Showing papers on "Pregnenolone published in 2006"
TL;DR: Investigating neuroactive steroid levels in post-mortem brain tissue from subjects with schizophrenia, bipolar disorder, nonpsychotic depression, and control subjects to determine if neuroactive steroids are altered in these disorders found them to be candidate modulators of the pathophysiology of schizophrenia and bipolar disorder and relevant to the treatment of these disorders.
159 citations
TL;DR: The detection limit and selectivity of this method and its small sample volume requirement allow analysis of endogenous concentrations of adrenal steroids in serum or plasma from children and adults and has an important potential role in the evaluation of the status of 4 of the enzymes involved in adrenal steroid biosynthesis.
Abstract: Background: Congenital adrenal hyperplasia is a group of autosomal recessive disorders caused by a deficiency of 1 of 4 enzymes required for the synthesis of glucocorticoids, mineralocorticoids, and sex hormones. Analysis of 11-deoxycortisol (11DC), 17-hydroxyprogesterone (17OHP), 17-hydroxypregnenolone (17OHPr), and pregnenolone (Pr) in blood allows detection of these enzyme defects.
Methods: The steroids were extracted from 200 μL of serum or plasma by solid-phase extraction, derivatized to form oximes, and extracted again with methyl t -butyl ether. Instrumental analysis was performed on an API 4000 tandem mass spectrometer with electrospray ionization in positive mode and multiple reaction-monitoring acquisition.
Results: The limits of detection were 0.025 μg/L for 11DC, 17OHP, and Pr and 0.10 μg/L for 17OHPr. The method was linear to 100 μg/L for 11DC, 17OHP, and Pr, respectively, and to 40 μg/L for 17OHPr. Within- and between-run (total) imprecision (CVs) were 72 h.
Conclusions: The detection limit and selectivity of this method and its small sample volume requirement allow analysis of endogenous concentrations of adrenal steroids in serum or plasma from children and adults. The method thus has an important potential role in the evaluation of the status of 4 of the enzymes involved in adrenal steroid biosynthesis.
118 citations
TL;DR: The cytochromes P450 (P450s) as mentioned in this paper catalyzes the first steps in different pathways of cholesterol degradation and play key roles in cholesterol homeostasis, catalyzing the first step in cholesterol degradation.
Abstract: By catalyzing the first steps in different pathways of cholesterol
degradation, cytochromes P450 (P450s) 7A1, 27A1, 11A1, and 46A1 play key roles
in cholesterol homeostasis. CYP7A1 is a microsomal liver-specific enzyme that
converts cholesterol to 7α-hydroxycholesterol. CYP27A1 is a ubiquitously
expressed mitochondrial P450 that metabolizes cholesterol to
27-hydroxycholesterol. CYP11A1 also resides in mitochondria but is expressed
mainly in steroidogenic tissues, where it catalyzes the conversion of
cholesterol to pregnenolone. Finally, CYP46A1 is a brain-selective microsomal
monooxygenase producing 24S-hydroxycholesterol from cholesterol.
Catalytic efficiencies of cholesterol-metabolizing P450s vary significantly
and probably reflect physiological requirements of different organs for the
rate of cholesterol turnover. P450s 7A1, 27A1, 11A1, and 46A1 represent a
unique system for elucidation of how different enzymes have adapted to fit
their specific roles in cholesterol elimination. Studies of
cholesterol-metabolizing P450s suggest that their activities could be
modulated post-translationally and that they should also be considered as
targets for regulation of cholesterol homeostasis.
112 citations
TL;DR: Hippocampal pyramidal neurons and granule neurons of adult male rats are equipped with a complete machinery for the synthesis of pregnenolone, dehydroepiandrosterone, testosterone, dihydrotestosterone and 17beta-estradiol, which is particularly important because estradiol rapidly modulates neuronal synaptic transmission such as long-term potentiation via synaptic estrogen receptors.
112 citations
TL;DR: Decreasing MAP2 expression by RNA interference does not modify PROG action, but it prevents the stimulatory effects of PREG and MePREG on neurite extension, showing that MAP2 is their specific receptor.
Abstract: The neurosteroid pregnenolone (PREG) and its chemically synthesized analog 3β-methoxypregnenolone (MePREG) bind to microtubule-associated protein 2 (MAP2) and stimulate the polymerization of microtubules. PREG, MePREG, and progesterone (PROG; the physiological immediate metabolite of PREG) significantly enhance neurite outgrowth of nerve growth factor-pretreated PC12 cells. However, PROG, although it binds to MAP2, does not increase the immunostaining of MAP2, contrary to PREG and MePREG. Nocodazole, a microtubule-disrupting agent, induces a major retraction of neurites in control cultures, but pretreatment with PREG/MePREG is protective. Decreasing MAP2 expression by RNA interference does not modify PROG action, but it prevents the stimulatory effects of PREG and MePREG on neurite extension, showing that MAP2 is their specific receptor.
110 citations
TL;DR: It is reported that pregnenolone, which is produced from cholesterol by the steroidogenic enzyme Cyp11a1 (cholesterol side-chain cleavage enzyme, P450scc), functions in promoting cell migration during epiboly.
Abstract: Embryonic cell movement is essential for morphogenesis and the establishment of body shapes, but little is known about its mechanism. Here we report that pregnenolone, which is produced from cholesterol by the steroidogenic enzyme Cyp11a1 (cholesterol side-chain cleavage enzyme, P450scc), functions in promoting cell migration during epiboly. Epiboly is a process in which embryonic cells spread from the animal pole to cover the underlying yolk. During epiboly, cyp11a1 is expressed in an extra-embryonic yolk syncytial layer. Reducing cyp11a1 expression in zebrafish using antisense morpholino oligonucleotides did not perturb cell fates, but caused epibolic delay. This epibolic defect was partially rescued by the injection of cyp11a1 RNA or the supplementation of pregnenolone. We show that the epibolic delay is accompanied by a decrease in the level of polymerized microtubules, and that pregnenolone can rescue this microtubule defect. Our results indicate that pregnenolone preserves microtubule abundance and promotes cell movement during epiboly.
99 citations
TL;DR: It is reported that responses mediated by recombinant rat N-methyl-D-aspartate receptors expressed in human embryonic kidney HEK293 cells are differentially affected by naturally occurring neurosteroid pregnenolone sulfate, and the structure of the extracellular loop between the third and fourth transmembrane domains of the NR2 subunit is critical for both the potentiating and inhibitory effects of pregnenolate sulfate.
92 citations
TL;DR: Radioimmunoassays showed an increase of PREG and 3α/5α-THP concentrations in neuropathic rat DH, which might be involved in endogenous mechanisms triggered by neuropathic rats to cope with the chronic pain state.
Abstract: The spinal cord (SC) is a biosynthetic center for neurosteroids, including pregnenolone (PREG), progesterone (PROG), and 3alpha/5alpha-tetrahydroprogesterone (3alpha/5alpha-THP). In particular, an active form of cytochrome P450 sidechain cleavage (P450scc) has been localized in sensory networks of the rat SC dorsal horn (DH). P450scc is the key enzyme catalyzing the conversion of cholesterol (CHOL) into PREG, the rate-limiting step in the biosynthesis of all classes of steroids. To determine whether neurosteroidogenesis might be involved in the pivotal role played by the DH in nociception, effects of neurogenic pain provoked by sciatic nerve ligature were investigated on P450scc expression, cellular distribution, and activity in the SC. P450scc mRNA concentration was threefold higher in the DH of neuropathic rats than in controls. The nerve ligature also increased the density of P450sccpositive neuronal perykarya and fibers in the ipsilateral DH. Incubation of spinal tissue homogenates with [3H]CHOL revealed that the amount of newly synthesized [3H]PREG from [3H]CHOLwas 80% higher in the DH of neuropathic rats. Radioimmunoassays showed an increase of PREG and 3alpha/5alpha-THP concentrations in neuropathic rat DH. The upregulation of PREG and 3alpha/5alpha-THP biosynthesis might be involved in endogenous mechanisms triggered by neuropathic rats to cope with the chronic pain state. 3alpha/5alpha-THP formation from PREG can also generate PROG, which decreases sensitivity to pain and protects nerve cells against degeneration. Because apoptotic cell death has been demonstrated in the DH during neuropathic pain, activation of neurosteroidogenesis in spinal tissues might also be correlated to the neuroprotective role of steroids in the SC.
91 citations
TL;DR: This work fractionated free steroids and their sulfate esters and converted them to heptafluorobutyrate or methyloxime-trimethylsilyl ether derivatives and provided a basis for elucidating the origins and regulation of brain steroids.
Abstract: Steroids in the brain arise both from local synthesis and from peripheral sources and have a variety of effects on neuronal function. However, there is little direct chemical evidence for the range of steroids present in brain or of the pathways for their synthesis and inactivation. This information is a prerequisite for understanding the regulation and function of brain steroids. After extraction from adult male rat brain, we have fractionated free steroids and their sulfate esters and then converted them to heptafluorobutyrate or methyloxime-trimethylsilyl ether derivatives for unequivocal identification and assay by gas chromatography analysis and selected ion monitoring mass spectrometry. In the free steroid fraction, corticosterone, 3alpha,5alpha-tetrahydrodeoxycorticosterone, testosterone, and dehydroepiandrosterone were found in the absence of detectable precursors usually found in endocrine glands, indicating peripheral sources and/or alternative synthetic pathways in brain. Conversely, the potent neuroactive steroid 3alpha,5alpha-tetrahydroprogesterone (allopregnanolone) was found in the presence of its precursors pregnenolone, progesterone, and 5alpha-dihydroprogesterone. Furthermore, the presence of 3beta-, 11beta-, 17alpha-, and 20alpha-hydroxylated metabolites of 3alpha,5alpha-tetrahydroprogesterone implicated possible inactivation pathways for this steroid. The 20alpha-reduced metabolites could also be found for pregnenolone, progesterone, and 5alpha-dihydroprogesterone, introducing a possible regulatory diversion from the production of 3alpha,5alpha-tetrahydroprogesterone. In the steroid sulfate fraction, dehydroepiandrostrone sulfate was identified but not pregnenolone sulfate. Although pharmacologically active, identification of the latter appears to be an earlier methodological artifact, and the compound is thus of doubtful physiological significance in the adult brain. Our results provide a basis for elucidating the origins and regulation of brain steroids.
84 citations
TL;DR: The substrate specificity, nuclear localization, and tissue localization of SULT2B1b suggest a role in regulating the responsiveness of cells to adrenal androgens via their direct inactivation or by preventing their conversion to more potent androgens and estrogens.
80 citations
TL;DR: No synergistic effects on pregnenolone or allopregnanolone were observed following olanzapine and fluoxetine coadministration compared to either compound alone, and it is possible that olanZapine- and flu oxetine-induced pregnenolsone elevations may contribute to the antidepressant actions of these agents.
Abstract: Olanzapine and fluoxetine elevate the GABAergic neuroactive steroid allopregnanolone to physiologically relevant concentrations in rodent cerebral cortex. It is unknown if these agents also alter pregnenolone or deoxycorticosterone. Since olanzapine and fluoxetine in combination have clinical utility and may demonstrate synergistic effects, we investigated neuroactive steroid alterations following olanzapine, fluoxetine or coadministration. Male rats received IP vehicle, olanzapine, fluoxetine or the combination of both agents in higher-dose (0, 10, 20 or 10/20 mg/kg, respectively) and lower-dose (0, 5, 10 or 5/10 mg/kg, respectively) experiments. Pregnenolone and allopregnanolone levels in hippocampus were determined by gas chromatography/mass spectrometry. Peripheral deoxycorticosterone and other steroid levels were determined by radioimmunoassay. Olanzapine, fluoxetine or the combination increased hippocampal pregnenolone and serum deoxycorticosterone in both higher- and lower-dose experiments, and elevated hippocampal allopregnanolone in higher-dose conditions. No synergistic effects on pregnenolone or allopregnanolone were observed following olanzapine and fluoxetine coadministration compared to either compound alone. Pregnenolone and its sulfate enhance learning and memory in rodent models, and therefore pregnenolone elevations may be relevant to cognitive changes in psychotic and affective disorders. Since pregnenolone decreases have been linked to depression, it is possible that olanzapine- and fluoxetine-induced pregnenolone elevations may contribute to the antidepressant actions of these agents.
TL;DR: The advances made in the understanding of biosynthesis of neurosteroids in the avian brain are summarized.
Abstract: The brain traditionally has been considered to be a target site of peripheral steroid hormones. In contrast to this classical concept, new findings over the past decade have shown that the brain itself also has the capability of forming steroids de novo, the so-called "neurosteroids". De novo neurosteroidogenesis in the brain from cholesterol is a conserved property of vertebrates. Our studies using the quail, as an excellent animal model, have demonstrated that the avian brain possesses cytochrome P450 side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3beta-HSD), cytochrome P450 17alpha-hydroxylase/c17,20-lyase (P450(17alpha,lyase)), 17beta-HSD, etc., and produces pregnenolone, progesterone, 3beta, 5beta-tetrahydroprogesterone, androstenedione, testosterone and estradiol from cholesterol. However, the biosynthetic pathway of neurosteroids in the avian brain from cholesterol may be still incomplete, because we recently found that the quail brain actively produces 7alpha-hydroxypregnenolone, a previously undescribed avian neurosteroid. This paper summarize the advances made in our understanding of biosynthesis of neurosteroids in the avian brain.
TL;DR: Pregnenolone induction may contribute to the clinical actions of clozapine and olanzapine in patients with schizophrenia and decreases in this NS have been associated with depressive symptoms in humans.
Abstract: Clozapine demonstrates superior efficacy in patients with schizophrenia, but the precise mechanisms contributing to this clinical advantage are not clear. Clozapine and olanzapine increase the GABAergic neuroactive steroid (NS) allopregnanolone, and it has been hypothesized that NS induction may contribute to the therapeutic actions of these agents. Pregnenolone administration improves learning and memory in rodent models, and decreases in this NS have been associated with depressive symptoms in humans. These pregnenolone characteristics may be relevant to the actions of antipsychotics. We therefore investigated potential pregnenolone alterations in rat hippocampus and cerebral cortex following clozapine, olanzapine, and other second generation agents as a candidate NS mechanism contributing to antipsychotic efficacy. In the first set of experiments, intact, adrenalectomized, and sham-operated male rats received vehicle or clozapine (20 mg/kg) IP. In the second set, male rats received vehicle, olanzapine (5 mg/kg), quetiapine (20 mg/kg), ziprasidone (10 mg/kg) or aripiprazole (5 mg/kg) IP. Pregnenolone levels were determined by gas chromatography/mass spectrometry. Clozapine markedly elevates pregnenolone in rat hippocampus, cerebral cortex, and serum; hippocampal levels were strongly correlated with serum levels (r = 0.987). Olanzapine also elevates pregnenolone levels, but to a lesser degree than clozapine. Pregnenolone induction may contribute to the clinical actions of clozapine and olanzapine.
TL;DR: Healthy women without underlying mood or anxiety disorder who were given a low-dose OCP did not experience adverse psychological symptoms despite a significant reduction in neuroactive steroids.
TL;DR: Increased levels of allopregnanolone rather than "endogenous benzodiazepines" offer a cogent explanation for the phenomenon of "increased GABAergic tone" previously proposed in HE.
TL;DR: DHEAS levels were inversely correlated with negative affect and craving measures, and may predict nicotine dependence severity, suggesting that this neuroactive steroid may be upregulated in smokers.
Abstract: Nicotine administration alters neuroactive steroids in rodent models, and serum levels of the neuroactive steroid DHEAS (dehydroepiandrosterone sulfate) appear to be higher in smokers. These molecules may be relevant to tobacco addiction and affective symptoms. This study aims to investigate DHEAS, allopregnanolone, pregnenolone, and other steroids in male smokers to determine potential associations with nicotine dependence severity and negative affect. Allopregnanolone and pregnenolone serum levels were determined by gas chromatography/mass spectrometry, while DHEAS and other steroid levels were determined by radioimmunoassay in 28 male smokers. Correlational analyses were performed to determine potential associations with rating measures, including the Fagerstrom Test for Nicotine Dependence (FTND), the addiction subscale of the Ikard Smoking Motivation Questionnaire (ISMQ), the craving item on the Reasons to Smoke (RTS) Questionnaire, and the negative affect and craving subscales of the Shiffman–Jarvik Withdrawal Questionnaire. DHEAS levels were inversely correlated with the negative affect subscale of the Shiffman–Jarvik Withdrawal Questionnaire (r=−0.60, p=0.002) and the RTS craving item (r=−0.43, p=0.03), and tended to be inversely correlated with the FTND scores (r=−0.38, p=0.067) and the ISMQ addiction subscale (r=−0.38, p=0.059), adjusting for age. Allopregnanolone levels were positively correlated with cotinine levels (r=0.57, p=0.006); pregnenolone levels tended to be positively correlated with cotinine levels (r=0.40, p=0.066). DHEAS levels were inversely correlated with negative affect and craving measures, and may predict nicotine dependence severity. Allopregnanolone levels were positively correlated with cotinine levels, suggesting that this neuroactive steroid may be upregulated in smokers. Neuroactive steroids may represent novel smoking cessation agents.
TL;DR: The overall results indicate that a low-oxygen condition decreases P4 synthesis by attenuating P450scc production and P 450scc activity in bovine luteal cells and suggest that oxygen deficiency is an essential condition for the progression of luteolysis in cattle.
Abstract: Oxygen deficiency caused by a decrease in the blood supply is known to induce various responses of cells. Because luteal blood flow has been shown to decrease during luteolysis, a low-oxygen condition seems to be an integral part of the environment during luteolysis. To determine whether a low-oxygen condition is associated with functional luteolysis, we examined the influence of reduced oxygen tension on the luteal progesterone (P4) generating system in cultured bovine midluteal cells. Luteal cells obtained from midcycle corpus luteum (d 8-12) were incubated under different O2 concentrations (20, 10, 5, 3% O2) with or without LH for 24 h. P4 production decreased with decreasing O2 concentration but was significantly stimulated by LH regardless of O2 concentration. After 8 h of culture, both basal and LH-stimulated P4 production was significantly lower under 3% O2 than under 20% O2. Low-oxygen condition also inhibited pregnenolone production. Cytochrome P450 side-chain cleavage enzyme (P450scc) mRNA expression, measured by quantitative PCR, decreased under low-oxygen condition in both non-LH-treated and LH-treated cells. Low-oxygen condition did not affect the expressions of steroidogenic acute regulatory protein mRNA or protein, whereas steroidogenic acute regulatory protein mRNA expression was stimulated by LH during 4 h of culture. Low-oxygen condition also did not affect 3 beta-hydroxysteroid dehydrogenase/Delta 5-Delta 4 isomerase mRNA expression or the activity of the enzyme in the cells, regardless of the incubation period. The overall results indicate that a low-oxygen condition decreases P4 synthesis by attenuating P450scc production and P450scc activity in bovine luteal cells and suggest that oxygen deficiency is an essential condition for the progression of luteolysis in cattle.
TL;DR: The results indicate that a substantial proportion of the progesterone is metabolized in the sequence progester one-->5beta-dihydroprogesterone-->P3alpha5beta-->conjugated P3alpha 5beta, which suggests a gonadal source of PI in the luteal phase.
Abstract: Background: Pregnanolone isomers (PI) with a hydroxy group in the 3α-position are neuroinhibitors operating via positive modulation of GABAA receptors. The 3β-PI and sulfates of PI and pregnenolone exert the opposite effect. In addition to the brain’s in situ synthesis, some circulating steroids can penetrate the blood-brain barrier. Methods: To assess the physiological impact of peripheral endogenous neuroactive pregnanolone isomers and their polar conjugates in women, serum allopregnanolone (P3α5α), isopregnanolone (P3β5α), pregnanolone (P3α5β), epipregnanolone (P3β5β), pregnenolone, estradiol (including their polar conjugates), and additional steroids were measured in 16 women in the follicular and luteal phases of the menstrual cycle using gas chromatography/mass spectrometry and RIA for the analysis. Linear models and Spearman’s correlations were used for data evaluation. Results and Discussion: The levels of conjugated PI were from one to almost three orders of magnitude higher in comparison with th...
TL;DR: Comparison of P4507B1 sequences in rat, human, and two mouse species showed that one amino acid change might explain important differences in KM for 7α‐hydroxylation, and suggested that such differences might contribute to the extent of immune response.
Abstract: In human and murine lymphoid organs, circulating 3 beta-hydroxysteroids, including pregnenolone (PREG), dehydroepiandrosterone (DHEA), and epiandrosterone (EPIA), are 7 alpha-hydroxylated by a cytochrome P450 identified in the hippocampus as P4507B1. Mouse and human lymphoid organs produced different patterns of 3 beta-hydroxysteroid 7 alpha-hydroxylation with the absence of pregnenolone and epiandrosterone hydroxylation in human and mouse, respectively. Both 7 alpha-hydroxy-DHEA and 7 alpha-hydroxy-EPIA triggered a significant increase of antitetanus toxoid and anti-Bordetella pertussis toxins IgGs production in cultures of activated B + T cells derived from human tonsils, whereas both 7 alpha-hydroxy-PREG and 7 alpha-hydroxy-DHEA increased the immune response in mouse. Paracrine action of 7 alpha-hydroxysteroids resulted from their production in cells of the lymphoid organs. Comparison of P4507B1 sequences in rat, human, and two mouse species showed that one amino acid change might explain important differences in KM for 7 alpha-hydroxylation, and suggested that such differences might contribute to the extent of immune response.
TL;DR: The results support the idea that the domain of PXR-controlled gene networks may be even more extensive than currently thought and may extend to functions apart from xenobiotic metabolism.
TL;DR: The results provide the first evidence for the regulation of neurosteroid biosynthesis by key proteins involved in the etiology of AD and suggest that pathogenic factors may induce neurodegeneration in humans through the reduction of the synthesis of endogenous neuroprotective neurosteroids in nerve cells.
Abstract: Studies performed with animals suggest neurosteroid involvement in neuroprotection. However in humans, the role of neurosteroidogenesis in the regulation of degenerative processes is unknown. To determine whether cellular factors intervening in degenerative mechanisms may interfere with the process of neurosteroidogenesis in humans, we combined pulse-chase experiments with HPLC and continuous flow scintillation detection to compare neurosteroid production in normal and transfected SH-SY5Y cells with key proteins involved in Alzheimer's disease (AD). Microscope analyses revealed that cell morphology was unchanged in stably transfected SH-SY5Y cells overexpressing human native tau (hTau40), mutant tau (P301L), and wild-type amyloid precursor protein (APPwt) compared to controls. Biochemical investigations showed that hTau40 enhanced progesterone (PROG), 17OHPROG, testosterone, and 3alpha-androstanediol neosynthesis from pregnenolone. In contrast, tau with the pathogenic P301L mutation was devoid of action on neurosteroidogenesis. Overexpression of APPwt inhibited PROG formation, did not affect 17OHPROG and testosterone, but increased 3alpha-androstanediol and estradiol synthesis. Extracellular treatment of control cells with aggregated amyloid peptide mimicked the action of APPwt expression on PROG but not on 3alpha-androstanediol and estradiol production. Moreover, PROG biosynthesis in APPwt cells was up-regulated in the presence of a gamma-secretase inhibitor. Our results provide the first evidence for the regulation of neurosteroid biosynthesis by key proteins involved in the etiology of AD. The data suggest that pathogenic factors may induce neurodegeneration in humans through the reduction of the synthesis of endogenous neuroprotective neurosteroids in nerve cells.
TL;DR: RT-PCR analysis revealed that gene expression of three steroidogenic enzyme show distinctly different tissue-specific patterns of expression in the Japanese eel, suggesting that some steroidogenic enzymes are also expressed in non-endocrine tissues and could potentially regulate the local and/or circulating steroid levels in teleosts, as they do in mammals.
TL;DR: The discovery of steroid function in cell movement is novel, and should provide new insights into the understanding of diverse functions of steroids.
TL;DR: Synaptic expression of P450(17α), P450arom, and estrogen receptors suggests “synaptocrine” mechanisms of brain steroids, which are synthesized at synapses and act as synaptic modulators.
Abstract: In the hippocampus, the center for learning and memory, cytochrome P450s (P450scc, P450(17alpha), and P450arom) as well as 17beta-, 3beta-hydroxysteroid dehydrogenases, and 5alpha-reductase participate in the synthesis of brain steroids from endogenous cholesterol. These brain steroids include pregnenolone, dehydroepiandrosterone, testosterone, dihydrotestosterone, and 17beta-estradiol. Both estrogens and androgens are synthesized in the adult male hippocampal neurons. Although the expression levels of steroidogenic enzymes are as low as 1/200 to 1/50,000 of those in testis or ovary, the levels of synthesized steroids are sufficient for the local usage within small neurons (i.e., intracrine system). This intracrine system contrasts with the endocrine system in which high expression levels of steroidogenic enzymes are necessary in endocrine organs in order to supply steroids to many other organs via blood circulation. Endogenous synthesis of sex steroids in the hypothalamus is also discussed. Rapid modulation by estrogens and xenoestrogens is discussed concerning synaptic plasticity such as the long-term potentiation, the long-term depression, or spinogenesis. Synaptic expression of P450(17alpha), P450arom, and estrogen receptors suggests "synaptocrine" mechanisms of brain steroids, which are synthesized at synapses and act as synaptic modulators.
TL;DR: Unlike the case with human and mouse SULT2B1 genes where differential splicing is necessitated since a portion of exon IA is fused with exon IB to complete the SULT 2B1b mRNA, this step is not required with the rat gene.
01 Jan 2006
TL;DR: A detailed discussion of specific enzymatic reactions and the products so formed can be found in this article, with a focus on the reaction of the cytochrome P450 side-chain cleavage enzyme.
Abstract: Testosterone represents the major circulating androgen in the male and is synthesized by a sequence of enzymatic reactions that converts the substrate for all steroid biosynthesis, cholesterol, initially to the first steroid produced, pregnenolone, and then through a number of steroid intermediates to testosterone. This chapter discusses the specific enzymatic reactions and the products so formed. Cholesterol synthesis involves the formation of mevalonic acid, squalene, lanosterol, and finally cholesterol. The uptake of cholesterol from the serum requires the interaction of circulating lipoproteins with specific cell surface receptors designed to interact with these lipoproteins and internalize them either in whole or in part. The initial enzymatic reaction in the biosynthesis of all steroids in all steroidogenic tissues is the conversion of cholesterol to pregnenolone. This reaction occurs through the activity of the cytochrome P450 side-chain cleavage enzyme. In the testis, testosterone is the major androgen produced by the Leydig cells and is responsible for the normal maintenance of spermatogenesis. However, testosterone can also be converted to the more potent androgen, dihydrotestosterone (DHT), through the action of the enzyme 5α-reductase.
TL;DR: Evidence is provided for a biologically active enzyme product 7α-hydroxyPREG and suggests that reduced CYP7B function in the hippocampus of memory-impaired aged rats may, in part, be overcome by administration of 7 α-hydroxylated metabolite PREG.
Abstract: Pregnenolone (PREG) and dehydroepiandrosterone (DHEA) have been reported to improve memory in aged rodents. In brain, these neurosteroids are transformed predominantly into 7α-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, 7α-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 7α-hydroxylated metabolite 7α-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 7α-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 [ 14 C]DHEA to [ 14 C]7α-hydroxyDHEA) was decreased selectively in memory-impaired aged rats compared with both young and memory-intact aged rats. 7α-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 7α-hydroxyPREG and suggests that reduced CYP7B function in the hippocampus of memory-impaired aged rats may, in part, be overcome by administration of 7α-hydroxyPREG.
TL;DR: The results revealed that the increases of progesterone production in the presence of hCG, CT, forskolin and 8-Br-cAMP were augmented by MBP, which supported that MBP promotes steroid hormone production by facilitating StAR expression in MLTC-1 cells.
TL;DR: The increased brain DHEA following cocaine self-administration may serve as a compensatory protective mechanism geared to attenuate the craving for cocaine.
TL;DR: The potentiating effect of PREGS on the secretion of GnRH induced by glutamate is consistent with the role of the steroid as a positive allosteric modulator of NMDA receptors.
Abstract: Immortalized hypothalamic GT1-7 neurons represent a good model system to investigate the control of GnRH secretion. Using these cells, we observed that the neuroactive steroid, pregnenolone sulfate (PREGS), is able to stimulate the release of GnRH in a dose-dependent manner through N-methyl-D-aspartate (NMDA) receptors, because its action is completely blocked by a specific NMDA receptor antagonist and magnesium. GT1-7 neurons express mRNAs for various mouse NMDA receptor subunits (zeta,1, epsilon3, epsilon4, and epsilon2, corresponding to the NR1, NR2C, NR2D, and NR2B rat subunits) and increase their spontaneous release of GnRH when incubated in the presence of exogenous glutamate or NMDA. In addition, we found that these neurons are able to release and synthesize glutamate, as demonstrated by the presence of glutamate accumulated in the defined incubation medium of the neurons, during the experiment and the expression of mRNA coding for vesicular glutamate transporter 2, a specific marker of glutamatergic neurons. The potentiating effect of PREGS on the secretion of GnRH induced by glutamate is consistent with the role of the steroid as a positive allosteric modulator of NMDA receptors. Together these results point to a novel mechanism by which the neuroactive steroid PREGS may potentiate an autocrine excitatory loop in GnRH neurons.