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A minimally toxic dose of methylene dianiline injures biliary epithelial cells in rats
M F Kanz1, G H Gunasena, L Kaphalia
1Department of Pathology, University of Texas Medical Branch, Galveston 77555-0609, USA.
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.
Insights
Methylene dianiline (DAPM) selectively injures bile duct cells in rats at a minimally toxic dose. This study defines DAPM as a specific bile duct toxicant, offering a model for studying biliary epithelial cell injury.
Area of Science:
- Toxicology
- Hepatology
- Cell Biology
Background:
- Methylene dianiline (DAPM) is known to induce hepatotoxicity and cholestasis in rats at specific doses.
- Understanding the selective toxicity of DAPM is crucial for developing models of biliary epithelial cell (BEC) injury.
Purpose of the Study:
- To determine if a minimally toxic dose of DAPM can serve as a model for selective BEC injury in vivo.
- To investigate the effects of DAPM on biliary and liver constituents and early cellular changes.
Main Methods:
- Rats received a 50 mg/kg oral dose of DAPM in ethanol or ethanol alone.
- Bile was collected for 6 hours post-administration.
- Liver tissues were assessed for biochemical, histochemical, and ultrastructural alterations at 3 and 6 hours.
Main Results:
- DAPM minimally affected bile salt and bilirubin excretion but increased biliary glucose and protein excretion.
- Significant necrosis of intrahepatic bile ducts was observed at 6 hours.
- BEC mitochondria and microvilli showed ultrastructural alterations by 3 hours, while hepatocytes remained largely unaffected.
Conclusions:
- DAPM at 50 mg/kg induces selective injury to bile duct cells, not hepatocytes.
- This dose of DAPM provides a valuable in vivo model for studying selective biliary epithelial cell toxicity.
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