Effects of the pyrethroid insecticide permethrin on membrane fluidity

Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids

Membrane lipids modulate the proteins embedded in the bilayer matrix by two non-exclusive mechanisms: direct or indirect. The latter comprise those effects mediated by the physicochemical state of the membrane bilayer, whereas direct modulation entails the more specific regulatory effects transduced via recognition sites on the target membrane protein. The nicotinic acetylcholine receptor (nAChR), the paradigm member of the pentameric ligand-gated ion channel (pLGIC) superfamily of rapid neurotransmitter receptors, is modulated by both mechanisms. Reciprocally, the nAChR protein exerts influence on its surrounding interstitial lipids. Folding, conformational equilibria, ligand binding, ion permeation, topography, and diffusion of the nAChR are modulated by membrane lipids. The knowledge gained from biophysical studies of this prototypic membrane protein can be applied to other neurotransmitter receptors and most other integral membrane proteins.

Membrane interaction and selectivity of novel alternating cationic lipid-nanodisc assembling polymers

Synthetic polymer nanodiscs are self-assembled structures formed from amphipathic copolymers encapsulating membrane proteins and surrounding phospholipids into water soluble discs. These nanostructures have served as an analytical tool for the detergent free solubilisation and structural study of membrane proteins (MPs) in their native lipid environment. We established the polymer-lipid nanodisc forming ability of a novel class of amphipathic copolymer comprised of an alternating sequence of N-alkyl functionalised maleimide (AlkylM) of systematically varied hydrocarbon chain length, and cationic N-methyl-4-vinyl pyridinium iodide (MVP). Using a combination of physicochemical techniques, the solubilisation efficiency, size, structure and shape of DMPC lipid containing poly(MVP-co-AlkylM) nanodiscs were determined. Lipid solubilisation increased with AlkylM hydrocarbon chain length from methyl (MM), ethyl (EtM), n-propyl (PM), iso-butyl (IBM) through to n-butyl (BM) maleimide bearing polymers. More hydrophobic derivatives formed smaller sized nanodiscs and lipid ordering within poly(MVP-co-AlkylM) nanodiscs was affected by nanodisc size. In dye-release assays, shorter N-alkyl substituted polymers, particularly poly(MVP-co-EtM), exhibited low activities against eukaryotic mimetic POPC membrane and increased their liposome disruption as POPC : POPG membrane mixtures increased in their anionic POPG component, resembling the charge profile of bacterial membranes. These trends in membrane selectivity were transferred towards native cell systems in which gram-positive Staphylococcus aureus and gram-negative Acenobacter baumannii bacterial strains were relatively susceptible to disruption by hydrophobic n-butyl- and n-propyl-poly(MVP-co-AlkylM) derivatives compared to human red blood cells (HRBCs), with a more pronounced selectivity resulting from poly(MVP-co-PM). Such selective membrane interaction by less hydrophobic polymers provides a framework for polymer design towards applications including selective membrane component solubilisation, biosensing and antimicrobial development.

Insecticide and fungicide effect on thermal and olfactory behavior of bees and their disappearance in bees' tissues

Plant protection products may affect the behavior of organisms which are not a target of control. The effect of Karate Zeon 050 CS (λ-Cyhalothrin -based insecticide; λ-CBI) and Amistar 250 SC (Azoxystrobin-based fungicide; ABF) was determined on Apis mellifera worker attraction towards their own colony odour, along with temperature preferences. Bees exposed to pesticides prefer the environment with the odour of their nest less often than the control group, and that insecticide-treated bees chose warmer environments than the control insects. The observed differences in the bees, especially with attraction towards their own colony, were dependent on the time of day. Chromatographic analyses indicated that λ-Cyhalothrin elimination was half that of Azoxystrobin in bee organisms, and both agents retarded each other's clearance. Mathematical modeling estimated that despite a relatively high disappearance rate, both compounds might have been bio-accumulated at relatively high level.

Treating honey bees with an extremely low frequency electromagnetic field and pesticides: Impact on the rate of disappearance of azoxystrobin and λ-cyhalothrin and the structure of some functional groups of the probabilistic molecules

The purpose of these laboratory tests was to assess the impact of 50 Hz EMF (electromagnetic field) on the disappearance of azoxystrobin (active ingredient (AI) of Amistar 250 SC) and λ-cyhalothrin (AI of Karate Zeon 050 CS) in the body of honey bees (Apis mellifera) and the structure of some functional groups of the probabilistic molecules in their organisms. Amistar 250 SC (an azoxystrobin-based fungicide; ABF) and Karate Zeon 050 CS (a λ-cyhalothrin-based insecticide; CBI) are plant protection products (PPPs) applied to bee-pollinated-crops. Chromatographic methods were used to assess the rate of AI disappearance. EMF affected the rate of disappearance of azoxystrobin and λ-cyhalothrin in bees within 6 h of intoxication. When these substances were used separately their disappearance in the presence of EMF slowed from 12.6% to 10.5% h^-1 and from 9.2% to 4.8% h^-1, respectively, and accelerated when used in a mixture, from 14.1% to 14.7% h^-1 and from 9.3% to 11.5% h^-1 respectively. Fourier Transform Infrared (FTIR) spectroscopy was used to analyze changes in the functional groups of the probabilistic molecules of the tested bees. To obtain the information about the spectra variations we used the Principal Component Analysis. It has been shown, that EMF statistically significantly interferes with amide I and II, symmetric PO₃^2- group from DNA, RNA and phospholipids vibrations. It also increased the number of changes of functional groups of the probabilistic molecules caused by ABF, but at the same time limited the changes in the functional groups studied in bees treated with CBI and a mixture containing both of them. In addition, exposure to EMF in bees treated with fungicide or insecticide, separately, and with both preparations caused differences (p < 0.05) in the secondary structure of proteins compared to controls. The obtained results indicate that EMF may affect the rate of metabolism and the detoxification process of pesticides in bees, depending on the AI of PPPs, applied individually or together. However, further detailed research is required to explain the mechanism of EMF as a detoxification modulator.

Evaluation of toxicological responses and promising biomarkers of topmouth gudgeon (Pseudorasbora parva) exposed to fipronil at environmentally relevant levels

Fipronil is an insecticide commonly used in agriculture. We report here on the sublethal and sub-chronic effects of fipronil on non-target topmouth gudgeon (Pseudorasbora parva) at environmentally relevant levels. The results showed that fipronil did not cause significant changes in brain acetylcholinesterase activities, glutathione S-transferase (GST) activities in the intestine, and GST, glutamic pyruvic transaminase (GPT), and glutamic oxaloacetic transaminase (GOT) activities in the liver tissues at environmentally relevant levels for 96-h exposure. In the further test for a 12-day exposure, dose-dependent responses of the serum GPT and GOT activities were observed in all treated groups with sublethal concentrations of fipronil. Furthermore, fipronil could reduce the liver mitochondrial membrane fluidity of P. parva, especially with high concentration of fipronil at high temperature. The results suggest that serum GPT and GOT in P. parva might be useful biomarkers for effects of fipronil exposure at environmentally relevant level, and reducing fluidity of liver mitochondrial membrane may be one toxic mechanism of fipronil.

Contaminant exposure effects in a changing climate: how multiple stressors can multiply exposure effects in the amphipod Hyalella azteca

Global climate change (GCC) is likely to intensify the synergistic effects between altered physicochemical parameters [of changing habitats] and other anthropogenic threats, such as water pollution, posing increased risks to aquatic biodiversity. As such, it is critical to understand how organisms will respond to changes in water temperature and salinity in the presence of contaminants. We exposed the epibenthic amphipod Hyalella azteca to a 3 × 3 factorial treatment design of three temperatures and three salinities ranging from 12 to 18 °C and 0 to 8 parts per thousand (ppt), respectively, in combination with a low-level environmentally relevant concentration of the pyrethroid insecticide bifenthrin (1 ng/L). Effects on survival and swimming behavior were evaluated after 96 h exposure. Transcription of a select suite of genes was monitored at 24, 48, and 96 h using quantitative polymerase chain reaction (qPCR). Our results not only demonstrate that the changes in salinity and temperature result in negative effects to invertebrate survival, behavior, and gene response, but that the effects were significantly more pronounced in the presence of bifenthrin. This is particularly important since greater thermal fluctuations, changes in timing and extent of glacial melt, and changes in precipitation, could result in H. azteca experiencing lower temperatures at times that coincide with increased spraying of pyrethroids. These environmentally relevant exposures using the standard test species H. azteca provide essential information for understanding effects caused by GCC in conjunction with increasing pesticide use, further highlighting the need to incorporate GCC impacts into risk assessments of contaminants of concern.

Disruption of phosphatidylcholine monolayers and bilayers by perfluorobutane sulfonate

Perfluoroalkyl acids (PFAAs) are persistent environmental contaminants resistant to biological and chemical degradation due to the presence of carbon-fluorine bonds. These compounds exhibit developmental toxicity in vitro and in vivo. The mechanisms of toxicity may involve partitioning into lipid bilayers. We investigated the interaction between perfluorobutane sulfonate (PFBS), an emerging PFAA, and model phosphatidylcholine (PC) lipid assemblies (i.e., dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholine) using fluorescence anisotropy and Langmuir monolayer techniques. PFBS decreased the transition temperature and transition width of PC bilayers. The apparent membrane partition coefficients ranged from 4.9 × 10(2) to 8.2 × 10(2). The effects on each PC were comparable. The limiting molecular area of PC monolayers increased, and the surface pressure at collapse decreased in a concentration-dependent manner. The compressibility of all three PCs was decreased by PFBS. In summary, PFBS disrupted different model lipid assemblies, indicating potential for PFBS to be a human toxicant. However, the effects of PFBS are not as pronounced as those seen with longer chain PFAAs.

Immunotoxicity of pyrethroid metabolites in an in vitro model

Risk assessment of man-made chemicals such as pesticides are mainly focused on parent compounds, and relatively little is known about their metabolites, especially with regard to target organ damages such as immunotoxicity. In the present study, the immunotoxicity of five synthetic pyrethroids (SPs) and three common metabolites was evaluated using an in vitro model by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cytoflow, and enzyme-linked immunosorbent assay (ELISA). Cell viability and apoptosis assays showed that both SPs and their metabolites possessed cytotoxicity to the monocytic cells. The aldehyde and acid derivatives were more effective than the other compounds at cytotoxicity, with inhibition of cell viability by 56.8 and 50.6% at 10⁻⁵ mol L⁻¹, and induction of 8.52 and 8.81% cell apoptosis, respectively. Exposure to SPs and their metabolites also led to changes in the secretion levels of tumor necrosis factor α (TNF α) and interleukins (ILs), and again the metabolites showed stronger effects than the parent compounds. The aldehyde derivative upregulated IL-12p70 level by 1.87-fold, and the alcohol and acid derivative increased the secretion of TNF α 5.88 and 7.96-fold, relative to the control group. In the in vitro model, the common metabolites of SPs clearly exerted greater immunotoxic effects to monocytes than the intact parent compounds. Results from the present study suggested the need for considering metabolites in achieving more comprehensive health risk assessment of man-made chemicals, including target organ toxicities such as immunotoxicity.

Partitioning of perfluorooctanoate into phosphatidylcholine bilayers is chain length-independent

The chain length dependence of the interaction of PFOA, a persistent environmental contaminant, with dimyristoyl- (DMPC), dipalmitoyl- (DPPC) and distearoylphosphatidylcholine (DSPC) was investigated using steady-state fluorescence anisotropy spectroscopy, differential scanning calorimetry (DSC) and dynamic light scattering (DLS). PFOA caused a linear depression of the main phase transition temperature T(m) while increasing the width of the phase transition of all three phosphatidylcholines. Although PFOA's effect on T(m) and the transition width decreased in the order DMPC>DPPC>DSPC, its relative effect on the phase behavior was largely independent of the phosphatidylcholine. PFOA caused swelling of DMPC but not DPPC and DSPC liposomes at 37 degrees C in the DLS experiments, which suggests that PFOA partitions more readily into bilayers in the fluid phase. These findings suggest that PFOA's effect on the phase behavior of phosphatidylcholines depends on the cooperativity and state (i.e., gel versus liquid phase) of the membrane. DLS experiments are also consistent with partial liposome solubilization at PFOA/lipid molar ratios>1, which suggests the formation of mixed PFOA-lipid micelles.

Chronic exposure to pyrethroid-based allethrin and prallethrin mosquito repellents alters plasma biochemical profile

Continuous exposure of humans to pyrethroid-based mosquito repellents for longer durations may lead to adverse health effects. No information is available on long-term use of these mosquito repellents pertaining to the biochemical changes in human subjects. Therefore, the present study is an attempt to evaluate the status of health in human volunteers exposed to two commercially available mosquito repellent pyrethroids, allethrin and prallethrin, in terms of changes in plasma biochemical profile. Results of this study showed less but significant increase in the levels of plasma glucose, phospholipids, nitrite and nitrate, lipidperoxides with a decrease in plasma cholesterol. No significant changes were observed in the contents of total protein, albumin, globulin, HDL-C and LDL-C. However, SGPT activity increased significantly in persons exposed to only allethrin. Though the present investigation involving a limited number of human subjects indicates the onset of both protective changes as well as derangement in metabolism, a detailed and rigorous study is greatly warranted to arrive at a definite conclusion about the effects of pyrethroid mosquito repellents.

Influence of structural factors on the enhanced activity of moxifloxacin: a fluorescence and EPR spectroscopic study

Partition coefficients of moxifloxacin in liposomes of dimyristoyl-L-alpha-phosphatidylcholine or dimyristoyl-L-alpha-phosphatidylglycerol and water were determined by spectrophotometry and fluorimetry. The K (p) values obtained were larger than those reported for most of the other fluoroquinolones, a consequence of the structural changes observed in the molecule of moxifloxacin, which in turn change its acid/base properties. Introduction of a methoxy group at position 8 and a diazabicyclonyl ring at position 7 in the basic fluoroquinolone structure alters the charge distribution at the physiological pH of 7.4, and these changes seem to be responsible for its improved antibacterial potency and broader spectrum of activity. Location studies have also been performed using fluorescence and electron paramagnetic resonance (EPR) spectroscopies. The results show that moxifloxacin must be located near the phospholipid headgroups, similar to other fluoroquinolones, but contributions from a hydrophobic component were also detected. These results suggest that the enhanced activity of this drug may be related to a more facilitated entrance into the bacterial cell, perhaps including a mediator step involving electrostatic interaction with a hydrophobic component; this step then controls the extent or orientation of insertion and improves the electrostatic interaction.

Nuclear magnetic resonance and thermal studies on the interaction between salicylic acid and model membranes

DSC and (1H and 31P) NMR measurements are used to investigate the perturbation caused by the keratolytic drug, salicylic acid (SA) on the physicochemical properties of the model membranes. Model membranes (in unilamellar vesicular (ULV) form) in the present studies are prepared with the phospholipids, dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), dipalmitoyl phosphatidic acid (DPPA) and mixed lipid DPPC-DPPE (with weight ratio, 2.5:2.2). These lipids have the same acyl (dipalmitoyl) chains but differed in the headgroup. The molar ratio of the drug to lipid (lipid mixture), is in the range 0 to 0.4. The DSC and NMR results suggest that the lipid head groups have a pivotal role in controlling (i) the behavior of the membranes and (ii) their interactions with SA. In the presence of SA, the main phase transition temperature of (a) DPPE membrane decreases, (b) DPPA membrane increases and (c) DPPC and DPPC-DPPE membranes are not significantly changed. The drug increases the transition enthalpy (i.e., acyl chain order) in DPPC, DPPA and DPPC-DPPE membranes. However, the presence of the drug in DPPC membrane formed using water (instead of buffer), shows a decrease in the transition temperature and enthalpy. In all the systems studied, the drug molecules seem to be located in the interfacial region neighboring the glycerol backbone or polar headgroup. However, in DPPC-water system, the drug seems to penetrate the acyl chain region also.

Salicylic acid-induced effects in the mixed-lipid (dipalmitoyl phosphatidylcholine–dipalmitoyl phosphatidylethanolamine) model membrane

The effect of the keratolytic drug salicylic acid (SA) on the thermotropic properties and fluidity of the mixed lipid membrane dipalmitoyl phosphatidylcholine (DPPC)-dipalmitoyl phosphatidylethanolamine (DPPE) had been studied using DSC, (1H and 31P) NMR, SAXS, and dynamic light scattering. The membrane was in multilamellar vesicular (MLV) and unilamellar vesicular (ULV) form with SA/(DPPC+DPPE) molar ratios, R(m), in the range from 0 to 0.5. It was found that the mechanism of interaction of SA with the lipid mixture exhibited similar patterns in both ULV and MLV. Both the NMR and DSC studies indicated that the drug molecules were probably localized in the lipid-water interfacial region neighboring the lipid headgroups or the glycerol moiety. The presence of the drug increased the fluidity of the membrane and the acyl chain order. However, studies on MLV showed that the presence of the drug in high concentration (R(m)0.2), caused destabilization of the DPPC-DPPE mixture, as indicated by the appearance of two endothermic transitions. DSC studies indicated that prolonged equilibration of the membrane led to reduced interaction between the lipid headgroups and the SA molecules. This reduced interaction could be due to the sequestering of the drug molecules into the lipid-water interfacial region, out of proximity to the polar headgroup or glycerol moiety. Effect of inclusion of cholesterol in the membrane systems was also studied.

Influence of pyrethroids and piperonyl butoxide on the Ca2+-ATPase activity of rat brain synaptosomes and leukocyte membranes

Pyrethroids are widely used insecticides of low acute toxicity in mammals but the consequences of long-term exposure are of concern. Their insecticidal action is related to neurotoxicity and, in addition, there are indications of mammalian immunotoxicity. In order to clarify structure-activity relationships of the membrane interactions of pyrethroids, the present study compared the influence of selected pyrethroids, i.e. permethrin and the more water soluble esbiol (S-bioallethrin), both type I, and cyfluthrin, type II, on the Ca(2+)-ATPase activity of rat brain synaptosomes and peritoneal leukocyte membranes. The pyrethroids were tested alone as well as mixed with the enhancing substance piperonyl butoxide (PBO) at concentration ratios of 1:5 and 1:10. At the highest concentration tested, permethrin (10 microM) alone inhibited the ATPase activity of leukocyte membranes by 20%, whereas the synaptosomes were affected less. Esbiol and cyfluthrin alone did not affect either membrane preparation significantly, whereas PBO (50 microM) alone caused 10-15% inhibition. Mixtures of either pyrethroid with PBO inhibited the ATPase activity of both types of membranes (up to 40% inhibition) in a synergistic manner, which always tended to be supra-additive. With esbiol a true potentiation took place. The synergistic interaction between pyrethroid and PBO was most apparent with mixtures of a concentration ratio of 1:5. The ATPase activity of leukocyte membranes tended to be more susceptible to inhibition than that of synaptosomes. The results are in accordance with the assumption that the mammalian toxicity of pyrethroids can be ascribed to a general disturbance of cell membrane function in neuronal tissue. The results indicate that it may also be the case in the immune apparatus.

Interaction of rifampicin and isoniazid with large unilamellar liposomes: spectroscopic location studies

The location of isoniazid and rifampicin, two tuberculostatics commonly used for the treatment of Mycobacterium tuberculosis and Mycobacterium avium complex infectious diseases, in bilayers of dimyristoyl-L-alpha-phosphatidylcholine (DMPC) and dimyristoyl-L-a-phosphatidylglycerol (DMPG) have been studied by 1H NMR and fluorimetric methods. Steady-state fluorescence intensity and fluorescence energy transfer studies between rifampicin and a set of functionalized probes [n-(9-anthroyloxy)stearic acids, n=2, 12] reveal that, in both systems, isoniazid is located at the membrane surface whereas rifampicin is deeply buried inside the lipid bilayers. Steady-state fluorescence anisotropy studies performed with the probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and trimethylammonium-diphenylhexa-triene (TMA-DPH), not only corroborate the above results, but also show that no changes in membrane fluidity were detected in either liposome. The 1H NMR results, in DMPC liposomes, confirm the location of rifampicin near the methylene group of the acyl chains of the lipid bilayers.

Cypermethrin-induced plasma membrane perturbation on erythrocytes from rats: reduction of fluidity in the hydrophobic core and in glutathione peroxidase activity

The effects of treatment with the synthetic insecticide cypermethrin on plasma membrane fluidity, lipid peroxidation and antioxidant status in rat erythrocytes were investigated. Rats were treated by gavage with a low dose (12.5 mg/kg body weight per day) of cypermethrin in corn oil for 60 days. DPH and TMA-DPH fluorescence anisotropy experiments show that cypermethrin treatment, compared with controls, induced a significant decrease in erythrocyte membrane fluidity measured by DPH, while no changes were observed using TMA-DPH. Cypermethrin treatment also induced a significant increase in the lipid peroxidation, measured by the formation of conjugated dienes. The increased oxidative stress resulted in a significant decrease in the activity of glutathione peroxidase. The results are discussed in terms of preferential localization of cypermethrin in the hydrophobic core of the membrane, where it increases lipid packing and consequently decreases membrane fluidity.

An index of lipid phase diagrams

There is a growing awareness of the utility of lipid phase behavior data in studies of membrane-related phenomena. Such miscibility information is commonly reported in the form of temperature-composition (T-C) phase diagrams. The current index is a conduit to the relevant literature. It lists lipid phase diagrams, their components and conditions of measurement, and complete bibliographic information. The main focus of the index is on lipids of membrane origin where water is the dispersing medium. However, it also includes records on acylglycerols, fatty acids, cationic lipids, and detergent-containing systems. The miscibility of synthetic and natural lipids with other lipids, with water, and with biomolecules (proteins, nucleic acids, carbohydrates, etc.) and non-biological materials (drugs, anesthetics, organic solvents, etc.) is within the purview of the index. There are 2188 phase diagram records in the index, the bulk (81%) of which refers to binary (two-component) T-C phase diagrams. The remainder is made up of more complex (ternary, quaternary) systems, pressure-T phase diagrams, and other more exotic miscibility studies. The index covers the period from 1965 through to July, 2001.

Effects of carbaryl, permethrin, 4-nonylphenol, and copper on muscarinic cholinergic receptors in brain of surrogate and listed fish species

We investigated the regulation of the muscarinic cholinergic receptor (MChR) in brain from seven species of fish, two surrogates and five threatened or endangered species exposed to a series of chemicals as a measure of compensatory response among species. Fish were classified as either cold water (rainbow trout-surrogate, apache trout, lahanton trout) or warm water (fathead minnow-surrogate, razorback sucker, bonytail chub, colorado squawfish) and were exposed to chemicals shown to affect cholinergic pathways (carbaryl and permethrin) and two chemicals whose relationships to the cholinergic system is less clear (4-nonylphenol and copper). Downregulation of MChR occurred in all warm water species, except colorado squawfish, and at carbaryl concentrations similar to those causing downregulation observed in rainbow trout. Permethrin exposure resulted in downregulation in fathead minnow and razorback sucker, but the concentrations required for observation of this phenomenon were much greater than observed in cold water species. Copper exposure caused a decrease in brain MChR in rainbow trout and apache trout, whereas 4-nonylphenol exposure resulted in a decrease in brain MChR in all three cold water species. Our results indicate that surrogates are useful in assessing sublethal physiological responses to chemicals with a known mechanism of action such as carbaryl and support use of surrogates for assessing physiological responses to chemicals with diverse, less clear mechanisms of action.