Amino Acid Analysis of Plasma.

Amino acid analysis of plasma metabolites.

Amino acid analysis is an important tool for the analysis of free amino acids and other similar biomolecules that contain primary and secondary amino groups within their structure and which are present in blood serum, plasma, and other body fluids such as urine and cerebrospinal fluid (CSF). CSF is a clear, colorless bodily fluid found in the brain and spine. During the last decades, it has become clear that amino acids play a crucial role as metabolites and as regulators of metabolic pathways in mammals, including humans. Since the blood serves as a common medium that links all organs in the body together, plasma amino acid concentrations could be affected by metabolic disturbances in a particular organ system. Therefore, amino acid profiling of blood plasma samples can be used to study the levels of amino acid metabolites.

Metabolite profiling usually refers to a set of metabolites, along with their concentrations, detected in a biological sample. Metabolite profiles can be very specific for certain classes of chemical compounds, such as lipids or amino acids. Similar to the genome, the full complement of genes of an organism, the metabolome, is described as the full complement of metabolites of an organism. The terms"metabolite" and"metabolome" have become established in the scientific literature since the year 2000. A Pubmed search for "metabolomics" showed that, as of Fall 2013, over 6,100 papers on this subject have already been published thus far. The combination of next-generation deep-sequencing technologies with mass spectrometry and other technologies such as amino acid analysis will surely provide more accurate data as a result of the extensive study of the metabolome in the near future.

Abnormal profiles in amino acid concentrations are observed in various diseases such as liver disease, end-stage renal disease, hepatocellular carcinoma, and others. In addition, several plasma peptides have also been identified as hormones important in metabolic physiology and diseases. One important peptide class includes the family of cardiac natriuretic peptides. These types of peptides have emerged as potent metabolic hormones that exhibit a wide range of biological actions and are involved in the control of metabolic homeostasis. Homeostasis is the ability or tendency of an organism or cell to maintain internal equilibrium.  A mammalian body achieves this by adjusting all physiological processes to coordinate responses of its parts to any situation or stimulus that tends to disturb the normal conditions or functions in order to maintain internal stability. Therefore, changes in plasma amino acid levels can reflect the metabolic status of a patient. For example, patients with severe hepatic disease have an amino acid imbalance in which low levels of branched chain amino acids and high levels of aromatic amino acids are observed in their systemic blood when analyzed.  Further, it is known that the increase in aromatic amino acids levels in the brain can lead to a decrease in the normal neurotransmitters and an increase in the neurologically inactive phenylethanolamine and octopamine. The intake of branched chain amino acids improves the plasma amino acid balance. Peptides with high levels of branched chain amino acids and low levels of aromatic amino acids are called high-Fischer-ratio oligopeptides. The Fischer ratio is the ratio between branched-chain amino acids (BCAA) and aromatic amino acids (AAA) which can be defined by the formula Fr = (Leu + Val + Ile)/(Tyr + Phe). This ratio has been used for the diagnosis of hepatic encephalopathy and its drug treatment efficacy. High Fischer ratio oligopeptides can be derived from various food proteins and their resulting amino acid content can be determined by amino acid analysis.

Kimura T, Noguchi Y, Shikata N, Takahashi M Plasma amino acid analysis for diagnosis and amino acid-based metabolic networks. Curr Opin Clin Nutr Metab Care. 2009 Jan;12(1):49-53. doi: 10.1097/MCO.0b013e3283169242.