Effect Of Dietary Silymarin On Lipid Metabolism Of Grass Carp(Ctenopharygodon Idellus)

Silymarin,a flavonolignan from the milk thistle(Silybum marianum L.),is mainly composed of four isomeric mixtures of active flavonolignans,including silybin A and B,isosilybin A and B,silychristin and silydianin.In mammal,silymarin has not only hepatoprotective and antioxidant properties,but hypolipidemic effects and decreasing fat deposition in the viscera.There is little information on effects of silymarin on lipid metobolism in fish.Increasing dietary lipids induces rapid growth and efficient feed conversion in several fish species.On the other hand,dietray high lipid levels and/or oxidized oil not only reduces growth performance but also leads to some side-effects such as unwanted fat accumulation in the liver or other tissues,hyperlipidemia,fatty liver,lipid peroxidation,and affecting meat flavor and quality,which has become one of key problems on the healthy development of aquaculture.Therefore,four chapter were included in this paper to investigate whether supplementation of silymarin in diets containing high lipid level or oxidized oil could affect growth performance,lipid metabolism and health status of grass carp(Ctenopharyngodon idellus)in vivo,and the mechanism of silymarin on lipid accumulation in hepatocytes and adipocytes of grass carp in vitro.Major results and conculsions were presented as follows:1.Silymarin supplementation suppressed lipid accumulation in hepatopancreas and intraperitoneal fat(IPF)tissue,and promoted antioxidant capacity in grass carp fed with high lipid diets.The juvenile fish(mean body weight =27.43 ± 0.17 g)were fed six isonitrogenous and isocaloric diets in a factorial design containing 0,100 or 200 mg kg-1silymarin(SM0,SM100,SM200)associated with either 4% or 8% lipid level(low lipid,LL,high lipid,HL,respectively)for 82 days.The results showed that silymarin supplementation in diets markedly promoted growth performance and protein ef?ciency.Silymarin supplementation notably suppressed hepatic lipid accumulation in grass carp fed with high lipid diets,due to upregulating lipolysis(HSL)and ?-oxidation(CPT1)genes.Silymarin reduced lipid accumularion in IPF tissue through downregulating lipogenesis gene in grass carp fed with high lipid diets.Silymarin supplementation notably reduced the elevated serum MDA content induced by HL treatments.Silymarin improved health status in grass carp fed with high-lipid diets by improving antioxidant capacity.2.Silymarin supplementation alleviated dietary oxidized oil induced side-effects ongrowth performance,and decreased lipid peroxidation and oxidative stress through enhancing antioxidative capabilities in grass carp.The juvenile fish(mean body weight =60.01±0.77 g)were fed eight isonitrogenous semi-purified diets in a factorial design containing 0,100 or 200 mg kg-1silymarin(SM0,SM100,SM200)associated with either2.5% or 6.5% lipid level(Low oxidized soybean oil level,LO;High oxidized soybean oil level,HO;respectively),2.5% low fresh soybean oil(LF,a LO control),and 6.5% high fresh soybean oil(HF,a HO control)for 80 days.There were no significant differences in FBW,WG,SGR,FCR,DFI,and SR among all groups.Despite no statistical differences,WG in the HOSM100 and HOSM200 group increased by 8.80% and 8.41% compared with the HOSM0 group,respectively,while LOSM100 and LOSM200 group increased by 19.77% and 10.16%in WG compared with the LOSM0 group,which further revealed that silymarin supplementation could alleviate dietary oxidized oil induced side-effects on fish.Silymarin supplementation notably enhanced CAT and GSH-Px activities in hepatopancreas,and decreased MDA contents in serum and hepatopancreas.Silymarin supplementation promoted health status in grass carp fed with the oxidized oil diets through decreasing lipid peroxidation and enhancing antioxidative capabilities3.Silymarin inhibited lipid accumulation and enhanced antioxidative ability in grass carp hepatocytes induced by oleic acid(OA)in vitro.Hepatocytes were treated with400 ?mol L-1OA containing with or without silymarin to observe the cell viability by3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)and the lipid accumulation by Oil Red O stain.We also tested the effects of silymarin on the antioxidant capacities and the expression of lipid metabolism related gene detected by RT-PCR in hepatocytes in grass carp.The results showed that SM100(100 ?g m L-1 silymarin)group significantly decreased lipid accumulation in the presence of 400 ?mol L-1 OA for 24 h.Reduced glutathione(GSH)contents were higher in SM100 group than that of the OA group.The expressions of FAS and SCD1 mRNA were significantly downregulated in SM100 group.These results demonstrated silymarin exerted an inhibitory effect on lipid accumulation by decreasing lipogenesis and enhanced antioxidative ability in grass carp hepatocytes.4.Silymarin suppressed lipid accumulation and improved antioxidant capability in grass carp adipocytes in vitro.Differentiated grass carp pre-adipocytes were treated with silymarin for 6 days.Treatment with 100 ?g mL-1silymarin(SM100 group)significantly reduced triglyceride accumulation at day 6.The adipogenic gene expression levels of PPAR?,C/EBP?,SREBP1 c,FAS,SCD1 and LPL and the protein expression level of PPAR? were significantly down-regulated in the SM100 group.Additionally,the SM100 group had significantly lower reactive oxygen species production and reduced glutathione contentscompared with the control in vitro.In conclusion,silymarin could inhibit excessive lipid accumulation in hepatopancreas and IPF tissue induced by high-lipid diets,and alleviated dietary oxidized oil induced side-effects on fish.Silymarin supplementation decreased lipid peroxidation and oxidative stress by improving antioxidant capability,and promoted health status in fish.