Detection of autoantibodies against reactive oxygen species modified glutamic acid decarboxylase-65 in type 1 diabetes associated complications.

BACKGROUND: Autoantibodies against glutamate decarboxylase-65 (GAD65Abs) are thought to be a major immunological tool involved in pathogenic autoimmunity development in various diseases. GAD65Abs are a sensitive and specific marker for type 1 diabetes (T1D). These autoantibodies can also be found in 6-10% of patients classified with type 2 diabetes (T2D), as well as in 1-2% of the healthy population. The latter individuals are at low risk of developing T1D because the prevalence rate of GAD65Abs is only about 0.3%. It has, therefore, been suggested that the antibody binding to GAD65 in these three different GAD65Ab-positive phenotypes differ with respect to epitope specificity. The specificity of reactive oxygen species modified GAD65 (ROS-GAD65) is already well established in the T1D. However, its association in secondary complications of T1D has not yet been ascertained. Hence this study focuses on identification of autoantibodies against ROS-GAD65 (ROS-GAD65Abs) and quantitative assays in T1D associated complications. RESULTS: From the cohort of samples, serum autoantibodies from T1D retinopathic and nephropathic patients showed high recognition of ROS-GAD65 as compared to native GAD65 (N-GAD65). Uncomplicated T1D subjects also exhibited reactivity towards ROS-GAD65. However, this was found to be less as compared to the binding recorded from complicated subjects. These results were further proven by competitive ELISA estimations. The apparent association constants (AAC) indicate greater affinity of IgG from retinopathic T1D patients (1.90 x 10⁻6 M) followed by nephropathic (1.81 x 10⁻6 M) and uncomplicated (3.11 x 10⁻7 M) T1D patients for ROS-GAD65 compared to N-GAD65. CONCLUSION: Increased oxidative stress and blood glucose levels with extended duration of disease in complicated T1D could be responsible for the gradual formation and/or exposing cryptic epitopes on GAD65 that induce increased production of ROS-GAD65Abs. Hence regulation of ROS-GAD65Abs could offer novel tools for analysing and possibly treating T1D complications.