Department of Medicine, University of California - San Diego, La Jolla, CA, USA.
BMC Evol Biol. 2010 May 6;10:133. doi: 10.1186/1471-2148-10-133.
Bile salts are the major end-metabolites of cholesterol and are also important in lipid and protein digestion and in influencing the intestinal microflora. We greatly extend prior surveys of bile salt diversity in both reptiles and mammals, including analysis of 8,000 year old human coprolites and coprolites from the extinct Shasta ground sloth (Nothrotherium shastense).
While there is significant variation of bile salts across species, bile salt profiles are generally stable within families and often within orders of reptiles and mammals, and do not directly correlate with differences in diet. The variation of bile salts generally accords with current molecular phylogenies of reptiles and mammals, including more recent groupings of squamate reptiles. For mammals, the most unusual finding was that the Paenungulates (elephants, manatees, and the rock hyrax) have a very different bile salt profile from the Rufous sengi and South American aardvark, two other mammals classified with Paenungulates in the cohort Afrotheria in molecular phylogenies. Analyses of the approximately 8,000 year old human coprolites yielded a bile salt profile very similar to that found in modern human feces. Analysis of the Shasta ground sloth coprolites (approximately 12,000 years old) showed the predominant presence of glycine-conjugated bile acids, similar to analyses of bile and feces of living sloths, in addition to a complex mixture of plant sterols and stanols expected from an herbivorous diet.
The bile salt synthetic pathway has become longer and more complex throughout vertebrate evolution, with some bile salt modifications only found within single groups such as marsupials. Analysis of the evolution of bile salt structures in different species provides a potentially rich model system for the evolution of a complex biochemical pathway in vertebrates. Our results also demonstrate the stability of bile salts in coprolites preserved in arid climates, suggesting that bile salt analysis may have utility in selected paleontological research.
胆盐是胆固醇的主要终代谢产物，在脂质和蛋白质消化以及影响肠道微生物群方面也很重要。我们极大地扩展了先前对爬行动物和哺乳动物中胆盐多样性的调查，包括对 8000 年前人类粪便化石和已灭绝的沙斯塔地懒（Nothrotherium shastense）粪便化石的分析。
虽然不同物种之间的胆盐存在显著差异，但胆盐谱通常在科内稳定，并且在爬行动物和哺乳动物的目内通常也稳定，并且与饮食差异没有直接相关性。胆盐的变化通常与爬行动物和哺乳动物的现有分子系统发育一致，包括最近对有鳞目爬行动物的分组。对于哺乳动物，最不寻常的发现是，Paenungulates（大象、海牛和岩蹄兔）的胆盐谱与 Rufous sengis 和南美土豚非常不同，这两种哺乳动物在分子系统发育中与 Paenungulates 一起被归类为 Afrotheria 目。对大约 8000 年前人类粪便化石的分析得出的胆盐谱与现代人类粪便中发现的胆盐谱非常相似。对沙斯塔地懒粪便化石（约 12000 年前）的分析表明，甘氨酸结合胆酸的存在为主，与生活在陆地上的树懒的胆汁和粪便分析相似，此外还有预期的来自草食性饮食的复杂植物甾醇和甾烷混合物。
在脊椎动物进化过程中，胆盐合成途径变得更长且更复杂，一些胆盐修饰仅在单一群体中发现，如有袋动物。不同物种中胆盐结构的进化分析为脊椎动物中复杂生化途径的进化提供了一个潜在的丰富模型系统。我们的研究结果还表明，在干旱气候中保存的粪便化石中的胆盐是稳定的，这表明胆盐分析可能在某些古生物学研究中具有实用价值。
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