In vitro and in vivo DNA damage of male and female rat liver nuclei by oncogenic and nononcogenic beta blockers.

The beta blocker DL-1-(2-nitro-3-methyl-phenoxy)-3-tert-butylamino-propan-2-ol (ZAMI 1305), hepatocarcinogenic to the female rat, and the nononcogenic beta blockers DL-1-(2-nitro-5-methyl-phenoxy)-3-tert-butylamino-propan-2-ol (ZAMI 1327), DL-propranolol, and DL-atenolol were tested for their capacity to damage liver DNA in vitro and in vivo. As revealed by alkaline sucrose gradient analysis, all the beta blockers tested, with the exception of DL-atenolol, caused a dose-dependent DNA fragmentation when they were added in vitro to nuclei isolated from livers of both male and female Wistar rats. Analysis of the DNA sedimentation patterns in neutral sucrose gradients demonstrated the absence of DNA fragmentation, thus indicating that the drugs did not induce double-strand DNA breaks. When the beta blockers were administered in vivo, liver DNA damage was observed only in female Wistar rats treated with ZAMI 1305. A single injection of ZAMI 1305 caused the onset of two distinct episodes of DNA damage. The first episode occurred within 5 minutes, and the damage was repaired within 1 hour after the injection; the second, apparently spontaneous, episode occurred 14 hours after the injection, and the damage was more pronounced than that seen in the first episode and took a much longer time to subside. However, a second injection of ZAMI 1305 into female Wistar rats 8 hours after the first injection did not induce the immediate short-lived episode of DNA damage but, like the first injection, it caused late DNA damage that peaked about 16 hours after drug administration.