Human lung type II cell derived A549 epithelial
cancer cells and HepG2 hepatocytes constitutively express
cytochrome P4504F2, a P450 we previously identified as a
tocopherol-omega-hydroxylase. To determine if A549 cells would metabolize tocochromanols via the
omega-hydroxylase pathway, we compared the metabolism of
tocopherols (alpha-, gamma-, delta-TOH) and
tocotrienols (alpha-, gamma-, delta-T3) in these 2 cell lines. Cultures were incubated with alpha-, gamma-, or delta-TOH, or the analogous T3s, and synthesis of their metabolites quantitated by GC-MS. A549 cells metabolized all tocochromanols 2-3 times more extensively than HepG2 cells (P < 0.001) except alpha-TOH, a difference not related to cell uptake of substrate but rather was reflective of greater microsomal TOH-
omega-hydroxylase enzyme activity. Notably, 9'-carboxychromanols were the major metabolites of all gamma- and delta-TOHs and T3s in A549 cultures, whereas 3'- and 5'-carboxychromanols predominated in HepG2 cultures. Accumulation of 9'-carboxychromanols in A549 cultures was due to their inefficient conversion to 7'-carboxychromanols relative to HepG2 cells.
Sesamin inhibited tocochromanol metabolism in both cells types, and neither cell type exhibited evidence of alternative (
sesamin-insensitive) pathways of metabolism. TOH-
omega-hydroxylase activity was undetectable in rat primary lung type II cells, suggesting that expression of activity was associated with transformation of normal type II cells to
cancer cells. Long-chain carboxychromanol metabolites of gamma-TOH and other forms of
vitamin E can be biosynthesized in A549 cultures for assessment of their
biological activity, including their potential inhibition of synthesis of inflammatory mediators.