Unbalanced estrogen metabolism in ovarian cancer

Greater exposure to estrogens is a risk factor for ovarian cancer. To investigate the role of estrogens in ovarian cancer, a spot urine sample and a saliva sample were obtained from 33 women with ovarian cancer and 34 age‐matched controls. Thirty‐eight estrogen metabolites, conjugates and DNA adducts were analyzed in the urine samples using ultraperformance liquid chromatography/tandem mass spectrometry, and the ratio of adducts to metabolites and conjugates was calculated for each sample. The ratio of depurinating estrogen–DNA adducts to estrogen metabolites and conjugates was significantly higher in cases compared to controls (p < 0.0001), demonstrating high specificity and sensitivity. DNA was purified from the saliva samples and analyzed for genetic polymorphisms in the genes for two estrogen‐metabolizing enzymes. Women with two low‐activity alleles of catechol‐O‐methyltransferase plus one or two high‐activity alleles of cytochrome P450 1B1 had higher levels of estrogen–DNA adducts and were more likely to have ovarian cancer. These findings indicate that estrogen metabolism is unbalanced in ovarian cancer and suggest that formation of estrogen–DNA adducts plays a critical role in the initiation of ovarian cancer.     

Critical depurinating DNA adducts: Estrogen adducts in the etiology and prevention of cancer and dopamine adducts in the etiology and prevention of Parkinson's disease

Endogenous estrogens become carcinogens when dangerous metabolites, the catechol estrogen quinones, are formed. In particular, the catechol estrogen‐3,4‐quinones can react with DNA to produce an excess of specific depurinating estrogen‐DNA adducts. Loss of these adducts leaves apurinic sites in the DNA, generating subsequent cancer‐initiating mutations. Unbalanced estrogen metabolism yields excessive catechol estrogen‐3,4‐quinones, increasing formation of depurinating estrogen‐DNA adducts and the risk of initiating cancer. Evidence for this mechanism of cancer initiation comes from various types of studies. High levels of depurinating estrogen‐DNA adducts have been observed in women with breast, ovarian or thyroid cancer, as well as in men with prostate cancer or non‐Hodgkin lymphoma. Observation of high levels of depurinating estrogen‐DNA adducts in high risk women before the presence of breast cancer indicates that adduct formation is a critical factor in breast cancer initiation. Formation of analogous depurinating dopamine‐DNA adducts is hypothesized to initiate Parkinson's disease by affecting dopaminergic neurons. Two dietary supplements, N‐acetylcysteine and resveratrol complement each other in reducing formation of catechol estrogen‐3,4‐quinones and inhibiting formation of estrogen‐DNA adducts in cultured human and mouse breast epithelial cells. They also inhibit malignant transformation of these cells. In addition, formation of adducts was reduced in women who followed a Healthy Breast Protocol that includes N‐acetylcysteine and resveratrol. When initiation of cancer is blocked, promotion, progression and development of the disease cannot occur. These results suggest that reducing formation of depurinating estrogen‐DNA adducts can reduce the risk of developing a variety of types of human cancer.     

The molecular etiology of breast cancer: evidence from biomarkers of risk

Estrogens can become endogenous carcinogens via formation of catechol estrogen quinones, which react with DNA to form specific depurinating estrogen-DNA adducts. The mutations resulting from these adducts can lead to cell transformation and the initiation of breast cancer. Estrogen metabolites, conjugates and depurinating DNA adducts in urine samples from 46 healthy control women, 12 high-risk women and 17 women with breast cancer were analyzed. The estrogen metabolites, conjugates and depurinating DNA adducts were identified and quantified by using ultraperformance liquid chromatography/tandem mass spectrometry. The levels of the ratios of depurinating DNA adducts to their respective estrogen metabolites and conjugates were significantly higher in high-risk women (p < 0.001) and women with breast cancer (p < 0.001) than in control subjects. The high-risk and breast cancer groups were not significantly different (p = 0.62). After adjusting for patient characteristics, these ratios were still significantly associated with health status. Thus, the depurinating estrogen-DNA adducts are possible biomarkers for early detection of breast cancer risk and response to preventive treatment.     

Relative imbalances in estrogen metabolism and conjugation in breast tissue of women with carcinoma: potential biomarkers of susceptibility to cancer

Exposure to estrogens has been associated with an increased risk of developing breast cancer. Breast biopsy tissues from 49 women without breast cancer (controls) and 28 with breast carcinoma (cases) were analyzed by HPLC with electrochemical detection for 31 estrogen metabolites and catechol estrogen quinone-glutathione conjugates. The levels of estrone and estradiol were higher in cases. More 2-catechol estrogen (CE) than 4-CE was observed in controls, but the 4-CE were three times higher than 2-CE in cases. In addition, the 4-CE were nearly four times higher in cases than in controls. Less O-methylation was observed for the CE in cases. The level of catechol estrogen quinone conjugates in cases was three times that in controls, suggesting in the cases a higher probability for the quinones to react with DNA and generate mutations that may initiate cancer. The levels of 4-CE and quinone conjugates were highly significant predictors of breast cancer. These results suggest that some catechol estrogen metabolites and conjugates could serve as biomarkers to predict risk of breast cancer.     

Analysis of potential biomarkers of estrogen-initiated cancer in the urine of Syrian golden hamsters treated with 4-hydroxyestradiol

Estrone (E1) and 17beta-estradiol (E2) are metabolized to catechol estrogens (CE), which may be oxidized to semiquinones and quinones (CE-Q). CE-Q can react with glutathione (GSH) and DNA, or be reduced to CE. In particular, CE-3,4-Q react with DNA to form depurinating adducts (N7Gua and N3Ade), which are cleaved from DNA to leave behind apurinic sites. We report the determination of 22 estrogen metabolites, conjugates and adducts in the urine of male Syrian golden hamsters treated with 4-hydroxyestradiol (4-OHE2). After initial purification, urine samples were analyzed by HPLC with multichannel electrochemical detection and by capillary HPLC/tandem mass spectrometry. 4-Hydroxyestrogen-2-cysteine [4-OHE1(E2)-2-Cys] and N-acetylcysteine [4-OHE1(E2)-2-NAcCys] conjugates, as well as the methoxy CE, were identified and quantified by HPLC, whereas the 4-OHE1(E2)-1-N7Gua depurinating adducts and 4-OHE1(E2)-2-SG conjugates could only be identified by the mass spectrometry method. Most of the administered 4-OHE2 was metabolically converted to 4-OHE1. Formation of thioether (GSH, Cys and NAcCys) conjugates and depurinating adducts [4-OHE1(E2)-1-N7Gua] indicates that oxidation of 4-CE to CE-3,4-Q and subsequent reaction with GSH and DNA, respectively, do occur. The major conjugates in the urine were 4-OHE1(E2)-2-NACCYS: The oxidative pathway of 4-OHE1(E2) accounted for approximately twice the level of products compared with those from the methylation pathway. The metabolites and methoxy CE were excreted predominantly (>90%) as glucuronides, whereas the thioether conjugates were not further conjugated. These results provide strong evidence that exposure to 4-OHE1(E2) leads to the formation of E1(E2)-3,4-Q and, subsequently, depurinating DNA adducts. This process is a putative tumor initiating event. The estrogen metabolites, conjugates and adducts can be used as biomarkers for detecting enzymatic oxidation of estrogens to reactive electrophilic metabolites and possible susceptibility to estrogen-induced cancer.     

Estrogens as endogenous genotoxic agents--DNA adducts and mutations

Estrogens induce tumors in laboratory animals and have been associated with breast and uterine cancers in humans. In relation to the role of estrogens in the induction of cancer, we examine formation of DNA adducts by reactive electrophilic estrogen metabolites, formation of reactive oxygen species by estrogens and the resulting indirect DNA damage by these oxidants, and, finally, genomic and gene mutations induced by estrogens. Quinone intermediates derived by oxidation of the catechol estrogens 4-hydroxyestradiol or 4-hydroxyestrone may react with purine bases of DNA to form depurinating adducts that generate highly mutagenic apurinic sites. In contrast, quinones of 2-hydroxylated estrogens produce less harmful, stable DNA adducts. The catechol estrogen metabolites may also generate potentially mutagenic oxygen radicals by metabolic redox cycling or other mechanisms. Several types of indirect DNA damage are caused by estrogen-induced oxidants, such as oxidized DNA bases, DNA strand breakage, and adduct formation by reactive aldehydes derived from lipid hydroperoxides. Estradiol and the synthetic estrogen diethylstilbestrol also induce numerical and structural chromosomal aberrations and several types of gene mutations in cells in culture and in vivo. In conclusion, estrogens, including the natural hormones estradiol and estrone, must be considered genotoxic carcinogens on the basis of the evidence outlined in this chapter.     

Formation of depurinating N3Adenine and N7Guanine adducts by MCF-10F cells cultured in the presence of 4-hydroxyestradiol

Metabolic conversion of endogenous estrogens, estradiol (E2) and estrone (E1), to the catechol estrogens 4-hydroxyE1(E2) [4-OHE1(E2)] has been implicated in the initiation of cancer in rodents and humans. Evidence collected in our laboratories has shown that 4-OHE1(E2) are enzymatically oxidized to E1(E2)-3,4-quinones [E1(E2)-3,4-Q], which have the potential to damage DNA by forming predominantly depurinating adducts, 4-OHE1(E2)-1-N3Ade and 4-OHE1(E2)-1-N7Gua, leading to the accumulation of mutations and probably cell transformation. The human breast epithelial cell line MCF-10F has been transformed by treatment with E2 or 4-OHE2. We have used MCF-10F cells to study the presence of adducts and conjugates after treatment with 4-OHE2. To mimic the intermittent exposure of breast cells to endogenous estrogens, MCF-10F cells were treated with 1 microM 4-OHE2 for a 24-h period at 72, 120, 192 and 240 h postplating. Culture media were collected at each point, extracted by solid-phase extraction and analyzed by HPLC connected with a multichannel electrochemical detector and/or ultraperformance liquid chromatography/tandem mass spectrometry. Media from successive treatments with 4-OHE2 showed the formation of methoxy and cysteine conjugates, and the depurinating adducts 4-OHE1(E2)-1-N3Ade. The amount of 4-OHE1(E2)-1-N3Ade adducts was higher after the third treatment; smaller amounts of the 4-OHE1(E2)-1-N7Gua adducts were detected after the second and third treatments. These results demonstrate that MCF-10F cells oxidize 4-OHE2 to E1(E2)-3,4-Q, which react with DNA to form the depurinating N3Ade and N7Gua adducts. This DNA damage can play an important role in the 4-OHE2-induced mutations and transformation of MCF-10F cells to malignant cells.     

Is estrogen plus progestin menopausal hormone therapy safe with respect to endometrial cancer risk?

Given the strong link between use of unopposed estrogens and development of endometrial cancers, estrogens are usually prescribed with a progestin, particularly for women with intact uteri. Some studies suggest that sequential use of progestins may increase risk; however, the moderating effects of usage patterns or patient characteristics, including body mass index (BMI), are unknown. We evaluated menopausal hormone use and incident endometrial cancer (n = 885) in 68,419 postmenopausal women with intact uteri enrolled in the National Institutes of Health‐American Association of Retired Persons Diet and Health study. Participants completed a risk factor questionnaire in 1996–1997 and were followed up through 2006. Hazard rate ratios (RRs) and 95% confidence intervals (CIs) were estimated using Cox regression. Among 19,131 women reporting exclusive estrogen plus progestin use, 176 developed endometrial cancer (RR = 0.88; 95% CI = 0.74–1.06). Long‐duration (≥10 years) sequential (<15 days progestin per month) estrogen plus progestin use was positively associated with risk (RR = 1.88; 95% CI = 1.36–2.60], whereas continuous (>25 days progestin per month) estrogen plus progestin use was associated with a decreased risk (RR = 0.64; 95% CI = 0.49–0.83). Increased risk for sequential estrogen plus progestin was seen only among thin‐to‐normal weight women (BMI < 25 kg/m²; RR = 2.53). Our findings support that specific categories of estrogen plus progestin use increases endometrial cancer risk, specifically long durations of sequential progestins, whereas decreased endometrial cancer risk was observed for users of short‐duration continuous progestins. Risks were highest among thin‐to‐normal weight women, presumably reflecting their lower endogenous estrogen levels, suggesting that menopausal hormones and obesity increase endometrial cancer through common etiologic pathways.     

Urinary estrogens and estrogen metabolites and subsequent risk of breast cancer among premenopausal women

Endogenous estrogens and estrogen metabolism are hypothesized to be associated with premenopausal breast cancer risk but evidence is limited. We examined 15 urinary estrogens/estrogen metabolites and breast cancer risk among premenopausal women in a case-control study nested within the Nurses' Health Study II (NHSII). From 1996 to 1999, urine was collected from 18,521 women during the mid-luteal menstrual phase. Breast cancer cases (N = 247) diagnosed between collection and June 2005 were matched to two controls each (N = 485). Urinary estrogen metabolites were measured by liquid chromatography-tandem mass spectrometry and adjusted for creatinine level. Relative risks (RR) and 95% confidence intervals (CI) were estimated by multivariate conditional logistic regression. Higher urinary estrone and estradiol levels were strongly significantly associated with lower risk (top vs. bottom quartile RR: estrone = 0.52; 95% CI, 0.30-0.88; estradiol = 0.51; 95% CI, 0.30-0.86). Generally inverse, although nonsignificant, patterns also were observed with 2- and 4-hydroxylation pathway estrogen metabolites. Inverse associations generally were not observed with 16-pathway estrogen metabolites and a significant positive association was observed with 17-epiestriol (top vs. bottom quartile RR = 1.74; 95% CI, 1.08-2.81; P(trend) = 0.01). In addition, there was a significant increased risk with higher 16-pathway/parent estrogen metabolite ratio (comparable RR = 1.61; 95% CI, 0.99-2.62; P(trend) = 0.04). Other pathway ratios were not significantly associated with risk except parent estrogen metabolites/non-parent estrogen metabolites (comparable RR = 0.58; 95% CI, 0.35-0.96; P(trend) = 0.03). These data suggest that most mid-luteal urinary estrogen metabolite concentrations are not positively associated with breast cancer risk among premenopausal women. The inverse associations with parent estrogen metabolites and the parent estrogen metabolite/non-parent estrogen metabolite ratio suggest that women with higher urinary excretion of parent estrogens are at lower risk.     

Catechol estrogen metabolites and conjugates in mammary tumors and hyperplastic tissue from estrogen receptor-alpha knock-out (ERKO)/Wnt-1 mice: implications for initiation of mammary tumors

A novel model of breast cancer was established by crossing mice carrying the Wnt-1 transgene (100% of adult females develop spontaneous mammary tumors) with the ERKO mouse line, in which mammary tumors develop despite a lack of functional estrogen receptor-alpha. To begin investigating whether metabolite-mediated genotoxicity of estrogens may play an important role in the initiation of mammary tumors, the pattern of estrogen metabolites and conjugates was examined in ERKO/Wnt-1 mice. Extracts of hyperplastic mammary tissue and mammary tumors were analyzed by HPLC with identification and quantification of compounds by multichannel electrochemical detection. Picomole amounts of the 4-catechol estrogens (CE) were detected, but their methoxy conjugates, as well as the 2-CE and their methoxy conjugates, were not. 4-CE conjugates with glutathione or its hydrolytic products (cysteine and N-acetylcysteine) were detected in picomole amounts in both tumors and hyperplastic mammary tissue, demonstrating the formation of CE-3,4-quinones. These preliminary findings show that the estrogen metabolite profile in the mammary tissue is unbalanced, in that the normally minor 4-CE metabolites were detected in the mammary tissue and not the normally predominant 2-CE. These results are consistent with the hypothesis that the mammary tumor development is primarily initiated by metabolism of estrogens to 4-CE and, then, to CE-3,4-quinones, which may react with DNA to induce oncogenic mutations.     

Lung cancer mortality risk among breast cancer patients treated with anti-estrogens

BACKGROUND:

The Women's Health Initiative randomized clinical trial reported that menopausal hormone therapy increases lung cancer mortality risk. If this is true, use of anti‐estrogens should be associated with decreased lung cancer mortality risk. The authors compared lung cancer incidence and mortality among breast cancer patients with and without anti‐estrogen therapy.

METHODS:

Our study included all 6655 women diagnosed with breast cancer between 1980 and 2003 and registered at the Geneva Cancer Registry. Among these women, 46% (3066) received anti‐estrogens. All women were followed for occurrence and death from lung cancer until December 2007. The authors compared incidence and mortality rates among patients with and without anti‐estrogens with those expected in the general population by Standardized Incidence Ratios (SIRs) and Standardized Mortality Ratios (SMRs).

RESULTS:

After a total of 57,257 person‐years, 40 women developed lung cancer. SIRs for lung cancer were not significantly decreased among breast cancer patients with and without anti‐estrogens (0.63, 95% confidence intervals [CI], 0.33‐1.10; and 1.12, 95% CI, 0.74‐1.62, respectively) while SMR was decreased among women with anti‐estrogens (0.13, 95% CI, 0.02‐0.47, P<.001) but not for women without anti‐estrogens (0.76, 95% CI, 0.43‐1.23).

CONCLUSIONS:

Compared with expected outcomes in the general population, breast cancer patients receiving anti‐estrogen treatment for breast cancer had lower lung cancer mortality. This study further supports the hypothesis that estrogen therapy modifies lung cancer prognosis. Cancer 2011. © 2011 American Cancer Society.     

Chapter 4: Estrogens as Endogenous Genotoxic Agents--DNA Adducts and Mutations

Estrogens induce tumors in laboratory animals and have beenassociated with breast and uterine cancers in humans. In relationto the role of estrogens in the induction of cancer, we examineformation of DNA adducts by reactive electrophilic estrogenmetabolites, formation of reactive oxygen species by estrogensand the resulting indirect DNA damage by these oxidants, and,finally, genomic and gene mutations induced by estrogens. Quinoneintermediates derived by oxidation of the catechol estrogens4-hydroxyestradiol or 4-hydroxyestrone may react with purinebases of DNA to form depurinating adducts that generate highlymutagenic apurinic sites. In contrast, quinones of 2-hydroxylatedestrogens produce less harmful, stable DNA adducts. The catecholestrogen metabolites may also generate potentially mutagenicoxygen radicals by metabolic redox cycling or other mechanisms.Several types of indirect DNA damage are caused by estrogen-inducedoxidants, such as oxidized DNA bases, DNA strand breakage, andadduct formation by reactive aldehydes derived from lipid hydroperoxides.Estradiol and the synthetic estrogen diethylstilbestrol alsoinduce numerical and structural chromosomal aberrations andseveral types of gene mutations in cells in culture and in vivo.In conclusion, estrogens, including the natural hormones estradioland estrone, must be considered genotoxic carcinogens on thebasis of the evidence outlined in this chapter.     

Potential for using aromatase inhibitors for preventing breast cancer

Substantial evidence supports the concept that estrogens cause breast cancer in animals and in women but the precise mechanism is unknown. The most commonly held theory is that estrogens stimulate proliferation of breast cells and thus statistically increase the chances for genetic mutations which could result in cancer. Another theory is that estrogen metabolism generates oxygen-free radicals and quinones which produce both stable and unstable DNA adducts. Both result in genetic mutations which accumulate and could ultimately cause cancer. A major criticism of the latter hypothesis is that breast tissue contains insufficient concentrations of estrogen for accumulation of genotoxic metabolites. Our hypothesis is that breast tissue estrogen levels, as a result of in situ synthesis, are much higher than previously thought. With sufficient amounts of aromatase in breast tissue, enough estradiol as substrate should be available to allow formation of substantial amounts of genotoxic metabolites. We postulate that aromatase overexpression may in this way cause breast cancer. As evidence supporting this concept, four animal models of aromatase overexpression and either breast cancer or pre-malignant lesions have been described. We have provided evidence that normal breast tissue can make estrogen and that certain stimulatory compounds can increase aromatase activity in the breast by nearly 10,000-fold. If our concepts are correct, it might be possible to prevent breast cancer by blocking the aromatase enzyme. Aromatase inhibitors might be more effective than antiestrogens in preventing breast cancer because of their dual role to block both initiation and promotion of breast cancer.     

Estrogens in female thyroid cancer: alteration of urinary profiles in pre- and post-operative cases

To evaluate the potential effect of estrogens in premenopausal female thyroid cancer, the concentrations of 14 estrogens were quantitatively determined in the urine of pre- and post-operative patients with thyroid papillary cancer (18 patients case, 26 approximately 54 years) and normal female subjects (20 cases, 31 approximately 52 years). The highly sensitive gas chromatography-mass spectrometry-selected ion-monitoring method was used for estrogens analysis. And an estrogen-oxidative metabolism and 16alpha-hydroxyestrone to 2-hydroxyestrone (16alpha-OH E1/2-OH E1) which is the two primary and competing site of estrogen-oxidation, were determined. Catechol estrogens, including 2-OH E1, were also increased without significant changes of the other estrogen metabolites in pre-operative patients with thyroid papillary cancer compared with normal subjects. The lowest mean value of 16alpha-OH E1/2-OH E1 was remarked in pre-operative patients, and it was significantly different from the ratio of post-operative cases. As a result, it is suggested that the increase of 2-hydroxylation in estrogen metabolism may have a significant association with female thyroid cancer.     

The relationship between physical activity and 2-hydroxyestrone, 16<Emphasis Type="Italic">α</Emphasis>-hydroxyestrone,and the 2/16 ratio in premenopausal women (United States)

Objectives: Estrogen is metabolized in the body through two mutually exclusive pathways yielding metabolites with different biological activities: the low estrogenic 2-hydroxyestrone (2-OHE1) and the highly estrogenic 16α-hydroxyestrone (16α-OHE1). The ratio of these metabolites (2/16) may be predictive of risk for developing breast cancer. Early evidence has demonstrated that exercise may alter estrogen metabolism to favor the weak estrogen, 2-OHE1. Methods : Seventy-seven eumenorrheic females completed physical activity logs for two weeks prior to providing a luteal phase urine sample. Concentrations of 2-OHE1 and 16α -OHE1 were measured and the 2/16 ratio computed. Hierarchical regression, controlling for age and body mass index (BMI), was used to determine relationships between estrogen metabolites and daily physical activity. Results : Regression analyses indicated significant positive relationships between physical activity and 2-OHE1 and the 2/16 ratio (p < 0.05) that appears to be independent of BMI. 16αOHE1 was not significantly related to physical activity. Conclusion : These results indicate that physical activity may modulate estrogen metabolism to favor the weak estrogen, 2-OHE1, thus producing a higher 2/16 ratio. This alteration in estrogen metabolism may represent one of the mechanisms by which increased physical activity reduces breast cancer risk.     

Lipid peroxidation and DNA adduct formation in lymphocytes of premenopausal women: Role of estrogen metabolites and fatty acid intake

A diet high in linoleic acid (an ω-6 PUFA) increased the formation of miscoding etheno (ε) - DNA adducts in WBC-DNA of women, but not in men (Nair et al., Cancer Epidemiol Biomark Prev 1997;6:597-601). This gender specificity could result from an interaction between ω-6 PUFA intake and estrogen catabolism, via redox-cycling of 4-hydroxyestradiol (4-OH-E(2) ) and subsequent lipid peroxidation (LPO). In this study, we investigated whether in premenopausal women LPO-derived adducts in WBC-DNA are affected by serum concentration of 2- and 4-hydroxyestradiol metabolites and by fatty acid intake. DNA extracted from buffy coat and plasma samples, both blindly coded from healthy women (N = 124, median age 40 year) participating in the EPIC-Heidelberg cohort study were analyzed. Three LPO-derived exocyclic DNA adducts, εdA, εdC and M(1) dG were quantified by immuno-enriched (32) P-postlabelling and estradiol metabolites by ultra-sensitive GC-mass spectrometry. Mean M(1) dG levels in WBC-DNA were distinctly higher than those of εdA and εdC, and all were positively and significantly interrelated. Serum levels of 4-OH-E(2) , but not of 2-OH-E(2) , metabolites were positively related to etheno DNA adduct formation. Positive correlations existed between M(1) dG levels and linoleic acid intake or the ratios of dietary linoleic acid/oleic acid and PUFA/MUFA. Aerobic incubation of 4-OH-E(2) , arachidonic acid and calf thymus DNA yielded two to threefold higher etheno DNA adduct levels when compared with assays containing 2-OH-E(2) instead. In conclusion, this study is the first to compare M(1) dG and etheno-DNA adducts and serum estradiol metabolites in human samples in the same subjects. Our results support a novel mechanistic link between estradiol catabolism, dietary ω-6 fatty acid intake and LPO-induced DNA damage supported by an in vitro model. Similar studies in human breast epithelial tissue and on amplification of DNA-damage in breast cancer patients are in progress.     

Induction by estrogens of lipid peroxidation and lipid peroxidederived malonaldehyde-DNA adducts in male Syrian hamsters: role of lipid peroxidation in estrogen-induced kidney carcinogenesis

Estrogen-induced kidney carcinogenesis in male Syrian hamstershas previously been postulated to be mediated by free radicalsgenerated by redox cycling of catecholestrogen metabolites.As part of our examination of this hypothesis, we have studiedthe induction of lipid peroxidation and lipid peroxide-derivedmalondialdehyde (MDA)-DNA adducts in kidney and liver of hamsterstreated with single injections of diethylstilbestrol (DES) orwith estradiol (E implants for various lengths of time. Treatmentof hamsters with 54) and 100 mg/kg DES increased concentrationsof both lipid hydroperoxides and of MDA-DNA adducts. In hamsterstreated with E Implants for up to 50 days, lipid peroxide levelsin liver were double control values 3 h after hormone implantation,and then decreased to plateau values of 30% over controls. Thosein kidney rose to 2- to 3-fold above controls 3 days after hormoneimplantation and then decreased to plateau values of 51% abovecontrols. MBA-DNA adduct levels were two or three times higherthan those of controls in liver and kidney of hamsters treatedwith hormone implants for 3 and 7 days. Renal lipid peroxideconcentrations were raised by chronic treat ment with E₂, butnot by weakly carcinogenic estrogens ethinylestradiol or 2-fluoroestradiol.In contrast, MDA- DNA adduct levels were raised by all threesteroidal estrogens 3 days after estrogen implantation. Theincreases in lipid peroxides and in MDA-DNA adducts in estrogen-treated hamsters support a mechanism of carcinogenesis by freeradical generation via redox cycling of catcholestrogen metabolites.Lipid peroxides are postulated to play a dual role in estrogen-inducedcarcinogenesis, (i) as cofactors for cytochrome P450-mediatedformation of catecholestrogen metabolites and their redox cycling,and (ii) as precursors of MDA, a DNA adduct-forming endogenouselectrophile.     

A population‐based cohort study on the use of hormone treatment and endometrial cancer in southern Sweden

Our aim was to determine the risk of endometrial cancer associated with long‐term use of combined hormone therapy (HT) and low‐potency estrogens. In this prospective population‐based cohort, 40,000 women aged 25–64 years, without prior cancer or hysterectomy, were included. The women answered 2 questionnaires at a 10‐year interval regarding HT use and personal details. Women were followed up for an average of 15.5 years through the National Cancer and Causes of Death Registry, representing 236,611 women years. Among the 17,822 postmenopausal women included, 166 cases of endometrial cancer were diagnosed. Only use of combined HT was related to a decreased risk of endometrial cancer (OR 0.3, 95% CI 0.1–0.8), the protective effect was found after 2 years, and increased with extended duration of use. “Only use” of low‐potency estrogens increased the risk of endometrial cancer almost to the same extent as use of high‐potency estrogens (OR 2.0, 95% CI 1.1–3.6 vs. OR 2.5, 95% CI 1.3–4.8), the increased risk was confined to non‐obese women in both groups. The risk was significantly increased for oral but not for local low‐potency estrogen users (OR 2.1, 95% CI 1.1–3.6 vs. OR 1.5, 95% CI 0.4–6.2, respectively). In long‐term estrogen users the risk was highest during the first 2 years, dropping slightly thereafter. Since low‐potency estrogen use increases the risk of endometrial cancer almost as much as high‐potency estrogen use, they should only be given if medically indicated. © 2009 UICC     

Relationships between critical period of estrogen exposure and circulating levels of insulin‐like growth factor‐I (IGF‐I) in breast cancer: evidence from a case‐control study

Epidemiological observations suggest that insulin‐like growth factor‐I (IGF‐I), a potent mitogenic and anti‐apoptotic peptide, plays a role in the etiology of breast cancer. Estrogen, which is crucial in breast carcinogenesis, both regulates and is influenced by IGF‐I family. A case‐control study was conducted to assess the role of IGF‐I as a biomarker for breast cancer and to evaluate the potential joint effect of circulating IGF‐I and critical period of estrogen exposure, as estimated by the interval between age at menarche and age at first full‐term pregnancy on the risk of breast cancer. Questionnaire information and blood samples were taken before treatment from 297 incident cases with breast cancer and 593 controls admitted for health examination at the Tri‐Service General Hospital, Taipei between 2004 and 2006. Plasma levels of IGF‐I and IGFBP‐3 were measured by immunoradiometric assay. Conditional logistic regression was used to calculate odds ratios (ORs) and their 95% confidence intervals (CIs). Our case‐control data indicate that breast cancer risk related to IGF‐I differs according to menopausal status. High circulating levels of IGF‐I increased risk of pre‐ but not postmenopausal breast cancer (top vs. bottom tertile, adjusted OR, 1.86; 95% CI, 1.01–3.44). Furthermore, elevated IGF‐I concentrations in conjunction with prolonged interval of critical period of estrogen exposure were associated with significantly increased risk of breast cancer, particularly among estrogen‐positive cases (adjusted OR, 2.42, 95% CI, 1.33–4.38). These results suggest that the joint effect of IGF‐I and estrogens may provide novel methods of breast cancer risk reduction among women.     

DNA adduct formation in liver and kidney of male Syrian hamsters treated with estrogen and/or alpha-naphthoflavone

Chronic administration of estrogens to male Syrian hamsters induces kidney tumors. Co-administration of estrogen plus alpha-naphthoflavone (ANF) suppresses this kidney carcinogenesis but induces liver tumors instead. In an attempt to elucidate the mechanism of the switch from estrogen-induced kidney to liver carcinogenesis in response to ANF treatment, patterns of kidney and liver DNA adducts were investigated by 32P-postlabeling analysis and compared to controls. Chronic treatment of hamsters with ANF alone or in combination with estradiol resulted in a flavone-specific DNA adduct pattern in livers of these animals. These spots, adducts 1 and 2, on 32P-postlabeling maps were taken as evidence of covalent ANF-DNA modifications. The kidney-specific estrogen-induced indirect DNA adducts, observed previously in hamsters treated chronically with estrogen, occurred in renal but not hepatic DNA of animals treated with estradiol alone or in combination with ANF. Pretreatment of hamsters with ANF for 3 days decreased by 75-80% the hepatic and renal diethylstilbestrol (DES)-DNA adducts, which are formed after injection of a single large dose of DES. It is concluded from these changes in DNA adduct patterns and levels that estrogen quinone-DNA adduction may play an etiological role in estrogen-induced kidney cancer. The prevention of estrogen-induced kidney tumors by ANF co-treatment may be a consequence of the decrease in renal concentrations of these adducts in response to ANF. Hepatic concentrations of estrogen quinone-DNA adducts also decrease, but ANF-DNA adducts, observed only in liver, may assume an etiological role in the induction of hepatomas.