Estrogen metabolism

Nutritional Influences on Estrogen Metabolism
By Douglas C. Hall, M. D.

ABSTRACT:
It is now well known that one of the most prominent causes of breast cancer, as well as many other hormone related health problems in both men and women, is excessive estrogen exposure from both endogenous and exogenous sources. Improving estrogen metabolism can be of benefit in women with various conditions and family histories, including a family history hi breast, uterine, or ovarian cancer, and conditions such as endometriosis, premenstrual syndrome, uterine fibroid tumors, fibrocystic or painful breasts, cervical dysplasia, and systemic lupus erythematosis. Beneficial modulation of estrogen metabolism can be accomplished through dietary and lifestyle modifications such as increasing fiber and reducing fat, increasing phytoestrogen intake, losing weight, and increasing exercise. In addition, many nutrients effectively reduce estrogen load by supporting preferred pathways of estrogen metabolism and detoxification. These include isoflavones, indole-3-carbinol, B vitamins, magnesium, limonene, calcium D-glucarate, and antioxidants. The influences of these nutrients on estrogen metabolism may have profound significance for diseases and conditions in which estrogen plays a role in clinical expression.

ESTROGEN PRODUCTION
The term "estrogen" is used to collectively describe the female hormones, the most potent of which is estradiol. The other important-but less powerful-estrogens are estrone and estriol. Estrogens affect the growth, differentiation, and function of diverse target tissues throughout the body-not just those involved in the reproductive process. Estrogens play an important role in bone formation and maintenance, exert cardioprotective effects, and influence behavior and mood. Estrogens also have important actions in male tissues, such as the prostate and testes.

In women, estrogens are synthesized from cholesterol in the ovaries in response to pituitary hormones. In an adult woman with normal cycles, the ovarian follicle secretes 70 to 500 ug of estradiol per day, depending on the phase of the menstrual cycle. Estradiol can be converted to estrone and vice versa, and both can be converted to estriol, the major urinary metabolite. Estrogens are also produced by the aromatization of androgens in fat cells, skin, bone, and other tissues.

After menopause, most endogenous estrogen is produced in the peripheral tissues by the conversion of androstenedione, which is secreted by the adrenal cortex, to estrone. In addition, some estrogen continues to be manufactured by aromatase in body fat, and the ovaries continue to produce small amounts of the male hormone testosterone, which is converted to estradiol. The total estrogen produced after menopause, however, is far less than that produced during a woman's reproductive years.

Estrogens circulate in the body bound mainly to the sex hormone binding globulin (SHBG); however, only unbound estrogens can enter target-tissue cells and induce biological activity. This is an important point, because it means that any change in the concentration of SHBG will alter estrogen metabolism by inducing changes in the availability of estrogen to the target cell.

ESTROGEN METABOLISM AND DETOXIFICATION
Metabolism of estrogen within the body is a complex subject. Estrone and estradiol are biochemically interconvertible and yield the same family of estrogen metabolites as shown for estrone in Figure I. Because these metabolites vary greatly in biological activity, the ultimate biologic effect of estrogen depends on how it is metabolized. The metabolism of estrogen takes place primarily in the liver through Phase I (hydroxylation) and Phase II (methylation, glucuronidation, and sulfation) pathways, with final excretion in the urine and feces.

* Hydroxylation
Cytochrome P-450 enzymes mediate the hydroxylation of estraliol and estrone, which is the major Phase I metabolic pathway for endogenous estrogens. This takes place at two primary sites on the estrogen molecule, either at the 2 carbon (C-2) position yielding 2-hydroxyestrone (2-0H) or at the 16a carbon (C-16a) position yielding 16a-OH. A minor contribution is made from hydroxylation at the 4 carbon (C-4) position yielding 4-0H. The 2-0H metabolite confers very weak estrogenic activity, and is generally termed the "good" estrogen. In contrast, the 16a-OH and 4-0H metabolites show persistent estrogenic activity and promote tissue proliferation. It is suggested that women who metabolize a larger proportion of their endogenous estrogen via the C-16a hydroxylation pathway may be at significantly elevated risk of breast cancer compared with women who metabolize proportionally more estrogen via the C-2 pathway. Furthermore, it is theorized that shifting estrogen balance toward a less estrogenic state through promotion of the C-2 pathway may prove beneficial for a variety of conditions related to estrogen dominance or imbalance.

* Methylation
The 2-0H and 4-0H metabolites (catechol estrogens) are readily oxidized to quinones, which are highly reactive and can damage DNA and promote carcinogenesis directly or indirectly through the generation of reactive oxygen species (ROS). This harmful pathway can be minimized through detoxification and excretion of the catechol estrogens via Phase II methylation by the catechol-O-methyltransferase (COMT) enzymes. This methylation requires S-adenosylmethionine (SAM) and I magnesium as cofactors. COMT is present in most tissues and converts catechols into their corresponding methyl ester metabolites, which are more water solubles. Recent data suggest that the methylation of 4-0H renders this harmful I metabolite significantly less active, while 2-methoxyestrone may manifest beneficial properties by inhibiting breast cancer. Therefore, supporting the methylation pathways promotes detoxification of estrogens and provides for more beneficial metabolites of estrogen.

* Glucuronidation
Glucuronidation is one of the key Phase II liver detoxification pathways for estrogens and other toxins. Glucuronic acid is conjugated with the estrogen to facilitate its elimination from the body. Unfortunately, some intestinal bacteria (mostly pathogenic) possess an enzyme, glucuronidase, that uncouples the bond between excreted estrogen and glucuronic acid in the large intestine, allowing the estrogen to reenter circulation (enterohepatic recirculation). Not surprising is the finding that excess glucuronidase activity is associated with an increased cancer risk, including breast cancer. The activity of glucuronidase is increased when the diet is high in fat and low in fiber, and can be reduced by establishing a proper bacterial flora by eating a diet high in plant foods and supplementing the diet with the "friendly bacteria" Lactobacillus acidophilus and Bifidobacterium infantis.

ESTROGEN RECEPTORS
Estrogens, like all steroid hormones, have a wide range of actions and affect almost all systems in the body, yet act in a tissue-specific manner. Estrogens act by binding with high affinity to the estrogen receptor (ER) in target cells. Once bound by estrogens, the receptor activates the transcription of estrogen-responsive target genes. Because the ER has a unique ability to bind with a wide variety of compounds with diverse structural features, many environmental toxins and plant compounds can bind to the ER with varying affinities and modulate estrogen activity.

Two forms of the estrogen receptor, a and b, have been identified that differ in tissue distribution, binding affinity, and biological function. Therefore, different target cells may respond differently to the same estrogenic stimulus depending on the ratio of expression of the two receptor subtypes in the cell. This helps to explain how phytoestrogens and the new designer estrogen drugs such as tamoxifen and raloxifene-called selective estrogen receptor modulators (SERMs )-behave like estrogens in some tissues but block its action in others. Unraveling the detailed physiological role of each receptor subtype is needed to further elucidate the complex nature of estrogen's mechanisms of action.

ESTROGEN AND CANCER RISK
Epidemiological and animal studies have identified estrogen exposure as a risk factor for several cancers, namely breast, endometrium, ovary, prostate, testis, and thyroid. Much of the evidence comes from the observation that cancer risk increases with increased exposure to endogenous or exogenous estrogens, and the positive relationship observed between blood levels of estrogens and cancer risk. Prolonged estrogen exposure can cause direct genotoxic effects by inducing cell proliferation in estrogen-dependent target cells (increasing the opportunity for the accumulation of random genetic errors), affecting cellular differentiation, and altering gene expression. Additionally, there is increasing evidence for indirect genotoxic effects of estrogens as well. The relative importance of each mechanism is likely a function of the specific estrogen, as well as the exposed tissue or cell type and its metabolic state.

Direct Genotoxic Effects
Evidence is accumulating that some estrogen metabolites may be directly responsible for the initial genetic damage leading to tumors. 16a-OH and 4-0H are the primary estrogen metabolites that have been associated with direct genotoxic effects and carcinogenicity. Some researchers believe increased levels of 16a-OH may increase the risk of breast cancer by increasing both cell proliferation and direct DNA damage; however, scientific consensus has not yet been reached. Conversely, 2-0H may induce apoptosis and thereby inhibit cell proliferation, an important mechanism in the prevention of cancer.

A recent 5-year prospective study of 10, 786 women was conducted to investigate the role of estrogen metabolism as a predictor of breast cancer, specifically the ratio of 2-0H to 16a-OH. The researchers found that premenopausal women who developed breast cancer had a decreased 2-0H:16a-OH ratio and a higher percentage of 16a-OH than 2-0H. Women with predominately 2-0H were 40% less likely to have developed breast cancer during the 5 years. Another recent case control study that began in 1977 found that postmenopausal women who developed breast cancer had a 15% lower 2-0H:16a-OH ratio than control subjects. Furthermore, those with the highest 2-0H:16a-OH ratios had about a 30% lower risk to breast cancer than women with lower ratios.

Diverse factors can add to the hormonal risk by decreasing the 2-0H: 16a-OH ratio, including numerous pesticides and carcinogens, certain drugs such as cyclosporin and cimetidine (Tagamet), obesity, and genetic predisposition. Dietary interventions such as increased consumption of cruciferous vegetables (e.g., broccoli and cabbage) and phytoestrogen-rich foods such as soy and flaxseeds can significantly promote C-2 hydroxylation and increase the 2-0H:16a-OH ratio.

Indirect Genotoxic Effects
Excessive production of ROS has been reported in breast cancer tissue, and free-radical toxicity, which manifests as DNA single- strand breaks, lipid peroxidation, and chromosomal abnormalities, has been reported in hamsters treated with estradiol. The oxidation of catechol estrogens (2-0H and 4-0H) yields reactive molecules called quinones. Quinones are thought to playa role in carcinogenesis by inducing DNA damage directly or as a result of redox cycling between the quinones and their semi-quinone radicals, which generates ROS. Supplementation with antioxidant nutrients can reduce the oxidation of the catechols and promote greater excretion of these metabolites through the methylation pathway.

RISK FACTORS FOR INCREASED ESTROGEN EXPOSURE
There are many lifestyle factors that can influence the body's production of estrogen. Obesity increases endogenous estrogen I production by fat tissue, where the enzyme aromatase converts I androgens into estrogen. Excess insulin in the bloodstream prompts the ovaries to secrete excess testosterone and reduces SHBG levels, thus increasing levels of free estrogen. Alcohol consumption increases estrogen levels, and epidemiological studies suggest that moderate alcohol consumption increases the risk of breast cancer, an effect that may be synergistically enhanced when combined with estrogen replacement therapy.

MANIFESTATIONS OF EXCESSIVE ESTROGEN EXPOSURE AND ESTROGEN DOMINANCE
An abundance of evidence makes it clear that excessive estrogen exposure from both endogenous and exogenous sources is a causal factor in the development of cancer in hormone-dependent tissues, such as the breast, endometrium, ovary, uterus, and prostate.

Furthermore, hormonal imbalances between progesterone, testosterone, and estrogen can lead to symptoms and conditions of estrogen dominance. These include premenstrual syndrome (PMS), endometriosis, uterine fibroid tumors, fibrocystic or painful breasts, cervical dysplasia, and systemic lupus erythematosis.

NUTRITIONAL MODULATION OF ESTROGEN METABOLISM
Multiple dietary and nutritional factors have the ability to influence estrogen synthesis and receptor activity, as well as the detoxification pathways through which estrogens are metabolized. Incorporating dietary changes with the use of select nutritional supplements can have profound effects in beneficially influencing estrogen balance and thus preventing estrogen-related.

Two major sources of exogenous estrogens are oral contraceptives and hormone replacement therapy. Another major source is environmental toxins found in pesticides, herbicides, plastics, refrigerants, and industrial solvents that are structurally similar to estrogen and have the ability to mimic harmful estrogens in the body. Furthermore, the hormones used to fatten livestock and promote milk production are found in meat and milk products, thereby increasing one's exposure to environmental estrogens.

While these lifestyle and environmental factors do influence the lifetime hormone burden of an individual, endogenous hormone levels also have agenetic basis that can be an important risk factor for hormone-dependent cancers and other conditions. Thus, family history can be a valuable indicator of potential problems in this area. All sources of estrogens-whether environmental, dietary, or endogenously produced--can affect ER function. These substances can bind to estrogen a or b receptors with varying affinities and for varying lengths of time, producing a wide range of estrogen-related effects diseases and conditions. A weight management program may also be very helpful in both reducing adipose aromatase activity and facilitating more desirable estrogen metabolism and excretion.

Dietary Fiber and Lignin
Insoluble dietary fibers such as lignin (found in flaxseeds and the bran layer of grains, beans, and seeds) can interrupt the enterohepatic circulation of estrogens in two ways, thus promoting their excretion and making them less available for reabsorption and further metabolism.36 First, dietary fiber, especially lignin, can bind unconjugated estrogens in the digestive tract, which are then excreted in the feces. Second, dietary fiber can beneficially affect the composition of intestinal bacteria and reduce intestinal b-glucuronidase activity, resulting in a lowered the conjugation of estrogen and reduced reabsorption. Dietary fiber intake also increases serum concentrations of SHBG, thus reducing levels of free estradiol.

Carbohydrates/Fats/Protein
Complex carbohydrates, such as those found in vegetables and whole grains, are preferred over simple carbohydrates for optimizing estrogen metabolism. Excess consumption of simple carbohydrates raises blood glucose and insulin levels, resulting in adverse influences on sex hormone balance. Conversely, complex carbohydrates attenuate glycemic and insulinemic responses.

The types and amounts of dietary fats may play a role in determining balance among estrogens in the body. For instance, high-fat diets may promote C-16a hydroxylation over C-2 hydroxylation. Furthermore, omega-3 fatty acids such as eicosapentaenoic acid (EPA) have been shown to increase C-2 hydroxylation and decrease C-16a hydroxylation of estradiol in breast cancer cells.

Inadequate dietary protein may lead to decreases in overall cytochrome P450 activity, including cytochrome P450-IA2, which detoxifies estradiol. Rice fortified with lysine and threonine is a source of protein frequently used to nutritionally support hepatic detoxification function, because of its low allergy potential. Soy is also an excellent source of protein that is low in fat and provides the health benefits of isoflavones.

Phytoestrogens
Phytoestrogens are plant compounds that have the capacity to bind to ERs and appear to have both estrogenic and anti-estrogenic effects, depending on the expression of ER subtypes in target cells and on the level of endogenous estrogen present. They are currently being extensively investigated as a potential alternative therapy for a range of conditions associated with estrogen imbalance including menopausal symptoms, PMS, and endometriosis, as well as prevention of breast and prostate cancer and protection against cardiovascular disease and osteoporosis. The two main classes of phytoestrogens are the isoflavones and lignans. Phytoestrogens beneficially influence estrogen synthesis and metabolism through a variety of mechanisms: 1) they have a similar structure to estradiol and can bind to the ER, 2.) they increase plasma SHBG levels, 3.) they decrease aromatase activity,46 and 4.) they shift estrogen metabolism away from the C-16a pathway to the C-2 pathway.

Therefore, it may be possible to demonstrate significant hormonal effects through dietary modification. For example, two recent studies found that increased isoflavone consumption increased urinary excretion of the genotoxic estrogens l6a-OH and 4-0H, indicative of their decreased formation, significantly increased the 2-0H:16a-OH ratio in both pre postmenopausal women.

Isoflavones- Soy is perhaps the most common food source of isoflavones, but others include legumes, alfalfa, clover, licorice, and kudzu root. There are several biologically active llavones, such as genistein, daidzein, and puerarin, with each Ilt source delivering a different profile. Higher intakes of soy ducts and isoflavones, such as consumed in traditional Japanese diets, are associated with low rates of hormone dependent can. The average daily isoflavone intake of Japanese women is 20 mg, while that of American women is 1 to 3 mg.

In two human studies, women given isoflavone supplements and milk for one month experienced longer menstrual cycles and serum estradiol levels.51.52 Longer menstrual cycles are beneficial because they result in decreased lifetime exposure to estrogen and lower the risk for breast cancer. Furthermore, in men with low levels of SHBG, consumption of a soymilk powder providing about 69 mg of isoflavones daily substantially increased their SHBG concentrations, an effect not observed in men with higher initial SHBG levels.

Lignans- These compounds are found in fiber-rich foods such flaxseed and other oil seeds, whole grains, legumes, and vegetables. Lignans stimulate the production of SHBG in the liver, and therefore reduce the levels of free estrogen insulation. They also inhibit aromatase activity, thus decreasing conversion of testosterone and androstenedione into estrogens in fat and breast cells. Lignans also have been shown to inhibit estrogen-sensitive breast cancer cell proliferation. Women consuming 10g of flaxseed per day experienced longer menstrual cycle length, increased progesterone-to-estrogen ratios, and fewer anovulatory cycles, all of which were considered to reflect improved ovarian function.

Resveratrol- This bioflavonoid occurs naturally in grapes and red wine and has been shown to inhibit breast cancer cell growth in vitro. It has been classified as a phytoestrogen based on its ability to bind to and activate the ER, with recent in vitro studies indicating that it exhibits estrogenic and anti-estrogenic activity and binds to ERa and ERb with comparable affinity. These estrogen modulatory effects may explain resveratrol's well- known anticancer and cardioprotective properties.

Vitamin E
Low serum vitamin E is associated with elevated estrogen levels, and supplementation may reduce symptoms of PMS. Vitamin E inhibits growth of breast cancer cells, possibly by inhibiting the expression of vascular endothelial growth factor, which encourages angiogenesis.63 Furthermore, vitamin E deficiency may negatively affect cytochrome P450 function, thus impacting estrogen detoxification.

Magnesium
Magnesium is an essential cofactor for the COMT enzyme, and therefore optimizes the methylation and excretion of catechol estrogens. Magnesium also promotes estrogen detoxification by directly increasing the activity of glucuronyl transferase, an enzyme involved in hepatic glucuronidation. Ovarian hormones influence magnesium levels, triggering decreases at certain times during the menstrual cycle as well as altering the calcium to magnesium ratio. These cyclical changes can produce many of the well-known symptoms of PMS in women who are deficient in magnesium and/or calcium.

Indole-3-Carbinol (l3C)
I3C is a naturally occurring compound derived from cruciferous vegetables such as broccoli, Brussels sprouts, and cabbage that actively promotes the breakdown of estrogen to the beneficial metabolite, 2-OH. Therefore, I3C is protective to estrogen-sensitive tissues and may be beneficial to those with health issues related to estrogen dominance.

The mechanism by which I3C promotes 2-OH formation involves the selective induction of Phase 1 metabolizing cytochrome P450 enzymes, which facilitate the 2-hydroxylation of estrogen. Through this metabolic role, I3C promotes an increased ratio of 2-OH to l6a-OH and may improve estrogen metabolism in women with poor diets or impaired detoxification. I3C may also reduce the activity of the enzyme required for the 4-hydroxylation of estrogen, thereby decreasing carcinogenic 4-OH formation.

According to a recent human study in both men and women, supplementation with 500 mg and 400 mg of I3C, respectively, resulted in significantly increased urinary excretion of 2-OH, while that of nearly all other metabolites including estradiol and l6a-OH was lower-indicative of their decreased formation. In another double-blind, placebo-controlled study of 57 women at increased risk for breast cancer, supplementation with I3C (300-400 mg/d for 4 weeks) proved to be a promising chemopreventive agent as measured by the increased 2-OH: l6a- OH ratio.

Not only does I3C promote healthier estrogen metabolism, but it may also act as a "weak," or anti-estrogen. Through competitive inhibition, 13C has been shown to prevent the receptor binding of "stronger," more stimulating estrogens!" Other mechanisms relating to I3C's influence on tissue health involve modulating ER activity, detoxifying xenoestrogens, modulating cell cycle regulation, and preventing the adhesion, migration, and invasion of cancer cell lines.

B Vitamins
The B vitamins, such as B6, B12 and folate, function as important cofactors for enzymes involved in estrogen conjugation and methylation. Therefore, decreased levels of B vitamins can disrupt estrogen detoxification and lead to increased levels of circulating estrogens. For instance, folate (as a precursor to SAM) is an essential cofactor for the methylation of catechol estrogens, 2-OH and 4-OH, which reduces their conversion to the carcinogenic quinones. Unfortunately, many individuals have agenetic polymorphism that interferes with their ability to metabolize folic acid to the active form utilized by the body. Supplementing with a metabolically active form of folate that doesn't require enzymatic conversion, such as L-5-methyl tetrahydrofolate, will ensure that these patients maintain adequate folate nutriture.

Another way in which certain B vitamins playa role in estrogen activity is through a potential to modulate the cell's response to activation of the ER. It has been demonstrated that elevated intra-cellular concentrations of the active form of vitamin B6 can lead to significantly decreased gene transcription responses when estrogen binds to the ER By modulating estrogen-induced gene expression in this way, vitamin B6 can attenuate the biological effects of estrogen. B vitamins also playa role in the prevention of cancer because they are crucial for DNA synthesis and repair as well as the process of DNA methylation, which is essential for DNA stability and integrity and is an important regulator of gene expression.

Calcium D-Glucarate
Calcium D-glucarate is a natural compound that appears to have some influence on breast cancer by aiding in detoxification and the regulation of estrogen. It not only inhibits b-glucuronidase, but also increases the activity of the glucuronidation Phase II pathway, with the net effect of increased estrogen and toxin elimination from the body. Calcium D-glucarate has been found in animal models to lower estradiol levels and inhibit the initiation, promotion, and progression of cancer.

Other Beneficial Phytonutrients
There are many other naturally occurring compounds derived from a variety of plant sources that promote healthy estrogen metabolism. Curcumin is a polyphenol complex from the curry spice turmeric, a member of the ginger family. A combination of curcumin and the isoflavone genistein has shown synergy in reducing xenoestrogen-induced growth of breast cancer cells. Curcumin also increases hepatic levels of glutathione and induces glutathione-S-transferase (GST) and glucuronyl transferase, important in the Phase II detoxification of quinones produced from the oxidation of catechol estrogens. Chrysin is a bioflavonoid that has been shown to inhibit aromatase activity, thus reducing the conversion of androgens into estrogen. Aromatase is found in breast tissue, and its inhibition may be useful in reducing the cell proliferative effects of estrogen. Preliminary research indicates that the herb rosemary promotes the 2-hydroxylation of estrogen in a similar fashion to 13C, and may inhibit 16a hydroxylation. Rosemary may also enhance estrogen detoxification.

Furthermore, many antioxidants and phytonutrients can reduce the oxidation of catechol estrogen metabolites into quinones. Notable players in this group include vitamins E and C, a-lipoic acid, N-acetylcysteine, the mineral selenium, curcumin, and green tea. D-Limonene, a naturally occurring monoterpene found in the oils of citrus fruits, promotes the detoxification of estrogen by inducing Phase I and Phase II enzymes in the liver, including GST. This compound has also shown great promise in the prevention and treatment of breast and other cancers.

There are also many hormone-modulating herbs that have along history of traditional use in treating women 's health conditions, including black cohosh, chasteberry, ginseng, dong quai, and licorice. While the mechanism of action of these herbs varies, many have been found to contain phytoestrogens. For a comprehensive discussion of the use of nutritional supplements and herbs in treating PMS, menopause, and other women's health conditions, please refer to the articles titled, Premenstrual Syndrome: A Natural Approach to Management; A Healthy Menstrual Cycle; A Natural Approach to Menopause; and Black Cohosh and Chastebeny: Herbs Valued by Women for Centuries.