The metabolism of hexachlorocyclohexanes and pentachlorocyclohexenes in flies and grass grubs

Studies on the metabolism, mode of action, and development of insecticides acting on the GABA receptor

γ-BHC and dieldrin are legacy insecticides that were extensively used after the second World War. When they were banned, their modes of action and metabolism were not known. This article aims at providing a picture of the metabolism of γ-BHC and the modes of action of γ -BHC and dieldrin. γ-BHC is metabolized via two independent metabolic pathways. One is a glutathione conjugation pathway resulting in the formation of dichlorophenyl mercapturic acid and the other is an oxidative metabolism catalyzed by microsomes to mainly 2,4,6-trichlorophenol (TCP) and (36/45)-1,2,3,4,5,6-hexachlorocyclohex-1-ene (HCCHE). Other metabolites of this pathway are 2,4,5-TCP, 2,3,4,6-tetrachlorophenol (TeCP), (36/45)- and (346/5)-1,3,4,5,6-pentachlorocyclohex-1-enes (PCCHE). Nowadays, γ-BHC and dieldrin are very important reagents which are used to study the GABA receptor in insects and mammals. They were found to be noncompetitive GABA antagonists blocking the chloride ion selective pores in the GABA-gated chloride channels and leading to inhibition of chloride ion conductance. [³H]EBOB binding data showed that γ-BHC, its analogs, dieldrin, and other cyclodiene insecticides interact with the same site on GABA receptor as picrotoxinin. Only γ-BHC, among other BHC isomers, exhibits this binding characteristic. Milbemycin, currently widely used as an insecticide, acaricide and nematicide, has been found to open the GABA-gated chloride channel.

Inhibition of housefly oxidative detoxication by phthaleins, fluoresceins and related compounds

1. Phenolphthalein, halogenated fluoresceins, and other triphenylmethane and diphenylmethane derivatives inhibited biphenyl hydroxylation, aldrin epoxidation and several O-dealkylations in insect abdomen homogenates. Phenolphthalein and eosin (50 muM) were 2-3 times more effective than SKF 525-A and piperonyl butoxide (50 muM) as inhibitors of biphenyl hydroxylation in vitro. 2. The phthaleins, Aurin and Aluminon, inhibited both epoxidation and hydroxylation to similar extents, but fluoresceins, Rhodamine B, Malachite Green, and basic diphenylmethane derivatives preferentially inhibited hydroxylation. 3. Tetrabromophenolphthalein ethyl ester and bis-(N-dimethyl-4-aminophenyl-methane inhibited biphenyl hydroxylation in vivo. Bis-(N-dimethyl-4-aminophenyl) methane synergized the toxic effects of 1-naphthyl N-methylcarbamate in live houseflies.

Cross specificity in some vertebrate and insect glutathione-transferases with methyl parathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitro-benzene and s-crotonyl-N-acetylcysteamine as substrates

1. Enzymes catalysing the reaction between GSH and methylparathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitrobenzene and S-crotonyl-N-acetylcysteamine were separated by (NH(4))(2)SO(4) precipitation from homogenates of sheep, rat and mouse livers and from homogenates of cockroaches, houseflies and grass grubs. 2. Electrofocusing of the preparations from each of these species separated a number of zones, each of which catalysed the reaction of GSH with all three substrates. 3. Ion-exchange chromatography on CM-cellulose also separated a number of fractions in which activity towards the three substrates coincided. 4. In both separation methods patterns of the activities were consistent with the presence in all species of several GSH transferases each having a degree of cross specificity towards the three substrates.

The inhibition of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) dehydrochlorinase and glutathione S-aryltransferase in grass-grub and housefly preparations

The inhibition of DDT [1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] dehydrochlorinase and glutathione S-aryltransferase by diphenylmethane and triphenylmethane derivatives was examined. Bis-(3,5-dibromo-4-hydroxyphenyl)methane and similar compounds were excellent inhibitors of both enzymes, but only DDT dehydrochlorinase was inhibited by compounds similar to bis-(N-dimethylaminophenyl)methane. Colour salts of the basic triphenylmethyl dyes were excellent inhibitors of both enzymes. All the inhibitors examined appeared to act by competition with glutathione for its binding site on the two enzymes.