Regulation of Sodium Channels by Aldosterone: Mechanisms and Implications

2. ΥΠΟΔΟΧΕΑΣ ΑΛΑΤΟΚΟΡΤΙΚΟΕΙΔΩΝ ΧΑΡΑΚΤΗΡΙΣΤΙΚΑ & ΠΛΕΙΟΤΡΟΠΕΣ ΔΡΑΣΕΙΣ 23 Ιανουαρίου 2014 Κωνσταντίνος Π. Μακαρίτσης Παθολογική Κλινική Πανεπιστημίου Θεσσαλίας

3. ΕΙΣΑΓΩΓΗ Η αλδοστερόνη απομονώθηκε για πρώτη φορά το 1953 και παράγεται στη σπειροειδή ζώνη του φλοιού των επινεφριδίων. Μείζονα ερεθίσματα για έκκριση αλδοστερόνης: Αγγειοτενσίνη ΙΙ Επίπεδα του Κ+ του πλάσματος Η αλδοστερόνη αυξάνει την επαναρρόφηση Να+ και ύδατος από το τελικό άπω εσπειραμένο και τη φλοιώδη μοίρα του αθροιστικού σωληναρίου του νεφρού.

4. NCCT ENaC Aldosterone NHEs NKCC2 N Engl J Med

5. Sodium Channels and Transporters • Approximately 2-3% of filtered sodium is reabsorbed in the cortical collecting tubule via the epithelial Na channel (ENaC). • ENaC is composed of 3 subunits, α, β, γ. All 3 subunits are required for a fully functional channel.

6. Aldosterone-Regulated Transport - Cortical Collecting Tubule

7. Aldosterone-Regulated Transport - Cortical Collecting Tubule X X Spironolactone Eplerenone Amiloride Triamterene N Engl J Med 1999;340:1177-87.

8. Sodium Channels and Transporters • Regulation of Na reabsorption depends on the number of channels inserted in the cell membrane. • Vasopressin (via increased cAMP) and aldosterone (via serum and glucocorticoid-regulated kinase [SGK]) increase the density of channels at the cell surface.

9. Regulation of ENaC membrane expression α β γ Insulin MR

10. Mineralocorticoid Receptor-MR Στοιχεία Παθοφυσιολογίας

11. Στοιχεία Παθοφυσιολογίας Η συγκέντρωση της αλδοστερόνης στο πλάσμα είναι πολύ μικρή (<1nmol/L) και κυκλοφορεί συνδεδεμένη με την αλβουμίνη σε ποσοστό περίπου 50%. Αντιθέτως, τα φυσικά γλυκοκορτικοειδή – κορτιζόλη και κορτικοστερόνη – κυκλοφορούν συνδεδεμένα με την τρανσκορτίνη (CBG) και την αλβουμίνη σε ποσοστό περίπου 95% Τα επίπεδα της κορτιζόλης στο πλάσμα είναι από 100-1000 φορές υψηλότερα από τα επίπεδα της αλδοστερόνης.

12. Στοιχεία Παθοφυσιολογίας Ο Mineralocorticoid Receptor-MR είναι μέλος της οικογένειας των πυρηνικών υποδοχέων των στεροειδών/θυρεοειδικών/ρετινοϊκών/λιπιδικών/ ”ορφανών” υποδοχέων, που απαρτίζεται από 49 μέλη στον άνθρωπο. Ο MR μεταβάλλει την έκφραση συγκεκριμένων γονιδίων, αλλά έχει δειχθεί ότι συμμετέχεικαι στις καλούμενες ταχείες μη γονιδιωματικές δράσεις (rapid non-genomic effects). Hypertension. 2011;57:1019-1025.

13. Aldosterone signaling PI3K Rapid non-Genomic Effects Genomic Effects Hypertension. 2011;57:1019-1025.

14. Στοιχεία Παθοφυσιολογίας Ο MR εκφράζεται στα επιθηλιακά κύτταρα νεφρού κατιόντος κόλου σιελογόνων και ιδρωτοποιών αδένων Ωστόσο, ο MR έχει εντοπιστεί και σε μη-επιθηλιακά κύτταρα ιπποκάμπου καρδιάς(καρδιακάμυϊκά κύτταρα, ενδοθηλιακά,ινοβλάστες, μακροφάγα) αγγείων (ενδοθηλιακά και λεία μυϊκά κύτταρα)

15. Mineralocorticoid Receptor-MR Έχει διαπιστωθεί, ότι ο MR παρουσιάζει παρόμοια χημική συγγένεια ως προς τη δέσμευση της αλδοστερόνης και της κορτιζόλης. Πώς η αλδοστερόνη ενεργοποιεί επιλεκτικά τον MR στα επιθηλιακά κύτταρα, καθώς αφενός δεν υπάρχει εκλεκτικότητα στο επίπεδο του υποδοχέα και αφετέρου τα επίπεδα της κορτιζόλης στο πλάσμα είναι από 100-1000 φορές υψηλότερα από τα επίπεδα της αλδοστερόνης;;; Molecular and Cellular Endocrinology 350 (2012) 289–298.

16. Mineralocorticoid Receptor-MR Η απάντηση στο ερώτημα αυτό προέκυψε με την ανακάλυψη του ρόλου του ενζύμου 11βHSD2 (11β-hydroxysteroid dehydrogenase type 2), το οποίο εκφράζεται σε υψηλές συγκεντρώσεις μαζί με τον MR στα επιθηλιακά κύτταρα, αλλά και στο τοίχωμα των αγγείων και στον πυρήνα της μονήρους δεσμίδας (NTS). Το ένζυμο αυτό (11βHSD2) καταλύει τη μετατροπή της κορτιζόλης σε κορτιζόνη, ενώ δεν επηρεάζει την αλδοστερόνη.Η κορτιζόνη δεν ενεργοποιεί τον MR, οπότε διευκολύνεται η επίδραση της αλδοστερόνης στον MR. Molecular and Cellular Endocrinology 350 (2012) 289–298.

18. CHIMERIC GENE GRA Congenital Adrenal Hyperplasia 11β-HSD2* * 11β-Hydroxy Steroid Dehydrogenase2 SAME Syndrome Glycyrrhizic acid Carvenoxolone

19. Mineralocorticoid Receptor-MR Hypertens Res 2004; 27: 781–789.

20. Mineralocorticoid Receptor-MR It has been subsequently shown that under normal conditions most epithelial MRs are occupied (~ 90%), but not activated by normal levels of endogenous glucocorticoids. MR–glucocorticoid complexes are presumably held inactive under normal conditions by the obligate co-generation of high levels of NADH, shown to be an inhibitor of transcription by co-repressor activation in other transcriptional systems. Biochimica et Biophysica Acta 1802 (2010) 1188–1192.

21. Mineralocorticoid Receptor-MR Under conditions of tissue damage, reactive oxygen species generation and intracellular redox change, cortisol becomes a mineralocorticoid receptor agonist, in the vessel wall and heart, mimicking the deleterious effects of elevated aldosterone inappropriate for salt status. Biochimica et Biophysica Acta 1802 (2010) 1188–1192.

22. MR and Evolution Aldosterone is postulated to have played a key role in the phylogenic transition from aquatic fishes to terrestrial tetrapods, given its major epithelial effects on sodium retention and potassium excretion. Thus, the aldosterone/MR pathway enabled animals to retain sodium in the body to sustain life on land, where there was little salt. In our modern industrialized societies, however, an abundance of salt and a pandemic of obesity synergistically cause inappropriate activation of the aldosterone/MR system, that causes salt-sensitive hypertension and cardiorenal disease. Hypertension 2010;55:813-818.

23. Phylogenetic perspectives on the aldosterone/MR system CVD Clin Exp Nephrol (2010) 14:303–314.

24. Effects of Aldosterone in Relation to Sodium Status High levels of aldosterone in response to dietarysalt restriction, promotes renal sodium conservation, but has no cardiovascular consequences. When aldosterone is produced in inappropriate amounts for the level of sodium status, it results in excessive renal sodiumretention, potassium wasting, hypertension, andcardiovascular damage. N Engl J Med. 2004;351:8-10.

25. Physiologic and Pathophysiologic Effects of Aldosterone on the Kidney and Heart in Relation to Dietary Salt levels High Low N Engl J Med. 2004;351:8-10.

26. Is aldosterone a cardiovascular risk factor? In primary aldosteronism and chronic high salt intake, aldosterone levels are inappropriate high for sodium status and aldosterone is clearly a cardiovascular risk factor. In essential hypertension and heart failure it might be cortisol which activates mineralocorticoid receptors. Thus, mineralocorticoid receptor activation, not aldosterone, is the risk factor. Biochimica et Biophysica Acta 1802 (2010) 1188–1192.

27. Deleterious actions of Increased MR Activation Increased MR Activation Cardiology in Review 2005;13:118–124.

28. MR, Aldosterone and Blood Pressure

29. MR, Aldosterone and blood pressure Aldosterone secretion is raised in response to sodium deficiency. Secretion of endogenous ouabain is raised in response to sodium loading. The role of aldosterone is to retain sodium in the face of chronic deficiency. The role of endogenous ouabain is to excrete sodium, via a pressure natriuresis effect. Endogenous ouabain increases blood pressure.

30. MR, Aldosterone and blood pressure Aldosterone secretion is raised in response to sodium deficiency. Secretion of endogenous ouabain is raised in response to sodium loading. The role of aldosterone is to retain sodium in the face of chronic deficiency. The role of endogenous ouabain is to excrete sodium, via a pressure natriuresis effect. Endogenous ouabain increases blood pressure.

31. MR, Aldosterone and blood pressure It is possible that the blood pressure elevating effects of aldosterone reflect not only direct effects on the vessel wall but also sodium retention with the resultant elevation of endogenous ouabain secretion. The combined elevation of aldosterone and endogenous ouabain levels in response to salt/mineralocorticoid imbalance may thus be an explanation of the hypertension produced.

32. Pathways of salt-sensitive hypertension Ouabain NCX1 ___ Nature Medicine, Nov 2004

33. ___ Ouabain N Engl J Med. 2007;356:1966-78. Aldosterone

34. MR in vascular constriction and relaxation

35. MR in vascular constriction and relaxation In all studies, the effects of Aldo are MR-dependent, implicating vascular MR in direct regulation of vascular tone. MR activation in vascular SMC and EC increases ROS and decreases bioavailable NO and thus would be expected to promote VSMC contraction by decreasing GC activity. Molecular and Cellular Endocrinology 350 (2012) 256–265. British Journal of Pharmacology (2011) 163 1163–1169.

36. MR in vascular constriction and relaxation Interestingly, when Aldo is infused into vessels intraluminally to target the endothelium a vasodilator response was found, that required the presence of the endothelium, MR, and NO generation via NOS. Co-incubation with NOS inhibitors resulted in a loss of vasodilation and/or enhanced contraction, again implicating endothelial MR in vasodilation and SMC MR in vasoconstriction. Molecular and Cellular Endocrinology 350 (2012) 256–265. British Journal of Pharmacology (2011) 163 1163–1169.

37. MR in vascular constriction and relaxation The effects of MR activation on vascular reactivity in “healthy” humans also remains somewhat controversial due to conflicting results from clinical studies with many demonstrating a constrictive response and some showing vascular relaxation. The discrepancies may be due to differences in the vascular health of the study participants in addition to differences in dose and duration of Aldo infusion. Molecular and Cellular Endocrinology 350 (2012) 256–265. British Journal of Pharmacology (2011) 163 1163–1169.

38. MR in vascular constriction and relaxation When patients with underlying cardiovascular diseases are studied, including patients with atherosclerosis, heart failure, and hypertension, the data are quite consistent with MR-activation promoting increased systemic vascular resistanceand reduced forearm blood flow. Molecular and Cellular Endocrinology 350 (2012) 256–265. British Journal of Pharmacology (2011) 163 1163–1169.

39. MR in vascular constriction and relaxation

40. MR in vascular constriction and relaxation Taken together, these data support that in healthy vessels, acute MR activation may evoke endothelium - dependent, NO - mediated vasodilation while, in the presence of endothelial dysfunction, vascular injury, or high vascular oxidative stress (as in patients with cardiovascular risk factors), MR activation promotes vasoconstriction. Molecular and Cellular Endocrinology 350 (2012) 256–265. British Journal of Pharmacology (2011) 163 1163–1169.

41. MR and Vascular Oxidative Stress

42. MR, Aldosterone and Vascular Oxidative Stress The interaction of ROS with NO also decreases the bioavailability of NO resulting in impaired EC-dependent vasorelaxation and the peroxinitrite formed can directly alter many vascular cell functions. Aldosterone also produces oxidative stress and endothelial dysfunction by decreasing the expression of G6PD, which reduces NADP+ to NADPH. Molecular and Cellular Endocrinology 350 (2012) 256–265. Clinical Science (2007) 113, 267–278.

43. MR, Aldosterone and Vascular Oxidative Stress peroxinitrite Molecular and Cellular Endocrinology 350 (2012) 256–265. Clinical Science (2007) 113, 267–278.

44. MR, Aldosterone and Vascular Oxidative Stress

45. MR and Vascular Inflammation

46. MR, Aldosterone and Vascular Inflammation Direct activation of MR has been shown to promote inflammatory gene expression. MR activation promotes expression of: adhesion molecules ICAM1 and VCAM1 interleukin-16 cytotoxic T-lymphocyte-ass. Protein 4 Infusion of Aldo increased circulating IL-6 Treatment with spironolactone reduced MCP-1 and PAI-1 levels Molecular and Cellular Endocrinology 350 (2012) 256–265.

47. MR, Aldosterone and Vascular Inflammation Vascular MR activation participates in the inflammatory response by up-regulating adhesion molecules, chemokines, cytokines, and growth factors that promote the recruitment and activation of inflammatory cells. Molecular and Cellular Endocrinology 350 (2012) 256–265.

48. MR and Vascular Remodeling

49. MR, Aldosterone and Vascular Remodeling Multiple animal models support that Aldo exacerbates vascular remodeling in association with endothelial damage in vivo and these effects are reversed by MR antagonists. Human studies have shown that patients with primary aldosteronism have significantly increased vascular medial thickness and narrowed vessel lumens compared to patients with similar degrees of essential hypertension and other forms of secondary hypertension. Molecular and Cellular Endocrinology 350 (2012) 256–265.

50. MR, Aldosterone and Vascular Remodeling Molecular and Cellular Endocrinology 350 (2012) 256–265.