Lack of tissue glucocorticoid reactivation in 11beta -hydroxysteroid dehydrogenase type 1 knockout mice ameliorates age-related learning impairments

Enhanced hippocampal long-term potentiation and spatial learning in aged 11beta-hydroxysteroid dehydrogenase type 1 knock-out mice

Glucocorticoids are pivotal in the maintenance of memory and cognitive functions as well as other essential physiological processes including energy metabolism, stress responses, and cell proliferation. Normal aging in both rodents and humans is often characterized by elevated glucocorticoid levels that correlate with hippocampus-dependent memory impairments. 11Beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) amplifies local intracellular ("intracrine") glucocorticoid action; in the brain it is highly expressed in the hippocampus. We investigated whether the impact of 11beta-HSD1 deficiency in knock-out mice (congenic on C57BL/6J strain) on cognitive function with aging reflects direct CNS or indirect effects of altered peripheral insulin-glucose metabolism. Spatial learning and memory was enhanced in 12 month "middle-aged" and 24 month "aged" 11beta-HSD1(-/-) mice compared with age-matched congenic controls. These effects were not caused by alterations in other cognitive (working memory in a spontaneous alternation task) or affective domains (anxiety-related behaviors), to changes in plasma corticosterone or glucose levels, or to altered age-related pathologies in 11beta-HSD1(-/-) mice. Young 11beta-HSD1(-/-) mice showed significantly increased newborn cell proliferation in the dentate gyrus, but this was not maintained into aging. Long-term potentiation was significantly enhanced in subfield CA1 of hippocampal slices from aged 11beta-HSD1(-/-) mice. These data suggest that 11beta-HSD1 deficiency enhances synaptic potentiation in the aged hippocampus and this may underlie the better maintenance of learning and memory with aging, which occurs in the absence of increased neurogenesis.

Physiology and neurobiology of stress and adaptation: central role of the brain

The brain is the key organ of the response to stress because it determines what is threatening and, therefore, potentially stressful, as well as the physiological and behavioral responses which can be either adaptive or damaging. Stress involves two-way communication between the brain and the cardiovascular, immune, and other systems via neural and endocrine mechanisms. Beyond the "flight-or-fight" response to acute stress, there are events in daily life that produce a type of chronic stress and lead over time to wear and tear on the body ("allostatic load"). Yet, hormones associated with stress protect the body in the short-run and promote adaptation ("allostasis"). The brain is a target of stress, and the hippocampus was the first brain region, besides the hypothalamus, to be recognized as a target of glucocorticoids. Stress and stress hormones produce both adaptive and maladaptive effects on this brain region throughout the life course. Early life events influence life-long patterns of emotionality and stress responsiveness and alter the rate of brain and body aging. The hippocampus, amygdala, and prefrontal cortex undergo stress-induced structural remodeling, which alters behavioral and physiological responses. As an adjunct to pharmaceutical therapy, social and behavioral interventions such as regular physical activity and social support reduce the chronic stress burden and benefit brain and body health and resilience.

Ectopic expression of Wnt10b decreases adiposity and improves glucose homeostasis in obese rats

The Wnt family of secreted glycoproteins had previously been shown to regulate diverse processes during early development. Wnt signaling also plays a key role in the homeostasis of adult tissues maintaining stem cell pluripotency and determining differentiating cell fate. The age-related decrease in Wnt signaling may contribute to increased muscle adiposity and diminished bone strength. In the current study, we investigated the long-term metabolic consequences of the upregulated Wnt/beta-catenin signaling in skeletal muscles of adult diet-induced obese (DIO) rats. To this end, we generated a recombinant adeno-associated virus (rAAV) vector encoding murine Wnt10b cDNA. The long-term expression of rAAV1-Wnt10b was tested after intramuscular injection in the female DIO rat. Animals fed high-fat diet and treated with rAAV1-Wnt10b showed a sustained reduction in body weight compared with controls, and expression of Wnt10b was accompanied by a reduction in hyperinsulinemia and triglyceride plasma levels as well as improved glucose homeostasis. Nuclear magnetic resonance methods revealed that ectopic expression of Wnt10b resulted in a decrease in both global and muscular fat deposits in DIO rats. The long-range effect of locally expressed Wnt10b was also manifested through the increased bone mineral density. The detailed analysis of molecular markers revealed fibroblast growth factor-4 and vascular endothelial growth factor as possible mediators of the systemic effect of Wnt10b transgene expression. Our data demonstrate that altering Wnt/beta-catenin signaling in the skeletal muscle of an adult animal invokes moderate responses with favorable metabolic profile, bringing the notion of alternative therapeutic modality in the treatment of obesity, diabetes, and osteoporosis.

Corticosteroids, 11beta-hydroxysteroid dehydrogenase isozymes and the rabbit choroid plexus

The epithelial cells of the choroid plexus (CP) are responsible for cerebrospinal fluid (CSF) secretion into the ventricles of the brain. The balance between CSF production and drainage, in part, facilitates a normal intracranial pressure. The secretion of Na(+) and anions by the CP creates an osmotic gradient driving water into the ventricles. This is opposite to classical Na(+) transporting tissues, such as the kidney, where Na(+) and water reabsorption is mediated by 11beta-hydroxysteroid dehydrogenase type 2 that protects the mineralocorticoid receptor by abrogating active cortisol to inactive cortisone. In the human ocular ciliary epithelium, Na(+) and water secretion is dependent on a novel mediator of ciliary epithelial Na(+) transport, 11beta-HSD type 1 (11beta-HSD1), that generates intraocular cortisol. In a mechanism analogous to that of the embryologically related ocular ciliary epithelium, we propose that autocrine regulation of intracranial cortisol is dependent on 11beta-HSD1 expression in the CP epithelial cells. By conducting immunolocalisation studies on brains from New Zealand White Albino rabbits, we defined the expression of 11beta-HSD1 in the secretory CP epithelial cells. Enzyme assays performed on intact rabbit CP whole tissue explants confirmed predominant 11beta-HSD1 activity, generating cortisol that was inhibited by glycyrrhetinic acid (an 11beta-HSD inhibitor). Using the real time-polymerase chain reaction, rabbit CP tissue was found to express levels of 11beta-HSD1, glucocorticoid receptor alpha and serum and glucocorticoid-regulated kinase 1 mRNA comparable to that expressed in rabbit ocular ciliary body, thereby highlighting the similarity between these two tissues. Furthermore, an enzyme-linked immunosorbent assay of rabbit CSF revealed a median cortisol concentration of 1.7 nmol/l (range 1.4-4.3 nmol/l, n = 9). Our data have identified a functional 11beta-HSD1 within the CP, mediating intracranial cortisol bioavailability. Expression of 11beta-HSD1 may be fundamental in the regulation of CSF secretion and the local generation of cortisol may represent a pathophysiological mechanism underlying cortisol-dependent neuroendocrine diseases.

Forebrain mineralocorticoid receptor overexpression enhances memory, reduces anxiety and attenuates neuronal loss in cerebral ischaemia

The nuclear mineralocorticoid receptor (MR), a high-affinity receptor for glucocorticoids, is highly expressed in the hippocampus where it underpins cognitive, behavioural and neuroendocrine regulation. Increased neuronal MR expression occurs early in the response to cellular injury in vivo and in vitro and is associated with enhanced neuronal survival. To determine whether increased neuronal MR might be causal in protecting against ischaemic damage in vivo we generated a forebrain-specific MR-overexpressing transgenic mouse (MR-Tg) under the control of the CamKII alpha promoter, and subjected mice to transient cerebral global ischaemia induced by bilateral common carotid artery occlusion for 20 min. We also separately assessed the effects of MR overexpression on hypothalamic-pituitary-adrenal (HPA) axis activity and cognitive and affective functions in noninjured animals. Our results showed that MR-Tg mice had significantly reduced neuronal death following transient cerebral global ischaemia compared to wild-type littermates. This effect was not associated with alterations in basal or poststress HPA axis function or in arterial blood pressure. MR-Tg mice also demonstrated improved spatial memory retention, reduced anxiety and altered behavioural response to novelty. The induction of neuronal MR appears to offer a protective response which has potential therapeutic implications in cerebral ischaemia and cognitive and affective disorders.

Local amplification of glucocorticoids by 11beta-hydroxysteroid dehydrogenase type 1 and its role in the inflammatory response

Glucocorticoids are widely used to treat chronic inflammatory conditions including rheumatoid arthritis. They promote mechanisms important for normal resolution of inflammation, notably macrophage phagocytosis of leukocytes undergoing apoptosis. Prereceptor metabolism of glucocorticoids by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) amplifies intracellular levels of glucocorticoids by oxoreduction of intrinsically inert cortisone (in humans, 11-dehydrocorticosterone in mice) into active cortisol (corticosterone in mice) within cells expressing the enzyme. Recently, we have shown in a mouse model of acute inflammation, high expression of 11beta-HSD oxoreductase but not dehydrogenase activity in cells elicited rapidly in the peritoneum by a single thioglycollate injection. 11beta-HSD oxoreductase activity remained high in peritoneal cells until the inflammation resolved. In vitro, the 11beta-HSD1 substrate, 11-dehydrocorticosterone, increased macrophage phagocytosis of apoptotic neutrophils to the same extent as corticosterone. This effect was dependent upon 11beta-HSD1: these cells solely expressed the type 1 11beta-HSD isozyme (not 11beta-HSD2), and carbenoxolone, an 11beta-HSD inhibitor, prevented the increase in phagocytosis elicited by 11-dehydrocorticosterone. Macrophages from 11beta-HSD1-deficient mice failed to respond to 11-dehydrocorticosterone. In vivo, 11beta-HSD1-deficient mice showed a delay in acquisition of macrophage phagocytic competence and had an increased number of free apoptotic neutrophils during sterile peritonitis. Importantly, in preliminary experiments, 11beta-HSD1-deficient mice exhibited delayed resolution of inflammation in experimental arthritis. These findings suggest 11beta-HSD1 may be a component of mechanisms engaged early during the inflammatory response that promote its subsequent resolution.

Liver-selective transgene rescue of hypothalamic-pituitary-adrenal axis dysfunction in 11beta-hydroxysteroid dehydrogenase type 1-deficient mice

11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) acts as a reductase in vivo, regenerating active glucocorticoids within cells from circulating inert 11-keto forms, thus amplifying local glucocorticoid action. 11beta-HSD1 is predominantly expressed in liver and also adipose tissue and brain. Mice deficient in 11beta-HSD1 (11beta-HSD1(-/-)) exhibit adrenal hyperplasia, raised basal corticosterone levels, and increased hypothalamic-pituitary-adrenal (HPA) axis responses to stress. Whereas reduced peripheral glucocorticoid regeneration may explain adrenal hypertrophy and exaggerated stress responses, elevated basal glucocorticoid levels support a role for 11beta-HSD1 within the brain in amplifying glucocorticoid feedback. To test this hypothesis, apolipoprotein E-HSD1 mice overexpressing 11beta-HSD1 in liver were intercrossed with 11beta-HSD1(-/-) mice to determine whether complementation of hepatic 11beta-HSD1 can restore adrenal and HPA defects. Transgene-mediated delivery of 11beta-HSD1 activity to the liver rescued adrenal hyperplasia and reversed exaggerated HPA stress responses in 11beta-HSD1(-/-) mice. Unexpectedly, elevated nadir plasma corticosterone levels were also restored to control levels. Consistent with this, CYP11B1 mRNA expression in the adrenal cortex of 11beta-HSD1(-/-) mice was increased by 50% but returned to control levels in 11beta-HSD1(-/-) mice bearing the apolipoprotein E-HSD1 transgene. 11beta-HSD1(-/-) mice have lower plasma glucose levels, but the fall in plasma corticosterone with sucrose supplementation was similar in 11beta-HSD1(-/-) and control mice, suggesting glucose deficiency is not the main mechanism whereby basal corticosterone levels are elevated in the null mice. Thus, regeneration of glucocorticoids by 11beta-HSD1 in the liver normalizes all aspects of HPA axis dysregulation in 11beta-HSD1(-/-) mice, without restoration of enzyme activity in key feedback areas of the forebrain. Therefore, hepatic glucocorticoid metabolism influences basal as well as stress-associated functions of the HPA axis.

Discovery and biological evaluation of adamantyl amide 11beta-HSD1 inhibitors

A series of adamantyl amide 11beta-HSD1 inhibitors has been discovered and chemically modified. Selected compounds are selective for 11beta-HSD1 over 11beta-HSD2 and possess excellent cellular potency in human and murine 11beta-HSD1 assays. Good pharmacodynamic characteristics are observed in ex vivo assays.

Development of an Enzyme-Linked Immunosorbent Assay for Serum 11-Dehydrocorticosterone in Rat and Mouse

We have developed an enzyme-linked immunosorbent assay (ELISA) for serum 11-dehydrocorticosterone (4-pregnen-21-ol-3,11,20-trione). The antiserum against 11-dehydrocorticosterone 21-hemisuccinate-conjugated bovine serum albumin was raised in rabbits. As an enzyme-labeled antigen, 11-dehydrocorticosterone 21-hemisuccinate was conjugated to horseradish peroxidase. Two ELISA systems were established: one without the extraction of steroids from serum (direct method), and another that used an HPLC purification step (HPLC method). The cross-reactivity of all steroids tested against the antibody was low except cortisone (92%); however, since cortisone levels in rats and mice are negligible, cortisone does not interfere with this direct ELISA. The measurable range of serum 11-dehydrocortiocosterone in both the direct and HPLC methods was 0.3-250 ng/ml and 0.78-400 ng/ml, respectively. Both methods displayed satisfactory parallel dilution, recovery and reproducibility; moreover, the values obtained with each method significantly correlated with the alternate method. To evaluate the two ELISA systems, the serum concentrations of 11-dehydrocorticosterone in normal rats and mice were determined by these two systems. The levels in Wistar rats fluctuated from 3 to 14 weeks of age (7.8+/-2.6 ng/ml) but at 1 week (1.7+/-1.2 ng/ml) were significantly low compared to other ages. No sex differences were found in rats and mice. Further, using the proposed direct method, chronological changes of rat serum 11-dehydrocorticosterone levels after 11-dehydrocorticosterone administration have been investigated together with corticosterone levels. These results verify that the proposed ELISA for 11-dehydrocorticosterone is useful for measuring 11beta-HSD activities in combination with the determination of serum corticosterone in rats and mice.

Central administration of a cytochrome P450-7B product 7 alpha-hydroxypregnenolone improves spatial memory retention in cognitively impaired aged rats

Pregnenolone (PREG) and dehydroepiandrosterone (DHEA) have been reported to improve memory in aged rodents. In brain, these neurosteroids are transformed predominantly into 7alpha-hydroxylated metabolites by the cytochrome P450-7B1 (CYP7B). The biological role of steroid B-ring hydroxylation is unclear. It has been proposed to generate bioactive derivatives that enhance cognition, immune, and other physiological processes. In support, 7alpha-hydroxylated DHEA increases the immune response in mice with greater potency than the parent steroid. Whether the memory-enhancing effects of PREG in rats is mediated via its 7alpha-hydroxylated metabolite 7alpha-hydroxyPREG is not known. We investigated this by treating memory-impaired aged rats (identified by their spatial memory performances in the Morris water maze task compared with young controls) with 7alpha-hydroxyPREG or PREG administered intracerebroventricularly using osmotic minipumps and then tested the rats during week 2 of steroid treatment in the eight-arm radial-arm version of the water maze (RAWM) that allows repeated assessment of learning. CYP7B bioactivity in hippocampal tissue (percentage conversion of [14C]DHEA to [14C]7alpha-hydroxyDHEA) was decreased selectively in memory-impaired aged rats compared with both young and memory-intact aged rats. 7alpha-hydroxyPREG (100 ng/h) but not PREG (100 ng/h) administration to memory-impaired aged rats for 11 d enhanced spatial memory retention (after a 30 min delay between an exposure trial 1 and test trial 2) in the RAWM. These data provide evidence for a biologically active enzyme product 7alpha-hydroxyPREG and suggests that reduced CYP7B function in the hippocampus of memory-impaired aged rats may, in part, be overcome by administration of 7alpha-hydroxyPREG.

Tissue Production of Cortisol by 11beta-Hydroxysteroid Dehydrogenase Type 1 and Metabolic Disease

Activation of intracellular glucocorticoid receptors is determined not only by the plasma concentrations of cortisol, under the influence of the hypothalamic-pituitary-adrenal (HPA) axis, but also by 11HSD enzymes within the target cell which interconvert cortisol with its inert metabolite cortisone. Data from cells in culture, isolated tissues, and transgenic mouse models have established that 11HSD type 1 regenerates glucocorticoids and amplifies glucocorticoid receptor activation. In humans, the rate of cortisol regeneration in peripheral tissues is of similar magnitude to adrenal secretion of cortisol at most times of day, and occurs principally in the splanchnic circulation. Approximately two-thirds of the splanchnic activity appears to reside in visceral adipose tissue, sufficient to allow visceral adipose tissue to "deliver" cortisol to the liver via the portal vein. In obesity, 11HSD1 activity in subcutaneous adipose tissue is increased, putatively explaining the link between obesity and other features of the metabolic syndrome. The regulation of 11HSD1, and the basis for its upregulation in obesity, are now being explored. Against this background, inhibition of 11HSD1 has become a major therapeutic target in metabolic syndrome. Preclinical results with novel selective 11HSD1 inhibitors are encouraging, and clinical proof of principle has been achieved with the nonselective inhibitor carbenoxolone. Although the parallels between metabolic syndrome and Cushing's syndrome were originally drawn with reference to patients with elevated plasma cortisol concentrations, it now appears that manipulating tissue concentrations of cortisol will allow the subtle level of control required for long-term therapy to reduce the risks of cardiovascular disease.

Discovery of adamantane ethers as inhibitors of 11beta-HSD-1: Synthesis and biological evaluation

A novel class of adamantane ethers 11beta-hydroxysteroid hydrogenase type I inhibitors has been discovered. These compounds have excellent HSD-1 potency and selectivity against HSD-2. The structure-activity relationships, selectivity, metabolism, PK, ex vivo pharmacodynamic data, and an X-ray crystal structure of one of these inhibitors bound to h-HSD-1 are discussed.

Adamantane sulfone and sulfonamide 11-beta-HSD1 Inhibitors

Potent and selective adamantane sulfone and sulfonamide inhibitors of 11-beta-HSD-1 have been discovered. Selected compounds from these series have robust pharmacokinetic profiles and strongly inhibit liver, fat, and brain HSD1 for extended periods after oral dosing.

Effects of stress hormones on the structure and function of the human brain

In response to stress, the hypothalamus-pituitary-adrenal axis is activated and glucocorticoids are secreted. These hormones exert multiple effects in the periphery as well as the brain. Acutely, they enhance memory consolidation, but at the same time the ability to retrieve previously learned information is reduced. In addition, glucocorticoids appear to interfere with working (short-term) memory. Chronically elevated glucocorticoid levels, as a result of endocrine or psychiatric disorders or as part of age-associated changes in the hypothalamus-pituitary-adrenal system, mostly have a negative influence on memory. In parallel, structural alterations are observed in the hippocampus and the prefrontal cortex. However, it seems that plasticity/reversibility is more common than previously thought. Moreover, several pharmacological interventions in animal models or small-scale human studies have revealed promising results. The advanced understanding of the CNS effects of glucocorticoids will ultimately lead to progress in the treatment of psychiatric and systemic diseases characterized by hypothalamus-pituitary-adrenal hyper- or hypo-activity.

11 beta-hydroxysteroid dehydrogenase type 1 induction in the arcuate nucleus by high-fat feeding: A novel constraint to hyperphagia?

11 beta-Hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) catalyzes regeneration of active intracellular glucocorticoids in fat, liver, and discrete brain regions. Although overexpression of 11 beta-HSD1 in adipose tissue causes hyperphagia and the metabolic syndrome, male 11 beta-HSD1 null (11 beta-HSD1-/-) mice resist metabolic disease on high-fat (HF) diet, but also show hyperphagia. This suggests 11 beta-HSD1 may influence the central actions of glucocorticoids on appetite and perhaps energy balance. We show that 11 beta-HSD1-/- mice express lower hypothalamic mRNA levels of the anorexigenic cocaine and amphetamine-regulated transcript and melanocortin-4 receptor, but higher levels of the orexigenic melanin-concentrating hormone mRNAs than controls (C57BL/6J) on a low-fat diet (11% fat). HF (58% fat) diet promoted transient ( approximately 8 wk) hyperphagia and decreased food efficiency in 11 beta-HSD1-/- mice and decreased melanocortin-4 receptor mRNA expression in control but not 11 beta-HSD1-/- mice. 11 beta-HSD1-/- mice showed a HF-mediated up-regulation of the orexigenic agouti-related peptide (AGRP) mRNA in the arcuate nucleus which paralleled the transient HF hyperphagia. Conversely, control mice showed a rapid (48 h) HF-mediated increase in arcuate 11 beta-HSD1 associated with subsequent down-regulation of AGRP. This regulatory pattern was unexpected because glucocorticoids increase AGRP, suggesting an alternate hyperphagic mechanism despite partial colocalization of 11 beta-HSD1 and AGRP in arcuate nucleus cells. One major alternate mechanism governing selective fat ingestion and the AGRP system is endogenous opioids. Treatment of HF-fed mice with the mu opioid agonist DAMGO recapitulated the HF-induced dissociation of arcuate AGRP expression between control and 11 beta-HSD1-/- mice, whereas the opioid antagonist naloxone given with HF induced a rise in arcuate AGRP and blocked HF-diet induction of 11 beta-HSD1. These data suggest that 11 beta-HSD1 in brain plays a role in the adaptive restraint of excess fat intake, in part by increasing inhibitory opioid tone on AGRP expression in the arcuate nucleus.

Inhibition of 11beta-HSD1 as a novel treatment for the metabolic syndrome: do glucocorticoids play a role?

The metabolic syndrome (syndrome X) is a cluster of risk factors and a common cause of cardiovascular disease in humans. Although the underlying mechanism for metabolic syndrome is still poorly understood, recent clinical data and studies with transgenic animals implicate elevated intracellular glucocorticoid tone in the etiology of metabolic syndrome. Development of selective inhibitors of 11beta-hydroxysteroid dehydrogenase (11beta-HSD)-1 and their use in rodent animal disease models encompassing several aspects of metabolic syndrome indicate the possibility of therapeutic intervention. This review will focus on recent advances in our understanding of the role of 11beta-HSD1 in metabolic disorders and other disease processes.

Local amplification of glucocorticoids by 11 beta-hydroxysteroid dehydrogenase type 1 promotes macrophage phagocytosis of apoptotic leukocytes

Glucocorticoids promote macrophage phagocytosis of leukocytes undergoing apoptosis. Prereceptor metabolism of glucocorticoids by 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) modulates cellular steroid action. 11beta-HSD type 1 amplifies intracellular levels of active glucocorticoids in mice by reactivating corticosterone from inert 11-dehydrocorticosterone in cells expressing the enzyme. In this study we describe the rapid (within 3 h) induction of 11beta-HSD activity in cells elicited in the peritoneum by a single thioglycolate injection in mice. Levels remained high in peritoneal cells until resolution. In vitro experiments on mouse macrophages demonstrated that treatment with inert 11-dehydrocorticosterone for 24 h increased phagocytosis of apoptotic neutrophils to the same extent as corticosterone. This effect was dependent upon 11beta-HSD1, as 11beta-HSD1 mRNA, but not 11beta-HSD2 mRNA, was expressed in these cells; 11-dehydrocorticosterone was ineffective in promoting phagocytosis by Hsd11b1(-/-) macrophages, and carbenoxolone, an 11beta-HSD inhibitor, prevented the increase in phagocytosis elicited in wild-type macrophages by 11-dehydrocorticosterone. Importantly, as experimental peritonitis progressed, clearance of apoptotic neutrophils was delayed in Hsd11b1(-/-) mice. These data point to an early role for 11beta-HSD1 in promoting the rapid clearance of apoptotic cells during the resolution of inflammation and indicate a novel target for therapy.

Targeting 11β-hydroxysteroid dehydrogenase type 1 in brain: therapy for cognitive aging?

Dementia care costs exceed those of cardiovascular diseases and cancer combined. Milder forms of functionally significant cognitive decline add further to the staggering human, societal and economic costs. However, the underlying mechanisms are poorly understood and few treatments are available. Cumulative exposure to high glucocorticoid levels is a major hypothesis of decline in cognitive function with aging. Current manipulations to maintain low circulating glucocorticoid levels throughout life (adrenalectomy with low-dose corticosterone replacement and neonatal handling), although effective in preventing the emergence of memory deficits with age in rodent models, are not clinically applicable. By contrast, recent data in cells, mice and humans suggest that inhibition of the tissue-selective glucocorticoid-amplifying enzyme, 11β-hydroxysteroid dehydrogenase type 1, may be an effective novel approach.

The biological actions of dehydroepiandrosterone involves multiple receptors

Dehydroepiandrosterone has been thought to have physiological functions other than as an androgen precursor. The previous studies performed have demonstrated a number of biological effects in rodents, such as amelioration of disease in diabetic, chemical carcinogenesis, and obesity models. To date, activation of the peroxisome proliferators activated receptor alpha, pregnane X receptor, and estrogen receptor by DHEA and its metabolites have been demonstrated. Several membrane-associated receptors have also been elucidated leading to additional mechanisms by which DHEA may exert its biological effects. This review will provide an overview of the receptor multiplicity involved in the biological activity of this sterol.

Do corticosteroids damage the brain?

Corticosteroids are an essential component of the body's homeostatic system. In common with other such systems, this implies that corticosteroid levels in blood and, more importantly, in the tissues remain within an optimal range. It also implies that this range may vary according to circumstance. Lack of corticosteroids, such as untreated Addison's disease, can be fatal in humans. In this review, we are principally concerned with excess or disturbed patterns of circulating corticosteroids in the longer or shorter term, and the effects they have on the brain.

Role of 11-beta-hydroxysteroid dehydrogenase type 1 in differentiation of 3T3-L1 cells and in rats with diet-induced obesity

AIM

To observe the roles of 11-beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in in vitro preadipocyte differentiation and in rats with diet-induced obesity (DIO).

METHODS

Protein expression of 11beta-HSD1 in the process of 3T3-L1 cell differentiation and in various tissues of the rats were detected by Western blot analysis; expression of 11beta-HSD1 mRNA and glucocorticoid receptor (GR) and other marker genes of preadipocyte differentiation were detected by using real-time PCR.

RESULTS

Lipid droplets in 3T3-L1 cells accumulated and increased after stimulation. A dramatically elevated protein level of 11beta-HSD1, especially in the late stages of 3T3-L1 cell differentiation, was detected. The relative mRNA levels of 11beta-HSD1, GR and cell differentiation markers LPL, aP2, and FAS were upregulated, and Pref-1 was downregulated during the differentiation. In DIO rats, bodyweight, visceral adipose mass index and the protein expression of 11beta-HSD1 increased, especially in adipose tissue, brain and muscles. Serum insulin, triglyceride, total cholesterol and low-density lipoprotein cholesterol were found to be increased in DIO rats, but without any obvious changes in blood glucose or tumor necrosis factor-alpha levels.

CONCLUSION

11beta-HSD1 may promote preadipocyte differentiation, and may be involved in the development of obesity.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

11Beta-hydroxysteroid dehydrogenase type 1--a role in inflammation?

Glucocorticoids are widely used for their potent anti-inflammatory effects. Endogenous glucocorticoids are immunomodulatory and shape both adaptive and innate immune responses. Over the past decade, it has become apparent that an important level of control over endogenous glucocorticoid action is exerted by the 11beta-hydroxysteroid dehydrogenase enzymes. The type 1 enzyme, 11beta-HSD1, reduces inert glucocorticoids into active forms, thereby increasing intracellular ligand availability to receptors. Although 11beta-HSD1 activity has been shown to play an important role in the metabolic actions of glucocorticoids, its role in the immune response has, until recently, remained unclear. Here we review recent evidence pertaining to the role of 11beta-HSD1 in the inflammatory response.

The role of 11beta-hydroxysteroid dehydrogenases in the brain

Glucocorticoids have a plethora of effects within the body to maintain homeostasis. In the brain they modify learning, memory and fear behaviours as well as regulating their own secretion by a negative feedback action. 11Beta-hydroxysteroid dehydrogenases (11beta-HSDs) are glucocorticoid metabolising enzymes that modify actions of glucocorticoids in a tissue specific manner. 11Beta-HSD1 regenerates active glucocorticoids from their inactive 11-keto derivatives, hence boosting tissue levels of corticosterone and cortisol. Removal of this enzyme (11beta-HSD1-/- mice) results in apparent lower intra-hippocampal corticosterone levels and reduces glucocorticoid-associated cognitive decline during ageing. This low corticosterone tissue environment is maintained even though there is a hyperactive hypothalamic-pituitary-adrenal axis and elevated basal and stress-induced plasma corticosterone levels. Conversely, the major central effects of 11beta-HSD2 are seen in development, as expression of 11beta-HSD2 is high in fetal and certain parts of the neonate brain, but is confined to a few discrete regions of the adult brain. 11Beta-HSD2 acts as a dehydrogenase, inactivating corticosterone or cortisol through conversion to 11-dehydrocorticosterone and cortisone. Loss of 11beta-HSD2 from the fetus and fetally derived tissues results in altered development of the cerebellum in the neonatal period and a life-long phenotype of anxiety, consistent with early life glucocorticoid programming.

Inhibition of 11beta-hydroxysteroid dehydrogenase type 1 in obesity

Excessive glucocorticoid exposure (Cushing's syndrome) results in increased adiposity associated with dysmetabolic features (including insulin resistance, hyperlipidaemia, and hypertension). Circulating cortisol levels are not elevated in idiopathic obesity, although cortisol production and clearance are increased. However, tissue glucocorticoid exposure may be altered independently of circulating levels by 11beta-hydroxysteroid dehydrogenase type 1 (11HSD1), an enzyme which generates active glucocorticoid within tissues, including in adipose tissue. Transgenic overexpression of 11HSD1 in mice causes obesity. In human obesity, 11HSD1 is altered in a tissue-specific manner with reduced levels in liver but elevated levels in adipose, which may lead to glucocorticoid receptor activation and contribute to the metabolic phenotype. The reasons for altered 11HSD1 in obesity are not fully understood. Although some polymorphisms have been demonstrated in intronic and upstream regions of the HSD11B1 gene, the functional significance of these is not clear. In addition, there is mounting evidence that 11HSD1 may be dysregulated secondarily to factors that are altered in obesity, including substrates for metabolism, hormones, and inflammatory mediators. 11HSD1 is a potential therapeutic target for the treatment of the metabolic syndrome. 11HSD1 knockout mice are protected from diet-induced obesity and associated metabolic dysfunction. Although many specific inhibitors of 11HSD1 have now been developed, and published data support their efficacy in the liver to reduce glucose production, their efficacy in enhancing insulin sensitivity in adipose tissue remains uncertain. The therapeutic potential of 11HSD1 in human obesity therefore remains highly promising but as yet unproven.

Stress and adult neurogenesis

Stress hormones have potent growth-inhibiting effects on a variety of peripheral tissues. Consistent with this general function, stress has been shown to inhibit cell proliferation and, ultimately, neurogenesis in the hippocampus. This effect appears to be common across mammalian species, life stages, and most types of stressors. Although some evidence points to a role for glucocorticoids in mediating this effect, contradictory data exist. This review considers the growing literature on this subject with specific emphasis on paradoxical findings and the role of glucocorticoids in modulating adult neurogenesis.

Polymorphisms in the gene encoding 11B-hydroxysteroid dehydrogenase type 1 (HSD11B1) and lifetime cognitive change

A rare polymorphism in the gene encoding 11B-hydroxysteroid dehydrogenase type 1 (HSD11B1: rs846911-C/A) has been associated with an increased risk of Alzheimer's disease. We tested the hypothesis that this and 2 other HSD11B1 polymorphisms (rs12086634-G/T and rs846910-A/G) were associated with lifetime cognitive change in humans. Subjects were 194 participants of the Scottish Mental Survey of 1932 who took the same well-validated mental test at age 11 and age 79. The subjects represented the highest and lowest quintiles with respect to cognitive decline between ages 11 and 79. Despite having non-significantly different IQs at age 11, by age 79 the groups had mean (S.D.) IQs of 80.3 (14.1) and 109.6 (9.1), respectively (p<.001). The polymorphism rs846911-C/A was absent from both groups. There were no significant differences in the frequency of polymorphisms of rs12086634-G/T (p=.91) and rs846910-A/G (p=.90) between the groups. We conclude that these variants in HSD11B1 are not significant contributors to the range of cognitive ageing examined here.

Mechanisms of Disease: selective inhibition of 11β-hydroxysteroid dehydrogenase type 1 as a novel treatment for the metabolic syndrome

The magnitude of the obesity and metabolic syndrome epidemic has heightened the need for the development of new and effective treatments. Although circulating cortisol concentrations are not elevated in obesity or in the metabolic syndrome, decreasing the tissue-specific generation of cortisol through inhibition of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) has been postulated as a therapeutic strategy. Observations in cohorts of obese patients, in comparison with those with type 2 diabetes, have suggested that the ability to decrease tissue-specific cortisol production might represent a protective mechanism to improve insulin sensitivity and prevent diabetes. In rodents, pharmacologic exploitation of this mechanism, through the development of inhibitors selective for 11beta-HSD1 (in preference to the type 2 isoform), dramatically improves insulin sensitivity. Here we review the published data and the rationale for treatment in humans, as well as discussing potential problems and adverse effects of future selective 11beta-HSD1 inhibitors.

11beta-HSD1 inhibition ameliorates metabolic syndrome and prevents progression of atherosclerosis in mice

The enzyme 11β–hydroxysteroid dehydrogenase (HSD) type 1 converts inactive cortisone into active cortisol in cells, thereby raising the effective glucocorticoid (GC) tone above serum levels. We report that pharmacologic inhibition of 11β-HSD1 has a therapeutic effect in mouse models of metabolic syndrome. Administration of a selective, potent 11β-HSD1 inhibitor lowered body weight, insulin, fasting glucose, triglycerides, and cholesterol in diet-induced obese mice and lowered fasting glucose, insulin, glucagon, triglycerides, and free fatty acids, as well as improved glucose tolerance, in a mouse model of type 2 diabetes. Most importantly, inhibition of 11β-HSD1 slowed plaque progression in a murine model of atherosclerosis, the key clinical sequela of metabolic syndrome. Mice with a targeted deletion of apolipoprotein E exhibited 84% less accumulation of aortic total cholesterol, as well as lower serum cholesterol and triglycerides, when treated with an 11β-HSD1 inhibitor. These data provide the first evidence that pharmacologic inhibition of intracellular GC activation can effectively treat atherosclerosis, the key clinical consequence of metabolic syndrome, in addition to its salutary effect on multiple aspects of the metabolic syndrome itself.

Genetic manipulation of 11β-hydroxysteroid dehydrogenases in mice

11β-Hydroxysteroid dehydrogenases (HSDs) interconvert active 11-hydroxy glucocorticoids (cortisol, corticosterone) and their inert 11-keto derivatives (cortisone, 11-dehydrocorticosterone). 11β-HSD type 1 is a predominant reductase that regenerates active glucocorticoids in expressing cells, thus amplifying local glucocorticoid action, whereas 11β-HSD type 2 catalyzes rapid dehydrogenation, potently inactivating intracellular glucocorticoids. Both isozymes thus regulate receptor activation by substrate availability. Spatial and temporal regulation of expression are important determinants of the physiological roles of 11β-HSDs, with each isozyme exhibiting a distinct, tissue-restricted pattern together with dynamic regulation during development and in response to environmental challenges, including diet and stress. Transgenic approaches in the mouse have contributed significantly toward an understanding of the importance of these prereceptor regulatory mechanisms on corticosteroid receptor activity and have highlighted its potential relevance to human health and disease. Here we discuss current ideas of the physiological roles of 11β-HSDs, with emphasis on the key contributions made by studies of 11β-HSD gene manipulation in vivo.

Molecular endocrinology and physiology of the aging central nervous system

Aging is associated with a progressive decline in physical and cognitive functions. The impact of age-dependent endocrine changes regulated by the central nervous system on the dynamics of neuronal behavior, neurodegeneration, cognition, biological rhythms, sexual behavior, and metabolism are reviewed. We also briefly review how functional deficits associated with increases in glucocorticoids and cytokines and declining production of sex steroids, GH, and IGF are likely exacerbated by age-dependent molecular misreading and alterations in components of signal transduction pathways and transcription factors.

11β-Hydroxysteroid dehydrogenase Type 1 as a novel therapeutic target in metabolic and neurodegenerative disease

11beta-hydroxysteroid dehydrogenase Type 1 (11HSD1) catalyses regeneration of active 11-hydroxy glucocorticoids from inactive 11-keto metabolites within target tissues. Inhibition of 11HSD1 has been proposed as a novel strategy to lower intracellular glucocorticoid concentrations, without affecting circulating glucocorticoid levels and their responsiveness to stress. Increased 11HSD1 activity may be pathogenic, for example, in adipose tissue in obesity. Experiments in transgenic mice and using prototype inhibitors in humans show benefits of 11HSD1 inhibition in liver, adipose and brain tissue in treating features of the metabolic syndrome and cognitive dysfunction with ageing. The clinical development of potent selective 11HSD1 inhibitors is now a high priority.

The role of glucocorticoid action in the pathophysiology of the Metabolic Syndrome

Glucocorticoids are stress hormones that modulate a large number of physiological actions involved in metabolic, inflammatory, cardiovascular and behavioral processes. The molecular mechanisms and the physiological effects of glucocorticoids have been extensively studied. However, the involvement of glucocorticoid action in the etiology of the Metabolic Syndrome has not been well appreciated. Recently, accumulating clinical evidence and animal genetics studies have attracted growing interest in the role of glucocorticoid action in obesity and insulin resistance. This review will discuss the metabolic effects in the context of glucocorticoid metabolism and establish the association of glucocorticoid action with the features of the Metabolic Syndrome, especially obesity and insulin resistance. Special discussions will be focused on corticosteroid-binding globulin and 11beta-hydroxysteroid dehydrogenase type 1, two proteins that mediate glucocorticoid action and have been implicated in the Metabolic Syndrome. Due to the complexities of the glucocorticoid biology and the Metabolic Syndrome and limited space, this review is only intended to provide a general link between the two areas with broad rather than in-depth discussions of clinical, pharmacological and genetic findings.

Conformational Flexibility in Crystal Structures of Human 11β-Hydroxysteroid Dehydrogenase Type I Provide Insights into Glucocorticoid Interconversion and Enzyme Regulation

Human 11beta-hydroxysteroid dehydrogenase type I (11beta-HSD1) is an ER-localized membrane protein that catalyzes the interconversion of cortisone and cortisol. In adipose tissue, excessive cortisol production through 11beta-HSD1 activity has been implicated in the pathogenesis of type II diabetes and obesity. We report here biophysical, kinetic, mutagenesis, and structural data on two ternary complexes of 11beta-HSD1. The combined results reveal flexible active site interactions relevant to glucocorticoid recognition and demonstrate how four 11beta-HSD1 C termini converge to form an as yet uncharacterized tetramerization motif. A C-terminal Pro-Cys motif is localized at the center of the tetramer and forms reversible enzyme disulfides that alter enzyme activity. Conformational flexibility at the tetramerization interface is coupled to structural changes at the enzyme active site suggesting how the central Pro-Cys motif may regulate enzyme activity. Together, the crystallographic and biophysical data provide a structural framework for understanding 11beta-HSD1 activities and will ultimately facilitate the development of specific inhibitors.

Nuclear envelope barrier leak induced by dexamethasone

Nuclear pore complexes (NPCs) are multiprotein channels that span the nuclear envelope. They strongly limit the efficiency of gene transfection by restriction of nuclear delivery of exogenously applied therapeutic macromolecules. NPC dilation could significantly increase this efficiency. Recently, it was shown in oocytes of Xenopus laevis that NPCs dilate from about 82 to 110 nm within min after injection of the glucocorticoid analog dexamethasone (dex). In the present paper we analyzed by means of atomic force microscopy the structural details of NPC dilation and correlated them with functional changes in nuclear envelope permeability. 5-11 min after Dex injection NPC dilation was found at its maximum (approximately 140 nm). In addition, a yet unknown configuration, so-called giant pore, up to 300 nm in diameter, was visualized. Giant pore formation was paralleled by an increase in nuclear envelope permeability tested by electrophysiology and confocal fluorescence microscopy. Even large macromolecules lacking any nuclear localization signal (77 kDa FITC-dextran, molecule diameter up to 36 nm) could gain access to the nucleus. We conclude that dex transiently opens unspecific pathways for large macromolecules. Dex treatment could be potentially useful for improving the efficiency of nuclear gene transfection.

Reduced brain CRH and GR mRNA expression precedes obesity in juvenile rats bred for diet-induced obesity

To assess the role of endogenous peptides involved in stress responsivity in the development of diet-induced obesity (DIO), selectively bred DIO and diet-resistant (DR) male were weaned onto a low fat (4.5%) chow diet at 3 weeks of age and then fed either chow or a 31% fat by energy content (high energy (HE)) diet for 9 days beginning at 4 weeks of age. Regardless of diet, DIO rats gained more weight than DR rats but did not show the selective DIO weight gain trait characteristic of older DIO rats fed HE diet. At this early age, both DR and DIO rats on HE diet ate more and had higher leptin levels but gained less body weight and had lower feed efficiency (body weight gain (g)/food intake (kcal)) than their chow-fed controls. HE diet also prevented the decline in 24h urine corticosterone levels from the third to fifth week observed in chow-fed rats. Terminally, DIO rats had lower hippocampal glucocorticoid receptor (GR) and amygdalar central nucleus corticotrophin-releasing hormone (CRH) mRNA than DR rats, regardless of their diets. Taken together with prior studies in these rats, there appears to be a critical period between 3 and 5 weeks of age when DIO and DR rats are not phenotypically different and hypothalamo-pituitary-adrenal (HPA) function is rapidly changing. The reduced expression of brain GR and CRH expression at the end of this period might contribute to the propensity of DIO rats to become obese selectively on HE diet after 5 weeks of age.

11beta-hydroxysteroid dehydrogenase type 1 as a modulator of glucocorticoid action: from metabolism to memory

Increases in plasma cortisol and glucocorticoid pharmacotherapy cause myriad adverse effects from obesity and diabetes to impairments in memory. The common metabolic syndrome phenotypically resembles the rare disorder Cushing's syndrome, but plasma cortisol levels are usually normal. 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyses the regeneration of active glucocorticoids (cortisol and corticosterone) from inert 11-keto forms in specific tissues, notably liver, adipose and brain. Recent work shows that obese humans and rodents have increased 11beta-HSD1 activity selectively in adipose tissue. By locally amplifying glucocorticoid action, this increase in activity might explain the Cushing's syndrome/metabolic syndrome paradox. Indeed, mice deficient in 11beta-HSD1 resist both the metabolic syndrome that develops with dietary obesity and glucocorticoid-associated cognitive impairments that develop with ageing. The ongoing development of selective 11beta-HSD1 inhibitors affords the opportunity to explore a new approach to some major common disorders.

11beta-hydroxysteroid dehydrogenase type 1: a tissue-specific regulator of glucocorticoid response

11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) interconverts inactive cortisone and active cortisol. Although bidirectional, in vivo it is believed to function as a reductase generating active glucocorticoid at a prereceptor level, enhancing glucocorticoid receptor activation. In this review, we discuss both the genetic and enzymatic characterization of 11beta-HSD1, as well as describing its role in physiology and pathology in a tissue-specific manner. The molecular basis of cortisone reductase deficiency, the putative "11beta-HSD1 knockout state" in humans, has been defined and is caused by intronic mutations in HSD11B1 that decrease gene transcription together with mutations in hexose-6-phosphate dehydrogenase, an endoluminal enzyme that provides reduced nicotinamide-adenine dinucleotide phosphate as cofactor to 11beta-HSD1 to permit reductase activity. We speculate that hexose-6-phosphate dehydrogenase activity and therefore reduced nicotinamide-adenine dinucleotide phosphate supply may be crucial in determining the directionality of 11beta-HSD1 activity. Therapeutic inhibition of 11beta-HSD1 reductase activity in patients with obesity and the metabolic syndrome, as well as in glaucoma and osteoporosis, remains an exciting prospect.

11Beta-hydroxysteroid dehydrogenase inhibition improves cognitive function in healthy elderly men and type 2 diabetics

In aging humans and rodents, inter-individual differences in cognitive function have been ascribed to variations in long-term glucocorticoid exposure. 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) regenerates the active glucocorticoid cortisol from circulating inert cortisone, thus amplifying intracellular glucocorticoid levels in some tissues. We show that 11beta-HSD1, but not 11beta-HSD2, mRNA is expressed in the human hippocampus, frontal cortex, and cerebellum. In two randomized, double-blind, placebo-controlled crossover studies, administration of the 11beta-HSD inhibitor carbenoxolone (100 mg three times per day) improved verbal fluency (P < 0.01) after 4 weeks in 10 healthy elderly men (aged 55-75 y) and improved verbal memory (P < 0.01) after 6 weeks in 12 patients with type 2 diabetes (52-70 y). Although carbenoxolone has been reported to enhance hepatic insulin sensitivity in short-term studies, there were no changes in glycemic control or serum lipid profile, nor was plasma cortisol altered. 11beta-HSD1 inhibition may be a new approach to prevent/ameliorate cognitive decline.

11 beta-hydroxysteroid dehydrogenase type 1 in obesity and the metabolic syndrome

11 beta-Hydroxysteroid dehydrogenase type 1 (11HSD1) catalyses the in vivo conversion of inactive to active glucocorticoids. It is a widespread, highly regulated enzyme which amplifies the ligand available for intracellular glucocorticoid receptors. Excessive glucocorticoid exposure causes central obesity, hypertension, dyslipidaemia and insulin resistance, as seen with elevated plasma cortisol in Cushing's syndrome. Transgenic mice over-expressing 11HSD1 in their white adipose tissue are obese, hypertensive, dyslipidaemic and insulin resistant. Further, 11HSD1 knockout mice are protected from these metabolic abnormalities. In human idiopathic obesity, circulating cortisol levels are not elevated but 11HSD1 mRNA and activity is increased in subcutaneous adipose. The impact of increased adipose 11HSD1 on pathways leading to metabolic complications remains unclear in humans. Pharmacological inhibition of 11HSD1 has been achieved in liver with carbenoxolone, which enhances hepatic insulin sensitivity. Newer selective 11HSD1 inhibitors are in development, which may achieve reduced cortisol action in adipose tissue and confer therapeutic benefit in obese patients.

11beta-Hydroxysteroid dehydrogenase Type 1 in obesity and Type 2 diabetes

Obesity and Type 2 diabetes mellitus are associated with abnormal regulation of glucocorticoid metabolism that are highlighted by clinical similarities between the sequelae of insulin resistance and Cushing's syndrome, as well as glucocorticoids' functional antagonism to insulin. 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activates functionally inert glucocorticoid precursors (cortisone) to active glucocorticoids (cortisol) within insulin target tissues, such as adipose tissue, thereby regulating local glucocorticoid action. Recent data, mainly from rodents, provide considerable evidence for a causal role of 11beta-HSD1 for the development of visceral obesity and Type 2 diabetes though data in humans are not unequivocal. This review summarizes current evidence on a possible role of 11beta-HSD1 for development of the metabolic syndrome, raising the possibility of novel therapeutic options for the treatment of Type 2 diabetes by inhibition or down-regulation of 11beta-HSD1 activity.

11β-Hydroxysteroid Dehydrogenases in the Brain

Glucocorticoids affect a wide range of processes in the brain, altering neurotransmission, electrophysiological activity, metabolism, cell division, and death. These actions are mediated by corticosteroid receptors (glucocorticoid and mineralocorticoid) that modify transcriptional activity of target genes. The amount of steroid available to activate these receptors is not only dependent on the circulating levels but also on pre-receptor metabolism of glucocorticoids occurring intracellularly. This metabolism is carried out by the enzymes 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). There are two distinct isozymes, the products of distantly related genes. 11beta-HSD type 2 inactivates glucocorticoids to its inert 11-keto derivative, while 11alpha-HSD type 1 elevates intracellular glucocorticoid levels by regenerating active glucocorticoids from circulating 11-dehydrocorticosterone or cortisone. This review highlights the important and very different roles the two enzymes play in the brain, outlining recent results obtained from studying mice with a targeted gene deletion in the 11beta-HSD1 or 11beta-HSD2 genes.

Alzheimer's disease: pathophysiological implications of measurement of plasma cortisol, plasma dehydroepiandrosterone sulfate, and lymphocytic corticosteroid receptors

Alzheimer's disease is often characterized by an increase in plasma cortisol without clinical evidence of hypercorticism. Twenty-three consecutive patients with Alzheimer's disease and 23 age- and sex-matched healthy controls were studied by measuring plasma cortisol and dehydroepiandrosterone sulfate (DHEAS) (by enzyme immunoassay), the number of type I and type II corticosteroid receptors in mononuclear leukocytes (by radio-receptor-assay), and the lymphocyte subpopulations (by cytofluorimetry). Results are expressed in terms of median and range. In Alzheimer's disease, plasma cortisol was higher than in controls (median 0.74, range 0.47-1.21 vs 0.47, 0.36-0.77 mmol/L; p < 0.001). Plasma DHEAS, the DHEAS/cortisol ratio, and the number of type II corticosteroid receptors were significantly lower in AD than in controls (DHEAS: median 1.81, range 0.21-3.69 vs 3.51, 1.35-9.07 micromol/L; DHEAS/ cortisol: 2.04, range 0.3-5.8 vs 6.8, range 2.7-24 and type II receptors: 1219, 1000-2700 vs 1950, 1035- 2750 receptors per cell; p < 0.001). No correlation was found between the hormonal parameters, age, and mini-mental test score. These data support the hypothesis of a dysregulation of the adrenal pituitary axis in Alzheimer's disease, which is probably the consequence of damage to target tissues by corticosteroids.

Regulation of aldosterone synthase gene expression in the rat adrenal gland and central nervous system by sodium and angiotensin II

We have developed a highly sensitive QRT-PCR method for the measurement of CYP11B1 (11beta-hydroxylase) and CYP11B2 (aldosterone synthase) mRNAs to study their expression in the rat brain in response to dietary sodium manipulation and angiotensin (Ang)II infusion. Male Wistar Kyoto rats (n = 6) were fed normal, high, or low sodium diets for 12 d or were administered AngII or vehicle for 7 d. CYP11B2 and CYP11B1 expression was measured in RNA from adrenal gland and discrete brain regions using real-time QRT-PCR. Sodium restriction increased adrenal CYP11B2 expression 57-fold from 1.0 x 10(5) +/- 0.6 x 10(5) to 57 x 10(5) +/- 22 x 10(5) copies/ microg RNA (mean +/- SEM; P < 0.05);in the hippocampus, 14-fold from 5.4 x 10(2) +/- 0.8 x 10(2) to 74 x 10(2) +/- 31 x 10(2) copies/ microg RNA (P < 0.05); and in the cerebellum, 5-fold from 1.9 x 10(3) +/- 0.7 x 10(3) to 9.9 x 10(3) +/- 3.0 x 10(3) copies/ microg RNA (P < 0.01). CYP11B2 gene expression in the brainstem and hypothalamus was not affected. High-sodium diet reduced adrenal CYP11B2 expression to 0.19 x 10(5) +/- 0.1 x 10(5) copies/ microg RNA (P < 0.05) but did not affect central nervous system (CNS) expression significantly. AngII significantly increased adrenal CYP11B2 expression but did not affect CNS expression. Brain CYP11B1 mRNA levels were 10- to 1000-fold higher than CYP11B2 but were unaffected by dietary sodium or AngII. To summarize, we have identified a local CYP11B2 response to sodium depletion in the hippocampus and cerebellum. This is the first such regulation of CYP11B2 transcription to be identified in the CNS.

Cortisol secretion in the elderly. Influence of age, sex and cardiovascular disease in a Chinese population

Adrenal function and aging have been the object of intense interest in recent years. In this study we analyzed morning (08:00 h) serum cortisol concentrations from a sample of Chinese subjects aged from 31 to 110 years. These levels differed according to age, health status and sex, although the sex difference was confirmed only among the healthy elderly. These results suggest that age (older than 60 years), disease and male sex are associated with increased morning serum cortisol levels in a Chinese population.