alpha-Tocopherol enhances degranulation in RBL-2H3 mast cells.

Based on the observation that 3 months alpha-tocopherol supplementation caused an up-regulation of the mRNA of vesicular transport proteins in livers of mice, the functional relevance was investigated in RBL-2H3 cells, a model for mast cell degranulation. In total, 24 h incubation with 100 muM alpha-tocopherol enhanced the basal and phorbol-12-myristyl-13-acetate/ionomycin-stimulated release of beta-hexosaminidase and cathepsin D as measured by enzymatic analysis as well as Western blotting and immunocytochemistry, respectively. beta-Tocopherol exerted the same effect, whereas alpha-tocopheryl phosphate and trolox were inactive, indicating that both the side chain and the 6-OH group at the chroman ring are essential for activation of degranulation. alpha-Tocopherol did not induce mRNA expression of soluble NSF-attachment protein receptor (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins, such as N-ethylmaleimide sensitive fusion protein, complexin-2, SNAP23 or syntaxin-3, in the RBL-2H3 cell model. In view of the well known alpha-tocopherol-mediated activation of protein phosphatases, which regulate soluble NSF-attachment protein receptor activities by dephosphorylation, underlying mechanisms are discussed in terms of preventing oxidative inactivation of protein phosphatases and so far unknown functions in certain membrane domains.