Identifying and Validating Plasma Circulating Renin‐Angiotensin System Components as Reliable Biomarkers of Rheumatoid Arthritis

Abstract

Objective The renin-angiotensin system (RAS) is an enzymatic cascade that controls the cardiovascular, renal, and adrenal functions responsible for maintaining arterial blood pressure and balancing body fluids and electrolytes. The RAS comprised of two opposing arms: i) classical arm, consists of Angiotensin (Ang) Converting Enzyme (ACE) /Ang II/ Ang II type 1 receptor (AT1R), which modulates a diverse range of biological effects, including vasoconstriction, vascular smooth muscle cell proliferation, and hypertrophy of heart vessel wall, ii) protective arm, consists of ACE2/Ang-(1-7)/Mas receptor (MasR), that acts as the counter regulatory within the RAS. Chronic imbalances of these two arms of the RAS leads to different pathophysiological conditions in renal, cardiovascular (CV), and central nervous systems. The urinary or plasma circulating level of ACE2 has been associated with different disease conditions such as renal, CV, and metabolic disorders. The plasma circulating level of ACE2 has been associated with different diseases. As a body's defense mechanism, the increased level of circulating ACE2 degrades Ang II and keeps its level within the normal range. Several studies links plasma or urinary ACE2 levels in patients with various disease. These patients exhibited reduced ACE2 activity and considerable high levels of circulating anti-ACE2 autoantibody, suggesting that an assessment of circulating ACE2, anti-ACE2, Ang II and Ang1-7 could provide a useful diagnostic biomarkers panel for patients with different inflammatory diseases. Methods This study was conducted based on an approved IRB and using twelve unidentifiable rheumatoid arthritis (RA) patients (five active and seven remission patients) samples, which were provided by the Institute of Arthritis Research. Diagnosis of RA was made using a RAPID3 questionnaire in tandem with comparing the measured amount of C-reactive protein and Vectra DA score. Levels of Ang-(1-7) and Ang II peptides were measured using liquid chromatography in tandem with mass spectrometry. Anti-ACE2 autoantibodies were measured using a previously-established ELISA method. Results The Mean ± SD results of the levels of Ang-(1-7) and Ang II peptides show that Ang-(1-7) level in the active RA group (1.29 ± 1.79) was significantly lower than in the remission RA group (7.62 ± 7.035). In contrast to Ang-(1-7), Ang II levels were significantly higher in the active RA patients (5.43 ± 4.05) when compared with the remission group (0.86 ± 0.43) (Fig.1). The mean ELISA score was significantly higher in the active RA patients (Fig.1) and was also correlated with Ang II levels in the active but not in the remission group (Fig. 2). These results suggest that anti-ACE2 antibody is associated with RA activity and intensity. Conclusion Our study suggests that estimation of the level of Ang-(1-7) and Ang II peptides in addition to assessing anti-ACE2 antibodies in patient's plasma can be considered as effective means of RA stage diagnosis. This approach also could be applied to other inflammatory conditions such as cardiovascular, renal and pulmonary diseases, diabetes and cancer.