A Comprehensive Review of the Current Knowledge of Chlorfenapyr: Synthesis, Mode of Action, Resistance, and Environmental Toxicology

Rational design and synthesis of new pyrrolone candidates as prospective insecticidal agents against Culex pipiens L. Larvae

As a result of its high reactivity, furan-2(3H)-one derivative 2 can be selected as a versatile and suitable candidate for building of novel nitrogen heterocyclic compounds. Consequently, furan-2(3H)-one derivative 2 and some nitrogen nucleophiles were utilized as starting materials for the formation of new pyridazinone and pyrrolone derivatives bearing naphthalene moiety. The continuous buildup of insecticide resistance is the main obstacle facing pest control measures. Pyrrole-based insecticides are a favourable choice due to their unique mode of action and no cross-resistance with traditional neurotoxic insecticides. The larvicidal activities of pyrrolone derivatives were assessed against field and laboratory strains of Culex pipiens larvae in comparison with chlorfenapyr (pyrrole insecticide). Compounds 17 (21.05 µg/mL) > 9 (22.81 µg/mL) > 15 (24.39 µg/mL) > 10 (26.76 µg/mL) > 16 (32.09 µg/mL) were most effective against lab strain of C. pipiens larvae relative to chlorfenapyr (25.43 µg/mL). While in field strain, 17 and 15 were the most toxic compounds followed by 9 > 10 > 16 > 2 with LC50 of 9.87, 10.76, 11.52, 12.68, 15.32 and 18.37 µg/mL, respectively, compared with chlorfenapyr with 14.03 µg/mL. The cytochrome P-450 monooxygenase activities were significantly increased in treated larvae of lab and field strains relative to untreated. The great variations in toxicity of the synthesized compounds were interpreted by structure-activity relationship study. The pyrrolone derivatives are effective against field and insecticide-resistant strains. Therefore, they are considered promising compounds to be integrated into pest management programs.

Substrate promiscuity of key resistance P450s confers clothianidin resistance while increasing chlorfenapyr potency in malaria vectors

Novel insecticides were recently introduced to counter pyrethroid resistance threats in African malaria vectors. To prolong their effectiveness, potential cross-resistance from promiscuous pyrethroid metabolic resistance mechanisms must be elucidated. Here, we demonstrate that the duplicated P450s CYP6P9a/-b, proficient pyrethroid metabolizers, reduce neonicotinoid efficacy in Anopheles funestus while enhancing the potency of chlorfenapyr. Transgenic expression of CYP6P9a/-b in Drosophila confirmed that flies expressing both genes were significantly more resistant to neonicotinoids than controls, whereas the contrasting pattern was observed for chlorfenapyr. This result was also confirmed by RNAi knockdown experiments. In vitro expression of recombinant CYP6P9a and metabolism assays established that it significantly depletes both clothianidin and chlorfenapyr, with metabolism of chlorfenapyr producing the insecticidally active intermediate metabolite tralopyril. This study highlights the risk of cross-resistance between pyrethroid and neonicotinoid and reveals that chlorfenapyr-based control interventions such as Interceptor G2 could remain efficient against some P450-based resistant mosquitoes.

The P450-Monooxygenase Activity and CYP6D1 Expression in the Chlorfenapyr-Resistant Strain of Musca domestica L

The house fly Musca domestica L. is one of the most common insects of veterinary and medical importance worldwide; its ability to develop resistance to a large number of insecticides is well known. Many studies support the involvement of cytochrome P-450-dependent monooxygenases (P450) in the development of resistance to pyrethroids, neonicotinoids, carbamates, and organophosphates among insects. In this paper, the monooxygenase activity and expression level of CYP6D1 were studied for the first time in a chlorfenapyr-resistant strain of house fly. Our studies demonstrated that P450 activity in adults of the susceptible strain (Lab TY) and chlorfenapyr-resistant strain (ChlA) was 1.56-4.05-fold higher than that in larvae. In females of the Lab TY and ChlA strains, this activity was 1.53- and 1.57-fold higher, respectively (p < 0.05), than that in males, and in contrast, the expression level of CYP6D1 was 21- and 8-fold lower, respectively. The monooxygenase activity did not vary between larvae of the susceptible strain Lab TY and the chlorfenapyr-resistant strain ChlA. Activity in females and males of the ChlA strain exceeded that in the Lab TY strain specimens by 1.54 (p = 0.08) and 1.83 (p < 0.05) times, respectively, with the same level of CYP6D1 expression. PCR-RFLP analysis revealed a previously undescribed mutation in the promoter region of the CYP6D1 gene in adults of the Lab TY and ChlA strains, and it did not affect the gene expression level. The obtained results show that the development of resistance to chlorfenapyr in M. domestica is accompanied by an increase in P450-monooxygenase activity without changes in CYP6D1 expression.

Multifaceted Effects of Subchronic Exposure to Chlorfenapyr in Mice: Implications from Serum Metabolomics, Hepatic Oxidative Stress, and Intestinal Homeostasis

As chlorfenapyr is a commonly used insecticide in agriculture, the health risks of subchronic exposure to chlorfenapyr remained unclear. This study aimed to extensively probe the health risks from subchronic exposure to chlorfenapyr at the NOAEL and 10-fold NOAEL dose in mice. Through pathological and biochemical examinations, the body metabolism, hepatic toxicity, and intestinal homeostasis were systematically assessed. After 12 weeks, a 10-fold NOAEL dose of chlorfenapyr resulted in weight reduction, increased daily food intake, and blood lipid abnormalities. Concurrently, this dosage induced hepatotoxicity and amplified oxidative stress in hepatocytes, a finding further supported in HepG2 cells. Moreover, chlorfenapyr resulted in intestinal inflammation, evidenced by increased inflammatory factors (IL-17a, IL-10, IL-1β, IL-6, IL-22), disrupted immune cells (RORγt, Foxp3), and compromised intestinal barriers (ZO-1 and occludin). By contrast, the NOAEL dose presented less toxicity in most evaluations. Serum metabolomic analyses unveiled widespread disruptions in pathways related to hepatotoxicity and intestinal inflammation, including NF-κB signaling, Th cell differentiation, and bile acid metabolism. Microbiomic analysis showed an increase in Lactobacillus, a decrease in Muribaculaceae, and diminished anti-inflammatory microbes, which further propelled the inflammatory response and leaded to intestinal inflammation. These findings revealed the molecular mechanisms underlying chlorfenapyr-induced hepatotoxicity and intestinal inflammation, highlighting the significant role of the gut microbiota.

Goethite and Hematite Nucleation and Growth from Ferrihydrite: Effects of Oxyanion Surface Complexes

The presence of oxyanions, such as nitrate (NO3-) and phosphate (PO43-), regulates the nucleation and growth of goethite (Gt) and hematite (Hm) during the transformation of ferrihydrite (Fh). Our previous studies showed that oxyanion surface complexes control the rate and pathway of Fh transformation to Gt and Hm. However, how oxyanion surface complexes control the mechanism of Gt and Hm nucleation and growth during the Fh transformation is still unclear. We used synchrotron scattering methods and cryogenic transmission electron microscopy to investigate the effects of NO3- outer-sphere complexes and PO43- inner-sphere complexes on the mechanism of Gt and Hm formation from Fh. Our TEM results indicated that Gt particles form through a two-step model in which Fh particles first transform to Gt nanoparticles and then crystallographically align and grow to larger particles by oriented attachment (OA). In contrast, for the formation of Hm, imaging shows that Fh particles first aggregate and then transform to Hm through interface nucleation. This is consistent with our X-ray scattering results, which demonstrate that NO3- outer-sphere and PO43- inner-sphere complexes promote the formation of Gt and Hm, respectively. These results have implications for understanding the coupled interactions of oxyanions and iron oxy-hydroxides in Earth-surface environments.

Time of exposure and assessment influence the mortality induced by insecticides against metabolic resistant mosquitoes

BACKGROUND

Increasing metabolic resistance in malaria vector mosquitoes resulted in the development of insecticide-treated nets (ITNs) with active ingredients (AI) that target them. Bioassays that accurately measure the mortality induced by these AIs on ITNs are needed. Mosquito metabolic enzyme expression follows a circadian rhythm. Thus, this study assessed (i) influence of the time of day of mosquito exposure and (ii) timing of assessment of mortality post exposure (24 and 72 h) to ITNs against vectors that are susceptible to pyrethroids and those with metabolic and knockdown resistance mechanisms.

METHODS

Two cone bioassay experiments were conducted following World Health Organization (WHO) guidelines. Firstly, on ITNs incorporated with 2 g AI/kg of deltamethrin (DM) alone, or combined with 8 g AI/kg piperonyl butoxide (PBO) synergist, during the day (9:00-14:00 h) and repeated in the evening (18:00-20:00 h). This was followed by a confirmatory experiment during the afternoon (12:00-14:00 h) and repeated in the night (22:00-24:00 h) using mosquitoes unexposed or pre-exposed to PBO for 1 h before exposure to DM ITNs. Each net piece was tested with a minimum of eight cones per time (N = 24). The outcome was mortality after 24 h (M24) or 72 h (M72) of holding.

RESULTS

The cone bioassays performed using metabolic resistant mosquitoes during the evening showed significantly lower M24 than those performed in the day for DM: odds ratio (OR) 0.14 [95% confidence interval (CI) 0.06-0.30, p < 0.0001] and DM PBO [OR 0.29 (95% CI 0.18-0.49, p < 0.0001). M72 was higher than M24 for metabolic resistant mosquitoes exposed to DM [OR 1.44 (95% CI 1.09-1.88), p = 0.009] and DM PBO [OR 1.82 (95% CI 1.42-2.34), p < 0.0001]. An influence of hour of experiment and time of assessment was not observed for mosquitoes that had knockdown resistance or that were pyrethroid-susceptible.

CONCLUSIONS

Time of day of experiment and hour of assessment of delayed mortality after exposure of mosquitoes are important considerations in evaluating insecticides that interact with mosquito metabolism to counter metabolic resistant mosquitoes. This is important when evaluating field-aged ITNs that may have lower concentrations of AI.

Delayed death of a child from chlorfenapyr poisoning: A case report and literature review

This was the first article reported a fatal case of chlorfenapyr poisoning in a child, and the typical symptoms before death include high fever, severe sweating, coma, and limb stiffness, and elevation of myocardial enzymes and myoglobin; neurological symptoms tend to appear earlier in children than in adults.

Chlorfenapyr poisoning: mechanisms, clinical presentations, and treatment strategies

BACKGROUND

Chlorfenapyr is used to kill insects that are resistant to organophosphorus insecticides. Chlorfenapyr poisoning has a high mortality rate and is difficult to treat. This article aims to review the mechanisms, clinical presentations, and treatment strategies for chlorfenapyr poisoning.

DATA RESOURCES

We conducted a review of the literature using PubMed, Web of Science, and SpringerLink from their beginnings to the end of October 2023. The inclusion criteria were systematic reviews, clinical guidelines, retrospective studies, and case reports on chlorfenapyr poisoning that focused on its mechanisms, clinical presentations, and treatment strategies. The references in the included studies were also examined to identify additional sources.

RESULTS

We included 57 studies in this review. Chlorfenapyr can be degraded into tralopyril, which is more toxic and reduces energy production by inhibiting the conversion of adenosine diphosphate to adenosine triphosphate. High fever and altered mental status are characteristic clinical presentations of chlorfenapyr poisoning. Once it occurs, respiratory failure occurs immediately, ultimately leading to cardiac arrest and death. Chlorfenapyr poisoning is difficult to treat, and there is no specific antidote.

CONCLUSION

Chlorfenapyr is a new pyrrole pesticide. Although it has been identified as a moderately toxic pesticide by the World Health Organization (WHO), the mortality rate of poisoned patients is extremely high. There is no specific antidote for chlorfenapyr poisoning. Therefore, based on the literature review, future efforts to explore rapid and effective detoxification methods, reconstitute intracellular oxidative phosphorylation couplings, identify early biomarkers of chlorfenapyr poisoning, and block the conversion of chlorfenapyr to tralopyril may be helpful for emergency physicians in the diagnosis and treatment of this disease.