High sodium intake modulates left ventricular mass in patients with G expression of +1675 G/A angiotensin II receptor type 2 gene

The rs1403543 Polymorphism of AGTR2, Which Encodes the Type-2 Angiotensin II Receptor, and Left Ventricular Mass in Polish Full-Term Newborns

BACKGROUND/OBJECTIVES

Left ventricular hypertrophy is a significant independent risk factor for increased cardiovascular morbidity and mortality. There are some reports indicating an association of rs1403543 (1675G>A) polymorphism in the AGTR2 gene, which encodes the type-2 angiotensin II receptor, with left ventricular hypertrophy or increased left ventricular mass (LVM) in adults. The aim of this study was to analyze the possible association of the AGTR2:rs1403543 polymorphism with LVM in full-term Polish healthy newborns.

METHODS

The study group comprised 207 consecutive, full-term, healthy newborns. LVM was assessed, on the 3rd day after birth, from the M-mode echocardiographic measurements of left ventricular dimensions using the Penn convention, with the Huwez et al.-modified equation mode. The AGTR2 polymorphism was identified by PCR-RFLP in genomic DNA extracted from cord blood leukocytes.

RESULTS

There were no significant differences in clinical and echocardiographic characteristics of male newborns in regard to the AGTR2:rs1403543 polymorphism. However, the LVM/body mass ratio in female newborns carrying at least one A allele (i.e., with genotype GA or AA) was significantly lower as compared to its value in reference (GG) homozygotes. In addition, in female newborns, the frequency of AGTR2 genotypes with at least one A allele was significantly higher in the lower tertile of LVM/body mass or LVM/body surface area (calculated using the Mosteller formula) ratios as compared with upper tertiles.

CONCLUSIONS

Our results suggest that the AGTR2:rs1403543 polymorphism may be associated with the physiological variability of cardiac mass in female newborns.

Exploring AT2R and its polymorphism in different diseases: An approach to develop AT2R as a drug target beyond hypertension

The Angiotensin II type 2 receptor (AT2R) is one of the critical components of the renin-angiotensin system (RAS), which performs diverse functions like inhibiting cell differentiation, cell proliferation, vasodilatation, reduces oxidative stress and inflammation. AT2R is relatively less studied in comparison to other components of RAS despite its uniqueness (sex-linked) and diverse functions. The AT2R is differentially expressed in different tissues, and its gene polymorphisms are associated with several diseases. The molecular mechanism behind the association of AT2R and its gene polymorphisms with the diseases remains to be fully understood, which hinders the development of AT2R as a drug target. Single nucleotide polymorphisms (SNPs) in AT2R are found at different locations (exons, introns, promoter, and UTR regions) and were studied for association with different diseases. There may be different mechanisms behind these associations as some AT2R SNP variants were associated with differential expression, the SNPs (A1675G/A1332G) affect the alternate splicing of AT2R mRNA, A1332G genotype results in shortening of the AT2R mRNA and subsequently defective protein. Few SNPs were found to be associated with the diseases in either females (C4599A) or males (T1334C). Several other SNPs were expected to be associated with other similar/related diseases, but studies have not been done yet. The present review emphasizes on the significance of AT2R and its polymorphisms associated with the diseases to explore the precise role of AT2R in different diseases and the possibility to develop AT2R as a potential drug target.

The Other Angiotensin II Receptor: AT2R as a Therapeutic Target

The active hormone of the renin-angiotensin system (RAS), angiotensin II (Ang II), is involved in several human diseases, driving the development and clinical use of several therapeutic drugs, mostly angiotensin I converting enzyme (ACE) inhibitors and angiotensin receptor type I (AT₁R) antagonists. However, angiotensin peptides can also bind to receptors different from AT₁R, in particular, angiotensin receptor type II (AT₂R), resulting in biological and physiological effects different, and sometimes antagonistic, of their binding to AT₁R. In the present Perspective, the components of the RAS and the therapeutic tools developed to control it will be reviewed. In particular, the characteristics of AT₂R and tools to modulate its functions will be discussed. Agonists or antagonists to AT₂R are potential therapeutics in cardiovascular diseases, for agonists, and in the control of pain, for antagonists, respectively. However, controlling their binding properties and their targeting to the target tissues must be optimized.

Increased myocardial sodium signal intensity in Conn's syndrome detected by 23Na magnetic resonance imaging

AIMS

Sodium intake has been linked to left ventricular hypertrophy independently of blood pressure, but the underlying mechanisms remain unclear. Primary hyperaldosteronism (PHA), a condition characterized by tissue sodium overload due to aldosterone excess, causes accelerated left ventricular hypertrophy compared to blood pressure matched patients with essential hypertension. We therefore hypothesized that the myocardium constitutes a novel site capable of sodium storage explaining the missing link between sodium and left ventricular hypertrophy.

METHODS AND RESULTS

Using 23Na magnetic resonance imaging, we investigated relative sodium signal intensities (rSSI) in the heart, calf muscle, and skin in 8 PHA patients (6 male, median age 55 years) and 12 normotensive healthy controls (HC) (8 male, median age 61 years). PHA patients had a higher mean systolic 24 h ambulatory blood pressure [152 (140; 163) vs. 125 (122; 130) mmHg, P < 0.001] and higher left ventricular mass index [71.0 (63.5; 106.8) vs. 55.0 (50.3; 66.8) g/m2, P = 0.037] than HC. Compared to HC, PHA patients exhibited significantly higher rSSI in the myocardium [0.31 (0.26; 0.34) vs. 0.24 (0.20; 0.27); P = 0.007], calf muscle [0.19 (0.16; 0.22) vs. 0.14 (0.13; 0.15); P = 0.001] and skin [0.28 (0.25; 0.33) vs. 0.19 (0.17; 0.26); P = 0.014], reflecting a difference of +27%, +38%, and +39%, respectively. Treatment of PHA resulted in significant reductions of the rSSI in the myocardium, calf muscle and skin by -13%, -27%, and -29%, respectively.

CONCLUSION

Myocardial tissue rSSI is increased in PHA patients and treatment of aldosterone excess effectively reduces rSSI, thus establishing the myocardium as a novel site of sodium storage in addition to skeletal muscle and skin.

Blood pressure, arterial stiffness and endogenous lithium clearance in relation to AGTR1 A1166C and AGTR2 G1675A gene polymorphisms

Introduction:

Although recently a matter of epidemiologic controversy, sodium overload and its interaction with genetic factors predispose to hypertension and related target organ complications.

Methods:

In 131 (66 male) treated hypertensives, we measured peripheral and central arterial pressures and pulse wave augmentation indexes (AIx_P, AIx_C1, AIx_C2), pulse wave velocity (PWV), daily urinary sodium excretion and did genetic studies of AGTR1 A1166C and AGTR2 G1675A polymorphisms. Proximal (FE_Li) and distal (FDR_Na) sodium reabsorption measurements were performed using endogenous lithium clearance.

Results:

In men, we found interaction between FDR_Na and AGTR2 G1675A polymorphism with respect to AIx_C1 (p_INT=0.01), AIx_C2 (p_INT=0.05) and AIx_P (p_INT=0.006). Arterial stiffness increased with higher sodium reabsorption in the distal tubule, in the presence of AGTR2 G allele with the opposite tendency in A allele carriers. In the subgroup with FDR_Na below median, as compared to those with FDR_Na above median, the AIx_C1 (139.6±3.8 vs 159.1±5.7%; p=0.009), AIx_C2 (26.3±1.8 vs 33.3±1.7%; p=0.016) and AIx_P (83.4±2.5 vs 96.5±2.6%; p<0.0001) were lower, in the G allele carrying men and GG homozygous women.

Conclusions:

The relation between sodium reabsorption in the distal tubule and the development of arterial stiffness depends on the AGTR2 G1675A polymorphism in blood pressure independent fashion.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Angiotensin II type 2 receptor gene polymorphisms in cardiovascular disease

Considerable progress in our understanding of the role of the angiotensin II type 2 (AT(2)) receptor in the development of cardiac hypertrophy and coronary artery disease has been achieved using in vitro and in vivo animal models. Our understanding in humans, however, has been hindered by the lack of availability of specific AT(2) receptor agonists and antagonists suitable for human study. Nevertheless, an alternative approach involving genotyping humans for a functional polymorphism within the AT(2) receptor gene (-1332G/A) has been used in several association studies to elucidate the pathogenic role of the AT(2) receptor in cardiovascular disease. Both the A allele and the G allele have independently been associated with left ventricular remodelling. However, the methods of measuring left ventricular mass, sodium balance, age and degree of remodelling appear to influence the outcome. An association of carriers of the G allele and premature coronary artery disease has also been established, particularly in males presenting with stenotic atherosclerosis requiring revascularisation. At the molecular level, it remains unclear as to whether carriers of the G allele express more or fewer AT(2) receptors when compared to carriers of the A allele. Consequently, it is presently not possible to definitively interpret the role of the AT(2) receptor in human cardiovascular disease from these association studies.