Experiment outline and Characterization of L. fermentum E15. (A) Experimental outline of L. fermentum E15 treated zebrafish larval fed by HCD. (B)L. fermentum E15 colonies on MRS agar cultured anaerobically after 48 h at 37°C. (C) Gram staining properties of L. fermentum E15.

Lactobacillus fermentum E15 can improve lipid accumulation induced by a HCD in the liver and blood vessels of zebrafish. (A) Representative images of lipid accumulation in zebrafish using Oil Red O staining. (B) Zebrafish IOD values. The data are presented as mean values ± SD (n = 20). (C) Zebrafish BMI index. The data are presented as mean values ± SD (n = 20). (D) H&E staining of zebrafish liver paraffin sections (lipid droplets indicated by blue arrows). *p < 0.05, ***p < 0.001, and ns indicates that it is not statistically significant. p < 0.05 was considered as statistically significant calculated by One-way ANOVA followed by Tukey’s test.

Lactobacillus fermentum E15 can improve lipid metabolic disorder and liver function abnormalities. The levels of (A) TC, (B) TG, (C) LDL-C, and (D) HDL-C in zebrafish larvae. Activities of (E) ALT and (F) AST in zebrafish larvae. The data are presented as mean values ± SD of three samples (n = 10 zebrfish for each sample). *p < 0.05, **p < 0.01, ***p < 0.001 and ns indicates that it is not statistically significant. p < 0.05 was considered as statistically significant calculated by One-way ANOVA followed by Tukey’s test.

Expression levels of mRNA associated with lipid metabolism in zebrafish larvae regulated by L. fermentum E15. (A) mRNA expression level of SREBP-1. (B) mRNA expression level of PPAR-γ. (C) mRNA expression level of Fasn. (D) mRNA expression level of PPAR-α. The data are presented as mean values ± SD of three samples (n = 20 zebrfish for each sample). *p < 0.05, **p < 0.01, ***p < 0.001 and ns indicates that it is not statistically significant. p < 0.05 was considered as statistically significant calculated by One-way ANOVA followed by Tukey’s test.

Effect of L. fermentum E15 on metabolic oxidative stress in HCD-fed zebrafish larvae. (A) Detection of ROS production in zebrafish larvae using DCFH-DA staining. (B) Quantification of ROS levels. The data are presented as mean values ± SD (n = 10). (C) SOD activity in zebrafish larvae. The data are presented as mean values ± SD of three samples (n = 10 zebrfish for each sample). (D) MDA levels in zebrafish larvae. The data are presented as mean values ± SD of three samples (n = 10 zebrfish for each sample). *p < 0.05, **p < 0.01, ***p < 0.001. p < 0.05 was considered as statistically significant calculated by One-way ANOVA followed by Tukey’s test.

Lactobacillus fermentum E15 can produce SCFAs. The levels of (A) acetic acid, (B) propionic acid, (C) butyric acid, and (D) isovaleric acid in the culture supernatant of L. fermentum E15. The data are presented as mean values ± SD (n = 3). The levels of (E) acetic acid, (F) propionic acid, (G) butyric acid, and (H) isovaleric acid in zebrafish after supplementing with L. fermentum E15. The data are presented as mean values ± SD of three samples (n = 20 zebrfish for each sample). *p < 0.05, **p < 0.01, ***p < 0.001. p < 0.05 was considered as statistically significant calculated by One-way ANOVA followed by Tukey’s test.

Lactobacillus fermentum E15 can alleviate HCD-induced lipid accumulation by activating the GPR43 receptor through the metabolism of SCFAs. (A) Representative images of lipid accumulation in zebrafish detected by Oil Red O staining. (B) IOD values in zebrafish. The data are presented as mean values ± SD (n = 20). The mRNA expression levels of GPR43 (C) and leptin A (D) detected by RT-qPCR. The data are presented as mean values ± SD of three samples (n = 20 zebrfish for each sample). *p < 0.05, **p < 0.01, ***p < 0.001 and ns indicates that it is not statistically significant. p < 0.05 was considered as statistically significant calculated by One-way ANOVA followed by Tukey’s test.