title: 17beta-Estradiol nitration by peroxidase/H2O2/NO2-: a chemical assessment.
abstract: Nitration of 17beta-estradiol by H(2)O(2) and nitrite in the presence of various peroxidases, viz. horseradish peroxidase, lactoperoxidase, and peroxidase-containing homogenates from bovine uteri, was systematically investigated to assess on a chemical basis its potential relevance to the mechanisms of impairment of estrogen functions under oxidative/nitrosative stress conditions. In the presence of excess nitrite 17beta-estradiol reacted smoothly to give 2-nitroestradiol (1), 4-nitroestradiol (2), and 2,4-dinitroestradiol (3). With 10-300 microM estradiol, formation yields of 1-3 were 12-55%, but dropped to 1% or less at lower estrogen concentration, for example, 1 microM, or in plasma as the reaction medium. Time course analysis showed that 2 is the prevalent nitration product under conditions of slow generation of nitrating species, suggesting some regioselectivity for estradiol nitration at C-4, whereas 1 prevails with bolus addition of reagents, due to faster degradation of 2. Competition experiments carried out with (15)NO(2)- showed that 2 is about twice more susceptible to nitration than 1 as determined by (15)N NMR analysis of the resulting 3. The biological effects of 1 and 2 were preliminarily tested on in vitro bovine embryo cultures. When 1 and 2 were substituted to the standard 17beta-estradiol in the oocyte maturation, a significant decrease in both cleavage and blastocyst efficiency was observed in the case of 1 but not 2. Overall, these results suggest that estradiol nitration is a potential pathway of hormonal dysfunction and toxicity but would require elevated estrogen levels of questionable physiological relevance.
authors.affiliation: Department of Organic Chemistry and Biochemistry, University of Naples Federico II, Complesso Universitario Monte S. Angelo, Via Cinthia 4, I-80126 Naples, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pezzella
authors.forename: Paola
authors.initials: P
authors.lastname: Manini
authors.forename: Paola
authors.initials: P
authors.lastname: Di Donato
authors.forename: Raffaele
authors.initials: R
authors.lastname: Boni
authors.forename: Alessandra
authors.initials: A
authors.lastname: Napolitano
authors.forename: Anna
authors.initials: A
authors.lastname: Palumbo
authors.forename: Marco
authors.initials: M
authors.lastname: d'Ischia
mesh_terms: D000818:Animals; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry* / Q000378:metabolism; D007784:Lactoperoxidase / Q000737:chemistry / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry*; D009865:Oocytes / Q000187:drug effects; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors; D014599:Uterus / Q000201:enzymology
chemical_list: D009573:Nitrites; D004958:Estradiol; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D007784:Lactoperoxidase; D010544:Peroxidases