Abstract
Background: Autoantibodies against glutamate decarboxylase-65 (GAD(65)Abs) are thought to be a major immunological tool involved in pathogenic autoimmunity development in various diseases. GAD(65)Abs 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 GAD(65)Abs is only about 0.3%. It has, therefore, been suggested that the antibody binding to GAD(65) in these three different GAD(65)Ab-positive phenotypes differ with respect to epitope specificity. The specificity of reactive oxygen species modified GAD(65) (ROS-GAD(65)) 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-GAD(65) (ROS-GAD(65)Abs) 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-GAD(65) as compared to native GAD(65) (N-GAD(65)). Uncomplicated T1D subjects also exhibited reactivity towards ROS-GAD(65). 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-GAD(65) compared to N-GAD(65).
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 GAD(65) that induce increased production of ROS-GAD(65)Abs. Hence regulation of ROS-GAD(65)Abs could offer novel tools for analysing and possibly treating T1D complications.