δ-Tocotrienol Improves Insulin Signaling and Decreases Inflammation in Neuroblastoma Cells

Objectives: Neuronal insulin resistance and inflammation are hallmarks of aging-related neuronal pathologies. Inflammation impairs insulin signaling, and insulin resistance in the brain is linked to cognitive decline. Delta-tocotrienol (δ-T3), a member of the vitamin E family, is a potent antioxidant with neuroprotective and anti-inflammatory properties. We aim to determine whether δ-T3 improves insulin signaling in neuronal cells via downregulation of inflammatory pathways. Methods: Murine neuro2a (N2a) neuroblastoma cells were pretreated with vehicle (veh) or δ-T3 (10 μM) for 6-8 hours. This was followed by treatment with control media or conditioned media (CM), collected from LPS-activated RAW 264.7 macrophages, and δ-T3 or veh for 16-18 hours. 20 minutes prior to collection of cell lysates, cells were treated with veh or insulin (100 nM). Total and phosphorylated Akt were measured via western blot. mRNA expression of the inflammatory cytokines, Il6 and Il23, was measured via real-time PCR. mRNA expression of Tlr4, Irs2, and Nfkb (an inflammatory transcription factor) was also measured. Data were analyzed using two-way ANOVA. Results: δ-T3 increased basal Akt phosphorylation and increased insulin signaling in N2a cells treated with CM (p< 0.05). Treatment with CM increased the expression of Il6, Il23, and Nfkb by 803%, 639%, and 453%, respectively. δ-T3 blunted the increases by 38% (p< 0.05), 34% (p< 0.05), and 35% (p< 0.01), respectively. δ-T3 decreased Tlr4 expression by 60% in control media (p< 0.05). Finally, CM increased Irs2 expression (p< 0.01), and δ-T3 blunted this increase by 57% (P< 0.01). Conclusions: Our data suggest that δ-T3 protects against inflammation-induced neuronal insulin resistance, likely through downregulation of the pro-inflammatory Il6, Il23, Tlr4, and Nfkb and activation of the insulin signaling pathway. δ-T3 may also act via suppression of the IRS2 signaling that leads to insulin resistance and glucose intolerance during aging. Funding Sources: Brains and Behaviors Program.