Coumestrol is a natural

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

in the class of

phytochemical Phytochemicals are naturally-occurring chemicals present in or extracted from plants. Some phytochemicals are nutrients for the plant, while others are metabolites produced to enhance plant survivability and reproduction. The fields of ext ...

s known as

coumestan Coumestan is a heterocyclic organic compound. Coumestan forms the central core of a variety of natural compounds known collectively as coumestans. Coumestans are oxidation products of pterocarpan that are similar to coumarin. Coumestans, inclu ...

s. Coumestrol was first identified as a compound with estrogenic properties by E. M. Bickoff in ladino

clover Clovers, also called trefoils, are plants of the genus ''Trifolium'' (), consisting of about 300 species of flowering plants in the legume family Fabaceae originating in Europe. The genus has a cosmopolitan distribution with the highest diversit ...

and

alfalfa Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial plant, perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, ...

in 1957. It has garnered research interest because of its estrogenic activity and prevalence in some foods, including

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source o ...

brussels sprout The Brussels sprout is a member of the Gemmifera cultivar group of cabbages (''Brassica oleracea''), grown for its edible buds. Etymology Though native to the Mediterranean region with other cabbage species, Brussels sprouts first appeared i ...

spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to Central Asia, Central and Western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common vegetable consumed eit ...

and a variety of

legume Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...

s. The highest concentrations of coumestrol are found in

, Kala Chana (a type of

chick pea The chickpea or chick pea (''Cicer arietinum'') is an annual legume of the family Fabaceae, subfamily Faboideae, cultivated for its edible seeds. Its different types are variously known as gram," Bengal gram, garbanzo, garbanzo bean, or Egypt ...

), and Alfalfa sprouts. Coumestrol is a

phytoestrogen A phytoestrogen is a plant-derived xenoestrogen (a type of estrogen produced by organisms other than humans) not generated within the endocrine system, but consumed by eating plants or manufactured foods. Also called a "dietary estrogen", it ...

, mimicking the

biological activity In pharmacology, biological activity or pharmacological activity describes the beneficial or adverse effects of a drug on living matter. When a drug is a complex chemical mixture, this activity is exerted by the substance's active ingredient or ...

estrogen Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

s. Phytoestrogens are able to pass through cell membranes due to their low molecular weight and stable structure, and they are able to interact with the enzymes and receptors of cells. Coumestrol binds to the

ERα Estrogen receptor alpha (ERα), also known as NR3A1 (nuclear receptor subfamily 3, group A, member 1), is one of two main types of estrogen receptor, a nuclear receptor (mainly found as a chromatin-binding protein) that is activated by the se ...

and

ERβ Estrogen receptor beta (ERβ) also known as NR3A2 (nuclear receptor subfamily 3, group A, member 2) 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 t ...

with similar

affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Pa ...

to that of

estradiol Estradiol (E2), also called oestrogen, 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 ...

(94% and 185% of the relative binding affinity of estradiol at the ERα and ERβ, respectively), although the estrogenic activity of coumestrol at both receptors is much less than that of estradiol. In any case, coumestrol has estrogenic activity that is 30 to 100 times greater than that of isoflavones. The chemical shape of coumestrol orients its two hydroxy groups in the same position as the two hydroxy groups in estradiol, allowing it to inhibit the activity of

aromatase Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze man ...

and 3α-hydroxysteroid dehydrogenase. These enzymes are involved in the biosynthesis of

steroid A steroid is an organic compound with four fused compound, fused rings (designated A, B, C, and D) arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes t ...

hormones, and inhibition of these enzymes results in the interference with hormone

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

Natural sources and dietary intake

Levels of coumestrol within individual plants of the same species are variable. Studies of coumestrol levels in alfalfa suggest that there may be a positive correlation between coumestrol production and infection of the plant by

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are found in almo ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

, and

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

. Higher levels of coumestrol are also found in plants which had been damaged by

aphids Aphids are small sap-sucking insects in the Taxonomic rank, family Aphididae. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Eriosomatinae, woolly ...

. Further study is required to fully explain the cause of the correlation between damage, infection, and coumestrol levels. According to the

United States Department of Agriculture The United States Department of Agriculture (USDA) is an executive department of the United States federal government that aims to meet the needs of commercial farming and livestock food production, promotes agricultural trade and producti ...

and

Iowa State University Iowa State University of Science and Technology (Iowa State University, Iowa State, or ISU) is a Public university, public land-grant university, land-grant research university in Ames, Iowa, United States. Founded in 1858 as the Iowa Agricult ...

database on isoflavanes and coumestrol, coumestrol is found in the following food items: Based on extrapolation from studies done on animals, the maximum tolerable daily intake of coumestrol for human beings has been estimated at 22 μg per kg of body mass. This was calculated by extrapolating from the lowest level at which adverse effects were seen in animals. Although due to the variability of the human diet, the exact amount of coumestrol the average person consumes has not been calculated, studies of phytoestrogen intake suggest that most human diets result in a negligible intake of coumestrol relative to the maximum tolerable daily intake.

Biological effects on mammals

Because coumestrol is an estrogen mimic, it is an

endocrine disruptor Endocrine disruptors, sometimes also referred to as hormonally active agents, endocrine disrupting chemicals, or endocrine disrupting compounds are chemicals that can interfere with endocrine (or hormonal) systems. These disruptions can cause ...

with the potential to affect all organ systems that are regulated hormonally via estrogens.

Nervous system

Coumestrol and other phytoestrogens have been shown to have an effect on sexual behavior in rats by antagonizing the action of estrogen within the brain; male rats that nursed from females with coumestrol in their diets were both less likely to mount a female rat and less likely to ejaculate, despite producing normal levels of

testosterone Testosterone is the primary male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...

. Exposure produced similar decreases of sexual behavior in female rats, as a result of the disruption of estrogen dependent gene expression in the brain. Effects were seen in three areas of the

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

, the

ventromedial nucleus The ventromedial nucleus of the hypothalamus (VMN, VMH or ventromedial hypothalamus) is a nucleus of the hypothalamus. In 2007, Kurrasch ''et al''. found that the ventromedial hypothalamus is a distinct morphological nucleus involved in termina ...

, the

paraventricular nucleus The paraventricular nucleus (PVN) is a nucleus in the hypothalamus, located next to the third ventricle. Many of its neurons project to the posterior pituitary where they secrete oxytocin, and a smaller amount of vasopressin. Other secretions ...

, and the medial preoptic area, all of which play a role in sexual behavior and sexual activity. Female rats that were exposed to coumestrol

neonatal In common terminology, a baby is the very young offspring of adult human beings, while infant (from the Latin word ''infans'', meaning 'baby' or 'child') is a formal or specialised synonym. The terms may also be used to refer to Juvenile (orga ...

ly did not adopt the

lordosis Lordosis is historically defined as an ''abnormal'' inward curvature of the lumbar spine. However, the terms ''lordosis'' and ''lordotic'' are also used to refer to the normal inward curvature of the lumbar and cervical vertebrae, cervical regio ...

position as much as those that were not exposed to coumestrol.

Reproductive system

Coumestrol has been shown to accelerate the onset of puberty in mice. Exposure to coumestrol immediately after birth resulted in an initial increase in uterine weight. However, continued exposure inhibited the growth of the

uterus The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...

and decreased levels of estrogen receptors within uterine tissue. The rats also showed altered vaginal development including cornification and

metaplasia Metaplasia () is the transformation of a cell type to another cell type. The change from one type of cell to another may be part of a normal maturation process, or caused by some sort of abnormal stimulus. In simplistic terms, it is as if the ...

of vaginal tissue, and delayed opening of the vagina. When

female mice were treated with coumestrol, similar reproductive irregularities occurred, and at 22 months old, atypical

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

distribution was observed in the uterine wall. When 2 day old male Wistar rats are injected with coumestrol daily, they exhibit a decrease in size in the lumens of their

seminiferous tubules Seminiferous tubules are located within the testicles, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa. Structure The epithelium of the tubule consists of a type of sustentacular cells ...

and germ cells go through increased rates of

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

. When bulls graze on pastures containing coumestrol, metaplasia occurs in the

prostate The prostate is an male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemica ...

and bulbourethral glands, and sperm maturation is suppressed. Female cows that consumed alfalfa experienced lower pregnancy rates and spontaneous abortions, as well as abnormal estrogen levels during pregnancy. A high coumestrol diet has also been shown to induce early development of the

vulva In mammals, the vulva (: vulvas or vulvae) comprises mostly external, visible structures of the female sex organ, genitalia leading into the interior of the female reproductive tract. For humans, it includes the mons pubis, labia majora, lab ...

and

udder An udder is an organ formed of two or four mammary glands on the females of dairy animals and ruminants such as cattle, goats, and sheep. An udder is equivalent to the breast in primates, elephantine pachyderms and other mammals. The udder is ...

of female lambs. In addition to these anatomical abnormalities, exposure to coumestrol has also been shown to alter the

estrus The estrous cycle (, originally ) is a set of recurring physiological changes induced by reproductive hormones in females of mammalian subclass Theria. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phas ...

cycle of a number of animals, including cows and sheep, resulting in lower rates of fertility.

Skeletal system

Coumestrol has been shown to decrease

bone resorption Bone resorption is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood. The osteoclasts are multi-nuclea ...

and promote the mineralization of bone ''in vitro'' and ''in vivo''; daily injections of coumestrol were shown to reduce bone loss in rats who had undergone an ovariectomy.

Genotoxicity

Coumestrol has been shown to have clastogenic properties at a certain concentration.. Studies have shown that coumestrol is a

mutagen In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer in ...

and induces formation of

micronuclei A micronucleus is a small cell nucleus, nucleus that forms whenever a chromosome or a fragment of a chromosome is not incorporated into one of the daughter nuclei during cell division. It usually is a sign of genotoxic events and chromosomal inst ...

in hamster cells of the V79 cell line as well as human lymphoblastoid cells in a dose-dependent manner. Exposure to coumestrol also causes single stranded breaks in hamster DNA, compromising genome stability.

Metabolism

Studies have shown that coumestrol has beneficial properties on carbohydrate metabolism in ovariectomized rats, decreasing glycogen levels in skeletal muscle. There is also data indicating that coumestrol lowers plasma cholesterol levels in chicks. These results point to a possibility of coumestrol having a positive role to play against human obesity and diabetes in the future.

Menopause

Coumestrol and other phytoestrogens are sometimes used as a substitute for hormone therapy in the treatment of menopausal symptoms such as hot flashes and night sweats. However, studies have indicated that phytoestrogen-enriched foods and supplements are not necessarily effective against these symptoms. In addition, studies indicate that coumestrol and other phytoestrogens have an antiestrogenic effect in the brain and, as a result, do not produce the mental health benefits which are seen in estrogen replacement therapy.

Breast cancer

Coumestrol and other phytoestrogens have also been investigated as a possible substitute for hormone therapy and

chemotherapy Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (list of chemotherapeutic agents, chemotherapeutic agents or alkylating agents) in a standard chemotherapy re ...

breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...

patients. The results of various studies regarding the use of phytoestrogens in treating breast cancer have been somewhat contradictory and ambiguous, and as a result, researchers cannot clearly define phytoestrogens like coumestrol as being chemoprotective agents or potentially having negative effects, such as inducing further growth of existing breast cancer tumors by activating ERα receptors. Researchers at Georgetown University Medical Center have investigated this matter and concluded that phytoestrogens may be used as an effective treatment for breast cancer because of their apoptotic properties, but that it is only safe to do so after menopause, when women have a much lower level of estrogen in their bodies, or when used conjunctively with anti-estrogen therapies.

Current and future research

Most research on the biological effects of coumestrol has been conducted on animals because of ethical concerns. There is a need for more human studies to better understand potential human health impacts due to exposure. In addition, further research is required to fully understand the biosynthesis pathway of coumestrol, although it is believed to be similar to that of flavones and isoflavones. Further research is required to understand the exact nature of the relationship between the levels of coumestrol in a plant and the plant's response to pathogens.