Quantitative proteomic analysis of N-linked glycoproteins in human tear fluid.

Human tear fluid is a complex biological fluid that is actually the extracellular fluid of the surface of the eye and can be considered a dilute protein solution. The quality of the tears are critical for vision as they provide the mirror smooth reflex for the surface of the eye and hence focusing of images on the retina. Changes in tear composition may reflect the health of the epithelial cells lining the ocular surface and they have been shown to be useful to discover biomarkers for eye diseases. Glycoproteins are potentially important biomarkers of disease and therapeutic targets and can also be found in human tears. In this chapter, we concentrated on technical details in quantitative proteomic analysis of N-linked glycoproteins in human tears by combining hydrazide chemistry enrichment of N-linked glycoproteins and iTRAQ technology.