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41-464: The retinoids are a class of chemical compounds that are natural derivatives of vitamin A or are chemically related to it. Synthetic retinoids are used in medicine where they regulate skin health, immunity and bone disorders. Retinoids have many important functions throughout the body, including roles in vision, regulation of skin proliferation and differentiation, growth of bone tissue, immune function, and male fertility. The biology of retinoids

82-424: A chemical compound ; the concept is most readily understood when considering pure chemical substances . It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction , into compounds or substances each having fewer atoms. A chemical formula is a way of expressing information about the proportions of atoms that constitute

123-664: A polyene side chain and a polar end group. The conjugated system formed by alternating C=C double bonds in the polyene side chain are responsible for the color of retinoids (typically yellow, orange, or red). Hence, many retinoids are chromophores . Alternation of side chains and end groups creates the various classes of retinoids. First generation retinoids are produced naturally in the body and interact with their normal biological counterparts, such as retinol binding protein 4 for retinol, retinoid receptors for all-trans-retinoic acid or 9-cis-retinoic acid . 13-cis retinoic acid has an unknown biological pathway but appears to act as

164-419: A solid-state reaction , or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases. Ionic compounds typically have high melting and boiling points , and are hard and brittle . As solids they are almost always electrically insulating , but when melted or dissolved they become highly conductive , because the ions are mobilized. An intermetallic compound

205-412: A continuous three-dimensional network, usually in a crystalline structure . Ionic compounds containing basic ions hydroxide (OH ) or oxide (O ) are classified as bases. Ionic compounds without these ions are also known as salts and can be formed by acid–base reactions . Ionic compounds can also be produced from their constituent ions by evaporation of their solvent , precipitation , freezing ,

246-503: A different chemical composition by interaction with a second chemical compound via a chemical reaction . In this process, bonds between atoms are broken in both of the interacting compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AD + CB , where A, B, C, and D are each unique atoms; and AB, AD, CD, and CB are each unique compounds. Cutaneous T-cell lymphoma The presentation depends if it

287-516: A disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, using the standard chemical symbols with numerical subscripts . Many chemical compounds have a unique CAS number identifier assigned by the Chemical Abstracts Service . Globally, more than 350,000 chemical compounds (including mixtures of chemicals) have been registered for production and use. The term "compound"—with

328-592: A growth factor. Second generation retinoids have a mixed effect and interact mainly with signaling in the skin. Third generation retinoids have narrow biological roles due to their constrained structure, with adapalene mimicking the effects of isotretinoin , bexarotene binding only the Retinoid X receptors , and tazarotene binding the Retinoic acid receptor beta and Retinoic acid receptor gamma forms. The only fourth generation retinoid, Trifarotene, binds selectively to

369-444: A meaning similar to the modern—has been used at least since 1661 when Robert Boyle's The Sceptical Chymist was published. In this book, Boyle variously used the terms "compound", "compounded body", "perfectly mixt body", and "concrete". "Perfectly mixt bodies" included for example gold, lead, mercury, and wine. While the distinction between compound and mixture is not so clear, the distinction between element and compound

410-566: A particular chemical compound, using chemical symbols for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H 2 O. In the case of non-stoichiometric compounds , the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e.g., for palladium hydride , PdH x (0.02 < x < 0.58)]. Chemical compounds have

451-496: A positively charged cation . The nonmetal will gain the electrons from the metal, making the nonmetal a negatively charged anion . As outlined, ionic bonds occur between an electron donor, usually a metal, and an electron acceptor, which tends to be a nonmetal. Hydrogen bonding occurs when a hydrogen atom bonded to an electronegative atom forms an electrostatic connection with another electronegative atom through interacting dipoles or charges. A compound can be converted to

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492-423: A range of viral (e.g., HTLV-1 , HTLV-2 , HIV , Epstein-Barr virus , Cytomegalovirus , HHV-6 , HHV-7 , HHV-8 (KSHV) , and Polyomaviruses such as Merkel cell polyomavirus ) and bacterial or fungal pathogens (including Staphylococcus aureus , Mycobacterium leprae , Chlamydophila pneumoniae , and dermatophytes ). The level of evidence varies among the different factors. A point-based algorithm for

533-447: A solid state dependent on how low the temperature of the environment is. A covalent bond , also known as a molecular bond, involves the sharing of electrons between two atoms. Primarily, this type of bond occurs between elements that fall close to each other on the periodic table of elements , yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on

574-469: A unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds . Chemical compounds can be molecular compounds held together by covalent bonds , salts held together by ionic bonds , intermetallic compounds held together by metallic bonds , or the subset of chemical complexes that are held together by coordinate covalent bonds . Pure chemical elements are generally not considered chemical compounds, failing

615-399: A variety of treatment options available and some CTCL patients are able to live normal lives with this cancer, although symptoms can be debilitating and painful, even in earlier stages. FDA approved treatments include the following: Histone deacetylase (HDAC) inhibitors are shown to have antiproliferative and cytotoxic properties against CTCL. Other (off label) treatments include: In 2010,

656-499: Is mycosis fungoides or Sézary syndrome , the most common, though not the only types. Among the symptoms for the aforementioned types are: enlarged lymph nodes , an enlarged liver and spleen , and non-specific dermatitis . The cause of CTCL remains largely unknown, but several external risk factors have been proposed as potential triggers and promoters of the disease. These include the use of hydrochlorothiazide diuretics, therapy-induced immunosuppression, and possible infections by

697-445: Is a central theme. Quicksilver ... with Aqua fortis will be brought into a ... white Powder ... with Sulphur it will compose a blood-red and volatile Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury. Boyle used the concept of "corpuscles"—or "atomes", as he also called them—to explain how a limited number of elements could combine into a vast number of compounds: If we assigne to

738-403: Is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. They can be classified as stoichiometric or nonstoichiometric intermetallic compounds. A coordination complex consists of a central atom or ion, which is usually metallic and is called

779-417: Is complex and their use in medicine has well-known benefits in diseases like acute promyelocytic leukemia (APL) or acne . On the other hand, retinoids are known to have many harmful effects on metabolism and cancer. Retinoids are divided into four generations based on their molecular structure and receptor selectivity. The basic structure of the hydrophobic retinoid molecule consists of a cyclic end group,

820-493: Is neutral overall, but consists of positively charged ions called cations and negatively charged ions called anions . These can be simple ions such as the sodium (Na ) and chloride (Cl ) in sodium chloride , or polyatomic species such as the ammonium ( NH 4 ) and carbonate ( CO 3 ) ions in ammonium carbonate . Individual ions within an ionic compound usually have multiple nearest neighbours, so are not considered to be part of molecules, but instead part of

861-586: Is not an ingredient that is safe for pregnant women. The Association of the American Academy of Dermatology (AAD) recommends that pregnant women consult a health care provider before trying any lotions or oils for stretch mark prevention. Chemical compounds A chemical compound is a chemical substance composed of many identical molecules (or molecular entities ) containing atoms from more than one chemical element held together by chemical bonds . A molecule consisting of atoms of only one element

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902-942: Is related to the mechanism of action as well as exposure. A medical sign of chronic or acute poisoning with retinol is hypervitaminosis A , which includes the presence of painful tender swellings on the long bones. Anorexia , skin lesions , hair loss , hepatosplenomegaly , papilloedema , bleeding , general malaise , pseudotumor cerebri , and death may also occur. Similar effects occur with other retinoids, except for 13-cis retinoic acid and its derivatives, such as adapalene . Retinoids provoke rapid elevation of circulating triglycerides leading to hypertriglyceridemia as well as cholesterol, leading to hypercholesterolemia . Retinoids are further shown to worsen many metabolic diseases, such as diabetes and congestive heart failure. Large-scale randomized, controlled clinical trials have conclusively shown that vitamin A, retinol and other retinoids increase mortality and cancer rates. In addition to

943-639: Is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction , which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds ; ionic compounds are held together by ionic bonds ; intermetallic compounds are held together by metallic bonds ; coordination complexes are held together by coordinate covalent bonds . Non-stoichiometric compounds form

984-452: The coordination centre , and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds, especially those of transition metals , are coordination complexes. A coordination complex whose centre is a metal atom is called a metal complex of d block element. Compounds are held together through a variety of different types of bonding and forces. The differences in

1025-449: The oxygen molecule (O 2 ); or it may be heteronuclear , a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H 2 O). A molecule is the smallest unit of a substance that still carries all the physical and chemical properties of that substance. An ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding . The compound

1066-896: The Corpuscles, whereof each Element consists, a peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos’d of them. In his Logick , published in 1724, the English minister and logician Isaac Watts gave an early definition of chemical element, and contrasted element with chemical compound in clear, modern terms. Among Substances, some are called Simple, some are Compound ... Simple Substances ... are usually called Elements, of which all other Bodies are compounded: Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... Followers of Aristotle made Fire, Air, Earth and Water to be

1107-459: The Earth. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. A molecule may be homonuclear , that is, it consists of atoms of one chemical element, as with two atoms in

1148-625: The RAR-y receptor. It was approved for use in the US in 2019. The major source of retinoids in human diet are plant pigments such as carotenes and retinyl esters derived from animal sources. Retinyl esters are transported through the chylomicron pathway to the liver or fat tissue while retinol or carotenes are transported from the enterocytes to the liver and are processed into retinyl esters by LRAT for storage. Most synthetic retinoids are absorbed when taken orally while topical retinoids cannot diffuse through

1189-524: The Truth ;; tho' they are not all agreed ... Compound Substances are made up of two or more simple Substances ... So a Needle is simple Body, being made only of Steel; but a Sword or a Knife is a compound because its ... Handle is made of Materials different from the Blade. Any substance consisting of two or more different types of atoms ( chemical elements ) in a fixed stoichiometric proportion can be termed

1230-472: The U.S. Food and Drug Administration granted orphan drug designation for naloxone lotion as a treatment for pruritus in cutaneous T-cell lymphoma to a pharmaceutical company called Elorac. Of all cancers involving lymphocytes , 2% of cases are cutaneous T cell lymphomas. CTCL is more common in men and in African-American people. The incidence of CTCL in men is 1.6 times higher than in women. There

1271-401: The body for much longer. Common skin conditions treated by topical retinoids include acne and psoriasis . photoaging , and skin wrinkles. In addition, retinoids are used to treat rare skin disorders including discoid lupus and mycosis fungoides . In Japan, isotretinoin may be used for neuroblastoma treatment although it is not approved in other countries due to a lack of consistency in

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1312-403: The demonstrated effects. Oral retinoids show considerable toxicity if they interact with retinoid receptors and thus are only approved in several severe diseases including acute promyelocytic leukemia , cutaneous T-cell lymphoma and heterotopic ossification . Toxic effects of retinoids occur with both acute or prolonged intake, depending on which retinoid is considered. The specific toxicity

1353-463: The diagnosis for early forms of cutaneous T-cell lymphoma was proposed by the International Society for Cutaneous Lymphomas in 2005. Cutaneous T-cell lymphoma may be divided into the several subtypes. Mycosis fungoides is the most common form of CTCL and is responsible for half of all cases. A WHO - EORTC classification has been developed. There is no cure for CTCL, but there are

1394-400: The fixed ratios. Many solid chemical substances—for example many silicate minerals —are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios; even so, these crystalline substances are often called " non-stoichiometric compounds ". It may be argued that they are related to, rather than being chemical compounds, insofar as

1435-508: The four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted. The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five : This seems to come nearer

1476-669: The harmful effects shared by other retinoids, bexarotene causes severe hypothyroidism . The Pharmacovigilance Risk Assessment Committee (PRAC), based on its review, confirmed that taking oral retinoids during pregnancy can have harmful effects on the baby as they may cause CNS, cranio-facial, cardiovascular and other defects. The use of acitretin, alitretinoin and isotretinoin should be prohibited in women of childbearing age unless they take measures to prevent pregnancy. The use of topical retinoids should also be excluded during pregnancy and in women planning pregnancy. Many lotions that claim to prevent or treat stretch marks contain retinol, which

1517-536: The periodic table tend to have similar electronegativities , which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet . Ionic bonding occurs when valence electrons are completely transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions. The metals in ionic bonding usually lose their valence electrons, becoming

1558-516: The skin barrier unless it is compromised. All classes of retinoid bind to many proteins. Natural retinoids such as retinol and retinyl esters bind to carrier proteins such as RBP4 , chylomicrons and VLDL while synthetic retinoids likely bind to these and other proteins. First generation retinoids are rapidly metabolized by Cytochrome p450 enzymes, typically of the Cyp26 family . Later generation retinoids are resistant to Cyp26 metabolism and remain in

1599-494: The two or more atom requirement, though they often consist of molecules composed of multiple atoms (such as in the diatomic molecule H 2 , or the polyatomic molecule S 8 , etc.). Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number . There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require

1640-455: The types of bonds in compounds differ based on the types of elements present in the compound. London dispersion forces are the weakest force of all intermolecular forces . They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole . Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, and to further freeze to

1681-421: The variability in their compositions is often due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound , or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure; such non-stoichiometric substances form most of the crust and mantle of

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