Study On The Mechanism Of Cereal Fiber Against Atherosclerosis

Atherosclerosis(atherosclerosis,AS)is the main pathological basis of cardiovascular disease,and cardiovascular disease caused by AS has become one of the leading cause of death in China.Cholesterol metabolism and inflammatory responses play an important role in the initiation and development of AS.Studies have shown that early intervention of nutrients has a positive effect on the prevention and treatment of AS.Numerous epidemiological studies have demonstrated that high dietary fiber(DF)intake can reduce the incidence and mortality of cardiovascular disease.And cereal fiber is more effective in reducing the risk of chronic metabolic diseases than DF from other food.Cereal fiber can effectively reduce serum cholesterol level and improve inflammatory response,but the mechanism of cereal fiber on anti-atherosclerosis is limited.Therefore,the present study explores the mechanism of cereal fiber against atherosclerosis.Objective:The present study explores the effects and underlying mechanism of oat fiber(mainly soluble DF)and wheat bran fiber(mainly insoluble DF)on the development of AS in Apo E-/-mice fed a high fat/cholesterol diet,and compares the differences between two cereal fiber.Methods:After a week of acclimatization,30 male,7-week-old Apo E-/-mice were randomly allocated to the following three dietary groups: Apo E-/-mice fed with a high-fat/cholesterol diet(Research diets D12451 + 1% cholesterol)as model group(AS),a high-fat/cholesterol diet plus oat fiber(O-fiber)group,and a high-fat/cholesterol diet plus wheat bran fiber(W-fiber)group for 18 weeks.Five 7-week-old C57BL/6 mice with the same genetic background fed with a normal diet(Research diets D10001)were used as control group(Chow).The body weight,food intake and energy intake were measured every week.After 18 weeks of intervention,all mice were fasted for 12-14 h and then the blood was taken from the orbital venous plexus.Serum lipids,free fatty acids(FFAs),and inflammatory cytokines including high-sensitivity C-reactive protein(hs-CRP),interleukin-6(IL-6),Interleukin-10(IL-10),Monocyte Chemoattractant-1(MCP-1),Interferon-?(IFN-?),Tumor Necrosis Factor-?(TNF-?),Interleukin-12p70(IL-12p70)were measured.At the end of the experiment,the aorta of mice were harvested and stained with Oil Red O or hematoxylineosin(HE)for atherosclerotic lesion quantification.CD36 immunohistochemical analysis was detected.The protein expressions involved in the nod-like receptor family pyrin domain containing 3(NLPR3)inflammasome pathway were detected by western blot in aortic tissues.Histological examination of the liver samples were carried out with HE or Oil Red O staining method.Liver homogenate TC,TG and FFAs were analyzed.The protein expressions involved in lipid metabolism and cholesterol reverse transport were detected by western blot in liver tissues.Mice feces were collected and the content of short-chain fatty acids(including acetic acid,propionic acid,butyric acid)was determined by HPLC method.The protein expressions involved in cholesterol absorption,metabolism and cholesterol reverse transport were detected by western blot in small intestine tissue.Results:1.Effects of cereal fiber on atherosclerotic lesion formation in Apo E-/-mice(1)Body weights of mice in each group increased steadily during the whole experiment.No significant differences in body weights,food intake and energy intake,were observed in the three groups of AS,O-fiber and W-fiber at the end of the experiment(P > 0.05).(2)In the AS model group,multiple atherosclerotic lesions were seen on the aortic sinus.Histomorphometric analysis revealed that O-fiber and W-fiber significantly decreased atherosclerotic lesion size(P < 0.01),and the effect of oat fiber on the improvement of atherosclerotic plaque was better than that of wheat bran fiber(P < 0.05).(3)HE staining and CD36 immunohistochemical analysis showed that,compared with the AS group,the formation of foam cells in the hyperplastic aorta was significantly decreased in the O-fiber and W-fiber groups(P < 0.01).2.Effects of cereal fiber on hepatic lipid disorder in Apo E-/-mice(1)Serum TC and LDL-c concentrations in the O-fiber group were significantly decreased compared with the AS group(P < 0.05),and the cholesterol-lowering effect of O-fiber was better than W-fiber(P < 0.05).There was no significant difference in serum HDL-c and FFAs among the three groups(P > 0.05).(2)HE staining and Oil red O staining showed that hepatic steatosis was obvious in the mice of AS group.O-fiber and W-fiber alleviated hepatic lipid accumulation.(3)Liver homogenate TC levels were significantly decreased by O-fiber and W-fiber(P <0.05),liver homogenate FFAs levels were significantly decreased by O-fiber(P <0.05).Cereal fiber has no effect on liver homogenate TG levels in Apo E-/-mice(P > 0.05).(4)Compared with the AS group,O-fiber and W-fiber intervention significantly reduced the protein expressions of SREBP-1,FAS,and ACC(P < 0.01),and the protein expressions of FAS in W-fiber group was lower than that of O-fiber group(P < 0.01).Protein expressions of SREBP-2 were significantly reduced in the two cereal fiber diet groups than that in the AS group(P < 0.01).W-fiber could significantly increase the expression of SR-B1 in the liver,which was superior to O-fiber(P < 0.01).Compared with AS group,O-fiber and W-fiber significantly increased protein expression of LXR-?,ABCG1 and ABCG5(P < 0.01).O-fiber and W-fiber had no effect on the protein expression of ABCA1 and ABCG8 in the liver of Apo E-/-mice.3.Effects of cereal fiber on intestinal cholesterol metabolism in Apo E-/-mice(1)O-fiber significantly increased fecal short-chain fatty acids(SCFA)content(P < 0.05),and SCFA content in O-fiber group was higher than that in W-fiber group(P < 0.05).(2)Compared with AS group,O-fiber and W-fiber significantly increased the protein expression of Sar1 B in the intestine(P < 0.01),and O-fiber was superior to W-fiber(P < 0.01).O-fiber and W-fiber significantly decreased the protein expression of NPC1L1 in the intestine(P < 0.01),O-fiber and W-fiber had no effect on the protein expression of SR-B1 in the intestine.(3)Compared with AS group,O-fiber and W-fiber significantly decreased the protein expression of SREBP-1,FAS,and ACC in the intestine(P < 0.05),and there was a significant difference between O-fiber and W-fiber groups in the effect of reducing protein expression of FAS and ACC(P < 0.01).O-fiber significantly increased the protein expression of SREBP-2 and LDLR in the intestine(P < 0.05).O-fiber and W-fiber significantly increased the protein expression of PPAR-? in the intestine(P < 0.01).(4)Compared with AS group,O-fiber significantly increased the protein expressions of LXR-?,ABCA1,ABCG1 and ABCG8 in the intestine(P < 0.01),W-fiber significantly increased the protein expressions of LXR-?,ABCA1 and ABCG1(P <0.01),and O-fiber was more significant than W-fiber on the effects of the protein expression of ABCA1,ABCG1 and ABCG8(P < 0.01).O-fiber and W-fiber had no effect on the protein expression of ABCG5 in the intestine.4.Effects of cereal fiber on NLRP3 inflammasome pathway in Apo E-/-mice(1)Serum hs-CRP,IL-10 and IL-12p70 levels in the O-fiber and W-fiber groups were significantly decreased(P < 0.05).A downward trend was observed in the indexes of MCP-1,IFN-?,TNF-? and IL-6,but there was no significant difference between cereal fiber group and AS group.(2)Compared with AS group,O-fiber decreased the protein expression of NLRP3,ASC,caspase-1,IL-1? and IL-18 in the aorta of Apo E-/-mice(P < 0.05),while W-fiber only decreased the protein expression of caspase-1 and IL-18(P < 0.05).O-fiber and W-fiber decreased the protein expression of TNF-?,My D88,NF-?B and VACM-1 in NK-?B(TLR4 / My D88 / NF-?B)pathway in the aorta(P <0.01),the protein expression of TLR4 was down-regulated only by O-fiber(P <0.05).Conclusions:1.Cereal fiber reduced the accumulation of macrophages in the aorta and ameliorated atherosclerotic plaque development,and oat fiber is superior to wheat bran fiber on anti-atherosclerosis effect.2.Cereal fiber can significantly reduce the levels of serum TC,LDL-c and liver homogenate TC in Apo E-/-mice fed a high fat/cholesterol diet,alleviated hepatic lipid accumulation,and the effect of oat fiber on lowering serum TC and LDL-c level was better than that of wheat bran fiber.Cereal fiber can delay the occurance of AS by regulating the related protein expressions involved in lipid metabolism and cholesterol reverse transport,lowering serum cholesterol level and improving liver steatosis.3.Cereal fiber can improve AS by increasing the content of fecal SCFA of Apo E-/-mice.The mechanisms mainly include that cereal fiber can increase the protein expression of Sar1 B and inhibit the protein expression of NPC1L1,then reduce the intestinal cholesterol absorption,cereal fiber can down-regulate the key protein expressions involved in lipid metabolism and then reduce fat synthesis,cereal fiber can activate PPAR-? and LXR-?,which can effectively regulate the expression of reverse cholesterol-related protein and promote the reversal of intestinal cholesterol,and the effect of oat fiber is better than that of wheat bran fiber.In addition,oat fiber can also increase the protein expression of LDLR by activating SREBP-2,and promote the removal of intestinal cholesterol.4.Cereal fiber can ameliorate AS via attenuating chronic inflammatory response.Oat fiber ameliorated AS mainly by regulating NLRP3 inflammasome pathway and TLR4/My D88/NF-?B pathway,while wheat bran fiber only had effects on TLR4/My D88/NF-?B pathway.