Odd chain fatty acid metabolism in mice after a high fat diet

Abstract

Epidemiological studies show that higher circulating levels of odd chain saturated fatty acids (FA: C15:0 and C17:0) are associated with lower risk of metabolic disease. These odd chain saturated fatty acids (OCSFA) are produced by α-oxidation in peroxisomes, de novo lipogenesis, from the diet and by gut microbiota. Although present at low concentrations, they are of interest as potential targets to reduce metabolic disease risk. To determine whether OCSFA are affected by obesogenic diets, we have investigated whether high dietary fat intake affects the frequency of OCSFA-producing gut microbiota, liver lipid metabolism genes and circulating OCSFA. FA concentrations were determined in liver and serum from pathogen-free SPF C57BL/6 J mice fed either standard chow or a high fat diet (HFD; 60% calories as fat) for four and twelve weeks. Post-mortem mouse livers were analysed histologically for fat deposition by gas chromatography-mass spectrometry for FA composition and by qPCR for the lipid metabolic genes fatty acid desaturase 2 (FADS2), stearoyl CoA desaturase 1 (SCD1), elongation of long-chain fatty acids family member 6 (ELOVL6) and 2-hydroxyacyl-CoA lyase 1 (HACL). Gut microbiota in faecal pellets from the ileum were analysed by 16S RNA sequencing. A significant depletion of serum and liver C15:0 (>50%; P < 0.05) and liver C17:0 (>35%; P < 0.05) was observed in HFD-fed SPF mice in parallel with hepatic fat accumulation after four weeks. In addition, liver gene expression (HACL1, ELOVL6, SCD1 and FADS2) was lower (>50%; P < 0.05) and the relative abundance of beneficial C3:0-producing gut bacteria such as Akkermansia, Lactobacillus, Bifidobacterium was lower after HFD in SPF mice. In summary, high dietary fat intake reduces serum and liver OCSFA, OCSFA-producing gut microbiota and is associated with impaired liver lipid metabolism. Further studies are required to identify whether there is any beneficial effect of OCSFA and C3:0-producing gut bacteria to counter metabolic disease.

Keywords: Free fatty acids; Gut microbiota; Liver; Odd-chain saturated fatty acids; Steatosis.

Graphical abstract

Fig. 1

(a) High fat diet increases body weight in specific pathogen free (SPF) mice. Body weight gain was significant during the first 2 weeks of experimental feeding. ****p < 0.0001 and **p < 0.01 for high fat diet (HFD) relative to control chow diet (CD) and was maintained at 4 weeks; p < 0.05. SPF CD: n = 10; SPF HFD: n = 10. Fatty acid concentration in the (b) serum and from (c) livers of SPF mice after four weeks following high fat diet (HFD) relative to control chow diet (CD). Values are given as median +/- 95% CI for n = 10 per group.

Fig. 2

Effect of high fat intake on saturated FA proportion in the serum (A-E) and liver (F-J) in SPF mice. Fatty acids were measured in the serum of mice by GC-MS. N = 10 per group, ****p < 0.0001 (HFD vs CD).

Fig. 3

Effect of high fat intake on unsaturated FA proportion in the serum (A-E) and liver (F-J) in SPF mice, ****p < 0.0001; *** p < 0.001; ** p < 0.01 (HFD vs CD) n = 10 per group.

Fig. 4

Hepatic steatosis (lipid vacuoles) in the livers of SPF mice on high fat diet but not control diet (a-b). Representative histology from chow diet group (CD) mouse and representative histology high fat diet (HFD) mouse liver. Liver sections stained with haematoxylin and eosin (H&E original magnification 20 ×). Effect of a 4-week HFD feeding on ELOVL6, HACL1, SCD1, and FADS2 mRNA expression in SPF mice (c-f). Mean relative transcript expression of genes related to specific fatty acid changes in mouse liver. Values are given as means ± S.E.M for n = 10; *p < 0.05, *** p < 0.0001; ****p < 0.0001 CD vs HFD.

Fig. 5

Specific dominant gut bacteria are affected by dietary fat. A: The composition of gut microbiota at phylum level; b: The heatmap of 35 differentially abundant genera between HFD and control treatment. Each column represented a sample from HFD and control treatment. (C: Controls (C1, C2, C3…); H: High fat diet (H1, H2, H3….).