A-Tocopheronic acid

Studies of the metabolism of vitamin E were triggered by the observations of Alaupovic and coworkers [126, 127]. When " [Cj-D-a-tocopherol-5-methyl was administered to rats or pigs and attempts were made to detect metabolic derivatives, two compounds were separated by chromatography. One of the compounds is " [C]-D-a-tocopherol quinone the other is either a dimer or a trimer of a-tocopherol. The dimer and trimer are terminal oxidation products of a-tocopherol and are excreted in the bile. a-Tocopherol quinone can be converted to a-hydroquinone. a-Tocopherol hydroquinone may be esterified in liver and eliminated in the feces after concentration in the bile and excretion in the intestine, or it may be oxidized in the kidney to a-tocopheronic acid, which may be converted into an a-tocopheronolactone conjugate, which is excreted in the urine. In conclusion, vitamin E is excreted as such in the urine or the bile after conversion to a dimer or a trimer, in the form of a conjugated hydroxy-quinone or tocopheronic acid (see Fig. 4-43). 

The latter can be further reduced to a-tocopherolhydroquinone, which is secreted in bile and feces as a glucuronide conjugate (5). Other oxidative urinary metabolites include a-tocopheronic acid and 2,5,7,8-tetramethyI-2-(2 -carboxy-... 

In urine, a-tocopherol is excreted after transformation to a-tocopheronic acid, a-tocopheronolactone, and two other acids. Recently, a new metabolite, i.e., a-CEHC (2,5,7,8-tetramethyl-2-(2 -carboxyethyl)-6-hydroxychroman), has been isolated and identified by GC-MS (8,9). 

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