Abstract
Abstract: :
Purpose: To determine the levels of γ–glutamyltranspeptidase activity (GGT; converts glutathione and glutamine to glutamate, modulates barrier permeability and affects melatonin synthesis) in human retinal pigmented epithelial (RPE) tissue from diabetic and non–diabetic human cadaver eyes. Methods: RPE tissue was dissected from human cadaver eyes obtained from Louisiana Eye Banks, cut into sections and weighed. GGT in sera from diabetic and non–diabetic patients were also assessed. The amount of GGT activity (glutaminase) was determined by conversion of L–γ–glutamyl–p–nitroanalide and expressed as nM converted/h/g RPE tissue or /ml serum. Results: While significant differences were detected between RPE from some eye pairs, the mean GGT levels in left and right cadaver eye pairs were not significantly different (p>0.3). The mean GGT level in RPE from non–diabetic human cadaver eyes (18,681±7,196 nM/g/h; n=56) was not significantly different from the mean GGT levels in 23 diabetic eyes. However, the GGT levels in RPE tissue from 10 insulin dependent diabetic (IDD) eyes was 2–fold lower than that in 13 non–insulin dependent diabetic (NIDD) eyes (p<0.00001). Concomitantly, the GGT in non–diabetic eyes were different from NIDD (p=.019) and IDD (p=0.006) eyes. Similarly, the mean GGT level in sera of 21 NIDD was higher than in sera of 10 IDD (p=0.02) and both were significantly different from the GGT levels in 45 non–diabetic sera (p=0.05). Conclusions:The GGT levels in RPE and serum are higher in NIDD patients than in non–diabetic persons, while the GGT levels in RPE and serum of IDD patients are lower than in non–diabetic persons.
Keywords: diabetic retinopathy • metabolism • retinal pigment epithelium