302 PROTEIN SUPPLEMENTATION TO IVM MEDIUM IN RELATION TO THE INCIDENCE OF APOPTOSIS IN BOVINE OOCYTES MATURED IN VITRO

Abstract

Mammalian embryos derived from in vitro fertilization display lower developmental competence and quality when compared to their in vivo counterparts. The composition of culture media significantly contributes to this phenomenon. Media supplemented with FBS or the serum derivate BSA are described as biochemically undefined. Those macromolecules were shown to exert a wide range of effects on cultured embryos, dependent on batch-to-batch variability. Therefore, replacement of these protein sources with a synthetic macromolecule such as polyvinyl pyrrolidone (PVP) or polyvinyl alcohol (PVA) provides a possibility to use a chemically defined culture medium (Ali et al. 2002 Biol. Reprod. 66, 901–905). Apoptosis as programmed cell death naturally occurs in mammalian oocytes and embryos; however, its incidence is significantly higher in vitro. The aim of this study was to investigate whether protein supplementation (FBS, fatty acid-free (faf)-BSA, PVP40) of IVM medium affects the incidence of apoptotic oocytes. In the present study, the IVM system previously described by Makarevich et al. (2002 Biol. Reprod. 66, 386–392) was used. Briefly, follicular oocytes aspirated from slaughterhouse ovaries were matured in vitro in one of three maturation media supplemented with FBS (10%), faf-BSA (6 mg mL⁻¹) or PVP40 (4 mg mL⁻¹). The terminal TUNEL assay kit was used to detect the DNA fragmentation in apoptotic cells (DeadEnd^TM Fluorometric TUNEL system, Promega, Madison, WI, USA). The data were analyzed by chi-square test of independence. Altogether, 630 oocytes collected during 12 IVM experiments were subjected to the Tunel test, and 563 (89.4%) of them were successfully investigated: 426 after maturation in vitro and 137 follicular, non-matured. The remaining 67 cells were lost during manipulation. The rate of Tunel-positive cells differed (P < 0.001) between matured (11.8%) and follicular oocytes (1.5%). Protein supplementation of IVM media did not significantly affect the rate of apoptotic oocyte occurrence, which was 9% in the faf-BSA group, 11.5% in the FBS group, and 15% in the PVP group. No differences were observed in the rate of Tunel-positive cells between oocytes at MII and MI stages. In conclusion, protein supplementation of IVM medium used in the present study did not affect the incidence of apoptotic oocytes after maturation in vitro.

This research was supported by the State Committee for Scientific Research as a Solicited Project PBZ-KBN-084 from 2003 to 2005 year.