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

Abstract

Leukotrienes generated by 5‐lipoxygenase (5‐LOX)‐catalyzed reaction are key regulators of inflammation. In ionophore A23187‐stimulated human neutrophils or differentiated HL60 cells, vitamin E forms differentially inhibited leukotriene B4 (LTB4) with IC50 of 5–20μM for γ‐tocopherol, δ‐tocopherol (δT) and γ‐tocotrienol, but much higher for α‐tocopherol. 13′‐carboxychromanol, a long‐chain metabolite of δT, suppressed neutrophil‐ and HL60 cell‐generated LTB4 with IC50 of 4–7μM and potently inhibited human recombinant 5‐LOX activity with IC50 of 1.5±1μM, but other metabolites, such as 9′‐carboxychromanol and 7,8‐dimethyl‐2‐(β‐carboxyethyl)‐6‐hydroxychroman (CEHC) did not show promising effects. 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. Further investigation showed that δT suppressed cytosolic Ca2+ increase and/or LTB4 formation triggered by ionophores, sphingosine 1‐phosphate and lysophosphatidic acid, but not by fMLP or thapsigargin, indicating that δT does not likely affect fMLP receptor‐mediated signaling or storage‐depletion induced calcium entry. Instead, δT 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.