Citation: Lekhanont K, Sathianvichitr K, Pisitpayat P,
Anothaisintawee T, Soontrapa K, Udomsubpayakul U. Association between the
levels of prostaglandin E
·Clinical Research·
Association
between the levels of prostaglandin E
Kaevalin Lekhanont1, Kanchalika Sathianvichitr1, Punyanuch Pisitpayat1, Thunyarat Anothaisintawee2, Kitipong Soontrapa3, Umaporn Udomsubpayakul4
1Department of Ophthalmology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand
2Department of Family Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand
3Department of Pharmacology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10400, Thailand
4Clinical Epidemiology and Biostatistics Unit, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand
Correspondence to: Kaevalin Lekhanont. Department of Ophthalmology, Ramathibodi Hospital, Mahidol University, Rama VI Rd., Rajathevi, Bangkok 10400, Thailand. lekhanont@yahoo.com
Received:
Abstract
AIM: To investigate the relationship between the levels of prostaglandin E2 (PGE2) in tears and dry eye disease severity based on both clinical symptoms and signs.
METHODS: Tear samples were collected from 36 non-Sjögren
syndrome dry eye patients (10 males and 26 females, mean age 50.11±11.17y). All
participants completed the Ocular Surface Disease Index (OSDI) questionnaire
and underwent a detailed ophthalmic examination including, tear film breakup
time (TBUT), ocular surface fluorescein staining, Schirmer I test, and
meibomian gland assessment. The level of PGE
RESULTS: The mean PGE2 level in tears of dry eye patients was 537.85±234.02 pg/mL. The tear PGE2 levels significantly positively correlated with OSDI scores (R=0.608, P<0.001), however, they did not significantly associate with TBUT (R=0.153, P=0.373), Schirmer scores (R=-0.098, P=0.570), ocular surface staining scores (R=0.282, P=0.095), and stage of MGD (R=-0.107, P=0.535). Male sex was significantly negatively correlated with tear PGE2 levels.
CONCLUSION: The levels of PGE
KEYWORDS: dry eye; prostaglandin E2; severity; tear; dry eye tests
DOI:10.18240/ijo.2019.07.12
Citation: Lekhanont
K, Sathianvichitr K, Pisitpayat P, Anothaisintawee T, Soontrapa K,
Udomsubpayakul U. Association between the levels of prostaglandin E
INTRODUCTION
Dry eye is a multifactorial disease of the ocular surface, characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles[1]. Although dry eye is thought of as a symptomatic disease, asymptomatic form with visible ocular surface staining, early tear film breakup time (TBUT), and even tear hyperosmolarity still exists[2]. Also, a poor correlation between the symptoms of dry eye and objectively recorded sign is often clinically observed. The reason for the mismatch between symptoms and signs of dry eye may be that there are multiple factors contributing to dry eye pain, such as tear hyperosmolarity, loss of lubrication, inflammatory mediators, and change in ocular surface sensation[3].
Prostaglandins (PGs) are one of well-known inflammatory mediators, playing a key role in the generation of the inflammatory response. They are lipid autacoids derived from arachidonic acid by the action of cyclooxygenase (COX) isoenzymes[4]. Stimulation of the ocular surface by tear hyperosmolarity might lead to the release of PGs in addition to other various cytokines and chemokines[5, 6]. These PGs themselves also have algaesic properties and may stimulate sensory nerve ending[4].
There are 4
principal bioactive PGs generated in vivo, including prostaglandin E2
(PGE2), prostacyclin (PGI2), prostaglandin D2 (PGD2) and prostaglandin F2α
(PGF2α)[4]. PGE2 is of particular interest because
it is involved in all processes of inflammation and the action of PGE2 on
peripheral sensory neurons and on central sites within the spinal cord and the
brain can result in pain[4, 7].
However, the role of PGE
Nonetheless,
the relationship between the level of PGE
SUBJECTS AND METHODS
Ethical Approval Institutional Review Board/Ethics Committee approval was obtained from the Mahidol University School of Medicine and all procedures conformed to the tenets of the Declaration of Helsinki. All participants were informed about the aim and protocol of the study and gave written informed consent prior to undergo the procedures.
Study
Design This was a cross-sectional pilot study
analyzing the level of PGE
Participants A total of 36 patients from dry eye clinic who have been diagnosed with dry eye disease were recruited into this study. The inclusion criteria were as follows: patients aged 18 years or over, documented history of dry eye disease for at least 3mo, having at least one or more of the dry eye symptoms often or all the time (dryness, foreign body sensation, burning, ocular discomfort, heaviness of the eyelids, photophobia or ocular fatigue), and fluorescein TBUT≤10s. Patients were excluded if: 1) They had a history of other coexisting ocular surface diseases except for meibomian gland dysfunction (MGD), ocular surgery or trauma within the past 3mo; 2) They were being treated with any eye drops or systemic medications in the group of ω-3 supplement, non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, immunomodulators, and antibiotics within the past 3mo; 3) They had been using any systemic medications which might affect tear film and meibomian gland function, including isotretinoin, antiandrogens, antidepressants, diuretics, anti-hypertension drugs, antihistamines, contraceptives, postmenopausal hormone therapy, and chemotherapy within the past 3mo; 4) They had diabetes mellitus; 5) They had a history of intensive and prolonged use of digital devices; 6) They had a history of contact lens wear within the past 3mo; 7) They had an abnormality of the nasolacrimal drainage apparatus or permanent or temporary occlusion of lacrimal puncta in any eye; and 8) They were pregnant or lactating women.
Interventions At baseline, the Ocular Surface Disease Index (OSDI) questionnaire (Allergan Inc., Irvine, CA, USA) was administrated by a single trained interviewer to assess symptom severity scores. This questionnaire comprises 12 questions and evaluates the frequency of symptoms over the preceding week. Each question is graded from 0 (“none of the time”) to 4 (“all of the time”). The total score, ranging from 0 to 100, is calculated based on the following formula: OSDI=(sum of scores for all questions answered ×100)/(total number of questions answered ×4). Higher scores represent greater ocular surface disease. The patients’ symptoms were categorized as normal (0-12), mild dry eye (13-22), moderate dry eye (23-32), or severe dry eye (33-100)[9].
A detailed examination of parameters of dry eye was performed sequentially at the same visit by another examiner as follows: slit-lamp examination, TBUT measurement, corneal and conjunctival fluorescein staining, Schirmer I test without anesthesia, and meibomian gland assessment[10].
TBUT was evaluated by introducing a fluorescein strip moistened with 1 drop of non-preserved normal saline into the inferior conjunctival fornix with minimal stimulation. The quantity of saline was also controlled by carefully shaking the fluorescein strip to remove excess fluid. The patient was asked to blink several times and then hold the eye open. The cornea was scanned with a slit-lamp using cobalt blue illumination. Time from the last complete blink to the first appearance of a random dry spot on the cornea was recorded in seconds. The test was repeated 3 times in each eye, and the mean time for 3 consecutive measurements was obtained. The test was considered positive if the average TBUT was less than 10s.
For corneal and conjunctival fluorescein staining, presence of any fluorescein staining of the ocular surface was recorded and graded using the Oxford scheme 6-point scale (from 0 through 5).
The Schirmer I test without
anesthesia was then performed. A standard 5×35-mm2 strip of dry
filter paper was placed in each lower fornix at the junction of the lateral and
middle thirds, taking care to avoid touching the cornea, and left in place for
5min. After 5min, the strips were removed, and the amount of wetting in
millimeters was recorded. The test results were considered positive if the
length of wetting obtained was less than
Lid margin abnormalities were
graded from 0 to 4 according to the number of these abnormalities present in each
eye: plugged meibomian gland orifices, vascular engorgement, posterior
displacement of the orifices, and irregularity of the lid margin. To assess an
obstruction of meibomian gland orifices, firm digital pressure was applied to
the lower tarsus. Meibum quality was evaluated in each of 8 glands of the
central third of the lower lid on a scale of 0 to 3 for each gland: 0, clear;
1, cloudy; 2, cloudy with debris (granular); and 3, thick, like toothpaste
(total score range, 0 to 24). Expressibility was assessed on a scale of 0 to
Tear
sampling was done on the next day to ensure that the previous diagnostic tests
would not disrupt tear film quality and quantity and result in false-positive
PGE2 elevation. Patients were instructed to lie down in a supine position and
tilt their heads to the same side of the eye in which tear was being collected.
Unstimulated tear samples were gathered from the inferior tear meniscus, using
a glass microcapillary tube (10 µL Microcaps®, Drummond Scientific,
Broomall, PA, USA). The microcapillary tube was placed gently at the lateral
canthus, taking care not to irritate the conjunctiva, cornea, or lid margin, to
avoid additional tear reflex as much as possible. Patients were allowed to
blink naturally. Up to 10 µL of tear samples was collected from each eye at the
same time of the day. The tear samples were immediately transported in an
insulated cooler at
Tear concentrations of PGE2 were measured by another examiner using a monoclonal enzyme-linked immunosorbent assay (ELISA) kit (Cayman Chemical, Ann Arbor, MI, USA) according to the manufacturer’s instructions. This PGE2 ELISA kit is a competitive assay that can be used for quantification of PGE2 and has a range from 7.8-1000 pg/mL and a sensitivity of approximately 15 pg/mL. Each kit contains PGE2 standard, PGE2 monoclonal antibody, AChE tracer, Ellman’s reagent, and a goat anti-mouse IgG coated 96-well plate. The diluted tear samples (50 µL) was placed in a 96-well plate in triplicates and 200 µL Ellman’s reagent was added to each well for 90min and the absorbance at 414 nm was recorded with a microplate reader (Molecular Devices, Sunnyvale, CA, USA). All measurements and interviews were conducted in a double-masked fashion by separate observers. Adverse reactions and complications were recorded.
Statistical
Analysis Statistical analyses were performed
with the statistical software package STATA version 14 (Stata Corp, College
Station, TX, USA). The data from the worse eye which was defined as having
lower TBUT value of each patient were used for analysis. If the TBUT values in
both eyes were equal, the scores of ocular surface fluorescein staining, MGD,
and Schirmer I test were used to define the worse eye. For continuous data,
normally distributed variables were presented as mean and standard deviation
(SD); non-normally distributed variables were presented as median and range.
Frequency and percentage were used for categorical data. Linear regression
analysis were applied to assess the independent association between tear PGE2
levels and other variables including demographics, dry eye symptom severity
scores (OSDI scores), TBUT, Schirmer I test, corneal staining score, and MGD
stage. Variables with P<
RESULTS
A total of 36 symptomatic dry eye patients were recruited and completed the study. There were 26 women (72.2%) and 10 men (27.8%). The mean age was 50.11±11.17y (51.70y for females and 45.18y for males; range, 27-72y). The average OSDI score, TBUT, ocular surface staining Oxford scale, Schirmer I score, and MGD stage based on the TFOS workshop on MGD[11] are shown in Table 1.
Table 1 Clinical information of 36 dry eye patients
Dry eye characteristic |
Mean±SD (median, range) |
Dry eye symptoms (OSDI score) |
23.51±8.94 (12.5-41.7) |
Fluorescein TBUT (s) |
6.66±1.61 (4-10) |
Ocular surface staining Oxford scale |
0.56±1.27 (0, 0-5) |
Schirmer I score without anesthesia (mm) |
8.11±3.56 (8, 2-16) |
Stage of MGD based on the TFOS workshop on MGD[10] |
0.94±1.09 (1, 0-4) |
Tear PGE2 level (pg/mL) |
537.85±234.02 (533.78, 149.68-972.56) |
OSDI: Ocular surface disease index; TBUT: Tear film breakup time; MGD: Meibomian gland dysfunction; TFOS: Tear Film and Ocular Surface Society; PGE2: Prostaglandin E2.
Based on scores generated by the OSDI questionnaire, 19 of the 36 patients (48.7%) reported mild dry eye symptoms, 12 (30.8%) reported moderate dry eye symptoms, and 8 (20.5%) reported severe dry eye symptoms. Thirty-four patients (94.4%) had symptoms plus at least 1 positive dry eye tests. Only 2 patients had only dry eye symptoms without positive dry eye tests. MGD of any severity was recorded in 23 patients (63.9%). Because all patients included into this study must have had at least one or more of the dry eye symptoms often or all the time, there was no asymptomatic or nonobvious MGD identified in our study. None of our patients had rheumatic disorders.
The mean tear PGE2 level was 537.85±234.02 pg/mL. The PGE2 levels in tears of dry eye patients significantly correlated with OSDI scores (R=0.608, P<0.001), as shown in Figure 1.
Figure 1 Correlation between tear PGE2 levels and the OSDI score.
There was
also a significant association between the OSDI category (mild, moderate,
severe) and the concentrations of PGE
Figure 2 Correlation between tear PGE2 levels and other dry eye clinical signs including ocular surface fluorescein staining score (Oxford scheme) (A), MGD stage (B), Schirmer I test without anesthesia (C), and fluorescein TBUT (D).
Univariate
analysis demonstrated a significant positive relationship between OSDI scores
and levels of PGE
Table 2 Univariate analysis of
the association between patient variables and levels of PGE
Variables |
PGE2 |
|||
Data coefficients |
95%CI |
t |
P |
|
Age |
-5.71 |
-12.74-1.31 |
-1.65 |
0.108 |
Male sex |
-155.87 |
-327.01-15.27 |
-1.85 |
0.073 |
OSDI scores |
15.91 |
8.66-23.15 |
4.46 |
0.000 |
OSDI category |
||||
Moderate symptoms |
174.02 |
15.47-332.57 |
2.23 |
0.032 |
Severe symptoms |
328.13 |
148.70-507.56 |
3.72 |
0.001 |
TBUT |
22.33 |
-27.89-72.55 |
0.90 |
0.373 |
Ocular surface fluorescein staining |
51.82 |
-9.55-113.20 |
1.72 |
0.095 |
Schirmer I scores |
-6.44 |
-29.24-16.36 |
-0.57 |
0.570 |
MGD stage |
-22.87 |
-97.00-51.26 |
-0.63 |
0.535 |
PGE2: Prostaglandin E2; OSDI: Ocular surface disease index; TBUT: Tear film breakup time; MGD: Meibomian gland dysfunction.
Table 3 Multivariate analysis of the association between
patient variables and levels of PGE
Variables |
PGE2 |
|||
Data coefficients |
95%CI |
t |
P |
|
OSDI scores |
14.20 |
7.17-21.23 |
4.11 |
0.000 |
Male sex |
-145.34 |
-281.81 to -8.87 |
-2.17 |
0.038 |
Ocular surface fluorescein staining |
37.90 |
-11.58-87.38 |
1.56 |
0.129 |
PGE2: Prostaglandin E2; OSDI: Ocular surface disease index.
DISCUSSION
Dry eye can
have a variety of symptoms such as irritation, blurred vision, and ocular pain
including dryness, burning, and foreign body sensation, as well as photophobia.
Within dry eye-related symptoms, some patients report recurring episodes of
transient pain whereas others complain of chronic pain. Besides hyperosmolar
tears itself, PGE2, the subtype of PGs, is recognized to be the principal
pro-inflammatory mediator and contributes to pain hypersensitivity by
modulating multiple sites in the nociceptive pathways, including peripheral and
central sensitization[7]. Furthermore, metabolites
of PGE2 may activate nociceptive neurons independent of PG receptors[14]. Clinically, the PGE2 level in the tears of dry eye
patients was higher than in that in the control group[8].
These clinical results were also supported by increased COX-2 and PGE synthase
expression levels seen in tear-producing tissue of dry eye mice[8]. In addition, topical COX-2 inhibitor reduced
inflammatory cells on the ocular surface, suggesting the role of COX-2/PGE2
axis in the pathogenesis of dry eye[6]. Topical
NSAIDs has also been observed to improve corneal fluorescein staining in a dry
eye mouse model[15]. However, the association
between the concentrations of PGE
Our study demonstrated that the increased tear PGE2 levels in non-Sjögren dry eye patients positively correlated with only their OSDI scores but not other clinical dry eye parameters including TBUT, Schirmer score, ocular surface staining score, and MGD stage. A previous study by Shim et al[8] showed that although tear PGE2 levels were elevated significantly in dry eye patients, the PGE2 concentrations alone did not associate with dry eye symptom scores. However, a reciprocal change in PGE2 and PGD2 levels correlated well with patients’ symptom scores. In another study by Walter et al[5], there was no correlation between dry eye symptoms and tear PGE2 levels. Additionally, tear PGE2 levels were not correlated with corneal sensation, TBUT, Schirmer score, meibomian gland atrophy, and meibum quality. Nonetheless, higher levels of PGE2 were associated with lower tear osmolarity, more meibomian gland plugging, and more corneal staining.
Differences
in outcomes between our study and the previous studies may be due to the
disparities in baseline characteristics of patient populations, dry eye
questionnaires, and tests used. Shim et al[8] included non-Sjögren dry eye patients similar to our study but their
patients appeared to be slightly older (mean age=57y) and had more severe dry
eye based on their eligible criteria of having all abnormal symptoms and signs.
Visual analog scale (VAS; 0
Interestingly,
our study revealed that male sex was negatively correlated with levels of PGE
Our findings
suggest that PGE2 may involve in pathogenesis of dry eye symptoms. Although the
role of PGE
Limitations of this study are no control group, a predominantly female population, small sample size, insufficient representation of the moderate to severe groups of dry eye, and no measurement of corneal sensation or other tear cytokines and chemokines. Future case-control studies enrolling more participants with representation in the greater disease severity range are needed to investigate the effects of PGs on dry eye symptoms. Measuring blood PGE2 levels synchronized with tear PGE2 levels will be more useful. The clinical role of PGE2 inhibition in improving dry eye symptoms should also be assessed. Additionally, other substances that may cause ocular irritation such as bradykinin or substance P should be evaluated for their relationship to dry eye. This might lead to the development of new and more effective treatments for this prevalent disease.
In summary, the
concentrations of PGE
ACKNOWLEDGEMENTS
This manuscript has been presented as a poster at the 8th Tear Film and Ocular Surface Society (TFOS) Conference in Montpellier, France (September 7-10, 2016).
Authors’ contributions: Design of the study (Lekhanont K, Sathianvichitr K); Conduct of the study (Lekhanont K, Sathianvichitr K, Pisitpayat P), collection (Lekhanont K, Sathianvichitr K, Pisitpayat P, Soontrapa K); management (Lekhanont K, Anothaisintawee T); analysis (Lekhanont K, Anothaisintawee T, Udomsubpayakul U); and interpretation of the data (Lekhanont K, Anothaisintawee T); and preparation, review, or approval of the manuscript (Lekhanont K, Sathianvichitr K, Pisitpayat P, Anothaisintawee T, Soontrapa K, Udomsubpayakul U).
Foundation: Supported by a Research Grant from
the Faculty of Medicine, Ramathibodi Hospital, Mahidol University and the SCG
Foundation.
Conflicts of Interest: Lekhanont K, None; Sathianvichitr K, None; Pisitpayat P, None; Anothaisintawee T, None; Soontrapa K, None; Udomsubpayakul U, None.
REFERENCES