Apoptosis, PCNA, and p53 in Fundulus grandis fish liver after in vivo exposure to N-methyl-N′-nitro-N-nitrcssoguanidine and 2-aminofluorene

Dysfunction in homeostatic mechanisms of cell death and proliferation are considered to be important in the pathogenesis of chemically induced neoplasia. p53 has been implicated in the regulation of cell death and proliferation. To determine whether expression of apoptosis, proliferating cell nuclear antigen (PCNA), and p53 differ between an alkylating agent and a polycyclic aromatic hydrocarbon, host response was measured through sequential immunohistochemical detection of apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method), PCNA PC-10, and p53 (PAb 240) in livers of the fish Fundulus grandis. Nine hundred fish were randomly assigned to 3 groups of 300 fish each and kept in separate aquarium tanks. One group of fish was exposed to 6.7 mu M N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 1 group was exposed to 6.9 mM 2-aminofluorene (2-AF), and the remaining group served as a control. A significant decrease (p = 0.005) in the level of apoptosis and a significant increase (p < 0.0001) in the level of p53 were found on experimental day 180 in the livers of MNNG-exposed fish. PCNA was significantly increased (p < 0.005) by day 9 of the experiment in both MNNG and 2-AF fish when compared with controls, but no significant differences existed between the 2 groups of treated fish. Response of fish liver cells to MNNG-mediated and 2-AF-mediated injury differs, at least initially, in the expression of p53, inhibition of apoptosis, and increased net cell proliferation. Concurrent use of a marker for cell death with a marker of proliferation greatly enhances the assessment of the effect of these compounds on liver cells.