Chronic Ethanol Ingestion Increases Expression of the Angiotensin II Type 2 (AT2) Receptor and Enhances Tumor Necrosis Factor-alpha- and Angiotensin II-Induced Cytotoxicity Via AT2 Signaling in Rat Alveolar Epithelial Cells

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

SARS-CoV-2, alcohol consumption and liver injury

Angiotensin converting enzyme 2 (ACE2) receptor sites for severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2), responsible for the disease called Covid-19 are present in the liver, especially in correspondence with cholangiocytes. Liver damage during SARS-Cov-2 infection can be due to several mechanism including direct cytopathic effect, synergy of intestinal damage / liver damage (lipopolysaccharides / Kupfer and other cells interaction), uncontrolled immune reaction (lymphopenia and significant increase in C reactive protein, ferritin, lactate dehydrogenase, D-dimer, interleukin (IL)-6, IL- 10, IL-2, interferon-gamma ...), sepsis, drug-induced liver injury, hypoxia and thromboembolic events. An increase in aspartate aminotransferase (AST) from 14 to 58% and alanine transaminase (ALT) from 21 to 76% has been reported. The mean level of AST and ALT has been reported to be higher in patients admitted to the intensive care unit than in those hospitalized in the ordinary hospital unit. The correlation of liver damage with worse prognosis is now a known fact, confirmed by numerous studies, in all pandemic phases. The consumption of alcohol reduces both innate and acquired immune activity and it has been hypothesized that this habit is correlated with liver increase of ACE2 receptors. Furthermore, non-alcoholic and alcoholic steatosis / steatohepatitis is a breeding ground for the development of oxidative stress. In this context, any encounter with SARS-Cov-2 infection can support and aggravate the systemic cytokine tsunami.

Angiotensin II receptor blocker inhibits tumour necrosis factor-alpha-induced cell damage in human renal proximal tubular epithelial cells

AIM

We investigated the effect of angiotensin II (AII) type 1 (AT1) and angiotensin II type 2 (AT2) receptor blockers on tumour necrosis factor alpha (TNF-alpha)-induced cell damage in human renal proximal tubular epithelial cells (RPTEC).

METHODS

The lactate dehydrogenase (LDH) and N-acetyl-beta-glucosaminidase (NAG) release into the medium after TNF-alpha treatment in RPTEC were determined using modified commercial procedures. In addition, the levels of caspase 3/7 activity in RPTEC were measured after TNF-alpha treatment with AlphaTau1 or AT2 receptor blockers. Finally we investigated the change of p22phox protein levels after TNF-alpha with AlphaTau1 or AT2 receptor blockers in RPTEC.

RESULTS

Tumour necrosis factor alpha (10(-8) mol/L) significantly increased LDH and NAG release into the medium from RPTEC. AlphaTau1 receptor blockers, olmesartan and valsartan (10(-9)-10(-6) mol/L) showed a significant reduction on TNF-alpha-induced LDH and NAG release in RPTEC. AT2 receptor blocker, PD123319 (10(-7)-10(-5) mol/L) also decreased TNF-alpha-induced LDH and NAG release in RPTEC. Blockade of both AlphaTau1 and AT2 receptor indicated additional reduction on TNF-alpha-induced LDH and NAG release. TNF-alpha (10(-8) mol/L) treatment showed small but significant increases of caspase 3/7 activity in RPTEC, and AT1 and AT2 receptor blockers (10(-8) mol/L) comparably decreased TNF-alpha-induced caspase 3/7 activity. Significant increases of p22phox protein levels were observed in TNF-alpha-treated group in RPTEC. However, only AlphaTau1 (10(-8) mol/L) but not AT2 (10(-5) mol/L) receptor blocker significantly decreased TNF-alpha-induced p22phox protein levels.

CONCLUSION

The present study demonstrates that TNF-alpha induces renal tubular cell damage in RPTEC and AT1/AT2 receptor blockers showed cytoprotective effects probably via at least partly different mechanism.

Acute and chronic alcohol abuse modulate immunity

This article represents the proceedings of the Alcohol and Immunology Research Interest Group (AIRIG) meeting, a satellite workshop held at the 37th Annual Meeting of the Society for Leukocyte Biology. The meeting was sponsored by the AIRIG and the National Institute on Alcohol Abuse and Alcoholism. The presentations were as follows: (1) Effects of Ethanol on Immune Response to Hepatitis C Virus by Jack R. Wands, (2) Alcohol and Alveolar Macrophage Dysfunction: The Role of Chronic Oxidant Stress by Lou Ann S. Brown, (3) T Cell Responses to Listeria monocytogenes in Mice on a Chronic Ethanol Exposure Protocol by Robert T. Cook, (4) Mechanisms of Acute and Chronic Alcohol Consumption on Severity of Viral Infections by the Liver and Pancreas by Thomas R. Jerrells, (5) Acute and Chronic Effects on Macrophage Ectodomain Shedding: Implications for Lung Host Defenses by Jay K. Kolls, (6) Increased Susceptibility to Pseudomonas Infection of Burn-Injured Mice Given Alcohol Before Injury by Elizabeth J. Kovacs, (7) Regulation of Tumor Necrosis Factor alpha Expression in Macrophages by Chronic Ethanol by Laura E. Nagy, and (8) Hepatitis C Virus Infection and Alcohol Use by Gyongyi Szabo. Meeting coorganizers were Elizabeth J. Kovacs, Lou Ann S. Brown, Thomas R. Jerrells, and Robert T. Cook.

Angiotensin II type 2 receptor gene deficiency attenuates susceptibility to tobacco-specific nitrosamine-induced lung tumorigenesis: involvement of transforming growth factor-beta-dependent cell growth attenuation

To clarify an involvement of angiotensin II signaling in lung neoplasia, we have examined the effect of angiotensin II receptor deficiency on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis. Male angiotensin II type 2 receptor (AT2)-null mice with an SWR/J genetic background and control wild-type mice were treated with NNK (100 mg/kg, i.p.) or saline vehicle. NNK treatment caused the development of lung tumors in all wild-type control mice (100 % tumor prevalence), but only 85% of AT2-null mice developed tumors. The tumor multiplicity in AT2-null mice (1.9 +/- 0.3) was significantly smaller than that in wild-type mice (4.1 +/- 0.9). Primary cultured lung fibroblasts prepared from both AT2-null and wild-type mice markedly increased the colony counts of A549 lung cancer cells in soft agar, but a consistently higher colony count was observed with the wild-type fibroblasts (fold increase in colony number, 5.6 +/- 0.5) than with the AT2-null fibroblasts (3.5 +/- 0.8). The underlying mechanism by which angiotensin II regulates cancer cell growth is due to the regulation of active transforming growth factor-beta (TGF-beta) production. Although the total level of TGF-beta was significantly stimulated when A549 cells were cocultured with either type of fibroblasts, the level of active TGF-beta in the conditioned medium was consistently higher with AT2-null fibroblasts than with wild-type fibroblasts. These results imply that the AT2 receptor negatively regulates the level of active TGF-beta and thus increases NNK-induced lung tumorigenesis. The AT2 receptor function in lung stromal fibroblasts may be a potential modulator of tumor susceptibility in chemical carcinogen-induced lung tumorigenesis.

Role of angiotensin II and the subfornical organ in the pharmacological actions of ethanol

AIMS

The current study was designed to evaluate if angiotensin II mediates the hypothermic effects of ethanol, and to determine if the effects of angiotensin are mediated centrally. We also tested the hypothesis that the subfornical organ (SFO) is a site responsible for the alterations in body temperature and aerial righting reflex mediated by ethanol and for the modulation of ethanol consumption in rats.

METHODS

Male Sprague-Dawley rats were used in a series of experiments to evaluate the role of both peripheral and central administration of losartan, a selective angiotensin type 1 receptor antagonist on ethanol-induced hypothermia. Subsequent studies were undertaken in SFO-lesioned rats to evaluate the effects of SFO-lesion on alcohol intake, the thermal response to alcohol and angiotensin, and the aerial righting reflex.

RESULTS

Selective antagonism of the angiotensin II type 1 receptor, administered either peripherally or centrally, attenuated not only the fall in colonic temperature but also attenuated the transient rise in tail skin temperature that was associated with administration of ethanol. The thermal responses to both angiotensin and ethanol were similarly attenuated in SFO-lesioned rats. Likewise the aerial righting reflex, which has previously been shown to be impaired by losartan treatment, was also significantly attenuated in SFO-lesioned animals. Alcohol intake, as determined by a 48 h, two-bottle preference test also revealed that SFO-lesioned animals consumed significantly less alcohol (ethanolic beer) than did controls.

CONCLUSION

Collectively, the results demonstrate that ethanol-induced temperature responses are mediated by the renin-angiotensin system and that this interaction is mediated centrally. In addition, the results demonstrate that the SFO is a site that mediates several neurobiological effects of ethanol, possibly via the renin-angiotensin system.