4-Hydroxyestrone, an Endogenous Estrogen Metabolite, Can Strongly Protect Neuronal Cells Against Oxidative Damage

Raloxifene Prevents Chemically-Induced Ferroptotic Neuronal Death In Vitro and In Vivo

Ferroptosis, a regulated form of cell death characterized by excessive iron-dependent lipid peroxidation, can be readily induced in cultured cells by chemicals such as erastin and RSL3. Protein disulfide isomerase (PDI) has been identified as an upstream mediator of chemically induced ferroptosis and also a target for ferroptosis protection. In this study, we discovered that raloxifene (RAL), a selective estrogen receptor modulator known for its neuroprotective actions in humans, can effectively inhibit PDI function and provide robust protection against chemically induced ferroptosis in cultured HT22 neuronal cells. Specifically, RAL can bind directly to PDI both in vitro and in intact neuronal cells and inhibit its catalytic activity. Computational modeling analysis reveals that RAL can tightly bind to PDI through forming a hydrogen bond with its His256 residue, and biochemical analysis further shows that when PDI's His256 is mutated to Ala256, RAL loses its inhibition of PDI's catalytic activity. This inhibition of PDI by RAL significantly reduces the dimerization of both the inducible and neuronal nitric oxide synthases and the accumulation of nitric oxide, both of which have recently been shown to play a crucial role in mediating chemically induced ferroptosis through subsequent induction of ROS and lipid-ROS accumulation. In vivo behavioral analysis shows that mice treated with RAL are strongly protected against kainic acid-induced memory deficits and hippocampal neuronal damage. In conclusion, this study demonstrates that RAL is a potent inhibitor of PDI and can effectively prevent chemically induced ferroptosis in hippocampal neurons both in vitro and in vivo. These findings offer a novel estrogen receptor-independent mechanism for RAL's neuroprotective actions in animal models and humans.

Protection of HT22 neuronal cells against chemically-induced ferroptosis by catechol estrogens: protein disulfide isomerase as a mechanistic target

Ferroptosis is a form of regulated cell death, characterized by excessive iron-dependent lipid peroxidation. Biochemically, ferroptosis can be selectively induced by erastin through glutathione depletion or through inhibition of glutathione peroxidase 4 by RSL3, which leads to accumulation of cytotoxic lipid reactive oxygen species (ROS). Protein disulfide isomerase (PDI) was recently shown to mediate erastin/RSL3-induced ferroptosis and thus also become a new target for protection against chemically-induced ferroptosis. The present study aims to identify endogenous compounds that can protect against erastin/RSL3-induced ferroptotic cell death. We find that 2-hydroxyestrone, 2-hydroxyestradiol, 4-hydroxyestrone and 4-hydroxyestradiol, four major endogenous catechol estrogens, are effective inhibitors of PDI, and can strongly protect against chemically-induced ferroptotic cell death in cultured HT22 mouse hippocampal neuronal cells. The CETSA assay showed that these catechol estrogens can bind to PDI in live cells. PDI knockdown attenuates the protective effect of these catechol estrogens against chemically-induced ferroptosis. Mechanistically, inhibition of PDI's catalytic activity by catechol estrogens abrogates erastin/RSL3-induced dimerization of nitric oxide synthase, thereby preventing the subsequent accumulation of cellular nitric oxide, ROS and lipid-ROS, and ultimately ferroptotic cell death. In addition, joint treatment of cells with catechol estrogens also abrogates erastin/RSL3-induced upregulation of nitric oxide synthase protein levels, which also contributes to the cytoprotective effect of the catechol estrogens. In conclusion, the present study demonstrates that the catechol estrogens are protectors of HT22 neuronal cells against chemically-induced ferroptosis, and inhibition of PDI's catalytic activity by these estrogens contributes to a novel, estrogen receptor-independent mechanism of cytoprotection.

Protein disulfide isomerase plays a crucial role in mediating chemically-induced, glutathione depletion-associated hepatocyte injury in vitro and in vivo

Recently we have shown that protein disulfide isomerase (PDI or PDIA1) is involved in mediating chemically-induced, glutathione (GSH) depletion-associated ferroptotic cell death through NOS activation (dimerization) and NO accumulation. The present study aims to determine the role of PDI in mediating chemically-induced hepatocyte injury in vitro and in vivo and whether PDI inhibitors can effectively protect against chemically-induced hepatocyte injury. We show that during the development of erastin-induced ferroptotic cell death, accumulation of cellular NO, ROS and lipid-ROS follows a sequential order, i.e., cellular NO accumulation first, followed by accumulation of cellular ROS, and lastly cellular lipid-ROS. Cellular NO, ROS and lipid-ROS each play a crucial role in mediating erastin-induced ferroptosis in cultured hepatocytes. In addition, it is shown that PDI is an important upstream mediator of erastin-induced ferroptosis through PDI-mediated conversion of NOS monomer to its dimer, which then leads to accumulation of cellular NO, ROS and lipid-ROS, and ultimately ferroptotic cell death. Genetic manipulation of PDI expression or pharmacological inhibition of PDI function each can effectively abrogate erastin-induced ferroptosis. Lastly, evidence is presented to show that PDI is also involved in mediating acetaminophen-induced liver injury in vivo using both wild-type C57BL/6J mice and hepatocyte-specific PDI conditional knockout (PDIfl/fl Alb-cre) mice. Together, our work demonstrates that PDI is an important upstream mediator of chemically-induced, GSH depletion-associated hepatocyte ferroptosis, and inhibition of PDI can effectively prevent this injury.

Sex as a Determinant of Age-Related Changes in the Brain

The notion of notable anatomical, biochemical, and behavioral distinctions within male and female brains has been a contentious topic of interest within the scientific community over several decades. Advancements in neuroimaging and molecular biological techniques have increasingly elucidated common mechanisms characterizing brain aging while also revealing disparities between sexes in these processes. Variations in cognitive functions; susceptibility to and progression of neurodegenerative conditions, notably Alzheimer's and Parkinson's diseases; and notable disparities in life expectancy between sexes, underscore the significance of evaluating aging within the framework of gender differences. This comprehensive review surveys contemporary literature on the restructuring of brain structures and fundamental processes unfolding in the aging brain at cellular and molecular levels, with a focus on gender distinctions. Additionally, the review delves into age-related cognitive alterations, exploring factors influencing the acceleration or deceleration of aging, with particular attention to estrogen's hormonal support of the central nervous system.

Strong Protection by 4-Hydroxyestrone against Erastin-Induced Ferroptotic Cell Death in Estrogen Receptor-Negative Human Breast Cancer Cells: Evidence for Protein Disulfide Isomerase as a Mechanistic Target for Protection

Ferroptosis is a recently identified form of regulated cell death, characterized by excessive iron-dependent lipid peroxidation. Recent studies have demonstrated that protein disulfide isomerase (PDI) is an important mediator of chemically induced ferroptosis and also a new target for protection against ferroptosis-associated cell death. In the present study, we identified that 4-hydroxyestrone (4-OH-E1), a metabolic derivative of endogenous estrogen, is a potent small-molecule inhibitor of PDI, and can strongly protect against chemically induced ferroptotic cell death in the estrogen receptor-negative MDA-MB-231 human breast cancer cells. Pull-down and CETSA assays demonstrated that 4-OH-E1 can directly bind to PDI both in vitro and in intact cells. Computational modeling analysis revealed that 4-OH-E1 forms two hydrogen bonds with PDI His256, which is essential for its binding interaction and thus inhibition of PDI's catalytic activity. Additionally, PDI knockdown attenuates the protective effect of 4-OH-E1 as well as cystamine (a known PDI inhibitor) against chemically induced ferroptosis in human breast cancer cells. Importantly, inhibition of PDI by 4-OH-E1 and cystamine or PDI knockdown by siRNAs each markedly reduces iNOS activity and NO accumulation, which has recently been demonstrated to play an important role in erastin-induced ferroptosis. In conclusion, this study demonstrates that 4-OH-E1 is a novel inhibitor of PDI and can strongly inhibit ferroptosis in human breast cancer cells in an estrogen receptor-independent manner. The mechanistic understanding gained from the present study may also aid in understanding the estrogen receptor-independent cytoprotective actions of endogenous estrogen metabolites in many noncancer cell types.

Hyaluronic Acid Conjugated with 17β-Estradiol Effectively Alleviates Estropause-Induced Cognitive Deficits in Rats

Women are at a higher risk of cognitive impairments and Alzheimer's disease (AD), particularly after the menopause, when the estrous cycle becomes irregular and diminishes. Numerous studies have shown that estrogen deficiency, especially estradiol (E2) deficiency, plays a key role in this phenomenon. Recently, a novel polymeric drug, hyaluronic acid-17β-estradiol conjugate (HA-E2), has been introduced for the delivery of E2 to brain tissues. Studies have indicated that HA-E2 crosses the blood-brain barrier (BBB) and facilitates a prolonged E2 release profile while lowering the risk of estrogen-supplement-related side effects. In this study, we used ovariohysterectomy (OHE) rats, a postmenopausal cognitive deficit model, to explore the effect of a 2-week HA-E2 treatment (210 ng/kg body weight, twice a week) on the cholinergic septo-hippocampal innervation system, synaptic transmission in hippocampal pyramidal neurons and cognitive improvements. Our study revealed an 11% rise in choline acetyltransferase (ChAT) expression in both the medial septal nucleus (MS nucleus) and the hippocampus, along with a 14-18% increase in dendritic spine density in hippocampal pyramidal neurons, following HA-E2 treatment in OHE rats. These enhancements prompted the recovery of cognitive functions such as spatial learning and memory. These findings suggest that HA-E2 may prevent and improve estrogen-deficiency-induced cognitive impairment and AD.

Protection against glutathione depletion-associated oxidative neuronal death by neurotransmitters norepinephrine and dopamine: Protein disulfide isomerase as a mechanistic target for neuroprotection

Oxidative stress is extensively involved in neurodegeneration. Clinical evidence shows that keeping the mind active through mentally-stimulating physical activities can effectively slow down the progression of neurodegeneration. With increased physical activities, more neurotransmitters would be released in the brain. In the present study, we investigated whether some of the released neurotransmitters might have a beneficial effect against oxidative neurodegeneration in vitro. Glutamate-induced, glutathione depletion-associated oxidative cytotoxicity in HT22 mouse hippocampal neuronal cells was used as an experimental model. We showed that norepinephrine (NE, 50 µM) or dopamine (DA, 50 µM) exerted potent protective effect against glutamate-induced cytotoxicity, but this effect was not observed when other neurotransmitters such as histamine, γ-aminobutyric acid, serotonin, glycine and acetylcholine were tested. In glutamate-treated HT22 cells, both NE and DA significantly suppressed glutathione depletion-associated mitochondrial dysfunction including mitochondrial superoxide accumulation, ATP depletion and mitochondrial AIF release. Moreover, both NE and DA inhibited glutathione depletion-associated MAPKs activation, p53 phosphorylation and GADD45α activation. Molecular docking analysis revealed that NE and DA could bind to protein disulfide isomerase (PDI). In biochemical enzymatic assay in vitro, NE and DA dose-dependently inhibited the reductive activity of PDI. We further revealed that the protective effect of NE and DA against glutamate-induced oxidative cytotoxicity was mediated through inhibition of PDI-catalyzed dimerization of the neuronal nitric oxide synthase. Collectively, the results of this study suggest that NE and DA may have a protective effect against oxidative neurodegeneration through inhibition of protein disulfide isomerase and the subsequent activation of the MAPKs‒p53‒GADD45α oxidative cascade.

Protective effect of vitamin C on DNA damage in surgery-induced cognitive dysfunction in APP/PS1 mice

Postoperative cognitive impairment is more likely to occur in elderly patients and in those with neurodegenerative diseases. The mechanisms underlying this impairment include neuroinflammation and oxidative stress. The increase in reactive oxygen species during oxidative stress causes cellular and molecular injury to neurons, including DNA damage, which aggravate brain dysfunction. Vitamin C has antioxidant effects and improves cognitive function in patients with Alzheimer's disease. However, it is unclear whether it can ameliorate surgery-induced cognitive impairment by inhibiting oxidative stress. In this study, 6-month-old mice overexpressing mutant amyloid precursor protein and presenilin-1 (APP/PS1) were subjected to laparotomy. The open field and fear conditioning tests were used to assess cognitive function. Mice that underwent surgery showed cognitive impairment without changes in spontaneous locomotor activity. Oxidative stress, DNA damage and inflammatory mediators were increased in the hippocampus after surgery. The expression levels of non-homologous end-joining DNA repair-associated proteins, including Ku heterodimer, DNA-dependent protein kinase catalytic subunit, X-ray repair cross complementing 4 (XRCC4) and XRCC4-like factor, were increased after surgery. Vitamin C pretreatment effectively attenuated cognitive dysfunction induced by surgery and reduced oxidative stress and DNA damage. Our findings suggest that DNA damage plays an important role in surgery-induced cognitive dysfunction, and that vitamin C pretreatment may have therapeutic potential as a preventative approach for the cognitive impairment.

In Silico Prediction of Steroids and Triterpenoids as Potential Regulators of Lipid Metabolism

This review focuses on a rare group of steroids and triterpenoids that share common properties as regulators of lipid metabolism. This group of compounds is divided by the type of chemical structure, and they represent: aromatic steroids, steroid phosphate esters, highly oxygenated steroids such as steroid endoperoxides and hydroperoxides, α,β-epoxy steroids, and secosteroids. In addition, subgroups of carbon-bridged steroids, neo steroids, miscellaneous steroids, as well as synthetic steroids containing heteroatoms S (epithio steroids), Se (selena steroids), Te (tellura steroids), and At (astatosteroids) were presented. Natural steroids and triterpenoids have been found and identified from various sources such as marine sponges, soft corals, starfish, and other marine invertebrates. In addition, this group of rare lipids is found in fungi, fungal endophytes, and plants. The pharmacological profile of the presented steroids and triterpenoids was determined using the well-known computer program PASS, which is currently available online for all interested scientists and pharmacologists and is currently used by research teams from more than 130 countries of the world. Our attention has been focused on the biological activities of steroids and triterpenoids associated with the regulation of cholesterol metabolism and related processes such as anti-hyperlipoproteinemic activity, as well as the treatment of atherosclerosis, lipoprotein disorders, or inhibitors of cholesterol synthesis. In addition, individual steroids and triterpenoids were identified that demonstrated rare or unique biological activities such as treating neurodegenerative diseases, Alzheimer's, and Parkinson's diseases with a high degree of certainty over 95 percent. For individual steroids or triterpenoids or a group of compounds, 3D drawings of their predicted biological activities are presented.

Sex-specific Changes in Brain Estrogen Metabolism Induced by Acute Trimethyltin Exposure

BACKGROUND/AIM

In this study, we investigated sex-specific effects of acute exposure to trimethyltin, a known neurotoxicant on metabolic steroids.

MATERIALS AND METHODS

We administered intraperitoneally 2.3 mg/kg trimethyltin to 4-week-old male mice and measured the levels of metabolic steroids 24 h after treatment. We also measured mRNA and protein levels of cytochrome P450 1B1 using real-time polymerase chain reaction and western blotting.

RESULTS

Cortisol levels in the cortex increased in both sexes following acute trimethyltin exposure. The estradiol levels decreased, and the 4-hydroxyestradiol levels increased only in females. We also observed increased cytochrome P450 1B1 mRNA and protein levels only in the female cortex.

CONCLUSION

Acute trimethyltin exposure induces distinct sex-specific metabolic changes in the brain before significant sexual maturation.

The Impact of Estrogen and Estrogen-Like Molecules in Neurogenesis and Neurodegeneration: Beneficial or Harmful?

Estrogens and estrogen-like molecules can modify the biology of several cell types. Estrogen receptors alpha (ERα) and beta (ERβ) belong to the so-called classical family of estrogen receptors, while the G protein-coupled estrogen receptor 1 (GPER-1) represents a non-classical estrogen receptor mainly located in the plasma membrane. As estrogen receptors are ubiquitously distributed, they can modulate cell proliferation, differentiation, and survival in several tissues and organs, including the central nervous system (CNS). Estrogens can exert neuroprotective roles by acting as anti-oxidants, promoting DNA repair, inducing the expression of growth factors, and modulating cerebral blood flow. Additionally, estrogen-dependent signaling pathways are involved in regulating the balance between proliferation and differentiation of neural stem/progenitor cells (NSPCs), thus influencing neurogenic processes. Since several estrogen-based therapies are used nowadays and estrogen-like molecules, including phytoestrogens and xenoestrogens, are omnipresent in our environment, estrogen-dependent changes in cell biology and tissue homeostasis have gained attention in human health and disease. This article provides a comprehensive literature review on the current knowledge of estrogen and estrogen-like molecules and their impact on cell survival and neurodegeneration, as well as their role in NSPCs proliferation/differentiation balance and neurogenesis.

Sirtuins-Mediated System-Level Regulation of Mammalian Tissues at the Interface between Metabolism and Cell Cycle: A Systematic Review

Sirtuins are a family of highly conserved NAD+-dependent proteins and this dependency links Sirtuins directly to metabolism. Sirtuins' activity has been shown to extend the lifespan of several organisms and mainly through the post-translational modification of their many target proteins, with deacetylation being the most common modification. The seven mammalian Sirtuins, SIRT1 through SIRT7, have been implicated in regulating physiological responses to metabolism and stress by acting as nutrient sensors, linking environmental and nutrient signals to mammalian metabolic homeostasis. Furthermore, mammalian Sirtuins have been implicated in playing major roles in mammalian pathophysiological conditions such as inflammation, obesity and cancer. Mammalian Sirtuins are expressed heterogeneously among different organs and tissues, and the same holds true for their substrates. Thus, the function of mammalian Sirtuins together with their substrates is expected to vary among tissues. Any therapy depending on Sirtuins could therefore have different local as well as systemic effects. Here, an introduction to processes relevant for the actions of Sirtuins, such as metabolism and cell cycle, will be followed by reasoning on the system-level function of Sirtuins and their substrates in different mammalian tissues. Their involvement in the healthy metabolism and metabolic disorders will be reviewed and critically discussed.

The role of sex hormones in women with multiple sclerosis: From puberty to assisted reproductive techniques

BACKGROUND

Multiple Sclerosis is a multifactorial chronic autoimmune disease, affecting predominantly females in the fertile age. Sex hormones changes during a woman's life, from puberty to menopause, including pregnancy and puerperium, may influence the onset and course of Multiple Sclerosis. The effect of estrogen levels on immune, clinical and radiological aspects of Multiple Sclerosis, also stimulated investigation on the effect of sexual hormones therapies, such as oral contraceptives and assisted reproductive technique, on the Multiple Sclerosis course.

SEARCH STRATEGY AND SELECTION CRITERIA

A literature search for original articles and reviews was conducted in the databases, including PubMed, Scopus, and ClinicalTrials.gov of the U.S. National Library of Medicine site from 1988 to 2020.

RESULTS AND CONCLUSION

This review reports the effects of the physiological and iatrogenic hormonal changes either on immune or clinical or paraclinical features in the different life stages of women affected by Multiple Sclerosis.