Pyrethroid insecticide hydrolysis

FIGURE 1.22 Hydrolysis of the pyrethroid insecticides fenvalerate and cypermethrin. 

Camilleri P (1984) Alkaline hydrolysis of some pyrethroid insecticides. J Agric Food Chem il 1122-1124. 

Ghiasuddin, S.M. and D.M. Soderlund. 1984. Hydrolysis of pyrethroid insecticides by soluble mouse brain esterases. Toxicol. Appl. Pharmacol. 74 390-396. 

Nakamura Y, Sugihara K, Sone T, Isobe M, Ohta S, Kitamura S (2007) The in vitro metabolism of a pyrethroid insecticide, permethrin, and its hydrolysis products in rats. Toxicology 235 176-184... 

Yang D, Wang X, Chen Y, Deng R, Yan B (2009) Pyrethroid insecticides isoform-dependent hydrolysis, induction of cytochrome P450 3A4 and evidence on the involvement of the pregnane X receptor. Toxicol Appl Pharmacol 237 49-58... 

Blood and various organs of humans and other animals contain esterases capable of acetylsalicylic acid hydrolysis. A comparative study has shown that the liver is the most active tissue in all animal species studied except for the guinea pig, in which the kidney is more than twice as active as the liver. Human liver is least active the enzyme in guinea pig liver is the most active. The relatively low toxicity of some of the new synthetic pyrethroid insecticides appears to be related to the ability of mammals to hydrolyze their carboxyester linkages. Thus mouse liver microsomes catalyzing (+)-/runs-resin e 111ri n hydrolysis are more than 30-fold more active than insect microsomal preparations. The relative rates of hydrolysis of this substrate in enzyme preparations from various species are mouse > > milkweed bug > > cockroach > > cabbage looper > housefly. 

Sogorb, M.A. and Vilanova, E., Enzymes involved in the detoxication of organophosphorus, carbamate and pyrethroid insecticides through hydrolysis, Toxicol. Lett., 128, 315-228, 2002. 

It is known that the (S)-forms are the essential stereoisomers for the insecticidal activities of both alcohols (4,5). Chemico-enzymatic processes are also reported in this article on the preparation of the optically active pyrethroid insecticides having the (S)-isomers of the two alcohols. Processes were developed that use enantioselective hydrolysis with a lipase. 

Takahashi, N., N. Mikami, T. Matsuda and J. Miyamoto. 1985a. Hydrolysis of the pyrethroid insecticide cypermethrin in aqueous media, J. Pesticide Sci., 10 643-648. 

Clothes-moth [13,175,269,270] larvae attack wool with a mixture of enzymes that catalyze the reduction of cystine residue disulfide cross-links and the hydrolysis of peptide bonds. Wool is usually moth-proofed by treatment with insecticides that are absorbed like dyes and show similar fastness. The wool textile industry applies insect-resistant agents mainly to carpet wools, which account for about 85% of the treated wool. Insect-resistant agents are of two classes those which have been developed specifically for use on wool, and those which consist of agricultural insecticides that have been specially formulated for use with wool. The former group is usually polychlorinated aromatic compounds, and the latter group is based on synthetic pyrethroid insecticides. 

Vistoli et al. (2010) studied the docking analysis of known substrates to develop both predictive models and molecular dynamics (MD) simulations to identify the in situ behavior of substrates and products. Pyrethroids and their respective carboxylesterase data (Ross et al. 2006) were used as substrates in the training set and in the external test sets for a series of docking experiments. A rich interaction pattern with hCESl was shared by aU the pyrethroid insecticides examined, and explains the marked efficacy with which the esterases hydrolyze the pyrethroids. Molecular dynamics simulations were used to examine the hydrolysis of heroin (CAS no. 561-27-3) to 6-O-acetylmorphine and morphine (CAS no. 57-27-2) by hCESl. 

In an attempt to circumvent the avaUabihty of analytical standards, several CYP450 studies were carried out using the substrate depletion method. This approach does not provide information on the products formed downstream, and may be of limited use in developing human enviromnental exposure PBPK/PD models that require extensive urinary metabolite data. Hydrolytic standards (i.e., alcohols and acids) were available to investigators who studied the carboxylesterase-catalyzed hydrolysis of several pyrethroid insecticides. The data generated in these studies are suitable for use in developing human exposure PBPK/PD models. 

Balance and tissue retention study. J Agric Food Chem 29 130-135 Crawford MJ, Croucher A, Hutson DH (1981b) The metabolism of the pyrethroid insecticide cypermethrin in rats excreted metabolites. Pestic Sci 12 399-411 Crow JA, Borazjani A, Potter PM, Ross MK (2007) Hydrolysis of pyrethroids by human and rat tissues examination of intestinal, liver and serum carboxylesterases. Toxicol Appl Pharmacol 221 1-12... 

Taking the pyrethroids, apart from fenvalerate, they are solids with low water solubility, marked lipophilicity, and low vapor pressure. Fenvalerate is a viscous liquid with an appreciable vapor pressure. Being esters, the pyrethroids are subject to hydrolysis at high pH. They are sufficiently stable to heat and light to be effective insecticides in the field. 

Pyrethroids are commercially important insecticides that usually contain a cyclopropyl unit that is m-substituted and a cyanohydrin derivative. They are usually sold as a mixture of isomers. However, asymmetric routes have been developed, especially because these compounds are related to chrysanthemic esters (Chapter 12).251 The pyrethroids can be resolved through salt formation or by enzymatic hydrolysis.252... 

Insecticides such as organophosphates, carbamates, pyrethroids, and some juvenoids, which contain ester linkages, are susceptible to hydrolysis. Esterases are hydrolases that split ester compounds by the addition of water to yield an acid and an alcohol. 

There are two types of esterases that are important in metabolizing insecticides, namely, carboxylesterases and phosphatases (also called phosphorotriester hydrolases or phosphotriesterases). Carboxylesterases, which are B-esterases, play significant roles in degrading organophosphates, carbamates, pyrethroids, and some juvenoids in insects. The best example is malathion hydrolysis, which yields both a- and (i-monoacids and ethanol (Figure 8.10). 

Since OPs inhibit serine hydrolases such as AChE by phosphorylating them, it follows that OPs are potential inhibitors of all other serine hydrolases. This means that OPs can be used as synergists, notably for the pyrethroids that are detoxified by ester hydrolysis, and OP-containing mixture have proven successful in several cases (34.) The usefulness of these mixtures can be prolonged by using them in rotations with other mixtures and/or insecticides. 

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