Vol. 61, Issue 1, 97-104, January 2002

Soluble Guanylyl Cyclase Activator YC-1 Protects White Matter Axons from Nitric Oxide Toxicity and Metabolic Stress, Probably through Na⁺ Channel Inhibition

G. Garthwaite, D. A. Goodwin, S. Neale, D. Riddall, and J. Garthwaite

The Wolfson Institute for Biomedical Research, University College London, London, United Kingdom

In the rat isolated optic nerve, nitric oxide (NO) activates soluble guanylyl cyclase (sGC), resulting in a selective accumulation of cGMP in the axons. The axons are also selectively vulnerable to NO toxicity. The experiments initially aimed to determine any causative link between these two effects. It was shown, using a NONOate donor, that NO-induced axonal damage occurred independently of cGMP. Unexpectedly, however, the compound YC-1, which is an allosteric activator of sGC, potently inhibited NO-induced axonopathy (IC₅₀ = 3 µM). This effect was not attributable to increased cGMP accumulation. YC-1 (30 µM) also protected the axons against damage by simulated ischemia, which (like NO toxicity) is sensitive to Na⁺ channel inhibition. Although chemically unrelated to any known Na⁺ channel inhibitor, YC-1 was effective in two biochemical assays for activity on Na⁺ channels in synaptosomes. Electrophysiological recording from hippocampal neurons showed that YC-1 inhibited Na⁺ currents in a voltage-dependent manner. At a concentration giving maximal protection of optic nerve axons from NO toxicity (30 µM), YC-1 did not affect normal axon conduction. It is concluded that the powerful axonoprotective action of YC-1 is unrelated to its activity on sGC but is explained by a novel action on voltage-dependent Na⁺ channels. The unusual ability of YC-1 to protect axons so effectively without interfering with their normal function suggests that the molecule could serve as a prototype for the development of more selective Na⁺ channel inhibitors with potential utility in neurological and neurodegenerative disorders.