title: A minimally toxic dose of methylene dianiline injures biliary epithelial cells in rats.
abstract: The threshold for hepatotoxicity and cholestasis induced by methylene dianiline (DAPM) in rats is between 25 and 75 mg/kg (Bailie et al., Environ. Health Perspect., 124, 25-30, 1993). Our objectives were to determine if a minimally toxic dose of DAPM provided a model system for studies of selective injury to biliary epithelial cells (BEC) in vivo. Thus, we examined the effects of 50 mg DAPM/kg on (1) biliary constituents, (2) liver constituents likely involved in DAPM biotransformation/detoxification, and (3) early morphological and histochemical changes in the liver. Male Sprague Dawley rats had biliary cannulas positioned under pentobarbital anesthesia. After 1 h of control bile collection, rats received 50 mg DAPM/kg po in 35% ethanol or 35% ethanol only. Bile was collected for another 6 h. Histochemical, ultrastructural, and biochemical liver alterations were assessed at 3 h or at 3 and 6 h. DAPM had minimal effects on biliary bile salt and bilirubin excretion over 6 h. Biliary glucose and protein excretion were increased approximately 2-fold starting in Hour 1, while inorganic phosphate excretion was not increased until Hour 2. Biliary glutathione excretion initially increased (Hour 1) but then declined steadily for 5 h. Microsomal cytochrome P-450 activities were transiently decreased at 3 h but had returned to control values by 6 h. Liver glutathione (GSH and GSSG) was not affected by DAPM at 3 or 6 h. Necrosis of intrahepatic bile ducts was severe at 6 h with moderate injury in smaller bile ducts. Ultrastructural alterations were observed in BEC mitochondria and microvilli at 3 h with no apparent alterations in hepatocyte mitochondria or tight junctions between cells. In addition, histochemical staining of liver sections and assays of mitochondrial enzyme activities in vitro at 3 h revealed no loss of mitochondrial function in hepatocytes. These results provide strong evidence for defining DAPM as a selective bile duct toxicant.
authors.affiliation: Department of Pathology, University of Texas Medical Branch, Galveston 77555-0609, USA.
authors.forename: M F
authors.initials: MF
authors.lastname: Kanz
authors.forename: G H
authors.initials: GH
authors.lastname: Gunasena
authors.forename: L
authors.initials: L
authors.lastname: Kaphalia
authors.forename: D K
authors.initials: DK
authors.lastname: Hammond
authors.forename: Y A
authors.initials: YA
authors.lastname: Syed
mesh_terms: D000485:Allergens / Q000008:administration & dosage / Q000633:toxicity; D000814:Aniline Compounds / Q000008:administration & dosage / Q000633:toxicity*; D000818:Animals; D001646:Bile / Q000187:drug effects / Q000378:metabolism; D001652:Bile Ducts / Q000187:drug effects* / Q000648:ultrastructure; D002273:Carcinogens / Q000008:administration & dosage / Q000633:toxicity*; D065607:Cytochrome P-450 Enzyme Inhibitors; D004847:Epithelial Cells / Q000187:drug effects* / Q000648:ultrastructure; D005947:Glucose / Q000032:analysis; D005978:Glutathione / Q000032:analysis; D019803:Glutathione Disulfide / Q000032:analysis; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology; D009336:Necrosis; D011506:Proteins / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D001559:Benzhydryl Compounds
chemical_list: D000485:Allergens; D000814:Aniline Compounds; D002273:Carcinogens; D065607:Cytochrome P-450 Enzyme Inhibitors; D005947:Glucose; D005978:Glutathione; D019803:Glutathione Disulfide; D011506:Proteins; C009505:4,4'-diaminodiphenylmethane; D001559:Benzhydryl Compounds