Effects of cholesterol-lowering statins on the aqueous humor outflow pathway

Abstract

Purpose: To investigate the effects of cholesterol-lowering statin drugs on trabecular meshwork cellular properties and aqueous humor outflow.

Methods: Primary cell cultures of porcine trabecular meshwork (PTM) and ciliary body (PCB) were treated with either lovastatin or compactin, to determine the effects of statins on cell shape, actin cytoskeletal organization, and cell-extracellular matrix interactions (focal adhesions) by immunofluorescence staining. Changes in myosin light-chain (MLC) phosphorylation were evaluated by Western blot analysis. Changes in Rho GTPase content of membrane fractions from lovastatin-treated PTM cells were assessed by Western blot analysis. A constant-flow, organ-culture perfusion system was used to measure the effects of statins on aqueous humor outflow facility in the anterior segments of porcine eyes.

Results: PTM and PCB cells treated with lovastatin or compactin exhibited dramatic changes in cell shape and cytoskeletal organization within 24 hours, consisting of cell rounding, actin depolymerization, and decreased focal adhesions. These effects were found to be reversible on supplementation with geranylgeranyl pyrophosphate. Both lovastatin and compactin decreased MLC phosphorylation in PTM and PCB cells. PTM cells treated with lovastatin exhibited marked decreases in membrane-bound Rho GTPase. In addition, perfusion of organ-cultured porcine eye anterior segments with 100 microM lovastatin for 96 hours caused a significant increase in aqueous humor outflow facility (110%) compared with control eyes, in a reversible manner.

Conclusions: This study demonstrates that the statin drugs lovastatin and compactin induce changes in cell shape and actin cytoskeletal organization and decrease MLC phosphorylation in PTM and PCB cells, all of which are events that are likely to lead to cellular and tissue relaxation. In addition, these effects of the statins appear to be mediated by inhibition of isoprenylation of the small GTP-binding proteins such as Rho GTPase. An important finding is that statins exert an ocular hypotensive response in an organ-culture perfusion model, indicating the potential for this class of drugs in glaucoma therapy.