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.
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Competing interests: None.
Funding: This work is supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists, 18791259 (2006–2008) and for Scientific Research, 21592216 (2009–2011), Japan.
Ethics approval: Ethics approval was provided by Tsukuba University Hospital.
Patient consent: Obtained.