Cortisol secretion and Alzheimer's disease progression

Glucocorticoids trigger Alzheimer disease-like pathobiochemistry in rat neuronal cells expressing human tau

Amyloid precursor protein (APP) mis-processing and aberrant tau hyperphosphorylation are causally related to the pathogenesis and neurodegenerative processes that characterize Alzheimer's disease (AD). Abnormal APP metabolism leads to the generation of neurotoxic amyloid beta (Abeta), whereas tau hyperphosphorylation culminates in cytoskeletal disturbances, neuronal dysfunction and death. Many AD patients hypersecrete glucocorticoids (GC) while neuronal structure, function and survival are adversely influenced by elevated GC levels. We report here that a rat neuronal cell line (PC12) engineered to express the human ortholog of the tau protein (PC12-htau) becomes more vulnerable to the toxic effects of either Abeta or GC treatment. Importantly, APP metabolism in GC-treated PC12-htau cells is selectively shifted towards increased production of the pro-amyloidogenic peptide C99. Further, GC treatment results in hyperphosphorylation of human tau at AD-relevant sites, through the cyclin-dependent kinase 5 (E.C. 2.7.11.26) and GSK3 (E.C. 2.7.11.22) protein kinases. Pulse-chase experiments revealed that GC treatment increased the stability of tau protein rather than its de novo synthesis. GC treatment also induced accumulation of transiently expressed EGFP-tau in the neuronal perikarya. Together with previous evidence showing that Abeta can activate cyclin-dependent kinase 5 and GSK3, these results uncover a potential mechanism through which GC may contribute to AD neuropathology.

Salivary cortisol awakening response in mild Alzheimer disease, caregivers, and noncaregivers

Alterations in the hypothalamic-pituitary-adrenal axis have been noted in people with Alzheimer disease (AD) and in the people caring for them. In a case-control study, we assessed whether the cortisol response at awakening and diurnal cortisol would reflect these changes. AD patients, their caregivers, and healthy senior noncaregivers collected saliva within 5 minutes of waking, 30 minutes after waking, before lunch, 1 hour after lunch, and at 11 pm or when getting ready for bed. They also completed a Perceived Stress Scale. Total cortisol for the day after adjusting for antidepressant use revealed a group effect [F(2,39)=12.49, P<0.0001], with mild AD patients and caregivers having higher cortisol values. Unlike the noncaregivers (t=-1.15, df=14, P>0.27), both cortisol values of the AD caregivers (t=-2.96, df=16, P<0.03) and the AD patients' (t=-2.5, df=14, P<0.01) increased between awakening and 30 minutes afterward. There were also group differences at awakening [F(2,48)=4.6, P=0.012] adjusting for antidepressant use and 30 minutes after waking adjusting for antidepressant use and awakening cortisol [F(2,46)=4.7, P=0.014<0.02). AD patients (r=0.45, P=0.08) and caregivers (r=0.44, P=0.10) with higher cortisol values 30 minutes after waking also showed a trend toward higher perceived stress scores. Salivary cortisol and cortisol response on awakening may enhance future studies relating free cortisol to subjective psychologic and physiologic markers.

Corticosterone and related receptor expression are associated with increased beta-amyloid plaques in isolated Tg2576 mice

Previously, we reported that the stress associated with chronic isolation was associated with increased beta-amyloid (Abeta) plaque deposition and memory deficits in the Tg2576 transgenic animal model of Alzheimer's disease (AD) [Dong H, Goico B, Martin M, Csernansky CA, Bertchume A, Csernansky JG (2004) Effects of isolation stress on hippocampal neurogenesis, memory, and amyloid plaque deposition in APP (Tg2576) mutant mice. Neuroscience 127:601-609]. In this study, we investigated the potential mechanisms of stress-accelerated Abeta plaque deposition in this Tg2576 mice by examining the relationship between plasma corticosterone levels, expression of glucocorticoid receptor (GR) and corticotropin-releasing factor receptor-1 (CRFR1) in the brain, brain tissue Abeta levels and Abeta plaque deposition during isolation or group housing from weaning (i.e. 3 weeks of age) until 27 weeks of age. We found that isolation housing significantly increased plasma corticosterone levels as compared with group-housing in both Tg+ mice (which contain and overexpress human amyloid precursor protein (hAPP) gene) and Tg- mice (which do not contain hAPP gene as control). Also, isolated, but not group-housed animals showed increases in the expression of GR in the cortex. Furthermore, the expression of CRFR1 was increased in isolated Tg+ mice, but decreased in isolated Tg- mice in both cortex and hippocampus. Changes in the components of hypothalamic-pituitary-adrenal (HPA) axis were accompanied by increases in brain tissue Abeta levels and Abeta plaque deposition in the hippocampus and overlying cortex in isolated Tg+ mice. These results suggest that isolation stress increases corticosterone levels and GR and CRFR1 expression in conjunction with increases in brain tissue Abeta levels and Abeta plaque deposition in the Tg2576 mouse model of AD.

Stress and glucocorticoid footprints in the brain-the path from depression to Alzheimer's disease

Increasingly, stress is recognized as a trigger of depressive episodes and recent evidence suggests a causal role of stress in the onset and progression of Alzheimer's disease (AD) pathology. Besides aging, sex is an important determinant of prevalence rates for both AD and mood disorders. In light of a recent meta-analysis indicating that depressed subjects have a higher likelihood of developing AD, a key message in this article will be that both depression and AD are stress-related disorders and may represent a continuum that should receive more attention in future neurobiological studies. Accordingly, this review considers some of the cellular mechanisms that may be involved in regulating this transition threshold. In addition, it highlights the importance of addressing the question of how aging and sex interplay with stress to influence mood and cognition, with a bias towards consideration of neuroplastic events in particular brain regions, as the basis of AD and depressive disorders.

The effect of stress on the expression of the amyloid precursor protein in rat brain

The abnormal processing of the amyloid precursor protein (APP) is a pivotal event in the development of the unique pathology that defines Alzheimer's disease (AD). Stress, and the associated increase in corticosteroids, appear to accelerate brain ageing and may increase vulnerability to Alzheimer's disease via altered APP processing. In this study, rats were repeatedly exposed to an unavoidable stressor, an open elevated platform. Previous studies in this laboratory have shown that a single exposure produces a marked increase in plasma corticosterone levels but animals develop tolerance to this effect between 10 and 20 daily sessions. Twenty-four hours after stress, there was an increase in the ratio of the deglycosylated form of APP in the particulate fraction of the brain, which subsequently habituated after 20 days. The levels of soluble APP (APPs) tended to be lower in the stress groups compared to controls except for a significant increase in the hippocampus after 20 days of platform exposure. Since APPs is reported to have neurotrophic properties, this increased release may represent a neuroprotective response to repeated stress. It is possible that the ability to mount this response decreases with age thus increasing the vulnerability to stress-induced AD-related pathology.

The stress system in depression and neurodegeneration: focus on the human hypothalamus

The stress response is mediated by the hypothalamo-pituitary-adrenal (HPA) system. Activity of the corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN) forms the basis of the activity of the HPA-axis. The CRH neurons induce adrenocorticotropin (ACTH) release from the pituitary, which subsequently causes cortisol release from the adrenal cortex. The CRH neurons co-express vasopressin (AVP) which potentiates the CRH effects. CRH neurons project not only to the median eminence but also into brain areas where they, e.g., regulate the adrenal innervation of the autonomic system and affect mood. The hypothalamo-neurohypophysial system is also involved in stress response. It releases AVP from the PVN and the supraoptic nucleus (SON) and oxytocin (OXT) from the PVN via the neurohypophysis into the bloodstream. The suprachiasmatic nucleus (SCN), the hypothalamic clock, is responsible for the rhythmic changes of the stress system. Both centrally released CRH and increased levels of cortisol contribute to the signs and symptoms of depression. Symptoms of depression can be induced in experimental animals by intracerebroventricular injection of CRH. Depression is also a frequent side effect of glucocorticoid treatment and of the symptoms of Cushing's syndrome. The AVP neurons in the hypothalamic PVN and SON are also activated in depression, which contributes to the increased release of ACTH from the pituitary. Increased levels of circulating AVP are also associated with the risk for suicide. The prevalence, incidence and morbidity risk for depression are higher in females than in males and fluctuations in sex hormone levels are considered to be involved in the etiology. About 40% of the activated CRH neurons in mood disorders co-express nuclear estrogen receptor (ER)-alpha in the PVN, while estrogen-responsive elements have been found in the CRH gene promoter region, and estrogens stimulate CRH production. An androgen-responsive element in the CRH gene promoter region initiates a suppressing effect on CRH expression. The decreased activity of the SCN is the basis for the disturbances of circadian and circannual fluctuations in mood, sleep and hormonal rhythms found in depression. Neuronal loss was also reported in the hippocampus of stressed or corticosteroid-treated rodents and primates. Because of the inhibitory control of the hippocampus on the HPA-axis, damage to this structure was expected to disinhibit the HPA-axis, and to cause a positive feedforward cascade of increasing glucocorticoid levels over time. This 'glucocorticoid cascade hypothesis' of stress and hippocampal damage was proposed to be causally involved in age-related accumulation of hippocampal damage in disorders like Alzheimer's disease and depression. However, in postmortem studies we could not find the presumed hippocampal damage of steroid overexposure in either depressed patients or in patients treated with synthetic steroids.

Plasma cortisol and progression of dementia in subjects with Alzheimer-type dementia

OBJECTIVE

Studies of subjects with dementia of the Alzheimer type have reported correlations between increases in activity of the hypothalamic-pituitary-adrenal (HPA) axis and hippocampal degeneration. In this study, the authors sought to determine whether increases in plasma cortisol, a marker of HPA activity, were associated with clinical and cognitive measures of the rate of disease progression in subjects with Alzheimer-type dementia.

METHOD

Thirty-three subjects with very mild and mild Alzheimer-type dementia and 21 subjects without dementia were assessed annually for up to 4 years with the Clinical Dementia Rating scale and a battery of neuropsychological tests. Plasma was obtained at 8 a.m. on a single day and assayed for cortisol. Rates of change over time in the clinical and cognitive measures were derived from growth curve models.

RESULTS

In the subjects with dementia, but not in those without dementia, higher plasma cortisol levels were associated with more rapidly increasing symptoms of dementia and more rapidly decreasing performance on neuropsychological tests associated with temporal lobe function. No associations were observed between plasma cortisol levels and clinical and cognitive assessments obtained at the single assessment closest in time to the plasma collection.

CONCLUSIONS

Higher HPA activity, as reflected by increased plasma cortisol levels, is associated with more rapid disease progression in subjects with Alzheimer-type dementia.

Plasma cortisol and progression of dementia in subjects with Alzheimer-type dementia

OBJECTIVE

Studies of subjects with dementia of the Alzheimer type have reported correlations between increases in activity of the hypothalamic-pituitary-adrenal (HPA) axis and hippocampal degeneration. In this study, the authors sought to determine whether increases in plasma cortisol, a marker of HPA activity, were associated with clinical and cognitive measures of the rate of disease progression in subjects with Alzheimer-type dementia.

METHOD

Thirty-three subjects with very mild and mild Alzheimer-type dementia and 21 subjects without dementia were assessed annually for up to 4 years with the Clinical Dementia Rating scale and a battery of neuropsychological tests. Plasma was obtained at 8 a.m. on a single day and assayed for cortisol. Rates of change over time in the clinical and cognitive measures were derived from growth curve models.

RESULTS

In the subjects with dementia, but not in those without dementia, higher plasma cortisol levels were associated with more rapidly increasing symptoms of dementia and more rapidly decreasing performance on neuropsychological tests associated with temporal lobe function. No associations were observed between plasma cortisol levels and clinical and cognitive assessments obtained at the single assessment closest in time to the plasma collection.

CONCLUSIONS

Higher HPA activity, as reflected by increased plasma cortisol levels, is associated with more rapid disease progression in subjects with Alzheimer-type dementia.

Diurnal cycle of salivary cortisol in older adult men and women with subjective complaints of memory deficits and/or depressive symptoms: relation to cognitive functioning

In populations of young and older adults, it has been shown that individuals may be categorized into one of three diurnal subgroups when salivary cortisol levels are assessed over a 2-day period and compared for their consistency across days: a typical subgroup, a flat subgroup, and an inconsistent subgroup. Interestingly, recent studies have reported that the typical subgroup represents the majority of the young and older adult population, a finding that is difficult to reconcile with previous studies showing increased cortisol levels in older adults with depression or cognitive impairments. In order to assess whether a typical diurnal cortisol profile is representative across different subgroups of older adults, we assessed diurnal cortisol cycle representation in a sample of older adults with subjective complaints of depression and/or memory problems. Furthermore, given the robust relationship between cortisol and cognitive function, the present study examined the association between the three diurnal subgroups and cognitive performance. Forty-two older individuals were recruited on the basis of reporting subjective complaints of either memory problems and/or depressive mood. Participants were asked to sample their saliva over a 2-day period and were then asked to undergo a neuropsychological evaluation that taps into short-term memory, declarative memory and language. The results showed that 69% of the sample presented a Flat cycle of salivary cortisol over a 2-day period while 19% presented an inconsistent pattern and 12% presented a typical pattern. Participants in the flat subgroup were significantly impaired on letter verbal fluency. Furthermore, a relationship was found between diurnal cortisol subgroup representation and subjective complaint profile. These findings show that older adults with complaints of memory problems and/or depressive symptoms do not present the typical profile of the diurnal cortisol cycle, and they provide a preliminary view of how diurnal cortisol profile relates to cognitive function during human aging.

Concentration dependent actions of glucocorticoids on neuronal viability and survival

A growing body of evidence based on experimental data demonstrates that glucocorticoids (GCs) can play a potent role in the survival and death of neurons. However, these observations reflect paradoxical features of GCs, since these adrenal stress hormones are heavily involved in both neurodegenerative and neuroprotective processes. The actual level of GCs appears to have an essential impact in this bimodal action. In the present short review we aim to show the importance of concentration dependent action of GCs on neuronal cell viability and cell survival in the brain. Additionally, we will summarize the possible GC-induced cellular mechanisms at different GC concentrations providing a background for their effect on the fate of nerve cells in conditions that are a challenge to their survival.

Reduction of neuronal intranuclear rodlets immunoreactive for tubulin and glucocorticoid receptor in Alzheimer's disease

Neuronal intranuclear rodlets were described in normal brain over a century ago, but their functional significance and pathological relevance is unknown. Here, we show co-localization of tubulin and glucocorticoid receptor-like immunoreactivity in these intranuclear inclusions in human brain. In addition, we provide evidence for a massive reduction in their areal density in Alzheimer's disease brain, but not in another common neurodegenerative condition, dementia with Lewy bodies. The marked reduction of these inclusions in Alzheimer's disease may support the concept of a role for stress hormones in Alzheimer's pathogenesis.

The stress system in the human brain in depression and neurodegeneration

Corticotropin-releasing hormone (CRH) plays a central role in the regulation of the hypothalamic-pituitary-adrenal (HPA)-axis, i.e., the final common pathway in the stress response. The action of CRH on ACTH release is strongly potentiated by vasopressin, that is co-produced in increasing amounts when the hypothalamic paraventricular neurons are chronically activated. Whereas vasopressin stimulates ACTH release in humans, oxytocin inhibits it. ACTH release results in the release of corticosteroids from the adrenal that, subsequently, through mineralocorticoid and glucocorticoid receptors, exert negative feedback on, among other things, the hippocampus, the pituitary and the hypothalamus. The most important glucocorticoid in humans is cortisol, present in higher levels in women than in men. During aging, the activation of the CRH neurons is modest compared to the extra activation observed in Alzheimer's disease (AD) and the even stronger increase in major depression. The HPA-axis is hyperactive in depression, due to genetic factors or due to aversive stimuli that may occur during early development or adult life. At least five interacting hypothalamic peptidergic systems are involved in the symptoms of major depression. Increased production of vasopressin in depression does not only occur in neurons that colocalize CRH, but also in neurons of the supraoptic nucleus (SON), which may lead to increased plasma levels of vasopressin, that have been related to an enhanced suicide risk. The increased activity of oxytocin neurons in the paraventricular nucleus (PVN) may be related to the eating disorders in depression. The suprachiasmatic nucleus (SCN), i.e., the biological clock of the brain, shows lower vasopressin production and a smaller circadian amplitude in depression, which may explain the sleeping problems in this disorder and may contribute to the strong CRH activation. The hypothalamo-pituitary thyroid (HPT)-axis is inhibited in depression. These hypothalamic peptidergic systems, i.e., the HPA-axis, the SCN, the SON and the HPT-axis, have many interactions with aminergic systems that are also implicated in depression. CRH neurons are strongly activated in depressed patients, and so is their HPA-axis, at all levels, but the individual variability is large. It is hypothesized that particularly a subgroup of CRH neurons that projects into the brain is activated in depression and induces the symptoms of this disorder. On the other hand, there is also a lot of evidence for a direct involvement of glucocorticoids in the etiology and symptoms of depression. Although there is a close association between cerebrospinal fluid (CSF) levels of CRH and alterations in the HPA-axis in depression, much of the CRH in CSF is likely to be derived from sources other than the PVN. Furthermore, a close interaction between the HPA-axis and the hypothalamic-pituitary-gonadal (HPG)-axis exists. Organizing effects during fetal life as well as activating effects of sex hormones on the HPA-axis have been reported. Such mechanisms may be a basis for the higher prevalence of mood disorders in women as compared to men. In addition, the stress system is affected by changing levels of sex hormones, as found, e.g., in the premenstrual period, ante- and postpartum, during the transition phase to the menopause and during the use of oral contraceptives. In depressed women, plasma levels of estrogen are usually lower and plasma levels of androgens are increased, while testosterone levels are decreased in depressed men. This is explained by the fact that both in depressed males and females the HPA-axis is increased in activity, parallel to a diminished HPG-axis, while the major source of androgens in women is the adrenal, whereas in men it is the testes. It is speculated, however, that in the etiology of depression the relative levels of sex hormones play a more important role than their absolute levels. Sex hormone replacement therapy indeed seems to improve mood in elderly people and AD patients. Studies of rats have shown that high levels of cumulative corticosteroid exposure and rather extreme chronic stress induce neuronal damage that selectively affects hippocampal structure. Studies performed under less extreme circumstances have so far provided conflicting data. The corticosteroid neurotoxicity hypothesis that evolved as a result of these initial observations is, however, not supported by clinical and experimental observations. In a few recent postmortem studies in patients treated with corticosteroids and patients who had been seriously and chronically depressed no indications for AD neuropathology, massive cell loss, or loss of plasticity could be found, while the incidence of apoptosis was extremely rare and only seen outside regions expected to be at risk for steroid overexposure. In addition, various recent experimental studies using good stereological methods failed to find massive cell loss in the hippocampus following exposure to stress or steroids, but rather showed adaptive and reversible changes in structural parameters after stress. Thus, the HPA-axis in AD is only moderately activated, possibly due to the initial (primary) hippocampal degeneration in this condition. There are no convincing arguments to presume a causal, primary role for cortisol in the pathogenesis of AD. Although cortisol and CRH may well be causally involved in the signs and symptoms of depression, there is so far no evidence for any major irreversible damage in the human hippocampus in this disorder.

Inhibitory effects of Bombusae concretio Salicea on neuronal secretion of Alzheimer's beta-amyloid peptides, a neurodegenerative peptide

Alzheimer's disease (AD) is characterized by the age-related deposition of beta-amyloid (A beta) 40/42 peptide aggregates in vulnerable brain regions. Multiple levels of evidence implicate a central role for A beta in the pathophysiology of AD. A beta is generated by the regulated cleavage of a = 700 amino acid A beta precursor protein (betaAPP). Full-length betaAPP can undergo proteolytic cleavage either within the A beta domain to generate secreted sbetaAPP alpha or at the N-terminal and C-terminal domain(s) of A beta to generate amyloidogenic A beta peptides. Several epidemiological studies have reported that estrogen replacement therapy protects against the development of AD in postmenopausal women. The aim of this study was to elucidate the antioxidant neuroprotective mechanism of Bombusae concretio Salicea (BC). BC was effective protectants against oxidative glutamate toxicity in the murine neuroblastoma cells (N2a) and human neuroblastoma cells (SK-N-MC). BC exhibited similar protective properties against oxidative glutamate toxicity and H2O2 toxicity. BC exhibited an antioxidant activity at approximately 20 microg/ml. BC of 5 microg/ml was ineffective in preventing the oxidative modification of LDL. The half-maximal effective concentration for BC was 16 microg/ml. These results suggested that BC supplementation in elderly men may be protective in the treatment of Alzheimer's disease (AD). We report here that treatment with BC increases the secretion of the nonamyloidogenic APP fragment, sbetaAPP alpha and decreases the secretion of A beta peptides from N2a cells and rat primary cerebrocortical neurons. These results raise the possibility that BC supplementation in elderly men may be protective in the treatment of AD.

Habituation to stress and dexamethasone suppression in rats with selective basal forebrain cholinergic lesions

Previous studies suggest a role for basal forebrain cholinergic neurons in enhancing the inhibitory influence of the hippocampus and medial prefrontal cortex (mPFC) on glucocorticoid stress responses mediated by the hypothalamic-pituitary-adrenocortical (HPA) axis. An inhibitory action of the basal forebrain cholinergic (BFC) system may occur through facilitation of stress-related information processing and maintenance of glucocorticoid receptor (GR) expression and negative feedback signaling in these target regions. The current study investigated the possibility that BFC input to the hippocampus contributes to habituation of the glucocorticoid response following repeated exposure to a stressor. Cholinergic lesions were made by microinjections of the immunotoxin 192 IgG-saporin into the medial septum/vertical limb of the diagonal band, and 3 weeks later rats were subjected to six daily sessions of restraint stress. Blood samples taken before, during and after acute stress revealed a significant increase in peak activation and protracted elevation of corticosterone in cholinergic lesioned rats. After 5 days of repeated stress, however, both groups habituated to the stressor, as indicated by similarly low corticosterone profiles throughout both the response and recovery period. Against that habituated background, rats were administered a dexamethasone challenge on day 6, so that feedback status could be examined. Dexamethasone-induced suppression of endogenous corticosterone before, during, and after stress was significantly attenuated in lesioned rats. The profile of dysfunction in glucocorticoid regulation after selective cholinergic lesions in young animals may be relevant to the adrenocortical hyperactivity and negative feedback deficits seen in conditions such as normal aging and Alzheimer's dementia, in which integrity of the basal forebrain cholinergic system is compromised.

Inhibition of adrenal cortical steroid formation by procaine is mediated by reduction of the cAMP-induced 3-hydroxy-3-methylglutaryl-coenzyme A reductase messenger ribonucleic acid levels

Elevated glucocorticoid levels are associated with many diseases, including age-related depression, hypertension, Alzheimer's disease, and acquired immunodeficiency syndrome. Cortisol-lowering agents could provide useful complementary therapy for these disorders. We examined the effect of procaine and procaine in a pharmaceutical formulation on adrenal cortical steroid formation. Procaine inhibited dibutyryl cyclic AMP (dbcAMP)-induced corticosteroid synthesis by murine Y1 and human H295R adrenal cells in a dose-dependent manner without affecting basal steroid formation. Treatment of rats with the procaine-based formulation reduced circulating corticosterone levels. This steroidogenesis-inhibiting activity of procaine was not observed in Leydig cells, suggesting that the effect was specific to adrenocortical cells. In search of the mechanism underlying this inhibitory effect on cAMP-induced corticosteroidogenesis, procaine was found to affect neither the cAMP-dependent protein kinase activity nor key proteins involved in cholesterol transport into mitochondria, cytochrome P450 side chain cleavage enzyme expression, and enzymatic activities associated with cholesterol metabolism to final steroid products. However, procaine reduced in a dose-dependent manner the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA) activity and the dbcAMP-induced HMG-CoA reductase mRNA levels by affecting mRNA stability. These data suggest that the inhibitory effect of procaine on cAMP-induced corticosteroid formation is due to the reduced synthesis of cholesterol. This modulatory effect of procaine on HMG-CoA reductase mRNA expression was also seen in dbcAMP-stimulated Hepa1-6 mouse liver hepatoma cells. Taken together, these results suggest that procaine may provide a pharmacological means for the control of hormone-induced HMG-CoA reductase mRNA expression and hypercortisolemia.

Methylprednisolone increases neuronal apoptosis during autoimmune CNS inflammation by inhibition of an endogenous neuroprotective pathway

Optic neuritis is one of the most common clinical manifestations of multiple sclerosis (MS), a chronic inflammatory disease of the CNS. High-dosage methylprednisolone treatment has been established as the standard therapy of acute inflammation of the optic nerve (ON). The rationale for corticosteroid treatment lies in the antiinflammatory and immunosuppressive properties of these drugs, as shown in experimental autoimmune encephalomyelitis (EAE), the animal model of MS. To investigate the influence of methylprednisolone therapy on the survival of retinal ganglion cells (RGCs), the neurons that form the axons of the ON, we used a rat model of myelin oligodendrocyte glycoprotein (MOG)-induced EAE. Optic neuritis was diagnosed by recording visual evoked potentials, and RGC function was monitored by measuring electroretinograms. Methylprednisolone treatment significantly increased RGC apoptosis during MOG-EAE. By Western blot analysis, we identified the underlying molecular mechanism: a suppression of mitogen-activated protein kinase (MAPK) phosphorylation, which is a key event in an endogenous neuroprotective pathway. The methylprednisolone-induced inhibition of MAPK phosphorylation was calcium dependent. Hence, we provide evidence for negative effects of steroid treatment on neuronal survival during chronic inflammatory autoimmune disease of the CNS, which should result in a reevaluation of the current therapy regimen.

Reversal of cycloheximide-induced memory disruption by AIT-082 (Neotrofin) is modulated by, but not dependent on, adrenal hormones

RATIONALE

AIT-082 (Neotrofin), a hypoxanthine derivative, has been shown to improve memory in both animals and humans. In animals, adrenal hormones modulate the efficacy of many memory-enhancing compounds, including piracetam and tacrine (Cognex).

OBJECTIVE

To investigate the role of adrenal hormones in the memory-enhancing action of AIT-082.

METHODS

Plasma levels of adrenal hormones (corticosterone and aldosterone) in mice were significantly reduced by surgical or chemical (aminoglutethimide) adrenalectomy or significantly elevated by oral administration of corticosterone. The effects of these hormone level manipulations on the memory-enhancing activity of AIT-082 and piracetam were evaluated using a cycloheximide-induced amnesia/passive avoidance model.

RESULTS

As previously reported by others, the memory enhancing action of piracetam was abolished by adrenalectomy. In contrast, the memory enhancement by 60 mg/kg AIT-082 (IP) was unaffected. However, a sub-threshold dose of AIT-082 (0.1 mg/kg, IP) that did not improve memory in control animals did improve memory in adrenalectomized animals. These data suggested that, similar to piracetam and tacrine, the memory enhancing action of AIT-082 might be inhibited by high levels of adrenal hormones. As expected, corticosterone (30 and 100 mg/kg) inhibited the action of piracetam, however no dose up to 100 mg/kg corticosterone inhibited the activity of AIT-082.

CONCLUSIONS

These data suggest that while AIT-082 function is not dependent on adrenal hormones, it is modulated by them. That memory enhancement by AIT-082 was not inhibited by high plasma corticosterone levels may have positive implications for its clinical utility, given that many Alzheimer's disease patients have elevated plasma cortisol levels.

Neuronal overexpression of "readthrough" acetylcholinesterase is associated with antisense-suppressible behavioral impairments

Molecular origin(s) of the diverse behavioral responses to anticholinesterases were explored in behaviorally impaired transgenic (Tg) FVB/N mice expressing synaptic human acetylcholinesterase (hAChE-S). Untreated hAChE-S Tg, unlike naïve FVB/N mice, presented variably intense neuronal overexpression of the alternatively spliced, stress-induced mouse "readthrough" mAChE-R mRNA. Both strains displayed similar diurnal patterns of locomotor activity that were impaired 3 days after a day-to-night switch. However, hAChE-S Tg, but not FVB/N mice responded to the circadian switch with irregular, diverse bursts of increased locomotor activity. In social recognition tests, controls displayed short-term recognition, reflected by decreased exploration of a familiar, compared to a novel juvenile conspecific as well as inverse correlation between social recognition and cortical and hippocampal AChE specific activities. In contrast, transgenics presented poor recognition, retrievable by tetrahydroaminoacridine (tacrine, 1.5 mg kg(-1)). Tacrine's effect was short-lived (24 h) suppression of the abnormal social recognition pattern in transgenics. Efficacy of antisense treatment was directly correlated with AChE-R levels and the severity of the impaired phenotype, being most apparent in transgenics presenting highly abnormal pre-treatment behavior. These findings demonstrate that neuronal AChE-R overproduction is involved in various behavioral impairments and anticholinesterase responses, and point to the antisense strategy as a potential approach for re-establishing cholinergic balance.

Salivary cortisol day profiles in elderly with mild cognitive impairment

It is unknown whether hypothalamus-pituitary-adrenal (HPA) axis dysfunction is associated with the memory impairments observed among elderly participants with mild cognitive impairment (MCI), a group considered at increased risk for Alzheimer's disease (AD). Therefore, salivary cortisol levels were measured at six points over the course of the day while at-home in MCI participants (n=16), normal elderly (n=28), and young controls (n=14). Results revealed that MCI participants did not show elevated salivary cortisol levels. The 9 a.m. cortisol level of the MCI group was significantly lower than the 9 a.m. level of the young controls, but did not differ from those of the normal elderly group. In contrast to the other two groups, within the MCI group mean cortisol levels were inversely related to immediate recall of paragraphs. No association was observed between mean cortisol levels and performance in paired associates and digit span. Whether cortisol levels, in conjunction with other factors, such as hippocampal volume, will lead to improved prediction of future decline to AD in participants with MCI remains to be established in longitudinal studies.

Cortisol is increased in postmortem cerebrospinal fluid of multiple sclerosis patients: relationship with cytokines and sepsis

Hypothalmo-pituitary-adrenal (HPA) axis activity is altered in patients with multiple sclerosis (MS), resulting in elevated basal levels and enhanced response of cortisol in stimulation tests. HPA axis hyperactivation in MS is thought to be the result of complex interactions of genetic, immunologic, and neuroendocrinological mechanisms. In order to investigate whether cytokine levels in the central nervous system are associated with the activation of the HPA axis in MS, we measured cortisol, interleukin (IL)-6, IL-10 and TNF-alpha levels in postmortem cerebrospinal fluid (CSF) of 18 patients with severe MS and 50 controls. We also investigated the cortisol and cytokine levels in the CSF of a group of MS patients and controls who died with sepsis, in order to see whether acute infectious situations affect the association between cortisol and cytokines. The cortisol levels in MS patients were increased by 80% in comparison to controls (p=0.008). There was no difference in IL-6 levels between the groups, while IL-10 and TNF-alpha levels of the majority of subjects were below detection limits. There was a positive correlation between cortisol and IL-6 only in control patients with sepsis (r=0.89, p=0.019), but not within the MS patents with sepsis or MS and control groups without sepsis. Cortisol levels in postmortem serum and CSF were highly correlated (r>0.78, p<0.001). We concluded that the basal level of cortisol is significantly increased in the CSF of MS patients and that IL-6 is not responsible for this rise. The relationship between cortisol and IL-6 in sepsis is discussed.

Mental deterioration correlates with response of natural killer (NK) cell activity to physiological modifiers in patients with short history of Alzheimer's disease

Natural killer (NK) cell activity of peripheral blood mononuclear (PBM) cells was measured in 16 subjects with mild to moderate senile dementia of Alzheimer's type (sDAT) chosen for short history of disease and no medication, and in 17 age- and sex-matched controls. Levels of cytotoxicity at baseline and after PBM cell exposure to modifiers either negative (cortisol 10(-6) M) or positive (rIL-2 650 IU/ml and rIFN-gamma 100 UI/ml, respectively) were related to indices of hypothalamic-pituitary-adrenal (HPA) function and Gottfries Bråne Rating Scale (GBS) score for mental deterioration. Spontaneous NK cell activity was not significantly different in sDAT subjects vs controls. In vitro inhibition by cortisol was lower in sDAT (P<0.05); cytokine-induced changes were greater (rIL-2, P<0.02; rIFN-gamma, P<0.05). Percent negative or positive variations from baseline significantly correlated with GBS scores (P<0.05 or less). Serum cortisol and cortisol/DHEAS molar ratio at 0800 h were significantly higher in sDAT (P<0.05 and P<0.02, respectively). Cortisol/DHEA ratio positively correlated with GBS scores (P<0.02). Moreover, the ratios of incremental area of response ACTH/cortisol and beta-endorphin/cortisol after 1 microg/kg ovine-corticotrophin-releasing hormone (o-CRH) positively correlated with percent increase of NK cell activity after rIL-2 (P<0.01). Data indicate that patients with mild cognitive impairment and short history of sDAT show abnormal responsiveness of NK cell activity to physiological modifiers while maintaining normal spontaneous activity. Furthermore, data are compatible with partial glucocorticoid resistance at the immune level. Progressing sDAT longitudinal studies are needed to address: i) the clinical applicability of these abnormalities as prognostic factors; ii) the role played by pro-opiomelanocortin (POMC)-derived peptides and adrenal androgens in the control of NK cell activity.

Effects of rapid tryptophan depletion on salivary and plasma cortisol in Alzheimer's disease and the healthy elderly

Serotonergic function is reduced in dementia of Alzheimer type (DAT) and abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis are also common. There is considerable interaction between the two systems. Effects of lowering brain serotonin on salivary and plasma cortisol were assessed in patients with DAT and in control subjects. A double-blind, cross-over design involving administration of two nutritionally balanced amino acid mixtures with or without tryptophan was used. Salivary and plasma cortisol were measured at intervals before and after the drink. DAT patients had higher salivary cortisol than controls. Despite a reduction of approximately 70% in plasma free tryptophan after 4 h in both groups, there was no effect on salivary or plasma cortisol. We conclude that, in subjects with DAT and healthy elderly subjects, acute tryptophan depletion had no effect on cortisol secretion.

Altered circadian cortisol secretion in Alzheimer's disease: clinical and neuroradiological aspects

We determined circadian salivary cortisol levels in 18 outpatients affected by probable Alzheimer's disease (AD) and looked for a possible correlation with both cognitive impairment and brain CT scan findings. The diagnosis of probable AD was made according to the NINCDS-ADRDA criteria. The severity of cognitive impairment was quantified using the Mini Mental State Examination (MMSE) and the Global Deterioration Scale (GDS). Cortisol levels were measured on saliva samples collected at 08:00 AM and 08:00 PM. For each sample, a duplicate cortisol measurement was performed on 50 microl of saliva by means of a modified commercial radioimmunoassay kit. At the same time, 11 of the 18 AD patients enrolled also underwent a brain CT scan to estimate cerebral atrophy by using linear indexes. The mean value of cortisol levels was significantly higher in AD patients than in controls at both the morning and the evening measurements, and the circadian fluctuation of cortisol was less marked in AD patients than in controls, although this difference did not reach statistical significance. Morning cortisol levels were significantly correlated to both the MMSE and the GDS scores. A significant correlation was also found between morning cortisol levels and all the cerebral atrophy indexes. By contrast, no correlation was observed between evening cortisol levels or cortisol circadian fluctuations and either cognitive impairment or cerebral atrophy. In conclusion, despite the potential biases deriving from the small sample and the limitations of the CT scan study, our results suggest that, in AD patients, hypercortisolemia is correlated with severity of the disease.

Action of glucocorticoids on survival of nerve cells: promoting neurodegeneration or neuroprotection?

Extensive studies during the past decades provided compelling evidence that glucocorticoids (GCs) have the potential to affect the development, survival and death of neurones. These observations, however, reflect paradoxical features of GCs, as they may be critically involved in both neurodegenerative and neuroprotective processes. Hence, we first address different aspects of the complex role of GCs in neurodegeneration and neuroprotection, such as concentration dependent actions of GCs on neuronal viability, anatomical diversity of GC-mediated mechanisms in the brain and species and strain differences in GC-induced neurodegeneration. Second, the modulatory action of GCs during development and ageing of the central nervous system, as well as the contribution of altered GC balance to the pathogenesis of neurodegenerative disorders is considered. In addition, we survey recent data as to the possible mechanisms underlying the neurodegenerative and neuroprotective actions of GCs. As such, two major aspects will be discerned: (i) GC-dependent offensive events, such as GC-induced inhibition of glucose uptake, increased extracellular glutamate concentration and concomitant elevation of intracellular Ca(2+), decrease in GABAergic signalling and regulation of local GC concentrations by 11 beta-hydroxysteroid dehydrogenases; and (ii) GC-related cellular defence mechanisms, such as decrease in after-hyperpolarization, increased synthesis and release of neurotrophic factors and lipocortin-1, feedback regulation of Ca(2+) currents and induction of antioxidant enzymes. The particular relevance of these mechanisms to the neurodegenerative and neuroprotective effects of GCs in the brain is discussed.

Corticotropin-releasing hormone protects neurons against insults relevant to the pathogenesis of Alzheimer's disease

We previously reported that mice over-expressing the human amyloid precursor protein gene with the double Swedish mutation of familial Alzheimer's disease (mtAPP), which exhibit progressive deposition of amyloid beta-peptide in hippocampal and cortical brain regions, have an impaired ability to maintain a sustained glucocorticoid response to stress. Corticotropin releasing hormone (CRH), which initiates neuroendocrine responses to stress by activating the hypothalamic-pituitary-adrenal (HPA) axis, is expressed in brain regions prone to degeneration in Alzheimer's disease. We therefore tested the hypothesis that CRH can modify neuronal vulnerability to amyloid beta-peptide toxicity. In primary neuronal culture, CRH was protective against cell death caused by an amyloid-beta peptide, an effect that was blocked by a CRH receptor antagonist and by an inhibitor of cyclic AMP-dependent protein kinase. The increased resistance of CRH-treated neurons to amyloid toxicity was associated with stabilization of cellular calcium homeostasis. Moreover, CRH protected neurons against death caused by lipid peroxidation and the excitotoxic neurotransmitter glutamate. The level of mRNA encoding CRH was unchanged in mtAPP mouse brain, whereas the levels of mRNAs encoding glucocorticoid and mineralocorticoid receptors were subtly altered. Our results suggest that disturbances in HPA axis function can occur independently of alterations in CRH mRNA levels in Alzheimer's disease brain and further suggest an additional role for CRH in protecting neurons against cell death.

Corticosteroids and cognition

The brain is a major target organ for corticosteroids. It has been observed that excessive circulatory levels of endogenous and exogenous corticosteroids are frequently associated with cognitive impairment in a wide variety of clinical disease states. Cognition and low levels of corticosteroids have been less well studied. In this paper we review the literature on glucocorticosteroid effects on cognition and delineate specific functions that appear to be causally affected. We draw a possible connection to specific areas of brain perturbation, including the hippocampus and frontal lobe regions. The possibility that cognitive dysfunction caused by glucocorticoids can be pharmacologically managed is introduced.

Relationships between cortisol, dehydroepiandrosterone sulphate and insulin-like growth factor-I system in dementia

Changes in the hypothalamus-pituitary-adrenal axis (HPAA) function, entailing elevated cortisol circulating titres, occur in aging and in some neurological conditions, such as Alzheimer's disease (AD). Excess cortisol has neurotoxic effects which affect hippocampal neurones. Dehydroepiandrosterone sulphate (DHEAS) has an antiglucocorticoid activity and neuroprotective effects, but its levels decrease with aging. Glucocorticoids influence the production of insulin-like growth factor-I (IGF-I) and modify its systemic and neurotrophic biological activity by inducing changes in IGF-binding proteins (IGFBPs). We looked for relationships between cortisol, DHEAS levels, and IGF-I - IGFBPs system in AD. Cortisol, DHEAS and GH levels at 02:00, 08:00, 14:00, 20:00 h, basal IGF-I, IGFBP-1 and IGFBP-3 levels were determined by RIAs or IRMA in 25 AD patients, aged 58-89 yr, and in 12 age-matched healthy controls. AD subjects had higher cortisol, lower DHEAS levels and increased cortisol/DHEAS ratio (C/Dr) than controls. In AD cases, total IGF-I, IGFBP-3, and IGF-I/IGFBP ratios were significantly lowered, while IGFBP-1 levels were significantly higher than in controls. We found a significant inverse correlation between IGF-I and IGFBP-3 levels vs C/Dr, and between both IGF-I/IGFBPs ratios vs mean cortisol levels. IGFBP-3 correlated directly with DHEAS. Cortisol was directly and IGF-I inversely correlated with cognitive impairment. In AD patients we found that alterations in HPAA function and elevated C/Dr are related to lowered total and free IGF-I levels. These findings and their relationship to cognitive impairment suggest that changes in hormonal set-up might influence the clinical presentation of the disease.

Hippocampal apoptosis in major depression is a minor event and absent from subareas at risk for glucocorticoid overexposure

Glucocorticoid (GC) overexposure in animals has been implicated in hippocampal dysfunctioning and neuronal loss. In major depression, hypercortisolemia, hypothalamic-pituitary-adrenocortical-axis alterations, and reduced hippocampal volumes are commonly observed; hence, hippocampal neurodegeneration is also expected. To study possible GC-related pathology, we investigated hippocampal tissue of 15 major-depressed patients, 16 matched controls, and 9 steroid-treated patients, using in situ-end-labeling for DNA fragmentation and apoptosis, and heat-shock protein 70 and nuclear transcription factor kappaB immunocytochemistry for damage-related responses. No obvious massive cell loss was observed in any group. In 11 of 15 depressed patients, rare, but convincing apoptosis was found in entorhinal cortex, subiculum, dentate gyrus, CA1, and CA4. Also in three steroid-treated patients, apoptosis was found. Except for several steroid-treated patients, heat-shock protein 70 staining was generally absent, nor was nuclear transcription factor-kappaB activation found. The detection in 11 of 15 depressed patients, in three steroid-treated, and in one control patient, demonstrates for the first time that apoptosis is involved in steroid-related changes in the human hippocampus. However, in absence of major pyramidal loss, its rare occurrence, that notably was absent from areas at risk for GC damage such as CA3, indicates that apoptosis probably only contributes to a minor extent to the volume changes in depression.

Plasma cortisol levels in elderly female subjects with Alzheimer's disease: a cross-sectional and longitudinal study

We investigated the plasma cortisol levels at a fasting state in elderly female Alzheimer's disease (AD), vascular dementia (VD), and non-demented subjects (n=66, 28 and 21, respectively). Twenty-eight AD subjects were followed for 40 months. The plasma cortisol levels in AD and VD subjects were significantly higher than those of non-demented subjects at baseline. In AD subjects in relatively early stages of the disease [Mini-Mental State Examination (MMSE)], at baseline, high plasma cortisol led to rapid declines in MMSE scores over a 40-month period.

Chronic corticosterone administration dose-dependently modulates Abeta(1-42)- and NMDA-induced neurodegeneration in rat magnocellular nucleus basalis

The impact of glucocorticoids on beta-amyloid(1-42) (Abeta(1-42)) and NMDA-induced neurodegeneration was investigated in vivo. Abeta(1-42) or NMDA was injected into the cholinergic magnocellular nucleus basalis in adrenalectomized (ADX) rats, ADX rats supplemented with 25%, 100%, 2x100% corticosterone pellets, or sham-ADX controls. Abeta(1-42)- or NMDA-induced damage of cholinergic nucleus basalis neurones was assessed by quantitative acetylcholinesterase histochemistry. Plasma concentrations of corticosterone and cholinergic fibre loss after Abeta(1-42) or NMDA injection showed a clear U-shaped dose-response relationship. ADX and subsequent loss of serum corticosterone potentiated both the Abeta(1-42) and NMDA-induced neurodegeneration. ADX+25% corticosterone resulted in a 10-90 nM plasma corticosterone concentration, which significantly attenuated the Abeta(1-42) and NMDA neurotoxicity. ADX+100% corticosterone (corticosterone concentrations of 110-270 nM) potently decreased both Abeta(1-42)- and NMDA-induced neurotoxic brain damage. In contrast, high corticosterone concentrations of 310-650 nM potentiated Abeta(1-42)- and NMDA-triggered neurodegeneration. In conclusion, chronic low or high corticosterone concentrations increase the vulnerability of cholinergic cells to neurotoxic insult, while slightly elevated corticosterone levels protect against neurotoxic injury. Enhanced neurotoxicity of NMDA in the presence of high concentrations of specific glucocorticoid receptor agonists suggests that the corticosterone effects are mediated by glucocorticoid receptors.

Testosterone reduces neuronal secretion of Alzheimer's beta-amyloid peptides

Alzheimer's disease (AD) is characterized by the age-related deposition of beta-amyloid (Abeta) 40/42 peptide aggregates in vulnerable brain regions. Multiple levels of evidence implicate a central role for Abeta in the pathophysiology of AD. Abeta peptides are generated by the regulated cleavage of an approximately 700-aa Abeta precursor protein (betaAPP). Full-length betaAPP can undergo proteolytic cleavage either within the Abeta domain to generate secreted sbetaAPPalpha or at the N- and C-terminal domain(s) of Abeta to generate amyloidogenic Abeta peptides. Several epidemiological studies have reported that estrogen replacement therapy protects against the development of AD in postmenopausal women. We previously reported that treating cultured neurons with 17beta-estradiol reduced the secretion of Abeta40/42 peptides, suggesting that estrogen replacement therapy may protect women against the development of AD by regulating betaAPP metabolism. Increasing evidence indicates that testosterone, especially bioavailable testosterone, decreases with age in older men and in postmenopausal women. We report here that treatment with testosterone increases the secretion of the nonamyloidogenic APP fragment, sbetaAPPalpha, and decreases the secretion of Abeta peptides from N2a cells and rat primary cerebrocortical neurons. These results raise the possibility that testosterone supplementation in elderly men may be protective in the treatment of AD.

The effect of corticosteroids on amyloid beta precursor protein/amyloid precursor-like protein expression and processing in vivo

In this study, we have investigated the effect of altered corticosteroid levels on the expression and processing of the amyloid beta precursor protein (A betaPP) and its amyloid precursor-like protein (APLP) homologue in rat brain. Four groups of animals were used in the study: sham operated, adrenalectomised, and adrenalectomised treated with either dexamethasone or aldosterone, with the A betaPP/APLP expression being determined by western blot analysis. While there were no changes in the levels of A betaPP/APLP following adrenalectomy, treatment with dexamethasone, but not aldosterone, resulted in a marked increase in protein expression levels with the level of increase varying between the brain regions examined. Corticosteroids had a more marked effect on the particulate rather than the soluble form of the protein, thus suggesting that elevated glucocorticoids may also be adversely influencing A betaPP/APLP processing.

Detrimental effects of chronic hypothalamic-pituitary-adrenal axis activation. From obesity to memory deficits

Increasing evidence suggests that the detrimental effects of glucocorticoid (GC) hypersecretion occur by activation of the hypothalamic-pituitary-adrenal (HPA) axis in several human pathologies, including obesity, Alzheimer's disease, AIDS dementia, and depression. The different patterns of response by the HPA axis during chronic activation are an important consideration in selecting an animal model to assess HPA axis function in a particular disorder. This article will discuss how chronic HPA axis activation and GC hypersecretion affect hippocampal function and contribute to the development of obesity. In the brain, the hippocampus has the highest concentration of GC receptors. Chronic stress or corticosterone treatment induces neuropathological alterations, such as dendritic atrophy in hippocampal neurons, which are paralleled by cognitive deficits. Excitatory amino acid (EAA) neurotransmission has been implicated in chronic HPA axis activation. EAAs play a major role in neuroendocrine regulation. Hippocampal dendritic atrophy may involve alterations in EAA transporter function, and decreased EAA transporter function may also contribute to chronic HPA axis activation. Understanding the molecular mechanisms of HPA axis activation will likely advance the development of therapeutic interventions for conditions in which GC levels are chronically elevated.