Diethylnitrosamine administration in vivo increases hepatic poly(ADP-ribose) levels in rats: results of a modified technique for poly(ADP-ribose) measurement.

Abstract

Poly(ADP-ribose) (polymer) is enzymatically synthesized on nuclear proteins in response to DNA strand breaks. NAD+ is the substrate for this reaction, which is catalyzed by poly(ADP-ribose)polymerase. This post-translational modification occurs in response to DNA strand breaks and is thought to play an important role in DNA repair. Polymer synthesis resulting from DNA damage has been described in cultured cells, but measurement is more difficult in animal tissues. In this study, modifications were made to an earlier method to measure carcinogen-induced increases in polymer levels in vivo. RNase I was added to the enzyme mixture used to digest polymer to ribosyladenosine (RAdo). This prevented the inhibition of snake venom phosphodiesterase by RNA. The HPLC analysis was improved, allowing elimination of the second boronate affinity chromatography step traditionally used to purify epsilon RAdo. Using this technique, we have studied the effect of i.p. diethylnitrosamine (DEN) injection on hepatic NAD+ and poly(ADP-ribose) levels in Fischer-344 rats. Hepatic polymer levels rose 8-fold from 26 to 218 pmol/g liver wet weight, 10 h following 200 mg DEN/kg body weight (n = 4-5). Liver NAD+ decreased concurrently, to 61% of basal levels at 16 h post-treatment (n = 4-5). Erythrocyte NAD+ concentrations remained unchanged, despite carcinogen administration. The DEN-induced effects on tissue polymer and NAD+ levels were dose dependent from 0 to 200 mg DEN/kg body weight (n = 4).