Metabolic benefits of annatto-extracted tocotrienol on glucose homeostasis, inflammation, and gut microbiome

Emerging evidence suggests that the gut microbiome plays an important role in the pathophysiology of both obesity and type 2 diabetes mellitus. We previously reported that dietary annatto-extracted tocotrienol exerts beneficial effects by modulating inflammatory responses in mice fed a high-fat diet (HFD). The purpose of this study was to test the hypothesis that tocotrienol supplementation when combined with an HFD would result in an altered gut microbiota composition. For 14 weeks, forty-eight male C57BL/6J mice were assigned to 4 groups-low-fat diet, HFD, HFD supplemented with annatto-extracted tocotrienol at 800 mg/kg diet (AT), and HFD supplemented with metformin at 200 mg/kg diet. Glucose homeostasis was assessed by glucose and insulin tolerance tests, serum and pancreas insulin levels, and histological assessments of insulin and glucagon in pancreatic tissue. The concentrations of adipokines were measured in white adipose tissues. For the gut microbiome analysis, cecal content was collected, DNA was extracted, and 16S rRNA gene sequencing was performed. AT supplementation improved glucose homeostasis and lowered resistin, leptin, and interleukin-6 levels in white adipose tissue. Relative to the HFD group, AT-supplemented mice showed a decrease in the Firmicutes to Bacteroidetes ratio and had a lower abundance of Ruminococcus lactaris, Dorea longicatena, and Lachnospiraceae family. The relative abundance of Akkermansia muciniphila was increased in the AT group compared to the low-fat diet group. The association between the metabolic improvements and the identified bacterial taxa suggests a potential metabolic modulation caused by AT supplementation through the gut microbiota composition in mice fed an HFD.