Primary aldosteronism (PA) is a known cause of hypertension. Individuals with this condition represent nearly 10% of the hypertensive population, and the prevalence of PA increases with the severity of the hypertensive disease [1]. The high prevalence of PA can be detected using the serum aldosterone/plasma renin activity ratio (ARR) for screening and aldosterone suppression as a confirmatory test (saline infusion, fludrocortisone suppression or captopril). The most frequent subtypes of the disease are idiopathic aldosteronism and aldosterone-producing adenoma. Other less frequent causes of PA are familial variants. Four forms of familial hyperaldosteronism (FH-1 to FH-IV) together with Primary Aldosteronism, Seizures, Neurological Abnormalities (PASNA) syndrome [2] [3] [4]. FH-I, also called glucocorticoid-remediable aldosteronism, accounts for only 0.5 to 1% of PA [5] .
A hallmark of familial hyperaldosteronism type I is the presence of a chimeric aldosterone synthase enzyme, which is formed by unequal crossing-over of the genes that encode 11β-hydroxylase (CYP11B1), and aldosterone synthase (CYP11B2) enzymes. These genes are 95% identical in nucleotide sequence [5–8]. The 11β-hydroxylase enzyme (CYP11B1 gene) is normally expressed in both: human adrenal fasciculate and glomerulose zones, catalyzes the biosynthesis of cortisol and aldosterone, respectively. In the fasciculate, this gene is regulated by adrenocorticotropic hormone (ACTH). The aldosterone synthase (CYP11B2 gene) is typically expressed only in the adrenal glomerulose, and its product catalyzes the final two steps of aldosterone biosynthesis, and it is regulated by angiotensin II. The generation of the chimeric enzyme (CYP11B1/CYP11B2 gene) results in ectopic expression of aldosterone synthase in the fasciculate zone which is regulated by ACTH instead of angiotensin II, causing severe hypertension, variable hyperaldosteronism, low plasma renin activity, and normal or decreased potassium.
In recent years, some evidence has indicated that female sex steroids may modify aldosterone levels and the serum aldosterone/plasma renin activity ratio (ARR) used in screening for primary aldosteronism (PA). In women in the luteal phase, aldosterone concentrations increase, which could give a false positive in the screening and confirmatory tests for PA [9]. Moreover, our previous study in a pregnant woman carrying familial hyperaldosteronism type I demonstrated an improvement in blood pressure, concomitant with the normalization of ARR. Following childbirth, progesterone and estradiol decreased, aldosterone increased, plasma renin activity was suppressed, and ARR was very high [10]. These observations support our previously reported in vitro study in which both the wild-type and chimeric aldosterone synthase enzyme activities were inhibited by progesterone, but estradiol demonstrated no effect [11].
On the other hand, little information on the role of male hormones in aldosterone synthase activity is available, although some authors have reported that males have a higher blood pressure than women [12]. Few studies have analyzed the effect of testosterone on aldosterone production, and the majority of these studies were performed using animal or experimental models. During our study with a male index case carrying FH-I and his pedigree consisting of 4 generations, we observed that aldosterone and ARR decreased with age [10]. Based on this family observation, we postulated that changes in male gonadal hormones observed during the transition from childhood to adulthood might also alter aldosterone levels, which in turn might explain the normalization of ARR in adulthood.
We had previously assessed the direct action of progesterone and estradiol on wild-type and chimeric aldosterone synthase activities using HEK-293 cells transiently transfected with wild-type aldosterone synthase or CYP11B1/CYP11B2 chimeric enzymes. Aldosterone production was determined using deoxycorticosterone (DOC) as a substrate. In this system, we demonstrated that progesterone inhibited wild-type aldosterone synthase with similar efficacy and higher potency than the chimeric enzyme, while estradiol had no effect on any of the enzymes [11]. Using these models, in this work, we explore the direct action of testosterone on wild-type aldosterone synthase (ASWT) and chimeric aldosterone synthase (ASCE).