Formaldehyde in cryoprotectant propanediol and effect on mouse zygotes

Cryopreservation of human zygotes and embryos has been routinely performedby in-vitro fertilization clinics for many years. Karran and Legge (1996)first reported that formaldehyde (FA) present in the cryoprotectivesolutions can have a deleterious effect on mouse oocytes. FA is acytotoxic, carcinogenic and mutagenic chemical. The effect of FA on mousezygotes was investigated. In addition, the concentrations of FA inpropanediol (PROH) obtained from various sources were determined. Pooled1-cell embryos were dispensed into droplets of modified Ham's F10 or humantubal fluid containing various concentrations of FA. Since bovine serumalbumin (BSA) may minimize toxicity additional trials were done as above inthe absence of BSA. FA concentration in the standard 1.5 M PROH, fromdifferent sources in water, was measured in the same assay using a standardcurve of 0-100 microM FA. FA in a complex medium had a significantdeleterious effect on embryo development and hatching but only at 1 mMconcentration (P < 0.000001; see Tables I-III). There was no significanteffect of FA at 100 microM. However, in a simple medium even 50 microM FAdecreased embryo hatching. FA was present in 1.5 M PROH from differentsources (range 1.0-35.3 microM concentration). It appears that FAconcentrations do not increase with storage because FA concentrations werelow even after opening and storage for 3 years on the shelf. This suggeststhat FA is a contaminant during the manufacturing process and may vary frommanufacturer to manufacturer and batch to batch. Until further studies aredone to confirm the lack of toxicity to embryos during cryopreservation(with or without FA scavengers) it may be prudent to screen all batches ofcryoprotectants for FA as part of quality control.