Abstract
Objectives
Fiber-rich foods such as pinto beans (PB) may exhibit prebiotic effects by preventing early immunosuppression and gut permeability associated with the onset of insulin resistance (IR). Thus, this study evaluated the early protective effects of PB supplementation on the cecal gut microflora, tight-junction protein abundances, gut inflammatory markers and glucose homeostasis in mice fed either a control (C) or a high-fat, high sucrose (HFS).
Methods
Six-wk-old, male C57BL/6 J mice were randomly assigned to four groups (n = 12/group) and fed a control (C, 10% kcal fat, 10% kcal sucrose) or HFS (45% kcal fat, 20% kcal sucrose) diet with or without 10% (wt/wt) freeze-dried PB for 30 d. Measures include fasting blood glucose (FBG), cecal bacteria analyses by 16 S rDNA sequencing, gene expression of gut antimicrobial peptides and markers of inflammation in the distal ileum by qPCR, and expression of tight junction proteins, STAT3 and MHC II in the distal ileum by immunoblotting. Statistical analyses include the Kruskal-Wallis/Dunn's post-hoc test, and a 2-way ANOVA using factors of HFS and PB.
Results
FBG was increased by HFS (main effect, P = 0.0070) while PB decreased FBG by at least 13% (main effect, P = 0.046). In the cecum, the sulfide-producing bacteria family Desulfovibrionaceae (genus Bilophilia) was decreased (≤49%, P ≤ 0.022) in the PB-fed mice compared to their controls. In contrast, the short chain fatty acid-producing family Lachnospiraceae, was elevated by at least 47% (P ≤ 0.0043) in the PB-fed groups compared to their controls. We also observed a 3-fold decrease (P = 0.012) in Ifng gene expression in the HFS group compared to control, together with a decrease in the phosphorylation of STAT3 in the distal ileum (P = 0.045). On the other hand, PB supplementation increased pSTAT3 (main effect, P = 0.022), MHC II (≥66%, main effect, P = 0.0040), with a trend to upregulate occludin (P = 0.055). Moreover, antimicrobial peptide genes, Reg3β and Reg3γ, and Il10 were upregulated by PB (main effect, P < 0.0094). Finally, a negative correlation between the genus Bilophilia and MHC II (Spearman, ρ = −0.5747, P = 0.0033) was observed
Conclusions
PB supplementation modulated the gut microbiome regardless of dietary fat content, and upregulated MHC II in the distal ileum. These effects may be central to its potential to protect against diet-induced IR
Funding Sources
Northarvest Bean Growers Association.