Estrogen metabolites as bioreactive modulators of tumor initiators and promoters

Genetic polymorphisms of estrogen metabolizing enzyme and breast cancer risk in Thai women

Estrogen and its metabolites are believed to play important roles in breast cancer, and its determinants include both genetic and lifestyle factors. The objective of the study is to investigate the association of breast cancer risk in Thailand with genetic polymorphisms in several genes involved in estrogen synthesis and metabolism. Five hundred and seventy patients with histopathologically confirmed breast cancer and 497 controls were included in the present study. Forty single nucleotide polymorphisms (SNPs) in the CYP1A1, CYP1A2, CYP1B1, CYP17, CYP19, CYP2C9, CYP2C19, AhR, ESR1, PGR, ERRG, COMT, HSD17B1, HSD17B2, EPHX1 and NQO1 genes were genotyped. Association of genotypes with breast cancer risk was evaluated using multivariate logistic regression, which suggested an altered risk for the following SNPs [gene, odds ratio (OR) and 95% confidence interval are shown]: heterozygote carriers of rs4917623 [CYP2C19, OR = 1.38 (1.04-1.84)], rs2066853 [AhR, OR = 1.34 (1.02-1.76)] and rs1857407 [ERRG, (OR = 0.72 (0.55-0.96)]; homozygote carriers of rs762551 [CYP1A2, OR = 2.75 (1.47-5.14)], rs4917623 [CYP2C19, OR = 1.48 (1.00-2.19) and rs945453 [ERRG, OR = 1.66 (1.04-2.65)]. In addition, a stratified analysis by menopausal status indicated that the association of the CYP1A2 (rs762551) and CYP17 (rs743572) polymorphisms with breast cancer risk were mainly evident in premenopausal, while ERRG (rs1857407) was significant in postmenopausal women. These findings suggest that CYP1A2, CYP2C19, AhR, ERRG and CYP17 polymorphisms may play an important role in estrogen metabolism and modify individual susceptibility to breast cancer in Thai women.

A liquid chromatography-mass spectrometry method for the simultaneous measurement of 15 urinary estrogens and estrogen metabolites: assay reproducibility and interindividual variability

BACKGROUND

Accurate, reproducible, and sensitive measurements of endogenous estrogen exposure and individual patterns of estrogen metabolism are needed for etiologic studies of breast cancer. We have developed a high-performance liquid chromatography-tandem mass spectrometry method to quantitate simultaneously 15 urinary estrogens and estrogen metabolites (EM): estrone; estradiol; 3 catechol estrogens; 5 estrogens in the 16alpha pathway, including estriol; and 5 methoxy estrogens.

METHODS

Overnight urines were obtained from 45 participants. For the reproducibility study, two blinded, randomized aliquots from 5 follicular and 5 luteal premenopausal women, 5 naturally postmenopausal women, and 5 men were assayed in each of four batches. Assay coefficients of variation and intraclass correlation coefficients were calculated with ANOVA models. Data from the additional 25 participants were added to compare EM levels by menstrual/sex group and assess interindividual variability.

RESULTS

For each EM, overall coefficients of variation were < or = 10%. Intraclass correlation coefficients for each menstrual/sex group were generally > or = 98%. Although geometric mean EM concentrations differed among the four groups, rankings were similar, with estriol, 2-hydroxyestrone, estrone, estradiol, and 16-ketoestradiol accounting for 60% to 75% of total urinary EM. Within each group, interindividual differences in absolute concentrations were consistently high; the range was 10- to 100-fold for nearly all EM.

CONCLUSION

Our high-performance liquid chromatography-tandem mass spectrometry method for measuring 15 urinary EM is highly reproducible, and the range of EM concentrations in each menstrual/sex group is quite large relative to assay variability. Whether these patterns persist in blood and target tissues awaits further development and application of this method.

The prevention of prostate cancer

From our better understanding of the natural history of prostate cancer, it is not unreasonable to believe that the disease is preventable. Prostate cancer has become a major healthcare problem worldwide, as life expectancy increases. Moreover, the cancer is slow growing, with a period of about 20-25 years from initiation to the stage when the clinically detectable phenotype can be identified. This review provides a simple overview of the endocrinology of prostate cancer and discusses some of the pharmaceutical agents that have been or are being tested to restrain, possibly arrest, the progression of this slowly growing cancer. Also discussed are many of the dietary factors that may influence the molecular or endocrine events implicated in its development. Dietary factors are considered responsible for the geographical differences in prostate cancer incidence and mortality. Since about 50% of all men worldwide, from both East and West, show evidence of microscopic cancer by 50 years of age, growth restraint would appear to be the pragmatic option to the possibility of preventing initiation.

Hormonal aspects in the causation of human breast cancer: epidemiological hypotheses reviewed, with special reference to nutritional status and first pregnancy

Epidemiology of breast cancer has identified early age at menarche, late first pregnancy, low parity and late menopause as risk factors, but in addition genetic factors, height, weight and living in western countries play a significant role. The international variation in incidence is almost exclusively due to non-genetic factors. Hypotheses in prevention-oriented research are reviewed: 1. obesity-related oestrogen production as a stimulus of the tumour in postmenopausal women; 2. nutritional status and energy expenditure during puberty and adolescence, developed for fertility and fecundity and extended later to breast cancer; 3. reproductive life during early adulthood, age at first pregnancy and its specific effects on breast tissues. The message of preventability of breast cancer is that mammary epithelial differentiation should come early. Our insight concerning events in puberty and early adulthood can be consolidated in one concept on the risk of extended proliferation of breast epithelium during early adulthood in the absence of full differentiation induced by pregnancy. The combined effects of Western-type nutrition, lack of exercise and Western-type women's emancipation sets the stage for breast cancer already at a young age. Since it is unlikely that emancipated women in affluent societies will return to the original life-style of getting pregnant as soon as it is biologically possible, a novel daring way of protection has to be considered. Could a "Breast Differentiation Pill" be developed to offer protection?

Estrogen Metabolism-Related Genes and Breast Cancer Risk: The Multiethnic Cohort Study

Common polymorphisms in genes that affect estrogen levels may be associated with breast cancer risk. We investigated the associations between breast cancer and sequence variants in several genes in the estradiol/estrone metabolism pathway (CYP1A1*2A, CYP1A2*1F, CYP1B1 Leu432Val, CYP3A4*1B, COMT Val158Met, SULT1A1Arg213His) as well as the Arg554Lys variant in AHR (a transcription factor for CYP1A1, CYP1A2, and CYP1B1) in a case-control study of 1,339 breast cancer cases and 1,370 controls nested in the Multiethnic Cohort Study. The Multiethnic Cohort Study is a large prospective study of men and predominantly postmenopausal women of Japanese, White, African American, Latino, and Native Hawaiian ancestry, residing in Hawaii and Los Angeles. We found no association between breast cancer and these polymorphisms, except for CYP1A2*1F which was inversely associated with risk. The odds ratio (95% confidence interval) for the AA, AC, and CC genotype was 1.0, 0.9 (0.7-1.0), and 0.7 (0.5-1.0), respectively (P for gene dosage effect=0.03). This association seemed somewhat stronger for estrogen receptor (ER)/progesterone receptor (PR)-negative tumors than for ER/PR-positive tumors, and no statistically significant interaction with estrogen-related risk factors was detected. The findings provide no evidence for a role of COMT Val58Met, CYP1A1*2A, CYP3A4*1B, CYP1B1 Leu432Val, SULT1A1 Arg213His, and AHR Arg554Lys in breast cancer etiology. They also provide support for an inverse association between CYP1A2*1F and breast cancer, which is consistent with the observation of lower circulating estrogen levels in premenopausal women with the CC genotype in a previous study.

Racial and ethnic disparities in breast cancer: a multilevel perspective

Although the etiology of racial and ethnic disparities in breast cancer is complex, the studies reviewed here suggest many possible culprits. In the authors' model, outcomes at the cellular level reflect not only genetic constitution and the hormonal milieu but also the interactions of predictors at multiple levels. At the societal level, important predictors include toxin and hormone exposure, access to care, quality of care, and social support. At the individual level, reproductive history, exogenous hormone use, diet,exercise, and response to stress all may influence cellular outcomes. The smooth transition from normal cell function to apoptosis occurs when the interactions between factors at the societal, individual, and cellular levels are harmonious. Perturbations at the societal level, however, such as inferior quality of care, or at the individual level, such as exogenous hormone use,can have profound effects on cell biology and predispose to neoplasia. When these perturbations are systematic and vary by race or ethnicity, disparities in breast cancer incidence and mortality result. Increasing incidence of breast cancer among both men and women likely reflects important trends at the societal and individual levels. These trends may include increased toxin exposure, increased obesity, and changes in the timing and number of births. Efforts to reduce breast cancer incidence and disparities must consider societal and individual factors and the important effects these factors can have on normal cell function.

Local biosynthesis and metabolism of oestrogens in the human breast

The origin of oestrogens at the level of the breast itself is discussed. In particular in postmenopausal women an accumulation of oestradiol at the site of breast tumours has been documented by a number of independent studies. The mechanism behind the high local oestrogens concentrations is thought to be the in situ production of these steroids by local processes with androstenedione as the main precursor. The presence of all enzymes required for this production has been demonstrated in a large proportion of breast tumours, with probably aromatase, hydroxysteroid dehydrogenase type 1 and sulfatase as the most important enzymes leading to the biologically highly active oestradiol. The individual enzymes that are relevant for the biosynthesis and the metabolism of oestrogens are discussed. The conclusion is reached that a number of these local processes may be involved in the promotion of premalignant lesions and in stimulation of growth of malignant tumours in the human breast.

Genetic instability favoring transversions associated with ErbB2-induced mammary tumorigenesis

It has been argued that genetic instability is required to generate the myriad mutations that fuel tumor initiation and progression and, in fact, patients with heritable cancer susceptibility syndromes harbor defects in specific genes that normally maintain DNA integrity. However, the vast majority of human cancers arise sporadically, in the absence of deficiencies in known "mutator" genes. We used a cII-based mutation detection assay to show that the mean frequency of forward mutations in primary mammary adenocarcinomas arising in mouse mammary tumor virus-c-erbB2 transgenic mice harboring multiple copies of the lambda bacteriophage genome was significantly higher than in aged-matched, wild-type mammary tissue. Analysis of the cII mutational spectrum within the mammary tumor genomic DNA demonstrated a >6-fold elevation in transversion mutation frequency, resulting in a highly unusual inversion of the transition/transversion ratio characteristic of normal epithelium; frameshift mutation frequencies were unaltered. Arising oncogenic point mutations within the c-erbB2 transgene of such tumors were predominantly transversions as well. Data from this model system support the notion that elaboration of a mutator phenotype is a consequential event in breast cancer and suggest that a novel DNA replication/repair gene is a relatively early mutational target in c-erbB2-induced mammary tumorigenesis.

Oestrogenic and antiandrogenic chemicals in the environment: effects on male reproductive health

Exposures of human populations to pesticides and industrial pollutants, and to synthetic chemicals present in foods, beverages, and plastics, have raised concern that these substances can interfere with endogenous sex hormone function. Interference with sex hormone action can, in turn, result in a variety of developmental and reproductive anomalies. Compounds in this class are thus referred to as endocrine disruptors (EDs). EDs that affect reproductive processes in vertebrates act primarily by altering oestrogenic and antiandrogenic activities. The recent cloning of a second oestrogen receptor (ER) subtype (ERbeta) and its widespread tissue distribution pattern indicates that the first ER to be cloned, ERalpha, may not be the only, or even the primary, mediator of oestrogen action. It is anticipated that this discovery will lead to development of antagonist compounds specific to either ER subtype, and help to determine the function of each receptor subtype in reproductive and other tissues. Growing evidence suggests that EDs interfere with reproductive function at low exposure levels and cause distinct effects at different concentrations within the same organ. Developing organisms have increased susceptibility to the actions of EDs because differentiating tissues are more vulnerable to changes in hormonal milieu. Thus, children are at greater risk of toxicant-related illnesses than adults. However, most data are collected from laboratory studies, and it remains to be determined that the levels of chemicals in the environment can impair human reproductive health. There is also significant genetic variability between human and animal species in their reactions to chemicals. The effects of low-dose, chronic, and multiple chemical exposures warrant further investigation in order to characterize the risk of environmental agents to humans. The aims of this review, which will focus on male reproduction, are to: 1) identify synthetic chemicals in the environment that fall into the ED class; 2) describe their mechanisms of toxicity in reproductive tissues; and, 3) outline the direction of future research efforts with respect to EDs.