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Pyridoxamine (PM) is one form of vitamin B6. Chemically it is based on a
pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...
ring structure, with hydroxyl, methyl, aminomethyl, and hydroxymethyl
substituent In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...
s. It differs from pyridoxine by the substituent at the 4-position. The hydroxyl at position 3 and aminomethyl group at position 4 of its ring endow pyridoxamine with a variety of chemical properties, including the scavenging of
free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabolic disorders Metabolism ...
species and carbonyl species formed in sugar and lipid degradation and chelation of metal ions that catalyze Amadori reactions.


Research

Pyridoxamine can form fairly weak complexes with a number of transition metal ions, with a preference for Cu2+ and Fe3+. The 3'-hydroxyl group of pyridoxamine allows for efficient
hydroxyl radical The hydroxyl radical, •HO, is the neutral form of the hydroxide ion (HO–). Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are pr ...
scavenging. Pyridoxamine inhibits the Maillard reaction and can block the formation of advanced glycation endproducts, which are associated with medical complications of
diabetes Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...
. Pyridoxamine is hypothesized to trap intermediates in the formation of Amadori products released from glycated
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s, possibly preventing the breakdown of glycated proteins by disrupting the
catalysis Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
of this process through disruptive interactions with the metal ions crucial to the
redox reaction Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
. One research study found that pyridoxamine specifically reacts with the
carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...
group in Amadori products, but inhibition of post-Amadori reactions (that can lead to advanced glycation endproducts) is due in much greater part to the metal chelation effects of pyridoxamine. A variety of preclinical studies in animal models of diabetes indicated that pyridoxamine improved
kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...
comparable or superior to aminoguanidine. Because of these results, pyridoxamine has been investigated for clinical utility in the treatment of diabetic nephropathy. Pyridoxamine also inhibits the formation of advanced lipoxidation endproducts during lipid peroxidation reactions by reaction with di
carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...
intermediates. In other preclinical research, pyridoxamine may be efficacious in treating
diabetic neuropathy Diabetic neuropathy includes various types of nerve damage associated with diabetes mellitus. The most common form, diabetic peripheral neuropathy, affects 30% of all diabetic patients. Studies suggests that cutaneous nerve branches, such as the s ...
and retinopathy associated with diabetes and
kidney stone Kidney stone disease (known as nephrolithiasis, renal calculus disease, or urolithiasis) is a crystallopathy and occurs when there are too many minerals in the urine and not enough liquid or hydration. This imbalance causes tiny pieces of cr ...
disease. In one study, pyridoxamine was more effective at protecting from
ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
-induced
gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...
epithelial Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...
than amifostine (the only radioprotector currently
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...
(FDA)-approved) due to pyridoxamine reactive oxygen species and reactive carbonyl species scavenging profile.


FDA Regulatory Activity

Pyridoxamine was marketed as a
dietary supplement A dietary supplement is a manufactured product intended to supplement a person's diet by taking a pill (pharmacy), pill, capsule (pharmacy), capsule, tablet (pharmacy), tablet, powder, or liquid. A supplement can provide nutrients eithe ...
, often as the hydrochloride
salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
, pyridoxamine dihydrochloride. However, in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, the FDA ruled in January 2009 that pyridoxamine must be regulated as a pharmaceutical drug because it is the active ingredient in Pyridorin, a drug designed by Biostratum, Inc., to prevent the progression of diabetic nephropathy."Big problem for BioStratum"
, '' Triangle Business Journal'', October 14, 2005
"FDA's pyridoxamine decision: FDA's decision regarding pyridoxamine has larger implications for dietary ingredients in general"
''
Entrepreneur Entrepreneurship is the creation or extraction of economic value in ways that generally entail beyond the minimal amount of risk (assumed by a traditional business), and potentially involving values besides simply economic ones. An entreprene ...
'', April, 2009
Pyridorin had success in early clinical trials, found to be effective in slowing the progression of diabetic neuropathy in a phase II trial on 224 patients. However, in 2005 Biostratum ran out of money and so was unable to begin a Phase III trial. Investors in Biostratum had realized that because Biostratum had no patent on pyridoxamine itself, and that pyridoxamine was commonly available for purchase as a dietary supplement, the company would be unable to charge enough money for the treatment (should it be approved as a prescription drug by the FDA) for the investors to get a reasonable return on the investment they had already made (about $100M) much less on the additional investment a Phase III trial would require. To solve this problem, Biostratum submitted a
citizen petition An FDA citizen petition is a process provided by the United States Food and Drug Administration (FDA) for individuals and community organizations to make requests to the FDA for changes to health policy. It is described in Title 21 of the Code of ...
to the FDA on July 29, 2005, seeking to disallow sales of pyridoxamine-containing supplements on the grounds that pyridoxamine, as the subject of an Investigational New Drug Application with the FDA, is a drug and not a dietary supplement. This petition was opposed by the Council for Responsible Nutrition, a
trade association A trade association, also known as an industry trade group, business association, sector association or industry body, is an organization founded and funded by businesses that operate in a specific Industry (economics), industry. Through collabor ...
of the dietary supplement industry. On January 12, 2009, the FDA ruled that products containing pyridoxamine are excluded from the definition of dietary supplements as defined by the Dietary Supplement Health and Education Act of 1994. The FDA stated that the status of Pyridorin as an investigational new drug, as a result of an application filed by BioStratum in July 1999 and effective on September 1, 1999, meant that "the marketing of pyridoxamine in a dietary supplement is essentially equivalent to the marketing of an investigational new drug as a dietary supplement" because there was an "absence of independent, verifiable evidence that the substance was marketed as a food or a dietary supplement prior to its authorization for investigation as a new drug." In 2006, Biostratum licensed its rights in Pyridorin to another company, NephroGenex In 2008, NephroGenex restarted the clinical development of Pyridorin, which as of 2012 is still ongoing. NephroGenex conducted and completed a Phase 2b study and initiated a Phase 3 study of Pyridorin as treatment for diabetic neuropathy in patients with Type 2 diabetes. In February 24, 2016 NephroGenex was forced to pause the Phase 3 trial and ultimately terminate it later that year due to a lack of funding. The company subsequently filed for Chapter 11 bankruptcy on April 30, 2016. NephroGenex shortly thereafter sought out a corporate partner for licensing or acquisition of Pyridorin. The company retained the services of an investment banking firm which reached out to many prospective buyers, which by September 2016 had failed to consummate a transaction. NephroGenex then decided to sell all its assets, including Pyridorin, through a bankruptcy auction that was to be held on November 14, but was forced to cancel the auction after it did not receive any qualifying bids. On December 16, 2016, the company filed a motion with the bankruptcy court, proposing a liquidation plan. On August 24, 2017, the company's Investigational New Drug (IND) Applications with the FDA were withdrawn. Medpace, the Clinical Research Organization that conducted the Pyridorin Phase 3 trial, proposed and received approval for a Planned Support Agreement which transferred ownership of NephroGenex to Medpace. The new NephroGenex, renamed Medpace Research Inc., partnered with OxiPath Health Inc. to form a new venture, ViGuard Health Inc., with the intention of marketing the oral formulation of pyridoxamine as a dietary supplement, to which end it submitted, on October 3, 2017 a citizen petition to the FDA requesting the Commissioner issue a regulation stating pyridoxamine is a dietary supplement as defined by the Dietary Supplement Health and Education Act of 1994 DSHEA).


See also

* Pyridoxamine-oxaloacetate transaminase * Pyridoxamine-pyruvate transaminase * Pyridoxamine-phosphate transaminase * List of investigational antipsychotics


References


External links

* Clinical trials testing Pyridoxamine (
clinicaltrials.gov ClinicalTrials.gov is a clinical trials registry, registry of clinical trials. It is run by the United States National Library of Medicine (NLM) at the National Institutes of Health, and holds registrations from over 444,000 trials from 221 cou ...
): *
Effect of Pyridorin in Patients With Diabetic Nephropathy
(NCT00320060) *
Effect of Pyridorin in Patients With Diabetic Nephropathy
(NCT00320021) *
Safety and Efficacy Study of Pyridorin in Patients With Nephropathy Due to Type 2 Diabetes
(NCT00734253) {{Vitamins Hydroxypyridines B vitamins Dietary supplements Aminomethyl compounds