Effect of dehydroepiandrosterone and its sulfate and fatty acid ester derivatives on rat brain membranes

A Bird's-Eye View of the Multiple Biochemical Mechanisms that Propel Pathology of Alzheimer's Disease: Recent Advances and Mechanistic Perspectives on How to Halt the Disease Progression Targeting Multiple Pathways

Neurons consume the highest amount of oxygen, depend on oxidative metabolism for energy, and survive for the lifetime of an individual. Therefore, neurons are vulnerable to death caused by oxidative-stress, accumulation of damaged and dysfunctional proteins and organelles. There is an exponential increase in the number of patients diagnosed with neurodegenerative diseases such as Alzheimer's (AD) as the number of elderly increases exponentially. Development of AD pathology is a complex phenomenon characterized by neuronal death, accumulation of extracellular amyloid-β plaques and neurofibrillary tangles, and most importantly loss of memory and cognition. These pathologies are most likely caused by mechanisms including oxidative stress, mitochondrial dysfunction/stress, accumulation of misfolded proteins, and defective organelles due to impaired proteasome and autophagy mechanisms. Currently, there are no effective treatments to halt the progression of this disease. In order to treat this complex disease with multiple biochemical pathways involved, a complex treatment regimen targeting different mechanisms should be investigated. Furthermore, as AD is a progressive disease-causing morbidity over many years, any chemo-modulator for treatment must be used over long period of time. Therefore, treatments must be safe and non-interfering with other processes. Ideally, a treatment like medicinal food or a supplement that can be taken regularly without any side effect capable of reducing oxidative stress, stabilizing mitochondria, activating autophagy or proteasome, and increasing energy levels of neurons would be the best solution. This review summarizes progress in research on different mechanisms of AD development and some of the potential therapeutic development strategies targeting the aforementioned pathologies.

Cortisol and DHEA in development and psychopathology

Dehydroepiandrosterone (DHEA) and cortisol are the most abundant hormones of the human fetal and adult adrenals released as end products of a tightly coordinated endocrine response to stress. Together, they mediate short- and long-term stress responses and enable physiological and behavioral adjustments necessary for maintaining homeostasis. Detrimental effects of chronic or repeated elevations in cortisol on behavioral and emotional health are well documented. Evidence for actions of DHEA that offset or oppose those of cortisol has stimulated interest in examining their levels as a ratio, as an alternate index of adrenocortical activity and the net effects of cortisol. Such research necessitates a thorough understanding of the co-actions of these hormones on physiological functioning and in association with developmental outcomes. This review addresses the state of the science in understanding the role of DHEA, cortisol, and their ratio in typical development and developmental psychopathology. A rationale for studying DHEA and cortisol in concert is supported by physiological data on the coordinated synthesis and release of these hormones in the adrenal and by their opposing physiological actions. We then present evidence that researching cortisol and DHEA necessitates a developmental perspective. Age-related changes in DHEA and cortisol are described from the perinatal period through adolescence, along with observed associations of these hormones with developmental psychopathology. Along the way, we identify several major knowledge gaps in the role of DHEA in modulating cortisol in typical development and developmental psychopathology with implications for future research.

Fatty acid esters of steroids: synthesis and metabolism in lipoproteins and adipose tissue

At the end of the last century ideas concerning the physiological role of the steroid fatty acid ester family were emerging. Estrogens, fatty acylated at C-17 hydroxyl group and incorporated in lipoproteins were proposed to provide antioxidative protection to these particles. A large number of studies involving non-estrogenic adrenal steroids, and their fatty acylated forms, demonstrated their lipoprotein-mediated transport into cells and subsequent intracellular activation, suggesting a novel transport mechanism for lipophilic steroid derivatives. After these important advances the main focus of interest has shifted away from C-19 and C-21 steroids to fatty acylated estrogens. However, interest in their lipoprotein-mediated transport has decreased because only minute amounts of these derivatives were detected in circulating lipoproteins, and their antioxidative activity remained unconfirmed under physiological circumstances. It now appears that the overwhelming majority of estradiol in postmenopausal women resides in adipose tissue, most of it in esterified form. This is poorly reflected in plasma levels which are very low. Recent data suggest that estrogen fatty acid esters probably represent a storage form. The future focus of investigation is likely to be on firstly, the enzymatic mechanisms regulating the esterification and de-esterification of estradiol and other steroids residing in adipose tissue and secondly, on the role of insulin and other hormones in the regulation of these enzymatic mechanisms. Thirdly, as a large proportion of fatty acid esterified C-19 and C-21 non-estrogenic steroids is transported in lipoproteins and as they are important precursors of androgens and estrogens, this field should be investigated further.

Estrogen and SERM neuroprotection in animal models of Parkinson's disease

A higher prevalence and incidence of Parkinson disease (PD) is observed in men and beneficial motor effects of estrogens are observed in parkinsonian women. Lesion of the dopamine (DA) nigrostriatal pathway in animals with 1-methyl 4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) provides a model of PD and this is based on its use in humans as side-product of a drug abuse. Presently treatment of PD is mainly symptomatic. The MPTP mouse is used to study the neuroprotective roles of estrogenic drugs on the DA system. Estrogens, but not androgens, are active neuroprotectants as well as progesterone and dehydroepiandrosterone. An estrogen receptor agonist PPT and the selective estrogen receptor modulator raloxifene are also neuroprotective. Striatal DA neurons of estrogen receptor alpha knockout mice are more susceptible to MPTP toxicity than wild-type mice and neuroprotection by estradiol is associated with the activation of the PI3-K pathway involving Akt, GSK3beta, Bcl2 and BAD.

Dehydroepiandrosterone protects vascular endothelial cells against apoptosis through a Galphai protein-dependent activation of phosphatidylinositol 3-kinase/Akt and regulation of antiapoptotic Bcl-2 expression

The adrenal steroid dehydroepiandrosterone (DHEA) may improve vascular function, but the mechanism is unclear. In the present study, we show that DHEA significantly increased cell viability, reduced caspase-3 activity, and protected both bovine and human vascular endothelial cells against serum deprivation-induced apoptosis. This effect was dose dependent and maximal at physiological concentrations (0.1-10 nM). DHEA stimulation of bovine aortic endothelial cells resulted in rapid and dose-dependent phosphorylation of Akt, which was blocked by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), the upstream kinase of Akt. Accordingly, inhibition of PI3K or transfection of the cells with dominant-negative Akt ablated the antiapoptotic effect of DHEA. The induced Akt phosphorylation and subsequent cytoprotective effect of DHEA were dependent on activation of Galphai proteins, but were estrogen receptor independent, because these effects were blocked by pertussis toxin but not by the estrogen receptor inhibitor ICI182,780 or the aromatase inhibitor aminoglutethimide. Finally, DHEA enhanced antiapoptotic Bcl-2 protein expression, its promoter activity, and gene transcription attributable to the activation of the PI3K/Akt pathway. Neutralization of Bcl-2 by antibody transfection significantly decreased the antiapoptotic effect of DHEA. These findings provide the first evidence that DHEA acts as a survival factor for endothelial cells by triggering the Galphai-PI3K/Akt-Bcl-2 pathway to protect cells against apoptosis. This may represent an important mechanism underlying the vascular protective effect of DHEA.

Dehydroepiandrosterone inhibits intracellular calcium release in beta-cells by a plasma membrane-dependent mechanism

Both dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) affect glucose stimulated insulin secretion, though their cellular mechanisms of action are not well characterized. We tested the hypothesis that human physiological concentrations of DHEA alter insulin secretion by an action initiated at the plasma membrane of beta-cells. DHEA alone had no effect on intracellular calcium concentration ([Ca(2+)](i)) in a rat beta-cell line (INS-1). However, it caused an immediate and dose-dependent inhibition of carbachol-induced Ca(2+) release from intracellular stores, with a 25% inhibition at zero. One nanometer DHEA. DHEA also inhibited the Ca(2+) mobilizing effect of bombesin (29% decrease), but did not inhibit the influx of extracellular Ca(2+) evoked by glyburide (100 microM) or glucose (15 mM). The steroids (androstenedione, 17-alpha-hydroxypregnenolone, and DHEAS) had no inhibitory effect on carbachol-induced intracellular Ca(2+) release. The action of DHEA depended on a signal initiated at the plasma membrane, since membrane impermeant DHEA-BSA complexes also inhibited the carbachol effect on [Ca(2+)](i) (39% decrease). The inhibition of carbachol-induced Ca(2+) release by DHEA was blocked by pertussis toxin (PTX). DHEA also inhibited the carbachol induction of phosphoinositide generation, with a maximal inhibition at 0.1 nM DHEA. Furthermore, DHEA inhibited insulin secretion induced by carbachol in INS-1 cells by 25%, and in human pancreatic islets by 53%. Taken together, this is the first report showing that human physiological concentrations of DHEA decrease agonist-induced Ca(2+) release by a rapid, non-genomic mechanism in INS-1 cells. Furthermore, these data provide evidence consistent with the existence of a specific plasma membrane DHEA receptor, mediating this signal transduction pathway by pertussis toxin-sensitive G-proteins.

Dehydroepiandrosterone (DHEA) such as 17beta-estradiol prevents MPTP-induced dopamine depletion in mice

Previous work from our laboratory has shown prevention of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced striatal dopamine (DA) depletion in mice by 17beta-estradiol, progesterone, and raloxifene. Dehydroepiandrosterone (DHEA), a neurosteroid, was shown to have neuroprotective activities in various paradigms of neuronal death but its effect in vivo in mice on MPTP toxicity has not been reported. We investigated the effects of 17beta-estradiol (2 microg/day) and DHEA (3 mg/day) for 5 days before and after an acute treatment of four MPTP (10 mg/kg) injections in male C57Bl/6 mice. Striatal DA concentrations and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured by HPLC. MPTP mice that received 17beta-estradiol or DHEA had striatal DA, DOPAC, and HVA concentrations comparable to intact animals and higher than striatal DA, DOPAC, and HVA levels in saline-MPTP-treated mice. MPTP treatment led to an increase of striatal DA turnover (assessed with the HVA/DA ratio); DHEA and 17beta-estradiol prevented this increase. 17beta-Estradiol did not affect striatal DA and metabolites concentrations in intact mice in this paradigm. Furthermore, in the substantia nigra DHEA and 17beta-estradiol prevented the MPTP-induced dopamine transporter and tyrosine hydroxylase mRNA decreases measured by in situ hybridization. Therefore, DHEA such as 17beta-estradiol is active in preventing the catecholamine-depleting effect of MPTP and our results suggest that this involves neuroprotection of DA neurons.