Department of Entomology and Nematology, University of Florida, Gainesville, FL 32610, USA; Emerging Pathogens Institute, University of Florida, Gainesville, FL 32610, USA.
National Center for Natural Products Research, School of Pharmacy, University of Mississippi, Oxford, MS 38677, USA.
Pestic Biochem Physiol. 2023 Aug;194:105532. doi: 10.1016/j.pestbp.2023.105532. Epub 2023 Jul 13.
Inhibitors targeting the 4-hydroxyphenyl pyruvate dioxygenase (HPPD) enzyme are well established herbicides and HPPD is also a primary enzyme within the tyrosine metabolism pathway in hematophagous arthropods, which is an essential metaboilic pathway post-blood feeding to prevent tyrosine-mediated toxicity. The objective of this study was to characterize the toxicity of triketone, pyrazole, pyrazolone, isoxazole, and triazole herbicides that inhibit HPPD to blood-fed mosquitoes and ticks. Topical exposure of nitisinone to blood-fed Aedes aegypti yielded high toxicity with an LD of 3.81 ng/insect (95% CI: 3.09 to 4.67 ng; Hillslope: 0.97, r: 0.99), yet was non-toxic to non-blood fed (NBF) mosquitoes. The rank order of toxicity was nitisinone > tembotrione > pyrazoxyfen > tebuconazole > mesotrione against blood-fed Ae. Aegypti, but nitisinone was approximately 30-fold more toxic than other chemicals tested. We also assessed the toxicity of HPPD-inhibiting herbicides to the lone star tick, Amblyomma americanum and similarly, nitisinone was toxic to Am. americanum with a lethal time to kill 50% of subjects (LT) of 23 h at 10 μM. Knockdown of the gene encoding the HPPD enzyme was performed through RNA-interference led to significant mortality after blood feeding in both, Ae. aegypti and Am. americanum. Lastly, a fluorescence assay was developed to determine relative quantities of L-tyrosine in Ae. aegypti and Am. americanum treated with HPPD inhibitors. L-tyrosine levels correlated with toxicity with nitisinone exposure leading to increased tyrosine concentrations post-blood feeding. Taken together, these data support previous work suggesting HPPD-inhibitors represent a novel mode of toxicity to mosquitoes and ticks and may represent base scaffolds for development of novel insecticides specific for hematophagous arthropods.
靶向 4-羟苯基丙酮酸双加氧酶（HPPD）的抑制剂是一种成熟的除草剂，也是吸血节肢动物酪氨酸代谢途径中的主要酶，该途径是吸血后防止酪氨酸介导毒性的关键代谢途径。本研究的目的是描述抑制 HPPD 的三酮、吡唑、吡唑啉酮、异噁唑和三唑类除草剂对吸血蚊子和蜱的毒性。局部暴露于尼替西农（nitisinone）给吸血的埃及伊蚊（Aedes aegypti），其 LD 为 3.81ng/虫（95%置信区间：3.09 至 4.67ng；坡度：0.97，r：0.99），但对非吸血（NBF）蚊子无毒。对吸血埃及伊蚊的毒性排序为：尼替西农＞替唑隆＞吡唑氧芬＞戊唑醇＞唑酮草酯，但尼替西农比其他测试的化学物质毒性高约 30 倍。我们还评估了 HPPD 抑制剂除草剂对孤星蜱（Amblyomma americanum）的毒性，同样，尼替西农对孤星蜱有毒，其半数致死时间（LT）为 23 小时，浓度为 10μM。通过 RNA 干扰敲低编码 HPPD 酶的基因，导致吸血后埃及伊蚊和孤星蜱的死亡率显著增加。最后，开发了一种荧光测定法来确定 HPPD 抑制剂处理的埃及伊蚊和孤星蜱中 L-酪氨酸的相对量。L-酪氨酸水平与毒性相关，尼替西农暴露导致吸血后酪氨酸浓度增加。综上所述，这些数据支持之前的工作，表明 HPPD 抑制剂是蚊子和蜱虫的一种新的毒性模式，可能代表针对吸血节肢动物的新型杀虫剂的基础支架。
