Abstract
Purpose: :
Studies have shown that topical treatment with adenosine A1 agonists acutely lowers IOP by increasing conventional outflow facility through a process requiring the secretion and activation of MMP-2. However, studies evaluating chronic dosing of adenosine A1 agonists have found the ocular hypotensive response to these agents is enhanced when compared to acute single-drop studies. These data provide evidence that chronic activation of adenosine A1 receptors leads to molecular or structural changes that enhances the functional response to these drugs. The purpose of this study was to determine the acute and sub-chronic effects of adenosine A1 agonists on the secretion of MMPs from cultured human trabecular meshwork cells.
Methods: :
Primary cultures of human trabecular meshwork cells were treated with the A1 receptor agonist,CHA (10-9 to 10-6 mol/L), for 2, 24, or 48 hours. To confirm that responses were mediated by A1 receptors and involved ERK1/2 activation, cells were pretreated with the A1 receptor antagonist, CPT (10-6 mol/L), or the ERK1/2 pathway inhibitor, U-0126 (10-6 mol/L), prior to the addition of CHA. At the end of the study period, media was collected, concentrated, and analyzed for MMP-1, MMP-2, and MMP-3.
Results: :
The addition of CHA (10-7 mol/L) for 2 hours produced a significant increase of 208±59% over control levels; however, no significant change in MMP-1 or -3 was observed. In cells treated with CHA for 24 hours, the secretion of MMP-1 and -3 were significantly increased by 150±39% and 72±18% over control levels, respectively. Following 48 hours of CHA treatment, the secretion of MMP-1 and -3 were significantly increased to 178±91% and 94±31% over control levels, respectively. Both the early increase in MMP-2 secretion and the later elevation in MMP-1 and -3 induced by CHA, were dose-related with an EC50s of 5.8 and 9.5 nmol/L, respectively. The increases in MMPs secretion measured at 2 and 24 hours were blocked by pretreatment with the adenosine A1 receptor antagonist, CPT, or the ERK1/2 pathway inhibitor, U-0126.
Conclusions: :
The addition of the adenosine A1 agonist, CHA, to human trabecular meshwork cells induces a biphasic increase in MMP secretion: an initial secretion of MMP-2 followed by the delayed secretion of MMP-1 and -3. Both the initial and delayed responses involve the activation of A1 receptors and are linked to stimulation of the ERK1/2 pathway. The identification of acute and delayed responses of adenosine A1 agonists may provide an explanation for previous observations that chronic treatment with these agents in vivo are more effective than single-drop studies.
Keywords: adenosine • trabecular meshwork • outflow: trabecular meshwork