Animal and human ocular surface response to a topical nonimmune mast-cell degranulating agent (compound 48/80)

Translational Preclinical Pharmacologic Disease Models for Ophthalmic Drug Development

Preclinical models of human diseases are critical to our understanding of disease etiology, pathology, and progression and enable the development of effective treatments. An ideal model of human disease should capture anatomical features and pathophysiological mechanisms, mimic the progression pattern, and should be amenable to evaluating translational endpoints and treatment approaches. Preclinical animal models have been developed for a variety of human ophthalmological diseases to mirror disease mechanisms, location of the affected region in the eye and severity. These models offer clues to aid in our fundamental understanding of disease pathogenesis and enable progression of new therapies to clinical development by providing an opportunity to gain proof of concept (POC). Here, we review preclinical animal models associated with development of new therapies for diseases of the ocular surface, glaucoma, presbyopia, and retinal diseases, including diabetic retinopathy and age-related macular degeneration (AMD). We have focused on summarizing the models critical to new drug development and described the translational features of the models that contributed to our understanding of disease pathogenesis and establishment of preclinical POC.

Treatment with galectin-1 eye drops regulates mast cell degranulation and attenuates the severity of conjunctivitis

Galectin-1 (Gal-1) is a β-galactoside-binding protein with diverse biological activities in the pathogenesis of inflammation, however the mechanisms by which Gal-1 modulates cellular responses in allergic inflammatory processes have not been fully determined. In this study, we evaluated the therapeutic potential of Gal-1 eye drops in an experimental model of conjunctivitis. Wistar rats received a topical application of compound (C)48/80 (100 mg/ml) into right eyes and a drop of vehicle into the contralateral eye. Another group of rats received Gal-1 (0.3 or 3 μg/eye) or sodium cromoglycate (SCG; 40 mg/ml) in both eyes and, after 15 min, right eye was challenged with C48/80. Conjunctivitis-induced by C48/80 was characterized by severe eyelid oedema and tearing, but clinical signs were ameliorated by eye drop doses of both Gal-1 (0.3/3 μg) and SCG. As expected, an increased proportion of degranulated mast cells (62%, P < 0.01) and lower histamine levels were observed after 6 h of C48/80 challenge, compared to control (32%). This effect was abrogated by Gal-1 and SCG, which reduced mast cell degranulation (31-36%), eosinophil migration and eosinophil peroxidase levels in the eyes. Gal-1 (3 μg) and SCG treatments also decreased IL-4 levels, as well as activation of mitogen activated protein kinases compared to untreated C48/80 eyes. Our findings suggest that Gal-1 eye drops represent a new therapeutic strategy for ocular allergic inflammation.

Levocabastine Eye Drops: A New Approach for the Treatment of Acute Allergic Conjunctivitis

Acute allergic conjunctivitis (AAC) is a common ocular allergic disorder and incident rates as high as 20% have been reported. Although a wide range of therapeutic agents are available for the treatment of AAC, the ideal treatment seems to have remained elusive. Levocabastine, a highly potent specific H1-receptor, appears to offer a promising alternative as a topical single-agent therapy. Levocabastine eye drops have been found to be well tolerated with an adverse-effect profile comparable to placebo and sodium cromoglycate. In addition, ocular levocabastine has been shown to have a rapid onset and long duration of action. The efficacy of levocabastine has been extensively investigated in conjunctival provocation tests and environmental studies. The available data suggest that ocular levocabastine is an effective therapeutic agent. Statistically significant differences in favour of levocabastine have been observed in comparisons with sodium cromoglycate, antazoline/naphazoline and oral terfenadine.

Effect of alcaftadine 0.25% on ocular itch associated with seasonal or perennial allergic conjunctivitis: a pooled analysis of two multicenter randomized clinical trials

PURPOSE

Seasonal and perennial allergic conjunctivitis represent the majority of cases of ocular allergy. This analysis was designed to evaluate the efficacy and safety of once-daily alcaftadine 0.25% in preventing ocular itching associated with seasonal or perennial allergic conjunctivitis.

SUBJECTS AND METHODS

Pooled data from two double-masked, multicenter, placebo-controlled studies using the conjunctival allergen challenge (CAC) model of allergic conjunctivitis were analyzed. Subjects randomized to receive treatment with alcaftadine 0.25% or placebo were challenged with seasonal (grass, ragweed, trees) or perennial (cat dander, cat hair, dog dander, dust mites, cockroach) allergens, 16 hours after treatment instillation. The primary efficacy measure was subject-evaluated mean ocular itching at 3 minutes post-CAC. Secondary measures included ocular itching at 5 and 7 minutes post-CAC. The proportion of subjects with minimal itch (itch score <1) and zero itch (itch score =0), and safety were also assessed.

RESULTS

A total of 189 subjects enrolled in the two studies were treated with alcaftadine or placebo. Overall, 129 subjects were challenged with seasonal allergens and 60 subjects were challenged with perennial allergens. Alcaftadine 0.25% achieved a statistically significant reduction in mean itch score at 3, 5, and 7 minutes post-CAC compared with placebo in subjects challenged with seasonal allergens (P<0.0001 at all time points) and those challenged with perennial allergens (P<0.0001 at all time points). A higher percentage of subjects treated with alcaftadine compared with placebo achieved minimal itch (P≤0.001 versus placebo at all time points) and zero itch (P<0.05 at all time points except 7 minutes for perennial) when challenged with either seasonal or perennial allergens. No treatment-related or serious adverse events were reported.

CONCLUSION

Once-daily alcaftadine 0.25% ophthalmic solution was well tolerated and demonstrated effective relief of ocular itching in subjects challenged with allergens classic for triggering either seasonal or perennial allergic conjunctivitis.

The safety and efficacy of alcaftadine 0.25% ophthalmic solution for the prevention of itching associated with allergic conjunctivitis

OBJECTIVE

The purpose of this study was to evaluate the safety and clinical efficacy of alcaftadine 0.25% ophthalmic solution, a new topical anti-allergic agent for the prevention of the signs and symptoms of allergic conjunctivitis induced by conjunctival allergen challenge (CAC).

STUDY DESIGN AND METHODS

This two-arm, double-masked, multi-center, placebo-controlled Phase III study (NCT00889330) enrolled healthy volunteers (N = 58) with a history of allergic conjunctivitis. Subjects ≥10 years of age with a reproducible, positive reaction to a CAC were randomized to receive either one drop of alcaftadine 0.25% ophthalmic solution bilaterally or vehicle bilaterally. After 16 hours (Visit 3) and 15 minutes (Visit 4), a CAC was performed and ocular and nasal symptoms of allergy were graded over a 20-minute period. Clinical and statistical significance were evaluated.

MAIN OUTCOME MEASURES

The primary endpoints were ocular itching and conjunctival redness. The secondary endpoints were all other signs and symptoms of allergic conjunctivitis. Visual acuity, slit lamp biomicroscopy and adverse event reporting were the predetermined safety measures.

RESULTS

Alcaftadine was effective in the prevention of ocular itching based on both clinically relevant and statistically significant differences compared with vehicle (placebo). Alcaftadine significantly reduced conjunctival redness, and almost all other allergic signs and symptoms at both 15 minutes and 16 hours after drug administration. No significant safety issues were reported. Between-group differences in ocular itching were higher 16 hours after drug administration than at 15 minutes after drug administration.

CONCLUSIONS

With an onset of action within 3 minutes and a duration of action of at least 16 hours, the statistically and clinically significant effect of alcaftadine 0.25% on itching make it an important addition to therapy for ocular allergy. Additional studies are warranted to better understand the mechanisms affording a fast onset and prolonged duration of action.

Time course of human conjunctival mast cell degranulation in response to compound 48/80

Compound 48/80, a non-immunogenic mast cell degranulatory agent, is known to produce the signs and symptoms of ocular allergy. Maximal mast cell degranulation of human conjunctiva occurred within the first hour after stimulation by a single topical dose of compound 48/80 (20 microliters, 7.5 mg/ml). The average percentage of fully degranulated mast cells in treated specimens (n = 9) was 31% (range 5-60%) versus 6% (range 0-20%) in control specimens (n = 5). Exact correlates of representative granulated, partially degranulated, and fully degranulated mast cells were determined by light and transmission electron microscopy.

Ocular anaphylaxis induced in the rat by topical application of compound 48/80. Dose response and time course study

In the present study we sought to develop a model of ocular anaphylaxis based on the topical application of compound 48/80 to the surface of the rat eye. Doses ranging from 50 to 1000 micrograms were found to produce graded edema of the conjunctiva and swelling of the lid. On histologic examination, 50 microns compound 48/80 produced no changes distinguishable from those in PBS-treated controls, 150 microns produced mild alterations, and 250, 500, and 1000 micrograms compound 48/80 produced a marked increase in degranulated mast cells and a mild influx of neutrophils. The time course of the response to 250 micrograms and 1000 micrograms of compound 48/80 was evaluated over a 72-h period. Both doses elicited epithelial damage. A mild reduction in the number of mast cell was seen at 6 h in rats receiving 250 or 1000 micrograms. The reduction persisted to 72 h in rats receiving 1000 micrograms. The number of neutrophils was increased at 1 and 6 h in eyes treated with 250 micrograms and at 1, 6, and 24 h in eyes treated with 1000 micrograms compound 48/80. The clinical and histologic changes induced by application of 250 micrograms compound 48/80 resemble those seen in patients with allergic conjunctivitis suggesting that a model of ocular anaphylaxis based on the topical application compound 48/80 will be clinically relevant and experimentally practical.

Late-phase reaction in ocular allergy

PURPOSE OF REVIEW

To determine if the late-phase reaction, which commonly occurs in allergic rhinitis and asthma, is also found in ocular allergy.

RECENT FINDINGS

Using PubMed, 542 articles were found; 18 articles in the allergy and ophthalmology literature were specifically related to late-phase reaction. Ocular late-phase reaction is clinically seen in 50-100% of allergic rhinoconjunctivitis patients, is associated with progression to systemic atopic disorders that is allergic rhinoconjunctivitis and occurs in several forms including biphasic, multiphasic and a prolonged response.

SUMMARY

The existing literature demonstrates that an ocular late-phase reaction also exists and has implications in the development severity of disease, change of reactivity and progression of the atopic disease state from a localized target organ, such as the nose or eye, to a more systemic atopic disorder. The existence of the clinically relevant allergic late-phase response is not only limited to the nose, skin and lungs but also includes the eyes. The appreciation that the late-phase response may be clinically very important as there is a continuum of ocular mast-cell activation during the waking hours of the day, a better understanding of its clinical impact may be a more appropriate focus in the development of future treatments.

Methodologies for the Study of Ocular Surface Disease

The ability to obtain reliable results from clinical trials of therapies for ocular allergic disease and dry eye disease is often limited because of inadequate control of variables, such as environment, patient life style, compliance, and individual fluctuations that occur from one assessment visit to another. The controlled allergen challenge (CAC) model of allergic conjunctivitis allows signs and symptoms of the disease to be elicited in a physiologically accurate and reproducible manner. The rigid criteria for subject selection, the controlled allergic reaction, and the standardized and quantified grading systems allow for a reproducible baseline from which statistically and clinically significant differences between formulations can be assessed. Similarly, the controlled adverse environment (CAE) model for dry eye mimics the environmental stimuli that lead to ocular surface drying. Preselected subjects have a reproducible, homogeneous baseline reaction from which the effects of various treatments can be significantly evaluated and compared. CAC and CAE provide accurate means to study highly variable and individual ocular surface disease.

Comparative efficacy of olopatadine 0.1% ophthalmic solution versus levocabastine 0.05% ophthalmic suspension using the conjunctival allergen challenge model

OBJECTIVE

To compare the efficacy of olopatadine and levocabastine in reducing ocular allergic itching and vascular hyperemia (redness) induced by conjunctival allergen challenge.

RESEARCH DESIGN AND METHODS

The study was a randomized, double-masked, contralateral study using the conjunctival allergen challenge (CAC) model. At Visit 1, subjects with a positive allergen skin test and a history of allergic conjunctivitis were administered increasing concentrations of allergen until at least a moderate grade 2 ocular itching and conjunctival redness response was obtained in both eyes. Allergic signs were graded on standardized 0-4 scales. Subjects who reacted positively were re-challenged at Visit 2 with the pre-determined concentration of allergen. Subjects who again responded with at least a grade 2 bilateral ocular itching and conjunctival redness score at Visit 2 were eligible for drug evaluation. At Visit 3, subjects received olopatadine in one eye and levocabastine in the contralateral eye according to a computer-generated randomization scheme generated prior to commencement of the study. Ocular discomfort was then graded in both eyes. Subjects were bilaterally challenged with the predetermined concentration of allergen 27 min after topical drug administration, such that the first post-challenge assessment was made 30 min post-drug instillation. Allergic signs and symptoms were evaluated at 3 min, 10 min, and 20 min postchallenge and safety and efficacy analyses were performed.

RESULTS

Sixty-eight subjects received study drug and were included in the safety and efficacy analyses. Ocular itching scores for olopatadine were significantly lower than levocabastine at 3 min and 10 min post-challenge (p < 0.001). Ocular redness scores for olopatadine were significantly lower than levocabastine at all time points post-challenge (p < 0.0001). Of all subjects, 4.41% reported ocular discomfort in the olopatadine eye and 26.5% in the levocabastine treated eye.

CONCLUSION

Olopatadine treated eyes had significantly less itching and redness than levocabastine treated eyes after conjunctival allergen challenge. Olopatadine was also associated with less discomfort upon instillation than levocabastine.

Animal models of ocular allergy and their clinical correlations

Ocular allergic diseases represent a wide spectrum of disorders, from the acute self-limited, mild form of seasonal allergic conjunctivitis to the chronic, severe, sight-threatening atopic keratoconjunctivitis. The least problematic forms are the most prevalent, and several animal models have contributed to elucidate their etiopathogenetic mechanisms and have served to test numerous anti-allergic compounds. The most severe and chronic, although less prevalent, ocular allergic problems have not benefited from a similar advance, with the subsequent lack of full understanding and a limited therapeutic armamentarium. Research in this field is currently concentrating efforts in developing more protracted models of ocular allergic inflammation involving the cornea and mimicking more closely the human disease caused by chronic ocular allergy. Most recent experimental models are demonstrating that inhibiting Th2 cells and their secreted cytokines might be one important therapeutic target for inhibiting chronic allergic inflammation in the ocular surface.

Allergic and immunologic disorders of the eye. Part I: immunology of the eye

Immuno-ophthalmology evolved during the 20th century as a subspecialty linking ophthalmologists and immunologists. This emerging subspecialty has focused on the use of immunology to better understand and treat ocular disorders. To help the allergist/clinical immunologist better appreciate the growing field of immuno-ophthalmology, this 2-part review series (Part II: Ocular Allergy will appear in the December issue of the Journal) will provide an overview of the impact that immunology has had on our understanding and treatment of allergic and immunologic eye diseases. The current review will focus on mechanisms by which mast cells, T cells, eosinophils, cytokines, and other inflammatory constituents contribute to the unique features of eye disease and their link to allergic responses that occur in other organs of the body.

Changes in histamine content following pharmacologically-induced mast cell degranulation in the rat conjunctiva

Compound 48/80 was applied into one eye of male Wistar rats and a drop of vehicle into the contralateral eye. Another group of rats received sodium cromoglycate in both eyes every 6 h for a period of 48 h. One eye was challenged with compound 48/80 30 min after the end of treatment with sodium cromoglycate. The eyes were monitored clinically and the histamine content of the conjunctiva was determined fluorometrically. The basal histamine levels in rat conjunctival homogenates were quantified. Pharmacologically-induced mast cell degranulation by a single application of 0.1 g ml(-1)of compound 48/80 resulted in significant decreases of conjunctival histamine levels 1, 12 and 24 h after challenge. Sodium cromoglycate prevented the effect of compound 48/80 when administered into the eye prior to the challenge with the non-immunogenic histamine releaser. Upon termination of the application, the membrane stabilizer was unable to reverse the reduced histamine levels in the conjunctival homogenates.

Immunomorphologic studies of mast cell heterogeneity, location, and distribution in the rat conjunctiva

Mast cells are crucial components of immediate and some delayed-type hypersensitivity reactions. They play a pivotal role in allergic conjunctivitis and other immunoinflammatory disorders of the ocular surface, yet little is known of their distribution and heterogeneity in the conjunctiva of potential animal models, such as the rat. In this study, mast cell types were investigated in histologic sections and corneal-conjunctival-lid whole mounts by using toluidine blue, alcian blue-safranin, and immunohistochemical staining methods (anti-rat mast cell proteinase [RMCP] antibodies). Quantitative analyses were performed on corneal-conjunctival-lid whole mounts by using the optical dissector procedure to obtain the density of mast cells per unit volume in different regions of the conjunctiva. Single and double immunohistochemical analyses revealed that the mast cells in the conjunctiva of the limbus, fornices, and lid margin were strongly RMCP I+, suggesting that they were of the connective tissue phenotype. Mast cells containing the mucosal mast cell proteinase RMCP II were not present in the normal conjunctiva. Histochemical analysis revealed that the maturity of the connective tissue mast cells, as assessed by the presence or absence of safranin (heparin)-positive granules in their cytoplasm varied in different regions. In the lid margin 60% to 78% of the mast cells were solely alcian blue-positive, whereas in the fornices 68% to 78% were safranin-positive. In the limbus the predominant type of mast cell was either safranin-positive or contained mixed granules. Mast cell densities were greatest close to the lid margin (10,000 to 12,000 cells/mm3), followed by the limbus (3400 to 4800 cells/mm3) and were rare in the remainder of the conjunctiva (500 to 1000 cells/mm3), with the exception of the region around the nictitating membrane. This study of rat conjunctival mast cells provides essential baseline data for future studies of the role of mast cells in models of allergic conjunctivitis.

Allergic conjunctivitis and uveitis models: reappraisal with some marketed drugs

The purpose of this study was to assess the activity of some marketed products in ocular non-immune and immune type I hypersensitivity reactions, and during intra-ocular type III hypersensitivity. In order to compare these activities, we improved and validated three different models of ocular allergic reaction already known for their ability to reproduce allergic conjunctivitis or uveitis. Allergic conjunctivitis was induced by ocular immediate hypersensitivity after instillation of compound 48/80 in the rat, or an active anaphylaxis reaction with ovalbumin immunisation and challenge in the guinea pig. Uveitis was induced by a reverse passive anaphylaxis reaction using intra-vitreal rabbit anti-bovine IgG anti-serum sensitisation and intravenous bovine gamma-globulin challenge in the rabbit. Clinical scores and blood-tissue permeability indices were studied. Using the same schedule of ocular instillation, the effects of Livostin (levocabastine 0.05%), Almide (lodoxamide 0.1%), Opticrom (sodium cromoglycate 2%), Ocufen (flurbiprofen 0.03%), Acular (ketorolac 0.5%) and 0.3% chlorpheniramine maleate were compared to positive and negative controls. We demonstrated the potent activity of chlorpheniramine maleate 0.3% and Livostin in both allergic conjunctivitis models. Significant activity was also evidenced with Almide, which was only active in the non-immune allergy model, while Opticrom was definitely not active in these models. In the uveitis model, Acular and Ocufen are active and potent drugs, while Livostin and Almide were not active. These results are discussed with respect to the models used and the mediators involved.

Comparison of Naphcon-A and its components (naphazoline and pheniramine) in a provocative model of allergic conjunctivitis

A double-masked, randomized, parallel group, placebo-controlled study demonstrated the efficacy of Naphcon-A (naphazoline HCl 0.025% and pheniramine maleate 0.3%). Seventy-two patients with a documented positive skin test or radioallergosorbent test were recruited. Three groups of 24 patients each received 1 drop of Naphcon-A instilled in one eye, and 1 drop of either naphazoline, pheniramine, or placebo in the other eye. After the instillation of test medication, a titrated dose of ragweed antigen was administered bilaterally, and ocular signs and symptoms were evaluated 10, 30, and 120 minutes later. All patients (excluding 4 who had persistent symptoms attributable to ragweed) were rechallenged with ragweed antigen at 120 minutes to assess the duration of action of the test medications. Naphcon-A was significantly more effective than placebo, naphazoline, and pheniramine in reducing redness. Naphcon-A and pheniramine were equally effective in relieving itching.

Effects of Mipragoside on ocular allergic inflammation in the rabbit

We evaluated the pharmacodynamic and pharmacokinetic profile of Mipragoside, a monosialoganglioside isopropyl-ester (as 0.5% w/w ophthalmic gel), on allergic inflammation of the eye induced by reverse passive Arthus reaction, on a non-immune mast cell degranulation elicited by compound 48/80 and on ocular inflammation produced by horse serum. Conjunctiva was sensitized by injection of rabbit antisera to bovine proteins and the allergic conjunctivitis was triggered by intravenous administration of bovine gamma globulin. The permeability of the blood-conjunctival barrier was evaluated by a fluorometric method. Compound 48/80 was topically administered at concentration of 50mg/ml and histological analysis of conjunctiva was performed. Horse serum was administered by intravenous injection at different days. The pharmacokinetic profile of topical 3H-Mipragoside on 48/80 model was investigated and compared with untreated animals. Mipragoside treatment significantly reduced (p < 0.05 vs placebo) the conjunctival vasopermeability induced by reverse passive Arthus reaction as well as successfully reduced the eosinophil levels in the conjunctival epithelium (p < 0.01 vs placebo) elicited by compound 48/80. Further, Mipragoside successfully reduced the primary signs of ocular inflammation produced by horse serum administration. A radiotracer technique was used to evaluate the disposition of 3H-Mipragoside in the rabbit ocular tissues. Disposition of the drug was monitored at 30, 60, 120 and 240 min. 3H-Mipragoside levels in the inflamed conjunctiva were significantly higher (p < 0.01) than in the control eye.

The level of tryptase in human tears. An indicator of activation of conjunctival mast cells

Tryptase, a neutral endoprotease, is secreted by activated mast cells in human tissues. Tryptase levels in various body fluids have been used as an indicator of mast cell activation. The authors determined tryptase levels in unstimulated tears collected from the following groups of patients: (1) normal control, (2) nonallergic ocular inflammation, (3) asymptomatic seasonal allergic conjunctivitis, (4) symptomatic seasonal allergic conjunctivitis, (5) vernal conjunctivitis, and (6) contact lens-associated giant papillary conjunctivitis. They also assessed the release of tryptase into the tear fluid after provoking the conjunctiva with (7) allergens, (8) compound 48/80, and (9) rubbing. Tryptase levels were elevated in tears of patients with active ocular allergy and also increased after provoking the conjunctiva with allergens in atopic subjects and with compound 48/80 and rubbing in nonatopic subjects. Tryptase levels in tear fluid may prove useful as a clinical indicator of mast cell involvement in ocular allergic disorders. In provocation experiments, tryptase levels may be used to evaluate and compare different mast cell stabilizing agents.

Human conjunctival mast cells: distribution of MCT and MCTC in vernal conjunctivitis and giant papillary conjunctivitis

The distribution and concentration of human tryptase-positive, chymase-negative mast cells (MCTS) and tryptase-positive, chymase-positive mast cells (MCTCS) were examined in conjunctival biopsy specimens from subjects with active vernal conjunctivitis (VC; n = 7), giant papillary conjunctivitis (GPC; n = 6), and allergic conjunctivitis (AC; n = 5), and from asymptomatic soft-contact lens wearers (SCL; n = 6) and normal control individuals (n = 19). Carnoy's fixed tissue sections were stained by a double immunohistochemical method using a biotinylated mouse monoclonal antichymase antibody with immunoperoxidase, followed by an alkaline phosphatase-conjugated mouse monoclonal antitryptase antibody. Epithelial mast cells (MCs) were found in all VC specimens (96% MCTCs) and in three GPC specimens (100% MCTCS) but in none of the other groups. In the substantia propria, MCTCS were the predominant type of MC observed in all specimens, accounting for 95% of the total MCs in the normal control group and 100% of the total MCs in the subjects with GPC, AC, and SCL. No significant differences were found in the total MC concentration of the substantia propria among the normal control subjects (11,054 +/- 6327 MCs per cubic millimeter), subjects in the SCL group (13,168 +/- 4685 MCs per cubic millimeter), subjects with GPC (17,313 +/- 8500 MCs per cubic millimeter), and subjects with AC (15,380 +/- 5660 MCs per cubic millimeter). In subjects with VC, the percentage of MCTs (18% +/- 13%) and the total MC concentration (24,689 +/- 18,978 MCs per cubic millimeter) in the substantia propria were significantly increased as compared to the normal control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of multiple applications of compound 48/80 on mast cells of rat conjunctiva

We sought to determine the effect on rat conjunctival mast cells of chronic exposure to a degranulating agent. Compound 48/80 (250 micrograms in 10 microliter) was applied daily to the ocular surface of rats for a total of 13 treatments administered in 17 days. A single application of compound 48/80 was given to rats for comparison. Four groups of animals (6 in each group) were evaluated 1 or 48 h after the last application of compound 48/80 in both chronic exposure and single exposure studies. Although a single exposure to compound 48/80 induced significant degranulation of mast cells in animals observed 1 h after treatment, no significant degranulation of mast cells was observed 1 h after the last dose of compound 48/80 was given to rats whose conjunctiva had been chronically exposed to this degranulating agent. Thus, multiple applications of compound 48/80 attenuated the mast cell response to compound 48/80. This acquired tolerance to compound 48/80 was reflected in the lessened clinical signs in rats receiving repeated applications compared with those given a single application.

Effects of ocular inflammation on tear proteins. I. Thiol protease inhibitors

Concentrations of protease inhibitors found in tears have been observed to vary during ocular inflammation. Possible stimuli for these variations were tested for by studying thiol protease inhibitor concentrations in models of ocular inflammation. Inflammatory responses were elicited either by topical application of arachidonic acid (AA), or compound 48/80. For each model, four rabbits were treated in one eye with the inflammatory stimulant and tear samples were collected before and up to five hours following treatment. Control animals were treated with buffer. When compared to pretreatment values, tears from AA-treated eyes showed decreased inhibitor at one and two hours and an increased inhibitor concentration at three hours. In the 48/80 model, inhibitory activity and protein levels were elevated when compared over time to the control group (p greater than or equal to 0.02, p greater than or equal to 0.0001 respectively). When compared to pretreatment values, inhibitor values were elevated at all times after treatment and protein values were elevated at one and three hours in this model. Serum proteins were also increased in the tears of rabbits treated with 48/80. The results suggest that one or more of the mediators released by basophil or mast cell degranulation stimulate increased tear protease inhibitory activity and tear serum proteins.

The release of histamine from the pars flaccida mast cells one cause of otitis media with effusion?

In this experimental study in the rat, compound 48/80--a potent degranulating drug of mast cells--was instilled in the external auditory meatus towards the tympanic membrane. Moreover, effusion material was produced in the attic space by blocking the tympanic isthmus with a piece of Gelfoam applied through the tympanic bulla. Both these procedures caused a degranulation of the pars flaccida mast cells and subsequently histamine was detected in the rinsing fluid collected from the middle ear cavity. A possible direct cause of the effusion material in the middle ear cavity may be a degranulation of the pars flaccida mast cells, thus resembling an allergic reaction Type I.