Fernandez M L, Vergara-Jimenez M, Conde K, Behr T, Abdel-Fattah G
Department of Nutritional Sciences, University of Arizona, Tucson, USA.
Am J Clin Nutr. 1997 Mar;65(3):814-22. doi: 10.1093/ajcn/65.3.814.
Dietary soluble-fiber sources such as pectin, guar gum, or psyllium decrease plasma concentrations of low-density-lipoprotein (LDL) cholesterol in guinea pigs by distinct mechanisms, including increases in LDL apolipoprotein (apo) B turnover and/or decreases in LDL apo B flux (J Lipid Res 1995; 36:2394-404). The present studies were undertaken to test whether changes in the rates of very-low-density lipoprotein (VLDL) apo B secretion, VLDL conversion to LDL, and hepatic uptake of VLDL were related to the cholesterol-lowering actions of these soluble fibers. Guinea pigs were fed (by wt) 12.5% pectin, 12.5% guar gum, 7.5% psyllium, or a control diet containing cellulose as the fiber source. Plasma cholesterol concentrations were significantly lower in guinea pigs fed pectin, guar gum, and psyllium by 42%, 46%, and 35%, respectively (P < 0.001), compared with those animals fed the control diet, whereas plasma triacylglycerol concentrations were lower only with guar gum intake. The secretion rate of triacylglycerol, determined after Triton was injected to block VLDL catabolism, was not different among dietary treatment groups whereas the secretion rate of apo B was lower with pectin, guar gum, and psyllium intakes (P < 0.01). In addition, pectin, guar gum, and psyllium significantly altered the composition of newly secreted VLDLs by increasing the number of triacylglycerol and phospholipid molecules in the secreted lipoprotein, indicating the presence of larger nascent VLDLs. In contrast, the average particle diameter of mature VLDLs as determined by electron microscopy was smaller in the dietary soluble-fiber groups in the following order: pectin < psyllium < guar gum. Plasma lecithin-cholesteryl acyltransferase and cholesteryl ester transfer protein activities were lower with intake of pectin, guar gum, and psyllium (P < 0.01). Injection of radiolabeled lipoproteins indicated that pectin, guar gum, and psyllium intakes resulted in more rapid VLDL and LDL apo B turnover and lower LDL apo B flux in guinea pigs fed guar gum and psyllium. These results suggest that the secretion rate of apo B, compositional changes in lipoproteins occurring in the intravascular compartment, and up-regulation of LDL receptors-associated with faster LDL apo B turnover rates-are secondary metabolic responses induced by dietary fiber that contribute to the lowering of plasma cholesterol concentrations.
膳食中的可溶性纤维来源，如果胶、瓜尔豆胶或车前子壳，通过不同机制降低豚鼠血浆中低密度脂蛋白（LDL）胆固醇的浓度，这些机制包括增加LDL载脂蛋白（apo）B的周转率和/或降低LDL apo B的通量（《脂质研究杂志》1995年；36:2394 - 404）。本研究旨在测试极低密度脂蛋白（VLDL）apo B分泌速率、VLDL向LDL的转化以及肝脏对VLDL的摄取变化是否与这些可溶性纤维的降胆固醇作用有关。给豚鼠喂食（按重量计）12.5%的果胶、12.5%的瓜尔豆胶、7.5%的车前子壳或含有纤维素作为纤维来源的对照饮食。与喂食对照饮食的动物相比，喂食果胶、瓜尔豆胶和车前子壳的豚鼠血浆胆固醇浓度分别显著降低42%、46%和35%（P < 0.001），而仅瓜尔豆胶摄入会使血浆三酰甘油浓度降低。注射曲拉通以阻断VLDL分解代谢后测定的三酰甘油分泌速率在各饮食处理组之间没有差异，而果胶、瓜尔豆胶和车前子壳摄入时apo B的分泌速率较低（P < 0.01）。此外，果胶、瓜尔豆胶和车前子壳通过增加分泌的脂蛋白中三酰甘油和磷脂分子的数量，显著改变了新分泌的VLDL的组成，表明存在更大的新生VLDL。相比之下，通过电子显微镜测定的成熟VLDL的平均粒径在膳食可溶性纤维组中按以下顺序较小：果胶 < 车前子壳 < 瓜尔豆胶。摄入果胶、瓜尔豆胶和车前子壳时，血浆卵磷脂胆固醇酰基转移酶和胆固醇酯转移蛋白活性较低（P < 0.01）。注射放射性标记的脂蛋白表明，在喂食瓜尔豆胶和车前子壳的豚鼠中，摄入果胶、瓜尔豆胶和车前子壳会导致VLDL和LDL apo B周转更快，LDL apo B通量更低。这些结果表明，apo B的分泌速率、血管内脂蛋白成分的变化以及与更快的LDL apo B周转率相关的LDL受体上调是膳食纤维诱导的次级代谢反应，有助于降低血浆胆固醇浓度。
