Dose and Time Dependent Effect of Dietary Blueberries on Diabetic Vasculature is Associated with Gut Microbes

Abstract

Background Evidence from our lab and others showed the vascular beneficial effects of dietary blueberries. However, dose‐ and time‐dependent effect of dietary blueberries on vascular complications in diabetes and the role of gut microbes in mediating this effect are unknown. We hypothesize that gut microbes are associated with the dose‐ and time‐dependent vascular beneficial effects of dietary blueberries. Methods 7‐week‐old db/db male mice (Jackson Lab), a widely‐used type 2 diabetic animal model, were fed a diet with or without freeze‐dried wild blueberry powder (FD‐BB) for 4 or 8 or 12 weeks (D4, D8, and D12). Diets contained 0%, 1.23% (B1), 2.46% (B2) and 3.7% (B3) of FD‐BB, which is equivalent to 0, ½, 1, and 2 human servings of wild blueberries. Age‐matched, non‐diabetic db/+ mice fed a standard diet for 4 or 8 or 12 weeks (C4, C8, and C12) were used as controls. After the treatment period blood glucose, body composition, glucose tolerance, and insulin tolerance were assessed. Vascular inflammation was determined by the binding of fluorescent labelled mouse monocytic WEHI78/24 cells to vascular endothelium and mRNA expression of vascular inflammatory chemokines and adhesion molecules (IL8/KC, MCP1/JE, ICAM1, VCAM1 and E‐selectin). Microbial profiling of cecum was done by 16s rRNA amplification. Results Diabetic mice (D4, D8 and D12) had increased blood glucose, impaired glucose and insulin tolerance, increased body fat, decreased lean body mass, enhanced binding of monocytes to the aortic vessel, and increased expression of selected inflammatory molecules as compared to their respective control mice (C4, C8 and C12). Blueberry treatment at all levels didn’t improve the metabolic parameters in diabetic mice. However, 3.7% FD‐BB treatment reduced the binding of WEHI78/24 monocyte to vascular endothelium and suppressed the mRNA expression of selected inflammatory molecules in diabetic mice (D4B3 vs D4, D8B3 vs D8, and D12B3 vs D12). Microbial profiling showed an alteration in the relative abundance of gut microbes at different taxonomic levels in diabetic mice as compared to their respective control mice. At the genera level, 7, 9 and 10 genera were altered after 4‐, 8‐ and 12‐weeks treatment in diabetic vs control mice. Blueberry supplementation at different dosages improved the relative abundance of selected gut microbes in diabetic mice (>4 genera) at different time points. Specifically, blueberry treatment increased the abundance of commensal microbe Bifidobacterium and decreased the abundance of opportunistic Clostridium genera in diabetic mice. Conclusion The beneficial effects of dietary blueberries on diabetic vasculature and gut microbiome varies with the doses and duration of treatment. In the present study, a dose of 3.7% FD‐BB in diet (equivalent to 1.5 human servings) was shown to exert potential beneficial effects on diabetic vasculature and is associated with specific gut microbes.