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 c onsidered to be important in the pathogenesis of chemically induced neoplas ia. p53 has been implicated in the regulation of cell death and proliferati on. To determine whether expression of apoptosis, proliferating cell nuclea r antigen (PCNA), and p53 differ between an alkylating agent and a polycycl ic aromatic hydrocarbon, host response was measured through sequential immu nohistochemical detection of apoptosis (terminal deoxynucleotidyl transfera se-mediated dUTP nick end-labeling method), PCNA PC-10, and p53 (PAb 240) i n livers of the fish Fundulus grandis. Nine hundred fish were randomly assi gned 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 remai ning group served as a control. A significant decrease (p = 0.005) in the l evel of apoptosis and a significant increase (p < 0.0001) in the level of p 53 were found on experimental day 180 in the livers of MNNG-exposed fish. P CNA was significantly increased (p < 0.005) by day 9 of the experiment in b oth MNNG and 2-AF fish when compared with controls, but no significant diff erences existed between the 2 groups of treated fish. Response of fish live r cells to MNNG-mediated and 2-AF-mediated injury differs, at least initial ly, in the expression of p53, inhibition of apoptosis, and increased net ce ll proliferation. Concurrent use of a marker for cell death with a marker o f proliferation greatly enhances the assessment of the effect of these comp ounds on liver cells.