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Glycerol monolaurate (GML) is a potential candidate for regulating metabolic syndrome and inflammatory response. However, the role of GML in modulating intestinal health in fish has not been well determined. In this study, a 70-d feeding trial was conducted to evaluate the effect of GML on intestinal barrier, antioxidant capacity, inflammatory response and microbiota community of large yellow croaker (13.05 ± 0.09 g) fed with high level soybean oil (SO) diets. Two basic diets with fish oil (FO) or SO were formulated. Based on the SO group diet, three different levels of GML 0.02% (SO0.02), 0.04% (SO0.04) and 0.08% (SO0.08) were supplemented respectively. Results showed that intestinal villus height and perimeter ratio were increased in SO0.04 treatment compared with the SO group. The mRNA expressions of intestinal physical barrier-related gene odc and claudin-11 were significantly up-regulated in different addition of GML treatments compared with the SO group. Fish fed SO diet with 0.04% GML addition showed higher activities of acid phosphatase and lysozyme compared with the SO group. The content of malonaldehyde was significantly decreased and activities of catalase and superoxide dismutase were significantly increased in 0.02% and 0.04% GML groups compared with those in the SO group. The mRNA transcriptional levels of inflammatory response-related genes (il-1β , il-6 , tnf-α and cox-2) in 0.04% GML treatment were notably lower than those in the SO group. Meanwhile, sequencing analysis of bacterial 16S rRNA V4–V5 region showed that GML addition changed gut microbiota structure and increased alpha diversity of large yellow croaker fed diets with a high level of SO. The correlation analysis results indicated that the change of intestinal microbiota relative abundance strongly correlated with intestinal health indexes. In conclusion, these results demonstrated that 0.02%–0.04% GML addition could improve intestinal morphology, physical barrier, antioxidant capacity, inflammatory response and microbiota dysbiosis of large yellow croaker fed diets with a high percentage of SO. • Dietary glycerol monolaurate improved intestinal antioxidant capacity and inflammation of large yellow croaker. • Dietary glycerol monolaurate could effectively modulate intestinal microbiota structure and composition. • Glycerol monolaurate at an appropriate level (0.02%–0.04%) improved intestinal health. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effect of supplemental glycerol monolaurate (GML) on growth performance, hepatic lipid metabolism, antioxidant capacity and mitochondrial function in large yellow croaker (Larimichthys crocea) fed diets with high soybean oil (SBO) level. The trial diet with 7% fish oil (FO) was designed as the negative control while the diet with 7% SBO was designed as the positive control. The other three diets were formulated with the administration of 400, 800 and 1600 mg/kg GML (0.04%, 0.08% and 0.16%) on basis of the positive control diet. Results showed that the specific growth rate (SGR) was increased and the feed conversion ratio (FCR) was decreased significantly in fish fed diets with GML supplementation compared with the positive control diet, while no difference was observed in the survival rate (SR) among dietary treatments. Fish fed the diet with 0.04% GML supplementation had significantly lower triglycerides and total cholesterol contents compared with those in the positive control group. The mRNA expression of lipogenesis-related genes (srebp1c and acc) were down-regulated while the mRNA expression of lipolysis and fatty acid β-oxidation-related genes (atgl , pparα and cpt1) were up-regulated in fish fed diets with 0.04% and 0.08% GML. Compared with the positive control diet, fish fed diets with 0.04% and 0.08% GML supplementation exhibited remarkably higher activities of superoxide dismutase, catalase and the content of glutathione, as well as lower malondialdehyde level. Furthermore, in fish fed diets with 0.04% and 0.08% GML, the morphology of mitochondria was improved and their number was increased. The mRNA expression of genes related to mitochondrial biogenesis (pgc1-α, tfam and nrf1) were significantly increased in fish fed with 0.04% and 0.08% GML supplementation. Meanwhile, the content of triphosadenine (ATP), the activity of citrate synthase (CS) and succinate dehydrogenase (SDH) in liver were increased significantly in 0.04% and 0.08% treatments compared with the positive control group. Conclusively, these results indicated that dietary GML supplementation (0.04%–0.08%) could promote growth performance, improve liver lipid metabolism, antioxidant capacity and enhance mitochondrial function in large yellow croaker fed with the SBO based diet. • Supplemental glycerol monolaurate improved lipid metabolism and enhanced antioxidant capacity of large yellow croaker. • The improvement of lipid metabolism and antioxidant capacity may be mediated by enhancing mitochondrial function. • The appropriate supplemental glycerol monolaurate level for decreasing hepatic lipid content was 0.04%–0.08%. [ABSTRACT FROM AUTHOR]

Low-density lipoprotein (LDL) is the main carrier of cholesterol transport in plasma, which participates in regulating lipid homeostasis. Studies in mammals have shown that high levels of LDL in plasma absorbed by macrophages trigger the formation of lipid-rich foam cells, leading to the development of atherosclerotic plaques. Although lipid-rich atherosclerosis-like lesions have been discovered in the aorta of several fish species, the physiological function of LDL in fish macrophages remains poorly understood. In the present study, LDL was isolated from the plasma of large yellow croaker (Larimichthys crocea), and mass spectrometry analysis identified two truncated forms of apolipoprotein B100 in the LDL protein profile. Transcriptomic analysis of LDL-stimulated macrophages revealed that differentially expressed genes (DEGs) were enriched in various pathways related to lipid metabolism, as confirmed by the fact that LDL increased total cholesterol and cholesteryl esters content. Meanwhile, the gene and protein expression levels of perilipin2 (PLIN2), a DEG enriched in the PPAR signaling pathway, were upregulated in response to LDL stimulation. Importantly, knocking down plin2 significantly attenuates LDL-induced cholesterol accumulation and promotes cholesterol efflux. Furthermore, the transcription factor PPARγ, which is upregulated in response to LDL stimulation, can enhance the promoter activity of plin2. In conclusion, this study suggests that LDL may upregulate plin2 expression through PPARγ, resulting in cholesterol accumulation in fish macrophages. This study will facilitate the investigation of the function of LDL in regulating lipid homeostasis in macrophages and shed light on the evolutionary origin of LDL metabolism in vertebrates. [Display omitted] • Characterization of apolipoprotein composition of LDL during evolution. • LDL significantly affects lipid metabolism homeostasis in fish macrophages. • LDL activates PLIN2 through PPARγ to promote cholesterol accumulation. [ABSTRACT FROM AUTHOR]