Glutamine: Role in the Fetus and Low-birthweight Infant

Abstract

After completing this article, readers should be able to: 1. Describe the glutamine-glutamate shuttle. 2. Delineate the effects of glutamine supplementation during total parenteral nutrition, chemotherapy, and radiotherapy in animals. 3. Describe the beneficial effects of glutamine supplementation in low-birthweight infants and in critically ill adults. 4. List the primary actions of glutamine in the intestine. The importance of glutamine for optimal growth of cells in culture has been known since the 1950s, when Eagle published his landmark paper in Science .1 His work demonstrated that of all the amino acids, cell growth in culture relied most on glutamine. Numerous subsequent studies have established the importance of glutamine for a variety of metabolic processes in the entire organism and are beginning to demonstrate that nutritional supplementation of this amino acid may be highly beneficial under certain circumstances. Glutamine and glutamate are structurally similar five-carbon amino acids. Glutamine is a neutral amino acid at pH 7.0 that contains an alpha-amino group and a deltaamide group. In glutamate, the amide nitrogen of glutamine is replaced by a carboxy-group, conferring to it a net negative charge at pH 7.0. This at least partially accounts for the transport of these two amino acids across cell membranes via different transport systems. The presence or absence of the amide group is responsible for different metabolic interactions of these amino acids. The array of metabolic processes in which glutamine is involved is highlighted by its relationship to its metabolites and the citric acid cycle (Fig. 1⇓ ).Glutamine, via glutamate, is readily converted to alpha-ketoglutarate, an integral component of the citric acid cycle. Deamidation of glutamine via glutaminase produces glutamate, a precursor of gamma-amino butyric acid (GABA), a neurotransmission inhibitor. Proline also is produced by the cyclization of glutamate. Proline is an important amino acid component of collagen and …