ACTIVATION OF APOPTOSIS IN EARLY MOUSE EMBRYOS BY 2'-DEOXYADENOSINE EXPOSURE

Adenosine deaminase (ADA) catalyzes the irreversible hydrolytic deamin ation of adenosine and deoxyadenosine to nontoxic derivatives. The imp ortance of this reaction in the female reproductive tract of mice is s uggested by pronounced utero-placental expression of ADA, and by embry olethality of the potent ADA-inhibitor deoxycoformycin (dCF) on day 7- 8 of gestation. The present study investigated the effects of dCF, ade nosine, and deoxyadenosine on the mouse neurula. Morphological cell de ath was monitored by the acridine orange reaction (AOR), and biochemic al cell death by internucleosomal DNA cleavage (IDC). A strong AOR app eared in day 7-8 embryos between 3 and 4.5 hr post-exposure to dCF in utero; there was no apparent effect on day 6 or day 9 embryos. Most em bryonic tissues were responsive, although the heart and extraembryonic membranes were resistant. Up to 75% of the embryonic chromatin was de graded in a regular pattern in concert with the AOR. Immediate activat ion of ''whole-body'' apoptosis was reproduced in short-term whole emb ryo culture with 0.1 mM deoxyadenosine in the presence of 0.01 mM dCF. This was not activated by exposure to dCF alone nor to adenosine; how ever, high concentrations of adenosine completely blocked the response to deoxyadenosine, whereas niacinamide inhibited the AOR without chan ging IDC. The cytotoxic effect of deoxyadenosine was correlated with a n expansion of embryonic dATP pools determined by high-performance liq uid chromatography analysis. The results suggest that deoxyadenosine i s the embryotoxic metabolite which accumulates in the antimesometrium of pregnant mice treated with dCF. Exposure to this metabolic toxin ac tivates apoptosis in day 7-8 embryos through an adenosine-sensitive, N AD-dependent mechanism. (C) 1994 Wiley-Liss, inc.