Impact of Dietary Arachidonic Acid on Gut Microbiota Composition and Gut-Brain Axis in Male BALB/C Mice

Abstract

Although arachidonic acid (ARA) is the precursor of the majority of eicosanoids, its influence as a food component on health is not well known. Therefore, we investigated its impact on the gut microbiota and gut-brain axis. Groups of male BALB/c mice were fed either a standard diet containing 5% lipids (Std-ARA) or 15%-lipid diets without ARA (HL-ARA) or with 1% ARA (HL + ARA) for 9 weeks. Fatty acid profiles of all three diets were the same. The HL-ARA diet favored the growth of Bifidobacterium pseudolongum contrary to the HL + ARA diet that favored the pro-inflammatory Escherichia-Shigella genus in fecal microbiota. Dietary ARA intake induced 4- and 15-fold colic overexpression of the pro-inflammatory markers IL-1β and CD40, respectively, without affecting those of TNFα and adiponectin. In the brain, dietary ARA intake led to moderate overexpression of GFAP in the hippocampus and cortex. Both the hyperlipidic diets reduced IL-6 and IL-12 in the brain. For the first time, it was shown that dietary ARA altered the gut microbiota, led to low-grade colic inflammation, and induced astrogliosis in the brain. Further work is necessary to determine the involved mechanisms.

Keywords: arachidonic acid; gut microbiota; gut–brain axis; hyperlipidic diet; inflammation.

Figure 1

Kinetics of animal body weight (A) and food consumption (B) in male BALB/C mice fed on standard diet (Std-ARA) or lipid-rich diets without arachidonic acid (HL-ARA) or with (HL + ARA) for 9 weeks. Mesenteric adipose tissue weight (C) at the end of the study. Data are represented as the mean ± standard error of the mean (SEM). n = 15 per diet group for body weight and food consumption and n = 5 for mesenteric adipose tissue weight. * p < 0.05 compared with the standard diet, data analyzed by one-way ANOVA test and Bonferroni’s multiple comparisons test for post hoc analysis.

Figure 2

Fecal phylum and genus compositions of mice fed on the Std-ARA, HL-ARA, and HL + ARA diets for 9 weeks. The fecal microbiota compositions were determined on 10 mice in each group by using the V3–V4 hyper-variable region of the 16S rRNA gene. The relative abundance of the various phyla is shown in bar plot (A). Bar plots show the relative abundance of the various genera in the Actinobacteria (B), the Proteobacteria (D), the Desulfobacteria (E), and the Firmicutes (F) phyla. The species composition of the Bifidobacterium genus is shown in bar plot (C).

Figure 3

Colon gene expression of IL-1β (A) and CD40 (B) at 9 weeks of diet. Data are represented as the mean ± standard error of the mean (SEM). n = 4–5 mouse per diet group. * p < 0.05 compared with the standard diet. Data analyzed by either one-way ANOVA test and Bonferroni’s multiple comparisons test for post hoc analysis or Kruskal–Wallis test and Dunn’s multiple comparisons test for post hoc analysis.

Figure 4

Gene expression of TNF-α in the liver (A) and mesenteric adipose tissue (B) at 9 weeks of diet. Data are represented as the mean ± standard error of the mean (SEM). n = 4–5 mouse per diet group. ** p < 0.01 compared with the standard diet. Data analyzed by one-way ANOVA test and Bonferroni’s multiple comparisons test for post hoc analysis.

Figure 5

Half-brain gene expression of IL-6 (A), IL-1β (B), CD40 (C), and IL-12 (D) at 9 weeks of diet. Data are represented as the mean ± standard error of the mean (SEM). n = 2 mouse per diet group. * p < 0.05, ** p < 0.01, and *** p < 0.001. Data analyzed by one-way ANOVA test and Bonferroni’s multiple comparisons test for post hoc analysis or Kruskal–Wallis-test and Dunn’s multiple comparisons test for post hoc analysis.

Figure 6

Western blot analysis of Iba1, GFAP, and α-tubulin in the cortex (A,B) and hippocampus (C,D). The protein levels were quantified by densitometry, normalized to the α-tubulin level, and expressed as a relative protein level. Data are represented as the mean ± standard error of the mean (SEM). n = 3 mouse per diet group. * p < 0.05 compared with the standard diet. Data analyzed by one-way ANOVA test and Bonferroni’s multiple comparisons test for post hoc analysis.

Figure 7

GFAP immunostaining (in green) in the hippocampus of mice fed the standard diet (Std-ARA) or hyperlipidic diets without arachidonic acid (HL-ARA) or with (HL + ARA) for 9 weeks. Nuclei were stained with DAPI (4’,6-diamidino-2-phenylindole, blue staining).