Haptoglobin as an early serum biomarker of virus-induced autoimmune type 1 diabetes in biobreeding diabetes resistant and LEW1.WR1 rats.

Proteomic profiling of serum is a powerful technique to identify differentially expressed proteins that can serve as biomarkers predictive of disease onset. In this study, we utilized two-dimensional (2D) gel analysis followed by matrix-assisted-laser desorption/ionization time-of-flight mass spectrometry analysis to identify putative serum biomarkers for autoimmune type 1 diabetes (T1D) in biobreeding diabetes resistant (BBDR) rats induced to express the disease. Treatment with toll-like receptor 3 ligand, polyinosinic:polycytidilic acid (pIC), plus infection with Kilham rat virus (KRV), a rat parvovirus, results in nearly 100% of young BBDR rats becoming diabetic within 11-21 d. Sera collected from prediabetic rats at early time points following treatment with pIC + KRV were analyzed by 2D gel electrophoresis and compared with sera from control rats treated with phosphate-buffered saline, pIC alone or pIC + H1, a non-diabetogenic parvovirus. None of the latter three control treatments precipitates T1D. 2D gel analysis revealed that haptoglobin, an acute phase and hemoglobin scavenger protein, was differentially expressed in the sera of rats treated with pIC + KRV relative to control groups. These results were confirmed by Western blot and enzyme-linked immunosorbent assay studies, which further validated haptoglobin levels as being differentially increased in the sera of pIC + KRV-treated rats relative to controls during the first week following infection. Early elevations in serum haptoglobin were also observed in LEW1.WR1 rats that became diabetic following infection with rat cytomegalovirus. The identification and validation of haptoglobin as a putative serum biomarker for autoimmune T1D in rats now affords us the opportunity to test the validity of this protein as a biomarker for human T1D, particularly in those situations where viral infection is believed to precede the onset of disease.