Fu P P, Von Tungeln L S, Chiu L H, Zhan D J, Deck J, Bucci T, Wang J C
National Center for Toxicological Research, Jefferson, Arkansas 72079, and Department of Chemistry, Soochow University, Taipei, Taiwan.
Chem Res Toxicol. 1998 Aug;11(8):937-45. doi: 10.1021/tx980079+.
It has been previously proposed that a nitropolycyclic aromatic hydrocarbon (nitro-PAH) with its nitro functional group perpendicular or nearly perpendicular to the aromatic moiety exhibits lower tumorigenicity than the corresponding parent aromatic hydrocarbon. We also hypothesized that reduction of the nitro group is not involved, or contributed less significantly in the metabolic activation of this class of nitro-PAHs. To verify this hypothesis, we selected 7-nitrodibenz[a,h]anthracene (7-NDB[a,h]A) for study. The X-ray crystallographic structure of 7-NDB[a,h]A was determined and indicated that the dihedral angle between the nitro functional group and the aromatic dibenz[a,h]anthracenyl moiety was 80.6 degrees, indicating the nitro group preferentially adopts a nearly perpendicular orientation. The tumorigenicity of 7-NDB[a,h]A and dibenz[a,h]anthracene (DB[a,h]A) was determined in the male B6C3F1 neonatal mouse. Mice were administered ip injections of 1/7, 2/7, and 4/7 of the total dose of 7-NDB[a,h]A (400 nmol in 35 microL of DMSO per mouse) within 24 h of birth and at 8 and 15 days of age, respectively, and sacrificed at 12 months of age. DB[a,h]A induced 78 and 96% hepatocellular adenomas and carcinomas, respectively. However, 7-NDB[a,h]A induced only 50 and 8% hepatocellular adenomas and carcinomas compared with the 8 and 4% hepatocellular adenomas and carcinomas induced by the solvent vehicle, DMSO. Aerobic metabolism of 7-NDB[a,h]A by liver microsomes of 15-day old male B6C3F1 neonatal mice resulted in trans-3,4-dihydroxy-3, 4-dihydro-7-nitrodibenz[a,h]anthracene (7-NDB[a,h]A trans-3, 4-dihydrodiol) and trans-10,11-dihydroxy-10, 11-dihydro-7-nitrodibenz[a,h]anthracene (7-NDB[a,h]A trans-10, 11-dihydrodiol) as predominant metabolites. Under anaerobic conditions, 7-NDB[a,h]A was not metabolized (nitroreduced). The DNA adduct levels in liver and lung tissues of male B6C3F1 mice treated with 7-NDB[a,h]A and sacrificed 24 h and 6 days after final dosing were determined by 32P-postlabeling/TLC. In all cases, the DNA adducts derived from 7-NDB[a,h]A trans-3,4-dihydrodiol and 7-NDB[a, h]A trans-10,11-dihydrodiol were formed. These results suggest that both of the metabolites, 7-NDB[a,h]A trans-3,4-dihydrodiol and 7-NDB[a,h]A trans-10,11-dihydrodiol, are involved in the metabolic activation of 7-NDB[a,h]A, leading to tumor induction in the neonatal mouse. Thus, our results described in this paper support our hypotheses that a nitro-PAH with a perpendicular nitro orientation exhibits lower tumorigenicity than the corresponding parent PAH and that nitroreduction contributes less significantly in the metabolic activation.
先前有人提出，带有垂直或近乎垂直于芳香部分的硝基官能团的硝基多环芳烃（nitro-PAH）比相应的母体芳烃具有更低的致瘤性。我们还假设，硝基的还原不参与这类硝基-PAH的代谢活化，或者在其中的作用不太显著。为了验证这一假设，我们选择了7-硝基二苯并[a,h]蒽（7-NDB[a,h]A）进行研究。测定了7-NDB[a,h]A的X射线晶体结构，结果表明硝基官能团与芳香二苯并[a,h]蒽部分之间的二面角为80.6度，这表明硝基优先采取近乎垂直的取向。在雄性B6C3F1新生小鼠中测定了7-NDB[a,h]A和二苯并[a,h]蒽（DB[a,h]A）的致瘤性。在出生后24小时内以及分别在8天和15天时，给小鼠腹腔注射7-NDB[a,h]A总剂量（每只小鼠400 nmol，溶于35 μL二甲基亚砜）的1/7、2/7和4/7，并在12个月龄时处死。DB[a,h]A分别诱导了78%和96%的肝细胞腺瘤和癌。然而，与溶剂二甲基亚砜诱导的8%和4%的肝细胞腺瘤和癌相比，7-NDB[a,h]A仅诱导了50%和8%的肝细胞腺瘤和癌。15日龄雄性B6C3F1新生小鼠的肝微粒体对7-NDB[a,h]A的需氧代谢产生了反式-3,4-二羟基-3,4-二氢-7-硝基二苯并[a,h]蒽（7-NDB[a,h]A反式-3,4-二氢二醇）和反式-10,11-二羟基-10,11-二氢-7-硝基二苯并[a,h]蒽（7-NDB[a,h]A反式-10,11-二氢二醇）作为主要代谢产物。在厌氧条件下，7-NDB[a,h]A未发生代谢（硝基还原）。通过32P后标记/TLC测定了末次给药后24小时和6天处死的用7-NDB[a,h]A处理的雄性B6C3F1小鼠肝脏和肺组织中的DNA加合物水平。在所有情况下，均形成了源自7-NDB[a,h]A反式-3,4-二氢二醇和7-NDB[a,h]A反式-10,11-二氢二醇的DNA加合物。这些结果表明，7-NDB[a,h]A反式-3,4-二氢二醇和7-NDB[a,h]A反式-10,11-二氢二醇这两种代谢产物均参与了7-NDB[a,h]A的代谢活化，从而导致新生小鼠发生肿瘤。因此，我们在本文中描述的结果支持了我们的假设，即具有垂直硝基取向的硝基-PAH比相应的母体PAH具有更低的致瘤性，并且硝基还原在代谢活化中的作用不太显著。
