Linoleic acid in Cell Culture

Importance and uses of linoleic acid in serum-free eukaryotic, including hybridoma and Chinese Hamster Ovary (CHO) cell, cultures

Linoleic Acid, a Serum-Free Medium Supplement, Useful In Biomanufacturing, Tissue Engineering, and Specialty Media

Fatty acids of the n-3, n-6 and n-9 families are important supplements for cell culture systems. They are important in cell culture systems used to biomanufacture heterologous proteins, such as monoclonal antibodies. Fatty acids have been shown to be important for the growth and productivity of Chinese Hamster Ovary (CHO) cells.

Linoleic acid is a n-6 unsaturated fatty acid that is not synthesized by animal cells and must be provided as a nutrient in cell culture. Linoleic acid is poorly soluble in aqueous media and susceptible to peroxidation. Historically, linoleic acid has been provided to cells in culture as a component of serum, albumin complex or esterified to molecules such as cholesterol . However, several classical media identify linoleic acid as a component of their basal formulae. While this is potentially useful when media are prepared and used fresh, it is a problem for media that are stored for use in commercial applications such as biomanufacturing and tissue engineering.

Historical media with free linoleic acid in their formulae include those based upon Ham's Nutrient Mixture, F-12: DMEM/Ham's Nutrient Mixture F-12 (50:50); F-12 Coon's Modification; MCDB Media, 105, 201, and 302; and Serum-Free/Protein Free Hybridoma Medium. Since these F-12 media derivatives also contain free iron, they are inherently unstable and not suitable as stored formulations.

The advent of serum-free, animal-protein-free and protein-free media formulations has increased the difficulty of delivering linoleic acid to cells in culture. The proper formulation of linoleic acid as a stable supplement is a challenge for the development of proprietary media useful for biomanufacturing and tissue engineering. For a more complete discussion of linoleic and other fatty acids as a cell culture additives, visit our Media Expert^®.

Primary Functions of Linoleic Acid in Cell Culture Systems:

• Long-term energy storage: energy derived from NADPH and ATP is stored in fatty acids. Fatty acids are esterified to a glycerol backbone to form a group of compounds known as mono-, di- and tri- glycerides (neutral fats). Energy is released when fatty acids are degraded.
• Fatty acids are precursors of other molecules: prostaglandins, prostacyclins, thromboxanes, phospho-lipids, glycolipids, and vitamins.
• Structural elements: fatty acids are important constituents of cell structures such as the membranes.

Chemical Attributes of Linoleic Acid that make it a Useful Serum-Free Medium Supplement:

Fatty acids (FA) are long-chain carboxylic acids that are insoluble in water. These fatty acid chains can be from 4 to 30 carbons long, but physiologically the most important fatty acids are from 16 to 22 carbons long. Since fatty acids are synthesized naturally by the addition of acetyl groups, they have an even numbers of carbon atoms-C2, C4, etc. They can be saturated or unsaturated. Natural fatty acids have their double bonds in the cis-configuration and are usually esterified to glycerol backbones to form complex lipids. Fatty acids that contain more than one double bond are called polyunsaturated fatty acids (PUFAs).

Whether a fatty acid is an n-3, n-6 or n-9 type is important, because animal cells cannot synthesize fatty acids of the n-3 or n-6 type. They must be provided in the diet and are considered essential fatty acids (EFAs).

Linoleic and linolenic acids are essential fatty acids (EFAs) produced by plants that must be provided to animal cells in vitro.

• Linoleic acid (18:2, n-6) is precursor to a number of other fatty acids; one of the most important is arachidonic acid (20:4, n-6), a PUFA with four double bonds that is a precursor of some prostaglandins. Serum albumin typically carries about 12% of all fatty acids as linoleic acid.
• Linolenic (n-3) is a precursor to fatty acids, such as the docosahexaenoic acids (22:6, n-3), a highly unsaturated PUFA with six double bonds.

If linoleic and linolenic fatty acids are not provided in sufficient quantity, cells cannot produce other important fatty acids, and fatty acid derivatives.