Abstract
Purpose:
This study was designed to determine the downstream targets of delta opioid-receptors for neuroprotection in glaucomatous injury.
Methods:
Brown Norway rats were used to elevate intraocular pressure (IOP) by injecting 50 µL of 2M hypertonic saline into the circumferential limbal veins. IOP was recorded as the average of 6-8 consecutive measurements prior to surgery (baseline IOP) and weekly after treatment, using a calibrated Tonolab tonometer. Animals were either treated with delta opioid-receptor agonist, SNC-121 or SNC-80 (1 mg/kg; i.p) or Br-cAMP (1 mg/kg; i.p), daily for 7 days. Pattern electroretinograms (PERG), retinal ganglion cells in flat mount, and axons were counted 4-6 week post injury. The changes in the expression patterns of PI3K/Akt and phospho-cyclic AMP-response element binding protein (p-CREB) were determined by Western blotting and immunohistochemistry.
Results:
PERG amplitudes were significantly reduced in ocular-hypertensive eyes (16.78±1.23 µvolts) when compared to normal eyes (22.24±1.42 µvolts) the 6th week, post injury. PERG deficits in hypertensive eyes were significantly improved by SNC-121 treatment (21.70±1.03 µvolts; P<0.05). There was a significant loss of RGCs and axons in the hypertensive eyes and the loss in RGCs and axons was fully blocked in SNC-121-treated animals by the 6th week, post injury. We found that SNC-121 activate and phosphorylate PI3K/Akt pathway and cyclic AMP-response element binding protein (CREB). A PI3K/Akt inhibitor, LY-294002 (1 mg/kg), fully blocked SNC-121 mediated retina neuroprotection. Moreover, PERG were significantly improved by Br-cAMP treatment when measured on 6th week, post injury.
Conclusions:
These data provide initial evidence that PI3K/Akt and CREB, a transcription factor, are the potential neuroprotective targets of delta opioid-receptors in glaucomatous injury. Data also provide clues that PI3K/Akt pathway and CREB may have negatively regulated the neurodegenerative pathways in SNC-121-induced retina neuroprotection.
Keywords: 615 neuroprotection •
688 retina •
715 signal transduction: pharmacology/physiology