Hartmann T, Theuring C, Beuerle T, Bernays E A, Singer M S
Institut für Pharmazeutische Biologie der Technischen Universität Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany.
Insect Biochem Mol Biol. 2005 Oct;35(10):1083-99. doi: 10.1016/j.ibmb.2005.05.011.
The polyphagous arctiid Grammia geneura appears well adapted to utilize for its protection plant pyrrolizidine alkaloids of almost all known structural types. Plant-acquired alkaloids that are maintained through all life-stages include various classes of macrocyclic diesters (typically occurring in the Asteraceae tribe Senecioneae and Fabaceae), macrocyclic triesters (Apocynaceae) and open-chain esters of the lycopsamine type (Asteraceae tribe Eupatorieae, Boraginaceae and Apocynaceae). As in other arctiids, all sequestered and processed pyrrolizidine alkaloids are maintained as non-toxic N-oxides. The only type of pyrrolizidine alkaloids that is neither sequestered nor metabolized are the pro-toxic otonecine-derivatives, e.g. the senecionine analog senkirkine that cannot be detoxified by N-oxidation. In its sequestration behavior, G. geneura resembles the previously studied highly polyphagous Estigmene acrea. Both arctiids are adapted to exploit pyrrolizidine alkaloid-containing plants as "drug sources". However, unlike E. acrea, G. geneura is not known to synthesize the pyrrolizidine-derived male courtship pheromone, hydroxydanaidal, and differs distinctly in its metabolic processing of the plant-acquired alkaloids. Necine bases obtained from plant acquired pyrrolizidine alkaloids are re-esterified yielding two distinct classes of insect-specific ester alkaloids, the creatonotines, also present in E. acrea, and the callimorphines, missing in E. acrea. The creatonotines are preferentially found in pupae; in adults they are largely replaced by the callimorphines. Before eclosion the creatonotines are apparently converted into the callimorphines by trans-esterification. Open-chain ester alkaloids such as the platynecine ester sarracine and the orchid alkaloid phalaenopsine, that do not possess the unique necic acid moiety of the lycopsamine type, are sequestered by larvae but they need to be converted into the respective creatonotines and callimorphines by trans-esterification in order to be transferred to the adult stage. In the case of the orchid alkaloids, evidence is presented that during this processing the necine base (trachelanthamidine) is converted into its 7-(R)-hydroxy derivative (turneforcidine), indicating the ability of G. geneura to introduce a hydroxyl group at C-7 of a necine base. The creatonotines and callimorphines display a striking similarity to plant necine monoesters of the lycopsamine type to which G. geneura is well adapted. The possible function of insect-specific trans-esterification in the acquisition of necine bases derived from plant acquired alkaloids, especially from those that cannot be maintained through all life-stages, is discussed.
多食性灯蛾科昆虫Grammia geneura似乎很好地适应了利用几乎所有已知结构类型的植物吡咯里西啶生物碱来进行自我保护。在其整个生命周期中都能保留的从植物中获取的生物碱包括各类大环二酯（通常存在于菊科千里光族和豆科植物中）、大环三酯（夹竹桃科）以及lycopsamine型的开链酯（菊科泽兰族、紫草科和夹竹桃科）。与其他灯蛾科昆虫一样，所有被隔离和处理过的吡咯里西啶生物碱都以无毒的N-氧化物形式保留。唯一既不被隔离也不被代谢的吡咯里西啶生物碱类型是具有前体毒性的奥托奈辛衍生物，例如不能通过N-氧化解毒的千里光宁类似物senkirkine。在隔离行为方面，G. geneura类似于之前研究过的高度多食性的黄猩猩灯蛾（Estigmene acrea）。这两种灯蛾科昆虫都适应利用含吡咯里西啶生物碱的植物作为“药物来源”。然而，与黄猩猩灯蛾不同的是，G. geneura并不合成由吡咯里西啶衍生的雄性求偶信息素羟基丹奈德，并且在对从植物中获取的生物碱的代谢处理上也有明显差异。从植物中获取的吡咯里西啶生物碱得到的奈西碱会重新酯化，产生两类不同的昆虫特异性酯生物碱，即同样存在于黄猩猩灯蛾中的克雷托诺碱，以及黄猩猩灯蛾中不存在的卡里莫芬碱。克雷托诺碱在蛹中含量较高；在成虫中，它们大部分被卡里莫芬碱取代。羽化前，克雷托诺碱显然通过酯交换反应转化为卡里莫芬碱。开链酯生物碱，如不具有lycopsamine型独特奈西酸部分的普拉替奈辛酯萨拉辛和兰花生物碱蝴蝶兰碱，会被幼虫隔离，但它们需要通过酯交换反应转化为相应克雷托诺碱和卡里莫芬碱才能转移到成虫阶段。对于兰花生物碱，有证据表明在这个过程中奈西碱（气管氨茴胺）会转化为其7-(R)-羟基衍生物（土麦冬碱），这表明G. geneura有能力在奈西碱的C-7位引入一个羟基。克雷托诺碱和卡里莫芬碱与G. geneura非常适应的lycopsamine型植物奈西单酯有显著相似性。本文讨论了昆虫特异性酯交换反应在获取源自植物生物碱的奈西碱，特别是那些不能在整个生命周期中保留的奈西碱方面可能发挥的作用。
