Oxalic acid (oxalate) is a strong dicarboxylic acid that is also a known uremic toxin. It is produced in the body by metabolism of glyoxylic acid or ascorbic acid. Glyoxylate is generated through glycine and hydroxyproline catabolism and can be converted to oxalate. In humans, this process takes place in the liver. Glycine and hydroxyproline comes from protein sources in the diet such as red meat and eggs. Glycine Is converted into glyoxylate in the peroxisome by the enzyme d-amino acid oxidase. Proline is converted to hydroxyproline in the endoplasmic reticulum using the enzyme prolyl 4-hydroxylase. The hydroxyproline metabolism to glyoxylate occurs in the mitochondria. Hydroxyproline dehydrogenase converts hydroxyproline to pyrroline hydroxycarboxylic acid. Delta-1-pyrroline-5-carboxylate dehydrogenase then catalyzes the formation of 4-hydroxy-L-glutamic acid from pyrroline hydroxycarboxylic acid. 4-hydroxy-2-oxoglutaric acid is then produced from 4-hydroxy-L-glutamic acid using the enzyme aspartate aminotransferase. Finally, 4-hydroxy-L-glutamic acid is converted to glyoxylate using 4-hydroxy-2-oxoglutarate aldolase. The glyoxylate formed enters the cytosol. in the cytosol, glyoxylate is converted oxalate using lactate dehydrogenase. Unused ascorbic acid can be also used to synthesize oxalate in the body. Although the specific reactions and enzymes involved are still unknown, there is a general sense of what metabolites are formed during oxalate synthesis from ascorbic acid. Ascorbic acid forms dehydroascorbic acid, which then forms 2,3-diketo-L-gulonate. 2,3-diketo-L-gulonate can be converted to oxalate. The oxalate formed in the liver form these 3 sources can enter the blood and have toxic effects in other tissues. Oxalate can promote cardiovascular disease, neurotoxicity and inflammation.

Metabolism and Physiological Effects of Oxalic acid References