Thiol-Disulfide homeostasis in tear fluid: Alterations associated with diabetic retinopathy

BackgroundThis study aimed to evaluate dynamic thiol/disulfide homeostasis in the tear fluid of patients with type 2 diabetes and to investigate its relationship with the presence of diabetic retinopathy (DR), considering it as a potential biomarker of oxidative stress.MethodsA total of 96 individuals were included in the study. Participants were divided into three groups: 32 patients with diabetic retinopathy (Group 1, DR (+)), 31 patients with diabetes but without retinopathy (Group 2, DR (-)), and 33 healthy volunteers (Group 3). All participants underwent a comprehensive ophthalmological examination, including best-corrected visual acuity, slit-lamp biomicroscopy, and fundus evaluation. Tear samples were collected using Schirmer strips and stored in phosphate-buffered Eppendorf tubes at -80 °C until analysis. Total thiol, native thiol, and disulfide levels were analyzed using a spectrophotometric method. Patients with a history of intraocular surgery, trauma, glaucoma, or systemic diseases other than diabetes were excluded.ResultsThere were statistically significant differences between the groups in terms of total thiol, disulfide, disulfide/total thiol, and disulfide/native thiol ratios (p < 0.001). Total thiol levels were significantly lower, while disulfide levels and ratios were significantly higher in the DR (+) group. No significant difference was found in native thiol levels (p = 0.194). HbA1c and fasting blood glucose levels were significantly higher in the DR (+) group compared to the other groups (p < 0.001). Central macular thickness was also significantly greater in the DR (+) group (p < 0.001). Correlation analysis revealed a positive and significant relationship between HbA1c and fasting blood glucose (r = 0.551; p < 0.01), whereas no significant correlation was found between central macular thickness and glycemic parameters.ConclusionThe increased disulfide levels and disulfide ratios in the tear fluid of patients with diabetic retinopathy suggest a shift in thiol/disulfide homeostasis toward oxidative stress. These tear-based biomarkers may serve as valuable tools for the early diagnosis and monitoring of diabetic retinopathy.