Biomarkers

Target: Ornithine

Ornithine or L-ornithine, also known as (S)-2,5-diaminopentanoic acid is a member of the class of compounds known as L-alpha-amino acids. L-alpha-amino acids are alpha amino acids which have the L-configuration of the alpha-carbon atom. L-ornithine is soluble (in water) and a moderately basic compound. Ornithine is a non-proteinogenic amino acid that plays a role in the urea cycle. It is considered to be a non-essential amino acid. A non-essential amino acid is an amino acid that can be synthesized from central metabolic pathway intermediates in humans and is not required in the diet. L-Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central part of the urea cycle, which allows for the disposal of excess nitrogen. Outside the human body, L-ornithine is abundant in a number of food items such as wild rice, brazil nuts, common oregano, and common grapes. L-ornithine can be found throughout most human tissues; and in most biofluids, some of which include blood, urine, cerebrospinal fluid (CSF), sweat, saliva, and feces. L-ornithine exists in all living species, from bacteria to plants to humans. L-Ornithine is also a precursor of citrulline and arginine. In order for ornithine that is produced in the cytosol to be converted to citrulline, it must first cross the inner mitochondrial membrane into the mitochondrial matrix where it is carbamylated by the enzyme known as ornithine transcarbamylase. This transfer is mediated by the mitochondrial ornithine transporter (SLC25A15; AF112968; ORNT1). Mutations in the mitochondrial ornithine transporter result in hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome, a disorder of the urea cycle (PMID: 16256388 ). The pathophysiology of the disease may involve diminished ornithine transport into mitochondria, resulting in ornithine accumulation in the cytoplasm and reduced ability to clear carbamoyl phosphate and ammonia loads (OMIM 838970 ). In humans, L-ornithine is involved in a number of other metabolic disorders, some of which include, ornithine transcarbamylase deficiency (OTC deficiency) (PMID: 16635166), argininemia, and guanidinoacetate methyltransferase deficiency (GAMT deficiency). Ornithine is abnormally reduced in the body in ornithine transcarbamylase deficiency. Specifically, in adults (>18 years old) with OTC deficiency, ornithine is reduced in the blood at a concentration of 41.0 +/- 16.0 μM (PMID: 16635166) compared to normal adults at a concentration of 109.0 +/- 32.0 μM (PMID: 16635166). Moreover, ornithine is found to be associated with cystinuria (PMID: 14586528), hyperdibasic aminoaciduria I (PMID: 5727921), and lysinuric protein intolerance (PMID: 27506743), which are inborn errors of metabolism. In adults (>18 years old) with cystinuria, ornithine is found to be significantly elevated in the urine at a concentration of 19-988.300 μmol/mmol creatinine (PMID: 14586528) compared to normal adults at a concentration of 1.5-2.6 μmol/mmol creatinine (PMID: 27012787). In adults (>18 years old) with hyperdibasic aminoaciduria I, ornithine is elevated in the urine at a concentration of 4.106-13.859 μmol/mmol creatinine (PMID: 5727921) compared to normal adults at a concentration of 1.882 +/- 1.968 μmol/mmol creatinine (PMID: 5727921). In adults (>18 years old) with lysinuric intolerance, ornithine is elevated in the blood at a concentration of 32.3 (22.4-53.9) μM (PMID: 27506743) compared to normal adults at a concentration of 74.3 (52.7-81.3) μM (PMID: 27506743). It has been claimed that ornithine improves athletic performance, has anabolic effects, has wound-healing effects, and is immuno-enhancing.