Department of Biology, Brandon University, 270-18th St., Brandon, Manitoba, Canada.
Vet Parasitol. 2009 Oct 28;165(1-2):96-108. doi: 10.1016/j.vetpar.2009.06.043. Epub 2009 Jul 8.
The avermectins and the milbemycins are structurally related classes of 16-membered macrocyclic lactones (ML) that have a broad spectrum of activity. Most studies on the mode of action of ML have used the avermectin, ivermectin (IVM). IVM activates glutamate-gated chloride channels that contain alpha-type subunits, resulting in a hyperpolarization of the neuronal membrane, leading to a flaccid paralysis. IVM kills Caenorhabditis elegans at therapeutic concentrations, making it a useful model to examine mechanisms of IVM toxicity and resistance. There have been suggestions that the milbemycins may exert effects that are different from the avermectins, however this hypothesis has been challenged. Using IVM and the milbemycin, moxidectin (MOX), we demonstrate that while the two drugs have some similar effects on C. elegans, there are also some differences in worm response. Following exogenous exposure to a gradient of IVM and MOX, ranging from 0 to 5000 nM, quantitative and qualitative differences in response to the two anthelmintic drugs were observed in the pharyngeal pump rate, larval development and motility of wild-type and glutamate-gated chloride channel (GluCl) subunit knockout strains of C. elegans. After exposure to equimolar drug concentrations, differences between the anthelmintic effects were observed in the motility phenotype in the wild-type, GluCl subunit knockout strains and multi-gene knockout strain of C. elegans that exhibits a marked reduction in IVM sensitivity; and transcription profiles of genes coding for GluCl subunits in both the wild-type and glc-2 knockout strain. The glc-2 deletion strain showed increased motility in response to 2.5nM MOX in the first 1.5h of exposure, compared with wild-type nematodes, whereas this strain showed little change in motility in response to IVM. The pharyngeal pump rate in the glc-2 deletion strain was sensitive to equimolar concentrations of IVM and MOX. The triple avr-14/avr-15/glc-1 knockout caused a loss of initial stimulation of motility seen in the wild-type, by 2.5 nM IVM, to a reduction in motility, whereas the response to MOX was little changed between this triple knockout strain and wild-type C. elegans. The results suggest that there are significant differences in the response of C. elegans to IVM and MOX. The product of the glc-2 gene may play a role in sensitivity to MOX, but not to IVM, while the products of avr-14, avr-15 and glc-1 may be important for the effects of IVM, but less so for MOX.
阿维菌素和米尔贝肟菌素是结构相关的 16 元大环内酯类（ML），具有广谱活性。大多数关于 ML 作用模式的研究都使用阿维菌素、伊维菌素（IVM）。IVM 激活含有α型亚基的谷氨酸门控氯通道，导致神经元膜超极化，导致弛缓性瘫痪。IVM 在治疗浓度下杀死秀丽隐杆线虫，使其成为研究 IVM 毒性和耐药性机制的有用模型。有人提出米尔贝肟菌素可能具有与阿维菌素不同的作用，但这一假设受到了挑战。我们使用 IVM 和米尔贝肟菌素，莫昔克丁（MOX），证明尽管这两种药物对秀丽隐杆线虫有一些相似的作用，但线虫的反应也存在一些差异。在暴露于从 0 到 5000 nM 的 IVM 和 MOX 梯度后，在对两种驱虫药的反应方面，在秀丽隐杆线虫的咽泵率、幼虫发育和运动方面观察到了定量和定性的差异，以及在野生型和谷氨酸门控氯通道（GluCl）亚基敲除的秀丽隐杆线虫菌株中观察到了定量和定性的差异。在暴露于等摩尔药物浓度后，在野生型、GluCl 亚基敲除菌株和多基因敲除菌株的运动表型中观察到驱虫效果的差异，后者对 IVM 的敏感性明显降低；以及编码 GluCl 亚基的基因在野生型和 glc-2 敲除菌株中的转录谱。与野生型线虫相比，在暴露于 2.5 nM MOX 的前 1.5 小时，glc-2 缺失菌株对 MOX 的反应表现出更高的运动性，而对 IVM 的运动性变化不大。glc-2 缺失菌株的咽泵率对 IVM 和 MOX 的等摩尔浓度敏感。avr-14/avr-15/glc-1 三重敲除菌株导致野生型对线虫运动的初始刺激减少，2.5 nM IVM 导致运动性降低，而 MOX 对该三重敲除菌株和野生型秀丽隐杆线虫的反应变化不大。结果表明，秀丽隐杆线虫对 IVM 和 MOX 的反应存在显著差异。glc-2 基因的产物可能在对线虫对 MOX 的敏感性中发挥作用，但对线虫对 IVM 的敏感性没有作用，而 avr-14、avr-15 和 glc-1 的产物可能对 IVM 的作用很重要，但对 MOX 的作用则不那么重要。
