Tear tryptase levels and allergic conjunctivitis

Proteases and Their Potential Role as Biomarkers and Drug Targets in Dry Eye Disease and Ocular Surface Dysfunction

Dry eye disease (DED) is a multifactorial disorder that leads to ocular discomfort, visual disturbance, and tear film instability. DED is accompanied by an increase in tear osmolarity and ocular surface inflammation. The diagnosis and treatment of DED still present significant challenges. Therefore, novel biomarkers and treatments are of great interest. Proteases are present in different tissues on the ocular surface. In a healthy eye, proteases are highly regulated. However, dysregulation occurs in various pathologies, including DED. With this review, we provide an overview of the implications of different families of proteases in the development and severity of DED, along with studies involving protease inhibitors as potential therapeutic tools. Even though further research is needed, this review aims to give suggestions for identifying novel biomarkers and developing new protease inhibitors.

The proteolytic effect of mast cell tryptase to eotaxin-1/CCL11·eotaxin-2/CCL24 and eotaxin-3/CCL26 produced by conjunctival fibroblasts

PURPOSE

To investigate the proteolytic effect of mast cell tryptase on eotaxin-1/CCL11, eotaxin-2/CCL24 and eotaxin-3/CCL26 produced by conjunctival fibroblasts.

STUDY DESIGN

Experimental.

METHODS

The production of eotaxin-1, -2 and -3 by conjunctival fibroblasts stimulated both with and without IL-4/IL-13 or/and TGF-β₁ was assessed by ELISA. The proteolytic activity of tryptase on eotaxins derived from conjunctival fibroblasts and recombinant eotaxins was also estimated by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).

RESULTS

Conjunctival fibroblasts produced eotaxin-1 and -3, but not eotaxin-2. Stimulation with IL-4/IL-13 and TGF-β₁ synergistically increased eotaxin-1 and -3 production. Tryptase reduced the immunoreactivity of eotaxin-1 and -3 but not of eotaxin-2, due to the proteolysis of these eotaxins but not the inhibition of their m-RNA expression.

CONCLUSION

Mast cell tryptase may exercise proteolytic activity on eotaxin-1 and -3 produced by conjunctival fibroblasts, resulting in partial suppression of the ability of eotaxin-1 and -3 to accumulate eosinophils in the conjunctiva. Eotaxin-2 in the tears may be a suitable biomarker of severity of allergic conjunctival disease.

Conjunctival allergen provocation test : guidelines for daily practice

Conjunctival allergen provocation test (CAPT) reproduces the events occurring by instilling an allergen on the ocular surface. This paper is the compilation of a task force focussed on practical aspects of this technique based on the analysis of 131 papers. Main mechanisms involved are reviewed. Indications are diagnosing the allergen(s)-triggering symptoms in IgE-mediated ocular allergy in seasonal, acute or perennial forms of allergic conjunctivitis, especially when the relevance of the allergen is not obvious or in polysensitized patients. Contraindications are limited to ongoing systemic severe pathology, asthma and eye diseases. CAPT should be delayed if receiving systemic steroids or antihistamines. Local treatment should be interrupted according to the half-life of each drug. Prerequisites are as follows: obtaining informed consent; evidencing of an allergen by skin prick tests and/or serum-specific IgE dosages; being able to deal with an unlikely event such as acute asthma exacerbation, urticaria or anaphylaxis, or an exacerbation of allergic conjunctivitis. Allergen extracts should be diluted locally prior to administration. Positive criteria are based on itching or quoted according to a composite score. An alternative scoring is based on itching. CAPT remains underused in daily practice, although it is a safe and simple procedure which can provide valuable clinical information.

Release of mast cell tryptase into saliva: a tool to diagnose food allergy by a mucosal challenge test?

BACKGROUND

Our aim was to examine whether measurement of the saliva mast cell tryptase (MCT) concentrations before and after a mucosal challenge test with the offending food would be helpful in diagnosing food allergy.

METHODS

We performed a retrospective analysis of 44 food challenge tests performed in 38 patients between 2006 and 2009. Patients with a suspected history of food allergy chewed the food until they developed symptoms or until the amount of time known from the patients' history to usually be required for the provocation of symptoms had passed. In 5 patients, saliva samples for the measurement of MCT were collected at minutes 0, 1, 4, 8, 11, and 16 after the first onset of symptoms. The remainder of the patients only had samples taken before chewing and 4 min after the end of the test period.

RESULTS

During repeated measurements, MCT peaked about 4 min after the onset of symptoms (p = 0.028). During 33 of the 44 tests (75.0%), we observed oral symptoms during testing; after 25 of the 33 (75.8%) tests evoking symptoms, the saliva MCT concentration increased. The MCT increase was negative in all other tests where no oral symptoms could be provoked.

CONCLUSIONS

The measurement of saliva MCT 4 min after the onset of symptoms may be helpful to diagnose food allergy. Because of numerous confounding variables, however, a negative saliva MCT increase does not exclude food allergy.

Mast Cell Chymase Induces Conjunctival Epithelial Cell Apoptosis by a Mechanism Involving Degradation of Fibronectin

PURPOSE

To determine the mechanism of conjunctival epithelial injury in vernal keratoconjunctivitis, we investigated the effects of human chymase on conjunctival epithelial cells in vitro.

METHODS

Human conjunctival epithelial cells were incubated with human chymase for 24 or 48 hr at levels of activity that were likely to exist in the tear fluid of patients with vernal keratoconjunctivitis. Morphologic changes of the cells were observed by phase contrast microscopy. To determine the number of detached cells, we used an automated cell counter, while apoptotic cells were quantitated by flow cytometry. The level of soluble fibronectin in conditioned medium was measured by ELISA.

RESULTS

Most of the cells in the incubation with chymase were detached by 24 hr. However, chymase-mediated apoptosis was a slower process and was only detected after incubation of cells with chymase for 36 to 48 hr. Both cell detachment and apoptosis were blocked when cells were incubated in fibronectin-coated plates. The increase of soluble fibronectin was dependent on the amount of chymase added and the exposure time. A caspase inhibitor (antiapoptotic agent) rescued cells from apoptosis but did not prevent cell detachment. These results indicate that chymase-induced apoptosis of conjunctival epithelial cells represents anoikis, which is a slowly occurring apoptotic process induced by lack of adhesion to an extracellular matrix.

CONCLUSIONS

Human mast cell chymase caused conjunctival epithelial cell detachment by degrading fibronectin, and this led to secondary apoptosis.

Mast Cell Chymase Decreases the Barrier Function and Inhibits the Migration of Corneal Epithelial Cells

PURPOSE

We investigated the in vitro effects of human mast cell chymase on corneal epithelial cells.

METHODS

Human corneal epithelial cells were incubated with human chymase at activity levels that were likely to exist in the tears of patients with vernal keratoconjunctivitis.

RESULTS

Incubation of chymase resulted in a decrease of barrier function of corneal epithelium. Occludin protein was cleaved by chymase. In the wound assay, incubation with chymase resulted in an inhibition of cell migration.

CONCLUSION

Human chymase causes the proteolysis of occludin and fibronectin, resulting in a decrease of barrier function and inhibition of the migration of corneal epithelial cells.

Constitutive expression of functionally active protease-activated receptors 1 and 2 in human conjunctival epithelial cells

Protease-activated receptors (PARs) are G-protein-coupled receptors which initiate inflammatory responses when activated by specific serine proteases. This study was conducted to examine whether human conjunctival epithelial cells (HCECs) express functionally active PAR1 and PAR2 using Chang conjunctival epithelial cells as in vitro model. We performed RT-PCR and immunofluorescence analyses to determine the expression of PAR1 and PAR2, and monitored the production of IL-6 after activating HCECs with PAR1 activating agents (thrombin or TFLLRN) or PAR2 activating agents (tryptase, trypsin, or SLIGKV). The results show that HCECs constitutively express PAR1 and PAR2 mRNA and proteins, and produce significant amounts of IL-6 when incubated with specific PAR-activating enzymes or agonist peptides. Thrombin- and tryptase-induced HCEC activation was blocked by PAR1 and PAR2 neutralizing antibodies, respectively, and by specific enzyme inhibitors. The constitutive expression of PAR1 and PAR2, and their activation by thrombin and tryptase, respectively, may have important implications in ocular inflammation.

Tryptase as Severity Marker in Drug Provocation Tests

BACKGROUND

In the absence of objective symptoms, it is difficult to assess an adverse reaction during drug provocation testing. We evaluated the value of serum tryptase levels to distinguish between positive, negative and, even more important, so-called 'hysterical' reactions (conversion symptoms). The latter are occasionally observed in drug provocation tests when the patient experiences ambiguous subjective symptoms.

METHODS

In a prospective single-center study, 303 patients underwent 785 drug provocation tests. Blood was taken for tryptase measurement on each test day before and after drug challenge, and the changes in serum tryptase levels in patients with no reactions were compared with those who experienced immediate reactions to a drug.

RESULTS

Thirty-four of 785 drug provocations were clinically judged as being positive. Despite objective symptoms, median serum tryptase values in the afternoon were even lower than baseline levels. However, this decrease was not statistically significant. In the 751 patients suffering no objective reactions, the median values of post-testing tryptase values were statistically significantly decreased as compared with pretesting values.

CONCLUSIONS

The measurement of serum tryptase levels does not appear to be helpful to differentiate mild allergic or nonallergic reactions from 'hysterical' ones. The milder decrease in the group with objective drug reactions might indicate slight mast cell activation in some patients. More severe clinical drug reactions led to stronger mast cell degranulation. Mild reactions did not increase the tryptase levels consistently.

Combinatorial approaches towards the discovery of new tryptase inhibitors

The synthesis and evaluation as tryptase inhibitors of a library of 2,5-diketopiperazine derivatives containing guanidine or amidine functional groups is reported. Among the compounds evaluated, derivatives 6{CG4-CG8} and 6{CG4-CG9} are the most active compounds and have marked selectivity towards tryptase in front of trypsin.

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.

Objective measurement of allergic reactions in the eye

PURPOSE OF REVIEW

Conjunctival allergen challenge has become a useful model of human ocular allergy and an accepted method for studying the effects of topical antiinflammatory medications. Conjunctival allergen challenge reactions are typically evaluated in a subjective fashion. Erythema and edema are graded by observation, using a 0 to 4 scale. Itching is graded on a 0 to 4 scale by questioning the subject. We have reviewed the recent literature on conjunctival allergen challenge, including recently developed methods aimed at objective assessment of ocular allergic reactions, such as the erythema, edema, sensation, or EES, method.

RECENT FINDINGS

Conjunctival erythema can be measured objectively using a spectroradiometer, or colorimeter, a device which measures the chromaticity of reflected light, and provides the x, or u', and y, or v', coordinates of any color. Edema of the eyelids and conjunctiva can be measured using a fractional millimeter reticule in the eyepiece of a slit lamp microscope. Ocular surface sensation can be evaluated using the aesthesiometer of Cochet and Bonnet, or by using a 'sensation index', a measurement that takes into account the intensity and duration of itching.

SUMMARY

CAC reactions can be measured objectively using the erythema, edema, sensation method, as well as subjectively by observation and questioning.

Atopic keratoconjunctivitis

Atopic keratoconjunctivitis (AKC) represents a disease usually classified under the term of allergic conjunctivitis together with seasonal allergic conjunctivitis (SAC), perennial allergic conjunctivitis (PAC) and vernal keratoconjunctivitis (VKC). However, AKC and VKC have clinical and pathophysiological features quite different from SAC and PAC, in spite of some common markers of allergy. This article aims to review personal studies suggesting that allergic conjunctivitis (similarly to asthma, rhinitis and atopic dermatitis) is a heterogeneous disease entity with different preferential pathogenetic mechanisms and a spectrum of clinical expression which varies according to individual cases. AKC and VKC may thus represent a model of atopy quite distinct from the classical type-1 hypersensitivity mechanism.

Conjunctival provocation testing: overview of recent clinical trials in ocular allergy

PURPOSE OF REVIEW

The conjunctival provocation test is a human model of ocular allergy that has been used to study the ocular response to allergenic stimuli and to evaluate antiallergic therapy. The review will discuss recent studies using the conjunctival provocation test and other models of ocular allergy, and evaluate the relative merits of different models.

RECENT FINDINGS

The conjunctival provocation test has allowed investigators to recruit large numbers of allergic individuals who, although asymptomatic, can be challenged with the conjunctival administration of allergen. Observations of the eye can be made before and after challenge, and cells and mediators may be sampled from the ocular surface. In addition, the effectiveness of antiallergic therapy can be evaluated, usually by pretreating the two eyes with different forms or doses of drug.

SUMMARY

Considerable useful information has been gained about the ocular allergic response and drug efficacy using the conjunctival provocation test and naturally occurring seasonal allergic conjunctivitis.

Serum Tryptase in Allergic Rhinitis: Effect of Cetirizine Treatment

Activated mast cells release a large range of potent mediators of allergic inflammation, including proteases. The tryptase serum levels were evaluated in 13 subjects suffering from allergic perennial rhinitis. Moreover, the effects of cetirizine treatment on serum tryptase were studied using the UniCap™ tryptase fluoroenzymeimmunoassay.

In allergic patients the serum tryptase values (M±SD: 6.1 ± 2.4 μg/L) were significantly (p < 0.02) higher than the values detected in controls (3.0 ± 1.2 μg/L). In allergic rhinitis, after antihistamine treatment, tryptase values (4.4 ± 1.8 μg/L) decreased significantly (p < 0.001). After two weeks from the cetirizine stop, the tryptase levels increased again (5.5 ± 2.6 μg/l).

The results demonstrate that mast cells are constantly activated in perennial allergic rhinitis. The antihistamine treatment is effective in reducing the tryptase release from mast cells, but the mechanism of action of cetirizine is still to understand.

Evidence of mast cell activity in the middle ears of children with otitis media with effusion

OBJECTIVES

This is the first study to report the presence of tryptase, a reflection of mast cell activity, in chronic middle ear effusion of patients whose atopic status was characterized.

DESIGN AND METHODS

Mediator activity of mast cells and eosinophils was measured prospectively from effusion of 33 randomly selected patients and 5 control subjects with chronic otitis media with effusion (OME). Atopy was determined by enzyme-linked immunosorbent assay. Middle ear biopsies from a second group of 8 OME patients and 4 controls were fixed in plastic and stained immunohistochemically for mast cells.

RESULTS

Sixty-one percent of patients had extensive activation of mast cells in their middle ears. Among those with elevated tryptase in their effusion, 95.6% were atopic and 94.7% also had elevated levels of effusion eosinophilic cationic protein (ECP). Tryptase levels were elevated only in the effusion of atopic patients, as compared with 5 controls (P < .01). Mast cells were present in 6 of 8 OME ears and absent in all 4 normal ears.

CONCLUSION

Mast cells and its mediator tryptase, both indicators of a Th2-driven immune response, are present in a majority of ears that have chronic effusion. These findings support the hypothesis that middle ear mucosa is capable of an allergic response and that the inflammation within the middle ear of most OME patients is allergic in nature.

Serum tryptase levels in adverse drug reactions

We evaluated the usefulness of individual tryptase levels and variations after adverse drug reactions in 64 patients. Our aim was to find a tool for the diagnosis of drug allergy. Thirty-seven subjects were confirmed to have drug allergy, 12 had nonsteroidal anti-inflammatory drug (NSAID) reactions, five had negative controlled drug challenges (NAAR), and 10 had symptoms after placebo intake (PLA). Serum tryptase levels greatly increased after anaphylactic shocks (2242%) and anaphylaxis (710.5%). Patients with allergic urticaria and those with idiosyncratic responses to acetylsalicylic acid (ASA) exhibited a small increase in serum tryptase (49.5% and 38.2%, respectively). In the other two groups (NAAR and PLA), no variation in this serum protease was observed. The time of appearance of the serum tryptase peak differed considerably among patients with similar clinical reactions (from 30 min to 6 h) and was independent of the latent period, severity of symptoms, or the amount of tryptase released. We conclude that serum tryptase determinations are helpful in the diagnosis of anaphylactic shock and anaphylaxis, but serial measurements may be needed to confirm mast-cell participation in milder reactions.