Alleviation of the two-cell block of ICR mouse embryos by polyaminocarboxylate metal chelators.

The present study was undertaken to examine the effects of various transition metal ion chelators, both polyaminocarboxylates (including nitrilotriacetate (NTA), ethylenediaminediacetate (EDDA), ethyleneglycolbistetraacetate (EGTA), ethylenediaminetetraacetate (EDTA) and diethylenetriaminepentaacetate (DTPA)) and non-polyaminocarboxylates (dipicolinic acid and deferoxamine), on the development in vitro of one-cell ICR strain mouse embryos to the four-cell and blastocyst stages. The order of stability constants of polyaminocarboxylates for transition metal ions such as zinc, copper and iron is as follows: NTA < or = EDDA < EGTA < EDTA < DTPA. Addition of 10 or 100 micromol polyaminocarboxylates x l(-1) to the medium significantly enhanced the development of most one-cell embryos (66-88%) beyond the two-cell stage compared with that (< 25%) in medium without polyaminocarboxylates. Although EDDA, EDTA and DTPA at 10 micromol x l(-1) induced the development of most one-cell embryos to the four-cell stage and beyond, a higher concentration (100 micromol x l(-1)) of NTA and EGTA was required to obtain a similar result. Therefore, the ability of polyaminocarboxylates to overcome the two-cell block is not correlated with their potency to chelate transition metal ions. In contrast, the non-polyaminocarboxylates dipicolinic acid and deferoxamine, at 10 and 100 micromol x l(-1), did not have the same effect. Taken together, the results indicate that the ability of polyaminocarboxylates to overcome the two-cell block in embryo development is due to some common feature or features other than the ability to chelate transition metal ions.