du Rand Esther E, Pirk Christian W W, Nicolson Susan W, Apostolides Zeno
Department of Biochemistry, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa; Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
J Insect Physiol. 2017 Apr;98:14-22. doi: 10.1016/j.jinsphys.2016.10.017. Epub 2016 Nov 11.
Honey bees (Apis mellifera) are generalist pollinators that forage for nectar and pollen of a very large variety of plant species, exposing them to a diverse range of secondary metabolites produced as chemical defences against herbivory. Honey bees can tolerate high levels of many of these toxic compounds, including the alkaloid nicotine, in their diet without incurring apparent fitness costs. Very little is known about the underlying detoxification processes mediating this tolerance. We examined the metabolic fate of nicotine in newly emerged worker bees using radiolabeled nicotine and LC-MS/MS analysis to determine the kinetic distribution profile of nicotine as well as the absence or presence and identity of any nicotine-derived metabolites. Nicotine metabolism was extensive; virtually no unmetabolised nicotine were recovered from the rectum. The major metabolite found was 4-hydroxy-4-(3-pyridyl) butanoic acid, the end product of 2'C-oxidation of nicotine. It is the first time that 4-hydroxy-4-(3-pyridyl) butanoic acid has been identified in an insect as a catabolite of nicotine. Lower levels of cotinine, cotinine N-oxide, 3'hydroxy-cotinine, nicotine N-oxide and norcotinine were also detected. Our results demonstrated that formation of 4-hydroxy-4-(3-pyridyl) butanoic acid is quantitatively the most significant pathway of nicotine metabolism in honey bees and that the rapid excretion of unmetabolised nicotine does not contribute significantly to nicotine tolerance in honey bees. In nicotine-tolerant insects that do not rely on the rapid excretion of nicotine like the Lepidoptera, it is possible that the 2'C-oxidation of nicotine is the conserved metabolic pathway instead of the generally assumed 5'C-oxidation pathway.
蜜蜂（西方蜜蜂）是多食性传粉者，它们采集多种植物的花蜜和花粉，从而接触到植物作为抵御食草动物的化学防御而产生的各种次生代谢产物。蜜蜂能够在其饮食中耐受高水平的许多此类有毒化合物，包括生物碱尼古丁，而不会产生明显的健康成本。对于介导这种耐受性的潜在解毒过程，人们知之甚少。我们使用放射性标记的尼古丁和液相色谱 - 串联质谱分析，研究了新羽化的工蜂体内尼古丁的代谢命运，以确定尼古丁的动力学分布概况以及任何尼古丁衍生代谢产物的有无及其身份。尼古丁的代谢很广泛；几乎没有未代谢的尼古丁从直肠中回收。发现的主要代谢产物是4 - 羟基 - 4 -（3 - 吡啶基）丁酸，它是尼古丁2'-氧化的终产物。这是首次在昆虫中鉴定出4 - 羟基 - 4 -（3 - 吡啶基）丁酸是尼古丁的分解代谢产物。还检测到了较低水平的可替宁、可替宁N - 氧化物、3'-羟基可替宁、尼古丁N - 氧化物和去甲可替宁。我们的结果表明，4 - 羟基 - 4 -（3 - 吡啶基）丁酸的形成在数量上是蜜蜂体内尼古丁代谢最重要的途径，并且未代谢尼古丁的快速排泄对蜜蜂的尼古丁耐受性贡献不大。在不依赖尼古丁快速排泄的耐尼古丁昆虫（如鳞翅目昆虫）中，尼古丁的2'-氧化可能是保守的代谢途径，而不是通常认为的5'-氧化途径。
