| Chitosan, a cation polysaccharide, has exhibited marked hypolipidemic effect, which attracts much attention in the world. However, the physicochemical properties of chitosans vary with the reaction conditions and materials, and then affect the physiological effects. Moreover, the hypolipidemic mechanism is still unclear although it has been provided as a weight-loss product. In this study, a series of chitosans with different properties were prepared and chosen in vitro and in vivo, then one with the best hypolipidemic effect was used to study its mechanism, which will be of great significance for the utilization and pharmacological investigation of chitosan.Chitosans with different degree of deacetylation (DD), molecular weight (Mw) and particle size were prepared by alkali fusion, then their binding capacities with fat, cholesterol and bile salts were studied in the conditions simulated human digestive tract and their hypocholesterolemic effects were also tested in rats. The results showed that the fat-binding capacities of chitosans strengthened with the increment of DD or Mw; the range of bile salt-binding capacities was 1.75~7.75 mg/g and the capacities strengthened with the Mw; particle size was the major factor influencing the cholesterol-binding capacity of chitosan and flake form showed the worst binding capacity; among 73%, 81% and 90% deacetylated chitosans, the last one could more effectively suppress body weight gain, and significantly reduce serum TC, LDL-C and elevate HDL-C level; molecular weight of chitosan had greater influence on the weight-loss effect compared with DD, and chitosan with higher Mw more significantly reduced feed efficiency and body weight gain, and plasma TG level.The distribution of chitosan in the tissues and plasma was studied. The determination method of FITC-CIS in the plasma and tissues was established, and the concentration in the digestive tract and the excretion in the feces and urine at the different time were observed following oral-administration of FITC-CIS in mice. The results showed that FITC-CIS was distributed mainly in the liver, kidney and muscle, the concentration in the liver was highest after1 h and that in the kidney was highest at the other time; in the stomach, the concentration of chitosan decreased with the time past by and fat in the diet was adsorbed by chitosan; the highest concentration was at 1 h and 2 h respectively in the small and large intestine; time with highest concentration in the feces or urine was corresponding with that in the large intestine or kidney, respectively; in the feces, the excretion of chitosan was most at 2.5~5 h and chitosan appears in the original form; in the urine, chitosan was excreted most at 6~12 h and degradated partially. The results proved directly that chitosan could bind fat in the diet in the digestive tract and then excrete with feces, and a portion of chitosan would be degradated in the body and regulate lipid metabolism.Chitosan with the best hypolipidemic effect was fed to rats accompanied with high-fat diet at the beginning and after the hyperlipemia to test the prevention and improvement effect. The results showed that compared with rats fed high-fat control diets, chitosan exhibited marked hypolipidemic effect, the body fat and liver index reduced significantly, and fatty liver symptom relieved; serum TG, TC and LDL-C concentrations reduced and HDL-C elevated significantly; liver TC and TG concentrations also lowered significantly; rats receiving chitosan had more excretion of fecal fat and cholesterol than those fed high-fat control diet, and the fatty acid composition in the fecal fat was the same as that in the diet, which indicated chitosan could reduce the absorption of fat in the diet; liver HL and LPL activities increased significantly, which indicated chitosan could regulate the lipase activity; chitosan could not only prevent the hyperlipemia induced by long term-administered high-fat diet but also relieve serum lipid level and liver fat accumulation in hyperlipemia rats; compared with cholestyramine which is a hypocholesterolemic medicine, chitosan with the same addition had worse effect, but it was safe and had no side effects.The molecular regulation of chitosan on several proteins correlated with lipid metabolism in the liver of rat was studied. The results showed that chitosan could significantly up-regulate LDL-R and PPARαmRNA level, moderately up-regulate LCAT and CYP7A1 mRNA level and down-regulate HMG CoA reducase mRNA level, which indicated chitosan could regulate the dynamic balance of cholesterol metabolism in the molecular level and then exert the hypolipidemic effect.The anti-oxidation activity of chitosan was studied in vitro and in vivo. The results showed that chitosan at an addition of 0.02% had anti-oxidation effect on the lard and crude rape oil, but the activity was worse than ascorbic acid, and when the addition increased, chitosan and ascorbic acid had similar activity; chitosan could significantly reduce serum FFA and MDA concentrations and elevate SOD, CAT and GSH-PX activities which were major anti-oxidation enzymes in the body, which indicated that chitosan regulated the anti-oxidation enzyme activities and then reduced the lipid peroxidization.In this study, chitosan with best hypolipidemic activity was chosen; the determination method of a novel fluorescence labeled chitosan in the plasma and tissues was established; the hypolipidemic mechanism of chitosan was elucidated on the mRNA expression of proteins correlated with lipid metabolism, the distribution and excretion of chitosan in mice, the reduction of lipid peroxidization and fat-binding activity in vitro.
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