There are two basic sources of phospholipids: synthetic and tissue-derived. Tissue-derived lipids are generally either egg-derived or bovine-derived. For clinical applications, neither of these sources is suitable due to stability problems and the possibility of viral or protein contamination. The U.S. Food and Drug Administration issued a letter restricting the source of bovine tissue used to isolate pharmaceutical products to countries and animals certified to be free of bovine spongiform encephalopathy (BSE). Cattle in the U.S. are not certified BSE-free and cannot be used to isolate pharmaceutical products. Egg sources are not currently restricted; however, additional testing for viral contamination may be required for pharmaceutical products. Regardless of the regulatory issues, animal-derived products do not offer any advantages to synthetic lipids. They are inherently less stable due to the polyunsaturated fatty acids, and in most cases the synthetic counterpart costs the same or less than the tissue-derived product.
Synthetic lipids from different sources are not necessarily equal either. Synthetic lipids can be prepared from glycerol or glycero-3-phosphocholine (GPC) derived from a plant or animal source. The latter is sometimes referred to as semi-synthetic lipid because a portion of the molecule is derived from a natural source. Lipids derived from glycerol require the chiral center be synthetically prepared which may lead to stereochemical impurities present in the final product. Lipids prepared using GPC obtained from an animal source may suffer from the same viral and protein contamination issues outlined above. The typical plant source for GPC is soybean lecithin.