Department of Entomology, Texas A&M University, TAMU 2475, College Station, TX 77843, USA.
Insect Biochem Mol Biol. 2013 Jul;43(7):580-7. doi: 10.1016/j.ibmb.2013.03.012. Epub 2013 Apr 6.
Insects cannot synthesize sterols de novo, so they typically require a dietary source. Cholesterol is the dominant sterol in most insects, but because plants contain only small amounts of cholesterol, plant-feeding insects generate most of their cholesterol by metabolizing plant sterols. Plants almost always contain mixtures of different sterols, but some are not readily metabolized to cholesterol. Here we explore, in two separate experiments, how dietary phytosterols and phytosteroids, in different mixtures, ratios, and amounts, affect insect herbivore sterol/steroid metabolism and absorption; we use two caterpillars species - one a generalist (Heliothis virescens), the other a specialist (Manduca sexta). In our first experiment caterpillars were reared on two tobacco lines - one expressing a typical phystosterol profile, the other expressing high amounts/ratios of stanols and 3-ketosteroids. Caterpillars reared on the control tobacco contained mostly cholesterol, but those reared on the modified tobacco had reduced amounts of cholesterol, and lower total sterol/steroid body profiles. In our second experiment, caterpillars were reared on artificial diets containing known amounts of cholesterol, stigmasterol, cholestanol and/or cholestanone, either singly or in various combinations and ratios. Cholesterol and stigmasterol-reared moths were mostly cholesterol, while cholestanol-reared moths were mostly cholestanol. Moth tissue cholesterol concentration tended to decrease as the ratio of dietary cholestanol and/or cholestanone increased. In both moths cholestanone was metabolized into cholestanol and epicholestanol. Interestingly, M. sexta generated much more cholestanol than epicholestanol, while H. virescens did the opposite. Finally, total tissue steroid levels were significantly reduced in moths reared on diets containing very high levels of cholestanol. We discuss how dietary sterol/steroid structural differences are important with respect to sterol/steroid metabolism and uptake, including species-specific differences.
昆虫自身不能从头合成固醇，因此它们通常需要从饮食中获取。胆固醇是大多数昆虫中的主要固醇，但由于植物中胆固醇含量很少，所以以植物为食的昆虫通过代谢植物固醇来产生大部分胆固醇。植物几乎总是含有不同固醇的混合物，但有些则不易转化为胆固醇。在这里，我们通过两个独立的实验来探索不同比例和含量的饮食性植物固醇和植物甾醇在不同混合物中的存在，会如何影响昆虫食草动物的固醇/甾醇代谢和吸收；我们使用了两种毛毛虫物种——一种是杂食性的（Heliothis virescens），另一种是专食性的（Manduca sexta）。在我们的第一个实验中，毛毛虫在两种烟草品系上被饲养——一种表达典型的植物固醇谱，另一种表达高量/高比例的甾醇和 3-酮固醇。在对照烟草上饲养的毛毛虫体内主要含有胆固醇，但在改良烟草上饲养的毛毛虫体内胆固醇含量降低，总固醇/甾醇的体谱也降低。在我们的第二个实验中，毛毛虫在含有已知量胆固醇、豆甾醇、胆甾烷醇和/或胆甾烷酮的人工饮食中被饲养，这些固醇可以单独或以不同的组合和比例存在。用胆固醇和豆甾醇饲养的蛾体内主要是胆固醇，而用胆甾烷醇饲养的蛾体内主要是胆甾烷醇。随着饮食中胆甾烷醇和/或胆甾烷酮比例的增加，蛾体内组织胆固醇浓度有下降的趋势。在两种蛾体内，胆甾烷酮都被代谢为胆甾烷醇和表胆甾烷醇。有趣的是，M. sexta 产生的胆甾烷醇比表胆甾烷醇多得多，而 H. virescens 则相反。最后，在以含有高浓度胆甾烷醇的饮食中饲养的蛾体内，总组织类固醇水平显著降低。我们讨论了饮食固醇/甾醇结构差异在固醇/甾醇代谢和吸收方面的重要性，包括物种特异性差异。
