NONENZYMATIC FORMATION OF FORMALDEHYDE IN MOUSE OOCYTE FREEZING MIXTURES

Three cryoprotectant solvents, dimethylsulphoxide, 1,2-propanediol and glycerol, were investigated for a nonenzymatic reaction product, form aldehyde. All three cryoprotectants demonstrated a direct relationship between increasing solvent molarity and increasing formaldehyde conce ntration which was independent of temperature and protein (bovine seru m albumin). Medium composition significantly influenced the formaldehy de concentration with HTF > T6 > M16 = M2. The formaldehyde could be e ffectively removed by reduced glutathione, cysteine and dithiothreitol with cysteine being the most effective scavenging agent. A reaction m echanism for this scavenging is proposed. The combination of cysteine and cryoprotectant reduced the zona pellucida 'hardening' effect in mo use oocytes.