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A 2-oxo monocarboxylic acid that is valeric acid carrying oxo- and methyl substituents at C-2 and C-3, respectively. An alpha-keto acid analogue and metabolite of isoleucine in man, animals and bacteria. Used as a clinical marker for maple syrup urine disease (MSUD)." []

2oxo-3R-methyl-pentanoic acid

Hydroxyphenyllactic acid or 4-hydroxyphenyllactate (the L-form) is a tyrosine metabolite. The level of L-hydroxyphenyllactic acid is elevated in patients with a deficiency of the enzyme p-hydroxyphenylpyruvate oxidase (EC 1.14.2.2) (PMID: 4720815). L-hydroxyphenyllactate is present in relatively higher concentrations in the cerebrospinal fluid and urine of patients with phenylketonuria (PKU) and tyrosinemia (PMID: 3126358). However, the D-form of hydroxyphenyllactate is of bacterial origin and is also found in individuals with bacterial overgrowth or unusual gut microflora (PMID: 3126358). Microbial hydroxyphenyllactate is likely derived from phenolic or polyphenolic compounds in the diet. Bifidobacteria and lactobacilli produce considerable amounts of phenyllactic and p-hydroxyphenyllactic acids (PMID: 23061754). It has also been shown that hydroxyphenyllactate decreases ROS (reactive oxygen species) production in both mitochondria and neutrophils and so hydroxyphenyllactate may function as a natural anti-oxidant (PMID: 23061754). Hydroxyphenyllactic acid is a microbial metabolite found in Acinetobacter, Bacteroides, Bifidobacteria, Bifidobacterium, Clostridium, Enterococcus, Escherichia, Eubacterium, Klebsiella, Lactobacillus, Pseudomonas and Staphylococcus (PMID: 19961416).

2-Pyrocatechuic acid is a normal human benzoic acid metabolite found in plasma (PMID 16351159), and is normally found with increased levels after consumption of many nutrients and drugs, i.e.: cranberry juice (PMID 14733499), aspirin ingestion. (PMID 3342084) It has been found associated with idiopathic oro-facial pain due to stress (oxidative stress might enhance the production of free radicals); it has been suggested that OH radicals are responsible for the production of many systemic and local tissue injury diseases which may initially manifest as pain syndrome, and 2-Pyrocatechuic acid is a biological marker for the detection and quantification of OH radicals, and patients had significantly increased circulating levels of 2-Pyrocatechuic acid after aspirin ingestion than control subjects. (PMID 7748148).

Phenyl hydrogen sulfate is an aryl sulfate that is phenol bearing an O-sulfo substituent. It has a role as a human xenobiotic metabolite. It is functionally related to a phenol. It is a conjugate acid of a phenyl sulfate. Aryl sulfate is a metabolite found in or produced by Escherichia coli (strain K12, MG1655). Phenyl hydrogen sulfate is a natural product found in Trypanosoma brucei with data available.

Phenol sulphate, also known as phenylsulfate or aryl sulphate, belongs to the class of organic compounds known as phenylsulfates. Phenylsulfates are compounds containing a sulfate group conjugated to a phenyl group. In normal humans, phenol sulphate is primarily a gut-derived metabolite that arises from the activity of the bacterial enzyme tyrosine phenol-lyase, which is responsible for the synthesis of phenol from dietary tyrosine (PMID: 31015435). Phenol sulphate can also arise from the consumption of phenol or from phenol poisoning (PMID: 473790). Phenol sulphate is produced from the conjugation of phenol with sulphate in the liver. In particular, phenol sulphate can be biosynthesized from phenol and phosphoadenosine phosphosulfate through the action of the enzyme sulfotransferase 1A1 in the liver. Phenol sulphate can be found in most mammals (mice, rats, sheep, dogs, humans) and likely most animals. Phenol sulphate is a uremic toxin (PMID: 30068866). It is a protein-bound uremic solute that induces reactive oxygen species (ROS) production and decreases glutathione levels, rendering cells vulnerable to oxidative stress (PMID: 29474405). In experimental models of diabetes, phenol sulphate administration has been shown to induce albuminuria and podocyte damage. In a diabetic patient cohort, phenol sulphate levels were found to significantly correlate with basal and predicted 2-year progression of albuminuria in patients with microalbuminuria (PMID: 31015435).

Protocatechuic acid, also known as protocatechuate or 3,4-dihydroxybenzoate, belongs to the class of organic compounds known as hydroxybenzoic acid derivatives. Hydroxybenzoic acid derivatives are compounds containing a hydroxybenzoic acid (or a derivative), which is a benzene ring bearing a carboxyl and a hydroxyl groups. The enzyme protocatechuate 3,4-dioxygenase uses 3,4-dihydroxybenzoate and O2 to produce 3-carboxy-cis,cis-muconate. Protocatechuic acid is a drug. In the analogous hardening of the cockroach ootheca, the phenolic substance concerned is protocatechuic acid. Protocatechuic acid is a mild, balsamic, and phenolic tasting compound. Outside of the human body, protocatechuic acid is found, on average, in the highest concentration in a few different foods, such as garden onions, cocoa powders, and star anises and in a lower concentration in lentils, liquors, and red raspberries. Protocatechuic acid has also been detected, but not quantified in several different foods, such as cloud ear fungus, american pokeweeds, common mushrooms, fruits, and feijoa. This could make protocatechuic acid a potential biomarker for the consumption of these foods. It is also found in Allium cepa (17,540 ppm). It is a major metabolite of antioxidant polyphenols found in green tea. Similarly, PCA was reported to increase proliferation and inhibit apoptosis of neural stem cells. In vitro testing documented antioxidant and anti-inflammatory activity of PCA, while liver protection in vivo was measured by chemical markers and histological assessment.

Gentisic acid, also known as gentisate or 2,5-dioxybenzoate, belongs to the class of organic compounds known as hydroxybenzoic acid derivatives. Hydroxybenzoic acid derivatives are compounds containing a hydroxybenzoic acid (or a derivative), which is a benzene ring bearing a carboxyl and a hydroxyl groups. Gentisic acid is also classified as a dihydroxybenzoic acid. It is a derivative of benzoic acid and a minor (1%) product of the metabolic break down of aspirin, which is excreted by the kidneys. Gentisic acid is found in essentially all organisms ranging from bacteria to fungi to plants to animals. Gentisic acid has been associated with a number of useful effects on human health and exhibits anti-inflammatory, antigenotoxic, hepatoprotective, neuroprotective, antimicrobial, and especially antioxidant activities (PMID: 31825145). It is widely distributed in plants as a secondary plant product such as Gentiana spp., Citrus spp., Vitis vinifera, Pterocarpus santalinus, Helianthus tuberosus, Hibiscus rosa-sinensis, Olea europaea, and Sesamum indicum and in fruits such as avocados, batoko plum, kiwi fruits, apple, bitter melon, black berries, pears, and some mushrooms (PMID: 31825145). Gentisic acid is found in higher concentrations in a number of foods such as tarragons, common thymes, and common sages and in a lower concentration in grape wines, rosemaries, and sweet marjorams. Gentisic acid has also been shown to act as a pathogen-inducible signal for the activation of plant defenses in tomato plants and cucumbers (PMID: 16321412; https://doi.org/10.1094/MPMI.1999.12.3.227).

Kynurenic acid (KYNA) is a well-known endogenous antagonist of the glutamate ionotropic excitatory amino acid receptors N-methyl-D-aspartate (NMDA), alphaamino-3-hydroxy-5-methylisoxazole-4-propionic acid and kainate receptors and of the nicotine cholinergic subtype alpha 7 receptors. KYNA neuroprotective and anticonvulsive activities have been demonstrated in animal models of neurodegenerative diseases. Because of KYNA's neuromodulatory character, its involvement has been speculatively linked to the pathogenesis of a number of neurological conditions including those in the ageing process. Different patterns of abnormalities in various stages of KYNA metabolism in the CNS have been reported in Alzheimer's disease, Parkinson's disease and Huntington's disease. In HIV-1-infected patients and in patients with Lyme neuroborreliosis a marked rise of KYNA metabolism was seen. In the ageing process KYNA metabolism in the CNS of rats shows a characteristic pattern of changes throughout the life span. A marked increase of the KYNA content in the CNS occurs before the birth, followed by a dramatic decline on the day of birth. A low activity was seen during ontogenesis, and a slow and progressive enhancement occurs during maturation and ageing. This remarkable profile of KYNA metabolism alterations in the mammalian brain has been suggested to result from the development of the organisation of neuronal connections and synaptic plasticity, development of receptor recognition sites, maturation and ageing. There is significant evidence that KYNA can improve cognition and memory, but it has also been demonstrated that it interferes with working memory. Impairment of cognitive function in various neurodegenerative disorders is accompanied by profound reduction and/or elevation of KYNA metabolism. The view that enhancement of CNS KYNA levels could underlie cognitive decline is supported by the increased KYNA metabolism in Alzheimer's disease, by the increased KYNA metabolism in down's syndrome and the enhancement of KYNA function during the early stage of Huntington's disease. Kynurenic acid is the only endogenous N-methyl-D-aspartate (NMDA) receptor antagonist identified up to now, that mediates glutamatergic hypofunction. Schizophrenia is a disorder of dopaminergic neurotransmission, but modulation of the dopaminergic system by glutamatergic neurotransmission seems to play a key role. Despite the NMDA receptor antagonism, kynurenic acid also blocks, in lower doses, the nicotinergic acetycholine receptor, i.e., increased kynurenic acid levels can explain psychotic symptoms and cognitive deterioration. Kynurenic acid levels are described to be higher in the cerebrospinal fluid (CSF) and in critical central nervous system (CNS) regions of schizophrenics as compared to controls. (PMID: 17062375 , 16088227). KYNA has also been identified as a uremic toxin according to the European Uremic Toxin Working Group (PMID: 22626821).

2,6-dihydroxybenzoic acid is a secondary metabolite of salicylic acid which has been hydrolyzed by liver enzymes during phase I metabolism.

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).

|FRAME: PHENOL Phenol| is an organic compound consisting of a phenyl group (-C₆H₅) bonded to a hydroxyl group.The word phenol is also used to refer to any compound that contains a six-membered aromatic ring, bonded directly to a hydroxyl group (-OH). Thus, |FRAME: Phenols phenols| are a class of organic compounds of which the phenol compound is the simplest member.

Coumarinic acid, also known as cis-o-coumaric acid or cis-o-hydroxycinnamic acid, is a hydroxy derivative of cinnamic acid. Cinnamic acid and its derivatives are used as important components in flavours, perfumes, synthetic indigo, and pharmaceuticals. There are three isomers of coumaric acid: o-coumaric acid, m-coumaric acid, and p-coumaric acid. These isomers differ by the position of the hydroxy substitution. p-Coumaric acid is the most abundant isomer in nature (Wikipedia). Coumarinic acid is found in pomegranate.

A hydroxycoumarin that is 4,7-dihydroxycoumarin bearing an additional amino substituent at positions 3." []

Myricetin 3-galactoside is found in allspice. Myricetin 3-galactoside occurs in Thea sinensis (tea) and other plant

3-hydroxyphenyllactate is a compound produced by gut (fecal fermentation) of tea or wine

A dicarboxylic acid that is malic acid (2-hydroxysuccinic acid) in which the hydrogen at position 2 is substituted by an isopropyl group." []

2-Isopropylmalic acid (CAS: 3237-44-3), also known as 3-carboxy-3-hydroxyisocaproic acid, belongs to the class of organic compounds known as hydroxy fatty acids. These are fatty acids in which the chain bears a hydroxyl group. 2-Isopropylmalic acid is a very hydrophobic molecule, practically insoluble (in water), and relatively neutral. 2-Isopropylmalic acid is an alpha-hydroxy organic acid regularly occurring in the urine of healthy individuals (PMID: 2338430, 544608), and in hemofiltrates (PMID: 7251751). 2-Isopropylmalic acid is elevated during fasting and diabetic ketoacidosis (PMID: 1591279). It is also a metabolite found in Acetobacter (PMID: 6035258).

A local anesthetic of the amide type now generally used for surface anesthesia. It is one of the most potent and toxic of the long-acting local anesthetics and its parenteral use is restricted to spinal anesthesia. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1006)

Phenol, is a toxic, colourless crystalline solid with a sweet tarry odor that resembles a hospital smell. It is commonly used as an antiseptic and disinfectant. It is active against a wide range of micro-organisms including some fungi and viruses, but is only slowly effective against spores. It has been used to disinfect skin and to relieve itching. Phenol is also used in the preparation of cosmetics including sunscreens, hair dyes, and skin lightening preparations. It is also used in the production of drugs (it is the starting material in the industrial production of aspirin), weedkillers, and synthetic resins. Phenol can be found in areas with high levels of motor traffic, therefore, people living in crowded urban areas are frequently exposed to traffic-derived phenol vapor. The average (mean +/- SD) phenol concentration in urine among normal individuals living in urban areas is 7.4 +/- 2.2 mg/g of creatinine. Exposure of the skin to concentrated phenol solutions causes chemical burns which may be severe; in laboratories where it is used, it is usually recommended that polyethylene glycol solution is kept available for washing off splashes. Notwithstanding the effects of concentrated solutions, it is also used in cosmetic surgery as an exfoliant, to remove layers of dead skin (Wikipedia). In some bacteria phenol can be directly synthesized from tyrosine via the enzyme tyrosine phenol-lyase [EC:4.1.99.2]. It can be produced by Escherichia and Pseudomonas. Phenol has been identified as a uremic toxin according to the European Uremic Toxin Working Group (PMID: 22626821).

7-Methylguanine is a metabolite of DNA methylation and depurination observed in normal human biofluids; however, it has been found significantly higher in the urine of smokers than in nonsmokers. (PMID 16059882). 7-Methylguanine has been identified in the human placenta (PMID: 32033212).

3,4-dimethoxybenzoic acid belongs to the family of M-methoxybenzoic Acids and Derivatives. These are benzoic acids in which the hydrogen atom at position 3 of the benzene ring is replaced by a methoxy group

Myricetin, also known as cannabiscetin or myricetol, belongs to the class of organic compounds known as flavonols. Flavonols are compounds that contain a flavone (2-phenyl-1-benzopyran-4-one) backbone carrying a hydroxyl group at the 3-position. Thus, myricetin is considered to be a flavonoid lipid molecule. A hexahydroxyflavone that is flavone substituted by hydroxy groups at positions 3, 3', 4', 5, 5' and 7. Myricetin is a very hydrophobic molecule, practically insoluble in water, and relatively neutral. Myricetin is found, on average, in the highest concentration within a few different foods, such as common walnuts, carobs, and fennels and in a lower concentration in welsh onions, yellow bell peppers, and jutes. Myricetin has also been detected, but not quantified in several different foods, such as napa cabbages, sesames, mixed nuts, lichee, and garden cress.

3-dehydroteasterone is a 3-oxo-5alpha-steroid, a (22S)-22-hydroxy C28-steroid, a 6-oxo steroid, a 22-hydroxy steroid and a 23-hydroxy steroid. It is functionally related to a teasterone. 3-Dehydroteasterone is a natural product found in Cryptomeria japonica, Triticum aestivum, and Lilium longiflorum with data available.

A C-glycosyl compound that is apigenin substituted by beta-D-glucopyranosyl and an alpha-L-arabinopyranosyl moieties at positions 6 and 8 via C-glycosidic linkages." []

Flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. FAD, also known as adeflavin or flamitajin b, belongs to the class of organic compounds known as flavin nucleotides. These are nucleotides containing a flavin moiety. Flavin is a compound that contains the tricyclic isoalloxazine ring system, which bears 2 oxo groups at the 2- and 4-positions. FAD is a drug which is used to treat eye diseases caused by vitamin b2 deficiency, such as keratitis and blepharitis. FAD exists in all living species, ranging from bacteria to humans. In humans, FAD is involved in the metabolic disorder called the medium chain acyl-coa dehydrogenase deficiency (mcad) pathway. Outside of the human body, FAD has been detected, but not quantified in several different foods, such as other bread, passion fruits, asparagus, kelps, and green bell peppers. It is a flavoprotein in which the substituent at position 10 of the flavin nucleus is a 5'-adenosyldiphosphoribityl group.

1-Methylguanine is a naturally occurring modified purine derived from tRNA, found in elevated levels in the serum and urine of cancer patients (PMID:2413515). Increase of 1-methylguanine in the urine of colorectal tumor bearing patients, has been justified either by a more rapid turnover of nucleic acids in tumor tissue or by an increase in the extent of their methylation (PMID:9069642).

3-Methylguanine is a methylated purine base. Methylated purine bases are known to be present in normal urine and to change under pathological conditions, in particular in the development of leukemia, tumors and immunodeficiency, by the altered turnover of nucleic acids typical of these diseases. (PMID 9069642).