Smith R D, Kehrer J P
Division of Pharmacology and Toxicology, College of Pharmacy, University of Texas, Austin 78712-1074.
Cancer Res. 1991 Jan 15;51(2):542-8.
A single i.p. dose of cyclophosphamide produces lung cell injury and fibrosis in mice. Although cyclophosphamide is activated by the cytochrome P-450 mixed function oxidase (MFO) system, a role for this system in the development of lung injury has not been established. The involvement of other metabolic pathways, such as cooxidation via prostaglandin H synthase, in the toxicity of cyclophosphamide has not been studied. The objectives of the current study were to assess the effects of various inhibitors of MFO and prostaglandin H synthase activity on the development of cyclophosphamide-induced lung damage and fibrosis in mice, to determine whether arachidonic acid as well as NADPH could support the activation of cyclophosphamide to an alkylating metabolite, and to assess the capacity of cyclophosphamide to serve as a reducing cosubstrate. In addition, the ability of a low dose of cyclophosphamide to prevent the lung injury from a later higher dose was determined. Treatment with SKF 525A, piperonyl butoxide, or 1-benzylimidazole, followed by a single 200 mg/kg dose of cyclophosphamide, did not diminish pulmonary thymidine incorporation (an index of cell division after injury) or hydroxyproline content (an indicator of fibrosis), compared to mice treated with cyclophosphamide alone. Pretreatment with 1-aminobenzotriazole reduced the incorporation of thymidine into lung DNA on days 3 and 10, but not on day 7, and also reduced lung hydroxyproline accumulation. Treatment with indomethacin, nordihydroguiaretic acid, or aspirin prior to cyclophosphamide greatly reduced levels of pulmonary thymidine incorporation and/or hydroxyproline content, compared to cyclophosphamide alone. Low dose pretreatment with cyclophosphamide did not prevent the lung injury or fibrosis from a subsequent higher dose. NADPH supported greater production of alkylating metabolites in liver than in lung microsomes. In contrast, the arachidonic acid-supported production of alkylating metabolites was greater in lung microsomes. No NADPH- or arachidonate-supported alkylating activity was evident in lung or liver cytosol. SKF 525A and 1-aminobenzotriazole inhibited the NADPH-supported reaction in liver, but not lung, while indomethacin and nordihydroguiaretic acid inhibited the arachidonic acid-supported reaction in lung but not liver. Cyclophosphamide was a moderately active reducing cosubstrate for 5-phenyl-4-pentenyl hydroperoxide in both lung and liver microsomes. These results demonstrate that pathways in lung tissue unrelated to MFOs can metabolize cyclophosphamide to an alkylating compound and that MFO-mediated activation of cyclophosphamide may not be essential for the development of the pulmonary toxicity associated with this drug.
腹腔注射单次剂量的环磷酰胺可导致小鼠肺细胞损伤和纤维化。尽管环磷酰胺是由细胞色素P - 450混合功能氧化酶（MFO）系统激活的，但该系统在肺损伤发生过程中的作用尚未明确。其他代谢途径，如通过前列腺素H合酶的共氧化作用，在环磷酰胺毒性中的作用尚未得到研究。本研究的目的是评估MFO和前列腺素H合酶活性的各种抑制剂对环磷酰胺诱导的小鼠肺损伤和纤维化发展的影响，确定花生四烯酸以及NADPH是否能支持环磷酰胺激活为烷基化代谢物，并评估环磷酰胺作为还原共底物的能力。此外，还确定了低剂量环磷酰胺预防后续高剂量环磷酰胺所致肺损伤的能力。与单独给予环磷酰胺的小鼠相比，用SKF 525A、胡椒基丁醚或1 - 苄基咪唑处理后再单次给予200 mg/kg环磷酰胺，并未降低肺组织中胸苷掺入量（损伤后细胞分裂的指标）或羟脯氨酸含量（纤维化的指标）。用1 - 氨基苯并三唑预处理可在第3天和第10天降低胸苷掺入肺DNA的量，但在第7天无此作用，同时也减少了肺组织中羟脯氨酸的积累。与单独给予环磷酰胺相比，在给予环磷酰胺之前用吲哚美辛、去甲二氢愈创木酸或阿司匹林处理可显著降低肺组织中胸苷掺入量和/或羟脯氨酸含量。低剂量环磷酰胺预处理不能预防后续高剂量环磷酰胺所致的肺损伤或纤维化。NADPH支持肝脏中烷基化代谢物的生成量比肺微粒体中的多。相反，花生四烯酸支持的烷基化代谢物生成在肺微粒体中更多。在肺或肝细胞溶胶中未观察到NADPH或花生四烯酸支持的烷基化活性。SKF 525A和1 - 氨基苯并三唑抑制肝脏中NADPH支持的反应，但不抑制肺中的反应，而吲哚美辛和去甲二氢愈创木酸抑制肺中花生四烯酸支持的反应，但不抑制肝脏中的反应。环磷酰胺在肺和肝微粒体中都是5 - 苯基 - 4 - 戊烯基氢过氧化物的中等活性还原共底物。这些结果表明，肺组织中与MFO无关的途径可将环磷酰胺代谢为烷基化化合物，且MFO介导的环磷酰胺激活可能不是该药物所致肺毒性发生的必要条件。
