Browsing Compounds

Guanidoacetic acid is a metabolite in the Urea cycle and metabolism of amino groups, and in the metabolic pathways of several amino acids. This includes glycine, serine, threonine, arginine and proline metabolism. Guanidinoacetic acid is also a precursor of creatine, an essential substrate for muscle energy metabolism.

Homogentisic acid, also known as melanic acid, is an intermediate in the breakdown or catabolism of tyrosine and phenylalanine. It is generated from the compound p-hydroxyphenylpyruvate through the enzyme p-hydroxyphenylpyruvate dehydrogenase. The resulting homogentisic acid is then broken down into 4-maleylacetoacetate via the enzyme homogentisate 1,2-dioxygenase. Homogentisic acid is also found in other organisms. For instance, it can found in Arbutus unedo (strawberry-tree) honey, in the bacterial plant pathogen Xanthomonas campestris as well as in the yeast Yarrowia lipolytica where it is associated with the production of brown pigments. Homogentisic acid can be oxidatively dimerized to form hipposudoric acid, one of the main constituents of the 'blood sweat' of hippopotamuses. When present in sufficiently high levels, homogentisic acid can function as an osteotoxin and a renal toxin. An osteotoxin is a substance that causes damage to bones and/or joints. A renal toxin causes damage to the kidneys. Chronically high levels of homogentisic acid are associated with alkaptonuria (OMIM: 203500), an inborn error of metabolism. Alkaptonuria is a rare inherited genetic disorder in which the body cannot process the amino acids phenylalanine and tyrosine. It is caused by a mutation in the enzyme homogentisate 1,2-dioxygenase (EC 1.13.11.5), which leads to an accumulation of homogentisic acid in the blood and tissues. Homogentisic acid and its oxidized form benzoquinone acetic acid are excreted in the urine, giving it an unusually dark color. The accumulating homogentisic acid (and benzoquinone acetic acid) causes damage to cartilage (ochronosis, leading to osteoarthritis) and heart valves as well as precipitating as kidney stones and stones in other organs. More specifically, homogentisic acid can be converted to benzoquinone acetic acid (BQA), and the resulting BQA can be readily converted to polymers that resemble the dark skin pigment melanin. These polymers are deposited in the collagen, a connective tissue protein, of particular tissues such as cartilage. This process is called ochronosis (as the tissue looks ochre); ochronotic tissue is stiffened and unusually brittle, impairing its normal function and causing damage. Homogentisic acid is the primary precursor of melanin synthesis in Vibrio cholerae.

Glycerol or glycerin is a colourless, odourless, viscous liquid that is sweet-tasting and mostly non-toxic. It is widely used in the food industry as a sweetener and humectant and in pharmaceutical formulations. Glycerol is an important component of triglycerides (i.e. fats and oils) and of phospholipids. Glycerol is a three-carbon substance that forms the backbone of fatty acids in fats. When the body uses stored fat as a source of energy, glycerol and fatty acids are released into the bloodstream. The glycerol component can be converted into glucose by the liver and provides energy for cellular metabolism. Normally, glycerol shows very little acute toxicity and very high oral doses or acute exposures can be tolerated. On the other hand, chronically high levels of glycerol in the blood are associated with glycerol kinase deficiency (GKD). GKD causes the condition known as hyperglycerolemia, an accumulation of glycerol in the blood and urine. There are three clinically distinct forms of GKD: infantile, juvenile, and adult. The infantile form is the most severe and is associated with vomiting, lethargy, severe developmental delay, and adrenal insufficiency. The mechanisms of glycerol toxicity in infants are not known, but it appears to shift metabolism towards chronic 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, liver, and kidney abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of untreated GKD. Many affected children with organic acidemias experience intellectual disability or delayed development. Patients with the adult form of GKD generally have no symptoms and are often detected fortuitously.

Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA. Guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with conjugated double bonds. Being unsaturated, the bicyclic molecule is planar. The guanine nucleoside is called guanosine. The first isolation of guanine was reported in 1844 from the excreta of sea birds, known as guano, which was used as a source of fertilizer. High affinity binding of guanine nucleotides and the ability to hydrolyze bound GTP to GDP are characteristics of an extended family of intracellular proteins. Guanine nucleotide-binding regulatory proteins may be involved in the activation of phospholipases C and A2 by hormones and other ligands. The binding of hormones to receptors that activate phospholipase C is decreased by guanine nucleotides and these hormones also stimulate a high-affinity GTPase activity in cell membranes. Effects of hormones on phospholipase C activity in cell-free preparations are dependent on the presence of guanine nucleotides. Hypoxanthine-guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8) is a purine salvage enzyme that catalyses the conversion of hypoxanthine and guanine to their respective mononucleotides. Partial deficiency of this enzyme can result in the overproduction of uric acid leading to a severe form of gout, whilst a virtual absence of HPRT activity causes the Lesch-Nyhan syndrome which is characterised by hyperuricaemia, mental retardation, choreoathetosis and compulsive self-mutilation. Peroxynitrite induces DNA base damage predominantly at guanine (G) and 8-oxoguanine (8-oxoG) nucleobases via oxidation reactions. G and 8-oxoG are the most reactive bases toward Peroxynitrite and possibly the major contributors to peroxynitrite-derived genotoxic and mutagenic lesions. The neutral G radical, reacts with NO2 to yield 8-nitroguanine and 5-nitro-4-guanidinohydantoin. (PMID: 16352449, 2435586, 2838362, 1487231).

Guanosine is a nucleoside comprising guanine attached to a ribose (ribofuranose) ring via a beta-N9-glycosidic bond. Guanosine can be phosphorylated to become GMP (guanosine monophosphate), cGMP (cyclic guanosine monophosphate), GDP (guanosine diphosphate), and GTP (guanosine triphosphate) (Wikipedia). This nucleoside exerts important neuroprotective and neuromodulator roles in the central nervous system, which may be related to inhibition of the glutamatergic neurotransmission activity. Guanosine is the specific extracellular guanine-based purines effector and its conversion occurs not only in the central nervous system but also peripherally (PMID: 16325434). Guanosine is found to be associated with purine nucleoside phosphorylase (PNP) deficiency, which is an inborn error of metabolism.

Fumaric acid is a precursor to L-malate in the Krebs tricarboxylic acid cycle. It is formed by the oxidation of succinate by succinate dehydrogenase. Fumarate is converted by fumarase to malate. A fumarate is a salt or ester of the organic compound fumaric acid, a dicarboxylic acid. (wikipedia).

Glycocholic acid is an acyl glycine and a bile acid-glycine conjugate. It is a secondary bile acid produced by the action of enzymes existing in the microbial flora of the colonic environment. In hepatocytes, both primary and secondary bile acids undergo amino acid conjugation at the C-24 carboxylic acid on the side chain, and almost all bile acids in the bile duct therefore exist in a glycine conjugated form (PMID:16949895 ). More specifically, glycocholic acid or cholylglycine, is a crystalline bile acid involved in the emulsification of fats. It occurs as a sodium salt in the bile of mammals. Its anion is called glycocholate. As the glycine conjugate of cholic acid, this compound acts as a detergent to solubilize fats for absorption and is itself absorbed. (PubChem). Bile acids are steroid acids found predominantly in bile of mammals. The distinction between different bile acids is minute, depends only on 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 ).

Glyceric acid is a colourless syrupy acid, obtained from oxidation of glycerol. It is a compound that is secreted excessively in the urine by patients suffering from D-glyceric aciduria, an inborn error of metabolism, and D-glycerate anemia. Deficiency of human glycerate kinase leads to D-glycerate acidemia/D-glyceric aciduria. Symptoms of the disease include progressive neurological impairment, hypotonia, seizures, failure to thrive, and metabolic acidosis. At sufficiently high levels, glyceric 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. Glyceric 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. In infants with acidosis, the initial symptoms include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of untreated glyceric aciduria. 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.

Glucosylceramide is a glycosphingolipid (ceramide and oligosaccharide)or oligoglycosylceramide with one or more sialic acids (i.e. n-acetylneuraminic acid) linked on the sugar chain. It is a component the cell plasma membrane which modulates cell signal transduction events. Gangliosides have been found to be highly important in immunology. Ganglioside GL1a carries a net-negative charge at pH 7.0 and is acidic. Gangliosides can amount to 6% of the weight of lipids from brain, but they are found at low levels in all animal tissues.Cerebrosides are glycosphingolipids. There are four types of glycosphingolipids, the cerebrosides, sulfatides, globosides and gangliosides. Cerebrosides have a single sugar group linked to ceramide. The most common are galactocerebrosides (containing galactose), the least common are glucocerebrosides (containing glucose). Galactocerebrosides are found predominantly in neuronal cell membranes. In contrast glucocerebrosides are not normally found in membranes. Instead, they are typically intermediates in the synthesis or degradation of more complex glycosphingolipids. Galactocerebrosides are synthesized from ceramide and UDP-galactose. Excess lysosomal accumulation of glucocerebrosides is found in Gaucher disease.

Formic acid is the simplest carboxylic acid. Formate is an intermediate in normal metabolism. It takes part in the metabolism of one-carbon compounds and its carbon may appear in methyl groups undergoing transmethylation. It is eventually oxidized to carbon dioxide. Formate is typically produced as a byproduct in the production of acetate. It is responsible for both metabolic acidosis and disrupting mitochondrial electron transport and energy production by inhibiting cytochrome oxidase activity, the terminal electron acceptor of the electron transport chain. Cell death from cytochrome oxidase inhibition by formate is believed to result partly from depletion of ATP, reducing energy concentrations so that essential cell functions cannot be maintained. Furthermore, inhibition of cytochrome oxidase by formate may also cause cell death by increased production of cytotoxic reactive oxygen species (ROS) secondary to the blockade of the electron transport chain. In nature, formic acid is found in the stings and bites of many insects of the order Hymenoptera, including bees and ants. The principal use of formic acid is as a preservative and antibacterial agent in livestock feed. When sprayed on fresh hay or other silage, it arrests certain decay processes and causes the feed to retain its nutritive value longer.

D-Galactose is an aldohexose that occurs naturally in the D-form in lactose, cerebrosides, gangliosides, and mucoproteins. D-Galactose is an energy-providing nutrient and also a necessary basic substrate for the biosynthesis of many macromolecules in the body. Metabolic pathways for D-Galactose are important not only for the provision of these pathways but also for the prevention of D-Galactose and D-Galactose metabolite accumulation. The main source of D-Galactose is lactose in the milk of mammals, but it can also be found in some fruits and vegetables. Utilization of D-Galactose in all living cells is initiated by the phosphorylation of the hexose by the enzyme galactokinase (E.C. 2.7.1.6) (GALK) to form D-Galactose-1-phosphate. In the presence of D-Galactose-1-phosphate uridyltransferase (E.C. 2.7.7.12) (GALT) D-Galactose-1-phosphate is exchanged with glucose-1-phosphate in UDP-glucose to form UDP-galactose. Glucose-1-phosphate will then enter the glycolytic pathway for energy production. Deficiency of the enzyme GALT in galactosemic patients leads to the accumulation of D-Galactose-1-phosphate. Classic galactosemia-a term that denotes the presence of D-Galactose in the blood is the rare inborn error of D-Galactose metabolism, diagnosed by the deficiency of the second enzyme of the D-Galactose assimilation pathway, GALT, which, in turn, is caused by mutations at the GALT gene. (PMID: 15256214, 11020650, 10408771).

Estrone is a major mammalian estrogen. The conversion of the natural C19 steroids, testosterone and androstenedione into estrone is dependent on a complex key reaction catalyzed by the cytochrome P450 aromatase (EC 1.14.14.1, unspecific monooxygenase), which is expressed in many tissues of the adult human (e.g. ovary, fat tissue), but not in the liver. The ovaries after menopause continue to produce androstenedione and testosterone in significant amounts and these androgens are converted in fat, muscle, and skin into estrone. When women between the ages of 45 and 64 years have prophylactic oophorectomy (when hysterectomy is performed for benign disease to prevent the development of ovarian cancer), evidence suggests that oophorectomy increases the subsequent risk of coronary heart disease (CHD) and osteoporosis. Whereas 14,000 women die of ovarian cancer every year nearly 490,000 women die of heart disease and 48,000 women die within 1 year after hip fracture. Therefore, the decision to perform prophylactic oophorectomy should be approached with great caution for the majority of women who are at low risk of developing ovarian cancer. Steroid sulfatase (EC 3.1.6.2, STS) hydrolyzes steroid sulfates, such as estrone sulfate to estrone which can be converted to steroids with potent estrogenic properties, that is, estradiol; STS activity is much higher in breast tumors and high levels of STS mRNA expression in tumors are associated with a poor prognosis. The biological roles of estrogens in tumorigenesis are certainly different between the endometrium and breast, although both are considered "estrogen-dependent tissues". 17beta-hydroxysteroid dehydrogenases (EC 1.1.1.62, 17-HSDs) are enzymes involved in the formation of active sex steroids. estrone is interconverted by two enzymes 17-HSD types. Type 1 converts estrone to estradiol and Type 2 catalyzes the reverse reaction. (PMID: 17653961, 17513923, 17470679, 17464097).

Glutamic acid (Glu), also referred to as glutamate (the anion), is one of the 20 proteinogenic amino acids. It is not among the essential amino acids. Glutamate is a key molecule in cellular metabolism. In humans, dietary proteins are broken down by digestion into amino acids, which serves as metabolic fuel or other functional roles in the body. 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).

Ethanolamine is a viscous, hygroscopic amino alcohol with an ammoniacal odor. It is widely distributed in biological tissue and is a component of lecithin. It is used as a surfactant, fluorometric reagent, and to remove CO2 and H2S from natural gas and other gases.

Gluconolactone is a lactone or oxidized derivative of glucose. Gluconolactone is a polyhydroxy acid (PHA) that is capable of chelating metals and may also function by scavenging free radicals, thereby protecting skin from some of the damaging effects of UV radiation. Also used as a pheromone by the oriental cockroach.

Estradiol is the most potent form of mammalian estrogenic steroids. Estradiol is produced in the ovaries. The ovary requires both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to produce sex steroids. LH stimulates the cells surrounding the follicle to produce progesterone and androgens. The androgens diffuse across the basement membrane to the granulosa cell layer, where, under the action of FSH, they are aromatized to estrogens, mainly estradiol. The ovary shows cyclical activity, unlike the testis that is maintained in a more or less constant state of activity. Hormone secretions vary according to the phase of the menstrual cycle. In the developing follicle LH receptors (LH-R) are only located on the thecal cells and FSH receptors (FSHR) on the granulosa cells. The dominant pre-ovulatory follicle develops LH-Rs on the granulosa cells prior to the LH surge. Thecal cells of the preovulatory follicle also develop the capacity to synthesize estradiol and this persists when the thecal cells become incorporated into the corpus luteum. After ovulation, the empty follicle is remodelled and plays an important role in the second half or luteal phase of the menstrual cycle. This phase is dominated by progesterone and, to a lesser extent, estradiol secretion by the corpus luteum. estradiol is also synthesized locally from cholesterol through testosterone in the hippocampus and acts rapidly to modulate neuronal synaptic plasticity. Localization of estrogen receptor alpha (ERalpha) in spines in addition to nuclei of principal neurons implies that synaptic ERalpha is responsible for rapid modulation of synaptic plasticity by endogenous estradiol. estradiol is a potent endogenous antioxidant which suppresses hepatic fibrosis in animal models, and attenuates induction of redox sensitive transcription factors, hepatocyte apoptosis and hepatic stellate cells activation by inhibiting a generation of reactive oxygen species in primary cultures. This suggests that the greater progression of hepatic fibrosis and hepatocellular carcinoma in men and postmenopausal women may be due, at least in part, to lower production of estradiol and a reduced response to the action of estradiol. estradiol has been reported to induce the production of interferon (INF)-gamma in lymphocytes, and augments an antigen-specific primary antibody response in human peripheral blood mononuclear cells. IFN-gamma is a potent cytokine with immunomodulatory and antiproliferative properties. Therefore, female subjects, particularly before menopause, may produce antibodies against hepatitis B virus e antigen and hepatitis B virus surface antigen at a higher frequency than males with chronic hepatitis B virus infection. The estradiol-Dihydrotestosterone model of prostate cancer (PC) proposes that the first step in the development of most PC and breast cancer (BC) occurs when aromatase converts testosterone to estradiol. (PMID: 17708600, 17678531, 17644764).

Estriol is a metabolite of estrone metabolized via 16alpha-hydroxyestrone through the enzyme 16alpha-hydroxysteroid dehydrogenase (EC 1.1.1.147) or to 2- or 4-hydroxyestrone (catechol estrogens) by the action of catecho-O-methyltransferase (EC 2.1.1.6). The latter metabolites can be formed in the brain and may compete with receptors for catecholamines. Metabolites are conjugated with sulfate or glucuronide before excretion by the kidney. During pregnancy, estriol constitutes 60-70% of the total estrogens, increasing to 300-500-fold in relation to non-pregnant women. The late term human fetus produces relatively large amounts of 16 alphahydroxy DHEA, which serves the mother as a precursor of estriol. It has been shown that 90% of the precursors for the formation of estriol are of fetal origin. If abnormal maternal serum screening results, specifically low levels of unconjugated estriol in the second trimester are detected, a diagnosis of Smith-Lemli-Opitz syndrome (SLOS),or RSH is suspected. SLOS is an autosomal recessive disorder caused by mutations of the gene encoding 7-dehydrocholesterol reductase (EC 1.3.1.21, DHCR7). (PMID: 16202579, 16112271, 16097001).

Malic acid 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 of 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.

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 salvage pathway. Hypoxanthine is also a spontaneous deamination product of adenine. Lesch-Nyhan disease is caused by deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase. (OMIN 308000).

Tyrosine is an essential amino acid that readily passes the blood-brain barrier. Once in the brain, it is a precursor for the neurotransmitters dopamine, norepinephrine and epinephrine, better known as adrenalin. These neurotransmitters are an important part of the body's sympathetic nervous system, and their concentrations in the body and brain are directly dependent upon dietary tyrosine. Tyrosine is not found in large concentrations throughout the body, probably because it is rapidly metabolized. Folic acid, copper and vitamin C are cofactor nutrients of these reactions. Tyrosine is also the precursor for hormones, thyroid, catecholestrogens and the major human pigment, melanin. Tyrosine is an important amino acid in many proteins, peptides and even enkephalins, the body's natural pain reliever. Valine and other branched amino acids, and possibly tryptophan and phenylalanine may reduce tyrosine absorption. A number of genetic errors of tyrosine metabolism occur. Most common is the increased amount of tyrosine in the blood of premature infants, which is marked by decreased motor activity, lethargy and poor feeding. Infection and intellectual deficits may occur. Vitamin C supplements reverse the disease. Some adults also develop elevated tyrosine in their blood. This indicates a need for more vitamin C. More tyrosine is needed under stress, and tyrosine supplements prevent the stress-induced depletion of norepinephrine and can cure biochemical depression. However, tyrosine may not be good for psychosis. Many antipsychotic medications apparently function by inhibiting tyrosine metabolism. L-dopa, which is directly used in Parkinson's, is made from tyrosine. Tyrosine, the nutrient, can be used as an adjunct in the treatment of Parkinson's. Peripheral metabolism of tyrosine necessitates large doses of tyrosine, however, compared to L-dopa. (http://www.dcnutrition.com).