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Diabetic and non-diabetic human cornea and tear γ-glutamyl transpeptidase activity

Authors Burnham J, Sakhalkar M, Langford M, Liang C, Redens T, Jain S

Received 31 August 2012

Accepted for publication 23 October 2012

Published 10 January 2013 Volume 2013:7 Pages 99—107

DOI https://doi.org/10.2147/OPTH.S37546

Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 2

Jordan M Burnham,1 Monali Sakhalkar,1 Marlyn P Langford,1 Chanping Liang,1 Thomas B Redens,1 Sushil K Jain2

1Department of Ophthalmology, 2Department of Pediatrics, Louisiana State University Health Sciences Center, Shreveport, LA, USA

Background: Diabetes-related eye disease is due in part to oxidative stress. Gamma-glutamyl transpeptidase (GGT) is a γ-glutamyl cycle enzyme that protects against oxidative stress via glutathione recapture. This study investigates corneal and Schirmer tears GGT activity in diabetic and non-diabetic adults aged 50 to 83 years old.
Methods: GGT activity was determined by colorimetric assay on 50 corneas from 14 diabetic (without keratopathy) and 20 non-diabetic donors and on Schirmer type 1 test strips (no anesthesia) of 14 diabetic and 14 non-diabetic subjects.
Results: Type 1 (T1) diabetic cornea GGT activity was 40% lower than Type 2 (T2) diabetic cornea GGT activity (P = 0.04), but GGT activity was similar for corneas (without keratopathy) from diabetic and non-diabetic donors (P ≥ 0.44 for all). The number of endothelial cells/unit of GGT activity in diabetic corneas was 22% higher (P = 0.1) than in non-diabetic corneas. GGT activity per Schirmer strip and GGT activity per mm of tears were 36% and 50% higher (P ≤ 0.008 for all) for non-diabetic (tear volume dependent) than diabetic donors (tear volume independent), respectively. GGT activity per mm was 50% lower in T1 than T2 diabetics (P = 0.02). Higher tear GGT activity in non-diabetic than diabetic females (P ≤ 0.05) was due to higher GGT activity in the African American females.
Conclusion: GGT activity was less in T1 than T2 diabetics, but comparable to non-diabetic corneas. Schirmer tear GGT activity in diabetic eyes was tear volume independent, less in T1 than T2, lower than in tear volume dependent, non-diabetic female eyes. Low cornea and tear GGT activity suggests loss of antioxidant potential and supports ocular antioxidant therapy for diabetic patients.

Keywords: cornea, diabetes, endothelium, epithelium, eye, γ-glutamyl transpeptidase, tear, oxidative stress

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