Amino Acid Turnover by Bovine Oocytes Provides an Index of Oocyte Developmental Competence In Vitro

Amino acid profiling has been used to distinguish between human embryos of differing developmental competence. We sought to determine whether amino acid profiling could be used to distinguish between metaphase II (MII) bovine oocytes with different developmental capabilities in vitro. Amino acid turnover was assayed during the final 6 h of in vitro maturation prior to oocytes undergoing individual fertilization in vitro. Following insemination, zygotes were immobilized in groups of 16 on the base of a Petri dish using Cell-Tak tissue adhesive to enable the developmental progress of each to be tracked to the blastocyst stage. Spent droplets of in vitro maturation medium were analyzed by high performance liquid chromatography, which revealed glutamine, arginine, and asparagine were depleted in the greatest quantities. Incompetent MII oocytes that failed to cleave by 72 h postfertilization depleted significantly more glutamine from (P = 0.0006) and released more alanine (P = 0.0001) into the medium than oocytes that cleaved. When cutoff values were selected for the turnover of alanine, arginine, glutamine, leucine, and tryptophan and modeled to predict fertilization and cleavage potential, oocytes that did not exceed the cutoff values for >= 2 of these key amino acids were more likely to cleave. The sensitivity, specificity, accuracy, and positive predictive value of this model were 60.5%, 76.8%, 63.5%, and 92.0%, respectively. Significant differences (P <= 0.015) in the consumption/production of alanine and glutamine were also observed when comparing uncleaved oocytes with those that produced blastocysts. The data show that noninvasive amino acid profiling can be used to measure oocyte developmental competence.