The rodent nongenotoxic hepatocarcinogen and peroxisome proliferator nafenopin inhibits intercellular communication in rat but not guinea-pig hepatocytes, perturbing S-phase but not apoptosis

Previously, we have shown that the peroxisome proliferator (PP), nafenopin, induces S-phase in␣rat hepatocytes and suppresses apoptosis in hepatocytes from both rat and guinea-pig. Here, we confirm and extend these findings by defining the time course of␣growth perturbation and by correlating this with species differences in loss of gap junctional intercellular communication (GJIC). GJIC is associated with nongenotoxic carcinogenesis, possibly reflecting a tumour suppresser role of the connexins. Fluorescence microscopy of Hoechst 33258-stained rat or guinea-pig hepatocyte monolayers showed 1% apoptosis during the first 8 h of culture, peaking to 2–2.5% at 20–24 h. Nafenopin suppressed apoptosis compared with controls in both rat and guinea-pig, measured at 20 h and 24 h onwards, respectively. The induction of S-phase in rat hepatocytes by nafenopin could be detected as early as 4 h after compound addition whereas S-phase was not altered by nafenopin in guinea-pig hepatocytes. Intercellular communication as measured by intercellular transfer of microinjected Lucifer Yellow CH was observed during the first 14 h of primary rat hepatocyte culture peaking at a maximum value of 88 ± 3.0% after 7 h. In hepatocyte cultures from guinea-pig, dye-coupling levels were maintained between 88 ± 3.0 and 93 ± 3.0% within 2–10 h of culture and by 12 h showed only a slight decrease to 72 ± 3.0%. In the rat, significant inhibition was observed at 4 h after administration of nafenopin since GJIC was reduced by 20 ± 5% compared with vehicle control. By contrast, in the presence of nafenopin, the level of dye-coupling between guinea-pig hepatocytes did not decrease but remained between 85 ± 5 and 93 ± 3.0%, similar to that observed in control guinea-pig cultures. The data obtained contribute to our understanding of the role of GJIC inhibition in the perturbation of cell survival and proliferation caused by nongenotoxic hepatocarcinogens.