Preferential Uptake of Gamma Tocopherol by Mast Cells. Does This Uptake Affect Mast Cell Cytokine Production?.

Abstract

Vitamin E, the main lipid soluble antioxidant, exists in eight different forms, of which α-tocopherol and γ-tocopherol are the two major forms. Previous experiments showed vitamin E uptake by macrophages that contribute to inflammation and immunity. On the other hand, vitamin E has structural similarity to the thiazolidinedione, troglitazone, a peroxisome proliferator-activated receptor (PPAR) agonist. In previous experiments we found that troglitazone (TGZ), a PPAR gamma agonist, had a negative effect on mast cell cytokine production. We therefore wondered whether vitamin E enters human mast cells, and if so, does this modulate mast cell cytokine production? We choose (interleukin) IL-6 for its pro-inflammatory properties and because it's known to be produced by mast cells in response to stimulants used in the experiment. In this study we try to answer these two questions. Cultured human mast cell line (HMC-1) was first incubated for 24 hrs with pharmacological concentrations of both alpha and gamma forms of vitamin E (10 μM). The mast cells were then activated with phorbol-12-myristate-13-acetate [PMA (50ng/ml)] and ionomycin (5μm) for 24 hours and cell-free supernatants collected. In additional experiments, IL-1ß (10ng/mL) was added to activate mast cells. IL-6 levels in the supernatants were determined in each well utilizing ELISA. Mast cell concentrations of alpha or gamma tocopherol were measured by high pressure liquid chromatography [HPLC] and electrochemical analysis. Mast cells pre-incubated in alpha and gamma forms of vitamin E at 10 μM did not affect mast cell IL-6 production. Mast cells, however, showed uptake of both forms of tocopherols but more pronounced uptake of the gamma form (13181.05 pmole/well of gamma compared to 8742.99 pmole/well of alpha tocopherol). We conclude that mast cells appear to store both alpha and gamma tocopherols but preferentially more gamma tocopherol. Though Vitamin E and PPAR agonists have similar structures, they did not show similar effect on mast cell cytokine production, suggesting they might have different mechanisms of action.