Mechanism Of Total Polar Compounds Generated From Frying Peanut Oil On Cytotoxicity In Hepg2 Cells

A series of chemical reactions such as oxidation reaction,polymerization and hydrolysis reaction have occurred during frying process under high temperature in different vegetable oils,resulting in total polar compounds(TPC)such as triglyceride oxide,triglyceride polymer and free fatty acid and so on.At present,domestic and foreign scholars mainly focus on the change of physical and chemical indexes and detection methods of frying oil,while researches on the safety of TPC in frying oil are limited.Therefore,this study systematically analyzed the effects on the physical and chemical properties of peanut oil with different frying time,further elucidated the content and distribution of TPC,and deeply clarified the influence of TPC on lipid metabolism,oxidative stress,cytotoxicity and their mechanisms in HepG2 cells.The aim of this study was to provide the scientific basis and theoretical supports for the safety of TPC and the rational utilization of frying oil.The main research contents and experimental results have been listed as follows:Firstly,with the increase of frying time,the changes of physical and chemical indexes and the distribution of TPC were investigated.With the increase of frying time,the peroxide value(POV)of frying peanut oil firstly increased and then decreased,while the acid value(AV),anisidine value(p-AV),carbonyl value(CGV)and viscosity increased.With the increase of frying time,the results of fatty acid and functional group composition showed that the increase amplitude of saturated fatty acid was 8.83%,and the content of polyunsaturated fatty acid and monounsaturated fatty acids decreased.Also,the decrease amplitude of polyunsaturated fatty acids(6.45%)was bigger than that of monounsaturated fatty acids(0.48%),accompanying with the generation of hydrolysis products and secondary oxidation products.With the increase of frying time,the content of TPC elevated from 3.26% at 0 h to 25.17% at 40 h.And TPC mainly included triglyceride oxide oligomer(TGO),triglyceride dioxide(TGD),triglyceride oxide monomer(ox-TG),diacylglycerol(DG)and free fatty acid(FFA).Among them,TGO and TGD showed an increasing trend,ox-TAG firstly increased and then stabilized,and DG and FFA showed irregular changes with the increase of frying time.The results showed that with the increase of frying time,TPC produced in frying peanut oil contained more polymerization products and oxidation products,while the hydrolysis products showed irregular changes.Secondly,the preparation method of TPC cell culture mother liquor was established,and the effect of mother culture liquor on the cell viability of HepG2 cells was explored.In this study,bovine serum albumin(BSA)was used as emulsifier to prepare cell culture mother liquor.We evaluated the effects of different BSA concentrations on particle size and potential,and then we found that 2% BSA had the best emulsifying performance.CCK-8(cell counting kit-8)test showed that 2% BSA had no toxic and side effects on HepG2 cells.Therefore,we chose 2% BSA to prepare TPC cell culture mother liquor for subsequent cell culture.Subsequently,the effects of TPC on lipid metabolism,oxidative stress and cytotoxicity of HepG2 cells were studied.It was presented that significant lipid deposition was induced by TPC over the concentration of 0.5 mg/mL.And the content of triglyceride in HepG2 cells increased from 0.02 to 0.17 mmol/mprot,accompanying with the down-regulation of lipidolysis genes PPARα,ACOX and CPT1;TPC could elevate the amounts of reactive oxygen species(ROS)in HepG2 cells,and simultaneously increase the malondialdehyde(MDA)in a time and dose dependent manner.On the contrary,antioxidant enzymes superoxide dismutase(SOD),glutathione(GSH)and catalase(CAT)respectively decreased in a time and dose dependent manner;In addition,TPC could induce the apoptosis of HepG2 cells,and the transition from G0/G1 to G2 phase in HepG2 cells was impeded with the increase of the concentrations of TPC.This study demonstrated that TPC could cause lipid deposition,oxidative stress and cytotoxicity.Finally,the production of cytotoxicity was verified.We explored the mediation effect of ROS on biological function by adding N-acetylcysteine(NAC),an inhibitor of reactive oxygen species(ROS).It was found that NAC could reverse apoptosis and cycle arrest induced by TPC in HepG2 cells,indicating that ROS was the upstream factor of cytotoxicity induced by TPC.It is proved that ROS produced by TPC could affect the biological function by mediating cytotoxicity in HepG2 cells.