Plasma immunoreactive endothelin in essential hypertension

Circulating Levels of Endothelin-1 and Big Endothelin-1 in Patients with Essential Hypertension

The role of endothelin-1 (ET-1) in the pathogenesis of hypertension (HTN) is not clearly established. There is evidence that its circulating levels are elevated in some forms of experimental and human HTN, but this was not a consistent finding. Based on these controversial data, we tested serum levels of ET-1 and Big ET-1 (the precursor of ET-1) in patients with essential HTN, comparing the results with those of healthy normotensive controls. The levels of ET-1 and Big ET-1 were measured by ELISA. Our results in patients with essential HTN showed that the mean levels of ET-1 (5.01 ± 2.1 pg/mL) were significantly higher (F = 6.34, p = 0.0144) than the mean levels in the control group (3.2 ± 1.0 pg/mL). The levels of Big ET-1 in patients with essential HTN (0.377 ± 0.1 pmol/L) were similar to those in the control group (0.378 ± 0.07 pmol/L) and did not differ significantly (F = 0.00, p = 0.9531). These data suggest that ET-1, but not Big ET-1, may play an important role in the pathogenesis of primary HTN.

Adaptation to 5 weeks of intermittent local vascular pressure increments; mechanisms to be considered in the development of primary hypertension?

The aims were to study effects of iterative exposures to moderate elevations of local intravascular pressure on arterial/arteriolar stiffness and plasma levels of vasoactive substances. Pressures in the vasculature of an arm were increased by 150 mmHg in healthy men (n = 11) before and after a 5-wk regimen, during which the vasculature in one arm was exposed to fifteen 40-min sessions of moderately increased transmural pressure (+65 to +105 mmHg). This vascular pressure training and the pressure-distension determinations were conducted by exposing the subjects' arm versus remaining part of the body to differential ambient pressure. During the pressure-distension determinations, venous samples were simultaneously obtained from pressurized and unpressurized vessels. Pressure training reduced arterial pressure distension by 40 ± 23% and pressure-induced flow by 33 ± 30% (P < 0.01), but only in the pressure-trained arm, suggesting local adaptive mechanisms. The distending pressure-diameter and distending pressure-flow curves, with training-induced increments in pressure thresholds and reductions in response gains, suggest that the increased precapillary stiffness was attributable to increased contractility and structural remodeling of the walls. Acute vascular pressure provocation induced local release of angiotensin-II (ANG II) and endothelin-1 (ET-1) (P < 0.05), suggesting that these vasoconstrictors limited the pressure distension. Pressure training increased basal levels of ET-1 and induced local pressure release of matrix metalloproteinase 7 (P < 0.05), suggesting involvement of these substances in vascular remodeling. The findings are compatible with the notion that local intravascular pressure load acts as a prime mover in the development of primary hypertension.NEW & NOTEWORTHY Adaptive responses to arterial/arteriolar pressure elevation have typically been investigated in cross-sectional studies in hypertensive patients or in longitudinal studies in experimental animals. The present investigation shows that in healthy individuals, fifteen 40-min, carefully controlled, moderate transmural pressure elevations markedly increase in vivo stiffness (i.e. reduce pressure distension) in arteries and arterioles. The response is mediated via local mechanisms, and it appears that endothelin-1, angiotensin-II, and matrix metalloproteinase 7 may have key roles.

The Efficacy of Tai Chi and Qigong Exercises on Blood Pressure and Blood Levels of Nitric Oxide and Endothelin-1 in Patients with Essential Hypertension: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Objective

Tai Chi and Qigong are the two similar traditional Chinese wellness exercises. A strong body of published clinical randomized controlled trials (RCTs) has investigated the health benefits of Tai Chi and Qigong exercises (TCQE) in patients with essential hypertension (EH). This is the first meta-analysis to evaluate the efficacy of TCQE on blood pressure (BP) and blood levels of nitric oxide (NO) and endothelin-1 (ET-1) in EH patients and explore the potential antihypertensive mechanism of TCQE.

Methods

We conducted a literature retrieval for Chinese and English studies in seven databases from their respective inceptions until January 14, 2020. All RCTs examining clinical efficacy of TCQE for EH patients were considered. The major therapeutic outcomes of TCQE were changes in the blood levels of NO, ET-1, and BP in EH patients. Methodological quality of the included RCTs was detected via The Cochrane Risk of Bias tool. We evaluated the data reported and performed the meta-analysis by Review Manager 5.3 software.

Results

9 RCTs involving 516 EH patients were included. The intervention duration lasted from 1.5 months to 6 months. The results of comprehensive analysis showed that compared with control interventions, experimental interventions were more effective in reducing the systolic blood pressure and the diastolic blood pressure and contributed higher blood levels of NO and lower blood levels of ET-1.

Conclusions

TCQE could be an effective complementary and alternative therapy for EH. The lower BP in EH patients who practice TCQE may have some connection with exercise-related increased blood NO levels and decreased blood ET-1 levels. However, further research is needed to make clear the efficacy of TCQE in management of EH and the mechanism of lowering BP in TCQE.

Endothelin-1In Continuous Ambulatory Peritoneal Dialysis and Hemodialysis Patients: A Preliminary Study

Objective

To determine the effects of continuous ambulatory peritoneal dialysis (CAPD) and hemodialysis (HD) on endothelin-1 (ET-1) levels in patients with endstage renal disease (ESRD) and to assess the relationship between plasma ET-1 levels and selected patient parameters.

Design

Prospective, non randomized comparison study.

Setting

Outpatient CAPD and HD units of a university medical center.

Participants

Twelve ESRD patients (6 on CAPD and 6 on HD) and 5 healthy normotensive subjects.

Interventions

CAPD patients had blood and peritoneal dialysate samples collected and measurements made following an overnight exchange. HD patients had blood collected and measurements made at 0 hours (basal) and again at 3 hours during a midweek HD session. Blood samples were also collected from normal subjects and served as ET-1 controls.

Measurements

ET-1 and patient parameters (creatinine, peritoneal dialysate volume, blood pressure, bodyweight, age, and treatment duration) were determined. Data are reported as the mean ± one standard deviation.

Results

Plasma and dialysate ET-1 levels in the CAPD group were 19.5±4.2 pglmL and 9.2±4.2 pglmL, respectively. The control group plasma and unused dialysate contained no detectable ET-1 «3.0 pg/mL, the limit of detection). The peritoneal clearance of ET-1 was less than that of creatinine (2. 29±0.69 mL/minute vs 4.22±0.66 mL/minute, p=0.005). The basal (0 hour) plasma ET-1 level in the HD group (16.5±7.8 pg/mL) did not differ from that of the CAPD group, p=0.423. Furthermore, no differences in patient parameters were detected between the CAPD and basal HD groups. Although the mean arterial pressure (MAP) decreased during HD, the plasma ET-1 level at 3 hours (13.5±5.4 pg/mL) remained unchanged from the basal level, p=0.307. An analysis of pooled data from the CAPD and HD groups revealed no significant correlation between plasma ET-1 and MAP, body weight, creatinine, or treatment duration. There was, however, a positive correlation between plasma ET-1 and age (r=0.643, p=0.024).

Conclusions

Plasma ET-1 levels are elevated in both CAPD and HD patients. Despite the clearance of ET-1 by the peritoneal membrane, plasma ET-1 levels in CAPD patients are elevated to the same extent as levels observed in HD patients. Preliminary results show a positive correlation between plasma ET-1 and age in the absence of renal function. This finding remains to be examined in a larger ESRD population.

Dysregulated aldosterone secretion in persons of African descent with endothelin-1 gene variants

Compared with persons of European descent (ED), persons of African descent (AD) have lower aldosterone (ALDO) levels, with the assumption being that the increased cardiovascular disease (CVD) risk associated with AD is not related to ALDO. However, the appropriateness of the ALDO levels for the volume status in AD is unclear. We hypothesized that, even though ALDO levels are lower in AD, they are inappropriately increased, and therefore, ALDO could mediate the increased CVD in AD. To test this hypothesis, we analyzed data from HyperPATH - 1,788 individuals from the total cohort and 765 restricted to ED-to-AD in a 2:1 match and genotyped for the endothelin-1 gene (EDN1). Linear regression analyses with adjustments were performed. In the total and restricted cohorts, PRA, ALDO, and urinary potassium levels were significantly lower in AD. However, in the AD group, greater ALDO dysregulation was present as evidenced by higher ALDO/plasma renin activity (PRA) ratios (ARR) and sodium-modulated ALDO suppression-to-stimulation indices. Furthermore, EDN1 minor allele carriers had significantly greater ARRs than noncarriers but only in the AD group. ARR levels were modulated by a significant interaction between EDN1 and AD. Thus, EDN1 variants may identify particularly susceptible ADs who will be responsive to treatment targeting ALDO-dependent pathways (e.g., mineralocorticoid-receptor antagonists).

Endothelial dysfunction in human essential hypertension

Although the endothelium has a number of important functions, the term endothelial dysfunction is commonly used to describe impairment in its vasodilatory capacity. It is increasingly recognized that this is related to hypertension, although whether it predates essential hypertension or is a consequence of it is still unknown. In this review, we explore the mechanisms of endothelial dysfunction in essential hypertension, its prognostic significance and methods of pharmacological reversal.

The Role of the Endothelin System in the Vascular Dysregulation Involved in Retinitis Pigmentosa

Retinitis pigmentosa is a clinical and genetic group of inherited retinal disorders characterized by alterations of photoreceptors and retinal pigment epithelium leading to a progressive concentric visual field restriction, which may bring about severe central vision impairment. Haemodynamic studies in patients with retinitis pigmentosa have demonstrated ocular blood flow abnormalities both in retina-choroidal and in retroocular vascular system. Moreover, several investigations have studied the augmentation of endothelin-1 plasma levels systemically in the body and locally in the eye. This might account for vasoconstriction and ischemia, typical in vascular dysregulation syndrome, which can be considered an important factor of reduction of the ocular blood flow in subjects affected by retinitis pigmentosa.

Genetic Polymorphisms in Endothelin-1 as Predictors for Long-Term Survival and the Cardiac Index in Patients Undergoing On-Pump Cardiac Surgery

Genetic variants within the endothelin-1 gene (EDN1) have been associated with several cardiovascular diseases and may act as genetic prognostic markers. Here, we explored the overall relevance of EDN1 polymorphisms for long-term survival in patients undergoing on-pump cardiac surgery. A prospectively collected cohort of 455 Caucasian patients who underwent cardiac surgery with cardiopulmonary bypass was followed up for 5 years. The obtained genotypes and inferred haplotypes were analyzed for their associations with the five-year mortality rate (primary endpoint). The EDN1 T-1370G and K198N genotype distributions did not deviate from Hardy–Weinberg equilibrium and the major allele frequencies were 83% and 77%, respectively. The cardiovascular risk factors were equally distributed in terms of the different genotypes and haplotypes associated with the two polymorphisms. The five-year mortality rate did not differ among the different EDN1 T-1370G and K198N genotypes and haplotypes. Haplotype analysis revealed that carriers of the G-T (compound EDN1 T-1370G G/K198N T) haplotype had a higher cardiac index than did non-carriers (p = 0.0008); however, this difference did not reach significance after adjusting for multiple testing. The results indicate that common variations in EDN1 do not act as prognostic markers for long-term survival in patients undergoing on-pump cardiac surgery.

Higher circulatory level of endothelin-1 in hypertensive subjects screened through a cross-sectional study of rural Bangladeshi women

Endothelin-1 (ET-1) is a potential marker of the endothelial dysfunction, which has been shown to be elevated in hypertensive subjects. No previous study has investigated the circulatory level of ET-1 and hypertension in a South Asian country. The present study assessed the circulating levels of ET-1 in subjects with or without hypertension and further examined the association of ET-1 with clinical and metabolic parameters. A total of 2543 rural Bangladeshi women with a mean age of 44.5 years were studied using a cross-sectional survey. Multiple regressions were used to examine the association between the circulatory ET-1 levels and hypertension. The prevalence of hypertension was 29.3%. The ET-1 levels were significantly higher in the hypertensive (mean 3.08 pg ml(-1), s.e. (0.19)) than in the non-hypertensive subjects (mean 2.01 pg ml(-1), s.e. (0.03)) (P = 0.001). After adjusting for age, the ET-1 level had significant positive associations with the diastolic blood pressure (P = 0.002), systolic blood pressure (P = 0.001), mean arterial pressure (P = 0.002) and fasting blood glucose (P = 0.002). In a tertile analysis, we found that hypertension in the subjects was significantly increased as the levels of ET-1 increased (P for the trend = 0.001). In a stepwise multiple regression analysis, after adjusting for age and all other potential variables, we found that the mean arterial pressure and the fasting plasma levels have significant associations with the ET-1 level. The present study demonstrates that there is a higher concentration of ET-1 among the hypertensive subjects in an apparently healthy population of Bangladeshi rural women. The relationship between ET-1 and hypertension requires further investigation to define the clinical utility and predictive value of serum ET-1 levels for hypertension for a South Asian population.

The role of endothelin-1 in the sympathetic nervous system in the heart

Endothelin-1 (ET1) is a peptide that was initially identified as a strong inductor of vascular contraction. In the last 25 years, there have been several biological processes identified in which ET1 seems to play a critical role. In particular, genetic studies have unveiled that ET1 is important for neuronal development, growth and function. Experimental studies identified ET1 as a regulator of the interaction between sympathetic neurons and cardiac myocytes. This might be of clinical importance since patients suffering from heart failure are characterized by disrupted norepinephrine homeostasis in the heart. This review summarizes the important findings on the role of ET1 for sympathetic neurons and norepinephrine homeostasis in the heart.

Adrenergic signaling and oxidative stress: a role for sirtuins?

The adrenergic system plays a central role in stress signaling and stress is often associated with increased production of ROS. However, ROS overproduction generates oxidative stress, that occurs in response to several stressors. β-adrenergic signaling is markedly attenuated in conditions such as heart failure, with downregulation and desensitization of the receptors and their uncoupling from adenylyl cyclase. Transgenic activation of β2-adrenoceptor leads to elevation of NADPH oxidase activity, with greater ROS production and p38MAPK phosphorylation. Inhibition of NADPH oxidase or ROS significantly reduced the p38MAPK signaling cascade. Chronic β2-adrenoceptor activation is associated with greater cardiac dilatation and dysfunction, augmented pro-inflammatory and profibrotic signaling, while antioxidant treatment protected hearts against these abnormalities, indicating ROS production to be central to the detrimental signaling of β2-adrenoceptors. It has been demonstrated that sirtuins are involved in modulating the cellular stress response directly by deacetylation of some factors. Sirt1 increases cellular stress resistance, by an increased insulin sensitivity, a decreased circulating free fatty acids and insulin-like growth factor (IGF-1), an increased activity of AMPK, increased activity of PGC-1a, and increased mitochondrial number. Sirt1 acts by involving signaling molecules such P-I-3-kinase-Akt, MAPK and p38-MAPK-β. βAR stimulation antagonizes the protective effect of the AKT pathway through inhibiting induction of Hif-1α and Sirt1 genes, key elements in cell survival. More studies are needed to better clarify the involvement of sirtuins in the β-adrenergic response and, overall, to better define the mechanisms by which tools such as exercise training are able to counteract the oxidative stress, by both activation of sirtuins and inhibition of GRK2 in many cardiovascular conditions and can be used to prevent or treat diseases such as heart failure.

Adrenergic signaling and oxidative stress: a role for sirtuins?

The adrenergic system plays a central role in stress signaling and stress is often associated with increased production of ROS. However, ROS overproduction generates oxidative stress, that occurs in response to several stressors. β-adrenergic signaling is markedly attenuated in conditions such as heart failure, with downregulation and desensitization of the receptors and their uncoupling from adenylyl cyclase. Transgenic activation of β2-adrenoceptor leads to elevation of NADPH oxidase activity, with greater ROS production and p38MAPK phosphorylation. Inhibition of NADPH oxidase or ROS significantly reduced the p38MAPK signaling cascade. Chronic β2-adrenoceptor activation is associated with greater cardiac dilatation and dysfunction, augmented pro-inflammatory and profibrotic signaling, while antioxidant treatment protected hearts against these abnormalities, indicating ROS production to be central to the detrimental signaling of β2-adrenoceptors. It has been demonstrated that sirtuins are involved in modulating the cellular stress response directly by deacetylation of some factors. Sirt1 increases cellular stress resistance, by an increased insulin sensitivity, a decreased circulating free fatty acids and insulin-like growth factor (IGF-1), an increased activity of AMPK, increased activity of PGC-1a, and increased mitochondrial number. Sirt1 acts by involving signaling molecules such P-I-3-kinase-Akt, MAPK and p38-MAPK-β. βAR stimulation antagonizes the protective effect of the AKT pathway through inhibiting induction of Hif-1α and Sirt1 genes, key elements in cell survival. More studies are needed to better clarify the involvement of sirtuins in the β-adrenergic response and, overall, to better define the mechanisms by which tools such as exercise training are able to counteract the oxidative stress, by both activation of sirtuins and inhibition of GRK2 in many cardiovascular conditions and can be used to prevent or treat diseases such as heart failure.

Physical activity opposes the age-related increase in skeletal muscle and plasma endothelin-1 levels and normalizes plasma endothelin-1 levels in individuals with essential hypertension

AIMS

Endothelin-1 has potent constrictor and proliferative activity in vascular smooth muscle, and essential hypertension and aging are associated with increased endothelin-1-mediated vasoconstrictor tone. The aim of this study was to investigate the effect of physical activity, hypertension and age on endothelin-1 levels in plasma and skeletal muscle and endothelin receptors in skeletal muscle in human subjects.

METHODS

In study 1, normotensive (46 ± 1 years, n = 11) and hypertensive (47 ± 1 years, n = 10) subjects were studied before and after 8 weeks of aerobic exercise training. In study 2, young (23 ± 1 years, n = 8), older lifelong sedentary (66 ± 2 years, n = 8) and older lifelong endurance-trained (62 ± 2 years, n = 8) subjects were studied in a cross-sectional design.

RESULTS

Skeletal muscle and plasma endothelin-1 levels were increased with age and plasma endothelin-1 levels were higher in hypertensive than normotensive individuals. Eight weeks of exercise training normalized plasma endothelin-1 levels in the hypertensive subjects and increased the protein expression of the ET(A) receptor in skeletal muscle of normotensive subjects. Similarly, individuals that had performed lifelong physical activity had similar plasma and muscle endothelin-1 levels as the young controls and had higher ET(A) receptor levels.

CONCLUSION

Our findings suggest that aerobic exercise training opposes the age-related increase in skeletal muscle and plasma endothelin-1 levels and normalizes plasma endothelin-1 levels in individuals with essential hypertension. This effect may explain some of the beneficial effects of training on the cardiovascular system in older and hypertensive subjects.

Regulation of insulin sensitivity by serine/threonine phosphorylation of insulin receptor substrate proteins IRS1 and IRS2

The insulin receptor substrate proteins IRS1 and IRS2 are key targets of the insulin receptor tyrosine kinase and are required for hormonal control of metabolism. Tissues from insulin-resistant and diabetic humans exhibit defects in IRS-dependent signalling, implicating their dysregulation in the initiation and progression of metabolic disease. However, IRS1 and IRS2 are regulated through a complex mechanism involving phosphorylation of >50 serine/threonine residues (S/T) within their long, unstructured tail regions. In cultured cells, insulin-stimulated kinases (including atypical PKC, AKT, SIK2, mTOR, S6K1, ERK1/2 and ROCK1) mediate feedback (autologous) S/T phosphorylation of IRS, with both positive and negative effects on insulin sensitivity. Additionally, insulin-independent (heterologous) kinases can phosphorylate IRS1/2 under basal conditions (AMPK, GSK3) or in response to sympathetic activation and lipid/inflammatory mediators, which are present at elevated levels in metabolic disease (GRK2, novel and conventional PKCs, JNK, IKKβ, mPLK). An emerging view is that the positive/negative regulation of IRS by autologous pathways is subverted/co-opted in disease by increased basal and other temporally inappropriate S/T phosphorylation. Compensatory hyperinsulinaemia may contribute strongly to this dysregulation. Here, we examine the links between altered patterns of IRS S/T phosphorylation and the emergence of insulin resistance and diabetes.

Brain endothelial barrier passage by monocytes is controlled by the endothelin system

Homeostasis of the brain is dependent on the blood-brain barrier (BBB). This barrier tightly regulates the exchange of essential nutrients and limits the free flow of immune cells into the CNS. Perturbations of BBB function and the loss of its immune quiescence are hallmarks of a variety of brain diseases, including multiple sclerosis (MS), vascular dementia, and stroke. In particular, diapedesis of monocytes and subsequent trafficking of monocyte-derived macrophages into the brain are key mediators of demyelination and axonal damage in MS. Endothelin-1 (ET-1) is considered as a potent pro-inflammatory peptide and has been implicated in the development of cardiovascular diseases. Here, we studied the role of different components of the endothelin system, i.e., ET-1, its type B receptor (ET(B)) and endothelin-converting enzyme-1 (ECE-1) in monocyte diapedesis of a human brain endothelial cell barrier. Our pharmacological inhibitory and specific gene knockdown studies point to a regulatory function of these proteins in transendothelial passage of monocytes. Results from this study suggest that the endothelin system is a putative target within the brain for anti-inflammatory treatment in neurological diseases.

Cholesterol, Cytokines and Diseases

A high level of cholesterol is associated with obesity, cardiovascular diseases and atherosclerosis. Immune response in atherosclerosis is mediated by chemokines which attract monocytes, leading to the innate immune response characterised by the production of cytokines. The immunoregulatory cytokines are an important bridge between innate and adductive immunity. TH1 cytokines are involved as effector T cells in inflammatory response, while TH2 cytokines can be anti-inflammatory such as IL-10 and IL-4. It is well known that statins enhance the production of TH2 cytokines whereas the secretion of TH1 cytokines is suppressed. For this purpose, we studied the significance of anti-inflammatory effect and suppression of inflammation by statins. In this paper we revisited the role of cholesterol and cytokines IL-18, IL-10, IL-12, TNF-α, interferon-γ, and chemokines in inflammatory diseases.

High level of plasma endothelin-1 predicts development of hypertension in normotensive subjects

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstrictor derived from the endothelium. However, most large scale cross-sectional studies in humans have indicated no relationship between plasma ET-1 levels and hypertension. The present study was designed to determine whether high plasma ET-1 levels predict the development of hypertension.

METHODS

A total of 1,492 subjects received a health examination in the Japanese cohort of Seven Countries Study in 1999, when, we examined blood pressure (BP), body mass index (BMI), and blood chemistries. Data on fasting ET-1 were obtained from 1,451 individuals. Seven years later, 1,261 subjects (494 males and 767 females) were re-examined (follow-up rate = 87%).

RESULTS

Of 814 normotensives (BP <140/90 mm Hg without antihypertensive medications) at baseline, 222 subjects developed hypertension. We divided the baseline plasma ET-1 levels into quartiles. The odds ratio for the development of hypertension after 7 years was 1.79 (95% confidence interval (CI): 1.08-2.96) in the highest quartile vs. the lowest quartile of ET-1 level after adjustment for confounding factors.

CONCLUSION

A high level of plasma ET-1 predicted the development of hypertension in normotensive subjects.

ET-1 plasma levels and ocular blood flow in retinitis pigmentosaThis article is one of a selection of papers published in the two-part special issue entitled 20 Years of Endothelin Research

Retinitis pigmentosa (RP) is an inherited retinal disorder clinically characterized by a pale, waxy optic nerve head, attenuated retinal blood vessels, and bone spicule pigment in the retina. Hemodynamic studies have demonstrated that RP is associated with a reduction in the retinal and choroidal blood flow. Retinal hemodynamic impairment is also present in early stages of RP, and various hypotheses have been advanced as to the cause. The authors studied 20 patients, 12 males and 8 females, aged 26–42 years (mean 35.1 years) and affected by simplex RP. The patients had a visual acuity of 0.9 ± 0.1, visual field mean defect of –6.52 ± 3.58 dB, and b-wave electroretinogram amplitude of 260.08 ± 8.24 µV. An increase in plasma levels of endothelin-1 (ET-1) was found: 1.910 ± 0.317 pg/mL versus 1.180 ± 0.210 pg/mL in non-RP controls (p < 0.02). Moreover both an ocular and systemic vascular impairment was detected by means of color Doppler imaging and laser Doppler flowmetry performed during a cold pressor test. We found a correlation between the increase of ET-1 plasma levels in RP and the decrease of peak systolic velocity in the ophthalmic artery (p < 0.03) and in the posterior ciliary arteries (p < 0.006). It is thought that an increase of ET-1 and retinal oxygen levels in RP could lead to vasoconstriction and a decrease of the retinal blood flow, worsening the abiotrophic process.

[Endothelin system function in diabetic nephropathy]

Diabetic Nephropathy (DN) is a major chronic complication of diabetes mellitus (DM), and one of the main causes of new cases for dialysis, being associated with increasing mortality. The main risk factors for DN are hypertension, hyperglycemia, dyslipidemia, and genetic susceptibility. The renin-angiotensin system (RAS) plays an important role in genesis and progression of DN and there is evidence of an interrelationship between this system and the endothelins. Endothelins are powerful vasoconstrictor peptides and act as modulators of vasomotor tone, cell proliferation, and hormone production. These peptides act through two types of receptors (ET-A and ET-B) and are expressed on endothelial cells and vascular smooth-muscle cells. Activation of this receptor in renal cells leads to a complex signaling cascade resulting in stimulation of mesangial cell hypertrophy, proliferation, contraction, and extracellular matrix accumulation. These hemodynamic renal alterations are associated with the onset and progress of renal disease in DM. Elevated endothelin-1 (ET-1) levels have been reported in patients with DM. There is evidence suggesting that an increase in the production of ET-1 leads to glomerular damage. The use of ET receptor antagonists has been reported as renoprotective, correcting the early hemodynamic abnormalities in experimental DM, reinforcing the importance of this system in DN.

Plasma Endothelin-1 Level in Japanese Normal Tension Glaucoma Patients

PURPOSE

To compare the plasma concentration of endothelin-1 (ET-1) among patients < 60 years of age with normal-tension glaucoma (NTG), primary open-angle glaucoma (POAG), and in age-matched normal participants.

METHODS

Plasma concentration of ET-1 was determined in 30 NTG 18 POAG patients, and 19 age-matched normal participants using an enzyme immunoassay.

RESULTS

The ET-1 level was 1.49 +/- 0.51 pg/ml in the NTG patients (49.4 +/- 8.8 years), 1.58 +/- 0.64 pg/ml in the POAG patients (44.7 +/- 10.7 years), and 1.33 +/- 0.50 pg/ml in the normal participants (49.9 +/- 5.6 years). The ET-1 levels were not significantly different among the three groups, and no significant correlation with the extent of visual field damage, intraocular pressure (IOP), refraction, or age was seen in the glaucoma patients.

CONCLUSIONS

The plasma ET-1 level showed no difference among NTG patients, POAG patients, and normal participants < 60 years of age in the Japanese population.

Endothelial dysfunction in patients with noncomplicated and complicated hypertension

Endothelial dysfunction plays an important role in the pathogenesis of hypertension. Other risk factors of atherosclerosis also affect its development. The aim of the study was to assess nitric oxide metabolites concentration (nitrites and nitrates No(x)) and endothelin (ET-1) in plasma and cyclic 3,5-guanosine monophosphate (cGMP) in 24 h-urine collection in patients with noncomplicated hypertension without risk factors of atherosclerosis and in hypertensive patients with coronary artery disease (CAD). Sixty-eight subjects were included in the study (44 men, 24 women), aged 47 +/- 76 years, allotted into four groups: I - controls (18 clinically healthy subjects); II - 12 subjects with hypertension without risk factors of atherosclerosis; III - 16 subjects with hypertension and risk factors of atherosclerosis; and IV - 22 subjects with hypertension and CAD. Plasma NO(x) concentration was determined using the Greiss method, plasma ET-1 by ELISA, and urine cGMP using the immunoenzymatic method. Plasma NO(x) concentration was 14.00 +/- 6.88 micromol/L in group I, in group II - 18.62 +/- 5.84 micromol, in group III - 9.96 +/- 4.72 micromol/L, and in group IV - 8.78 +/- 3.72 micromol/L. Statistically significant differences were between groups I and III (p < 0.05) and I and IV (p < 0.04) and groups II and III (p < 0.01) and II and IV (p < 0.01). The concentration of cGMP in 24 h urine collection was in group I - 40 +/- 24 pmol/L; in group II - 54 +/- 41 pmol/L; in group III - 38 +/- 32 pmol/L; and in group IV - 42 +/- 36 pmol/L. There were no significant differences between the groups. Plasma ET-1 concentration was 3.86 +/- 0.52 pg/mL in group I, in group II - 4.05 +/- 0.71 pg/mL, in group III - 4.22 +/- 0.79 pg/mL and in group IV - 4.38 +/- 0.75 pg/mL. Statistically significant differences were between group I and III (p < 0.05), I and IV (p < 0.03), and between group II and IV (p < 0.04). Endothelial dysfunction was not found in hypertensive patients without a family history of cardiovascular diseases and without other risk factors of atherosclerosis. Deterioration of endothelial function was observed in patients with hypertension with risk factors of atherosclerosis. It was most pronounced in those with CAD.

Impact of endothelin-1 Lys198Asn polymorphism on coronary artery disease and endorgan damage in hypertensives

OBJECTIVE

Endothelin is the most potent endogenous vasoconstrictor and is involved in several vascular disorders such as arterial hypertension. Its intense interaction with other vasoactive hormone systems revealed the consideration about the endothelin gene as an interesting candidate for influencing the development of essential hypertension and hypertensive endorgan damage. The purpose of this study was to investigate the role of endothelin-1 Lys198Asn polymorphism in patients with severe arterial hypertension as well as associated endorgan damages.

METHODS

In 400 hypertensive patients and 150 normotensive controls we examined the endothelin-1 Lys198Asn polymorphism by DNA sequencing and patients were divided according to their genotype (GG, GT, and TT). Moreover, the frequency of endothelin-1 Lys198Asn polymorphism was investigated with respect to the prevalence of several actual or historical endorgan damages (renal disorder, coronary artery disease, vascular events, vascular damage, and congestive heart failure) in hypertensive patients.

RESULTS

Genotype distribution for endothelin-1 Lys198Asn polymorphism was 57.3% (GG), 41.3% (GT), and 1.43% (TT) in normotensive individuals; and in hypertensive individuals was 54.75% (GG), 43% (GT) and 2.25% (TT). Genotype distribution was unaffected in patients with severe hypertension, renal disorder, vascular events, vascular damage, and congestive heart failure. We, however, found a significant difference in hypertensive individuals with coronary artery disease and TT genotype (P=0.004).

CONCLUSION

Homozygous TT carrier contributes to a higher prevalence of coronary artery disease, especially for three-vessel disease in hypertensive individuals. Thus, the polymorphism at position 198 could serve as a possibility to differentiate high-risk subgroups in the heterogeneous population of hypertensive patients.

Polymorphisms of the endothelin-1 gene associate with hypertension in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) associates with excess cardiovascular (CV) morbidity and mortality. Hypertension, a highly prevalent entity in RA, has been associated with the endothelin-1 (ET-1) gene locus (EDN1) in some groups, such as Afro-Caribbean, the obese, and in low-renin states, but not in the general population as a whole. High levels of plasma ET-1 have been observed in RA. This study evaluated the potential association of EDN1 gene locus and serum ET-1 levels with hypertension in patients with RA. Genomic DNA and serum samples were collected from 397 well-characterized RA patients; DNA was also available from 401 local general population controls without RA. To explore the overall relevance of EDN1, two suitable single-nucleotide polymorphisms (SNPs), rs1800541 and rs5370, were selected and haplotype analysis was performed. Both SNPs were identified using real-time polymerase chain reaction (PCR) and melting curve analysis. Genetic analysis was related to hypertension as dichotomous trait and to blood pressure indices as continuous variables. Serum endothelin levels were also assessed in the RA patients. No genotype or haplotype differences were observed between RA and control subjects. Within RA, logistic regression analysis of each SNP separately revealed a threefold increase in the adjusted odds of being hypertensive of rs5370 TT homozygotes compared to GG homozygotes (OR = 2.89, 95%CI: 1.02 to 8.19). After adjustment for multiple potential confounders, haplotype analysis revealed an additive effect of the rs1800541-rs5370 T-T haplotype on hypertension (OR = 2.96, 95%CI: 1.28 to 6.86; p = .011), systolic blood pressure (SBP) (beta = 6.75 +/- 2.57 mm Hg; p = .009), and pulse pressure (PP) (beta = 4.37 +/- 2.12 mm Hg; p = .040). There was an increased prevalence of raised ET-1 levels amongst hypertensive RA patients, whereas a similar trend was observed for T-T haplotype carriers. RA patients who carry the rs1800541-rs5370 T-T EDN1 haplotype appear more likely to be hypertensive with an increased SBP and PP. These findings, if replicated in future studies, could be used as a screening tool for RA patients at increased hypertension, and thus cardiovascular, risk.

Dietary isoflavones in the prevention of cardiovascular disease--a molecular perspective

The Food and Drugs Administration has approved a health claim for soy based on clinical trials and epidemiological data indicating that high soy consumption is associated with a lower risk of coronary artery disease. Soy products contain a group of compounds called isoflavones, with genistein and daidzein being the most abundant. A number of cardioprotective benefits have been attributed to dietary isoflavones including a reduction in LDL cholesterol, an inhibition of pro-inflammatory cytokines, cell adhesion proteins and inducible nitric oxide production, potential reduction in the susceptibility of the LDL particle to oxidation, inhibition of platelet aggregation and an improvement in vascular reactivity. There is increasing interest in the use of nutrigenomic methods to understand the mechanisms by which isoflavones induce these changes, and in the use of nutrigenetics to understand why the effects vary between individuals. Nutrigenomics is a rapidly growing field making use of molecular biology methodologies, such as microarray technology and proteomics, to study how specific nutrients or diets affect gene expression and cellular protein levels. The analysis of differential gene expression and protein levels in endothelial cells, macrophages and smooth muscle cells is critical to elucidating the sequence of events leading to the formation of atherosclerotic lesions, and to understanding the potential anti-atherogenic properties of soy isoflavones. An increasing number of studies demonstrate a significant impact of genetic variation on changes in cardiovascular risk factors in response to dietary intervention. Nutrigenetic effects of this type have recently been reported for dietary isoflavones, and may help to explain some of the disparities in the current literature concerning isoflavones and cardiovascular health.

Dual endothelin receptor blockade acutely improves insulin sensitivity in obese patients with insulin resistance and coronary artery disease

OBJECTIVE

Endothelin (ET)-1 is a vasoconstrictor and proinflammatory peptide that may inhibit glucose uptake. The objective of the study was to investigate if ET (selective ET(A) and dual ET(A)+ET(B)) receptor blockade improves insulin sensitivity in patients with insulin resistance and coronary artery disease.

RESEARCH DESIGN AND METHODS

Seven patients (aged 58 +/- 2 years) with insulin resistance and coronary artery disease completed three hyperinsulinemic-euglycemic clamp protocols: a control clamp (saline infusion), during ET(A) receptor blockade (BQ123), and during combined ET(A) (BQ123) and ET(B) receptor blockade (BQ788). Splanchnic blood flow (SBF) and renal blood flow (RBF) were determined by infusions of cardiogreen and p-aminohippurate.

RESULTS

Total-body glucose uptake (M) differed between the clamp protocols with the highest value in the BQ123+BQ788 clamp (P < 0.05). The M value corrected by insulin was higher in the BQ123+BQ788 than in the control clamp (P < 0.01) or the BQ123 clamp (P < 0.05). There was no difference between the control clamp and the BQ123 clamp. Mean arterial pressure did not change during the control clamp, whereas it decreased during both the BQ123 (P < 0.01) and BQ123+BQ788 (P < 0.05) clamps. RBF increased and renal vascular resistance decreased in the BQ123+BQ788 clamp (P < 0.05) but not in the BQ123 clamp. There was no change in SBF in either clamp.

CONCLUSIONS

Dual ET(A)+ET(B) receptor blockade acutely enhances insulin sensitivity in patients with insulin resistance and coronary artery disease, indicating an important role for endogenous ET-1.

Circulating levels of endothelin-1 in a homogenous Gulf Arab population with untreated essential hypertension

BACKGROUND

Racial variations are reported in the natural history of hypertension. For example, hypertension is significantly more prevalent in blacks than whites. Endothelial cells are important regulators of vascular tone and homeostasis, in part through secretions of vasoactive substances including endothelin-1 (ET-1), a small peptide with potent vasopressor actions. In black hypertensives, ET-1 levels are higher than in normotensive blacks and in both hypertensive and normotensive whites. Since ET-1 might play a significant role in the development and severity of hypertension in the indigenous Arab population of the United Arab Emirates, we investigated the circulating levels of ET-1 in this homogenous population.

PATIENTS AND METHODS

ET-1 levels were measured in plasma samples from 60 untreated hypertensive Arabs and compared with 60 age- and sex-matched normotensive controls.

RESULTS

ET-1 levels were significantly higher in hypertensives (mean 10.1 +/- 1 pmol/L) than normotensives (mean 2.2 +/- 0.5 pmol/L). Body mass index (BMI) was slightly higher among the hypertensives. For all subjects these levels significantly (P < 0.001) correlated with systolic blood pressure and less significantly (P < 0.05) with diastolic blood pressure and body weight. The correlation between ET-1 and both systolic and diastolic blood pressure was persistently significant after adjusting for BMI.

CONCLUSION

Plasma concentrations of ET-1 are significantly higher in hypertensive Gulf Arabs as compared with reported levels in white hypertensives and ET-1 could be a risk factor for cardiovascular diseases in this population. The endothelial system might be particularly important with respect to hypertension in this racial group and merits further study.

Target-organ damage in adolescent hypertension. Analysis of potential influencing factors, especially nitric oxide and endothelin-1

BACKGROUND AND PURPOSE

To assess the role of the nitric oxide-endothelin imbalance in the development of target-organ damages (carotid intima-media thickness and left ventricular mass index) in adolescent hypertension.

METHODS

125 adolescents--67 hypertensive and 58 normotensive--underwent routine anthropology (height, weight) and blood pressure measurements, and laboratory (glucose, cholesterol and triglyceride levels) testing as well as sampling blood for determination of the plasma concentrations of nitric oxide (NOx) and endothelin-1 (ET-1), followed by measurement of the carotid intima-media thickness (IMT) and left ventricular mass index (LVMI).

RESULTS

Plasma concentration of NOx was significantly lower (27.7+/-13.7 vs. 35.8+/-7.0 micromol/l, respectively, p<0.001) and ET-1 was higher (3.11+/-3.9 vs. 1.09+/-1.07 fmol/ml, respectively, p<0.001) in hypertensive adolescents than that of controls. NOx negatively, endothelin positively correlated with blood pressure values, especially with systolic BP. An inverse relationship has been found between NOx and ET-1 concentrations (r=-0.29, p<0.003). In this adolescent population body weight, systolic blood pressure and plasma ET-1 were the most important factors influencing IMT, whereas LVMI correlated with height and weight and systolic BP of the teenagers.

CONCLUSIONS

NO/endothelin imbalance seems to play a role in the development of hypertension and target-organ damages in adolescence. Further studies are encouraged in order to clarify the pathophysiological role of NO/endothelin imbalance in adolescent hypertension.

Genistein affects the expression of genes involved in blood pressure regulation and angiogenesis in primary human endothelial cells

BACKGROUND

Several lines of evidence suggest that the dietary isoflavone genistein (Gen) has beneficial effects with regard to cardiovascular disease and in particular on aspects related to blood pressure and angiogenesis. The biological action of Gen may be, at least in part, attributed to its ability to affect cell signalling and response. However, so far, most of the molecular mechanisms underlying the activity of Gen in the endothelium are unknown.

METHODS AND RESULTS

To examine the transcriptional response to 2.5 microM Gen on primary human endothelial cells (HUVEC), we applied cDNA array technology both under baseline condition and after treatment with the pro-atherogenic stimulus, copper-oxidized LDL. The alteration of the expression patterns of individual transcripts was substantiated using either RT-PCR or Northern blotting. Gen significantly affected the expression of genes encoding for proteins centrally involved in the vascular tone such as endothelin-converting enzyme-1, endothelin-2, estrogen related receptor alpha and atrial natriuretic peptide receptor A precursor. Furthermore, Gen countered the effect of oxLDL on mRNA levels encoding for vascular endothelial growth factor receptor 165, types 1 and 2.

CONCLUSIONS

Our data indicate that physiologically achievable levels of Gen change the expression of mRNA encoding for proteins involved in the control of blood pressure under baseline conditions and reduce the angiogenic response to oxLDL in the endothelium.

G protein-coupled receptor kinase 2 mediates endothelin-1-induced insulin resistance via the inhibition of both Galphaq/11 and insulin receptor substrate-1 pathways in 3T3-L1 adipocytes

G protein-coupled receptor kinases (GRKs) regulate seven-transmembrane receptors (7TMRs) by phosphorylating agonist-activated 7TMRs. Recently, we have reported that GRK2 can function as a negative regulator of insulin action by interfering with G protein-q/11 alpha-subunit (Galphaq/11) signaling, causing decreased glucose transporter 4 (GLUT4) translocation. We have also reported that chronic endothelin-1 (ET-1) treatment leads to heterologous desensitization of insulin signaling with decreased tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and Galphaq/11, and decreased insulin-stimulated glucose transport in 3T3-L1 adipocytes. In the current study, we have investigated the role of GRK2 in chronic ET-1-induced insulin resistance. Insulin-induced GLUT4 translocation was inhibited by pretreatment with ET-1 for 24 h, and we found that this inhibitory effect was rescued by microinjection of anti-GRK2 antibody or GRK2 short interfering RNA. We further found that GRK2 mediates the inhibitory effects of ET-1 by two distinct mechanisms. Firstly, adenovirus-mediated overexpression of either wild-type (WT)- or kinase-deficient (KD)-GRK2 inhibited Galphaq/11 signaling, including tyrosine phosphorylation of Galphaq/11 and cdc42-associated phosphatidylinositol 3-kinase activity. Secondly, ET-1 treatment caused Ser/Thr phosphorylation of IRS-1 and IRS-1 protein degradation. Overexpression of KD-GRK2, but not WT-GRK2, inhibited ET-1-induced serine 612 phosphorylation of IRS-1 and restored activation of this pathway. Taken together, these results suggest that GRK2 mediates ET-1-induced insulin resistance by 1) inhibition of Galphaq/11 activation, and this effect is independent of GRK2 kinase activity, and 2) GRK2 kinase activity-mediated IRS-1 serine phosphorylation and degradation.

The pharmacology of bosentan

This article describes the pharmacological properties and the overall preclinical and clinical profiling of bosentan (Ro 47-0203), a non-peptide endothelin receptor antagonist with oral activity. Bosentan is a combined and competitive antagonist of both ETA and ETB receptors that is selective for the endothelin system. In vitro and in vivo, bosentan potently antagonises the vascular response elicited by the endothelins. Preclinical efficacy is demonstrated in a variety of pathological models including pulmonary and essential hypertension, renal failure of ischaemic and nephrotic origin and cerebral vasospasm following subarachnoid haemorrhage. Effects are particularly marked in experimental models of heart failure (HF) where bosentan acts as a potent vasodilator that improves overall left ventricular performance. After chronic treatment, bosentan also improves survival in rats with HF. As a result of the first encouraging clinical results that show pulmonary and systemic vasodilation, long-term studies are ongoing in the treatment of congestive heart failure (CHF).

Endothelin in the splanchnic vascular bed of DOCA-salt hypertensive rats

Vascular capacitance is reduced by endothelin-1 (ET-1) in deoxycorticosterone (DOCA)-salt hypertensive rats. This may contribute to hypertension development. Because the splanchnic blood vessels (especially veins) are important in determining vascular capacitance, we tested the hypothesis that ET-1 levels in the splanchnic vasculature are elevated in hypertensive DOCA-salt compared with normotensive rats. Tissue ET-1 content was measured by ELISA in aorta, vena cava, superior mesenteric artery and vein, and small mesenteric arteries and veins from normotensive sham-operated (sham) and 4-wk DOCA-salt rats. We also determined ET-1 concentration in aortic and portal venous blood (draining the nonhepatic splanchnic organs) in anesthetized and conscious sham and DOCA-salt rats before and after acute blockade of ETB receptor-mediated plasma clearance of ET-1. Results showed a higher ET-1 content in veins than in arteries of similar size. However, ET-1 content was similar in vessels from sham and DOCA-salt rats, except in aorta and superior mesenteric artery, where ET-1 content was greater in DOCA-salt rats. ET-1 concentration was significantly higher in portal venous than in aortic blood, indicating net nonhepatic splanchnic release (nNHSR) of ET-1. However, nNHSR of ET-1 was similar in sham and DOCA-salt rats. Although nNHSR of ET-1 increased significantly after ETB receptor blockade in sham rats, it was completely unchanged in DOCA-salt rats. These data suggest that, despite the absence of ETB receptor-mediated plasma clearance of ET-1, neither the venous peptide content nor the net release of ET-1 is increased in the splanchnic vasculature of DOCA-salt rats. These results argue against the hypothesis that increased venomotor tone in DOCA-salt hypertension is caused by increased ET-1 concentration around splanchnic venous smooth muscle cells.

Heart failure-the importance of ethnicity

Heart failure is a major public health problem in the Western world. Aetiological factors involved in its development include hypertension, diabetes, and ischaemic heart disease--all of which differ in prevalence, and possibly mechanism, between patients of differing ethnicity. Unfortunately, epidemiological and therapeutic trials have involved almost exclusively white populations, and evidence from these trials cannot necessarily be assumed to be generalisable to populations that include high proportions of patients from other ethnic origins. This review will discuss the mechanistic and therapeutic differences that exist in heart failure between those of European origin, and patients from the major ethnic minority groups of the UK.

Plasma endothelin-1 level is related to renal function and smoking status but not to blood pressure

OBJECTIVE

Endothelin-1 (ET-1) is a potent vasoconstrictor derived from the endothelium. Several studies with small numbers of humans have showed high plasma ET-1 levels in hypertension, but other studies have not. Furthermore, it has been shown in a small number of subjects that ET-1 is elevated in uraemic patients. However, there have been no epidemiological surveys as to whether ET-1 level is related to hypertension or end-organ damage.

METHODS

A total of 1492 subjects received a health examination in 1999. The data for fasting ET-1 of 1450 individuals were obtained. A specific radioimmunoassay was used to measure ET-1 levels. We also measured body mass index (BMI), systolic and diastolic blood pressure (BP), haemoglobin A1c, cholesterol, blood urea nitrogen (BUN), creatinine and uric acid. We performed carotid B-mode ultrasonography and electrocardiography. Smoking habit was evaluated by questionnaire.

RESULTS

Mean ET-1 was 4.93 +/- 1.73 pg/ml in men and 4.84 +/-1.54 pg/ml in women. ET-1 increased with age (P < 0.001). Systolic (P < 0.001) and diastolic (P < 0.05) BP, hypertensive medication (P < 0.05), BUN (P < 0.01), creatinine (P < 0.001), uric acid (P < 0.001), intimal-medial thickness (P < 0.001), smoking (P < 0.05) and age (P < 0.001), were significantly associated with ET-1 by univariate analysis. By the use of multiple stepwise regression analysis, age (P < 0.001), creatinine (P < 0.001) and smoking (P < 0.05) remained significant. However, no relation was shown between ET-1 and BP.

CONCLUSION

Our data suggest that high ET-1 is not related to hypertension, but to subclinical renal dysfunction and smoking.

Evaluation of the Lys198Asn and -134delA Genetic Polymorphisms of the Endothelin-1 Gene

Endothelin-1 (ET-1) is a potent vasoconstrictor and shows various pharmacological responses. Two single nucleotide polymorphisms in the ET-1 gene (EDN1) have been reported to be associated with blood pressure (BP). One is the Lys198Asn polymorphism, which showed a positive association with BP in overweight people. Another is the 3A/4A polymorphism (-134delA) located in the 5'-untranslated region. In this study, we investigated the expression of the Lys198Asn polymorphism in ET-1 in vitro, as well as the association between either of the two polymorphisms and the plasma ET-1 level. We expressed both the major (Lys-type) and minor type (Asn-type) preproET-1 in three different cell lines, and measured the levels of ET-1 and big ET-1 in the culture supernatant. There was no significant difference in the levels of ET-1 or big ET-1 between the Asn-type and Lys-type transfectant. In the association study, the plasma levels of ET-1 in 54 hypertensive patients having an amino acid substitution from Lys to Asn at position 198 were not different from those of hypertensives without the substitution. However, we found a significant difference in ET-1 levels between individuals with the 3A/3A and 3A/4A genotypes. Our transient expression study indicates that the Lys198Asn polymorphism may not directly affect ET-1 and big ET-1 production. Another variant in the EDN1 gene in linkage disequilibrium with the Lys198Asn polymorphism may be responsible for the association with BP, or the interaction between the EDN1 Lys198Asn polymorphism and other factors such as obesity may be involved in the mechanisms elevating BP in vivo.

Secretion of interleukin-1beta by astrocytes mediates endothelin-1 and tumour necrosis factor-alpha effects on human brain microvascular endothelial cell permeability

Evidence suggests that endothelin-1 (ET-1) plays an essential role in brain inflammation. However, whether ET-1 contributes directly to blood-brain barrier (BBB) breakdown remains to be elucidated. Using an in vitro BBB model consisting of co-cultures of human primary astrocytes and brain microvascular endothelial cells (BMVECs), we first investigated the expression of ET-1 by BMVECs upon stimulation with tumour necrosis factor (TNF)-alpha, which plays an essential role in the induction and synthesis of ET-1 during systemic inflammatory responses. Increased ET-1 mRNA was detected in the human BMVECs 24 h after TNF-alpha treatment. This was correlated with an increase in ET-1 levels in the culture medium, as determined by sandwich immunoassay. Both TNF-alpha and ET-1 increased the permeability of human BMVECs to a paracellular tracer, sucrose, but only in the presence of astrocytes. The increase in BMVEC permeability by TNF-alpha was partially prevented by antibody neutralization of ET-1 and completely by monoclonal antibody against IL-1beta. Concomitantly, TNF-alpha induced IL-1beta mRNA expression by astrocytes in co-culture and this effect was partially prevented by ET-1 antibody neutralization. In parallel experiments, treatment of human primary astrocytes in single cultures with ET-1 for 24 h induced IL-1beta mRNA synthesis and IL-1beta protein secretion in the cell culture supernatant. Taken together, these results provide evidence for paracrine actions involving ET-1, TNF-alpha and IL-1beta between human astrocytes and BMVECs, which may play a central role in BBB breakdown during CNS inflammation.

Role of endothelin in human hypertension

Endothelin-1 (ET-1) is a pleiotropic hormone produced primarily by the endothelium. Synthesis of ET-1 is stimulated by the major signals of cardiovascular stress, such as vasoactive agents (angiotensin II, norepinephrine, vasopressin, and bradykinin), cytokines (e.g., tumor necrosis factor alpha and transforming growth factor beta), and other factors, including thrombin and mechanical stress. ET-1 induces vasoconstriction, is proinflammatory, promotes fibrosis, and has mitogenic potential, important factors in the regulation of vascular tone, arterial remodeling, and vascular injury. These effects are mediated via two receptor types, ETA and ETB. The role ET-1 plays in normal cardiovascular homeostasis and in mild essential hypertension in humans is unclear. However, certain groups of essential hypertensive patients may have ET-1-dependent hypertension, including blacks (subjects of African descent), salt-sensitive hypertensives, patients with low renin hypertension, and those with obesity and insulin resistance. ET-1 has also been implicated in severe hypertension, heart failure, atherosclerosis, and pulmonary hypertension. In all of these conditions, plasma immunoreactive ET levels are elevated and tissue ET-1 expression is increased. Accordingly, it is becoming increasingly apparent that ET-1 plays an important role in cardiovascular disease and in some forms of hypertension in humans. Data from clinical trials using combined ETA-ETB receptor blockers have already demonstrated significant blood-pressure-lowering effects. Thus, targeting the endothelin system may have important therapeutic potential in the treatment of hypertension, particularly by contributing to the prevention of target organ damage and the management of cardiovascular disease.

The vascular endothelin system is not overactive in normotensive hemodialysis patients

BACKGROUND

The hemodynamic significance of elevated endothelin-1 (ET) plasma levels in hemodialysis (HD) patients is unknown. Therefore, we studied the role of ET in the regulation of vascular tone in normotensive HD patients and matched healthy controls (C).

METHODS

The forearm blood flow (FBF) responses to adenosine, norepinephrine, the ET-A receptor antagonist BQ-123 (40 nmol/min), the ET-B receptor antagonist BQ-788 (1 and 50 nmol/min), and ET (5 pmol/min) were measured. Results are percent of baseline change +/- SEM (baseline = 100%).

RESULTS

Responses to adenosine and norepinephrine were both unchanged in HD. In HD, BQ-123 increased FBF less than in C (133 +/- 9 vs. 178 +/- 27%; P = 0.02). BQ-788 failed to change FBF in C but decreased FBF to 83 +/- 4% in HD. Compared to BQ-123 alone, BQ-123 plus BQ-788 (50 nmol/min) caused an additional increase of FBF (234 +/- 32%, P < 0.001) in C, but not in HD (139 +/- 14%). This additional increase was absent when BQ-788 was co-infused at 1 nmol/min. ET reduced FBF comparably in both groups.

CONCLUSIONS

Resistance vessels of HD patients have unremarkable contractile properties, as shown by responses to adenosine and norepinephrine. In HD, the basal vascular ET-mediated tone is reduced. The main action of the ET-B receptor in C is vasoconstrictive, which also is blunted in HD. The intact response to exogenous ET indicates the normal function of ET receptors in HD. Our results could be explained by a reduced generation or reduced metabolic clearance rate of ET in normotensive HD patients. Controversy remains concerning the role of the ET-B receptor when comparing the present data with previously published literature.

HIV-1-induced production of endothelin-1 in an in vitro model of the human blood-brain barrier

Evidence suggests that the HIV-1 envelope glycoproteins play a role in the central nervous system (CNS) complications of AIDS. Endothelin-1 (ET-1) has also been implicated in brain injury and the progression of the AIDS dementia complex (ADC). Here, we used a real-time reverse transcription polymerase chain reaction assay and an immunometric assay to show that in vitro model of the blood-brain barrier (BBB) consisting of a monolayer co-culture of astrocytes and human brain microvascular endothelial cells (A-HBMEC) increased its expression of ET-1 mRNA and secretion of ET-1 peptide when infected with HIV-1. The enhanced expression of ET-1 occurred independently of viral replication as it was also induced by the viral glycoprotein coat HIV-1g120SF. These results show that one mechanism by which HIV-1 might affect the CNS is by inducing release of ET-1 by the BBB.

Saphenous vein endothelin system expression and activity in African American patients

OBJECTIVE

Plasma endothelin (ET)-1 levels are significantly higher in African American hypertensive patients than in white hypertensive patients. However, whether the molecular components of vascular ET-1 biosynthesis and function are altered in this population remains to be established. Accordingly, the overall goal of this study was to investigate the effects of race on vascular mRNA and protein levels of ET-converting enzyme (ECE)-1 subisoforms, ET-1, and ET receptor profiles in hypertension.

METHODS AND RESULTS

Saphenous vein samples were obtained from African American (n=13) and white (n=15) patients undergoing coronary artery grafting surgery. The expression of preproET-1 and of ECE-1a was upregulated approximately 2- and 3-fold, respectively, in African Americans. In endothelium-intact vessels, the ET(A) expression was higher in whites. In endothelium-denuded vessels, the ET(B) mRNA was 3-fold higher in African Americans, suggesting that vasoconstriction-promoting ET(B) receptors are upregulated in this population. Vascular tissue ET-1 levels and ECE-1 activity were also augmented in African American patients.

CONCLUSIONS

This study demonstrated that the biosynthetic pathway of ET-1 is activated to a higher degree and that the ET(B) receptor subtype expression is altered in the peripheral vasculature of African American hypertensive patients. The augmented synthesis and altered expression of ET(B) receptors may both contribute to the increased incidence of hypertension and related complications in this patient population.

Participation of renal and circulating endothelin in salt-sensitive essential hypertension

Salt sensitivity of blood pressure is a cardiovascular risk factor, independent of and in addition to hypertension. In essential hypertension, a conglomerate of clinical and biochemical characteristics defines a salt-sensitive phenotype. Despite extensive research on multiple natriuretic and antinatriuretic systems, there is no definitive answer yet about the major causes of salt-sensitivity, probably reflecting the complexity of salt-balance regulation. The endothelins, ubiquitous peptides first described as potent vasoconstrictors, also have vasodilator, natriuretic and antinatriuretic actions, depending on their site of generation and binding to different receptors. We review the available data on endothelin in salt-sensitive essential hypertension and conclude that abnormalities of renal endothelin may play a primary role. More importantly, the salt-sensitive patient may have blood pressure-dependency on endothelin in all states of salt balance, thus predicting that endothelin receptor blockers will have a major therapeutic role in salt-sensitive essential hypertension.

Mechanism of action of hypotensive prostaglandins in patients with essential hypertension

Despite extensive investigation, the biological mechanisms causing essential hypertension (EHT) remain unclear. To clarify the means by which hypotensive prostaglandins (Hypo-PGs, mainly PGE1 and PGE2) act in patients with EHT, the interaction between intravenously infused Hypo-PGs and pressor substances such as an adrenergic neurotransmitter, noradrenaline (NA) and angiotensin II (AII) was examined both in patients with EHT and in perfused isolated rabbit ear artery preparations. In patients with EHT, Hypo-PGs were shown to reduce the pressor responses to intravenously infused NA or AII, although no significant difference was found between the pressor responses to NA under basal conditions and the responses during intravenous infusion of Hypo-PGs. Animal studies were undertaken to investigate the inhibitory action of Hypo-PGs on the vasoconstrictive responses to electrical stimulation of the perivascular sympathetic nerves (VSNS) and to exogenous NA at pre- and postjunctional sites in blood vessel walls. The suppressive action of Hypo-PGs on the response to VSNS was shown to be more potent than that to their action on the response to exogenous NA. Thus, it was concluded that the hypotensive action of intravenously infused Hypo-PGs in patients with EHT may be more dependent on prejunctional sites than on the postjunctional sites in the walls of blood vessels.