Acid peptidase activity released from in vitro produced porcine embryos: a candidate marker to predict developmental...

The ability to efficiently create high quality embryos, competent to produce normal viable offspring in vitro, facilitates diverse technological advancements in animal agriculture and assisted reproduction. Current methods for evaluation of embryos are predominantly based on morphological characteristics which are prone to potential bias of the scorer. Metabolic and genetic markers have also been explored for quality assessment, but they are cost prohibitive or require longer periods of time for evaluation. We hypothesized that secreted enzymes could provide another means of embryo quality assessment. In this report, we provide evidence that medium conditioned by porcine embryos often has proteolytic activity that operates in acidic conditions (acid peptidase activity or APA). The APA could be inhibited by pepstatin A, suggesting that the activity is derived from one or more aspartic peptidases. We also provide evidence that single embryos, incubated for as few as 24 hr, released enough APA that it was possible to measure it accurately at day 5 of culture. We also observed that such activity on day 6 could be positively correlated with advanced developmental stage and embryo quality. In addition, those embryos that were graded identically by morphological evaluations often differed in the amount of APA--with some being significantly higher than the experimental threshold value. Therefore, the APA of embryos might serve as an additional marker for evaluation of embryos.