A Novel Imidazo[1,5-b]isoquinolinone Derivative, U63A05, Inhibits Syk Activation in Mast Cells to Suppress IgE-Mediated Anaphylaxis in Mice

The Complexity of Sesquiterpene Chemistry Dictates Its Pleiotropic Biologic Effects on Inflammation

Sesquiterpenes (SQs) are volatile compounds made by plants, insects, and marine organisms. SQ have a large range of biological properties and are potent inhibitors and modulators of inflammation, targeting specific components of the nuclear factor-kappaB (NF-κB) signaling pathway and nitric oxide (NO) generation. Because SQs can be isolated from over 1600 genera and 2500 species grown worldwide, they are an attractive source of phytochemical therapeutics. The chemical structure and biosynthesis of SQs is complex, and the SQ scaffold represents extraordinary structural variety consisting of both acyclic and cyclic (mono, bi, tri, and tetracyclic) compounds. These structures can be decorated with a diverse range of functional groups and substituents, generating many stereospecific configurations. In this review, the effect of SQs on inflammation will be discussed in the context of their complex chemistry. Because inflammation is a multifactorial process, we focus on specific aspects of inflammation: the inhibition of NF-kB signaling, disruption of NO production and modulation of dendritic cells, mast cells, and monocytes. Although the molecular targets of SQs are varied, we discuss how these pathways may mediate the effects of SQs on inflammation.

Cytokine Storm Syndrome in SARS-CoV-2 Infections: A Functional Role of Mast Cells

Cytokine storm syndrome is a cascade of escalated immune responses disposing the immune system to exhaustion, which might ultimately result in organ failure and fatal respiratory distress. Infection with severe acute respiratory syndrome-coronavirus-2 can result in uncontrolled production of cytokines and eventually the development of cytokine storm syndrome. Mast cells may react to viruses in collaboration with other cells and lung autopsy findings from patients that died from the coronavirus disease that emerged in 2019 (COVID-19) showed accumulation of mast cells in the lungs that was thought to be the cause of pulmonary edema, inflammation, and thrombosis. In this review, we present evidence that a cytokine response by mast cells may initiate inappropriate antiviral immune responses and cause the development of cytokine storm syndrome. We also explore the potential of mast cell activators as adjuvants for COVID-19 vaccines and discuss the medications that target the functions of mast cells and could be of value in the treatment of COVID-19. Recognition of the cytokine storm is crucial for proper treatment of patients and preventing the release of mast cell mediators, as impeding the impacts imposed by these mediators could reduce the severity of COVID-19.

Mast cell stabilisers

Mast cells play a critical role in type 1 hypersensitivity reactions. Indeed, mast cell mediators are implicated in many different conditions including allergic rhinitis, conjunctivitis, asthma, psoriasis, mastocytosis and the progression of many different cancers. Thus, there is intense interest in the development of agents which prevent mast cell mediator release or which inhibit the actions of such mediators once released into the environment of the cell. Much progress into the design of new agents has been made since the initial discovery of the mast cell stabilising properties of khellin from Ammi visnaga and the clinical approval of cromolyn sodium. This review critically examines the progress that has been made in the intervening years from the design of new agents that target a specific signalling event in the mast cell degranulation pathway to those agents which have been developed where the precise mechanism of action remains elusive. Particular emphasis is also placed on clinically used drugs for other indications that stabilise mast cells and how this additional action may be harnessed for their clinical use in disease processes where mast cells are implicated.

Twenty-first century mast cell stabilizers

Mast cell stabilizing drugs inhibit the release of allergic mediators from mast cells and are used clinically to prevent allergic reactions to common allergens. Despite the relative success of the most commonly prescribed mast cell stabilizer, disodium cromoglycate, in use for the preventative treatment of bronchial asthma, allergic conjunctivitis and vernal keratoconjunctivitis, there still remains an urgent need to design new substances that are less expensive and require less frequent dosing schedules. In this regard, recent developments towards the discovery of the next generation of mast cell stabilizing drugs has included studies on substances isolated from natural sources, biological, newly synthesized compounds and drugs licensed for other indications. The diversity of natural products evaluated range from simple phenols, alkaloids, terpenes to simple amino acids. While in some cases their precise mode of action remains unknown it has nevertheless sparked interest in the development of synthetic derivatives with improved pharmacological properties. Within the purely synthetic class of inhibitors, particular attention has been devoted to the inhibition of important signalling molecules including spleen TK and JAK3. The statin class of cholesterol-lowering drugs as well as nilotinib, a TK inhibitor, are just some examples of clinically used drugs that have been evaluated for their anti-allergic properties. Here, we examine each approach under investigation, summarize the test data generated and offer suggestions for further preclinical evaluation before their therapeutic potential can be realized.

Deficiency in steroid receptor coactivator 3 enhances cytokine production in IgE-stimulated mast cells and passive systemic anaphylaxis in mice

Background

Steroid receptor coactivator 3 (SRC-3) is a multifunctional protein that plays an important role in malignancy of several cancers and in regulation of bacterial LPS-induced inflammation. However, the involvement of SRC-3 in allergic response remains unclear. Herein we used passive systemic anaphylaxis (PSA) and passive cutaneous anaphylaxis (PCA) mouse models to assess the role of SRC-3 in allergic response.

Results

SRC-3-deficient mice exhibited more severe allergic response as demonstrated by a significant drop in body temperature and a delayed recovery period compared to wild-type mice in PSA mouse model, whereas no significant difference was observed between two kinds of mice in PCA mouse models. Mast cells play a pivotal role in IgE-mediated allergic response. Antigen-induced aggregation of IgE receptor (FcϵRI) on the surface of mast cell activates a cascade of signaling events leading to the degranulation and cytokine production in mast cells. SRC-3-deficient bone marrow derived mast cells (BMMCs) developed normally but secreted more proinflammatory cytokines such as TNF-α and IL-6 than wild-type cells after antigen stimulation, whereas there was no significant difference in degranulation between two kinds of mast cells. Further studies showed that SRC-3 inhibited the activation of nuclear factor NF-κB pathway and MAPKs including extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 in antigen-stimulated mast cells.

Conclusions

Our data demonstrate that SRC-3 suppresses cytokine production in antigen-stimulated mast cells as well as PSA in mice at least in part through inhibiting NF-κB and MAPK signaling pathways. Therefore, SRC-3 plays a protective role in PSA and it may become a drug target for anaphylactic diseases.

Mediators released during human anaphylaxis

A range of mediators are generated during anaphylaxis, with redundancy of effects, multiple overlapping pathways, and involvement of several cell types. Key steps in the reaction occur at the site of initial contact, and mediators may not be detectable systemically. Furthermore, the potencies of various mediators vary enormously, and clinical effects may occur below our level of detection. We also do not know what converts (amplifies) a local reaction into systemic anaphylaxis. Murine models have identified several novel mediators that may propagate and/or regulate this process and also indicate that circulating neutrophils may play an important role in reaction amplification. Differential expression of various genes within specific intracellular signalling pathways of mediator release may further explain the varying severities of anaphylactic reactions. As our knowledge of the mechanisms of activation, key mediators, and the regulation of mediator release improves, new treatments for prevention and acute management may emerge.