| Dyslipidemia is a common clinical metabolic disease and an important risk factor for type 2 diabetes(T2DM),ischemic stroke and atherosclerotic cardiovascular disease(ASCVD).The main manifestations of dyslipidemia in Chinese adults are elevated TG concentrations and reduced HDL-C concentrations.The prevalence of dyslipidemia in China has soared in the past three decades.Fasting blood lipids are mainly detected in daily clinical practice.While individuals stay in a postprandial state during the most time in a day,diets have nonnegligible impacts on blood lipids concentrations.Postprandial triglycerides(PTG)is closely related to metabolic diseases as T2 DM,Non-alcoholic fatty liver diseases and ASCVD.However,there are few studies focus on PTG metabolism in our population,further researches are required.Triglycerides(TG)are mainly carried by very low-density lipoproteins(VLDL)and chylomicrons(CM)to transport in the blood stream.The main apolipoproteins of these lipoproteins are apolipoprotein B100(ApoB100),apolipoprotein C(ApoC),and apolipoprotein B48(ApoB48),among which ApoB48 plays an essential role in TG metabolism.ApoB48 synthesis in intestinal epithelial cells and is an indispensable factor in dietary impact on PTG.Many studies have found that ApoB48 is closely related to diseases such as insulin resistance(IR),T2 DM,and ASCVD.The binding of ApoB48 to TG in dietary lipids is affected by various proteins such as microsomal triglyceride transfer proteins(MTTP).Meanwhile,the synthesis and secretion of ApoB48 are closely related to dietary factors.However,whether ApoB48 has a significant impact on PTG levels remains unclear.There are only a few drugs for TG management,and fenofibrate is currently commonly used in the treatment of hypertriglyceridemia.Fenofibrate is a fibrate drug,and its main mechanism,to date,is known to act as a lipid-lowering agent by activating peroxisome proliferator activated receptor alpha(PPARα).Previous studies have found that fenofibrate can affect proteins taking vital roles in lipids metabolism,such as apolipoprotein CⅢ,but it is still unclear whether fenofibrate has impacts on intestinal ApoB48.Therefore,the main aim of this study was to explore the suitable range of Chinese populations for PTG testing,while the relationship between ApoB48 and postprandial hypertriglyceridemia(PHTG)was analyzed by comparing postprandial ApoB48 concentrations among different PTG populations.In addition,by establishing an animal model of hyperlipidemia using golden hamsters,the possible mechanism of ApoB48 on postprandial hyperteriglycerides was explored.By comparing the metabolic effects of fenofibrate on blood glucose and lipids,as well as the effects on ApoB48 expression within the intestinal epithelium,novel lipidlowering mechanism of fenofibratewere explored,aiming to provide possible new targets for the early prevention and treatment of dyslipidemia.Part one Clinical study of a suitable population for having oral high fat tolerance testObjective: The aim of the present study was to determine the PTG response and identify who would benefit from diagnostic PTG measurements using oral high-fat tolerance test.Methods:A total of 400 Chinese adults were enrolled and underwent oral highfat tolerance tests(OFTT),which were well tolerated.The participants were assigned to groups according to their fasting triglyceride concentrations to evaluate the practicability of PTG testing.A PTG concentration > 2.5 mmol/L was defined as high(HPTG).Results:1.Comparison of baseline indicators in groups with different FTG concentrations.All subjects were firstly divided into four groups according to their FTG concentrations: Group A: FTG < 1.0 mmol/L;Group B: 1.0 mmol/L≤ FTG < 1.7 mmol/L,Group C: 1.7 mmol/L ≤ FTG < 2.0 mmol/L,Group D: FTG≥ 2.0 mmol/L.BMI,systolic blood pressure(SBP),diastolic blood pressure(DBP),waist circumference(WC),fasting glucose(FBG),fasting insulin(FINS),HOMA-IR,TG,TC,LDL-C and ApoB levels increased while HDL-C decreased with increasing FTG levels,differences between groups were statistically significant.2.Lipids changes after OFTT in groups with different FTG concentrations2.1 TG increased gradually after OFTT in the fourvgroups of subjects with different FTG concentrations.PTG peaked at 4 hours postprandial in Group A and B,while PTG peaked at 6 hours after the OFTT in Group C and D.In addition,PTG of Group A and B almost returned to the FTG concentrations at 10 h after the OFTT whereas the PTG of Group C and Group D were still significantly higher than FTG concentrations at 10 h postprandial.2.2 Referring to the population recommended by the 2011 Greek consensus of 1.0 mmol/L ≤ FTG < 2.0 mmol/L for the detection of PL in OFTT,all subjects were redivided into 3 groups: Group E in those with FTG < 1.0 mmol/ L;1.0 mmol/L ≤ FTG < 2.0 mmol/L for Group F;And those with FTG ≥ 2.0 mmol/L were assigned to Group G.TG peaked at 4h postprandial after OFTT in subjects of Group E and F,while PTG in Group G had a delayed and increased peak.3.Comparison of PHTG prevalence in groups with different FTG concentrationsThe prevalence of PHTG in the four groups allocated according to the Chinese dyslipidemia guidline was 9.2%,75.0%,98.6% and 100%.The PHTG prevalence in the three groups assigned according to the Greek consencus was 9.2%.79.8% and 98.9%.Summary: Performing an OFTT to detect PTG in the Chinese population with 1.0 mmol/L ≤ FTG < 2.0 mmol/L helps identify more PHTG patients and results in a larger clinical benefit.Part two Correlation study of fasting apolipoprotein B48 and postprandial hypertriglyceridemeiaObjective: The aim of this study was to explore the possible mechanism of PHTG by measuring ApoB and ApoB48 concentrations in subjects with normal fasting triglyceride concentrations,and by exploring the impact of ApoB48 on postprandial TG after ingesting a high-fat meal.Methods:According to the inclusion and exclusion criteria,125 volunteers with normal FTG were included.All subjects underwent OFTT after 10 hours of fasting,and blood samples were taken at 2,4,6,8 and 10 hours before and after the OFTT.Blood glucose and lipids metabolism and other related indicators were measured.All subjects were divided into two groups according to PTG level: Subjects with PTG ≤ 2.5 mmol/L were defined as the Control group(Con),and the PHTG group consisted of subjects with TG > 2.5 mmol/L at any time after OFTT.Changes of blood lipids and ApoB48 levels in the two groups were analyzed and compared.Results:1.Basic parameters between two groupsFasting TC,TG,LDL-C,triglyceride-rich lipoproteins(TRLs),nonHDL-C,ApoB,ApoB48 levels of subjects in PHTG group were significantly higher than those in Con group,while HDL-C levels were significantly lower than those in Con group(P < 0.05).2.Lipid profiles in the two groupsPTG of subjects in Con group peaked at 2 hours postprandial,while PTG of subjects in PHTG group reached its peak at 4 hours after OFTT.At each time points after OFTT,the levels of TC,TG,LDL-C,TRLs,NonHDL-C,ApoB and ApoB48 in PHTG group were significantly higher than those in Con group,while the levels of HDL-C were significantly lower than those in Con group(P < 0.05).3.Correlation analysis and regression analysis of ApoB48 and other basic indicatorsFasting ApoB48 was positively correlated with TC,TG,LDL-C,TRLs,Non-HDL-C(P < 0.001).After adjusted for age,sex,BMI,ApoB48 is an independent risk factor for PHTG(P = 0.034,OR = 1.215).Summary: Fasting serum ApoB48 concentrations are strongly associated with PHTG,while changes of postprandial ApoB48 levels coincide with profiles of postprandial triglyceride changes Part three Establishment of hyperlipidemia golden hamster model and effects of intestinal epithelial apolipoprotein B48 expression levels on postprandial blood lipidsObjective: The effects of long-term high-fat diet on mRNA expression levels of ApoB48 in intestinal epithelial tissues were analyzed by establishing a hyperlipidemia model using golden hamsters fed a highfat diet,and effect of different ApoB48 mRNA expression levels in intestine on postprandial triglyceride concentrations were explored using a single high-fat loading experiment.Methods:Thirty 8-weeks-old golden hamsters were randomly divided into control group(Con)and high-fat-diet group(HF).Con group was fed with normal chow diet and HF was fed with high-fat die for 12 weeks.The FBG levels,blood lipids concentrations of TC,TG,HDL-C,and LDL-C And insulin concentrations were measured.All golden hamsters were given olive oil by gavage according to 450 μL/100 g body weight,and the TC,TG,HDL-C,and LDL-C indexes were detected by blood sampling in the vein of the inner canthal vein before at 0.5,1,2,3,and 4 h after gavage.Protein and mRNA expression levels of ApoB48,MTTP,NPC1L1,CD36 and PPARα were detected by real-time polymerase chain reaction(RTPCR)and Western blot analysis.Results:1.Changes of general indexes of golden hamsters in two groups after12-weeks of high-fat diet.During 12 weeks of feeding,both groups of golden hamsters were in good condition and their body weights increased gradually.Since week 2,body weights of the golden hamsters in the HF group were significantly higher than those in the Con group;However,there was no significant difference in the caloric intake between the two groups of golden hamsters;In the HF group,golden hamsters exhibit insulin resistance,fasting glucose,TC,TG,FFA,ApoB,ApoB48,and Non-HDL-C together with TG / HDLC concentrations were significantly higher in the HF group than in the Con group;2.OFTT outcomes.TG,ApoB,and ApoB48 concentrations of golden hamsters in the Con group peaked at 2 hours after the OFTT and almost returned to the fasting level at 4h postprandial,while the TG,ApoB,and ApoB48 concentrations of golden hamsters in HF group increased continuously during the 4 hours after OFTT.3.Changes in intestinal ApoB48 and related protein levels and mRNA expression levels in groups with various postprandial TG responsesThe mRNA expression levels of ApoB48,NPC1L1,MTTP,CD36 and PPARα in HPTG group with elevated PTG were all significantly higher than those in the group with lower PTG.The mRNA expression levels of ApoB48,NPC1L1,MTTP,CD36 and PPARα in the HPC group,where golden hamsters were fed with common chow diet but PTG elevated were not significantly different from those of the high-fat diet NH group with normal PTG.Summary:1.Hyperlipidemia model was successfully established in golden hamsters using high-fat diets,and insulin resistance together with delayed and increased postprandial TG peaks were found.2.Postprandial triglyceride concentrations in hyperlipidemic golden hamsters consistently correlated with ApoB48 expression levels in the intestine of golden hamsters and with expression levels of MTTP,NPC1L1 and CD36.Part four Exploration of the lipid-lowering mechanism of fenofibrate by inhibiting the expression of ApoB48 and related proteins in intestinal epithelial tissuesObjective: The effects of fenofibrate on mRNA and protein expression levels of ApoB48 in intestinal tissues and factors related to lipids absorption in the intestine were investigated by administering fenofibrate to high-fat diets fed hyperlipidemia golden hamsters,and the lipid-lowering mechanism of fenofibrate was explored.Methods:Same as part 3.Thirty golden hamsters were randomly divided into control group(Con)and high-fat diet group(HF).Golden hamsters in the Con group were fed a normal chow diet and the HF group was fed a highfat diet.Ten golden hamsters were randomly selected from the HF group after 12 weeks as the high-fat diet with fenofibrate intervention group(HFF)and were given fenofibrate(50 mg/kg/d)by gavage.The Con and HF groups were given the same volume of sodium chloride solution containing0.1% DMSO by gavage.Golden hamsters were sacrificed after 12-weeks intervention,serum and intestinal tissue samples were retained to detect biochemical indexes such as serum blood glucose,lipids and insulin concentrations.H&E staining and oil red O staining of intestinal tissue were performed to observe the morphological changes.Protein and mRNA expression levels of ApoB48,MTTP,NPC1L1,CD36 and PPARα were detected by real-time polymerase chain reaction(RT-PCR)and Western blot analysis.Results:1.Basic parameters of golden hamsters after fenofibrate interventionCaloric intake and body weights of golden hamsters were slightly reduced after fenofibrate intervention compared with those in the HF group,but the differences were not statistically significant.Perirenal fat,subcutaneous fat and epididymal fat visceral index were significantly decreased.In the HFF group,there was no significant difference in fasting blood glucose concentrations compared with the HF group.HOMA-IR significantly decreased while QUICKI increased.After fenofibrate intervention,fasting TC and TG concentrations of golden hamsters gradually decreased,and the concentrations of TG,FFA and ApoB48 were significantly decreased(P < 0.05).PTG peaked at 3 hours after the OFTT in golden hamsters intervened by fenofibrate,and the peak value was lower than that in the HF group.2.Lipids content of intestinal tissues in golden hamstersThe content of TC in the jejunum and ileum of golden hamsters in HF group was significantly higher than that in Con group,while the content of TG in the liver,duodenum,jejunum and ileum was significantly higher than that in Con group(P < 0.05).Fenofibrate intervention for 12 weeks significantly decreased TC content in jejunum and ileum,and duodenum and jejunum and ileum TG content were also significantly decreased compared with HF group.3.Comparison of histological outcomesH&E staining of the liver tissue showed that,fenofibrate could attenuate the disorder of intestinal tissue structure and abnormal intestinal villus morphology caused by high-fat diet.In oil red O staining,obvious lipids deposition in the intestinal tissue was seen in the HF group,which was alleviated by fenofibrate intervention,and the red lipid droplets were significantly reduced.4.Changes in protein and mRNA expression levels of ApoB48 and related factors in the intestine of golden hamsters after fenofibrate intervention.After fenofibrate intervention,the protein and mRNA expression levels of ApoB48,NPC1L1,MTTP and CD36 in the intestine were significantly reduced compared with the HF group(P< 0.05).Summary: 1.Fenofibrate intervention can reduce serum TC,TG,ApoB,ApoB48,FFA,Non-HDL-C and TG / HDL-C concentrations and improved IR in golden hamsters induced by high-fat diets.2.Fenofibrate may exert lipid-lowering effects through reducing intestinal TG absorption by modulating the mRNA and protein expression levels of ApoB48,MTTP as well as NPC1L1.Conclusion:1.Adults with 1.0 mmol/L ≤ FTG < 2.0 mmol/L can obtain larger clinical benefits by undergoing an OFTT to detect the postprandial blood lipids concentrations.2.Fasting apolipoprotein B48 is closely related to postprandial hypertriglyceridemia.3.Increased protein and mRNA expression of ApoB48 in the intestinal epithelium is one of the mechanisms underlying postprandial hypertriglyceridemia.Fenofibrate can inhibit intestinal lipid absorption and decrease serum TG,FFA,ApoB48 levels by inhibiting the expression of ApoB48,MTTP,and NPC1L1 in the intestine. |
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