Determination of Hepatotoxicity and Its Underlying Metabolic Basis of 1,2-Dichloropropane in Male Syrian Hamsters and B6C3F1 Mice

Abstract

1,2-Dichloropropane (1,2-DCP) has recently been reclassified from not classifiable as to its carcinogenicity to humans (Group 3) to carcinogenic to humans (Group 1) by the International Agency for Research on Cancer. This was based on the findings of epidemiological studies in Japan that occupational exposure to paint stripers containing 1,2-DCP was associated with increased cholangiocarcinomas. It is known that 1,2-DCP is negative for cholangiocarcinogenicity in rats and mice. However, its toxicity and carcinogenicity has not been examined in hamsters and little is known about the regulation of its metabolism in hamsters. The purpose of this study was to determine the hepatobiliary toxicity of 1,2-DCP in hamsters and to characterize and compare the altered patterns of hepatic xenometabolic enzymes in hamsters and mice. Male Syrian hamsters and male B6C3F1 mice were treated with various doses of 1,2-DCP for 4 h or 3 days or 4 weeks. These experiments demonstrated that a high dose of 1,2-DCP induced centrilobular hepatocellular necrosis in hamsters. CYP2E1 is possibly the key enzyme responsible for bioactivation and the consequent hepatocytotoxicity of 1,2-DCP, and GSH conjugation catalyzed by GST-T1 may exert a cytoprotective role in hamsters and mice. Notably, the expression pattern of GST-T1 in bile duct epithelial cells differed between hamsters and mice: GST-T1 was expressed in bile duct epithelial cells of mice but not hamsters. This indicates that responses to 1,2-DCP in the bile duct of hamsters might differ from that of mice, and suggests that long-term studies are necessary to clarify the chalangiocarcinogenicity of 1,2-DCP in hamsters, though no biliary toxicity was observed in the present short-term experiments.

Keywords: 1,2-DCP; CYP2E1; GST-T1; hamster; hepatotoxicity; mouse.

FIG. 1.

Hepatotoxic effects of 1,2-DCP in hamsters in the 4-h and 3-day experiments. A, Effects of 500 mg/kg b.w. 1,2-DCP in the 4-h experiment: fatty change characterized by increased microvacuoles (A2) and Oil Red O-positive vesicles (A4) in the treated hamsters compared with the controls (A1 and A3, respectively); CYP2E1 was increased in centrilobular hepatocytes (A6) compared with the controls (A5); and GST-T1 was decreased in centrilobular hepatocytes but increased in periportal hepatocytes (A8) in the treated hamsters compared with the controls (A7). B, Effects of 500 → 250 mg/kg b.w. 1,2-DCP in the 3-day experiment: centrilobular hepatocellular necrosis and fatty change in the treated hamsters (B2); CYP2E1 was increased in hepatocytes throughout the lobule (B4) compared with the controls (B3); GST-T1 was decreased in centrilobular hepatocytes but increased in periportal hepatocytes (B6) in treated hamsters compared with the controls (B5); and expression of GST-T1 was not observed in bile duct epithelial cells in either the control (B7: high magnification of B5) or treated hamsters (B8: high magnification of B6).

FIG. 2.

Hepatotoxic effects of 1,2-DCP in hamsters in the 4-week experiment. Fatty change was observed in the treated hamsters (A); CYP2E1 was increased in centrilobular hepatocytes (C) compared with the controls (D), and GST-T1 was decreased in centrilobular hepatocytes but increased in periportal hepatocytes (E) in the treated hamsters compared with the controls (F). The protein level of CYP2A, but not CYP1A1, was increased by treatment with both the low and high doses of 1,2-DCP (G). 1,2-DCP did not affect cell proliferation of hepatocytes or bile duct epithelial cells (H).

FIG. 3.

Hepatotoxic effects of 1,2-DCP in mice in the 4-h and 3-day experiments. A, Effects of 500 mg/kg b.w. 1,2-DCP in the 4-h experiment: fatty change characterized by increased microvacuoles (A2) and Oil Red O-positive vesicles (A4) in the treated mice compared with the controls (A1 and A3, respectively). A mottled pattern of cytoplasmic staining with GST-T1 was observed in control mice (A5) while GST-T1 was increased throughout the lobule in the treated mice (A6). Bile duct epithelial cells were positive for GST-T1 in the control (A7: high magnification of A5) and treated mice (A8: high magnification of A5). 1,2-DCP treatment had no effect on GST-T1 expression in bile duct epithelial cells. B, Effects of 500 mg/kg b.w. 1,2-DCP in the 3-day experiment: centrilobular hepatocellular necrosis is evident in the treated mice (B2); centrilobular hepatocellular necrosis occurred within the CYP2E1-positive area in the treated mice (B4), while the area and staining density of CYP2E1 in hepatocytes around the necrotic area is comparable to the control mice (B3); GST-T1 was decreased throughout the lobule in the treated mice (B6) compared with the controls (B5).

FIG. 4.

Hepatotoxic effects of 1,2-DCP in mice in the 4-week experiment: GST-T1 was decreased in the centrilobular hepatocytes in the treated mice (A) compared with the controls (B); mRNA expression levels of CYPs of families 1-4 and GST-T1 in livers (C), *P < 0.05 versus control; the protein level of CYP2A, but not CYP1A1, was increased by treatment with both the low and high dose of 1,2-DCP (D); 1,2-DCP did not affect cell proliferation of hepatocytes or bile duct epithelial cells (E).

FIG. 5.

Proposed mechanisms of 1,2-DCP-induced hepatotoxicity.