CLINICAL THERAPEUTICS® / VOL. 25, NO. 10, 2003
`
`Double-Masked, Randomized, Placebo-Controlled
`Clinical Study of the Mast Cell–Stabilizing
`Effects of Treatment with Olopatadine in the
`Conjunctival Allergen Challenge Model in Humans
`
`Andrea Leonardi, MD,1 and Mark B. Abelson, MD2,3
`1Ophthalmology Unit, University of Padova, Padova, Italy, 2Schepens Eye Research Institute,
`Harvard Medical School, Boston, and 3Ophthalmic Research Associates, Inc., North Andover,
`Massachusetts
`
`ABSTRACT
`
`Objective: The purpose of this study was to assess the effects of olopatadine
`on the release of mast cell–derived mediators after conjunctival allergen challenge
`(CAC) in humans.
`Methods: This was a double-masked, randomized, placebo-controlled clinical
`trial. Subjects with a clinical history of seasonal allergic conjunctivitis (but no cur-
`rent symptoms or treatment at baseline) were studied. At visit 1, subjects under-
`went bilateral CAC with increasing doses of allergen every 15 minutes until a sig-
`nificant clinical reaction was obtained, then were evaluated at 15 minutes and 5
`hours after CAC. At visit 2 (2 weeks later), subjects were rechallenged to confirm
`the allergic response. Subjects exhibiting positive reactions at both visits (at both 15
`minutes and 5 hours) were randomized and instructed to treat 1 eye with olopata-
`dine and the contralateral eye with placebo (commercially available artificial
`tears) in a double-masked fashion twice daily for the 5 days immediately preced-
`ing visit 3. At visit 3, bilateral CAC was performed with the same dose as at visit
`2. Itching and redness were recorded. Tear cytology for inflammatory cell counts
`(ie, neutrophils, eosinophils, and lymphocytes) was carried out using precolored
`slides, and cell numbers were counted at 400× magnification. Tear histamine was
`assessed using radioimmunoassay histamine measurement. Intercellular adhesion
`molecule (ICAM)-1/CD54 monoclonal antibody was used for immunohisto-
`chemical staining of conjunctival epithelial cells obtained by impression cytology.
`
`Accepted for publication August 18, 2003.
`Printed in the USA. Reproduction in whole or part is not permitted.
`
`Copyright © 2003 Excerpta Medica, Inc.
`
`0149-2918/03/$19.00
`
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`CLINICAL THERAPEUTICS®
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`Slides were examined by 3 masked investigators and redness was classified on a
`scale of 0 (absent) to 3 (very intense).
`Results: Ten subjects completed the trial. Olopatadine significantly reduced
`postchallenge itching and redness compared with placebo (P < 0.01 and P < 0.03,
`respectively). Olopatadine also reduced the number of neutrophils and the total
`number of cells at 30 minutes (both P = 0.015), and the number of eosinophils
`(P < 0.001), neutrophils (P < 0.004), lymphocytes (P = 0.011), and total number
`of cells (P = 0.001) at 5 hours postchallenge compared with placebo. Tear hista-
`mine levels were significantly lower after challenge in the eyes pretreated with
`olopatadine compared with placebo (mean [SD], 7 [8] vs 22 [12] nmol/L;
`P = 0.04). Olopatadine significantly reduced tear histamine levels compared with
`those measured in the same eyes after CAC at visit 2 (P = 0.001), whereas placebo
`did not affect histamine levels. Olopatadine also significantly reduced ICAM-1
`expression compared with placebo at 30 minutes and 5 hours postchallenge
`(P < 0.03 and P < 0.01, respectively).
`Conclusion: In the present study, olopatadine significantly reduced the levels of
`histamine, cellular infiltrate, and ICAM expression compared with placebo after
`CAC, suggesting that it reduced the release of mast cell–derived mediators in hu-
`mans. This inhibition of mediator release correlated with reduction of itching and
`redness. (Clin Ther. 2003;25:2539–2552) Copyright © 2003 Excerpta Medica, Inc.
`Key words: olopatadine, histamine, mast cell–stabilizing allergic conjunctivi-
`tis, conjunctival allergen challenge.
`
`INTRODUCTION
`More than 15% of the general US population (and up to 30% in some industri-
`alized countries) has ocular allergy, the most common manifestations of which are
`seasonal and perennial allergic conjunctivitis.1 These 2 conditions are character-
`ized by itching, redness, tearing, chemosis, and eyelid swelling,2 all of which can
`be attributed to conjunctival mast cell degranulation.3 The reaction begins once
`allergens penetrate the tear film and bind to immunoglobulin E (IgE) receptors
`on the surface of conjunctival mast cells. This process results in mast-cell activa-
`tion and subsequent degranulation, causing exocytosis of preformed and newly
`formed proinflammatory and allergic mediators. Of these, histamine plays a ma-
`jor role in eliciting the clinical signs and symptoms of ocular allergy.4 Activation
`of neuronal type 1 histamine receptors (H1) induces itching, whereas activation
`of vascular endothelial cells through the action of both H1 and H2 histamine re-
`ceptors leads to vasodilation (ie, hyperemia) and transudation of fluid into tissue
`(ie, eyelid swelling and chemosis). Other mediators released include tryptase,
`chymase, prostaglandins, leukotrienes, heparin, and vasoactive peptides.5 In ad-
`
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`A. Leonardi and M.B.Abelson
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`dition, mast-cell degranulation releases cytokines, which trigger the activation of
`vascular endothelial cells and the expression of chemokines and adhesion mole-
`cules, such as intercellular adhesion molecule-1 (ICAM-1)/CD54. In chronic severe
`allergy such as atopic keratoconjunctivitis (AKC) and vernal keratoconjunctivitis
`(VKC), these factors lead to a latent recruitment phase that ushers in inflammatory
`mediators and their eventual infiltration of the conjunctival mucosa.6,7
`The temporal progression of an allergic reaction can often be delineated by the
`expression of signs and symptoms and the types of cells present at the site. Be-
`cause the pathophysiology of many allergic reactions can be similar, the study of one
`inflammatory condition can provide insight when examining another. Reactions in
`both the lung and the nose involve a secondary immunologic phase of cellular in-
`filtration after the initial reaction, which is caused by chemoattractant factors re-
`leased by mast cells. This second phase sometimes prolongs the initial reaction or
`triggers a second round of signs and symptoms. However, despite many similari-
`ties, these early and late reactions are tissue specific, a distinction that must be
`taken into account when determining clinical significance. Unlike those in nasal
`and lung tissues, ocular allergies rarely exhibit a second clinical phase. Although
`in some cases the cellular mechanisms are similar, in allergic conditions, tissue-
`specific distinctions exist.8
`In seasonal and perennial conjunctivitis, there is essentially 1 clinical phase. On
`conjunctival provocation, histamine-induced signs and symptoms are evident
`within minutes. The itching associated with an early-phase ocular allergic reaction
`has been shown to peak ~3.5 minutes after provocation,9 coinciding with mast-cell
`degranulation.10 A cellular late-phase reaction is seen only when higher concentra-
`tions of allergen are used and only occur in a subset of allergic patients. However,
`in allergic conjunctivitis, the cellular infiltrate is usually at the subclinical level,
`meaning that changes at the cellular level (if they occur at all) do not produce clin-
`ically visible signs or symptoms.11 In fact, conjunctival scrapings of patients with
`mild ocular allergic disease reveal only an infrequent finding of eosinophils.11,12
`The expression of adhesion molecules such as ICAM-1 and the presence of mi-
`gratory inflammatory mediators have been documented to follow the early-phase
`reaction. The presence of ICAM-1 and cellular infiltrate consisting primarily of
`neutrophils when a late phase was induced via extremely high-level allergen ex-
`posure was observed as early as 20 minutes after provocation and extended to
`6 hours, at which point lymphocytes and monocytes also became evident among
`infiltrate cells.6,13 Unlike findings on the early phase of the ocular allergic reac-
`tion, these observations have not been found to correlate with any clinically rele-
`vant manifestation of a late-phase response in the vast majority of patients. The
`induction of inflammatory mediators and cellular infiltration occurs at a subclin-
`ical level, except in rare cases (<5% of ocular allergy cases) with more chronic
`conditions such as AKC or VKC.14,15
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`CLINICAL THERAPEUTICS®
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`Several classes of ophthalmic medications are available for the treatment of the
`early-phase clinical signs and symptoms associated with seasonal and perennial
`allergic conjunctivitis. Two such classes are antihistamines and mast-cell stabiliz-
`ers. Antihistamines antagonize the binding of histamine at its receptors, blocking
`the activation of nerve cells and endothelial cells. Mast-cell stabilizers inhibit the
`degranulation of mast cells, preventing the cascade of events that triggers the
`signs and symptoms of the disease. Therapies such as olopatadine, ketotifen, and
`azelastine, which offer a combination of these 2 mechanisms, have become avail-
`able commercially. These antiallergy agents claim to exert both mast cell–stabilizing
`and antihistaminic effects. Mast-cell stabilization has been shown with olopata-
`dine in preclinical research in human conjunctival mast cells,16 with ketotifen in
`human conjunctival tissues, and with azelastine in cultured mast cells derived
`from umbilical cord blood and rat peritoneal mast cells.17–19
`The conjunctival allergen challenge (CAC) model was designed to reproduce,
`in a standardized way, the immediate ocular allergic response.20 It has been
`shown that a small dose of allergen causes a mild, short-term reaction with spon-
`taneous recovery, whereas in a subset of patients, a large dose can cause an
`intense and persistent reaction that progresses to cellular recruitment.21 This
`modified CAC model has been used to demonstrate the prophylactic effects of a
`mast-cell stabilizer (lodoxamide22) and a topical corticosteroid (desonide phos-
`phate23) on the induction of a CAC-induced prolonged ocular allergic reaction.
`Because mast-cell degranulation is responsible for the release of inflammatory
`mediators and the cellular infiltrate that may occur in selected patients, the ex-
`tent of mast-cell stabilization exhibited by a medication can be determined by
`the quantification of mast cell–derived mediators in the conjunctiva up to 6 hours
`after challenge. Olopatadine is the only drug of its category indicated for the
`treatment of all the signs and symptoms of allergic conjunctivitis, which include
`itching, tearing, lid swelling, redness, and chemosis.24 It is a selective H1 recep-
`tor antagonist with mast cell–stabilization properties.25
`The present study was performed to assess the effects of olopatadine on the re-
`lease of mast cell–derived mediators after modified CAC in humans. The olopata-
`dine molecule is thought to have multiple mechanisms of action, which we sought
`to clarify in this study. In addition to a clinical evaluation, the objective parame-
`ters of tear histamine levels, tear cytology, and ICAM-1 immunohistochemical ex-
`pression were analyzed to evaluate the mast cell–stabilizing capability of this drug.
`
`SUBJECTS AND METHODS
`Subjects with a clinical history of seasonal allergic conjunctivitis were enrolled in
`this double-masked, randomized, placebo-controlled clinical trial. Informed writ-
`ten consent was obtained from all subjects. All subjects were asymptomatic and
`free of any topical or systemic medication, and had positive skin-test results
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`A. Leonardi and M.B.Abelson
`
`(wheal diameter >3 mm) or positive specific serum IgE (CAP system, Pharmacia
`Diagnostics, Uppsala, Sweden). The allergen that induced the greatest response
`by skin test and was most clinically correlated with seasonal symptoms was cho-
`sen for use in the CAC procedure.
`Conjunctival challenge was performed according to the standardized proce-
`dure described by Abelson et al20 and modified for the induction of prolonged
`reaction and cellular infiltration.21 At visit 1, the allergen dose that induced a
`positive conjunctival reaction was determined by challenging both eyes with al-
`lergen in serial dilutions, increasing the dose every 15 minutes until a significant
`clinical reaction was obtained (≥3 score for itching and redness on 0–4 scales
`[0 = none; 4 = severe]). Subjects underwent monitoring 15 minutes postchal-
`lenge and then returned 5 hours later for further evaluation. Subjects showing
`positive signs and symptoms at 15 minutes and at 5 hours returned 2 weeks
`later for visit 2. At visit 2, a second challenge was conducted with the final dose
`determined at visit 1 to confirm the prolonged conjunctival reaction. Fifteen
`minutes was considered the standard time for looking at the early phase of the
`reaction, and 5 hours was selected as the second time point because this is when
`the cellular infiltrate peaks in those patients who develop this response after a
`high-dose challenge.6,13 Subjects with positive reactions at visits 1 and 2 were
`randomized and instructed to treat 1 eye with olopatadine and the contralateral
`eye with placebo (commercially available artificial tears) in a double-masked
`fashion twice daily for the 5 days immediately preceding visit 3. At visit 3, 15
`minutes after the final dose of treatment, subjects underwent bilateral CAC with
`the same dose as at visit 2.
`Slit-lamp examinations were conducted at each visit to note safety parameters,
`and patients were asked whether they experienced any adverse events. The sub-
`ject graded itching and the investigator graded redness. Parameters were evalu-
`ated in each eye before drug instillation; at baseline before challenge; at 5, 10,
`20, and 30 minutes; and at 5 hours postchallenge. Both itching and redness were
`assessed using the 5-point scale (0–4) described previously.
`Tear samples (50 µL) were collected from both eyes with a capillary tube before
`CAC and within 10 minutes after challenge at visits 2 and 3. Samples were col-
`lected from the outer canthus with a microcapillary tube, immediately transferred
`to a plastic tube, and then centrifuged for 10 minutes at 1000 rpm to separate the
`cells from the tear fluid. The supernatant tear-fluid samples were immediately
`frozen and stored at –20°C until analyzed by radioimmunoassay histamine mea-
`surement with a commercial kit (Immunotech, Marseille, France) intended for the
`quantitative determination of histamine levels in biologic samples. This method is
`based on the competition between the histamine in the sample and the tracer for
`the binding sites on the antibody-coated tube. Procedures followed the manufac-
`turer’s recommendations. The sensitivity of the assay (limit of detection) is 0.2 nM.
`
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`Tear cytology was performed at 30 minutes and 5 hours after CAC to deter-
`mine inflammatory cell counts. Tears were collected with a capillary tube at both
`time points. Because the procedure was not a scraping, no anesthetic was neces-
`sary. The 5-hour time point was selected because this is when the peak effect of
`mast-cell chemotactic agents on cellular infiltration is evident.7,13,21,22 Tear sam-
`ples (2 µL) were collected and placed on precolored slides (Testimplets, Roche,
`Mannheim, Germany). The numbers of neutrophils, eosinophils, and lympho-
`cytes were immediately counted in 5 fields of 0.15 mm2 using a microscope (Carl
`Zeiss International, Stuttgart, Germany) at 400× magnification. Conjunctival im-
`pression cytology specimens were collected from both eyes at visit 1 (baseline
`before CAC) and at visit 3 at 30 minutes postchallenge using 0.22-µm filters
`(GSWPO1300, Millipore Corporation, Billerica, Massachusetts). In each eye,
`1 semilunar filter was applied without exerting pressure onto the inferior
`bulbar conjunctiva. Membranes were removed immediately after contact,
`moistened in phosphate-buffered saline (pH 7.4), and firmly pressed onto a
`gelatin-covered slide to achieve maximum transfer of conjunctival cells for
`immunohistochemistry.
`ICAM-1/CD54 monoclonal antibody (CD 54, Bender MedSystems GmbH,
`Vienna, Austria) was used for immunohistochemical staining of conjunctival epithe-
`lial cells obtained by impression cytology at 30 minutes and 5 hours. A sensitive
`immunoenzymatic alkaline phosphatase–monoclonal anti-alkaline phosphatase
`complex procedure was employed to detect ICAM-1 expression on epithelial cells
`according to Ciprandi et al.6 Slides were examined by 3 masked investigators. The
`positive red reaction in the epithelium was analyzed in 5 representative fields
`(400× magnification) from the impression cytology specimens. It was classified as
`very intense (3), intense (2), slight (1), or absent (0).
`Data were analyzed by Student t test. The level of statistical significance was
`fixed in the protocol as P < 0.05, and the level of clinical significance was prospec-
`tively defined as ≥1 unit difference between placebo- and olopatadine-treated
`eyes.
`
`RESULTS
`Clinical Signs and Symptoms
`Eighteen subjects were initially enrolled; 10 achieved a qualifying allergic
`reaction at the necessary time points to continue in the study. Mean (SD) age
`was 31.5 (11.3) years (range, 20–50 years); 7 patients were women and 3 were
`men. All 10 qualified subjects completed the trial as planned. No changes
`or adverse events were reported based on slit-lamp examinations and patient
`interviews.
`The CAC-induced reaction was bilaterally symmetrical and reproducible (ie, no
`significant difference was found in the CAC score at visit 1 vs visit 2). The pro-
`
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`A. Leonardi and M.B.Abelson
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`longed allergic reaction was characterized by mild redness and mild eyelid
`swelling.
`Olopatadine reduced signs and symptoms compared with placebo. The primary
`symptom, itching (Figure 1), and the primary sign, redness (Figure 2), were sig-
`nificantly reduced by olopatadine compared with placebo (P < 0.01 and P < 0.03,
`respectively). Olopatadine demonstrated a clinically significant (≥1 unit difference)
`reduction in redness and itching during the 30-minute post-CAC assessments.
`
`Tear Histamine
`Tear histamine levels at baseline (before challenge) were very low or unde-
`tectable and were significantly increased after challenge at visit 2. Olopatadine
`significantly reduced mean (SD) tear histamine levels after challenge at visit 3
`(7 [8] nM/L) compared with levels measured in the same eyes after the visit-2
`(untreated) challenge (30 [27] nM/L, P = 0.001), whereas placebo did not signif-
`icantly modify histamine levels compared with those at visit 2 (22 [12] vs 23 [22]
`nM/L) (Figure 3). Comparing histamine levels between the 2 treatments at visit 3,
`
`Olopatadine
`Placebo
`
`*†
`
`*†
`
`*†
`
`†
`
`3.0
`
`2.5
`
`2.0
`
`1.5
`
`1.0
`
`0.5
`
`0
`
`Mean Itching Score (0–4 Scale)
`
`0 min
`
`5 min
`
`10 min
`
`20 min
`
`30 min
`
`5 h
`
`Time Postchallenge
`
`Figure 1. Mean (SD) itching scores on a 0 to 4 scale (0 = none; 4 = severe) in 10 sub-
`jects who instilled olopatadine or placebo eyedrops twice daily for 5 days
`before undergoing conjunctival allergen challenge. *P < 0.01 versus placebo.
`†Clinically significant (≥1 unit difference) reduction versus placebo.
`
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`*†
`
`*†
`
`*†
`
`*
`
`Olopatadine
`Placebo
`
`*†
`
`CLINICAL THERAPEUTICS®
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`3.5
`
`3.0
`
`2.5
`
`2.0
`
`1.5
`
`1.0
`
`0.5
`
`0
`
`Mean Redness Score (0–4 Scale)
`
`0 min
`
`5 min
`
`10 min
`
`20 min
`
`30 min
`
`5 h
`
`Time Postchallenge
`
`Figure 2. Mean (SD) redness scores on a 0 to 4 scale (0 = none; 4 = severe) in 10
`subjects who instilled olopatadine or placebo eyedrops twice daily for 5 days
`before undergoing conjunctival allergen challenge. *P < 0.03 versus placebo.
`†Clinically significant (≥1 unit difference) reduction versus placebo.
`
`olopatadine significantly reduced the levels compared with placebo (7 [8] vs 22
`[12] nM/L, P = 0.04) (Figure 3).
`
`Tear Cytology
`Before challenge, tear cytology was negative in all eyes at both visits 2 and 3.
`Compared with placebo, olopatadine significantly reduced the number of neu-
`trophils and the total number of cells at 30 minutes (both P = 0.015), and the
`number of eosinophils (P < 0.001), neutrophils (P < 0.004), lymphocytes (P =
`0.011), and the total number of cells (P = 0.001) at 5 hours (Figure 4).
`
`ICAM-1
`Expression of ICAM-1 on epithelial cells was low or absent at baseline (before
`CAC). Increased ICAM-1 expression was evident at 30 minutes and, to a lesser
`extent, at 5 hours after challenge. Olopatadine pretreatment significantly reduced
`ICAM-1 expression compared with placebo at 30 minutes and 5 hours postchal-
`lenge (P < 0.03 and P < 0.01, respectively) (Figure 5).
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`A. Leonardi and M.B.Abelson
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`Olopatadine
`Placebo
`
`*†
`
`Visit 2
`
`Visit 3
`
`Tear Histamine Levels Postchallenge
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
`Mean Histamine (nmol/L)
`
`Figure 3. Mean (SD) tear histamine levels after conjunctival allergen challenge at visit 2
`(before instillation of olopatadine or placebo eyedrops) and at visit 3 (after in-
`stillation) among 10 subjects. *P = 0.04 versus placebo. †P = 0.001 versus visit 2.
`
`DISCUSSION
`The CAC model reproduces, both clinically and histologically, the progression of
`the ocular allergic reaction.13,21,22,24 In the present study, subjects whose signs
`and symptoms persisted at 5 hours were selected and pretreated with olopatadine
`and placebo contralaterally to examine the effects of olopatadine on the markers
`of mast cell–derived mediators following CAC. Olopatadine significantly reduced
`signs and symptoms throughout the test period compared with placebo
`(P < 0.05). Reductions in itching and redness, which result from histamine re-
`lease from mast cells, were significantly reduced both clinically (≥1 unit) and sta-
`tistically (P < 0.01 and P < 0.05, respectively).
`The findings of the present study are supported by data from previous in vitro or
`nonhuman studies. In a guinea pig model of allergic reaction,26 olopatadine signif-
`icantly prevented the increase of histamine (P < 0.05) and slightly (but not signifi-
`cantly) inhibited peptide-leukotrienes. Mast cells also produce several cytokines,27
`such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-4, IL-6, and IL-13,
`which may activate the expression of chemokines and adhesion molecules,
`initiating the recruitment of inflammatory cells.28 Olopatadine was previously
`
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`Olopatadine 30 min
`Placebo 30 min
`Olopatadine 5 h
`Placebo 5 h
`
`‡
`
`†
`
`*
`
`§
`
`||
`
`†
`
`Eosinophils
`
`Neutrophils
`
`Lymphocytes
`
`Total Cells
`
`Tear
`
`25
`
`20
`
`15
`
`10
`
`5
`
`0
`
`Mean No. of Cells
`
`Figure 4. Mean (SD) tear cytology at 30 minutes and 5 hours after conjunctival allergen
`challenge among 10 subjects. *P < 0.001 versus placebo. †P < 0.015 versus
`placebo. ‡P < 0.004 versus placebo. §P = 0.011 versus placebo. ||P = 0.001
`versus placebo.
`
`shown to inhibit TNF-α release from purified human conjunctival mast cells and to
`inhibit the upregulation of ICAM-1 expression on epithelial cells.29 This last effect
`seems to be mediated through a TNF-α–specific mechanism. Therefore, inhibition of
`mast-cell activation and the reduced expression of ICAM-1 are necessary to inhibit the
`induction of inflammatory cell recruitment and infiltration. Another study showed
`decreased eotaxin levels in tears of allergic subjects treated with olopatadine.30
`The measurement of histamine, cellular infiltrate, and adhesion molecule ex-
`pression in the present study provides an assessment of mast-cell degranulation
`and the release of proinflammatory mediators from the mast-cell. After stimula-
`tion by antigen, mast cells release a series of proinflammatory mediators (eg, his-
`tamine, prostaglandins, leukotrienes) that induce the signs and symptoms of the
`acute reaction. Also released are cytokines and chemokines that recruit immune
`cells and stimulate adhesion molecules, although both of these processes occur at
`subclinical levels that do not produce clinical signs or symptoms, except in rare,
`extreme cases (<5% of all cases of ocular allergy). Olopatadine significantly re-
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`A. Leonardi and M.B.Abelson
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`Olopatadine
`Placebo
`
`*
`
`†
`
`30 min
`
`5h
`
`Time Postchallenge
`
`3.0
`
`2.5
`
`2.0
`
`1.5
`
`1.0
`
`0.5
`
`0.0
`
`Mean Expression Score (0–3 Scale)
`
`Figure 5. Conjunctival intercellular adhesion molecule (ICAM)-1 expression at 30 min-
`utes and 5 hours after conjunctival allergen challenge among 10 subjects.
`*P < 0.03 versus placebo. †P < 0.01 versus placebo.
`
`duced the levels of histamine (P < 0.05), cellular infiltrate (P < 0.015), and ICAM
`expression (P < 0.03) compared with placebo at all time points after CAC. From
`these data, we infer that olopatadine decreases the release of mediators from mast
`cells; with fewer mediators released, fewer cells are recruited to migrate to the
`site. In the present study, a lower number of infiltrated cells was indeed evident
`after olopatadine pretreatment (P < 0.015). In addition, as demonstrated in this
`study, true mast cell–stabilizing activity leads to reduction of all signs and symp-
`toms of allergic conjunctivitis mediated by mast cell–derived substances. Drugs
`with mast cell–stabilizing properties may provide insight into the prevention of
`other signs of the disease, such as eyelid swelling, which is caused by both his-
`tamine and vasoactive peptides released from the mast cell.31–33
`
`CONCLUSIONS
`In the present study, olopatadine significantly reduced the levels of histamine, cel-
`lular infiltrate, and ICAM expression compared with placebo after CAC. The re-
`sults suggest the ability of a combination mast-cell stabilizer and antihistamine
`to reduce the release of mast-cell mediators, including histamine (the primary
`
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`mediator of allergy), in the eyes of allergic human subjects. Although this study
`examined prophylactic use in seasonal allergic conjunctivitis, the activity shown
`here may have further implications for the use of combination antihistamine and
`mast cell–stabilizer medications such as olopatadine in the treatment of the less
`common but more severe chronic allergic conditions (eg, AKC, VKC), in which
`cellular infiltration is present clinically and implicated in the disease process.
`However, these areas would warrant further study. The results of this study also
`appear to indicate mechanisms of action of olopatadine beyond an antihistamine
`and mast cell–stabilizing effect.
`
`ACKNOWLEDGMENTS
`This research was supported by an unrestricted grant from Alcon Laboratories,
`Inc. (Fort Worth, Texas). The authors wish to acknowledge Iva Fregona and
`Chiara DeDomincis for technical assistance. Editorial assistance provided by
`Lauren Nichols and Kate Fink.
`
`REFERENCES
`1. Bielory L. Update on ocular allergy treatment. Expert Opin Pharmacother. 2002;3:
`541–553.
`2. Abelson MB, Schaefer K. Conjunctivitis of allergic origin: Immunologic mechanisms
`and current approaches to therapy. Surv Ophthalmol. 1993;38(Suppl):115–132.
`3. Abelson MB, Chapin MJ. Current and future topical treatments for ocular allergy.
`Compre Ophthalmol Update. 2000;1:303–320.
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