Background The novel coronavirus disease (2019-nCoV) has been affecting global health since the end of 2019 and there is no sign that the epidemic is abating . The major issue for controlling the infectious is lacking efficient prevention and therapeutic approaches. Chloroquine (CQ) and Hydroxychloroquine (HCQ) have been reported to treat the disease, but the underlying mechanism remains controversial. Purpose The objective of this study is to investigate whether CQ and HCQ could be ACE2 blockers and used to inhibit 2019-nCoV virus infection. Methods In our study, we used CCK-8 staining, flow cytometry and immunofluorescent staining to evaluate the toxicity and autophagy of CQ and HCQ, respectively, on ACE2 high-expressing HEK293T cells (ACE2 h cells). We further analyzed the binding character of CQ and HCQ to ACE2 by molecular docking and surface plasmon resonance (SPR) assays, 2019-nCoV spike pseudotyped virus was also used to observe the viropexis effect of CQ and HCQ in ACE2 h cells. Results Results showed that HCQ is slightly more toxic to ACE2 h cells than CQ. Both CQ and HCQ could bind to ACE2 with K D = (7.31 ± 0.62) e −7 M and (4.82 ± 0.87) e −7 M, respectively. They exhibit equivalent suppression effect for the entrance of 2019-nCoV spike pseudotyped virus into ACE2 h cells. Conclusions CQ and HCQ both inhibit the entrance 2019-nCoV into cells by blocking the binding of the virus with ACE2. Our findings provide novel insights into the molecular mechanism of CQ and HCQ treatment effect on virus infection.

Mast cells are unique immune cells that function as sentinels in host defence reactions, including immediate hypersensitivity responses and allergic responses. The mast cell-specific receptor named MAS-related G protein-coupled receptor X2 (MRGPRX2) triggers mast-cell degranulation, a key process in anaphylactoid reactions. It is widely observed that antimicrobials can induce pseudo-allergic reactions (i.e. IgE-independent mechanism) with symptoms ranging from skin inflammation to life-threatening systemic anaphylaxis. However, their direct involvement and the mechanisms underlying anaphylactoid reactions caused by antimicrobials have not been demonstrated. Structurally different antimicrobials were screened by Ca imaging using MRGPRX2 overexpressing HEK293 cells. MRGPRX2 related anaphylactoid reactions induced by these components were investigated by body temperature drop and mast cell degranulation assays. We showed that MRGPRX2 is involved in allergic-like reactions to three types of antimicrobials in a dose-dependent manner. However, mast cells lacking the receptor show reduced degranulation. Furthermore, mice without MAS-related G protein-coupled receptor B2 (the orthologous gene of MRGPRX2) exhibited reduced substance-induced inflammation. Interestingly, β-lactam and antiviral nucleoside analogues did not induce anaphylactic reactions, which were also observed in vitro. These results should alarm many clinicians that such drugs might induce anaphylactoid reactions and provide guidance on safe dosage of these drugs.

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Graphical abstract Traditional Chinese medicines played an important role in the treatment of COVID-19 in 2020. Ephedra sinica , one of the major constituent herbs of multi-component herbal formula, has been widely used to treat COVID-19 in China. However, its active components are still unclear. The objectives of this study are to screen and evaluate active components from the traditional Chinese medicine Ephedra sinica for the treatment of COVID-19. In our study, we established an ACE2/CMC bioaffinity chromatography model, and then developed an ACE2/CMC-HPLC-IT-TOF-MS system for the active compounds screening and identification from Ephedra sinica extract. We performed molecular docking and surface plasmon resonance (SPR) assays to assess the binding characteristics (binding mode and K D value). We used CCK-8 staining to assess the toxicity of screened compounds, and also used SARS-CoV-2 pseudovirus to observe the viropexis effect of screened compounds in ACE2 h cells. In this current work, one fraction was fished out, separated and identified as ephedrine (EP), pseudoephedrine (PEP), and methylephedrine (MEP). Binding assays showed that the three compounds could bind with ACE2 in a special way to some amino acid residues, similar to the way SARS-CoV-2 bound with ACE2. Additionally, the three compounds, especially EP, can inhibit the entrance of SARS-CoV-2 spike pseudovirus into ACE2 h cells because they can reduce the entrance ratio of pseudovirus in the pseudovirus model. Overall, the ACE2/CMC-HPLC-IT-TOF-MS system was established and verified to be suitable for ACE2-targeted bioactive compound screening. EP, PEP, and MEP with ACE2-binding features were screened out from Ephedra sinica , and acted as blockers inhibiting SARS-CoV-2 spike pseudovirus entering ACE2 h cells. Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03233-7.

Anaphylactoid reactions are common clinical acute adverse drug reactions that can exacerbate a patient’s condition and produce effects that may become life-threatening. Therefore, it is important to establish a novel method to evaluate drugs for anaphylactoid reactions. In this study, we developed a sensitive and rapid method to detect histamine release from LAD2 cells using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and constructed a relative release index based on various release curve parameters, including allergen release time and sudden change rate, to evaluate the potential and strength of allergen-induced anaphylactoid reactions. This LAD2 release model was used to evaluate anaphylactoid reactions induced by ciprofloxacin, norfloxacin, lomefloxacin, moxifloxacin, and baicalin. The results positively correlated with those obtained with an Evans blue ear test and negatively correlated with the Ca2+ influx EC50. In summary, the current study established a novel in vitro method to analyze the properties of histamine release from LAD2 cells and characterize the sensitization and strength of sensitization of drugs or components that may induce anaphylactoid reactions.