Re: Using single media to day 5 . fertsert paper
Low oxygen and oil overlay
To address your question, indirectly perhaps, there appears to be good evidence that peroxides in the oil overlay, used by many of us, can reach a concentration that is detrimental to eggs and embryos, and the effect of these peroxides is at least due to interaction with albumin in the media. See Otsuki et al 2007 F&S 88:741-743, and Otsuki et al 2009 F&S 91:1745-1749. There appears to be some differences in ‘beginning' concentrations of peroxides in the oil according to batch and/or distributor. The authors investigated storage conditions, and found that time and temperature of storage increased peroxide levels in the oil, and they intimated that exposure to atmospheric oxygen may also increase peroxide levels over time.
There is also a recent publication, just looking at differences in oil by manufacturer in cycles with human embryos, and the authors did find differences in outcomes by manufacturer, and interestingly, sensitivity to oil by manufacturer according to stage of development. See Sifer et al 2009 Eur J Obstet Gyn Reprod Biol 147:52-56. The authors suggested that the processing of oil by each manufacturer could be different, and that the original stock materials used by each manufacturer could be different.
And of course, the biotoxicity testing used by manufacturers is likely different. Along these lines, a recent ASRM abstract by Hughes et al 2009, found that group culture of mouse embryos reduced the sensitivity of the assay to peroxide contaminants in the oil – this demonstrated that yes, peroxides can impact embryo development, as measured by cell numbers and apoptosis. I also like the idea that this abstract also supports group culture of embryos.
Washing oil varies from clinic to clinic, and by manufacturer, and there has been a good debate over whether or not washing oil really helps. There is a recent ASRM abstract by Khan et al 2009, where the oil was washed and evaluated for triton X-100 contamination before and after washing, and washing did help, but it did not completely remove the surfactant. And interestingly, washing oil was found to make the oil more susceptible to sunlight, though most of us do not expose the oil to anything by room lighting – see Provo and Herr 1998 Theriogenology 49:214. Lighting in the laboratory is another fascinating topic.
The rate at which peroxides form in the oil is not clear – days or months from when the bottle of oil is processed, stored, and then opened. Also, I'm not sure if manufacturers gas the oil bottle dead space with sterile nitrogen, or argon, or another inert gas prior to closure, although I would assume so, or at least they would use a sterile gas of some sort.
If you do not use oil overlay, there are two publications addressing reactive oxygen species in culture media and the antioxidant capacity of the media with regard to human embryo development. The experiments were carried out under a 5/5/90 atmosphere, and though the topic of low oxygen vs atmospheric oxygen for culture was not directly addressed, the authors commented "Perhaps one of the most obvious ways of reducing oxidative damage in IVF clinics is to reduce exposure of the gametes and embryos to environments that contain free radicals or that allow their generation". See Bedaiwy et al 2004 F&S 82:593-600, and Bedaiwy et al 2006 F&S 86:304-309.
So, does use of low oxygen in culture impact release of toxins into the culture milieu? Perhaps so, if the oil itself is affected by oxygen and temperature across the culture time frame. And the effect could be very subtle, and we may not see an immediate impact.
So I guess that if you have the ability to use low oxygen in human IVF, and as there are more and more publications supporting the use of low oxygen, then it would be a reasonable course of action.
Mike
Michael L. Reed
