Abstract
Compared with wild grass carp (Ctenopharyngodon idellus), intensively cultured fish displayed disordered lipid metabolism, showing excess lipid deposition in the hepatopancreas and muscle. Lotus leaf prevents fat accumulation in humans and may have similar effects on fish. This study explored the regulatory mechanisms by which the dietary addition of an alcoholic extract of lotus leaf (AELL) reduced lipid deposition in the hepatopancreas and muscle of juvenile grass carp. The fish (average initial weight: 34.00 ± 0.40 g) were fed four experimental diets containing different AELL levels (0, 0.07, 0.14, and 0.21%) for 8 weeks. Serum components, lipid droplet size, triacylglycerol (TAG) content, enzymatic activities, and mRNA levels of genes related to lipid metabolism in the hepatopancreas and muscle were analyzed. The results show that dietary AELL supplementation significantly reduced the TAG content and lipid droplet area in the histological sections as well as the fatty acid synthase (FAS) activity in both the hepatopancreas and muscle but enhanced the activities of lipoprotein lipase (LPL) and carnitine palmitoyltransferase I (CPT1) in both tissues. In addition, dietary AELL supplementation decreased the mRNA expression of genes involved in fatty acid uptake (cd36, fatp1/fatp4/fatp6, fabp10/fabp11, acsl1/acsl4) and de novo lipid synthesis (pgd, g6pd, and fasn) as well as the transcription factors pparg and srebf1 in the hepatopancreas and muscle but increased the mRNA levels of genes relating to lipid catabolism (cpt1a, lipe, pnpla2, lpl), lipid transportation (apob), and the transcription factor ppara in both tissues. In conclusion, dietary AELL supplementation reduced lipid accumulation in the hepatopancreas and muscle by affecting the gene expression of proteins with known effects on lipid metabolism in juvenile grass carp.
Highlights
Grass carp (Ctenopharyngodon idellus) is an important commercial freshwater fish in high demand within China (FAO, 2018)
MK929573 fasn, fatty acid synthase; srebf1, sterol-regulator element-binding protein; acaca, acetyl-CoA carboxylase alpha; lpl, lipoprotein lipase; cd36: CD36 molecule; pgd, phosphogluconate dehydrogenase; g6pd, glucose-6-phosphate dehydrogenase; cpt1a, carnitine palmitoyltransferase 1A; lipe, lipase E, hormone sensitive type; pnpla2, patatin-like phospholipase domain-containing protein 2; ppara: peroxisome proliferator-activated receptor alpha; pparg: peroxisome proliferator-activated receptor gamma; fatp1, long-chain fatty acid transport protein 1; fatp4, long-chain fatty acid transport protein 4; fatp6, long-chain fatty acid transport protein 6; fabp10, fatty acid binding protein 10; fabp11, fatty acid binding protein 11; acsl1, acyl-CoA synthetase long chain family member 1; acsl4, acyl-CoA synthetase long chain family member 4; vldlr, very low-density lipoprotein receptor; lrp1, low-density lipoprotein receptor-related protein; apob, apolipoprotein B. This is the first investigation on the effect of dietary alcoholic extract of lotus leaf (AELL) on the lipid content of serum, muscle, and hepatopancreas in fish and the related molecular effects
The results show that dietary AELL can decrease serum TAG, cholesterol, and low-density lipoprotein (LDL) levels and increase the serum highdensity lipoprotein (HDL) level of grass carp
Summary
Grass carp (Ctenopharyngodon idellus) is an important commercial freshwater fish in high demand within China (FAO, 2018). Modern intensive aquaculture is based on formulated feeds that promote fish growth and increase grass carp production (Zhao et al, 2018). The flavonoids in the alcoholic extract of the lotus leaf are a group of polyphenolic compounds that mainly includes kaempferitrin, hyperoside, astragalin, phloridzin, and quercetin (478.51, 232.74, 12.62, 5.67, and 0.49 mg g−1, respectively) (Chen et al, 2020). These have important physiological functions, including anti-inflammatory, anti-allergic, anti-obesity, and antioxidant activities (Agrawal, 2011; Ahn et al, 2013). The biological potential to lower blood lipid and the anti-obesity effects of lotus leaf extract have been shown in humans (Lee et al, 2015; Zhang et al, 2015) and rats (Su et al, 2015; Ding et al, 2017) and indicate that dietary lotus leaf extract may have the potential to suppress excess lipid accumulation in fish
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