IOP lowering effect of topical trans-resveratrol involves adenosine receptors and TGF-ß2 signaling pathways.

Trans-resveratrol was earlier shown to lower intraocular pressure (IOP) in rats; however, its mechanisms of action remain unclear. It has been shown to modulate adenosine receptor (AR) and TGF-ß2 signaling, both of which play a role in regulating IOP. Hence, we investigated effects of trans-resveratrol on AR and TGF-ß2 signaling. Steroid-induced ocular hypertensive (SIOH) rats were pretreated with A1AR, phospholipase C (PLC) and ERK1/2 inhibitors and were subsequently treated with single drop of trans-resveratrol. Metalloproteinases (MMP)-2 and -9 were measured in aqueous humor (AH). In another set of experiments, effect of trans-resveratrol on AH level of tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA) was determined after single and multiple drop administration in SIOH rats. Effect of trans-resveratrol on ARs expression, PLC and pERK1/2 activation and MMPs, tPA and uPA secretion was determined using human trabecular meshwork cells (HTMC). Further, effect of trans-resveratrol on TGF-ß2 receptors, SMAD signaling molecules and uPA and tPA expression by HTMC was determined in the presence and absence of TGF-ß2. Pretreatment with A1AR, PLC and ERK1/2 inhibitors antagonized the IOP lowering effect of trans-resveratrol and caused significant reduction in the AH level of MMP-2 in SIOH rats. Trans-resveratrol increased A1AR and A2AAR expression, cellular PLC, pERK1/2 levels and MMP-2, tPA and uPA secretion by HTMC. Additionally, it produced TGFßRI downregulation and SMAD 7 upregulation. In conclusion, IOP lowering effect of trans-resveratrol involves upregulation of A1AR expression, PLC and ERK1/2 activation and increased MMP-2 secretion. It downregulates TGFßRI and upregulates SMAD7 hence, inhibits TGF-ß2 signaling.

Topical trans-resveratrol ameliorates steroid-induced anterior and posterior segment changes in rats.

Steroid-induced hypertension and glaucoma is associated with increased extracellular meshwork (ECM) deposition in trabecular meshwork (TM). Previous studies have shown that single drop application of trans-resveratrol lowers IOP in steroid-induced ocular hypertensive (SIOH) rats. This IOP lowering is attributed to activation of adenosine A1 receptors, which may lead to increased matrix metalloproteinase (MMP)-2 activity. This study evaluated the effect of repeated topical application of trans-resveratrol for 21 days in SIOH animals on IOP, changes in MMP-2 level in aqueous humor, trabecular meshwork and retinal morphology and retinal redox status. We observed that treatment with trans-resveratrol results in significant and sustained IOP reduction in SIOH rats. This IOP reduction is associated with significantly higher aqueous humor total MMP-2 level; significantly reduced TM thickness and increased number of TM cells. Treatment with trans-resveratrol also significantly increased ganglion cell layer (GCL) thickness, the linear cell density in the GCL and inner retina thickness; and significantly reduced retinal oxidative stress compared to the SIOH vehicle-treated group. In conclusion, repeated dose topical application of trans-resveratrol produces sustained IOP lowering effect, which is associated with increased level of aqueous humor MMP-2, normalization of TM and retinal morphology and restoration of retinal redox status.

Anterior and posterior segment changes in rat eyes with chronic steroid administration and their responsiveness to antiglaucoma drugs.

Steroid-induced ocular hypertension (SIOH) is associated with topical and systemic use of steroids. However, SIOH-associated anterior and posterior segment morphological changes in rats have not been described widely. Here we describe the pattern of intraocular pressure (IOP) changes, quantitative assessment of trabecular meshwork (TM) and retinal morphological changes and changes in retinal redox status in response to chronic dexamethasone treatment in rats. We also evaluated the responsiveness of steroid-pretreated rat eyes to 5 different classes of antiglaucoma drugs that act by different mechanisms. Up to 80% of dexamethasone treated animals achieved significant and sustained IOP elevation. TM thickness was significantly increased and number of TM cells was significantly reduced in SIOH rats compared to the vehicle-treated rats. Quantitative assessment of retinal morphology showed significantly reduced thickness of ganglion cell layer (GCL) and inner retina (IR) in SIOH rats compared to vehicle-treated rats. Estimation of retinal antioxidants including catalase, superoxide dismutase and glutathione showed significantly increased retinal oxidative stress in SIOH animals. Furthermore, steroid-treated eyes showed significant IOP lowering in response to treatment with 5 different drug classes. This indicated the ability of SIOH eyes to respond to drugs acting by different mechanisms. In conclusion, SIOH was associated with significant morphological changes in TM and retina and retinal redox status. Additionally, SIOH eyes also showed IOP lowering in response to drugs that act by different mechanisms of action. Hence, SIOH rats appear to be an inexpensive and noninvasive model for studying the experimental antiglaucoma drugs for IOP lowering and neuroprotective effects.

Role of adenosine receptors in resveratrol-induced intraocular pressure lowering in rats with steroid-induced ocular hypertension.

BACKGROUND: Steroid-induced ocular hypertension is currently treated in the same way as primary open-angle glaucoma. However, the treatment is often suboptimal and is associated with adverse effects. We evaluated the oculohypotensive effects of topical trans-resveratrol in rats with steroid-induced ocular hypertension and involvement of adenosine receptors (AR) in intraocular pressure (IOP) lowering effect of trans-resveratrol. METHODS: The oculohypotensive effect of unilateral single-drop application of various concentrations of trans-resveratrol was first studied in oculonormotensive rats. Concentration with maximum effect was similarly studied in rats with steroid-induced ocular hypertension. Involvement of AR was studied by observing the alterations of IOP in response to trans-resveratrol after pretreating animals with AR subtype-specific antagonists. Additionally, we used computational methods, including 3D modelling, 3D structure generation and protein-ligand interaction, to determine the AR-trans-resveratrol interaction. RESULTS: All concentrations of trans-resveratrol produced significant IOP reduction in normotensive rat eyes. Maximum mean IOP reduction of 15.1% was achieved with trans-resveratrol 0.2%. In oculohypertensive rats, trans-resveratrol 0.2% produced peak IOP reduction of 25.2%. Pretreatment with A1 antagonist abolished the oculohypotensive effect of trans-resveratrol. Pretreatment with A3 and A2A AR antagonists produced significant IOP reduction in both treated and control eyes, which was further augmented by trans-resveratrol application in treated eyes. Computational studies showed that trans-resveratrol has highest affinity for A2B and A1, followed by A2A and A3 AR. CONCLUSION: Topically applied trans-resveratrol reduces IOP in rats with steroid-induced ocular hypertension. Trans-resveratrol-induced oculohypotension involves its agonistic activity at the A1 AR.