Mechanisms Mediating Anti-Inflammatory Effects of Delta-Tocotrienol

Inflammation is a major underlying cause for obesity-associated metabolic diseases. Hence, anti-inflammatory dietary components are used to improve obesity-related disorders. First hypothesized that T3, a member of the vitamin E family, reduced adiposity, insulin resistance and hepatic triglyceride accumulation through its anti-inflammatory properties. Secondly, that T3 reduces inflammation via inhibition of NF-κB and/or JNK pathway in adipocytes. To test the first hypothesis, C57BL/6J male mice were fed a HF diet with or without supplementation of T3 (HF+T3) at 400 mg/kg and 1600mg/kg for 14 weeks and were compared to mice fed a low-fat diet (LF) or HF supplemented with metformin as an anti-diabetic control. Glucose tolerance tests were administered two weeks prior to the end of treatments. Histology, qPCR and protein analyses were performed to assess inflammation and fatty acid metabolism in adipose and liver tissues. Significant improvements in glucose clearance and reduced liver triglycerides were observed in T3-supplemented groups compared to the HF group. Body weight and fat pad weight were not significantly reduced in HF+T3 groups, however, we observed smaller fat cell size and reduced macrophage infiltration in their adipose tissues compared to other groups. These changes were at least in part mechanistically explained by a reduction of mRNA and protein expression of pro-inflammatory adipokines and increased expression of anti-inflammatory adipokines in HF+T3 mice. Moreover, T3 dose-dependently increased fatty acid oxidation and reduced fatty acid synthesis in adipose tissue and liver. To test our second hypothesis, 3T3-L1 cells were pretreated with varying doses of T3 (0.0001 – 100 µM) for 4 hours then with LPS for 1 hour or 18 hours to induce inflammation. Cell viability was tested using MTT assay. Q-PCR and Western blots were performed to assess specific genes and proteins, respectively, related to inflammation and the NF-B and JNK pathways. There were no significant effects on cell viability for doses lower than 25 µM. We used 1 µM and 5 µM doses and found that these doses reduced expression of a pro-inflammatory cytokine IL-6. Additionally, gene expression of downstream transcripts of NF-B, including MIP2, a chemokine that attracts additional macrophages, and COX2, an enzyme that is responsible for formation of mediators of inflammatory reactions, were downregulated by T3. In addition, the 1 µM T3 reduced phosphorylation of the p65 subunit in NF-κB. None of these doses affected IB protein levels. In addition, we did not see any reduction in the JNK pathway at the protein level, which is consistent with other studies. In conclusion, our study suggests that T3 may promote metabolically healthy obesity by reducing fat cell hypertrophy and decreasing inflammation via inhibition of NF-B in both liver and adipose tissue.