Prostaglandins increase trabecular meshwork outflow facility in cultured human anterior segments

Abstract

Purpose: To determine the effect of latanoprost free acid and prostaglandin E1 (PGE1) on outflow facility in cultured human anterior segments. Clinical studies find prostaglandin treatment increases uveoscleral outflow, but do not agree whether trabecular outflow increases. Cultured anterior segments eliminate the uveoscleral pathway and enable a direct assessment of trabecular outflow.

Design: Laboratory investigation.

Methods: One anterior segment of an eye pair was placed in perfusion organ culture and received a continuous infusion of drug while the fellow anterior segment received vehicle. Histologic changes were assessed. Zymography and Western blots were used to analyze matrix metalloprotease (MMP) activity. Scleral hydraulic conductivities were measured.

Results: Latanoprost significantly increased outflow facility (67% +/- 11% vs control 6% +/- 10%, P < .001). Facility changes occurred within one hour of receiving drug, reaching a new baseline by 24 hours. Facility changes were reversible, requiring about 48 hours to return to pre-drug values. PGE1 caused less facility change (13% +/- 17% vs control 1% +/- 11%, P = .02). Prostaglandin treated anterior segments had regions of focal detachment and loss of Schlemm canal endothelial cells, with loss of extracellular matrix underlying some areas. MMPs were not consistently increased in Western blots, zymography, or immunohistochemistry. Scleral hydraulic conductivity increased, but not enough to account for total facility increase.

Conclusions: Prostaglandins increase outflow facility in perfusion organ culture of human anterior segments. MMP activity was not consistently increased, and scleral hydraulic conductivity was not increased sufficiently to account for total facility increase. The histologic changes suggest a direct trabecular meshwork effect.

FIGURE 1

Reversibility of latanaprost free acid treatment on intraocular pressure (IOP) in human cultured anterior segments. Latanaprost free acid was given for 24 hours causing a prompt decrease in pressure. After removal of latanaprost free acid, pressure returned to baseline over 48 hour period.

FIGURE 2

Prostaglandin-E1 (PGE1) effect on human trabecular meshwork. (Top) Control anterior segment (an 86-year-old female). Outflow facility remained stable during culture. Schlemm canal cells are intact (arrowheads). Trabecular cells have normal nucleoli and position on lamellae (600×). (Bottom) Fellow anterior segment that received PGE1. Outflow facility increased 54% over 72 hours, with IOP dropping from 20 mm Hg to 14 mm Hg. Schlemm canal cells show intercellular separations (arrows) and loosening from underlying extracellular matrix (asterisks). Trabecular cells are intact, with normal nuclei and position on lamellae. SC = Schlemm canal (600×).