Pesticide interactions: Effects of organophosphorus pesticides on the metabolism,toxicity, and persistence of selected pyrethroid insecticides

The organophosphorus pesticides profenofos, sulprofos, O-ethyl O-(4-nitrophenyl) phenylphosphonothioate (EPN), and S,S,S,-tributyl phosphorotrithioate (DEF) administered intraperitoneally to mice at 0.5 to 5 mg/kg strongly inhibit the liver microsomal esterase(s) hydrolyzing trans-permethrin. Profenofos, EPN, and DEF at 25 mg/kg increase the intraperitoneal toxicity of fenvalerate > 25-fold and of malathion > 100-fold. Topically applied profenofos, sulprofos, and DEF significantly synergize the toxicity of cis-cypermethrin to cabbage looper larvae and house fly adults but these phosphorus compounds are much less effective in synergizing the toxicity of trans-permethrin. The magnitude of synergism appears to depend on the species, organophosphorus compound, and pyrethroid involved. Profenofos, sulprofos, and EPN do not significantly alter the persistence of trans-permethrin on bean foliage.     

Human metabolism of atrazine

Atrazine (ATZ) metabolism by human liver microsomes (HLM), cytochrome P450 (CYP) isoforms, and human liver (HL) S9 fractions, was investigated using HPLC/PDA and LC/MS/MS. CYP-dependent metabolites from pooled HLM are desethylatrazine (DEA), desisopropylatrazine (DIA), 1-hydroxyisopropylatrazine (HIATZ), and 2-hydroxyethyl atrazine (HEATZ). DEA and DIA were major metabolites in pooled HLM. CYP1A2 and 2C19, respectively, were major isoforms for DEA and DIA production. CYP3A4, while less active, is generally at high concentrations, produces both DEA and DIA and is significant. The percent total normalized rates (%TNR) for CYP1A2 and 3A4 in pooled HLM were 63% and 24% for DEA, and 35% and 56% for DIA production. Single donor HLM samples, showed correlations for CYP1A2 (r = 0.92) and 3A4 (r = 0.81) for DEA and DIA production, while variations in production of DEA and DIA were 8.5- and 6.0-fold, respectively. Pooled S9 fractions also mediate glutathione conjugation of atrazine, DEA and DIA.     

Enzymatic hydrolysis of diazoxon by rat tissue homogenates

The enzymatic hydrolysis of ³²P-labeled diazoxon was studied using tissue homogenates of rat and American cockroach. The order of the hydrolytic activities of rat tissues for diazoxon was as follows: liver > blood > lung > heart > kidney > brain. A liver enzyme hydrolyzing diazoxon to diethyl phosphoric acid and 2-isopropyl-4-methyl-6-hydroxypyrimidine was located in the microsomes. The activity of the microsomal enzyme was inhibited by EDTA, heavy and rare earth metal ions, and SH reagents. Ca²⁺ activated the enzyme and protected it from inactivation. Mitochondrial and soluble enzymes from liver and a serum enzyme also hydrolyzed diazoxon and they were also activated by Ca²⁺. The removal of calcium bound to the microsomal enzyme protein by dialysis against EDTA led to a partially irreversible change of the enzyme. The hydrolysis of diazoxon by the Ca²⁺-requiring microsomal and serum enzymes was more rapid than that of paraoxon. Hydrolysis of diazoxon did not occur in American cockroach homogenates. This difference in the capacity to hydrolyze diazoxon between mammals and insects is discussed in relation to the selective toxicity of diazinon.     

Comparative effects of two plant growth regulators; indole-3-acetic acid and chlorogenic acid on human and horse serum butyrylcholinesterase

Butyrylcholinesterase (BChE), a major detoxification enzyme found abundantly in many tissues and organisms, constitutes the first line defense in the serum of higher organisms and is a marker for toxic exposure. In this study, the interaction of two plant growth regulators, indole-3-acetic acid (IAA) and chlorogenic acid (CA) with purified human and horse serum BChE is investigated. The time dependent interaction of IAA with the two enzyme species was concentration dependent and rapid. Through kinetic studies, IAA was found to be linear-mixed type inhibitor for human serum BChE, and uncompetitive inhibitor for the horse serum enzyme. For the human BChE, α and the K_i value was calculated as 2.15 ± 1.09 and 3.09 ± 0.98 mM, respectively, and for the horse enzyme the K_i value was calculated as 1.05 ± 0.09 mM. The time dependent interaction of CA with the two enzyme species was biphasic. At low CA concentrations, CA stimulated the activities of both enzyme species whereas at high CA concentrations, inhibition was observed. At high concentrations, the inhibition kinetics for both enzymes fitted the non-competitive inhibition model. The K_i values calculated for human and horse BChE were 2.75 ± 0.14 and 0.96 ± 0.07 mM, respectively. The differences in the interaction of these two growth regulators with the two enzymes species arises from the structural differences between the human and horse serum BChE which can be considered as a triple human mutant BChE.     

Comparative molluscicidal action of extract of Ginko biloba sarcotesta, arecoline and niclosamide on snail hosts of Schistosoma japonicum

In search for new local plant molluscicides for the control of the vectors of schistosomiasis, we compared the molluscicidal action of the extract of Ginkgo biloba sarcotesta by benzinum (EGSB) to that of arecoline (ARE) and niclosamide (NIC) against Oncomelania hupensis snails. NIC showed the highest toxicity on snails with 24 h LC₅₀ vales of 0.12 mg/L and LC₉₀ of 0.98 mg/L, while the LC₅₀ and LC₉₀ of EGSB were much lower than that of ARE. Sublethal in vivo 24 h exposure to 40% and 80% LC₅₀ of NIC, EGSB and ARE altered the activities of different enzymes in different body tissues of snails. EGSB could significantly inhibit Choline esterase (ChE), Alanine aminotransferase (ALT), Alkaline phosphatase (ALP) and Malic dehydrogenase (MDH) activities both in the cephalopodium and liver. ARE could significantly cause a reduction in ChE, ALP activities in the cephalopodium and ChE, ALT, ALP, Succinodehydrogenase (SDH), MDH activities in the liver. NIC significantly altered activities of ChE, ALT, ALP, SDH, and MDH in the cephalopodium and ChE, ALT, ALP, SDH activities in the liver. All molluscicides could not affect Lactate dehydrogenase (LDH) activity in the cephalopodium and the liver. Maximum inhibition of ALT and MDH activities was found in the cephalopodium and liver of snails treated with 80% of 24 h LC₅₀ of EGSB. However, NIC and ARE caused maximum reduction in ALP and SDH activities, respectively. The results indicated that molluscicidal action of EGSB was different to that of ARE and NIC in some extent.     

Expression of a wheat cytochrome P450 monooxygenase cDNA in yeast catalyzes the metabolism of sulfonylurea herbicides

A wheat cytochrome P450 cDNA (CYP71C6v1) was cloned by RT-PCR and heterologously expressed in yeast. The microsomal fractions derived from this strain could catalyze the metabolism of some sulfonylurea herbicides such as chlorsulfuron, triasulfuron, metsulfuron-metyl, bensulfuron-metyl, and tribenuron-metyl, but not sulfonylurea herbicides such as thifensulfuron and pyrazosulfuron. Kinetic parameters K_m for chlorsulfuron and triasulfuron were 57 (±15) μM and 38 (±16) μM in vitro, respectively. Analysis of the metabolites demonstrated that the CYP71C6v1 functioned as a 5-phenyl ring hydroxylase when chlorsulfuron and triasulfuron were the substrates.     

Synergism of resistance to phosalone and comparison of kinetic properties of acetylcholinesterase from four field populations and a susceptible strain of Colorado potato beetle

The susceptibility to phosalone and biochemical characteristics of acetylcholinesterase (AChE) were compared between susceptible (SS) strain and four field populations of Colorado potato beetle (CPB) collected from commercial potato fields of Hamedan Province in west of Iran. Bioassays involving topical application of phosalone to fourth instars revealed up to 252 fold resistance in field populations compared with the SS strain. Synergism studies showed that although esterase and/or glutathione S-transferase metabolic pathways were present and active against phosalone, they were not selected for and did not have a major role in resistance. It is likely that piperonyl butoxide (PBO) reduced phosalone toxicity by inhibiting bio-activation of phosalone. The affinity (K_m) and hydrolyzing efficiency (V_max) of AChE to selected substrates, namely, acetylthiocholine iodide (ATC), propionylthiocholine iodide (PTC), and butyrylthiocholine iodide (BTC) were examined. AChE inhibition by higher substrate concentration was evident only in the SS strain. In resistant field populations, Aliabad (Aa), Bahar (B) and Dehpiaz (Dp), substrate inhibition at higher concentrations was not seen. There was no definite optimal concentration found for any of the substrates examined. When ATC, PTC, and BTC were used as substrate, the reaction rates of AChE from Yengijeh (Yg) population increased as the concentration of all three substrates were increased, but were almost constant at concentration of ATC ? 3.98, PTC ? 2.8, and BTC ? 5 mM. The susceptible form of AChE had the most efficient ATC hydrolysis but very low BTC hydrolysis activity. In contrast, AChEs from field populations elicited relatively reduced ATC hydrolysis, but relatively increased BTC hydrolysis. The in vitro inhibition potency of some organophosphates (OPs), on AChEs of the field populations and SS strain was determined. The rank order from the most potent inhibitor to the least as determined by their bimolecular reaction constants (K_i) was ethyl paraoxon > diazoxon > methyl paraoxon for AChE from Aa, B, Dp, and Yg populations, respectively, whereas the rank order for the susceptible strain was methyl paraoxon > ethyl paraoxon > diazoxon.     

In vitro and in vivo effects of some pesticides on carbonic anhydrase enzyme from rainbow trout (Oncorhynchus mykiss) gills

Here we investigated the in vitro and in vivo effects of the pesticides, deltamethrin, diazinon, propoxur and cypermethrin, on the activity of rainbow trout (rt) gill carbonic anhydrase (CA). The enzyme was purified from rainbow trout gills using Sepharose 4B-aniline-sulfanilamide affinity chromatography method. The overall purification was approx. 214-fold. SDS-polyacrylamide gel electrophoresis showed a single band corresponding to a molecular weight of approx. 29 kDa. The four pesticides dose-dependently inhibited in vitro CA activity. IC₅₀ values for deltamethrin, diazinon, propoxur and cypermethrin were 0.137, 0.267, 0.420 and 0.460 μM, respectively. In vitro results showed that pesticides inhibit rtCA activity with rank order of deltamethrin > diazinon > propoxur > cypermethrin. Besides, in vivo studies of deltamethrin were performed on CA activity of rainbow trout gill. rtCA was significantly inhibited at three concentrations (0.25, 1.0 and 2.5 μg/L) at 24 and 48 h.     

Inhibition of Na-K-ATPase in different tissues of freshwater fish Channa punctatus (Bloch) exposed to monocrotophos

Freshwater fish, Channa punctatus, commonly known as the snakehead fish, was exposed to two sublethal concentrations (0.96 and 1.86 mg/L) (selected on the basis of 1/20 and 1/10 of 96 h LC₅₀ value) of monocrotophos for two exposure periods (15 and 60 days). Effects of monocrotophos on Na⁺, K⁺-ATPase in liver, kidney, muscle, intestine, brain, heart and gills were determined. Results indicate that Na⁺, K⁺-ATPase activity in tissues decreased as concentration of monocrotophos and exposure period increased. Monocrotophos induced significant inhibitory effects on the Na⁺, K⁺-ATPase activity of C. punctatus, ranging from gills (70%) > Kidney (63%) > brain (57%) > intestine (52%) > liver (50%) > muscle (47%) > heart (44%) inhibition at a sublethal concentration of 0.96 mg/L. Significant inhibition was detected in Na⁺, K⁺-ATPase activity, ranging from gills (90%) > heart (78%) > kidney (78%) > muscle (74%) > intestine (71%) > brain (67%) > liver (63%) at sublethal concentration of 1.86 mg/L. After subacute exposure (15 days) only gills and brain showed significant inhibition after higher concentration (1.86 mg/L). However, it is evident that exposure duration is more important than dose in the inhibition of the activity of enzyme. At lower concentration initial stimulation of the activity of Na⁺, K⁺-ATPase activity was also noticed. It is suggested that the inhibition of the ATPase by monocrotophos blocked the active transport system of the gill epithelial as well as chloride cells, glomerular and epithelial cells of the tubules and thus altered the osmoregulatory mechanism of the fish. In fact, the impairment of the activity of enzymes which carry out key physiological roles could cause alterations of the physiology of the whole organism.     

Isolation of insect microsomal oxidases by rapid centrifugation

Only about 60% of the total relative gravitational force conventionally used to sediment microsomes is needed to prepare highly active microsomes from the midgut tissues of an insect larva. A rapid preliminary centrifugation for 2 min at 39,000g_max effectively removed contaminating microorganisms, tissue debris, nuclei, and mitochondria. The supernatant was recentrifuged for 20 min to 210,000g to sediment the microsomes. There were no losses of microsomal oxidase activities or degradation of cytochrome P-450 to the inactive form (P-420) resulting from the application of the higher gravitational force. Incorporation of 1 mM EDTA in the buffer and washing the microsomes resulted in an improved yield of the cytochrome compared to that in microsomes prepared in sucrose. Yields of microsomal protein, cytochrome P-450, and NADPH-cytochrome c reductase in the rapidly isolated microsomes were as good as those in conventionally prepared microsomes. The apparent kinetic characteristics of several microsomal oxidation activities and optical difference spectra of Types 1 and 2 ligands were identical in the rapidly and conventionally prepared microsomes. The morphological appearance of the microsomes was examined by electron microscopy. Microsomal pellets prepared by either method were indistinguishable. The rapid procedure saves significant time in microsome preparation and yields microsomal oxidase activities as good or slightly better than those prepared by usual centrifuged procedures.     

Functional expression of Helicoverpa armigera CYP9A12 and CYP9A14 in Saccharomyces cerevisiae

Elevated oxidative detoxification is a major mechanism responsible for pyrethroid resistance in Helicoverpa armigera from Asia. Constitutive overexpression of CYP9A12 and CYP9A14 was associated with pyrethroid resistance in the YGF strain of H. armigera. CYP9A12 and CYP9A14 were functionally expressed in the W(R) strain of yeast (Saccharomyces cerevisiae) transformed with a plasmid shuttle vector pYES2. The cell lysates prepared from yeast transformed with CYP9A12 and CYP9A14, respectively, exhibited considerable O-demethylation activities against two model substrates p-nitroanisole (0.59 and 0.42 nmol p-nitrophenol min⁻¹ mg protein⁻¹) and methoxyresorufin (2.98 and 5.41 pmol resorufin min⁻¹ mg protein⁻¹), and clearance activity against the pyrethroid esfenvalerate (8.18 and 4.29 pmol esfenvalerate min⁻¹ mg protein⁻¹). These results provide important evidence on the role of CYP9A12 and CYP9A14 in conferring pyrethroid resistance in H. armigera, and also demonstrate that the yeast expression system can provide necessary redox environment for insect P450s to metabolize xenobiotics.     

The role of tyrosinase in the inactivation of house fly microsomal mixed-function oxidases

The low mixed-function oxidase activity of house fly microsomes has been associated with low cytochrome P-450 content and NADPH-cytochrome c reductase activity. The microsomal cytochrome P-450 content and NADPH-cytochrome c reductase activity could be decreased by the addition of catechol and increased by the addition of cyanide to the homogenates. Similar results were obtained with rat liver microsomes treated with tyrosinase and catechol. During the inactivation of rat liver microsomal enzymes by tyrosinase and catechol, crosslinking of microsomal proteins occurred. These results suggest that the instability of house fly microsomal mixed-function oxidase may be due in part to the action of contaminating tyrosinase on endogenous substrates.     

Acetylcholinesterase in selected plant-parasitic nematodes: Inhibition, kinetic and comparative studies

The in vitro inhibition potency of some organophosphates (OPs) and carbamates (CAs) which are widely used to control plant-parasitic nematodes on acetylcholinesterase (AChE) of Meloidogyne javanica, Heterodera avenae and Tylenchulus semipenetrans, the major pathogens responsible for the damage of a wide range of crops in Al-Qassim region, Saudi Arabia was examined. AChE of H. avenae activity was 1.58- and 1.51-fold greater than that of T. semipenetrans or M. javanica, respectively. The order of inhibition potency of the tested compounds against T. semipenetrans AChE was: carbofuran > paraoxon > oxamyl > fenamiphos > phorate-sulfoxide > aldicarb, where the corresponding concentrations that inhibited 50% of the nematode AChE activity (I₅₀) were 5 × 10⁻⁸, 7 × 10⁻⁷, 7.5 × 10⁻⁷, 2 × 10⁻⁶, 2 × 10⁻⁴ and 2 × 10⁻³ M, respectively. Paraoxon, fenamiphos and carbofuran exhibited high inhibition potency against M. javanica AChE where the I₅₀ values were below 1 nM. Phorate-sulfoxide and aldicarb were potent inhibitors of M. javanica AChE with I₅₀ values of 3.8 and 8 nM, respectively, while oxamyl exhibited low inhibition potency with I₅₀ of 15 nM. Fenamiphos and paraoxon showed the highest I₅₀ values of <100 μM against H. avenae followed by oxamyl (I₅₀ < 1 mM), whereas paraoxon, carbofuran and aldicarb showed low potency with I₅₀ values >1 mM. All the tested compounds exhibited high inhibition potency to AChE of M. javanica than T. semipenetrans or H. avenae. Except phorate-sulfoxide in M. javanica the inhibition pattern and implied mechanism for all the tested compounds for the three nematodes is suggested to be a linear mixed type (a combination of competitive and non-completive type).     

Effects of dietary pyridoxine on growth and biochemical responses of Labeo rohita fingerlings exposed to endosulfan

A sixty-day experiment was carried out to study the effect of dietary pyridoxine (PN) on growth performance, RNA/DNA ratio and some biochemical parameters of Labeo rohita fingerlings exposed to sub-lethal dose of endosulfan (1/10th of 96 h static non-renewal LC₅₀ = 0.2 ppb) to assess the role of pyridoxine in ameliorating the negative effects of endosulfan. Two hundred seventy fingerlings (6.5 ± 0.26 g) were randomly distributed into six treatments in triplicates (15 fish/tank). Five iso-nitrogenous (35.45-35.75% crude protein) purified diets were prepared with graded levels of pyridoxine. Six treatment groups were T₀ (10 mg PN + without endosulfan), T₁ (0 mg PN + endosulfan), T₂ (10 mg PN + endosulfan), T₃ (50 mg PN + endosulfan), T₄ (100 mg PN + endosulfan) and T₅ (200 mg PN + endosulfan). Weight gain (%), specific growth rate (SGR), tissue glycogen, and protease activity were significantly (P < 0.05) higher in pyridoxine fed groups compared to their non-pyridoxine fed counterpart. Protease activity was positively correlated (R² = 0.931) with (%) weight gain. Glucose-6-phosphate dehydrogenase (G6PDH) activity was significantly (P < 0.05) higher in non-pyridoxine fed group and decreased in pyridoxine fed counterparts. There were no significant (P > 0.05) effect of dietary pyridoxine on feed conversion ratio (FCR), protein efficiency ratio (PER), survival, gastro-somatic index (GSI), hepato-somatic index (HSI) and liver and muscle DNA levels of L. rohita fingerlings. RNA levels, both in liver and muscle, increased significantly (P < 0.05) in pyridoxine fed groups. A positive correlation was observed between growth and RNA levels, both in liver (R² = 0.91) and muscle (R² = 0.88). RNA/DNA ratio showed a third order polynomial relationship with dietary pyridoxine, both in liver (Y = −0.014x³ + 0.1613x² − 0.5333x + 0.7933, R² = 0.987) and muscle (Y = −0.0407x³ + 0.4763x² − 1.6358x + 2.4667, R² = 0.9345). The overall results obtained in present study indicated that dietary pyridoxine supplementation at 100 or 200 mg PN/kg diet ameliorates the negative effects of endosulfan and restores optimal growth of L. rohita fingerlings.     

Evaluation of molluscicidal activities of Arisaema tubers extracts on the snail Oncomelania hupensis

Four extracts of Arisaema erubescens tubers by acetic acetal (AAE), benzinum (BZE), n-butanol (NBE) and chloroform (CFE) were obtained to evaluate their molluscicidal activities against the snail Oncomlania hupensis. The responses of choline esterase (ChE), alkaline phosphatase (ALP), esterase (EST), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) to the extracts (NBE) were also investigated. In the four extracts (AAE, BZE, NBE and CFE), NBE showed the highest toxicity on the snails after 48 h exposure. NBE also showed the time- and concentration-dependent effect, for example, the LC₉₀ values of the NBE were decreased from 365.5 mg/L (24 h) to 36.4 mg/L (96 h). At the end of exposure to NBE (LC₅₀ concentration), the activities of ChE and ALP in snail tissues (cephalopodium and liver) decreased significantly. Isozyme electrophoresis profiles indicated that responses of isozymes (EST, SOD and GSH-Px) to NBE were more intense in liver than in cephalopodium. After 72 h exposure to NBE, the EST activity in snail liver decreased and some enzyme bands (EST1 and EST4) disappeared. But the activities of SOD 1 and GSH 2 in liver increased after 48 h exposure. The results indicated that NBE was the highest toxic component in the four extracts. The decline of the detoxification ability and the oxidative damage in snail tissues might be the main reason for the molluscicidal activities.     

Effects of carbaryl and azinphos methyl on juvenile rainbow trout (Oncorhynchus mykiss) detoxifying enzymes

In this study, the effects of sublethal exposures to the anticholinesterase insecticides azinphos methyl (AzMe) and carbaryl on the detoxifying responses of juvenile rainbow trout Oncorhynchus mykiss were investigated. Juvenile specimen were exposed to sublethal concentrations of AzMe (2.5 and 5 μg/L) and carbaryl (1 and 3 mg/L) for 24, 48 and 96 h. Carboxylesterase (CbE), catalase (CAT) and glutathione S-transferase (GST) activities as well as reduced glutathione (GSH) and cytochrome P450-1A (CYP1A) levels were monitored in liver and/or kidney. In all exposed groups liver CbE was significantly inhibited. Liver and kidney GSH level was reduced after sublethal exposure to both compounds. Carbaryl induced CAT activity during the first 48 h of exposure, followed by a significant decrease, whereas AzMe continuously decreased CAT activity. GST activity and CYP1A were transiently induced at 24 h by carbaryl exposure (3 mg/L) but sublethal exposure to AzMe did not affect GST activity or CYP1A. Our results show that the O. mykiss detoxifying system are a target for carbaryl and AzMe action, probably affecting redox balance. Although the responses showed similar trends in both organs, they were more important in liver than in kidney. The early inhibitory effect in CAT activity and GSH content produced by AzMe may be associated with a high degree of oxidative stress. Early induction of CYP1A, GST and CAT by carbaryl followed by enzyme inhibition suggests a milder or delayed oxidative stress, revealing differences between both pesticides metabolization. CbE inhibition is a good biomarker for AzMe and carbaryl exposure.     

Comparison of the inhibition effect of different anticoagulants on vitamin K epoxide reductase activity from warfarin-susceptible and resistant rat

Anti-vitamin K drugs are widely used as anticoagulant in human thromboembolic diseases. Similar compounds have also been used as rodenticides to control rodent population since 1950s. Massive use of first generation anticoagulants, especially warfarin, has lead to the development of genetic resistances in rodents. Similar resistances have been reported in human. In both cases, polymorphisms in VKORC1 (Vitamin K epoxide reductase subunit 1), the subunit 1 of the VKOR (Vitamin K epoxide reductase) complex, were involved. In rats (Rattus norvegicus), the Y139F mutation confers a high degree of resistance to warfarin. Little is known about the in vitro consequences of Y139F mutation on inhibitory effect of different anticoagulants available. A warfarin-susceptible and a warfarin-resistant Y139F strain of wild rats (Rattus norvegicus) are maintained in enclosures of the Lyon College of Veterinary Medicine (France). Using liver microsomes from susceptible or resistant rats, we studied inhibition parameters by warfarin (K_i = 0.72 ± 0.1 μM; 29 ± 4.1 μM), chlorophacinone (K_i = 0.08 ± 0.01 μM; 1.6 ± 0.1 μM), diphacinone (K_i = 0.07 ± 0.01 μM; 5.0 ± 0.8 μM), coumachlor (K_i = 0.12 ± 0.02 μM; 1.9 ± 0.2 μM), coumatetralyl (K_i = 0.13 ± 0.02 μM; 3.1 ± 0.4 μM), difenacoum (K_i = 0.07 ± 0.01 μM; 0.26 ± 0.02 μM), bromadiolone (K_i = 0.13 ± 0.02 μM; 0.91 ± 0.07 μM), and brodifacoum (K_i = 0.04 ± 0.01 μM; 0.09 ± 0.01 μM) on VKOR activity. Analysis of the results leads us to highlight different anticoagulant structural elements, which influence inhibition parameters in both susceptible and Y139F resistant rats.     

Endocrine disruption and metabolic changes following exposure of Cyprinus carpio to diethyl phthalate

Diethyl phthalate (DEP) enter into aquatic environment from industries manufacturing cosmetics, plastic and many commercial products and can pose potential fish and human health hazard. This experiment evaluated effects of DEP in adult male (89 g) common carp (Cyprinus carpio) by exposing them to fractions of LC₅₀ (1/500-1/2.5) doses with every change of water for 28 days. Vitellogenin induction metabolic enzymes, somatic indices and bioaccumulation were studied on 7th, 14th, 21st and 28th day. The 96th hour LC₅₀ of DEP in fingerlings was found to be 48 mg/L. Compared to control, except increase (P < 0.01) in alkaline phosphatase activity (EC 3.1.3.1) and liver size, there was decrease (P < 0.01) in activity of acid phosphatase (EC 3.1.3.2), aspartate aminotransferase (EC 2.6.1.1), alanine aminotransferase (EC 2.6.1.2) and testiculosomatic index following exposure to 1, 5 and 20 ppm DEP. Significant (P < 0.01) dose dependant vitellogenin induction was observed with exposure of fish to 0.1, 1 and 5 ppm DEP. The bioaccumulation of DEP in testis, liver, brain, gills and more importantly in muscle tissues of fish increased significantly (P < 0.01) with increase of dose from 1 to 5 ppm. Significant interaction (P < 0.01) of dose and duration of exposure indicated that exposure period of a week to two was sufficient to bring about changes in quantifiable parameters studied. Fish exposed to 20 ppm DEP became lethargic and discolored during onset of the 4th week. This is the first report describing metabolic changes and vitellogenin induction following exposure of C. carpio to DEP dose that is as low as 1/500th fraction of LC₅₀.     

Structure-activity relationships of pheromonostasis induced by ACCase-inhibitor herbicides in the moth Helicoverpa armigera

Many moth sex pheromone blends are derived from fatty acids and their production is regulated by a Pheromone Biosynthesis Activating Neuropeptide (PBAN). In prior work we showed that the herbicide Diclofop-acid, an acetyl-coenzyme A carboxylase (ACCase) inhibitor, inhibits PBAN-induced sex pheromone production in vitro. In this work we extend our study showing that several other herbicides, belonging to the 2-aryloxyphenoxypropionate (‘FOP’) and the cyclohexandione-oxime (‘DIM’) families significantly inhibit pheromone production by adult females whilst survival is unaffected by treatment. Enzyme activity in vitro and kinetic analysis revealed a K_m of 0.35 μM with K_i values of 0.1 and 0.28 μM due to Tralkoxydim and Diclofop inhibition, respectively. Inhibitory activity on PBAN-induced pheromone production by all herbicides tested revealed a potency order: Tralkoxydim > Clodinafop > Cycloxidim > Haloxyfop > Diclofop > Fenoxaprop > Fluazifop > Quizalofop, Quizalofop being inactive. Differences in inhibition efficiencies may be attributed to different binding sites on the enzyme or to the polarity and solubility of these compounds.     

Structure-activity relationships of 1,2,3-benzothiadiazole insecticide synergists as inhibitors of microsomal oxidation

The activities of 47 substituted 1,2,3-benzothiadiazoles as inhibitors of microsomal epoxidation and/or hydroxylation in enzyme preparations from rat liver or armyworm (Spodoptera eridania) gut have been evaluated. Many were found to be effective inhibitors of microsomal oxidation, the most active being the 6-butyl and 6-propoxy derivatives with I₅₀ values of 4.9 × 10^?7 and 7.0 × 10^?7M, respectively, for the epoxidation reaction. Regression analyses have established that activity of the 5-, 6-, and 5,6-substituted compounds can be satisfactorily described in equations in terms of π², π, and σ whereas that of the 4-substituted derivatives depends on π and the steric parameter E₈.