DICARBOXYLIC-ACIDS, AN ALTERNATE FUEL SUBSTRATE IN PARENTERAL-NUTRITION - AN UPDATE

Dicarboxylic acids (DA) are formed from the omega-oxidation of monocarboxylic acids when the beta-oxidation of free fatty acids is impaired. Medium-chain DA have the peculiar characteristic of being water soluble due to the presence of two carboxylic terminal groups in the molecule. Contrary to both long- and medium-chain triglycerides which are administered as emulsions, they can be given by a peripheral vein as inorganic salts. DA are beta-oxidized at level of both peroxisomes and mitochondria via carnitine-independent pathway. The products of beta-oxidation of odd-chain DA are acetyl-CoA and malonyl-CoA, which can not be oxidized further, are used in lipogenesis. Moreover even-chain DA produce acetyl-CoA and succinyl-CoA, which is a gluconeogenetic precursor. Azetaic acid (C9), does not show acute or chronic toxicity effects in animals but much of it is lost in urine (more than 50% of the given dose). Sebacic acid (C10) is lost in urine to a smaller extent (about 12% of the administered dose) and its energy density (6.64 Kcal/g) is greater than that of C9 (4.97 Kcal/g). Dodecanedioic acid (C12) seems to be the best candidate for parenteral nutrition, because it is eliminated in the urine only in minimal amounts (3.90% of the given dose), it is rapidly utilized by tissues, and it has a high energy density (7.20 Kcal/g).