Abstract
Purpose :
Vitamin D is an important biological hormone with known anti-inflammatory function, but relatively little is known about vitamin D’s function and availability at the ocular surface. Dry eye disease (DED) is a common multifactorial disease that has a significant inflammatory component. This study evaluates vitamin D metabolite levels in the human tear film and the expression of vitamin D-related genes at the ocular surface during DED.
Methods :
A 500 µl pooled tear sample (n=30 subjects) was collected by microcapillary tube and analyzed by mass spectrometry (LC/MS/MS) for vitamin D metabolite levels. To evaluate vitamin D ocular surface gene expression, 10 normal and 11 DED subjects (age- and sex-matched) were recruited. Following assessment of DED clinical signs Schirmer’s test, corneal and conjunctival staining, TBUT, and meibography and symptoms (OSDI and VAS dryness and comfort questionnaires), conjunctival impression cytology (CIC) samples were collected from each eye using the EyePrim device. RNA was collected and analyzed by qPCR for vitamin D receptor (VDR) and hydroxylase (CYP27B1, CYP24A1) relative expression. Blood samples were also collected from each subject by blood spot card for evaluation of circulating vitamin D levels (ZRT Labs).
Results :
Vitamin D metabolites were identified in human tear samples by LC/MS/MS analysis [1,25D3 (3.5 pmol/L), 25D3 (23.5 pmol/L), 25D2 (11.5 pmol/L), and 24,25D3 (35.5pmol/L)]. In CIC samples, VDR expression was significantly decreased in DED subjects (4.8 ± 0.4) compared to normal subjects (7.3 ± 0.8 ΔCt value). CYP27B1 expression was also decreased in DED subjects (p<0.05); however, there was no change in CYP24A1 expression between the two groups. There was a positive correlation between CYP27B1 and VDR mRNA expression (r=0.63, p< 0.001). For circulating vitamin D analysis (25D3), no significant difference was found between normal and DED subjects.
Conclusions :
This is the first study that demonstrates vitamin D metabolites in human tears, providing a source of vitamin D to the ocular surface. In addition, based on the clinical study results, vitamin D-related gene expression is lower in dry eye subjects, suggesting that vitamin D activity could be important in protecting the ocular surface from dry eye inflammation. Interestingly, these changes were localized to the ocular surface and were not impacted by hormone levels in the blood.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.