Laboratoire d'Ecologie Alpine (LECA), Grenoble-Alpes University, Savoie Mont-Blanc University, CNRS, 38041, Grenoble, France.
Vector Control Product Evaluation Centre (VCPEC) Institut Pierre Richet (VCPEC IPR)/INSP, Bouaké, Côte d'Ivoire.
Malar J. 2023 Sep 4;22(1):256. doi: 10.1186/s12936-023-04673-5.
The widespread use of pyrethroid insecticides in Africa has led to the development of strong resistance in Anopheles mosquitoes. Introducing new active ingredients can contribute to overcome this phenomenon and ensure the effectiveness of vector control strategies. Transfluthrin is a polyfluorinated pyrethroid whose structural conformation was thought to prevent its metabolism by cytochrome P450 monooxygenases in malaria vectors, thus representing a potential alternative for managing P450-mediated resistance occurring in the field. In this study, a controlled selection was used to compare the dynamics of resistance between transfluthrin and the widely used pyrethroid deltamethrin in the mosquito Anopheles gambiae. Then, the associated molecular mechanisms were investigated using target-site mutation genotyping and RNA-seq.
A field-derived line of An. gambiae carrying resistance alleles at low frequencies was used as starting material for a controlled selection experiment. Adult females were selected across 33 generations with deltamethrin or transfluthrin, resulting in three distinct lines: the Delta-R line (selected with deltamethrin), the Transflu-R line (selected with transfluthrin) and the Tiassale-S line (maintained without selection). Deltamethrin and transfluthrin resistance levels were monitored in each selected line throughout the selection process, as well as the frequency of the L1014F kdr mutation. At generation 17, cross-resistance to other public health insecticides was investigated and transcriptomes were sequenced to compare gene transcription variations and polymorphisms associated with adaptation to each insecticide.
A rapid increase in resistance to deltamethrin and transfluthrin was observed throughout the selection process in each selected line in association with an increased frequency of the L1014F kdr mutation. Transcriptomic data support a broader response to transfluthrin selection as compared to deltamethrin selection. For instance, multiple detoxification enzymes and cuticle proteins were specifically over-transcribed in the Transflu-R line including the known pyrethroid metabolizers CYP6M2, CYP9K1 and CYP6AA1 together with other genes previously associated with resistance in An. gambiae.
This study confirms that recurrent exposure of adult mosquitoes to pyrethroids in a public health context can rapidly select for various resistance mechanisms. In particular, it indicates that in addition to target site mutations, the polyfluorinated pyrethroid transfluthrin can select for a broad metabolic response, which includes some P450s previously associated to resistance to classical pyrethroids. This unexpected finding highlights the need for an in-depth study on the adaptive response of mosquitoes to newly introduced active ingredients in order to effectively guide and support decision-making programmes in malaria control.
在非洲广泛使用拟除虫菊酯杀虫剂导致了疟蚊产生很强的抗药性。引入新的有效成分有助于克服这种现象，并确保病媒控制策略的有效性。四氟甲醚菊酯是一种多氟拟除虫菊酯，其结构构象被认为可以防止其被疟原虫载体中的细胞色素 P450 单加氧酶代谢，因此代表了管理现场发生的 P450 介导的抗性的潜在替代方法。在这项研究中，使用对照选择来比较转氟氯菊酯和广泛使用的拟除虫菊酯溴氰菊酯在疟蚊 Anopheles gambiae 中的抗性动态。然后，使用靶标突变基因分型和 RNA-seq 研究相关的分子机制。
使用携带低频率抗性等位基因的田间衍生的 An. gambiae 品系作为对照选择实验的起始材料。成年雌性经过 33 代的选择，用溴氰菊酯或转氟氯菊酯处理，产生了三个不同的品系：Delta-R 品系（用溴氰菊酯选择）、Transflu-R 品系（用转氟氯菊酯选择）和 Tiassale-S 品系（未经选择维持）。在整个选择过程中，监测每个选择品系中溴氰菊酯和转氟氯菊酯的抗性水平，以及 L1014F kdr 突变的频率。在第 17 代时，研究了对其他公共卫生杀虫剂的交叉抗性，并对转录组进行测序，以比较与适应每种杀虫剂相关的基因转录变化和多态性。
在每个选择品系中，随着 L1014F kdr 突变频率的增加，对溴氰菊酯和转氟氯菊酯的抗性迅速增加。转录组数据支持与溴氰菊酯选择相比，转氟氯菊酯选择引起更广泛的反应。例如，在 Transflu-R 品系中，包括已知的拟除虫菊酯代谢物 CYP6M2、CYP9K1 和 CYP6AA1 在内的多种解毒酶和角质层蛋白被特异性过度转录，以及与 An. gambiae 中的抗性相关的其他基因。
本研究证实，在公共卫生环境中，成年蚊子反复接触拟除虫菊酯可以快速选择各种抗性机制。特别是，它表明，除了靶标突变外，多氟拟除虫菊酯转氟氯菊酯还可以选择广泛的代谢反应，其中包括一些先前与经典拟除虫菊酯抗性相关的 P450。这一意外发现强调了需要深入研究蚊子对新引入的有效成分的适应性反应，以便有效地指导和支持疟疾控制决策计划。
