X-Message-Number: 30165
Date: Tue, 18 Dec 2007 06:39:17 -0800 (PST)
Subject: cryoprotectants contaminated with formaldehyde

[A lowered temperature does not reduce cryoprotectant "induced"
formaldehyde generation, possibly because formaldehyde was a contaminant
of the cryoprotectants themselves. This points to various sources of
cryoprotectants having different cytotoxicities, depending on their
formaldehyde content. The addition of formadehyde scavengers to
cryopreservation solutions may eliminate this source of toxicity.]

Hum Reprod. 1998 Apr;13(4):979-82. Links
Formaldehyde in cryoprotectant propanediol and effect on mouse zygotes.
  Mahadevan MM, McIntosh Q, Miller MM, Breckinridge SM, Maris M, Moutos DM.
University of Arkansas for Medical Sciences, Department of Obstetrics and
Gynecology, Little Rock, USA.
Cryopreservation of human zygotes and embryos has been routinely performed
by in-vitro fertilization clinics for many years. Karran and Legge (1996)
first reported that formaldehyde (FA) present in the cryoprotective
solutions can have a deleterious effect on mouse oocytes. FA is a cytotoxic,
carcinogenic and mutagenic chemical. The effect of FA on mouse zygotes was
investigated. In addition, the concentrations of FA in propanediol (PROH)
obtained from various sources were determined. Pooled 1-cell embryos were
dispensed into droplets of modified Ham's F10 or human tubal fluid
containing various concentrations of FA. Since bovine serum albumin (BSA)
may minimize toxicity additional trials were done as above in the absence of
BSA. FA concentration in the standard 1.5 M PROH, from different sources in
water, was measured in the same assay using a standard curve of 0-100 microM
FA. FA in a complex medium had a significant deleterious effect on embryo
development and hatching but only at 1 mM concentration (P < 0.000001; see
Tables I-III). There was no significant effect of FA at 100 microM. However,
in a simple medium even 50 microM FA decreased embryo hatching. FA was
present in 1.5 M PROH from different sources (range 1.0-35.3 microM
concentration). It appears that FA concentrations do not increase with
storage because FA concentrations were low even after opening and storage
for 3 years on the shelf. This suggests that FA is a contaminant during the
manufacturing process and may vary from manufacturer to manufacturer and
batch to batch. Until further studies are done to confirm the lack of
toxicity to embryos during cryopreservation (with or without FA scavengers)
it may be prudent to screen all batches of cryoprotectants for FA as part of
quality control.
PMID: 9619557

Hum Reprod. 1996 Dec;11(12):2681-6.
Non-enzymatic formation of formaldehyde in mouse oocyte freezing mixtures.
  Karran G, Legge M. Department of Biochemistry, University of Otago,
Dunedin, New Zealand.
  Three cryoprotectant solvents, dimethylsulphoxide, 1,2-propanediol and
glycerol, were investigated for a non-enzymatic reaction product,
formaldehyde. All three cryoprotectants demonstrated a direct
relationship between increasing solvent molarity and increasing
formaldehyde concentration which was independent of temperature and
protein (bovine serum albumin). Medium composition significantly
influenced the formaldehyde concentration with HTF > T6 > M16 = M2. The
formaldehyde could be effectively removed by reduced glutathione,
cysteine and dithiothreitol with cysteine being the most effective
scavenging agent. A reaction mechanism for this scavenging is
proposed. The combination of cysteine and cryoprotectant reduced the zona
pellucida 'hardening' effect in mouse oocytes.
PMID: 9021372

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