Anti‐inflammatory effects of Angiotensin‐(1‐7) through Renin‐Angiotensin System and Arachidonic Acid Pathway
Authors: Khajehpour Sana , Aghazadeh‐Habashi Ali 
Published: May 2022

ObjectiveRheumatoid arthritis (RA) is a prevalent chronic inflammatory disease that affects 1‐2% of the population worldwide. Renin‐angiotensin system (RAS) and Arachidonic acid (ArA) pathway are associated with the pathogenesis of inflammatory diseases (Fig. 1). Inflammatory conditions such as RA disrupt the balance between pro‐ and anti‐inflammatory components of these two pathways. The RAS is composed of two opposing axes. Ang II is one of its components that is implicated in the up‐regulation of pro‐inflammatory mediators and contributes to the pathogenesis of RA. On the other hand, Ang‐(1‐7), counteracts the inflammatory effects of Ang II. Several studies have shown a cross‐talk between the RAS and ArA metabolites, especially eicosanoids such as 20‐hydroxyeicosatetraenoic acid (20‐HETE) and epoxyeicosatrienoic acids (EETs). Ang II stimulates 20‐HETE synthesis in microvessels and decreases EET levels by increasing their degradation. In this study, using Ang‐(1‐7) and its long‐acting bone‐targeting conjugate, we studied the impact of Ang‐(1‐7) anti‐inflammatory effects on the RAS, ArA pathways and their interrelation.MethodsTwenty‐four male Sprague‐Dawley rats were randomly divided into healthy control and adjuvant arthritic (AA) rats. The rats in the AA group were injected with Mycobacterium butyrium in squalene to induce AA. AA rats were further divided into and treated with four groups INF, Ang‐(1‐7), and Ang. Conj. After 21 days of treatment, animals’ plasma samples were collected for analysis of Ang II, Ang‐(1‐7), 20‐HETE, and different EETs. The quantification was done using an LC‐MS/MS system in positive ESI mode for Ang peptides and negative for HETE and EETs. The one‐way ANOVA with Tukey posthoc test was used to test the significance difference (p‐value < 0.05).ResultsThe Ang peptide analysis shows that the level of Ang‐(1‐7) in control (0.75 ± 0.08) and INF (0.19 ± 0.05) rats was significantly different. However, treating with Ang‐(1‐7) peptide (0.90 ± 0.17) or Ang. Conj. peptide conjugate (1.45 ± 0.22) could increase the Ang‐(1‐7) peptide level in rats. In contrast to Ang‐(1‐7), Ang II levels in the INF group were significantly different from control, Ang‐(1‐7), and Ang. Conj. (Fig. 2A). Analyzing the level of total EETs and 20‐HETE in plasma reveals that the total EETs/20‐HETE ratio decreases in INF rats (0.10 ± 0.02) significantly, whereas this ratio increased in Ang‐(1‐7) (3.48 ± 0.65), and Ang. Conj. (7.73 ± 1.21) in comparison to the control (6.90 ± 1.03) group (Fig. 2B). Our finding reveals a positive correlation between the level of Ang II and 20‐HETE, Ang‐(1‐7), and total‐EETs. This trend was reversed when Ang II was correlated with total EETs or the ratio of total‐EETs/20‐HETE (Fig. 3B). Concentrations are reported as ng/mL.ConclusionThe physiological balance of CYP‐mediated ArA metabolites and the RAS components are disturbed by the inflammation, resulting in the augmentation of pro‐inflammatory arms of both pathways. Our approach of using Ang‐(1‐7) and its long‐acting bone targeting conjugate could reverse such an effect and promote anti‐inflammatory effect in the AA animal model.