Orotic acid (BioDeep_00000001401)

描述信息

Orotic acid is classified as a pyrimidinemonocarboxylic acid. That is it is a uracil bearing a carboxy substituent at position C-6. It is also classified as a pyrimidinedione and a carboxylic acid. Orotic acid is a minor dietary constituent. Indeed, until it was realized that it could be synthesized by humans, orotic acid was known as vitamin B-13. The richest dietary sources of orotic acid are cows milk and other dairy products as well as root vegetables such as carrots and beets. Dietary intake probably contributes to a basal rate of orotic acid excretion in urine because fasting decreases excretion by ~50\\\\%. However, it is now apparent that most urinary orotic acid is synthesized in the body, where it arises as an intermediate in the pathway for the synthesis of pyrimidine nucleotides. Orotic acid is converted to UMP by UMP synthase, a multifunctional protein with both orotate phosphoribosyltransferase and orotidylate decarboxylase activity. The most frequently observed inborn error of pyrimidine nucleotide synthesis is a mutation of the multifunctional protein UMP synthase (UMP synthase deficiency or orotic aciduria). This disorder prevents the conversion of orotic acid to UMP, and thus to other pyrimidines. As a result, plasma orotic acid accumulates to high concentrations, and increased quantities appear in the urine. Indeed, urinary orotic acid is so markedly increased in individuals harboring a mutation in UMP synthase that orotic acid crystals can form in the urine. The urinary concentration of orotic acid in individuals suffering from orotic aciduria can be of the order of millimoles of orotic acid per millimole creatinine. By comparison, the urinary level in unaffected individuals is ~ 1 ¬umol/mmol creatinine (PMID: 17513443). Orotic aciduria is characterized by megaloblastic anemia and orotic acid crystalluria that is frequently associated with some degree of physical and mental retardation. These features respond to appropriate pyrimidine replacement therapy and most cases appear to have a good prognosis. When present in sufficiently high levels, orotic acid can act as an acidogen and a metabotoxin. An acidogen is an acidic compound that induces acidosis, which has multiple adverse effects on many organ systems. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of orotic acid are associated with at least seven inborn errors of metabolism, including argininemia, LPI syndrome (lysinuric protein intolerance), hyperornithinemia-hyperammonemia-homocitrullinuria (HHH), OTC deficiency, citrullinemia type I, purine nucleoside phosphorylase deficiency, and orotic aciduria. Orotic acid is broadly classified as an organic acid. Abnormally high levels of organic acids in the blood (organic acidemia), urine (organic aciduria), the brain, and other tissues lead to general metabolic acidosis. Acidosis typically occurs when arterial pH falls below 7.35. In infants with acidosis, the initial symptoms include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of the untreated IEMs mentioned above. Many affected children with organic acidemias experience intellectual disability or delayed development. In adults, acidosis or acidemia is characterized by headaches, confusion, feeling tired, tremors, sleepiness, and seizures.
Orotic acid, also known as orotate or orotsaeure, is a member of the class of compounds known as pyrimidinecarboxylic acids. Pyrimidinecarboxylic acids are pyrimidines with a structure containing a carboxyl group attached to the pyrimidine ring. Orotic acid is slightly soluble (in water) and a moderately acidic compound (based on its pKa). Orotic acid can be synthesized from uracil. Orotic acid can also be synthesized into dihydroorotic acid. Orotic acid can be found in a number of food items such as okra, atlantic herring, black chokeberry, and prunus (cherry, plum), which makes orotic acid a potential biomarker for the consumption of these food products. Orotic acid can be found primarily in most biofluids, including saliva, amniotic fluid, blood, and urine, as well as in human liver and pancreas tissues. Orotic acid exists in all living species, ranging from bacteria to humans. In humans, orotic acid is involved in the pyrimidine metabolism. Orotic acid is also involved in few metabolic disorders, which include beta ureidopropionase deficiency, dihydropyrimidinase deficiency, MNGIE (mitochondrial neurogastrointestinal encephalopathy), and UMP synthase deficiency (orotic aciduria). Moreover, orotic acid is found to be associated with hyperornithinemia-hyperammonemia-homocitrullinuria, orotic aciduria I, ornithine transcarbamylase deficiency, and n-acetylglutamate synthetase deficiency. Orotic acid is a non-carcinogenic (not listed by IARC) potentially toxic compound. The compound is manufactured in the body via a mitochondrial enzyme, dihydroorotate dehydrogenase or a cytoplasmic enzyme of pyrimidine synthesis pathway. It is sometimes used as a mineral carrier in some dietary supplements (to increase their bioavailability), most commonly for lithium orotate . Chronically high levels of orotic acid are associated with at least 4 inborn errors of metabolism including: Argininemia, Citrullinemia Type I, Purine nucleoside phosphorylase deficiency and Orotic Aciduria (T3DB).
Orotic acid (6-Carboxyuracil), a precursor in biosynthesis of pyrimidine nucleotides and RNA, is released from the mitochondrial dihydroorotate dehydrogenase (DHODH) for conversion to UMP by the cytoplasmic UMP synthase enzyme. Orotic acid is a marker for measurement in routine newborn screening for urea cycle disorders. Orotic acid can induce hepatic steatosis and hepatomegaly in rats[1][2][3].

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