Role of renin-angiotensin system and metabolites of angiotensin in the mechanism of gastric mucosal protection

Gut microbiota and renin-angiotensin system: a complex interplay at local and systemic levels

Gut microbiota is a potent biological modulator of many physiological and pathological states. The renin-angiotensin system (RAS), including the local gastrointestinal RAS (GI RAS), emerges as a potential mediator of microbiota-related effects. The RAS is involved in cardiovascular system homeostasis, water-electrolyte balance, intestinal absorption, glycemic control, inflammation, carcinogenesis, and aging-related processes. Ample evidence suggests a bidirectional interaction between the microbiome and RAS. On the one hand, gut bacteria and their metabolites may modulate GI and systemic RAS. On the other hand, changes in the intestinal habitat caused by alterations in RAS may shape microbiota metabolic activity and composition. Notably, the pharmacodynamic effects of the RAS-targeted therapies may be in part mediated by the intestinal RAS and changes in the microbiome. This review summarizes studies on gut microbiota and RAS physiology. Expanding the research on this topic may lay the foundation for new therapeutic paradigms in gastrointestinal diseases and multiple systemic disorders.

ACE2 as therapeutic agent

The angiotensin-converting enzyme 2 (ACE2) has emerged as a critical regulator of the renin-angiotensin system (RAS), which plays important roles in cardiovascular homeostasis by regulating vascular tone, fluid and electrolyte balance. ACE2 functions as a carboxymonopeptidase hydrolyzing the cleavage of a single C-terminal residue from Angiotensin-II (Ang-II), the key peptide hormone of RAS, to form Angiotensin-(1-7) (Ang-(1-7)), which binds to the G-protein-coupled Mas receptor and activates signaling pathways that counteract the pathways activated by Ang-II. ACE2 is expressed in a variety of tissues and overwhelming evidence substantiates the beneficial effects of enhancing ACE2/Ang-(1-7)/Mas axis under many pathological conditions in these tissues in experimental models. This review will provide a succinct overview on current strategies to enhance ACE2 as therapeutic agent, and discuss limitations and future challenges. ACE2 also has other functions, such as acting as a co-factor for amino acid transport and being exploited by the severe acute respiratory syndrome coronaviruses (SARS-CoVs) as cellular entry receptor, the implications of these functions in development of ACE2-based therapeutics will also be discussed.

Anti-diarrheal therapeutic potential of diminazene aceturate stimulation of the ACE II/Ang-(1-7)/Mas receptor axis in mice: A trial study

The angiotensin (Ang) II converting enzyme (ACE II) pathway has recently been shown to be associated with several beneficial effects on the body, especially on the cardiac system and gastrointestinal tract. ACE II is responsible for converting Ang II into the active peptide Ang-(1-7), which in turn binds to a metabotropic receptor, the Mas receptor (MasR). Recent studies have demonstrated that Diminazene Aceturate (DIZE), a trypanosomicide used in animals, activates the ACE II pathway. In this study, we aimed to evaluate the antidiarrheal effects promoted by the administration of DIZE to activate the ACE II/Ang-(1-7)/MasR axis in induced diarrhea mice models. The results show that activation of the ACE II pathway exerts antidiarrheal effects that reduce total diarrheal stools and enteropooling. In addition, it increases Na⁺/K⁺-ATPase activity and reduces gastrointestinal transit and thus inhibits contractions of intestinal smooth muscle; decreases transepithelial electrical resistance, epithelial permeability, PGE2-induced diarrhea, and proinflammatory cytokines; and increases anti-inflammatory cytokines. Enzyme-linked immunosorbent assay (ELISA) demonstrated that DIZE, when activating the ACE II/Ang-(1-7)/MasR axis, can still interact with GM1 receptors, which reduces cholera toxin-induced diarrhea. Therefore, activation of the ACE II/Ang-(1-7)/MasR axis can be an important pharmacological target for the treatment of diarrheal diseases.

[Expressions of Renin, angiotensin converting enzyme, angiotensin receptor 1, and angiotensin receptor 2 in synovial tissue of osteoarthritis at different stages]

OBJECTIVE

To study the expressions of Renin, angiotensin converting enzyme (ACE), angiotensin receptor 1 (AT1R), and AT2R in synovial tissue of osteoarthritis (OA) at different stages.

METHODS

The patients who were treated with upper knee amputation because of trauma or total knee arthroplasty for OA between January 2018 and December 2018 were enrolled. Among them, 32 patients who met the selection criteria were included in the study. According to the Kellgren-Lawrence (K-L) X-ray classification, they were allocated to normal synovial group (group A, n=9), moderate OA synovial group (group B, n=11, K-L level 3), and advanced OA synovial group (group C, n=12, K-L level 4). The relative expressions of Renin, ACE, AT1R, and AT2R mRNAs and proteins were detected by real-time fluorescence quantitative PCR (qRT-PCR) and Western blot.

RESULTS

The relative expressions of Renin, ACE, and AT1R mRNAs and proteins were significantly higher in group B and group C than in group A ( P<0.05). The relative expressions of ACE and AT1R mRNAs and proteins and Renin protein were significantly higher in group C than in group B ( P<0.05). However, the relative expressions of AT2R mRNA and protein were lower in group B and group C than in group A ( P<0.05), and in group C than in group B ( P<0.05).

CONCLUSION

The expressions of Renin, ACE, and AT1R in synovial tissue of osteoarthritis significantly increase as the K-L level increased, and the expression of AT2R decreases. Renin, ACE, AT1R, and AT2R have a certain degree of correlation with the development of OA.

Changes to the gut microbiota induced by losartan contributes to its antihypertensive effects

BACKGROUND AND PURPOSE

Hypertension is associated with gut dysbiosis. Here we have evaluated the effects of the angiotensin receptor antagonist losartan on gut microbiota in spontaneously hypertensive rats (SHR) to assess their contribution to its antihypertensive effects.

EXPERIMENTAL APPROACH

Twenty-week-old Wistar Kyoto rats (WKY) and SHR were treated with losartan for 5 weeks (SHR-losartan). Faecal microbiota transplantation (FMT) was performed from donor SHR-losartan group to recipient untreated-SHR. Blood pressure (BP) was measured using tail-cuff plethysmography. Composition of the gut microbiota was assessed by amplification of the V3-V4 region of 16S rRNA gene. T cells were analysed in gut/aorta by flow cytometry.

KEY RESULTS

Faeces from SHR showed gut dysbiosis, characterised by higher Firmicutes/Bacteroidetes ratios, lower acetate- and higher lactate-producing bacteria, and lower levels of strict anaerobic bacteria, effects which were restored to normal by losartan. Improvement of gut dysbiosis was linked to higher colonic integrity and lower sympathetic drive in the gut. In contrast, hydralazine reduced BP, but it neither restored gut dysbiosis nor colonic integrity. FMT from SHR-losartan to SHR reduced BP, improved the aortic endothelium-dependent relaxation to ACh, and reduced NADPH oxidase activity. These vascular changes were accompanied by both increased Treg and decreased Th17 cell populations in the vascular wall.

CONCLUSION AND IMPLICATIONS

In SHR, losartan treatment reduced gut dysbiosis and sympathetic drive in the gut, thus improving gut integrity. The changes induced by losartan in gut microbiota contributed, in part, to protecting the vasculature and reducing BP, possibly by modulating the immune system in the gut.

Global transcriptome‑wide analysis of the function of GDDR in acute gastric lesions

Acute gastric lesions induced by stress are frequent occurrences in medical establishments. The gastric dramatic downrelated gene (GDDR) is a secreted protein, which is abundantly expressed in normal gastric epithelia and is significantly decreased in gastric cancer. In our previous study, it was found that GDDR aggravated stress-induced acute gastric lesions. However, the role of GDDR in acute gastric lesions remains to be fully elucidated. In the present study, RNA sequencing was performed in order to examine the gene expression profile regulated by GDDR in acute gastric lesions. The dataset comprised four stomach samples from wild-type (WT) mice and four stomach samples from GDDR-knockout mice. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to analyze the differentially-expressed genes (DEGs). Weighted correlation network analysis was used to identify clusters of highly correlated genes. Cytoscape was used to construct a protein-protein interaction network (PPI) of the DEGs. Based on the GO analysis, the upregulated DEGs were distinctly enriched in muscle contraction and response to wounding; and the downregulated DEGs were significantly enriched in the regulation of nitrogen compound metabolic process and regulation of RNA metabolic process. The results of the KEGG pathway analysis showed that the upregulated DEGs were enriched in ECM-receptor interaction and the signaling pathway of cGMP-PKG, and the downregulated DEGs were enriched in the renin-angiotensin system and glycerolipid metabolism. The co-expression network revealed a group of genes, which were associated with increased wound healing in the WT mice. Significant pathways were identified through the PPI network, including negative regulation of the signaling pathway of glucocorticoid receptor, regulation of cellular stress response, and regulation of hormone secretion. In conclusion, the present study improves current understanding of the molecular mechanism underlying acute gastric lesions and may assist in the treatment of gastric lesions.

Significance of angiotensin 1-7 coupling with MAS1 receptor and other GPCRs to the renin-angiotensin system: IUPHAR Review 22

Angiotensins are a group of hormonal peptides and include angiotensin II and angiotensin 1-7 produced by the renin angiotensin system. The biology, pharmacology and biochemistry of the receptors for angiotensins were extensively reviewed recently. In the review, the receptor nomenclature committee was not emphatic on designating MAS1 as the angiotensin 1-7 receptor on the basis of lack of classical G protein signalling and desensitization in response to angiotensin 1-7, as well as a lack of consensus on confirmatory ligand pharmacological analyses. A review of recent publications (2013-2016) on the rapidly progressing research on angiotensin 1-7 revealed that MAS1 and two additional receptors can function as 'angiotensin 1-7 receptors', and this deserves further consideration. In this review we have summarized the information on angiotensin 1-7 receptors and their crosstalk with classical angiotensin II receptors in the context of the functions of the renin angiotensin system. It was concluded that the receptors for angiotensin II and angiotensin 1-7 make up a sophisticated cross-regulated signalling network that modulates the endogenous protective and pathogenic facets of the renin angiotensin system.