patients with essential hypertension.

Blood pressure, seasonal body fat, heart rate, and ecological differences in Caboclo populations of the Brazilian Amazon

This study compares blood pressure (BP) and related cardiovascular risk factors among three Caboclo communities from the Brazilian Amazon. Its purpose is to investigate possible risk differentials related to variable ecological settings and Western influences. Caxiuanã is characterized as a more "traditional" group, while Aracampina and Santana are viewed as more "transitional" in lifestyle. A total of 348 subjects from the three communities were evaluated in the wet or the dry season or in both. Measurements across the communities were compared by season and sex. Results suggest little seasonal variation in average BP, BP change, body fat, or body fat change among men. Conversely, there is substantial seasonal and inter-community variation among women. Additional analyses reveal (1) an inconsistent association between age and BP across the communities; (2) that BMI is not associated with BP transitional communities in either season but is associated with both systolic and diastolic pressure in the most traditional community; and (3) little to no sex effect on BP. These results suggest increased Western influence affects body composition particularly of women. However, increased BMI and fat among transitional Caboclo women does not directly translate into higher BP; rather, their BP appears to be more affected by seasonal stresses. Finally, conditions during the wet season diminish age-related variation in BP, suggesting that during the wet season these Caboclo may be less active.

Blood pressure in relation to three candidate genes in a Chinese population

OBJECTIVE

In a prospective analysis of a Caucasian population, we recently found that the genes encoding angiotensin-converting enzyme (ACE, I/D polymorphism), alpha-adducin (Gly460Trp) and aldosterone synthase (-344C/T) jointly influence the incidence of hypertension. We therefore investigated the association between blood pressure and these three genes in a Chinese population.

METHODS

We genotyped 479 Han Chinese from 125 nuclear families recruited in northern China via random sampling (approximately 75%) and at specialized hypertension clinics (approximately 25%). We performed population-based and family-based association analyses using generalized estimating equations (GEE) and the quantitative transmission disequilibrium test (QTDT), respectively, while controlling for covariables.

RESULTS

The participants included 239 (49.9%) women and 132 (27.6%) hypertensive patients, of whom 77 took antihypertensive drugs. The blood pressure, measured at the subjects' homes, averaged 126/80 mmHg. Mean values of urinary sodium, potassium and Na/K ratio were 226 mmol/day, 37 mmol/day and 6.31, respectively. In adjusted GEE analyses, systolic blood pressure was 9.3 mmHg (95% confidence interval 3.6-15.0 mmHg; P = 0.001) and 14.6 mmHg (95% confidence interval 3.4-25.8 mmHg; P = 0.01) higher in the ACE DD than II subjects among the alpha-adducin TrpTrp (n = 141) and aldosterone synthase CC (n = 33) homozygotes, respectively (P < or =0.05 for interactions of the ACE genotype with the alpha-adducin and aldosterone synthase polymorphisms). Among 40 informative offspring homozygous for the alpha-adducin Trp allele, systolic blood pressure was significantly associated with transmission of the ACE D allele (beta = 5.5 mmHg; P = 0.046).

CONCLUSIONS

The ACE I/D, alpha-adducin Gly460Trp and aldosterone synthase -344C/T polymorphisms interact to influence systolic blood pressure in Chinese, suggesting that these genes might indeed predispose to hypertension, especially in an ecogenetic context characterized by a high salt intake.

Sympathetic and angiotensin-dependent hypertension during cage-switch stress in mice

The goal of this study was to determine the dependence of the acute hypertensive response to a novel model of acute psychosocial stress on the sympathetic and renin-angiotensin systems. Baseline mean arterial pressure (MAP), heart rate (HR), and locomotor activity were measured with telemetry in mice for a 1-h period and averaged 98 ± 1 mmHg, 505 ± 3 beats/min, and 5 ± 1 counts, respectively. Stress was induced by placing a mouse into a cage previously occupied by a different male mouse, and this increased MAP, HR, and activity in the control group by 40 ± 2 mmHg, 204 ± 25 beats/min, and 68 ± 6 counts, respectively. Each variable gradually returned to baseline levels by 90 min after beginning cage switch. Pretreatment with terazosin (10 mg/kg ip) significantly reduced the initial increase in MAP to 12 ± 6 mmHg, whereas MAP for the last 45 min was superimposable on control values. Atenolol (10 mg/ml drinking water) had no effect to blunt the initial increase in MAP but had a growing effect from 10 min onward, decreasing MAP all the way to baseline by 60 min after starting cage switch. Captopril (2 mg/ml drinking water) treatment caused a very similar response. All three treatments significantly decreased the area under the blood pressure curve, and the blood pressure effect could not be attributed uniformly to effects on HR or activity. These data suggest that our novel model of psychosocial stress causes an initial α1-receptor-dependent increase in MAP. The later phase of the pressor response is blocked similarly by a β1-receptor antagonist and an ACE inhibitor, independent of HR, suggesting that the β1-dependent blood pressure effect is due, in large part, to the renin-angiotensin system.

Low-renin hypertension, altered sodium homeostasis, and an alpha-adducin polymorphism

Defining the genetic basis of common forms of human essential hypertension is most informative when correlated with physiological mechanisms that underlie blood pressure regulation. A polymorphism of the alpha-adducin gene as been associated with elevated blood pressure in the rat, but previous studies of the 460Trp polymorphism of the human alpha-adducin gene have not clearly identified an association with hypertension. In this study, the frequency of the 460Trp allele was 19% and 9 of 279 subjects (3.2%) were homozygous for the 460Trp allele. The systolic blood pressure response to changes in dietary sodium was significantly greater in subjects homozygous for the 460Trp allele (25 +/- 4 mm Hg) compared with subjects heterozygous for 460Trp (12 +/- 2 mm Hg) or homozygous for the 460Gly allele (14 +/- 1 mm Hg). Intracellular erythrocyte sodium content, sodium-lithium countertransport, and renal fractional excretion of sodium were significantly decreased in subjects homozygous for the 460Trp polymorphism (P<0.05). There was a significant association between homozygosity for the 460Trp allele and low-renin hypertension. Subjects heterozygous for the 460Trp allele did not have increased salt-sensitivity or an increased frequency of low-renin hypertension. Therefore, this study demonstrates a common genetic basis for altered cellular sodium homeostasis, impaired renal sodium handling, and salt-sensitivity of systolic blood pressure in individuals homozygous for the 460Trp polymorphism of the alpha-adducin gene. Homozygosity for this alpha-adducin allele may be an important determinant for approximately 10% of individuals with low-renin hypertension.

Effects of three candidate genes on prevalence and incidence of hypertension in a Caucasian population

BACKGROUND

The genes encoding angiotensin converting enzyme (ACE, I/D), alpha-adducin (ADD, Gly460Trp) and aldosterone synthase (AS, -344C/T) share the potential of influencing blood pressure (BP) via sodium homeostasis. However, most studies in humans focused on single-gene effects and disregarded epistasis, the suppression or potentiation of a gene by other non-allelic genes.

METHODS

We studied the singular and combined effects of the aforementioned candidate genes: (1) in relation to BP, plasma renin activity (PRA) and urinary aldosterone in 1461 subjects randomly selected from a Caucasian population; and (2) in relation to the incidence of hypertension in a subgroup of 678 initially normotensive subjects followed up for 9.1 years (median).

RESULTS

In cross-sectional analyses, AS/CC homozygosity was associated with slightly lower systolic BP (-1.32 mmHg; P = 0.08). AS/TT homozygotes showed both lower PRA and higher urinary aldosterone excretion (P < or = 0.05). In multiple-gene analyses, compared with the whole study population, ADD/Trp subjects had a higher relative risk of hypertension in the presence of the AS/T allele (1.29; P = 0.05), whereas in combination with AS/CC homozygosity ADD/Trp subjects had the smallest relative risk (0.48; P = 0.003). Hypertension developed in 229 subjects (36.6 cases per 1000 person-years). ACE/DD homozygosity, in comparison with the other ACE genotypes, was associated with increases in the incidence of hypertension, which amounted to 31% (P = 0.005) in single-gene analyses, to 59% (P = 0.004) in carriers of the ADD/Trp allele and to 122% (P = 0.0007) in AS/CC subjects. Among subjects who had both the ADD/Trp allele and the AS/CC genotype, ACE/DD homozygotes manifested a 252% (P = 0.001) higher incidence of hypertension.

CONCLUSIONS

Epistatic interactions between the ACE, ADD and AS genes contribute to the prevalence and incidence of hypertension in Caucasians. The clinical relevance of the risk-conferring haplotypes identified in our prospective study was underscored by their positive predictive values, which under the assumption of a 20% life-time risk of hypertension, ranged from 29.8-40.1%.

The renin-angiotensin-aldosterone system and carotid artery disease in mild-to-moderate primary hypertension

BACKGROUND

The evidence linking activation of the renin-angiotensin system with accelerated cerebro-vascular atherosclerosis remains controversial. We therefore prospectively investigated the relationships of plasma renin activity and aldosterone levels with carotid artery lesions (CAL) in essential hypertension.

METHODS

We evaluated the prevalence and severity of CAL and the intimal-medial thickness (IMT) with a high-resolution echo-Doppler technique in 107 cerebrovascularly asymptomatic consecutive primary hypertensives (55 male, 52 female) and in 70 (42 male, 28 female) normotensive controls. We also measured supine plasma renin activity (PRA) and aldosterone before and 45 min after captopril administration, while daily urinary excretion of sodium was measured.

RESULTS

Both the prevalence (59.4 versus 26.2%) and severity of sex- and age-adjusted and unadjusted CAL and IMT were significantly higher in hypertensives than in controls. Regression analysis showed different predictors of IMT (age and captopril-stimulated-PRA, R2 = 0.27, P < 0.0001), score of CAL (mean blood pressure, R2 = 0.15, F=12.73, P< 0.0001) and maximal stenosis (pulse pressure and known duration of hypertension R2 = 0.29, F = 14.58, P< 0.0001). Sex- and age-adjusted IMT did not differ between quartiles of renin-sodium profile. However, patients in the quartile with the highest PRA had the lowest score of CAL and an inverse relationship between age-adjusted PRA and IMT and CAL was found.

CONCLUSIONS

These results, besides confirming an association of both IMT and CAL with primary hypertension and ageing, demonstrate that CAL and IMT have different correlates. However, they do not support the contention that a high renin-sodium profile carries an excess risk of CAL in primary hypertensives with no clinical evidence of cerebro-vascular disease.

Coronary microvascular endothelial cells cosecrete angiotensin II and endothelin-1 via a regulated pathway

Although endothelial cells produce angiotensin II (ANG II) and endothelin-1 (ET-1), it is not clear whether a single cell produces both peptides, with cosecretion in response to stimulation, or whether different subpopulations of endothelial cells secrete one or the other peptide, with secretion in response to different stimuli. Exposure of cultured coronary microvascular endothelial cells to cycloheximide for 60 min had no effect on ANG II or ET-1 secretion. This result suggested the existence of a preformed intracellular pool of ANG II and ET-1, which is a precondition for regulated secretion. Exposure of endothelial cells to isoproterenol, high extracellular potassium, or cadmium, all of which stimulate peptide secretion via different signaling pathways, significantly (P > 0.001) increased the secretion of both ANG II and ET-1 in a cell size-dependent manner. Sodium nitroprusside and S-nitroso-N-acetyl penicillamine significantly (P > 0.001) decreased ANG II and ET-1 secretion, whereas N(omega)-nitro-L-arginine-methyl ester enhanced it. The similar regulation of ANG II and ET-1 secretion and the presence of both peptides around individual endothelial cells indicate that the autocrine/paracrine regulation of cardiovascular function by endothelial cells is accomplished via cosecretion of ANG II and ET-1.

Different patterns of renal prostaglandins I2 and E2 in patients with essential hypertension with low to normal or high renin activity

OBJECTIVE

Differences in renal synthesis between prostaglandins I2 and E2, and the relationships of the amounts synthesized to renin release were investigated in patients with essential hypertension.

METHODS

Of 12 inpatients, six had low to normal plasma renin activity and six had high renin activity. Before and 30 min after intravenous injection of aspirin D,L-lysine (18 mg/kg), abdominal aortic and renal venous plasma was sampled and assayed for renin activity, 6-ketoprostaglandin F1alpha (as an index of prostaglandin I2), and prostaglandin E2.

RESULTS

In patients with low to normal renin activity, mean +/- SD plasma levels of 6-keto-prostaglandin F1alpha were lower in the right and left renal veins (3.6 +/- 1.4 and 4.1 +/- 1.5 pg/ml, respectively) than in the aorta (5.5 +/- 2.0 pg/ml), but in the other patients, the levels in these veins (7.0 +/- 2.4 and 6.5 +/- 1.5 pg/ml) were higher than in the aorta (5.4 +/- 0.9 pg/ml). Plasma prostaglandin E2 levels in both veins were higher than in the aorta in both groups and, at each site, the levels were similar in the two groups. Aspirin suppressed renin release in the patients with high renin activity.

CONCLUSIONS

In patients with essential hypertension with low to normal renin activity, either less prostaglandin I2 than prostaglandin E2 is produced in the kidney or else more is metabolized there, and in such patients with high renin activity, the renal synthesis of prostaglandin I2, more than that of prostaglandin E2, seems to be related to the increased renin release.

Transcription factor decoy to study the molecular mechanism of negative regulation of renin gene expression in the liver in vivo

Renin is synthesized in high quantities in the juxtaglomerular cells of the kidney, but little or none is synthesized in the liver. Our previous in vitro and biochemical studies have demonstrated that tissue-specific expression of the mouse renin gene is regulated by the specific interaction between negative regulatory element (NRE) in the 5'-flanking region of the renin gene and NRE binding protein (NREB). In this study, we examined the hypothesis that this interaction between the NRE in the promoter region of the rat renin gene and the NREB in the liver contributes to the suppressed renin gene expression in this tissue in vivo. We used in vivo transfection of NRE transcription factor decoy (TFD) double-stranded oligonucleotide into the rat liver via portal vein infusion. A gel mobility shift assay showed that transfected NRE TFD blocked endogenous NREB binding with the rat renin gene. This resulted in enhanced hepatic renin mRNA expression, immunohistochemical detection of renin in the liver, and consequently, increased plasma renin concentration. Taken together, these results document the importance of NREB in the inhibition of renin gene expression in rat liver in vivo and suggest the possibility of in vivo renin gene modulation by the TFD approach.

Bi-directional actions of estrogen on the renin-angiotensin system

Estrogen stimulates the renin-angiotensin system by augmenting both tissue and circulating levels of angiotensinogen and renin. We show, however, that angiotensin converting enzyme (ACE) activity in the circulation and in tissues is reduced in two animal models of postmenopausal chronic hormone replacement. We observed a reduction of ACE activity in association with a significant increase in plasma angiotensin I (Ang I) and hyperreninemia in ovariectomized monkeys treated with Premarin (conjugated equine estrogen) replacement for 30 months. Plasma angiotensin II (Ang II) levels were not increased in monkeys treated with estrogen, suggesting that the decrease in ACE curtailed the formation of the peptide. The Ang II/Ang I ratio, an in vivo index of ACE activity, was significantly reduced by estrogen treatment, further supporting the biochemical significance of estrogen's inhibition of ACE. In ovariectomized transgenic hypertensive (mRen2)27 rats submitted to estrogen replacement treatment for 3 weeks, ACE activity in plasma and tissue (aorta and kidney) and circulating Ang II levels were reduced, whereas circulating levels of angiotensin-(1-7) (Ang-(1-7)) were increased. Ang-(1-7), the N-terminal fragment of Ang II, is a novel vasodilator and antihypertensive peptide. Thus, the net balance of these effects of estrogen on the reninangiotensin vasoconstrictor/vasodilator system is to promote the anti-hypertensive effect.

Pathologic consequences of increased angiotensin II activity

Advances in molecular medicine and pharmacology have allowed clinicians to critically reassess the renin-angiotensin system. Angiotensin II (AII) participates in the control of cardiovascular function and electrolyte balance, and plays a part in the regulation of cellular oncogenes and the expression of growth factors. The expression of the proteins of the renin-angiotensin system in organs other than the kidneys suggests that these diverse actions are associated with the peptide in the local environment. Tissue renin-angiotensin activity has prompted the investigation of alternate pathways for the production of AII and characterization of novel forms of angiotensin peptides that counteract the vasoconstrictor and proliferative actions of AII. The heptapeptide angiotensin-(1-7) appears to be critically involved in regulating the angiotensinogen activity of AII through stimulation of vasodilator prostaglandins and release of nitric oxide. Study in this area has been accelerated by the identification of receptors that convey the actions of angiotensin peptides at the cellular level and the pharmacologic characterization of agents that inhibit the ability of AII to bind to target receptors. The introduction of a new class of orally active AII-receptor blockers has provided a specific test of the role of AII in the development of essential hypertension and the potential for improved therapy for hypertension and cardiac and vascular sequelae.

Angiotensin-converting enzyme gene polymorphism in essential hypertensive patients in Japanese population

Association between angiotensin-converting enzyme (ACE) gene polymorphism and essential hypertension in a Japanese population with the same socioeconomic background was investigated. Insertion-deletion (I/D) polymorphism of the ACE gene located on intron 16 was detected by polymerase chain reaction. Association between ACE gene polymorphism and family history of essential hypertension as well as the development of vascular damage in eye fundi were also investigated. Variation at ACE loci did not contribute to essential hypertension and the vascular damages in eye fundi. These results suggest that the ACE gene was not directly responsible for essential hypertension in this particular Japanese population with the same socioeconomic background.

Renin inhibition: a novel therapy for cardiovascular disease

The renin-angiotensin system (RAS) is a major contributor in the regulation of blood pressure, and pharmacologic manipulation of this system has resulted in a beneficial class of therapeutic agents, which include angiotensin-converting enzyme (ACE) inhibitors. However, ACE inhibitors are not specific for RAS, and in addition, they can affect bradykinin and prostaglandin, which can also cause changes in vascular tone. Under development are renin inhibitors that are specific for angiotensinogen and act at the initial, rate-determining step of the RAS cascade. The various pharmacologic approaches to renin inhibition include specific renin antibodies, synthetic derivatives of the prosegment of renin precursor, pepstatin analogs, and angiotensinogen analogs. The last approach is the most promising for patient therapy. Multiple studies have shown the effectiveness of the renin inhibitors in both primates and human beings. Further research is now directed toward the development of an agent with good oral bioavailability for patient treatment and as a biologic probe for helping to understand the role of the RAS in control of blood pressure and blood volume.

Losartan: first of a new class of angiotensin antagonists for the management of hypertension

Angiotensin receptor antagonists represent a new class of drugs for the treatment of patients with hypertension. Reduction of blood pressure in patients with essential hypertension requires increased activity of the renin-angiotensin system. Losartan, the first orally active, nonpeptide angiotensin antagonist, specifically competes with angiotensin II (Ang II) for the AT1 receptor and reversibly alters the receptor. Maximum blood pressure reductions occur after doses of approximately 50 mg, although some patients will require 100 mg; the parent compound and a metabolite are responsible for a smooth 24-hour effect on blood pressure. Once-daily dosing with losartan has been documented to be safe. The drug's safety has been evaluated in 4,058 patients; of these patients, more than 1,200 were treated for longer than 6 months and more than 800 were treated for longer than 1 year with doses of 10 mg to 150 mg. Overall, no hypertensive patients were withdrawn from treatment because of elevated serum creatinine or potassium levels, and there were no reports of angioedema. In addition, some reductions in plasma uric acid levels were noted. Cough occurred significantly less often in patients treated with losartan than in those treated with hydrochlorothiazide or lisinopril. In contrast to angiotensin-converting enzyme (ACE) inhibitors, losartan does not activate bradykinin-nitric oxide-prostanoid vasodilation.

New monoclonal antibodies directed against the propart segment of human prorenin as a tool for the exploration of prorenin conformation

Six monoclonal antibodies (MAbs) directed against human prorenin were produced by immunizing BALB/c mice with a peptide corresponding to the sequence (-17 to +9) of prorenin. The new MAbs were screened for their ability to first bind to the immobilized peptide and then to prorenin previously captured by an anti-total renin MAb. The specificity of the MAbs was confirmed by the total lack of binding to active renin. Using BIAcore technology, equilibrium affinity constants of the MAbs were determined and ranged from 3.2 x 10(8) to 5.7 x 10(9) l/mol. Immunoradiometric assays (IRMA) for prorenin were performed using the anti-total renin MAb and the anti-prorenin MAbs. The best results were obtained when an anti-prorenin MAb was immobilized and the anti-total renin MAb was used as tracer in a one-step procedure. Moreover, the signal was significantly increased by the presence of the renin inhibitor SR 43845 suggesting that the inhibitor-induced conformational change of prorenin could be detected by the MAbs.

Oxidized LDL and lipoprotein(a) stimulate renin release of juxtaglomerular cells

Atherogenic lipoproteins accumulate in the arterial wall and may potentially stimulate neighboring cells. In the glomerulus the vascular pole resembles afferent arteries in close vicinity to the juxtaglomerular apparatus. We examined the effects of native and oxidized LDL and lipoprotein(a) [Lp(a)] on renin release of juxtaglomerular cells (JG cells) prepared in primary culture from mouse kidneys. Renin activity of JG cells was measured in culture supernatants and cells between the 20th and 40th hour of culturing. Spontaneous renin release into the cell supernatant was 26 +/- 1% of total activity. Control stimulation of JG cells by melittin or forskolin dose-dependently increased renin release up to 90 +/- 2%. Incubation of JG cells with native LDL (50 and 300 micrograms/ml) or native Lp(a) (30 micrograms/ml) did not alter renin release. Oxidized LDL increased renin release to 34 +/- 1% and 43 +/- 1% at 50 and 300 micrograms/ml, while oxidized Lp(a) stimulated renin release to 33 +/- 1%, 42 +/- 1%, and 71 +/- 2% at 1, 10, and 30 micrograms/ml, respectively. Coincubation with superoxide dismutase and catalase, enzymes removing O2- and H2O2, completely eliminated oxidized LDL and Lp(a)-stimulated renin release. In the absence of lipoproteins, renin release was significantly stimulated by activation of O2- formation by the xanthine/xanthine oxidase reaction. These data indicate that oxidized LDL and Lp(a) stimulate renin release in JG cells by a mechanism involving oxygen-derived radicals. Thus, oxidatively modified atherogenic lipoproteins may contribute to renin-dependent hypertension in renoparenchymatous kidney disease.

Appraisal of a glycopeptide cloaking strategy for a therapeutic oligopeptide: glycopeptide analogs of the renin inhibitor ditekiren

Among the limitations to the practical therapeutic oligopeptide are low oral availability, indifferent aqueous solubility, and an astonishing efficient sequestration and biliary elimination by a multi-capacity liver transporter. Given the purposed use of N- and O- linked saccharides as functional appendages of eukaryotic peptides and proteins, a strategy of glycopeptide mimicry was examined for the oligopeptide renin inhibitor, ditekiren. The anticipation was that the saccharide would impart significant aqueous solubility, and might impact beneficially on the remaining two limitations. Execution of this approach was achieved by the removal of the (dimethylethoxy)carbonyl amino terminus of ditekiren, and its substitution by Boc-L-asparagine N-linked mono- and disaccharides. Potent hypotensive activity, as measured by a human renin-infused rat assay, is observed for virtually all of these structures (N-linked beta-pyranose D-N-acetyglucosaminyl, D-glucosaminyl, D-N-acetylgalactosaminyl, D-mannosyl, D-galactosyl, D-maltosyl, D-cellobiosyl, D-chitobiosyl, but not L-fucosyl). The basis for this dramatic improvement (relative to ditekiren in the same assay) is the diversion of the peptide clearance from rapid liver biliary clearance to slower urinary clearance (Fisher, J. F.; Harrison, A. W.; Wilkinson, K. F.; Rush, B. R.; Ruwart, M. J. J. Med. Chem. 1991, 34, 3140). Guided by the human renin-infused rat hypertension assay, an evaluation of the linker-saccharide pairing was made. Loss of hypotensive activity is observed upon substitution of the Boc-L-asn by Boc-D-asn, and by removal of the Boc amino terminus of the glycopeptide. Potent hypotensive activity is preserved by replacement of the Boc-L-asn linker by succinate, malate, tartrate, and adipate linkers. With the longer adipate spacer, attachment of the saccharide to the P-3 phenylalanine--with omission of the P-4 proline--retains activity. These data suggest value to the glycopeptide guise for preserving the in vivo activity, and for the beneficial manipulation of pharmacodynamics, of this renin inhibitory oligopeptide. This strategy may have general applicability.

Mechanism of cAMP regulation of renin gene transcription by proximal promoter

Renin is produced mainly by the kidney, and cAMP is a main positive regulator of its synthesis. This study was undertaken to analyze the molecular mechanism of cAMP-mediated regulation of Ren-1C gene transcription by the proximal promoter. We first showed that the promoter region from -365 to +16 of the mouse renin gene (Ren-1C) mediated the cAMP-induced chloramphenicol acetyltransferase gene expression in embryonic kidney-derived 293 cells. Deletion analysis and heterologous promoter assay disclosed that the proximal promoter region from -75 to +16 was able to activate chloramphenicol acetyltransferase expression by cAMP, and indicated that the proximal promoter element from -75 to -47 (RP-2 element) overlapping the TATA-like region was able to confer cAMP responsiveness. Electrophoretic mobility shift assay and DNase I footprinting analysis demonstrated that novel nuclear factors in 293 cells interacted with the RP-2 element, and that cAMP increased the binding activity of these nuclear factors to the RP-2 element. Furthermore, we demonstrated that cAMP enhanced the binding of nuclear factors derived from juxtaglomerular cells, the main production site of renin in the kidney, to the RP-2 element in vivo. These results suggest that the RP-2 element plays an important role in the cAMP-mediated regulation of Ren-1C gene transcription through the proximal promoter.

Oxygen-derived radicals stimulate renin release of isolated juxtaglomerular cells

We assessed effects of reactive oxygen metabolites on renin release of juxtaglomerular cells (JG-cells) prepared in primary culture from mouse kidneys. Renin activity was measured in culture supernatants and cells. Basal renin release was increased by incubation of JG-cells with xanthine/xanthine oxidase from 26 +/- 1% up to 58 +/- 3% of total activity. This increase was slightly inhibited by superoxide dismutase, and was eliminated by addition of catalase, implicating H2O2 as an intermediate product in the stimulatory cascade. H2O2 applied exogenously dose-dependently stimulated renin release up to 55 +/- 2%; this effect was also prevented by catalase. We propose that reactive oxygen metabolites stimulate renin release in isolated JG-cells. This could have important implications in inflammatory kidney diseases.

Renin inhibition: a new approach to cardiovascular therapy

The renin-angiotensin system (RAS) functions as a primary regulator in the short-term and long-term control of blood pressure. Pharmacologic inhibition of the RAS with angiotensin-converting enzyme (ACE) inhibition is effective for treating systemic hypertension and congestive heart failure. As a more specific therapy, the development of renin inhibitors has evolved through various approaches: specific renin antibodies, peptides developed from prosegments of renin precursor, oligopeptides related to pepstatin a universal inhibitor of aspartyl proteinase enzyme, and analogs of angiotensinogen (the renin substrate). Angiotensinogen analogs are promising as therapeutic agents because of high potency, metabolic stability, and good oral bioavailability. Ongoing research is directed towards the application of renin inhibition, the treatment of various cardiovascular disorders, and as a biological probe for understanding the role of the RAS in control of blood pressure and blood volume.

Effect of angiotensin II and enalapril on transfer of low-density lipoprotein into aortic intima in rabbits

To assess the mechanism behind a possible atherosclerosis-promoting effect of angiotensin II, the influence of angiotensin II, noradrenaline, and enalapril on transfer of low-density lipoprotein (LDL) into the arterial wall was investigated in conscious rabbits. Intravascular infusion of angiotensin II (1.4 micrograms/kg per minute) initially increased the mean blood pressure from 70 to 80 mm Hg to 125 to 150 mm Hg; this effect was transient, and the blood pressure returned to baseline values within 2 hours, despite continuous infusion of angiotensin II. The normalized influx of LDL into the aortic intima, determined after in vivo exposure to 125I-LDL for 1 hour, was 88 +/- 17 (n = 6), 12 +/- 12 (n = 5), and 28 +/- 6 (n = 5) nL/cm2 per hour (mean +/- SEM) during angiotensin II infusion at high blood pressure, during angiotensin II infusion after the blood pressure had been normalized, and during continuous saline infusions, respectively (P < .05 for high blood pressure versus low blood pressure and saline). When noradrenaline was used to increase blood pressure to a level similar to that induced by angiotensin II, the normalized influx of LDL in noradrenaline-treated rabbits was also increased markedly. Production of endogenous angiotensin II was inhibited with enalapril (2.9 mg/kg per day). Compared with placebo rabbits, enalapril-treated rabbits had a 92% lower plasma angiotensin-converting enzyme activity and a 23% lower blood pressure. The normalized influx of LDL, however, was similar in the two groups at 18 +/- 2 (n = 10) and 20 +/- 3 (n = 10) nL/cm2 per hour, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension and the kidney--an overview

The kidney plays a major role in the genesis of any type of hypertension, as demonstrated by experiments which show that hypertension can be "transplanted" when the kidney itself is transplanted. Hypertension is common in patients with renal disease, and may occur even at normal glomerular filtration rates. The mechanisms that promote hypertension and are involved in renal disease comprise both activation of pressor mechanisms and failure of depressor mechanisms, the latter having been considerably less well studied. The major pressor mechanisms are an abnormal pressure-natriuresis relationship and inappropriate activity of the renin-angiotensin system.