Chiara Lanzani

ACE and α-Adducin Polymorphism as Markers of Individual Response to Diuretic Therapy

Abstract—Renin-angiotensin system reactivity and the constitutive capacity of the renal tubule to reabsorb sodium play a role in the individual response to diuretic therapy; therefore we evaluated the blood pressure (BP) response to hydrochlorothiazide in 87 never-treated individuals with mild essential hypertension, according to ACE gene I/D and &agr;-adducin Gly460Trp polymorphism. These genotypes where chosen because previous data showed their interaction in determining the BP response to salt probably was the result of their involvement in the activation of the renin-angiotensin system (ACE) and in the constitutive capacity of the kidney to reabsorb sodium (&agr;-adducin) (treatment for 2 months). BP was measured after 3 run-in visits and after the first and second months of treatment by means of a standardized procedure. Data were analyzed by ANOVA, t test, and multivariate ANOVA for repeated measures (covarying for gender, age, and body mass index). Although basal mean BP (MBP) was similar in the different ACE and &agr;-adducin genotypes, patients carrying at least one I allele of ACE and one 460Trp allele of &agr;-adducin had the largest MBP decrease with treatment (12.7±1.9 mm Hg), the effect of the combination of genotypes being additive but not epistatic. These patients had an odds ratio of 15.75 of being a responder to hydrochlorothiazide compared with patients with Gly460Gly+DD, with the least MBP decrease (3.4±1.7 mm Hg). &agr;-Adducin and ACE I/D polymorphism may be useful to predict the interindividual degree of response to hydrochlorothiazide; the analysis of the combination of the 2 genotypes increases the accuracy of the prediction of response to the drug.

Common noncoding UMOD gene variants induce salt-sensitive hypertension and kidney damage by increasing uromodulin expression

Hypertension and chronic kidney disease (CKD) are complex traits representing major global health problems. Multiple genome-wide association studies have identified common variants in the promoter of the UMOD gene, which encodes uromodulin, the major protein secreted in normal urine, that cause independent susceptibility to CKD and hypertension. Despite compelling genetic evidence for the association between UMOD risk variants and disease susceptibility in the general population, the underlying biological mechanism is not understood. Here, we demonstrate that UMOD risk variants increased UMOD expression in vitro and in vivo. Uromodulin overexpression in transgenic mice led to salt-sensitive hypertension and to the presence of age-dependent renal lesions similar to those observed in elderly individuals homozygous for UMOD promoter risk variants. The link between uromodulin and hypertension is due to activation of the renal sodium cotransporter NKCC2. We demonstrated the relevance of this mechanism in humans by showing that pharmacological inhibition of NKCC2 was more effective in lowering blood pressure in hypertensive patients who are homozygous for UMOD promoter risk variants than in other hypertensive patients. Our findings link genetic susceptibility to hypertension and CKD to the level of uromodulin expression and uromodulins effect on salt reabsorption in the kidney. These findings point to uromodulin as a therapeutic target for lowering blood pressure and preserving renal function.

Adducin- and Ouabain-Related Gene Variants Predict the Antihypertensive Activity of Rostafuroxin, Part 2: Clinical Studies

Five genetic variants that affect Na,K-ATPase interactions predict the blood pressure response to rostafuroxin but not to losartan and hydrochlorothiazide. Help for Hypertension As if changing its mind about how best to detoxify the body, the kidney first secretes a filtrate that contains almost everything in the blood but then recaptures much of it by pumping essential water, salts, and other molecules back in. The Na+, K+-ATPase, or sodium pump, recaptures sodium salts, and because Na+ is the prime determinant of extracellular fluid volume in the body, regulation of this pump controls blood pressure. Now a pair of papers describes how an antihypertension drug can correct abnormal sodium pumping and how this understanding of the drug’s mechanism points to a genetic signature that can predict whether a patient will respond to the drug. One cause of hypertension is a particular variant(s) of the protein adducin, a modulator of protein exposure on the cell surface that stimulates the sodium pump; a second is high concentrations of endogenous ouabain, an activating ligand for the pump. Both factors abnormally enhance the pump function through the triggering of the Src signaling pathway. Rostafuroxin, a derivative of digitoxigenin, acts as an antihypertensive agent by interfering with both of these ways to activate the sodium pump, preventing an increase in renal tubular Na+ transport and the resulting hypertension. In the first of the companion papers (Ferrandi et al.), the authors explore how rostafuroxin accomplishes its pressure-lowering feat. They show that the drug inhibits the Na+, K+ ATPase-Src-EGFR-ERK signaling activated by mutant adducin or ouabain, normalizing renal cell sodium transport, in two different rodent models of hypertension and in human cells. Upon closer examination of rostafurotoxin’s effects on Src-related phosphorylation in vitro, it became clear that the drug disrupts the ability of the variant adducin and the oubain-bound sodium pump to bind and activate Src at its SH2 domain. In the second of the companion papers (Lanzani et al.), the authors apply these results to patients by examining genetic variants that control the mechanisms of hypertension explored in the first paper. Lanzani et al. inspected genetic alterations in genes that encode enzymes that control ouabain synthesis and transport as well as two variants of adducin. They then tested the ability of these genetic variants to predict the response to rostafuroxin in a group of never-before treated patients with hypertension. Individuals who carried certain combinations of these genetic variants responded well to rostofuroxin, displaying a mean drop in the placebo-corrected blood pressure of about 14 mmHg, a clinically meaningful value. The same genetic signature did not predict the blood pressure response to other antihypertensive drugs with different mechanisms of action. The authors suggest that this genetic signature may exist in about a quarter of hypertensive patients. Finally, rostfuroxin may do more than lower blood pressure. Organ damage is known to be a downstream effect of an overactive Src signaling pathway—one of the byproducts of the hypertension mechanisms studied in this pair of papers. Because rostafuroxin interferes with Src signaling, the drug may curb the secondary damage to the heart, kidney, and brain caused by high blood pressure. Thus the kidney’s seemingly schizophrenic filtering actually represents a multilevel, fine-tuned control of the sodium pump as a means of managing blood pressure. Rostafuroxin can selectively correct hypertension in patients whose pumping mechanism is out of kilter, an advance toward personalized treatment of high blood pressure. Twenty years of genetic studies have not contributed to improvement in the clinical management of primary arterial hypertension. Genetic heterogeneity, epistatic-environmental-biological interactions, and the pathophysiological complexity of hypertension have hampered the clinical application of genetic findings. In the companion article, we furnished data from rodents and human cells demonstrating two hypertension-triggering mechanisms—variants of adducin and elevated concentrations of endogenous ouabain (within a particular range)—and their selective inhibition by the drug rostafuroxin. Here, we have investigated the relationship between variants of genes encoding enzymes for ouabain synthesis [LSS (lanosterol synthase) and HSD3B1 (hydroxy-δ-5-steroid dehydrogenase, 3β- and steroid δ-isomerase 1)], ouabain transport {MDR1/ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1]}, and adducin activity [ADD1 (adducin 1) and ADD3], and the responses to antihypertensive medications. We determined the presence of these variants in newly recruited, never-treated patients. The genetic profile defined by these variants predicted the antihypertensive effect of rostafuroxin (a mean placebo-corrected systolic blood pressure fall of 14 millimeters of mercury) but not that of losartan or hydrochlorothiazide. The magnitude of the rostafuroxin antihypertensive effect was twice that of antihypertensive drugs recently tested in phase 2 clinical trials. One-quarter of patients with primary hypertension display these variants of adducin or concentrations of endogenous ouabain and would be expected to respond to therapy with rostafuroxin. Because the mechanisms that are inhibited by rostafuroxin also underlie hypertension-related organ damage, this drug may also reduce the cardiovascular risk in these patients beyond that expected by the reduction in systolic blood pressure alone.

Plasma Ouabain-Like Factor During Acute and Chronic Changes in Sodium Balance in Essential Hypertension

Abstract—An ouabain-like factor has been implicated repeatedly in salt-sensitive hypertension as a natriuretic agent. However, the response of plasma ouabain-like factor to acute and chronic variation of body sodium is unclear. We studied 138 patients with essential hypertension who underwent an acute volume expansion/contraction maneuver (2 days) and 20 patients who entered a blind randomized crossover design involving chronically controlled sodium intake and depletion (170 to 70 mmol/d; 2 weeks each period). In both studies, plasma levels of ouabain-like factor were higher during sodium depletion (acute: 338.8±17.4 and 402.7±22.8 pmol/L for baseline and low sodium, respectively, P <0.01; chronic: 320.4±32.0 versus 481.0±48.1 pmol/L, P =0.01). No significant change in plasma ouabain-like factor was observed after a 2-hour saline infusion (333.4±23.9 pmol/L) or controlled sodium (402.1±34.9 pmol/L). When patients were divided into salt-sensitive or salt-resistant groups, no differences in plasma ouabain-like factor were observed in the 2 groups at baseline or in response to the 2 protocols: salt resistant (n=69, 340.1±25.9 pmol/L) versus salt sensitive (n=69, 337.4±23.6 pmol/L) and chronic salt resistant (n=11, 336.0±53.2) versus salt sensitive (n=9, 301.1±331.4 pmol/L). However, circulating ouabain-like factor was increased by sodium depletion in both groups. These results demonstrate that circulating ouabain-like factor is raised specifically by maneuvers that promote the loss of body sodium. Acute expansion of body fluids with isotonic saline is not a stimulus to plasma ouabain-like factor. Moreover, basal levels of plasma ouabain-like factor do not differ among patients with salt-sensitive or salt-resistant hypertension. Taken together, these new results suggest that ouabain-like factor is involved in the adaptation of humans to sodium depletion and argue against the hypothesis that ouabain-like factor is a natriuretic hormone.

Plasma and tissue expression of the long pentraxin 3 during normal pregnancy and preeclampsia

OBJECTIVE: Cell death normally occurs during pregnancy and is critical during its common complication, preeclampsia. The long pentraxin 3 (PTX3) gene is generated in tissues that cope with excessive or deregulated cell death and inhibits the cross-presentation of cell-associated antigens. We examined whether PTX3 is expressed during pregnancy and possibly involved in the development of preeclampsia. METHODS: Women with preeclampsia (n = 30), women with uncomplicated pregnancies (n = 66), age-matched healthy women (n = 50), women who developed acute bacterial infections (n = 20), and women with rheumatoid arthritis (n = 20) were studied. The concentrations of PTX3 were measured in the blood by a sandwich enzyme-linked immunosorbent assay (ELISA) and in placentas by immunohistochemistry. The concentrations of PTX3 and C-reactive protein in the various groups were compared by nonparametric tests (the Mann-Whitney U and the Kruskal-Wallis tests). The odds of developing preeclampsia were assessed using logistic regression. RESULTS: PTX3 was expressed in amniotic epithelium and chorionic mesoderm, trophoblast terminal villi, and perivascular stroma in placentas from pregnancies of uncomplicated subjects. Circulating levels steadily rose during normal gestation and peaked during labor. Serum levels of PTX3 were strikingly higher in preeclampsia compared with normal control pregnancies (5.08 ± 1.34 and 0.59 ± 0.07 ng/mL, respectively, P < .001). Sites of higher expression in the placentas from preeclamptic patients include infarcts and fibrinoid zones. CONCLUSION: Defects in the homeostatic response to cell death/remodeling events, revealed by enhanced levels of PTX3, could be implicated in preeclampsia. LEVEL OF EVIDENCE: II-2

Physiological Interaction Between α-Adducin and WNK1-NEDD4L Pathways on Sodium-Related Blood Pressure Regulation

The kidney plays an important role in salt and blood pressure (BP) homeostasis. In previous studies, variants in the genes for &agr;-adducin (ADD1), WNK1, and NEDD4L, which all regulate renal sodium absorption, have been associated with increased BP. However, findings have been inconsistent. We tested whether this is because of physiological interactions between the effects of variants in these genes. We assessed the single and combined effects of the ADD1 (Gly460Trp), WNK1 (rs880054 A/G), and NEDD4L (rs4149601 G/A) polymorphisms on renal and BP response to an acute Na load (n=344 subjects), BP decrease after 1 month of treatment with 12.5 mg of hydrochlorothiazide (n=193), and ambulatory 24-hour BP (n=690). Individually, the variants showed modest effects on some of the studied phenotypes. We found the ADD1 Trp allele to be permissive for the effects of variants of the other genes. In combination, the same variants (ADD1 Trp/WNK1 GG/Nedd4L GA+AA) showed a consistent effect on renal Na handling (P=0.009) and acute BP response to a saline infusion (P=0.021), BP lowering after thiazide treatment (P=0.008), and nocturnal systolic BP (P=0.044). Physiological interaction between the ADD1 and WNK1-NEDD4L pathways influences the effects of variants in these genes on sodium-related BP regulation. Relatively common alleles in the ADD1, WNK1, and NEDD4L genes when present in combination may have significant effects on renal sodium handling, BP, and antihypertensive response to thiazides.

Genomic Association Analysis of Common Variants Influencing Antihypertensive Response to Hydrochlorothiazide

To identify novel genes influencing blood pressure response to thiazide diuretic therapy for hypertension, we conducted genome-wide association meta-analyses of ≈1.1 million single-nucleotide polymorphisms in a combined sample of 424 European Americans with primary hypertension treated with hydrochlorothiazide from the Pharmacogenomic Evaluation of Antihypertensive Responses study (n=228) and the Genetic Epidemiology of Responses to Antihypertensive study (n=196). Polymorphisms associated with blood pressure response at P<10–5 were tested for replication of the associations in independent samples of hydrochlorothiazide-treated European hypertensives. The rs16960228 polymorphism in protein kinase C, &agr; replicated for same-direction association with diastolic blood pressure response in the Nordic Diltiazem study (n=420) and the Genetics of Drug Responsiveness in Essential Hypertension study (n=206), and the combined 4-study meta-analysis P value achieved genome-wide significance (P=3.3×10−8). Systolic or diastolic blood pressure responses were consistently greater in carriers of the rs16960228 A allele than in GG homozygotes (>4/4 mm Hg) across study samples. The rs2273359 polymorphism in the GNAS-EDN3 region also replicated for same-direction association with systolic blood pressure response in the Nordic Diltiazem study, and the combined 3-study meta-analysis P value approached genome-wide significance (P=5.5×10−8). The findings document clinically important effects of genetic variation at novel loci on blood pressure response to a thiazide diuretic, which may be a basis for individualization of antihypertensive drug therapy and identification of new drug targets.

Role of the adducin family genes in human essential hypertension

Objective In both humans and rats, polymorphisms of the alpha adducin (ADD1) gene are involved in renal sodium handling, essential hypertension and some of its organ complications. Adducin functions within cells as a heterodimer composed of various combinations of three subunits that are coded by three genes (ADD1, 2, 3) each located on a different chromosome. Design These characteristics provide the biochemical basis for investigating epistatic interactions among these loci. Methods We examined the three adducin gene polymorphisms and their association with ambulatory blood pressure (ABPM) and with plasma levels of renin activity (PRA), endogenous ouabain (EO), in 512 newly discovered and never-treated hypertensive patients. Results Relative to carriers of the wild type (Gly/Gly) ADD1 gene, patients carrying the mutated Trp ADD1 allele had higher blood pressure (systolic blood pressure (SBP) 143.2 ± 1.0 versus 140.6 ± 0.6 mmHg P = 0.027 and diastolic blood pressure (DBP) 94.2 ± 0.77 versus 92.3 ± 0.5 mmHg, P = 0.03), lower PRA and EO, consistent with the hypothesis of the renal sodium retaining effect of the Trp allele. Polymorphisms in the ADD2 and ADD3 genes taken alone were not associated with these variables. However, the differences in SBP and DBP between the two ADD1 genotypes were greatest in carriers of the ADD3 G allele (around + 8 mmHg). The significance of the interaction between ADD1 and ADD3 ranged between P = 0.020 to P = 0.006 according to the genetic model applied. Conclusions The interaction of ADD1 and ADD3 gene variants in humans is statistically associated with variation in blood pressure, suggesting the presence of epistatic effects among these loci.

Genes involved in vasoconstriction and vasodilation system affect salt-sensitive hypertension.

The importance of excess salt intake in the pathogenesis of hypertension is widely recognized. Blood pressure is controlled primarily by salt and water balance because of the infinite gain property of the kidney to rapidly eliminate excess fluid and salt. Up to fifty percent of patients with essential hypertension are salt-sensitive, as manifested by a rise in blood pressure with salt loading. We conducted a two-stage genetic analysis in hypertensive patients very accurately phenotyped for their salt-sensitivity. All newly discovered never treated before, essential hypertensives underwent an acute salt load to monitor the simultaneous changes in blood pressure and renal sodium excretion. The first stage consisted in an association analysis of genotyping data derived from genome-wide array on 329 subjects. Principal Component Analysis demonstrated that this population was homogenous. Among the strongest results, we detected a cluster of SNPs located in the first introns of PRKG1 gene (rs7897633, p = 2.34E-05) associated with variation in diastolic blood pressure after acute salt load. We further focused on two genetic loci, SLC24A3 and SLC8A1 (plasma membrane sodium/calcium exchange proteins, NCKX3 and NCX1, respectively) with a functional relationship with the previous gene and associated to variations in systolic blood pressure (the imputed rs3790261, p = 4.55E-06; and rs434082, p = 4.7E-03). In stage 2, we characterized 159 more patients for the SNPs in PRKG1, SLC24A3 and SLC8A1. Combined analysis showed an epistatic interaction of SNPs in SLC24A3 and SLC8A1 on the pressure-natriuresis (p interaction = 1.55E-04, p model = 3.35E-05), supporting their pathophysiological link in cellular calcium homeostasis. In conclusions, these findings point to a clear association between body sodium-blood pressure relations and molecules modulating the contractile state of vascular cells through an increase in cytoplasmic calcium concentration.

Genetics of Essential Hypertension: From Families to Genes

Family studies demonstrated the contribution of genetic factors to the development of primary hypertension. However, the transition from this phenomenologic-biometric approach to the molecular-genetic one is more difficult. This last approach is mainly based on the Mendel paradigm; that is, the dissection of the poligenic complexity of hypertension is brought about on the assumption that the individual genetic variants underlying the development of hypertension must be more frequent in hypertensive patients than in controls and must cosegregate with hypertension in families. The validity of these assumptions was clearly demonstrated in the so-called monogenic form of hypertension. However, because of the network of the feedback mechanisms regulating BP, it is possible that that the same gene variant may have an opposite effect on BP according to the genetic and environmental backgrounds. Independent groups of observations (acute BP response to saline infusion, incidence of hypertension in a population follow-up of 9 yr, age-related changes on BP) discussed in this review suggest a positive answer to this question. Therefore the impact of a given genetic variant on BP level must be evaluated within the context of the appropriate genetic epistatic interactions. A negative finding or a minor genetic effect in a general population may become a major gene effect in a subset of people with the appropriate genetic and environmental backgrounds.