van Duursen Majorie B M, Sanderson J Thomas, van der Bruggen Marieke, van der Linden Jeroen, van den Berg Martin
Institute for Risk Assessment Sciences (IRAS), Utrecht University, The Netherlands.
Toxicol Appl Pharmacol. 2003 Aug 1;190(3):241-50. doi: 10.1016/s0041-008x(03)00166-2.
In human breast tissue, estrone (E(1)) and estradiol (E(2)) are mainly hydroxylated by cytochrome P450 1A1 (CYP1A1) and 1B1 (CYP1B1) to 2-hydroxyestrogens (2-OHE(1/2)) and 4-hydroxyestrogens (4-OHE(1/2)), respectively. Several studies show that 4-OHE(1/2), but not 2-OHE(1/2), may act as a carcinogen and a high estrogen 4-/2-hydroxylation ratio appears to be a marker for the presence of neoplasms. In this study, we investigated the effects of several dioxin-like compounds on estrogen 2- and 4-hydroxylation in a malignant (MCF-7) and a nontumorigenic (MCF-10A) human mammary epithelial cell line. 2- and 4-methoxyestrogen (MeOE(1/2)) formations were used as measures of the 2- and 4-hydroxylation pathways, respectively. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), and 3,3'4,4',5,5'-hexachlorobiphenyl (PCB 169) concentration dependently induced 2-MeOE(1/2) formation and ethoxyresorufin-O-deethylation (EROD) activity through induced CYP1A1 expression in MCF-7 and MCF-10A cells. 2,3',4,4',5-pentachlorobiphenyl (PCB 118) had no such effect. Effects on CYP1B1 expression and 4-MeOE(1/2) formation were less pronounced; only TCDD caused an induction, whereas PCB 169 was a potent and selective inhibitor of 4-MeOE(1/2) formation (IC(50) 0.7 and 2.2 nM PCB 169 in MCF-7 and MCF-10A cells, respectively). MCF-10A cells were less responsive toward dioxin-like compounds and the apparent EC(50) values for CYP1A1 and CYP1B1 induction in this study were 10-100 fold higher than in MCF-7 cells. The constitutive 4-/2-MeOE(1/2) ratios were 2.99 +/- 0.78 and 0.93 +/- 0.40 in MCF-7 and MCF-10A, respectively. Incubation with dioxin-like compounds resulted in a concentration-dependent decrease in the 4-/2-MeOE(1/2) ratio, but an increase in potentially carcinogenic estrogen metabolites in both MCF-7 and MCF-10A cells. This indicates that even though the 4-/2-OHE(1/2) ratio may be used as indicator for the presence of neoplasms, it is readily lowered by dioxin-like compounds and its value as a prognostic parameter for cancer risk should be further examined.
在人体乳腺组织中，雌酮（E(1)）和雌二醇（E(2)）主要分别被细胞色素P450 1A1（CYP1A1）和1B1（CYP1B1）羟基化为2-羟基雌激素（2-OHE(1/2)）和4-羟基雌激素（4-OHE(1/2)）。多项研究表明，4-OHE(1/2)而非2-OHE(1/2)可能具有致癌作用，且较高的雌激素4-/2-羟基化比率似乎是肿瘤存在的一个标志物。在本研究中，我们研究了几种二噁英类化合物对恶性（MCF-7）和非致瘤性（MCF-10A）人乳腺上皮细胞系中雌激素2-和4-羟基化的影响。分别以2-甲氧基雌激素（MeOE(1/2)）和4-甲氧基雌激素（MeOE(1/2)）的生成作为2-和4-羟基化途径的指标。2,3,7,8-四氯二苯并-p-二噁英（TCDD）、2,3,4,7,8-五氯二苯并呋喃（PCDF）、3,3',4,4',5-五氯联苯（PCB 126）和3,3'4,4',5,5'-六氯联苯（PCB 169）通过诱导MCF-7和MCF-10A细胞中CYP1A1的表达，浓度依赖性地诱导2-MeOE(1/2)的生成和乙氧基异吩嗪酮-O-脱乙基酶（EROD）活性。2,3',4,4',5-五氯联苯（PCB 118）没有这种作用。对CYP1B1表达和4-MeOE(1/2)生成的影响不太明显；只有TCDD引起诱导，而PCB 169是4-MeOE(1/2)生成的强效选择性抑制剂（MCF-7和MCF-10A细胞中PCB 169的IC(50)分别为0.7和2.2 nM）。MCF-10A细胞对二噁英类化合物的反应较小，本研究中CYP1A1和CYP1B1诱导的表观EC(50)值比MCF-7细胞高10 - 100倍。MCF-7和MCF-10A中组成型4-/2-MeOE(1/2)比率分别为2.99±0.78和0.93±0.40。用二噁英类化合物孵育导致4-/2-MeOE(1/2)比率浓度依赖性降低，但MCF-7和MCF-10A细胞中潜在致癌性雌激素代谢物增加。这表明，尽管4-/2-OHE(1/2)比率可作为肿瘤存在的指标，但它很容易被二噁英类化合物降低，其作为癌症风险预后参数的价值应进一步研究。
