Tai H L, McReynolds J H, Goldstein J A, Eugster H P, Sengstag C, Alworth W L, Olson J R
Department of Pharmacology and Therapeutics, University at Buffalo, New York 14214.
Toxicol Appl Pharmacol. 1993 Nov;123(1):34-42. doi: 10.1006/taap.1993.1218.
Previous studies have established that TCDF is rapidly metabolized and excreted in rats and that pretreatment of rats with TCDD increases the rate of hepatic metabolism of this compound. The extrahepatic metabolism of TCDF was investigated to assess which enzyme was involved in the metabolism of this compound. Very little metabolism of TCDF was detected in control microsomes (0.3-3.0 pmol/mg/hr), while TCDF metabolism was increased 40- to 200-fold in TCDD-induced rat liver, kidney, and lung microsomes. Since TCDD induces cytochrome P4501A1 and P4501A2 (CYP1A1 and CYP1A2) in the rat liver but only CYP1A1 in kidney and lung, these results suggest that CYP1A1 metabolizes TCDF. To test this hypothesis, TCDF metabolism was investigated in the presence and absence of selective chemical inhibitors and antibodies to CYP1A1 and 1A2. 1-Ethynylpyrene, a suicide inhibitor of CYP1A1 and antibody to rat CYP1A1, produced a dose-dependent inhibition of TCDF metabolism in TCDD-induced rat liver microsomes. Conversely, 2-ethynylnaphthalene, a suicide inhibitor of CYP1A2 and antibody to rat CYP1A2, had no inhibitory effect on the hepatic microsomal metabolism of TCDF. Together, the results strongly indicate that rat CYP1A1 is the primary enzyme responsible for the metabolism of TCDF. 4-Hydroxy-2,3,7,8-TCDF was also identified as the major TCDF metabolite formed by rat CYP1A1. TCDF was also metabolized by human liver microsomes and recombinant yeast microsomes expressing human CYP1A1 and reductase but not by yeast microsomes expressing human CYP1A2 with or without reductase. A similar HPLC profile of TCDF metabolites was observed with microsomes from human liver and yeast expressing human CYP1A1. However, based on ethoxyresorufin-O-deethylase activity, a marker of CYP1A1, the relative rate of TCDF metabolism is about 100-fold greater in TCDD-induced rat liver microsomes than in yeast microsomes expressing human CYP1A1 and reductase. Thus, although TCDF is metabolized by rat and human CYP1A1, the results indicate that there are marked quantitative differences in metabolism which suggest that TCDF will be more persistent in humans.
先前的研究已经证实，四氯二苯并呋喃（TCDF）在大鼠体内能迅速代谢并排泄，并且用2,3,7,8-四氯二苯并二噁英（TCDD）对大鼠进行预处理会增加该化合物的肝脏代谢速率。对TCDF的肝外代谢进行了研究，以评估哪种酶参与了该化合物的代谢。在对照微粒体中检测到TCDF的代谢极少（0.3 - 3.0皮摩尔/毫克/小时），而在TCDD诱导的大鼠肝脏、肾脏和肺微粒体中，TCDF的代谢增加了40至200倍。由于TCDD在大鼠肝脏中诱导细胞色素P4501A1和P4501A2（CYP1A1和CYP1A2），但在肾脏和肺中仅诱导CYP1A1，这些结果表明CYP1A1代谢TCDF。为了验证这一假设，在存在和不存在针对CYP1A1和1A2的选择性化学抑制剂及抗体的情况下，对TCDF的代谢进行了研究。1-乙炔基芘，一种CYP1A1的自杀性抑制剂以及大鼠CYP1A1抗体，在TCDD诱导的大鼠肝脏微粒体中对TCDF代谢产生了剂量依赖性抑制。相反，2-乙炔基萘，一种CYP1A2的自杀性抑制剂以及大鼠CYP1A2抗体，对TCDF的肝脏微粒体代谢没有抑制作用。总之，结果强烈表明大鼠CYP1A1是负责TCDF代谢的主要酶。4-羟基-2,3,7,8-TCDF也被鉴定为大鼠CYP1A1形成的主要TCDF代谢产物。TCDF也可被人肝脏微粒体以及表达人CYP1A1和还原酶的重组酵母微粒体代谢，但不能被表达人CYP1A2（无论有无还原酶）的酵母微粒体代谢。在来自人肝脏和表达人CYP1A1的酵母微粒体中观察到了相似的TCDF代谢产物高效液相色谱图谱。然而，基于CYP1A1的标志物乙氧基异吩噁唑酮-O-脱乙基酶活性，TCDF在TCDD诱导的大鼠肝脏微粒体中的相对代谢速率比表达人CYP1A1和还原酶的酵母微粒体中大约高100倍。因此，尽管TCDF可被大鼠和人CYP1A1代谢，但结果表明在代谢方面存在显著的定量差异，这表明TCDF在人体内将更具持久性。
