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Effects of Latrunculin-B on Outflow Facility and Trabecular Meshwork Structure in Human Eyes

¹From the Departments of Mechanical and Industrial Engineering and ²Ophthalmology, University of Toronto, Toronto, Ontario, Canada.

PURPOSE. To determine the effect of the F-actin-disrupting agent latrunculin-B on aqueous outflow facility and trabecular meshwork architecture in human eyes.

METHODS. After baseline facility measurement in human eye bank eyes (n = 9 pairs), one eye of each pair received anterior chamber exchange and continued perfusion with medium containing 1 µM latrunculin-B. Contralateral eyes were treated in a similar manner with vehicle. Eyes were fixed by anterior chamber exchange and perfusion with universal fixative at 8 mm Hg (corresponding to a physiologic pressure of 15 mm Hg in vivo), and outflow pathway tissues were examined by transmission and scanning electron microscopy.

RESULTS. Perfusion of eyes with 1 µM latrunculin-B caused a continuous and ongoing increase in outflow facility, resulting in a net facility difference of 64% 2 hours after drug administration (P < 0.006). Transmission electron microscopy showed subtle and focal detachment of the inner wall of Schlemm’s canal, rarefaction of the juxtacanalicular tissue (JCT), and cell-cell and cell-matrix detachment. Scanning electron microscopy showed collapsed vacuoles in the inner wall of Schlemm’s canal and a marked increase in the number and size of border (paracellular) pores in the inner wall.

CONCLUSIONS. Latrunculin-B increases outflow facility in postmortem human eyes. The mechanism of facility increase is most likely due to loss of mechanical integrity of the trabecular meshwork as a consequence of reduction in cell-cell and cell-matrix adhesion. The facility increase and the extent of inner wall separation from the JCT that we observed were both qualitatively similar to that reported in living monkey eyes, but the magnitude of the facility increase and morphologic changes were much less than in the living monkey. This supports the idea that inner wall separation from the JCT may modulate outflow facility.

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