Immunohistochemical localisation of d-β-aspartic acid in pingueculae

Background:d-β-Aspartic acid residues, which are biologically uncommon, have been reported to accumulate in various proteins of the living body with age. In the present study, d-β-aspartic acid-containing proteins were found to be localised in pingueculae, which represent one of the most prominent age-related ocular changes.Methods:Surgical specimens of conjunctivae with or without pingueculae were obtained from eight patients. Immunohistochemical localisation of d-β-aspartic acid-containing proteins was performed using a polyclonal antibody against d-β-aspartic acid-containing peptides.Results:Strong immunoreactivity to d-β-aspartic acid-containing peptides was detected in the subepithelial amorphous materials of all surgical specimens with pingueculae. In contrast, no immunoreactivity to d-β-aspartic acid-containing peptides was detected in the specimens without pingueculae.Conclusions:Pingueculae are thought to be aggregates of proteins that contain d-β-aspartic acid residues. It is known that the conversion of l- to d-aspartyl residues is accelerated by ultraviolet irradiation. In addition, d-β-aspartic acid-containing proteins, in general, tend to aggregate with each other and accumulate in the tissues. These facts indicate that ultraviolet irradiation-induced racemisation of aspartic acid is closely related to the development of pingueculae.