D-GALACTOSAMINE

Description

Galactosamine is a model hepatotoxicant, induces hepatitis characterized by neutrophilic infiltration, and kills the animal by fulminant hepatic failure. Galactosamine, an amino derivative of sugar galactose, has been used as a model hepatotoxicant since the first reports of hepatotoxicity in late 1970s by Keppler and associates. Galactosamine-induced hepatitis has been a model of choice to study various aspects of liver disease, including mechanisms of toxicant-induced apoptosis and necrosis, liver tissue repair, neutrophil infiltration and transmigration, and the role of endotoxin or lipopolysaccharide (LPS) in initiating liver injury.
Humans and animals synthesize galactosamine in the body. Galactosamine (a type of hexosamine) is formed when an amino group replaces one of the hydroxy groups of a sixcarbon sugar, or hexose. The human body utilizes uridine diphosphate (UDP)-N-acetyl-D-glucosamine or glucosamine as a precursor to synthesize this compound, and is most often found in the form N-acetyl-D-galactosamine (often referred to as N-acetylgalactosamine). Most importantly, galactosamine is a constituent of hyaluronic acid, a powerful water-binding agent. Many different types of tissues in human body contain hyaluronic acid, which acts as a lubricating agent in the synovial fluid of joints and in connective tissues. Hyaluronic acid also acts as a lubricating agent in the vitreous humor of the eyeball. Hyaluronic acid has considerable medicinal value; it is often used in wound healing, burn dressings, osteoarthritis treatment, cataract or corneal transplantation surgery, and various types of plastic surgeries.

Definition

ChEBI: The pyranose form of D-galactosamine.

Toxicity evaluation

Galactosamine induces liver injury by interfering with the uridine pool in the cell, which is essential for RNA and protein synthesis. Galactosamine ismetabolized via the Leloir pathway of galactose metabolism, which leads to the generation of uridine derivatives of galactosamine. The two enzymes of the Leloir pathway, galactokinase and UDP-galactose uridyltransferase, convert galactosamine into galactosamine-1-phosphate and UDP-galactosamine, respectively,due to their lowsubstrate specificity.UDPgalactosamine blocks the final enzyme in Leloir pathway, the UDP-galactose-40 epimerase, resulting in the accumulation of UDP-galactosamine in the cells. This results in the depletion of uridine triphosphate (UTP), UDP, uridine monophosphate (UMP), and the sugar derivative of uridine such as UDP-glucose and UDP-galactose essential for RNA and protein synthesis. Orotate, a precursor of the hexosamine biosynthesis pathway, has been used as an antidote to galactosamine toxicity.