Hydrocortisone and dexamethasone dose-dependently stabilize mast cells derived from rat peritoneum

Brain Leukocytes as the Potential Therapeutic Target for Post-COVID-19 Brain Fog

After recovering from the acute phase of coronavirus disease 2019 (COVID-19), many patients struggle with additional symptoms of long COVID during the chronic phase. Among them, the neuropsychiatric manifestations characterized by a short-term memory loss and inability to concentrate are called "brain fog". Recent studies have revealed the involvement of "chronic neuro-inflammation" in the pathogenesis of brain fog following COVID-19 infection. In the COVID-related brain fog, similarly to neurodegenerative disorders caused by neuro-inflammation, brain leukocytes, such as microglia and lymphocytes, are hyperactivated, suggesting the overexpression of delayed rectifier K⁺-channels (Kv1.3) within the cells. In our previous patch-clamp studies, drugs, such as antihistamines, statins, nonsteroidal anti-inflammatory drugs, antibiotics and anti-hypertensive drugs, suppressed the Kv1.3-channel activity and reduced the production of pro-inflammatory cytokines. Additionally, newer generation antihistamines, antibiotics and corticosteroids strongly stabilize mast cells that directly activate microglia in the brain. Taking such pharmacological properties of these commonly used drugs into account, they may be useful in the treatment of COVID-related brain fog, in which the enhanced innate and adaptive immune responses are responsible for the pathogenesis.

Mast Cell's Role in Cytokine Release Syndrome and Related Manifestations of COVID-19 Disease

In this narrative review, firstly, we describe the characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the pathogenesis of its infection in humans. Later, the importance of mast cells in SARS-CoV-2 infection and their role in Coronavirus Disease 2019 (COVID-19) will be discussed. SARS-CoV-2 is a transmissible agent frequently detected in some mammalian species and also in humans. Literature data published in PubMed that covered mast cells' role in cytokine release syndrome and related manifestations of COVID-19 disease were reviewed by the authors independently and collectively. Recommendations for the management of cytokine release syndrome and related manifestations were made by the authors. Mast cells are concentrated in environments where they encounter viruses, bacteria, and toxins, especially in the skin, nasal mucosa, lungs, airways, gastrointestinal tract, and meninges, to prevent their entry into the human body. Once SARS-CoV-2 enters the host, it stimulates one of the mast cells, together with pre-existing innate immune cells that form a defensive barrier in the submucosa of the respiratory tract and nasal cavities against pathogenic microorganisms. The roles of mast cells in SARS-CoV-2-induced hyperinflammation and cytokine storms have recently been one of the hot topics in the literature. Physicians should keep in mind the mast cells' role in cytokine release syndrome and related manifestations of COVID-19 disease. Mast cell-targeting therapies (e.g., H1 and H2 receptor antagonists) can reduce the severity and course of the disease when used after complications associated with COVID-19 are suspected or seen.

The edematogenic effect of Micrurus lemniscatus venom is dependent on venom phospholipase A2 activity and modulated by non-neurogenic factors

Coral snakes mainly cause neurotoxic symptoms in human envenomation, but experimental studies have already demonstrated several pharmacological activities in addition to these effects. This investigation was carried out with the aim of evaluating (1) non-neurogenic mechanisms involved in the inflammatory response induced by Micrurus lemniscatus venom (MLV) in rat hind paws, (2) participation of PLA₂ in this response, and (3) neutralizing efficiency of commercial anti-elapid antivenom on edema. MLV promoted a rapid, significant increase in vascular permeability, influx of leukocytes, and disorganization of collagen bundles, as demonstrated by histological analysis. Several pretreatments were applied to establish the involvement of inflammatory mediators in MLV-induced edema (5 µg/paw). Treatment of animals with chlorpromazine reduced MLV-induced edema, indicating participation of TNF-α. However, the inefficiency of other pharmacological treatments suggests that eicosanoids, leukotrienes, and nitric oxide have no role in this type of edema formation. In contrast, PAF negatively modulates this venom-induced effect. MLV was recognized by anti-elapid serum, but this antivenom did not neutralize edema formation. Chemical modification of MLV with p-bromophenacyl bromide abrogated the phospholipase activity and markedly reduced edema, demonstrating PLA₂ participation in MLV-induced edema. In conclusion, the non-neurogenic inflammatory profile of MLV is characterized by TNF-α-mediated edema, participation of PLA₂ activity, and down-regulation by PAF. MLV induces an influx of leukocytes and destruction of collagen fibers at the site of its injection.

COVID-19 and Lung Mast Cells: The Kallikrein-Kinin Activation Pathway

Mast cells (MCs) have relevant participation in inflammatory and vascular hyperpermeability events, responsible for the action of the kallikrein-kinin system (KKS), that affect patients inflicted by the severe form of COVID-19. Given a higher number of activated MCs present in COVID-19 patients and their association with vascular hyperpermeability events, we investigated the factors that lead to the activation and degranulation of these cells and their harmful effects on the alveolar septum environment provided by the action of its mediators. Therefore, the pyroptotic processes throughout caspase-1 (CASP-1) and alarmin interleukin-33 (IL-33) secretion were investigated, along with the immunoexpression of angiotensin-converting enzyme 2 (ACE2), bradykinin receptor B1 (B1R) and bradykinin receptor B2 (B2R) on post-mortem lung samples from 24 patients affected by COVID-19. The results were compared to 10 patients affected by H1N1pdm09 and 11 control patients. As a result of the inflammatory processes induced by SARS-CoV-2, the activation by immunoglobulin E (IgE) and degranulation of tryptase, as well as Toluidine Blue metachromatic (TB)-stained MCs of the interstitial and perivascular regions of the same groups were also counted. An increased immunoexpression of the tissue biomarkers CASP-1, IL-33, ACE2, B1R and B2R was observed in the alveolar septum of the COVID-19 patients, associated with a higher density of IgE+ MCs, tryptase+ MCs and TB-stained MCs, in addition to the presence of intra-alveolar edema. These findings suggest the direct correlation of MCs with vascular hyperpermeability, edema and diffuse alveolar damage (DAD) events that affect patients with a severe form of this disease. The role of KKS activation in events involving the exacerbated increase in vascular permeability and its direct link with the conditions that precede intra-alveolar edema, and the consequent DAD, is evidenced. Therapy with drugs that inhibit the activation/degranulation of MCs can prevent the worsening of the prognosis and provide a better outcome for the patient.

Potential prophylactic efficacy of mast cell stabilizers against COVID-19 vaccine-induced anaphylaxis

To fight against coronavirus disease 2019 (COVID-19), the vaccination is currently the most effective approach. However, in addition to common systemic side effects, the vaccines can cause serious allergic reactions or anaphylaxis. In anaphylaxis, the exposure to the allergen causes a sudden release of chemical mediators from mast cells, for which adrenaline is the drug of first choice. In our previous basic studies, in addition to adrenaline, anti-allergic drugs (olopatadine, loratadine, tranilast and ketotifen), antibiotics (clarithromycin), corticosteroids (hydrocortisone and dexamethasone) and certain food constituents (caffeine and catechin) inhibited the process of exocytosis and showed their effectiveness as highly potent mast cell stabilizers. In these studies, since mast cells were pre-incubated with these drugs or the food constituents before exocytosis was induced, the findings strongly indicated their prophylactic efficacy in stabilizing mast cells. Considering such pharmacological properties of these commonly prescribed medications or the food constituents, their prophylactic use may potentially be beneficial in preventing anaphylaxis caused by COVID-19 vaccination.

Resiniferatoxin promotes adult worm expulsion in Trichinella spiralis-infected rats by Th2 immune response modulation

BACKGROUND

The immune response during T spiralis infection is characterized by an increase in eosinophils and mast cells, as well as Th2 cytokine production, such as interleukin (IL)-4, IL-10 and IL-13, promoting T spiralis expulsion from the host. However, this response damages the host, favouring the parasite survival. In the search for new pharmacological strategies that protect against T spiralis infection, a recent study showed that treatment with resiniferatoxin (RTX) modulates the Th1 cytokines production, reducing muscle parasite burden.

OBJECTIVE

To evaluate the effect of RTX treatment on the Th2 cytokines production, the number of eosinophils, mast cells and the intestinal expulsion of T spiralis.

METHODS

Serum levels of IL-4, IL-10 and IL-13 were quantified by ELISA; the number of eosinophils, mast cells and the adult worms of T spiralis in the small intestine was quantified.

RESULTS

RTX treatment increased serum levels of IL-4, IL-10 and IL-13, and it decreases intestinal eosinophilia, however, favours the mastocytosis, promoting T spiralis intestinal expulsion.

CONCLUSIONS

These findings suggest that RTX is capable to modulate the Th2 immune response, promoting T spiralis expulsion, which contributes to the defence against T spiralis infection, placing the RTX as a potential immunomodulatory drug.

Aloe-emodin, a naturally occurring anthraquinone, is a highly potent mast cell stabilizer through activating mitochondrial calcium uniporter

Mast cells play a fundamental role in immune system. Upon stimulation, they are activated via IgE dependent or independent pathway and then release granules which contain plenty of preformed constituents. Mast cell stabilizers are commonly used clinically for inhibiting the degranulation of mast cells. In the current study, we firstly identified aloe-emodin, a naturally occurring anthraquinone, was a prominent mast cell stabilizer. It could strikingly dampen IgE/FcεRI- and MAS-related G protein coupled receptor (Mrgpr)-mediated mast cell degranulation in vitro and in vivo. Mechanism study indicated that aloe-emodin rapidly and reversibly decreased cytosolic Ca²⁺ (Ca²⁺_[c]) concentration through enhancing the mitochondrial Ca²⁺ (Ca²⁺_[m]) uptake. After genetically silencing or pharmacologic inhibiting mitochondrial calcium uniporter (MCU), the effects of aloe-emodin on the Ca²⁺_[c] level and mast cell degranulation were significantly weakened. In contrast to six clinical drugs with mast cell stabilizing properties (amlexanox, tranilast, ketotifen, cromolyn disodium salt, dexamethasone and pimecrolimus), aloe-emodin showed an impressive and potent inhibitory action on the mast cell degranulation. Collectively, aloe-emodin is a highly potent mast cell stabilizer. By directly activating MCU, it decreases Ca²⁺_[c] level to suppress mast cell degranulation. Our study may provide a promising candidate for the treatment of mast cell activation-related diseases.

Catechin synergistically potentiates mast cell-stabilizing property of caffeine

Caffeine and catechin, contained in coffee and tea, are commonly consumed substances worldwide. Studies revealed their health promoting functions, such as anti-oxidant, anti-cancer and anti-bacterial properties. Additionally, studies also revealed their roles in ameliorating the symptoms of allergic disorders, indicating their anti-allergic properties. In the present study, using the differential-interference contrast (DIC) microscopy, we examined the effects of caffeine and catechin on the degranulation from rat peritoneal mast cells. Both caffeine and catechin dose-dependently decreased the numbers of degranulating mast cells. At concentrations equal to or higher than 25 mM, caffeine and catechin markedly suppressed the numbers of degranulating mast cells. In contrast, at relatively lower concentrations, both substances did not significantly affect the numbers of degranulating mast cells. However, surprisingly enough, low concentrations of catechin (1, 2.5 mM) synergistically enhanced the suppressive effect of 10 mM caffeine on mast cell degranulation. These results provided direct evidence for the first time that caffeine and catechin dose-dependently inhibited the process of exocytosis. At relatively lower concentrations, caffeine or catechin alone did not stabilize mast cells. However, low concentrations of catechin synergistically potentiated the mast cell-stabilizing property of caffeine.

Stabilizing mast cells by commonly used drugs: a novel therapeutic target to relieve post-COVID syndrome?

Regardless of the severity of coronavirus disease 2019 (COVID-19), a high proportion of patients struggle with persistent respiratory or systemic symptoms after recovery. This is called "postCOVID syndrome", for which pulmonary fibrosis is one of the pathogenesis. Besides T-lymphocytes and macrophages, mast cells also contribute to the development of cytokine storm and thus stimulate the activity of fibroblasts. Additionally, by the exocytotic release of fibroblast-activating factors, mast cells directly facilitate the progression of pulmonary fibrosis. In our previous basic studies, anti-allergic drugs (olopatadine, ketotifen), antibiotics (clarithromycin) and corticosteroids (hydrocortisone, dexamethasone) inhibited the process of exocytosis and showed their potency as highly effective mast cell stabilizers. Given such pharmacological properties of these commonly used drugs, they may be useful in the treatment of post-COVID-19 pulmonary fibrosis and in relieving the symptoms of post-COVID syndrome.

α 1-Adrenergic Receptor Blockade by Prazosin Synergistically Stabilizes Rat Peritoneal Mast Cells

BACKGROUND

Adrenaline quickly inhibits the release of histamine from mast cells. Besides β 2-adrenergic receptors, several in vitro studies also indicate the involvement of α-adrenergic receptors in the process of exocytosis. Since exocytosis in mast cells can be detected electrophysiologically by the changes in the membrane capacitance (Cm), its continuous monitoring in the presence of drugs would determine their mast cell-stabilizing properties.

METHODS

Employing the whole-cell patch-clamp technique in rat peritoneal mast cells, we examined the effects of adrenaline on the degranulation of mast cells and the increase in the Cm during exocytosis. We also examined the degranulation of mast cells in the presence or absence of α-adrenergic receptor agonists or antagonists.

RESULTS

Adrenaline dose-dependently suppressed the GTP-γ-S-induced increase in the Cm and inhibited the degranulation from mast cells, which was almost completely erased in the presence of butoxamine, a β 2-adrenergic receptor antagonist. Among α-adrenergic receptor agonists or antagonists, high-dose prazosin, a selective α 1-adrenergic receptor antagonist, significantly reduced the ratio of degranulating mast cells and suppressed the increase in the Cm. Additionally, prazosin augmented the inhibitory effects of adrenaline on the degranulation of mast cells.

CONCLUSIONS

This study provided electrophysiological evidence for the first time that adrenaline dose-dependently inhibited the process of exocytosis, confirming its usefulness as a potent mast cell stabilizer. The pharmacological blockade of α 1-adrenergic receptor by prazosin synergistically potentiated such mast cell-stabilizing property of adrenaline, which is primarily mediated by β 2-adrenergic receptors.

A Jack of All Trades: Impact of Glucocorticoids on Cellular Cross-Talk in Osteoimmunology

Glucocorticoids (GCs) are known to have a strong impact on the immune system, metabolism, and bone homeostasis. While these functions have been long investigated separately in immunology, metabolism, or bone biology, the understanding of how GCs regulate the cellular cross-talk between innate immune cells, mesenchymal cells, and other stromal cells has been garnering attention rather recently. Here we review the recent findings of GC action in osteoporosis, inflammatory bone diseases (rheumatoid and osteoarthritis), and bone regeneration during fracture healing. We focus on studies of pre-clinical animal models that enable dissecting the role of GC actions in innate immune cells, stromal cells, and bone cells using conditional and function-selective mutant mice of the GC receptor (GR), or mice with impaired GC signaling. Importantly, GCs do not only directly affect cellular functions, but also influence the cross-talk between mesenchymal and immune cells, contributing to both beneficial and adverse effects of GCs. Given the importance of endogenous GCs as stress hormones and the wide prescription of pharmaceutical GCs, an improved understanding of GC action is decisive for tackling inflammatory bone diseases, osteoporosis, and aging.

Modulation of Mast Cell Reactivity by Lipids: The Neglected Side of Allergic Diseases

Mast cells (MCs) have long been mainly regarded as effector cells in IgE-associated allergic disorders with potential immunoregulatory roles. Located close to the allergen entry sites in the skin and mucosa, MCs can capture foreign substances such as allergens, toxins, or noxious substances and are exposed to the danger signals produced by epithelial cells. MC reactivity shaped by tissue-specific factors is crucial for allergic responses ranging from local skin reactions to anaphylactic shock. Development of Th2 response leading to allergen-specific IgE production is a prerequisite for MC sensitization and induction of FcεRI-mediated MC degranulation. Up to now, IgE production has been mainly associated with proteins, whereas lipids present in plant pollen grains, mite fecal particles, insect venoms, or food have been largely overlooked regarding their immunostimulatory and immunomodulatory properties. Recent studies, however, have now demonstrated that lipids affect the sensitization process by modulating innate immune responses of epithelial cells, dendritic cells, and NK-T cells and thus crucially contribute to the outcome of sensitization. Whether and how lipids affect also MC effector functions in allergic reactions has not yet been fully clarified. Here, we discuss how lipids can affect MC responses in the context of allergic inflammation. Direct effects of immunomodulatory lipids on MC degranulation, changes in local lipid composition induced by allergens themselves and changes in lipid transport affecting MC reactivity are possible mechanisms by which the function of MC might be modulated.

Second-Generation Histamine H1 Receptor Antagonists Suppress Delayed Rectifier K+-Channel Currents in Murine Thymocytes

BACKGROUND/AIMS

Voltage-dependent potassium channels (Kv1.3) are predominantly expressed in lymphocyte plasma membranes. These channels are critical for the activation and proliferation of lymphocytes. Since second-generation antihistamines are lipophilic and exert immunomodulatory effects, they are thought to affect the lymphocyte Kv1.3-channel currents.

METHODS

Using the patch-clamp whole-cell recording technique in murine thymocytes, we tested the effects of second-generation antihistamines, such as cetirizine, fexofenadine, azelastine, and terfenadine, on the channel currents and the membrane capacitance.

RESULTS

These drugs suppressed the peak and the pulse-end currents of the channels, although the effects of azelastine and terfenadine on the peak currents were more marked than those of cetirizine and fexofenadine. Both azelastine and terfenadine significantly lowered the membrane capacitance. Since these drugs did not affect the process of endocytosis in lymphocytes, they were thought to have interacted directly with the plasma membranes.

CONCLUSIONS

Our study revealed for the first time that second-generation antihistamines, including cetirizine, fexofenadine, azelastine, and terfenadine, exert suppressive effects on lymphocyte Kv1.3-channels. The efficacy of these drugs may be related to their immunomodulatory mechanisms that reduce the synthesis of inflammatory cytokine.

Glucocorticoids decrease the numbers and activation of mast cells by inducing the transactivation receptors of AGEs

Glucocorticoids (GCs) are potent anti-allergic compounds that function, at least in part, by inhibiting signaling pathways in mast cells. We hypothesized that the GC-induced mastocytopenia and suppression of mast cell activation are mediated by the advanced glycation end products (AGEs)/receptors of AGEs (RAGEs) signaling axis. We evaluated the role of AGEs in GC-mediated mastocytopenia and impaired mast cell degranulation in male Wistar rats and Swiss-Webster mice subcutaneously injected with dexamethasone or prednisolone (0.1 mg/kg) once a day for 21 consecutive days. The animals were treated with either the AGE inhibitor aminoguanidine (250 mg/kg), the RAGE antagonist FPS-ZM1 (1 mg/kg) or the galectin-3 antagonist GSC-100 (1 mg/kg) daily for 18 days, starting 3 days following GC treatment. Aminoguanidine inhibited GC-induced mast cell apoptosis and restored mast cell numbers in the pleural cavity of GC-treated rats. Aminoguanidine also reversed the GC-induced reduction in histamine release triggered by allergens or compound 48/80 in vitro. GC treatment induced RAGE and galectin expression in mast cells, and blocking these agents by FPS-ZM1 or GSC-100 significantly reversed mast cell numbers in the peritoneal cavity and mesenteric tissue of GC-treated mice. In addition, the combination of GC and AGE-induced mast cell apoptosis in vitro was inhibited by both FPS-ZM1 and GSC-100. We concluded that the GC-induced mastocytopenia and suppression of mast cell stimulation are associated with the gene transactivation of RAGE and galectin-3.