Effects of epigallocatechin-3-gallate (EGCG) on in vitro maturation and fertilization of porcine oocytes

The beneficial properties of green tea and especially of its principal active polyphenol, epigallocatechin-3-gallate (EGCG), have led to an increased demand for dietary supplements with highly enriched EGCG concentrations. In order to investigate the possible reproductive-related consequence of EGCG supplementation, the effects of this catechin on in vitro maturation (IVM) and fertilization (IVF) of oocyte, using the pig as experimental model, were examined. In the first series of experiments EGCG, at concentrations ranging from 0 to 25 microg/ml, was added during in vitro maturation of pig oocytes. EGCG had no effect on nuclear maturation of pig oocytes and on fertilization traits considered after IVF at any of the doses tested. By contrast, a significant (p<0.05) decrease in the number of embryos that developed to blastocysts following parthenogenetic activation was recorded when 25 microg/ml EGCG was added to IVM medium; in addition this catechin concentration significantly (p<0.05) inhibited progesterone production by cumulus cells after 48 h of culture. When induction of sperm capacitation was performed in presence of EGCG, a significantly lower percentage of spermatozoa showing a Hsp70-capacitated pattern and a significant reduction of sperm H(2)O(2) production were evident at a concentration of 25 microg/ml EGCG (p<0.05). During gamete coincubation EGCG reduced, in a dose response manner, the number of reacted spermatozoa suspended in fertilization medium and increased the number of sperm bound to ZP. Supplementation of 10 microg/ml EGCG during IVF significantly increased the fertilization rate while higher EGCG concentrations (25 microg/ml) decreased the percentage of fertilized oocytes (p<0.05). In conclusion, our data suggest that high EGCG concentrations could affect in vitro maturation and fertilization in pig; it cannot be totally excluded that excessive EGCG concentrations could induce reproductive-related consequences also in vivo.