Dispensable, Indispensable, and Conditionally Indispensable Amino Acid Ratios in the Diet
Friedman Mendel in Absorption and Utilization of Amino Acids, 2019
This chapter discusses the determination of reasonable dietary ratios of amino acids (AA) and the effect of those ratios on physiological responses. The AA may be divided into the nutritional classifications of indispensable (IAA), conditionally indispensable, and dispensable (DAA) based on absolute ability or relative rates of synthesis in vivo. The chapter examines views and approaches to the formulation of the AA portion of diets and the possible application of the Saturation Kinetics Model (SKM) to their improvement. The SKM is based on the concept that an organism is characterized by a sequence of homeostatically constrained steady states. Physiological responses are the result of a series of enzymatically mediated steps, one of which is rate limiting and displays saturation kinetics. The study of proteins gives some empirical insight into optimal IAA/DAA ratios and is important for formulating protein based diets. AA must be studied individually to determine optimal ratios.
Single Amino Acids
Luke R. Bucci in Nutrition Applied to Injury Rehabilitation and Sports Medicine, 2020
This chapter explores the use of individual amino acids for enhancement of musculoskeletal healing. Proteins are composed of amino acids linked together into discrete chains. Amino acid metabolism encompasses and directly impacts almost every aspect of cellular function. Amino acids are referred to as either essential (indispensable) or nonessential (dispensable). Arginine is one of the basic amino acids, along with lysine, histidine, ornithine, and citrulline. Initial work on arginine found that it was a dietary essential amino acid during periods of growth in rats, but not in stable adults. Studies in injured rats found that arginine administration enhanced wound healing, ulcer healing, fracture repair rates, nitrogen balance, or protein synthesis. Significant analgesia compared to saline infusion was measured for 6 to 24 h after arginine infusion. Analgesia was blocked by naloxone administration, an opioid peptide antagonist. The branched-chain amino acids are indispensable in the diet.
Amino Acids
Michael B. Smith in Biochemistry, 2020
There is an important class of difunctional molecule that is critical to an understanding of biological processes. Amino acids comprise the backbone of peptides, and thereby of enzymes. This chapter discusses the structure, nomenclature, and characteristics of amino acids. The basic amine reacts intramolecularly with the acidic proton of acetic acid to form a conjugate base and a conjugate acid in the same molecule. An intermolecular example of this reaction occurs when methanamine (methyl amine) and acetic acid are mixed together, and the product is methylammonium acetate. There are two enantiomers for each amino acid, based on the zwitterionic forms of a generic amino acid with one alkyl group R and one hydrogen atom.
Amino acid kinetics and the response to nutrition in patients with cancer
Published in International Journal of Radiation Biology, 2019
Barbara S. van der Meij, Laisa Teleni, Marielle P. K. J. Engelen, Nicolaas E. P. Deutz
Purpose: Amino acids are involved in many physiological processes in the body and serve as building blocks of proteins which are the main component of muscle mass. Often patients with cancer experience muscle wasting, which is associated with poor outcomes. The purpose of this paper is to discuss amino acid kinetics in cancer, review the evidence on the response to nutrition in patients with cancer, and to give recommendations on the appropriate level of amino acid or protein intake in cancer. Current evidence shows that amino acid kinetics in patients with cancer are disturbed, as reflected by increased and decreased levels of plasma amino acids, an increased whole body turnover of protein and muscle protein breakdown. A few studies show beneficial effects of acute and short-term supplementation of high protein meals or essential amino acid mixtures on muscle protein synthesis. Conclusions: Cancer is associated with disturbances in amino acid kinetics. A high protein intake or supplementation of amino acids may improve muscle protein synthesis. Future research needs to identify the optimal level and amino acid mixtures for patients with cancer, in particular for those who are malnourished.
Serum and plasma amino acids as markers of prediabetes, insulin resistance, and incident diabetes
Published in Critical Reviews in Clinical Laboratory Sciences, 2018
C. Gar, M. Rottenkolber, C. Prehn, J. Adamski, J. Seissler, A. Lechner
Presently, routine screening misses many cases of prediabetes and early type 2 diabetes (T2D). Therefore, better biomarkers are needed for a simple and early detection of abnormalities of glucose metabolism and prediction of future T2D. Possible candidates for this include plasma or serum amino acids because glucose and amino acid metabolism are closely connected. This review presents the available evidence of this connectivity and discusses its clinical implications. First, we examine the underlying physiological, pre-analytical, and analytical issues. Then, we summarize results of human studies that evaluate amino acid levels as markers for insulin resistance, prediabetes, and future incident T2D. Finally, we illustrate the interconnection of amino acid levels and metabolic syndrome with our own data from a deeply phenotyped human cohort. We also discuss how amino acids may contribute to the pathophysiology of T2D. We conclude that elevated branched-chain amino acids and reduced glycine are currently the most robust and consistent amino acid markers for prediabetes, insulin resistance, and future T2D. Yet, we are cautious regarding the clinical potential even of these parameters because their discriminatory power is insufficient and their levels depend not only on glycemia, but also on other components of the metabolic syndrome. The identification of more precise intermediates of amino acid metabolism or combinations with other biomarkers will, therefore, be necessary to obtain in order to develop laboratory tests that can improve T2D screening.
Levels of amino acids in human hepatocellular carcinoma and adjacent liver tissue
Published in Nutrition and Cancer, 1995
Takashi Nishizaki, Takashi Matsumata, Akinobu Taketomi, Kazuharu Yamamoto, Keizo Sugimachi
Total parenteral nutrition can be used to overcome amino acid imbalance in cancer patients. Because there is little documentation of treatment for amino acid imbalance in patients with hepatocellular carcinoma (HCC), we designed a study 1) to compare tissue levels of amino acids between HCC and the adjacent liver and 2) to determine which serum amino acids correlate to tumor volume. A significant elevation of methionine and a significant decrease of glycine and cystine were observed in HCC compared with adjacent liver tissue, and a significant correlation was found between tumor volume and serum methionine levels (x = ‐0.636, p < 0.01). Thus the tumor tissue competes successfully with host tissue for nitrogen substrates, particularly methionine, and an accelerated protein synthesis in HCC consumes large amounts of these amino acids. The possibility of methionine‐depleted treatment could be considered for patients with HCC.
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