A novel cytochrome P450 expressed primarily in brain

Advances in steroid research from the pioneering neurosteroid concept to metabolomics: New insights into pregnenolone function

Advances in neuroendocrinology have led to major discoveries since the 19th century, identifying adaptive loops for maintaining homeostasis. One of the most remarkable discoveries was the concept of neurosteroids, according to which the brain is not only a target but also a source of steroid production. The identification of new membrane steroid targets now underpins the neuromodulatory effects of neurosteroids such as pregnenolone, which is involved in functions mediated by the GPCR CB1 receptor. Structural analysis of steroids is a key feature of their interactions with the phospholipid membrane, receptors and resulting activity. Therefore, mass spectrometry-based methods have been developed to elucidate the metabolic pathways of steroids, the ultimate approach being metabolomics, which allows the identification of a large number of metabolites in a single sample. This approach should enable us to make progress in understanding the role of neurosteroids in the functioning of physiological and pathological processes.

Biotransformation of Efavirenz and Proteomic Analysis of Cytochrome P450s and UDP-Glucuronosyltransferases in Mouse, Macaque, and Human Brain-Derived In Vitro Systems

Antiretroviral drugs such as efavirenz (EFV) are essential to combat human immunodeficiency virus (HIV) infection in the brain, but little is known about how these drugs are metabolized locally. In this study, the cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT)-dependent metabolism of EFV was probed in brain microsomes from mice, cynomolgus macaques, and humans as well as primary neural cells from C57BL/6N mice. Utilizing ultra high performance liquid chromatography high-resolution mass spectrometry (uHPLC-HRMS), the formation of 8-hydroxyefavirenz (8-OHEFV) from EFV and the glucuronidation of P450-dependent metabolites 8-OHEFV and 8,14-dihydroxyefavirenz (8,14-diOHEFV) were observed in brain microsomes from all three species. The direct glucuronidation of EFV, however, was only detected in cynomolgus macaque brain microsomes. In primary neural cells treated with EFV, microglia were the only cell type to exhibit metabolism, forming 8-OHEFV only. In cells treated with the P450-dependent metabolites of EFV, glucuronidation was detected only in cortical neurons and astrocytes, revealing that certain aspects of EFV metabolism are cell type specific. Untargeted and targeted proteomics experiments were used to identify the P450s and UGTs present in brain microsomes. Eleven P450s and 11 UGTs were detected in human brain microsomes, whereas seven P450s and 14 UGTs were identified in mouse brain microsomes and 15 P450s and four UGTs, respectively, were observed in macaque brain microsomes. This was the first time many of these enzymes have been noted in brain microsomes at the protein level. This study indicates the potential for brain metabolism to contribute to pharmacological and toxicological outcomes of EFV in the brain. SIGNIFICANCE STATEMENT: Metabolism in the brain is understudied, and the persistence of human immunodeficiency virus (HIV) infection in the brain warrants the evaluation of how antiretroviral drugs such as efavirenz are metabolized in the brain. Using brain microsomes, the metabolism of efavirenz by both cytochrome P450s (P450s) and UDP-glucuronosyltransferases (UGTs) is established. Additionally, proteomics of brain microsomes characterizes P450s and UGTs in the brain, many of which have not yet been noted in the literature at the protein level.

Cytochrome P450 expression and regulation in the brain

The regulation of brain cytochrome P450 enzymes (CYPs) is different compared with respective hepatic enzymes. This may result from anatomical bases and physiological functions of the two organs. The brain is composed of a variety of functional structures built of different interconnected cell types endowed with specific receptors that receive various neuronal signals from other brain regions. Those signals activate transcription factors or alter functioning of enzyme proteins. Moreover, the blood-brain barrier (BBB) does not allow free penetration of all substances from the periphery into the brain. Differences in neurotransmitter signaling, availability to endogenous and exogenous active substances, and levels of transcription factors between neuronal and hepatic cells lead to differentiated expression and susceptibility to the regulation of CYP genes in the brain and liver. Herein, we briefly describe the CYP enzymes of CYP1-3 families, their distribution in the brain, and discuss brain-specific regulation of CYP genes. In parallel, a comparison to liver CYP regulation is presented. CYP enzymes play an essential role in maintaining the levels of bioactive molecules within normal ranges. These enzymes modulate the metabolism of endogenous neurochemicals, such as neurosteroids, dopamine, serotonin, melatonin, anandamide, and exogenous substances, including psychotropics, drugs of abuse, neurotoxins, and carcinogens. The role of these enzymes is not restricted to xenobiotic-induced neurotoxicity, but they are also involved in brain physiology. Therefore, it is crucial to recognize the function and regulation of CYP enzymes in the brain to build a foundation for future medicine and neuroprotection and for personalized treatment of brain diseases.

The interoceptive hippocampus: Mouse brain endocrine receptor expression highlights a dentate gyrus (DG)-cornu ammonis (CA) challenge-sufficiency axis

The primeval function of the mammalian hippocampus (HPC) remains uncertain. Implicated in learning and memory, spatial navigation, and neuropsychological disorders, evolutionary theory suggests that the HPC evolved from a primeval chemosensory epithelium. Deficits in sensing of internal body status ('interoception') in patients with HPC lesions argue that internal sensing may be conserved in higher vertebrates. We studied the expression patterns in mouse brain of 250 endocrine receptors that respond to blood-borne ligands. Key findings are (i) the proportions and levels of endocrine receptor expression in the HPC are significantly higher than in all other comparable brain regions. (ii) Surprisingly, the distribution of endocrine receptor expression within mouse HPC was found to be highly structured: receptors signaling 'challenge' are segregated in dentate gyrus (DG), whereas those signaling 'sufficiency' are principally found in cornu ammonis (CA) regions. Selective expression of endocrine receptors in the HPC argues that interoception remains a core feature of hippocampal function. Further, we report that ligands of DG receptors predominantly inhibit both synaptic potentiation and neurogenesis, whereas CA receptor ligands conversely promote both synaptic potentiation and neurogenesis. These findings suggest that the hippocampus acts as an integrator of body status, extending its role in context-dependent memory encoding from 'where' and 'when' to 'how I feel'. Implications for anxiety and depression are discussed.

Alterations in cholesterol metabolism as a risk factor for developing Alzheimer's disease: Potential novel targets for treatment

Alzheimer's disease (AD) is the most common form of dementia and it is characterized by the deposition of amyloid-β (Aβ) plaques and neurofibrillary tangles in the brain. However, the complete pathogenesis of the disease is still unknown. High level of serum cholesterol has been found to positively correlate with an increased risk of dementia and some studies have reported a decreased prevalence of AD in patients taking cholesterol-lowering drugs. Years of research have shown a strong correlation between blood hypercholesterolemia and AD, however cholesterol is not able to cross the Blood Brain Barrier (BBB) into the brain. Cholesterol lowering therapies have shown mixed results in cognitive performance in AD patients, raising questions of whether brain cholesterol metabolism in the brain should be studied separately from peripheral cholesterol metabolism and what their relationship is. Unlike cholesterol, oxidized cholesterol metabolites known as oxysterols are able to cross the BBB from the circulation into the brain and vice-versa. The main oxysterols present in the circulation are 24S-hydroxycholesterol and 27-hydroxycholesterol. These oxysterols and their catalysing enzymes have been found to be altered in AD brains and there is evidence indicating their influence in the progression of the disease. This review gives a broad perspective on the relationship between hypercholesterolemia and AD, cholesterol lowering therapies for AD patients and the role of oxysterols in pathological and non-pathological conditions. Also, we propose cholesterol metabolites as valuable targets for prevention and alternative AD treatments.

Thyroid hormones induce doxorubicin chemosensitivity through enzymes involved in chemotherapy metabolism in lymphoma T cells

Thyroid hormones (THs) – 3,3′,5-triiodo-L-thyronine (T3) and L-thyroxine (T4) – are important regulators of the metabolism and physiology of most normal tissues. Cytochrome P450 family 3A members are drug metabolizing enzymes involved in the activation and detoxification of several drugs. CYP3A4 is the major enzyme involved in the metabolism of chemotherapeutic drugs. In this work, we demonstrate that THs induce a significant increase in CYP3A4 mRNA levels, protein expression and metabolic activity through the membrane receptor integrin αvβ3 and the activation of signalling pathways through Stat1 and NF-κB. We reasoned that TH-induced CYP3A4 modulation may act as an important regulator in the metabolism of doxorubicin (Doxo). Experiments in vitro demonstrated that in CYP3A4-knocked down cells, no TH-mediated chemosensitivity to Doxo was observed. We also found that THs modulate these functions by activating the membrane receptor integrin αvβ3. In addition, we showed that the thyroid status can modulate CYP450 mRNA levels in tumor and liver tissues, and the tumor volume in response to chemotherapy in vivo. In fact, Doxo treatment in hypothyroid mice was associated with lower tumors, displaying lower levels of CYP enzymes, than euthyroid mice. However, higher mRNA levels of CYP enzymes were found in livers from Doxo treated hypothyroid mice respect to control. These results present a new mechanism by which TH could modulate chemotherapy response. These findings highlight the importance of evaluating thyroid status in patients during application of T-cell lymphoma therapeutic regimens.

Mining for Oxysterols in Cyp7b1-/- Mouse Brain and Plasma: Relevance to Spastic Paraplegia Type 5

Deficiency in cytochrome P450 (CYP) 7B1, also known as oxysterol 7α-hydroxylase, in humans leads to hereditary spastic paraplegia type 5 (SPG5) and in some cases in infants to liver disease. SPG5 is medically characterized by loss of motor neurons in the corticospinal tract. In an effort to gain a better understanding of the fundamental biochemistry of this disorder, we have extended our previous profiling of the oxysterol content of brain and plasma of Cyp7b1 knockout (-/-) mice to include, amongst other sterols, 25-hydroxylated cholesterol metabolites. Although brain cholesterol levels do not differ between wild-type (wt) and knockout mice, we find, using a charge-tagging methodology in combination with liquid chromatography-mass spectrometry (LC-MS) and multistage fragmentation (MSⁿ), that there is a build-up of the CYP7B1 substrate 25-hydroxycholesterol (25-HC) in Cyp7b1-/- mouse brain and plasma. As reported earlier, levels of (25R)26-hydroxycholesterol (26-HC), 3β-hydroxycholest-5-en-(25R)26-oic acid and 24S,25-epoxycholesterol (24S,25-EC) are similarly elevated in brain and plasma. Side-chain oxysterols including 25-HC, 26-HC and 24S,25-EC are known to bind to INSIG (insulin-induced gene) and inhibit the processing of SREBP-2 (sterol regulatory element-binding protein-2) to its active form as a master regulator of cholesterol biosynthesis. We suggest the concentration of cholesterol in brain of the Cyp7b1-/- mouse is maintained by balancing reduced metabolism, as a consequence of a loss in CYP7B1, with reduced biosynthesis. The Cyp7b1-/- mouse does not show a motor defect; whether the defect in humans is a consequence of less efficient homeostasis of cholesterol in brain has yet to be uncovered.

Electricity-driven 7α-hydroxylation of a steroid catalyzed by a cytochrome P450 monooxygenase in engineered yeast

Schematic diagram of the cytochrome P450 monooxygenase-catalyzed BES.

Mammalian Cells Engineered To Produce New Steroids

Steroids can be difficult to modify through traditional organic synthesis methods, but many enzymes regio- and stereoselectively process a wide variety of steroid substrates. We tested whether steroid-modifying enzymes could make novel steroids from non-native substrates. Numerous genes encoding steroid-modifying enzymes, including some bacterial enzymes, were expressed in mammalian cells by transient transfection and found to be active. We made three unusual steroids by stable expression, in HEK293 cells, of the 7α-hydroxylase CYP7B1, which was selected because of its high native product yield. These cells made 7α,17α-dihydroxypregnenolone and 7β,17α-dihydroxypregnenolone from 17α-hydroxypregnenolone and produced 11α,16α-dihydroxyprogesterone from 16α-hydroxyprogesterone. The last two products were the result of CYP7B1-catalyzed hydroxylation at previously unobserved sites. A Rosetta docking model of CYP7B1 suggested that these substrates' D-ring hydroxy groups might prevent them from binding in the same way as the native substrates, bringing different carbon atoms close to the active ferryl oxygen atom. This new approach could potentially use other enzymes and substrates to produce many novel steroids for drug candidate testing.

Identification of 7α,24-dihydroxy-3-oxocholest-4-en-26-oic and 7α,25-dihydroxy-3-oxocholest-4-en-26-oic acids in human cerebrospinal fluid and plasma

Dihydroxyoxocholestenoic acids are intermediates in bile acid biosynthesis. Here, using liquid chromatography – mass spectrometry, we confirm the identification of 7α,24-dihydroxy-3-oxocholest-4-en-26-oic and 7α,25-dihydroxy-3-oxocholest-4-en-26-oic acids in cerebrospinal fluid (CSF) based on comparisons to authentic standards and of 7α,12α-dihydroxy-3-oxocholest-4-en-26-oic and 7α,x-dihydroxy-3-oxocholest-4-en-26-oic (where hydroxylation is likely on C-22 or C-23) based on exact mass measurement and multistage fragmentation. Surprisingly, patients suffering from the inborn error of metabolism cerebrotendinous xanthomatosis, where the enzyme CYP27A1, which normally introduces the (25 R)26-carboxylic acid group to the sterol side-chain, is defective still synthesise 7α,24-dihydroxy-3-oxocholest-4-en-26-oic acid and also both 25 R- and 25 S-epimers of 7α,12α-dihydroxy-3-oxocholest-4-en-26-oic acid. We speculate that the enzymes CYP46A1 and CYP3A4 may have C-26 carboxylase activity to generate these acids. In patients suffering from hereditary spastic paraplegia type 5 the CSF concentrations of the 7α,24- and 7α,25-dihydroxy acids are reduced, suggesting an involvement of CYP7B1 in their biosynthesis in brain.

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Dihydroxy-3-oxocholest-5-en-26-oic are found in human CSF and plasma.

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Hydroxy groups may be at 7α,24, 7α,25, or 7α,12α.

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Another acid is hydroxylated at 7α and in the side-chain probably at C-22 or C-23.

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In patients with CTX acids with 25 R or 25 S stereochemistry are found.

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In patients with SPG5 the concentrations of acids in CSF are reduced.

Hereditary spastic paraplegia type 5: natural history, biomarkers and a randomized controlled trial

Spastic paraplegia type 5 (SPG5) is a rare subtype of hereditary spastic paraplegia, a highly heterogeneous group of neurodegenerative disorders defined by progressive neurodegeneration of the corticospinal tract motor neurons. SPG5 is caused by recessive mutations in the gene CYP7B1 encoding oxysterol-7α-hydroxylase. This enzyme is involved in the degradation of cholesterol into primary bile acids. CYP7B1 deficiency has been shown to lead to accumulation of neurotoxic oxysterols. In this multicentre study, we have performed detailed clinical and biochemical analysis in 34 genetically confirmed SPG5 cases from 28 families, studied dose-dependent neurotoxicity of oxysterols in human cortical neurons and performed a randomized placebo-controlled double blind interventional trial targeting oxysterol accumulation in serum of SPG5 patients. Clinically, SPG5 manifested in childhood or adolescence (median 13 years). Gait ataxia was a common feature. SPG5 patients lost the ability to walk independently after a median disease duration of 23 years and became wheelchair dependent after a median 33 years. The overall cross-sectional progression rate of 0.56 points on the Spastic Paraplegia Rating Scale per year was slightly lower than the longitudinal progression rate of 0.80 points per year. Biochemically, marked accumulation of CYP7B1 substrates including 27-hydroxycholesterol was confirmed in serum (n = 19) and cerebrospinal fluid (n = 17) of SPG5 patients. Moreover, 27-hydroxycholesterol levels in serum correlated with disease severity and disease duration. Oxysterols were found to impair metabolic activity and viability of human cortical neurons at concentrations found in SPG5 patients, indicating that elevated levels of oxysterols might be key pathogenic factors in SPG5. We thus performed a randomized placebo-controlled trial (EudraCT 2015-000978-35) with atorvastatin 40 mg/day for 9 weeks in 14 SPG5 patients with 27-hydroxycholesterol levels in serum as the primary outcome measure. Atorvastatin, but not placebo, reduced serum 27-hydroxycholesterol from 853 ng/ml [interquartile range (IQR) 683-1113] to 641 (IQR 507-694) (-31.5%, P = 0.001, Mann-Whitney U-test). Similarly, 25-hydroxycholesterol levels in serum were reduced. In cerebrospinal fluid 27-hydroxycholesterol was reduced by 8.4% but this did not significantly differ from placebo. As expected, no effects were seen on clinical outcome parameters in this short-term trial. In this study, we define the mutational and phenotypic spectrum of SPG5, examine the correlation of disease severity and progression with oxysterol concentrations, and demonstrate in a randomized controlled trial that atorvastatin treatment can effectively lower 27-hydroxycholesterol levels in serum of SPG5 patients. We thus demonstrate the first causal treatment strategy in hereditary spastic paraplegia.

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.

27-hydroxycholesterol: A novel player in molecular carcinogenesis of breast and prostate cancer

Several studies have suggested an etiological role for hypercholesterolemia in the pathogenesis of breast cancer and prostate cancer (PCa). However, the molecular mechanisms that underlie and mediate the hypercholesterolemia-fostered increased risk for breast cancer and PCa are yet to be determined. The discovery that the most abundant cholesterol oxidized metabolite in the plasma, 27 hydroxycholesterol (27-OHC), is a selective estrogen receptor modulator (SERM) and an agonist of Liver X receptors (LXR) partially fills the void in our understanding and knowledge of the mechanisms that may link hypercholesterolemia to development and progression of breast cancer and PCa. The wide spectrum and repertoire of SERM and LXR-dependent effects of 27-OHC in the context of all facets and aspects of breast cancer and prostate cancer biology are reviewed in this manuscript in a very comprehensive manner. This review highlights recent findings pertaining to the role of 27-OHC in breast cancer and PCa and delineates the signaling mechanisms involved in the governing of different facets of tumor biology, that include tumor cell proliferation, epithelial-mesenchymal transition (EMT), as well as tumor cell invasion, migration, and metastasis. We also discuss the limitations of contemporary studies and lack of our comprehension of the entire gamut of effects exerted by 27-OHC that may be relevant to the pathogenesis of breast cancer and PCa. We unveil and propose potential future directions of research that may further our understanding of the role of 27-OHC in breast cancer and PCa and help design therapeutic interventions against endocrine therapy-resistant breast cancer and PCa.

Contribution of cholesterol and oxysterols to the pathophysiology of Parkinson's disease

Neurodegenerative diseases are a major public health issue worldwide. Some countries, including France, have engaged in research into the causes of Parkinson's disease, Alzheimer's disease, and multiple sclerosis and the management of these patients. It should lead to a better understanding of the mechanisms leading to these diseases including the possible involvement of lipids in their pathogenesis. Parkinson's disease is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra and the accumulation of α-synuclein (Lewy bodies). Several in vivo studies have shown a relationship between the lipid profile [cholesterol, oxidized cholesterol products (oxysterols) formed either enzymatically or by auto-oxidation], the use of drugs regulating cholesterol levels, and the development of Parkinson's disease. Several oxysterols are present in the brain and could play a role in the development of this disease, particularly in the accumulation of α-synuclein, and through various side effects, such as oxidation, inflammation, and cell death. Consequently, in Parkinson's disease, some oxysterols could contribute to the pathophysiology of the disease and constitute potential biomarkers or therapeutic targets.

Comparative aspects of neurosteroidogenesis: From fish to mammals

It is now clearly established that the central and peripheral nervous systems have the ability to synthesize de novo steroids referred to as neurosteroids. The major evidence for biosynthesis of neuroactive steroids by nervous tissues is based on the expression of enzymes implicated in the formation of steroids in neural cells. The aim of the present review is to summarize the current knowledge regarding the presence of steroidogenic enzymes in the brain of vertebrates and to highlight the very considerable contribution of Professor Kazuyoshi Tsutsui in this domain. The data indicate that expression of steroid-producing enzymes in the brain appeared early during vertebrate evolution and has been preserved from fish to mammals.

7α-Hydroxypregnenolone, a key neuronal modulator of locomotion, stimulates upstream migration by means of the dopaminergic system in salmon

Salmon migrate upstream against an opposing current in their natal river. However, the molecular mechanisms that stimulate upstream migratory behavior are poorly understood. Here, we show that 7α-hydroxypregnenolone (7α-OH PREG), a newly identified neuronal modulator of locomotion, acts as a key factor for upstream migration in salmon. We first identified 7α-OH PREG and cytochrome P450 7α-hydroxylase (P450_7α), a steroidogenic enzyme producing 7α-OH PREG, in the salmon brain and then found that 7α-OH PREG synthesis in the brain increases during upstream migration. Subsequently, we demonstrated that 7α-OH PREG increases upstream migratory behavior of salmon. We further found that 7α-OH PREG acts on dopamine neurons in the magnocellular preoptic nucleus during upstream migration. Thus, 7α-OH PREG stimulates upstream migratory behavior through the dopaminergic system in salmon. These findings provide new insights into the molecular mechanisms of fish upstream migration.

CYP7B1 Enzyme Deletion Impairs Reproductive Behaviors in Male Mice

In addition to androgenic properties mediated via androgen receptors, dihydrotestosterone (DHT) also regulates estrogenic functions via an alternate pathway. These estrogenic functions of DHT are mediated by its metabolite 5α-androstane-3β, 17β-diol (3β-diol) binding to estrogen receptor β (ERβ). CYP7B1 enzyme converts 3β-diol to inactive 6α- or 7α-triols and plays an important role as a regulator of estrogenic functions mediated by 3β-diol. Using a mutant mouse carrying a null mutation for the CYP7B1 gene (CYP7B1KO), we examined the contribution of CYP7B1 on physiology and behavior. Male, gonadectomized (GDX) CYP7B1KO and their wild type (WT) littermates were assessed for their behavioral phenotype, anxiety-related behavioral measures, and hypothalamic pituitary adrenal axis reactivity. No significant effects of genotype were evident in anxiety-like behaviors in open field (OFA), light-dark (L/D) exploration, and elevated plus maze (EPM). T significantly reduced open arm time on the EPM while not affecting L/D exploratory and OFA behaviors in CYP7B1KO and WT littermates. T also attenuated the corticosterone response to EPM in both genotypes. In GDX animals, T was able to reinstate male-specific reproductive behaviors (latencies and number of mounts, intromission, and ejaculations) in the WT but not in the CYP7B1KO mice. The male reproductive behavior defect in CYP7B1KO seems to be due to their inability to distinguish olfactory cues from a behavioral estrus female. CYP7B1KO mice also showed a reduction in androgen receptor mRNA expression in the olfactory bulb. Our findings suggest a novel role for the CYP7B1 enzyme in the regulation of male reproductive behaviors.

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.

The interaction between metabolism, cancer and cardiovascular disease, connected by 27-hydroxycholesterol

Oxysterols are metabolites of cholesterol that are produced in liver and other peripheral tissues as a means to eliminate cholesterol to bile acid. Recent studies have revealed that the most abundant circulating oxysterol 27-hydroxycholesterol (27HC) is the first identified endogenous selective estrogen receptor modulator. 27HC levels correlate well with that of cholesterol, and also rise progressively with age. 27HC affects estrogen receptor function by the antagonism of estrogen action and also by the direct modulation of the receptor function, and similar to estrogen/estrogen receptors, 27HC has many actions in various tissues. This review article introduces the recent progress in the understanding of the role of 27HC in breast cancer and cardiovascular dysfunction.

Brain and pineal 7α-hydroxypregnenolone stimulating locomotor activity: identification, mode of action and regulation of biosynthesis

Biologically active steroids synthesized in the central and peripheral nervous systems are termed neurosteroids. However, the biosynthetic pathways leading to the formation of neurosteroids are still incompletely elucidated. 7α-Hydroxypregnenolone, a novel bioactive neurosteroid stimulating locomotor activity, has been recently identified in the brain of newts and quail. Subsequently, the mode of action and regulation of biosynthesis of 7α-hydroxypregnenolone have been determined. Moreover, recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity in juvenile chickens, connecting light-induced gene expression with locomotion. This review summarizes the advances in our understanding of the identification, mode of action and regulation of biosynthesis of brain and pineal 7α-hydroxypregnenolone, a potent stimulator of locomotor activity.

Cytochromes p450: roles in diseases

The cytochrome P450 superfamily consists of a large number of heme-containing monooxygenases. Many human P450s metabolize drugs used to treat human diseases. Others are necessary for synthesis of endogenous compounds essential for human physiology. In some instances, alterations in specific P450s affect the biological processes that they mediate and lead to a disease. In this minireview, we describe medically significant human P450s (from families 2, 4, 7, 11, 17, 19, 21, 24, 27, 46, and 51) and the diseases associated with these P450s.

7-Dehydrocholesterol-derived oxysterols and retinal degeneration in a rat model of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a recessive disease characterized by markedly elevated levels of 7-dehydrocholesterol (7-DHC) and reduced levels of cholesterol in tissues and fluids of affected individuals, due to defective 3β-hydroxysterol-Δ(7)-reductase (Dhcr7). Treatment of Sprague Dawley rats with AY9944 (an inhibitor of Dhcr7) leads to similar biochemical features as observed in SLOS. Eighteen oxysterols previously have been identified as oxidation products of 7-DHC (most of them distinct from cholesterol (Chol)-derived oxysterols) in solution, in cells, and in brains obtained from Dhcr7-KO mice and AY9944-treated rats, formed either via free radical oxidation (peroxidation) or P450-catalyzed enzymatic oxidation. We report here the identification of five 7-DHC-derived oxysterols, including 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), 4α- and 4β-hydroxy-7-DHC, 24-hydroxy-7-DHC and 7-ketocholesterol (7-kChol, an oxysterol that is normally derived from Chol), in the retinas of AY9944-treated rats by comparing the retention times and mass spectrometric characteristics with corresponding synthetic standards in HPLC-MS analysis. Levels of 4α- and 4β-hydroxy-7-DHC, DHCEO, and 7-kChol were quantified using d(7)-DHCEO as an internal standard. Among the five oxysterols identified, only 7-kChol was observed in retinas of control rats, but the levels of 7-kChol in retinas of AY9944-rats were 30-fold higher. Intravitreal injection of 7-kChol (0.25μmol) into a normal rat eye induced panretinal degeneration within one week; by comparison, contralateral (control) eyes injected with vehicle alone exhibited normal histology. These findings are discussed in the context of the potential involvement of 7-DHC-derived oxysterols in the retinal degeneration associated with the SLOS rat model and in SLOS patients.

Endogenous synthesis of corticosteroids in the hippocampus

BACKGROUND

Brain synthesis of steroids including sex-steroids is attracting much attention. The endogenous synthesis of corticosteroids in the hippocampus, however, has been doubted because of the inability to detect deoxycorticosterone (DOC) synthase, cytochrome P450(c21).

METHODOLOGY/PRINCIPAL FINDINGS

The expression of P450(c21) was demonstrated using mRNA analysis and immmunogold electron microscopic analysis in the adult male rat hippocampus. DOC production from progesterone (PROG) was demonstrated by metabolism analysis of (3)H-steroids. All the enzymes required for corticosteroid synthesis including P450(c21), P450(2D4), P450(11β1) and 3β-hydroxysteroid dehydrogenase (3β-HSD) were localized in the hippocampal principal neurons as shown via in situ hybridization and immunoelectron microscopic analysis. Accurate corticosteroid concentrations in rat hippocampus were determined by liquid chromatography-tandem mass spectrometry. In adrenalectomized rats, net hippocampus-synthesized corticosterone (CORT) and DOC were determined to 6.9 and 5.8 nM, respectively. Enhanced spinogenesis was observed in the hippocampus following application of low nanomolar (10 nM) doses of CORT for 1 h.

CONCLUSIONS/SIGNIFICANCE

These results imply the complete pathway of corticosteroid synthesis of 'pregnenolone →PROG→DOC→CORT' in the hippocampal neurons. Both P450(c21) and P450(2D4) can catalyze conversion of PROG to DOC. The low nanomolar level of CORT synthesized in hippocampal neurons may play a role in modulation of synaptic plasticity, in contrast to the stress effects by micromolar CORT from adrenal glands.

Neurosteroid biosynthesis in the brain of amphibians

Amphibians have been widely used to investigate the synthesis of biologically active steroids in the brain and the regulation of neurosteroid production by neurotransmitters and neuropeptides. The aim of the present review is to summarize the current knowledge regarding the neuroanatomical distribution and biochemical activity of steroidogenic enzymes in the brain of anurans and urodeles. The data accumulated over the past two decades demonstrate that discrete populations of neurons and/or glial cells in the frog and newt brains express the major steroidogenic enzymes and are able to synthesize de novo a number of neurosteroids from cholesterol/pregnenolone. Since neurosteroidogenesis has been conserved during evolution from amphibians to mammals, it appears that neurosteroids must play important physiological functions in the central nervous system of vertebrates.

ERbeta: recent understanding of estrogen signaling

The discovery of a second estrogen receptor, ERbeta, and the finding that 5alpha-androstane-3beta,17beta-diol (3betaAdiol) strongly binds to ERbeta, have opened up a new aspect of estrogen signaling. Some of the major shifts in our understanding come from finding ERbeta in tissues which do not express ERalpha but are estrogen-responsive; these were called sites of 'indirect estrogen action'. Two key sites that fall into this category are the brain and the prostate. Studies of ERbeta in the past 10 years have led us to hypothesize that estrogen signaling depends on the balance between ERalpha and ERbeta, and that inadequate predominance of one or the other isoform could lead to disease.

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.

Prolactin increases the synthesis of 7alpha-hydroxypregnenolone, a key factor for induction of locomotor activity, in breeding male Newts

We recently found that the Japanese red-bellied newt, Cynops pyrrhogaster, actively produces 7alpha-hydroxypregnenolone, a previously undescribed amphibian neurosteroid. 7alpha-Hydroxypregnenolone stimulates locomotor activity of male newts. Locomotor activity of male newts increases during the breeding period as in other wild animals, but the molecular mechanism for such a change in locomotor activity is poorly understood. Here we show that the adenohypophyseal hormone prolactin (PRL) stimulates 7alpha-hydroxypregnenolone synthesis in the brain, thus increasing locomotor activity of breeding male newts. In this study, cytochrome P450(7alpha) (CYP7B), a steroidogenic enzyme catalyzing the formation of 7alpha-hydroxypregnenolone, was first identified to analyze seasonal changes in 7alpha-hydroxypregnenolone synthesis. Only males exhibited marked seasonal changes in 7alpha-hydroxypregnenolone synthesis and CYP7B expression in the brain, with a maximum level in the spring breeding period when locomotor activity of males increases. Subsequently we identified PRL as a key component of the mechanism regulating 7alpha-hydroxypregnenolone synthesis. Hypophysectomy decreased 7alpha-hydroxypregnenolone synthesis in the male brain, whereas administration of PRL but not gonadotropins to hypophysectomized males caused a dose-dependent increase in 7alpha-hydroxypregnenolone synthesis. To analyze the mode of PRL action, CYP7B and the receptor for PRL were localized in the male brain. PRL receptor was expressed in the neurons expressing CYP7B in the magnocellular preoptic nucleus. Thus, PRL appears to act directly on neurosteroidogenic magnocellular preoptic nucleus neurons to regulate 7alpha-hydroxypregnenolone synthesis, thus inducing seasonal locomotor changes in male newts. This is the first report describing the regulation of neurosteroidogenesis in the brain by an adenohypophyseal hormone in any vertebrate.

Sumoylated PPARalpha mediates sex-specific gene repression and protects the liver from estrogen-induced toxicity in mice

As most metabolic studies are conducted in male animals, understanding the sex specificity of the underlying molecular pathways has been broadly neglected; for example, whether PPARs elicit sex-dependent responses has not been determined. Here we show that in mice, PPARalpha has broad female-dependent repressive actions on hepatic genes involved in steroid metabolism and immunity. In male mice, this effect was reproduced by the administration of a synthetic PPARalpha ligand. Using the steroid oxysterol 7alpha-hydroxylase cytochrome P4507b1 (Cyp7b1) gene as a model, we elucidated the molecular mechanism of this sex-specific PPARalpha-dependent repression. Initial sumoylation of the ligand-binding domain of PPARalpha triggered the interaction of PPARalpha with GA-binding protein alpha (GABPalpha) bound to the target Cyp7b1 promoter. Histone deacetylase and DNA and histone methylases were then recruited, and the adjacent Sp1-binding site and histones were methylated. These events resulted in loss of Sp1-stimulated expression and thus downregulation of Cyp7b1. Physiologically, this repression conferred on female mice protection against estrogen-induced intrahepatic cholestasis, the most common hepatic disease during pregnancy, suggesting a therapeutic target for prevention of this disease.

Cerebrospinal fluid steroidomics: are bioactive bile acids present in brain?

In this study we have profiled the free sterol content of cerebrospinal fluid by a combination of charge tagging and liquid chromatography-tandem mass spectrometry. Surprisingly, the most abundant cholesterol metabolites were found to be C(27) and C(24) intermediates of the bile acid biosynthetic pathways with structures corresponding to 7alpha-hydroxy-3-oxocholest-4-en-26-oic acid (7.170 +/- 2.826 ng/ml, mean +/- S.D., six subjects), 3beta-hydroxycholest-5-en-26-oic acid (0.416 +/- 0.193 ng/ml), 7alpha,x-dihydroxy-3-oxocholest-4-en-26-oic acid (1.330 +/- 0.543 ng/ml), and 7alpha-hydroxy-3-oxochol-4-en-24-oic acid (0.172 +/- 0.085 ng/ml), and the C(26) sterol 7alpha-hydroxy-26-norcholest-4-ene-3,x-dione (0.204 +/- 0.083 ng/ml), where x is an oxygen atom either on the CD rings or more likely on the C-17 side chain. The ability of intermediates of the bile acid biosynthetic pathways to activate the liver X receptors (LXRs) and the farnesoid X receptor was also evaluated. The acidic cholesterol metabolites 3beta-hydroxycholest-5-en-26-oic acid and 3beta,7alpha-dihydroxycholest-5-en-26-oic acid were found to activate LXR in a luciferase assay, but the major metabolite identified in this study, i.e. 7alpha-hydroxy-3-oxocholest-4-en-26-oic acid, was not an LXR ligand. 7Alpha-hydroxy-3-oxocholest-4-en-26-oic acid is formed from 3beta,7alpha-dihydroxycholest-5-en-26-oic acid in a reaction catalyzed by 3beta-hydroxy-Delta(5)-C(27)-steroid dehydrogenase (HSD3B7), which may thus represent a deactivation pathway of LXR ligands in brain. Significantly, LXR activation has been found to reduce the symptoms of Alzheimer disease (Fan, J., Donkin, J., and Wellington C. (2009) Biofactors 35, 239-248); thus, cholesterol metabolites may play an important role in the etiology of Alzheimer disease.

CYP7B1: one cytochrome P450, two human genetic diseases, and multiple physiological functions

The CYP7B1 cytochrome P450 enzyme hydroxylates carbons 6 and 7 of the B ring of oxysterols and steroids. Hydroxylation reduces the biological activity of these substrates and facilitates their conversion to end products that are readily excreted from the body. CYP7B1 is expressed in the liver, reproductive tract, and brain and performs different physiological functions in each tissue. Hepatic CYP7B1 activity is crucial for the inactivation of oxysterols and their subsequent conversion into bile salts. Loss of CYP7B1 activity is associated with liver failure in children. In the reproductive tract, the enzyme metabolizes androgens that antagonize estrogen action; mice without CYP7B1 have abnormal prostates and ovaries. The role of CYP7B1 in brain is under investigation; recent studies show that spastic paraplegia type 5, a progressive neuropathy, is caused by loss-of-function mutations in the human gene.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Two novel CYP7B1 mutations in Italian families with SPG5: a clinical and genetic study

Hereditary spastic paraplegias (HSPs) are a heterogeneous group of neurodegenerative disorders characterized by progressive weakness and spasticity in the lower limbs. Spasticity may occur in isolation (''pure'' HSP) or may be accompanied by other features. Although autosomal recessive HSPs usually have clinically complex phenotypes, mutations within a few genes underlie pure forms. Recently the gene (CYP7B1) responsible for SPG5, a pure recessive HSP, has been identified. The six CYP7B1 coding exons were analysed in four Italian families. Complete clinical assessment was performed in all patients. Blood CYP7B1 mRNA levels were assessed in three patients and six controls. Brain MRI and (18)F-fluoro-deoxy-glucose positron emission tomography (PET) scan were conducted in three patients. Two novel homozygous mutations were identified. Both result in a frameshift and the introduction of a premature stop codon at the C-terminal of the protein. Patients have reduced blood CYP7B1 mRNA levels, suggesting nonsense mediated RNA decay. Although clinical assessment showed a pure form of spastic paraplegia, MRI demonstrated white matter abnormalities in three patients and PET scan revealed cerebellar hypometabolism in one. Based on the results, we report the first Italian families with SPG5 molecular characterization and describe two novel truncating mutations in CYP7B1. The recessive character, the truncating nature of the mutations, and the reduced peripheral blood CYP7B1 mRNA levels suggest that the development of the disease is associated with a loss of function. SPG5 is considered a pure form of HSP, but MRI and PET findings in our patients suggest that SPG5 phenotype may be broader than the pure presentation.

Discovering oxysterols in plasma: a window on the metabolome

While the proteome defines the expressed gene products, the metabolome results from reactions controlled by such gene products. Plasma represents an accessible "window" to the metabolome both in regard of availability and content. The wide range of the plasma metabolome, in terms of molecular diversity and abundance, makes its comprehensive analysis challenging. Here we demonstrate an analytical method designed to target one region of the metabolome, that is, oxysterols. Since the discovery of their biological activity as ligands to nuclear receptors there has been a reawakening of interest in oxysterols and their analysis. In addition, the oxysterols, 24S- and 27-hydroxycholesterol, are currently under investigation as potential biomarkers associated with neurodegenerative disorders such as Alzheimer's disease and multiple sclerosis; widespread analysis of these lipids in clinical studies will require the development of robust, sensitive and rapid analytical techniques. In this communication we present results of an investigation of the oxysterols content of human plasma using a newly developed high-performance liquid chromatography-mass spectrometry (HPLC-MS) method incorporating charge-tagging and high-resolution MS. The method has allowed the identification in plasma of monohydroxylated cholesterol molecules, 7alpha-, 24S-, and 27-hydroxycholesterol; the cholestenetriol 7alpha,27-dihydroxycholesterol; and 3beta-hydroxycholest-5-en-27-oic acid and its metabolite 3beta,7alpha-dihydroxycholest-5-en-27-oic acid. The methodology described is also applicable for the analysis of other sterols in plasma, that is, cholesterol, 7-dehydrocholesterol, and desmosterol, as well as cholesterol 5,6- seco-sterols and steroid hormones. Although involving derivatization, sample preparation is straightforward and chromatographic analysis rapid (17 min), while the MS method offers high sensitivity (ng/mL of sterol in plasma, or pg on-column) and specificity. The methodology is suitable for targeted metabolomic analysis of sterols, oxysterols, and steroid hormones opening a "window" to view this region of the metabolome.

7Alpha-hydroxypregnenolone mediates melatonin action underlying diurnal locomotor rhythms

Melatonin regulates diurnal changes in locomotor activity in vertebrates, but the molecular mechanism for this neurohormonal regulation of behavior is poorly understood. Here we show that 7alpha-hydroxypregnenolone, a previously undescribed avian neurosteroid, mediates melatonin action on diurnal locomotor rhythms in quail. In this study, we first identified 7alpha-hydroxypregnenolone and its stereoisomer 7beta-hydroxypregnenolone in quail brain. These neurosteroids have not been described previously in avian brain. We then demonstrated that 7alpha-hydroxypregnenolone acutely increased quail locomotor activity. To analyze the production of 7alpha-hydroxypregnenolone, cytochrome P450(7alpha), a steroidogenic enzyme of this neurosteroid, was also identified. Subsequently, we demonstrated diurnal changes in 7alpha-hydroxypregnenolone synthesis in quail. 7Alpha-Hydroxypregnenolone synthesis and locomotor activity in males were much higher than in females. This is the first demonstration in any vertebrate of a clear sex difference in neurosteroid synthesis. This sex difference in 7alpha-hydroxypregnenolone synthesis corresponded to the sex difference in locomotion. We show that only males exhibited marked diurnal changes in 7alpha-hydroxypregnenolone synthesis, and these changes occurred in parallel with changes in locomotor activity. Finally, we identified melatonin as a key component of the mechanism regulating 7alpha-hydroxypregnenolone synthesis. Increased synthesis of 7alpha-hydroxypregnenolone occurred in males in vivo after melatonin removal via pinealectomy and orbital enucleation (Px plus Ex). Conversely, decreased synthesis of this neurosteroid occurred after melatonin administration to Px plus Ex males. This study demonstrates that melatonin regulates synthesis of 7alpha-hydroxypregnenolone, a key factor for induction of locomotor activity, thus inducing diurnal locomotor changes in male birds. This is a previously undescribed role for melatonin.

Neonatal dietary cholesterol and alleles of cholesterol 7-alpha hydroxylase affect piglet cerebrum weight, cholesterol concentration, and behavior

This experiment was designed to test the effect of polymorphism in the cholesterol 7-alpha hydroxylase (CYP7) gene locus and dietary cholesterol (C) on cerebrum C in neonatal pigs fed sow's milk formulas. Thirty-six pigs (18 male and 18 female) genetically selected for high (HG) or low (LG) plasma total C were weaned at 24-36 h after birth and assigned in a 2 x 2 x 2 factorial arrangement of treatments with 2 diets (0 or 0.5% C), 2 sexes, and 2 genotypes (HG and LG). Individually housed pigs consumed diets ad libitum for 42 d. Open-field behavior was tested at wk 2 and 4. All pigs were killed at 42 d of age, the cerebrum was weighed, and C content and concentration measured. All data were analyzed by general linear model ANOVA. Cerebrum weight was greater in HG than LG pigs (P < 0.03) but was not affected by diet or sex. Pigs fed C tended to have a higher cerebrum C concentration than those deprived (P = 0.12). At 2 wk, LG pigs explored a novel open-field environment less often (P < 0.001) than did HG pigs. At 4 wk, some LG pigs explored the open field but fewer (P < 0.001) vs. HG pigs retreated back to the safe area. There were no genotype x diet, genotype x sex, or diet x sex interactions affecting cerebrum weight, or C content or concentration. Polymorphism in the CYP7 gene locus affected cerebrum weight and behavior and dietary C tended to increase cerebrum C concentration in neonatal pigs. These findings in neonatal pigs have considerable potential importance in human infant nutrition and behavioral development.

Liquid chromatography-mass spectrometry utilizing multi-stage fragmentation for the identification of oxysterols

In humans, the brain accounts for about 20% of the body's free cholesterol, most of which is synthesized de novo in brain. To maintain cholesterol balance throughout life, cholesterol becomes metabolized to 24S-hydroxycholesterol, principally in neurons. In mouse, rat, and probably human, metabolism to 24S-hydroxycholesterol accounts for about 50% of cholesterol turnover; however, the route by which the remainder is turned over has yet to be elucidated. Here, we describe a novel liquid chromatography (LC) multi-stage fragmentation mass spectrometry (MS(n)) methodology for the identification, with high sensitivity (low pg), of cholesterol metabolites in rat brain. The methodology includes derivatization to enhance ionization, exact mass analysis at high resolution to identify potential metabolites, and LC-MS(n) (n=3) to allow their characterization. 24S-hydroxycholesterol was confirmed as a major oxysterol in rat brain, and other oxysterols identified for the first time in brain included 24,25-, 24,27-, 25,27-, 6,24,- 7alpha,25-, and 7alpha,27-dihydroxycholesterols. In addition, 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al and its aldol, two molecules linked to amyloidogenesis of proteins, were characterized in rat brain.

Cytochrome P450s and cholesterol homeostasis

By participating in pathways of cholesterol biosynthesis and elimination, different cytochrome P450 (P450 or CYP) enzymes play an important role in maintenance of cholesterol homeostasis. CYP51 is involved in cholesterol biosynthesis, whereas CYP 7A1, 27A1, 46A1, 7B1, 39A1, and 8B1 are the key enzymes in cholesterol catabolism to bile acids, the major route of cholesterol elimination in mammals. Cholesterol transformations to steroid hormones are also initiated by the P450 enzyme CYP11A1. Finally, one of the major drug-metabolizing P450s CYP3A4 seems to contribute to bile acid biosynthesis as well. The 9 P450s will be the focus of this review and assessed as drug targets for cholesterol lowering.

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.

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.

The value of alternative testing for neurotoxicity in the context of regulatory needs

Detection and characterisation of chemical-induced toxic effects in the central and peripheral nervous system represent a major challenge for employing newly developed technologies in the field of neurotoxicology. Precise cellular predictive test batteries for chemical-induced neurotoxicity are increasingly important for regulatory decision making, but also the most efficient way to keep costs and time of testing within a reasonable margin. Current in vivo test methods are based on behavioural and sensory perturbations coupled with routine histopathological investigations. In spite of the empirical usefulness of these tests, they are not always sensitive enough and often, they do not provide information that facilitates a detailed understanding of potential mechanisms of toxicity, thus enabling predictions. In general, such in vivo tests are unsuitable for screening large number of agents. One way to meet the need for more powerful and comprehensive tests via an extended scientific basis is to study neurotoxicity in specific cell types of the brain and to derive generalised mechanisms of action of the toxicants from such series of experiments. Additionally, toxicokinetic models are to be developed in order to give a rough account for the whole absorption, distribution, metabolism, excretion (ADME) process including the blood-brain barrier (BBB). Therefore, an intensive search for the development of alternative methods using animal and human-based in vitro and in silico models for neurotoxic hazard assessment is appropriate. In particular, neurotoxicology represents one of the major challenges to the development of in vitro systems, as it has to account also for heterogeneous cell interactions of the brain which require new biochemical, biotechnological and electrophysiological profiling methods for reliable alternative ways with a high throughput.

Codependence of growth hormone-responsive, sexually dimorphic hepatic gene expression on signal transducer and activator of transcription 5b and hepatic nuclear factor 4alpha

Targeted disruption of the signal transducer and activator of transcription 5b gene (STAT5b) leads to decreased expression in male mouse liver of a male-predominant cytochrome (Cyp) 2d protein, whereas female-predominant Cyp2b proteins are increased. Presently, we characterize the effects of STAT5b deficiency on 15 specific, individual Cyp RNAs and other sexually dimorphic liver gene products. All seven male-specific RNAs investigated were decreased to normal female levels in STAT5b-deficient male liver, whereas five of eight female-specific RNAs, designated class I female genes, were increased in expression up to 200-fold or more. STAT5b deficiency had a much more modest effect on the expression of these genes in females. Hypophysectomy and GH replacement studies demonstrated positive GH pulse regulation of all seven male RNAs and negative GH pulse regulation of class I, but not class II, female RNAs in wild-type, but not in STAT5b-deficient, male mice. A majority of the sex-specific genes responded in parallel to the loss of STAT5b and the loss of hepatocyte nuclear factor 4alpha, indicating that both transcription factors are essential and suggesting they may coregulate sexually dimorphic liver gene expression. Continuous GH treatment of intact male mice, which overrides the endogenous male, pulsatile plasma GH pattern, down-regulated all seven male RNAs and induced expression of the five class I female RNAs within 4-7 d; however, induction of class II female RNAs was delayed until d 7-14. Given the slow responses of all 15 genes to changes in plasma GH status, GH regulation of sex-specific Cyp expression is proposed to be indirect and mediated by STAT5b- and hepatocyte nuclear factor 4alpha-dependent factors that may include repressors of female-specific Cyps and other targets of GH action.

CYP7B expression and activity in fibroblast-like synoviocytes from patients with rheumatoid arthritis: regulation by proinflammatory cytokines

OBJECTIVE

The cytochrome P450 enzyme CYP7B catalyzes the conversion of dehydroepiandrosterone (DHEA) into 7alpha-hydroxy-DHEA (7alpha-OH-DHEA). This metabolite can stimulate the immune response. We previously reported that the severity of murine collagen-induced arthritis is correlated with CYP7B messenger RNA (mRNA) expression and activity in the arthritic joint. The purpose of this study was to investigate the presence of 7alpha-OH-DHEA in synovial samples and the cytokine regulation of CYP7B activity in fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA).

METHODS

The presence of 7alpha-OH-DHEA was examined in synovial biopsy tissues, synovial fluid, and serum by radioimmunoassay. The effect of cytokines on CYP7B mRNA expression and CYP7B activity in FLS was examined by determining the formation of the CYP7B enzyme product 7alpha-OH-DHEA with the use of high-performance liquid chromatography.

RESULTS

The CYP7B enzyme product 7alpha-OH-DHEA was found in synovial biopsy tissues, synovial fluid, and serum from RA patients. The proinflammatory cytokines tumor necrosis factor alpha (TNFalpha), interleukin-1alpha (IL-1alpha), IL-1beta, and IL-17 up-regulated CYP7B activity in an FLS cell line 2-10-fold. Enhanced CYP7B activity was correlated with an increase in CYP7B mRNA. The cytokine transforming growth factor beta inhibited CYP7B activity. Moreover, CYP7B activity was detected in 10 of 13 unstimulated synovial fibroblast cell lines. Stimulation with TNFalpha increased CYP7B activity in all cell lines tested.

CONCLUSION

Exposure to the proinflammatory cytokines TNFalpha, IL-1alpha, IL-1beta, and IL-17 increases CYP7B activity in synovial tissue. Increased CYP7B activity leads to higher levels of the DHEA metabolite 7alpha-OH-DHEA in synovial fluid, which may contribute to the maintenance of the chronic inflammation observed in RA patients.

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.

Crossing the barrier: net flux of 27-hydroxycholesterol into the human brain

Side chain oxidized oxysterols have a unique ability to traverse lipophilic membranes. We tested the hypothesis that there is a net flux of 27-hydroxycholesterol from the circulation into the brain using plasma samples collected from the internal jugular vein and an artery of healthy male volunteers. Two independent studies were performed, one in which total levels of 27-hydroxycholesterol were measured and one in which the free fraction of 27-hydroxycholesterol was measured. In the majority of subjects studied, the level of 27-hydroxycholesterol was higher in the artery than in the vein, and uptake from the circulation was calculated to be about 5 mg/24 h. The distribution of 27-hydroxycholesterol in human brain was found to be consistent with an extracerebral origin, with a concentration gradient from the white to the gray matter--a situation opposite that of 24S-hydroxycholesterol, which os exclusively formed in brain. In view of the fact that the blood-brain barrier is impermeable to cholesterol and that 27-hydroxycholesterol is a potent regulator of several cholesterol-sensitive genes, the flux of 27-hydroxycholesterol into the brain may be and important link between intra- and extracerebral cholesterol homeostasis.

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.

C19‐5‐ene Steroids in Nature

Dehydroepiandrosterone (DHEA), produced from cholesterol in the adrenals, is the most abundant steroid in our circulation. It is present almost entirely as the sulfate ester, but the free steroid is the form that serves as a precursor of estrogens and androgens, as well as 7- and 16-oxygenated derivatives. Mammalian tissues reduce the 17-keto Group of DHEA to produce androstenediol-a weak estrogen and full-fledged androgen. Its androgen activity is not inhibited by the anti-androgens commonly used to treat prostate cancer. It is probably responsible for the growth of therapy-resistant prostate cancer. DHEA is hydroxylated at the 7 alpha position, and this derivative is oxidized by 11 beta-hydroxysteroid dehydrogenase to form 7-keto DHEA. The latter is reduced by the same dehydrogenase to form 7 beta-hydroxy DHEA. When fed to rats, each of the latter three steroids induce the formation of two thermogenic enzymes in the liver. The late-term human fetus produces relatively large amounts of 16 alphahydroxy DHEA, which serves the mother as a precursor of estriol.

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.