The effect of β receptor blockade through propranolol on corneal neovascularization

Overactivation of Norepinephrine-β2-Adrenergic Receptor Axis Promotes Corneal Neovascularization

Purpose

To investigate the role of the sympathetic nervous system in corneal neovascularization (CNV) and to identify the downstream pathway involved in this regulation.

Methods

Three types of CNV models were constructed with C57BL/6J mice, including the alkali burn model, suture model, and basic fibroblast growth factor (bFGF) corneal micropocket model. Subconjunctival injection of the sympathetic neurotransmitter norepinephrine (NE) was administered in these three models. Control mice received injections of water of the same volume. The corneal CNV was detected using slit-lamp microscopy and immunostaining with CD31, and the results were quantified by ImageJ. The expression of β2-adrenergic receptor (β2-AR) was stained with mouse corneas and human umbilical vein endothelial cells (HUVECs). Furthermore, the anti-CNV effects of β2-AR antagonist ICI-118,551 (ICI) were examined with HUVEC tube formation assay and with a bFGF micropocket model. Additionally, partial β2-AR knockdown mice (Adrb2+/-) were used to establish the bFGF micropocket model, and the corneal CNV size was quantified based on the slit-lamp images and vessel staining.

Results

Sympathetic nerves invaded the cornea in the suture CNV model. The NE receptor β2-AR was highly expressed in corneal epithelium and blood vessels. The addition of NE significantly promoted corneal angiogenesis, whereas ICI effectively inhibited CNV invasion and HUVEC tube formation. Adrb2 knockdown significantly reduced the cornea area occupied by CNV.

Conclusions

Our study found that sympathetic nerves grow into the cornea in conjunction with newly formed vessels. The addition of the sympathetic neurotransmitter NE and activation of its downstream receptor β2-AR promoted CNV. Targeting β2-AR could potentially be used as an anti-CNV strategy.

Propranolol eye drops in patients with corneal neovascularization

RATIONALE

Studies performed in animal models of corneal neovascularization suggested the possible efficacy of a treatment with propranolol. Corneal neovascularization is one of the most feared complications of Stevens-Johnson syndrome that frequently involves ocular surface. We report the first 2 patients with severe ocular neo-vascularization treated with different degrees of success, with propranolol eye drops.

PATIENT CONCERNS

Two patients with corneal neovascularization complicating the Stevens-Johnson syndrome, not responsive to steroids and cyclosporine, were treated with propranolol eye drops.

DIAGNOSES

Corneal neovascularization was detected by ophthalmoscopic evaluation.

INTERVENTIONS

Topical treatment with propranolol eye drops at different concentrations.

OUTCOMES

Both patients reported dramatic subjective benefits (reduction of photophobia and discomfort) without adverse effects, and in the patient with a less advanced disease, an objective reduction of neovascularization and an improved visual acuity was observed.

LESSONS

This experience suggests that propranolol might be an inexpensive, safe and effective treatment in counteracting the progression of corneal neovascularization.