Signaling Pathway in the Osmotic Resistance Induced by Angiotensin II AT2 Receptor Activation in Human Erythrocytes

Acute In Vivo Administration of Compound 21 Stimulates Akt and ERK1/2 Phosphorylation in Mouse Heart and Adipose Tissue

The angiotensin II type 2 (AT2) receptor has a role in promoting insulin sensitivity. However, the mechanisms underlying the AT2 receptor-induced facilitation of insulin are still not completely understood. Therefore, we investigated whether acute in vivo administration of AT2 receptor agonist compound 21 (C21) could activate insulin signaling molecules in insulin-target tissues. We report that, in male C57BL/6 mice, an acute (5 min, 0.25 mg/kg; i.v.) injection of C21 induces the phosphorylation of Akt and ERK1/2 at activating residues (Ser473 and Thr202/Tyr204, respectively) in both epididymal white adipose tissue (WAT) and heart tissue. In WAT, the extent of phosphorylation (p) of Akt and ERK1/2 induced by C21 was approximately 65% of the level detected after a bolus injection of a dose of insulin known to induce maximal activation of the insulin receptor (IR). In the heart, C21 stimulated p-Akt to a lesser extent than in WAT and stimulated p-ERK1/2 to similar levels to those attained by insulin administration. C21 did not modify p-IR levels in either tissue. We conclude that in vivo injection of the AT2 receptor agonist C21 activates Akt and ERK1/2 through a mechanism that does not involve the IR, indicating the participation of these enzymes in AT2R-mediated signaling.

In Vitro Metabolite Profiling and Anti-Inflammatory Activities of Rhodomyrtus Tomentosa with Red Blood Cell Membrane Stabilization Methods

Background

Rhodomyrtus Tomentosa (Karamunting) is one of South Kalimantan's biodiversity. In previous research on asthma and coal dust exposure models, nebulization with an ethanol extract of R. tomentosa leaves has been shown to reduce inflammatory cells. This study aimed to investigate the anti-inflammatory activity on the stabilization of red blood cell membranes and to identify the chemical compounds present in extracts of R. tomentosa leaves.

Methods

Anti-inflammatory effect of R. tomentosa leaves was evaluated by in vitro red blood cell membrane stabilization methods. Nonsteroidal anti-inflammatory sodium diclofenac was used as the reference drug. The content of chemical compounds in the ethanol extract of R. tomentosa leaves was identified using Ultra Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS).

Results

The results of inhibition of red blood cells membrane lysis showed the n-hexane fraction (concentration 25 ppm), ethyl acetate fraction (concentration 50 ppm), and a fraction of water (concentration 50 ppm) with an inhibition level of 54.5%, 81.8%, 63.6%, respectively. The ethyl acetate fraction showed the highest inhibition of hemolysis. This result is not significantly different from the standard anti-inflammatory sodium diclofenac (90.09%). Oleanonic acid and ursonic acid were two similar metabolites in subfractions ethyl acetate 1, 2, and 3, which may have anti-inflammatory properties.

Conclusion

R. Tomentosa leaves can have potency as an anti-inflammatory by increasing the red blood cell membrane stability equal to lysosome cells, depending on the concentration.

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.

ATR1 Angiotensin II Receptor Reduces Hemoglobin S Polymerization, Phosphatidylserine Exposure, and Increases Deformability of Sickle Cell Disease Erythrocytes

Angiotensin II (Ang II) regulates blood volume and stimulates erythropoiesis through AT1 (ATR1) and AT2 (ATR2) receptors, found in multiple tissues, including erythrocytes. Sickle cell disease (SCD) patients present altered Ang II levels. Hemoglobin S polymerization, deformability and phosphatidylserine translocation are important features of mature erythrocytes, therefore, our hypothesis is Ang II affects these parameters and, if it does, what would be the influence of AT1R and AT2R on these effects. A polymerization assay (PA), deformability, and annexin V binding were performed in SCD erythrocytes samples adding Ang II, ATR1 antagonist (losartan or eprosartan), and ATR2 antagonist (PD123319). Through the PA test, we observed a dose-dependent polymerization inhibition effect when comparing Ang II to control. Losartan did not affect the level or the rate of Ang II inhibition, while PD123319 showed an increased level of protection against polymerization, and eprosartan brought levels back to control. Ang II was able to reduce the translocation of phosphatidylserine from the inner to the outer leaflet, a marker of eryptosis, in the presence of PD123319. Also, ATR1 showed a positive effect increasing deformability. Our data shows that ATR1 is important for maintenance of erythrocyte physiological function in SCD and for prolonging its life.

Red Blood Cell-Conditioned Media from Non-Alcoholic Fatty Liver Disease Patients Contain Increased MCP1 and Induce TNF-α Release

Background

Non-alcoholic fatty liver disease (NAFLD) constitutes a global pandemic. An intricate network among cytokines and lipids possesses a central role in NAFLD pathogenesis. Red blood cells comprise an important source of both cytokines and signaling lipids and have an important role in molecular crosstalk during immunometabolic deregulation. However, their role in NAFLD has not been thoroughly investigated.

Methods

Conditioned media from erythrocytes derived from 10 NAFLD patients (4 men, 6 women, aged 57.875±15.16) and 10 healthy controls (4 men, 6 women, aged 39.3±15.55) was analyzed for the cytokines IFN-γ, TNF-α, CCL2, CCL5, IL-8, IL-1β, IL-12p40, IL-17, MIP-1β, the signaling lipids sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA), and cholesterol. Their effect on the cytokine profile released by RAW 264.7 macrophages was also studied.

Results

MCP1 levels were greater in conditioned growth medium from NAFLD patient erythrocytes than in that from healthy controls (37±40 vs 6.51±5.63 pg/ml). No statistically significant differences were found between patients and healthy controls with regard to S1P, LPA, cholesterol, or eight other cytokines. TNF-a release by RAW 264.7 cells was greater after incubation with patient-derived erythrocyte-conditioned medium than in medium without RAW 264.7 cells from either healthy or NAFLD subjects.

Conclusion

Erythrocytes may contribute to liver infiltration by monocytes, and macrophage activation, partially due to CCL2 release, in the context of NAFLD..