Mary C. Ingram

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.

Evidence of Coexisting Changes in 11β-Hydroxysteroid Dehydrogenase and 5β-Reductase Activity in Subjects With Untreated Essential Hypertension

Abstract We compared corticosteroid metabolite excretion rates and patterns in a group of 68 subjects with untreated essential hypertension and a matched group of 48 normotensive control subjects. The ratio of tetrahydrocortisol plus allotetrahydrocortisol to tetrahydrocortisone and the ratio of allotetrahydrocortisol to tetrahydrocortisol were significantly higher in the hypertensive group. This is qualitatively similar to the situation found in patients with the syndrome of apparent mineralocorticoid excess or subjects treated with licorice or carbenoxolone where hypertension is known to arise from deficiencies of 11β-hydroxysteroid dehydrogenase and 5β-reductase activities. The equivalent ratios for corticosterone metabolites were not different between groups, but total corticosterone metabolite excretion was higher in the hypertensive group. Plasma cortisol levels were lower in hypertensive than in control subjects, but corticosterone levels were higher. This evidence supports a previous suggestion that the activities of these two enzymes may be reduced in essential hypertension, but the contribution of these changes to hypertension is not known.

An influence of variation in the aldosterone synthase gene (CYP11B2) on corticosteroid responses to ACTH in normal human subjects.

OBJECTIVE Previous evidence suggests that the efficiency of 11β‐hydroxylase is at least partly heritable and also that it may be mildly impaired in essential hypertension. In both cases, assessment of activity was based on the response of 11‐deoxycorticosterone (DOC) and 11‐deoxycortisol to ACTH. The gene (CYP11B1) coding for this enzyme is highly homologous with and lies a relatively short distance downstream from the gene coding for aldosterone synthase (CYP11B2) on chromosome 8. Two polymorphisms of CYP11B2 have been described. The first involves a change of −344C to T in a putative steroidogenic factor‐1 (SF‐1) binding site and the other, the intron conversion, an exchange of intron 2 for that of CYP11B1. These polymorphisms are in linkage dysequilibrium. Their effects on 11β‐hydroxylation were studied.

Polymorphic Variation in the 11β-Hydroxylase Gene Associates With Reduced 11-Hydroxylase Efficiency

The −344 C/T and intron 2 conversion variants in the CYP11B2 gene, encoding aldosterone synthase, have been associated with markers of impaired 11β-hydroxylase activity. We hypothesize that this association is because of variations in the adjacent 11β-hydroxylase gene (CYP11B1) and arises through linkage disequilibrium between CYP11B1 and CYP11B2. The pattern of variation across the entire CYP11B locus was determined by sequencing 26 normotensive subjects stratified by and homozygous for the −344 and intron conversion variants. Eighty-three variants associated with −344 and intron conversion were identified. Haplotype analysis revealed 4 common haplotypes, accounting for 68% of chromosomes, confirming strong linkage disequilibrium across the region. Two novel CYP11B1 polymorphisms upstream of the coding region (−1889 G/T and −1859 A/G) were identified as contributing to the common haplotypes. Given the potential for such mutations to affect transcriptional regulation of CYP11B1, these were analyzed further. A total of 512 hypertensive subjects from the British Genetics of Hypertension Study population were genotyped for these polymorphisms. A significant association was identified between the −1889 polymorphism and urinary tetrahydrodeoxycortisol/total cortisol metabolite ratio, indicating reduced 11β-hydroxylase efficiency. A similar pattern was observed for the −1859 polymorphism, but this did not achieve statistical significance. Functional studies in vitro using luciferase reporter gene constructs show that these polymorphisms significantly alter the transcriptional response of CYP11B1 to stimulation by adrenocorticotropic hormone or forskolin. This study strongly suggests that the impaired 11β-hydroxylase efficiency associated previously with the CYP11B2 −344 and intron conversion variants is because of linkage with these newly identified polymorphisms in CYP11B1.

Corticosteroid Production by Fetal Rat Hippocampal Neurons

11β-hydroxylase and aldosterone synthase catalyse the final stages of corticosterone and aldosterone synthesis respectively. Previously, we established that they are expressed in the rat brain, particularly the cerebellum and the hippocampus. Primary cultures of fetal rat neurons were studied. RT-PCR and immunohistochemistry established that neurons express 11β -hydroxylase and aldosterone synthase mRNAs and protein. After incubating the cells with 10μM DOC for 24 hours, medium was analysed for aldosterone and corticosterone. Median % conversion of DOC to corticosterone was 7.6% compared to 0.4% in controls. Median % conversion of DOC to aldosterone was 6.2% compared to 0.06% in controls. Corticosteroids mediate a number of functions of mammalian brain, including blood pressure homeostasis, salt appetite and neuronal excitability. Local production of these steroids could have significant effects on these processes.

Aldosterone synthase gene variation and adrenocortical response to sodium status, angiotensin II and ACTH in normal male subjects

objective  Aldosterone synthase, a key enzyme in the terminal steps of aldosterone synthesis, is encoded by the CYP11B2 gene. A polymorphism in the 5′ coding region of this gene (−344 C/T) is associated with hypertension, particularly with elevation of the aldosterone to renin ratio. A second polymorphism (a conversion in intron 2 to resemble that of the neighbouring 11β‐hydroxylase (CYP11B1) gene) is found in close linkage dysequilibrium with the variant at −344 C/T. The mechanism by which these variants predispose to cardiovascular disease and the precise intermediate phenotype associated with them remains speculative.

Effect of variation in CYP11B1 and CYP11B2 on corticosteroid phenotype and hypothalamic–pituitary–adrenal axis activity in hypertensive and normotensive subjects

Background  Aldosterone is important in the development of hypertension. We have shown that a single nucleotide polymorphism (SNP) (–344T) in the 5′ regulatory region (UTR) of the gene encoding aldosterone synthase (CYP11B2) associates with aldosterone excess and hypertension as well as altered adrenal 11‐hydroxylation efficiency (deoxycortisol to cortisol). This conversion is carried out by the enzyme 11β‐hydroxylase, encoded by the adjacent gene, CYP11B1. We proposed that the effects of CYP11B2 are explained by linkage disequilibrium (LD) across the CYP11B locus. We have demonstrated high LD across this locus and identified two SNPs in the 5′ UTR of CYP11B1 (–1859 G/T, –1889 A/G) that associate with reduced transcription in vitro and altered 11‐hydroxylation efficiency in vivo. Accordingly, we hypothesized that the reduced adrenal 11‐hydroxylation may lead to chronic resetting of the pituitary–adrenal axis, with chronically increased ACTH drive resulting in aldosterone excess.

Phenotypic consequences of variation across the aldosterone synthase and 11‐beta hydroxylase locus in a hypertensive cohort: data from the MRC BRIGHT Study

Background  Aldosterone is an important cardiovascular hormone; 15% of hypertensive subjects have alteration in aldosterone regulation, defined by a raised ratio of aldosterone to renin (ARR). Studies of the aldosterone synthase gene (CYP11B2) have focused on a single nucleotide polymorphism in the 5′promoter region (–344 C/T). In normotensive subjects, the T allele associates with raised levels of the 11‐deoxysteroids, deoxycorticosterone and 11‐deoxycortisol which are substrates for 11β‐hydroxylase, encoded by the adjacent and homologous gene, CYP11B1. We have speculated that this altered 11β‐hydroxylase efficiency leads to increased ACTH drive to the adrenal gland to maintain cortisol production and reported herein the association between the –344 C/T single nucleotide polymorphism (SNP) and adrenal steroid production in subjects with essential hypertension.

11 beta-hydroxylase activity in glucocorticoid suppressible hyperaldosteronism: Lessons for essential hypertension?

Corticosteroid 11 beta-hydroxylation is catalysed by 11 beta-hydroxylase and aldosterone synthase. Using plasma steroid ratios, the level of this process in patients with glucocorticoid-suppressible hyperaldosteronism (GSH) was compared with that in unaffected control subjects and in patients with Conns syndrome. Based on both 11-deoxycortisol:cortisol (S:F) and 11-deoxycorticosterone:corticosterone (DOC:B) ratios, patients with GSH showed impaired resting 11 beta-hydroxylase activity. In GSH, but not in the other groups, the S:F ratio was significantly correlated with basal plasma aldosterone concentration. ACTH infusion increased the S:F ratio in all these patient groups, suggesting a common partial deficiency. The results also indicate that 11 beta-hydroxylation may be rate-limiting in normal subjects. In control subjects and patients with Conns syndrome, the DOC:B ratio was not affected by ACTH. However, in GSH patients, this ratio fell markedly, indicating an increased efficiency of 11 beta-hydroxylation of DOC (but not S). This may be due to the activation by ACTH of the zona fasciculata chimaeric aldosterone synthase characteristic of this disease. Plasma aldosterone, corticosterone and DOC concentrations, appeared to be more sensitive to ACTH in GSH than the other groups. The defect in 11 beta-hydroxylation in GSH accounts for the increased levels of DOC reported in the condition, and may contribute to the phenotypic variability.

Sodium status, corticosteroid metabolism and blood pressure in normal human subjects and in a patient with abnormal salt appetite

1. A patient with severe hypertension was found to have mildly impaired 11β‐hydroxysteroid dehydrogenase (11β‐HSD) activity on the basis of urinary steroid metabolite ratios, low plasma aldosterone, angiotensin II and renin levels and marginally low levels of plasma potassium.