5.0

Detected but not Quantified

Homovanillic acid

Homovanillic acid (HVA), also known as homovanillate, belongs to the class of organic compounds known as methoxyphenols. Methoxyphenols are compounds containing a methoxy group attached to the benzene ring of a phenol moiety. HVA is also classified as a catechol. HVA is a major catecholamine metabolite that is produced by a consecutive action of monoamine oxidase and catechol-O-methyltransferase on dopamine. HVA is typically elevated in patients with catecholamine-secreting tumors (such as neuroblastoma, pheochromocytoma, and other neural crest tumors). HVA levels are also used in monitoring patients who have been treated for these kinds tumors. HVA levels may also be altered in disorders of catecholamine metabolism such as monoamine oxidase-A (MOA) deficiency. MOA deficiency can cause decreased urinary HVA values, while a deficiency of dopamine beta-hydrolase (the enzyme that converts dopamine to norepinephrine) can cause elevated urinary HVA values. Within humans, HVA participates in a number of enzymatic reactions. In particular, HVA and pyrocatechol can be biosynthesized from 3,4-dihydroxybenzeneacetic acid and guaiacol. This reaction is catalyzed by the enzyme known as catechol O-methyltransferase. In addition, HVA can be biosynthesized from homovanillin through the action of the enzyme known aldehyde dehydrogenase. HVA has recently been found in a number of beers and appears to arise from the fermentation process (https://doi.org/10.1006/fstl.1999.0593). HVA is also a metabolite of Bifidobacterium (PMID: 24958563) and the bacterial breakdown of dietary flavonoids. Dietary flavonols commonly found in tomatoes, onions, and tea, can lead to significantly elevated levels of urinary HVA (PMID: 20933512). Likewise, the microbial digestion of hydroxytyrosol (found in olive oil) can also lead to elevated levels of HVA in humans (PMID: 11929304).

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