Effect of Ornithine α-Ketoglutarate on Intestinal Microbiota and Serum Inflammatory Cytokines in Dextran Sulfate Sodium Induced Colitis

Abstract

Ornithine α-ketoglutarate (OKG), a nutritional compound, is an amino acid salt with anti-oxidative and anti-inflammatory effects on humans and animals. Ulcerative colitis (UC), as an inflammatory bowel disease (IBD), leads to chronic intestinal inflammatory dysfunction. This study evaluated the optimal dosage of OKG in healthy mice. Then, a mouse model of acute colitis was established using dextran sodium sulfate (DSS), and the preventive effect of OKG on DSS-induced colitis in mice was explored through analysis of serum inflammatory cytokines and fecal microbiota. Initially, the mice were randomly divided into a control group, a group given a low dose of OKG (LOKG: 0.5%), a group given a medium dose of OKG (MOKG: 1%), and a group given a high dose of OKG (HOKG: 1.5%); they remained in these groups for the entire 14-day experimental period. Our results demonstrated that 1% OKG supplementation increased body weight, serum growth hormone (GH), insulin (INS), alkaline phosphatase (ALP), Tyr, and His and decreased urea nitrogen (BUN), NH₃L, and Ile. Then, a 2 × 2 factor design was used for a total of 40 mice, with diet (a standard diet or a 1% OKG diet) and challenge (4% DSS or not) as the main factors. During days 14 to 21, the DSS mice were administered 4% DSS to induce colitis. The results revealed that OKG alleviated weight loss and reversed the increases in colonic histological damage induced by DSS. OKG also increased serum IL-10 secretion. Moreover, OKG enhanced the abundance of Firmicutes and decreased that of Bacteriodetes at the phylum level and particularly enhanced the abundance of Alistipes and reduced that of Parabacterioides at the genus level. Our results indicated that OKG promotes growth performance and hormone secretion and regulates serum biochemical indicators and amino acid concentrations. Furthermore, 1% OKG supplementation prevents DSS-induced colitis in mice via altering microbial compositions and reducing the secretion of inflammatory cytokines in serum.

Keywords: colitis; dextran sulfate sodium; inflammatory cytokines; intestinal microbiota; ornithine α-ketoglutarate.

Figure 1

Effects of OKG on growth performance of healthy mice. (A) body weight (IBW: initial body weight; FBW: final body weight), (B) average daily weight gain, and (C,D) serum concentrations of growth hormone and insulin. Values within a row with different superscripts (the symbols “a, b”) differ significantly (p < 0.05).

Figure 2

Effects of OKG on body weight, DAI, and colon length of mice with DSS-induced colitis. (A) The experimental design; (B) body weight. (C–E) disease activity index (DAI) and colon length. * p < 0.05 and ** p < 0.01 indicate a statistically significant difference for the challenge (water or DSS). ^# p < 0.05 and ^## p < 0.01 indicate a statistically significant difference for the dietary treatment (basal or OKG).

Figure 3

Effects of OKG on the histological scores (right) and histological sections (left) of mice with DSS-induced colitis. ** p < 0.01 indicate a statistically significant difference for challenge (water or DSS). ^## p < 0.01 indicate a statistically significant difference for dietary treatment (basal or OKG).

Figure 4

Effects of OKG on the serum TNF-α (A), IFN-γ (B), IL-1β (C), and IL-10 (D) levels of mice with DSS-induced colitis. ** p < 0.01 indicate a statistically significant difference for challenge (water or DSS). ^## p < 0.01 indicate a statistically significant difference for dietary treatment (basal or OKG).

Figure 5

Effects of OKG on the observed index (A), Shannon index (B), Simpson index (C), Chao index (D), ACE index (E), and PD index (F) of mice with DSS-induced colitis. ** p < 0.01 indicate a statistically significant difference for challenge (water or DSS).

Figure 6

Effects of OKG on the relative abundance of microbiota at the phylum level (A) and Taxonomic differences between various groups at the phylum level (B) of mice with DSS-induced colitis. * p < 0.05 and ** p < 0.01 indicate a statistically significant difference for challenge (water or DSS). ^# p < 0.05 and ^## p < 0.01 indicate a statistically significant difference for dietary treatment (basal or OKG).

Figure 7

Effects of OKG on the relative abundance of microbiota at the genus level (A) and Taxonomy differences between various groups at the genus level (B) of mice with DSS-induced colitis. * p < 0.05 and ** p < 0.01 indicate a statistically significant difference for challenge (water or DSS). ^# p < 0.05 and ^## p < 0.01 indicate a statistically significant difference for dietary treatment (basal or OKG).

Figure 8

Predictive functional profiling of microbial communities via PICRUSt. KEGG pathway annotations at level 1 (A) and level 2 (B). * p < 0.05 and ** p < 0.01 indicate a statistically significant difference for challenge (water or DSS).