Increased levels of Nε- Carboxy methyl lysine (Nε-CML) are associated with topographic alterations in retinal pigment epithelium: A preliminary study

PurposeTo evaluate the association of serum levels of Nε- Carboxy methyl lysine (Nε-CML), an advanced glycation end product with topographic alterations in retinal pigment epithelium (RPE) in diabetic retinopathy on spectral domain optical coherence tomography (SD-OCT).MethodConsecutive cases of type 2 diabetes mellitus with no retinopathy (n = 20); non-proliferative diabetic retinopathy (n = 20); proliferative diabetic retinopathy (n = 20) and healthy controls (n = 20) between the ages of 40 and 65 years were included. RPE alterations were graded on segmentation map of SD-OCT: grade 0, No RPE alterations; grade 1, RPE alterations in up to two quadrants and grade 2, RPE alterations in more than two quadrants. Serum level of Nε-CML and glycated hemoglobin (HbA1c) was analyzed using the standard protocol. Statistical analysis was done.ResultsSignificant increase in Nε-CML was observed with increased severity of diabetic retinopathy (F = 34.1; p < 0.0001). Fisher exact test revealed significant increase in grades of RPE alterations with increased severity of diabetic retinopathy (p < 0.001). Univariate ordinal regression analysis was done to calculate the risk of progression in grades of RPE alteration with individual changes in variables like duration of diabetes (odds ratio = 1.37; p = 0.001), HbA1c (odds ratio = 1.37; p = 0.002) and Nε-CML (odds ratio = 1.37; p < 0.0001). Multivariate ordinal regression analysis for predicting progression in grades of RPE alteration revealed Nε-CML to be an independent predictor of increase in grades of RPE alteration (adjusted odds ratio = 1.07; p < 0.01) when duration of diabetes and HbA1c were held constant.ConclusionIncrease in serum levels of Nε- Carboxy methyl lysine is significantly associated with topographic alterations in RPE. Grades of RPE alteration increase significantly with increased severity of diabetic retinopathy.