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

Estrogenized HSA induced high-affinity autoantibodies in breast cancer - Novel biomarker for early detection

Objective

Breast cancer (BC) is the second most prevalent cancer worldwide. Estrogen has been increasingly recognized as a major contributor to the development of BC, playing a more critical role than previously understood. Estrogen derived nucleic acid and protein adducts have been shown to play significant roles in BC development and progression. However, the alterations in molecular mechanism(s) and immune pathways arising as a result of estrogenization still remain elusive.

Patients and methods

4-hydroxyestradiol (4-OHE2) was used for adduct formation with protein human serum albumin (HSA) (4-OHE2-HSA). The affinity of antibodies for 4-OHE2-HSA was evaluated in breast cancer patients. Immunoassays (direct binding ELISA, inhibition ELISA, and quantitative precipitin titration assay) were used to assess autoantibodies against estrogenized HSA in BC patients (n = 85) and healthy controls (n = 45).

Results

Estrogenization of HSA altered both its structure and function and compromised its interactions with various HSA-binding proteins. BC patients demonstrated high-affinity antibodies against 4-OHE2-HSA as compared to HSA (p < 0.05). Additionally, cytokines Interleukin (IL)-1, IL-6 and tumor necrosis factor-alpha (TNF-α) were significantly elevated in BC patients as compared to the control group. Several factors, such as chemotherapy, estrogen receptors (ERs), and combination of surgery and chemotherapy, influenced the production of antibodies in cancer patients. The affinity constant for estrogenized HSA was 1.31 × 10-7 M, while for HSA and 4-OHE2, it was 1.68 × 10-6 M and 1.36 × 10-6 M, respectively.

Conclusions

Estrogenized HSA is highly immunogenic, resulting in functional alterations. High affinity antibodies were detected in BC patients against 4-OHE2-HSA. Consequently, 4-OHE2-HSA may serve as a novel molecular target for potential cancer therapeutics. Furthermore, autoantibodies against 4-OHE2-HSA could serve as a potential biomarker for early detection of BC.

The Importance of Hypoxia-Related to Hemoglobin Concentration in Breast Cancer

The importance of hemoglobin (Hgb) as a novel prognostic biomarker in predicting clinical features of cancers has been the subject of intense interest. Anemia is common in various types of cancer including breast cancer (BC) and is considered to be attributed to tumoral hypoxia. Cancer microenvironments are hypoxic compared with normal tissues, and this hypoxia is associated with Hgb concentration. Recent preclinical documents propose a direct or indirect correlation of intratumoral hypoxia, specifically along with acidity, with Hgb concentration and anemia. Analysis of the prognostic value of Hgb in BC patients has demonstrated increased hypoxia in the intratumoral environment. A great number of studies demonstrated that lower concentrations of Hgb before or during common cancer treatments, such as radiation and chemotherapy, is an essential risk factor for poor prognostic and survival, as well as low quality of life in BC patients. This data suggests a potential correlation between anemia and hypoxia in BC. While low Hgb levels are detrimental to BC invasion and survival, identification of a distinct and exact threshold for low Hgb concentration is challenging and inaccurate. The optimal thresholds for Hgb and partial pressure of oxygen (pO2) vary based on different factors including age, gender, therapeutic approaches, and tumor types. While necessitating further investigations, understanding the correlation of Hgb levels with tumoral hypoxia and oxygenation could improve exploring strategies to overcome radio-chemotherapy related anemia in BC patients. This review highlights the collective association of Hgb concentration and hypoxia condition in BC progression.

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.

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.

16α-Hydroxyestrone: Mass Spectrometry-Based Methodologies for the Identification of Covalent Adducts Formed with Blood Proteins

Elevated levels of the estrone metabolite, 16α-hydroxyestrone (16αOHE1), have been linked with multiple diseases. As an electrophilic reactive metabolite, covalent binding to proteins is thought to constitute one of the possible mechanisms in the onset of deleterious health outcomes associated with 16αOHE1. Whereas mass spectrometry (MS)-based methodologies are currently considered the best suited to monitor the formation of protein covalent adducts, the application of these approaches for the identification of covalent adducts of 16αOHE1 is yet to be provided. In the present study, with the ultimate goal of determining the most adequate methodology for searching for 16αOHE1-derived covalent adducts, we explored multiple liquid chromatography-electrospray ionization tandem high-resolution mass spectrometry (LC-ESI-HRMS/MS)-based approaches to investigate the nature and specific locations of the covalent adducts produced in human hemoglobin (Hb) and human serum albumin (HSA) modified in vitro with 16αOHE1. The application of a "bottom up" proteomics approach, involving the nanoLC-ESI-HRMS/MS analysis of tryptic peptides, allowed the identification of multiple sites of 16αOHE1 adduction in Hb and HSA. As expected, the majority of the adducted peptides occurred in lysine residues following stabilization of the Schiff base formed with 16αOHE1 by reduction or via Heyns rearrangement, yielding the stable α-hydroxyamine and ketoamine adducts, respectively. Noteworthy is the fact that a serine residue was also identified to be covalently modified with 16αOHE1, which to our knowledge constitutes a first-hand report of a keto electrophile as target of hydroxyl-based nucleophilic amino acids. The N-alkyl Edman degradation resulted to be unsuitable for the identification of 16αOHE1adducts formed with the N-terminal valine of Hb, most probably due to stereochemical restraints of the tested derivatizing agents (fluorescein isothiocyanate and phenyl isothiocyanate) on assessing these bulky covalent adducts. Nonetheless, the digestion of adducted proteins to amino acids resulted in the detection of 16αOHE1-derived keto and α-hydroxyamine Lys adducts. The simplicity of this methodology might be beneficial for clinical studies, with the possibility of offering quantitative information with the preparation of synthetic standards of these adducts. The results obtained are crucial not only for the identification and quantification of biomarkers of exposure to 16αOHE1 but also for clarifying the role of protein binding in the onset of diseases associated with elevated levels of this reactive metabolite.

Imbalances in the disposition of estrogen and naphthalene in breast cancer patients: a potential biomarker of breast cancer risk

Elevation of naphthoquinones and estrogen quinones, which are reactive metabolites of naphthalene and estrogen, is thought to be an important indicator of naphthalene- and estrogen-induced carcinogenesis. We compared background levels of naphthalene and estrogen quinone-derived adducts in serum albumin (Alb) from 143 women with breast cancer and 119 healthy controls. Cysteinyl adducts of naphthoquinones, including 1,2-naphthoquinone (1,2-NPQ) and 1,4-naphthoquinone (1,4-NPQ), and estrogen quinones, including estrogen-2,3-quinones (E₂-2,3-Q) and estrogen-3,4-quinones (E₂-3,4-Q), were characterized after adduct cleavage. Levels of estrogen quinones and naphthoquinones were positively correlated in healthy controls, but not in breast cancer patients (p < 0.05). Compared with controls, levels of 1,2-NPQ and E₂-3,4-Q were elevated by two- to ten-fold in cancer patients (p < 0.001). To explore the correlation between estrogen- and naphthalene-derived quinone adducts and disease status, we performed linear discriminant analysis of the ratio of 1,2-NPQ-Alb to (1,2-NPQ-Alb plus 1,4-NPQ-Alb) versus the ratio of E₂-3,4-Q-2-S-Alb to (E₂-2,3-Q-4-S-Alb plus E₂-3,4-Q-2-S-Alb) in patients and controls. These two groups were separable using albumin adducts of estrogen quinones and naphthoquinones, with 99.6% overall correct classification rate (overall accuracy). The findings of this study suggest that differences in the disposition of estrogen and naphthalene, and the subsequent elevation of cumulative E₂-3,4-Q and 1,2-NPQ may serve as biomarkers of breast cancer risk.

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.

Mass Spectrometry-Based Methodologies for Targeted and Untargeted Identification of Protein Covalent Adducts (Adductomics): Current Status and Challenges

Protein covalent adducts formed upon exposure to reactive (mainly electrophilic) chemicals may lead to the development of a wide range of deleterious health outcomes. Therefore, the identification of protein covalent adducts constitutes a huge opportunity for a better understanding of events underlying diseases and for the development of biomarkers which may constitute effective tools for disease diagnosis/prognosis, for the application of personalized medicine approaches and for accurately assessing human exposure to chemical toxicants. The currently available mass spectrometry (MS)-based methodologies, are clearly the most suitable for the analysis of protein covalent modifications, providing accuracy, sensitivity, unbiased identification of the modified residue and conjugates along with quantitative information. However, despite the huge technological advances in MS instrumentation and bioinformatics tools, the identification of low abundant protein covalent adducts is still challenging. This review is aimed at summarizing the MS-based methodologies currently used for the identification of protein covalent adducts and the strategies developed to overcome the analytical challenges, involving not only sample pre-treatment procedures but also distinct MS and data analysis approaches.