Ellagic acid embryoprotection in vitro: distribution and effects on DNA adduct formation.

Ellagic acid (EA) is a naturally occurring plant phenol that was recently demonstrated to protect cultured rat embryos from the embryotoxic effects of N-methyl-N-nitrosourea (MNU). The teratogenic mechanism of action of MNU, as well as other methylating agents, is debated: both cell death and mutation have been proposed. In some model systems, EA has been reported to selectively decrease the mutagenic DNA adduct O6-methylguanine (O6MG) when compared to the cytotoxic DNA adduct N7-methylguanine (N7MG). The present study was initiated to determine 1) the distribution of 14C-EA and 3H-MNU in the rat whole embryo culture model system and 2) the effects of EA on MNU-induced DNA adduct formation in this model system. 14C-EA (50 μM for 2 hr, known embryoprotective concentration; no MNU added) was used to demonstrate access of EA to the embryo within the 2 hr exposure period. The majority of EA (99.5%) remained in the media while tissue concentrations of 57.0 and 47.9 pmol/mg were attained in the yolk sacs and embryos, respectively. Similarly, MNU (75 μM for 1 hr, known effective concentration; no EA added) was distributed between the media, yolk sacs, and embryos at 99.7%, 73.7 and 112.9 pmol/mg, respectively. When non-radiolabeled EA (50 μM for 2 hr) was used to protect embryos prior to exposure to 3H-MNU (75 μM for 1 hr), the distribution of MNU in the model system was unchanged. When O6MG and N7MG addjuction rates in yolk sac DNA, embryo DNA, and pooled data were compared between protected (50 μM EA for 2 hr followed by 75 μM MNU for 1 hr), and non-protected tissues (vehicle for 2 hr followed by 75 μM MNU for 1 hr), EA decreased O6MG formation by 35.2–49.7% while N7MG was not decreased. The decreases in O6MG formation were only statistically significant (P < 0.05) when yolk sac and embryo data were pooled. EA apparently interrupts the embryotoxic pathogenesis of MNU by decreasing O6MG formation within the embryo and/or yolk sac. © 1993 Wiley-Liss, Inc.