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Lactic acid is an organic acid. It is a chiral molecule, consisting of two optical isomers, L-lactic acid and D-lactic acid, with the L-isomer being the most common in living organisms. Lactic acid plays a role in several biochemical processes and is produced in the muscles during intense activity. In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal. This is governed by a number of factors, including monocarboxylate transporters, lactate concentration, the isoform of LDH, and oxidative capacity of tissues. The concentration of blood lactate is usually 1-2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion. There are some indications that lactate, and not glucose, is preferentially metabolized by neurons in the brain of several mammalian species, including mice, rats, and humans. Glial cells, using the lactate shuttle, are responsible for transforming glucose into lactate, and for providing lactate to the neurons. Lactate measurement in critically ill patients has been traditionally used to stratify patients with poor outcomes. However, plasma lactate levels are the result of a finely tuned interplay of factors that affect the balance between its production and its clearance. When the oxygen supply does not match its consumption, organisms adapt in many different ways, up to the point when energy failure occurs. Lactate, being part of the adaptive response, may then be used to assess the severity of the supply/demand imbalance. In such a scenario, the time to intervention becomes relevant: early and effective treatment may allow tissues and cells to revert to a normal state, as long as the oxygen machinery (i.e. mitochondria) is intact. Conversely, once the mitochondria are deranged, energy failure occurs even in the presence of normoxia. The lactate increase in critically ill patients may, therefore, be viewed as an early marker of a potentially reversible state (PMID: 16356243). When present in sufficiently high levels, lactic acid can act as an oncometabolite, an immunosuppressant, an acidogen, and a metabotoxin. An oncometabolite is a compound that promotes tumor growth and survival. An immunosuppressant reduces or arrests the activity of the immune system. 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 lactic acid are associated with at least a dozen inborn errors of metabolism, including 2-methyl-3-hydroxybutyryl CoA dehydrogenase deficiency, biotinidase deficiency, fructose-1,6-diphosphatase deficiency, glycogen storage disease type 1A (GSD1A) or Von Gierke disease, glycogenosis type IB, glycogenosis type IC, glycogenosis type VI, Hers disease, lactic acidemia, Leigh syndrome, methylmalonate semialdehyde dehydrogenase deficiency, pyruvate decarboxylase E1 component deficiency, pyruvate dehydrogenase complex deficiency, pyruvate dehydrogenase deficiency, and short chain acyl CoA dehydrogenase deficiency (SCAD deficiency). Locally high concentrations of lactic acid or lactate are found near many tumors due to the upregulation of lactate dehydrogenase (PMID: 15279558). Lactic acid produced by tumors through aerobic glycolysis acts as an immunosuppressant and tumor promoter (PMID: 23729358). Indeed, lactic acid has been found to be a key player or regulator in the development and malignant progression of a variety of cancers (PMID: 22084445). A number of studies have demonstrated that malignant transformation is associated with an increase in aerobic cellular lactate excretion. Lactate concentrations in various carcinomas (e.g. uterine cervix, head and neck, colorectal region) at first diagnosis of the disease, can be relatively low or extremely high (up to 40 µmol/g) in different individual tumors or within the same lesion (PMID: 15279558). High molar concentrations of lactate are correlated with a high incidence of distant metastasis. Low lactate tumors (< median of approximately 8 µmol/g) are associated with both an overall longer and disease-free survival compared to high lactate lesions (lactate > approximately 8 µmol/g). Lactate-induced secretion of hyaluronan by tumor-associated fibroblasts creates a milieu favourable for cell migration and metastases (PMID: 22084445). An acidic environment (pH 6-6.5), which is common in many tumors, allows tumor cells to evade the immune response, and therefore allows them to grow unchecked. Locally high concentrations of lactic acid are known to markedly impede the function of normal immune cells and will lead to a loss of T-cell function of human tumor-infiltrating lymphocytes (PMID: 22084445). Lactic acid is also an organic acid and acts as a general acidogen. 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, kidney abnormalities, liver damage, 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. Lactic acid is also a microbial metabolite, urinary lactic acid is produced by Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia, Enterobacter, Acinetobacter, Proteus mirabilis, Citrobacter frundii, Enterococcus faecalis, Streptococcus group B, Staphylococcus saprophyticus (PMID: 22292465), Bacillus, Corynebacterium, Rhizopus and Saccharomyces cerevisiae (PMID: 26360870).

Lactic acid is an organic acid. It is a chiral molecule, consisting of two optical isomers, L-lactic acid and D-lactic acid, with the L-isomer being the most common in living organisms. Lactic acid plays a role in several biochemical processes and is produced in the muscles during intense activity. D-Lactic acid is the end product of the enzyme glyoxalase II (or hydroxyacyl-glutathione hydrolase) (EC 3.1.2.6), which converts the intermediate substrate S-lactoyl-glutathione to reduced glutathione and D-lactate (OMIM: 138790). Lactic acid is a microbial metabolite found in Aerococcus, Bacillus, Carnobacterium, Corynebacterium, Enterococcus, Escherichia, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Rhizopus, Saccharomyces, Streptococcus, Tetragenococcus, Vagococcus and Weissella (PMID:26287368; PMID:26360870).

3-Hydroxypropionic acid is a carboxylic acid. It is an intermediate in the breakdown of branched-chain amino acids and propionic acid from the gut. Typically it originates from propionyl-CoA and a defect in the enzyme propionyl carboxylase. This leads to a buildup in propionyl-CoA in the mitochondria.  Such a buildup can lead to a disruption of the esterified CoA:free CoA ratio and ultimately to mitochondrial toxicity. Detoxification of these metabolic end products occurs via the transfer of the propionyl moiety to carnitine-forming propionyl-carnitine, which is then transferred across the inner mitochondrial membrane. 3-Hydroxypropionic acid is then released as the free acid. As an industrial chemical, it is used in the production of various chemicals such as acrylates in industry. When present in sufficiently high levels, 3-hydroxypropionic 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 hydroxypropionic acid are associated with many inborn errors of metabolism including biotinidase deficiency, malonic aciduria, methylmalonate semialdehyde dehydrogenase deficiency, methylmalonic aciduria, methylmalonic aciduria due to cobalamin-related disorders, and propionic acidemia. Hydroxypropionic acid is 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. Infants with acidosis have symptoms that include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart, liver, and kidney abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of the 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. 3-Hydroxypropionic acid is also a microbial metabolite found in Escherichia, Klebsiella and Saccharomyces (PMID: 26360870).

Dimethyl carbonate is used for cold sterilisation of beverages. Effective against typical beverage-spoiling microorganisms, like yeasts and fermentative bacteria Dimethyl carbonate, often abbreviated DMC, is a flammable clear liquid boiling at 90 °C. It has recently found use as a methylating reagent. Its main benefit over other methylating reagents such as iodomethane and dimethyl sulfate is its lesser toxicity and its biodegradability. Also, it is now prepared from catalytic oxidative carbonylation of methanol with carbon monoxide and oxygen, instead of from phosgene making its production non-toxic and environmentally friendly. This allows dimethyl carbonate to be considered a green reagent

Glyceraldehyde is a triose monosaccharide with chemical formula C3H6O3. It is the simplest of all common aldoses. It is a sweet, colourless crystalline solid that is an intermediate compound in carbohydrate metabolism. The word "glyceraldehyde" comes from combining glycerine and aldehyde, as glyceraldehyde is merely glycerine with one hydroxide changed to an aldehyde. Glyceraldehyde is produced from the action of the enzyme glyceraldehyde dehydrogenase, which converts glycerol to glyceraldehyde using NADP as a cofactor. When present at sufficiently high levels, glyceraldehyde can be a cytotoxin and a mutagen. A cytotoxin is a compound that kills cells. A mutagen is a compound that causes mutations in DNA. Glyceraldehyde is a highly reactive compound that can modify and cross-link proteins. Glyceraldehyde-modified proteins appear to be cytotoxic, depress intracellular glutathione levels, and induce reactive oxygen species (ROS) production (PMID:14981296). Glyceraldehyde has been shown to cause chromosome damage to human cells in culture and is mutagenic in the Ames bacterial test.

3-(3-Hydroxyphenyl)propanoic (hMPP) acid is one of the major metabolites of ingested caffeic acid (PMID: 15479001) and of the phenolic degradation products of proanthocyanidins (the most abundant polyphenol present in chocolate) by the microflora in the colon (PMID: 12663291). mHPP is suspected to have antioxidants properties and is actively absorbed by the monocarboxylic acid transporter (MCT) in intestinal Caco-2 cell monolayers (PMID: 15479001, 12663291). hMPP has been found to be a metabolite of Clostridium, Escherichia, and Eubacterium (PMID: 28393285, 19520845). 3-(3-Hydroxyphenyl)propanoic acid is a flavonoid metabolite. 3-(3-Hydroxyphenyl)propanoic acid is a phenolic acid metabolite formed by the gut microflora detected after the consumption of whole grain.

3-(2-Hydroxyphenyl)propanoic acid is found in bilberry. 3-(2-Hydroxyphenyl)propanoic acid is found in Melilotus alba (whilte melilot).

Ethyl 2-aminobenzoate is found in citrus. Ethyl 2-aminobenzoate is a flavouring ingredient. Ethyl 2-aminobenzoate is present in orange juice, orange peel and concord grape.

Indolelactic acid (CAS: 1821-52-9) is a tryptophan metabolite found in human plasma, serum, and urine. Tryptophan is metabolized by two major pathways in humans, either through kynurenine or via a series of indoles, and some of its metabolites are known to be biologically active. Indolelactic acid is present in various amounts, significantly higher in umbilical fetal plasma than in maternal plasma in the protein-bound form (PMID 2361979, 1400722, 3597614, 11060358, 1400722). Indolelactic acid is also a microbial metabolite; urinary indole-3-lactate is produced by Clostridium sporogenes (PMID: 29168502).

Salicylic acid is a monohydroxybenzoic acid that is benzoic acid with a hydroxy group at the ortho position. It is obtained from the bark of the white willow and wintergreen leaves. It has a role as an antiinfective agent, an antifungal agent, a keratolytic drug, an EC 1.11.1.11 (L-ascorbate peroxidase) inhibitor, a plant metabolite, an algal metabolite and a plant hormone. It is a conjugate acid of a salicylate. It is a colorless solid, it is a precursor to and a metabolite of aspirin (acetylsalicylic acid). It is a plant hormone. The name is from Latin salix for willow tree. It is an ingredient in some anti-acne products. Salts and esters of salicylic acid are known as salicylates. Salicylic acid modulates COX1 enzymatic activity to decrease the formation of pro-inflammatory prostaglandins. Salicylate may competitively inhibit prostaglandin formation. Salicylate's antirheumatic (nonsteroidal anti-inflammatory) actions are a result of its analgesic and anti-inflammatory mechanisms. Salicylic acid works by causing the cells of the epidermis to slough off more readily, preventing pores from clogging up, and allowing room for new cell growth. Salicylic acid inhibits the oxidation of uridine-5-diphosphoglucose (UDPG) competitively with nicotinamide adenosine dinucleotide and noncompetitively with UDPG. It also competitively inhibits the transferring of glucuronyl group of uridine-5-phosphoglucuronic acid to the phenolic acceptor. The wound-healing retardation action of salicylates is probably due mainly to its inhibitory action on mucopolysaccharide synthesis. Salicylic acid is biosynthesized from the amino acid phenylalanine. In Arabidopsis thaliana, it can be synthesized via a phenylalanine-independent pathway.

4-Hydroxybenzoic acid, also known as p-hydroxybenzoate or 4-carboxyphenol, 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. 4-Hydroxybenzoic acid is a white crystalline solid that is slightly soluble in water and chloroform but more soluble in polar organic solvents such as alcohols and acetone. It is a nutty and phenolic tasting compound. 4-Hydroxybenzoic acid exists in all living species, ranging from bacteria to plants to humans. 4-Hydroxybenzoic acid can be found naturally in coconut. It is one of the main catechins metabolites found in humans after consumption of green tea infusions. It is also found in wine, in vanilla, in Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), at relatively high concetrations (892±52 mg/kg). It is also found in cloudy olive oil and in the edible mushroom Russula virescens. It has been detected in red huckleberries, rabbiteye blueberries, and corianders and in a lower concentration in olives, red raspberries, and almonds. In humans, 4-hydroxybenzoic acid is involved in ubiquinone biosynthesis. In particular, the enzyme 4-hydroxybenzoate polyprenyltransferase uses a polyprenyl diphosphate and 4-hydroxybenzoate to produce diphosphate and 4-hydroxy-3-polyprenylbenzoate. This enzyme participates in ubiquinone biosynthesis. 4-Hydroxybenzoic acid can be biosynthesized by the enzyme Chorismate lyase. Chorismate lyase is an enzyme that transforms chorismate into 4-hydroxybenzoate and pyruvate. This enzyme catalyses the first step in ubiquinone biosynthesis in Escherichia coli and other Gram-negative bacteria. 4-Hydroxybenzoate is an intermediate in many enzyme-mediated reactions in microbes. For instance, the enzyme 4-hydroxybenzaldehyde dehydrogenase uses 4-hydroxybenzaldehyde, NAD+ and H2O to produce 4-hydroxybenzoate, NADH and H+. This enzyme participates in toluene and xylene degradation in bacteria such as Pseudomonas mendocina. 4-hydroxybenzaldehyde dehydrogenase is also found in carrots. The enzyme 4-hydroxybenzoate 1-hydroxylase transforms 4-hydroxybenzoate, NAD(P)H, 2 H+ and O2 into hydroquinone, NAD(P)+, H2O and CO2. This enzyme participates in 2,4-dichlorobenzoate degradation and is found in Candida parapsilosis. The enzyme 4-hydroxybenzoate 3-monooxygenase transforms 4-hydroxybenzoate, NADPH, H+ and O2 into protocatechuate, NADP+ and H2O. This enzyme participates in benzoate degradation via hydroxylation and 2,4-dichlorobenzoate degradation and is found in Pseudomonas putida and Pseudomonas fluorescens. 4-Hydroxybenzoic acid is a popular antioxidant in part because of its low toxicity. 4-Hydroxybenzoic acid has estrogenic activity both in vitro and in vivo (PMID 9417843).

Cyclo(L-Phe-L-Pro) is an organic molecular entity. It has a role as a metabolite. Cyclo(L-Phe-L-Pro) is a natural product found in Nigrospora oryzae, Epichloe typhina, and other organisms with data available.

3-Hydroxybenzoic acid, also known as 3-hydroxybenzoate or 3-carboxyphenol, 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. 3-Hydroxybenzoic acid exists in all living organisms, ranging from bacteria to humans. Outside of the human body, 3-hydroxybenzoic acid is found, on average, in the highest concentration in american cranberries and beers. 3-hydroxybenzoic acid has also been detected, but not quantified in a few different foods, such as bilberries, citrus, and corns. As well, 3-Hydroxybenzoic Acid can be found in the pineapple fruit. It can also be formed by a Pseudomonas species from 3-Chlorobenzoic acid. 3-Hydroxybenzoic acid is a monohydroxybenzoic acid. 3-Hydroxybenzoic acid can be obtained by the alkali fusion of 3-sulfobenzoic acid between 210-220 °C. 3-Hydroxybenzoic acid is a component of castoreum, the exudate from the castor sacs of the mature North American beaver (Castor canadensis) and the European beaver (Castor fiber), used in perfumery.

A glutamic acid derivative that is L-glutamic acid in which the two hydrogens on the amino group are substituted by a phthaloyl group." []

Jasmonic acid is found in apple. Esters are present in Jasminum grandiflorum (royal jasmine) and are responsible for its odour. Jasmonic acid is a member of the jasmonate class of plant hormones. It is biosynthesized from linolenic acid by the octadecanoid pathway

7-epijasmonic acid, also known as (+)-epijasmonate, is a member of the class of compounds known as jasmonic acids. Jasmonic acids are lipids containing or derived from a jasmonic acid, with a structure characterized by the presence of an alkene chain linked to a 2-(3-oxocyclopentyl)acetic acid moiety. Thus, 7-epijasmonic acid is considered to be an octadecanoid lipid molecule. 7-epijasmonic acid is practically insoluble (in water) and a weakly acidic compound (based on its pKa). 7-epijasmonic acid can be found in a number of food items such as broad bean, flaxseed, corn, and eggplant, which makes 7-epijasmonic acid a potential biomarker for the consumption of these food products.

5-Methoxyindoleacetate, also known as 5-methoxy-IAA or 5-MIAA, belongs to the class of organic compounds known as indole-3-acetic acid derivatives. Indole-3-acetic acid derivatives are compounds containing an acetic acid (or a derivative) linked to the C3 carbon atom of an indole. 5-Methoxyindoleacetic acid is formed through oxidative deamination. It is identified in the urine, and the concentration is determined to be 1.3 µg/mL using GC-MS (PMID: 12908946). An increase in urinary 5-MIAA excretion was shown in patients with cancer of the stomach, rectum, and lung (PMID: 2446428).

3-O-caffeoylquinic acid methyl ester is a quinic acid. Methyl chlorogenate is a natural product found in Gelasia latifolia, Takhtajaniantha austriaca, and other organisms with data available. See also: Manilkara zapota fruit (part of).

3,3'-dimethoxybenzidine appears as colorless crystals or a light brown powder. Turns violet on standing. Carcinogen. 3,3'-Dimethoxybenzidine is a member of biphenyls. 3,3'-Dimethoxybenzidine is used as an intermediate in the production of dyes and pigments. No information is available on the acute (short-term), chronic (long-term), reproductive, developmental, or carcinogenic effects of 3,3'-dimethoxybenzidine in humans. Animal studies have reported effects on the liver, kidneys, spleen, and bladder, and endocrine effects, gastritis, intestinal hemorrhage, and weight loss from chronic oral exposure. Increased incidences of tumors in several organs have been reported in rats orally exposed to 3,3'-dimethoxybenzidine or its salt. EPA has classified 3,3'-dimethoxybenzidine as a Group B2, probable human carcinogen. Dianisidine is a colorless, highly toxic, crystalline compound that turns violet when exposed to air. Dianisidine is used exclusively as an intermediate for the production of dyes and pigments. Exposure to this substance causes skin irritation and sensitization. Dianisidine is reasonably anticipated to be a human carcinogen based on evidence of carcinogenicity in experimental animals. (NCI05) 3,3'-Dimethoxybenzidine (o-Dianisidine) can cause cancer according to an independent committee of scientific and health experts. Highly toxic compound which can cause skin irritation and sensitization. It is used in manufacture of azo dyes.

(R)-indole-3-lactic acid is a propanoic acid derivative having an (R)-hydroxy substituent at the 2-position and a 1H-indol-3-yl group at the 3-position. It is functionally related to a propionic acid and a 1H-indole. It is a conjugate acid of a (R)-indole-3-lactate. (2R)-2-hydroxy-3-(1H-indol-3-yl)propanoic acid is a natural product found in Malassezia furfur with data available.

1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [N-methyl-(R)salsolinol, NM(R)Sal] is the most potent toxin among isoquinolines. Endogenous isoquinolines with and without catechol structure have been proposed to be neurotoxins specific for dopamine neurons. (PMID 9085193). (R)salsolinol N-methyltransferase synthesizes N-methyl(R)salsolinol, which is further oxidized into 1,2-dimethyl-6,7-dihydroxyisoquinolinium ion by non-enzymatic and enzymatic oxidation. (PMID 14697894). Dopamine-derived N-methyl(R)salsolinol is an endogenous MPTP-like neurotoxin to cause Parkinson's disease. In the cerebrospinal fluid from newly diagnosed untreated patients with Parkinson's disease, the level of this toxin was found to increase significantly, compared to control and a disease control, multiple system atrophy. L-DOPA therapy did not seem to affect the level of this toxin. The results suggest that N-methyl(R)salsolinol level in the cerebrospinal fluid may indicate remaining dopamine neurons in the parkinsonian brain. (PMID 10076861). N-methyl(R)salsolinol (NM(R)Sal) induces apoptosis (but not necrosis) in SH-SY5Y cells, and the apoptotic cascade is initiated by mitochondrial permeability transition and activated by stepwise reactions. (PMID 12200198).

1,2-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline is an endogenous amine in parkinsonian and normal human brain. (PMID 2049084). Endogenous isoquinolines with and without catechol structure have been proposed to be neurotoxins specific for dopamine neurons. (PMID 9085193).