Fernando Elijovich

DC isoketal-modified proteins activate T cells and promote hypertension

Oxidative damage and inflammation are both implicated in the genesis of hypertension; however, the mechanisms by which these stimuli promote hypertension are not fully understood. Here, we have described a pathway in which hypertensive stimuli promote dendritic cell (DC) activation of T cells, ultimately leading to hypertension. Using multiple murine models of hypertension, we determined that proteins oxidatively modified by highly reactive γ-ketoaldehydes (isoketals) are formed in hypertension and accumulate in DCs. Isoketal accumulation was associated with DC production of IL-6, IL-1β, and IL-23 and an increase in costimulatory proteins CD80 and CD86. These activated DCs promoted T cell, particularly CD8+ T cell, proliferation; production of IFN-γ and IL-17A; and hypertension. Moreover, isoketal scavengers prevented these hypertension-associated events. Plasma F2-isoprostanes, which are formed in concert with isoketals, were found to be elevated in humans with treated hypertension and were markedly elevated in patients with resistant hypertension. Isoketal-modified proteins were also markedly elevated in circulating monocytes and DCs from humans with hypertension. Our data reveal that hypertension activates DCs, in large part by promoting the formation of isoketals, and suggest that reducing isoketals has potential as a treatment strategy for this disease.

Differential Regulation of Natriuresis by 20-Hydroxyeicosatetraenoic Acid in Human Salt-Sensitive Versus Salt-Resistant Hypertension

Background—Twenty-hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P450 metabolite of arachidonic acid that produces vasoconstriction and inhibition of renal tubular sodium transport. In Dahl rats, a 20-HETE deficiency plays a role in salt-sensitive (SS) hypertension. In humans, there are no data on regulation of 20-HETE by salt intake or on a role for this compound in SS hypertension. Methods and Results—Thirteen salt-resistant (SR) and 13 SS hypertensive subjects had urine 20-HETE excretion measured during salt-loading and depletion. In all patients, 20-HETE was 66.6% higher in the salt-replete (1.75±0.25 &mgr;g/h) than in the salt-depleted state (1.05±0.16, P <0.003). There was no difference in 20-HETE excretion between SR and SS patients in either state of salt balance. In SR patients, sodium excretion during salt-loading correlated with 20-HETE (r =0.61, P <0.03) but not with blood pressure. In contrast, in SS patients, sodium excretion did not correlate with 20-HETE but did correlate with blood pressure (r =0.66, P <0.02). Finally, in the SS group only, there was a negative correlation between body mass index and 20-HETE excretion (r =−0.79, P <0.002) that was present during both salt-loading and depletion. Conclusions—We demonstrate for the first time that 20-HETE excretion is regulated by salt intake in hypertension. We find a disrupted relationship between sodium excretion and 20-HETE in SS patients, which results in dependence of their salt excretion on blood pressure and may be related to the magnitude of their obesity. We conclude that salt-sensitivity of blood pressure in essential hypertension may result from impairment of a natriuretic mechanism dependent on 20-HETE.

Evidence for Linkage Between Essential Hypertension and a Putative Locus on Human Chromosome 17

Several clinical and animal studies indicate that essential hypertension is inherited as a multifactorial trait with a significant genetic and environmental component. In the stroke-prone spontaneously hypertensive rat model, investigators have found evidence for linkage to blood pressure regulatory genes (quantitative trait loci) on rat chromosomes 2, 10, and X. In 1 human study of French and UK sib pairs, evidence for linkage has been reported to human chromosome 17q, the syntenic region of the rat chromosome 10 quantitative trait loci (QTL). Our study confirms this linkage (P=0.0005) and refines the location of the blood pressure QTL.

The T8590C Polymorphism of CYP4A11 and 20-Hydroxyeicosatetraenoic Acid in Essential Hypertension

A role for a deficit in transport actions of 20-hydroxyeicosatetraenoic acid (20-HETE) in hypertension is supported by the following: (1) diminished renal 20-HETE in Dahl-S rats; (2) altered salt- and furosemide-induced 20-HETE responses in salt-sensitive hypertensive subjects; and (3) increased population risk for hypertension in C allele carriers of the T8590C polymorphism of CYP4A11, which encodes an enzyme with reduced catalytic activity. We determined T8590C genotypes in 32 hypertensive subjects, 25 of whom were phenotyped for salt sensitivity of blood pressure and insulin sensitivity. Urine 20-HETE was lowest in insulin-resistant, salt-sensitive subjects (F=5.56; P<0.02). Genotypes were 13 TT, 2 CC, and 17 CT. C allele frequency was 32.8% (blacks: 38.9%; whites: 25.0%). C carriers (CC+CT) and TT subjects were similarly distributed among salt- and insulin-sensitivity phenotypes. C carriers had higher diastolic blood pressures and aldosterone:renin and waist:hip ratios but lower furosemide-induced fractional excretions of Na and K than TT. The T8590C genotype did not relate to sodium balance or pressure natriuresis. However, C carriers, compared with TT, had diminished 20-HETE responses to salt loading after adjustment for serum insulin concentration and resetting of the negative relationship between serum insulin and urine 20-HETE to a 1-&mgr;g/h lower level of 20-HETE. The effect of C was insulin independent and equipotent to 18 &mgr;U/mL of insulin (&Dgr;20-HETE= 2.84−0.054×insulin−0.98×C; r2=0.53; F=11.1; P<0.001). Hence, genetic (T8590C) and environmental (insulin) factors impair 20-HETE responses to salt in human hypertension. We propose that genotype analyses with sufficient homozygous CC will establish definitive relationships among 20-HETE, salt sensitivity of blood pressure, and insulin resistance.

Regulation of Plasma Endothelin by Salt in Salt-Sensitive Hypertension

BackgroundSalt dependency of blood pressure (BP) characterizes most models of experimental hypertension in which endothelins play a significant vasoconstrictor role. Despite this, there are no data on the regulation of plasma endothelin by salt balance in human hypertension. Methods and ResultsPlasma endothelin was measured in 47 patients with essential hypertension. Endothelin, catecholamine, and plasma renin activity (PRA) responses to 24-hour sodium deprivation (↓Na) were assessed in 29 of these patients. Endothelin was higher in hypertensive patients (4.6±0.2 fmol/mL) than in 20 control subjects (3.3±0.3 fmol/mL, P <0.002), was correlated with BP, and was negatively associated with PRA (P <0.04). Salt-sensitive, salt-resistant, and indeterminate groups were defined by the tertiles of the t statistic for the difference in BP before and after ↓Na. Systolic BP falls were −15±1, −2±2, and −9±1 mm Hg, respectively. PRA, its response to ↓Na, and its level after ↓Na were lowest (albeit nonsignificant) in salt-sensitive patients. Baseline catecholamine and endothelin levels did not differ among the groups. In response to ↓Na, catecholamines increased more significantly in salt-sensitive patients (+2.4±0.9 nmol/L) than in the other groups (0.4±0.2 and 0.7±0.2 nmol/L for indeterminate and salt-resistant groups, respectively;P <0.03), whereas endothelin increased in the salt-sensitive group (0.8±0.3 fmol/mL), decreased in the salt-resistant group (−0.4±0.3 fmol/mL), and sustained minimal change in the indeterminate group (0.2±0.3 fmol/mL) (P <0.04). Thus, endothelin levels in the salt-depleted state were highest in salt-sensitive patients (5.2±0.4 fmol/mL) versus the other groups (3.4±0.4 and 4.4±0.4 fmol/mL for salt-resistant and indeterminate groups, respectively) (P <0.02). Changes in endothelin during ↓Na and levels after ↓Na were correlated with changes in catecholamines (P <0.02). ConclusionsOur data suggest that salt-depleted salt-sensitive hypertensives with blunted renin responses exhibit enhanced catecholamine-stimulated endothelin levels and may therefore respond better than unselected patients with essential hypertension to endothelin receptor blockers.

Salt Sensitivity of Blood Pressure A Scientific Statement From the American Heart Association

Salt-sensitivity of blood pressure is an abnormal phenotype that confers increased cardiovascular morbidity. We discuss its underlying renal mechanisms, including the role of systems that regulate renal salt handling. We review knockout and congenic strains that have unraveled participation of several genes in rodents inbred to produce pure salt-sensitive and salt-resistant substrains. In humans, salt-sensitivity is a continuous variable, hence, defined with arbitrary cutoffs for blood pressure responses to salt-loading or deprivation. Nonetheless, clustering of phenotypic characteristics in salt-sensitive subjects suggests an inherited component for this trait. This is supported by relationships between salt-sensitivity and gene polymorphisms in renal transporters, vasoactive substances and oxidative systems. Identification of biochemical or genetic markers of salt-sensitivity for use in the clinic would improve risk stratification of hypertensive and prehypertensive subjects. Understanding of its pivotal mechanisms may lead to specific therapies to decrease the cardiovascular risk associated with this trait in humans.

20-HETE and Furosemide-Induced Natriuresis in Salt-Sensitive Essential Hypertension

Abstract—Cyclooxygenase metabolites of arachidonic acid modulate the natriuretic effect of furosemide. It is not known whether 20-HETE, a monooxygenase metabolite of arachidonic acid that also inhibits sodium transport, participates in the action of furosemide. We measured urine sodium (UNaV) and 20-HETE during furosemide diuresis (40 mg three times over 12 hours) in 12 salt-sensitive (SS) and 11 salt-resistant (SR), salt-replete hypertensive subjects (126±24 mmol/24 hours positive sodium balance produced by 160-mmol-sodium diet and 2 L saline infusion). Individual systolic blood pressure decreases from the salt-replete to the salt-depleted state were the index of salt-sensitivity. SS had low plasma renin with blunted responses to changes in salt balance, inappropriate plasma aldosterone, and an increased aldosterone/renin ratio. UNaV by furosemide was less in SS (263±25 mmol/12 hours) than in SR (351±25 mmol/12 hours, P <0.02) patients. 20-HETE was not different between SS and SR patients before (1.92±0.38 versus 1.37±0.34 &mgr;g/h) or after furosemide (1.52±0.27 versus 2.01±0.40 &mgr;g/h), but furosemide changed 20-HETE excretion in opposite direction in SR (0.63±0.26) versus SS (−0.40±0.17, P <0.005) patients. In all patients together, %&Dgr;20-HETE by furosemide correlated with %&Dgr;UNaV (r =0.56, P <0.01) and negatively with salt-sensitivity of blood pressure (r =−0.55, P <0.01). In SS, &Dgr;20-HETE by furosemide correlated with &Dgr;aldosterone/renin ratio (r =0.60, P <0.05), whereas 20-HETE during furosemide had a negative correlation with body mass index (r =−0.73, P <0.01). Our data suggest that 20-HETE modulates the natriuretic response to furosemide, and impaired natriuresis of SS involves a mechanism that alters the 20-HETE response to furosemide and is linked to salt-sensitivity of blood pressure.

20-HETE and Circulating Insulin in Essential Hypertension With Obesity

Abstract—Analogous to observations in Dahl salt-sensitive (SS) rats, we have shown that 20-hydroxyeicosatetraenoic acid (20-HETE) is involved in the pathogenesis of SS essential hypertension. A strong negative correlation between urine 20-HETE and body mass index (BMI) remains unexplained. We measured BP, urine sodium (UNaV), and 20-HETE in obese hypertensive subjects during a 24-hour salt load (160 mmol NaCl diet+2 L intravenous saline). We classified them into insulin-resistant (IR) (n=14) and insulin-sensitive (IS) (n=12), with the average insulin sensitivity index (SI=22.5×[fasting glucose×insulin]−1) of 3 days (cutoff for IR, SI <0.161 mL · L/&mgr;U · mmol). IR were older (50±1 versus 44±2, P <0.03), more obese (BMI 38.2±1.4 versus 32.0±1.5 kg/m2, P <0.01), and had higher insulin (39.2±2.3 versus 22.0±1.1 &mgr;U/mL, P <0.0001) and lower SI (0.084±0.009 versus 0.222±0.013, P <0.0001) than IS. Blood pressure, UNaV, and sodium balance did not differ between groups. SI correlated negatively with age (r =−0.39, P <0.05) and BMI (r =−0.53, P <0.01). Urine 20-HETE was less in IR than in IS when normalized by serum insulin (0.91±0.25 versus 2.24±0.46 &mgr;g · 24 hours−1/&mgr;U · mL−1, P <0.02), but not if uncorrected. Urinary 20-HETE excretion correlated negatively with insulin (r =−0.40, P <0.04), whereas the relationship between 20-HETE and SI was not statistically significant. Our data suggest that increased circulating insulin, not the state of insulin resistance, suppresses urine 20-HETE excretion in obese hypertensive subjects. Findings in experimental models suggest that an inhibitory effect of insulin on cytochrome P4504A, rather than effects of insulin on membrane-bound arachidonic acid or on its release to the cytosol, may explain our observation.

Effect of Salt on Isoprostanes in Salt-Sensitive Essential Hypertension

The controversy over beneficial versus harmful effects of salt on cardiovascular outcomes may be caused by different effects of salt on intermediate phenotypes of hypertension not characterized in epidemiological studies. Hence, we investigated acute effects of salt on oxidative stress in hypertensive subjects classified as salt sensitive (SS, n=14) or salt resistant (SR, n=13) by an inpatient protocol of salt loading (460 mmol NaCl) and salt depletion (10 mmol NaCl and furosemide). Oxidative stress was assessed by measuring the plasma isoprostane 8-iso-PGF2α. SS had lower plasma renin activity, higher aldosterone/renin ratios, and exaggerated endothelin and catecholamine responses to salt depletion compared with SR. Baseline lipid-bound isoprostanes (749±70 pmol/L) were 83% of the total and were slightly but not significantly higher in SS than SR. Baseline free isoprostanes did not differ between groups. After salt loading, lipid-bound isoprostanes were higher in SS (945±106) than SR (579±57; P<0.01). Salt depletion significantly decreased them in SS (−174±84) and increased them in SR (+129±58), equalizing their levels (771±61 versus 708±91; P value not significant). Free isoprostanes were decreased by salt depletion only if data in all of the patients were analyzed together. Total isoprostanes followed the pattern of the lipid-bound fraction. Correlations between salt depletion-induced changes in lipid-bound isoprostanes, plasma renin activity (r=0.45; P<0.02), and aldosterone/renin ratios (r=−0.41; P<0.04) suggested that the more SS the patient, the greater the reduction of oxidative stress by salt depletion. Our research is the first to show that salt affects oxidative stress acutely in humans, particularly in SS hypertension, which may explain the controversial results of epidemiological studies on salt and morbidity and may have implications for therapy.

Essential Hypertension of Caribbean Hispanics: Sodium, Renin, and Response to Therapy

Little is known about essential hypertension in Hispanic Americans, despite the fact that they are the fastest‐growing minority in the United States and have a disproportionate degree of hypertensive target organ damage. The authors studied 89 Caribbean Hispanic hypertensive patients who participated in six double‐blind, randomized trials of antihypertensive agents. Demographics, laboratory data, sodium excretion, plasma renin activity, and atrial natriuretic peptide were obtained after 3–4 weeks on placebo. Blood pressure responses to angiotensin‐converting enzyme (ACE) inhibitors, β blockers, calcium channel blockers, hydrochlorothiazide (HCTZ), and fixed combinations of ACE inhibitors and HCTZ, were compared to the placebo values after 8–12 weeks of treatment. Patients had a multiple risk factor profile (obesity and diabetes) and a wide spectrum of blood pressure elevation, left ventricular hypertrophy, and hypertensive renal damage. Urine sodium excretion rates indicated inability to comply with salt restriction in 65% of patients. Plasma renin activity was lower than that of Hispanic normotensive controls, and 62% of patients had low‐renin essential hypertension by renin profiling to sodium excretion. On analysis of variance, blood pressure reductions by calcium channel blockers, HCTZ, and ACE inhibitor/HCTZ combinations were significantly greater than that with placebo, while those of ACE inhibitors and β blockers as monotherapy were not. The authors conclude that essential hypertension of Caribbean Hispanics is associated with multiple risk factors and is largely of the low‐renin type. Responses to therapy are consistent with those observed in other populations with the low‐renin phenotype and suggest salt‐sensitivity of blood pressure in this population. Confirmation of the latter has implications for prevention and treatment of essential hypertension in Hispanics.