A comparative evaluation of treatments with 17β-estradiol and its brain-selective prodrug in a double-transgenic mouse model of Alzheimer's disease

Brain Specific Estrogen Ameliorates Cognitive Effects of Surgical Menopause in Mice

Menopause is a major endocrinological shift that leads to an increased vulnerability to the risk factors for cognitive impairment and dementia. This is thought to be due to the loss of circulating estrogens, which exert many potent neuroprotective effects in the brain. Systemic replacement of estrogen post-menopause has many limitations, including increased risk for estrogen-sensitive cancers. A more promising therapeutic approach therefore might be to deliver estrogen only to the brain thus limiting adverse peripheral side effects. We examined whether we could enhance cognitive performance by delivering estrogen exclusively to the brain in post-menopausal mice. We modeled surgical menopause via bilateral ovariectomy (OVX). We treated mice with the pro-drug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED), which can be administered systemically but is converted to 17β-estradiol only in the brain. Young (2.5-month) and middle-aged (11-month-old) female C57BL/6J mice received ovariectomy and a subcutaneous implant containing vehicle (cholesterol) or DHED. At 3.5 months old (young group) and 14.5 months old (middle-aged group), mice underwent behavior testing to assess memory. DHED did not significantly alter metabolic status in middle-aged, post-menopausal mice. In both young and middle-aged mice, the brain-specific estrogen DHED improved spatial memory. Additional testing in middle-aged mice also showed that DHED improved working and recognition memory. These promising results lay the foundation for future studies aimed at determining if this intervention is as efficacious in models of dementia that have comorbid risk factors.

Sex and Brain: The Role of Sex Chromosomes and Hormones in Brain Development and Parkinson's Disease

Sex hormones and genes on the sex chromosomes are not only key factors in the regulation of sexual differentiation and reproduction but they are also deeply involved in brain homeostasis. Their action is crucial for the development of the brain, which presents different characteristics depending on the sex of individuals. The role of these players in the brain is fundamental in the maintenance of brain function during adulthood as well, thus being important also with respect to age-related neurodegenerative diseases. In this review, we explore the role of biological sex in the development of the brain and analyze its impact on the predisposition toward and the progression of neurodegenerative diseases. In particular, we focus on Parkinson's disease, a neurodegenerative disorder that has a higher incidence in the male population. We report how sex hormones and genes encoded by the sex chromosomes could protect from the disease or alternatively predispose toward its development. We finally underline the importance of considering sex when studying brain physiology and pathology in cellular and animal models in order to better understand disease etiology and develop novel tailored therapeutic strategies.

Effects of xenobiotics on CYP1 enzyme-mediated biotransformation and bioactivation of estradiol

Endogenous estradiol (E2) exerts diverse physiological and pharmacological activities, commonly used for hormone replacement therapy. However, prolonged and excessive exposure to E2 potentially increases estrogenic cancer risk. Reportedly, CYP1 enzyme-mediated biotransformation of E2 is largely concerned with its balance between detoxification and carcinogenic pathways. Among the three key CYP1 enzymes (CYP1A1, CYP1A2, and CYP1B1), CYP1A1 and CYP1A2 mainly catalyze the formation of nontoxic 2-hydroxyestradiol (2-OH-E2), while CYP1B1 specifically catalyzes the formation of genotoxic 4-hydroxyestradiol (4-OH-E2). 4-OH-E2 can be further metabolized to electrophilic quinone intermediates accompanied by the generation of reactive oxygen species (ROS), triggering DNA damage. Since abnormal alterations in CYP1 activities can greatly affect the bioactivation process of E2, regulatory effects of xenobiotics on CYP1s are essential for E2-associated cancer development. To date, thousands of natural and synthetic compounds have been found to show potential inhibition and/or induction actions on the three CYP1 members. Generally, these chemicals share similar planar polycyclic skeletons, the structural motifs and substituent groups of which are important for their inhibitory/inductive efficiency and selectivity toward CYP1 enzymes. This review comprehensively summarizes these known inhibitors and/or inductors of E2-metabolizing CYP1s based on chemical categories and discusses their structure-activity relationships, which would contribute to better understanding of the correlation between xenobiotic-regulated CYP1 activities and estrogenic cancer susceptibility.

Alzheimer's Disease and Sex-Dependent Alterations in the Striatum: A Lesson from a Mouse Model

In the last years, many clinical studies highlighted sex-specific differences in the pathophysiology of Alzheimer's disease (AD). The recent paper published in the Journal of Alzheimer's Disease shows the influence of sex on amyloid-β plaque deposition, behavior, and dopaminergic signaling in the 5xFAD mouse model of AD, with worse alterations in female mice. This commentary focuses on the importance of recognizing sex as a key variable to consider for a more precise clinical practice, with the challenge to develop sex-specific therapeutic interventions in neurodegenerative diseases such as AD.

A Green Blue LED-Driven Two-Liquid-Phase One-Pot Procedure for the Synthesis of Estrogen-Related Quinol Prodrugs

Quinol derivatives of estrogens are effective pro-drugs in steroid replacement therapy. Here, we report that these compounds can be synthesized in one-pot conditions and high yield by blue LED-driven photo-oxygenation of parent estrogens. The oxidation was performed in buffer and eco-certified 2-methyltetrahydrofuran as the two-liquid-phase reaction solvent, and in the presence of meso-tetraphenyl porphyrin as the photosensitizer. Two steroidal prodrugs 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED) and 10β-Hydroxyestra-1,4-diene-3,17-dione (HEDD) were obtained with high yield and selectivity.

Advances in prodrug design for Alzheimer's Disease: the state of the art

INTRODUCTION

: Alzheimer's disease (AD) is the most common cause of dementia with a memory loss and other cognitive abilities and is a complex and multifactorial neurodegenerative disease that remains today a challenge for drug discovery. Like many pathologies of the central nervous system, one of the first hurdles is the development of a compound with a sufficient brain exposure to ensure a potential therapeutic benefit. In this direction, the development of prodrugs has been an intense field of research in the last years.

AREAS COVERED

: Two main strategies of prodrugs development are analysed in this review. First, the application of the classical modulation of an active compound to incorporate a drug carrier or to prepare bioprecursor has been exemplified in the field of AD. This approach has led to several examples engaged in the clinical trials. In a second chapter, a series of innovative prodrugs based on a polypharmacological approach is described to take into account the complexity of AD.

EXPERT OPINION

: In the past 10 years, at least 6 prodrugs have been approved by the FDA for the treatment of central nervous system pathologies. Most of them have been developed in order to improve membrane permeability of the parent drugs. Facing the limitation of Alzheimer's disease drug discovery, the development of prodrugs will likely play a central role in the next years. Indeed, beside addressing the challenge of distribution, prodrug could also tackle the complex multifactorial origin of the disease with the rise of innovative pleiotropic prodrugs.

Targeting the non-classical estrogen pathway in neurodegenerative diseases and brain injury disorders

Estrogens can alter the biology of various tissues and organs, including the brain, and thus play an essential role in modulating homeostasis. Despite its traditional role in reproduction, it is now accepted that estrogen and its analogues can exert neuroprotective effects. Several studies have shown the beneficial effects of estrogen in ameliorating and delaying the progression of neurodegenerative diseases, including Alzheimer's and Parkinson's disease and various forms of brain injury disorders. While the classical effects of estrogen through intracellular receptors are more established, the impact of the non-classical pathway through receptors located at the plasma membrane as well as the rapid stimulation of intracellular signaling cascades are still under active research. Moreover, it has been suggested that the non-classical estrogen pathway plays a crucial role in neuroprotection in various brain areas. In this mini-review, we will discuss the use of compounds targeting the non-classical estrogen pathway in their potential use as treatment in neurodegenerative diseases and brain injury disorders.

Intranasal administration of DHED protects against exhaustive exercise-induced brain injury in rats

DHED (10β,17β-dihydroxyestra-1,4-dien-3-one) is a brain-selective prodrug of 17β-estradiol and has been reported to have a strong neuroprotective effect. In this study, the exhaustive swimming rat model was used to investigate the therapeutic effects and mechanisms of intranasal DHED treatment. Male eight-week-old healthy Sprague Dawley rats were randomly divided into three groups: control group (Cont), exhaustive swimming (ES), and DHED + exhaustive swimming (DHED). The open-field test and beam-walking test were performed to measure exploratory behavior and general activity in rats. Immunofluorescence staining, western blotting, ELISA analysis and related assay kits were applied to measure brain damage, inflammatory cytokines, and apoptosis pathways. Behavioral data shows that DHED intranasal administration can prevent neurobehavioral impairment caused by exhaustive swimming. Using a series of bioanalytical assays, we demonstrated that DHED markedly abated neuronal injury compared to the exhaustive swimming group, as evidenced by the reduced expression of apoptosis-regulated proteins, the improvement of neural survival, and the prevention of myelin loss. In addition, mitochondrial fission was attenuated distinctly, and a dynamic equilibrium was restored. Intranasal administration of DHED likewise significantly suppressed reactive gliosis and the release of inflammatory cytokines in the rat cerebral motor cortex. Consistent with previous reports, DHED treatment ameliorated changes of excitatory neurotransmitters. These results provide strong support for the promising therapeutic effects of DHED on neuroprotection during exhaustive swimming. The underlying mechanisms may rely on mitochondrial dynamics, neuroinflammation, and the balance of neurotransmitters.

From Menopause to Neurodegeneration-Molecular Basis and Potential Therapy

The impacts of menopause on neurodegenerative diseases, especially the changes in steroid hormones, have been well described in cell models, animal models, and humans. However, the therapeutic effects of hormone replacement therapy on postmenopausal women with neurodegenerative diseases remain controversial. The steroid hormones, steroid hormone receptors, and downstream signal pathways in the brain change with aging and contribute to disease progression. Estrogen and progesterone are two steroid hormones which decline in circulation and the brain during menopause. Insulin-like growth factor 1 (IGF-1), which plays an import role in neuroprotection, is rapidly decreased in serum after menopause. Here, we summarize the actions of estrogen, progesterone, and IGF-1 and their signaling pathways in the brain. Since the incidence of Alzheimer’s disease (AD) is higher in women than in men, the associations of steroid hormone changes and AD are emphasized. The signaling pathways and cellular mechanisms for how steroid hormones and IGF-1 provide neuroprotection are also addressed. Finally, the molecular mechanisms of potential estrogen modulation on N-methyl-d-aspartic acid receptors (NMDARs) are also addressed. We provide the viewpoint of why hormone therapy has inconclusive results based on signaling pathways considering their complex response to aging and hormone treatments. Nonetheless, while diagnosable AD may not be treatable by hormone therapy, its preceding stage of mild cognitive impairment may very well be treatable by hormone therapy.

Long-term ovarian hormone deprivation alters functional connectivity, brain neurochemical profile and white matter integrity in the Tg2576 amyloid mouse model of Alzheimer's disease

Premenopausal bilateral ovariectomy is considered to be one of the risk factors of Alzheimer's disease (AD). However, the underlying mechanisms remain unclear. Here, we aimed to investigate long-term neurological consequences of ovariectomy in a rodent AD model, TG2576 (TG), and wild-type mice (WT) that underwent an ovariectomy or sham-operation, using in vivo MRI biomarkers. An increase in osmoregulation and energy metabolism biomarkers in the hypothalamus, a decrease in white matter integrity, and a decrease in the resting-state functional connectivity was observed in ovariectomized TG mice compared to sham-operated TG mice. In addition, we observed an increase in functional connectivity in ovariectomized WT mice compared to sham-operated WT mice. Furthermore, genotype (TG vs. WT) effects on imaging markers and GFAP immunoreactivity levels were observed, but there was no effect of interaction (Genotype × Surgery) on amyloid-beta-and GFAP immunoreactivity levels. Taken together, our results indicated that both genotype and ovariectomy alters imaging biomarkers associated with AD.

Aminoguanidine ameliorates ovariectomy-induced neuronal deficits in rats by inhibiting AGE-mediated Aβ production

Advanced glycation end products (AGEs) have been reported to cause neurodegeneration, senile plaque formation and spatial learning and memory deficits. There is much evidence describing the beneficial effects of aminoguanidine (AG) on the central nervous system; AG is able to inhibit the receptor for AGEs and beta-amyloid (Aβ) deposition in the brain, thus preventing cognitive decline and neurodegeneration. In this study, we investigated whether AG protects against ovariectomy-induced neuronal deficits and Aβ deposition in rats. Animals in the ovariectomy group (OVX) group, and those in the OVX+AG group were treated with AG (100 mg/kg/day) for 8 weeks. Learning and memory were evaluated using the electric Y maze. AGE and Aβ_1-40 biochemical assessments were performed using enzyme-linked immunosorbent assay (ELISA) kits. Furthermore, evaluations of brain amyloid precursor protein 695 (APP₆₉₅) mRNA expression by RT-PCR and AGE expression by immunohistochemistry were carried out. Ovariectomized rats exhibited memory impairment and Aβ production disorder with upregulated APP₆₉₅ mRNA and AGE expression levels. AG pretreatment relieved the ovariectomy-induced learning and memory disorder and significantly ameliorated the Aβ production disturbance and AGE generation. Additionally, pathological changes in morphology were also significantly recovered. Our data reveal that AG plays a potentially neuroprotective role against ovariectomy-induced learning and cognitive impairment and Aβ production disorder.

Advanced glycation end products (AGEs) have been reported to cause neurodegeneration, senile plaque formation and spatial learning and memory deficits. There is much evidence describing the beneficial effects of aminoguanidine (AG) on the central nervous system; AG is able to inhibit the receptor for AGEs and beta-amyloid (Aβ) deposition in the brain, thus preventing cognitive decline and neurodegeneration. In this study, we investigated whether AG protects against ovariectomy-induced neuronal deficits and Aβ deposition in rats. Animals in the ovariectomy group (OVX) group, and those in the OVX+AG group were treated with AG (100 mg/kg/day) for 8 weeks. Learning and memory were evaluated using the electric Y maze. AGE and Aβ_1-40 biochemical assessments were performed using enzyme-linked immunosorbent assay (ELISA) kits. Furthermore, evaluations of brain amyloid precursor protein 695 (APP₆₉₅) mRNA expression by RT-PCR and AGE expression by immunohistochemistry were carried out. Ovariectomized rats exhibited memory impairment and Aβ production disorder with upregulated APP₆₉₅ mRNA and AGE expression levels. AG pretreatment relieved the ovariectomy-induced learning and memory disorder and significantly ameliorated the Aβ production disturbance and AGE generation. Additionally, pathological changes in morphology were also significantly recovered. Our data reveal that AG plays a potentially neuroprotective role against ovariectomy-induced learning and cognitive impairment and Aβ production disorder.

Brain Selective Estrogen Treatment Protects Dopaminergic Neurons and Preserves Behavioral Function in MPTP-induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra and loss of both motor and non-motor features. Several clinical and preclinical studies have provided evidence that estrogen therapy reduces the risk of PD but have limitations in terms of adverse peripheral effects. Therefore, we examined the potential beneficial effects of the brain-selective estrogen prodrug, 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED) on nigrostriatal dopaminergic neurodegeneration and behavioral abnormalities in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Wild-type mice were treated with daily subcutaneous injections of DHED (50 and 100 µg/kg) or vehicle for four weeks. To produce PD-like symptoms, mice were injected with MPTP (18 mg/kg in saline; intraperitoneally) four times at 2-hr intervals for one day. After behavioral examination, mice were sacrificed, and the brains were isolated for neurochemical and morphological examinations. MPTP injected mice exhibited loss of dopaminergic neurons and fibers in substantia nigra and striatum respectively, along with impaired motor function at day 7 post MPTP injection. These phenotypes were associated with significantly increased oxidative stress and inflammatory responses in the striatum regions. DHED treatments significantly mitigated behavioral impairments and dopaminergic neurodegeneration induced by MPTP. We further observed that DHED treatment suppressed oxidative stress and inflammation in the striatum of MPTP treated mice when compared to vehicle treated mice. In conclusions, our findings suggest that DHED protects dopaminergic neurons from MPTP toxicity in mouse model of PD and support a beneficial effect of brain-selective estrogen in attenuating neurodegeneration and motor symptoms in PD-related neurological disorders. Graphical Abstract.

Ovariectomy Influences Cognition and Markers of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most devastating and costly diseases, and prevalence of AD increases with age. Furthermore, females are twice as likely to suffer from AD compared to males. The cessation of reproductive steroid hormone production during menopause is hypothesized to cause this difference. Two rodent AD models, APP21 and APP+PS1, and wild type (WT) rats underwent an ovariectomy or sham surgery. Changes in learning and memory, brain histology, amyloid-β (Aβ) deposition, levels of mRNAs involved in Aβ production and clearance, and synaptic and cognitive function were determined. Barnes maze results showed that regardless of ovariectomy status, APP+PS1 rats learned slower and had poor memory retention. Ovariectomy caused learning impairment only in the APP21 rats. High levels of Aβ42 and very low levels of Aβ40 were observed in the brain cortices of APP+PS1 rats indicating limited endogenous PS1. The APP+PS1 rats had 43-fold greater formic acid soluble Aβ42 than Aβ40 at 17 months. Furthermore, levels of formic acid soluble Aβ42 increased 57-fold in ovariectomized APP+PS1 rats between 12 and 17 months of age. The mRNA encoding Grin1 significantly decreased due to ovariectomy whereas levels of Bace1, Chat, and Prkcb all decreased with age. The expression levels of mRNAs involved in Aβ degradation and AβPP cleavage (Neprilysin, Ide, Adam9, and Psenen) were found to be highly correlated with each other as well as hippocampal Aβ deposition. Taken together, these results indicate that both ovariectomy and genotype influence AD markers in a complex manner.

Retina-Targeted Delivery of 17β-Estradiol by the Topically Applied DHED Prodrug

The purpose of this study was to explore retina-targeted delivery of 17β-estradiol (E2), a powerful neuroprotectant, by its bioprecursor prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED) administered as eye drops in animal models. Compared to the parent hormone, DHED displayed increased transcorneal flux ex vivo both with and without the presence of 2-hydroxypropyl-β-cyclodextrin used as a penetration-enhancing excipient in rat, rabbit, and pig. In vitro, the prodrug also showed facile bioactivation to E2 in the retina but not in the cornea. After topical administration to rats and rabbits, peak DHED-derived E2 concentrations reached 13 ± 5 ng/g and 18 ± 7 ng/g in the retina of female rats and rabbits, respectively. However, the prodrug remained inert in the rest of the body and, therefore, did not cause increase in circulating hormone concentration, as well as wet uterine and anterior pituitary weights as typical markers of E2′s endocrine impact. Altogether, our studies presented here have demonstrated the premise of topical retina-selective estrogen therapy by the DHED prodrug approach for the first time and provide compelling support for further investigation into the full potential of DHED for an efficacious and safe ocular neurotherapy.

The Critical Period for Neuroprotection by Estrogen Replacement Therapy and the Potential Underlying Mechanisms

17β-Estradiol (estradiol or E2) is a steroid hormone that has been broadly applied as a neuroprotective therapy for a variety of neurodegenerative and cerebrovascular disorders such as ischemic stroke, Alzheimer's disease, and Parkinson's disease. Several laboratory and clinical studies have reported that Estrogen Replacement Therapy (ERT) had no effect against these diseases in elderly postmenopausal women, and at worst, increased their risk of onset and mortality. This review focuses on the growing body of data from in vitro and animal models characterizing the potential underlying mechanisms and signaling pathways that govern successful neuroprotection by ERT, including the roles of E2 receptors in mediating neuroprotection, E2 genomic regulation of apoptosis- related pathways, membrane-bound receptor-mediated non-genomic signaling pathways, and the antioxidant mechanisms of E2. Also discussed is the current evidence for a critical period of effective treatment with estrogen following natural or surgical menopause and the outcomes of E2 administration within an advantageous time period. The known mechanisms governing the duration of the critical period include depletion of E2 receptors, the switch to a ketogenic metabolic profile by neuronal mitochondria, and a decrease in acetylcholine that accompanies E2 deficiency. Also the major clinical trials and observational studies concerning postmenopausal Hormone Therapy (HT) are summarized to compare their outcomes with respect to neurological disease and discuss their relevance to the critical period hypothesis. Finally, potential controversies and future directions for this field are discussed throughout the review.

A Novel Prodrug Approach for Central Nervous System-Selective Estrogen Therapy

Beneficial effects of estrogens in the central nervous system (CNS) results from the synergistic combination of their well-orchestrated genomic and non-genomic actions, making them potential broad-spectrum neurotherapeutic agents. However, owing to unwanted peripheral hormonal burdens by any currently known non-invasive drug administrations, the development of estrogens as safe pharmacotherapeutic modalities cannot be realized until they are confined specifically and selectively to the site of action. We have developed small-molecule bioprecursor prodrugs carrying the para-quinol scaffold on the steroidal A-ring that are preferentially metabolized in the CNS to the corresponding estrogens. Here, we give an overview of our discovery of these prodrugs. Selected examples are shown to illustrate that, independently of the route of administrations and duration of treatments, these agents produce high concentration of estrogens only in the CNS without peripheral hormonal liability. 10β,17β-Dihydroxyestra-1,4-dien-3-one (DHED) has been the best-studied representative of this novel type of prodrugs for brain and retina health. Specific applications in preclinical animal models of centrally-regulated and estrogen-responsive human diseases, including neurodegeneration, menopausal symptoms, cognitive decline and depression, are discussed to demonstrate the translational potential of our prodrug approach for CNS-selective and gender-independent estrogen therapy with inherent therapeutic safety.

Female Sex and Brain-Selective Estrogen Benefit α-Synuclein Tetramerization and the PD-like Motor Syndrome in 3K Transgenic Mice

Many studies report a higher risk for Parkinson's disease (PD) and younger age of onset in men. This, and the fact that the neuropathological process underlying PD symptoms may begin before menopause, suggests that estrogen-based hormone therapy could modify this higher risk in males. However, the effects of female sex or estrogen on α-synuclein (αS) homeostasis and related PD neuropathology remain unknown. Here, we used an αS tetramer-abrogating mouse model of PD (3K) that amplifies the familial E46K PD mutation to investigate the effects of female sex and brain-selective estrogen treatment on αS tetramerization and solubility, formation of vesicle-rich αS⁺ aggregates, dopaminergic and cortical fiber integrity, and associated motor deficits. In male 3K mice, the motor phenotype became apparent at ∼10 weeks and increased to age 6 months, paralleled by PD-like neuropathology, whereas 3K females showed a significant delay in onset. At 6 months, this beneficial phenotypic effect in 3K females was associated with a higher αS tetramer-to-monomer ratio and less decrease in dopaminergic and cortical fiber length and quantity. Brain-selective estrogen treatment in symptomatic 3K mice significantly increased the tetramer-to-monomer ratio, turnover by autophagy of aggregate-prone monomers, and neurite complexity of surviving DAergic and cortical neurons, in parallel with benefits in motor performance. Our findings support an upstream role for αS tetramer loss in PD phenotypes and a role for estrogen in mitigating PD-like neuropathology in vivo Brain-selective estrogen therapy may be useful in delaying or reducing PD symptoms in men and postmenopausal women.SIGNIFICANCE STATEMENT The mechanisms responsible for the male-to-female preponderance in Parkinson's disease (PD) are not well understood yet important for treatment efficacy. We previously showed that abrogating native α-synuclein (αS) tetramers produces a close PD model, including dopaminergic and cortical fiber loss and a progressive motor disorder responsive to l-DOPA. Here, we analyzed sex and use 10b-17β-dihydroxyestra-1,4-dien-3-one treatment of symptomatic 3K males, and demonstrate that the beneficial effects of female sex on PD-like neuropathology can be reinstated by elevating estrogen in the male brain. The study provides evidence that 17β-estradiol restores the tetramer-to-monomer ratio by autophagy turnover of excess αS monomers, vesicle and fiber integrity in brain regions critically involved in motor behavior. These data provide the basis for understanding sex differences in αS homeostasis and the development of therapeutic approaches to treating men and postmenopausal women with PD.

The mechanism(s) of action of antioxidants: From scavenging reactive oxygen/nitrogen species to redox signaling and the generation of bioactive secondary metabolites

Small molecule, dietary antioxidants exert a remarkably broad range of bioactivities, and many of these can be explained by the influence of antioxidants on the redox homeostasis. Such compounds help to modulate the levels of harmful reactive oxygen/nitrogen species, and therefore participate in the regulation of various redox signaling pathways. However, upon ingestion, antioxidants usually undergo extensive metabolism that can generate a wide range of bioactive metabolites. This makes it difficult, but otherwise a need, to identify the ones responsible for the different activities of antioxidants. By better understanding their ways of action, the use of antioxidants in therapy can be improved. This review provides a summary on the role of the in vivo metabolic changes and the oxidized metabolites on the mechanisms behind the bioactivity of antioxidants. A special attention is given to metabolites described as products of biomimetic oxidative chemical reactions, which can be considered as models of free radical scavenging. During such reactions a wide variety of metabolites are formed, and they can exert completely different specific bioactivities as compared to their parent antioxidants. This implies that exploring the free radical scavenging-related metabolite fingerprint of each antioxidant molecule, collectively defined here as the scavengome, will lead to a deeper understanding of the bioactivity of these compounds. Furthermore, this paper aims to be a working tool for systematic studies on oxidized metabolic fingerprints of antioxidants, which will certainly reveal an often-neglected segment of chemical space that is a treasury of bioactive compounds.

Treatment with a brain-selective prodrug of 17β-estradiol improves cognitive function in Alzheimer's disease mice by regulating klf5-NF-κB pathway

10β,17β-dihydroxyestra-1,4-dien-3-one (DHED) which is a brain-selective prodrug of 17β-estradiol has been reported to improve the cognitive function in Alzheimer’s disease (AD) mice model. However, little is known about the potential mechanism for cognitive improvement. In the present study, we used AD mice to investigate the effects and mechanisms of DHED treatment. Female Tg2576 transgenic AD mice were ovariectomized and then treated by implanting Alzet osmotic minipumps containing DHED or vehicle subcutaneously for 8 weeks. Consistent with previous report, DHED treatment ameliorated cognitive function of AD mice with decreasing Aβ levels in the hippocampus. Besides, we also found DHED treatment could reduce oxidative and inflammatory stress and the level of p-tau. The mechanisms underlying the cognitive function improvement may be linked with estrogen receptor (ER)-klf5-NF-κB pathway, demonstrated by decreased expression of klf5 and the secretion of inflammatory cytokines. However, the effects of DHED treatment could be reversed when ERα was inhibited by ICI182780. Taken together, our findings uncovered a new mechanism for DHED to improve the cognitive function of AD mice and may provide a viable therapy to treat AD.

10β,17α-Dihydroxyestra-1,4-dien-3-one: A Bioprecursor Prodrug Preferentially Producing 17α-Estradiol in the Brain for Targeted Neurotherapy

Uterotrophic effect of 17α-estradiol, the C17 epimer of the main human estrogen 17β-estradiol, was shown to manifest in animal models at doses lower than those necessary for central outcome raising concerns about its potential to treat maladies of the central nervous system. We introduce here 10β,17α-dihydroxyestra-1,4-dien-3-one (α-DHED) that acts as a bioprecursor prodrug producing 17α-estradiol with remarkable selectivity to the brain and, therefore, without appreciable exposure of the periphery to the parent steroid. This distinguishing feature of α-DHED is shown by using an estrogen-responsive mouse model with complementary LC-MS/MS measurement of drug contents in target tissues. Our data warrant further research to fully establish the potential of α-DHED for a safe and efficacious 17α-estradiol-based neurotherapy.

An exploratory investigation of brain-selective estrogen treatment in males using a mouse model of Alzheimer's disease

Estrogens are neuroprotective, and studies suggest that they may mitigate the pathology and symptoms of Alzheimer's disease (AD) in female models. However, central estrogen effects have not been examined in males in the context of AD. The purpose of this follow-up study was to assess the benefits of a brain-selective 17β-estradiol estrogen prodrug, 10β,17β-hydroxyestra-1,4-dien-3-one (DHED), also in the male APPswe/PS1dE9 double-transgenic mouse model of the disease. After continuously exposing 6-month old animals to DHED for two months, their brains showed decreased amyloid precursor and amyloid-β protein levels. The DHED-treated APPswe/PS1dE9 double transgenic subjects also exhibited enhanced performance in a cognitive task, while 17β-estradiol treatment did not reach statistical significance. Taken together, data presented here suggest that DHED may also have therapeutic benefit in males and warrant further investigations to fully elucidate the potential of targeted estrogen therapy for a gender-independent treatment of early-stage AD.

[Anti-ageing therapies in Alzheimer's disease]

Alzheimer's disease is the most common cause of dementia in the elderly population. Currently, there are no effective treatments to prevent or delay the natural course of the disease. Numerous studies have provided information about the molecular processes underlying biological ageing and, perhaps more importantly, potential interventions to slow ageing and promote healthy longevity in laboratory model systems. The main issue addressed in this review is whether an intervention that has anti-ageing properties can alter the appearance and/or progression of Alzheimer's disease, a disease in which age is the biggest risk factor. Different anti-ageing interventions have been shown to prevent (and in some cases possibly restore) several parameters recognised as central symptoms to the development of Alzheimer's disease. In addition, they are taking the first steps towards translating these laboratory discoveries into clinical applications.