In vitro inhibition of human conjunctival mast-cell degranulation by ketotifen

Tryptase and Exogenous Trypsin: Mechanisms and Ophthalmic Applications

Ocular injuries caused by inflammation, surgery or accidents are subject to a physiological healing process that ultimately restores the structure and function of the damaged tissue. Tryptase and trypsin are essential component of this process and they play a role in promoting and reducing the inflammatory response of tissues, respectively. Following injury, tryptase is endogenously produced by mast cells and can exacerbate the inflammatory response both by stimulating neutrophil secretion, and through its agonist action on proteinase-activated receptor 2 (PAR2). In contrast, exogenously introduced trypsin promotes wound healing by attenuating inflammatory responses, reducing oedema and protecting against infection. Thus, trypsin may help resolve ocular inflammatory symptoms and promote faster recovery from acute tissue injury associated with ophthalmic diseases. This article describes the roles of tryptase and exogenous trypsin in affected tissues after onset of ocular injury, and the clinical applications of trypsin injection.

Topical Ketotifen Fumarate Inhibits Choroidal Mast Cell Degranulation and Loss of Retinal Pigment Epithelial Cells in Rat Model for Geographic Atrophy

Purpose

This study evaluates whether topical ketotifen fumarate (KTF) can prevent geographic atrophy (GA)-like phenotypes in a rat model.

Methods

Pharmacokinetics (PKs) of KTF after topical administration twice daily for 5 days was analyzed in rat retina, retinal pigment epithelium (RPE)/choroid/sclera, and in plasma by an liquid chromatography tandem mass spectrometry (LC-MS/MS) method. Rats were then given hydrogel implants +/- 48/80 in the superior subconjunctival space and topically treated with 1% and 0.25% of KTF or phosphate buffer saline (PBS) twice daily. Rats were euthanized at 1, 2, 4, and 8 weeks postinjection. Choroidal mast cells (MCs) were stained with nonspecific esterase and the RPE monolayer was labeled with RPE65 and ZO-1 in whole mount choroids. Retinal and choroidal areas were determined in cryosections stained with picrosirius red. Dark-adapted electroretinogram (ERG) was also performed to evaluate retinal function.

Results

PK results showed the highest level of KTF (average 5.6 nM/mg) in the RPE/choroid/sclera in rats given topical 1% KTF. Topical 1% KTF significantly reduced choroidal MC degranulation at 1 week and 2 weeks (both P < 0.001) and RPE loss at 4 weeks (P < 0.001) as well as retinal and choroidal thinning (both P < 0.001) and reduction in ERG amplitude at 8 weeks (P < 0.05) compared to PBS. Similar results were obtained with 0.25% KTF.

Conclusions

Both 1% and 0.25% KTF eye drops effectively reduced MC degranulation, RPE loss, and retinal and choroidal thinning while preventing the decline of ERG amplitude in a GA-like rat model. These data suggest that topical KTF might be a new therapeutic drug for treating GA.

Translational Relevance

The results of this study demonstrate that topical KTF successfully reduced GA-like phenotypes in a rat model and may provide a novel therapy for GA.

In vitro safety of ketotifen as a topical nasal rinse

BACKGROUND

Ketotifen is a second-generation noncompetitive H1-antihistamine and mast-cell stabilizer. It is commonly used to treat or prevent allergic conjunctivitis, asthma, chronic urticaria, anaphylaxis, mast-cell, and other allergic-type disorders. However, it has never been studied in aspirin-exacerbated respiratory disease (AERD), an aggressive phenotype of chronic rhinosinusitis with nasal polyps, where the mast cell plays a prominent role its pathogenesis.

METHODS

Human sinonasal epithelial cells were grown at an air-liquid interface (ALI). Ketotifen powder was dissolved in saline to make 4 test solutions at 1.04, 2.08, 10.4, and 20.8 µg/mL. Control (saline) or ketotifen solution was added apically to ALI cultures from tissue of 5 unique patients, and ciliary beat frequency (CBF) changes were recorded. Lactate dehydrogenase was measured at 24 and 48 hours to estimate long-term cellular toxicity.

RESULTS

Apical application of ketotifen at all concentrations was neither ciliotoxic nor ciliostimulatory, with no change in CBF over a period of 15 minutes after application. Cellular toxicity for all concentrations at 24 and 48 hours after application was <3% and <7%, respectively, that of lysed cultures.

CONCLUSION

Topical application of ketotifen to an in vitro model of sinonasal epithelium is safe, as evaluated by CBF and lactate dehydrogenase. Ketotifen is neither ciliotoxic nor ciliostimulatory, and no long-term cellular toxicity was observed. Ketotifen may have promise as a topical nasal rinse in the treatment of AERD.

Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?

INTRODUCTION

An increasing number of patients present with multiple symptoms affecting many organs including the brain due to multiple mediators released by mast cells. These unique tissue immune cells are critical for allergic reactions triggered by immunoglobulin E (IgE), but are also stimulated (not activated) by immune, drug, environmental, food, infectious, and stress triggers, leading to secretion of multiple mediators often without histamine and tryptase. The presentation, diagnosis, and management of the spectrum of mast cell disorders are very confusing. As a result, neuropsychiatric symptoms have been left out, and diagnostic criteria made stricter excluding most patients. Areas covered: A literature search was performed on papers published between January 1990 and November 2018 using MEDLINE. Terms used were activation, antihistamines, atopy, autism, brain fog, heparin, KIT mutation, IgE, inflammation, IL-6, IL-31, IL-37, luteolin, mast cells, mastocytosis, mediators, mycotoxins, release, secretion, tetramethoxyluteolin, and tryptase. Expert opinion: Conditions associated with elevated serum or urine levels of any mast cell mediator, in the absence of comorbidities that could explain elevated levels, should be considered 'Mast Cell Mediator Disorders (MCMD).' Emphasis should be placed on the identification of unique mast cell mediators, and development of drugs or supplements that inhibit their release.

The Role of Mast Cells in Stroke

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin. Through the release of preformed mediators stored in their granules and newly synthesized molecules, they are able to initiate, modulate, and prolong the immune response upon activation. Their presence in the central nervous system (CNS) has been documented for more than a century. Over the years, MCs have been associated with various neuroinflammatory conditions of CNS, including stroke. They can exacerbate CNS damage in models of ischemic and hemorrhagic stroke by amplifying the inflammatory responses and promoting brain–blood barrier disruption, brain edema, extravasation, and hemorrhage. Here, we review the role of these peculiar cells in the pathophysiology of stroke, in both immature and adult brain. Further, we discuss the role of MCs as potential targets for the treatment of stroke and the compounds potentially active as MCs modulators.

Pharmacotherapy of mast cell disorders

PURPOSE OF REVIEW

Mast cell disorders (MCDs) comprise mastocytosis and disorders referred to as mast cell activation syndrome and are caused by abnormal accumulation and/or activation of mast cells in tissues. Clinical signs and symptoms are protean; therefore, finding suitable treatment options for individual patients entails a challenge for clinicians. The purpose of this manuscript is to review the literature on the available therapeutic interventions in patients with MCD.

RECENT FINDINGS

Pharmacotherapy is mainly directed against the effects of mast cells and their mediators. The current recommendations are exclusively based on expert opinions due to the lack of controlled clinical trials. The targeted therapies aiming at blocking mutant KIT variants and/or downstream signaling pathways are currently being developed and may be considered in severely affected, therapy-refractory patients.

SUMMARY

There is currently no method for predicting the best available approach to control symptoms in individual patients with MCD. Therefore, a stepwise, individual-based approach in pharmacotherapy options appears to be most successful strategy and is recommended in all patients. The core component of the treatment in most patients is to control symptoms caused by mast cell mediator release, whereas cytoreductive therapies are mainly reserved for patients with advanced/aggressive systemic mastocytosis.

Mastocytosis: the puzzling clinical spectrum and challenging diagnostic aspects of an enigmatic disease

Mastocytosis is a complex disorder characterized by the accumulation of abnormal mast cells (MC) in the skin, bone marrow and/or other visceral organs. The clinical manifestations result from MC-derived mediators and, less frequently, from destructive infiltration of MCs. Patients suffer from a variety of symptoms including pruritus, flushing and life-threatening anaphylaxis. Whilst mastocytosis is likely to be suspected in a patient with typical skin lesions [i.e. urticaria pigmentosa (UP)], the absence of cutaneous signs does not rule out the diagnosis of this disease. Mastocytosis should be suspected in cases of recurrent, unexplained or severe insect-induced anaphylaxis or symptoms of MC degranulation without true allergy. In rare cases, unexplained osteoporosis or unexplained haematological abnormalities can be underlying feature of mastocytosis, particularly when these conditions are associated with elevated baseline serum tryptase levels. The diagnosis is based on the World Health Organization criteria, in which the tryptase level, histopathological and immunophenotypic evaluation of MCs and molecular analysis are crucial. A somatic KIT mutation, the most common of which is D816V, is usually detectable in MCs and their progenitors. Once a diagnosis of systemic mastocytosis (SM) is made, it is mandatory to assess the burden of the disease, its activity, subtype and prognosis, and the appropriate therapy. Mastocytosis comprises seven different categories that range from indolent forms, such as cutaneous and indolent SM, to progressive forms, such as aggressive SM and MC leukaemia. Although prognosis is good in patients with indolent forms of the disease, patients with advanced categories have a poor prognosis.

Mast Cell Stabilizer (Ketotifen) in Fibromyalgia: Phase 1 Randomized Controlled Clinical Trial

OBJECTIVES

Compared with pain-free controls, patients with fibromyalgia (FM) have more mast cells in the skin. Whether mast cells are involved in the pathogenesis of FM is unclear. We sought to determine the effects of a mast cell stabilizer (ketotifen) on FM symptoms.

MATERIALS AND METHODS

Fifty-one FM patients were randomized to daily oral ketotifen 2 mg bid (n=24) for 8 weeks or placebo (N=27). Mean age of patients was 51.2 years (SD=8.4); 88% were female and 88% were white; 22% were taking concomitant opiates; and mean pressure pain sensitivity (range, 0 to 20) was 10.0 (0.4). At study entry, the weekly average pain intensity was 6.4 (1.1) and the mean score on the Revised Fibromyalgia Impact Questionnaire-Revised was 66.8 (14.0).

RESULTS

We found no statistically significant treatment group differences from baseline in either group for the 2 primary measures: weekly average pain intensity (ketotifen -1.3 [1.9] vs. placebo -1.5 [1.9], P=0.7); and Fibromyalgia Impact Questionnaire-Revised score (-12.1 [19.5] vs. -12.2 [18.1], P=0.9). No secondary outcome measures (Brief Pain Inventory pain intensity and pressure pain sensitivity) reached statistical significance; results did not differ in the intent-to-treat and completer analyses. Other than transient sedation (6 [28.6%] vs. 1 [4.0%]), ketotifen was well tolerated.

DISCUSSION

The study results question whether skin mast cells play a major role in the pathogenesis of FM. However, given the role of mast cells in peripheral and central nociception, and the minimal side effects of ketotifen, a randomized clinical trial using increasing doses of ketotifen may be warranted.

Effect of ketotifen in obese patients with type 2 diabetes mellitus

AIM

Mast cells are found to be an important contributor in obesity induced insulin resistance. We evaluate the effect of ketotifen in obese patient with type 2 diabetes (T2DM) treated with glimepiride.

METHOD

In a randomized controlled study we recruited forty-eight obese patients with T2DM from Internal Medicine Department at Tanta University Hospital, Egypt. They were classified into three groups: group 1, those who received glimepiride (GL) 3mg/d alone; group 2, those who received GL 3mg/d+ketotifen 1mg once daily; and group 3, those who received GL 3mg/d+ketotifen 1mg twice daily. Fasting blood samples were obtained before and 12weeks after treatment for biochemical analysis of glycemic and inflammatory biomarkers. Data were statistically analyzed by paired Student's t-test and one way analysis of variance; p<0.05 was considered statistically significant.

RESULTS

The obtained data suggested that the addition of ketotifen in twice daily dose has a beneficial effect on all measured parameters except adiponectin. However, glimepiride plus ketotifen once daily only affected the level of inflammatory biomarkers without any significant effect on other parameters.

CONCLUSIONS

The co-administration of ketotifen twice daily plus glimepiride improves glycemic and inflammatory process in obese patients with T2DM.

The progress and promise of zebrafish as a model to study mast cells

Immunological and hematological research using the zebrafish (Danio rerio) has significantly advanced our understanding of blood lineage ontology, cellular functions and mechanisms, and provided opportunities for disease modeling. Mast cells are an immunological cell type involved in innate and adaptive immune systems, hypersensitivity reactions and cancer progression. The application of zebrafish to study mast cell biology exploits the developmental and imaging opportunities inherent in this model system to enable detailed genetic and molecular studies of this lineage outside of traditional mammalian models. In this review, we first place the importance of mast cell research in zebrafish into the context of comparative studies of mast cells in other fish species and highlight its advantages due to superior experimental tractability and direct visualization in transparent embryos. We discuss current and future tools for mast cell research in zebrafish and the notable results of using zebrafish for understanding mast cell fate determination and our development of a systemic mastocytosis model.

Spectrum of mast cell activation disorders

Mast cell (MC) activation disorders present with multiple symptoms including flushing, pruritus, hypotension, gastrointestinal complaints, irritability, headaches, concentration/memory loss and neuropsychiatric issues. These disorders are classified as: cutaneous and systemic mastocytosis with a c-kit mutation and clonal MC activation disorder, allergies, urticarias and inflammatory disorders and mast cell activation syndrome (MCAS), idiopathic urticaria and angioedema. MCs are activated by IgE, but also by cytokines, environmental, food, infectious, drug and stress triggers, leading to secretion of multiple mediators. The symptom profile and comorbidities associated with these disorders, such as chronic fatigue syndrome and fibromyalgia, are confusing. We propose the use of the term 'spectrum' and highlight the main symptoms, useful diagnostic tests and treatment approaches.

Evidence for the role of mast cells in colon-bladder cross organ sensitization

This study examined the contribution of mast cells to colon-bladder cross organ sensitization induced by colon irritation with trinitrobenzene sulfonic acid (TNBS-CI). In urethane anesthetized rats 12 days after TNBS-CI, the voiding interval was reduced from 357 s to 201 s and urothelial permeability, measured indirectly by absorption of sodium fluorescein from the bladder lumen, increased six-fold. These effects were blocked by oral administration of ketotifen (10 mg/kg, for 5 days), a mast cell stabilizing agent. TNBS-CI in wild type mice produced a similar decrease in voiding interval (from 319 s to 209 s) and a 10-fold increase in urothelial permeability; however this did not occur in KitªWª/KitªW-vª mast cell deficient mice. Contractile responses of bladder strips elicited by Compound 48/80 (50 μg/ml), a mast cell activating agent, were significantly larger in strips from rats with TNBS-CI (145% increase in baseline tension) than in control rats (55% increase). The contractions of strips from rats with TNBS-CI were reduced 80-90% by pretreatment of strips with ketotifen (20 μM), whereas contractions of strips from control animals were not significantly changed. Bladder strips were pretreated with SLIGRL-NH2 (100 μM) to desensitize PAR-2, the receptor for mast cell tryptase. SLIGRL-NH2 pretreatment reduced by 60-80% the 48/80 induced contractions in strips from rats with TNBS-CI but did not alter the contractions in strips from control rats. These data indicate that bladder mast cells contribute to the bladder dysfunction following colon-bladder cross-sensitization.

Bepotastine besilate, a highly selective histamine H(1) receptor antagonist, suppresses vascular hyperpermeability and eosinophil recruitment in in vitro and in vivo experimental allergic conjunctivitis models

To elucidate the ocular pharmacological properties of bepotastine besilate, a selective histamine H(1) receptor antagonist, when compared with other histamine H(1) receptor antagonists, using guinea pig allergic conjunctivitis models and in vitro models of eosinophil recruitment and mast cell membrane stabilization. Conjunctival vascular hyperpermeability was studied in guinea pigs passively sensitized with anti-ovalbumin antiserum or following subconjunctival injection of histamine. Modulation of eosinophil recruitment was evaluated for both platelet-activating factor (PAF)-induced eosinophil infiltration in guinea pigs and leukotriene B(4)-induced in vitro chemotaxis of guinea pig peritoneal eosinophils. Membrane-stabilizing effects of bepotastine also were studied with rat peritoneal mast cells stimulated with the ionophore A23187. Histamine H(1) receptor antagonists including bepotastine besilate were topically administered before ovalbumin, histamine or PAF challenges for in vivo experiments or were added directly to mast cell and eosinophil medium in vitro. Bepotastine besilate significantly inhibited conjunctival vascular hyperpermeability in a dose-dependent manner with maximal effect for bepotastine besilate 1.5%. In separate in vivo experiments, bepotastine besilate 1.0% was significantly more effective than levocabastine 0.025% in the passive sensitization model or olopatadine 0.1% in the histamine-induced hyperpermeability model. Bepotastine besilate 1.0% further suppressed PAF-induced eosinophil infiltration into conjunctival tissue more effectively than ketotifen 0.05%. Chemotaxis of guinea pig peritoneal eosinophils and histamine release from rat peritoneal mast cells in vitro were also inhibited by addition of bepotastine. Olopatadine had a weak effect as compared to that of bepotastine on eosinophil chemotaxis and no effect on mast cell histamine release in our study conditions. Bepotastine besilate was more potent than olopatadine, ketotifen, or levocabastine in reducing vascular hyperpermeability in various animal models of allergic conjunctivitis. Mast cell function and eosinophil chemotaxis were also inhibited in vitro with bepotastine, suggesting bepotastine acts as an inhibitor of allergic response through multiple mechanisms: histamine H(1) receptor antagonism, mast cell stabilization, and inhibition of eosinophil migration to ocular inflammatory sites.

Comparison of the effects of ketotifen fumarate 0.025% and olopatadine HCl 0.1% ophthalmic solutions in seasonal allergic conjunctivities: a 30-day, randomized, double-masked, artificial tear substitute-controlled trial

BACKGROUND

Topical antiallergic agents, such as antihistamines and mast-cell stabilizers, are the main therapeutic options for seasonal allergic conjunctivitis (SAC). Ketotifen fumarate and olopatadine HCl have dual action that offers a combination of these 2 mechanisms. Although clinical studies comparing the efficacy of these 2 drugs have shown that both were effective in the treatment of SAC, the results were contradictory and did not include the effects of these drugs on inflammatory markers.

OBJECTIVES

The aims of this study were to compare the clinical efficacy of topical ketotifen and olopatadine eye drops and to determine the effects of these 2 drugs on the expression of cell adhesion molecules (CAMs) and inflammatory markers in conjunctival surface cells in patients with SAC.

METHODS

This 30-day, randomized, double-masked, artificial tear substitute (ATS)-controlled clinical trial was conducted at the Department of Ophthalmology, Karadeniz Technical University, School of Medicine, Trabzon, Turkey. Patients with SAC were included in the study and randomly assigned to 1 of 3 groups: topical ketotifen fumarate 0.025% ophthalmic solution, topical olopatadine HCl 0.1% ophthalmic solution, or ATS (control group). All drugs were administered 2 drops per eye BID for 30 days. At the beginning of the study (day 0; baseline), on day 15, and on day 30, clinical scores (itching, tearing, redness, eyelid, swelling, and chemosis) and conjunctival impression cytology specimens were obtained. The percentages of cells expressing intercellular adhesion molecule 1, vascular CAM-1, human leukocyte antigen-DR, and beta1-integrin (CD29) from conjunctival impression cytology specimens were determined using flow cytometry. Patients were questioned about adverse events (AEs) at each visit. Ocular discomfort on installation of the drugs was recorded as an AE.

RESULTS

Thirty-nine patients (20 men, 19 women; age range, 18-61 years) with SAC were included. Twelve patients received ketotifen; 13, olopatadine; and 14, ATS. In both active-treatment groups, the improvements of clinical scores (tearing and itching) were more pronounced compared with those in the ATS group, although the day-30 difference in tearing score between the olopatadine and ATS groups was not statistically significant. No significant within-group or between-group differences in mean scores for redness, chemosis, or eyelid swelling were found. The expression rates of CAMs and inflammatory markers in conjunctival surface cells were significantly more reduced with ketotifen and olopatadine compared with ATS. However, clinical and flow cytometric parameters were improved with ATS at 15 and 30 days compared with baseline. No AEs were observed during the study period.

CONCLUSIONS

In this short-term study in a selected, small study population with SAC, ketotifen and olopatadine diminished the expression of CAMs and inflammatory markers on the conjunctival surface cells effectively. Both active treatments were more efficacious compared with ATS and were well tolerated.

Mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4h-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] prevents mucosal mast cell hyperplasia and intestinal dysmotility in experimental Trichinella spiralis inflammation in the rat

Trichinella spiralis infection in rats induces hypermotility and an abnormal response to cholecystokinin (CCK) similar to motor disturbances observed in irritable bowel syndrome. Mast cell hyperplasia is also characteristic of this experimental model. The aim of our study was to correlate mast cell activity with the development of dysmotility and to demonstrate whether the mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] could prevent the development of intestine hypermotility. Sprague-Dawley rats were infected with T. spiralis and, 5 days after infection, treated with the mast-cell stabilizer ketotifen (10 mg/kg/day). Twelve days after infection, intestinal spontaneous motor activity and response to CCK were evaluated by means of strain-gauge transducers. Immunohistochemistry for rat mast cell protease II (RMCPII), cyclooxygenase (COX)-2, and inducible nitric-oxide synthase (iNOS) was performed in intestinal specimens. In addition, RMCPII and myeloperoxidase were determined in serum. Infected control rats showed hypermotility, mast cell hyperplasia, increased RMCPII levels, increased myeloperoxidase, and overexpression of COX-2 and iNOS. In contrast, ketotifen-treated rats showed spontaneous intestinal motility and CCK response similar to the noninfected control rats. Mast cell hyperplasia and RMCPII were reduced in ketotifen-treated rats. Inflammatory parameters were less modified by ketotifen, but those animals that received the longest ketotifen treatment showed a slight amelioration in these parameters. These results indicate that mast cells are implicated in the development of hypermotility. The treatment with ketotifen prevented hypermotility and mast cell hyperplasia and diminished mucosal mast cell activity.

Ketotifen induced inhibition of histamine release in a non-IgE model of middle ear effusion

The inhibitory effects of ketotifen, a histamine H1-receptor antagonist and mast cell stabilizer, were examined on a non-IgE experimental model of middle ear effusion. Thirty rats were divided into three groups. Group A (n = 9) was subjected to mechanical stimulation of the external auditory canal (EAC); group B (n = 11) was pre-treated with intraperitoneal administration of 0.2 mg ketotifen, 90 min before mechanical stimulation of the EAC; and group C (n = 10), the control group, was neither exposed to mechanical stimulation nor given ketotifen. Thirty minutes after completion of the experiment, the eardrums were inspected, histamine levels were determined by a fluorometric assay, and the pars flaccida underwent histological assessment. An attic effusion was observed in group A; a similar phenomenon but to a lesser extent was also seen in group B. Statistical analysis confirmed that the mean histamine concentration of the rinsing fluid obtained from group A was significantly higher than that of group C (p = 0.004) or group B (p = 0.008). No significant difference was found between the mean histamine concentration of groups C and group B (p = 0.311). Histological assessment revealed that the thickness of the pars flaccida of group A was considerably greater than that of groups C and B and was characterized by marked edema. Furthermore, the pars flaccida mast cell population was significantly depleted compared with groups C and B. The data indicate that mechanical stimulation of the EAC triggered the pars flaccida mast cells to degranulate in a non-mediated IgE fashion and that histamine is implicated in most of these histological changes. It is concluded that administration of ketotifen before mechanical stimulation of the EAC had a stabilizing effect and abolished mast cell degranulation, therefore, may be considered as a potential therapeutic agent for the treatment of middle ear disease in the pediatric population.