Natural Forms of Vitamin E and 13′-Carboxychromanol, a Long-Chain Vitamin E Metabolite, Inhibit Leukotriene Generation from Stimulated Neutrophils by Blocking Calcium Influx and Suppressing 5-Lipoxygenase Activity, Respectively

Leukotrienes generated by 5-lipoxygenase (5-LOX)-catalyzed reaction are key regulators of inflammation. In ionophore-stimulated (A23187; 1-2.5 mu M) human blood neutrophils or differentiated HL-60 cells, vitamin E forms differentially inhibited leukotriene B-4 (LTB4) with an IC50 of 5-20 mu M for gamma-tocopherol, delta-tocopherol (delta T), and gamma-tocotrienol, but a much higher IC50 for alpha-tocopherol. 13'-Carboxychromanol, a long-chain metabolite of delta T, suppressed neutrophil-and HL-60 cell-generated LTB4 with an IC50 of 4-7 mu M and potently inhibited human recombinant 5-LOX activity with an IC50 of 0.5-1 mu M. In contrast, vitamin E forms had no effect on human 5-LOX activity but impaired ionophore-induced intracellular calcium increase and calcium influx as well as the subsequent signaling including ERK1/2 phosphorylation and 5-LOX translocation from cytosol to the nucleus, a key event for 5-LOX activation. Further investigation showed that delta T suppressed cytosolic Ca2+ increase and/or LTB4 formation triggered by ionophores, sphingosine 1-phosphate, and lysophosphatidic acid but not by fMLP or thapsigargin, whereas 13'-carboxychromanol decreased cellular production of LTB4 regardless of different stimuli, consistent with its strong inhibition of the 5-LOX activity. These observations suggest that delta T does not likely affect fMLP receptor-mediated signaling or store depletion-induced calcium entry. Instead, we found that delta T prevented ionophore-caused cytoplasmic membrane disruption, which may account for its blocking of calcium influx. These activities by vitamin E forms and long-chain carboxychromanol provide potential molecular bases for the differential anti-inflammatory effects of vitamin E forms in vivo. The Journal of Immunology, 2011, 186: 1173-1179.