Analysis of tear fluid proteins in insulin-dependent diabetes mellitus

Secretory immunoglobulin A, lactoferrin, lysozyme and tear specific pre-albumin were analyzed in stimulated tear fluid of 25 diabetic patients without retinopathy and in 29 diabetic patients with (pre) proliferative retinopathy using high performance liquid chromatography. Results were compared to those obtained in 26 healthy controls to determine the effect of diabetes mellitus on the exocrine function of the main lacrimal gland. Sodium dodecyl sulfate polyacrylamide gel electrophoresis onto minigels was performed on 20 tear samples for verification of high performance liquid chromatography fractions recorded. The mean total protein values in tear fluid (Bradford assay) of diabetics without retinopathy, with retinopathy and healthy controls did not differ significantly (mean in mg/ml +/- SD: 6.4 +/- 2.2, 5.9 +/- 2.0 and 5.7 +/- 1.7, respectively; Mann-Whitney; p > 0.02). High performance liquid chromatography showed an increased secretory immunoglobulin A and decreased peak 5 OD280 (+56% and -38%, respectively; p < 0.02) in patients without retinopathy, whereas in patients with retinopathy lysozyme was increased (+27%; p < 0.01) and tear specific pre-albumin and peak 5 OD280 decreased (-24% and -42%, respectively; p < 0.04), when compared to healthy controls. These inconsistent differences do not uniformly suggest an exocrine dysfunction of the main lacrimal gland in diabetic patients.