- Chemically defined medium
A chemically defined medium is a growth medium suitable for the in vitro cell culture of human or animal cells in which all of the chemical components are known. The term chemically defined medium was defined by Jayme and Smith (2000) as a 'Basal formulation which may also be protein-free and is comprised solely of biochemically-defined low molecular weight constituents'.
A chemically defined medium is entirely free of animal-derived components and represents the purest and most consistent cell culture environment.
By definition chemically defined media cannot contain either fetal bovine serum, bovine serum albumin or human serum albumin as these products are derived from bovine or human sources and contain complex mixes of albumins and lipids. The term chemically defined media is often misused in the literature to refer to serum albumin-containing media. Animal serum or albumin is routinely added to culture media as a source of nutrients and other ill-defined factors, despite technical disadvantages to its inclusion and its high cost. Technical disadvantages to using serum include the undefined nature of serum, batch-to-batch variability in composition, and the risk of contamination. There are increasing concerns about animal suffering inflicted during serum collection that add an ethical imperative to move away from the use of serum wherever possible.
Chemically defined media differ from serum-free media in that bovine serum albumin or human serum albumin with either a chemically defined recombinant version (which lacks the albumin associated lipids) or synthetic chemical such as the polymer polyvinyl alcohol which can reproduce some of the functions of BSA/HSA. The next level of defined media, below chemically defined media is Protein-Free Media. These media contain animal protein hydrolysates and are complex to formulate although are commonly used for insect or CHO cell culture. Animal culture media can be divided into five subsets based on the level of defined media (Jayme and Smith, 2000): From lowest definition to highest these are: 1, Serum-containing media; 2, Reduced-serum media; 3, Serum-free media, 4, Protein-free media; 5, Chemically-defined media.
The term 'defined media' is commonly used to refer to serum-free media. Media formulations containing the media supplement B27 (supplied by Invitrogen) are often erroneously referred to as chemically defined media (e.g. Yao et al., 2006) despite this product containing bovine serum albumin (Chen et al., 2008) using the above definitions this type of media is referred to as serum-free media.
Other variants of serum-free media include:
Animal protein-free media, containing human serum albumin, human transferrin, human insulin, but animal-derived lipids (as with StemPro 34).
Xeno-free media, containing human serum albumin, human transferrin, human insulin, and chemically defined or human lipids.
Recombinant, xeno-free media, containing recombinant human serum albumin or a synthetic replacement, recombinant human insulin, recombinant human transferrin, and chemically defined lipids.
Jayme DW, Smith SR (2000). "Media formulation options and manufacturing process controls to safeguard against introduction of animal origin contaminants in animal cell culture.". Cytotechnology 33: 27–36. PMID 19002808.
Yao S, Chen S, Clark J, Hao E, Beattie GM, Hayek A, Ding S. (2006). "Long-term self-renewal and directed differentiation of human embryonic stem cells in chemically defined conditions.". PNAS 103: 6907–6912. doi:10.1073/pnas.0602280103. PMC 1458992. PMID 16632596. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1458992.
Chen, Y., Stevens, B., Chang, J., Milbrandt, J., Barres, B. A., Hell, J. W. (2008). "NS21: re-defined and modified supplement B27 for neuronal cultures.". J. Neurosci. Methods 171: 239–247. doi:10.1016/j.jneumeth.2008.03.013. PMC 2678682. PMID 18471889. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2678682.
Summers, M.C., Biggers, J. (2003). "Chemically defined media and the culture of mammalian preimplantation embryos: historical perspective and current issues.". Human Reproduction Update 9: 557–582. PMID 14714592.
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