4-Hydroxycatecholestrogen metabolism responses to exercise and training: possible implications for menstrual cycle irregularities and breast cancer

Linking Physical Activity to Breast Cancer via Sex Hormones, Part 1: The Effect of Physical Activity on Sex Steroid Hormones

The effect of physical activity on breast cancer risk may be partly mediated by sex steroid hormones. This review synthesized and appraised the evidence for an effect of physical activity on sex steroid hormones. Systematic searches were performed using MEDLINE (Ovid), EMBASE (Ovid), and SPORTDiscus to identify experimental studies and prospective cohort studies that examined physical activity and estrogens, progestins, and/or androgens, as well as sex hormone binding globulin (SHBG) and glucocorticoids in pre- and postmenopausal women. Meta-analyses were performed to generate effect estimates. Risk of bias was assessed, and the GRADE system was used to appraise quality of the evidence. Twenty-eight randomized controlled trials (RCT), 81 nonrandomized interventions, and six observational studies were included. Estrogens, progesterone, and androgens mostly decreased, and SHBG increased, in response to physical activity. Effect sizes were small, and evidence quality was graded moderate or high for each outcome. Reductions in select sex steroid hormones following exercise supports the biological plausibility of the first part of the physical activity-sex hormone-breast cancer pathway. The confirmed effect of physical activity on decreasing circulating sex steroid hormones supports its causal role in preventing breast cancer.See related reviews by Lynch et al., p. 11 and Drummond et al., p. 28.

Association of Active and Sedentary Behaviors with Postmenopausal Estrogen Metabolism

PURPOSE

Physical activity may reduce endogenous estrogens, but few studies have assessed effects on estrogen metabolism and none have evaluated sedentary behavior in relation to estrogen metabolism. We assessed relationships between accelerometer-measured physical activity and sedentary behavior and 15 urinary estrogens and estrogen metabolites (EM) among postmenopausal controls from a population-based breast cancer case-control study conducted in Poland (2000-2003).

METHODS

Postmenopausal women (N = 542) were ages 40 to 72 yr and not currently using hormone therapy. Accelerometers, worn for 7 d, were used to derive measures of average activity (counts per day) and sedentary behavior (<100 counts per minute per day). Estrogen metabolites were measured in 12-h urine samples using liquid chromatography-tandem mass spectrometry. Estrogen metabolites were analyzed individually, in metabolic pathways (C-2, -4, or -16), and as ratios relative to parent estrogens. Geometric means of estrogen metabolites by tertiles of accelerometer-measures, adjusted for age and body mass, were computed using linear models.

RESULTS

High activity was associated with lower levels of estrone and estradiol (P trend = 0.01), whereas increased sedentary time was positively associated with these parent estrogens (P trend = 0.04). Inverse associations were observed between high activity and 2-methoxyestradiol, 4-methoxyestradiol, 17-epiestriol, and 16-epiestriol (P trend = 0.03). Sedentary time was positively associated with methylated catechols in the 2- and 4-hydroxylation pathways (P trend ≤ 0.04). Women in the highest tertile of activity had increased hydroxylation at the C-2, -4, and -16 sites relative to parent estrogens (P trend ≤ 0.02), whereas increased sedentary time was associated with a lower 16-pathway/parent estrogen ratio (P trend = 0.01).

CONCLUSIONS

Higher activity was associated with lower urinary estrogens, possibly through increased estrogen hydroxylation and subsequent metabolism, whereas sedentary behavior may reduce metabolism.

Association between physical activity and urinary estrogens and estrogen metabolites in premenopausal women

OBJECTIVE

The objective of the study was to evaluate in premenopausal women the relationships of physically active and sedentary behaviors reported for adulthood and adolescence with a comprehensive profile of estrogen metabolism.

METHODOLOGY

Fifteen estrogens and estrogen metabolites (jointly termed EM) were measured using liquid chromatography-tandem mass spectrometry in luteal phase urines from 603 premenopausal women in the Nurses' Health Study II. Geometric means of individual EM, metabolic pathway groups, and pathway ratios were examined by level of exposure after adjustment for age, body mass index, alcohol intake, menstrual cycle length, and sample collection timing.

RESULTS

High overall physical activity in adulthood (42+ metabolic equivalent h/wk vs. <3 metabolic equivalent h/wk) was associated with a 15% lower level of urinary estradiol (Ptrend=0.03) and 15% lower level of 16-hydroxylation pathway EM (Ptrend=0.03). Levels of 2- and 4-hydroxylation pathway EM did not differ significantly by physical activity. High overall activity was also positively associated with four ratios: 2-pathway EM to parent estrogens (Ptrend=0.05), 2-pathway catechols to parent estrogens (Ptrend=0.03), 2-pathway catechols to methylated 2-pathway catechols (Ptrend<0.01), and 2-hydroxyestrone to 16α-hydroxyestrone (Ptrend=0.01). Similar patterns of association were noted for walking and vigorous physical activity, but there was little evidence of associations with sedentary behaviors or activity during adolescence.

CONCLUSIONS

High levels of physical activity were associated with lower levels of parent estrogens and 16-hydroxylation pathway EM and preferential metabolism to 2-pathway catechols. The results of our analysis, the largest, most comprehensive examination of physical activity and estrogen metabolism to date, may be useful in future studies investigating the etiology of diseases linked to both physical activity and endogenous estrogen.

Physical activity and cancer prevention--mechanisms

PURPOSE

This paper presents potential mechanisms by which exercise or physical activity may affect cancer development.

METHODS

Analysis of published and unpublished experimental and epidemiological data from the cancer-activity literature and from other fields of study are compiled to provide a summary of potential mechanisms by which exercise may mediate cancer development.

RESULTS

Exercise appears to have a beneficial effect relative to cancer development, and the reader is referred to other sections of this symposium. To date however, the mechanism(s) remains unknown. Potential mechanisms influenced by exercise include alterations in steroid hormones or insulin/insulin-like growth factors, immune modulation, alterations in free radical generation, changes in body composition or weight, and direct effects on the tumor. Cancer is a complex process. It is clear that multiple mechanisms may be operative and that the characteristics of the individual, type of exercise, as well as type of cancer and stage of carcinogenesis will affect which mechanisms may affect the disease. More experimental research in both animal models and in human clinical studies is needed to understand the basic biological mechanisms underlying the effect of physical activity on cancer.

CONCLUSION

In general, physical activity is associated with reduced risk of cancer development, yet to date, the mechanisms remain unknown.

Molecular epidemiology of sporadic breast cancer. The role of polymorphic genes involved in oestrogen biosynthesis and metabolism

The major known risk factors for female breast cancer are associated with prolonged exposure to increased levels of oestrogen. The predominant theory relates to effects of oestrogen on cell growth. Enhanced cell proliferation, induced either by endogenous or exogenous oestrogens, increases the number of cell divisions and thereby the possibility for mutation. However, current evidence also supports a role for oxidative metabolites, in particular catechol oestrogens, in the initiation of breast cancer. As observed in drug and chemical metabolism, there is considerable interindividual variability (polymorphism) in the conjugation pathways of both oestrogen and catechol oestrogens. These person-to-person differences, which are attributed to polymorphisms in the genes encoding for the respective enzymes, might define subpopulations of women with higher lifetime exposure to hormone-dependent growth promotion, or to cellular damage from particular oestrogens and/or oestrogen metabolites. Such variation could explain a portion of the cancer susceptibility associated with reproductive effects and hormone exposure. In this paper the potential role of polymorphic genes encoding for enzymes involved in oestrogen biosynthesis (CYP17, CYP19, and 17beta-HSD) and conversion of the oestrogen metabolites and their by-products (COMT, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, GSTT1 and MnSOD) in modulating individual susceptibility to breast cancer are reviewed. Although some of these low-penetrance genes appeared as good candidates for risk factors in the etiology of sporadic breast cancer, better designed and considerably larger studies than the majority of the studies conducted so far are evidently needed before any firm conclusions can be drawn.

Urinary estrogen metabolites and breast cancer: differential pattern of risk found with pre- versus post-treatment collection

INTRODUCTION

The products of estrogen metabolism may affect breast carcinogenesis. The 16alpha-hydroxyestrone (16-OHE) metabolite has a higher affinity for the estrogen receptor (ER) than the 2-hydroxyestrone (2-OHE) metabolite, while conjugated 2-OHE metabolite may inhibit angiogenesis. We investigated the association between the relative concentrations of these metabolites in urine (2-OHE/16-OHE) and breast cancer in a case-control study of Chinese women living in Shanghai.

METHODS

Incident breast cancer cases between 25 and 65 years of age (n=110) were identified from hospital or population tumor registries in Shanghai, China. Controls (n=110) were randomly selected from a complete registry of the Shanghai population, and individually matched to cases by menopausal status, age, and pre-treatment or post-treatment urine collection time. Urine samples were collected prior to any breast cancer treatment or surgery among 78 case-control pairs, while urine was collected after surgery, and perhaps other treatments, among 32 case-control pairs. A commercial enzyme-immunoassay kit was used to measure urinary estrogen metabolite concentrations. Conditional logistic regression was used to calculate odds ratios summarizing the 2-OHE/16-OHE and breast cancer association within subjects providing either pre-treatment or post-treatment urine samples.

RESULTS

Subjects with a higher urinary 2-OHE/16-OHE ratio were less likely to be diagnosed with breast cancer, but only when urine samples were collected prior to breast cancer treatment (OR(Tertile3(T3)versusTertile1(T1))=0.5, 95% CI (0.2, 1.1)). In contrast, a higher 2-OHE/16-OHE ratio was significantly associated with breast cancer among subjects providing urine specimens after treatment initiation (OR(T3versusT1)=8.7, 95% CI (1.6, 47.1)). This observed cross-over modification occurred within both pre-menopausal and post-menopausal women, and independent of body mass index or recent dietary intake.

CONCLUSION

Cross-study differences in urine collection protocols may explain observed inconsistencies in the 2-OHE/16-OHE and breast cancer association. Our case-control analysis using pre-treatment urine samples suggested that a lower 2-OHE/16-OHE ratio was associated with an increased risk of pre-menopausal and post-menopausal breast cancer diagnosis among Chinese women.

Influence of exercise and menstrual cycle phase on plasma homocyst(e)ine levels in young women--a prospective study

Plasma total homocysteine (tHcy) has been identified as an independent risk factor for cardiovascular diseases (CVD). The difference in tHcy between the sexes has most often been related to the sex hormones, but also to a higher muscle mass in men. The purpose of this study was to assess the effects of acute exercise, brief exhaustive training, and menstrual cycle phase on circulating plasma tHcy concentrations. Fifteen untrained eumenorrheic women (mean age [+/-SD]: 18.7+/-0.4 yr, body fat: 25.8+/-3.4%, VO2max: 43.8+/-2.3 ml x kg(-1) x min(-1)) volunteered for the present study, which covered two menstrual cycles. During the second cycle the subjects participated in two exhaustive 5-day training programs on a cycle ergometer: one in the follicular (FPh) and one in the luteal phase (LPh). Pre- and posttraining plasma tHcy and total estrogen (E) responses were determined in blood samples obtained immediately before, during and immediately after incremental exercise to exhaustion. tHcy levels showed a large between-subject variation, but differences between FPh and LPh levels were consistent (P=0.063). Mean tHcy levels at rest were 9.44+/-1.65 micromol/L and 8.93+/-1.71 micromol/L during the FPh and LPh, respectively. Brief exhaustive training did not elicit any changes in plasma tHcy concentrations, although posttraining LPh E levels were lower (P<0.01). Overall, the differences between FPh and LPh values for tHcy and E were attenuated by training. Acute exercise increased plasma tHcy concentrations (P<0.001). At exhaustion, tHcy levels increased by 17% and 16% during the FPh and LPh, respectively. This was also significantly above tHcy levels at submaximal exercise (P=0.044). After a short period of training tHcy levels did not increase as much during acute exercise as they did before training; however, the increments were still significant (P=0.048). In conclusion, acute exercise in women produces significant increases in plasma tHcy concentrations, whereas brief exhaustive training does not significantly alter plasma tHcy levels. Our findings also suggest that plasma tHcy concentrations are menstrual cycle phase-dependent and that there is a close association between estrogen status and tHcy levels.

Premenstrual syndromes: closing the 20th century chapters

The need to re-evaluate premenstrual syndromes became apparent in 1997-1998 and early 1999. The success stories of some symptomatic treatment modalities and more sophisticated studies of pathobiology chart the pathways for future progress: the shift from a descriptive diagnosis to diagnoses based on etiology, the recognition of diversified vulnerabilities and their expression in particular situations, and specific treatment modalities.

Relationship between the risk of breast cancer and physical activity. An epidemiological perspective

The possible protective effect of physical exercise on the risk of breast cancer has gained attention during the last few years. According to the current concepts of biological mechanisms underlying the possible protection, physical activity may alter menstrual function by reducing the number of ovulatory menstrual cycles via a hormone-related pathway and, thus, reducing the cumulative exposure to progesterone and estrogen. Experimental studies on the effects of exercise suggest changes in menstrual characteristics and in ovarian hormone serum levels. The majority of epidemiological studies, in spite of limitations in estimating physical activity and partly incomplete control of confounding factors, suggest a protective effect of physical activity. Whether physical activity offers a means of primary prevention of breast cancer is still an open issue.

Sex steroid metabolism and menstrual irregularities in the exercising female. A review

This article aims to clarify why, and by which mechanisms, exercise may influence the normal menstrual cycle. Therefore, the vast amount of literature on this subject is reviewed and a critical appraisal of the most widespread hypotheses if offered. The strikingly low body mass which frequently accompanies exercise-related menstrual irregularities (ERMI) has led some authors to develop a hypothesis which postulates that a critical percentage of body fat is essential to trigger normal menstruation. The relevance of any reference to anorexia nervosa to support this view lacks consistency: female athletes differ in many ways from patients with anorexia nervosa, not least in their excellent physical status which is essential to deliver first-class performances. ERMI is not identical to the so-called female athlete triad, a complicated pathology that involves ERMI, premature osteoporosis and disordered eating. ERMI itself does not seem to have any substantial pathological effects as long as attention is paid to preventing osteoporosis or stress fractures which may result from prolonged hypo-estrogenaemia. In the female athlete with ERMI who wishes to conceive, the accompanying subfertility may necessitate a response other than a prompt reduction in training intensity, as this is hardly a first choice for any top athlete. During recent years, a number of prospective studies have greatly contributed to our understanding of the complexity of the mechanisms involved in ERMI. Older hypotheses, such as those considering hyperprolactinaemia as the cornerstone of ERMI, have now been firmly rejected. The present hypotheses emphasise the importance of caloric deficiency and limited energy availability, although they still fail to identify the actual mechanism that causes ERMI. There is, however, evidence that ERMI is produced by a disturbance of the hypothalamic gonadotrophin-releasing hormone oscillator. This disturbance is caused by either an insufficient estrogen or progesterone feedback or by an imbalance of local opioid peptide and catecholamine activities mediated by gamma-aminobutyric acid (GABA), corticotrophin-releasing hormone and insulin-like growth factor-1. More recent experiments have also linked ERMI with changes in steroid metabolism, in particular, an increasing activity of catecholestrogens possibly leading to enhanced intracerebral noradrenaline (norepinephrine) levels that may interfere with normal gonadotrophin release. This article demonstrates that the outcome of the many studies of ERMI is characterised by much controversy and numerous methodological flaws. The importance and complexity of some recent findings necessitate a comprehensive study which links older and newer findings within a critical perspective.

Exercise-induced changes in enzymatic O-methylation of catecholestrogens by erythrocytes of eumenorrheic women

The present study was designed to assess the effects of acute exercise and short-term intensive training on catechol-O-methyltransferase (COMT) activity. COMT inactivates catecholamines and converts primary catecholestrogens (CE) into their O-methylated form yielding the 2- (2-MeOE) and 4-methoxyestrogens (4-MeOE). Blood samples were obtained from 15 previously untrained eumenorrheic women (mean +/- SE, VO2max: 43.8 mL x kg-1 x min-1 +/- 0.6) before and after a 5-d intensive training period, at rest and during incremental exercise. COMT activity was determined in the erythrocytes (RBC-COMT) after incubation of blood lysate with primary CE. The formation of both 2- and 4-MeOE was significantly higher (P < 0.05) during the luteal (LPh) than during the follicular phase (FPh). The amount of 2-MeOE formed (FPh: 4.2 +/- 0.2%; LPh: 4.9 +/- 0.2%) was significantly greater than the produced amount of 4-MeOE (FPh: 1.4 +/- 0.1%; LPh: 1.5 +/- 0.1%) (P < 0.05). Both before and after training, incremental exercise did not significantly alter RBC-COMT activity although we observed a trend for RBC-COMT activity increasing proportionally with the exercise intensity. After a brief period of exhaustive training, during rest the formation of 2-MeOE (FPh: +16.7%, LPh: +15.7%) and 4-MeOE (FPh: +28.6%; LPh: +40%) was significantly (P < 0.05) increased. The results of the present study are consistent with earlier findings reporting increased plasma concentrations of O-methylated CE following training. It is concluded that RBC-COMT activity is increased by brief intensive training, but not by acute exercise. We speculate that an increase in COMT-catalyzed O-methylation of CE may indicate that less COMT is available to deactivate norepinephrine.