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Carla Siegfried, Ying-Bo Shui, Fang Bai, David Beebe; Evaluation of the antioxidant status of human aqueous humor. Invest. Ophthalmol. Vis. Sci. 2013;54(15):758.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies suggest that oxidative stress plays a role in glaucoma development, yet there is a gap in understanding the components of antioxidant protection in the eye. To explore these factors in disease states such as glaucoma and cataract, as well as after vitrectomy surgery, which increases the risk of glaucoma (Koreen, et al. Retina 2012), we measured the contribution of ascorbic acid (AsA) to the Total Reactive Antioxidant Potential (TRAP) of the aqueous humor in patients undergoing intraocular surgery.
Consenting patients undergoing cataract and/or glaucoma surgery were included. An Oxylab pO2TM optical oxygen sensor (Oxford Optronix) was used to measure pO2 in the anterior chamber (AC) angle, mid-AC, and near the corneal endothelium. In pseudophakes and eyes undergoing lens extraction, pO2 was measured in the posterior chamber and near the anterior lens surface. Aqueous humor samples (n=40) were collected and stored in the gas phase of a liquid nitrogen tank. AsA assay (colorimetric in triplicate) and TRAP assays (chemiluminescence) were performed as previously described. Ascorbate oxidase added to each sample revealed the antioxidant potential not attributable to AsA.
Antioxidant potential contributed by AsA accounted for 40-83% (mean=65%) of TRAP. In post-vitrectomy eyes, the AsA level in aqueous humor was significantly lower (p=0.002) and the contribution of AsA to TRAP was also decreased (p=0.007). The contribution of AsA to TRAP was decreased in females (p=0.017) with a similar trend in African vs. European Americans (p=0.065). Multivariate regression analyses will be performed after pending analysis of an additional 40 samples. Since all patients had cataract and/or glaucoma, TRAP or AsA levels did not correlate with the presence of these diseases, or with oxygen levels at any location in the eye.
AsA accounts for a significant component of TRAP in human aqueous humor. Prior vitrectomy surgery, a risk factor for the development of nuclear cataracts and open angle glaucoma, is associated with significantly lower AsA and TRAP values. Depletion of these antioxidants in at-risk subjects (females and African Americans) provides further support for the importance of antioxidant protection in cataract and glaucoma.
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