Similar effects of selective laser trabeculoplasty and prostaglandin analogs on the permeability of cultured Schlemm canal cells.

PURPOSE: To evaluate whether selective laser trabeculoplasty and prostaglandin analogs regulate the permeability of cultured human Schlemm canal cells by inducing intercellular junction disassembly. DESIGN: Laboratory investigation. METHODS: Intercellular junctions were made visible in living cells by making them fluoresce after transfection with a plasmid expressing the zonula occludens 1 protein tagged with green fluorescent protein. Schlemm canal cells were treated by direct laser irradiation; by exposure to media conditioned by either lasered Schlemm canal cells or trabecular meshwork cells; by exposure to the prostaglandin analogs latanoprost, bimatoprost, and travoprost; or by the addition of the nonprostaglandin agents brimonidine, timolol, and dorzolamide. Junction disassembly was monitored using fluorescence microscopy, and permeability alterations were measured as changes in conductivity using flow meters. RESULTS: The direct laser irradiation of Schlemm canal cells caused a 3-fold increase in conductivity. Exposure of the cells to media conditioned by lasered Schlemm canal cells or trabecular meshwork cells induced junction disassembly and a 2- to 4-fold increase in conductivity. Exposure to prostaglandin analogs also induced junction disassembly and a 4- to 16-fold increase in conductivity, whereas the 3 nonprostaglandin agents tested were ineffective in both regards. CONCLUSIONS: Exposure to factors secreted by lasered Schlemm canal cells and lasered trabecular meshwork cells and the application of prostaglandin analogs induced junction disassembly while increasing the permeability of Schlemm canal cells. These findings support our hypothesis that selective laser trabeculoplasty and prostaglandin analogs share a common mechanism that likely mediates their pressure-lowering effects.

Constitutive secretion of chemokines by cultured human trabecular meshwork cells.

Trabecular meshwork endothelial (TME) cells secrete a number of factors, such as enzymes and cytokines, which modulate the functions of the cells and the extracellular matrix of the conventional aqueous outflow pathway. TME cells usually secrete these factors in response to stimuli such as mechanical stretching, laser irradiation and pro-inflammatory cytokines. Here, we report that cultured human TME cells isolated from two non-glaucomatous individuals secrete significant quantities of the chemotactic cytokines IL8, CXCL6 and MCP1 in the absence of any stimulation. The secretion of these chemokines was augmented by treatment with the pro-inflammatory cytokines TNFalpha and IL1beta. By way of comparison, there was little or very low production of the three chemokines by human non-pigmented ciliary epithelial cells in the absence of stimulation. Our findings provide support to our recent observations that monocytes, presumably under the influence of chemotactic signals, circulate through the trabecular meshwork in the normal state and also that cytokines regulate the permeability of Schlemm's canal endothelial cells. In addition, the fact that normal TME cells constitutively secrete chemotactic cytokines strengthens the notion that cytokines play a key role in the homeostasis of the outflow of the aqueous humor and, possibly, in the pathogenesis of glaucoma.

From the bedside to the bench and back again: predicting and improving the outcomes of SLT glaucoma therapy.

PURPOSE: To determine whether selective laser trabeculoplasty (SLT) and prostaglandin analogues (PGAs) have a common mechanism of action that involves increasing conductivity across Schlemm's canal endothelial cells (SCEs) and inducing a similar decrease in intraocular pressure (IOP) in a given patient. METHODS: The intercellular junctions in SCEs were made visible by transfection of a plasmid containing a GFP-tagged gene for ZO-1 protein. Transfected SCEs were treated with media conditioned by lasered trabecular meshwork endothelial cells (TMEs), or with latanoprost, bimatoprost, or travoprost. Non-transfected SCEs were exposed to brimonidine, timolol, or brinzolamide. Confocal microscopy and conductivity measurements documented the in vitro treatment effects. Clinically, the IOP in the first SLT-treated eye of 24 patients was measured (1) while on PGA therapy, (2) at "baseline" several weeks after discontinuing PGA therapy, and (3) approximately 90 days after SLT treatment. RESULTS: Both the in vitro addition of any of the 3 PGAs and of media conditioned by lasered TMEs induced similar SCE effects involving junction disassembly, paracellular pathway widening, and increased conductivity. Clinically, PGAs decreased IOP by a mean of 5.58 mmHg and SLT decreased IOP by 6.60 mmHg from a baseline of 21.52 mmHg. CONCLUSIONS: Exposure to media conditioned by lasered TMEs, or the addition of PGAs, induces the disassembly of intercellular junctions opening up the SCE barrier. Clinically, a positive PGA response predicts both a successful SLT outcome and the magnitude of the decrease in IOP after SLT. We hypothesize that SLT and PGA therapies may share a common mechanism of action.

Inhibition of cardiovascular cell proliferation by angiotensin receptor blockers: are all molecules the same?

BACKGROUND: Few studies have directly compared the effects of different angiotensin receptor blockers (ARBs) on mechanisms involved in the pathogenesis of cardiovascular disease. METHODS: We studied the ability of different ARBs to inhibit the proliferation of vascular smooth muscle cells (VSMCs) and cardiac fibroblasts (CFs) in continuous culture and in quiescent cells stimulated to proliferate by platelet-derived growth factor (PDGF) and insulin. We also investigated whether the antiproliferative effects of ARBs depended on their ability to block angiotensin II receptors or activate the peroxisome proliferator-activated receptor gamma (PPAR gamma). RESULTS: Dose-response studies showed that candesartan, eprosartan, and irbesartan had little or no effect on the proliferation of VSMC or CF in continuous culture even when tested at concentrations as high as 10 mumol/l or when tested in cells stimulated with PDGF/insulin. In contrast, telmisartan inhibited VSMC and CF proliferation by 50-70% (P < 0.05) in a dose-dependent and reversible fashion and significantly inhibited the increases in cyclin D1 levels and cell proliferation induced by PDGF/insulin. Antiproliferative effects of telmisartan were also observed in Chinese hamster ovary (CHO-K1) cells that lack functional angiotensin II receptors and in human VSMCs treated with the PPAR gamma antagonist GW9662. CONCLUSION: Telmisartan, but not candesartan, irbesartan, or eprosartan, can significantly inhibit the proliferation of VSMC and CF in culture when tested at concentrations near those that can be achieved in plasma with usual oral dosing. Telmisartan can also inhibit the proliferation of cells that lack angiotensin II receptors and cells treated with a PPAR gamma antagonist suggesting that the antiproliferative effects of telmisartan may involve more than just angiotensin II receptor blockade or activation of PPAR gamma.