Fertilization and early embryology: Non-enzymatic formation of formaldehyde in mouse oocyte freezing mixtures

Three cryoprotectant solvents, dimethylsulphoxide, 1,2-propanedioland glycerol, were investigated for a non-enzymatic reactionproduct, formaldehyde. All three cryoprotectants demonstrateda direct relationship between increasing solvent molarity andincreasing formaldehyde concentration which was independentof temperature and protein (bovine serum albumin). Medium compositionsignificantly influenced the formaldehyde concentration withHTF T6 M16 = M2. The formaldehyde could be effectively removedby reduced glutathione, cysteine and dithiothreitol with cysteinebeing the most effective scavenging agent A reaction mechanismfor this scavenging is proposed. The combination of cysteineand cryoprotectant reduced the zona pellucida ‘hardening’effect in mouse oocytes.