Simplification of the diagnostic work-up of primary aldosteronism and investigation of immunology mechanisms

Background Primary aldosteronism (PA) is the most common cause of arterial hypertension characterized by high levels of aldosterone, resulting in excessive mineralocorticoid receptor (MR) stimulation, and extensive hypertensive-mediated organ damage (HMOD). Current guidelines recommend one or more exclusion tests in patients performed the screening test with the measurement of aldosterone-to-renin ratio (ARR) to avoid further lateralization procedures in those who tested false-positive. To date the diagnostic gain provided by these exclusion tests over the ARR was examined only in few studies, and, therefore, stands on a weak level of evidence. Moreover, growing experimental evidence has shown that immune system, especially T cells is involved in aldosterone-induced HOMD through MR activation. MR activation in animal models of hyperaldosteronism promoted T cells differentiation to the pro-inflammatory T helper 17 (Th17) subsets while decreasing the number of anti-inflammatory T regulatory (Tregs). Alteration of the balance between Th17 and Tregs contributed to the pathogenesis of hypertension and the associated complications. Furthermore, our previous work provided proof on the MR gene expression and protein expression in both human CD4+ and CD8+ T cells by Droplet Digital PCR and immunoblotting, respectively. However, up to now, there was no relevant research focused on the function of Th17 and Tregs in PA patients, and evaluate the effect of MR antagonists and surgery on these cells in patients with PA. Aims - To meta-analyze available studies of exclusion tests to furnish a more accurate picture of their diagnostic accuracy and gain in the work-up of PA with a higher level of confidence. - To investigate the levels of circulating Th17 and Tregs in PA patients and evaluate the effect of MR antagonists and surgery on these cells in PA patients. Materials and methods - Eligible studies reported on the diagnostic performance of the ARR and the exclusion tests for identifying unilateral PA (uPA) were selected using the “gold” standard (biochemical cure after adrenalectomy), or, whenever unavailable, a “golden” standard (adrenal imaging and/or AVS) as reference. Then, pooled sensitivity, specificity, the summary receiver operating characteristic (sROC) curve, and corresponding area under the curve (sAUC) were examined. - Blood samples from PA patients were obtained at 3-time points: before surgery, when patients had high PAC and were not treated with MR antagonists (T0); before surgery when patients had high PAC and were treated with MR antagonists (T1); one month after surgery when patients had normal PAC (T2). Immunologic markers on Th17 (CD4+IL17+), pathogenic IL-23-dependent Th17 (CD4+IL17+IL23R+), and Tregs (CD4+CD25+FoxP3+) were analyzed by multicolor flow cytometry. Results - By increasing the overall sample size of the patients studied by these tests and comprising the experience gained in multiple centers, we found that two most popluar exclusion tests, captopril challenge test (CCT) and saline infusion test (SIT), had no diagnostic gain over ARR for diagnosing uPA. - The percentage of circulating Th17 in PA patients was significantly lower after treatment of MR antagonists and post-surgery biochemical cure; meanwhile, there was a decrease in pathogenic Th17 one month after surgery. Although there were no differences in the percentage of Tregs at these 3-time points, Th17/Tregs ratio was markedly decreased after treatment with MR antagonists and post-surgically cure of the hyperaldosteronism. Conclusions This meta-analysis revealed that the use of exclusion tests in patients with a high post-test probability of uPA, as identified by ARR values, could be unnecessary, if not confounding. Meanwhile, our current study showed that treatment with MR antagonists and post-surgery biochemical cure can decrease the percentage of circulating Th17 and the ratio of Th17/Tregs in PA patients.