Ruth Andrew

Understanding the role of glucocorticoids in obesity: tissue-specific alterations of corticosterone metabolism in obese Zucker rats

The role of glucocorticoids in obesity is poorly understood. Observations in obese men suggest enhanced inactivation of cortisol by 5alpha-reductase and altered reactivation of cortisone to cortisol by 11betahydroxysteroid dehydrogenase type 1 (11betaHSD1). These changes in glucocorticoid metabolism may influence corticosteroid receptor activation and feedback regulation of the hypothalamic-pituitary-adrenal axis (HPA). We have compared corticosterone metabolism in vivo and in vitro in male obese and lean Zucker rats, aged 9 weeks (n = 8/group). Steroids were measured in 72-h urine and 0900 h trunk blood samples. 5alpha-Reductase type 1 and 11betaHSD activities were assessed in dissected tissues. Obese animals were hypercorticosteronemic and excreted more total corticosterone metabolites (2264+/-623 vs. 388+/-144 ng/72 h; P = 0.003), with a greater proportion being 5alpha-reduced or 11-oxidized. 11-Dehydrocorticosterone was also elevated in plasma (73+/-9 vs. 18+/-2 nM; P = 0.001) and urine (408+/-111 vs. <28 ng/72 h; P = 0.01). In liver of obese rats, 5alpha-reductase type 1 activity was greater (20.6+/-2.7% vs. 14.1+/-1.5%; P<0.04), but 11betaHSD1 activity (maximum velocity, 3.43+/-0.56 vs. 6.57+/-1.13 nmol/min/mg protein; P = 0.01) and messenger RNA levels (0.56+/-0.08 vs. 1.03+/-0.15; P = 0.02) were lower. In contrast, in obese rats, 11betaHSD1 activity was not different in skeletal muscle and sc fat and was higher in omental fat(36.4+/-6.2 vs. 19.2+/-6.6; P = 0.01), whereas 11betaHSD2 activity was higher in kidney (16.7+/-0.6% vs. 11.3+/-1.5%; p = 0.01). We conclude that greater inactivation of glucocorticoids by 5alpha-reductase in liver and 11betaHSD2 in kidney combined with impaired reactivation of glucocorticoids by 11betaHSD1 in liver may increase the MCR of glucocorticoids and decrease local glucocorticoid concentrations at these sites. By contrast, enhanced 11betaHSD1 in omental adipose tissue may increase local glucocorticoid receptor activation and promote obesity.

Dehydroepiandrosterone 7-hydroxylase cyp7b: predominant expression in primate hippocampus and reduced expression in alzheimer's disease☆

Neurosteroids such as dehydroepiandrosterone (DHEA), pregnenolone and 17beta-estradiol are synthesized by cytochrome P450s from endogenous cholesterol. We previously reported a new cytochrome P450 enzyme, CYP7B, highly expressed in rat and mouse brain that metabolizes DHEA and related steroids by hydroxylation at the 7alpha position. Such 7-hydroxylation can enhance DHEA bioactivity in vivo. Here we show that the reaction is conserved across mammalian species: in addition to mouse and rat, DHEA hydroxylation activity was present in brain extracts from sheep, marmoset and human. Northern blotting using a human CYP7B complementary deoxyribonucleic acid (cDNA) probe confirmed the presence of CYP7B mRNA in marmoset and human hippocampus; CYP7B mRNA was present in marmoset cerebellum and brainstem, with lower levels in hypothalamus and cortex. In situ hybridization to human brain revealed higher levels of CYP7B mRNA in the hippocampus than in cerebellum, cortex, or other brain regions. We also measured CYP7B expression in Alzheimers disease (AD). CYP7B mRNA was significantly decreased (approximately 50% decline; P<0.05) in dentate neurons from AD subjects compared with controls. A decline in CYP7B activity may contribute the loss of effects of DHEA with ageing and perhaps to the pathophysiology of AD.

Increased glucocorticoid production and altered cortisol metabolism in women with mild to moderate Alzheimer’s disease

BACKGROUNDnAbnormalities at several levels of the hypothalamic-pituitary-adrenal axis, which may promote glucocorticoid dependent neurodegeneration, have been reported in patients with Alzheimers disease. In this study we have explored the possibility that peripheral cortisol metabolism is enhanced and glucocorticoid production is increased compensatory in patients with mild to moderate Alzheimers disease.nnnMETHODSnUrinary excretion of cortisol and its principal conjugated metabolites was studied in ten women with mild to moderate Alzheimers disease, seven healthy elderly women and seven young women.nnnRESULTSnThere was an age-related fall in glucocorticoid production (median, 2009 [range 1828--4201] vs. 9315 [range 3613--16,244] microg/24 hours in elderly vs. young control subjects). A-ring metabolism (i.e., the irreversible inactivation of cortisol by 5 alpha- and 5 beta-reductases) was reduced in old age. However, patients with Alzheimers disease showed persistence of cortisol metabolite excretion. Glucocorticoid production was significantly increased in patients with Alzheimers disease versus healthy elderly control subjects (median, 7269 [range 6005-15,335] vs. 2009 [range 1828--4201] microg/24 hours), and patients with Alzheimers disease had increased A-ring reduction of cortisol.nnnCONCLUSIONSnAn increased glucocorticoid production is an early feature of Alzheimers disease and may be secondary to enhanced metabolic clearance of cortisol by A-ring reduction.

Growth hormone replacement inhibits renal and hepatic 11β–hydroxysteroid dehydrogenases in ACTH‐deficient patients

The commonest side‐effects of GH replacement therapy relate to sodium retention but its mechanism is unclear. In rats, GH inhibits renal and hepatic 11β–hydroxysteroid dehydrogenase (11β–HSD) activities. In man, this action might impair inactivation of cortisol to cortisone in the distal nephron thereby allowing cortisol to activate mineralocorticoid receptors. In this study, we examined the effects of GH replacement on cortisol metabolism.

Contrasting effects of intrauterine growth retardation and premature delivery on adult cortisol secretion and metabolism in man

objective Among babies born at term, intrauterine growth retardation (IUGR) predicts adult hypertension and hyperglycaemia. This might be due to elevated circulating glucocorticoids in adulthood, as described in animal models and in several cohorts of men who were low birthweight at term. Recently, we found that premature low birthweight babies also have adult cardiovascular risk factors, irrespective of IUGR. We have now investigated cortisol secretion in this group.