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K.G. Howell, A.M. Vrabel, D.H. Johnson, M.P. Fautsch; Myocilin Levels Are Elevated in the Aqueous of Patients With POAG . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1847.
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To determine the levels of myocilin in the aqueous humor of normal and glaucomatous eyes. Laboratory studies suggest excess myocilin can raise intraocular pressure.
Aqueous humor samples were collected at the start of surgery from patients undergoing cataract or glaucoma surgery. Cataract patients had no other ocular disease and were considered "normal", glaucoma cases had either primary open angle glaucoma (POAG) or pseudoexfoliative glaucoma (PEX–GL) and were on topical medications. Protein concentrations were determined by Bradford protein assay. Equal volumes of aqueous (25 µl) and human recombinant myocilin protein standards (0, 5, 15, and 30 ng) were separated on 4–15% gradient SDS–PAGE gels and transferred to polyvinylidene diflouride membrane. Myocilin protein was detected with an antibody specific to the N–terminus (amino acids 108–131). Using Image J densitometry software, myocilin concentrations in the surgical samples were determined following comparison to standards. Kruskal–Wallis and pair–wise Wilcoxon test with Bonferroni corrections were performed.
The mean myocilin level in normal aqueous humor was 0.26 ± 0.18 ng/µl (range: 0 to 0.64 ng/µl; n=26). No difference was found by gender. Myocilin levels were higher in POAG (0.63 ± 0.50 ng/µl; range: 0 to 2.19 ng/ul; n=28; p=0.009). Levels were also higher in PEX–GL (0.54 ± 0.29 ng/µl; range: 0.05 to 1.11 ng/µl; n=19; p=0.006). Aqueous humor total protein levels were higher in PEX–GL than normal or POAG (316 ± 114 ng/µl vs 231 ± 91, p=0.030; POAG: 231 ± 76; p=0.027). The amount of myocilin in proportion to the total protein concentration was higher in POAG than normal (0.27% ± 0.19% vs 0.13% ± 0.09%, p=0.012) while in PEX–GL, the value was between the others (0.19% ± 0.13%, p=0.18). The three groups were of similar age, with a mean of 74 years in each.
Myocilin levels in human aqueous humor were elevated in POAG and PEX samples when compared to normal.
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