Synthetic serum substitute (SSS): a globulin-enriched protein supplement for human embryo culture

Abstract

Objective: The purpose of the present study was to evaluate whether an IVF protein supplement prepared from human serum albumin (HSA) and human globulins would retain performance characteristics equivalent to those reported for the commercial plasma expanders, Plasmatein (Alpha Therapeutics, Los Angeles, California) and Plasmanate (Cutter Biological, Miles Inc., Elkhart, Indiana).

Methods: Pronuclear-stage human embryos were randomly divided and cultured in human tubal fluid medium (HTF) supplemented with either HSA (5 mg/mL) or Plasmatein (10%, v/v; 5 mg/ml) as a means of indirectly assessing the effect alpha- and beta-globulins have on embryonic development. Those results coupled with the known composition characteristics of Plasmatein were used as the starting basis to formulate test lots of synthetic serum substitute (SSS).

Results: Significantly (P < 0.05) more of the human embryos cultured in Plasmatein supplemented medium reached the four-cell or greater stage by 40 hr postinsemination than a comparable group cultured in HSA alone. Lot 1 of SSS, formulated with HSA (84% of total protein) and human globulins (16% of total protein) and an aqueous lipoprotein fraction derived from human plasma (Excyte IV; Miles Diagnostics, Kankakee, Illinois), produced accelerated early embryonic growth relative to control murine embryos grown in the presence of Plasmatein, however, the percentage of the embryos reaching the hatched blastocyst stage was decreased (45 vs 100%). Human embryos from seven patients, randomized to HTF medium supplemented with Plasmatein or lot 1 of SSS, showed equivalent growth at 36-40 hr postinsemination. A microprecipitate developed in media supplemented with lot 1 after several days of culture. The Excyte IV concentration was reduced and, ultimately, eliminated from the subsequent and final prototype lots of SSS. Murine embryos grown in the presence of lipoprotein free SSS showed significantly accelerated (P < 0.01) growth at 17 hr postthaw compared to Plasmatein and all embryos progressed to hatching by 41 hr. Human embryos, randomized to either Plasmatein or lot 3 of SSS, showed significantly accelerated growth (P < 0.01) when scored at 38 hr following insemination.

Conclusion: Synthetic serum substitute provides a convient, standardized means of adding protein to media used in assisted reproductive technology (ART) procedures.