Browsing Compounds

7-Dehydrocholesterol is a zoosterol (a sterol produced by animals rather than plants). It is a provitamin-D. The presence of this compound in skin enables humans to manufacture vitamin D3 from ultraviolet rays via an intermediate isomer provitamin D3. It is also found in breast milk.

Carnosine (beta-alanyl-L-histidine) is found exclusively in animal tissues. It is a dipeptide of the amino acids beta-alanine and histidine. Carnosine has the potential to suppress many of the biochemical changes that accompany ageing (e.g. protein oxidation, glycation, AGE formation, and cross-linking) and associated pathologies (PMID: 16804013). It is highly concentrated in muscle and brain tissues. Some autistic patients take it as a dietary supplement and attribute an improvement in their condition to it. Supplemental carnosine may increase corticosterone levels. This may explain the "hyperactivity" seen in autistic subjects at higher doses. Carnosine also exhibits some antioxidant effects. The antioxidant mechanism of carnosine is attributed to its chelating effect against metal ions, superoxide dismutase (SOD)-like activity, and ROS and free radicals scavenging ability (PMID: 16406688). Carnosine is a biomarker for the consumption of meat. Carnosine is found to be associated with carnosinuria, which is an inborn error of metabolism.

Adenine is a purine base. Adenine is found in both DNA and RNA. Adenine is a fundamental component of adenine nucleotides. Adenine forms adenosine, a nucleoside, when attached to ribose, and deoxyadenosine when attached to deoxyribose; it forms adenosine triphosphate (ATP), a nucleotide, when three phosphate groups are added to adenosine. Adenosine triphosphate is used in cellular metabolism as one of the basic methods of transferring chemical energy between chemical reactions. Purine inborn errors of metabolism (IEM) are serious hereditary disorders, which should be suspected in any case of neonatal fitting, failure to thrive, recurrent infections, neurological deficit, renal disease, self-mutilation and other manifestations. Investigation usually starts with uric acid (UA) determination in urine and plasma. (OMIM 300322, 229600, 603027, 232400, 232600, 232800, 201450, 220150, 232200, 162000, 164050, 278300). (PMID: 17052198, 17520339).

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).

Aldosterone is a steroid hormone produced by the adrenal cortex in the adrenal gland to regulate sodium and potassium balance in the blood. Specifically it regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium. It is synthesized from cholesterol by aldosterone synthase, which is absent in other sections of the adrenal gland. It is the sole endogenous member of the class of mineralocorticoids. Aldosterone increases the permeability of the apical (luminal) membrane of the kidney's collecting ducts to potassium and sodium and activates their basolateral Na+/K+ pumps, stimulating ATP hydrolysis, reabsorbing sodium (Na+) ions and water into the blood, and excreting potassium (K+) ions into the urine.

Dihydrobiopterin (BH2) is an oxidation product of tetrahydrobiopterin. Tetrahydrobiopterin is a natural occurring cofactor of the aromatic amino acid hydroxylase and is involved in the synthesis of tyrosine and the neurotransmitters dopamine and serotonin. Tetrahydrobiopterin is also essential for nitric oxide synthase catalyzed oxidation of L-arginine to L-citrulline and nitric oxide.

Butyric acid, a four-carbon fatty acid, is formed in the human colon by bacterial fermentation of carbohydrates (including dietary fiber), and putatively suppresses colorectal cancer (CRC). Butyrate has diverse and apparently paradoxical effects on cellular proliferation, apoptosis and differentiation that may be either pro-neoplastic or anti-neoplastic, depending upon factors such as the level of exposure, availability of other metabolic substrate and the intracellular milieu. In humans, the relationship between luminal butyrate exposure and CRC has been examined only indirectly in case-control studies, by measuring fecal butyrate concentrations, although this may not accurately reflect effective butyrate exposure during carcinogenesis. Perhaps not surprisingly, results of these investigations have been mutually contradictory. The direct effect of butyrate on tumorigenesis has been assessed in a no. of in vivo animal models, which have also yielded conflicting results. In part, this may be explained by methodology: differences in the amount and route of butyrate administration, which are likely to significantly influence delivery of butyrate to the distal colon. (PMID: 16460475) Butyric acid is a carboxylic acid found in rancid butter, parmesan cheese, and vomit, and has an unpleasant odor and acrid taste, with a sweetish aftertaste (similar to ether). Butyric acid is a fatty acid occurring in the form of esters in animal fats and plant oils. Interestingly, low-molecular-weight esters of butyric acid, such as methyl butyrate, have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives. Butyrate is produced as end-product of a fermentation process solely performed by obligate anaerobic bacteria.

Acetic acid is one of the simplest carboxylic acids. It is an important chemical reagent and industrial chemical that is used in the production of plastic soft drink bottles, photographic film; and polyvinyl acetate for wood glue, as well as many synthetic fibres and fabrics. In households diluted acetic acid is often used as a cleaning agent. In the food industry acetic acid is used as an acidity regulator. The acetyl group, derived from acetic acid, is fundamental to the biochemistry of virtually all forms of life. When bound to coenzyme A it is central to the metabolism of carbohydrates and fats. However, the concentration of free acetic acid in cells is kept at a low level to avoid disrupting the control of the pH of the cell contents. Acetic acid is produced and excreted by certain bacteria, notably the Acetobacter genus and Clostridium acetobutylicum. These bacteria are found universally in foodstuffs, water, and soil, and acetic acid is produced naturally as fruits and some other foods spoil. Acetic acid is also a component of the vaginal lubrication of humans and other primates, where it appears to serve as a mild antibacterial agent.

Betaine (or N,N,N-trimethylglycine) was named after its discovery in sugar beet (Beta vulgaris) in the 19th century. It is a small N-trimethylated amino acid, existing in zwitterionic form at neutral pH. It is now often called glycine betaine to distinguish it from other betaines that are widely distributed in microorganisms, plants, and animals. Many naturally occurring betaines serve as organic osmolytes, substances synthesized or taken up from the environment by cells for protection against osmotic stress, drought, high salinity, or high temperature. Intracellular accumulation of betaines permits water retention in cells, thus protecting from the effects of dehydration (Wikipedia). Betaine functions as a methyl donor in that it carries and donates methyl functional groups to facilitate necessary chemical processes. In particular, it methylates homocysteine to methionine, also producing N,N-dimethylglycine. The donation of methyl groups is important to proper liver function, cellular replication, and detoxification reactions. Betaine also plays a role in the manufacture of carnitine and serves to protect the kidneys from damage. Betaine comes from either the diet or by the oxidation of choline. Betaine insufficiency is associated with metabolic syndrome, lipid disorders, and diabetes, and may have a role in vascular and other diseases (PMID: 20346934). Betaine is important in development, from the pre-implantation embryo to infancy. Betaine is also widely regarded as an anti-oxidant. Betaine has been shown to have an inhibitory effect on NO release in activated microglial cells and may be an effective therapeutic component to control neurological disorders (PMID: 22801281). As a drug, betaine hydrochloride has been used as a source of hydrochloric acid in the treatment of hypochlorhydria. Betaine has also been used in the treatment of liver disorders, for hyperkalemia, for homocystinuria, and for gastrointestinal disturbances (Martindale, The Extra Pharmacopoeia, 30th Ed, p1341).

Ascorbic acid is found naturally in citrus fruits and many vegetables and is an essential nutrient in human diets. It is necessary to maintain connective tissue and bone. The biologically active form of ascorbic acid is vitamin C. Vitamin C is a water soluble vitamin. Primates (including humans) and a few other species in all divisions of the animal kingdom, notably the guinea pig, have lost the ability to synthesize ascorbic acid and must obtain it in their food. Vitamin C functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant. [PubChem] Ascorbic acid is an electron donor for enzymes involved in collagen hydroxylation, biosynthesis of carnitine and norepinephrine, tyrosine metabolism, and amidation of peptide hormones. Ascrobic acid (vitamin C) deficiency causes scurvy. The amount of vitamin C necessary to prevent scurvy may not be adequate to maintain optimal health. The ability of vitamin C to donate electrons also makes it a potent water-soluble antioxidant that readily scavenges free radicals such as molecular oxygen, superoxide, hydroxyl radical, and hypochlorous acid. In this setting, several mechanisms could account for a link between vitamin C and heart disease. One is the relation between LDL oxidation and vitamins C and E. Vitamin C in vitro can recycle vitamin E, which can donate electrons to prevent LDL oxidation in vitro. As the lipid-phase vitamin E is oxidized, it can be regenerated by aqueous vitamin C. Other possibilities are that vitamin C could decrease cholesterol by mechanisms not well characterized, or could improve vasodilatation and vascular reactivity, perhaps by decreasing the interactions of nitric oxide with oxidants. (PMID: 10799361).

Adenosine monophosphate, also known as 5'-adenylic acid and abbreviated AMP, is a nucleotide that is found in RNA. It is an ester of phosphoric acid with the nucleoside adenosine. AMP consists of the phosphate group, the pentose sugar ribose, and the nucleobase adenine. AMP can be produced during ATP synthesis by the enzyme adenylate kinase. AMP has recently been approved as a 'Bitter Blocker' additive to foodstuffs. When AMP is added to bitter foods or foods with a bitter aftertaste it makes them seem 'sweeter'. This potentially makes lower calorie food products more palatable.

Melibiose is disaccharide consisting of one galactose and one glucose moiety in an alpha (1-6) glycosidic linkage. This sugar is produced and metabolized only by enteric and lactic acid bacteria and other microbes. It is not an endogenous metabolite but may be obtained from the consumption of partially fermented molasses, brown sugar or honey. Antibodies to melibiose will appear in individuals affected by Chagas' disease (Trypanosoma cruzi infection). Melibiose is not metabolized by humans, but can be broken down by gut microflora, such as E. coli. In fact, E. coli is able to utilize melibiose as a sole source of carbon. Melibiose is first imported by the melibiose permease, MelB and then converted to β-D-glucose and β-D-galactose by the α-galactosidase encoded by melA. Because of its poor digestability Melibiose (along with rhamnose) can be used together for noninvasive intestinal mucosa barrier testing. This test can be used to assess malabsorption or impairment of intestinal permeability. Recent studies with dietary melibiose have shown that can strongly affected the Th cell responses to an ingested antigen. It has been suggested that melibiose could be used to enhance the induction of oral tolerance. (PMID 17986780).

Adenosine is a nucleoside that is composed of adenine and D-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. For instance, adenosine plays an important role in energy transfer as adenosine triphosphate (ATP) and adenosine diphosphate (ADP). It also plays a role in signal transduction as cyclic adenosine monophosphate (cAMP). Adenosine itself is both a neurotransmitter and potent vasodilator. When administered intravenously adenosine causes transient heart block in the AV node. Due to the effects of adenosine on AV node-dependent supraventricular tachycardia, adenosine is considered a class V antiarrhythmic agent. Overdoses of adenosine intake (as a drug) can lead to several side effects including chest pain, feeling faint, shortness of breath, and tingling of the senses. Serious side effects include a worsening dysrhythmia and low blood pressure. When present in sufficiently high levels, adenosine can act as an immunotoxin and a metabotoxin. An immunotoxin disrupts, limits the function, or destroys immune cells. A metabotoxin is an endogenous metabolite that causes adverse health effects at chronically high levels. Chronically high levels of adenosine are associated with adenosine deaminase deficiency. Adenosine is a precursor to deoxyadenosine, which is a precursor to dATP. A buildup of dATP in cells inhibits ribonucleotide reductase and prevents DNA synthesis, so cells are unable to divide. Since developing T cells and B cells are some of the most mitotically active cells, they are unable to divide and propagate to respond to immune challenges. High levels of deoxyadenosine also lead to an increase in S-adenosylhomocysteine, which is toxic to immature lymphocytes.

Ammonia is a colourless alkaline gas and is one of the most abundant nitrogen-containing compounds in the atmosphere. It is an irritant with a characteristic pungent odor that is widely used in industry. Inasmuch as ammonia is highly soluble in water and, upon inhalation, is deposited in the upper airways, occupational exposures to ammonia have commonly been associated with sinusitis, upper airway irritation, and eye irritation. Acute exposures to high levels of ammonia have also been associated with diseases of the lower airways and interstitial lung. Small amounts of ammonia are naturally formed in nearly all tissues and organs of the vertebrate organism. Ammonia is both a neurotoxin and a metabotoxin. In fact, it is the most common endogenous neurotoxin. A neurotoxin is a compound that causes damage to neural tissue and neural cells. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Ammonia is recognized to be central in the pathogenesis of a brain condition known as hepatic encephalopathy, which arises from various liver diseases and leads to a build up ammonia in the blood (hyperammonemia). More than 40% of people with cirrhosis develop hepatic encephalopathy. Part of the neurotoxicity of ammonia arises from the fact that it easily crosses the blood-brain barrier and is absorbed and metabolized by the astrocytes, a population of cells in the brain that constitutes 30% of the cerebral cortex. Astrocytes use ammonia when synthesizing glutamine from glutamate. The increased levels of glutamine lead to an increase in osmotic pressure in the astrocytes, which become swollen. There is increased activity of the inhibitory gamma-aminobutyric acid (GABA) system, and the energy supply to other brain cells is decreased. This can be thought of as an example of brain edema. The source of the ammonia leading to hepatic encephalopathy is not entirely clear. The gut produces ammonia, which is metabolized in the liver, and almost all organ systems are involved in ammonia metabolism. Colonic bacteria produce ammonia by splitting urea and other amino acids, however this does not fully explain hyperammonemia and hepatic encephalopathy. The alternative explanation is that hyperammonemia is the result of the intestinal breakdown of amino acids, especially glutamine. The intestines have significant glutaminase activity, predominantly located in the enterocytes. On the other hand, intestinal tissues only have a little glutamine synthetase activity, making it a major glutamine-consuming organ. In addition to the intestine, the kidney is an important source of blood ammonia in patients with liver disease. Ammonia is also taken up by the muscle and brain in hepatic coma, and there is confirmation that ammonia is metabolized in muscle. Excessive formation of ammonia in the brains of Alzheimer's disease patients has also been demonstrated, and it has been shown that some Alzheimer's disease patients exhibit elevated blood ammonia concentrations. Ammonia is the most important natural modulator of lysosomal protein processing. Indeed, there is strong evidence for the involvement of aberrant lysosomal processing of beta-amyloid precursor protein (beta-APP) in the formation of amyloid deposits. Inflammatory processes and activation of microglia are widely believed to be implicated in the pathology of Alzheimer's disease. Ammonia is able to affect the characteristic functions of microglia, such as endocytosis, and cytokine production. Based on these facts, an ammonia-based hypothesis for Alzheimer's disease has been suggested (PMID: 17006913, 16167195, 15377862, 15369278). Chronically high levels of ammonia in the blood are associated with nearly twenty different inborn errors of metabolism including: 3-hydroxy-3-methylglutaryl-CoA lyase deficiency, 3-methyl-crotonylglycinuria, argininemia, argininosuccinic aciduria, beta-ketothiolase deficiency, biotinidase deficiency, carbamoyl phosphate synthetase deficiency, carnitine-acylcarnitine translocase deficiency, citrullinemia type I, hyperinsulinism-hyperammonemia syndrome, hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, isovaleric aciduria, lysinuric protein intolerance, malonic aciduria, methylmalonic aciduria, methylmalonic aciduria due to cobalamin-related disorders, propionic acidemia, pyruvate carboxylase deficiency, and short chain acyl CoA dehydrogenase deficiency (SCAD deficiency). Many of these inborn errors of metabolism are associated with urea cycle disorders or impairment of amino acid metabolism. High levels of ammonia in the blood (hyperammonemia) lead to the activation of NMDA receptors in the brain. This results in the depletion of brain ATP, which in turn leads to the release of glutamate. Ammonia also leads to the impairment of mitochondrial function and calcium homeostasis, thereby decreasing ATP synthesis. Excess ammonia also increases the formation of nitric oxide (NO), which in turn reduces the activity of glutamine synthetase, and thereby decreases the elimination of ammonia in the brain (PMID: 12020609). As a neurotoxin, ammonia predominantly affects astrocytes. Disturbed mitochondrial function and oxidative stress, factors implicated in the induction of the mitochondrial permeability transition, appear to be involved in the mechanism of ammonia neurotoxicity. Ammonia can also affect the glutamatergic and GABAergic neuronal systems, the two prevailing neuronal systems of the cortical structures. All of these effects can lead to irreversible brain damage, coma, and/or death. Infants with urea cycle disorders and hyperammonemia initially exhibit vomiting and increasing lethargy. If untreated, seizures, hypotonia (poor muscle tone, floppiness), respiratory distress (respiratory alkalosis), and coma can occur. Adults with urea cycle disorders and hyperammonemia will exhibit episodes of disorientation, confusion, slurred speech, unusual and extreme combativeness or agitation, stroke-like symptoms, lethargy, and delirium. Ammonia also has toxic effects when an individual is exposed to ammonia solutions. Acute exposure to high levels of ammonia in air may be irritating to skin, eyes, throat, and lungs and cause coughing and burns. Lung damage and death may occur after exposure to very high concentrations of ammonia. Swallowing concentrated solutions of ammonia can cause burns in the mouth, throat, and stomach. Splashing ammonia into eyes can cause burns and even blindness.

Arginosuccinic acid is a basic amino acid. Some cells synthesize it from citrulline, aspartic acid and use it as a precursor for arginine in the urea cycle or Citrulline-NO cycle. The enzyme that catalyzes the reaction is argininosuccinate synthetase. Argininosuccinic acid is a precursor to fumarate in the citric acid cycle via argininosuccinate lyase. Defects in the arginosuccinate lyase enzyme can lead to arginosuccinate lyase deficiency. Argininosuccinate (ASA) lyase deficiency results in defective cleavage of ASA. This leads to an accumulation of ASA in cells and an excessive excretion of ASA in urine (arginosuccinic aciduria). In virtually all respects, this disorder shares the characteristics of other urea cycle defects. The most important characteristic of ASA lyase deficiency is its propensity to cause hyperammonemia in affected individuals. ASA in affected individuals is excreted by the kidney at a rate practically equivalent to the glomerular filtration rate (GFR). Whether ASA itself causes a degree of toxicity due to hepatocellular accumulation is unknown; such an effect could help explain hyperammonemia development in affected individuals. Regardless, the name of the disease is derived from the rapid clearance of ASA in urine, although elevated levels of ASA can be found in plasma. ASA lyase deficiency is associated with high mortality and morbidity rates. Symptoms of ASA lyase deficiency include anorexia, irritability rapid breathing, lethargy and vomiting. Extreme symptoms include coma and cerebral edema.

Androstenedione is a delta-4 19-carbon steroid that is produced not only in the testis, but also in the ovary and the adrenal cortex. Depending on the tissue type, androstenedione can serve as a precursor to testosterone as well as estrone and estradiol. It is the common precursor of male and female sex hormones. Some androstenedione is also secreted into the plasma, and may be converted in peripheral tissues to testosterone and estrogens. Androstenedione originates either from the conversion of dehydroepiandrosterone or from 17-hydroxyprogesterone. It is further converted to either testosterone or estrone. The production of adrenal androstenedione is governed by ACTH, while production of gonadal androstenedione is under control by gonadotropins.

Bilirubin is a bile pigment that is a degradation product of heme. In particular, bilirubin is a yellow breakdown product of normal heme catabolism. Its levels are elevated in certain diseases and it is responsible for the yellow colour of bruises. Bilirubin is an excretion product and the body does not control its levels. Bilirubin levels reflect the balance between production and excretion. Thus, there is no "normal" level of bilirubin. Bilirubin consists of an open chain of four pyrroles (tetrapyrrole). In contrast, the heme molecule is a closed ring of four pyrroles, called porphyrin (Wikipedia). Bilirubin is found to be associated with Crigler-Najjar syndrome type I, which is an inborn error of metabolism.

beta-Alanine is the only naturally occurring beta-amino acid - an amino acid in which the amino group is at the beta-position from the carboxylate group. It is formed in vivo by the degradation of dihydrouracil and carnosine. It is a component of the naturally occurring peptides carnosine and anserine and also of pantothenic acid (vitamin B-5), which itself is a component of coenzyme A. Under normal conditions, beta-alanine is metabolized into acetic acid. beta-Alanine can undergo a transanimation reaction with pyruvate to form malonate-semialdehyde and L-alanine. The malonate semialdehyde can then be converted into malonate via malonate-semialdehyde dehydrogenase. Malonate is then converted into malonyl-CoA and enter fatty acid biosynthesis. Since neuronal uptake and neuronal receptor sensitivity to beta-alanine have been demonstrated, beta-alanine may act as a false transmitter replacing gamma-aminobutyric acid. When present in sufficiently high levels, beta-alanine can act as a neurotoxin, a mitochondrial toxin, and a metabotoxin. A neurotoxin is a compound that damages the brain or nerve tissue. A mitochondrial toxin is a compound that damages mitochondria and reduces cellular respiration as well as oxidative phosphorylation. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of beta-alanine are associated with at least three inborn errors of metabolism, including GABA-transaminase deficiency, hyper-beta-alaninemia, and methylmalonate semialdehyde dehydrogenase deficiency. beta-Alanine is a central nervous system (CNS) depressant and is an inhibitor of GABA transaminase. The associated inhibition of GABA transaminase and displacement of GABA from CNS binding sites can also lead to GABAuria (high levels of GABA in the urine) and convulsions. In addition to its neurotoxicity, beta-alanine reduces cellular levels of taurine, which are required for normal respiratory chain function. Cellular taurine depletion is known to reduce respiratory function and elevate mitochondrial superoxide generation, which damages mitochondria and increases oxidative stress (PMID: 27023909). Individuals suffering from mitochondrial defects or mitochondrial toxicity typically develop neurotoxicity, hypotonia, respiratory distress, and cardiac failure. beta-Alanine is a biomarker for the consumption of meat, especially red meat.

cAMP or cyclic AMP is an adenine nucleotide containing one phosphate group which is esterified to both the 3'- and 5'-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and ACTH. cAMP is synthesized from ATP by adenylate cyclase. Adenylate cyclase is located at the cell membranes. Adenylate cyclase is activated by the hormones glucagon and adrenaline and by G protein. Liver adenylate cyclase responds more strongly to glucagon, and muscle adenylate cyclase responds more strongly to adrenaline. cAMP decomposition into AMP is catalyzed by the enzyme phosphodiesterase.

Acetoacetic acid (AcAc) is a weak organic acid that can be produced in the human liver under certain conditions of poor metabolism leading to excessive fatty acid breakdown (diabetes mellitus leading to diabetic ketoacidosis). It is then partially converted into acetone by decarboxylation and excreted either in urine or through respiration. Persistent mild hyperketonemia is a common finding in newborns. Ketone bodies serve as an indispensable source of energy for extrahepatic tissues, especially the brain and lung of developing rats. Another important function of ketone bodies is to provide acetoacetyl-CoA and acetyl-CoA for synthesis of cholesterol, fatty acids, and complex lipids. During the early postnatal period, acetoacetate and beta-hydroxybutyrate are preferred over glucose as substrates for synthesis of phospholipids and sphingolipids in accord with requirements for brain growth and myelination. Thus, during the first two weeks of postnatal development, when the accumulation of cholesterol and phospholipids accelerates, the proportion of ketone bodies incorporated into these lipids increases. On the other hand, an increased proportion of ketone bodies are utilized for cerebroside synthesis during the period of active myelination. In the lung, AcAc serves better than glucose as a precursor for the synthesis of lung phospholipids. The synthesized lipids, particularly dipalmityl phosphatidylcholine, are incorporated into surfactant, and thus have a potential role in supplying adequate surfactant lipids to maintain lung function during the early days of life (PMID: 3884391). The acid is also present in the metabolism of those undergoing starvation or prolonged physical exertion as part of gluconeogenesis. When ketone bodies are measured by way of urine concentration, acetoacetic acid, along with beta-hydroxybutyric acid or acetone, is what is detected.