Phenylpyrazole insecticides are a class of chemically-related broad-spectrum insecticides. [1] The chemical structures of these insecticides are characterized by a central pyrazole ring with a phenyl group attached to one of the nitrogen atoms of the pyrazole.
Phenylpyrazole insecticides were developed in response to increasing pesticide resistance to other chemicals. Now, along with neonicotinoids, they are some of the most widely-used pesticides. [1]
Phenylpyrazole insecticides function by blocking GABA-gated chloride channels in insects (IRAC group 2B). [1] Mammals do not have this type of chloride channel, making them much less susceptible to its effects. However, they do have the capacity to disrupt epithelial cells in the human intestine and adversely impact human health. [2]
Examples include:
Bifenthrin is a pyrethroid insecticide. It is widely used against ant infestations.
Abamectin (also called avermectin B1) is a widely used insecticide and anthelmintic. Abamectin, is a member of the avermectin family and is a natural fermentation product of soil dwelling actinomycete Streptomyces avermitilis. Abamectin differs from ivermectin, the popular member of the avermectin family, by a double bond between carbons 22 and 25. Fermentation of Streptomyces avermitilis yields eight closely related avermectin homologs, with the B1a and B1b forms comprising the majority of the fermentation. The non-proprietary name, abamectin, refers to a mixture of B1a (~80%) and B1b (~20%). Out of all the avermectins, abamectin is the only one that is used both in agriculture and pharmaceuticals.
Picrotoxin, also known as cocculin, is a poisonous crystalline plant compound. It was first isolated by the French pharmacist and chemist Pierre François Guillaume Boullay (1777–1869) in 1812. The name "picrotoxin" is a combination of the Greek words "picros" (bitter) and "toxicon" (poison). A mixture of two different compounds, picrotoxin occurs naturally in the fruit of the Anamirta cocculus plant, although it can also be synthesized chemically.
Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds containing at least one covalently bonded atom of chlorine. The chloroalkane class includes common examples. The wide structural variety and divergent chemical properties of organochlorides lead to a broad range of names, applications, and properties. Organochlorine compounds have wide use in many applications, though some are of profound environmental concern, with TCDD being one of the most notorious.
Chloride channels are a superfamily of poorly understood ion channels specific for chloride. These channels may conduct many different ions, but are named for chloride because its concentration in vivo is much higher than other anions. Several families of voltage-gated channels and ligand-gated channels have been characterized in humans.
The GABAA receptor (GABAAR) is an ionotropic receptor and ligand-gated ion channel. Its endogenous ligand is γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system. Accurate regulation of GABAergic transmission through appropriate developmental processes, specificity to neural cell types, and responsiveness to activity is crucial for the proper functioning of nearly all aspects of the central nervous system (CNS). Upon opening, the GABAA receptor on the postsynaptic cell is selectively permeable to chloride ions and, to a lesser extent, bicarbonate ions.
Fipronil is a broad-spectrum insecticide that belongs to the phenylpyrazole insecticide class. Fipronil disrupts the insect central nervous system by blocking the ligand-gated ion channel of the GABAA receptor and glutamate-gated chloride (GluCl) channels. This causes hyperexcitation of contaminated insects' nerves and muscles. Fipronil's specificity towards insects is believed to be due to its greater binding affinity for the GABAA receptors of insects than to those of mammals, and for its action on GluCl channels, which do not exist in mammals. As of 2017, there does not appear to be significant resistance among fleas to fipronil.
Aldrin is an organochlorine insecticide that was widely used until the 1990s, when it was banned in most countries. Aldrin is a member of the so-called "classic organochlorines" (COC) group of pesticides. COCs enjoyed a very sharp rise in popularity during and after World War II. Other noteworthy examples of COCs include dieldrin and DDT. After research showed that organochlorines can be highly toxic to the ecosystem through bioaccumulation, most were banned from use. Before the ban, it was heavily used as a pesticide to treat seed and soil. Aldrin and related "cyclodiene" pesticides became notorious as persistent organic pollutants.
The avermectins are a group of 16-membered macrocyclic lactone derivatives with potent anthelmintic and insecticidal properties. These naturally occurring compounds are generated as fermentation products by Streptomyces avermitilis, a soil actinomycete. Eight different avermectins were isolated in four pairs of homologue compounds, with a major (a-component) and minor (b-component) component usually in ratios of 80:20 to 90:10. Avermectin B1, a mixture of B1a and B1b, is the drug and pesticide abamectin. Other anthelmintics derived from the avermectins include ivermectin, selamectin, doramectin, eprinomectin.
The epithelial sodium channel(ENaC), (also known as amiloride-sensitive sodium channel) is a membrane-bound ion channel that is selectively permeable to sodium ions (Na+). It is assembled as a heterotrimer composed of three homologous subunits α or δ, β, and γ, These subunits are encoded by four genes: SCNN1A, SCNN1B, SCNN1G, and SCNN1D. The ENaC is involved primarily in the reabsorption of sodium ions at the collecting ducts of the kidney's nephrons. In addition to being implicated in diseases where fluid balance across epithelial membranes is perturbed, including pulmonary edema, cystic fibrosis, COPD and COVID-19, proteolyzed forms of ENaC function as the human salt taste receptor.
Chlorethoxyfos is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is registered for the control of corn rootworms, wireworms, cutworms, seed corn maggot, white grubs and symphylans on corn. The insecticide is sold under the trade name Fortress by E.I. du Pont de Nemours & Company.
Pyriprole is for veterinary use on dogs against external parasites such as fleas and ticks.
Emamectin is the 4″-deoxy-4″-methylamino derivative of abamectin, a 16-membered macrocyclic lactone produced by the fermentation of the soil actinomycete Streptomyces avermitilis. It is generally prepared as the salt with benzoic acid, emamectin benzoate, which is a white or faintly yellow powder. Emamectin is widely used in the US and Canada as an insecticide because of its chloride channel activation properties.
Tefluthrin is the ISO common name for an organic compound that is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids such as tefluthrin are often preferred as active ingredients in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. It is effective against soil pests because it can move as a vapour without irreversibly binding to soil particles: in this respect it differs from most other pyrethroids.
Early twenty-first century pesticide research has focused on developing molecules that combine low use rates and that are more selective, safer, resistance-breaking and cost-effective. Obstacles include increasing pesticide resistance and an increasingly stringent regulatory environment.
Fluralaner, (INN) sold under the brand name Bravecto among others, is a systemic insecticide and acaricide that is administered orally or topically. The US Food and Drug Administration (FDA) approved it for flea treatment in dogs in May 2014, and approved the combination fluralaner/moxidectin as a topical treatment for cats in November 2019. The EU approved fluralaner in March 2014. Australia approved it for the treatment and prevention of ticks and fleas on dogs in January 2015. For treating mites in chickens, a solution for use in drinking water is available under the brand name Exzolt and was approved for use in the EU in 2017.
Chloride channel openers refer to a specific category of drugs designed to modulate chloride channels in the human body. Chloride channels are anion-selective channels which are involved in a wide variety of physiological functions and processes such as the regulation of neuroexcitation, transepithelial salt transport, and smooth muscle contraction. Due to their distribution throughout the body, diversity, functionality, and associated pathology, chloride channels represent an ideal target for the development of channel modulating drugs such as chloride channel openers.
A chloride channel blocker is a type of drug which inhibits the transmission of ions (Cl−) through chloride channels.
The Calcium-Dependent Chloride Channel (Ca-ClC) proteins (or calcium-activated chloride channels, are heterogeneous groups of ligand-gated ion channels for chloride that have been identified in many epithelial and endothelial cell types as well as in smooth muscle cells. They include proteins from several structurally different families: chloride channel accessory, bestrophin, and calcium-dependent chloride channel anoctamin channels ANO1 is highly expressed in human gastrointestinal interstitial cells of Cajal, which are proteins which serve as intestinal pacemakers for peristalsis. In addition to their role as chloride channels some CLCA proteins function as adhesion molecules and may also have roles as tumour suppressors. These eukaryotic proteins are "required for normal electrolyte and fluid secretion, olfactory perception, and neuronal and smooth muscle excitability" in animals. Members of the Ca-CIC family are generally 600 to 1000 amino acyl residues in length and exhibit 7 to 10 transmembrane segments.
Afoxolaner (INN) is an insecticide and acaricide that belongs to the isoxazoline chemical compound group.
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