DEVELOPMENTAL EXPOSURE OF MALE GERM-CELLS TO 5-AZACYTIDINE RESULTS INABNORMAL PREIMPLANTATION DEVELOPMENT IN RATS

Methylation of cytosine residues in mammalian DNA is established durin g gametogenesis and embryogenesis; it plays an important role in gene regulation and normal embryonic development and has also been implicat ed in genomic imprinting. In the present study, we evaluated whether p aternal administration of 5-azacytidine, a drug that is incorporated i nto DNA and blocks DNA methylation, could alter male germ cell develop ment and function. A drug that does not block methylation, 6-azacytidi ne, served as a control. Adult male Sprague-Dawley rats (n = 4-8 per g roup) were treated i.p., three times per week for 4 and 11 wk, with sa line or 2.5 (low dosage) or 5.0 (high dosage) mg/kg of 5-azacytidine a nd 6-azacytidine. After each of the treatment periods, males were mate d to determine effects on fertility and embryo development. Although n either 6-azacytidine nor 4 wk of 5-azacytidine treatment affected male reproductive organ weights or sperm counts, 11 wk of 5-azacytidine re sulted in dose-dependent reductions in testis and epididymal weights a nd sperm counts. Both dosages of 5-azacytidine resulted in significant increases in preimplantation loss, and the high dosage of 5-azacytidi ne caused a decrease in fertility. Examination of embryos on Day 2 of gestation revealed a striking dose-dependent increase in the average n umber of abnormal embryos per litter sired by the males treated with 5 -azacytidine (saline, 0.33 +/- 0.24; low dosage, 2.64 +/- 0.92; high d osage, 10.09 +/- 0.95). In summary, paternal administration of 5-azacy tidine interfered with normal male germ cell development and resulted in alterations in fertilization and early embryo development. We sugge st that 5-azacytidine-induced alterations in germ cell DNA methylation patterns may be one of the underlying mechanisms, since similar dosag es of the analogue 6-azacytidine had no effect on male reproduction an d progeny outcome.