Urinary alpha-tocopherol metabolites in alpha-tocopherol transfer protein-deficient patients.

Patients with alpha-tocopherol transfer protein (alpha-TTP) defects experience neurological symptoms characteristic of vitamin E deficiency and depend on continuous high alpha-tocopherol supplements. We investigated the excretion of 2,5,7, 8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), a urinary metabolite of alpha-tocopherol, as a putative marker for the alpha-tocopherol status of alpha-TTP-deficient patients and control subjects. In three patients vitamin E supplementation was stopped for short periods of time, during which plasma alpha-tocopherol concentrations and urinary alpha-CEHC excretion were measured. In the patients, plasma alpha-tocopherol decreased below normal (<5 micromol/l) but alpha-CEHC excretion remained above the range of unsupplemented control subjects (0.118-0.306 mg/day, n = 6). In healthy subjects, however, alpha-CEHC excretion was increased only after surpassing a plasma alpha-tocopherol threshold of 30-40 micromol/l. Such a threshold did not exist in patients. The general mechanism of alpha-tocopherol degradation did not appear to differ between patients and control subjects. The presumed mechanism of omega- and subsequent beta-oxidation was supported by the detection of alpha- CPHC, an alpha -CEHC homolog with a side chain longer by 3 carbon atoms, both in supplemented patients and in control subjects.