Hemoglobin adducts as biomarkers of estrogen homeostasis: Elevation of estrogenquinones as a risk factor for developing breast cancer in Taiwanese Women

Investigation of the abasic sites induced by hydrogen peroxide and methyl methanesulfonate in calf thymus DNA and BEAS-2B cells

The primary goals of this study were to investigate the formation of abasic sites (AP sites) induced by methyl methanesulfonate (MMS) and hydrogen peroxide (H2O2), and to characterize specific types of these pro-mutagenic DNA lesions in calf thymus DNA (CT-DNA), and BEAS-2B human lung normal cell line. Furthermore, these profiles were compared with those observed in leukocytes derived from healthy controls (HC), breast cancer patients (BCP) before treatment, and 5-year survivors. Results indicated that both H2O2 and MMS induced the concentration- and time-dependent formation of AP sites in CT-DNA. To characterize the specific types of AP sites induced by H2O2 or MMS, we performed AP site cleavage assay using putrescine, T7 exonuclease (T7 Exo), and exonuclease III (Exo III). Results showed that the AP sites induced by H2O2 in CT-DNA were predominantly 5'-and 3'-nicked AP sites and no intact AP sites were detected. By contrast, the majority of AP sites generated by MMS in CT-DNA are not excisable and are classified as residual and intact AP sites. Similar approaches were performed in human BEAS-2B cells and comparable observations were confirmed in the cell-based model. Further investigation indicated that the profile of the AP sites observed in Taiwanese HC is identical to that of BEAS-2B cells treated with H2O2 whereas the pattern of AP sites detected in BCP is similar to that of CT-DNA exposed to H2O2, suggesting that these AP sites were produced primarily through reactive oxygen species (ROS) generation. More than 70 % of the AP sites in leukocytes derived from BCP were 5'-nicked and residual AP sites. Furthermore, the characteristics of the AP sites detected in 5-year survivors are comparable with the ones in HC by using putrescine cleavage assay. Overall, we speculate that deficiency in the DNA repair cascade may play a role in mediating the formation of specific types of AP sites detected in BCP.

Analysis of the Abasic Sites in Breast Cancer Patients With 5 Year Postoperative Treatment Without Recurrence in Taiwan

PURPOSE

This prospective study aimed to investigate estrogen-induced carcinogenesis by assessing the background levels of abasic sites (apurinic/apyrimidinic sites, AP sites) in Taiwanese breast cancer patients following 5 years of postoperative treatment without recurrence (5-year survivors) (n = 70). The study also sought to compare the extent of these DNA lesions with those found in healthy controls and in breast cancer patients prior to treatment.

METHODS

Abasic sites were measured using an aldehyde reactive probe and quantified as the total number of abasic sites per total nucleotides. Characterization of the abasic sites in subjects recruited for this study was conducted using the abasic site cleavage assay using putrescine or T7 exonuclease (T7 Exo) and/or exonuclease III (Exo III).

RESULTS

The number of abasic sites detected in 5 year survivors (26.7 ± 10.2 per 106 total nucleotides, n = 70) was significantly reduced by 46.9% compared to those in breast cancer patients before treatment (50.3 ± 59.2 per 106 total nucleotides, P < 0.001), and was similar to the levels observed in healthy controls (23.3 ± 13.5 per 106 total nucleotides, P > 0.05). Further investigation into the specific types of abasic sites indicated that the number of abasic sites excisable by putrescine in controls, breast cancer patients, and 5-year survivors were 63.3%, 78.6%, and 67.7%, respectively. These findings suggest the involvement of oxidative stress rather than depurination/depyrimidination of DNA adducts in the formation of abasic sites. Further analyses were performed using exonuclease cleavage assay to characterize the specific types of abasic sites including 5'-cleaved, 3'-cleaved, intact, and residual abasic sites. Results demonstrated that the proportion of residual abasic sites detected in controls, breast cancer patients, and 5-year survivors were estimated to be 32.7%, 48.8%, and 34.0%, respectively.

CONCLUSION

Overall, these findings suggest clear evidence of treatment-related effects on the reduction of levels of abasic sites as well as on the profile of abasic sites in 5 year survivors.

Profiling of Protein Adducts of Estrogen Quinones in 5-Year Survivors of Breast Cancer Without Recurrence

Aims

The aim of this study was to simultaneously analyze estrogen quinone-derived adducts, including 17β-estradiol-2,3-quinone (E₂-2,3-Q) and 17β-estradiol-3,4-quinone (E₂-3,4-Q), in human albumin (Alb) and hemoglobin (Hb) derived from breast cancer patients with five-year postoperative treatment without recurrence in Taiwan and to evaluate the treatment-related effects on the production of these adducts.

Settings and Design

Cohort

Methods and Material: Blood samples derived from breast cancer 5-year survivors without recurrence were collected. Albumin and hemoglobin adducts of E₂-3,4-Q and E₂-2,3-Q were analyzed to evaluate the degree of disposition of estrogen to quinones and to compare these adduct levels with those in patients before treatment.

Statistical Analysis

All data are expressed as mean ± standard deviation of three determinations. We used Student’s t-test to examine subgroups. Data were transformed to the natural logarithm and tested for normal distribution for parametric analyses. Linear correlations were investigated between individual adduct levels by simple regression. Statistical analysis was performed using the SPSS Statistics 20.0.

Results

Result confirmed that logged levels of E₂-2,3-Q-derived adducts correlated significantly with those of E₂-3,4-Q-derived adducts (correlation coefficient r=.336-.624). Mean levels of E₂-2,3-Q-4-S-Alb and E₂-3,4-Q-2-S-Alb in 5-year survivors were reduced by 60-70% when compared to those in the breast cancer patients with less than one year of diagnosis/preoperative treatment (P<.001).

Conclusions

Our findings add support to the theme that hormonal therapy including aromatase inhibitors and Tamoxifen may dramatically reduce burden of estrogen quinones. We hypothesize that combination of treatment-related effects and environmental factors may modulate estrogen homeostasis and diminish the production of estrogen quinones in breast cancer patients.

Quo vadis blood protein adductomics?

Chemicals are measured regularly in air, food, the environment, and the workplace. Biomonitoring of chemicals in biological fluids is a tool to determine the individual exposure. Blood protein adducts of xenobiotics are a marker of both exposure and the biologically effective dose. Urinary metabolites and blood metabolites are short term exposure markers. Stable hemoglobin adducts are exposure markers of up to 120 days. Blood protein adducts are formed with many xenobiotics at different sites of the blood proteins. Newer methods apply the techniques developed in the field of proteomics. Larger adducted peptides with 20 amino acids are used for quantitation. Unfortunately, at present the methods do not reach the limits of detection obtained with the methods looking at single amino acid adducts or at chemically cleaved adducts. Therefore, to progress in the field new approaches are needed.

Quantification of the Endogenous Adduction Level on Hemoglobin and Correlation with Albumin Adduction via Proteomics: Multiple Exposure Markers of Catechol Estrogen

Catechol estrogens (CEs) are genotoxic metabolites whose detection is challenging due to their low concentrations and high variability in the blood. By intact protein and free CE measurement of the spiked hemolysate, endogenous CEs were revealed to mainly (>99%) exist as hemoglobin (Hb) adducts in red blood cells. In order to detect endogenous CE-Hb adducts, we developed a two-step method that involved protein precipitation and solid phase extraction to purify Hb from red blood cells, and the method was coupled with proteomics using liquid chromatography-tandem mass spectrometry. Using bottom-up proteomics and standard additions, we identified C93 and C112 of Hb-β as the main adduction sites of Hb, and this accounted for CE-induced oxidization of adducted peptides by sample preparation. The non-adducted, adducted, and oxidized tryptic peptides that covered the same Hb-β sequences were targeted by parallel reaction monitoring to determine the adduction level in red blood cells. A quantification limit (S/N < 8) below the endogenous CE-Hb adduction level with relative standard errors that ranged from 5 to 22% was achieved and applied to clinical samples. The human serum albumin (HSA) adduction levels from the same patient were also determined using a previously developed method (Anal. Chem. 2019, 91, 15922-15931). A positive correlation (R² = 0.673) between the CE-HSA and CE-Hb adduction level was obtained from all clinical samples, and both levels were significantly (p < 0.005) higher for patients with breast cancer compared to healthy controls. However, double indexes derived from the red blood cell and the serum, respectively, provide higher precision and confidence in predicting cancer risk than the single index. This study reported an efficient sample preparation for proteomics-based Hb adducts and revealed the potential of using multiple blood proteins for developing more reliable and specific markers based on protein adductomics.

Mode of action-based risk assessment of genotoxic carcinogens

The risk assessment of chemical carcinogens is one major task in toxicology. Even though exposure has been mitigated effectively during the last decades, low levels of carcinogenic substances in food and at the workplace are still present and often not completely avoidable. The distinction between genotoxic and non-genotoxic carcinogens has traditionally been regarded as particularly relevant for risk assessment, with the assumption of the existence of no-effect concentrations (threshold levels) in case of the latter group. In contrast, genotoxic carcinogens, their metabolic precursors and DNA reactive metabolites are considered to represent risk factors at all concentrations since even one or a few DNA lesions may in principle result in mutations and, thus, increase tumour risk. Within the current document, an updated risk evaluation for genotoxic carcinogens is proposed, based on mechanistic knowledge regarding the substance (group) under investigation, and taking into account recent improvements in analytical techniques used to quantify DNA lesions and mutations as well as "omics" approaches. Furthermore, wherever possible and appropriate, special attention is given to the integration of background levels of the same or comparable DNA lesions. Within part A, fundamental considerations highlight the terms hazard and risk with respect to DNA reactivity of genotoxic agents, as compared to non-genotoxic agents. Also, current methodologies used in genetic toxicology as well as in dosimetry of exposure are described. Special focus is given on the elucidation of modes of action (MOA) and on the relation between DNA damage and cancer risk. Part B addresses specific examples of genotoxic carcinogens, including those humans are exposed to exogenously and endogenously, such as formaldehyde, acetaldehyde and the corresponding alcohols as well as some alkylating agents, ethylene oxide, and acrylamide, but also examples resulting from exogenous sources like aflatoxin B1, allylalkoxybenzenes, 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx), benzo[a]pyrene and pyrrolizidine alkaloids. Additionally, special attention is given to some carcinogenic metal compounds, which are considered indirect genotoxins, by accelerating mutagenicity via interactions with the cellular response to DNA damage even at low exposure conditions. Part C finally encompasses conclusions and perspectives, suggesting a refined strategy for the assessment of the carcinogenic risk associated with an exposure to genotoxic compounds and addressing research needs.

Detection and Characterization of Catechol Quinone-Derived Protein Adducts Using Biomolecular Mass Spectrometry

The catechol quinone (CQ) motif is present in many biologically relevant molecules throughout endogenous metabolic products, foods, drugs, and environmental pollutants. The CQ derivatives may undergo Michael addition, and has been shown to yield covalent bonds with nucleophilic sites of cysteine, lysine, or histidine residue of proteins. The CQ-adducted proteins may exhibit cytotoxicity or biological functions different from their un-adducted forms. Identification, characterization, and quantification of relevant protein targets are essential but challenging goals. Mass spectrometry (MS) is well-suited for the analysis of proteins and protein modifications. Technical development of bottom-up proteomics has greatly advanced the field of biomolecular MS, including protein adductomics. This mini-review focuses on the use of biomolecular MS in (1) structural and functional characterization of CQ adduction on standards of proteins, (2) identification of endogenous adduction targets, and (3) quantification of adducted blood proteins as exposure index. The reactivity and outcome of CQ adduction are discussed with emphases on endogenous species, such as dopamine and catechol estrogens. Limitations and advancements in sample preparation, MS instrumentation, and software to facilitate protein adductomics are also discussed.

Albumin and hemoglobin adducts of estrogen quinone as biomarkers for early detection of breast cancer

Cumulative estrogen concentration is an important determinant of the risk of developing breast cancer. Estrogen carcinogenesis is attributed to the combination of receptor-driven mitogenesis and DNA damage induced by quinonoid metabolites of estrogen. The present study was focused on developing an improved breast cancer prediction model using estrogen quinone-protein adduct concentrations. Blood samples from 152 breast cancer patients and 71 healthy women were collected, and albumin (Alb) and hemoglobin (Hb) adducts of estrogen-3,4-quinone and estrogen-2,3-quinone were extracted and evaluated as potential biomarkers of breast cancer. A multilayer perceptron (MLP) was used as the predictor model and the resultant prediction of breast cancer was more accurate than other existing detection methods. A MLP using the logarithm of the concentrations of the estrogen quinone-derived adducts (four input nodes, 10 hidden nodes, and one output node) was used to predict breast cancer risk with accuracy close to 100% and area under curve (AUC) close to one. The AUC value of one showed that both data sets were separable. We conclude that Alb and Hb adducts of estrogen quinones are promising biomarkers for the early detection of breast cancer.

Genetic polymorphisms in APE1 Asp148Glu(rs3136820) as a modifier of the background levels of abasic sites in human leukocytes derived from breast cancer patients and controls

BACKGROUND

Apurinic/apyrimidinic (abasic/AP) sites are among the most common endogenous DNA lesions. AP sites, if not repaired, could result in genomic instability as well as chromosome aberrations. Information regarding the direct assay of the number of abasic sites in human leukocytes and its association with risk of breast cancer has not been reported.

METHODS

In this study, we investigated the association between certain risk factors for breast cancer and the background levels of AP sites in leukocytes derived from 148 Taiwanese women with breast cancer and 140 cancer-free controls. The risk factors studied include age, body mass index (BMI), and polymorphisms of apurinic/apyrimidinic endonuclease (APE1) [APE1 Asp148Glu(rs3136820)].

RESULTS

Mean levels of AP sites were estimated to be 23.3 and 50.3 per 10⁶ nucleotides in controls and breast cancer patients, respectively (~twofold, p < 0.001). In subjects with age <50 or BMI < 27 (kg/m²), the levels of AP sites in breast cancer patients were ~2-3-fold greater than those of controls (p < 0.05). Additionally, results from the AP site 3'-cleavage assay indicated that the AP sites detected in both controls and patients were likely to be oxidant-mediated 5'-cleaved AP sites (~61-64 %). The number of AP sites in breast cancer patients was ~twofold greater in subjects with Asp/Glu + Glu/Glugenotypes than those with Asp/Asp genotype (p < 0.001).

CONCLUSIONS

We confirmed that cumulative body burden of AP sites is a significant predictor of the risk of developing breast cancer and that genetic predisposition and environment factors may modulate the induction of oxidative DNA lesions in breast cancer patients.

Mechanisms of estrogen carcinogenesis: The role of E2/E1-quinone metabolites suggests new approaches to preventive intervention--A review

Studies in hamsters, mice and rats have demonstrated that estradiol (E2), its interconvertible metabolite estrone (E1) and their catechol metabolites, in particular 4-hydroxy E2/E1, are carcinogenic in the kidney, uterus and mammary gland. Observational studies and clinical trials consistently show that sustained exposure to E2/E1 is associated with the development of sporadic breast cancer. The weight of evidence supports the contribution of two complementary pathways in the initiation, promotion and progression of breast cancer. One pathway involves activation of nuclear and cytoplasmic signaling pathways through the binding of estrogen to nuclear and membrane-bound estrogen receptors leading to increased cell proliferation. The other pathway involves the oxidative metabolism of E2/E1 to catechols and then reactive quinones that can contribute to oxidative DNA damage and form specific, mutagenic depurinating adducts with adenine and guanine which then in turn can serve as biomarkers for the occurrence of these processes. Both pathways can serve as portals to preventive intervention. Antiestrogens are used clinically to block receptor-mediated signaling to block tumor growth. Various chemopreventive agents such as sulforaphane (SFN) and resveratrol have been shown in cell culture to block oxidative metabolism of E2/E1 and thus prevent DNA damage. Pretreatment of MCF-7 and MCF-10F cells with and inhibitor of catechol-O-methyltransferase (COMT) followed by treatment with E2 or 4-OH E2 caused increased oxidative DNA damage (8-oxo-dG) and depurinating DNA adducts showing the importance of E2-catechol O-methylation by COMT as a protective pathway. E2 treatment of MCF-10A cells with E2 or 4-OH E2 caused an increase in E2-adenine and guanine adducts. Treatment with sulforaphane increased

NAD(P)H

quinone oxidoreductase 1 (NQO1) and glutathione-S-transferase A1 (GSTA1) expression without affecting expression of catechol-O-methyltransferase (COMT) or cytochrome P450 1B1. Pretreatment with SFN decreased depurinating DNA adducts while increasing levels of 4-OCH3E1/2 and 4-OHE1/2-glutathione conjugates. Treatment of MCF-10F cells with E2 or 4-OH-E2 also caused increased depurinating DNA adducts and neoplastic transformation while pretreatment with resveratrol caused a reduction in adduct levels and neoplastic transformation. Increased levels of estrogen-quinone conjugates and DNA adducts have also been detected in urine of women at increased risk for and with breast cancer. These observations support the notion that targeting the estrogen/estrone metabolism pathway may be another way to reduce breast cancer risk.