Albumin is the one of the most abundant serum proteins found in plasma and is present in all mammals. Albumin is a complex protein that has many functions in the body including maintaining osmotic pressure of the circulatory system and binding a variety of molecules including toxins. It also binds and transports fatty acids. With these roles in vivo, it is logical that it would provide value in mammalian cell culture.
Role in Mammalian Cell Culture
Fetal bovine serum has been an important part of culturing mammalian cells for decades. Its composition of proteins, nutrients, growth factors, etc. provides cells with a complete cocktail from which to grow. However, with the desire to move toward serum-free media came the need to find alternative supplements to provide cells support in culture. Since the major protein in serum is albumin and it plays many roles in the human body, it was an obvious choice in lieu of serum. It has since become a popular media supplement from both human and bovine sources. While there is much literature published on albumin and its role in cell culture, there is still much to be learned.
Bovine Serum Albumin
As a by-product of the meat industry, bovine serum albumin is greatly available and as a large component of FBS, it was a logical choice as a media supplement when FBS was removed. Due to its availability, there is a temptation to think of it as a commodity product, however, albumin’s complexity prevents such a simple definition. Consequently viewing it as a commodity presents challenges in the way it is used in cell culture.
For example, it is well recognized that both human and bovine serum albumin are able to enhance cell culture through its ability to bind lipids and deliver them to the cells. Albumin contains several fatty acid binding sites and fatty acids bind these albumin sites primarily by hydrophobic binding. However, the fatty acid profile for commercially available albumins varies (Alfano, 2016). The primary reason for this variability is based on how the albumin is purified. The manufacturing method dictates how much fatty acid is present in the final product. Some cells like the additional fatty acids, but others do not. Cell response often depends on the cell line and the type and amount of fatty acids present.
The article series, “Is Bovine Albumin Too Complex to Be Just a Commodity?, by Frank J. Mannuzza and Joseph G. Montalto discusses the challenge of performance variability and present a compelling argument for creating a better link between manufacturing method and product application. They suggest that the industry must understand which aspects of albumin are critical to performance quality and then identify the manufacturing method that supports the presence of these critical quality attributes in the final product.
Bovine serum albumin (BSA) is purified from serum using one of three different purification methods: cold-organic solvent fractionation, heat shock and ion exchange chromatography. Mannuzza and Montalto point out that each method produces a BSA that can meet standard specifications, but often ignored are the attributes not measured in a standard Certificate of Analysis. These unmeasured attributes, like fatty acid profiles, hormone profiles, contaminants and presence of IgG, transferrin and other peptides can be critical to a BSA’s performance in a particular application.
Different manufacturing methods also create a lack of heterogeneity in the BSA market, thus causing performance variability both lot-to-lot and among suppliers. This variability causes end users to conduct lot qualification, which is time consuming and costly to both end users and suppliers. Mannuzza and Montalto suggest that the best way to address this issue is to match the BSA to its intended use.
I was very interested in this topic as performance variability and lot qualification is a frequent criticism of BSA use. I was fortunate to be able to talk with Foster Harris, Vice President of Business Development, MP Biomedicals about these issues and to get a supplier’s perspective. Our interview is below:
What do you see as the primary applications for BSA, are there any emerging uses?
The broad primary applications are for diagnostic, mammalian cell culture and bacterial media use. MP Biomedicals focuses on the last two. I am unaware of any new potential uses that haven’t already been tried or considered.
What do you see as the biggest challenge with performance variability for Bovine Serum Albumin?
Some of it has to do with the fact we are working with a biologic (cell culture and viral media use) so each animal’s plasma is somewhat different than that of another. Some has to do with process and handling within a company as people are not robots and there could be differences between how one technician follows the process steps vs. another individual. Some of it also has to do with the components utilized in the development process. As an example: we use Gel from a company who have been making it for 40 years, whereas other companies may just be making their own on site. Therefore, the lot-to-lot variation could be attributed to the Gel used and the expertise of the company selling the Gel.
Can you describe the types of Bovine Serum Albumin you offer and why you feel it is important to have variety?
It is important to have a variety of options for the customer to choose from as each customer has their own application for BSA use. Not all BSA is the same and not all applications are the same.
We offer BSA from other manufacturers who use the Heat Shock process from U.S. origin cattle and we plan to also offer NZ origin Heat Shock BSA in the near future, which widely known as the highest quality designation.
MP Biomedicals manufactures four standard grades: Low Fatty Acid, Low Endotoxin, Low Protease and Low IGG.
How do you advise customers on selecting which BSA is best for their application?
There are BSA grades that are designed to work in different applications. The sales person directing the customer to the appropriate BSA grade needs to understand each of the BSAs and what their intended use is. It really is a matter of learning which BSA is best suited for an application. Sometimes the customer may have more than one option depending upon their end use. As an example: Stem Cell Media – Low Endotoxin and Low Fatty Acid could be recommended depending on whether the customer adds fatty acids and lipids to their media or they don’t add these components. Additionally, our NZ BSA is manufactured in a GMP approved facility and following GMP quality guidelines. Some customers need that certification for their intended use.