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Mitchell A. Watsky, Yan-ping Lin, John L. Ubels, Zhaohong Yin, Bruce D. Hammock; Vitamin D In Tear, Aqueous And Vitreous Humor, And Production By Corneal Epithelium. Invest. Ophthalmol. Vis. Sci. 2011;52(14):318.
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The purpose of this study was to measure vitamin D metabolite concentrations in the aqueous and vitreous compartments of the eye and in tear. Because in addition to skin the eye is the only major organ exposed to sunlight, we also determined if the corneal epithelium can synthesize vitamin D following UV-B exposure.
Assessment of vitamin D metabolites was performed using a UPLC-MS/MS method developed in the Hammock lab utilizing the Diels-Alder reaction. Vitamin D2 and D3 forms were distinguished by different transitions in UPLC-MS/MS detection. A benefit of the Diels-Alder reaction is a detection limit for most vitamin D metabolites of 25 pg/ml. For tear measurements, pilocarpine-stimulated tear fluid was collected from New Zealand white rabbits. For intraocular measurements, rabbits were killed and eyes were enucleated. Aqueous humor was drawn from the anterior chamber and the anterior segment was dissected from the globe to collect vitreous humor. Plasma vitamin D was also measured. To test for epithelial vitamin D synthesis, a human corneal epithelial cell line was irradiated with two doses of UV-B (10 and 20mJ/cm2/day for three days)and vitamin D was measured in control or 7-dehydrocholesterol spiked culture medium.
Both 25(OH)D3 and 1,25(OH)2D3 were found in tear, and D2 and D3 metabolites were found in measurable quantities in aqueous and vitreous humor. No unhydroxylated D3 (pre-vitamin D) was found in aqueous or vitreous humor. Aqueous and vitreous 1,25(OH)2D3 levels most closely matched plasma levels. Both pre-vitamin D and 25(OH)D3 were found in the culture medium of UV-B irradiated epithelial cells. The presence of 7-dehydrocholesterol in the medium resulted in significantly increased vitamin D metabolite levels.
There are significant concentrations of vitamin D metabolites in tear fluid and aqueous and vitreous humor. In addition, the corneal epithelium is capable of synthesizing 25(OH)D3 following UV-B exposure.
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