Modulatory Effects of Natural Curcuminoids on P-Glycoprotein ATPase of Insecticide-Resistant Pest Helicoverpa armigera (Lepidopetera: Noctüidae)

Disruptive Effects of Two Curcuminoids (Demethoxycurcumin and Bisdemethoxycurcumin) on the Larval Development of Drosophila melanogaster

Juvenile hormones (JHs) play a central role in insect development, reproduction, and various physiological functions. Curcuminoids generally exhibit a wide range of biological activities, such as antioxidant, anti-inflammatory, antibacterial, and insecticidal, and they exhibit insect growth inhibitory effects. However, research on insecticidal properties of curcuminoids has been limited. Moreover, to the best of our knowledge, studies on JHs of insects and curcuminoids are lacking. Therefore, this study aimed to identify the substances that act as JH disruptors (JHDs) from edible plants. Demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC), two curcuminoids from the turmeric plant Curcuma longa L. inhibited the formation of a methoprene-tolerant (Met)-Taiman (Tai) heterodimer complex in Drosophila melanogaster, as shown through in vitro yeast two-hybrid assays. An artificial diet containing 1% (w/v) DMC or BDMC significantly reduced the number of D. melanogaster larvae in a concentration-dependent manner; larval development was disrupted, preventing the progression of larvae to pupal stages, resulting in an absence of adults. Building on the results obtained in this study on curcuminoids, researchers can use our study as a reference to develop eco-friendly pesticides.

Insights into the Use of Eco-Friendly Synergists in Resistance Management of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is the most notorious insect pest of potato globally. Injudicious use of insecticides for management of this pest has resulted in resistance to all major groups of insecticides along with many human, animal health, and environmental concerns. Additionally, the input cost of insecticide development/discovery is markedly increasing because each year thousands of chemicals are produced and tested for their insecticidal properties, requiring billions of dollars. For the management of resistance in insect pests, synergists can play a pivotal role by reducing the application dose of most insecticides. These eco-friendly synergists can be classified into two types: plant-based synergists and RNAi-based synergists. The use of plant-based and RNAi-based synergists in resistance management of insect pests can give promising results with lesser environmental side effects. This review summarizes the resistance status of CPB and discusses the potential advantage of plant-based and RNAi-based synergists for CPB resistance management. It will motivate researchers to further investigate the techniques of using plant- and RNAi-based synergists in combination with insecticides.

Structure-based alteration of tryptophan residues of the multidrug transporter CmABCB1 to assess substrate binding using fluorescence spectroscopy

ABCB1, also known as P-glycoprotein, is an essential component of many physiological barriers and extrudes a variety of hydrophobic chemicals out of the cell. Structures of ABCB1 provided insights into the structural changes that occur upon ATP binding and the characteristic architecture of the substrate binding site. Yet, the structure-function relationship between substrate binding and transporting still remains largely obscured because there is no robust method for accurately measuring substrate binding constants. The methods currently used cannot identify whether the bound substrates are located in the inner chamber of the molecule in the transmembrane region or not because of the low spatial resolution. Here, we report a system for measuring the affinity of substrate binding to the Cyanidioschyzon merolae ABCB1 (CmABCB1) using site-specific tryptophan (Trp) fluorescence quenching. We designed a CmABCB1 mutant with an extrinsic Trp residue introduced into the inner chamber. Trp fluorescence was quenched by three substrates and one inhibitor, including rhodamine 6G, in a saturable fashion, allowing for accurate estimation of the dissociation constant (KD ) for each molecule. The KD for rhodamine 6G is similar to that determined using a reciprocal fluorescence quenching assay using rhodamine 6G fluorescence, suggesting that Trp fluorescence of the mutant was quenched by the interaction between the extrinsic Trp and substrates bound in the inner chamber. Structural comparison of the ABCB1 structures suggests that the system presented in this study could be ideal method of choice to determine the substrate binding affinities of compounds bound to the chamber of mammalian ABCB1.

ATP-binding cassette transporters ABCF2 and ABCG9 regulate rice black-streaked dwarf virus infection in its insect vector, Laodelphax striatellus (Fallén)

The majority of plant viral disease is transmitted and spread by insect vectors in the field. The small brown planthopper, Laodelphax striatellus (Fallén), is the only efficient vector for rice black-streaked dwarf virus (RBSDV), a devastating plant virus that infects multiple grain crops, including rice, maize, and wheat. Adenosine triphosphate (ATP)-binding cassette (ABC) transporters participate in various biological processes. However, little is known about whether ABC transporters affect virus infection in insects. In this study, RBSDV accumulation was significantly reduced in L. striatellus after treatment with verapamil, an effective inhibitor of ABC transporters. Thirty-four ABC transporter genes were identified in L. striatellus and expression analysis showed that LsABCF2 and LsABCG9 were significantly upregulated and downregulated, respectively, after RBSDV infection. LsABCF2 and LsABCG9 were expressed during all developmental stages, and LsABCG9 was highly expressed in the midgut of L. striatellus. Knockdown of LsABCF2 promoted RBSDV accumulation, while knockdown of LsABCG9 suppressed RBSDV accumulation in L. striatellus. Our data showed that L. striatellus might upregulate the expression of LsABCF2 and downregulate LsABCG9 expression to suppress RBSDV infection. These results will contribute to understanding the effects of ABC transporters on virus transmission and provide theoretical basis for virus management in the field.

Determination of effective concentrations of drug absorption enhancers using in vitro and ex vivo models

BACKGROUND

Achievement of an effective concentration of the pharmaceutically active ingredient in the blood and/or at the target site is an important aspect in the formulation of drugs and therefore needs to be quantified. Any concentration above therapeutic levels can cause toxic effects whereas low concentrations can be sub-therapeutic. This paper investigated different concentrations of selected commercially sourced analytical-grade pure chemicals as potential drug absorption enhancers in vitro and ex vivo to determine the lowest effective concentrations for optimizing drug absorption in oral dosage forms.

METHODS

Recombinant cytochrome (CYP) 3A4 enzyme and recombinant p-glycoprotein membrane models were utilized for the investigation of in vitro inhibitory effects of drug absorption enhancers. Promega (2015) protocols were adopted for both assays. The everted porcine intestinal ex vivo model was employed for assessing effects of the drug absorption enhancers on the absorption of propranolol.

RESULTS

The lowest effective CYP3A4 inhibitory concentrations were observed for curcumin (75µM and 100 µM), quercetin (75 and 100 µM) and glycyrrhizic acid (50 µM) while the most effective p-glycoprotein (P-gp) inhibition concentrations were curcumin (10, 15, 25, 50, 75 and 100 µM), sinomenine (50, 75, and 100 µM), quercetin (75 and 100 µM) and naringin (50 µM). Additive effects were observed between combinations of quercetin (75 µM) and curcumin (100 µM); quercetin (75 µM) and curcumin (75 µM); quercetin (75 µM) and curcumin (50 µM), and quercetin (75 µM) with curcumin (10 µM), which increased the basal ex vivo absorption of propranolol from 1.24 ± 0.03 µg/mL to 5.19 ± 0.12 µg/mL, 4.17 ± 0.05 µg/mL, 3.86 ± 0.10 µg/mL, and 4.07± 0.05 µg/mL respectively, after 2 hours.

CONCLUSION

Incorporation of the drug absorption enhancers (e.g., curcumin and quercetin), at specific concentrations, in dosage forms could improve the bioavailability of the BCS Class III and IV drugs that are substrates of CYP3A4 and p-glycoprotein.

Enterodiol is Actively Transported by Rat Liver Cell Membranes

The interaction of enterodiol and the well-described polyphenol epigallocatechin gallate (EGCG) with hepatic membranes has been matter of interest in the last few years. On one hand, EGCG is only able to bind to the phospholipid polar head groups, as it has been already described in synthetic lipid bilayers and erythrocyte membranes but cannot get inserted into the hydrophobic core or be transported into the lumen of membrane vesicles. On the other, enterodiol has no interaction with non-energized membranes either, but it is able to interact and even be transported upon addition of ATP. In fact, the ATPase activity undergoes a twofold increase in the presence of enterodiol but not in the presence of EGCG. This is the first report on the transport of enterodiol by liver membranes, and it may help explain the rather high blood concentrations of this estrogenic enterolignan compared to EGCG, which is extensively metabolized by the intestine and the liver. The present results suggest that a fraction of enterodiol may escape the liver inactivation by being pumped out from the hepatocytes to the bloodstream.

MOLECULAR CLONING, EXPRESSION PATTERN OF MULTIDRUG RESISTANCE ASSOCIATED PROTEIN 1 (MRP1, ABCC1) GENE, AND THE SYNERGISTIC EFFECTS OF VERAPAMIL ON TOXICITY OF TWO INSECTICIDES IN THE BIRD CHERRY-OAT APHID

The ATP-binding cassette (ABC) transporters are important transmembrane proteins encoded by a supergene family. The majority of ABC proteins are primary active transporters that bind and hydrolyze ATP to mediate the efflux of a diverse range of substrates across lipid membranes. In this study, we cloned and characterized a putative multidrug resistance associated protein 1 (MRP1) from Rhopalosiphum padi encoded by ABCC1. Structural analysis showed that this protein has structural features typical of the ABC transporter family. Phylogenetic analysis indicated that the amino acid sequence was highly similar that of the corresponding protein from Acyrthosiphon pisum. Real-time quantitative polymerase chain reaction (PCR) analysis showed that ABCC1 was expressed throughout all R. padi developmental stages, with the highest level of expression in the fourth larval instar. We also examined ABCC1 expression in four different tissue types and found that it was most highly expressed in the midgut. Exposing R. padi to imidacloprid and chlorpyrifos increased ABCC1 expression. Furthermore, ABCC1 expression was higher in the imidacloprid-resistant (IR) and chlorpyrifos-resistant (CR) strains than in an insecticide-susceptible strain (SS) of R. padi. Exposing R. padi to verapamil in combination with insecticides significantly increased the toxicity of the insecticides. The respective synergy factor of CR and IR R. padi strain was 1.33 and 1.26, which was lower than that (2.72 and 1.64, respectively) of the SS. Our results clarify the biological function of ABCC1 in R. padi, particularly its role in insecticide resistance, and suggest novel strategies for pest management that use ABC transporter inhibitors to increase the effectiveness of insecticides.

The ABC gene family in arthropods: comparative genomics and role in insecticide transport and resistance

About a 100 years ago, the Drosophila white mutant marked the birth of Drosophila genetics. The white gene turned out to encode the first well studied ABC transporter in arthropods. The ABC gene family is now recognized as one of the largest transporter families in all kingdoms of life. The majority of ABC proteins function as primary-active transporters that bind and hydrolyze ATP while transporting a large diversity of substrates across lipid membranes. Although extremely well studied in vertebrates for their role in drug resistance, less is known about the role of this family in the transport of endogenous and exogenous substances in arthropods. The ABC families of five insect species, a crustacean and a chelicerate have been annotated in some detail. We conducted a thorough phylogenetic analysis of the seven arthropod and human ABC protein subfamilies, to infer orthologous relationships that might suggest conserved function. Most orthologous relationships were found in the ABCB half transporter, ABCD, ABCE and ABCF subfamilies, but specific expansions within species and lineages are frequently observed and discussed. We next surveyed the role of ABC transporters in the transport of xenobiotics/plant allelochemicals and their involvement in insecticide resistance. The involvement of ABC transporters in xenobiotic resistance in arthropods is historically not well documented, but an increasing number of studies using unbiased differential gene expression analysis now points to their importance. We give an overview of methods that can be used to link ABC transporters to resistance. ABC proteins have also recently been implicated in the mode of action and resistance to Bt toxins in Lepidoptera. Given the enormous interest in Bt toxicology in transgenic crops, such findings will provide an impetus to further reveal the role of ABC transporters in arthropods.

Mosquitocidal properties of natural product compounds isolated from Chinese herbs and synthetic analogs of curcumin

Because of resistance to current insecticides and to environmental, health, and regulatory concerns, naturally occurring compounds and their derivatives are of increasing interest for the development of new insecticidal compounds against vectors of disease-causing pathogens. Fifty-eight compounds, either extracted and purified from plants native to China or synthetic analogs of curcumin, were evaluated for both their larvicidal activity against Aedes aegypti (L.) and their ability to inhibit binding of cholesterol to Ae. aegypti sterol carrier protein-2 in vitro. Of the compounds tested, curcumin analogs seem especially promising in that of 24 compounds tested five were inhibitors of Ae. aegypti sterol carrier protein-2 with EC50 values ranging from 0.65 to 62.87 microM, and three curcumin analogs exhibited larvicidal activity against fourth instar Ae. aegypti larvae with LC50 values ranging from 17.29 to 27.90 microM. Adding to the attractiveness of synthetic curcumin analogs is the relative ease of synthesizing a large diversity of compounds; only a small fraction of such diversity has been sampled in this study.