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Marta Sacchetti, Vincenzo Scorcia, Flavio Mantelli, Augusto Pocobelli, Alessandro Lambiase, Stefano Bonini; Neuropeptide levels in normal cornea and in keratoconus.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1020. doi: https://doi.org/.
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Neuropeptides released by corneal sensory nerve endings and epithelial cells play a key role in maintaining ocular surface homeostasis. Nevertheless, their levels in normal and pathologic corneas have not yet been assessed. In this study we aimed to investigate the levels of the major neuropeptides in normal cornea and in keratoconus.
Six normal cadaveric (3 M, 3 F, 56±8 years) corneas were obtained from the Rome Eye Bank, 12 corneas with keratoconus (6 M, 6 F, 45±15 years) and 4 with leukoma (2 M, 2 F, 52±11 years) were obtained at the time of keratoplasty. Corneas were mechanically dissected and neuropeptides were extracted using the water/acetic acid protocol. Tissue concentration of Substance-P (SP), Calcitonine gene related peptide (CGRP), and Vasointestinal peptide (VIP) was assessed by ELISA following the manufacturer instructions. Data are expressed as pg/mg of protein, and presented as mean±SD. Statistical analysis was done by T-test with a p value <0.05 considered significant.
SP, CGRP and VIP were all detected in both normal and pathologic cornea. Corneas with keratoconus showed significantly higher CGRP (228±128 vs 113±25 pg/mg, p=0.031) and VIP (12.4±6 vs 6.8±2.1 pg/mg, p=0.019) levels as compared to controls. A similar difference in neuropetide levels was evidenced when comparing keratoconous to leukoma, although it did not reach statistical significance. No changes in VIP and CGRP content were observed in corneas with leukoma when compared to controls. A high variability in SP values was detected in all the samples evaluated leading to no significant differences between groups.
This study is one of the first to quantify SP, CGRP and VIP in the human cornea, and to indicate a possible correlation with pathological conditions. Alterations in the local levels of VIP and CGRP in keratoconous, but not in corneas with a leukoma, may reflect an alteration of corneal innervation and trophism and could represent an additional pathogenic mechanism involved in keratoconous progression.
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