Studies of the enzyme complex responsible for pregnenolone and dehydroepiandrosterone 7 alpha-hydroxylation in mouse tissues

The Origin of 7α-Hydroxy-Dehydroepiandrosterone and Its Physiological Role: a History of Discoveries

Nearly 60 years has elapsed since the first isolation and identification of 7α-hydroxy-dehydroepiandrosterone, and in that time much information has been gained on its occurrence, metabolism, ontogeny, immunomodulatory activity, cell proliferation, cortisol control in local tissues and neuroactivity. Additional knowledge about this steroid may elucidate its role in obesity, neurodegenerative disturbances such as Alzheimer’s disease, or psychiatric disorders such as schizophrenia or depression. This review aims to provide a comprehensive summary of the available literature on 7α-hydroxy-dehydroepiandrosterone.

Synthesis of 3α-deuterated 7α-hydroxy-DHEA and 7-oxo-DHEA and application in LC-MS/MS plasma analysis

7-Oxygenated metabolites of dehydroepiandrosterone (DHEA) are known for their neuroprotective and immunomodulatory properties. These neuroactive steroids are currently predominately analysed by mass spectrometry, for which the use of internal deuterated standards is necessary. The aim of this study was to synthesize the deuterated derivatives of 7α-hydroxy-DHEA and 7-oxo-DHEA and test them in liquid chromatography-tandem mass spectrometry (LC-MS/MS) in order to enhance the performance characteristics of this method. Here we report the synthesis of 3α deuterium-labelled 7α-hydroxy-DHEA and 7-oxo-DHEA. Deuterium was introduced into the 3α position by reduction of the corresponding 3-ketone with a protected 17-carbonyl group using NaBD4. Our new procedure allows the easier synthesis of deuterated steroid labelled compounds. The use of these deuterated steroids enabled us to improve the human plasma LC-MS/MS analysis of 7α-hydroxy-DHEA and 7-oxo-DHEA in terms of sensitivity, precision and recovery.

7-oxygenated Derivatives of Dehydroepiandrosterone and Obesity

7-hydroxy/oxo derivatives of dehydroepiandrosterone are potential regulators of the local cortisol activity due to their competition in the cortisolcortisone balance mediated by 11β-hydroxysteroid dehydrogenase. 7-hydroxydehydroepiandrosterone is marketed as anti-obesity medication, though no clinical study aimed at the benefit of administering 7-oxygenated derivatives of dehydroepiandrosterone has appeared until now. We tried to show whether there exist differences in levels of circulating 7-hydroxy/oxo-dehydroepiandrosterone derivatives between lean and obese boys and girls. From a cohort of adolescents investigated within the frame of anti-obesity programme 10 obese boys and 10 obese girls were compared with age-matched lean boys and girls in their anthropometric data, and concentrations of both epimers of 7-hydroxydehydroepiandrosterone and 7-oxo-dehydroepiandrosterone were determined by the RIA method. The basal levels of 7α-hydroxy-dehydroepiandrosterone were significantly higher in obese boys than in lean boys but not in girls. The association was found for anthropometric parameters and 7α-hydroxy-dehydroepiandrosterone, however again only in boys and not in girls. Higher levels of 7α-hydroxydehydroepiandrosterone its positive association with anthropometric data in obese boys may serve as a sign that, at least in boys, 7-oxygenated 5-ene-steroids may take part in regulating the hormonal signal for fat formation or distribution.

Steroid hormones in prediction of normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) is a treatable neurological disorder affecting elderly people with the prevalence increasing with age. NPH is caused by abnormal cerebrospinal fluid (CSF) reabsorption and manifested as a balance impairment, urinary incontinence and dementia development. These symptoms are potentially reversible if recognized early. Diagnosis of NPH is difficult and can be easily mistaken for other neurodegenerative disorders, which makes NPH one of the major misdiagnosed diseases worldwide. The aim of the study was to find out the appropriate combination of indicators, based on CSF steroids, which would contribute to a clearer NPH diagnosis. The levels of CSF cortisol, cortisone, dehydroepiandrosterone (DHEA), 7α-OH-DHEA, 7β-OH-DHEA, 7-oxo-DHEA, 16α-OH-DHEA and aldosterone (all LC-MS/MS) were determined in our patients (n=30; NPH, 65-80 years) and controls (n=10; 65-80 years). The model of orthogonal projections to latent structures (OPLS) was constructed to predict NPH. Cortisone, 7α-OH-DHEA, 7β-OH-DHEA, 7-oxo-DHEA, aldosterone, 7α-OH-DHEA /DHEA, 7-oxo-DHEA/7α-OH-DHEA, 7β-OH-DHEA/7-oxo-DHEA and 16α-OH-DHEA/DHEA in the CSF were identified as the key predictors and the model discriminated patients from controls with 100% sensitivity and 100% specificity. The suggested model would contribute to early and accurate NPH diagnosis, enabling promptly treatment of the disease.

Determination of seven selected neuro- and immunomodulatory steroids in human cerebrospinal fluid and plasma using LC-MS/MS

Dehydroepiandrosterone (DHEA) and its 7-oxo- and 7-hydroxy-metabolites occurring in the brain are considered neurosteroids. Metabolism of the latter is catalysed by 11β-hydroxysteroid dehydrogenase (11β-HSD) which also interconverts cortisol and cortisone. The concurrent metabolic reaction to DHEA 7-hydroxylation is the formation of 16α-hydroxy-DHEA. The LC-MS/MS method using triple stage quadrupole-mass spectrometer was developed for simultaneous quantification of free DHEA, 7α-hydroxy-DHEA, 7β-hydroxy-DHEA, 7-oxo-DHEA, 16α-hydroxy-DHEA, cortisol and cortisone in human plasma and cerebrospinal fluid (CSF). The method employs 500 μL of human plasma and 3000 μL of CSF extracted with diethyl ether and derivatized with 2-hydrazinopyridine. It has been validated in terms of sensitivity, precision and recovery. In plasma, the following values were obtained: limit of detection: 2-50p g/mL; limit of quantification: 5-140 pg/mL; within-day precision 0.58-14.58%; between-day precision: 1.24-13.89% and recovery: 85-113.2%). For CSF, the values of limit of detection: 2-28 pg/mL; limit of quantification: 6-94 pg/mL; within-day precision; 0.63-5.48%; between-day precision: 0.88-14.59% and recovery: 85.1-109.4% were acquired. Medians and concentration ranges of detected steroids in plasma and CSF are given in subjects with excluded normal pressure hydrocephalus (n=37; 65-80 years). The method enables simultaneous quantification of steroids important for the estimation of 11β-HSD activity in human plasma and CSF. It will be helpful in better understanding various degenerative diseases development and progression.

Dehydroepiandrosterone: a neuroactive steroid

Dehydroepiandrosterone (DHEA) and its sulfate bound form (DHEAS) are important steroids of mainly adrenal origin. They are produced also in gonads and in the brain. Dehydroepiandrosterone easily crosses the brain-blood barrier and in part is also produced locally in the brain tissue. In the brain, DHEA exerts its effects after conversion to either testosterone and dihydrotestosterone or estradiol via androgen and estrogen receptors present in the most parts of the human brain, through mainly non-genomic mechanisms, or eventually indirectly via the effects of its metabolites formed locally in the brain. As a neuroactive hormone, DHEA in co-operation with other hormones and transmitters significantly affects some aspects of human mood, and modifies some features of human emotions and behavior. It has been reported that its administration can increase feelings of well-being and is useful in ameliorating atypical depressive disorders. It has neuroprotective and antiglucocorticoid activity and modifies immune reactions, and some authors have also reported its role in degenerative brain diseases. Here we present a short overview of the possible actions of dehydroepiandrosterone and its sulfate in the brain, calling attention to various mechanisms of their action as neurosteroids and to prospects for the knowledge of their role in brain disorders.

7α-hydroxylation of dehydroepiandrosterone does not interfere with the activation of glucocorticoids by 11β-hydroxysteroid dehydrogenase in E(t)C cerebellar neurons

The neuroprotective action of dehydroepiandrosterone (DHEA) in the absence of a known specific receptor has been attributed to its metabolism by different cell types in the brain to various steroids, with a preference to its 7-hydroxylated products. The E(t)C cerebellar granule cell line converts DHEA almost exclusively to 7α-hydroxy-DHEA (7α-OH-DHEA). It has been postulated that DHEA's 7-OH and 7-oxo metabolites can decrease glucocorticoid levels by an interactive mechanism involving 11β-hydroxysteroid dehydrogenase (11β-HSD). In order to study the relationship of 7-hydroxylation of DHEA and glucocorticoid metabolism in intact brain cells, we examined whether E(t)C cerebellar neurons, which are avid producers of 7α-OH-DHEA, could also metabolize glucocorticoids. We report that E(t)C neuronal cells exhibit 11β-HSD1 reductase activity, and are able to convert 11-dehydrocorticosterone into corticosterone, whereas they do not demonstrate 11β-HSD2 dehydrogenase activity. Consequently, E(t)C cells incubated with DHEA did not yield 7-oxo- or 7β-OH-DHEA. Our findings are supported by the reductive environment of E(t)C cells through expression of hexose-6-phosphate dehydrogenase (H6PDH), which fosters 11β-HSD1 reductase activity. To further explore the role of 7α-OH-DHEA in E(t)C neuronal cells, we examined the effect of preventing its formation using the CYP450 inhibitor ketoconazole. Treatment of the cells with this drug decreased the yield of 7α-OH-DHEA by about 75% without the formation of alternate DHEA metabolites, and had minimal effects on glucocorticoid conversion. Likewise, elevated levels of corticosterone, the product of 11β-HSD1, had no effect on the metabolic profile of DHEA. This study shows that in a single population of whole-cells, with a highly reductive environment, 7α-OH-DHEA is unable to block the reducing activity of 11β-HSD1, and that 7-hydroxylation of DHEA does not interfere with the activation of glucocorticoids. Our investigation on the metabolism of DHEA in E(t)C neuronal cells suggest that other alternate mechanisms must be at play to explain the in vivo anti-glucocorticoid properties of DHEA and its 7-OH-metabolites.

Neuroactive steroids in periphery and cerebrospinal fluid

Some peripheral steroids penetrate the blood-brain barrier (BBB), providing at least substances for the CNS steroid metabolome. That is why the predictive value of the peripheral steroids appears to be comparable with that of the cerebrospinal fluid (CSF) steroids. The concentrations of the CSF steroids are pronouncedly lower in comparison with the ones in circulation. The available data indicate that the levels of pregnenolone sulfate substantially increase in the rat brain tissue after the administration of pregnenolone into the circulation. In the human circulation there are about two orders of magnitude higher levels of pregnenolone sulfate compared to the free pregnenolone. Our data show insignificant correlation between CSF and serum pregnenolone, but a borderline one between CSF pregnenolone and serum pregnenolone sulfate. Therefore in humans, the circulating pregnenolone sulfate might be of an importance for pregnenolone concentration in the CNS. In contrast to free pregnenolone, dehydroepiandrosterone (DHEA) in the CSF correlates with both unconjugated and conjugated DHEA in the serum. These data as well as the low C17-hydroxylase-C17,20-lyase activity in the CNS might indicate that DHEA levels in the CNS are influenced by peripheral levels of DHEA and its sulfate. According to the information, available part of the neurosteroids may be synthesized de novo in the CNS, but substantial part of the steroid metabolites may be also synthesized in the CNS from the steroid precursors or directly transported through BBB from the periphery. The processes mentioned above may be complimentary in some cases. Brain synthesis may provide minimal level of neurosteroids, which are indispensable for the CNS functions. Thus, brain steroids of peripheral origin may reflect various physiological situations or even pathologies. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

The 7-hydroxylation of dehydroepiandrosterone in rat brain

Dehydroepiandrosterone (DHEA) is an important neurosteroid with multiple functions in the central nervous system including neuroprotection. How DHEA exerts its neuroprotection function has not been fully elucidated. One possible mechanism is via its active metabolites, 7alpha-OH DHEA and 7beta-OH DHEA. The purpose of this research is to understand how DHEA is metabolized to 7alpha-OH DHEA and 7beta-OH DHEA by brain tissue. DHEA was incubated with rat brain microsomes and mitochondria and the 7alpha-OH DHEA and 7beta-OH DHEA formed by these fractions were analyzed by LC/MS. For the first time, we observed that DHEA could be metabolized to 7alpha-OH DHEA and 7beta-OH DHEA in mitochondria but the formation of 7alpha-OH DHEA and 7beta-OH DHEA demonstrated different enzymatic kinetic properties. Adding NADPH, an essential cofactor, to mitochondria incubation mixtures increased only the formation of 7alpha-OH DHEA, but not that of 7beta-OH DHEA. Addition of estradiol to the incubation mixtures inhibited only the formation of 7alpha-OH DHEA, but not that of 7beta-OH DHEA. Western blot analysis showed that both microsomes and mitochondria contained cytochrome P450 7B. We also found that 7alpha-OH DHEA could be converted to 7beta-OH DHEA by rat brain homogenates. Our data suggest that 7alpha-OH DHEA and 7beta-OH DHEA are formed by different enzymes and that 7beta-OH DHEA can be formed from both DHEA and 7alpha-OH DHEA, although the overall level of 7beta-OH DHEA was very low.

Anti-inflammatory effects and changes in prostaglandin patterns induced by 7beta-hydroxy-epiandrosterone in rats with colitis

High dose levels of dehydroepiandrosterone and its 7-hydroxylated derivatives have been shown to reduce oxidative stress and inflammatory responses in dextran sodium sulfate (DSS)-induced colitis in rats. Another endogenous steroid, 7beta-hydroxy-epiandrosterone (7beta-hydroxy-EpiA) has been shown to exert neuroprotective effects at much smaller doses. Our aims were to evaluate whether 7beta-hydroxy-EpiA pre-treatment prevents DSS-induced colitis and to determine whether the effects involve changes in anti-inflammatory prostaglandin (PG) D(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) levels. Rats were administered 0.01, 0.1 and 1mg/kg 7beta-hydroxy-EpiA i.p. once a day for 7 days. Thereafter, colitis was induced by administration of 5% DSS in drinking water for 7 days. Levels of the PGs and the expression of cyclooxygenase (COX-2) and PG synthases were assessed during the course of the experiment. Administration of 7beta-hydroxy-EpiA caused a transient increase in COX-2 and PGE synthase expression within 6-15h and augmented colonic tissue levels of 15d-PGJ(2) levels starting at day 2. Treatment with DSS resulted in shortened colon length, depleted mucus in goblet cells and induced oxidative stress. COX-2 and mPGES-1 synthase expression were enhanced and accompanied by increased PGE(2), D(2) and 15d-PGJ(2) production. Although all dose levels of 7beta-hydroxy-EpiA reduced PGE(2) production, only the lowest dose (0.01mg/kg) of the steroid completely prevented colitis damage and tissue inflammation. 7beta-Hydroxy-EpiA pre-treatment prevents the occurrence of DSS-induced colitis through a shift from PGE(2) to PGD(2) production, associated with an early but transient increase in COX-2 expression and a sustained increase in the production of the anti-inflammatory prostaglandin 15d-PGJ(2).

Dehydroepiandrosterone metabolites and their interactions in humans

Dehydroepiandrosterone (DHEA) is 7alpha-hydroxylated by the cytochrome P4507B1 in the liver, skin and brain, which are targets for glucocorticoids. 7alpha-Hydroxy-DHEA produced anti-glucocorticoid effects in vivo but the interference between the glucocorticoid hormone binding with its receptor could not be determined. In the organs mentioned above, circulating inactive cortisone is reduced to active cortisol by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). 7alpha-Hydroxy-DHEA is also a substrate for this enzyme. Studies of 11beta-HSD1 action on 7alpha-hydroxy-DHEA show the reversible production of 7beta-hydroxy-DHEA through an intermediary 7-oxo-DHEA. Both the production of 7alpha-hydroxysteroids and their interference with the activation of cortisone into cortisol are basic to the concept of native anti-glucocorticoids. The cytochrome P4507B1 responsible for 7alpha-hydroxy-DHEA production and 11beta-HSD1 are key enzymes for the modulation of glucocorticoid action in humans. This is a promising new area for research.

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.

The native anti-glucocorticoid paradigm

Circulating 3beta-hydroxysteroids including dehydroepiandrosterone (DHEA) are 7alpha-hydroxylated by the cytochrome P450-7B1 in the liver, skin and brain, which are the target organs of glucocorticoids. Anti-glucocorticoid effects with 7alpha-hydroxy-DHEA were observed in vivo without an interference with glucocorticoid binding to its receptor. In the organs mentioned above, the circulating inactive cortisone was reduced into active cortisol by the 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). We demonstrated that 7alpha-hydroxy-DHEA was also a substrate for this enzyme. Studies of the 11beta-HSD1 action on 7alpha-hydroxy-DHEA showed the reversible production of 7beta-hydroxy-DHEA through an intermediary 7-oxo-DHEA, and the kinetic parameters favored this production over that of active glucocorticoids. Both the production of 7alpha-hydroxysteroids and their interference with the activation of cortisone into cortisol are basic to the concept of native anti-glucocorticoids efficient at their production site. This opens a promising new area for research.

DHEA Metabolism in Arthritis: A Role for the p450 Enzyme Cyp7b at the Immune-Endocrine Crossroad

For dehydroepiandrosterone (DHEA) both immunosuppressive and immuno-stimulating properties have been described. The immunosuppressive effects may be explained by the conversion of DHEA into androgens and/or estrogens. The described immuno-stimulating effects of DHEA may be due to the conversion of DHEA into 7alpha-hydroxy-DHEA (7alpha-OH-DHEA) by the activity of the p450 enzyme, Cyp7b. 7alpha-OH-DHEA is thought to have anti-glucocoticoid activity preventing the anti-inflammatory action of endogenous glucocorticoids. To investigate a putative role of Cyp7b in the arthritic process, tissues from both the murine collagen-induce arthritis (CIA) model and from patients with rheumatoid arthritis (RA) were studied. We determined the Cyp7b expression levels in synovial tissue and the level of 7alpha-OH-DHEA in both serum and arthritic joints of mice with CIA. Our studies showed that the severity of arthritis correlates with increased Cyp7b activity. Next, we investigated Cyp7b expression and activity in RA patients where the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) are known to control the disease process. Fibroblast-like synoviocytes (FLS), isolated from RA synovial biopsies were found to express Cyp7b mRNA. In addition, Cyp7b enzymatic activity was detected in these cells. We also investigated whether Cyp7b activity is regulated by cytokines. Proinflammatory (e.g., TNF-alpha and IL-1beta) cytokines were found to stimulate Cyp7b activity and the anti-inflammatory cytokine transforming growth factor-beta (TGF-beta) was found to suppress Cyp7b activity in FLS. Next, we studied which signal transduction pathway is involved in the TNF-alpha-mediated induction of Cyp7b activity in human FLS. The results show a role for nuclear factor kappa B (NFkappaB) and activator protein-1 (AP-1) in the regulation of Cyp7b expression. Finally, we established that the effects of DHEA or 7alpha-OH-DHEA on the immune system can not be explained by glucocorticoid receptor (GR) engagement. The role of the p450 enzyme Cyp7b in DHEA metabolism and its relevance in the arthritic process will be discussed.

Protection against dextran sodium sulfate-induced colitis by dehydroepiandrosterone and 7alpha-hydroxy-dehydroepiandrosterone in the rat

In this study the anti-oxidant effect of DHEA and 7alpha-hydroxy-DHEA against oxidative stress induced by colitis was investigated in vivo in rats. The two steroids were intraperitoneally injected once daily (50 mg/kg body weight) for 7 days before the induction of colitis that was effected by a daily treatment of 5% (w/v) dextran sodium sulfate (DSS) in drinking water for 7 days. This was quantified by the evidence of weight loss, rectal bleeding, increased wall thickness, and colon length. The inflammatory response was assessed by neutrophil infiltration after a histological examination and myeloperoxidase (MPO) activity measurement. Two markers of oxidative damage were measured in colon homogenates after the onset of DSS treatment: protein carbonyls and thiobarbituric acid-reacting substances. The colonic metabolism of corticosterone by 11beta-hydroxysteroid dehydrogenases types 1 and 2 (11beta-HSD) was investigated in control and treated animals. Results indicated that colitis caused a decrease in body weight and colon length. Severe lesions were observed in the colon with a reduced number of goblet cells which contained less mucins. The lesions were associated with increased MPO activity and oxidative damage. Colonic inflammation down and up regulated the 11beta-HSD2 and 11beta-HSD1, respectively. Treatments by DHEA and 7alpha-hydroxy-DHEA attenuated the inflammatory response when MPO activity decreased; but this did not increase the colonic oxidation of corticosterone into 11-dehydrocorticosterone. Both DHEA and 7alpha-hydroxy-DHEA exerted a significant anti-oxidant effect against oxidative stress induced by colitis through reducing the oxidative damage to proteins and lipids. This resulted in a moderate increase in the amount of colonic mucus. Both DHEA and 7alpha-hydroxy-DHEA may prove useful in the prevention or treatment of colitis.

Synthesis of 7alpha-hydroxy-dehydroepiandrosterone and 7beta-hydroxy-dehydroepiandrosterone

The fermentation of dehydroepiandrosterone synthesized from the starting material diosgenin using Mucor racemosus produced 7alpha-hydroxy-dehydroepiandrosterone and 7beta-hydroxy-dehydroepiandrosterone. The bioactivity of the microbial metabolites is also discussed. The species M. racemosus was isolated by screening among stains from soil samples collected from various parts of China.

Neurosteroids: metabolism in human intestine microsomes

Both dehydroepiandrosterone (DHEA) and epiandrosterone (EpiA) are substrate for cytochrome P450 species and enzymes that produce 7alpha- and 7beta-hydroxylated metabolites in the brain and other organs. In contrast to DHEA and EpiA, the 7-hydroxylated derivatives were shown to mediate neuroprotection, and 7beta-hydroxy-EpiA was the most potent. The suggested use of any of these steroids as drugs administered per os for neuroprotection requires the assessment of their metabolism in the human intestine and liver. To achieve this, we produced radio-labeled 7alpha-hydroxy-DHEA, 7beta-hydroxy-DHEA, 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA that were used as substrates in incubations with human intestine microsomes supplemented with reduced or oxidized cofactors. Identity of the radio-labeled metabolites obtained was determined by gas chromatography/mass spectrometry after comparison with authentic steroid references. The proportions of metabolites produced resulted from their radioactivity contents. The only metabolite obtained with DHEA, EpiA, 7alpha-hydroxy-DHEA and 7beta-hydroxy-DHEA substrates was its 17beta-reduced derivative, thus inferring the presence of 17beta-hydroxysteroid oxidoreductases in the human intestine microsomes. In addition to the 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA substrates, their 17beta-reduced metabolites were obtained with 7beta-hydroxy-EpiA and 7alpha-hydroxy-EpiA, respectively. The identity of the enzyme responsible for the 7alpha-hydroxy-EpiA/7beta-hydroxy-EpiA inter-conversion is unknown. The incubation conditions used produced these metabolites in low but significant yields that suggest their presence in the portal blood before access to the liver.

HUMAN LIVER S9 FRACTIONS: METABOLISM OF DEHYDROEPIANDROSTERONE, EPIANDROSTERONE, AND RELATED 7-HYDROXYLATED DERIVATIVES

Dehydroepiandrosterone (DHEA) and 3beta-hydroxy-5alpha-androstan-17-one (epiandrosterone, EpiA) are both precursors for 7alpha- and 7beta-hydroxylated metabolites in the human brain. These 7-hydroxylated derivatives were shown to exert anti-glucocorticoid and neuroprotective effects. When these steroids are administered per os to humans, the first organ encountered is the liver, where extensive metabolism takes place. The objective of this work was to assess the cofactor dependence and metabolism of DHEA, EpiA, and their 7-hydroxylated derivatives in S9 fractions of human liver, using a radiolabeled steroid substrate for quantification and gas chromatography-mass spectrometry for identification. The best transformation yields were obtained with NADPH and were larger in female than in male. Results showed that both DHEA and EpiA mainly transformed into their 17beta-hydroxylated derivatives, 7- or 16alpha-hydroxylated metabolites under NAD(P)H conditions, and 5alpha-androstane-3,17-dione for EpiA under NAD(P)+ conditions. In turn, 7alpha-hydroxy-DHEA and 7beta-hydroxy-DHEA were partly transformed into each other via a 7-oxo-DHEA intermediate and were reduced into the 17beta-hydroxy derivative, respectively. The same type of transformations occurred for 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA, except that no 7-oxo-EpiA intermediate was obtained. These findings determine the presence of enzymes responsible for the 7alpha- and 16alpha-hydroxylation in the human liver, the 11beta-hydroxysteroid dehydrogenase type 1 responsible for the oxidoreduction of the 7-hydroxylated substrates, and the 17beta-hydroxysteroid dehydrogenase responsible for the reduction of 17-oxo-steroids into 17beta-hydroxysteroids.

Immunohistochemical detection of the human cytochrome P4507B1: production of a monoclonal antibody after cDNA immunization

The cytochrome P4507B1 (P4507B1) is responsible for the 7alpha-hydroxylation of dehydroepiandrosterone (DHEA) and other 3beta-hydroxysteroids in the brain and other organs. The cDNA of human P4507B1 was used for DNA immunization of mice. The best responding mouse led to the production of monoclonal antibodies (mAbs). The clone D16-37 produced an IgM specific for P4507B1 with no cross-reaction with other human P450s. This antibody permitted the immunohistochemical detection of P4507B1 in slices of human hippocampus. P4507B1 was expressed in neurons only. This new tool will be used for the extensive examination of the P4507B1 presence and determination of its levels in slices of human normal and diseased brain and in other human tissues.

Dehydroepiandrosterone and its 7-hydroxylated metabolites do not interfere with the transactivation and cellular trafficking of the glucocorticoid receptor

The human brain is a target tissue for glucocorticoids (GC). Dehydroepiandrosterone (DHEA) is a neurosteroid produced in the brain where it is transformed into 7alpha-hydroxy-DHEA and 7beta-hydroxy-DHEA. The antiglucocorticoid effects of both 7-hydroxylated metabolites have been investigated with evidence in mice that neither form of DHEA interfered with the binding of GC to its glucocorticoid receptor (GR), but contributed to a decreased nuclear uptake of the activated GR. Our objective was to use COS-7 cell culture to research DHEA, 7alpha-hydroxy-DHEA and 7beta-hydroxy-DHEA interferences with GR trafficking. These cells did not carry out the 7alpha-hydroxylation of DHEA and the oxidation of cortisol into cortisone. The cDNA of the human GR was inserted into pcDNA3 for a transient transfection of COS-7 cells. Human GR transactivation activity was measured from a luciferase-MMTV reporter gene. The transfected COS-7 cells were cultured using 10(-12) to 10(-5) M dexamethasone (DEX) or cortisol, which triggered the reporter expression. Treatment with 10(-12) to 10(-5) M DHEA, 7alpha-hydroxy-DHEA and 7beta-hydroxy-DHEA caused no change in the GC-induced GR transactivation. A reconstruction of the process associated EGFP to the human GR cDNA. Confocal microscopic examination of COS-7 cells transiently expressing the fusion protein EGFP-GR showed nuclear fluorescence 60 min after incubation with 10(-8) M DEX or cortisol. The addition of 10(-5) M DHEA, 7alpha-hydroxy-DHEA or 7beta-hydroxy-DHEA did not change its kinesis and intensity. These results contribute to the knowledge of DHEA, 7alpha-hydroxy-DHEA and 7beta-hydroxy-DHEA, in relation to antiglucocorticoid activity. We conclude that direct interference with GR trafficking can be discounted in the case of these hormones, therefore proposing new possibilities of investigation.

The human cytochrome P4507B1: catalytic activity studies

The cytochrome P4507B1 (P4507B1) in the human hippocampus is responsible for the production of 7alpha-hydroxylated derivatives of dehydroepiandrosterone (DHEA) and other 3beta-hydroxylated neurosteroids. Minor quantities of the 7beta-hydroxylated derivatives are also produced. Neuroprotective action of these 7-hydroxysteroids was reported. Recombinant human P4507B1 was prepared from yeast coexpressing the human hippocampal P450 cDNA and the human P450 reductase genes. Microsomal P4507B1 activity was tested in the presence of NADPH and (14)C-labeled steroid substrates to deduce kinetic parameters and to study inhibitor responses. The K(M) values obtained for DHEA, pregnenolone, epiandrosterone, 5alpha-androstane-3beta,17beta-diol and estrone were 1.90 +/- 0.06, 1.45 +/- 0.03, 1.05 +/- 0.12, 0.8 +/- 0.04 and 1.20 +/- 0.26 microM, respectively. Production of limited amounts of 7beta-hydroxylated derivatives was also observed, but only with DHEA, 5alpha-androstane-3beta,17beta-diol and epiandrosterone. K(M) values determined for 7beta-hydroxylation were identical to those for 7alpha-hydroxylation. The DHEA 7alpha-hydroxylation was inhibited by estrone and estradiol (mixed type inhibition) and by the [25-35] beta-amyloid peptide (non-competitive inhibition). These results indicate that in human, the 7-hydroxylation catalysed by P4507B1 preferentially takes place on DHEA, 5alpha-androstane-3beta,17beta-diol and epiandrosterone with major and minor formation of 7alpha- and 7beta-hydroxylated derivatives, respectively. Both estrogens and a beta-amyloid component inhibit the P4507B1-mediated production of the 7-hydroxysteroid metabolites.

Simultaneous determination of dehydroepiandrosterone and its 7-oxygenated metabolites in human serum by high-resolution gas chromatography--mass spectrometry

A highly sensitive and specific method has been developed for the simultaneous measurement of free (unconjugated) or sulfate-conjugated forms of dehydroepiandrosterone (DHEA), 7alpha-hydroxy-DHEA (7alpha-OH-DHEA), 7beta-hydroxy-DHEA (7beta-OH-DHEA), and 7-oxo-DHEA (7-oxo-DHEA) in human serum. This method is based upon a stable isotope-dilution technique by gas chromatography-selected-ion monitoring mass spectrometry. Free steroids were extracted from serum with an organic solvent and the sulfate-conjugated steroids remained in aqueous phase. Free steroids were purified by solid-phase extraction, while sulfate-conjugated steroids were hydrolyzed by sulfatase and deconjugated steroids were purified by solid-phase extractions. The extracts were treated with O-methylhydroxylamine hydrochloride and were subsequently dimethylisopropylsilylated. The resulting methyloxime-dimethylisopropylsilyl (MO-DMIPS) ether derivatives were quantified by gas chromatography-selected-ion monitoring mass spectrometry in a high-resolution mode. The detection limits of MO-DMIPS ether derivatives of DHEA, 7alpha-OH-DHEA, 7beta-OH-DHEA and 7-oxo-DHEA were 1.0, 0.5, 0.5 and 2.0pg, respectively. Coefficients of variation between samples ranged from 10.6 to 22.9% for free 7-oxygenated DHEA to less than 10% for DHEA and sulfate-conjugated 7-oxygenated DHEA. The concentrations of these steroids were measured in 18 sera samples from healthy volunteers (9 males and 9 females; aged 23-78 years). Free DHEA, 7alpha-OH-DHEA, 7beta-OH-DHEA and 7-oxo-DHEA levels ranged between 0.21-3.55, 0.001-0.194, 0.003-0.481, and 0.000-0.077ng/ml, respectively, and the sulfate-conjugated steroid levels of these metabolites ranged between 253-4681, 0.082-3.001, 0.008-0.903, and 0.107-0.803ng/ml, respectively. The free DHEA-related steroid concentrations were much lower than those previously measured by RIA and low-resolution GC-MS. The present method made it possible to determine simultaneously serum DHEA-related steroid levels with sufficient sensitivity and accuracy.

The allylic 7-ketone at the steroidal skeleton is crucial for the antileukemic potency of chlorambucil’s active metabolite steroidal esters

We have investigated the role of the allylic 7-ketone in oxidized Delta5-steroids on antileukemic activity. We synthesized and studied a series of oxidized and non-oxidized steroidal esters of p-N,N-bis(2-chloroethyl)aminophenylacetic acid (PHE), chlorambucil's active metabolite. In a comparative study of these 7-keto derivatives, on a molecular basis, regarding their ability to induce sister chromatid exchanges (SCEs) and to inhibit cell proliferation in normal human lymphocytes in vitro, the results with these 7-keto derivatives, on a molecular basis, correlated well with their antileukemic potency against leukemia P388- and L1210-bearing mice, which proved to be significantly increased compared to that of the non-oxidized derivatives. Our results indicate that the role of the steroidal skeleton it is not only for the transportation of the alkylating agent into the cell, but also contributes directly to the mechanism of antileukemic action, by an as-yet unknown way. The main conclusion from this study is that the existence of the allylic 7-keto group in the skeleton of the Delta5-steroidal esters impressively enhances their antileukemic activity, while the toxicity remains at clinically acceptable levels, suggesting that this structural modification should be further investigated.

Antioxidant effects of dehydroepiandrosterone and 7alpha-hydroxy-dehydroepiandrosterone in the rat colon, intestine and liver

This study examined in healthy male Wistar rats the in vivo antioxidant effect of dehydroepiandrosterone (DHEA) and 7alpha-hydroxy-DHEA administered by intraperitoneal injections (50 mg/kg body weight) for 2 or 7 days. Markers of oxidative damage to lipids (thiobarbituric acid-reacting substances, TBARS) and to proteins (protein carbonyls) were assessed in colon, small intestine, and liver homogenates. DHEA and 7alpha-hydroxy-DHEA caused a decrease in body weight. DHEA treatment significantly increased liver, colon, and small intestine cell weights. After 7 days, DHEA exerted an antioxidant effect in all organs studied. In the colon, oxidative damage protection was accompanied by a goblet cell proliferation and increase in acidic mucus production. After 2 days, the antioxidant effect of 7alpha-hydroxy-DHEA was mainly observed in the liver. Nonprotein sulfhydryl groups (mostly glutathione levels) were altered by DHEA in the liver whereas they remained unchanged after 7alpha-hydroxy-DHEA treatment. The results indicate that in healthy animals, DHEA exerts a protective effect, particularly in the colon, by reducing the tissue susceptibility to oxidation of both lipids and proteins. This effect was not limited to a specific tissue, whereas the metabolite 7alpha-hydroxy-DHEA exerted its antioxidant effect towards the two markers of oxidative damage earlier than DHEA, and mainly in the liver.

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 Alzheimer's 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.

In vitro metabolism of dehydroepiandrosterone (DHEA) to 7alpha-hydroxy-DHEA and Delta5-androstene-3beta,17beta-diol in specific regions of the aging brain from Alzheimer's and non-demented patients

The description of dehydroepiandrosterone (DHEA) as a neuroactive neurosteroid has raised the important question of whether the steroid itself and/or its metabolite(s) are active in the brain. Classical transformations of DHEA in brain and peripheral tissues include its conversion to testosterone and estradiol. In the human brain, the metabolism of DHEA to other metabolites is still poorly understood, particularly in aging people and Alzheimer's patients. The present study describes the in vitro transformation of DHEA into 7alpha-hydroxy-DHEA and Delta5-androstene-3beta,17beta-diol, for the first time in the aging brain of patients with Alzheimer's disease in comparison with non-demented controls. Formal identification of DHEA metabolites is provided by gas chromatography-mass spectrometry, thus indicating the presence of NADPH-dependent 7alpha-hydroxylase and 17beta-hydroxysteroid oxidoreductase activities. Under our experimental conditions, the synthesis of 7alpha-hydroxy-DHEA and Delta5-androstene-3beta,17beta-diol occurs in the frontal cortex, hippocampus, amygdala, cerebellum and striatum of both Alzheimer's patients and non-demented controls. In both groups of patients, the pattern of DHEA metabolism is similar, but significant higher synthesis of 7alpha-hydroxy-DHEA in the frontal cortex and Delta5-androstene-3beta,17beta-diol in the cerebellum and striatum were observed compared with those in other brain regions. In addition, a trend toward a significant negative correlation is found between the density of cortical amyloid deposits and the amount of 7alpha-hydroxy-DHEA formed in the frontal cortex and that of Delta5-androstene-3beta,17beta-diol in the hippocampus. Therefore, the biosynthesis of 7alpha-hydroxy-DHEA and/or Delta5-androstene-3beta,17beta-diol is likely to regulate DHEA cerebral concentrations and may contribute to the control of DHEA activity in the aging brain including in Alzheimer's disease.

Use of bioconversion for the preparation of [4-14C]-labeled 7 alpha- and 7 beta-hydroxylated derivatives of dehydroepiandrosterone and epiandrosterone

The 7 alpha- and 7 beta-hydroxylated derivatives of [4-14C]-dehydroepiandrosterone were prepared with use of the yeast-expressed human cytochrome p4507B1. Epiandrosterone (EPIA), 5 alpha-androstane-3beta,17 beta-diol, and 5 alpha-androstane-3,17-dione were obtained after incubation of [4-14C]-5 alpha-dihydrotestosterone with Escherichia coli-expressed (3beta,17 beta)-hydroxysteroid dehydrogenase from Pseudomonas testosteroni. The 7 alpha- and 7 beta-hydroxylated derivatives of [4-14C]-EPIA produced were prepared after incubation with mycelium of Rhizopus nigricans. Each labeled steroid was purified by chromatography and identified by crystallization to constant specific activity after isotopic dilution with each authentic steroid carrier. Production yields and radio-purity measurements allowed the use of such procedures for the preparation of the described radio-steroids for studies of metabolism and mode of action.

Steroid and sterol 7-hydroxylation: ancient pathways

B-ring hydroxylation is a major metabolic pathway for cholesterols and some steroids. In liver, 7 alpha-hydroxylation of cholesterols, mediated by CYP7A and CYP39A1, is the rate-limiting step of bile acid synthesis and metabolic elimination. In brain and other tissues, both sterols and some steroids including dehydroepiandrosterone (DHEA) are prominently 7 alpha-hydroxylated by CYP7B. The function of extra-hepatic steroid and sterol 7-hydroxylation is unknown. Nevertheless, 7-oxygenated cholesterols are potent regulators of cell proliferation and apoptosis; 7-oxygenated derivatives of DHEA, pregnenolone, and androstenediol can have major effects in the brain and in the immune system. The receptor targets involved remain obscure. It is argued that B-ring modification predated steroid evolution: non-enzymatic oxidation of membrane sterols primarily results in 7-oxygenation. Such molecules may have provided early growth and stress signals; a relic may be found in hydroxylation at the symmetrical 11-position of glucocorticoids. Early receptor targets probably included intracellular sterol sites, some modern steroids may continue to act at these targets. 7-Hydroxylation of DHEA may reflect conservation of an early signaling pathway.

Dehydroepiandrosterone (DHEA) stimulates neurogenesis in the hippocampus of the rat, promotes survival of newly formed neurons and prevents corticosterone-induced suppression

Treating adult male rats with subcutaneous pellets of dehydroepiandrosterone (DHEA) increased the number of newly formed cells in the dentate gyrus of the hippocampus, and also antagonized the suppressive of corticosterone (40 mg/kg body weight daily for 5 days). Neither pregnenolone (40 mg/kg/day), a precursor of DHEA, nor androstenediol (40 mg/kg/day), a major metabolite, replicated the effect of DHEA (40 mg/kg/day). Corticosterone reduced the number of cells labelled with a marker for neurons (NeuN) following a 28-day survival period, and this was also prevented by DHEA. DHEA by itself increased the number of newly formed neurons, but only if treatment was continued throughout the period of survival. Subcutaneous DHEA pellets stimulated neurogenesis in a small number of older rats ( approximately 12 months old). These results show that DHEA, a steroid prominent in the blood and cerebral environment of humans, but which decreases markedly with age and during major depressive disorder, regulates neurogenesis in the hippocampus and modulates the inhibitory effect of increased corticoids on both the formation of new neurons and their survival.

Dehydroepiandrosterone (DHEA) metabolism in Saccharomyces cerevisiae expressing mammalian steroid hydroxylase CYP7B: Ayr1p and Fox2p display 17beta-hydroxysteroid dehydrogenase activity

We have engineered recombinant yeast to perform stereospecific hydroxylation of dehydroepiandrosterone (DHEA). This mammalian pro-hormone promotes brain and immune function; hydroxylation at the 7alpha position by P450 CYP7B is the major pathway of metabolic activation. We have sought to activate DHEA via yeast expression of rat CYP7B enzyme. Saccharomyces cerevisiae was found to metabolize DHEA by 3beta-acetylation; this was abolished by mutation at atf2. DHEA was also toxic, blocking tryptophan (trp) uptake: prototrophic strains were DHEA-resistant. In TRP(+) atf2 strains DHEA was then converted to androstene-3beta,17beta-diol (A/enediol) by an endogenous 17beta-hydroxysteroid dehydrogenase (17betaHSD). Seven yeast polypeptides similar to human 17betaHSDs were identified: when expressed in yeast, only AYR1 (1-acyl dihydroxyacetone phosphate reductase) increased A/enediol accumulation, while the hydroxyacyl-CoA dehydrogenase Fox2p, highly homologous to human 17betaHSD4, oxidized A/enediol to DHEA. The presence of endogenous yeast enzymes metabolizing steroids may relate to fungal pathogenesis. Disruption of AYR1 eliminated reductive 17betaHSD activity, and expression of CYP7B on the combination background (atf2, ayr1, TRP(+)) permitted efficient (>98%) bioconversion of DHEA to 7alpha-hydroxyDHEA, a product of potential medical utility.

Neurosteroid 7-hydroxylation products in the brain

The neurosteroids pregnenolone (PREG) and dehydroepiandrosterone (DHEA) are precursors for both oxidized and hydroxylated metabolites in the brain. Thus, brain production of 7-hydroxylated derivatives is second to that in the liver, and P4507B1-containing hippocampus is the major site for 7 alpha-hydroxylation. Other P450s and/or oxido-reductive mechanisms may be responsible for 7 beta-hydroxylation. In addition to regulating neurosteroid brain levels, when produced, the 7-hydroxylated derivatives of PREG and DHEA were investigated for antiglucocorticoid-mediated neuroprotective potencies, and both 7 alpha- and 7 beta-hydroxy-DHEA were efficient in preventing the nuclear uptake of [3H]dexamethasone-activated glucocorticoid receptor in brain cells. Activation of 7 alpha-hydroxylation by increased close contacts of astrocytes and after glucocorticoid treatment suggested that the regulated production of 7 alpha-hydroxysteroids was a key event for the neuroprotection conferred by neurosteroids.

Involvement of steroids and cytochromes P(450) species in the triggering of immune defenses

In vertebrates the wide variety of cytochromes P(450) (P(450)) is a key for elimination of low molecular weight xenobiotics and for the production and metabolism of steroid hormones. In contrast, xenobiotics of large molecular weight are processed and eliminated after the immune response. The suppression of immune response by native P(450)-produced glucocorticoid (GC) hormones constitutes a first link between P(450) and immunity. In the last decade, mechanisms and molecules responsible for the triggering of immune response were investigated and results showed that many tissues and organs transform native 3beta-hydroxysteroids into 7-hydroxylated metabolites that trigger immunity. Present data suggest that 7-hydroxysteroids are native anti-GCs that block the GC-induced immunosuppression. Because specific P(450) are responsible for the production of 7-hydroxylated steroids resulting into increased immunity, a second link exists between P(450) and immunity. Taken together, these findings support the proposal that P(450) are keys to all of the known defense mechanisms of vertebrates against all xenobiotic forms.

7-Hydroxydehydroepiandrosterone epimers in human serum and saliva. Comparison of gas chromatography-mass spectrometry and radioimmunoassay

Recent reports demonstrated that 7-hydroxylated metabolites of dehydroepiandrosterone (DHEA) possess immunomodulatory and antiglucocorticoid properties. Increased 7alpha-OH-DHEA levels were found in patients with Alzheimer's disease. Hence, measurement of steroids in patients with autoimmune diseases or disturbances in the central nervous system could be of interest. A new sensitive GC-MS method for the determination of 7-hydroxydehydroepiandrosterone epimers was developed and compared with previously developed radioimmunoassays. Besides serum, these steroids were, for the first time, measured in saliva where their concentrations were about five times lower. 7alpha- and 7beta-epimer levels correlated well in both body fluids and they were larger in male.

Ergosteroids IV: synthesis and biological activity of steroid glucuronosides, ethers, and alkylcarbonates

The 7-oxo derivative of dehydroepiandrosterone is more active than the parent steroid and is devoid of adverse side effects in rats, monkeys and humans. In anticipation of possible therapeutic use we have sought more active, longer lasting forms of 7-oxo- and 7beta-hydroxydehydroepiandrosterones. The 7-oxo- and 7-hydroxy steroids have been converted to glucuronides, ethers and carbonate esters. The syntheses of these compounds are described and their ability to induce the formation of liver thermogenic enzymes when fed to rats is reported. Some of the new derivatives were found to be somewhat more effective than the equimolar amounts of 7-oxo-DHEA with which they were compared in each experiment.

Neurosteroid hydroxylase CYP7B: vivid reporter activity in dentate gyrus of gene-targeted mice and abolition of a widespread pathway of steroid and oxysterol hydroxylation

The major adrenal steroid dehydroepiandrosterone (DHEA) enhances memory and immune function but has no known dedicated receptor; local metabolism may govern its activity. We described a cytochrome P450 expressed in brain and other tissues, CYP7B, that catalyzes the 7alpha-hydroxylation of oxysterols and 3beta-hydroxysteroids including DHEA. We report here that CYP7B mRNA and 7alpha-hydroxylation activity are widespread in rat tissues. However, steroids related to DHEA are reported to be modified at positions other than 7alpha, exemplified by prominent 6alpha-hydroxylation of 5alpha-androstane-3beta,17beta-diol (A/anediol) in some rodent tissues including brain. To determine whether CYP7B is responsible for these and other activities we disrupted the mouse Cyp7b gene by targeted insertion of an IRES-lacZ reporter cassette, placing reporter enzyme activity (beta-galactosidase) under Cyp7b promoter control. In heterozygous mouse brain, chromogenic detection of reporter activity was strikingly restricted to the dentate gyrus. Staining did not exactly reproduce the in situ hybridization expression pattern; post-transcriptional control is inferred. Lower level staining was detected in cerebellum, liver, and kidney, and which largely paralleled mRNA distribution. Liver and kidney expression was sexually dimorphic. Mice homozygous for the insertion are viable and superficially normal, but ex vivo metabolism of DHEA to 7alpha-hydroxy-DHEA was abolished in brain, spleen, thymus, heart, lung, prostate, uterus, and mammary gland; lower abundance metabolites were also eliminated. 7alpha-Hydroxylation of 25-hydroxycholesterol and related substrates was also abolished, as was presumed 6alpha-hydroxylation of A/anediol. These different enzyme activities therefore derive from the Cyp7b gene. CYP7B is thus a major extrahepatic steroid and oxysterol hydroxylase and provides the predominant route for local metabolism of DHEA and related molecules in brain and other tissues.

Metabolism of DHEA by cytochromes P450 in rat and human liver microsomal fractions

Administration of dehydroepiandrosterone (DHEA) to rodents produces many unique biological responses, some of which may be due to metabolism of DHEA to more biologically active products. In the current study, DHEA metabolism was studied using human and rat liver microsomal fractions. In both species, DHEA was extensively metabolized to multiple products; formation of these products was potently inhibited in both species by miconazole, demonstrating a principal role for cytochrome P450. In the rat, use of P450 form-selective inhibitors suggested the participation of P4501A and 3A forms in DHEA metabolism. Human liver samples displayed interindividual differences in that one of five subjects metabolized DHEA to a much greater extent than the others. This difference correlated with the level of P4503A activity present in the human liver samples. For one subject, troleandomycin inhibited hepatic microsomal metabolism of DHEA by 78%, compared to 81% inhibition by miconazole, suggesting the importance of P4503A in these reactions. Form-selective inhibitors of P4502D6 and P4502E1 had a modest inhibitory effect, suggesting that these forms may also contribute to metabolism of DHEA in humans. Metabolites identified by LC-MS in both species included 16alpha-hydroxy-DHEA, 7alpha-hydroxy-DHEA, and 7-oxo-DHEA. While 16alpha-hydroxy-DHEA appeared to be the major metabolite produced in rat, the major metabolite produced in humans was a mono-hydroxylated DHEA species, whose position of hydroxylation is unknown.

7 alpha-hydroxy-dehydroepiandrosterone and immune response

In human and murine lymphoid organs, circulating 3 beta-hydroxysteroids, including pregnenolone (PREG), dehydroepiandrosterone (DHEA), and epiandrosterone (EPIA), are 7 alpha-hydroxylated by a cytochrome P450 identified in the hippocampus as P4507B1. Mouse and human lymphoid organs produced different patterns of 3 beta-hydroxysteroid 7 alpha-hydroxylation with the absence of pregnenolone and epiandrosterone hydroxylation in human and mouse, respectively. Both 7 alpha-hydroxy-DHEA and 7 alpha-hydroxy-EPIA triggered a significant increase of antitetanus toxoid and anti-Bordetella pertussis toxins IgGs production in cultures of activated B + T cells derived from human tonsils, whereas both 7 alpha-hydroxy-PREG and 7 alpha-hydroxy-DHEA increased the immune response in mouse. Paracrine action of 7 alpha-hydroxysteroids resulted from their production in cells of the lymphoid organs. Comparison of P4507B1 sequences in rat, human, and two mouse species showed that one amino acid change might explain important differences in KM for 7 alpha-hydroxylation, and suggested that such differences might contribute to the extent of immune response.

Ontogeny of the neurosteroid enzyme Cyp7b in the mouse

The function of the major adrenal steroid dehydroepiandrosterone (DHEA) is not known. It has been reported to improve learning and memory in mice and can exert neuroprotective and trophic effects, particularly in the hippocampus. We recently described a cytochrome P450 (Cyp7b), that catalyses the 7alpha-hydroxylation of DHEA and related steroids and sterols. In this paper, we have used mRNA in situ hybridisation to map the ontogeny of cyp7b in the foetal and adult mouse. Cyp7b mRNA is highly expressed throughout from embryonal (E) day 12.5 (the earliest day studied). There is also expression throughout the body, including the spine, thymus, developing kidneys, lungs and urogenital region. Widespread expression becomes more restricted towards birth: in newborn mice expression is largely limited to the hippocampus, with some expression being detected in kidney. The overall decline in mRNA, and increasing restriction to the hippocampus, is reflected in the DHEA hydroxylation activity of brain homogenates. This pattern of cyp7b mRNA expression in specific organs could be consistent with a protective role in foetal development, with highest expression seen when the foetus is most vulnerable to steroid excess (i.e.) early gestation.

Dexamethasone-induced apoptosis of mouse thymocytes: prevention by native 7alpha-hydroxysteroids

Dehydroepiandrosterone (DHEA) has been shown to decrease the dexamethasone (DEX)-induced apoptosis of thymocytes and to be one of the native 3beta-hydroxysteroids extensively 7alpha-hydroxylated in thymus. This led us to question whether DHEA or 7alpha-hydroxy-DHEA is responsible for the decrease in DEX-induced apoptosis of thymocytes and whether this property is shared with other native 3beta-hydroxysteroids and their 7alpha-hydroxylated metabolites. Treatment of mice with DHEA or 7alpha-hydroxy-DHEA prior to DEX led to a smaller decrease in thymus weight than with DEX alone and to a disappearance of the DEX-induced changes in thymocyte phenotypes. Thymocyte apoptosis induced by DEX treatment was significantly lowered in DHEA- and 7alpha-hydroxy-DHEA-treated thymi, even after 18 h culture with additional 10-6 mol/L DEX. Extensive apoptosis of thymocytes cultured with 10-7 mol/L DEX was brought back to control levels when 10-5 mol/L 7alpha-hydroxy-DHEA or 10-5 mol/L 7alpha-hydroxy-epiandrosterone was added. After use of DHEA and epiandrosterone or pregnenolone, less significant and no significant changes were obtained, respectively. These findings imply that the 7alpha-hydroxylation of 3beta-hydroxysteroids may be a prerequisite for an exquisite regulation of the thymocyte-positive selection driven by the glucocorticoids produced in thymic epithelial cells.

The 7alpha-hydroxysteroids produced in human tonsils enhance the immune response to tetanus toxoid and Bordetella pertussis antigens

Human tonsils were assessed for their ability to 7alpha-hydroxylate pregnenolone (PREG), dehydroepiandrosterone (DHEA) and 3-epiandrosterone (EPIA). Both 7alpha-hydroxy-DHEA and 7alpha-hydroxy-EPIA were produced by homogenates of either whole tonsils or of lymphocyte-depleted tonsil fractions. In contrast, isolated lymphocytes were found to be unable to carry out 7alpha-hydroxylation. When co-cultures of tonsil-derived T and B lymphocytes were set up under stimulatory conditions, IgGs were released in the supernatants and could be quantitated, and immunomodulating properties of different steroids were monitored. When PREG was added to a mixture of tonsil-derived B and T lymphocytes, a decrease of non-specific and specific IgG was observed. An increase in specific anti-tetanus toxoid and anti-Bordetella pertussis antigen IgGs was obtained with either 1 microM 7alpha-hydroxy-DHEA or 1 microM 7alpha-hydroxy-EPIA. In contrast, DHEA and EPIA were unable to trigger such an effect. When cultures of isolated tonsillar B cells were used, none of the steroids tested showed significant effects on specific IgG productions. These data led to the conclusion that human tonsillar cells transform DHEA and EPIA, but not PREG, into 7alpha-hydroxylated metabolites. These metabolites could act on target tonsillar T lymphocytes which in turn act upon B lymphocytes for increasing specific IgG production.

Transformation of 3-hydroxy-steroids by Fusarium moniliforme 7alpha-hydroxylase

Transformation of physiologically important 3-hydroxy-steroids by the DHEA-induced 7alpha-hydroxylase of F. moniliforme was investigated. Whereas DHEA was almost totally 7alpha-hydroxylated, PREG, EPIA and ESTR were only partially converted into their 7alpha-hydroxylated derivatives because hydroxylation at other undetermined positions as well as reduction of ketone at C17 or C20 into hydroxyl also occurred. Cholesterol was not transformed by the enzyme. Kinetic parameters of the 7alpha-hydroxylation for these substrates were determined and confirmed that DHEA was the best substrate of the 7alpha-hydroxylase. Inhibition studies of DHEA 7alpha-hydroxylation by the other 3-hydroxy-steroids were also carried out and proved that DHEA, PREG, EPIA and ESTR shared the same active site of the enzyme. Induction effects of these steroids were compared, and DHEA appeared to be the best inducer of the 7alpha-hydroxylase of F. moniliforme.

Immunoassay of 7-hydroxysteroids: 1. Radioimmunoassay of 7beta-hydroxy dehydroepiandrosterone

High sensitivity radioimmunoassay of 3beta,7beta-dihydroxy-5-androsten-17-one (7beta-OH-DHEA) has been developed and evaluated. The method is based on polyclonal rabbit antisera raised against its 19-O-(carboxymethyl)oxime bovine serum albumin conjugate and bridge- and position homologous [125I]iodotyrosine methyl ester as a tracer. Alternatively, [3H]tracer has been prepared, which was recognized by the antiserum as well, but the assay sensitivity was lower. The identity of measured immunoreactive material was confirmed by high performance liquid chromatography which separated 7beta-OH-DHEA from its 7alpha-isomer. Using radioiodinated tracer, the sensitivity of the method was 3.48 fmol (1.06 pg) per tube, the mean recovery of standard added to steroid-free serum was 98.5%. Free (unconjugated and not-esterified) 7beta-OH-DHEA amounted in average 5.8% of the total 7beta-OH-DHEA present in human serum. It was measured in 42 normal subjects (28 females and 14 males) and in 92 randomly selected patients with various endocrinopathies. The mean values +/- SD in normals were 2.05 +/- 1.02 nmol l(-1), the broad range of values from undetectable levels to 10.3 nmol l(-1) was found in the patients. Serum levels of free 7beta-OH-DHEA in the patients significantly correlated with DHEA and its sulfate.

Change of 7alpha-hydroxy-dehydroepiandrosterone levels in serum of mice treated by cytochrome P450-modifying agents

Dehydroepiandrosterone (DHEA) is 7alpha-hydroxylated in liver, brain and other organs of murine and in other species. Several works suggest that the 7alpha-hydroxy-DHEA produced may be one of the native antiglucocorticoids, and compounds modifying its production may prove useful in investigation of 7alpha-hydroxy-DHEA production and effects. After treatment of mice with dexamethasone, phenobarbital, trilostane, melatonin or metyrapone, we have used gas chromatography-mass spectrometry with negative ion detection for measurement of 7alpha-hydroxy-DHEA levels in serum of control and treated animals. The 7alpha-hydroxylating rates of liver and brain microsomes from the same animals were also measured. Results showed that serum levels of 7alpha-hydroxy-DHEA were significantly increased after treatment by all compounds except metyrapone. Significantly increased 7alpha-hydroxy-DHEA levels were directly related with significantly increased 7alpha-hydroxylation yields in liver and not in brain. In contrast, metyrapone decreased 7alpha-hydroxylation in liver and brain. These findings indicate that in brain and in liver, different enzyme systems may be responsible for production of 7alpha-hydroxy-DHEA and that treatment-induced modifications of circulating 7alpha-hydroxy-DHEA levels are mainly due to change of 7alpha-hydroxylating rates in liver.

Inhibition studies of dehydroepiandrosterone 7 alpha- and 7 beta- hydroxylation in mouse liver microsomes

Hydroxylations of dehydroepiandrosterone (DHEA) at the 7 alpha- and 7 beta- positions have been reported in numerous murine tissues and organs, including liver, and the responsible cytochrome P450 (P450) species await identification. Using thin layer chromatography and gas chromatography-mass spectrometry, we report identification of 7 alpha-hydroxy-DHEA and 7 beta-hydroxy-DHEA metabolites produced in mouse liver microsome digests and kinetic studies of their production with apparent KM values of 3.19 +/- 0.292 microM and 2.82 +/- 0.241 microM for 7 alpha- and 7 beta-hydroxylation, respectively. Investigation of P450 inhibitor and of steroid hormone effects on both 7 alpha- and 7 beta-hydroxylation of DHEA showed that, 1) different P450s were involved in 7 alpha- and 7 beta-hydroxylation of DHEA because metyrapone inhibited solely 7 alpha-hydroxylation, 2) P450 2D6, 2B1, and 2B11 were not responsible for 7 alpha- and 7 beta-hydroxylation of DHEA because respective specific inhibitors quinidine and chloramphenicol triggered no inhibition, 3) aside from P450 7b, P450 1A1, and 1A2 may be responsible for a fraction of DHEA 7 alpha- and 7 beta-hydroxylation because alpha-naphthoflavone and furafylline, which inhibit specifically P450 1A1 and 1A2, decreased the 7 alpha- and 7 beta-hydroxylation partly, 4) comparison of these findings with those obtained with brain microsomes suggested that tissue-specific P450 species are responsible for the 7 alpha- and 7 beta-hydroxylation of DHEA, 5) 7 alpha-hydroxylation of DHEA may be shared with other 3 beta-hydroxysteroids, such as 3 beta-hydroxy-5 alpha-androstan-17-one, 5-androstene-3 beta,17 beta-diol and pregnenolone, which acted in a noncompetitive manner. Taken together, these findings will be of use for identification of the P450 species responsible for 7 alpha- and 7 beta-hydroxylation of DHEA and for studies of their activities in liver.

Seasonal changes in the production of two novel and abundant ovarian steroids in the channel catfish (Ictalurus punctatus)

Timely and appropriate changes in steroid plasma titers are necessary for successful reproduction in all vertebrates. Gonadal steroidogenesis of the most intensively cultured teleost species in North America, the channel catfish (Ictalurus punctatus), is poorly understood so a year-long study was conducted to investigate seasonal changes in ovarian steroidogenesis. Incubations of ovarian tissue were conducted monthly with [3H]pregnenolone and the medium was analyzed by high-performance liquid chromatography (HPLC) with radioactivity detection. The suite of steroids produced by the catfish ovary included the expected sex steroids (estradiol and testosterone) and 18 additional ovarian metabolites, including five steroids that have yet to be identified. Androstenedione, 20beta-dihydroprogesterone, 5|P-dihydrotestosterone, estriol, 11beta-hydroxyandrostenedione, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11beta-hydroxytestosterone, and progesterone were characterized by a combination of HPLC and thin-layer chromatography. Two of the most abundant steroids were isolated and analyzed by gas chromatography coupled with mass spectrometry (GC-MS). One of the steroids, 7alpha-hydroxypregnenolone (7P5), is a novel steroid in teleosts and was produced late in vitellogenic growth of the oocyte. Evidence suggests that the enzyme responsible for converting pregnenolone to 7P5, 7alpha-hydroxylase, is a cytochrome P450. The second abundant steroid metabolite was partially characterized by GC-MS as an hydroxylated form of 17-hydroxy-pregnenolone (chi,17P5). This steroid was most abundant when the ovary was regressed and during early vitellogenesis and rapidly decreased prior to spawning. In mammals, 7P5 has been identified as an important neurosteroid; however, the reproductive significance of 7P5 and chi,17P5 in catfish is unknown.

Hydroxylation of pregnenolone at the 7 alpha- and 7 beta- positions by mouse liver microsomes. Effects of cytochrome p450 inhibitors and structure-specific inhibition by steroid hormones

Hydroxylations of pregnenolone (PREG) at the 7 alpha-and 7 beta-positions have been reported in numerous murine tissues and organs, including liver, and the responsible cytochrome P450 (P450) species await identification. Using thin-layer chromatography and gas chromatography-mass spectrometry and crystallization to constant specific activity, we report identification of 7 alpha-hydroxy-PREG and 7 beta-hydroxy-PREG metabolites produced in mouse liver microsomes and kinetic studies of their production with apparent KM values of 2.45 +/- 0.124 microM and 3.41 +/- 0.236 microM for 7 alpha- and 7 beta-hydroxylation, respectively. Investigation of P450 inhibitors and of steroid hormone effects on both 7 alpha- and 7 beta-hydroxylation of PREG showed that 1) different P450 were involved because metyrapone and antipyrine inhibited solely 7 alpha-and 7 beta-hydroxylation, respectively; 2) P450 1A2, 2D6, 2B1, and 2B11 were not responsible for 7 alpha and 7 beta-hydroxylation of PREG because respective specific inhibitors furafylline, quinidine, and chloramphenicol triggered no inhibition; 3) P450 1A1 was responsible for only part of the 7 beta-hydroxylation of PREG because alpha-naphthoflavone, which inhibits specifically P450 1A1, did not suppress entirely 7 beta-hydroxylation while ketoconazole, antipyrine, and metyrapone extensively decreased the 7 beta-hydroxylation; 4) comparison of these findings with those obtained with brain microsomes suggests that tissue-specific P450 species are responsible for the 7 alpha-and 7 beta-hydroxylation of PREG; and 5) 7 alpha-hydroxylation of PREG may be shared with other 3 beta-hydroxysteroids such as isoandrosterone, 5-androstene-3 beta, 17 beta-diol, and dehydroepiandrosterone, which acted in a competitive manner. Taken together, these findings will be of use for identification of the P450 species responsible for 7 alpha- and 7 beta-hydroxylation of PREG and for studies of their activities in liver and other organs.