GLP-1 Mediates Regulation of Colonic ACE2 Expression by the Bile Acid Receptor GPBAR1 in Inflammation

Background & Aims: ACE2, a carboxypeptidase that generates Ang-(1-7) from Ang II, is highly expressed in the lung, small intestine and colon. GPBAR1, is a G protein bile acid receptor that promotes the release of the insulinotropic factor glucagon-like peptide (GLP)-1 and attenuates intestinal inflammation. Methods: We investigated the expression of ACE2, GLP-1 and GPBAR1 in two cohorts of Crohn’s disease (CD) patients and three mouse models of colitis and Gpbar1−/− mice. Activation of GPBAR1 in these models and in vitro was achieved by BAR501, a selective GPBAR1 agonist. Results: In IBD patients, ACE2 mRNA expression was regulated in a site-specific manner in response to inflammation. While expression of ileal ACE2 mRNA was reduced, the colon expression was induced. Colon expression of ACE2 mRNA in IBD correlated with expression of TNF-α and GPBAR1. A positive correlation occurred between GCG and GPBAR1 in human samples and animal models of colitis. In these models, ACE2 mRNA expression was further upregulated by GPABR1 agonism and reversed by exendin-3, a GLP-1 receptor antagonist. In in vitro studies, liraglutide, a GLP-1 analogue, increased the expression of ACE2 in colon epithelial cells/macrophages co-cultures. Conclusions: ACE2 mRNA expression in the colon of IBD patients and rodent models of colitis is regulated in a TNF-α-and GLP-1-dependent manner. We have identified a GPBAR1/GLP-1 mechanism as a positive modulator of ACE2

Hijacking SARS-CoV-2/ACE2 Receptor Interaction by Natural and Semi-synthetic Steroidal Agents Acting on Functional Pockets on the Receptor Binding Domain

The coronavirus disease 2019 (COVID-19) is a respiratory tract infection caused by the severe acute respiratory syndrome coronavirus (SARS)-CoV-2. In light of the urgent need to identify novel approaches to be used in the emergency phase, we have embarked on an exploratory campaign aimed at repurposing natural substances and clinically available drugs as potential anti-SARS-CoV2-2 agents by targeting viral proteins. Here we report on a strategy based on the virtual screening of druggable pockets located in the central β-sheet core of the SARS-CoV-2 Spike's protein receptor binding domain (RBD). By combining an in silico approach and molecular in vitro testing we have been able to identify several triterpenoid/steroidal agents that inhibit interaction of the Spike RBD with the carboxypeptidase domain of the Angiotensin Converting Enzyme (ACE2). In detail, we provide evidence that potential binding sites exist in the RBD of the SARS CoV-2 Spike protein and that occupancy of these pockets reduces the ability of the RBD to bind to the ACE2 consensus in vitro. Naturally occurring and clinically available triterpenoids such as glycyrrhetinic and oleanolic acids, as well as primary and secondary bile acids and their amidated derivatives such as glyco-ursodeoxycholic acid and semi-synthetic derivatives such as obeticholic acid reduces the RBD/ACE2 binding. In aggregate, these results might help to define novel approaches to COVID-19 based on SARS-CoV-2 entry inhibitors

Discovery of a AHR pelargonidin agonist that counter-regulates Ace2 expression and attenuates ACE2-SARS-CoV-2 interaction

The severe acute respiratory syndrome (SARS)-CoV-2 is the pathogenetic agent of Corona Virus Induced Disease (COVID)19. The virus enters the human cells after binding to the angiotensin converting enzyme (ACE)2 receptor in target tissues. ACE2 expression is induced in response to inflammation. The colon expression of ACE2 is upregulated in patients with inflammatory bowel disease (IBD), highlighting a potential risk of intestinal inflammation in promoting viral entry in the human body. Because mechanisms that regulate ACE2 expression in the intestine are poorly understood and there is a need of anti-SARS-CoV-2 therapies, we have settled to investigate whether natural flavonoids might regulate the expression of Ace2 in intestinal models of inflammation. The results of these studies demonstrated that pelargonidin activates the Aryl hydrocarbon Receptor (AHR) in vitro and reverses intestinal inflammation caused by chronic exposure to high fat diet or to the intestinal braking-barrier agent TNBS in a AhR-dependent manner. In these two models, development of colon inflammation associated with upregulation of Ace2 mRNA expression. Colon levels of Ace2 mRNA were directly correlated with Tnf-α mRNA levels. Molecular docking studies suggested that pelargonidin binds a fatty acid binding pocket on the receptor binding domain of SARS-CoV-2 Spike protein. In vitro studies demonstrated that pelargonidin significantly reduces the binding of SARS-CoV-2 Spike protein to ACE2 and reduces the SARS-CoV-2 replication in a concentration-dependent manner. In summary, we have provided evidence that a natural flavonoid might hold potential in reducing intestinal inflammation and ACE2 induction in the inflamed colon in a AhR-dependent manner

Development of FXR, PXR and CAR agonists and antagonists for treatment of liver disorders

The farnesoid-x-receptor (FXR), the constitute-androstane-receptor (CAR) and the pregnane-x-receptor (PXR) are ligand regulated nuclear receptors highly expressed in the liver and intestine supervising essential steps in the metabolism of xeno and endo-biotics in entero-hepatic tissues. Primary and secondary bile acids function as receptor agonists/ activators for these receptors. Activation of FXR by steroidal and non steroidal ligands promotes bile acids secretion by activating bile acids transporters in the apical membrane of hepatocytes. These effects are coordinated with a reduction in bile acids uptake at the basolateral membrane. However, FXR agonists interfere with the regulatory activity of CAR on hepatocyte’s basolateral transporters. Because these effects might worsen live injury in a subset of patients with obstructive cholestasis, development of FXR antagonists might be of clinical relevance. Structure-activity relationship studies have shown that available FXR antagonists are poorly specific for FXR, however the recent discovery of selective antagonists from marine sponges has ground the identification/development of specific FXR antagonists that are currently used in pre-clinical models of liver injury. PXR agonists are endowed with a wide array of biological activities but their effects on the expression/activity of phase I and II metabolizing enzymes is likely to limit their pharmacological development. Nevertheless a combination between FXR agonists and CAR and PXR agonists might hold utility in treating subset of patients with liver disorders. In addition, development of tissue specific FXR antagonists is an attractive opportunity to target subsets of genes in the intestine and liver avoid side-effects linked to FXR activation

Nitric oxide and inflammation.

There are several pre-clinical studies on the involvement of NO in inflammation. From this large amount of information it is clear that virtually every cell and many immunological parameters are modulated by NO. Thus, the final outcome is that NO cannot be rigidly classified as an anti-inflammatory or pro-inflammatory molecule. This peculiar aspect of the pathophysiology of NO has hampered the development of new drugs based on the concepts developed. Recent therapeutic approach are targeted to increase endogenous NO by activating the gene and some promising early data are available. At the present stage one of the most promising approach in the inflammation field is represented by a new class of NO-releasing compounds namely NO-NSAIDs that have recently enrolled in phase 2 clinical studies

The emerging roles of hydrogen sulfide in the gastrointestinal tract and liver.

Hydrogen sulfide, like nitric oxide, was best known as a toxic pollutant before becoming recognized as a key regulator of several physiologic processes. In recent years, evidence has accumulated to suggest important roles for hydrogen sulfide as a mediator of several aspects of gastrointestinal and liver function. Moreover, alterations in hydrogen sulfide production could contribute to disorders of the gastrointestinal tract and liver. For example, nonsteroidal anti-inflammatory drugs can reduce production of hydrogen sulfide in the stomach, and this has been shown to contribute to the generation of mucosal injury. Hydrogen sulfide has also been shown to play a key role in modulation of visceral hyperalgesia. Inhibitors of hydrogen sulfide synthesis and drugs that can generate safe levels of hydrogen sulfide in vivo have been developed and are permitting interventional studies in experimental models and, in the near future, humans

Farnesoid-X-receptor from medicinal chemistry to clinical application

The farnesoid X receptor (FXR) is a bile sensor that acts in coordination with other nuclear receptors to regulate essential steps in bile acid uptake, metabolism and excretion. In addition, FXR is an ancillary receptor involved in lipid and glucose homeostasis. Steroidal and non-steroidal FXR ligands are currently available. Both groups have shown limitations in the preclinical studies regarding absorption, metabolism, specificity of target and intrinsic toxicity. FXR ligands endowed with agonistic activity are under development for the treatment of cholestatic liver diseases, including primary biliary cirrhosis and metabolic disorders linked to insulin resistance. Despite the fact that results from preclinical models are encouraging, targeting FXR holds potential for side effects (i.e., impaired cholesterol disposal and cholestasis). Thus, results from FXR gene-ablated mice and mice administered an FXR antagonist support a role for FXR antagonists or modulators (i.e., FXR agonists that selectively activate specific subsets of FXR target genes in a tissue) or co-regulator-specific manner