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DE Brooks, FJ Ollivier, GS Schultz, TD Blalock, SE Andrew, AM Komaromy, TJ Cutler, ME Lassaline, ME Kallberg, G Van Setten; Connective Tissue Growth Factor (CTGF) In Horse Tear Film . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4205.
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Purpose: Healing of corneal ulcers in horses is often associated with profound fibrosis and scar formation that can result in varying degrees of visual impairment. Connective tissue growth factor (CTGF) is a fibrogenic cytokine involved in corneal wound healing. Transforming growth factor ß activates keratocytes to produce CTGF. CTGF enhances fibroblasts to proliferate and produce more collagen and its overexpression has been proposed to play an important role in pathways that lead to fibrosis. The purpose of this study was to determine if CTGF was present in the tear fluid of normal horse eyes and the eyes of horses with corneal ulcers in order to evaluate the role of CTGF in corneal wound healing and corneal scar formation in horses. Methods: Samples of tear fluid (10µL) were obtained with glass capillary tube from 44 horses (n=65 eyes) after a light sedation. Sampling was done from normal eyes (n=32), eyes with a corneal ulceration (n=21), and the unaffected contralateral eyes of horses with ulcers (n=12). CTGF levels in the tears were determined by enzyme immunoassay (ELISA). Results: CTGF was detected in 23 normal unaffected eyes (72%) and 8 normal contralateral eyes (67%), with the mean CTGF levels (± SD) being 51.5 ± 108.8 and 13.4 ± 13.6 ng/ml respectively. CTGF was found in 8 of the 21 eyes with corneal ulcers (38%) with the mean CTGF level (± SD) being 26.3 ± 67.8 ng/ml. Conclusion: This study demonstrates, for the first time, the presence of CTGF in the horse tear film, antigenic similarity between human and equine CTGF, and the feasibility of measuring CTGF protein in horse tears using the human CTGF ELISA. CTGF was present at detectable levels in approximately 70% of the tears from normal horse eyes, and at a lower level (50 ng/ml vs 13 ng/ml) in approximately 70% of the normal, contralateral eyes of horses with corneal ulcers. CTGF was detectable in about 40% of tears from ulcerated horse eyes at a level of about 25 ng/ml. The reduced level of CTGF in tears from ulcerated eyes and in contralateral non-ulcerated eyes may be due to dilution from increased tear volume, the absence of CTGF at specific stages of the healing period, and/or the exhaustion of CTGF synthesis by lacrimal gland cells. It will be important to evaluate CTGF levels at various stages of the healing process of corneal ulcers (early and late) in horses, and to correlate CTGF levels to the degree of corneal scarring in order to thoroughly understand the role of CTGF in corneal fibrosis in horses.
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