Introduction
Rho proteins are small molecules that help control how cells maintain their shape, move, divide, and die. Rho kinases (ROCKs) are proteins activated by Rho that play a key role in managing these cell processes. Two types of ROCKs, ROCK1 and ROCK2, help organize the cell's internal structure. ROCKs are found in all tissues, including the cornea, where they help with healing and cell development. In the cornea, ROCKs are important for keeping it clear and aiding in wound healing. ROCK inhibitors (RKIs) can boost corneal repair and cell regeneration, and they are being explored for treating corneal diseases, glaucoma, and other eye conditions.
What Is the Mechanism of Rho Kinase Inhibitors?
-
Preventing Damage with Rho Kinase Inhibitors: Rho kinase inhibitors are used to treat diabetic retinopathy by stopping the attachment of harmful white blood cells to the eye's blood vessels. These inhibitors reduce certain proteins that act as anchor sites for these cells, preventing further damage to the eye's blood vessels. In studies with rats that had diabetes, a Rho kinase inhibitor called fasudil reduced white blood cell adhesion by 68 percent. These inhibitors also help protect retinal cells from damage caused by low oxygen and oxidative stress.
-
Slowing Endothelial Damage: Rho kinase inhibitors also help protect the tiny blood vessels in the retina by restoring the activity of an enzyme that produces nitric oxide. Nitric oxide is important because it helps keep blood vessels open and prevents cell death. In the same rat study, the inhibitors increased nitric oxide production by 35 percent, which helped protect retinal blood vessels and reduce cell damage. Blocking nitric oxide production reversed the protective effects of the Rho kinase inhibitors, highlighting its importance in the treatment.
What Are the Functions of Rho Kinase Inhibitors?
Rho-kinase (ROCK) is a protein part of a larger family called AGC kinases. It works with a smaller protein called Rho to help control various cell functions, such as how cells move, change shape, divide, and express genes.
-
Functions of ROCK: ROCK helps control how cells contract (tighten up), move, and change shape. It also affects cell death (apoptosis) by affecting the cell's structure.
-
Cell Death and ROCK: ROCK can cause cell death by making cells contract too much and damage themselves. In the corneal endothelium (the cornea's inner layer), ROCK inhibitors can prevent this damage by stopping excessive contraction. These inhibitors can quickly slow down cell death, often within a day.
What Are the Uses of Rho Kinase Inhibitors?
-
Rho-kinase inhibitors (RKIs) can be applied as eye drops or injected into the eye.
-
For conditions like Fuchs endothelial corneal dystrophy (FECD), RKIs like Y-27632 help keep the cornea clear and improve vision.
-
RKIs like Ripasudil hydrochloride hydrate can also be useful for patients without central descemetorhexis surgery.
-
RKIs are effective in treating high-eye pressure conditions like ocular hypertension and primary open-angle glaucoma.
-
They work by making fluid drain from the eye easier and reducing damage to drainage tissues.
-
RKIs also lower oxidative stress, which harms the eye's drainage system.
-
RKIs can improve blood flow to the retina and optic nerve, which is beneficial for retinal diseases like diabetic retinopathy.
-
They help by reducing blood vessel constriction and improving overall retinal health.
Which Drugs of Rho Kinase Inhibitors Are Used in Glaucoma?
Two common Rho kinase inhibitors (RKIs) are Ripasudil (K-115) and Netarsudil (AR-13503). Ripasudil is used to treat glaucoma in Japan, and it can cause some redness and bleeding in the eye, but no other major eye problems have been reported. Netarsudil is used for glaucoma in the United States and affects norepinephrine, a chemical that influences various body functions. It can cause redness, pain at the application site, and corneal changes. RKIs are also helpful for treating corneal issues. They can prevent cell death and promote cell growth in the cornea, which might be useful for conditions like Fuchs' dystrophy and damage from cataract surgery. They help by boosting certain proteins that control cell division, although these benefits might be more noticeable in younger patients.
Topical Ripasudil is often used alongside a specific surgical procedure (Descemet Stripping Only) to help patients recover vision more quickly and maintain better corneal health. RKIs can be delivered as eye drops or through an injection into the front part of the eye with cultured corneal cells.
How Are Rho Inhibitors Used in Eyes?
Currently, the first step in treating glaucoma to prevent its progression and damage to the optic nerve is medication to reduce intraocular pressure (IOP). These medications work either by increasing the outflow of eye fluid or reducing its production. For example, prostaglandin analogs and alpha agonists help increase fluid outflow, while beta-blockers, carbonic anhydrase inhibitors, and alpha agonists reduce fluid production. However, these drugs do not directly target the trabecular meshwork, the main site of fluid resistance. ROCK inhibitors are a new type of drug that targets the trabecular meshwork to lower IOP. Only four ROCK inhibitors have been tested in clinical trials: SNJ-1656 (Y-39983), AR-12286, Ripasudil (K-115), and Netarsudil (AR-13324), with Ripasudil and Netarsudil, approved for treating glaucoma in Japan, China, and the USA.
-
Netarsudil: Netarsudil, sold as Rhopressa (0.02 percent ophthalmic solution), is used in the USA to reduce IOP in patients with open-angle glaucoma or ocular hypertension. It is applied topically once a day and works by relaxing the trabecular meshwork, increasing fluid outflow, reducing scleral venous pressure, and directly lowering IOP. Clinical trials showed that Netarsudil effectively lowers IOP, comparable to Timolol, another glaucoma medication. While it is generally safe, common side effects include conjunctival congestion, subconjunctival hemorrhage, corneal verticillata, and eye pain.
-
For Steroid-Induced Glaucoma: Netarsudil may also be useful for patients with glaucoma caused by long-term steroid use. Steroid-induced glaucoma occurs due to changes in the cell structure of the trabecular meshwork, increasing fluid resistance and IOP. Studies suggest that ROCK inhibitors can disrupt these changes and improve fluid outflow. Clinical trials indicate that Netarsudil can help prevent steroid-induced IOP increases, though more research is needed.
-
Drug Combinations: Combining Netarsudil with other glaucoma medications like Latanoprost can enhance its effectiveness. Studies show that using a fixed-dose combination of Netarsudil and Latanoprost significantly reduces IOP more than either drug alone. This combination is well tolerated and can be an effective treatment before considering surgery for glaucoma.
-
Corneal Edema: Rho-kinase inhibitors have benefited patients with Iridocorneal endothelial syndrome (ICE) syndrome. A patient with corneal swelling from ICE syndrome may experience a significant reduction in the swelling and improved vision after using Netarsudil eye drops for four weeks.
What Are the Side Effects of Rho Kinase Inhibitors?
Rho kinase inhibitors have multiple effects. They help improve blood flow by relaxing the muscles in blood vessels, which leads to vasodilation. However, this can also cause redness in the eyes. These inhibitors can also affect the liver, potentially causing liver damage. In some cases, liver damage can be serious or even life-threatening.
Conclusion
Rho-kinase inhibitors (RKIs) are promising drugs with various benefits for treating eye conditions. They improve corneal healing, reduce intraocular pressure in glaucoma, and protect retinal cells from damage. While RKIs offer significant advantages, such as promoting cell regeneration and reducing eye pressure, they also have potential side effects, including eye redness and possible liver damage. Their application is expanding to treat common and rare eye diseases, making them valuable tools in ophthalmology.
