Allopurinol, an inhibitor of xanthine oxidase, improves the development of IVM/IVF bovine embryos (>4 cell) in vitro under certain culture conditions

Abstract

To determine the origin of free oxygen radicals in the culture medium of bovine embryos, the effect of allopurinol, an inhibitor of xanthine oxidase, on the development of embryos (>4 cell) in modified synthetic oviduct fluid (m-SOF) medium was examined. When embryos were cultured in the presence of 0.2 mM allopurinol under high oxygen tension (5% CO 2 in air), the blastocyst rate significantly (P<0.05) increased compared with the absence of allopurinol (allopurinol (+) 42 vs (−) 25%; Day 6, 63 vs 51%; Day 7, 69 vs 58%; Day 8). However, allopurinol had no effect on embryo development under low oxygen tension (5% CO 2, 5% O 2, 90% N 2). Moreover, it was found that the developmental rate and the total cell number of blastocysts decreased (development rate: 60 vs 28%, cell number: 132 vs 74) when the embryos were cultured in medium containing 0.01 U/mL xanthine oxidase (XOD) and 0.1 mM hypoxanthine (HXT), and the damaging effect of XOD and HXT was removed by the addition of 0.2 mM allopurinol. The beneficial effect of allopurinol was also observed when the glucose concentration was increased to 4.5 mM from 1.5 mM (control: 22% vs allopurinol: 34%; Day 8), but no beneficial effects were observed in the media without glucose (control: 55% vs allopurinol: 59%). Taken together, these results suggested that a portion of the free oxygen radicals are generated from the XOD and HXT reactions under culture conditions, and this generation is enhanced by high oxygen tension in the gas atmosphere or by high glucose concentrations in the medium.