Diet-induced metabolic improvements in a hamster model of hypercholesterolemia are strongly linked to alterations of the gut microbiota

Abstract

The mammalian gastrointestinal microbiota exerts a strong influence on host lipid and cholesterol metabolism. In this study, we have characterized the interplay among diet, gut microbial ecology, and cholesterol metabolism in a hamster model of hypercholesterolemia. Previous work in this model had shown that grain sorghum lipid extract (GSL) included in the diet significantly improved the high-density lipoprotein (HDL)/non-HDL cholesterol equilibrium (T. P. Carr, C. L. Weller, V. L. Schlegel, S. L. Cuppett, D. M. Guderian, Jr., and K. R. Johnson, J. Nutr. 135:2236-2240, 2005). Molecular analysis of the hamsters' fecal bacterial populations by pyrosequencing of 16S rRNA tags, PCR-denaturing gradient gel electrophoresis, and Bifidobacterium-specific quantitative real-time PCR revealed that the improvements in cholesterol homeostasis induced through feeding the hamsters GSL were strongly associated with alterations of the gut microbiota. Bifidobacteria, which significantly increased in abundance in hamsters fed GSL, showed a strong positive association with HDL plasma cholesterol levels (r = 0.75; P = 0.001). The proportion of members of the family Coriobacteriaceae decreased when the hamsters were fed GSL and showed a high positive association with non-HDL plasma cholesterol levels (r = 0.84; P = 0.0002). These correlations were more significant than those between daily GSL intake and animal metabolic markers, implying that the dietary effects on host cholesterol metabolism are conferred, at least in part, through an effect on the gut microbiota. This study provides evidence that modulation of the gut microbiota-host metabolic interrelationship by dietary intervention has the potential to improve mammalian cholesterol homeostasis, which has relevance for cardiovascular health.

FIG. 1.

Characterization of the gut microbiota composition of hamsters fed different amounts of GSL as determined by pyrosequencing of 16S rRNA tags (V3 region). Composition of the gut microbiota of hamsters fed 0%, 1%, and 5% GSL (n = 7 per group) at the family level (A) and the genus level (B). (C) Rarefaction curves of OTUs from sequences of fecal samples from individual hamsters fed 0% GSL (red), 1% GSL (green), and 5% GSL (blue). (D) Shannon diversity indices of the gut microbiota of individual hamsters fed 0% GSL (red), 1% GSL (green), and 5% GSL (blue). OTUs were identified using 97% cutoffs for rarefaction and Shannon diversity indices.

FIG. 2.

Impact of GSL on the gut microbiota composition of hamsters fed 0% GSL (n = 7), 1% GSL (n = 7), and 5% GSL (n = 8) as determined by DGGE and qRT-PCR. (A) DGGE showing fingerprints of DNA isolated from the fecal samples of hamsters. Lanes 1 to 32 contain DNA from individual hamsters. Lane M contains markers from reference strains. Bands C and F showed significant increases in staining intensity in fecal fingerprints of hamsters fed 5% GSL. The bands A, C, and F marked by an arrow were excised, purified, and sequenced (Table 2). (B) Phylogenetic tree of DGGE band F with sequences that revealed highest similarities in GenBank. The tree was inferred using the unweighted-pair group method using average linkages, and the percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) are shown next to the branches. A neighbor-joining tree resulted in essentially the same phylogeny (data not shown). (C) Cell numbers of total bifidobacteria in hamster fecal samples as determined by qRT-PCR. (D) Quantification of the Bifidobacterium animalis-like phenotype detected by DGGE in hamster fecal samples by qRT-PCR. (E) Correlation of cell numbers of bifidobacteria with daily GSL intake.

FIG. 3.

Specific bacterial populations in the guts of hamsters show high associations with both cholesterol metabolic phenotypes and GSL intake. (A and B) Correlations between cell numbers of total bifidobacteria (A) and the Bifidobacterium animalis-like phenotype (B) with HDL cholesterol. (C) Correlation between proportion of Coriobacteriaceae and non-HDL cholesterol. (D) Correlation between unclassified members of the family Coriobacteriaceae and cholesterol absorption. Data from control animals (0% GSL) were excluded from the analysis.

FIG. 4.

Metabolic network showing the associations between daily GSL intake, gut microbiota composition, and host cholesterol metabolism in hamsters fed 0%, 1%, and 5% GSL. Results of the correlations of cell numbers of bifidobacteria and proportions of Coriobacteriaceae and phenotypic markers were obtained with data from animals fed 1% and 5% GSL. Red connections indicate a positive correlation, while blue connections show correlations that are inverse. Green connections show associations with no statistical significance. Metabolic data were obtained by Carr and coworkers in a previous study (8).