Modified Danzhi Xiaoyao Powder (MDXP) improves the corneal damage in dry eye disease (DED) mice through phagocytosis.

ETHNOPHARMACOLOGICAL RELEVANCE: Modified Danzhi Xiaoyao Powder (MDXP) is a traditional Chinese medicine formula remedy for treating Dry Eye Disease (DED). It showed the function of dispersing stagnated liver Qi for relieving Qi stagnation and clearing heat, which can be effective in treating conditions such as Dry Eye Disease (DED) and irregular menstruation due to liver depression and fire transformation. AIM OF THE STUDY: This study investigated the mechanism of the effect of MDXP in mice with DED. MATERIALS AND METHODS: A DED model was induced in mice using chronic painful stimulation (tail clamping) in combination with Benzalkonium Chloride Solution drops administered in a dry box for 28 days. After modeling, the MDXP groups were given Chinese medicine with different dosages by gavage for 14 days. The following parameters were recorded in each group: body mass, anal temperature, tear secretion, tear film rupture time, and corneal fluorescein staining. Behavioral changes were evaluated by elevating cross-maze and open-field experiments. The levels of inflammatory factors serum tumor necrosis factor-α (TNF-α), interleukin 1ß (IL-1ß), fcγR-mediated phagocytosis pathway cell division control protein 42 homolog (CDC42), actin-related protein 2/3 complex subunit 2 (ARPC2), and actin-related protein 3 (ACTR3) were measured by using Enzyme-linked immunoassay (ELISA), immunohistochemical staining, and real-time fluorescent qualitative polymerase chain reaction (RT-qPCR). RESULTS: MDXP increased body mass and lowered body temperature, prolonged tear film break-up time, promoted tear secretion, repaired corneal damage, decreased horizontal and vertical scores, elevated percentage of open arm times and boom opening time percentage, and reduced the expression levels of inflammatory factors of TNF-α, IL-1ß and pathway-related proteins CDC42, ARPC2, and ACTR3 in mice. MDXP also reduced the expression levels of inflammatory factors of TNF-α and IL-1ß in human corneal endothelial cells (HCECs), mouse mononuclear macrophage cells (RAW264.7), and human myeloid leukemia mononuclear cells (THP-1). CONCLUSIONS: MDXP can relieve tension and anxiety, inhibit apoptosis, reduce phagocytosis, reduce the expression of pro-inflammatory factors, repair corneal damage, and improve the symptoms in DED mice. The mechanism of action may be through the fcγR-mediated phagocytosis pathway.

An oncogenic lncRNA, GLCC1, promotes tumorigenesis in gastric carcinoma by enhancing the c-Myc/IGF2BP1 interaction.

Accumulating evidence has shown that long non-coding RNAs (lncRNAs) are vital regulators of the expression of various genes in multiple human diseases. The aim of this study was to investigate the role of glycolysis-associated lncRNA of colorectal cancer (GLCC1) in the progression of gastric carcinoma as well as the underlying mechanism. The expression levels of GLCC1 and c-Myc were determined in 47 pairs of gastric carcinoma tissues and cell lines using quantitative real-time polymerase chain reaction (qRT-PCR). Next, the functional roles of GLCC1 and c-Myc in the proliferation, apoptosis, migration, and invasion of gastric carcinoma cells (BGC823 and SGC7901 cells) were determined by siRNA-mediated knockdown of these molecules, and the cells were evaluated by Cell Counting Kit-8 (CCK-8), flow cytometry, and Transwell assays. In addition, RIP and RNA pull-down assays were used to examine the interaction between GLCC1 and c-Myc/IGF2BP1. Further mechanistic studies were conducted using western blotting. lncRNA GLCC1 and c-Myc were observed to be significantly increased in both gastric carcinoma tissues and cell lines. Knockdown of GLCC1 or c-Myc suppressed cell proliferation, migration, and invasion but promoted apoptosis in both the BGC823 and SGC7901 cell lines. Mechanistically, c-Myc was identified as a downstream regulator involved in the GLCC1-mediated biological effects in gastric carcinoma. The RNA pull-down and RIP assays further showed that the upregulation of lncRNA GLCC1 enhanced the interaction of the IGF2BP1 protein with c-Myc mRNA, thus promoting the stabilization of c-Myc mRNA. Altogether, we demonstrated that lncRNA GLCC1 modulates gastric cancer cell migration and invasion by enhancing the c-Myc/IGF2BP1 interaction, and lncRNA GLCC1 may serve as a potential therapeutic target for preventing the development and progression of human gastric carcinoma.

Recent discoveries in HIV-1 reverse transcriptase inhibitors.

HIV-1 reverse transcriptase inhibitors (RTIs) are indispensable components of highly active antiretroviral therapy (HAART), which has achieved great success in controlling AIDS epidemic in reducing drastically the morbidity and mortality of HIV-infected patients. RTIs are divided into two categories, nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs). In this review, the recent discoveries in NRTIs and NNRTIs, including approved anti-HIV drugs and noteworthy drug candidates in different development stages, are summarized, and their future direction is prospected.

Indazolyl-substituted piperidin-4-yl-aminopyrimidines as HIV-1 NNRTIs: Design, synthesis and biological activities.

A series of indazolyl-substituted piperidin-4-yl-aminopyrimidines (IPAPYs) were designed from two potent HIV-1 NNRTIs piperidin-4-yl-aminopyrimidine 3c and diaryl ether 4 as the lead compounds by molecular hybridization strategy. The target molecules 5a-q were synthesized and evaluated for their anti-HIV activities and cytotoxicities in MT-4 cells. 5a-q displayed moderate to excellent activities against wild-type (WT) HIV-1 with EC50 values ranging from 1.5 to 0.0064 µM. Among them, 5q was regarded as the most excellent compound against WT HIV-1 (EC50 = 6.4 nM, SI = 2500). And also, it displayed potent activities against K103 N (EC50 = 0.077 µM), Y181C (EC50 = 0.11 µM), E138K (EC50 = 0.057 µM), and moderate activity against double mutants RES056 (EC50 = 8.7 µM). Moreover, the structure-activity relationships (SARs) were summarized, and the molecular docking was performed to investigate the binding mode of IPAPYs and HIV-1 reverse transcriptase.

Neurotoxicity and mode of action of fluralaner on honeybee Apis mellifera L.

BACKGROUND: Fluralaner, a novel pesticide that targets the γ-aminobutyric acid (GABA) receptor (GABAR) subunit of resistant to dieldrin (RDL), exhibits strong potential to be an insecticide to control agricultural insect pests. However, the risk and action of fluralaner to economic insects, e.g., honeybee Apis mellifera Linnaeus, remains unclear. RESULTS: In this study, both oral and contact toxicity of fluralaner to honeybee were found to be 0.13 µg adult-1 . Abamectin, dieldrin, ethiprole, α-endosulfan, fipronil and fluralaner strongly inhibited the GABA-induced current in A. mellifera RDL (AmRDL), expressed in Xenopus laevis oocytes, with median inhibitory concentration (IC50 ) values of 7.99, 868.1, 27.10, 412.0, 11.21 and 13.59 nM, respectively. The binding free energy and electrophysiological response of AmRDL and insecticides were opposite. The correlation values between toxicity (to A. mellifera) and binding free energy/electrophysiological inhibition (to AmRDL) were at a moderate level. CONCLUSION: In conclusion, we report for the first time the notable risk of fluralaner to honeybee in vivo and compared the actions of GABAR-targeted insecticides on the AmRDL receptor. © 2019 Society of Chemical Industry.

Recent progress in HIV-1 inhibitors targeting the entrance channel of HIV-1 non-nucleoside reverse transcriptase inhibitor binding pocket.

Since the entrance channel was proposed as a new binding site in non-nucleoside reverse transcriptase inhibitor binding pocket (NNIBP) of HIV-1 reverse transcriptase (RT) in 2012, a huge number of HIV-1 inhibitors acting on this target have sprung up, aiming to discover promising inhibitors with excellent antiviral activities, physicochemical properties, and so on. From 2012 to 2018, many noteworthy compounds have been continuously discovered. In this review, the recent progress in HIV-1 inhibitors targeting the entrance channel of HIV-1 NNIBP was summarized and reviewed, which would provide useful clues and inspiration for further design of HIV-1 inhibitors.

Advances in diarylpyrimidines and related analogues as HIV-1 nonnucleoside reverse transcriptase inhibitors.

HIV-1 nonnucleoside reverse transcriptase inhibitors (NNRTIs) have been playing an important role in the fight against acquired immunodeficiency syndrome (AIDS). Diarylpyrimidines (DAPYs) as the second generation NNRTIs, represented by etravirine (TMC125) and rilpivirine (TMC278), have attracted extensive attention due to their extraordinary potency, high specificity and low toxicity. However, the rapid emergence of drug-resistant virus strains and dissatisfactory pharmacokinetics of DAPYs present new challenges. In the past two decades, an increasing number of novel DAPY derivatives have emerged, which significantly enriched the structure-activity relationship of DAPYs. Studies of crystallography and molecular modeling have afforded a lot of useful information on structural requirements of NNRTIs, which contributes greatly to the improvement of their resistance profiles. In this review, we reviewed the discovery history and their evolution of DAPYs including their structural modification, derivatization and scaffold hopping in continuous pursuit of excellent anti-HIV drugs. And also, we discussed the prospect of DAPYs and the directions of future efforts.

Attenuation of Pseudomonas aeruginosa biofilm by hordenine: a combinatorial study with aminoglycoside antibiotics.

Pseudomonas aeruginosa is a ubiquitous pathogen that is the leading cause of chronic infections. Bacterial biofilm formation facilitates CF development and restricts the anti-bacterial potential of many current antibiotics. The capacity of P. aeruginosa to form biofilms and resist antibiotics is closely correlated with quorum sensing (QS). Disrupting QS by QS inhibitors is a promising strategy for treating chronic infections. Here, we evaluated the effect of hordenine, a recently characterized QS inhibitor, on the susceptibility of aminoglycoside antibiotics against P. aeruginosa biofilms. Hordenine significantly enhanced the susceptibility of aminoglycoside antibiotics tobramycin, gentamycin, and amikacin against P. aeruginosa PAO1 biofilm formation. Combinations of hordenine and aminoglycoside antibiotics showed potent efficiency in disrupting the preformed biofilms of P. aeruginosa. Microscopic observations showed flat, scattered, and unstructured biofilm architecture after treatment with hordenine. Mechanistic study further revealed that hordenine treatment led to the downregulation of genes involved in QS and biofilm formation. Thus, our results suggest that hordenine has the potential to function as an antibiotic accelerant in treating P. aeruginosa infections.

Effect of Qingguang'an II on expressions of OX42 protein and IL-1ß mRNA of retinal microglia cells of rats with chronic high intraocular pressure.

The study investigated the effects of Qingguang'an II (a Chinese medicinal preparation) on expressions of OX42 protein and interleukin-1ß (IL-1ß) mRNA of retinal microglia cells of rats with chronic high intraocular pressure (IOP). SD rats were randomly divided into 6 groups, that were: A: blank group; B: model group; C: Qingguang'an II low dose group; D: Qingguang'an II medium dose group; E: Qingguang'an II high dose group; F: Yimaikang disket (a Chinese medicinal preparation) group. Experimental rats in B, C, D, E, F groups were established the model of chronic high IOP by cauterizing of superficial scleral vein. Tissues of eyes were obtained after intragastric administration for 2 and 4wk. At the time-point of 2wk, OX42 protein and IL-1ß mRNA in group B were statistically expressed in higher level comparing with other groups (P<0.05). Moreover, at the time-point of 4wk, OX42 protein and IL-1ß mRNA in groups C, D and E were statistically expressed in lower level comparing with group F (P<0.05). Besides, OX42 protein and IL-1ß mRNA in groups C and D were statistically expressed in higher level comparing with group E (P<0.05). OX42 protein and IL-1ß mRNA in groups C and D were expressed in similar level (P>0.05). The study indicated that, in the protection of optic nerve of rats with chronic high IOP, the high dose of Qingguang'an II at the time-point of 4wk was the better choice.

Design and synthesis of hybrids of diarylpyrimidines and diketo acids as HIV-1 inhibitors.

Based on the strategy of molecular hybridization, diketo acid fragment as a classical phamacophore of integrase inhibitors was introduced to reverse transcriptase inhibitors diarylpyrimidines to design a series of diarylpyrimidine-diketo acid hybrids (DAPY-DKAs). The target molecules 10b and 11b showed inhibitory activities against WT HIV-1 with EC50 values of 0.18µM and 0.14µM, respectively. And the results of molecular docking demonstrated the potential binding mode and revealed that the DKA moiety and its ester could both be tolerated in the nonnucleoside binding site (NNBS) of HIV-1 RT.

[MRI findings of cerebral schistosomiasis in acute stage：establishment of experimental model of acute cerebral schistosomiasis with rabbits].

OBJECTIVE: To establish an experimental model of acute cerebral schistosomiasis japonica and explore the MRI manifestations of acute cerebral schistosomiasis. METHODS: Rabbits were divided into 3 groups with 10 rabbits in each group. The rabbits in the experimental group were directly injected with suspension fluid of Schistosoma japonicum eggs (0.9 mg, 1 ml) by the cranial drilling method, those in the negative control group were given saline (1 ml) by the same method above-mentioned, and those in the blank control group were not given any treatment. Antibiotic was given to the first two groups after the operation. The clinical manifestations of the 3 groups were observed, and the magnetic resonance imaging (MRI) was performed in 30 days post-operation, and then the brain tissues were taken for pathological examinations. RESULTS: All the rabbits in the experimental group exhibited inappetence, various neurological symptoms including hemiplegia, and weight loss after the operation; while those in the negative control group showed inappetence in 3 days after the operation, and 1 week later, the symptom disappeared; there were no adverse reactions in the blank control group. MRI of the experimental group showed nodular or patchy enhancement on T1WI enhancement, brain edema, abnormal ventricular dilatation, and needle augmentation. SWI displayed hypointense in the abnormal enhanced nodules and flaky hypointense on the operation brain. In the negative control group, 2 rabbits showed abnormal enhancement of the needle canal, and 1 showed mild dilatation of the ventricle. The blank control group showed normal manifestations. The pathological examinations showed abnormal appearances in 10 rabbits of the experimental group, including 6 with S. japonicum egg granuloma nodules, nonspecific granuloma nodules coexisted with perivascular inflammation; no granuloma nodules were found in the negative control group, but 2 rabbits showed vascular inflammation; the blank control group showed the normal brain tissue. CONCLUSIONS: An experimental model of acute cerebral schistosomiasis is successfully established in rabbits by intracranial injection of schistosome eggs. The MRI examination combined with the clinical manifestations can improve the accuracy of early diagnosis of cerebral schistosomiasis.

CT perfusion imaging of the stomach: a quantitative analysis according to different degrees of adenocarcinoma cell differentiation.

OBJECTIVES: To evaluate clinical usefulness of computed tomography perfusion imaging (CTPI) in gastric cancer. MATERIALS AND METHODS: Twenty subjects without gastric diseases (control group) and fifty patients with gastric cancer were studied prospectively using CTPI examinations. Four perfusion parameter values, i.e., blood flow (BF), blood volume (BV), mean transit time, and permeability surface (PS), were calculated. The gastric cancer group was divided into three groups: well differentiated, moderately differentiated, and poorly differentiated gastric adenocarcinoma. RESULTS: Comparing the three groups, differences between the well-differentiated group and the moderately differentiated group or the poorly differentiated group were all statistically significant for BF, BV, and PS. CONCLUSION: The BF, BV, and PS values could serve as indicators of the degree of malignancy of gastric cancer.

The synthetic melanocortin (CKPV)2 exerts anti-fungal and anti-inflammatory effects against Candida albicans vaginitis via inducing macrophage M2 polarization.

In this study, we examined anti-fungal and anti-inflammatory effects of the synthetic melanocortin peptide (Ac-Cys-Lys-Pro-Val-NH2)2 or (CKPV)2 against Candida albicans vaginitis. Our in vitro results showed that (CKPV)2 dose-dependently inhibited Candida albicans colonies formation. In a rat Candida albicans vaginitis model, (CKPV)2 significantly inhibited vaginal Candida albicans survival and macrophages sub-epithelial mucosa infiltration. For mechanisms study, we observed that (CKPV)2 inhibited macrophages phagocytosis of Candida albicans. Meanwhile, (CKPV)2 administration inhibited macrophage pro-inflammatory cytokines (TNF-α, IL-1ß and IL-6) release, while increasing the arginase activity and anti-inflammatory cytokine IL-10 production, suggesting macrophages M1 to M2 polarization. Cyclic AMP (cAMP) production was also induced by (CKPV)2 administration in macrophages. These above effects on macrophages by (CKPV)2 were almost reversed by melanocortin receptor-1(MC1R) siRNA knockdown, indicating the requirement of MC1R in the process. Altogether, our results suggest that (CKPV)2 exerted anti-fungal and anti-inflammatory activities against Candida albicans vaginitis probably through inducing macrophages M1 to M2 polarization and MC1R activation.

3D-QSAR studies of insecticidal anthranilic diamides as ryanodine receptor activators using CoMFA, CoMSIA and DISCOtech.

To explore the three-dimensional quantitative structure-activity relationships (3D-QSAR) and the pharmacophore model of a new class of potent activators of the anthranilic diamide ryanodine receptor (RyR), comparative molecular field analysis (CoMFA), comparative molecular similarity indices analysis (CoMSIA) and distance comparison technique (DISCOtech) were performed on 38 anthranilic diamides. Successful CoMFA and CoMSIA models yielded "leave-one-out" (LOO) cross-validated correlation coefficient (q(2)) values of 0.785 and 0.788 and non-cross-validated correlation coefficient (r(2)) values of 0.958 and 0.981, respectively. Results were graphically interpreted in terms of field contribution maps. A DISCOtech pharmacophore model containing an aromatic ring center, a hydrophobic ring center, a hydrogen bond-donor and a hydrogen bond-acceptor was constructed. This model indicated that hydrophobic interaction and hydrogen bonds have important roles in the interactions between activators and RyRs, which was consistent with CoMSIA results. The information obtained from CoMFA, CoMSIA and DISCOtech models enabled interpretation of the structure-activity relationships of anthranilic diamides. Based on the constructed models, some vital features for the interaction of anthranilic diamides with RyRs were identified, which may prove helpful in designing more potent RyR activators.

Selectivity of Imidacloprid for fruit fly versus rat nicotinic acetylcholine receptors by molecular modeling.

For better understanding of the mechanisms of selective binding of the representative nicotinic acetylcholine receptor (nAChR) agonist neonicotinoid Imidacloprid (IMI), three-dimensional models of fruit fly alpha 1 beta 2 and rat alpha 4beta 2 nAChRs were generated by homology modeling, using the crystal structure of the acetylcholine-binding protein (AChBP) of Lymnaea stagnalis and the nAChR of mus musculus as the templates, respectively. The conformational stability of the two models was studied by molecular dynamics (MD) and the quality of the models was confirmed. Especially, insecticide Imidacloprid was docked into the putative binding site of the fruit fly alpha 1 beta 2 and rat alpha 4 beta 2 nAChRs by Surflex-docking. The calculated docking energies were in agreement with the experimental data and the putative binding sites were also consistent with the results from labeling and mutagenesis experiments. Furthermore, the mechanisms of Imidacloprid selectively acting on fruit fly versus rat nAChRs were discussed.

CoMFA and molecular docking studies of benzoxazoles and benzothiazoles as CYP450 1A1 inhibitors.

For better understanding of the molecular interactions of inhibitors with CYP450 1A1, a series of benzoxazoles and benzothiazoles were analyzed by comparative molecular field analysis (CoMFA) and molecular docking. Two conformer-based alignment strategies were employed to construct reliable CoMFA models. The best CoMFA model yielded a predictive correlation coefficient r(2)(pred) value of 0.809. Furthermore, a three-dimensional model of CYP450 1A1 was generated by homology modeling using CYP450 1A2 as a template, and docking of 48 CYP450 1A1 inhibitors into the putative binding sites of the CYP450 1A1 were studied. The results obtained from this study will be helpful in the design of potentially active CYP450 1A1 inhibitors.

[Construction and identification of recombinant retroviral vector and stable cell line expressing latent membrane protein 2A of Epstein-Barr virus].

AIM: To clone EBV-LMP2A gene, construct and identify the recombinant retroviral vector and stable cell strains expressing EBV LMP2A. METHODS: The full-length EBV LMP2A gene was generated by RT-PCR amplification from B95.8 cells which contain complement nucleotide sequence of EBV LMP2A gene. The gene was ligated to T-vector and sequenced to construct retroviral vector consisting with LMP2A. To produce retroviral virus, packing cells, 293T cells were co-transfected with recombinant retroviral expression vector pGEZ-LMP2A and two auxiliary viral vectors pHIT456 and pHIT60 by lipofectAMINE2000. Viral titration was performed according to the instructions of the manufacturer. To establish L929 cell line stable expressing LMP2A, L929 cells were infected with recombinant retrovirus three times and selected by Zeocine. The Zeocine-resistant clones (L929/LMP2A) were screened for LMP2A expression by RT-PCR and Western blot. RESULTS: The recombinant retrovirus vector carrying LMP2A gene was constructed successfully. Transfection yield a titer of 5 x 10(8) infectious particles/L. The infected L929 cells were selected by Zeocine. Results of RT-PCR and Western blot indicated that L929 transgenetic cells could stably express EBV-LMP2A. CONCLUSION: The L929 cell line stably expressing LMP2A provides suitability for extraction of the LMP2A protein and preparations of the vaccine for the therapy of EBV-associated diseases.

[Redox factor 1 increases proliferation of neonatal rat cardiac fibroblasts].

OBJECTIVE: To investigate the function of REF1 in the proliferation and collagen synthesis of neonatal rat cardiac fibroblasts, and the underlying mechanisms. METHODS: Neonatal rat cardiac fibroblasts were transfected with the adenoviral vector containing rat wild type Ref1 (Ad-Ref1) or mutated Ref1 (Ad-mutRef1). The mutations resulted in Cys to Ala at amino acids 65 and 93, which eliminated the redox function of the REF1 protein. MTT was used to check the cell viability and flow cytometry was used to analyze the cell proliferation with the count of cell numbers and the percentage of cells in S phase of the cell cycle. The expressions of Ref1, collagen I (Col I) and collagen III (Col III) were determined by RT-PCR and Western blot. The translocation of REF1 was examined by fluorescence staining and revealed under fluorescence microscope. Electrophoretic mobility shift assay (EMSA) was used to check the effect of REF1 on AP1 DNA binding ability. The high glucose medium (25 mmol/L) was applied to culture cardiac fibroblasts. The effect of high glucose on AP1 DNA binding activity, the expression and translocation of REF1 were examined. RESULTS: MTT analysis showed that Ad-Ref1 promoted the relative viability of cardiac fibroblasts (0.671+/-0.044 vs control 0.364+/-0.007, n=6, P<0.01). The percentage of cells in S phase of the cell cycle was increased significantly in the Ad-Ref1 transfected cells (16.8%+/-0.62% vs control 9.04%+/-0.43%, n=3, P<0.05), as demonstrated by flow cytometry analysis. The expressions of Col I and Col III at mRNA level were increased when cells transfected with Ad-Ref1, while Ad-mutRef1 did not show such effects. Compared with the redox-deficient mutant Ad-mutRef1 (C65/93A), EMSA results demonstrated that Ad-Ref1 resulted in a marked increase in AP1 DNA binding. We also found that the cardiac fibroblasts cultured in high glucose (25 mmol/L) medium resulted in an increase in AP1 DNA binding activity, which was similar as seen in Ad-Ref1 transfected cells. There was also an increased accumulation of nuclear REF1 protein when cells were cultured in high glucose medium, although the expressions of REF1 at both mRNA and protein levels were not affected. CONCLUSION: REF1 can increase proliferation and collagen synthesis of cardiac fibroblasts, which may be related to its ability to up-regulate AP1 DNA binding.

Homology modeling of human alpha 1 beta 2 gamma 2 and house fly beta 3 GABA receptor channels and Surflex-docking of fipronil.

To further explore the mechanism of selective binding of the representative gamma-aminobutyric acid receptors (GABARs) noncompetitive antagonist (NCA) fipronil to insect over mammalian GABARs, three-dimensional models of human alpha 1 beta 2 gamma 2 and house fly beta 3 GABAR were generated by homology modeling, using the cryo-electron microscopy structure of the nicotinic acetylcholine receptor (nAChR) of Torpedo marmorata as a template. Fipronil was docked into the putative binding site of the human alpha 1 beta 2 gamma 2 and house fly beta 3 receptors by Surflex-docking, and the calculated docking energies are in agreement with experimental results. The GABA receptor antagonist fipronil exhibited higher potency with house fly beta 3 GABAR than with human alpha 1 beta 2 gamma 2 GABAR. Furthermore, analyses of Surflex-docking suggest that the H-bond interaction of fipronil with Ala2 and Thr6 in the second transmembrane segment (TM2) of these GABARs plays a relatively important role in ligand selective binding. The different subunit assemblies of human alpha 1 beta 2 gamma 2 and house fly beta 3 GABARs may result in differential selectivity for fipronil.