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Bilirubin
Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the destruction of aged or abnormal red blood cells. In the first step of bilirubin synthesis, the heme molecule is stripped from the hemoglobin molecule. Heme then passes through various processes of porphyrin catabolism, which varies according to the region of the body in which the breakdown occurs. For example, the molecules excreted in the urine differ from those in the feces. The production of biliverdin from heme is the first major step in the catabolic pathway, after which the enzyme biliverdin reductase performs the second step, producing bilirubin from biliverdin.Boron W, Boulpaep E. Medical Physiology: a cellular and molecular approach, 2005. 984–986. Elsevier Saunders, United States. Ultimately, bilirubin is broken down within ...
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Jaundice
Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme metabolism, liver dysfunction, or biliary-tract obstruction. The prevalence of jaundice in adults is rare, while jaundice in babies is common, with an estimated 80% affected during their first week of life. The most commonly associated symptoms of jaundice are itchiness, pale feces, and dark urine. Normal levels of bilirubin in blood are below 1.0  mg/ dl (17  μmol/ L), while levels over 2–3 mg/dl (34–51 μmol/L) typically result in jaundice. High blood bilirubin is divided into two types – unconjugated and conjugated bilirubin. Causes of jaundice vary from relatively benign to potentially fatal. High unconjugated bilirubin may be due to excess red blood cell breakdown, large bruises, genetic conditions s ...
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Biliverdin Reductase
Biliverdin reductase (BVR) is an enzyme () found in all tissues under normal conditions, but especially in reticulo-macrophages of the liver and spleen. BVR facilitates the conversion of biliverdin to bilirubin via the reduction of a double-bond between the second and third pyrrole ring into a single-bond. There are two isozymes, in humans, each encoded by its own gene, biliverdin reductase A (BLVRA) and biliverdin reductase B (BLVRB). Mechanism of catalysis BVR acts on biliverdin by reducing its double-bond between the pyrrole rings into a single-bond. It accomplishes this using NADPH + H+ as an electron donor, forming bilirubin and NADP+ as products. BVR catalyzes this reaction through an overlapping binding site including Lys18, Lys22, Lys179, Arg183, and Arg185 as key residues. This binding site attaches to biliverdin, and causes its dissociation from heme oxygenase (HO) (which catalyzes reaction of ferric heme --> biliverdin), causing the subsequent reduction to bil ...
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Heme Breakdown
Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, heme is a coordination complex "consisting of an iron ion coordinated to a porphyrin acting as a tetradentate ligand, and to one or two axial ligands." The definition is loose, and many depictions omit the axial ligands. Among the metalloporphyrins deployed by metalloproteins as prosthetic groups, heme is one of the most widely used and defines a family of proteins known as hemoproteins. Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase. The word ''haem'' is derived from Greek ''haima'' meaning "blood". Function Hemoproteins have diverse biological functions inc ...
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Heme
Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, heme is a coordination complex "consisting of an iron ion coordinated to a porphyrin acting as a tetradentate ligand, and to one or two axial ligands." The definition is loose, and many depictions omit the axial ligands. Among the metalloporphyrins deployed by metalloproteins as prosthetic groups, heme is one of the most widely used and defines a family of proteins known as hemoproteins. Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase. The word ''haem'' is derived from Greek ''haima'' meaning "blood". Function Hemoproteins have diverse biological functions incl ...
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Stercobilin
Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: A cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. Kay IT, Weimer M, Watson CJ (1963)“The formation in vitro of stercobilin from bilirubin”Journal of Biological Chemistry. 238:1122-3. It is the chemical responsible for the brown color of human feces and was originally isolated from feces in 1932. Stercobilin (and related urobilin) can be used as a marker for biochemical identification of fecal pollution levels in rivers. Metabolism Stercobilin results from breakdown of the heme moiety of hemoglobin found in erythrocytes. Macrophages break down senescent erythrocytes and break the heme down into biliverdin, which rapidly reduces to free bilirubin. Bilirubin binds tightly to plasma proteins (especially albumin) in the blood stream and is transported to the liver, where it is conjugated with one or two glucuronic acid re ...
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Biliverdin
Biliverdin (latin for green bile) is a green tetrapyrrolic bile pigment, and is a product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: a cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. It is the pigment responsible for a greenish color sometimes seen in bruises. Metabolism Biliverdin results from the breakdown of the heme moiety of hemoglobin in erythrocytes. Macrophages break down senescent erythrocytes and break the heme down into biliverdin along with hemosiderin, in which biliverdin normally rapidly reduces to free bilirubin. Biliverdin is seen briefly in some bruises as a green color. In bruises, its breakdown into bilirubin leads to a yellowish color. Role in disease Biliverdin has been found in excess in the blood of humans suffering from hepatic diseases. Jaundice is caused by the accumulation of biliverdin or bilirubin (or both) in the circulatory system and tissues. Jaundiced skin and sclera (whites of the eyes) ...
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Phototherapy
Light therapy, also called phototherapy or bright light therapy is intentional daily exposure to direct sunlight or similar-intensity artificial light in order to treat medical disorders, especially seasonal affective disorder (SAD) and circadian rhythm sleep-wake disorders. Treating skin conditions such as neurodermatitis, psoriasis, acne vulgaris, and eczema with ultraviolet light is called ultraviolet light therapy. Medical uses Nutrient deficiency Vitamin D deficiency Exposure to light at specific wavelengths of Ultraviolet B (abbreviated as UV-B or UVB) enables the body to produce vitamin D to treat vitamin D deficiency. Skin conditions Light therapy treatments for the skin usually involve exposure to ultraviolet light. The exposures can be to a small area of the skin or over the whole body surface, as in a tanning bed. The most common treatment is with narrowband UVB, which has a wavelength of approximately 311–313 nanometers. Full body phototherapy can be de ...
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Urobilin
Urobilin or urochrome is the chemical primarily responsible for the yellow color of urine. It is a linear tetrapyrrole compound that, along with the related colorless compound urobilinogen, are degradation products of the cyclic tetrapyrrole heme. Metabolism Urobilin is generated from the degradation of heme, which is first degraded through biliverdin to bilirubin. Bilirubin is then excreted as bile, which is further degraded by microbes present in the large intestine to urobilinogen. Some of this remains in the large intestine, and its conversion to stercobilin gives feces their brown color. Some is reabsorbed into the bloodstream and then delivered to kidney. When urobilinogen is exposed to air, it is oxidized to urobilin, giving urine its yellow color. Importance Many urine tests (urinalysis) monitor the amount of urobilin in urine, as its levels can give insight on the effectiveness of urinary tract function. Normally, urine would appear as either light yellow or colorless. ...
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Tetrapyrrole
Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( =- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon atoms and one nitrogen atom. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life. Some tetrapyrroles form the active core of compounds with crucial biochemical roles in living systems, such as hemoglobin and chlorophyll. In these two molecules, in particular, the pyrrole macrocycle ring frames a metal atom, that forms a coordination compound with the pyrroles and plays a central role in the biochemical function of those molecules. Structure Linear tetrapyrroles (called bilanes) include: *Heme breakdown products (e.g., bilirubin, biliverdin) * Phycobilins (found in cyanobacteria) *Luciferins as found in dinoflagellates and euphausiid shrimps (krill) F ...
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Hy's Law
Hy's law is a rule of thumb that a patient is at high risk of a fatal drug-induced liver injury if given a medication that causes hepatocellular injury (not Hepatobiliary injury) with jaundice. The law is based on observations by Hy Zimmerman, a major scholar of drug-induced liver injury.United States Department of Health and Human Services, Food and Drug Administration, Center for Drug Evaluation and Research (CDER) Center for Biologics Evaluation and Research (CBER)Guidance for Industry Drug-Induced Liver Injury: Premarketing Clinical Evaluation, Final, July 2009/ref> Some have suggested the principle be called a hypothesis or observation. Hy's Law cases have three components: * The drug causes hepatocellular injury, generally defined as an elevated ALT or AST by 3-fold or greater above the upper limit of normal. Often with aminotransferases much greater (5-10x) the upper limit of normal. * Among subjects showing such aminotransferase elevations, they also have elevation of thei ...
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Glucuronic Acid
Glucuronic acid (from Greek γλεῦκος "''wine, must''" and οὖρον "''urine''") is a uronic acid that was first isolated from urine (hence the name). It is found in many gums such as gum arabic (c. 18%), xanthan, and kombucha tea and is important for the metabolism of microorganisms, plants and animals. Properties Glucuronic acid is a sugar acid derived from glucose, with its sixth carbon atom oxidized to a carboxylic acid. In living beings, this primary oxidation occurs with UDP-α-D-glucose (UDPG), not with the free sugar. Glucuronic acid, like its precursor glucose, can exist as a linear (carboxo-) aldohexose ( 60,000 are too large for renal excretion and will be excreted with bile into the intestine. Neonates are deficient in this conjugating system, making them particularly vulnerable to drugs such as chloramphenicol, which is inactivated by the addition of glucuronic acid, resulting in gray baby syndrome. Bilirubin is excreted in the bile as bilirubin dig ...
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Bile
Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bile) and stored and concentrated in the gallbladder. After eating, this stored bile is discharged into the duodenum. The composition of hepatic bile is (97–98)% water, 0.7% bile salts, 0.2% bilirubin, 0.51% fats (cholesterol, fatty acids, and lecithin), and 200 meq/L inorganic salts. The two main pigments of bile are bilirubin, which is yellow, and its oxidised form biliverdin, which is green. When mixed, they are responsible for the brown color of feces. About 400 to 800 millilitres of bile is produced per day in adult human beings. Function Bile or gall acts to some extent as a surfactant, helping to emulsify the lipids in food. Bile salt anions are hydrophilic on one side and hydrophobic on the other side; consequently, they tend ...
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