Selective permeability of mouse blood-aqueous barrier as determined by 15 N-heavy isotope tracing and mass spectrometry

Significance The aqueous fluid of the eye is composed of proteins from both blood circulation and ocular production. The main filter between the blood bed and the intraocular fluid is referred to as the blood-aqueous barrier. Here we devised an approach to address the selectivity of the barrier using nitrogen-15–labeled serum proteins as tracers. Following systemic injection of the labeled serum to normal nitrogen-14 mice, the labeled proteins subsequently entered the aqueous fluid and were measured by mass spectrometry. This new quantitative method captured the dynamic redistribution patterns of approximately 500 serum proteins entering normal eye and the eye recovering from injury. We discovered inhibitory complement proteins crossed the blood-ocular barrier of the wounded eye but not of the normal eye.