Lacy S A, Mangum J B, Everitt J I
CIIT, Research Triangle Park, NC 27709.
Toxicology. 1992;73(2):147-60. doi: 10.1016/0300-483x(92)90098-y.
Xenobiotics metabolized in rat pulmonary tissue are often selectively cytotoxic to individual lung cell populations. A non-homogeneous distribution of xenobiotic biotransformation enzymes, e.g., cytochrome P-450 (P-450)- and glutathione (GSH)-associated enzymes, in rat lung tissue may underlie this observed cell-selective pneumotoxicity. To evaluate this hypothesis, the relative activities of P-450- and GSH-associated enzymes were measured in sonicated, freshly isolated preparations containing enriched complements of individual toxicant-sensitive lung cell types, including non-ciliated bronchiolar epithelial (Clara) cells (24% pure), alveolar type II cells (86% pure) and pulmonary endothelial cells (identified by membrane-associated angiotensin converting enzyme activity). Lung cell fractions were isolated by centrifugal elutriation from male F344 rats that 48 h earlier received a single i.p. injection of either P-450-inducer beta-naphthoflavone (50 mg beta-NF/kg body weight) or corn oil vehicle. The enriched Clara cell fraction possessed (per 10(6) cells) greater P-450 and reduced GSH contents and higher enzyme activities (i.e., NADPH- and NADH cytochrome c reductases, benzyloxy (BROD)-, pentoxy (PROD)- and etoxyresorufin (EROD)-O-dealkylases, GSH transferase, GSH peroxidase, GSH reductase and NADPH quinone oxidoreductase) than either the enriched type II cell or endothelial cell preparations. However, the relative biochemical activities for the enriched fractions (Clara greater than type II greater than endothelial) generally reflected respective sonicate cellular protein content. Treatment of rats with beta-NF resulted in: (a) an induction in EROD activity in the enriched preparations of type II cells, Clara cells and endothelial cells (125-, 89- and 35-fold, respectively); (b) higher NADPH quinone oxidoreductase activities, which were increased to the greatest degree (3-fold) in the enriched type II cell fraction and (c) a small elevation in GSH transferase activity measured in the enriched Clara cell fraction. Although the enriched rat lung cell preparations possessed unique biochemical profiles for constitutive and beta-NF-inducible P-450- and GSH-associated enzymes, additional studies with higher purity preparations (e.g., Clara cells) will be required to more fully evaluate the relationship between relative cellular complements of xenobiotic biotransformation enzymes and pneumotoxicant susceptibility.
在大鼠肺组织中代谢的外源化合物通常对单个肺细胞群体具有选择性细胞毒性。大鼠肺组织中外源化合物生物转化酶（如细胞色素P-450（P-450）和谷胱甘肽（GSH）相关酶）的非均匀分布可能是观察到的这种细胞选择性肺毒性的基础。为了评估这一假设，在含有丰富的单个对毒物敏感的肺细胞类型（包括无纤毛细支气管上皮（克拉拉）细胞（纯度为24%）、II型肺泡细胞（纯度为86%）和肺内皮细胞（通过膜相关血管紧张素转换酶活性鉴定））的新鲜分离的超声破碎制剂中，测量了P-450和GSH相关酶的相对活性。通过离心淘析从48小时前单次腹腔注射P-450诱导剂β-萘黄酮（50mgβ-NF/kg体重）或玉米油载体的雄性F344大鼠中分离肺细胞组分。富集的克拉拉细胞组分（每10^6个细胞）比富集的II型细胞或内皮细胞制剂具有更高的P-450和更低的GSH含量以及更高的酶活性（即NADPH和NADH细胞色素c还原酶、苄氧基（BROD）、戊氧基（PROD）和乙氧基试卤灵（EROD）-O-脱烷基酶、GSH转移酶、GSH过氧化物酶、GSH还原酶和NADPH醌氧化还原酶）。然而，富集组分（克拉拉细胞＞II型细胞＞内皮细胞）的相对生化活性通常反映了各自超声破碎细胞的蛋白质含量。用β-NF处理大鼠导致：（a）II型细胞、克拉拉细胞和内皮细胞的富集制剂中EROD活性诱导（分别为125倍、89倍和35倍）；（b）更高的NADPH醌氧化还原酶活性，在富集的II型细胞组分中增加程度最大（3倍）；（c）在富集的克拉拉细胞组分中测量的GSH转移酶活性略有升高。尽管富集的大鼠肺细胞制剂对于组成型和β-NF诱导型P-450和GSH相关酶具有独特的生化特征，但需要用更高纯度制剂（如克拉拉细胞）进行更多研究，以更全面地评估外源化合物生物转化酶的相对细胞组成与肺毒物敏感性之间的关系。
