The Protective Effects of AT2R Agonist, CGP42112A, Against Angiotensin II-Induced Oxidative Stress and Inflammatory Response in Astrocytes: Role of AT2R/PP2A/NFκB/ROS Signaling

Angiotensin II type 2 receptor agonist attenuates LPS-induced acute lung injury through modulating THP-1-derived macrophage reprogramming

Acute respiratory distress syndrome (ARDS) is a devastating respiratory disorder, characterized by overwhelming inflammation in the alveoli without effective pharmacological treatment. We aimed to investigate the effect and mechanism of angiotensin II type 2 receptor (AT2R) agonist, Compound 21 (C21), on the lipopolysaccharide (LPS)-induced acute lung injury (ALI) model. The protective effect of C21 was evaluated via enzyme-linked immunosorbent assay (ELISA), Western blot (WB), real-time PCR, and fluorescence microscopy in LPS-challenged THP1-derived macrophages. Besides, the in vivo efficacy of C21 was assessed using cell counting, ELISA, protein quantification, hematoxylin-eosin (H&E) staining, and WB in an LPS-induced ALI mouse model. The results showed that C21 significantly inhibited the secretion of pro-inflammatory cytokines (CCL-2, IL-6), overproduction of intracellular ROS, and activation of inflammatory pathways (NF-κB/NLRP3, p38/MAPK) in THP-1 cell-derived macrophages stimulated by LPS. In in vivo study, intraperitoneal injection of C21 could reduce airway leukocytes accumulation and chemokine/cytokine (keratinocyte chemoattractant (KC), IL-6) generation, as well as alleviate diffuse alveolar damage induced by LPS. Conclusively, the AT2R agonist C21 significantly inhibited LPS-stimulated excess inflammatory responses and oxidative stress in macrophages. Meanwhile, C21 could effectively alleviate acute inflammation and tissue damage in the lungs of ALI mice challenged by LPS. The results of this study bring new hope for the early treatment of ALI/ARDS.

Brain Renin-Angiotensin System: From Physiology to Pathology in Neuronal Complications Induced by SARS-CoV-2

Angiotensin-converting enzyme 2 (ACE2), a key enzyme in the renin-angiotensin system (RAS), is expressed in various tissues and organs, including the central nervous system (CNS). The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease-2019 (COVID-19), binds to ACE2, which raises concerns about the potential for viral infection in the CNS. There are numerous reports suggesting a link between SARS-CoV-2 infection and neurological manifestations. This study aimed to present an updated review of the role of brain RAS components, especially ACE2, in neurological complications induced by SARS-CoV-2 infection. Several routes of SARS-CoV-2 entry into the brain have been proposed. Because an anosmia condition appeared broadly in COVID-19 patients, the olfactory nerve route was suggested as an early pathway for SARS-CoV-2 entry into the brain. In addition, a hematogenous route via disintegrations in the blood-brain barrier following an increase in systemic cytokine and chemokine levels and retrograde axonal transport, especially via the vagus nerve innervating lungs, have been described. Common nonspecific neurological symptoms in COVID-19 patients are myalgia, headache, anosmia, and dysgeusia. However, more severe outcomes include cerebrovascular diseases, cognitive impairment, anxiety, encephalopathy, and stroke. Alterations in brain RAS components such as angiotensin II (Ang II) and ACE2 mediate neurological manifestations of SARS-CoV-2 infection, at least in part. Downregulation of ACE2 due to SARS-CoV-2 infection, followed by an increase in Ang II levels, leads to hyperinflammation and oxidative stress, which in turn accelerates neurodegeneration in the brain. Furthermore, ACE2 downregulation in the hypothalamus induces stress and anxiety responses by increasing corticotropin-releasing hormone. SARS-CoV-2 infection may also dysregulate the CNS neurotransmission, leading to neurological complications observed in severe cases of COVID-19. It can be concluded that the neurological manifestations of COVID-19 may be partially associated with changes in brain RAS components.

Angiotensin Type 2 Receptor Pharmacological Agonist Relieves Neurocognitive Deficits via Reducing Neuroinflammation and Microglial Engulfment of Dendritic Spines

Mechanically ventilated patients suffering critical illness are at high risk of developing neurocognitive impairments. Angiotensin type 2 receptor (AGTR2) has been demonstrated to be anti-inflammatory and neuroprotective. The present study thus aimed to investigate whether AGTR2 can alleviate cerebral dysfunction in mice subjected to cochallenge with lipopolysaccharide (LPS) and mechanical ventilation (MV), and to reveal the underlying mechanism. We utilized a mice model that received a single injection of LPS (1 mg/kg, intraperitoneally) followed 2 h later by MV (10 ml/kg, lasting for 2 h). Pretreatment with the AGTR2 pharmacological agonist C21 (0.03, 0.3, and 3 mg/kg, intraperitoneally, once daily, lasting for 10 days). Locomotor activity and behavioral deficits were evaluated 24 h post-MV by open-field and fear-condition tests. Brain hippocampus and prefrontal cortex tissues were collected for immunofluorescence staining and western blotting to evaluate the resulting impacts on microglia, including morphological traits, functional markers, synaptic engulfment, superoxide production, and signaling molecules. Compared with vehicle-control, pre-administrated C21 reduced the branch endpoints and length of microglia processes in a dose-dependent manner in mice subjected to LPS/MV. The neuroprotective effect of AGTR2 was behaviorally confirmed by the improvement of memory decline in LPS/MV-treated mice following C21 pretreatment. In addition to morphological alterations, C21 reduced microglial functional markers and reduced microglial-dendrite contact and microglial engulfment of synaptic protein markers. In terms of the underlying molecular mechanism, AGTR2 stimulation by C21 leads to activation of protein phosphatase 2A, which subsequently mitigates microglial PKCδ and NF-κB activation, and inhibites NOX2-derived ROS production. The AGTR2 agonist C21 alleviates behavioral deficits in those mice subjected to LPS/MV, via mechanisms that involve reactive microglia and abnormal synaptic plasticity in NOX2-derived ROS and the PKCδ-NFκB pathway.

Syntheses, Structural Characterization, and Cytotoxicity Assessment of Novel Mn(II) and Zn(II) Complexes of Aroyl-Hydrazone Schiff Base Ligand

This work describes the syntheses, structural characterization, and biological profile of Mn(II)- and Zn(II)-based complexes 1 and 2 derived from the aroyl-hydrazone Schiff base ligand (L1). The synthesized compounds were thoroughly characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), UV-vis, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and single-crystal X-ray diffraction (s-XRD). Density functional theory (DFT) studies of complexes 1 and 2 were performed to ascertain the structural and electronic properties. Hirshfeld surface analysis was used to investigate different intermolecular interactions that define the stability of crystal lattice structures. To ascertain the therapeutic potential of complexes 1 and 2, in vitro interaction studies were carried out with ct-DNA and bovine serum albumin (BSA) using analytical and multispectroscopic techniques, and the results showed more avid binding of complex 2 than complex 1 and L1. The antioxidant potential of complexes 1 and 2 was examined against the 2,2-diphenyl picrylhydrazyl (DPPH) free radical, which revealed better antioxidant ability of the Mn(II) complex. Moreover, the antibacterial activity of synthesized complexes 1 and 2 was tested against Gram-positive and Gram-negative bacteria in which complex 2 demonstrated more effective bactericidal activity than L1 and complex 1 toward Gram-positive bacteria. Furthermore, the in vitro cytotoxicity assessment of L1 and complexes 1 and 2 was carried out against MDA-MB-231 (triple negative breast cancer) and A549 (lung) cancer cell lines. The cytotoxic results revealed that the polymeric Zn(II) complex exhibited better and selective cytotoxicity against the A549 cancer cell line as was evidenced by its low IC₅₀ value.

Angiotensin-(1-9) in hypertension

Angiotensin-(1-9) [Ang-(1-9)] is a peptide of the non-canonical renin-angiotensin system (RAS) synthesized from angiotensin I by the monopeptidase angiotensin-converting enzyme type 2 (ACE2). Using osmotic minipumps, infusion of Ang-(1-9) consistently reduces blood pressure in several rat hypertension models. In these animals, hypertension-induced end-organ damage is also decreased. Several pieces of evidence suggest that Ang-(1-9) is the endogenous ligand that binds and activates the type-2 angiotensin II receptor (AT2R). Activation of AT2R triggers different tissue-specific signaling pathways. This phenomenon could be explained by the ability of AT2R to form different heterodimers with other G protein-coupled receptors. Because of the antihypertensive and protective effects of AT2R activation by Ang-(1-9), associated with a short half-life of RAS peptides, several synthetic AT2R agonists have been synthesized and assayed. Some of them, particularly CGP42112, C21 and novokinin, have demonstrated antihypertensive properties. Only two synthetic AT2R agonists, C21 and LP2-3, have been tested in clinical trials, but none of them like an antihypertensive. Therefore, Ang-(1-9) is a promising antihypertensive drug that reduces hypertension-induced end-organ damage. However, further research is required to translate this finding successfully to the clinic.