Insecticidal activity and microsomal metabolism of biooxidizable lindane analogs

The insecticidal activity of lindane analogs, in which some chlorine atoms were replaced by other groups susceptible to microsomal oxidative metabolism, was determined against mosquitos, house flies, and German cockroaches. When tested with a synergist, piperonyl butoxide, one of the methylthio analogs was as active as lindane, whereas several others were also highly active. By examining the ratio of synergized and unsynergized LD₅₀ values (synergistic ratio value), the highly insecticidal methylthio, methoxy, and methyl analogs appear to undergo metabolic detoxication effectively in house flies. By means of in vitro metabolism experiments using microsomal fraction from house fly abdomen, the methoxy, ethoxy, and methylthio analogs were shown to be metabolized rapidly at similar rates. The synergized insecticidal activities of these compounds against various insect species relate linearly with each other, suggesting that the oxidative degradation is inhibited by the synergist to a similar extent and that the transport process to the site of action is not a limiting factor in determining the relative insecticidal activity.     

Oxidative metabolism of lindane and its isomers with microsomes from rat liver and house fly abdomen

Lindane and other hexachlorocyclohexane isomers produced 2,4,6-trichlorophenol as the major oxidative metabolite when incubated in the presence of NADPH under aerobic condition. A mechanism for the formation of 2,4,6-trichlorophenol is proposed, which includes direct oxygenation of the cyclohexane ring. The proposed mechanism is supported by data from studies of model chemical reactions of the pentachlorocyclohexanol isomers. Pathways leading to 1,2,4-trichlorobenzene, tetrachlorobenzene isomers, 2,4,5-trichlorophenol, and tetrachlorophenol isomers are discussed, and are considered to include the route through pentachlorocyclohexene and hexachlorocyclohexene. Reductive dechlorination of lindane under anaerobic condition was observed using microsomes and NADPH.     

The mechanism of resistance to lindane and hexadeuterated lindane in the Third Yumenoshima strain of house fly

The factors which cause lindane resistance in the Third Yumenoshima strain, a strain of house flies highly resistant to insecticides, were studied using hexadeuterated lindane. Hexadeuterated lindane has the same physicochemical properties as lindane, but the former is much less biodegradable than the latter. The LD₅₀ ratio of lindane to hexadeuterated lindane in this strain, deuterium isotope effect on LD₅₀ values, was larger than that in S_NAIDM, a susceptible (nonresistant) strain. The penetration rates of labeled and nonlabeled lindane through the insect cuticle were about the same for both strains. Thus, penetration rate does not cause resistance. The metabolic degradation of lindane in the resistant strain in vivo occurred much faster than in the susceptible strain. This was also the case for lindane degradation processes in vitro such as microsomal oxidation and glutathione conjugation. In both strains, significant isotope effects were observed in the degradation rates in vitro of labeled and nonlabeled lindane. Therefore, principal biodegradation and detoxication pathways should include reactions which cleave the CH bonds. When the much less biodegradable d₆ counterpart of lindane was applied to both strains, the susceptible strain became much more highly intoxicated than the other within 20 to 30 min. This indicates that a combination of both greater degradability and probably lower sensitivity at the action site are the main factors underlying resistance in the Third Yumenoshima strain.     

Diffusive movement of simazine and lindane in river-bed sediments

River-bed sediments are active zones for pesticide deposition and subsequent movement by diffusion, mass transport and sorption to solids. The aim of this work was to investigate the importance of diffusion as a means of pesticide movement. In laboratory experiments, simazine and lindane were introduced to well-mixed aqueous solutions overlying two different river sediments. Sediment cores were sectioned horizontally and analyzed for pesticide content by supercritical fluid extraction. Experiments were used to determine sorption isotherms of the compounds to suspended sediments at 10°C. Vertical profiles of the pesticides in the sediments showed that the compounds reached a maximum depth of 89 mm over a period of 37 days. A mathematical model was developed to describe pesticide transport by diffusion within the sediment porewaters and sediment sorbed phases, taking into account sorption of the compounds to sediment particles. Effective diffusion coefficients ((0.5–1.6)×10^-10 m² s^-1) were obtained for simazine and lindane in the characterized sediments. These were used to calculate values for diffusion in the dissolved phase (0.38×10^-10 and 6·16×10^-10 m² s^-1 for simazine and lindane respectively) and diffusion in the sorbed phase (0.39×10^-10 m² s^-1 for simazine and negligible for lindane). Sorption onto the sediment significantly influenced the rate of penetration of the compounds into the sediment; thus although lindane had a larger effective diffusion coefficient than simazine, its larger sorption affinity and negligible diffusion in the sorbed phase led to less penetration into the sediment. © 1998 Society of Chemical Industry     

Metabolic detoxication and synergistic ratio of lindane analogs in house flies

Biodegradability of lindane analogs using house fly whole body, microsomes, and microsome supernatant fraction was examined. It decreased in the order of alkoxy ～ methylthio > methyl analogs > lindane in the whole body experiments, as well as with microsomes in the presence of NADPH. With the supernatant in the presence of glutathione, a different trend was observed. The synergistic effects of piperonyl butoxide when used together with lindane analogs were mostly explained in terms of the inhibition of the microsomal metabolism. Piperonyl butoxide was also shown to inhibit the penetration of compounds into the fly body and to make the central nervous system of the American cockroach less sensitive to the action of insecticides causing after and repetitive discharges. It was observed that the value of the percentage of metabolic disappearance of insecticides after a certain period decreases as the dose level initially applied in the whole body experiments increases. The synergistic ratio parallels the percentage of disappearance value after the insecticidal activity test period when a dose corresponding to the unsynergized LD₅₀ is initially applied. When quantitative comparisons are required for biodegradability of insecticides using house flies as the test insects, it should be on the basis of direct metabolism experiments using a fixed dose throughout the series of insecticides, but not on the basis of the synergistic ratio.     

虱螨脲对棉铃虫叶酸一碳库代谢途径的影响

为了探究虱螨脲对棉铃虫的作用机理,用虱螨脲(200 mg/L)处理棉铃虫3龄幼虫,通过转录组测序、叶酸含量测定、叶酸饲喂试验和分子对接技术分析了虱螨脲对棉铃虫叶酸一碳库代谢途径的影响。结果表明,棉铃虫幼虫差异基因数量随虱螨脲处理后时间的延长而增多,主要富集在叶酸一碳库、氧化还原活性、几丁质结合、氨基酸合成、嘌呤合成与代谢以及离子跨膜运输等途径上,其中叶酸一碳库代谢通路在处理后0.5 h极显著富集(P=6.35×10^-5)。棉铃虫幼虫的叶酸含量随着虱螨脲处理后时间的延长而显著降低,处理后24 h叶酸含量为4.53μg/100 g,约为对照组的1/2;用含叶酸的饲料饲喂虱螨脲处理的棉铃虫幼虫,能够明显降低其中毒症状。分子对接结果表明,胞质10-甲酰基四氢叶酸脱氢酶(cytosolic 10-formyltetrahydrofolate dehydrogenase)与虱螨脲共形成12个氢键和6个卤键,具有最低的结合能(-10.4 kcal/mol),推测其是虱螨脲的潜在作用靶标之一。研究结果进一步丰富了虱螨脲的作用机理,为以叶酸途径为靶标的杀虫剂开发提供了理论指导。     

Transport and distribution of lindane and simazine in a riverine environment: measurements in bed sediments and modelling

Aquatic sediments often remove hydrophobic contaminants from fresh waters. The subsequent distribution and concentration of contaminants in bed sediments determines their effect on benthic organisms and the risk of re-entry into the water and/or leaching to groundwater. This study examines the transport of simazine and lindane in aquatic bed sediments with the aim of understanding the processes that determine their depth distribution. Experiments in flume channels (water flow of 10 cm s(-1)) determined the persistence of the compounds in the absence of sediment with (a) de-ionised water and (b) a solution that had been in contact with river sediment. In further experiments with river bed sediments in light and dark conditions, measurements were made of the concentration of the compounds in the overlying water and the development of bacterial/algal biofilms and bioturbation activity. At the end of the experiments, concentrations in sediments and associated pore waters were determined in sections of the sediment at 1 mm resolution down to 5 mm and then at 10 mm resolution to 50 mm depth and these distributions analysed using a sorption-diffusion-degradation model. The fine resolution in the depth profile permitted the detection of a maximum in the concentration of the compounds in the pore water near the surface, whereas concentrations in the sediment increased to a maximum at the surface itself. Experimental distribution coefficients determined from the pore water and sediment concentrations indicated a gradient with depth that was partly explained by an increase in organic matter content and specific surface area of the solids near the interface. The modelling showed that degradation of lindane within the sediment was necessary to explain the concentration profiles, with the optimum agreement between the measured and theoretical profiles obtained with differential degradation in the oxic and anoxic zones. The compounds penetrated to a depth of 40-50 mm over a period of 42 days.     

Intoxication effects of lindane (γ-BHC) on the carbohydrate metabolism in the climbing perch, Anabas testudineus (Bloch)

The effects of an acute lethal (0.59 mg/liter) and a sublethal (0.075 mg/liter) concentration of lindane on the levels of glycogen (liver and muscle), glucose (blood), and lactic acid (liver, muscle, and blood) of a freshwater fish, Anabas testudineus (Bloch) were determined. A marked decrease in the liver glycogen and significant increase in blood glucose and muscle glycogen at 1 hr of exposure to 0.075 mg/liter lindane was noted. These results indicate extensive utilization of energy stores in the liver and simultaneous buildup of fuel reserves in the muscle. After 3 hr of exposure, glycogenesis possibly becomes operative in liver through the Cori cycle. The activity of the cycle was observed in the fish in all the subsequent periods of exposure studied. At 120 hr, the decreases observed in muscle and liver glycogen indicate near exhaustion of glycogen stores. Though changes in glycogen content of both muscle and liver were similar in 0.59 mg/liter lindane, they have less adaptive value since mortality of fish was significantly high at all three peroids studied.     

Metabolism of lindane in house flies: Metabolic desaturation,dehydrogenation and dehydrochlorination,and conjugation with glutathione

In lindane-treated house flies, a cis-dehydrogenated metabolite, $\text{(}\text{36}\text{45}\text{)-}\text{hexachlorocyclohexene}$, was identified by gas-liquid chromatography and mass spectrometry. The in vitro metabolism study showed that in the presence of NADPH the microsomal fraction of house flies converted lindane to three hexane-soluble metabolites. This conversion was inhibited by piperonyl butoxide, SKF-525A, and carbon monoxide. These metabolites were identified as $\text{(}\text{36}\text{45}\text{)-}\text{hexachlorocyclohexene}$, $\text{(}\text{36}\text{45}\text{)- and (}\text{346}\text{5}\text{)-pentachlorocyclohexene}$ (PCCHE) by gas-liquid chromatography. They, as well as lindane, were excellent substrates for the reaction with the postmicrosomal fraction in the presence of glutathione. While the reaction with lindane-d₆ showed a significant deuterium isotope effect (6.82), that of $\text{(}\text{36}\text{45}\text{)-}\text{PCCHE-d}{}_5$ did not (1.18). Enzymatic conjugation with glutathione probably occurs at the stage of PCCHE.     

Deuterium isotope effects on the formation of mercapturic acids from lindane in rats

Metabolism experiments with rats showed that significant isotope effects ($\text{k}{}_{\mathrm{<mtext>H</mtext>}}\text{k}{}_{\mathrm{<mtext>D</mtext>}}\text{= 2.4}\text{to}\text{3.5}$) were associated with the in vivo formation of dichloro and trichlorophenylmercapturic acids from a 1:1 mixture of normal and hexadeuterated lindane. This is evidence that rate-determining dehydrogenation and dehydrochlorination, both of which proceed with significant isotope effects, are essential in the pathway of dichloro- and trichlorophenylmercapturic acid formation from lindane. No significant primary isotope effects were associated ($\text{k}{}_{\mathrm{<mtext>H</mtext>}}\text{k}{}_{\mathrm{<mtext>D</mtext>}}\text{= 1.31 ± 0.17}$) with the formation of monochlorophenylmercapturic acid. This suggests that the 1,2-dechlorination to tetrachlorocyclohexene followed by glutathione conjugation is the probable pathway that produces this metabolite from lindane.     

Inheritance of resistance to lindane in a laboratory-selected strain of Tribolium castaneum (Herbst)

Studies on the inheritance of resistance to lindane in a laboratory-selected strain of Tribolium castaneum, by making crosses between the resistant and a susceptible strain, showed that resistance in this strain is controlled by an autosomally inherited single gene which is incompletely dominant.     

Glutamate-activated chloride channels: Unique fipronil targets present in insects but not in mammals

Selectivity to insects over mammals is one of the important characteristics for a chemical to become a useful insecticide. Fipronil was found to block cockroach GABA receptors more potently than rat GABA_A receptors. Furthermore, glutamate-activated chloride channels (GluCls), which are present in cockroaches but not in mammals, were very sensitive to the blocking action of fipronil. The IC₅₀s of fipronil block were 30 nM in cockroach GABA receptors and 1600 nM in rat GABA_A receptors. Moreover, GluCls of cockroach neurons had low IC₅₀s for fipronil. Two types of glutamate-induced chloride current were observed: desensitizing and non-desensitizing, with fipronil IC₅₀s of 800 and 10 nM, respectively. We have developed methods to separately record these two types of GluCls. The non-desensitizing and desensitizing currents were selectively inhibited by trypsin and polyvinylpyrrolidone, respectively. In conclusion, in addition to GABA receptors, GluCls play a crucial role in selectivity of fipronil to insects over mammals. GluCls form the basis for development of selective and safe insecticides.     

Balance of conversion of [14C]lindane in lettuce in hydroponic culture

After application of [¹⁴C]lindane to the nutrient medium (1.45 ppm), 14.1% of the radioactivity was taken up by 12 lettuce plants during 4 weeks; in the nutrient medium, 7.8% was recovered after the same time interval. The radioactivity in the nutrient extract comprised: unchanged lindane (about 82%); free 2,3,4,6-tetrachlorophenol, free pentachlorophenol, conjugates of pentachlorophenol, and an unidentified polar compound (a total of 15%); 1,2,3-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, pentachlorobenzene, hexachlorobenzene, 2,3,4,5,6-pentachlorocyclohex-1-ene, and probably 1,2,3,4,5,6-hexachlorocyclohexene (a total of 3%). The radioactivity extracted from plants consisted of unchanged lindane (about 77%); free 2,3,4,6-tetrachlorophenol, conjugates of a tetrachlorophenol and pentachlorophenol, and a strongly hydrophilic compound that was not identified (a total of 20%); 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, pentachlorobenzene, 2,3,4,5,6-pentachlorocyclohex-1-ene, and probably 1,2,3,4,5,6-hexachlorocyclohexene (a total of 3%). Identification was carried out by means of comparisons of chromatographic properties and of the mass spectra with those of authentic reference compounds. The significance of hexachlorobenzene as a metabolite of lindane is discussed.     

Blood parasites of small wild mammals in Czechoslovakia]

The author investigated 4,853 specimens of wild living small mammals (43 species: Insectivora, Chiroptera, Lagomorpha, Rodentia, Carnivora) from Czechoslovakia for blood parasites. Trypanosomes were found in Talpa europaea, Sorex alpinus, Crocidura suaveolens, Myotis myotis, Apodemus sylvaticus, Apodemus flavicollis, Mus musculus, Rattus norvegicus, Clethrionomys glareolus and Microtus agrestis. Babesia was detected in Myotis emarginatus, Myotis myotis, Clethrionomys glareolus, Microtus arvalis and Microtus agrestis. Grahaemella was found in Talpa europaea, Sorex araneus, Neomys fodiens, Neomys anomalus, Myotis emarginatus, Myotis myotis, Apodemus sylvaticus, Apodemus flavicollis, Apodemus microps, Apodemus agrarius, Mus musculus, Clethrionomys glareolus, Arvicola terrestris, Pitymys subterraneus, Microtus arvalis, Microtus agrestis, and Microtus oeconomus. Spontaneous Bartonella-infection was ascertained in one Microtus arvalis and, in erythrocytes of one Sorex araneus, parasitic organisms very similar to Bartonella were found.     

Electrocorticogram disturbances detected in rats exposed from early stages of life to residual doses of lindane

Functional brain alterations induced by lindane were examined in Rat chronically exposed to low doses of lindane (1 and 2 μg L⁻¹ in drinking water) from conception. Histological and electrophysiological investigations were conducted at 14 weeks of age. Lindane did not induce histological changes. It did not significantly modify the sleep-wakefulness cycle and EEG did not show major alterations. The spectral EEG analysis, by recording cortical variations in both energy spectrum and energy levels of different frequency bands, showed an increase in the 11-15 Hz activity in both groups exposed to lindane. This activity was characterised by spindles well-depicted during slow wave sleep or associated with fast activity during wakefulness and theta activity in paradoxical sleep. These data suggest that chronic exposure to lindane doses as low as 1 μg L⁻¹ in drinking water could lead to central electrophysiological effects possibly involving GABA-benzodiazepine mechanisms.     

Propanil metabolism in rice: A comparison of propanil amidase activities in rice plants and callus cultures

Propanil amidase is an enzyme found in rice, which hydrolyzes the herbicide 3,4-dichloropropionanilide, propanil. The activity of the enzyme as measured in rice plants was found to be two to four times greater in plants with four leaves than in plants with fewer than four leaves. The higher amidase activity of the four-leaf plants was localized in the unexpanded leaves.Rice root callus suspension in cultures also demonstrated propanil amidase activity. In vivo experiments indicated that the herbicide was metabolized by the tissue culture. Propanil amidase activity as determined in vitro, however, was detected only after the culture had developed to late stationary phase.     

Effect of antioxidant supplementation on free radical scavenging system and immune response in lindane treated scabies patients

The scabicide, lindane induces oxidative stress and immunological alterations. The present study was undertaken to assess the ameliorative effects of antioxidant supplementation in lindane treated scabies patients. Scabies patients were treated with either 1% lindane or 1% lindane along with antioxidant (Lycored or Vitamin-E). Oxidative stress and immunological parameters were evaluated in blood samples and compared with healthy controls. Lindane caused a significant increase in malonedialdehyde (MDA) levels and decrease in reduced glutathione (GSH) and ferric reducing ability of plasma (FRAP), which was attenuated by anti-oxidant therapy. The IL-1α levels were significantly enhanced in scabies patients per se and remained unaffected after lindane/anti-oxidant treatment. The TNF-α and nitroblue tetrazolium (NBT) reduction levels were not significantly different in all the groups. Topical application of lindane induces significant free radical generation and may cause immunological alterations which can be reversed by antioxidant therapy.