Anti-inflammatory activity of H1-receptor antagonists: review of recent experimental research

Testing of the inhibitory effects of loratadine and desloratadine on SARS-CoV-2 spike pseudotyped virus viropexis

Currently, there is an urgent need to find a treatment for the highly infectious coronavirus disease (COVID-19). However, the development of a new, effective, and safe vaccine or drug often requires years and poses great risks. At this critical stage, there is an advantage in using existing clinically approved drugs to treat COVID-19. In this study, in vitro severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike pseudotyped viral infection experiments indicated that histamine H₁ antagonists loratadine (LOR) and desloratadine (DES) could prevent entry of the pseudotyped virus into ACE2-overexpressing HEK293T cells and showed that DES was more effective. Further binding experiments using cell membrane chromatography and surface plasmon resonance demonstrated that both antagonists could bind to ACE2 and that the binding affinity of DES was much stronger than that of LOR. Molecular docking results elucidated that LOR and DES could bind to ACE2 on the interface of the SARS-CoV-2-binding area. Additionally, DES could form one hydrogen bond with LYS31 but LOR binding relied on non-hydrogen bonds. To our knowledge, this study is the first to demonstrate the inhibitory effect of LOR and DES on SARS-CoV-2 spike pseudotyped virus viropexis by blocking spike protein-ACE2 interaction. This study may provide a new strategy for finding an effective therapeutic option for COVID-19.

High pressure assisted synthetic approach for novel 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine and 5,6-dihydrobenzo[h]quinoline derivatives and their assessment as anticancer agents

A novel, expedient and effective methodology for the synthesis of distinctly substituted 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine and 5,6-dihydrobenzo[h]quinoline systems has been developed with a new synthetic platform. This process includes ammonium acetate-mediated cyclocondensation reactions of 3-oxo-2-arylhydrazonopropanals with benzosuberone and tetralone precursors, respectively, using the high-pressure Q-tube reactor, which has been found to be superior to both conventional heating and microwave irradiation. The novel protocol benefits from its high atom efficiency, economy, ease of workup, broad substrate scope and is also applicable to gram-scale synthesis. To identify and confirm the newly synthesized targeted compounds, the X-ray single-crystal as well as all possible spectroscopic methods were utilized. The cytotoxicity of the newly synthesized 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine 4a-j and 5,6-dihydrobenzo-[h]quinolines derivatives 6a-e were preliminary examined toward three cell lines of human cancer; lung cancer (A549), breast cancer (MCF-7) and colon cancer (HCT-116), by applying the MTT colorimetric assay. The achieved results reflected the promising profile of the prepared compounds in this study against cancer cells and have shown that members from the synthesized 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine 4a-j exhibited promising cytotoxicity's against MCF-7, and A549 cancer cells respectively, while the HCT-116 (colon) cancer cells were inhibited by certain examples of 5,6-dihydrobenzo[h]quinoline derivatives 6c,d. These promising results could serve as a good primary base for further research into the design of anticancer drugs.

Design, synthesis, and in vitro antituberculosis activity of benzo[6,7]cyclohepta[1,2-b]pyridine-1,3,4-oxadiazole derivatives

A new antitubercular agents, benzo[6,7]cyclohepta[1,2-b]pyridine-1,3,4- oxadiazole hybrids (6a-o), have been designed and synthesized involving oxidative cyclization of hydrazones by use of di(acetoxy)iodobenzene, characterized by IR,¹ H NMR,¹³ C NMR, and HRMS, and further confirmed by X-ray analysis. All the newly synthesized compounds 4a-o evaluated for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (ATCC27294). Among the compounds tested, the compounds 4o (MIC: 1.56 μg/ml) and 4l, 4m (MIC: 3.125 μg/ml) are promising lead analogues and have shown lower cytotoxicity.

Three-component, one-pot synthesis of benzo[6,7]cyclohepta[1,2-b]pyridine derivatives under catalyst free conditions and evaluation of their anti-inflammatory activity

An efficient three-component protocol is described for the synthesis of benzo[6,7]cyclohepta[1,2-b]pyridine derivatives using β-chloroacroleins, 1,3-dicarbonyls and ammonium acetate under catalyst free conditions by using ethanol as reaction media. The mild reaction conditions, operational simplicity and high yields are the advantages of this protocol and the broad scope of this one-pot reaction makes this procedure promising for practical usages. All the final compounds were screened for anti-inflammatory activity. Among the compounds tested, the compounds 5a, 5b, 5c, 5d, 5f, and 5k exhibited significant inhibition of IL-1β and MCP-1 secretion as a measure of anti-inflammatory activity.

Sequential engagement of FcεRI on Mast Cells and Basophil Histamine H(4) Receptor and FcεRI in Allergic Rhinitis

Histamine H(4) receptor (H(4)R)-deficient mice (H(4)R(-/-)), H(4)R antagonist-treated wild-type (WT) mice, and WT mice depleted of basophils failed to develop early (EPR) or late phase (LPR) nasal responses following allergen sensitization and challenge. Basophil transfer from WT but not H(4)R(-/-) mice restored the EPR and LPR in H(4)R(-/-) mice. Following passive sensitization with OVA-specific IgE, FcεRI(-/-) recipients of WT basophils plus OVA and histamine developed an EPR and LPR. OVA-IgE passively sensitized FcεRI(-/-) recipients of H(4)R(-/-) basophils and OVA and histamine challenge failed to develop an EPR or LPR, and basophils were not detected in nasal tissue. In contrast, recipients of basophils from IL-13(-/-) and IL-4(-/-)/IL-13(-/-) mice developed an EPR but not an LPR. These results demonstrate the development of allergic rhinitis proceeded in two distinct stages: histamine release from FcεRI-activated mast cells, followed by histamine-mediated recruitment of H(4)R-expressing basophils to the nasal cavity and activation through FcεRI.

Synthesis and biological evaluation of cyanoguanidine derivatives of loratadine

Cyanoguanidine derivatives of loratadine (3a-i) were synthesized and screened for antitumor and anti-inflammatory activity. The most promising compound 3c (R=n-C(8)H(17)) possessed at least twofold higher in vitro cytotoxicity than 5-fluorouracil against mammary (MCF-7 and MDA-MB 231) as well as colon (HT-29) carcinoma cells. The mode of action, however, is so far unclear. The participation of the COX-1/2 enzymes on the cytotoxicity, however, is very unlikely. Nevertheless all compounds showed stronger in vivo anti-inflammatory activity than ibuprofen in the xylene-induced ear swelling assay in mice.

Neurophysiological and neurochemical basis of modern pruritus treatment

Chronic pruritus of any origin is a frequent discomfort in daily medical practice, and its therapy is challenging. Frequently, the underlying origin may not be identified and symptomatic therapy is necessary. Conventional treatment modalities such as antihistamines often lack efficacy, and hence new therapeutic strategies are necessary. The neuronal mechanisms underlying chronic pruritus have been partly identified during the past years and offer new therapeutic strategies. For example, mast cell degranulation, activation of neuroreceptors on sensory nerve fibres and neurogenic inflammation have been identified to be involved in induction and chronification of the symptom. Accordingly, controlling neuroreceptors such as cannabinoid receptors by agonists or antagonists showed high antipruritic efficacy. Pruritus is transmitted to the central nervous system by specialized nerve fibres and sensory receptors. It has been demonstrated that pruritus and pain have their own neuronal pathways with broad interactions. Accordingly, classical analgesics for neuropathic pain (gabapentin, antidepressants) also exhibit antipruritic efficacy upon clinical use. In summary, these recent developments show that highlighting the basis of pruritus offers modern neurophysiological and neurochemical therapeutic models and the possibility to treat patients with refractory itching of different origin.

Evaluation of Histamine H1-, H2-, and H3-Receptor Ligands at the Human Histamine H4 Receptor: Identification of 4-Methylhistamine as the First Potent and Selective H4 Receptor Agonist

The histamine H(4) receptor (H(4)R) is involved in the chemotaxis of leukocytes and mast cells to sites of inflammation and is suggested to be a potential drug target for asthma and allergy. So far, selective H(4)R agonists have not been identified. In the present study, we therefore evaluated the human H(4)R (hH(4)R) for its interaction with various known histaminergic ligands. Almost all of the tested H(1)R and H(2)R antagonists, including several important therapeutics, displaced less than 30% of specific [(3)H]histamine binding to the hH(4)R at concentrations up to 10 microM. Most of the tested H(2)R agonists and imidazole-based H(3)R ligands show micromolar-to-nanomolar range hH(4)R affinity, and these ligands exert different intrinsic hH(4)R activities, ranging from full agonists to inverse agonists. Interestingly, we identified 4-methylhistamine as a high-affinity H(4)R ligand (K(i) = 50 nM) that has a >100-fold selectivity for the hH(4)R over the other histamine receptor subtypes. Moreover, 4-methylhistamine potently activated the hH(4)R (pEC(50) = 7.4 +/- 0.1; alpha = 1), and this response was competitively antagonized by the selective H(4)R antagonist JNJ 7777120 [1-[(5-chloro-1H-indol-2-yl)-carbonyl]-4-methylpiperazine] (pA(2) = 7.8). The identification of 4-methylhistamine as a potent H(4)R agonist is of major importance for future studies to unravel the physiological roles of the H(4)R.

Roles of histamine and its receptors in allergic and inflammatory bowel diseases

Mast cell has a long history of being recognized as an important mediator-secreting cell in allergic diseases, and has been discovered to be involved in IBD in last two decades. Histamine is a major mediator in allergic diseases, and has multiple effects that are mediated by specific surface receptors on target cells. Four types of histamine receptors have now been recognized pharmacologically and the first three are located in the gut. The ability of histamine receptor antagonists to inhibit mast cell degranulation suggests that they might be developed as a group of mast cell stabilizers. Recently, a series of experiments with dispersed colon mast cells suggested that there should be at least two pathways in man for mast cells to amplify their own activation-degranulation signals in an autocrine or paracrine manner. In a word, histamine is an important mediator in allergic diseases and IBD, its antagonists may be developed as a group of mast cell stabilizers to treat these diseases.