Abstract
We measured the urinary excretion of retinol-binding protein (RBP), β2-microglobulin (β2-m), albumin, and N-acetyl-β-D-glucosaminidase as well as serum glucose, RBP, β2-m, hemoglobin A1c, and creatinine in type 2 diabetes mellitus 158 patients. In urinary RBP, there was a significant difference between the patients who had nephropathy and those without complications. In the cases with nephropathy, urinary RBP had a significantly high value, but no significant difference was observed in the case with retinopathy. There were no significant correlations between urinary RBP and serum RBP. The index of correlation was 0.351.
According to western blot, there were 11, 6, and 6 bands for serum RBP, urinary RBP, and urinary transthyretin (TTR), respectively. The main bands for all three had molecular mass (MM) of 150 kDa. RBP combined with TTR is thought not to be able to pass through kidney glomeruli due to its high MM. The main band of urinary RBP is free RBP according to previous reports. Nevertheless, the main band had a MM of 150 kDa and represented combined TTR. This result contradicts previous reports about urinary RBP.
On the other hand, for urinary RBP4, the only band was of 150 kDa for cases without retinopathy, but for the cases with retinopathy, a sub-band was seen at 50 kDa and an extremely light-colored band was seen at 55 kDa, which suggests the possibility of early detection of retinopathy by examining these bands.
