Rho Kinase Inhibitors
Rho is a group of small GTP-binding proteins. These proteins aid in regulation of cell structure, motility, division, and apoptosis. Rho kinases (ROCKs) are effectors of the Rho pathways (Rho activates ROCKs). There are two identified types of ROCKs referred to as ROCK1 and ROCK2. Both are serine/tyrosine kinases. One of the main functions of ROCKs is to aid in reorganization of the actin cytoskeleton. Cell growth, movement, and death can occur through this reorganization. ROCKs are ubiquitous and expressed in all tissue types, although the concentration of the particular isoform may vary by tissue.
ROCKs are expressed in the cornea, and appear to be involved in corneal healing and cell differentiation. Corneal endothelial cells (CEC) are responsible for maintaining the clarity of the cornea and express ROCKs. The use of ROCK inhibitors (RKIs) has been shown to improve corneal wound healing and endothelial regeneration. Because of this, RKIs are a promising therapeutic agent for corneal disease, but have also found applications in glaucoma and vitreoretinal disease.
Rho kinase plays a part in the guanine nucleotide exchange factors, factors that cycle between the bound and unbound conformations of GTP1. Rho kinase specifically works downstream of RhoA protein, a Rho GTPase. Guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs), and guanine nucleotide dissociation inhibitors (GDIs) switch RhoA between its active GTP bound conformation and inactive GDP bound conformation.
Activated RhoA turns on a coiled-coil serine/threonine kinase called Rho kinase. The two isoforms of ROCK, ROCK1 (ROKβ) and ROCK2 (ROKα), have similar effects but may also have different effects depending on the isoform. Once active, Rho kinase phosphorylates myosin light chain, myosin phosphatase substrate 1, LIM kinase, CP1-17, calponin and the ERM proteins. These factors serve a number of cellular roles including cell adhesion, actomyosin contraction, cell migration, and cell proliferation. These factors have a critical role in outflow of aqueous humor. As mentioned previously, ROCK has recently been shown to affect the corneal layers through cell proliferation, cell migration, including wound healing and progression through the cell cycle.
Indications for Rho Kinase Inhibitors in Ophthalmology
In the setting of corneal endothelial disease, both topical and anterior chamber injections with RKIs have been found to be beneficial. In Fuchs endothelial corneal dystrophy (FECD), a form of anterior segment dysgenesis, use of ROCK inhibitor (Y-27632) eye drops have been successful in preserving corneal clarity and visual acuity. The use of RKI eye drops (Ripasudil hydrochloride hydrate) as a salvage treatment for patients who have failed central descemetorhexis has also been found to be successful in a subset of patients. These findings support a pharmacologic approach to a commonly surgical problem in CEC disease.
In conjunction with other topical glaucoma therapies, RKIs have been shown to be effective in diseases of increased intraocular pressure (IOP) in both animal and human models. Such diseases include ocular hypertension (predisposes patient to glaucoma) and primary open-angle glaucoma (POAG). The mechanism of ROCK inhibitors’ ability to decrease IOP is through direct action on the trabecular meshwork and Schlemm’s canal cells (increases permeability), which play a large role in the resistance of aqueous humor outflow. RKIs also decrease reactive oxidative species damage to the trabecular meshwork which is a known component of glaucoma pathophysiology. See Medical Management for Primary Open-Angle Glaucoma for more information on the use of RKIs in glaucoma.
The ROCK pathway has also been implicated in retinal disease such as diabetic retinopathy. It is known that Rho and ROCK are expressed in central nervous tissue and retinal ganglion cells which may promote vasoconstriction through endothelin-1. Therefore, use of RKIs promotes vasodilation and improved retinal blood flow, especially to the optic nerve head.
Commonly Used Rho Kinase Inhibitors
Two commonly used RKIs are Ripasudil (K-115) and Netarsudil(AR-13503). Ripasudil has been clinically approved to treat glaucoma in Japan. Side effects of Ripasudil include dose-dependent conjunctival hyperemia and non-dose dependent conjunctival hemorrhage. It has not shown any other ophthalmological side effects. Netarsudil is both an RKI and a norepinephrine transport inhibitor. As a norepinephrine transport inhibitor, it decreases the reuptake of norepinephrine increasing its effects on the body and the alpha-adrenergic receptors. It has also been clinically approved to treat glaucoma, specifically in the United States, and its intraocular pressure lowering effect has been shown to increase with latanoprost. Side effects of Netarsudil include conjunctival hyperemia and corneal verticillata, instillation site pain, and conjunctival hemorrhages.
Rho kinase inhibitors have also been shown to treat corneal endothelial dysfunction. They inhibit apoptosis and increase proliferation of monkey corneal endothelial cells, and these effects may be seen in humans. Recent studies have shown that topical application of RKIs as eyedrops has also successfully treated Fuchs’ endothelial dystrophy and endothelial damage after cataract surgery, although more tests are necessary. The mechanism proposed for increased cell cycle growth with corneal endothelial cells involve increased cyclin D levels which suppress phosphorylation of cyclin-dependent kinase inhibitor 1B, p27/kip115. Both factors regulate cell division in corneal cells; however these effects may only be seen in younger patients.
Because of these properties, topical ripasudil is often given in conjunction with the descemet stripping only(DSO) procedure. Patients treated with topical ripasudil recovered vision more quickly and had higher endothelial cell density at 3,6 and 12 months.
There have been two proposed methods of delivery of ROCK inhibitors to heal the corneal endothelium, including topical eye drops and an anterior chamber injection with cultured endothelial cells.
- Riento K, Ridley AJ. ROCKs: multifunctional kinases in cell behaviour. Nat Rev Mol Cell Biol. 2003;4(6):446-456. doi:10.1038/nrm1128
- Leung T, Manser E, Tan L, Lim L. A Novel Serine/Threonine Kinase Binding the Ras-related RhoA GTPase Which Translocates the Kinase to Peripheral Membranes. J Biol Chem. 1995;270(49):29051-29054. doi:10.1074/jbc.270.49.29051
- Matsui T, Amano M, Yamamoto T, et al. Rho-associated kinase, a novel serine/threonine kinase, as a putative target for small GTP binding protein Rho. EMBO J. 1996;15(9):2208-2216. http://www.ncbi.nlm.nih.gov/pubmed/8641286. Accessed May 25, 2019.
- Ishizaki T, Maekawa M, Fujisawa K, et al. The small GTP-binding protein Rho binds to and activates a 160 kDa Ser/Thr protein kinase homologous to myotonic dystrophy kinase. EMBO J. 1996;15(8):1885-1893. http://www.ncbi.nlm.nih.gov/pubmed/8617235. Accessed May 25, 2019.
- Nakagawa O, Fujisawa K, Ishizaki T, Saito Y, Nakao K, Narumiya S. ROCK-I and ROCK-II, two isoforms of Rho-associated coiled-coil forming protein serine/threonine kinase in mice. FEBS Lett. 1996;392(2):189-193.
- Leung T, Chen XQ, Manser E, Lim L. The p160 RhoA-binding kinase ROK alpha is a member of a kinase family and is involved in the reorganization of the cytoskeleton. Mol Cell Biol. 1996;16(10):5313-5327. doi:10.1128/mcb.16.10.5313
- Moura-Coelho N, Tavares Ferreira J, Bruxelas CP, Dutra-Medeiros M, Cunha JP, Pinto Proença R. Rho kinase inhibitors—a review on the physiology and clinical use in Ophthalmology. Graefe’s Arch Clin Exp Ophthalmol. 2019;257(6):1101-1117. doi:10.1007/s00417-019-04283-5
- Yin J, Yu F-SX. Rho kinases regulate corneal epithelial wound healing. Am J Physiol Physiol. 2008;295(2):C378-C387. doi:10.1152/ajpcell.90624.2007
- Anderson S, DiCesare L, Tan I, Leung T, SundarRaj N. Rho-mediated assembly of stress fibers is differentially regulated in corneal fibroblasts and myofibroblasts. Exp Cell Res. 2004;298(2):574-583. doi:10.1016/J.YEXCR.2004.05.005
- Meekins LC, Rosado-Adames N, Maddala R, Zhao JJ, Rao P V., Afshari NA. Corneal Endothelial Cell Migration and Proliferation Enhanced by Rho Kinase (ROCK) Inhibitors in In Vitro and In Vivo Models. Investig Opthalmology Vis Sci. 2016;57(15):6731. doi:10.1167/iovs.16-20414
- Wilson RS, Roper-Hall MJ. Effect of age on the endothelial cell count in the normal eye. Br J Ophthalmol. 1982;66(8):513-515. doi:10.1136/bjo.66.8.513
- Okumura N, Koizumi N, Ueno M, et al. ROCK Inhibitor Converts Corneal Endothelial Cells into a Phenotype Capable of Regenerating In Vivo Endothelial Tissue. Am J Pathol. 2012;181(1):268-277. doi:10.1016/J.AJPATH.2012.03.033
- Okumura N, Koizumi N, Ueno M, et al. Enhancement of corneal endothelium wound healing by Rho-associated kinase (ROCK) inhibitor eye drops. Br J Ophthalmol. 2011;95(7):1006-1009. doi:10.1136/bjo.2010.194571
- Rao PV, Pattabiraman PP, Kopczynski C. Role of the Rho GTPase/Rho kinase signaling pathway in pathogenesis and treatment of glaucoma: Bench to bedside research. Exp Eye Res. 2017;158:23-32. doi:10.1016/j.exer.2016.08.023
- Moshirfar M, Parker L, Birdsong OC, et al. Use of Rho kinase Inhibitors in Ophthalmology: A Review of the Literature. Med hypothesis, Discov Innov Ophthalmol J. 2018;7(3):101-111. http://www.ncbi.nlm.nih.gov/pubmed/30386798. Accessed May 25, 2019.
- Koizumi N, Okumura N, Ueno M, Kinoshita S. New Therapeutic Modality for Corneal Endothelial Disease Using Rho-Associated Kinase Inhibitor Eye Drops. Cornea. 2014;33:S25-S31. doi:10.1097/ICO.0000000000000240
- Moloney G, Petsoglou C, Ball M, et al. Descemetorhexis Without Grafting for Fuchs Endothelial Dystrophy—Supplementation With Topical Ripasudil. Cornea. 2017;36(6):642-648. doi:10.1097/ICO.0000000000001209
- Inoue T, Tanihara H. Rho-associated kinase inhibitors: A novel glaucoma therapy. Prog Retin Eye Res. 2013;37:1-12. doi:10.1016/J.PRETEYERES.2013.05.002
- Honjo M, Tanihara H, Inatani M, et al. Effects of rho-associated protein kinase inhibitor Y-27632 on intraocular pressure and outflow facility. Invest Ophthalmol Vis Sci. 2001;42(1):137-144. http://www.ncbi.nlm.nih.gov/pubmed/11133858. Accessed May 27, 2019.
- Fujimoto T, Inoue T, Ohira S, et al. Inhibition of Rho Kinase Induces Antioxidative Molecules and Suppresses Reactive Oxidative Species in Trabecular Meshwork Cells. J Ophthalmol. 2017;2017:1-23. doi:10.1155/2017/7598140
- Hein TW, Rosa RH, Yuan Z, Roberts E, Kuo L, Kuo L. Divergent roles of nitric oxide and rho kinase in vasomotor regulation of human retinal arterioles. Invest Ophthalmol Vis Sci. 2010;51(3):1583-1590. doi:10.1167/iovs.09-4391
- Tanihara H, Inoue T, Yamamoto T, Kuwayama Y, Abe H, Araie M. Phase 2 Randomized Clinical Study of a Rho Kinase Inhibitor, K-115, in Primary Open-Angle Glaucoma and Ocular Hypertension. Am J Ophthalmol. 2013;156(4):731-736.e2. doi:10.1016/J.AJO.2013.05.016
- Wang R-F, Williamson JE, Kopczynski C, Serle JB. Effect of 0.04% AR-13324, a ROCK, and Norepinephrine Transporter Inhibitor, on Aqueous Humor Dynamics in Normotensive Monkey Eyes. J Glaucoma. 2015;24(1):51-54. doi:10.1097/IJG.0b013e3182952213
- Okumura N, Kinoshita S, Koizumi N. Application of Rho Kinase Inhibitors for the Treatment of Corneal Endothelial Diseases. J Ophthalmol. 2017;2017:2646904. doi:10.1155/2017/2646904
- Peh GSL, Adnan K, George BL, et al. The effects of Rho-associated kinase inhibitor Y-27632 on primary human corneal endothelial cells propagated using a dual media approach. Sci Rep. 2015;5(1):9167. doi:10.1038/srep09167
- Macsai MS, Shiloach M. Use of Topical Rho Kinase Inhibitors in the Treatment of Fuchs Dystrophy After Descemet Stripping Only. Cornea. 2019 May;38(5):529-534. doi: 10.1097/ICO.0000000000001883. PMID: 30720541.
- Elhalis H, Azizi B, Jurkunas UV. Fuchs endothelial corneal dystrophy. Ocul Surf. 2010;8(4):173–84.