Dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEAS) protect hippocampal neurons against excitatory amino acid-induced neurotoxicity

Dehydroepiandrosterone (DHEA) supplementation for cognition and well-being

BACKGROUND

In view of the theoretical rationale for beneficial effects of DHEA and DHEAS in aging and dementia, we believe it is timely to undertake a thorough investigation of well-conducted studies in this area. This will provide a basis for confirmation of any effect of DHEA/S administration in humans, in large-scale and properly controlled trials, which would evaluate effective dosage, acceptable route and duration of administration and side effect profiles. This is especially pertinent at this time as DHEA is currently being sold in large quantities in health food stores, particularly in the USA. In some cases the recommended dose is different for men and women (50mg/day for men and 25mg/day for women) and the basis for this recommendation needs to be explored.

OBJECTIVES

To establish whether administration of DHEA, or its sulphate, DHEAS, improves psychological well-being and/or improves cognitive function or reduces the rate of decline of cognitive function in older adults or in individuals with dementia.

SEARCH STRATEGY

All available electronic databases, hand searched journals, personal communications and conference abstracts were searched for randomised controlled trials of DHEA in well-being and cognition. The total yield from searching was 415 and the detailed breakdown is given in the body of this review.

SELECTION CRITERIA

All relevant randomised controlled trials of DHEA or DHEAS were considered for inclusion in the review. Studies where groups are matched, rather than randomised, were also considered.

DATA COLLECTION AND ANALYSIS

Data for the specified outcomes were independently extracted by two reviewers (FAH & JvN) and cross-checked. Any discrepancies were discussed and resolved. Where possible and appropriate, data were pooled and the mean differences estimated.

MAIN RESULTS

The published DHEA trials fall into 2 categories: 1. four German studies in which DHEA was administered for a period of two weeks or less; 2. a USA study in which DHEA was administered for three months. Well-being was assessed in both sets of studies and a significant improvement was reported in the longer duration USA study, while no effect was reported in the shorter duration studies. The USA study used an open-ended questionnaire for self-assessment of well-being and stated that 67% of men and 82% of women reported enhanced well-being on DHEA compared with placebo. There was no significant change on an analogue measure of libido. The German studies assessed mood and well-being with a number of standardised scales and reported no significant effects of DHEA on any of them. Only the German studies examined performance on cognitive tests, i.e. memory, verbal fluency, speed of processing, etc. They reported no significant benefit of DHEA.

REVIEWER'S CONCLUSIONS

The data at present offer limited support for improvement in a sense of well-being following DHEA treatment. This effect was reported only in the longer-term study which used a crude measure of well-being. The data offer no support at present for an improvement in memory or other aspects of cognitive function following DHEA treatment, although cognitive function was only measured in the short-duration trials. In view of the growing public enthusiasm for DHEA supplementation, particularly in the USA, it is clear that high-quality trials need to be undertaken in older adults, in which (a) the duration of DHEA treatment is in excess of two weeks, (b) the number of participants is large enough to detect effects if they exist, and (c) the outcome measures include validated scales for assessment of mood and well-being, and objective tests of cognitive function. Recently, studies of DHEA supplementation in clinical depression and Alzheimer's Disease have been completed in the USA. As soon as the results are available these studies will be reviewed. Currently, two trials (in France and the USA) in normal elderly are in progress.

Actions of dehydroepiandrosterone and its sulfate in the central nervous system: effects on cognition and emotion in animals and humans

Dehydroepiandrosterone (DHEA) and its sulfate ester, DHEAS, exert multiple effects in the rodent central nervous system (CNS). Most of them seem to be mediated through their non-genomic action on several neurotransmitter receptors. DHEA(S) increases neuronal excitability, enhances neuronal plasticity and also has neuroprotective properties. In line with these observations DHEA(S) treatment in rodents enhances memory in several paradigms. Even more studies show antiamnestic effects of the steroids. However, DHEA(S) has also anxiolytic and anti-aggressive properties. In humans cross-sectional and longitudinal studies suggest that DHEAS might be associated with global measures of well-being and functioning; however, a relationship with cognition could not be detected to date. Moreover, studies investigating DHEAS levels in neurodegenerative diseases have produced conflicting results. Experimental studies in elderly humans have revealed preliminary evidence for mood enhancing and antidepressant effects of DHEA treatment, while positive effects on measures of memory and attention could not be found. However, electrophysiological studies demonstrated that DHEA treatment has effects on the human CNS. Several reasons for the discrepancy between data obtained in rodents and humans are discussed and research perspectives are outlined which might help to improve interpretation of results obtained in the two species.

Stress, aging, and brain oxidative damage

Stress may contribute to aging acceleration and age-related degenerative diseases. Stress and adaptation to stress require numerous homeostatic adjustments including hormones, neurotransmitters, oxidants, and other mediators. The stress-induced hormones, neurotransmitters, and oxidants all have beneficial, but also harmful effects if out of balance. Therefore, the homeostasis of stress and adaptation should be governed by the hormone balance, neurotransmitter balance, and oxidant balance, as well as the interactions among these substances. The imbalance and the over-interaction of these balances may ultimately cause increased oxidant generation and oxidative damage to biomolecules. This increased oxidative damage may add to the oxidant burden associated with normal aerobic metabolism, which in itself, generates oxidants, causes accumulation of oxidative damage in mitochondria, and contributes to normal aging. Therefore, the stress-associated increase of oxidative damage may, in part, contribute to stress-associated aging acceleration and age-related neurodegenerative diseases.

Changes with aging of steroidal levels in the cerebrospinal fluid of women

OBJECTIVE

Age-related changes of steroid levels in the central nervous system (CNS) are not well understood. To investigate whether steroidal conditions in the CNS of women change with aging and menopause, steroid levels have been measured in serum and cerebrospinal fluid (CSF), and examined correlations with aging.

METHODS

Serum and CSF concentrations of estradiol (E2), cortisol, dehydroepiandrosterone (DHEA), DHEA sulfate (DHEAS) and albumin were measured in 80 female patients who underwent operations for benign gynecological diseases. They had no endocrinological or neurological disorders and were aged 17-71 years; 62 patients were in premenopause and 18 were in postmenopause.

RESULTS

Serum levels of E2 decreased markedly after menopause, while levels of DHEA and DHEAS decreased gradually with age. There was no significant change with age of serum cortisol levels. The CSF concentrations of E2 (0.2-3 pg/ml) decreased with age [correlation coefficient (r)= 0.31, P < 0.01]. The CSF DHEA levels (0.1-0.8 ng/ml) did not change with age although not significantly, but CSF cortisol levels (0.1-0.6 microg/dl) increased with age (r = 0.35, P < 0.01). The CSF DHEAS concentrations were below the sensitivity of the radioimmunoassay (RIA) (1 ng/ml). The CSF/serum ratios of cortisol increased with age (r = 0.30, P < 0.01), as did those of DHEA (r = 0.55, P < 0.01). Although serum albumin levels did not change throughout life, CSF albumin levels and CSF/serum albumin ratios increased gradually with age (r = 0.28, P = 0.052; r = 0.23, P = 0.114, respectively), but there was no significance. There were marked decreases of serum E2 and DHEA levels and CSF E2 levels in postmenopausal women (P < 0.05), but CSF cortisol levels increased (P < 0.05) and DHEA levels in CSF were maintained after menopause.

CONCLUSION

These results indicate that steroids in CSF become cortisol dominated and deficient in estrogens with aging, especially after menopause.

Endogenous levels of dehydroepiandrosterone sulfate, but not other sex hormones, are associated with depressed mood in older women: the Rancho Bernardo Study

OBJECTIVE

The purpose of this study was to determine whether endogenous steroid hormone levels are associated with depressed mood in community-dwelling older women.

DESIGN

A cross-sectional population-based study.

SETTING

Rancho Bernardo, California

PARTICIPANTS

A total of 699 non-estrogen using, community-dwelling, postmenopausal women (aged 50 to 90 years) from the Rancho Bernardo cohort who were screened for depressed mood and had plasma obtained for steroid hormone assays in 1984-1987.

MEASUREMENTS

Plasma levels of total and bioavailable (non-SHBG-bound) estradiol and testosterone, estrone, androstenedione, cortisol, dehydroepiandrosterone, and (DHEA) and its sulfate (DHEAS) were measured by radioimmunoassay. Mood and depression were assessed using the Beck Depression Inventory.

RESULTS

Only DHEAS levels were significantly and inversely associated with depressed mood, and the association was independent of age, physical activity, and weight change (P = .0002). Age, sedentary lifestyle, and weight loss were positively associated with depressed mood. Alcohol intake, cigarette smoking, marital status, type of menopause, and season of testing were unassociated with depressed mood. A subset of 31 women with categorically defined depression had lower DHEAS levels compared with 93 age-matched nondepressed women (1.17 +/- 1.08 vs 1.57 +/- .98 micromol/L; P = .01).

CONCLUSIONS

These results add to the evidence that DHEA/S is a neuroactive steroid and point to the need for careful long-term clinical trials of DHEA therapy in older women with depressed mood.

Neurosteroid modulation of dendrodendritic inhibition in the mouse olfactory bulb

The present report describes neurosteroid modulation of olfactory bulb function by examining the effects of intrabulbar infusion of dehydroepiandrosterone sulfate (DHEAS), a neurohormone discovered in rat brain, on field potentials in the granule cell layer evoked by paired-pulse stimulation of the mouse lateral olfactory tract. Infusion of DHEAS (5 nmol) significantly decreased the test response without affecting the conditioning response. As a consequence, DHEAS selectively potentiated paired-pulse depression, which is believed to be due to granule cell-mediated inhibition of the mitral/tufted cells. The granule-to-mitral/tufted dendrodendritic synapse is GABAergic. Taken together, these results suggest that DHEAS potentiates the GABAergic dendrodendritic inhibition exerted by the granule cells on the mitral/tufted cells.

Dehydroepiandrosterone (DHEA) protects hippocampal cells from oxidative stress-induced damage

It has been postulated that decreases in plasma levels of dehydroepiandrosterone (DHEA) may contribute to the development of some age-related disorders. Along with neuroprotective and memory enhancing effects, DHEA has been shown to display antioxidant properties. Moreover, oxidative stress is known to cause lipid peroxidation and degenerative changes in the hippocampus, an area involved in memory processes and especially afflicted in Alzheimer's disease (AD). Accordingly, we investigated the antioxidant effects of DHEA in models of oxidative stress using rat primary hippocampal cells and human hippocampal tissue from AD patients and age-matched controls. A pre-treatment of rat primary mixed hippocampal cell cultures with DHEA (10-100 microM) protected against the toxicity induced by H2O2 and sodium nitroprusside. Moreover, DHEA (10-100 microM) was also able to prevent H2O2/FeSO4-stimulated lipid oxidation in both control and AD hippocampal tissues. Taken together, these data suggest that DHEA may be useful in treating age-related central nervous system diseases based on its protective effects in the hippocampus.

Dehydroepiandrosterone: biosynthesis and metabolism in the brain

Dehydroepiandrosterone (DHEA) is abundantly found in brain tissues of several species, including human. However, the cellular origin and pathway by which DHEA is synthesized in brain are not yet known. We have, therefore, initiated pilot experiments to explore gene expression of cytochrome P450 17alpha-hydroxylase (P450c17), the key steroidogenic enzyme for androgen synthesis, and evaluate DHEA production by highly purified astrocytes, oligodendrocytes, and neurons. Using RT-PCR, we have demonstrated for the first time that astrocytes and neurons in the cerebral cortex of neonatal rat brain express P450c17. The presence of P450c17 in astrocytes and neurons was supported by the ability of these cells to metabolize pregnenolone to DHEA in a dose-dependent manner as determined by RIA. These data were further confirmed by production of androstenedione by astrocytes using progesterone as a substrate. However, cortical neurons express a low transcript of P450c17 messenger RNA and produce low levels of DHEA and androstenedione compared with astrocytes. Oligodendrocytes neither express the messenger RNA nor produce DHEA. The production of DHEA by astrocytes is not limited to cerebral cortex, as hypothalamic astrocytes produce DHEA at a level 3 times higher than that produced by cortical astrocytes. Cortical and hypothalamic astrocytes also have the capacity to metabolize DHEA to testosterone and estradiol in a dose-dependent manner. However, hypothalamic astrocytes were 3 times more active than cortical astrocytes in the metabolism of DHEA to estradiol. In conclusion, our data presented evidence that astrocytes and neurons express P450c17 and synthesize DHEA from pregnenolone. Astrocytes also have the capacity to metabolize DHEA into sex steroid hormones. These data suggest that as in gonads and adrenal, DHEA is biosynthesized in the brain by a P450c17-dependent mechanism.

Stress and the aging hippocampus

The "glucocorticoid cascade hypothesis" of hippocampal aging has stimulated a great deal of research into the neuroendocrine aspects of aging and the role of glucocorticoids, in particular. Besides strengthening the methods for investigating the aging brain, this research has revealed that the interactions between glucocorticoids and hippocampal neurons are far more complicated than originally envisioned and involve the participation of neurotransmitter systems, particularly the excitatory amino acids, as well as calcium ions and neurotrophins. New information has provided insights into the role of early experience in determining individual differences in brain and body aging by setting the reactivity of the hypothalamopituitary-adrenal axis and the autonomic nervous system. As a result of this research and advances in neuroscience and the study of aging, we now have a far more sophisticated view of the interactions among genes, early development, and environmental influences, as well as a greater appreciation of events at the cellular and molecular levels which protect neurons, and a greater appreciation of pathways of neuronal damage and destruction. While documenting the ultimate vulnerability of the brain to stressful challenges and to the aging process, the net result of this research has highlighted the resilience of the brain and offered new hope for treatment strategies for promoting the health of the aging brain.

Pregnenolone sulfate modulates NMDA receptors, inducing and potentiating acute excitotoxicity in isolated retina

Pregnenolone sulfate (PS) acts as a positive allosteric modulator of N-methyl-D-aspartate (NMDA) receptor-mediated responses. In the retina, we previously observed that the synthesis of pregnenolone and PS increases after stimulation of NMDA receptors and blockade of the synthesis reduces retinal cell death. This study was carried out to explore in the isolated and intact retina the possible role of PS in NMDA-induced excitotoxicity. Lactate dehydrogenase (LDH) measurements and morphological analysis revealed that a 90-min exogenous application of PS at 0.1-500 microM concentrations potentiated NMDA-induced cell death and at 50-500 microM concentrations caused cytotoxicity. After 45 min, either NMDA or PS caused no significant LDH release; but their co-application resulted in a high degree of toxicity. In addition, we found that a mild NMDA insult developed into serious damage when even low PS concentrations (0.1-10 microM) were used. Toxicity-inducing and -potentiating effects were specific to PS modulatory action on NMDA receptors, in that they were blocked by 4-(3-phosphonopropyl)2-piperazinecarboxylic acid (CPP) and MK-801 but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and neither dehydroepiandrosterone sulfate nor pregnenolone caused LDH release. Prevention of degenerative signs was seen in retinae pretreated with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), a Cl- channel blocker, thus indicating a Na+/Cl--dependent acute mode of excitotoxic cell death responsible for PS toxicity. The positive interaction between the neurosteroid and NMDA receptors was further proved by a PS dose-dependent increase in NMDA-induced stimulation of [3H] MK-801 binding to retinal membranes. The results suggest a crucial role of PS in retinal vulnerability and propose the toxicity-potentiating effects as an important key in linking NMDA-induced endogenous synthesis to acute excitotoxicity.

Neurosteroids, brain damage, and mental illness

The steroidal environment of the brain has marked consequences for both its structure and function. Social or physical stress has deleterious results on hippocampal function. This can be replicated by raising corticoids, which are also highly responsive to stress. Corticosterone, the major glucocorticoid in the rat, induces neuronal death in primary hippocampal cultures. Elevated corticoids also induce mood changes, and these are well known to be associated with stress, particularly chronic stress such as social adversity accentuated by intercurrent aversive life events. DHEA, a second adrenal steroid, has a very different developmental history, increasing rapidly during childhood, reaching a peak in youth, and declining thereafter in both blood and CSF. DHEA, in contrast to corticoids, has brain protective actions. It reduces the neurotoxic actions of glutamate analogues (such as NMDA) as well as those of corticoids. Evidence from several sources suggests that DHEA can act as an antiglucocorticoid. DHEA levels are reduced in major depressive disorders in both adolescents and adults, and a raised cortisol/DHEA ratio (together with intercurrent life events) predicts delayed recovery. DHEA may have a role in the treatment of depression. Together, these findings suggest that altered steroidal environment, whether induced by stress or aging, can have appreciable results on the cellular structure of the brain as well as on its function, although links between the two sets of findings are still tentative.