▪ Abstract The synthesis and excretion of bile acids comprise the major pathway of cholesterol catabolism in mammals. Synthesis provides a direct means of converting cholesterol, which is both hydrophobic and insoluble, into a water-soluble and readily excreted molecule, the bile acid. The biosynthetic steps that accomplish this transformation also confer detergent properties to the bile acid, which are exploited by the body to facilitate the secretion of cholesterol from the liver. This role in the elimination of cholesterol is counterbalanced by the ability of bile acids to solubilize dietary cholesterol and essential nutrients and to promote their delivery to the liver. The synthesis of a full complement of bile acids requires 17 enzymes. The expression of selected enzymes in the pathway is tightly regulated by nuclear hormone receptors and other transcription factors, which ensure a constant supply of bile acids in an ever changing metabolic environment. Inherited mutations that impair bile acid synthesis cause a spectrum of human disease; this ranges from liver failure in early childhood to progressive neuropathy in adults.
▪ 摘要:在哺乳动物体内,
胆汁酸的合成和排泄构成了
胆固醇分解的主要途径。合成提供了一种将既疏
水又不溶于
水的
胆固醇直接转化为
水溶性且容易排泄的分子——
胆汁酸的直接方法。完成这种转化的
生物合成步骤也赋予了
胆汁酸的清洁剂特性,这些特性被机体利用来促进从肝脏排泄
胆固醇。这种在
胆固醇排泄中的作用被
胆汁酸溶解膳食
胆固醇和必需营养素以及促进它们传递到肝脏的能力所平衡。合成完整的
胆汁酸需要17种酶。途径中的选择性酶的表达受到核激素受体和其他转录因子的严格调控,这些因子确保在不断变化的代谢环境中始终有足够的
胆汁酸供应。遗传突变会影响
胆汁酸的合成,导致一系列人类疾病,从儿童早期的肝衰竭到成年人的渐进性神经病变。