Eleanor Davies

Cortisol Effects on Body Mass, Blood Pressure, and Cholesterol in the General Population

The effects of excess cortisol secretion on blood pressure and fat deposition are well documented, but the importance of this glucocorticoid in controlling these processes in normal individuals is less clear. We studied the relationship between cortisol excretion rate (tetrahydrocortisol [THF]+allo-THF+tetrahydrocortisone [THE]) and a range of important cardiovascular risk factors in 439 normal subjects (238 male) sampled from the North of Glasgow (Scotland) population. There were marked gender differences: female subjects were lighter and had lower blood pressures and cortisol levels, whereas HDL cholesterol was higher. The pattern of cortisol metabolism was also different; the index of 11beta-hydroxysteroid dehydrogenase activity (THF+allo-THF/THE) was lower and that of 5alpha-reductase (allo-THF/THF) was higher. There was a strong correlation of blood pressure (positive), cholesterol (positive), and HDL cholesterol (negative in women, positive in men) with age. Cortisol excretion rate did not correlate with blood pressure but correlated strongly with parameters of body habitus (body mass index and waist and hip measurements [positive]) and HDL cholesterol (negative). With multiple regression analysis, there remained a significant association of cortisol excretion rate with HDL cholesterol in men and women and with body mass index in men. These results suggest that glucocorticoids regulate key components of cardiovascular risk.

A Lifetime of Aldosterone Excess: Long-Term Consequences of Altered Regulation of Aldosterone Production for Cardiovascular Function

Up to 15% of patients with essential hypertension have inappropriate regulation of aldosterone; although only a minority have distinct adrenal tumors, recent evidence shows that mineralocorticoid receptor activation contributes to the age-related blood pressure rise and illustrates the importance of aldosterone in determining cardiovascular risk. Aldosterone also has a major role in progression and outcome of ischemic heart disease. These data highlight the need to understand better the regulation of aldosterone synthesis and its action. Aldosterone effects are mediated mainly through classical nuclear receptors that alter gene transcription. In classic epithelial target tissues, signaling mechanisms are relatively well defined. However, aldosterone has major effects in nonepithelial tissues that include increased synthesis of proinflammatory molecules and reactive oxygen species; it remains unclear how these effects are controlled and how receptor specificity is maintained. Variation in aldosterone production reflects interaction of genetic and environmental factors. Although the environmental factors are well understood, the genetic control of aldosterone synthesis is still the subject of debate. Aldosterone synthase (encoded by the CYP11B2 gene) controls conversion of deoxycorticosterone to aldosterone. Polymorphic variation in CYP11B2 is associated with increased risk of hypertension, but the molecular mechanism that accounts for this is not known. Altered 11beta-hydroxylase efficiency (conversion of deoxycortisol to cortisol) as a consequence of variation in the neighboring gene (CYP11B1) may be important in contributing to altered control of aldosterone synthesis, so that the risk of hypertension may reflect a digenic effect, a concept that is discussed further. There is evidence that a long-term increase in aldosterone production from early life is determined by an interaction of genetic and environmental factors, leading to the eventual phenotypes of aldosterone-associated hypertension and cardiovascular damage in middle age and beyond. The importance of aldosterone has generated interest in its therapeutic modulation. Disadvantages associated with spironolactone (altered libido, gynecomastia) have led to a search for alternative mineralocorticoid receptor antagonists. Of these, eplerenone has been shown to reduce cardiovascular risk after myocardial infarction. The benefits and disadvantages of this therapeutic approach are discussed.

Extra‐adrenal production of corticosteroids

1. The major corticosteroids aldosterone and cortisol (corticosterone in rodents) are secreted from the adrenal cortex under the regulation of the renin–angiotensin system and the hypothalamic–pituitary–adrenal axis.

Is Altered Adrenal Steroid Biosynthesis a Key Intermediate Phenotype in Hypertension

Approximately 10% of patients with hypertension have a high ratio of aldosterone to renin, but the reason for this and the relationships among low-renin essential hypertension, elevation of the ratio, and true primary aldosteronism are unclear. We have previously reported that a polymorphism of the gene (C-to-T conversion at position -344) encoding aldosterone synthase is associated with hypertension, particularly in patients with a high ratio. However, the most consistent association with this variant is a relative impairment of adrenal 11beta-hydroxylation. In this review, we propose that altered conversion of deoxycortisol to cortisol leads to a subtle, chronic increase in adrenocortrophin drive to the adrenal cortex, with eventual development of hyperplasia. In combination with other genetic or environmental factors (such as dietary sodium intake), we suggest that this might be responsible for the long-term development of a resetting of the aldosterone response to angiotensin II, giving rise to the phenotype of hypertension with a raised ratio. In some subjects, this may progress further to true primary aldosteronism with a dominant adrenal nodule. Thus, there may be a genetically influenced continuum from hypertension with a normal ratio, through hypertension with a raised ratio, and primary aldosteronism.

Depot-specific steroidogenic gene transcription in human adipose tissue

Context  Sex steroids (androgens and oestrogens) and corticosteroids (glucocorticoids and mineralocorticoids) have a major impact on fat distribution. Several genes involved in steroid synthesis and metabolism, such as 11β‐hydroxysteroid dehydrogenase type 1 and aromatase, are known to be expressed within adipose tissue, thus modulating local steroid levels; however, our knowledge of which genes are expressed and at what level is incomplete.

Bile acids modulate glucocorticoid metabolism and the hypothalamic–pituitary–adrenal axis in obstructive jaundice ☆

Background & Aims Suppression of the hypothalamic–pituitary–adrenal axis occurs in cirrhosis and cholestasis and is associated with increased concentrations of bile acids. We investigated whether this was mediated through bile acids acting to impair steroid clearance by inhibiting glucocorticoid metabolism by 5β-reductase. Methods The effect of bile acids on glucocorticoid metabolism was studied in vitro in hepatic subcellular fractions and hepatoma cells, allowing quantitation of the kinetics and transcript abundance of 5β-reductase. Metabolism was subsequently examined in vivo in rats following dietary manipulation or bile duct ligation. Finally, glucocorticoid metabolism was assessed in humans with obstructive jaundice. Results In rat hepatic cytosol, chenodeoxycholic acid competitively inhibited 5β-reductase (Ki 9.19 ± 0.40 μM) and reduced its transcript abundance (in H4iiE cells) and promoter activity (reporter system, HepG2 cells). In Wistar rats, dietary chenodeoxycholic acid (1% w/w chow) inhibited hepatic 5β-reductase activity, reduced urinary excretion of 3α,5β-tetrahydrocorticosterone and reduced adrenal weight. Conversely, a fat-free diet suppressed bile acid levels and increased hepatic 5β-reductase activity, supplementation of the fat-free diet with CDCA reduced 5β-reductase activity, and urinary 3α,5β-reduced corticosterone. Cholestasis in rats suppressed hepatic 5β-reductase activity and transcript abundance. In eight women with obstructive jaundice, relative urinary excretion of 3α,5β-tetrahydrocortisol was significantly lower than in healthy controls. Conclusion These data suggest a novel role for bile acids in inhibiting hepatic glucocorticoid clearance, of sufficient magnitude to suppress hypothalamic–pituitary–adrenal axis activity. Elevated hepatic bile acids may account for adrenal insufficiency in liver disease.

Familial and phenotypic associations of the aldosterone Renin ratio.

CONTEXT The aldosterone to renin ratio (ARR) is a marker of aldosterone excess, widely used to screen for primary aldosteronism (PA). The significance of a raised ARR in normotensive and hypertensive subjects and the phenotypic and familial factors affecting it are unclear. OBJECTIVE We estimated the distribution and heritability of the ARR and tested for associations between ARR and blood pressure (BP) with 11 polymorphisms at the CYP11B1/CYP11B2 locus. DESIGN AND SETTING A total of 1172 individuals from 248 Caucasian families ascertained via a hypertensive proband were evaluated. MAIN OUTCOME MEASURE Plasma aldosterone was measured by RIA, and plasma renin concentration was measured by the LIAISON Direct Renin chemiluminescent immunoassay. RESULTS Unadjusted and adjusted ARR were continuously distributed in normotensives and hypertensives, with no evidence of a cutoff that would identify a separate population with PA. Median ARR was 4.19 ng/liter per mIU/liter (range, 0.04-253.16). ARR levels were higher in females and associated with age, body mass index, and potassium. Antihypertensive agents had significant predictable effects on the ARR. Renin was negatively associated, and ARR was positively associated with ambulatory BP readings (P < 0.001) in subjects not taking antihypertensives. The heritability of the ARR was 38.1% (P < 10(-8)). Plasma aldosterone, but not ARR, was influenced by the intron 2 conversion variation in the CYP11B2 gene (beta = -0.07; P = 0.04). CONCLUSIONS The ARR is continuously distributed, is influenced by genetic and environmental factors, and is not a marker of a distinct pathological abnormality but possibly reflects the long-term influence of aldosterone on cardiovascular homeostasis.

Programming of Hypertension Associations of Plasma Aldosterone in Adult Men and Women With Birthweight, Cortisol, and Blood Pressure

Abstract—Animal models suggest that explanations for the association of low birthweight with adult hypertension may include chronic activation of the hypothalamic-pituitary-adrenal or renin-angiotensin-aldosterone axes. In humans, low birthweight predicts elevated plasma cortisol, but associations with aldosterone have not been reported. We measured aldosterone in serum samples from 205 men and 106 women from 67 to 78 years of age, from Hertfordshire, UK, for whom birthweight was recorded. Participants underwent an overnight low-dose (0.25 mg) dexamethasone suppression test and a low-dose (1 &mgr;g) ACTH (corticotropin) stimulation test and were genotyped for the -344 C/T polymorphism of the CYP11B2 gene encoding aldosterone synthase. Median aldosterone was 6.22 ng/dL (range 0.15 to 38.74) and was higher in men than women (P<0.0001). Higher aldosterone levels after both dexamethasone and ACTH stimulation were associated with higher blood pressure (r=0.20, P=0.001; r=0.33, P<0.0001, respectively) and with lower birthweight (r=−0.16, P=0.008; r=−0.21, P=0.001, respectively). These associations remained significant after adjusting for age, gender, obesity, and genotype. Our findings supplement previous evidence that aldosterone is an important regulator of blood pressure and suggest that factors in early life that retard fetal growth and program activation of the hypothalamic-pituitary-adrenal axis in humans result not only in higher glucocorticoid activity but also in increased mineralocorticoid activity.

α-Adducin and Angiotensin I–Converting Enzyme Polymorphisms in Essential Hypertension

This study focused on two genes that have previously been implicated in hypertension and may influence renal sodium handling, adducin, and angiotensin I–converting enzyme (ACE). We compared their polymorphic frequencies and interaction in patients with essential hypertension (n=128) and individually age- and gender-matched normotensive control subjects. The &agr;-adducin G460W polymorphism was genotyped by DNA amplification and restriction digestion. The ACE I/D polymorphism was assayed by a triple-primer method, with a “nested” polymerase chain reaction primer situated completely within the insertion sequence of the I allele. The distributions of genotypes and alleles for the two polymorphisms were not significantly different between the case and control populations, and the cross-classification of cases by &agr;-adducin and ACE genotype gave a distribution similar to that of control subjects. We have previously reported that the distributions of genotypes for two linked polymorphisms in the aldosterone synthase gene (one in the steroidogenic factor-1 [SF-1] binding site and the other an intronic conversion [IC]) were significantly different between this cohort of essential hypertensives and matched control subjects. The cross-classification of cases by &agr;-adducin and SF-1, &agr;-adducin and IC, ACE and SF-1, and ACE and IC genotype gave a distribution similar to that of control subjects. Hence, no evidence was found to suggest an association between either the &agr;-adducin G460W or the ACE I/D polymorphism and hypertension in a careful case-control study. Furthermore, the &agr;-adducin G460W, ACE I/D, and aldosterone synthase SF-1 and IC polymorphisms do not appear to interact in our hypertensive population.

MicroRNA-24 Is a Novel Regulator of Aldosterone and Cortisol Production in the Human Adrenal Cortex

Dysregulation of aldosterone or cortisol production can predispose to hypertension, as seen in aldosterone-producing adenoma, a form of primary aldosteronism. We investigated the role of microRNA (miRNA) in their production, with particular emphasis on the CYP11B1 (11&bgr;-hydroxylase) and CYP11B2 (aldosterone synthase) genes, which produce the enzymes responsible for the final stages of cortisol and aldosterone biosynthesis, respectively. Knockdown of Dicer1, a key enzyme in miRNA maturation, significantly altered CYP11B1 and CYP11B2 expression in a human adrenocortical cell line. Screening of nondiseased human adrenal and aldosterone-producing adenoma samples yielded reproducible but distinctive miRNA expression signatures for each tissue type, with levels of certain miRNA, including microRNA-24 (miR-24), differing significantly between the 2. Bioinformatic analysis identified putative binding sites for several miRNA, including miR-24, in the 3′ untranslated region of CYP11B1 and CYP11B2 mRNAs. In vitro manipulation of miR-24 confirmed its ability to modulate CYP11B1 and CYP11B2 expression, as well as cortisol and aldosterone production. This study demonstrates that Dicer-dependent miRNA, including miR-24, can post-transcriptionally regulate expression of the CYP11B1 and CYP11B2 genes. Normal adrenal tissue and aldosterone-producing adenoma differ significantly and reproducibly in their miRNA expression profiles, with miR-24 significantly downregulated in the latter. Adrenal miRNA may, therefore, be a novel and valid target for the therapeutic manipulation of corticosteroid biosynthesis.