Dexamethasone effects on cortisol secretion in Alzheimer's disease: some clinical and hormonal features in suppressor and nonsuppressor patients

Deep phenotyping of Alzheimer's disease leveraging electronic medical records identifies sex-specific clinical associations

Alzheimer's Disease (AD) is a neurodegenerative disorder that is still not fully understood. Sex modifies AD vulnerability, but the reasons for this are largely unknown. We utilize two independent electronic medical record (EMR) systems across 44,288 patients to perform deep clinical phenotyping and network analysis to gain insight into clinical characteristics and sex-specific clinical associations in AD. Embeddings and network representation of patient diagnoses demonstrate greater comorbidity interactions in AD in comparison to matched controls. Enrichment analysis identifies multiple known and new diagnostic, medication, and lab result associations across the whole cohort and in a sex-stratified analysis. With this data-driven method of phenotyping, we can represent AD complexity and generate hypotheses of clinical factors that can be followed-up for further diagnostic and predictive analyses, mechanistic understanding, or drug repurposing and therapeutic approaches.

Stress-Induced Neurodegeneration: The Potential for Coping as Neuroprotective Therapy

Stress responses are essential for survival, but become detrimental to health and cognition with chronic activation. Chronic hypothalamic-pituitary-adrenal axis release of glucocorticoids induces hypothalamic-pituitary-adrenal axis dysfunction and neuronal loss, decreases learning and memory, and modifies glucocorticoid receptor/mineralocorticoid receptor expression. Elderly who report increased stress are nearly 3 times more likely to develop Alzheimer's disease, have decreased global cognition and faster cognitive decline than those reporting no stress. Patients with mild cognitive impairment are more sensitive to stress compared to healthy elderly and those with Alzheimer's disease. Stress may also transduce neurodegeneration via the gut microbiome. Coping styles determine hippocampal mineralocorticoid receptor expression in mice, indicating that coping modifies cortisol's effect on the brain. Identifying neuroprotective coping strategies that lessen the burden of stress may prevent or slow cognitive decline. Treatments and education designed to reduce stress should be recognized as neuroprotective.

Transcriptomics in tissue glucocorticoid sensitivity

BACKGROUND

Synthetic glucocorticoids are widely used in the treatment of several inflammatory, autoimmune and lymphoproliferative disorders. However, considerable variation in response to therapeutic doses of glucocorticoids has been documented among individuals. The aim of our study was to identify novel glucocorticoid sensitivity-determining genes using genome-wide expression profiling in healthy subjects.

METHODS

One hundred one healthy subjects [mean age ± standard error of the mean (SEM); 26.52 ± 0.50 years] were given 0.25 mg dexamethasone at midnight, and serum cortisol concentrations were determined at 08:00 hours the following morning. Subjects were stratified into the 10% most glucocorticoid-sensitive and 10% most glucocorticoid-resistant according to the serum cortisol concentrations. Genomic DNA, RNA and plasma samples were obtained in the 22 subjects one month later.

RESULTS

Transcriptomic analysis showed variability between glucocorticoid-resistant and glucocorticoid-sensitive subjects. One hundred thirty-three genes were upregulated and 49 downregulated in the glucocorticoid-resistant compared to the glucocorticoid-sensitive group. Further analysis revealed differences between 3 glucocorticoid-resistant and 3 glucocorticoid-sensitive subjects. The majority of the 1058 upregulated genes and 1139 downregulated genes were found to participate in telomere maintenance, systemic lupus erythematosus and Alzheimer's disease. Interestingly, Synuclein A, a key molecule in Parkinson's disease, was upregulated in the subgroup of glucocorticoid-sensitive subjects.

CONCLUSIONS

We have identified differences in tissue sensitivity to glucocorticoids among healthy subjects at the transcriptomic level. These differences are associated with differential expression of genes related to autoimmune and neurological disorders.

Dysregulation of stress systems and nitric oxide signaling underlies neuronal dysfunction in Alzheimer's disease

Stress is a multimodal response involving the coordination of numerous body systems in order to maximize the chance of survival. However, long term activation of the stress response results in neuronal oxidative stress via reactive oxygen and nitrogen species generation, contributing to the development of depression. Stress-induced depression shares a high comorbidity with other neurological conditions including Alzheimer's disease (AD) and dementia, often appearing as one of the earliest observable symptoms in these diseases. Furthermore, stress and/or depression appear to exacerbate cognitive impairment in the context of AD associated with dysfunctional catecholaminergic signaling. Given there are a number of homologous pathways involved in the pathophysiology of depression and AD, this article will highlight the mechanisms by which stress-induced perturbations in oxidative stress, and particularly NO signaling, contribute to neurodegeneration.

Dehydroepiandrosterone and Dehydroepiandrosterone Sulfate in Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background and Purpose: Previous studies found inconsistent results for the relationship between Alzheimer's disease and the levels of dehydroepiandrosterone and dehydroepiandrosterone sulfate. This study performed a systematic review and meta-analysis to evaluate previous studies' results on this relationship. Method: Studies related to this outcome were obtained using a systematic search from the electronic databases of PubMed, Embase, Web of Science, and Psyc-ARTICLES in March 2018. The random-effects model was used to measure the strength of the association between Alzheimer's disease and the levels of dehydroepiandrosterone and dehydroepiandrosterone sulfate, using the standardized mean difference. Results: Thirty-one eligible studies were included in the final analysis. There was no statistically significant association between the level of dehydroepiandrosterone and Alzheimer's disease (standardized mean difference: 0.51, 95% confidence interval: -0.44 to 1.45, Z = 1.06, p = 0.29). On the other hand, lower level dehydroepiandrosterone sulfate was observed in patients with Alzheimer's disease than in controls (standardized mean difference: -0.69, 95% confidence interval: -1.17 to -0.22, Z = -2.84, p < 0.01). Conclusion: Decreased dehydroepiandrosterone sulfate concentrations may be an important indicator for Alzheimer's disease, although whether dehydroepiandrosterone sulfate could be used as a diagnostic tool requires further research.

Delirium pathophysiology: An updated hypothesis of the etiology of acute brain failure

BACKGROUND

Delirium is the most common neuropsychiatric syndrome encountered by clinicians dealing with older adults and the medically ill and is best characterized by 5 core domains: cognitive deficits, attentional deficits, circadian rhythm dysregulation, emotional dysregulation, and alteration in psychomotor functioning.

DESIGN

An extensive literature review and consolidation of published data into a novel interpretation of known pathophysiological causes of delirium.

RESULTS

Available data suggest that numerous pathological factors may serve as precipitants for delirium, each having differential effects depending on patient-specific patient physiological characteristics (substrate). On the basis of an extensive literature search, a newly proposed theory, the systems integration failure hypothesis, was developed to bring together the most salient previously described theories, by describing the various contributions from each into a complex web of pathways-highlighting areas of intersection and commonalities and explaining how the variable contribution of these may lead to the development of various cognitive and behavioral dysfunctions characteristic of delirium. The specific cognitive and behavioral manifestations of the specific delirium picture result from a combination of neurotransmitter function and availability, variability in integration and processing of sensory information, motor responses to both external and internal cues, and the degree of breakdown in neuronal network connectivity, hence the term acute brain failure.

CONCLUSIONS

The systems integration failure hypothesis attempts to explain how the various proposed delirium pathophysiologic theories interact with each other, causing various clinically observed delirium phenotypes. A better understanding of the underlying pathophysiology of delirium may eventually assist in designing better prevention and management approaches.

The relationship between stress and Alzheimer's disease

Stress is critically involved in the development and progression of disease. From the stress of undergoing treatments to facing your own mortality, the physiological processes that stress drives have a serious detrimental effect on the ability to heal, cope and maintain a positive quality of life. This is becoming increasingly clear in the case of neurodegenerative diseases. Neurodegenerative diseases involve the devastating loss of cognitive and motor function which is stressful in itself, but can also disrupt neural circuits that mediate stress responses. Disrupting these circuits produces aberrant emotional and aggressive behavior that causes long-term care to be especially difficult. In addition, added stress drives progression of the disease and can exacerbate symptoms. In this review, I describe how neural and endocrine pathways activated by stress interact with ongoing neurodegenerative disease from both a clinical and experimental perspective.

ATP-sensitive potassium-channel inhibitor glibenclamide attenuates HPA axis hyperactivity, depression- and anxiety-related symptoms in a rat model of Alzheimer's disease

Affective disorders including depression and anxiety are among the most prevalent behavioral abnormalities in patients with Alzheimer's disease (AD), which affect the quality of life and progression of the disease. Dysregulation of the hypothalamic-pituitary-adrenal-(HPA) axis has been reported in affective disorders and AD. Recent studies revealed that current antidepressant drugs are not completely effective for treating anxiety- and depression-related disorders in people with dementia. ATP-sensitive-potassium-(K_ATP) channels are well-known to be involved in AD pathophysiology, HPA axis function and the pathogenesis of depression and anxiety-related behaviors. Thus, targeting of K_ATP channel may be a potential therapeutic strategy in AD. Hence, we investigated the effects of intracerebroventricular injection of Aβ25-35 alone or in combination with glibenclamide, K_ATP channel inhibitor on depression- and anxiety-related behaviors as well as HPA axis response to stress in rats. To do this, non-Aβ25-35- and Aβ25-35-treated rats were orally treated with glibenclamide, then the behavioral consequences were assessed using sucrose preference, forced swim, light-dark box and plus maze tests. Stress-induced corticosterone levels following forced swim and plus maze tests were also evaluated as indicative of abnormal HPA-axis-function. Aβ25-35 induced HPA axis hyperreactivity and increased depression- and anxiety-related symptoms in rats. Our results showed that blockade of K_ATP channels with glibenclamide decreased depression- and anxiety-related behaviors by normalizing HPA axis activity in Aβ25-35-treated rats. This study provides additional evidence that Aβ administration can induce depression- and anxiety-like symptoms in rodents, and suggests that K_ATP channel inhibitors may be a plausible therapeutic strategy for treating affective disorders in AD patients.

Hypothalamic Dysfunction and Multiple Sclerosis: Implications for Fatigue and Weight Dysregulation

Signs and symptoms of multiple sclerosis are usually attributed to demyelinating lesions in the spinal cord or cerebral cortex. The hypothalamus is a region that is often overlooked yet controls many important homeostatic functions, including those that are perturbed in multiple sclerosis. In this review we discuss how hypothalamic dysfunction may contribute to signs and symptoms in people with multiple sclerosis. While dysfunction of the hypothalamic-pituitary-adrenal axis is common in multiple sclerosis, the effects and mechanisms of this dysfunction are not well understood. We discuss three hypothalamic mechanisms of fatigue in multiple sclerosis: (1) general hypothalamic-pituitary-adrenal axis hyperactivity, (2) disordered orexin neurotransmission, (3) abnormal cortisol secretion. We then review potential mechanisms of weight dysregulation caused by hypothalamic dysfunction. Lastly, we propose future studies and therapeutics to better understand and treat hypothalamic dysfunction in multiple sclerosis. Hypothalamic dysfunction appears to be common in multiple sclerosis, yet current studies are underpowered and contradictory. Future studies should contain larger sample sizes and standardize hormone and neuropeptide measurements.

Cortisol: Mediator of association between Alzheimer's disease and diabetes mellitus?

Numerous epidemiologic studies have identified an independent association between Alzheimer's disease (AD) and diabetes mellitus (DM), which remains unexplained. This review contends that the association is mediated by mild hypercortisolemia that is manifested in AD by early stages, as empirical evidence indicates that hypercortisolemia is diabetogenic even at subclinical levels. Subclinical Cushing's syndrome is discussed as the paradigm. It is proposed that hypercortisolemia increases the risk of pre-diabetes and DM during early AD and the preceding decades. That hypercortisolemia is exhibited during the AD prodromal stage has yet to be determined, but may be inferred from concurrent metabolic parameters as documented in the literature. Studies refuting association between AD and DM also are evaluated, and the relationship between AD and DM is deduced to be more complex than directly causal, with DM of longstanding duration having a protective role. Association between DM and AD may require reappraisal by APOE ε4 carrier status, in view of newly identified roles of APOE ε4 in pre-diabetes. That association of APOE ε4 with DM in AD may have been underestimated in epidemiologic studies also is highlighted. At the core of arguments and mechanisms presented in this review is the circadian rhythm of cortisol secretion, which is the main determinant of glycemic control in humans. Alterations to that rhythm and to the hypothalamic-pituitary-adrenal axis occurring in AD are examined. Consequently the cause of hypercortisolemia in AD, and therefore of association between AD and DM, is proposed to be adrenal hyper-responsiveness to adrenocorticotropic hormone.

Associations between Sleep, Cortisol Regulation, and Diet: Possible Implications for the Risk of Alzheimer Disease

Accumulation of proteinaceous amyloid β plaques and tau oligomers may occur several years before the onset of Alzheimer disease (AD). Under normal circumstances, misfolded proteins get cleared by proteasome degradation, autophagy, and the recently discovered brain glymphatic system, an astroglial-mediated interstitial fluid bulk flow. It has been shown that the activity of the glymphatic system is higher during sleep and disengaged or low during wakefulness. As a consequence, poor sleep quality, which is associated with dementia, might negatively affect glymphatic system activity, thus contributing to amyloid accumulation. The diet is another important factor to consider in the regulation of this complex network. Diets characterized by high intakes of refined sugars, salt, animal-derived proteins and fats and by low intakes of fruit and vegetables are associated with a higher risk of AD and can perturb the circadian modulation of cortisol secretion, which is associated with poor sleep quality. For this reason, diets and nutritional interventions aimed at restoring cortisol concentrations may ease sleep disorders and may facilitate brain clearance, consequentially reducing the risk of cognitive impairment and dementia. Here, we describe the associations that exist between sleep, cortisol regulation, and diet and their possible implications for the risk of cognitive impairment and AD.

Hypothalamic-pituitary-adrenal (HPA) axis and aging

Human aging is associated with increasing frailty and morbidity which can result in significant disability. Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to aging-related diseases like depression, cognitive deficits, and Alzheimer's disease in some older individuals. In addition to neuro-cognitive dysfunction, it has also been associated with declining physical performance possibly due to sarcopenia. This article reviews the pathophysiology of HPA dysfunction with respect to increased basal adrenocorticotropic hormone (ACTH) and cortisol secretion, decreased glucocorticoid (GC) negative feedback at the level of the paraventricular nucleus (PVN) of the hypothalamus, hippocampus (HC), and prefrontal cortex (PFC), and flattening of diurnal pattern of cortisol release. It is possible that the increased cortisol secretion is secondary to peripheral conversion from cortisone. There is a decline in pregnolone secretion and C-19 steroids (DHEA) with aging. There is a small decrease in aldosterone with aging, but a subset of the older population have a genetic predisposition to develop hyperaldosteronism due to the increased ACTH stimulation. The understanding of the HPA axis and aging remains a complex area with conflicting studies leading to controversial interpretations.

Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases?

There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.

Neuropathology of stress

Environmental challenges are part of daily life for any individual. In fact, stress appears to be increasingly present in our modern, and demanding, industrialized society. Virtually every aspect of our body and brain can be influenced by stress and although its effects are partly mediated by powerful corticosteroid hormones that target the nervous system, relatively little is known about when, and how, the effects of stress shift from being beneficial and protective to becoming deleterious. Decades of stress research have provided valuable insights into whether stress can directly induce dysfunction and/or pathological alterations, which elements of stress exposure are responsible, and which structural substrates are involved. Using a broad definition of pathology, we here review the "neuropathology of stress" and focus on structural consequences of stress exposure for different regions of the rodent, primate and human brain. We discuss cytoarchitectural, neuropathological and structural plasticity measures as well as more recent neuroimaging techniques that allow direct monitoring of the spatiotemporal effects of stress and the role of different CNS structures in the regulation of the hypothalamic-pituitary-adrenal axis in human brain. We focus on the hypothalamus, hippocampus, amygdala, nucleus accumbens, prefrontal and orbitofrontal cortex, key brain regions that not only modulate emotions and cognition but also the response to stress itself, and discuss disorders like depression, post-traumatic stress disorder, Cushing syndrome and dementia.

Neurobiological and neuropsychiatric effects of dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS)

DHEA and DHEAS are steroids synthesized in human adrenals, but their function is unclear. In addition to adrenal synthesis, evidence also indicates that DHEA and DHEAS are synthesized in the brain, further suggesting a role of these hormones in brain function and development. Despite intensifying research into the biology of DHEA and DHEAS, many questions concerning their mechanisms of action and their potential involvement in neuropsychiatric illnesses remain unanswered. We review and distill the preclinical and clinical data on DHEA and DHEAS, focusing on (i) biological actions and putative mechanisms of action, (ii) differences in endogenous circulating concentrations in normal subjects and patients with neuropsychiatric diseases, and (iii) the therapeutic potential of DHEA in treating these conditions. Biological actions of DHEA and DHEAS include neuroprotection, neurite growth, and antagonistic effects on oxidants and glucocorticoids. Accumulating data suggest abnormal DHEA and/or DHEAS concentrations in several neuropsychiatric conditions. The evidence that DHEA and DHEAS may be fruitful targets for pharmacotherapy in some conditions is reviewed.

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.

The relevance of neurosteroids to clinical psychiatry: from the laboratory to the bedside

Neurosteroids are important neuroactive molecules with suggested central involvement in several neurophysiological and psychiatric disease processes. The discovery of neurosteroids followed the revelation that the brain exhibited the capacity to synthesize its own steroids in situ and thus be a potential site of steroidogenesis. In contrast to some steroids that exhibit traditional genomic steroid actions, most neurosteroids appear to regulate neuronal function by means of "non-genomic" mechanisms influencing neuronal excitability. Neurosteroids are synthesized either from CNS cholesterol or from peripheral steroid precursors and exhibit a wide range of modulatory effects on neurotransmitter receptor activity, most notably at the gamma-aminobutyric acid A (GABA(A)) receptor. Neurosteroids play an important role in neurodevelopment and neuroprotective effects, many aspects of which may have particular applicability to psychiatric disorders including various gender differences. Neurosteroids appear to be relevant to the pathophysiology and pharmacological treatment of many psychiatric disorders including the most notable mood and anxiety disorders, but also psychotic, childhood, eating, dementia, stress and postpartum disorders. It has been suggested that neurosteroids may become potential targets for pharmacological intervention in the future with further neurosteroid investigation contributing to a more comprehensive understanding of human behavior and psychopathology.

Gene analysis of the glucocorticoid receptor alpha in Alzheimer's disease

BACKGROUND

In Alzheimer's disease (AD), the hypothalamic-pituitary-adrenal (HPA) axis is hyperactive and the sensitivity to dexamethasone is decreased, suggesting a possible involvement of glucocorticoid receptor alpha (GRalpha) defects in the aetiopathology of the disease.

METHODS

We, therefore, searched for the presence of mutations in the human GRalpha (hGRalpha) gene, focusing on the hormone-binding domain due to its importance in mediating glucocorticoids' effects. RNA isolated from peripheral blood mononuclear cells (PBMCs) of 15 patients with Alzheimer's disease and 20 healthy individuals was subjected to reverse transcription-polymerase chain reaction amplification (RT-PCR) analysis followed by denaturing gradient gel electrophoresis (DGGE).

RESULTS

No mutations could be detected in the region of the hGRalpha gene examined.

CONCLUSIONS

We conclude that the hormone-binding domain of GRalpha is not altered in Alzheimer's disease and molecular defects in other gene regions of the GRalpha or in its isoform GRbeta warrant further investigation in Alzheimer's disease.

Dementia: a neuroendocrine perspective

The etiology of Alzheimer's disease (AD) has not been as yet completely defined. Genetic, environmental and neurophysiological aspects should all be taken into account. The disease has also neuroendocrine implications, some of which are discussed in this review. It is known that stress and glucocorticoids may affect neurone survival. On the contrary, some data indicate that DHEA and DHEAS exert a neuroprotective action. In AD, changes in hypothalamic-pituitary-adrenal axis function have been reported. Experimental and clinical evidence indicates that glucocorticoid hypersecretion and DHEAS levels decrement may add to hippocampal dysfunction in aging and in AD. Glucocorticoid and beta-amyloid concur in the mechanism of neurone damage, as well as excitatory amino acids (EAA), Ca++ and reactive oxygen species (ROS). The neuroprotective effects exerted by IGFs are also hindered in aging and even more in AD. Production and biological actions of IGFs are negatively influenced by cortisol hypersecretion and DHEAS decrease in patients with AD.