Moorthy B, van Golen K L, Randerath K
Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030.
Toxicol Appl Pharmacol. 1992 Apr;113(2):218-26. doi: 10.1016/0041-008x(92)90117-b.
I-compounds are recently discovered, age-dependent covalent DNA modifications, which are detectable by 32P-postlabeling assay for DNA adducts. The effects of the catatoxic antiglucocorticoid, pregnenolone-16 alpha-carbonitrile (PCN), on hepatic and renal I-compound levels have been studied in male and female Sprague-Dawley rats together with the levels of microsomal cytochrome P450 and rates of ethylmorphine N-demethylation. PCN (50 mg/kg ip) was dissolved in corn oil and administered to rats once daily for 4 days, and animals were killed at 1 day or 8 days after the last treatment. Hepatic and renal I-compounds were analyzed by 32P-postlabeling in control and PCN-treated animals at both time points. Microsomal cytochrome P450 and ethylmorphine N-demethylase activities were also determined. Total levels of liver nonpolar and polar I-compounds were reduced in female rats by 37 and 51%, respectively, compared to controls, at 1 day. Ten out of sixteen individual I-compounds were also markedly reduced in female rat liver DNA as a result of PCN administration. In contrast to females, total levels of liver I-compounds were not significantly altered in males by PCN at 1 day; however, two individual I-compounds were lowered. I-compound levels recovered 8 days after termination of PCN treatment in both males and females. Total levels of renal I-compounds were not affected by PCN treatment in either males or females. [3H]Methylthymidine incorporation studies showed an increase in mean DNA synthesis rate at 1 day in liver of both males and females, but this was significant in males only. Marked induction of hepatic microsomal cytochrome P450 (2.2-fold) and ethylmorphine N-demethylase (4.0-fold) activity was observed in female rats treated with PCN at 1 day as compared to controls. The extent of induction of these enzymes was much higher in females than males. At 8 days the levels of cytochrome P450 and ethylmorphine N-demethylase activity had returned to uninduced values. The results are consistent with a pivotal role for PCN-inducible cytochrome P450 in the metabolism of I-compounds.
I-化合物是最近发现的、与年龄相关的共价DNA修饰，可通过DNA加合物的32P后标记分析检测到。已在雄性和雌性Sprague-Dawley大鼠中研究了抗糖皮质激素孕烯醇酮-16α-腈（PCN）对肝脏和肾脏I-化合物水平的影响，同时研究了微粒体细胞色素P450水平和乙基吗啡N-去甲基化速率。将PCN（50mg/kg，腹腔注射）溶于玉米油中，每天给大鼠给药一次，共给药4天，在最后一次给药后1天或8天处死动物。在两个时间点对对照动物和PCN处理的动物的肝脏和肾脏I-化合物进行32P后标记分析。还测定了微粒体细胞色素P450和乙基吗啡N-脱甲基酶活性。与对照组相比，雌性大鼠肝脏中非极性和极性I-化合物的总水平在1天时分别降低了37%和51%。由于给予PCN，雌性大鼠肝脏DNA中16种单个I-化合物中的10种也显著降低。与雌性相反，PCN在1天时对雄性大鼠肝脏I-化合物的总水平没有显著影响；然而，有两种单个I-化合物水平降低。在PCN治疗终止8天后，雄性和雌性大鼠的I-化合物水平均恢复。PCN治疗对雄性或雌性大鼠肾脏I-化合物的总水平均无影响。[3H]甲基胸苷掺入研究表明，雄性和雌性大鼠肝脏在1天时平均DNA合成速率均增加，但仅在雄性中显著。与对照组相比，在1天时用PCN处理的雌性大鼠中观察到肝脏微粒体细胞色素P450（2.2倍）和乙基吗啡N-脱甲基酶（4.0倍）活性显著诱导。这些酶的诱导程度在雌性中比雄性高得多。在8天时，细胞色素P450水平和乙基吗啡N-脱甲基酶活性已恢复到未诱导值。结果表明PCN诱导的细胞色素P450在I-化合物代谢中起关键作用。
