Protection against inflammatory neurodegeneration and glial cell death by 7β-hydroxy epiandrosterone, a novel neurosteroid

Regio- and Stereoselective Steroid Hydroxylation at C7 by Cytochrome P450 Monooxygenase Mutants

Steroidal C7β alcohols and their respective esters have shown significant promise as neuroprotective and anti-inflammatory agents to treat chronic neuronal damage like stroke, brain trauma, and cerebral ischemia. Since C7 is spatially far away from any functional groups that could direct C-H activation, these transformations are not readily accessible using modern synthetic organic techniques. Reported here are P450-BM3 mutants that catalyze the oxidative hydroxylation of six different steroids with pronounced C7 regioselectivities and β stereoselectivities, as well as high activities. These challenging transformations were achieved by a focused mutagenesis strategy and application of a novel technology for protein library construction based on DNA assembly and USER (Uracil-Specific Excision Reagent) cloning. Upscaling reactions enabled the purification of the respective steroidal alcohols in moderate to excellent yields. The high-resolution X-ray structure and molecular dynamics simulations of the best mutant unveil the origin of regio- and stereoselectivity.

Dehydroepiandrosterone and Dehydroepiandrosterone Sulfate in Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background and Purpose: Previous studies found inconsistent results for the relationship between Alzheimer's disease and the levels of dehydroepiandrosterone and dehydroepiandrosterone sulfate. This study performed a systematic review and meta-analysis to evaluate previous studies' results on this relationship. Method: Studies related to this outcome were obtained using a systematic search from the electronic databases of PubMed, Embase, Web of Science, and Psyc-ARTICLES in March 2018. The random-effects model was used to measure the strength of the association between Alzheimer's disease and the levels of dehydroepiandrosterone and dehydroepiandrosterone sulfate, using the standardized mean difference. Results: Thirty-one eligible studies were included in the final analysis. There was no statistically significant association between the level of dehydroepiandrosterone and Alzheimer's disease (standardized mean difference: 0.51, 95% confidence interval: -0.44 to 1.45, Z = 1.06, p = 0.29). On the other hand, lower level dehydroepiandrosterone sulfate was observed in patients with Alzheimer's disease than in controls (standardized mean difference: -0.69, 95% confidence interval: -1.17 to -0.22, Z = -2.84, p < 0.01). Conclusion: Decreased dehydroepiandrosterone sulfate concentrations may be an important indicator for Alzheimer's disease, although whether dehydroepiandrosterone sulfate could be used as a diagnostic tool requires further research.

The Quantitation of 7β-Hydroxy-Epiandrosterone in the Plasma and Seminal Plasma of Men With Different Degrees of Fertility

7β-hydroxy-epiandrosterone (7β-OH-EpiA) is an endogenous androgen metabolite that has been shown to exert neuroprotective, anti-inflammatory and anti-estrogenic effects. However, to the best of our knowledge no information is available about this androgen steroid in relation to sperm quality. We analyzed 7β-OH-EpiA in plasma and seminal plasma using a newly developed isotope dilution ultra-high performance liquid chromatography – mass spectrometry method. Validation met the requirements of FDA guidelines. Levels of 7β-OH-EpiA were measured in 191 men with different degrees of infertility. One-way analysis of variance followed by multiple comparison and correlation analysis adjusted for age, BMI and abstinence time were performed to evaluate the relationships between this steroid and sperm quality. Concentrations of 7β-OH-EpiA in seminal plasma were significantly higher in severely infertile men in comparison with healthy men and slightly infertile men. The same trend was found when blood plasma was evaluated. Furthermore, plasma 7β-OH-EpiA negatively correlated with sperm concentration (-0.215; p<0.01) and total count (-0.15; p<0.05). Seminal 7β-OH-EpiA was negatively associated with motility (-0.26; p<0.01), progressively motile spermatozoa (-0.233; p<0.01) and nonprogressively motile spermatozoa (-0.188; p<0.05). 7β-OH-EpiA is associated with lower sperm quality and deserves more research in that respect.

Central intracrine DHEA synthesis in ageing-related neuroinflammation and neurodegeneration: therapeutic potential?

It is a well-known fact that DHEA declines on ageing and that it is linked to ageing-related neurodegeneration, which is characterised by gradual cognitive decline. Although DHEA is also associated with inflammation in the periphery, the link between DHEA and neuroinflammation in this context is less clear. This review drew from different bodies of literature to provide a more comprehensive picture of peripheral vs central endocrine shifts with advanced age—specifically in terms of DHEA. From this, we have formulated the hypothesis that DHEA decline is also linked to neuroinflammation and that increased localised availability of DHEA may have both therapeutic and preventative benefit to limit neurodegeneration. We provide a comprehensive discussion of literature on the potential for extragonadal DHEA synthesis by neuroglial cells and reflect on the feasibility of therapeutic manipulation of localised, central DHEA synthesis.

Sex differences in the effect of prenatal testosterone exposure on steroid hormone production in adult rats

Maternal hyperandrogenism during pregnancy might have metabolic and endocrine consequences on the offspring as shown for the polycystic ovary syndrome. Despite numerous experiments, the impact of prenatal hyperandrogenic environment on postnatal sex steroid milieu is not yet clear. In this study, we investigated the effect of prenatal testosterone excess on postnatal concentrations of luteinizing hormone, corticosterone and steroid hormones including testosterone, pregnenolone, progesterone, estradiol and 7beta-hydroxy-epiandrosterone in the offspring of both sexes. Pregnant rats were injected daily with either testosterone propionate or vehicle from gestational day 14 until parturition. The hormones were evaluated in plasma of the adult offspring. As expected, females had lower testosterone and higher pregnenolone, progesterone and estradiol in comparison to males. In addition, corticosterone was higher in females than in males, and it was further elevated by prenatal testosterone treatment. In males, prenatal testosterone exposure resulted in higher 7beta-hydroxy-epiandrosterone in comparison to control group. None of the other analyzed hormones were affected by prenatal testosterone. In conclusion, our results did not show major effects on sex hormone production or luteinizing hormone release in adult rats resulting from testosterone excess during their fetal development. However, maternal hyperandrogenism seems to partially affect steroid biosynthesis in sex-specific manner.

Association of serum dehydroepiandrosterone sulfate and cognition in older adults: sex steroid, inflammatory, and metabolic mechanisms

OBJECTIVE

Dehydroepiandrosterone sulfate (DHEAS) levels and cognitive function decline with age, and a role for DHEAS in supporting cognition has been proposed. Higher DHEAS levels may be associated with better cognitive performance, although potential mechanisms for this relationship are not well established.

METHOD

We performed a cross-sectional study of the relationship between serum DHEAS and three aspects of cognition--executive function, working memory, and processing speed--in 49 men and 54 women, aged 60-88 years, with low serum DHEAS levels. We examined three potential mechanisms of DHEAS action--sex hormone sufficiency, inflammatory status, and glucose regulation.

RESULTS

After adjustment for multiple covariates, higher serum DHEAS levels were associated with better working memory (standardized beta coefficient 0.50, p < .05), with a trend toward better executive function (standardized beta coefficient 0.37, p < .10) in men only. There was a nonsignificant trend toward a negative association between levels of tumor necrosis factor α (TNFα) and working memory in the combined population (standardized beta coefficient -0.22, p < .10). None of the glucoregulatory measures was associated with cognitive function.

CONCLUSIONS

The relationship between DHEAS and cognition is complex and differs by sex and cognitive domain. This study supports the need for further investigations of the sex-specific effects of DHEAS on cognition and its underlying mechanisms of action.

Clinical utility of neuroprotective agents in neurodegenerative diseases: current status of drug development for Alzheimer's, Parkinson's and Huntington's diseases, and amyotrophic lateral sclerosis

INTRODUCTION

According to the definition of the Committee to Identify Neuroprotective Agents in Parkinson's Disease (CINAPS), "neuroprotection would be any intervention that favourably influences the disease process or underlying pathogenesis to produce enduring benefits for patients" [Meissner W, et al. Trends Pharmacol Sci 2004;25:249-253]. Preferably, neuroprotective agents should be used before or eventually during the prodromal phase of the diseases that could start decades before the appearance of symptoms. Although several symptomatic drugs are available, a disease-modifying agent is still elusive.

AREAS COVERED

The aim of the present review is to give an overview of neuroprotective agents being currently investigated for the treatment of AD, PD, HD and ALS in clinical phases.

EXPERT OPINION

Development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages, both conceptual and methodological. Novel solutions might be offered by evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multi-target approaches and network pharmacology.

The DHEA metabolite 7β-hydroxy-epiandrosterone exerts anti-estrogenic effects on breast cancer cell lines

7β-Hydroxy-epiandrosterone (7β-OH-EpiA), an endogenous androgenic derivative of dehydroepiandrosterone, has previously been shown to exert anti-inflammatory action in vitro and in vivo via a shift from prostaglandin E2 (PGE2) to 15-deoxy-Δ(12,14)-PGJ2 production. This modulation in prostaglandin production was obtained with low concentrations of 7β-OH-EpiA (1-100nM) and suggested that it might act through a specific receptor. Inflammation and prostaglandin synthesis is important in the development and survival of estrogen-dependent mammary cancers. Estrogen induced PGE2 production and cell proliferation via its binding to estrogen receptors (ERs) in these tumors. Our objective was to test the effects of 7β-OH-EpiA on the proliferation (by counting with trypan blue exclusion), cell cycle and cell apoptosis (by flow cytometry) of breast cancer cell lines MCF-7 (ERα+, ERβ+, G-protein coupled receptor 30: GPR30+) and MDA-MB-231 (ERα-, ERβ+, GPR30+) and to identify a potential target of this steroid in these cell lineages (by transactivations) and in the nuclear ER-negative SKBr3 cells (GPR30+) (by proliferation assays). 7β-OH-EpiA exerted anti-estrogenic effects in MCF-7 and MDA-MB-231 cells associated with cell proliferation inhibition and cell cycle arrest. Moreover, transactivation and proliferation with ER agonists assays indicated that 7β-OH-EpiA interacted with ERβ. Data from proliferation assays on the MCF-7, MDA-MB-231 and SKBr3 cell lines suggested that 7β-OH-EpiA may also act through the membrane GPR30 receptor. These results support that this androgenic steroid acts as an anti-estrogenic compound. Moreover, this is the first evidence that low doses of androgenic steroid exert antiproliferative effects in these mammary cancer cells. Further investigations are needed to improve understanding of the observed actions of endogenous 7β-OH-EpiA.

Oxidative metabolism of dehydroepiandrosterone (DHEA) and biologically active oxygenated metabolites of DHEA and epiandrosterone (EpiA)--recent reports

Dehydroepiandrosterone (DHEA) is a multifunctional steroid with a broad range of biological effects in humans and animals. DHEA can be converted to multiple oxygenated metabolites in the brain and peripheral tissues. The mechanisms by which DHEA exerts its effects are not well understood. However, evidence that the effects of DHEA are mediated by its oxygenated metabolites has accumulated. This paper will review the panel of oxygenated DHEA metabolites (7, 16 and 17-hydroxylated derivatives) including a number of 5α-androstane derivatives, such as epiandrosterone (EpiA) metabolites. The most important aspects of the oxidative metabolism of DHEA in the liver, intestine and brain are described. Then, this article reviews the reported biological effects of oxygenated DHEA metabolites from recent findings with a specific focus on cancer, inflammatory and immune processes, osteoporosis, thermogenesis, adipogenesis, the cardiovascular system, the brain and the estrogen and androgen receptors.

7beta-Hydroxy-epiandrosterone-mediated regulation of the prostaglandin synthesis pathway in human peripheral blood monocytes

7alpha-Hydroxy-DHEA, 7beta-hydroxy-DHEA and 7beta-hydroxy-EpiA are native metabolites of dehydroepiandrosterone (DHEA) and epiandrosterone (EpiA). Since numerous steroids are reported to interfere with inflammatory and immune processes, our objective was to test the effects of these hydroxysteroids on prostaglandin (PG) production and related enzyme gene expression. Human peripheral blood monocytes were cultured for 4 and 24 h in the presence of each of the steroids (1-100 nM), with and without addition of TNF-alpha (10 ng/mL). Levels of PGE(2), PGD(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) were measured in the incubation medium, and cell content of cyclooxygenase (COX-2), and PGE and PGD synthases (m-PGES1, H-PGDS, L-PGDS), and peroxisome proliferator activated receptor (PPAR-gamma) was assessed by quantitative RT-PCR and Western blots. Addition of TNF-alpha resulted in elevated PG production and increased COX-2 and m-PGES1 levels. Among the three steroids tested, only 7beta-hydroxy-EpiA decreased COX-2, m-PGES1 and PPAR-gamma expression while markedly decreasing PGE(2) and increasing 15d-PGJ(2) production. These results suggest that 7beta-hydroxy-EpiA is a native trigger of cellular protection through simultaneous activation of 15d-PGJ(2) and depression of PGE(2) synthesis, and that these effects may be mediated by activation of a putative receptor, specific for 7beta-hydroxy-EpiA.

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).

7alpha- and 7beta-hydroxy-epiandrosterone as substrates and inhibitors for the human 11beta-hydroxysteroid dehydrogenase type 1

The human 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) catalyzes both the NADP(H)-dependent oxido-reduction of cortisol and cortisone and the inter-conversion of 7alpha- and 7beta-hydroxy-dehydroepiandrosterone (DHEA) through a 7-oxo-DHEA intermediate. As shown with human liver and intestine fractions, 7alpha-hydroxy-epiandrosterone (7alpha-hydroxy-EpiA) and 7beta-hydroxy-EpiA were readily inter-converted with no evidence for a 7-oxo-EpiA intermediate. Whether this inter-conversion resulted from action of the 11beta-HSD1 or from an unknown epimerase is unresolved. Furthermore, whether these steroids could inhibit the cortisol-cortisone oxido-reduction remains a question. The recombinant human 11beta-HSD1 was used to test these questions. NADP(+) supplementation only provided the production of 7beta-hydroxy-EpiA out of 7alpha-hydroxy-EpiA with a V(max)/K(M) ratio at 0.1. With NADPH supplementation, both 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA were formed in low amounts from 7beta-hydroxy-EpiA and 7alpha-hydroxy-EpiA, respectively. These inter-conversions occurred without a trace of the putative 7-oxo-EpiA intermediate. In contrast, the 7-oxo-EpiA substrate was efficiently reduced into 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA, with V(max)/K(M) ratios of 23.6 and 5.8, respectively. Competitive and mixed type inhibitions of the 11beta-HSD1-mediated cortisol oxidation were exerted by 7alpha-hydroxy-EpiA and 7beta-hydroxy-EpiA, respectively. The 11beta-HSD1-mediated cortisone reduction was inhibited in a competitive manner by 7-oxo-EpiA. These findings suggest that the active site of the human 11beta-HSD1 may carry out directly the epimeric transformation of 7-hydroxylated EpiA substrates. The low amounts of these steroids in human do not support a physiological importance for modulation of the glucocorticoid status in tissues.

First synthesis of 7α- and 7β-amino-DHEA, dehydroepiandrosterone (DHEA) analogues and preliminary evaluation of their cytotoxicity on Leydig cells and TM4 Sertoli cells

Efficient syntheses of new DHEA analogues, and their apoptotic and necrotic effects on Leydig cells and TM4 Sertoli cells are described. The key step in the synthetic strategy of 7-amino-DHEA derivatives involves a bromination on C-7 position to give an epimeric mixture of bromides which were substituted by azides and reduced to give 7alpha- and 7beta-amino-3beta-hydroxyandrost-5-en-17-ones. No cytotoxic effect induced by apoptosis mechanism was observed on Leydig and TM4 Sertoli cells by treatment with these amino-DHEA analogues. A necrotic effect was induced only in TM4 Sertoli cells. The best activity was obtained with 7alpha,beta-amino-androst-5-en-3beta-ol and 7beta-amino-3beta-hydroxy-androst-5-en-17-one.

Fatigue in progressive multiple sclerosis is associated with low levels of dehydroepiandrosterone

BACKGROUND AND OBJECTIVE

Fatigue is one of the most limiting symptoms in multiple sclerosis (MS) and the mechanisms underlying its origin are poorly understood. Our aim was to test whether fatigue in MS is associated with endocrine markers.

METHODS

We longitudinally studied 73 progressive MS patients. Fatigue was assessed at baseline and at 3, 6, 12 and 24 months using the Fatigue Severity Scale (FSS). Given the longitudinal design of our study, patients were labelled as sustained fatigued when FSS scores were >5.0 at all time points, and as non-fatigued when FSS scores were < or = 5.0 at all time points. Serum levels of dehydroepiandrosterone (DHEA), its sulphated conjugate (DHEAS) and cortisol were measured at each time point.

RESULTS

Twenty-nine patients scored >5.0 in the FSS at all time points, and 9 patients (12.3%) scored 5.0 at all time points. Mean baseline levels of DHEAS and DHEA were lower in MS patients with sustained fatigue when compared to patients without fatigue (P = 0.01 and P = 0.03 respectively). Analysis of DHEAS and DHEA over time showed significantly lower hormone levels in patients with fatigue [F(1,31) = 6.14, P=0.019 for DHEAS; F(1,32) = 6.63, P=0.015 for DHEA].

CONCLUSIONS

Fatigue in progressive MS could be related to low serum levels of DHEA and DHEAS. Our results suggest that these hormones should be considered as biological markers of fatigue in MS patients and that hormone replacement may thus be tested as an option to treat fatigue in MS patients.

Inter-conversion of 7alpha- and 7beta-hydroxy-dehydroepiandrosterone by the human 11beta-hydroxysteroid dehydrogenase type 1

The dehydroepiandrosterone (DHEA) 7alpha-hydroxylation in humans takes place in the liver, skin, and brain. These organs are targets for the glucocorticoid hormones where 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activates cortisone through its reduction into cortisol. The putative interference of 7alpha-hydroxy-DHEA with the 11beta-HSD1-catalyzed reduction of cortisone into cortisol has been confirmed in preliminary works with human liver tissue preparations of the enzyme demonstrating the transformation of 7alpha-hydroxy-DHEA into 7-oxo-DHEA and 7beta-hydroxy-DHEA. However, the large production of 7beta-hydroxy-DHEA could not be explained satisfactorily. Therefore our objective was to study the role in the metabolism of oxygenated DHEA by recombinant human 11beta-HSD1 expressed in yeast. The 7alpha- and 7beta-hydroxy-DHEA were each oxidized into 7-oxo-DHEA with quite dissimilar K(M) (70 and 9.5 microM, respectively) but at equivalent V(max). In contrast, the 11beta-HSD1-mediated reduction of 7-oxo-DHEA led to the production of both 7alpha- and 7beta-hydroxy-DHEA with equivalent K(M) (1.1 microM) but with a 7beta-hydroxy-DHEA production characterized by a significantly greater V(max). The 7alpha-hydroxy-DHEA produced by the cytochrome CYP7B1 in tissues may exert anti-glucocorticoid effects through interference with the 11beta-HSD1-mediated cortisone reduction.

Neuroprotection and neurodegenerative diseases: from biology to clinical practice

Neurodegenerative diseases and, in particular, Alzheimer disease, are characterized by progressive neuronal loss correlated in time with the symptoms of the disease considered. Whereas the symptoms of those incapacitating diseases are beginning to be managed with a relative efficacy, the ultimate objective of therapy nonetheless remains preventing cell (neuronal and/or astrocytic) death in a neurocytoprotective approach. In biologic terms, in the light of progress at basic research level, three strategies may be envisaged: (1) antagonizing the cytotoxic causal events (excess intracellular calcium, accumulation of abnormal proteins, excitotoxic effects of amino acids, oxidative stress, processes related to inflammation, etc.); (2) stimulating the endogenous protective processes (anti-free radical or DNA repair systems, production of neurotrophic factors, potential cytoprotective action of steroids, etc.); (3) promoting damaged structure repair strategies (grafts) or deep brain or cortical neurostimulation with a view to triggering (beyond the symptomatic actions) potential 'protective' cell mechanisms. The clinical transition of the various strategies whose efficacy is being tested in animal and/or cell models, experimental analogs of the diseases, and thus the objective demonstration in humans of pharmacological and/or surgical neurocytoprotection, is currently the subject of considerable methodological debate (What are the right psychometric assessment criteria? What are the most pertinent laboratory or neuroradiological markers, etc.?). A number of clinical trials have been completed or are ongoing with drugs that are reputed to be neuroprotective. Thus, elements of the response are beginning to be generated with a view to determining whether it will soon be possible to effectively slow or even stop the neurodegenerative process whose etiology, in most cases, remains obscure.

Neuroactive steroids: old players in a new game

It is now clear that the study of the effects exerted by steroids on the nervous system may be considered as one of the most interesting and promising topics for biomedical research. Indeed, new effects, mechanisms of action and targets are becoming more and more evident suggesting that steroids are not only important key regulators of nervous system function but they may also represent a new therapeutic tool to combat certain diseases of the nervous system. The present review summarizes recent observations on this topic indicating that while the concept of the nervous system as a target for steroid hormones has been appreciated for decades, a promising new era for the study of these molecules and their actions in the nervous system has been initiated in the last few years.

The identification and simultaneous quantification of 7-hydroxylated metabolites of pregnenolone, dehydroepiandrosterone, 3beta,17beta-androstenediol, and testosterone in human serum using gas chromatography-mass spectrometry

7-Hydroxy-metabolites of dehydroepiandrosterone (DHEA) and 3beta,17beta-androstenediol (AD) possess immunomodulatory and neuroprotective properties; therefore, the measurement of these steroids in patients with autoimmune diseases or disturbances in the CNS may be of interest. A gas chromatography-mass spectrometry (GC-MS) method for the determination of 7-hydroxy-metabolites of pregnenolone, DHEA, AD, and testosterone including the parent steroids was applied to serum samples from 12 adult men (27-66 years), 13 male adolescents (13-20 years), 5 boys (6-10 years), 15 women in the follicular phase of the menstrual cycle (22-45 years), 17 women in the luteal phase (22-45 years), and 4 girls (6-10 years). The steroids were age and sex dependent, but independent of the menstrual cycle. The ratio of the 7alpha-hydroxy-metabolites to their parent steroids were age dependent, exhibiting an increasing trend (p < 0.0001, ANOVA) from pregnenolone (5%) to AD (20%). The ratio of 7beta- to 7alpha-metabolites ranged from 0.6 to 1. These results are consistent with models suggesting 7alpha-hydroxylation of the parent steroid, conversion to a 7-oxo-steroid and finally to the 7beta-hydroxylated-metabolite. Partial correlations suggested that 7-hydroxylation might reduce the concentration of circulating androgens. Despite the three times lower concentration of AD-metabolites, their antiglucocorticoid, immunomodulatory, and neuroprotective effects may be comparable to that of DHEA based on their reported greater biological activity.

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.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.

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.

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.