The Colonic Microbiome and Epithelial Transcriptome Are Altered in Rats Fed a High-Protein Diet Compared with a Normal-Protein Diet

Abstract

Background: A high-protein diet (HPD) can produce hazardous compounds and reduce butyrate-producing bacteria in feces, which may be detrimental to gut health. However, information on whether HPD affects intestinal function is limited.Objective: The aim of this study was to determine the impact of an HPD on the microbiota, microbial metabolites, and epithelial transcriptome in the colons of rats.Methods: Adult male Wistar rats were fed either a normal-protein diet (20% protein, 56% carbohydrate) or an HPD (45% protein, 30% carbohydrate) for 6 wk (n = 10 rats per group, individually fed). After 6 wk, the colonic microbiome, microbial metabolites, and epithelial transcriptome were determined.Results: Compared with the normal-protein diet, the HPD adversely altered the colonic microbiota by increasing (P < 0.05) Escherichia/Shigella, Enterococcus, Streptococcus, and sulfate-reducing bacteria by 54.9-fold, 31.3-fold, 5.36-fold, and 2.59-fold, respectively. However, the HPD reduced Ruminococcus (8.04-fold), Akkermansia (not detected in HPD group), and Faecalibacterium prausnitzii (3.5-fold) (P < 0.05), which are generally regarded as beneficial bacteria in the colon. Concomitant increases in cadaverine (4.88-fold), spermine (31.2-fold), and sulfide (4.8-fold) (P < 0.05) and a decrease in butyrate (2.16-fold) (P < 0.05) in the HPD rats indicated an evident shift toward the production of unhealthy microbial metabolites. In the colon epithelium of the HPD rats, transcriptome analysis identified an upregulation of genes (P < 0.05) involved in disease pathogenesis; these genes are involved in chemotaxis, the tumor necrosis factor signal process, and apoptosis. The HPD was also associated with a downregulation of many genes (P < 0.05) involved in immunoprotection, such as genes involved in innate immunity, O-linked glycosylation of mucin, and oxidative phosphorylation, suggesting there may be an increased disease risk in these rats. The abundance of Escherichia/Shigella, Enterococcus, and Streptococcus was positively correlated (Spearman's ρ > 0.7, P < 0.05) with genes and metabolites generally regarded as being involved in disease pathogenesis, suggesting these bacteria may mediate the detrimental effects of HPDs on colonic health.Conclusion: Our findings suggest that the HPD altered the colonic microbial community, shifted the metabolic profile, and affected the host response in the colons of rats toward an increased risk of colonic disease.