Circulating adrenomedullin in erythrocopietin-induced hypertension

Erythropoietin-Induced Hypertension: A Review of Pathogenesis, Treatment, and Role of Blood Viscosity

Anemia is a common complication of certain chronic diseases and can be treated by stimulating hematopoietic cells to increase red blood cell count, and this action is achieved by recombinant human erythropoietin. In this review article, we have discussed about hypertension, which develops as a result of erythropoietin therapy. We have explored the pathogenesis of erythropoietin-induced hypertension and discussed some ways to prevent and treat this condition. Also, an attempt has been made to find out the role of blood viscosity in erythropoietin-induced hypertension. We conducted a comprehensive review of literature by collecting data from online databases like PubMed and Google Scholar. We mainly studied clinical trials that unraveled the mechanism of hypertension caused by erythropoietin. Hypertension is mainly caused due to enhanced vascular responsiveness to constrictors and impaired action of vasodilators. Role of blood viscosity in the pathogenesis of hypertension is doubtful due to the lack of consistency in the studies. Incidence of hypertension can be reduced by achieving slow correction of anemia and by switching to subcutaneous route of administration. Conventional anti-hypertensives have been found to be beneficial in the treatment. In some severe and persistent cases, temporary discontinuation of erythropoietin may be needed.

Evaluation of transcriptional levels of the natriuretic peptides, endothelin-1, adrenomedullin, their receptors and long non-coding RNAs in rat cardiac tissue as cardiovascular biomarkers of aging

Chronological age is considered one of the major risk factors for cardiovascular disease and mortality. The study aimed to evaluate the transcriptional levels of the natriuretic peptides (NP), endothelin (ET)-1, adrenomedullin (ADM), their receptors and long non-coding (Lnc) RNA MIAT, MALAT-1, CARMEN and XIST in rat cardiac tissue as cardiovascular biomarkers of aging. Three groups of male Wistar rats were studied: A (n = 6; young), B (n = 13; adult), C (n = 10; old). Total RNA was extracted from left ventricle and analyzed by Real-Time PCR. Echocardiographic and histological analyses were performed. A significant increase of Atrial NP (ANP) and Brain NP (BNP) mRNA was observed in C while C-type NP (CNP) remained in a steady-state in B and C; ET-1 mRNA increased significantly as a function of age. Any difference was observed for NP receptors. ETA expression was statistically lower in B than A while ETB were similar in all the three groups. The ADM showed an opposite trend to that of the other peptides decreasing significantly as a function of age and presenting a counter-regulation of calcitonin receptor-like receptor (CLR) and receptor activity modifying protein (RAMP)-2. LncRNA transcripts decreased significantly as a function of age except for XIST. ADM and LncRNA trend suggest that the animals are subjected to "successful aging" as also confirmed by histological analysis. Applying a multivariate logistic regression analysis, only LnANP (p = 0.003) and LnADM (p = 0.023) resulted significantly associated with aging identifying them, for the first time, as independent markers of aging. The study underlining the importance of a multi-label biomolecular approach in the evaluation of aging.

Adrenomedullin in vascular diseases

A novel vasodilator, adrenomedullin (AM), which acts as an autocrine/paracrine factor in cardiovascular system, has antiproliferative and antimigrative effects. AM gene transfer prevents the development of cuff-induced vascular injury. Moreover, AM knockout mice exhibited an increase in angiotensin (Ang) II/salt loading-induced coronary arterial lesion, hypoxia-induced pulmonary vascular damage, and cuff-induced vascular injury associated with enhancement in reactive oxygen species (ROS) generation. In addition, AM expression was stimulated by ROS, and AM directly inhibits oxidative stress so that AM might be a negative feedback substance against ROS-induced organ damages. In addition, AM increases nitric oxide and ameliorates insulin resistance, leading to oxidative stress. Consequently, endogenous AM might compensatively inhibit the development of vascular diseases at least partly through an antioxidative effect.

Lessons from the adrenomedullin knockout mouse

Because vasolidator peptide adrenomedullin (AM) exhibits complicated action, we developed AM knockout mice in order to elucidate the physiological and pathophysiological role of AM. The AM(-/-) mice were embryonic lethal, so we could not evaluate directly the role of AM in this mutant mice. Thus, we loaded angiotensin II (AngII) and salt in AM(+/-) mice, which were viable and fertile. As a result, AngII and salt loading caused coronary vascular damage and left ventricular hypertrophy in AM(+/-) mice more greatly than AM(+/+) mice. Moreover, cuff placement of femoral artery stimulated intimal thickening more severely. This treatment increased local AM levels in AM(+/+) mice but not in AM(+/-) mice. The accelerated organ damage in AM(+/-) mice was accompanied with enhanced production of oxidative stress. Thus, our data suggest that intrinsic AM play a vascular protective role.

Regulation of cell growth and apoptosis by adrenomedullin

Adrenomedullin, originally discovered in human pheochromocytoma, has been shown to have potent vasodilatory activity. However, like other vasoactive peptide hormones, its physiological roles have been found to extend far beyond the regulation of vascular tonus, and to include such functions as the regulation of cell proliferation and differentiation. There is a growing body of evidence that adrenomedullin exerts a wide range of effects on cell growth and apoptotic death, and that these effects are dependent on cell type and experimental conditions. Signaling pathways independent of cyclic AMP, such as protein tyrosine kinase(s) and mitogen-activated protein kinases, may play key roles in the regulation of mitogenesis and apoptosis by adrenomedullin.

Cardioprotective effect of adrenomedullin in heart failure

Many neurohumoral factors participate in the pathophysiology of heart failure, and adrenomedullin (AM) may be involved in their derangement. This work reviews the accumulating evidence in support of a compensatory role of AM in heart failure, and describes the possible mechanisms of this role. It has been established that plasma AM levels are increased in patients with heart failure in proportion to the severity of the disease. Furthermore, recent studies suggest that plasma AM level is an independent prognostic indicator of heart failure. Thus, AM may be not only a biochemical marker for evaluating the severity of heart failure, but also a prognostic indicator of this syndrome. In patients with heart failure, AM production is increased not only in the plasma, but also in the heart. AM secretion from the failing human heart is also increased, but this increase is small and responds slowly to the stimulus. This phenomenon may be explained by the fact that AM is secreted via a constitutive pathway and that AM is an autocrine and/or a paracrine factor in the heart. An experiment using cultured myocytes suggested that cytokines and mechanical stress are important stimuli for AM production in the heart. Regarding the action of AM in the heart, recent studies have suggested that AM exerts an inotropic action both in vitro and in vivo. AM also attenuates cardiac hypertrophy in myocytes and inhibits proliferation and collagen production in cardiac fibroblasts. These results suggest that AM may be an antifibrotic, antihypertrophic, and positive inotropic factor in the failing and hypertrophied heart. Because AM has many cardiorenal actions, AM administration may be useful for the treatment of heart failure. Indeed, acute administration of AM has been shown to improve the hemodynamics, renal function, and hormonal parameters in patients with heart failure. Moreover, recent studies have shown that AM gene therapy or long-term AM infusion significantly improved cardiac hypertrophy and fibrosis, and prolonged the survival time in an animal model of hypertension and heart failure. In conclusion, these findings suggest that AM plays a compensatory role in the pathophysiology of heart failure and that administration of AM may be a new and promising approach for the treatment of patients with this syndrome.

Plasma levels of adrenomedullin and atrial and brain natriuretic peptides in the general population: their relations to age and pulse pressure

Adrenomedullin (AM) and atrial and brain natriuretic peptides (ANP and BNP) exert vasodilator and natriuretic actions and are thought to share roles in counteracting the progression of hypertension or heart failure as circulating or locally-acting hormones. However, little data is available with regard to their roles in subjects who have no apparent cardiovascular diseases. The present study was carried out to identify the factors that affect plasma levels of AM, ANP and BNP in the general population. We measured the plasma levels of AM, ANP and BNP in 184 local residents who had a scheduled regular health checkup, and compared the findings with those for other clinical parameters. Univariate analyses showed that the plasma levels of AM, ANP and BNP were significantly correlated with age. The plasma levels of ANP and BNP were also significantly correlated with systolic blood pressure (SBP) and with pulse pressure (PP), an indicator of the stiffness of the great vessels. Multivariate analyses conducted using a stepwise method revealed that age was a significant, independent variable for the plasma levels of AM, ANP and BNP. In addition, PP was a significant factor for the plasma levels of ANP and BNP, while the plasma AM was significantly associated with body mass index (BMI). Thus, the plasma levels of AM, ANP and BNP all increased in association with aging, and those of ANP and BNP increased in association with PP, suggesting possible relationships between the plasma levels and age-related changes in the cardiovascular system.

Association of angiotensinogen gene polymorphism with erythropoietin-induced hypertension: a preliminary report

The association of the angiotensinogen (AGT) gene variation at codon 235, the T235 variant, with hypertension induced by erythropoietin (Epo) was investigated in patients with progressive renal disease requiring treatment for renal anemia with Epo. The subjects for the study were patients with renal diseases with serum creatinine concentration exceeding 2 mg/dl and a hematocrit (Ht) of less than 30%. During the run-in period, blood pressure was well controlled with an appropriate salt restricted diet and/or antihypertensive treatment. The patients were then given 6,000 IU of Epo once a week until the Ht rose by 5%. For the overall patient group, AGT gene polymorphism analysis revealed T235T (T/T) in 31 cases (61%), M235T (M/T) in 19 cases (37%), and M235M (M/M) in 1 case (2%). In response to treatment with Epo, hypertension (defined as an increase in mean blood pressure greater than 10 mmHg) was found in 11 cases (22%), all of who carried the homozygous T allele (T/T). On the other hand, the frequency of T/T in patients who did not develop hypertension was 50% (T/T:T/M=20:19 cases), indicating a significant difference (p=0.003 by Chi-square). Variables estimated to be associated with Epo-induced hypertension were the T allele, gender (male), and the degree of increase in Ht, in descending order. Our preliminary research indicates that individuals who carry two copies of the T allele, i.e., who are homozygous for T, are highly susceptible to development of hypertension when subjected to Epo. These results suggest that the AGT T235 variant may be the primary gene responsible for the development of Epo-induced hypertension.