Methotrexate and folic acid are commonly used for studies on intestinal folate transport and absorption because of their availability specifically labeled with tritium, their stability, and their relatively low cost.

In order to maintain an adequate folate status, the intake of folates/folic acid should be appropriate and the absorption processes of folates/folic acid in the small intestine should function properly.

Both vitamin B 12 and folate are present in food as coenzymatically active forms bound to protein, from which they must be freed by processing or digestion prior to absorption. Folate is actively absorbed primarily from the upper third of the small intestine.

Folate (vitamin B 9) refers to the many forms of folic acid and its related compounds, including tetrahydrofolic acid (the active form), methyltetrahydrofolate (the primary form found in blood), methenyltetrahydrofolate, folinic acid, folacin, and pteroylglutamic acid.

Folic acid (pteroylglutamic acid) occurs largely as polyglutamates in food, and must be hydrolyzed to the monoglutamate form for absorption, a reaction mediated by folate conjugase on the brush border of enterocytes in the proximal small intestine [4].

2021年12月14日 · Folic acid is a manmade (synthetic) form of folate. Your body can’t store large amounts of natural folate. But your body can easily absorb folic acid. As a result, it’s added to some of the foods you eat. Grains such as rice, bread, pasta and some cereals are enriched (fortified) with folic acid.

Folate is the natural form of vitamin B9, water-soluble and naturally found in many foods. It is also added to foods and sold as a supplement in the form of folic acid; this form is actually better absorbed than that from food sources—85% vs. 50%, respectively. Folate helps to form DNA and RNA and is involved in protein metabolism.

Folic acid absorption is an active process that occurs primarily in the duodenum and jejunum. Following absorption, folic acid present in human and canine portal blood is not methylated, although methylation may occur later in the liver following reduction.

When consumed, food folates are hydrolyzed to the monoglutamate form in the gut prior to absorption by active transport across the intestinal mucosa [2]. Passive diffusion also occurs when pharmacological doses of folic acid are consumed.

Important unresolved issues are addressed, including the mechanism of intestinal folate absorption in the absence of PCFT and regulation of PCFT gene expression. The impact of a variety of ions, organic molecules, and drugs on PCFT-mediated folate transport is described.