The efficacy and safety of topical diquafosol ophthalmic solution for the treatment of dry eye: A systematic review of randomized clinical trials

Di Wu1,4, PhD, Wang Qi Chen2, Ryan Li3, Yan Wang4, MD, PhD

1 Tianjin Medical University. 22 Qixiangtai Rd, Heping, Tianjin, China, 300070

2 University of California, Berkeley, College of Chemistry. 419 Latimer Hall, Berkeley, CA 94720

3 University of Toronto, Faculty of Arts and Science. Sidney Smith Hall, 100 St. George Street Toronto, Ontario, Canada M5S 3G3

4 Tianjin Eye Hospital & Eye Institute, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Medical University. No 4. Gansu Rd, Heping District, Tianjin, China, 300020

Corresponding author: Yan Wang, MD, PhD. Tianjin Eye Hospital & Eye Institute, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Medical University. No 4. Gansu Rd, Heping District, Tianjin, China, 300020 Tel: 86-22-27305083. Email: wangyan7143@vip.sina.com

None of the authors has a financial interest related to this study.

Keywords: diquafosol, dry eye, keratoconjunctivitis sicca, randomized clinical trials, systematic review

Purpose: To evaluate the efficacy and safety of topical diquafosol ophthalmic solution treatment for dry eye.

Methods: Randomized clinical trials (RCTs) from MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) were identified to evaluate the efficacy and safety of topical administration of diquafosol for dry eye patientsents. Data evaluation was based on endpoints including Schirmer’s test, tear film break-up time test (TFBUT), ocular surface staining score, subjective symptom score and adverse events.

Results: A total of 8 RCTs involving 1516 patients were selected abiding pre-specified criteria. Significant improvement of Schirmer’s test values and TFBUT were reported in 40% (2/5) and 80% (4/5) studies, respectively. Ocular surface staining scores significantly decreased in 100% (Fluorescein corneal staining: 6/6; Rose Bengal corneal and conjunctival staining: 4/4) RCTs. Symptoms significantly improved in 75% (6/8) RCTs in dry eye patients. No severe adverse events were reported with the concentrations of diquafosol from 0.5% - 5%. Heterogeneity in study design prevented meta-analysis from statistical integration and summarization.

Conclusions: Topical diquafosol appears to be a safe therapeutic option for the treatment of dry eye. The high variability of the selected RCTs compromised the strength of evidence and limits the determination of efficacy. However, the topical administration of diquafosol showed appears to be beneficial in improving the integrity of the epithelial cell layer of ocular surface and mucin secretion in dry eye patients. This review indicates a need for standardized criteria and methods for evaluation to assess the efficacy of diquafosol in the future clinical trials.

INTRODUCTION

Dry eye or keratoconjunctivitis sicca (KCS) is a multifactorial disease characterized by increased osmolarity of the tear film and inflammation of the ocular surface.1 Based on population-based epidemiologic studies, The International Dry Eye Workshop (2007) reported the prevalence of dry eye to be a range of approximately 5%-35% at various ages.2-9 Furthermore, tAside from the disturbance of vision function, the burden of dry eye also may include the impact on daily activities, social and physical functioning, and quality of life.10

The pathogenesis of dry eye is a cyclic amplification of the damage and discomfort associated with the disease. The cascade of inflammatory events in dry eye caused by tTear hyperosmolarity and tear film instability have been regarded as the causative and core mechanism causing ocular surface damage, symptoms of discomfort and a cascade of inflammatory events in dry eye.1 The activation of inflammatory signaling pathways (e.g., MAP kinases and NFκB) and the release of inflammatory cytokines elicits apoptotic death of surface epithelial cells, including the goblet cells (GCs).11-13 GCs secrete gel-forming mucin that plays an essential role in maintaining the integrity of the tear film.14,15 The reduction of GCs leads to a corresponding reduction of mucin, which exacerbates tear film instability and ocular surface hyperosmolarity, triggering the progression of dry eye into a vicious cycle. Therefore, increasing mucin secretion is would be an important therapeutic target in dry eye syndrome in an effort to break from this cycle.

Diquafosol, a pharmacological agent under investigation, has been known as a purinergic P2Y2 receptor agonist that promotes fluid transfer and mucin secretion by activating P2Y2 receptors expressed on ocular surface.16,17-20 Previous studies have shown that the stimulation of water and mucin secretion by diquafosol is related to the activation of phospholipase C via G proteins caused by the combination of diquafolsol and P2Y2 receptor, which consequently increases the concentration of calcium ion within conjunctival epithelial cells and in GCs.19,21 Animal in vivo studies, conducted on dogs, rabbits, or age-related dry eye murine model, demonstrated that the topical administration of diquafosol appeared to be effective in improving mucin MUC5AC concentration and aqueous tear secretion.22-24

Even though tThere is evidence demonstrating the improvement of aqueous tear secretion in animal models22-24, but, no consensus on the efficacy of diquafosol as a clinical therapy for dry eye has been established. Diquafosol ophthalmic solution was approved in Japan in April 2010 as a novel therapeutic option for dry eye, but it has not yet been accepted by United States Food and Drug Administration (FDA).25 So far, several randomized clinical trials (RCTs) have been performed concerning diquafosol and dry eye. To our knowledge, there has been no reported systematic review or meta-analysis to provide recommendations to evaluate the treatment effects of diquafosol for dry eye. This present report aimed to systematically review the results of RCTs on safety and efficacy of diquafosol ophthalmic solution in different dry eye types.

MATERIALS AND METHODS

This review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).26 A previously written protocol can be found in the Appendix 1. The details of the protocol abide the recommendations from Cochrane Handbook for Systematic Reviews of Interventions (Cochrane Handbook).27

Eligibility Criteria

Types of Studies: RCTs studying the effect of diquafosol administration as an ophthalmic solution for dry eye disease.

Types of Participants: Male or female participants of any age ≥18 with either subjective or objective diagnosis of dry eye were considered. Methods of diagnosis can be tear film break-up time (TFBUT) test, ocular surface staining, symptoms of ocular dryness, and/or Schirmer’s test.

Types of Intervention: Topical diquafosol administration as an ophthalmic solution of any vehicles, dose and regiments were included.

Types of Outcome: Clinical outcomes including symptom score, ocular surface staining score, TFBUT, Schirmer’s test, and adverse events.

Literature Search

The Cochrane highly sensitive search strategy was applied to MEDLINE (1966-2014), EMBASE (1980-2014), and Cochrane Central Register of Controlled Trials (CENTRAL, the Cochrane Library, Issue 9, 2014) database, with language restriction to English, Chinese, and French. The initial electronic database search was conducted on July 21st 2014, using the following terms to search all databases and registers: diquafosol; diquafosol tetrasodium; diquafosol sodium; P2Y2 agonist, P2Y2; dry eye; Sjögren syndrome; keratoconjunctivitis; keratoconjunctivitis sicca. The search strategy is available in the Appendix 2. Two authors (Wu, D; Chen, W) conducted the search independently. In addition, all references of included studies and those of published relevant reviews278, 289 wereare hand searched.

Study Selection

The study selection process was independently completed by two authors (Wu, D; Chen, W) independently. All titles and abstracts identified from the search strategy were scanned and reports that were apparently either notneither about diquafosol, norot randomized, nor desired they had no associated clinical outcomes were excluded. After an initial screening, Ffull texts of potentially eligible studies were obtained and verified inclusion using a prior constructed eligibility form. Disagreements were resolved by discussion.

Data Extraction

A data extraction sheet based on “Checklist of items to consider in data collection or data extraction” from Cochrane Handbook, pilot-tested it on 3 randomly selected included studies and refined accordingly.2930 The following data from included studies were extracted: risk of bias items, study design, characteristics of participants (total number, age, sex, diagnostic criteria, country), type of intervention (duration, regimen, concentration), and type of outcome measures (including outcomes listed in the eligibility of criteria, missing participants, and length of follow up). Any unclear or absence of information was confirmed with original investigators.

Risk of Bias in Individual Studies

Risk of Bias was assessed based on the ‘Risk of bias’ tool described in Handbook (Version 5.1.0).3031 To determine the validity of eligible randomized trials, an assessment of the adequacy of sequence randomization, concealment of allocation, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective outcome reporting and ‘other issues’ was completed. The bias was defined as high risk, low risk, or unclear provided by criteria defined in the Cochrane Handbook for evaluating risk of bias.

Summary Mmeasures

The primary outcome of this systematic review was the evaluation of the efficacy of topical diquafosol treatment on dry eye by tear function tests (Schirmer’s test and TFBUT test). Secondary outcomes of this study included: ocular surface staining score (fluorescein or Rose Bengal staining), subjective symptom score; and safety parameters (ocular and systemic adverse events).

Statistical analysis

All selected information was subjected to analysis by RevMan 5 (Review Manager Version 5.2, Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2012). A chi-squared test evaluated statistical heterogeneity between studies, with significant heterogeneity (P<0.05) ceasing meta-analysis

RESULT

Due to the presence of between-study heterogeneity induced by the variation of comparison, follow-up time points, and diquafosol concentrations for evaluating different outcome measures, it is inappropriate to report these outcomes in conjunction with meta-analysis. As an alternative, data yielded from included RCTs were subjected to descriptive analysis.

Study Selection

Of 375 potentially relevant citations identified from electronic databases (23 from MEDLINE, 89 from EMBASE, and 19 from CENTRAL), and hand searches (244 from all references of included studies and previous relevant reviews), 31 articles were retrieved for full-text review after adjusting for duplicates and titles and abstracts screening. A Selectively, a total of 8 RCTs were included in this systematic review.312-389 DThe details of the selection process are given in Figure1.

Study Characteristics

Table 1 shows the characteristics of the 8 included studies that dated from 2001 to 2014. All 8 studies (see Table 1) selected for the review were RCTs published in English. Seven of which were full text312-378 and one was conference abstract389. A total of four trials were performed in Japan,312,334,345,367 three in America,323,378,389 and one in Korea.356 Two studies were conducted following two trials each.334, 378 One study included a RCT and a non-RCT.334 Only the RCT was enrolled in this review. The other study comprising of with two trials evaluated the safety of diquafosol and its efficacy separately.378

Methods:

In all, there were five multicenter studies.32,33,35,37,39 Of the eight studies, four specified the washout period before the randomization with a mean washout period from previous treatments of 1.5±0.58 weeks. The mean follow-up time was 1.94±1.94 months.32,33,35,39 (Table 1)

Participants:

The included studies involved 1516 patients with dry eye. Mean age was 59.87 (range: 36.7 - 65.3) years old, and 73.0% were female (see Table 2). All studies included provided specified criteria of dry eye diagnosis. Four studies evaluated diquafosol efficacy in specific dry eye populations: one study included patients with short BUT type of dry eye (eyes with Schirmer values ≤ 5 mm were excluded),334, one study included patients with aqueous-tear deficient dry eye but not evaporative dry eye,356 one study included patients with dry eye refractory to sodium hyaluronate monotherapy,-37 and one study enrolled patients with mild-to-moderate dry eye.378 (see Table 2). In the remaining 4 studies, type or severity of DED of enrolled patients was not specified.

Intervention:

Of the 8 included studies, one study recruited 32 patients and tested topical diquafosol in 1 randomly selected eye, and the other eye was assigned as control.367 Three studies enrolled 286, 150 and 17 patients respectively, and only one eye from each patient was selected into study. 312,334,356 However, Nno explicit explanation relating to the selection of two eyes was documented. Two studies that recruited 286 and 158 patients remained unclear in the number of eyes included in trials.345,389 In the remaining 2 studies (three trials), 527 and 60 enrolled patients were grouped respectively and randomly to receive either topical diquafosol in both eyes, or placebo in both eyes.323,378

Different concentrations of diquafosol were evaluated in the 8 studies included in this systematic review with a range from 0.5% to 5%. Detailed information of regimen can be found in Table 1.

Outcomes:

All studies included in this systematic review evaluated efficacy of diquafosol ophthalmic solution primarily using Schirmer I test (without anesthesia, in 5 studies33,34,36-38), Shirmer II test (with anesthesia, in 1 study38), TFBUT (in 5 studies32,34-37), ocular surface staining (in 7 studies32-37,39), and symptom score (in 7 studies32-37,39). Five studies evaluated adverse events.32,33,35,37,38

Risk of Bias Within Studies

The outcome of ‘Risk of Bias’ assessment is summarized in Figure 2. In terms of selection bias, four of the eight RCTs specified the methods of random sequence generation.334-367 Two studies provided the method of allocation concealment.334,367 Regarding performance biases (blinding of participants and personnel), four of the eight included studies were double masked,312,323,345,378 and two were open-label study design,334,356 which were judged as high risk in both performance bias and detection bias. Among the eight included RCTs, six were judged as low risk of attrition bias because the dropouts patients’ number werewas reported clearly and the percentages werewas believed unlikely to affect the outcome.312-367 Six RCTs included in this systematic review were judged to be free from reporting bias, as all of the studies’ pre-specified outcomes were addressed in result.312,334-378 One However, one study didn’t report the result of TFBUT, which was addressed as an endpoint for efficacy assessment in methodologies.323 For the only one conference abstract enrolled in this review, there was no sufficient information to assess the risk of bias within study.

Outcome of Efficacy

Schirmer I/II Test

Schirmer’s test is a method of assessment indicative of volume tear fluid secretion. In the result of the included studies, two out of five studies showed significant improvement.323,356 (Table 3) Hwuang356 reported improvement in both monotherapy and in combination (diquafosol/ sodium hyaluronate) throughout a three months period from 1.12 to 3.27mm(/5min). Tauber323 reported of the subjects with intermediate or high tear volume in diquafosol (1%, 2%) treatment group was significantly higher than placebo group at six weeks. The other three studied showed no significant improvement compared with baseline values.334,367,378 No significant improvement reported from Schirmer II test assessed.378

TFBUT

TFBUT is indicative of tear film stability. Of the included studies, five assessed TFBUT.312, 334-367 All five studies reported improvement. Four out of five studies323-356 reported a significant improvement compared with baseline or control values (Table 3) with a range from 0.9-3.9s, and one study showed improvement but is not statistically significant312.

Ocular surface staining

Ocular surface staining was used to evaluate the integrity of the superficial cell layers of the ocular surface.3940 Sixeven of the included studies312,323,345-367,389 evaluated fluorescein corneal (FC) staining and four312,345-367 evaluated Rose Bengal (RB) corneal and conjunctival staining. FC staining results all reported statistically significant amelioration from -0.35 to -2.12. RB staining results all showed statistically significant improvement from -0.21 to -3.06.

Subjective ocular symptoms

All 8 studies included in this review evaluated subjective ocular symptoms, including one evaluated ocular surface disease index score (OSDI).356 A significant alleviation of at least one ocular symptom was reported by six studies.312-367 Diquafosol eye drop treatment showed significant improvement of dry eye sensation or ocular dryness in four out of five trials evaluating this symptom312, 334, 367, 378 and foreign body sensation in three out of six trials323, 367, 378. No However, no mitigation was observed in eye discharge (evaluated in 4 studies312, 334, 345, 367), ocular discomfort (evaluated in 3 studies312, 345, 367) and tearing (evaluated in 2 studies312,334).

Others

One trial assessed tear film stability by performing stability analysis system (TSAS) measurements with video-keratography.34 No significant improvement was observed following diquafosol treatment.

One trial evaluated goblet cell density and squamous metaplasia degree with performing conjunctival impression cytology, and showed significant improvement in both assessments after diquafosol treatment.36

Outcome of Safety

Of the 8 studies included, 5 of which evaluated the safety and adverse events of topical administration of diquafosol and reported no serious adverse events.312,323,345,367,378

DISCUSSION

The PRISMA statement, a more updated version of QUOROM statement, serves as a guideline in the development of a 27-item checklist and a four-phase flow diagram, which are essential for transparent reporting of a systematic review.26 The adoption of the PRISMA statement mitigates problems with incomplete or inadequate delivery of information such as missing reports and minimizing bias, thus maximizing the reliability of findings. Thise systematic review combines evidence and findings across studies to evaluate efficacy and safety of diquafosol with a more holistic view than permitted in a single study.

One consideration of this systematic review is the clinical safety of diquafosol. FromConsidering clinical safety of diquafosol, the evaluation, no demonstrated noion sof serious ocular or systemic adverse effect wasis found. Furthermore, the occurrence of adverse events does not increase with the increase of the concentration of diquafosol (0.5%-5%). Therefore, as a secretion stimulating treatment for dry eye, diquafosol, as a secretion stimulating treatment for dry eye, is clinically safe.

Another consideration, based on the result of clinical tests evaluated in the included RCT, is the efficacy of diquafosol. Ocular surface damage can be evaluated by vital staining, a hallmark of dry eye disease.401 From the included RCTs, a significant improvement wereas found in all studies that evaluated ocular surface staining. This result is congruent with evidence found in a rat dry eye model.24 In accordance with the pathology of dry eye and mechanism of diquafosol, the staining scores are indicative of either the improvement of aqueous tear production or mucin secretion. Aqueous tear production can be evaluated clinically using Schirmer’s test. The result from the included RCT is inconsistent and inconclusive of improvement in aqueous tear secretion. On the other hand, mucin production, evaluated by TFBUT, was reported to improve by the majority of the included studies (4/5). From these trends, one can see a possible correlation between the function of diquafosol and the improvement of mucine secretion as well as the mitigation of ocular surface damage, while however, aqueous tear production does not seem to have a strong association with diquafosol efficacy.

Even though there are discernable trends in the result, the evidence is not sufficiently robust to determine the efficacy of diquafosol primarily due to the high heterogeneous nature of participants, intervention, comparator, outcome and study design of the included studies. Firstly, tThe participants of the selected studies have high variability in patient selection criteria. For example, among the selected studies, some studies includes while other excludes patients with Sjögren syndrome. In another case, while most of the studies require Schirmer’s test value less than 5, one study only includes patients with short TFBUT and Schirmer’s test value greater than 5.334 Furthermoer, tThe interventions of the selected study have variation in dosage, combination of therapy (e.g. sodium hayaluronate + diquafosol), and concentration. The comparators of the selected studies also have a high variation including placebo, artificial tears and sodium hayaluronate. The outcomes of the studies have variation in time point, test, scales, and reporting formats. The study design has variability as well; some include double-mask, no blinding and washout/no washout period.

Aside from heterogeneity, among the RCTs evaluating topical diquafosol treatment in patients with dry eye, there remain several other concerns that do not allow us toinhibit us to formulate conclusions adopting an evidence-based approach to dry eye. First, the randomized trial did not evaluate a sufficient number of patients. The only 3 studies with a larger number of participants (286-527) are sponsored by pharmaceutical companies, of which only one study includes patients over 300 participants. Furthermore, among the included study, only two designed a follow up period of more than 3 months. In the report of the International Dry Eye Workshop (2007), the Diagnostic Methodology Subcommittee regarded dry eye as a chronic, symptomatic ocular surface disease.412 Therefore, it is logical to assume that a longer follow-up period is necessaryneeded. In addition, the follow up period of most study end as intervention period ends. Only two studies extended the follow-up one week after the conclusion of the intervention period, one of which states that “…After discontinuation of study medication, corneal staining scores in the diquafosol groups, but not the placebo group, worsened slightly and were no longer significantly different when compared with placebo”.33 Indicating further concern with the design of the selected studies. Moreover, the limited ethnicities of the selected studies (Japan & United States) may compromise the understanding of the various response to drug therapy by different race and ethnicity. The several issues previously discussed prevent us from effectively implementing a statistical approach.

This systematic review has several limitations on a study and review level including the quality of the studies varied. Concerning randomization, limitations include inability to limitations include unable to assess the quality of the selected studies due to unclear reports ofting of the randomization method. Regarding the review process, no unpublished data was selected and the language of the searched studies was restricted to English, Chinese, and French.

In summary, the safety of diquafosol is established based on the included study. Although there is a possible correlation between diquafosol and mucin secretion and between diquafosol and surface damage assuagement, the high heterogeneity of the selected study affects the strength of the findings leading to limitationlimits thein determination ofing the efficacy of diquafosol on dry eye. For future trials, this review indicates a need for a neutral organization to perform a multi-centered, large sample sized, long term evaluation of the efficacy of diquafosol. Some aspects to consider for future trials include concentration of diquafosol [varied] and the duration of efficacy of diquafosol post treatment. Further suggestions include a standardized comparator in evaluation of any particular drug for dry eye.

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Figure 1. Flow diagram of systematic process for report identification.

Figure 2. Risk of bias summary in included studies. Green (+) = low risk; Red (-) = high risk; Yellow (?) = unclear.

Supplemental Digital Content：

Appendix 1: Protocol of the present systematic review

Appendix 2: Search Strategy

1