Netarsudil

The medical condition glaucoma is a leading cause of progressive visual impairment and blindness across the world with primary open-angle glaucoma (POAG) being the major type of glaucoma.

Elevated intraocular pressure (IOP) resulting from increased resistance to aqueous humor outflow is considered a major risk for the development and progression of POAG, but various clinical studies have demonstrated that the reduction and tight control of IOP can delay or prevent POAG and the vision loss associated with it. Ordinary physiological IOP results from aqueous humor produced by the ocular ciliary body and its outflow through two main outflow pathways: the conventional (trabecular) and the unconventional (uveoscleral) pathways.

Under ordinary physiological conditions, diagnostic tracers have shown that the conventional trabecular pathway accounts for up to 90% of aqueous humor outflow. Through this pathway, aqueous humor drains from the anterior chamber sequentially through the uveal and corneoscleral meshwork beams, juxtacanalicular connective tissue (JCT) region, and inner wall (IW) endothelial cells of Schlemm's canal (SC) until finally entering the lumen of SC. From there aqueous humor drains into the collector channels, intravascular plexus, epscleral veins, and finally into the blood circulation.

In glaucomatous eyes, elevated IOP is the result of abnormally increased resistance to aqueous outflow in the conventional trabecular pathway due to apparent increases in the contractile tone and stiffness of the trabecular pathway meshwork (TM), changes in extracellular matrix composition, and/or a decrease in the conductance of the IW endothelial cells of SC.

Subsequently, as a rho kinase inhibitor, the novelty of netarsudil lies in its ability or specificity to apply its mechanism of action directly and specifically at the diseased TM of the conventional trabecular outflow pathway. In particular, rho kinases are serine/threonine kinases that function as important downstream effectors of Rho GTPase. Such activity in the TM and SC drives actomysin contraction, promotes extracellular matrix production, and increases cell stiffness. Acting as an inhibitor of rho kinase, netarsudil consequently reduces cell contraction, decreases the expression of fibrosis-related proteins, and reduces cell stiffness in the TM and SC cells. As a result, netarsudil has been able to demonstrate increases in trabecular outflow facility, increases in the effective filtration area of the TM, cause expansion of the TM tissue, and dilate episcleral veins.

Furthermore, netarsudil is also believed to possess inhibitory action against the norepinephrine transporter (NET). Such inhibition of the NET prevents reuptake of norepinephrine at noradrenergic synapses, which results in an increase in the strength and duration of endogenous norepinephrine signaling. As a consequence of this enhanced signaling, norepinephrine-induced vasoconstriction that can reduce blood flow to the ciliary body may subsequently be responsible for a mechanism in which the formation of aqueous humor may be delayed, prolonged, or reduced as well.