Conjunctival Mast Cells Research Articles

Pharmacology, clinical efficacy and safety of olopatadine hydrochloride

Olopatadine is a multimechanism anti-allergic agent that inhibits H1 receptor activation and stabilizes mast cell membranes, blocking the release of allergic and inflammatory mediators. Studies in human conjunctival mast cells clearly demonstrate, in the relevant tissue and species, olopatadine’s inhibition of histamine release, which was subsequently confirmed in allergen-challenged subjects. Its comfort and tolerability may be related to the absence of perturbation of cell membranes, in contrast to many anti-allergics, whose disruption of membranes lead to histamine release even at therapeutically relevant concentrations. In preclinical and clinical studies, olopatadine had greater efficacy and comfort than other anti-allergic agents available today for ophthalmic use.

Mast cell hyperplasia induced by multiple challenge with cedar pollen in sensitised guinea pigs

Because immediate allergic symptoms are aggravated by repetitive antigen challenges in a guinea pig model of Japanese cedar pollen-induced conjunctivitis, we determined whether conjunctival mast cells are different in number between the acute and chronic stages. Sensitised guinea pigs were challenged by dropping a pollen suspension into their eyes once a week. Conjunctival tissue sections were stained with toluidine blue. Ophthalmic lavage was performed to assay for mast cell mediators. At the 20th and 40th challenges, the number of mast cells increased by 4- to 5-fold compared with the 1st challenge. Although mast cell degranulation was insignificant 10 min after the 1st challenge, the 20th and 40th challenges produced significant degranulation. After multiple challenges, the amount of histamine and tryptase-like activity in the lavage fluid was dramatically increased. Increased mast cells are associated with aggravated symptoms. Mast cell mediators may be involved in pathogenesis at the chronic stage.

Regulation of the soluble receptor for TNFα on conjunctival epithelial cells and correlation with ICAM-1 upregulation by TNFα and IgE-activated conjunctival mast cells

Regulation of the soluble receptor for TNFα on conjunctival epithelial cells and correlation with ICAM-1 upregulation by TNFα and IgE-activated conjunctival mast cells

Regulation of Soluble Receptor for TNFα on Conjunctival Epithelial Cells and Correlation with ICAM-1 Upregulation by TNFα and IGE-Activated Conjunctival Mast Cells

The influences of Ge addition on crystallization kinetics, microstructure and high-temperature magnetic property of nanocrystalline FeAlSiBCuNbGe alloy have been investigated. The results showed that doping a small amount of Ge into Fe72.7Al0.8Si17.5B5Cu1Nb3 alloy can lower the activation energy and therefore decrease the glass forming ability. The primary crystalline temperature Tx1 and secondary crystallization temperature Tx2 were slightly decreased. But the addition of Ge enhances the Curie temperature of amorphous phase, which significantly improved high-temperature magnetic softness. Average grain sizes were increased and thickness of intergranular amorphous layer was decreased due to the addition of Ge to alloys. The optimum annealing temperature for Fe72.7Al0.8Si17.5B5Cu1Nb2.6Ge0.4 alloy was obtained at 843 K. The reason for the enhancement in high-temperature magnetic softness was systematically analyzed in terms of the evolution of microstructure.

A review of olopatadine for the treatment of ocular allergy

Ocular allergy affects > 20% of the general population and many therapeutic preparations are available to individuals experiencing the most common forms – seasonal and perennial allergic conjunctivitis. 0.1% Olopatadine topical ophthalmic solution is currently approved for the treatment of allergic signs and symptoms in patients ≥ 3 years of age. Olopatadine is available in Europe as Opatanol® and in > 30 other countries as Patanol®. It inhibits mast cell degranulation and antagonises histamine receptors to manage the itching, redness, chemosis, tearing and lid swelling of the ocular allergic reaction, and its mast cell stabilising ability has been demonstrated both in vitro (using human conjunctival mast cells) and in vivo (human clinical experience). This article reviews both the laboratory and clinical information available on olopatadine, prefaced by a discussion of the current understanding of the ocular allergic reaction and followed by the future implications for this compound. Both laboratory and clinical studies have established the efficacy, safety and comfort of olopatadine in several study design models and comparisons to other antiallergy medications. The application of olopatadine, specifically in the management of lid swelling, an allergic sign recalcitrant to therapy and nasal allergic symptoms has also been established. In the future, a new formulation containing 0.2% olopatadine exhibits a duration of action up to 24 h, supporting once-daily dosing.

Mechanisms of Antihistamines and Mast Cell Stabilizers in Ocular Allergic Inflammation

Mast cells play a central role in allergic reactions and inflammation. Successful anti-allergic therapies have typically targeted mast cell mediators, particularly histamine. Antihistaminic compounds interact with the various histamine receptors found on many cells, whereas other compounds such as disodium cromoglycate, are referred to as mast cell stabilizers, as they inhibit degranulation. Some of the most successful compounds developed recently are dual-action, in that they have both anti-histaminic and mast cell stabilizing activities. Recent trends in pharmaceutical intervention, however, have been focused on the secondary effects of mast cell mediators on epithelial cell adhesion molecule expression and mediator release in the process of allergic inflammation. Since, the ocular mucosa is highly exposed to environmental allergens it is commonly involved in allergic reactions and, as such, has been a useful and accessible model in which to test new therapies in vivo. These ocular allergen provocation studies permit analysis of ocular surface cells and evaluation of tear film mediators. Furthermore, techniques to purify conjunctival mast cells have facilitated the study of the effects of mast cell stabilizing compounds on other mast cell mediators, such as cytokines, and the direct effects of mast cell mediators on epithelial cells in vitro. This review will discuss current understanding of how anti-histamines and mast cell stabilizers work, particularly in the context of molecular mechanisms of ocular allergic inflammation.

Histological study on mast cells in conjunctiva of NC/Nga mice.

To investigate the pathological findings in conjunctiva of NC/Nga mice, which develop atopic dermatitis spontaneously, we focused our study on the density of mast cells as determined by histological methods. NC/Nga mice were divided into five groups; the 4W-group comprised four 4-week-old mice without treatment, the 10W-group comprised four 10-week-old mice without treatment, the 16W-group comprised four 16-week-old mice without treatment, the Dx group comprised three 16-week-old mice undergoing topical 0.1% dexamethasone (Dx) ointment treatment, and the FK506 group comprised three 16-week-old mice undergoing topical 0.1% FK506 ointment treatment. For the histological examination, the lids and eyeballs of the mice were removed and fixed with Carnoy's solution and thin sections were made. The Carnoy-fixed specimens were stained with toluidine blue or H&E and examined histologically. Toluidine blue-stained tissue sections were examined for the density per square millimeter of mast cells, which were identified as metachromatic cells in the conjunctival tissue and lid cutaneous tissue by light microscopy. Mast cell density in the conjunctiva was 8.6 +/- 8.2 cells/mm(2) in the 4W-group, 29.2 +/- 22.0 cells/mm(2) in the 10W-group, 41.0 +/- 21.1 cells/mm(2) in the 16W-group, 22.7 +/- 17.1 cells/mm(2) in the Dx group, and 33.6 +/- 27.7 cells/mm(2) in the FK506 group. Mast cell density increased significantly with age among the 4W-, 10W-, and 16W-groups ( P < 0.001). The mast cell density of lid cutaneous tissue was higher than the conjunctival mast cell density. Mast cell density was significantly higher in the 16W-group than in the Dx group, but not significantly higher than in the FK506 group. An increase in mast cell density with age indicates that NC/Nga mice develop atopic keratoconjunctivitis-like signs. Dexamethasone ointment has a suppressive effect on the increase in mast cell density.

Double-masked, randomized, parallel-group study comparing olopatadine 0.1% ophthalmic solution with cromolyn sodium 2% and levocabastine 0.05% ophthalmic preparations in children with seasonal allergic conjunctivitis

Background: It is estimated that >50% of medications have not been tested in children. Physicians need pediatric data to guide them in treating children. Olopatadine hydrochloride ophthalmic solution 0.1% is a topical antiallergic agent that is both an antihistamine with high affinity and selectivity for the histamine H 1 receptor and a mast cell stabilizer that inhibits the release of histamine and other proinflammatory mediators from human conjunctival mast cells. The efficacy and tolerability of olopatadine has been demonstrated by comparative studies in adults and children with seasonal allergic conjunctivitis (SAC). Objective: Pediatric patient data were extracted from 2 clinical trials to assess the efficacy and tolerability of olopatadine hydrochloride ophthalmic solution 0.1% compared with those of cromolyn sodium ophthalmic solution 2% and levocabastine ophthalmic solution 0.05% as treatment for SAC in children. Methods: In study 1, conducted at 15 centers in 7 countries (Europe and Australia) from October 1995 to December 1997, olopatadine was instilled BID and placebo (vehicle) BID for 6 weeks and compared with cromolyn instilled QID. Study 2, conducted at 17 centers in 8 countries (Europe and Australia) from November 1998 to June 2000, compared olopatadine BID with levocabastine BID. In both studies, children of either sex and any race, aged 4 to 11 years, and having proven grass pollen allergies were assigned to treatment in a double-masked, randomized fashion. Slit-lamp examination, the physician's impression scale, and self-ratings were used to obtain efficacy data. Data analyses were based on pollen concentrations. The tolerability assessments were based on visual acuity, pupil diameter, intraocular pressure, and a dilated fundus examination. Results: Study 1 comprised 30 children (olopatadine [n = 13] and cromolyn sodium [n = 17]; 18 boys, 12 girls; mean age, 7.9 years [range, 4–11 years]). Study 2 comprised 22 children (olopatadine [n = 10] and levocabastine [n = 12]; 12 boys, 10 girls; mean age, 8.6 years [range, 5–11 years]). In study 1, ocular itching ( P = 0.010), redness seen on slit-lamp examination (P = 0.003), and eyelid swelling ( P = 0.034) were significantly less intense with olopatadine than with cromolyn sodium during the peak pollen period. In study 2, redness seen on slit-lamp examination ( P = 0.040) and self-rated ocular redness ( P = 0.024) were significantly less intense with olopatadine than levocabastine during the peak pollen period. Olopatadine was well tolerated. Conclusion: Olopatadine hydrochloride ophthalmic solution 0.1% was more effective than both cromolyn sodium 2% and levocabastine 0.05% ophthalmic preparations in controlling ocular signs and symptoms of SAC in children and was well tolerated when administered twice daily for 6 weeks.

The effects of olopatadine, desloratadine, ketotifen, azelastine, and epinastine on membrane stability

Rationale To compare surface activity of olopatadine, desloratadine, ketotifen, azelastine, and epinastine and their effects on membrane stability using model and natural membranes. Methods Argon-buffer interface and a monolayer of 1-stearoyl-2-oleoyl- sn-glycero-3-phosphocholine (SOPC) were used as models for surface activity measurements. Lysis of natural membranes was determined by leakage of 6-carboxyfluorescein, hemoglobin, LDH and histamine from erythrocyte ghosts, intact erythrocytes, human corneal epithelial and conjunctival mast cells, respectively. Results Surface measurements revealed a range of affinities for the argon-buffer interface (i.e., K d, S=0.06-17.7mM) and SOPC-monolayer (i.e., K d, L=0.04mM to 1.05mM) in the order of: clemastine ≥ desloratadine ≥ azelastine ≥ ketotifen ≥ epinastine. Because of apparent low affinity for both argon-buffer interface and SOPC monolayer K d,S values could not be established for olopatadine. Consequently, olopatadine was devoid of hemolytic activity, even at maximum solubility concentrations (i.e., 10mM) when tested with intact erythrocytes or erythrocyte ghosts. This behavior was mirrored in human corneal epithelial cells and human conjunctival mast cells, where ketotifen, azelastine and epinastine caused significant membrane lysis as assessed by lactate dehydrogenase and histamine release, respectively. Conclusions Disruption of cell membranes by desloratadine, clemastine, azelastine, ketotifen and epinastine is a consequence of their intrinsic surface activity and interaction with the cell membrane. Olopatadine is unique amongst the antihistamines tested by causing minimal perturbation and diruption of cell membranes.

The promotion of eosinophil degranulation and adhesion to conjunctival epithelial cells by IgE-activated conjunctival mast cells

Allergen-mediated mast cell activation is a key feature of ocular allergic diseases. Evidence of eosinophil-derived mediators in tears and conjunctival biopsy specimens has been associated with chronic ocular allergic inflammation. To examine the role of conjunctival mast cell mediators in eosinophil adhesion to conjunctival epithelial cells and eosinophil degranulation. Conjunctival cells were obtained by enzymatic digestion of cadaveric conjunctival tissues. Eosinophils were obtained from peripheral blood samples using negative magnetic bead selection. The effect of IgE-activated mast cell supernates on eosinophil degranulation and adherence to epithelial cells was compared with supernates obtained from mast cells pretreated with a degranulation inhibitor (olopatadine). Eosinophil adhesion was measured by eosinophil peroxidase assay, and eosinophil degranulation was measured by eosinophil-derived neurotoxin radioimmunoassay. IgE-activated conjunctival mast cell supernates stimulated adhesion of eosinophils to epithelial cells (20.4% +/- 6.3% vs 3.1% +/- 1.0%; P = .048). Degranulation was not required for this process (no effect of olopatadine). IgE-activated mast cell supernates stimulated eosinophil-derived neurotoxin release (108.89 +/- 8.27 ng/10(6) cells vs 79.45 +/- 5.21 ng/10(6) cells for controls, P = .02), which was significantly inhibited by pretreatment of mast cells with a degranulation inhibitor (79.22 +/- 4.33 ng/10(6) cells vs 61.09 +/- 5.39 ng/10(6) cells for olopatadine pretreated and untreated, respectively, P = .02). Mediators released from conjunctival mast cells promote eosinophil adhesion to conjunctival epithelial cells and eosinophil degranulation. Degranulation inhibition studies suggest that different mast cell mediators are involved in regulation of these events.

Epithelial cells in ocular allergy.

Conjunctival epithelial cells do not act only as mechanical barriers, preventing the entry of particles, bacteria, viruses, and noxious substances into the eye but they are also active participants in the regulation of allergic inflammation via expressing adhesion/effector molecules (intercellular adhesion molecule-1, vascular cell adhesion molecule-1, human leukocyte antigen-DR, CD40/CD40L, Fas/Fas ligand) on their surfaces and releasing numerous proinflammatory cytokines, such as eotaxin, regulated on activation normal T-cell expressed and released (RANTES), macrophage inflammatory protein-1, interleukin (IL)-8, IL-6, and tumor necrosis factor-a, which are necessary for the proliferation, differentiation, activation, and chemotaxis of various inflammatory cells into the conjunctiva. Histamine, released from the conjunctival mast cells, might stimulate the synthesis of proinflammatory molecules such as IL-6 and IL-8 by the epithelial cells through the receptors that couple to inositol phosphate generation and, therefore, amplify the allergic response. The relationship between the epithelium and allergy should be considered in detail in future studies aiming at an effective control and treatment of all forms of allergic conjunctivitis.

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

Ketotifen relieves the symptoms of allergic conjunctivitis through multiple mechanisms of action. One such mechanism may involve stabilization of conjunctival mast cells. Because of inter- and intra-species variation, however, this hypothesis cannot be adequately tested using mast cells from animals or other human tissues. We therefore employed human conjunctival mast cells. The mast cells were prepared using human conjunctival tissues obtained from US eye banks. Cell suspensions were sensitized with human IgE and incubated with ketotifen fumarate or control. After antigenic challenge of sensitized cells with anti-IgE, levels of histamine and tryptase, two mast-cell granule markers, were measured in the supernatant fluid. Cell viability was assessed with a Trypan Blue assay. Ketotifen at concentrations of approximately 10(-11) to 10(-4) M inhibited mast-cell histamine release by 90% or more. Similarly, ketotifen at approximately 10(-10) to 10(-4) M inhibited tryptase release by 90% or more (apart from a single anomalous reading). At all ketotifen concentrations that stabilized mast cells, cell viability was preserved. Moreover, ketotifen did not impair cell viability unless concentrations were increased above the clinically relevant range, i.e., above the order of magnitude of 10(-4) M. These data demonstrate that ketotifen can stabilize human conjunctival mast cells, without impairing cell viability.

Interactions of olopatadine and selected antihistamines with model and natural membranes

Objective: Olopatadine, an effective topical ocular human conjunctival mast cell stabilizer/antihistaminic antiallergic drug, was evaluated and compared to selected classical antihistamines for their interaction with model and natural membranes to ascertain potential functional consequences of such interactions. Methods: The model membranes examined consisted of the argon-buffer interface and monomolecular films of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) at the argon-buffer interface. Interactions with the model membranes were detected as changes in surface tension, i.e., surface pressure. Functional consequences of these interactions were assessed with natural membranes by 6-carboxyfluorescein leakage, hemoglobin release, lactate dehydrogenase release, and histamine release from appropriate cell types. Results: Measurements at the argon-buffer interface revealed intrinsic surface activity for all agents that ranged from highly surface-active to weakly surface-active in the order of: desloratadine > clemastine > azelastine = ketotifen > diphenhydramine > pyrilamine > emedastine > epinastine =olopatadine. This order of amphipathic behavior was confirmed for most of the compounds by estimates of their dissociation constants (K d,L ) determined from interactions with SOPC monolayers adjusted to a surface pressure approximating that of natural membranes. Epinastine was the only antihistamine that showed a disproportionately greater increase in surface activity toward SOPC in monolayer when compared to other antihistamines. Dissociation constants could not be established for olopatadine because of its low affinity for both the argon-buffer interface and the SOPC monolayer. Functional consequences of these interactions were assessed with natural membranes by 6-carboxyfluorescein leakage (erythrocyte ghosts), hemoglobin release (erythrocytes), lactate dehydrogenase release (conjunctival mast cells, corneal epithelial cells), and histamine release (conjunctival mast cells). Aside from olopatadine and emedastine, all antihistamines promoted a concentration- dependent leakage of hemoglobin from intact erythrocytes. The concentration of drug required to cause half-maximal hemoglobin release (H 50 ) from erythrocytes correlated linearly (r = 0.98) with the SOPC dissociation constants (K d,L ) estimated for the different antihistaminic agents interacting with SOPC monolayers.A similarly high correlation (r = 0.85) emerged from a plot with a slope approaching unity that related drug concentrations required for half-maximal hemoglobin leakage from erythrocytes to threshold doses of drug that caused histamine release from human conjunctival mast cells. Olopatadine was the only agent that did not promote membrane perturbation as monitored by either hemoglobin release from intact erythrocytes, LDH release from human conjunctival mast cells, or 6-carboxyfluorescein release from erythrocyte ghosts. Assessment of the lytic potential of marketed concentrations of ketotifen (0.025%), azelastine (0.05%), and epinastine (0.05%) revealed significant membrane perturbation of human conjunctival mast cells and, importantly, human corneal epithelial cells as indexed by LDH release. This was in contrast to marketed concentrations of olopatadine (0.1%) which maintained normal mast cell and corneal epithelial cell membrane function. Conclusions: Combined, these results support the notion that the disruption of natural cell membranes by surface-active antihistamines occurs not through a receptor-mediated process, but is the consequence of a direct interaction of these agents with the cell membrane. This is corroborated by surface pressure-concentration isotherms for adsorption of five different antihistaminic agents to SOPC monolayers where 50% lysis occurred at a surface pressure of 42.9 ± 1.1mN/m. Olopatadine appears to be unique among the agents tested by demonstrating low intrinsic surface activity, thus limiting its interaction with natural membranes. At concentrations of about half-maximal compound solubility (i.e., 5.0mM or a 0.19% drug solution), olopatadine generated SOPC monolayer surface pressures (i.e., 39.82 ± 0.10 mN/m) that were below those that promoted membrane perturbation and onset of hemoglobin leakage. Olopatadine’s restricted interaction with membrane phospholipids limits the degree of membrane perturbation and release of intracellular constituents, including histamine, LDH,and hemoglobin, which is believed to contribute to olopatadine’s topical ocular comfort and patient acceptance.

A comparison of the efficacy and tolerability of olopatadine hydrochloride 0.1% ophthalmic solution and cromolyn sodium 2% ophthalmic solution in seasonal allergic conjunctivitis

Background: Treatments for allergic conjunctivitis have various mechanisms of action. Cromolyn sodium stabilizes conjunctival mast cells by preventing calcium influx across the cell membrane, whereas olopatadine hydrochloride is both an antihistamine and a mast cell stabilizer. Objective: This study compared the efficacy and tolerability of olopatadine and cromolyn in controlling the ocular signs and symptoms of seasonal allergic conjunctivitis. Methods: This was a multicenter, randomized, double-masked, parallel-group trial. One group instilled olopatadine 0.1% ophthalmic solution and placebo BID, and the other instilled cromolyn 2% ophthalmic solution QID, both for 6 weeks. The formulation of cromolyn used in this study is currently available only in Europe and Australia. Results: The intent-to-treat efficacy and safety analyses included 185 patients, 91 in the olopatadine group and 94 in the cromolyn group. At 30 minutes after the first instillation, respective decreases of ∼30% and ∼20% were reported in self-rated ocular itching and redness with both treatments; by 4 hours, itching had decreased by ∼38% in both groups. Differences between treatments were not statistically significant. At 4 hours, redness had decreased by ∼38% and ∼26% in the respective treatment groups. By day 42, both treatments had produced significant reductions from baseline in ocular signs and symptoms; however, the reductions in itching and redness were significantly greater with olopatadine compared with cromolyn (both variables, P < 0.05). The difference in physicians' impression of overall improvement on days 30 and 42 significantly favored olopatadine over cromolyn (both days, P < 0.05). Most patients (62.2%) had reacted positively to grass pollen at baseline. The regression slopes correlating itching and redness with pollen count were 5 times lower for olopatadine compared with cromolyn ( P = 0.002 and P = 0.016, respectively), indicating that olopatadine's efficacy increased as the pollen count increased. Conclusions: Six weeks' instillation of olopatadine 0.1% ophthalmic solution BID had a significantly greater effect on the ocular signs and symptoms of allergic conjunctivitis compared with 6 weeks' instillation of cromolyn 2% ophthalmic solution QID. Both treatments were well tolerated by patients in all age groups; however, olopatadine appeared to have better local tolerability in children aged <11 years.

Pathophysiology of ocular allergy: the roles of conjunctival mast cells and epithelial cells.

Allergic eye disease is associated with IgE-mediated conjunctival inflammation leading to signs of immediate hypersensitivity, including redness, itching, and tearing. Pathologic studies using conjunctival mast cells demonstrate that these cells, when sensitized with IgE antibody and exposed to environmental allergens, release mediators involved with allergic inflammation. The type, release kinetics, and concentration of these mediators in the conjunctiva have not been completely characterized. The ability to isolate and purify mast cells and epithelial cells from human conjunctival tissue has permitted the study of mediator release and cell-to-cell signaling in this tissue. Our laboratory has developed in vitro and in vivo models to better understand how inflammatory cells are recruited to and infiltrate conjunctival tissues. These models demonstrate that mast-cell activation may supply sufficient cytokine signaling to initiate and direct the well-orchestrated trafficking of eosinophils to the ocular surface, facilitate their adhesion, and cause release of potent mediators of ocular inflammation.

The central role of conjunctival mast cells in the pathogenesis of ocular allergy

Ocular allergic diseases are characterized by specific activation of conjunctival mast cells with subsequent release of preformed and newly formed mediators. Mast-cell numbers on the ocular surface are increased in all forms of allergic conjunctivitis. Mast-cell activation plays a central role in the development of the ocular allergic reaction, which can be divided into an early and a late inflammatory phase. Mast-cell mediators have been measured in tears of patients suffering from various forms of allergic conjunctivitis, and in sensitized patients after specific ocular allergen challenge. Histamine and tryptase are the most studied mediators in tears of allergic patients. Several cytokines, such as IL-4 and TNF-a, are also produced and released by conjunctival mast cells, and probably play a role in the immunoregulation on the ocular surface. In vitro studies of the characteristics and biologic functions of conjunctival mast cells highlight their central role in the pathogenesis of ocular allergy, and have led to new opportunities to evaluate anti-allergic compounds. This review discusses the role of conjunctival mast cells in the development of ocular allergic diseases.

Mechanisms of antihistamines and mast cell stabilizers in ocular allergic inflammation.

Mast cells play a central role in allergic reactions and inflammation. Successful anti-allergic therapies have typically targeted mast cell mediators, particularly histamine. Antihistaminic compounds interact with the various histamine receptors found on many cells, whereas other compounds such as disodium cromoglycate, are referred to as mast cell stabilizers, as they inhibit degranulation. Some of the most successful compounds developed recently are dual-action, in that they have both anti-histaminic and mast cell stabilizing activities. Recent trends in pharmaceutical intervention, however, have been focused on the secondary effects of mast cell mediators on epithelial cell adhesion molecule expression and mediator release in the process of allergic inflammation. Since, the ocular mucosa is highly exposed to environmental allergens it is commonly involved in allergic reactions and, as such, has been a useful and accessible model in which to test new therapies in vivo. These ocular allergen provocation studies permit analysis of ocular surface cells and evaluation of tear film mediators. Furthermore, techniques to purify conjunctival mast cells have facilitated the study of the effects of mast cell stabilizing compounds on other mast cell mediators, such as cytokines, and the direct effects of mast cell mediators on epithelial cells in vitro. This review will discuss current understanding of how anti-histamines and mast cell stabilizers work, particularly in the context of molecular mechanisms of ocular allergic inflammation.

Anti-IgE activated conjunctival mast cells mediate upregulation of eosinophil adhesion to conjunctival epithelial cells and eosinophil degranulation

Anti-IgE activated conjunctival mast cells mediate upregulation of eosinophil adhesion to conjunctival epithelial cells and eosinophil degranulation

Olopatadine inhibits anti-immunoglobulin E-stimulated conjunctival mast cell upregulation of ICAM-1 expression on conjunctival epithelial cells.

Olopatadine is a clinically effective dual-action (antihistamine/mast cell stabilizer) ophthalmic antiallergic agent. We have previously demonstrated that olopatadine inhibits tumor necrosis factor alpha (TNF-alpha) release from purified human conjunctival mast cells and that supernates from stimulated mast cells upregulate intercellular adhesion molecule 1 (ICAM-1) expression on epithelial cells via TNF-alpha. To investigate the effect of olopatadine on the TNF-alpha-mediated mast cell upregulation of ICAM-1 expression on conjunctival epithelial cells. Human conjunctival mast cells and epithelial cells were purified (>95%) from cadaveric tissue. Conjunctival mast cells were preincubated with three doses (30, 300, or 3,000 microM) of olopatadine or buffer alone for 30 minutes followed by 90-minute challenge with anti-immunoglobulin E (10 microg/mL). The resulting supernates were incubated with conjunctival epithelial cell monolayers for 24 hours along with the following treatments: rTNF-alpha, mast cell supernate + anti-TNF-alpha, recombinant (r)TNF-alpha + anti-TNF-alpha, the three doses of olopatadine, olopatadine supernates, olopatadine supernates + rTNF-alpha. ICAM-1 expression was measured using flow cytometry. Anti-IgE-stimulated human conjunctival mast cell supernates upregulated human conjunctival epithelial cell ICAM-1 expression to the same extent as rTNF-alpha. ICAM-1 upregulation could be completely blocked with anti-TNF-alpha. Preincubation of conjunctival mast cells with olopatadine significantly blocked the ability of supernates to upregulate ICAM-1 on conjunctival epithelial cells. ICAM-1 expression could be restored by adding rTNF-alpha to the olopatadine-preincubated mast cell supernates. Olopatadine is able to significantly decrease the anti-immunoglobulin E mast cell supernate-mediated upregulation of ICAM-1 on human conjunctival epithelial cells in vitro. This seems to be mediated through an effect on a TNF-alpha-specific mechanism.

Conjunctival mast cells in ocular allergic disease.

Allergic eye disease is a common clinical problem adversely affecting the quality of life for millions of sufferers. This ocular process is associated with IgE-mediated conjunctival inflammation leading to signs of immediate hypersensitivity including redness, itching, and tearing. Pathologic studies have shown that the conjunctiva contains mast cells that when sensitized with IgE antibody and exposed to environmental allergens can release mediators of allergic inflammation. The type, release kinetics, and concentration of these mediators in the conjunctiva have not been completely characterized. The ability to isolate and purify mast cells and epithelial cells from human conjunctival tissue has permitted the study of mediator release and cell-to-cell signaling in this tissue. Our laboratory has developed in vitro and in vivo models to better understand how inflammatory cells are recruited to and infiltrate conjunctival tissues. These models demonstrate that mast cell activation may supply sufficient cytokine signaling to initiate and direct the well-orchestrated trafficking of eosinophils to the ocular surface, facilitate their adhesion, and cause release of potent mediators of ocular inflammation.