Aldosterone synthase is encoded on chromosome 8q22[1] by the CYP11B2 gene.[1] The gene contains 9 exons and spans roughly 7000 base pairs of DNA.[1] CYP11B2 is closely related with CYP11B1. The two genes show 93% homology to each other and are both encoded on the same chromosome.[4] Research has shown that calcium ions act as a transcription factor for CYP11B2 through well defined interactions at the 5'-flanking region of CYP11B2.[1]
Aldosterone synthase is a member of the cytochrome P450 superfamily of enzymes.[5] The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids.
Function
Adrenocorticotropic hormone is assumed to play a role in the regulation of aldosterone synthase likely through stimulating the synthesis of 11-deoxycorticosterone which is the initial substrate of the enzymatic action in aldosterone synthase.[6]
Renin–angiotensin system schematic showing aldosterone activity on the right
In human metabolism the biosynthesis of aldosterone largely depends on the metabolism of cholesterol. Cholesterol is metabolized in what is known as the early pathway of aldosterone synthesis[7] and is hydroxylated becoming (20R,22R)-dihydroxycholesterol which is then metabolized as a direct precursor to pregnenolone. Pregnenolone can then followed one of two pathways which involve the metabolism of progesterone or the testosterone and estradiol biosynthesis. Aldosterone is synthesized by following the metabolism of progesterone.
In the potential case where aldosterone synthase is not metabolically active the body accumulates 11-deoxycorticosterone. This increases salt retention leading to increased hypertension.[8]
Methyl oxidase deficiency
Lack of metabolically active aldosterone synthase leads to corticosterone methyl oxidase deficiency type I and II. The deficiency is characterized clinically by salt-wasting, failure to thrive, and growth retardation.[9] The in-active proteins are caused by the autosomal recessive inheritance of defective CYP11B2 genes in which genetic mutations destroy the enzymatic activity of aldosterone synthase.[9] Deficient aldosterone synthase activity results in impaired biosynthesis of aldosterone while corticosterone in the zona glomerulosa is excessively produced in both corticosterone methyl oxidase deficiency type I and II. The corticosterone methyl oxidase deficiencies both share this effect however type I causes an overall deficiency of 18-hydroxycorticosterone while type II overproduces it.[9]
Enzymatic inhibition
Inhibition of aldosterone synthase is currently being investigated as a medical treatment for hypertension, heart failure, and renal disorders.[10] Deactivation of enzymatic activity reduces aldosterone concentrations in plasma and tissues which decreases mineralocorticoid receptor-dependent and independent effects in cardiac vascular and renal target organs.[10] Inhibition has shown to decrease plasma and urinary aldosterone concentrations by 70 - 80%, rapid hypokalaemia correction, moderate decrease of blood pressure, and an increase plasma renin activity in patients who are on a low-sodium diet.[10] Ongoing medical research is focusing on the synthesis of second-generation aldosterone synthase inhibitors to create an ideally selective inhibitor as the current, orally delivered, LCl699 has shown to be non-specific to aldosterone synthase.[10]
↑Peter M, Dubuis JM, Sippell WG (1999). "Disorders of the aldosterone synthase and steroid 11β-hydroxylase deficiencies". Horm. Res. 51 (5): 211–22. doi:10.1159/000023374. PMID10559665.
↑Strushkevich N, Gilep AA, Shen L, Arrowsmith CH, Edwards AM, Usanov SA, Park HW (February 2013). "Structural insights into aldosterone synthase substrate specificity and targeted inhibition". Molecular Endocrinology. 27 (2): 315–324. doi:10.1210/me.2012-1287. PMID23322723.
↑Mornet E, Dupont J, Vitek A, White PC (June 1989). "Characterization of two genes encoding human steroid 11-beta-hydroxylase (P-45011-beta)". J Biol Chem. 264 (15): 20961–20967. PMID2592361.
Helmberg A (1993). "Twin genes and endocrine disease: CYP21 and CYP11B genes". Acta Endocrinol. 129 (2): 97–108. doi:10.1530/acta.0.1290097. PMID8372604.
Slight SH, Joseph J, Ganjam VK, Weber KT (1999). "Extra-adrenal mineralocorticoids and cardiovascular tissue". J. Mol. Cell. Cardiol. 31 (6): 1175–84. doi:10.1006/jmcc.1999.0963. PMID10371693.
Stowasser M, Gunasekera TG, Gordon RD (2002). "Familial varieties of primary aldosteronism". Clin. Exp. Pharmacol. Physiol. 28 (12): 1087–90. doi:10.1046/j.1440-1681.2001.03574.x. PMID11903322.
Padmanabhan N, Padmanabhan S, Connell JM (2002). "Genetic basis of cardiovascular disease--the renin–angiotensin–aldosterone system as a paradigm". Journal of the renin–angiotensin–aldosterone system (JRAAS). 1 (4): 316–24. doi:10.3317/jraas.2000.060. PMID11967817.
Lifton RP, Dluhy RG, Powers M, Rich GM, Gutkin M, Fallo F, Gill JR Jr, Feld L, Ganguly A, Laidlaw JC, et al. (1993). "Hereditary hypertension caused by chimaeric gene duplications and ectopic expression of aldosterone synthase". Nat. Genet. 2 (1): 66–74. doi:10.1038/ng0992-66. PMID1303253.
Mitsuuchi Y, Kawamoto T, Naiki Y, Miyahara K, Toda K, Kuribayashi I, Orii T, Yasuda K, Miura K, Nakao K, et al. (1992). "Congenitally defective aldosterone biosynthesis in humans: the involvement of point mutations of the P-450C18 gene (CYP11B2) in CMO II deficient patients". Biochem. Biophys. Res. Commun. 182 (2): 974–9. doi:10.1016/0006-291X(92)91827-D. PMID1346492.
Curnow KM, Tusie-Luna MT, Pascoe L, Natarajan R, Gu JL, Nadler JL, White PC (1992). "The product of the CYP11B2 gene is required for aldosterone biosynthesis in the human adrenal cortex". Mol. Endocrinol. 5 (10): 1513–22. doi:10.1210/mend-5-10-1513. PMID1775135.
Kawainoto T, Mitsuuchi Y, Ohnishi T, Ichikawa Y, Yokoyama Y, Sumimoto H, Toda K, Miyahara K, Kuribayashi I, Nakao K, et al. (1991). "Cloning and expression of a cDNA for human cytochrome P-450aldo as related to primary aldosteronism". Biochem. Biophys. Res. Commun. 173 (1): 309–16. doi:10.1016/S0006-291X(05)81058-7. PMID2256920.
Mornet E, Dupont J, Vitek A, White PC (1990). "Characterization of two genes encoding human steroid 11 beta-hydroxylase (P-450(11) beta)". J. Biol. Chem. 264 (35): 20961–7. PMID2592361.
Martsev SP, Chashchin VL, Akhrem AA (1985). "[Reconstruction and study of a multi-enzyme system by 11 beta-hydroxylase steroids]". Biokhimiia. 50 (2): 243–57. PMID3872685.
Shizuta Y, Kawamoto T, Mitsuuchi Y, Miyahara K, Rösler A, Ulick S, Imura H (1995). "Inborn errors of aldosterone biosynthesis in humans". Steroids. 60 (1): 15–21. doi:10.1016/0039-128X(94)00023-6. PMID7792802.
Mitsuuchi Y, Kawamoto T, Miyahara K, Ulick S, Morton DH, Naiki Y, Kuribayashi I, Toda K, Hara T, Orii T, et al. (1993). "Congenitally defective aldosterone biosynthesis in humans: inactivation of the P-450C18 gene (CYP11B2) due to nucleotide deletion in CMO I deficient patients". Biochem. Biophys. Res. Commun. 190 (3): 864–9. doi:10.1006/bbrc.1993.1128. PMID8439335.
Fardella CE, Rodriguez H, Montero J, Zhang G, Vignolo P, Rojas A, Villarroel L, Miller WL (1997). "Genetic variation in P450c11AS in Chilean patients with low renin hypertension". J. Clin. Endocrinol. Metab. 81 (12): 4347–51. doi:10.1210/jc.81.12.4347. PMID8954040.
Nomoto S, Massa G, Mitani F, Ishimura Y, Miyahara K, Toda K, Nagano I, Yamashiro T, Ogoshi S, Fukata J, Onishi S, Hashimoto K, Doi Y, Imura H, Shizuta Y (1997). "CMO I deficiency caused by a point mutation in exon 8 of the human CYP11B2 gene encoding steroid 18-hydroxylase (P450C18)". Biochem. Biophys. Res. Commun. 234 (2): 382–5. doi:10.1006/bbrc.1997.6651. PMID9177280.
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