Evaluation of drug-muscarinic receptor affinities using cell membrane chromatography and radioligand binding assay in guinea pig jejunum membrane

Repositioning of histamine H1 receptor antagonist: Doxepin inhibits viropexis of SARS-CoV-2 Spike pseudovirus by blocking ACE2

The spread of the corona virus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been intensifying in the past year, posing a huge threat to global health. There is an urgent need for effective drugs and vaccines to fight the COVID-19, but their advent may not be quite fast. Drug repurposing is a feasible strategy in the current situation, which could greatly shorten drug development time and help to response quickly to the novel virus outbreak. It has been reported that histamine H₁ receptor antagonists have broad-spectrum antiviral effects. Therefore, in this study, we aim to screen potential drugs among histamine H₁ receptor antagonists that may inhibit SARS-CoV-2 infection. Based on the model of angiotensin-converting enzyme 2 (ACE2) overexpressing HEK293T cell membrane chromatography (CMC), five FDA-approved histamine H₁ receptor antagonists were found to have bioaffinity to ACE2. Then we determined the interaction between these drugs and ACE2 by frontal analysis and surface plasmon resonance (SPR), which consistently demonstrated that these hits bind to ACE2 at micromolar levels of affinity. Through the pseudovirus assay, we finally identified that doxepin could inhibit SARS-CoV-2 spike pseudovirus from entering the ACE2-expressing cell, reducing the infection rate to 25.82%. These preliminary results indicate that the histamine H₁ receptor antagonist, doxepin, is a viable drug candidate for clinical trials. Therefore, we hope the work timely provides rational help for developing anti-SARS-CoV-2 drugs to control the rapid spread of SARS-CoV-2.

Advances in cell membrane chromatography

Cell membrane chromatography (CMC) is a biomimetic chromatographic method based on the ability of membrane receptors to selectively interact with their ligands in vivo. Using membrane receptors as a stationary phase, the CMC method helps in determining the binding characteristics between ligands and membrane receptors and in efficiently identifying specific target components in a complex sample that produce the cellular biological effects of ligands (drugs, antibodies, enzymes, cytokines, etc.). CMC is an analytical tool for revealing characteristics of ligand-receptor interactions, screening and discovering target substances, and accurately controlling the quality of drugs. Since establishment of CMC in the early 1990s, with the rapid development of cell biology, significant progress has been made in the development of high-expression receptors, engineered cell cultures, and standardized preparations, which allowed in vitro immobilization of cell membrane receptors and miniaturization of binding assays. A variety of CMC models have been established using different membrane receptors as a stationary phase, and many new methods have been developed by combining CMC with high-performance liquid chromatography (HPLC)/mass spectrometry or HPLC-IT-TOF technologies. CMC methods have been widely used to study drug-receptor interactions and to screen complex samples for effective or harmful components.

Prospects for multitarget lipid-raft-coated silica beads: a remarkable online biomaterial for discovering multitarget antitumor lead compounds

Application of lipid raft biomaterial with multiple cancer-related receptors for screening novel multitarget antitumour lead compounds.

Development and thermodynamic evaluation of novel lipid raft stationary phase chromatography for screening potential antitumor agents

Novel lipid raft stationary phase chromatography (LRSC), with lipid rafts that contain abundant tropomyosin-related tyrosine kinase A receptors immobilized on the stationary phase, was developed for a high-throughput screening of potentially active antitumor agents. Lestaurtinib was used as a model compound to determine the operational parameters of the LRSC. Of all the factors considered, the particle size of column packing, the column temperature and the flow rate were of immense importance in determining the performance of the established LRSC system. In order to profoundly comprehend the binding interaction between the model drug and the receptors on the column, thermodynamic studies were employed. The results revealed that the interaction was spontaneous and exothermic, a typical enthalpy-driven process. Additionally, the primary forces were hydrogen bonding and van der Waals forces. In evaluating the applicability of the method, active extracts from Albizziae Cortex were screened out using the LRSC system under the optimized conditions. The bioactive components were successfully confirmed by the MTT assay. In conclusion, it could be said that the LRSC is a good model for screening potential antitumor agents because of its viability, rapid response and scalable features.

Efficient screening of a novel antimicrobial peptide from Jatropha curcas by cell membrane affinity chromatography

A novel method named cell membrane affinity chromatography was used to screen antimicrobial peptides from Jatropha curcas . A cationic antimicrobial peptide (KVFLGLK, JCpep7) was successfully isolated and identified. Antimicrobial assays indicated that JCpep7 was active against the tested microorganisms ( Salmonella typhimurium ATCC 50013, Shigella dysenteriae ATCC 51302, Pseudomonas aeruginosa ATCC 27553, Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 23631, and Streptococcus pneumoniae ATCC 49619) with minimal inhibitory concentration (MIC) values ranging from 24 to 64 μg/mL. The antimicrobial mechanisms based on Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) techniques showed that JCpep7 killed microbes principally via breaking of their cell walls and membranes, followed by cell lysis. The results indicated that cell membrane affinity chromatography could be a promising approach for high-throughput screening of antimicrobial peptides from J. curcas .

Ganoderma atrum polysaccharide protects cardiomyocytes against anoxia/reoxygenation-induced oxidative stress by mitochondrial pathway

It is now well established that oxidative stress plays a causative role in the pathogenesis of anoxia/reoxygenation (A/R) injury. Ganoderma atrum polysaccharide (PSG-1), the most abundant component isolated from G. atrum, has been shown to possess potent antioxidant activity. The goals of this study were to investigate the effect of PSG-1 against oxidative stress induced by A/R injury and the possible mechanisms in cardiomyocytes. In this work, primary cultures of neonatal rat cardiomyocytes pretreated with PSG-1 were subjected to A/R and subsequently monitored for cell viability by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The levels of intracellular reactive oxygen species (ROS), apoptosis, and mitochondrial membrane potential (Deltapsi(m)) were determined by flow cytometry. Western blot analysis was used to measure the expression of cytochrome c, Bcl-2 family, and manganese superoxide dismutase (MnSOD) proteins, and the activities of caspase-3 and caspase-9 were determined by a colorimetric method. The results showed that PSG-1 protected against cell death caused by A/R injury in cardiomyocytes. PSG-1 reduced the A/R-induced ROS generation, the loss of mitochondrial membrane potential (Deltapsi(m)), and the release of cytochrome c from the mitochondria into cytosol. PSG-1 inhibited the A/R-stimulated activation of caspase-9 and caspase-3 and alteration of Bcl-2 family proteins. Moreover, PSG-1 significantly increased the protein expression of MnSOD in cardiomyocytes. These findings suggest that PSG-1 significantly attenuates A/R-induced oxidative stress and improves cell survival in cardiomyocytes through mitochondrial pathway.

Acute effect of sidestream cigarette smoke extract on vascular endothelial function

Acute exposure to passive smoking adversely affects vascular function by promoting oxidative stress and endothelial dysfunction. However, it is not known whether tobacco sidestream (SS) smoke has a greater deleterious effect on the endothelium than non-tobacco SS smoke and whether these effects are related to nicotinic endothelial stimulation. To test these hypotheses, endothelial-dependent relaxation and superoxide anion production were assessed in isolated rat aortas incubated with tobacco SS smoke, non-tobacco SS smoke, or pure nicotine. Tobacco SS smoke decreased the maximal relaxation to acetylcholine (Ach) from 79 +/- 6% to 57 +/- 7.3% (% inhibition of phenylephrine-induced plateau, P < 0.001) and increased superoxide anion production from 31 +/- 9.7 to 116 +/- 24 count/10 sec/mg (P < 0.01, lucigenin-enhanced chemiluminescence technique). The non-tobacco SS smoke extract had no significant effect on the response to Ach but increased superoxide anion production in the aortic wall to 133 +/- 2 count/10 sec/mg (P < 0.001). Furthermore, concentration-response curves to Ach and superoxide production remained unaltered with nicotine (0.001, 0.01, or 0.1 mM). In conclusion, despite similar increases in vascular wall superoxide production with tobacco and non-tobacco SS smoke, only the tobacco SS smoke extracts affected endothelium-dependent vasorelaxation. Nicotine alone does not reproduce the effects seen with tobacco SS smoke, suggesting that the acute endothelial toxicity of passive smoking cannot simply be ascribed to a nicotine-dependent mechanism.

Comparison of alpha1-adrenergic receptor cell-membrane stationary phases prepared from expressed cell line and from rabbit hepatocytes

A G-protein-coupled receptor-cell-membrane stationary phase (CMSP) has been prepared by immobilizing cell membranes on the surface of silica, as carrier. The resulting HEK293 alpha1A adrenoceptor cell-membrane stationary phase can be used for rapid on-line chromatographic determination of potential subtype-selective alpha1-adrenoceptor ligand-binding affinities for alpha 1-adrenoceptor subtypes. The objective of the research was to study whether cell lines stably overexpressing subtype receptors could improve the sensitivity and specificity of cell-membrane chromatography (CMC) compared with use of homogenized tissue and cells in primary culture. Effects of mobile-phase ionic strength, sample concentration, and the presence of competitive agents on ligand-receptor interaction in CMSP were also evaluated. We found that cell lines stably overexpressing subtype receptors led to improved sensitivity and specificity in CMC. The technique leads to useful procedures-cell-membrane stationary phases may, for example, facilitate exploration of ligand-receptor interaction and determination of ligand-receptor binding affinity in initial screening and separation of lead compounds or active components in Chinese traditional natural medicine and herbs. This might eventually be an important contribution and an addition to our collection of techniques.

Muscarinic receptors autoantibodies purified from mammary adenocarcinoma-bearing mice sera stimulate tumor progression

The ability of tumor cells to stimulate adaptive immunity, particularly by inducing anti-tumor antibodies (Abs), has been extensively reviewed. LM3 is a tumorigenic cell line derived from a murine mammary metastatic adenocarcinoma that spontaneously overexpressed mAchR. Here we investigate the ability of Abs purified from the sera of LM3 tumor-bearing mice, directed against muscarinic acetylcholine receptors (mAchR) to modulate tumor cells' proliferation and angiogenesis. We observed that IgG from early tumor bearers (ETB), 14-day LM3 tumor, and from late tumor bearers (LTB), 28-day LM3 tumor, displaced tritiated quinuclidinyl benzilate binding to LM3 tumor cells, confirming Abs interaction with cholinoceptors, while IgG from normal mice did not modify the antagonist binding to mAchR at any concentration tested. In addition, Abs from ETB and LTB immunoblotted a protein of 70 kDa on murine tumor cells and on heart homogenates that was also recognized by a specific anti-M(2) receptor monoclonal antibody. We also observed that IgG purified from ETB-stimulated LM3 cells' proliferation in a more effective manner than the muscarinic agonist carbachol (CARB) did. IgG from LTB-potentiated LM3 cells induced angiogenesis by increasing the number of blood vessels and VEGF-A production in peritumoral skin "via" mAchR, in an agonist similar manner. All effects were blocked by preincubating cells with the non-selective antagonist atropine. In conclusion, autoAbs purified from LM3 tumor-bearing mice sera exert different pro-tumor actions depending on the stage of tumor development: in ETB, they stimulate tumor cells' proliferation, while in LTB they potentiate tumor neovascularization.

Establishment of the model of white blood cell membrane chromatography and screening of antagonizing TLR4 receptor component from Atractylodes macrocephala Koidz

A model of white blood cell membrane chromatography (WB-CMC) was established to screen active component from Atractylodes macrocephala Koidz. The component can antagonize Toll-like receptor 4 (TLR4) and inhibit inflammatory reaction. In the model of WB-CMC, cell membrane stationary phase (CMSP) was prepared by immobilizing the rabbit white blood cell membrane (WBCM) onto the surface of silica carrier and taxinol was used as a model molecule. The active component which can act on WBCM and its receptor (such as TLR4) as an effective target in A. macrocephala was determined by using a replacement experiment. The anti-inflammatory effects of the active component were tested by using pharmacological methods in vivo. The results indicated that the retention characteristics of atractylenolide I as active component was similar to that of taxinol in the model of WB-CMC. And so, atractylenolide I acted on the WBCM and TLR4 and its anti-inflammatory activity was related with antagonizing TLR4. Therefore, the interaction between the active component and WBCM and its receptor can be simulated by the model of WB-CMC in vitro. This model can be used to screen active components and to study effective characteristics for acting on definite targets.