Estrogen and neurodegenerative diseases

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Estradiol, the major estrogen sex hormone in humans Estradiol.svg
Estradiol, the major estrogen sex hormone in humans

Neurodegenerative diseases can disrupt the normal human homeostasis and result in abnormal estrogen levels. [1] For example, neurodegenerative diseases can cause different physiological effects in males and females. In particular, estrogen studies have revealed complex interactions with neurodegenerative diseases. Estrogen was initially proposed to be a possible treatment for certain types of neurodegenerative diseases but a plethora of harmful side effects such as increased susceptibility to breast cancer and coronary heart disease overshadowed any beneficial outcomes. On the other hand, Estrogen Replacement Therapy has shown some positive effects with postmenopausal women. Estrogen and estrogen-like molecules form a large family of potentially beneficial alternatives that can have dramatic effects on human homeostasis and disease. Subsequently, large-scale efforts were initiated to screen for useful estrogen family molecules. Furthermore, scientists discovered new ways to synthesize estrogen-like compounds that can avoid many side effects.[ citation needed ]

Contents

Estrogen

17-alpha- vs 17-beta-estradiol 17-alpha- vs 17-beta-estradiol.svg
17-alpha- vs 17-beta-estradiol

Estrogen is a lipid hormone in humans can regulate many physiological processes. [2] It is largely related to menstrual and estrous and its biological function is mediated by binding to two receptors: Estrogen Receptor alpha (ERα) and Estrogen Receptor beta (ERβ). These two receptors are tissue specific and have different influences on their downstream genes. [3] A decrease in estrogen levels can lead to osteoporosis, cognitive disorders, and can affect many important genes related to normal physiological function.[ citation needed ]

Estrogen can be divided into four classes: 1) Animal Estrogens that includes estrone (E1), estradiol (E2), and estriol (E3); 2) Plant Estrogens (Phytoestrogens); 3) Fungi Estrogens (Mycoestrogens) and 4) Synthetic Estrogens (xenoestrogens). Xenoestrogens contain a large number of compounds that are synthesized or naturally exist. These estrogens imitate estrogen structure and can be designed to satisfy the need of new drugs. They may have a significant impact on neurodegenerative disease treatment due to their ease of synthesis and targeted specificity.[ citation needed ]

Application

The application of estrogen on medicine can be divided into a number of aspects. The best known ones are breast cancer and coronary heart disease. Estrogen also plays very important role in animal metabolism balance. These unexpected diseases hindered estrogen to get involved in neurodegenerative disease therapy. So, when applying estrogen-like drugs to relieve neurodegenerative diseases, the concentration should be restrictly controlled to avoid these side effects.[ citation needed ]

Neurodegenerative Diseases

Parasagittal MRI of human head in patient with benign familial macrocephaly prior to brain injury (ANIMATED) Parasagittal MRI of human head in patient with benign familial macrocephaly prior to brain injury (ANIMATED).gif
Parasagittal MRI of human head in patient with benign familial macrocephaly prior to brain injury (ANIMATED)

Neurodegenerative diseases are diseases caused along the process of neurodegeneration. Neurodegeneration includes structural and functional loss of neurons or even the death of the neurons. The causes of such diseases can be various but can be concluded into four aspects: genetic mutation, protein misfolding, intracellular mechanisms and programmed cell death. Main classes of neurodegenerative diseases are Alzheimer's disease, Parkinson's disease, Huntington's disease and Amyotrophic lateral sclerosis.[ citation needed ]

Efforts Made on Therapy

Different neurodegenerative diseases have different causes and are not well studied until now. There is no clear cure for such diseases but some efforts have been made to research deeper into them. The 10th Global College of Neuroproetction and Neuroregeneration Annual Conference together with the International Association of Neurorestoratology VI was held to discuss on neurorestoration, neuroprotection and neuroregeneration in various clinical neurodegenerative diseases like Alzheimer's, Parkinson's, Huntington's disease, stroke and brain or spinal cord injuries. [4] The main aim was to enhance health care by the use of stem cells, nanodrug delivery of drugs and stem cells, use of multimodal drugs as well as a combination of different approaches. They concluded that the future of neuroprotection could be achieved by the use of stem cells and nanodrug delivery in chronic neurological disorders. [4]

Estrogen and neurodegenerative diseases

Although estrogen is best known for its effects on the maturation and differentiation of the primary and secondary sex organs, increasing evidence suggests that its influence extends beyond this system, and its activity in the CNS may initiate, or influence our susceptibility to neurodegenerative decline. Estrogen has been proposed to act as a neuroprotectant at several levels, and it is probable that deprivation of estrogen as a result of menopause exposes the aging or diseased brain to several insults. In addition, estrogen deprivation is likely to initiate or enhance degenerative changes caused by oxidative stress, and to reduce the brain's ability to maintain synaptic connectivity and cholinergic integrity leading to the cognitive decline seen in aged and disease-affected individuals. [5] There is sufficient evidence that estradiol is a powerful neuroprotectant which might have use against AD, stroke and Parkinson's disease both in women and men. [5]

Estrogen and Alzheimer's disease

This figure shows how APP cleavage produces toxic Abeta in Alzheimer's disease. APP cleavage produce toxic Abeta.png
This figure shows how APP cleavage produces toxic Abeta in Alzheimer's disease.

Amyloid plaques formed by amyloid-β (Aβ) deposition and neurofibrillary tangles formed by tau protein phosphorylation are dominant physiological features of Alzheimer's disease. Amyloid precursor protein (APP) proteolysis is fundamental for production of Aβ peptides implicated in AD pathology. [6] By using a cell line that contains high levels of estrogen receptors, scientists found that treatment with physiological concentrations of 17 beta-estradiol is associated with accumulation in the conditioned medium of an amino-terminal cleavage product of APP (soluble APP or protease nexin-2), indicative of non-amyloidogenic processing. [7]

Estrogen and Parkinson's disease

Recommendations on the use of postmenopausal hormonal replacement therapy in women with Parkinson's disease or those genetically at risk. [8] But another group of scientists found a positive association between estrogen use and lower symptom severity in women with early PD not yet taking L-dopa. [9]

Estrogen and Huntington's disease

Huntington's disease (HD) is a polyglutamine disorder based on an expanded CAG triplet repeat [10] leading to cerebral and striatal neurodegeneration. [11] Potential sex differences concerning the age of onset and the course of the disease are poorly defined, as the difficulties of matching female and male HD patients regarding their CAG repeat lengths limit comparability. [12]

Estrogen and Amyotrophic lateral sclerosis

ALS occurs more commonly in men than in women, and women get the disease later in life compared to men. [13] This suggested the possible protective role of estrogen in ALS. By conducting treatment of 17β-estradiol to ovariectomy treated mice, scientists found significantly delay of disease progression. [14]

Estrogen Replacement Therapy

Estrogen Replacement Therapy (HRT) is a kind of hormone replacement therapy. Its goal is to mitigate discomfort caused by diminished circulating estrogen after menopause. The 2002 Women's Health Initiative of the National Institutes of Health found disparate results for all cause mortality with hormone replacement, finding it to be lower when HRT was begun earlier, between age 50–59, but higher when begun after age 60. In older patients, there was an increased incidence of breast cancer, heart attacks and stroke, although a reduced incidence of colorectal cancer and bone fracture. [15] Some of the WHI findings were again found in a larger national study done in the UK, known as The Million Women Study. As a result of these findings, the number of women taking hormone treatment dropped precipitously. [16] The Women's Health Initiative recommended that women with non-surgical menopause take the lowest feasible dose of HRT for the shortest possible time to minimize associated risks. [15]

Main Pathways

The role of estrogens is mostly mediated by two nuclear receptors (ER alpha and ER beta) and a membrane-associated G-protein (GPR30 or GPER), and it is not limited to reproduction, but it extends to the skeletal, cardiovascular and central nervous systems. Various pathologies such as cancer, inflammatory, neurodegenerative and metabolic diseases are often associated with dysfunctions of the estrogen system. Therapeutic interventions by agents that affect the estrogen signaling pathway might be useful in the treatment of many dissimilar diseases. [17] These pathways also shown great impact on neurodegenerative disease.[ citation needed ]

Application

The receptors of estrogen are specially distributed in different tissues, which have different influence on their downstream genes. The activation of the two different estrogen receptors has different effects on human. ERα and ERβ also mediate Selective estrogen-receptor modulators' (SERMs') function, [18] but the selective ERα agitator can always cause some side effects such as breast cancer or endometrial hyperplasia, while the selective ERβ agitator may play an active effect on such diseases. So, the selective ERβ agitator has more clinical value for neurodegenerative diseases). In post-menopausal women, high levels of testosterone and estrogen higher the risk 2-3 times than lower level situation. Women that are not taking hormone replacement therapy (HRT) have lesser risk of breast cancer because of the insulin level increase. [19]

Nonsteroidal estrogens and neurodegenerative diseases

Nonsteroidal estrogens include xenoestrogens, phytoestrogens and mycoestrogens. They are very useful in neurodegenerative diseases' therapy when considering about the side effects caused by estradiol. As the development of chemical synthesis, it becomes possible for people to construct new molecules. Drug companies can exploit naturally existing compounds and synthetic compounds that have estrogen-like activity to produce patented proprietary drugs, especially the contraceptives. [20] Phytoestrogens are plant derived estrogens and have similar structures with 17beta-estradiol thus may cause estrogenic or anti-estrogenic effects. [21]

Application

Nonsteroidal estrogens prevalently exist in our environment and have both positive and negative effects on our daily life. But as a possible way to get access to neurodegenerative disease treatment, scientists have developed multiple ways to screen these estrogens and select the ones that have less side effects. Bipartite recombinant yeast system and dual fluorescence report system are designed to screen these potential chemicals. [22] [23]

Related Research Articles

<span class="mw-page-title-main">Estradiol</span> Chemical compound

Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of female reproductive cycles such as estrous and menstrual cycles. Estradiol is responsible for the development of female secondary sexual characteristics such as the breasts, widening of the hips and a female-associated pattern of fat distribution. It is also important in the development and maintenance of female reproductive tissues such as the mammary glands, uterus and vagina during puberty, adulthood and pregnancy. It also has important effects in many other tissues including bone, fat, skin, liver, and the brain.

<span class="mw-page-title-main">Estrone</span> Chemical compound

Estrone (E1), also spelled oestrone, is a steroid, a weak estrogen, and a minor female sex hormone. It is one of three major endogenous estrogens, the others being estradiol and estriol. Estrone, as well as the other estrogens, are synthesized from cholesterol and secreted mainly from the gonads, though they can also be formed from adrenal androgens in adipose tissue. Relative to estradiol, both estrone and estriol have far weaker activity as estrogens. Estrone can be converted into estradiol, and serves mainly as a precursor or metabolic intermediate of estradiol. It is both a precursor and metabolite of estradiol.

Hot flashes are a form of flushing, often caused by the changing hormone levels that are characteristic of menopause. They are typically experienced as a feeling of intense heat with sweating and rapid heartbeat, and may typically last from two to 30 minutes for each occurrence.

<span class="mw-page-title-main">Selective estrogen receptor modulator</span> Drugs acting on the estrogen receptor

Selective estrogen receptor modulators (SERMs), also known as estrogen receptor agonist/antagonists (ERAAs), are a class of drugs that act on the estrogen receptor (ER). A characteristic that distinguishes these substances from pure ER agonists and antagonists is that their action is different in various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues.

Fulvestrant, sold under the brand name Faslodex among others, is an antiestrogenic medication used to treat hormone receptor (HR)-positive metastatic breast cancer in postmenopausal women with disease progression as well as HR-positive, HER2-negative advanced breast cancer in combination with abemaciclib or palbociclib in women with disease progression after endocrine therapy. It is given by injection into a muscle.

<span class="mw-page-title-main">Equol</span> Isoflavandiol estrogen metabolized from daidzein

Equol (4',7-isoflavandiol) is an isoflavandiol estrogen metabolized from daidzein, a type of isoflavone found in soybeans and other plant sources, by bacterial flora in the intestines. While endogenous estrogenic hormones such as estradiol are steroids, equol is a nonsteroidal estrogen. Only about 30–50% of people have intestinal bacteria that make equol.

<span class="mw-page-title-main">Estrogen receptor</span> Proteins activated by the hormone estrogen

Estrogen receptors (ERs) are a group of proteins found inside cells. They are receptors that are activated by the hormone estrogen (17β-estradiol). Two classes of ER exist: nuclear estrogen receptors, which are members of the nuclear receptor family of intracellular receptors, and membrane estrogen receptors (mERs), which are mostly G protein-coupled receptors. This article refers to the former (ER).

<span class="mw-page-title-main">Raloxifene</span> Chemical compound

Raloxifene, sold under the brand name Evista among others, is a medication used to prevent and treat osteoporosis in postmenopausal women and those on glucocorticoids. For osteoporosis it is less preferred than bisphosphonates. It is also used to reduce the risk of breast cancer in those at high risk. It is taken by mouth.

<span class="mw-page-title-main">Tibolone</span> Chemical compound

Tibolone, sold under the brand name Livial among others, is a medication which is used in menopausal hormone therapy and in the treatment of postmenopausal osteoporosis and endometriosis. The medication is available alone and is not formulated or used in combination with other medications. It is taken by mouth.

<span class="mw-page-title-main">Estrogen receptor beta</span> Protein-coding gene in the species Homo sapiens

Estrogen receptor beta (ERβ) also known as NR3A2 is one of two main types of estrogen receptor—a nuclear receptor which is activated by the sex hormone estrogen. In humans ERβ is encoded by the ESR2 gene.

Antiestrogens, also known as estrogen antagonists or estrogen blockers, are a class of drugs which prevent estrogens like estradiol from mediating their biological effects in the body. They act by blocking the estrogen receptor (ER) and/or inhibiting or suppressing estrogen production. Antiestrogens are one of three types of sex hormone antagonists, the others being antiandrogens and antiprogestogens. Antiestrogens are commonly used to stop steroid hormones, estrogen, from binding to the estrogen receptors leading to the decrease of estrogen levels. Decreased levels of estrogen can lead to complications in sexual development. Antiandrogens are sex hormone antagonists which are able to lower the production and the effects that testosterone can have on female bodies.

<span class="mw-page-title-main">Coumestrol</span> Chemical compound

Coumestrol is a natural organic compound in the class of phytochemicals known as coumestans. Coumestrol was first identified as a compound with estrogenic properties by E. M. Bickoff in ladino clover and alfalfa in 1957. It has garnered research interest because of its estrogenic activity and prevalence in some foods, including soybeans, brussels sprouts, spinach and a variety of legumes. The highest concentrations of coumestrol are found in clover, Kala Chana, and Alfalfa sprouts.

Hormone replacement therapy (HRT), also known as menopausal hormone therapy or postmenopausal hormone therapy, is a form of hormone therapy used to treat symptoms associated with female menopause. Effects of menopause can include symptoms such as hot flashes, accelerated skin aging, vaginal dryness, decreased muscle mass, and complications such as osteoporosis, sexual dysfunction, and vaginal atrophy. They are mostly caused by low levels of female sex hormones that occur during menopause.

<span class="mw-page-title-main">8-Prenylnaringenin</span> Chemical compound

8-Prenylnaringenin (8-PN; also known as flavaprenin, (S)-8-dimethylallylnaringenin, hopein, or sophoraflavanone B) is a prenylflavonoid phytoestrogen. It is reported to be the most estrogenic phytoestrogen known. The compound is equipotent at the two forms of estrogen receptors, ERα and ERβ, and it acts as a full agonist of ERα. Its effects are similar to those of estradiol, but it is considerably less potent in comparison.

<span class="mw-page-title-main">Nonsteroidal estrogen</span> Class of drugs

A nonsteroidal estrogen is an estrogen with a nonsteroidal chemical structure. The most well-known example is the stilbestrol estrogen diethylstilbestrol (DES). Although nonsteroidal estrogens formerly had an important place in medicine, they have gradually fallen out of favor following the discovery of toxicities associated with high-dose DES starting in the early 1970s, and are now almost never used. On the other hand, virtually all selective estrogen receptor modulators (SERMs) are nonsteroidal, with triphenylethylenes like tamoxifen and clomifene having been derived from DES, and these drugs remain widely used in medicine for the treatment of breast cancer among other indications. In addition to pharmaceutical drugs, many xenoestrogens, including phytoestrogens, mycoestrogens, and synthetic endocrine disruptors like bisphenol A, are nonsteroidal substances with estrogenic activity.

<span class="mw-page-title-main">WAY-200070</span> Chemical compound

WAY-200070 is a synthetic, nonsteroidal, highly selective agonist of ERβ. It possesses 68-fold selectivity for ERβ over ERα (EC50 = 2 nM and 155 nM, respectively). WAY-200070 has been found to enhance serotonergic and dopaminergic neurotransmission in the central nervous system, and produces antidepressant- and anxiolytic-like effects in animals. It has been proposed as a potential novel antidepressant/anxiolytic agent. WAY-200070 has also been found to produce antidiabetic effects in animals, and may also be beneficial for the treatment of certain inflammatory conditions.

<span class="mw-page-title-main">Endoxifen</span> Chemical compound

Endoxifen, also known as 4-hydroxy-N-desmethyltamoxifen, is a nonsteroidal selective estrogen receptor modulator (SERM) of the triphenylethylene group as well as a protein kinase C (PKC) inhibitor. It is under development for the treatment of estrogen receptor-positive breast cancer and for the treatment of mania in bipolar disorder. It is taken by mouth.

ERA-45 is a synthetic estrogen and a selective agonist of the ERα. It shows 286-fold selectivity for transactivation of the ERα over the ERβ, with EC50 values of 0.37 nM for the ERα (7-fold weaker than estradiol) and 13 nM for the ERβ (20,000-fold weaker than estradiol). However, another found only about 35-fold potency for transactivation of the ERα over the ERβ. The drug has no antagonistic activity at either receptor. ERA-45 induced prostate cancer development in preclinical models when it was given in combination with testosterone, whereas testosterone alone did not do so. In contrast, the selective ERβ agonist ERB-26 was protective against the development of prostate cancer produced by these two drugs. These findings suggest opposing roles of the ERα and ERβ in the prostate gland. The chemical structure of ERa-45 does not appear to have been disclosed.

<span class="mw-page-title-main">High-dose estrogen therapy</span> Type of hormone therapy

High-dose estrogen therapy (HDE) is a type of hormone therapy in which high doses of estrogens are given. When given in combination with a high dose of progestogen, it has been referred to as pseudopregnancy. It is called this because the estrogen and progestogen levels achieved are in the range of the very high levels of these hormones that occur during pregnancy. HDE and pseudopregnancy have been used in medicine for a number of hormone-dependent indications, such as breast cancer, prostate cancer, and endometriosis, among others. Both natural or bioidentical estrogens and synthetic estrogens have been used and both oral and parenteral routes may be used.

<span class="mw-page-title-main">Estrogen (medication)</span> Type of medication

An estrogen (E) is a type of medication which is used most commonly in hormonal birth control and menopausal hormone therapy, and as part of feminizing hormone therapy for transgender women. They can also be used in the treatment of hormone-sensitive cancers like breast cancer and prostate cancer and for various other indications. Estrogens are used alone or in combination with progestogens. They are available in a wide variety of formulations and for use by many different routes of administration. Examples of estrogens include bioidentical estradiol, natural conjugated estrogens, synthetic steroidal estrogens like ethinylestradiol, and synthetic nonsteroidal estrogens like diethylstilbestrol. Estrogens are one of three types of sex hormone agonists, the others being androgens/anabolic steroids like testosterone and progestogens like progesterone.

References

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  20. ↑ "Natural Estrogens".
  21. ↑ Phytoestrogen
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