Bile duct epithelial cells exposed to alpha-naphthylisothiocyanate produce a factor that causes neutrophil-dependent hepatocellular injury in vitro.

The acute hepatotoxicity induced by alpha-naphthylisothiocyanate (ANIT) in rats is manifested as neutrophil-dependent necrosis of bile duct epithelial cells (BDECs) and hepatic parenchymal cells. This hepatotoxicity mirrors that of drug-induced cholangiolitic hepatitis in humans. Since BDECs are primary targets of ANIT-induced toxicity, we hypothesized that after exposure to ANIT, BDECs produce a factor(s) that causes neutrophil chemotaxis and neutrophil-dependent hepatocellular injury. To test this hypothesis BDECs were isolated from male Sprague Dawley rats and incubated with ANIT (6.25, 12.5, 25, or 50 microM) or vehicle for 24 h. The conditioned medium (CM) was collected and placed in the bottom chamber of a two-chambered chemotaxis system, while isolated neutrophils were placed in the top chamber. Chemotaxis was indicated by neutrophil migration through a membrane to the bottom chamber. CM from BDECs exposed to each concentration of ANIT was chemotactic, whereas CM from vehicle-treated BDECs was not. ANIT alone caused a modest degree of chemotaxis at 50 microM. The conditioned media were added to isolated hepatocytes or to hepatocyte-neutrophil cocultures and incubated for 24 h. Hepatocyte toxicity was indicated by alanine aminotransferase release into the culture medium. CM from vehicle-treated BDECs did not cause hepatocyte killing in either hepatocyte-neutrophil cocultures or hepatocyte cultures. In contrast, the addition of CM from ANIT-treated BDECs (CM-BDEC-A) to hepatocyte-neutrophil cocultures resulted in hepatocyte killing. The same CM was not cytotoxic to hepatocyte cultures devoid of neutrophils. The hepatocyte killing could not be explained by residual ANIT in the CM, which was below the limit of detection (< or = 0.5 microM). The addition of antiproteases afforded protection against neutrophil-dependent hepatocellular injury induced by CM-BDEC-A. These results indicate that ANIT causes BDECs to release a factor(s) that attracts neutrophils and stimulates them to injure hepatocytes in vitro.