Calcitroic acid (1α-hydroxy-23-carboxy-24,25,26,27-tetranorvitamin D₃) is a major metabolite of 1α,25-dihydroxyvitamin D₃ (calcitriol). Often synthesized in the liver and kidneys, calcitroic acid is generated in the body after

vitamin D Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...

is first converted into calcitriol, an intermediate in the fortification of bone through the formation and regulation of calcium in the body. During this deactivation process, oxidation reactions at C24 and C23 occur which ultimately lead to side-chain cleavage which helps in the formation of calcitroic acid. These pathways managed by calcitriol are thought to be inactivated through its hydroxylation by the

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

CYP24A1 Cytochrome P450 family 24 subfamily A member 1 (abbreviated CYP24A1) is a member of the cytochrome P450 superfamily of enzymes encoded by the ''CYP24A1'' gene. It is a mitochondrial monooxygenase which catalyzes reactions including 24-hydroxylatio ...

, also called calcitriol 24-hydroxylase. Specifically, it is thought to be the major route to inactivate vitamin D metabolites. Hydroxylation and further metabolism of calcitriol in the liver and the kidneys yields calcitroic acid, a water soluble compound that is excreted in bile. A recent review suggested that current knowledge of calcitroic acid is limited, and more studies are needed to identify its physiological role. Calcitroic acid is fairly newly introduced in studies considering it was isolated and characterized approximately 40 years ago. This explains why current knowledge is limited on the vitamin d metabolite. In case where a higher concentration of this acid is used in vitro, studies determined that calcitroic acid binds to vitamin D receptor (VDR) and induces gene transcription. In vivo, studies determined that calcitroic acid, along with

citrulline The organic compound citrulline is an α-amino acid. Its name is derived from ''citrullus'', the Latin word for watermelon. Although named and described by gastroenterologists since the late 19th century, it was first isolated from watermelon in 1 ...

, may be used to quantify the amount of ionizing radiation an individual has been exposed to.

Uses and Functions

Calcitriol is given to those who cannot produce enough active vitamin D such as those with renal diseases. Dosage intake is dependent upon the specific medical condition and the body's response to therapy.

References

Secosteroids Vitamin D Indenes Human metabolites {{biochem-stub