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(±)-erythro-Isoleucine is a flavouring ingredient, dietary supplement, and a nutrient. Branched-chain amino acids (BCAA) are essential amino acids whose carbon structure is marked by a branch point. These three amino acids are critical to human life and are particularly involved in stress, energy and muscle metabolism. BCAA supplementation as therapy, both oral and intravenous, in human health and disease holds great promise. BCAA denotes valine, isoleucine, and leucine which are branched chain essential amino acids. Despite their structural similarities, the branched amino acids have different metabolic routes, with valine going solely to carbohydrates, leucine solely to fats, and isoleucine to both. The different metabolism accounts for different requirements for these essential amino acids in humans: 12 mg/kg, 14 mg/kg, and 16 mg/kg of valine, leucine, and isoleucine respectively. Furthermore, these amino acids have different deficiency symptoms. Valine deficiency is marked by neurological defects in the brain, while isoleucine deficiency is marked by muscle tremors. BCAA are decreased in patients with liver disease such as hepatitis, hepatic coma, cirrhosis, extrahepatic biliary atresia, or portacaval shunt. Aromatic amino acids (AAA)-tyrosine, tryptophan, and phenylalanine (as well as methionine) are increased in these conditions. Valine, in particular, has been established as a useful supplemental therapy to the ailing liver. All the BCAA probably compete with AAA for absorption into the brain. Supplemental BCAA with vitamin B6 and zinc help normalize the BCAA:AAA ratio. The BCAA are not without side effects. Leucine alone, for example, exacerbates pellagra and can cause psychosis in pellagra patients by increasing excretion of niacin in the urine. Leucine may lower brain serotonin and dopamine. The ratio of leucine to other BCAA is greatest in pork, where leucine is 7 to 8 g and the other BCAA together are only 3 to 4 g (http://www.dcnutrition.com).

Isoleucine (Ile) or L-isoleucine is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-isolecuine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Isoleucine is found in all organisms ranging from bacteria to plants to animals. It is classified as a non-polar, uncharged (at physiological pH) aliphatic amino acid. Isoleucine is an essential amino acid in humans, meaning the body cannot synthesize it and that it must be obtained from the diet. In plants and microorganisms, isoleucine is synthesized starting from pyruvate and alpha-ketobutyrate. Isoleucine is classified as a branched chain amino acid (BCAA). BCAAs include three amino acids: isoleucine, leucine and valine. They are alpha amino acids whose carbon structure is marked by a beta branch point. Despite their structural similarities, BCAAs have different metabolic routes, with valine going solely to carbohydrates (glucogenic), leucine solely to fats (ketogenic) and isoleucine being both a glucogenic and a ketogenic amino acid. Isoleucine is catabolized via with alpha-ketoglutarate where upon it is oxidized and split into propionyl-CoA and acetyl-CoA. Propionyl-CoA is converted into succinyl-CoA, a TCA cycle intermediate which can be converted into oxaloacetate for gluconeogenesis (hence glucogenic). The acetyl-CoA can be fed into the TCA cycle by condensing with oxaloacetate to form citrate or used in the synthesis of ketone bodies or fatty acids. The different metabolism of BCAAs accounts for different requirements for these essential amino acids in humans: 12 mg/kg, 14 mg/kg and 16 mg/kg of valine, leucine and isoleucine are required respectively. Furthermore, these amino acids have different deficiency symptoms. Valine deficiency is marked by neurological defects in the brain, while isoleucine deficiency is marked by muscle tremors. BCAAs are decreased in patients with liver disease, such as hepatitis, hepatic coma, cirrhosis, extrahepatic biliary atresia. An inability to break down isoleucine, along with other amino acids, is associated with maple syrup urine disease (MSUD) (PMID: 34125801). Isoleucine, like other BCAAs, is associated with insulin resistance. In particular, higher levels of isoleucine are observed in the blood of diabetic mice, rats, and humans (PMID 25287287). Mice fed an isoleucine deprivation diet for one day have improved insulin sensitivity, and feeding of an isoleucine deprivation diet for one week significantly decreases blood glucose levels (PMID: 24684822).

L-Norleucine, also known as L-aminohexanoate or caprine, belongs to the class of organic compounds known as l-alpha-amino acids. These are alpha amino acids which have the L-configuration of the alpha-carbon atom. Thus, L-norleucine is considered to be a fatty acid lipid molecule. An unnatural amino acid that is used experimentally to study protein structure and function. L-Norleucine is a very hydrophobic molecule, practically insoluble in water, and relatively neutral. L-Norleucine exists in all eukaryotes, ranging from yeast to humans. Outside of the human body, L-Norleucine has been detected, but not quantified in cow milk. This could make L-norleucine a potential biomarker for the consumption of these foods. It binds reversibly to the kringle domain of plasminogen and blocks the binding of plasminogen to fibrin and its activation to plasmin.

2-amino-3-(4-chlorophenyl)propanoic acid is a phenylalanine derivative. A selective and irreversible inhibitor of tryptophan hydroxylase, a rate-limiting enzyme in the biosynthesis of serotonin (5-HYDROXYTRYPTAMINE). Fenclonine acts pharmacologically to deplete endogenous levels of serotonin.

2-Amino-4-methylpentanoic acid

An aromatic amino acid that is alanine in which one of the methyl hydrogens is substituted by a phenyl group." []

Tetracycline is a broad spectrum polyketide antibiotic produced by the Streptomyces genus of Actinobacteria. It exerts a bacteriostatic effect on bacteria by binding reversible to the bacterial 30S ribosomal subunit and blocking incoming aminoacyl tRNA from binding to the ribosome acceptor site. It also binds to some extent to the bacterial 50S ribosomal subunit and may alter the cytoplasmic membrane causing intracellular components to leak from bacterial cells.

Oleamide is an amide of the fatty acid oleic acid. It is an endogenous substance: it occurs naturally in the body of animals. It accumulates in the cerebrospinal fluid during sleep deprivation and induces sleep in animals. It is being studied as a potential medical treatment for mood and sleep disorders, and cannabinoid-regulated depression. The mechanism of action of oleamide's sleep inducing effects is an area of current research. It is likely that oleamide interacts with multiple neurotransmitter systems. Oleamide is structurally related to the endogenous cannabinoid anandamide, and has the ability to bind to the CB1 receptor as a full agonist.

Phenylalanine (Phe), also known as L-phenylalanine is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-phenylalanine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Phenylalanine is found in all organisms ranging from bacteria to plants to animals. It is classified as an aromatic, non-polar amino acid. In humans, phenylalanine is an essential amino acid and the precursor of the amino acid tyrosine. Like tyrosine, phenylalanine is also a precursor for catecholamines including tyramine, dopamine, epinephrine, and norepinephrine. Catecholamines are neurotransmitters that act as adrenalin-like substances. Interestingly, several psychotropic drugs (mescaline, morphine, codeine, and papaverine) also have phenylalanine as a constituent. Phenylalanine is highly concentrated in the human brain and plasma. Normal metabolism of phenylalanine requires biopterin, iron, niacin, vitamin B6, copper, and vitamin C. An average adult ingests 5 g of phenylalanine per day and may optimally need up to 8 g daily. Phenylalanine is highly concentrated in a number of high protein foods, such as meat, cottage cheese, and wheat germ. An additional dietary source of phenylalanine is artificial sweeteners containing aspartame (a methyl ester of the aspartic acid/phenylalanine dipeptide). As a general rule, aspartame should be avoided by phenylketonurics and pregnant women. When present in sufficiently high levels, phenylalanine can act as a neurotoxin and a metabotoxin. A neurotoxin is a compound that disrupts or attacks neural cells and neural tissue. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of phenylalanine are associated with at least five inborn errors of metabolism, including Hartnup disorder, hyperphenylalaninemia due to guanosine triphosphate cyclohydrolase deficiency, phenylketonuria (PKU), tyrosinemia type 2 (or Richner-Hanhart syndrome), and tyrosinemia type III (TYRO3). Phenylketonurics have elevated serum plasma levels of phenylalanine up to 400 times normal. High plasma concentrations of phenylalanine influence the blood-brain barrier transport of large neutral amino acids. The high plasma phenylalanine concentrations increase phenylalanine entry into the brain and restrict the entry of other large neutral amino acids (PMID: 19191004). Phenylalanine has been found to interfere with different cerebral enzyme systems. Untreated phenylketonuria (PKU) can lead to intellectual disability, seizures, behavioural problems, and mental disorders. It may also result in a musty smell and lighter skin. Classic PKU dramatically affects myelination and white matter tracts in untreated infants; this may be one major cause of neurological disorders associated with phenylketonuria. Mild phenylketonuria can act as an unsuspected cause of hyperactivity, learning problems, and other developmental problems in children. It has been recently suggested that PKU may resemble amyloid diseases, such as Alzheimer's disease and Parkinson's disease, due to the formation of toxic amyloid-like assemblies of phenylalanine (PMID: 22706200). Phenylalanine also has some potential benefits. Phenylalanine can act as an effective pain reliever. Its use in premenstrual syndrome and Parkinson's may enhance the effects of acupuncture and electric transcutaneous nerve stimulation (TENS). Phenylalanine and tyrosine, like L-DOPA, produce a catecholamine-like effect. Phenylalanine is better absorbed than tyrosine and may cause fewer headaches. Low phenylalanine diets have been prescribed for certain cancers with mixed results. For instance, some tumours use more phenylalanine than others (particularly melatonin-producing tumours called melanomas).

Hypoxanthine, also known as purine-6-ol or Hyp, belongs to the class of organic compounds known as purines. Purines are a bicyclic aromatic compound made up of a pyrimidine ring fused to an imidazole ring. Hypoxanthine is also classified as an oxopurine, Hypoxanthine is a naturally occurring purine derivative and a reaction intermediate in the metabolism of adenosine and in the formation of nucleic acids by the nucleotide salvage pathway. Hypoxanthine exists in all living species, ranging from bacteria to plants to humans. Hypoxanthine has been detected, but not quantified in, several different foods, such as radish (var.), mountain yams, welsh onions, greenthread tea, and common beets. Hypoxanthine is occasionally found as a constituent of nucleic acids, where it is present in the anticodon of tRNA in the form of its nucleoside inosine. Biologically, hypoxanthine can be formed a number of ways. For instance, it is one of the products of the action of xanthine oxidase on xanthine. However, more frequently xanthine is formed from oxidation of hypoxanthine by xanthine oxidoreductase. The enzyme hypoxanthine-guanine phosphoribosyltransferase converts hypoxanthine into IMP in the nucleotide salvage pathway. Hypoxanthine is also a spontaneous deamination product of adenine. Under normal circumstances hypoxanthine is readily converted to uric acid. In this process, hypoxanthine is first oxidized to xanthine, which is further oxidized to uric acid by xanthine oxidase. Molecular oxygen, the oxidant in both reactions, is reduced to H2O2 and other reactive oxygen species. In humans, uric acid is the final product of purine degradation and is excreted in the urine. Within humans, hypoxanthine participates in a number of other enzymatic reactions. In particular, hypoxanthine and ribose 1-phosphate can be biosynthesized from inosine through its interaction with the enzyme purine nucleoside phosphorylase. Hypoxanthine is also involved in the metabolic disorder called the purine nucleoside phosphorylase deficiency. Purine nucleoside phosphorylase (PNP) deficiency is a disorder of the immune system (primary immunodeficiency) characterized by recurrent infections, neurologic symptoms, and autoimmune disorders. PNP deficiency causes a shortage of white blood cells, called T-cells, that help fight infection. Affected individuals develop neurologic symptoms, such as stiff or rigid muscles (spasticity), uncoordinated movements (ataxia), developmental delay, and intellectual disability. PNP deficiency is associated with an increased risk to develop autoimmune disorders, such as autoimmune hemolytic anemia, idiopathic thrombocytopenic purpura (ITP), autoimmune neutropenia, thyroiditis, and lupus.

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).

Citric acid (citrate) is a tricarboxylic acid, an organic acid with three carboxylate groups. Citrate is an intermediate in the TCA cycle (also known as the Tricarboxylic Acid cycle, the Citric Acid cycle or Krebs cycle). The TCA cycle is a central metabolic pathway for all animals, plants, and bacteria. As a result, citrate is found in all living organisms, from bacteria to plants to animals. In the TCA cycle, the enzyme citrate synthase catalyzes the condensation of oxaloacetate with acetyl CoA to form citrate. Citrate then acts as the substrate for the enzyme known as aconitase and is then converted into aconitic acid. The TCA cycle ends with regeneration of oxaloacetate. This series of chemical reactions in the TCA cycle is the source of two-thirds of the food-derived energy in higher organisms. Citrate can be transported out of the mitochondria and into the cytoplasm, then broken down into acetyl-CoA for fatty acid synthesis, and into oxaloacetate. Citrate is a positive modulator of this conversion, and allosterically regulates the enzyme acetyl-CoA carboxylase, which is the regulating enzyme in the conversion of acetyl-CoA into malonyl-CoA (the commitment step in fatty acid synthesis). In short, citrate is transported into the cytoplasm, converted into acetyl CoA, which is then converted into malonyl CoA by acetyl CoA carboxylase, which is allosterically modulated by citrate. In mammals and other vertebrates, Citrate is a vital component of bone, helping to regulate the size of apatite crystals (PMID: 21127269). Citric acid is found in citrus fruits, most concentrated in lemons and limes, where it can comprise as much as 8% of the dry weight of the fruit. Citric acid is a natural preservative and is also used to add an acidic (sour) taste to foods and carbonated drinks. Because it is one of the stronger edible acids, the dominant use of citric acid is as a flavoring and preservative in food and beverages, especially soft drinks and candies. Citric acid is an excellent chelating agent, binding metals by making them soluble. It is used to remove and discourage the buildup of limescale from boilers and evaporators. It can be used to treat water, which makes it useful in improving the effectiveness of soaps and laundry detergents. The salts of citric acid (citrates) can be used as anticoagulants due to their calcium chelating ability. Intolerance to citric acid in the diet is known to exist. Little information is available as the condition appears to be rare, but like other types of food intolerance it is often described as a "pseudo-allergic" reaction.

Leucine (Leu) or L-leucine is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-leucine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Leucine is found in all organisms ranging from bacteria to plants to animals. It is classified as a non-polar, uncharged (at physiological pH) aliphatic amino acid. Leucine is essential in humans, meaning the body cannot synthesize it, and it must be obtained from the diet. Human dietary sources are foods that contain protein, such as meats, dairy products, soy products, beans and legumes. L-Leucine is a branched chain amino acid (BCAA). The BCAAs consist of leucine, valine and isoleucine (and occasionally threonine). BCAAs are essential amino acids whose carbon structure is marked by a branch point at the beta-carbon position. BCAAs are critical to human life and are particularly involved in stress, energy and muscle metabolism. BCAA supplementation as therapy, both oral and intravenous, in human health and disease holds great promise. BCAAs have different metabolic routes, with valine going solely to carbohydrates (glucogenic), leucine solely to fats (ketogenic) and isoleucine being both a glucogenic and a ketogenic amino acid. The different metabolism accounts for different requirements for these essential amino acids in humans: 12 mg/kg, 14 mg/kg and 16 mg/kg of valine, leucine and isoleucine respectively. The primary metabolic end products of leucine metabolism are acetyl-CoA and acetoacetate; consequently, it is one of the two exclusively ketogenic amino acids, with lysine being the other. Leucine is the most important ketogenic amino acid in humans. The vast majority of l-leucine metabolism is initially catalyzed by the branched-chain amino acid aminotransferase enzyme, producing alpha-ketoisocaproate (alpha-KIC). alpha-KIC is metabolized by the mitochondrial enzyme branched-chain alpha-ketoacid dehydrogenase, which converts it to isovaleryl-CoA. Isovaleryl-CoA is subsequently metabolized by the enzyme isovaleryl-CoA dehydrogenase and converted to beta-methylcrotonyl-CoA (MC-CoA), which is used in the synthesis of acetyl-CoA and other compounds. During biotin deficiency, HMB can be synthesized from MC-CoA via enoyl-CoA hydratase and an unknown thioesterase enzyme, which convert MC-CoA into HMB-CoA and HMB-CoA into HMB respectively. Leucine has the capacity to directly stimulate myofibrillar muscle protein synthesis (PMID 15051860). This effect of leucine arises results from its role as an activator of the mechanistic target of rapamycin (mTOR) (PMID 23551944) a serine-threonine protein kinase that regulates protein biosynthesis and cell growth. The activation of mTOR by leucine is mediated through Rag GTPases. Leucine, like other BCAAs, is associated with insulin resistance. In particular, higher levels of leucine are observed in the blood of diabetic mice, rats, and humans (PMID 25287287). BCAAs such as leucine have different deficiency symptoms. Valine deficiency is marked by neurological defects in the brain, while isoleucine deficiency is marked by muscle tremors. Persistently low leucine levels can result in decreased appetite, poor feeding, lethargy, poor growth, weight loss, skin rashes, hair loss, and desquamation. Many types of inborn errors of BCAA metabolism exist and these are marked by various abnormalities. The most common form is maple syrup urine disease, marked by a characteristic urinary odor. Other abnormalities are associated with a wide range of symptoms, such as mental retardation, ataxia, hypoglycemia, spinal muscle atrophy, rash, vomiting and excessive muscle movement. Most forms of BCAA metabolism errors are corrected by dietary restriction of BCAAs and at least one form is correctable by supplementation with 10 mg of biotin daily. - BCAAs are useful because they are metabolized primarily by muscle. Stress states - e.g surgery, trauma, cirrhosis, infections, fever and starvation--require proportionately more BCAAs than other amino acids and probably proportionately more leucine than either valine or isoleucine. BCAAs and other amino acids are frequently fed intravenously (TPN) to malnourished surgical patients and in some cases of severe trauma. BCAAs, particularly leucine, stimulate protein synthesis, increase reutilization of amino acids in many organs and reduce protein breakdown. Furthermore, leucine can be an important source of calories, and is superior as fuel to the ubiquitous intravenous glucose (dextrose). - Leucine also stimulates insulin release, which in turn stimulates protein synthesis and inhibits protein breakdown. These effects are particularly useful in athletic training. Huntington's chorea and anorexic disorders both are characterized by low serum BCAAs. These diseases, as well as forms of Parkinson's, may respond to BCAA therapy.

Xanthine, also known as 2,6-dioxopurine, belongs to the class of organic compounds known as xanthines. These are purine derivatives with a ketone group conjugated at carbons 2 and 6 of the purine moiety. Xanthine is also classified as an oxopurine. An oxopurine in which the purine ring is substituted by oxo groups at positions 2 and 6 and N-9 is protonated. Xanthine exists in all living species, ranging from bacteria to plants to humans. In plants, several stimulants can be derived from xanthine, including caffeine, theophylline, and theobromine. Derivatives of xanthine (known collectively as xanthines) are a group of alkaloids commonly used for their effects as mild stimulants and as bronchodilators, notably in the treatment of asthma or influenza symptoms. Within humans, xanthine participates in a number of enzymatic reactions. In particular, xanthine can be biosynthesized from guanine; which is mediated by the enzyme guanine deaminase. In addition, xanthine and ribose 1-phosphate can be biosynthesized from xanthosine through the action of the enzyme purine nucleoside phosphorylase. In humans and other primates, xanthine can be converted to uric acid by the action of the xanthine oxidase enzyme. People with rare genetic disorders, specifically xanthinuria and Lesch–Nyhan syndrome, lack sufficient xanthine oxidase and cannot convert xanthine to uric acid. Individuals with xanthinuria have unusually high concentrations of xanthine in their blood and urine, which can lead to health problems such as renal failure and xanthine kidney stones. Individuals with Lesch-Nyhan syndrome have a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). The HGPRT deficiency causes a build-up of uric acid in all body fluids. This results in both high levels of uric acid in the blood and urine, associated with severe gout and kidney problems. Neurological signs include poor muscle control and moderate intellectual disability.

Oxytetracycline is a tetracycline analog isolated from the actinomycete streptomyces rimosus and used in a wide variety of clinical conditions. [PubChem]Oxytetracycline inhibits cell growth by inhibiting translation. It binds to the 30S ribosomal subunit and prevents the amino-acyl tRNA from binding to the A site of the ribosome. The binding is reversible in nature. Oxytetracycline is lipophilic and can easily pass through the cell membrane or passively diffuses through porin channels in the bacterial membrane. Oxytetracycline is a clinically used broad-spectrum antibacterial antibiotic. It is approved by FDA for use in fish and animal feeds. Oxytetracycline is known as a broad-spectrum antibiotic due to its activity against such a wide range of infections. It was the second of the tetracyclines to be discovered. Oxytetracycline, like other tetracyclines, is used to treat many infections common and rare. Its better absorption profile makes it preferable to tetracycline for moderately severe acne, but alternatives sould be sought if no improvement occurs by 3 months

The amino acid betaine derived from glycine." []

Glutamic acid (Glu), also known as L-glutamic acid or as glutamate, the name of its anion, is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-glutamic acid is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Glutamic acid is found in all organisms ranging from bacteria to plants to animals. It is classified as an acidic, charged (at physiological pH), aliphatic amino acid. In humans it is a non-essential amino acid and can be synthesized via alanine or aspartic acid via alpha-ketoglutarate and the action of various transaminases. Glutamate also plays an important role in the body's disposal of excess or waste nitrogen. Glutamate undergoes deamination, an oxidative reaction catalysed by glutamate dehydrogenase leading to alpha-ketoglutarate. In many respects glutamate is a key molecule in cellular metabolism. Glutamate is the most abundant fast excitatory neurotransmitter in the mammalian nervous system. At chemical synapses, glutamate is stored in vesicles. Nerve impulses trigger release of glutamate from the pre-synaptic cell. In the opposing post-synaptic cell, glutamate receptors, such as the NMDA receptor, bind glutamate and are activated. Because of its role in synaptic plasticity, it is believed that glutamic acid is involved in cognitive functions like learning and memory in the brain. Glutamate transporters are found in neuronal and glial membranes. They rapidly remove glutamate from the extracellular space. In brain injury or disease, they can work in reverse and excess glutamate can accumulate outside cells. This process causes calcium ions to enter cells via NMDA receptor channels, leading to neuronal damage and eventual cell death, and is called excitotoxicity. The mechanisms of cell death include: Damage to mitochondria from excessively high intracellular Ca2+. Glu/Ca2+-mediated promotion of transcription factors for pro-apoptotic genes, or downregulation of transcription factors for anti-apoptotic genes. Excitotoxicity due to glutamate occurs as part of the ischemic cascade and is associated with stroke and diseases like amyotrophic lateral sclerosis, lathyrism, and Alzheimer's disease. Glutamic acid has been implicated in epileptic seizures. Microinjection of glutamic acid into neurons produces spontaneous depolarization around one second apart, and this firing pattern is similar to what is known as paroxysmal depolarizing shift in epileptic attacks. This change in the resting membrane potential at seizure foci could cause spontaneous opening of voltage activated calcium channels, leading to glutamic acid release and further depolarization (http://en.wikipedia.org/wiki/Glutamic_acid). Glutamate was discovered in 1866 when it was extracted from wheat gluten (from where it got its name. Glutamate has an important role as a food additive and food flavoring agent. In 1908, Japanese researcher Kikunae Ikeda identified brown crystals left behind after the evaporation of a large amount of kombu broth (a Japanese soup) as glutamic acid. These crystals, when tasted, reproduced a salty, savory flavor detected in many foods, most especially in seaweed. Professor Ikeda termed this flavor umami. He then patented a method of mass-producing a crystalline salt of glutamic acid, monosodium glutamate.

Oxipurinol is a xanthine oxidase inhibitor. Oxipurinol is potentially used for treatment of congestive heart failure. PMID: 15139781.

Cholic acid is a major primary bile acid produced in the liver and is usually conjugated with glycine or taurine. It facilitates fat absorption and cholesterol excretion. Bile acids are steroid acids found predominantly in the bile of mammals. The distinction between different bile acids is minute, and depends only on the presence or absence of hydroxyl groups on positions 3, 7, and 12. Bile acids are physiological detergents that facilitate excretion, absorption, and transport of fats and sterols in the intestine and liver. Bile acids are also steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine, and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH, and consequently require a carrier for transport across the membranes of the enterohepatic tissues. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients. Bile acids have potent toxic properties (e.g. membrane disruption) and there are a plethora of mechanisms to limit their accumulation in blood and tissues (PMID: 11316487, 16037564, 12576301, 11907135). When present in sufficiently high levels, cholic acid can act as a hepatotoxin and a metabotoxin. A hepatotoxin causes damage to the liver or liver cells. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Among the primary bile acids, cholic acid is considered to be the least hepatotoxic while deoxycholic acid is the most hepatoxic (PMID: 1641875). The liver toxicity of bile acids appears to be due to their ability to peroxidate lipids and to lyse liver cells. Chronically high levels of cholic acid are associated with familial hypercholanemia. In hypercholanemia, bile acids, including cholic acid, are elevated in the blood. This disease causes liver damage, extensive itching, poor fat absorption, and can lead to rickets due to lack of calcium in bones. The deficiency of normal bile acids in the intestines results in a deficiency of vitamin K, which also adversely affects clotting of the blood. The bile acid ursodiol (ursodeoxycholic acid) can improve symptoms associated with familial hypercholanemia.

Sphingosine, also known as (4E)-sphingenine or sphing-4-enine, belongs to the class of organic compounds known as 1,2-aminoalcohols. These are organic compounds containing an alkyl chain with an amine group bound to the C1 atom and an alcohol group bound to the C2 atom. Sphingosine is an 18-carbon amino alcohol with an unsaturated hydrocarbon chain, which forms a primary part of sphingolipids. Sphingolipids are a class of cell membrane lipids that include sphingomyelin. Thus, sphingosine is considered to be a sphingoid base lipid. Sphingosine is a very hydrophobic molecule, practically insoluble (in water), and relatively neutral. Sphingosine is found in all living organisms ranging from bacteria to plants to humans. Sphingosine is synthesized from palmitoyl CoA and serine in a condensation required to yield dehydrosphingosine. Dehydrosphingosine is then reduced by NADPH to dihydrosphingosine (sphinganine), and finally oxidized by FAD to sphingosine. Within humans and other mammals, sphingosine participates in a number of enzymatic reactions. In particular, sphingosine can be converted into sphingosine 1-phosphate through its interaction with the enzyme sphingosine kinase 2. sphingosine 1-phosphate is an important signaling molecule. In addition, sphingosine can be biosynthesized from sphingosine 1-phosphate; which is mediated by the enzyme sphingosine-1-phosphate phosphatase 2. Sphingosine and its derivative sphinganine are the major bases of the sphingolipids in mammals. In humans, sphingosine is involved in globoid cell leukodystrophy.

Malic acid (CAS: 6915-15-7) is a tart-tasting organic dicarboxylic acid that plays a role in many sour or tart foods. Apples contain malic acid, which contributes to the sourness of a green apple. Malic acid can make a wine taste tart, although the amount decreases with increasing fruit ripeness (Wikipedia). In its ionized form, malic acid is called malate. Malate is an intermediate of the TCA cycle along with fumarate. It can also be formed from pyruvate as one of the anaplerotic reactions. In humans, malic acid is both derived from food sources and synthesized in the body through the citric acid cycle or Krebs cycle which takes place in the mitochondria. Malate's importance to the production of energy in the body during both aerobic and anaerobic conditions is well established. Under aerobic conditions, the oxidation of malate to oxaloacetate provides reducing equivalents to the mitochondria through the malate-aspartate redox shuttle. During anaerobic conditions, where a buildup of excess reducing equivalents inhibits glycolysis, malic acid's simultaneous reduction to succinate and oxidation to oxaloacetate is capable of removing the accumulating reducing equivalents. This allows malic acid to reverse hypoxia's inhibition of glycolysis and energy production. In studies on rats, it has been found that only tissue malate is depleted following exhaustive physical activity. Other key metabolites from the citric acid cycle needed for energy production were found to be unchanged. Because of this, a deficiency of malic acid has been hypothesized to be a major cause of physical exhaustion. Notably, the administration of malic acid to rats has been shown to elevate mitochondrial malate and increase mitochondrial respiration and energy production. Malic acid has been found to be a metabolite in Aspergillus (Hugo Vanden Bossche, D.W.R. Mackenzie and G. Cauwenbergh. Aspergillus and Aspergillosis, 1987).

Triethylamine is used as a food additive [EAFUS] ("EAFUS: Everything Added to Food in the United States. [http://www.eafus.com/]")

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).

Elaidamide

Hexylamine is used as a food additive [EAFUS] ("EAFUS: Everything Added to Food in the United States. [http://www.eafus.com/]")

Citraconic acid, also known as 2-methylmaleate or methylmaleic acid, belongs to the class of organic compounds known as methyl-branched fatty acids. These are fatty acids with an acyl chain that has a methyl branch. Usually, they are saturated and contain only one or more methyl group. However, branches other than methyl may be present. Citraconic acid is a dicarboxylic acid consisting of maleic acid having a methyl substituent at the 2-position. Citraconic acid exists as a white solid. It is the cis-isomer of mesaconic acid and is one of the pyrocitric acids formed upon the heating of citric acid. Citraconic acid has been detected in the urine of both normal and fasting individuals (PMID: 6778884). Citraconic acid is also elevated in the urine of individuals with methylmalonic acidaemia who have suffered ketotic attacks (PMID: 116077). Altered serum levels of citraconic acid have been detected in patients with primary biliary cholangitis (PMID: 28400566).

2-Hydroxyphenethylamine, also known as beta-phenethanolamine or 2-amino-1-phenylethanol, belongs to the class of organic compounds known as aralkylamines. These are alkylamines in which the alkyl group is substituted at one carbon atom by an aromatic hydrocarbyl group. It is the simplest member of the class of phenylethanolamines that is 2-aminoethanol bearing a phenyl substituent at the 1-position. 2-Hydroxyphenethylamine exists in all living organisms, ranging from bacteria to humans. 2-Hydroxyphenethylamine ia an amine found in the brain. It may be modulator of sympathetic functions. Its derivatives are adrenergic agonists and antagonists.

L-alloisoleucine is a branched chain amino acid and is a stereo-isomer of L-isoleucine. It is a common constituent of human plasma (albeit at low levels). L-alloisoleucine is produced as a byproduct of isoleucine transamination. L-Isoleucine is one of the four common amino acids (the 3 others being threonine, hydroxyproline, and hydroxylysine) that have two asymmetric carbon atoms which produce four structural possibilities for the same chemical composition. L-alloisoleucine differs from L-isoleucine by having having different stereochemistry around its beta carbon. Plasma L-alloisoleucine, which is derived from L-isoleucine in vivo, can be used for the diagnosis of maple syrup urine disease (MSUD), a genetic disorder. Indeed, plasma L-alloisoleucine levels above 5 umol/L is the most specific and most sensitive diagnostic marker for all forms of MSUD (PMID: 10508118). In MSUD the degradation of the essential branched-chain L-amino acids leucine, valine, and isoleucine and their derived 2-oxoacids is impaired because of an inherited deficiency in branched-chain 2-oxoacid dehydrogenase complex (EC 1.2.4.4) activity. The accumulation of branched-chain compounds in blood and other body fluids can exert neurotoxic effects.

Guanosine (G), also known as 2-amino-inosine, belongs to the class of organic compounds known as purine nucleosides. Purine nucleosides are compounds comprising a purine base attached to a ribosyl or deoxyribosyl sugar moiety. Guanosine consists of a guanine base attached to a ribose (ribofuranose) ring via a beta-N9-glycosidic bond. Guanosine is a white, crystalline powder with no odor and mild saline taste. It is very soluble in acetic acid, and slightly soluble in water, but insoluble in ethanol, diethyl ether, benzene, and chloroform. Guanosine exists in all living species, ranging from bacteria to plants to humans. High levels of guanosine can be found in clovers, coffee plants, and the pollen of pines. It has been detected, but not quantified in, several different foods, such as leeks, garlic, chicory roots, green bell peppers, and black-eyed peas. Guanosine plays an important role in various biochemical processes including the synthesis of nucleic acids such as RNA and intracellular signal transduction (cGMP). The antiviral drug acyclovir, often used in herpes treatment, and the anti-HIV drug abacavir, are both structurally similar to guanosine. Guanosine can be phosphorylated to become guanosine monophosphate (GMP), cyclic guanosine monophosphate (cGMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP). In humans, guanosine is involved in intracellular signalling through the adenosine receptors A1R and A2AR (PMID: 31847113). Evidence from rodent and cell models has shown a number of important neurotrophic and neuroprotective effects of guanosine. In particular, it is effective in preventing deleterious consequences of seizures, spinal cord injury, pain, mood disorders and aging-related diseases, such as ischemia, Parkinson’s and Alzheimer’s diseases (PMID: 27699087). Studies with rodent models of Parkinson’s disease have shown that guanosine decreases neuronal apoptotic cell death and increases dopaminergic neurons at substantia nigra pars compacta, accompanied by an improvement of motor symptoms in Parkinson’s disease (i.e. a reduction of bradykinesia). Guanosine promotes neurite arborization, outgrowth, proliferation and differentiation. Systemic administration of guanosine for eight weeks (8 mg/kg) has been shown to stimulate neuroprogenitors proliferation in the subventricular zone (SVZ) in a mouse model of Parkinsonism (PMID: 27699087). The effect of guanosine treatment is accompanied by an increased number of fibroblast growth factor (FGF-2)-positive cells which is an important regulator of neuroprogenitor/stem cell proliferation, survival and differentiation (PMID: 27699087). Guanosine prevents reactive oxygen species (ROS) generation and cell death in hippocampal slices subjected to the oxygen/glucose deprivation (PMID: 31847113).

Taurocholic acid is a bile acid and is the product of the conjugation of cholic acid with taurine. Its sodium salt is the chief ingredient of the bile of carnivorous animals. Bile acids are steroid acids found predominantly in the bile of mammals. The distinction between different bile acids is minute, depending only on the presence or absence of hydroxyl groups on positions 3, 7, and 12. Bile acids are physiological detergents that facilitate excretion, absorption, and transport of fats and sterols in the intestine and liver. Bile acids are also steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine, and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH, and consequently require a carrier for transport across the membranes of the enterohepatic tissues. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients. Bile acids have potent toxic properties (e.g. membrane disruption) and there are a plethora of mechanisms to limit their accumulation in blood and tissues (PMID: 11316487, 16037564, 12576301, 11907135). Taurocholic acid, as with all bile acids, acts as a detergent to solubilize fats for absorption and is itself absorbed. It is used as a cholagogue and choleretic (a bile purging agent). Hydrolysis of taurocholic acid yields taurine, a nonessential amino acid. Taurocholic acid is one of the main components of urinary nonsulfated bile acids in biliary atresia. Raised levels of taurocholate in fetal serum in obstetric cholestasis may result in the development of a fetal dysrhythmia and sudden intra-uterine death (PMID: 3944741, 11256973).