Peripheral steroid sulfatase inhibition potentiates improvement of memory retention for hippocampally administered dehydroepiandrosterone sulfate but not pregnenolone sulfate

Memory, mood and associated neuroanatomy in individuals with steroid sulphatase deficiency (X-linked ichthyosis)

Steroid sulphatase (STS) cleaves sulphate groups from steroid hormones, and steroid (sulphate) levels correlate with mood and age-related cognitive decline. In animals, STS inhibition or deletion of the associated gene, enhances memory/neuroprotection and alters hippocampal neurochemistry. Little is known about the consequences of constitutive STS deficiency on memory-related processes in humans. We investigated self-reported memory performance (Multifactorial Memory Questionnaire), word-picture recall and recent mood (Kessler Psychological Distress Scale, K10) in adult males with STS deficiency diagnosed with the dermatological condition X-linked ichthyosis (XLI; n = 41) and in adult female carriers of XLI-associated genetic variants (n = 79); we compared results to those obtained from matched control subjects [diagnosed with ichthyosis vulgaris (IV, n = 98) or recruited from the general population (n = 250)]. Using the UK Biobank, we compared mood/memory-related neuroanatomy in carriers of genetic deletions encompassing STS (n = 28) and non-carriers (n = 34,522). We found poorer word-picture recall and lower perceived memory abilities in males with XLI and female carriers compared with control groups. XLI-associated variant carriers and individuals with IV reported more adverse mood symptoms, reduced memory contentment and greater use of memory aids, compared with general population controls. Mood and memory findings appeared largely independent. Neuroanatomical analysis only indicated a nominally-significantly larger molecular layer in the right hippocampal body of deletion carriers relative to non-carriers. In humans, constitutive STS deficiency appears associated with mood-independent impairments in memory but not with large effects on underlying brain structure; the mediating psychobiological mechanisms might be explored further in individuals with XLI and in new mammalian models lacking STS developmentally.

Pre- and postsynaptic modulation of hippocampal inhibitory synaptic transmission by pregnenolone sulphate

Neurosteroids are important endogenous modulators of GABA_A receptor-mediated neurotransmission within the CNS and play a vital role in maintaining normal healthy brain function. Research has mainly focussed on neurosteroids such as allopregnanolone and tetrahydro-deoxycorticosterone (THDOC) which are allosteric potentiators of GABA_A receptors, whilst the sulphated steroids, including pregnenolone sulphate (PS), which inhibit GABA_A receptor function, have been relatively neglected. Importantly, a full description of PS effects on inhibitory synaptic transmission, at concentrations that are expected to inhibit postsynaptic GABA_A receptors, is lacking. Here, we address this deficit by recording inhibitory postsynaptic currents (IPSCs) from rat hippocampal neurons both in culture and in acute brain slices and explore the impact of PS at micromolar concentrations. We reveal that PS inhibits postsynaptic GABA_A receptors, evident from reductions in IPSC amplitude and decay time. Concurrently, PS also causes an increase in synaptic GABA release which we discover is due to the activation of presynaptic TRPM3 receptors located close to presynaptic GABA release sites. Pharmacological blockade of TRPM3 receptors uncovers a PS-evoked reduction in IPSC frequency. This second presynaptic effect is caused by PS activation of inwardly-rectifying Kir2.3 channels on interneurons, which act to depress synaptic GABA release. Overall, we provide a comprehensive characterisation of pre- and postsynaptic modulation by PS of inhibitory synaptic transmission onto hippocampal neurons which elucidates the diverse mechanisms by which this understudied neurosteroid can modulate brain function.

Hormonal modulation of novelty processing in women: Enhanced under working memory load with high dehydroepiandrosterone-sulfate-to-dehydroepiandrosterone ratios

Several studies have suggested that dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS) may enhance working memory and attention, yet current evidence is still inconclusive. The balance between both forms of the hormone might be crucial regarding the effects that DHEA and DHEAS exert on the central nervous system. To test the hypothesis that higher DHEAS-to-DHEA ratios might enhance working memory and/or involuntary attention, we studied the DHEAS-to-DHEA ratio in relation to involuntary attention and working memory processing by recording the electroencephalogram of 22 young women while performing a working memory load task and a task without working memory load in an audio-visual oddball paradigm. DHEA and DHEAS were measured in saliva before each task. We found that a higher DHEAS-to-DHEA ratio was related to enhanced auditory novelty-P3 amplitudes during performance of the working memory task, indicating an increased processing of the distracter, while on the other hand there was no difference in the processing of the visual target. These results suggest that the balance between DHEAS and DHEA levels modulates involuntary attention during the performance of a task with cognitive load without interfering with the processing of the task-relevant visual stimulus.

The hormonal pathway to cognitive impairment in older men

In older men there is a multiple hormonal dysregulation with a relative prevalence of catabolic hormones such as thyroid hormones and cortisol and a decline in anabolic hormones such as dehydroepiandrosterone sulphate, testosterone and insulin like growth factor 1 levels. Many studies suggest that this catabolic milieu is an important predictor of frailty and mortality in older persons. There is a close relationship between frailty and cognitive impairment with studies suggesting that development of frailty is consequence of cognitive impairment and others pointing out that physical frailty is a determinant of cognitive decline. Decline in cognitive function, typically memory, is a major symptom of dementia. The "preclinical phase" of cognitive impairment occurs many years before the onset of dementia. The identification of relevant modifiable factors, including the hormonal dysregulation, may lead to therapeutic strategies for preventing the cognitive dysfunction. There are several mechanisms by which anabolic hormones play a role in neuroprotection and neuromodulation. These hormones facilitate recovery after brain injury and attenuate the neuronal loss. In contrast, elevated thyroid hormones may increase oxidative stress and apoptosis, leading to neuronal damage or death. In this mini review we will address the relationship between low levels of anabolic hormones, changes in thyroid hormones and cognitive function in older men. Then, giving the contradictory data of the literature and the multi-factorial origin of dementia, we will introduce the hypothesis of multiple hormonal derangement as a better determinant of cognitive decline in older men.

Perimenopausal regulation of steroidogenesis in the nonhuman primate

Human aging is characterized by a marked decrease in circulating levels of dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEAS), hormonal changes associated with cognitive decline. Despite beneficial effects of DHEA supplementation in rodents, studies in elderly humans have generally failed to show cognitive improvement after treatment. In the present study we evaluate the effects of age and estradiol supplementation on expression of genes involved in the de novo synthesis of DHEA and its conversion to estradiol in the rhesus macaque hippocampus. Using reverse transcription polymerase chain reaction (RT-PCR) we demonstrate the expression of genes associated with this synthesis in several areas of the rhesus brain. Furthermore, real-time PCR reveals an age-related attenuation of hippocampal expression level of the genes CYP17A1, STS, and 3BHSD1/2. Additionally, short-term administration of estradiol is associated with decreased expression of CYP17A1, STS, SULT2B1, and AROMATASE, consistent with a downregulation not only of estrogen synthesis from circulating DHEA, but also of de novo DHEA synthesis within the hippocampus. These findings suggest a decline in neurosteroidogenesis may account for the inefficacy of DHEA supplementation in elderly humans, and that central steroidogenesis may be a function of circulating hormones and menopausal status.

Pregnenolone sulfate in the brain: a controversial neurosteroid

Pregnenolone sulfate (PREGS) has been shown, either at high nanomolar or at micromolar concentrations, to increase neuronal activity by inhibiting GABAergic and by stimulating glutamatergic neurotransmission. PREGS is also a potent modulator of sigma type 1 (sigma1) receptors. It has been proposed that these actions of PREGS underlie its neuropharmacological effects, and in particular its influence on memory processes. On the other hand, the PREGS-mediated increase in neuronal excitability may become dangerous under particular conditions, for example in the case of excitotoxic stress or convulsions. However, the physiopathological significance of these observations has recently been put into question by the failure to detect significant levels of PREGS within the brain and plasma of rats and mice, either by direct analytical methods based on liquid chromatography/mass spectrometry (LC/MS) or enzyme linked immunosorbent assay (ELISA) with specific antibodies against PREGS, or by indirect gas chromatography/mass spectrometry (GC/MS) analysis with improved sample workup. These recent results have not come to the attention of a large number of neurobiologists interested in steroid sulfates. However, although available direct analytical methods have failed to detect levels of PREGS above 0.1-0.3 ng/g in brain tissue, it may be premature to completely exclude the local formation of biologically active PREGS within specific and limited compartments of the nervous system. In contrast to the situation in rodents, significant levels of sulfated 3beta-hydroxysteroids have been measured in human plasma and brain. Previous indirect measures of steroid sulfates by radioimmunoassays (RIA) or GC/MS had detected elevated levels of PREGS in rodent brain. The discrepancies between the results of different assay procedures have revealed the danger of indirect analysis of steroid sulfates. Indeed, PREGS must be solvolyzed/hydrolyzed prior to RIA or GC/MS analysis, and it is the released, unconjugated PREG which is then quantified. Extreme caution needs to be exercised during the preparation of samples for RIA or GC/MS analysis, because the fraction presumed to contain only steroid sulfates can be contaminated by nonpolar components from which PREG is generated by the solvolysis/hydrolysis/derivatization reactions.

Dehydroepiandrosterone sulfate prevents ischemia-induced impairment of long-term potentiation in rat hippocampal CA1 by up-regulating tyrosine phosphorylation of NMDA receptor

We have reported that dehydroepiandrosterone sulfate (DHEAS) reduces the threshold for long-term potentiation (LTP) in Shaffer collateral-CA1 synapses through the amplification of Src-dependent NMDA receptor signaling. The present study is a follow-up of the above reports, aiming at evaluating the effects of DHEAS on the impaired LTP in reversible forebrain ischemic rats. Transient (20 min) incomplete forebrain ischemia led to an impaired LTP in the hippocampal CA1 region without damages to the basal synaptic transmission between the Shaffer collaterals and pyramidal neurons. Repetitive administrations of DHEAS (20 mg/kg for 3 days) from the first 3 h of reperfusion, but not acute DHEAS application (50 microM), prevent the impairment of LTP produced by ischemia. Co-administration of the specific sigma(1) receptor antagonist NE100 with DHEAS completely prevented the protective effect of DHEAS. In contrast, progesterone (PRGO) not only had no protective effect against the ischemic LTP impairment, but also attenuated the protective effect of DHEAS on the impaired LTP. Tyrosine phosphorylation of NMDA receptor subunit 2B (NR2B) significantly decreased after ischemia, whereas that of NR1 had no obvious change. Furthermore, the repetitive administration of DHEAS improved the reduction in tyrosine phosphorylation of NR2B. These findings suggest that the repetitive activation of sigma(1) receptor induced by DHEAS might prevent the ischemic LTP impairment through regulating the tyrosine phosphorylation of NR2B.

Dehydroepiandrosterone and its metabolites: differential effects on androgen receptor trafficking and transcriptional activity

Dehydroepiandrosterone (DHEA) is a multi-functional steroid that has been implicated in a broad range of biological effects in humans and rodents. Recent studies demonstrated that DHEA acts genomically through the androgen receptor (AR) in addition to its well-known effects on cell surface receptors. However, the relative contribution of DHEA and its major metabolites, including DHEA-Sulfate (DHEA-S), 7alpha-OH-DHEA, 7beta-OH-DHEA, 7-oxo-DHEA, androstenedione (Adione), and androstenediol (Adiol), in the production of genomic effects remains controversial, in part because the metabolism of DHEA varies in different cells and tissues. In the current study, the ability of DHEA and its metabolites to promote AR intracellular trafficking and regulate AR-mediated reporter gene expression, which are characteristic effects of androgens, was determined. Intracellular trafficking of AR-GFP protein was assessed in COS-7 cells while AR transcriptional activity was tested in CV-1 cells transiently co-transfected with AR expression plasmid and an MMTV-ARE-CAT reporter. The results demonstrated that DHEA, the 3beta-HSD metabolite Adione, and the 17beta-HSD metabolite Adiol, were androgenic. Each promoted AR-GFP intracellular trafficking, the formation of nuclear clusters, and AR-dependent transcriptional activity in a dose-dependent manner. In contrast, DHEA-S, 7alpha-OH-DHEA, 7beta-OH-DHEA, and 7-oxo-DHEA were ineffective and exhibited minimal androgenic activity, even at relatively high concentrations (10(-6) M). These results provide the first systematic comparison of the (i) androgenic activity of DHEA and its sulfated and hydroxylated metabolites, (ii) relative androgenicity of DHEA itself vs. the established androgens Adione and Adiol, and (iii) ability of DHEA and its major metabolites to promote AR-GFP intracellular trafficking. In addition to partitioning DHEA and its metabolites into compounds with (DHEA, Adione, Adiol) and without (DHEA-S, 7alpha-OH-DHEA, 7beta-OH-DHEA, and 7-oxo-DHEA) androgenic activity, the findings improve our understanding of the intracellular processes mediating the genomic effects of DHEA through AR.

Neuroprotection and neurodegenerative diseases: from biology to clinical practice

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

Chronic administration of dehydroepiandrosterone sulfate (DHEAS) primes for facilitated induction of long-term potentiation via sigma 1 (sigma1) receptor: optical imaging study in rat hippocampal slices

Dehydroepiandrosterone sulfate (DHEAS), one of the most abundant neurosteroids synthesized de novo in the nervous system, has well characterized effects on memory and cognitive performances. However, little is known about the underlying synaptic mechanisms. In this study, we investigated the effects of chronic administration of DHEAS (20 mg/kg for 7 days) on the plasticity of Schaffer collateral-CA1 synapses by applying an optical recording technique on the hippocampal slices stained with voltage-sensitive dyes. We report here that chronically administered DHEAS significantly facilitated the induction of frequency-dependent LTP, termed DHEAS-facilitated LTP. While tetanus of at least 50 pulses (at 100 Hz) were required to induce LTP in control rats, only 20 pulses were needed in DHEAS-treated animals. In contrast DHEA, the non-sulfated form of DHEAS, had no facilitating effect on the induction of LTP. We found that chronically administered DHEAS did not alter the presynaptic glutamate release in response to both single pulse and tetanic stimulation, suggesting that certain alterations happened in postsynaptic neurons. Co-administration of the sigma 1 (sigma1) receptor antagonists, haloperidol or NE100, with DHEAS completely inhibited the DHEAS-facilitated LTP. However, acute administration of sigma1 receptor antagonists to the slices did not affect the induction of DHEAS-facilitated LTP, suggesting that sigma1 receptor is a key target of chronic actions of DHEAS but is not involved in the induction of DHEAS-facilitated LTP. Our findings provide evidence that chronically administered DHEAS plays a priming role in inducing a facilitated synaptic plasticity probably via a chronic activation of sigma1 receptor in rat hippocampal CA1 pyramidal cells.

Sulfonation in pharmacology and toxicology

Sulfonation has a major function in modulating the biological activities of a wide number of endogenous and foreign chemicals, including: drugs, toxic chemicals, hormones, and neurotransmitters. The activation as well as inactivation of many xenobiotics and endogenous compounds occurs via sulfonation. The process is catalyzed by members of the cytosolic sulfotransferase (SULT) superfamily consisting of at least ten functional genes in humans. The reaction in intact cells may be reversed by arylsulafatase present in the endoplasmic reticulum. Under physiological conditions, sulfonation is regulated, in part, by the supply of the co-substrate/donor molecule 3'-phosphadensoine-5-phosphosulfate (PAPS), and transport mechanisms by which sulfonated conjugates enter and leave cells. Variation in the response of individuals to certain drugs and toxic chemicals may be related to genetic polymorphisms documented to occur in each of the above pathways. Sulfonation has a major function in regulating the endocrine status of an individual by modulating the receptor activity of estrogens and androgens, steroid biosynthesis, and the metabolism of catecholamines and iodothyronines Sulfonation is a key reaction in the body's defense against injurious chemicals and may have a major function during early development since SULTs are highly expressed in the human fetus. As with many Phase I and Phase II reactions, sulfonation may also serve as the terminal step in activating certain dietary and environmental agents to very reactive toxic intermediates implicated in carcinogenesis.

Neurosteroid paradoxical enhancement of paired-pulse inhibition through paired-pulse facilitation of inhibitory circuits in dentate granule cells

Neurosteroids are produced in the brain independently of peripheral endocrine glands to act locally in the nervous system. They exert potent promnesic effects and play significant roles in mental health-related disorders. In part, neurosteroids act by affecting ligand-gated ion channels and metabotropic receptors through rapid non-genomic processes. We have previously demonstrated that neurosteroids also affect synaptic transmission presynaptically in the CA1 region of the hippocampus. Here we describe the effects of the most abundant neurosteroid in the rodent brain, pregnenolone sulfate (PregS), on signal processing in the dentate subfield of the hippocampus. We show that PregS acts presynaptically at low concentrations (300 nM) to enhance paired-pulse facilitation (PPF) in perforant pathway terminals on dentate granule cells. Similar effects were found with two steroid sulfatase inhibitors demonstrating a potential contribution of endogenous steroids to dentate synaptic plasticity. This enhanced presynaptic facilitation paradoxically increases paired-pulse inhibition (PPI) at short interpulse intervals. Based on these data, a model of dentate gyrus circuit interactions is proposed for the presynaptic action of PregS on the filtering dynamics of the dentate subfield at frequencies similar to those of the endogenous signals from the entorhinal cortex. These modeling studies are consistent with experimental measurements demonstrating positive modulation by PregS at low frequencies and negative modulation at high frequencies. These studies show an important role for the presynaptic action of neurosteroids in modulating input signals to the hippocampus.

DHEA and DHEA sulfate differentially regulate neural androgen receptor and its transcriptional activity

The mechanism of action of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEA-S), two interconvertable neurosteroids, has not been fully characterized in the central nervous system (CNS). Previous studies demonstrated that DHEA was intrinsically androgenic, suggesting that it may act through a genomic pathway. However, it is not known whether DHEA-S also produces androgenic effects, an important question given that the concentration of DHEA-S in brain is some 7-12 times that of DHEA. The current study compared the potential androgenic effects of DHEA-S with DHEA by examining their capacity to induce two characteristic effects of an androgenic compound. These included the ability to (1) up-regulate neural androgen receptor (AR) protein level in mouse brain and immortalized GT1-7 hypothalamic cells and (2) assess their effect on reporter gene expression through AR in CV-1 cells cotransfected with pSG5-AR and pMMTV-ARE-CAT reporter. Semi-quantitative Western blot analysis showed that DHEA treatment significantly augmented AR in mouse brain and GT1-7 cells in a dose-dependent manner and that these effects were not blocked by trilostane (TRIL), a known 3beta-hydroxysteroid dehydrogenase inhibitor. DHEA also promoted AR-mediated reporter gene expression as a function of dose and the effect was comparable with or without the addition of TRIL. In contrast, DHEA-S treatment failed to increase AR level in the mouse brain or GT1-7 cells and modestly induced AR-mediated reporter gene expression only at substantially elevated concentrations compared to DHEA. The findings demonstrate that DHEA is capable of exerting androgenic effects through AR while the androgenicity of DHEA-S is negligible. The implications of the results for models of the mechanism of action of DHEA and its sulfate ester, DHEA-S, in the brain are considered.

Anti-aging medicine--the good, the bad, and the ugly

Complementary and alternative medicine has flourished since the beginning of time because of a human need to postpone the aging process and to reverse disease. Complementary and alternative medicine sells, because in some cases it works as well or better than mainstream medicine. In addition, many practitioners of complementary medicine understand Hippocrates' aphorism: "It is more important to know the person that has the disease than the disease the person has." It is important to recognize that spending time with the patient is often as therapeutic as drugs. CAM offers patients the time, touch, attention, and level of personal interaction that are increasingly uncommon in contemporary medical care. There is a major need for large and appropriately designed studies to test the effectiveness of complementary techniques. As in other areas of health care, studies in the elderly are consistently lacking. With the growing interest in CAM, it is important for medical providers to keep an open mind--to both the potential benefits and potential harms of alternative treatments. When treatments are shown to be dangerous or ineffective, we must educate the public and work to remove these therapies from the market place. When treatments are proven effective, Western and Eastern medical providers must work together with patients to provide the most appropriate and comprehensive health care.

Hormonal fountains of youth

Any hope of a fountain of youth to stop people from getting older is a long way off, with science just beginning to understand the complex genetic, physical, and hormonal causes of aging. Clearly, modem research has demonstrated that the concept of a hormonal fountain of youth is predominantly mythology. The best evidence supporting use of hormonal replacement is vitamin D and estrogen replacement to prevent hip fractures. Other than that, treatment should be limited to hormone replacement in persons who have endocrine disease.

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

It has been demonstrated that neuroprotective effects of dehydroepiandrosterone (DHEA) may be mediated by its 7alpha- and 7beta-hydroxy derivatives. Epiandrosterone is also converted to 7beta-hydroxy epiandrosterone (7beta-OH EPIA) in numerous tissues. The aim of the present study was to establish whether treatment with 7beta-hydroxy epiandrosterone has a neuroprotective effect in animal models of Alzheimer's disease (AD) lesions. Intra-amygdaloid administration of amyloid beta [Abeta(25-35)] increased the number of tau-positive cells in the ipsilateral hippocampus. Intracerebroventricular administration of ethylcholine aziridinium (AF64A) caused cholinergic damage in the septum, and glial lesions in the lateral septal nucleus and in the lateral zones of the hippocampus. These effects were almost completely prevented when animals were treated subcutaneously (b.i.d.) for 10 days with 0.1 mg/kg 7beta-hydroxy epiandrosterone. These findings indicate that 7beta-hydroxy epiandrosterone has powerful cytoprotective effects suggesting that (a) this neurosteroid may have therapeutic potential in various neurodegenerative conditions such as Alzheimer's disease, and (b) 7beta-hydroxy steroids may constitute a novel class of endogenous neuroprotective agents.

Dehydroepiandrosterone (DHEA) and the aging brain: flipping a coin in the "fountain of youth"

The physiological role of dehydroepiandrosterone (DHEA) and its sulphated ester DHEA(S) has been studied for nearly 2 decades and still eludes final clarification. The major interest in DHEA derives from its unique pattern of activity. Its levels exhibit a dramatic age-related decline that supports significant involvement of DHEA(S) in the aging process. Particularly relevant to the aging process is the functional decline that involves memory and cognitive abilities. DHEA is derived mainly from synthesis in the adrenal glands and gonads. It can also be detected in the brain where it is derived from a synthesis that is independent from peripheral steroid sources. For this reason DHEA and other steroid molecules have been named "neurosteroids." Pharmacological studies on animals provided evidence that neurosteroids could be involved in learning and memory processes because they can display memory-enhancing properties in aged rodents. However, human studies have reported contradictory results that so far do not directly support the use of DHEA in aging-related conditions. As such, it is important to remember that plasma levels of DHEA(S) may not reflect levels in the central nervous system (CNS), due to intrinsic ability of the brain to produce neurosteroids. Thus, the importance of neurosteroids in the memory process and in age-related cognitive impairment should not be dismissed. Furthermore, the fact that the compound is sold in most countries as a health food supplement is hampering the rigorous scientific evaluation of its potential. We will describe the effect of neurosteroids, in particular DHEA, on neurochemical mechanism involved in memory and learning. We will focus on a novel effect on a signal transduction mechanism involving a classical "cognitive kinase" such as protein kinase C. The final objective is to provide additional tools to understand the physiological role and therapeutic potentials of neurosteroids in normal and/or pathological aging, such as Alzheimer's disease.

Steroid and sterol 7-hydroxylation: ancient pathways

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

Neurosteroids in learning and memory processes

The discovery that neurosteroids could be synthesized de novo in the brain independent from the periphery and display neuronal actions led to great enthusiasm for the study of their physiological role. Pharmacological studies suggest that neurosteroids may be involved in several physiological processes, such as learning and memory. This chapter summarizes the effects of the administration of neurosteroids on learning and memory capabilities in rodents and in models of amnesia. We address the central mechanisms involved in mediating the modulation of learning and memory processes by neurosteroids. In this regard, the neurosteroid-modulated neurotransmitter systems, such as gamma-aminobutyric acid type A, N-methyl-D-aspartate, and cholinergic and sigma opioid systems, appear to be potential targets for the rapid memory alteration actions of neurosteroids. Moreover, given that some neurosteroids affect neuronal plasticity, this neuronal change could be involved in the long-term modulation of learning and memory processes. To understand the role of endogeneous neurosteroids in learning and memory processes, we present some physiological studies in rodents and humans. However, the latter do not successfully prove a role of endogenous neurosteroids in age-related memory impairments. Finally, we discuss the relative implication of a given neurosteroid vs its metabolites. For this question, a new approach using the quantitative determination of traces of neurosteroids by mass spectrometry seems to have potential for examining the role of each neurosteroid in discrete brain areas in learning and memory alterations, as observed during aging.

Aggressive behavior induced by the steroid sulfatase inhibitor COUMATE and by DHEAS in CBA/H mice

The steroid sulfatase enzyme (STS) regulates the formation of dehydroepiandrosterone (DHEA) from dehydroepiandrosterone-sulfate (DHEAS). DHEAS is a well-known negative allosteric modulator of the GABA(A) receptor-gated chloride channels. It is classified as an excitatory neurosteroid. The implication of GABA(A) receptor activity in aggressive behavior in rodents is well-documented. In addition a genetic correlation between STS level in the liver and aggressive behavior across 12 strains of mice suggest that STS activity could be involved in aggression in mice. We assessed herein whether COUMATE (an STS inhibitor) and DHEAS modulate aggression in CBA/H mice. We hypothesized that inhibiting STS activity in vivo followed by DHEAS injections which increase the level of sulfated steroid that cross the blood-brain barrier and then modulate neurotransmitter receptors could modify the attack behavior in mice. COUMATE (10 mg/kg) was administrated p.o. alone or in combination with the neurosteroid DHEAS (0-50 mg/kg) i.p. Animals were thereafter tested for aggression. A single dose of COUMATE significantly inhibited STS activity both in the brain (70.57%) and in the liver (87%) 24 h following administration. Behavioral tests showed that the inhibitor and DHEAS enhanced aggressive behavior when animals were simultaneously subjected to both molecules. These results confirm the correlation between aggressive behavior and STS concentration in mice. In addition, we confirm that the steroid metabolism can modulate the behavior in rodents.

Dehydroepiandrosterone and the relationship with aging and memory: a possible link with protein kinase C functional machinery

A progressive decline of cognitive and memory functions, compared to the average young-life performance, characterizes brain aging. The changes in performance may depend upon altered activity of neurotransmitters acting on attention and memory trace formation (acetylcholine, catecholamines, glutamate, for example) or the failure of the transduction mechanisms linked to receptor activation. One of the fundamental cellular changes associated with brain aging is the alteration of mechanisms involving the activity of the calcium-phospholipid-dependent protein kinase C (PKC). A crucial event for the activation of protein kinase C is its translocation from the cytosol to different intracellular sites and recent studies have demonstrated the key role played by several anchoring proteins in this mechanism. The defective activation of PKC-dependent pathways during aging is due to a defective mechanism of translocation of the kinase because of reduced levels of the major anchoring protein RACK-1 (receptor for activated C kinase). Pharmacological strategies aimed at the correction of age-associated memory deficits have been mostly focused on neurotransmitters using direct or indirect agonists. More recently, attention has been paid to the memory enhancing properties of some steroid hormones, namely 'neurosteroids'. Among these the activities of dehydroepiandrosterone (DHEA), pregnenolone (PREG) and their sulfates, have been extensively studied. These neuroactive steroids, can regulate neuronal function through their concurrent influence on transmitter-gated ion channels and gene expression. We addressed the possibility that DHEA, among other neurosteroids, could modulate directly the age-associated impairment of PKC signal transduction and provide experimental evidence that DHEA can revert the alteration of RACK-1 anchoring protein expression.

Role of pregnenolone, dehydroepiandrosterone and their sulfate esters on learning and memory in cognitive aging

Aging is a general process of functional decline which involves in particular a decline of cognitive abilities. However, the severity of this decline differs from one subject to another and inter-individual differences have been reported in humans and animals. These differences are of great interest especially as concerns investigation of the neurobiological factors involved in cognitive aging. Intensive pharmacological studies suggest that neurosteroids, which are steroids synthesized in the brain in an independent manner from peripheral steroid sources, could be involved in learning and memory processes. This review summarizes data in animals and humans in favor of a role of neurosteroids in cognitive aging. Studies in animals demonstrated that the neurosteroids pregnenolone (PREG) and dehydroepiandrosterone (DHEA), as sulfate derivatives (PREGS and DHEAS, respectively), display memory-enhancing properties in aged rodents. Moreover, it was recently shown that memory performance was correlated with PREGS levels in the hippocampus of 24-month-old rats. Human studies, however, have reported contradictory results. First, improvement of learning and memory dysfunction was found after DHEA administration to individuals with low DHEAS levels, but other studies failed to detect significant cognitive effects after DHEA administration. Second, cognitive dysfunctions have been associated with low DHEAS levels, high DHEAS levels, or high DHEA levels; while in other studies, no relationship was found. As future research perspectives, we propose the use of new methods of quantification of neurosteroids as a useful tool for understanding their respective role in improving learning and memory impairments associated with normal aging and/or with pathological aging, such as Alzheimer's disease.

The effect of steroid sulfatase inhibition on learning and spatial memory

Steroid sulfatase inhibitors can enhance the concentration of the neurosteroid DHEAS in rat brain. Previous studies have demonstrated that the steroid sulfatase inhibitor (p-O-sulfamoyl)-N-tetradecanoyl tyramine (DU-14) could reverse scopolamine induced amnesia in rats in a passive avoidance memory paradigm. The intent of this study was to determine whether chronic pretreatment with DU-14 could reverse scopolamine amnesia and/or enhance spacial memory in the place, probe and cued versions of the Morris water maze (MWM). Rats were divided into four groups and administered IP for 15 days either DU-14 (30.0 mg/Kg) or corn oil (1.0 ml/Kg) vehicle. On training days animals were administered either scopolamine (1.0 mg/Kg) or saline (1.0 ml/Kg). The groups administered DU-14 displayed a significant enhancement in learning and spacial memory in the place version of the MWM, when compared to respective vehicle-scopolamine and vehicle-saline groups. In the probe version, the DU-14-saline group remained in the target quadrant of the maze significantly longer than any of the other groups indicating enhanced retention. In the cued version of the MWM, treatment with DU-14 did not significantly change escape latency suggesting that the steroid sulfatase inhibitor did not alter motivation or locomotion. These results suggest that the chronic administration of steroid sulfatase inhibitors enhance learning and spatial memory in rats.