SANTA BARBARA, CALIF. – Unique protein signatures in the media surrounding embryos may soon provide a noninvasive means of identifying viability and aneuploidy, Dr. William B. Schoolcraft predicted at a conference on in vitro fertilization and embryo transfer sponsored by the University of California, Los Angeles.
Biopsies performed during preimplantation genetic diagnosis or comprehensive chromosome screening are "very invasive procedures" that are comparable to surgery or a forceps delivery, said Dr. Schoolcraft.
Removal of the embryo from an incubator, exposure to the heat of a laser, and traumatic manipulation may cause subtle harm, resulting in short- or long-term complications, he added.
But fascinating developments in the laboratory have confirmed dynamic, day-by-day evolutions in the pattern of proteins that are taken up – and secreted – by embryos in culture, providing evidence of distinctive signatures indicating viability, gene expression, and prospects for implantation, Dr. Schoolcraft noted.
To date, his group has identified more than 250 proteins in spent media from embryos, 74 of which are uniquely expressed in that environment.
"Some are excreted only by early embryos, some by embryos throughout preimplantation development, and most interestingly, some proteins are just excreted by embryos on day 3 to day 5, suggesting they might be markers for viability," said Dr. Schoolcraft, medical director of the Colorado Center for Reproductive Medicine, Lone Tree.
Indeed, 14 biomarkers are differentially expressed in culture on day 5, which holds great promise for selection of the embryos that are most likely to be successfully implanted.
Nine specific proteins have been identified as candidate biomarkers, including lipocalin-1, which has proved to demonstrate increased expression in aneuploid blastocyst secretome, the material secreted from the embryo.
Significant differences in pregnancy rates have also been found based on reactive oxygen species in the spent media of day 3 embryos, highlighting "another potential marker" for embryo viability and health, said Dr. Schoolcraft.
"The concept would be that in addition to morphology – certainly not in place of morphology – we would be able to look at spent media and identify proteins" that suggest high viability, and select only those embryos that "don’t possess a signature of aneuploidy," he said.
Dr. Schoolcraft reported that he had no relevant financial disclosures.