AT₁R (angiotensin type 1 receptor) and AT₂R (angiotensin type 2 receptor) are well known to be involved in the complex cardiovascular actions of AngII (angiotensin II). However, shorter peptide fragments of AngII are thought to have biological activity in their own right and elicit effects that oppose those mediated by AngII. In the present study, we have used HEK (human embryonic kidney)-293 cells stably transfected with either AT₁R or AT₂R to perform a systematic analysis of binding affinities of all the major angiotensin peptides. Additionally, we tested the novel AT₂R agonist Compound 21, as well as the MasR (Mas receptor) agonist and antagonist AVE0991 and A-779 respectively, for their ability to bind to AT₁R or AT₂R. Candesartan, CGP42214 and PD123319 were used as reference compounds. Binding studies using ¹²⁵I-[Sar¹Ile⁸]AngII on the AT₁R-transfected HEK-293 cells revealed only AngII, AngIII [angiotensin III; angiotensin-(2–8)] and candesartan to have high affinity for AT₁R. In the AT₂R-transfected HEK-293 cells, competition for ¹²⁵I-[Sar¹Ile⁸]AngII binding was observed for all ligands except candesartan, AVE0991 and A-779, the latter two compounds having negligible affinity at either AT₁R or AT₂R. The rank order of affinity of ligands at AT₂R was CGP42112>AngII≥AngIII>Compound 21≥PD123319≫AngIV [angiotensin IV; angiotensin-(3–8)]>Ang-(1–7) [angiotensin-(1–7)]. Of note, although AngIV and Ang-(1–7) exhibited only modest affinity at AT₂R compared with AngII, these two angiotensin peptides, together with AngIII, had substantial AT₂R selectivity over AT₁R. Collectively, our results suggest that shorter angiotensin peptides can act as endogenous ligands at AT₂R.

Significance: Six million people die each year from stroke, and 5 million survivors are left with a permanent disability. Moreover, the neuronal damage caused by stroke often triggers a progressive decline in cognitive function that doubles the risk of dementia for stroke survivors. Despite this massive global disease burden, there are no approved drugs for treating the neuronal injury caused to the brain by the oxygen deprivation occurring during an ischemic stroke. The precipitous drop in brain pH resulting from stroke activates acid-sensing ion channel 1a. We show that inhibition of these channels using a “double-knot” spider venom peptide massively attenuates brain damage after stroke and improves behavioral outcomes, even when the peptide is administered 8 h after stroke onset.

The glucagon like peptide-1 receptor (GLP-1R) agonist liraglutide attenuates induction of plasminogen activator inhibitor type-1 (PAI-1) and vascular adhesion molecule (VAM) expression in human vascular endothelial cells (hVECs) in vitro and may afford protection against endothelial cell dysfunction (ECD), an early abnormality in diabetic vascular disease. Our study aimed to establish the dependence of the in vitro effects of liraglutide on the GLP-1R and characterise its in vivo effects in a mouse model of ECD. In vitro studies utilised the human vascular endothelial cell line C11-STH and enzyme-linked immunosorbent assays (ELISA) for determination of PAI-1 and VAM expression. In vivo studies of vascular reactivity and immunohistochemical analysis were performed in the ApoE^-/- mouse model. In vitro studies demonstrated GLP-1R-dependent liraglutide-mediated inhibition of stimulated PAI-1 and VAM expression. In vivo studies demonstrated significant improvement in endothelial function in liraglutide treated mice, a GLP-1R dependent effect. Liraglutide treatment also increased endothelial nitric oxide synthase (eNOS) and reduced intercellular adhesion molecule-1 (ICAM-1) expression in aortic endothelium, an effect again dependent on the GLP-1R. Together these studies identify in vivo protection, by the GLP-1R agonist liraglutide, against ECD and provide a potential molecular mechanism responsible for these effects.